One limit on the output of a highly rated supercharged diesel engine is the thermal loading imposed by combustion on the walls of the combustion chamber; that is, on the piston, cylinder head, valves, and liner wall. The test readings usually available, whether on works test or in the field are not sufficient for any direct comparison of thermal loading for engines of the same type operating under different site conditions, at different loads and/or with different turbocharger matches. Various factors involved in thermal loading owing to combustion are assessed by cycle and heat-transfer calculations using a digital computer. An approximate formula is derived, for one type of engine, that enables a rapid comparison to be made using the normally available test information. Experimental values for piston temperature obtained by thermocouple measurement on engines in development tests are plotted against the “heat loading factor” obtained from this formula. It is concluded that the formula provides a useful guide for use during development and for nonstandard conditions in service generally.

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