Cyclically Resolved Flame and Flow Imaging in an SI Engine Operating with Future Ethanol Fuels

This work was concerned with study of the in-cylinder flow field and flame development in a spark ignition research engine equipped with Bowditch piston optical access. High-speed natural light (chemiluminescence) imaging and simultaneous in-cylinder pressure data measurement and analysis were used to understand the fundamentals of flame propagation for a variety of ethanol fuels blended with either gasoline or iso-octane. PIV was undertaken on the same engine in a motoring operation at a horizontal imaging plane close to TDC (10 mm below the fire face) throughout the compression stroke (30°,40°,90° and 180°bTDC) for a low load engine operating condition at 1500rpm/0.5 bar inlet plenum pressure. Up to 1500 cycles were considered to determine the ensemble average flow-field and turbulent kinetic energy. Finally, comparisons were made between the flame and flow experiments to understand the apparent interactions. The results revealed the relative influence of the bulk air motion on the overall development of the propagating kernel, with a tendency noted for the flame to migrate towards the hotter exhaust side of the engine despite no apparent complimentary bulk air motion in this direction in the two dimensional plane studied. This offset motion occurred with all fuels and may have significant consequences in similar central direct injection engine layouts. The phenomenon has been noted recently elsewhere in similar optical pent-roofed engines but without both flow and flame imaging being available.