Verification of the Impact of Coefficient of Drag Variation due to Natural Wind on Fuel Consumption based on Actual Driving Data

It is often assumed that the actual fuel economy on public roads is affected by natural wind and that this could be contributing to discrepancy between catalog fuel economy and actual fuel economy, owing to the increased yaw angle and drag coefficient (CD). However, the impact of yaw characteristics alone on fuel economy during actual driving has not been verified or proven as it is difficult to obtain actual driving data under uniform conditions. For this reason, shape optimization is normally performed at zero-yaw through the aerodynamic development phases. In this paper, two vehicles with different yaw sensitivity characteristics are driven simultaneously, and fuel economy measurements are performed simultaneously with ambient airflow, environment, and vehicle conditions, and the results where the conditions of the two vehicles match are extracted to clarify the impact of the differences of yaw characteristics on fuel economy. The obtained results matched the values predicted by theoretical calculations for the impact of yaw angle on fuel economy and estimated the ratio of the rate of change in fuel efficiency (⊿FE) to the rate of change in drag coefficient (⊿CD) to be +2.4%/-10ct. This is a numerical confirmation of the impact of yaw angle on fuel economy through verification based on actual driving data, and is an important indicator in optimizing aerodynamic characteristics. This research demonstrates the importance of the yaw angle in aerodynamic development and suggests a new direction for shape optimization.