Effect of Initial Fuel Distribution and Subsequent Mixing on Emissions From Lean, Premixed Flames

Abstract

Results presented here illustrate how optimizing the fuel distribution at injection reduces the subsequent mixing needed for ultralow emissions in lean, premixed gaseous flames. An experimental facility was developed for bluff body stabilization of a high pressure natural gas flame at the exit of a 4” diameter mixing tube. Fuel was injected through two concentric ring manifolds. NOx and CO drop dramatically from diffusion flame to perfectly premixed levels with increasing mixing distance. Furthermore, for each mixing distance, there is an optimum fuel split that results in minimum NOx and CO emissions. Computational fluid dynamics and laser sheet flow visualization show the recirculation zones and fluid mixing that affect fuel injection requirements. Although improved fuel injection and greater mixing will both drive the NOx-CO curve to the origin, improving the initial fuel distribution reduces the requirement for subsequent mixing.