Characteristics of pure oxygen/methane flames in a rapidly mixed tubular flame burner

Recently pure oxygen combustion has received keen interest from viewpoints of saving energy and reducing the emissions (NOx and CO2). To avoid potential hazards of flame flash back, an inherently safe technique of rapidly mixed tubular flame has been adopted in this study, in which fuel and oxygen are individually injected into the cylindrical burner. The flame structure and stability were experimentally investigated under various equivalence ratios. Detailed observations show that a steady tubular flame can be established close to the lean extinction limit; however, as the equivalence ratio was raised, steady combustion evolved into periodic oscillations; around stoichiometry the flame became steady, and thereafter evolved into unsteady state in the rich condition. Based on pressure fluctuation measurements and frequency spectral analyses, high frequency (around 2000 Hz) combustion-driven oscillation was observed. Steady tubular flame has been attained at the stoichiometric condition. Through comparing with the stoichiometric methane/air flame, the methane/oxygen flame illustrates remarkable advantages.