What is fuel knock?

[ayousef]

So, I read this terminology more than a few times and cant figure out how fuel could cause knock. Im assuming this is real knock, or is this false knock caused (one way or the other) by fuel?

Also while on the subject, why would advancing SOI reduce knock-retard, is it because it gives the fuel more time to atomize before the spark fires? Is there a downside to too early of an SOI.

I ask because im working on a nice histogram (which I will share) that automatically calculates the minimum SOI, with the maximum being dictated by the camshaft specs (exhaust valve closing, or intake valve opening whichever occurs later).

thanks!

[ridanakr]

i dont know what did you mean with fuel knock!!
may you mean spark knock as what we know.
you have to know that there is real & fake knock.

the real knock happening because of:
1/ if the spark advanced too much.
2/ if the air/fuel stoich leaned out.

and fake knock happen because of:
1/ dirty air filter
2/ vibration or leak in exhaust system
3/ if the road you testing the car on have road bumps.
4/ if there is mechanical problem making high vibration to the engine block.
5/ etc...

i hope you get the idea.