Monday, January 22, 2007

Little engine that could?

By Efrain Viscarolasaga

In 1816, inventor Robert Stirling developed the idea for an alternative to the internal combustion engine. Ever since, the Stirling engine has been touted as one of the most efficient possible engine designs.

Because price and size challenges have kept the idea mostly theoretical, it's also been called one of the most impractical for commercial use.

In North Haven, Conn., Precision Combustion Inc. has been working on a catalytic burner for Stirling engines that could make such engines a possibility -- and the U.S. Army has taken notice.

Last week, PCI landed a Phase I Small Business Innovation Research (SBIR) grant to further develop its burner for use as part of a portable power source that could help soldiers power batteries in the field and run remote sensors, quietly, for long periods of time.

"The (Stirling) engine design is pretty well established, and engine manufacturers are working to put it into applications today," said Kevin Burns, president of PCI. "But the question is how we can get the price and size down for commercial applications."

PCI has already been working on commercial applications for its catalytic burner with SunPower Inc., a maker of Stirling engines and other power devices in Ohio. SunPower has developed a commercial niche for such engines for use in fossil- and biomass-fueled electric generators and vehicle power units.

PCI will use what it has learned in past developments and apply it to the Army's needs.

"They want to take our very compact burner and make it even more compact," said Burns.

The new grant, awarded through the U.S. Army's Communications-Electronics Research Development and Engineering Center (CERDEC), will provide PCI with $70,000 to develop a compact catalytic burner to run on military standard fuels, such as JP-8, and provide the heat source to drive a Stirling engine. The award also contains an option for another $30,000, if the Army research center in Fort Monmouth, N.J., continues the project after the initial design.

The final units are expected to weigh about 5 pounds and will be capable of producing about 35 watts of electricity, according to Burns.

The Stirling engine is a power source of great interest for several military field applications, according to Army research officials. The engine works via temperature changes within a cylinder to move a piston manipulated by the expansion and contraction of the air mass. It creates no exhaust and has no valves, making for an extremely quiet device -- one capable of efficiency rates upwards of 80 percent. Modern diesel engines are about 40 percent efficient, with gasoline internal-combustion engines even less efficient.

But while the theory has been around since the early 19th century, it faces several challenges in modern applications, including price and size.

Salvatore Scuderi, president of The Scuderi Group in West Springfield, a maker of a split-cycle engine design based on fluid- and thermo-dynamics, said Stirling engines hold promise, but size has always been a problem. That can be exacerbated in an industry pushing for smaller units. "For vehicle applications, such as an automobile, it is not very viable because you would need an engine bigger than the car to get the right power density," he said. "But for remote, generator applications, they could work."

PCI and Scuderi aren't the only ones working to improve engines and power supply efficiency. In Woburn, Wilson TurboPower Inc. has combined two power technologies based on MIT research to create a heat exchanger that can be used in almost any application in which heat is transformed into energy, from furnaces to fuel cells to engines.

While PCI's initial focus will be to help the Army research center develop a viable power supply for soldiers in the field, there could also be commercial applications for the new technology. One such application is in commercial trucking, whose drivers keep their diesel engines running at night to keep electricity on in the truck, said Burns.

Founded in 1986, the 30-person firm has been awarded 28 Phase 2 SBIR grants and launched several commercial products from those, including an air-purification unit used on the International Space Station and catalytic fuel processors for solid-oxide fuel cells.