Investigation of the effect of compression ratio on the combustion behavior and emission performance of HVO blended diesel fuels in a single-cylinder light-duty diesel engine

Hydrotreated vegetable oil (HVO) is a renewable high quality paraffinic diesel that can be obtained by the hydrotreating of a wide range of biomass feedstocks, including vegetable oils, animal fats, waste oils, greases and algal oils. HVO can be used as a drop-in fuel with beneficial effects for the engine and the environment. The main objective of this study was to explore the potential of HVO as a candidate bio blendstock for new experimental formulations of diesel fuel to be used in advanced combustion systems at different compression ratios and at high EGR rates in order to conform to the Euro 6 NOx emission standard. The experiments were carried out in a single-cylinder research engine at three steady-state operating conditions and at three compression ratios (CR) by changing the piston. The set of fuels comprised a commercial EN590-compliant diesel fuel and four experimental fuels formulated ad hoc to investigate the effect of natural cetane provided by the HVO in comparison with artificial cetane. The fuel quality has proved to affect the specific fuel consumption, the maximum pressure gradient and the regulated emissions at all the tested CR. The use of high-cetane number HVO blends reduced the HC and CO emissions derived from incomplete combustion at all operating conditions, while the effect on PM emissions was dependent on the combustion mode, whether conventional diesel combustion or premixed charge combustion ignition (PCCI). The comparison of results obtained with the HVO blends and the base fuel treated with the cetane improver suggests that the cetane number was the single most influent factor on engine performance.