73-28 DWP
Evaluation of the Ethyl Corporation Lean Thermal
Reactor System
June 1973
Emission Control Technology Division
Office of Air § Water Programs
Environmental Protection Agency
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Background
The Ethyl Corporation has had a long term development program
on emission control systems utilizing lean thermal reactors.
Because their system represents a thoroughly tested example
of this type of control technique the Office of Air and Water
Programs contacted the Ethyl Corporation and requested an
evaluation of their system. A test program was undertaken
by the Test and Evaluation Branch.
Device Description
This system incorporated lean carburetion, EGR, and thermal
reactors. A more detailed description, prepared by Ethyl,
is attached.
Test Program
A 1972 Fury III with a 360 CID engine and the Ethyl lean
thermal reactor system was tested. Three tests were conducted
in accordance with the 1975 Federal Test Procedure (FTP) as
described in the November 15, 1972, Federal Register. All
test work was conducted at 4500 pounds inertia weight.
Results
The results from the tests are reported in the attached table.
These results demonstrate that emission levels well below 1975
interim standards can be achieved with this sytem. For com-
parative purposes an average 1972 FTP result was calculated
using results from the first two bags of the reported 1975
test work. Comparison of this data with 1973 certification
emissions levels and fuel economy are shown. This vehicle
demonstrated significantly better emissions and fuel economy
than a similar 1973 certification vehicle. General impression
of vehicle driveability was good.
Conclusions
Ethyl Corporation's lean thermal reactor system installed on
a 1972 Fury (360 CID engine) demonstrated the potential for
achieving emission levels well below 1975 interim standards.
This vehicle as equipped with Ethyl's system als9 demonstrated
good fuel economy and driveability and was lead insensitive.
The vehicle tested did not, however, meet either the statutory
1975 or 1976 standards.
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Emissions and Fuel Economy
1975 FTP
Fuel
Test
Test
Test
1
2
3
HC
gin/mi
.78
.78
.87
CO
gin/mi
5
5
5
.93
.51
.77
NOx
gm/mi
1
1
1
.42
.30
.42
co2 c
gin/mi
756
769
746
.49
.51
.8.0
onsumption
mpg
11
11
11
.23
.05
.96
Average .81
5.74
1.38
757.60
11.41
1975
Interim
Standards 1.5
1976
Interim 0.4
Standards
15.0
3.4
3.1
0.40
Emissions and Fuel Economy
1972 FTP
Fuel
Avg . 3
tests
1973
OP"*.
Results
HC
gm/mi
1.06
2.6
CO
gin/mi
7.07
38.0
NOx
gm/mi
1.42
2.4
CO 2
gin/mi
755.91
...
Consumption
mpg
11.23
9.7
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APPENDIX
LEAN REACTOR SYSTEMS
Carburetion, Mixture and Air Heating, EGR, Ignition Advance,
and Automatic Starting Sequence Device
Carburetion
The effectiveness of the lean reactor system depends primarily on
improved carburetion. The advantages of lean operation have long been
known; but, with conventional carburetion, problems can limit its usefulness.
Problems in making conventional engines lean are that some cylinders may
become much leaner than others, or mixtures within the individual cylinders
may vary. By causing combustion to be poor in some cylinders, this can
produce an increase in hydrocarbon emissions rather than the expected
decrease. Driveability difficulties also can result from poor combustion in
the excessively lean cylinders. Both of these problems tend to increase
when exhaust gas is recirculated for reduction of NOX. Another problem
is that, when an engine is made only moderately lean, NOX increases.
However, this increase occurs only until air-fuel ratios of 15-16:1 have
been reached and, as the mixture is made leaner bey-ond this point, NOX
decreases. Earlier research showed that problems of lean mixtures could
be overcome and the limits of satisfactory lean operation extended if the
air-fuel mixture was very well mixed and evenly divided among the cylinders.
The 3-venturi carburetor was developed to provide a high degree of atomiza-
tion and mixing, along with close-tolerance metering of the air-fuel mixture.
This carburetor utilizes high air velocities for mixing. Other design charac-
teristics also help. These include the geometry of the fuel nozzle and the
use of perforations in the primary throttle plate through which the mixture
passes under some conditions. Also, a mixing tube extends into the intake
manifold beneath the primary throttle.
High air velocities are' produced by the use of a small primary
venturi for light loads and two variable secondary Venturis for higher power
conditions. Thus, the high velocities present under all conditions not only
provide mixing but also give strong metering signals at any engine condition.
These signals, in turn, promote metering accuracy. In addition, the strong
venturi signal permits elimination of the separate idle system and allows
fuel for idling and light load conditions to be provided through the main
nozzle of the primary venturi, which also benefits mixing. Other refine-
ments incorporated in the carburetor include a device for temperature-
compensating the idle mixture ratio, an internal control to increase mixture
flow during deceleration, and a temperature-modulated choke that closely
relates both the degree and duration of choking to engine and under-hood
tmnporatures, Ueo of those aysfcoms, evpn in corrjuncHon w5!:1i F.OTI, \"*<'-
mita an idling air-fuel ratio of about L'l ,'Aii a.ua opai-atiiig aii'-iudi ratiot>
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of 17-18:1 across the speed range. Enrichment to 12:1 A/F occurs at full
power.
Mixture and Air Heating
Quick warm-up is a critical factor in advanced emission control
systems. Several systems are used in the lean reactor to improve perfor-
mance and emissions during the first few minutes after starting. As
mentioned earlier, choking is carefully regulated and the idle air-fuel mix-
ture is temperature compensated. In addition, the intake manifold is modi-
fied in the hot-spot section beneath the carburetor throats to transfer heat
rapidly from the exhaust gas side of the manifold crossover to the intake
side. This provides more rapid vaporization of fuel on the cold start. This
modification consists of discs of finned stainless steel that replace portions
of the normal cast iron structure in the hot-spot area. A crossover heat
control valve directs exhaust gas from one side of the engine through the
crossover and out the other side during the cold-start period. After warm-
up, this valve opens and the exhaust gas bypasses the hot-spot area. Car-
buretor air also is preheated rapidly by the use of a muff-type preheater
installed at one reactor outlet. The conventional temperature control valve
in the air cleaner opens after warm-up to maintain carburetor air at the
normal temperature.
Exhaust Gas Recirculation System
A modulating EGR system is used to vary the amount of EGR used
during different driving modes. The primary signal used to modulate EGR
is venturi vacuum--a measure of engine airflow. This vacuum signal
operates a vacuum motor and, in turn, a contoured cam that positions a
pintle valve located between the exhaust source and the intake manifold.
This basic system is subject to additional controls that actuate a solenoid
valve that either blocks or opens the vacuum line to the vacuum motor.
These controls are shown in Figure A-l. A temperature-sensing switch in
the air cleaner blocks out EGR until carburetor air temperature exceeds
60°F, at which time the engine"can tolerate the dilution. This overcomes
cold-start problems and drive-away deficiencies at low temperatures.
Similarly, to prevent problems caused by charge dilution from exhaust gas
immediately after the engine starts, a time delay in the circuit prevents
the onset of EGR until 40 seconds after the engine starts. EGR also is shut
off during idle and heavy deceleration by a throttle switch that senses the
closed throttle position. Under full-throttle conditions, EGR is shut off by
a manifold vacuum switch as a safety measure to permit full power develop-
ment. A speed switch also interrupts EGR use at speeds above 60-65 mph.
Interruption of EGR at high speeds causes reactor temperatures to decrease
by a bout ZOO"}/1, Thus, thin contvol puvmitti tho uao of high reactor
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temperatures at moderate speeds without excessive temperatures at
extremely high speeds, and contributes both to good performance of the
system and durability of the reactors.
Ignition Advance System
Figure A-2 shows the system used to control distributor vacuum
advance. A solenoid valve opens or closes the vacuum line to the vacuum
advance unit and permits vacuum advance under some operating conditions
but not under others. EGR and ignition timing are related to each other to
maintain good driveability and emission control. Under stabilized engine
operating temperatures, no vacuum advance is applied until EGR has begun
to flow. Then the solenoid opens and vacuum advance is applied. Spark
advance coming on at this point offsets the sluggishness of EGR. However,
when the engine is cold and EGR has not yet become operative, vacuum
advance is desirable for good engine starting and performance. Thus,
temperature overrides are used to apply vacuum advance regardless of
EGR until the temperatures of both the engine block and the air cleaner
exceed 60 °F. Similarly, to prevent overheat problems, vacuum advance is
applied if engine coolant temperature exceeds 220°F. Another circuit main-
tains vacuum advance at high speeds regardless of EGR. Characteristics
of the vacuum advance have been modified to provide greater-than-normal
advance when manifold vacuum is low. This is done to compensate for the
low manifold vacuums that accompany lean mixtures and EGR. The distri-
butor also incorporates a solenoid that can retard ignition timing 10°. This
solenoid is actuated for a few seconds after starting and is controlled by the
automatic starting sequence device (ASD), as described below.
Automatic Starting Sequence Device
To obtain low emissions, it is essential that an engine warm up
quickly with minimum choking. In some experimental cars, momentary use
(about 10 seconds) is made of higher speeds, retarded timing and greater
throttle opening during initial starting to hasten warm-up. Retarded timing
has three effects. One is to reduce hydrocarbon emissions. A second is to
increase the temperature of the exhaust gas. The third is to reduce engine
power output, which permits a larger throttle opening for a given engine
speed* Figure A-3 shows how these factors have been combined into a
simple, automatic starting sequence device. Physically this device con-
sists of a small vacuum-operated piston mounted near the carburetor.
Vacuum is applied through a solenoid valve. When the engine first starts,
the solenoid opens and vacuum is applied to the piston. The piston advances
the throttle in a manner similar to the conventional choke-ope rated high-
speed idle. At the same time, the piston closes electrical contacts to
actuate tho solenoid that retards the distributor about 10° and blocks o/f
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vacuum advance. Thus the device causes a high idle speed with a heavily
retarded spark for about 10 seconds after starting. Then the system dis-
engages and will not reindex to repeat the cycle unless the ignition switch
has been turned off for a few seconds. Thus it does not complicate opera-
tion in the event of an engine stall.
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Vtnturi Vacuum
' Mf /Speed Switch
>60 mph
Time Delay Switch
Control Cam
Ign.
Switch
^Vacuum Motor
Figure A-l. Exhaust Gas Recycle System
-| n Air Cleaner
J— " Temperature
<80ef
Engine
r\ Temperature
•^<6flef >220°f
C.
ijASDJ
1
Switch
Vacuum Motor
Recycle Position
Retard
Solenoid
Vacuum
Advance
-Vacuum Atfvanci
Solenoid
Figure A-2. Modified Ignition System
Retard
Solenoid
Vacuum
Advance
\> Solenoid -^T~
Thuttlo Uvar ^=°={ | Vac Tank
Time Delay
8 sec.&
Temp. Switch
/Ignition Switch
-0=©
Figure A-3. Automatic Start Device (ASO)
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