Characteristic analysis of low-velocity gas filtration combustion in an inert packed bed

Abstract

This paper investigates the low-velocity filtration combustion of lean methane–air mixtures occurring in inert packed beds by using a modified one-temperature model, considering the axial thermal diffusion owing to the convective gas–solid heat transfer. Based on the scaling analysis of various transport terms in different conservation equations, a high-activation energy asymptotic method is applied in the flame zone and results in a set of powerful analytical solutions for combustion macrocharacteristics under the fully developed conditions. These are then combined with the eigenvalue method of the modified one-temperature model in the whole flow region to study the flame behaviour analytically and numerically. Our results have shown that the combustion wave velocity is a key characteristic parameter in the filtration combustion process. Compared with other existing theoretical results, the present analytical solutions demonstrate the intricate relationships among the combustion wave velocity, the flame speed, the peak flame temperature and the effects of the variable thermo-physical properties, and show better prediction performance for the combustion wave velocity, the flame speed and the peak flame temperature. Excellent agreements with experimental results have been observed, especially for very lean filtration combustion with stream-wise propagating combustion fronts.