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The development of new high power diesel engines is continually going for increased mean effective pressures and consequently increased thermal loads on combustion chamber walls close to the limits of endurance. Therefore accurate CFD simulation of conjugate heat transfer on the walls becomes a very important part of the development. In this study the heat transfer and temperature on piston surface was studied using conjugate heat transfer model along with a variety of near wall treatments for turbulence. New wall functions that account for variable density were implemented and tested against standard wall functions and against the hybrid near wall treatment readily available in a CFD software Star-CD.

The development of diesel engines is constantly leading to greater increases in the power density. The heat load into the combustion chamber walls increases with the increased power density. Estimating correct local heat fluxes inside the combustion chamber is one of the most challenging tasks in engine simulation. In this study, the heat load of the piston was estimated with the help of the modern simulation tools CFD and FEM. The objective of the work was to evaluate the thermal stress of a research engine designed for an exceptionally high maximum and mean pressure. The local heat transfer coefficient and gas temperature were simulated with a CFD code with the standard and modified wall functions and used as boundary values for the FEM analysis. As a reference case, a model of a production engine with measured piston surface temperatures was used to validate the combined CFD and FEM analysis.

Accurate heat release analysis of cylinder pressure data is a powerful tool used in the development of diesel engines. However, significant errors in the calculated heat release values can occur due to shortcomings in both the experimental measurements and in the heat release model and this can produce misleading results. This paper shows the effect of such common errors on the calculated gross heat release data obtained when analysing simulated and experimental direct injection diesel engine pressure diagrams using a traditional single-zone First Law heat release model. The work reveals that the greatest uncertainty in most cases will be caused by assuming the wrong rate of heat transfer between the cylinder charge and combustion chamber walls. To overcome this limitation, an alternative heat release model is proposed and shown to give very good results over a wide range of operating conditions.