Numerical study of methane and air combustion inside a small tube with an axial temperature gradient at the wall

A numerical study on CH4 and air premixed combustion inside a small tube with a temperature gradient at the wall was undertaken to investigate the effects of inlet velocity, equivalence ratio and combustor size on combustion characteristics. The simulation results show that the inlet velocity has a significant influence on the reaction zone, and the flame front shifts downstream as the inlet velocity increases. The results also show that, the inlet velocity has no obvious effects on the flame temperature. The highest flame temperature is obtained if the equivalence ratio is set to 1. It is disclosed that the combustor size strongly influences the combustion characteristics. The smaller the combustor size is, the more difficult it is to maintain the steady combustion. The smallest combustor size that the stable flame can be sustained is determined mainly by the wall temperature of the micro-combustor under the given conditions. The higher the wall temperature is, the smaller the smallest combustor size. Therefore increasing wall temperature is an effective way to realize flame stabilization for a given combustor size.

Research highlights
► Combustor size has a strong influence on combustion characteristics.
► There is a smallest combustor size for maintaining stable combustion under the given conditions.
► Large inlet velocity shifts the flame front downstream.
► Inlet velocity has no significant effects on the flame temperature.