Effects of ammonia substitution on combustion stability limits and NOx emissions of premixed hydrogen–air flames

Abstract The combustion stability limits and nitrogen oxide (NO x ) emissions of burner-stabilized premixed flames of ammonia (NH 3 )-substituted hydrogen (H 2 )–air mixtures at normal temperature and pressure are studied to evaluate the potential of partial NH 3 substitution to improve the safety of H 2 use. The effects of NH 3 substitution, nitrogen (N 2 ) coflow and mixture injection velocity on the stability limits and NO x emissions of NH 3 –H 2 –air flames are experimentally determined. Results show a reduction of stability limits with NH 3 substitution and coflow, supporting the potential of NH 3 as a carbon-free, green additive in H 2 –air flames and indicating a different tendency from that for no coflow condition. The NO x emission index is almost constant even with enhanced NH 3 substitution, though the absolute value of NO x emissions increases in general. At fuel-rich conditions, the NO x emission index decreases with increasing mixture injection velocity and the existence of coflow. The thermal deNO x process in the post-flame region is involved in reducing NO x emissions for the fuel-rich flames.