Flow and flame dynamics of confined buoyant inverse diffusion flames

PIV experiments and simulation were performed to investigate non-reacting and reacting buoyant inverse diffusion flames, with emphasis on flow and flame dynamics. The results show that in non-reacting inverse diffusion flames the initial shear flow and the buoyancy effect induce opposite-direction vorticities, which interact with each other and cause flow instability. This instability can be quantified by the Richardson number, Ri, which measures the gravitational effect relative to the initial shear flow. So the instability is strongest at Ri = 1 when the two mechanisms of vorticity are comparable to each other. In the reacting inverse diffusion flame, the density gradient is reversed due to chemical heat release and so is the buoyancy-induced vorticity that it shares the same direction with the vorticity of the initial shear flow. As a result, the near-field flow instability is suppressed while the initial shear flow would continue growing under the gravitational effect until instability develops in the far field.