Effects of micro-combustor geometry and size on the heat transfer and combustion characteristics of premixed hydrogen/air flames

Abstract

major challenge in the development of micro-combustors is flame instabilities—resulting in a non-uniform wall temperature distribution and lower combustion efficiency. To overcome these issues, this research investigates the combustion characteristics of premixed hydrogen/air mixture in a micro-combustor with a cavity, bluff body, rib with bluff body and rib configurations. A detailed chemical reaction mechanism is also developed which consists of 13 species and 19 reactions. The obtained results are validated with published experimental findings. Having the model validated, a parametric study has been conducted to examine the effect of thermal conductivity coefficient, equivalent ratio, aspect ratio and geometrical configurations on heat transfer and combustion characteristics of hydrogen/air flames. It is demonstrated that increasing the thermal conductivity coefficient improves the preheating of the fresh mixture at upstream. However, this causes more heat loss from the outer walls to the surroundings. Moreover, increasing the equivalence ratio of a mixture reduces the negative effects arising from the heat losses on combustion stability. At higher inlet velocities, the location of a maximum temperature shifts towards downstream, which reduces the flame and average wall temperature. Among these configurations, a micro-combustor with bluff body is a more promising option to improve the flame stability and combustion efficiency.