## Fig xA Schematic of the experimental

Detailed governing and entropy transport equations were given in our earlier work, please refer to [25]. The volumetric entropy generation rates by various irreversible processes can be calculated as below.equation(1)g=-1T2q·∂T∂r-1TP:∂∂rv-∑iniVi·∂∂rμiT-1T∑iμiKi

The first term on the right hand shows the effect of energy flux. In which only the effect of conduction is included. The second term is the rate of entropy generation by viscous effect in terms of tensor. The effects of mass AP1903 and chemical reaction on entropy generation rates are represented in the third and fourth terms. As entropy generation is independent of flow physics, the volumetric entropy generation rate can be calculated by post-processing the variables in the steady state. The total entropy generation in the computational domain isequation(2)Sgen=∫VgdVSgen=∫VgdV

4. Results and discussion

To validate the numerical simulation model, experimental test was carried out in the micro combustor (B1) with a gap length of 2 mm and gap height of 0.4 mm. Fig. 4 shows the combustion picture in B1 under different H2/air equivalence ratios, flow velocity is kept at 5 m/s. It is found that the combustor with higher equivalence ratio shows higher temperature distribution. This is attributed to more thermal energy released in the case with higher equivalence ratio.