EPA-450/3-77-042
November 1977
MOTOR VEHICLE
EMISSIONS CONTROL
BOOK SEVEN
CATALYTIC CONVERTER
SYSTEMS
U.S. E^VIR()^ME^TAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 2771 1
\
01
9
-------
EPA-450/3-77-042
MOTOR VEHICLE EMISSIONS CONTROL
BOOK SEVEN
CATALYTIC CONVERTER SYSTEMS
by
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
-------
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-450/3-77-042
ii
-------
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
111
-------
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
-------
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.
v
-------
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
-------
CONTENTS
Introduction to Emissions Control 7-1
Hydrocarbons 7-1
Carbon Monoxide 7-1
Oxides of Nitrogen 7-2
Formation of Hydrocarbons 7-2
Formation of Carbon Monoxide 7-3
Formation of Oxides of Nitrogen 7-3
Ignition Timing 7-3
Carburetion 7-5
System Introduction 7-7
System/Component Purpose 7-9
System/Component Function 7-11
Monolith Type Converter 7-13
Pellet Type Converter 7-15
Catalysts 7-17
Catalyst Protection Systems 7-21
System Inspection 7-33
System Testing 7-35
System Summary 7-37
Answers 7-39
vii
-------
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).
48
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.
7-1
-------
7-2
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.
-------
7-3
FORMATION OF CARBON MONOXIDE
Carbon monoxide is 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
-------
7-4
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 tempertures 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 1s
that combustion temperatures are not as high. This 1s 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 1s 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.
-------
7-5
CARBURETION
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.
-------
CAT
7-7
SYSTEM INTRODUCTION
From what you have already learned you know that hydrocarbons and carbon
monoxide are undesirable products of combustion. You also know that
these two pollutants are exhausted to the atmosphere through the tailpipe
of the automobile. Many of the emissions control systems are designed to
help reduce these tailpipe emissions. These are the TAG system, the AIR
system, EGR system, and the Spark Control system. These systems are
effective in reducing the tailpipe emissions but the EPA requirements
for 1975 and 1976 called for emissions levels to be lower than could be
accomplished by these systems alone.
The automobile manufacturers found that a device called the catalytic
converter could reduce the HC and CO emissions to a value that would meet
EPA requirements for 1975 and 1976. The catalytic converter also helped
to improve the driveability of the automobile. Since the catalytic con-
verter is very effective in reducing HC and CO emissions the engine could
be retuned to provide more power and performance and to provide better
fuel economy.
Most 1975 and newer automobiles are equipped with catalytic converters.
However, some automobiles manufactured during these years do not use
catalytic converters since they meet the federal standards for HC and CO
without their use.
1. The catalytic converter was first installed on
model year automobiles.
-------
7-8
2. Catalytic converters are installed on most 19 and
newer automobiles.
3. The device called a
can reduce the HC and CO emissions to a value that meets
EPA requirements for 1975 and 1976.
-------
CAT
7-9
SYSTEM/COMPONENT PURPOSE
The catalytic converter system is a unique emissions control system in
many ways. One aspect which makes it unique is the fact that the entire
system only has one component. This is the catalytic converter itself.
The purpose of the catalytic converter is to reduce the amount of hydro-
carbons and carbon monoxide in the automobile exhaust. The catalytic
converter provides an additional area for oxidation or burning of the
HC and CO.
Another aspect of the catalytic converter system which makes it different
from all the other systems is the fact that it needs a protection system.
The catalyst protection system is usually built into the AIR system
operation. By diverting the AIR injection air to the atmosphere instead
of the exhaust manifold, it is possible to protect the catalytic conver-
ter. The purpose of the catalyst protection system is to protect the
catalytic converter from damage due to overheating.
4. One aspect which makes the catalytic converter system
unique is that the entire system has only
component.
5. Catalytic converter systems reduce the amount of hydro-
carbons (HC) and carbon monoxide (CO) in the automobile
exhaust by providing an additional area for
to occur.
6. The catalyst protection system's purpose is to protect
the catalytic converter from damage caused by
-------
CAT
7-11
SYSTEM/COMPONENT FUNCTION
As you recall from the previous section of the book, the catalytic
converter provides an additional area to oxidize or burn the HC and CO
after it leaves the engine. This in turn will reduce the total amount
of hydrocarbons and carbon monoxide in the exhaust gases. Since you are
now familiar with the purpose of the catalytic converter system, let's
take a closer look at how it accomplishes its job.
The catalytic converter is a component which looks much like another
SINGLE EXHAUST SYSTEM
WITH CATALYTIC CONVERTER
MUFFLER
EXHAUST
CATALYTIC
CONVERTER
DUAL EXHAUST SYSTEM
WITH CATALYTIC CONVERTER
EXHAUST
PIPE
ASSEMBLY
CATALYTIC
CONVERTERS
FIGURE 7-1,
-------
7-12
muffler. It is usually located in the exhaust system ahead of the
muffler and fairly close to the exhaust manifold. There is one catalytic
converter used on cars equipped with single exhaust systems. Cars which
are equipped with a dual exhaust system however, will usually have two
catalytic converters. They will be located close to both exhaust
manifolds. Figure 7-1 shows the location of the catalytic converters
used for both systems.
As you can see in figure 7-2, there is one difference which distinguishes
the catalytic converter from an ordinary muffler. This difference is the
material from which the catalytic converter is constructed. The outer
skin or shell of the catalytic converter is made of stainless steel.
Stainless steel is used for catalytic converter construction because it
is more durable and corrosion-resistant than the metal used in ordinary
mufflers.
CATALYTIC CONVERTER
MUFFLER
FIGURE 7-2
Since the catalytic converter is a fairly expensive component, it is
desirable to construct it in this manner to assure a long component life
span.
-------
CAT
7-13
There are two basic internal designs used for catalytic converters.
These are the monolith design and the pellet design. Both types have
their advantages and disadvantages as well as differences in construction,
We will first look at the monolith type catalytic converter.
7. A catalytic converter looks like a
8. The two internal designs of catalytic converters are the
design and the design.
MONOLITH TYPE CONVERTER
Figure 7-3 shows a cut-away view of the monolith type catalytic converter.
Contained inside the stainless steel shell is a flow diffuser, a honeycomb
monolith, and a stainless steel mesh. As the arrow in figure 7-3 indicates
the exhaust gases enter the monolith type catalytic converter and first
MONOLITH CONVERTER
FLOW DIFFUSER
EXHAUST
GASES
HONEYCOMB
MONOLITH
STAINLESS STEEL
SHELL
STAINLESS
STEEL MESH
FIGURE 7-3
-------
7-14
encounter the flow diffuser. This flow diffuser is designed to spread
or diffuse the exhaust gases for a more even flow through the monolith
element.
The monolith element is a honeycomb type design. This monolith has
hundreds of small passages which the exhaust gases flow through. A
ceramic material is used to make this monolith element. As figur* 7-4
shows, this ceramic material is coated with a very thin loytr of
platinum and palladium. This coating of platinum and palladium Is thft
key to the catalytic converter as we shall see later.
MONOLITH CONVERTER
EXHAUST
GASES
COATING OF
PLATINUM AND
PALLADIUM
FIGURE 7-4
Surrounding the monolith element, as you can see in figure 7-3, is a
stainless steel mesh. This mesh has been put into the catalytic converter
shell to cradle the monolith element. This mesh protects the fragile
ceramic element from damage due to road shock.
Now you should be familiar with this monolith design catalytic converter.
We will now look inside a pellet type converter. As you will see, this
converter is quite different in design but it does the very same job.
-------
CAT
7-15
PELLET TYPE CONVERTER
Figure 7-5 shows a cut-away view of the pellet type catalytic converter,
This type of catalytic converter contains baffles, baffle plates, insu-
lation and aluminum oxide pellets inside its stainless steel shell. As
PELLET - STYLE
CATALYTIC CONVERTER
INSULATION
INSULATION
ALUMINUM OXIDE PELLETS
FIGURE 7-5
the exhaust gases enter this type of catalytic converter, they first
encounter a baffle which directs the gases upward. The only way for the
EXHAUST GAS FLOW-THRU
PELLET-STYLE CATALYTIC
CONVERTER
INSULATION
EXHAUST /
GASES
INSULATION
ALUMINUM OXIDE PELLETS COATED
WITH PLATINUM AND PALLADIUM
FIGURE 7-6
-------
7-16
gases to flow through the converter is to pass through the holes in the
baffle plate. These gases then pass down through the bed of aluminum
oxide pellets and are directed out of the converter by another baffle.
The arrows in figure 7-6 show the path which the exhaust gases take
when flowing through the pellet type catalytic converter.
This type of catalytic converter also has insulation in its shell to keep
the heat contained inside the converter. The aluminum oxide pellets are
coated with platinum and palladium just like the ceramic core of the
monolith type.
MONOLITH CONVERTER
ADVANTAGES
MORE RESISTANT
TO VIBRATION
SMALL, THEREFORE
FAST HEAT-UP
LESS EXHAUST
BACK PRESSURE
DISADVANTAGES
NOT REPAIRABLE
MORE EXPENSIVE
TO MANUFACTURE
REQUIRES MORE
PLATINUM AND
PALLADIUM
PELLET CONVERTER
ADVANTAGES
DISADVANTAGES
LESS EXPENSIVE
TO MANUFACTURE
USES LESS PLATINUM
AND PALLADIUM
REPAIRABLE
(PELLETS CAN BE
REPLACED)
SLOWER WARM-UP
BECAUSE OF LARGER
SIZE
HIGHER EXHAUST
BACK PRESSURE
NOT AS DURABLE
FIGURE 7-7
-------
CAT
7-17
Both styles of catalytic converters operate in the same way. However,
each has their own advantages and disadvantages. Figure 7-7 contains
charts which list these for each type of catalytic converter.
9. When the exhaust gases enter the monolith type catalytic
converter, they first encounter a
10. The monolith element is a type design,
11. The monolith element is made of a
material.
12. The pellet type converter uses small
diameter.
pellets approximately 1/8" to 3/16" in
13. The small pellets are coated with a very thin layer of
and
CATALYSTS
Platinum and palladium are the key to the catalytic converter. These two
elements are used in both types of catalytic converters. These elements
act as the catalytic agents or the catalysts. A catalyst is a substance
that is used to speed up a chemical reaction or chemical change. Both
types of converters use about 70 percent platinum and 30 percent palladium.
-------
7-18
Platinum is a more efficient catalyst but it is also very expensive.
Palladium is less efficient as a catalyst but is less expensive. By
using both catalysts it is possible to have a catalytic converter which
has the needed efficiency and a reasonable cost.
The catalyst is a substance used to speed up a chemical reaction or
chemical change. As you can see in figure 7-8, in automobile applica-
tions the catalyst speeds up the change of HC and CO. These harmful
Q V-r^7 CATALYTIC
CO) -* CONVERTER -*
FIGURE 7-8
gases are converted to HpO and CC^. These are harmless substances,
water vapor and carbon dioxide. The catalytic converter does this by
adding oxygen, or oxidizing the HC and CO.
In order for the catalytic converter to oxidize the HC and CO, a burning
must take place. This burning takes place in the catalytic converter
itself. When this secondary burning takes place in the catalytic con-
verter, heat will be given off. The temperature of this burn will
usually be about 200°F hotter than the exhaust temperature. The
catalytic converter needs heat to function correctly. In fact, the
converter won't start to operate until the exhaust temperatures reach
-------
SECONDARY COMBUSTION OR
BURNING OCCURS IN THE
CATALYTIC CONVERTER
no
MUFFLER
CAT
7-19
FIGURE 7-9
500°F. When the automobile is operating normally the temperature inside
the catalytic converter will be approximately 1400°F. When the inside
of the converter is at this temperature the outer shell will heat to
about 700°F.
CONVERTER OPERATING
TEMPERATURES
INSIDE
TEMPERATURE
1200-1600° F
SHELL TEMPERATURES 600-800°F
FIGURE 7-10
-------
7-20
Much higher temperatures can occur in the catalytic converter. Whenever
an overly rich mixture is present during the combustion process, the
catalytic converter will become hotter. This rich mixture can be caused
by a spark plug misfire. It could also result from a carburetor mal-
function such as a partially closed choke plate. If this overly rich
condition occurs, an increased oxidation or burning will take place in
the catalytic converter. This increased burning will lead to a rapid
increase in the catalytic converter temperature. If this temperature
reaches approximately 2500°F, the aluminum oxide pellets or the ceramic
core of the converter will be damaged. When the catalytic converter is
damaged from overheating it will have to be replaced. For this reason,
cars equipped with catalytic converters should not be run with spark
plug wires that are open, disconnected or shorted. If the shorting or
disconnecting of a spark plug is required for any reason, the engine
should not be operated for over 30 seconds. Any condition which allows
an overly rich mixture to reach the catalytic converter should be
corrected immediately to prevent catalytic converter damage.
14. Platinum and palladium are used in both converters, as
the catalytic agents or the .
15. A substance that is used to speed up a
is called a catalyst.
16. ________________ is the better of the two catalysts, but
it is very expensive.
-------
CAT
7-21
17. The purpose of the oxidizing catalytic converter is to
oxidize or add to certain harmful elements
and compounds in the exhaust gas.
18. In automotive applications, the chemical compounds that
require oxidizing are and
19. In order to prevent possible damage, any condition which
allows an excessively rich air/fuel mixture to reach the
should be corrected
immediately.
CATALYST PROTECTION SYSTEMS
Since the catalytic converter can be severely damaged if overheated, many
manufacturers have installed a catalyst protection system on their auto-
mobiles. The purpose of the catalyst protection system is to protect the
catalytic converter from damage due to overheating. We will now look
more closely at some catalyst protection systems and learn how they
function.
Figure 7-11 shows a catalyst protection system which is used by the
Chrysler Corporation on many of their automobiles. This system is
designed to protect the catalytic converter during periods of decelera-
tion. Normally when the automobile decelerates, the air/fuel mixture
becomes excessively rich. This system prevents this condition from
occurring. When the engine speed exceeds 2000 RPM the throttle position
-------
7-22
ELECTRONIC
CONTROL UNIT
CATALYST PROTECTION SYSTEM
BALLAST RESISTOR .IGNITION SWITCH
TO
BATTERY
START
RUN
THROTTLE
POSITION
SOLENOID
ELECTRONIC
SPEED
SWITCH
^ BATTERY
FIGURE 7-11
solenoid is energized by a signal from the electronic speed switch. When
the throttle is then released, this throttle position solenoid will hold
the throttle at a preset point corresponding to 1500 RPM. The electronic
speed switch senses when engine speed drops below 2000 RPM and it then
de-energizes the throttle position solenoid. This allows the throttle
plates to fully close to the curb idle position. By keeping the throttle
plates at a 1500 RPM position, this catalyst protection system allows
enough air to enter the engine during deceleration. This extra air prevents
an excessively rich mixture and protects the catalytic converter from
overheating.
Ford uses a catalyst protection system that is built into the operation
of the AIR system. The AIR system provides the necessary air for the
proper operation of the catalytic converter. Figure 7-12 shows this
catalyst protection system.
This system protects the catalytic converter by diverting injection air
to the atmosphere during four specific engine conditions. There are
rich engine warm up, engine deceleration, overheated engine operation and
-------
CATALYST PROTECTION SYSTEM (TYPED
VACUUM DIFFERENTIAL
VALVE
• tKtN IIAL. I
VALVE Mra
HI-
FLOOR PAN
SWITCH
BY-PASS
VALVE
MANIFOLD
VACUUM
TEMPERATURE
SWITCH
CAT
7-23
FIGURE 7-12
periods of excessive floor pan temperatures caused by the catalytic
converter.
As you can see in figure 7-12, the main components of this system are the
by-pass or diverter valve, the vacuum differential valve (VDV), the
vacuum solenoid, the ported vacuum switch (PVS), the air cleaner
temperature switch and the floor pan switch.
The by-pass valve used in this system works in a different way than a
normal AIR by-pass valve. This valve will inject air into the exhaust
manifold any time a vacuum signal is present. Whenever this vacuum drops
to 0 the by-pass valve will divert the air to the atmosphere.
The vacuum solenoid is connected into the system in such a way that it
must be energized to allow the vacuum signal to reach the by-pass valve.
The switches in this system are closed during normal engine operation.
If any of these switches open the solenoid will de-energize. This will
prevent the vacuum from reaching the by-pass valve and the injection air
will be dumped to the atmosphere. Figure 7-13 shows the catalyst
-------
7-24
CATALYST PROTECTION SYSTEM (TYPE I)
VDV
BY-PASS
VALVE
COLD ENGINE
CONDITION
SOLENOID
DE-ENERGIZED!
FLOOR PAN
SWITCH -
225°-250°
B+
TEMPERATURE
MANIFOLD VACUUM SWITCH - 65°
FIGURE 7-13
protection system in this "open switch" position. You can see that the
temperature switch is below 65°F.
The vacuum differential valve is used to dump injection air for the first
few seconds of deceleration. Under normal cruising operation, a vacuum
VACUUM DIFFERENTIAL VALVE
(VDV) - CATALYST SYSTEM
BY - PASS
TIMING
ORIFICE
DIAPHRAGM
SPRING
TO BY-PASS VACUUM
VALVE VALVE CLOSED
MANIFOLD
VACUUM
FILTER
NORMAL OPERATION
FIGURE 7-14
-------
CAT
7-25
will be present on both sides of the diaphragm. This is made possible
by the small timing orifice connecting both sides of the diaphragm.
This condition may be seen in figure 7-14.
In this position the vacuum differential valve will allow the vacuum
signal to reach the by-pass valve. This in turn will permit the by-pass
valve to inject air into the exhaust manifold. During the first few
seconds of deceleration the higher intake manifold vacuum will act on the
lower side of the diaphragm. This will pull the diaphragm down against
the spring pressure. When this happens the vacuum dump valve will open
allowing air to bleed into the vacuum line. This will cause the by-pass
valve to divert injection air to the atmosphere. This may be seen in
figure 7-15. When the vacuum on both sides of the diaphragm becomes
equal the vacuum dump valve will close and the by-pass valve will again
direct injection air to the exhaust manifold.
VACUUM DIFFERENTIAL VALVE
(VDV) - CATALYST SYSTEM
BY-PASS
TIMING
ORIFICE
DIAPHRAGM
SPRING
*
FILTER-
TO BY-PASS VACUUM DUMf
VALVE VALVE OPEN
MANIFOLD
VACUUM
FILTER
DECELERATION
FIGURE 7-15
20. Ford modified the
system operation to protect the
catalytic converter.
-------
7-26
21. Ford's catalyst protection system includes the diverter
valve, the vacuum valve, the
vacuum solenoid, the ported vacuum switch, the air
cleaner temperature switch and the floor pan switch.
22. A
vacuum source is used for the operation
of Ford's by-pass valve.
23. With no vacuum signal, the
dump air to atmosphere.
valve will
Ford used another type of catalyst protection system on some of their
later cars. This system was designed to prevent EGR system operation
during cold engine operation, and prevent air injection during extended
periods of engine idle. Figure 7-16 shows the components of this catalyst
protection system.
THERMACTOR
WITH TVS
SWITCH AND
VACUUM DELAY
VALVE
EGR VALVE AIR CLEANER
TVS SWITCH
BELOW
60° F
VACUUM
DELAY VALVE
BYPASS
VALVE
CHECK
VALVE
AIR \
PUMP
TO SPARK
PORT
COLD
ENGINE
OPERATION
FIGURE 7-16
-------
CAT
7-27
Figure 7-16 shows this system with the thermal vacuum switch (TVS)
closed. This will occur anytime the intake air is below 60°F. In this
position the TVS switch will block the ported vacuum signal. In this
state of operation the EGR system will not operate and the AIR system
will dump its air to the atmosphere.
When the intake air temperature rises above approximately 60°F, the TVS
switch opens. As the throttle is opened, a ported vacuum signal is
available to operate the EGR system. This same ported vacuum signal
passes through the vacuum delay valve to the by-pass valve. This
vacuum at the by-pass valve causes injection air to be directed to the
exhaust manifold. This operation is shown in figure 7-17.
THERMACTOR
WITH TVS
SWITCH AND
VACUUM DELAY
VALVE
EGR VALVE AIR CLEANER
TVS SWITCH
ABOVE
60° F
VACUUM
DELAY VALVE
BYPASS
VALVE
CHECK
vVALVE
TO SPARK
PORT
WARM
ENGINE
OPERATION
FIGURE 7-17
During periods of extended idle, the throttle plates are nearly closed,
and there is no ported vacuum signal. The vacuum which is trapped between
the by-pass valve and the vacuum delay valve will slowly bleed through
the delay valve. When this vacuum bleeds off and approaches 0" the
by-pass valve will divert injection air to the atmosphere. This vacuum
will bleed off in approximately 30 to 60 seconds. Figure 7-18 shows the
-------
7-28
THERMACTOR
WITH TVS
SWITCH AND
VACUUM DELAY
VALVE
EGR VALVE
VACUUM
DELAY VALVE
BYPASS
VALVE
AIR \
PUMP
CHECK
y VALVE
NO VACUUM
SIGNAL
OPERATION DURING
EXTENDED IDLE
OR EXTENDED
DECELERATION
FIGURE 7-18
catalyst protection system in this operating condition. By removing this
injection air from the exhaust system the amount of oxidation or burning
which takes place in the catalytic converter will be reduced. This
prevents the excessively high temperature that would otherwise occur in
the catalytic converter.
HEAT SHIELDS
INTERIOR
INSULATING
PADS.
HEAT
SHIELDS
CATALYTIC
CONVERTER
LOWER SHIELD
FIGURE 7-19
-------
CAT
7-29
Since the catalytic converter may reach very high skin temperatures,
some manufacturers have protected the under carriage of their automobiles,
Figure 7-19 shows the heat shields used to protect the under carriage
components from the catalytic converters additional heat. In addition,
vehicles designed for heavy duty operation, such as trailer towing, will
have special insulation beneath the carpeting. This will decrease the
heat buildup inside the vehicle.
You should now have a basic understanding of the protection systems
required for the catalytic converter. However, you must be aware that
the catalyst protection systems will vary greatly between individual
automobile manufacturers and models. For this reason, you should always
consult the manufacturer's service manual.
All automobiles using a catalytic converter must use lead-free or un-
leaded fuel. This is because the lead in leaded fuel will coat the
platinum and palladium catalyst material. This coating of lead will
destroy the effectiveness of the catalytic converter and the catalyst
will need to be replaced.
LEADED FUEL DESTROYS
CATALYST EFFECTIVENESS
LEAD COATS THE CATALYST
MAKING IT INEFFECTIVE
FIGURE 7-20
-------
7-30
Since leaded gasoline will destroy a catalytic converter a special fuel
tank filler neck has been installed on all catalytic converter equipped
automobiles. This is shown in figure 7-21. A special small diameter
UNLEADED FUEL FILLER INLET
UNLEADED
FUEL
NOZZLE
LEADED FUEL
NOZZLE
RESTRICTOR
UNLEADED
FUEL FILLER
FIGURE 7-21
«
unleaded fuel nozzle must be used to fill the tank. The unleaded fual
nozzle is the only nozzle that will fit in the new small diameter filler
neck. In addition, a spring loaded door inside the filler neck is used.
This prevents fuel from being added by any other means except the small
diameter fuel nozzle.
24. Some manufacturers have added
sheilds to protect
under carriage components from the catalytic converter's
additional heat.
25.
fuel must be used with any vehicle
equipped with a catalytic converter.
-------
CAT
7-31
Now you should be familiar with the function of the catalytic converter
system. We can now take a brief look at the inspection and testing
procedures for this system.
-------
CAT
7-33
SYSTEM INSPECTION
An inspection of the catalytic converter system should be made periodi-
cally and previous to any testing of the system. This inspection will
require no tools or instruments and will take 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 done. The cata-
lytic converter or converters should be in place. In
addition, all catalyst protection system components and
connecting hoses should be in place.
In order for the catalytic converter system to function as it
was designed, the catalytic converter must be installed
correctly. In addition, the catalyst protection system must
be installed correctly in order to protect the catalytic
converter from damage due to overheating.
2. Check the catalyst protection system connecting hoses for
cracks, deterioration and loose connections.
Any air leaks into the catalyst protection system hoses can
reduce the effectiveness of the system. If air leaks are
excessive the catalyst protection system may fail to operate
at all. An excessive air leak can also cause a lean misfire
in the engine cylinders.
3. Check the catalytic converter itself for evidence of physi-
cal damage.
Look for large dents, ruptures, or punctures. Also check for
evidence of converter overheating. This can be seen by high
temperature discoloration or signs of scorching on the vehicle
underbody.
-------
7-34
VISUAL INSPECTION
PUNCTURE
DISCOLORATION
LARGE DENT
CHECK FOR: |. LARGE DENTS
2. RUPTURES
3. PUNCTURES
4. EVIDENCE OF OVERHEATING-
CONVERTER DISCOLORATION/
UNDERBODY SCORCHING
FIGURE 7-22
If the catalytic converter has been excessively damaged it
will fail to operate as it was designed and will have to be
replaced.
26. When inspecting the catalytic converter, check for evi-
dence of physical damage such as dents or punctures.
Also, check for evidence of converter
27. Any
into the catalyst protection system
hoses can reduce the effectiveness of the system.
28. An excessive air leak in the catalyst protection system
can cause a lean in the engine cylinders,
-------
CAT
7-35
SYSTEM TESTING
For specific information on testing and setting catalyst protection
system components, it is recommended that the manufacturer's shop or
service manual or a good emissions control manual be used. This is
required because of protection system variations between different
models and manufacturers.
-------
CAT
7-37
SYSTEM SUMMARY
PURPOSE
Catalytic converter systems reduce the amount of hydrocarbons (HC) and
carbon monoxide (CO) gas in automobile emissions by providing an additional
area for exhaust gases to oxidize or burn. This is accomplished by using
a chemical catalyst to speed up the oxidizing process.
MAIN COMPONENTS
Outer Shell - Shaped much like a muffler, the outer shell of the catalytic
converter is made of stainless steel to increase durability and rust
resistance.
Monolith Element - Used on monolith design converters, the monolith ele-
ment is a honeycomb of small ceramic passageways. A very thin layer of
platinum and palladium is used to cover the ceramic element. The entire
element is surrounded by a stainless steel mesh for protection.
Aluminum Oxide Pellets - Used on pellet designed converters, a bed of
Aluminum Oxide pellets l/8"-3/16" diameter are coated with a thin layer
of platinum and palladium. The exhaust gas is directed to flow through
these pellets.
Platinum and Palladium - Common elements in both the monolith and pellet
design converters are the two noble metals, platinum and palladium, used
as catalytic agents. (A catalyst is a substance that is used to speed up
a chemical reaction.) Both types of converters are approximately 70%
platinum and 30% palladium in the thin film covering their interior
elements.
SYSTEM FUNCTION
As exhausted gas leaves the manifold it enters the catalytic converter.
There the gas is directed to flow over the interior monolith or pellets
covered by the catalytic agents, platinum and palladium. When this
happens, the exhaust gases increase their temperatures and continue to
-------
7-38
oxidize, removing hydrocarbon (HC) and carbon monoxide (CO) emissions
from the exhaust before it enters the muffler. As the heat developed
in the catalytic converters is very high, auto manufacturers are
devising various methods of control and insulation to insure its
safe operation.
-------
CAT
7-39
ANSWERS
1. 1975
2. 1975
3. catalytic converter
4. one
5. oxidation or burning
6. overheating
7. muffler
8. monolith, pellet
9. flow diffuser
10. honeycomb
11. ceramic
12. aluminum oxide
13. platinum, palladium
14. catalyst
15. chemical reaction or chemical change
16. platinum
17. oxygen
18. hydrocarbons, carbon monoxide
19. catalytic converter
20. AIR
21. differential
22. manifold
23. bypass
24. heat
25. lead free or unleaded
26. overheating
27. air leaks
28. misfire
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse be/ore completing/
1 RtPORT NO.
EPA-450/3-77-042
3. RECIPIENT'S ACCESSION- NO.
4. TITLE ANDSUBTITLE
Motor Vehicle Emissions Control - Book Seven
5. REPORT DATE
November 1977
Catalytic Converter Systems
6. PERFORMING ORGANIZATION CODE
7, AUTHOR(S)
B.D. Hayes
M.T. Maness
8. PERFORMING ORGANIZATION REPORT NO.
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
Report
i£
^G
14. 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 Catalytic Converter Systems which are
an integral part of automobiles today. The mechanic's increased knowledge should
help him keep "emissions controlled" vehicles operating as designed. 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 pro-
perly.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Catalytic Converter
Photochemical
System Inspection
Hydrocarbons
Carbon Monoxide
)xides of Nitrogen
Oxidation
Honeycomb
Ceramic
Monolith Converter
Pellet Converter
Muffler
Aluminum Oxide
13. DISTRIBUTION STATEMENT
Release Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
46
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
•frU.S. GOVERNMENT PRINTING OFFICE: 1978 .7k 5- 22V
------- |