Effects of O2 enrichment on NH3/air flame propagation and emissions

The potential utilization of ammonia as a carbon-free fuel under oxygen (O2)-enriched condition is demonstrated, suggesting its practically appropriate burning conditions by measuring and predicting the combustion characteristics of outwardly-propagating spherical O2-enriched NH3/air premixed flames at normal temperature and pressure. Measured and computed laminar burning velocities and predicted flame structure exhibit that the O2-enriched ammonia/air flames become thinner and propagate faster with O2 enrichment. Observed flame morphologies and measured and computed Markstein numbers reveal that all the present O2-enriched flames are stable in terms of the flamefront cellular instability due to preferential diffusion and the effects of O2 enrichment on the instability are negligible. Volume-based 35-40% O2 in the nonfuel mixtures demonstrates the proper burning intensity for practical applications, comparable to the typical hydrocarbon/air flames. In the present flame configuration, however, local nitrogen oxides emissions are found to be high, which should be substantially reduced in the practical systems. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.