Analysis of the Impact of the WLTP Procedure on CO2 Emissions of Passenger Cars 2019-24-0240
Until 2017, the pollutant emissions and fuel consumption Type Approval (TA) procedure for light duty vehicles in Europe was based on the New European Driving Cycle (NEDC), a test cycle performed on a chassis dynamometer. However several studies highlighted significant discrepancies in terms of CO2 emissions between the TA test and the real world, due to the limited representativeness of the actual test procedure. Therefore, the European authorities decided to introduce a new, up-to date, test procedure capable to closer represent real world driving conditions, called Worldwide Harmonized Light Vehicles Test Procedure (WLTP). This work aims to analyse the effects of the new WLTP on vehicle CO2 emissions through both experimental and simulation investigations on two different Euro 5 vehicles, a petrol and a diesel car, representatives of average European passenger cars. The study also considers the effect of the engine warm-up and the impact of the start-stop technology in this new TA scenario. It was found that, although the higher test mass and Road Loads (RLs), as well as the higher driving cycle dynamics imposed by the WLTP, generated an increase of cycle energy demand of 44% for the petrol car and of 23% for the diesel car, the CO2 emissions increased in the same proportion only for the diesel car, while they increased only of 10% for the petrol car, thanks to the increase of the internal combustion engine efficiency along the WLTC cycle. Finally, the effectiveness of the start-stop was found to be reduced by about one half for both vehicles when passing from the NEDC to the WLTP.