NO2/NO emissions of gasoline passenger cars and light-duty trucks with Euro-2 emission standard

Abstract

The total amount, as well as the partitioning, of the NOx emissions of six gasoline passenger cars and 10 light-duty trucks, all of Euro-2 emission standard, was measured in this study. The measurements were carried out in the NEDC and FTP75 cycles, in the German “Bundesautobahnzyklus” (federal motorway cycle) and in Swiss real-world cycles. All the vehicles were provided by private owners and brought directly from the road to the chassis dynamometer. In order to obtain results which are as realistic as possible, no servicing was carried out. Depending on their mass, gasoline light-duty trucks of the Euro-2 emission standard have a legal HC+NOx limit which is 20–40% higher than for gasoline passenger cars of the same generation. The measurements show that light-duty trucks emit about eight times more NOx in Swiss real-world cycles compared to passenger cars. However, this cannot be due to the higher engine load alone; there have to be major differences in engine construction, engine tuning or in the layout of the exhaust gas aftertreatment system. It can be observed that the overall catalyst efficiencies of light-duty trucks are substantially lower than those of passenger cars. Apart from this difference in total NOx emissions, an interesting difference in the partitioning of NO and NO2 for passenger cars and light-duty trucks can be observed. On average, about 5.3 mass-percent of the NOx emissions from the measured passenger cars are emitted as NO2, without a clear effect on the velocity pattern driven. In contrast to the behaviour of passenger cars, the measured light-duty trucks show a strong dependence on the velocity pattern. They emit on average 18.4 mass-percent NO2, but this figure goes up to 38.3 percent for motorway driving. The measurements show that the NO2 mass fraction depends strongly on the absolute NOx emission level: the more NOx is emitted, the higher is the NO2 mass fraction.