Thermal performance of a micro combustor with heat recirculation

In this paper, numerical and experimental investigations in a three‐step microcombustor have been carried out to understand the effect of heat recirculation on flame stabilization behavior with premixed fuel–air mixtures. External heating cup is utilized to enhance the heat recirculation. From numerical simulations, it was observed that the extent of heat recirculation is a function of cup dimensions, cup material, and flow velocity and mixture equivalence ratio. Heat recirculation has been observed to significantly enhance the flame stability limits and upper flame stability limits were observed for the range of flow rates investigated during the present work. Stable flames exist for smaller flow rates with a minimum thermal input of ~2.2 W at Φ = 0.5. X‐shaped spinning flames exist for inter‐mediate flow rate conditions with and without heat recirculation for a broad range of equivalence ratios. These X‐shaped flames rotate around the axis at ~100–150 Hz frequency. The average combustor wall temperature increases with the flow velocity for the stable flame mode and remain mostly uniform and well distributed for the X‐shaped spinning flame mode. Heat recirculation helps in increasing the mean wall temperature of the combustor by ~100–400 K.

► Flame stability limits of backward step microcombustors with heat recirculation.
► Enhanced stability limits with heat recirculation.
► Heat recirculation enhances wall temperature distribution.
► Regimes of existence of spinning modes depends on extent of heat recirculation.