UNIT 7
EMISSION CONTROL SYSTEMS
TEXT A
Overview of Emission Control Systems
PROFESSIONAL ENGLISH
UNIT 7
EMISSION CONTROL SYSTEMS
TEXT A
Overview of Emission Control Systems
PCV System
EGR System
Evaporative Control System
Air Injection
Catalytic Converter
PROFESSIONAL ENGLISH
本次课学习目标
掌握排放控制系统的组成
掌握排放控制系统的原理
掌握有关的英文专业术语
了解翻译技巧 — 重复
NEW WORDS
dilute [dai'lju:t] v.冲淡,变淡,变弱,稀释
crossover ['kr?s?ouv?] n.转线路,天桥,交叉
channel ['t∫?nl] n.海峡，水道，信道，频道，通道
route [ru:t] n.路线,路程,通道； v.发送
lean （ out） [li:n] v.贫化，变瘦
thermal ['θ?:m?l] a.热的,热量的
transducer [tr?nz'dju:s?] n.传感器，变频器，变换器
orifice ['?rifis] n.孔，口，节流孔
linear ['lini?] a.线的,直线的,线性的
potentiometer [pten∫i'?m
it?]
n.电位计,电势计
fume [fju:m] n.(浓烈或难闻的 )烟,气体； v.用烟熏,
冒烟,发怒
prohibit [pr?'hibit] v.禁止,阻止
adhere [?d'hi?] v.粘附,胶着,坚持
pop [p?p] n.砰的一声,爆裂声,流行乐曲,流行艺术
a.流行的,热门的,通俗的
v.发出爆裂声,爆开,射击,突然出现
diverter [dai'v?:t?] n.分流器，换向器，分流阀
divert [di'v?:t] v.转移,转向
catalytic [?k?t?'litik] a.催化的
muffler ['m?fl?] n.消声器
pellet ['pelit] n.小球
honeycomb ['h?nikoum] n.蜂房，蜂巢
platinum ['pl?tin?m] n.白金,铂
palladium [p?'leidi?m] n.钯
catalyst ['k?t?list] n.催化剂
render ['rend?] v.致使，表演，实施
PHRASES AND EXPRESSIONS
脉宽调制pulse width
modulation
EGR阀位置（ EVP）传感器EGR valve position
(EVP) sensor
锥形端tapered tip
通气孔bleed port
背压back pressure
大节气门开度（简写为 WOT）wide-open throttle
废气再循环阀EGR valve
节气门开度throttle opening
在最坏的情况下at worst
空气喷射air injection
催化转换器catalytic converter
空气泵air pump
分流阀diverter valve
清污阀purge valve
与 … 一道（同时），以及，除 … 之外（还）
along with
活性炭罐charcoal canister
Overview of Emission Control Systems
To minimize pollution of the atmosphere from incompletely
burned and evaporating gases and to maintain good
driveability and fuel economy,a number of emission control
systems are used on all vehicles,They include positive
crankcase ventilation (PCV) system,evaporative emission
control (EVAP) system,exhaust gas recirculation (EGR)
system,air injection (AIR) system and three-way catalytic
converter (TWC) system.
PCV System
The purpose of the positive crankcase ventilation (PCV)
system is to take the vapors produced in the crankcase and
piston blow-by,and redirect them into the air/fuel intake system
to be burned during combustion,These vapors dilute the
air/fuel mixture,they have to be carefully controlled and
metered so as not to affect the performance of the engine,This
is the job of the positive crankcase ventilation (PCV) valve,
At idle,when the air/fuel mixture is very critical,just a little
of the vapors are allowed in to the intake system,At high
speed when the mixture is less critical and the pressures in
the engine are greater,more of the vapors are allowed in to
the intake system [1],When the valve or the system is
clogged,vapors will back up into the air filter housing or at
worst,the excess pressure will push past seals and create
engine oil leaks [2],If the wrong valve is used or the system
has air leaks,the engine will idle rough,or at worst engine oil
will be sucked out of the engine.
EGR System
Exhaust gas recirculation (EGR) systems reduce the
amount of oxides of nitrogen produced during the combustion
process,The EGR system dilutes the air/fuel mixture with
controlled amounts of exhaust gas,Since exhaust gas does
not burn,this reduces the peak combustion temperatures,
At lower combustion temperatures,very little of the nitrogen in
the air will combine with oxygen to form NOX,Most of the
nitrogen is simply carried out with the exhaust gases,For
driveability,it is desirable to have the EGR valve opening (and
the amount of gas flow) proportional to the throttle opening,
Driveability is also improved by shutting off the EGR when the
engine is started up cold,at idle,and at full throttle,Since the
NOX control requirements vary on different engines,there are
several different systems with various controls to provide these
functions,
EGR Valves
Most of these systems use a vacuum-operated EGR valve to
regulate the exhaust gas flow into the intake manifold,Exhaust
crossover passages under the intake manifold channel the
exhaust gas to the valve,(Some in-line engines route the
exhaust gas to the valve through an external tube.) Typical
mounting of the EGR valve is either on a plate under the
carburetor or directly on the manifold.
The EGR valve is a vacuum-operated,flow control valve,
Opening the EGR valve by control vacuum at the diaphragm,
allows exhaust gases to flow through the valve and into the
intake manifold,Here,the exhaust gas mixes with the air/fuel
mixture,The effect is to dilute or lean out the mixture,so that it
still burns completely but with a reduction in combustion
chamber temperatures.
There are also various designs of EGR valves,The positive
back pressure EGR valve has a bleed port and valve positioned
in the center of the diaphragm,A light spring holds this bleed
valve open,and an exhaust passage is connected from the
lower end of the tapered valve through the stem to the bleed
valve,When the engine is running,exhaust pressure is applied
to the bleed valve,At low engine speeds,exhaust pressure is
not high enough to close the bleed valve,If control vacuum is
supplied to the diaphragm chamber,the vacuum is bled off
through the bleed port,and the valve remains closed,（略）
In a negative back pressure EGR valve,a normally closed
bleed port is positioned in the center of the diaphragm,An
exhaust passage is connected from the lower end of the tapered
valve through the stem to the bleed valve,When the engine is
running at lower speeds,there is a high-pressure pulse in the
exhaust system,However,between these high-pressure pulses
there are low-pressure pulses,As the engine speed increases,
more cylinder firings occur in a given time,and the high-pressure
pulses become closer together in the exhaust system.（略）
A digital EGR valve contains up to three electric solenoids that
are operated directly by the PCM,Each solenoid contains a
movable plunger with a tapered tip that seats in an orifice,When
any solenoid is energized,the plunger is lifted and exhaust gas is
allowed to recirculate through the orifice into the intake manifold,
The solenoids and orifices are different sizes,The PCM can
operate one,two,or three solenoids to supply the amount of
exhaust recirculation required to provide optimum control of NOx
emissions.
The linear EGR valve contains a single electric solenoid
that is operated by the PCM,A tapered pintle is positioned
on the end of the solenoid plunger,When the solenoid is
energized,the plunger and tapered valve are lifted,and
exhaust gas is allowed to recirculate into the intake manifold,
The EGR valve contains an EGR valve position or lift sensor,
which is a linear potentiometer,The signal from this sensor
varies from approximately 1V with the EGR valve closed to
4.5V with the valve wide open,
The PCM pulses the EGR solenoid winding on and off with
a pulse width modulation principle to provide accurate control
of the plunger and EGR flow,The EGR valve position (EVP)
sensor acts as a feedback signal to the PCM to inform the
PCM if the commanded valve position was achieved.
Fig.7-2 A electronic EGR system
Fig.7-2 A electronic EGR system
Internal Exhaust Gas Recirculation (EGR)
EGR reduces the levels of oxides of nitrogen (nitric oxide NO,
and small quantities of nitrogen dioxide NO2,collectively
referred to as NOX) in engine exhaust gases at part load,The
aim of an internal EGR system is to control the recirculation of
exhaust gas without the use of external pipework on the engine.
In a conventional plenum throttled engine,at part throttle there
is a pressure differential between the inlet and exhaust ports,
Towards the end of the exhaust stroke on a four stroke engine,
the inlet valve opens and a period follows when inlet and
exhaust valves are open simultaneously,During this valve
overlap period,the inlet port depression causes residual
exhaust gas in the combustion chamber to flow back into the
inlet port,The resultant pressure drop in the combustion
chamber causes gases in the exhaust port to flow back into the
combustion chamber,These residual exhaust gases dilute the
incoming air/fuel charge,
This dilution of the charge reduces the peak combustion
temperatures and pressures,which reduces the amount of
NOX in the exhaust gases,Excess dilution can lead to
incomplete or unstable combustion which results in an increase
in hydrocarbon (HC) levels,The optimum amount of dilution
varies with engine speed and load,Conventionally,the dilution
requirements for optimized running conditions are achieved by
using an external EGR system which recirculates metered
quantities of exhaust gas by external pipes and a control valve.
Evaporative Control System
Gasoline evaporates quite easily,In the past these
evaporative emissions were vented into the atmosphere,20%
of all HC emissions from the automobile are from the gas tank,
In 1970 legislation was passed,prohibiting venting of gas tank
fumes into the atmosphere,An evaporative control system was
developed to eliminate this source of pollution,The function of
the fuel evaporative control system is to trap and store
evaporative emissions from the gas tank and carburetor,
A charcoal canister is used to trap the fuel vapors,The fuel
vapors adhere to the charcoal,until the engine is started,and
engine vacuum can be used to draw the vapors into the engine,
so that they can be burned along with the fuel/air mixture,This
system requires the use of a sealed gas tank filler cap,This
cap is so important to the operation of the system that a test of
the cap is now being integrated into many state emission
inspection programs,Pre-1970 cars released fuel vapors into
the atmosphere through the use of a vented gas cap,Today
with the use of sealed caps,redesigned gas tanks are used,
The tank has to have the space for the vapors to collect so that
they can then be vented to the charcoal canister,A purge
valve is used to control the vapor flow into the engine,The
purge valve is operated by engine vacuum,One common
problem with this system is that the purge valve goes bad and
engine vacuum draws fuel directly into the intake system [3],
This enriches the fuel mixture and will foul the spark plugs,
Most charcoal canisters have a filter that should be replaced
periodically,This system should be checked when fuel
mileage drops,
In some engines,the powertrain control module (PCM)
allows intake manifold vacuum to draw vapors into the
combustion chambers during certain operating conditions,All
of these engines use a duty cycle purge system,The PCM
controls the vapor flow by operating the duty cycle EVAP
purge solenoid (Fig.7-3).
Fig.7-3 An ECM-controlled
EVAP system
Air Injection
Since no internal combustion engine is 100% efficient,there
will always be some unburned fuel in the exhaust,This
increases hydrocarbon emissions,To eliminate this source of
emissions an air injection system was created,Combustion
requires fuel,oxygen and heat,Without any one of the three,
combustion cannot occur,Inside the exhaust manifold there is
sufficient heat to support combustion,if we introduce some
oxygen that any unburned fuel will ignite,This combustion will
not produce any power,but it will reduce excessive
hydrocarbon emissions,Unlike in the combustion chamber,this
combustion is uncontrolled,so if the fuel content of the exhaust
is excessive,explosions,which sound like popping,will occur,
There are times when under normal conditions,such as
deceleration,when the fuel content is excessive [4],Under
these conditions we would want to shut off the air injection
system,
a) cold mode
Fig.7-4 Air management system operation
b) worm mode
Fig.7-4 Air management system operation
This is accomplished through the use of a diverter valve,which
instead of shutting the air pump off,diverts the air away from
the exhaust manifold,Since all of this is done after the
combustion process is complete,this is one emission control
that has no effect on engine performance,
Later versions of the air injection system are under ECM
control (Fig.7-4),When the engine is cold,the ECM energizes a
control solenoid,This allows air to flow to an air switching valve,
The air switching valve is energized to direct air to the exhaust
ports.
On a warm engine,or in "closed loop" mode,the ECM de-
energizes the air switching valve,directing air between the beds
of the catalytic converter,This provides extra oxygen for the
oxidizing catalyst to decrease HC and CO levels,while keeping
oxygen levels low in the first bed of the converter,This enables
the reducing catalyst to effectively decrease the levels of oxides
of nitrogen (NOX).
Catalytic Converter
Automotive emissions are controlled in three ways,One is to
promote more complete combustion so that there are fewer by-
products,The second is to reintroduce excessive hydrocarbons
back into the engine for combustion and the third is to provide
an additional area for oxidation or combustion to occur,This
additional area is called a catalytic converter,The catalytic
converter looks like a muffler,It is located in the exhaust
system ahead of the muffler,Inside the converter are pellets or
a honeycomb made of platinum or palladium,The platinum or
palladium is used as a catalyst (a catalyst is a substance used
to speed up a chemical process),As hydrocarbons or carbon
monoxide in the exhaust are passed over the catalyst,it is
chemically oxidized or converted to carbon dioxide and water,
As the converter works to clean the exhaust,it develops heat,
The dirtier the exhaust,the harder the converter works and
the more heat that is developed,In some cases the
converter can be seen to glow from excessive heat,If the
converter works this hard to clean a dirty exhaust,it will
destroy itself,Also leaded fuel will put a coating on the
platinum or palladium and render the converter ineffective.
小结
PCV System
EGR System
EGR Valves
negative back pressure EGR valve
The linear EGR valve
digital EGR valve
linear EGR valve
Internal Exhaust Gas Recirculation (EGR)
Evaporative Control System
charcoal canister
purge valve (EVAP purge solenoid)
duty cycle
Air Injection
Catalytic Converter
作业
熟记相关专业词汇
P169 EXERCIES Ⅰ & Ⅱ
EMISSION CONTROL SYSTEMS
TEXT A
Overview of Emission Control Systems
PROFESSIONAL ENGLISH
UNIT 7
EMISSION CONTROL SYSTEMS
TEXT A
Overview of Emission Control Systems
PCV System
EGR System
Evaporative Control System
Air Injection
Catalytic Converter
PROFESSIONAL ENGLISH
本次课学习目标
掌握排放控制系统的组成
掌握排放控制系统的原理
掌握有关的英文专业术语
了解翻译技巧 — 重复
NEW WORDS
dilute [dai'lju:t] v.冲淡,变淡,变弱,稀释
crossover ['kr?s?ouv?] n.转线路,天桥,交叉
channel ['t∫?nl] n.海峡，水道，信道，频道，通道
route [ru:t] n.路线,路程,通道； v.发送
lean （ out） [li:n] v.贫化，变瘦
thermal ['θ?:m?l] a.热的,热量的
transducer [tr?nz'dju:s?] n.传感器，变频器，变换器
orifice ['?rifis] n.孔，口，节流孔
linear ['lini?] a.线的,直线的,线性的
potentiometer [pten∫i'?m
it?]
n.电位计,电势计
fume [fju:m] n.(浓烈或难闻的 )烟,气体； v.用烟熏,
冒烟,发怒
prohibit [pr?'hibit] v.禁止,阻止
adhere [?d'hi?] v.粘附,胶着,坚持
pop [p?p] n.砰的一声,爆裂声,流行乐曲,流行艺术
a.流行的,热门的,通俗的
v.发出爆裂声,爆开,射击,突然出现
diverter [dai'v?:t?] n.分流器，换向器，分流阀
divert [di'v?:t] v.转移,转向
catalytic [?k?t?'litik] a.催化的
muffler ['m?fl?] n.消声器
pellet ['pelit] n.小球
honeycomb ['h?nikoum] n.蜂房，蜂巢
platinum ['pl?tin?m] n.白金,铂
palladium [p?'leidi?m] n.钯
catalyst ['k?t?list] n.催化剂
render ['rend?] v.致使，表演，实施
PHRASES AND EXPRESSIONS
脉宽调制pulse width
modulation
EGR阀位置（ EVP）传感器EGR valve position
(EVP) sensor
锥形端tapered tip
通气孔bleed port
背压back pressure
大节气门开度（简写为 WOT）wide-open throttle
废气再循环阀EGR valve
节气门开度throttle opening
在最坏的情况下at worst
空气喷射air injection
催化转换器catalytic converter
空气泵air pump
分流阀diverter valve
清污阀purge valve
与 … 一道（同时），以及，除 … 之外（还）
along with
活性炭罐charcoal canister
Overview of Emission Control Systems
To minimize pollution of the atmosphere from incompletely
burned and evaporating gases and to maintain good
driveability and fuel economy,a number of emission control
systems are used on all vehicles,They include positive
crankcase ventilation (PCV) system,evaporative emission
control (EVAP) system,exhaust gas recirculation (EGR)
system,air injection (AIR) system and three-way catalytic
converter (TWC) system.
PCV System
The purpose of the positive crankcase ventilation (PCV)
system is to take the vapors produced in the crankcase and
piston blow-by,and redirect them into the air/fuel intake system
to be burned during combustion,These vapors dilute the
air/fuel mixture,they have to be carefully controlled and
metered so as not to affect the performance of the engine,This
is the job of the positive crankcase ventilation (PCV) valve,
At idle,when the air/fuel mixture is very critical,just a little
of the vapors are allowed in to the intake system,At high
speed when the mixture is less critical and the pressures in
the engine are greater,more of the vapors are allowed in to
the intake system [1],When the valve or the system is
clogged,vapors will back up into the air filter housing or at
worst,the excess pressure will push past seals and create
engine oil leaks [2],If the wrong valve is used or the system
has air leaks,the engine will idle rough,or at worst engine oil
will be sucked out of the engine.
EGR System
Exhaust gas recirculation (EGR) systems reduce the
amount of oxides of nitrogen produced during the combustion
process,The EGR system dilutes the air/fuel mixture with
controlled amounts of exhaust gas,Since exhaust gas does
not burn,this reduces the peak combustion temperatures,
At lower combustion temperatures,very little of the nitrogen in
the air will combine with oxygen to form NOX,Most of the
nitrogen is simply carried out with the exhaust gases,For
driveability,it is desirable to have the EGR valve opening (and
the amount of gas flow) proportional to the throttle opening,
Driveability is also improved by shutting off the EGR when the
engine is started up cold,at idle,and at full throttle,Since the
NOX control requirements vary on different engines,there are
several different systems with various controls to provide these
functions,
EGR Valves
Most of these systems use a vacuum-operated EGR valve to
regulate the exhaust gas flow into the intake manifold,Exhaust
crossover passages under the intake manifold channel the
exhaust gas to the valve,(Some in-line engines route the
exhaust gas to the valve through an external tube.) Typical
mounting of the EGR valve is either on a plate under the
carburetor or directly on the manifold.
The EGR valve is a vacuum-operated,flow control valve,
Opening the EGR valve by control vacuum at the diaphragm,
allows exhaust gases to flow through the valve and into the
intake manifold,Here,the exhaust gas mixes with the air/fuel
mixture,The effect is to dilute or lean out the mixture,so that it
still burns completely but with a reduction in combustion
chamber temperatures.
There are also various designs of EGR valves,The positive
back pressure EGR valve has a bleed port and valve positioned
in the center of the diaphragm,A light spring holds this bleed
valve open,and an exhaust passage is connected from the
lower end of the tapered valve through the stem to the bleed
valve,When the engine is running,exhaust pressure is applied
to the bleed valve,At low engine speeds,exhaust pressure is
not high enough to close the bleed valve,If control vacuum is
supplied to the diaphragm chamber,the vacuum is bled off
through the bleed port,and the valve remains closed,（略）
In a negative back pressure EGR valve,a normally closed
bleed port is positioned in the center of the diaphragm,An
exhaust passage is connected from the lower end of the tapered
valve through the stem to the bleed valve,When the engine is
running at lower speeds,there is a high-pressure pulse in the
exhaust system,However,between these high-pressure pulses
there are low-pressure pulses,As the engine speed increases,
more cylinder firings occur in a given time,and the high-pressure
pulses become closer together in the exhaust system.（略）
A digital EGR valve contains up to three electric solenoids that
are operated directly by the PCM,Each solenoid contains a
movable plunger with a tapered tip that seats in an orifice,When
any solenoid is energized,the plunger is lifted and exhaust gas is
allowed to recirculate through the orifice into the intake manifold,
The solenoids and orifices are different sizes,The PCM can
operate one,two,or three solenoids to supply the amount of
exhaust recirculation required to provide optimum control of NOx
emissions.
The linear EGR valve contains a single electric solenoid
that is operated by the PCM,A tapered pintle is positioned
on the end of the solenoid plunger,When the solenoid is
energized,the plunger and tapered valve are lifted,and
exhaust gas is allowed to recirculate into the intake manifold,
The EGR valve contains an EGR valve position or lift sensor,
which is a linear potentiometer,The signal from this sensor
varies from approximately 1V with the EGR valve closed to
4.5V with the valve wide open,
The PCM pulses the EGR solenoid winding on and off with
a pulse width modulation principle to provide accurate control
of the plunger and EGR flow,The EGR valve position (EVP)
sensor acts as a feedback signal to the PCM to inform the
PCM if the commanded valve position was achieved.
Fig.7-2 A electronic EGR system
Fig.7-2 A electronic EGR system
Internal Exhaust Gas Recirculation (EGR)
EGR reduces the levels of oxides of nitrogen (nitric oxide NO,
and small quantities of nitrogen dioxide NO2,collectively
referred to as NOX) in engine exhaust gases at part load,The
aim of an internal EGR system is to control the recirculation of
exhaust gas without the use of external pipework on the engine.
In a conventional plenum throttled engine,at part throttle there
is a pressure differential between the inlet and exhaust ports,
Towards the end of the exhaust stroke on a four stroke engine,
the inlet valve opens and a period follows when inlet and
exhaust valves are open simultaneously,During this valve
overlap period,the inlet port depression causes residual
exhaust gas in the combustion chamber to flow back into the
inlet port,The resultant pressure drop in the combustion
chamber causes gases in the exhaust port to flow back into the
combustion chamber,These residual exhaust gases dilute the
incoming air/fuel charge,
This dilution of the charge reduces the peak combustion
temperatures and pressures,which reduces the amount of
NOX in the exhaust gases,Excess dilution can lead to
incomplete or unstable combustion which results in an increase
in hydrocarbon (HC) levels,The optimum amount of dilution
varies with engine speed and load,Conventionally,the dilution
requirements for optimized running conditions are achieved by
using an external EGR system which recirculates metered
quantities of exhaust gas by external pipes and a control valve.
Evaporative Control System
Gasoline evaporates quite easily,In the past these
evaporative emissions were vented into the atmosphere,20%
of all HC emissions from the automobile are from the gas tank,
In 1970 legislation was passed,prohibiting venting of gas tank
fumes into the atmosphere,An evaporative control system was
developed to eliminate this source of pollution,The function of
the fuel evaporative control system is to trap and store
evaporative emissions from the gas tank and carburetor,
A charcoal canister is used to trap the fuel vapors,The fuel
vapors adhere to the charcoal,until the engine is started,and
engine vacuum can be used to draw the vapors into the engine,
so that they can be burned along with the fuel/air mixture,This
system requires the use of a sealed gas tank filler cap,This
cap is so important to the operation of the system that a test of
the cap is now being integrated into many state emission
inspection programs,Pre-1970 cars released fuel vapors into
the atmosphere through the use of a vented gas cap,Today
with the use of sealed caps,redesigned gas tanks are used,
The tank has to have the space for the vapors to collect so that
they can then be vented to the charcoal canister,A purge
valve is used to control the vapor flow into the engine,The
purge valve is operated by engine vacuum,One common
problem with this system is that the purge valve goes bad and
engine vacuum draws fuel directly into the intake system [3],
This enriches the fuel mixture and will foul the spark plugs,
Most charcoal canisters have a filter that should be replaced
periodically,This system should be checked when fuel
mileage drops,
In some engines,the powertrain control module (PCM)
allows intake manifold vacuum to draw vapors into the
combustion chambers during certain operating conditions,All
of these engines use a duty cycle purge system,The PCM
controls the vapor flow by operating the duty cycle EVAP
purge solenoid (Fig.7-3).
Fig.7-3 An ECM-controlled
EVAP system
Air Injection
Since no internal combustion engine is 100% efficient,there
will always be some unburned fuel in the exhaust,This
increases hydrocarbon emissions,To eliminate this source of
emissions an air injection system was created,Combustion
requires fuel,oxygen and heat,Without any one of the three,
combustion cannot occur,Inside the exhaust manifold there is
sufficient heat to support combustion,if we introduce some
oxygen that any unburned fuel will ignite,This combustion will
not produce any power,but it will reduce excessive
hydrocarbon emissions,Unlike in the combustion chamber,this
combustion is uncontrolled,so if the fuel content of the exhaust
is excessive,explosions,which sound like popping,will occur,
There are times when under normal conditions,such as
deceleration,when the fuel content is excessive [4],Under
these conditions we would want to shut off the air injection
system,
a) cold mode
Fig.7-4 Air management system operation
b) worm mode
Fig.7-4 Air management system operation
This is accomplished through the use of a diverter valve,which
instead of shutting the air pump off,diverts the air away from
the exhaust manifold,Since all of this is done after the
combustion process is complete,this is one emission control
that has no effect on engine performance,
Later versions of the air injection system are under ECM
control (Fig.7-4),When the engine is cold,the ECM energizes a
control solenoid,This allows air to flow to an air switching valve,
The air switching valve is energized to direct air to the exhaust
ports.
On a warm engine,or in "closed loop" mode,the ECM de-
energizes the air switching valve,directing air between the beds
of the catalytic converter,This provides extra oxygen for the
oxidizing catalyst to decrease HC and CO levels,while keeping
oxygen levels low in the first bed of the converter,This enables
the reducing catalyst to effectively decrease the levels of oxides
of nitrogen (NOX).
Catalytic Converter
Automotive emissions are controlled in three ways,One is to
promote more complete combustion so that there are fewer by-
products,The second is to reintroduce excessive hydrocarbons
back into the engine for combustion and the third is to provide
an additional area for oxidation or combustion to occur,This
additional area is called a catalytic converter,The catalytic
converter looks like a muffler,It is located in the exhaust
system ahead of the muffler,Inside the converter are pellets or
a honeycomb made of platinum or palladium,The platinum or
palladium is used as a catalyst (a catalyst is a substance used
to speed up a chemical process),As hydrocarbons or carbon
monoxide in the exhaust are passed over the catalyst,it is
chemically oxidized or converted to carbon dioxide and water,
As the converter works to clean the exhaust,it develops heat,
The dirtier the exhaust,the harder the converter works and
the more heat that is developed,In some cases the
converter can be seen to glow from excessive heat,If the
converter works this hard to clean a dirty exhaust,it will
destroy itself,Also leaded fuel will put a coating on the
platinum or palladium and render the converter ineffective.
小结
PCV System
EGR System
EGR Valves
negative back pressure EGR valve
The linear EGR valve
digital EGR valve
linear EGR valve
Internal Exhaust Gas Recirculation (EGR)
Evaporative Control System
charcoal canister
purge valve (EVAP purge solenoid)
duty cycle
Air Injection
Catalytic Converter
作业
熟记相关专业词汇
P169 EXERCIES Ⅰ & Ⅱ
