Reducing aerodynamic drag and rolling resistance from heavy-duty trucks
This report summarizes the commercial technologies available in the U.S. and Europe that can be used to improve the fuel efficiency of heavy freight trucks by reducing aerodynamic drag and rolling resistance, and evaluates their applicability to Chinese heavy trucks. These technologies are most effective when applied to the largest, combination trucks (truck plus trailer) that spend significant time traveling at highway speeds, which are responsible for a large share of fuel consumption. There are numerous commercially-available devices designed for retrofit onto both trucks and trailers.
There are at least twenty companies that sell aerodynamic aids for U.S. heavy trucks and trailers. For trucks, these aids include: roof and side fairings, vortex generators and air dams. For trailers, these aids include: gap reducers, nose cones, side skirts, under body fairings, and boat tails/end fairings. Some US suppliers and domestic manufacturers are selling roof fairings and side fairings for use on new tractors and for retrofits on in-use fleet in China. Virtually all tire companies that supply the U.S. heavy truck market sell low rolling resistance tires and several also sell single-wide tires. Additional companies sell automatic tire monitoring or inflation systems to maintain proper tire pressure, also to reduce rolling resistance.
Wind tunnel and in-use testing on test tracks indicates that individual aerodynamic aids can reduce distance-specific fuel use (l/100km) from U.S. trucks by 1% to 15%; packages of several different types of devices together can reduce fuel use by 25% or more. Testing has also demonstrated that low rolling resistance tires can reduce fuel use from U.S. trucks by approximately 3% while the use of single-wide tires in lieu of traditional dual tire sets on truck rear axles and trailer axles can reduce fuel use by up to 9%. Automatic tire inflation systems have been shown to reduce fuel use by 0.5% to 1.2%.
The fuel efficiency benefit of aerodynamic aids is sensitive to truck speed: the faster a truck typically travels, the greater the reduction in fuel use. Rolling resistance is insensitive to speed, but is proportional to truck weight: low rolling resistance tires therefore provide greater benefits on heavier trucks than on lighter trucks. In comparison to U.S. trucks, Chinese freight trucks typically travel at lower speeds (70 km/hr compared to 105 km/hr), but operate at significantly higher gross weight (49,000 kg or more compared to 36,000 kg). As such, the expected benefits of aerodynamic aids will be smaller for Chinese trucks than for U.S. trucks, but the expected benefits of reduced rolling resistance will be greater.
For Chinese trucks typically traveling at 70 km/hr, a full package of retrofit aerodynamic aids applied to both the truck and the trailer might be expected to reduce fuel use by 11% or more. This would provide an annual fuel savings of 6,500 liters or more for a typical Chinese heavy combination truck. If combined with low rolling resistance tires and automatic tire inflation systems for both the truck and trailer, fuel use might be reduced by up to 20%, saving up to 11,800 liters of fuel per truck annually.
This report does not review the costs and economic benefits of aerodynamic or low rolling resistance technologies nor does it provide a detailed review of availability in China. These are areas of potential future research.