Gus Peterson tests one of his tabletop models of the Stirling cycle engine at the Monument Show-N-Shine. The Eagle/ HEATHER SHEEDY

MONUMENT – Gus Peterson of Monument can turn heat into power, and he uses a unique approach not involving solar panels.

Peterson, a hobbyist who researches power engines, has a couple of tabletop models of the Stirling cycle engine, which will run on the flame from a cigarette lighter. One of them has an 18-inch parabolic mirror, that concentrates all the sunlight in that 18-inch circle on the end of the displacer cylinder that is to be heated. It is capable of running 1,000 revolutions per minute.

“Now that means that the displacer, in its cylinder, is heating, then cooling that body of air 16 times a second and sending the pulses to the work cylinder,” Peterson explained.

The Stirling cycle engine is an external combustion heat engine, in contrast to popular internal combustion heat engines of today. The classic example of an external combustion heat engine is the steam engine, as used on railroads; steam traction engines; and stationary engines as used in mills. In those applications, the combustion took place in a fire box, under a boiler, and the high-pressure steam was piped to the engine, Peterson explained.

A Stirling cycle engine is not a steam engine, but sometimes is called a “hot air” engine. It operates with a sealed cylinder, piston, and connecting rod that rotates a crankshaft as the piston travels inward and outward in the cylinder, much like internal combustion engines. The Stirling engine alternates heat, and then cools the body of gas that is trapped in the cylinder, which causes a “pushing-pulling” effect on the piston-connecting rod assembly, and causing the crankshaft to rotate. The machine has a cylinder next to the work cylinder that is heated on one end with a fire, and cooled on the other end with cooling fins.

A displacer inside, connected to the crankshaft, moves forward and back in its cylinder, causing the gas body to rotate between the hot end and the cool end. This gives the push-pull effect needed to make the work piston turn the crankshaft, Peterson explained. The displacer cylinder is plumbed to the working cylinder so the surge effect is transmitted directly between them.

“This concept was tested by many, then patented in 1816 by Scotch minister Robert Stirling (sometimes spelled with an ‘e’). For almost 125 years it was used mostly for pumping water heated from various fuel sources (corn cobs, coal, wood, buffalo chips). It was used extensively in England mines and smaller pumps for individual homes, where the whole family, including children, were employed to feed the firebox. At one time, a kitchen cooling fan was available, powered by a Stirling engine, fueled with liquid fuel, possibly coal oil,” he said.

Scientists, in their search for a way to generate electricity, have considered solar-powered Stirling engines, and devised panels to harness that energy, with tests in the Southwest, Peterson said.

“I have a feeling that the concept was crushed with the development of photo-voltaic cells, since they convert sunlight to electricity directly without going through the steps of developing a mechanical motion,” he said.