Assumption:

The burning process is not being affected by the mixing rate between the fuel and the oxidizer.

The flame height is defined as the point along the z axis on which inter diffusion of the fuel and oxidizer is reached for the first time .

(Figure 28.3)

The time, t required for oxidizer element to reach axis of the jet is given by

By the Einstein diffusion equation, we can have

Where D₁₂ is the fuel air diffusion coefficient, is the average square displacement.

where is the volumetric flow rate, is average thermal conductivity of mixture, is the average of specific heat of mixture.