EPA-650/2-75-055
May 1975 Environmental Protection Technology Series
DETERMINATION
OF AIRCRAFT
TURBINE ENGINE
PARTICULATES
I
55
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U.S. Environmental Protection Agency
Office of Research and Development
Washington, 0. C. 20460
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EPA-650/2-75-055
DETERMINATION OF AIRCRAFT
TURBINE ENGINE PARTICULATES
by
Keith M. Johansen and Emerson L. Kumm
Airesearch Manufacturing Company of Arizona, Inc.
P. O. Box 5217
Phoenix, Arizona 85010
Contract No. 68-02-1236
ROAP No. 26ACU-31
Program Element No. 1AA010
EPA Project Officer: Dr. Ronald L. Bradow
Chemistry and Physics Laboratory
National Environmental Research Center
Research Triangle Park, N. C. 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
WASHINGTON, D.C. 20460
May 1975
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EPA REVIEW NOTICE
This report has been reviewed by the National Environmental Research
Center - Research Triangle Park, Office of Research and Development,
EPA, and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These series are:
1. ENVIRONMENTAL HEALTH EFFECTS RESEARCH
2 . ENVIRONMENTAL PROTECTION TECHNOLOGY
3. ECOLOGICAL RESEARCH
4. ENVIRONMENTAL MONITORING
5. SOCIOECONOMIC ENVIRONMENTAL STUDIES
6. SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS
9. MISCELLANEOUS
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to
develop and demonstrate instrumentation, equipment and methodology
to repair or prevent environmental degradation from point and non-
poiiit sources of pollution. This work provides the new or improved
technology required for the control and treatment of pollution sources
to meet environmental quality standards.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
Publication No. EPA-650/2-75-055
11
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4-2
ABSTRACT
The objective of this twelve-month program was to
develop measurement techniques for particulate emissions
from aircraft gas turbine engines. The ultimate goal was
to establish optimum representative sampling procedures,
parameters, devices, and instruments to estimate the mass
of these particulates emitted from gas turbines as they
exist in the open atmosphere.
A series of tests with a turboprop engine, Garrett/
AiResearch Model TPE331, was used as a basis for determin-
ing the feasibility of gravimetrically measuring the parti-
culate emissions from aircraft engines. Limited tests were
also conducted with two turbofan engines, the Garrett/
AiResearch Model TFE731-2 and the Pratt & Whitney Model
JT3D-9.
Several different filter materials were tested to
determine the one most suitable for the particulate measure-
ments. DM450 Metricel filter material (a copolymer of
acrylonitrile and polyvinyl chloride) was selected.
It was concluded that satisfactory correlations
between particulate mass emissions and smoke number can
be obtained with a given engine operating at given condi-
tions, but that correlations obtained under different
operating conditions even with the same engine have sub-
stantially different slopes. Thus, reflective smoke
numbers do not seem to accurately assess the particulate
emission rate of a significant variety of aircraft gas
turbine engines.
111
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4-3
It was determined that the particulate mass emission
rate from the engines varies intermittently with time and
that ambient dust levels can have a significant effect on
measured results. Deposits of particulate matter in the
sampling probe and transfer line were not significant.
A uniform distribution of particulate concentrations
was measured at the exhaust plane of the TPE331 Engine.
However, samples obtain from the JTOD Turbofan Engine indi-
cated a significant variation in particulate concentration
at the exhaust plane of this engine. The cause for this
variation was not determined. Data from both the JT8D-9
and TFE731-2 engines indicated significant variations during
the initial portion of the tests and subsequently stabilized
at a relatively constant level.
It was difficult to compare the results of gravimetric
measurements of engine particulate emissions with the con-
ventional smoke number. The latter is principally affected
by small carbon particles whereas the former can be affected
by both ambient dust ingested at the engine inlet and rela-
tively large particles which form as carbon deposits on the
walls of the combustor and are intermittently dislodged and
discharged from the engine.
It is recommended that a combination of the two methods
be the subject of further research, in order to relate gas
turbine particulate emissions to air quality standards.
This report was submitted in fulfillment of Contract
Ho. EPA 68-02-1236 by AiResearch Manufacturing Company of
Arizona under the sponsorship of the Environmental
Protection Agency. Work was completed in July 1974.
iv
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TABLE OF CONTENTS
Page
Abstract ii
List of Figures v
List of Tables vii
Acknowledgements viii
Sections
I Conclusions 1
II Recommendations 4
III Introduction 5
IV Test Equipment and Experimental Techniques 10
V TPE331 Engine Emission Characteristics 24
VI Particulate Measurement Method Development 43
VII Discussion of Results 76
VIII References 79
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FIGURES
1 TPE331-5-251, S/N 21 With 12 Point Sampling
Probe
2 Particulate Sampling System for Gas Turbine
Engines 12
3. Twelve-Point Averaging Probe Used For
Particulate Sampling
4 Single Point Traversing Probe Inlet 14
5 Twelve-Point Averaging Probe Mounted Behind
the JT8D-9 Engine 15
6 Smoke Number vs. Weight flow (100 Percent
Power) 18
7 Glove Box Used for Weighing Filters 21
8 TPE331 Equal Area Mapping Diagram 26
9 TPE331 Exhaust Mapping Smoke Number 27
10 Weight Increase versus Smoke Number
at 90-Percent Power 28
11 Particulate Emissions of Engine Repeated
Tests 31
12 Smoke Number of Engine Repeated Tests 32
13 Smoke Number versus Particulate
Concentrations for Champagne Results 34
14 TPE331 Dust and Smoke Measurements 36
15 Smoke Number Correlation at Taxi Idle
Condition 37
16 Smoke Number Correlation at 100 Percent
Power 3 8
17 Weight Flow versus Smoke Number at
Taxi Idle Condition 40
18 TPE331 Dust and Smoke Number Measurements 41
vi
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FIGURES (Contd)
No. Page
19 Particulate Sampling System for Gas
Turbine Engines
44
20 TPE331-5-X21 Exhaust Gas Particulate
Concentration versus Smoke Number 51
21 Variable Sample Transfer Line Length
with Reference TPE331 Engine 53
22 Particulate Passing Through a DM450 Metricel
Filter 54
23 Statistical Experiment Particulate Variable
Probe and Sample Flow 56
24 'JT8D-9 Test Setup 58
25 JT8D-9 Combustor Can/Probe Relationship 59
26 JT8D-9 Discharge Flow Particulate
Concentration 61
27 Smoke Number Data from DM450 Metricel Filters 62
28 JT8D-9 Smoke Number by Probe Rake Position
No. 1 64
29 Dilution Test Setup 66
30 TPE331 Exhaust Gas Particulate Sampling with
Dilution Device 67
31 Cascade Impactor Test Schematic 70
32 Cumulative Mass Distribution of Particulates
as a Function of Particulate Size 75
yn
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TABLES
No.
1 National Ambient Air Quality Standards
(Federal Register, April 30, 1971)
2 Measurement Deviation of Particulate or Filters 22
3 TPE331 -Engine Emissions 25
4 Repeatability Test Results 33
5 Variable Probe/Filter Flow Rates - TPE331 45
6 Summary of Analysis of Relationship off
Variables from Multiple Regression by the
Student "T" Test 47
7 Summary of Analysis of Relationship of
Variables by Coefficient of Correlation 48
3 Analysis of Variance of Regression Against
Smoke Number at 0.04245 Cubic Meters Gas Sample 49
9 Particulate Concentrations for Reference Engine 55
10 Cascade Impactor Test Sequence 71
11 Particulate to Gas Weight Ratio Collected by
Anderson Cascade Impactor Stage 7 2
12 Particulate Size Versus Weight Percentage
Emitted at Various Power Levels by the TPE331
Reference Engine 74
Vlll
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ACKNOWLEDGEMENTS
This report was prepared by the AiResearch Manufactur-
ing Company of Arizona, a division of The Garrett
Corporation, under EPA Contract Number 68-02-1236.
The period of performance of this program was 29 June
1973 through 30 June 1974. The AiResearch Program Manager
was Keith M. Johansen. Emerson L. Kumm was the Principal
Investigator and Peter C. Amundsen was responsible for all
engine tests and emissions data acquisition.
All tests with the TPE331 and TFE731 Engines were run
at the AiResearch Test Facilities in Phoenix, Arizona. An
additional series of tests with a JT8D-9 Engine were con-
ducted on subcontract at Aviation Power Supply (APS) in
Burbank, California. The cooperation of Allen R. Stokke,
Manager, and John C. Bogena, Foreman of Engine Test
Facilities at APS during these tests is gratefully acknow-
ledged.
The EPA Project Officer was Dr. Ronald L. Bradow. His
technical direction and assistance during the program pro-
vided significant contribution.
IX
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I. CONCLUSIONS
General conclusions from this program were as
follows:
o Accurate gravimetric measurements of gas turbine
engine particulate emissions can be obtained.
o Smoke number (reflectance) measurements do
not correlate with gravimetric measurements
of engine particulate emissions.
o As with smoke number (reflectance) measurements,
it is difficult to relate gravimetric measure-
ments of engine particulate emissions to ambient
air quality standards.
o For the engines tested, a reduction in partic-
ulate mass emission concentration was noted
at higher engine power levels, even though
the smoke number increases.
o The carbon deposits in the sampling probe and
transfer lines were typically less than 5 per-
cent of the material collected by the filters.
Also, there was not a significant trend between
transfer line length and measured particulate
emissions.
o The cost of obtaining gravimetric measurements of
production engine particulate emissions would be
substantially higher than the conventional smoke
number measurements.
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The background, data and measurement techniques presented
in this report permits considerably more accurate tests
and measurements to be made of gas turbine particulate
emissions than was previously possible.
The gravimetric measurement data presented herein
indicates that the particulate concentration (emission
rate) varies intermittently during engine operation and
that significant stratification of the particulates can
exist at the exit plane of some engines. It was assumed
that small carbon particles are produced at a relatively
uniform rate in fuel-rich zones within the combustor.
Larger particulates are probably derived indirectly
from ambient dust ingested at the engine inlet and from
carbon deposits which form within the combustor.
The conventional smoke number measurement depends
chiefly on the very small carbon particulate material for
which the atmosphere has a long retention time, but the
gravimetric measurement includes the larger particles which
do not remain suspended in the atmosphere. Hence, it is
difficult to relate gravimetric measurement of particulate
mass emissions measurements to ambient air quality stan-
dards. The situation is complicated by the many variables
that influence the combustion of fuel and the variety of
combustion chambers that are used in gas turbine engines.
Accurate gravimetric measurements can be obtained if
the sample gas volume is 0.028 M3 or larger. Within the
range of parameters tested, probe flow-rate and filter
flow-rate did not significantly effect the test results.
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The particulate size measured from the TPE331 Engine
was shown to be somewhat uniformly distributed from
large material (over 9 microns) to very small materials
(approximately 0.3 microns).
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II- RECOMMENDATIONS
It is recommended that the sampling apparatus and tech-
niques developed in this program be used for additional
research to attempt to correlate particulate emissions with
smoke number and to relate this data to ambient air quality
standards. This would include further testing to study the
effects of nonisokinetic sampling (and its effect on probe
sampling efficiency), dilution, ambient dust ingested at the
engine inlet, stratification of particulate concentrations
in the engine exhaust plane, nonconstant particulate emis-
sion rates, and particle size distribution.
The use of DM450 Metricel filter material for engine
smoke number measurement is recommended since it provides a
more accurate reflectance measurement than the Whatman No. 4
material currently used.
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III. INTRODUCTION
BACKGROUND
n \ *
The standards for the control of air pollution from
aircraft gas turbine engines established by the Environmental
Protection Agency specifically regulate emissions of carbon
monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO ), and
iC
smoke. Smoke is defined as the particulate matter in the
engine exhaust that obscures the transmission of light.
The convention in the formulation of the air quality
standards has been to specify primary and secondary stan-
dards for particulates as mass per unit volume of air (refer
to Table 1). However, the current method of dealing with
determinations of gas turbine particulate emissions is to
specify a smoke number that is an indicator of the rela-
tive visibility of the exhaust gas.
The procedure used for determining this smoke number
involves a measurement of the optical reflectivity of the
particulates collected on a specific type of porous filter
element by the passage of a known volume of engine exhaust
gas through the filter. The difficulty in attempting to
use this procedure as an indicator of the particulate mass
emitted is that the reflectivity is largely a function of
the relative size of the particulates collected, and may
not necessarily be related in any discrete manner to the
total mass of the sample, particularly since particle sizes
*Superscript numbers in parenthesis designate references
presented in Section VIII of this report.
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Table 1. NATIONAL AMBIENT AIR QUALITY STANDARDS.
(Federal Register, April 30, 1971)
Pollutant
Carbon monoxide
(Primary and secondary)
Hydrocarbons (Non-methane)
(Primary and secondary)
Nitrogen dioxide
(Primary and secondary
Particulate matter
(Primary)
(Secondary)
Photochemical oxidants
(Primary and secondary)
Sulfur dioxide
(Primary)
(Secondary)
Standard Description
(a)
(b)
(a)
(a)
(a)
(b)
(a)
(b)
(a)
(a)
(b)
(a)
(b)
(c)
Note: Primary standards provide for
other undesirable effects on
*Change to 100 micrograms per cubic
**Change to 700 micrograms per cubic
10 milligrams per cubic meter (9ppm) , maximum 8-hour concentration
not to be exceeded more than once per year.
40 milligrams per cubic meter (35 ppm) , maximum 1-hour concentration
not to be exceeded more than once per year.
160 micrograms per cubic meter (0.24 ppm), maximum 3-hour concentra-
tion (6 to 9 am) not to be exceeded more than once per year. For use
as a guide in devising implementation plans to meet oxidant standards.
100 micrograms per cubic meter (0.05 ppm), annual arithmetic mean.
75 micrograms per cubic meter, annual geometric mean.
260 micrograms per cubic meter, maximum 24-hour concentration not to
be exceeded more than once per year.
60 micrograms per cubic meter, annual geometric mean, as a guide to
be used in assessing implementation plans to achieve the 24-hour
standard.
150 micrograms per cubic meter, maximum 24-hour concentration not to
be exceeded more than once per year.
160 micrograms per cubic, meter (0.08 ppm), maximum 1-hour concentra-
tion not to be exceeded more than once per year .
80 micrograms per cubic meter (0.03 ppm), annual arithmetic mean.
365 micrograms per cubic meter (0.14 ppm), maximum 24-hour concentra-
tion not to be exceeded more than once per year.
60 micrograms per cubic meter CO. 02 ppm], annual arithmetic mean.
260 micrograms per cubic meter (0.1 ppm), maximum 24-hour concentra-
tion not to be exceeded more than once per year.*
1300 micrograms per cubic meter (0.5 ppm), maximum 3-hour concentra-
tion not to be exceeded more than once per year.**
protection of public health; secondary standards for prevention of
public welfare.
meter as of August 1974 - EPA.
meter as of August 1974 - EPA.
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in gas turbine exhausts can be nonhomogenous. There may
also be a great variation in particle size that changes with
operating mode for a given engine, and varies with different
types of engines. An additional consideration is that the
smoke number and plume visibility of a high-bypass-ratio,
exhaust-mixing turbofan engine may be much lower than that
of a nonbypass type (i.e., turbojet or turboshaft) engine
that has essentially identical-mass emissions per unit oper-
ating time. This difference is due to the dilution effect
of the bypass air on the sample.
(2)
Research by Champagne indicates that the smoke num-
ber index can be identical for two particulate emission sam-
ples that differ in total mass by a factor of as much as
two. The smoke number is primarily influenced by the re-
flectivity of the smaller particles on the filter paper.
The larger particles will have little effect on the reading
obtained, irrespective of their mass quantity.
It is necessary to sum the operating-time weighted
emission rates from each of the pertinent engine operating
modes in order to obtain a complete indication of the effect
of the engine on environmental quality. However it is not
possible to make this kind of assessment with accuracy
through the use of conventional smoke number reflectance
data. A direct mass (gravimetric) measurement of engine
particulate emissions was therefore considered a means to
provide a more accurate assessment of gas turbine engine
contribution to ambient air concentrations without the re-
quirement to extrapolate from optical density measurements.
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OBJECTIVE
The objective of the two-phase, 12-month program was to
assess the feasibility of gravimetric measurement technique
for determining particulate emissions from gas turbine en-
gines. The goal of the program was to establish optimum
sampling procedures, parameters, devices, and instruments to
estimate the mass of these particulates emitted from air-
craft gas turbines as they exist in the open atmosphere.
SCOPE
Particulate emission data was obtained from three dif-
ferent gas turbine engine types for this program:
(1) TPE331-5-251 - A single-shaft turboprop engine
rated at 840 shaft horsepower.
(2) TFE731-2 - A two-spool turbofan engine rated at
3500 pounds thrust.
(3) JT8D-9-A - A two-spool turbofan engine rated
at 14,500 pounds thrust.
The TPE331 Engine (Serial No. X-21) was used for the
majority of the tests. All TPE331 Engine tests were con-
ducted with the inlet air temperature controlled to 15°C.
During Phase I, gaseous and smoke* emissions from this
engine were measured to verify that the emission charac-
teristics of this engine was representative of other
engines of the same model. A test was also conducted
with several 'candidate filter materials to select a
suitable material for gravimetric measurement of engine
^Conventional smoke number per EPA Standards (Reference 1)
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particulates. In addition, the exhaust plane of this engine
was mapped with a single-point probe to determine particu-
late inhomogeneities and thus, the applicability of using a
12-point averaging probe for subsequent tests.
During Phase II, several series of tests were conducted
with the TPE331 Engine to assess effects of the various
sampling and engine operating parameters including probe-
flow rate, filter-flow rate, sample volume, line length,
dilution ratio, and engine power. Additional TPE331 Engine
tests with an Andersen Cascade Impactor were conducted to
determine particulate size and distribution as a function
of engine power. Tests with a TFE731-2 Engine were con-
ducted to determine the requirement for isokinetic sampling.
Particulate emissions data were obtained from a JT8D-9
Engine in order to determine whether or not there are signi-
ficant particulate inhomogeneities in the engine exhaust
and, if present, whether these inhomogeneities can be
related to the can-annular combustor configuration used
in the engine. (The TPE331 and TFE731 Engines have annular,
reverse-flow combustor configurations.)
A statistical analysis of the data was conducted to
assess the suitability of the gravimetric method for gas
turbine engine exhaust particulate measurements and to
define optimum test procedures and conditions.
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IV. TEST EQUIPMENT AND EXPERIMENTAL TECHNIQUES
TEST EQUIPMENT DESIGN
The testing in this program for particulate emissions
from gas turbine propulsion engines resulted in some modi-
fications of the 12-point probe pickup and lines as speci-
fied by the EPA^ ' for measurement of smoke exhaust emis-
sions. These modifications resulted in reducing the amount
of particulate deposited in the probe and sample transfer
line to a very small percentage of the amounts collected on
the filters. Figure 1 shows the location of the sampling
probe at the exit plane of the TPE331 Engine. Figure 2
shows the EPA specified sampling system. Details of the
final 12-point probe used with the TPE331 and the TFE731
Engines in this investigation are given in Figure 3. The
EPA specifications were used to locate the 12-point probe
relative to the exhaust nozzle for sampling the exhaust
particulate emissions. Steady-state flow was established
using the bypass around the filter before switching to
the filter element.
The exit plane of the TPE331-5-251, used as the refer-
ence engine in this program, was also examined by a single-
point traversing probe. A sketch of the single-point
traversing probe inlet is given in Figure 4.
The 12-point averaging probe used on the JT8D-9 Engine
required a special support to withstand the force of the
exhaust gas flow. A photograph of the installation is shown
in Figure 5 and illustrates the special stiffeners for
supporting the probe orifices.
10
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..
Figure 1. TPE331-5-251, S/N 21 with 12-point
sampling probe.
11
MP-46750
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TURBINE
EXHAUST
DISCHARGE
NOZZLE
TRANSFER LINE
INSULATED SECTION
(a)
(a) CERAPAPER - 1 MM
JOHN MANVILLE CO.
13 MM - OVERALL
THICKNESS
SAMPLING PROBE
EXHAUST
GAS
FLOW
0.95 CM O.D.
0.80 MM WALL
I 120 CM (MIN.)
Li.
DIVERTER
VALVE
(3 WAY)
FIBERGLASS TAPE
OUTER WRAP
HEATED 80°C
SECTION
BYPASS
LINE
NEEDLE
CO ^
VALVE
V(
MEA!
©
T T
DLUME
3UREMENT
~
^
•\
NEEDLE SHUTOFF
ROTOMETER
VALVE VALVE
VACUUM PUMP
Figure 2. Particulate sampling system
for gas turbine engines.
12
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0.635 CM OD
X 0.071 CM WALL
TUBING CRES 301 —3
r::
3.9 MM 4.90 MM
3.6 MM 4.88 MM 6'35
T
2.54 CM X 0.05 CM WALL
TUBING CRES 304
WELDED BOTH ENDS
6 SWAGELOK
WELDED AND
DRILLED THRU
0.79 CM DIA.
CRES 316
50o TOTAL
IANGLE INSERT
CRES 304
I 5.3 ^j
MM
DIMENSION
A (mm)
B (mm)
C (mm)
D (mm)
PAP223080-1
TFE731
128.0
99.0
74.0
255.0
PAP223080-3
TPE331
110.0
84.0
45.0
128.0
Figure 3. Twelve-point averaging .probe
for particulate sampling.
13
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WELD
10
•^•"W \J
+ 5
\
0
n
11.1
11.
2
13.80
13.69
\
\
NOTES:
1. DIMENSIONS
IN MM
2. CRES 304
MATERIAL
15.88 (NOMINAL)
Figure 4. Single point traversing
probe inlet.
14
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INSULATED SAMPLE
TRANSFER LINE
Figure 5. Twelve-point averaging probe mounted
behind the JT8D-9 engine.
15
MP-49414
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The vacuum pump adequately provided the required flow
rate of 0.85 m /hr used initially in the program. (The
effect of different sample flow rates was subsequently in-
vestigated as discussed in Section VI.) The probe orifice
pressure loss was counter balanced by the engine exhaust
dynamic head. The pressure drop in the stainless-steel
sample transfer line (0.64 cm outside-diameter, 0.08 cm wall
thickness, and 9.14 meters long) was 7.4 cm of Hg and the
pressure drop across the filter was 15 cm of Ilg with the
flow of 0.85 m3/hr (STP).
The sample transfer line was heated with electrical
heater tape to maintain a minimum gas temperature of 80°C.
Since this heater tape would be damaged if exposed directly
to the hot engine exhaust stream, a short section downstream
of the probe (approximately 0.5 m long) was insulated but
unheated.
FILTER SELECTION
Following the engine gaseous emission measurement
tests, particulate samples were obtained using the follow-
ing materials (listed in the order tested):
(1) Whatman No. 4
(2) DM450 Metricel - Gelman Instrument Company
(3) DM800 Metricel - Gelman Instrument Company
(4) Versapor - Gelman Instrument Company
(5) AA Millipore - Millipore Corporation
The tests were run in compliance with the EPA regula-
tions. Particulate samples were obtained at four engine
power points: taxi/idle, 30-, 90-, and 100-percent cor-
rected rated power. After setting the engine on power,
16
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four samples (flow volumes of 0.0028, 0.0085, 0.0142, and
0.0198 m ) of each filter type were taken. Additional
testsx using Whatman No. 4 were conducted following the
AA Millipore tests at taxi/idle and 100 percent power to
determine repeatability.
Typical results of the particulate data analysis are
presented in Figure 6. Smoke number* measurements were
obtained from all the filter specimens at each of the four
engine conditions. The smoke number data resulted in
straight line correlations on a semi-log grid. The Whatman
No. 4 material produced lower smoke numbers than the other
materials. Good correlation of the data (from the Whatman
No. 4 material) taken before and after the test indica-
ted no change in engine performance during the tegt
sequence.
The four candidate filter materials were measured
gravimetrically for all engine operating conditions. The
(2)
correlation given by D. L. Champagne was used to obtain
a comparison of particulate weight from the four candidate
filter materials and smoke number from the Whatman No. 4
filters. For an initial evaluation see Figure 6(a).
*The term "smoke number" is defined by Reference (1) as a
specific analysis of smoke spot reflectance with Whatman
No. 4 filter material and at an exhaust gas sampling of
0.023 Ib. per square inch of filter area (1.62 x 10~3
Kg/cm2). However, the smoke number data presented in
this report were obtained from reflectance analysis of
samples of several filter materials and at various ex-
haust gas volume flow rates, and therefore are not all
smoke number measurements by the conventional definition.
17
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100
100
0.0001
(a)
Whatman #4
Material
0.001
W/A, kg/cm
Filter
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(b) Metrical Filter Material
Open symbols - DM450
Closed symbols - DM800
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100 si
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(c) Versapore Filter
Material
(d) Millipore AA Filter
Material
O Smoke Number
A Particulate Mass
Figure 6. Smoke number and particulate mass versus weight
flow per unit filter area for candidate filter
materials (100% power).
18
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It was subsequently shown that the weighing procedures
used for filter material screening were inadequately con-
trolled and thus produced inaccurate results. However,
the Metricel material (DM450 and DM800) produced the most
consistent smoke number and gravimetric results. It was
evident also that the particulate deposit on the filters
was not proportional to the sample gas volume even though
there was good correlation with the smoke number. This
phenomena will be discussed in detail later in this report
(see "Repeatability Tests" pages 29 through 42).
The Metricel filters are rated by Gelman for a maximum
operating temperature of 77°C. A brief test was conducted
with sample gas temperatures of 150°C and 80°C to determine
whether the higher temperature would adversely effect the
filtering characteristics of the material. The filters from
the tests with high gas temperatures showed no visible
evidence of deterioration and the smoke numbers from both
tests were identical. The DM450 Metricel filter was chosen
for all subsequent testing.
FILTER WEIGHING PROCEDURE
A significant effort in the program was devoted to the
development of a practical system for weighing the filters
to the desired accuracy ( + 5 micrograms). Items influencing
the weighing accuracy include:
(a) Static charge on the filter.
(b) Changes in local humidity (the variation in the
weight of a filter that is caused by changes in
the ambient humidity was found to be significant
as compared to the particulate weight being
measured).
19
-------
(c) Standardization (zero and calibration) of
balance.
^eighings were conducted initially in a "Clean Room"
with and without a glove box. Although the humidity was
accurately controlled in the "Clean Room", air currents in-
duced electrical charges which also influenced the accuracy
of the balance.
It was subsequently determined that repeatable weighing
of the filter elements (weighing about 60 mg each) could be
made with an electrobalance* (absolute accuracy is specified
to be +1 microgram) in a metal and glass glove box as shown
in Figure 7. Plastic Petri dishes were used to hold and
catalog the individual filter elements before and after
tests.
Since it was not possible to maintain the same absolute
humidity in the glove box for the pre- and post-test filter
weight measurements, the filters were grouped in batches of
ten with two reference (untested) filters in each batch.
The filters were calibrated inside the sealed glove box in
open trays for 24 to 36 hours before weighing.
Initially, weighings were made in the glove box with a
hot plate and water beaker using a relative humidity con-
troller to evaporate water and maintain a humidity above
the room humidity. This was subsequently shown to be un-
necessary.
The average mean deviation of 63 reference filters was
determined to be 5.5 micrograms. By applying the average
mean deviation of the reference filter weight to the mean
*Cahn Electrobalance Model 4100 - Cahn Instruments/Division
of Ventron, Paramount, California 90723.
20
-------
WATER
BEAKER
RELATIVE
HUMIDITY
INDICATOR
TEMPERATUR
AND
HUMIDITY
RECORDER
Figure 7. Glove box used for weighing filters
21
HP-46817
-------
particulate weights for the three gas sample volumes, the
percentage effect of the weighing error on the actual weight
measurements was determined. This is shown in Table 2. The
standard mean deviation of the weighings of the reference
filters as a percent of the particulate weighings is shown
to decrease as the gas sample size increases. A value of
5-percent indicates that a reasonable weighing precision
was achieved with the largest gas sample.
Table 2. MEASUREMENT DEVIATION OF PARTICULATE OR FILTERS
Quantity
test
filters
22
23
23
Gas
sample, (STP)
cubic meters
0.0085
0.014
0.020
Mean
particulate
weight,
micrograms
52.2
86.0
109.7
Reference filter
average mean
deviation,
percent
10
6
5
The procedure finally adopted to achieve the desired
accuracy consisted of the following steps:
(a) The filters were exposed to a constant relative
humidity and temperature environment for a^ least
24 hours to equilibrate.
(b) An ionizer (a radio-active source) was placed
inside the weighing chamber of the balance to
remove the static charge from the filters, walls
of the chamber, and the weighing pans. Both
sides of the filter were exposed to the ionizer
for approximately 1 minute before being weighed.
(c) Ten filters were weighed as a group (this
typically required 15 minutes).
22
-------
(d) The first filter was then reweighed and the
balance zeroed. If the first filter weight or
balance zero setting changed by more than 2
micrograms, the ten filters were weighed again.
(e) The relative humidity and temperature in the
glove box, (or in the proximity of the balance
when weighing in the open laboratory environment)
was recorded before and after weighing each lot
of ten filters.
(f) When weighing in the open laboratory environment,
the balance and filters were located in an area
where there was a minimum of air currents (i.e.,
away from an air conditioning vent) in order to
minimize exposure to local humidity changes and
airborne dust.
PROBE AND LINE DEPOSITS
After each test series, the probes and lines were
flushed with a solvent* and the filtrate was weighed. The
filtrate was also examined under a high power microscope to
determine the approximate percentage of carbon in the probe
and line deposits. From the test results discussed in a
later section, the large center support tube acted to separ-
ate and collect material grossly larger than obtained on the
filter elements.
The test arrangments using the Andersen Cascade
Impactor and an EPA furnished Gas Diluter are discussed in
the sections relating to those tests.
*Dow Clean (1,1,1 trichloroethane)
23
-------
V- TPE331 ENGINE EMISSION CHARACTERISTICS
GASEOUS AND SMOKE EMISSIONS
The TPE331 Engine (S/N X21) was used for the major
portion of the tests in this program and was therefore de-
signated to be the reference engine. Gaseous and smoke
emissions measurements were obtained from this engine to
demonstrate that it was typical of production engines.
The emission measurements were conducted in compliance
with EPA regulations using commercial aviation
(ASTM D1655-71T, Jet A) fuel and constant temperature (15°C)
inlet air. The inlet air relative humidity was 32 percent.
The particulate concentrations are reported in terms of
micrograms per gram of exhaust gas since the exhaust gas
sample was calculated in grams. Micrograms per cubic
meter (STP) may be obtained by multiplying the micrograms
per gram by 1225.4
Emission data was taken at four power settings:
o Taxi/idle (5 percent power, 65 percent speed)
o 30 percent corrected rated power
o 90 percent corrected rated power
o 100 percent corrected rated power
The resultant gaseous emissions and smoke number data and
the production baseline range for this engine model is sum-
marized in Table 3. The data indicated that while the
gaseous emissions are typical of TPE331 Engines, the smoke
number is relatively low. The conventional smoke number
(SN) is taken at the semi-log graph extrapolated value of
gas weight flow to filter area ratio of 0.0230 Ibs/in or
0.00162 Kg/cm2.
24
-------
Table 3. TPE331 ENGINE EMISSIONS
Engine
TPE331-X-21
Production
baseline
range
Gaseous emission,
kg pollutant per 1000 hp-hr cycle
HC
27.4
24-34
CO
19.1
18-25
N0x
3.5
3.2-4.1
Smoke
number
16
14-23
In order to assess particulate mass and smoke number
inhomogenieties at the reference engine exhaust plane, an
exhaust-plane map was obtained. The exhaust plane of the
engine was divided into twenty-one equal areas as shown in
Figure 8. With the use of a single-point probe, two samples
were obtained at the centroid of each of these areas for
each of the four engine power conditions.
The resulting maps are presented in Figure 9. The
smoke numbers for a given power setting do not vary signi-
ficantly across the exhaust plane except near the edges
(primarily at the top). It was believed that lift forces
on the probe may have caused some displacement resulting in
external air ingestion.
The numbers in parenthesis on Figure 9 are approxima-
tions of particulate concentrations determined from mea-
sured smoke number at each point. These approximations
were obtained from plots of DM450 Metrical particulate
mass versus smoke number as shown in Figure 10. Since
there was considerable scatter* on these plots, a group of
tests was conducted to investigate the repeatability of
*Attempts by Champagne^ ' and Shaffernocker to cor-
relate engine particulate mass emissions and smoke numbers
have produced similar results.
25
-------
(33.27, 102.62)
DIMENSIONS - MILLIMETERS
X, Y COORDINATES
QUADRANTS ARE SYMMETRICAL
Figure 8
TPE331 equal area
mapping diagram.
26
-------
a. IDLE POWER
b. 30% POWER
c. 90% POWER
d. 100% POWER
NOTES: 1.
PARTICULATE-TO-GAS WEIGHT RATIO, Ug/g,
GIVEN IN PARENTHESIS.
2. FILTER MATERIAL - DM450 METRICEL.
Figure 9. TPE331 Exhaust mapping
smoke number.
27
-------
200
tr>
EH
ffi
U
H
p
u
H
EH
100
90
80
70
60
50
40
30
20
10
NOTES:
1. REFERENCE ENGINE
2. OPEN SYMBOLS - 12-POINT AVERAGE PROBE
3. CLOSED SYMBOLS - SINGLE - POINT PROBE
4. 0.85 M3/HR. FLOW RATE
5. DM450 METRICEL FILTERS
x
•
^
— *
xx
A^X
/&
-------
gravimetric data. These tests are discussed in the
following section.
REPEATABILITY TESTS
Considerable scatter was noted in the particulate mass
measurements under constant test conditions and procedures.
Initially, the scatter was thought to be attributed to in-
accurate filter weight measurements. However, subsequent
investigations showed weight measurements of the filters to
be accurate within +5 micrograms and therefore not a major
contributor to the data scatter. Other possible sources of
error that were also investigated and discounted included
sampling line leakages and instrumentation inaccuracies.
Therefore several series of tests were conducted to deter-
mine whether the rate of particulate emission from the
engine was constant.
In the first test, 92 samples were obtained consecu-
tively (to eliminate ambient changes) using the four engine
3
power conditions* and four sample gas volumes (0.0028 m ,
33 3
0.0085 m , 0.0142 m , and 0.0198 m ). For some of these
samples, two filters were placed in series in order to
determine if some of the particulate mass was passing
through the filters. For these samples, the indicated mass
concentration was assumed to be the total mass collected by
the two filters.
As a result of the typical +5 micrograms weighing in-
accuracy, the 16 filters of the 0.0028 m sample volumes
exhibited very large variations in measured particulate
*The major portion of the tests was at 30 percent power.
29
-------
weight concentration and were, therefore, not included in
the analysis.
The test results plotted in Figure 11 show that the
particulate concentration varies significantly from one test
sample to the next. However, the smoke numbers (reflectance
readings) of the DM450 Metrical filters (shown in Figure
12) are relatively uniform.
From these results, it was tentatively concluded that
particulate mass was emitted from the engine at a non-
constant rate. Apparently carbon deposits that accumulate
on the combustor wall occasionally (and erratically due to
engine vibration) break off and are discharged through the
engine exhaust. These would generally be larger particles
and would tend to produce significant scatter in the mea-
sured mass emissions. Since these would be relatively
large particles but few in number, the measured smoke
number would not be significantly effected.
Further, it was anticipated that as the sample volume
is increased (with a constant sample flow rate), the data
scatter would be reduced since longer sampling times would
be required and this would tend to provide a better average
of the erratic particulate mass emissions. The particulate
concentrations measured for three sample volumes at the four
engine power setting^ are summarized in Table 4. As ex-
pected, a reduction in the particulate concentration
standard mean deviation occurs with increasing sample
/
volume for the tests at 30-percent power.
30
-------
O
H
EH
EH
W
O
H
I
o
EH
I
W
U
H
EH
14.0
12.0
: REFERENCE ENGINE
12-.POINT AVG. PROBE
0.85M3/HR.
DM450 METRICEL FILTERS
A- 0.0085M3
D- 0.0142M3
O- 0.0198M
TWO
FILTERS
IN SERIES
I
TWO FILTERS
IN SERIES
OPEN LAB.
WEIGHINGS
50
60
70
80
90
100
TEST NUMBERS IN SEQUENCE
Figure 11. Particulate emissions of engine
repeated tests.
-------
OJ
100
80
w zn
PQ " U
CO
40
20
NOTE:
i
TWO
IN
1. T
2. 1
3. 0
4. D
FILTEE
SERIES
PE331-5
2-POINT
.85 M3/
M450 ME
S
-251, }
AVERAC
HR
TRICEL
£21 ENG
SING PR
FILTER
-GL^
(
LAB(
TftTT?
INE
DBE
5
3PEN
3RATORY
IGHINGS
c
TAX:
100% E
)0% POW:
[-IDLE -
OWER —i
ER-i
If
1 1
0 °
10 20 30 40 50 60
TEST NUMBER IN SEQUENCE
70
80
90
Figure 12. Smoke number of engine repeatability tests.
-------
Table 4. REPEATABILITY TEST RESULTS
Number
of
tests
19
20
20
Total
59
6
9
9
Engine
power ,
%
30
30
30
30
taxi/
idle
90
100
Sample
size,
m3
0-0085
0.0142
0-0198
Group
A
Group A
Group A
Group A
Group A
Particulate
concentration
yg/g
5.43
5.09
4.40
4.96
5.64
3.95
3.75
Particulate
concentration
standard mean
deviation,
yg/g
2.89
2.27
1.25
2.23
1.43
1.74
1.98
(2)
Although not directly related to repeatability, it is
important to note from the data presented in Table 4, that
the particulate concentration decreases at higher engine
power levels even though the smoke number increases. This
trend as well as the level of particulate concentrations
differ significantly with results reported by Champagne.
By using a value of 1225.4 grams of air (dry) to a cubic
meter (standard sea level conditions), Champagne's results
were replotted and are illustrated in Figure 13. As
shown, the data from the reference TPE331 Engine (Table 4)
shows a different trend and higher particulate concentra-
tions than are indicated in Champagne's curves. The dis-
crepancy between this data and the data reported by
Champagne may be attributable to the fact that the TPE331
Engine is a single-spool turboshaft engine configuration
whereas Champagne's data is predominantly from a two-spool
turbojet engine (J79).
33
-------
-L UU . U
80.0
60.0
40.0
5 20.0
£°
^co 1 0 . 0
^ 8.0
2 6.0
EH
^ 4.0
EH
M
O
H
is 2.0
CO
0
o i n
EH -1- • u
H °'8
EH
5 °-6
ID
H 0.4
EH
0.2
0.1
H
0
H
1
H
«j
-
5 . 64 -/
4.96^
3.95-^
3.75-Y
/
1 /
/
'
O PH
o\o.O
0 P^
oo.
o\°
^^
P
r -
/
POWER
0\°
O
0
rH
X
/
CHAMP
>
/
/
/
/
jt
/
\
/
/ \
y
/
k
/
/
/
/
NOTE: NO CORRECTION
FOR PARTICLES
PASSING THROU
SINGLE FILTER
r->TT
DATA REPORTED
GIVES RANGE +1 a
OR STANDARD ~
MEAN DEVIATION
10 20 30 40 50
SMOKE NUMBER
60
70
Figure 13. Smoke number versus particulate
concentration for Champagne
results.
34
-------
In order to further investigate the possibility that
data scatter would be reduced at larger sample volumes
(longer sampling time), additional samples were obtained at
the 30 percent power and sample volumes of 0.0198 m3,
0.0283 m3, and 0.0340 m3
The results are shown in Figure 14 reaffirms that
engine exhaust gas particulates can vary significantly dur-
ing the test sequence even through little or no change is
noted in the smoke number. Figure 14 also presents the
measurement of the ambient dust taken at the engine exhaust,
both with and without the engine windmilling. The ambient
dust loading is higher than was previously assumed and it is
evident that future tests should sample such dust during the
test series, preferably at the engine inlet and simulta-
neously with the exhaust gas sample so that each measurement
can be corrected for dust ingestion.
These results, as well as previous results, indicate
that gravimetric measurements of exhaust gas particulates
are susceptible to considerable scatter. However, the smoke
number as given by the DM450 Metrical filters appear to be
consistent and relatively constant for each engine power
setting and/or sample volume. The smoke number variation
of the reference engine with power setting from taxi-idle
to 100% power is readily discernible with the DM450 Metricel
filters but very little absolute change is perceived on
the conventional Whatman #4 filter. The higher sensitivity
of the DM450 Metricel filter to smoke number measurement as
compared to the Whatman No. 4 filters indicates that this
material should be given more general useage. Figures 15
and 16 show how consistent the measurements are from a
series of reference engine tests conducted to obtain the
smoke number for the standard reference W/A = 0.0230 Ib.
2
gas sample/sq. in. of filter area (0.00162 Kg/cm ).
35
-------
to
o
H
EH
EH
O
H
W
U
O
EH
CO
w
EH
U
H
EH
ft
12.0
10.0
tn
6
O
CO
4.0
2.0
0
n AMBIENT DUST (VOL. = 0.028;
O SMOKE NUMBER OF DM450 METR]
(12-POINT AVERAGING PROBE.
O 30% POWER (VOL. = 0.0198M3)
<0> 30% POWER (VOL. = 0.0283M3)
A 30% POWER (VOL. = 0.0340M3
O(
m
am13!
,n n
1 D H
^_A^v/V/^
°000(
1
}UUU
>0oo<>^
JM3)
[GEL FIL,r.
)
>000°<
0
<
o
><>o
CER
>Q000<
>
OA
A A
A y
poooo
>
AAAA
100
80
60
40
20
H
H
«
O
s
en
10
15
20
25
30
35
40
TEST NUMBER - IN SEQUENCE
Figure 14. TPE331, dust and smoke measurements.
-------
H
En
EH
H
w
EH
ffi
. w
(N
g
o
H1 0.0020
0.0010
0.0009
0.0008
0-0007
0.0006
0.0005
0.0004
0.0003
0.0002
0
0.00162 Kg/cm
CO. 0230 lb/in2)
Reference value
for smoke number
determination
NOTES:
3,
4,
REFERENCE ENGINE
TPE331-5-251
12-POINT AVERAGING
PROBE.
0.85 M /HR.
DM450 METRICEL
FILTERS
20
40 60
SMOKE NUMBER
80
100
Figure 15
Smoke number correlation at
taxi-idle condition.
37
-------
0. 004
0 003
j
e
u
tn
X
A nn 9
<
&
«»
<
Pn
<
«
W
EH
|j 0.0010
1 — 1
n onnQ
EH
H n 0008
p
0. 0007
p,
H
^ 0. 0006
EH
Ed
g 0.0005
H
&
W n 0004
<
Ul
0. 0003
0.0002
/
/
/
/
/
/O
t
/
/
/
/
O/
/
/
/
1
if*""N ^
o7
/
o/
/
/
f
/\
/
7o
/
/
X
^-^
0.00162 Kc
S
j/cm
(0.0230 lb/in2)
Reference value
for smoke number
determination
xV NOTES: 1. REFERENCE ENGINE
V TPE331-5-251
^ 2. 12-POINT AVERAGING
PROBE .
3
3. 0.85 M /HR.
4. DM450 METRICEL
F:
ILTER
20
40 60
SMOKE NUMBER
80
100
Figure 16. Smoke number correlation at 100 percent power.
38
-------
The standard reference value can be obtained from a
flow sample of approximately 0.01 m3 with the 47 mm filter
diameter. The filter has an exposed (filter) area of 7.81
2
cm . The DM450 Metricel filter has not been used for tur-
bine engine smoke number measurement evidently because with
engines of smoke number greater than 35, the spot saturates
with respect to reflectance measurements, before the refer-
ence volume/area (0.0016 .kg/cm2) sample can be achieved.
A check on the conventional smoke number of the
reference engine was obtained with Whatman No. 4 to deter-
mine what measureable change in engine smoke emission may
have occurred over the test program (10 months). The data,
shown in Figure 17, was taken at the taxi/idle operating
condition and compared to previous data. The engine smoke
number was unchanged from the value of 10.0. This indicates
the overall engine emissions over the test period were
quite constant.
With improvement in filter weighing techniques as
previously described, additional repeatability tests were
conducted with the TPE331 reference engine at 30-percent
power in a continuing effort to define the factors influ-
encing the data scatter. Data derived from these tests is
presented in Figure 10. The particulate concentrations
measured in these tests were nearly constant; the mean
particulate concentration was 1.49y.g/g with a standard
deviation of 0.09yg/g.
Ambient dust measurements made with the twelve-point
averaging probe in normal test position in the exhaust
plane with the engine windmilling at 20-percent speed
39
-------
CN
D
tn
9
#
rf!
H
EH
iJ
H
PH
EH
H
w
o
H
0.0060
0.0040
0.0020
0.0010
0.0008
0.0006
0.0004
0.0002
- DATA 1ST TEST
- DATA 2ND TEST
- DATA 3RD TEST
REFERENCE
ENGINE
TPE331-5-251
12-POINT
AVERAGING PROBE
WHATMAN NO. 4
FILTERS
T = 15°P
INLET D °
10 20
SMOKE NUMBER
30
40
Figure 17. Weight flow versus smoke number
at taxi-idle condition.
40
-------
NOTES: TPE331-5-251, X21 30% POWER
12-POINT AVERAGINE-PROBE DM450 METRICEL FILTER
100
O S
a D
en 3
80
60
40
<
D
o o c
> O
D
» (
o o
Q D
1 °
1
O
O O <
] D
0 O
> <
Q Q
>
G.O
. 0
tn
•\
^2.0
en n
IS °
9 n
oJ
*^
0
n
>0 0 (
> no <>(
"\ O
} I
• m
1
3
D 0.0141 M
O 0.0283 M3
O 0.0424 M
SHADED SYMBOLS-
AMBIENT DUST
]onoG<
>ODon<
• ^
• ^
25
JO
10 15 20
TEST NUMBER IN SEQUENCE
Figure 18. TPE331 dust and smoke measurements.
-------
showed insignificant concentrations. In the previous test,
Figure 14, measured values ranged nominally from 1.5 to
3.0 yg/g with several points exceeding 3.0 yg/g while
ambient dust concentration measurements ranged from 1.0
to 2.0 yg/g. These represent extraordinarily high con-
centrations of ambient dust (1000 to 2000 yg/in. ) and
presumably they were at least partially the result of
local traffic and turbulence in the vicinity of the test
facility. It is apparent however, that ambient dust can
have a significant effect on the measured particulate
concentration. In order to quantitatively separate the
effect of particulates aspirated through the engine at a
specific data point from those resulting from other vari-
ables that may contribute to the observed scatter (i.e.,
variation in engine carbon particulate production), it would
be necessary to measure inlet particulates with a separate
filter system.
A review of all the repeatability data obtained re-
sulted in the following conclusions:
(a) Filter weighing, instrumentation, and test errors
did not significantly contribute to the observed
scatter.
(b) The particulate concentrations emitted by the
engine and ambient dust can vary irregularly
with time.
(c) The smoke number was relatively constant for each
sample volume in spite of the observed particulate
weight scatter.
42
-------
SECTION VI.
PARTICULATE MEASUREMENT
METHOD DEVELOPMENT
EFFECT OF SAMPLING PARAMETERS
The test arrangement shown in Figure 19, was used to
test the variable parameters shown in Table 5. The refer-
ence engine with the 12-point averaging probe was used. A
Graeco-Latin parameter test square^ using the symbol
designations of Table 5 resulted in a test formulation for
varying the probe and filter flow rates and sample volumes
as follows:
1
2
3
a
Aa
BB
CY
GRID I
b
BY
Ca
A3
c
CB
AY
Ba
GRID II
a 3 Y
A la 2c 3b
B 2b 3a Ic
C 3c Ib 2a
The results are given in terms of particulate weight
to gas flow weight ratio as determined by weighing the
filters and by measuring the DM 450 Metricel smoke number.
Due to the variable test results previously obtained, three
series of tests were made of each grid. The data was
statistically analyzed by regressing sample volume (X.^ ,
probe-flow rate (X ), and filter-flow rate (X3) on parti-
culate concentration and smoke number. Table 6 summarizes
the results.
With the use of the Student "t" test
(4)
it is evident
that the sample volume has a high level of significance
(99.95 percent probability) in the linear relationship with
43
-------
12.2 CM
0.851 CM ID (TYP)
SWAGELOK
(TYP)
1—6.35 CM-
DETAIL A - FLOW DIVIDER
EXHAUST
DISCHARGE
NOZZLE
I INSULATED
SECTION
VACCUM
PUMP
FLOW
DIVIDER1
DIVERTERj
VALVE
HEATED
SECTION
VOLUME
MEASUREMENT
FILTER
HOLDER
NEEDLE
VALVE
ROTOMETER
Figure 19. Particulate sampling system for gas turbine engines.
-------
Table 5. VARIABLE PROBE/FILTER FLOW RATES - TPE331
Block:
Engine - TPE331-5-251, S/N X21
Probe transition line-1.9 meters insulated
Temperature controlled line - 11.3 meters, 80°C
No sample dilution
Sample flow diagram - Figure 19
Variable parameters:
Engine operating conditions
Probe flow rate
Filter flow rate
Gas sample volume
b = 30% power
c = 90% power
A = 0.85 m3/hr
B = 1.70 m3/hr
C = 2.55 m3/hr
a = 0.425 m3/hr
3=0. 638 m /hr
Y = 0.85 m3/hr
1 = 0.0198 m3
2 = 0.0283 m3
3 = 0.0425 m3
Cn
-------
smoke number. Table 6 also shows that the relationship be-
tween volume and particulate concentration at 30- and 90-per-
cent power has a lower level of significance, (60 to 75
percent) than at taxi/idle (99.57 percent). The coefficients
of correlation between these variables are shown in Table 7.
There is the expected good correlation of sample volume with
smoke number and a low level of significance between volume
and particulate concentration.
It had been postulated that low probe-flow rates should
provide erroneously high measured particulate concentrations
(and perhaps smoke number). The analysis of the variable
probe-flow rate data and variable filter-flow rate data does
not provide a strong substantiation for this postulate. At
90-percent power, there is a good correlation of probe- and
filter-flow rate with smoke number; however, at the lower
power conditions there is a low correlation. At all power
conditions, there is a low to moderate correlation between
flow-rate and particulate concentration.
As expected and observed previously, the data also
indicated that the prediction error is reduced at large
sample volumes. Therefore, the data obtained at the largest
gas sample volume [0.0425 m ] was analyzed over the complete
power range to further investigate the significance of probe-
flow rate and filter-flow rate on particulate concentration
and smoke number. The analysis of variance table for this
data is presented in Table 8. It is observed that the coef-
ficients of correlation are very low (0.11 and 0.14) and the
Student "t" test shows a low level of significance (below
75 percent) with respect to smoke number. Thus, it was
concluded that the range of variations in probe-flow and
filter-flow rates used during the test do not affect the
46
-------
Table 6. SUMMARY OF ANALYSIS OF RELATIONSHIP OF VARIABLES
FROM MULTIPLE REGRESSION BY THE STUDENT "T" TEST.
Dependent
variable
Smoke number
Concentration
of
particulate
Power
level
90%
30%
Idle
90%
30%
Idle
Student "t" test for significance of relationship
Volume
(0.0198, 0.0283, 0.0425 m3)
t=19.828>t =3.965
at 99.95% level
t=5.978>t =3.965
at 99.95% level
t=9.772>t =3.965
at 99.95% level
t=0.936>t =0.257
at 60% level
t=1.292>t =0.689
at 75% level
t=-3.259<-2.898
at 99.5% level
Probe flow rate
0.85, 1.70, 2.55 m /h
t=-8.658t =0.257
at 60% level
t=-0.789t =0.257
at 60% level
t=2.056>t =1.740
at 95% level
t=0.921>t =0.689
at 75% level
Filter flow rate
(0.425, 0.638, 0.85 m /h)
t=4.910t =0.257
at 60% level
t=2.474>t =2.110
at 97.5% level
t=2.162>t =2.110
at 97.5% level
t=-2.325
-------
Table 7. SUMMARY OF ANALYSIS OF RELATIONSHIP
OF VARIABLES BY COEFFICIENTS OF
CORRELATION.
Dependent
variable
Smoke number
Concentration
of
particulate
Power
level
90%
30%
Idle
90%
30%
Idle
Correlation coefficient
Volume
(0.0198, 0.0283, 0.0425m3)
0.983
High correlation
0.848
High correlation
0.934
High correlation
0.243
Low correlation
0.326
Low correlation
-0.657
Moderate
correlation
Probe-flow rate
0.85, 1.70, 2.55 m3/h
-0.918
High correlation
0.093
Low correlation
-0.206
Low correlation
0.145
Low correlation
0.482
Low correlation
0.239
Low correlation
Filter-flow rate
0. 425, 0.638, 0.85 m3/h
-0.795
High correlation
0.057
Low correlation
0.098
Low correlation
0.552
Moderate
correlation
0.500
Moderate
correlation
-0.528
Moderate
correlation
-------
Table 8. ANALYSIS OF VARIANCE OF REGRESSION AGAINST SMOKE NUMBER
AT 0.0425 CUBIC METERS GAS SAMPLE VOLUME.
Coefficient of determination 0.0521
Multiple corp. coefficient 0.2282
Sum of squares attributable to regression 15.62083
Sum of squares of deviation from regression 284.37917
Variance of estimate 18.95861
Std. error of estimate 4.35415
Intercept (a value)
87.77083
Analysis of variance for the multiple linear regression
Source of variation D.F.
Due to regression 2
Deviation about regression... 15
Total.... 17
Sum of
squares
15.62083
284.37917
300.00000
Mean
squares
7.81042
18.95861
F
value
0.4120
Variable
no.
Mean
Std.
deviation
Reg.
coeff.
Std. error
of rfg. coe.
Computed
T value
Partial
corp. coe.
Sum of sq.
added
Prop. var.
cum.
1
2
3
0.81667
0.41667
86.00000
0.46177
0.08587
4.20084
1.08333
-6.63333
2.51387
12.10840
0.43094
-.54783
0.11059
-.14005
9.93103
5.68980
0.03310
0.01897
Comp. check on final coeff.
-6.63333
X - Probe flow rate
X - Filter flow rate
X - Smoke number
-------
measured particulate concentration or smoke number signifi-
cantly over the complete engine operational range.
An attempt was made to correlate smoke number with
particulate concentration at different power levels and gas
sample volumes. For this analysis, the effects of probe-
flow rate and filter-flow rate were ignored and only the
larger sample volumes were considered. The resulting
correlation is presented in Figure 20- Two curve fits were
made because the data at taxi/idle was acquired at 65-
percent engine speed, whereas at the other power conditions,
the engine speed was 100 percent. Therefore, the curve
between taxi/idle and 30-percent power is considered an
interpolation, while the data between 30- and 90-percent
power may be represented quite accurately by the curve.
In summary, the following observations and conclusions
were derived from this statistical analysis.
(a) The exhaust gas sample volume should be 0.0283
m or larger to obtain minimum variation of
particulate concentration due to size of gas
sample.
(b) For the TPE331 Engine and within the range of
values tested, probe-flow rate•and filter-flow
rate do not significantly affect smoke number
or particulate concentration at the above
recommended sample volume.
(c) Additional data obtained at several other
engine power conditions (including taxi/idle
at 100-percent speed) could provide a more
complete correlation between particulate
concentration and smoke number.
(d) The conventional exhaust gas smoke number
correlates very well with the volume of the
gas sample.
50
-------
POWER LEVEL
O IDLE POWER (65% NJ.)
Q 30% POWER (100% N]_)
& 90% POWER C100%
0.0198 M GAS
SAMLE VOLUME
0.0283 M3
0.0425 M
14
40
60 70
SMOKE NUMBER
80
90
100
NOTE: OPERATING CONDITIONS
PHOENIX ALTITUDE (335 m)
STATIC OPERATION, T
15°C
Figure 20.
TPE331-5-X21 exhaust gas
particulate concentration
versus smoke number.
51
-------
PARAMETRIC SAMPLING
The reference engine was tested using two sample trans-
fer line lengths of 4.57 meters and 9.14 meters. Stainless
steel tubing with a diameter of 0.9525 centimeters with an
0.0508 centimeter wall was used. The engine was operated at
taxi/idle, 30-percent, and 90-percent rated power. The re-
sulting exhaust gas particulate concentrations and smoke
numbers are given in Figure 21. There does not appear to
be a significant trend with a change in transfer line length.
Although the particulate concentration measured in the taxi/
idle operation with the 9.14 meter line was lower than with
the 4.57 meter line, small increases were observed at the
30-percent and 90-percent power operations.
Deposits of carbon in the probe and transfer lines
decreased through the program of testing on the various
engines due chiefly to the employment of a larger insulated
.transfer line of 0.9525 cm O.D. as compared to the initial
uninsulated transfer line of 0.635 cm O.D. at the rated flow
of 0.85 m /hr. The final average probe and line deposition
rates of carbon amounted typically to less than 5 percent of
the material collected by the filters.
Another parameter of significance in the overall ac-
curacy of the results concerns the amount of particulates
passing through a single DM 450 Metrical filter at normal
gas flow rate of 0.85 m /hr. The data presented in Figure
22 includes the results of testing conducted at the four
power conditions. The material measured on the second of
two filters (also DM 450 Metricel) positioned in series
is shown to increase significantly as the engine power is
increased. This may be due smaller size of particulate
material generated at the higher power.
52
-------
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O 0.0142 M SAMPLE
3
Q 0.0198 M SAMPLE
20 40 60 80
ENGINE POWER, percent
100
Figure 22. Particulates passing through a DM450
Metricel filter.
54
-------
The particulate-to-gas concentrations/ as compared to
the Champagne correlation (shown previously in Figure 13,
if corrected for the material passing through the filter
shown in Figure 22, would result in the concentrations for
the reference engine tests listed in Table 9.
TABLE 9. PARTICULATE CONCENTRATIONS
FOR REFERENCE ENGINE.
Engine
power setting
TPE331-5-251-S/N21
Taxi/Idle
30%
90%
100%
Particulate c
microgram
Two filters
5.81
5.63
4.87
4.68
oncentration ,
s/gram
One filter
5.64
4.96
3.95
3.75
TFE731-2 Engine Tests
A test was conducted with, a TFE731-2 Engine to
measure particulate concentrations at various probe flow
rates and gas sample volumes in order to assess the
effects of non-isokinetic sampling. The TFE731 is a
turbofan engine and thus has an exhaust gas velocity of
approximately twice that of the TPE331. For these tests,
the filter flow rate and engine power were held constant
at 0.85 m3/hr and 90 percent of rated thrust, respectively.
Combinations of the two variables were tested in a random
sequence for a total of twenty individual tests.
The resultant data (Figure 23) did not indicate an
optimum gas sample volume or probe flow rate. Thus
55
-------
Ul
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EH
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ffi
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CO
O
EH
CO
EH
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EH
oo
CO
0
A
-O-
0.02
D_
A
D
A
0. 04
GAS SAMPLE VOLUME, m
0.06
PROBE FLOW RATE
O - 0.85 M /HR
A - 2.55 M3/HR
NOTES: 1. TFE731 TURBOFAN ENGINE
2. 0.85 M3/HR FILTER FLOW
5 10 15
TEST NUMBER IN SEQUENCE
3. 90% POWER
4. 12-POINT AVERAGING PROBE
Figure 23. Statistical experiment, particulates
variable probe anu. sample flow.
-------
apparently obviating the requirement for isokinetic sam-
pling. A plot of the particulate concentration based on
the test sequence is also presented in Figure 23. This
plot indicates that the engine particulate output fluctu-
ated significantly during the initial portion (approximately
30 minutes) of the test and then stabilized at a relatively
constant lower value. As previously discussed, this
characteristic has also been evidenced by the TPE331
Reference Engine in earlier tests. The particulate con-
centration of the TFE731 at 90-percent power appears to
be about twice that of the TPE331 at the same percentage
of rated power.
JT8D-9 Engine Tests
A series of tests were conducted with a JT8D-9 Turbofan
Engine at Aviation Power Supply in Burbank, California, to
determine possible particulate inhomogeneities in the exhaust
flow of an engine having a can-annular combustion system.
"For these tests, particulate samples were obtained with a
12-point averaging probe located 7.6 cm downstream of the
engine exhaust nozzle as shown in Figure 24. Data was ob-
tained at 30- and 85-percent engine power conditions with
both DM 450 Metricel and Whatman.No. 4 filters. The probe
was placed at six different circumferential positions as
depicted in Figure 25. The positions of the probe ori-
fices relative to the engine exhaust nozzle and the nine
combustor cans are also shown. A photograph of the instal-
lation was presented previously in Figure 6.
The probe orifices were located at the center of the
equal annular areas in the same manner as the 12-point aver-
aging probes used in the tests performed with the TFE731
and TPE331. However, the probes used in the TFE731 and
57
-------
FAN
FLOW
CORE
FLOW
75.7 CM
7.6 CM
—12-POINT
AVERAGING
PROBE
HEATED TRANSFER
SAMPLE LINE
OD = 0.9525 CM
LENGTH = 7.32 M
Figure 24. JT8D-9 test setup.
58
-------
PROBE ORIFICES
EXHAUST NOZZLE
COMBUSTOR CAN EXIT
PROBE POSITION
Figure 25. JT8D-9 combustor can/probe relationship,
59
-------
while the probe for the JT8D-9 Engine was exposed to both
fan and core flow. The probes at the smallest radius tended
to be immersed in the core engine exhaust, while the probes
at the largest radius were exposed to the fan exhaust. The
probes at the intermediate radial position were exposed to
mixed flow. DM450 Metricel filters were used to collect
the particulates at a probe flow rate of 0.85 ra /hr. Nearly
all testing was done with a gas sample volume of 0.0141 m
which was necessary because of the very large quantity of
particulate material observed in initial tests (probe posi-
tion Ho. 1). Subsequent tests at other probe positions
produced much lower particulate deposits. After obtaining
samples at the six rake positions, testing was repeated at
the initial probe rake position (No. 1). Ambient dust was
measured twice during the test series.
Test results are given in Figure 26. The average
particulate concentration at 30-percent power is 1.75 +1.43
x 10 grams/gram and the average particulate concentration
at 85 percent power is 15.61 +27.5 x 10~ grams/gram. The
particulate weight obtained at 85-percent power in position
No. 1 was unusually high with considerable scatter. The
test results at the other rake positions also evidenced some
scatter and variation with position. The particulate con-
centration at 30-percent power was very low, particularly
in certain probe rake positions, and may be due to the fact
that the probe samples both fan and engine exhaust flows.
Smoke numbers measured from the DM450 Metricel filters
used in the test are presented in Figure 27. Two important
facts evident from the data are:
60
-------
25
20
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PH ffi O
f-M CH
AA
r"
0 10
20
30 40
50
60 70
80
TEST NUMBER IN SEQUENCE
Figure 26. JT8D-9 discharge flow
particulate concentration.
61
-------
CTi
NJ
-1. UU
90
80
70
PH 60
£ SO
S -^ ^
H
0 40
a
en
30
20
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n i — \ rn Fl
i j i , 1 1 i < — '
D 8
O 3
u°°°
1 . I 1 ' 1 1 ' 1 I . 1
5% POWER
0% POWER
GO ^
O°
Oo0
3 4
PROBE POSITION
Figure 27.
Smoke number CReflectance} data, from JT8D-9
Engine with DM450 Metrics! filters.
-------
(1) As with the previous engine tests, the particu-
late concentration data exhibited a large amount^
of scatter where as the smoke number data was
relatively uniform.
(2) The smoke number data is affected by the probe
position (particularly at 30-percent power) thus
indicating nonhomogenieties in the engine
exhaust.
Conventional smoke numbers (using Whatman No. 4
filters) were obtained. This data is compared to Pratt and
Whitney data in Figure 28. The current measurements are
somewhat higher than the overall correlation given in
PWA-4339, but one sigma equals 3.9, which includes most of
the results. The Von Brand Soiling Index using Whatman
No. 4 filter paper should give essentially the same results
as those shown in Figure 28.
After the JT8D-9 engine test, the probe and lines were
flushed. Although negligible amount of carbon was found,
the probe contained an unusually large deposit of small
metal particles (approximately 20 mg). It was postulated
that since the engine had recently been overhauled, there
may have been a seal or blade-tip rub that produced the
metal particulates. This would also explain some of the
exceptionally high data scatter noted previously in Figure
26.
Particulate Sampling with Exhaust Gas Dilution
An exhaust sample dilution apparatus developed by
Environmental Research Corporation under contract to EPA
63
-------
35
H
P
30
25
20
15
10
0-
WHATMAN
NO. 4
(
2
AT 0.0016 KG/ CM
/
/
TESTS AT
<& X
m/
^/
/
APS, 4/2:
/
/
/
s
/
/
3/74
(
/
<
VBSI
D
/J
/
(VON BRAND
qOTT.TT'
JG INDEX) -
PWA - 4339,
FEB. 1972
EPA CONTRACT
68-04-0627
a = 3.9
20
40
60
80
100
PERCENT OF RATED THRUST
Figure 28. JT8D-9 smoke number by probe
rake-position no. 1.
64
-------
was provided by EPA for use in this program. The con-
struction, and method of operation of the dilution device
is given in Reference 5. In theory the diluter provides
a means to rapidly cool the engine exhaust gas sample to
ambient temperature and thereby condense the unburned
hydrocarbons. The diluted exhaust gas sample would there-
fore contain only solid particulates. Also, since the
sample flow rate was the same as had been used in the
previous tests (0.85 m /hr), the sampling time would be
increased proportional to the dilution rate thus providing
a very accurate average of the engine particulate emission
rate.
A flow diagram of the test arrangement is illustrated
in Figure 29. A single point probe was used in lieu of
the 12-point averaging probe to match the pressure drop
capabilities of the diluter. An insulated line (1.2 meters
long with 1.27 cm diameter) was used for a transition line
between the probe and sample inlet on the diluter. The
temperature of the diluted sample was slightly above the
ambient temperature because of radiation and convection
cooling together with the direct dilution.
The TPE331 reference engine was tested at two power
conditions (30- and 90-percent power) over a range of
dilution ratios. The diluted sample flow rate was 0.85 m /
hr and a gas volume of 0.0283 m was passed through a DM450
Metricel filter. The test results in terms of the exliaust
particulate are presented in Figure 30. The mean parti-
culate concentration and standard deviation of data
obtained previously (Table 4) with the TPE331 at 30- and
90-percent power is also shown on Figure 30. Except for
65
-------
SINGLE POINT PROBE
- INSULATED 1.22-METER
1.27 CM S3 TUBING
VIEW
AA
DILUTEE
HEATED 7.32-METER
0.9525 CM OD, 0.051 CM
WALL S3 TUBING
TO SMOKE
CART
35 CM
1.27 CM
0.4763 CM DIAMETER
ORIFICE
Figure 29. Dilution test setup.
66
-------
TPE331-5-251
S/N21
DILUTION RATIOS
GIVEN AT EACH
POINT
~ 30% POWER
A - 90% POWER
30% POWER — --
(TABLE 4)
012.5:1
DATA AT
90% POWER
(TABLE 4)
TEST NUMBER IN SEQUENCE
Figure 30.
TPE331 exhaust gas particulate sampling
with dilution device.
67
-------
two data points at 90-percent power, particulate concentra-
tion in the diluted sample is somewhat lower than the con-
centration measured previously without dilution. This
suggests that some of the deposit on the filters tested
without dilution is unburned hydrocarbons. The large
discrepancies in the two samples at 90-percent power could
not be determined.
There are other major limitations associated with the
use of the dilution device:
(1) The diluter itself was received in a somewhat
damaged mechanical condition and leakages during
its operation in the tests make very question-
able the overall accuracy of the results. Also,
it is possible that some deposits may have
accumulated in the interior walls of the diluter.
(2) A single-point probe must be used because of
the low pumping capacity of the device. Thus,
the resulting data may not be representative
if the particulate concentration in the engine
exhaust is stratified (nonhomogenous).
(3) Particulate sampling with the dilution device
was very time consuming since the operating
time to obtain the same filter flow rate
varied directly with the dilution ratio.
Thus, a dilution ratio of 20:1 required
engine operation for 20 times the duration
of the direct sampling for the same filter
particulate weight gain.
63
-------
(4) Probe and line deposits were significantly
lower in the above tests - apparently due to
the larger transfer line size.
Cascade Impactor Tests for Particulate Size
A test was conducted with the TPE331 Engine, the 12-
point averaging probe, and a 7 stage Anderson cascade
impactor (a dry impingement device) to determine the size
and distribution of particles emitted from the engine.
The theory of operation for the cascade impactor is as
follows: An exhaust gas sample is drawn through a series
of jets on each impaction stage. Since the jet diameters
progressively decrease from stage to stage, the velocity
imparted to a particle continually increases. Thus at
each stage, successively smaller particles are separated
from the gas stream and deposited on the impaction plates.
A filter located downstream of the impactor collects all
particles with diameter smaller than the last stage
cut-off limit.
A schematic of the test setup is shown in Figure 31.
Type A Glass fiber filters (80 mm diameter) were used on
each stage. The impactor was wrapped with insulation to
reduce convective heat loss. The temperature of gas at
the impactor inlet was typically 120°C and at the discharge
was typically 38°C during the tests. Condensation was not
visually apparent on any of the filter plates. Also,
microscopic and gravimetric analysis of the filtrate
obtained from the probe and line flushings did not reveal
any carbon.
The test conditions are presented in Table 10. The
data is presented in Table 11. It is noteworthy that the
69
-------
ENGINE
EXHAUST
DUCT
12 POINT AVERAGING PROBE
-LINE 1
NOTE:
3-WAY
CONSTANT
AREA BALL
VALVE
1 , T3, T5 ARE METAL
TEMPERATURES T2 AND
T4 ARE GAS TEMPERA-
TURES
FLOW
ADJUSTMENT
VALVES
TO
.VACUUM
CART
3-WAY BALL
VALVE
FILTER
HOLDER
TOGGLE
VALVE
LINE:
1: 1.27CM OD x 0.124CM
WALL x 1.37M-2.54CM
DIA LDS MOLDABLE
0.9525CM FLEXIBLE
LINE TEFLON CORE
4.57M LONG
0.9525CM x 0.051CM
WALL SS, 3.66M
LONG ELECTRICALLY
HEATED
Figure 31.
Cascade impactor test
schematic.
70
-------
Table 10. CASCADE IMPACTOR TEST SEQUENCE
Test number
1
2
3
4
5
6
7
8
9
10
11
Engine power,
percent
Idle
Idle
Idle
30
30
30
90
90
90
100
100
Sample time,
minutes
20
20
45
20
30
45
20
30
20
20
30
71
-------
Table 11.
PARTICULATE TO GAS WEIGHT RATIO COLLECTED BY ANDERSEN
CASCADE IMPACTOR STAGES - FINAL SERIES.
Impactor
stage
number
1
2
3
4
5
6
7
Subtotal
Impactor
exhaust flow
Total
Taxi-idle
test minutes
20
30
45
wc/w ug/g
t) (j
1.70
1.66
1.57
1. 60
1.67
1.74
1.88
11.82
5.89
17.71
1.41
1.52
1.51
2.31
1.63
1.67
1.82
11.87
4.85
16.72
1.18
1.13
1.08
0 . 99
1.23
1.25
1.39
8.25
6.05
14.30
30% Power
test minutes
20
30
45
w /w yg/g
S G
0.17
0 .26
0 .28
0 .65
0 .28
0 .30
0 .41
2.35
1.42
3.77
0 .07
0 .22
0.16
0.67
0 .27
0.25
0.27
1.91
1.64
3.55
0.21
0.14
0.17
0.52
0 .24
0 .24
0 .26
1.78
2.23
4.01
90% Power
test minutes
20
30
45
w /w vg/g
S G
0.48
0.20
0.35
0 .37
0 .49
0 .45
0.53
2.88
2.14
5.02
0 .46
0.18
0 .29
0 .30
0 .38
0 .30
0 .41
2.32
1.60
3.92
0.36
0 .09
0 .26
0.31
0.34
0 .28
0.15
1.79
2.23
4.02
100% Power
test minutes
20
30
WC/W Ug/g
b (j
0 .76
0 .29
0 .34
0 .46
0.57
0 .55
0.50
3.47
1.45
4.92
1.08
0 .30
0 .37
0 .42
0 .53
0.39
0 .36
3.45
2.08
5.53
NOTES :
(1) Type A glass fiber plates used on impactor stages
(2) DM450 Metricel used to filter exhaust flow from impactor
(3) TPE331 Reference engine
(4) Test setup - Figure 31
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particulate concentrations measured on each stage were of
the same order of magnitude for each test indicating a
wider range and more uniform distribution of particles
than has been anticipated.
Assuming that the 50-percent effective stage cutoff
diameter (D50) as given for Anderson Cascade Impactor at
1.7 m /hr to be equivalent to the mass median diameter,
the results of Table 11 were converted into the particle
size distribution data of Table 12.
Reference 6 gives the following D values for the
different stages of the Andersen cascade impactor:
DS (microns) Stage
9.2 1
5.8 2
3.3 3
1.8 4
0.86 5
0.54 6
0.30 7
Additional analysis of the data in Table 11 (30-minute
test) was conducted to determine and illustrate the cumu-
lative mass distribution of particulate emission as a
function of particulate size and engine power level. As
shown in Figure 32, approximately half (50- to 60-percent)
of the particulate mass is below DSQ (MMD) of 1 micron.
Also, at 30-percent power there is no significant emission
of particles having an MMD greater than 10 micron while
at 100-percent power, approximately 20 percent of the
particulate mass emission is contained in particulates
larger than 10 microns.
73
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Table 12. PARTICULATE SIZE VERSUS WEIGHT
PERCENTAGE EMITTED AT VARIOUS
POWER LEVELS BY THE TPE331
REFERENCE ENGINE.
Particulate
size
microns
9.2 +
5.8
3.3
1.8
0.86
0.54
0.30
J_|G Ot3 f\ •**> r\
, , 0.30
than
Particulate Weight Percentage
Taxi-idle
8.80
8.84
8.54
10.06
9.30
9.56
10.45
34.46
30%
Power
3.97
5.84
5.38
16.24
6.97
6.97
8.30
46.69
90%
Power
10.03
3.65
6.95
7.57
9.35
7.96
8.42
46.06
100%
Power
17.61
5.65
6.79
8.42
10.53
9.00
8.23
33.78
NOTE: As derived from Andersen cascade impactor.
74
-------
Q
t-r
<
MH
EH
100
CO
CO
w
EH
CJ
H
EH
Pi
H
O
O
W
W
§
CO
O
CO
CO
f=-i
EH
t—^
f-i
CJ
20
CASCADE IMPACTOR TEST
30 MINUTE SAMPLE TIME
TPE331 TURBOPROP ENGINE EXHAUST EMISSION
INLET AIR TEMPERATURE = 50°F
JET A FUEL
TAXI/IDLE
0 30% POWER
90% POWER
100% POWER
D , MICRONS
Figure 32. Cumulative mass distribution of particulates
as a function of particulate size.
75
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Previous information on smoke particulate size from
the J-57 Engine ' indicated such particles were very
small—a geometric median diameter of 0.53 microns with a
standard deviation of 1.63. Much larger particulates are
indicated by the data from the test with a much larger
range of sizes.
76
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VII. DISCUSSION OF RESULTS
The test results obtained in this program varied
substantially from some theoretical estimates and pre-
liminary assumptions as to gas turbine smoke generation.
Particulate stratification in the exhaust gas flow and
variation of particulate concentration with time was
obtained in testing on all engines. The conventional smoke
number varied only slightly with changes in particulate
concentration being chiefly dependent on the smaller, more
physicologically damaging particulate material not removed
in the atmosphere by gravity. Particulate concentration
in gas turbine exhaust flow as obtained in this study is
of the order of 5 micrograms per gram as compared to 0.05
to 0.20 micrograms per gram typical of urban areas in the
U.S.
It appears that the particulates produced by gas
turbine engines are generated in at least two major paths -
small particles of smoke directly from fuel rich combustion
and from combustor carbon deposits released intermittently
to be shattered into grossly larger particulate by the
turbine blades. This would appear to explain the variation
in particulate concentration with test duration, the more
uniform results with increased sample volume, and the wide
range in particulate size obtained on a cascade impactor.
The experimental technique as developed in this study
cannot compare test results to any true absolute measure-
ments. Hence, the statistical approach necessarily required
considerable point by point evaluation of the techniques
employed. Accurate weighings of filter particulates in the
77
-------
microgram range was achieved by using reference filters
subjected to the same humidity and temperature changes as
the test filters to correct for the weight change of the
test filters (due to water absorption or desorption) and
by following a precise weighing procedure. A specific 12
point averaging probe design as used with a larger insulated
transfer line and heated connecting line was found to gener-
ate little or no carbon deposits. Variation of the probe
flow rates and sample flow rate showed suprisingly small
effect on the particulate concentration measurement. Using
the procedures detailed in this report it now appears
possible to obtain consistent test results for the measure-
ment of particulates.
The particulate generation of a gas turbine can change
significantly and vary between engines of even the same
type. This is basically believed due to the sensitivity of
the combustion process to all the combustion factors; fuel,
£uel nozzle, airflow, pressure, temperature, combustor
geometry, thermal changes, etc. The probe pickup effi-
ciency was also thought to be affected significantly by the
flow capture area ratio which depended on the degree of
isokinetic sampling but this appeared in test results to
have little significance. The exhaust gas mass flow
variation across the exit nozzle is appreciable but as
this varies from engine to engine, the 12 point averaging
probe was designed only with a constant exhaust gas flow
area per probe.
Due to the stratification of the particulates in the
exhaust gas, it is apparently necessary to examine the flow
with several different positions of even the 12 point
averaging probe to obtain a good measurement. For any
specific engine, measurements would also have to be made
78
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at several power levels and over a time duration to deter-
mine intermitten emissions. Thus, the amount of tests to
reasonably specify the particulate emissions of a new engine
could easily involve 40 hours of engine test time and 480
filter samples. Considering the labor involved in the
weighing procedure, it becomes obvious that cost for
measuring the mass of gas turbine exhaust particulates
is substantial. Also, due to the sensitivity of the com-
bustion process on carbon generation, changes in parti-
culate output with engine time, changes in fuel and
operating conditions may be significant. Hence, it does
not appear possible to achieve the original objective of
an economical method for "determining the mass of insoluble
particulates contained in samples of aircraft gas turbine
exhausts, and to relate that quantity to the level of
particulates emitted to the free atmosphere." Never-
theless, the equipment as developed can and should be
used for obtaining better and more accurate engine smoke
numbers using both Whatman No. 4 and DM450 Metricel
filters on a routine basis, and for particulate sampling
on an occasional check basis.
79
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SECTION VIII
REFERENCES
1. Federal Register, Volume 38, Number 136, July 17,
1973.
2. Champagne, D. L., "Standard Measurement of Aircraft
Gas Turbine Engine Exhaust Smoke," ASME Paper - Gas
Turbine Conference March - April 1, Houston, Texas,
1971.
3. Shaffernocker, W. M., and Stanforth, C. M., "Smoke
Measurement Techniques," SAE Paper 680347, 1968.
4. Davies, 0. L., The Design and Analysis of Industrial
Experiments, Hafner Publishing Company, 1956.
5. Tomaides, M, , "Develop a Portable Primary Particulate
Diluter-Sampler for Miscellaneous Mobile Sources,"
ERE Report 7265, September 20, 1972, EPA Contract
No. 68-02-0589.
6. Flesch, Jerome P., et al., "Calibrating Particulate
Air Samplers with Monodisperse Aerosols: Application
to the Andersen Cascade Impactor," Am. Ind. Hygiene
Assoc. Journal, p. 513, Nov-Dec 1967.
7. Stockham, John, et al., "Study of Visible Exhaust
Smoke from Aircraft Jet Engines," IIT Research Inst.,
June, 1971, p. 7.
80
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BIBLIOGRAPHIC DATA
SHEET
1. Report No.
EPA-650/2~75~055
4. Title and Subtitle
DETERMINATION OF AIRCRAFT TURBINE ENGINE
PARTICULATES
3. Recipient's Accession No.
5. Report Date
May 1975
6.
7. Authot(s)
KEITH M. JOHANSEN, EMERSON L. KUMM
8. Performing Organization Repc.
No.
73-210332(12)
9. Performing Organization Name and Address
AIRESEARCH MANUFACTURING COMPANY OF ARIZONA
402 SOUTH 36th STREET
Phoenix, AZ 85034
10. Project/Task/Work Unit No.
2 6ACV-31/1AA010
11. Contract/Grant No.
68-02-1236
12. Sponsoring Organization Name and Address
NATIONAL ENVIRONMENTAL RESEARCH CENTER
RESEARCH TRIANGLE PARK
NORTH CAROLINA 27711
13. Type of Report & Period
Covered
Final,
14.
15. Supplementary Notes
16. Abstracts
SAME AS REPORT
17. Key Words and Document Analysis. 17o. Descriptors
GAS TURBINE ENGINES.
EMISSIONS MEASUREMENT
SMOKE
PARTICULATE MEASUREMENT
17b. Identifiers/Open-Ended Terms
17c. COSATI Field/Group
18. Availability Statement
AVAILABLE TO THE PUBLIC
RELEASE UNLIMITED
19. Security Class (This
Report)
UNCLASSIFIED
^."Security Class (This"
Page
UNCLASSIFIED
21. No. of Pages
89'
22. Trice
FORM NTIS-35 (10-70)
USCOMM-DC 40329-P7)
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