EPA/AA/CTAB/89-06
Technical Report
A Resistively Heated Catalytic Converter With Air
Injection For Oxidation Of Carbon Monoxide And
Hydrocarbons At Reduced Ambient Temperatures
by
Gregory K. Piotrowski
September 1989
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 technical information and to inform the public of
technical developments which may form the basis for a final EPA
decision, position or regulatory action.
U. S. Environmental Protection Agency
Office of Air and Radiation
Office of Mobile Sources
Emission Control Technology Division
Control Technology and Applications Branch
2565 Plymouth Road
Ann Arbor, Michigan 48105
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Table of Contents
Page
Number
I. Summary 1
II. Introduction 1
III. Description of Test Program 5
IV. Vehicle Description 5
V. Test Facilities and Analytical Methods 7
VI. Discussion 7
A. Selection of Air Pump Flow Rates 7
B. Discussion of Test Results 9
VII. Highlights From Testing 17
VIII.Future Effort 18
IX. Acknowledgments 18
X. References 19
APPENDIX A - Test Vehicle Specifications A-l
APPENDIX B - Individual FTP Results B-l
APPENDIX C - Bag I/Bag 3 Emission Levels Over the FTP
Cycle C-l
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I. Summary
A resistively-heated metal monolith catalytic converter
together with a belt-driven air pump was evaluated on a
gasoline-fueled vehicle. The purpose of this work was the
oxidation of carbon monoxide (CO) and hydrocarbon (HC)
emissions at 20° F ambient conditions.
CO emissions were reduced to 3.9 grams per mile over the
Federal Test Procedure (FTP) cycle with resistive heating of
the converter for 1-1/2 minutes and excess air added in front
of the catalyst for 3 minutes at the start of the test. This
was a 68 percent increase in efficiency from CO measured in the
absence of catalyst resistive heating and excess air addition.
Bag 1 CO from the FTP cycle was reduced to 63.5 grams with
catalyst resistive heating/air addition, an increase in
efficiency of almost 70 percent from the no-resistive
heating/no-air addition catalyst operating scheme.
Bag 1 HC was reduced to 2.88 grams with the catalyst
resistive-heating/air-addition scheme referred to above. This
was a 67 percent increase in efficiency from no-heat/no-air
catalyst configuration levels. HC emissions were reduced to
0.20 grams per mile over the FTP with catalyst resistive
heating/air addition.
II. Introduction
The motor vehicle certification process adopted in the
United States requires the measurement of emissions over the
Federal test procedure (FTP) cycle.[1] The ambient
temperature range allowed for this testing is 68°F to 86°F;
test cell temperatures at the EPA test facility in Ann Arbor,
generally range between 72°F and 77°F.[2]
Motor vehicle hydrocarbon and carbon monoxide emissions,
however, are sensitive to a number of variables, to include
ambient temperature. Black et all. [3] measured emissions from
nine high sales volume 4-cylinder engine equipped vehicles;
these vehicles had accumulated driving mileages ranging from
2,800 to 61,600 miles. Mean total hydrocarbons over the FTP
ranged from 0.21 g/mi at 70°F to 0.59 g/mi at 20°F with this
fleet. CO levels ranged from 2.46 g/mi at 70°F to 7.50 g/mi at
20 °F. Commercial summer and winter unleaded gasolines were
used for this 70°F and 20°F testing, respectively. Black and
others documented similar trends for non-catalyst gasoline,
catalyst-equipped gasoline and methanol engines in an earlier
study.[4] Other authors have also documented this
phenomena.[5,6]
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Light-duty automotive emissions of CO are of particular
concern to the U.S. EPA. The National Ambient Air Quality
Standards (NAAQS) for CO are 10 mg/mj (9 ppm) over 8 hours,
and 40 mg/ml (35 ppm) over a 1-hour time period. [7] During
1987, 59 cities or metropolitan areas exceeded the CO standards
on one or more days.[8] These metropolitan regions represented
a population of over 86 million people. It has been observed
that 90 percent of these violations occurred on days when the
ambient temperature dropped below the 68°F floor specified in
the transient driving requirements in certification
regulations.[9] An earlier study [10] also noted that 83
percent of the exceedances of the NAAQS for CO had been
occurring outside of the temperature range of 68°F to 86°F at
that time.
The relative importance of increases in Bag 1 CO emissions
to weighted FTP averages due to colder ambient conditions has
been demonstrated by the U.S. EPA. A small fleet of in-use
vehicles was tested over the FTP cycle at 75°F, 50°F, and 20°F
ambient conditions.[8] Bag 1 CO levels increased 529 percent
from 75°F levels when the vehicles were tested at 20 °F.
Similar increases in CO over the Bag 1 portion of the FTP were
noted in earlier EPA studies.[6,11] The stabilized and hot
transient portions of the FTP show increases in CO at lower
ambient temperatures; these increases, as a fraction of 20°F
test levels versus 75°F test levels are less than half of those
determined from Bag 1 testing. Bag 1 CO emission levels are
also comparatively much higher than CO from the stabilized and
hot transient portions of the FTP at 75°F and lower ambient
conditions.[6,8,11]
Higher Bag 1 CO emissions at lower ambient temperatures
may be caused by several factors. First, drivetrain friction
is greater at colder temperature. An engine therefore must
convert more energy to obtain similar acceleration and constant
speed at lower ambients until the difference in frictional
resistance between 75°F and the colder ambient conditions is
overcome. Fuel distribution, wall wetting, etc. may become
problems of greater concern as ambient temperature decreases
because of increasingly poorer fuel atomization. An increased
period of fuel enrichment may be necessary to overcome
driveability problems caused by poorer fuel distribution and
inefficient combustion at lower temperatures. Catalytic
converters also may take longer to "light-off," or come to
effective operating temperature at lower ambients.
A resistively heated metal monolith catalyst has been
evaluated on both methanol and gasoline-fueled vehicles
[12,13,14]. Camet Inc., a subsidiary of W.R. Grace, provided
this catalyst for our evaluation. This catalyst can be heated
to a temperature of 1000°F in a very short period of time prior
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to cold starting; catalyst specifications and power
requirements have been provided in a previous paper. [12] This
catalyst, therefore, may improve cold start CO emissions at
reduced ambient conditions by reaching light-off temperature
faster than a typical light-duty vehicle catalyst.
One part of the testing described in [13] above was an
evaluation of the resistively heated converter on a
gasoline-fueled vehicle at 20 °F ambient conditions. The
catalyst was evaluated in four different modes. First, the
converter was tested in a three-way catalyst configuration; no
resistive heating was applied nor was extra air added in front
of the catalyst (oxidation-catalyst mode) during this testing.
The catalyst was then resistively heated during Bags 1 and 3;
again, no additional air was added in front of the catalyst.
The catalyst was preheated for 10 seconds prior to cold start
in Bag 1; resistive heating continued for 30 seconds following
cold start. No resistive heating was applied during Bag 2.
Resistive heating was applied for 5 seconds prior to hot start
in Bag 3; heating continued for 20 seconds following hot start.
Two different resistive-heating/oxidation-catalyst
simulation strategies were evaluated. The first strategy
involved the same heating scheme as given above; air at 30 psi
(2.4 SCFM) was added in front of the catalyst during the
simultaneous resistive-heating/engine-running portions. of Bags
1 and 3. The second strategy involved increasing the
post-start resistive heating period in Bag 1 to 50 seconds.
Air at 30 psi was added during the resistive-heating/
engine-running portions of Bag l and 3.
At 20°F Bag l CO emissions were approximately 100 times
greater than those from Bag 3 when no heat or air was applied
to the catalyst. A comparison of Bag 3 CO levels between 20°F
and 72°F ambient testing conducted during that project
indicated that the catalyst was operating with similar
efficiencies over this portion of the FTP under those widely
different ambient temperature conditions. Clearly, a strategy
to substantially lower FTP emissions of CO at 20°F ambient
conditions would have to lower these Bag 1 emissions occurring
at cold start and during catalyst warm up.
Heating the catalyst without the addition of bottled air
did not lower emissions of CO over the FTP at 20°F. The
catalyst was preheated for 10 seconds prior to engine start and
for 30 seconds following start during Bag 1. Average CO
emissions over Bags 1 and 3 were not reduced by resistive
heating. Weighted FTP average emissions for CO were also
unchanged from no-heat/no-air mode testing. Though only a
small number of tests were conducted, resistive heating during
the early part of Bag 1 without the addition of excess air
appeared to provide very little emissions benefit over the
no-heat/no-air configuration.
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The use of resistive heating and the simultaneous addition
of excess air appeared to cause a slight reduction in emissions
of CO. When air at 2.4 SCFM was added during catalyst
heating/engine operation CO emissions fell to 175.6 grams over
Bag 1; this compares to 190.5 grams for the no heat/no air
configuration. This represents an almost 9 percent increase in
CO efficiency over Bag 1. Weighted FTP efficiencies increased
over 7 percent for CO through the use of this heating/air
addition strategy.
Increasing the amount of time the catalyst was resistively
heated during Bag 1 while adding air at 2.4 SCFM during the
simultaneous heating/engine-running period was then evaluated.
The Bag 1 preheat time was kept at 10 seconds; the time that
the catalyst was resistively heated after cold start was
increased to 50 seconds, an increase from the 30-second
post-start heating time of the previous configuration.
The increased heating period did not lower CO emissions
below levels from the previously tested configuration. CO
weighted FTP average emissions were essentially unchanged from
levels with the catalyst in the no-heat/no-air mode. CO
emissions over Bags 1 and 3 were also unchanged from levels
measured with the no-heat/no-air configuration.
CO by percent in undiluted exhaust (ahead of the CVS) was
continuously monitored during the Bag 1 portion of the tests,
which utilized the 10/50 heating scheme and addition of air
over the catalyst at 2.4 SCFM. CO was measured at 9 percent of
undiluted exhaust during the first 3 minutes of Bag l at 20°F
ambient conditions. CO concentration dropped sharply during
the period of 180 to 240 seconds into a test; after
approximately 4 minutes of engine operation, CO had fallen to a
stable value much less than l percent. The level did not
change after that time. Any reduction of CO during this 3-4
minute period could substantially reduce weighted FTP CO
emissions.
The goal of the testing described here was to lower
emissions of CO and HC over the first 3-4 minutes of the FTP
cycle at 20°F ambient conditions. This was to be accomplished
by resistively heating the catalytic converter and through the
use of air added in front of the catalyst in conjunction with
the resistive heating. The catalyst would be resistively
heated for a longer period of time than in the configurations
previously tested; [13] air would be added in front of the
catalyst with a belt-driven air pump, rather than from a bottle
of compressed air.
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III. Description of Test Program
The work discussed in Section VI of this report was
conducted in two separate phases.
We were concerned that our earlier work [13] showed only
a slight improvement in CO emissions at lower ambients with
resistive catalyst heating and air addition during the Bag 1
portion of the FTP. Our earlier work utilized bottled air for
the air added in front of the catalyst; this was done for sake
of convenience. It is possible, however, that the amount of
air added during Bag 1 was insufficient to fully oxidize excess
CO and HC emissions during engine warm up. Conversely, the
addition of excess air at 20°F might have had an undesired
cooling effect on the resistively heated catalyst at cold start.
The first part of this project therefore involved a rough
calculation of the amount of excess air necessary to oxidize CO
and HC emissions from the test vehicle during cold start and
engine warm up at 20°F ambient conditions. An average engine
speed over the initial portion of Bag 1 for the test vehicle
was determined. A belt-driven air pump was mounted on the
vehicle and pump flowrate at different engine speeds was
measured. A valve to divert part of this excess air to the
atmosphere was added to the system; pump output curves for
various settings of this diverter valve were then generated. A
diverter valve setting was chosen that provided air at the
necessary flowrate and average engine speed calculated above.
The second part of this work involved the evaluation of
the catalyst over the FTP cycle with various resistive heating/
air-addition schemes. The catalyst configurations tested are
given in Table l; the catalyst was evaluated in the same
underfloor location as in our earlier work [13]. Each test
here was conducted after an overnight soak at 20°F conditions.
Figure 1 is a diagram of the Bag 1 and Bag 2 portions of
the FTP cycle. The Bag 1 or cold transient portion of the test
consists of the first 505 seconds of the cycle. The 90 and 180
second time intervals corresponding to catalyst resistive
heating and air pump use referred to in Table 1 are noted on
Figure 1.
IV. Vehicle Description
The test vehicle was a 1987 Volkswagen Golf 4-door sedan,
equipped with automatic transmission, continuous fuel injection
(Bosch CIS), and radial tires. The 1.78-liter engine had a
rated maximum power output of 85 horsepower at 5,250 rpm. The
vehicle was tested at 2,500 Ibs inertia weight and 7.7 actual
dynamometer horsepower. Approximately 13000 odometer miles had
been accumulated on this vehicle prior to the start of this
work.
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Table 1
Catalyst Resistive Heating/Air-Addition Schemes
_ Catalyst As Originally Supplied _
Catalyst
Configuration
Baseline
Number 1
Number 2
Number 3
Number 4
Resistive Heating
None
10/50, Bag 1*
None
10/80, Bag 1
10/170, Bag 1
Excess Air Supplied
None
None
3 minutes, Bag 1**
3 minutes, Bag 1
3 minutes, Bag 1
**
Signifies heating for 10 seconds prior to vehicle start,
50 seconds following vehicle start.
Signifies addition of air during the 3 minutes of Bag 1
immediately following cold start.
SPEED
MfH
20
Figure 1
Driving Trace. Bags '1 And 2 Of The FTP Cycle
90 Seconds
TtANSIENH-STAIIUZED
200
400 600 800 1000
TIME-SEC.
1200 1370
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A more detailed description of the vehicle is provided in
Appendix A.
V. Test Facilities and Analytical Methods
Emissions testing was conducted on a Labeco Electric
single-roll chassis dynamometer, using a direct-drive variable
inertia flywheel unit and road load power control unit. The
Philco-Ford CVS has a nominal capacity of 350 CFM. The EPA
cold test cell has the capability to cold soak a vehicle to
20° F conditions and to supply 20° F air to the engine
during the FTP cycle.
Exhaust HC emissions were measured with a Beckman Model
400 FID. CO was measured using a Horiba Model AIA 23 infrared
detector, while NOx emissions at 20°F were determined by
chemiluminescent technique using a Beckman Model 951A NOx
analyzer.
VI. Discussion
A. Selection of Air Pump Flow Rates
As previously mentioned, our earlier work with this
resistively heated converter [13] resulted in only a slight
improvement in CO emissions at 20°F conditions with resistive
heating and air addition in front of the catalyst. We were
concerned, however, that the amount of air added was
insufficient to fully oxidize excess CO and HC emissions
occuring during cold start. We wished to keep the amount of
air added during the catalyst warm-up period to a minimum; any
additional air at 20°F flowing over the catalyst might have an
undesired cooling effect.
The air pump we utilized for this work was a belt-driven
vane pump of the type generally referred to as the Saginaw air
pump.[15] The pump's output was therefore determined
experimentally. The test vehicle was not originally equipped
with this pump. The engine alternator was removed and the pump
mounted in its place. The battery was recharged during vehicle
operation on the chassis dynamometer by a battery charger.
A five-step procedure was used to determine how much air
to flow over the catalyst. This procedure called for making
simplifying assumptions; these assumptions were made in the
interest of saving time and effort. The procedure is outlined
and explained below.
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1. Determine the period of the FTP cycle of interest as
the time period during which "excess" CO emissions are produced
from the test vehicle.
2. Calculate how much additional air must be added over
the catalyst to completely oxidize excess CO (and HC)
emissions. Express this requirement as a flowrate.
3. Determine the range of engine speeds over the period
of interest. By weighting engine speeds against time, estimate
an average engine speed over the time period of interest.
4. Map the output of the air pump as a function of
engine speed and diverter valve setting.
5. Choose the diverter valve setting which provides the
calculated air flowrate at the average engine speed determined
above.
The period of higher CO emissions in Bag 1 was determined
in a qualitative manner. The 'difference in CO emission levels
between Bag 1 and 3 of the FTP from the test vehicle at 20°F
was assumed to be related to cold start. Therefore, the
"excess" CO emissions of interest to us could be expressed as
the difference between Bag l and 3 levels. The same assumption
was made concerning HC emissions. Tailpipe CO emissions from
the test vehicle over Bag 1 at 20°F were then continuously
sampled using a Sun Emissions Analyzer. CO concentrations were
very high at cold start; after approximately 3.2-4.0 minutes of
driving the Bag 1 cycle, however, the concentration had
declined in a step-change manner. The concentrations measured
after this step-change varied only slightly during the
remainder of Bag 1; this behavior was noted on several tests.
We attributed the step-change reduction in emissions to
catalyst light-off, and defined the first 3.2 minutes of Bag 1
as the period of high CO production for the test vehicle.
Because our air pump was belt driven, its output was a
function of engine speed. The vehicle was run over Bag 1 of
the FTP with continuously measured engine speed. A rough
measure of engine speed versus time interval over the
3.2-minute period of interest was made, and an average engine
speed of 1,413 rpm was determined.
The excess CO and HC emissions were assumed to occur
during the first 3.2 minutes of Bag 1. Using an empirical
ratio of CH 1:1.85 for HC, an additional air requirement of 5.4
SCFM was calculated. Stoichiometric conversion of CO and HC
was postulated; any cooling effect on the catalyst caused by
the addition of air was therefore minimized.
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Figure 2 contains the curves generated when air pump flow
was mapped with respect to engine speed and diverter valve
setting. A hand-operated valve was used to divert some of the
pump output to the atmosphere; the valve-open notation in
Figure 2 refers to the position of the actuator. The airflow
to the catalyst was measured by flowing it through a
rotameter. An allowance for backpressure in the exhaust pipe
was not made; airflow in front of the catalyst may have been
slightly lower because of this. In order to obtain 5.4 SCFM at
1,413 engine rpm, it was necessary to open the valve to the
one-third open position.
B. Discussion of Test Results
The primary goal of this experimentation was the reduction
of CO emission levels from the test vehicle over the FTP cycle
at 20°F ambient conditions. Figure 3 presents CO emission
levels over the FTP for several resistive-heating/air-addition
schemes for the Camet catalyst. Figure 4 presents Bag 1 CO
emissions in grams for the same heat/air schemes.
Heating the catalyst in the absence of air from the air
pump provided virtually no additional CO emissions reduction.
The level of CO emissions was roughly 12 grams per mile in both
heated and unheated catalyst configurations. The no heat/no
air scheme had slightly lower weighted FTP average CO
emissions; this was due in large part to a single test during
which CO emissions were measured at 10 grams per mile. Bag 1
CO levels were also similar in both cases, with the final no
heat/no air test accounting for much of the difference. The
significance of Bag 1 to the weighted FTP average is apparent
when Bag 2 and 3 averages are considered; for the
no-heat/no-air configuration here, Bag 2 and 3 CO emissions
were 1.2 grams each.
The addition of air greatly reduced Bag 1 CO emissions
even in the absence of catalyst resistive heating. Bag 1 CO
was reduced roughly 50 percent, to 105 grams, through the
addition of air. Weighted average FTP CO emissions were also
reduced, to 6.3 grams per mile, with the no-heat/3-minutes air
addition catalyst operating scheme. This level of CO emissions
is well below the recently proposed 20°F standard of 10.0 grams
per mile. [16] In each test in which air addition was called
for, this operation was conducted in the same manner. A
technician opened the manually controlled diverter valve to the
one-third open position immediately after Bag 1 cold start.
The valve was held in this position and air was admitted over
the catalyst for 3 minutes of the cycle. At the end of this
3-minute period, the valve was manually closed and pump air was
diverted to the atmosphere during the remainder of the test.
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FIGURE 2
CAMET CATALYST EVALUATION
AIR PUMP CALIBRATION
VALVE 1/2 OPEN
REQUIRED OUTPUT
VALVE FULL OPEN
VALVE 1/3 OPEN
AIR PUMP FLOW (SCFM)
1000
I I I I I I I I I I I I I I I I I I I I I I I I I I
1200 1400 1600 1800 2000 2200 2400
ENGINE SPEED (RPM)
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FIQURE 3
CO, AVERAGE FTP
20 DEQ. F AMBIENT CONDITIONS
CATALYST HEAT/AIR ADDITION SCHEME
NO HEAT, NO AIR
10/50*, NO AIR
NO HEAT, 3 MINS AIR
10/80, 3 MINS AIR
10/170, 3 MINS AIR
•DENOTES HEAT 10 SECONDS PRIOR TO,
50 SECONDS FOLLOWING COLD START
CO, GRAMS/MILE
0 2 4 6 8 10 12 14
CO, GRAMS/MILE
FIGURE 4
CO, BAG 1 OF FTP
20 DEG. F AMBIENT CONDITIONS
CATALYST HEAT/AIR ADDITION SCHEME
NO HEAT, NO AIR
10/50*. NO AIR
NO HEAT. 3 MINS AIR
10/80, 3 MINS AIR
10/170, 3 MINS AIR
•DENOTES HEAT 10 SECONDS PRIOR TO,
50 SECONDS FOLLOWING COLD START
CO. GRAMS
201.1
210
50 100 150 200 250
CO, GRAMS
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Resistively heating the catalyst was next attempted with
the simultaneous addition of air from the air pump. Resistive
heating was applied at 10 seconds prior to cold start and
continued for 80 seconds following cold start. Air was
admitted in front of the catalyst immediately following cold
start; air addition continued for 3 minutes.
The combination of resistive heating and air addition
provided a substantial improvement in CO emissions over the use
of air addition alone. Bag 1 CO emissions were reduced to 63.5
grams, an almost 70 percent decrease in emissions from
no-heat/no-air levels. This was also an almost 40 percent
improvement over emission levels from the configuration which
employed the addition of air for 3 minutes and no resistive
heating.
The improvement in Bag 1 emissions translates into a
substantial improvement in weighted FTP CO emissions. Average
FTP CO emissions for this heated-catalyst/air-addition
configuration were 3.9 grams per mile, close to the current
light-duty car standard. The importance of Bag 1 emissions to
weighted FTP emissions is again evident because this 3.9 grams
per mile represents a 70 percent improvement from
no-heat/no-air configuration levels, the same improvement
realized in Bag 1 emissions.
Extending the period of catalyst resistive heating while
leaving other variables unchanged did not appear to improve CO
emission levels. The period of catalyst heating was increased
to 3 minutes, approximately the time period relating to the
production of significant guantities of CO mentioned
previously. CO emissions were slightly higher in Bag 1 than
those experienced with heating for 90 seconds only. Only two
tests were conducted with the heating period extended to a full
3 minutes, however. The data from this limited amount of
testing did not indicate that an improvement in CO emission
levels would occur by merely extending the period of resistive
heating beyond 90 seconds.
We are unable to account for the increase in CO emissions
that occurred when the heating period was extended to 3
minutes. It was expected that emissions would have remained at
the same level or decreased when the heating period was
extended. This phenomena could be related to the part of the
driving cycle covered by the additional resistive heating; a
sharp deceleration and short idle period are included in this
extended period of heating. This would not have been an
expected result, however. The resistive heating/air addition
schemes have not yet been optimized for this lower ambient
temperature application; more work must be done to determine
the cause of this phenomena.
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HC emission levels over the FTP in grams per mile for the
catalyst configurations tested are presented in Figure 5.
Figure 6 contains average Bag 1 HC emission levels in grams.
The application of 1 minute of resistive heating without
air addition had no effect on Bag 1 HC emissions at 20°F
ambient conditions. Average HC emissions were 8.95 grams over
Bag 1 with resistive heating only; this compares to 8.70 grams
when no resistive heating or air addition was utilized.
Similar to our experience with CO emissions, however, the use
of additional air without resistive catalyst heating
substantially reduced HC emissions from no-heat/no-additional
air configuration levels. Bag 1 HC emissions were reduced to
4.56 grams by the addition of air during the first 3 minutes;
this represents a 50 percent increase in efficiency from the
no-heat/no-air configuration. FTP HC emissions were reduced to
0.30 grams per mile, a decrease of 44 percent from the 0.54
grams per mile experienced with the no-heat/no-air addition
configuration.
The combination of resistive heating and air addition
lowered HC emissions below levels obtained through the addition
of air in front of the catalyst alone. Bag 1 HC was reduced to
2.88 grams with the 10/80 heating scheme; this represents
reductions in emissions of 67 and 37 percent respectively from
levels obtained with the no-heat/no-air and the
no-heat/3-minutes air addition configurations. Average total
HC emissions over the FTP were reduced to 0.20 grams per mile
with this configuration; this is below the 0.25 grams per mile
non-methane hydrocarbon standard referred to in the President's
proposed Clean Air Act Amendments legislation.[16]
Extending the period of resistive heating from 1.5 to 3
minutes with air addition did not improve Bag 1 HC efficiency.
Bag 1 HC emissions were 3.00 grams, approximately the same
level as the emissions from the configuration utilizing 1.5
minutes of resistive heating. Average FTP HC emissions for the
3-minute resistive heating configuration were 0.21 grams per
mile, essentially unchanged from the 0.20 grams per mile
measured withheating for 1.5 minutes. Again, only two tests
were conducted with the heating period extended to a full 3
minutes. The data from this limited amount of testing did not
indicate that an improvement in HC emission levels would occur
by merely extending the period of resistive heating beyond 90
seconds.
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FIGURE 5
HC, AVERAGE FTP
20 DEG. F AMBIENT CONDITIONS
CATALYST HEAT/AIR ADDITION SCHEME
NO HEAT, NO AIR
10/50*. NO AIR
NO HEAT, 3 MINS AIR
10/80, 3 MINS AIR
10/170, 3 MINS AIR
HC, GRAMS/MILE
0.00 0.20
•DENOTES HEAT 10 SECONDS PRIOR TO,
50 SECONDS FOLLOWING COLD START
0.40 0.60
HC, GRAMS/MILE
FIGURE 6
HC, BAG 1 OF FTP
20 DEG. F AMBIENT CONDITIONS
CATALYST HEAT/AIR ADDITION SCHEME
NO HEAT, NO AIR
10/50*. NO AIR
NO HEAT, 3 MINS AIR
10/80, 3 MINS AIR
10/170, 3 MINS AIR
HC, GRAMS
J
•DENOTES HEAT 10 SECONDS PRIOR TO,
50 SECONDS FOLLOWING COLD START
0.00 3.00 6.00 9.00 12.00
HC, GRAMS
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The reduction of NOx emissions at 20°F ambient conditions
was not a goal of this project. We had noticed an increase in
Bag 1 NOx at 20°F in our previous work when resistive heating
and the addition of air was employed. [13] We therefore
monitored NOx emissions during this testing to determine the
effects of resistive heating and air addition on NOx levels.
NOx emissions over the FTP in grams per mile for the tested
catalyst configurations are presented in Figure 7. Figure 8
contains average Bag 1 NOx emission levels in grams.
The addition of air caused an increase in Bag 1 NOx
emissions to approximately 2.8 grams; NOx emissions over the
FTP rose to almost 0.9 grams per mile as a result. NOx
emissions approaching 0.7 grams per mile over the FTP were
measured in the absence of additional air. Catalyst resistive
heating, in the absence of air added by the air pump, did not
appear to substantially increase NOx emissions. Figures 7 and
8 may suggest that the additional air from the pump during Bag
1 may account for a substantial increase in NOx irrespective of
the catalyst resistive heating scheme.
Another phenomena relating to NOx emissions that was noted
during this project was an apparent increase in NOx over time
from tests with the same catalyst configuration. Individual
FTP test results from this work are given in Appendix B; Bag 1
emissions in grams from these tests are presented in Appendix C.
The first 4 tests listed in Table B-l refer to catalyst
testing without resistive heating/air addition. The first 2
tests were conducted at the start of the program. The third
test was conducted at the midpoint of the program, and the
fourth was the last test of the program.
NOx levels during the first two tests were approximately
0.57 grams per mile over the FTP. NOx rose to 0.83 grams per
mile during the third test conducted at the midpoint of the
program. HC and CO emissions did not change substantially
however, between the third and the two initial tests. NOx rose
to 0.98 grams per mile on the final no heat/no air test
conducted at the end of the program. HC emissions measured on
this fourth test were approximately at the same level as HC
emissions over the first 3 no heat/no air tests; CO was lower
on this final test than previously measured levels with the
same catalyst configuration.
Only a limited number of tests were conducted with the no
heat/no air catalyst configuration; it may be difficult to draw
conclusions from this limited amount of testing. Increasing
NOx emissions may be occurring, however, because of some effect
related to the noble metal catalyst itself, rather than the
resistive heating. If this is the case, it would be difficult
to ascertain precisely the effects on NOx formation from
catalyst resistive heating/air addition.
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-16-
FIQURE 7
NOx, AVERAGE FTP
20 DEQ. F AMBIENT CONDITIONS
CATALYST HEAT/AIR ADDITION SCHEME
NO HEAT, NO AIR
10/50*, NO AIR
NO HEAT, 3 MINS AIR
10/80, 3 MINS AIR
10/170, 3 MINS AIR
NOx, GRAMS/MILE
•DENOTES HEAT 10 SECONDS PRIOR TO,
50 SECONDS FOLLOWING COLD START
J
0.0 0.3 0.6 0.9 1.2
NOx, GRAMS/MILE
FIGURE 8
NOx, BAG 1 OF FTP
20 DEG. F AMBIENT CONDITIONS
CATALYST HEAT/AIR ADDITION SCHEME
NO HEAT, NO AIR
10/50*. NO AIR
NO HEAT, 3 MINS AIR
10/80, 3 MINS AIR
10/170. 3 MINS AIR
-DENOTES HEAT 10 SECONDS PRIOR TO.
50 SECONDS FOLLOWING COLD START
I NOx, GRAMS
0 0.5 1 1.5 2 2.5 3 3.5
NOx, GRAMS
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-17-
The goal of this project at its inception was primarily
the oxidation of CO and secondarily HC at lower ambients;
consideration was not given to the conversion of NOx or the
prevention of NOx formation. The exact noble metal loading of
the catalytic material on the substrate is available from the
manufacturer, Garnet, Inc. Different choices for the catalytic
mixture might have been possible had NOx control been used as a
criteria for evaluation. The location of the catalyst in the
exhaust stream and its configuration in a single underfloor can
may also have substantially influenced NOx emissions.
VII. Highlights From Testing
1. CO emissions over the FTP with the catalyst in the
no resistive heating/no additional air configuration were 12.0
grams per mile. These emissions were not reduced by
resistively heating the catalyst in the absence of additional
air from the air pump.
The use of the air pump over the first 3 minutes of Bag 1
without resistively heating the catalyst reduced CO emissions
over the FTP by almost 50 percent, to 6.3 grams per mile.
Heating the catalyst for 1-1/2 minutes together with 3 minutes
of air addition during Bag 1 reduced CO to 3.9 grams per mile
over the FTP, an increase in efficiency of 68 percent over no
resistive heat/no air configuration levels.
2. HC emissions in Bag 1 were not reduced by catalyst
resistive heating in the absence of additional air from the air
pump. The 10/80 resistive heating/3-minutes air addition
scheme reduced HC emissions in Bag 1 to 2.88 grams; this was a
67 percent reduction in emissions from no heat/no air
configuration levels. HC emissions over the FTP were reduced
to 0.20 grams per mile with this resistive heating/air-addition
scheme.
3. NOx emissions over Bag 1 of the FTP were measured at
2.0 grams with the no resistive heating/no additional air
catalyst configuration. Bag 1 NOx increased to 2.8 grams with
the addition of air for 3 minutes. Resistively heating the
catalyst in the absence of additional air did not cause a
substantial rise in NOx emissions, however.
It is unclear whether resistively heating the catalyst
with the addition of excess air caused the rise in NOx
emissions from no heat/no air configuration levels. During the
last test of the no resistive heating/no air addition
configuration, the final test in this program, NOx emissions
over the FTP were measured at 0.98 grams per mile. This is a
substantial increase from levels measured earlier in the
program with this configuration. The control of NOx emissions
should be considered a criteria for evaluation in future
efforts with this technology at lower ambient temperatures.
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-18-
VIII.Future Effort
We are currently evaluating this resistively heated
substrate with two different catalysts (palladium-only, and a
base-metal configuration) for use as light-duty methanol
vehicle catalysts. This work is being conducted at 72°F
ambient conditions and will be the subject of a future EPA
technical report.
Future efforts may utilize catalysts better suited to take
advantage of the substrate's resistive heating characteristic.
For example, an optimized system for low temperature CO control
may require an oxidation catalyst rather than a three-way
catalyst. The position of the converter in the exhaust stream
is another factor which may be addressed in a future effort.
We placed the resistively-heated catalyst in the same
underfloor location as the stock converter in order to compare
test results [12, 13]. The underfloor location used may not be
the most desirable location in the exhaust stream for the
converter if the design is tailored to a specific application,
such as low temperature CO control.
The use of a two-catalyst system for specific applications
may also be evaluated. A resistively heated substrate
catalyzed specifically for formaldehyde control might be used
with a second catalyst for optimal control of a variety of
emissions from a methanol-fueled vehicle. A thermostatically
controlled bypass valve might also be incorporated into this
system.
The air addition strategy used in this work was simplified
to facilitate project completion in a minimum amount of time.
The optimum air strategy for low temperature CO oxidation was
therefore probably not determined here. Future work may
involve refinement of the air addition strategy for lower
temperature CO control.
IX. Acknowledgements
The catalyst used in this test program was supplied by
Camet, located in Hiram, OH. Garnet is a manufacturer and sales
agent for W. R. Grace and Company. The test vehicle used in
this program was supplied by Volkswagen of America.
The author thanks James Garvey and Rodney Branham of the
Test and Evaluation Branch (TEB), Emission Control Technology
Division (ECTD), who conducted the driving cycle tests. The
author also recognizes the efforts of Jennifer Criss of CTAB
for typing and formating this report.
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-19-
X. References
1. 1975 Federal Test Procedure, Code of Federal
Regulations, Title 40, Part 86, Appendix I(a), Urban
Dynamometer Driving Schedule.
2. Conversation with A. McCarthy, EOD/OMS/OAR, Ann
Arbor, MI, June 28, 1989.
3. "The Influence of Ambient Temperature on Tailpipe
Emissions From 1984-1987 Model Year Light-Duty Gasoline Motor
Vehicles," Black, F., et al., Atmospheric Environment, Vol. 23,
No. 2, pp. 307-320, 1989.
4. "Motor Vehicle Emissions Under Reduced Ambient
Temperature Idle Operating Conditions," Black, F., et al.,
Atmospheric Environment, Vol. 21, No. 10, pp. 2077-2082, 1987.
5. "The Effect of Ambient Temperature Variation on
Emissions and Fuel Economy," Spindt, R. S. and F. P. Hutchins,
SAE Paper 790228, 1979.
6. "The Impact of Low Ambient Temperature on Three-Way
Catalyst Car Emissions," J. N. Braddock, SAE Paper 810280, 1981.
7. Air Pollution, 2nd Edition, Wark, K. and C. F.
Warner, Harper and Row Publishers, New York, N.Y., 1981.
8. "Vehicle Emission Characteristics Under Cold Ambient
Conditions," Larson, R. E., SAE Paper 890021, 1989.
9. "Ambient Temperatures During CO Exceedance: Program
and Policy Implications," Joy, R. W. , and T. C. Austin, Third
Annual Mobile Sources/Clean Air Conference, Estes Park, CO,
September 1987.
10. "Carbon Monoxide and Non-FTP Ambient Temperature,"
Bruetsch, R. I., EPA/AA/CTAB/TA/81-7, February 1981.
11. "Effect of Ambient Temperatures On Vehicle Emissions
and Performance Factors," Spindt, R. S. and R. E. Dizak, et
al., EPA-460/3-79-006A, September 1979.
12. "Evaluation Of A Resistively Heated Metal Monolith
Catalytic Converter On A MlOO Neat Methanol-Fueled Vehicle,"
Piotrowski, G. K. and D. M. Blair, EPA/AA/CTAB/88-09, August
1988.
13. "Evaluation Of A Resistively Heated Metal Monolith
Catalytic Converter On A Gasoline-Fueled Vehicle," Piotrowski,
G. K., EPA/AA/CTAB/88-12, December 1988.
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-20-
X. References (cont'd)
14. "Resistive Materials Applied To Quick Light-Off
Catalysts," Hellman, K. H., et al., SAE Paper 890799, March
1989.
15. "The General Motors Air Injection Reactor Air Pump,"
Thompson, W. B., SAE Paper 660108, January 1966.
16. "Overview of the Clean Air Act Amendments of 1989,"
White House Summary Statement, reprinted in Inside EPA Weekly
Report, July 28, 1989.
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A-l
APPENDIX A
TEST VEHICLE SPECIFICATIONS
Vehicle Type
1987 Volkswagen Golf
Fuel
Indolene clear
Engine:
Displacement
Bore
Stroke
Compression ratio
Maximum output SAE net
1.78 liter
8.10 cm
8.64 cm
9.0 to 1
85 hp at 5250 rpm
Fuel System
Continuous injection system
(fuel injection) with Lambda
feedback control, electric
fuel pump
Transmission:
Type
Torque converter stall
torque ratio
Hydradynamic torque converter
and planetary gearing with
three forward and one reverse
gears
2.50
Torque converter stall speed 2400-2600 rpm
Gear ratios;
1
2
3
Axle
2.71
1.50
1.00
3.41
Curb weight
2340 Ibs
Equivalent test weight
2500 Ibs
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B-l
APPENDIX B
INDIVIDUAL FTP RESULTS
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B-2
Table B-l
Garnet Catalyst - 20°F Ambient Conditions
Individual FTP Results
Test Number/Type
892792/no heat, no air
892810/no heat, no air
893132/no heat, no air
894564/no heat, no air
892854/heat 10/50 Bag 1,
5/20 Bag 3 no air
893128/heat 10/50 Bag 1,
5/20 Bag 3 no air
892853/no heat, 3 minutes
air Bag 1
893133/no heat, 3 minutes
air Bag 1
893850/no heat, 3 minutes
air Bag 1
892811/heat 10/80 Bag l,
3 minutes air Bag 1
892812/heat 10/80 Bag 1,
3 minutes air Bag 1
893129/heat 10/80 Bag 1,
3 minutes air Bag 1
893130/heat 10/80 Bag 1,
3 minutes air Bag 1
893848/no heat 10/80 Bag 1,
3 minutes air Bag 1
893849/heat 10/80 Bag 1,
3 minutes air Bag 1
893851/heat 10/80 Bag 1,
HC
(g/mi)
0.53
0.58
0.51
0.55
0.55
0.55
0.27
0.33
0.29
0.20
0.21
0.21
0.20
0.15
0.22
0.22
CO
.(g/mi)
11.88
13.07
12.73
10.12
11.53
13.44
5.92
6.45
6.56
3.51
3.98
3.96
4.12
4.00
3.94
4.01
C02
( g/mi )
353.
387.
361.
370.
360.
367.
362.
376.
386.
371.
376.
360.
360.
379.
383.
381.
NOX
(g/mi)
0.57
0.56
0.83
0.98
0.65
0.73
0.77
0.90
0.95
0.61
0.64
0.66
0.84
0.96
1.09
0.95
3 minutes air Bag 1
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B-3
Table B-l (cont'd)
Garnet Catalyst - 20°F Ambient Conditions
Individual FTP Results
Test Number/Type
893852/heat 10/80 Bag 1,
3 minutes air Bag 1
893847/heat 10/80 Bag 1,
3 minutes air Bag 1
894261/heat 10/170 Bag 1,
3 minutes air Bag 1
894169/heat 10/170 Bag 1,
HC
( q/mi )
0.20
0.16
0.22
0.21
CO
3.49
3.71
3.98
5.15
C02
(q/mi)
370.
397.
381.
369.
NOX
(q/mi)
1.05
1.10
0.89
0.91
3 minutes air Bag 1
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C-l
APPENDIX C
BAG I/BAG 3 EMISSION LEVELS
OVER THE FTP CYCLE
-------
C-2
Table c-1
Garnet Catalyst - 20°F Ambient
Bag I/Bag 3 Emission Levels Over
Conditions
The FTP Cycle
Test Number/Type
892792/no heat,
no air
892810/no heat,
no air
893132/no heat,
no air
894564/no heat,
no air
HC
qms/gms
8.39/0.22
9.46/0.22
8.30/0.20
8.66/0.30
892854/heat 10/50 8.96/0.20
Bag 1, 5/20 Bag 3
no air
893128/heat 10/50 8.94/0.18
Bag 1, 5/20 Bag 3
no air
892853/no heat,
3 minutes air
Bag 1
893133/no heat,
3 minutes air
Bag 1
893850/no heat,
3 minutes air
Bag 1
4.14/0.23
5.14/0.25
4.39/0.23
892811/heat 10/80 2.92/0.22
Bag l, 3 minutes
air Bag 1
892812/heat 10/80 3.08/0.20
Bag 1, 3 minutes
air Bag 1
893129/heat 10/80 3.27/0.19
Bag 1, 3 minutes
air Bag 1
893130/heat 10/80 2.92/0.22
Bag 1, 3 minutes
air Bag 1
CO
gms/qms
199.74/1.09
222.62/1.22
215.05/1.22
166.80/2.03
194.14/0.82
C02 NOx
gms/qms gms/gms
1366/1186 1.07/1.70
1534/1223 1.55/1.63
1376/1183 2.26/2.56
1416/1204 3.19/2.79
1379/1169 1.65/1.92
227.40/1.08 1398/1197 1.87/1.93
100.00/1.01 1496/1158 1.71/2.34
107.83/1.50 1536/1227 2.99/2.57
108.01/1.90 1606/1269 3.57/2.89
58.76/1.21 1589/1175 1.77/1.75
67.24/0.92 1617/1182 1.83/1.74
66.61/1.11 1576/1200 2.05/1.80
69.98/0.90 1501/1176 2.28/2.16
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C-3
Table C-l (cont'd)
Camet Catalyst - 20°F Ambient
Bag I/Bag 3 Emission Levels Over
Conditions
The FTP Cycle
Test Number/Type
HC
gms/gms
893848/heat 10/80 2.13/0.19
Bag l, 3 minutes
air Bag 1
893849/heat 10/80 2.98/0.18
Bag l, 3 minutes
air Bag l
893851/heat 10/80 3.26/0.19
Bag 1, 3 minutes
air Bag 1
893852/heat 10/80 2.94/0.22
Bag 1, 3 minutes
air Bag 1
893847/heat 10/80 2.40/0.17
Bag 1, 3 minutes
air Bag 1
894261/heat 10/170 3.23/0.24
Bag 1, 3 minutes
air Bag 1
894169/heat 10/170 2.77/0.24
Bag 1, 3 minutes
air Bag 1
CO
gms/gms
56.64/2.25
59.49/1.21
63.97/1.71
82.21/1.80
C02 NOx
gms/gms gms/gms
65.42/1.34 1557/1218 2.64/2.92
63.03/1.63 1522/1257 3.50/2.96
64.23/1.48 1595/1196 3.52/2.70
1602/1248 3.46/3.04
1668/1209 3.58/2.49
1587/1204 3.43/2.77
1513/1183 2.69/2.33
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