An external combustion engine (EC engine) is a heat engine where an (internal) working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. A heat engine is a physical or theoretical device that converts Thermal energy to mechanical output FLUID ( F ast L ight '''U'''ser '''I'''nterface D esigner is a graphical editor that is used to produce FLTK Source code An engine is a mechanical device that produces some form of output from a given input A heat exchanger is a device built for efficient Heat transfer from one medium to another whether the media are separated by a solid wall so that they never mix or the media The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable work. FLUID ( F ast L ight '''U'''ser '''I'''nterface D esigner is a graphical editor that is used to produce FLTK Source code In Physics, mechanical work is the amount of Energy transferred by a Force.  The fluid is then cooled, compressed and reused (closed cycle), or (less commonly) dumped, and cool fluid pulled in (open cycle air engine).
"Combustion" refers to burning fuel with an oxidizer, to supply the heat. Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of Fuel is any material that is burned or altered in order to obtain energy An oxidizing agent or oxidising agent (also called an oxidant, oxidizer or oxidiser) can be defined as either a Chemical compound Engines of similar (or even identical) configuration and operation may use a supply of heat from other sources such as nuclear, solar, geothermal or exothermic reactions not involving combustion; but are not then strictly classed as external combustion engines.
The working fluid can be a gas as in a Stirling engine, or steam as in a steam engine. This page is about the physical properties of gas as a state of matter A Stirling engine is a closed-cycle regenerative Heat engine with a Gaseous working fluid Uses A Steam engine uses the expansion of steam in order to drive a Piston or Turbine to perform Mechanical work. A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. The fluid can be of any composition; gas is by far the most common, although even single-phase liquid is sometimes used. This page is about the physical properties of gas as a state of matter Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of In the case of the steam engine, the fluid changes phases between liquid and gas. A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties