A new emission reduction approach in MILD combustion through asymmetric fuel injection

This paper presents investigations with asymmetric liquid fuel injection (kerosene and biodiesel) into a combustor operating in MILD (moderate or intense low oxygen dilution) combustion regime with thermal inputs varying from 25 kW (6.34 MW/m3)-53 kW (13.3 MW/m3). Effect of air-preheat temperature on temperature distribution and pollutant emissions is investigated by varying the incoming air temperature from 300 to 800 K. The position of asymmetric fuel injection is optimized based on numerical studies to maximize internal recirculation rate, Rdil. Maximum Rdil values of 4.54 and 3.52 are obtained for asymmetric and symmetric fuel injection cases respectively. Different fuel injection pressures of 14, 30, and 48 bar with the same nozzle are used to achieve different mass flow rates of 2.5/2.45, 3.12/3.10, and 4.46/4.3 kg/h for kerosene/biodiesel fuels respectively. Shadowgraphy studies show that measured Sauter Mean Diameters (SMD) vary from 34 to 19 µm and 108 to 37 µm for kerosene and biodiesel respectively, with fuel injection pressure varying from 14 to 48 bar. The combustor showed increased flame stability up to a global equivalence ratio of ϕ = 0.2 for asymmetric fuel injection compared to ϕ = 0.6 in symmetric fuel injection case, due to higher temperatures measured in the central zone of combustor.