Publication

Abstract : A micro combustor integrated with a micro-mixing mechanism was employed to investigate the flame stabilization characteristics of hydrogen–air mixtures from lean to ultra-lean inlet conditions. Stable flames were successfully sustained at remarkably low equivalence ratios, including ϕg = 0.5, 0.4, 0.3, 0.2 and 0.125. The lean stability limit for H2–air flames was determined to be ϕg = 0.125 using both 2D and 3D numerical models. At lower inlet velocities, low-temperature chemistry occurs near the micro-mixing slot, where localized heat release promotes the formation of a pure diffusion flame in the main reaction zone. The 2D and 3D models were compared in terms of flame stabilization and showed close agreement, thereby validating the use of the 2D model for higher aspect ratios. The local equivalence ratio at the central slot interface (ϕinter), identified as a critical parameter influencing flame stabilization and found to be in a range of 0.5 to 7.0. Heat recirculation analysis was conducted to quantify the heat flux from flame to bluff body and bluff body to unburnt gas or mixture at lean to ultra-lean conditions. Even though the wall temperature is relatively low at ultra-lean conditions, it presents a potential advantage for energy harvesting applications, specifically favorable circumstances for the integration of thermoelectric generator (TEG) modules in direct contact with the combustor wall or utilizing EGT, thereby enabling power generation with minimal fuel consumption. A maximum firing rate of 904 W was achieved without any indication of flame lift-off, demonstrating enhanced flame stabilization of hydrogen.