Infrared High-Speed Thermography of Combustion Chamber Wall Impinged by Diesel Spray Flame: Imaging Velocimetry of the Radially Striped Infrared Radiation Pattern

As a new method to examine the extremely unsteady and spatially varying wall heat transfer phenomena on diesel engine combustion chamber wall, high-speed imaging of infrared thermal radiation from the chromium coated window surface impinged by a diesel spray flame has been conducted in a constant volume combustion chamber. The infrared radiation from a back surface of the chromium layer was successfully visualized at 10kHz frame rate and 128 × 128 pixel resolution through the window. The distributions of infrared radiation, temperature and heat flux exhibited coherent and streaky structure with radial stripes extending and waving from a stagnation point likely reflecting the near-wall turbulent structure in a wall impinging diesel flame. The experiments were conducted with various parameters such as fuel injection pressure, ambient gas oxygen concentration, wall impinging distance, wall surface roughness and wall materials. Imaging velocimetry analysis was applied to the movement of the radially striped infrared radiation pattern in order to discuss potential correlation between the distributions of the movement velocity and the heat flux. The coherent and streaky radial stripes have been consistently observed at all tested conditions suggesting a potential of near-wall turbulence control, for example by structured surface such as riblets, to reduce cooling loss under varieties of engine operating conditions and engine specifications.