Tractive-Energy-Based Formulae for the Impact of Aerodynamics on Fuel Economy Over the EPA Driving Schedules 830304

A fuel consumption analysis has been made to determine the impact of changes in aerodynamic drag on fuel economy over the Environmental Protection Agency (EPA) driving schedules. It is based on the tractive energy required by vehicles to negotiate those schedules — specifically, on the fraction that is required to overcome drag. Formulae for this energy fraction that are applicable to any automobile have been previously derived. In conjunction with empirical inputs on closed-throttle fuel rate and the fuel consumption fraction for engine and vehicle accessories, an expression for the aerodynamic influence coefficient relating any percentage reduction in drag to the corresponding attainable percentage reduction in on-road fuel consumption has been formulated. The simple formula is used to show the effect of drag changes of various magnitude on EPA Urban, Highway, and Composite fuel consumptions. The equivalent reductions in vehicle mass and tire rolling-resistance coefficient required to produce the same fuel saving are also shown.