Thermal and combustion performance of a swirl-stabilized meso-combustor for micro-power generation

Abstract

Combustion-driven thermoelectric and thermophotovoltaic power systems taking advantage of meso‑ and micro-scale combustors, that are direct energy conversion modules, have attracted growing interest. So, in this research, three double annulus axial swirlers are implemented to investigate the effect of swirl direction of the fuel and air flows with respect to each other on thermal performance and combustion characteristics of a non-premixed meso‑scale combustor. This study comprehensively evaluates several key performance metrics of the meso‑combustor, including its operational envelope, flame characteristics, exhaust gas temperature, mean outer wall temperature and its uniformity, pollutant emissions, wall heat losses, and thermal efficiency. It is found that adding swirl to the co-axial airflow significantly enhances the operational envelope, expanding it by >600 % in comparison to zero-swirl airflow configuration. Co-rotating swirling flows is reported to have a more positive influence on flame blow-out than counter-rotating swirling flows. Furthermore, the flame lift-off height decreases with an increase in airflow rate for a set fuel flow rate, with the lift-off heights in the co-swirl configuration demonstrating the least sensitivity to increases in fuel flow rate. Analysis of the combustion products reveals that CO concentration has a U-shaped dependency of the equivalence ratio, where the co-swirl mode exhibits lower CO concentrations by approximately 31 % compared to the counter-swirl mode. Additionally, the co-swirl mode displays the superior values of exhaust gas temperature (∼ 3.3 %), combustion efficiency (∼ 34 %), mean outer wall temperature (4.6 %), radiation efficiency (∼ 15 %), and thermal efficiency (∼ 3.5 %) compared with counter-swirl mode under identical operating conditions.