Fuel consumption simulation of HDVs in the EU: comparisons and limitations

The CO2 certification procedures for HDVs in the EU and the United Stated use a combination of component testing and vehicle simulation to assign official CO2 emission and fuel consumption values. This paper analyzes the model structure, simulation flow, and limitations of the regulatory simulation tool used in the EU (VECTO) and compares it against the regulatory tool used in the United States (GEM). The analysis shows fundamental differences in the modeling approach between the regions. VECTO uses a backward-looking model architecture, in which the simulation flow occurs in the opposite direction of the actual energy and torque flows. GEM, on the other hand, uses a forward-looking architecture in which the driver interacts directly with the vehicle through the accelerator pedal, and the simulation proceeds in the same direction as the energy and torque flows.