LOUISVILLE, KY. Navistar is showing a prototype dual-fuel 13L MaxxForce engine in a 2011 International ProStar Plus at this week’s Mid-America Trucking Show here. The engine, which runs on diesel and liquefied natural gas (LNG), was built in partnership with Clean Air Power.

“Recognizing the abundant supply of natural gas in the United States and Canada, we feel compelled to invest in our products in such a way that enables our customers to expand their usage of very low emissions technologies through our engines,” said Jim Hebe, senior vice president, North American sales operations, Navistar. “The use of natural gas certainly accomplishes this and we are proud to be developing the broadest, most energy-efficient line of trucks in the industry, helping deliver real-world savings to the bottom line.”

The engine is being tested in a 2011 ProStar Plus model, a 122-in. BBC tractor with 430 hp. and 1,550 lbs.-ft. of torque. It uses diesel pilot injection for combustion on the compression stroke and mixes air and LNG on the intake stroke. The result is an engine that runs on a mixture of 15% diesel and 85% natural gas.

Minimal changes to a stock 13L MaxxForce engine are required, the company said, other than the addition of a natural gas injection system. Chassis changes include the addition of a 26-in. diameter, 119-gal. LNG tank that provides a 400 mi. range, a coolant heated fuel vaporizer, and an LNG regulator and filter.

Navistar said it is working with the EPA to define the regulatory requirements of an EPA-compliant dual fuel engine.

“As we assess changing market conditions, the ability to offer customers choice is important not only in our U.S. markets, but in our global markets as well,” Hebe added. “As we develop this product for our International truck customers, we will also be able to leverage the technology in other markets and products as appropriate.”

Navistar also announced that its MaxxForce 15 engine is ready for production in International ProStar Plus models.

“With the addition of our MaxxForce 15, our line-up of MaxxForce Advanced EGR big bore engines truly differentiates us from the competition,” said Jim Hebe, Navistar’s senior vice president, North American sales operations. “The introduction of the ProStar Plus with MaxxForce 15 now gives customers the ultimate combination in durability and power.”

The MaxxForce 15 offers up to 500 hp. with 1,850 lbs.-ft. of torque in the ProStar Plus. The International PayStar heavy-duty vocational trucks will have up to 550 hp. available.

The engine uses the MaxxForce Advanced EGR system and produces peak torque at 1,000 rpm and holds steady to 1,600 rpm, which reduces gear-shifting needs uphill and allows for shifting at lower speeds when accelerating, Navistar said.