Transient surface-heat-flux measurements in the exhaust of a SI engine

Surface-heat-flux measurements were performed at two locations in a straight-pipe extension of the exhaust-port of a SI engine. The measured surface-heat-flux history was characterised by a double peak, during the exhaust valve-open period. The largest peak resulted from the action of high-velocity, blowdown gases exiting the combustion chamber at the beginning of the exhaust process. The significantly lower second peak was due to the slower piston-driven gas motion that occurred during the displacement phase. During the closed-valve period, the local surface-heat-flux was found to be relatively low (10-45 kW/m(2)) in comparison to the peak heat flux (80-288 kW/m(2)), and to exhibit minimal decay. The predicted heat-flux histories from an engine-simulation analysis, which employed a heat transfer correlation developed by the authors, were in good agreement with the corresponding measured histories during blowdown, however, predictions were relatively poor during the displacement phase, both in magnitude and behaviour.