PM Module Emission Control for SI Engines Lecture19 Emission Control by Engine Design Variables Notes | EduRev

: PM Module Emission Control for SI Engines Lecture19 Emission Control by Engine Design Variables Notes | EduRev

 Page 1


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_1.htm[6/15/2012 3:03:36 PM]
 Module 5:Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
EMISSION CONTROL FOR SI ENGINES/VEHICLES
The Lecture Contains:
AN OVERVIEW AND CONTROL OF ENGINE-OUT EMISSIONS
Categorization of Emission Control Techniques
ENGINE DESIGN PARAMETERS
Engine Compression Ratio
 High Turbulence Combustion Chambers
Fuel System
Valve Gear Design
Variable Swept Volume and Downsizing
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 2


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_1.htm[6/15/2012 3:03:36 PM]
 Module 5:Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
EMISSION CONTROL FOR SI ENGINES/VEHICLES
The Lecture Contains:
AN OVERVIEW AND CONTROL OF ENGINE-OUT EMISSIONS
Categorization of Emission Control Techniques
ENGINE DESIGN PARAMETERS
Engine Compression Ratio
 High Turbulence Combustion Chambers
Fuel System
Valve Gear Design
Variable Swept Volume and Downsizing
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_2.htm[6/15/2012 3:03:36 PM]
 Module 5:Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
AN OVERVIEW AND CONTROL OF ENGINE-OUT EMISSIONS
During 1950s the road vehicles were found to be the principal source of air pollution in the US cities.
Carbon monoxide, unburned fuel (hydrocarbons), nitrogen oxides and smoke particulates were identified
as the main air pollutants. Now, carbon dioxide has been added to the list of harmful gaseous emissions
due to its global warming effect.  Initially, to solve the local air pollution problem during 1960s efforts
were mainly focused on reduction of CO from gasoline vehicles and black smoke emissions from diesel
vehicles. Another area of priority attention was the prevention of blue smoke emissions caused by
excessive consumption of engine lubricating oil which resulted from worn out piston rings, cylinder bore
etc. 
The first emission control for the spark ignition engines involved adjustments of air-fuel ratio. It was
followed by control and adjustment of other engine parameters such as mixture control under idling,
acceleration and deceleration, spark timing, precision manufacturing of key engine components such as
piston, rings, cylinder head gasket to minimize crevice volume, cams, valves etc. Positive crankcase
ventilation (PCV) system was introduced on gasoline vehicles during mid 1960’s to prevent release into
atmosphere of hydrocarbon-rich crankcase blow by gases
As the emission standards were tightened, exhaust aftertreatment devices such as catalytic converters
were introduced for the first time in 1974-75 and more advanced modifications in engine design and fuel
system were employed. Electronic fuel and engine management become necessary during 1980s to
meet the then emission regulations. Further advancements in engine, fuel system and emission control
technology have emerged in the meantime.  Multi-valve cylinder engines became common and variable
valve actuation was applied in production vehicles during late 1980s. In mid 1990s, gasoline direct
injection stratified charge (DISC) engines were put into production by Japanese auto-manufacturers. 
Besides all-round advancements in engine technology and aftertreatment systems happening all the
time, in the past few years alternative power trains also for vehicles have been developed which provide
a higher fuel efficiency in addition to low emissions. Hybrid electric vehicles (HEV) are already in market
place. The HEV has IC engine as a primary source of power but employ electric propulsion powered by
storage batteries as the main propulsion unit. Fuel cell vehicles using hydrogen as energy source are in
an advanced stage of development and they completely eliminate the use of IC engines as a propulsion
system
Categorization of Emission Control Techniques
The emission control techniques may be grouped into the following broad categories:
Engine design and fuel system parameters
Engine add-ons to enable reduction of engine-out emissions and
Exhaust aftertreatment
 
 
 
 
 
 
 
 
 
 
 
 
Page 3


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_1.htm[6/15/2012 3:03:36 PM]
 Module 5:Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
EMISSION CONTROL FOR SI ENGINES/VEHICLES
The Lecture Contains:
AN OVERVIEW AND CONTROL OF ENGINE-OUT EMISSIONS
Categorization of Emission Control Techniques
ENGINE DESIGN PARAMETERS
Engine Compression Ratio
 High Turbulence Combustion Chambers
Fuel System
Valve Gear Design
Variable Swept Volume and Downsizing
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_2.htm[6/15/2012 3:03:36 PM]
 Module 5:Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
AN OVERVIEW AND CONTROL OF ENGINE-OUT EMISSIONS
During 1950s the road vehicles were found to be the principal source of air pollution in the US cities.
Carbon monoxide, unburned fuel (hydrocarbons), nitrogen oxides and smoke particulates were identified
as the main air pollutants. Now, carbon dioxide has been added to the list of harmful gaseous emissions
due to its global warming effect.  Initially, to solve the local air pollution problem during 1960s efforts
were mainly focused on reduction of CO from gasoline vehicles and black smoke emissions from diesel
vehicles. Another area of priority attention was the prevention of blue smoke emissions caused by
excessive consumption of engine lubricating oil which resulted from worn out piston rings, cylinder bore
etc. 
The first emission control for the spark ignition engines involved adjustments of air-fuel ratio. It was
followed by control and adjustment of other engine parameters such as mixture control under idling,
acceleration and deceleration, spark timing, precision manufacturing of key engine components such as
piston, rings, cylinder head gasket to minimize crevice volume, cams, valves etc. Positive crankcase
ventilation (PCV) system was introduced on gasoline vehicles during mid 1960’s to prevent release into
atmosphere of hydrocarbon-rich crankcase blow by gases
As the emission standards were tightened, exhaust aftertreatment devices such as catalytic converters
were introduced for the first time in 1974-75 and more advanced modifications in engine design and fuel
system were employed. Electronic fuel and engine management become necessary during 1980s to
meet the then emission regulations. Further advancements in engine, fuel system and emission control
technology have emerged in the meantime.  Multi-valve cylinder engines became common and variable
valve actuation was applied in production vehicles during late 1980s. In mid 1990s, gasoline direct
injection stratified charge (DISC) engines were put into production by Japanese auto-manufacturers. 
Besides all-round advancements in engine technology and aftertreatment systems happening all the
time, in the past few years alternative power trains also for vehicles have been developed which provide
a higher fuel efficiency in addition to low emissions. Hybrid electric vehicles (HEV) are already in market
place. The HEV has IC engine as a primary source of power but employ electric propulsion powered by
storage batteries as the main propulsion unit. Fuel cell vehicles using hydrogen as energy source are in
an advanced stage of development and they completely eliminate the use of IC engines as a propulsion
system
Categorization of Emission Control Techniques
The emission control techniques may be grouped into the following broad categories:
Engine design and fuel system parameters
Engine add-ons to enable reduction of engine-out emissions and
Exhaust aftertreatment
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_3.htm[6/15/2012 3:03:36 PM]
 Module 5: Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
ENGINE DESIGN PARAMETERS
The following engine parameters have large influence on emissions and hence have undergone
substantial modifications since the pre-emission control era.
Engine compression ratio,
Combustion chamber design – low crevice volume, high turbulence
Spark timing
Air-fuel ratio
Fuel system design: carburetor giving way to fuel injection
Multivalves and variable valve actuation
Engine temperature control
Engine Compression Ratio
Engine compression ratio affects
Surface to volume ratio  of the combustion chamber
Engine combustion temperature
Thermodynamic efficiency
Fuel octane number for knock free  engine operation
The premium high performance car engines during 1960s employed CR of 10 to 11:1. The engine CR
was lowered to 8.5 to 9.0:1 when stringent emission standards were legislated for the first time in 1975. 
The combustion chamber with a lower CR has lower surface/volume ratio resulting in a reduction in
volume of quench layer on the combustion chamber surface. Typical effect of surface/volume ratio of
combustion chamber is shown on Fig, 5.1. Moreover, for a low CR engine the crevice volume would
also be proportionately lower. These factors in turn would reduce HC emissions.  Higher exhaust
temperatures resulting with low CR would promote oxidation of HC and CO in exhaust system.
At low CR the peak combustion temperatures are lower and hence low NOx formation.
Introduction of catalytic converters made the use of unleaded gas necessary. As the petroleum refinery
economics dictated the use of unleaded gasoline of a low octane number, engine CR had to be
lowered.
The principal disadvantage of low CR engine is that it has a poorer fuel efficiency that also results in
higher CO2 emissions. 
 The premium high performance car engines during 1960s employed CR of 10 to 11:1. The engine CR
was lowered to 8.5 to 9.0:1 when stringent emission standards were legislated for the first time in 1975.
However, due to development of high turbulence engine combustion chambers and use of port fuel
injection system it has been possible to use a somewhat higher engine CR. The modern gasoline
engines have CR mostly in the range of 9.0 to 9.5:1.
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 4


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_1.htm[6/15/2012 3:03:36 PM]
 Module 5:Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
EMISSION CONTROL FOR SI ENGINES/VEHICLES
The Lecture Contains:
AN OVERVIEW AND CONTROL OF ENGINE-OUT EMISSIONS
Categorization of Emission Control Techniques
ENGINE DESIGN PARAMETERS
Engine Compression Ratio
 High Turbulence Combustion Chambers
Fuel System
Valve Gear Design
Variable Swept Volume and Downsizing
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_2.htm[6/15/2012 3:03:36 PM]
 Module 5:Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
AN OVERVIEW AND CONTROL OF ENGINE-OUT EMISSIONS
During 1950s the road vehicles were found to be the principal source of air pollution in the US cities.
Carbon monoxide, unburned fuel (hydrocarbons), nitrogen oxides and smoke particulates were identified
as the main air pollutants. Now, carbon dioxide has been added to the list of harmful gaseous emissions
due to its global warming effect.  Initially, to solve the local air pollution problem during 1960s efforts
were mainly focused on reduction of CO from gasoline vehicles and black smoke emissions from diesel
vehicles. Another area of priority attention was the prevention of blue smoke emissions caused by
excessive consumption of engine lubricating oil which resulted from worn out piston rings, cylinder bore
etc. 
The first emission control for the spark ignition engines involved adjustments of air-fuel ratio. It was
followed by control and adjustment of other engine parameters such as mixture control under idling,
acceleration and deceleration, spark timing, precision manufacturing of key engine components such as
piston, rings, cylinder head gasket to minimize crevice volume, cams, valves etc. Positive crankcase
ventilation (PCV) system was introduced on gasoline vehicles during mid 1960’s to prevent release into
atmosphere of hydrocarbon-rich crankcase blow by gases
As the emission standards were tightened, exhaust aftertreatment devices such as catalytic converters
were introduced for the first time in 1974-75 and more advanced modifications in engine design and fuel
system were employed. Electronic fuel and engine management become necessary during 1980s to
meet the then emission regulations. Further advancements in engine, fuel system and emission control
technology have emerged in the meantime.  Multi-valve cylinder engines became common and variable
valve actuation was applied in production vehicles during late 1980s. In mid 1990s, gasoline direct
injection stratified charge (DISC) engines were put into production by Japanese auto-manufacturers. 
Besides all-round advancements in engine technology and aftertreatment systems happening all the
time, in the past few years alternative power trains also for vehicles have been developed which provide
a higher fuel efficiency in addition to low emissions. Hybrid electric vehicles (HEV) are already in market
place. The HEV has IC engine as a primary source of power but employ electric propulsion powered by
storage batteries as the main propulsion unit. Fuel cell vehicles using hydrogen as energy source are in
an advanced stage of development and they completely eliminate the use of IC engines as a propulsion
system
Categorization of Emission Control Techniques
The emission control techniques may be grouped into the following broad categories:
Engine design and fuel system parameters
Engine add-ons to enable reduction of engine-out emissions and
Exhaust aftertreatment
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_3.htm[6/15/2012 3:03:36 PM]
 Module 5: Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
ENGINE DESIGN PARAMETERS
The following engine parameters have large influence on emissions and hence have undergone
substantial modifications since the pre-emission control era.
Engine compression ratio,
Combustion chamber design – low crevice volume, high turbulence
Spark timing
Air-fuel ratio
Fuel system design: carburetor giving way to fuel injection
Multivalves and variable valve actuation
Engine temperature control
Engine Compression Ratio
Engine compression ratio affects
Surface to volume ratio  of the combustion chamber
Engine combustion temperature
Thermodynamic efficiency
Fuel octane number for knock free  engine operation
The premium high performance car engines during 1960s employed CR of 10 to 11:1. The engine CR
was lowered to 8.5 to 9.0:1 when stringent emission standards were legislated for the first time in 1975. 
The combustion chamber with a lower CR has lower surface/volume ratio resulting in a reduction in
volume of quench layer on the combustion chamber surface. Typical effect of surface/volume ratio of
combustion chamber is shown on Fig, 5.1. Moreover, for a low CR engine the crevice volume would
also be proportionately lower. These factors in turn would reduce HC emissions.  Higher exhaust
temperatures resulting with low CR would promote oxidation of HC and CO in exhaust system.
At low CR the peak combustion temperatures are lower and hence low NOx formation.
Introduction of catalytic converters made the use of unleaded gas necessary. As the petroleum refinery
economics dictated the use of unleaded gasoline of a low octane number, engine CR had to be
lowered.
The principal disadvantage of low CR engine is that it has a poorer fuel efficiency that also results in
higher CO2 emissions. 
 The premium high performance car engines during 1960s employed CR of 10 to 11:1. The engine CR
was lowered to 8.5 to 9.0:1 when stringent emission standards were legislated for the first time in 1975.
However, due to development of high turbulence engine combustion chambers and use of port fuel
injection system it has been possible to use a somewhat higher engine CR. The modern gasoline
engines have CR mostly in the range of 9.0 to 9.5:1.
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_3.htm[6/15/2012 3:03:36 PM]
Fig 5.1
Effect of surface/volume ratio of combustion chamber on HC
emissions
 
Page 5


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_1.htm[6/15/2012 3:03:36 PM]
 Module 5:Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
EMISSION CONTROL FOR SI ENGINES/VEHICLES
The Lecture Contains:
AN OVERVIEW AND CONTROL OF ENGINE-OUT EMISSIONS
Categorization of Emission Control Techniques
ENGINE DESIGN PARAMETERS
Engine Compression Ratio
 High Turbulence Combustion Chambers
Fuel System
Valve Gear Design
Variable Swept Volume and Downsizing
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_2.htm[6/15/2012 3:03:36 PM]
 Module 5:Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
AN OVERVIEW AND CONTROL OF ENGINE-OUT EMISSIONS
During 1950s the road vehicles were found to be the principal source of air pollution in the US cities.
Carbon monoxide, unburned fuel (hydrocarbons), nitrogen oxides and smoke particulates were identified
as the main air pollutants. Now, carbon dioxide has been added to the list of harmful gaseous emissions
due to its global warming effect.  Initially, to solve the local air pollution problem during 1960s efforts
were mainly focused on reduction of CO from gasoline vehicles and black smoke emissions from diesel
vehicles. Another area of priority attention was the prevention of blue smoke emissions caused by
excessive consumption of engine lubricating oil which resulted from worn out piston rings, cylinder bore
etc. 
The first emission control for the spark ignition engines involved adjustments of air-fuel ratio. It was
followed by control and adjustment of other engine parameters such as mixture control under idling,
acceleration and deceleration, spark timing, precision manufacturing of key engine components such as
piston, rings, cylinder head gasket to minimize crevice volume, cams, valves etc. Positive crankcase
ventilation (PCV) system was introduced on gasoline vehicles during mid 1960’s to prevent release into
atmosphere of hydrocarbon-rich crankcase blow by gases
As the emission standards were tightened, exhaust aftertreatment devices such as catalytic converters
were introduced for the first time in 1974-75 and more advanced modifications in engine design and fuel
system were employed. Electronic fuel and engine management become necessary during 1980s to
meet the then emission regulations. Further advancements in engine, fuel system and emission control
technology have emerged in the meantime.  Multi-valve cylinder engines became common and variable
valve actuation was applied in production vehicles during late 1980s. In mid 1990s, gasoline direct
injection stratified charge (DISC) engines were put into production by Japanese auto-manufacturers. 
Besides all-round advancements in engine technology and aftertreatment systems happening all the
time, in the past few years alternative power trains also for vehicles have been developed which provide
a higher fuel efficiency in addition to low emissions. Hybrid electric vehicles (HEV) are already in market
place. The HEV has IC engine as a primary source of power but employ electric propulsion powered by
storage batteries as the main propulsion unit. Fuel cell vehicles using hydrogen as energy source are in
an advanced stage of development and they completely eliminate the use of IC engines as a propulsion
system
Categorization of Emission Control Techniques
The emission control techniques may be grouped into the following broad categories:
Engine design and fuel system parameters
Engine add-ons to enable reduction of engine-out emissions and
Exhaust aftertreatment
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_3.htm[6/15/2012 3:03:36 PM]
 Module 5: Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
ENGINE DESIGN PARAMETERS
The following engine parameters have large influence on emissions and hence have undergone
substantial modifications since the pre-emission control era.
Engine compression ratio,
Combustion chamber design – low crevice volume, high turbulence
Spark timing
Air-fuel ratio
Fuel system design: carburetor giving way to fuel injection
Multivalves and variable valve actuation
Engine temperature control
Engine Compression Ratio
Engine compression ratio affects
Surface to volume ratio  of the combustion chamber
Engine combustion temperature
Thermodynamic efficiency
Fuel octane number for knock free  engine operation
The premium high performance car engines during 1960s employed CR of 10 to 11:1. The engine CR
was lowered to 8.5 to 9.0:1 when stringent emission standards were legislated for the first time in 1975. 
The combustion chamber with a lower CR has lower surface/volume ratio resulting in a reduction in
volume of quench layer on the combustion chamber surface. Typical effect of surface/volume ratio of
combustion chamber is shown on Fig, 5.1. Moreover, for a low CR engine the crevice volume would
also be proportionately lower. These factors in turn would reduce HC emissions.  Higher exhaust
temperatures resulting with low CR would promote oxidation of HC and CO in exhaust system.
At low CR the peak combustion temperatures are lower and hence low NOx formation.
Introduction of catalytic converters made the use of unleaded gas necessary. As the petroleum refinery
economics dictated the use of unleaded gasoline of a low octane number, engine CR had to be
lowered.
The principal disadvantage of low CR engine is that it has a poorer fuel efficiency that also results in
higher CO2 emissions. 
 The premium high performance car engines during 1960s employed CR of 10 to 11:1. The engine CR
was lowered to 8.5 to 9.0:1 when stringent emission standards were legislated for the first time in 1975.
However, due to development of high turbulence engine combustion chambers and use of port fuel
injection system it has been possible to use a somewhat higher engine CR. The modern gasoline
engines have CR mostly in the range of 9.0 to 9.5:1.
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_3.htm[6/15/2012 3:03:36 PM]
Fig 5.1
Effect of surface/volume ratio of combustion chamber on HC
emissions
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture19/19_4.htm[6/15/2012 3:03:37 PM]
 Module 5: Emission Control for SI Engines
 Lecture19:Emission Control by Engine Design Variables
 
High Turbulence Combustion Chambers
Small cylinders with hemispherical and pentroof type combustion chambers are now more commonly
used in SI engines.
Small cylinder engines can be operated at higher speeds whicht increases turbulence and tends
to reduce HC emissions..
Smaller cylinders have smaller amount of burned gases that form the high temperature adiabatic
core. More heat transfer takes place from the burned gases as the walls are nearer to the bulk
gases. It results in lower NO
x
.
The compact hemispherical combustion chambers shape (Fig 5.2a) provides the lowest surface
to volume ratio and minimum tendency to engine knock.
The hemispherical combustion chamber although may employ multiple valves,  the two valve
configuration is more common as it is difficult to accommodate 4-valves at the necessary valve
positioning angles. The valve heads along with the surface of combustion chamber form a profile that
looks like a hemisphere. Both the intake and exhaust valves are inclined increasing valve port area that
results in higher volumetric efficiency. The chamber has a low surface to volume ratio.  The intake ports
are provided with a suitably curved geometry to generate high rate of air swirl.
Fig 5.2 (a)
Hemispherical combustion chamber (generally with two
valves)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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