Emissions from different alternative diesel fuels operating with single and split fuel injection

Abstract

Few factors affect diesel combustion and emissions more significantly than the composition of the fuel and the fuel injection process. In this paper, both of these factors are considered by comparing conventional, synthetic and vegetable oil-derived diesel fuels and by comparing a single pulse injection and a split (pilot and main) injection process. This paper focuses on characterization of the combustion process and emissions produced by three substantially different diesel fuels: an ultra low sulfur diesel fuel (BP15), a pure soybean methyl ester (B100), and a synthetic, practically free of sulfur and aromatic compounds, Fischer–Tropsch fuel (FT) produced in a gas-to-liquid process. The study was carried out in a direct injection (DI) 2.5 L common-rail turbodiesel engine working at four engine operation modes, spanning conditions of most interest in the engine map. In all modes the engine was tested with single and split injection (pilot and main), with constant start of injection (SOI), and without exhaust gas recirculation (EGR). Using the results from thermodynamic analysis, this study confirms that the ignition character of the fuel affects the start of the combustion process, notably for the whole combustion process when the single injection is used, and during the combustion process after the pilot injection when the split injection is used. In general, the FT fuel can reduce both NOx and PM specific emissions in all modes under both single and split injection modes, bypassing the nitrogen oxides-particulate matter (NOx–PM) trade-off. Finally, this work confirms that biodiesel can reduce the particle concentration. However, in some cases an increase of PM mass emission has been observed and this increase of the PM mass emission is due to unburned or partially burned hydrocarbon (HC) emissions.