Extinction limits and structure of counterflow nonpremixed methane-ammonia/air flames

Abstract An experimental and computational investigation on the fundamental combustion characteristics of methane (CH 4 )-ammonia (NH 3 ) blends is conducted to confirm their potential as a clean fuel with low carbon dioxide (CO 2 ) emissions and determine their reasonable burning conditions, considering counterflow nonpremixed CH 4 NH 3 /air flames. Extinction limits and structure of the nonpremixed CH 4 NH 3 /air flames are measured and predicted. Results show that flames gradually become orange and the flame thickness increases with NH 3 addition, compared with the pure CH 4 /air flames. Also, flames can sustain less NH 3 at high strain rates. Compared with the pure CH 4 /air flames, CH 4 NH 3 /air flames exhibit remarkable reduction of CO 2 emissions with moderate reduction of combustion stability limits and no remarkable temperature drop in the flame, supporting the potential of CH 4 NH 3 blends as a clean fuel with low CO 2 emissions. However, additional investigations for reducing the enhanced NO x emissions mainly via the fuel NO x mechanism with NH 3 addition are needed. Finally, the quantitative discrepancy among the present measurements and predictions merits the development of a new reaction mechanism which is optimized for the reaction of CH 4 NH 3 fuel blends and air.