This paper reports the study of the effects of alternative diesel fuel and the impact for the air-fuel mixture preparation. The injection process characterization has been carried out in a non-evaporative high-density environment in order to measure the fuel injection rate and the spatial and temporal distribution of the fuel. The injection and vaporization processes have been characterized in an optically accessible single cylinder Common Rail diesel engine representing evaporative conditions similar to the real engine.
The tests have been performed by means of a Bosch second generation common rail solenoid-driven fuel injection system with a 7-holes nozzle, flow number 440 cc/30s @100bar, 148deg cone opening angle (minisac type). Double injection strategy (pilot+main) has been implemented on the ECUs corresponding to operative running conditions of the commercial EURO 5 diesel engine. First and second generation biodiesel, like Soybean Methyl Ester (SME) and Gas To Liquid (GTL), have been used and their behaviour has been compared to the reference diesel fuel. Images of evolving fuel, acquired in non-evaporative conditions and in the combustion chamber of the optical diesel engine, have been processed extracting the main parameters of the jet evolution. The different characteristics of the investigated fuels have produced differences in spray global performances in terms of penetrations and cone-angles. Different spatial distributions of the liquid fuel in the chamber have been assessed by the analysis of the luminous intensity along the jet direction. Finally, a comparison of the tip penetration in both evaporative and non evaporative systems has been carried out.
