One company thinks it has the answer for truck operators that want to use natural gas but are concerned about range issues: a dual-fuel system that can be retrofitted to existing diesel engines.

American Power Group, a subsidiary of Green Man Technologies, has for a decade been converting large onsite diesel backup generators to this dual-fuel system. About two years ago, it started working to adapt the technology for use in vehicles. So far, testing indicates potential fuel savings of 25 to 30 percent per year, according to CEO Lyle Jensen.

The engine starts under diesel power, but under pulling power or acceleration operates in dual-fuel mode, displacing about half the diesel with compressed natural gas. If you run out of CNG, it automatically converts to full-diesel mode.

One of the things that stood out about this technology, Jensen explains, is that it is non-invasive. It doesn't require expensive custom fuel injectors and other heat-sensitive custom componentry, bringing the cost of the system down. Instead, the system introduces CNG through a proprietary air mixer, pre-turbo.

"So we deliver what I would call an enriched-air fuel through the turbo into the air intake manifold." As long as they stay below a level of 70 percent displacement, he says, thermal issues should not be a problem.

This type of technology had been tried elsewhere in the world, Jensen says, but the problem was controlling the safety and reliability of the displacement. So to fine-tune it, the company turned to Robert Natkin, who Jensen calls "one of the smartest powertrain guys I've ever met." Natkin, a former powertrain engineer for Ford, "fell in love with the concept," Jensen says. With his help, they created a third-generation design that converted the analog system to a digital ECU-based system.

The new system can access the diesel engine's electronic control unit and monitor key operating metrics to make sure the dual-fuel system is operating within all the required OEM and emissions parameters. The response is measured in nanoseconds. If temperature or pressure readings exceed the OEM metrics, the control system will automatically shut off the dual-fuel and return the engine to full diesel operation.

In December, APG announced it had received exemptions from the U.S. Environmental Protection Agency that allow it to test and verify its third-generation version in 11 trucks. The testing is to verify that the system does not affect vehicle emissions.

Last month, Casella Waste Systems in Rutland, Vt., agreed to convert one of its refuse trucks to the dual fuel system and begin on-the-road trials. Jensen expects a second and third round of exemptions for fleet testing, with hopes of adding 50 more in the first half of this year.

Once each engine model is approved by the EPA via this testing, the company hopes to start offering the system commercially for those models in the latter half of the year.

More info: www.americanpowergroupinc.com.

From the February 2011 issue of Heavy Duty Trucking magazine.