Abstract
In the last years, increasing attention has been paid to biofuels for their potential to reduce both CO_2 emissions, considered one of the major greenhouse gas (GHG), and particulate matter mass emissions. Biodiesel can be classified in 1^<st> and 2^<nd> generation fuels. First generation biodiesel is produced from vegetable oils and animal fats through a transesterification process. The 2^<nd> generation of alternative fuel was obtained from the well-known Fischer-Tropsch synthesis process. The physical properties and chemical composition of biofuels are quite similar with respect to the conventional diesel fuel even if they can alter the combustion processes in terms of performance and emissions. In this paper, the effect of the alternative diesel fuels on particle formation and emissions was analyzed by means of optical techniques and conventional methods. The measurements were carried out on a direct injection (DI) Common Rail (CR) transparent research diesel engine. In-cylinder broadband UV-visible measurements were used to acquire information about the soot size distribution. The particulate emissions were characterized at the exhaust by means of an electrical low pressure impactor (ELPI), for the particle counting and sizing, and an opacimeter, for the smoke opacity (particulate mass concentration) measurement. The engine was fuelled with conventional diesel and two alternative fuels, chosen as representative of the first generation biofuel, namely RME, and second generation biofuel, GTL, at two engine operating conditions, 1500 rpm x 2 bar and 2000 rpm x 5 bar of BMEP, typical of New European Driving Cycle.
