Numerical study of a low emission gas turbine like combustor for turbulent ammonia/air premixed swirl flames with a secondary air injection at high pressure

The present study is dedicated to understand the emission characteristics of turbulent premixed ammonia/air swirl flames in a gas turbine like combustor at high pressure with and without secondary air injection. Ammonia has recently created an attention as a sustainable energy source not only because of its carbon free nature but also owing to its high hydrogen capacity of 17.8% in weight. Thus, in the present study, the effect of pressure on NO, unburnt NH₃, and H₂ emissions in ammonia/air premixed combustion was discussed by having space and time average emissions (STAE) at the exit of cylindrical combustor for various equivalence ratios and high pressures up to 0.5 MPa. The study found that NO emission decreases with an increase in pressure whereas unburnt NH₃ emission in rich flame conditions also decreases with increase in pressure, and the study realizes that, at the equivalence ratio of 1.2, NO and unburnt NH₃ emissions are minimal and in the same order of 200 ppm of mole fraction, even though still there is an unburnt H₂ emission of 6% volumetric exhaust flow at the operating pressure of 0.5 MPa. Subsequently, secondary air injection system was introduced to the combustor, and eventually, the study realizes a low emission combustor with the STAE of NO in the order of 100 ppm of mole fraction at 16% of O₂ concentration and zero NH₃ and H₂ emissions, at the primary zone equivalence ratio of 1.2.