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KNOCKING PHENOMENON IN C.I ENGINES / DIESEL KNOCK

If the delay period is long , a large amount of fuel will be injected and accumulated in combustion chamber. The auto Ignition of this large amount of fuel may cause high rate of pressure rise. This high pressure rise causes heavy vibration of the engine and creates lot of noise. 

This Phenomenon of Combustion causing heavy pressure rise during uncontrolled combustion is called "Diesel Knock". Diesel Knock generally starts at the very beginning of the combustion process due to sudden auto ignition of large amount of fuel whereas the knocking in the S.I engine generally starts at the end of combustion period.



The following method can be adopted to prevent diesel knock.

* By reducing the delay period by doping e. g adding 1% of ethyl nitrate or any nitrate so as to accelerate the combustion.

* By increasing the turbulence of the compressed air injected. It promotes homogenous mixture by strapping the fuel from the spray.

* By arranging the fuel injector in such a way to inject only a small quantity of a fuel in beginning

* By supercharging,  i . e, increasing the inlet pressure of air.

* By Increasing the injector pressure which encourages the atomization of fuel.

* By raising the temperature of the coolant, intake of the air as well as cylinder head and         combustion chamber. 

* By increasing the compression ratio to produce a temperature much higher than that required for the spontaneous ignition of the fuel. 

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