Autoignition of methane/coal particle/air mixture under constant-volume conditions

Abstract

Autoigniton of methane/air mixture loaded with uniform coal particles is simulated using the Eulerian-Lagrangian method. A zero-dimensional constant-volume approach is employed to investigate the impacts of particle diameter, particle concentration, and initial gas pressure on the two-phase mixture ignition process. Different stages are found from the ignition transient: particle heating, particle/gas thermal runaway, two-phase heat exchanges, and thermal quasi-equilibrium of two phases. Moreover, the ignition delay time of the two-phase mixture changes nonmonotonically with the particle size. Also, as the particle concentration increases, the magnitude of the differences in two-phase mixture ignition delays gradually decreases. At low particle concentrations, the particle temperature rises and then rapidly drops due to burnout of the fixed carbon, while the two-stage gas temperature increase is found. In addition, the two-phase mixture is more easily ignited under high pressure conditions. The particle ignition is more sensitive to pressure change than the gas ignition. An ignition diagram of methane/coal two-phase mixture with various particle concentrations, initial pressure and diameters is determined based on parametric studies. It is shown that particle addition promotes the gas ignition when the particles are small. Moreover, the particles can have inhibitory effects on gas ignition at high particle concentrations, and lower pressure. The results from this study are significant for explosion hazard mitigation implementations and detonation propulsion systems with pulverized solid fuels.