Heat transfer from gases to the wall of the combustion chamber of a diesel engine consists of two modes of heat transmission: convection and radiation. The quantitative relation between the two components has been directly measured only to a small extent in diesel engines. In order to prepare the derivation of an equation that would express more accurately the instantaneous heat transfer rate, the heat flux at each crank angle flowed from the gases to the cylinder wall was measured experimentally in diesel engines. The radiant heat flux was extracted from the above-mentioned total heat flux by using a thermocouple covered with a sapphire window.
Integrating the instantaneous values of both radiant and total heat fluxes, the ratio of the former flux to the latter was determined versus the value of indicated mean effective pressure.