Energetic and pollutant emission analysis of a small diesel engine fuelled with diesel and diesel/RME blend

This paper shows an energetic analysis of a small diesel engine for micro-cogeneration applications at different engine operating conditions. The aim is to evaluate the opportunity to perform cogeneration at different engine speeds in order to strictly satisfy with the electrical demand while also providing heat from the engine. The investigation was carried out on a prototype three-cylinder engine with 1000 cc of displacement. The engine is equipped with a direct common-rail injection system that reaches a maximum pressure of 1400 bar. The engine is provided with two emission reduction systems: a cooled EGR and an oxidation catalyst for the reduction of NOx, and CO/HC emissions, respectively. Tests were carried out with conventional diesel fuel and a biodiesel blend; in particular, a 20% v/v concentration of rapeseed methyl ester (RME) mixed with diesel fuel was used. Combustion characteristics of the engine were analysed by means of both in-cylinder pressure and rate of heat release traces. The heat recovery from the engine cooling water and from the exhaust gas was calculated. Gaseous emissions were measured at the exhaust. A smoke meter was used to measure the particulate matter concentration. The sizing and the counting of the particles were performed by means of an engine exhaust particle sizer spectrometer. The results presented in this paper can be useful for the design of more efficient and cleaner energy systems. It was found out that the adding of 20% v/v of RME to diesel fuel does not affect significantly both the fuel conversion efficiency and the engine energetic flows. The adding of 20% v/v of RME to diesel fuel results in lower exhaust emissions. Nevertheless, at high engine speed, B20 emits larger particles because of the more advanced combustion with respect to diesel fuel. It can be argued that the B20 combustion process can be optimized phasing properly the injection.