Navistar’s International SuperTruck II prototype, developed through a project with the U.S. Department of Energy, has achieved 16 miles per gallon (14.7 liters per 100 km) using a hybrid-electric powertrain, among other technologies.

The thresholds build on advances tested in the OEM’s first SuperTruck, developed in 2009. It achieved 13 mpg (18 L/100 km).

Other enhancements in SuperTruck II included reduced weights and rolling resistance, aerodynamic improvements, and powertrain improvements, the company says.

“With co-funding by the DOE, Navistar engineers experimented with prospective technologies not currently available in the Class 8 truck market to accelerate the impact of sustainable mobility,” said Russ Zukouski, chief engineer, global innovation and principal investigator for the SuperTruck program.

“The team concentrated its design on high-voltage electrification, utilizing hybrid technology on a path toward full electrification that has the potential to be commercialized in fully electric vehicles and improve customers’ total cost of ownership (TCO) and business operations.”

The results boosted freight efficiency over the 2009 vehicle by 170%, as well as 55% brake thermal efficiency. The manufacturer also measured the total cost of ownership for underlying technologies, and high-voltage systems.

A composite trailer

“Navistar is the only OEM to build a trailer to provide the most accurate testing results possible,” added Dean Oppermann, chief engineer – advanced truck. “It includes a 100% composite box designed for minimum aerodynamic drag with light weight, integrated cross members, controlled underbody flow with composite aero treatments, next-generation solar panels with connectivity options, and ride height control.”

Navistar partnered with Bosch on the high-voltage accessories and technologies.

Engine improvements, meanwhile, touched on combustion, friction, gas exchange and airflows. A redesigned cylinder head and the dual-overhead cam engine, along with an enhanced fuel system, boosted fuel economy 2%.

Aftertreatment upgrades including diesel exhausted fluid (DEF) dosing, improved mixing and lower restrictions, and new selective catalytic reduction (SCR) formulas.

“A full system approach was required to achieve 55.2% brake thermal efficiency,” said Jim Cigler, chief engineer – advanced engine. “Navistar was able to identify new ways to push our engines to the next level of efficiency.”