EPA-AA-EVRB - 9 2 - 01
TECHNICAL REPORT
DEVELOPMENT OF CONVERSION FACTORS FOR HEAVY-DUTY
BUS ENGINES G/BHP-HR TO G/MILE
by
MATTHEW KITCHEN
and
WILLIAM DAMICO
Engine and Vehicle Regulations Branch
Regulation Development and Support Division
July 27, 1992
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. T:
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 I?A
decision, position, or regulatory action.
Engine and Vehicle Regulation Branch
Regulatory Development and Support Division
Office of Mobile Sources
Office of Air and Radiation
U.S. Environmental Protection Agency
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ABSTRACT
This technical report calculates conversion factors to
convert emission results from EPA's heavy-duty truck transient
test (expressed in g/bhp-hr), to equivalent levels for various
in-use bus applications (expressed in g/mile). Conversion
factors are calculated by comparing emission results from a bus
engine operated on the EPA heavy-duty truck transient test cycle
and various bus specific chassis test cycles. Pollutant specific
conversion factors are developed for inter-city, urban, and heavy
urban bus applications.
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1.0 Introduction
The Environmental Protection Agency (EPA) emissions testing
and certification program for heavy-duty vehicles, unlike the EPA
programs for light-duty vehicles, focuses on engines and exhaust
systems rather than total vehicles. Consequently, standards for
heavy-duty vehicles are written in terms of grams of emission per
unit of work done, such as grams per brake-horsepower per hour
(g/bhp-hr), rather than grams per mile (g/mi). This approach to
regulating heavy-duty vehicles has several advantages in terms of
setting and enforcing emissions standards. On the other hand,
the g/bhp-hr values available for certified engines do not lend
themselves to the calculation of emissions inventories, which are
typically expressed in g/mi figures. In order to calculate
emission inventories, the emission factors for heavy-duty engines
need to be converted from units of g/bhp-hr to units of g/mi.
Thus a bhp-hr/mi conversion factor methodology is necessary.
EPA has previously calculated bhp-hr/mi conversion factors
(both for heavy-duty vehicles in general and for various sub-
classes of heavy-duty vehicles) for use in estimating emissions
inventories. These conversion factors were based on estimates of
the average amount of work that must be expended by the engine to
propel the vehicle one mile. However, the conversion factors for
buses, most notably urban buses, did not accurately reflect the
effects that different types of bus operations have on the
relative levels of emissions of specific pollutants. In order to
more accurately model the emissions from urban buses, improved
conversion factors are needed to relate the g/bhp-hr results of
the engine dynamometer test to the g/mi emission factors for
various types of bus operation.
Pollutant specific conversion factors for urban buses can be
calculated if emissions data from chassis tests of buses (given
in g/mi) and from the engines which power these buses (given in
g/bhp-hr) are available. These data would preferably be from a
set of bus/engine pairs with the bus chassis tested over a
variety of test cycles. During the past decade, a relatively
small number of buses have been emissions tested using a variety
of test cycles. EPA has collected data from the only two test
programs which have run reliable chassis tests on buses and for
which dynamometer results are also available. From these data,
updated estimates of appropriate bhp-hr/mi conversion factors for
buses are derived.
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2.0 Background
Historically, conversion factors for heavy-duty vehicles
have been generated by relating the total amount of work done
over the engine test cycle to the work required on the road.
This was done by comparing fuel consumption values and assumed
that emissions per unit of work done were constant and
independent of the specific vehicle duty cycle. Thus, when
engines are tested for emissions purposes, the brake-specific
fuel consumption (BSFC) is measured.* Using this information,
along with the density of the fuel used in the emissions testing
and the fuel economy of the vehicle in which the engine is being
used, the bhp-hr/mi conversion factor for that vehicle can be
calculated using the formula:
Bhp-hr
Where: CF = conversion factor
FE =» fuel economy
BSFC = brake specific fuel consumption
p = fuel density
Using this procedure, as well as data for various weight classes
of vehicles and fuel types, EPA produced a report in 1988 which
calculated sub-class and fuel-type specific conversion factors
for heavy-duty vehicles of model years ranging from 1962 to
2000. [1] This conversion factor was non-pollutant specific and
was 3.241 bhp-hr/mile.
This approach provided reasonable estimates of average
heavy-duty vehicle emissions. However, it failed to reflect the
differences in emissions related to different vehicle operating
cycles. Since urban buses generally operate in ways which are
quite different from other heavy-duty vehicles, such as line hau.'
trucks, it is desirable to develop conversion factors based on
direct comparisons of g/bhp-hr engine test data with g/mi bus
test data. Furthermore, since the vehicle operating cycle may
well affect various pollutants differently, it is also desirable
to do this on a'pollutant-specific basis. In order to properly
derive such conversion factors, data must be obtained from a
vehicle tested using both a chassis dynamometer cycle simulating
The brake specific fuel consumption of an engine is the
average mass of fuel consumed per Bhp-hr of work performed by the
engine.
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the operations of an urban bus and from the engine alone when
removed and tested over the engine dynamometer certification
teat. In the past, a scarcity of data of this type has limited
the ability to calculate pollutant specific conversion factors.
However, data obtained recently from Environment Canada have made
such calculations possible for buses. These data along with
previously existing chassis test data can be used to calculate
seta of pollutant specific conversion factors for buses. The
remainder of this report will present both the available data and
the analysis made on these data.
3.0 Description of Teat Cycle*
Five different bus test cycles and one truck test cycle were
used in the studies reviewed in this technical report. The truck
cycle consists of the chassis test version of the EPA heavy-duty
diesel transient engine test. The bus cycles are those known as
the Central Business District test cycle, The New York Bus
Composite test cycle, the EPA unfiltered bus test cycle, the EPA
filtered bus test cycle, and the New York Bus test cycle. The
origins, uses and ramifications of each test cycle are addressed
below.
The truck chassis cycle is intended to represent the same
vehicle operations as the EPA heavy-duty transient engine
dynamometer test for heavy-duty diesel engines. This is the
cycle which is uaed to certify bus engines to Federal emissions
standards. The cycle is composed of three different driving
patterns. These patterns are the "New York Non-Freeway" which
lasts for 254 seconds and covers a distance of 0.53 miles at an
average speed of 7.56 mph, the "Los Angeles Non-Freeway" which
lasts for 285 seconds and covers a distance of 1.15 miles with an
average speed of 14.55 mph, and the "Los Angeles Freeway" which
lasts for 254 seconds and covers 3.33 miles at an average speed
of 44.94 mph. The New York Non-Freeway segment is run both at
the beginning and end of this cycle, and the LA patterns are each
run once in between.
The EPA filtered and unfiltered bus cycles were derived from
the bus data in the same data collection program (known as
CAPE21) that was used to design the heavy-duty certification test
procedure. The unfiltered cycle is 1191 seconds in duration with
an average speed of 8.77 mph and a total distance covered of 2.9
miles. This cycle is intended to represent a composite of the
different types of bus operations. Consequently it has both a
segment which represents low speed stop and go driving and a
segment which represents higher but constantly varying speeds.
One characteristic of this cycle is that it contains small,
closely spaced, rapid changes in vehicle speeds. Some users of
this cycle believe that such high frequency changes are probably
not often seen in actual driving conditions. Therefore, a
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special version of this test cycle with the high frequency speed
changes smoothed out has also been used. This test cycle is
referred to as the EPA filtered cycle.
The Central Business District cycle (CBD), as its name
implies, attempts to simulate driving in a heavily built up urban
environment. The CBD test cycle is 600 seconds in duration with
an average speed of 12.37 mph over a distance of 2.06 miles. The
cycle consists of fifteen segments of equal length, wherein the
bus accelerates from idle to 20 mph, holds at that speed for 20
seconds, and then decelerates back down to idle. This cycle is a
simplified simulation of urban bus operation on a fixed route
with fairly frequent, equidistant stops. The CBD test cycle is
part of the Advanced Bus Design cycle created by the Department
of Transportation and the Urban Mass Transit Association as part
of the specifications for assessing bus performance.
The New York Bus Composite cycle (NYBC) is essentially a
"compressed" version of the EPA unfiltered bus test cycle. If is
1029 seconds in duration with an average speed of 8.77 mph over a
distance of 2.51 miles. The first part of the cycle simulates
non-freeway driving, with abundant idle time. The second part of
the cycle simulates freeway driving of a highly variable
transient nature.
The final cycle used in this study is the New York Bus (NYB)
cycle. This bus cycle attempts to simulate some of the toughest
bus driving conditions which exist in the United States today.
Data for this cycle was collected from a mid-town Manhattan route
in New York City. The cycle consists of very rapid accelerations
to speeds ranging from 15 to 50 mph and then rapid decelerations
to idle. The bus sits at idle for long periods of time before it
accelerates rapidly again. Thus, rapid stop and go traffic with
long passenger transfer times are simulated.
In summary, these cycles thoroughly characterize the range
of expected bus operation. The CBD, EPA filtered, EPA unfiltered
and New York Composite cycles approximate the operation of the
average urban bus. The Heavy-Duty Transient Chassis cycle
represents the lightest duty a bus would be expected to be
operated over, such as travelling from city to city, while the
New York Bus cycle represents the heaviest duty a bus would be
expected to encounter, such as transit operations in a heavily
built-up urban inner city area (see Table 3-1).
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TABLS 3-1 SUMMARY OF BUS CYCLSS
BUS CYCLS
EPA Truck
EPA Unfiltered
CBD
NYBC
NYB
TIME
(seconds)
1047
1191
600
1029
600
DISTANCE TRAVELLED
(miles)
5.54
2.90
2.06
2.51
0.65
AVG SPEED
(mph) I
18.52
8.77
12.37
8.77
3.89
CBD= Central Business District, NYBC=» New York Bus Composite
Cycle, NYB= New York Bus Cycle
4.0
Test Programs
Based on a review of available test data, data from two teat
programs are used for the analysis conducted in this technical
report. These test programs are the circa 1984 Southwest
Research Institute (SwRI) chassis testing, and 1990 work at the
Vehicle Emissions Testing Laboratory of Environment Canada.
Results from these tests contain chassis test data on buses which
have also had their engines emissions tested on an engine
dynamometer. These two reports will serve as the sources of data
for deriving the sets of pollutant specific conversion factors.
(A summary of these two test programs is included in Table 4-1.)
Results from other test programs which involved chassis testing
on bus cycles are summarized in Appendix A. These results are
included for reference purposes only as their lack of correlation
to engine test results precludes their use in calculating
conversion factors.
4.1
Southwest Research Institute
The Southwest Research Institute testing used in this report
was conducted in the mid-1980's using a set of buses from San
Antonio. The San Antonio buses were tested as part of a program
to evaluate the then proposed heavy-duty transient test cycle.
Four of the San -Antonio buses were powered by 1980 Detroit Diesel
Corporation six-cylinder naturally aspirated engines (DDC 6V-71N)
while a fifth bus was equipped with a 1978 Detroit Diesel
Corporation eight-cylinder naturally aspirated, engine (DDC
8V-71N). All five buses were tested using the chassis version of
the heavy-duty transient test cycle (the truck chassis cycle).
Four of the buses were also tested using the EPA unfiltered bus
test cycle. The engine of the remaining bus, one of the 1980 DDC
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6V-71N engines, was removed from the bus and tested using the
engine dynamometer test procedure. The results from these tests
were published in a report in October of 1984. [2] Appendix B
contains vehicle descriptions and emissions data from all the
buses tested at SwRI during this test program.
Data collected included hydrocarbon (HC), carbon monoxide
(CO), oxides of nitrogen (NOx) and particulate matter (PM)
emissions. Unfortunately, the Southwest Research Institute
testing did not include transient engine dynamometer testing and
chassis testing on the same vehicle and engine pair. Had it done
so, a direct g/BHP-hr to g/mile pollutant specific conversion
factor set could have been constructed for the EPA unfiltered bus
chassis cycle using data from a single bus-engine pair. It is
useful, however, to indirectly construct a g/bhp-hr to g/mile
conversion factor set, using the data from several bus tests,
keeping in mind that the reliability of these conversion factors
is reduced somewhat.
4.2 Environment Canada
The Vehicle Emission Testing Laboratory (VETL) of
Environment Canada is a relatively new facility. However, during
the short period since testing began at this facility, several
buses have been tested. This facility is equipped to run only
chassis dynamometer cycles. In one program, two passenger buses
with Orion 45 cabs and Cummins L10 engines were tested at the
VETL.
The data from the Orion 45 passenger buses were the result
of a joint project between Environment Canada's Mobile Source
.Emissions Division (MSEO) and Ontario Bus Industries Inc. The
goal of this project was to characterize g/mi emissions from two
new diesel-fueled urban buses. Three bus cycles were used during
this program: the CBD, New York Bus Cycle, and the NYBC cycle.
A chassis version of the EPA truck heavy-duty transient test was
also utilized. Fortunately, the two Cummins L10 engines used in
these buses had been tested prior to installation using the
engine dynamometer test cycle at SwRI as part of a production
engine emissions audit performed by Cummins. The Cummins Engine
Company agreed to supply the emissions results from these two
engines. Therefore, chassis versus engine results, as well as
the effects of different operating parameters investigated in
this testing, can all be examined using the data from these
tests. This data is presented in Appendix C.[3]
The data from the Vehicle Emissions Testing Laboratory of
Environment Canada included HC, CO, Nox, PM, aldehydes, methane,
and volatile organic compounds (VOC) emissions, and was provided
for two Cummins L10 equipped buses. For the purposes of this
report we will concentrate on the regulated emissions HC, CO, Nox
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and PM. Since the engines had been dynamometer tested at SwRI as
part of a production engine emissions audit performed by Cummins,
chassis versus engine results, as well as the effects of
different operating parameters investigated in this testing, can
all be examined using the data from these tests. Each bus was
tested at least twice with different combinations of fuel,
inertia loadings and horsepower ratings. For the purposes of
this report, the data which most closely approximated EPA heavy-
duty test conditions was used.
TABLE 4-1
SUMMARY OF TEST PROGRAMS CITED
TEST PROGRAM
SWRI
ENV CANADA
BUSES TESTED
3 1980 DDC 6V-71N
1 1980 DDC 6V-71N
1 1978 DDC 8V-71N
2 1983 DDC 6V-92TA
1 1982 DDC 6V-92TA
2 Cummins L10
BUS CYCLES ;
j
EPA HD Transient (chassis)
EPA Unfiltered (chassis) i
EPA HD Transient (chassis) ]
EPA Engine Dynamometer i
EPA HD Transient (chassis)
EPA Unfiltered (chassis)
EPA HD Transient (chassis) ;
EPA Unfiltered (chassis)
EPA Filtered (chassis)
CBD (chassis)
EPA HD Transient (chassis)
EPA Unfiltered (chassis)
EPA Filtered (chassis)
EPA HD Transient (chassis) !
CBD (chassis)
NYBC (chassis)
NYB (chassis)
5.0
Methodology and Results
Where the emissions data are available from both the engine
and chassis tests of the same bus, the pollutant specific bhp-
hr/mi conversion factors can be directly calculated for that bus
and the chassis cycle used merely by dividing the chassis
emissions results by the engine emissions results. In order to
construct a set of conversion factors for a full range of buses
currently operating, test results would be needed for two-stroke
and four-stroke bus engines both prior to the advent of
particulate emissions control standards and after particulate
emissions control standards. However, data for only pre-contrrl
two-stroke and post-control four-stroke engines are available.
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(EPA started regulating bus PM emissions in 1988, therefore pre-
control refers to pre-1988 bus engines and post control refers to
1988 and later bus engines.)
The data from the 1984 study at SwRI provides directly
comparable engine and chassis emissions information for one bus
equipped with a two-stroke 1980 DDC 6V-71 engine which was tested
over the transient engine dynamometer test cycle and the truck
chassis test cycle (labeled SwRI in table 5-1). The Canadian
data provides engine and chassis data for two four-stroke buses
equipped with 1990 Cummins L-10 engines (labeled 30293 and 30295
in table 5-1). The bhp-hr/mi conversion factors for these test
sequences are presented in Table 5-1. The actual certification
test results for these two engines are presented in appendix C.
[4]
TABLE 5-1 Pollutant Specific Conversion Factor* Calculated
Directly
Bus
SWRI
30295
30293
30295
30293
30295
30293
30295
30293
Chassis
Cycle
HDT
HDT
HDT
CBD
CBD
NYB
NYB
NYBC
NYBC
Fuel
Economy
(mpg)
N/A
4.02
4.06
2.93
3.33
1.60
1.69
3.11
3.46
Pollutant Specific
Conversion Factors (bhp-
hr/mile)
HC
1.68
1.74
1.37
2.09
2.04
5.65
5.22
2.15
2.93
CO
4.62
4.05
4.55
8.45
9.23
24.00
27.14
12.37
12.21
Nox
2.86
3.86
3.20
5.34
3.89
7.19
6.73
4.44
3.52
PM
3.17
3.17
3. 44 ;
6.61
6.05 !
18.99'
17.29 :
11. 33 :
7. 07
HDT=Heavy-Duty Transient, CBD=Central Business District
NYB=New York Bus, NYBC=New York Bus Composite
In addition to the one bus which was tested on the transient
engine dynamometer test cycle and truck chassis test cycle during
the 1984 study performed by SwRI, four other buses powered with
1978 and 1980 DDC engines were tested using both the truck
chassis test cycle and the EPA unfiltered bus cycle. In all
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testa, fuel consumption was measured, making it possible to
report the emission results in units of g/kg of the fuel
consumed, as well as g/mi. Since the one bus from which the
engine was removed and tested was not operated over a bus cycle,
it is not possible to directly convert from g/bhp-hr to g/mi for
a bus cycle. However, this set of conversion factors could be
calculated by chaining together the engine and chassis emissions
data for the one bus for which engine data is available with the
chassis data for both the truck and bus chassis cycles for the
remainder of the buses. This is done by multiplying the bhp-
hr/mi emission conversion factor for the bus tested on both
cycles (i.e., ratio of engine dynamometer to truck chassis cycle
emissions) by the ratio of the bus chassis cycle to truck chassis
cycle emissions results for the buses tested on both cycles.
Slightly different results are obtained depending on whether the
ratio of the g/mi data is used or the ratio of the g/kg data.
The conversion factors calculated using these pollutant specific
conversion factors are presented in Table 5-2. The methodology
of chaining together emission factors is presented in Appendix D.
TABLB 5-2 Conversion Factors Calculated Using SwRZ Data
Chassis
Cycle
EPA Unfiltered
Pollutant Specific Conversion Factors
(bhp-hr/mi)
HC
2.21
CO
6.17
Nox
3.40
PM :
4.37 ;
As can be seen from Table 5-1, the 1980 bus with a two-
stroke engine yielded approximately the same truck chassis test
cycle conversion factors as the two buses equipped with 1990
four-stroke engines. Although the limited data supports only
tentative conclusions, it does appear that conversion factors are
not a strong function of design technology. However, they
clearly are heavily dependent on the chassis cycle used and the
pollutant of concern, as can be seen in Table 5-1.
In comparing the conversion factors calculated from the
Environment Canada data to the conversion factors calculated from
the SwRl data, -(if. engine dynamometer to New York bus composite
chassis cycle as contained in Table 5-1 versus engine dynamometer
to EPA unfiltered chassis cycle as contained in Table 5-2), it
may be seen that the conversion factors for CO and PM from the
SwRl study do not match those from the Canadian study. (This
comparison is appropriate because the New York composite and EPA
unfiltered bus cycle are similar.) This discrepancy is believed
to be mostly attributable to the aspiration techniques and
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strategy connected with the efforts to comply with the
particulate regulations. These strategies are only fully
effective at high engine speeds, which are achieved during the
engine dynamometer cycle but are not seen very often during the
New York composite or EPA unfiltered bus cycles. Therefore, this
discrepancy may indicate a difference in the level of control of
the emissions of CO and particulates between truck type operation
and bus type operations.
6.0 Calculation of Conversion Factors
Based on the above analysis, it is possible to construct
conversion factors applicable to buses over a range of in-use
driving patterns. The basic premise is that the data from the
two Cummins L-10 four-stroke bus engines tested at the Canadian
laboratory will provide conversion factors representative of all
bus engines based on the above-discussed good correlation with
the SwRI data. It is immediately evident from Table 5-1 that the
g/mi emissions factors are strongly influenced by the type of
operations of the vehicle. Since urban buses experience a wide
variety of operating practices and conditions, it is evident that
they will exhibit a range of g/mi emission factors. Therefore, a
range of conversion factors will be developed.
The buses tested in the Canadian program were tested using
chassis cycles which represented a range of operating duty
cycles. One method of gauging the severity of the duty of an
operating cycle is to look at the fuel consumption of the
vehicles when tested on that cycle. In general, the lower the
fuel economy, the more severe (i.e., stop and go with lots of
acceleration and deceleration) the operation of the cycle.
.Referring back to the fuel consumption rates of Table 5-1 for the
buses operated over the four chassis cycles at the Canadian
laboratory, it can be seen that the Heavy-Duty Truck chassis
cycle has the lightest duty of the four cycles with an average
fuel economy of 4.04 miles per gallon while the New York Bus
cycle has the heaviest duty with an average fuel economy of 1.65
miles per gallon. The CBD and New York composite cycles are more
in the mid-range of duty factors and fuel consumption rates with
average fuel economies of 3.13 miles per gallon and 3.29 miles
per gallon respectively. Since these are both close to the urban
bus average fuel economy of approximately 3.3 miles per gallon
[5], the average of these two middle duty cycles provides
reasonable estimates of conversion factors for average bus
operations. The New York City cycle provides the maximum duty
conversion factor for bus operation. This cycle is
representative of driving in heavily congested inner city areas.
The truck chassis cycle provides the minimum duty conversion
factor. This cycle would be more representative of inter-city
bus routes. The range of conversion factors obtained from the
Canadian study is presented in Table 6-1.
10
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TABLS 6-1 BANGS Or BOS CONVERSION FACTORS (bhp-hr/mil«)
Operating
Level
Inter-city
Urban
Heavy Urban
HC
1.6
2.3
5.4
CO
4.3
10.6
25.6
NOx
3.5
4.3
7.0
' PM
3.3
7.9
18.1
7.0 CONCLUSION
Table 6-1 contains the pollutant-specific bus conversion
factors for inter-city, urban, and heavy urban bus operating
levels. It should be noted that these factors are based on very
limited data. In order to develop more statistically reliable
conversion factors, further testing needs to be conducted. Data
which allow direct comparisons between identical engines at
equivalent mileage accumulation levels in terms of engine tested
g/bhp-hr and chassis tested g/mile, need to be developed.
Further testing in the area of conversion factor cross-
applicability to both two and four stroke engines also needs to
be developed. Using the methodology developed in this report and
with new data from further testing, more refined g/bhp-hr to
g/mile conversion factors for a variety of bus operating
conditions could be developed.
11
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REFERENCES
1. "Heavy-Duty Vehicle Emission Conversion Factors II 1962-2000",
Standards Development and Support Branch, Emission Control
Technology Division, Office of Mobile Sources, Office of Air and
Radiation, EPA, EPA-AA-SDSB-89-01, October 1988.
2. "Characterization of Heavy-Duty Motor Vehicle Emissions Under
Transient Driving Conditions," Mary Ann Warner-Selph and Harry E.
Dietzmann, Southwest Research Institute, EPA report number
EPA/600/3-84/104, October 1984 (NTIS number PB85-124154/REB).
3. "Evaluation of Regulated Exhaust Emissions from Urban Buses,"
Greg Rideout, Vehicle Emissions Testing Laboratory, Environment
Canada, June 1990.
4. Cummins Engine Company,. Inc. SwRI Letter Report 08-3952,
January 7, 1991.
5. "1989 Transit Operating and Financial Statistics," American
Public Transit Association.
12
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AIPSNDIX A
SlfPPLKMSNTAL INFORMATION
Southw««t R«««arch Institute
In addition to the five buses from San Antonio tested by the Southwest
Research Institute for the study published in 1984, three other buses from
Houston were also tested in the same time frame. Two of these buses were
ecpaipped with 1983 model Detroit Diesel Corporation six-cylinder turbocharged
engines (DDC 6V-92TA) while the third bus had a 1982 model DDC 6V-92TA
engine. In addition to the truck chassis cycle and the unfiltered EPA bus
chassis cycle, two additional chassis cycles were run on these buses. All
three buses were tested using a version of the EPA bus chassis cycle with the
high frequency transients filtered out (EPA filtered) . In addition, two of
the buses were tested using the Central Business District test cycle. This
data is in Table A-l below.
Ch«vron Raa«arch Company Data
The Chevron Research Company in Richmond, California has been performing
chassis tests on urban buses since early in 1988. The purposes of this
series of tests are mainly to test alternative fuela and fuel formulations as
well as to test unproven bus technologies. However, conventional diesel
buses were also tested in the program to use as comparisons/controls. In the
first set of tests, a CMC coach with a 1982 model DDC 6V-92 engine was tested
over the CBD and unfiltered EPA bus chassis cycles as well as some steady-
state cycles.1 The test engine used in this bus had accumulated 95,700
miles.
-As part of an as yet unfinished and unpublished set of tests, Chevron
has also tested a late model diesel bus from the Southern California Regional
Transit District fleet. This bus is equipped with a recent model 1989
Detroit Diesel 6V-92TA engine and was a relatively low mileage bus with only
34,000 miles. The inertial and road load simulated were not explicitly
stated but appear to have been calculated using the standard techniques for
buses. The only cycle used in the testing so far is the CBD cycle. The
average emissions results from three runs of the test cycle using a blend of
two commercially available diesel fuels from southern California have been
made available for publication. This data is contained in table A-2 below.
Ntttr York City Tranait Authority
The New York City Transit Authority has performed testing on buses as
far back as 1980. For purposes of this report, only a small set of data from
New York's ongoing particulate trap study is being included. This study,
which is intended to perform developmental and comparative testing of
particulate trap systems for buses in actual revenue service, has been
ongoing since May of 1989. The data used in this report are taken from one
bus tested in August of 1990. This bus consisted of a CMC RTS model crach
with a 1989 DDC 6V-92TA engine, a three-speed automatic transmission ar.d a
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gross vehicle weight rating of 36,900 pounds. At the time of the testing,
tho bus had accumulated 83,921 miles. During the testing, #1 diesel fuel was
ua«d. Although this bus was one of the buses used for trap developmental
testing, the data included here were collected from tests performed with the
trap system removed and a stock muffler put in its place. Three different
transient cycles were performed consisting of the CBD cycle, the New York Bus
cycle and the NYBC cycle. Unfortunately the dynamometers available to the
New York City Transit Authority could not simulate the full road load of the
bu.3 chassis 30 the test results had to be adjusted for this fact, making the
results somewhat questionable. This data is contained in table A-3 below.
1.24 Environment Canada
Another VETL program did comparative testing using four diesel buses and
three light-duty vehicles. The results of the VETL comparative testing
between buses and light-duty vehicles were published in June of 1990. Three
of the buses tested were typical of the types of urban buses common in the
United States having testing inertia weights of 28,200 pounds and using DDC
1982 6V-71 N, DDC 1989 6V-92 TA and 1990 DDC 6V-92 TA engines. The fourth
busi was somewhat larger than the typical U.S. urban bus with a testing weight
of 35,000 pounds and a 1984 Cummins NHHTC-300 engine. The bus with the 1982
Detroit Diesel engine was tested both before and after routine maintenance.
Th«> only transient cycle used during the testing was the EPA truck chassis
cycle. The buses were operated using commercial #1 diesel fuel.
-------
TABLE A-l: SwRI CHASSIS TESTING RESULTS
BUSES
HOUSTON- 1
6V-92TA
1983
55,000 miles
HOUSTON- 2
6V-92TA
1983
100,000 miles
HOUSTON- 3
6V-92TA
1982
139,000 miles
CYCLE
EPA Truck
EPA Unfilt
EPA Filter
EPA Truck
EPA Unfilt
EPA Filter
CBD
EPA Truck
EPA Unfilt
EPA Filter
CBD
EMISSION FACTORS (G/MI)
MPG
4.9
3.8
4.6
5.2
4.25
4.8
3.7
4.9
3.9
4.7
3.5
HC
1.2
2.1
2.4
1.8
2.87
3.1
2.8
2.7
4.7
5.1
4.1
CO
11.7
38.4
5.1
5.8
te.H
1^*
T- —
5.1
15.9
12.6
25.7
10.0
28.6
NOx
24.0
32.2
30.5
19.2
26.7
24.9
29.6
15.7
21.9
20.9
23.3
PM
2.6
5.5
1.7
1.6
2.1
1.4
2.8
3.9
6.3
3.4
6.3
EPA Truck= EPA Heavy-Duty Transient Cycle
EPA Unfilt= EPA Unfiltered Cycle
EPA Filter- EPA Filtered Cycle
CBD=» Central Business District Cycle
TABLE A-2: CHEVRON TESTING RESULTS
BUSES
DDC 6V-92TA
1982
34,000 *
CYCLE
CBD
Unfilt
CBD
CBD
CBD
Unfilt
Unfilt
Unfilt
EMISSION FACTORS (G/MI)
MPG
3.9
4.8
NA
4.2
4.0
4.0
5.1
4.9
HC
6.9
4.0
3.3
6.4
6.6
5.0
3.7
3.9
CO
59.0
51.0
31.8
56.0
55.9
59.8
47.4
49.2
NOx
30.0
28.0
34.0
28.0
28.1
33.4
' 26.2
26.5
PM
5.6
2.4
5.4
5.3
5.3
2.4
2.3
2.4
CBD=» Central Business District
* Average of three tests.
Unfilt- EPA Unfiltered
-------
TABLE A-3: NEW YORK CITY TBSTINO RESULTS
BUSES
DOC 6V-92TA
1389
83, 921
CYCLE
CBD
NYB
NYBC
NYBC
EMISSION FACTORS (G/MI)
MPG
4.1
1.7
3.6
3.6
HC
2.8
8.5
3.8
3.9
CO
5.3
11.9
6.0
6.0
NOx
26.3
77.5
32.1
32.5
PM
1.0
2.1
1.1
1.1
CBEi= Central Business District
NYEiC= New York Bus Composite
NYB= New York Bus
-------
APPENDIX B
SwlEtt CHASSIS T1STIKO RESULTS
BUSES
SAN ANTONIO-1
6V- 7 IN
1980
164,000 miles
SAN ANTONIO-2
6V- 7 IN
1980
132,000 miles
SAN ANTONIO- 3
6V- 7 IN
1980
137,000 miles
SAN ANTONIO- 4
8V- 7 IN
1978
247,000 miles
SAN ANTONIO- 5
6V- 7 IN
1!)80
915,000 miles
CYCLE
EPA Truck
EPA Unfilt
EPA Truck
EPA Unfilt
EPA Truck
EPA Unfilt
EPA Truck
EPA Unfilt
EPA Truck
Engine
(Dyno)
g/bhp-hr
EMISSION FACTORS (G/MI)
MPG
4.7
3.8
4.9
4.0
4.7
3.7
4.6
3.9
NA
NA
HC
2.5
3.6
2.9
4.0
2.9
2.9
2.7
3.8
2.8
1.7
CO
86.3
128.8
28.8
51.5
52.6
102.3
18.2
27.4
34.4
7.5
Nox
16.4
20.8
22.2
27.0
16.4
19.8
27.4
30.1
17.4
6.1
PM
7.1
10.0
2.3
3.3
5.8
8.9
2.5
2.9
2.1
0.7
EPA Truck- EPA Heavy-Duty Transient Cycle, EPA Unfilt= EPA Unfiltered Cycle,
EPA Filter- EPA Filtered Cycle
CBD- Central Business District Cycle
-------
APPENDIX C
ENVIRONMENT CANADA TESTING RESULTS
BUS
Cummins L10
30295
Cummins L10
30293
CYCLE
EPA Truck-C
EPA Truck-H
CBD
NYB
NYBC
EPA Truck-C
EPA Truck-H
CBD
NYB fti
NYBC Af I
FUEL
CONSUMPTION
(L/100 KM)
76.7
70.3
96.6
176.9
90.9
69.4
63.7
84.8
81.5
167.2
EMISSIONS (G/MI)
THC
1.3
1.13
1.4
3.7
1.4
1.1
1.0
1.5
2.1
3.8
CO
10.8
12.8
26.8
76.1
39.2
12.3
13.7
27.9
36.9
82.0
Nox
19.3
19.9
27.6
37.2
23.0
16.1
16.6
20.3
18.3
35.0
PM
1.9
1.5
3.1
8.8
5.6
2.1
1.7
3.0
3.5
8.5
EPA Truck-C= EPA Heavy-Duty Transient Cycle Cold Start
EPA Truck-H=> EPA Heavy-Duty Transient Cycle Hot Start
CBD»« Central Business District Cycle
NYB" New York Bus Cycle
NYBC= New York Bus Composite Cycle
SwRI DYNAMOMETER RESULTS (g/bhp-hr)
Bus Number
30295
30293
HC
0.65
0,73
CO
3.17
3.02
NOx
5.17
5.20
PM !
0.465 i
0.491 ;
-------
CALCULATION OF BUS CONVERSION FACTORS
Bua
Cycle
Heavy-duty
Transient
Cycle
Central
Business
District
New York
Bus Cycle
New York
Composite
Cycle
Pollutant
Category
HC
CO
NOx
PM
HC
CO
NOx
PM
HC
CO
NOx
PM
HC
CO
NOx
PM
Bus 130295 (4s)
Dyno
Teat
Results
(SwRI)
0.65
3.17
5.17
0.465
0.65
3.17
5.17
0.486
0.65
3.17
5.17
0.486
0.65
3.17
5.17
0.465
Chassis
Test
Results
(Ontario)
1.13
12.84
19.94
1.475
1.38
28.8
27.59
3.075
3.67
78.08
37.16
8.83
1.4
39.21
22.96
5.57
bhp-hr/
mile
1.74
4.05
3.86
3.17
2.09
8.45
5.34
8.61
5.65
24.00
7.19
18.90
2.15
12.37
4.44
11.96
Bus 130293 (4s)
Dyno
Test
Results
(SwRI)
0.73
3.02
5.2
0.491
0.73
3.02
5.2
0.491
0.73
3.02
5.2
0.491
0.73
3.02
5.2
0.491
Chassis
Test
Results
(Ontario)
1
13.74
16.62
1.69
1.49
27.86
20.25
2.97
3.81
81.95
35
8.49
2.14
38.87
18.31
3.47
bhp-hr/
mile
1.37
4.58
3.20
3.44
2.04
9.23
3.89
6.05
5.22
27.14
8.73
17.29
2.93
12.21
3.52
^07
-------
APPENDIX D
CHAINED EMISSION FACTOR DATA (SwRI)
engine
1982
6V-71N
1980
6V-71N
1980
6V-71N
1980
6V-71N
1980
8V-71H
cycle
EPA Truck
Engine
EPA Truck
Engine
EPA Truck
EPA Bus
EPA Truck
EPA Bus
EPA Truck
EPA Bus
EPA Truck
EPA Bus
EPA Truck
EPA Bus
EPA Truck
EPA Bus
EPA Truck
EPA Bus
EPA Truck
EPA Bus
Emissions
*c
2.8
3.4
4.2
1.7
2.5
3.6
3.9
4.5
2.9
4.0
4.7
5.2
2.6
2.9
4.4
3.5
2.7
3.8
4.1
4.9
CO
34.4
9.5
51.9
7.5
86.3
9.7
132
158
28.8
51.5
45.8
66.8
52.6
102.4
79.8
124
18.2
27.4
27.4
34.8
Nox
17.4
10.6
26.4
6.1
16.4
20.8
25.2
25.6
22.2
27.0
35.4
35.1
16.4
19.8
24.9
24
27.4
30.1
41.4
38.2
PM
2.0
1.0
3.1
0.7
7.1
10.0
10.9
12.3
2.3
3.3
3.7
4.3
5.8
8.9
8.8
10.7
2.5
2.9
3.7
3.7
Units
g/mi
g/mi *
gAg
g/Bhp-hr
g/mi
g/mi
g/kg
g/kg
g/mi
g/mi
g/kg
g/kg
g/mi
g/mi
g/kg
g/kg
g/mi
g/mi
g/kg
g/kg
Bus/Truck chassis
HC
1.7
0.66
2.5
1.5
1.2
1.4
1.1
1.0
0 08
1.4
1.2
CO
4.6
0.66
7.0
0 .1
1.2
1.8
1.5
1.9
1.6
1.5
1.3
NOx
2.9
0.66
4.3
1.3
1.0
1.2
1.0
1.2
1.0
1.1
.9
PM
3.2
0.66
4.8
1.4
1.1
1.4
1.2
1.5
1.2
1.2
1.0
-------
CHAINED EMISSION DATA CONVERSION FACTOR CALCULATION
BHP-HR/MILK CONVERSION FACTORS
BASIS
g/mi
g/kg
HC
2.21
1.79
CO
6.17
6.32
NOx
3.40
2.77
PM
4.37
3.55
EQUATION D-2
CHAINED CONVERSION FACTOR CALCULATION
N
Where:
A is the Bhp-hr/mile engine dynamometer to truck chassis cycle
conversion factor of the SwRI bus tested.
B is the bus chassis cycle emission value.
T is the truck chassis cycle emission value.
N is the number of comparable cycle sets.
1. "Emissions and Fuel Economy Test Results for Methanol and
Diesel-Fueled Buses," Gilles A. Eberhard,'Matthew Ansari, and S.
Kent Hoekman; Chevron Research Company; Air & Waste Management
Association 82nd Annual Meeting & Exhibition June 25-30, 1989.
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