High-speed IR thermography of radiant heat transfer on chamber wall impinged by diesel spray flame

To elucidate the mechanism of radiant heat transfer in the combustion chamber of diesel engines, radiant heat flux on diesel-spray-impinged wall surface was measured by high-speed IR thermography as a new method to examine the extremely unsteady and spatially varying wall heat transfer phenomena. High-speed imaging of infrared thermal radiation from the wall surface impinged by a diesel spray flame was performed using a high-speed infrared camera operating at 10,000 fps with a spatial resolution of 128 pixels × 128 pixels for a 30 mm field of view. To measure only the radiant heat flux—not the total heat flux—using high-speed IR thermography, a simple approach was taken by placing a MgF 2 window patch on the chromium-coated quartz window. This blocked the convective heat transfer from the spray flame to the chromium-coated quartz window. The radiant heat flux distribution spread circularly, preceding the convective heat transfer, and did not exhibit the radial stripes observed in the total heat flux measurements. This indicates a clear distinction between radiant and total heat flux phenomenon, demonstrating that the radiant heat flux was successfully isolated. As a result, it was demonstrated that the ratio of radiant heat flux to the total heat flux was almost 100% from the start of injection until impinging on the wall, and then gradually decreased. However, the time-averaged ratio for 5 ms after the start of injection was approximately 50%, which is significantly higher than previously reported. In addition, in case of DGM fuel, the total heat flux increased, however, the radiant heat flux decreased compared to that of diesel fuel.