Editing Ramjet (section)

==Related engines==

===Air turboramjet===
{{Excerpt|Air turborocket|Air turboramjet|paragraphs=1}}

===Supersonic-combustion ramjets (scramjets)===
{{Main|Scramjet}}
Ramjet diffusers slow the incoming air to a subsonic velocity before it enters the combustor. [[Scramjet]]s are similar to ramjets, but the air flows through the combustor at supersonic speed. This increases the pressure recovered from the streaming air and improves net thrust. Thermal choking of the exhaust is avoided by having a relatively high supersonic air velocity at combustor entry. Fuel injection is often into a sheltered region below a step in the combustor wall. The [[Boeing X-43]] was a small experimental ramjet<ref>[http://www.boeing.com/history/chronology/chron17.html "Boeing: History – Chronology 2002–2004"] {{webarchive|url=https://web.archive.org/web/20111114144020/http://www.boeing.com/history/chronology/chron17.html |date=November 14, 2011}}.</ref> that achieved {{convert|5|Mach|m/s km/h|sigfig=2}} for 200 seconds on the [[X-51A Waverider]].<ref>[https://www.af.mil/News/Article-Display/Article/116538/x-51-waverider-makes-historic-hypersonic-flight/ "USAF vehicle breaks record for hypersonic flight"] {{webarchive|url=https://web.archive.org/web/20160410144856/http://www.wpafb.af.mil/news/story.asp?id=123206524 |date=April 10, 2016}}.</ref>

===Standing oblique detonation ramjets (Sodramjets)===
{{Excerpt|Shcramjet|paragraphs=1}}

===Precooled engines===
{{Main|Precooled jet engine}}
A variant of the ramjet is the 'combined cycle' engine, intended to overcome the ramjet's limitations. One example of this is the [[Reaction Engines SABRE|SABRE]] engine, which uses a precooler, behind which is the ramjet and turbine machinery.

The [[ATREX]] engine developed in Japan is an experimental implementation of this concept. It uses [[liquid hydrogen]] fuel in a single-fan arrangement. The liquid fuel is pumped through a [[heat exchanger]] in the air intake, simultaneously heating the fuel and cooling the incoming air. This cooling is critical to efficient operation. The hydrogen then continues through a second heat exchanger position after the combustion section, where the hot exhaust is used to further heat the hydrogen, turning it into a high pressure gas. This gas is then passed through the tips of the fan to provide driving power to the fan at subsonic speeds. After mixing with the air, it is burned in the combustion chamber.

The [[Reaction Engines Scimitar]] was proposed for the [[LAPCAT]] [[hypersonic]] airliner, and the [[Reaction Engines SABRE]] for the [[Reaction Engines Skylon]] spaceplane.

===Nuclear-powered ramjet===

====United States====
{{Main|Project Pluto}}
During the [[Cold War]], the United States designed and ground-tested a nuclear-powered ramjet called [[Project Pluto]]. This system, intended for use in a [[cruise missile]], used no combustion; a high-temperature, unshielded [[nuclear reactor]] heated the air. The ramjet was predicted to be able to fly at supersonic speeds for months. Because the reactor was unshielded, it was dangerous to anyone in or around the vehicle flight path (although its exhaust wasn't radioactive). The project was ultimately cancelled because [[ICBM]]s seemed to serve the purpose better.<ref>{{cite web |title=Project Pluto |url=https://msts.sites.nv.doe.gov/wp-content/uploads/2023/04/DOENV_763.pdf |access-date=March 5, 2024 |url-status=live |archive-url=https://web.archive.org/web/20120303003018/http://www.nv.doe.gov/library/factsheets/DOENV_763.pdf |archive-date=3 March 2012}}</ref>

This type of engine could be used for the exploration of planetary atmospheres such as Jupiter's.<ref>IAC-03-Q.4.09 [https://arc.aiaa.org/doi/10.2514/6.IAC-03-Q.4.09 Application of the MITEE Nuclear Ramjet for Ultra Long Range Flyer Missions in the Atmospheres of Jupiter and the Other Giant Planets] - [[International Astronautical Congress|IAC]] 2003 Bremen</ref>

====Russia====
{{Main|9M730 Burevestnik}}
On 1 March 2018 President Vladimir Putin announced a nuclear-powered ramjet cruise missile capable of extended long range flight. It was designated 9M730 "Burevestnik" (Petrel) and has the [[NATO reporting name]] SSC-X-9 "Skyfall".<ref>{{cite tweet |author=Ankit Panda |user=nktpnd |title=Update from a source: Russia's Burevestnik nuclear-powered cruise missile has a NATO designator — SSC-X-9 SKYFALL. (USIC also calls this missile the KY30.) |number=1064991343624237059 |date=2018-11-20 |access-date=2023-01-24}}</ref> On 9 August 2019, an explosion and release of radioactive material was recorded at the [[State Central Navy Testing Range]]. Recovery efforts were underway to raise a test article that had landed in the [[White Sea]] during testing in 2018 when the nuclear power source of the missile [[Nyonoksa radiation accident|detonated and killed 5 researchers]].<ref>{{cite web |title=Russian nuclear engineers buried after 'Skyfall nuclear' blast |website=aljazeera.com |language=en |url=https://www.aljazeera.com/news/2019/8/13/russian-nuclear-engineers-buried-after-skyfall-nuclear-blast |access-date=2023-01-24}}</ref>

===Ionospheric ramjet===
The upper atmosphere above about {{convert|100|km}} contains [[monatomic]] oxygen produced by the sun through photochemistry. A concept was created by NASA for recombining this (thin) gas back to diatomic molecules at orbital speeds to power a ramjet.<ref>[https://ntrs.nasa.gov/citations/19930085302 Preliminary survey of propulsion using chemical energy stored in the upper atmosphere] by Lionel V. Baldwin and Perry L. Blackshear.</ref>

===Bussard ramjet===
{{Excerpt|Bussard ramjet|paragraphs=1}}

===Ramjet mode for an afterburning turbojet===
{{Main|Pratt & Whitney J58}}
An afterburning turbojet or bypass engine can be described as transitioning from turbo to ramjet mode if it can attain a flight speed at which the [[engine pressure ratio]] (epr) has fallen to one. The turbo afterburner then acts as a ramburner.<ref>[https://apps.dtic.mil/dtic/tr/fulltext/u2/a311466.pdf Article title] p. 18-1</ref> The intake ram pressure is present at entry to the afterburner but is no longer augmented with a pressure rise from the turbomachinery. Further increase in speed introduces a pressure loss due to the presence of the turbomachinery as the epr drops below one.

A notable example was the propulsion system for the [[Lockheed SR-71 Blackbird]] with an epr=0.9 at Mach 3.2.<ref name="enginehistory.org">{{cite conference |title=SR-71 Propulsion System P&W J58 Engine (JT11D-20) |first=Peter |last=Law |year=2013 |url=http://www.enginehistory.org/Convention/2013/SR-71Propul/SR-71Propul.shtml |access-date=2020-01-18}}</ref> The thrust required, airflow and exhaust temperature, to reach this speed came from a standard method for increasing airflow through a compressor running at low corrected speeds, compressor bleed, and being able to increase the afterburner temperature as a result of cooling the duct and nozzle using the air taken from the compressor rather than the usual, much hotter, turbine exhaust gas.<ref name="bleedpatent">{{cite patent |country=US |number=3344606 |title=Recover Bleed Air Turbojet |inventor=Robert B. Abernethy |pubdate=October 3, 1967}}</ref>