Study of Non-equilibrium Process and Turbulence Generation in the Diffusive Combustion

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This study aims at the clarification of the non-equilibrium process and turbulence generation in the diffusive combustion. The contents of the present study are summarized as follows :1. Numerical simulation were performed to predict fluid motions induced by interactions between density and pressure gradients due to the presence of a vortex string situated in a deviated position from the jet flame axis. Deformation and stretching of the flame front take place once the vorticity production becomes stronger than the dissipation due to viscosity. When either the pressure gradient or the density gradient is high, the vorticity production proceeds at a high rate, which promotes the deformation of flame front and accelerates the heat release.2. The flow instability of a jet diffusion flame was investigated based on a linearized stability theory. The equation of disturbance was solved numerically for a two-dimensional parallel flow with density variation. Results show that the existence of a hot layr at the jet boundary makes the flow more stable, raising the critical wave number and critical Reynolds number at which turbulence neither grows nor declines. The increase of the critical wave number is due mainly to the interaction between the flow and density gradient, and the local change of the viscous dissipation raises the critical Reynolds number thereby leading to a wider stability limit.3. Particle image velocimetry (PIV) for measuring velocity vectors was applied to the flow in a methane jet flame and a cold methane jet. Characteristics of turbulent eddies were clarified from the distribution of fluctuating velocity and vorticity. Results show that eddies generated inside flame front entrain the combustion products into the fuel stream, at the same time the dissipation of turbulence eddies takes place by the laminarization due to local heat-release.