Quote Originally Posted by aimless View Post
I would like to add some ideas, that are probably not mentioned:

Deflagration (in firearms and engines) is desired .

Firearms and engines (even the BARAKUDA air rifle) are designed in the way, that the direction of the deflagration is predetermined (e.g. engines-from the spark-plug to the piston)

So dieseling -if occuring- can be e.g. ignited on the piston-sealing OR on the port; with quite different results as you can imagine.......but IMO will not lead to recocking. Even if the pressure-wave is directed towards the piston (as I wrote before).
I can certainly accept that in a detonation, because it is supersonic, then shockwaves can be directed (and even focussed) and therefore cause localised effects. The shaped charge explosives use exactly this effect (Munroe effect IIRC).

I am not sure about the effects of direction in a deflagration reaction. By definition this is subsonic, so the surrounding gasses can flow and will equalise the pressure within the confinement at near sonic speeds, that is to say the pressure equalisation will be achieved faster than the combustion (I think). Thus the gasses produced by the burning, and heat, will expand uniformly away from the point of ignition, and will act equally in all directions. By comparison with the velocity of a piston, this is all over very quickly.

Your point about where the combustion actually starts is a good one and I can see that this could lead to different effects. With absolutely no data, I would speculate that combustion is more likely to start away from the cooling effect of the container walls, but there is also the problem that the fuel/air mixture is unlikely to be evenly concentrated and it may be that the necessary critical conditions exist only in one (random) area.

Whatever, I have experienced re-cocking in an air pistol when I was deliberately introducing fuel. It was at that point I decided to cease further experimentation as I realised that pressures could become unsafe. BTW the gun was not damaged in any detectable way by these few experiments and it still works just fine today, with it's original seals. I guess I was lucky to have worked up to it and stopped before it got too exciting.