I have gleaned quite a bit of information recently from the forum on CD ignition systems.
Also, I see that RCIGN and some others have successfully used glowplug ignition on "gas engines".

What I really want to understand is:-
At what timing BTDC does the charge decide to fire?
What makes it decide?
Is it governed by compression ratio?
Is it governed by temperature?
Do different grades of plug change the timing?
Does engine wear affect the timing?
Do glowplugs work best with Alcohol fuels?
Can they work with petrol (gasoline)?
Is nitro necessary?
Is starting easy?

Possibly many of these questions have been answered before, but these are the ones which interest me most and I thought that it would be good to have them all answered on one thread if possible.