TD5 Defender - Exhaust Gas Recirculation (EGR) System
17
EMISSION CONTROL
8
DESCRIPTION AND OPERATION
EXHAUST GAS RECIRCULATION
The exhaust gas recirculation (EGR) valve permits a controlled amount of exhaust gas to combine with the fresh
air entering the engine. The exhaust gas reduces the combustion temperature by delaying the fuel burning rate,
which assists in reducing the quantity of oxides of nitrogen.
On EU3 models, an EGR cooler is employed to further reduce the combustion temperature. By passing the
exhaust gas through a bundle of pipes flooded by coolant, the density of the exhaust gas going into the engine is
increased. This process further reduces the amount of NO
2
in the exhaust.
Recirculation of too much exhaust gas can result in higher emissions of soot, HC and CO due to insufficient air.
The recirculated exhaust gas must be limited so that there is sufficient oxygen available for combustion of the
injected fuel in the combustion chamber. To do this the ECM is used to control the precise quantity of exhaust gas
to be recirculated in accordance with the prevailing operating conditions. Influencing factors include:
•
The mass of air flow detected by the MAF sensor.
•
The ambient air temperature detected by the AAP sensor. This is used to initiate adjustments to reduce the
amount of smoke produced at high altitudes.
•
The mass of air flow detected by the MAF sensor.
•
The ambient air temperature detected by the AAP sensor. This is used to initiate adjustments to reduce the
amount of smoke produced at high altitudes.
Other factors which are taken into consideration by the engine management system for determining the optimum
operating condition include:
•
Manifold inlet air temperature
•
Coolant temperature
•
Engine speed
•
Fuel delivered
The main components of the EGR system are as follows.