Effect of Fuel/Air Mixing on NOx Emissions and Stability in a Gas Premixed Combustion System

Abstract

Understanding the mixing properties in lean premixed combustors is of critical importance to realize low NO x emissions and stable combustion over a wide range of operating conditions. This goal can be partially achieved if spatial and temporal homogeneity of the fuel/air distribution is ensured and if the mixing profile remains less sensible to perturbations of the flow field. Fuel/air oscillations are one of the mechanisms leading to thermoacoustic instabilities and should be minimized. In this paper, experimental techniques (Laser Induced Fluorescence, Particle Image Velocimetry, flame transfer function measurements) are used to investigate the response of different mixing profiles of a lean premixed swirl burner to simulated acoustic forcing of different amplitudes. Results for reacting and cold flow investigations are presented. The flame transfer function appeared to be the most reliable tool to predict the impact of the mixing profile on system stability, but the cold flow investigations gave additional information on the mixing mechanisms at the burner outlet.