A numerical study of pulsating flame propagation in mixtures of gas and particles

Abstract

Pulsating flame propagation in mixtures consisting of gas and particles is calculated numerically using a simplified model of particle-cloud combustion. The key heat transfer processes are based on the radiation heat transfer between particles and the heat transfer between gas and particles. Therefore, the model in which the flame propagates into a gas mixture seeded with inert particles is used to simplify the problem. The basic mechanisms of pulsating flame propagation can be explained as follows. When the burning velocity is rapid, there is insufficient time for the particles to be heated by radiation from the burned region. Therefore, the burning velocity slows down because the heat is absorbed by cold particles in and behind the flame. On the other hand, when the burning velocity is slow, the particles in front of the flame are sufficiently heated by radiation from the hot particles behind the flame so that the flame gathers speed. After passing through this period, the flame meets the cold particles, and its speed is again decreased. Thus, the flame oscillates in propagation. Pulsating flame propagation appears under certain conditions of the equivalence ratio, the weight concentration of particles, and the particle diameter. In the case of low weight concentration of particles and large particles, radiation preheating is not sufficient so that pulsation does not occur. Also, in the case of small particles, the particle temperature rises quite fast and the temperature in the system equilibrates rapidly so that the pulsation disappears. Tendencies of calculaton results agree with those of experimental results obtained from the PMMA particle cloud in microgravity.