Calculation of Heat Flux Integral Length Scales from Spatially-Resolved Surface Temperature Measurements in an Engine 910721

Instantaneous heat flux rates were measured in a spark ignited CFR engine. A new heat flux probe was used which had seven thin film platinum resistance thermometers, spaced 1 mm apart, on a Macor substrate. Instantaneous heat flux was measured at each sensor location and the integral length scale of heat flux was calculated from the spatial cross correlation data. A swirl flow condition was generated by use of a shrouded intake valve, and tumble flow was created by rotating the shrouded valve 90°. An unshrouded valve gave a more quiescent flow condition.
Under motoring conditions, peak heat flux was 70% higher for swirl flow conditions than quiescent flow conditions, and the total heat rejected during the closed portion of the cycle was 50% higher with the swirl flow than the quiescent flow. The peak heat flux for swirl flow compared to tumble flow was 30% higher and the total heat rejection was 10% greater. Heat flux integral length scales near TDC of compression were on the order of 1 mm and were greater for swirl flows than for either the tumble flow or the quiescent flow.
The heat flux integral length scale did not change for a change in compression ratio from 10 to 6, corresponding to a change in TDC clearance height from 12 mm to 22 mm.
Combustion had the effect of increasing the heat flux integral length scale over the unburned case. It is reasoned that the increased viscosity of the burned gases caused preferential dissipation of the shorter length scales.


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