Macrostructure and NO_x emission evolution characteristics of lean‐premixed flames under combustion instability

Abstract

Effects of combustion instability on flame macrostructures and NO x emissions were conducted experimentally in a model gas turbine combustor. Two variables of the CH 4 flame were investigated-the flow rate and the equivalence ratio. Results indicate that flame macrostructure changes when the equivalence ratio increases from 0.50 to 1.00, the average total length of flame front firstly decreases from 105 to 75 mm, and then increases to 110 mm. While the average length of flame root decreases from 25 to 5 mm. The appearance of the flame front evolves from a "M" shape to a reversed "V" shape, but the appearance of the flame root changes from elongated V shape to a flatted V shape. The envelop diagram of different combustion instability signifies that there are mode shifting of flame-acoustic interactions in the combustion chamber. Under instability conditions, the temperature and velocity distribution of the flame front or flame root affects the NO x emissions. Along the radial direction, the peak temperature in the inner recirculation region and the outer recirculation region drops. This article explored the dynamic characteristics of lean-premixed flames under combustion instability, which could be instructive to the designing of stable and clean combustors in industrial gas turbines.