An energy-use analysis is presented to examine the potential energy-savings and range-extension benefits of aerodynamic improvements to tractors and trailers used in commercial transportation. The impetus for the study was the observation of aerodynamically-redesigned/optimized tractor shapes of emerging zero-emission tractors that have the potential for significant drag reduction over conventional aerodynamic tractors.
Using wind-tunnel test results, a series of aerodynamic performance models were developed representing a range of tractor and trailer combinations. From current-day day-cab and sleeper-cab tractors to aerodynamically-optimized zero-emission cab concepts, paired with standard dry-van trailers or low-drag trailer concepts, the study examines the potential of implementing various fleet configurations for different operational duty cycles.
An energy-use analysis was implemented to estimate the energy-rate contributions associated with inertial accelerations, grade forces, rolling resistances, and aerodynamic-drag forces for three types of duty cycles: Long Haul, Regional Haul, and Urban Delivery. Speed-dependent wind-averaged-drag models, adapted for local wind-speed magnitudes, were implemented. A second method for estimating Long Haul cycle energy use, based on wind-climate simulations over a large highway network, was also used for verification and cross comparison with the Long Haul duty-cycle based methodology.
Results demonstrate that Urban Delivery operations expend a smaller magnitude, and smaller relative proportion, of energy use to overcome aerodynamic drag, but that significant savings are nonetheless possible for these operations with aerodynamic improvements to the trucks. Over the range of aerodynamic improvements examined, the analyses reveal the potential for 4-27% energy-rate savings and 5-37% range extension the Long Haul cycle, 3-13% energy-rate savings and 3-15% range extension the Regional Haul cycle, and with 2-11% energy-rate savings and 2-12% range extension estimated for the Urban Delivery Cycle. Relative to current-day fleet compositions, trailer-aerodynamic improvements are shown to have about twice the potential for energy savings and range reduction than do tractor-aerodynamic improvements.