posted on 2010-11-10, 14:16authored byJonathan C. Henson
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.
History
School
Mechanical, Electrical and Manufacturing Engineering