EFFECTS OF HEIGHT ABOVE BURNER AND OXYGEN CONTENT ON SOOT FORMATION AND NANOSTRUCTURE IN A CO-FLOW LAMINAR DIFFUSION FLAME FUELED WITH METHANE

Abstract

Soot is particulate matter that comes from the incomplete combustion of hydrocarbon fuels. It is a well-known respiratory irritant and can cause build-up in combustion equipment. For both reasons, soot mitigation strategies have become a topic of much research. One such method is known as oxygen-enhanced combustion, which is the practice of enriching the oxidizer stream in a combustion system to higher-than-air oxygen percentages. This has the benefit of reducing soot formation, leading to fewer emissions. This work aims to qualify and quantify the effect of a 100% oxygen oxidizer stream on the soot. This effect is being quantified by measurement of soot primary particle diameter, flame temperature, and soot nanostructure metrics such as fringe length, fringe tortuosity, and fringe lattice spacing gleaned from high-resolution TEM images. It is qualified by observation of soot particle population density and degree of agglomeration of aggregates from low and median resolution TEM images. It was found that methane/100% oxygen flames share similar trends to methane/air flames based on soot evolution, particle population density, degree of agglomeration, and primary particle density, but the values for these metrics are lower for the oxygen flame, suggesting increased oxidation and therefore less soot formation/growth. Soot nanostructure metrics for both flames showed little change with HAB, reinforcing the assertion that methane is a non-graphitizing fuel. It was also found that the only metric that changed with increased oxygen concentration was fringe length, suggesting that the apparent increase in structural order in soot produced by methane/100% oxygen flames is only due to increase graphitic plane length.