Numerical investigation on the combustion characteristics of turbulent premixed ammonia/air flames stabilized by a swirl burner

The present study is dedicated to understand the combustion characteristics of turbulent premixed swirl flames for ammonia (NH3)/air mixture in gas turbine combustors by a numerical investigation. Although, NH3 has been identified recently as a sustainable fuel because of the carbon-free nature, some physical and chemical characteristics of NH3, such as very low laminar burning velocity, production of large amount of fuel NO during the combustion, hampered the utilization of the NH3 as a commercial fuel. Hence, the large eddy simulation (LES) numerical technique was used to produce a detailed and multi-scale information about the reacting flow field and the chemical species distributions of turbulent premixed NH3/air flames by three dimensional calculations. The study realized that a swirl burner successfully stabilizes the NH3/air premixed flames without any additives. In addition, the study found that even though there is an enormous NO emission than that of the ordinary hydrocarbon fuel at the stoichiometric condition, in the rich flame condition, NO emission is significantly decreased, whereas unburnt NH3 increases with respect to the equivalence ratio. Accordingly, there is an impressive operating condition for NH3/air mixtures, which gives a minimal NO and unburnt NH3 emissions even for turbulent swirl flames. The present study found that, at the initial mixture temperature of 500 K, the equivalence ratio of 1.225 gives the minimal NO and NH3 emissions, and this is the best operating point for the selective catalytic reduction (SCR) process in the downstream of the burner.