EPA-420-S-74-100
AUTOMOBILE EMISSIONS AND ENERGY CONSUMPTION
John P. DeKany and Thomas C. Austin
Environmental Protection Agency
For Presentation at the
Air Pollution Control Association
Spring Seminar
Montebello, Quebec
May 20-22, 1974

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The impact of automobile emission
control on fuel economy is a subject
receiving increasing attention by the
public, industry and Government. Many
schemes have been promoted in the in-
terest of achieving reduced fuel con-
sumption by the passenger car popula-
tion. Some of the more popular schemes
are:
1.	Vehicle miles traveled (VMT)
reductions (using gas rationing
or other approaches).
2.	Shifting new car production to
small cars.
3.	Removing emission controls from
existing cars.
4.	Relaxing automobile exhaust
emission standards.
To determine the impact on both
emissions and fuel economy of the
latter two schemes, the U.S. Environ-
mental Protection Agency's (EPA)
Emission Control Technology Division
(ECTD) has performed extensive eval-
uations. Further studies have also
considered the impact of vehicle
weight and other parameters on auto-
mobile fuel economy.
DATA SOURCES & CALCULATION PROCEDURES
Input data for EPA's fuel economy
studies come from four major sources:
1.	New car certification testing
2.	In-use car surveillance testing
3.	Prototype vehicle testing
4.	Special projects testing
The new car certification testing
is run by EPA at the Motor Vehicle
Emission Laboratory in Ann Arbor,
Michigan. Over two thousand vehicles
are submitted annually by the auto-
mobile manufacturers for testing.
Most of these vehicles are tested
after 4,000 .miles of operation but
many vehicles are tested at mileages
as high as 50,000 miles.
In-use surveillance testing is done for
EPA by various contractors located
throughout the United States. This
ABSTRACT
U.S. automobile emission standards
have resulted in a 12% loss in sales-
weighted fuel economy for model year
1974 vehicles due the types of control
systems the industry has chosen to use.
Increasing concern over fuel economy
is causing some manufacturers to adopt
control techniques for model year 1975
which will result in improved economy
and lower emissions simultaneously.
Techniques appear to be available which
will allow this trend to continue into
future model years. The extent of the
improvements possible will depend on
the demands of the market, the response
of the industry, and the existence of fuel
economy related regulations or legislation.

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program is run to determine the actual
emission levels from the vehicles in
the hands of the public. Vehicles are
randomly selected from registration
lists and a variety of model years and
vehicle makes are included in the pro-
gram.
Prototype vehicle testing is routine-
ly performed at the Ann Arbor laboratory.
Many vehicles are volunteered to EPA for
testing by automobile manufacturers and
independent developers who may be inter-
ested in either lab-to-lab correlation
at low emission levels or in public
disclosure of their developments through
the test reports which ECTD publishes on
the prototype testing. Other vehicles
are solicited by EPA from automobile
manufacturers and independent developers
for testing. These vehicles are ones
that have not been volunteered but in
which EPA has some particular interest.
Special projects testing is done by
EPA for a variety of reasons. Examples
of extensive special projects in the
past are:
1.	A study of the effects of tampering
with emission controls.
2.	A study of fuel economy characteristics
of rotary engine-powered vehicles versus
conventional engine-powered vehicles.
Host of the relevant data from the four
major sources was accumulated using either
the 1972 Federal Test Procedure (FTP) (1)
(2)* or the 1975 FTP (3). In this paper
the fuel economy values calculated from
the 1975 FTP were converted to the equiv-
alent 1972 FTP value to maintain consis-
tency .
The FTP is a chassis dynamometer test
performed indoors, in a closely controlled
environment. The driving cycle followed,
which is often referred-to as the "LA4",
represents a 7.5 mile trip in an urban
area. Average vehicle speed over the cycle
is approximately 20 miles per hour (mph)
and the vehicle makes 2.4 stops per mile.
The speed range encountered during the
LA4 cycle is from zero (idle) to 57 mph.
The details of the speed vs. time trace,
which the driver of the vehicle follows,
reflect the irregularities in speed which
actually occur in customer driving. Essen-
tially no driving is done at exactly steady
state conditions. The use of the chassis
dynamometer makes the use of this realistic
and detailed driving cycle possible. Even
with the use of a driver's aid, such
cycles are difficult to repeat during
road or track testing where traffic and
road conditions are not constant. Each
cycle is run from a cold start. That is,
the vehicle is parked for at least 12
hours in a 68-86"F ambient prior to the
start of the simulated trip.
Fuel economy data derived from the
FTP are obtained by the carbon balance
method. Basically this involves using
the unburned hydrocarbon (H£), carbon
monoxide (CO), and carbon dioxide (CO2)
emissions measured during the test to cal-
culate the amount of fuel consumed during
the test. This method is based on the
fact that the HC, CO and CO2 emissions
are essentially all of the carbon con-
taining compounds emitted by the vehicle
and the fuel itself consists of hydro-
carbon compounds. Knowing the carbon
emitted in the form of HC, CO and CO2,
one can calculate the carbon that was
used in the form of gasoline. A more
detailed explanation and a derivation
of the carbon balance technique can be
found in reference (4). The same refer-
ence also shows the correlation of the
carbon balance technique and weigh
methods. Good engineering practice in
both the running of the emission test and
the fuel weighing results in excellent
correlation.
When more than one test is used to
determine the average fuel economy for
a vehicle or a group of vehicles, the
reciprocal economies are averaged.
In statistical terms the harmonic mean
of the individual test data, rather
than th'e arithmetic mean, was used.
This procedure results in the average
~Numbers in parentheses designate
references at the end of the paper.

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economy values reflecting the total
miles traveled during the testing
divided by the total gallons used. A
more detailed explanation of the sig-
nificance of the harmonic mean to av-
erage fuel economy data can be found
in reference (5).
EMISSION CONTROL TECHNIQUES
There are three separate sources
of emissions from most uncontrolled
passenger cars:
1.	evaporative emissions
2.	crankcase emissions
3.	exhaust emissions
Evaporative emissions have been re-
duced with the use of sealed gas tank
caps, revised air cleaner geometry and
activated charcoal traps connected to
fuel system vents.
Crankcase emissions have been essen-
tially eliminated with installation of
positive crankcase ventilation (PCV)
systems which recycle to the intake
manifold the blowby gases that were
formerly vented to the ambient.
Many different techniques have been
developed to reduce exhaust emissions.
Modifications have been made upstream of
the combustion chamber, in the combustion
chamber, and downstream of the combustion
chamber.
Upstream of the combustion chamber,
modifications can include intake air heat-
ing systems, improved chokes, recalibrated
and improved carburetion, and redesigned
intake manifolding. On many vehicles, com-
binations of these modifications are used
to obtain leaner combustion, which results
in decreased HC and CO emissions. Exhaust
gas recirculation (EGR) systems can be
used to achieve oxides of nitrogen (NOx)
reductions. The recirculated exhaust gas
reduces NOx formation during the combustion,
process by lowering peak flame temperatures
and reducing oxygen concentration in the
cylinder.
Combustion chamber-related modifications
can include revised geometry, lowered com-
pression ratio and retarded spark timing.
These modifications are used to obtain
a lower surface to volume ratio (S/V) at
the time of the combustion. Reduced S/V
results in lower unburned hydrocarbon
emissions because wall quenching is re-
duced. Retarded spark timing also results
in higher exhaust gas temperatures (due
to the reduced expansion occuring after
combustion) which promotes post cylinder
oxidation reactions in the exhaust system.
Valve timing modifications have been made
to create "internal EGR" on some engines.
Other engines, however, have had valve
timing changes made to reduce the amount
of internal EGR so that HC and CO emissions
would be lowered.
Post combustion chamber modifications
can include air injection, revised ex-
haust manifold geometry, afterburners,
thermal reactors and catalytic convert-
ers. These techniques are normally used
to promote oxidation reactions in the
exhaust gas to reduce the HC and CO
content, but in a reducing atmosphere
catalysts can also be used to reduce
NOx.
EFFECT OF EMISSION CONTROLS
GENERAL EFFECTS -'Contrary to popular
belief, emission controls can affect
fuel economy both positively and neg-
atively. Table 1 summarizes the effects
of the more common control approaches.
Spark retard is the control technique
that has been most responsible for the
negative economy impact that emission
controls have on current (1974) models.
The reduction in burned gas expansion
and the reduced exposure of the charge
to high temperatures which occurs with
retarded timing may work very effectively
to reduce HC and NOx emissions, but less
work is extracted from the fuel. The
degree to which fuel economy is adversely
affected depends on the extent of the
retard used. Many retard systems work
only during transient conditions or
during operation in lower trans-
mission gears. This allows control
of emissions during urban, stop and

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go, operation without adverse fuel
economy effects during highway
cruising.
Reduced compression ratios are less
effective at reducing HC and NOx emissions
and have been used mainly to allow the
use of low lead or unleaded fuels which
are generally of lower octane rating.
A reduction in compression ratio from
9:1 to 8:1 results in an economy loss
of about 3.5% in urban driving (4).
Rich air/fuel ratios are sometimes
used to promote oxidation reactions in
the exhaust manifold. Rich calibration,
however, results in poor fuel utilization
in the cylinder, as there is insufficient
oxygen available to completely bum all
of the fuel. Rich ratios also reduce the
ratio of specific heats (k) of the intake
charge, which reduces efficiency. Rich
calibrations are sometimes used to offset
the poor driveability induced by the use
of EGR systems that recycle excessive
amounts of exhaust gas during light load
operation. Excessive EGR can reduce flame
speed which reduces engine efficiency.
Lean air/fuel ratios used on many
current models improve economy by re-
ducing the throttling required for a given
engine load (thereby reducing pumping
losses) and increasing the ratio of
specific heats of the intake charge. Quick
warm-up systems and intake air heaters
extend the degree of enleanment possible.
Proportional EGR (PEGR) systems do not
recirculate excessive amounts of exhaust
gas during light loads where the engine
least needs and can least tolerate EGR.
PEGR systems recirculate exhaust gas in
proportion to the intake air flow. Some
systems employ even higher percentage
flow rates at high loads than light loads.
This type of EGR system can be used to
provide significant NOx reductions with a
simultaneous fuel economy improvement (6).
The benefits are due to reduced throttling
losses and an increase in the specific heat
ratio of the intake charge. Most current
(1974) vehicles do not use proportional
EGR systems, but several systems are fully
developed and may be installed on some
1975 models.
Catalytic converters and thermal
reactors are often associated with changes
in fuel economy but in themselves they
have essentially no effect. Any related
fuel economy effect is due to engine
calibrations made to optimize the
performance of these after-treatment
devices. Both positive and negative
overall effects are possible, depend-
ing on the specific type of catalyst
or reactor used.
TABLE 1
Fuel Economy Effect of Various
Emission Control Techniques
Positive	Little or	Negative
.Effect	no Effect	Effect
Lean Air/Fuel Ratios
Proportional EGR
Quick Warm-up Systems
Intake Air Heaters
Catalysts
Thermal Reactors
Air Injection
Evaporative Emission
Controls
Positive Crankcase
Rich Air/Fuel Ratios
Conventional EGR
Spark Retard
Reduced Compression
Ratio
Ventilation

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Air injection systems require
some engine power to drive the air
pump but the effect on economy is
very small.
EFFECT ON THE 197A MODELS - The effect
of the 1974 Federal emission standards
(3.4 grams per mile [gpm] HC, 39 gpm
CO, 3.1 gpm NOx) on fuel economy depends
on the combination of control techniques
a manufacturer uses. The choice of con-
trol techniques can be dictated by cost
constraints, the desire to retain high
performance and high economy, and by
the extent of control required to meet
the standards. Not all cars require
equivalent control on a percentage basis
to meet a given standard. Lighter vehicles,
because of the lower exhaust volumes, emit
less HC and NOx emissions than heavier
cars (7) and, therefore, need less control.
This allows the manufacturers of lighter
vehicles to more easily avoid the use of
control techniques that adversely affect
economy.
Figure 1 shows that the lighter veh-
icles have avoided fuel economy penalties
due to emission standards. Figure 1 is
based on 654 tests of uncontrolled (1957-
1967 model year) vehicles and 464 tests
of 1974 models. Most new cars in inertia
weight^ (IW) classes 3500 pounds and
below achieve superior fuel economy in
urban driving to uncontrolled cars of
equal weight. Vehicles in weight classes
4000 pounds and above, however, have
suffered severe penalties, ranging from
13% to 21% on the average.
Not all models have followed the trend
indicated in Figure 1. Some manufacturers
have developed more sophisticated systems.
The adoption of improved fuel metering
systems, like electronic fuel injection,
"Inertia weight" is equal to the vehicle's
curb weight plus 300 pounds load rounded
to the nearest class.
FIGURE 1
PERCENT CHANGE IN FUEL ECONOMY BETWEEN
UNCONTROLLED AND '74 MODELS vs. INERTIA WEIGHT
Inertia Weight

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FIGURE 2
FUEL ECONOMY vs. VEHICLE WEIGHT
a
o
C9
U
«
04
«
01
25
20
15
10
1 ¦ 1
		 1 I ¦ I	1	
—1	1	
"
1957-1967 Vehicles
©	9

1974 Vehicles
O	-o
-

-

>0-^ —


^-o	
—



1 t l
1 1	1	1
i i
2000 2500 3000 3500 4000
	 Inertia Height
4500 5000
5500
by_some manufacturers is an example of
what can be done to reduce emissions and
improve fuel economy and performance si-
multaneously. Some manufacturers, howeyer,
have done worse than indicated in Figure 1
by choosing low cost or no cost systems
(e.g., massive spark retard) at the sac-
rifice of economy and performance.
Figure 2 presents additional infor-
mation about the comparison of 1974
models to uncontrolled cars. Fuel economy
is plotted vs. inertia weight class for
both data sets. The reduced power re-
quirements of the lighter vehicles
result in superior fuel economy. The
advantage of the light cars is even
more pronounced for the 1974 models, as
the heavier models have suffered fuel
economy penalties due to emission
controls.
Sales Weighted Effect - Since the effect
of emission controls has not been the
same for all weight classes of vehicles,
the overall effect of the 1974 Federal
standards can be determined only by
considering the effect on various weight
classes. To avoid the confounding effects
of market shifts it is necessary to select
a fixed sales distribution to be used in
determining the change in fuel economy due
to emission controls from one model year to
another. If the sales distribution (by
weight class) of uncontrolled cars was
used to determine the sales-weighted
economy of uncontrolled cars, and the
sales distribution of 1974 cars was used to
determine the sales-weighted economy of
1974 cars, the difference in sales-weighted
fuel economy would include not only the
effect of emission controls but the effect
of market shifts in the various weight
classes. The effect of market shifts have
been avoided in our analysis of the data by
fixing the sales distribution (at that
experienced for model year 1973) for both
uncontrolled and 1974 model year vehicles.
The 1973 sales distribution was selected
because it is the most recent one avail-
able. This distribution has been reported
in reference (8) and is also shown in
Appendix A.

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Using the 1973 sales distribution, the
change in sales-weighted fuel economy
from uncontrolled cars (1957-1967 average)
to the 1974 models is -12.3%. Sales-
weighted fuel economy for the 1974 models
is 11.4 miles per gallon (mpg) and 13.0 mpg
for the '57-'67 average. Figure 3 shows
the trend in sales-weighted economy
(fixed '73 sales distribution) from un-
controlled to 1974. The average loss for
the controlled model years, 1968-1974,
is 7.0%.
EFFECT OF TAMPERING
In response to suggestions that re-
moval of emission controls from in-use
vehicles could result in significant
improvements in fuel economy, an in-
house program was run to investigate
the effects of tampering with emission
control systems. It is obvious that
many emission control techniques are
difficult to eliminate. Changing camr-
shafts, compression ratios, distributors,
carburetors, and cylinder heads would be
extremely costly. It is also apparent that
many techniques used to reduce emissions
also improve economy. Keeping these
things in mind, the program was de-
signed to achieve maximum fuel econ-
omy at minimum cost.
A total of ten late model vehicles
(1973 and 1974) were procured for the
evaluation. Sub-compact, compact, inter-
mediate, and full-size cars were included.
Vehicles were tested according to the
following plan:
1.	Tune to manufacturer's specifi-
cations .
2.	Test for emissions and fuel
economy.
3.	Optimize for fuel economy.
4.	Test for emissions and fuel
economy.
5.	Time to manufacturer's speci-
fications .
6.	Send out to independent garage
or tune-up shop for fuel economy
optimization.
7.	Test for emissions and fuel
economy.
FIGURE 3
FUEL ECONOMY vs. MODEL YEAR
I
3
u
«
pi
a
«
16
15
14
13
12
11
_L

T
T
T
T

-L

X
'57-'67 *68
'69
•70 *71 '72
Model Year
'73
'74

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Fuel economy optimization done by
EPA included EGR removal, vacuum advance
restoration, initial advance optimization,
idle speed reduction, and air pump re-
moval. Intake air preheaters, evaporative
control systems and PCV systems were
Intentionally not altered.
Fuel economy optimization done by the
eight independent garages and tune-up
shops often consisted of the same modi-
fications made by EPA (done somewhat
differently) and sometimes included valve
adjustments, leaner idle settings, richer
idle settings, altered centrifugal ad-
vance, leaner main metering jets, and
air cleaner inversion.
The results of the tampering done by
EPA and the independent garages and
tune-up shops were quite different as
shown in Table 2. Both EPA and the
independent garages and tune-up shops
were successful in causing significant
increases in exhaust emissions, but only
EPA achieved fuel economy improvements.
Changes which the independent garages and
tune-up shops made that tended to improve
economy were often offset by changes that
caused fuel penalties. The percent change
in fuel economy resulting from the in-
dependent garage tampering ranged from
-15.5% to +9.0%. Only four of the
thirteen attempts showed any improvement.
Of significant note, the one garage of
the eight that advertised its expertise
in emission control removal failed to
improve economy on both cars sent to it.
Despite the fact that this garage was
unable to improve economy, the modifi-
cations made resulted in an increase in
emissions. On the average, HC was up 16%,
CO up 50% and NOx was up 50%.
Although the results of the EPA program
may be too limited to establish firm esti-
mates for the effects of large scale
tampering, it appears that the gains in
fuel economy would be modest at best
while the adverse impact on exhaust
emissions would be substantial.
FUTURE TRENDS
1975 MODEL YEAR - Future fuel economy
trends will depend on many factors.
The choice of emission controls used
will have a significant effect. General
Motors (GM) has stated (9) that its
decision to use the catalytic converter
to achieve the 1975 Federal Interim
Standards (1.5 gpm HC, 15 gpm CO,
3.1 gpm NOx) will result in fuel
economy improvements. Preliminary
GM data (9) indicated that, for some
models, 20% improvements in fuel
economy could be achieved simul-
taneously with 50% reductions in
HC and CO emissions. GM has also
reported (10) that on the average
it expects a 13% increase in econ-
omy for 1975.
TABLE 2
SUMMARY OF TAMPERING RESULTS
ON FUEL ECONOMY AND EMISSIONS
Change from Manufacturer's Specifications
HC	CO	NOx	MPG
EPA Tampering	+65%	+21%	+116%	+7.0%
Tune-up Shop Tampering +39%
+89%
+63%
-3.5%

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While the catalytic converter
itself has essentially no effect on
fuel economy, the catalyst can re-
duce HC and CO emissions enough so
that control techniques which reduce
economy can be eliminated. With
engine calibrations essentially
optimized for best economy, the use
of a good catalyst system can allow
the vehicle to meet stringent emission
standards.
Part of the fuel economy optimi-
zation done on some 1975 models
Includes the use of proportional EGR.
Contrary to popular belief, the in-
stallation of a good EGR system can
result in improved economy (10). A
little known advantage of proportional
EGR systems is that they allow the
use of higher compression ratios, as
recirculated exhaust gas has anti-
knock qualities. These anti-knock
qualities are not realized with the
EGR systems on current (1974) models
because insufficient EGR flow rates
are provided during operation at higher
load where knock can be a problem.
While GM will be using the catalyst
system to optimize for economy in 1975,
other manufacturers will be achieving
improvements without catalysts. Saab,
for example, reported (11) improved
fuel economy due to the use of improved
fuel metering systems. It appears un-
likely that all manufacturers will
experience fuel economy improvements
for 1975, but with GM expecting signifi-
cant improvements and representing nearly
half of the U.S. market it is not unreason-
able to anticipate an improvement of approx-
imately 10% due to changes being made to
emission control systems. Figure 4 shows
the historical economy trend from the
years of uncontrolled cars to 1974 and
the effect on sales-weighted economy if
a 10% improvement due to improved systems
is realized in 1975. The point labeled
"Improved Systems" and the points for
model years 1974 and earlier are all based
on 1973 sales fractions.
FIGURE 4
FUEL ECONOMY vs. MODEL YEAR
T
T
T
T
§
«
0
n
01
p«
«
16
15
14
13
12
11
Altered Model Mix Assumed,
No System Improvements O
Improved
Systems
-L
a.
J.
'57-'*! '68 '69
•70 '71 '72 '73 *74
Model Tear
'75

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POST-1975 - Fuel economy trends beyond	EFFECT OF MARKET SHIFTS - Large improvei-
1975 are difficult to predict at this	ments in fuel economy are possible without
time because of uncertainty over future	improving engine efficiency if the market
emission standards and the uncertainty	shifts toward the lighter weight classes,
over future public demand for improved	Figure 4 shows the effect of a hypothetical
economy. The time table for future stand-	redistribution of vehicles sales. The
ards can be expected to have significant	actual sales distribution of the 1973 models
effect. Several prototype control systems	is shown with the solid line in Figure 5.
being designed to meet the "statutory"	The dashed line is the distribution that
HC and CO levels of .41 gpm HC and 3.4	would result if the 4500 pound and heavier
gpm CO have shown potential for fuel	classes were eliminated and sales were
economy improvements over 1974 cars, at	distributed evenly between the 2000 and
NOx levels near .4 gpm. The "3-way" cat-	4000 pound classes. This change in sales
alyst approach, which employs fuel injection	distribution would cause the average
modulated by an oxygen sensor in the ex-	inertia weight to drop from 3970
haust stream, has been reported by Volvo	pounds to 3000 pounds. With no im-
(12) to give 8% better fuel economy than the	provement in engine efficiency the
corresponding 1974 model. Gould has re-	increase in sales-weighted economy
ported (13) fuel economy data that indicate	over the 1974 case would be 37%.
dual catalyst type systems can also achieve
.41 gpm HC, 3.4 gpm CO and 0.4 gpm NOx with The hypothetical shift in sales
fuel economy superior to 1974 model cars.	distribution could be accomplished
The use of advanced control systems like	without sacrifices in passenger room
those currently under investigation by	and comfort. Recent analysis (14) has
Volvo and Gould could depend on the need	shown that functionally designed auto-
for such systems to meet stringent	mobiles, a rarity in the current market,
emission standards in the future.	offer substantially -more interior room

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than heavier cars designed with, "styling"
in mind. Reference (14) showed that the
new Volkswagen Dasher compared to the new
Ford Mustang II has essentially equivalent
room for the front seat passengers but 14%
more rear leg room, 25% more rear shoulder
room, and 158% more luggage room, despite
the fact that the Mustang is 27% heavier
and two inches longer than the Dasher.
ALTERNATE ENGINES - The use of alternate
engine technology can also result in
substantial fuel economy improvements
in the future. The alternate engines
with the greatest potential are those
employing unthrottled internal com-
bustion operation. Three types of engines
that can operate in this manner are:
1.	stratified charge
2.	variable displacement Otto cycle
3.	Diesel
Open chamber stratified charge
engines have demonstrated significant
advantages over conventional engines
when they are not throttled, but without
throttling they have difficulty achiev-
ing stringent emission standards. Unless
the engine is throttled exhaust temp-
eratures drop because of the greater
heat capacity of the charge per unit of
fuel during the very lean conditions
that exist at low power levels. Low
exhaust temperatures make thermal or
catalytic reactions in the exhaust
system difficult. More development work
appears to be required before strati-
fied charge engines will be able to
meet the dual requirements of low
emissions and improved fuel economy.
Variable displacement engines offer
significant fuel economy potential because
of their theoretical ability to maintain
nearly peak efficiencies throughout the
load and speed range of the engine. Un-
like the exhaust of the un throttled
stratified charge engine, the exhaust of
the unthrottled variable displacement
engine stays hot enough to be compatible
with after-treatment systems. The exhaust
remains hot at low power outputs because
power fs reduced by reducing the intake
air volume (by engine displacement re-
duction) as-well as the fuel volume. The
development status of variable displacement
engines is significantly behind stratified
charge and Diesel engines.
The Diesel engine appears to be the
only alternate engine capable of meeting
stringent emission standards and giving
significantly better fuel economy in the
short term. Tests reported by EPA (15)
and others (16) show that pre-chamber
Diesel-powered passenger caTs, currently
available on the world market, have demon-
strated the ability to meet levels below
.41 gpm HC, 3.4 gpm CO and 1.5 gpm NOx
with no emission controls. Fuel economy
of the Diesel cars currently available
is much better than conventional cars of
equivalent weight.
Figure 6 shows the EPA data on the
1974 model gasoline-powered vehicles com-
pared to Diesel-powered vehicles tested
by EPA. The 3000 IW class Diesels were
the Opel Rekord 2100D and the Peugeot 504D.
The 3500 class Diesels were the Mercedes
220D, Mercedes 240D and the Nissan (Datsun)
220C. The 4500 class data point is based
on data from a Ford pick-up truck retro-
fitted with a six-cylinder Nissan engine.
All fuel economy results shown in Figure 6
are on the basis of the 1972 FTP.
Through the two sets of data points in
Figure 6 are drawn the best fit curves of
the form.(mpg) x (TW) = C, where "C" is
a constant. Previous work (17) has shown
this equation provides a good fit for the
miles per gallon versus inertia weight data
from a representative population of passen-
ger cars. The dashed curve through the
Diesel data points was used to calculate
a sales-weighted fuel economy for a
hypothetical "all Diesel" model year
using 1973 sales fractions. The resultant
sales-weighted economy for the all Diesel
case was 20.5 mpg compared to 11.4 mpg
for the all gasoline engine case. This
analysis indicates a potential for a 79%
improvement in sales-weighted fuel economy
due to a complete shift to.Diesel cars
with no change in model mix.
It should be pointed out that the
Diesel vehicles used to generate the
dashed curve in Figure 6 all had low
power to weight ratios. Top speeds of

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FIGURE 6
FUEL ECONOMY vs. VEHICLE WEIGHT
FOR CONVENTIONAL & DIESEL POWERED VEHICLES
g
a
P
14
w
AO
35
30
25
20
15
10
T
\
T
\
\
\
\
\
\
\
\
\ Diesel Powered Vehicles
1974 Gasoline Powered Vehicles
_L
I
I
2000 2500 3000 3500 4000
Inertia Weight
4500 5000
5500
these vehicles averaged 80-85 miles
per hour (mph) and zero to 60 mph
acceleration times were in the 25
second bracket. Reference (4) showed
that the fuel economy advantage of the
Diesel is approximately cut in half
if It is compared to gasoline-powered
cars of equivalent performance instead
of being compared to the average gas-
oline-powered cars. Reference (4) also
pointed out, however, that the Diesel
engine has the capability to have its
performance increased substantially
without suffering economy losses
through the use of supercharging. It
may not be necessary to sacrifice
vehicle performance to obtain the
fuel economy advantage shown in
Figure 6.
SUMMARY AND CONCLUSIONS
The systems used to meet the Federail
light duty emission standards in effect
since 1968 have been responsible for
an average 7% loss in fuel economy.
The 1974 models have suffered most
with a 12.3% loss. Recently increased

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concern over fuel economy, however,
is causing a reversal of the down-
ward trend. Improved emission control
systems, Both catalytic and non-cat-
alytic, being developed for 1975 are
likely to result in significant fuel
economy improvements being made simul-
taneously with significant emission
reductions. For some of the catalytic
systems it appears that a relaxation
of the 1975 Federal Interim Standards
would do nothing to improve economy
further.
The potential for fuel economy Im-
provements by tampering with the emission
control systems installed in current cars
does not appear to be significant and
large emission increases result when
tampering is done.
Future fuel economy trends could be
greatly influenced by a shift in sales
distributions. A drop in average car
weight of 1000 pounds could result in a
37% improvement in fuel economy. Dramatic
improvements also appear to be possible
if the usage of the Diesel engine is
expanded. The effect of future emission
standards appears to be insignificant when
compared to the effect of market shifts
or increased Diesel usage.
REFERENCES
1.	Federal Register, Volume 35, No. 219,
November 10, 1970.
2.	Federal Register, Volume 36, No. 55,
March 20, 1971.
3.	Federal Register, Volume 36, No. 128,
July 2, 1971.
4.	T.C. Austin and Karl H. Hellman,
"Passenger Car Fuel Economy - Trends and
Influencing Factors", SAE paper 730790,
September 1973.
5.	"Automotive Fuel Economy", U.S. Environ-
mental Protection Agency, Office of Air
and Water Programs, Mobile Source Air
Pollution Control, October 1973.
6.	J.J. Gumbleton, R.A. Bolton and
H.W. Lang, "How EGR Affects Engine Per-
formance", Automotive Engineering,
April 1974.
7.	"A Study of Emissions from Light Duty
Vehicles in Six Cities", report number
APTD-1497, prepared for EPA by Automotive
Environmental Systems, Inc., Westminster,
California, March 1973.
8.	"Passenger Car Weight Trend Analysis",
report number EPA-460/3-73-006B, prepared
for EPA by the Aerospace Corporation,
El.Segundo, California, January 1974.
9.	Statement of General Motors Corporation,
Submitted to the House Subcommittee on
Conservation and Natural Resources, by
E.S. Starkman and C. Marks, July 1973.
10.	"General Motors Advanced Emission
Control System Development Progress", Vol.11,
submitted to EPA, November 1973.
11.	"Emission Control Status Report",
submitted to EPA by Saab-Scania AB,
December 1973.
13.	Personal communication with
Dr. Robert Fedor, Gould Inc,. March 1974.
14.	T. Hogg, "Trimming Off the Fat",
Ward's Auto World, Vol. 10, No. 3,
March 1974.
15.	"Exhaust Emissions from Three
Diesel-powered Passenger Cars",
Report No. 73-19 AW, Emission Control
Technology Division, EPA, Ann Arbor,
March 1973.
16.	K.J, Springer and R.A. Ashby,
"The Low Emission Car for 1975 - Enter
the Diesel", Paper No. 739133, Inter-
society Energy Conversion Engineering
Conference, August 1973.
17.	"Fuel Economy and Emission Control'1,
U.S. Environmental Protection Agency,
Office of Air and Water Programs, Mobile
Source Air Pollution Control Program,
November 1972.

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CtorreMeJL
APPENDIX A
Urban Fuel Economy of Uncontrolled and
Controlled Passenger Cars

Fuel Consumption (Ci) in Litres/100 Kilometers
(L/100 Km) for Various Model Years
ly/J Sales
Class
Fractions
(fi)
'74
'73
'72
'71
•70
•69
•68
•57-'67
2000
.0128
.001H
9.8
9.9
10.2
10.4
10.1
10.6
12.2
10.2
2250
. 0438
.0% o
11.3
10.7
10.7
11.0
12.2
11.6
11.5
10.8
2500
.0573
,oHS3
11.9
11.9
12.0
12.2
13.4
12.5
12.1
12.3
2750
.0945

12.9
13.4
11.8
12.8
12.7
12.0*
12.0
13.7
3000
.0577
. i m
15.5
15.1
16.4
15.9
14.8
15.3
14.8
15.3
3500
.1181
.1132.
16.8
16.9
17.6
19.2
17.7
17.7
17.7
17.4
4000
.1221
.1 c>M0
21.6
21.8
21.3
20.2
19.5
19.7
19.6
18.7
4500
.2545

24.8
23.4
22.0
22.0
21.5
20.9
20.8
20.2
5000
.1681
.poS
26.1
25.3
24.6
24.6
23.4
25.9
25.3
21.7
5500
.0681
.(AT*
28.3
27.2
25.3
21.7
23.7
21.8
21.8*
22.4
ales weighted fuel
onsumption (Efici)
n L/100 km	20.7 20.1 19.5 19.4 19.0 19.0 18.9 18.1
ales weighted fuel
conomy.235.2. in
E f ici
iles per gallon	11.4 11.7 12.1 12.1 12.4 12.4 12.5 13.0
*No data available, corresponding value from *68 or '69 used.
NOTE: IW class 1750 was deleted from the analysis because of its
low sales fraction (.0030) and a lack of fuel economy data.

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