Measurements of Instantaneous Heat Flux to Metal and Ceramic Surfaces in a Diesel Engine

The effects of surface materials and extent of insulation on the heat transfer to the head of an open-chamber diesel were studied. A large instrumentation plug designed to incorporate plates of various materials on the gas-side surface was utilized with a special research head. Instantaneous rates of heat transfer to the plate gas-side surface were measured. Measurement results obtained with a zirconia plate and an insulated metal plate are compared to data for an uninsulated metal plate. The insulation of the metal plate increased its gas-side surface temperature over the uninsulated case by about the same amount achieved with a 6.35-mm-thick zirconia plate. The magnitude of the surface temperature swing for zirconia is not as high as expected from conduction theory, but is substantially higher than that for the uninsulated metal. Significant reductions of steady state heat fluxes were achieved with both the zirconia and the insulated metal compared to the uninsulated metal. However, peak values of surface heat fluxes for the insulated metal were found to be higher than those for the uninsulated metal. Substantial reductions in peak values of surface heat flux were achieved with zirconia over the uninsulated metal. Surface temperature levels for zirconia were not as high as possible because of limitations placed on the thermal loading by the design of the research engine head.