Propagation and emissions of premixed methane-ammonia/air flames

Abstract

In order to investigate the possible use of methane (CH4)-ammonia (NH3) blends as a low carbon fuel, the combustion characteristics of expanding spherical premixed CH4-NH3/air flames are studied, measuring and predicting their laminar burning velocities (SL∞), Markstein numbers (Ma) and structure. Results show that the premixed CH4-NH3/air flames are thicker and propagate slower than the pure CH4/air flames, with reduced carbon dioxide (CO2) emissions. Meanwhile, both flames are cellularly stable for the present various test conditions, showing 0.3 < Ma < 2.1, and this observation is weakly affected by the concentration of NH3 in the fuel blend. Moderate reduction in SL∞, i.e., reasonable burning intensity for practical applications, of the CH4-NH3/air flames even with reduced CO2 emissions supports the possible use of CH4-NH3 blends as a low carbon fuel. However, the problem of high local nitrogen oxides (NOx) emissions in the present flame configuration should be resolved for their practical application. The quantitative discrepancies between the measurements and predictions for a few conditions despite their generally and qualitatively good agreement indicate that a new mechanism optimized for the oxidation of CH4-NH3 blends at atmospheric condition is needed since no reaction mechanism for it is currently available.