What is an external combustion engine?
An external combustion engine is a reciprocating engine for which combustion takes place outside the cylinders. An early example is the steam engine, which typically burned coal outside of the engine to turn water into steam. The Stirling engine is an external combustion engine that uses a working fluid to move pistons in cylinders. In an internal combustion engine, on the other hand, a fuel is burned inside engine cylinders. Though steam engines have largely been replaced, Stirling engines have many potential applications. While combustion gases do not enter the cylinders of an external combustion engine, they must be in thermal contact with the engine for it to function. In a steam engine, the heat from burning coal is transferred to water through the walls of a boiler. This heat turns water into steam, which is directed into the cylinders of the engine. At the appropriate time, the steam pushes on a piston that turns a crankshaft. In this way, a steam engine transforms the chemical
