Updated Emission Modeling for Large Sl Engines Memorandum


                                                                    EPA420-F-00-049
                   UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                                  ANN ARBOR, Ml 481 05
November 10, 2000
                                                                           OFFICE OF
                                                                        AIR AND RADIATION

MEMORANDUM
SUBJECT:   Updated Emission Modeling for Large SI Engines

FROM:      Alan Stout, Mechanical Engineer
             Assessment and Modeling Division

THRU:      Glenn Passavant, Senior Program Manager
             Assessment and Modeling Division

TO:          Docket A-98-01
       The Environmental Protection Agency (EPA) has developed the NONROAD Emissions
Model to compute nationwide emission levels for a wide variety of nonroad engines. The purpose
of this memorandum is to describe the inputs to the NONROAD model and present estimated
emission contributions from nonroad spark-ignition engines rated above 19 kW (25 hp).  These
engines are referred to in this document as Large SI engines.  These modeling results support the
Agency's final finding that these engines contribute to air pollution in the United States.

       The NONROAD model incorporates information on emission rates, operating data, and
engine population to determine annual emission levels of various pollutants.  Operating data and
population are determined separately for dozens of different applications. The model uses the
following equation to calculate total emissions for each group of engines; individual parameters are
described further below:

Emissions = EF x DF x p x LF x TF x Hours x Units

Where,
EF = emission factor in g/hp-hr
DF = deterioration factor (dimensionless)
P = rated engine power in horsepower
LF = load factor (dimensionless)
TF = transient adjustment factor (dimensionless)
Hours = operating hours per year for each unit
Units = population of engines operating in a given year

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Emission and Deterioration Factors
Engine emissions are measured on an engine dynamometer, with results reported as a mass
of emissions per unit of work (g/kW-hr or g/hp-hr). Southwest Research Institute recently compiled
a listing of test data from past and current testing projects.1 These tests were all conducted on new
or nearly new engines. Table 1 summarizes this test data. All engines were operated on the steady-
state ISO C2 duty cycle, except for two engines that were tested on the steady-state D2 cycle. The
results from the different duty cycles were comparable. Lacking adequate test data for engines
fueled by natural gas, we model those engines to have the same emission levels as those fueled by
liquefied petroleum gas (LPG), based on the similarity between engines using the two fuels (in the
case of hydrocarbon emissions, this is based on nonmethane measurements). The listed emission
levels for gasoline engines represent a composite of emissions from air-cooled and water-cooled
engines.

Table 1
New-Engine Emission Factors for Large SI Engines (g/hp-hr)
Fuel
LPG
Gasoline
NOx
11.99
7.13
THC
1.68
6.22
CO
28.23
203.4
PM
0.06
0.06
Emission levels often change as an engine ages. In most cases, emission levels increase with
time, especially for engines equipped with technologies for controlling emissions. We developed
deterioration factors for uncontrolled Large SI engines based on measurements with comparable
highway engines.2 Table 2 shows the deterioration factors that apply at the median lifetime
estimated for each type of equipment. For example, a deterioration factor of 1.26 for hydrocarbons
multiplied by the emission factor of 6.22 g/hp-hr for new gasoline engines indicates that modeled
emission levels increase to 7.84 g/hp-hr when the engine reaches its median lifetime. The
deterioration factors are linear multipliers, so the modeled deterioration at different points can be
calculated by simple interpolation.

Table 2
Deterioration Factors
Pollutant
THC
CO
NOx
Median Life
Deterioration Factor
1.26
1.35
1.03
Operating Parameters

The NONROAD model relies on the OE Link database from Power Systems Research to

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provide market information for individual engine models, each with an established power rating."
Engines typically operate at a variety of speeds and loads, such that operation at rated power is rare.
To take into account the effect of operation at idle and partial load conditions, a load factor indicates
the degree to which average engine operation is scaled back from full load. For example, at a 0.3
(or 30 percent) load factor, an engine rated at 100 hp would be producing an average of 30 hp over
the course of normal operation. For highly mobile equipment, this can vary widely (and quickly)
between 0 and 100 percent of full power. Table 3 shows the load factors that apply to the various
applications of nonroad equipment.

Emissions during transient operation can be significantly higher than during steady-state
operation. Based on emission measurements from highway engines comparable to uncontrolled
Large SI engines, we have measured transient emission levels that are 30 percent higher for HC and
45 percent higher for CO relative to steady-state measurements.3 The NONROAD model therefore
multiplies steady-state emission factors by 1.3 for HC and 1.45 for CO to estimate emission levels
during normal, transient operation. Test data do not support adjusting NOx emission levels for
transient operation. Also, the model applies no transient adjustment factor for generators, pumps, or
compressors, since engines in these applications are less likely to experience transient operation.

Power Systems Research also specifies a value for annual operating hours that apply to
various applications, as shown in Table 3. These figures represent an average annual usage that
applies over the course of an engine's lifetime.

Population

The NONROAD model generally uses population data based on information from Power
Systems Research, which is based on historical sales information adjusted according to survival and
scrappage rates. We are, however, using different population estimates for forklifts based on a
recent market study.4 That study identified a 1996 population of 491,321 for Class 4 through 6
forklifts, which includes all forklifts powered by internal combustion engines. Approximately 80
percent of those were estimated to be fueled by propane, with the rest running on either gasoline or
diesel fuel. Assuming an even split between gasoline and diesel for these remaining forklifts leads
to a total population of spark-ignition forklifts of 442,000. The NONROAD model therefore uses
this estimate for the forklift population, which is significantly higher than that estimated by Power
Systems Research. Table 3 shows the estimated population figures used in the NONROAD model
for each application, adjusted for the year 2000.

The split between LPG and gasoline in various applications warrants further attention.
Engines are typically sold without fuel systems, which makes it difficult to assess the distribution of
engines sales by fuel type. Also, engines are often retrofitted for a different fuel after a period of
operation, making it still more difficult to estimate the prevalence of the different fuels. The high
percentage of propane systems for forklifts, compared with about 60 percent estimated by Power
aPower Systems Research is a firm that provides marketing data on engines and
equipment. The OE Link database is a compilation of historical annual sales for individual
engine models sold in the U.S. The database is available from Power Systems Research (612-
454-0144).

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Systems Research, can be largely attributed to expenses related to maintaining fuel supplies. LPG
cylinders can be readily exchanged with minimal infrastructure cost as compared to gasoline
storage. Natural gas systems typically offer the advantage of pipeline service, but the cost of
installing high-pressure refueling equipment is an obstacle to increased use of natural gas systems.

Some applications of nonroad SI equipment face much different refueling situations. Lawn
and garden equipment is usually not centrally fueled and therefore operates almost exclusively on
gasoline, which is more readily available. Agriculture equipment is predominantly powered by
diesel engines. Most of these operators likely have storage tanks for diesel fuel. For those who use
spark-ignition engines in addition to, or instead of, the diesel models, we would expect them in
many cases to be ready to invest in gasoline storage tanks as well, resulting in little or no use of
LPG or natural gas for those applications. For construction, general industrial, and other equipment,
there may be a mix of central and noncentral fueling, and motive and portable equipment. We
therefore believe that estimating an even mix of LPG and gasoline for these engines is most
appropriate. The estimated distribution of fuel types for the individual applications used in the
NONROAD model are listed in Table 3.

An additional issue related to population figures is the level of growth factored into emission
estimates for the future. The NONROAD model incorporates application-specific growth figures
based on projections from Power Systems Research. The projected growth is reflected in the
population estimates included in Table 3. The model also projects growth rates separately for the
different fuels for each application.
MODELING RESULTS

Total mobile-source emission estimates for the years 2000 and 2007 are summarized in
Tables 4 and 5. These tables show relative contributions of the different mobile source categories to
the overall mobile source emissions inventory. The emission figures are projected to change
somewhat between 2000 and 2007. Population growth and the effects of other regulatory control
programs are factored into the later emissions estimates. Of the total mobile-source emissions in
2007, Large SI engines are estimated to contribute about 3 percent of HC, NOx, and CO emissions,
and about 0.3 percent of PM emissions. The appendix shows how the different Large SI
applications contribute to the total emissions for the category.

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                                      Table 3
Operating Parameters and Population Estimates for Various Applications of Large SI Engines
Application
Forklift
Generator
Welder
Commercial turf
Pump
Air compressor
Baler
Irrigation set
Aerial lift
Scrubber/sweeper
Chipper/grinder
Leaf blower/vacuum
Oil field equipment
Trencher
Specialty vehicle/cart
Skid/steer loader
Rubber-tired loader
Gas compressor
Paving equipment
Terminal tractor
Bore/drill rig
Ag. tractor
Concrete/industrial saw
Roller
Crane
Other material handling
Paver
Other agriculture equipment
Other construction
Avg.
Rated HP
69
59
67
28
45
65
44
97
52
49
66
79
44
54
66
47
71
110
39
93
78
82
46
55
75
67
48
162
126
Load
Factor
0.30
0.68
0.58
0.60
0.69
0.56
0.62
0.60
0.46
0.71
0.78
0.94
0.90
0.66
0.58
0.58
0.71
0.60
0.59
0.78
0.79
0.62
0.78
0.62
0.47
0.53
0.66
0.55
0.48
Hours
per Year
1800
115
408
682
221
484
68
716
361
516
488
282
1104
402
65
310
512
6000
175
827
107
550
610
621
415
386
392
124
371
2000
Population
504,696
146,246
19,246
55,433
35,981
17,472
18,659
5,367
38,901
13,363
13,015
11,797
7,855
3,627
9,145
7,436
3,177
788
1,109
2,716
2,607
1,599
2,266
1,362
1,240
1,605
1,367
5,501
1,276
2007
Population
603,099
217,525
27,008
64,265
50,340
24,404
20,977
3,917
38,565
13,252
15,102
13,621
7,845
3,950
9,635
8,099
3,460
1,005
1,207
2,687
2,839
1,798
2,468
1,483
1,351
1,591
1,488
6,102
1,390
Percent
LPG/CNG
95
100
50
0
50
50
0
50
50
50
50
0
100
50
50
50
50
100
50
50
50
0
50
50
50
50
50
0
50

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Application
Pressure washer
Aircraft support
Crushing/processing equip
Surfacing equipment
Tractor/loader/backhoe
Hydraulic power unit
Other lawn & garden
Refrigeration/AC
Total Population
Avg.
Rated HP
39
99
63
40
58
50
61
55

Load
Factor
0.85
0.56
0.85
0.49
0.48
0.56
0.58
0.46

Hours
per Year
115
681
241
488
870
450
61
605

2000
Population
1,227
910
235
314
360
330
402
169
915,678
2007
Population
1,722
1,131
256
342
392
351
466
201
1,127,323
Percent
LPG/CNG
50
50
50
50
50
50
0
100

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                     Table 4
        Modeled Annual Emission Levels for
Mobile Source Categories in 2000 (thousand short tons)
Category
Large SI
Recreational SI
NonroadSK19kW
Marine SI
Nonroad CI
Marine CI
Locomotive
Aircraft
Total Nonroad
Total Highway
Total Mobile Source
NOx
tons
306
21.3
106
32
2,625
1,001
1,192
178
5,461
7,988
13,449
percent
2%
0.16%
0.8%
0.2%
20%
7%
9%
1%
41%
59%
100%
HC
tons
125
587
1,460
928
316
31
47
183
3,677
3,772
7,449
percent
2%
8%
20%
12%
4%
0%
1%
2%
49%
51%
100%
CO
tons
2,294
4,231
18,359
2,144
1,217
133
119
1,017
29,514
49,701
79,215
percent
3%
5%
23%
3%
2%
0.2%
0.2%
1%
37%
63%
100%
PM
tons
1.6
5.6
50
38
253
42
30
39
459
240
699
percent
0.2%
0.8%
7%
5%
36%
6%
4%
6%
66%
34%
100%
                     Table 5
        Modeled Annual Emission Levels for
Mobile Source Categories in 2007 (thousand short tons)
Category
Large SI
Recreational SI
Nonroad SKI 9 kW
Marine SI
Nonroad CI
Marine CI
Locomotive
Aircraft
Total Nonroad
Total Highway
Total Mobile Source
NOx
tons
369
22.4
96
42
2,253
1,018
773
200
4,773
5,529
10,302
percent
4%
0.22%
0.9%
0.4%
22%
10%
8%
2%
46%
54%
100%
HC
tons
141
616
933
733
214
33
43
205
2,918
2,317
5,235
percent
3%
12%
18%
14%
4%
1%
1%
4%
56%
44%
100%
CO
tons
2,517
4,445
21,406
2,056
1,128
142
119
1,200
33,013
44,276
77,289
percent
3%
6%
28%
3%
1%
0.2%
0.2%
2%
43%
57%
100%
PM
tons
1.9
5.9
58
33
226
44
27
41
437
186
623
percent
0.3%
0.9%
9%
5%
36%
7%
4%
7%
70%
30%
100%

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REFERENCES

1. "Three-Way Catalyst Technology for Off-Road Equipment Powered by Gasoline and LPG
Engines—Interim Report Volume 2: Cost-Effectiveness Analysis" Jeff J. White, et al, May 1998,
p.  15 (Docket A-98-01, document U-D-4).

2 . "Revisions to the June 2000 Release of NONROAD to Reflect New Information and Analysis
on Marine and Industrial Engines," EPA memorandum from Mike Samulski to Docket  A-98-01
(Document IV-B-1).

3 . "Regulatory Analysis and Environmental Impact of Final emission Regulations for 1984 and
Later Model Year Heavy Duty Engines," U.S. EPA, December 1979, p.  189 (Docket A-98-01,
document IV-B-2).

4 . "The Role of Propane in the Fork Lift/Industrial Truck Market: A Study of its Status, Threats,
and Opportunities," Robert E. Myers for the National Propane Gas Association, December 1996
(Docket A-98-01, document U-D-2).

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             APPENDIX
Emission Modeling Outputs by Application

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                        2000 Emission Levels by Application
                                       2007 Emission Levels by Application
APPLICATION

FORKLIFTS
GENERATORS
GAS COMPRESSORS
COMMERCIAL TURF
OIL FIELD EQUIP.
WELDERS
AERIAL LIFTS
CHIPPER/GRINDER
AIR COMPRESSORS
PUMPS
SCRUB/SWEEPER
IRRIGATION SETS
LEAFBLOWER/VACUUM
TERMINAL TRACTORS
RUBBER-TIRED LOADER
OTH LAWN&GARDEN
SKID/STEER LOADER
TRENCHERS
CONCRETE/IND. SAWS
OTH AG.EQUIP.
SWATHERS
AIRPORT GSE
AG. TRACTOR
HYD POWER UNIT
ROLLERS
OTHER CONSTR.
BALERS
SPECIALTY VEH/CARTS
OTH MAT'L HANDLING
CRANES
BORE/DRILL RIGS
PAVERS
TRACT/LDR/BACKHOE
PRESSURE WASHERS
PAVING EQUIP.
HYDR. POWER UNITS
REFRIGERATION/AC
CRUSH/PROC EQUIP.
SURFACING EQUIP.
RAILWAY MAINT.
FRONT MOWERS
OTHER LAWN&GARDEN
PLATE COMPACTORS
COMBINES

TOTALS
NOx
247,543
9,020
5,979
4,986
4,659
3,912
3,632
3,512
3,329
2,683
2,627
2,498
2,166
1,768
883
818
669
558
531
497
452
376
359
356
308
307
276
241
225
196
184
182
93
50
48
45
35
32
32
11
9
7
3
o
6
HC*
56,558
1,402
1,000
6,348
961
2,227
2,045
2,111
1,928
1,473
1,472
1,308
2,742
1,014
523
460
421
331
314
603
573
214
456
211
182
182
350
228
150
116
109
108
55
29
29
27
7
19
19
7
12
9
4
4
CO
1,242,159
24,476
17,877
241,464
18,846
74,983
68,709
71,922
65,182
36,621
49,412
43,082
104,089
34,212
17,791
15,437
14,487
11,243
10,667
22,809
21,745
7,198
17,328
7,163
6,203
6,203
13,307
5,164
5,212
3,943
3,706
3,669
1,884
980
969
926
138
652
648
232
457
336
165
136
PM
1,178
42
30
47
22
25
23
23
21
27
16
15
20
11
6
5
4
4
o
J
5
4
2
3
2
2
2
3
4
2
1.3
1.2
1.2
0.6
0.3
0.3
0.3
0.2
0.2
0.2
0.1
0.1
0.1
0.03
0.03
NOx
297,973
13,199
7,632
5,781
4,653
5,633
3,842
4,077
4,741
3,827
2,784
1,623
2,501
1,859
978
866
737
618
587
546
506
482
404
393
341
339
310
254
226
217
204
202
103
72
53
47
41
36
35
13
11
8
3
o
3
HC*
64,892
2,018
1,277
7,367
960
2,940
1,689
2,450
2,531
1,912
1,222
1,228
3,173
836
549
381
439
347
329
670
638
246
513
221
191
191
391
239
118
121
114
113
58
38
30
30
8
20
20
8
14
10
4
4
CO
1,357,677
35,025
22,820
280,270
18,827
96,845
53,038
83,456
83,883
46,876
38,288
43,716
120,514
26,386
18,417
11,954
14,944
11,630
11,044
25,338
24,178
8,042
19,495
7,408
6,421
6,407
14,807
5,407
3,908
4,074
3,825
3,795
1,950
1,253
1,001
1,024
163
674
671
254
523
385
167
152
PM
1,408
60
38
55
22
34
22
26
29
36
16
12
24
11
6
5
5
4
4
5
5
3
4
2
2
2
3
4
1.4
1.4
1.3
1.3
0.6
0.4
0.3
0.3
0.2
0.2
0.2
0.1
0.1
0.1
0.03
0.03
306,100
88,343
2,293,833
1,557
368,760
100,549
2,516,932
1,854
*The hydrocarbon figures include exhaust emissions, but exclude evaporative emissions.
                                              A-l

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