Quote:
Originally Posted by Ecky
Knock is from the shock waves caused by multiple flame fronts interacting, doing damage. You really do not want multiple ignition points.
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I dissagree to some extent. Engines with multiple sparkplugs aren't more likely to have knock, for an example. I believe the multiple flame fronts as being an old myth.
What I understand knock (detonation) to be is when a pocket of air and fuel (regardless of the number of flame fronts) reaches a critical temperature and pressure so that it spontaneously combusts. Normally combustion occurs along a flame front and therefore causes a gradual presure wave. If a whole pocket of air and fuel suddenly ignite then you have a much more sudden expanssion of gasses resulting in a sonic (or maybe even hypersonic??) pressure wave. These knock pressurewaves are very stronge and will bounce around causing spots along the tops of the pistons and in the combustion chamber to have very high pressure and very high temperature compacted ripples of exhaust gas smack into the metal.