Comparison of Real World Emissions in Urban Driving for Euro 1-4 Vehicles Using a PEMS

An on-board emission measurement system (PEMS), the Horiba OBS 1300, was installed in Euro 1-4 SI cars of the same model to investigate the impact of vehicle technology on exhaust emissions, under urban driving conditions with a fully warmed-up catalyst. A typical urban driving loop cycle was used with no traffic loading so that driver behavior without the influence of other traffic could be investigated. The results showed that under real world driving conditions the NOx emissions exceeded the legislated values and only at cruise was the NOx emissions below the legislated value. The higher NOx emissions during real-world driving have implications for higher urban Ozone formation. With the exception of the old EURO1 vehicle, HC and CO emissions were under control for all the vehicles, as these are dominated by cold start issues, which were not included in this investigation. The CO and HC emissions for hot catalysts were low and modeling of real world emissions for the parts of journeys where the catalysts was hot, using legislated emissions per km, would over predict the real world CO and HC emissions. Cold start emissions should be treated as a separate emissions quantity that occurs with all cold start journeys at the start of the journey and should not be spread out over the 11km of the NEDC or 18km of the US FTP75 test cycles as at present. The fuel consumption and CO2 emissions were of the order of double the legislated NEDC values for real world emissions for Euro 1-4 vehicles. The higher acceleration rates after junctions were the principle cause of the higher fuel consumption and NOx emissions.