View source for Pulse detonation engine

{{short description|Rocket engine that uses detonation waves to combust fuel and oxidizer}}

A '''pulse detonation engine''' ('''PDE''') is a type of [[Air propulsion|propulsion]] system that uses [[detonation wave]]s to [[Combustion|combust]] the fuel and [[oxidizer]] mixture.<ref>{{cite journal |last1=Kailasanath |first1=K. |title=Review of Propulsion Applications of Detonation Waves |journal=[[AIAA Journal]] |date=September 2000 |volume=38 |issue=9 |pages=1698–1708 |doi=10.2514/2.1156 |bibcode=2000AIAAJ..38.1698K |url=https://arc.aiaa.org/doi/abs/10.2514/2.1156?journalCode=aiaaj |access-date=28 November 2021|url-access=subscription }}</ref><ref>{{cite journal |last1=Roy |first1=G.D. |last2=Frolov |first2=S.M. |last3=Borisov |first3=A.A. |last4=Netzer |first4=D.W. |title=Pulse detonation propulsion: challenges, current status, and future perspective |journal=Progress in Energy and Combustion Science |date=January 2004 |volume=30 |issue=6 |pages=545–672 |doi=10.1016/j.pecs.2004.05.001 |bibcode=2004PECS...30..545R |url=https://www.sciencedirect.com/science/article/abs/pii/S0360128504000383 |access-date=28 November 2021|url-access=subscription }}</ref>

The engine is pulsed because the mixture must be renewed in the [[combustion chamber]] between each detonation wave and the next. Theoretically, a PDE can operate from [[subsonic flight|subsonic]] up to a [[hypersonic]] flight speed of roughly [[Mach number|Mach]] 5. An ideal PDE design can have a thermodynamic [[Fuel efficiency|efficiency]] higher than other designs like [[turbojet]]s and [[turbofan]]s because a detonation wave rapidly compresses the mixture and adds heat at constant volume. Consequently, [[moving parts]] like [[Axial compressor|compressor spools]] are not necessarily required in the engine, which could significantly reduce overall weight and cost. Key issues for further development include fast and efficient mixing of the fuel and oxidizer, the prevention of [[Autoignition temperature|autoignition]], and integration with an inlet and nozzle.

{{As of|May 2023}}, no practical PDE has been put into production, but several testbed engines have been built and one was successfully integrated into a low-speed demonstration aircraft that flew in sustained PDE powered flight in 2008.

== History ==
[[File:PDE-powered aircraft.jpg|thumb|300px|In-flight picture of the pulsed-detonation–powered, and heavily modified, [[Rutan Long-EZ]] on January 31, 2008]]

PDEs have been considered for propulsion since 1940.<ref>Hoffmann, N., ''Reaction Propulsion by Intermittent Detonative Combustion,'' German Ministry of Supply, Volkenrode Translation, 1940.</ref>

The first known flight of an aircraft powered by a pulse detonation engine took place at the [[Mojave Airport & Spaceport|Mojave Air & Space Port]] on 31 January 2008.<ref>Norris, G., "Pulse Power: Pulse Detonation Engine-powered Flight Demonstration Marks Milestone in Mojave," ''Aviation Week & Space Technology'', Vol. 168, No. 7, 2008, pp. 60.</ref>  The project was developed by the [[Air Force Research Laboratory]] and Innovative Scientific Solutions, Inc.  The aircraft selected for the flight was a heavily modified [[Scaled Composites]] [[Rutan Long-EZ|Long-EZ]], named ''Borealis''.<ref>''Borealis'' display poster text at Museum of USAF</ref> The engine consisted of four tubes producing pulse detonations at a frequency of 80&nbsp;Hz, creating up to 200 pounds of thrust (890 newtons).  Many fuels were considered and tested by the engine developers in recent years, but a refined [[octane]] was used for this flight.  A small rocket system was used to facilitate the liftoff of the Long-EZ, but the PDE operated under its own power for 10 seconds at an altitude of approximately 100 feet (30 m). The flight took place at a low speed whereas the appeal of the PDE engine concept lies more at high speeds, but the demonstration showed that a PDE can be integrated into an aircraft frame without experiencing structural problems from the 195-200&nbsp;dB detonation waves.  No more flights are planned for the modified Long-EZ, but the success is likely to fuel more funding for PDE research. The aircraft itself has been moved to the [[National Museum of the United States Air Force]] for display.<ref>[https://www.af.mil/News/Article-Display/Article/123534/pulsed-detonation-engine-flies-into-history/ "Pulse Detonation Engine Flies Into History"], ''Air Force Print News Today'', 16 May 2008, accessed 16 August 2008</ref>

In June 2008, the [[Defense Advanced Research Projects Agency]] (DARPA) unveiled [[Blackswift]], which was intended to use this technology to reach speeds of up to Mach 6.<ref name="wired">{{Cite news |title = Explosive Engine Key to Hypersonic Plane|first = Noah|last = Shachtman|author-link = Noah Shachtman|url = https://www.wired.com/dangerroom/2008/06/the-military-wa/|magazine = [[Wired (magazine)|Wired]]|publisher = [[Condé Nast Publications]] |location = San Francisco, California |date = 24 June 2008|access-date = 2009-06-27}}<!-- [http://blog.wired.com/defense/2008/06/the-military-wa.html ''Wired'' article] --></ref> However the project was reported cancelled soon afterward, in October 2008.

== Operation ==

The basic operation of the PDE is similar to that of the [[Pulsejet|pulse jet engine]]. In the pulse jet, air is mixed with fuel to create a flammable mixture that is then ignited in an open chamber. The resulting combustion greatly increases the pressure of the mixture to approximately 100 atmospheres (10 MPa),<ref>[http://www.publicaddress.net/default,4114.sm "Pulse Detonation Engines"], An interview with Dr John Hoke, head researcher from Innovative Scientific Solutions Incorporated PDE program under contract to the United States Air Force Research Laboratory,  broadcast on New Zealand radio, 14 April 2007</ref> which then expands through a nozzle for thrust.

To ensure that the mixture exits to the rear, thereby pushing the aircraft forward, a series of shutters are used to close off the front of the engine. Careful tuning of the inlet ensures the shutters close at the right time to force the air to travel in one direction only through the engine. Some pulse jet designs used a tuned resonant cavity to provide the valving action through the airflow in the system. These designs normally look like a U-shaped tube, open at both ends.

In either system, the pulse jet has problems during the combustion process. As the fuel burns and expands to create thrust, it is also pushing any remaining unburnt charge rearward, out of the nozzle. In many cases some of the charge is ejected before burning, which causes the famous trail of flame seen on the [[V-1 flying bomb]] and other pulse jets. Even while inside the engine, the mixture's volume is constantly changing which inefficiently converts fuel into usable energy.

All regular jet engines and most rocket engines operate on the ''[[deflagration]]'' of fuel, that is, the rapid but [[Speed of sound|subsonic]] [[combustion]] of [[fuel]]. The pulse detonation engine is a concept currently{{When|date=May 2023}} in active development to create a jet engine that operates on the supersonic ''[[detonation]]'' of fuel. Because the combustion takes place so rapidly, the charge (fuel/air mix) does not have time to expand during this process, so it takes place under almost [[Isochoric process|constant volume]]. Constant volume combustion is more efficient than open-cycle designs like [[gas turbine]]s, which leads to greater [[fuel efficiency]].

As the combustion process is so rapid, mechanical shutters are difficult to arrange with the required performance. Instead, PDEs generally use a series of valves to time the process carefully.{{Cn|date=May 2023}}

Most PDE research is military in nature, as the engine could be used to develop a new generation of high-speed, long-range [[reconnaissance aircraft]] that would fly high enough to be out of range of any current anti-aircraft defenses, while offering range considerably greater than the [[SR-71]], which required a massive tanker support fleet.{{Cn|date=May 2023}}

Key difficulties in pulse detonation engines are achieving DDT without requiring a tube long enough to make it impractical and drag-imposing on the aircraft (adding a U-bend into the tube extinguishes the detonation wave); reducing the noise (often described as sounding like a jackhammer); and damping the severe vibration caused by the operation of the engine.{{Cn|date=May 2023}}

== Uses ==

If both fuel and oxidizer are carried by the vehicle a pulse detonation engine is independent of the atmosphere and it can be used in [[spaceflight]]. On 26 July 2021 (UTC), Japan's space agency [[JAXA]] successfully tested a pulse detonation rocket engine in space on a [[S-520]] sounding rocket flight.<ref name="jaxa">{{cite news |last1=Hebden |first1=Kerry |title=Japan successfully tests rocket engine propelled by shock waves |url=https://room.eu.com/news/japan-successfully-tests-rocket-engine-propelled-by-shock-waves |access-date=20 August 2021 |work=Room, The Space Journal of Asgardia |date=28 July 2021}}</ref>  The upper stage of the rocket used a [[rotating detonation engine]] (RDE) as the main engine and a S-shaped pulse detonating engine was used to de-spin the stage after the main engine burn. PDE operated three times in the flight for a total of 14 cycles.<ref>{{Cite journal |last1=Buyakofu |first1=Valentin |last2=Matsuoka |first2=Ken |last3=Matsuyama |first3=Koichi |last4=Kawasaki |first4=Akira |last5=Watanabe |first5=Hiroaki |last6=Itouyama |first6=Noboru |last7=Goto |first7=Keisuke |last8=Ishihara |first8=Kazuki |last9=Noda |first9=Tomoyuki |last10=Kasahara |first10=Jiro |last11=Matsuo |first11=Akiko |last12=Funaki |first12=Ikkoh |last13=Nakata |first13=Daisuke |last14=Uchiumi |first14=Masaharu |last15=Habu |first15=Hiroto |display-authors=1 |date=2023 |orig-date=2022 |title=Flight Demonstration of Pulse Detonation Engine Using Sounding Rocket S-520-31 in Space |url=https://www.researchgate.net/publication/363205605 |journal=Journal of Spacecraft and Rockets |volume=60 |issue=1 |pages=181–189 |doi=10.2514/1.A35394 |bibcode=2023JSpRo..60..181B |issn=0022-4650}}</ref>

== See also ==

* [[Nuclear pulse propulsion]]
* [[Rotating detonation engine]]
* [[Scramjet]]
* [[Gluhareff Pressure Jet]]
* [[Aurora aircraft]]

== References ==

{{refs}}

== External links ==

* [https://innssi.com/pulsed-detonation-engine/ Innovative Scientific Solutions Inc.]
* [http://www.aardvark.co.nz/pjet/pde.shtml Pulse Detonation Engines]
* [https://web.archive.org/web/20060313223530/http://www.popsci.com/popsci/aviationspace/e46d5b4a1db84010vgnvcm1000004eecbccdrcrd.html Popular Science]
* [https://patents.google.com/patent/US2942412 1952 Pulse Detonation Jet Propulsion Patent by William Bollay]
* [http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=11&f=G&l=50&d=PTXT&S1=5542247&OS=5542247&RS=5542247 Apparatus powered using laser-supplied energy, US patent Issued on 6 August 1996 Boyd B. Bushman]
* [https://www.slideshare.net/slideshow/pde-propulsion-options-35968274/35968274 Pulse Detonation Propulsion Options]
* [http://www.defenselink.mil/comptroller/defbudget/fy2010/budget_justification/pdfs/03_RDT_and_E/Vol_1_DARPA/DARPA_PB10_RDTE-05-04-09.pdf DARPA May 2009 notes on PDE]
* [https://aeroenginesaz.com/en/extras_PDE-pulse-detonation-engine PDE (Pulse Detonation Engine)]
* [https://innssi.com/pulsed-detonation-engine/ Pulsed Detonation Engine]
* [https://www.youtube.com/watch?v=x5OJrOA-WoQ New Engine for supersonic and Hypersonic speed by DRDO | The PDEs]

{{Emerging technologies|transport=yes}}

{{Use dmy dates|date=February 2015}}
[[Category:Jet engines]]
[[Category:Aircraft engines]]