Impacts of inlet step on the performance of a micro-combustor

A Computational Fluid Dynamic (CFD) study on hydrogen-air premixed combustion in a micro-combustor is investigated by solving three-dimensional (3D) governing equations. The effects of inlet geometry on the flame temperature, flame stability and micro combustor efficiency under different inlet flow rates and various equivalence ratios were studied by a simulation of two micro-combustors with similar dimensions, in which one of them was designed with inlet step and the other without inlet step. The simulated results confirm that the temperature is higher in a micro-combustor with inlet step compared to that of the simple geometry. Thus the flame stability can be ensured by application of the step in the inlet of the micro-combustor. In a moderate equivalence ratio of lean mixture (Ø=0.5), the peak of maximum temperature takes place in the micro-combustor with inlet step in a lower velocity (V_1a=4m/s) which was recorded around 1747°K. By enhancing the inlet flow rate of hydrogen-air mixture, the flame length raises and the flame is blown further downstream of both combustors. Also, in both micro-combustors fueled by lean hydrogen-air mixture, more heat can be released when the equivalence ratio is larger and a higher temperature level is recorded (1931°K). Indeed, in the fixed hydrogen-air mixture, inlet flow rate (=1.57×10^-6 m³/s) when Ø=0.6, a maximum temperature was recorded in the micro-combustor with inlet step and consequently the temperature of exhaust gases was higher. In the same physical and chemical conditions, the micro-combustor with inlet step has higher performance efficiency.