Exhaust Emission Factors
for Nonroad Engine Modeling—
Compression-Ignition
Report No. NR-009A
February 13, 1998
revised June 15, 1998
Megan Beardsley and Chris Lindhjem
U.S. EPA Office of Mobile Sources, Assessment and Modeling Division
Purpose
This report describes and documents exhaust emission factors used for compression
ignition (CI) engines in the U.S. Environmental Protection Agency's (EPA) NONROAD
emission inventory model. It covers factors for all diesel-fueled engines. Emission factors for
spark ignition engines (including gasoline and natural gas/propane) are covered in a separate
report, NR-010. Other EPA reports will describe additional issues relating to emission factors
including adjustments to emission rates due to variations in fuel and temperature (NR-001) and
adjustments to emission rates as equipment deteriorates with time and use (NR-011).
Introduction
The NONROAD model estimates air pollution from more than 80 types of compression
ignition (CI) and spark ignition (SI) nonroad sources including such items as lawnmowers,
motorboats, portable generators and construction equipment. By bringing together information
on equipment populations, equipment use, and emission factors, the NONROAD model
estimates mass emissions of hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOX),
sulfur dioxide (SO2), particulate matter (PM) and carbon dioxide (CO2) for specific states and
counties for past and future years, providing a flexible tool that can be applied to a wide variety
of air quality modeling and planning functions.
The NONROAD calculations rely on emission factors—estimates of the amount of
pollution emitted by a particular type of equipment during a unit of use. Typically emission
factors for nonroad sources are reported in grams per horsepower-hour, but they also may be
reported in grams per mile, grams per hour, and grams per gallon. The emission factors in the
NONROAD model are based on emissions test data, adjusted when necessary to account for the
effects of fuel sulfur and in-use operation that differ from the typical test conditions. Emission
1
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factors are stored in NONROAD's data input files. Emission changes with the age of the engine,
often called 'deterioration,'are described in Report No. NR-011.
Currently EPA is preparing a version of the NONROAD model. A final version of
NONROAD is planned for release late in 1998. EPA expects to use the CI emission factors
described here in both the and the final version of the model. If comments on this document or
other information gathered during stakeholder and peer review cause us to rethink this approach,
we will document the changes in a subsequent report.
Background
There is little test data available on nonroad engines. In developing the emission factors
for NONROAD we have considered data from various sources.
Previous Inventories
Prior to the NONROAD model, there have been three major efforts to estimate nonroad
emission inventories from CI engines. These are:
• EPA's Nonroad Engine and Vehicle Emission Study ("NEVES"). [1] Published in
November, 1991, this study was mandated by Congress to determine whether nonroad
sources made a significant contribution to urban air pollution. It covers HC, CO, NOX,
PM, SOX and other pollutants. It provides inventories for 19 ozone and 16 CO
nonattainment areas.
• California Air Resources Board's (ARE) nonroad model ("OFF-ROAD") [2], designed to
estimate nonroad emissions for the state of California only. A version of this model was
released in late summer 1997. It covers HC, CO, NOX, PM, SO2, and CO2.
• EPA's "Nonroad Engine Model"-- Designed as an internal tool for analyzing various
control scenarios, EPA has used this model primarily to estimate the effect of recently
proposed regulations on emissions from compression-ignition (CI) engines over 37 kW
(50 hp).[3] The model computes national-level inventories of nonroad diesel HC, NOX,
CO and PM.
All of these models/studies estimate emissions from uncontrolled engines. The
California model also includes California emission standards, and the EPA's Nonroad Engine
Model includes proposed Federal emission standards. The sources of the emission factors used
in these inventories are described in Appendix A. Many of the emission factors are based on
data from the 1970s and early 1980s.
New Data
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In addition to the data considered in developing previous emission factors, there is a
limited amount of new emission test data on newer (post-1988) uncontrolled engines. The post-
1988 engines were not designed to meet any new emission regulations, but the test data indicates
that emissions from these post-1988 engines (especially hydrocarbons and particulate matter) are
lower than the emission factors used in earlier inventories. EPA's review of this data is
described in Appendix B.
Emission Standards
In addition to estimating emissions from uncontrolled engines, the NONROAD model is
designed to account for the effect of federal emissions standards. NONROAD will not cover
California emission standards or proposed federal standards that are not yet final. However,
because EPA expects to finalize a set of recently proposed standards for nonroad diesel engines
before the release of the final NONROAD model, these proposed standards have been included
in the version of the model. Thus, this document describes emission factors under two
regulations that establish three tiers of emission standards:
• "Determination of Significance for Nonroad Sources and Emission Standards for New
Nonroad Compression Ignition Engines at or above 37 Kilowatts." This rule establishes
"Tier 1" standards for CI engines at or above 50 hp (37 kW). [4]
• "Control of Emissions from Nonroad Diesel Engines." This proposed rule lists "Tier 1"
and "Tier 2" standards for CI engines below 50 hp, and "Tier 2" and "Tier 3 " standards
for engines of 50 hp and greater. [5] " "
Of course, if changes are made to the proposed rule, the final version of the model will
reflect those changes. The standards are phased in over a number of years, and NONROAD's
emission factors will follow the final schedule implementing the new standards.
The NONROAD emission factors for engines subject to the existing and proposed rules
are based on the factors used in the regulatory support documents for the proposed rule, "Draft
Regulatory Impact Analysis: Control of Emissions from Nonroad Diesel Engines." However, as
explained below, the NONROAD model's emission factors for pre-control engines differ from
the RIA in their use of EPA's new data on cleaner post-88 engines.
Steady State Emission Factors-HC. CO. NOx and PM
Nonroad engines are primarily tested with steady-state tests. However, the steady-state
operation typically used for emission testing is not always representative of the operation of
engines in many nonroad applications. Some of the differences can be due to load or engine
speed, and other differences can be due to transient demands. We will apply "in-use adjustment
factors" to the emission factors derived from steady state tests. The derivation and application of
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these factors are described in Appendix C. EPA will create input files for NONROAD by
applying in-use adjustment factors to the steady-state emission factors described in this section.
The remainder of this section describes steady-state fuel consumption and emission
factors for HC, CO, NOX and PM. These factors are listed in Table 1. We have used engine
model year and horsepower as categories to group NONROAD emission factors. These
groupings are consistent with emission standards for CI engines and with emissions test data.
Data on pre-controlled engines (see Appendix B) indicates that engines of more than 100 hp have
significantly different emission characteristics than engines under 100 hp. Perhaps for future
versions of NONROAD, emission factors may be distinguished by technologies such as turbo-
charging, fuel metering pumps, and cylinder size; however, there is not enough emissions data at
present to support such distinctions in NONROAD emission factors.
Fuel sulfur levels affect PM emissions. NONROAD users can adjust for local fuel sulfur
levels, but the model has a default diesel fuel sulfur level of 0.33 mass percent, the national
average for nonroad diesel [6], and the emission factors in NONROAD's input files are intended
to be consistent with the default fuel sulfur level. Where emission tests were known to have been
performed with fuels with other sulfur contents the test results have been adjusted as described in
Appendix B.
Due to lack of data, the brake-specific fuel consumption (BSFC) for the 1988-and-later
uncontrolled engines is used for all engines, both earlier uncontrolled engines and later engines
subject to emissions standards. While it is likely that fuel consumption varies between these
categories, there is not sufficient data available at this time for EPA to specify alternate values.
Pre-1988. Engines < =50 hp:
There are no known tests of pre-1988 CI engines of less than 50 hp. Thus NONROAD
will use the same emission factors as for the 1988 through Tier 1 years for engines of this size
described below.
Pre-1988. Engines > 50 hp:
For pre-1988 CI engines of 50 hp or greater, NONROAD's steady-state emission factors
are based on the emission factors used in NEVES. These vary by application. However, NEVES
includes an adjustment for in-use operation. Since NONROAD uses a different in-use
adjustment factor than NEVES (see Appendix C), the NEVES adjustment is removed to
determine pre-1988 average steady-state emissions.
Because the testing fuel is generally unknown, we assume that the NEVES PM factors are
appropriate for the default fuel sulfur content of 0.33 wt.% sulfur used in NONROAD.
A conversion from gram per gallon to gram per horsepower-hr was made to NEVES
emission rates for the greater than 50 horsepower engines for the diesel recreational marine
categories; inboard, outboard, and sailboat auxiliary. Outboard and sailboat auxiliary engines
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above 50 hp were converted from the NEVES gram per gallon to gram per horsepower using the
higher fuel consumption of 0.408 Ibs/hp-hr and 7.1 Ibs/gallon fuel density because these engines
are primarily less than 100 hp. The NEVES emission rate for inboard engines was converted
using the lower fuel consumption rate of 0.367 Ibs/hp-hr because these engines are primarily
above 100 horsepower.
1988 to Tier 1. Engines <= 50 hp:
For 1988-and-later pre-control engines less than or equal to 50 hp, we will use the
emission factors described in the documentation for ARB's OFF-ROAD model. [2] We have
combined the direct injection and indirect injection factors using the technology fractions listed
in the EPA's Regulatory Impact Analysis (RIA) for the proposed new emission standards. [5]
Again, because the sulfur content of fuels used in generating these emission factors is unknown,
we have assumed that the PM emission factors are appropriate for default fuel sulfur of 0.33%
sulfur.
1988 to Tier 1. Engines > 50 hp:
Recent studies have indicated that, in general, emission rates from 1988-and-later pre-
control engines of greater than 50 hp are lower than the rates used in NEVES, necessitating a
revision to the NEVES emission factors.
For these engines we will use emission factors calculated from recent studies. These
studies are described in detail in Appendix B. As explained in Appendix B, a correction for fuel
sulfur content is applied.
Tier 1. Engines < =25 hp
The NONROAD model's emission factors for Tier 1 <25 hp are based on data from
ARB, which already regulates engines <25 hp. EPA expects engines meeting federal Tier 1
standards to employ similar technology and emit at similar levels. As described in the RIA, EPA
weighted the California data using the national fractions of direct and indirect injection engines
for this size category. [5]
HC and NOX — California certification data was used to split the combined HC+NOX
standard into single pollutant emission factors.
CO - California certification data was used.
PM — Emission factors for PM are estimated to be the Tier 1 standard for PM. We
assume that engines will meet the standard on default sulfur fuel.
Tier 1. Engines 25-50 hp
Data is not available on engines meeting this proposed standard. As in the RIA, emission
factors were estimated based on California data on smaller engines, but weighted to reflect the
estimated national fractions of direct and indirect injection engines for this size category . [5]
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HC and NOX — California certification data for engines 11-25 hp was used to split the
combined HC-NOX standard into single pollutant emission factors.
CO — California certification data for engines 11-25 hp was used.
PM — Emission factors for PM are estimated to be the Tier 1 standard for PM. We
assume that engines will meet the standard on default sulfur fuel.
Tier 1. Engines 50-175 hp
EPA has limited Tier 1 certification data on Tier 1 engines 50-175 hp.
NOx—EPA estimates that Tier 1 NOX emissions are at the Tier 1 standard.
HC and CO—Emission factors are estimated using EPA's Tier 1 certification data.
PM—Because no emission standard was promulgated for Tier 1, PM emissions for pre-
control, 1988-and-later engines were used.
Tier 1. Engines >175 hp
EPA has limited Tier 1 certification data on Tier 1 engines > 175 hp.
NOx—EPA estimates that Tier 1 NOX emissions are at the Tier 1 standard.
HC and CO—Emission factors are estimated using EPA's Tier 1 certification data.
PM—Because pre-Tier 1 PM emissions were below the Tier 1 standard (when the
standard was adjusted for fuel sulfur), we have assumed that Tier 1 PM emissions are at
the same PM levels as pre-control, 1988-and-later engines.
Tier 2. Engines < =50 hp
Data is not available on engines meeting this proposed standard. Emission factors were
estimated as in the RIA based on ARB data.
HC and NOx—As in the RIA, EPA assumes minimum HC emissions of 0.6 g/hp-hr (0.8
g/kW-hr) based on ARB data on indirect injection (IDI) engines under 25 hp (19 kW).
EPA used this value to split the combined HC+NOx standard into single pollutant
emission factors.
CO—The same as under Tier 1.
PM-Because of uncertainties in PM emissions, NONROAD does not estimate a reduced
PM emission rate from the Tier 1 level at this time. EPA will continue to evaluate this
emission rate based on available data.
Tier 2. Engines > 50 hp
Data is not available on engines meeting this proposed standard.
NOx and HC—As in the RIA, NONROAD uses the proposed European NOx standard to
split the Tier 2 combined HC+NOx standard into single pollutant emission factors.
CO— The same as under Tier 1.
PM-Because of uncertainties in PM emissions, NONROAD does not estimate a reduced
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PM emission rate from the Tier 1 level at this time. EPA will continue to evaluate this
emission rate estimate based on available data.
Tier3
The proposed Tier 3 standard applies only to engines greater than 50 hp and less than or
equal to 750 hp. Data is not available on engines meeting this proposed standard.
NOx and HC-For Tier 3 HC and NOX, NONROAD follows the RIA in using
engineering judgement to assume minimum HC emissions of 0.2 g/hp-hr. This rate is
then subtracted from the combined HC+NOx standard to split the standard into single-
pollutant emission factors.
CO-We estimate at this time that CO will be the same as Tier 1.
PM-EPA has not yet established the Tier 3 PM standards. Therefore, we are estimating
the same credit as Tier 2.
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Table 1—Steady-State Emission Factors* for CI Engines in the NONROAD Model
Engine
Power (hp)
>0to 11
>llto 16
>16 to 25
>25 to 50
>50 to 100
>100 to 175
Model
Year
pre-88
88-99
00-04
05-
pre-88
88-99
00-04
05-
pre-88
88-99
00-04
05-
pre-88
88-98
99-03
04-
pre-88
88-97
98-03
04-07
08-
pre-88
88-96
97-02
03-06
07-
Regulation
-
~
Tierl
Tier 2
-
~
Tierl
Tier 2
-
~
Tierl
Tier 2
-
~
Tierl
Tier 2
~
~
Tierl
Tier 2
Tier3
~
~
Tierl
Tier 2
Tier3
BSFC
(Ib/hp-hr)
0.408**
0.408**
0.408**
0.408**
0.408
0.367
Emission Factors (g/hp-hr)
HC
1.5
1.5
1.6
0.6
1.5
1.5
0.7
0.6
1.8
1.8
0.7
0.6
1.8
1.8
0.8
0.6
CO
5.0
5.0
5.6
5.6
5.0
5.0
2.0
2.0
5.0
5.0
2.0
2.0
5.0
5.0
2.5
2.5
NOX
10.0
10.0
5.9
5.0
10.0
10.0
5.2
5.0
6.9
6.9
5.2
5.0
6.9
6.9
5.5
5.0
PM
1.0
1.0
0.75
0.75
1.0
1.0
0.6
0.6
0.8
0.8
0.6
0.6
0.8
0.8
0.6
0.6
Vary by application, see NEVES
0.99
0.7
0.4
0.2
3.49
1.0
1.0
1.0
8.30
6.9
5.2
o o
J.J
0.72
0.72
0.72
Same as Tier 2
Vary by application, see NEVES
0.68
0.4
0.4
0.2
2.70
1.0
1.0
1.0
8.38
6.9
4.5
2.8
0.40
0.40
0.40
Same as Tier 2
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Table 1, continued.
Engine
Power (hp)
>175 to 300
>300 to 600
>600 to 750
>750
Model
Year
pre-88
88-95
96-02
03-05
06-
pre-88
88-95
96-00
01-05
06-
pre-88
88-95
96-01
02-05
06-
pre-88
88-99
00-05
06-
Regulation
Tierl
Tier 2
Tier3
~
~
Tierl
Tier 2
TierS
~
~
Tierl
Tier 2
TierS
~
~
Tierl
Tier 2
BSFC
(Ib/hp-hr)
0.367
0.367
0.367
Emission Factors (g/hp-hr)
HC
CO
NOX
PM
Vary by application, see NEVES
0.68
0.4
0.4
0.2
2.70
1.0
1.0
1.0
8.38
6.9
4.5
2.8
0.40
0.40
0.40
Same as Tier 2
Vary by application, see NEVES
0.68
0.3
0.3
0.2
2.70
1.0
1.0
1.0
8.38
6.9
4.5
2.8
0.40
0.40
0.40
Same as Tier 2
Vary by application, see NEVES
0.68
0.3
0.3
0.2
2.70
1.0
1.0
1.0
8.38
6.9
4.5
2.8
0.40
0.40
0.40
Same as Tier 2
Vary by application, see NEVES
0.68
0.3
0.3
2.70
1.0
1.0
8.38
6.9
4.5
0.40
0.40
0.40
*Prior to listing in NONROAD input files, these ISO-C1 emission factors are adjusted for in-use
operation as explained in Appendix C.
**BSFC for engines <50 hp is assumed to be the same as 50-100 hp engines
Emission Factors—CO2 and SO2
Emission factors for CO2 and SO2 are rarely measured, instead they typically are
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calculated based on brake-specific fuel consumption (BSFC).
The NONROAD model uses in-use adjusted BSFC to compute CO2 emissions directly.
BSFC and engine activity provides the means to estimate the tons of fuel consumed. We
assumed that all of the carbon in the fuel is converted to CO2. The average carbon fraction of
the fuel is estimated to be 87%. This does not require a CO2 emission factors input file.
The model does not require an SO2 emission factors input file either. EPA will calculate
SO2 emission factor as shown in the equation below.
SO2 = (BSFC * 453.6* (1 - 0.022) - HC) * 0.0033 * 2
where
SO2 is in g/hp-hr
BSFC is the in-use adjusted fuel consumption in Ib/hp-hr
453.6 is the conversion factor from pounds to grams
1-0.022 is an adjustment for sulfur converted to direct PM
HC is the in-use adjusted hydrocarbon emissions in g/hp-hr
0.0033 is the default wt. fraction of sulfur in nonroad die sel fuel
2 is the grams of SO 2 formed from a gram of sulfur
This equation includes corrections for the fraction of sulfur that is converted to direct PM
and for the fraction of sulfur remaining in unburned fuel. The direct PM correction factor
(0.022) was calculated by assuming that the direct sulfur PM is H2SO4:7H20 (sulfuric acid
hydrated seven times) and converting the direct sulfur PM (described in Appendix B) to a molar
fraction of sulfur which is subtracted from the fuel consumption. We also assume that the
unburned fuel, as indicated by HC emissions, has the same sulfur level as the base fuel.
References
[1] EPA, "Nonroad Engine and Vehicle Emission Study" (NEVES), U.S. EPA, Office of Air
and Radiation, 21A-2001. November, 1991.
[2] EEA, "Documentation of Input Factors for the New Off-Road Mobile Source Emissions
Inventory Model," ("Inputs...") Energy and Environmental Analysis, Inc. for California Air
Resources Board. February, 1997.
[3] Caffrey, P., "Memorandum: Operation of the Nonroad Emissions Model" from Peter
Caffrey, U.S. EPA Office of Mobile Sources, Engine Programs and Compliance Division, to the
Docket A96-40, Draft 6/13/97.
[4] 59 FR 31306, June 17 1994.
10
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[5] EPA, "Draft Regulatory Impact Analysis: Control of Emissions from Nonroad Diesel
Engines." U.S. EPA Office of Mobile Sources, Engine Programs and Compliance Division.
August 1997.
[6] Korotney, David. "Estimates for In-Use Nonroad Diesel Fuel Levels," Memorandum to
Docket A-96-40. July 1, 1997.
11
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Appendix A
Sources of Previous Emission Factors for
Nonroad Compression Ignition Engines
There is little test data available on nonroad engines. Table Al lists the data sources used
for EPA's Nonroad Engine and Vehicle Study's (NEVES) diesel emission factors. These factors
were also used for EPA's internal Nonroad Emission Model. Table A2 lists the data sources
used for California's Air Resources Board (ARB) OFF-ROAD diesel emission factors. The
studies listed in the tables are described below.
Table Al—Data sources for NEVES Diesel Emission Factors
Application
Lawn and Garden and
Light Commercial
Agriculture
Construction
Logging (skidders)
Industrial and
Airport Service Equipment
Recreational Marine
(Inboard)
Emissions Test
Data Source
None
Cal/ERT, 1982
EMA
SwRI, 1973
Cal/ERT, 1982
EMA
SwRI, 1973
NMMA
Notes
NEVES emission factors
were based on factors for
"continuous service diesel <
50 hp" SwRI, 1991, which
are based on Radian, 1988
factors for truck/container
refrigeration units.
NEVES emission factors
were based on EMA when
possible. For PM and for
applications not available
from EMA, factors were
taken from AP-42, which
relies on Cal/ERT for most
emission factors and on
SwRI, 1973 for PM and
SOx.
Al
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Table A2—Data sources for ARB Diesel Emission Factors
Horsepower Class
Emissions Test
Data Source
Notes
0-15 hp
Manufacturers' data—
2 Yanmar engines
1 Deutz engine
15-25hp
Manufacturers (ARB Off-
Road Equipment Study,
1990)
25-50 hp
Manufacturers Submissions
(ARB Off-Road Equipment
Study, 1990)
50-125 hp
Manufacturers (CA HD
Construction Study, 1988)
125-250
250+
Manufacturers (CA HD
Construction Study, 1988)
ARB factors on all engines
from 125 hp and above are
based on the same data, but
the weighting between turbo-
charged and naturally
aspirated engines is different
in the two horsepower
categories listed here.
Description and Citations of Sources used for Previous Emission Factors
Radian, 1988. Radian's estimates of HC, CO, NOx and PM for truck/container
refrigeration units are not based on testing, but on Radian's estimates for "typical small
direct injection and indirect injection diesel engines." (Weaver, C.S., "Feasibility and
Cost Effectiveness of Controlling Emissions from Diesel Engines in Rail, Marine,
Construction, Farm and Other Mobile Off-Highway Equipment." Final Report by Radian
Corporation for U.S. EPA, Office of Policy Analysis, under contract 68-01-7288,
February, 1988.)
SwRI, 1973. Southwest Research Institute tested 8 diesel engines for HC, CO, NOx and
PM. Emissions of SOx were calculated for no. 2 diesel fuel assuming sulfur content of
0.22%. BSFC is not stated. The emissions tests were given different weightings to
estimate industrial, construction and farm equipment emission factors. (Hare, C.T and
K. J. Springer. Exhaust Emission from Uncontrolled Vehicles and Related Equipment
Using Internal Combustion Engines, Final Report, Part 5, Heavy Duty Farm,
A2
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Construction and Agricultural Engines. San Antonio TX: Southwest Research Institute,
October 1973.)
EMA. Emission factors for 17 applications based on unknown number of tests, unknown
horsepower engines. Engine vintage unknown, but data was submitted by the Engine
Manufacturers Association to EPA prior to NEVES (1991). (Listed in NEVES table I-
06.)
Cal/ERT, 1982. Data from 13 engine manufacturers representing 391 models of
construction equipment. Raw data was aggregated by an accounting firm prior to analysis
and reporting. (Environmental Research and Technology, Inc. "Feasibility, Cost and Air
Quality Impact of Potential Emission Control Requirements on Farm, Construction and
Industrial Equipment in California", Document PA841, sponsored by the Farm and
Industrial Equipment Institute, Engine Manufacturers Association, and Construction
Industry Manufacturers Association, May 1982.)
NMMA. The National Marine Manufacturers Association submitted data to EPA on HC,
CO, NOx and BSFC for 3 diesel inboard motors. Engine vintage unknown, but data was
submitted to EPA prior to NEVES (1991). (NEVES, Table 1-1 l(e).)
ARE Off-Road Study, 1990. A study of lawn and garden and utility emissions.
(Manufacturer Submissions to ARB on Exhaust Emission Standards for Utility and Lawn
and Garden Equipment Engines. California ARB, October 1990. EPA requests
assistance in locating this study)
ARB Heavy Duty Construction Study, 1988.' Reports HC, NOx and PM emission factors
based on emission information from four manufacturers. Does not include information
on test programs. It is not clear how data collected in the study was used to create the
inputs for the ARB model. (Energy and Environment Analysis, Inc. " Feasibility of
Controlling Emissions from Off-Road, Heavy-Duty Construction Equipment." Final
Report to the California Air Resources Board. Arlington, VA, December 1988.)
A3
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Appendix B
1988-1995 Steady-State Emission Factors and Fuel Sulfur Adjustment
for Nonroad Compression Ignition Engines
Introduction
EPA's 1991 Nonroad Engine and Vehicle Emission Study (NEVES) (1) used emission
factors for diesel engines based primarily on tests of older engines. All the NEVES particulate
matter (PM) emission factors are from tests conducted in 1972 and many of the other emissions
factors in NEVES are based on data from tests prior to 1982.
To better characterize emissions from more recent, pre-controlled engines, EPA analyzed
available emission test data on 1988-1995 nonroad diesel engines. This analysis provides the
basis for NONROAD emission factors for 1988-and-later engines greater than 50 hp, as
described in the main body of this report. The analysis indicated a significant difference in
emissions based on engine power. Engines between 50 and 100 horsepower in general had
higher emissions and fuel consumption than engines larger than 100 horsepower. Table Bl
summarizes these results.
Table Bl— Average Emission Test Results for 1988 to 1995 Model Year Engines
Engine
(Reference)
Average (50
to lOOhp)
Average
(>=100hp)
HC
(g/hp-hr)
0.99
0.68
CO
(g/hp-hr)
3.49
2.70
NOx
(g/hp-hr)
8.30
8.38
PM
(g/hp-hr)
0.722
0.402
BSFC
(Ib/hp-hr)
0.408
0.367
A summary of test results for individual engines is presented in Table B2. Note that
testing was conducted using the current certification test procedure, also known as ISO-C1. The
procedure uses eight steady-state modes weighted by time to produce one number in units such as
grams per horsepower-hour. EPA adjusted this test data to account for differences between the
test fuel and typical in-use fuel sulfur levels of 0.33 wt. percent as explained below.
Bl
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Table B2-Summary of ISO-C1 Emission Results for 1988 through 1995 Engines
Engine
(Reference)
Ford New
Holland (2)
John Deere
7068T (2)
Volvo TD
71G(avg. of
2) (3)
Volvo TD73
KBE (avg. of
2) (3)
Weterbeke
32BEDA (4)
Caterpillar
3176B(4)
Cummins
KTA19-M3
(4)
Caterpillar
3306
(Nonroad) (5)
Cummins 4BT
(Nonroad) (5)
John Deere
403 9D (6)
Caterpillar
3116(7)
Caterpillar
3054 (7)
John Deere
4039 (7)
John Deere
7076 (7)
Model
Year
1991
1990
1984
1992
1995
1995
1995
1990
1990
1991
1991
1991
1994
1993
Age
(Hrs)
0
0
0
0
0
0
0
0
0
0
2,511
1,964
2,265
3,300
Fuel
Sulfur
(wt. %)
0.26
0.26
0.046
0.046
0.033
0.033
0.033
0.26
0.26
0.25
0.28
0.035
0.28
0.035
0.28
0.035
0.28
0.035
Power
Level
(hp)
127
139
144
139
95
451
599
285
100
72
201
85
86
174
HC
(g/hp-hr)
1.02
0.45
0.47
0.64
1.95
0.09
0.68
1.1
0.8
0.6
0.07
0.66
0.41
0.53
CO
(g/hp-hr)
7.70
2.98
1.64
0.85
7.43
2.94
3.26
1.4
2.1
3.5
2.51
1.00
2.17
2.05
NOx
(g/hp-hr)
7.48
11.74
12.68
4.52
7.99
6.37
8.78
6.5
11
7.2
9.38
7.53
11.22
10.22
PM
(g/hp-hr)
1.10
0.41
0.149
0.12
1.50
0.213
0.257
0.18
0.39
0.59
0.406
0.350
0.387
0.340
0.384
0.256
0.250
0.205
BSFC
(Ib/hp-hr)
0.358
0.349
0.373
0.386
0.484
0.358
0.359
0.354
0.365
0.385
0.352
0.393
0.389
0.385
B2
-------
(table continued from previous page)
Consolidated
Diesel
6TA-830 (7)
John Deere
6619 (7)
Consolidated
Diesel 4039
(7)
Caterpillar
3306 (7)
Average
(50 to 100 hp)
Average
(>=100 hp)
1990
1993
1988
1990
4,370
4,970
3,570
6,700
0.28
0.035
0.28
0.035
0.28
0.035
0.28
0.035
0.33
0.33
226
275
71
278
0.86
0.82
1.32
1.27
0.99
0.68
1.50
4.69
3.37
1.46
3.49
2.70
6.53
7.29
7.57
6.52
8.30
8.38
0.397
0.338
0.662
0.556
0.581
0.484
0.248
0.245
0.722*
0.402*
0.365
0.397
0.389
0.373
0.408
0.367
* Adjusted to the national average fuel sulfur level of 0.33 weight percent
Fuel Sulfur Adjustment
PM emissions from diesel engines are highly dependent on the sulfur content of the fuel
the engine is burning. PM emissions from diesel engines are generally comprised of unburned or
partially burned fuel, engine oil, and sulfur compounds. When the engine burns fuel, the fuel
sulfur is oxidized to both sulfur dioxide and sulfur trioxide. The sulfur trioxide rapidly absorbs
water to form hydrated sulfuric acid which condenses and is collected on filters as particulate
matter (PM) during emission testing.
Because the sulfur content of diesel fuel can vary considerably, it is important to account
for fuel sulfur in establishing emission factors for PM. To adjust emission test data to the default
sulfur level used in NONROAD (0.33 wt. percent), EPA followed the approach described below.
EPA measured particulate emissions from nine nonroad diesel engines using fuel with
two different sulfur levels, a typical highway diesel fuel at a sulfur level of 0.035 weight percent
and a typical nonroad diesel fuel doped to a sulfur level of 0.28 weight percent to simulate more
closely the average nonroad diesel fuel sulfur level of 0.33 weight percent. Most data from this
study is listed in Table B2, above. In addition, the study included a 1997 John Deere nonroad
engine. This engine is not shown in Table B2 because it certified for the Tier 1 emission
regulations and should not be used to determine an overall emission factor for pre-controlled
engines. Its PM emissions for high and low sulfur levels were 0.186 and 0.129 g/hp-hr,
respectively, with an average fuel consumption of 0.350 Ib/hp-hr. (7) Test results from this study
B3
-------
(including all 9 engines tested) were used to determine the emission adjustment associated with
fuel sulfur level. Other fuel parameter differences such as cetane and fuel distillation that might
also have affected particulate emissions were ignored for this analysis.
The study found that emissions of all pollutants were reduced by using highway fuel as
compared to the nonroad fuel; however, only the average PM reduction was statistically
significant at the 90% confidence level.
The particulate sulfur emission rate should be proportional to the fuel consumption and
the fuel sulfur level. By dividing the difference in particulate emissions by the fuel consumption,
EPA calculated the average effect of fuel sulfur levels for the nine engines. This analysis
provided the constant "A" in the equation below, which describes the relationship between
particulate emissions and fuel sulfur content, with the national average sulfur level of 0.33
weight percent (8) as the default sulfur level.
PMBase = PM + BSFC * A * (0.0033 - Fuel Sulfur)
where
PMBase = PM emissions with default fuel, in g/hp-hr
PM = PM emissions with test fuel, in g/hp-hr
BSFC = Brake Specific Fuel Consumption in g/hp-hr
A = 0.157gPM/hp-hr/Weight Fraction sulfur/BSFC
0.0033= the default weight fraction of fuel sulfur for nonroad die sel
Fuel Sulfur = Weight Fraction of sulfur in test fuel
EPA then used this equation for all tests listed in Table B2 to correct PM emissions from
the test-fuel sulfur level to a fuel sulfur level of 0.33 wt.% before computing the averages listed
in Table Bl and at the bottom of Table B2.
References
(l)"Nonroad Engine and Vehicle Emission Study" (NEVES), U.S. EPA, Office of Air and
Radiation, 21A-2001. November, 1991.
(2) Doorlag, M. and M. Samulski. "Heavy-Duty Engine Testing Report: Non-Road Engine
Configurations, Test Results 1991" EPA Technical Report, 1991.
(3) Hedbom, A. "Emission tests of two Volvo//VME Heavy Duty Off Road Engines."
Motortestcenter, Hanige, Sweden. MTC 9307A. March. 1994.
(4) Carroll, J.N. and C. M. Urban. "Emission Testing of Nonroad Compression Ignition
Engines." Draft Final Report. Southwest Research Institute, 6886-802. September 1995.
B4
-------
(5) Fritz, S. G., "Dynamometer Testing of Heavy-Duty Diesel Engines to Support
Non-Road Regulations," SwRI Report No. 08-3426-010, Work Assignment 0-10 of
EPA Contract No. 68-CO-0014 (September 1991).
(6) Smith, Michael. "Dynamometer Testing of Nonroad Diesel Engines to Support Nonroad
Regulations." Southwest Research Institute, 08-4855-150, EPA Docket A-91-24, June 1992.
(7) Fritz, S. G., "Emission Factors for Compression Ignition Nonroad Engines Operated on
Number 2 Highway and Nonroad Diesel Fuel," Southwest Research Institute. EPA contract #
68-C5-0077, SwRI 08-7601-822. Report expected 1998.
(8) Korotney, David. "Estimates for In-Use Nonroad Diesel Fuel Levels," Memorandum to
Docket A-96-40. July 1, 1997.
B5
-------
Appendix C
Adjustment for In-Use Operation of
Nonroad Compression Ignition Engines
Nonroad engines often operate under conditions unlike that of the steady-state ISO-C1
testing procedure typically used in emissions testing. This alternate operation can cause a change
in the emission characteristics of nonroad compression ignition (CI) engines. As in NEVES, the
NONROAD model accounts for in-use operation in CI engines by applying an adjustment to
emission factors generated using the ISO-C1 tests. Unlike NEVES, the NONROAD model uses
in-use adjustment factors derived from emission testing designed to represent operational
behavior of nonroad equipment. Note that the in-use adjustments are not applied by the
NONROAD model, but are applied by EPA during the creation of the NONROAD emission
factor input files.
Development of In-Use Adjustment Factors
In NEVES, EPA adjusted the ISO-C1-derived emission factor data available at the time
to account for in-use operation by applying a set of multipliers. These factors were derived from
a comparison of only a few engines tested with both the ISO-C1 test procedure and the highway
Federal Test Procedure (FTP). (1) These factors shown in Table CI were applied in NEVES
only to engines used in applications judged to be sufficiently transient in nature.
Table CI NEVES Test Cycle Adjustment from ISO-C1 Emission Factors
NEVES
Adjustment
HC
1.4
CO
2.0
NOx
1
PM
1.6
The NEVES adjustment was derived from tests of engines operating on steady-state
cycles and the Federal Test Procedure for highway heavy-duty engines. However, the highway
test procedure may not simulate engine behavior when used in nonroad applications. Therefore,
a joint EMAVEPA project was initiated to develop more realistic test cycles for nonroad engine
emissions characterization. The project developed cycles to represent typical operation of an
agricultural tractor, a crawler dozer, and a backhoeMoader. (2) The cycles were developed from
data acquired from instrumenting one piece of each type of equipment. This data was used to
construct appropriate test cycles from statistical criteria developed by EMA and EPA. Southwest
Research Institute (SwRI) then tested nine late-model nonroad engines using the steady-state
ISO-C1 certification procedure and the three nonroad test cycles. (3) These test results average
to the adjustment factors shown in Table C2.
CI
-------
Table C2 In-use Adjustment Factor (Ratio of Application Test Cycle to Steady-State ISO-C1
Emissions)
Test Cycle
Agricultural Tractor
BackhoeVLoader
Crawler Dozer
HC
0.89
2.19
0.93
CO
0.42
2.31
1.27
NOx
0.99
1.03
0.99
PM
0.64
2.04
1.21
BSFC
0.98
1.18
0.98
Table C3 lists summarizes the cycle specific results for individual engines. Individual
engine steady-state results are listed in Table B2 of Appendix B with the exception of the John
Deere 6101. The ISO-C1 results for the John Deere 6101 were 0.47 g/hp-hr for HC, 0.86 for CO,
5.55 for NOx, 0.186 for PM, and 0.350 Ib/hp-hr for BSFC. The John Deere 6101 engine was not
included in Appendix B because it was designed for and meets the Tier 1 emission standard.
Therefore the average ISO-C1 results shown in Table Cl are lower than the average given in
Appendix B, Table B2.
C2
-------
Table C3 Summary of the Emission Results of Various Nonroad Test Cycles
Engine
Caterpillar 3 116 (3)
Caterpillar 3054 (3)
John Deere 4039(3)
John Deere 7076 (3)
Consolidated Diesel
6TA-830 (3)
John Deere 6619 (3)
Consolidated Diesel
4039 (3)
Caterpillar 3306 (3)
John Deere 6101 (3)
Average
Test Cycle
Ag. Tract.
Backhoe
Dozer
Ag. Tract.
Backhoe
Dozer
Ag. Tract.
Backhoe
Dozer
Ag. Tract.
Backhoe
Dozer
Ag. Tract.
Backhoe
Dozer
Ag. Tract.
Backhoe
Dozer
Ag. Tract.
Backhoe
Dozer
Ag. Tract.
Backhoe
Dozer
Ag. Tract.
Backhoe
Dozer
Ag. Tractor
Backhoe
Dozer
ISO-C1
HC
(g/hp-hr)
0.04
0.36
0.09
0.46
1.22
0.51
0.20
1.00
0.33
0.54
1.13
0.52
0.90
2.08
0.83
0.87
1.99
0.80
0.86
2.89
1.22
1.33
2.30
1.16
0.50
1.07
0.51
0.63
1.56
0.66
0.71
CO
(g/hp-hr)
0.75
7.47
7.30
0.47
3.34
1.06
0.56
2.62
1.42
0.57
4.82
2.22
1.07
9.86
3.76
1.16
6.89
3.31
2.50
3.31
2.10
0.82
5.14
2.70
0.32
1.92
1.17
0.91
5.04
2.77
2.18
NOx
(g/hp-hr)
9.40
9.46
8.70
9.46
5.45
8.28
11.70
9.57
11.70
9.45
14.35
10.14
5.62
6.69
6.06
6.77
8.29
7.01
7.28
6.52
7.40
6.46
7.22
6.54
4.93
6.36
5.25
7.90
8.21
7.88
7.98
PM
(g/hp-hr)
0.280
0.652
0.713
0.263
0.759
0.384
0.173
0.447
0.254
0.168
0.522
0.303
0.304
1.698
0.805
0.283
1.102
0.698
0.430
0.725
0.413
0.201
0.813
0.436
0.125
0.430
0.246
0.247
0.794
0.473
0.389
BSFC
(Ib/hp-hr)
0.357
0.411
0.362
0.377
0.446
0.372
0.361
0.471
0.372
0.366
0.493
0.370
0.377
0.438
0.370
0.400
0.466
0.398
0.367
0.436
0.364
0.372
0.415
0.370
0.362
0.434
0.362
0.371
0.446
0.371
0.377
C3
-------
Because the in-use adjustment factors used in NEVES were based on limited testing and
unrepresentative test procedures, EPA plans to replace in them NONROAD with the more
representative factors shown in Table C2. These factors will be continually evaluated and
improved, but, because of the need to produce a working version of NONROAD, EPA is
including the above SwRI-derived factors in the version as the best available estimation. EPA is
aware that some of these factors are quite different than those used in NEVES and will have a
large impact on the corresponding emission inventories. Users of this version of NONROAD
should note that these factors, and the list of applications to which the factors are applied, may
change in later releases. EPA may reconsider the in-use adjustment factors due to comments
received during testing and peer review or due to the following issues and activities planned by
EPA:
• Generation of additional in-use test cycles and engine testing on these cycles
• Evaluation of technology effects on adjustment factors
• Contribution of load factor differences to the SwRI-derived adjustment factors
• Representativeness of engine\equipment model and work activity used to generate
the data upon which the nonroad cycles were generated
• Appropriateness of statistical criteria (such as time in mode weighting factors)
used to generate the backhoeMoader, crawler dozer, and agricultural tractor cycles
EPA also plans to continue investigating the effects of in-use behavior which may change
the understanding of the correction from the ISO-C1 steady-state test results. This continuing
evaluation may prompt EPA to revise the emission factors used in NONROAD as part of a new
release of the model. EPA is interested in comments about the approach outlined here.
Applying In-use Adjustment Factors
To apply the in-use adjustment factors listed in Table C2 to the entire CI equipment
population, EPA matched nonroad applications with the test cycle that most closely represents
the nonroad activity for the application. Table C4 lists the nonroad application used in the
NONROAD model and the in-use adjustment most representative of that application. If steady-
state operation is typical of an application no adjustment was made, and the cycle adjustment is
listed as 'none'. Some applications have no diesel engines, and therefore an adjustment is not
applicable and is indicated by 'NW.
The steady-state emission factors listed in the main body of this report were then
multiplied by the appropriate in-use adjustment factor to create NONROAD's emission factor
inputs for CI engines.
Table C4 Diesel Engines, In-Use Emission Factor Adjustment by Application Category
sec
2270000000
2270001000
SCC Description
All Diesel Off-Highway Vehicle: Total
Recreational Vehicles Total
Cycle Adjustment
C4
-------
(table continued from previous page)
2270001010
2270001020
2270001030
2270001040
2270001050
2270001060
2270002000
2270002003
2270002006
2270002009
2270002012
2270002015
2270002018
2270002021
2270002024
2270002027
2270002030
2270002033
2270002036
2270002039
2270002042
2270002045
2270002048
2270002051
2270002054
2270002057
2270002060
2270002063
2270002066
2270002069
2270002072
2270002075
2270002078
2270002081
2270003000
2270003010
2270003020
2270003030
2270003040
2270003050
2270003060
2270004000
2270004010
2270004011
2270004015
2270004016
2270004020
2270004021
2270004025
2270004026
Recreational Vehicles Motorcycles: Off-Road
Recreational Vehicles Snowmobiles
Recreational Vehicles All Terrain Vehicles
Recreational Vehicles Minibikes
Recreational Vehicles Golf Carts
Recreational Vehicles Speciality Vehicle Carts
Construction Equipment Total
Construction Equipment Pavers
Construction Equipment Tampers/Rammers
Construction Equipment Plate Compactors
Construction Equipment Concrete Pavers
Construction Equipment Rollers
Construction Equipment Scrapers
Construction Equipment Paving Equipment
Construction Equipment Surfacing Equipment
Construction Equipment Signal Boards
Construction Equipment Trenchers
Construction Equipment Bore/Drill Rigs
Construction Equipment Excavators
Construction Equipment Concrete/Industrial Saws
Construction Equipment Cement & Mortar Mixers
Construction Equipment Cranes
Construction Equipment Graders
Construction Equipment Off-highway Trucks
Construction Equipment Crushing/Proc. Equipment
Construction Equipment Rough Terrain Forklifts
Construction Equipment Rubber Tire Loaders
Construction Equipment Rubber Tire Dozers
Construction Equipment Tractors/Loaders/Backhoes
Construction Equipment Crawler Dozer
Construction Equipment Skid Steer Loaders
Construction Equipment Off-Highway Tractors
Construction Equipment Dumpers/Tenders
Construction Equipment Other Construction Equipment
Industrial Equipment Total
Industrial Equipment Aerial Lifts
Industrial Equipment Forklifts
Industrial Equipment Sweepers/Scrubbers
Industrial Equipment Other General Industrial Equipment
Industrial Equipment Other Material Handling Equipment
Industrial Equipment AC\Refrigeration
Lawn & Garden Equipment Total
Lawn & Garden Equipment Lawn mowers (Residential)
Lawn & Garden Equipment Lawn mowers (Commercial)
Lawn & Garden Equipment Rotary Tillers < 6 HP
Lawn & Garden Equipment Rotary Tillers < 6 HP (Commercial)
Lawn & Garden Equipment Chain Saws < 6 HP
Lawn & Garden Equipment Chain Saws < 6 HP (Commercial)
Lawn & Garden Equipment Trimmers/Edgers/Brush Cutters
Lawn & Garden Equipment Trimmers/Edgers/Brush Cutters (Commercial)
N\A
N\A
N\A
N\A
N\A
Backhoe
Dozer
N\A
Backhoe
Unused SCC
Dozer
Dozer
Dozer
Dozer
Mone
Backhoe
Dozer
Backhoe
Dozer
Mone
Dozer
Dozer
Backhoe
Dozer
Backhoe
Backhoe
Dozer
Backhoe
Dozer
Backhoe
Backhoe
Backhoe
Dozer
Dozer
Backhoe
Ag. Tractor
Mone
Backhoe
Mone
N\A
N\A
N\A
N\A
N\A
N\A
N\A
N\A
C5
-------
(table continued from previous page)
2270004030
2270004031
2270004035
2270004036
2270004040
2270004041
2270004045
2270004046
2270004050
2270004051
2270004055
2270004056
2270004060
2270004061
2270004065
2270004066
2270004070
2270004071
2270004075
2270004076
2270005000
2270005010
2270005015
2270005020
2270005025
2270005030
2270005035
2270005040
2270005045
2270005050
2270005055
2270005060
2270006000
2270006005
2270006010
2270006015
2270006020
2270006025
2270006030
2270007000
2270007005
2270007010
2270007015
2270007020
2270008000
2270008005
2270008010
2270009000
2270009010
2270010000
Lawn & Garden Equipment Leafblowers/Vacuums
Lawn & Garden Equipment Leafblowers/Vacuums (Commercial)
Lawn & Garden Equipment Snowblowers
Lawn & Garden Equipment Snowblowers (Commercial)
Lawn & Garden Equipment Rear Engine Riding Mowers
Lawn & Garden Equipment Rear Engine Riding Mowers (Commercial)
Lawn & Garden Equipment Front Mowers
Lawn & Garden Equipment Front Mowers (Commercial)
Lawn & Garden Equipment Shredders < 6 HP
Lawn & Garden Equipment Shredders < 6 HP (Commercial)
Lawn & Garden Equipment Lawn & Garden Tractors
Lawn & Garden Equipment Lawn & Garden Tractors (Commercial)
Lawn & Garden Equipment Wood Splitters
Lawn & Garden Equipment Wood Splitters (Commercial)
Lawn & Garden Equipment Chippers/Stump Grinders
Lawn & Garden Equipment Chippers/Stump Grinders (Commercial)
Lawn & Garden Equipment Commercial Turf Equipment
Lawn & Garden Equipment Commercial Turf Equipment (Commercial)
Lawn & Garden Equipment Other Lawn & Garden Equipment
Lawn & Garden Equipment Other Lawn & Garden Equipment (Commercial)
Farm Equipment Total
Farm Equipment 2-Wheel Tractors
Farm Equipment Agricultural Tractors
Farm Equipment Combines
Farm Equipment Balers
Farm Equipment Agricultural Mowers
Farm Equipment Sprayers
Farm Equipment Tillers > 6 HP
Farm Equipment Swathers
Farm Equipment Hydro Power Units
Farm Equipment Other Agricultural Equipment
Farm Equipment Irrigation Sets
Light Commercial Total
Light Commercial Generator Sets
Light Commercial Pumps
Light Commercial Air Compressors
Light Commercial Gas Compressors
Light Commercial Welders
Light Commercial Pressure Washers
Logging Equipment Total
Logging Equipment Chain Saws > 6 HP
Logging Equipment Shredders > 6 HP
Logging Equipment Skidders
Logging Equipment Fellers/Bunchers
Airport Service Equipment Total
Airport Service Equipment Airport Support Equipment
Airport Service Equipment Terminal Tractors
Underground Mining Equipment Total
Other Underground Mining Equipment
Oil Field Equipment Total
Mone
Mone
Mone
Mone
Mone
Mone
Mone
Mone
Mone
Mone
Mone
Mone
N\A
N\A
N\A
N\A
Unused SCC
Mone
Mone
Mone
Ag. Tractor
Ag. Tractor
Ag. Tractor
Ag. Tractor
Ag. Tractor
Ag. Tractor
Ag. Tractor
Ag. Tractor
Mone
Ag. Tractor
Mone
Mone
Mone
Mone
Mone
Mone
Mone
N\A
None
Dozer
Backhoe
Backhoe
Backhoe
Backhoe
C6
-------
(table continued from previous page)
2270010010
2282005025
2285003015
2282005000
2282005005
2282005010
2282005015
Other Oil Field Equipment
Recreational Pleasure Craft, Sailboat Aux. Outboard
Railway Maintenance
Recreational Pleasure Craft, Total
Recreational Pleasure Craft, Inboards
Recreational Pleasure Craft, Outboards
Recreational Pleasure Craft, Personal Water Craft
None
None
Backhoe
None
None
N\A
References
(1) EPA, "Nonroad Engine and Vehicle Emission Study" (NEVES), U.S. EPA, Office of Air
and Radiation, 21A-2001. November, 1991
(2) Jackson, C., "Nonroad Composite Cycle Development and Data Analysis." EPA Office of
Mobile Sources. Report expected 1998.
(3) Fritz S.G., "Emission Factors for Compression Ignition Nonroad Engines Operated on
Number 2 Highway and Nonroad Diesel Fuel," Southwest Research Institute. EPA contract
#68-C5-0077, SwRI 08-7601-822. Report expected 1998.
C7
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