EPA-AA-SDSB-81-4
Technical Report
An Evaluation of Three-Way Control
Single and Dual Bed Catalysts As Applied to
Heavy-Duty Gasoline Engines
by
Thomas Nugent
April 1981
NOTICE
Technical Reports do not necessarily represent final EPA decisions
or positions. They are intended to present technical analysis of
issues using data which are currently available. The purpose in
the release of such reports is to facilitate the exchange of tech-
nical information and to inform the public of technical develop-
ments which may form the basis for a final EPA decision, position
or regulatory action.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
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Table of Contents
Page
I. Introduction 1
II. Discussion 1
A. Equipment 1
B. Procedure 7
C. Engine History 7
D. Problems 8
III. Results 9
IV. Conclusions 20
References 23
Appendix A 24
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I. Introduction
A test program to evaluate the applicability of three-way
control (TWC) and dual-bed catalysts (TWC and Oxidation Catalysts)
in combination with a closed-loop control stoichiometric (feed-
back) carburetor on a production 1978 IHC 404 CID heavy-duty gaso-
line engine was conducted at EPA's Office of Mobile Source Air
Pollution control Laboratory (OMSAPC) Ann Arbor, Michigan. Test-
ing was conducted according to the federal test procedure for the
heavy-duty transient cycle.[1]
The test program consisted of forty-six cold-start tests,
fifty-eight confirmatory hot-start tests run to insure accuracy
and precision of the cold-start tests, and fourteen hot-start
tests run to identify the effects of air/fuel ratio control points
on NOx emissions. The effects of various combinations of cata-
lysts, EGR, air/fuel ratio control points, carburetor response
times and air pump capacity on emissions, fuel economy and engine
power were examined.
This project and data developed through this project has been
presented previously in an SAE paper jointly developed by EPA and
Engelhard Industries. The paper was formally presented at the
1981 SAE international Congress and Exposition.[2]
This EPA Technical Report provides background for the SAE
document. All individual test results are presented and an ex-
panded review is done of the conduct of the test program and
specific problem situations encountered in conducting the proj-
ect. This report will only highlight results of this study. A
more detailed analysis of results can be found in the SAE publica-
tion.
II. Discussion
A. Equipment
Tests were conducted by EPA with supportive expertise pro-
vided by Engelhard Industries, the supplier of all catalysts and
oxygen sensors utilized in the test program. The feedback Carbur-
etor and Logic Control Box were purchased by EPA from the Holley
Carburetor Company.
The engine, an IHC 404 1978 production engine with a Califor-
nia calibration representative of 1979 technology, was loaned to
EPA for testing purposes, through the cooperative efforts of the
International Harvester Company. Technical specifications for
equipment utilized in this program are described in Table l.[2]
The Holley Model 2210 experimental feedback carburetor was a
direct bolt on replacement of the original Model 2210 on the 1978
engine. A 10 Hz electric solenoid valve controlled both the idle
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Table 1
Technical Specifications: TWC Catalyst Program
Engine: 1978 Production IHC 404 cubic inch V-8
heavy-duty truck engine
Three-Way Catalysts;
Oxidation Catalysts:
Feedback Carburetor:
Logic Box;
Two, 151-CID monolithic, 50 grams/ft3
loading, Platinum-rhodium ratio of 5:1,
(manufactured by Engelhard), Corning
substrate of 300 cells/in2.
Two, 113-CID monolithic, 50 grams/ft3
loading, platinum-palladium ratio of 4:1,
(manufactured by Engelhard), Corning sub-
strate of 300 cells/in2.
Holley 2210 modified for experimental use
by Holley Carburetor Co., Division of Colt
Industries, for stoichiometric closed-loop
control of idle and main-jets. Engelhard
designed microswitch with throttle engage-
memt during the last approximate 9 degrees
of throttle movement prior to wide open
throttle. Microswitch activation provided
a fixed 4.6 percent CO (A/F ratio = 12.9)
enrichment (in place of the conventional
power valve which provided upto 6.0 percent
CO at wide open throttle on the 1978 pro-
duction carburetor). Standard accelerator
pump, choke and throttle deceleration posi-
tioner were retained.
Holley Model 8 experimental-type designed
and built with adjustable,
- air/fuel ratio control point
(350 mv to 800 mv)
- response time (CRT)
- AC gain (a gain parameter in the logic
box)
- wide open throttle (WOT) open-loop over-
ride
- cold start open loop override*
* Provides an open-loop air/fuel ratio near stoichiometric from
the carburetor jets so that the choke may provide enrichment.
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Table 1 (cont'd)
Technical Specifications; TWO Catalyst Program
Exhaust Gas Oxygen
Sensor; Standard production Robert Bosch part No.
0258001001.
Air Pump: Each pump delivers 7.21-8.30 CFM @ 1000
pump RPM and 1.6 inches Hg backpressure,
(IHC no. 446746-C92, 461369-C91).
EGR System; Standard 1978 production.
Air Mixers; Located between the TWC and oxidation
catalysts.
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and main jet circuits. Choke calibration and idle speed were
standard (1978). The idle mixture screws were adjusted to provide
approximately 50 percent duty cycle on the solenoid valve in order
to achieve maximum control flexibility.
A throttle actuated microswitch deactivated the closed-loop
control near the wide open throttle (WOT) position providing en-
richment to about a 12.9 air/fuel ratio (4.6 percent CO) as a com-
promise for maximum horsepower, engine durability, and overall
emissions. At all throttle positions between idle and the near
WOT position the closed-loop control system was intended to pro-
vide stoichiometric air/fuel ratio conditions so that the TWC
catalysts could function properly. It should be noted that when
the microswitch was activated near WOT, resulting in an air/fuel
ratio of 12.9, the TWC single-bed catalyst provided little overall
conversion of HC, CO or NOx. However, since air was added between
the two beds in the TWC dual-bed catalyst system the second bed or
oxidation catalyst removed a large fraction of the HC and CO emis-
sions.
The engine utilized a deceleration throttle positioner which
opened the trottle slightly during deceleration (whenever the RPM
exceeded 1800 at high manifold vacuums) in order to reduce mis-
firing and excessively rich mixtures.
The Holley Model 8 logic box contained the adjustment fea-
tures listed in Table 1. The millivolt control point established
the operating point for the oxygen sensor output voltage and
thereby determined the air/fuel ratio relative to the stoichio-
metric condition. This relationship is represented by Figure 1.
The characteristic response time (CRT) determined the speed at
which the air/fuel ratio cycled around the millivolt control
point. A cold start override was controlled by a thermostatic
switch in the engine coolant circuit which was set to activate the
closed-loop system at 120°F.
The original 1978 production engine utilized air injection
from one air pump into the exhaust ports of each cylinder bank.
This air path was sealed for the conversion to the TWC catalyst
system. The air pump was instead routed to the air mixer between
the dual-beds as shown in Figure 2. The air pump was not used
when the TWC single-bed catalysts were used alone. No attempt was
made to divert air into exhaust ports upon cold start in order to
reduce cold start HC and CO emissions (where the TWC catalyst ini-
tially acts as an oxidation catalyst). Doing so would surely de-
crease emissions, as demonstrated in the 1978 production version
where the air, directed into the exhaust ports, had a very sub-
stantial effect on HC emissions.[2]
Tests were conducted in a standard EPA heavy-duty gasoline
transient test cell. The cell utilized a double-ended dynamom-
eter, water coolant system, electronic instrumentation an ambient
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Figure
SrOICMIOMETRIC
Oxygen
Sensor
Output
Voltage
(millivolts)
Air/fuel ratio
Typical curve of oxygen sensor output voltage vs. air/fuel ratio
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TO AIR
MIXERS'
ELECTRIC
DYNAMOMETER
MICRO
SWITCH
LOGIC BOX
TWC CATALYSTS
OXIDATION'
CATALYSTS
FIG. 2.'-.SCHEMATIC OF EXHAUST SYSTEM IN TEST CELL CONFIGURATION
FOR DUAL BED CATALYST TESTING IN THIS PROGRAM
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air handling/humidity conditioning system all of which serve as
independent units for each test cell. Computer and CFV/CVS sys-
tems are shared between cells. A more complete description of
test cell facilities can be found in EPA's 1972-1973 baseline en-
gine report.[3]
Other equipment utilized in this test program was either
standard 1978 production or fabricated to meet special require-
ments of the program.
B. Procedure
All testing activities conducted through this program follow
OMSAPC standard procedures for heavy-duty gasoline transient test-
ing. Specific procedures can be found in the Code of Federal
Regulations, 40 CFR, Part 86, Subpart N.
Briefly, with the engine and emission control system set up
for the configuration to be tested, one heavy-duty transient
cold-start test and three confirmatory hot-start tests (individual
hot-start portions of the cold-start transient tests) were run. A
twenty minute soak was conducted between each test. As each
sample was collected it was analyzed by EPA technicians on
in-house analyzer A009. Raw emission figures were turned in for
computer processing upon completion of the test sequence for each
version. Processing was usually complete by the following day
with the configuration not being changed until confirmatory emis-
sion results and satisfactory cycle performance were obtained.
Upon analysis of emission results the subsequent configuration to
be tested was determined and testing scheduled.
In the instances where major version changes, such as carbur-
etor substitution occured, or where major engine repairs were con-
ducted the engine was analyzed with a Sun 2001 Diagnostic Computer
to insure proper tune prior to testing.
C. Engine History
This engine was initially utilized in an EPA program to
determine engine emission sensitivity to the 1984 heavy-duty tran-
sient test cycle. Data developed through the sensitivity program
was presented through SAE publication.[4] The engine was also
utilized in a 1979 test program involving the application of var-
ious oxidation catalyst and air pump configurations. Data devel-
oped in this program was utilized in the development of the 1984
heavy-duty gaseous emission regulations.[1] The data was not pub-
lished separately. Testing of the TWC/feedback carburetor system
begain on January 17, 1980 at EPA's MVEL. Initial baseline and
early catalyst testing was conducted in test cell D103W. Due to
other priority testing requirements the engine was moved, at ap-
proximately mid-program (6-26-80), to test cell D104E where the
test program was completed on December 19, 1980. The engine was
removed from the test cell on December 23, 1980.
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D. Problems
A number of minor problems inherent with test programs of
this nature were encountered. These included thermocouple fail-
ure, air handling limitations and resulting high cell temperature
problems, torque cell failures, computer downtime, analyzer down-
time, logic control box missettings and various miscalibrations.
These did not seriously disrupt the program. A number of more
serious situations however did delay program completion.
During the soak portion of the cold-start test conducted on
May 29, 1980 a fuel regulator failure (a test cell component)
resulted in engine flooding and raw fuel collection in the cylin-
ders. As the system was dismantled to dispell the fuel four of
the eight spark plugs were broken. The test configuration was
resumed with replacement of the fuel regulator and all eight spark
plugs. The problem of engine modification from the baseline con-
figuration (new spark plugs), and potential subsequent data varia-
tion was noted and testing resumed.
A NOx correlation testing program on another engine required
the IHC engine to be move to a new test cell midway through test-
ing (from test cell D103W to cell D104E). The NOx study was de-
signed to determine the difference in bag versus continuous NOx
measurement during transient heavy— duty gasoline engine emission
tests. Cell D103W is physically located next to diesel cell D102
which is equipped with a continuous NOx measurement capability.
Locating the NOx correlation engine in cell D103W allowed, with
minor modification (creation of a passageway through the common
wall separating the two cells) , simultaneous normal bag sampling
and continuous NOx sampling to occur.
The transfer of the TWC test engine to another testing cell
was not felt to have been a significant problem since the same
physical parameters or limits apply to all test cells and since
each test must be compared to the cycle performance specifica-
tions. Any parameter exceeding its stated limits (temperature,
humidity etc.) or not passing the cycle performance specifications
is susceptible to being voided regardless of where the test was
run. It of course, would have been of preference not to have
moved the engine .
In mid- July a knock was detected in the engine that
ponded to a noticable emission increase. An engine check discoved
a misgapped spark plug. The plug was regapped and testing
tinued with emissions returning to near expected levels. However,
by mid-August the knock had intensified and engine analysis indi-
cated a broken piston. Probably the f orementioned misgapped plug
was closed by a piece of the broken piston that had since disin-
tegrated with continued engine use. It was further determined
that arching was occuring from several plug wire boots and that
the oxygen sensor had lost some of its low temperature sensitivity
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through damage from either the piston failure or spark plug mis-
firing. The piston, oxygen sensor (aged at Engelhard), plug wires
and plug boots were replaced.
In late September while running consecutive hot-start tests
to determine NOx emission levels at various millivolt set points
(determinant of air/fuel ratio) and ignition failure resulted in a
complete burnout of the TWC catalysts. The ignition failure was
caused by a short (insulation melt) in the primary lead to the
coil. EPA technician responsiveness resulted in damage being con-
fined to the TWC catalysts and oxygen sensor.
To insure that the oxidation catalysts were not damaged the
complete dual-bed system and oxygen sensor were replaced. The
replacement catalysts, supplied by Engelhard, were loaded identi-
cally to those destroyed in the burn out. The catalysts were aged
by running a seris of cold-start tests with forced cool-downs over
a two day period. A total of approximately eight break-in hours
of testing were run.
All tests determined to have been affected by any of the
forementioned problems were voided and those versions rerun.
III. Results
A description of configurations tested as well as emission
and fuel economy figures can be found for cold-start tests in
Table 2.* The most favorable emission results were obtained in
the dual-bed configuration (Figure 2) with EGR (version 45c). The
HC level of 0.68 g/Bhp-hr, CO level of 3.60 g/Bhp-hr and NOx level
of 0.74 g/Bhp-hr are well below the 1984 heavy-duty emission stan-
dards of 1.3 g/Bhp-hr for HC, 15.5 g/Bhp-hr for CO and the statu-
tory NOx standard of 1.7 g/Bhp-hr. The NOx standard is not part
of the 1984 regulation but is being developed as a separate rule-
making. These test levels represent conversion efficiencies of
approximately 73 percent for HC, 91 percent for CO and 86 percent
for NOx as compared to the stock single exhaust configuration
(version 00). Emission values for version 13 (version 45 without
EGR), version 21 (version 45 with a fast carburetor response) and
version 23 (version 45 with a slow carburetor response) also meet
these standards.
The need to test both single and dual-bed configurations was
required since before testing it could not be determined if the
dual-bed configuration would be required to meet the HC and CO
emission standards.
A considerable number of confirmatory hot start tests were
run to verify the cold^-s^art data but the test results were not
used further in the a^TlaW- - •"--- L-^ ----- ^--- -- --•
Appendix A. V__S
used further in the a^ilaysis. This hot start data is given in \/
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Version
Number
00
09
10
11
Table 2
IHC 404 Cold Start Tests
Emissions
HC
CO
NOx
BSFC
Engine Configuration
(g/BHP-hr) (g/BHP-hr) (g/BHP-hr) (Ib. fuel/BHP-hr)
1978 production engine, 2.55
1978 EGR, air pump with 2.48
air to exhaust ports,
standard carburetor, con-
ventional single exhaust.
1978 production engine, 2.65
1978 EGR, air pump with 2.65
air to exhaust ports,
standard carburetor,
fabricated single ex-
haust split into dual ex-
hausts, straight pipes
representing dummy cata-
lysts, no air mixers.
1978 production engine, 2.31
1978 EGR, air pump with 3.05
air to exhaust ports, 3.01
standard carburetor, fab-
ricated exhaust, single
exhaust split into dual
exhausts, two dummy TWC
catalysts, straight pipes
representing dummy oxida-
tion catalysts, no air
mixers.
1978 production engine, 3.58
no EGR, one air pump, 4.63
air to air mixers be- 4.57
tween the two dummy TWC 4.49
and two dummy oxidation
catalysts, feedback car-
buretor, open-loop at
wide open throttle and
under 120°F, medium car-
buretor response, 530 mil-
livolt control point, fab-
ricated exhaust.
40.85
42.13
54.11
50.65
65.25
72.82
74.23
50.96
58.00
57.70
48.93
6..00
4.66
5.56
5.07
4.68
4.54
4.42
7.81
8.41
8.23
7.94
0.671*
0.674*
0.663*
0.689*
0.732
0.701*
0.713*
0.692
0.655**
0.642**
0.648**
* Test conducted after installation of new piston and catalysts.
** Test conducted after installation of new piston.
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Version
Number
12
13
15
16
17
18
19
Table 2 (cont'd)
IHC 404 Cold Start Tests
Emissions
HC
CO
NOx
BSFC
Engine Configuration (g/BHP-hr)" (g/BHP-hr)" (g/BHP-hr) (Ib. fuel/BHP-hr)
Version 11, except the 4.24
system is completely
closed-loop.
1978 production engine, 0.84
no EGR, one air pump, 0.49
air to air mixers be- 0.97
tween the two TWC and 0.77
two oxidation catalysts,
feedback carburetor,
open-loop at WOT and un-
der 120°F, medium carbur-
etor response, 530 milli-
volt control point, fab-
ricated exhaust.
1978 production engine, 0.76
no EGR, no air pump, two
TWC catalysts, no oxida-
tion catalysts, feedback
carburetor, open-loop at
WOT and under 120°F, fast
carburetor response, 530
millivolt control point,
fabricated exhaust.
Version 15 except the 0.89
system is completely
closed-loop.
Version 15 with the car- 1.25
buretor response in the
slow position.
Version 15 except the 1.41
system is completely
closed-loop with the car-
buretor response in the
slow position.
1978 production engine, 1.27
no EGR, no air pump, 1.46
two TWC catalysts, no
oxidation catalysts, feed-
51.05
5.74
2.96
3.11
5.38
21.35
18.53
20.12
17.08
25.27
22.15
7.85
1.04
0.94
1.78
1.62
0.70
0.71
1.67
1.37
1.41
1.64
0.685
0.686
0.708
0.673
0.724
0.682
0.693
0.686
0.672
0.712
0.698
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Table 2 (cont'd)
IHC 404 Cold Start Tests
Emissions
Version HC CO NOx BSFC
Number Engine Configuration (g/BHP-hr) (g/BHP-hr) (g/BHP-hr) (Ib. fuel/BHP-hr)
back carburetor, open-
loop at WoT and under
120°F, medium carburetor
response, 530 millivolt
control point, fabricated exhaust.
20 Version 19 except the 1.30 17.07 1.53 0.699
system is completely
closed-loop.
21 1978 production engine, 0.71 4.11 2.07 0.698
no EGR, one air pump,
air to air mixers be-
tween the two TWC and
two oxidation catalysts,
feedback carburetor,
open-loop at WOT and un-
der 120°F, fast carbur-
etor response, 530 milli-
volt control point, fab-
ric ted exhaust.
23 Version 21 with the car- 0.70 3.19 1.55 0.714
buretor response time in
the slow position.
24 Version 21 except the 0.79 3.05 2.05 0.736
system is completely
closed-loop with the car-
buretor response in the
slow position.
26 1978 production engine, 0.87 3.22 1.93 0.738
no EGR, one air pump,
air to air mixers be-
tween the two TWC and
two oxidation catalysts,
feedback carburetor,
completely closed-loop,
medium carburetor re-
sponse, 530 millivolt
control point, fabri-
cated exhaust.
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Version
Number
27
35
37
41
43
Table 2 (cont'd)
IHC 404 Cold Start Tests
Emissions
HC
CO
NOx
BSFC
Engine Configuration
1978 production engine,
no EGR, two air pumps,
air to air mixers be-
tween the two TWC cat-
alysts and two oxida-
tion catalysts, feed-
back carburetor, open-
loop at WOT and under
120°F, fast carburetor
response, 530 millivolt
control point, fabri-
cated exhaust.
1978 production engine,
EGR, one air pump,
air to air mixers be-
tween the two TWC and
two oxidation catalysts,
feedback carburetor,
open-loop at WOT and un-
der 120°F, medium carbur-
etor resonse, 350 milli-
volt control point, fab-
ricated exhaust.
1978 production engine,
EGR, no pump, two
TWC catalysts, no ox-
idation catalysts, feed-
back carburetor, open-
loop at WOT and under
120°F, medium carbure-
tor response, 350 milli-
volt control point, fab-
ricated exhaust.
Version 35 without EGR.
Version 19 at the 350
millivolt control point.
(g/BHP-hr) (g/BHP-hr) (g/BHP-hr) (Ib. fuel/BHP-hr)
0.90
0.81
0.94
0.75
0.62
1.20
0.78
4.00
3.59
9.72
17.98
3.28
20.47
28.79
1.90
3.11
3.01
3.26
3.89
4.25
3.69
0.728
0.737
0.704
0.741*
0.691
0.643**
0.711*
* Test conducted after installation of new piston and catalysts.
** Test conducted after installation of new piston.
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Version
Number
45a.
45c,
45f
45m.
49
Table 2 (cont'd)
IHC 404 Cold Start Tests
53
Engine Configuration
1978 production engine,
EGR, one air pump, air
to air mixers between
the two TWC and two ox-
idation catalysts, feed
back carburetor, open-
loop at WOT and under
120°F, medium carbure-
tor response, 530 mil-
livolt control point,
fabricated exhaust.
Version 45 at the 710 0.68
millivolt control point.
Version 45 at the 630 0.56
millivolt control point.
Version 45 at the 630 0.65
millivolt control point.
1978 production engine, 4.35
EGR, one air pump, 5.29
air to air mixers be-
tween the two dummy TWC
and two dummy oxidation
catalysts, feedback
carburetor, open-loop
at WOT and under 120°F,
medium carburetor re-
sponse, 530 millivolt
control point, fabri-
cated exhaust, (version
11 with EGR).
Version 49 at the 350 4.47
millivolt control point.
Emissions
HC
(g/BHP-hr)
0.84
0.75
0.43
0.53
CO
(g/BHP-hr)
2.95
3.39
2.73
3.75
NOx
(g/BHP-hr)
1.13
1.94
1.42
1.44
BSFC
(Ib. fuel/BHP-hr)
0.713
0.649**
0.714*
0.750*
3.60
3.29
3.33
51.98
46.06
0.74
0.71
3.78
5.36
4.69
0.704*
0.737*
0.748*
0.669
0.688*
41.37
5.89
0.682
* Test conducted after installation of new piston and catalysts.
** Test conducted after installation of new piston.
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Version
Number
55
Table 2 (cont'd)
IHC 404 Cold Start Tests
Engine Configuration
Version 49 without EGR
at the 350 millivolt
control point.
Emissions
HC
(g/BHP-hr)
4.44
4.87
CO
(g/BHP-hr)
47.87
39.21
NOx
(g/BHP-hr)
8.33
7.74
BSFC
(Ib. fuel/BHP-hr)
0.760
0.659*
Test conducted after installation of new piston and catalysts.
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In the single bed catalyst configurations (TWC catalysts
only) version 15-20, 37 and 43 approximate the HC and NOx stan-
dards but fall short of CO standards by some 25 percent. For this
reason further discussion will be confined to dual-bed system con-
figurations. The reader is referred to the SAE document as refer-
enced for further analysis of single bed configurations.[2]
The effect of EGR on NOx emissions can be seen in the dualbed
configurations at the 350 millivolt (MV) control point with EGR
(version 35) as compared to the similar configuration without EGR
(version 41.) Here an approximate 20 percent decrease in NOx
emissions and a corresponding 6 percent decrease in fuel economy
can be seen. The NOx levels however, 3.11 g/Bhp-hr for version 35
and 3.89 g/Bhp-hr for version 41 both exceed the proposed NOx
standard.
Configurations at the 530 millivolt control point that meet
the proposed standard indicated a 9 percent increase in NOx emis-
sions with actual NOx levels of 1.48 g/Bhp-hr with EGR (version
45, 4 test average) and 1.35 g/Bhp-hr without EGR (version 13, 4
test average). These averages are misleading however since some
of the version 45 tests were conducted after installation of a new
piston and catalysts (discussed in section D). The only version
45 test conducted before piston and catalysts change yielded a NOx
value of 1.13 g/Bhp-hr or a 17 percent reduction in NOx emis-
sions. In general, the application of EGR resulted in significant
NOx emissions reduction.
The air/fuel ratio (millivolt control point) effect on emis-
sions is principally related to NOx. The stoichiometric point is
located at approximately the 530 MV control point with rich
air/fuel ratios at higher MV control points and lean air/fuel
ratios at lower MV control points. Tests indicate a MV control
point independence in dual-bed configurations with regard to HC
and CO control. The NOx relationship is demonstrated by the
series of hot-start tests (version 45) run at various MV control
points (Table 3). Here, a requirement for richer than stoichio-
metric air/fuel ratios to meet the proposed NOx standard is indi-
cated. This engine would have to run at approximately the 550 MV
control point to meet the NOx standard of 1.7 g/Bhp-hr (air/fuel
ration about 0.2 rich of stoichiometric.)
The critical response time (CRT) determines the speed at
which the air/fuel ratio cycles around the MV control point from
full rich to full lean. A fast CRT of 0.2 seconds, a medium CRT
of 2.8 seconds and a slow CRT of 5.6 seconds were evaluated. The
slow response time, according to closed-loop theory, produces the
tightest control under steady state conditions but not necessarily
under transient conditions. This is represented by the following
test data. Versions 21 and 23 represent individual cold-start
tests while version 13 is the simple mean of four cold-start tests.
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Table 3
IHC 404 Hot Start Tests*
Version
Number
45a.
45b.
45c.
45d.
45e.
45f .
45g.
45h.
45i.
*5j.
45k.
Engine Configuration
1978 production engine,
EGR, one air pump,
air to air mixers be-
tween the two TWC and
two oxidation catalysts,
feedback carburetor,
open-loop at WoT and
under 120°F, medium car-
buretor response, 530
millivolt control point,
fabricated exhaust .
Version 45 at the 740
millivolt control point.
Version 45 at the 710
millivolt control point.
Version 45 at the 685
millivolt control point.
Version 45 at the 655
millivolt control point.
Version 45 at the 630
millivolt control point.
Version 45 at the 605
millivolt control point.
Version 45 at the 575
millivolt control point.
Version 45 at the 550
millivolt control point.
Version 45 at the 495
millivolt control point .
Version 45 at the 440
millivolt control point.
HC
(g/BHP-hr)
0.30
0.30
0.43
0.42
0.40
0.36
0.33
0.39
0.31
0.38
0.38
0.32
Emissions
CO NOx
(g/BHP-hr) (g/BHP-hr)
0.61 2.02
0.81 1.97
0.89 0.93
0.94 0.92
1.07 1.18
0.84 1.00
0.74 1.21
0.82 1.63
0.64 1.54
0.69 1.88
1.02 2.28
0.77 3.01
BSFC
(Ib. fuel/BHP-hr)
0.693
0.665
0.689
0.689
0.687
0.658
0.678
0.608
0.675
0.684
0.647
0.653
All tests conducted after installation of new piston.
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-18-
Table 3 (cont'd)
IHC 404 Hot Start Tests
Emissions
Version
Number
451.
45m.
Engine Configuration
Version 45 at the 385
millivolt control point.
Version 45 at the 350
HC
(g/BHP-hr)
0.27
0.24
CO
(g/BHP-hr)
0.56
0.55
NOx
(g/BHP-hr)
3.45
3.85
BSFC
(Ib. fuel/BHP-hr)
0.667
0.633
millivolt control point.
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-19-
Emission g/Bhp-hr Ib. fuel/Bhp-hr
Version CRT (sec.) HC CO NOx BSFC
23 5.6 0.70 3.19 1.55 0.714
13 2.8 0.77 4.30 1.29 0.698
21 0.2 0.71 4.11 2.07 0.698
Upon analysis of individual cold-start tests for version 13
(Table 2) and the Los Angeles Freeway (LAF) portion of the tran-
sient test as presented in the referenced SAE document it was
determined that the best balance of emissions and fuel economy was
obtained with the 2.8 second CRT. This is further exemplified by
the near normal oxygen sensor voltage trace as indicated in the
same SAE document.[2]
The effect of open-loop at WOT on emissions is presented by
the comparisn of two dual-bed, 530 MV control point configurations
both without EGR; the open-loop at WOT version 13 and the same
configuration in the completely closed-loop mode version 26. Ver-
sion 13 figures represent the simple mean of four cold-start tests.
Emission g/Bhp-hr Ib. fuel/Bhp-hr
Version WOT-Mode HC CO NOx BSFC
13 open 0.77 4.30 1.29 0.690
26 closed 0.87 3.22 1.93 0.738
Although open-loop enrichment may result in higher emissions (CO)
it was found necessary to run open-loop at WOT in order to main-
tain maximum engine horsepower levels required by heavy-duty vehi-
cles.
Maximum horsepower levels were determined from WOT map tests
run to establish speed-load parameters for the computer driven
transient tests. Results indicate an average horsepower value of
167 for the standard 1978 production engine (version 10). The
average in the dual-bed, open-loop at WOT configuration (version
45) is 162 horsepower, representing a 3 percent loss in maximum
horsepower. The corresponding completely closed-loop configura-
tion (version 46) resulted in an average horsepower of 148 an 11
percent drop from standard 1978 production. Due to this horse-
power loss subsequent testing was concentrated in the open-loop at
WOT mode.[2] Actual emission testing was not conducted on version
46; mapping was done for horsepower determination only.
The effect of air pump capacity is demonstrated by a compari-
son of a dual-bed, 530 MV control point, fast CRT configuration
without EGR and one air pump (version 21) and the same configura-
tion with two air pumps (version 27). Full air from both air
pumps was directed to the air mixers. Indicated figures repre-
sent one cold-start test for each version.
-------
-20-
Emission g/Bhp-hr Ib. fuel/Bhp-hr
Version Airpump No. HC_ CO NOx BSFC
21 1 0.71 4.11 2.07 0.698
27 2 0.90 4.00 1.90 0.728
Since a reduction in fuel economy was shown with two air
pumps and further since several other configurations produced CO
emissions under the 4 g/Bhp-hr level achieved with two air pumps,
all subsequent testing was conducted in the single air pump mode.
In analyzing the fuel consumption figures, given in pounds of
fuel/Bhp-hr or Brake Specific Fuel Consumption (BSFC), consider-
able variation for any given version is indicated. Thus it is
difficult to determine fuel economy trends for the various ver-
sions. Table 4 indicates BSFC for baseline configurations and the
dual-bed closed-loop system with and without EGR.[2]
Although slight fuel economy differences can be found between
individual versions, no significant fuel consumption differences
can be identified between baseline and closed-loop configurations
with and without EGR, between single vs. dual-bed catalyst modes
or between open vs. closed-loop at WOT modes.
Due to the experimental nature of this program several test
runs were accepted as valid that exceeded various cycle perfor-
mance specifications. High engine idle rates that occur during
the early portions of the transient cold-start test were
considered the primary cause of. this situation. This problem
could not be corrected by either software or hardware adjustments
due to time and equipment constraints. Since the problem was
limited to the first sample bag overall emission effects were not
considered significant enough to void marginal tests.
A problem observed with the preferred feedback system was
intermittent engine hesitation on strong accelerations. This
occurred even with a warm engine and intensified with the addition
of EGR. The problem, which occured around the stoichiometric
air/fuel ratio, is generally controlled with the rich mixtures
typical of current heavy-duty engines. It is theorized that the
problem could be best corrected through manufacturing design
changes.
The SAE publication should be referred to for a more complete
discussion of results of the test project.[2]
IV. Conclusions
The results of this test program indicated that at low mile-
age a TWC dual-bed catalyst system with a closed-loop stoichio-
metric carburetor can yield emissions substantially below the 1984
HC and CO standards and the statutory NOx standard for heavy-duty
gasoline engines.
-------
-21-
Table 4
Heavy-Duty Transient Test
Fuel Consumption 2/
Fuel Consumption
Configuration (Lbs. Fuel/BHP-hr)
1978 Production Engine (See Table II) 0.671 1 run
Version 00 0.674 1 run
Version 9 0.663 1 run
0.689 1 run
Version 10 0.732 1 run
0.713 1 run
0.701 1 run
Avg. of above 0.692 (7 runs)
Same Engine with Closed-Loop System 0.705 Avg. 17 runs
(of various versions)
With EGR St'd. Dev. = 0.032
Same Engine with Closed-Loop System 0.697 Avg. 16 runs
(of various versions)
Without EGR St'd Dev. = 0.032
-------
-22-
Engine-out HC and CO emissions were sufficiently high how-
ever, that the TWC single-bed catalyst alone could not be utili-
zed. Dual-bed catalysts were required and were able to produce
high conversion efficiencies. A number of key improvements to the
air/fuel preparation and distribution as well as improved quality
of combustion in the engine are required to alleviate the problem
of hesitation upon acceleration. These improvements are con-
sidered feasible since they have been accomplished with light-duty
passenger car engines.
Improved air/fuel distribution is also very important in
order to achieve maximum engine horsepower at the leanest possible
(but still net rich) air/fuel ratios. Maximum horsepower with the
closed-loop carburetor and catalysts was approximately 3 percent
below the maximum horsepower of the 1978 production engine. With
implementation of the above improvements this loss should approach
zero.
Brake specific fuel consumption was essentially the same
(within data scatter) as obtained with the 1978 production engine.
It would appear from this test program, even with systems
that were not optimized, that TWC closed-loop systems could pro-
vide efficient emission control of heavy-duty gasoline engines as
well as the same overall advantages as currently achieved with
similar systems on light-duty passenger car gasoline engines.
Design improvements to the heavy-duty truck engine would appear
justified as a result of the feasibility study.[2]
-------
-23-
References
1. "Gaseous Emission Regulations for 1984 and Later Model Year
Heavy-Duty Engines," Federal Register, Vol. 45, No. 14, Monday,
January 21, 1980.
2. Hansel, Dr. James G.; Cox, Timothy; Nugent, Thomas, "The
Application of a Three-Way Conversion Catalyst System to a Heavy-
Duty Gasoline Engine," SAE Paper 810086 (1981).
3. Cox, Timothy; Diatchun, Zachary; Nugent, Thomas; Passavant,
Glenn; Ragsdale, Larry, "1972-73 Heavy-Duty Engine Baseline Pro-
gram and NOx Emission Standard Development," EPA Technical Report
EPA-AA-SDSB-80-01, March 1981.
4. Cox, Timothy P., "Heavy-Duty Gasoline Engine Emission Sensi-
tivity to Variations in the 1984 Federal Test Cycle," SAE Paper
801370 (1980).
-------
-24-
Version
Number
11
12
13
15
16
Appendix A
IHC 404 Confirmatory Hot Start Tests
Engine Configuration
no EGR, one air pump,
air to air mixers be-
tween the two dummy TWC
and two dummy oxidation
catalysts, feedback car-
buretor, open-loop at
wide open throttle and
under 120°F, medium car-
buretor response, 530 mil-
livolt control point, fab-
ribated exhaust.
Version 11, except the
system is completely
closed-loop.
1978 production engine,
no EGR, one air pump,
air to air mixers be-
tween the two TWC and
two oxidation catalysts,
feedback carburetor,
open-loop at WOT and un-
der 120°F, medium carbur—
ator response, 530 milli-
volt control point, fab-
ricated exhaust.
1978 production engine,
no EGR, no air pump, two
TWC catalysts, no oxida-
tion catalysts, feedback
carburetor, open-loop at
WOT and under 120°F, fast
carburetor response, 530
millivolt control point,
fabricated exhaust.
Version 15 except the
system is completely
closed-loop.
:ion
mgine,
tump,
i be-
HC
(g/BHP-hr)
3.28
3.18
3.32
CO
(g/BHP-hr)
47.70
46.37
48.81
Emissions
NOx
(g/BHP-hr)
8.18
7.66
8.53
BSFC
(Ib. fuel/BHP-hr)
0.707
0.689
0.698
3.38
3.43
3.53
0.21
0.23
0.33
0.41
0.51
0.47
46.10
44.11
43.94
0.96
0.84
1.14
2.23
2.32
0.85
8.41
7.98
8.47
0.93
0.90
1.67
1.45
1.55
1.74
0.51
6.45
0.55
0.63
0.49
0.58
19.59
16.86
23.64
16.33
16.20
16.52
0.76
0.75
0.67
0.80
0.80
0.82
0.698
0.690
0.704
0.679
0.692
0.709
0.717
0.724
0.664
0.700
0.765
0.707
0.706
0.686
0.712
-------
-25-
Version
Number
17
19
20
21
23
24
Appendix A (cont'd)
IHC 404 Confirmatory Hot Start Tests
Engine Configuration
Version 15 with the
carburetor response in
the slow position.
no EGR, no air
two TWC catalysts, no
oxidation catalysts,
feedback carburetor,
open-loop at WOT and
under 120°F, medium
carburetor response,
530 millivolt control
Version 19 except the
system is completely
closed-loop.
no EGR, one air pump,
air to air mixers be-
tween the two TWC and
two oxidation catalysts,
feedback carburetor,
open-loop at WOT and un-
der 120°F, fast carbur-
etor response, 530 milli-
volt control'point, fab-
ricated exhaust.
Version 21 with the car-
buretor response time in
the slow position.
Version 21 except the
system is completely
closed-loop with the car-
buretor response in the
slow position.
Emissions
HC
:ion (g/BHP-hr)
:he 0.88
tse in 0.84
L. 0.85
ingine, 0.86
imp, 0.90
i, no 0.84
its, 0.78
:or, 0.85
and 0.75
.um
ise,
i i- m~\
LULU -L
I exhaust .
: the 1.04
:ely 0.76
0.86
ingine, 0.45
lump, 0.37
CO
(g/BHP-hr)
17.36
18.66
18.93
16.27
20.65
16.50
20.80
25.52
19.25
15.09
14.70
15.16
2.22
1.92
NOx
(g/BHP-hr)
1.77
1.76
1.65
1.51
1.17
1.44
1.41
1.12
1.59
1.51
1.36
1.37
2.11
2.02
BSFC
(Ib. fuel/BHP-hr)
0.686
0.699
0.683
0.693
0.686
0.676
0.696
0.740
0.700
0.691
0.695
0.697
0.698
0.695
0.34
0.40
0.71
0.39
0.40
0.85
0.96
0.57
0.72
0.73
2.17
2.14
.91
.95
1.97
0.710
0.712
0.735
0.729
0.726
-------
-26-
Version
Number
26
27
35
37
Appendix A (cont'd)
IHC 404 Confirmatory Hot Start Tests
Engine Configuration
no EGR, one air pump,
air to air mixers be-
tween the two TWC and
two oxidation catalysts,
feedback carburetor,
completely closed-loop,
medium carburetor re-
sponse, 530 millivolt
control point, fabri-
cated exhaust.
1978 production engine, 0.64
no EGR, two air pumps, 0.58
air to air mixers be-
tween the two TWC cat-
alysts and two oxida-
tion catalysts, feed-
back carburetor, open-
loop at WOT and under
120°F, fast carburetor
response, 530 millivolt
control point, fabri-
cated exhaust.
1978 production engine, 0.28
EGR, one air pump, 0.33
air to air mixers be-
tween the two TWC and
two oxidation catalysts,
feedback carburetor,
open-loop at WOT and un-
der 120°F, medium carbur-
etor response, 350 milli-
volt control point, fab-
ricated exhaust.
1978 production engine, 0.42
EGR, no air pumps, two 0.43
TWC catalysts, no oxi-
dation catalysts, feed-
back carburetor, open-
loop at WOT and under
120°F, medium carbure-
tor response, 350 mil-
livolt control point,
fabricated exhaust.
:ion
mgine ,
lump,
i be-
HC
(g/BHP-hr)
0.45
0.42
0.42
CO
(g/BHP-hr)
0.75
0.79
0.87
Emissions
NOx
(g/BHP-hr)
1.71
1.83
1.76
BSFC
(Ib. fuel/BHP-hr)
0.727
0.727
0.722
2.10
2.10
0.98
1.40
5.48
7.75
2.04
2.12
3.08
3.14
3.07
3.14
0.726
0.725
0.726
0.717
0.682
0.688
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-27-
Version
Number
41
43
45a.
49
Appendix A (cont'd)
IHC 404 Confirmatory Hot Start Tests
Engine Configuration
no EGR, one air pump,
air to air mixers be-
tween the two TWC and
two oxidation catalysts,
feedback carburetor,
open-loop at WOT and un-
der 120°F, medium carbure-
tor response, 350 milli-
volt control point, fab-
ricated exhaust.
1978 production engine, 0.92
no EGR, no air pump, 1.02
two TWC catalysts, no
oxidation catalysts, feed-
back carburetor, open-
loop at WOT and under
120°F, medium carburetor
response, 530 millivolt
control point, fabricated
exhaust.
1978 production engine, 0.38
EGR, one air pump, air 0.41
to air mixers between
the two TWC and two ox-
idation catalysts, feed-
back carburetor, open-
loop at WOT and under
120°F, medium carbure-
tor response, 530 milli-
volt control point, fab-
ricated exhaust.
1978 production engine, 3.70
EGR, one air pump, 3.51
air to air mixers be-
tween the two dummy
TWC and two dummy
oxidation
Emissions
HC
:ion (g/BHP-hr)
:ngine, 0.47
lump, 0.50
CO
(g/BHP-hr)
1.23
1.17
NOx
(g/BHP-hr)
3.93
3.89
BSFC
(Ib. fuel/BHP-hr)
0.689
0.688
19.46
23.82
1.39
0.85
48.65
48.31
3.03
2.63
0.99
1.13
5.51
5.45
0.649**
0.636**
0.697
0.705
0.722
0.642
** Test conducted after installation of new piston.
-------
-28-
Version
Number
49
53
55
Appendix A (cont'd)
IHC 404 Confirmatory Hot Start Tests
Emissions
HC
CO
NOx
BSFC
Engine Configuration
catalysts, feedback
carburetor, open-loop
at WOT and under 120°F
medium carburetor re-
sponse, 530 millivolt
control point, fabri-
cated exhaust, (version
11 with EGR).
Version 49 at the 350
millivolt control point.
Version 49 without EGR
at the 350 millivolt
control point.
(g/BHP-hr) (g/BHP-hr) (g/BHP-hr) (Ib. fuel/BHP-hr)
3.54
3.42
3.72
3.71
33.16
33.89
38.78
39.34
5.85
5.95
8.68
8.74
0.672
0.662
0.645
0.649
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