Thermal Loading of a Petrol Engine

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Abstract
This paper reports the results of an investigation into the thermal loading of a modern 1·975 1, four-cylinder petrol engine operating at engine speeds of up to 100 rev/s. The effects of engine speed and load, mixture strength, ignition advance, compression ratio, coolant temperature and pressure, antifreeze, detonation, olefin content of fuel, and a piston modification on the local heat fluxes and metal temperatures have been determined and the maximum levels established. The methods of temperature measurement were fixed and traversing thermocouples for the cylinder head and liner, fixed thermocouples for the valve seats and spark plug, disappearing-filament optimal pyrometer and hardness recovery for the exhaust valve, differential thermocouples for the gross heat losses, and intermittent-contact fixed thermocouples for the piston. The greatest heat fluxes occurred at the centre of the combustion chamber, in the valve bridge and exhaust-valve seat region, and decreased towards the outside of the combustion chamber and down the cylinder liner. For the form of combustion chamber investigated the heat flux varied as the 0·6 power of the gross fuel consumption and the operating variables generally gave only second-order effects. The piston temperature is fairly sensitive to ignition advance, compression ratio, and high-speed detonation.

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