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VA
VALVE
DESCRIPTION
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OPERATION
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VALVE
DESCRIPTION
Exhaust gas recirculation reduces the quantity of
fresh air supplied to the cylinders per stroke without
having to throttle the air supply. As a result, emis-
sions are reduced. If a quantity of exhaust gas is
mixed with the air that is to be used to burn the fuel
in the cylinders, the oxygen content is reduced,
because the exhaust gas is low in oxygen. The result
is that the combustion rate is reduced, as is the com-
bustion temperature. This reduces the quantity of
NOx that are emitted in the exhaust gas (Fig. 1).
OPERATION
The mass of the air supplied to the cylinders per
stroke is the decisive factor for determining the opti-
mum quantity of exhaust gas for the operating con-
dition. This is calculated from the Mass Air Flow
sensor information.
The ECM evaluates this signal as well as that
from the Charge Air Pressure sensor, and outputs a
PWM signal in accordance with one of the maps
stored in it. The signal is sent to the exhaust gas
recirculation valve. The map is formulated to keep
the NOx as low as possible. The EGR valve is actu-
ated by an electric positioning motor.
EMISSIONS CONTROL
EXHAUST GAS RECIRCULATION
TABLE OF CONTENTS
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EMISSIONS CONTROL 25 - 1
REMOVAL
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INSTALLATION
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Fig. 1 EXHAUST GAS RECIRCULATION
1 - EGR VALVE
2 -CHARGE AIR PRESSURE SENSOR
3 - EXHAUST MANIFOLD
4 - EGR DUCT IN CYLINDER HEAD
5 - INTAKE MANIFOLD
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