Kinetics Reduction For Combustion Chemistry And Investigation Of Methane Turbulent Jet Flame Using Direct Numerical Simulation

Combustion is a type of fundamental approach for energy conversion, in the frame work of energy and power engineering, which has wide application in many kinds of power equipments; such as furnace and combustor in boiler, gas turbine, internal combustion engine, aircraft engine and so on. However, combustion problems in practice become remarkably complex, due to the involvement of turbulent flow. In diffusion flame, turbulence has significant influence on the mixing between fuel and oxidizer; while turbulence also changes the characteristics of flame propagation, in the case of premixed combustion. As a result, insightful research on turbulent combustion phenomena is the prerequisite to design and retrofit power equipments with the aim to improve combustion efficiency and reduce pollutant emission.The primary focus of this thesis is to meticulously investigate the interaction between turbulence and combustion in different types of combustion using DNS (Direct Numerical Simulation), in order to provide new references for turbulent combustion model development and finally benefit engineering practice. Direct numerical simulation, is a recently-developed method to model turbulence, which has the capacity to completely record turbulence without introducing any model errors. If combined with real chemistry kinetics, it can be used to simulate turbulent combustion in detail, and duplicate the factual interaction between turbulence and combustion. The work is expanded along the thread of direct numerical simulation, and the research object is methane turbulent jet flame, a widely-applied type of flame.To improve computation efficiency, some effort to reduce chemical kinetics was taken. The detailed method and step to fulfill chemistry reduction for turbulent combustion modeling was given, with the example to reduce a NOx-invovled chemical scheme. Then, a methane/air premixed lean flame in turbulent jet flow was simulated using DNS, to deeply study the effects of vortex-induced curvature, stretch, compression and strain rate on premixed flame and heat release. Furthermore, PDF method was employed to explain the correlation among these actions on premixed flame. This research gained good comments from domestic researchers.After that, a methane/air diffusion flame was investigated using 3D DNS and reduced chemical kinetics. In this case, the fuel-oxidizer mixing and ignition processes, with the influence from turbulence, were carefully recorded, which could instruct the development of novel theoretical models of turbulent non-premixed combustion.