Exhaust Gas Recirculation (EGR) is a proven technology to reduce the oxides of nitrogen (NOx) emitted from the IC engines. This works by re-circulating some quantity of the burnt exhaust gases back into the fresh intake air stream, thus reducing the availability of fresh O2. This reduces the rate of burning of the fuel/air mixture and avoids formation of high combustion temperatures which otherwise are conducive for the formation of the NOx emissions. For achieving BS IV, the NOx emission needs to be reduced by 30% in comparison with BS III limits. Therefore, the exhaust gas that is being re-circulated to the intake air is cooled in an EGR cooler which further suppresses the increase in combustion temperatures.
The engine coolant from the oil cooler plate enters the EGR cooler and cools the EGR gas and also the EGR valve stem area and exits from there to the radiator. EGR gas from the exhaust manifold passes across the EGR valve (incase if the EGR valve is opened) and gets cooled in the EGR cooler and rushes to the fresh air intake pipe. This entire heat exchange pattern is of a counter flow type. The EGR cooler encompasses a bundle of heat exchanger core where-in the heat transfer between the hot EGR gas and the engine coolant takes place. To avoid early formation of scales in the heat exchanger core, practice of using water as an engine coolant is highly discouraged. The engine coolant should be a mixture of 1:1 ethylene glycol and water. The entire EGR valve-cooler assembly will be hot after an engine shutdown.
The EGR valve has DC stepper motor and a gear train which converts the rotary motion of the DC motor shaft to the linear movement of the valve. The DC motor assembly also encompasses inside, a position sensor which gives the feedback of the EGR valve position to the ECU. To operate the EGR valve the ECU supplies current with a controlled duty-cycle to the DC motor terminals. Upon actuation, the position sensor in the DC motor assembly, gives feedback to the ECU and makes a close-loop operating cycle.
To check the proper functioning of EGR valve steps to be followed are:
1) Switch OFF the ignition key.
2) Remove the wiring harness connector from the EGR valve connector.
3) Remove the EGR valve-cooler assembly from the engine such that the EGR valve head is visible from the gas inlet side.
4) Connect the wiring harness connector to the removed EGR valve assembly.
5) Switch ON the ignition key and then switch it OFF.
6) During the switch OFF the valve will open by 5 to 6 mm and close once.
This check is intentionally done by the ECU to ensure whether the EGR valve is operating without getting stuck during its operation.
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