Effects of a wave-shaped piston bowl geometry on the performance of heavy duty Diesel engines fueled with alcohols and biodiesel blends

Abstract

The effects of a new wave-shaped piston bowl design on combustion characteristics and engine out emissions were tested in a heavy duty Diesel engine fueled with conventional Diesel and fossil-free blends containing n-butanol, n-octanol, 2-ethylhexanol, hydrotreated vegetable oil, and rapeseed methyl ester. The compositions of the blends were chosen such that their cetane numbers matched that of fossil Diesel. Engine experiments were performed at four operating points from the European Stationary Cycle, with no modification of engine settings when switching between different fuels. A standard piston with omega geometry was tested using fossil Diesel and the fossil-free nBu30H (30% n-butanol and 70% hydrotreated vegetable oil by volume) blend, and the results obtained were compared to those achieved with the wave piston. In general, the fossil-free blends yielded significantly lower soot emissions than fossil Diesel but slightly higher NOx emissions. Relative to the standard piston, the wave piston accelerated the combustion of both Diesel and fossil-free blends, especially the diffusion combustion. The wave piston’s positive effects on thermal efficiency and soot emissions were more pronounced for conventional Diesel fuel than for oxygenated nBu30H.