Multidimensional Modeling of Radiative Heat Transfer in Diesel Engines

During combustion in a diesel engine radiation heat transfer is the same order of magnitude as the convection heat transfer. Therefore for a reliable engine simulation the radiation transfer equation should be solved simultaneously with the flow and energy equations. A rigorous solution for the radiative transfer is, however, neither warranted nor cost effective. An approximation is needed at a level consistent with those used in modeling the fuel spray, the chemical kinetics, the soot and the turbulence. The approximation should account for the anisotropic behavior of radiation in the engine and be easily integrated into finite difference codes.

This paper illustrates use of the first and the third order spherical harmonics approximation to the radiative transfer equation and the delta-Eddington approximation to the scattering phase function for droplets in the flow. Solutions are presented for an axisymmetric, finite cylindrical geometry and assumed distributions for temperature, soot and fuel droplets chosen to be representative of conditions in a diesel engine during combustion. Results are obtained numerically by an accurate finite difference scheme. Important goals of this paper are to investigate the importance of scattering by fuel droplets and of accounting for spatial variations in the extinction coefficient on the radiative flux distributions at the walls of a disc shaped diesel engine.