Editing Jet engine (section)

==Types of jet engine==
There are a large number of different types of jet engines, all of which achieve forward thrust from the principle of ''jet propulsion''.

===Airbreathing===
{{Main article|Airbreathing jet engine}}
Commonly aircraft are propelled by airbreathing jet engines. Most airbreathing jet engines that are in use are [[turbofan]] jet engines, which give good efficiency at speeds just below the speed of sound.

==== Turbojet ====
{{Main article|Turbojet}}
[[File:Jet engine.svg|thumb|right|Turbojet engine]]
A [[turbojet]] engine is a [[gas turbine]] engine that works by compressing air with an inlet and a compressor ([[Axial compressor|axial]], [[Centrifugal compressor|centrifugal]], or both), mixing fuel with the compressed air, burning the mixture in the [[combustor]], and then passing the hot, high pressure air through a [[turbine]] and a [[propelling nozzle|nozzle]]. The compressor is powered by the turbine, which extracts energy from the expanding gas passing through it. The engine converts internal energy in the fuel to increased momentum of the gas flowing through the engine, producing thrust. All the air entering the compressor is passed through the combustor, and turbine, unlike the [[turbofan]] engine described below.<ref>{{Cite book|last1=Mattingly|first1=Jack D.|title=Elements of Propulsion: Gas Turbines and Rockets|series=AIAA Education Series|year=2006|publisher=American Institute of Aeronautics and Astronautics|location=Reston, VA |page=6|isbn=978-1-56347-779-9}}</ref> 

==== Turbofan ====
{{Main article|Turbofan}}
[[File:Turbofan operation lbp.svg|thumb|right|Schematic diagram illustrating the operation of a low-bypass turbofan engine.]]
[[Turbofan]]s differ from turbojets in that they have an additional fan at the front of the engine, which accelerates air in a duct bypassing the core gas turbine engine. Turbofans are the dominant engine type for medium and long-range [[airliner]]s.

Turbofans are usually more efficient than turbojets at subsonic speeds, but at high speeds their large frontal area generates more [[Aerodynamic drag|drag]].<ref>Mattingly, pp. 9–11</ref> Therefore, in supersonic flight, and in military and other aircraft where other considerations have a higher priority than fuel efficiency, fans tend to be smaller or absent.

Because of these distinctions, turbofan engine designs are often categorized as [[Low-bypass turbofan|low-bypass]] or [[High-bypass turbofan|high-bypass]], depending upon the amount of air which bypasses the core of the engine.  Low-bypass turbofans have a [[bypass ratio]] of around 2:1 or less.
==== Propfan ====
{{Main article|Propfan}}
A [[propfan]] engine is a type of airbreathing jet engine which combines aspects of [[turboprop]] and [[turbofan]]. Its design consists of a central gas turbine which drives open-air [[contra-rotating propellers]]. Unlike turboprop engines, in which the propeller and the engine are considered two separate products, the propfan’s gas generator and its unshrouded propeller module are heavily integrated and are considered to be a single product. {{Citation needed|date=November 2024}} Additionally, the propfan’s short, heavily twisted [[Variable-pitch propeller (aeronautics)|variable pitch]] blades closely remember the ducted fan blades of turbofan engines.

Propfans are designed to offer the speed and performance of turbofan engines with fuel efficiency of turboprops. However, due to low fuel costs and high cabin noise, early propfan projects were abandoned.<ref>{{Cite web |last=Flight International (2007-07-12). |title=Whatever happened to propfans? |url=https://www.flightglobal.com/whatever-happened-to-propfans/74180.article |url-status=live |archive-url=https://web.archive.org/web/20071020123934/http://flightglobal.com/articles/2007/06/12/214520/whatever-happened-to-propfans.html |archive-date=October 20, 2007 |access-date=2024-11-28 |website= |language=en}}</ref> Very few aircraft have flown with propfans, with the [[Antonov An-70]] being the first and only aircraft to fly while being powered solely by propfan engines.

==== Advanced technology engine ====
{{Main article|Advanced Technology Engine}}
The term Advanced technology engine refers to the modern generation of jet engines.<ref>{{cite book |title=A Dictionary of Aviation |first=David W. |last=Wragg |isbn=9780850451634 |edition=first |publisher=Osprey |year=1973 |page=4}}</ref> The principle is that a turbine engine will function more efficiently if the various sets of turbines can revolve at their individual optimum speeds, instead of at the same speed. The true advanced technology engine has a triple spool, meaning that instead of having a single drive shaft, there are three, in order that the three sets of blades may revolve at different speeds. An interim state is a twin-spool engine, allowing only two different speeds for the turbines.

==== Ram compression ====
{{Further|Ramjet|Scramjet}}
Ram compression jet engines are airbreathing engines similar to gas turbine engines in so far as they both use the [[Brayton cycle]]. Gas turbine and ram compression engines differ, however, in how they compress the incoming airflow. Whereas gas turbine engines use axial or centrifugal compressors to compress incoming air, ram engines rely only on air compressed in the inlet or diffuser.<ref name="m14">Mattingly, p. 14</ref> A ram engine thus requires a substantial initial forward airspeed before it can function. Ramjets are considered the simplest type of air breathing jet engine because they have no moving parts in the engine proper, only in the accessories.<ref>{{Cite book
|last1=Flack |first1=Ronald D.|title=Fundamentals of Jet Propulsion with Applications|series=Cambridge Aerospace Series|year=2005|publisher=Cambridge University Press|location=New York|page=16|isbn=978-0-521-81983-1}}</ref>

Scramjets differ mainly in the fact that the air does not slow to subsonic speeds. Rather, they use supersonic combustion. They are efficient at even higher speed. Very few have been built or flown.

====Non-continuous combustion====
{| class="wikitable"
|-
!'''Type'''
!'''Description'''
!'''Advantages'''
!'''Disadvantages'''
|-
![[Motorjet]]
|Works like a turbojet but a [[piston engine]] drives the compressor instead of a turbine.
|Higher exhaust velocity than a propeller, offering better thrust at high speed
|Heavy, inefficient and underpowered. Example: [[Caproni Campini N.1]].
|-
![[Pulsejet]]
|Air is compressed and combusted intermittently instead of continuously. Some designs use valves.
|Very simple design, used for the [[V-1 flying bomb]] and more recently on model aircraft
|Noisy, inefficient (low compression ratio), works poorly on a large scale, valves on valved designs wear out quickly
|-
![[Pulse detonation engine]]
|Similar to a pulsejet, but combustion occurs as a [[detonation]] instead of a [[deflagration]], may or may not need valves
|Maximum theoretical engine efficiency
|Extremely noisy, parts subject to extreme mechanical fatigue, hard to start detonation, not practical for current use
|}