Numerical simulations of lean propane-air flames propagating in circular tubes under quenching conditions

Flame extinction in internal combustion engines can be observed when a flame front enters a small gap between the cylinder and piston or above the piston rings. This phenomenon is caused by the interaction of the flame with the walls. Cooling of the reaction zone by the wall is the reason for the flame extinction. Simplifying the problem to the propagation of a premixed laminar flame in the narrow channels with isothermal wall allowed employing numerical methods to analyze this phenomenon. The aim of this work was to examine flame behavior during its propagation in the narrow circular tube. A numerical analysis of the freely propagating flame was conducted. In this study, the propagation and quenching of a laminar premixed propane/air flame in circular tube was investigated numerically. The flame chemistry is modeled by one-step overall reaction. The considerations are limited to flames propagating downwards in lean propane-air mixtures. Quenching diameter as a function of equivalence ratio was determined. One of the most important flame parameters - flame propagation velocity (under quenching conditions) was compared with adiabatic burning velocity and limit burning velocity predicted by Zeldovich. It was found satisfactory agreement between numerical calculations and theoretical considerations. Numerical results show also that there is a close dependence between preheat zone and dead space for flames propagating in a wider tube.