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A phenomenological heat transfer model for direct injection diesel engines has been developed. Utilizing the thermodynamic results of a combustion model as an input, the model is able to predict the temporal variation of the heat losses from the cylinder gas to the cylinder walls. Additionally, the division into isothermal combustion chamber subsurfaces allows the consideration of the spatial variation of the wall heat fluxes. The physical mechanisms such as flow dependent convection, heat radiation due to hot soot particles and isolation effects of deposited soot layers are described in detail. Thus, the effects of these mechanisms on the overall heat transfer can be studied. The heat transfer model was verified successfully by comparison to measured wall heat fluxes in a single-cylinder direct injection diesel engine. It is shown that the effects of engine speed and load, turbo-charging and soot deposition can be predicted with good accuracy.