Effects of radiation on large-scale spherical flame propagation

One-dimensional numerical simulations are conducted for large-scale spherical flame propagation in near-stoichiometric methane/air mixture. With the help of adaptive mesh refinement, we simulate the spherical flame propagation up to a radius of 4 m inside an extremely large computational domain of 20 m. The emphasis is placed on quantifying the radiation effects on large-scale spherical flame propagation. Besides the adiabatic model neglecting radiative loss, two radiation models are used in simulation: one is the optically thin model considering only radiation emission and the other is the statistical narrow band model considering both radiation emission and absorption. The effects of radiative loss and radiation absorption on large-scale spherical flame propagation are quantified through comparison among results predicted by these three models. It is shown that for the near stoichiometric methane/air mixture, radiation has little influence on small-scale spherical flame propagation with radius below 4 cm; while radiative loss and radiation absorption both have great impact on large-scale spherical flame propagation with radius up to 4 m. Spherical flames without and with self-acceleration are both considered in 1D simulation. Radiation effects on the propagation speed and acceleration exponent of the large-scale self-accelerating spherical flame are assessed. It is found that radiation effects on acceleration exponent are exaggerated when radiation absorption is neglected. In experiments for large-scale spherical flame propagation, the acceleration exponent is not strongly affected by radiation due to radiation absorption.