PB-224 859
NAS REPORT ON TECHNOLOGICAL FEASIBILITY OF 1975-76
MOTOR VEHICLE EMISSION STANDARDS
AN EVALUATION OF ALTERNATIVE POWER SOURCES FOR
LOW-EMISSION AUTOMOBILES, NATIONAL ACADEMY OF SCIENCES
NATIONAL ACADEMY OF SCIENCES
PREPARED FOR
ENVIRONMENTAL PROTECTION AGENCY
APRIL 1973
Distributed By:
National Technical Information Service
U. S. DEPARTMENT OF COMMERCE
-------
BIBLIOGRAPHIC DATA
SHEET
1. Report No.
4. 1 itlu .iiiu Subtitle.-
* *» *•
An Evaluation of Alternative Power Sources for Low-Emission
Automobiles, National Academy of Sciences
PB 224 859
5. Report Date
April 1973
6.
7. Author(y)
Committee on Motor Vehicle Emissions - CMVE/NAS
8. Performing Organization Rept.
No.
Performing Organization Name and Address
Committee on Motor Vehicle Emissions
National Academy of Sciences
2101 Constitution Avenue
Washington. D.C. 20418
10. Project/Task/U'ork Unit No.
11. Contract/Grant No..
68-01-0402
12. Sponsoring Organization Name and Address
Environmental Protection Agency
Office of Air and Water Programs - Mobile Source Air Pol. Cor
401 M Street SW Room 1219 East Tover
Washington, D.C. 20460
13. .Type of Report & Period
Covered
trol.
panel report
14.
15. Supplementary Notes
committee report supported by seven panel reports also available from NTJS
16. Abstracts
The panel has evaluated several near and long term alternative power
systems including diesel, gas turbine ranking cycle and Stirling engines.
In addition electric vehicles and alternative fuels were studies. Various
aspects of each engine-system was considered including emissions,
fuel economy, noise, cost size and weight, produceability and driveability.
The report also discusses the lead time necessary to beginrtlimited and mass
production of each system.
17. Key Words and Document Analysis. 17a. Descriptors
air pollution
motor vehicles
emission control
17b. Klentificrs/Open-Ended Terms
alternative engines
diesel
gas turbine
Stirling
rankine
17e. COSATl Field/Group
18. Availability Statement
Release unlimited
I Ox
19.. Security Class (This
Report)
UNCLASSIFIED
20. Security Class (This
Page
UNCLASSIFIED
21. No. of Pages
22.. Price
FORM NTI3-3S (REV. 3-72)
USCOMM-OC I49S2-P72
42OR73OO4
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AN EVALUATION OF ALTERNATIVE POWER SOURCES
FOR LOW-EMISSION AUTOMOBILES
Report of the
Panel on Alternate Power Sources
to the
COMMITTEE ON MOTOR VEHICLE EMISSIONS
NATIONAL ACADEMY OF SCIENCES
April 1973
-------
NOTICE
The Conmittee on Motor Vehicle Emissions has evaluated the
technological feasibility of meeting the light-duty motor vehicle
emissions standards as prescribed by the Clean Air Amendments of
1970. This study was performed under the sjxmsjjrship of the National
Academy of Sciences and with the express approval of the Governing
Board of the National Research Council.
The Committee obtained much of its information from eight
panels of consultants, each panel dealing with a particular subject
area of importance in the Committee deliberations. Panel members
were selected by the Committee on the basis of recognized competence
in specific areas.
The panel reports are reports of the panels to the Committee.
Before publication, each panel report was reviewed by appointed
members of the Committee. The views represented by the panels are
one of the sources of information provided to the Committee and were
used as a partial basis for the Committee judgments.
ii
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PREFACE
In'leg!siating the Clean Air Amendments of 1970, the Congress
asked the Environmental Protection Agency to contract with the Nptional
Academy of Sciences to conduct a comprehensive study and investigation
of the technological feasibility of meeting the motor vehicle emissions
standards prescribed in accordance with the law. In responding to this
request, pursuant to a contract with the Environmental Protection Agency,
the Academy established a Committee on Motor Vehicle Emissions and
charged it with the conduct of this study. The Committee published the
results of its work in a report to the Environmental Protection Agency
dated February 12, 1973.
As means of providing itself with authoritative information and
expertise in the various critical aspects of the problem it undertook to
study, the Committee appointed specialist panels to undertake investi-
gations and report their findings. The following report, An Evaluation
of Alternative Power Sources for Low-Emission Automobiles, presents the
findings of one of those panels.
Taken together, the special panel reports constitute a very
substantial accumulation of data and analysis brought together by many
specialists in many investigations in a very fast-moving area of tech-
nological development. In its published report, the Committee on Motor
Vehicle Emissions has, of course, brought together that part of all this
information and analysis required to fulfill its stated obligation to
the Environmental Protection Agency. The separate reports of the
specialist panels are published for the public record and to complete
the documentary record.
Members of the Panel on Alternate Power Sources were:
John Bjerklie
Schnectady, New York
Panel Chairman
Elton J. Cairns David G. Wilson
Senior Scientist Department of Mechanical
Chemical Engineering Division Engineering
Argonne National Laboratory Massachusetts Institute of
Technology
Henry J. Korp
Howell Corporation Clarence Zener
University Professor
Charles Tobias Carnegie-Mellon University
Department of Chemical
Engineering Kurt H. Weil
University of California Special Consultant to the Panel
iii
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CONTENTS
PAGE
1. INTRODUCTION AND SUMMARY 1
Comparison 5
2. DIESEL ENGINES 28
Summary 28
Introduction 29
State of The Art 30
Problems 32
Future Engines 35
Potential 37
Potential Availability 37
References 38
3. GAS TURBINES 41
Summary ' 41
Introduction 42
Description 42
Characteristics 46
Simplicity 46
Large Power-Weight Ratio 46
Acceptable Volume 46
Emissions 46
Cost 47
Fuel Consumption 48
Driveability 48
Ability To Withstand Abuse and Neglect 49
Safety 49
Noise 50
State of The Art 50
State of The Art of Components 52
Compressors 52
Heat Exchangers 52
Burners 55
Turbines 55
Control Systems 56
Transmissions 57
iv
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CONTENTS (continued)
PAGE
Problems 58
NOX Emissions 58
First Cost 58
Fuel Consumption 59
Critical Materials 59
Design Power Limitations 59
Expectations for the Future 60
Potential Availability 60
References . 61
Discussions 61
Visits and Papers Made Available to the Panel 61
4. ELECTRICALLY DRIVEN VEHICLES 65
Summary 65
Introduction 67
All-Electric Vehicles 70
Battery-powered Vehicles 70
Fuel Cells 78
Hybrid Electric Vehicles 83
Potential Availability 84
References 85
Discussions 85
Papers 85
5. KANKINE ENGINES 87
Summary 87
Introduction 88
State of the Art 94
Steam Engines 94
Other Fluids 99
Problems 101
Potential Developments 102
Future Possibilities 103
Potential Availability 104
References' 104
v
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CONTENTS (continued)
PAGE
Discussions 104
EPA-OAP Contractors' Coordinating Meetings
Reports and Handouts 105
Papers and Reports 105
6. STIRLING ENGINE 108
Summary 108
Introduction 109
State of The Art 110
Problems 115
Potential Developments 115
Future Possibilities 117
Potential Availability 118
References '. 118
Discussions 118
Papers 119
7. OTHER ENGINES 121
Potential Availability 124
References 126
Discussions 126
8. COMBUSTION 127
References 129
Discussions 129
Papers 130
9. ALTERNATIVE FUELS 132
Summary 132
Introduction 132
Reformed Fuel 133
Liquefied Natural Gas (LNG) and Liquefied Propane
G£S (LPG) 134
vi
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CONTENTS (continued)
PAGE
Ammonia 135
Hydrogen 135
References 138
10. ALTERNATIVE METHODS OF POLLUTION REDUCTION 139
Summary ' 139
Introduction 140
Encouragement of Small Cars 140
Societal Changes for Fewer Car-Miles 141
Direct Encouragement of Mass-Transportation Systems 143
Encouragement of Transfer of Freight From Trucks
To Railroad 144
General 145
APPENDIX
A. Visits Conducted by the Panel 147
Orientation Visit 147
EPA Incentive Program Contractors' Visits 147
Other Domestic Visits 148
Conferences Held at University ,of California 150
European Visits 150
vii
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TABLES
PAGE
1-1 Relative Status of Various Alternative Engines 6
1-2 Comparisons of Alternative Engines Under Various
Conditions 7
l-3(a) Evaluation of Present Diesel Engine 9
(b) Evaluation of Light-Duty Diesel Engine 10
(c) Evaluation of Advanced Diesel Engine 11
(d) Evaluation of Gas Turbine Engine 12
(e) Evaluation of Advanced Gas Turbine 13
(f) Evaluation of Presently Available Battery-Powered
Electric Systems 14
(g) Evaluation of Advanced Battery-Powered Electric
Systems 15
(h) Evaluation of Advanced Fuel Cell 16
(i) Evaluation of Present Steam Engines 17
(j) Evaluation of Advanced Steam Engine 18
(k) Evaluation of Advanced Organic Fluid Rankine Engine 19
(1) Evaluation of Present Stirling Engine 20
(m) Evaluation of Advanced Stirling or Ericsson Engine 21
(n) Evaluation of Advanced Out-of-Cylinder Internal-
Combustion Engines 22
(o) Evaluation of Closed Positive-Displacement Brayton
Engine 23
(p) Evaluation of Best Combined Power Plant (Diesel-
Brayton with Secondary Firing) 24
1-4 Approximate Costs To Reach Any Production Status 27
4-1 Characteristics of Batteries and Electric Vehicles 73
4-2 Some Specifications for Three Electric Automobiles 77
4-3 Ranges for Electric Vehicles Under Various Driving
Conditions 79
FIGURES
1-1 Normplized Production Status -- Total Industry 26
3-1 Gas Turbine Configurations for Automobiles 44,45
3-2 Effect of Regenerator Therm*! Effectiveness
on Fuel Consumption 54
4-1 Specific Power vs Specific Energy Capabilities
of Various Batteries 72
5-1 Rankine Cycle Engine Schematics 90,91,92
viii
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1. INTRODUCTION AND SUMMARY
The Panel on Alternative Power Systems was charged with
considering the possibility of using engines other than spark-
ignition gasoline-fueled Otto-cycle engines for automobiles. The
major aspects of these considerations were emission levels and the
delay before the engines could become available. Numerous visits were
made to manufacturers and technologists to discuss various engines
and concepts. Questionnaires on engines and 'concepts were sent out
and the replies were evaluated. Many ideas freely offered by
interested individuals and organizations were also considered. A list
of these visits and discussions is included in Appendix A.
Several points became evident:
1. There are heat engines that can be used in automobiles to
permit the 1976 emissions standards to be met (though not necessarily
by 1976).
2. There are electrical means at hand that can allow the
1976 emissions standards to be met (though not for full-size cars of
high performance).
3. Some of the alternative power plants could be placed in
limited production by 1976; some could begin limited production im-
mediately.
4. Most of the alternative power plants could be placed in
token or limited production by 1980.
5. None of them could be placed in mass production to meet
total industry requirements before 1980.
6. No alternative power plant will be available for mass pro-
duction—even by 1980--that will have no compromise in some respect
regarding the engine or the automobile.
7. Only one or two alternative power plants can be considered
to be potentially unqualified successes as replacements for the spark-
ignition gasoline engine at some future date.
- 1 -
-------
Despite the late availability of alternative engines, the promise of
low emissions justifies a close look at their potential place in the
future.
The indicated time frame (post-1980) before the impact of any
alternative engine can be felt is coincidental with the rise of other
social and economic problems related to transportation and energy.
This implies that the future of any alternative power plant depends
on the concurrent evolution of the transportation industry, the energy
business, and engine technology—one will not lead the other, but each
may limit the other. A further implication is that any viable al-
ternative power plant must fit into this as yet undetermined future
while imposing as few limitations as possible on the other industries.
The future power plants must be able to use the fuels or energy of the
future and they must possess great versatility.
The anticipated time schedule is short enough so that the
power plants must also be considered in the context of present fuels
and present systems as well as future systems. That is, a major re-
quirement for candiate alternative power plants is that they must fit
into a technical, social, and economic evolution starting how.
The time span over which economic and social pressures will be
great enough to force the transportation and energy systems into great
change is also relatively short—probably 15 to 30 years. This is
so short as to preclude more than one major technical evolution before
quasi-stability is reached. Based simply on the time span over which
major engine changes have been assimilated into the industry in the
past—15 to 20 years for jet engines on air transports, 15 years and
still waiting for the Wankel engine—the span of 15 to 30 years will
permit only one complete engine change. Also, since billions of dol-
lars are involved in engine change, the nation's economy probably can
stand but one change in the next 15 to 30 years.
On the other hand, the economy can stand the gradual evolution
of several types of engines, so that the total mix of power plant types
can be in a state of continual flux. New concepts could then be intro-
duced at will, so long as they are introduced gradually in limited ap-
- 2 -
-------
plications at the start.
Although automotive emissions are an overriding concern for
this panel, it is apparent that the other aspects of power plant char-
acter are at least as important to the user and to industry. At this
time the need to satisfy the requirements of the auto industry (the
largest block of the transportation industry), the liquid hydrocarbon
fuel industry (the largest block of the energy industry), and the
social community (which has been handmaiden to the development of the
auto and oil industries) is apparent. These needs can be translated
into the following evaluation points for alternative power plants:
fl CO
Emissions— Serviceability—'—
Energy source versatility— Design horsepower versatility—'—
Fuel economy—'— Control ease—
Noise^ Producibilitj4
Safety^ Size-
Cost— Weight^
c d
Starting ease— Integrability—
c c
Driveability— Response to abuse and neglect—
A close look at this list can only emphasize the real competi-
tor against which all candidate power plants must be matched—the spark-
ignition gasoline-powered Otto-cycle engine. With minor qualifications
this engine meets all of the above requirements except emissions.
It has already been demonstrated that engines that are superior
to spark-ignition engines in only one or a few aspects (for instance,
The engine evaluation points are marked to distinguish their major signi-
ficance as follows:
9
—Must be met by law
—Necessary for future society
C
•Required by the consumer
-Contributes to the ability of the manufacturer to sell engines that
satisfy the consumer (usually by way of reducing cost)
- 3 -
-------
the dlesel engine) cannot compete in the American automobile market
within the present economic system. Thus the 70+ years of gasoline-
engine dominance is an earned dominance and not one simply of con-
venience to the large manufacturers.
Recognizing that neither the existing auto-road transportation
system nor the 1976 emission standards are unassailable, one other con-
sideration should be introduced in evaluating power plants. That is,
which candidates become viable under various possible interpretations
of the ground rules. The basic ground rules are to meet the emission
standards while maintaining good performance. But over the next 10 to
15 years taking some deviations may be the most practical approach.
The questions then are, What candidates are viable
1. If the power plant must fit into present autos and maintain
present automobile performance while meeting 1976 emission standards?
(This is termed "one-to-one substitution.")
2. If the power plant must operate an automobile so that the
1976 emission standards are met, but the auto may be of substandard
size or have substandard performance? (This is termed "de-rated auto.")
3. If the power plant must operate a full-size1 automobile with
present-day performance but can have slightly relaxed emissions compared
with 1976 (a suggested relaxation being no worse than 1975 California
standards)? (This is termed "de-rated emissions.")
4. If the power plant powers an automobile of substandard size
and/or performance and has slightly relaxed emissions, but not as great
in either case as for 2 and 3? (This is termed "compromise de-rate.")
These various possibilities now allow various rates of social, economic,
and technical evolution, various economic Impositions on the consumer,
various impositions on the technical and business innovators, and
various departures from the familiar. The status of various alterna-
tive engines is summarized below.
- 4 -
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COMPARISON
Table 1-1 shows the relative status of the various alternative
engines. The various forms of alternative engines in present and ad-
vanced states of development are compared with the precontrol gasoline
engine. The comparison points are those discussed previously as the
ones that must be considered for any engine contending for use in
automobiles. The precontrol gasoline engine is rated "1" wherever
quantitative comparison can be made, and ratings of poor, fair, good,
and excellent are used where qualitative comparison is all that is
possible. The best engines will have quantitative ratings as appli-
cable of less than 1 and the qualitative ratings as close to excellent
as possible.
Present production status, the earliest probable date for
limited production, and the earliest possible date for mass production
are also indicated. The production status categories in order of
approach to mass production are prototype, concept feasibility, pre-
production, limited production, and mass production. If a single
suitable prototype has not been produced, the production status is
indicated as the number of years (-x) estimated for reaching that
milepost. Table 1-2 shows the same findings compared under different
circumstances.
The use of some alternative fuels, H? for instance, can convert
the heat engines listed under De-rated emissions in Table 1-2 to low-
emission engines and can be considered for one-to-one substitution.
Likewise, a gasoline engine converted to run to H_ would be a viable
alternative engine. In any case, an acceptable means for handling and
storing hydrogen would have to be developed.
The engines within each comparison situation listed in Table 1-2
would ordinarily be sorted out for viability by normal economic and
sociologic processes, and it is only because of an imposition of a
crisis situation on air standards that the technical aspects enter in
at this time.
- 5 -
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TABLE 1-1
Relative Status of Various Alternative Engines
Emissions
Fuel Versatility
Fuel Consumption
. Noise
Safety
Cost
Starting Ease
Response to Abuse
and Neglect
1 Driveablllty
O* Serviceability
1 Design HP Versatility
Control Ease
Produclbility
Size
Weight
Integrablllty
Present Production
Status
Earliest Ltd. Prod.
Earliest Mass Prod.
•GD
e
Q
1975
2/3
F-G
E
2
Evde
E
G
E
F
E
G
2 1/4
2-2%
F
Ltd
Prod
Nov
1976
dvanced
lesel
< 0
1976?
3/4
G
E
1
Evde
E
G
E
E
E
G
3/4
3/4
E
-4
yrs
1980
1983
as
urbine
U H
1975
E
1-2
E
E
2-3
Evde
G
G-E
E
F
F
F
1
3/4-1
E
Cone.
Feas.
1978
1984
dvanced
33 Turbine
5
E
F
P-F
G
F
E($)
G
-
-
P
Ltd
Prod.
Nov
1976
•a
S &
c a
> *j
•o Q
0
3 (2
1976
E
%-3/4
E
G
10
Evde
?
E
G
E?
G?
E
3+
E
-15
yrs
1992
1996
re-Control
asollne
04 O
G-E
1
G
E
1
G
E
E
E
E
E
E
1
E
Mass
Prod.
Nov
Nov
P - Poor C.P.P. - .Central Power Plants
F - Fair Evde - Excellent, vlth delay
G - Good Yrs - Years to prototype
E - Excellent E($) - Excellent, but costly
-------
TABLE 1-2
Comparisons of Alternative Engines Under Various Conditions
Comparison Situation
Best Probable Candidates
(Sometime)
Remarks
(Availability)
One-To-One Substitution No certain candidate
but advanced Stirling,
advanced gas turbine,
and advanced battery
or advanced fuel cell
are best chances
De-rated Auto
De-rated Emissions
Compromise De-rate
Advanced Stirling
Rankine
Battery
Advanced battery .
Advanced fuel cell
Advanced gas turbine
Gas turbine
Advanced Stirling
Light-duty diesel
Advanced battery
Advanced gas turbine
Advanced fuel cell
Present diesel
Light-duty diesel
Present gas turbine
Advanced gas turbine
Advanced Stirling
Advanced fuel cell
Advanced battery
- 7 -
Future
Considerable
de-rate, future
Great de-rate
present
Some de-rate,
future
Future
Future
De-rate to
California, 1975
Future
De-rate to
California, 1975
Future
Future
Future
Some performance and
emissions derate
No great degradation
need be imposed on
any of these
Future
Future
-------
Those candidates that appear to merit earliest consideration are
as follows:
Diesel: Can be considered now for special applications such as
taxis, police cars, light duty urban trucks and vans.
Advanced diesel: Earliest probable compromise solution for
general car population; fits many applications in present transportation
systems. Can be considered for future transportation systems.
Advanced gas turbine: Suitable with little or no compromise to
larger vehicles; some question about suitability in urban driving and
in small cars; good fit to future energy system; can be considered for
future transportation systems.
Advanced Stirling: Potentially can fit all requirements and
be the best, but needs intense development; good fit to future energy
system. Can be considered for future transportation systems.
Advanced battery: Very good fit to future energy system.
Advanced fuel cells also fit this group as soon as it is clear that it
is mostly engineering that is required for its development rather than
a major technical and/or economic "breakthrough."
The present unsettled nature of the evolving socioeconomic
situation regarding transportation and energy precludes a choice for
one power plant at this time. It is logical to proceed in improving
the characteristic^ of all likely engines, batteries, and fuel cells.
By this means the most, viable candidates will surface.
Table 1-3(a-p) evaluates each of the engine classes considered.
All the evaluation points are listed, and qualitative or approximate
quantitative comparison is made to the pre-emission-controls gasoline
engine.
The following are brief qualification's' for some of the evalua-
tion items in Table 1-3:
Starting ease: An engine that has sure starting is considered
excellent irrespective of time lag, but time lag is noted.
- 8 -
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TABLE l-3(a)
Evaluation of Present Diesel Engine
Emissions in Grams per Mile
CO HC NO
2 to 3
2.5
0.6 to 1.0 1.5 to 1.8
0.15 1.65
Remarks '
State of art, 50 to 70 HP
Expected by Daimler-Benz
With slight modification,
present-type diesel could
meet 1975
standards
Sourcest Perkins, Ricardo, Southwest Research Institute, Ford, Daimler-
Benz, GM.
Other Criteria:
Criterion
Fuel versatility
Fuel consumption..
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP
versatility
Control ease
Producibility
Size
Weight
Integrability
Present production
status
Rating
Fair
2/3
Fair to good
Excellent
2
Excellent
Excellent
Good
Excellent
Fair
Excellent
Good
2%
2 to 2%
Fair
Limited
production
Remarks
Sources
15-sec starting
Poor torque at low
RPM
Injector problem
Daimler-Benz,
Volvo, CAV,
GM, Ford
Size and weight
p roblems; rad iator
size a 1%
Remaining potential problems; odor, smoke, white smoke, particulates,
noise.
Note; Numerical ratings are in comparison with equivalent 1968 gasoline
engine - 9 -
-------
TABLE 1-3(b)
Evaluation of Light-Duty Diesel Engine
Emissions
CO
3.36
0.52
__
in Gram?
HC
0.34
0.22
__
per Mile
0.6 - 0.7
0.42
0.54
0.22
Remarks
Daimler-Benz estimate
Caterpillar proposal
Best production prototype
Best lab measurements
Sources: Mercedes-Benz, Cummins, and Caterpillar.
™—•"•""•"""^ •'"''' '"'
Other Criteria:
Criterion
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP
versatility
Control ease
Producibility
Size
Weight
Integrab11ity
Present production
status
Ratine ,
Fair
2/3 to 3/4
Fair to good
Excellent
1%
Excellent
Excellent
Good
Excellent
>
Excellent
Excellent
Good
1.35
1.55
Good
- 2 years
Remarks
Sources
15-sec start
Cummins,
Caterpillar
Low torque at low RPM
Injector problem
Radiator size -
Caterpillar,
Cummins
Caterpillar,
Cummins
Remaining potential problems; .odor, smoke, white smoke, particulates
(could affect life when EGR is used).
Note; Numerical ratings are in comparison with equivalent 1968 gasoline
engine.
- 10 -
-------
TABLE l-3(c)
a
Evaluation of Advanced Diesel Engine—
Emissions
CO HC
OK OK
Other Criteria;
Criterion
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP
versatility
Control ease
Producibility
Size
Weight
Integrability
Present production
status
Rating
Fair to good
3/4
Good
Excellent
1
Excellent
Excellent
Good
Excellent
Excellent
Excellent
Good to good+
3/4
3/4
Excellent
-4 years
Sources and Remarks
Better than 1975 (Ricardo)
Remarks
May use spark assist
15-sec starting
Shaft speed has to be
kept up
Injector problem (may
use only one)
Radiator--l%
Remaining potential problems; For both concepts, combustion work is just
beginning and there are lubrication
problems. There are also seal problems
with the rotary engine.!
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine.
Two concepts were considered as advanced diesel engines—the rotary
(Wankel) diesel and the high-speed two-stroke diesel. (See remarks
in Remaining Potential Problems category above.)
- 11 -
-------
TABLE l-3(d)
Evaluation of Gas Turbine Engine
Emissions In Grams per Mile
CO
3.1
0.9
3.5
0.6
Remarks :
HC NO
— — x
0.35 4.2
0.26 2.9
0.3 2.7
0.25 3.1
The present type o:
Sources
General Motors (measured)
Noel Penny Turbines
(estimates)
Chrysler
Garrett AiResearch
modified to meet 1975 emission standards.
Criteria
Criterion
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP
versatility
Control ease
Producibility
Size
Weight
Integrability
Present production
status
Rating
Excellent
2 @ low load
1 @ high load
Excellent
Excellent
2 to 3
Good
Good
Good to excellent
Excellent
Fair
Fair
Poor to fair
1
3/4 to 1
Excellent
Remarks
Some whine
Materials and manufacturing
costs include up to 12 Ib
of super a Hoy per engine
(high nickel and Cobalt)
15-30 sec starting,
sizable power needed
May improve with
development
More controls required to
reach excellent
Problem below 100 to 150 HP
Partly set by driveability
Could improve
Concept feasibility Cost has caused rejection.
Remaining potential problems; NO emissions, cost, lower power fuel
consumption
Note: Numerical ratings are in comparison with equivalent 1968
gasoline engine.
- 12 -
-------
TABLE 1-3(e)
Evaluation of Advanced Gas Turbine
Criterion
Emissions
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP
versatility
Control ease
Producibility
Size
Weight
Integrability
Present production
status
/ ,
Concept requirements:
Rating : Remarks
Will probably meet
1976 standards
Excellent
1% to 1 3/4 @ low load
3/4 to 1 @ high load
Excellent
Excellent
1
Good
Some whine
Assumes considerable
ceramic parts
15-sec starting--
sizable power needed
Problem below 100 HP
Set by driveability
Excellent
Excellent
Excellent
Fair
Fair
Good
1
1/2 to 3/4
Excellent
-2 to -4 years
Variable combustor, ceramics for major parts;
lowest cost and fuel consumption may require
infinitely variable transmission (not presently
available) to allow best operating speed and
simplest configuration.
Remaining potential problems: Low power, fuel consumption too high.
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine.
. - 13 -
-------
TABLE l-3(f)
Evaluation of Presently Available Battery-Powered Electric Systems
Criterion
Emissions
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP
versatility
Control ease
Producibility
Size
Weight
Integrability
Present production
status
Rating
As in Central Power
Plant
As in Central Power
Plant
3/4 to 1 (based on heat
equivalent)
Excellent
Fair
Greater than 5 where
usable
Excellent
Fair
Fair to good
Good
Can obtain fair
performance in-
dependent of size;
high performance not
available
Excellent (costly)
Good
Cannot be matched to
family size or compact
car with performance
comparable to gasoline
fueled vehicle
Poor
Limited production
Remarks
Relocated in Central
Power Plant
Possible problem in
accident
Limited applications
only
Short range (less than
50 miles)
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine.
- 14 -
-------
TABLE 1-3 (g)
Evaluation of Advanced Battery-Powered Electric Systems
Criterion
Emissions
Fuel versatility .
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP versati-
lity
Control ease
Producibility
Size
Weight
Integrability
Present production
status
Rating
As in central power
plant
As in central power
; plant
2/3 to 1 (based on
heat equivalence)
Excellent
Good
2 to 3%
Excellent
Excellent
Good
Excellent
Excellent
Good
1 to 1%
1%
Excellent
-4 years
Remarks
/
Relocated to central
plant
Possible problem in
accident
Temperature automatically
maintained at all times
Costly
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine.
- 15 -
-------
TABLE l-3(h)
Evaluation of Advanced Fuel Cell
Criterion Rating Remarks
Emissions Low Will meet 1976 standards
Fuel versatility Excellent^
Fuel consumption % to 3/4
Noise Excellent
Safety Good Depends on operating temp-
erature and electrolyte
Cost 10
Starting ease Excellent With possible delay
Response to abuse
and neglect ?
Driveability Excellent
Serviceability Good
Design HP versatility Probably excellent
Control ease Good
Producibility Excellent
Size 3+
Weight 3
Integrability Probably excellent
Present production
status -15 years
3
— With regard to fuel versatility, fuel cells can be designed to use
any of a wide range of fuels, but, once designed, a given fuel cell
is limited to operation on a rather narrow range of fuels. But the
ability of this concept to make use of a wide range of fuels is
excellent.
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine.
- 16 -
-------
TABLE 1-3(1)
Evaluation of Present Steam Engines
Emissions in Grams per mile
GM measurement on SE-101
GM measurement on SE-124
Range of values obtained
CO
3.0
1.2
2-4
HC
0.5
0.2
0.5-2.0
Bx
2.0
1.7
0.5-2.0
Remarks; Present steam engines can probably, be modified to meet 1976
standards and may achieve the levels of advanced steam
engines.
Other Criteria:
Criterion
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Rating
Excellent
1% to 1% (probable),
1% to 2 (measured)
Good to excellent
Good
Poor to excellent
Good
Good
Poor to excellent
Design HP versatility Fair to good
Control ease Poor
Producibility Poor
Size
Weight
Integrability
Present production
status
1 3/4 to 3
Poor
-4 years
Remarks
Fan and blowers are noisy
Question on boilers under
all conditions
includes up to 10 Ib
nickel
H_0 must be liquid at
s.tart. 30-sec to
,. 1-min start time
Question on maintaining
seals
With steam chest
Poor, if internals cannot
be made essentially
service-free
Boiler manufacturing tech-
nique has to be developed
This compares 135 HP steam
to 200 HP gasoline
Radiator to 4 times gaso-
line engine, boiler
heavy and large
Note; Numerical ratings are in comparison with equivalent 1968 gasoline
engine. - 17 -
-------
TABLE l-3(j)
Evaluation of Advanced Steam Engine
Emissions In Grams per Mile
CO HC NO
— — —x
0.1 0.02 0.2
Remarks
Estimated from measurements provided
by Steam Engine Systems; OK for 1976.
Other Criteria;
Criterion
Fuel versatility
Fuel consumption
Noise
Safety .
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP
versatility
Control ease
Producibility
Size
Weight
Integrability
Present production
status
Rating
Excellent
1% to 1%
Excellent
Good to excellent
2% to 3
Excellent
Good
Good
Excellent
Good
Poor
Good
1
1% to 1%
Poor
-2 to -4 years
Remarks
Assumes quieted fans
Assumes solution to water
freezing problem; 30-to
60-sec start time
Especially with turbine
prime mover
With steam chest
This compares 135 HP
steam to 200 HP gasoline
engine
Boiler plus radiator to
4 times gasoline engine
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine.
- 18 -
-------
TABLE l-3(k)
Evaluation of Advanced Organic Fluid Rankine Engine
Emissions in Grams per Mile
CO HC NO
0.3 0.01 0.06
0.22 0.14 0.29
Remarks
Estimated from Faxve measurements
Estimated from Thermo Electron
measurements
OK for 1976.
Other Criteria:
Criterion
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Rating
Excellent
u
Excellent
Good to excellent
2% to 3%
Excellent
Fair
Driveability Good
Serviceability Excellent
Design HP versatility Good
Control ease Poor
Producibility Fair
Size
Weight
Integrability
Present production
status
1 to 1%
1 to 1%
Poor
-3 to -5 years
Remarks
Assumes quieted fans
30-sec to 1-min
Maintaining seals
a problem
With vapor chest
Hermetic or near-hermetic
sealing a problem
This compares 135 HP
Rankine to 200 HP
gasoline
Boiler and radiator to
6 times gasoline engine
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine.
- 19 -
-------
TABLE 1-3(1)
Evaluation, of Present Stirling Engine
Emissions in Grams'per Mile
CO HC NO
— — TC
0.31 0.1 0.175
0.15 0.04 0.15
Remarks
Estimated from measurements
Stabilized test; no cold start.
OK for 1976.
Other Criteria;
Criterion
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Ratings
Excellent
2/3
Excellent
Excellent
1% to 2
Excellent
Poor
Good
Poor to Excellent
Design HP versatility Excellent
Control ease Good
Producibility
Size
Weight
Integrability
Present production
status
Good
3/4 to 1
1 to 1 1/4
Good
-2 to -3 years
Remarks
Includes 8-9 Ib nickel
and 8-9 Ib chromium
15-30 sec start
Sealing is a problem
Improved control needed
(dead volume control
looks OK)
Excellent if seal problems
solved
Improved control needed
(dead volume control
looks OK) i
Radiator 2% to 3 times
.size of gasoline engine
radiator
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine. j
- 20 -
-------
TABLE 1-3. (m)
Evaluation of Advanced Stirling or Ericsson Engine
Criterion
Emissions
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP versatility
Control ease
Producibility
Size
Weight
Integrability
Present production
status
Rating
At least as good as
present Stirling
Excellent
% to 3/4
Excellent
Excellent
1
Excellent
Excellent
Excellent
Excellent
Excellent
Excellent
Excellent
3/4
2/3
Good
-5 to -10 years
Remarks
OK for 1976
15-sec start
Radiator to 2% times size
of gasoline engine
radiator
Sources; Kinergetics, Philips, and United Stirling were major sources;
also some consultants.
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine.
- 21 -
-------
TABLE 1-3(n)
Evaluation of Advanced Out-of-Cyllnder Internal-Combustion Engines
Emissions
CO HC NO
^MM —•• WM^|
Low Low ?
Other Criteria;
Criteria Rating Remarks and Sources
Fuel versatility Excellent Many suggestions by
Fuel consumption 1 numerous inventors;
Noise Good several papers and
Safety Excellent consultants served as
Cost 1% to 2 the sources.
Starting ease Excellent
Response to abuse
and neglect Excellent
Driveability Excellent
Serviceability Excellent
Design HP versatility Excellent
Control ease Excellent
Froducibility Excellent
Size 1%
Weight 1%
Integrability Fair to good
Present production
status -5 to -10 years
Note; Numerical ratings are in comparison with equivalent 1968
gasoline engine. :
•22 -
-------
TABLE l-3(o)
Evaluation of Closed Positive-Displacement Brayton Engine
Criterion
Emissions
Fuel versatility
Fuel consumption
Noise
Safety
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP versatility
Control ease
Producibility
Size
Weight
Integrability
Present production
status
Ratine
Should be like
Stirling Engines
Excellent
3/4 to 1
Excellent
Excellent
1 to 1%
Excellent
Fair to excellent
Good
Poor to excellent
Excellent
Good
Excellent
1
1 to 1%
Good
-5 to -10 years
Remarks
OK for 1976
Depends on working fluid
Improved control needed
Depends on working fluid
and seals
Improved control needed
3 to 3% times radiator
Sources; Several papers and inventors served as the sources.
Note: Numerical ratings are in comparison with equivalent 1968
gasoline engine.
- 23 -
-------
TABLE l-3(p)
Evaluation of Best Combined Power Plant
(Diesel-Brayton with Secondary Firing)
Emissions
CO
OK
HC
OK
NO
?
Other Criteria;
Criterion
Fuel versatility
Fuel consumption
Noise
Safety i
Cost
Starting ease
Response to abuse
and neglect
Driveability
Serviceability
Design HP versatility
Control ease
Producibility
Size
Weight
Integrability
Present production
status
Rating
Good
% to 3/4
Good
Excellent
1% to 2%
Good
Excellent
Excellent
Excellent
Fair
Fair
Good
As low as 1
1 to 1%
Poor to fair
-5 to -10 years
Remarks
15-30 sec, sizable
start power needed
Probably best above
100 to 150 HP
Amounts to two small
engines side by side
Note; |Numerical ratings are in comparison with equivalent 1968
gasoline engine.
- 24 -
-------
.Response to abuse and neglect: Basically this measures the
amount of trouble to be expected when the engines are put into the
hands of the public; closely akin to .reliability and dependability.
\> . ; '
Driveability (does not include starting): How well does a car
perform when equipped with the engine: A car equipped with an engine
that is overweight or underpowered for its package size will have poor
driveability. Also, an engine with sluggish controls will have poor
driveabillty.
Serviceability: Ease, cost, and rapidity of servicing.
Design HP versatility: Ability of an engine type to satisfy
a wide variety of power levels for various sizes and types of vehicles.
Control ease: Required tuning and cost of all controls, as well
as number of controlled parameters.
Producibility: Best producibility means most conventional
tooling.
The state of development is estimated in terms of the normalized
production status curve, Figure 1-1. In this curve the 0 year is when
a suitable prototype is available. That is, one engine of a configu-
ration that is probably manufacturable, that exhibits the desired
traits, and that has been developed and operated for a sufficiently
long time to prove its desirability. Positive years are the years
required after such availability for each successive state of pro-
duction to be reached. Negative years are our estimates for each
undeveloped engine. That estimated time must be added to the positive
years to get an estimate of the total number of years from the present
to reach a particular production level.
Estimates of engineering and tooling costs for each successive
production step are listed in Table 1-4. One estimate is made for the
/
nonautomotive industry aiming for limited production (and where recall
and other risks are built into the engine cost) and another is made
for the auto industry which must work out all the potential cost and
business risks by development beforehand. The curves are for engines
using conventional tooling. Engines requiring unconventional tooling
will have extended times to reach a given production status.
- 25 -
-------
Mass Production
Limited Production
Preproduction
Concept Feasibility
Suitable
Prototype
Nonauto industry &
optimistic auto
industry schedule
Units/Year
107
108
10s
10*
103
102
10
1
-2
4 6
YEARS FROM SUITABLE PROTOTYPE
(Assumes optimum spending)
8
10
FIGURE 1-1 Normalized production status — total industry.
-------
TABLE 1-4
Approximate Costs To Reach Any Production Status
Production Status
Cost To Make Each Step
For Major Auto
Company
: For Non-auto Company
Aiming Only at
Limited Production
Prototype
(1 unit)
$5 - 20xl06 R&D
$2
- 20xl06 R&D
Concept feasibility
(to 100 units)
$108 - dev.
(Mktg, tooling,
engines)
$10 - 20x10 dev
(Mktg, tooling,
engines)
Pre-produc tion
(to 1000 units)
$50 x 106 tooling $10 - 20xl06 tooling
Limited production
(to 100,000 units/yr)
Q
$10 - tooling
50x10 - tooling
Limit for non-auto
company
Mass production
(over 300,000
units/year)
Q
$10 - retooling
+ $25xl06/year
- 27 -
-------
2. DIESEL ENGINES
SUMMARY
The diesel engine characteristics are such that 1975 standards
might be met with full-size automobiles by incorporating several im-
provements. No manufacturer presently has technology to ensure meet-
ing the 1976 NO standard of 0.4 grams per mile.
3t
New developments in diesel engines, such as a two-stroke engine
with a new, low-emission combustion method, and the use of positive-
displacement rotary prime movers such as the Wankel configuration, offer
the future possibility of meeting, or nearly meeting 1976 standards with
an engine that is smaller and cheaper than the present (1970) gasoline
engine. The concepts are at present far removed from being in the
automobile engine prototype stage.
There is a good possibility that an automotive diesel engine
having sufficient specific power and low enough emissions to meet the
1976 emissions standards can be built. But there is much engineering
work still to be done before the concept can be proven. The potential
problems of smoke, white smoke, odor, cold-weather starting, and noise
still remain. It appears that good single prototypes of the advanced
engine cannot be available before 1975. Limited production might be
possible by 1980.
With only relatively minor engine modifications, such as
improved injection nozzles, present diesel-powered cars (of the size
of Mercedes-Benz cars) can be made to meet the 1975 standards. For
larger cars to be powered by diesel engines of present design tech-
nology, 1975 emission levels could probably be met if modifications such
as injection retard, EGR, and possibly turbocharge are used. The basic
engines are now in limited production. Mass production could start in
4 to 6 years. Diesel engines are suitable for medium-performance or
substandard-sized automobiles, such as the Mercedes-Benz as presently
powered by diesel.
- 28 -
-------
A passenger-car diesel engine designed according to existing
technology may have a possible disadvantage in slightly higher weight
and larger size than a spark-ignition engine of comparable output. It
may cost more basically, but the difference shrinks when the emission
controls for gasoline engines are added in, since the add-ons for diesels
to meet 1975 standards are minimal. The diesel will give much better
fuel economy and will require less maintenance, which should quickly
make up any first-cost difference with normal driving mileage. The
efficient diesel will tolerate a wide range of fuels, which becomes of
' f
greater interest as our concerns with conservation of fuels increase.
Because fuel of lower volatility is used, diesel engines have an
additional safety factor, and there will be lower emissions at the
filling station.
INTRODUCTION
Diesel engines differ from gasoline engines in their method
of combusting the fuel. Air in the cylinders is compressed and heated
until its temperature ignites the injected diesel fuel. In gasoline-
powered engines, the carbureted air-fuel mixture is ignited with an
electric spark. Diesels normally operate with more air than is nec-
essary to support combustion. This excess air ensures more complete
combustion, practically eliminating carbon monoxide emissions and pro-
ducing fairly low unburned hydrocarbons. Hydrocarbon emissions do not
meet 1976 standards unless the engine is modified from present design.
Unfortunately, the high combustion temperatures do produce NO
X,
emissions, which are presently higher than the 1976 standards.
Diesel engines are produced in four-stroke and two-stroke
versions; four-stroke engines have one power stroke for two revolutions,
while two-stroke engines produce one power stroke for every revolution.
Four-stroke engines are further differentiated as direct-injection or
precombustion-chamber diesels. Direct-injection diesels use fuel in-
jected directly into the combustion chamber formed by the cylinder
- 29 -
-------
walls and the top of the piston. In precombustion-chamber diesels,
fuel is injected into a small chamber adjacent .to the cylinder. Burn-
ing starts there where better air-fuel mixing can occur and then pro-
ceeds into the main combustion chamber. Burning lasts longer in the
precombustion-chamber engine than in the direct-injection engine and
a cleaner exhaust is obtained. This is aided by the fact that there
is normally a rich mixture in the pre-chamber so that NO generation
3t
is low.
The two-stroke engine, which provides better fuel economy, is
typically used in city buses and in some medium-duty diesel applica-
tions. There are recent indications that smaller versions of the
engine may find their way into light-pickup and possibly passenger-car
use. Heavy-duty diesels designed to power long-haul trucks originally
j
used precombustion-chamber engines that had high specific power; now
i
that exhaust emissions are of great concern, this system is used in
all applications where clean exhaust is mandatory, including diesel-
driven automobiles and taxis.
STATE OF THE ART
Recent data (1, 2, 3, 4) show that several current four-stroke
and one two-stroke diesel engines can meet 1976 standards for carbon
monoxide and unburned hydrocarbons. They meet or nearly meet the NO
3£
standard for 1975 (3.0 grams per mile). A single set of data for a
diesel automobile (2) produced results that met the 1975 specification.
There have been no results obtained on diesel engines showing ability
to meet the 1976 standard of 0.4 grams of NO per mile.
, • *t i i
To varying degrees, all of the companies visited were optimistic
that diesel engines could be manufactured to meet all but the very
severe 1976 NO standard. None was really willing to exert a great
A,
deal of effort in competing for the passenger-car market unless assur-
ances were given that if they produced a better low-emission vehicle or
engine their equipment would be purchased in some substantial quantity
- 30 -
-------
for some period of time. Investments for such studies, and the tooling
to go with any large-scale production, are too great to allow specula-
tion on the part of these companies that their engines would be bought.
Present diesel engines for light-duty vehicles have much lower
power density and greater specific weight than the equivalent gasoline
engine. This is partly due to cost factors--cast iron is cheaper for
large parts that have to withstand shock and thermal stress than is
aluminum, for instance. But the major reason is that the nature of
diesel engine combustion dictates a high peak pressure that must
last for a considerably longer time per stroke than does the pressure
pattern of the gasoline engine. This means that the diesel engine
cylinder must be massive to stand normal operation for even a short
time. Also, some types of diesel engines are limited in operating
speed by the rate of the combustion process. A slower-speed engine
is a bigger engine. So both of the effects brought on by the combus-
i
tion process dictate that the diesel engine will be larger and heavier
than the equivalent gasoline engine.
The pre-chamber diesel can« operate at much higher speed than
the direct-injection diesel. This, coupled with its naturally
cleaner exhaust, makes the pre-chamber type more tractable as a start-
ing point for a low-emission engine than does the direct-injection
engine. Generally, those contacted (3, 5, 6) indicated that a re-
designed diesel engine that will meet the emission standards and power
a full-size family car will weigh 15 percent to 25 percent more than
an equivalent spark-ignition engine.
Tests have shown that it is possible to reduce emissions on
the diesel by such mechanical changes as turbo-charging, intercooling
and simultaneously using lower compression ratios, possibly as low as
10 to 1 (5). This approach reduces the emission of NO and the smoke
X
produced. It should be noted that smoke levels meeting federal regu-
lations are being achieved by many current diesel engines and impro-
vements are being made continually.
Another proven approach uses conventional natural aspiration
with usual compression ratios (14 and over). This is coupled with
- 31 -
-------
other modifying features (injection retard, no dribble injectors, EGR)
(3, 4, 5, 7, 8, 9, 10, 11) and has been shown to decrease NO to levels
3t
approaching the 1976 standard.
Injection retarded from normal helps considerably to reduce
NO emissions as do other programmed injection means. The degree of
X
improvement is not sufficient to meet the standards by itself. However,
retard, plus EGR appears to be all that is required to meet 1975 stand-
ards. Turbo-charge is required over and above this to keep the smoke
at legal levels. Exhaust-gas recirculation (EGR) used to reduce NO
X
formation tends to increase smoke and, therefore, the quantity of re-
circulation that can be used is limited. EGR also detracts from power,
so it would only be used at lower power where most light-duty vehicles
operate anyway. Because of increased particulate matter in the engine,
diesel exhaust recirculation may cause wear problems.
Improved injectors (Daimler-Benz) have helped some companies
lower the unburned hydrocarbons. The dribble of fuel at the end of
injection contributes to higher unburned "hydrocarbons. Thus, preven-
tion of dribble is the main feature of the newer injectors.
There have been cases of excessive white smoke (unburned fuel
particles) at startup, especially at low temperatures. Improved in-
jection equipment and procedures, are under development to overcome
that problem (Cummins, Caterpillar). Particulates can be handled with
fairly simple filters (Daimler-Benz). Characteristic diesel-engine
odors can be modified to be acceptable in these advanced-design diesels.
PROBLEMS
, i
1 i
It appears that any diesel engine will be slightly noisier at
best than the equivalent gasoline engine. This is minimized in pre-
chamber diesels, in Wankel configurations, and in the new two-stroke
engine, but it is not completely eradicated as a problem. Also, there.
apparently will always be some tendency to smoke although this is
minimized with turbo-charged engines. Another potentially persistent
- 32 -
-------
problem, not completely understood as yet, is white smoke on cold start.
Starting remains a problem to be finally solved for low temperatures,
even though the present methods appear satisfactory down to at least
0°F. New methods of preheating are being tried that show promise of
certain starts at least to -15°F. Present start time is as good as now
—of 15 sec for preheat is maintained. Odor, while nearly eliminated
in the new two-stroke engine, persists to some degree in all other
engines. Odor may persist as a deterrent to adoption of the diesel
engine for large populations of vehicles. Diesel odor even now can be
detected in London, one of the world's cities most populated with diesel
engines. The London air is not objectionable, but the vehicle popu-
lation is not 100 percent diesel.
Even to meet a modified NO standard with engines powerful
2f>
enough to meet the EPA automobile-performance requirements will re-
quire new engineering approaches. Basically, considerations must be
given to producing a passenger-car-type diesel engine whose durability
and efficiency are not quite as good as is presently produced for
industrial applications. Truckers expect 300,000 to 400,000 miles
of relatively maintenance-free engine life. This is many times the
life expected for the average passenger car. Such an approach will
tend to decrease weight and size of the engine, and, in turn, its
cost, which will make the engine more attractive as an alternative
to the emission-controlled spark-ignition engine. A difficulty with
this approach is that the engine combustion characteristics demand
more massive construction, which inherently leads to a long life engine,
even if you do not want it.
The major detracting factor for driveability is the engine's
starting characteristics. However, further studies to make use of
combustion heating units and/or proper cold-starting glow plugs are
under way. Another driveability drawback is,that torque drops rapidly
at low rpm, so compared with the gasoline engine the shaft speed has
to be kept high. With regard to acceleration, current high-weight,
few-cylinder engines with high inertia of the rotating syestem are
sluggish, but the contemplated modern light-design, more cylinder
- 33 -
-------
engines should require less flywheel effect and should be "snappier"
engines.
Driveability with turbo-charged engines is not as good as with
naturally aspirated diesels or gasoline engines. This is because of
severe torque and power loss at low engine speed—the turbo-charger is
not working. This requires keeping the engine speed up—a feature that
can be built into an automatic transmission or that can be developed by
using the proper driving techniques. In the extreme, a modified
transmission with more than three speeds may be required, but this is
more costly.
Noise, especially noticeable at idle, is difficult to control.
Retarding injection timing and controlled injection rates are very help-
ful in this regard. Also, by allowing some excess weight to exist at
the cylinders there is some noise control. In addition, designing for
smaller cylinders (turbo-charging, higher speed) allows less noise
radiation.
Engine costs will be higher for the diesel engine compared with
the uncontrolled gasoline engine, but this initial cost should be more
than offset by the better fuel economy and reduced maintenance that
will be provided with the diesel. The cost increase is due to extra
weight, the fuel injection system, and the turbo-charger, if used.
The injector system is reported by various manufacturers to cost
between 15 percent and 50 percent of the basic engine cost. The
injector system, therefore, poses a great challenge for cost reduction,
which is particularly difficult because of the precision parts required.
The pre-chamber diesel can lead to the use of less expensive injectors
because of the more forgiving nature of its combustion system.
: If greater changes are required for NO reduction, the cost
. ' i
could increase dramatically. One method that could be used is water
injection for flame cooling. This will require a new pump, a second
injection system, another tank, treatment of freezing, etc. However,
water is very effective as a NO control agent--a 1:1 water-to-fuel
ratio is sufficient to cut NO by over 50 percent.
-------
Diesel engines tolerate a fairly wide cut of fuel including
conventional #2 diesel fuel, kerosene, or #1 diesel fuel, and even low-
octane gasoline coul^ be used in emergencies if a little lubricating
oil or canned additive containing lubricant and cetane-improver were
added. Evaporative losses of diesel fuels to the atmosphere will be
much less than.for gasoline. The more efficient diesel engine should
be of more and more interest as our concern with fuel consumption
increases.
FUTURE ENGINES
The use of new materials, such as fiberglass for the engine
cooling fan to replace the present metal fan, may provide a real
advantage in reducing weight, increasing horsepower, reducing noise,
and improving operating economy.
The spark-assisted diesel engine is another way to permit
lowering the compression ratio and widening the range of fuels that
can be used. The advent of this method could potentially reduce
emissions. Such an engine falls between diesel engines and spark-
ignition gasoline engines. In working toward this type from the gaso-
line engine spark-ignition engine, it would be called a stratified-
charge engine. The amount of work from that end has been much more
extensive than from the diesel end, and need not be reviewed here
except to say that it could be considered as a logical alternative to
the normal spark-ignition engine. (For more information on stratified-
charge engines, see the report of the Panel on Emission Control Systems.)
The work of Austin Tool Company in Los Angeles on a small, high
speed pre-chamber engine with retard injection and recirculation was
started as an incentive contract awarded by EPA. The work has been
discontinued, despite the fact that the approach is logical and was not
being pursued vigorously by the automobile industry. An EPA incentive
contract requires that the first engine tests be carried out at the
expense of the contractor. This became impossible in that case.
- 35 -
-------
The tests conducted before Austin Tool Company had to abandon
the project were inconclusive. A number of the concepts being tried
were also considered to be important by diesel engine manufacturers
(as stated herein) if low emissions are to be reached. The engine
was to be installed in a small car adapted to Los Angeles' unique
transportation requirements as a potential solution to the Los Angeles
basin air problem. The termination of the work has delayed development
of an alternative engine that could go far toward achieving local high
air quality. Los Angeles would be an attractive limited market whose
air quality problem now requires the major engine changes to be imposed
in the future throughout the rest of the country. The same solution
could have been very valuable in New York City.
Major new technology is being offered to the diesel engine
field. There appear to be at least two possible methods of greatly
reducing the size, weight, and cost of the engine and simultaneously
achieving similar or improved emissions. These new concepts are not
proven, but first indications are that life and performance can be
achieved. The first of these alternative approaches to diesel engine
design is to use a two-stroke engine with a highly modified combustion
system. The measured emissions on the first try were below 1975
levels (6). The combustion system is new. The successful use of
such a two-stroke, low-emission engine will in one step nearly double
the power density and halve the specific weight.
The second approach is to use a Wankel configuration so that
air throughput rate can be increased and size can be reduced. Two
variations have been noted: (a) the Rolls-Royce two-staged device
(one Wankel rotor feeding a second, high-pressure Wankel rotor for
compression, and expansion taking place through the high-pressure
rotor and then through the low-pressure rotor), and (b) a turbo-charged,
single-stage Wankel configuration. The former readily achieves start-
ing, but has not demonstrated superior fuel consumption, life, or
emissions. The second one shows better emissions than the first.
The Wankel configuration in one stage has difficulty achieving
a compression ratio greater than 10 or 12. Thus, the Rolls-Royce
- 36 -
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engine should be the easiest to operate. However, the other one has
the best chance of being compact (a turbo-charger is much smaller than
the large low-pressure Wankel stage used by Rolls-Royce). Starting
may be a difficulty with a low-compression ratio turbo-charged engine.
Some of the new starting methods being pursued (Volvo, Cummins) should
help considerably.
POTENTIAL
• • ' i '
Diesel engines of low power (Daimler-Benz and Perkins) are
available now in limited production for medium-size, medium-performance
automobiles. Diesel engines, of 150 HP or more that would give low
emissions meeting the 1975 NO emission standard could be produced in
3t
limited quantities by 1976 or 1977. These would be engines having
retarded injection and EGR. They could be either naturally aspirated
engines of normal compression ratio (18 to 20) or they could be low-
t
compression ratio and turbo-charged. Two or three years later a
reasonably sized (2000 units) pilot run could be produced. Five more
years may be required before volume production could be reached. As
noted, most companies interviewed would expect to work with present
passenger-car manufacturers and/or would need assurances of support
and purchase of their engines before they move ahead to design these
passenger-car diesel engines. A general consensus was that eventually
such engines should be used in specialty vehicle applications having
a high-load factor and used mostly in urban areas, such as taxis, light
pickup and delivery trucks, and some cars.
\
Potential Availability
Diesel engines that are suitable for some vehicles and that
could lead to considerable air pollution reduction if used properly and
intensively are presently available in limited-to-medium production.
Achieving mass-production is mostly a matter of tooling and could
- 37 -
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probably be accomplished so that existing designs could be in mass-
production in 1976.
Advanced diesel engines suitable for automobiles are estimated
to be four years from a suitable prototype (assuming optimum expenditure
rate). Following the curve of Figure 1-1, this indicates mass-production
in another six to eight years.
REFERENCES
Fact-Finding Visits Made by the Panel
Perkins Chrysler
CAV Rolls-Royce
Cummins Daimler-Benz
Caterpillar Volvo
GM Detroit Diesel Ricardo
Ford McCulloch
Papers and Letters Made Available to the Panel
1. Statement of Rudolf Uhlenhaut, Director, Passenger Car Development,
Daimler-Benz, before the U.S. Senate Committee on Public Works,
March 14, 1972.
2. Springer, K. J., Emissions from a gasoline-and-diesel-powered
Mercedes 220 passenger car, Southwest Research Institute, June 1971.
... i .
3. Perkins Engines, Ltd., Presentation to the Panel, June 26, 1972.
4. Bosecker, R. E., and Webster, D. F., Precombustion chamber diesel
Engine emissions—A progress report, SAE paper 710672.
5. Cummins Engine Company, Inc., Presentation to the Panel, March 24, 1972.
- 38 -
-------
6. Dooley, J., Prepared material on high speed 2-stroke diesel engine
for the Panel.
7. Khan, I. M., Wang, C.H.T., and Langridge, B. E., Effect of air swirl
on smoke and gaseous emissions from direct-injection diesel engines,
SAE paper 720102.
8. Khan, I. M., Greeves, G., and Probert, D. M., Prediction of soot
and nitric oxide concentrations in diesel engine exhaust, Paper
C142/71, Institution of Mechanical Engineers.
9. Ford, H. S., Merrior, D. F., and Hames, R. J., Reducing hydrocarbon
and odor in diesel exhaust by fuel injector design, SAE paper
700734.
10. Hames, R. J., Merrion, D. F., and Ford, H. S., Some Effects of
fuel injection system parameters on diesel exhaust emissions,
SAE paper 710671.
11. Kahn, I. M., and Wang, C.H.T., Factors affecting emissions of
smoke and gaseous pollutants from direct injection diesel engines,
Paper C151/71, Institution of Mechanical Engineers.
12. Ricardo and Company, Exhaust emission tests on the Rolls-Royce
2-R6 Wankel diesel, D. P. 15070, April 18, 1972.
13. Dooley, J. L., McCulloch Corporation, Letter to the Panel,
March 10, 1972.
14. Kahn, I. M., and Grigg, H. C., Progress of diesel combustion re-
search, CIMAC, 9th International Congress on Combustion Engines,
1971.
- 39 -
-------
15. Russell, M. F., Improvements to conventional diesel engines to
reduce noise, Institution of Mechanical Engineers, 1970.
16. Broome, D. and Khan, I. M., The mechanisms of soot release from
combustion of hydrocarbon fuels with particular reference to the
diesel engine, Conference on Air Pollution Control in Transport
Engines, November 1971.
17. Feller, F., The 2-stage rotary engine—A new concept in diesel
power, Proceedings of the Institution of Mechanical Engineers,
1970-71, Vol. 185 13/71, pp. 139-158.
18. Millington, B. W., The small high speed diesel engine, Proceedings,
The Institute of Road Transport Engineers, July 1965.
19. Pitchford, J. H., Millington, B. W., and Howarth, M. H., What
problems still restrain the small automotive diesel engine?
1964 FISITA Conference.
20. Puttick, J. R., Recycle diesel underwater powerplants, SAE
paper 710827.
21. Torpey, P. M., Whitehead, M. J., and Wright, M., Experiments in
the control of diesel emissions, Institution of Mechanical
Engineers, C124/71, Nov. 1971.
22. Broome, D., Higher BMEP in automotive diesels, Automot. Design
Eng., March 1966. • ;
23. Walder, C. J., Some problems encountered in the design and
development of high speed diesel engines, SAE Paper 978A.
24. Reducing exhaust emissions from diesels, Autotnt. Design Eng.,.
Sept. 1971.
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3. GAS TURBINES
SUMMARY
Gas turbines are a feasible method of propulsion for standard-
size U.S. passenger cars. In prototype form, they have demonstrated
acceptable or superior weight, size, high-speed fuel consumption,
driveability, maintainability, resistance to abuse and neglect, and
safety. Carbon monoxide and hydrocarbon emissions are below the 1976
standards; NO emissions are presently above the 1976 standard, but
X
several approaches have shown that it is technically feasible to lower
NO to 1976 requirements, especially for low-pressure-ratio engines.
These concepts can probably be incorporated into a prototype by 1976.
The added controls or costs of reaching 1976 NO standards are not yet
A
known.
/ All gas turbines to date have shown poor fuel consumption at low
design power and while operating at low fractions of the design power.
Highly regenerated units tend to limit this effect, but the possibility
of economical gas turbines having a design power below 150 HP and
operating efficiently under lightly loaded conditions is still a
controversial point.
The retail costs of future gas turbines installed in automobiles
are highly uncertain. Estimates made by various highly qualified
individuals or organizations run from a price below that of the cleaned-
up spark-ignition engine to two, three, or four times higher. These
estimates depend on the use of materials similar to those used in
today's engines.
Future possibilities for gas turbines improve as the use of
ceramics for many parts is proven. If ceramics become widely avail-
able for the hot parts of gas turbines, it is generally agreed that
the engines would eventually cost less than the spark-ignition alter-
native. In addition, the employment of critical resources such as nickel
- 41 -
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would be greatly reduced.
A realistic schedule for advanced gas turbines to be produced in
quantity would be for limited production of advanced engines by 1982
and mass-production by 1984.
INTRODUCTION
Description
Gas turbines are internal-combustion engines (in their most usual
form) with air being drawn from the atmosphere and being subjected to
compression, heating in a burner, and expansion, with all these pro-
cesses occurring simultaneously and continuously in different compo-
nents. The same processes take place in spark-ignition and compression-
ignition engines, but there the processes occur successively in the
same component (one cylinder). In automobile-vehicle-size gas turbines,
air compression usually takes place in a centrifugal compressor, while
expansion can be handled by either axial- or radial-flow turbines.
This description is not rigorous, because various exceptions can
be found in existing engines and concepts. For instance, in some
large gas turbines gases other than air (such as hydrogen and carbon
dioxide) are used, in which case the exhaust from the turbine is
cooled and returned to the compressor. Such a machine is termed a
"closed-cycle" gas turbine. They have been used for large stationary
plants where cooling water is available and where the heat source is
coal or a nuclear reactor (1). Closed-cycle gas turbines have been
proposed for automobiles (2) but do not seem attractive because of
the need for both a gas cooler and a gas heater, and because the
turbine-inlet temperature must thereby be limited. A high turbine
temperature is necessary if a reasonably high efficiency is to be
obtained.
The description given above of a so-called "simple-cycle" gas
turbine must also be modified to take account of the more usually
- 42 -
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encountered variations. A gas turbine may contain a heat exchanger in
which the compressed air is heated by the hot exhaust gas. It may
contain just one rotating shaft connecting the turbine with the com-
pressor (and with the output shaft), or the turbine expansion may
take place in two or more turbines, with at least one turbine stage
driving a separate output shaft. This is called a "two-shaft" gas
turb ine.
There may also be two separately driven stages of compression,
with,or without a separate power turbine for the output shaft. This
arrangement is known as a "two-spool" gas turbine, and was the form
under development at the Ford Motor Company in the 1950's (3). It is
now considered to be too complex and expensive for use in automobile
gas turbines.
The four principal types of gas turbine being generally considered
for automobiles are, then, the single- and two-shaft varieties with
and without heat exchange. These are shown in schematic form in
Figure 3-1, along with a closed-cycle version of the single shaft
engine. Thermodynamic requirements dictate that, for reasonable
I
efficiency, the cycles without heat exchange have high pressure ratios
(from 10 to 20) and low air mass flows, while the heat exchange cycles
use low-pressure ratios (4 to 6) and higher mass flows.
The single-shaft engines have only a limited range of shaft speeds
from full to zero power, and, therefore, require a sophisticated (and
as-yet unavailable) transmission. The two-shaft gas turbines can
deliver torque from zero to full speed and a simple transmission is
i
possible, although prototype cars have generally been fitted with a
standard three-speed automatic transmission incorporating hydraulic
couplings (4).
- 43 -
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Combustor
FueN
Air_
in
N
V
Compressor
Turbine
Single Shaft-Simple Cycle
>* To infinitely variable
transmission
Exhaust
Turbine
Single Shaft-Heat Recovery Cycle
Regenerator or recuperator
Exhaust
5 To infinitely variable
transmission
Combustor
in
Air
in ""**
N
)
H
A
\
<
A
\
l
fc-^ CUU«.
Compressor 2-Turbines
Two Shaft-Simple Cycle
- 44 -
To transmission
-------
Air,
in
\
Regenerator
or
Recuperator
Exhaust
" Fuel
V
Compressor
Combustor
To transmission.
2-Turbines
Two Shaft-Heat Recovery Cycle
Power control
Heater Combustor
Exhaust
Turbine
dor 2)
Air coolant
Closed-Heat Recovery Cycle (Single-shaft version shown)
To transmission
FIGURE 3-1 Gas turbine configurations for automobiles.
- 45 -
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CHARACTERISTICS
Simplicity
Basically, the gas turbine is simple. It may contain only one
moving part—the rotor—which turns steadily with near-perfeet balance.
There is, therefore, little to go wrong once a machine has been
developed, and many industrial gas turbines have run for over 100,000
hours with 98 percent or better availability (5).
However, the rotor may consist of two or more very complex, precise,
and expensive castings, and the stator may likewise be built from a
large number of precision-made parts.
Large Power-Weight .Ratio
Aircraft gas turbines are capable of producing several equivalent
horsepowers per pound of engine weight. This advantage over other
prime movers, decreases as the engine design power is reduced, but gas
turbines of automotive size are still lighter than standard-automobile
spark-ignition engines of equivalent power.
Acceptable Volume
Gas turbines in large sizes can be far smaller than any competitive
prime mover, but in automobile applications the space required by the
heat exchangers (which are normally used) causes the overall.volume to
be equivalent to that of a gasoline engine with accessories. The
alternative high-pressure-ratio nonregenerative gas turbine can be
considerably smaller than the corresponding-power spark-ignition
engine.
Emissions
In its bare form,gas turbine emissions are much lower than those
- 46 -
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of the bare spark-ignition engine, giving negligible hydrocarbons and
carbon monoxide. The nitrogen oxides are far less than those of the
spark-ignition engine, though they are not negligible. To meet the
1976 standards, the NO emissions must be reduced to about 20 percent
x
of present levels. A most important feature of gas turbine emissions
is that the design or production level is likely to be maintained
without degradation throughout the life of the engine. The engine
will give maximum performance when the emissions are at their design
or minimum level, and thus there is no incentive for the operator to
tamper with emission control characteristics.
Cost
Costs of mass-produced goods can be judged only by adding a small
factor to the basic raw-material costs (and even here the effects of
mass production on the raw-material costs have to be estimated. A few
years ago, according to George Huebner, then chief engineer of Chrysler
Corporation, the raw materials alone had cost $8.00 per horsepower in
the Chrysler turbine that was put into 50 passenger cars and loaned out
for trial (6). He compared this with $2.00 per horsepower for the
total production costs of spark-ignition engines.
Since then, many organizations have made their own estimates or
have been commissioned to do so by the EPA. Most have arrived at far
lower estimates. The most detailed published estimates were made for
the EPA by Williams Research Corporation, an experienced manufacturer
of small gas turbines (7). Its conclusions were that in quantity pro-
duction, the gas turbine could have a production cost slightly lower
than that of the gasoline engine, but current engines would be 20 per-
cent more expensive.
These estimates were made assuming that current materials (including
up to 20 pounds of hot parts using high proportions of nickel, chromium,
and cobalt) would be used. There are presently under way programs of
vigorous research into the use of ceramics for all stationary hot parts
and, as a longer-term aim, for rotating parts (8). The successful
- 47 -
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development of ceramic components would Immediately bring the gas tur-
bine engine into the prospect of having a substantially lower production
cost than any competitors and of making a minimum impact, on the country's
scarce resources of alloying materials.
Fuel Consumption
The Chrysler gas turbines referred to above achieved fuel con-
sumptions better than the gasoline engines they replaced in all con-
ditions of driving except when a substantial amount of idling in
traffic was involved (9). It is to be expected that the next generation
of gas turbine engines will be somewhat improved, while the fuel
consumption of spark-ignition engines will worsen. If ceramic turbines
were developed, a substantial rise in turbine-inlet temperature would
be possible, leading to a sharp reduction in fuel consumption.
(Specific fuel consumption decreases by about 10 percent for each
100 F increase in turbine-inlet temperature.)
Driveability
The driving characteristics of present gas turbines, typified by
the Chrysler Corporation turbine presently fitted in a Dodge chassis,
are virtually indistinguishable from a standard spark-ignition engine
with an automatic transmission. In earlier turbines, acceleration
delay (caused by the need to accelerate the compressor and compressor-
turbine shaft before an increase in torque would be experienced by
the power turbine) and lack of engine braking caused minor problems
in adjusting to driving a turbine car. The use of variable-angle
power-turbine nozzles has almost eliminated these problems. There
are other developments aimed at removing the last traces of hesitation.
As to starting ability, gas turbines are far more certain than
existing gasoline engines in cold weather. With further emission
controls, gasoline engines seem likely to become more temperamental
on starting, so that certainty of starting may eventually be its most
- 48 -
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important aspect.
The starting time of the engines will be somewhat longer, 10 to 15
seconds, as against a second or two for present spark-ignition engines,
but is small enough to be acceptable.
Ability To Withstand Abuse and Neglect
Once developed ("debugged"), gas turbines require little maintenance.
Gas turbines in airline service are now running many thousands of hours
between overhauls. A substantial degree of abuse can usually be
tolerated. For instance, the Rover gas turbine, which has placed high
in the 24-hour Le Mans race, completed the last five or six hours with
a bolt about 1% inches long embedded in the heat-exchanger matrix (10),
However, the same bolt introduced into the air intake downstream of
the air filter at full-speed conditions would almost certainly-"wipe
out" the engine.
The oil does not have to be changed in gas turbines, and if the
fuel filter needs changing it will merely cause a reduction in power
rather than an increase in wear. It is anticipated that routine
service will be done by mechanics trained to present levels. Major
maintenance may require more thoroughly trained mechanics.
If future turbines use ceramic components there will probably be
a simultaneous reduction in the need for maintenance and a reduction
in the ability of turbines to withstand abuse.
Safety
The gas turbine is an extremely safe propulsion unit for two
principal reasons: The exhaust is nontoxic, and the fuel is less
liable than gasoline to explode or burst into flame during collisions.
Although the engine may contain parts rotating at 100,000 RPM, with
peripheral velocities of 1800 ft per sec, the casing* are normally
designed to contain the parts even if they should "run away" and
burst at overspeed.
- 49 -
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The casing of a gas turbine is normally of sheet metal or cast
aluminum, or of other construction that will contribute substantially
to the energy absorption through crushing which might occur on a frontal
collision.
Noise
While a jet engine is extremely noisy, a small gas turbine with
an intake filter and muffler and a regenerative heat exchanger in the
exhaust can be as quiet as the equivalent spark-ignition engine and
can be more quiet over some frequencies. The present Chrysler turbine
in a Dodge chassis confirms this. As a gas turbine uses no muffler as
such, and as the ducting has to be constructed of corrosion-resistant
materials, the noise level is unlikely to suffer degradation during its
life — in other words, show-room noise levels should be maintained*
This would be a substantial improvement over present-day automobiles.
State of the Art
Gas turbines have been fitted in passenger automobiles since
1950 (Rover in Britain, 11). Confidence in their characteristics
reached the point that Chrysler Corporation loaned 50 turbine-powered
cars to about 250 of the general public for personal use during the
I9601si Further developments in engines and in matching them to
vehicles has continued at Chrysler since that time, though at a
slower pace. General Motors and Ford have also had substantial gas-
turbine programs formerly aimed principally at trucks, though now
with substantial automobile activity. Williams Research Corporation
has .fitted gas turbines to prototype cars for problem evaluation.
Overseas, Rover has made several prototype cars and has allowed its
engines to be used for racing.as a development effort. Most other
large automobile manufacturers have had gas turbine programs ranging
from keeping abreast of developments to running component and proto-
type tests.
- 50 -
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Early gas turbines were heavy consumers of fuel. Improvement
in component efficiencies (to which the gas turbine is very sensitive)
and, most important, the development of the ceramic-matrix rotary heat
exchanger, has made full-power fuel consumption better than that of
the present spark-ignition engine. The part-load fuel consumption
presently matches that of the gasoline engine at about half powers
and is worse at lower powers.
These remarks apply to low-pressure-ratio, heat-exchanger
engines. This type of engine has the virtue that the heat exchanger
improves in thermal ratio (effectiveness) at reduced flows. While
the efficiencies of the compressor and turbine(s) suffer a loss in
efficiency at low loads, though severe, it is not catastrophic to fuel
economy.
i
The principal single-shaft alternative of the gas turbine type
of engine uses a high pressure ratio and no heat exchanger. It can
give good full-load specific fuel consumption. However, the part-load,
part-speed performance of high-pressure-ratio compressors is very poor,
and essentially rules this engine out of consideration for automobiles
in this form.
Some manufacturers have proposed getting around this part-load
problem by running a high-pressure-ratio engine at full speed in a
closed cycle, and by varying power level through varying the mean-
pressure level while maintaining shaft speed and all temperature levels,
Such an approach, while giving a nearly constant design-point fuel
consumption over most of the load range, requires a gas heater (which
lowers the potential turbine-inlet temperature and therefore increases
the fuel consumption); a gas cooler, which will be several times
larger than the conventional radiator; and an infinitely variable
transmission. The manufacturing costs of this complex arrangement
make it unattractive, in the panel's opinion.
- 51 -
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STATE OF THE ART OF COMPONENTS
Compressors
Although there have been a few proposals to use axial-flow
compressors, all known automobile gas turbine developments have been
based on single- or two-stage centrifugal compressors. The peak
efficiency of this type of compressor (the total-to-static polytropic
efficiency from inlet to outlet) could probably be 86 percent for
pressure ratios up to 5 to 1. Some present compressors seem to have
reached to within one or at most two points of that figure (12).
(There are, however, some compressors with much poorer performance.)
Further development of peak efficiency of these better compressors
cannot, therefore, yield large returns. It is probable that larger
overall gains are still to be had by improvement of the part-speed
efficiencies. Axial compressors would have efficiencies two to three
points higher, but would be expensive and fragile.
There have been some programs aimed at producing pressure
ratios of 10 to 1 and higher in a single centrifugal stage. Such
developments are unlikely to be of value to automobile gas turbines
for the reasons previously given.
Heat Exchangers '
A gas turbine heat exchanger adds considerably to the bulk of
the unit. A heat exchanger normally becomes smaller (for the same
performance) as the passage size is reduced—but the cost and the
tendency to fouling both increase if fixed-surface heat exchangers
are used. The flow losses become smaller as the mean through
velocity is reduced, which entails a large "face" area, again not an
advantageous condition, in general, for fixed-surface heat exchangers.
However, the rotating-matrix heat exchanger (or "regenerator")
satisfies all these desiderata and has become predominant for
automobile gas turbines.
-- 52 -
-------
Formerly these rotating matrices were made of coiled stainless-
steel strips, alternately plain and corrugated (Chrysler, General
Motors). Corning has developed a glass-ceramic material called Cercor
which has not only greatly reduced the material costs (and nickel-
chromium requirements), but has almost eliminated thermal growth and
the sealing problems it entails. Although all the problems with ceramic
heat-exchanger materials and with sealing have not been entirely solved,
there appears to be no insurmountable problem. Several other
manufacturers are now working in the area.•
Regenerators have been built with design-point thermal ratios
or effectiveness (the actual heat transferred as a proportion of the
maximum available heat transfer) of 90 percent and leakage flows of
about 2 percent. Some contractors are using lower values of the
thermal ratio, 75 and even 60 percent (14) in their predictions, but
it is the panel's view that these low .figures do not reflect an
accurate benefit-cost optimization for society. The thermal effective-
ness has a strong effect on the thermal efficiency at all power
levels (Figure 3-2), thermal effectivenss increasing as the power
level is reduced, and an engine with a fuel consumption little better
than those of present-day automobiles is not the best solution for
the future when energy becomes more dear. The impending shortage of
energy, especially in petroleum products, will require improvements in
fuel consumption, and, as it has been demonstrated that there is room
for a heat exchanger of 90 percent thermal ratio within the engine
compartment of standard automobiles at a comparatively small increase
in cost, we believe that 90 percent should be regarded as a reasonable
norm.
Leakage also has a strong effect on cycle efficiency. Regene-
rator leakage consists of carryover loss of gases trapped within the
matrix, and seal leakage. Some manufacturers have encountered dif-
ficulties producing seals that maintain low leakage levels. There
seem to be reasons to be confident that present difficulties, where
they are encountered, are of a developmental rather than of a
fundamental nature and that they will be resolved.
- 53 -
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20
15
03
O>
O>
a
*
1
c
g
'^
a.
§
o
o
"55
u.
« 10
o
6>
2
a>
"8
Pressure Ratio 4.6
PR 6.7
PR 6.7
I
I
I
60 70 80
Regenerator Effectiveness (Percent)
90
100
FIGURE 3-2 Effect of regenerator thermal effectiveness on
fuel consumption (Data from Garrett report to EPA (14), June
1972; 175 hp. engine). .
- 54 -
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Burners
With regard to the simple combustion of the fuel, automobile
gas turbine burners have negligible problems compared with those for
high-altitude aircraft operating in a wide range of conditions. Burners
and hot ducts presently use high-temperature materials and ares
therefore, expensive, but there seems to be an excellent chance that
future burners will be constructed of ceramics. Present burners pro-
duce very low levels of carbon monoxide and of hydrocarbons. The
nitrogen oxide emissions, however, are about 2 g per mile on the federal.
driving cycle--five times the 1976 limit.
To produce acceptably low NO , the present form of primary-
X
zone stoichiometric burning must be abandoned (13). A large number
of alternative approaches are being proposed and followed for the
reduction of NO (14). They can be classified into two categories:
x
The principal approach is to burn at low equivalence ratios, and a second
approach is to extract heat from the flame at the point of formation.
Burners with NO emissions that apparently meet the 1976
X
limits have been tested in the laboratory (15). Other approaches are
in the early stages but can be considered to have the potential of
meeting the requirements (14. 16). There seems reason to be confident
that engine tests will demonstrate successful low-emission burners by
1975. Some of these burners will probably include the complication
of variable geometry, requiring a control-system input with its
attendant additional costs, and liability to malfunction and inter-
ference.
Turbines
In single-shaft low-pressure-ratio machines, single-stage
radial turbines may be used. A radial turbine may also be used as
the second stage in a multi-state unit—for instance, as the power
turbine in a two-shaft machine. Axial-flow turbines have generally
been preferred, having slightly higher efficiencies in general
- 55 -
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(perhaps 88 percent versus 86 percent and lower rotating Inertia).
The efficiency of radial turbines is likely to be increased with
improvement of the turbine diffuser (17). The aerodynamic design of
turbines of the comparatively low loading demanded for automobile
engines is well established, and design efforts are concentrated
toward achieving cost reductions principally through material selection;
higher-temperature capability, again principally through material
development and through cooling of the turbine blades; and variable-
angle nozzle development for lower cost and greater reliability.
Turbine-inlet temperatures for uncooled automotive turbines
are presently in the range of 1650°F to 1850°F. Increases in
turbine-inlet temperature bring about considerable gains in specific
fuel consumption or overall cycle efficiency. Commercial aircraft
are using 1900°F for take-off conditions and military aircraft 2200°F,
both with blade cooling. The small blades required for automotive use
do not favor blade cooling of the present convective patterns.
Transpiration-cooled blades are running in test engines at'3000 F and
higher but, again, are large blades suitable for aircraft and industrial
engines (18).
The most promising developments under way for automotive gas
turbines are in ceramic turbine components, which would simultaneously
allow turbine-inlet temperatures of 2500°F or higher to be used with-
out the need of penalizing cooling air, and would permit almost the
entire engine to be made of low-cost, readily available materials
(25c per pound versus $6.00 to $9.00 per pound for metals). There
seems to be an excellent chance that the static parts of experimental
gas turbines will be successfully tested by 1974, and perhaps turbine
rotors by 1978.
Control Systems
As gas-turbine engines are made smaller, the control systems
tend to remain the same size. Eventually, in the case of small air-
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craft engines, they become almost as prominent as the engine itself.
Automobile gas turbines require a different control system from aircraft
engines, and there is a need for development engineering and cost
reduction. There has been little effort in the use of, for instance,
integrated circuits or of fluidics in small-gas-turbine control
systems, either of which might permit a substantial degree of size
reduction and cost cutting in large-scale production. Work on improved
control systems is now under way, and there appear to be no fundamental
reasons impeding the development of control systems of acceptable cost
and sophistication. EPA is funding programs with these aims.
Transmissions
More development is needed on transmissions tailored to gas
turbines. The EPA has two contracts in this area (14). Early applica-
tions of gas turbines used transmissions without gear-shifting capabil-
ities. As two-shaft gas turbines develop double full-load torque when
stationary, early prototype automobiles were able to operate success-
fully. However, later prototypes were generally fitted with standard
automobile three-speed automatic transmissions. These usually include a
hydraulic coupling, which involves considerable power losses and is
hardly necessary since the power turbine of a two-shaft gas turbine is
itself a form of pneumatic coupling. Improvements in performance and
costs can, therefore, be expected when transmissions are developed to
suit the characteristics of gas turbines.
The single-shaft gas turbines proposed at present (14) have
special transmission needs. No output is developed below about 70
percent speed. Some form of closely controlled speed ratio or infinite-
variable transmission will therefore be needed. Automobiles have been
offered with infinitely variable transmissions from time to time, and the
Dutch DAF is presently made with an infinitely variable belt drive as
standard. This is a small car of about 2000 pounds and is powered by an
engine of about 70 HP. At the other extreme of vehicle weight and power,
some earth-moving equipment uses hydrostatic infinitely variable trans-
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missions. The proponents of the use of single-shaft gas turbines have
claimed that the elimination of a separate power turbine and its bearings
will result in a substantial cost saving, while an infinitely variable
transmission can be developed which will cost no more, and perhaps less,
than existing automobile automatic transmissions. Such claims have been
met witli some skepticism, but they are not beyond possibility.
Problems
Inasmuch as gas turbines have been successfully fitted to
vehicles that were put into the hands of selected recipients from
the general public and received enthusiastically, there are no basic
problems in fitting this prime mover to the standard family automobile.
However, the problems previously mentioned have to be overcome before
gas turbine automobiles could be sold on a widespread competitive
basis.
NO Emissions
x
Present emissions contain a proportion of nitrogen oxides
higher than those called for by the 1976 standards, although 1975
standards can be met easily. There seem to be excellent possibilities
of meeting these standards in prototype engines before 1976.
First Cost
While estimates of the manufacturing costs of gas turbine
engines in mass-production differ widely, it is the panel's view
that they are likely to be initially at least 50 percent higher than
equivalent spark-ignition engines with required emission controls.
The development of ceramic components would give the potential of
costs well below those of present gasoline engines.
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Fuel Consumption
The part-load fuel consumption of gas turbines is poor, with
the exception of closed-cycle machines. Higher turbine-inlet tempera-
tures through the use of ceramic components would alleviate this
problem considerably. Were traffic-control systems introduced to
reduce traffic stalls and crawls, gas-turbine fuel consumption would
be substantially better than that of spark-ignition engines.
Critical Materials
With present materials of construction, some estimates of the
use of nickel, chromium, and cobalt for a production of 1 million
engines per year are that the cobalt required would be 156 percent and
the nickel 38 percent of current U.S. consumption (19). This is based
on 2.02 Ib of cobalt and 12.2 Ib of nickel per engine. Other estimates
(14) were that nickel consumption would increase by only 27 percent
and cobalt by 8 percent. So wide a diversity of views reflects
current variations in design approaches.
While it is certain that gas turbines will be capable of far
longer lifetimes than present automobile engines and that a large
proportion of the critical materials--of whatever level is used--
will be available for recycling, it is obviously undesirable for so
large a proportion of the country's (and the world's) resources to be
so used.
Again, the development of ceramic hot-part materials would be
a complete solution to this problem.
Design Power Limitations
Gas turbines can be made to be more efficient the larger the
power output. The present studies have been made for standard family
U.S. automobiles. If it becomes desirable for purposes of energy con-
servation to encourage the use of smaller cars, requiring perhaps
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60 HP, the specific fuel consumption of gas turbines is likely to be
considerably worse than present designs. (The actual fuel consumption
per mile will, of course, be lower.) While gas turbines will probably
become highly acceptable for use on trucks and buses, and will be a
strong contender for the larger automobiles, they may not be the best
choice for smaller vehicles.
Expectations for the Future
Within this decade the automobile gas turbine of over 150 HP
has a good probability of substantially matching or bettering the
spark-ignition engine in first cost, running costs, emissions,
reliability, driveability, and maintenance. Gas turbines may be
competitive at power levels as low as 80 HP. Engines with these
desirable characteristics could commence mass-production on a pilot
basis (50,000 per year) in 1982 or 1983, with a level of one million
per year being reached by 1985. Ceramic-based gas turbines would use
fewer critical materials than any competing power unit.
POTENTIAL AVAILABILITY
The gas turbine in its favorite automotive form has been put
through concept feasibility at the Chrysler Corporation. It has since
retreated back to research and development and an occassional single-
unit demonstration.
The advanced gas turbines, whose R&D has been concentrating
more on achieving lower cost and emissions, are estimated to be about
four years away from a suitable prototype with optimum funding. An
additional 7 to 10 years of optimum effort would then be required to
bring them to mass production.
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REFERENCES
Discussions
Chrysler
Ford
General Motors
Williams Research
AiResearch
Daimler-Benz
British Leyland Motor Co.
Noel Penney Turbines
Turbokonsult
The Zwick Co. (Combustion)
Thermo-Mechanical Systems
(Air cycles)
Visits and Papers Made Available to the Panel
1. Keller, C., The origin and development of the closed-cycle gas-
turbine system, Escher Wyss News, vol. 39, no. 1, 1966.
2. AiResearch presentation to the Panel.
3. Keller, C., Development of the Ford 704 gas turbine engine,
SAE paper 291A.
4. Kronegard, S. 0., and Rosen, C.G.A., Matching gas turbine pro-
pulsion systems to vehicles, SAE paper 680539.
5. Garner, P. B., Total energy, in Gas Turbine Engineering Handbook,
pp. 255-270.
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6. Huebner, G. J., Unpublished address to the MIT student ASME,
1968.
7. Williams Research presentation at June 1972 EPA-OAP Contractors'
Coordinating Meeting.
8. Norton and Owens-Illinois presentation, EPA-CAP, Contractor's
Coordinating Meeting, June 1972.
9. Huebner, G. J., Jr., The Chrysler Gas Turbine Story.
10. Phillips, P. A., and Spear, P., The Chrysler gas. turbine story,
Proceedings, Institute of Mechanical Engineers, vol. 170, part 2A,
no. 9, 1965.
11. Penney, N., Rover case history of small gas turbines, SAE paper
no. 634A.
12. Dallenback, F., The aerodynamic design and performance of
centrifugal and mixed flow compressors, Vol. Technical Progress
Series, SAE, 1961.
13. Mikus, T., and Heywood, J. B., The automotive gas turbine and
nitric-oxide emissions, Department Mechanical Engineering, MIT,
1972. (To be published in Combustion Sci. and Technol.)
14. EPA Contractors Coordinating Meetings: September 1971,
February 1972, June 1972.
15. Zwlck, E. B., presentation to the Panel.
16. Ford, Presentation to the Panel.
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17. Drum, N. J., Investigation of turbulent bpundary layers in an
axial-to-radial diffuser, MS thesis, MIT, June 1971.
18. Moskowitz, S. L., and Lombards, S., 2750 Degree F engine test of
a transpiration air-cooled turbine, Trans. ASME J. for Power,
April 1971.
19. Thermomechanical Systems, Presentation to the Panel.
' ' ' . '
20. Cadwell, R. G., Chapman, W. I., and Walch, H. C., The Ford turbine
--An engine designed to compete with the diesel, SAE paper
720168.
21. Wright, E. S., Davison, W. R., and Greenwald, L. E., A feasibility
analysis of a simple cycle gas turbine engine for automobiles,
SAE paper 720238.
22. Cornelius, W., and Wade, W. R., The formation and control of
nitric oxide in a regenerative gas turbine burner, SAE paper
700708.
23. Amann, C. A., Wade, W. R., and Yu, M. K., Some factors affecting
gas turbine passenger car emissions, GMR-1120.
24. Wade, W. R., and Cornelius, W., Emission characteristics of
continuous combustion systems of vehiclular powerplants—Gas
turbine, steam, Stirling, GMR 1135, 1971.
25. Noel Penney Turbines, Marketing report made available to the
Panel.
26. EPA-OAP Contractors Coordinating Meeting, 2nd and 3rd Summary
Report, including handouts of AiResearch, United Aircraft,
Williams Research, and General Electric.
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Comparative Summary of Advanced Gas Turbine Optimization Studies.
Gas Turbine Combustion program handouts by Solar, AiResearch,
General Electric, Mechanical Technology, Inc., United Aircraft,
Northern Research, and Williams Research.
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4. ELECTRICALLY DRIVEN VEHICLES
SUMMARY
Electrically driven vehicles, in principle, provide freedom from
pollution and have high energy efficiency, flexibility of performance,
durability, and low maintenance costs. The limiting factor relating
to the technical and economic feasibility of electric vehicles is the
vehicular power source. Electric drive systems having excellent charac-
teristics have been demonstrated; development of optimal electric drive
systems is not considered to be limiting in the ultimate realization
of electric automobiles.
Fuel-cell powered electric vehicles in which the free energy of
fossil fuels is directly converted into electrical energy for motive
power do not emit CO or NO ; unused hydrocarbons can be easily removed
j£,
from the exhaust. Fuel cell systems which contain a reformer (which
produces a hydrogen-rich fuel stream) are also capable of very low
HC, CO, and NO emission.
2t
Fuel cells are not heat engines and are not subject to the
Carnot efficiency limitation. For this reason they may operate at
high energy conversion efficiency, resulting in superior fuel economy.
Fuel consumption rates one half those of present-day automobiles may be
expected.
Although some fuel-cell systems have been successfully deployed
in space missions, these are not adaptable for applications requiring
low cost. Current advanced developments directed toward stationary
'applications in commercial and consumer markets are in the field-test
stage. These represent important cost reductions and performance im-
provements relative to the aerospace units. With further significant
cost and performance improvements, vehicular applications in small
quantities may become feasible within 10 to 15 years.
Vehicles employing rechargeable batteries as power sources do not
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have emissions resulting from the combustion of fuels by the vehicles.
The site of emissions is transferred to central power stations where
such emissions are understood to be more effectively controlled and at
a lower cost. Because of the high efficiency of batteries and of
electric drives, the net fuel economy of such vehicles promises to be
better than that of present-day automobiles. Furthermore, if we move
toward an electric economy, batteries may assume a unique role in the
transportation system.
In contrast to fuel cells, there has been extensive experience in
the performance characteristics of at least one battery system: lead-
acid. This battery is rugged, efficient, reliable, and can respond
instantaneously to large changes in load. Presently available
special-purpose vehicles powered by lead-acid batteries can provide
ranges of up to 50 miles and modest acceleration, marginally acceptable
under urban driving conditions, at a high cost. Other currently
available rechargeable batteries such as zinc/silver-oxide and cadmium/
nickel-oxide, while superior in selected respects to the lead-acid
system, are inherently unsuitable for vehicular applications because of
cost and/or materials availability limitations. Still other battery
systems currently in various stages of development offer significant
performance improvements, and may meet the cost and materials avail-
ability criteria necessary for vehicular applications. The zinc/nickel-
oxide battery is expected to allow a vehicle Design with acceptable
acceleration and a range of about 80 miles between recharges.
The most promising of the advanced battery systems are sodium/
sulfur and lithium/sulfur batteries, which operate at temperatures in
the range 300-400°C and are maintained at operating temperature by
their reject heat and appropriate thermal insulation. These batteries
are expected to have specific energies of 100 w-hr/lb and specific
powers of 100-200 w/lb, permitting the design and construction of
electric vehicles with excellent acceleration capabilities and a range
of about 200 miles between recharges. Single prototype vehicles are
now in various stages of preparation. About seven to eight years of
optimum effort will probably be required for the development of pilot
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quantities of these batteries for more extensive vehicle test purposes.
Still other promising battery systems are in early stages of exploration.
Hybrid electric-heat engine power plants are claimed to enable
reduction of the emission of air pollutants. The expected improvement
in driveability by using the electrical part of the system for power
surges should allow the heat engine to operate cleanly and economically
at one setting or with a slowly varying setting over a range. There
are significant penalties in the areas of cost and complexity that must
be overcome before the hybrid can be considered to be a viable contender.
Even if the technical and economic criteria can be met, it is doubtful
if introduction of this new and relatively complex power-plant scheme
will represent any more than an interim solution in respect to pollution
abatement and effective use of natural resources.
INTRODUCTION
The incentive for using electrically powered vehicles is based on
three fundamental considerations:
1. The vehicle itself is either nonpolluting (in the case of a
battery power source) or (in the case of a fuel-cell power source) the
•-V
levels of noxious gases (HC, CO, NO ) are well below the 1976 limits
X
set by the Clean Air Act.
2. Because of the inherent high efficiency of batteries, not
only is the site of pollution transferred from the vehicle to the
central power plant, but the total use of fossil fuels, and therefore
the total pollution, is significantly reduced relative to that using
the 1C engine. The use of fuel cells for vehicle propulsion also
reduces the demand for fossil fuels.
3. Since battery driven vehicles can be expected to be charged
largely during time periods when off-peak power is readily available,
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a higher utilization of power-plant investments (a higher load factor)
and therefore reduced energy costs for the overall system would result
X
if electric cars were to be introduced in significant numbers. As
nuclear power generation assumes an increasing importance in the total
energy generation spectrum, the use of off-peak capacity for recharging
the batteries of electric vehicles would offer an even more significant
advantage in respect to efficient use of plant investment, as well as
a reduction of operating costs.
Electric automobiles of marginal performance were made in the
tens of thousands around the turn of the century. At present their use
is restricted to special vehicles numbering in the hundreds of thousands
(golf carts, fork lift trucks, and urban delivery vans and light
trucks). Electric vehicles available today do not have the range and
acceleration capability even approaching the smallest gasoline driven
car (1).
The central problem as it has been evident all along, is the
lack of availability of batteries with sufficiently high specific
energy (w-hr/lb) and specific power (w/lb) capability. Several cur-
rently available battery types are characterized by high energy-
conversion efficiency and reliability, although at moderately high
to very high cost, for application as a motive power source. The
improvements needed are in the range of a 5- to 10-fold increase in
specific energy, while retaining (and even improving by 50-100 percent)
the specific power capability. In addition, before broad applications
in the personal vehicle area become possible, the cost per unit of
energy storage capability ($/kw-hr) has to be lowered by a factor of
2 to 3 compared with the least expensive system available today--the
lead-acid battery. As already demonstrated in various experimental
vehicle programs, the development of the electric drive (motor and
control gear) that would provide desired vehicle performance and dri-
veability does not appear to be a limiting factor in the technological
and economic feasibility of the electric automobile (2, 3). On the
basis of what we know today and given sufficient time for further
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development, there are no reasons why the motor and control gear could
not be mass produced at moderate costs, perhaps somewhat below that of
the present engine, transmission, and associated gear. Although the
complete cost of the power plant, including batteries (or fuel cells)
promises to be above that of the present power train and gasoline tank,
this difference ultimately may not be very significant compared with
a cleaned up (or clean) fossil-fuel driven internal or external com-
bustion engine. The increased initial cost should in part be offset
by lower energy and maintenance costs.
Much concern has been expressed about the demand electrically
driven vehicles would place on the present or currently-anticipated
central power generation capacity and on the power distribution net-
work. Considering the installed power generation capacity in the
United States at the end of 1971, 367 x 10° kw, and the average power
actually used, 200 x 10 kw, the difference between the two would have
sufficed to provide the total energy actually used by every vehicle
driven today in the country (4, 5).
However impressive the above comparison may be, it is by no
means suggested that such a high proportion of the total electric
energy generated would ever be required for electric cars. Penetration
of electric vehicles into the U.S. transportation scheme can occur only
very gradually, for reasons which are completely divorced from the
availability of power. Even in the late 1980's only a small fraction
of all vehicles is likely to be powered electrically. This level of
penetration will represent an Insignificant percentage demand on the
total generating capacity as it already exists, not even considering
the planned expansion by 1980-1990. Considering the estimated energy
demand (without electric cars) of 10*3 kwh for the year 2000 (2), an all-
electric family car population of 180 million, driven 43.4 km every
day, would add less than 15 percent to the anticipated demand (1).
Insofar as the possible need for a greatly expanded distribution
network is concerned, it should be noted that for a completely dis-
charged battery of a family car driven 200 miles, a household circuit
would only have to provide on the order of 10 kw for 12 hours. This
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type of load can at present be handled by many households in off-peak
periods. Future household circuits will be able to handle, for reasons
other than the electric car, the usually much lower average demands for
battery charging.
The average cost of electricity, even taking into account the
cost of any possible expansion of the distribution network, should be
favorably affected by power demands created by electric cars.
ALL-ELECTRIC VEHICLES
Battery-Powered Vehicles
x In principle, battery-powered electric vehicles provide an
attractive alternative to conventional vehicles powered by spark-
ignition engines. Batteries can be pollution-free and provide effi-
cient, silent, responsive power. The use of electrically rechargeable
batteries shifts the source of pollution away from the densely-populated
areas to the power-generating stations, where emissions can be effec-
tively and economically controlled.
In the past, many battery-powered vehicles have been used and
are still in use, but their acceleration and range (miles between re-
charges) are far lower than those of similar spark-ignition engine
vehicles. The problem has been that batteries having sufficient energy
storage capability (expressed as specific energy, w-hr/lb), power de-
livery capability (expressed as specific power, w/lb), and lifetime
have not been available at any cost. Experience with special-purpose
and demonstration battery-powered vehicles has shown that efficient,
flexible, and powerful electric motor and controller systems can be.con-
structed and operated in electric automobiles using presently available
technology (2,3,6,7). The costs of the electric drive systems (minus
battery) appear to be capable of being reduced to acceptable levels.
A battery-powered automobile capable of performing according to
existing urban and suburban driving profiles, with a range of at least
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200 miles under these conditions and a battery weight 25 percent of the
total automobile weight, requires a battery with a specific energy of
100 w-hr/lb and specific power of at least 70 w/lb (8). Batteries of
lower specific energy provide shorter ranges, and those with lower specif-
ic power provide lower acceleration capability.
Figure 4-1 shows a plot of the specific power versus specific
energy capabilities of various batteries (9). The curves for batteries
that are now commercially available (see Table 4-1) show that these
batteries are not capable of providing the specific power and specific
1 . I
energy required for a high-performance with a range of 200 miles. But
vehicles of more modest performance, such as urban delivery vans and
urban buses, can be contemplated, although at an Increased investment
cost (see Table 4-1, and compare to a goal of about $10/kw-hr to be
competitive with spark-ignition engine vehicles).
The lead-acid (Pb/PbO?) battery represents a well-developed
technology and is unlikely to undergo significant, rapid Improvements
in cost or performance. Vehicles (both passenger and commercial) of
*
marginal performance for urban use (50 miles range, 50 MPH ) are now
available in limited quantities from at least ten manufacturers. There
are now tens of thousands of industrial vehicles of this type and about
200,000 lead-acid battery-driven golf carts in the United States (1).
A large variety of electric Industrial and consumer vehicles are
available in England and Japan (1). In the United States, orders are
being placed this year for hundreds of lead-acid battery-driven pass-
enger vehicles (1).
In terms of acceleration and cycle life the Cd/NiJ) battery
offers increased performance (see Table 4-1) but at a very high price,
making this approach impractical. Battery manufacturers do not forsee
a Cd/Ni-0. battery cost of less than about $400/kw-hr, even In very
large quantities, using presently available technology. Furthermore,
cadmium is a relatively high-cost ($3/lb) material of low production
rate and low reserves.
All vehicle performance figures quoted in this discussion relate to
vehicles having 25 percent of their weight allotted to batteries. Some-
what higher ranges and speeds are possible with a higher battery weight.
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1.000
o>
*,
-100
1
a.
o
a
to
10
r 1,0001—
10 100
Specific Energy (W-hr/lb)
\
1,000
I I
10 100
Specific Energy (W-hr/kg)
1,000
FIGURE 4-1 Specific power vs specific energy capabilities of various
batteries.
- 72 -
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TABLE 4-1
Characteristics of Batteries8 and Electric Vehicles
Battery
Pb/Pb02
Cd/Rl203
Zn/«2<>3
Zn/Ag20
li(Al)/
TeCU (C)
Ha/S
Ll/S
Electrolyte
H2S04(aq)
KOH(aq)
KOH (aq)
KOH(aq)
L1C1-KC1
Ha20.xAl203
or glass
L1C1-KC1
Operating
Temp. °C
Ambient
Ambient
Ambient
Ambient
360-500
300-350
375-400
Specific
Energy
w-hr/lba
10-20
10-20
25-35
40-55
(50-60)
(80-100)
(100-120)
Peak
Specific
Power w/lb
75
150
100
100
(120-150)
75-100
(100-200)
Range,0
Miles
20-40
20-40
40-80
80-100
90-110
150-200
(200-240)
Acceleration
Fair
Excellent
Good
Good
Excellent
Good
Excellent
Cycle
Life
300
1000
(300)
100
(1500)
(1000)
(1000)
Costf
S/kw-hr
20-50
>150
>100
>400e
(10-30)
(10-30)
Time
Dev.
Status Year
*
Available
Available
Laboratory cells
and batteries 4
Available
~1 kwh proto-
type batteries 5
~1 kwh lab
batteries 7
Small lab bat-
teries, sealed
cells 8
Figures in parentheses are estimates for the future, based on present laboratory data.
Urban-suburban driving profile average power level.
Urban-suburban driving requires peak power, at least 70 w/lb, with 100 w/lb preferred.
d
Urban-suburban driving profiles.
Deep discharge.
Authors' estimate; includes allowance for salvage value.
$/kw-hr of energy storage capability (one cycle).
-------
--• The Zn/Ni 0 battery offers a significantly higher specific
energy than is available from Pb/PbO. or Cd/Ni 0 batteries (25-35
'' ' $ •••'•" "
w-hr/lb versus 10-20 w^hr/lb); however, this system is still in the
preprototype stage andvonly hand-made laboratory cells and batteries are
available now.. A battery of this type, when developed, could probably
provide acceptable performance for urban (and perhaps suburban)" vehicles,
having a range of 40-80 miles, depending on the driving profile. It is
estimated that 4 to 5 years would be required (at an optimum funding
level) before small numbers of Zn/Ni-03 batteries could be made avail-
able for testing in electric vehicles. Present estimates indicate that
the future selling price for Zn/Ni 0- batteries in large-scale produc-
tion may be as low as $100/kw-hr. Processing costs are the main
problem, because materials costs are not very high, nor are the
materials in short supply.
The Zn/Ag 0 battery offers specific energy and specific power
capabilities higher than those available from other aqueous-
electrolyte rechargeable batteries. The feature prohibiting its use as
a power source for electric automobiles is that it requires a large
inventory of silver, which is expensive and in short supply. Further-
more, a significant improvement in the cycle life would be necessary;
before its use could be seriously contemplated. As an engineering
exercise, a high-performance electric automobile containing Zn/Ag.O
batteries was constructed and tested (3). This vehicle demonstrated
conclusively that electric vehicles matching performance (but not the
range) of their gasoline engine counterparts can indeed be built using
presently available technology. The cost, however, is higher, even
discounting the cost of the battery.
A review of the state of battery science and technology (9)
reveals that only medium-temperature (300-400°C) electrochemical cells
have demonstrated in laboratory-experiments significant promise of
meeting both the specific energy goal necessary for a range (in urban-..
suburban driving) of 200 miles or more between recharges (100 w-hr/lb)
and the specific power necessary for very rapid acceleration and high-
speed gassing maneuvers consistent with freeway driving (100-200 w/lb).
• *r '
-£74 - *.
-------
Tliesc cells, which operate at 300-500°C (the temperature to be maintained
by thermal insulation and Waste heat from the battery generated during
operation), make use of nonaqueous electrolytes (ionically-conductive
ceramics, glasses, or molten salts) and (usually) liquid electrodes.
The negative electrodes are sodium or lithium; the positive electrodes
are sulfur or chalcogen (the chalcogens are the members of Group VI B
of the periodic chart, and include sulfur, selenium, and tellurium)
containing mixtures or compounds. Data for the three most advanced
types of medium-temperature batteries are shown in Table 4-1.
f
The Li(Al)/TeCl,(C) cell (10) makes use of tellurium, which is
relatively expensive and probably in short supply, thereby limiting its
applicability. However, this cell has reached the most advanced state
of development of all medium-temperature cells. Sealed cells have
been developed and produced in small pilot quantities for laboratory
testing, and some 12-cell batteries have been constructed and tested.
These 1/4 kw-hr batteries have demonstrated cycle lives of 100 cycles
(individual cells of this type have been cycled more than 200 times).
It is believed that this work will continue, with the construction of
somewhat larger batteries for testing by the U.S. Army at Fort Belvoir.
Approximately five years would be required, at an optimum level of
effort, for the development of prototype batteries for electric auto-
mobile propulsion. The range to be anticipated is about 100 miles,
if 50-60 w-hr/lb can be achieved. The cost can be anticipated to be
relatively high, and the tellurium supply will probably be limiting.
From a materials point of view, the sodium/sulfur (11) and
lithium/sulfur (8) cells are more promising for widespread use in high-
performance electric automobiles. The sodium/sulfur cell contains
either a ceramic (beta alumina, Na.O'xAl.O.) or a glass (sodium-ion
conducting) electrolyte which separates liquid sodium from liquid
sulfur. The construction of these cells can be relatively simple,
allowing mass production at a reasonable cost (estimated to be
$10-30/kw-hr). For a range of 200 miles, a cycle life of 1000 cycles
ought to be;more than adequate (200,000 miles over the lifetime of the
battery). Cycle lives of more than 100 cycles have been demonstrated
by single laboratory cells. Sodium/sulfur batteries having a power
- 75 -
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level of up to 400 watts have already been constructed and tested; a
30 kw battery is already under construction for use in a demonstration
vehicle (12). It is estimated that about seven years of optimum effort
may be required for the development of pilot quantities of sodium/sulfur
batteries for electric automobiles. These vehicles can be expected to
have a range of 150-200 miles, with good acceleration capabilities.
The lithium/sulfur cell using a molten LiCl-KCl electrolyte
(8,9), which shows promise of even higher specific energy (100-120
w-hr/lb) and specific power (100-200 w/lb), is in the small lab cell
and small battery stage of development. Unsealed cells have delivered
1000-2000 cycles (operating continuously for 6 mos- 1 yr); sealed cells
have delivered 100-200 cycles during about 1000 hours of operation;
a sealed 3-cell battery has delivered 6 cycles during 200 hours of
operation. It is projected that about 8 years of development at the
optimum rate will be required to reach the pilot test stage in electric
automobiles. The ultimate cost may be in the range of $10-30/kw-hr.
The performance of an electric vehicle with Li/S batteries as the power
source should essentially match that of present gasoline-engine
vehicles. The range is expected to be 200 miles or more. The cost of
the vehicle is expected to be somewhat higher than the present-day
vehicle.
In order to provide some design-related information for elec-
tric automobiles, some estimates have been made for the weights of the
various major components of three classes of electric vehicles:
future full-size electric family auto; future compact electric auto;
and urban subcompact auto of marginal performance, available now. |
Table 4-2 shows the weight distribution by components. The family and
compact autos are assumed to be powered by lithium/sulfur batteries
having the same performance per unit electrode area as typical labora-
tory cells of 1971; the urban auto is assumed to be powered by lead-
acid batteries available now. The weights of the components have been
estimated by the authors and are Intended to be representative of
currently available electric vehicles (1).
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TABLE 4-2
Some Specifications for Three Electric Automobiles
Type
Curb weight
Test weight
Weight of power plant:
Battery
Motor
Controls
Transmission and drive train
Air conditioner and heater
Miscellaneous
Total
Accessory power:
Lights, radio, etc
Air conditioner
Air Draft Coefficient
Frontal area of vehicle
Transmission efficiency
Family
4300 Ib
4600 Ib
1075 lba
150 Ib
200 Ib
70 Ib
80 Ib
25 Ib
1600 Ib
250W
3000W
0.5
24 ft2
0.82
Compact
1800 Ib
2200 Ib
600 Ib
100 Ib
110 Ib
50 Ib
20 Ib
20 Ib
900 Ib
250W
0.5
20 ft2
0.82
Urban
1650 Ib
1850 Ib
~900 lbb
~100 Ib
~30 Ib
50 Ib
~20 Ib
1100 Ib
~150W
~0.5
~20 ft2
~0.75
* Lithium/sulfur battery assumed for performance calculations.
Lead-acid battery assumed for performance calculations; authors estimates of typical
weights for available vehicles.
c Include in curb weight and test weight.
-------
Computer calculations of the ranges of the family and compact
autos were performed, using published driving profiles, specific
battery designs, and laboratory cell performance data as inputs (8,13,14),
The results, shown in Table 4-3, indicate that electric automobiles
powered by batteries having a specific energy near 100 w-hr/lb and a
specific power near 100 w/lb can be expected to meet present-day
urban-suburban driving patterns, and have a range of 125-250 miles
between recharges. Presently available lead-acid battery-powered urban
vehicles can provide a range of about 50 miles between recharges, with
marginal acceleration, at a cost premium.
Fuel Cells
Direct conversion of the free energy of combustion of fuels to
electrical energy has been shown to be technologically feasible;
operating hardware has served as the auxiliary power source of the
Gemini and Apollo space vehicles. A general review of thermodynamic
and kinetic principles and of engineering and technological aspects
has been given, among others, by Liebhafsky and Cairns (15). The state
of the art to 1967 has been reviewed by the Panel of Electrically
Powered Vehicles of the U.S. Department of Commerce (16).
Using hydrogen (or an alcohol), a fuel cell system emits only
water vapor and CO,,. When the primary fuel is a hydrocarbon, which
has to be reformed into hydrogen and carbon dioxide, emissions of NO
A
also occur, at levels, however, well below the limits specified for
1976. Emission of NO results from the burning of fuel to heat the
x
reformer. A special class of fuel cells operating at high temperatures
(*j 1,000°C) can accept H or mixtures of H and CO as a fuel; these
are not expected to emit NO , only water and CO . Thus from the point
X £,
of view of pollution abatement, fuel cells based on either hydrogen or
hydrocarbons can perform entirely satisfactorily.
Fuel cells may be described as continuous feed primary batter-
ies; the reactants are continuously fed to the reaction sites (the fuel
to the anode, air or oxygen to the cathode). The reaction conditions
in the cell itself are time invariant. Efficiency remains high over a
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Table 4-3
Ranges fo» Electric Vehicles under Various Driving Conditions
Vehicle Family Compact Urban
Accessory Power, watts 250 250 0
Regenerative Braking Efficiency 0 0.5 0
Urban driving range,
average miles 200 250 ~50
Suburban driving range,
average miles 150 125
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very broad range (25-125 percent) of the nominal load rating for a
well-designed fuel cell power plant. Fuel-cell systems carry the fuel
in separate tanks, similar to heat engines, instead of in the reaction
vessel itself, as batteries do. In principle, therefore, fuel cells
should be capable of providing a similar range to the present-day
automobile. The energy conversion efficiency of fuel cells, in
principle, is significantly higher than any mobile or stationary power
plant presently in use. Since the conversion process is not subject
to the Carnot limitation, the heat rejected to the surroundings amounts
to the sum of TAS of the net reaction and of the irreversible losses due
to conduction in the electrolyte and those losses associated with such
processes as the charge transfer reactions at the electrode surfaces,
and mass transfer. Efficiencies of 40 to 60 percent (based on the heat
of combustion) at moderate power drain have been convincingly demon-
strated in prototype hardware (17,18). High energy-conversion effi-
ciency gives a powerful incentive for serious consideration of appli-
/
cation of fuel cells as power sources in automobiles.
In its present stage of development, certain fuel cell hardware
was proven to be very reliable over long periods of continuous or in-
terrupted use, capable of handling large overloads for short periods of
time. The operating period required for economic feasibility is
approximately 16,000 hours. A complete power conversion system (19,20)
is currently undergoing field testing for stationary energy conversion
from natural gas to electricity. The inherent problems in the develop-
ment of fuel cells for general consumer use are associated with capital
cost per unit power capability and lifetime.
Significant effort has been devoted to the development of fuel
cells--including some directed to automotive applications—in the past
twenty years. Of the numerous private enterprises that have had major
programs in this area, today only one (Pratt and Whitney Aircraft
Division of United Aircraft) has a massive commitment in fuel-cell
development and in limited manufacture (19,20). The continued engine-
ering developmental effort of P&W has resulted in noteworthy advances
in the state of the art and suggests a revision of prognostication for
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potential application of fuel cells as power sources in personal
vehicles (16,20).
Major advances as related to phosphoric acid electrolyte cells
can be summarized as follows:
1. Significant reduction of platinum catalyst loadings of
les from 12 g,
of performance (21).
electrodes from 12 g/ft2 (1965) to below 2 g/ft2 (1972), without loss
2. Development of sophisticated manufacturing technology for
the mass production of cell stacks involving modules of thin cells.
Extensive use of low-cost electronically conducting materials (carbon)
and insulators (polymers) is bringing the cost of cell hardware to
within the realm of economic feasibility for consumer use.
3. Development of simple, small, and inexpensive catalytic
reformers, which convert the hydrocarbon fuel into hydrogen, CO„, and
water vapor. The power plant emits HO, CO. and low levels of NO .
£• £ Jn»
Based on known technology, complete units in the range greater
than 10 kw may become feasible at a cost of $100/kw (includes reformer
and DC-AC converter). Further reduction of cost may be possible if and
when noble-metal catalyst loadings can be still further lowered, or
eventually completely replaced. Developmental efforts continue with
an objective of further reducing costs on (a) other cell types involving
acid electrolytes; (b) KOH electrolyte; and (c) high temperature, molten
electrolytes. The use of other hydrogen-containing fuels (e.g.,
ammonia, hyrazine, alcohols) is also promising.
In respect to application in personal vehicles, no meaningful
\
predictions can be made at this time. A few vehicles powered by fuel
cells have been constructed and road tested (22,23) to define develop-
ment goals on the besic electric drive components (the motor, electric
drive, and power source). The overall thermal efficiency has already
been proven to be at least twice as high as that of the gasoline engine
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in average use. Heavy weight, large volume, and high initial cost
(these did not involve presently available fuel cell technology) ap-
peared to be the problems directly related to fuel cells.
Estimates based on currently available technology indicate
that power levels in the range of 50 w/lb may be accessible, at
$100/kw (power system cost). This power capability is not sufficient to
match the performance of the present family car, and the cost per
kilowatt is five to ten times higher than would be necessary to match
the equivalent gasoline-engine-powered vehicle. Nevertheless, the
advancements made in fuel-cell technology indicate that they should no
longer be dismissed from consideration as a potentially economically
feasible alternative power source. However, it is unlikely that fuel
cells with appropriate power and cost characteristics can be developed
and ready for broad application in the personal vehicle sector in less
than 15 years.
Fuel cells are in a stage of development that does not permit
firm predictions to be made about their potential availability for
application in personal vehicles. If noble metal catalyst loadings
can be further reduced (or entirely eliminated) and if manufacturing
technology for the cell stacks can be advanced to the point where cost
is lowered to the range of $30-50 per kw, the incentive for the deploy-
ment of fuel cells as a power source in vehicles becomes strong.
Depending on primary fuel, they are pollution free, or nearly so,
efficient, and potentially very durable. The electric power source
affords broad possibilities for the design of prime movers yielding
favorable vehicle performance characteristics and good driveability.
A further incentive for seeking the advancement of fuel cell
technology with applications in vehicles as a definite goal may be
derived from the energy source-distribution picture, as it is esti-
mated to evolve over the next 15-30 years. It is generally agreed that
up into the first decades of the twenty-first century, fossil fuels will
provide a major fraction of the primary energy. Use of fuel cells in
transportation would improve the efficiency of use of these resources.
On the other hand, considering the shift toward an all-electric ri
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economy, the distribution of electrical energy from central stations
may involve central generation of a suitable fuel (H-, NH,, etc.) and
its distribution in a network of pipelines. The end use could then
include reconversion by fuel cells into electric motive power in
vehicles. The high inherent thermal efficiency of fuel cells therefore
could be of interest even when fossil fuels cease to be a major factor
in the energy economy.
HYBRID ELECTRIC VEHICLES
A number of schemes have been proposed for the operation of
hybrid electric vehicles in which a heat engine is combined with a
battery, an electric drive, and a control system (24,25,26). The
intention is to minimize the emission of pollutants by operating a
suitably-tuned heat engine (SI, diesel, gas turbine, etc.) at a fixed
operating point while providing the varying component of the propulsion
power from a battery-powered electric motor. It is possible to use the
electric motor mechanically in parallel with the heat-engine drive (24),
or in series with it. The use of the electric motor adds significantly
to the driveability of the vehicle when the SI engine is tuned for
minimum emissions (yielding low power and poor driveability).
It may be necessary to allow the heat engine to follow the
demand, probably with a slowed response in order to have a vehicle
capable of a wide range of power levels. Because of the fact that the
battery will usually be operated at high current densities, the overall
energy efficiency will be low (perhaps below 50 percent), resulting in
higher fuel consumption than would otherwise be the case. While this
scheme has been shown to be technically feasible, the 1976 emission
standards have not been met for a significant period, and presently-
available batteries have been shown to have an inadequate lifetime.
The combination of increased fuel consumption, increased complexity
and cost, and the need for improvements in emission control equipment
and batteries makes the attractiveness of heat engine-electric hybrid
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vehicle at best a marginal solution to the pollution problem.
It is possible that the 1976 emissions standards could be met
by heat engine-electric hybrid vehicles, but it appears that this
solution to the problem is likely to be of an interim nature, since
future improvements in either heat engines or batteries (including
fuel cells) could displace the more complicated and less efficient
hybrid system. Recognizing the likely interim nature of this approach
to minimizing motor vehicle emissions, it is difficult to imagine that
industry would undertake the development and large-scale production
of heat engine-electric hybrid vehicles.
To put it succinctly, a good hybrid power plant would need a
fairly clean engine and a better battery than what we have ^oday.
The combination of these two could yield a vehicle emission performance
acceptable under the 1976 standards. However, if these were available
they could be solutions in themselves. Therefore, if one considers
the developmental and manufacturing costs, and the strong likelihood
that hybrid vehicles would have only an interim significance in the
transportation spectrum, it appears unlikely that they will play a
significant role in the solution to the automotive emission problem.
POTENTIAL AVAILABILITY
Battery-operated vehicles exist now, and limited-production
battery-powered automobiles could be said to exist, albeit with low
performance and small size. Mass production of these limited perform-
ance vehicles could be achieved in four to six years if required.
Advanced battery power plants are estimated to be about; four
years from a suitable prototype assuming optimum funding. If this
schedule could be held, mass-produced electric-powered vehicles of high
performance could conceivably become available in an additional seven
to ten years.
Advanced fuel cells are estimated to be at least 15 years away
from a suitable prototype, even with suitable funding.
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REFERENCES
Discussions
General Motors Corporation
Ford Motor Company
Chrysler Corporation
Petro-Electric Motors, Ltd.
U.S. Army Mobility Equipment Research & Development Center
General Electric Company
Pratt 6e Whitney, Division of United Aircraft Corp,
Papers
1. Proceedings of the Second International Electric Vehicle
Symposium, Electric Vehicle Council, New York, 1972.
2. Agerwal, P. D., and Levy, I. M., SAE paper 670178.
3. Rishavy, E. A., Bond, W. D., and Zechin, T. A., SAE paper
670175.
4. Salihi, J., IEEE Spectrum, June 1972, p. 44.
5. Kyle, M. L., Cairns, E. J., and Webster, D. S., Lithium/sulfur
batteries for off-peak energy storage--A comparison of energy
storage and peak power generation system, Argonne National
Laboratory Report (in press).
6. Foote, L. R., and Hough, J. F., SAE paper 700024.
7. Martland, L, Lyne, A. E., and Foote, L. R., SAE paper 680428.
8. Kyle, M. L., Shimotake, H., Steusenberg, R. H., Martino, F. J.,
Rubishko, R., and Cairns, E. J., 1971 IECEC, p. 80.
9. Cairns, E. J., Steunenberg, R. K., and Shimotake, H., in Kirk-
Othmer Encyclopedia of Chemical Technology Supplement, 1971.
10. Metcalfe, j. E., Chaney, E. J., and Rightmire, R. A., 1971
IECEC, p. 685.
11. Rummer, J. F., and Weber, N., SAE paper 670179.
- 85 -
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12. Jones, I. W., Electricity Research Council Laboratory,
Capenhurst, England, private communication to E. J. Cairns,
May 1972.
13. Cairns, E. J., ejt a^., Development of high-energy batteries
for electric vehicles, Argonne National Laboratory Report
no. ANL-7888, Dec. 1971.
14. Cairns, E. J., Gay, E. C., Shimotake, H., and Selman, J. R.,
Presentation: 1972 ISE meeting, Stockholm; sec also extended
abstract.
15. Liebhafsky, H. A., and Cairns, E. J., Fuel Cells and Fuel
Batteries: A Guide to Their Research and Development,
New York: Wiley, 1968.
16. Panel on Electrically Powered Vehicles, U.S. Dept. of Commerce,
The automobile and air pollution: A program for progress,
Part II, pp. 67-73, Dec. 1966.
17. Vielstich, W., Fuel Cells, Modern Processes for the Electro-
technical Production of Energy, New York: Wiley-Interscience,
1970.
18. Wyczalek, F. A., Frank, D. A., and Smith, G. E., A vehicle
fuel cell system, SAE paper 670181.
19. "Target" Program, United Aircraft.
20. Podolny, W. H., Fuel cell powerplants for rural electrifica-
tion, United Nations Rural Electrification Symposium, New
Delhi, Dec. 1971.
21. Presentation of Army MERDC, Ft. Belvoir, to the Panel.
22. Marks, C., Rishavy, E. A., Wyczalek, F. A., Electrovan—
A fuel cell powered vehicle, SAE paper 670176.
23. Kordesch, K. V., Hydrogen Air/Lead Battery Hybrid System for
Vehicle Propulsion.
24. Gelb, G. H,, Richardson, N. A., Wang, T. C., and Berman, D.,
SAE paper 710235.
25. Lapedes, D. E., Proc. Ind. Internal Elec. Vehicle Symp.
Electric Vehicle Council, New York, 1971.
26. Barpal, I. R., 1971 IECEC, p. 842.
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5. RANKINE ENGINES
SUMMARY
Rankine-engine burner-boiler components have been tested for
emission and show promise that the 1976 standards can be met with
Rankine-engine-powered, standard-size automobiles. Various approaches
to the design indicate that Rankine engines can be made to fit into
full-size automobiles. These findings are contracted by EPA to be
demonstrated with working units in automobiles by 1975.
Engine noise promises to be low except for the condenser fans,
which could be troublesome because of large air-flow requirements.
Starting should be easy, although time-consuming (one minute being a
practical estimate). The driveability of Rankine-powered automobiles
can be satisfactory if the power-to-weight ratio of the engine can be
improved considerably over demonstrated units.
One full-size automobile has been fitted with a 150 HP steam
engine. Emissions did not meet 1976 standards and there were other
detracting features that can be traced partly to the underdeveloped
nature of the engine. Lower-power steam engines have been fitted
into medium-size automobiles and demonstrated. Low power density is
a general characteristic of these engines, traceable to poor effi-
ciency. The steam turbine engine can achieve efficiency comparable to
positive displacement steam engines, but it requires a multispeed or
infinitely variable transmission. Effective ways of building multi-
stage turbines and the verifications of methods of using steam turbines
with few critical controls would make the steam-turbine approach for
an automobile more viable than a positive-displacement steam engine.
Newer forms of Rankine engines that use organic fluids flowing
through either reciprocating or turbine machinery offer the possibility
of trouble-free operation (no freezing, easy starting) at the expense
of poorer fuel economy compared with steam. These units will be of
larger size and will be more difficult to integrate into automobiles
than will steam engines.
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The Rankine cycle in any version will tend to have relatively
uniform specific fuel consumption over the operating range. This leads
to reasonable fuel economy (although poorer than gasoline-powered auto-
mobiles of similar size and power) over typical driving schedules with
either steam or with the best organic fluid.
To achieve an engine with reasonable fuel economy the controls
must be complex and the engine must be as large as possible within the
allowable envelope. Thus, any Rankine engine will be pushed to the
allowable limits on size, weight, and cost for a given application and
the auto will be underpowered and overpriced by considerable margins
compared to the same application with a spark-ignition engine. Despite
its potentially low emissions, good driveability, and low noise, most of
the other evaluation criteria for automobile engines are not satisfied
by the Rankine engine, independent of type.
It is questionable whether even limited production of full-
power engines could be available before 1980. Limited production of
existing designs for low-power applications could begin by 1976-77.
Major questions remain to be answered with respect to safety, opera-
bility, and reliability in the hands of the public, and with respect to
overall driving versatility. Unit cost and the ability to be phased
into production are even larger questions for which answers are
lacking.
A suitable full-size, prototype Rankine engine will not be
available until 1975 (EPA schedule). Further development of a manu-
facturable prototype must be followed by field development, tooling
development, and test trials as normally instituted on any new engine
by the auto .companies. This state is anticipated to be longer for
closed-cycle machines than for open-cycle engines, such as for gasoline
engines. An estimated earliest date for mass-production for an
advanced Rankine engine is 1985.
INTRODUCTION
The Rankine engine is basically a closed system operating with
a working fluid that is liquefied, pumped, vaporized, expanded, and
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recondensed. The expander can be a turbine or a positive-displacement
device of either rctary or piston type. The pump, likewise, can be
rotary, rotary positive-displacement, or reciprocating. Schematic
flow systems for the various Rankine systems are shown in Figure 5-1.
The best-known working fluid is water, as used in steam engines,
However, in the last few decades more consideration has been given to
other fluids that tend to overcome the basic limitations of steam,
i.e., freezing, corrosion, and low fractions of Carnot efficiency
achievable in simple cycles. Liquid metals were considered for some
applications. But for more generally useful systems organic fluids,
or easy-to-use inorganic fluids, came under consideration. The
simplest of these systems considered stable hydrocarbons or halo-
genated hydrocarbons. Depending on the fluid, the vaporizer could be
either a boiler or a heater containing the fluid at supercritical
pressure. Again, depending on the fluid, internal heat recovery using
a recuperator can be used to increase the cycle efficiency at the
expense of additional equipment.
The Rankine engine ideally can achieve up to 85 percent of
Carnot efficiency with some fluids, where Carnot efficiency is figured
on the basis of average absolute temperature of heat addition (Tfl)
and average absolute temperature of heat rejection (T"r):
T - T
a r
Carnot
T
a
However, with adjustment for pumping power, component inefficiencies,
heat losses, and unavailable burner-exhaust heat, a more characteristic
fraction of Carnot efficiency achievable by Rankine engines is 30 to
40 percent. The basic limitation of Rankine-cycle efficiency is the
maximum and minimum temperatures to which the working fluid can be
exposed. Maximum temperature is limited by either corrosion of the
high-temperature parts or degradation of the working fluid. Minimum
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Boil
pum
c
Flow __^_
diagram
Boiler/
er feed vapor reservoir Flow
1 (2j • 1 1 ttirKinA •
y~wV»*-^^^ °'
« . -*— Air reciprocator .
•« Combustor i"r K
fcxhaust • ' /ucl
; r
I
L
Cooling
medium
^*
Condenser
Sump and 1
Soir <=3p>
m Tn
transmission
(3)
~] Jet condenser
(sometimes
J used)
J
—V ) Sump or boost
^—^ pump
O
i
1-2 Preheating and Boiling
2-3 Expansion
3-4 Condensation
4-1 Pumping
Expanded vapor
contains some-moisture
Entropy
"Wet" vapor cycle
thermal diagram
FIGURE 5-1 Rankine. cycle engine schematics. A. "Wet" vapor
(water, liquid metals, some refrigerants, some hydrocarbons).
-------
"Dry" vapor cycle
thermal diagram
1-2 Preheating and boiling
2-3 Expansion
3-4 Recuperation
4-5 Desuperheat and
condensation
5-6 Pumping
6-1 Recuperation
Entropy
Control
Boiler feed pump
f^^~". ^^
Exhaust M_C°mbustor
Jet condenser
(sometimes used)
Desupemeater
and condenser
To
transmission
Sump or
boost pump
FIGURE 5-1 (continued) Rankine cycle engine schematics. B. "Dry" vapor
(most hydrocarbons and many halogenated hydrocarbons, many refrigerants),
-------
Supercritical vapor cycle
thermal diagram
Entropy
NO
to
1-2 Heating
2-3 Expansion
3-4 Recuperation
4-5 Desuperheating and
condensing
5-6 Pumping
6-1 Recuperation
©
Heater
and vapor
reservoir
/WWVvw^A^VU
Q^_ Rest of flow
diagram as in B
1 1— Fuel
Combustor
FIGURE 5-1 (concluded) Rankine cycle engine
schematics. G. Supercritical vapor (hexa-
fluorobenzene, AEF-78, P-1D, torqane).
-------
temperature is limited by the minimum practical vapor pressure (and cor-
responding temperature) in the condenser (lower pressure means lower
allowable flow losses) or by the condenser-wall temperature desired
for reasonable-size radiators (lower temperature means larger conden-
sers). These limitations result in practical system efficiencies as
follows:
Stable Common
Working Fluid Steam Organic Organic
Maximum temperature 1000°F 750°F 500°F
Minimum temperature 200°F 250°F 200°F
fa .3 to .4 .4 .4
Cycle efficiency .20 to .27 .22 .15
Overall efficiency .16 to .22 .18 .12
Q
Achievable fraction of Carnot efficiency.
The nature of Rankine cycles is that the peak efficiency does not drop
rapidly from the peak value at part load.
The vapor generator has to be sized to provide the horsepower
equivalent in BTU/hr divided by the cycle efficiency. Thus, high
efficiency is required to keep the boiler size down. All of the heat
represented by cycle inefficiencies must be rejected from the cycle
by the condenser. This means that high efficiency is required if the
condenser is to be compact. The vapor generator and the condenser
must both be sized for maximum power, although ram-air effects can be
used to minimize the condenser-fan-power requirements.
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STATE OF THE ART
Steam Engines
There are on going contracts from the Environmental Protection
Agency and the Department of Transportation for three bus engines and
one automobile engine using steam as the working fluid (1). The bus
engines are represented by turbine expanders and piston-type expanders,
and the automobile engine is a piston type (Steam Engine System, 5).
In addition, General Motors has demonstrated operating steam engines
(2) in two automobiles. The Pritchard car in Australia (28) also has
a piston-type expander, as does the Willjams Brothers car in the
United States.
The piston prime mover for steam engines poses many development
problems, but the key ones are the lubricating problem and the blow-by
problem (Lear Motors observations). EPA has let contracts to study the
lubrication problem (1). The blow-by problem is one that appears to
be solvable if crossheads are used. Crossheads also help the lubri-
cation problem by removing the side load from the pistons exposed to
steam. Crossheads tend to make the prime mover high and bulky. But
the conservative approach is to use them, and they are still used by
most of the steam-engine developers.
The steam rates (the higher the efficiency the lower the steam
rates) for the modern engines are presently no better than that of
the Doble engine of several decades ago (3), although the McCulloch
engine (a modernized Doble) was better (3). Also, the start-up time
is no better than that achieved by Doble. However, present engines
tend to be a little smaller than Dobles, which was achieved partly at
the expense of poorer efficiency.
Emission measurements have been made on the GM car (4) and on
the burner-vaporizer of the Steam Engine Systems engine (1). The former
does not meet the 1976 standards; the latter does, but so far only in
the laboratory and not on a complete engine (an assumed mpg and
simulated operation was used to convert ppm to grams of emissions per
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mile.) There is little problem of achieving low enough CO, and hydro-
carbons can be held down easily, especially if the combustors are well
insulated. However, NO is somewhat of a problem. Several approaches
have been used to minimize it. In the successful tests at SES, well-
prepared premixed fuel is the key (1), along with overall lean operation.
Other successful tests will be mentioned in the next section on organic
fluid engines (5,6).
The SES design for a full-size car is to deliver 135 HP and
will allow the EPA-designated auto performance to be achieved. Its
design to date shows it able to fit well within the present engine
compartment although the condenser occupies the complete front of the
car out to the fender. Their approach to the freezing problem offers
the hope that freezing need not be considered as a deterrent to
adopting steam.
The larger of the GM engines (mounted in a slightly elongated
Pontiac Grand Prix) was designed, built, installed and tested over a
period of nine months (2). It operated well. The results of the
testing are satisfactory enough to consider it as a reasonable
starting point for future development. However, lubrication, controls,
fan noise, condenser size, system bulk, and SFC, as exemplified by
this engine, indicate problems typical of the generic engine type
rather than the state of development. That is, engineering can be
used to improve the situation somewhat, but no large improvements can
be expected. The above problems revolve around the basic limitations
on efficiency already mentioned, the use of steam in a reciprocating
prime mover, and the fact that the design point for the engine
(including heat exchangers) has to consider maximum power. The degree
of engine improvement to be expected with any amount of engineering
and using the same basic approach is not great. Thus the GM (SE-101)
engine indicates the nature of steam engines designed for use in
automobiles. So, in general, the considerations are (Reference 2,
and discussions with GM, Ford, Chrysler, Lear, and reports on the
California Bus Program) as follows:
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Noise—Fan and combustor-air-blower noise is the predominant
noise and is very noticeable at idle. (An additional component on the
fan can be used to cut this noise at low power.)
SFC—Tends to be up to 50 percent poorer than the gasoline
engines normally fitted for full-size autos (can be improved somewhat
if the engines are enlarged or made more sophisticated).
Control ease—Many controls must be used for controlling power
and efficiency well enough to keep the engine size within bounds.
Driveability and versatility—Start-up time is the main de-
traction (one to several minutes). Improved design may be able to cut
this to less than one minute. Also high-power periods must be limited
in duration for automotive size boilers and vapor reservoirs.
Starting ease—Satisfactory (assuming the freezing problem is
in fact solved).
Size—Small improvements may be possible, but good SFC requires
using all the available room.
Weight—Invoking boiler codes results in a weight penalty;
this can be improved by updating legal requirements to fit engine
requirement.
Safety—Probably satisfactory.
Emissions can undoubtedly be improved (1), and it is probably safe to
say that the 1976 emissions standards can be met. The engine must
still be evaluated when placed in the hands of the disinterested
public.
The cost of the engine cannot yet be evaluated properly. The
boiler will be one of the high-cost components. The high-temperature
portions of the boiler have to be stainless steel to avoid corrosion
and overstressing, and the weight estimate for this alone can vary
j . i
from 50 to 100 pounds depending on the design compromises. The con-
denser is large, massive, and costly, especially when the fans and
their controls are included. The controls are also costly, consisting
of the steam cut-off valves, the combustor blower/fuel-flow controls,
the air-fuel mixture-control element, the boiler-feed-pump flow control,
and the safety controls (overtemperature, overpressure, and overspeed).
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Various estimates of steam-engine costs range from similar to
gasoline engines without emission controls to three or four times this
cost. The reciprocating prime mover portion of the engine will be
smaller and lighter than a gasoline engine. The requirement for cross-
heads and/or better sealing of the piston and the more difficult
lubrication problem in the panel's opinion will tend to make the prime
mover cost about the same as for a bare gasoline engine. But the
price of boiler, condenser, controls, and auxiliaries must be added in.
The controls for past compact Rankine engines have amounted to 10 to 20
percent of the total cost of the engine, or roughly half the cost of
the prime mover (panel opinion as the result of discussions with manu-
facturers who have made Rankine engines). The figures are not so high
with larger, higher-efficiency, steady-load engines not necessarily
operating at constant speed. The attempt to make compact engines with
least penalty to efficiency coupled with wide load and speed variation
leads to the difficult control problem and concomitant high costs.
The boiler without the burner is a high-cost item because of
its material requirements. Cost reduction will derive from smaller
size, but at the expense of less reliability (because of increased
heat-transfer requirements) and poorer driveability (lowering cost by
lowering vapor-reservoir volume limits reserve vapor, which requires
that all the vapor must be generated as used--even for sudden power
increases). A practical boiler may require a cost comparable to that
of the prime mover, in the panel's opinion.
The condenser cost must be from four to six times the cost of
an equivalent gasoline-engine radiator. Also the radiators are so
large that two fans instead of one are normally required. Estimating
the probable cost of the condenser by comparison with mass-produced
radiators leads to its cost estimations about half the cost of the
prime mover. These estimates by the panel lead to a total cost of a
complete engine that is easily operable by the public of up to three
times the cost of the prime mover.
The steam turbine engine has all the basic limitations and
advantages that the positive-displacement steam engine has except that
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the prime mover (turbine assembly) can be very small and cheap and the
development problems (particularly lubrication and sealing) can be
easier (Lear). But the power-transmission problem is multiplied. Thus,
the turbo-engine (excluding the transmission) may then be 15 to 20
percent cheaper than the reciprocating steam engine. The turbine, even
if lower in efficiency than a positive displacement device, can utilize
high expansion ratios and could achieve system efficiency similar to
a positive displacement engine.
The transmission required for the steam engine depends on the
prime-mover type. The reciprocating engine theoretically requires
only a forward and reverse gear. However, both SES and GM recommend
the use of the standard automatic transmission presently used in most
automobiles (1,2). This allows the prime mover to avoid low-speed
operation, thus easing the control problem somewhat.
The turbine requires at least a standard transmission, but
would operate better and better as the transmission approaches an
infinitely variable speed ratio (Lear). This would allow highly
variable output speed with constant input speed. At this time no
practical infinitely variable transmissions are available. If they
were available they would have been used for gasoline engines, since
they too perform better at constant high shaft speed. Recent in-
vestigations of transmissions suggest that, if they become available,
the price will be up to one and one half times that of conventional
transmissions (1). Further, Lear Motors feels that at least a five-
speed transmission is required for their DOT bus. The quality of ride
in that bus with a three-speed transmission is poor because of the
jolts as the transmission shifts. Thus the cost of the transmission
for a steam-turbine power plant for an automobile can be expected to
be higher than that for present automobiles. The cost of the transmis-
sion for the reciprocating engine can be expected to equal that for
present automobiles. (Other references used to evaluate the discus-
sions with manufacturers and to help formulate panel opinions on steam
engines are References 18 through 24.)
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OTHER FLUIDS
The major reason for considering fluids other than water was to
ease the operating and design problem. That is, the freezing problem
may be avoidable, lubrication may be eased, a turbine prime mover may
be more tractable (lower speed, lower stress), and, possibly, efficiency
can be increased. Aside from liquid metals (which avoid hardly any
of these problems) most of the "other fluids" are organics, either pure
hydrocarbons or halogenated hydrocarbons (Sundstrand, MERDC, 7, 8, 9,
10). The basic results of the search to date for fluids that are
"better" than steam are that freezing can be avoided, lubrication can be
eased, and turbines can be more tractable. This means that both reci-
procators and turbines can be considered.
The technical cost of these potential advantages is that the
thermal stability of the fluid can be a major problem (serving to limit
achievable efficiency, and therefore to put lower limits on the size of
heat-exchange components). The rate of fluid flow is usually large
(which follows with high-molecular-weight fluids and results in more
expensive fluid handling components such as pumps), and the system must
be virtually hermetically sealed. Also, most of the potentially
suitable fluids are retrograde—they become dry on isentropic expansion
from the saturated line and use the "dry" vapor cycle (Figure 5-1).
Therefore, most of these fluids require the use of a recuperator to
desuperheat the expanded vapor by using it to preheat the boiler-feed
liquid. The more retrograde the fluid, normally the bigger and more
perfect the recuperator must be to maintain the ability to achieve a
reasonable fraction cf Carnot efficiency.
Some of these fluids are best used supercritically (Figure 5-1).
That is, the fluid is pressurized above the critical pressure and
vaporized without density discontinuities. This aids the boiler design,
but does not relieve any of the restrictions.
In short, to show any real improvement over steam, "other
fluids" should be close to non-retrograde, and should have very good
thermal stability, reasonable lubricating properties, and a low freezing
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point; they should be compatible with air and water even at high temp-
eratures, should have a molecular weight well above that of water, and
should be inexpensive. The search for this ideal fluid is well docu-
mented (Monsanto in References I, 11, 12, 13). The thermal stability
and cost problems are the most difficult. The Monsanto results to
date have not produced one that will allow operation at temperatures
above 750°F. While this is very respectable, it offers no efficiency
advantage to organic Rankine systems over steam systems.
Engines have been designed for common refrigerant fluids of
reasonable stability (1, 8), and very stable fluids of high cost
(1, Aerojet). Generally, the design approaches using the more exotic
higher-cost fluids have also used the most sophisticated and expensive
systems in an attempt to realize maximum potential from the fluid.
The measured or predicted overall system efficiency varies from less
than 10 percent (simplest) to about 15 to 18 percent (most sophisti-
cated) . The fluids to date have not allowed significant gains in
performance, size, weight, safety, or system cost. The controls alone
of one 40 W organic fluid turbo-Rankine generator set cost about 30
percent of the total, estimated at over $15Q/WH .(Sundstrarid).
There have been no gains in emissions over that achievable
with steam, since a similar burner system and control is usable in
both. Thermo Electron (8, 1) has operated a burner-boiler to simulate
their 130 HP engine running over the Federal driving cycle. They used
an exhaust heat regenerator. The results were very good (see Table in
Introduction).
There is another possible source of greatly increased system
cost if the use of highly stable organic fluids is found to be neces-
sary. That is, these fluids can be expected to cost several dollars
per pound in mass-production, and up to 40 pounds may be required in a
given system (1, 8, Aerojet). Also, the cost of the recuperator
required for most of these fluids is not inconsiderable, since it is
normally made of corrosion-resistant material in compact heat-exchanger
form.
The high molecular weight fluids pose a valving problem for
positive displacement equipment because of the large quantities that
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must flow into the cylinders at each stroke and the low sonic speed of
these fluids, which leads to shock losses and noise.
The overall advantages of "other fluids" over steam are at
this time, essentially non-existent, especially when compared with the
steam turbine system. Even in comparison with the reciprocating steam
system, there is only a possible advantage in better lubricating
properties than steam. (Additional references used to help the panel
form its evaluations and opinions were 25, 26 and 27*)
PROBLEMS
The basic problems with the Rankine systems can be summarized
as follows:
Cost--The engine may cost several times the cost for gasoline
engines; there is also probability that a more expensive transmission
will be required with turbine systems.
Size—Condenser and boilers are the biggest components and
are adversely affected by low cycle efficiency.
Weight—May be comparable to gasoline engines if the turbine
systems are used.
SFC--Adversely affected by low-cycle efficiency, and will
likely be worse than gasoline engines.
Control ease—Simple controls lead to poor efficiency.
Sophisticated controls for good system operation lead to high cost.
Response to abuse and neglect—Inadvertent breaking of seals
(a highly probable situation with any sealed system in the hands of
the public) will allow contamination by air and water, a potentially
incapacitating failure (except for steam systems). Lubrication may be
a problem for steam reciprocators.
This list is self documented by the type of work being carried on
under contract to EPA (1). This includes advanced condenser core
development; lubrication in steam; the three main system contracts
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(Aerojet, Thermo Electron, Steam Engine Systems) covering prime mover
development, boiler-burner development, and system controls; transmis-
sion studies (MTI, Sundstrand); and the search for ideal fluids
(Monsanto). The existing Rankine engines now mounted in automobiles
are in low-power, low-performance autos. The attempts to adapt Rankine
engines to full-size, conventional performance autos have emphasized
the problems mentioned above.
POTENTIAL DEVELOPMENTS
There are many variations of the Rankine cycle other than those
mentioned previously. Chief among those that appear to be promising is
the "D-cycle" (14). This system uses compression of wet steam to com-
plete the boiling, expansion, heat rejection loop rather than using
complete condensation followed by pumping as in the usual Rankine system.
In the extreme case both the isentropic expansion and the isentropic
compression take place within the vapor dome of the fluid (steam being
well suited). This leads thermodyhamically to a Carnot cycle, one of
the several recognized maximum efficiency cycles. The "D" cycle has
not been proven in real machinery suitable for an automobile. Also,
the imposition of realistic expander and compressor efficiencies will
detract seriously from the ideal efficiency used in promoting the
concept.
Some improvements in boiler-burner sizes may be expected that
could reduce overall cost by as much as 10 percent (15,16). Rotary-
positive displacement prime movers (such as the Wankel configuration)
are possible in Rankine systems (17), but with the same problems that
piston prime movers have in vapor systems.
Turbines used with steam offer the best possibility for an
automobile Rankine engine, but at low power the present turbines
suffer some efficiency or shaft speed problems. An inexpensive version
of a multistage steam turbine would seem to be in the realm of design
possibility, and this would contribute to some overall system cost '-
reduction while leading to lower shaft speeds with good efficiency.
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FUTURE POSSIBILITIES
The Rankine engine for full-size automobiles must be highly
optimized to achieve high efficiency and power, good fuel economy,
small size and weight, and low cost. But such optimization implies that
some component costs and the control costs must increase. On the other
hand, lower-powered Rankine engines can be built now, albeit at fairly
high cost. Thus, it is anticipated that the automobile Rankine engine
will be low powered and/or costly. Fuel economy in a real automobile
is projected to be, at best, similar to present gasoline powered autos
and will probably be somewhat worse. A sophisticated control will be
required to achieve good fuel economy and small enough size to be useful
in existing design automobiles.
A large unknown exists as to the behavior of Rankine engines in
the hands of the public.
Emissions suitable for 1976, even in the high powered readable
versions, can probably be met. The Rankine engine will be easy to
start, although starting will take up to a minute or so. Noise can be
made acceptable, especially in a turbine version with controlled con-
denser fans.
In comparison with other heat engines that have better efficien-
cy, lower volume, lower cost, better integrability in automobiles, and
better producibility, the Rankine engine is less suitable for use in
low-emission cars.
Allowing for the possibility of new concepts in boilers and
controls and assuming that a cheaper approach to multistage steam
turbines is found, especially if it could allow for some flexibility
in exhaust pressure and inlet conditions so that controls could be
simplified, it is tempting to say that the Rankine engine could get
another lease on life for automobile application. But even using the
best existing all-around working fluid (water), the condenser require-
ments are still there and the-relatively low efficiency is still there.
This best of all worlds could possibly project the Rankine system into
a technically competitive position with emission-controlled gasoline
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engines but at about 50 percent to 100 percent more engine cost,
POTENTIAL AVAILABILITY
i
i
Prototype steam Ranklne engines of low power now exist. If they
were deemed to be "suitable" they could be put Into limited production in
four to five years, since some development is still needed to make them
really suitable even for limited production.
More advanced Rankine engines (for instance, those in the EPA
advanced automotive powerplant system program) are scheduled to be
demonstrated by 1975. If they were then deemed to be "suitable" they
could be put into limited production by 1979, with mass-production
being reached in another four years.
Advanced Rankine engine prototypes of the type required to
make them as suitable as possible for automobiles are estimated to
be four to six years away at optimum development rates. This leads to
an estimated probable date for mass-production by 1985 with optimum
expenditure rates (assuming a slightly longer concept feasibility
stage than required for open cycle engines such as gasoline, diesel,
and gas turbine engines).
REFERENCES
Discussions
General Motors Lear Motors
Chrysler Aerojet
Ford MERDC
Thermo Electron Kinetics Corporation
Sundstrand Aviation Paxve
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EPA-OAP Contractor's Coordinating Meetings
Reports and handouts by
. v
Thermo Electron
Aerojet
Steam Engine Systems
California Bus Program:
Lear
Steam Power Systems
Brobeck
Combustors:
Solar
SES
TECO
Aerojet
6E
Condensers and Regenerators:
AiResearch
Working Fluids:
Monsanto
Lubrication:
General Electric
Papers and Reports
1. EPA-OAP Contractor Coordinating Meeting for Sept. 1972,
Feb. 1972, and June 1972.
2. Vickers, P. T., Amann, C. A., Mitchell, H. R., and
Cornelius, W., The design features of the GM SE-101—A vapor cycle
powerplant, SAE paper 700163.
3. Bell, J. L. and A. F., Description of a modern automotive
steam powerplant, SAE paper S338.
4. Vickers, P. T., Mondt, J. R., Haverdink, W. H., and Wade,
W. R., General Motor's steam powered passenger cars—Emissions, fuel
economy and performance, SAE paper 700670.
5. Report TE 4133-53-72, System and component specifications,
thermo-electron Rankine-cycle automotive power plant, 1972 for Galaxy
500, Thermo-Electron, 1971.
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6. Zwick, W. B., Mills, T. R., and Flo Rito, R., Evaluation of
a low NO burner, Final report; Contract EHS 70-125, Environmental
Protection Agency, July 1971.
7. Paxve Proposal EHSD 71 NEC 32 to HEW.
8. Morgan, D. T., Rankine-cycle power system with organic-based
fluid and reciprocating expander for low emission automotive propulsion,
Technical report of the Conference on Low Pollution Power Systems
Development; Committee on the Challenges of Modern Society, Feb. 1971.
9. Doerner, W. A., Dletz, R. J., Van Buskirk, 0. R,, Levy, S. B.,
Rennold, P. J., and Bechtold, M., A Rankine cycle engine with rotary
heat exchangers, SAE paper 720053.
10. Hryniszak, W., Aspects of broadening the choice of heat
engine in the future, 36th Andrew Laing lecture, Northeast Coast
Institution of Engineers and Shipbuilders, Transactions, vol. 84,
1967. ,
11. Bjerklie, J. W., and Luchter, S., Rankine cycle working
fluid selection and specification rationale, SAE paper 690063.
12. Percival, W. H., Fluorochemical vapor machine, SAE paper
931B.
13. Hryniszak, W., Hutchinson, M., and Renton, 0., Special
fluid power plants, ASME paper 66-GT-84.
14. Information made available by D-Cycle Power Systems, Inc.
15. Strack, W. C., Condensers and boilers for steam-powered
cars: A parametric analysis of their size, weight, and required fan
power, NASA Technical Note D-5813.
16. Compton, W. A., Low emissions from controlled combustion.
for automotive rankine cycle engines, Presentation at EPA-OAP Contractor
Coordinating Meetings, Sept, 1972, Feb. 1972, and June 1972.
17, Tauson, P. 0., Rotary steam engine, SAE paper 699031,
presented at 1969 IECEC. !
18„ Joint Hearings before the Committee on Commerce and the
Sub-committee on Air and Water Pollution of the Committee on Public
Works, U.S. Senate, Automobile steam engine and other external
combustion engines, May 27 and 28, 1968. ,
19. Ayres, R. U., and Renner, R. A., Automotive emission
control: Alternative to the internal combustion engine, 5th Technical
Meeting, West Coast Section, Air Pollution Control Assoc., Oct. 1970.
106 -
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20. Palmer, R. M., An exercise in steam car design, Institution
of Mechanical Engineers, Proceedings 1969-70, vol. 184, part 2A, no. 10,
pp. 195-217.
21. The search for a low-emission vehicle, Staff Report for
the Committee on Commerce, U.S. Senate, U.S. Gov. Printing Office,
#26-248.
22. Fraas, A.. P., Control of mobile steam power plants, SAE
paper 70.
23. Miner, S. S., Developments in automotive steam powerplants,
SAE paper 690043.
24. Peterson, J. R., The effect of swirl flow upon the perform-
ance of monotube steam generators, SAE paper 700116.
Bjerklie, J. W., and Sternlicht, B., Critical comparison of
low-emission Otto and Rankine engines for automotive use, SAE paper
690044.
26. Barber, R. Ee, Bond, J. C., and Alford, E. H., The design
and development of a turbine-gearbox for use in an automotive organic
Rankine cycle system, SAE paper 710564.
27. Schuster, J. R., and Berenson, P. J., Flow stability of a
five-tube forced-convection boiler, ASME paper 67-WA/HT-20.
28. Information made available from a report prepared by Capt.
R. C. Alexander, U.S. Navy Res., Washington, D.C., regarding The
Pritchard steam power system for automobile use.
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6. STIRLING ENGINE
SUMMARY
At the present state of development Stirling engines are very
efficient and eventually could allow high-performance full-size
automobiles to meet the 1976 emission standards. Tests indicate
that the 1976 emissions standards can be met as easily as with Rankine
engines, the only other heat engine showing promise for really low
emission levels without much more combustion development. Any form
of heat energy or fuel source can be used to operate a Stirling engine.
The engineering problems remaining to be solved before it could be
adopted as a practical engine for limited application relate to the
reliability of the heater assembly, sealing of the working fluid, and
to the development of a simple, versatile power-output-control
system. Considerably more engineering is necessary before the engine
can be considered a suitable automobile power plant.
New developments are occurring rapidly in Stirling engines
that tend to make them smaller, more reliable, simpler, and possibly
even more efficient. The potential for the advanced engine, therefore,
is great. Size, weight, producibility, safety, response to abuse
and neglect, starting ease, emissions, and cost potential—all show
indications of being competitive with or better than diesels in the
present generation of development and equal to or better than gasoline
engines in the next generation of development.
The single limiting factor of the advanced Stirling engine is
that the solution of the engineering problems will take between four
and ten years before the first prototype suitable for present-type
automobiles could be. demonstrated.
Of the alternative heat engines potentially suitable for auto-
mobiles, the Stirling engine can have the fewest limitations in all-
around future applications, but it is the least well developed and
will require the longest to develop at the existing rate.
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INTRODUCTION
The Stirling engine derives its power output by using heating
and cooling to vary the pressure of a fluid within a closed volume,
the pressure variations being transmitted to a piston. This is done
at high efficiency by alternately and regeneratively transferring the
working fluid to the heater and the cooler. Thus, the engine contains,
at a minimum, one power piston and one displacer piston, one regenerator,
one heater, and one cooler. Valved regenerative engines that function
through volume control have been termed Ericsson engines. This conven-
tion will be adhered to here.
The ideal efficiency of either the Stirling or Ericsson cycle
is 100 percent of Carnot efficiency figured between peak cycle-fluid
temperature and minimum cycle-fluid temperature. The basic engine
forms can be made to approximate the ideal Stirling cycle. (References
3, 14, and 15 are descriptive of Stirling engine application and
development.)
The basic engines can consist of both the power piston and
the displacer in a single cylinder (the rhombic-drive engine developed
at the Philips Research Labs, Eindhoven, The Netherlands (1,2,3) or
the power piston and displacer in separate cylinders (4), or multiple
pistons acting as both power piston and displacer, each mounted in
its own cylinder (2,3,4,5). Many variations and combinations are
possible.
Most of the work on Stirling engines has been done at the
Philips Research Lab. In the last 15 years other work has been done
chiefly at General Motors (4,6,7), United Stirling (8,9), MAN, Ohio
University (3), University of Calgary (3), University of Bath (3),
and McDonnell Douglas. Many smaller groups have also delved into
Stirling engines.
Until very recently the basic drawback that prevented its
adoption as a power plant has been its size and cost. The displacer
and piston must be held in the proper phase relationship, the heater
has to transfer much heat into a confined area, the regenerator must
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be almost 100 percent effective, the sealing of the fluid must be long
lasting, the heat exchanger and piping volumes must be kept very low,
and the pressure drops must be low. This translates to a requirement
for much effort on optimization, expensive seals, expensive heaters,
and high internal pressures.
The incentives for continuing work are that the recent engines
have better fuel economy than any other usefully demonstrated heat
engine, that they can be designed for any fuel, that noise is very low,
that size is now low, and that practical solutions to all the problems
of present engines are visible.
STATE OF THE ART
The most advanced Stirling engines that could potentially be
adapted to automobiles are running in laboratories at Eindhoven
(Philips) (1,2,3,10,11) and in Malmo (United Stirling) (8,9). The
development working fluid is helium, and the demonstrated overall
efficiency is above 32 percent in both cases. Neither engine ,is
presently generating maximum possible power. Both of these engines
employ the double-acting principle first originated by Philips and
exploited by GM for a torpedo engine. The Philips engine has four
cylinders arranged to drive a swashplate. The United Stirling engine
utilizes a steep-V engine of four cylinders driving throuhg a con-
ventional crankshaft. Both engines use crossheads. The Philips
engine uses a rolling rubber seal on each piston rod called the "roll-
sock" seal (very descriptive of the action). The United Stirling
engine uses sliding seals.
The Philips engine designed for autos weighs about 800 Ib.
(10). At full pressure (220 atmospheres) and rpm (4500 rpm) it is
designed to generate 175 horsepower. The combustor uses a regene-
rative heat exchanger to conserve the waste heat that remains after
heating the working fluid at the heater (this will be called an
economizer hereafter). The peak wall temperature is about 1000°F.
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Projected fuel economy varies from 26+ mpg at 40 mph (steady and level)
to 18.2 mpg at 70 mph. The expected customer average mileage for city
and suburban driving is 12 percent higher than for a gasoline engine
powered automobile without emission controls. A mock-up of the engine in
a Ford Torino occupies the bottom of the engine compartment, leaving
more than sufficient room for all auxiliaries and accessories. The
engine compartment appears to be less crowded than it was with the
*»
gasoline engine it replaced. The engine now running in .the lab is of
smaller physical size than the one in the mock-up. It generates 60 HP
at 220 atmospheres mean pressure and 4500 rpm.
Heater heads at this time consist of many small tubes manifolded
together and heated by an atmospheric-pressure flame. In the heater,
the thermal stresses coupled with pressure stress in the hot tubes
require the use of high-alloy metal in the amount of several pounds
per engine. The engine is estimated to use 8 to 9 pounds of nickel
and the same amount of chromium. This is mostly in the heater and it
contributes largely to the present cost of the engine. A ceramic-core
economizer is used in the projected auto'engines as the exhaust-heat-
recovery unit. There is no severe sealing chore to be done on this
core since both sides are at atmospheric pressure.
The regenerator consists of many layers of fine-mesh screen
made of stainless steel. This unit must be as small and have as low a
pressure drop as possible to allow the engine to be at its best. These
conflicting requirements have to be optimized for each design.
The cooler consists of cooling coils through which water is
circulated, the water then being cooled in a normal-type radiator.
The radiator for an optimized Stirling engine is about twice the size
of an optimized radiator for an equivalent-power diesel engine. This
is because almost all the waste heat is rejected through the radiator
of a Stirling engine, while only about 50 percent of the diesel waste
heat is thus rejected (for comparison, only about 40 percent of the
waste heat of a gasoline engine is removed via the radiator). Use of
water as an intermediate coolant has the advantage that its mass can
serve as a thermal flywheel so as to allow the engine to be over-
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powered for several seconds. This is an advantage since it allows the
design power to be lower than actual peak power required on fast trans-
sierits.
The United Stirling engine occupies a space about 20"x30"x20"
and is of a size that can fit conveniently into the engine compartment
of a subcompact car. The engine is presently operating with a mean
pressure of 75 atmospheres at 2000 rpm and generating 10 HP. At double
the pressure and 4000 rpm the engine will generate 55 HP—a value suf-
ficient to replace the present Pinto or Vega gasoline engine. The en-:
gine will weigh about 250 Ib. Again, there is no reason to suspect
that these projections will not be met.
Both Philips and United Stirling have a Stirling-powered bus
and boat. Riding them is like coasting downhill or cruising under
sail. All these mounted engines have rhombic drive, helium fluid,
and sliding seals.
Noise and vibration are minimal with the Stirling engine. Fan
noise and burner-blower noise are the biggest sources. The fan noise
is slightly greater than for a diesel or gasoline engine, but lower
than for a Rankine engine. Measured levels for the Philips bus
according to the SAE code were 68 dbA. At 40 mpg in the front seat the
level was 65 dbA. Above the engine with the hatch open it was 76 dbA.
Most of the noises in the moving bus were gears and road noise.
Similarly, for the United Stirling bus the noise one meter:.1 from the
unprotected engine was measured as 86 dbA for the Stirling engine,
which compared to 103 to 107 dbA for the diesel engine it replaced.
The approximate road mileage of the buses now operating appears
to be comparable to diesel-powered buses. The Stirling-powered buses
also have equivalent driving performance. Starting procedure by the
operator is no more complicated than for diesel engines, and only
slightly longer in time compared with a diesel engine using glow-plug
start. Starting is certain.
It remains to be seen how the engines will operate in the hands
of the disinterested public. The roll-sock seal has so far suffered
when used outside the lab—hence the use of sliding seals in the
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vehicular engines.
Emissions were measured from a heater head designed to simulate
the one used in the projected automobile application at Philips. The
federal driving cycle was simulated so far as fuel-flow sequencing was
concerned. The results were interpreted in g/mile assuming 30 percent
engine efficiency. The results are:
CO .31
HC .1
N0x .175
The combustor used some exhaust-gas recirculation for two reasons: to
achieve good fuel af.omization with the EGR as the atomizing gas, and
to reduce the flame temperature for NO control.
Both the swashplate and V-4 engines are comparable in weight to
the gasoline engine they will replace. About 800 Ib for the 175 HP
swashplate engine is expected, and the 55 HP V-4 will weight about
250 Ib. Projections using advanced design heater heads show that the
V-4 engine should be capable of 100 HP, leading to only 2.5 Ib/HP.
Safety should be very good in these engines. Hydrogen will
eventually be used in them, increasing power output still more. The
fluid content of Stirling engines in the 150 to 200 HP category is 15
to 20 grams. This represents only about 2000 BTU if burned completely.
Even in an explosion in an engine compartment, which would be very
difficult to generate unless the hydrogen were trapped in the presence
of air and an ignition source, there would be more noise than visible
effect. Venting the compartment upwards would effectively reduce any
possible hazard to insignificance.
The use of hydrogen introduces the problems of hydrogen em-
brittlement and fluid loss by diffusion through the walls of the engine.
Philips has worked on the problem and has some results with coated walls
that show diffusion to have been slowed to one fifteenth of its rate
with untreated walls. Work remains to be done on this problem.
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The cost of the new double-acting Stirling engines (V-4 and
swashplate) is comparable to gasoline engines taken on a dollars-per-
pound basis. The cost for the heater head, the seals, and the larger
radiator is additional. For-these engines the heater head represents
the greatest cost difficulty and in production engines may be about
one fourth to one half the cost of the complete engine. The double-
acting engines are slightly heavier than the equivalent gasoline
engine at this time. The high-pressure components are small but do
contribute to the weight difference.
The Philips control system involves pressurizing and depressuriz-
ing the engine-volume so as to change the power output. Power can be
reduced easily by bypassing the cylinder, and it can be increased
rapidly by dumping fluid into the loop. The bypass process represents
lost heat, since it is valved from the highest pressure (and hottest)
part of the loop to a low-pressure reservoir. A compressor is needed to
replace the bypassed fluid into a high-pressure reservoir for replace-
ment back into the loop as desired. The compressor represents weight
and cost not appearing in a comparable gasoline engine.
The United Stirling system is much simpler, quicker, and less
lossy. It works on the principle that the pressure excursion inside
the working volume becomes less as dead volume is opened to the loop.
Thus even though fluid does not flow in and out of the dead volume,
the pressure excursions around the design mean pressure is changed.
This changes the power output at the power piston. Use of several
dead-volume chambers of different sizes allows power to be changed
simply by opening and closing pressure-balanced valves—like playing
an organ. Engineering of the double-acting Stirling engine is nearing
completion, and in about two to three years a prototype suitable for
an automobile could be available. Limited production could begin in
another three to four years. Thus, Stirling engines for limited
application may be available by 1978.
A large part of the engine can be made by present techniques.
However, the heater-head, burner, and regenerator would be new to the
auto industry. '•'•
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PROBLEMS
The problems with Stirling engines are evident from the discus-
sion above:
Control type has to be optimized
Heater-head reliability, size, and cost has to
be improved
Sealing has to be improved
Hydrogen and helium working fluids may not be
completely practical
s,
The first three are being worked on actively by several groups; the
last one is being worked on actively by one group.
Control by the varying dead-volume method may be satisfactory
for automobiles since it is quick, sure, and efficient. It remains
to be well proven.
The heater-head problem can be solved in part by using heat-
pipe technology as is being done at both Philips and United Stirling.
The heat pipe ensures plenty of area for the flame heat to get into
the system and also ensures extremely rapid heat transfer into the
confined zone of the head. An added benefit is that the dead volume
at the heater can be minimized to get even more power out of a given
engine. (The V-4 engine power could approach 100 HP.)
Philips is pursuing engineering perfection on the roll-sock seal
and experimenting with coatings to prevent hydrogen diffusion. (They
report success to the extent that they believe they may have to replace
the hydrogen inventory only once a year.)
United Stirling is engineering a sliding rod seal instead of the
roll-sock, and is developing a small electrolysis unit for generating
hydrogen to replace lost fluid.
POTENTIAL DEVELOPMENTS
A third group, Kihergetics, has attempted to solve all problems
at once, and their demostrations have indicated some success in prin-
ciple (12). They have devised an internal-combustion Stirling cycle
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that uses air as the working fluid. The cycle is partly open in that
some gas is exhausted and replaced by fresh air at each stroke. Internal
combustion replaces the heater-head. This allows very small dead volume
at the heater. The combustion is very lean and done in vitiated air so
that the fuel is easily vaporized (or well atomized) and pre-mixed.
Measured emissions are low enough to meet the 1976 standards.
Since air is used as the working fluid, some leakage is allow-
able as it represents only a loss rather than an incapacitating problem.
The control problem is transferred to one of throttling the inlet air
and fuel. This is also easily accomplished. Air is the most available
working fluid possible, so represents no basic problem of cost. Also,
the engine materials are easily used in air. .
The Kinergetics engine must utilize a compressor by which the
air is admitted to the system. The fuel system also represents a
slightly more severe problem than does the normal Stirling engine since
it must be put in at high pressure (unless carbureted at the inlet and
allowed to proceed through the colder parts of the system). The engine
has not been run long enough to demonstrate freedom from fouling, etc.
The Ericsson engine (3,13) may be another approach to the same
problems. Hydrogen and helium are normally used in Stirling engines
so as to reduce pressure losses through heat exchangers that can be
small. The heater and cooler dead volume has to be small to allow
achievement of maximum power density. The regenerator has to be small
to allow achievement of best power density and to allow maximum effi-
ciency, since the "ineffective" portion of the fluid is exposed to
cyclic temperature changes during which some heat is lost from the
system. The Ericsson engine can isolate the heater-head and the cooler
with valving so that power density is not lost even if they are en- .
larged to allow better heat transfer at low temperature differentials
(thereby doing much to solve the heater-head problem). Also, the re-
cuperator (used instead of a regenerator) is at constant temperature,
thereby avoiding a small effect on efficiency due to heat loss from
this dead volume. The recuperator should be of small volume for maxi-
mum power density. Theoretically, the Ericsson engine will have the
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same power density as the Stirling engine if the recuperator volume
equals the volume of all three heat exchangers of the present Stirling
engine. This would allow the total system pressure drop to be low
compared to the Stirling engine so that engine efficiency can be higher
than for Stirling engines. These changes in operation may be suffi-
cient to permit the use of air, thereby ridding the system of a seal
problem.
Control of the Ericsson can be accomplished similarly to the
Stirling engine. Air leakage would be replaced by a small compressor
sized to match the maximum leakage (which should be only a small per-
centage of the flow.)
Either of the new concepts will take four to five years to
develop as suitable for prototype design. Thus the new concepts
would take at least two years longer than the normal Stirling engine
to reach limited production. However, it is possible they could be
more suitable for mass production and, if so slated, could be in pro-
duction potentially by 1982 to 1984.
FUTURE POSSIBILITIES
The present Stirling engines are very good performers that show
promise of being able to compete with diesels on a cost, reliability,
and SFC basis. They will beat diesels on a noise basis. There are
many possible approaches for improvement, some of which are being
taken.
If Stirling engine development were to cease, the existing
engines would not be good candidates now for automobiles. However,
the amount of improvement possible by a more generalized approach than
heretofore taken is great in terms of increased reliability and lower
cost. It is this possibility that makes the Stirling engine a "dark
horse" 'with the potential to match or beat the gasoline engine on all
significant evaluation points.
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POTENTIAL AVAILABILITY
Continued development of existing Stirling engines should bring
forth a prototype suitable for automobiles in two to three years. Those
being installed now are "first" prototypes from which the "suitable"
prototype should evolve. Present-type Stirling engines could then enter
limited production in four more years (1979), followed by mass pro-
duction in an additional four years (1983).
More-advanced-type Stirling engines (in the sense that they
would be more suitable for use by the public and for easier and cheaper
manufacture) will take longer to develop, estimated at from five to
ten years to reach suitable prototype stage (even with optimum spending).
Thus, it could be 1981 at the earliest for limited production and
1984-85 for mass production.
REFERENCES
Discussions
GM
Ford
Chrysler
Volvo
British Leyland Motor Co,
Perkins
Daimler-Benz
MAN
Philips
United Stirling
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Papers
1. Meijer, R. J., The Philips Stirling engine, De Ingenieur,
paper 621.41.
2. R.A.J.O. van Witterveen, The Stirling-cycle engine,
Committee on the Challenges of Modern Society, Air Pollution, Technical
Report, Conference on Low Pollution Power Systems Development, Eindhoven,
Feb. 1971.
3. Walker, G., Stirling cycle machines, University of Bath,
1971^ to be published as a text book, spring of 1973.
4. Mattair, J. N., Heffner, F. E., and Miklos, A. A., The
Stirling engine for underwater vehicle applications, SAE paper 690731.
5. Meijer, R. J., Prospects of the Stirling engine for
vehicular propulsion, Philips Tech. Rev., Paper P-96, vol. 31, no.5/6,
pp. 168-185, 197.
6. Lienesch, J. H., and Wade, W. R0, Stirling engine progress
report: Smoke, odor, noise, and exhaust emissions, General Motors
Research Publication, GMR-740, Jan. 10, 1968.
7. Maki, E. R., and DeHart, A0 0., A new look at swash-plate
drive mechanisms, SAE paper 710829.
8. Neelen, G.T.M., Ortegren, L.G.H., Kuhlmann, P., and
Zacharias, F., Stirling engines in traction applications, CIMAC, 9th
Int. Cong, on Combustion Engines, 1971.
9. Ortegren, L. G., Stirling engine activities at United
Stirling (Sweden), CIMAC, 9th Int. Cong, on Combustion Engines, 1971.
10. Michels, A.P.J., CVS test simulation of a 128 KW Stirling
passenger car engine, 1972 IECEC.
11. Michels, A.P.J., The NO-content in the exhaust gases of
a Stirling engine, paper 719134, 1971 IECEC.
12. PC-3040, Technical brief Ketobi engine system concept,
Kinergetics, Inc., May 1972.
13. Bjerklie, J. W., Comparison of C0» cycles for automotive
power plants, IECEC, 1972.
14. Walker, G., Stirling engines for isotope power generation,
Paper EN/1B57, Second Int. Symposium on Power from Radioisotopes,
Madrid, June 1972.
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15. Potential capabilities of the Stirling engine for space
power, Technical Documentary Report No. ASD-TDR-62-1099, Director of
Aeromechanics, ASD, Wright-Patterson AFB, Project No. 3145, Task No.
314502.
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7. OTHER ENGINES
In the past, consideration has been given to a wide variety of
other engines having some potential advantage over the gasoline or
diesel engines. Four classes of such engines are of some interest:
Those that use clean-burning fuels, one that uses pure oxygen instead
of air, those that are reciprocating engines but with combustion
occurring outside the cylinders, and those that are reciprocating
versions of the gas turbine (reciprocating Brayton cycle). The only
ones with significant operating time are those that use clean-burning
fuels (this is mentioned in the chapter on Alternative Fuels).
Engines using pure oxygen instead of air have been operated
at Ricardo's in Britain in an investigation of submarine power plants
(1). Flame temperatures similar to conventional engines are achieved
by diluting the incoming oxygen with recirculated exhaust products--
CO- and HO. The method was found to be workable, although some
difficulty with "gumming" was experienced because of the recirculatlon.
This was overcome during the program, but long life was not demonstrated
before termination of the contract. The engine was run slightly derated
to preserve its integrity.
An automobile using 02 requires nearly four pounds of oxygen
for every pound of hydrocarbon fuel. The size and cost of such a
tank (either cryogenic 0- or compressed 0_) would require expensive
tankage, would require an automobile to lose carrying capacity (or
to be bigger) and would raise the power-plant cost by at least 50
percent and probably closer to 100 percent (if sufficient oxygen for
a 200-mile range were to be carried).
The alternative, generating CL from air, can be considered in
terms of a cryogenic air-cycle separator. About 20 percent of the
engine power would have to be used to operate a turbo-compressor type
LOX (liquid oxygen) generator. At least a small LOX reservoir would
have to be carried. Also, the machinery tends to be expensive, in
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this case being comparable to the heart of a simple cycle gas turbine
A rough estimate is that the power plant cost would increase by at
least 50 percent, the total volume and weight would increase appre-
ciably (probably occupying space outside the engine compartment), and
the fuel consumption would be about 25 percent greater than an engine
using air.
The Boston Reformed Fuel Car (2) utilizes a chemical reformer
in which water and heat are added to a hydrocarbon fuel to form CO-
and H2. (This is discussed in more detail in the Chapter on Alternative
Fuels.)
The class of engines that use combustion outside the cylinder
operates by using the normal piston action to compress the air. The
air is then discharged into a chamber (either a closed volume or a
more or less continuous flow combustor) where combustion takes place.
The hot gases are then valved into an expansion chamber where they are
expanded and discharged as in a conventional engine. The compression
and expansion process can take place in either the same cylinders
(3,4) or in a separate cylinder (5,6) depending on the valving arrange-
ment.
The potential for low emissions exists because of long combus-
tion times that can burn out unburned hydrocarbons and CO. But long
time could work to disadvantage for NO because of the high pressures
J&
at which the burning takes place, thus allowing the reactions to
approach closer to equilibrium than in normal reciprocating engine
combustion. The continuous combustion version will tend to act like
a very high pressure gas turbine combustor, an unknown quality as far
as NO is concerned.
x
The performance of such engines is limited by materials.
Efficiency is related to the peak operating temperature as in any heat
engine. Thus, the continuous combustion version cannot logically
operate at temperatures much higher than can gas turbines. The engine
variety that uses the same cylinder for compression and expansion can
operate at somewhat higher temperatures. Water cooling of the corn-
bus tors can go far to improve the integrity and the efficiency of
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either of these conceptual engines so that overalj. SFC may approach that
of the spark-ignition gasoline engine. This, however, probably tends
to allow NO to increase. As a class, these engines are untried and
x
theoretically show some deficiency in volume and efficiency.
The last class of engine to be considered (the closed Brayton
cycle reciprocating engine) is similar in that compression and expansion
occur in cylinders (7). By adjusting the relative sizes of the com-
pressor and expander, maximum benefit can be gained. The system is
best used if the engine operates in a closed loop with a fluid at high
pressure. This keeps the size down. However, the same basic limitations
occur with this engine as with the others—operating temperature is
limited by materials. Since the loop is closed, fluids other than air
can be used to gain efficiency advantages (at the expense of worrying
about the leakage and fluid replacement). This engine is then a re-
ciprocating version of the closed gas turbine already mentioned in a
previous chapter. Use of recuperators and efficient components can
allow the engine to approach or even exceed the efficiency of the
equivalent gas turbine. These engines have an advantage over gas
turbines in that design power and off-design operation can both be
achieved with reasonably low efficiency degradation down to very low
power levels. (Similar engines taken in context with rotary engines
using external combustion are discussed in Chapters 8 and 9.)
The closed reciprocating engine requires an external heater and
a radiator similar to the Stirling or Ericsson engines. The achievable
efficiencies are not as high as for the Stirling or the Ericsson engines.
The valving problem is greater than that for the Ericsson engine.
Valving for this type engine calls for controlled cutoff and fast
action, especially at low power. Losses can be great with this type
of valve if the normal poppet valve system is used. A completely new
valving concept designed for low loss may be in order if these kinds of
engines are to be developed.
Engines of different types used together as hybrid systems to
achieve high efficiency practically always lead to higher costs for a
given installation. Examples of these are
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Basic Heat Engine Second Engine
Gasoline or diesel Rankine, gas turbine,
Stirling--powered by
waste heat
Diesel Turbosupercharger geared to
shaft—with or without
afterfirlng
The most successful systems of;this $ype have been the turbocharged
diesel and the turbosupercharged gasoline engine. Their increased
cost has led to low acceptability except in very specific applications
that can make good use of the better fuel economy or higher power
density.
In summary, the only "other engines" that appear to show
promise are the closed reciprocating version of the Brayton cycle some
variation of the turbocharged diesel, and the spark-ignition engine
using clean-burning fuels. The former is in the concept stage only
and shows less promise than other similar engines that are also in
the concept or technical feasibility stage (Stirling or Ericsson engines)
and that have already been discussed.
POTENTIAL AVAILABILITY
Essentially all of the possible "other engines" can be con-
sidered at the "starting block." Thus, none of them are any further
advanced at this time than the advanced Rankine or advanced Stirling
engine. While there may be an arguable case that a few of these can
be easier to develop than either the advanced Rankine or advanced
Stirling engines, it usually takes a relatively fixed period at optimum
expenditure rate to bring any new engine to the "suitable" prototype
stage, if, indeed, it ever reaches it. Thus, a first prototype is
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seldom a suitable prototype, and a second or third working prototype is
usually required. Consequently, at this point it is difficult to
estimate development time and all the "other engines" must be put in
the same time bracket as the advanced Rankine and advanced Stirling
enginesi. (The latter, at least, will shortly have the advantage of
$
having gone through the "first" prototype in the form of what we have
called the "present" Stirling.)
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REFERENCES
Discussions
Chrysler
OST (Jack Hope)
Thermomechanical Systems
DOT, Office of High Speed Ground Transportation
Papers and Reports
1. Puttick, J. R., Recycle diesel underwater powerplants,
SAE paper 710827.
2. Newkirk, M. S., and Abel, J. L., The Boston reformed fuel
car, SAE paper 720670.
3. Thermomechanical Systems, Presentation to the Panel.
4. Wall, M. R., Method and apparatus for increasing the
efficiency of combusticn engines, U.S. Patent 3 446 013, 1969.
5. Warren, G. B., and Bjerklie, J. W., Proposed reciprocating
internal combustion engine with constant pressure combustion, SAE paper
690045.
6. Bjerklie, J. W., A free piston Brayton engine for low
power, 1971 IECEC.
7. Bjerklie, J. W., Comparison :of CO- cycles for automotive
power plants, 1972 IECEC.
8. Ward, E. J., Spriggs, J. A., and Varney, F. M., New prime
movers for ground transportation--Low pollution, low fuel consumption,
1972 IECEC.
9. External combustion piston engine, Thermomechanical Systems
Co., EPA-OAP Contract EHSH 71-003.
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8. COMBUSTION
The combustion process is at the heart of the problem of
automobile emissions whenever chemically fueled heat engines are used
for developing propulsive power. This is true whether the fuel is
carried in the auto or is used to convert to electricity first--as for
electric cars. However, the main concern here is for the combustion
process in a self-contained heat engine on the auto carrying its own
fuel supply.
The emissions of major concern are unburned hydrocarbons, carbon
monoxide, and oxides of nitrogen. Other emissions of some concern are
particulates, soot, and oxides of sulfur. Sulfur and lead particulates
can only be handled by fixing the content of the fuel. Likewise,
pxides of nitrogen production are subject to fuel content as well as
the flame properties. Fuel nitrogen is the nitrogen actually contained
in the molecules of fuel (as opposed to dissolved air and nitrogen).
High percentages (over 50 percent) of this fuel nitrogen can be con-
verted to oxides of nitrogen. Usually automotive fuel contains low
enough nitrogen that the NO so generated would be much lower than the
X
1976 standards. Thermal NO generated by virtue of flame properties
X
and dependent on nitrogen contained in the air, is usually the NO of
2C
major concern.
Those emissions that are subject to control by combustion
control are soot, smoke, unburned hydrocarbons, carbon monoxide, and
oxides of nitrogen (thermal NO ). Until a few years ago, most com-
X
bustion work was devoted to achieving the highest possible efficiency
over the widest possible range of operating parameters. This implied
good control over everything except oxides of nitrogen. In internal
combustion systems such as in Otto-cycle and Diesel-cycle engines,
some compromise on highest possible efficiency was usually granted in
favor of smooth operation, easy starting, and fast response. Smoke
was usually controlled because it is visible. Gas turbine conbustors
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were usually regarded as very "clean" although they did smoke under,
certain circumstances.
Of the alternative engines, it can be accurately stated that
unburned hydrocarbons and carbon monoxide are low enough to meet 1976
standards or can easily be made to meet them. It can also be stated
that oxides of nitrogen are (or can be) low enough to meet the 1975
standards. The combustion problem therefore comes down to a question
of tighter control of oxides of nitrogen for the 1976 standards.
The generation of oxides of nitrogen in flames (thermal NO )
JC
has been traced to the occurrence of hot spots in the flame zone of
over ~-3500°F. In the usual combustion system, however, there is a
fuel-rich zone surrounded by an air zone. This implies that combustion
must take place in large part at or near stoichiometric mixture, that
is, at flame temperatures over, or near, 4000°F. Much of the NO seems
X
to form after the luminous flame zone. The higher the combustion pres-
sure, the higher NO in systems studied to date. Thus, while atmos-
X
pheric pressure systems (Rankine and Stirling-cycle combustors) can
be made to meet the 1976 emission standards, gas turbine combustors
(at 4 atmospheres and above) have not been completely successful in
limiting the NO emissions to 0.4 g/mile.
3C
With this situation, the only way to control the NO in the
3C
higher pressure systems (gas turbines, extra-cylinder-combustion
reciprocating engines) is to somehow quench the NO -forming reactions
2t
in their early stages. This has been done with some success by heat
extraction from the primary combustion zone leading to reduced peak
temperatures. This has been done by water cooling, radiation cooling,
and by injecting air into the primary zone, essentially reducing the
amount of combustion taking place there and cooling the products of
combustion so NO does not form. These steps have led to partial
2v
control of NO but have not yet been proven to be a panacea.
X.
Other approaches are to prevent the possibility of near-
stoichiometric combustion from taking place. This can be done by
arranging a combustion zone to hold a flame at a low enough flame
temperature to limit the rate of NO production and to thoroughly mix
3t
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and prepare the fuel so that no rich zones can appear, even in the form
of large droplets. There has been good success with this approach in
limiting emissions, but it has not yet been made into a practical com-
bustion system.
Many of the references listed describe the original problem.
Others describe the approaches so far tested. The GM Symposium on
Emissions in Continuous Flow Combustion Systems was a key meeting to
collect in one place and at one forum the most recent worldwide data
and considerations on emissions of the type encountered in gas turbines
and external combustion engines (Rankine, Stirling, closed gas turbine,
closed reciprocating Brayton cycle engines, etc.).
The combustion work being funded by EPA-GAP is continuing and
is reported publically in the Contractor Coordinating Meetings. The
auto industry is also continuing its own work. Industry has not yet
found a way to design a low-emission fixed-geometry gas-turbine com-
bustor. However, the atmospheric-pressure combustors appear to have
low enough emissions without variable geometry.
A discourse on combustion will not be undertaken here, since
the actual emission levels so far achieved are covered in the status
tables for each engine, and the general problems and approaches are
mentioned above.
REFERENCES
Discussions
EPA-OAP Contractors Coordinating Meetings: Sept. 1971, Jan.
1972, June 1972. Summaries and handouts from Solar, GE, United
Aircraft, Aerojet, Northern Research, AiResearch, MTI, Paxve.
Symposium on Emissions from Continuous Combustion Systems,
General Motors, 1971 (book published and available).
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Papers
I, McJones, R. W., and Corbiel, R. J., Natural gas fueled
vehicle exhaust emissions and operational characteristics, SAE paper
700078.
(•.
2. Genslak, S. L., Evaluation of gaseous fuels for automobiles,
SAE paper 720125.
3. Hazard, H., and McComis, C., Battelle Memorial Institute,
The effect of fuel nitrogen content on emission of NO from a low- :
emission automotive Rankine-cycle combustor, Low-emission automotive
Rankine-cycle combustor, EPA-OAP Topical report, March 1972.
4. Zwick, E. B'., Mills, J. R., and Fio Rito, R., Evaluation
of low NO burner, final report, EPA-OAP contract EHS 70-125, Paxve Inc.
July 1971?
5. Klapatch, R. D., and Koblish, J. R., Nitrogen dioxide
control with water injection in gas turbines,. ASME paper 71-WA/GT-9.
6. Fenimore, C. P., Formation of nitric oxide in premixed
hydrocarbon flames, General Electric Company.
7. Fenimore, C. P., Hilt, M. B., and Johnson, R. H., Formation
and measurements of nitrogen oxides in gas turbines, ASME paper
70-Wa/GT-3.
8. Singh, P. P., Young, W. Ee, and Ambrose, M. J., Formation
and control of oxides of nitrogen emission from gas turbine combustion
systems, ASME paper 72-GT-22.
9. Hilt, M. B., and Johnson, R. H., Nitroc oxide abatement :
in heavy duty gas turbine combustors by means of aerodynamics and
water injection, ASME paper 72-GT-530
10. Hazard, H. R., NO emissions from experimental compact
combustors, ASME paper 72-GT-153.
11. Bell, A. W., deVolo, N. B., and Breen, B. P., Nitric
oxide reduction by controlled combustion processes, WSC/paper 70-5.
12. Starkman, E. S., Mizutami, Y., Sawyer, R. F., and
Teixeira, D. P., The role of chemistry in gas turbine emissions,
University of California, Berkeley.
13. El-Messiri, I. A., and Newhall, H. K., the role of
combustion product quenching in the divided chamber engine, 1971
IECEC.
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14. Cornelius, W., and Wade, W. R., The formation and control
of nitric oxide in a regenerative gas turbine burner, SAE paper
700708.
15. Schaub, F. S., and Beightel, K. V., NO emission reductions
methods for large bore diesel and natural gas enginls, ASME paper
71-WA/DGP-Z.
16. Smith, D. S., Sawyer, R. F., and Starkman, E. S., Oxides
of nitrogen from gas turbines, 60th Annual Meeting, Air Pollution
Control Assoc., paper #67-125.
17. Sawyer, R. F., Teixeira, D. P., and Starkman, E. S., Air
pollution characteristics of gas turbine engines, Report no. TS-69-1,
Thermal Systems Division, ME Dept., University of California, Berkeley.
18. Newhall, H. K., and El-Messiri, I. A., A combustion
chamber designed for minimum engine exhaust emissions, SAE paper
700491.
19. Newhall, H. K., and Shahed, S. M., Kinetics of nitric
oxide formation in high pressure hydrogen-air flames, WSCI paper
70-3.
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9. ALTERNATIVE FUELS
SUMMARY
Alternative fuels to the conventional liquid hydrocarbons can
have a significant effect on emissions. Hydrogen, methane, and
methanol, for instance, can be used in slightly modified existing
engines, and tests indicate that hydrogen, at least, can allow
existing automobiles to meet the 1976 standards.
All these alternative fuels can be used in gas turbines and
in the external combustion engines. The use of these fuels in die.sel
engines may require the incorporation of a spark assist to achieve
suitable combustion. This would be similar to a stratified-charge
gasoline engine running on a cleaner-burning fuel.
The possibilities of alternative fuels are only beginning to
be explored, but could be very hopeful. Especially is this true if
the alternative fuels can also fit into whatever future energy
economy the nation develops.
We suggest that much more work be done in research and develop-
ment in this area.
INTRODUCTION
Emissions are a function not only of the engine type but also
of the fuel that the engine burns. The conditions of steady burning
at a constant low pressure allows properly designed burners for ex-
ternal combustion engines to have emissions below the 1976 standard
using conventional fuels. Current research promises to produce a
burner for gas turbines that will also have satisfactory emissions
using conventional fuels. The transient burning condition in diesels
and in spark-ignited engines is the reason for unacceptably high
1
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emissions. One approach to solving this problem Is to modify the
standard spark-Ignition engine. The review of such modifications is
outside the scope of this Panel. It is pertinent to point out here,
however, that such modifications may require a fuel modification. Thus,
the removal of lead alkyl is probably necessary to avoid poisoning of
the afterburner catalysts. In addition, sulfur and other additives
must be restricted to low levels. Also, fuel molecules containing
nitrogen can be expected to convert over 50 percent of this nitrogen
to nitric oxide (11). A second approach to solving the emissions
problem is the development of new types of engines. This approach
is the purview of this panel and is the subject of most of the other
chapters. A third approach is the use of alternative fuels and is
the subject of this chapter.
REFORMED FUEL
One company is attempting to develop an automobile that uses
a modified spark-ignition engine operating on a gas mixture composed
largely of H and CO-, produced by the steam reformation of unleaded
gasoline (12). A steam reformer is to be located in the trunk of the
automobile, and is intended to produce the hydrogen-rich gaseous
fuel mixture in response to engine demand. A surge tank is provided
to store H- and C0? for startup and transient demands.
The status of the program is as follows: Operation of the
modified engine has been demonstrated on tanks of H? + C0? mixture
of the composition expected from the reformer. Small reformer units
have been operated, but they have not produced reformate at the rate
demanded by the engine. A great deal of additional work will be
required to develop a reformer with the required fuel (H9 + C0?)
production rate that is compact enough to fit into the rear compart-
ment of the automobile. After that, the questions of endurance and
cost remain to be answered.
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LIQUEFIED NATURAL GAS (LNG) AND LIQUEFIED PROPANE GAS (LPG)
Both industrial and governmental groups have evaluated natural
gas and propane (LPG) to determine their capability of reducing emissions
from automobiles (13,14), One engine manufacturer showed that emission
levels approaching the 1975-76 standards can be achieved, but exhaust
gas recirculation is still required to reduce NO formation to the
3C
1975-76 standard. When using LPG there is an 8 percent loss in peak
engine power (350 cubic inch 1970 engine) compared with using gasoline
and a 14-1/2 percent loss using natural gas. There is a substantial
loss in economy (30 percent), and driveability is impaired. The use of
LPG for starting and warmup in a dual-fuel car using gasoline for con-
ventional operation was attempted. Cold-start emissions are decreased
but a 50 pound LPG container is required for approximately 20 gallons
of gasoline use.
Another manufacturer showed on an experimental natural gas
6-cylinder engine sized for bus operation that the use of compressed
(CNG) or liquefied (LNG) natural gas would produce emissions that
would meet 1975 standards. The 1976 NO standard could be met only
X
with EGR, a catalytic afterburner, and a great reduction in perfor-
mance. Compared with a diesel engine with similar power output, the
natural gas engine had on the average of 15 percent higher fuel consump-
tion. The emissions were odorless once there was no particulate matter
present. Of course greater safety hazards exist and additional pre-
cautions had to be taken.
There are over 5,000 cars converted to run on gaseous fuels in
the Los Angeles basin where gas supplies and liquid systems have been
joined together to provide the gaseous fuels to the car operators.
Emissions are lower and maintenance is reduced, but there is a dis-
advantage in the heavy, bulky tank required to hold the gaseous fuel.
The EPA, the Bureau of Mines, and General Service Administration
have all worked with gaseous fuels. EPA's position is to consider .
conversion of fleet-operated vehicles in those metropolitan areas
where logistical and economic factors are favorable in terms of
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availability of fuel and conversion equipment and where major air
pollution problems are attributable to motor vehicles.
AMMONIA
Studies with ammonia as an automotive fuel are going on at a
southern university where the students are considering the longer-
range view that an alternative fuel will be required when our gasoline
supplies are gone. Ammonia can be produced from air and water. There
is less consideration of emissions in this program. Emissions of
nitrogen-containing compounds may be much higher.
HYDROGEN
Hydrogen gas has three unique properties that, when taken
together, give it a unique potential as a vehicular fuel:
1. The exhaust gas contains no carbon in any form. The
problems of unburnt hydrocarbons and of poisonous CO do not, therefore,
exist. With hydrogen as a fuel one needs no afterburner or other
secondary reaction vessels.
2. The flammability limit of hydrogen is exceptionally high.
The volume percentage of hydrogen in air can range over a factor of
19 and still be ignited by a spark. This contrasts with the factor of
5 for gasoline vapor. Because of this high flammability range, very
lean mixtures of hydrogen gas may be used, thereby ensuring that NO
3C
will stay within acceptable standards. With hydrogen as a fuel, one
needs no exhaust-gas-recirculation to reduce NO .
Ji
3. The supply of hydrogen gas is inexhaustible. Currently,
the cheapest way of making hydrogen gas is to use natural gas as a
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base material. When nautral gas approaches exhaustion 'and its price
goes too high, the cheapest way of making hydrogen gas will be to use
coal as the base material. When the price of coal becomes too high,
the cheapest.way of making hydrogen will be to use water and electric
power as the base materials. All the water which is used in the
electrolytic process of making hydrogen is eventually reformed when
the hydrogen is burned. In the 15-30 year span we are discussing,
the required electric power may possibly be coming directly from the
sun's heat or by way of the sun's heat captured by the upper layers of
the tropical water, hydroelectric power, waves, wind, or from renewable
vegetation. Under any circumstances, the electric power will not come
from the burning of fossil fuels.
The recognition of the potential of hydrogen as a fuel of the
future, the fuel that will provide for our transportation, heat our
homes, and power our industry, has struck a sympathetic chord in the
scientific community of this country. As a result, an outburst of
literature on the hydrogen economy appeared in 1972 (1-10). Unfortu-
nately, the literature was not accompanied by a corresponding experi-
mental activity.
Austin (4) has reviewed the scant experimental work on hydrogen
pertinent to its use as a vehicular fuel. An engine burning hydrogen
gas at stoichiometric ratio has only one tenth the concentration of
NO in its exhaust as xjhen burning gasoline vapor at its stoichiometric
ji
ratio. Furthermore, at an air/fuel ratio of 1.75 times stoichiometric,
the NO content of the hydrogen exhaust is reduced by a further factor
X
of 20, well below the 1975 standards. Several experimenters have
reported conversion of internal combustion engines to hydrogen fuel
retaining satisfactory performance, but with no emission data. The
cryogenic fuel tank plus its hydrogen fuel would weigh 40 percent less
than the conventional tank with its gasoline for the same cruising
radius, but would occupy 5 times the volume. The cost of such tanks
has not yet been explored for the mass-production market, but promises
to be quite large. It is not improbable chat the manufacturing cost of
such a tank would be at least one fourth of the cost of the complete
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power-plant cost. Hydrogen storage in pressurized tanks promises to
be both expensive and heavy. Also, the behavior of hydrogen containers
in case of accident with full loads of hydrogen is an unknown, but it
is a problem being studied in some quarters, such as at Oklahoma State
University. Hydrogen storage in various hydrides has been explored for
space applications and other special purposes. All of these methods
are presently very expensive, and much engineering is required to make
the scheme tractable.
As we see it, the maximum potential of hydrogen as a fuel
would be obtained with a diesel-type engine. With such an engine, the
fuel mixture would be very clean during the great bulk of the driving
time, particularly in cities, where full power is not used. At these
times NO emissions would be negligible. Only at peak power would a
*£
near-stoichiometric ratio be used, with an accompanying rise in NO
2t
emissions, usually occurring in environments that are ventilated
(rural areas).
Sound experimental work and socio economic impact studies on
the use of hydrogen as a vehicular fuel is required before unqualified
success can be claimed for the approach.
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REFERENCES
1. Gregory, D. P., Ng, D.Y.C., and Long, G. M., The hydrogen
economy, Chapter 8 in Electrochemistry of Cleaner Environments, editor
J. O'M. Bockris ed., Plenum Press, 1972.
2. Gregory, D. P., A new concept in energy transmission, Publ.
Util. Fortnight., Feb. 3, 1972, p. 3.
3. Williams, L. G. , The cleaning of America, Astronaut.
Aeronaut., Feb. 1972, p.42.
4. Austin, A. L., A survey of hydrogen's potential as a
vehicular fuel, Lawrence Livermore Laboratory, UCRL-51228, June 19,
1972.
5. Bockris, J. O'M., A hydrogen economy, Science, p. 1323,
June 23, 1972.
6. Hydrogen: Likely fuel of the future, Chem. Engin. News,
p. 14, June 26, 1972.
7. Bockris, J. O'M., and Appleby, A. J., The hydrogen economy--
An ultimate economy? Environ. This Month, p. 29, July 1972.
8. Hydrogen fuel use calls for new source, Chem. Engin. News,
p. 16, July 3, 1972.
9. Hydrogen fuel economy: Wide-ranging changes, Chem. Engin.
News, p'. 27, July 10, 1972.
10. Clark, W., Hydrogen may emerge as the master fuel to power
a clean-air future, Smithsonian, p. 13, Aug. 1972.
11. Hazard, H. and McComis, C., The effect of fuel nitrogen
content on emissions of NOx from a low-emission automotive Rankine-
cycle combustor, Bettelle Memorial Institute, Topical Report to EPA-
OAP, March 1972.
12. Newkirk, M. S. and Abel, J. L., The Boston reformed fuel
car, SAE paper 720670.
13. Genslak, S. L., Evaluation of gaseous fuels for automobiles,
SAE paper 720125.
14. McJones, R. W. , and Corbiel, R. J. , Natural gas fuelled
vehicles exhaust emissions arid operational characteristics, SAE
paper 700078.
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10. ALTERNATIVE METHODS OF POLLUTION REDUCTION
SUMMARY
Many possibilities exist for reducing the effects of automobile
emissions on air quality other than reducing the automobile emissions
themselves. Many of these are self evident:
Smaller cars
More and better public transportation
Fiscal policies that encourage less driving,
less emissions per car, more use of public
transportation
Staggered hours of driving
Restricted times for urban driving of some
vehicles
Encouragement of existing lower emission engines
(diesel) for limited urban use (taxis, delivery
vehicles)
Blocked-off city business centers
The skillful planning of these and other alternatives may go further
to reduce the overall emissions than will imposition of tight auto
emission standards.
It is not reasonable to expect automobile cleanup to be all
that is necessary for urban air cleanup. It is also not reasonable
to expect clean autos to be a requirement where clean air is not a
problem. A balanced attack on the overall transportation/energy
problem, however, can allow great reduction in urban air pollution
without unduly burdening the car owner. It is one of the hopes for
alternative engines that some of the low emission types will fit into
whatever ultimate solutions are arrived at for the transportation/
energy problems.
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INTRODUCTION
The other chapters in this report discuss the ability of
various types of engines to conform to the 1976 emission standards
while performing a standard duty cycle. The present chapter discusses
auto pollution reduction by methods other than engine development. Such
alternative methods include changes in the duty cycle required of a
given car, as well as those changes for society that will demand fewer
car-miles.
Some of these changes are entirely within the responsibility
of EPA. Some would require the cooperation of other federal agencies.
In such cases EPA should take the initiative in establishing the
appropriate cooperative programs.
ENCOURAGEMENT OF SMALL CARS
As smaller engines are refined to perform as well as large
engines with respect to specific fuel consumption and parts per million
of emissions, the grams per mile of emissions will become more a
function of vehicle weight. Then the amount of pollution control
accessories required for a given level of control will also be a
function of vehicle weight, dictating a rising curve of added cost
versus car weight. The pollution control standards will therefore
encourage the use of small versus large cars.
A shift from large to small cars would be beneficial for
meeting air pollution standards. The present EPA Incentive Procurement
Program, as well as the R & D program, is based on a 4,000-lb car
performing as effectively in city and country driving as present-day
cars. This perpetuates the philosophy of the large car, whereas a
2,000-lb car performing effectively in city driving only could be
very effective in minimizing automotive emissions in urban areas.
By reducing both the required weight and performance, in acceleration
and hill-climbing ability, there would be more assurance that the
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automobile industry could produce an acceptable car meeting the 1976
pollution standards. The realization of such a change in small cars
would more easily allow the urban areas to meet 1976 standards without
drastic changes in engine types.
SOCIETAL CHANGES FOR FEWER CAR-MILES
This country has demonstrated that appropriate economic in-
centives can stimulate an outburst of ingenuity from its citizens. The
government can, therefore, most effectively achieve a given societal
goal by using this ingenuity. One way of bringing this ingenuity to
bear upon air pollution is through taxation. Such a tax must be
selective in applying only to those regions where pollution is serious,
i.e., to the interiors of cities.
An accurate and low-cost method of applying such a tax has
been developed for the Road Research Laboratory in Britain. Each
car is equipped with a meter which is tripped by. stations suitably
located along the city streets. Technology exists today for both the
meters and the triggering stations. The meter would of course be
calibrated for the pollution potential of its car in addition to other
societal-cost factors. The economic incentive thereby provided would
encourage each individual to reduce his travel cost by either driving
a smaller car, joining a commuter pool, or using public transportation.
such a tax would also discourage the cruising of taxi cabs. The re-
duction in car-miles within a city would have a side benefit. The
stops and congestion-induced idling per car-mile would be greatly re-
duced.
There is every reason to add to the taxes paid by automobile
users the other external costs which are presently borne by society
as a whole or by local residents. Work at the Road Research Laboratory
in Britain has indicated that the congestion costs alone might be $2
per vehicle mile for city-center driving in rush hours, and a proportion
of these costs could be levied. An increment could be added for
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emissions and noise. Such charges would vary widely with time of day
and with location.
There would be five major results of such a taxation policy.
1. Governmental regulation of pollution and research into
methods of its control would be paid for by those responsible for the
pollution. A substantial burden would be removed from taxation revenue.
2. Residents and property owners could be compensated on
simple formulas for a proportion of the nuisance resulting from the
proximity of major highways.
3. Congestion would be eliminated because the costs of travel
during periods of congestion would be so high that people would choose
to travel at other times or by alternative means. Vehicle emissions
would fall sharply with elimination of congested traffic flow.
4. Bus and other public transport services would become much
more viable because of increased patronage, increased road speeds, and
the removal of what amounts to society's present heavy subsidy of
private motor vehicles.
5. As large, heavy vehicles bring about higher costs to society
than do small, light cars and as they would, therefore, bear a higher
tax rate, there would be further incentive toward the use of those
automobiles that require lower quantities of raw materials and of fuel.
Much simpler forms of taxation may also serve the same purposes.
Hence, a free public transportation system in the central business
district (CBD) in conjunction with parking lots and high-cost toll
gates around the district could enhance the move toward less congestion
and lowered emissions in the CBD.
With regard to the need to conserve resources of all types,
and especially of fuels, government will soon be faced with the
need for regulation by one or two alternatives: taxation or rationing.
Taxation of all raw materials, including fuels, at a rate inversely
proportional to the number of years the known reserves will last at
present rates of consumption may be appropriate. These rates would
be negotiated with industry on an annual basis. The proceeds of these
taxes should go toward establishing reliable energy supplies -- perhaps
through solar-energy research or the stockpiling of critical fuels. It
is apparent that present road fuels should quadruple in price to
achieve an incentive towards conservation comparable to that in Europe,
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for instance.
Such taxation policies should produce a more rapid change in
our transportation systems with less cost to society than would a
system of government rationing coupled with government financing of
research and development of new transportation concepts. Not only
would public transportation flourish, with its higher efficiency, but
the Incentive to develop more efficient automobile engines would rise,
as it has done in Europe with the trend to diesel engines.
It is apparent that the days are numbered for the large family
automobile powered by engines of 150 to 400 HP burning petroleum fuels.
One view of the future is that vehicles will be powered by hydrogen
produced by nuclear reactors. Another view is that such a system will
be too wasteful of energy and that travel will take place in small
slow-speed battery-driven vehicles over short distances and that auto-
mated guideways would transport these small vehicles, small buses, and
freight containers nonstop within and between cities. American industry
is well capable of bringing about such a transformation with ease and
economy if it is given the incentives. The taxation policies suggested
would provide such incentives.
Considerable government effort is needed for the initiation of
some such tax system.
DIRECT ENCOURAGEMENT OF MASS-TRANSPORTATION SYSTEMS
In the previous section we described a tax, one effect of which
would tend to push people into mass transportation systems. We shall
now describe a change in legal structures that would attract rather
than push people into rapid transit systems. The details of this change
in legal structure have been discussed in length by George Jernsted of
Westinghouse Electric.
Rapid commuter transit systems have been plagued by the
economic fact that nowhere in the world are they profitable. The
full ingenuity of the private enterprise system has, therefore,
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not focused on the problem of rapid transit systems. The change
in legal structure herein described would render new rapid transit
systems potentially profitable. The planning and implementation of
such systems could then be left to the private domain.
Suppose a new community is being planned and that it has a
rapid transit station. This station would be the natural center for a
business plus apartment buildings complex. The mere presence of the
station would render the surrounding land more valuable. Calculations
have shown that a fair share of the added land value would essentially
pay for the capital cost of the community's just contribution to the
rapid transit system. One way of transferring this added land value
would be for the rapid transit system to have condemnation authority.
Governmental agencies could work towards establishing a prototype system,
for adoption by states, under which rapid transit systems could become
potentially profitable.
ENCOURAGEMENT OF TRANSFER OF FREIGHT FROM TRUCKS TO RAILROAD
The increase in ton-miles of freight per year has closely
followed the increase predicted 25 years ago. Unexpectedly, however,
the increase has been absorbed almost entirely by the trucking industry.
Particularly unfortunate for the railroads has been the catastrophic
loss to the trucking industry of most of the manufactured goods they
once hauled.
From the standpoint of air pollution, this transfer of freight
from rail to truck is most unfortunate. Trucks require at least three
times as much fuel per ton-mile as does the railroad, and correspond-
ingly cause at least three times as much pollution.
The reason for the transfer of the manufacturer's trade from
railroad to trucks is understandable. The average speed of a boxcar,
from origin to destination, has remained at 6 miles per hour for many
years. This is so low that the depreciation of the goods in transit
is comparable to the freight charge itself. No wonder that the manu-
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facturers prefer trucks over rail despite the higher costs.
The reasons for the slow motion of freight may be traced to the
origins of the railroad system. This system was completed by 1910, when
the only competition was barge and mule haulage. At that time it was
certainly faster than its competition. Wisely, the railroads, therefore,
concentrated on low cost per ton-mile. This meant that at every fork
or intersection, the train has to be disassembled and new trains
assembled. For this purpose, freight yards were established. The time
spent by boxcars in freight yards gradually increased with the length
of trains, and now greatly exceeds the time the boxcar spends traveling
en route.
A study conducted at Carnegie-Mellon University has shown that
a simple change in viewpoint of the railroads could drastically improve
their service. This change is to organize their trains so as to mini-
mize the cost of transportation plus the depreciation of the goods in
transit and to charge an appropriately higher tariff. This study showed
that both the manufacturers and the railroad would receive a higher
profit, and 40% fewer freight cars would be needed to carry the present
traffic. Such a system would presumably result in a large transfer of
freight from trucks to rail.
The ICC could help to provide the railroad industry the economic
incentive for recapturing the manufacturers' trade.
GENERAL
The foregoing discussions are some relatively specific ideas
for reducing overall fuel consumption, thereby limiting emissions no
matter what kind of engine is used. The side effects are that urban
congestion can be minimized and natural resources conserved. Other
side effects are changes in the auto and energy businesses.
Obviously, there are many ideas that could be put to work with
similar benefits and/or changes so long as the major objective is im-
proved transportation efficiency in urban areas. The future trans-
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portation system, whatever it is — auto/road, all public bus, or some-
thing else -- must be more efficient than at present if the urban areas
are to become clean and uncongested. We could have, as a result,
a "livable city."
The alternative, which is a possible solution, although probably
a poor one, is the desecration of urban areas and a move of business as
well as people to the suburban and rural areas. This could lead
ultimately to an even more complicated and unwieldy transportation
system wholly dependent on the automobile -- a continuation of the
present problem rather than a solution of it. The effect on society
of this alternative may be more upsetting for society as a whole than
would be the overall effect of achieving the "livable city" with its
high-efficiency transporation system.
Whatever transportation system evolves has to be satisfactory by
user standards if it is to succeed. As was pointed out, imposed
economic incentives can go far toward guiding the public's selection
of standards, similar to the way in which past guidance has been toward
the auto/road system — low fuel tax, good roads and more of them,
nonsupport of adequate public transportation, etc. In any case, the
new systems, if there are to be any, must evolve, and fairly slowly, if
they are to succeed. They must also pay'their way as they go or suffer
the same fate as interurban rail transportation. But, by viewing the
entire transportation process as a single system rather than looking
at each of its segments (buses, or trolleys, or commuter trains, or
trucks, or taxis, or personal autos) as a separate system, more
efficiency can be achieved to the benefit of the public. It could be
accomplished in an evolutionary manner when viewed as a single system,'
and the chances of great suffering by any one business or public sector
would be minimized.
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APPENDIX A
Visits Conducted by the Panel
ORIENTATION VISIT
Office of Air Programs
Environmental Protection Agency
Ann Arbor, Michigan
November 1971
DOMESTIC AUTOMOBILE MANUFACTURERS
General Motors Corporation (all alternative engines)
December 20, 1971
Ford Motor Company (all alternative engines)
December 21, 1971
Chrysler Corporation (all alternative engines)
December 22, 1971
EPA INCENTIVE PROGRAM CONTRACTORS' VISITS
International Materials Corporation
(reformed-fuel/Otto-cycle engine)
January 6, 1972
Thermo Electron Company (organic fluid,
reciprocating Rankine engine)
January 7, 1972
Petro-Electric Motors (lead-acid battery/
Otto-cycle engine hybrid)
January 24, 1972
Austin Tool Company (diesel engine)
January 17, 1972
Paxve Corporation (organic fluid, turbo-
Ranklne engine)
January 17, 1972
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OTHER DOMESTIC VISITS
Office of Air Programs
Contractors Coordinating Meeting
January 18-21, 1972, September 28-29, 1971
Dr. David Ragone
Dartmouth College, Hanover, New Hampshire
(review of files of Technical Advisory
Committee on Advanced Automotive Power Systems)
February 14, 1972
Meeting of Technical Advisory Committee on
Advanced Automotive Power Systems
Battery Systems
February 3-4, 1972
Symposium on Batteries for Traction and Propulsion
sponsored by the Columbus Section of the
Electrochemical Society 3
March 7-8, 1972, Columbus, Ohio
Senate Hearings (gas turbines and Rankine engines)
March 14, 1972
Meeting with Kinetics Corporation at NAS offices
(organic fluid positive displacement Rankine engine)
February 1972
Meeting with Philips Corporation at NAS Office
(Stirling engine)
February 1972
Caterpillar Tractor Company (diesel engines)
March 23, 1972, Peoria, Illinois
Cummins Engine Company (diesel engines)
March 24, 1972, Columbus, Indiana
Lear Motors (steam, turbo-Rankine engine)
March 29, 1972, Reno, Nevada
Aerojet Liquid Rocket Company (organic fluid,
turbo-Rankine engine)
March 30, 1972, Sacramento, California
Department of Air Resources
Metropolitan District of New York
April 7, 1972
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Garrett AlKesearch (gas turbines)
Phoenix, Arizona
April 18, 1972
Perkirts Engine Company (diesel engines)
Farmington, Michigan
April 19, 1972
Williams Research (gas turbines)
Walled Lake, Michigan
April 19, 1972
Detroit Diesel (diesel engines)
Detroit, Michigan
April 20, 1972
Meeting with Ford, Philips, and EPA (Stirling engine)
Ford Motor Company
Dearborn, Michigan
April 28, 1972
Presentation of Preliminary Evaluation to CMVE
Detroit, Michigan
May 18, 1972
IR&T Presentation to DOT
Washington, D.C.
May 19, 1972
AAPS Coordination Meeting
Ann Arbor, Michigan
June 20, 1972
MERDC (all-alternative engines)
Fort Belvoir, Virginia
July 26, 1972
General Electric (batteries)
Schenectady, New York
July 27, 1972
Panel Chairman's Meeting
National Academy of Sciences
July 27, 1972
Pratt and Whitney Aircraft (batteries and fuel cells)
East Hartford, Connecticut
July 28, 1972
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CONFERENCES HELD AT UNIVERSITY OF CALIFORNIA
BERKELEY, CALIFORNIA
AUGUST 14, 1972
McCulloch Engine Co. (diescl engine)
Revom, Inc. (rotary diesel engine) }
Kinergetics, Inc. (internal-combustion Stirling engine)
Zwick Company (low-emission burners)
Thermomechanical Systems (air engines)
Professor Joe Walker
University of Calgary (Stirling engines)
Alberta, Canada
August 15, 1972
Preparation of Final Panel Report
University of California
Berkeley, California
August 15-18, 1972
EUROPEAN VISITS
Perkins Engine Company (diesel engines)
Peterborough, England
June 26, 1972
Rolls Royce (rotary diesel engines)
Crewe, England
June 27, 1972
Ricardo
Consulting Engineers (diesel engines)
* Shoreham by the Sea
Sussex, England
June 28, 1972
CAV (diesel technology, including injectors) /
. London, England
June 29, 1972
j
BICERI ;
Consulting Engineers (diesel engines)
Slough, England
June 29, 1972
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British Leyland Motor Company
(diesel engines, gas turbines, and Stirling engines)
Coventry, England
June 30, 1972
Noel Penney Turbines (gas turbines)
Solihull, England
June 30, 1972
Daimler-Benz (diesel engines, gas turbines)
July 3, 1972
M.A.N., (Stirling engines)
Augsburg, Germany
July 4, 1972
Philips (Stirling engines)
Eindhoven, Netherlands
July 5, 1972
United Stirling (Stirling engines)
Malmo, Sweden
July 6, 1972
Volvo (diesel engines)
Gothenberg, Sweden
July 7, 1972
Deutsch Automobilegesellsehaft (electric automobiles)
Stuttgart, Germany
September 5, 1972
British Railways Board (batteries)
Derby, England
September 8, 1972
CGE (batteries)
Marcoussis, France
September 6, 1972
Alsthom-Jersey (batteries, fuel cells)
Massy, France
September 7, 1972
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