A soot map for methane-oxygen counterflow diffusion flames

Abstract

We report on the development of a soot map that separates non-sooting from sooting regions of laminar, counterflow, methane-oxygen-nitrogen diffusion flames at atmospheric pressure. Soot formation is studied at a constant global strain rate of 20 s m 1 as a function of the amounts of methane (0-100%) in the fuel stream and of oxygen (0-100%) in the oxidizer stream. Visual evidence for incipient soot formation is obtained by increasing the mole fraction of oxygen in the oxidizer stream for a given mole fraction of methane in the fuel stream. As the percent methane in the fuel stream increases, less percent oxygen in the oxidizer stream is required for soot inception. A detailed soot model duplicates the experimentally observed soot map and suggests that soot formation under our conditions is associated with a peak flame temperature near 2550 K and a peak soot volume fraction around 1 ppm. Similarly, peak soot inception can be correlated with a temperature of ∼1750 K anywhere along the soot limit curve.