LAUSR

Abstract 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.