EPA/AA/TDG/93-06
Technical Report
Evaluation of Three Catalysts Formulated for Methane Oxidation
on a CNG-Fueled Pickup Truck
by
Gregory K. Piotrowski
Ronald M. Schaefer
December 1993
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
Regulatory Programs and Technology Division
Technology Development Group
2565 Plymouth Road
Ann Arbor, MI 48105
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
ANN ARBOR. MICHIGAN 48105
DEC 22 1993 OFFICE OF
AIR AND RADIATION
MEMORANDUM
SUBJECT: Exemption From Peer and Administrative Review
FROM: Karl H. Hellman, Chief l//^
Technology Development Group
TO: Charles L. Gray, Jr., Director
Regulatory Programs and Technology Division
The attached report entitled "Evaluation of Three Catalysts
Formulated for Methane Oxidation on a CNG-Fueled Pickup Truck,"
(EPA/AA/TDG/93-06) describes the emission results obtained from the
evaluation of three specialized methane catalysts supplied by three
different catalyst manufacturers. The catalysts were evaluated
using a CNG-fueled Dodge Dakota pickup truck.
Since this report is concerned only with the presentation of
data and its analysis and does not involve matters of policy or
regulations, your concurrence is requested to waive administrative
review according to the policy outlined in your directive of April
22, 1982.
Concurrence:
Date:
Cjiarles L. Gray/ Jr. , Director, RPT
Attachment
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Table of contents
Page
Number
I. Summary 1
II. Introduction 2
III. Description of Catalytic Converters 2
IV. Description of Test Vehicle 7
V. Test Facilities and Analytical Methods 9
VI. Test Procedures 10
VII. Discussion of Test Results 11
A. Electrically Heated Methane Catalyst 11
B. Main Underfloor Catalysts 15
VIII.Conclusions 21
IX. Acknowledgements 21
X. References 22
APPENDIX A - Fuel Properties/Test Data Sheet A-l
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I. summary
Three fresh catalysts formulated for methane oxidation were
evaluated by U.S. EPA on a compressed natural gas (CNG) vehicle.
The first catalyst was an electrically heated, compact, quick
lightoff converter, provided by W. R. Grace Company. The other two
catalysts were larger in volume and were similar in size to the
stock main catalyst on the test vehicle. These two larger volume
catalysts were provided by Kemira Oy and AlliedSignal. No
durability miles were accumulated on any of the catalysts.
The CNG-fueled test vehicle was a 1991 Dodge Dakota pickup
equipped with a 318-CID engine provided by Stewart & Stevenson
Power, Inc. Although the truck was equipped for dual fuel (either
gasoline or CNG) operation, all the testing described here was
performed with CNG fuel operation over the Federal Test Procedure
(FTP) driving cycle.
The Grace quick lightoff catalyst was tested without the use
of a larger main catalyst downstream. The effect of electrical
heating and secondary air injection upstream of this catalyst were
also investigated. The two larger volume catalysts were also
tested in an underfloor location. The effect of secondary air
assist was also evaluated on these two catalysts.
The low-volume Grace catalyst caused substantial emission
level reductions in non-methane hydrocarbons (NMHC), carbon
monoxide (CO), and oxides of nitrogen (NOx). With 20/40-second
heat assist (resistive heating applied for 20 seconds prior to key-
on and 40 seconds after key-on in Bag 1 only) , NMHC and CO emission
levels were measured at 0.10 grams/mile and 11.6 grams/mile
respectively over the FTP cycle, over 60 percent reductions from
engine-out levels. The lowest NOx levels were obtained without any
catalyst assist and were measured at 0.8 grams/mile over the FTP
cycle, over a 50 percent reduction from engine-out levels.
The two larger volume main catalysts both resulted in
emissions over the FTP cycle that were below the levels of the
California ultra-low emission vehicle (ULEV) standards, with and
without secondary air assist. The test data taken for this report
did not permit the calculation of non-methane organic gases (NMOG)
as required by the California regulations, nor was a Reactivity
Adjustment Factor (RAF) applied to the data. Nevertheless, it is
the opinion of the authors that the test results are low enough
that a 0.04 grams/mile NMOG level would be met at zero miles with
a fresh catalyst. The Kemira Oy catalyst without air assist
resulted in NMHC/CO/NOx emission levels of 0.02/0.4/0.2 grams/mile
over the FTP. These emission levels were attained at zero
accumulated system miles. The AlliedSignal catalyst (smaller in
volume than the Kemira Oy unit) resulted in similar low levels of
0.01/0.8/0.2 grams/mile without air assist. Secondary air assist
provided little additional emission reductions from the unassisted
catalyst levels for both units.
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II. Introduction
The current U.S. highway vehicle fleet is almost totally
dependent on petroleum-based (i.e., gasoline and Diesel) fuels.
Alternatives to petroleum-based fuels may become increasingly
important in future years because of their potential contribution
to a solution for air quality problems as well as a means to lessen
the demand for imported oil in the U.S. [1,2]
One candidate for serious consideration as an alternative
motor vehicle fuel is compressed natural gas (CNG). CNG is
composed primarily of methane (CH4) , but it may contain up to 10
percent higher weight hydrocarbons (mostly ethane, propane and
butane). [3] Ozone-forming photochemically reactive fuel-related
emissions from CNG vehicles consist primarily of non-methane
hydrocarbons (NMHC). CNG-fueled vehicle exhaust is 90-95 percent
methane, a relatively non-reactive hydrocarbon (HC) species.
Gasoline vehicle exhaust HC consists of 65-95 percent more reactive
non-methane hydrocarbon species, however. [1] It is estimated that
CNG-fueled vehicles may have 36-93 percent lower volatile organic
compound (VOC) emissions, determined on a reactivity-equivalent
basis, than gasoline-fueled vehicles (depending on the
configuration of the CNG vehicles as either dual-fuel or optimized
for CNG). [l]
The large methane fraction of the HC exhaust emissions from
CNG-fueled vehicles is a problem for engine designers, because
methane is the most difficult HC to oxidize catalytically. Some
vehicle emission tests conducted at General Motors Research
Laboratories showed that poor methane conversion on lean calibrated
CNG-fueled vehicles occurred over the FTP cycle when commercial
three-way catalysts were used. [4] Recently further General Motors
research indicated good methane conversion occurred when a
palladium/alumina catalyst was used together with slightly rich
feedstream conditions. [5] Other catalyst development work to date
suggests that with proper engine controls, selected catalyst
formulations can effectively control methane emissions from CNG-
fueled vehicles. [6]
EPA's Technology Development Group routinely conducts and
publishes the results from emission control technology evaluations
to spur further interest in new technologies. Recently, three
catalyst companies furnished EPA with samples of fresh, unaged
catalysts specifically formulated for use on CNG-fueled vehicles.
These catalysts were evaluated on a CNG-fueled pickup truck at the
EPA National Vehicle and Fuel Emissions Laboratory. The results
from this evaluation are presented in this report.
III. Description of Catalytic Converters
The first converter evaluated here was a quick lightoff
electrically heated catalyst supplied by Grace Company. This
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single-segment, metallic foil substrate had a total volume of 0.22
liters (Figure 1) . The energy required for electrically hearing
this catalyst was supplied from a dedicated 12-volt, 115 amp-hour,
deep-cycle battery. The current delivered to the catalyst averaged
about 500 amps during the time of resistive heating. A switch and
engine starter motor relay were used to supply energy from the
dedicated battery when desired. Table 1 contains more detailed
specifications of the Grace electrically heated catalyst. The
catalyse pictured here is much smaller in volume than a
conventional main converter and was not designed as a substitute
for a main underfloor catalyst.
Figure l
Grace Electrically Heated Catalyst
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Table 1
Grace Electrically Heated Methane Catalyst
List of Detailed Specifications
Catalyst diameter
Catalyse length
Catalyst volume
Total substrate weight
Cells per square inch
Noble metal loading
Ratio of noble metals
Specifications
2.51 inches
2.75 inches
13.24 in'
335 grams
160
30 g/ftj
?t:Pd:Rh 0:1:0
The second converter evaluated was provided by Kemira Oy of
Finland. This unit was cylindrical in shape and had the largest
volume (4.71 dmj) of the three converters evaluated. This converter
was designed for heavy-duty truck applications utilizing CNG fuel.
This converter utilized a single metallic foil substrate and was
mounted in the underfloor location for our testing. A picture of
this unit is provided as Figure 2; a more detailed list of
specifications for the Kemira Oy catalyst is provided in Table 2.
Figure 2
Kemira Ov Methane Catalyst
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Table 2
Kemira Oy Methane Catalyst
List of Detailed Specificationa
Prototype identification number
Total weight of converter
Substrate;
Diameter
Length
Volume
Cells per square inch
Total surface area
Cross section
Precious metal loading
Total precious metal
Precious metal ratio
Foil material
Foil thickness
Weight of substrate
Shell material
Shell thickness
Specification
5382
7300g
200mm
150mm
4.71 dm3
600
18.8m2
314.2cm2
1.77g/dm3
8.34g
1:1:0 Pt:Pd:Rh
W 1.4767
0.05mm
4118g
W 1.4512
1.5mm
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-he last converter evaluated in this program was supplied by
AlliedSignal Inc. This catalyst had a total substrate volume
between the two other units (2.78dnr) and was similar in size to the
stock catalyst on the truck. This catalyst utilized two ceramic
substrates with similar sizes and loadings and was also evaluated
in the underfloor location. A picture of this converter is
provided in Figure 3 below, and a detailed list of catalyst
specifications is provided in Table 2.
Figure 3
AlliedSianal Methane catalyst
Table 3
AlliedSignal Methane Catalyst
List of Detailed Specifications
Material
Total catalyst volume
Cross section (oval)
Length
Cells per square inch
Noble metal loading
Ratio of noble metals
Ceramic
169.66 in3
4.5 x 7.0 in
3.4 in
400
100 g/ft3
0:10:1 Pt:Pd:Rh
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IV. Description of Test Vehicle
The test vehicle used for this evaluation was a 1991 Dodge
Dakota pickup truck. The truck was converted to CNG operation by
Stewart & Stevenson Power, Inc. of Commerce City, Colorado, using
their patented Gaseous Fuel Injection (GFI) system. The truck had
dual-fuel (gasoline or CNG) capability; fuel selection was governed
by a switch inside the passenger compartment. Figure 4 depicts the
GFI system.
Figure 4
Gaseous Fuel Injection System
TYPICAL INSTALLATION
Battery Power
Switched Power
Fuel Injector
Starter Solenoid
Colt Negative
Knock Sensor
Fuel Gauge
TDC or Tachometer
Intake Air Temp
Manifold Skin Temp
Selector Switch
Oxygen Sensor
Figure A1: NGV System Schematic
High Pessure Fuel Line
Metering Valve
and Computer
Pressure
Regulator
Fuel
Nozzles
MAP
Vacuum
Line Tee
GFL
Engine
Coolant
High pressure CNG was supplied from storage cylinders to a
single-stage regulator where the pressure was reduced to 100 psig.
Two CNG storage tanks were located inside the passenger compartment
and were capable of filling to approximately 3,500 psig pressure.
EPA, however, filled these tanks only to a maximum 2,500 psig
pressure when refueling. With this fill level, it was possible to
conduct approximately four tests over the FTP cycle before the
truck was refueled. EPA also installed two excess flow valves at
the outlet of each storage tank for safety purposes.
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One hundred psig fuel passes from the pressure regulator to a
primary fuel filter and then to a regulator referred to as a compu-
valve. The compu-valve commands the appropriate combination of
solenoids and injectors to operate for the required period of time
necessary to meter the desired amount of fuel. The metered fuel
then passes from the metering valve to spray nozzles in the intake
system of the engine, in this case the air cleaner. These nozzles
introduce fuel into the intake air stream and promote nixing of the
inlet air and fuel.
The GFI system used speed density calculations for both fuel
flow and air flow and solved for the correct air/fuel mixture based
on a fixed (software) stoichiometric value of the fuel consumption
in the area of operation. Speed density calculations are based on
engine speed and the temperature and pressure of the inlet air and
fuel. The GFI system senses manifold absolute pressure, barometric
absolute pressure, and fuel absolute pressure. Temperatures
monitored include intake air temperature, manifold skin temperature
(air temperature at engine intake valve), and fuel regulated
temperature. The first two sensors are remotely located, and the
last is embedded in the metering valve.
Figure 5 is a picture of the test vehicle. The truck was
tested at 4,750 Ibs equivalent test weight and 13.0 actual
dynamometer horsepower. The vehicle was loaned to U.S. EPA by
Stewart & Stevenson Power, Inc.
Figure 5
CNG-Fueled Dodge Dakota Test Vehicle
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V. Teat Facilities and Analytical Methods
Emissions -testing at EPA was conducted on a Clayton model ECE-
50 double-roll chassis dynamometer, using a direct-drive variable
inertia flywheel unit and road load power control unit. The Philco
Ford constant volume sampler has a nominal capacity of 600 standard
cubic feet per minute. NOx emissions were determined by a Beckman
Model 951A chemi luminescent NOx analyzer. Methane (CH4) emissions
were measured with a Model 8205 Bendix methane analyzer.
Hydrocarbon emissions were determined using a Beckman Model 400
flame ionization detector. CO and C02 were measured using a Bendix
Model 8501-5CA infrared analyzer.
Procedures were developed for the determination of both total
and non-methane hydrocarbons and fuel economy for natural gas
vehicles based on the properties of the natural gas fuel. The
natural gas used to refuel the test vehicle was obtained from a
commercial pipeline located near the EPA motor vehicle laboratory.
This fuel was not specifically analyzed, but it was assumed to be
typical of natural gas used in the Detroit area for home heating
applications. The properties used in these calculations (Appendix
A) were provided to EPA by a local gas company. Appendix A also
presents natural gas fuel economy and a gasoline equivalent fuel
economy value.
The properties of the natural gas fuel included mole percent
compositions of nitrogen, carbon dioxide, helium, hydrogen, and
hydrocarbons. These values were used to calculate specific gravity
and net (lower) heating value. This data was then used to
determine the properties seen in Appendix A such as:
1. Composite H/C ratio for the total hydrocarbon components
in the fuel, H/CTHC;
2. Composite H/C ratio for all non-methane hydrocarbon
components in the fuel,
3. Non-methane carbon weight fraction (CWFNMHC) of the fuel,
grams of carbon per gram of non-methane hydrocarbon, excluding C02
and inert gases not consumed in the combustion process;
4. Mass fraction, grams of fuel per gram of carbon, where
carbon is based on carbon in hydrocarbon components (and C02) in
the fuel, g NGV fuel/g C in NGV fuel; and
5. Energy density of the fuel in BTU's per gram of fuel,
expressed as net (lower) heating value, BTU/g NGV fuel.
From these properties, corrected total and non-methane
hydrocarbon values were obtained based on the fuel's components in
their proper mole fractions. Calculations for CO, C02, and NOx
exhaust emissions were unchanged from procedures described in
Section 86.144-78, Title 40, of the Code of Federal Regulations.
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Specific calculations for determining adjusted total and non-
methane hydrocarbon emissions were detailed in a previous EPA
technical report describing testing of several natural gas
vehicles. [7]
VI. Test Procedures
The goal of this program was the evaluation of three catalytic
converters on a natural gas fueled truck. Three separate catalyst
manufacturers supplied EPA with prototype converters for
evaluation.
The first catalyst evaluated was an electrically-heated quick
lightoff converter supplied by the W. R. Grace Company. EPA
conducted this evaluation with and without catalyst heat and air
assist. Resistive heating was applied to the catalyst for 20
seconds prior to key-on in the Bag 1 portion of the FTP and for 40
seconds after key-on in Bag 1. No resistive heat was applied to
the catalyst for the remainder of the FTP. The effect of secondary
air assist when combined with the resistive heating strategy
described previously was also investigated. This air assist period
was 60 seconds after key-on in the Bag 1 portion of the FTP only.
The air assist time was limited to 60 seconds so that the
conversion of NOx emissions would not be inhibited. Air flow to
the catalyst was kept constant at 5 standard cubic feet per minute
and was provided by a shop air hose.
The two additional catalysts did not arrive at EPA until
approximately six months after the testing with the Grace catalyst
was complete. No emission tests were performed with the Dakota
truck during this six-month period; the truck was started and
driven periodically to keep the battery charged.
The second catalyst evaluated was provided to EPA by Kemira Oy
of Finland. Three different configurations of this catalyst were
evaluated. A straight pipe was inserted in place of the stock
underfloor catalyst to enable the determination of engine-out
levels. The engine-out levels measured during this testing were
significantly different than those measured prior to testing the
Grace catalyst, so they are reported separately. The Kemira Oy
catalyst was then installed on the truck and tested without any
assist. The last configuration utilized the Kemira Oy catalyst
with 60 seconds of air assist after start in Bag 1. Again, the air
assist rate was kept constant at 5 standard cubic feet per minute.
The third catalyst evaluated was supplied by AlliedSignal
Inc., located in Tulsa, Oklahoma. This catalyst was tested using
procedures similar to those used for the Kemira Oy catalyst
evaluation. The engine-out emissions measured prior to
installation of the AlliedSignal catalyst were similar to those
obtained before the Kemira Oy testing.
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VII. Discussion of Test Results
A. Electrically Heated Methane Catalyst
The results from the EHC evaluation are reported separately
because of its much smaller catalyst volume than the others tested.
The engine-out emissions measured here differed significantly to
those reported in the next section. There was a substantial delay
between this testing and the testing described in the next section.
The direct effect of this time delay on vehicle hardware and
emissions is not known. It is also possible that the difference in
elevation at the Stewart & Stevenson facility in Colorado (where
the vehicle was converted) and the EPA laboratory in Michigan may
have contributed to the change in engine-out emission levels
experienced here over time.
Resistive heating and air assist were used only during the
cold-start portion of Bag 1 of the FTP. The first 505 seconds of
the FTP are referred to as Bag 1; the cold-start portion consists
of the initial minutes of Bag 1 during which the engine and exhaust
system heat to a relatively steady-state temperature. The
following discussion comments on differences in exhaust emission
levels which may be related to catalyst reactions, heat assist, or
air assist. All testing was conducted at an ambient temperature of
728-73°F. Bag 1 emission levels are given in grams over the test
segment (Bag 1) . Composite FTP emissions are reported in grams per
mile.
Figure 6 presents Bag 1 total hydrocarbon emission levels
obtained during testing with the Grace catalyst. "Engine-out"
levels were obtained with no catalyst present in the exhaust
system. "Stock Catalyst" represents testing with the stock
catalyst in the exhaust system. "No assist" represents testing
with only the low-volume Grace electrically heated catalyst in the
underfloor location without any catalyst assist. "Heat assist"
utilized a 20/40-second resistive heat assist. "Heat & air assist"
utilized both a 20/40-second resistive heat scheme and a 60-second
air assist after start in Bag 1 only.
The stock catalyst caused a 42 percent reduction in Bag l
total hydrocarbons from engine-out levels, from 7.44 grams to 4.34
grams. The small-volume Grace catalyst without any assist lowered
total hydrocarbons to 5.36 grams over Bag 1. When heat assist was
applied to the Grace converter, Bag 1 total hydrocarbon (THC)
levels were similar to those measured with the larger volume stock
catalyst at 4.53 grams, a 40 percent reduction from engine-out
levels.
Combined catalyst resistive heating/air assist caused a slight
increase in Bag 1 THC to 4.66 grams. This was unexpected; the
addition of air over the catalyst may have caused the catalyst to
cool slightly, delaying lightoff. It is not known how significant
any cooling effect may have been, as catalyst skin temperature and
inlet/outlet air temperatures were not monitored.
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Figure 6
Grace Methane Catalyst Evaluation
Bag 1 Total Hydrocarbon Emission Levels
Catalyst Configuration
Engine-out
Stock Catalyst
Grace Catalyst
No assists^
Heat assist^
Heat & air assist^
7.44
4.34
5.36
4.53
4.66
2468
Total Hydrocarbons (grams)
10
Figure 7 presents Bag 1 carbon monoxide (CO) emission levels
using the Grace catalyst for the same catalyst configurations
described above. The stock catalyst was again very effective at
reducing Bag 1 CO levels from engine-out levels, from 145.0 grams
to 32.9 grams. Bag 1 CO levels were measured at 80.3 grams, almost
a 45 percent reduction from engine-out levels with the unassisted
Grace EHC. Resistive heating further lowered Bag 1 CO levels to
51.0 grams, a 65 percent reduction from engine-out levels. Again,
adding air assist to resistive heating had a detrimental effect on
Bag 1 CO emissions. In this configuration, Bag 1 CO levels were
measured at 57.6 grams, 13 percent higher than resistive heating
alone. Each configuration evaluated, however, had higher CO
emissions than the larger volume stock converter.
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Figure 7
Grace Methane Catalyst Evaluation
Bag 1 Carbon Monoxide Emission Levels
Catalyst Configuration
Engine-out
Stock Catalyst
Grace Catalyst
145
No assist
Heat assisl
Heat & air assist^
32.9
80.3
:57.6 i
0 20 40 60 80 100 120 140 160
Carbon Monoxide (grams)
Table 4 presents individual bag emission levels with the
small-volume Grace EHC. Methane (CH4) and non-methane hydrocarbons
(NMHC) followed a trend similar to those discussed in Figure 6 for
total hydrocarbons. Oxides of nitrogen (NOx) emissions were also
reduced significantly over Bag 1 with the unassisted Grace
catalyst, from 6.4 grams engine-out to 2.6 grams. Resistive heating
slightly increased Bag l NOx levels to 3.1 grams. There was no
noticeable change when heat and air assist were combined, compared
to heat-assist-only levels when considering NOx.
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Table 4
. Grace Methane Catalyst Evaluation
Individual Bag Emission Levels (grams)
Catalyst
Configuration
THC
CH4
NMHC
CO
C02
NOX
Bag 1:
Engine-out
Stock catalyst
No assist
Heat assist
Heat & air
assist
7.44
4.34
5.36
4.53
4.66
6.18
4.34
4.73
4.11
4.22
1.26
**
0.62
0.43
0.44
145.0
32.9
80.3
51.0
57.6
1632
1774
1686
1718
1744
6.4
1.7
2.6
3.1
3.0
Bag 2:
Engine-out
Stock catalyst
No assist
Heat assist
Heat & air
assist
6.43
2.57
5.04
4.52
4.62
5.18
2.50
4.56
4.16
4.20
1.25
0.08
0.48
0.37
0.42
119.2
11.3
71.2
42.0
43.8
1758
1944
1848
1855
1876
5.8
2.0
1.8
2.5
2.4
Bag 3:
Engine-out
Stock catalyst
No assist
Heat assist
Heat & air
assist
5.62
3.38
4.45
4.03
4.08
4.55
3.38
3.94
3.64
3.62
1.08
**
0.50
0.40
0.46
90.2
14.9
64.8
39.8
41.2
1388
1518
1430
1448
1469
8.4
2.7
3.1
4.0
3.9
** Less than 0.005 grams measured.
Table 5 presents composite FTP emission levels as well as a
computed natural gas fuel economy (CNG MPG) value based on the
properties of the fuel used with the Grace EHC.
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Table 5
Grace Methane Catalyst Evaluation
FTP Emission Levels (grams/mile)
Catalyst
Configuration
Engine-out
Stock catalyst
No assist
Heat assist
Heat & air
assist
THC
1.72
0.86
1.32
1.18
1.20
CH4
1.40
0.85
1.18
1.07
1.08
NMHC
0.32
0.01
0.14
0.10
0.12
CO
31.2
4.6
19.0
11.6
12.3
C02
436
480
453
459
464
NOX
1.8
0.5
0.6
0.8
0.8
CNG
MPG
13.7
13.7
13.8
14.0
13.8
The lowest composite emission levels of THC and CO using the
Grace catalyst occurred with the resistive heat assist only. THC
were measured at 1.18 grams/mile in this configuration, which also
resulted in the lowest non-methane hydrocarbon level at 0.10
grams/mile. This configuration resulted in a 11.6 grams/mile
composite level for CO. Not unexpectedly, the lowest composite NOx
level measured with the low-volume Grace catalyst occurred without
any heat or air assist at 0.6 grams/mile. Natural gas fuel economy
was not appreciably influenced by the use of the Grace catalyst.
B.
Main Underfloor Catalysts
Two larger volume main catalysts were also evaluated; these
were supplied by Kemira Oy and by AlliedSignal Inc. These
catalysts were evaluated using three different configurations:
"engine-out" (no catalyst present in the exhaust system), "no
assist" (catalyst without supplemental air assist), and "air
assist" (60 seconds of air assist to the catalyst after key-on in
Bag 1 only). Engine-out emission levels here, measured before
testing each of these catalysts, were very similar and are averaged
in the figures below. They differed substantially, however, from
engine-out levels measured prior to the Grace catalyst testing
described in the previous section.
Figure 8 presents Bag 1 emission levels of total hydrocarbons
when utilizing these two larger volume catalysts.
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Figure 8
Larger Volume Main Catalyst Evaluation
Bag 1 Total Hydrocarbon Emission Levels
Catalyst Configuration
Engine-out
Kemira Oy
No assist
Air assist
AlliedSignal
No assist
Air Assist
5.88
1.82
2.06
01 23456
Total Hydrocarbons (grams)
Both catalysts were very effective at reducing Bag 1 total
hydrocarbons. With the Kemira Oy catalyst, Bag 1 hydrocarbons
levels were reduced from the averaged engine-out level of 5.88
grams to 1.82 grams without any catalyst assist, a 69 percent
reduction. Similarly, the AlliedSignal catalyst reduced Bag 1
hydrocarbon levels to 1.79 grams, almost a 70 percent reduction
from engine-out levels. Adding secondary air assist upstream of
each catalyst did not additionally decrease Bag l hydrocarbon
emissions; in fact, these levels slightly increased above
unassisted catalyst levels.
Similar trends were noted in Bag 1 CO emission levels as with
Bag 1 hydrocarbons, as seen in Figure 9 below. The larger volume
Kemira Oy catalyst reduced Bag 1 CO by almost 96 percent from
engine-out levels, even without air assist. (Engine-out CO levels
were measured at 55.1 grams, the unassisted Kemira Oy catalyst at
2.5 grams.) As with Bag 1 HC, when 60 seconds of air assist was
added to the Kemira Oy catalyst, Bag 1 CO levels increased
slightly.
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Figure 9
Larger Volume Main Catalyst Evaluation
Bag 1 Carbon Monoxide Emission Levels
Catalyst Configuration
Engine-out
Kemira Oy
No assist
Air assist
AlliedSignal
No assist
Air Assist
2.5
3.1
5.1:
4.5:
55.1
10 20 30 40 50
Carbon Monoxide (grams)
60
The fresh AlliedSignal catalyst also effectively reduced Bag
1 CO levels from the 55.1-gram engine-out level. Without catalyst
assist, Bag 1 CO levels were measured at 5.1 grams when using the
AlliedSignal catalyst, almost a 91 percent reduction from engine-
out levels. When air assist was applied to this catalyst during
the first minute of Bag 1, CO levels were further reduced to 4.5
grams.
Tables 6 and 7 present individual Bag emission levels using
both the Kemira Oy and AlliedSignal catalysts. Different engine-
out levels are presented in each table here and were obtained prior
to initiating testing with either catalyst. These values were
averaged in the previous two figures for simplicity.
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Table 6
Kemira Oy Methane Catalyst Evaluation
Individual Bag Results (grams)
Catalyst
Configuration
EC
NOX
C02
CO
CH4
NMHC
Bag 1:
Engine-out
No assist
Air assist
5.79
1.82
2.06
7.8
0.6
0.6
1678
1773
1758
54.0
2.5
3.1
5.40
1.67
1.98
0.39
0.16
0.08
Bag 2:
Engine-out
No assist
Air assist
5.25
0.51
0.56
7.1
0.5
0.3
1814
1905
1900
44.0
1.3
1.6
5.03
0.49
0.55
0.44
0.02
0.01
Bag 3:
Engine-out
No assist
Air assist
4.95
1.39
1.46
9.3
1.7
1.6
1423
1504
1498
39.9
0.7
0.8
4.53
1.36
1.44
0.42
0.04
0.02
-------
-19-
Table 7
AlliedSignal Methane Catalyst Evaluation
Individual Bag Results (grams)
Catalyst
Configuration
EC
NOX
CO2
CO
CH4
NMHC
Bag i:
Engine-out
No assist
Air assist
5.96
1.79
1.85
8.4
0.5
0.7
1673
1852
1765
56.2
5.1
4.5
5.54
1.66
1.65
0.39
0.13
0.19
Bag 2:
Engine-out
No assist
Air assist
5.59
0.57
0.56
7.7
0.2
0.2
1797
1907
1914
Bag 3:
Engine -out
No assist
Air assist
5.03
1.29
1.39
10.3
1.4
1.6
1419
1524
1495
49.8
2.6
2.5
5.26
0.56
0.56
0.32
0.01
**
41.2
1.7
1.5
4.70
1.28
1.39
0.33
0.01
**
** Less than 0.005 grains measured.
-------
-20-
Tables 8 and 9 present composite FTP emission levels when
using both the Kemira Oy and AlliedSignal catalysts.
Table 8
Kemira Oy Methane Catalyst Evaluation
FTP Composite Emission Levels (grams/mile)
catalyst
Configuration
Engine-out
No assist
Air assist
EC
1.45
0.28
0.30
NOX
2.1
0.2
0.2
C02
451
472
470
CO
12.2
0.4
0.5
CH4
1.33
0.26
0.29
NMHC
0.12
0.02
0.01
CNG
MPG
14.0
13.9
14.0
Table 9
AlliedSignal Methane Catalyst Evaluation
FTP Composite Emission Levels (grams/mile)
Catalyst
Configuration
Engine-out
No assist
Air assist
HC
1.48
0.28
0.29
NOX
2.3
0.2
0.2
COj
446
479
473
CO
13.0
0.8
0.7
CH4
1.39
0.27
0.28
NMHC
0.09
0.01
0.01
CNG
MPG
14.0
13.7
13.9
In the absence of any catalyst assist, use of either the
Kemira Oy or AlliedSignal catalyst resulted in low emission levels
over the FTP; these levels were below the levels of the California
ULEV Standards of 0.04/1.7/0.2 grams/mile for NMHC/CO/NOx
respectively. The test data taken for this report did not permit
the calculation of non-methane organic gases (NMOG) as required by
the California regulations, nor was a Reactivity Adjustment Factor
(RAF) applied to the data. Nevertheless, it is the opinion of the
authors that the test results are low enough that a 0.04 grams/mile
NMOG level would be met at zero miles with a fresh catalyst. The
bulk of the total hydrocarbons are methane emissions, therefore,
non-methane hydrocarbon values are very low (0.02 grams/mile with
the Kemira Oy catalyst and 0.01 grams/mile with the AlliedSignal
unit). CO levels were very low with each catalyst and well below
the ULEV CO level of 1.7 grams/mile. NOx emissions with either
catalyst was measured at 0.2 grams/mile. Again, these emission
levels were attained at zero accumulated system miles.
-------
-21-
Adding air assist provided little benefit in reducing
composite FTP emission levels. The only noticeable benefit from
air assist resulted with the Kemira Oy catalyst and non-methane
hydrocarbon emissions. When air assist was used with this
catalyst, non-methane emissions were reduced from the already low
0.02 grams/mile to 0.01 grams/mile.
VIII.Conclusions
1. It is difficult to compare the results from the
evaluation of the Grace EHC with those from the other catalysts
tested because of the operation and smaller volume of the Grace
converter. Despite its small size, the unassisted EHC was
effective at reducing Bag 1 THC, CO and NOx emission levels.
Resistive heating in Bag 1 further lowered Bag 1 emissions of
THC and CO. Emissions over the Bag 2 and 3 segments of this heat-
assist testing were also lowered. The addition of catalyst air
assist did not appear to further lower emission levels. Testing
using air assist without resistive heating was not conducted.
2. The Kemira Oy catalyst was very effective in reducing
emission levels of NMHC, CO and even NOx. Engine out NMHC
emissions were reduced to extremely low levels, as low as 0.02
grams/mile over the FTP. CO emissions were also very low. The use
of catalyst air assist did not further lower CO emissions, to our
surprise. NOx emissions were also reduced to approximately 0.2
grams/mile. NOx reduction activity was not greatly affected by the
use of catalyst air assist during the Bag 1 segment of this
testing.
3. The emissions levels with the AlliedSignal catalyst were
very similar to those from the evaluation of the Kemira Oy
catalyst.
IX. Acknowledgements
The first catalyst evaluated in this test program was supplied
to EPA by the W.R. Grace and Company. The second catalyst was
supplied by Kemira Oy, located in Vihtavuori, Finland. The last
catalyst used in this program was provided by AlliedSignal Inc.,
located in Tulsa, Oklahoma. The natural gas fueled Dodge Dakota
truck was loaned to EPA by Stewart & Stevenson Power, Inc., located
in Commerce City, Colorado. The authors would like to thank these
companies for their cooperation and support.
The authors also appreciate the efforts of James Garvey,
Robert Moss, and Ray Ouillette of the Technology Evaluation and
Testing Support Branch who conducted the driving cycle tests and
emission sampling. The word processing and editing efforts of
Jennifer Criss and Lillian Johnson of the Technology Development
Group are also appreciated.
-------
-22-
X. References
1. "Analysis of the Economic and Environmental Effects of
Compressed Natural Gas as a Vehicle Fuel," Special Report, Office
of Mobile Sources, U.S. EPA, April 1990.
2. "Assessment of the Costs and Benefits of Flexible and
Alternative Fuel Use In The U.S. Transportation Sector," DOE/PE-
0080, January 1988.
3. Gas Engineers Handbook. First Edition, Industrial Press,
New York, NY, 1965.
4. "Exhaust Emissions from Dual-Fuel Vehicles Using
Compressed Natural Gas and Gasoline," Cadle et al., Air and Water
Management Association, Pittsburgh, PA, June 1990.
5. "Methane Oxidation over Noble Metal Catalysts as Related
to Controlling Natural Gas Vehicle Exhaust Emissions," Oh, S., P.
Mitchell and R. Siewert, Catalytic Control of Air Pollution, pp!2-
25, American Chemical Society, 1992.
6. Letter from B. Bertelsen, Executive Director,
Manufacturers of Emission Controls Association to W. Reilly,
Administrator, U.S. EPA, January 4, 1993.
7. "1992 Natural Gas Vehicle Challenge: EPA Emissions and
Fuel Economy," Breutsch, R. I. and M. E. Reineman, EPA/AA/TDG/92-
05, June 1992.
-------
APPENDIX A
NATURAL GAS VEHICLE TEST ANALYSIS
Dyno: D209 Test No: 93-1543
Input Data for 1B7GL23Y8NS529176
"
Tost No. MFR Vehicle ID Veh Version
93-1548 20 1B7GL23Y8NS529176 0
Identification
REQIO MFR Initials Driver ID Oper ID LA4 Prep ID
22024 0 54768 54721 54768
Flags
EVAP Rag PARTIC RETEST RFCC
0 000
RUNCHQ
0
Disposition and Accounting
Veh Disp Test Olsp Void Cod* TPS
0 000
Dynamometer and Analyzer Site
Dyno IW Set TWHP Coast Down
D209 4750 13 0:00
Odometer
1766
Dyno/CVS Distance VMIX Seconds
Bag 1
Bag 2
Bag 3
Units
8378 4983 505.00
8999 8512 864.00
8375 4964 505.00
Ft
Exhaust
HCRD
Bag 1
Bag 2
Bag 3
CO
Bag 1
Bag 2
Bag 3
C02
Bag 1
Bag 2
Bag 3
NOx
Bag 1
Bag 2
Bag 3
Methane
Bag 1
Bag 2
Bag 3
NGFuel
Properties
COMMENTS:
THIS TEST WAS CO
Range Meter
14 86.3
14 49.7
1 4 74.2
18 71
18 38.1
18 56.5
22 69.9
22 47
22 81
15 64.2
15 3S.3
^M ' ''
>* 10.4
Fuel Meter
Units
page 1/3
Processed: 06/25/93 11:18
Test Type
05
Tire
0
9 Preps
0
Procedure
02
Test No.
93-1548
Test Date Key Start
6/10/93 9:53
Prep Date Prep Key Off
6/9/93 16:21
Ace Code Ace Code
0 0
CVS
27C
Reading
0
0
0
0
Analyzer HF1D
A203 A 2 03
Ambient Conditions
Barometer 29.05
Ambient 76.5
Dew Point 47.8
Temp Units D
Background
Range
14
14
14
Meter
3.4
3.2
3.4
18
18
18
0.2
0.3
0.3
22
22
22
4
4.1
4.1
15
15
15
0.2
0.2
0.2
18
18
18
THC . NMHC NQ CNGTHC
H/C Ratio H/C Ratio NQ/C Ratio CWF
3.886 2.891 1.441 0.667
0
0
o
suika hU AT THE US. EPA NATIONAL VEHICLE AND FUEL EMISS
0.7
0.7
0.7
C02
WF
0.090
IONS LABORATC
HCRD
Bag 1
Bag 2
Bag 3
CO
Bag 1
Bag 2
Bag 3
CO2
Bagi
Bag 2
Bag 3
NOX
Bag 1
Bag 2
Bag3
Methane
Bag 1
Bag 2
Bag 3
GHV Specific
BTU/ft*3 Gravity
JOOO 0.593
RY - BOD. ANN ARBOR, MICHIGAJ
-------
APPENDIX A (CONT'D)
NATURAL GAS VEHICLE TEST ANALYSIS page 2/3
Dyno: 0209 Test No: 93-1548 Processed: 06/25/93 11:18
Raw Emission Determination for 1B7QL23Y8NS529176
Ambient
Conditions
HC
Bag 1
Bag 2
Bag 3
CO
Bagi
Bag 2
Bag 3
CO2
Bag 1
Bag 2
Bag 3
NOx
Bag 1
Bag 2
Bag 3
Methane
Bag 1
Bag 2
Bag 3
NMHCo
Bag 1
Bag 2
Bag 3
THC Reso Adlus*
Bagi
Bag 2
Bag3
COMMENTS:
THISfESfWA$
-------
APPENDIX A (CONT'D)
NATURAL GAS VEHICLE TEST ANALYSIS pag0 3/3
Oyno: 0209 Test No: 93-1548 Processed: 06/25/93 11:18
Emission. Mass, and Fuel Economy for 1B7GL23Y8NS529176
Natural Gas
Properties
Natural Gas
Properties
Dvno/CVS
Bag 1
Bag 2
Bag 3
CVS Corrected
Concentrations
Bag 1
Bag 2
Bag 3
CVS Mas*
Emissions
Bag 1
Bag 2
Bag 3
Total Mass
Emissions
Bag 1
Bag 2
Bag 3
Mass
Emissions
Bag 1
Bag 2
Bag 3
Composite
Emissions
Unrounded
Rounded
Natural Gas
Fuel Economy
THIS TbAT (JlJWC
Natural Gas
Fuel Economy
THIS IHSTCONC
THC
H/C Ratio
3.8860
NG
NG/C Ratio
1.4410
VMIX
4983
8512
4964
CH4C
oom
57.30
31.40
48.33
CH4
grams
5.39
5.05
4.53
CH4
grams
5.39
5.05
4.53
CH4
fl/Rll
1.501
iJSi
1 .33408
1.33S
gram* C
per mil*
129.349
THC
Density
18.749
NG
CWF
0.694
Roll Revs
8378
8999
8375
NMHCc
ppm
0.00
0.00
0.00
MAJLIS
run iw
gram*
0.00
0.00
0.00
UAJLJO
ranmw
gram*
0.00
0.00
0.00
NMHC
a/ml
0.000
0.000
0.000
NMMC
a/ml
0.00000
0.000
gram* NO
per grim* C
1.441
THC
CWF
0.754
CNGTHC
CWF
0.667
Mile*
3.593
3.860
3.592
TOTAL HC
ppm
57.30
31.40
48.33
TOTAL HC
gram*
5.39
5.05
4.53
TOTAL HC
gram*
5.39
5.05
4.53
TOTAL HC
a/ml
1.501
1.308
1.261
TOTAL HC
a/mi
1 .33498
1.335
Ijftm^
IwVK*
H/C Ratio
2.8910
Specific
Gravity
0.593
Dllut Factor
NMHC NMHC
Density CWF
17.568 0.805
CO2
WF
0.096
GHV NHV NG
BTU/ft*3 BTU/a Density
7000 43.967 20.470
Numerator Dilut Factor Correct
9.656 13.374 0.9252272
20.608 0.9514749
15.543 0.9356608
COc
ppm
325.85
159.11
247.83
CO
gram*
53.53
44.65
40.56
CO
gram*
53.53
44.65
40.56
CO
g/ml
14.898
11.569
11.292
CO
a/mi
12.183
12.2
JOTEu AT THE U.S. EPA NATIONAL VEHlCLb AMD filSL EMLSSIOr
FCng
Numerator
129.349
FCng
Denominator
14.205
X'I'HU AT THE U.S. EPA NATION
FCna
9.106
AL VEHICLE AN1
CO2na
1 7.894
CO2c NOxe
% pom
0.650 31.79
0.414 17.35
0.556 38.33
coa NO*
grams grams
1677.33 7.70
1824.15 7.18
1430.91 9.25
CO2 NOX
gram* gram*
1677.33 7.70
1824.15 7.18
1430.91 9.25
C02 NOX
g/ml g/ml
466.795 2.144
472.625 1.861
398.361 2.576
C02 NOX
g/ml g/ml
451.01 2.1159
451 2.12
UTG BTU'* NG BTU'S NQ
per gallon per mil* MPG
114132 8195.182 13.93
S LABORATORY. ANN ARBOR. MICHIGAN
gr C / mil* Proposed
Numerator Denominator CFR MPG
1658.878 124.464
13.33
------- |