VII.2 Combustion regimes

Although all combustion processes are chemical reactions between fuels and oxidiser, the details of the processes vary greatly, so much so that we must treat them in different ways. In particular we divide combustion into two main categories :

Non-premixed combustion

In non-premixed combustion regions of fuel and oxidiser are separate, and combustion occurs on the interface between the two regions. Examples include various types of burner where a jet of fuel is injected into a region of air, and diesel combustion, where the fuel is broken up into individual droplets, and combustion occurs at the surface of the droplets.

Premixed combustion

In premixed combustion the fuel and oxidiser are mixed at the molecular level before combustion occurs. In such a case there are distinct regions of unburnt and burnt mixtures, separated by the flame. Examples include internal combustion (IC) engines.

Of course these are the extreme cases. In technical applications the optimum regime often lies somewhere between the two, where the fuel and oxidiser are permitted to mix partially but not completely before combustion occurs. This is known as Partially Premixed Combustion.

Some other examples of the different regimes