Stirling engines have been studied since 200 years ago, when Robert Stirling invented the basic concept behind them. estir Co., an in-company venture of Panasonic led by Teruyuki Akazawa, thought that it would make a good business reusing the otherwise wasted heat from Panasonic’s plants, and reimplemented Stirling engines, seeking to make them more efficient than ever.
The air in a cylinder of the engine goes through a cycle of repeated expansion and contraction as it is heated by the air and cooled by the water, moving the engine’s piston up and down.
The main issue with Stirling engines is that they have only been known to work best at temperatures of over 1000°C, and plants can usually only supply less than 500°C. That is why Stirling engines research as replacements for gasoline ones had been abandoned from the 1990s.
To make the engine work at lower temperatures, such as those produced by Panasonic’s plants, Akazawa thought of reducing the internal friction of the engine. Using oil as lubricant was not an option, because oil can burn and clog the engine at several hundred degrees.
Instead, after several trial-and-error experiments, Akazawa used a mechanism called “Scotch yoke” to give the linear motion of the piston a rotary one. Thus, he and his company succeeded making the engine work without oil lubrication. Akazawa had previously worked on the development of an air-conditioning system without using motor oil.
A prototype Stirling engine works since June 2009, with an output of 500 W. The second version of the engine is running since December and outputs 10 kW. This one, Akazawa says, can produce enough juice to feed 12 to 20 average households, if it works 24/7.
Akazawa said, “I hope it’ll become standard procedure for all manufacturing plants to be equipped with Stirling engines to generate electricity from waste heat.” The 43-year-old president of estir, persuaded his boss at Panasonic to revisit development of the Stirling engine. He told the boss at the time, “I want to revive the abandoned engine mechanism using the latest technologies, which are more sophisticated.”
According to a study performed by the Energy Conservation Center in Japan in 2000, 95% of the waste heat from industrial plants has a temperature under 400 degrees Celsius, and only 3% is 500 degrees or hotter, so Akazawa’s Stirling engine revival is welcomed by the industry.