By Indian Institute of Technology, copy of image in Robert Stirling's patent of 1816. Wikimedia Commons

A remarkable engine now called the Stirling engine was developed and patented in 1816 by a 25-year-old Scottish clergyman named Robert Stirling.  Stirling was devoted to the clergy but inherited a love of engineering from his father and his grandfather, who was the inventor of the threshing machine.  Some historians believe that Robert invented his new engine to replace the dangerous steam engines of that time.  Even though the Stirling engine was utilized in small, domestic projects, it was never developed for common use and was eventually overtaken by cheaper and more efficient versions of the steam engine and small, internal combustion engines.

The mechanical premise of the Stirling engine was basic but innovative; all it required to run was a source of heat.  The Stirling engine operated by cyclic compression and expansion of air or other gas (the working fluid) at different temperatures, where there was a net conversion of heat energy to mechanical work.  In contrast to internal combustion engines, Stirling engines had the potential to use renewable heat sources more easily, to be quieter, and to be more reliable with lower maintenance.  A layman's overview of the Stirling engine is available in Dr. William Watson’s latest white paper, "In the OSTI Collections: Stirling Engines."

It wasn't until the 20th century that a revival of Reverend Stirling's forgotten engine took place.  The Phillips Company developed experimental Stirling engines for a wide variety of applications and continued to work in the field until the late 1970s.  In 1996, the Swedish navy outfitted their submarines with Stirling engines.  Today, DOE databases provide a myriad of free DOE research project reports and publications where Stirling engines are being used in applications such as thermal storage, solar-only electrical generation, and spacecraft power generation.