EPA-460/3-76-021
January 1976
SULFATE AND PARTICULATE
EMISSIONS
FROM AN OXIDATION
CATALYST EQUIPPED ENGINE
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Mobile Source Air Pollution Control
Emission Control Technology Division
Ann Arbor, Michigan 48105
-------
EPA'-460/3-76-021
SULFATE AND PARTICULATE
EMISSIONS
FROM AN OXIDATION
CATALYST EQUIPPED ENGINE
by
Ander Laresgoiti and George S. Springer
Department of Mechanical Engineering
The University of Michigan
Ann Arbor, Michigan 48104
Grant No. R-801476
EPA Project Officer: Gordon J. Kennedy
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Mobile Source Air Pollution Control
Emission Control Technology Division
Ann Arbor, Michigan 48105
January 1976
-------
This report is issued by the Environmental Protection Agency to report
technical data of interest to a limited number of readers. Copies are
available free of charge to Federal employees, current contractors and
grantees, and nonprofit organizations - in limited quantities - from the
Library Services Office (MD35) , Research Triangle Park, North Carolina
27711; or, for a fee, from the National Technical Information Service,
5285 Port Royal Road, Springfield, Virginia 22161.
This report was furnished to the Environmental Protection Agency by
Department of Mechanical Engineering, The University of Michigan,
Ann Arbor, Michigan, in fulfillment of-Grant No. R-801476. The contents
of this report are reproduced herein as received from The University of
Michigan. The opinions, findings, and conclusions expressed are those
of the.author and not necessarily those of the Environmental Protection
Agency. Mention of company or product names is not to be considered
as an endorsement by the Environmental Protection Agency.
Publication No. EPA-460/3-76-021
11
-------
CONTENTS
Page
LIST OF FIGURES iv
ABSTRACT vi
ACKNOWLEDGMENTS vii
Chapter
I. INTRODUCTION 1
II. EXPERIMENTAL APPARATUS 3
2.1 Engine and Fuel 3
2.2 Simulated Exhaust System 4
2.3 Catalysts 6
2.4 Sampling Train 6
III. EXPERIMENTAL PROCEDURE 15
3.1 Test Conditions 15
3.2 Engine and Exhaust Conditioning 15
3.3 Test Procedure 18
3.4 Measurement of Sulfuric Acid Content 19
IV. RESULTS 20
4.1 Particulate Emission 20
4.2 Sulfuric Acid Emission 29
4.3 Sulfur Conversion 30
4.4 Space Velocity 32
4.5 Secondary Air and Air Fuel Ratio 32
4.6 Concluding Remarks 37
APPENDICES
A. ENGINE SPECIFICATIONS AND OPERATING CONDITIONS 39
B. PHYSICAL AND CHEMICAL PROPERTIES OF INDOLENE HO 0 FUEL
SUPPLIED BY AMOCO OIL COMPANY 42
C. ENGINE AIR FLOW RATE AND FUEL FLOW RATE 43
D. CALCULATION OF THE CONVERSION OF S02 TO SOs 44
REFERENCES 54
ill
-------
LIST OF FIGURES
Figure Page
2.1 Experimental Apparatus 5
2.2 Schematic of Sampling Train 7
2.3 Geometry of Probes Used 8
2.4 Particle Collection Unit 10
2.5 Feedback Control Mechanism 12
2.6 Operational Amplifier Circuit 13
4.1 Particulate Emission versus Exhaust Gas Temperature Without
the Catalyst for 35 km h" and 88 km h" Cruise Conditions
and for the 7 Mode Federal Test F rocedure 21
4.2 Particulate Emission versus Exhaust Gas Temperature for
88 km h"1 Cruise Condition, with and without Pelleted Catalyst. 23
4.3 Particulate and Sulfate Emissions and Sulfur Conversion as a
Function of Speed, Temperature, and Fuel Sulfur Content for
the Pelleted and Monolithic Catalysts 24
4.4 Fuel Consumption versus Speed 26
4.5 Particulate and Sulfate Emissions versus Fuel Sulfur Content
for 35 km h"1 Cruise Condition and for the 7 Mode Federal
Test Procedure (Pelleted Catalyst) 27
4.5 Particulate and Sulfate Emissions versus Fuel Sulfur Content
for 35 km h"1 Cruise Condition and for the 7 Mode Federal
Test Procedure (Monolithic Catalyst) 28
4.7 Sulfur Conversion versus Temperature with Speed as Parameter
(Pelleted and Monolithic Catalysts) 31
IV
-------
Figure Page
4.8 Effects of Flow Rate Through the Catalyst on Sulfur Conver-
sion, H2S04 Emission and Particulate Emission (Pelleted Catalyst) • 33
4.9 Effects of Flow Rate Through the Catalyst on Sulfur Conversion,
H2S04 Emission and Particulate Emission (Monolithic Catalyst) 34
4.10 Effects of Secondary Air on Sulfur Conversion, H^SO. Emission,
and Particulate Emission (Pelleted Catalyst) 35
4.11 Effects of Secondary Air on Sulfur Conversion, H-SO. Emission,
and Particulate Emission (Monolithic Catalyst) 36
4.12 Effects of Air Fuel Ratio on Sulfur Conversion, H2S04 Emission,
and Particulate Emission (Monolithic Catalyst) 38
D.I Plug Flow Reactor Model Used in the Calculation of SO- Conversion- 45
D.2 Percent Conversion of S02 into SOj at Chemical Equilibrium 47
D.3 SO- Concentrations at the Catalyst Inlet as a Function of
Temperature and Fuel Sulfur Content 49
D.4 Relationship between Fractions of S02 Converted into SO, and
S0_ Concentrations as a Function of Temperature 52
D.5 Rate Constant as a Function of Temperature for the Reaction
S02 + 1/2 02 *=? S03 53
-------
ABSTRACT
Particulate and sulfuric acid emissions were studied in the exhaust of a
production Chevrolet V-8 engine. Tests were run without a catalyst in the ex-
haust system and with the engine equipped with a pelleted or a monolithic
catalyst. Particles were collected at points along a specially constructed
exhaust system. The weight and sulfuric acid content of the particulate matter,
and the percent of fuel sulfur emitted as H2S04 were determined under different
operating conditions. The effects of the following parameters were studied
during the tests: a) engine speed (tests were performed at various constant
speeds in the range 35-96 Km h~ and under the 7 mode Federal Test Procedure) ,
b) catalyst temperature in the range 573-773 K, c) fuel sulfur content in the
range 0.1-0.3%, d) flow rate through the catalyst, e) amount of secondary air,
and f) air-fuel ratio. The results showed that the sulfuric acid and particu-
late emissions and the sulfur conversion depend mostly on the speed, catalyst
temperature, and fuel sulfur content. Within the temperature range and secondary
air range studied, the type of catalyst, the air-fuel ratio, and the amount
of secondary air did not seem to affect the results significantly.
VI
-------
ACKNOWLEDGMENTS
This work was supported by the United States Environmental Protection
Agency under Grant No. R801476-01.
VII
-------
-1-
I. INTRODUCTION
Gasolines contain a small amount of sulfur which, if the engine is not
equipped with a catalyst, is emitted mostly in the form of sulfur dioxide.
When the engine is equipped with an oxidizing catalyst some of the sulfur
dioxide is converted into sulfur trioxide which, combining rapidly with water
vapor in the exhaust, is emitted in the form of sulfuric acid. Thus, while
oxidation catalysts reduce gaseous emissions they give rise to the emission
of sulfuric acid [1-9]. In addition, the installation of oxidation catalysts
in automobile exhaust systems causes an increase in the amount of particulate
matter emitted [2,3,4,5].
Owing to the possible problems created by the increased sulfuric aci'd
and particulate emissions from catalyst equipped engines, it would be desirable
to understand the mechanisms and parameters which control such emissions,
and to determine the amounts of sulfuric acid and particulates emitted. In
recent years several investigations have been addressed to this problem.
Nevertheless many aspects of the problem remain unresolved. Sulfuric acid and
particulate emissions from actual engines operating at steady and cyclic
speeds were reported in refs. [2-7]. These studies do not indicate fully the
important role of the catalyst temperature because this temperature was either
not reported [5], or was varied only over a limited range (793-939 K) [2-7].
Sulfate emissions in simulated catalyst-exhaust systems were studied by Mikkor
et al [8]and Hammerle and Mikkor [9]. The storage of sulfates in catalysts
was investigated by Hammerle and Mikkor [9].
Results are not yet available to indicate the full effects of engine
variables, fuel sulfur content, and catalyst temperature on the sulfuric acid
and particulate emissions from an actual spark ignition engine equipped with
-------
-2-
oxidation catalysts. The overall objective of this investigation was, there-
fore, to study the influence of these parameters on emissions from a Chevrolet
V-8 engine operating onatest stand dynamometer. Specifically, the amount of
particulate matter and sulfuric acid emitted and the percent of the fuel sulfur
emitted as sulfuric acid (sulfur conversion) were measured as a function of
a) engine speed (both steady and cyclic), b) fuel sulfur content, c) catalyst
temperature, d) flow rate through the catalyst, e) amount of secondary air,
and f) air fuel ratio. The tests were performed with both a pelleted and a
monolithic oxidation catalyst.
-------
-3-
II. EXPERIMENTAL APPARATUS
The apparatus employed in this study was essentially the same as the one
used by Sampson and Springer [10] and by Ganley and Springer [11]. Therefore,
only a brief summary will be given to indicate the changes made and to facili-
tate the reading of the report.
The apparatus consisted of the engine, the simulated exhaust system,
and the sampling train. These components are described in the following sec-
tions.
2.1 Engine and Fuel
The engine used was a 350 CID 250 HP Chevrolet V-8 production engine.
The engine specifications are given in Appendix A.
The engine was mounted on a Midwest Dynamatic eddy current dynamometer
test stand located in a test cell in the Automotive Engineering Laboratory
at The University of Michigan. The engine and dynamometer were instrumented
to monitor and control coolant temperature, oil temperature and pressure,
manifold vacuum, exhaust pressure, and engine speed and load. The air flow
rate to the engine was measured by a rounded approach air cart manufactured
by General Motors Corporation. The fuel flow rate was measured with a burette.
Tests were conducted using Indolene HO 0 (clear) fuel. Di-t-butyl-disul-
fide was added to adjust the sulfur content of the fuel to the desired value.
The physical and chemical properties of the fuel are given in Appendix B.
The engine was lubricated with Valvoline 10 W 40 oil, which is typical
of commercially available motor oils. The oil, oil filter, and PCV valve
were changed at 40 hour intervals.
-------
-4-
2.2 Simulated Exhaust System
Tests were first conducted under cyclic conditions without the catalysts.
Then, in turn a pelleted and a monolithic catalytic reactor were installed
in the exhaust system and tests were performed with each catalyst under steady
and cyclic operating conditions. In the following paragraphs the basic ex-
haust system without the reactor is first described. The changes made to in-
stall the reactors are outlined subsequently.
The exhaust system, connected to the engine, consisted of the standard
exhaust manifolds and cross-over pipe, a surge tank, a 4.27 m long 50.8 mm
diameter pipe, and a sharp edged orifice (Fig. 2.1).
The surge tank was a 304 mm diameter 609 mm long steel cylinder,
insulated with a wrapping of Kaowool. The surge tank was added to reduce the
pressure and flow fluctuations in the exhaust (Sampson and Springer [10]).
The simulated exhaust system consisted of three 609 mm long black pipe
sections, a 180° bend followed by 3 additional 609 mm sections of black iron
pipe. There were six holes in each of the sections. Three 1/8 NPT holes were
located along the top and three 1/4 NPT holes along the sides to allow for the
installation of thermocouples and sampling probes, respectively. All holes
were fitted with plugs when not in use.
A 22.2 mm sharp edged orifice (Orifice A), made to ASME specifications,
was placed at the end of the simulated exhaust system. The purpose of this
orifice was to measure the exhaust flow rates during cyclic sampling, as
described in the next section.
-------
SECONDARY
AIR
AIR PUMP
/ VALVE
ORIFICE D
EXHAUST
MANIFOLDS
/ CHEVROLET
V-8 ENGINE
FLEXIBLE
TUBING
NSULATION
SURGE TANK
SIMULATED
EXHAUST
SYSTEM
iVA A AIA.TTIJ1
CATALYTIC
REACTOR
ORIFICE A
TO EXHAUST
VENT
MQ. 2.1. 1-xpcrimental nrparntus. Circles represent thermocouple nncl sampling locations.
-------
-6-
2.3 Catalysts
Emissions with two catalysts were investigated. One was a pelleted cat-
alyst supplied by General Motors Corporation, the other was a monolithic cat-
alyst supplied by Engelhard Industries{Appendix A).
The catalytic reactors were installed in place of the first segment of
the simulated exhaust system. No other modifications of the exhaust system
were necessary.
After the tests with the pelleted catalytic reactor were completed the
reactor was removed and the monolithic catalytic reactor was installed in its
place. The monolithic reactor was designed to process only half the volume
of the exhaust gas. Therefore, for the monolithic reactor only four of the
eight cylinders (the1 right bank of cylinders) were connected to the simulated
exhaust. The other four cylinders were connected directly to the test cell
exhaust vent.
For both catalysts-secondary air was injected into.the simulated ex-
haust (before the surge tank) by an air pump driven by a V belt from the
crankshaft pulley. The amount of secondary air was controlled by a valve and
was measured by an 18 mm sharp edged orifice (Orifice D, Fig. 2.1) made to
ASME specifications.
2.4 Sampling Train
The sampling train consisted of a probe, a particle collection unit, a
heat exchanger, a flow control mechanism, and two vacuum pumps (Fig. 2.2).
Each of these components is described below.
Two different size probes were utilized in the course of this study.
They were constructed of 316 stainless steel tubing and had the dimensions
given in Fig. 2.3. The larger probes were used when the sample was undiluted.
-------
-7-
EXHAUST PIPE
FROM ENGINE
^ TO EXHAUST
VENT
PROBE
FU3W CONTROL
MECHANISM
PARTICLE
COLLECTION
UNIT
BLEED U
VALVE
L
1
I
TO EXHAUST
VENT
VACUUM
PUMPS
.-inipl
tr;iin.
-------
-8-
PROBE
I
n
A
3.98
2.66
B
6.35
4.99
C
114.2
51.5
D
160.3
56.1
R
24.6
11.5
All Dimensions in mm
Material: 316 Stainless Steel
l:iji. 2.3. (icnmctry of j:rohcs n^cil in tliu stiuly.
-------
-9-
The smaller ones were used when the sample was diluted with ambient air
during cyclic sampling the larger probes were used in both cases). The probes
were located in the center of the exhaust pipe facing the direction of the
flow.
The particle collection unit consisted of a single filter (Fig- 2.4).
The matter collected on the filter was analyzed to determine particulate and
H2S04 emission.
The filters used were Gelman 47 mm diameter type A glass fiber placed
in a modified Gelman 2220 filter holder.
The entire collection unit was surrounded with beaded heaters and enclosed
in a 25 mm thick wrapping of kaowool held in a sheet metal shell. The current
to the heaters was controlled by voltage controllers. The temperature of the
gas sample was measured with chromel-alumel thermocouples inserted into the
gas stream on both sides of the filter holders.
The exhaust gases could be diluted with ambient air to lower the dew
point of the gas mixture and thus avoid condensation of water in the filter.
The flow rate of the dilution air was controlled by the mechanism described
below.
The flow rate through the probe and the amount of dilution air must be
carefully regulated through the tests. The flow rate through the probe must
be adjusted to the proper value for isokinetic sampling (Ganley and Springer
[11]). The dilution air was kept constant at an 8:1 dilution ratio.
At steady operating speeds flow rates of the dilution air and the total sample
were measured by wet test meters installed in the system and the flow rates
were set appropriately. Under cyclic operating conditions the flow rates
through the probe and the dilution system were modified and adjusted
-------
-10-
FROM PROBE
DILUTION,
AIR —
DILUTION
AIR
CONTROL
MECHANISM
INSULATION
HEATERS
FILTER
TO WET
TEST METER
r-chcmntJc of the collection unit. Open circles represent
thermocouple locations.
-------
-11-
continuously. To accomplish this a special flow control system was designed
(Fig. 2.5). The flow rate through the probe was regulated as follows. A
standard 1.3 mm diameter sharp edged orifice (Orifice B) was installed in
the sampling line (Fig. 2.5). The pressure drop across this orifice was mea-
sured by a Ptran 0 - 0.1 psi differential pressure sensitive transistor im-
mersed in a silicon oil bath to minimize temperature fluctuations. The pres-
sure drop across the orifice in the exhaust system (Orifice A) was measured
by a Rahm PT (C) 71 potentiometer type differential pressure transducer. The
signals from the two transducers were compared on an Analog Devices 118A Op-
erational Amplifier. A schematic of the amplifier circuit is given in Fig.
2.6. The difference in the two signals was amplified by an AST/SERVO Systems
Model A-176 DC error signal servoamplifier (Fig. 2.6) and fed to a Kollsman
8090160650, 115 volt 2 phase, 2 pole motor generator. This motor generator
was connected to a stainless steel Whitey 1RS4 type valve through a 50:1 ratio
link "high-precision" gear box. The flow rate through the probe was regulated
by the valve.
The amount of dilution air was controlled by a similar control system
(Fig. 2.5). The orifice in the dilution air line was 5.6 mm in diameter.
The pressure transducer used wasa Bourns Model 503 differential pressure trans-
ducer and the valve used to control the flow was a Whitey 1RS8 brass valve.
The voltage necessary for the pressure transducers was provided by a Kepco
Model CK18-3 and a Thornton 201D type DC power supply while the servoamplifier
and the motor generator were connected to the 117 volt AC line. The ori-
fices were calibrated under steady state conditions. The orifice in the ex-
haust system (Orifice A) was calibrated with a rounded approach air cart
manufactured by General Motors Corporation. The orifices in the sampling line
(Orifice B) and in the dilution air line (Orifice C) were calibrated using the
wet test meters.
-------
EXHAUST
TO EXHAUST
VENT
PROBE
ORIFICE A
PRESSURE
TRANSDUCER
MOTOR
GENERATOR
WA/M II IftJ
VACUUM
ni IftlBC
rUMrb
\
|
1
MOTOR •»
^PMPRATOR
I GEAR
BOX
PARTICLE
COLLECTION
UNIT
_
SERVO-
AMPLIFIER
TRANSDUCER
OPERATIONAL
AMPLIFIER
CIRCUIT
i-o
I
ORIFICE C
L—- DILUTION
AIR
TRANSDUCER
AMPLIFIER
CIRCUIT
Fi». 2.5.
Schematic of the automatic control system.
-------
BIAS VOLTAGE
VOLTS
-7
lOkfl
f ^-^ I\J l\Alr
o—fpVvww—
-L ir* L.n
* lOkli
vww-
SAMPLING PROBE ±
PRESSURE
TRANSDUCER VOLTAGE
10 kA
rVWW—'
lOkfi
-WWW
I
EXHAUST PRESSURE
TRANSDUCER VOLTAGE
0-10 VOLTS
OPERATIONAL
AMPLIFIER
BIAS VOLTAGE
+15 VOLTS
SERVO -
AMPLIFIER
l;i». 2.6. Operational :unolifior circuit. Circles with I1 represent potentiometers.
-------
-14-
Two high vacuum pumps were used to provide the flow through the sampling
train.
-------
-15-
III. EXPERIMENTAL PROCEDURE
All tests were performed following the same sequence of steps: a) the
engine and exhaust system were conditioned, b) particulate samples were col-
lected, c) the weight of the collected particles was measured, and d) the
samples were analyzed for sulfate content.
3.1 Jest Conditions^
A summary of the test conditions under which the samples were taken is
given in Table (3.1).
In test series I and II samples were collected at different positions
along the simulated exhaust system. In all other tests the samples were
collected at one position 400 mm downstream of the catalytic reactor. Tests
III through XX were performed first with the pelleted reactor. The tests were
then repeated with the monolithic catalytic reactor.
The last column in the table describes the various variables studied
during each test.
3.2 Engine and Exhaust Conditioning
Before taking any data the engine and exhaust system were operated at
the test conditions to allow the emissions to stabilize.
Prior to the present study the engine had been operating with Indolene
HO 0 (clear) fuel. Therefore, before Test I the engine was conditioned for
six hours only. The results obtained in these tests did not change with
time indicating that the six hours conditioning time was sufficient.
When a different catalytic reactor was installed, the system was condi-
tioned the equivalent of 2500 km at 88 km h"1 with fuel containing 0.1% sulfur
(in addition, the pelleted catalyst had been previously conditioned the equi-
valent of 8,000 km at 88 km h"1 with fuel containing 0.017% sulfur). Before the
start of each new series of tests, the engine and the exhaust system were
conditioned for three-hours.
-------
Table 3.1 Test Conditions
Test
Series
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
Catalyst
None
Pelleted
Pelleted §
Monolithic
Pelleted 5
Monolithic
Pelleted §
Monolithic
Pelleted 5
Monolithic
Pelleted f,
Monolithic
Pelleted f,
Monolithic
Pelleted §
Monolithic
Pelleted 5
Monolithic
Pelleted §
Monolithic
Pelleted &
Monolithic
Engine
Speed (RPM)
_
1800
1800
1800
1800
1800
1800
2000
2000
2000
2000
1300
Engine
Load BMP
-
24.5
24.5
24.5
24.5
24.5
24.5
30.0
30.0
30.0
30.0
11.7
A/F
Ratio
-
14.6
15.0
15.0
15.0
13.5
16.7
15.0
15.0
17.0
15.0
15.0
Initial
Spark Advance
4°
4°
4°
4°
-8°
4°
4°
4°
4°
4°
4°
4°
Road
Speed
Equivalent
Cyclic
88 km h-1
Cruise
88 km h"1
Crui se
88 km h"1
Cruise
88 km h"1
Cruise
88 km h"1
Cruise
88 km h"1
Cruise
96 km h"1
Cruise
96km h"1
Cruise
96 km h"1
Cruise
96 km h"1
Cruise
64 km h"1
Cruise
Test
-
H2S04 Condensation
Secondary Air
and Space Velocity
Fuel Sulfur
Content
Spark Retard
A/F Ratio
A/F Ratio
Secondary Air
Fuel Sulfur
Content
A/F Ratio
Space Velocity
Secondary Air
-------
Test
Series
XIII
XIV
XV
XVI
XVII
XVIII
XIX
XX
Catalyst
Pelleted §
Monolithic
Pelleted 5
Monolithic
Pelleted §
Monolithic
Pelleted §
Monolithic
Pelleted f,
Monolithic
Pelleted S
Monolithic
Pelleted &
Monolithic
Pelleted S
Monolithic
Engine
Speed (RPM)
1300
1300
1300
1300
750
750
750
-
Engine
Load BMP
11.7
11.7
11.7
11.7
3.9
3.9
3.9
-
A/F
Ratio
15.0
13.7
16.5
15.0
13.0
13.0
13.0
-
Initial
Spark Advance
4°
4°
4°
4°
4°
4°
4°
-
Road
Speed
Equivalent
64 km h"1
Cruise
64 Km h"1
Cruise
64 km h"1
Cruise
64 km h"1
Cruise
35 km h"1
Cruise
35 km h"1
Cruise
35 km h'1
Cruise
FTP
Test
Fuel Sulfur
Content
A/F Ratio
A/F Ratio
Space Velocity
Secondary Air
Fuel Sulfur
Content
Space Velocity
Fuel Sulfur
Content
-------
-18-
3.3 Test Procedure
A typical test was performed in the following manner. The probe was
placed in the location under study, the filters were weighed, placed in the
collection unit, and the system was warmed up.
For steady state sampling the engine was run at fast idle for 5 minutes.
Then the speed was increased to the operating speed and the torque was in-
creased until the desired load was reached. The engine was then run for about
80 minutes to allow for temperatures and particulate emissions to stabilize.
This is particularly important for tests with catalytic reactors because the
reactors tend to store H-SO. x^hile cold and release it when they warm up [9].
For cyclic tests the system was warmed up through 10 cycles before sampling.
After the engine warmed up, the temperature of the collection unit was
adjusted to the appropriate value and sampling started. When the sampling was
not diluted its temperature was adjusted to the same value as that of the
exhaust gas at the location of the probe. When the sample was diluted the
temperature of the collection unit was kept at a temperature which was lower
than the temperature of the exhaust at the location of the probe.
During steady operation (test II through XIX) the temperatures of the
sample and the catalyst were recorded every five minutes. During cyclic op-
eration the temperatures were measured at the end of each cycle. It is noted
that the catalyst temperature was measured with a thermocouple inserted into
the reactor.
In addition to these temperatures the following parameters were re-
corded throughout each test: a) temperature and pressure of the gas through
the wet test meters, b) the engine speed and load, c) fuel flow rate d) air
flou rate, e) manifold vacuum, f) atmospheric pressure, and g) room tempera-
ture.
-------
-19-
After each test the filters were placed for 24 hours in an airtight con-
tainer containing CaCl2 as desiccant. After 24 hours the filters were weighed
and prepared for chemical analysis. The weight of the filter indicated the
amount of particulates in the exhaust. The chemical analysis provided the sul-
fate content of the particulate sample.
3.4 Measurement of Sulfuric Acid Content
The surfuric acid content of the collected particulate sample was de-
termined by the Barium-Thorin Titrimetric procedure [12,13].
The filter was placed in a covered Pyrex flask containing 50 ml of de-
ionized water. After 12 hours, 25 ml of the liquid were taken from the flask,
and placed in a centrifuge for 15 minutes to separate out filter fibers.
Following the centrifuging 15 ml of the liquid were passed through a cation
exchange resin to remove all positive ion interferences. This liquid was
then diluted with deionized water to give a total volume of 25 ml. Ten ml
of this solution were mixed with 40 ml of isopropanol. Two drops of thorin
indicator solution were added to this liquid. The liquid sample thus prepared
was titrated with a 0.001 molar solution of Ba(C104)2 diluted in a mixture
containing 20% deionized water and 80% isopropanol. The change in color of
the liquid was monitored with a Baush and Lomb Spectronic 20 colorimeter by
measuring the change in absorbance of the solution at a wavelength of 520 nm.
The amount of titrant added up to the end of the titration was proportional to
the H2S04 concentration in the sample.
The titrant solution was calibrated against a solution of H2S04 of "known1
concentration. This "known" solution was calibrated by titrating it with a
NaHCO solution using a glass electrode ph meter to monitor the titration.
•J
-------
-20-
IV. RESULTS
The major objective of this investigation was to evaluate the parameters
which affect the sulfate and particulate emissions from spark ignition engines
equipped either with a monolithic or with a pelleted catalyst. Particular
attention was focused on the effects of engine speed, catalyst temperature,
fuel sulfur content, air fuel ratio, and amount of secondary air on the
amount of particulate matter emitted, on the amount of sulfuric acid emitted,
and on the sulfur conversion rate.
It is important to note that in the following tests the effects of the
various parameters were separated. This was accomplished by varying one
parameter at a time. For example the temperatures of the catalysts were
regulated by heating tapes and were thus unaffected by the engine speed or
the secondary air. This must be borne in mind when evaluating the data and
when comparing them to the results in the previous tests where generally sev-
eral parameters were varied simultaneously.
4.1 Particulate Emission
In order to establish the proper sampling conditions for the catalyst
equipped engine, the particulate emission from the engine was measured both
with and without the catalysts. For the engine operating on unleaded fuel
and without the catalyst, particulate emission as a function of exhaust tem-
perature is shown in Fig. 4.1 for 35 and 88 km h"1 cruise conditions (steady
speeds) and for the 7 mode Federal Test Procedure. For exhaust gas tem-
peratures above 390 K the particulate emission remains constant. Particulates
collected above this temperature are mostly carbon formed in the combustion
chamber due to the dehydrogenation of hydrocarbons [10,11,14]. Below 390 K
there is a large increase in particulate emission due mostly to condensation
of high molecular weight organic compounds present in the exhaust gas [15-18].
-------
-21-
0.02-
e
o»
z
g
en
O.OI
o
a:
88 km If1
7mode FTP
-
35kmh~'
\ L_
300 400 500 600
EXHAUST GAS TEMPERATURE K
y\,,. ,1.1. !';irtidilute emission versus exhaust pas temperature
1-cilcral Test Procedure, and 35 km h~' and
tions. Tndolcnc II l 0 fuel f
during 7 Mode
88 Km h"1 cruise condi-
fit to data.
-------
-22-
It is noted that during the 7 mode Federal Test Procedure approximately
twice the amount (by weight) of particulates is emitted as at 35 km h
steady speed (35 km h'1 corresponds to the average speed of the cycle). A
similar trend was observed by Ter Haar et al [19].
Particulate emission as a function of exhaust gas temperature was also
measured with fuel containing 0.017% sulfur (Fig. 4.2). These tests were per-
formed both with and without the catalyst with the objective of determining
the exhaust gas temperature at which most of the sulfuric acid condensed.
Above •* 390 K the results with and without the catalyst agree closely, sug-
gesting that most particles collected are carbon directly emitted from the
combustion chamber [10,11,14]. Deposition in the catalyst may account for the
small difference in the results. There is a sharp increase in the amount of
particulate matter emitted below 390 K. In the absence of the catalyst this
increase is due to condensation of heavy hydrocarbons [15-18]. For the cat-
alyst equipped engine the increase is most likely due to condensation of sul-
furic acid. Below 350 K the amount of particulate matter emitted remained
constant when using a catalyst, indicating that most of the sulfuric acid con-
densed out of the gas stream. Therefore, in all subsequent tests the collec-
tion unit was kept in the 305-315 K temperature range by diluting the sample
with ambient air (dilution ratio 8:1). These temperatures are appropriate
also when fuels with higher sulfur content (i.e. sulfur content higher than
0.017%) are used since in this case the condensation process is completed at
even higher temperatures.
For steady engine speeds the effects of speed, fuel sulfur content and
catalyst temperature on the amount of particulate matter emitted are shown in
Fig. 4.3. The lines shown" in this figure were calculated by the following
expression
-------
-23-
0.02
6
o»
O
LJ
UJ
O
QC
0.01
No Catalyst
With Pelleted Catalyst
o
300 400 500 600
EXHAUST GAS TEMPERATURE K
4.2.
PnrticuJatc emission with nnd without a nellcteSK
Indolene 110 0 fuel with 0.0179. sulfur content. C ) Fi
to data.
-------
-24-
50
c?
CD
^•40
in
g 30
20
10
in
S=Ot%
50
40
30
20
10
723K
673K
50
40
30
20
10
0 20 40 60 80 100120
SPEED km h'1
0 20 40 60 80100120
SPEED km h'1
S--OJX
773K
723K
8. ^
673K
573K
0 20406080100120
SPEED km h'1
03
0.2
O.I
5*02%
773K .
573K
0.3
02
O.I
5=03%
673K
573K
2040 6080100120
SPEED km h'1
0 2040 6080100120
SPEED km h'1
0 20406080100120
SPEED km h'1
1.0
en
06
0.4
I02
Fuel Sulfur
Content =O.I%
Catalyst
Temperature-
1.0
0.8
06
0.4
02
- S*O2%
773K
673K .
573K
1.0
08
06
0.4
02
673K .
573K
0 2O 40 60 8O tOO 120
SPEED km h'1
0 20 40 60 80 100 120
SPEED kmh'1
0 20 40 60 80 100 120
SPEED km h'1
Fig. 4.3. Effects of speed, catalyst temperature, and fuel sulfur con-
tent on sulfur conversion, H2S04 emission and particulate ,
emission. Indolene HO 0 fuel, A/F = 15.0, excess air = 25%.(*»59<-
O f-elleted catalyst date. • T.olithic catalyst data.
, Solid lines were calculated.
-------
-25-
_ 4 /C \f AS_J (3.04 ) ^ k*"1"' (4.1)
' \loo) \iooj \
where A is a constant which is obtained by matching eq. (4.1) to the data.
The data give A in the 2.2-2.8 range. The lines in Fig. 4.3 were computed
using the average value of A=2.4. C is the percent conversion of S02 into
S03 (see top of Fig. 4.3), F is the fuel consumption in g km (Fig. 4.4)
and S is the fuel sulfur content (percent sulfur per weight in the fuel).
Particulate emission under cyclic operation (7 mode Federal Test Pro-
cedure) are shown in Figs. 4.5 and 4.6. In these figures the ranges of par-
ticulate emissions at the steady speed corresponding to the average speed of
the cycle (35 km h"1) are also shown. For the 7 mode Federal Test Procedure
the amount of particulate matter emitted increased linearly with the fuel
sulfur content. A similar increase in particulate matter with fuel sulfur
content was observed with the pelleted catalyst. With the monolithic catalyst
at the steady 35 km h speed the particulate emission seems to be insen-
sitive to the fuel sulfur content. This can be explained by noting that the
rate of reaction at which the SO- to SO., conversion occurs depends on the
concentration of S02 in the exhaust gas at the inlet to the catalyst and on
the catalyst temperature [20]. At low S02 concentrations and at high tempera-
tures the mechanism limiting the formation of SOj is the adsorption of S02
by the catalyst. Under these conditions the reaction rate varies nearly
linearly with the S02 concentration. At high S02 concentrations or low tem-
peratures the rate of reaction becomes constant. In this region the reaction
is controlled by desorption of S03 from the catalyst. In between the adsorp-
tion and desorption controlled regions the reaction is governed mostly by
chemical reaction. The amount of particulate matter emitted is proportional
-------
-26-
120
100
80
60
8
UJ
2O
T T
20
1 T
J I I L
40 60
SPEED km h
80
-i
100
-1.-1. Fuel consumption versus .spccil f ) Tit to data,
-------
0.016
0.012
UJ
UJ
0.008
o
^0.004
a.
PELLETED
7mode FTP
593-648K
0.01-
0.008
g
c/> O006
oo
LU
*
c/)
CM
0.004
Q.002
0 O.I 02 0.3
FUEL S CONTENT %
7mode FTP
593-648K
573K
423 K -\
35 km h't
0 O.I 0.2 0.3
FUEL S CONTENT %
^^^
ludolcnc 110 0 i'uel.
-------
1 0.016
o»
—' 1
_ MONOLITHIC
7mode FTP
1 453-473^
J/5 0.012
en
UJ
0.008-
o
0.004
473K
35km h"1-
0.01
0.008 -
0.006
LU
^0.004 -
0.002 -
7mode FTP
SSkmh'1-
0.1 0.2 0.3
FUEL S CONTENT %
1 6
'
0.1 0.2 0.3 0
FUELS CONTENT %
Particulatc and IbSO/j emissions during 7 Mode Federal Test Procedure and 35 km h-1 cruise
condition. Monolithic catalyst. Temperatures indicated correspond to catalyst temperature
CO
I
Tndolene 110 0 fuel.
-------
-29-
to the sulfuric acid (i.e. S03 formed) in the exhaust (see next section). Thus,
the fact that the amount of particulate matter emitted remained constant indi-
cates that the reactions in the catalyst are in the desorption controlled
region (high S02 concentration, low catalyst temperature) where the S02 con-
centration at the catalyst inlet does not affect the reaction. Since the amount
of S07 is proportional to the fuel sulfur content, in this region the fuel
sulfur content does not influence the results significantly. At higher catalyst
temperatures the reactions are not in the desorption region and the amount of
particulates emitted depends on the fuel sulfur content.
4.2 Sulfuric Acid Emission
The effects of speed, fuel sulfur content, and catalyst temperature on
the amount of sulfuric acid emitted are shown in Fig. 4.3. There is a dis-
tinct similarity between the amounts of sulfuric acid and particulate matter
emitted, because the particulates are composed mostly of sulfuric acid and
uater. The solid lines in Fig. 4.3 were calculated by the expression
.
ioo
The parameters C, F and S were defined in conjunction with eq. (4.1). Note
that the sulfuric acid emission has a minimum at about 90 km h . As will be
shorn in the next section the sulfur conversion decreases continuously with
speed. However, the fuel consumption increases with speed (Fig. 4.4) giving
rise to the minimum in the sulfuric acid emissions.
The sulfuric acid emission for the 7 mode Federal Test Procedure is
shown in Fig. 4.5 and 4.6. As expected the trend in the results is the same
as for the particulate emission because of the relationship between the
amounts of sulfuric acid and particulate matter emitted.
-------
-30-
4.5 Sulfur Conversion
The sulfur conversion (percent weight of sulfur in fuel converted to
sulfuric acid) as a function of speed, fuel sulfur content, and catalyst tem-
perature are shown in Fig. 4.3. The data points are from the measurements.
The lines were computed according to the procedure described in Appendix D.
Note that for all the temperatures tested the sulfur conversion increases
with temperature indicating that the catalytic reaction is kinetically limited
(as opposed to being limited by chemical equilibrium) [20].
The results, crossplotted using temperature as the abcissa and speed as
the variable parameter, are shown in Fig. 4.7. The conversions were extra-
polated to higher temperatures by calculating the reaction rate constants for
higher temperatures using Arrhenius1 equation (see Appendix D). The curves on
the left side of the peaks correspond to reactions in the kinetically limited
region, the ones on the right correspond to reactions in the region limited
by chemical equilibrium. The data of Creswick et al [3], Trayser et al [4],
and Holt et al [7] obtained with a pelleted and monolithic catalyst are also
included in Fig. 4.7. The data reported by these investigators were shifted
"0 K to the right (as suggested by Dr. W.R. Pierson) to account for the fact
that these investigators measured the catalyst temperature at the catalyst exit
and not inside the catalyst.
Mikkor et al [8] also measured sulfur conversion. Their data are not
included here because instead of an engine they used a simulated exhaust system.
Nevertheless, their results show a trend similar to the curves in Fig. 4.7.
Figure 4.3 indicates that an increase in speed produces a decrease in
sulfur conversion. The reason for this is that at higher speeds the flow rate
through the catalyst increases decreasing the residence time inside the catalyst
-------
80
"
8
o
LU
UJ
-I
LJ
CO
60
40
20
^•Present Study
p,« Troyser eta I. (1975)
*Creswicketal.(l975)
wHoltetol. (1975)
550
SSkmh
'1
88kmh~L
96kmh~'
600
700
800
900
1000
CATALYST TEMPERATURE K
4.7 Sulfur conversion as a function of temperature and speed. Indolene HO 0 fuel with
0.1% sulfur content. A/F = 15.0. Excess air 25% (>v5% 02). Open and closed
symbols represent pelleted and monolithic catalyst data, respectively.
^ 1.IJ 1.:
-------
-32-
Note that at catalyst temperatures above *• 900 K the reactions are in the
chemical equilibrium region where the reactions are not affected by the flow
rate, as observed by Holt et al [7].
Figure 4.3 also shows the effect of fuel sulfur content on the sulfur
conversion. The conversion is insensitive to the fuel sulfur content above
^ 573 K indicating that the catalytic oxidation of S02 is limited by adsorp-
tion of S02 by the catalyst (see Section 4.1). Below ** 573 K the conversion
decreases with fuel sulfur content indicating that the limiting mechanism is
desorption of SO, from the catalyst.
4.4 Space Velocity
The effects of space velocity (i.e. the velocity of the exhaust gas
through the catalyst) on particulate and sulfuric acid emissions and on the
sulfur conversion are shown in Figs. 4.8 and 4.9. In general, a reduction in
space velocity and a corresponding increase in residence time result in an
increase of sulfuric acid conversion and hence an increase in the amounts of
sulfuric acid and particulate matter emitted.
4.5 Secondary Air and Air Fuel Ratio
Sulfur conversion, sulfuric acid, and particulate emissions as a function
of secondary air injected into the exhaust before the catalyst are given in
Figs. 4.10 and 4.11. The amount of secondary air does not seem to affect the
results suggesting that there is sufficient oxygen for the reaction to be
completed. These results tend to agree with those reported by Mikkor et al [8]
At smaller amounts of secondary air, the secondary air might affect the re-
sults but the amounts needed to observe these effects could not be achieved
in the present tests.
-------
w
50
40
20
PELLETED
{^\Tofa 1 Exhaust
-
ffik(O.5)x Total Exhaust
i-iH 1 1
I
1
1
-
hT1 64Kmh~' 88kmh~' 96kmh~'
473K 6I3K 673K 723K
0.14
76 0.12
jt
|o.08
ui 0.06
0*
JiO.04
Q02
-
_
-
—
S
r/f
\
_
-
35 km IT' 64 km h"1 88 km h'1 96 km h~'
473K 613 K 673K 723K
.0.3
o
to
0.2
ui
0.1
-
—
I
—
1
-
35 km h-* 64 km h~' 88 km h'1 96 km h'1
473 K 613 K 673 K 723 K
Fi- 4 S !M-fccts of flow rate thromrh a pelleted catalyst on sulfur conversion, II2SO/| emission, nnd
""' ' ivjrticulatc emission. O^cn symbols arc for the entire exhaust passing throu«:h the catnlvst.
Shaded svmbols are for reduced flow rates. Indolene 110 0 fuel with 0.1% sulfur content.
25% excess air (A* 5% 02). A/F = 15.0. Temperatures given are catalyst temperatures.
-------
t>U
»
?,50
0)
< 40
o
U)
t 30
UJ
J20
u.
S 10
v>
MONOLITHIC
-
Q To/to/ Exhaust
W\(O.4)x Total Exhaust
-
' „. nl H
i
1
-
0.14
Tg 0.12
z Ol
2
t» 0.08
(O
2S 0.06
v
^0.04
0.02
-
-'
_
_
-
: .nl
ml Hi
-
-
-
—
^
/»
P
/X/
1
-
-
-
'E
z
o
PARTICULATE EMISSI
' - e 8
__•„• n
i
—
-
35 km h'1 64 km h'1 88 km h'1 96 km h'1
398 K 573 K 623 K 673 K
35 km h'164 km h'1 88 km h'1 96 km If
398 K 573 K 623 K 673 K
35 km h"164 km h"1 88 km h'1 96 km h'1
398 K 573 K 623K 673 K
4.9. Effects of flow rate through a monolithic catalyst on sulfur conversion, II2S04 emission, and
particul.-Jtc emission. Open symbols are for the entire exhaust passing through the catalyst.
Shaded symbols are for reduced flow rates. Tndolene 110 0 fuel with 0.1"<; sulfur content, 25";
excess air («* 5% 02) A/F = 15.0. Temperatures given are catalyst temperatures.
-------
-3.r>
tn
evj
cn
40
£30
^20
UJ
u_
5 10
~ o
o
10
20 30
PELLETED
Speed Catalyst Temp
773 K
* 96 km h'1
oSSkmh'1
a 64 km h'1
o35 km h'1
— Fit to Data
A/F=I5.0
723 K
658 K
427 K
0.14
0.12
J O.I
o>
z 0.08
g
en 0.06
UJ n04
0*0.01
^.,0.02
<
i 1 i i i
A
A*
O
n £%
~ v.^^^
D
e
o»
UJQ3
ui
3 0.2
o
feoi
10 20 30 0 10 20
EXCESS AIR OVER STOICHIOMETRIC %.
30
Hi;. /1. 10. I'.ffcct of sccoiulury ;nr on sulfur conversion, 1I2SU/1 emission,
and particulatc emission For n pelleted catalyst. Tndolene
IK) O Fuel with 0.1". suH-'ur content.
-------
a ^
Ul CO
-J f 10
z
ff*
CO
*.tt f\
& 0
0.06
i
n:
(/>_ OO4
CO i Vx.V^T
^^ /^/NO
^ 0.02
5-
.A.
0
i i i i i
* •*
^ i i i i
10 20 3
i i i i i -
-
-------
-37-
The air fuel ratio does not seem to influence the results provided the
catalyst temperature is kept constant, and sufficient oxygen is supplied (through
secondary air injection) to the catalyst to oxidize the unburned hydrocarbons,
carbon monoxide, and sulfur dioxide (Fig. 4.12).
4.6 Concluding Remarks
The foregoing results indicate that the particulate emission, sulfuric
acid emission, and sulfur conversion are nearly the same for both the mono-
lithic and the pelleted catalyst provided the speed, the fuel sulfur content,
and the catalyst temperature are the same for both catalysts. This implies
that the emission is governed mostly by the operating parameters and depends
less on the type of catalyst (pelleted or monolithic).
As noted before, in the present tests the operating conditions were set
to indicate the effects of the various parameters individually on the emis-
sions. In applying the results to actual operating conditions the appropriate
combination of these parameters must be selected.
-------
-38-
FfcRTICULATE ^804 %S IN FUEL EMITTED
EMISSION 9 km'1 EMISSION 9 km'1 AS HgSC^
g P P p
— S 8 — ro 8 — o> 5
- MONOLITHIC
• -
- •
• •
i i i i
3 14 15 16 17
i i i i
•
e
i i i i
3 14 15 16 17
i i i i
. • _
V
•
i i i i
3 14 15 16 17
AIR FUEL RATIO
Fir.. /1.12. l.ffcct of air fuel rntJo on sulfur conversion, IbSO/i emission,
and ^articulate emission for :i monolithic c;ital«st. 8fi Km h
cruise condition. Excess air 25% («»5% 02) catalyst temperature
623 K, Indolene HO 0 fuel with 0.1% sulfur content.
( ) fit to data.
-------
-39-
APPENDIX A
ENGINE SPECIFICATIONS AND OPERATING CONDITIONS
A.I Engine Specifications
Displacement 350 cubic inches
Horsepower (adv.) 250 at 4800 RPM
Carburetor 2 barrel Rochester
Compression ratio 9.0:1
Bore 4.00 inches
Stroke 3.48 inches
Spark plugs AC R455
Point dwell 30 degrees
A. 2 Steady Speeds
All tests at steady speeds were performed at conditions corresponding
to a full sized 1970 Chevrolet cruising under road load conditions. The
engine speed was calculated from
A/- S* R (A.I)
znr
where S* is the car speed, R is the rear axle ratio, and r is the radius of
the rear tires. For a standard Chevrolet R is 3.07 and r is 351 mm [21].
The load on the engine was calculated from
5HP- _V_ (o.oo27 w + o.ooSl#v (A-2)
~ (>oo \
where V is the vehicle speed (km h"1) , W is the total weight of the car
(17796.8 N) and A is the projected area of the automobile (2.88 m ) [21 ].
-------
-40-
A.3 Cyclic Operating Conditions
The cycle under which the engine was run was an approximation to the 7
mode Federal Test Procedure, Table A.I [22, 23]. The cycle used in the tests
is given in Table A.2.
A.4 Catalysts Specifications
Pelleted Catalyst:
The pelleted catalyst was a General Motors extrudate catalyst with & 5
to 2 platinum-palladium ratio and a nominal loading of 0.332 troy oz/cu ft.
Monolithic Catalyst:
The monolithic catalyst was an Engelhard PTX, type IIB catalyst.
-------
-41-
Table A.I Actual 7 Mode Federal Test Procedure
(The load is to be kept constant at 14 HP)
Mode
I
II
III
IV
V
VI
VII
Speed
km h"
0 (idling)
0-48
48-48
48-24
24-24
24-80
80-15
10-0 (idling)
Time , s
20
14
15
11
15
29
25
8
Cumulative
time, s
20
34
49
60
75
104
129
137
Table A.2 Approximation to the 7 Mode Federal Test Procedure
(For every new mode the torque was set to the value
necessary to produce 14 HP at the maximum rpm).
Mode
I
II
III
IV
V
VI
VII
RPM
700 (idling)
700-1150
1150-1150
1150-900
900-900
900-1800
1800
700
Time, s
20
14
15
11
15
29
25
8
Cumulative
time, s
20
34
49
60
75
104
129
137
-------
-42-
APPENDIX B
PHYSICAL AND CHEMICAL PROPERTIES OF INDOLENE HO 0
FUEL SUPPLIED BY AMOCO OIL COMPANY
Test
ASTM Method
Specification Test Values
Control Limit
API Gravity
Distillation % F
Initial Boiling Point
10% Evap.
50% Evap.
90% Evap.
Maximum
10% Slope
Reid Vapor Pressure
Oxidation Stability Minutes
Gum, mg/100 ml (after Heptane wash)
TMEL grm. lead/gal.
Sulfur-Weight, %
Olefin, %
Aromatic, %
Saturates, %
Octane Research (Clear)
Octane Research (3cc TEL/gal)
Phosphorus, gins. /gal.
Sensitivity (Clear)
Sensitivity (3cc TEL/gal)
D287
D86
D86
D86
D86
D86
D86
D86
D323
D525
D381
D526
D1266
D1319
D1319
D1319
D2699
D2699
D3231
58.0-61.0
75-95
120-135
200-230
300-325
NMT 415
NMT 3.2
8.7-9.2
NMT 600
NMT 4.0
NMT 0.05
NMT 0.10
NMT 10
NMT 35
Remainder
95.0-98.5
NLT 103.0
NMT 0.005
7.0-10.5
NMT 9.0
59.6-61.9
86-93
129-135
220-221
315-318
398-406
2.9-3.9
8.9-9.0
600+
0.2-3.0
0.0-0.01
0.01-0.017
3.9-7.4
26.1-29.5
63.1-71.1
96.6-97.4
105.0-106.2
0.000-0.003
8.3-9.4
7.1-8.5
-------
-43-
APPENDIX C
ENGINE AIR FLOW RATE AND FUEL FLOW RATE
C.I Air Flow Rate
The air flow rate was measured during each test using a rounded approach
air cart manufactured by General Motors Corporation. The pressure drop across
the orifice was measured with a micromanometer and was related to the air
flow rate by the expression
where K is a constant, Ap is the pressure drop across the nozzle (inches of
water) , T . is the room temperature (deg K) and p&t is the atmospheric pres
3.1 IT
sure (in Hg) .
C.2 Fuel Flow Rate
The fuel volume flow rate was measured with a burette. In calculating
the mass flow rate the fuel density was taken to be 0.74 g cm .
-------
-44-
APPENDIX D
CALCULATION OF THE CONVERSION OF S02 TO S03
S0_ is produced by the reaction
In order to calculate the rate constant k it is assumed that the above reac-
tion is a first order, reversible reaction. For such a reaction the rate con
stant (dm3/(h)x(catalyst mass in kg)) is given by [fco]
CD.2)
where (-r^) is the rate of disappearance of S02 (moles of S02 reacted/
catalyst mass kg x h ) , Cso2 is the concentration of S02 (moles/dm3) at a
given position inside the catalyst, (CS02)E is the chemical equilibrium con-
centration of S02 (mole/dm3). rSQ2 and CS02 are not known directly but must
be determined from the information available which are the amount of S02
entering the catalyst (reactor) and the amount of S03 leaving the catalyst. .
In order to utilize the available information we assume that the reaction
takes place in a plug flow type reactor shown in Fig. D.I. For a differential
element containing a dm mass of the catalyst an S02 mass balance gives [20]
dm. CD-3)
Upon integration eq. (D.3) becomes
(r*ti
1*1
-------
CATALYTIC REACTOR
/
FS02
,dm
r+
I
Ji.
tn
^SO
''"
out
SOg'out
I1-1- I'll'}1, flow reactor in the calculation o' c:')-> conversion. X«;)9 denotes the fraction of SO->
transfori'icd to SO-. I;;:MO denotes the nolar flow rate o^ SOo (mol/scc). The subscripts
in and out represent tlic"conditions at the inlet and outlet of the catalytic reactor.
-------
m
-46-
is the mass of the catalyst in the reactor, (Fso2) is the m°lar flow of
S02, (XSo2) is the fraction of S02 converted into S02. The subscripts in
and out represent the conditions at the inlet and outlet of the reactor, re-
spectively,
(D.5)
By assuming that (XsoO = °» and substituting eq. (D.2) into (D.4) we ob-
'£• •
in
tain
«*• , - / , * **>, , . CD.6)
(f*0 \- ~ J kl^oT^'EJ
V -S^ajiit "0
With the definitions
(/"_ \ _ /^,.
(D.7a)
(y
^^
E ~ (C ) 4-fr \ ™ (C \ (D.Tb)
eq. (D.6) yields
(^soJottfr
The subscript E denotes chemical equilibrium. Integration of eq. (D.8) gives
Th° follov;inK calculations were performed for m = 1 kg. (XSO)E as a func-
tion of temperature was obtained by Hammerle et al [9]. Their result is
reproduced here in Fig. D.2. txS02)ont was measurcd in
-------
o
CO
o:
ui r
100
8
CD
o
LJ
ui
••••"*
ro
O
80
60
CM
O
CO
20
500
600
700 800 900
TEMPERATURE K
1000 MOO
fig. D.2. Conversion of SO™ to SO at chemical equilibrium (from Hammerle and Mikkor (9))
-------
-48-
the present experiments. The results of the measurements are shown in the
top three plots of Fig. 4.3. Note that S conversion is the same as
100 x (XS02)out-
(CS02) • was determined as follows. The catalyst was operated with 25
percent access over stoichiometric. This corresponds to an "air fuel ratio"
of 19:1 through the catalyst. The "air fuel ratio" through the catalyst is
defined as
of ft*£ ium&t m Me ff*
The amount of sulfur per kg of exhaust gas is
~
where S is the percent sulfur in the fuel by weight. The number of moles of
SO- per kg of exhaust gas is
CD'12)
since one mole of S in the fuel gives rise to one mole of S02-
Equations (D.10), (D.ll) and (D.12) give
1000 r j \nofe (D. 13)
or
where P . is the density of the exhaust gas. This density was calculated
by assuming that the density of the exhaust gas is the same as the density
of air at the temperature and pressure of the exhaust. The results are shown
in Fig. D.3.
-------
-49-
id5
O
UJ
111
o
o
I
Id7
FUEL SULFUR
CONTENT:
0.1 % .
500 600
J_
_L
700 800 9OO 1000 1100 I2OO
TEMPERATURE K
Fig. D.3. c:oni:cntr;itn-ii ol SO2 -'it tlic inlet '>T the cjt.ilyst
.is ,-i riniction ol" tci'ipcraturc ;md fuel sulfur content.
-------
-50-
In eq. (D.9) (FS02) . is the number of moles of S02 entering the catalyst
per hour
tes
__ 3 fal turned (_S_WJ_\ mo es (D 15)
_ - j— \iool\3Zl kou-r
The results for (FS02)in are 8iven in Table °.l.
In order to obtain k, eq. (D.9) was plotted in Fig. D.4 for various tem-
peratures. The slope of the lines gives the rate constant. The rate con-
stant as a function of inverse temperature is represented in Fig. D.5.
Arrhenius' equation gives the rate constant as [20]
£.
- ft e" *r CD. 16)
where A and E are two constants, R is the ideal gas constant (R = 8.28 joule/
gmol K) and T is the absolute temperature (degrees K) . From the line in
Fig. D.5 the values for A and E are E = 87,450 joule/gmol K, A = 3.3 x 10 .
By knowing k the sulfur conversion can be readily calculated' from eq. (D.9),
i.e.
.^._ ,
(D.17)
irt
-------
-51-
Table D.I Molar Flow of S02 into the Catalyst
Speed
km h"1
96
88
64
22
Fuel
Consumption
kg h -1
10.0
8.3
5.8
3.0
(FSOo) in
g moles Yi~
0.32
0.26
0.19
0.09
-------
10.0
i> hctwcen fractions of SO., converted into S03 and the S02 concentrations as a
function of'temperature. (V
-------
-53-
0.0011 0.0013
0.0015
I/T K'1
0.0017
MO. li.fi. '\-ito constant ;is ?i "unction o1' 1 ci'inrv.-n IIT Tor I'M-
ri-.-ictinn S')-> + I/? 'l^-cs
-------
-54-
REFERENCES
1. Pierson, W.R.; "Sulfuric Acid Generation by Automotive Catalysts,"
Paper No. 42, Symposium on Auto Emission Catalysis, Division of Colloid
and Surface Chemistry, ACS 170th National Meeting, Chicago (August 1975).
2. Pierson, W.R., Hammerle, R.H., and Kuiraner, J.T.; "Sulfuric Acid Aero-
sol Emissions from Catalyst-Equipped Engines," SAE Paper 740287 (1974).
3. Creswick, F.A., Blosser, E.R., Trayser, D.A., and Foster, J.F.j "Sulfuric
Acid Emissions from an Oxidation-Catalyst Equipped Vehicle," SAE Paper
750411 (1975).
4. Trayser, D.A., Blosser, E.R., Creswick, F.A., and Pierson, W.R.; "Sul-
furic Acid and Nitrate Emissions from Oxidation Catalysts," SAE Paper
750091 (1975).
5. Bradow, R.L., and Moran, J.B.; "Sulfate Emissions from Catalyst Cars:
A Review," SAE Paper 750090 (1975).
6. Begeman, C.R., Jackson, M.W., and Nebel, G.J.; "Sulfate Emissions from
Catalyst-Equipped Automobiles," SAE Paper 741060 (1974).
7. Holt, E.L., Bachman, K.C., Leppard, W.R., Wigg, E.E. , and Somers, J.H.;
"Control of Automotive Sulfate Emissions," SAE Paper 750683 (1975).
8. Mikkor, M., Hammerle, R.H., and Truex, T.; "Effects of Hydrocarbons,
Carbon Monoxide and Oxygen on Sulfuric Acid Emission from an Automotive
Catalyst," Paper No. 43, Symposium on Auto Emission Catalysts, Division
of Colloid and Surface Chemistry, ACS 170th Annual Meeting, Chicago
(August 1975) .
9. Hammerle, R.H. , and Mikkor, M. ; "Some Phenomena which Control Sulfuric
Acid Emission from Automotive Catalysts," SAE Paper 750097 (1975).
-------
-55-
10. Sampson, R.E., and Springer, G.S.; "Effects of Temperature and Fuel
Lead Content on Particulate Formation in Spark Ignition Engine Exhaust,"
Environmental Science and Technology, _7» 55-60 (1973).
11. Ganley, J.T., and Springer, G.S.; "Physical and Chemical Characteristics
of Particulates in Spark Ignition Engine Exhaust," Environmental Science
and Technology, £, 340-347 (1974).
12. Fritz, J.S., and Yamamura, S.S.; "Rapid Microtitration of Sulfate,"
Analytical Chemistry, 27_, 1461-1464 (1955).
13. Fielder, R.S., and Morgan, C.H.; "An Improved Titrimetric Method for
Determining Sulfur Trioxide in Flue Gas," Analytica Chimica Acta, 23.
538-540 (1960).
14. Street, J.C., and Thomas, A.; "Carbon Formation in Premixed Flames,"
Fuel, 34, 4-36 (1955).
15. McKee, H.C., and McMahon.W.A., "Automobile Exhaust Particulates Source
and Variation," Journal of the Air Pollution Control Association, 10,
456-462 (1960).
16. McKee, H.C., McMahon, W.A., and Roberts, L.R.; "A Study of Particulates
in Automobile Exhaust," Proc. of the Semi-Annual Tech. Conf., Air Pollu-
tion Control Association, 208-227 (1957).
17. Dubois, L., Zdrojewski, A., Jennawar, P., and Monkman, J.L.; "The Iden-
tification of the Organic Fraction of Air Sample," Atmospheric Environ-
ment, 4_, 199-207 (1970).
18. Cukor, P., Ciaccio, L.L., Lanning, E.W., and Rubino, R.L.; "Some Chem-
ical and Physical Characteristics of Organic Fractions in Air-Borne
Particulate Matter," Environmental Science and Technology, 6_, 633-637
(1972).
-------
-56-
19. Ter Haar, G.L., Lenane, D.L., Hu, J.N., and Brandt, M.; "Composition,
Size and Control of Automotive Exhaust Particulates," Journal of the
Air Pollution Control Association, 22, 39-46 (1972).
20. Levenspiel, 0.; "Chemical Reaction Engineering," John Wiley and Sons,
Inc., 1972, p. 460-524.
21. "Passenger Car Data," Ethyl Corporation, Petroleum Chemicals Division,
100 Park Avenue, New York, N.Y. (1970).
22. Control of Air Pollution from New Motor Vehicle Engines, Federal
Register 31, Part II, 5170-5178 (March 1966).
23. Control of Air Pollution from New Motor Vehicles and New Motor Vehicle
Engines, Federal Register 33, Part II, 8304-8324 (June 1968).
-------
TECHNICAL REPORT DATA .
(Please read Initnicttons on the reverse before completing)
1 REPORT NO
EPA-460/3-76-Q21
2.
I. RECIPIENT'S ACCESSION
4. TITLE AND SUBTITLE
Sulfate and Particulate Emissions from An Oxidation
Catalyst Equipped Engine.
i. REPORT DATE
January 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHORtS)
Ander Laresgoiti
George S. Springer
8. PERFORMING ORGAf
9. PERFORMING ORG -\NIZATION NAME AND ADDRESS
The University of Michigan
Ann Arbor, Michigan 48104
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
R 801476
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. Environmental Protection Agency
2565 Plymouth Road
Ann Arbor, Michigan 48105
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Particulate and sulfuric acid emissions were studied in the exhaust of a production
1970 Chevrolet 350 CID 2-barrel engine; with and without a pelleted and monolithic
oxidation catalyst treating the exhaust. Particulates were collected at various
points along a specially-constructed exhaust system. Total mass and the sulfuric
acid content of the paxticulates were measured, as well as the percent conversion of
fuel sulfur content into emitted sulfuric acid under variations in the following
operating conditions:
a. Cyclic and constant engine speeds
b. Catalyst temperatures
c. Fuel sulfur contents.
d. Catalyst exhaust flow rates.
e. Secondary air flows.
f. Air-fuel ratios
It was found that the total mass and sulfuric acid content of the particulates, as
well as % conversion of fuel sulfur content depend mostly on engine speed, catalyst
temperature, and fuel-sulfur content.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Air Pollution
Total Particulates
Sulfuric Acid
Fuel Sulfur Content
Oxidation Catalyst
Motor Vehicle Emissions
Automotive Emissions
13 DISTRIBUTION STATEMENT
Not Restricted
19 SECURITY CLASS (This Report I
Unclassified
21. NO. OF PAGES
68
20. SECURITY CLASS (Thispage)
22. PRICE
EPA Form 2220-1 (9-73)
------- |