Dave,


You often choose to argue with what I say, often when I am right and I usually am.

A richer mixture is slower to ignite, since it is colder than a leaner mixture, so ignition does take place later in the cycle, when the piston is closer to TDC.

As the piston rises it heats the mixture by compressing it. It will need the piston to compress the cooler rich mixture further, to allow it to be ignited, than if the mixture was leaner and warmer to begin with.

And as you wrote, a richer mixture does take more time to burn.


So, from where I am looking, the richness of the mixture, the magnitude of which is achieved using the fuel needles, is the glow engine's equivalent of turning the distributor in the direction of its rotor's rotation, or in the opposite direction, in your car's engine.


And about detonation, a rich mixture can even cause detonation, due to the sheer volume of the fuel, increasing the resultant compression pressures (liquid fuel is incompressible).
Please see the current thread about "Engine throws the prop nut, starts backward...".