Premixed and Diffusion Flames

In a premixed flame, the fuel and oxidizer are mixed before reaching the flame. The stoichiometry of the mixture can be controlled by changing the fuel to oxidized ratio, and an inert gas such as nitrogen may be used to dilute the reactants and alter the flame temperature.

In a diffusion flame, only fuel is supplied to the burner (of fuel and an inert diluent gas such as nitrogen). The oxidizer is supplied from the ambient air and the mixing and combustion reactions take place together. The structure of the flame, with its central fuel core and the outer reaction zone can be seen by looking at the colors associated with these regions. Soot formed in the reaction acts as a "black body" and the yellow color of the outer and higher regions of the flame indicate its presence.