A real world assessment of European medium-duty vehicle emissions and fuel consumption

Abstract

Emissions of road vehicles have a significant impact on climate change and air quality and in order to address these problems there have been regulatory actions globally in the last decades. Such actions have focused mainly on light and heavy-duty vehicles, which comprise the highest share of the fleet and are responsible for the majority of emissions in the field. However, there are also medium-duty vehicles with a maximum permissible mass between 3.5 and 12 tonnes in the European categories, which have been mostly overlooked until recently. These vehicles could have a low market share, but they are important as they circulate mainly in urban and suburban areas under transient conditions and often with congestion. This has a detrimental impact on the environment and human health due to greenhouse gas and pollutant emissions. However, there are limited studies for this vehicle category. The current work undertook to address this issue by focusing on medium-duty vehicles in Europe by attempting to establish a methodology to calculate reference emission values for CO₂, NO_x and CO to improve fleet monitoring. For this reason, two state-of-the-art vehicles were measured on-road under the EU verification test procedure. Naturally, the measurements represented the anticipated average European conditions of the route in terms of speed profile, road grade and distance. In order to provide emissions values that are representative of the European conditions a normalization process was needed. For this reason, the measurements were used to set up vehicle simulations in VECTO, the official simulation tool of the European Commission for calculating type-approval fuel consumption and CO₂ emissions. In this way, the simulations provided values ranging from 297 g/km to 373 g/km. Using the ratio of fuel consumption for NO_x and CO from the measurements, it was possible to derive reference pollutant values. For NO_x, they were found to be between 0.0557 and 0.0963 g/km, while for CO the values were at 0.047 g/km. These values could be used as emissions factors as in the Guidebook, which is the official tool for monitoring fleet emissions of the European Commission. The Guidebook offers several approaches to calculate emissions, depending on data availability with the most sophisticated being a calculation method using vehicle speed, loading share and road grade. Taking this into consideration, the current work developed a similar methodology using the simulation time-series to derive regression coefficients that enable the calculation of CO₂, NO_x and CO emissions under different operating conditions. In this way, this methodology can be applied to representative vehicles of the medium and heavy-duty categories that have been through the verification test procedure to determine representative emission factors for these vehicles. This methodology could be used to improve fleet emissions monitoring, but also as a simple simulation tool for any further studies in the field.