Originally Posted By: Merkava_4
Originally Posted By: Ducked
No it isn't
Quote:
What is knocking?
During the propagation of flame front (after spark begins) the charge near the flame front expands which leads to further compression of end charge (charge which are away from the spark plug) which results in further increase in temperature of end charge. Due to this, if temperature of the end charge becomes equal to (or more than) self-ignition temperature of fuel, a separate secondary flame front will be formed. When this two flame fronts (primary and secondary flame front)
collide, a very high energy wave is formed which affects engine performance and CC adversely, this phenomenon is called knocking.
LINK
Quote:
Whenever these
colliding pressure fronts meet, their destructive power is unleashed on the engine parts, often leading to a mechanical destruction of the motor. The pinging sound of detonation is just these pressure waves pounding against the insides of the combustion chamber and piston top.
LINK
You can find any amount of tosh on this topic on the internyet, so its quite hard to support any argument with a quick link.
The sources would have to be read carefully and critically to validate or refute them, I havn't had my coffee yet, and I'm not particularly qualified for the job. These ones might be fine, dunno.
But I can make one observation on one of them.
You're saying that knocking is due to colliding flame fronts, right?
The second sentence of your second reference goes
"The actual "knocking" or "ringing" sound of detonation is due to these pressure waves pounding against the insides of the combustion chamber and the piston top,
and is not due to 'colliding flame fronts'" (my bolding)
Knocking is a synonym for detonation, i.e. the supersonic explosion of the fuel-air mixture, which produces a characteristic ringing of the engine structure.
Thats it. Thats what it is.
It "classically" follows spark ignition, but recent descriptions of LSPI suggest it can also be initiated by a pre-ignition event, which isn't all that surprising.
This doesn't remove or confuse the difference between pre-ignitiopn and knocking/detonation, but your original statement does.
Pre-ignition is ignition that occurs
before the timed ignition by the spark.
Thats it. Thats what it is.