A Comparison of Light-duty Vehicle Emissions over Different Test Cycles and in Real Driving Conditions

The European Commission is examining test procedures to ensure that light-duty vehicle emissions are well controlled both in real use and over the legislative test cycle. At the same time, the UN Working Party on Pollution and Energy (GRPE) has developed a Worldwide harmonised Light vehicles Test Procedure (WLTP) that is expected to be used for Type Approval in the EU in the future. To identify and understand the differences in emissions that may arise between these new methodologies and between them and existing procedures, AECC has conducted a series of tests on modern light-duty vehicles using both on-road emissions measurements and chassis dynamometer tests. For the on-road measurements Portable Emissions Measurement Systems were used to measure emissions over pre-selected routes. Chassis dynamometer emissions tests were conducted over the current legislative test cycle (NEDC New European Driving Cycle), the Common Artemis suite of test cycles (CADC), the new Worldwide Light-duty Test Cycle (WLTC – the test cycle for WLTP) and a set of cycles produced by a Random Cycle Generator based on ‘short trip’ segments from the EU driving database that was used to construct WLTC. This paper examines the results of these tests and highlights the key differences between the various chassis dynamometer test cycles and between them and the on-road measurements using PEMS equipment. The test results show that there can be substantial differences for some pollutants measured as ‘real driving emissions’ (RDE) using PEMS equipment, compared to the test cycles.