Radiation extinction of laminar diffusion flame over a plane porous burner in zero gravity: Numerical modeling

The dynamics of the formation and extinction of laminar diffusion flames of methane and ethylene formed in an oxidizing medium in zero gravity above the surface of a flat porous burner have been studied numerically. The calculations reproduce the conditions of experiments carried out within the framework of the BRE–Flamenco project of the Advanced Combustion Microgravity Experiment (ACME) program aimed at the study of combustion in zero gravity. A three-dimensional non-stationary model taking into account multistep and multicomponent chemical mechanisms of oxidation of fuels, soot formation and oxidation, and the thermal radiation of combustion products was tested for jet laminar diffusion flame of methane under normal gravity and for ethylene flame inder short-term zero gravity in free fall in the test tower. Calculations for flames formed under long-term zero gravity were performed for the range of fuel consumption typical of combustion of solid and liquid combustible materials. In all cases considered, combustion proceeds in an unsteady mode, despite the constant fuel consumption. The flame growth stage is accompanied by a continuous decrease in temperature in the reaction zone due to heat loss by radiation followed by local extinction and pulsations of the flame and the complete cessation of combustion. The effect of the type and fuel consumption on the duration of the flame and the dynamics of its decay is analyzed. The sensitivity of the calculation results to the chemical mechanism is found. It is established that the proportion of energy emitted by the flame in zero gravity is an order of magnitude higher than that for the flame under normal gravity. Radiant heat loss are shown to cause instability and extinction of the flame.