Question

The tendency of a diesel engine to knock increases, if:
(1) Engine speed is increased
(2) Engine H.P. is increased
(3) Octane number of fuel is increased
(4) Compression ratio is increased

Answer 1

engine h.p is increased

Answer 2

2.) Engine speed is increased

In the normal working of diesel engine , initially the air is compressed and then the fuel is injected at high pressure.

Due to the high compression ratio, the fuel ignites and explodes to give the power stroke.

Now the requirement of this combustion model is that the highly atomized fuel should start burning as soon as it is sprayed in the cylinder. But, if the fuel sprayed initially is not able to mix properly due to a variety of reasons, it keeps on concentrating in the combustion chamber.This increases the concentration of fuel in the chamber and at some point, the large quantity of fuel ignites sending pulses throughout the chamber. This leads to knocking in a diesel engine.

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