In a jet flame,

Fuel Diffuses radially outward.
Oxidizer Diffuses radially inward.
Mixing Takes place at certain radial location and thus flame is established.

Flame Surface

• Location where fuel and oxidizer meet in stoichiometric proportion.
• As the reaction zone is quite thin, flame can be assumed as a thin surface.

Reaction Zone

Occurs in an annular region inside the flame surface.