The combustion operator is used in conjunction with a Cooling operator and Gaseous Dynamics to simulate fire, fuel and resulting explosion behaviors using fluid simulations.

It contains three different fire models:

1. Simple fire combustion
This model does not use any fuel channels but assumes that the combustion directly takes place whereever the user defines it to. It is more an artistic model that is easy to handle because it is partly of procedural nature.

2. Fuel-Fire combustion
This model uses a fuel channel that can be ignited and then start combustion. This is still a simple but more complex algorithm that allows you to simulate spreading of fire. This generates diffuse flames.

3. Fuel-Oxygen-Fire combustion
This model uses a fuel channel and can be ignited then start combustion. It furthermore takes into account a fuel-oxygen ratio in order to more realistically calculate combustions. This is a more complex algorithm but can also generate nice plumes.

A little (but rough) combustion stages overview:
Once the ignition temperature of a fuel is reached, temperature is rising until it reaches a critical point (the Cooling point). After this point the temperature drops quickly (that's why flames disappear visually so fast). It's good to keep this in mind.