A state-of-the-art micro-mixing micro-combustor with enhanced flame stabilization characteristics using H2-air mixtures

• Micro-mixing slot transforms NPF to PPF. • The stable flame region was determined to be within the range 7 < ϕ inter < 21. • The wall temperature uniformity improved as the mixture became leaner. • As the mixture becomes leaner, stability limit increases further. • Stability limit is improved by 28% compared to other combustors. A novel micro-mixing micro-combustor was developed and the flame stabilization characteristics were investigated numerically. The Combustor exhibited excellent lean stability limits, with stability limits increasing as the fuel–air mixture became leaner. Stability limits achieved for the equivalence ratios 1.0, 0.8 and 0.6 were 8 m/s, 14 m/s and 16 m/s respectively (although the exact blow-off limit for each case is expected to be higher). The limits are higher than those reported in previous studies on hydrogen fueled combustors. As the Reynolds number exceeded 500, simulations above 6 m/s were performed using a turbulent model to account for the transition to turbulence. An all-new criterion to predict the flame stabilization was suggested by specifying the range of local equivalence ratio at central slot interface (φ inter ) as 7 ≤ φ inter ≤ 21 (cold flow) for both laminar and turbulent regimes when 0.6 ≤ φ g ≤ 1.0. The uniformity of wall temperature demonstrated significant improvement at lean equivalence ratios in both the laminar and turbulent regimes, which is crucial for practical applications such as thermoelectric generators (TEGs) and similar systems. Furthermore, the introduction of micro-mixing resulted in the transformation of the diffusion flame into a partially premixed flame. The underlying mechanisms driving this transformation in flame structure were analyzed and discussed in detail. Regarding the enhancement of stability limits, the firing rates of existing combustors were compared with the that of the present combustor and the results revealed a significant 28 % hike at the lift-off condition, which would be even higher when the exact blow-off limits are determined.