In spite of the recent trend, voted toward the reduction of renewable energy sources deriving from crops, the EC Commission proposes that the proportion of energy from renewable sources in the transportation sector should be at least 20 % of its final energy consumption by the year 2020. In this framework, the activities aiming to study the effects on engine performances, emissions and fuel consumption of alternative diesel fuel receive continue stimulations and supports. In this paper, results of the different behavior of biodiesel fuels in the injection process and their impact on the air-fuel mixture preparation are reported. The injection process characterization has been carried out in a non-evaporative high-density ambient in order to measure the fuel injection rate and the spatial and temporal distribution of the fuel. Moreover, the injection and combustion processes have been characterized in an optically accessible single cylinder Common Rail diesel engine that represented evaporative conditions similar to the real engine.
The studied injections have been chosen for engine working conditions of 1500 rpm at 2 bar of BMEP. A double injection strategy (pilot+main) has been adopted and a pilot energizing time has been calibrated to deliver 1.0 mm3. First generation of biodiesels like Rapeseed Methyl Ether (RME) and Soybean Methyl Ether (SME) and second generation of biodiesel like gas to liquid (GTL) have been mixed with reference diesel fuel (50% + 50%) and characterized in non-evaporating ambient while pure diesel fuel and its GTL mixture have been studied in evaporating ambient.
Images of evolving fuel in non-evaporative conditions, captured by a high resolution CCD camera at different instant from the start of injection and for different operative conditions, have been processed extracting the main parameters of the jet evolution: tip penetration, spray-cone angle, spray density distribution. These data have been also acquired in the combustion chamber of the optical diesel engine by means of a high resolution CCD camera synchronized with the injection events. Moreover the combustion processes have been studied and the pollutant emissions have been measured for several engine working conditions and biodiesel mixes.