Effect of Compression and Expansion on Instantaneous Heat Transfer in Reciprocating Internal Combustion Engines

Abstract

Instantaneous heat flux at the surface of a cylinder head in a motored diesel engine has been measured, at various speeds, using a fast-response surface thermocouple. Heat flux during compression was found to be much larger than heat flux during expansion, the maximum heat flux occurred about 8° before top dead centre and there was a significant heat flux even when gas temperature and wall temperature were equal. During expansion, heat flowed from the surface to the gas even though the bulk gas temperature was greater than the surface temperature. These effects are predicted by solutions of the equation of thermal energy and are shown to be related to the volumetric rate of compression or expansion. A simple modification of Annand's equation gives good results and is recommended for general cycle calculations.