A STUDY OF CONFINED DIFFUSION FLAMES

A numerical simulation of an axisymmetric confined diffusion flame formed between a H2-N2 jet and coflowing air at 30 cm/s is presented. For the initial computations, the restrictions of the Burke-Schumann theory are imposed and the results of the computation are compared with the analytical solution for flame location. For both the underventilated and overventilated flames, the results of the computations are in excellent agreement with the analytical solution. However, the flame behavior becomes more complex as the restrictions are relaxed. When variable diffusion coefficients and densities are included in the calculation, small radial velocities are induced and the flame interface is slightly distorted. When heat release is included, the flame is shorter and an unsteady mixing region forms at the fuel-oxidizer interface. The instabilities are damped when viscous effects are included. Large-scale instabilities form in the oxidizer region with a frequency of approximately 15-20 Hz when gravity is included in the calculation.