Numerical simulation of spark ignition engines with special emphasis on radiative heat transfer
thesisposted on 10.11.2010 by Jonathan C. Henson
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
The in-cylinder combustion dynamics of spark-ignition (SI) engines involves a complex interaction of physical and chemical processes. Despite significant progress In the numerical simulation of these phenomena with computational fluid dynamics (CFD), there is a need for generalised models to describe the emission, absorption and scattering of thermal radiation within the 'participating' combustion gases. Therefore, the present work advances the predictive capability of nurnerical methods for radiation transport in participating media for inclusion into an established finite-volume CFD code. The research focuses on three radiation methods: discrete transfer, YIX and a pathlengthbased Monte Carlo algorithm. The three-dimensional formulation and coding of each method combines the best available knowledge from heat transfer, statistical and graphics literature. In particular, the tracing and searching of complex arbitrary geometries utilises an efficient ray-triangle intersection algorithm in a novel way to handle cell face distortion and edge intersections with minimum computation. A new general weighted-sum-ofgray- gases model (WSGG) is implernented in order to first resolve the spectral (nongray) dependence of high-temperature gas radiative properties prior to solution by one of the three radiation methods. The present methods are first verified against published benchmark solutions for radiating media in the absence of other modes of heat transfer. Subsequently, the discrete transfer- WSGG model is coupled with the engine-specific CFD code KIVA-11 for studies of the flow field, flame propagation and infrared emission in pancake and pentroof SI engines. Here, the Favre-averaged Navier-Stokes, energy and radiation conservation equations are solved over a nonorthogonal, curvilinear mesh of arbitrary hexahedrons, body-fitted to the combustion chamber geometry. Flexible algebraic and elliptic mesh generation tools are developed for this purpose. Additional k-F- turbulence terms for variable density flows, the EDC model for mixing-controlled combustion, the Shell model for auto-ignition and the capability to simulate ports and valves with wave action are new features added to KIVA-11 to ensure a good description of the turbulent, chemically reacting flow field as a basis for the radiation studies. Comparisons with experimental measurements from optical engine studies are presented.
- Mechanical, Electrical and Manufacturing Engineering