EPA-420-P-98-020
Median Life, Annual Activity, and Load Factor Values
for Nonroad Engine Emissions Modeling
Report No. NR-005A
December 9, 1997
revised June 15, 1998
Christian E. Lindhjem
and
Megan Beardsley
Nonroad Engine Emissions Modeling Team
Assessment and Modeling Division
EPA, Office of Mobile Sources
Purpose
EPA's NONROAD model computes emission inventories for nonroad engines. This
report documents the default input values of median life, annual activity, and load factor for
various types of nonroad engines. These values are used to calculate the fleet age distributions
for each engine type included in this model. Annual activity and load factor values are also used
to calculate the yearly emissions for each engine type included in the model.
Introduction
This report documents the default annual activity and load factor values. These estimates
are used to determine emissions from engines by using the following equation. The discussion of
the other default values of population, power, and emission factors are the subject of other
reports.
Emissions = (Pop) (Power) (LF) (A) (EF)
where Pop = Engine Population
Power = Average Power (hp)
LF = Load Factor (fraction of available power)
A = Activity (hrs/yr)
EF = Emission Factor (g/hp-hr)
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This report also documents the default values for the median life of engines. The first
step in developing the age distribution is the determination of how long an engine is used in
years. The median life, annual activity, and load factor are all variables used in estimating the
median lifetime of nonroad engine. The median lifetime in years is determined from the median
life expressed in units of hours at full load, the annual activity expressed in units of hours per
year, and the load factor expressed in units of the fraction of available power as shown in the
equation below.
»f j- T --c v e \ Median Life (hrs)
Median Lifetime (years) = J ^ '
Activity (hrslyr) * Load Factor
The fleet of engines' age distribution and scrappage rates are estimated as functions of the
engine age expressed in the fraction of median lifetime. For instance, when engines of a given
model year are used to their median lifetime, 50% of the engines sold in that model year have
been scrapped and are not in use. In order to determine the engine population at any given in-use
year, the number of engines in every model year remaining in service needs to be calculated
based on the estimated median lifetime in years calculated with the equation above. A further
discussion of how the age distributions and scrappage rates are used to incorporate fleet turnover
is the subject of another report. (1)
For most applications, equipment is used until the engine no longer works; that is, median
engine life is considered synonymous with median equipment life. Marine vessels and other
large equipment such as mining and construction applications are exceptions to this rule, because
they typically use replacement engines when the original engine cannot be rebuilt instead of
purchasing entirely new equipment. Installing a new engine is assumed to have the same effect
on emissions as replacing the equipment, so engine life remains the relevant value for age
determination for these applications.
Values Used in NONROAD for Median Life, Annual Activity, and Load Factor
The estimates for median life, activity, and load factor used as default data files in
NONROAD are described in this work. The NONROAD model classifies engine applications
and fuel types with the use of a source categorization code (SCC). The descriptions shown in the
tables below were translated to SCC's by the fuel type and application description. For diesel
and gasoline engines, this translation is straightforward because the structure of the SCC's
differentiates engines by fuel type. For application-specific engines, the description of the
application is used to determine the appropriate SCC. The translation procedure of using
application description and fuel type to denote SCC's is also described in the report describing
default equipment populations. (2)
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Median Life in Hours at Full Load
Engine life varies with engine type and power level. The NONROAD model uses the
median life estimates that the California Air Resources Board in its OFFROAD model uses. (3)
These estimates are listed by horsepower class and engine type in Table 1. The horsepower
classes are defined in Table 2.
Liquid petroleum gas (LPG) and compressed natural gas (CNG) engines are primarily
four-stroke spark-ignition engines and hence have many similarities with four-stroke gasoline
engines. Because LPG and CNG engines are similar in design to gasoline engines, their median
life is likely to be similar to the median life of gasoline engines. For this reason and the lack of
relevant data to the contrary, LPG and CNG engines are assumed to have the same median life as
gasoline engines in the NONROAD model.
The values described represent the only comprehensive review of the engine life
associated with the engine type and power level available. They represent median values of
engine life, not distinguishing the engine by make or model. Individual engine models may have
longer or shorter median lives. Surveys of engine life by application or engine type are
encouraged to improve the estimates shown below.
Table 1 Expected Engine Life in Hours at Full Load (3)
Engine
Type
Diesel
2-stroke
Gasoline
4-stroke
Gasoline
CNG/
LPG
HP1
1250
150
200
200
HP 2
2500
200
400
400
HP 3
2500
750
750
750
HP 4
4000
—
1500
1500
HP 5
4000
—
3000
3000
HP 6
4000
—
3000
3000
HP 7
6000
—
3000
3000
HP 8
6000
—
3000
3000
HP 9
6000
—
3000
3000
HP 10
—
—
3000
3000
-------
Table 2 Horsepower Classes for Median Life (3)
HP Class
HP 1
HP2
HP3
HP4
HP5
HP6
HP7
HP8
HP9
HP 10
Diesel
<15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
751+
—
2-stroke
<2
3-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
751+
4-stroke
<5
6-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
751+
Small (<25 hp) Spark-Ignition Engine Median Life
The median life (the point where 50% of engines have been scrapped) for several
applications of nonroad engines have been estimated previously in terms of years of use. (4) For
the purpose of the NONROAD model, the median life was converted from units of years to units
of hours at full load using load factors and median hours of use which are shown in Table 5
below. To do this, we used the second equation shown above. Median life in years from Table 3
was multiplied by hours per year and load factor given in Table 5 to create the column in Table 3
and used as an input to the NONROAD model.
The final values for the median life used in NONROAD for these selected applications
are shown in Table 3. Lower or higher power level engines used the default values from ARB to
distinguish power level among these applications because these engines are expected to be
significantly different than the engines estimated previously.
Table 3: Median Life for the Bulk of Several Small Spark-Ignition Engine Applications
Application
Lawn Mowers
Use
Residential
Commercial
Power
(min.)
1
1
Power
(max.)
6
6
Median Life
(Hours at Full Load)
47.9
268
Median Life
(Years) (4)
5.8
2
-------
Trimmer/Edger/Cutter
Chainsaws
Leaf Blower\ Vacuum
Tillers
Snowblowers
Commercial Turf
Rear Engine Rider
Lawn and Garden
Tractor
Residential
Commercial
Residential
Commercial
Residential
Commercial
Residential
Commercial
Residential
Commercial
Commercial
Residential
Commercial
Residential
Commercial
0
0
0
0
0
0
0
0
0
0
3
3
6
3
6
3
3
6
6
6
6
11
11
6
6
25
16
16
25
25
19.4
157.6
28
136.4
21.5
324.3
39.4
830.7
12.3
209.4
988.9
79.3
627
114.8
920
4.3
2.3
4.3
0.9
4.3
2.3
5.8
4.4
4.4
4.4
2.9
5.8
2.9
5.8
2.9
Activity in Hours per Year
The default input values for the activity estimates come from Power Systems Research
(PSR), an independent research firm. This firm conducts several yearly surveys of equipment
owners and determines a median usage rate for engines by application and fuel type. (5) These
usage rates are shown in Table 4 for 2 and 4 stroke gasoline and diesel engines. The PSR
methodology is described and evaluated in a report by Pechan. (6)
The PSR data represents the most comprehensive review of application specific activity
available to the NONROAD team. It may be possible to determine activity regionally for a few
specific types of nonroad equipment, and the results compared with the PSR estimates used in
NONROAD. If such information becomes available, the Nonroad Engine Emissions Modeling
Team would consider using such information in future versions of the model.
No data exist regarding activity levels for LPG and CNG engines. These engines are
similar to gasoline engines because they employ spark-ignition. Therefore, LPG and CNG
engines are more likely to be used in applications where gasoline engines are used, so they are
assumed to have the same usage pattern as gasoline engines.
-------
Load Factor
PSR also estimates the load factor from surveys of equipment users. PSR calculates the
fraction of load from the estimate of hours of usage per year, the fuel consumption per year, and
the fuel consumption rate at rated power for each engine in the field. A median fraction of
available power is determined for specific applications. The load factors are also shown in Table
4. As was the case for activity levels, LPG and CNG engines are assigned the load factors for
gasoline engines.
The load factor is determined from actual and maximum fuel consumption rates for
various pieces of equipment. If alternative surveys become available, they would be considered
for future versions. For reference, the PSR methodology is explained in detail in the Pechan
report. (6)
Table 4: PSR Estimates of Activity and Load Factor for Gasoline and Diesel Engines*
3SR Application Description
jenerator Sets
Mr Compressors
3umps
til Field Equipment
Jnderground Mine Equipment
lefrigeration/AC
Tactical Military Equipment
Terminal Tractors
\Velders
7orklifts
)ther Material Handling
^ocomotive
scrubbers/Sweepers
surfacing Equipment
7orest Equipment
Vlarine Auxiliary
Shippers/Grinders
Cranes
ixcavators
scrapers
jraders
brawler Dozers
lubber Tire Dozer
lubber Tire Loader
Srush/Processins Equipment
sec
22xx006005
22xx006015
22xx006010
22xx010010
22xx009010
22xx003060
not modeled
22xx003070
22xx006025
22xx003020
22xx003050
not modeled
22xx003030
22xx002024
22xx007015
not modeled
22xx004066
22xx002045
22xx002036
22xx002018
22xx002048
22xx002069
22xx002063
22xx002060
22xx002054
Activity
Diesel
(Hrs/year)
338
815
403
1231
1533
1341
260
1257
643
1700
421
848
1220
561
1276
2608
465
806
859
914
821
936
899
761
955
Load Factor
Diesel
(% of Max. Power)
74
48
74
92
68
28
62
82
45
30
59
63
68
45
71
67
73
43
57
72
61
64
59
68
78
Activity
Gasoline
(Hrs/year)
115
484
221
1104
260
605
225
827
208
1800
386
15
516
488
35
175
488
415
378
540
504
700
900
512
241
Load Factor
Gasoline
(% of Max. Power)
68
56
69
90
80
46
68
78
51
30
53
91
71
49
70
61
78
47
53
70
64
80
75
71
85
-------
3aving Equipment
)ther Construction
Sore/Drill Rigs
skid Steer Loader
lollers
)ff-Highway Truck
3avers
Trenchers
FractorVLoaderVBackhoe
rrigation Sets
Agricultural Tractor
)ther Agricultural Equipment
Combines
swathers
Balers
3owerboats (Inboard Marine)
z%%%
Frimmer/Edger/Cutter* *
Agricultural Mowers
snowb lower**
Cement/Material Mixers
3ressure Washer
Tillers**
Jumpers/Tenders
3late Compactors
specialty Vehicle/Carts
^awn and Garden Tractor**
\erial Lifts
^awn Mowers**
xaf Blower/Vacuum* *
Commercial Turf Equipment**
)ff-Highway Tractors
sprayers
^hainsaws**
snowmobiles**
^ight Plants\Signal Boards
)ther General Industrial
22xx002021
22xx002081
22xx002033
22xx002072
22xx002015
22xx002051
22xx002003
22xx002030
22xx002066
22xx005060
22xx005015
22xx005055
22xx005020
22xx005045
22xx005025
2282010005
2282020005
22xx004025
22xx004026
22xx005030
22xx004035
22xx004036
22xx002042
22xx006030
22xx005040
22xx002078
22xx002009
22xx001060
22xx004055
22xx004056
22xx003010
22xx004010
22xx004011
22xx004030
22xx004031
22xx004071
22xx003070
22xx005035
2260004020
2260004021
2260007005
22xx001020
22xx002027
22xx003040
622
606
466
818
745
1641
821
593
1135
749
475
381
150
110
95
200
60
363
400
275
145
172
566
484
435
544
384
320
120
1068
855
90
70
50
535
878
53
62
75
55
56
57
62
75
55
65
70
51
70
55
58
35
43
43
65
56
30
78
38
43
65
57
46
55
40
55
65
58
60
40
78
51
175
371
107
310
621
450
392
402
870
716
550
124
125
95
68
100
34
175
45
84
115
43
127
166
65
104
361
76
56
733
155
80
26
121
318
713
59
48
79
58
62
80
66
66
48
60
62
55
74
52
62
38
68
48
78
59
85
71
41
55
58
62
46
70
75
60
70
65
92
81
72
54
-------
Wood Splitter
)ther Lawn Garden**
^oncrete/lnd. Saws
sailboat Auxiliary***
lailway Maintenance
\ircraft Support
lear Engine Rider**
lough Terrain Forklifts
lydro Power Unit
7ront Mowers
jas Compressors
Mi-Terrain Vehicles\Off-road
Vlotorcycles
3ersonal Water Craft****
Vlini-Bikes
jolf Carts
rampers/Rammers
shredders
brawler Tractor (Agricultural
Tractor with Crawler Tracks)
'-Wheel Tractors
Outboard Engines****
22xx004060
22xx004061
22xx004075
22xx004076
22xx002039
22820xx020
22820xx025
228500x015
22xx008005
22xx004040
22xx002057
22xx005050
22xx004055
22xx004056
22xx006020
22xx001030
2282005015
22xx001040
22xx001050
22xx002006
22xx004050
22xx004051
22xx007010
No population
not used
22xx005010
2282005010
9989090010
265
433
580
68
943
732
480
662
790
480
8500
0
0
0
1150
460
120
936
544
150
55
65
73
32
47
51
64
60
48
56
60
0
0
0
49
43
40
64
62
29
76
61
610
62
184
681
86
413
450
86
8500
135
100
55
1080
160
50
700
286
100
69
58
78
35
62
56
67
63
56
65
60
72
42
62
46
55
80
80
62
32
* Gasoline values are used for LPG and CNG engines.
** See discussion below of Small Spark-Ignition Engines for alternate use and load factors.
*** Gasoline sailboat auxiliary is included in outboard and powerboats (inboard in the SCC
nomenclature)
**** New values for gasoline recreational marine shown below
Small (<25 hp) Spark-Ignition Engines Activity and Load Factor
Regulations to be proposed for small spark-ignition engines are described in greater detail
in another report (2), and the supporting documentation for those regulations include estimates of
activity and load for a few important applications. (4) The activity and load factors and power
levels for these applications, mainly lawn and garden equipment, were derived from data
supplied during discussions regarding the proposed regulations. These alternate values are
shown in Table 5 and represent a departure from the PSR values shown above. For applications
not shown in Table 5, the PSR values were used because the PSR survey includes such categories
-------
as construction, agricultural, commercial, and many other engines applications already
considered commercial and not included in the data submitted for the rulemaking.
Many of the small spark-ignited engines are used in lawn and garden equipment
applications, and lawn and garden equipment is used both by commercial and residential users.
The commercial users are grounds keepers for nonresidential, large apartment complexes, and
some single-family homes. Commercial equipment therefore has significantly different usage in
terms of hours per year and weekday and weekend day than residential equipment. To account
for these differences in equipment usage, separate SCC's were defined to distinguish commercial
from residential lawn and garden equipment.
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Table 5: Usage and Load Factors for Several Small Spark-Ignition Engine Applications
Application
Lawn Mowers
Trimmer/Edger/Cutter
Chainsaws
Leaf Blower\ Vacuum
Tillers
Snowblowers
Commercial Turf
Rear Engine Rider
Lawn and Garden Tractor
Use
Residential
Commercial
Residential
Commercial
Residential
Commercial
Residential
Commercial
Residential
Commercial
Residential
Commercial
Commercial
Residential
Commercial
Residential
Commercial
Annual Hours
25
406
9
137
13
303
10
282
17
472
8
136
682
36
569
45
721
Load Factor
(fraction of power)
0.33
0.33
0.50
0.50
0.50
0.50
0.50
0.50
0.40
0.40
0.35
0.35
0.50
0.38
0.38
0.44
0.44
Recreational Marine Engines
As described in another report (2), recreational marine engines are divided into three
applications; inboard, outboard, and personal watercraft. The outboard category includes the
inboard\outboard sterndrive engines formerly considered as a separate application in the SCC
system because the engine types are similar. The inboard engines are most closely associated
with the PSR category 'powerboats' in Table 3. Personal watercraft were included in the PSR
category formerly reserved for Off-Road Motorcycles which are now included with All Terrain
Vehicles.
10
-------
A study of recreational boating activity indicates that boating activity may be
considerably different than PSR estimates. (5, 7) In order to determine and estimate for activity
in hours per year, it was necessary to estimate the number of engines (E), yearly fuel
consumption of the engines (FC), brake-specific fuel consumption (BSFC), average horsepower
(Hp), and a load factor (LF) by type of engine as described in the equation below.
Activity (hrs/year) =(FC) / [(E) * (Hp) * (LF) * (BSFC)]
According to the report (7), the fuel consumption and number of boats by boat type were
determined and given in Tables II-3 (page II-6) and II-8 for gasoline-fueled engines. Cabin
cruisers and other cabin boats were assumed to be inboard gasoline. Personal watercraft were
determined uniquely, and all other boats were assumed to be driven by outboard-style engines.
The total number of inboard, outboard, and personal watercraft boats were estimated to be
998,000, 9,065,000, and 200,000 respectively. Table II-9 shows the fraction of boats that have
one and two engines where 26.8% of inboard boats have two engines; 2.7% of outboard boats
have two engines; and no personal watercraft engines. So it is estimated that there were
1,265,000 inboard, 9,309,755 outboard, and 200,000 personal watercraft engines nationally in
1990-1991, the time period for the survey.
Total fuel consumption was determined from Table II-3 based on the criteria described
above to be 257,173,000 gallons for inboard, 672,009,000 gallons for outboard, and 25,063,000
for personal watercraft for the survey year.
To determine the fuel consumption of the engines, data was submitted to EPA which
indicated fuel consumption as a function of power level and is shown in Table 6. (8) The
fraction of engines by power level was determined from PSR data for the 1990 in-use year and
associated with fuel consumption estimates to determine an average fuel consumption of 0.216
for outboard, 0.100 for inboard, and 0.160 for personal watercraft in units of gallons/hp-hr.
Table 6 Fuel Consumption by Power Level
Engine Type
2-stroke
4-stroke
Power Level
0-16 hp
>16hp
0-25 hp
25-40 hp
>40hp
Fuel Consumption
(gallons/hp-hr)
0.27
0.16
0.14
0.12
0.10
11
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The average power for the three types of engines was determined from the PSR estimates
of the 1990 in-use populations. Price Waterhouse estimate average power level by boat length
and type of boat rather than a direct measure of average power level. The average power level of
outboard engines was determined to be 37 horsepower from PSR compared with roughly 66 for
the Price Waterhouse estimate. The average power level for inboard engines was estimated to be
166 from PSR compared with 179 for the Price Waterhouse. The average power level for
personal watercraft was estimated to be 52 from PSR compared with 50 for Price Waterhouse.
By using the PSR data for average power level, we are consistent with the use of PSR in
determining the population distributions for this version of NONROAD.
Other supplied comments indicates that EPA should revise the load factor to accurately
reflect the duty cycle in the certification test of 20.7% of rated power. In-use data of load factor
is not available, and the PSR estimates of load factor (32% for outboard, 38% for inboard, and
42% for personal watercraft) are not currently documented.
Using the combined information and estimates, the average activity is estimated to be 75
hours per year for inboard, 45 hours per year for outboard, and 73 hours per year for personal
watercraft engines compared with the PSR estimate of 100 hours for all types of recreational
marine gasoline engines. It is helpful to remember that this implied activity is related to the
number of hours that the engine actually operates, not necessarily how many hours the boat is in-
use on the water.
References
(1) EPA, "Growth and Scrappage Methodology Report for NONROAD," NR-008, Jan. 1998.
(2) EPA, "Nonroad Engine Population Estimates," NONROAD Documentation, NR-006,
Dec., 1997.
(3) ARE, "Documentation of Input Factors for the New Off-Road Mobile Source Emissions
Inventory Model," Energy and Environmental Analysis, Inc., February, 1997. Table 3-1.
(4) EPA, "Statement of Principles for Nonroad Phase 2 Small Spark-Ignited Engines;
Proposed Rule," 62 FR 14740, March, 27, 1997.
(5) Power Systems Research, "Reference Guide, US Parts Link Edition 6.2," St.Paul, MN.
(6) E.H. Pechan, "Evaluation of Power Systems Research (PSR) Nonroad Population Data
Base," prepared for Office of Mobile Sources, U.S. Environmental Protection Agency,
September 1997, EPA Contract No. 68-D3-0035, Work Assignment No. III-107, Pechan
Report No. 97.09.003/1807.
(7) Price Waterhouse, "National Recreational Boating Survey," Draft Final Report, Prepared
for the U.S. Fish and Wildlife Service and the U.S. Coast Guard, March 9, 1992.
(8) Ted Morgan, "Emission Data for Recreational Marine Engines," communication to Ken
ZerafaoftheEPA, September 13, 1991.
(9) Ted Morgan, communication to Rich Wilcox of the EPA, April 13, 1998.
12
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