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

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