Duty Cycle Effects On Small Engine Emissions
98-MA4A.01
Peter Gabele
U.S. Environmental Protection Agency, MD-46, Research Triangle Park, North Carolina 27711
ABSTRACT
The paper presents emissions data obtained from seven lawn mower engines that were tested
using three duty cycles; a six mode steady-state test, a quasi-steady-state test, and a transient test.
A comparison of emissions from the three duty cycles is made for non-methane organic gases,
carbon monoxide, nitrogen oxides, detailed hydrocarbons (percent of total organic emissions that
are paraffin, olefin, aromatic, or acetylene), and toxic compounds (benzene, 1,3-butadiene,
formaldehyde, and acetaldehyde). Differences in ozone potential are also determined and
reported for each duty cycle. The study includes both regulated and unregulated (not certified to
any emission standard) test engines that have a wide range of emission rates. Results indicate
that regulated emission rate differences due to duty cycle are fairly small (less than ten percent
on the average). For over half of the regulated emissions data, there is no significant difference
in emission rates between data obtained using the steady-state and the transient duty cycle.
Emission comparisons are even better between the quasi-steady-state and steady-state data.
Ozone potential and toxic emissions are ten to twenty percent higher with the transient test cycle
and organic composition appears unaffected by duty cycle selection.
INTRODUCTION
Emissions from small non-handheld engines are normally determined using a six-mode, steady-
state test procedure. The contribution of these engines to the emissions inventory has been
determined using results based on tests with this steady-state duty cycle. The engine is operated
in each mode until engine temperature has stabilized, then exhaust samples are taken for analysis.
The basic procedure, known as the SAE J1088, was developed and refined over time by the
Society of Automotive Engineers.1 Test procedures similar to the J1088 were adopted by the
California Air Resources Board and the U.S. Environmental Protection Agency for use in
certifying new nonroad spark-ignition engines at or below 19 kW.
Historically, steady-state tests for small engines have been appropriate because they are simpler
and less expensive to perform than transient tests. The loads experienced by the engine during
the test represent those experienced in actual operation and emissions occurring during modes
where the engine normally resides are weighted more heavily than those that are used less.
Criticism of steady-state tests centers on their inability to simulate real-world conditions as well
as transient tests do. Experience with motor vehicle engines has shown that emissions and fuel
consumption results from steady-state tests are considerably lower than transient test results.
Important emissions occurring during the transients may not be captured by the test. For engines
that operate in steady-state applications, the test is a non-problem, but for many small engine
applications, transient operation cannot be avoided.

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Lawn mower engines, the most popular small engine application, operate through a series of
transients where engine torque varies as a function of grass condition and type of lawn mower.
A transient duty cycle for lawn mowers known as the Grass Cutting Duty Cycle (GCDC) was
developed by recording real-time measurements of engine torque while mowing different lawns.2
This duty cycle takes into account differences in load due to the type of mower (e.g., mulcher
versus side discharge), and differences due to the condition of the grass being cut (e.g., short/tall,
wet/dry).
Use of a transient test to certify small engines may not be justified at this time due to the costs
and complexities of the test. But there are emission inventory concerns about the use of steady-
state data that should be addressed. Errors in the inventory result if these tests fail to produce
real-world emission results. It may be necessary to use transient test data for inventory purposes,
or apply correction factors, if possible, to the steady-state data. On the other hand, if emissions
are not significantly impacted by duty cycle, resources can be directed elsewhere.
Results from two previous studies comparing regulated (HC, CO, and NOx) and carbon dioxide
(C02) emission rates from steady-state, quasi-steady-state, and transient duty cycles have been
published.2,3 One study reported few differences while the other reported significant ones. No
known attempt has been made to compare speciated hydrocarbon (HC) emissions data from
different duty cycles. In fact, there is a lack of published speciated HC data for small engines.
The Southwest Research Institute has conducted a number of small engine emissions'
characterization studies that speciate hydrocarbons using a quasi-steady-state duty cycle recently
named the C6M (Composite Six-Mode) duty cycle.4,5,6 But no attempt has been made to
compare speciated data from one duty cycle with that of another.
It is important to know if transient operation influences the organic composition of emissions.
Organic composition of the exhaust gas determines both the photochemical reactivity and the
toxicity of the emissions. Emission studies of on-road sources have recognized the importance
of the transient cycle and have used it exclusively in tests which measure toxic and reactive
emission rates. Tests that provide small engine emissions data for human exposure models must
adequately simulate real-world emissions since exposure to these sources most often occurs in
situations where transient operation is the norm (e.g., during lawn and garden work).
This study investigates the effect of duty cycle on regulated and unregulated (including speciated
HCs) emissions. Emissions from steady-state, quasi-steady-state, and transient duty cycles are
examined. Results are obtained in testing six four-stroke and one two-stroke lawn mower
engines using the 1990 baseline gasoline.
EXPERIMENTAL METHOD
Test Equipment
The test cell has an eddy-current dynamometer that can absorb up to 12 kW. The dynamometer's
low moment of inertia (1.55x10"3kg-m2) enables better simulation of small engine transient loads
when operating at rapidly changing speeds. An engine-dynamometer controller consists of two
separate units: a dynamometer controller that varies excitation current to the dynamometer to
maintain either speed or torque, and a throttle controller that controls the engine's throttle to
maintain desired torque, speed, or throttle position. The engine-dynamometer controller is
2

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interfaced to a computer that commands second-by-second speed, torque, or throttle position
called for by the duty cycle. During these tests, engine torque is controlled by the dynamometer
torque control and engine speed is controlled by the throttle controller.
During the test, engine torque, speed, and power, and various pressures and temperatures at the
constant volume sampler (CVS) are needed in order to calculate emission rates. These are
brought into a computer in real-time and downloaded to a spreadsheet after the test. Real-time
regulated emissions (hydrocarbons (HC), CO, and nitrogen oxides (NOJ are brought into a
separate computer and also downloaded to the spreadsheet following the test. The spreadsheet
contains a record of second-by-second data enabling the calculation of real-time or modal
emission rates.
Engine exhaust is directed to a constant volume sampler (CVS) via a bell-mouthed opening
positioned near the engine's exhaust outlet (see Figure 1). Dilution air from the engine room
forms an envelope around the exhaust and diluted exhaust is drawn into the CVS at a rate of
about 600 SCFM. Heated sample lines are used to draw samples from the CVS for aldehyde,
real-time, and bag analyses. The bags are first analyzed for regulated emissions, then a sample is
drawn off for HC speciation.
The test facility shares much of its sampling and analytical equipment with a chassis
dynamometer emissions laboratory. Personnel assigned to the test cell are highly skilled in the
characterization of emissions from gasoline and diesel engines.
Test Procedure
Exhaust gas emissions are generated by operating the engines over three different duty cycles:
the federal small engine certification cycle (6-Mode), the C6M cycle, and the GCDC. The
GCDC was developed by an EPA regulation negotiation test procedure task group and the C6M
was developed by Southwest Research Institute (SwRI).2,7 The C6M is a modification of the
certification test for small (less than 19 kilowatts), non-handheld, engines that basically
combines the sample taken during the six separate steady-state modes into one large sample. It is
a quasi-steady-state duty cycle since emissions are collected during the transients that occur
when shifting from mode-to-mode. The GCDC is a transient test with constantly varying loads
being applied to the engine while the engine's speed is held steady using a throttle controller or
the engine's governor.
The 6-Mode Test - The 6-Mode test is conducted by taking exhaust gas samples while the
engine is operating at six different steady-state load points. Five of the load points are defined as
100, 75, 50, 25, and 10 percent of rated torque at 85 percent of rated speed; the sixth point is at
idle load. The sample is taken for a 600 second period after all engine and sampling system
readings have stabilized.
The C6M Test Cycle - The engine is run through six modes (same modes as in 6-Mode test)
while emissions are sampled continuously. The time spent in each mode is proportional to the
weight given the mode in the certification procedure. For example, if the weight of a mode is
twice that of a second mode in the certification test, the length of time spent in that mode is twice
that of the second mode. Instead of having twelve (six sample and six background) bags to
analyze following the test, the C6M has only two (a sample and a background) bags. This
greatly reduces the cost and simplifies the analysis component. During the C6M test, engine
3

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speed is maintained at 85 percent of rated speed except at idle when it decreases to the lowest
speed inside a smooth operating regime. Equivalency between the C6M and the certification test
has not established due to resource restraints, but Southwest Research concluded that the C6M
produces results which are useful to a research program. Table 1 specifies the test parameters of
the C6M.
The GCDC - The GCDC is derived in part from mulching and side discharge data when cutting
grass under the following conditions: short dry, short wet, long dry, and long wet. These eight
conditions plus one that simulates the bagging of long dry grass are all represented in the
GCDC. The entire test extends for 1000 seconds and Figure 2 shows a trace of the torque versus
time with one of the engines being operated using the GCDC. During the test, engine speed is
maintained at 85 percent of rated speed using a throttle controller.
Table 2 shows the average or weighted engine speed, torque, and power for each test engine with
all three duty cycles. The 6-Mode and C6M test values are obtained using the modal weighting
factors given in the federal regulation.8 The GCDC values are the average of the six replicate
samples for each duty cycle. It is noted that the average and weighted power measured for the
GCDC was consistently less than that for the other two test procedures. Had this study been
designed from the standpoint of certification concerns rather than inventory concerns, the loads
for the 6-Mode test would have been forced equal to those for the GCDC. This can be done by
simply changing the weighting factors assigned to the 6-Mode to values that take into account
the frequency distribution of loads in the GCDC.
The test matrix that was used is shown in Table 3. Six replicate C6M and GCDC tests and three
replicate 6-Mode tests were performed with each engine.
Gaseous Emissions Measurement
Exhaust emission rates were determined for HC, CO and NO, using standard sampling,
analytical, and calculation procedures.8 They were also determined using a real-time sampling
and analysis procedure that enabled integrated results over that test period to be compared to bag
sample results for quality control (QC) purposes. The NMOG emissions were determined by
taking the sum of the individual non-methane HC emissions following analysis with a gas
chromatography- flame ionization detector (GC/FID), then adding in the oxygenate and aldehyde
emissions.
Dilute exhaust samples were collected in 60-L Tedlar bags for hydrocarbon speciation. The GC
speciation methodologies are essentially the same as those used in the Auto/Oil Air Quality
Improvement Research Program.9 A background sample was taken during the test. Integrated
GC-FID peak measurements were compared to the HC measurements obtained using the
standard FID procedure for QC purposes.
Aldehydes were sampled through a heated sample line (110°C) and collected on
dinitrophenylhydrazine (DNPH) -coated silica gel cartridges. Two cartridges were drawn during
each test: one from the exhaust gas and one from the background. The aldehyde samples, trapped
on the cartridge as individual DNPH aldehyde derivatives, were then analyzed by high-
performance liquid chromatography.9
4

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Emissions' Reactivity
Ozone-forming potential of the exhaust volatile organic compounds (VOC) is based upon the
incremental reactivity approach developed by Carter and Atkinson.10 Application of this concept
has led to the development of the Maximum Incremental Reactivity (MIR) method, that
expresses the reactivity of exhaust NMOG and CO from the test engine,11 The method assigns a
specific reactivity level to each of the organic species and to CO, and calculates a reactivity-
weighted emission (RWE) rate for each specie by multiplying the specie's specific reactivity
times its emission rate. The RWE rate for an exhaust sample is obtained by summing all of the
individual RWE rates for each specie present. The RWE rate, expressed in units of grams ozone
per kilowatt-hour, is a useful measure of the ozone potential of the CO and organic emissions in
urban atmospheres where the VOC-to-NOx ratios are relatively low (approximately 6). The
specific reactivity of the organic emissions can easily be obtained by dividing the organic RWE
rate by its emission rate.
Test Engines and Fuel
Six four-stroke engines were used in this study. The two having OHV configurations were
regulated engines (#0034 & #2122) designed to comply with the Phase 1 emission standard for
small non-handheld engines. One two-stroke engine (#4468) was tested to investigate its
sensitivity to duty cycle. Approximately ten percent of the in-use lawn mowers are those
powered by 2-stroke engines.12 Three of the engines were tested with their governors in-place
and four with them removed (#1001, #1035, #0034, & #4468 ). A more complete description of
the engines is given in Table 4.
The test fuel used in this study was a 1990 Baseline Gasoline designated "RFA." A detailed
description of the fuel is given in Table 5.
RESULTS AND DISCUSSION
The regulated and unregulated emission summaries are given in Table 6 for the seven engines
tested. Average emission rates and percent differences relative to 6-Mode emission rates are
given in each table. In Table 6, the percent difference was obtained by averaging the percent
differences for each of the seven engines. The engine-by-engine emission rates, standard
deviations, and percent differences compared to the 6-Mode test data are given in tables in the
appendix. The emission rate values accompanied by standard deviations in Table A-l represent
the average of six runs for all C6M and GCDC data, and the average of three runs for the 6-Mode
emission rates.
The average emission rates for the seven engines are strongly affected by emissions from the one
2-stroke engine that was tested. The 2-stroke engine's organic emission rates were about twenty
times higher than the average 4-stroke emission rate. This resulted in elevated 2-stroke
emissions of ozone precursors and toxic compounds. The average MLR ozone potential for the 4-
stroke engines is 88 g 03/kW-h compared to 1387 g 03/kW-h for the 2-stroke engine. For toxic
emission rates the comparison is 1.2 g/kW-h for the 4-stroke engines versus 12.4 g/kW-h for the
2-stroke engine.
5

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Results given in Tabic 6 illustrate that emission rates for the C6M and GCDC tests compare
fairly well with those from the 6-Mode test. The 6-Mode steady-state test is viewed as the
reference method since it has been used extensively to determine emission rates from small
engines and is the current EPA certification method. The regulated emissions data from each of
the test engines lends itself to statistical analysis because replicate testing was performed with all
of the duty cycles. The C6M and GCDC duty cycles were each run six times and the 6-Mode
test was run three times for regulated emission analyses. The C6M emission rates were not
significantly (95 percent confidence level) different from the 6-Mode rates for over 70 percent of
the regulated emissions data. Comparison between emission rates for the transient test (GCDC)
and the 6-Mode test is not as good, but there were still no significant differences for over 55
percent of the data.
Only one sample was taken for speciated organic emissions data (detailed hydrocarbons and
aldehydes) collected using the 6-Mode test; therefore, no attempt is made to compare these data
statistically with the mean emission rates from the GCDC and C6M tests. Generally, GCDC
regulated and unregulated emission rates, with the exception of NOx, are higher than those of the
6-Mode and C6M tests. This happens primarily because the loads with the GCDC (see Table 2)
are less than those with the other two duty cycles. As engine loads decrease, emission rates,
expressed in units of g/kW-h, usually increase. Emission rates from the GCDC and the 6-Mode
test agree better when the weighting factors used in the 6-Mode test are changed to account for
the load frequency distributions. For example, using such weighting factors causes the HCs for
the 6-Mode test to be greater than those for the GCDC by an average of 5.8 percent. From Table
6, the HCs are less with the 6-Mode test an average 10.2 percent using the standard weighting
factors. This study is concerned with duty cycle emission rate differences from an emissions
inventory standpoint; therefore, the comparisons using the modified 6-Mode test are interesting
but less relevant to the discussion.
The overall summaries of Table 6 show that unregulated emission rates and organic composition
also appear roughly the same for each of the three duty cycles. Some percentages (differences
relative to the 6-Mode test) may seem high but these are often the result of small differences
between small numbers. In many cases the standard deviations for the mean values reported are
greater than the differences due to duty cycle. The magnitude of the emission rate differences of
this study tend to agree with those reported in an earlier study. In that study, a current
technology lawn mower engine was tested using both steady-state (California test) and transient
(GCDC) test procedures.2 Replicate tests were run with each procedure and the differences in the
corresponding mean emission rates are within 25 percent for each pollutant.
Another study that examined duty cycle effects for 19 two- and four-stroke engines came up with
much larger differences than those reported here.3 Hydrocarbon and CO emission rates were
twice as high in the transient test compared to the steady-state test for two lawn mower engines.
Emissions from other engines demonstrated similar increases in HC and CO emission rates as the
duty cycle became more transient in nature. Replicate tests were not conducted and the engines
tested were new with overhead valve configurations. Engines #0034 and #2122 of this study
have overhead valve configurations but did not display such dramatic increases in HC and CO
during transient testing.
6

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CONCLUSIONS
The data support the notion that emission rates from small engines have not been seriously
underestimated due to the use of a steady-state test procedure. However, the study's results are
based on a limited test matrix due to resource constraints. Conclusions regarding emissions and
duty cycle effects may not be representative of the entire lawn mower fleet. A better
understanding of the overall problem will evolve as these results are pooled with those of similar
studies.
The study is primarily interested in determining if emissions with transient testing are
significantly different from those with a steady-state testing. Emissions are characterized from
seven lawn mower engines using three duty cycles. With each engine, six replicate tests for
emissions were run using both the transient GCDC and the quasi-steady-state C6M. Three
replicate tests for regulated emissions and one for unregulated emissions were run with the 6-
Mode steady-state test. Emissions obtained using the two non-steady-state duty cycles are not
dramatically different from the 6-Mode results. Results with the C6M are closer to those of the
6-Mode test. A comparison of results from the seven engines leads to the following conclusions
regarding emissions from the quasi-steady-state (C6M) test relative to those from the 6-Mode
test:
•	Hydrocarbon, CO, and NOx emission rates are not significantly different for over 70
percent of the comparisons.
•	Overall, the HC and NOx emission rates are four and two percent lower, respectively, and
the CO emission rates are five percent higher.
•	Individual toxic emission rates range from zero to seven percent higher.
•	The organic composition in terms of HC family fractions and their contribution to the
ozone potential is about the same.
The following conclusions are made regarding GCDC emission rates relative to those from the 6-
Mode test:
•	Hydrocarbon, CO, and NO, emission rates are not significantly different for over 50
percent of the comparisons.
•	Overall, HC and CO emission rates are 10 and 9 percent higher, respectively, and the NOx
emission rates are two percent lower.
•	Individual toxic emission rates range from 3 to 19 percent higher.
•	The organic composition in terms of HC family fractions and their contribution to the
ozone potential are about the same.
ACKNOWLEDGMENTS
The author wishes to acknowledge the help he has received from those who have contributed to
this study. Particular thanks go to Jerry Faircloth, and Versal Mason for their on-site support;
and Colleen Loom is and Kim Wood for their GC analyses. This study could not have proceeded
as smoothly as it did without the support of each of these individuals.
7

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DISCLAIMER
The information in this document has been funded wholly or in part by the United States
Environmental Protection Agency, It has been subject to Agency review and approved for
publication. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
REFERENCES
1.	"Test Procedure for the Measurement of Gaseous Exhaust Emissions from Small Utility
Engines", SAE Recommended Practice J1088, Warrendale, PA., February 1993.
2.	Carpenter, T., Buszkiewicz, T., Trimble, T., "Transient versus steady-state test procedure
evaluation of 4-cycle utility engines," Society of Automobile Engineers Technical Paper
No.961736, Warrenton, PA., September, 1996.
3.	Sun, X., Brereton,G., Morrison, K., Patterson, D., "Emissions Analysis of Small Utility
Engines," SAE Technical Paper No. 952080, March 1995.
4.	Hare, C.T., Carroll, J.N., "Reactivity of Exhaust Emissions from a Small Two-Stroke Engine
and a Small Four-Stroke Engine Operating on Gasoline and LPG," Small Engine Technology
Conference, SAE Technical Paper No. 931540, Pisa, Italy, December, 1993.
5.	Hare, C.T., White, J .J., "Toward the Environmentally-Friendly Small Engine: Fuel, Lubricant,
and Emission Measurement Issues," Small Engine Technology Conference, SAE Technical
Paper No. 911222, Yokohama, Japan, October, 1991.
6.	White, J.W., Carroll, J.N., Hare, C.T., Lourenco, J.G., "Emission Factors for Small Utility
Engines," SAE Technical Paper No. 910560, March, 1991.
7.	Hare, C.T., White, J.J., "A Next Generation Emission Test Procedure for Small Utility
Engines - Part 1, Background and Approach," SAE Technical Paper No. 901595, Milwaukee,
WI, September, 1990.
8.	Federal Register, "Control of Air Pollution; Emission for New Nonroad Spark-Ignition
Engines At or Below 19 Kilowatts;" Fed. Reg. 40 CFR Part 86, Final Rule, July 3, 1995.
9.	Siegl, W.O., Richert, J.F.O., Jensen, T.E., Schuetzle, D., Swarin, S.J., Loo, J.F., Prostak, A.,
Nagy, D., Schlenker, A.M., "Improved Emissions Speciation Methodology for Phase II of the
Auto/Oil Air Quality Research Program - Hydrocarbons and Oxygenates," SAE Technical Paper
No. 930142, SP-1000, October, 1993.
10.	Carter, W.P.L. and Atkinson, R.J., "An Experimental Study of Incremental Hydrocarbon
Reactivity," Environ. Sci. Technol. 21, 864-880., 1987.
11.	Lowi, Alvin Jr., and Carter, W. P. L., "A Method for Evaluating the Atmospheric Ozone
Impact of Actual Vehicle Emissions," SAE Technical Paper No. 900710, March 1990.
12.	"Nonroad engine and vehicle emission study", EPA-21A-2001, Office of Mobile Sources,
U.S. Environmental Protection Agency , November, 1991 (report available on request to the
author).
8

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APPENDIX
Table A-la. Emission rates, compositions, and ozone potentials (standard deviations in
parentheses) for the seven engines and three duty cycles examined in the study.

Engine 1001
Engine 1035
Engine 2615

6Mode
C6M
GCDC
6Mode
C6M
GCDC
6Mode
C6M
GCDC
Regulated Emissions (g/kW-h)
HC
29.2
31.3
31.1
13.8
13.9
15.7
14.2
15.5
16.4

(1.6)
(1.9)
(1.2)
(0.9)
(0.6)
(1.1)
(1.2)
(0.5)
(0.5)
CO
443
420
431
286
281
276
523
622
599

(27.3)
(64)
(19)
(38)
(32)
(43)
(44)
(19)
(19)
NOx
3.7
3.7
• 3.3
4.3
4.6
3.6
1.9
1.7
2.1

(0.9)
(0.4)
(0.6)
(0.7)
(0.8)
(0.6)
(0.6)
(0.3)
(0.1)
C02
1280
1273
1573
1208
1227
1456
. 1006
1006
1186

(78)
(69)
(34)
(51)
(57)
(79)
(77)
(44)
(45)
NMOG
26.7
27.7
29.6
12.6
12.7
14.6
12.0
14.3
15.3


(2.8)
(1.2)

(0.6)
(0.7)

(0.7)
(1.0)
Toxic Emissions (g/kW-h

1,3 Butadiene
0.26
0.37
0.40
0.19
0.21
0.24
0.10
0.10
0.11


(0.07)
(0.08)

(0.03)
(0.03)

(0.02)
(0.01)
Benzene
1.18
1.25
1.32
0.65
0.64
0.75
0.71
0.87
0.90


(0.07)
(0.05)

(0.03)
(0.05)

(0.05)
(0.05)
Formaldehyde
0.36
0.41
0.37
0.20
0.17
0.20
0.14
0.16
0.15


(0.06)
(0.02)

(0.02)
(0.01)

(0.01)
(0.01)
Acetaldehyde
0.08
0.10
0.09
0.04
0.03
0.04
0.02
0.03
0.03


(0.01)
(0.00)

(0)
(0)

(0)
(0)
Reactivity
MIR (g
140
150
156
75
75
82
77
91
95
CykW-h)

(12)
•(70)

(3)
(5)

(3)
(5)
Specific
4.33
4.60
4.50
4.71
4.67
4.62
4.07
4.04
4.08
Reactivity

(0.16)
(0.09)

(0.12)
(0.06)

(0.11)
(0.09)
(g cyg









NMOG)









MIR Fractions
Paraffin
6%
5%
6%
4%
4%
4%
4%
4%
4%


(1%)
(0)

(0)
(0)

(0)
(0)
Olefin
36%
41%
41%
44%
44%
45%
30%
28%
30%


(5%)
(1%)

(2%)
(2%)

(1%)
(1%)
Aromatic
35%
34%
34%
26%
27%
28%
25%
27%
28%


(5%)
(1%)

(1%)
(1%)

(2%)
(3%)
Acetylene
1%
2%
2%
2%
2%
2%
2%
2%
2%


(0)
(0)

(0)
(0)

(0)
(0)
Aldehyde
3%
3%
3%
3%
3%
3%
2%
2%
2%


(0)
(0)

(0)
(0)

(0)
(0)
CO
18%
15%
15%
21%.
20%
19%
37%
37%
34%


(1%)
(2%)

(2%)
(2%)

(2%)
(2%)
HC Family Fractions
Paraffin
32%
27%
30%
26%
25%
25%
32%
32%
31%


(2%)
(1%)

(1%)
(0)

(1%)
(1%)
Olefin
25%
28%
28%
32%
32%
31%
24%
22%
23%


(3%)
(1%)

(1%)
(1%)

(0)
(1%)
Aromatic
35%
35%
34%
30%
31%
31%
31%
32%
32%


(5%)
(1%)

(1%)
(1%)

(2%)
(2%)
Acetylene
8%
10%
9%
11%
12%
12%
13%
14%
14%


(1%)
(0)

(1%)
(0)

(2%)
(2%)

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Table A-lb.

Engine 0954
Engine 0034
Engine 2122
Engine 4468

6Mode
C6M
GCDC
6Mode
C6M
GCDC
6Mode
C6M
GCDC
6Mode
C6M
GCDC
Regulated Emissions (g/kW-h)
HC
24.7
20.6
23.5
12.5
10.5
13.3
8.4
8.3
9.9
339
304
367

(5.2)
(3.2)
(3.0)
(3.3)
(0.1)
(1.2)
(0.5)
(0.5)
(1.0)
(44)
(9)
(16)
CO
487
506
510
360
405
467
381
389
414
952
912
1042

(29)
(13)
(17)
(32)
(28)
(21)
(12)
(19)
(7)
(57)
(14)
(24)
NOx
3.6
3.4
3.0
7.5
8.0
6.8
4.5
4.0
4.2
0.43
0.42
0.52

(0.3)
(0.6)
(0.4)
(1.0)
(0.5)
(0.4)
(0.3)
(0.3)
(0.4)
(0.34)
(0.30)
(0.60)
O
O
1456
1381
1556
1178
1236
1491
1302
1302
1523
1283
1305
1471

(216)
(51)
(96)
(104)
(26)
(32)
(23)
(44)
(32)
(38)
(83)
(60)
NMOG
23.2
21.7
25.0
11.6
12.2
14.6
9.7
7.5
8.9
370
320
379


(2.6)
(2.3)

(0.8)
(1.0)

(0.7)
(0.9)

(19)
(32)
Toxic Emissions (g/kW-h)
1,3 Butadiene
0.15
0.11
0.13
- 0.14
0.17
0.20
0.09
0.08
0.09
1.12
0.99
1.15


(0.07)
(0.10)

(0.03)
(0.03)

(0.02)
(0.01)

(0.05)
(0.36)
Benzene
1,06
1.12
1.28
0.61
0.66
0.84
0.65
0.58
0.70
9.26
8.11
9.47


(0.11)
(0.14)

(0.08)
(0.06)

(0.05)
(0.04)

(0.5)
(1.44)
Formaldehyde
0.19
0.20
0.22
0.22
0.23
0.26
0.14
0.13
0.15
1.51
1.15
1.24


(0.03)
(0.01)

(0.05)
(0.01)

(0.01)
(0.08)

(0.08)
(0.05)
Acetaldehyde
0.04
0.04
0.04
0.04
0.05
0.05
0.03
0.03
0.03
0.42
0.38
0.45


(0.01)
(0.00)

(0)
(0)

(0)
(0.02)

(0.07)
(0.02)
Reactivity
MIR (g CykW-h)
112
105
118
66
72
85
58
51
57
1387
1206
1473


(6)
(7)

(5)
(5)

(3)
. (2)

(100)
(130)
Sp. React.
3.71
3.60
3.61
4.03
4.14
4.10
3.91
3.95
3.90
3.61
3.61
3.74
(g CVg NMOG)

(0.26)
(0.11)

(0.12)
(0.06)

(0.11)
(0.18)

(0.14)
(0.18)
MIR Fractions
Paraffin
10%
10%
10%
6%
5%
5%
6%
4%
4%
15%
15%
15%


(2%)
(1%)

(0)
(0)

(0)
(1%)

(1%)
(1%)
Olefin
33%
31%
32%
33%
35%
34%
27%
26%
27%
29%
28%
28%


(3%)
(3%)

(1%)
(1%)

(1%)
(1%)

(2%)
(2%)
Aromatic
30%
29%
31%
26%
25%
26%
28%
24%
24%
50%
50%
51%


(5%)
(3%)

(2%)
(2%)

(2%)
(3%)

(4%)
(3%)
Acetylene
2%
2%
2%
2%
2%
2%
2%
2%
2%
1%
1%
1%

(0)
(0)

(0)
(0)

(0)
(0%)

(0%)
(0%)
Aldehyde
2%
2%
2%
3%
3%
3%
2%
3%
3%
1%
1%
1%

(0)
(0)

(0)
(0)

(0)
(1%)

(0%)
(0%)
CO
23%
26%
23%
29%
30%
30%
35%
41%
39%
4%
4%
4%


(1%)
(2%)

(1%)
(2%)

(2%)
(2%)

(0.3%)
(0.3%)
HC Family Fractions
Paraffin
42%
42%
42%
36%
32%
25%
34%
30%
30%
46%
47%
46%


(5%)
(2%)

(1%)
(0)

(1%)
(4%)

(2%)
(1%)
Olefin
21%
20%
20%
24%
25%
31%
21%
22%
23%
15%
15%
15%


(2%)
(2%)

(1%)
(1%)

(0)
(1%)

(1%)
(1%)
Aromatic
29%
28%
29%
30%
31%
31%
35%
35%
34%
34%
34%
35%


(4%)
(3%)

(3%)
(1%)

(2%)
(3%)

(2%)
(2%)
Acetylene
8%
9%
9%
10%
12%
12%
11%
13%
13%
4%
4%
4%

(1%)
(1%)

(1%)
(0)

(2%)
(1%)

(0%)
(0.6%)

-------
Table A-2. Emission rate, composition, and ozone potential comparisons of C6M and GCDC
results to the 6-Mode results for each of the seven engines examined.
Engine #
1001
1035
2615
0954
0034
2122
4468

C6M
GCDC
C6M
GCDC
C6M
GCDC
C6M
GCDC
C6M
GCDC
C6M
GCDC
C6M
GCDC
Regulated Emissions (percent different from 6-Mode test)
HC
+9.1
+6.5
+0.8
+13.8
+9.5
+15.5
-16.6
-4.9
-16.0
+9.0
-1.2
+17.9
-10
8.3
CO
+0.2
-2.7
-1.5
-3.2
+18.8
+14.4
+3.7
+4.5
+12.5
+29.8
+2.2
+8.6
-4.2
9.5
NOx
+10.1
-1.1
+6.4
-15.6
-13.9
+10.4
-7.1
-17.5
+6.6
-9.3
-10.9
-5.5
-2.3
21
O
O
-2.2
+22.8
+1.6
+20.5
-0.1
+17.8
-5.2
+6.9
+4.9
+26.6
-0.1
+16.8
1.7
15
NMOG
+5.2
+10.7
+1.0
+15.6
+19.5
+28.0
-6.1
+8.0
+4.5
+25.3
-22.3
-8.1
-13
2.4
Toxic Emissions (percent different from 6-Mode test)
1,3 Butadiene
+44.3
+53.9
+0.8
+21.3
+1.4
+18.0
-18.6
-6.4
+21.4
+46.4
-15.2
-3.2
-11
2.7
Benzene
+6.0
+12.1
+0.5
+14.6
+21.4
+25.8
+5.7
+20.7
+8.2
+37.7
-11.9
+6.0
-12
2.3
Formaldehyde
+14.6
+2.0
+2.2
+1.7
+16.1
+13.5
-2.0
+10.0
+1.7
+14.2
-9.5
0
-24
-18
Acetaldehyde
+20.6
+6.3
+1.4
+11.3
+23.7
+32.0
-5.0
0
+15.0
+25.0
0
0
-9.5
4.8
Reactivity (percent different from 6-Mode test)
MIR
+6.8
+11.0
-0.5
+9.9
+18.6
+23.3
-6.6
+4.8
+8.7
+23.9
-13.1
-2.5
-13
6.2
Sp. Reactivity
+6.1
+3.7
-0.9
-1.9
-0.8
+0.3
-3.2
-2.7
+2.5
+14.3
+1.0
-0.2
0
3.6
MIR Fractions
percent different from 6-Mode test)
Paraffin
-20.0
-5.0
-12.5
-3.7
+10.0
+7.5
-2.0
-1.0
-16.6
-35.8
-31.6
-26.8
0
0
Olefin
+14.4
+14.7
+0.6
+2.7
-5.5
0
-5.7
-3.3
+5.4
+36.9
-4.4
+3.2
-3.4
-3.4
Aromatic
-3.2
-4.3
+4.2
+6.5
+6.3
+11.1
-3.0
+3.0
-5.0
+6.5
-13.5
-13.5
0
2
Acetylene
+75.0
+70.0
+7.5
+20.0
+2.5
-3.5
-1.5
-10.0
-10.0
+20.0
-15.0
-16.0
0
0
HC Family Fractions (percent different from 6-Mode test

Paraffin
-15.6
-6.9
-4.4
-3.6
+1.2
-3.5
+0.5
-0.7
-12.2
-11.7
-12.0
-11.4
2.2
0
Olefin
+13.7
+11.4
-1.8
-2.8
-9.4
-5.7
-5.2
-5.2
+7.9
+3.3
+4.7
+7.6
0
0
Aromatic
0
-2.9
+2.5
+3.1
+2.5
+4.0
-3.1
-0.3
-0.6
+3.6
+0.5
-2.5
0
3
Acetylene
+19.8
+5.1
+8.7
+8.8
+8.9
+10.5
+18.7
+17.5
+19.0
+21.0
+16.3
+18.1
0
0
11

-------
Tabic 1. C6M duty cycle description.
COMPOSITE SIX MODE TEST CYCLE
Mode Points
1 | 2 | 3 | 4 | 5
6
Speed
Intermediate (85% of Rated Speed)
Idle
Load
Percent
100
75
50
25
10
0
Time in
Mode (sec.)
108
240
348
360
84
60
Table 2. Average or weighted torque, speed, and load for each engine/duty cycle condition.
Engine #
1001
1035
2615
2122
0034
0954
4468
6-Mode







Torque (n-m)
2.41
3.60
3.61
3.09
2.75
2.57
1.94
RPM
3047
3047
3047
2950
3056
3045
3042
Power (kW)
0.77
1.04
1.03
0.94
0.88
0.81
0.61
C6M







Torque (n-m)
2.25
3.23
3.23
3.10
2.71
2.60
1.96
RPM
2996
3013
3090
2938
3029
3051
3055
Power (kW)
0.72
1.03
1.04
0.95
0.87
0.83
0.63
GCDC







Torque (n-m)
1.85
2.62
2.65
2.53
2.20
2.13
1.59
RPM
3051
3059
3047
2977
3056
3052
3058
Power (kW)
0.59
0.82
0.84
0.78
0.70
0.67
0.50
Table 3. Test matrix with number of replicate measurements for each duty cycle.

Day 1
Day 2
Day 3
Day 4
Day 5
Regulated
6-Mode
3C6M
3 GCDC
6-Mode
6-Mode
Emissions

3 GCDC
3C6M


Speciated
Modes 1
same as
same as
Modes 3
Modes 5
HCs&
& 2 of 6-
above
above
& 4 of 6-
& 6 of 6-
aldehydes
Mode


Mode
Mode

-------
Table 4. Engine descriptions.
Engine Mfr, and
Number
Model #
Age & Time In-
Use (years)
Type
Engine
Displace-
Ment (cc)
Rated Power
@ rpm
Max. Test Torque
@ rpm
Valve Type
Briggs & Stratton
(#2615)
I2G702
1 yr.
60 hrs.
4-strokc
190
5.0 hp@3600
5.0 ft-!b@3060
Valve in
head, L-hcad
Briggs & Stratton
(#1035)
124702
4 yr.
In use 1 year
4-stroke
190
5.0 hp@3600
5.0 ft-Ib@3060
Valve in
head, L-head
Briggs & Stratton
(#1001)
92902
10 yr.
In use 2 years
4-stroke
148
3.5 hp@3600
3.5ft-lb@3060
Valve in
head, L-head
Briggs & Stratton
(#0954)
I0A902
New
(10 hours)
4-stroke
160
4.0 hp@3600
4.0 ft-ib@3060
Valvc-in-head
L-head
Honda
(#0034)
GXV140
New
(IS hours)
4-stroke
135
4.4 hp@3600
4.2 ft-lb@3060
Overhead-
valve
Kawasaki
(#2122)
FC150V
New
(10 hours)
4-stroke
153
5.5 hp@3600
4.8 ft-lb@2790
Overhead-
valve
Lawn-Boy
(#4468)
10227
New
(8 hours)
2-stroke
127
2.8 hp@3060
3.0 ft-ib@3060
Reed valves
Table 5. Fuel description.
Fuel Type
RFA


Specific Gravity
0.7469
Sulfur, wt %
0.0315
Benzene, ppmC%
2.11


Aromalics, vol. %
Olefins, vol. %
Paraffin, vol. %
MTBE, vol. %
31.8
11.5
56.7
0.1


Research Octane No.
Motor Octane No.
Octane Index
92.2
83.8
88.1


Carbon, wt %
13.3
Hydrogen, wt %
86.7


Rcid vapor pressure, psi
8.65
Distillation, C° IBP
10%
50%
90%
EP
35
51
102
165
216
13

-------
Table 6. Average emission rates, compositions, and ozone potentials fr^.n the seven engines
tested, and comparison of C6M and GCDC emissions to 6-Mode test (each percentage given is
the average of the percent differences obtained with each of the seven engines).

6Mode
C6M
GCDC

C6M
GCDC
Primary Emissions g/kW-h

Ave. of differences
HC
63
57
68

-3.5%
10.2%
CO
490
505
534

4.6%
8.7%
NOx
3,7
3.7
3.4

-1,6%
-2.5%
C02
1245
1247
1465

0.1%
18.0%
NMOG
66
59
69

-1.6%
11.7%
Toxic Emissions g/kW-h


1,3 Butadiene
0.29
0.29
0.33

3.2%
18.9%
Benzene
2.02
1.89
2.18

2.6%
17.0%
Formaldehyde
0.39
0.35
0.37

-0.1%
3.4%
Acetaldehyde
0.10
0.09
0.10

6,6%
11,7%
Reactivity


MIR (g 03/kW-h)
273
250
295

0.1%
10.9%
Specific Reactivity
(g 03/g NMOG)
4.05
4.09
4.08

0.7%
2,4%
MIR Fractions


Paraffin
7%
7%
7%

-10.4%
-9.3%
Olefin
33%
33%
34%

0,2%
7.3%
Aromatic
31%
31%
32%

-2.0%
1.6%
Acetylene
2%
2%
2%

8.4%
11,5%
Aldehyde
2%
2%
2%

7%
8%
CO
24%
25%
23%

2%
-3%
HC Family Fractions


Paraffin
35%
34%
33%

-5.8%
-5.4%
Olefin
23%
23%
24%

1.4%
1.2%
Aromatic
32%
32%
32%

0.3%
1.1%
Acetylene
9%
11%
10%

13.1%
11.6%
14

-------
Background Sample Line

Flow Controller e=C>jB|
Aldehyde Cartridge c=o=4|
Aldehyde Pampc=C5>®
Background
Engine-Dynamometer
Test Stand
CVS Line

To

HSL*
HSL*
Sample Bag
Real-Time
Analysis Bench
k Heated Sample Line (HSL)
Figure 1. Schematic of small engine gas sampling system.
7
6
5
4
3
2
1
0
V"
253
1013
506
760
Time, sec-
Figure 2. Torque-time trace for GCDC test.

-------
TECHNICAL REPORT DATA
1. REPORT NO.
EPA6Q0/A-98-048
2,
3 .R
4. TITLE AND SUBTITLE
Duty Cycle Effects on Small Engine Emissions
S.REPORT DATE
6.PERFORMING ORGANIZATION CODE
7. AUTHOR(S!
Peter Gabele
8.PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
National Exposure Research Laboratory
Human Exposure & Atmospheric Sciences Division
Source Apportionment & Characterization Branch
10.PROGRAM ELEMENT NO.
1 i, CONTRACT/GRANT NO.
APRD Internal Grant 826
12. SPONSORING AGENCY NAME AND ADDRESS
I3.TYPE OF REPORT AND PERIOD COVERED
Journal Article
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The paper presents emissions data obtained from seven lawn mower engines that were tested using three duty
cycles; a six mode steady-state test, a quasi-steady-state test, and a transient test, A comparison of emissions from
the three duty cycles is made for non-methane organic gases, carbon monoxide, nitrogen oxides, detailed
hydrocarbons (percent of total organic emissions that are paraffin, olefin, aromatic, or acetylene), and toxic
compounds (benzene, 1,3-butadiene, formaldehyde, and acetaldehyde). Differences in ozone potential are also
determined and reported for each duty cycle. The study includes both regulated and unregulated (not certified to
any emission standard) test engines that have a wide range of emission rates. Results indicate that regulated
emission rate differences due to duty cycle are fairly small (less than ten percent on the average). For over half of
the regulated emissions data, there is no significant difference in emission rates between data obtained using the
steady-state and the transient duty cycle. Emission comparisons are even better between the quasi-steady-state and
steady-state data. Ozone potential and toxic emissions are ten to twenty percent higher with the transient test cycle
and organic composition appears unaffected by duty cycle selection.
17,	KEY WORDS AND DOCUMENT ANALYSIS
». DESCRIPTORS
b.IDENTIFIERS/ OPEN ENDED
TERMS
c.COSATI



18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21.NO. OF PAGES

20. SECURITY CLASS (IMs Page)
UNCLASSIFIED
22. PRICE
I

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