Substantial advances in European road vehicle emissions have been achieved over the past three 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 effects that fuels can have on emissions, in this case from commercial road vehicles. A bus certified to Euro VI emissions level and a delivery truck certified to Euro V emissions level have been tested on a chassis-dyno over the World Harmonized Vehicle Cycle (WHVC) and Transport for London Urban Inter-Peak (TfL UIP) test cycles with six fuels: an EN590-compliant B5 (petroleum diesel containing 5% biodiesel by volume), a bioderived 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 (CNI). Results show reduced NO_x reductant (AdBlue) consumption with paraffinic diesel in the Euro VI bus due to lower engine-out NO_x emissions. More surprisingly, higher hydrocarbon emissions were observed with some low-density hydrocarbon fuels in the Euro V truck. Compared to B5, B30 with and without CNI did not affect tank-to-wheel (TTW) CO₂, volumetric fuel consumption or NO_x by statistically significant margins. When considered with the findings of a complementary light-duty study, it is apparent that low-density diesel fuels could offer overall benefits to both emissions affecting local air quality and to greenhouse gas emissions on a TTW basis. The addition of higher fatty acid methyl ester (FAME) levels to fuels can be used to increase renewable fuel contribution resulting in no penalty in NO_x emissions from modern technology vehicles. Compatibility of these fuels with the existing vehicle fleet would require further specific consideration. Outside of fuel properties considerations, Euro VI aftertreatment systems can increase N₂O emissions at the tailpipe through chemical reactions in the catalyst. This can translate into about 10% contribution of N₂O emissions to the overall GHG emissions of the vehicle.

Auxiliary diesel heaters are commonly used in all types of vehicles in cold climates and conditions around the world. Electric buses used in public transport utilise diesel-burning auxiliary heaters to provide thermal comfort for passengers under cold weather conditions while maintaining the operational range otherwise reduced by electric heating. However, the downside of utilising diesel burners is that they cause similar exhaust pollutants to conventional diesel vehicles. Because the emission control for auxiliary heaters is lax, the diesel burners typically lack any exhaust aftertreatment (EAT), resulting in potentially high local emissions. As the public transport sectors around the world seem to transit from traditional internal combustion engine-vehicles to battery electric applications, the significance of the emissions caused by diesel auxiliary heaters is continuously increasing. EVs are generally considered zero-emission vehicles but the implementation of diesel burners is evidently conflicting with this concept. Nevertheless, publicly available experimental results from studies around this topic are surprisingly limited. The data of the few available publications are not directly comparable because there is no direct procedure or protocol for determining the exhaust pollutants from auxiliary heaters in real-world conditions at present. As a result, assessing the direct effect of the pollutants caused by electric vehicles utilising auxiliary heaters in the public transport is challenging. This study addresses this problem by introducing two methods for measuring auxiliary heater emissions; first, a field-test method that is applicable for a quick screening of the emissions of multiple heater units; secondly, a laboratory test method for a more detailed emission characterisation in a simulated real-world operation environment. In these experiments, the primarily objective was to study the emissions of the auxiliary heaters, including CO₂, CO, NO_x and soot. The heater operation was found to be cyclic with numerous start-ups during its typical operation. The cyclic operation resulted in concurrent emission peaks in CO and soot. Measurements of actual operation showed auxiliary heater utilisation rates similar to the controlled measurements, although the whole temperature range of the controlled measurements was not reached in real-world conditions. The measurements conducted during the field screening revealed high variations between emissions of individual units. A further screening of auxiliary heaters would provide a better outlook for the mitigation of their emissions.