Combustion characteristics of CH₄ nonpremixed flame with recession distance

A lot of research on the stability of nonpremixed flames has focused on the fuel-nozzle and quarl geometries. Of the work carried out, only a smill amount has focused on the stability of the nonpremixed flame according to the recession distance and air-nozzle geometry. Therefore, in this study, a coaxial-diffusion-type gas burner with a swirler is designed for the systematic investigation of the combustion characteristics of a CH₄ flame depending on the recession distance and secondary air-nozzle geometry. 1 st air is flowed through the swirler, and 2nd air is flowed through each nozzle. It is shown that the secondary air velocity greatly influences the flame length and shape. There is an optimum recession distance for each nozzle for the best combustion efficiency. In this study, it is shown that the optimized recession distance is nearly half the outer diameter of the air-supply nozzle.