This paper discusses the process of combustion, as revealed by high speed cinematography, in a small high speed diesel. Two direct injection types and one prechamber type were examined, and combustion sequences are shown. The phenomena are complex, but the main features are:
In small engines much of the fuel strikes the chamber wall and moves along it.
Swirl is greater than has hitherto been supposed, squish much less.
Most of the flame is of the carbon-rich diffusion type.
Soot from very rich mixture is always formed at high loads, but can burn later leaving a clean exhaust.
Combustion knock does not seem to be related to the total fuel in the chamber on ignition, but rather to the amount of fast burning mixture present.