Fuel Savings from Truck Aerodynamic Drag Reducers and Correlation with Wind-Tunnel Data

Abstract

A 9347 km (5809 mi) cross-country fuel economy experiment was conducted to demonstrate typical fuel savings that can be obtained using drag-reducing devices on tractor-trailer trucks, and to ascertain the degree of correlation of the experimentally determined fuel savings with the fuel savings that could be predicted using data from drag reduction experiments on models in a wind-tunnel. Three trucks were used in the experiment. One truck was equipped with a commerically available wind deflector/vortex stabilizer system, another was equipped with a prototype streamline fairing/gap seal system developed at the University of Maryland, and the remaining vehicle was operated without any drag-reducing devices in order to obtain a basis from which to determine the fuel savings. The fuel savings per unit distance that resulted from use of the commerical drag reducing system was 0.029±.006 liter/km (0.012±.002 gal/mi), while that realized with the University-of-Maryland-developed prototype system was 0.057±.003 liter/km (0.024±.001 gal/mi). An analysis of the conditions under which these results were obtained indicated that they were conservative estimates of the fuel savings that would be realized with long-term operating of the vehicles and devices used in the experiment. Fuel savings predictions were performed using wind-tunnel drag reduction data, and relative airspeed and yaw angle data continuously measured in the fuel economy experiments. The measured fuel savings due to the commercial system was 75 ± 15% of the predicted value, and that due to the University of Maryland system was 78 ±4% of the predicted value. The differences obtained appear related to the nonsimulation of wind turbulence in the wind-tunnel experiments. Nomenclature A-aerodynamic drag reference area (product of height of trailer above ground and its width) BSFC = brake specific fuel consumption of engine C D = body-axis aerodynamic drag coefficient CF = relative fuel consumption calibration factor D A = body-axis aerodynamic drag force DR = rolling resistance drag force d = distance traveled by vehicle FC = volumetric fuel consumption FCD = volumetric fuel consumption per unit distance FR = fuel consumption rate on a mass basis FS = volumetric fuel savings P(I,J) = frequency of occurrence of wind condition (/,/) A/z -change in elevation / = index for wind angle band J = index for wind speed band P a = power required by accessories A/ = rolling time V = vehicle speed V r = speed of air relative to vehicle V w = wind speed W ~ vehicle weight d = slope angle of road surface j f = specific weight of fuel n D =driveline efficiency 0 = wind angle relative to vehicle heading \l/ = yaw angle p = air density

Aerodynamic drag reduction of class 8 heavy vehicles: a full-scale wind tunnel study

“…In addition, the non-moving ground plane beneath the vehicle produces a boundary layer that may underestimate the performance of the trailer underbody devices. As has been observed in previous studies, these types of effects can lead to differences between the estimated fuel savings from wind tunnel data and that actually observed on the road [4,5,6,16,29,50,65]. To remedy this potential shortcoming, future studies will include fuel economy data from both track testing and subsequent fleet evaluations of select devices.…”

“…Prior to that time, heavy vehicles were primarily designed for functionality and ease of manufacturing and, therefore, little thought was given to aerodynamics, which resulted in box-shaped tractors and trailers. To improve the fuel economy of these vehicles, several conference workshops and numerous research programs and studies were conducted on heavy vehicle aerodynamics [5,6,8,9,10,11,12,16,21,28,29,33,36,37,38,39,47,48,50,53,56,57,58,64]. Although the entire vehicle was investigated for various avenues of reducing drag, the primary focus of these efforts was the aerodynamics of the tractor and the front of the trailer.…”

A Review of Reynolds Number Effects on the Aerodynamics of Commercial Ground Vehicles

“…In aerodynamics the most critical criteria is Reynolds number which guides vehicle design principles and governs the use of testing and analysis tools. A review of the literature [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,…”

“…These data sets are for aerodynamically sharp-edged (i.e. small edge radii) bluff body vehicles that are known to have aerodynamic forces and moments that vary little with Reynolds number, see Anderson [2], Buckley [13,15], Cooper [20, 23] and Watkins [92,93,94,95,96,97].…”

“…The information presented in this paper has been extracted from published works and where available accepted correlation parameters and summary data plots are presented. The evaluation of complete vehicles made use of references 6,8,9,11,13,15,16,18,20,21,22,23,24,26,27,29,33,36,37,44,45,48,49,50,51,52,56,64,70,73,74,77,80,81,82,83,84,85,86,87,91,93,94,95,96,97,100 …”