Effects of trapezoidal bluff bodies on blow out limit of methane/air combustion in a micro-channel

•The shape change of bluff body has a slight effect on blow out limit at the same ζ.•The combustion recirculation zone expands with increasing blockage ratio.•The optimum blockage ratio is 0.4 for trapezoidal bluff body in our study.•Blow out limit can reach up to 2 m/s with the optimum blockage ratio of 0.4.