湍流甲烷OXY型有氧燃烧中PIV速度矢量场检测方案(CCD相机)

Carbon capture and storage (CCS) is an important strategy for reducing CO2 emissions,with oxy-fuel combustion being one of the most promising technologies becauseof it is high efficiency and low cost. In oxy-combustion, CH4/0 2/CO 2 mixtures burnat low temperatures (~1700 K), high pressures (~40 bar), where laminar burning velocitiesare about 7 times lower than in traditional CH4 /Air mixtures. Thus oxy-fuelcombustors are more prone to blowoff and dynamic instabilities. In this thesis weexamine turbulent oxy-combustion flame stabilization physics at the large and smallscales using experimental studies and numerical simulations.Experimental measurements are used to establish the stability characteristics offlame macrostructures in a swirl stabilized combustor. We show that the transitionin the flame macrostructure to a flame stabilized along both the inner and outershear layers (Flame IV), scales according to the extinction strain rate, similar to airflames. To achieve accurate scaling, extinction strain rates must be computed at thethermal conditions of the outer shear layer, emphasizing the role of heat interactionswith the wall boundary layer. Care must be exercised while modeling the chemicalstructure of oxy-flames. We show that the kinetics of CO2 (used as a diluent in oxycombustion)is important in determining the consumption speed and flame extinctionstrain rate. Specifically, the extinction strain rate was found to be heavily impactedby the reaction C02+ H - CO + OH.Large Eddy Simulations (LES) models, first validated for various combustor geometries,fuels and oxidizers, are used to examine the stabilization mechanisms ofthese flames. First, we demonstrate the importance of choosing the correct globalchemical kinetics mechanism in predicting the flow structures in multi-dimensionalsimulations and develop a priori criterion of selecting a reduced mechanism based onthe extinction strain rate. Besides flame macrostructures, recirculation zone lengthsare found to linearly scale with extinction strain rates. This scaling holds regardlessof fuel or oxidizer type, Reynold's number, inlet temperature, or combustor geometry.It is thus very important that a chemical mechanism is able to correctly predict extinctionstrain rates if it is to be used in CFD simulations. We use the validated LESframework to model the transition to Flame IV in the swirl combustor for methaneoxy-combustion mixtures. The 3D turbulent flame structure strongly resembles aID strained adiabatic laminar flame structure in the combustor interior, and nonadiabaticflames near the combustor wall. The results support the earlier conclusionsregarding the use of the extinction strain rate and the wall thermal boundary conditionin scaling and modeling turbulent combustion dynamics.