Heavy liquid fuels also undergo a great number of pyrolysis reactions that give more easily oxidized, gaseous fuels.

These reactions are endothermic and require constant energy input from the ongoing combustion reactions.

A lack of oxygen or other improperly designed conditions result in these noxious and carcinogenic pyrolysis products being emitted as thick, black smoke.

This shows the reaction to soot precursors under hot, high pressure, fuel rich conditions.