Analysis of tailpipe emissions, thermal efficiency and fuel consumption for urban real world driving using a SI passenger car as a probe vehicle

Air quality issues in urban areas are always a big concern. Air pollution especially NO2 and PM exceedances in cities are common. This is particularly true with congested traffic and the monitoring station is at the roadside. It is well known that road transport in the urban area is a major source of air pollution. Though all the vehicles have to comply the EU emission standards, the emissions were tested using the legislated standard driving cycles, which could not represent real world driving emissions. This is because compared to the legislated driving cycle, the real world driving uses different powers, different average speeds, different traffic congestion, different road gradients, different maximum acceleration rates, different cold start conditions, different numbers of stop/start events and occurs at different ambient temperatures and pressures and will inevitably have different emissions. In recognition of importance of real driving emissions, the EU plans to introduce RDE (Real driving emission) test procedure in 2017.
This work investigated real world emissions on a congested road by a roadside air quality monitoring station that exceeds European air quality standards for NOx and PM using a portable emissions measurement system (PEMS) and a Euro 4 SI passenger car. The PEMS used was the Temet FTIR with Horiba OBS pitot tube exhaust mass flow sensor and gas sampler. Twenty nine hot start repeat journeys were conducted at different times of the day (morning and evening rush hours, lunch time, night) so that a range of traffic conditions were included and eight cold start tests for the same journeys were conducted and compared with the hot start results and shown to give significantly higher emissions. The vehicle was equipped with thermocouple, lambda sensor and GPS for travel parameter analysis. The GHG including CO2, CH4 and N2O, nitrogen species in the exhaust gases including NO, NO2, N2O, NH3 and HCN and other emissions were analysed. The results were compared to the NEDC and WLTC. One of the suggestions from this work is that the proposal for the EU RDE test procedure do not include congested traffic driving and cold start which will compromise its expected purpose and effect.