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 knock are experienced in a petrol engine, these knocks are termed as “Detonation”.
This engineering term, you might have experienced in your motorbike.
There are power and efficiency loss along with the rough running of an engine is 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, 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 reduce delay period considerably and hence prevent diesel knock.
02) For spontaneous ignition of the fuel, we require 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 compression ratio increased 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 promotes 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 in starting of the engine.
If we increase the injection pressure, which encourages the atomization of fuel and prevent 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 not aware of the phenomenon behind this.
Now above description will clear the doubt about diesel knock in your automotive engine.
Besides this information, you are suggested to read something more from below engineering books
To get the more details about the topic, I further recommended reading