Characterization of PCCI Combustion in a Single Cylinder CI Engine Fuelled with RME and Bio-Ethanol

This paper reports experiments on a single-cylinder direct-injection compression ignition engine operating in premixed charge compression ignition (PCCI) combustion mode. The engine was fuelled with pure rapeseed methyl ester (RME) and bio-ethanol. RME was injected in the combustion chamber by common rail (CR) injection system at 800 bar and bio-ethanol in the intake manifold by commercial port fuel injection system at 3.5 bar. The effects of different percentage of bio-ethanol were studied by means of both the in-cylinder heat release analysis and the high-speed UV-visible chemiluminescence visualization. The pollutant formation and exhaust emissions of the engine operating in dual fuel mode were evaluated.

The increase of the bio-ethanol content improved the brake thermal efficiency slightly even if the brake fuel consumption increased. However, the choice to inject two biofuels decreases both the smoke opacity and NO_x concentration. These results were analyzed considering the data obtained by spectroscopy measurements in the combustion chamber. In particular, the high presence of radical species such as OH, HCO, and H₂CO contribute to describe the chemical reactions and physical processes involved in dual fuel combustion mode.