Robert Stirling patents the Stirling air engine

Background. Robert Stirling was a Scottish clergyman and engineer who invented the Stirling engine. In 1816, he patented his air engine, which was designed as an industrial prime mover to rival the steam engine. The engine operated by cyclically expanding and contracting air, converting heat energy to mechanical work.

Patent Scope. The 1816 patent described a closed-cycle air engine, contrasting with Cayley's engine where air was forced through a furnace and exhausted. Stirling's design worked air in a closed circuit. The patent also covered a heat exchanger called an 'economiser,' which stored heat from the working gas during one part of the cycle and returned it during another.

Engine Principle. The Stirling engine is a closed-cycle regenerative heat engine with a permanent gaseous working fluid. The inclusion of the regenerator differentiates it from other closed-cycle hot air engines. The working fluid is heated by energy supplied from outside the engine's interior space, and a displacer moves the fluid to a location where it is cooled, creating a partial vacuum.