Experiments Study And Flamelet Model Simulations On MILD Combustion Under Normal Temperature Air

MILD combustion is known as one of the most promising new combustiontechnologies in21st century, which has high efficiency and low NOx, CO, SO_xemissions.This paper has discussed the characteristics of MILD combustion using normaltemperature air with the method of experimental study and CFD simulation. A pilot scalefurnace of20kW has been designed and built. The experiment has been carried out bytaking LPG(>96%C3H8) as fuel with normal temperature air. The temperature field ismeasured and flue gas component is sampled and analyzed.Experimental results present that MILD combustion can also been realized without airpreheating. Temperature distribution in the furnace is uniform and there is no visual flame.It is indicated that the combustion reaction has lower rate and occurs in the wholechamber.Also the levels of oxygen and NO are very low in the furnace (average4.2%and29ppm separately). There is high level of CO distribution in the center part of furnace,besides of which CO is undetectable. It is also found that no CO and low NO (only17ppm)is detected in the exits which proves that MILD combustion has high ability of emissionreduction.Numerical simulation is also taken to predicted MILD combustion of C3H8without airpreheating by the software of FLUENT. Three kinds of turbulence model-standard k-εmodel, realizable k-ε model, Reynolds Stress model are chosen combined with the LaminarFlamelet model and DO radiation model. The results show that the prediction oftemperature field and the trend of CO concentration using Reynolds Stress model combinedwith Flamelet model are better than the other two groups, but the simulation of O2distribution on three kinds of combination has the similar results. The trend of NO can bemore accurately predicted by using FLUENT NO model. The modeling results of CO andNO in the exit are in accordance with experiment.Research shows that intense flue gas recirculation and high-speed gas/air jet play avery important role of MILD combustion under normal temperature air, and models onflow and combustion still need development. It is also considered that the characteristics of this technology-no air preheating, uniform temperature distribution and low NO emissionswill be very beneficial to its application and promotion.