Numerical investigation on the combustion of air-methane mixture in a frustum microcombustor

Low energy density of conventional lithium batteries used in mobile devices is a good reason for more investigations on micro power-generators. Micro combustor is a key component of micro powergenerators. Micro combustor is a key component of micro power-generators. Criticize of stable burning and low thermal efficiency of conventional micro combustors is a hot topic for debate. In this work the combustion of air-methane mixture in a ۲D axisymmetric frustum micro combustor is modeled numerically. Effects of geometry on the combustor wall temperature and flame stability is discussed. Numerical results showed maximum flame temperature variations is not uniform with respect to uniform frustum slope angle changes. Temperature all over the diverging frustum wall decreases as frustum slope increases. In this case the wall temperature distribution is not uniform because of low-temperature regions at the outlet plane and subsequently extinction and flame blow-out is probable. Converging frustums with slope angles lowerthan ۳ degrees has a uniform temperature, velocity, and turbulent intensity distribution all over the combustor and consequently a robust combustion is forecasted. In frustums with slope angles greater than ۳ and lower than ۷ degrees the temperature at the outlet plane is very high and there exist the risk of upstream burning which may lead to hot spots and a material failure in some cases. Slope angles exceeding these values could cause choking and clogging at the outlet plane which in turn may cause the reverse motion of the flame leading edge especially at the centerline of the combustor.

Keywords:

micro power-supplier , combustion stability , frustum micro-combustor , air-methane combustion , hotspot