External combustion engine in the context of "Working fluid"

A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be transformed by a connecting rod and crank into rotational force for work. The term "steam engine" is most commonly applied to reciprocating engines as just described, although some authorities have also referred to the steam turbine and devices such as Hero's aeolipile as "steam engines". The essential feature of steam engines is that they are external combustion engines, where the working fluid is separated from the combustion products. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In general usage, the term steam engine can refer to either complete steam plants (including boilers etc.), such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine.

Steam-driven devices such as the aeolipile were known in the first century AD, and there were a few other uses recorded in the 16th century. In 1606 Jerónimo de Ayanz y Beaumont patented his invention of the first steam-powered water pump for draining mines. Thomas Savery is considered the inventor of the first commercially used steam powered device, a steam pump that used steam pressure operating directly on the water. The first commercially successful engine that could transmit continuous power to a machine was developed in 1712 by Thomas Newcomen. In 1764, James Watt made a critical improvement by removing spent steam to a separate vessel for condensation, greatly improving the amount of work obtained per unit of fuel consumed. By the 19th century, stationary steam engines powered the factories of the Industrial Revolution. Steam engines replaced sails for ships on paddle steamers, and steam locomotives operated on the railways.

An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to components of the engine. The force is typically applied to pistons (piston engine), turbine blades (gas turbine), a rotor (Wankel engine), or a nozzle (jet engine). This force moves the component over a distance. This process transforms chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.

The first commercially successful internal combustion engines were invented in the mid-19th century. The first modern internal combustion engine, the Otto engine, was designed in 1876 by the German engineer Nicolaus Otto. The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar two-stroke and four-stroke piston engines, along with variants, such as the six-stroke piston engine and the Wankel rotary engine. A second class of internal combustion engines use continuous combustion: gas turbines, jet engines and most rocket engines, each of which are internal combustion engines on the same principle as previously described. In contrast, in external combustion engines, such as steam or Stirling engines, energy is delivered to a working fluid not consisting of, mixed with, or contaminated by combustion products. Working fluids for external combustion engines include air, hot water, pressurized water or even boiler-heated liquid sodium.

A steam car is a car (automobile) propelled by a steam engine. A steam engine is an external combustion engine (ECE), whereas the gasoline and diesel engines that eventually became standard are internal combustion engines (ICE). ECEs have a lower thermal efficiency, but carbon monoxide production is more readily regulated.

The first experimental steam-powered cars were built in the 18th and 19th centuries, but it was not until after Richard Trevithick developed the use of high-pressure steam around 1800 that mobile steam engines became a practical proposition. By the 1850s there was a flurry of new steam car manufacturers.