What is the basic explanation for knock and detonation? Can someone kind to explain or point me to the right direction?

 

Detonation when the air/fuel mixture in the cylinder explodes, instead of burning rapidly.
(To be really technical, detonation is when the flame front moving through the cylinder exceeds
the speed of sound.)

This is bad for two main reasons:

1) The sudden shock load can break parts - the repeated shock loads of constant
detonation is like running a jackhammer in your engine.
2) The temperature inside a detonating cylinder is much hotter than normal, and can get hot enough to melt aluminum.

Symptoms of detonation:

1) A loud pinging or rattle/knocking noise. It sounds like a bunch of marbles inside a
tin can. (This is why detonation is commonly called "knock")
2) Higher than normal exhaust gas temperatures
3) Little "flyspecks" of aluminum on spark plug center electrodes and the center
insulator. This is the dead giveaway indicator for detonation. Examine your plugs with a
magnifying glass. Little ***** of aluminum clinging to the plugs means that you are detonating.
(It's aluminum from the pistons being vaporized and condensing on the plugs)
4) Engine damage (holes in pistons, melted spark plug ground electrodes, etc.

Causes of detonation:

1) Low octane fuel
2) High static compression ratio
3) High boost levels
4) Excessive spark advance
5) Lean fuel mixture (may be insufficient fuel pump capacity/pressure, insufficient
injector flow, air flow sensor out of range)
6) High inlet air temperature / low air density


From;
http://members.shaw.ca/costall/1000Q/

 

Ive had this happen a few time......Not to fun.

 

Thanks.... that is a good write-up and easy to understand...