Some Repeatability and Reproducibility Issues in Real Driving Emission Tests

The new European Commission Regulations for vehicle certification include a new laboratory procedure for fuel consumption and require Real Driving Emissions (RDE) to be gauged on-road with Portable Emissions Measurement Systems (PEMS). The goal of this investigation is to underline some critical issues in the development of RDE cycles with particular reference to the repeatability on-road and the reproducibility on-track. More specifically, the study includes an optimization of the route for RDE cycles to ensure robustness with respect to traffic conditions, an analysis of emissions variability on-road in hot weather and a discussion about the possibility to reproduce RDE cycles on-track. The tests were performed with a start&stop Diesel Class3b vehicle that was equipped with a PEMS instrumentation and tested over an optimized route in summer in the southern Italy. The tests on the track were performed on the testing facilities of the Nardò Technical Center. The emissions levels measured in the on-road and on-track test were found to be strongly affected by ambient conditions together with engine load and speed and cycle specification in terms of speed and acceleration. This result underlines the necessity of improving the corrections for NO_x versus ambient temperature and humidity used in the European Regulation and suggests the possibility to correlate the emissions of NO_x and CO₂ to some parameters of RDE tests: vehicle speed and acceleration, engine load and speed, ambient temperature and humidity.