Army not yet sold on hybrid vehicles.

The Army's decision to stop funding the production of hybrid-electric Humvees is a clear sign that military vehicles will continue to be a tough sell in the world of fuel-efficient technologies.

During the past decade, the Army has supported a number of development programs to equip military vehicles with hybrid-electric engines, but none has transitioned yet to full production. The hybrid Humvee was viewed as one of the more promising efforts, with at least six prototypes in the works.

Although the Army continues to struggle with the enormous logistics burdens of transporting millions of gallons of fuel to combat zones, it has not yet been convinced that hybrid-electric engines are the way to go. Hybrid systems, though more fuel efficient, have proved to be more expensive and less rugged than advocates had hoped.

"We have to prove that it works as tooted," said Claude Bolton, assistant secretary of the Army for acquisition, technology and logistics. "It has yet to be seen" whether hybrid vehicles will ever be accepted in the Army's truck fleets, he told an industry conference.

Another hybrid prototype now in development is the Army's wrecker, the Heavy Expanded Mobility Tactical 'Duck. The manufacturer of the HEMTT, Oshkosh Truck Corp., equipped the vehicle with a hybrid system similar to one now in use in civilian trucks, such as fire engines.

But the Army is not yet persuaded that the HEMTT should be hybrid, said Lt. Col. Lisa Kirkpatrick, program manager for Army heavy trucks.

"We need to test it against conventional power train," she said. "I have told Oshkosh co be prepared to go back to conventional power train if hybrid electric doesn't work. ... I don't know if hybrid electric will deliver what it promises."

Gary Schmiedel, a program engineer at Oshkosh, said "there is a lot of capability, a lot of opportunity in hybrid technology," but that more work needs to be done.

Among the hurdles is the ability to operate in extreme temperatures. Military trucks must be able to run in temperatures as low as minus 50 and as high as 150. "There is more work to do there," Schmiedel said in a presentation. "It's about managing the energy storage."

Hybrid systems today could not survive the intense heat in combat zones such as Iraq, unless the vehicles were equipped with advanced cooling systems. "It's an expensive infrastructure investment," he said.

The advantages of hybrid propulsion go beyond fuel efficiency, Schmiedel said. They include design flexibility and the generation of additional electricity to power battlefield devices, such as radios and computers.

He said hybrid vehicles could achieve 30-40 percent reduction in fuel consumption compared to conventional diesel engines, depending on the scenario. The more stop-start activity, generally, the higher the efficiency. "If" you have a uniform, consistent load on the road, that is not a particularly good application for hybrid drive train," he said. "The more aggressive the mission profile, the more economy gains you realize."

In a hybrid system, a diesel engine serves as the prime mover, and is coupled to a generator. The diesel can be substituted with a gas engine or turbine.

Hybrid propulsion is expected to play a prominent role in the Army's next-generation combat vehicles, but it's nut yet clear exactly how it will be applied in the Future Combat Systems program. An FCS program review in August could determine whether vehicles developed under FCS will have hybrid or conventional engines, said Robert V. Sorge, a project director at General Dynamics Land Systems. He said that hybrid propulsion will be assessed against conventional diesel and turbine engines. Although the Army generally supports hybrid systems in FCS, he said, there are still concerns about efficiency, case of integration, as well as questions on how much electric power Army vehicles really need.