The Interaction of Flow-Field and Turbulence on Flame Development using High-Speed Combustion PIV

Abstract

The current gasoline engines are being pushed by researchers as well as the manufacturers to meet with the stringent demands and regulations regarding its efficiency, fuel economy and harmful emissions. Ultra-lean burning accompanied by higher turbulence and flow level are currently the best options for these engines to successfully meet these criteria. This study explores the turbulent flame structure inside an real operating engine environment in an attempt to improve the knowledge base of this area and hence provide useful information for engine developers, researchers and simultation models. A newly developed high-speed PIV technique that allows time-resolved measurement of both flame front and flow field simultaneously was applied to observe the flame structure and its relationship to the engine flow and turbulence. The results images demonstrated that the flame propagation is quite influenced by the general flow field and large scale eddies in which it can enhance, diminish and guide the flame propagation. This effect is especially notable in lean burning cases. Flame front generally grows in the direction of existing strong bulk in-cylinder flow and does not propagate if encountering a counter flow. The turbulence level of the unburned area is enhanced in these existing bulk flow stream as the flame propagates through them. Small scale eddies have a strong effect on flame curvatures and wrinkleness which can also help to push the flame propagation through difficult bulk-flow conditions.