EXPERIMENTAL INVESTIGATION ON PERFORMANCE AND EMISSIONS OF AN AUTOMOTIVE DIESEL ENGINE FUELLED WITH BIOFUELS

Biodiesel is the biofuel most commonly used in Europe, covering approximately 80% of the biofuel market. However, the relationship between biofuel industry and food prices push towards the adoption of new generation biodiesels which could minimize the impact of biofuels production on human food chain. Biodiesel sourced from non-edible seed oils like Jatropha Curcas could therefore be a viable solution for biodiesel production, since allows green cover to wasteland. More recently, also Hydrotreated Vegetable Oil (HVO), obtained by means of a refinery-based process that converts vegetable oils into paraffinic hydrocarbons, has been gaining an increasing attention. The effects of using high percentage blends of ultra low sulphur diesel and biofuels (FAME and HVO) in a Euro 5 small displacement passenger car diesel engine on combustion process, full load performance and part load emissions have been evaluated in this work. Moreover, a characterization of Particulate Matter (PM) in terms of mass, chemical composition and particles number and size distribution was assessed as well. The impacts that fuels with different physical and chemical properties may have on injection, combustion and on ECU calibration process were evaluated by means of specific tests campaign involving different injection timings under part load operation. Results highlighted that the implementation of models for blending detection, on engines ECUs, could be of crucial importance for a wider usage of biofuels in transportation sector. In addition, the effects on engine torque were analyzed, for both a standard ECU calibration (i.e. without any special tuning for the different fuel characteristics) and for a specifically adjusted ECU calibration obtained by properly increasing the injected fuel quantities to compensate for the lower Lower Heating Value (LHV) of the biofuels: with the latter, the same torque levels measured under diesel operation could be observed with the biodiesel too, with lower smoke levels, thus highlighting the potential for maintaining the same level of performance while achieving substantial emissions benefits. Moreover, the effects of biodiesel blends on brake specific fuel consumption and on engine-out exhaust emissions (CO2, CO, HC, NOx and smoke) were also evaluated at several part load operating conditions, representative of the New European Driving Cycle (NEDC). Both standard and specific calibrations were evaluated, highlighting an average rise of fuel consumption in good agreement with LHV decrease, at same fuel conversion efficiency and CO2 emissions. A decrease of NOx emissions when using a specifically adjusted engine calibration, along with a considerable smoke emission reduction were observed as well. Due to increasing concerns about the hazardous effects that particulate matter could have on human health, PM emissions were evaluated under normal engine operating mode at part load operation. PM gravimetric analysis at medium and high load operating points showed a good correlation with soot measurements carried out by means of standard laboratory equipment (i.e. smokemeters). On the contrary, at low loads, the same instrument underestimated the Soluble Organic Fraction (SOF) fraction of PM especially when biofuel was used. Thermo-gravimetric analysis confirmed the outcomes from gravimetric analysis: the significance of standard measurements which are commonly carried out during the engine calibration activity should be carefully considered when biofuels are adopted. Finally, the assessment of the toxicological potential of PM when HVO and Rapeseed Methyl Ester (RME) were used was carried out. Results highlighted that PM from HVO had a higher mutagenic effect respect to PM emissions obtained with other fuels.