Experimental characterization of diesel combustion using glycerol derived ethers mixtures

In this paper the characteristics of a mixture of glycerol-based ethers usable in a compression ignition engine are investigated, in terms of efficiency and emissions. Alternative pathways for the energetic exploitation of biodiesel derived glycerol became of increasing interest as the biodiesel production was increased worldwide. Because of its detrimental physical and chemical properties, raw glycerol is hardly usable in conventional internal combustion engines (ICE). However, etherification of glycerol with tert-butyl alcohol and isobutylene allows obtaining a mixture mainly composed of higher glycerol ethers (GEM) suitable for compression ignition engines. Thus, the aim of this research study was to test a mixture of mono-, di- and tri-tert-butyl ethers of glycerol in blend with a commercial diesel fuel in a compression ignition engine, evaluating the fuel efficiency and the impact on the pollutant emissions. The tests were performed on a single cylinder research engine derived from a Euro5 compliant four cylinder engine. The test methodology considers the comparison among three fuel blends: 1) a mixture consisting of 90% v/v diesel and 10% v/v of GEM; 2) a blend consisting of 80% v/v diesel and 20% v/v of GEM; 3) a reference diesel. The tests were carried out in five characteristic key points of the NEDC emission homologation cycle (New European Driving Cycle). These points allow estimation of the blends impact on the performance of a real four-cylinder engine (one cylinder of which is represented by the research engine) over the NEDC. The results have shown the possibility to burn the diesel/GEM blends without significant impact on combustion characteristics and efficiencies while, due to the oxygen content of the GEM, important benefits are obtained in terms of NOx-PM trade-offs and emission particles at the exhaust. At medium-high load conditions there is a maximum decrease of about 70% in terms of PM emissions compared to a slight increase of NOx. At low load conditions, a maximum increase of HC and CO of about 50% has been detected