Infrared high-speed thermography of combustion chamber wall impinged by diesel spray flame

Abstract

As a demonstration of 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 wall surface impinged by a diesel spray flame was attempted using a high-speed infrared camera. A 35 mm-diameter chromium-coated quartz window surface was impinged by a diesel spray flame with an impinging distance of 27 mm from the nozzle orifice in a constant volume combustion chamber. The infrared thermal radiation from the back surface of the 0.6 µm thick chromium layer was successfully visualized at 10 kHz frame rate and 128 × 128 pixel resolution through the quartz window. The infrared radiation exhibited coherent and streaky structure with radial stripes extending and waving from the stagnation point. The width of the radial stripes, spatial amplitude and the period of the waving movement were comparable to the ones for turbulent heat transfer on the engine cylinder wall previously measured with a heat flux sensor, suggesting that they are resulting from the turbulent structure in the wall-impinging diesel flame. The radiation intensity was calibrated to temperature and converted to heat flux via 3-D numerical analysis of transient thermal conduction in the quartz window. The peak-to-peak variation amplitudes of temperature and heat flux among the radial stripes during the diesel spray flame impingement were about 20 K and 2.3 MW/m², corresponding to 13% of 150 K maximum temperature swing amplitude and 18 MW/m² maximum heat flux, respectively.