A Methodology for Monitoring On-Road CO ₂ Emissions Compliance in Passenger Vehicles

The European Union road transport CO₂ emissions regulation foresees mandatory targets for passenger vehicles. However, several studies have shown that there is a divergence between official and real-world values that could range up to 40% compared to the NEDC reference value. The introduction of the Worldwide Harmonized Test Protocol (WLTP) limited this divergence, but it is uncertain whether it can adequately address the problem, particularly considering future evolutions of vehicle technology. In order to address this issue, the recent EU CO₂-standards regulation introduces the monitoring of on-road fuel consumption and subsequently CO₂ emissions by utilizing On-Board Fuel Consumption Meters (OBFCM). In the near future, all vehicles should provide instantaneous and lifetime-cumulative fuel consumption signals at the diagnostics port. Currently, the fuel consumption signal is not always available. The current study investigates a monitoring approach that obtains and normalizes on-road vehicle operation data of existing vehicles and estimates on-road CO₂ emissions through vehicle simulation. The first step is to reconstruct the engine fuel consumption map, based on laboratory vehicle measurements in order to use it as reference data. Subsequently, a methodology is developed to set up a vehicle simulation model aiming at using the signals retrieved through the OBD port, under real-world operation, and to emulate data availability under a monitoring scheme. Subsequently, the methodology is validated with reference data from both measurements and simulations. In the current study, three vehicles were tested over both cold and hot conditions and it was found that under real-world conditions the divergence in the overall calculated CO₂ emissions was below ±5% between simulated and measured values.