A Comparison of Tailpipe Gaseous Emissions from the RDE and WLTP Test Procedures on a Hybrid Passenger Car

Non-plugin hybrids represent a technology with the capability to significantly reduce fuel consumption (FC), without any changes to refuelling infrastructure. The EU market share for this vehicle type in the passenger car segment was 3% in 2018 and this powertrain type remains of interest as an option to meet the European Union (EU) fleet average CO₂ limits. EU legislative procedures require emissions limits to be met during the chassis dynamometer test and in the on-road real driving emissions (RDE) test, while official CO₂/FC figures are quantified via the laboratory chassis dynamometer test only. This study employed both legislative test procedures and compared the results. Laboratory (chassis) dynamometer testing was conducted using the Worldwide Harmonised Light Vehicles Test Procedure (WLTP). On-road testing was carried out in accordance with RDE requirements, measuring the concentration of regulated gaseous emissions and the number of solid particles (PN). Dynamic parameters and other characteristic properties were determined for each RDE test. Compliance with such requirements allowed the assessment of harmful compound emissions to which the latest requirements of the standard for non-plugin hybrid vehicles were applied. Comparisons of the results from the two test procedures revealed varying behaviour from compound to compound, with differences caused by certain characteristics of the RDE/WLTP tests, such as the proportion of urban driving, the frequency of stops and the mean speed, as well as ambient temperature. Overall, harmful emissions were shown to be low under almost all driving conditions, even for test conditions generally thought to cause higher emissions.