J.M. Joo, D.H. Um, O.C. Kwon
Sungkyunkwan University, KR
hydrogen, ammonia, carbon-free, nonpremixed flames, extinction limits, NOx
The effects of ammonia (NH3) substitution on the extinction and nitrogen oxide (NOx) emissions of nonpremixed hydrogen (H2)-air flames at normal temperature and pressure were experimentally studied to evaluate the potential of partial NH3 substitution to improve the safety of H2 use and provide a database of nonpremixed NH3-substituted H2-air flames. Results show reduction of combustion stability limits with NH3 substitution. The NOx emission index EINOx increases with enhanced NH3 substitution in general. For given coflowing air injection velocities EINOx decreases and then increases with increasing fuel injection velocities, though the absolute value of NOx emissions monotonically increases. The effects of recirculation of burned gas in the combustion chamber that encloses the coflow burner reduce EINOx for low fuel injection velocities Vfuel, while the reduced flame length due to the lift-off behavior and thereby the reduced radiant heat losses enhance EINOx for high Vfuel. The present observations support the potential of NH3 as a carbon-free, green additive for improving the safety of H2 use with reasonable levels of NOx emissions.