|NOx comparisons of the different blends. Click to enlarge.|
A research project, sponsored by the German Union for the Promotion of Oil and Protein Plants (UFOP) and Shell Research Limited, has made comparative exhaust gas studies using Shell Middle Distillate (GTL—gas-to-liquids synthetic fuel) with lubrication additives; fossil diesel fuel (DF); rapeseed oil methyl ester (RME, or biodiesel); premium diesel fuel (PDF—comprised of 60% DF; 20% RME and 20% GTL); and a blend of 95% GTL and 5% RME (B5GTL).
Overall, GTL consistently produced lower emissions than regular DF, with particularly low oxides of nitrogen emission and significantly lower mutagenicity. Biodiesel showed advantages in the hydrocarbon, carbon monoxide and particle mass emissions.
The premium diesel blend shared those low emissions, but caused—like the biodiesel—high emissions of ultra fine particles. B5GTL showed the expected combination of GTL with little shifting to RME; by contrast, the premium diesel blend obtained non-linear effects, including a lower particle mass emission but also unexpectedly high mutagenicity.
|PM comparisons of the different blends. Click to enlarge.|
The research was a network project of the Institute for Technology and Biosystems Engineering of the German Federal Agricultural Research Centre (FAL) in cooperation with the Steinbeis Transfer Center for Biofuels and Environmental Measurement Technology in Coburg and the Center for Occupational and Social Medicine at the University of Göttingen where the environmental impacts of different diesel fuels were examined.
The researchers conducted the preliminary test series on a 6-cylinder, 205 kW, Mercedes-Benz Euro-3 truck engine without exhaust gas after-treatment. The results—particularly the non-linear emissions and impact changes—suggest that the studies must be extended to Euro 4 vehicles with exhaust gas after-treatment in order to identify the advantages and dangers of random mixtures of fuels, to recognize the interactions, and to pass them on the engine developers.
The project is also the start of the future formulation of an engine and environmentally-tolerable biofuel that lies in between neat BTL and neat RME.