Mixture of glycerol ethers as diesel bio-derivable oxy-fuel: Impact on combustion and emissions of an automotive engine combustion system

The effects on combustion and emissions of a bio-derivable glycerol-based ethers mixture (GEM) usable in a compression ignition engine have been investigated. The tests were performed on a single cylinder research engine derived from a Euro5 compliant four cylinder engine for passenger car application. The experimental methodology has considered the comparison among three fuels: (1) a reference diesel; (2) a mixture consisting of 90 vol.% diesel and 10 vol.% of GEM; (3) a blend consisting of 80 vol.% diesel and 20 vol.% of GEM. The tests were carried out in some characteristic key points of the New European Driving Cycle (NEDC) emission homologation cycle. These points allowed an estimation of the blend impact on the performance of a real four-cylinder engine (one cylinder of which is represented by the research engine) over the NEDC. Both regulated and unregulated pollutant emissions have been measured during the test campaign. In particular, apart from the regulated emissions, the concentration of aldehydes and carbonaceous particles at the engine exhaust has been determined in some test points. The results have shown the possibility to burn the diesel/GEM blends without any significant impact on combustion characteristics and efficiencies, while, due to the oxygen content of the GEM, important benefits were obtained in terms of NOx-PM trade-off and emissions of particles at the exhaust. At medium-high load conditions, there was 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. Regarding the emissions of aldehydes, the results showed that the GEM addition favoured the increasing of carbonyl compounds at low engine loads, while at higher loads no significant variation has been detected by burning GEM.