Thermal coupling and energy flows between coolant, engine structure and lubricating oil during engine warm up

The thermal behaviour of a modern 2.4 l DI diesel engine used in light duty commercial and private car applications has been investigated to identify how cold operating penalties can be minimised. PROMETS (Programme for Modelling Engine Thermal Systems) has been used to simulate the effects of thermal systems changes. The code has been modified to include new systems elements. The results show how the balance of energy transfers changes as the engine warms up and point to the importance of oil interaction with components in the lower parts of the engine which have a large thermal capacity. These include elements supporting the main bearings, the crankshaft and the lower liner. The interaction can hold down the rise in oil temperature and retard the fall in oil viscosity which in turn has a strong influence on friction losses. The performance of thermal system variants has been compared to identify the fuel economy benefits.

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