Robert Stirling

Robert Stirling (born 1790, Perthshire, Scotland—died June 6, 1878, Galston, Ayrshire) was a Scottish clergyman best known as the inventor of the Stirling engine, a type of external-combustion engine. He also invented optical devices and other instruments.

Stirling’s first patent was granted in 1816 for what became known as the Stirling cycle engine. His company manufactured engines from 1818 to 1922, during which time they were used to pump water on farms and to generate electricity. Later attempts to develop the Stirling engine for commercial use proved largely unsuccessful, though its potential for quiet operation, multiple fuel sources, high efficiency, low pollution, and high power density continues to hold considerable attraction for researchers.

Stirling’s engines were powered by an external heat source to force pistons forward and backward within the cylinders that contained them. Instead of igniting a fuel source to promote a rapid expansion of air to drive each piston, as in modern internal-combustion engines, Stirling closed-cycle engines used a gaseous working fluid that was permanently encased within the engine. The working fluid, which expanded from heating and contracted from cooling, shuttled between hot and cold cylinders. As the cylinder filled up with fluid, it would drive the piston backward, which would in turn drive a flywheel.

Stirling received additional patents in 1827 and 1840 for improvements in the design of his engine. He was made a posthumous inductee to the Scottish Engineering Hall of Fame in 2014.