Fuel effects on modern diesel passenger car and commercial vehicle emissions (Concawe Review 31.1)
As both vehicle technology and emissions legislation continue to evolve, Concawe has conducted studies to examine the multidimensional effects that fuels can have on greenhouse gases (GHGs) and pollutant emissions from diesel passenger cars (PCs) and commercial vehicles (CVs). Three diesel passenger cars spanning Euro 5, 6b and 6d-TEMP were tested in the PC study over the Worldwide harmonized Light-duty Test Cycle (WLTC), and a Euro VI bus and Euro V delivery truck were tested in the CV study over the World Harmonized Vehicle Cycle (WHVC) and Transport for London Urban Inter-Peak (TfL UIP) cycle. Test fuels used in the studies were common to both the PC and CV work: an EN 590-compliant B5, hydrotreated vegetable oil (HVO) sustainable paraffinic fuel, a 50/50% v/v blend of the aforementioned fuels, a low density petroleum-derived B5, a B30 containing 30% v/v sustainable fatty acid methyl ester (FAME) and the same B30 additised with a high dose of cetane number improver (CNI).
The expected tank-to-wheels reductions in CO2 were detected from low-density fuels versus EN 590 B5 due to their lower carbon intensity. Some benefits in pollutant emissions from low-density fuels were detected in older vehicle technologies but are reduced below any detection threshold in later technology vehicles due primarily to exhaust after-treatment (AT) effectiveness, and an engine-out benefit in NOx in the Euro VI bus manifested as a reduction in consumption of SCR (selective catalytic reduction) reductant (AdBlue). The increased NOx emissions from B30 reported in some previous studies were not evident in any vehicle except the Euro 5 PC with no NOx AT.
The addition of CNI to B30 did not counter the increase in NOx observed in one vehicle, and it is postulated that this would be broadly the case in modern vehicles. N2O emissions from the vehicles fitted with NOx AT catalysts (lean NOx traps and SCR) can contribute around 5–7% of the total GHGs emitted, whereas this is less than 0.5% in vehicles without NOx AT, highlighting the challenges of optimising vehicle technology to minimise both GHG and pollutant emissions. Overall, this work illustrates the complex and evolving interactions between fuels and vehicle technology affecting emissions.