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The findings presented in this paper are part of a long term project aimed at raising the science of heat transfer in internal combustion engine cooling galleries. Initial work has been undertaken by the authors and an experimental facility is able to simulate different sizes of coolant passages. External heat is applied and data for the forced convective, nucleate boiling and transition or critical heat flux (CHF) regimes has been obtained. The results highlighted in this paper attempt to quantify the effects of cooling passage surface roughness on the nucleate boiling regime. Tests have been conducted using aluminium test pieces with surface finishes described as smooth, intermediate and as-cast. It has been found that the as-cast surface increases the heat flux density in the nucleate boiling region over that of the smooth and intermediate surfaces.

Precision cooling has a number of advantages over the conventional cooling of combustion engines. It is primarily used to prevent component failures and is generally intended to create an even distribution of temperature within the cylinder head and block. This leads to lower thermal stresses and higher component durability. Precision cooling in the form of forced convection and nucleate boiling can be used to greater effect than that of traditional precision cooling concentrating on forced convection only. This paper describes the analytical and experimental precision cooling strategy that has been used to investigate nucleate and transition boiling. Analytical details of the models are described and preliminary experimental data is provided for comparison. The major finding indicates that the diameter of the internal cooling passage is one of the significant factors that influences the critical heat flux.

Modern architectures for diesel cylinder heads, especially high performance, direct injection heads for passenger cars and light trucks, require an optimized combination of design and material properties. In aluminium castings, microstructural gradients and associated fatigue and mechanical properties can result from the process selection, e. g. gravity or low pressure, and from the variable cooling rates which have to be applied to the different parts of the casting in order to get a progressive solidification and a sound part. It is thus essential to understand the relationship between the microstructure resulting from the combination of process, material choice and heat treatment, and the properties of the material. As the most widely used material for aluminium diesel as well as gasoline cylinder heads, the 319 alloy has been selected for its superior strength. We have carried out tensile testing and thermo - mechanical fatigue testing on a range of materials.