Scale effects on combustion phenomena in a microcombustor

Abstract

Investigation of the combustion phenomena in a constant volume microcombustor was carried out on a constant volume microcombustor that is subject to significant heat loss to the wall in order to estimate the effects of combustor dimension art flame propagation. A cylindrical combustor of a variable height that is comparable to quenching limit of the combustible mixture of H-2 and air was built. Flame visualization and measurement of transient pressure during the flame propagation were made. Measurements were made at the chamber height ranging from 0.67 nun to 3 mm. A simple theoretical model that takes into account the heat loss to the wall during flame propagation was used to derive available work of the burnt gas from the pressure measurements. For a chamber depth of less than 1 nun, the pressure increase by combustion was negligible and the sensible heat in the burnt gas was not adequate to be converted to mechanical power For a chamber height greater than 2 mm, however, the amount of heat generated by combustion was sufficient to produce a few Joules of theoretical work even after experiencing increased heat loss due to the small scale of the chamber.