The MILD (moderate or intense low-oxygen dilution) combustion is characterized by low emission, stable combustion, and low noise for various kinds of fuel. This paper reports a numerical investigation of the effect of different nozzle configurations, such as nozzle number N, reactants jet velocity V, premixed and nonpremixed modes, on the characteristics of MILD combustion applied to one F class gas turbine combustor. An operating point is selected considering the pressure p = 1.63 MPa, heat intensity Pintensity = 20.5 MW/m3 atm, air preheated temperature Ta = 723 K, equivalence ratio φ = 0.625. Methane (CH4) is adopted as the fuel for combustion. Results show that low-temperature zone shrinks while the peak temperature rises as the nozzle number increases. Higher jet velocity will lead to larger recirculation ratio and the reaction time will be prolonged consequently. It is helpful to keep high combustion efficiency but can increase the NO emission obviously. It is also found that N = 12 and V = 110 m/s may be the best combination of configuration and operating point. The premixed combustion mode will achieve more uniform reaction zone, lower peak temperature, and pollutant emissions compared with the nonpremixed mode.
Numerical study of flame structure in the mild combustion regime
