Diesel knock is experienced in the diesel engine. When a high-pressure wave strikes the cylinder wall, cylinder head, and piston, it results in diesel knock.
When sudden and violent knocks are experienced in a petrol engine, these knocks are termed “Detonation”.
This engineering term, you might have experienced in your motorbike.
There is power and efficiency loss along with the rough running of an engine observed.
In severe cases, it may wreck the engine also.
A considerable amount of air-fuel mixture may ignite at the same instant and result in a combustion knock or heavy thud rather than pink.
To prevent diesel knock, the following important methods can be used very effectively
01) Add 1% of ethyl nitrate or any nitrate to accelerate the combustion of fuel.
This process is known as “Doping” and reduces the delay period considerably and hence prevents diesel knock.
02) For spontaneous ignition of the fuel, we require a much higher temperature this can be achieved by raising the compression ratio.
The rate of pressure rise increases resulting in smooth running of the engine.
If the compression ratio increases in a petrol engine, the engine is more liable to detonate, but in a diesel engine, it reduces the diesel knock.
03) Diesel knock can be reduced by increasing the turbulence of the compressed air injected promoting a homogeneous mixture by stripping the fuel from the spray.
04) Arrange the fuel injector in such a way that it should start injecting only a small quantity of fuel at starting of the engine.
If we increase the injection pressure, which encourages the atomization of fuel and prevents knock.
05) By raising the temperature of the coolant that of the intake air as well as the cylinder head and combustion chamber.
06) Also by increasing the inlet pressure of air (Supercharging), we can prevent diesel knock.
Many times we noted this sudden noise but were not aware of the phenomenon behind this.
Now above description will clear the doubt about diesel knocking on your automotive engine.
Besides this information, you are suggested to read something more from below engineering books
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