Experimental and kinetic modelling investigation on NO, CO and NH3 emissions from NH3/CH4/air premixed flames

Abstract Ammonia (NH 3 ) is regarded as one of the most viable alternatives to produce carbon-free energy. However, its low flammability and high NO x emissions associated with its combustion inhibit the implementation of pure NH 3 as a fuel. Dual-fuel approaches with NH 3 and more reactive fuels have been proposed; however, information on pollutant emissions is still scarce. The present work focuses on quantifying the gaseous pollutant emissions from the combustion of mixtures of NH 3 and CH 4 as a function of the equivalence ratio and amount of NH 3 in the fuel mixture. A premixed laminar burner was fired with various mixtures of NH 3 /CH 4 in air with equivalence ratios of 0.8, 0.9 and 1, and a fixed thermal input of 300 W. The NH 3 molar fraction in the fuel mixture was varied from 0 (pure CH 4 ) up to 0.7. Gas temperatures along the burner axis and emissions of NO x , CO and NH 3 were measured for all conditions. The results were compared with kinetic simulations using recent chemical kinetic mechanism models. The experimental results showed that the NO x concentration initially increases as the fraction of NH 3 in the fuel mixture rises up to 0.5, decreasing afterwards. Furthermore, NO x emissions decrease as the equivalence ratio is reduced towards fuel-lean conditions. CO and NH 3 emissions are fairly low indicating complete combustion of CH 4 and NH 3 . The chemical kinetic mechanisms considered showed fair agreement with the experimental trends, with the NO x and CO emissions being over-predicted for most conditions.