Flame Holding Characteristics in Flame-Base of Lean-Rich Combustion. Numerical Unsteady-State Analysis of Laminor Lean-Rich Combustion Flames.

Abstract

Recently much attention has been paid on lean-rich combustion as one of the methods to reduce NOx emission level. In this investigation NOx emission characteristics of the lean-rich combustion were numerically analyzed by taking a set of elementary reactions into consideration. It was found that decreasing the equivalence ratio of the rich flame effectively reduces the NOx level, while it makes the rich flame slightly unstable. In this paper, therefore, unsteady structure and stability characteristics of the attached flames after ignition are examined by using the numerical analysis with a set of elementary reactions installed. According to the results, the combined effects of convection and diffusion of fuel, active species and heat from the rich-side flame to the lean-side flame in the attached regions near the rim are found to control the structure and stability of the leanrich combustion. It is considered that the vortex region formed behind the rim performs an important part in the flame stabilization of the lean-rich combustion.