Fuel Effects on Regulated and Unregulated Emissions from Three Light-Duty Euro 5 and Euro 6 Diesel Passenger Cars

Substantial advances in European road vehicle emissions have been achieved over the past 3 decades driven by strengthening revisions in emissions legislation and enabled by advances in fuel, vehicle engine and emissions control technologies. As both vehicle technology and emissions legislation in Europe continue to evolve, Concawe has conducted a study to examine the opportunities that fuels can provide to further reduce emissions from light-duty diesel passenger cars. Three European diesel cars spanning Euro 5, Euro 6b and Euro 6d-TEMP emissions certification levels have been tested over the cold-start WLTC (Worldwide harmonized Light-duty Test Cycle) with 6 fuels: an EN590-compliant B5 (petroleum diesel containing 5% biodiesel by volume), a bio-derived paraffinic diesel, a 50:50 blend of the aforementioned fuels, a low density petroleum-derived B5, a B30 and the same B30 additized with a high dose of cetane number improver. Results have shown that low density fuels with high hydrogen to carbon (H/C) ratio are capable of delivering benefits in tank-to-wheels CO₂ (carbon dioxide), CO (carbon monoxide), HC (hydrocarbons), other greenhouse gases and NO_x (oxides of nitrogen), whereas no further benefits were measured in NH₃ (ammonia) or in PN (particle number) at the low baseline levels produced by the vehicles. Compared to B5, B30 gave a significant increase in NO_x at the tailpipe from the Euro 5 car and engine-out from the Euro 6d-TEMP car but no tailpipe detriments in NOx were measurable in either of the Euro 6 cars, due to the good performance of their NOx aftertreatment devices. The latter results show that some fuel qualities previously important to control emissions such as PN or NOx have become less impactful with the latest engine technologies. The addition of cetane number improver to the B30 did not reduce NOx. The findings suggest that high H/C ratio diesel fuels could offer benefits to both emissions affecting local air quality and to greenhouse gas emissions on a tank-to-wheels basis. The addition of higher FAME (Fatty Acid Methyl Ester) levels to fuels can be used to increase renewable fuel contribution resulting in no penalty in NOx emissions from newer technology vehicles. Compatibility of these fuels with the existing vehicle fleet would require further specific consideration.