23-04-2012, 01:08 PM
ABNORMAL COMBUSTION: KNOCK AND SURFACE IGNITION in si engine
ABNORMAL COMBUSTION KNOCK AND SURFACE IGNITION in si engine.pptx (Size: 474.06 KB / Downloads: 72)
ABNORMAL COMBUSTION: KNOCK AND SURFACE IGNITION in si engine
NORMAL COMBUSTION:-
A combustion process which is initiated solely by a timed spark and in which the flame front moves completely across the combustion chamber in a uniform manner at a normal velocity.
There are two primary abnormal combustion phenomena: knock and surface ignition.
Knock is the engine sound that results from spontaneous ignition of the unburned fuel-air mixture ahead of the flame (the “end gas”).
Surface ignition is the ignition of the fuel-air mixture by any hot surface, other than the spark discharge, prior to arrival of the flame.
ENGINE KNOCK
Knock is most important at wide open throttle engine operation.
It is an engine / fuel / vehicle problem, and limits the compression ratio that can be used for a fuel with given knock resistance.
It is usually characterized in terms of the pressure waves produced inside the cylinder when knock occurs, and the vibration of the engine structure that knock produces.
Noise and Roughness.
Mechanical Damage.
Carbon Deposits.
Increase in heat transfer.
Decrease in power output and efficiency.
Pre-ignition.