United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-96/020 April 1996
EPA Project Summary
Criteria Pollutant Emissions from
Internal Combustion Engines in the
Natural Gas Industry
Gerald S. Workman Jr., Rachel G. Adams, and Gunseli Sagun Shareef
This report contains emission data
for oxides of nitrogen, carbon monox-
ide, methane, ethane, nonmethane hy-
drocarbons, and nonmethane-ethane
hydrocarbons from stationary internal
combustion (1C) engines and gas tur-
bines used in the natural gas industry.
The emission factors calculated from
test results were from five test cam-
paigns conducted as part of the Gas
Research Institute's air toxics study,
three of which were cofunded by the
U.S. Environmental Protection Agency
(EPA). Test results for individual en-
gines tested are presented, along with
full load engine family-specific factors,
and the calculated emission factors are
evaluated relative to the emission fac-
tors published in EPA report AP-42.
Units tested included eleven 2-stroke
engines and five 4-stroke engines, with
and without controls, and two gas tur-
bines. This data will enhance the cur-
rent data base in AP-42 for stationary
1C engines. It will not only enlarge the
population of engine types covered, but
will enhance the emission factor qual-
ity of several engine categories which
have a limited data set.
This Project Summary was developed
by the National Risk Management Re-
search Laboratory's Air Pollution Pre-
vention and Control Division, Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Background
One function of the Air Pollution Pre-
vention and Control Division (APPCD) of
the U.S. Environmental Protection
Agency's (EPA's) Office of Research and
Development is improving current air pol-
lutant emission inventory methodologies,
especially for pollutants associated with
tropospheric ozone formation. As part of
the improvement of emission inventory
methodologies, APPCD supports field
emission measurement efforts. These data
are used by EPA's Office of Air Quality
Planning and Standards (OAQPS) to en-
hance their reference document "Compi-
lation of Air Pollutant Emission Factors"
(AP-42), which contains emission factors
for oxides of nitrogen (NOX), carbon mon-
oxide (CO), methane (CH4), ethane (C2H6),
nonmethane hydrocarbon (NMHC), and
nonmethane-ethane hydrocarbon (NMEHC)
emissions from the large, stationary inter-
nal combustion (1C) reciprocating and tur-
bine engines used in the natural gas in-
dustry. In AP-42, emission factors for some
types of engines, especially those with air
pollution controls, are based on an inad-
equate amount of emissions test data. To
improve the understanding of emissions
from these sources, additional testing is
needed to enhance the emissions data-
base, giving OAQPS the ability to revise
AP-42.
Emissions characterization of 1C engines
in the natural gas industry is currently
underway through a program sponsored
by the Gas Research Institute (GRI), with
the primary focus on determining the po-
tential for air toxics emissions. Since in-
formation on NOx, CO, CH4, C2H6, NMHC,
and NMEHC emissions is needed to com-
pletely characterize the 1C engine emis-
sions, EPA/APPCD provided cofunding to
the GRI program to support gathering such
data for enhancement of the emissions
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database currently used in AP-42 for the
development of emission factors. The work
described in this document was conducted
as part of this joint effort between GRI
and EPA and involved:
• Field measurements of NOx, CO, CH4,
C2H6, and total hydrocarbon (THC)
emissions at three test sites (joint
EPA/GRI effort);
• Incorporation of field data, collected
by GRI at two earlier test sites, into
the data set for evaluation; and
• Evaluation of all test data for use in
enhancing the emissions database
currently in AP-42.
Results
Table 1 summarizes full load emission
factors for NOx, CO, CH4, C2H6, THC,
NMHC, and NMEHC expressed in grams
per horsepower-hour and pounds per mil-
lion British thermal units. The emission
factors were averaged by engine family,
and are presented for 2-stroke, lean-burn;
2-stroke, clean-burn; 4-stroke, lean-burn;
4-stroke, clean-burn; and 4-stroke, rich-
burn engines; and gas turbines. Separate
emission factors were calculated for en-
gines using emission control equipment;
e.g., nonselective catalytic reduction
(NSCR) selective catalytic reduction
(SCR), CO oxidation catalyst, or precom-
bustion chamber (PCC). Only data from
test periods during which the engines were
operated within 90% of rated load and
95% of rated speed were used to calcu-
late the average emission factors, except
when the engine tested was the only one
of a particular classification included in
the test program, and the engine did not
meet the minimum load and speed criteria
during any of the test periods.
The NOx, CO, and THC emission fac-
tors are based on continuous emissions
monitoring system (CEMS) measurements
while the CH4 and C2H6 emission factors
are based on gas chromatography (GC).
Emission factors expressed as NMHC and
NMEHC are calculated by subtracting the
CH4 and CH4/C2H6 concentrations, respec-
tively, from the THC concentrations. In
some cases, the difference between the
measured THC and CH4/C2H6 concentra-
tions was less than the analytical preci-
sion of the instruments. In these cases,
NMHC/NMEHC emissions were not quan-
tified.
Except for the 2-stroke, lean-burn en-
gine family, the information presented in
Table 1 is considered limited since the
emission factors are based on tests con-
ducted on only one to three engines/tur-
bines. As expected, there are differences
between the emission factors calculated
in this study and those in AP-42. The
differences between the data from this
study and AP-42 can be attributed to the
variability associated with the population
of engines tested, and differences in the
type of instrumentation used during the
two studies.
Conclusions
Based on examination of the test re-
sults from this study, the following conclu-
sions are offered to enhance the emis-
sions database currently in AP-42:
• Incorporate emissions data used to
develop the emission factors for un-
controlled 2-stroke, lean-burn; 4-
stroke, lean-burn; and 4-stroke, rich-
burn engines; and gas turbines into
the current AP-42 emissions data-
base. Although the current factors are
"A" quality, incorporation of these data
will broaden the population of the en-
gines covered.
Incorporate the data used to develop
the emission factors for 2-stroke,
clean-burn engines into the current
AP-42 emissions database. The cur-
rent AP-42 factors are "C" quality.
The additional data may upgrade the
emission factor quality rating for this
category.
Use data for NSCR-controlled 4-
stroke, rich-burn engine, PCC-con-
trolled 4-stroke, lean-burn engine, and
the 2-stroke, clean-burn engine with
a CO oxidation catalyst to build and/
or improve an emissions database
for these categories.
The current version of AP-42 has
separate emission factors for "clean-
burn" and "PCC" controlled engines.
"Clean-burn" is a trade name used by
one manufacturer to describe modifi-
cations to a lean-burn engine to lower
emissions. A PCC is a primary com-
ponent of the "clean-burn" modifica-
tion to these engines. An engine
equipped with PCC may also have all
of the other clean-burn modifications,
as did the one engine with PCC tested
under this program. Consideration
should be given to combining the
emissions database for these control
scenarios under a single generic de-
scription.
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Table 1. Full Load Average Emission Factors
Engine Family
2-stroke; lean-burn
Emission
Control
—
No. of Engines/
Runs?
7/16
Units
(g/hp-hr)"
(Ib/MMBtu)
N0x
14
3.4
CO
0.63
0.15
CH4
4.6
1.1
C2H4
0.31
0.059
THC
5.7
1.4
NMHC
1.1
0.28
NMEHC
0.80
0.19
2-stroke' clean-burn
4-stroke; lean-burn
4-stroke; clean-burn
4-stroke; rich-burn
Gas turbine
—
CO
catalyst
—
SCR
catalyst
PCC
—
NSCR
catalyst
—
1/3
1/1
3/6
1/2
1/1
P/1
1f/2
2/4
(g/hp-hr)
(Ib/MMBtu)
(g/hp-hr)
(Ib/MMBtu)
(g/hp-hr)
(Ib/MMBtu)
(g/hp-hr)
(Ib/MMBtu)
(g/hp-hr)
(Ib/MMBtu)
(g/hp-hr)
(Ib/MMBtu)
(g/hp-hr)
(Ib/MMBtu)
(g/hp-hr)
(Ib/MMBtu)
0.48
0.14
0.54
0.17
14
3.7
5.0
1.3
0.56
0.14
18
5.2
0.050
0.015
1.4
0.31
1.4
0.41
0.11
0.030
0.83
0.21
0.43
0.11
2.0
0.51
15
4.2
0.26
0.075
0.1&
0.03&
NA
NA
NA
NA
5.5
1.5
NA
NA
NA
NA
NA
NA
NA
NA
ND
ND
0.38C
0.1 1C
NA
NA
0.16
0.044
0.15
0.036
NA
NA
NA
NA
NA
NA
ND
ND
6.8
2.0
6.3
1.9
4.1
1.1
2.7
0.69
8.0
2.0
3.0
0.85
1.7
0.49
ND
ND
— c
— c
— c
— c
c,d
c,d
c,d
c,d
—c
C
—c
— c
— c
—c
ND
ND
— c
— c
c
c
_,,<*
c,d
c,d
—C'"
C
c
—c
c
c
— c
ND
ND
NA = Not available. ND = Not detected. NSCR = nonselective catalytic reduction. SCR = selective catalytic reduction.
PCC = Pre-combustion chamber.
'For some pollutants, the number of engines/runs used in the average is less than the total number tested.
"There is uncertainty in the horsepower measurements made by the engine analyst for 4 of the 16 runs.
CGC hardware malfunction during Campaign 4 prevented collection of data for methane and/or ethane.
''Difference between recorded methane and THC measurements was less than the precision of either instrument.
'Based on one engine tested at 91 % speed and below 90% load.
'Based on one engine tested at 90% speed.
gTest results below the detection limits were averaged as zero.
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G. Workman, R. Adams, andG. Shareefare with Radian Corp., Research Triangle
Park, NC 27709
Charles C. Masser is the EPA Project Officer (see below).
The complete report consists of two volumes, entitled "Criteria Pollutant Emissions
from Internal Combustion Engines in the Natural Gas Industry:"
"Volume I. Technical Report" (Order No. PB96-168265; Cost: $25.00)
"Volume II. Appendices A-l" (Order No. PB96-168273; Cost: $57.00)
The above reports will be available only from: (cost subject to change)
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
National Risk Management Research Laboratory (G-72)
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-96/020
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