Tell me about ignition advance/retard

[Sergeant Pluck]

I know what it is mechanically - as in, at what point the spark fires in relation to how far ahead/behind of TDC - but how does it alter the engine characteristics? For instance what effect does a given state of advance/retard have on fuel consumption, power characteristics, emissions, etc etc - and answer me this: if the fuel mixture is ignited BEFORE the piston reaches TDC (or even at TDC), why doesn't the bike go backwards or the engine just blow up

Learn me up please, I need some theory

Pluck

 

[Mzokk]

and answer me this: if the fuel mixture is ignited BEFORE the piston reaches TDC (or even at TDC), why doesn't the bike go backwards or the engine just blow up

Learn me up please, I need some theory

Pluck

speed of the piston Vs speed of the flame front from the ignition and the design of the combustion chamber. Pinking (detonation) can occur when the ignition is slightly too advanced causing a shock wave against the piston as it hits the expanding flame front on the way up causing the remaining mixture to explode. (though the gases are still expanding so it does push the piston down.) The exact point point of ignition before TDC depends on the engine design speed of the piston, design of the combustion chamber, compression ratio and the Octane rating of the petrol (resistance to detonation)

Found this explains it better than I could

http://en.wikipedia.org/wiki/Engine_knocking

 

[Sergeant Pluck]

speed of the piston Vs speed of the flame front from the ignition and the design of the combustion chamber. Pinking (detonation) can occur when the ignition is slightly too advanced causing a shock wave against the piston as it hits the expanding flame front on the way up causing the remaining mixture to explode. (though the gases are still expanding so it does push the piston down.) The exact point point of ignition before TDC depends on the engine design speed of the piston, design of the combustion chamber, compression ratio and the Octane rating of the petrol (resistance to detonation)

Found this explains it better than I could

http://en.wikipedia.org/wiki/Engine_knocking

Excellent - thank you - that, and one of the links at the bottom are exactly what I was after - explains everything I wanted to know

Pluck