Steam engine

[1] A steam engine is a heat engine doing mechanical work via steam as working fluid, using force made by steam pressure to push a piston back forth in a cylinder, a pushing force transformed by a connecting rod and crank into rotational force for work. 

The term "steam engine" is often used to reciprocate engines as just depicted, though some authorities also refer to the steam turbine and devices like Hero's aeolipile. The engines' crucial features are being external combustion engines, where the working fluid separates from the combustion products. The ideal thermodynamic cycle used to analyze this process is the Rankine cycle. Generally, the term steam engine refers to either full steam plants (like boilers), like railway steam locomotives and portable engines, or to only piston or turbine machinery, as in the beam engine and stationary steam engine.