Flammability diagram

Flammability diagrams show the regimes of flammability in mixtures of fuel, oxygen and an inert gas, typically nitrogen. Mixtures of the three gasses are usually depicted in a triangular diagram, known as a ternary plot. Such diagrams are available in the speciality literature. The same information can be depicted in a normal orthogonal diagram, showing only two substances, implicitly using the feature that the sum of all three components is 100 percent. The diagrams below only concerns one fuel; the diagrams can be generalized to mixtures of fuels.

Triangular diagrams are not commonplace. The easiest way to understand them is to briefly go through three basic steps in their construction.

Triangular diagram showing all possible mixtures of methane, oxygen and nitrogen. Any mixture of methane and air will lie on the blue air-line

Any stoichiometric mixture of methane and oxygen will lie on the red stoichiometric line

The actual flammability envelope defining flammable mixtures of methane

Same diagram, but with alternative axis layout

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