Mechanical Engineering - IC Engines and Nuclear Power Plants - Discussion

@All.

Why Wall Temperature Reduces Knock in CI Engines.

In a diesel (CI) engine, knocking is caused by a long ignition delay. When the ignition delay is long, a large amount of fuel accumulates in the combustion chamber before the first flame appears. When this large mass of fuel finally ignites, it burns almost instantaneously, causing a violent pressure rise known as "diesel knock".

Increasing the wall temperature helps reduce this delay through the following mechanisms:.

Faster Vaporization: Hotter walls transfer more heat to the incoming air and fuel droplets, causing the fuel to vaporize and mix with air much faster.

Reduced Ignition Delay: Higher temperatures accelerate the chemical pre-flame reactions, shortening the time between fuel injection and the start of combustion.

Smoother Pressure Rise: Because the fuel ignites sooner after being injected, less fuel accumulates in the chamber, leading to a more controlled and gradual pressure rise.

If the combustion chamber is already hot enough then it will supply the heat to the fuel and fuel will burn readily and that too before the spark and therefore a premature ingnition will take place. I think this is (premature ignition) what causes knocking in SI engines.

I think the correct answer is A.

Because if the wall temperature is higher then there would be the chances of preignition which leads to knocking.

It is because of uniform temperature allover and tus instantaneous combustion will reduce knocking tendency.

In CI engine knocking is caused by ignition delay, so an increase in wall temperature reduce knocking.

No, @Mck.

It is actually, increases in the temp of cooling water increases the knocking tendency.

Knocking will increase when in case IC engines, where as in CI engines knocking will decreases.

@Ujjwal.

Pre-ignition cannot occur because fuel will not be there inside the chamber.

Then why cooling water temp increases the knocking?

In petrol engine increase the knoking tendency.