ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS Notes | EduRev

: ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS Notes | EduRev

 Page 1


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_1.htm[6/15/2012 3:03:58 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
  
ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
The Lecture Contains:
Crankcase Emission Control (PCV System)
Evaporative Emission Control
Exhaust Gas Recirculation
Water Injection
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 2


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_1.htm[6/15/2012 3:03:58 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
  
ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
The Lecture Contains:
Crankcase Emission Control (PCV System)
Evaporative Emission Control
Exhaust Gas Recirculation
Water Injection
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_2.htm[6/15/2012 3:03:58 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
 
ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
Crankcase Emission Control (PCV System)
A small amount of charge in the cylinder leaks past piston rings into crankcase of the reciprocating
engines.   Near top dead centre (TDC) when the rings change their position in the grooves at the end
of compression stroke, combustion has already begun and the cylinder pressures are high.  A significant
part of charge stored in the piston- ring-cylinder crevice leaks into the crankcase. These gases are
known as ‘crankcase blow by’ and their flow rate increases as the engine is worn out and the piston -
cylinder clearances and ring gaps increase. In the homogeneous charge engines, the crankcase blow by
gas is high in HC concentration. Only a small fraction of the gas stored in the ring crevices and hence
blow by gases may consist of partially burnt mixture. This source contributes about 20 percent of total
hydrocarbons emitted by an uncontrolled car.
Figure
5.6
Schematic of a PCV
system.
The crankcase blowby gases in the uncontrolled engines were ventilated to atmosphere under the effect
of pressure difference occurring naturally between the crankcase and atmosphere. For control of
crankcase emissions, the blowby gases are recycled back to the engine assisted by a positive pressure
drop between the crankcase and intake manifold. When engine is running and intake charge is throttled
the intake manifold is at a lower pressure than the crankcase. The blow-by gases mix with the intake
charge to be burned inside the engine cylinder to CO
2
 and H
2
O. A typical PCV system is shown in Fig.
5.6.  A tube connects crankcase or cylinder head cover to the intake manifold below throttle valve, which
leads the blowby gases back to the engine. Due to suction effect of intake manifold as the pressure in
the crankcase falls, ventilation air 
from the air cleaner is drawn into the crankcase that continuously purges it. A one-way valve (PCV
 
 
 
 
 
 
 
 
 
 
Page 3


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_1.htm[6/15/2012 3:03:58 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
  
ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
The Lecture Contains:
Crankcase Emission Control (PCV System)
Evaporative Emission Control
Exhaust Gas Recirculation
Water Injection
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_2.htm[6/15/2012 3:03:58 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
 
ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
Crankcase Emission Control (PCV System)
A small amount of charge in the cylinder leaks past piston rings into crankcase of the reciprocating
engines.   Near top dead centre (TDC) when the rings change their position in the grooves at the end
of compression stroke, combustion has already begun and the cylinder pressures are high.  A significant
part of charge stored in the piston- ring-cylinder crevice leaks into the crankcase. These gases are
known as ‘crankcase blow by’ and their flow rate increases as the engine is worn out and the piston -
cylinder clearances and ring gaps increase. In the homogeneous charge engines, the crankcase blow by
gas is high in HC concentration. Only a small fraction of the gas stored in the ring crevices and hence
blow by gases may consist of partially burnt mixture. This source contributes about 20 percent of total
hydrocarbons emitted by an uncontrolled car.
Figure
5.6
Schematic of a PCV
system.
The crankcase blowby gases in the uncontrolled engines were ventilated to atmosphere under the effect
of pressure difference occurring naturally between the crankcase and atmosphere. For control of
crankcase emissions, the blowby gases are recycled back to the engine assisted by a positive pressure
drop between the crankcase and intake manifold. When engine is running and intake charge is throttled
the intake manifold is at a lower pressure than the crankcase. The blow-by gases mix with the intake
charge to be burned inside the engine cylinder to CO
2
 and H
2
O. A typical PCV system is shown in Fig.
5.6.  A tube connects crankcase or cylinder head cover to the intake manifold below throttle valve, which
leads the blowby gases back to the engine. Due to suction effect of intake manifold as the pressure in
the crankcase falls, ventilation air 
from the air cleaner is drawn into the crankcase that continuously purges it. A one-way valve (PCV
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_2.htm[6/15/2012 3:03:58 PM]
valve) is used to control the flow of blowby gases PCV valve restricts flow of blowby gases during idling
and very light loads which otherwise would cause excessive leaning of the charge by ventilation
air.Under normal engine operation, PCV valve is fully open providing free flow of the gases while under
high intake manifold vacuum the flow is restricted.
 
 
Page 4


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_1.htm[6/15/2012 3:03:58 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
  
ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
The Lecture Contains:
Crankcase Emission Control (PCV System)
Evaporative Emission Control
Exhaust Gas Recirculation
Water Injection
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_2.htm[6/15/2012 3:03:58 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
 
ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
Crankcase Emission Control (PCV System)
A small amount of charge in the cylinder leaks past piston rings into crankcase of the reciprocating
engines.   Near top dead centre (TDC) when the rings change their position in the grooves at the end
of compression stroke, combustion has already begun and the cylinder pressures are high.  A significant
part of charge stored in the piston- ring-cylinder crevice leaks into the crankcase. These gases are
known as ‘crankcase blow by’ and their flow rate increases as the engine is worn out and the piston -
cylinder clearances and ring gaps increase. In the homogeneous charge engines, the crankcase blow by
gas is high in HC concentration. Only a small fraction of the gas stored in the ring crevices and hence
blow by gases may consist of partially burnt mixture. This source contributes about 20 percent of total
hydrocarbons emitted by an uncontrolled car.
Figure
5.6
Schematic of a PCV
system.
The crankcase blowby gases in the uncontrolled engines were ventilated to atmosphere under the effect
of pressure difference occurring naturally between the crankcase and atmosphere. For control of
crankcase emissions, the blowby gases are recycled back to the engine assisted by a positive pressure
drop between the crankcase and intake manifold. When engine is running and intake charge is throttled
the intake manifold is at a lower pressure than the crankcase. The blow-by gases mix with the intake
charge to be burned inside the engine cylinder to CO
2
 and H
2
O. A typical PCV system is shown in Fig.
5.6.  A tube connects crankcase or cylinder head cover to the intake manifold below throttle valve, which
leads the blowby gases back to the engine. Due to suction effect of intake manifold as the pressure in
the crankcase falls, ventilation air 
from the air cleaner is drawn into the crankcase that continuously purges it. A one-way valve (PCV
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_2.htm[6/15/2012 3:03:58 PM]
valve) is used to control the flow of blowby gases PCV valve restricts flow of blowby gases during idling
and very light loads which otherwise would cause excessive leaning of the charge by ventilation
air.Under normal engine operation, PCV valve is fully open providing free flow of the gases while under
high intake manifold vacuum the flow is restricted.
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_3.htm[6/15/2012 3:03:59 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
 
Evaporative Emission Control
In the uncontrolled vehicles, fuel vapours from the fuel tank and carburettor were vented into the
atmosphere that constituted about 20% of all hydrocarbon emissions from a gasoline passenger car.
 From 1970, evaporative emission control was required to be employed on production gasoline vehicles
in the USA.
The evaporative emission control system consists of a device to store fuel vapours produced in
the fuel system due to evaporation.
A canister containing activated charcoal is used to store the fuel vapours.
The vapours produced in the fuel tank normally collect in the fuel tank itself and are vented to
the charcoal canister when fuel vapour pressure becomes excessive.  The fuel vapours from the
tank and carburettor led to and adsorbed into the charcoal. In the PFI engines only the fuel tank
is connected to the canister.
When engine is running, the vacuum created in the intake manifold is used to   draw fuel
vapours from the canister into the engine. Purging air is sucked through the canister which leads
the fuel vapours from canister to the engine. An electronically controlled  purge valve is used.
During engine acceleration additional mixture enrichment can be tolerated and under these
operating conditions the stored fuel vapours are usually purged into the intake manifold.
This system is a fully closed system. A sealed fuel tank filler cap is used and a stable fuel tank
pressure is maintained by the purging process of the canister.
A typical schematic layout of evaporative control system is shown in Fig. 5.7. Given below are some of
the measures adopted to achieve near zero evaporative emissions as required in California;
Sealed fuel tank is kept under vacuum to prevent permeation of fuel through walls of a polymer
fuel tank and leakage of fuel vapours through filler cap.
Fuel tubing made of high density polymer or steel to reduce/prevent fuel permeation.
Better canister technology and more effective activated charcoal.
Employment of refuelling vapour recovery (ORVR) system as during vehicle refuelling maximum
share of fuel evaporative emissions  escape..
A carbon trap to arrest the escape of fuel vapours from intake manifold. When the vehicle is
standing and is under hot soak fuel vapours can escape past the throttle body into atmosphere.
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 5


Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_1.htm[6/15/2012 3:03:58 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
  
ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
The Lecture Contains:
Crankcase Emission Control (PCV System)
Evaporative Emission Control
Exhaust Gas Recirculation
Water Injection
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_2.htm[6/15/2012 3:03:58 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
 
ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
Crankcase Emission Control (PCV System)
A small amount of charge in the cylinder leaks past piston rings into crankcase of the reciprocating
engines.   Near top dead centre (TDC) when the rings change their position in the grooves at the end
of compression stroke, combustion has already begun and the cylinder pressures are high.  A significant
part of charge stored in the piston- ring-cylinder crevice leaks into the crankcase. These gases are
known as ‘crankcase blow by’ and their flow rate increases as the engine is worn out and the piston -
cylinder clearances and ring gaps increase. In the homogeneous charge engines, the crankcase blow by
gas is high in HC concentration. Only a small fraction of the gas stored in the ring crevices and hence
blow by gases may consist of partially burnt mixture. This source contributes about 20 percent of total
hydrocarbons emitted by an uncontrolled car.
Figure
5.6
Schematic of a PCV
system.
The crankcase blowby gases in the uncontrolled engines were ventilated to atmosphere under the effect
of pressure difference occurring naturally between the crankcase and atmosphere. For control of
crankcase emissions, the blowby gases are recycled back to the engine assisted by a positive pressure
drop between the crankcase and intake manifold. When engine is running and intake charge is throttled
the intake manifold is at a lower pressure than the crankcase. The blow-by gases mix with the intake
charge to be burned inside the engine cylinder to CO
2
 and H
2
O. A typical PCV system is shown in Fig.
5.6.  A tube connects crankcase or cylinder head cover to the intake manifold below throttle valve, which
leads the blowby gases back to the engine. Due to suction effect of intake manifold as the pressure in
the crankcase falls, ventilation air 
from the air cleaner is drawn into the crankcase that continuously purges it. A one-way valve (PCV
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_2.htm[6/15/2012 3:03:58 PM]
valve) is used to control the flow of blowby gases PCV valve restricts flow of blowby gases during idling
and very light loads which otherwise would cause excessive leaning of the charge by ventilation
air.Under normal engine operation, PCV valve is fully open providing free flow of the gases while under
high intake manifold vacuum the flow is restricted.
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_3.htm[6/15/2012 3:03:59 PM]
 Module 5: Emission Control for SI Engines
 Lecture20:ADD-ON SYSTEMS FOR CONTROL OF ENGINE-OUT EMISSIONS
 
Evaporative Emission Control
In the uncontrolled vehicles, fuel vapours from the fuel tank and carburettor were vented into the
atmosphere that constituted about 20% of all hydrocarbon emissions from a gasoline passenger car.
 From 1970, evaporative emission control was required to be employed on production gasoline vehicles
in the USA.
The evaporative emission control system consists of a device to store fuel vapours produced in
the fuel system due to evaporation.
A canister containing activated charcoal is used to store the fuel vapours.
The vapours produced in the fuel tank normally collect in the fuel tank itself and are vented to
the charcoal canister when fuel vapour pressure becomes excessive.  The fuel vapours from the
tank and carburettor led to and adsorbed into the charcoal. In the PFI engines only the fuel tank
is connected to the canister.
When engine is running, the vacuum created in the intake manifold is used to   draw fuel
vapours from the canister into the engine. Purging air is sucked through the canister which leads
the fuel vapours from canister to the engine. An electronically controlled  purge valve is used.
During engine acceleration additional mixture enrichment can be tolerated and under these
operating conditions the stored fuel vapours are usually purged into the intake manifold.
This system is a fully closed system. A sealed fuel tank filler cap is used and a stable fuel tank
pressure is maintained by the purging process of the canister.
A typical schematic layout of evaporative control system is shown in Fig. 5.7. Given below are some of
the measures adopted to achieve near zero evaporative emissions as required in California;
Sealed fuel tank is kept under vacuum to prevent permeation of fuel through walls of a polymer
fuel tank and leakage of fuel vapours through filler cap.
Fuel tubing made of high density polymer or steel to reduce/prevent fuel permeation.
Better canister technology and more effective activated charcoal.
Employment of refuelling vapour recovery (ORVR) system as during vehicle refuelling maximum
share of fuel evaporative emissions  escape..
A carbon trap to arrest the escape of fuel vapours from intake manifold. When the vehicle is
standing and is under hot soak fuel vapours can escape past the throttle body into atmosphere.
 
 
 
 
 
 
 
 
 
 
 
 
 
Objectives_template
file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture20/20_3.htm[6/15/2012 3:03:59 PM]
Figure
5.7
Schematic of an evaporative emission control system for a PFI
engine.
 
 
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