Aerotherm Project 7212
TECHNICAL SUPPORT AND ASSISTANCE FOR THE DEVELOPMENT
OF STANDARDS OF PERFORMANCE FOR STATIONARY
INTERNAL COMBUSTION ENGINES
S. Youngblood, M. MacDonald, L. Cooper
Acurex Corporation/Aerotherm Division
485 Clyde Avenue
Mountain View, California 94042
January 1977
AEROTHERM REPORT TR-76-234
Prepared for
EPA Project Officer - John R. Busik
EPA Task Officer - John N. McDermon
Industrial Environmental Research Laboratories
U.S. Environmental Protection Agency
Research Triangle Park
North Carolina 27711
Contract 68-01-3158
Task 14
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TABLE OF CONTENTS
Section Page
1 INTRODUCTION 1
1.1 Scope of Work 1
1.2 Summary of Results 2
1.2.1 Additions to Data Base 2
1.2.2 Scatter Analysis 2
1.2.3 Field Applicability 4
2 ADDITIONS TO DATA BASE 5
3 SCATTER ANALYSIS: SOURCES OF VARIATIONS IN NO LEVELS FROM LARGE BORE
ENGINES x 7
3.1 Effect of Measurement Methods
3.1.1 Previous Studies of Exhaust Measurement Variation 8
3.1.2 Variations in NOX Emissions to the NOX Instrument 11
3.1.3 Variations in NOX Levels Related to Sampling Procedures 19
3.1.4 Comparison of Manufacturer's Measurement Error 29
3.2 Effect of Ambient Conditions on NOV 33
X
3.2.1 Effect of Ambients on NOX Emissions from 1C Engines 34
3.2.2 Selection of Ambient Correction Factors for Large Bore Engines 35
3.2.3 Effect of Ambient Correction on Reduction of Data Scatter 69
'3.3 Effect of Engine Variability 75
3.3.1 Production Variations 75
3.3.2 Model Variations 77
3.3.3 Variations with Number of Cylinders 80
3.3.4 Variations in NOX Level Due to Other Engine Variables 80
FIELD APPLICABILITY 87
4.1 Summary of Manufacturers' "114" Responses 87
4.2 Summary of DEMA and AGA Comments on Control Techniques 89
REFERENCES 91
NOMENCLATURE 93
m
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LIST OF ILLUSTRATIONS
Figure
1 Nondispersive Infrared Absorption Analyzer
1 5
2 Chemiluminescent Analyzer
on
3 Schematic of Exhaust Sampling System
?7
4 Sampling Practices
5 Measurement Error Relative to EPA Procedure
6 1969 Humidity Range in Engine Test Cells, Dearborn, Michigan 36
7 Effect of Ambient Humidity on 1C engines NO emissions 37
8 Effect of Ambient Temperature on 1C Engine NO Levels 38
X
9 Effect of Humidity on Emissions Scatter for Six HD Gasoline Engines 39
10 Effect of Humidity and Temperature on Emissions Scatter for Six HD Diesel
Engines 40
11 Effect of Humidity on A/F Ratio and NO Emissions from HD Gasoline Engines ... 42
X
12 Effect of Temperature on A/F Ratio and NOV Emissions for HD Gasoline Engines . . 44
X
13 Effect of Barometer Pressure on A/F Ratio and NO Emissions for HD Gasoline
Engines 45
14 Exhaust Gas Concentration Versus A/F 46
15 Effect of Fuel Distribution on NO Emissions 47
16 Effect of Ignition Timing and A/F on NO Exhaust Emissions, 1600 rmp, 23 bhp
Road at mbt 47
17 Effect of A/F Ratio and Ambient Humidity on NO Emissions of a LD Gasoline
Engine 49
18 Comparison of SI Ambient Humidity Correction Factors 50
19 Water to Fuel Range vs. Ratio Air-to-Fuel 52
20 Effect of Humidity and Temperature on NO Emission for Different CI Engines ... 54
21 Comparison of CI and SI Ambient Humidity Correction Factors 56
22 Correction Factors for Temperature for CI Engines 57
23 Gas Turbine Humidity Correction Factor 59
24 Observed Ambient Humidity Influence on NO Production 60
X
25 Comparison of Existing Gas Turbine Ambient Temperature Correction with HD Diesel
Temperature Correction 62
26 Gas Turbine Temperature Correction Factors 63
27 Relationship of NOX Level and Load to f/a Ratio for a Turbocharged Diesel Engine
Operating at Two Ambient Temperatures 64
IV
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LIST OF ILLUSTRATIONS Concluded.
Figure Page
28 Effect of Ambient Correction on Scatter in NOX Emissions of Uncontrolled
4-TC Engines 72
29 NO Production Variation with Number of Cylinders 81
X
30 Variation in NO Level with Number of Cylinders 82
31 Variation in NO Level with Speed 83
32 NO Variation with Manifold Temperature 84
33 N0x Variation with Torque (BMEP) 86
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LIST OF TABLES
Table Pa9e
1 Additions to Data Base ................ ....... . 6
2 Accuracy of NO Measurements ....................... 10
3 Instruments Used By Manufacturers to Measure NO Emissions . ... 12
4 Sources of NO Instrument Error ........................ 16
5 Comparison of CL and NDIR, NDIR/NDUV Measurements ............... 18
6a Sources of Sampling Error: The Sample Transfer ................ 21
6b Sources of Sampling Error: Instrument Related .......... ... 22
7 Comparison of Sampling Practices ...................... 24
8 Sources of Error for DEMA, SAE, and EMD Emission Practices ........... 26
9 Large Bore Engine Manufacturer's Sampling Practice .............. 30
10 Manufacturer's Sampling Error as a Percent, Relative to EPA Procedure ..... 31
11 Ambient Humidity Correction Factors for SI Engines .- .............. 48
12 Existing 1C Engine Ambient Correction Factors for Application to Large Bore
Engines .................................. 70
13 Scatter in NO Emissions of Uncontrolled 4-TC Engines ............ 71
14 Variations in NO Emissions from GMC/EMD Production Engines .......... 76
15 Potential Scatter in NO Emissions from Production Engines Due to Ambient
Humidity and Temperature Variations ..................... 78
16 Variation in NOX Due to Model Differences . ... ........... 79
vi
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SECTION 1
INTRODUCTION
In June 1974 the Aerotherm Division of Acurex Corporation was engaged by the EPA to gather
data and information available on the effectiveness of various emission control techniques for re-
ducing emissions of NO , CO, and HC from stationary internal combustion engines. These data were
documented in a draft Standards Support and Environmental Impact Statement (SSEIS) which was submit-
ted to the Industrial Studies Branch (ESED/OAQPS) in March 1976.
The draft SSEIS has undergone review within EPA and has also been circulated among various in-
dustry groups representing manufacturers and users of stationary internal combustion engines. Since
the development of standards of performance for stationary internal combustion engines is so complex,
a number of questions and issues have been raised during this review of the Standards Support and En-
vironmental Impact Statement.
The objective of this current study is to answer the questions and issues which have arisen
as a result of the draft document review and to perform various services for the EPA in connection
with the pending recommendation and promulgation of standards of control. This supplemental report
documents work completed under contract 68-01-3158, Task 14. The following section briefly outlines
the scope of work completed under this task order.
1.1 SCOPE OF WORK
The work completed under this task order is divided into three tasks as described in the work
plan. These tasks are listed below by the section number of this report where they are discussed.
• Section 2: The purpose of this task was to collect and incorporate into the existing data
base additional emissions data supplied by the eight manufacturers of large bore engines.
The responses to a June 16, 1976 Section "114" request for information were the primary
source of this information
t Section 3: The sources of data scatter for the reported emissions data were evaluated
according to the following breakdown:
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- Measurement Techniques: Assess the extent to which scatter in the data is attributable
to variations in the measurement practices among the eight manufacturers
- Variations in Ambient Conditions: Determine to what extent variations in ambient inlet
air humidity, temperature, and pressure affect exhaust emissions, and investigate the
application of correction factors to adjust emissions to standard inlet air conditions
— Engine Variability: Investigate to what extent the scatter in the data is related to;
(a) inherent differences among engines of a common generic configuration, and (b) differ-
ences among identical engines and models of the same manufacturers
• Section 4: The final task under this contract was to reevaluate the field applicability
of the various controls that were identified in the draft document
1 .2 SUMMARY OF RESULTS
The following are highlights of the major conclusions reached during the completion of this
task order.
1.2.1 Additions to Data Base
• The data base of uncontrolled engines containing ambient information has increased nearly
200 percent after incorporation of the additional data obtained. The corresponding data
for controlled engines increased 100 percent. Thus, substantial emissions data now exists
for correction to standard ambient inlet conditions
• No manufacturer reported the response of an engine's exhaust emissions to systematic
variations of inlet air conditions. Thus, ambient correction factors could not be derived
directly from the data
1.2.2 Scatter Analysis
Measurement Methods
• Measurement practices were shown to contribute significant uncertainty for some of the
manufacturer's data
• The error in each manufacturer's measurement method was estimated. It is recommended
that the reported N0x levels be banded by the appropriate uncertainty limits
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Effect of Ambient Conditions
• Variations in ambient conditions were shown to contribute significantly to the scatter in
reported emission levels. This scatter can be reduced by correcting observed levels to
standard ambient conditions
• Ambient correction factors were selected from the literature based on smaller bore engines
to be applied to large bore data, since no factors existed for large bore engines. These
factors are:
— Corrections_for humidity only in SI engines. Factors could not be derived for changes
in ambient pressure or temperature due to inconsistent variations in response to these
inlet parameters
— Corrections for temperature and humidity for CI engines. These factors were based on
specific engine types (e.g., 4-TC, 2-BS, etc.). No factors exist for the effect of
ambient pressure variations on emissions from CI engines
• Scatter in 4-TC diesel and dual fuel uncontrolled emissions was decreased slightly by
application of an ambient correction factor. Scatter increased somewhat for 4-TC uncon-
trolled natural gas emissions. Thus, other sources of scatter, such as measurement
methods and engine variability are believed to account for most of the data scatter
t Existing correction factors (based on small bore engines) were recommended for application
to large bore data, until manufacturers can obtain data to develop factors based on large
bore engines. It is recommended that standardized limits be established for those ambient
parameters for which no factors presently exist
Effect of Engine Variability
• Two manufacturers reported that NO levels vary from 3 to 8 percent for measurements of
X
identical engines (production models). However, some of the reported variation was shown
to possibly be related to variations in ambient conditions
• No clear trend could be established for the effect of number of cylinders on emission
levels for either diesel or natural gas engines
• NO emissions for any type engine (given strokes/cycle, fuel, and air charging) vary more
A
from manufacturer to manufacturer than they do among models within a manufacturer's line.
It is expected that differences among manufacturers are related to differences in speed,
BMEP, and manifold air temperature
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• Limited data show that NO emissions from 4-TC diesel and dual fuel engines decrease some-
what with increasing speed
• NO emissions from 4-TC, natural gas (SI) engines increase directly with design manifold
air temperature. NO levels from diesel and dual fuel (CI) engines increase slightly with
design manifold air temperature
• No trend in NO emissions could be established for differences in BMEP among diesel, dual
fuel, and natural gas engines
.2.3 Field Applicability
• There is a general consensus among manufacturers that 1 to 3 years is required to fully
develop N0x control techniques, including the evaluation of engine durability. This com-
pares to 9 to 15 months estimated in the draft SSEIS
• In general, manufacturers reported potential cost impacts of NO controls (e.g., increased
X
maintenance) rather than technical limitations that would prevent the application of po-
tential NOX control techniques
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SECTION 2
ADDITIONS TO DATA BASE
Following the completion of the draft SSEIS and its presentation to the NAPCTAC in March, EPA
received comments from engine manufacturers and the AGA. As a result of these comments EPA sent
Section 114 letters on June 16, 1976 to the relevant engine manufacturers requesting additional in-
formation. Seven of eight manufacturers of large bore engines responded with new or revised exhaust
emissions data, information on ambient conditions during emission tests, sales data, and field operat-
ing experience. These new data are summarized in Table 1 and compared with the existing data base.
Entries in this table are engine models for which we have controlled and/or uncontrolled data. As
this table illustrates, the uncontrolled data base containing ambient information has more than
doubled and the controlled data with ambients has increased 150 percent. Thus, a substantial data
base exists for which ambient variations in temperature and humidity can be considered; however, none
of the manufacturers supplied emissions data, systematically, as a function of ambient variations.
Therefore, a correction factor for ambients cannot be developed directly.
Two manufacturers, DeLaval and White-Alco, supplied emissions data (uncontrolled) for the first
time. Their submission included data for many of their present production models. Cooper Energy
Services, White Superior, and Ingersoll-Rand also reported exhaust emissions (both uncontrolled and
controlled) for additional, previously unmeasured engine models. Both Colt and Waukesha reported
additional emissions data (uncontrolled and controlled) for previously measured engine models.
These new emissions data have been incorporated into the existing data base. The uncontrol-
led data containing ambient temperature and humidity were used to perform the scatter analysis re-
ported in Section 3.2.3. Further evaluation of the controlled data base (with ambients) will be
completed using a computer analysis developed under contract 68-02-2530.
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TABLE 1. ADDITIONS TO DATA BASE
Fuel
Strokes
Air Charging
Existing data,
uncontrol led
Additional data,
uncontrol led
Existing data,
control led
Additional data,
controlled
Diesel
2
BS
5
3
TC
5
4
4
4
4
NA
2
2
TC
7
13
6
7
Dual Fuel
2
BS
TC
2
1
2
1
4
NA
TC
3
3
3
2
Gas
2
BS
1
1
1
1
TC
1
11
1
11
4
NA
4
1
4
1
TC
8
5
5
2
Total
38
39
31
29
U_>
CO
1—
Fuel
Strokes
Air Charging
Anbient data,
existing uncontrolled
Ambient data,
new uncontrolled
Ambient data,
existing controlled
Ambient data,
new controlled
Diesel
2
BS
2
2
TC
1
4
1
4
4
NA
0
0
TC
3
13
3
6
Duel Fuel
2
BS
TC
2
1
2
1
4
NA
TC
3
3
3
2
Gas
2
BS
0
1
0
1
TC
0
11
0
11
4
NA
3
1
3
1
TC
2
4
2
1
Total
16
38
16
27
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SECTION 3
SCATTER ANALYSIS: SOURCES OF VARIATIONS IN NOX
LEVELS FROM LARGE BORE ENGINES
This task is concerned with refining the exhaust emissions data which were reported in the
draft SSEIS and in subsequent responses from the engine manufacturers. The draft reported the ef-
fectiveness of various emission control techniques as part of an effort to develop standards of per-
formance to limit exhaust emissions from stationary reciprocating 1C engines. The reported data,
however, may not be directly comparable because the manufacturers used different measurement tech-
niques and the ambient conditions varied from test-to-test. Consequently, these measurements methods
are examined in detail in Section 3.1 to determine to what extent the reported emission levels differ
due to differences in the procedures. Similarly, Section 3.2 seeks relationships between exhaust
emissions and varying ambient conditions. Specifically that section examines: (1) how variations
in ambient temperature, humidity, and pressure affect NO emissions, (2) what correction factors
X
exist for adjusting measured exhaust emissions to standard conditions, and (3) the extent to which
scatter in emissions levels can be reduced by applying an appropriate ambient correction factor.
This current study will make a preliminary evaluation of ambient scatter by attempting to correct
the uncontrolled data base only. The controlled data will be corrected and evaluated under contract
68-02-2530.
In addition to these two types of scatter, differences in emissions data may be attributable
to inherent differences among engines of a common generic configuration, or inherent differences
among identical engines of the same manufacturers and model. These kinds of scatter are examined
in Section 3.3 (after correction for ambient conditions where possible). A fourth source of scatter
is related to the extent to which the data represent a "cut-and-try" approach to emission reduction,
rather than a systematic approach to obtain the greatest reduction in emissions. This kind of scat-
ter will be examined under contract 68-02-2530, after the controlled data base has been corrected for
variations in measurement methods and ambient conditions.
Thus, the following sections evaluate scatter due to: (1) measurement methods, (2) ambient
conditions, and (3) engine variability.
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3.1 EFFECT OF MEASUREMENT METHODS
Previous studies have indicated that sampling instrumentation and procedures significantly
affect emission levels. Furthermore, no one standard procedure has been adopted by all of the man-
ufacturers reporting emissions. That is, the eight manufacturers who reported emission data used
either chemiluminescent (CL) or nondispersive infrared (NDIR) and ultraviolet (NDUV) instruments and
one of four emission measurement procedures (SAE, EPA, EMD, or DEMA). Therefore, this section will
present a detailed discussion of the instrument and sample acquisition practices used by the engine
manufacturers. The purpose of this discussion is to identify possible variations in exhaust emission
levels attributable to particular measurement equipment and/or procedures. Specifically, this sec-
tion will :
t Establish which instruments, sampling trains, and procedures were used by each manufac-
turer who reported NO emissions
X
• Summarize the potential sources of uncertainty relating to each measurement practice
• Evaluate the variability among manufacturers' emissions data due to these uncertainties
The following discussion will begin by illustrating typical measurement uncertainties in present
sampling practices. This analysis will show that significant uncertainties in measurements can arise
due to differences in both instrument and sampling procedures. Therefore, both of these sources of
error will be discussed as they apply to the instruments and procedures used by the eight large bore
engine manufacturers. Then these practices will be compared and the uncertainty in each manufactur-
er's NO measurements estimated.
3.1.1 Previous Studies of Exhaust Measurement Variation
Before evaluating each manufacturer's sampling practice, it is of interest to examine the
present "state-of-the-art" of internal combustion engine exhaust measurements of NO . Three recent
studies have been conducted to compare the measurements of NO made by different laboratories from
the same emission source. In two of these studies N0x measurements were made, simultaneously, in
the same laboratory using identical procedures. In the other study, the same emission source was
sent to each laboratory. These studies illustrate the magnitude of emission variations attributable\
to instruments and sampling procedures. They also indicate the reproducibility of emissions measure-
ments, both within a laboratory and amongst different laboratories. The results of these studies
will serve as a basis for comparing potential data variations due to the measurement practices of
the eight large bore engine manufacturers considered in the current study.
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A series of cooperative emissions tests was conducted by the Coordinating Research Council
(CRC) to evaluate measurement methods used to analyze diesel exhaust emissions from truck-size
engines. In Phase III of this program, six laboratories sent sampling teams to one location to make
simultaneous measurements (using NDIR analyzers) of a multicylinder engine (Reference 1). The engine
used in this study was a 6 cylinder, 300 cubic inch, 4 stroke direct injection diesel. The proce-
dures that were used during this test program to measure NO, CO, and C0« evolved into SAE Recommended
Practice J-177 (Reference 2). In Phase IV of that program, the same engine was circulated to 15
laboratories to: (1) verify that the generally good agreement of Phase III emission levels were the
result of improved sampling procedures, and (2) obtain NO/NO data using CL analyzers (Reference 3).
X
Table 2 shows the results of these two cooperative tests. Although the Phase III variations
appear reasonable, the Phase IV results indicate poor agreement amongst the laboratories. These
larger errors were attributed to poor calibration procedures (span gases out of spec, instruments
not calibrated) and possibly some variation in engine performance. In addition, it was noted that
the average NO concentration measured at rated load by the CL analyzers was approximately 23-percent
lower than that measured by NDIR.
A more recent cooperative test program conducted by the CRC evaluated EPA's revised heavy duty
diesel engine NO/NO measurement methods and instrumentation (Reference 4). Six participants made a
series of NO/NO measurements on a multicylinder engine, simultaneously, and produced the range of
error shown below. A range is shown because the results were analyzed in three different groupings:
(1) all data, (2) those which remained after eliminating questionable results from participants who
encounter sampling problems, and finally, (3) those which were left after excluding both questionable
data and results obtained from instruments with long sample transfer times.
13 mode St'd Dev.
g/hp-hr g/hp-hr St'd Dev./Mean, %
NO 8.03 - 8.21 .42 - .29 5.9 - 3.5
NOX 8.05 - 8.16 .30 - .17 3.8 - 2.1
All but one of the participants used a CL analyzer, and the results from the one NDIR analyzer (a
new reduced interference design) were equivalent to these from the CL analyzers. Thus, based on
simultaneous tests using the same instruments, sampling practices, and emissions source, errors in
emission measurements among laboratories ranged from 3 to 6 percent for NO, and 2 to 4 percent for
NO . In addition, the repeatability within a laboratory ranged from 2 to 7 percent for NO and 1 to
3 percent for N0x-
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TABLE 2. ACCURACY OF NO MEASUREMENTS (REFERENCES 1 AND 3)
A
Source
NO:
NDIR
CL
N02:
NDUV
CL
Phase III
6 Labs, Simultaneous Measurements
Standard Deviation
as % of Average
5
—
—
—
Spread in Data
as % of Average
10
—
—
—
Phase IV
15 Labs, Round Robin
Standard Deviation
as % of Average
8
36
21
88
Spread in Data
as % of Average
27
15
39
166
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In contrast to the above program, the eight large bore engine manufacturers used one of four
test procedures (SAE, EPA, DEMA, or EMD) and either CL or NDIR/NDUV instruments. Furthermore, the
NDIR's were not reduced interference designs. Hence, their data are likely to vary more than the
truck engine results due to measurement practices. The following discussion will first examine the
sources of such variations from differences in both instruments and sampling practices. Then an
attempt will be made to suggest uncertainty bounds on the emissions data from each manufacturer.
3.1.2 Variations in NOX Emissions Related to the NOX Instrument
Since the development of commercial chemiluminescent analyzers (1971), various studies have
been conducted to compare their operation with the already established NDIR analyzer. All of these
studies have shown the NDIR analyzer to record consistently higher levels of NO than the CL analyzer
for a given source (References 3,5, and 6). Three of the large bore engine manufacturers reported
N0x emissions using NDIR's and the other five used CL analyzers.
Table 3 shows the NO instruments used by each of the manufacturers. Scott Research Labora-
X
tories made the emission measurements for Ingersoll-Rand and White-Alco, since neither manufacturer
presently owns emission measurement equipment. Note that an electrochemical instrument was used by
Shell Oil Research in 1971 to measure NO from one Cooper-Bessemer and one Ingersoll-Rand engine.
None of the manufacturers has used this instrument since then; therefore, no attempt will be made to
correlate those emissions with instrument differences,. Only Waukesha and GMC/EMD continue to measure
NO emissions with NDIR analyzers, and Waukesha has recently acquired a CL analyzer. Thus, all but
one manufacturer will be using CL instruments in the future. In the following paragraphs, the prin-
ciple of operation of the NDIR and CL instruments and associated sources of error will be briefly
reviewed. Then the results of NDIR/CL comparisons will be summarized to seek a method of expressing
emissions on an ''equivalent instrument" basis.
3.1.2.1 NDIR Instrumentation
The NDIR instrument was introducted nearly 20 years ago and has continued to be used widely
as a CO and COp detector. In addition, it was used extensively to detect NO, HC, and SO,,, but other
methods are now supplanting it for these species. Its principle of operation depends upon absorption
of infrared radiation by the gaseous sample. Figure 1 illustrates a typical NDIR instrument. Built-
in optical and gaseous filters are used to produce a narrow infrared beam bandwidth to compensate for
interference (absorption) by other constituents.
Despite these precautions, water vapor and COp, to some extent, may cause positive interfer-
ences (high readings) even though refrigerant and chemical driers are used to remove water vapor.
11
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TABLE 3. INSTRUMENTS USED BY MANUFACTURERS TO MEASURE NO EMISSIONS
A
ro
Manufacturer
Colt
Cooper Energy
De Laval
Ingersoll-Randa
Waukesha
White Superior
(Div. Cooper Energy)
White-Alcoa
GMC/EMD
CL (with Thermal Converter)
NO/NO
A
Thermo Electron 10A
Thermo Electron 10A
Scott 125
Scott 125
Scott 125
Scott 125
NDIR/NDUV
NO, N02/N02
NO: Beckman
IR 18A
NO: Horiba
AIA-2
NO/Beckman 31 5B
N02/Beckman 255
Electrochemical
N0/N02
Envirometrics NS-200
NO: Dynasciences NX-130
N02: Envirometrics NS-200
Measurements made by Scott Environmental Technology Lab.
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Infrared
source
Reference
cell
OJ
Recorder
signal
Diaphragm
distended
Sample out
— Component
of interest
O —Other molecules
Control unit
Figure 1. Nondispersive infrared absorption analyzer.
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Desicants, however, have been found to cause significant interferences as well as water vapor (see
later discussion and Section 3.1.3). In addition to these problems, the response of the NDIR instru-
ment to the specie of interest is nonlinear in some instrument designs, necessitating a carefully
constructed calibration curve using at least four, and preferably six to eight, calibration gases.
3.1.2.2 Chemiluminescent Analyzers
Chemiluminescent analyzers, in contrast to NDIR instruments, have been developed only recently
(1971) for source sampling. Nevertheless, the CL instrument has gained increasing application for
the measurement of NO (NO + N02) and NO. In this type of instrument ozone, Og, is reacted with
nitric oxide, NO, to produce a chemically excited state of NO*, which emits light as it decays to
stable NO,,. The intensity of this emitted light is proportional to the NO concentration present in
the sample. The analyzer uses a photomultiplier to detect the light.
Figure 2 is a schematic of a CL analyzer and illustrates the reaction of ozone with NO in the
reaction chamber of the instrument. The instrument is easier to calibrate than some NDIR's due to
its linear response to NO, and thus requires fewer calibration gases. Note that a N02 -* NO con-
verter is depicted in Figure 2. This device consists of a stainless steel tube which is heated to
~1200°F and essentially converts all N0? in the sample to NO. In this way just NO or both NO and
N02 can be measured, depending on whether the sample gas is fed directly to the reaction chamber or
passed through the converter first. The N02 level is then deduced by subtracting the NO level from
the total NO reading.
Potential problems encountered in this instrument include quenching of the excited N0? by
other species, converter inefficiencies, and interferences caused by chemiluminescence of other gases.
In general, quenching (by C02 or H20) is negligible in CL instruments; water is removed from the
sample before analysis and the use of low pressure (vacuum) reaction chambers reduces quenching by
C02. Some quenching problems have been observed during measurement of fuel-rich automotive exhausts.
Quenching effects, however, have not been observed during measurements on truck-size diesels, whose
exhausts are similar to those of large bore stationary engines (i.e., -15 percent oxygen).
Converter problems are avoided by thermal conditioning of new converters and by making regular
checks of converter efficiency (>90 percent). Interferences are minimized by the instrument manu-
facturer through the choice of spectral filters and photodetectors.
3.1.2.3 Sources of Instrument Error
Sources of error for each of the instruments listed in Table 3 are summarized in Table 4.
Note that neither the quenching effect nor the converter problems of the CL analyzer should occur
14
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en
Sample gas
Photo-
multiplier
tube
N02 * NO
Converter
Ozone
1
-- L"ht
Principle of Operation
NO + 03 - NO* + 02
NO* •+ N09 + hv (Light)
$ c. f-
o
<
Vent (to vacuum source)
Reaction chamber
Figure 2. Chemiluminescent analyzer.
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TABLE 4.
SOURCES OF N0x INSTRUMENT ERROR
Chemil uminescent,
N0/N02
• Quenching of CL by
third body reactions3
(C02, H20)
• N0,/N0 converter13
L.
- NOX -* Ng at high
temperature, low
02, high CO and HC
— N02 •* NO incomplete
due to improper
converter condi-
tioning
- NH3 -* NO, N02
at high temperature
especially with
some catalytic con-
verters in rich ex-
hausts
- N02 ->• NO at low
temperatures, low 02
NDIR, NOC
• Water vapor in-
terference causes
higher NOX readings.
Also COg inter-
ference to some
extent; optical
filters and water
removal minimize
interferences
• Use of chemical
driers lead to
N02 adsorbtion
and N02 * NO
conversion
• Calibration curve
non-linear, requires
frequent checks us-
ing 4 to 6 calibra-
tion gases
NDUV, N02d
• Interference caused
by carbon particles
and other species ,
results in a drift-
ing, high reading.
Electrochemical ,e
N0/N02
• Not much appl i ca-
tion in source
sampl ing
• SOg interferences
• Nonlinearity in
30 to 300 ppm
range
• Susceptible to
error due to
temperature
changes
aNot present in properly designed instruments. (See References 7, 8, 9.)
Condition CL converter to avoid error; perform regular converter efficiency. Most of these errors occur
in rich exhausts unlike the lean exhausts (~15 percent oxygen) of large bore engines. (See References 4,
10.)
cSee References 5 and 10
See Reference 10
eSee Reference 11
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when measuring large bore engine exhausts with a properly operated and maintained CL analyzer. Pres-
ent NDIR analyzers, on the other hand, are susceptible to errors due to interference despite sample
conditioning to remove water. This interference combined with the relative ease of operation and
accuracy of CL analyzers has led to an increasing perference of CL's for NO measurements. As an
X
example, EPA's proposed revisions to the Heavy Duty Diesel and Gasoline Engine Sampling Procedure
specify CL analyzers. The following section summarizes comparisons of CL and NDIR/NDUV measurements
of N0x- These comparisons will be the basis for expressing NDIR/NDUV measurements as equivalent CL
levels.
3.1.2.4 Correlations of CL to NDIR/DNUV
As discussed above, NDIR analyzers are subject to water vapor interference despite sample
conditioning to remove water vapor. These interferences cause the instrument to indicate higher
N0x levels than are actually present. A comprehensive study conducted by TRW (with Scott Research
Labs) using constant volume sampling (CVS) of automative exhausts determined that
[NO]NDIR = 1.07 [NO]CL - 4.2 (1)
where [NO] denotes NO concentration in ppm (Reference 5). Both analyzers had similar water removal
systems (condenser and chemical driers); hence, the difference was due to a gas interference only.
In addition to this finding, the study established that chemical driers promoted NO,, -*- NO conversion.
Comparison of an NDIR with water removal to a CL without water removal indicated that
[NO]NDIR 1.12 [NO]CL+ 8.4 (2)
Furthermore, a comparison of two CL analyzers, one (CLg) preceded by a water trap and chemical
drier and the other (CL.) without either, indicated that
[NOxJ = .873 [N0x] '* 6.6 (3)
13 M
Thus, the net effect of the drier and water trap is to destroy about 12 percent of the NO in the
X
sample.
The results of this study and others that corroborate these effects are summarized in Table 5.
The bias of NDIR analyzer ranges from 3 to 30-percent higher based on these studies. As this table
indicates, the particular correction that applies to any one of the three manufacturers that used an
NDIR analyzer (and NDUV for N02) will depend on their sampling setup and procedures (e.g., type and
location of water trap, and the NO, present). Therefore, the appropriate correction for NDIR instru-
ment bias will be identified after a discussion of each manufacturer's sampling practices.
17
-------
TABLE 5. COMPARISON OF CL AND NDIR, NDIR/NDUV MEASUREMENTS
Source
TRW Study
(Reference 5)
Clemens Memo
(Reference 12)
SAE 750204
Phase IV
(Reference 3)
SAE 730213
(Reference 6)
CRC Report #487
(Reference 4)
Comparison
N°xCL/N°xNDIR/NDUV = '82
NOxCL/N°xNDIR/NDUV = "75
NOxCL/NOxNDIR = '9
(NOCL/NONDIR = '88)
NOCL/NONDIR = .77
N°xCL/N°xNDIR/DUV = *94
N°xCL/N°xNDIR = "985
Comments
No water removal from CL sample.
Water trap and drier used for both CL and NDIR.
Used TRW comparison for NO (no water removal for CL)
and assumed that N02 was 2 percent of total NO in a
diesel exhaust. x
Result questionable due to other sampling errors.
None of eight large-bore manufacturers used DUVa
instrument.
NDIR instrument is "third" generation, low interfer-
ence analyzer, not comparable to NDIR's used by
large-bore manufacturers.
co
Dispersive Ultraviolet
-------
3-1-3 Variations in NOX Levels Related to Sampling Procedures
In addition to the choice of instrumentation, differences in sampling procedures can cause
variations in reported emission levels. This was clearly illustrated in Table 2 for the Phase IV
cooperative tests where 15 laboratories made measurements of an identical source. Since four basic
sampling procedures (DEMA, SAE, EMD, EPA) were used by the eight large bore engine manufacturers,
some variation between their reported emission levels can probably be attributed to differences in
their sampling practices. The sources of these errors will be identified and the four sampling pro-
cedures compared and evaluated in this section.
3.1.3.1 Sources of Sampling Error
The two major problems encountered in measuring engine exhausts are: (1) chemical changes
that occur during transfer of the sample to the analyzer, and (2) error due to improper operation of
the analyzer. Figure 3 is a simple schematic of an engine sampling system. In transferring the ex-
haust gas sample to the analyzer, care must be taken to ensure that all of the NO (NO + N02) or NO
(when only an NDIR is used) originating from the engine exhaust reaches the analyzer. For these
reasons sample lines are heated to prevent condensation or kinetic conversion of constituents. High
sample flowrates (short sample residence times) are maintained to minimize sample degradation during
its transfer from the engine to the analyzer, and water removal devices are employed to minimize
instrument interferences from water vapor. Similarly, it is important that the analyzer be calibra-
ted and all components, such as NO^^NO converters (on CL instruments), be functioning properly.
Therefore, adequate analyzer specifications and calibration procedures are essential for accurate
emission measurements.
Table 6a presents a more detailed summary of sources of sample transfer error. As this table
indicates, heated sampling lines coupled with low sample residence times are essential to preserve
the initial amounts of NO and N02 contained in the sample gas. Furthermore, leak checks of the en-
tire sampling system (particularly on the vacuum side) should always be performed to assure that the
sample gas reaches the analyzer undiluted. Water removal is required with NDIR analyzers; therefore,
care must be taken to minimize the time available for NO to be converted to N02 which can then be
absorbed by the condensed water from the sample gas. Chemical driers (desiccants) are an unacceptable
water removal device since they promote the NO,, -*• NO reaction and absorb N02 (see Section 3.1.2).
Table 6b summarizes important analyzer related procedures required for accurate measurements.
Care must also be exercised in operating emission measurement instruments. Frequent calibrations
should be performed using accurate, certified blends of calibration gases. Zero and span checks
19
-------
Sample Line
1N5
O
Exhaust
Probe
Enqine
Water
Removal
NO Analyzer
A
Figure 3. Schematic of exhaust sampling system.
-------
TABLE 6a. SOURCES OF SAMPLING ERROR: THE SAMPLE TRANSFER
Sampling System
Source
Error
Correction
t Unheated
sampling line
• Large sample
residence times
• Sample line
connections and
fittings
• Water removal
— Refrigerant
— Chemical
drier (desiccant)
NO •* N02i N02 adsorbed
during water removal:
Observed 40-percent
loss of NO when sample
residence times were
35-40 sec (Reference 13)
Heated Line: N02 ad-
sorbed during water re-
moval : 6-7% NOy loss
for system response
times9 greater than
35 sec (Reference 13)
Cold Line: 12-percent
NOX loss for sample
residence time of
13 sec (Reference 14)
Leaks that dilute sample
gas: Observed 25-percent
loss of NOv due to pre-
filter leak (Reference 13)
2 adsorbed in condenser;
NO
(Reference 5)
N02 -> NO and drier "eats"
N02« Negative or positive
errors with cold lines
(SAE procedure) depending
on how drier conditioned
(Reference 5 and 13)
Heat line to 375°F
Use short sample line
and/or flowrates to
limit system response
to 15 sec or less.
Leak check system be-
fore testing
CL: Locate condenser
after converter.
NDIR: Maintain high
sample flow through
condenser, remove
H20 as it forms.
Do not use chemical
driers
System response time = sample residence time + instrument response time
21
-------
TABLE 6b. SOURCES OF SAMPLING ERROR; INSTRUMENT RELATED
Instrumentation
Source
Error
Correction
• Instrument drift,
ozone shortage (CL),
plugged capillary
• Converter
malfunction (CL)
t Visual rather than
stripchart readings
t Calibration and
span gases
Low NO readings
/\
Not all N0£ converted to
NO, results in low NOX
reading also possible for
NO to exceed NOX levels
Analyzer meter only ac-
curate to ±3 percent.
Visual averaging less
consistent than chart
averaging (Reference 13)
Change of constituents
with time, or erroneous
certification
Calibrate instrument
frequently. Zero and
span before and after
each measurement for
all instrument ranges.
Instrument should meet
minimum performance
criteria.
Perform converter
checks regularly. Use
known standard to check
converter efficiency.
Use stripchart, aver-
age levels over an
interval for which
steady state condi-
tions exist.
Use certified gases of
specified blends.
Cross-check span and
calibration gases.
22
-------
also serve to indicate potential instrument problems as well as necessary gain adjustments. Span
gases should be frequently cross-checked with calibration gases or checked against a NBS standard
since even certified gases can be in error.
Some calibration curves for NDIR analyzers are nonlinear; therefore, several calibration gases
(minimum of four) should be used to calibrate the instrument (Reference 13). These instruments also
experience some hysterysis after sitting unused; therefore, frequent calibration is necessary. Also,
calibration points should be curve-fit using a higher-order polynomial. In addition, efficiencies
of N0x converters (on CL analyzers) should be checked regularly. Finally, strip chart recordings
of data are superior to visual analyzer meter readings since a permanent record is produced, and
emission levels can be averaged over a time interval more accurately and consistently.
3.1.3.2 Sampling Procedures: EPA, DEMA, SAE, EMD
Having completed this brief review of sources of sampling error, we can examine each of the
four measurement practices presently used by the eight large bore engine manufacturers. Table 7 is
a comparison of the EPA, DEMA, SAE, and EMD emission measurement practices (References 15, 16, 17,
and 18). The information for the EPA procedures is based on the revised EPA Heavy Duty Diesel Emis-
sions Regulations as proposed in the Federal Register, Volume 41, No. 101, May 24, 1976. This re-
vised procedure requires CL analyzers for NO/NO measurement, establishes instrument and calibration
X
specifications, and defines sample transfer configurations and practices.
This comprehensive EPA regulation was recently verified through cooperative testing by both
manufacturers of mobile diesel engines and the EPA-Ann Arbor mobile sources laboratory (Reference 4).
The six participants in this program (see Section 3.1.1) made essentially equivalent NO measurements
for a series of eight tests. Two participants, however, did experience a small, but consistent NO/NO
crossover (NO levels greater than NO levels). Nevertheless, the standard deviation of measured NO
x x
levels was generally small, ranging from 2 to 4 percent (of the mean level). Therefore, the EPA
practice will be the basis of comparison for the other measurement practices.
The potential sources of measurement error of the other three procedures (OEMA, SAE, and EMD)
are summarized in Table 8. The sampling trains for these three procedures, as well as the EPA setup
are illustrated in Figure 4. The DEMA procedure specifies a CL analyzer and the SAE/EMD procedures
require an NDIR instrument. The EMD practice also utilizes an NDUV analyzer, in series after the
NDIR, to measure NO,, in the sample.
Table 8 clearly indicates that there are several sources of measurement error possible for the
DEMA procedure, largely as a result of its failure to define instrument and sample transfer practices.
23
-------
TABLE 7. COMPARISON OF SAMPLING PRACTICES
Test Procedure
DEMA: No time between modes specified
EPA: 5 minutes
SAE: 20 minutes
EMD: 30 minutes
DEMA: Data recorded and averaged over 10 minutes
EPA: Data recorded over last 2 minutes
SAE: Data recorded over last 5 minutes
EMD: Data recorded over last 3 minutes
Instrument Calibration - DEMA and EPA are CL; SAE is NDIR; EMD is NDIR/NDUV
DEMA: Analyzers calibrated semimonthly. No details of calibration given.
EPA: Check NOX converter once per week (must be at least 90-percent
efficient); leak check system, calibrate analyzer, check sample
line residence time, and quench check every 30 days
SAE: Calibrate monthly
EMD: Checked and calibrated monthly, semiannually and annually
DEMA: Number of calibration gases not specified
EPA: Span analyzer with calibration gases having nominal concentrations
of 30, 60, and 90 percent of full scale concentrations
SAE: Use calibration gases that are 25, 50, 75, and 100 percent of
instrument range used.
EMD: Use 4 calibration gases
DEMA: No specifications for calibration or span gas blends and dilutents
EPA: Blends and dilutents specified and accurate within 2 percent of
true concentration or traceable within 1 percent of NBS blends.
Span gas traceable to within 1 percent of calibration gas.
SAE: ±2 percent accuracy on gas analysis certification
EMD: ±2 percent accuracy blends and dilutents defined by EMD
DEMA: No analyzer specifications required
EPA: Specifications for response-time, precision, noise, zero and
span drift, and linearity
SAE: Accuracy should be ±2 percent full-scale deflection or better
EMD: Same as SAE
24
-------
TABLE 7. Concluded
Sample Transfer
DEMA: Stainless steel (S.S.) probe, configuration not specified
EPA: Specifies number and size of holes in S.S. probe
SAE: S.S. probe, no configuration specified
END: S.S. probe, configuration specified
DEMA: Sampling line material not specified
EPA: Stainless steel, teflon, or proven inert
SAE: Stainless steel or teflon after exhaust cooled
EMD: Stainless steel
DEMA: Line heated to 200°F for NOX (375°F for HCy)
EPA: 375°F + 18°F - 9°F
SAE: Unheated
EMD: Unheated
DEMA: No sample line length specified
EPA: <50 feet or sample line residence and instrument response time is
less than or equal to 15 seconds
SAE: No length specified
EMD: No length specified
DEMA: Chemical driers can be used
EPA: Not allowed
SAE: Refrigerant and chemical drier specified
EMD: Same as SAE
DEMA: Recommend water removal at probe or at analyzer before N02 -> NO converter
EPA: Condenser at analyzer after converter
SAE: Condenser and drier before analyzer
EMD: Same as SAE for NDIR. NDUV does not use water removal.
25
-------
TABLE 8. SOURCES OF ERROR FOR DEMA, SAE, EMD EMISSION PRACTICES
DEMA (CL)
ro
CJ1
• Unheated sampling lines permitted
• No specification of sample residence
time in sampling line, or system re-
sponse time
• Leak checks are not specified
f Water removal device can be located
at analyzer, but before F^-^NO
absorption in water trap
• Chemical driers permitted
• No instrument specifications
• Converter efficiency checks not
specified
t No calibration procedures specifed
• Calibration and span gas specifica-
tions not defined
EMD (NDIR/NDUV)/SAE (NDIR)
• Unheated sample lines
0 No sample residence or system
response time specified
• Leak checks not specified
0 Allow chemical drier
0 Calibration procedures not specific
(e.g., what constitutes out-of-
calibration, how calibration points
are curve fit, etc.)
0 Calibration and span gas blends and
dilutents not specified by SAE.
EMD has "own" specifications.
-------
EPA-HD Diesel and Gasoline (Proposed) Regulations
nnfififlfifiy N°;
UUUUUUU/V con
-* NO j
verter J
50' or sample residence +
instrument response time <15 seconds
EMD and SAE J-177 Recommended Practices
Sample line
(Not heated)
Li
Fi Itrr »•- . -- .
CL
00
O
O
NDIR
ro
DEMA SETUP
(Near Probe)
Condenser
Sample line not heated
No length specified
Filter
>
" NO
Converter
CL
" -QQQQ/
Heated 200"F *
10°F no length specified
Condenser
- NO
Converter
>
CL
Figure 4. Sampling practices,
-------
Its most obvious shortcoming is the potential degradation of the NO and N02 in the sample gas as it
passes from the probe through an unheated sample line (of unspecified length) and condenser before
entering the CL analyzer High residence times would also promote N0x loss for this configuration.
One large bore engine manufacturer demonstrated that the sample residence time must be less than
3 seconds to prevent significant loss of N02 in the sample (12-percent loss for a 13-second residence
time) as it passed through a cold sample line and condenser (see Table 6).
Similarly, SAE and END practices can also lead to a loss of N0x as the sample passes through
an unheated sample line, a condenser, and a desiccant before reaching the analyzer. As discussed
previously, the desiccant converts NOp to NO and absorbs NOg.
Comparisons of the SAE sampling train with the proposed EPA train indicated that SAE measured
concentrations of NO are understated by 15 to 40 percent during the first few measurement modes of
the federal 13-mode composite cycle, then are equal in the seventh or eighth modes, and finally are
overstated by about 10 percent in the last modes (Reference 13). These results and the study con-
ducted by TRW suggest that the desiccant requires a period of time to equilibrate. If a new drier
were used before each 13-mode test (permissible under present EPA regulations), NO levels would tend
to be low (since levels would be understated until the drier had equilibrated, possible not until
the last, rated speed, low power modes were being measured). If the drier was not replaced, or if
it was preconditioned, the NO levels would tend to be overstated. This is probably the case for
those large bore engine manufacturers who used driers, since their engines are typically operated
about an hour before they are stabilized and measurements are begun.
The EMD procedure is similar to the SAE procedure with the exception that both NO and NO- are
measured using NDIR and NDUV analyzers. Results from Reference 5 based on automotive exhausts indi-
cated that NDIR/NDUV N0x measurements were about 20-percent higher than CL readings (no water removal
for CL sample). Apparently, the positive biases (interference and drier) more than offset potential
N0x loss due to the cold sampling in that study. In addition to the positive NDIR biases, NDUV
analyzers have a history of stability problems, usually manifested as a drifting (high) reading.
One study attributed this error to interference due to carbon particle buildup (see Reference 10).
3.1.3.3 Summary and Conclusion of DEMA, SAE, and EMD Practices
In summary, it appears that the DEMA practices will generally lead to negative errors due to
N0x loss in transporting the sample from the engine to the analyzer. At this time the absolute error
associated with this practice is unknown relative to the EPA procedure. Limited results (see Table 5)
28
-------
suggest this error could be as much as -10 to -15 percent depending on the amount of N0? in the
sample (estimated to be 2 to 10 percent of the total NOV) and the extent that NO is converted to NO,
X c,
during the sample transfer.
The positive bias of the SAE procedure gives a +12-percent error in the NO reading. The EMD
procedure, which measures both NO and N02 causes a +20-percent error in the NO reading. Nevertheless,
both procedures could experience as much as a -40 percent error in the NO or NO reading if the
chemical drier has not stabilized. Thus, the uncertainties in N0x measurements for the SAE and EMD
practices appear to be significantly greater than the DEMA practice.
Finally, the EPA procedures defined for the heavy duty diesel engines are clearly superior to
the other three procedures. This practice appears to have minimized the various sources of measure-
ment error and should give more accurate and consistent NO readings. Therefore, each of the manu-
facturer's sampling practices will be evaluated in the following section by comparing it to the EPA
procedure.
3.1.4 Comparison of Manufacturer's Measurement Error
Table 9 summarizes each manufacturer's practice in terms of procedures that could lead to
measurement error. Note that three of the four DEMA manufacturers using cold sample lines have lo-
cated their water traps near the analyzer instead of at the engine as is recommended in the DEMA
practice. Therefore, this setup will promote additional loss of NO in the exhaust sample. In
X
addition, Colt and Waukesha have relatively high sample residence times which will also promote
NO loss.
X
The potential errors in measurement resulting from these practices are estimated in Table 10
relative to the EPA procedure. (Blanks appear in Table lOfor items which do not apply to a particu-
lar manufacturer.) These errors are depicted for each manufacturer in Figure 5. Errors due to sys-
tem leaks are not included in the figure since this error cannot be generalized. Also, the error
bands were constructed assuming that errors of the same sign were additive. Note that these uncer-
tainties substantially exceed the 4-percent scatter in NO levels observed during verification tests
X
of the EPA procedure.
NDIR and NDIR/NDUV instrument biases have been included in this figure and are based on the
TRW study (Reference 5). Note that the potential negative 40-percent error of Table 10 is not included
in Figure 5 since the manufacturers generally operate the engine long enough before measurements are
taken to condition the drier. As the data for Waukesha indicates, sampling errors can be as large as
instrument bias; although in the case of the Cooper and 6MC/EMD data, instrument biases predominate.
29
-------
TABLE 9. LARGE BORE ENGINE MANUFACTURER'S SAMPLING PRACTICE
Practi ce/
Manufacturer
DEMA (CL)
Colt
Cooper
Delaval
White Superior
SAE (NDIR)
Waukesha
Cooper
EMD (NDIR/NDUV)
GMC/EMD
EPA (CL)
White/Alco
Ingersoll-Rand
Sample Line
Heated
No
No
No
Yes
No
No
No
Yes
Yes
Length, ft
20
20
33
30
33
18-75
40
60-80
60
Residence
Time, Sec
14
3
2
4
-15
<3
6
6-8
6
Water Removal
Refrig
Yes
Yes
Yes
Yes
Yes
Yes
Yesa
Yes
Yes
Drier
Yes
Yes
Yesa
Location
Before
Analyzer
Before
Analyzer
Before
Analyzer
Before
Analyzer
Before
Analyzer
Before
Analyzer
Before
Analyzer
After
Converter
After
Converter
Data
Recording
Stripchart
Visual
Visual
Visual
Stripchart
Visual
Stripchart
Stripchart
Stripchart
Leak
Check
Yes
No
No
Yes
No
No
Yes
Yes
Yes
Converter Eff.
Check (CL)
2/yr
No
No
?
--
--
--
Yes
Yes
aEMD measures N0? with NDUV. No water traps are used.
-------
TABLE 10. MANUFACTURER'S SAMPLING ERROR AS A PERCENT, RELATIVE TO EPA PROCEDURE
Manufacturer' s
Practice
DEMA
Colt
Cooper
Delaval
White Superior
SAE
Waukesha
Cooper
EMD
GMC/EMD
Sampling
Cold line, large
residence time
-12a
-12a
Water trap before analyzer
Cold lineb
-5
-5
-5
-5
-5
-5
Hot line
<-5c
Leak
Checkd
-25
-25
-25
-25
Recording6
±3
±3
±3
NDIRf
and
Drier
NDUV
<-40
1+10
f-40
-40
+20
Converter
Check9
i-
aPotential loss of NOx based on Data from Reference 14.
bAssumes that five percent of NO converted to N02 and lost in water trap. Based on data
from Reference 12.
cLoss assumed to be less than five percent since heated sample line used.
dLoss cannot be generalized. Twenty-five percent loss based on one example reported in
Reference 12.
eBased on Reference 12.
Errors based on Reference 12. Forty percent error for unconditioned driers.
9Failure to perform converter checks could result in understated NOx values due to
incomplete conversion of NOg to NO.
-------
OJ
ro
100 X
+20-
+10-
NO observed \
NO correct 7
/
-10-
-20-
-30-
-40-
-50-
Mfg
Practice
55 - <
@ H @ ca H "" £3
^••J ~~~
Colt Cooper Del aval Superior Waukesha Cooper GMC/EMD
DEMA SAE EMD
Does not include potential error due to system leaks, and assumes chemical drier is conditioned.
Figure 5. Measurement error relative to EPA procedure.1
-------
Conclusions
The above analyses of instruments and measurement practices suggest the following conclusions
about the reported data:
• The exhaust data which were reported using the DEMA, SAE, or EMD practices should be
banded by the appropriate uncertainty level. In general measurement uncertainties are
expected to range from -15 to +5 percent for DEMA data and -20 to +20 percent for the
SAE/EMD data.
• Waukesha's data should not be used for setting numerical values of a standard since: (1)
only NO was measured, (2) other significant sampling problems could have been present,
and (3) the amount of N0~ in the exhaust was unknown so that correction of NO to NO + N0«
would be speculative.
• The Ingersoll-Rand and White-Alco exhaust emissions data appear to have the least measure-
ment error (±5 percent) since their sampling procedure was essentially identical to the
EPA procedure. The previous analyses also lead one to conclude that the EPA practice is
the best existing sampling procedure and should be used as a guideline when stipulating a
measurement procedure for an NSPS. Both the DEMA and SAE/EMD practices require better
and more carefully specified sampling procedures. In addition, the NDIR/NDUV instrument
bias relative to CL instruments is so large that it yields unacceptable measurement uncer-
tainty. Cooperative testing of the revised EPA procedure indicate that measurement un-
certainty using the best sampling procedures is about ±5 percent.
3.2 EFFECT OF AMBIENT CONDITIONS ON NO
Previous studies have recognized that variations in ambient conditions can significantly af-
fect observed exhaust emissions, particularly NO levels (References 6 and 19). As a consequence,
EPA has adopted ambient correction factors for regulated mobile sources based on experimental studies
These factors are used to correct observed NO levels to values at a standard temperature (85°F) and
humidity (75 grains FLO/lb dry air) for heavy duty (HD) diesel engines and to correct to standard
humidity, only, for both heavy and light duty gasoline vehicles (References 20 and 21). Since NO
emissions from large bore engines will also depend on ambient conditions, these data should also be
corrected to standard conditions.
Although the eight large bore engine manufacturers provided ambient conditions (barometric
pressure and inlet air temperature and humidity) for much of their emission data, none of them re-
ported emission data for a given engine operated under varying ambient conditions. Thus, at this
33
-------
time it is not possible to directly derive ambient correction factors for large bore engines. Never-
theless, the response of these large bore engines to changes in ambient conditions may be similar to
that observed in the smaller bore diesel and gasoline engines for which ambient correction factors
have been developed. Therefore, the discussion in this section will evaluate the applicability of
existing ambient correction factors to large bore engines. It will also examine the potential ap-
plication of gas turbine correction factors and analytically derived expressions.
Section 3.2.1 will discuss variations in N0x levels resulting from ambient differences and the
reduction in data scatter after applying ambient correction factors developed for smaller bore diesel
and gasoline engines. Then, in Section 3.2.2, the existing correction factors and potential ana-
lytical expressions are evaluated in detail and appropriate correction factors are selected to cor-
rect the emissions data from the eight large bore engine manufacturers of this study. The results
obtained after applying this correction to the uncontrolled data base are summarized in Section 3.2.3
and further recommendations are made for ambient correction factors for large bore engines.
3.2.1 Effect of Ambients on NOX Emissions from 1C Engines
Enforcement of NO emission standards for mobile 1C engines must rely on ambient correction
factors to adjust NO measurements to standard ambient conditions, since the observed levels may
differ considerably from levels that would be measured at standard atmospheric conditions for which
control standards are set. Several studies have shown the effect of ambient humidity on NO emis-
X
sions (References 22, 23, and 25).
Figure 6 taken from one of these studies, illustrates the variation in specific humidity each
month during the year 1969 for Dearborn, Michigan. For this area, ambient humidity varied from 20
to 120 grains H20/lb dry air over the year. The effect of this variation on NO emissions is shown
in Figure 7 using the correction factors that have been derived from experimental work for gasoline
and diesel engines. The N0x levels are shown to deviate as much as 25 percent from levels measured
at standard conditions. Moreover, the correction factors used vary significantly as well, depending
on the particular study and type of emission source.
Variations in ambient temperature have also been shown to affect NO emissions. This effect
X
is illustrated in Figure 8 and ranges from 5 to 25 percent depending on the particular study. Al-
though the effect for diesel engines is not as large as that produced by ambient humidity variations,
the change in brake specific emissions (g/hp-hr) can be significant. This is particularly true for
some large bore spark ignition engines, which emit as much as 20 g/hp-hr. For these sources a 5-
percent ambient correction means a change in the reported level of about 1 g/hp-hr.
34
-------
Variations in barometric pressure also can be expected to affect NO emission (References 22
and 26). Only one study, however, has evaluated this ambient variation (Reference 22). This in-
vestigation used carbureted gasoline engines and found NO variations of as much as 40 percent due
X
to changes in ambient pressure. These changes were attributed largely to variations in A/F ratio
in the carbureted gasoline engines. However, a correction factor for this effect could not be de-
rived for the different carbureted engines because each engine's emissions response to changes in
barometric pressure was too inconsistent to generalize a correction.
Despite the lack of a quantifiable correction for changes in ambient pressure, several studies
have shown that scatter in emissions data taken at different ambient humidities and temperatures can
be reduced, significantly, by applying the appropriate correction factors. For example, Figure 9 il-
lustrates the reduction in data scatter that is achieved with emissions from HD gasoline engines by
correcting for humidity only. The average standard deviation from the six engines was reduced by
a factor of about six by the use of a correction for humidity.
Figure 10 illustrates a similar result for ambient temperature and humidity correction of
diesel engine emissions. The average scatter after correction was reduced to about one third of the
scatter before correction. Note, that in absolute terms, the reduction in scatter for diesel engines
was smaller (-0.5 g/hp-hr) compared to the reduction for gasoline engines (~1.5 g/hp-hr). Both
studies, nevertheless, indicate that scatter in emissions data can be reduced significantly, by cor-
recting observed NO levels to standard conditions.
3.2.2 Selection of Ambient Correction Factors for Large Bore Engines
As stated previously, ambient correction factors have been developed for automobile and truck
size gasoline (SI) and diesel (CI) engines. The following sections will discuss the application of
the existing SI factors to natural gas engines and the existing CI factors to large bore diesel and
dual fuel engines. In addition, gas turbine ambient correction factors will be examined for applica-
tion to large bore engine emissions. As these sections will illustrate, no satisfactory ambJent
temperature correction factor has been developed J^_ajiy__sj^j:^rTjI_jji!£rJiaJ—CM^
only one study has considered ambient temperature corrections for CI engines.. Therefore, Section
3.2.2.4 will discuss an analytical approach to correct emissions for variations in ambient temperature,
3.2.2.1 Ambient Correction Factors Developed for SI Engines
A survey of the literature showed that correction factors for gasoline-fueled engines have
been developed only for ambient humidity variations (Reference 19). One of the studies also evalu-
ated the effect of ambient temperature and barometric pressure variations on exhaust emissions, but
35
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ro
TD
o
Q.
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QJ
CL
OJ
fO
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cn
-o
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140'
120-
100-
80-
60-
40 -J
20 -J
i i i i i i I I I i i i
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 6. 1969 humidity range in engine test cells, Dearborn, Michigan
(from Reference 24).
36
-------
O)
-p
(J
O)
1-
o
O
CO
03
1.0 for humidity >75 grains/lb dry air.
'From Reference 19.
'From Reference 20.
Figure 7. Effect of ambient humidity on 1C engines NOX emissions.'
-------
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1.5 .
-o
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(D (-1-
• .90 °- g.
- .80
Natural gas engine
aBased on range of ± 30°F from standard temperature of 85°F. K >1 for temperature
less than 855F.
Reference 6
cBased on change in NOX emissions with manifold inlet temperature. Assume change
in ambient is equal to change in manifold temperature. From Reference 26.
Figure 8. Effect of ambient temperature on 1C engine N0x levels.
-------
GO
2.0 -
s_
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o.
-C
CD
C
o
> 1.0
ro
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A Average
Before Ambient Correction
After Ambient Correction
11
12
NO Level, g/hp-hr
X
13 14
a
15
16
aAverage level (Federal. Test Cycle Composite) for four ambient humidities; 30, 45,
75, 120 grains/lb dry air.
Figure 9. Effect of humidity on emissions scatter for six HD gasoline
engines (Reference 22).
-------
s_
_c
Q.
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Dl
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o
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03
OJ
Q
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Before Ambient Correction
After Ambient Correction
1
5.2
2
7.3
3
7.6
4
7 A
5
9.5
6
13.3
Engine #
NOX Emission,
g/hp-hr @ 75 grains/
Ib. dry air, 85°F,
29.92 inches Hg.
For Federal 13 mode composite cycle for HD diesel engines.
Ambient humidity varied from 35 to 125 grains/lb dry; temperature from 70 to 115°F.
Figure 10. Effect of humidity and temperature on emissions scatter for six
HD diesel engines13 (Reference 6).
-------
found that engine-to-engine variations were too great to generalize a correction factor for either
temperature or pressure (Reference 22). These studies will be briefly discussed in the following
paragraphs, and then the ambient humidity correction factors will be compared and evaluated for ap-
plication to the large bore natural gas-fueled engines in this study.
The Automobile Manufacturer's Association contracted with the Ethyl Corporation to conduct a
study on the effect of ambient air humidity, temperature, and pressure on heavy duty (HD) gasoline
engines (Reference 22). The results of this study for the effect of humidity later became the cor-
rection factor designated in the Federal Register for HD gasoline engines (Reference 20).
This correction factor was derived from emission measurements conducted on seven engines in
accordance with the Gasoline Fueled Heavy-Duty Engine procedures in the 1970 Federal Register. The
test engines were installed in an engine dynamometer test cell where humidity, temperature, and
pressure were varied. The engines tested were gasoline fueled, spark ignited, carbureted, heavy duty
truck engines ranging in size from 38 to 75 CID per cylinder. The compression ratios varied from 7
to 9.4, and air-to-fuel ratios varied from 14.4 to 15.7. The objective of study was to develop fac-
tors to adjust composite mass emissions to a standard condition of 75 grains H^O/lb dry air, 90°F
inlet air temperature, and a barometric pressure of 29.92 inches of mercury.
Figure 11 illustrates the effect of humidity on both A/F ratio and NO emissions (Federal 9
mode composite cycle). As this figure illustrates, a reasonably good correlation was established
between changes in ambient humidity and NO emissions. Note also that A/F ratios are essentially
constant or decrease slightly with increasing inlet air humidity. The ambient correction factor was
of the form
K = 0.634 + 0.00654(H) - 0.0000222(H)2 (1)
where N0x corrected = N0x observed
H = specific humidity, grains H20/lb dry air
Figures 12 and 13 illustrate the effect of temperature and pressure on A/F and N0x emissions
for these same engines. Obviously, engine-to-engine variations were too great to generalize a cor-
rection factor for either temperature or barometric pressure.
Both physical reasoning and these results indicate that changes in ambient temperature and_
pressure affect the A/F ratio more than do changes in humidity. Moreover, it is well known that the
effect of A/F ratio variations on NO emissions depends on the engine operating point on the N0x vs.
A/F curve (see Figure 14). For example, a decrease in A/F ratio for an engine operating at A in
41
-------
o
4->
14—
1_
s
14
13
16
15
14
16
15
14
16
15
14
16
16
Q 1 1 1 |
8 — —
Engine 1
till
i
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i
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Engine 2
i i I i
I
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Engine 5
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it;
14
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w CV Q
Engine 7
1 I 1 1
i
8 -
— _
4-/t,3o3
20 40 60 80 100
Humidity, grains H^O/lb dry air
120
-C
I
o.
20.0-
18.0-
16.0-
14.0-
12.0-
10.0-
8.0-
20
Each number represents an
engine's datum point.
Curves show M02 values predicted
by the R^ factor equation which
is good only to 120 grains.
I
40
60
80
Humidity, grains
TOO
dry air
Figure 11. Effect of humidity on A/F ratio and N0x emissions for HD gasoline engines (from Reference 22}
-------
Figure 14 would result in a decrease in NO emissions, whereas a decrease in A/F ratio for an engine
X
at C would cause an increase in NO emissions. The author concluded, therefore, that engines operat-
ing at different A/F ratios with different metering characteristics should exhibit varying (possibly
contradictory) effects on exhaust emissions for similar changes in inlet air conditions.
The author also indicated that changes in inlet air conditions could affect fuel distribution
to the engine, and this in turn affects N0v emissions. This effect is illustrated in Figure 15.
A
In addition, changes in inlet air conditions which change the engine A/F ratio also change the min-
imum spark advance for best torque (mbt). Figure 16 illustrates how NO emissions vary with A/F
for the mbt setting and other settings retarded from mbt. Since some of the engines in that study
had no vacuum advances, they experienced, in effect, retarded mbt settings as their A/F ratio changed.
Thus, their emissions would respond differently to A/F changes than engines with vacuum advances.
Therefore, the development of a general correction factor for ambient temperature and pressure was
not possible, although variations in these parameters affected emissions significantly.
In two other studies ambient humidity corrections were developed from LD gasoline vehicles
(References 23 and 25). In the first study, a correction factor was derived from emission tests at
76°F and at four ambient humidities on a fleet of eight passenger cars operated on a chassis dynamo-
meter set to simulate seven different road loads of the Federal 7 mode composite cycle for LD vehicles.
These passenger cars were powered by gasoline-fueled, spark ignited, carbureted engines ranging in
size from 42 to 59 CID per cylinder. The compression ratios varied from 8.5 to 10.5, and air-to-fuel
ratios from 14.6 to 16.4.
Corrections for ambient humidity were derived for both the Federal Test Cycle composite load
factor is considered more applicable to large bore carbureted SI engines which typically operate at
a constant load (nearly rated load). These factors are
K = 0.796 + 0.175(H/100) + 0.129(H/100)2 (2a)
composite factor
K = 0.844 + 0.151(H/100) + 0.075(H/100)2 (2b)
constant load, 50 mph
The results of this study were adopted by California to correct emissions for ambient humidity for
gasoline powered vehicles under 6,000 pounds (Reference 27).
43
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14 9- O~O .
11 ' ' '
if
15 T- 'o~~o-
n ' ' '
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,5
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16
15
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16
15
14
15
14
13
16
15
14
11
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1
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12
NO
14
i
16
l
18
20
Air-Fuel Ratio
Figure 14. Exhaust gas concentration versus A/F (from
Reference 22).
-------
2000.
1600
1500
g- 1000J
725
500-
Most Uniform
Fuel Distri-
bution
Least Uniform
Fuel Distribution
I 1600 - 725
I 1600
= 55%
I 1 I
13 14 15 16 17 18 19 20
Air-Fuel Ratio
Figure 15. Effect of fuel distribution
on NO emissions (from
Reference 22).
2200
Q.
Q-
600
Retard (% decrease in
power)
Air-Fuel Ratio
Figure 16. Effect of ignition timing and A/F
on NO exhaust emissions, 1600 rpm,
23 bhp road at mbt (from
Reference 22).
-------
In the second study, a similar test program on gasoline vehicles was conducted to develop
an ambient humidity correction factor that was adopted by EPA to correct LD gasoline vehicles
(References 21 and 25). This factor is
K = I/O 0.0047(H-75))
(3)
In yet another study, an ambient correction factor for humidity was developed for typical re-
search engines where A/F and mbt settings were held constant (Reference 24). The author of this
study also noted the effect of A/F ratio on N0x emissions as illustrated in Figure 17. Based on this
figure, the author of Reference 22 reasoned that composite correction factors would vary from constant
load factors since NO emissions vs. humidity curves changed with A/F ratio. Despite the validity
of these observations, the correction factor derived in this study is probably less applicable to
large bore engines than those derived for gasoline vehicles, since in practice A/F ratios and spark
settings of large bore engines are not necessarily held constant as they were in this study, (e.g.,
spark timing is fixed as load changes for some engines, and varies with load for other engines).
Comparison of Existing Humidity Correction Factors for SI Engines
Based on the preceding discussion, three ambient humidity correction factors are potentially
applicable to large bore, natural gas fueled engines, particularly four-stroke, carbureted versions.
These factors are summarized in Table 11. Figure 18 is a comparison of the three factors over a
typical range of ambient humidities. Note that only one of the factors plotted is a constant load
factor (Equation 2b); the other three are based on composite test cycles.
TABLE 11. AMBIENT HUMIDITY CORRECTION FACTORS FOR SI ENGINES
Equation No.
(1]
(2a)
(2b)
(3)
Correction Factor
K 0.634 + 0.00654(H) - 0.0000222(H)2 Compo-
site Factor (9 Mode Federal HD Gasoline Test
Cycle)
K 0.796 + 0.175(H/100) + 0.129(H/1002)
Composite Factor (Federal Test Cycle, LD
Gasoline Vehicles)
K 0.844 + 0.151(H/100) + 0.075(H/100)2
50 mph, Constant Load
K 1/(1 0.0047(H-75)) Composite Factor
(Federal Test Cycle, LD Gasoline Vehicles)
Reference
22
23
23
25
48
-------
CL
CL
CO
c:
o
to
CO
'i
cu
o
3500-
3000-
2500
2000
1500
1000
O 20 grains moisture
A 90 grains moisture
D 160 grains moisture
per pound dry air
15
16
17
18
Air-Fuel Ratio
15.7 A/F
14.9 A/F
14.4 A/F
20 90 160
Humidity grains H 0/1 b dry air
Figure 17. Effect of A/F ratio and ambient humidity on NO emissions of a LD
gasoline engine (from Reference 22).
-------
O)
4->
O
o>
S-
O
"O
s_
0)
1.25 -
1.20 -
1.15 -
Q eqn (1)
0 eqn (2a)
eqn (2b)
20 40 60 80 100 120
Ambient Humidity (grains H^O/lb dry air)
Figure 18. Comparison of SI ambient humidity correction factors
50
-------
As Figure 18 illustrates, there is a considerable difference in correction depending on the
study. The results from the EPA/Scott study show the greatest sensitivity to ambient humidity varia-
tion while the results for HD gasoline engines show the least. This is not unexpected in view of the
previous discussion regarding the variation in engine responses to changes in inlet conditions de-
pending on A/F ratio, fuel metering and distribution, and ignition (distribution operation) charac-
teristics of different engines. The correction based on constant load has been chosen as the most
suitable correction to be applied to large bore SI engines, since these engines are typically opera-
ted at constant load. Thus, this correction factor is most applicable to carbureted (4-NA) natural
gas engines.
Application of any of the correction factors of Figure 18 to other engine types (e.g., turbo-
charged units) is questionable due to major differences in inlet air intake systems. For example,
data from the draft SSEIS indicate that N0x reductions due to water induction are directly propor-
tional to water-to-fuel (w/f) rates, up to w/f ratios of one. Moreover, w/f rates due to ambient
humidity are a function of A/F ratio, as Figure 19 illustrates. Based on this figure, the w/f rate
of a carbureted natural gas engine (trapped A/F -17) is about 30-percent lower for a specific humid-
ity of 100, than the w/f ratio of a turbocharged engine with a trapped A/F ratio of 25 (trapped A/F
ratios for turbocharged SI engines typically range from 20 to 25, References 28 and 29). Note, also,
that the curves of constant humidity diverge with increasing A/F ratio. Therefore, it can be anti-
cipated that NO emissions of engines with different A/F ratios will respond differently to identical
changes in ambient humidity. Thus, the application of the constant load humidity correction factor
(based on carbureted gasoline engines) to other than carbureted large bore, SI engines is questionable
Similar conclusions can also be reasoned regarding the application of ambient temperature and
pressure correction factors to NO emissions from engines whose air intake as well as fuel systems
differ substantially. As discussed earlier, however, no factors have been developed for SI engines
for either temperature or pressure.
3.2.2.2 Ambient Correction Factors Developed for CI Engines
A survey of the literature established that two sources have reported ambient correction fac-
tors for truck-size diesel engines (References 6 and 19). A study by Krause, et al., was sponsored
by_ the Automobile Manufacturer's Association and the Engine Manufacturer's Association and resulted
in correction factors for both temperature and humidity. These corrections were later adopted by
j:he EPA for HD diesel engines (Reference 20)^ The other source, Reference 19, reported corrections
for humidity only.
51
-------
0.80
en
ro
OJ
4->
co
CC r—
OJ
c rs
O 4-
•r- E
+-> -Q
U i—
13 -^
-o o
C (XI
S- J3
cu •—
"3
0.60-
0.40-
0.20-
Figure 19. Water to fuel range vs. ratio air-to-fuel.
-------
In Krause's study, a correction factor was derived for six different engines run over a 13-
mode cycle (Reference 6). Emission procedures used were similar to "California Procedures for Diesel
Engines in 1973 and Subsequent Model Year Vehicles Over 6001 Pounds Gross Vehicle Weight." The
heavy duty truck engines tested were diesel fueled, compression ignition engines ranging in size
from 69 to 155 CID. The compression ratios varied between 14.9 and 18.7. Inlet air conditions were
controlled to one of 19 combinations of humidity and temperature. The humidity conditions ranged
from 35 to 125 grains HgO/lb dry air, and the temperature was varied between 70°F and 115°F. Baro-
metric pressure was controlled to 28.00 ± 0.2 inch Hg. at the air cleaner inlet.
The engines in the study were of the following types:
• 4-stroke turbocharged, direct injection (4-TC)
• 4-stroke turbocharged, prechamber (4-TC, PC)
• 4-stroke naturally aspirated, MAN chamber (4-NA, MAN)
i 4-stroke naturally aspirated (4-NA)
t 2-stroke blower scavenged (2-BS)
• 4-stroke turbocharged, aftercooled (4-TC,AC)
Unlike turbocharged large bore engines, which are nearly always aftercooled, only one of the
turbocharged engines in this study was aftercooled. That engine as well as the 4-NA and the 2-BS
units were similar in design to large bore engines. A correction factor was developed for all of the
engines as well as for individual units. The factor was of the form
K l/[A(H-75) + B(T-85)]
where NO corrected = (K)x (NO observed) and A and B are related to A/F ratio (load). The reference
ambient conditions are 75 grains H-0/lb dry air and 85°F. Figure 20 is a plot of the coefficients
A and B for each engine as a function of load (or A/F ratio).
Average values of A and B for all engines (as function of A/F) were also determined. This
result does not appear wholly justified given the variations in response to ambient humidity and
temperature exhibited by the different engine types depicted in Figure 20. Note that the 4-TC, AC
unit is significantly less sensitive to ambient temperature variations over the load range than the
other designs. Therefore, separate ambient correction factors for 2-BS, 4-NA, and 4-TC, AC units
from this study were used on the corresponding large bore designs instead of just one average value
53
-------
0.010
4-TC
2-BS
4-NA
4-TC
4-TC
-0.004
100
16.7
A/F
Figure 20. Effect of humidity and temperature on NO emission for
different CI engines.
54
-------
of all engines. The coefficients A and B were determined for rated load conditions using average
rated load A/F ratios that were reported for the large bore engines.
The second source (Reference 19) which examined ambient humidity effects reported correction
factor based on experimental tests of a 2-BS and a 4-NA engine.
Ambient humidity corrections from both of these sources (assuming inlet temperature is held
constant, hence, the B term of Krause's factor drops out) are illustrated in Figure 21. The SI
(gasoline) factors discussed in Section 3.2.2.1 are also plotted for comparison. Note that there is
little variation in correction factors for different diesel engine types with the exception of the
2-BS unit from Reference 19. Moreover, the diesel fueled (CI) engines appear less sensitive to am-
bient humidity changes than SI units, particularly for humidities less then 75 grain H20/lb dry air.
Initially, one might expect the diesel units to be more responsive to inlet humidity variations,
since these units operate at higher A/F ratios (approximately 25 to 40), and therefore, induct more
nearly at stoichiometric ratios (-15 to 17, depending on the fuel). Diesel engines, however, have a
greater thermal inertia than SI engines according to their higher trapped A/F ratios. Apparently the
higher thermal inertia in the diesel units more than offsets their higher effective water induction
rate; thus their NO emissions are less sensitive to changes in ambient humidity than SI engines.
X
This explanation is corroborated by experiments which have demonstrated that water injection, as a
control technique, produces significantly greater NO reductions in SI units than for CI (diesel)
units (see Section 5.3.8 of the draft SSEIS).
The Krause study (Reference 6) also investigated the effect of ambient temperature on NO
emissions. Figure 22 presents the correction factors that were derived for engine types similar to
those in the present study (humidity is assumed constant, hence, the A term of Krause's factor drops
out). The reference temperature is taken as 85°F. This figure shows that the naturally aspirated
and blower scanvenged engines NO emissions are more sensitive to inlet air temperature changes than
the aftercooled design. Since Krause's study systematically examined the effect of both inlet tem-
perature and humidity for a number of CI engine types, his factors were selected for application to
similar large bore engine types.
3.2.2.3 Potential Application of Gas Turbine Ambient Correction Factors to Reciprocating 1C Engines
Since no ambient correction factors have been developed specifically for large bore engines,
all existing correction factors for internal combustion engines were examined including those for
gas turbines. There is a considerable amount of technical literature on gas turbine ambient correc-
tion factors as a result of the promulgation of emission standards for aircraft engines and the pro-
55
-------
-o
O)
•M
O
O)
i.
o
o
1.25 -
1.20
1.15
1.10
1.05
OJ
I 1.0
.95
.90 •
.85
.80
.75
O 4-TC (AC), 4-NA
V 2-BS
A 4-NA j
Ref. 19
2-BS
SI factors
(See Figure is)
/ Ambient Humidity (grains H20/lb dry air)
20
40 60 80 100 120
Figure 21. Comparison of CI and SI ambient humidity
correction factors.
56
-------
1.10 T
in
1.05 - -
01
QJ
O
O
CU
S-.
ta
1.0
.95 - -
O 4-TC (AC)
Q 4-NA
V 2-BS
.90 - -
50 60 70 80 90 100 110 120
Ambient Air Temperature, °F
Figure 22. Correction factors for temperature for CI
engines (Reference 6).
-------
posed emission standards for stationary gas turbines (References 30, 31, 32, 33, 34, and 35). This
section describes these various factors and their potential application to the large bore engine data
in the present study.
Gas turbine combustion characteristics have some common features with those in diesel engines.
Both the gas turbine primary combustion zone and the diesel combustion chamber can be characterized
as a well-stirred reactor, and both use similar distillate fuels or natural gas. On the other hand,
the gas turbine combustion is a steady-state, constant pressure process, whereas the diesel is an
unsteady, variable pressure combustion process. Nevertheless, the similarities of the two systems
warrant an investigation of existing gas turbines correction factors.
Many investigators have developed ambient humidity correction factors based on a model that
relates NO formation to combustion parameters of temperature, pressure, equivalence ratio and res-
idence time (using the kinetic rate equations for NO formation) (Reference 34). Humidity enters
this model though its effect on reaction (flame) temperature. Most researchers have shown that the
effect of humidity on NO formation takes the form
K
NO
x corrected Fxp [K ,„ H n
N0x observed " (Hobserved "reference'J
where H ^ specific humidity at reference (standard) conditions
K empirical constant that ranges from 14 to 30, generally taken as 19 (Reference 30)
Figure 23 is a plot of this correction factor and shows that it agrees reasonably well with
the HD diesel (4-TC, AC) factor discussed in Section 3.2.2.2 (the gas turbine factor was adjusted
to a reference humidity of 75 grains H^O/lb dry air to correspond with the reference humidity of the
HD factor).
Other sources have shown similar agreement of humidity effects on NOX emissions of diesel
engines and gas turbine as illustrated in Figure 24. The gas turbine humidity correction factor was
derived from empirical data based on water injection as a means of NO control in gas turbines. The
X
ambient humidity was converted into an effective water-to-fuel ratio by multiplying the ambient
humidity loading by the near stoichiometric A/F ratio existing at combustion. Then the empirically
derived water injection correction factor of Ambrose (Reference 36) was used to calculate the per-
centage reduction in NOX- It is reasoned that the overall A/F ratio is inappropriate since much of
the water vapor in the inlet air never reaches the primary combustion zone because it is vented for
engine cooling or enters downstream as dilution or wall cooling air. Based on this result one can
conclude that changes in humidity appear to affect NOX formation in gas turbines in much the same
58
-------
en
10
"0
O)
-------
CTl
o
1.0 -r
Predicted Curve
QJ
_
E
to
>» 0.9
-a
0 n
CM U.
un
ro
•P
(T5
0.6 -
0.5 -
s
0
Experimental
Curve
Experimental Lab Data
Field Data
Diesel Engine Data
0.0 35 70 105 140 175 210 245
Specific Humidity grains H?0/lbm dry air
230
315
Figure 24. Observed ambient humidity influence on NO production
(from Reference 36). x
-------
way as in diesel (1C) engines. However, it should be remembered that a number of adequate humidity
correction factors have been developed for 1C engines; therefore this gas turbine result is of
limited value, but serves to reinforce the more global application of these corrections.
Gas turbine temperature corrections were also examined for application to reciprocating engine
data. Figure 25 is a comparison of the HD diesel (4-TC, AC) correction factor with various gas
turbine factors. Obviously, there is little agreement with the exception of one factor. Presumably
these differences arise from differences in inlet air compressor and combustor design. The gas tur-
bine factors, however, have some flexibility in that they are related to the combustor inlet para-
meters of pressure and temperature. Therefore, an attempt was made to relate changes in NO forma-
tion of reciprocating engines to changes in ambient temperature by estimating the precombustion
cylinder temperature in a typical reciprocating engine using the compressor pressure ratio and the
assumption of isentropic compression to calculate temperature. This calculated temperature was then
used with the gas turbine factors. Figure 26 presents the results of this approach for several
different forms of gas turbine factors. Again, these results do not correlate well with the HD
diesel factor, probably due to the empirical nature of the gas turbine equations and the large dif-
ferences in air intake systems between engines and turbines.
On the basis of this brief review, gas turbine ambient correction factors do not make a use-
ful contribution as potential ambient correction factors for reciprocating engines.
3.2.2.4 An Analytical Approach for the Ambient Temperature Correction of NO Emissions
Since no temperature correction factor has been reported in the literature (see Section
3.2.2.1) for SI engines, and no systematic emissions data exist (either SI or CI) from which to base
a temperature correction for large bore engines in general, an attempt was made to develop a semi-
analytical approach for relating changes in ambient temperature to changes in NO level from large
bore engines. This approach was used to estimate how changes in ambient temperature affect NO
levels.
The analytical approach is based on the fact that ambient temperature changes affect NO emis-
sions by their direct impact on both fuel/air (f/a) ratio and peak flame temperature. As the ambient
temperature rises, the inlet air becomes less dense. Since the air intake volume is essentially con-
stant, the engine will inject a smaller mass of air; that is, the f/a ratio will increase. This
change in f/a ratio is related to a change in NO level for both SI and CI engines (see Figure 27).
The temperature of the air in a diesel engine or fuel/air mixture in a dual fuel or natural
gas engine after compression is correspondingly changed by a change in ambient (inlet) air tempera-
61
-------
CTi
ro
o
01
s_
o
o
S-
OJ
to
HD Diesel Reference 6
gas turbine
Reference 37
80
100
120
140
Temperature, °F
Figure 25. Comparison of existing gas turbine ambient temperature correction
with HD diesel temperature correction.
-------
O-l
CO
-a
CD
-M
O
a>
s-
S-
o
o
O)
-------
TREF
en
NO
TREF
\
REF
Load
Af/a
(f/a)REF (f/a)
f/a
Figure 27. Relationship of NO level and load to f/a ratio
for a turbocharged diesel engine operating at
two ambient temperatures.
-------
ture. That is, an increase in inlet air temperature results in an even greater charge temperature
after compression. This increase in charge temperature leads to a higher peak flame temperature and,
consequently, greater NOX levels. The increase in N0x level due to an inlet air temperature increase
is related to specific engine design parameters such as f/a ratio, degree of aftercooling, and com-
pression ratio, as well as the fundamental nature of the combustion process (i.e., CI or SI). There-
fore, the relationship between N0x level and inlet air temperature is anticipated to be highly de-
pendent on the particular engine design.
The discussion above indicates that NOX level is primarily a function of both f/a ratio and
inlet air temperature. That is,
NOX = g(f, T)
A
where f = f/a, fuel/air ratio
T 5 T,, ambient inlet temperature
a
N E NO , oxides of nitrogen
The subscript R denotes a reference ambient condition
Since we are interested in predicting changes in NO level rather than absolute NO level we
may mathematically represent a change in NO to a change in ambient temperature as
X
dN (§) df * (f) dT
°r
(l!
dN. = 3N_ df 3|i
dT 3f dT 3T
Where the derivatives on the right side of Equation (1) remain to be evaluated. The first partial
3N
derivative, -53-, represents the change in NO emissions due to a change in f/a at constant ambient
dT X
3N
temperature, while the second partial, •**-, represents the change in NO,, due to temperature variations
d I X
at constant f/a. This mathematical formulation can be portrayed graphically as shown in Figure 27.
The diagram shows NO vs. fuel-to-air ratio, the downsloping curves, and load vs. fuel-to-air ratio,
the upsloping curves, for a typical turbocharged diesel engine. The basic problem is to find the
change in NO at constant load due to some ambient temperature change. For example, assume the am-
bient temperature, T, is greater than the reference temperature, TR. Starting at the uncorrected
fuel-to-air ratio one locates point A on the NO production curve and point B on the load curve.
X
Then moving over, at constant load, to the reference temperature load curve, one locates point C and,
hence, the reference fuel-to-air ratio. Now, knowing the reference fuel-to-air ratio, one can move
65
-------
from point D to point E on the reference temperature curve. Thus, the change in N0x production re-
sulting in this change of ambient temperature is indicated as ANO .
X
The change in NO level with f/a for a constant ambient temperature, -^, is presumed known
for a given engine or engine type. This relationship can be established from data that can be ob-
tained in the laboratory on a sample engine. In addition, it is assumed that the N0x vs. f/a plots
of Figure 27 have similar slopes for different ambient temperatures. Therefore, only N0x vs. f/a
data at one ambient temperature are required to evaluate the derivative.
The derivative df/dT, expresses the rate of change of f/a ratio with a change in ambient
temperature. The author of Reference 38 has derived the following expression relating f/a to ambient
temperature (at constant load) for both turbocharged and naturally aspirated engines.
B
(2)
/i. i \
and B (1 + n) (1 ei) n
where k C /Cv, rati° °^ specific heats
n = turbocharger adiabatic compressor efficiency
n = turbocharger exponent from equation T. r constant where .5
-------
Since B is always less than 2 and T is 70°F = 530°R, a nominal change in ambient temperature of
R
25°F makes
Since this term is small compared to unity, we can approximate the derivative by
df „ fR
dt b Tj^
Thus, the term from Equation (1) that predicts the change in NO due to a change in f/a is evaluated
as
3N df = /8N\/B\/!R
An expression is now required to relate the change in NO level to a change in ambient inlet
air temperature, i.e., the partial derivative vf of Equation (1). This dependence can be evaluated
by first relating changes in ambient temperature to changes in flame temperature using the following
relationship from Reference 39 suggested by the authors of Reference 40.
Y
T + -
(Q-L)-f + Cp(Too - TB)
(5)
where T-. = droplet diffusion flame temperature from Reference 39.
T^ E isentropic compression temperature
= TM(CR)k
CR E compression ratio of engine
TM E manifold air temperature, related to T. by degree of turbocharging and aftercooling
Tn = boiling point temperature of the fuel
Q E heat of combustion per unit mass of fuel
L s latent heat of vaporization of the fuel
Y E ambient oxygen mass fraction
i = stoichiometric oxygen to fuel ratio (by mass)
C E specific heat of the fuel/air mixture
67
-------
Then, the change in flame temperature is related to a change in N0x production using the Arrhenius
relation
dNO K
-gt*= EXP(-K/RTn); £ 123,000°R
If it is assumed that the rate of NO production is time independent, one can readily integrate the
Arrhenius equation to yield the following expression for the ratio of NO produced at a given ambient
temperature, T, and a corresponding flame temperature, T^, to that at the reference condition.
NR
The partial derivative can then be approximated in finite difference form by
».•(> 30
3T- T TR
Now by substituting Equations (4), (6), and (7) into Equation (1) we obtain:
Rf N
dN DTR 3N
r (T Tin
|K * f 0 f 0 P ' 1
1 cvn ^ '*• T)tK
R T x T
i\ ' f n A f f R
L ix. i x.r\ j
dT TR 8f T-TR
(8)
A preliminary evaluation of this expression for a turbocharged diesel engine predicts a 1-
percent change in NO per 1°F change in ambient inlet air temperature. For a constant intercooler
effectiveness and turbocharger compressor efficiency, a one degree change in ambient temperature
corresponds to a one degree change in manifold inlet temperature. Therefore, this analytical
expression can be checked using N0x emissions data vs. manifold air temperature (at constant load)
for a turbocharged, diesel engine.
Emissions data for the manifold air cooling control (see Figures 5 to 11 of the draft SSEIS)
indicates that this technique produces a 0.1- to 0.3-percent change in NO per degree Fahrenheit for
diesel engines. Emissions data reported by Ingersoll-Rand (and from Figures 5 to 11 of the draft),
show about a 1-percent change in NO per 1°F change in manifold air temperature for turbocharged SI
engines (Reference 26). Since NO emissions from SI engines are more responsive to changes in mani-
fold air temperature, it appears that this analytical approach overestimates the effect of inlet air
temperature on N0x emissions from this turbocharged CI engine. The assumptions which were made with
regard to the constancy of the NO production rate with peak flame temperature may be more valid for
SI engines than CI engines owing to differences in the combustion processes of each.
68
-------
The approach outlined here has the potential to incorporate many different parameters into a
single correction factor. Additional terms could be added for any other operating parameters that
have a significant effect on NO emissions, either directly or by their impact on f/a or T^. Once
the appropriate relations are established, it may be possible to predict changes in NO levels as a
X
result of changes in any one of these variables caused by ambient variations.
These goals are somewhat ambitious; therefore, the most logical first step is to gather avail-
able data taken at different ambient conditions and apply the method to prove its validity. At this
time, however, there is insufficient information for either SI or CI engines to substantiate this
approach.
3.2.3 Effect of Ambient Correction on Reduction of Data Scatter
Having selected potential ambient correction factors for large bore engines, we are now in a
position to determine whether the use of these corrections will reduce the scatter in the existing
data base. For the purpose of this preliminary study, ambient correction factors will be applied
only to the uncontrolled data of four-stroke turbocharged diesel, dual fuel, and natural gas engines.
Emissions data from this engine type contained the most complete ambient information (before incor-
poration of additional Colt and Cooper emissions data) and, therefore, provided a better statistical
sample for determining the effect of ambient corrections on the scatter.
3.2.3.1 Effect of Ambient Corrections on NO Emissions Scatter
X
The ambient correction factors were selected from existing 1C engine factors discussed in Sec-
tions 3.2.2.1 and 3.2.2.2. These factors are summarized in Table 12. The ones for CI engines are
based on small bore diesel engine types which correspond to each of the large bore designs. The 4-TC,
AC factor (see Table 12), was used to correct both the 4-TC diesel and dual fuel results.
The SI correction factor is for humidity only and is based on a typical 4-NA carbureted gaso-
lene engine operating at a constant load. The other humidity factors (see Table 11), for similar
gasoline engines all were based on composite test cycles; therefore, the factor based on a constant
load was selected for application to the large bore data. As was indicated in Section 3.2.2.2, this
factor may not be valid for other engine types (such as the 4-TC units); nevertheless, it was selec-
ted for this preliminary evaluation since no humidity correction factors have been developed for
other types of SI engines.
The results of correcting the data are summarized in Table 13 and Figure 28. As the table in-
dicates, the standard deviation in the data was only reduced from 1.9 to 1.7 g/hp-hr for diesel data
and from 4.2 to 3.9 g/hp-hr for the dual fuel data, whereas it increased from 1.4 to 1.8 g/hp-hr for
the natural gas data.
69
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TABLE 12. EXISTING 1C ENGINE AMBIENT CORRECTION FACTORS FOR APPLICATION TO LARGE BORE ENGINES
Fuel
Correction Factor
Comments
Diesel &
Dual Fuel
K = l/(l+A(H-75) + B (T-85))
H = observed humidity, grains hLO/lb dry air
T = observed inlet, air temperature, °F
See Section 3.2.2.2 rated
load correction for humidity
and temperature (from Refer-
ence 6).
Type
2-BS
4-NA
4-TC, AC
A
-0.00242
-0.00231
-0.00231
B
0.00235
0.00255
0.0017
Natural Gas, SI
K = 0.844 + 0.151 (H) + 0.075 (H)
See Section 3.2.2.1 rated
load correction for humidity
only (from Reference 22).
NO corrected = (K) NO observed
X A
-------
TABLE 13. SCATTER IN NOX EMISSIONS OF UNCONTROLLED 4-TC ENGINES
Fuel/#
Natural Gas/4
Dual Fuel/3
Diesel/11
Engine
Type
4-TC
4-TC
4-TC
NOX Level grams/hp-hr
Uncorrected
Mean
17.5
8.1
8.1
St'd Dev.
1.4
4.2
1.9
Corrected
Mean
15.5
8.2
7.7
St'd Dev.
1.8a
3.9b
1.7b
Humidity correction only
^Humidity and temperature correction
71
-------
20 - -
O Uncorrected
Q corrected
o
.9
15 ..
ro
i
Q.
1-
CT>
10 --
5 ..
Natural gas Dual Fuel
Diesel fuel
Figure 28. Effect of ambient correction on scatter in NO emissions of
uncontrolled 4-TC engines. x
-------
An increase in standard deviation does not necessarily imply that the correction factor is in-
valid (nor does a decrease confirm validity). That is, it may be possible for NOX levels which are
higher than the sample average to increase when corrected for ambients (e.g., because they were mea-
sured at high humidity and/or low temperature) and, correspondingly, for the lower NO levels to be
X
decreased by the ambient corrections.
The increase in scatter of the natural gas data after correction, however, may be the result
of (1) the application of a humidity factor to 4-TC engines that was based on 4-NA carbureted gaso-
line engines and (2) the inability to correct for ambient temperature variations which may have had
a significant effect on the reported emissions. This increase in scatter is contrary to the results
illustrated in Figures 9 and 10 (of Section 3.2.1) where the scatter in a sample of both SI and CI
engines was reduced significantly after correction for ambient variations. Note that the scatter re-
ported in these figures is based on an average for each engine over a range of ambients rather than
an average of the entire sample of engines and, therefore, excludes other sources of scatter, such
as engine variability.
A more valid test of the applicability of a correction factor would be its ability to predict
changes in NO production caused by changes in ambients for an individual engine. This was not pos-
sible since no systematic data set exists which can be used to develop and test corrections.
3.2.3.2 Conclusions Regarding Ambient Correction Factors/
The primary finding of this study is that the scatter in the N0y data was reduced only slightly
by the application of ambient correction factors. Apparently other variables, such as measurement
uncertainties (discussed in Section 3.1) or engine design parameters (see Section 3.3), account for_
most of the differences in NO levels reported by the manufacturers.
The search for ambient correction factors also revealed that neither humidity nor temperature
corrections exist for turbocharged natural gas engines (2 to 4 stroke). These engine types consti-
tute a significant fraction of the existing sources and, presumably, will continue to be produced.
Therefore new sources of this kind would be subject to performance standards for emissions. Enforce-
ment of a standard based on measurements "in the field" would require application of ambient correction
factors or, alternatively, specification that the measurements be made within given ambient limits.
An experimental program to systematically investigate the effect of variations in ambient temperature
and humidity on NO emissions from natural gas engines would be one approach to the problem of estab-
lishing ambient correction factors.
73
-------
In addition to the lack of humidity and temperature correction factors, no factors exist to
correct NOX emissions for variations in ambient pressure for carbureted natural gas engines. Studies
of carbureted gasoline enjines_^4^^) have shown that ambient pressure variations affect NO emis-
sions substantially j?,y_J=lli]]^^j^4;jTe A/' Fratio (see Fielure 13). However, researchers were unable to
generalize a correction factor for this effect. In view of the absence of such a correction factor,
barometric pressure in a given location should be specified to within certain limits, and qualifi-
cation measurements of large bore naturally aspirated or blower scavenged engines should be conducted
within these limits. This approach, however, is unsatisfactory for relating measurements made at
higher elevations, e.g., Colorado, to a measurement made at standard ambient conditions.
The application of ambient correction factors to emissions data from dual fuel engines based on
the data from diesel engines is subject to question. Although the combustion of the gas/air mixture in
these dual fuel engines is initiated after compression by the injection of pilot oil, it proceeds essen-
tially as a premixed flame rather than by droplet burning. Hence, the combustion process has many
similarities to that in natural gas engines. Moreover, trapped A/F ratios of dual fuel engines are
generally less than those of diesel engines but greater than those of SI units. Therefore, these
engines experience different effective ambient water-to-fuel induction rates and thermal inertias
(see Sections 3.2.2.1 and 3.2.2.2) than their diesel counterparts. Consequently, one can reason that
NO emissions from dual fuel engines will respond differently than diesel engines to variations in
ambient humidity and temperature. Therefore, dual fuel engines may require different correction
factors than diesel engines. There is no data at this time, however, to prove or disprove this hypo-
thesis.
In summary, ambient correction factors depend on the snqjjie^t^ge^ Although correction for
large bore engines can be inferred from tests on truck size units, this approach is imperfect because
of the differences in combustion characteristics and the fact that not all large bore engine types
are represented in the test samples. Nevertheless, it does have enough validity that it can be used
as a basis for correcting emission data until the manufacturers develop and demonstrate their own
correction factors. In the absence pfii>anvcoirre>ctionii.factors for temperature or pressure, limits
should be specified for values of ambient pressure and temperature to minimize variations of exhaust
measurements. These Jlimits ^wi 11 be eva1uated_aj:te£itex^imjjijjig_the expanded data base during the
follow-on work effort.
74
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3.3 EFFECT OF ENGINE VARIABILITY
The emission data supplied by the manufacturers show a great deal of scatter, that is, NO
levels from uncontrolled engines can vary by as much as a factor of 2 to 3. Some of this scatter
can be attributed to the use of different measurement techniques or the fact that the results were
not corrected for ambient conditions. This scatter also could be the result of: (1) variations in
production for a particular model, (2) variations between different models of the same type (i.e.,
same strokes/cycle, air charging and fuel), or (3) different number of cylinders for a given model.
In this section the uncontrolled data base is evaluated for these kinds of scatter. Furthermore,
the data are examined for trends in emissions due to speed, bmep, and manifold air temperatures.
All of these analyses use data that have been correlated for ambient variations by the methods de-
scribed in Section 3.2.3.
3.3.1 Production Variations
Unfortunately, there is little data available to determine variations in emissions of produc-
tion models. Most of the manufacturers have concentrated on obtaining emissions in their laborato-
ries for different engine models. At this time there has been little impetus for large bore station-
ary engine manufacturers to make exhaust measurements of engines leaving the production line.
Nevertheless, Colt and GMC/EMD reported variations in production models.
Colt reported less than a 3-percent difference in two NO measurements, one in 1972, the other
in 1975, from a two-stroke blower scavenged diesel engine (Reference 41). Such a small difference was
unexpected, and Colt suggests (in their August 2, 1976 "114" response) that the variation would more
likely be of the order of 10 percent for production units, but they have no data to verify this esti-
mate. Colt has measured NO levels of production spark ignited engines (2-TC-G) within 3 percent of
X
each other under similar ambient conditions (Reference 42).
GMC/EMD has reported average NO levels and standard deviations for samples of their 2-TC and
X
2-BS diesel models (Reference 43). These results are summarized in Table 14. As this table suggests,
these variations in NO levels of production engines may have been a result of ambient variations. In-
let air temperatures varied over a wide range for both the turbocharged and blower scavenged units, and
humidity was not recorded. An attempt was made to determine whether these observed variations in
emissions could be due to changing ambient conditions. First, a correction was computed for each
extreme of the reported temperature range using the methodology presented in Section 3.2.2.2. These
two maximum possible variations were then compared to the reported data to determine if temperature
variations alone could account for the scatter. Next a correction was computed for both the reported
75
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TABLE 14. VARIATIONS IN NOX EMISSIONS FROM GMC/EMD PRODUCTION ENGINES (FROM
REFERENCE 43)
en
Type
2-TC-D
2-BS-D
# Cylinders
20
16
16
12
# Units
11
10
13
8
Variation (standard deviation
as a % of average)
± 8
± 8
± 6
± 5
Ambient
Temperature
J 67-97°F
63-128°F
-------
temperature variation and an assumed humidity variation, ranging from 35 to 115 grains H-O/lb dry
air. These corrections were then compared with the production variability scatter. The comparisons
are listed in Table 15.
Based on these corrections, temperature variations alone could not account for all the scatter
of turbocharged units, although they would do so for blower scavenged units. If humidity were to
vary over the range used for the calculations presented in Table 15, then ambient variations of tem-
perature and humidity could account for all the scatter reported for these engines. It should be
noted, however, that the ambient correction factors are based on data from smaller, truck-size
engines, and therefore, may not be applicable to these larger units.
3.3.2 Model Variations
Variations in NOX levels may be attributed to different engine models with an engine type for
a given manufacturer. For example, N0x levels for a manufacturer's 4-TC-G models may vary due to
differences in bore, stroke, turbocharger, configuration (inline cylinders vs. vee), compression
ratio, aftercooler, and other engine design parameters. In an effort to identify the magnitude of
model-to-model variations, average N0x levels and standard deviations were evaluated for different
models from each manufacturer.
Table 16 presents the results of this study. GMC/EMD, White Alco, and Colt are not included
in this table since they each manufacture one engine model, which can be configured for different
fuels. For example Colt markets their 38D8-1/8 opposed piston engine model as a gas, diesel, or dual
engine, either blower scavenged or turbocharged. GMC/EMD and White Alco manufacture one basic diesel-
fueled, turbocharged design which differs primarily in number of cylinders and speed ratings. CMC/
EMD also markets blower scavenged units.
The other five manufacturers listed in Table 16 produce different engine models within a given
engine type. NO levels reported by Cooper for four 2-TC models varied by 13 percent about the aver-
X
age. These engines differ in bore, speed, number of cylinders, and torque (bmep), but they were all
operated at the same inlet and manifold air temperature. Delaval's data indicate only 4- to 5-per-
cent variation between models for both gas and diesel fueled units. The percent variations shown for
Waukesha, Ingersoll-Rand and White Superior should not be compared to the Cooper and Delaval results
because differences due to ambient conditions could not be factored out; these manufacturers did not
report ambient data. To the extent that one can draw any conclusions from such a small sample size,
it appears that NO emissions for any type of engine (given strokes/cycle, fuel, and air charging)
X
vary more from manufacturer to manufacturer than they do among models in a manufacturer's line.
77
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TABLE 15. POTENTIAL SCATTER IN NOX EMISSIONS FROM PRODUCTION ENGINES DUE TO
AMBIENT HUMIDITY AND TEMPERATURE VARIATIONS
co
Type
2-TC-D
2-BS-D
# Cylinders
20
16
16
12
Inlet Air
Temperature
Range
) 67-97°F
)
) 63-128°F
f
Scatter,
Uncorrected
for Ambient
± 8
± 8
± 6
± 5
Correction for
Temperature
Range9
) +3 to -2
) (67 to 97°F)
) +5 to -9
) (63 to 128°F)
Correction
for Temperature
& Humidity
Range^
+16 to -11
+15 to -14
aUsing HD diesel ambient correction factor (see Section 3.2.2.2)
= !/0 + B(T-85J) where B - .0017 for 2-TC-D (based on 4-TC-D)
2_BS_D
T = test temperature
(Reference temperature of 85°F)
Using HD diesel ambient correction factor.
K
correction
+ A(H-75) + B(T-75)) where A = -0.00231 for 2-TC-D (based on 4-TC-D)
= -0.00242 for 2-BS-D
H - test humidity ranging from 35 to
115 grains H20/lb dry air
(Reference humidity = 75 grains
H20/lb dry air)
-------
TABLE 16. VARIATION IN N0v DUE TO MODEL DIFFERENCES
A
Manufacturer
Cooper
Del aval
Ingersoll-Rand
White Superior
Waukesha
Gasa
4-TC
#
2
3C
2C
3C
AVG
17.6
18.0
20.4
12.8
SD
0.6
1.8
2.4
0.6
%
4
10
12
4
2-TC
#
4
AVG
14.6
SD
1.8
%
13
Dieselb
4-TC
#
3
2C
AVG
9.2
7.9
SD
0.5
0.7
%
5
9
aAmbient correction for humidity only (see Table 12)
Ambient correction for humidity and temperature (see Table 12)
cNo ambient correction, ambients not recorded
SD - Standard deviation
% - SD/AVG
-------
Emission variations that are due to differences among manufacturers could be related to differences
in speed, bmep, or manifold air temperature. This possibility will be addressed in Section 3.3.4.
3.3.3 Variations with Number of Cylinders
Several manufacturers have suggested that NO levels will vary for a basic engine design de-
X
pending on the number of cylinders due to interaction with the manifold and turbocharger Figure
29 is a plot of NO level (corrected for ambients) vs. number of cylinders. Based on this grouping,
it appears thatNO^IeveJ^fecjreasesiw^ for 4-TCjJ
units, and that 4-TC-D NOy emissions aj^e^
Figure 30 presents a different interpretation. NO levels (corrected for ambients) have been
X
plotted vs. number of cylinders for each manufacturer's units. This would tend to reduce other sources
of emission variation, such as design differences among manufacturers that may have been reflected in the
previous figure. Figure 29 indicates that there is no clear trend between NO emissions and number
of cylinders for either diesel or gas units. The effect of changing the number of cylinders introduces
a scatter of 3 to 9 percent. Note that EMD data could not be corrected for ambients, and therefore,
this data may not represent the effect of differences in the number of cylinders.
3.3.4 Variations in NOX Level Due to Other Engine Variables
The results of Sections 3.3.1 through 3.3.3 suggest that the variations observed in NOx
levels reported by all the manufacturers for engines of a given type may be a result of design para-
meters that differentiate one manufacturer's engines from those of the others. Consequently, uncon-
trolled NOX data (corrected for ambients) were plotted vs. speed (rpm), manifold air temperature, and
torque (bmep).
Figure 31 illustrates NOX level variation with speed for two engine types. There are too few
data points to indicate any trend for 4-TC units, although the 4-TC dual fuel and diesel NO levels
X
appear to decrease with increasing speed, as would be expected for lower exhaust gas chamber resi-
dence times.
NOV level variation with manifold air temperature is depicted in Figure 32. The 4-TC-G NOV
X X
levels appear to be very sensitive to the design air manifold temperature, but the diesel and dual
fuel levels do not. These results confirm expectations from physical reasoning that NO levels from pre-
mixed vaporized fuel combustion in SI engines may be strongly influenced by the degree of aftercool-
ing. CI engines are characterized by droplet combustion, and NO emissions under these conditions
would depend more on local A/F ratio than on overall air temperature.
80
-------
4-TC (
( • Natural gas
( O Diesel
CXI
Q.
-£=
CD
20
15
10
8
O
O
I I I I I I I I I I I I I I I I I I I
*
O
«*
4 8 12 16 20
Number of cylinders
Figure 29. NO production variation with number of cylinders,
y\
-------
co
ro
i
CL
20
18
16
14
?, 12
rt
x
I 10
8
6
9.0/0.6, 1%
Delaval
O 2-BS-C
B 2-TC-D
V 4-TC-D
V 4-TC-G
x a a/x
17.2/1.6, 9% Delaval
15.8/1.2, 8% EMD
12.5/0.4, 3% EMD
7.9/0.6, 7% Alco
4
2
0
x
a
mean
st'd. dev.
12 16
# cylinders
20
Figure 30. Variation in NO level with number of cylinders,
A
-------
CO
GO
25
20
15
-C
I
Q.
S-
01
X
g 10
8
o
• 4-TC Nat. qas
(SI) *
o 4-TC Diesel and
dual fuel
(CI)
8
o
I I
I I I I I I I I I I I I I I I I I I I I I I I
Q I I I I I I I I I I
0 200 400 600 800 1000 1200 1400
Speed ,RPM
Figure .31. Variation in NO level with speed.
A
-------
00
25
20
15
I
a.
.c
i.
cn
10
A4-TC natural qas
0 (SI) J
Q4-TC diesel and
dual fuel
(CI)
I I I I I I I I I i
80 100 120 140 160 180 200
T °F
I *• I
Figure 32. NO variation with manifold temperature.
A
-------
Finally, Figure 33 illustrates the variation of NOX level with bmep (torque) for 4-TC-G and
4-TC-D, DF units. The data are scattered. If one ignores the cluster of CI data around 150 psi, one
can conjecture a trend of decreasing brake specific NOX emissions with increasing bmep for these
units. No trend is apparent for SI units, except that they are not manufactured with bmep's exceed-
ing 200 psi.
Based on these preliminary studies, it appears that certain engin_e_jjeslgn parameters (e.g..
rpm, bmep, or manifold air temperatffif?J.,imM...^^1.SLM,,,more of the scatter in NOV levels for engines of
a given type than variations in ambient humidity or temperature. These_factors will be investigated
further under contract 68-02-2530.
85
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25
20
• 4-TC Natural gas (SI)
O 4-TC Diesel and
dual fuel (CI)
s_
_c
Q-
_c
en
15
O
O
CD
CTi
10
O
O
I I I I I I I I I I I I I I I I I I I I I I I
I I I I I I I I I
100
150
200
BMEP, psi
250
Figure 33. NO variation with torque (BMEP).
/\
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SECTION 4
FIELD APPLICABILITY
Since manufacturers have applied NO control techniques only to engines in their emissions labora-
X
tories, they have expressed concern for possible technical limitations of these controls when used
under "field" conditions. The primary objectives of this task are (1) to evaluate manufacturers' re-
sponses regarding the adverse effects of control techniques they have tested and (2) to assess the
technical limitations that exist for field application of various control techniques.
This section will primarily discuss the first objective. The second objective requires addi-
tional contact with manufacturers and field users. The second objective will be accomplished during
the Affected Facilities task (under Contract 68-02-2530). Thus, by coupling these tasks a consider-
able amount of consultation can be consolidated. Therefore, some conclusions regarding the field
applicability of the various control techniques will be reserved.
4.1 SUMMARY OF MANUFACTURERS' "114" RESPONSES
In response to the June 16, 1976 Section "114" request for information, six of the eight large
bore engine manufacturers commented on potential or observed adverse effects of the emission control
devices they had tested. Their comments are summarized and briefly discussed below. DeLaval and
White Alco were unable to comment since neither has done any development work on the various control
techniques.
In general, the responses produced a consensus that any control technique to reduce NOV emis-
A
sions must undergo a period of durability testing before being released for field application. For
example, Inge rsolj-Rand concluded that none of the methods of NO reduction (other than water induc-
tion) that they had demonstrated during short test runs produced immediate adverse effects such
as misfiring, detonation, or excess thermal stress. More extensive testing would be required to
assess long term durability.,
Colt also expressed the need for long term testing of the order of one or more years to
evaluate the effect of any N0v control on engine components and maintenance. This time estimate
appears to be consistent with the 9 to 15 months allotted for development of existing (rather than
emerging) control techniques discussed in Section 5.3.14 of the draft SSEIS. These existing controls
87
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were classified as changes to operating conditions, e.g., retard or A/F, or additions of existing
hardware, e.g., increased manifold aircooling, or turbocharging.
GMC/EMD, however, stated that at least three years of durability testing was a normal evalua-
tion period for assessing any technical changes that were to be made to a production engine. Thus,
GMC/EMD's time estimate is more nearly equal to the estimates in the draft SSEIS for major develop-
ment programs for controls such as modified combustion chambers or water induction.
Colt, on the other hand, establjsJied_t^t_alt£j^iiQ^^ of a 4-TC dual fuel
•*••'" " ^**aanni-«r™.i"-i-r3maa»s™B~—- •'•*••
engine the effect of retard (4 degrees) was to increase the maintenance period for valve recondition-
1n9^y£S~E£T^en^' Their estimate of the incremental cost for this increase in maintenance was
approximately 0.3 percent of the estimated total annual operating cost of this engine which appeared
in Table 7-10 of the draft SSEIS. These economic aspects will be given further consideration during
Task 5 (Cost Revisions) of the follow-on work effort. It ij_jrrteresting to note that Colt was the
only manufacturer to quantify an adverse effect_of_a control technique.
Furthermore, Cooper and Waukesha noted the customary increases in fuel consumption, CO, and
smoke levels associated with the application of NO controls. Both manufacturers, however, indi-
X
cated that they had insufficient technical information (e.g., exhaust temperature histories) to
assess the potential adverse effects of the techniques they applied. Waukesha believed techniques
"""*' *"•* Hi*
such as retard might cause iincreased maintenance dueiiit10--exc£-Ssiiv-ei_exhaust temperatures reqjri£J_ng
more frequent valve replacement. Waukesha and Cooper indicated that a development program would be
required to determine the adverse effects of various NOX reduction control techniques.
In addition, to this information, Cooper indicated that certain controlled levels that they
reported in their new emissions data (2-TC natural gas, production engines, see Section 2), were un-
acceptable due to misfiring. These NO levels represented the greatest NO reduction possible and
X X
caused the greatest increases in fuel consumption. All of these control approaches which caused
excessive misfiring were combinations of retard (3 to 4 degrees), manifold air cooling (30°F), and
lean A/F ratio.
Finally, White Superior indicated that engines sold for compressor applications are typically
required to meet a 10-percent overload capability during two hours of the day. Thus, White concluded
that some of the controls they had applied would require derating of the engine, since, in some cases
these engines could not meet his overload limit. White is presently compiling this information for
submittal to EPA.
In conclusion, all of the manufacturers have stated they believe some adverse effects will re-
sult from the application of NOX controls. Only Colt has quantified an adverse effect of a control
-------
technique. This effect appears to be primarily economic (i.e., an increased maintenance cost) rather
than a technical limitation.
Other manufacturers feel that development programs are necessary to quantify adverse long
term effects of N0x controls. Their estimates range from 1 to 3 years for all control techniques,
rather than the 9 to 15 months estimated in the draft SSEIS for retard, manifold air cooling, derate,
turbocharging and A/F changes.
4.2 SUMMARY OF DEMA AND AGA COMMENTS ON CONTROL TECHNIQUES
Two organizations, DEMA and AGA also commented on the field applicability of NO control tech-
niques discussed in the March 1976 draft SSEIS (References 44 and 45). In general, these comments re-
flect a concern for the increased cost of purchase and operation of controlled engines, rather than
technical limitations which would prevent the application of a control technique. These cost aspects
will be given more consideration under Task 5 of the follow-on work effort. Their comments related to
technical limitations are summarized below by the specific control technique. Conclusions regard-
ing the field application of these techniques will be reserved until after Task 1, Affected Facilities,
is completed as discussed in the introduction of this section.
Retard (R)
The primary concern is the possibility of reduced exhaust valve life due to higher exhaust
gas temperatures. Increased fuel consumption is also noted with the application of this control as
well as some amount of derate with large amounts of retard in naturally aspirated or blower scavenged
engines. Manufacturers believe 10-percent derate is a practical limit for marketing BS or NA engines.
Reduced Manifold Air Temperature (MAT)
The amount of cooling is limited by the cooling media (i.e., radiator, cooling tower, pond).
The practical limit is approximately the ambient air temperature plus 20 degrees. Lower manifold
temperatures require ground water or refrigeration. Also, increased cooling implies increased de-
scaling costs.
Air-to-Fuel Change (A/F)
A/F changes have limited application to blower scavenged engines due to increased parasitic
horsepower and manifold air temperatures. Both of these effects would tend to offset a reduction
in brake specific NO emissions. In addition, the durability of the blower is unknown for higher blower
speeds. Beyond a certain amount of A/F change in a 4-NA engine, maximum load capability will decrease
89
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implying derate. Dual fuel engines will require turbocharger development and careful turbocharger
to engine matching because combustion of dual fuel engines is more sensitive to A/F than diesel
units. Increases in A/F for turbocharged gas engines are limited by combustion deterioration.
Derate (D)
Derating will cause marketing problems for 2-BS units due to increased installed cost and
fuel consumption. Derate is generally not effective in reducing brake specific N0x emissions on
turbocharged engines due to the relatively flat A/F curve over the power range.
Turbocharging
Turbocharging of NA or BS engines results in a low rated turbocharged engine with higher in-
stalled costs and fuel consumption. In addition, manufacturers indicated that a turbocharged BS or
NA engine requires the performance and development effort of any "new1' engine. Also, turbocharged
engines incur higher maintenance costs (primarily for the turbocharger) than NA or BS units.
Internal Exhaust Gas Recirculation (IEGR)
In essence this technique produces a marginally scavenged engine (particularly BS units),
therefore carbon buildup, higher temperatures (increased maintenance) and poorer combustion (in-
creased fuel cost) will result.
External Gas Recirculation (EEGR)
The concern here is that only one manufacturer has limited data for this technique. It is
believed that considerable development is required. The requirement for cooling will mean higher
installed and maintenance costs.
90
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REFERENCES
1. Coordinating Research Council (CRC) "Cooperative Evaluation of Techniques for Measuring NO and
CO in Diesel Exhaust: Phase III," CRC Report, 1972.
2. "Measurement of C02, CO, and NO in Diesel Exhaust," SAE Recommended Practice J177a. March, 1974.
3. J. M. Perez, L. C. Broering, and J. H. Johnson, "Cooperative Evaluation of Techniques for Measur-
ing NO and CO (Phase IV Tests)," SAE Paper 750204.
4. Coordinating Research Council (CRC) "Cooperative Study of Heavy Duty Diesel Emission Measurement
Methods," CRC Report 487, July, 1976.
5. "A Study of Mandatory Engine Maintenance for Reducing Vehicle Exhaust Emissions, Volume VI: A
Comparison of Oxides of Nitrogen Measurements," TRW Systems Group, CRC APRAC CAPE 13-68-12,
July 1972.
6. S. R. Krause, D. F. Merrion, and G. L. Green, "Effect of Inlet Air Humidity and Temperature on
Diesel Exhaust Emissions," SAE Paper 730213.
7. H. G. Maahs, "Interference of Oxygen, Carbon Dioxide, and Water Vapor on the Analysis for Oxides
of Nitrogen by Chemiluminescence."
8. R. D. Matthews, R. F. Sawyer, and R. W. Schefer, "Interference in Chemiluminescent Measurement
of NO and NOg Emissions from Combustion Systems," Draft of Paper Submitted to Combustion and
Flame Fall, 1976.
9. J. E. Sigsby, Jr., et al., "Chemiluminescent Method for Analysis of Nitrogen Compounds in Mobile
Source Emissions," Environmental Science and Technology. Volume 7, No. 1, January 1973.
10. J. H. Tuttle, R. A. Shisler, and A. M. Mellor, "Nitrogen Dioxide Formation in Gas Turbine Engines:
Measurements and Measurement Methods," Purdue University Report No. PURDU-CL-73-06, December 1973.
11. Monsanto Research Corporation, "Instrumentation for the Determination of Nitrogen Oxides Content
of Stationary Source Emissions," Volume I, October 1971 and Volume II, January 1972.
12. W. B. Clemens (EPA/Ann Arbor), "Impact on Existing Standards Due to Proposed Instrumentation
Changes in the Heavy Duty Federal Test Procedure," Interoffice Memo, September 18, 1974.
13. Personal Communication between S. B. Youngblood (Acurex/Aerotherm) and W. B. Clemens (EPA/Ann
Arbor) July 22, October 19, and November 1, 1976.
14. F. S. Schaub and K. V. Beightol, "NOX Emission Reduction Methods for Large Bore Diesel and
Natural Gas Engines," ASME Paper 71-WA/DGP-2.
15. "Revised Heavy Duty Engine Regulations for 1979 and Later Model Years," Federal Register,
Volume 41, No. 101, May 24, 1976.
16. Diesel Engine Manufacturers Association (DEMA), "DEMA Exhaust Emission Measurement Procedure for
Low and Medium Speed Internal Combustion Engines," 1974.
17. SAE J177a, See Reference 2.
18. "General Motors Corporation Statement on Draft SSEIS for Stationary Reciporcating Internal Com-
bustion Engines," May 14, 1976.
19. Coordinating Research Council (CRC), "Effect of Humidity of Air Intake on Nitric Oxide Formation
in Diesel Exhaust," CRC Report 447, December 1971.
20. "Emission Regulations for Heavy Duty Gasoline and Diesel Engines," See Reference 15.
21. Environmental Protection Agency (45 CFR Part 1201), "Control of Air Pollution from New Motor
Vehicles and New Motor Vehicle Engine," (Notice of Proposed Rule Making), February 1971.
22. S. R. Krause, "Effect of Engine Intake-Air Humidity, Temperature, and Pressure on Exhaust Emissions,"
SAE Paper 710835.
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23. W. J. Brown, et al. , "Effect of Engine Intake-Air Moisture on Exhaust Emissions," SAE Paper
700107
24. J. A. Robinson, "Humidity Effects on Engine Nitric Oxide Emissions at Steady-State Conditions,"
SAE Paper 700467.
25. Scott Research Laboratories, "Effect of Laboratory Ambient Conditions on Exhaust Emissions,"
Project No. 2846.
26. Private Communication between R. W. Sheppard (Ingersol1-Rand) and D. R. Goodwin (EPA), August 1976.
27. State of California, Air Resources Board, 1973, "California Exhaust Emission Standards for
Gasoline Powered Motor Vehicles," Proposed, November 18, 1970.
28. C. R. McGowin, "Emissions Control of a Stationary Two-Stroke Spark-Gas Engine by Modification
of Operating Conditions," Shell Development Company Report, 1972.
29. Personal Communication between A. R. Fleischer (Delaval Turbine Inc.) and D. R. Goodwin (EPA),
July 30, 1976.
30. G. L. Touchton and N. R. Diebeluis, "A Correlation of Nitrogen Oxides Emissions with the Gas
Turbine Operating Parameters," ASME Paper 76-GT-14.
31. H. Shaw, "Effect of Water on Nitric Oxide Production in Gas Turbines Combustors," ASME Paper
75-GT-70.
32. W. S. Blazowski and D. E. Walsh, "Prediction of Aircraft Gas Turbine NOX Emission Dependence on
Engine Operating Parameters and Ambient Conditions," AIAA Paper 73-1275.
33. J. M. Vaught, "The Effect of Inlet Temperature and Pressure on an Industrial Turbine Engine
Exhaust Emission," ASME Paper 75-WA/GT-ll.
34. W. S. Y. Hung, "An Experimentally Verified NOX Emission Model for Gas Turbine Combustors,"
ASME Paper 75-GT-71.
35. J. W. Marzeski and W. S. Blazowski, "Ambient Temperature and Pressure Corrections for Aircraft
Gas Turbine Idle Pollutant Emissions," ASME Paper 76-GT-130.
36. Gas Turbine International , May-June 1974.
37. Private Communication between S. B. Youngblood (Acurex/Aerotherm) and J. McDermon (EPA),
October 1976.
38. T. Wu and K. J. McAulay, "Predicting Diesel Engine Performance at Various Ambient Conditions,"
SAE Paper 730148.
39. F. A. Williams, Combustion Theory, Addison-Wesley, Chapter 3 and 4, 1965.
40. R. P Wilson, Jr., E. B. Muir, and F. A. Pellicciotti, "Emissions Study of a Single-Cylinder
Diesel Engine," SAE Paper 740123.
41. Private Communication between C. L. Newton (Colt) and D. R. Goodwin (EPA), August 2, 1976.
42. Private Communication between C. L. Newton (Colt) and D. R. Goodwin (EPA), April 2, 1976.
43. Private Communication between G. P Hanley (GMC) and D. R. Goodwin (EPA), January 29, 1975.
44. Private Communication between F S. Schaub (DEMA) and D. R. Goodwin (EPA), May 12, 1976.
45. Private Communication between G. H. Ewing (AGA) and D. R. Goodwin, September 24, 1976.
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NOMENCLATURE
Abbreviation
Fuel
0
DF
G
Strokes/Cycle
2
4
Air Charging
BS
NA
TC
Pollutants
N0x
NO
N02
CO
co2
HCT
CH4
Instruments
CL
NDIR
NDUV
Other
A/F
f/a
SI
CI
H
T
Explanation
Diesel
Dual fuel
Gas (i.e., natural gas)
2-stroke/cycle engine
4-stroke/cycle engine
Blower scavenged
Naturally aspirated
Turbocharged (and intercooled)
NO + N02
Nitrogen oxide
Nitrogen dioxide
Carbon monoxide
Carbon dioxide
Total hydrocarbons
Methane
Chemiluminescent
Nondispersive infrared
Nondispersive ultraviolet
Air-to-fuel ratio
Fuel-to-air ratio
Spark ignition
Compression ignition
Humidity grains HpO/lb dry air
Ambient air intake temperature
93
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NOMENCLATURE
Abbreviation
Fuel
D
OF
G
Strokes/Cycle
2
4
Air Charging
BS
NA
TC
Pollutants
N0x
NO
N02
CO
co2
HCT
CH4
Instruments
CL
NDIR
NDUV
Other
A/F
f/a
SI
CI
H
T
Explanation
Diesel
Dual fuel
Gas (i .e., natural gas)
2-stroke/cycle engine
4-stroke/cycle engine
Blower scavenged
Naturally aspirated
Turbocharged (and intercooled)
NO + N02
Nitrogen oxide
Nitrogen dioxide
Carbon monoxide
Carbon dioxide
Total hydrocarbons
Methane
Chemiluminescent
Nondispersive infrared
Nondispersive ultraviolet
Air-to-fuel ratio
Fuel-to-air ratio
Spark ignition
Compression ignition
Humidity grains HUO/lb dry air
Ambient air intake temperature
93
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