ElktonJohn,
I noticed your interest in "just what happens" in the environment of an internal combustion engine at the point of ignition, we have the same interest. One thing that fascinated me about diesel at the point of ignition by compression is the manner in which the injected fuel cloud burns. The seemingly best picture I could come up with as to reliability of the source was some old Mercedes Manuals. This is their abbreviated picture: We're coming up the compression stroke, greatly raising the temperature; at some point BTDC the injector sprays it's cloud of pure diesel; the cloud is elongated (and obviously changing across the whole of the fuel release). This cloud has the highest density in the middle of the elongated stream and becomes less and less dense as we move outwards. So, the inner cloud is initially too rich to even ignite, so, the initial ignition takes place in multiple spots at the outer edges of the cloud. That initial ignition is totally a function of the high temps created by the compression. Some of the middle section of the cloud also ignites by compression from the rising piston and the high pressure (so temps) created by the outer cloud igniting from multiple spots. There is a precise time frame in which all this is happening, but I don't have those #'s in front of me. So, after the ignition sequence I've described up to this point, compression no longer dominates as the fuel igniter. What dominates now is the radiative heat from the burn pattern of the outer cloud and more and more of the inner cloud. The fascinating thing to me is that I had always thought of diesel engines (even though I was a diesel mechanic in the Service and went through courses at Aberdeen Proving Ground, and the civilian Detroit Diesel / Allison Automatic in Iowa) as being totally compression dominant devices. And, most certainly, a diesel with compression problems runs poorly to not at all. But, it is the engineering of the pistons and combustion chamber and fuel injector that results in the engine utilizing the two components of complete ignition, that is: 1) compression 2) radiant heat from multiple compression initiated burn sights at the outer, lean edges of the cloud. (Though the piston & initial compression mediated ignition produces, well, more compression, it is the radiant heat from burning diesel that dominates as the igniter of the initially rich inner cloud which becomes leaner and leaner as we step through the cycle).
This makes it very easy to see why we want a diesel fuel of proper cetane rating; one can go too high and one can go too low. If one is to use #2 diesel or #1 diesel or bio-diesel, or mixes, the engine sounds different dependent on which fuel it is burning, so what is going on in the combustion chamber is altered; not necessarily for better or for worse, but that same engine has something different enough going on from beginning to end of fuel burn as a function of fuel type. In light of this discussion.