Scaling up ethanol fueled step micro-combustor for higher power generation

Abstract

Stepped micro-combustors can be reliably used for portable power generation applications and can be scaled up in size to meet higher power requirements. The previous studies in stepped micro-combustors did not focus on the use of liquid fuels and the effect of scaling up (in size). This work numerically investigates ethanol combustion in stepped micro-combustors across increasing sizes, examining key performance parameters such as heat recirculation, flame structure, exergy destruction, and entropy generation. The finite volume method (FVM) and detailed chemistry are used to study the effect of scaling on premixed ethanol-air micro-combustor for five different micro-combustors of surface area to volume ($S/V$) ratio ranging from 2000 (smallest) to 1000 (largest). With scaling up, i.e., reducing surface area to volume ($S/V$) ratio, flame stabilizes closer to the inlet tube, with reduced heat recirculation through combustor walls. The reduced preheating of the incoming air–fuel mixture affects the chain branching reaction, which reduces flame speed. Scaling up increases the exergy efficiency (reaching a maximum of 86% at $S/V$ ratio of 1000 at 25 W) and reduces the entropy generation rate (73% decrease at 25 W). With the reduction in the $S/V$ ratio (from 2000 to 1333), a significant enhancement (42% ) in the radiative power of the micro-combustor is observed (for 35 W thermal power). The combustor with an $S/V$ ratio of 1600 consistently showed superior temperature uniformity at all power levels, with the flame stabilizing at step 2 for all the input power levels investigated here. The results will enable scaling up micro-combustor designs that can support higher input thermal power, enhance energy conversion efficiency, and minimize losses.