NACFE: SuperTruck Innovations Pave the Way for Zero-Emission Trucks

The Department of Energy’s SuperTruck program, by allowing truck makers and researchers a more holistic approach to the development of designing a more efficient tractor trailer, is resulting in technologies that will not only improve the efficiency of diesel engines, but also will help in developing longer-range zero-emission trucks.

That’s one of the major themes of a new report from the North American Council for Freight Efficiency, SuperTruck 2: Empowering Future Trucking.

“We’ve been interested in the SuperTruck projects since they were funded during the Obama administration,” said Mike Roeth, NACFE executive director, introducing the report to trucking journalists at the American Trucking Associations’ Technology & Maintenance Conference annual meeting in New Orleans.

“Because these trucks really align with the work we do around efficiency. And while you’re not going to see a full-blown SuperTruck on your dealer lot any time soon, the reality is you buy little pieces of the technology proven on these trucks every model year.”

“We concluded that the SuperTruck 2 teams achieved great improvements and delivered efficiency technologies to make zero-emission solutions more successful,” said Rick Mihelic, NACFE director of emerging technologies and lead author of the report.

“There is a significant amount of work represented by these trucks,” Mihelic told reporters at TMC. “They represent about 10 years’ worth of research and development by all the truck manufacturers.

“One interesting aspect of the SuperTruck program is that every technology tested has to have a viable path to production,” Mihelic noted. “If it is tested and proven worthwhile on a SuperTruck, that technology will go into a production vehicle at some point in time.”

Lessons Learned from the SuperTruck 2 Program

The new report focuses on lessons learned from the SuperTruck 2 program. It documents the significant technologies investigated, developed and demonstrated by the SuperTruck 2 teams, and the potential for these technologies to influence future production truck designs.

In 2009, the DOE funded the first SuperTruck project to inspire truck makers to demonstrate new technologies that could greatly improve freight energy efficiency, reduce vehicle operating costs and improve environmental sustainability.

The successful demonstrations led to DOE funding the even more aggressive SuperTruck 2 program beginning in 2016.

Five teams participated in SuperTruck 2, led by:

• Cummins and Peterbilt
• Daimler Truck North America
• Volvo Trucks
• Navistar
• Paccar

From 2016 through 2024, each of these five teams succeeded in innovating complete tractor-trailer systems capable of exceeding freight efficiency performance improvements of more than 100% versus each team’s Model Year 2009 baseline diesel tractors with standard 53-foot dry van box trailers, NACFE said in its report.

SuperTruck 2 teams had essentially two goals:

1. Demonstrate a 55% brake thermal efficiency (BTE) engine in an engine test stand.
2. Demonstrate a complete tractor-trailer vehicle system that exceeded a 100% improvement in freight-ton-efficiency (FTE) versus their selected MY2009 baseline vehicle with a gross vehicle weight of 65,000 lbs. in a representative on-highway long-haul duty cycle of their own choosing.

SuperTruck 1 vehicles demonstrated fuel economy numbers in the range of 11 to 13 mpg and freight-ton efficiency figures greatly exceeding their target 50% improvement versus their MY2009 baseline.

The SuperTruck 2 technologies had a target of exceeding 100% versus those same baselines and fuel mileage as much as 16 mpg by further optimizing diesel technologies, and incorporating 48V mild hybridization and in one case, full high-voltage hybridization.

Innovation Diffusion

One of NACFE’s key conclusions in the report is what they call “innovation diffusion.”

Both Roeth and Mihelic noted during the TMC press conference that in their experiences as engineers for OEMs, designers are typically given one specific area of the vehicle focus on — be it the bumper, the hood, the engine or something else.

“SuperTruck really challenges the OEMs and their engineers to look at the entire truck,” Mihelic said. “So they are able to work on the truck as a complete system and design it from that perspective.”

The SuperTruck vehicles are real-world trucks evaluated by expert teams that have skin in the game with their own money, resources and reputations, along with funding from the government, NACFE said.

Teams often include participants not typically allowed behind the wall of proprietary development at OEMs, including national laboratories and university researchers.

Potentially excellent ideas that normally sit on shelves from lack of management engagement or interest can make it into full system development of vehicles.

"Development perspectives that may be hamstrung with component-level development are set free to bloom by participating in a complete vehicle system perspective where, for example, performance gains in one area are achieved by weight reductions or simplification in completely unrelated areas of the vehicle.

“SuperTruck projects empower designers to literally think outside the mental boxes they typically must work within under normal organizational product development,” NACFE said.

Technologies Used in SuperTruck 2

The NACFE report goes into detail about how the five teams approached the challenge and the technologies and strategies they used, including in areas such as:

• Aerodynamics
• Rolling resistance
• Lift axles and improved tandems
• Lightweighting
• Reducing friction and parasitic loss
• 48V hybridization
• Cab Configuration
• Software/advanced predictive cruise control

In aerodynamics, for instance, projects used tractor and trailer aerodynamics, replaced mirrors with cameras, and developed ways to manage the tractor-trailer gap.

To reduce the area the tractor-trailer carves in space as it moves through the air, SuperTruck 1 and 2 teams investigated several concepts to reduce the overall height of the tractor-trailer when operating at highway speeds, sometimes called kneel-down systems that reduce the suspension height.

Another approach to reducing height is using smaller diameter tires, which eliminates the need to reduce the tractor-trailer height while the vehicle is moving, but adds the complexity of being able to raise the trailer floor height to mate to existing docks.

These types of systems also can improve airflow under the tractor-trailer by providing better sealing from the ground skirts installed on the vehicles.

48V Hybridization

NACFE called mild hybridization “one of the most insightful aspects of SuperTruck.”

Traditional truck diesel engines not only provide the force to move the truck down the road, but the engine also powers additional systems such as power steering, alternator, pumps, cooling fans, and a range of accessories collectively categorized as front engine accessory drive (FEAD). The FEAD takes power from the engine through a series of belts and pulleys. Those mechanical connections add power-stealing friction or what is collectively termed parasitic loss.

SuperTruck 2 teams investigated reducing parasitic losses by replacing the belt-driven systems with electric ones. Electric accessories generally have less frictional losses, less vibration and create less heat.

Truck electrical systems have operated for decades on 12 volt (12V) electrical systems. However, higher voltages allow more efficient use of electricity, such as in electric motors. SuperTruck 2 allowed OEMs to pursue 48V systems to replace the FEAD. The industry term adopted for this is “mild hybridization.”

48V systems also can be used for energy recovery during decelerations.

The Navistar SuperTruck 2 team pushed the envelope beyond just 48V mild hybridization by developing a full high-voltage hybrid. This concept incorporates the benefits of 48V accessories replacing the diesel engine driven FEAD ones but adds high voltage systems for motive power to move the truck can recover energy during decelerations.

Waste Heat Recovery

One technology that ended up being conspicuously absent from the SuperTruck 2 demonstrators was waste heat recovery.

Waste heat recovery attempts to repurpose heat normally lost to the environment. Diesel engines traditionally have had thermal efficiencies between 35% and 55%. That means that anywhere from two-thirds to one-half of the energy in the fuel is simply dumped to the environment and not used to move the vehicle. Waste-heat recovery systems attempt to capture and reuse that lost heat to help propel the vehicle. A variety of concepts for WHR have been investigated over decades, many funded through the DOE.

The SuperTruck 2 teams investigated waste heat recovery but most did not include it in their demonstration vehicles.

NACFE’s interpretation of the five SuperTruck 2 teams’ investigation of WHR is that all seemed to concur WHR is a necessary technology to get to a 55% BTE engine, but commercializing WHR may not be required or financially viable to achieve significant vehicle level freight efficiency gains for production trucks powered by diesel engines.

'Universal Ideas' Applicable Beyond Diesel

Another of NACFE’s key conclusions is what it calls “universal ideas.”

Many tractor-trailer system efficiency gains are universally applicable to all powertrain choices, the report points out. Reducing the energy required to move freight over a distance means less operational cost.

Another way to view that is that less energy required per mile can translate into greater net range for the same amount of energy, and/or greater payload.

Future trucks will build from technologies demonstrated in SuperTruck 2 to achieve increased range and freight capacity. For example, a 100% improvement in mpg easily demonstrated by SuperTruck 2 teams would make a battery-electric vehicle currently capable of 300 miles on a charge capable of going 600 miles.

While there are many ways to improve the efficiency of tractor-trailers, NACFE said, there are some technologies that achieve greater gains, regardless of the type of power system, be that diesel, electric, or something else:

• Aerodynamic improvement
• Rolling resistance improvement
• Weight reduction
• Parasitic loss reduction

These four common improvement factors are very pertinent to evolving technologies, NACFE said, including:

• Battery-electric vehicles
• Fuel-cell electric vehicles
• Alternative fuel vehicles such as renewable natural gas, compressed natural gas, hydrogen internal combustion engines (H2 ICE), propane, and all the hybrid permutations of these zero- and near-zero emission technologies.

“SuperTruck 2 investigations essentially are breeding grounds to propagate innovation well beyond just the subject vehicles,” the report said.

In the Works: SuperTruck 3

The SuperTruck 3 program awards were announced in November of 2021. Technology goals were summarized by the White House as “the DOE is working with manufacturers and industry partners to reimagine vehicle transportation across the country to achieve our climate goals — from lowering carbon emissions to increasing efficiency and affordability.”

Where SuperTruck 1 and 2 were focused on heavy-duty trucking, SuperTruck 3 has a broader focus including medium-duty as well as heavy-duty trucks. These projects include full battery electric and hydrogen fuel cell vehicles for medium- and heavy-duty trucks.

The five major teams awarded funding for SuperTruck 3 are led by:

• Paccar (including Kenworth and Peterbilt)
• Volvo Group North America
• Daimler Truck North America
• Ford
• General Motors

With reporting from Executive Editor Jack Roberts.