Combustion characteristics of non-premixed methane micro-jet flame in coflow air and thermal interaction between flame and micro tube

The combustion characteristics of non-premixed methane micro-jet flame in coflow air were investigated experimentally and numerically. A detailed reaction mechanism was employed in the two-dimension numerical computation. The thermal interaction between the flame and solid tube was considered by using fluid-solid coupled thermal boundaries in the numerical computation. Four typical flames, lifted flame, attached flame, hemisphere flame and umbrella flame, were observed in different fuel flow velocity ranges in experiments. The flame heights, blow off and extinction limits in coflow airs at different velocities were measured. The OH and CH distributions of non-premixed micro-jet flames were obtained by experiments, and the computational results agree well with those from the experiments. The computational temperature distributions show that there are thermal interactions between flames and solid tube. The heat exchanges through surfaces of the solid tube were analyzed in detail. The fresh fuel gas in the solid tube is preheated by the thermal recirculation. Consequently, the combustion intensity of the micro-jet flame is enhanced. The thermal interaction is essentially affected by the flame shape, and it is significant for the hemisphere flame.