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Fuel-Savings from Aerodynamic Efficiency Improvements for Combination Tractor-Trailers Relative to Vehicle Speed
Abstract:
Commercial, class-8 tractor-trailers were tested to develop a relationship between vehicle speed and fuel savings associated with trailer aerodynamic technologies representative of typical long-haul freight applications. This research seeks to address a concern that many long-distance U.S. freight companies hold that, as vehicle speed is reduced, the fuel savings benefits of aerodynamic technologies are not realized. In this paper, the reductions in fuel consumption were measured using the SAE J1231 test method and thru-engine fueling rates recorded from the vehicle’s electronic data stream. Constant speed testing was conducted on road at different speeds and corresponding testing was conducted on track to confirm results. Data was collected at four (4) vehicle speeds: 35, 45, 55, and 62 miles per hour. Two different trailer aerodynamic configurations were evaluated relative to a baseline tractor trailer.
Reductions in fuel consumption displayed a strong relationship to vehicle speed, with aerodynamic improvements demonstrating a maximum reduction of fuel consumption of nine (9) percent relative to the baseline at 62 miles per hour. Results at high vehicle speeds are consistent with earlier wind tunnel studies published for trailer aerodynamic technologies. Reductions in fuel consumption demonstrated at 35, 45 and 55 miles per hour are consistent with anticipated performance based on changes in the coefficient of drag for the aerodynamic technology packages tested. At speeds as slow as 35mph, a trailer side skirt and full trailer aerodynamic package demonstrated fuel savings of over 2 and 3 percent, respectively. Fuel savings results at high speeds were relatively insensitive to baseline selection when compared to five (5) different baselines.
The relationships derived from the tests provide a good fit (i.e., high R2 values) to mathematical regression models and suggest these curves can be used to estimate reductions in fuel consumption savings for aerodynamic technologies for modern class-8 tractor-trailers operating at different vehicle speeds. When applying the SAE J1321 approach (i.e., use of a control vehicle and calculating fuel savings relative to a baseline), ECU-derived fuel savings generally agree with the gravimetric measurement.