Flame Structure and NOx Formation of Counterflow Flame Using Oxygen-Enriched Air.

Abstract

In this study, numerical simulations of the counterflow diffusion flame and the counterflow double flame with oxygen-enriched air were made by using the GRI chemical reaction mechanism (NOx included) in order to elucidate the effects of oxygen concentration and equivalence ratio of mixture on the flame structure and NOx formation. The following conclusions were reached: (1) In the case of counterflow diffusion flame, as the oxygen concentration increases, the width of high-temperature zone becomes larger, so that NO formation by the thermal NO mechanism increases, but that by the prompt NO mechanism decreases and becomes negative. (2) In the case of counterflow double flame, as the equivalence ratio becomes large, the NO formation by the prompt NO mechanism at the position of the fuel-rich premixed flame decreases, and that by the thermal NO mechanism at the position of the diffusion flame keeps approximately constant. (3) In the both flames, NO formation has a maximum at about YO2=0.8, and it decreases steeply above YO20.8, because the nitrogen concentration decreases.