Fleets switching their tractors to 6x2 axle configurations could realize fuel savings of 2.5%. However, factors such as low fuel prices, higher tire wear, driver perception, residual value, and improved efficiency of 6x4 axles have contributed to their limited adoption.
Fleets should expect to see an average 1%–3% improvement in fuel economy from automatic manual transmissions, which use a computer to shift the manual transmission at the optimal time. Improved driver recruitment and retention are big factors behind many fleet owners’ decisions to specify these transmissions over manual transmissions.
Many fuel efficiency technologies are available to fleets, but no truck could or should have all of them. Fleets must analyze the range of options and compare them against their own operations to determine which offer the fastest payback. There are a variety of test methods, and each has its appropriate application. Understanding what each test method involves, its benefits and challenges, and how it deviates from real-world performance will help fleets have a better understanding of how to interpret the data.
Downspeeding is one of the primary powertrain-focused strategies for improving fuel economy in heavy-duty trucks. With downspeeding, the rear gear ratio is sped up in order to lower the speed of the engine, bringing fuel-efficiency improvements. Downspeeding allows the engine to operate at the most efficient rpm while generating the minimal horsepower required to maintain a 65 mph cruise speed.
Electronic Engine Parameters
While engine parameters have been around since the mid-1980s, not all fleets are using them to optimize for fuel efficiency. Fleets that are already managing their electronic engine parameters can see fuel-economy gains of around 0.5 mpg from optimizing the parameters, but gains can be even higher, in the 5%–8% range, for fleets that previously did not use parameters to optimize for fuel efficiency.
Idling burns 8% of total fuel burned, and more importantly, two-thirds of that idling time can be reasonably avoided using currently available technologies. Idling as a source of inefficiency can be addressed via a variety of methods. Reducing idling also improves productivity, lowers maintenance costs, and reduces truck and engine wear.
Fleets can save 2,000 lbs. by investing to a limited degree in lightweighting, and as much as 4,000 lbs. with an aggressive investment. Lightweighting can take place in various areas of the tractor and trailer, including the powertrain, axle suspensions, wheel ends, drive shaft, frame, fifth wheel, and more.
Low Rolling Resistance Tires
Low rolling resistance tires, whether in a dual or a wide-base configuration, will save significant amounts of fuel compared with tires that are not designed for low rolling resistance. More and more fleets are recognizing that the benefits of low rolling resistance tires outweigh the challenges.
Low-Viscosity Engine Lubricants
Class 8 over-the-road fleets can realistically expect fuel savings in the range of 0.5%–1.5% from switching from 15W-40 to 5W/10W-30 engine oil. In addition, switching from 5W/10W-30 oil to the fuel-efficient FA-4 is expected to add a further 0.4%–0.7% of fuel savings.
Maintenance for Fuel Efficiency
Even a vehicle that is running safely and reliably may still enjoy substantial fuel-economy savings from additional or more optimized maintenance. Adding up all of the potential reductions in fuel economy of 10 key components shows that maintenance can in fact address 30%–50% of fuel consumption.
Two-truck platooning is an emerging technology designed to boost fuel economy performance for tractor-trailers engaged in long- and regional-haul highway applications. Platooning combines existing commercial vehicle safety technology with emerging vehicle-to-vehicle communications and autonomous vehicle control technology to electronically “tether” tractor-trailers together in a convoy formation at highway speeds. Once a platoon of trucks is established, the vehicles, safety systems work in unison to draw the trucks together at significantly reduced following distances to overcome each vehicle’s inherent aerodynamic drag.
Using solar panels to harvest the sun’s energy is growing in acceptance for residential and commercial properties. It is now emerging as an excellent solution as well for Class 8 over-the-road tractors and trailers. On trailers they can charge batteries for such things as refrigeration units or powered tailgates. For tractors, they are mostly commonly used in concert with a Battery HVAC system to augment the power needed for driver hotel loads. Banks of batteries can be combined for starting the tractor and for these hotel loads and control strategies incorporated to most efficiently manage the entire systems. Fleets are reporting extended run time for air conditioning and reduced downtime due to dead batteries. NACFE is planning to conduct a full Confidence Report on the benefits and challenges of Solar in early 2018.
Tire Pressure Systems
Proper tire inflation pressure is critical to the optimal operation of a commercial vehicle. Underinflated tires result in decreased fuel efficiency and increased tire wear.
Tractor aerodynamics increase fuel efficiency by lowering air resistance so that less fuel is needed to move down the road as speed increases. The per-vehicle fuel-economy benefit of optimizing the aerodynamics of a tractor can be quite high. If the aerodynamic features are removed from the OEM’s aerodynamic base model, a fleet can expect to lose about 10% in fuel economy.
Trailer aerodynamic devices help to increase fuel efficiency by lowering air resistance, so that it takes less fuel to move down the road as speed increases. The per-vehicle fuel-economy benefit of trailer aerodynamic devices can be high, ranging from 1% to over 10%, depending on the devices chosen. Trailer aerodynamic devices can also improve stability and rollover, splash and spray, and driver fatigue.
Variable Engine-Driven Accessories
Variable engine-driven accessories are evolving as potential fuel-saving strategies for long- and regional-haul fleets. Some accessories have been available for years, while others are just recently emerging. Since these accessories provide essential vehicle functions, the potential efficiency gains would be accomplished through the implementation of new designs and technology to minimize the energy necessary to provide these essential functions.