Experimental and computational thermal analysis of vortex flame in meso-scale combustor

Abstract

The demand for compact, lightweight and powerful energy sources has significantly increased in recent years. The miniaturization of small-size power supply appliances with high energy density is becoming an important issue around the world. The reduction of the combustor size has encountered some challenges. The crucial problem in meso-scale combustion systems is limited flame stability region as well as short residence time. In addition, the increase of surface to volume ratio in meso-scale combustion expedites flame quenching. In this study, specially designed meso-scale vortex combustor is developed at the High Speed Reacting Flow Laboratory (HiREF), Faculty of Mechanical Engineering, Universiti Teknologi Malaysia (UTM). The objectives of this study are to experimentally investigate the flame stability, heat loss and exhaust gas emissions in meso-scale vortex combustor. Computational investigations of the mixing flow and combustion characteristics of vortex flames in meso-scale combustor have also been completed. The minimum equivalence ratio to have a stable flame is 0.2 when the mass flow rate is 40 mg/s. The ratio of heat loss to combustion heat release is 0.55 at stoichiometric equivalence ratio and lowest mass flow rate. The experimental study was carried out in vortex combustion for NOx, CO2 and O2 productions, with results in good agreement between the experimental production and computational prediction. The level of NOx is well below 10 ppm for all mass flow rates and equivalence ratios. The inlet air and fuel flow fields were found to have a forced vortex tangential velocity. Moreover, mixing between the air and fuel inlet flow was found to have a unique shape as a toroidal jet structure. The swirl number was found to drop almost five times within 70% of the combustor height. Both experimental and numerical analysis showed that the vortex flame has a toroidal jet structure with a non-reacting core. One of the findings in the current study is decreasing flame height in the meso-scale vortex combustor. The vortex flame has a substantially reduced height ranging from 9.2 mm to almost 7.5 mm for different conditions of equivalence ratio. The maximum flame height happened close to the stoichiometry equivalence ratio. Outside wall temperature has increased about 22% by changing the mass flow rate of air from 40 mg/s to 170 mg/s at stoichiometric equivalence ratio.