19 May 2014

Impact of FAME on the performance of three Euro 4 light-duty diesel vehicles – Part 1: Fuel consumption and regulated emissions

Report no. 6/14: By 2020, EU legislation will require that 10% of the total transport fuel energy demand is met by the use of renewable energy, primarily by blending bio-components. Although many types of blending components for diesel fuels are being considered to achieve this requirement, Fatty Acid Methyl Esters (FAME) are the most likely to be used in significant volumes over the coming decade. FAME products have been used in Europe for many years, both as blends and as neat fuels, in certain niche markets.

One unanswered question concerning FAME/diesel fuel blends is the effect of FAME on fuel consumption. Since FAME has a slightly lower energy content compared to hydrocarbon-only fuels, a higher volumetric fuel consumption is expected unless the vehicle is able to compensate in some way for the energy loss associated with the bio-component in diesel fuel. To answer this question, Concawe completed a vehicle study in which four diesel fuel blends with FAME (as Rapeseed Methyl Ester (RME)) were tested in three Euro 4 light-duty passenger cars, each equipped with different after-treatment technologies. The FAME contents of these fuels varied from 0% to 50% v/v in order to accentuate the effect of FAME on the energy content of the blended diesel fuels.

The programme was statistically designed to give a robust and repeatable testing schedule so that fuel consumption and tailpipe emissions data could be reliably collected over regulatory and transient driving cycles. The vehicle study was conducted for Concawe by the Laboratory for Applied Thermodynamics of the Aristotle University of Thessaloniki, Greece. Fuel consumption data for all three vehicles over all driving cycles show that the volumetric fuel consumption increases in direct proportion with increasing FAME content and the decreasing volumetric lower heating value (energy content) of the FAME/diesel fuel blends. There was no detectable change in the energy efficiency of the vehicles on different fuel blends and they were not able to compensate for the lower energy content of the FAME/diesel blends through improved performance. Increasing the FAME content also reduced the PM but increased the NOx, HC, and CO emissions.

The overall impact of FAME on tailpipe emissions was small when compared to the variations in emissions seen for different driving cycles and for different vehicles over the same driving cycle. No significant difference in emissions performance was observed for the two types of Diesel Particulate Filter (DPF) aftertreatment systems that were tested in these vehicles. It is expected that these results will be of importance to those interested in the impact of FAME in diesel fuel on Well-to-Wheels fuel consumption and on tailpipe emissions from modern light-duty passenger cars.