Doubt related to ignition delay, pre-ignition,knocking, ideal running:

Hi CEans i am little confused on the following question so i am destined here to find the real answer for the following questions.
1)What would be the throttle position when we are in ideal condition(vehicle was kickstarted but haven't moved.Whether it would be lightly opened or closed because we haven't given he throttle so how?)
2)I am clear that pre-ignition and knocking but when i was searching for the detailed answer it had been listed that 'Knocking (also called knock, detonation, spark knock, pinging or pinking) in spark-ignition Internal combustion engine - Wikipedia occurs when combustion of the Air Fuel Ratio in the cylinder starts off correctly in response to ignition by the Spark Plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front." in wikipedia.explain briefly.
3)Ignition delay-whether there is a delay in sparking or delay in catching of fire in fuel mixture?


  • Siddhant Mukherjee
    Siddhant Mukherjee
    The answers:

    1) When you start any engine and you do not give any throttle the engine does not stop. This is because, the throttle is set open slightly. if you look at your motor bke's carburetor carefully, You will find a screw over there which will be attached to a cam like system. This is the screw which helps you set the throttle valve lower limit of opening. If you set it to a point, the throttle valve will never close below that point.

    2) and 3)

    The answer to your questions lie in the fundamentals of knocking in S.I and C.I engines. In SI engines, knocking occurs when there is a two way combustion (due to spark plug and due to any hot spot) , a shock wave is produced which destroys the output power due to mutual cancellation of pressure waves.
    In CI engines knocking is due to ignition delay. It is the delay of fuel catching fire. ignition delay occurs in CI engines when fuel is not properly atomized. A cluster of fuel will have higher heat capacity and thus take more time to heat up and reach self ignition temperature.During this time the atomized fuel in form of mist will burn and later when the clusters burn they again create shocks and the pressure waves cancel out resulting in loss of power.

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