\ EPA-450/3-77-038/
November 1977
MOTOR VEHICLE
EMISSIONS CONTROL
BOOK THREE
REACTION SYSTEMS
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U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 277 1 1
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EPA-450/3-77-038
MOTOR VEHICLE EMISSIONS CONTROL
BOOK THREE
AIR INJECTION REACTION SYSTEMS
B.D. Hayes, Project Director
M.T. Maness, Associate Project Director
R.A. Ragazzi, Principal Investigator
R.A. Barrett, Graduate Research Assistant
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
EPA Grants No. T008135-01-0 and T900621-01-0
EPA Region VIII Project Officer: Elmer M. Chenault
EPA Project Officer: Bruce Hogarth
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Control Programs Development Division
Research Triangle Park, North Carolina 27711
November 1977
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Copies of this publication are available free of charge to Federal employees,
current contractors and grantees, and nonprofit organizations - as supplies
permit - from the Library Services Office (MD-35), Environmental Protection
Agency, 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 the
Department of Industrial Sciences, Colorado State University, Fort Collins,
Colorado, 80523, through Grants No. T008135-01-0 and No. T900621- 01-0.
The contents of this report are reproduced herein as received from Colorado
State University. The opinions, findings, and conclusions expressed are
those of the authors 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-450/3-77-038
11
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MOTOR VEHICLE EMISSIONS CONTROL
-- SERIES OF SEVEN BOOKS --
MOTOR VEHICLE EMISSIONS STAFF., COLORADO STATE UNIVERSITY
BOOK ONE - POSITIVE CRANKCASE VENTILATION SYSTEMS
BOOK TWO - THERMOSTATIC AIR CLEANER SYSTEMS
BOOK THREE - AIR INJECTION REACTION SYSTEMS
BOOK FOUR - FUEL EVAPORATION CONTROL SYSTEMS
BOOK FIVE - EXHAUST GAS RECIRCULATION SYSTEMS
BOOK SIX - SPARK CONTROL SYSTEMS
BOOK SEVEN - CATALYTIC CONVERTER SYSTEMS
ill
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ACKNOWLEDGMENTS
The Motor Vehicle Emissions Control Staff of the Department
of Industrial Sciences at Colorado State University would
like to acknowledge the efforts extended by the Environmental
Protection Agency, Research Triangle Park, and Region VIII
Environmental Protection Agency, Manpower Development
Division.
A special thanks must be extended to the automotive vehicle
equipment and parts manufacturers for their cooperation and
assistance in the development of this training material.
iv
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INSTRUCTIONS FOR THE USE OF THIS BOOK
This book is one of a series designed specifically to teach the concepts
of automobile emissions control systems. Each book is designed to be
used as self-instructional material. Therefore, it is important that
you follow the step-by-step procedure format so that you may realize the
full value of the emissions system which is being presented. The topics
are taught in incremental steps and each topic treatment prepares the
student for the next topic. Each book is divided into sections which
include the introduction, purpose, function, inspection and testing of
the emissions system presented.
As you proceed through this series, please begin with book one and read
the following books in sequence. This is important because there are
several instances where material covered in a given book relies on
previously covered material in another book.
To receive the full benefits of the book, please answer the self-
evaluation statements related to the material. These statements are
separated from the text by solid lines crossing the page. The answers
to the statement can be found at the end of the book as identified by
the table of contents. You should check for the correct answer after
you respond to each statement. If you find that you have made a mistake,
go back through the material which relates to the statement or statements.
Fill-in-the-blank statements are utilized for self-evaluation purposes
throughout the material. An example statement would appear like this:
The American flag is red, white, and
You would write "blue" in the blank and immediately check your answer at
the end of the book.
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The material, statements and illustrations should be easy to follow and
understand. In several illustrations a small ghost named "VEC" (Vehicle
Emissions Control) has been used to make the picture easier to understand.
Upon completion of this series, you should be able to better understand
the emissions control systems and devices which are an integral part of
automobiles today. Your increased knowledge should help you keep these
"emissions controlled" vehicles operating as they were designed to
operate. Respectable fuel economy, performance and driveability, as well
as cleaner air, can be obtained from the automobile engine that has all
of its emissions systems functioning properly.
vi
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CONTENTS
Introduction to Emissions Control 3-1
Hydrocarbons 3-1
Carbon Monoxide 3-1
Oxides of Nitrogen 3-2
Formation of Hydrocarbons 3-2
Formation of Carbon Monoxide .3-3
Formation of Oxides of Nitrogen 3-3
Ignition Timing 3-3
Carburetion 3-5
System Introduction 3-7
System/Component Purpose 3-11
Air Pump 3-12
Inlet Filters 3-13
Pressure Relief Valve 3-15
Diverter Valve 3-16
Gulp Valve 3-18
Check Valve 3-18
Air Injection Manifold 3-20
System/Component Function 3-23
Air Pump 3-23
Pressure Relief Valve 3-24
Diverter Valve 3-24
Gulp Valve 3-29
Check Valve 3-30
Air Injection Manifold 3-32
System Inspection 3-35
System Testing . , 3-37
Air Pump Test 3-37
Gulp Valve Test 3-37
Diverter Valve Test 3-38
Check Valve Test 3-40
Summary 3-43
Answers 3-45
vii
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INTRODUCTION TO EMISSIONS CONTROL
As we all know emissions systems and devices have been installed on the
automobile engine because of the air pollution problem. In order for
you to understand these emissions systems and devices you should have a
background of the problem. All of the emissions control systems were
installed on the engine to reduce just three specific exhaust products.
These are known as products of combustion. The three products which the
emissions systems are designed to reduce are hydrocarbons, carbon monoxide
and oxides of nitrogen.
HYDROCARBONS
Gasoline, like all petroleum products, is made up of hundreds of hydro-
carbon compounds. The name "hydrocarbon" has been given to these com-
pounds because they are made up of hydrogen and carbon atoms. This is
also the reason hydrocarbons have the abbreviation (HC).
Hydrocarbons are gasoline vapors or raw gasoline itself. One reason
hydrocarbon emissions must be controlled is because it is one of the
major components of photochemical smog. Photochemical or "Los Angeles"
smog forms when hydrocarbons and oxides of nitrogen combine in the
presence of sunlight. In order to avoid this smog condition the hydro-
carbon emissions from automobiles must be controlled. Hydrocarbons
also act as an irritant to our eyes and some are suspected of causing
cancer and other health problems.
CARBON MONOXIDE
Another product of combustion that must be controlled is carbon monoxide.
Carbon monoxide has the abbreviation (CO). CO is also hazardous to our
health when it is mixed with the air we breathe. It can cause headaches,
reduce mental alertness and even cause death if enough of it is in the
air. Carbon monoxide is also a problem in that it speeds the formation
of photochemical smog. For these reasons CO emissions must be controlled.
3-1
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3-2
OXIDES OF NITROGEN
Oxides of nitrogen are the last harmful products of combustion we will
discuss. Nitrogen oxides have been given the abbreviation (NO ). As
/\
you already know, oxides of nitrogen and hydrocarbons combine to form
photochemical smog. The sunlight which triggers the formation of photo-
chemical smog has another effect on oxides of nitrogen. Some of the
oxides of nitrogen are broken down and a gas called ozone is formed.
Ozone is a lung and eye irritant and it also deteriorates rubber and
affects the growth of vegetation. Since the nitrogen oxides have these
effects they must also be controlled.
Now that you are familiar with the emissions which must be controlled
let's find out where they originate.
FORMATION OF HYDROCARBONS
Hydrocarbons, you will recall, are fuel vapors or raw fuel. For this
reason hydrocarbon emissions will result from any uncontained supply
of gasoline. Hydrocarbon emissions also come from the tailpipe. If
the automobile engine could achieve "complete combustion," all of the
unburned fuel or hydrocarbons would be used up. However, it is impos-
sible for today's automobile engines to achieve "complete combustion."
Any time the fuel mixture in the combustion chamber is not completely
burned, some hydrocarbons will be emitted from the tailpipe. The two
main'reasons why hydrocarbons are not completely burned are because of
engine misfire and "quench areas." When an engine misfire occurs, none
of the raw fuel or hydrocarbons are burned. When this happens they are
simply exhausted directly to the atmosphere. Quench areas are places in
the combustion chamber where the flame goes out before the fuel is com-
pletely burned. Small cavities such as where the head gasket seals the
cylinder head to the block is a quench area. Another quench area is
located between the top of the piston and the first compression ring.
These areas are sources of hydrocarbon emissions.
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3-3
FORMATION OF CARBON MONOXIDE
Carbon monoxide fs partially burned fuel. Carbon monoxide is formed in
the combustion chamber whenever there is not enough air to burn all the
fuel. This means that whenever a "rich" air/fuel mixture is pulled into
the combustion chamber carbon monoxide will be formed. After the flame
goes out the carbon monoxide is exhausted through the tailpipe and into
the air.
FORMATION OF OXIDES OF NITROGEN
Oxides of nitrogen are also formed in the combustion chamber. These
oxides result from the nitrogen which Is contained in our air. In some
cases combustion temperatures in the automobile engine can exceed 4500°F.
At temperatures above approximately 2500°F, nitrogen oxides will start
forming. Therefore, if combustion chamber temperatures exceed 2500°F,
oxides of nitrogen will be produced and then exhausted to our atmosphere.
Now that you understand how these emissions are formed in the automobile
engine, we will see how changes in ignition timing and carburetor adjust-
ment affect the amount of these pollutants.
As you know, changes in timing and carburetion can have a large effect
on how an engine performs. These changes in timing and carburetion also
can have drastic effects on the amount of pollutants which are present
in the automobile's exhaust. The amount of hydrocarbons, carbon monoxide
and oxides of nitrogen which are present in the exhaust gases will vary
as timing and carburetion adjustments are changed.
IGNITION TIMING
Prior to emissions controlled automobiles, advancing the spark timing
was a common practice. Setting the spark timing this way caused the
spark plug to fire before the piston reached top dead center. This
advanced spark timing allowed the maximum amount of heat energy to be
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3-4
exerted on the piston. As a result the best performance and fuel econ-
omy could be obtained. Unfortunately, this also produced high hydro-
carbon and nitrogen oxide emissions levels.
In order to reduce emissions levels, ignition spark timing was retarded.
By firing the spark plug after the piston reaches top dead center, not
as much of the heat energy is converted to work on the piston. The
extra heat energy which is not used on the piston now passes through
the exhaust valve and into the exhaust manifold. This keeps the exhaust
gas temperatures higher. These higher exhaust temperatures allow burning
of the air/fuel mixture to continue in the exhaust manifold. This further
oxidation or burning in the exhaust manifold helps to reduce HC and CO
emissions.
Another advantage of retarded timing from an emissions standpoint is
that combustion temperatures are not as high. This is due to the fact
that the maximum combustion pressure will be lower. Since the combustion
temperatures will be lower and the formation of oxides of nitrogen de-
pends on temperature, a smaller amount of these pollutants will be ex-
hausted to the atmosphere.
There is one more advantage to using retarded spark timing. As you know,
when ignition timing is retarded the engine's idle speed will drop. This
decrease in idle speed occurs because less heat energy is applied to the
combustion chamber and more heat energy is being supplied to continue the
burning process in the exhaust manifold. In order to regain an acceptable
idle speed, the throttle plates must be opened wider. This wider throttle
plate opening allows more air to pass through the carburetor. This increase
in air flow will reduce the amount of residual exhaust gases in the cylinder,
This in turn will allow a more burnable mixture which can be made leaner.
Since the mixture can be leaner there will be more air in the combustion
chamber. As you know, the more air that is made available during com-
bustion the lower will be the HC and CO emissions.
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3-5
CARBURET I ON
Adjustments made to the carburetor air/fuel ratio can also have a large
effect on the amount of pollutants which come from the automobile engine.
When idle mixture settings become richer there is less air present for
the combustion process. This lack of air results in an increase in hydro-
carbon and carbon monoxide emissions.
When idle mixture screws are turned in, the amount of fuel is reduced
and the mixture becomes leaner. This leaner mixture contains more air
and therefore more oxygen is available for more complete burning of the
fuel. This results in lower HC and CO emissions levels.
As the idle mixture screws are turned in, the idle air/fuel mixture be-
comes leaner. If this mixture becomes too lean a "lean misfire" will
occur. A "lean misfire" will occur because the fuel is so diluted or
thinned out by the air that the mixture will not ignite. This leads to
a very large increase in hydrocarbon emissions. This happens because
the failure of the mixture to ignite results in that amount of raw fuel
being emitted to the atmosphere.
The carbon monoxide emissions decrease when a lean misfire condition is
present. Carbon monoxide is partially burned fuel. Since no combustion
takes place during a lean misfire condition no CO is formed and the total
amount of CO produced by the engine will be less.
A lean misfire usually occurs in one or more cylinders. This condition
may also move from cylinder to cylinder while the engine is running.
This is caused by the uneven distribution of the air/fuel mixture
delivered to each cylinder. This condition occurs mainly because of
problems with intake manifold design.
Now you should understand how changes in timing and carburetion adjust-
ment can affect emissions levels. With this knowledge you will be able
to understand how each emissions control system we will discuss helps to
reduce the air pollution caused by the automobile.
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AIR
3-7
SYSTEM INTRODUCTION
The next system we are going to discuss is the AIR system. As you remem-
ber from the introduction of this book, hydrocarbons and carbon monoxide
emissions must be controlled. The AIR system greatly helps reduce these
two emissions. Before we go any further with this system let's briefly
review what happens after the exhaust gases leave the combustion chamber.
As you recall when ignition spark timing is retarded the exhaust gas
temperatures will be hotter. Using retarded timing helped to continue the
burning or "oxidizing" of the unburned hydrocarbons and carbon monoxide.
This takes place because there is a small amount of air in the exhaust
manifold and when the hot exhaust gases come in contact with this air
they can continue to burn. The amount of burning which takes place in
the exhaust manifold depends on just how much air is availalbe. Unfortu-
nately, there is not enough air in the manifold to burn all the hydrocar-
bons and carbon monoxide which are present in the exhaust gases.
The AIR system is designed to supply more air to the exhaust manifold and
actually burn the unburned portion of the exhaust gases. This reduces
the harmful hydrocarbon, HC, and carbon monoxide, CO, emissions. These
exhaust gases should be further oxidized before they go out the tailpipe.
Because of the incomplete combustion taking place in the cylinders,
carbon monoxide and hydrocarbons are pushed out of the cylinders during
the exhaust stroke. If the hydrocarbons and carbon monoxide in the
exhaust manifold continued to burn, the harmful gas, carbon monoxide,would
change to the harmless gas, carbon dioxide which has a symbol CCL. The
HC that is burned in the exhaust manifold because of the AIR system, is
reduced to water vapors which have a symbol ^0.
The AIR system injects air into the exhaust manifold. This is how this
system got its name. AIR stands for air injection reaction. However,
different manufacturers have their own name for this system. Figure 3-1
shows the different names which are used for this system. Even though
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3-8
n
VEHICLE
MANUFACT.
AMERICAN
MOTORS^tORP
CHRYSLER
CORPORATION
fi)RD MOTOR
COMPANY
GENERAL
MOTORS CORR
AIR INJECTION
SYSTEM
A, G.
(AIR GUARD)
AIR
INJECTION
THERMACTOR
A.I.R.
(AIR INJECTOR
REACTOR)
^^
FIGURE 3-1
each manufacturer uses a different name for this system they all have the
same purpose and all function in the same way.
The AIR system was first used on automobile engines in 1966. During 1966
and 1967 most of the automobiles which were equipped with an AIR system
were sold in California. Starting in 1968 AIR systems were installed on
many engines throughout the country. Many of the foreign automobiles
which are imported into this country also have air injection systems.
Since the AIR system does its job after the combustion takes place in the
cylinder, the system is very beneficial. It does an effective job of
reducing HC and CO from the exhaust. It also allows the manufacturers to
change carburetion and ignition timing to give better driveability.
1. The amount of secondary burning or oxidizing which takes
place in the exhaust manifold depends on how much
is available.
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2. The AIR system injects fresh air into the
AIR
3-9
3. AIR is the abbreviation for
4. The AIR system does its job after
takes place in the cylinders.
5. and
are effectively reduced by the AIR system.
6. By using the AIR system manufacturers could change
and ignition timing to give us
better driveability.
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AIR
3-11
SYSTEM/COMPONENT PURPOSE
Now that you are familiar with how the AIR system helps control the
emissions of hydrocarbons and carbon monoxide it is time to take a
closer look at the components of this system. First you will look at
each component separately to find out what part it plays in the AIR
system.
The components of the AIR system are shown in figure 3-2. As you can
see this system is composed of an air pump, a diverter valve, a check
MANIFOLD VACUUM
SIGNAL LINE
DIVERTER
VALVE
MANIFOLD
FIGURE 3-2
valve, an air injection or distribution manifold and the connecting hoses
and vacuum lines. V8 engines use two check valves and two injection
manifolds.
Figure 3-3 shows where these components are usually located on a V8
engine.
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3-12
CONNECTING
HOSE
CHECK
VALVE
CONNECTING
CHECK
VALVE
FIGURE 3-3
AIR PUMP
Since the AIR system supplies the exhaust manifold(s) with additional
air to oxidize or burn the hydrocarbons and carbon monoxide, a means of
"pumping" outside air into the exhaust manifold must be used. This is
the job of the air pump. The air pump is a belt driven pump and as you
can see in figure 3-4, it is located much like other belt driven engine
components.
FIGURE 3-4
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AIR
3-13
The air pump drav/s fresh air from the engine compartment through an
inlet, usually located in the pump itself. Part of this air inlet serves
as a filter to remove any foreign matter from the air. If dirt or dust
is allowed into the air pump it could possibly damage the pump and render
the system useless.
INLET FILTERS
The most popular air pump inlet and filter arrangement is shown in
figure 3-5.
AIR INLET
FIGURE 3-5
The air enters the pump and is filtered by a centrifugal fan filter.
This filter is actually part of the pump itself.
The second method which can be used is the external filter shown in
figure 3-6.
As you can see the filter and air inlet are separated from the pump
itself. A hose is used to connect the filter to the pump.
Figure 3-7 shows the location of the pump discharge or outlet.
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3-14
AIR INLET
FIGURE 3-6
PULLEY
PUMP
DISCHARGE
AIR IN
TO DIVERTER VALVE
FIGURE 3-7
A hose is connected to the pump outlet so the supply air can move on to
the diverter valve and injection manifolds.
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AIR
3-15
An
supplies the air for the air injection
system.
8. Before air enters the pump it passes through an
to remove any dust particles.
9. The AIR system uses a
driven pump.
PRESSURE RELIEF VALVE
The air pump is usually equipped with a pressure relief valve. This
valve is shown in figure 3-8. This pressure relief valve limits the
maximum pressure from the pump. This is done to prevent exhaust system
PRESSURE RELIEF VALVE
FIGURE 3-8
overheating at high engine speeds. Limiting the maximum pump pressure
can also be done at the diverter valve. For this reason, not all air
pumps will have a built-in pressure relief valve.
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3-16
DIVERIER VALVE
A diverter or anti-backfire valve and its various connections is shown
in figure 3-9.
TO AIR
MANIFOLD 8
CHECK VALVE
/
DIVERTED AIR
TO ATMOSPHERE
INTAKE
MANIFOLD
VACUUM
?> AIR
ANIFOLD
CHECK
vALVE
FROM
AIR
PUMP
FIGURE 3-9
This valve has been called several different names. The purpose of the
valve, regardless of its name, is the same. The valve's job is to prevent
backfire by momentarily diverting the air pump's output. This is done so
that air does not reach the exhaust valve area during the initial stages
of engine deceleration. Engine deceleration takes place when you take your
foot off the gas pedal. When this occurs the throttle plates in the
carburetor close creating a high vacuum condition just beneath the throttle
plates. Because of this vacuum condition rich air/fuel mixture is drawn
into the cylinders. This rich mixture cannot burn completely during the
power stroke so much of the mixture is pushed out past the exhaust valves
and into the exhaust manifold. If the AIR system was allowed to inject
fresh air into the exhaust ports under this condition, an undesirable
backfire would occur. This backfire would take place as soon as the fresh
air mixed with the overly rich exhaust gases. This valve is called a
diverter valve because it diverts the air from the air pump away from the
exhaust manifold and out to the atmosphere. It's called an anti-backfire
valve because it prevents backfiring during deceleration.
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AIR
3-17
A muffler was installed on the diverter valve to prevent the loud noise
when the valve diverts the air to the atmosphere. On newer engines, the
muffler is internal and you cannot see it. The older type diverter
valves had an external muffler. Figure 3-10 shows both types of diverter
valves.
DIVERTER VALVES
EXTERNAL MUFFLER
INTERNAL MUFFLER
FIGURE 3-10
10. Most air pumps are equipped with a
valve.
11. Maximum pump pressure is limited by the pressure relief
valve. This is done to prevent exhaust system
at high speeds.
12. In order to prevent a
in the exhaust
system during deceleration, the AIR system uses a diver-
ter valve.
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3-18
13. The diverter valve is usually very noisy when it diverts
air to the atmosphere. To prevent this noise a
was installed.
GULP VALVE
Some manufacturers use another type of anti-backfire valve which 1s called
a gulp valve. This valve allows air from the air pump to be sent to the
intake manifold when the engine decelerates. This air will dilute the
rich fuel mixture before it goes into the cylinder, thus preventing a
backfire. Figure 3-11 shows a gulp valve.
GULP VALVE
FIGURE 3-11
CHECK VALVE
The next component of the AIR system we shall discuss is the check
valve. A check, valve is used to prevent exhaust gases from reaching the
hoses, pump or anti-backfire valve.
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AIR
3-19
The air pump has enough pressure to keep the air flowing toward the air
pipe assemblies. But what would happen if the pump stopped pumping air
for some reason or if an air hose would break? Exhaust gases would go
into the air pipe assembly instead of the tailpipe. It is the check
valve's job to prevent this from occuring. The check valve prevents hot
exhaust gases from backing up into the hoses and pump. A check valve is
shown in figure 3-12. The check valve is a one-way valve. This means
CHECK VALVE
FIGURE 3-12
that it will permit air to flow 1n only one direction or one way. On an
in-line engine there is only one check valve, because there is only one
air injection manifold. There are two air injection manifolds on V8
engines and therefore two check valves. Check valves are usually mounted
on the air injection manifold and connect to the diverter valve with a
rubber hose.
14. The gulp valve used by some manufacturers diverts air
from the air pump to the _______________
during the first few seconds of deceleration.
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3-20
15. During the first few seconds of deceleration the gulp
valve will dilute the rich fuel mixture before it goes
into the cylinder, thus preventing a .
16. When exhaust pressure is higher than the system air
pressure, the valve prevents the back flow of
exhaust gas into the air supply hoses.
AIR INJECTION MANIFOLD
The last component of the AIR system we shall discuss is the air injection
manifold. Some manufacturers call their injection manifold an air
distribution manifold. The purpose of the air injection manifold is to
distribute the pump air to the exhaust ports of each cylinder. As you
can see in figure 3-13, only one manifold is used for an in-line engine.
AIR INJECTION MANIFOLDS
6 CYLINDER
8 CYLINDER
FIGURE 3-13
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AIR
3-21
A V8 engine will use two injection manifolds. These manifolds usually
have one outlet or nozzle for each cylinder. In some applications, how-
ever, this may not be the case. Because of design limitations some V8
engines have only seven nozzles. These nozzles are usually located very
near the exhaust valves. Figure 3-14 shows the exhaust valve and air
injection nozzle location usually found on an AIR equipped automobile.
FIGURE 3-14
17. The air injection manifold distributes the pump air to
the ports of each cylinder.
18. Some V8 engines have only
design limitations.
nozzles because of
Now that you are familiar with all of the AIR system components it is time
to take a closer look at how they function.
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AIR
3-23
SYSTEM/COMPONENT FUNCTION
You will recall from the last section of this chapter that an AIR system
has four basic components. These are the air pump, anti-backfire valve,
check valve and the air injection manifold. Now we shall look more
closely at each of these components so you can understand how they do
their job.
AIR PUMP
As you remember the belt driven air pump supplies the system with air to
be injected into the exhaust manifold. This pump is a rotary vane type
pump. The air pump is made up of a pump housing, a rotor, and vanes.
Most air pumps have between 2 and 5 vanes. Figure 3-15 shows a simplified
view of the inside of the air pump. After the air is filtered to remove
CROSS SECTION OF AIR PUMP
VANE
ROTOR
PUMP
HOUSING
VANE SEALS
OUTLET
INLET
FIGURE 3-15
any dirt or dust it enters the inlet of the pump. As the vanes move
around the pump housing they pull air through the inlet and push it out
through the outlet. The arrows in figure 3-15 show the flow direction of
air through the pump.
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3-24
PRESSURE RELIEF VALVE
A spring loaded valve is used as a pressure relief valve on those air
pumps which have a built-in relief valve. As you recall, maximum pump
pressure must be limited to prevent exhaust system overheating at high
engine speeds. When pressure in the pump exceeds a maximum pressure
level the relief valve spring will be compressed, opening the valve.
With this condition the excess air will pass through the valve to the
atmosphere. When the pump pressure drops back to a safe level the
relief valve will close and the pump will operate normally again.
19. Maximum pump pressure is limited by the pressure relief
valve to prevent exhaust system overheating at
engine speeds.
20. When pump pressure exceeds its preset maximum pressure
level, the relief valve will vent the excess pressure to
the
DIVERTER VALVE
The purpose of the diverter or anti-backfire valve is to divert pump air
to the atmosphere during the first few seconds of engine deceleration.
Now let's see how this valve accomplishes this. A combination diverter
and pressure regulator valve is shown in figure 3-16. This diverter
valve is made up of two valve plates, a spring loaded stem, a diaphragm
and a diaphragm spring. The diverter valve has an inlet connection for
the air supply from the pump, an outlet for air to reach the injection
manifold, and a signal line from the intake manifold. This manifold
vacuum line provides the signal which tells the diverter valve when to
"dump" its air to the atmosphere.
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AIR
3-25
DIAPHRAGM
SPRING
TO CHECK
VALVE
VALVE
PLATES
MANIFOLD
VACUUM
TO CHECK
VALVE
TO AIR
PUMP
STEM
FIGURE 3-16
When the engine is operating vacuum will be applied to both the upper and
lower sides of the diaphragm. This is accomplished by the use of a
timing orifice located in the diaphragm itself. Figure 3-17 shows the
location of this orifice. In this position the diaphragm spring will
raise the stem and unseat the upper valve plate. When the diverter valve
TIMING
ORIFICE
DIAPHRAGM
SPRING
VALVE
PLATES
MANIFOLD
VACUUM
STEM
FIGURE 3-17
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3-26
is operating in this manner, air will flow from the valve inlet past the
upper valve plate and out through the valve outlet. This flow of air
through the diverter valve is shown in figure 3-18.
TO AIR
INJECTION
MANIFOLD
TO AIR
INJECTION
MANIFOLD
FROM AIR
PUMP
FIGURE 3-18
A high intake manifold vacuum will result when the carburetor throttle
plates close during deceleration. This high vacuum condition will act
on the diaphragm in the diverter valve pulling it downward. The
diaphragm spring will compress, thus moving the stem downward. When this
happens the lower valve plate will be unseated and the air will be
diverted through a muffler to the atmosphere. Figure 3-19 shows how
the air will flow through the diverter valve when it is in the dump
position.
Since the diaphragm has a timing orifice built into it which connects
the upper and lower sides of the diaphragm the unequal vacuum conditions
will stabilize. When the vacuum on both sides of the diaphragm becomes
equal the diaphragm spring will push the stem up again and unseat the
upper valve plate. When this happens the air will again flow to the
injection manifold(s). This equalizing of the two vacuum chambers
will usually take approximately 2 to 3 seconds. Thus the air will only
be diverted to the atmosphere for the first few seconds of deceleration
when the excessively rich mixture is liable to cause a backfire.
-------
VENT
AIR
3-27
SEATED
FIGURE 3-19
When the engine is turning at a high RPM excessive pump pressure will be
produced. It is the diverter pressure regulator valve's job to limit
this pressure. As you can see in figure 3-20, when the excessive pump
pressure acts upon the diverter pressure regulator valve, the lower valve
5PSI
VENT
5PSI
FIGURE 3-20
-------
3-28
plate will unseat. This will vent pump air to the atmosphere to hold
the pressure to a pre-determined maximum.
21. The purpose of the anti-backfire valve is to divert pump
air to the atmosphere during the first few seconds of
engine .
22. The vacuum signal which tells the diverter valve when to
"dump" its air to the is provided
by the intake manifold.
23. The unequal vacuum conditions created in the diverter
valve diaphragm chambers will equalize through the built-
in during deceleration.
24. When the vacuum on both sides of the diverter valve
diaphragm becomes equal the air will again flow to the
25. It usually takes approximately two to three
for the two vacuum chambers in the diverter valve to
equalize.
-------
AIR
3-29
GULP VALVE
This second type of anti-backfire valve is known as a gulp valve. As you
can see in figure 3-21, this valve is teed into the supply line between
the air pump and the injection manifold. In order to prevent backfire on
deceleration the gulp valve diverts pump air to the intake manifold.
•0
*
V,
DISTRIBUTION
.MANIFOLD
rTt\
AIR
Q ' f- — '
Y
CHECK
VALVE
JLi
J V
r
ii ii .. ..
q
r . f
SIGNAL LINE
TO
INTAKE
J MANIFOLD^
^ J
^ i ^ i^~~^^
D f A,
J> ' K
GULP VALVE IN
R DISCHARGE
)
FAKE MANIFOLD^
FIGURE 3-21
Figure 3-22 shows an inside view of the gulp valve. You will notice that
the upper diaphragm chamber and valve stem are much the same as the
INTAKE
MANIFOLD
VACUUM
SIGNAL
AIR FROM
AIR PUMP
AIR DISCHARGE
TO INTAKE
MANIFOLD
'AIR VALVE
FIGURE 3-22
-------
3-30
diverter valve. An intake manifold vacuum signal is used to dump the
gulp valve in the same manner as the diverter valve. When a high intake
manifold vacuum occurs the diaphragm will be pulled down against spring
force. This will open the valve and pump air will pass through the gulp
valve to the intake manifold. A small timing orifice in the diaphragm
will slowly equalize the vacuum on both sides of the diaphragm returning
the valve to a closed position. This will take only a few seconds as
does a diverter valve. After the gulp valve closes the air will again
flow to the injection manifold.
CHECK VALVE
The check valve which is usually mounted on the air injection manifold
is a one-way valve. This valve will allow air to pass from the pump
side to the injection manifold side. It will not allow air flow from the
injection manifold side to the air pump side.
This valve, as you can see in figure 3-23, is a simple spring loaded
device. When the air pump pressure exceeds the exhaust system pressure
CHECK
VALVE^
rrrm
AIR INJECTION MANIFOLD
FIGURE 3-23
the air will flow through the check valve as shown in figure 3-24. The
check valve spring will be compressed and the air will flow around the
-------
AIR
3-31
CHECK VALVE
FIGURE 3-24
valve plate and through the valve to the air injection manifold. If for
any reason the exhaust system pressure is greater than the air pump
pressure the valve plate will seat preventing flow through the valve.
This condition is shown in figure 3-25.
FIGURE 3-25
-------
3-32
26. Another type of anti-backfire valve is known as a
valve.
27. Gulp valves are teed into the supply line between the
and the air pump.
28. The gulp valve diverts pump air to the
to prevent backfire on deceleration,
29. Usually mounted on the injection manifold is a check
valve. A check valve will allow flow in
direction.
30. The check valve used in the AIR system will allow air to
pass through it from the side to the injection
manifold side.
AIR INJECTION MANIFOLD
As you recall the purpose of the air injection or distribution manifold
is to distribute the pump air to each cylinder. This manifold is made of
tubing with the cylinder nozzles all connected to a common line. With
this arrangement all the cylinders will receive air. Some engines may
have passageways cut in the cylinder head instead of using an injection
manifold. These passageways distribute and inject air in the same manner
as an injection manifold.
-------
AIR
3-33
AIR INJECTION MANIFOLDS
6 CYLINDER
8 CYLINDER
FIGURE 3-26
31. To complete the AIR system the air pump, diverter valve,
check valve, and manifold are connected
with hoses and pipes.
Now you should understand the AIR system. It is now time to look at the
maintenance procedures required to keep this system operating properly.
-------
A1K
3-35
SYSTEM INSPECTION
An Inspection of the AIR system should be made periodically and previous
to any testing of the system. This inspection will require only simple
tools and takes only a few minutes. Many problems may be avoided or
corrected by these steps.
1. Check to see that all components are properly installed on
the engine and no modifications have been made. Air pump,
drive belt, anti-backfire valve, check valve, manifold and
all connecting hoses should be in place.
In order for the AIR system to function as it was designed
all components must be installed correctly.
2. Inspect the air inlet filter if the system is so equipped.
If the filter is excessively dirty it should be replaced.
If the air inlet filter is dirty the air supply for the
pump may be restricted. This will result in reduced effec-
tiveness of the entire system.
3. The air pump drive belt should be inspected for excessive
wear. If the belt condition is unacceptable it should be
replaced. In addition, this belt must be tightened according
to manufacturer's specifications.
If the drive belt is worn or too loose, the pump efficiency
will be reduced and the effectiveness of the entire system
will suffer.
4. Check the system connecting hoses for cracks, deterioration
and loose connections.
-------
3-36
Any air leaks in the system will reduce the AIR system's
effectiveness. In addition, if air leaks into the anti-
backfire valve's signal line, a backfire condition on
deceleration may occur.
32. The AIR system should be inspected periodically and
before the system.
33. All of the AIR system must be
installed correctly in order for the system to function
as it was designed.
-------
AIR
3-37
SYSTEM TESTING
The AIR system should be tested periodically or anytime it is suspected
to be working improperly. The components of the AIR system which require
testing are the air pump, anti-backfire valve and the check valve(s).
AIR PUMP TEST
Manufacturer's specifications should be consulted when testing the air
pump as with all other test procedures. Figure 3-27 shows the procedure
recommended by one manufacturer. They recommended the pump be tested
FIGURE 3-27
using a special test tee and pressure gauge connected into the outlet hose
of the pump. • The pump air pressure is then measured at a specified
engine speed.
GULP VALVE TEST
The anti-backfire valve must also be tested to see that it is operating
correctly. The gulp valve, if used,can be tested as shown in figure 3-28.
With the engine idling the by-pass hose should be pinched shut somewhere
between the valve and the intake manifold. If the valve is operating
properly the idle RPM should not change. Now the vacuum signal line should
-------
3-38
AIR TO
INTAKE MANIFOLD
FIGURE 3-28
be removed for about 5 seconds, then replaced. If the gulp valve is oper-
ating correctly, the engine will run rough for about 1-3 seconds. Always
check the manufacturer's specifications before conducting this test. On
certain foreign models youwill damage the air pump by pinching the hose shut.
DIVERTER VALVE TEST
Figure 3-29 shows the first step to testing the diverter type anti-backfire
FIGURE 3-29
-------
AIR
3-39
valve. With the engine idling, hold your fingers by the vent port. No
air should be felt escaping from the vent. The engine should then be
sped up to produce excessive pump pressure. As shown in figure 3-30,
some air should be felt escaping from the combination pressure regulator
FIGURE 3-30
diverter valve or the pump relief valve. When the engine is decelerated
from the high engine speed hold your fingers by the diverter valve vent.
As you can see in figure 3-31, you should feel all the air from the pump
FIGURE 3-31
-------
3-40
being vented for 1 to 3 seconds. If the valve fails to operate properly,
you should check the vacuum signal line before replacing the valve. Figure
3-32 shows that manifold vacuum should be present in this line.
FIGURE 3-32
CHECK VALVE TEST
The last component to be tested in the AIR system is the check valve.
To test the check valve you must first remove the air supply hose from
FIGURE 3-33
-------
AIR
3-41
the check valve. With the engine running, carefully hold your hand over
the check valve and feel for any leakage. There should be no exhaust
escaping from the check valve. The engine should now be shut off and a
simple test made to assure that the check valve is not stuck closed. As
you can see in figure 3-34, when you push down on the check valve with a
screwdriver or solid rod the valve plate should move freely.
FIGURE 3-34
Lastly to test for leaks with the engine operating, use soap and water
on a brush while watching for bubbles at the connections.
After you have performed these tests you will be sure that the AIR system
is operating properly and helping to keep our air clean.
34. One test which should be done to the diverter valve is to
decelerate the engine from a high speed while holding your
fingers by the vent. As the
engine slows down you should feel all the air from the
pump being vented for only 1 to 3 seconds.
-------
3-42
35. When testing a check valve you should push down on the
check valve with a screwdriver or solid rod. The
^^ should move freely.
-------
AIR
3-43
SYSTEM SUMMARY
PURPOSE
The purpose of the air injection system is to supply additional oxygen
(air) at the exhaust ports near the exhaust valves to extend the combus-
tion process into the exhaust system. This reduces the unburned hydro-
carbon and carbon monoxide emissions.
MAIN COMPONENTS
Air Pump - Supplies filtered low pressure air to the system.
Diverter Valve - Diverts air pump output to atmosphere during decelera-
tion to prevent backfire and has a built-in pressure relief valve to
protect the system.
Check Valve - Prevents hot exhaust gases from backing up into the hoses
and pump.
Air Manifold - Distributes air to each cylinder.
Air Nozzles - Injects air to each exhaust passage near the exhaust valves.
Manifold Vacuum Signal Line - Senses manifold vacuum to actuate the
diverter valve.
SYSTEM FUNCTION
During normal operating conditions the air pump supplies air to the diver-
ter valve which then passes the air on to the air nozzles for injection
into the exhaust manifold. There the hot exhausted gases receive the
fresh oxygen charge and undergo further combustion. During deceleration
there is high intake manifold vacuum and an excessively rich fuel mixture.
If fresh oxygen were supplied to these exhaust gases, reignition and
engine backfire could result. The diverted valve senses the high intake
manifold vacuum and vents air from the pump to the atmosphere.
-------
AIR
3-45
ANSWERS
1. air
2. exhaust manifold
3. air injection reaction
4. combustion
5. hydrocarbons, carbon monoxide
6. carburetion
7. air pump
8. air filter
9. belt
10. pressure relief
11. overheating
12. backfire
13. muffler
14. intake manifold
15. backfire
16. check
17. exhaust
18. seven
19. high
20. atmosphere
21. deceleration
22. atmosphere
23. timing orifice
24. injection manifold or exhaust ports
25. seconds
26. gulp
27. injection or distribution manifold
28. intake manifold
2 9. one
30. pump
31. injection or distribution
32. testing
33. components
34. diverter valve
35. valve plate
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/3-77-038
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Motor Vehicle Emissions Control - Book Three
Air Injection Reaction Systems
5. REPORT DATE
November 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
B.D.
M.T.
Hayes
Maness
R.A. Ragazzi
R.A. Barrett
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
T008135-01-0
T900621-01-0
12. SPONSORING AGENCY NAME AND ADDRESS
Control Programs Development Division
Office of Air Quality Planning and Standards
Office of Air and Waste Management
U.S. Environmental Protection Agency
13. TYPE OF REPORT AND PERIOD COVERED
Final RennrE
14.
Final Rep<
SPONSORING
AGENCY CODE
EPA 200/04
15. SUPPLEMENTARY NOTES Research Triangle Park, North Carolina 27711
16. ABSTRACT
This book is one of a series designed specifically to teach the concepts of auto-
mobile emissions control systems. It is intended to assist the practicing mechanic
or the home mechanic to better understand the Air Injection Reaction Systems which
are an integral part of automobiles today. The mechanic's increased knowledge
should help him keep "emissions controlled" vehicles operating as designed. Re-
spectable fuel economy, performance and driveability, as well as cleaner air, can
be obtained from the automobile engine that has all of its emissions systems
functioning properly.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Air Injection
Reaction Systems
Photochemical
Intake Manifold
Exhaust Manifold
System Inspector
Carbon Monoxide
Oxides of Nitrogen
Carburetion
Combustion
Backfire
Muffler
Exhaust
? DfSTRfBTfiTO'N'STATEMENI
Release Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
fcU.S. GOVERNMENT PRINTING OFFICE: 1978 .7k 5 - 22"y
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