Hi EXDAC,
Here we go, dual electronic ignition will help solve the problem, why I don't have the option to install it in my AEIO 580 lycoming ?
Piston Angular velocity affects timing: ( The time betwen the spark and optimal propagation of combustion inside the cylinder so that it reaches peak pressure after TDC - Top Dead Center-) in an engine with magnetoes is fixed, expressed in degrees at the crankshaft flange around 23 degreees before TDC called timing advance.
This to allow for propagation of flame so that it reaches peak pressure after TDC. But this work within a limited range of RPM's.
The timing is indeed fixed but the piston travels faster or slower (Angular velocity) accoprding to RPM's.
This changes the propagation of the flame in the cylinder in the sense that if peak pressure is reached later (After TDC, high Rpms) there will be loss of performance but no damage.
If it happens before ( Slow rpm's slow moving piston high manifold pressure) then we have a a rising piston in cylinder likely to work against a peaking pressure before TDC.
Peak pressures lead to premature self ignition of mixture .
Here lies the danger:
Detonation, it can damage the engine.
Lead thetraetyl was discovered in the US prior to WW2 . Its purpose was to delay the propagation of the flame inside the cylinders to prevent self ignition and detonation.
This is also the reason the German aircraft engines had trouble reaching the power to cubic displacement ratio US engines were capable of. They did not have the equivalent fuels, They were limited by detonation.
In the automotive industry, with the advent of electronics and stringent emission controls, timing is no longer fixed, it is variable delayed or advanced,, computer controlled and depends on the angular velocity of the piston and internal pressures. There is also a knock sensor capable of sensing the advent of detonation ( It was devised for anti pollution purposes, but regulates timing advance so as to optimise the full combustion of mixture in cylinder, therefore performance).
Detonation means higher pressure inside cylinder, high operating temperatures, and low engine output. Warbird flying ? This can be a problem without the right fuel...