A Study on Radiant Heat Transfer in Combustion Chamber of DI Diesel Engines

In order to clarify the mechanism of radiant heat transfer in the combustion chamber of DI diesel engines, radiant heat fluxes at various points on the piston head of a rapid compression and expansion machine were measured by using thin-film thermocouples. The ambient oxygen volume fraction, the swirl ratio, and the diameter and the number of the fuel injection nozzle hole were varied as experimental parameters. Measured radiant heat fluxes were compared with the total heat fluxes measured at the similar measurement locations to the radiant heat fluxes, the flame temperature and KL-factor obtained by the two-color method. In addition, in order to investigate the effects of the flame distribution and the reflectivity of the wall on the spatial distribution of the radiant heat loss, numerical simulations of the radiant heat transfer between the luminous flame and the chamber wall were also carried out via Monte-Carlo method. The results showed that the magnitude of the radiant heat flux is smaller than that of the total heat flux by one order, regardless of the changes in the oxygen volume fraction, swirl ratio and fuel injection nozzles. It is also shown that the spatial distribution of the radiant heat loss inside the piston cavity is uniform due to high reflectivity of the chamber wall made of aluminum alloy.