Wisconsin engineer, entrepreneur move ‘green’ diesel engine closer to market

A University of Wisconsin–Madison engineer is collaborating with a Wisconsin entrepreneur to produce a diesel engine that could be a quieter, more efficient power source for a variety of household and industrial applications, including lawn equipment and electric generators.

The pair has just received a $850,000 grant to fabricate and test a prototype engine, bringing it that much closer to commercialization.

The engine, a modified external combustion design by Brookfield, Wis., entrepreneur Gerald Kashmerick of Kashmerick Engines LLC, uses external combustion, burning fuel in a high-pressure chamber outside of the piston cylinder. As an external combustion engine, it can be powered by a wide range of liquid and gaseous fuels, and customers could change which fuel they use with a simple turn of a valve. The engine, called the “K6,” also uses six strokes instead of four to reduce the pressure of exhaust gases, which allows it to harvest more energy rather than expelling it with the gas.

“If you expand all of the combustion products from the air in the compression stroke at once, as in a typical engine, you end up with a pretty high pressure at the end of the stroke. So when you open the exhaust valve to dump expanded gas out to the environment, you lose all of that energy stored in the high-pressure exhaust gases and you create a lot of noise,” says Timothy Shedd, a UW–Madison associate professor of mechanical engineering.

But slowly decompressing the gases would waste less of that energy and make for a much quieter engine. “Just a shush-shush-shush instead of a bang-bang-bang,” Shedd says. “No muffler should be needed.”

He says the engine could be up to about 30 percent more efficient than a standard diesel engine, depending on the engine load and speed. Shedd, working with graduate student Matthew Carlson, developed thermodynamic models demonstrating the engine’s potential and helped design parts that would be exposed to particularly high temperatures.

Shedd and Carlson have worked to ensure the K6 engine could function as advertised. They compare its performance to that of traditional engines. They also have worked with Kashmerick to help him design parts of the engine that will be subject to high temperatures.

Thanks to a U.S. Department of Defense Small Business Innovation Research (SBIR) grant, the team can now create a physical prototype. Shedd says the prototype will allow detailed testing of the engine’s actual capabilities, and bring the technology closer to commercialization.

According to Shedd, what’s unique about the engine is not so much its individual mechanisms, but rather, the combination of the external combustion engine with the six-stroke cycle.

“The K6 engine represents a unique combination of previous concepts,” he says. “In addition, many new engine concepts require some really special parts to function, often so ‘special’ that they can’t be made in reality or can’t be manufactured in mass quantities.”

In contrast, he says, the K6 can be made by modifying existing diesel engines in a way that is both realistic and manufacturable. Furthermore, the K6 wouldn’t require computer control for operation, making an individual engine as much as $100 cheaper, and much simpler to build.

On the down side, the engine requires extra rotations to perform the extra strokes, meaning the process loses more energy to friction and has less power. “Testing of the prototype should demonstrate the engine is still a winning combination for some types of uses,” Shedd says.

“Our modeling results suggest that not only does the engine seem feasible, it is possible its performance and efficiency could rival traditional engines, particularly at part-load operation where many utility engines operate,” Shedd adds.

Among the engine’s potential applications are power washers, electric generators, lawn equipment, welders, marine propulsion and even hybrid vehicle engines, which rarely run at full power.

Shedd says he expects to have a prototype running by late fall or early winter.