Abstract：The important features for realizing MILD combustion (moderate or intense low-oxygen dilution combustion) are high-speed air jet with high-temperature flue gas backflow and burning after rapid mixing with reactants. The optimization design of the structural parameters of combustion chamber and the internal flow field organization are the key factors to realize MILD combustion of liquid fuel under air condition at normal temperature. Numerical simulation was used to investigate the effects of combustion chamber height, fuel distribution and air nozzle position on flow field, temperature field distribution and NOx emissions. The results show that the combustion chamber height mainly affects the velocity attenuation of air jet and the internal circulation rate to determine the circulation of the overall airflow in combustion chamber. The position change between the air nozzle and the fuel nozzle determines the fuel distribution in combustion chamber and the mixing with high temperature flue gas. When the relative distance between air nozzle and fuel nozzle is small, the strong backflow can make the fuel distribution in the combustion chamber more uniform. The ability of diluting fresh reactant of flue gas is enhanced, and then the combustion in combustion chamber is moderated with decreased peak temperature thermal NO emission. When the air nozzle is far away from the exit of combustion chamber, the concentrated large area of reflux leads to the evenly distributed reactants in the combustion chamber, and the overall combustion reaction becomes more uniform and moderate, which is beneficial to the realization of MILD combustion.
WEINBERG F J. Combustion temperatures: the future?[J]. Nature, 1971, 233（5317）: 239-241.
[2]
SORRENTINO G, CAVALIERE A, SABIA P, et al. Diffusion ignition processes in MILD combustion: a mini-review[J]. Frontiers in Mechanical Engineering， doi：10.3389/fmech.2020.00010.
TIAN Y, ZHANG J H, ZHU J Z, et al. Feasibility analysis of flameless combustion in high-parameter gas turbine combustor[J]. Scientia Sinica(Technologica), 2020, 50(1): 17-30. (in Chinese)
[4]
XING F, KUMAR A, HUANG Y, et al. Flameless combustion with liquid fuel: a review focusing on fundamentals and gas turbine application[J]. Applied Energy, 2017, 193: 28-51.
[5]
LAMMEL O, SCHUTZ H, SCHMITZ G, et al. FLOX combustion at high power density and high flame temperatures[J]. Journal of Engineering for Gas Turbines and Power, doi：10.1115/1.4001825.
[6]
SI J C, WANG G C, MI J C. Characterization of MILD combustion of a premixed CH4/air jet flame versus its conventional counterpart[J]. ACS Omega, 2019, 4(27): 22373-22384.
[7]
MI J C, LI P F, DALLY B B, et al. Importance of initial momentum rate and air-fuel premixing on mode-rate or intense low oxygen dilution (MILD) combustion in a recuperative furnace[J]. Energy & Fuels, 2009, 23(6): 5349-5356.
[8]
FLAMME M．New combustion systems for gas turbines(NGT)[J]．Applied Thermal Engineering，2004，24(11/12): 1551-1559．
[9]
TORRESI M, CAMPOREALE S M, FORTUNATO B. Diluted combustion in a aerodynamically staged swirled burner fueled by diesel oil[C]∥Processes and Techno-logies for a Sustainable Energy，2010: 1-8．
[10]
REDDY V M, KUMAR S. Development of high intensity low emission combustor for achieving flameless combustion of liquid fuels[J]. Propulsion & Power Research, 2013, 2(2):139-147.
[11]
REDDY V M, BISWAS P, GARG P, et al. Combustion characteristics of biodiesel fuel in high recirculation conditions[J]. Fuel Processing Technology, 2014, 118:310-317.
BAI P B, XING Y M, WANG Z. Experiment study and simulation esearch for the atomization characteristics of the internal mixing nozzle[J]. Fluid Machinery, 2015, 43(2): 1-6. (in Chinese)
[14]
WNNING J A， WNNING J G. Flameless oxidation to reduce thermal no-formation[J]. Progress in Energy & Combustion Science, 1997, 23(1):81-94.
WU Y F, ZHAO G L, LIU Z X, et al. Verification experiment for MILD combustion evaluation standards[J]. Thermal Power Generation, 2018, 47(1): 106-111. (in Chinese)
2022, Vol. 43 
