Effects of heat and momentum losses on the stability of premixed flames in a narrow channel

Abstract

To understand fundamental characteristics of combustion in a small-scale device, the effects of the momentum and heat loss on the stability of laminar premixed flames in a narrow channel are investigated by two-dimensional high-fidelity numerical simulations. A general finding is that momentum loss promotes the Saffman-Taylor (S-T) instability, which is additive to the Darrieus-Landau (D-L) instabilities, while the heat loss effects result in an enhancement of the diffusive-thermal (D-T) instability. It is also found that heat loss amplifies the sensitivity of the growth rate to the Lewis number variation, and the critical Lewis number of neutral stability also increases with heat loss. The two competing effects between the heat and momentum losses play an intricate role in determining the overall instability and cell formation patterns. The simulations of multiple cell interactions revealed that D-T instability mechanism is primarily responsible for the splitting into smaller flame cells, while the D-L and S-T mechanisms favour larger flame cells through merging. The relative sensitivity of the flame instability to the momentum or heat loss effect is also examined by a numerical experiment for different Lewis number cases.