Editing Engine (section)

=== Heat engine ===
{{Main|Heat engine}}

==== Combustion engine ====
Combustion engines are [[heat engine]]s driven by the heat of a [[combustion]] process.

==== Internal combustion engine ====
[[File:A three-horsepower internal combustion engine that ran on coal gas LCCN2006691790.jpg|thumb|254x254px|A three-horsepower internal combustion engine that ran on coal gas]]
{{Main|Internal combustion engine}}The ''internal combustion engine'' is an engine in which the [[combustion]] of a fuel (generally, [[fossil fuel]]) occurs with an oxidizer (usually air) in a [[combustion chamber]]. In an internal combustion engine the expansion of the high [[temperature]] and high [[pressure]] gases, which are produced by the combustion, directly applies [[force]] to components of the engine, such as the [[piston]]s or [[turbine blade]]s or a [[propulsive nozzle|nozzle]], and by moving it over a distance, generates mechanical [[work (physics)|work]].<ref name=r1 >{{cite encyclopedia|first=Charles Lafayette II |last=Proctor |url=https://www.britannica.com/EBchecked/topic/290504/internal-combustion-engine |title=Internal Combustion engines |encyclopedia=Encyclopædia Britannica Online |access-date=2011-05-09}}</ref><ref name=r2 >{{cite web |url=http://www.answers.com/topic/internal-combustion-engine?cat=technology |title=Internal combustion engine |publisher=Answers.com |access-date=2011-05-09 |archive-date=2011-06-28 |archive-url=https://web.archive.org/web/20110628184840/http://www.answers.com/topic/internal-combustion-engine?cat=technology |url-status=live }}</ref><ref name=r3>{{cite web|url=http://inventors.about.com/gi/dynamic/offsite.htm?site=http://www.bartleby.com/65/in/intern-co.html |archive-url=https://archive.today/20120721063446/http://inventors.about.com/gi/dynamic/offsite.htm?site=http://www.bartleby.com/65/in/intern-co.html |archive-date=2012-07-21 |title=Columbia encyclopedia: Internal combustion engine |publisher=Inventors.about.com |access-date=2011-05-09 }}</ref><ref name=r4 >{{cite web |url=http://www.infoplease.com/ce6/sci/A0825332.html |title=Internal-combustion engine |publisher=Infoplease.com |year=2007 |access-date=2011-05-09 |archive-date=2011-05-15 |archive-url=https://web.archive.org/web/20110515152409/http://www.infoplease.com/ce6/sci/A0825332.html |url-status=live }}</ref>

==== External combustion engine ====
{{Main|External combustion engine}}
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]]. The [[fluid]] then, by expanding and acting on the [[Mechanism (engineering)|mechanism]] of the engine produces motion and usable [[Mechanical work|work]].<ref>{{cite web |url=http://www.merriam-webster.com/dictionary/external%20combustion |title=External combustion |publisher=Merriam-Webster Online Dictionary |date=2010-08-13 |access-date=2011-05-09 |archive-date=2018-06-27 |archive-url=https://web.archive.org/web/20180627202610/https://www.merriam-webster.com/dictionary/external%20combustion |url-status=live }}</ref> 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. 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, but as external thermal engines.

The working fluid can be a gas as in a [[Stirling engine]], or [[steam]] as in a steam engine or an organic liquid such as n-pentane in an [[Organic Rankine cycle]].  The fluid can be of any composition; gas is by far the most common, although even single-phase [[liquid]] is sometimes used.  In the case of the steam engine, the fluid changes [[Phase (matter)|phases]] between liquid and gas.

==== Air-breathing combustion engines ====

''Air-breathing combustion engines'' are combustion engines that use the [[oxygen]] in atmospheric air to [[oxidise]] ('burn') the fuel, rather than carrying an [[oxidiser]], as in a [[rocket]]. Theoretically, this should result in a better [[specific impulse]] than for rocket engines.

A continuous stream of air flows through the air-breathing engine. This air is compressed, mixed with fuel, ignited and expelled as the [[exhaust gas]]. In [[reaction engine]]s, the majority of the combustion energy (heat) exits the engine as exhaust gas, which provides thrust directly.

;Examples
Typical air-breathing engines include:
* [[Reciprocating engine]]
* [[Steam engine]]
* [[Gas turbine]]
* [[Airbreathing jet engine]]
* [[Turboprop|Turbo-propeller engine]]
* [[Pulse detonation engine]]
* [[Pulse jet]]
* [[Ramjet]]
* [[Scramjet]]
* [[Liquid air cycle engine]]/[[Reaction Engines SABRE]].

==== Environmental effects ====
The operation of engines typically has a negative impact upon [[air quality]] and ambient [[noise pollution|sound levels]]. There has been a growing emphasis on the pollution producing features of automotive power systems. This has created new interest in alternate power sources and internal-combustion engine refinements. Though a few limited-production battery-powered electric vehicles have appeared, they have not proved competitive owing to costs and operating characteristics.{{Citation needed|date=November 2012}} In the 21st century the diesel engine has been increasing in popularity with automobile owners. However, the gasoline engine and the Diesel engine,  with their new emission-control devices to improve emission performance, have not yet been significantly challenged.{{Citation needed|date=November 2012}} A number of manufacturers have introduced hybrid engines, mainly involving a small gasoline engine coupled with an electric motor and with a large battery bank, these are starting to become a popular option because of their environment awareness.

==== Air quality ====
[[Exhaust gas]] from a spark ignition engine consists of the following: [[nitrogen]] 70 to 75% (by volume), [[water vapor]] 10 to 12%, [[carbon dioxide]] 10 to 13.5%, [[hydrogen]] 0.5 to 2%, [[oxygen]] 0.2 to 2%, [[carbon monoxide]]: 0.1 to 6%, unburnt [[hydrocarbons]] and partial [[oxidation]] products (e.g. [[aldehyde]]s) 0.5 to 1%, [[nitrogen monoxide]] 0.01 to 0.4%, [[nitrous oxide]] <100 ppm, [[sulfur dioxide]] 15 to 60 ppm, traces of other compounds such as fuel additives and lubricants, also halogen and metallic compounds, and other particles.<ref>Paul Degobert, Society of Automotive Engineers (1995), ''Automobiles and Pollution''</ref> Carbon monoxide is highly toxic, and can cause [[carbon monoxide poisoning]], so it is important to avoid any build-up of the gas in a confined space. [[Catalytic converter]]s can reduce toxic emissions, but not eliminate them. Also, resulting greenhouse gas emissions, chiefly [[carbon dioxide]], from the widespread use of engines in the modern industrialized world is contributing to the global [[greenhouse effect]] – a primary concern regarding [[global warming]].

==== Non-combusting heat engines ====
{{Main|heat engine}}
Some engines convert heat from noncombustive processes into mechanical work, for example a nuclear power plant uses the heat from the nuclear reaction to produce steam and drive a steam engine, or a gas turbine in a rocket engine may be driven by decomposing [[hydrogen peroxide]]. Apart from the different energy source, the engine is often engineered much the same as an internal or external combustion engine.

Another group of noncombustive engines includes [[thermoacoustic heat engine]]s (sometimes called "TA engines") which are thermoacoustic devices that use high-amplitude sound waves to pump heat from one place to another, or conversely use a heat difference to induce high-amplitude sound waves. In general, thermoacoustic engines can be divided into standing wave and travelling wave devices.<ref>{{cite book |url=https://www.scribd.com/doc/147785416/Experimental-Investigations-on-a-Standing-Wave-Thermoacoustic-Engine#fullscreen |first=Mahmoud |last=Emam |title=Experimental Investigations on a Standing-Wave Thermoacoustic Engine, M.Sc. Thesis |publisher=Cairo University |location=Egypt |year=2013 |access-date=2013-09-26 |archive-date=2013-09-28 |archive-url=https://web.archive.org/web/20130928064211/http://www.scribd.com/doc/147785416/Experimental-Investigations-on-a-Standing-Wave-Thermoacoustic-Engine#fullscreen |url-status=live }}</ref>

[[Stirling engines]] can be another form of non-combustive heat engine. They use the Stirling thermodynamic cycle to convert heat into work. An example is the alpha type Stirling engine, whereby gas flows, via a [[recuperator]], between a hot cylinder and a cold cylinder, which are attached to reciprocating pistons 90° out of phase. The gas receives heat at the hot cylinder and expands, driving the piston that turns the [[crankshaft]]. After expanding and flowing through the recuperator, the gas rejects heat at the cold cylinder and the ensuing pressure drop leads to its compression by the other (displacement) piston, which forces it back to the hot cylinder.<ref>{{cite journal |first=Khaled M. |last=Bataineh |title=Numerical thermodynamic model of alpha-type Stirling engine |journal=Case Studies in Thermal Engineering |volume=12 |year=2018 |pages=104–116 |issn=2214-157X |doi=10.1016/j.csite.2018.03.010|doi-access=free }}</ref>