Pulse detonation engine - AbsoluteAstronomy.com

A pulse detonation engine, or "PDE", is a type of propulsion

Air propulsion

Air propulsion is the generation of thrust during flight by an aircraft or a creature such as a bird, bat or insect.-Aircraft:An aircraft propulsion system must serve two purposes. First, the thrust from the propulsion system must balance the drag of the airplane when the airplane is cruising...

system that uses detonation waves to combust

Combustion

Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

the fuel and oxidizer mixture. The engine is pulsed because the mixture must be renewed in the combustion chamber between each detonation wave initiated by an ignition source. Theoretically, a PDE can operate from subsonic up to a hypersonic

Hypersonic

In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above...

flight speed of roughly Mach 5. An ideal PDE design can have a thermodynamic efficiency

Fuel efficiency

Fuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...

higher than other designs like turbojets and turbofan

Turbofan

The turbofan is a type of airbreathing jet engine that is widely used for aircraft propulsion. A turbofan combines two types of engines, the turbo portion which is a conventional gas turbine engine, and the fan, a propeller-like ducted fan...

s because a detonation wave rapidly compresses the mixture and adds heat at constant volume. Consequently, moving parts

Moving parts

The moving parts of a machine are those parts of it that move. Machines comprise both moving and fixed parts. The moving parts have controlled and constrained motions....

like compressor spools

Axial compressor

Axial compressors are rotating, airfoil-based compressors in which the working fluid principally flows parallel to the axis of rotation. This is in contrast with other rotating compressors such as centrifugal, axi-centrifugal and mixed-flow compressors where the air may enter axially but will have...

are not necessarily required in the engine, which could significantly reduce overall weight and cost. PDEs have been considered for propulsion for over 70 years. Key issues for further development include fast and efficient mixing of the fuel and oxidizer, the prevention of autoignition

Autoignition temperature

The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion...

, and integration with an inlet and nozzle.

To date, 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. 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. However the project was cancelled soon afterward, in October 2008.

Concept

All regular jet engines and most rocket engines operate on the deflagration
Deflagration
Deflagration is a term describing subsonic combustion that usually propagates through thermal conductivity; hot burning material heats the next layer of cold material and ignites it. Most "fire" found in daily life, from flames to explosions, is deflagration...

of fuel, that is, the rapid but subsonic

Speed of sound

The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....

combustion

Combustion

of fuel

Fuel

Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

. The pulse detonation engine is a concept currently in active development to create a jet engine that operates on the supersonic detonation
Detonation
Detonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations are observed in both conventional solid and liquid explosives, as well as in reactive gases...

of fuel.

The basic operation of the PDE is similar to that of the pulse jet engine

Pulse jet engine

A pulse jet engine is a type of jet engine in which combustion occurs in pulses. Pulsejet engines can be made with few or no moving parts, and are capable of running statically....

; air is mixed with fuel to create a flammable mixture that is then ignited. The resulting combustion greatly increases the pressure of the mixture to approximately 100 atmospheres (10 MPa), 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.

The main difference between a PDE and a traditional pulse jet engine

Pulse jet engine

A pulse jet engine is a type of jet engine in which combustion occurs in pulses. Pulsejet engines can be made with few or no moving parts, and are capable of running statically....

is that the mixture does not undergo subsonic combustion but instead, supersonic detonation. In the PDE, the oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

and fuel

Fuel

combination process is supersonic, effectively an explosion instead of burning. The other difference is that the shutters are replaced by more sophisticated valves. In some PDE designs from General Electric

General Electric

General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

, the shutters are eliminated through careful timing, using the pressure differences between the different areas of the engine to ensure the "shot" is ejected rearward.

The main side effect of the change in cycle is that the PDE is considerably more efficient. In the pulse jet engine

Pulse jet engine

A pulse jet engine is a type of jet engine in which combustion occurs in pulses. Pulsejet engines can be made with few or no moving parts, and are capable of running statically....

the combustion pushes a considerable amount of the fuel/air mix (the charge) out the rear of the engine before it has had a chance to burn (thus the trail of flame seen on the V-1 flying bomb

V-1 flying bomb

The V-1 flying bomb, also known as the Buzz Bomb or Doodlebug, was an early pulse-jet-powered predecessor of the cruise missile....

). Even while inside the engine the mixture's volume is continually changing, which is an inefficient way to burn fuel. In contrast the PDE deliberately uses a high-speed combustion process that burns all of the charge while it is still inside the engine at a constant volume.

This is said to increase the amount of heat produced per unit of fuel above any other engines, although conversion of that energy into thrust would remain inefficient. A combustion process able to produce more heat per unit of fuel would, of course, be incredibly valuable in countless applications.
Another side effect, not yet demonstrated in practical use, is the cycle time. A traditional pulsejet tops out at about 250 pulses per second due to the cycle time of the mechanical shutters, but the aim of the PDE is thousands of pulses per second, so fast that it is basically continuous from an engineering perspective. This should help smooth out the otherwise highly vibrational pulsejet engine — many small pulses will create less volume than a smaller number of larger pulses for the same net thrust. Unfortunately, detonations are many times louder than deflagrations.

The major difficulty with a pulse-detonation engine is starting the detonation. While it is possible to start a detonation directly with a large spark, the amount of energy input is very large and is not practical for an engine. The typical solution is to use a deflagration-to-detonation transition (DDT)—that is, start a high-energy deflagration, and have it accelerate down a tube to the point where it becomes fast enough to become a detonation. Alternatively the detonation can be sent around a circle and valves ensure that only the highest peak power can leak into exhaust.

This process is far more complicated than it sounds, due to the resistance the advancing wavefront encounters (similar to wave drag

Wave drag

In aeronautics, wave drag is a component of the drag on aircraft, blade tips and projectiles moving at transonic and supersonic speeds, due to the presence of shock waves. Wave drag is independent of viscous effects.- Overview :...

). DDTs occur far more readily if there are obstacles in the tube. The most widely used is the "Shchelkin spiral

Shchelkin spiral

The Shchelkin spiral is a device that assists the transition from deflagration to detonation in a pulse detonation engine. The spiral is named after Kirill Ivanovich Shchelkin, a Russian physicist who described it in his 1965 book Gas Dynamics of Combustion.In pulse detonation engines, direct...

", which is designed to create the most useful eddies with the least resistance to the moving fuel/air/exhaust mixture. The eddies lead to the flame separating into multiple fronts, some of which go backwards and collide with other fronts, and then accelerate into fronts ahead of them.

The behavior is difficult to model and to predict, and research is ongoing. As with conventional pulsejets, there are two main types of designs: valved and valveless. Designs with valves encounter the same difficult-to-resolve wear issues encountered with their pulsejet equivalents. Valveless designs typically rely on abnormalities in the air flow to ensure a one-way flow, and are very hard to achieve in a regular DDT.

NASA maintains a research program on the PDE, which is aimed at high-speed, about Mach 5

Mach number

Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...

, civilian transport systems. However 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

Reconnaissance aircraft

A reconnaissance aircraft is a manned military aircraft designed, or adapted, to carry out aerial reconnaissance.-History:The majority of World War I aircraft were reconnaissance designs...

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 to use in operation.

While most research is on the high speed regime, newer designs with much higher pulse rates in the hundreds of thousands appear to work well even at subsonic speeds. Whereas traditional engine designs always include tradeoffs that limit them to a "best speed" range, the PDE appears to outperform them at all speeds. Both Pratt & Whitney

Pratt & Whitney

Pratt & Whitney is a U.S.-based aerospace manufacturer with global service operations. It is a subsidiary of United Technologies Corporation . Pratt & Whitney's aircraft engines are widely used in both civil aviation and military aviation. Its headquarters are in East Hartford, Connecticut, USA...

and General Electric

General Electric

General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

now have active PDE research programs in an attempt to commercialize the designs.

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.

First PDE powered flight

The first flight of an aircraft powered by a pulse detonation engine took place at the Mojave Air & Space Port on January 31, 2008. The project was developed by the Air Force Research Laboratory

Air Force Research Laboratory

The Air Force Research Laboratory is a scientific research organization operated by the United States Air Force Materiel Command dedicated to leading the discovery, development, and integration of affordable aerospace warfighting technologies; planning and executing the Air Force science and...

and Innovative Scientific Solutions, Inc. The aircraft selected for the flight was a heavily modified Scaled Composites

Scaled Composites

Scaled Composites is an aerospace company founded by Burt Rutan and currently owned by Northrop Grumman that is located at the Mojave Spaceport, Mojave, California, United States...

Long-EZ

Rutan Long-EZ

-See also:-External links:****...

, named Borealis. The engine consisted of four tubes producing pulse detonations at a frequency of 80 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

Octane

Octane is a hydrocarbon and an alkane with the chemical formula C8H18, and the condensed structural formula CH36CH3. Octane has many structural isomers that differ by the amount and location of branching in the carbon chain...

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). Obviously, this 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 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

National Museum of the United States Air Force

The National Museum of the United States Air Force is the official museum of the United States Air Force located at Wright-Patterson Air Force Base northeast of Dayton, Ohio. The NMUSAF is the world's largest and oldest military aviation museum with more than 360 aircraft and missiles on display...

for display.

Popular culture

In the sci-fi novel Aelita
Aelita (novel)
Aelita also known as Aelita or, The Decline of Mars is a 1923 science fiction novel by Russian author Alexei Tolstoy.-Plot summary:...

(1923), two Russians travel to Mars in a pulse detonation rocket utilizing "a fine powder of unusual explosive force" (p. 19).
In the drama television series JAG
JAG (TV series)
JAG is an American adventure/legal drama television show that was produced by Belisarius Productions, in association with Paramount Network Television and, for the first season only, NBC Productions...

, the Season Nine episode "The One That Got Away" (original air date October 17, 2003) features the Aurora
Aurora aircraft
Aurora was a rumored mid-1980s American reconnaissance aircraft. There is no substantial evidence that it was ever built or flown and it has been termed a myth.The U.S. government has consistently denied such an aircraft was ever built...

— which, in the show is a super-secret hypersonic
Hypersonic
In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above...

aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

under development by the CIA, that uses a pulse-detonation engine.
In the movie Stealth
Stealth (film)
Stealth is a 2005 American science fiction action film starring Jessica Biel, Josh Lucas, Jamie Foxx, and Sam Shepard. The film was directed by Rob Cohen, director of The Fast and the Furious and xXx....

(2005), the advanced fighters use pulse-detonation engines with scramjet
Scramjet
A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow...

boosters.
The PDE has been used as a story point in a number of modern novels such as Dan Brown
Dan Brown
Dan Brown is an American author of thriller fiction, best known for the 2003 bestselling novel, The Da Vinci Code. Brown's novels, which are treasure hunts set in a 24-hour time period, feature the recurring themes of cryptography, keys, symbols, codes, and conspiracy theories...

's thriller, Deception Point
Deception Point
Deception Point is a 2001 techno-thriller novel by Dan Brown. The plot concerns a meteorite found within the Arctic Circle that may provide proof of extraterrestrial life, and attempts by dark forces to prevent this finding from becoming public.-Plot:...

(the second page of the book states that all technologies in the story are non-fictional and exist, albeit without referencing any sources), and Victor Koman
Victor Koman
Victor Koman is an American science fiction and fantasy writer and agorist. A three time winner of the Prometheus Award, Koman is mainly popular in the libertarian community. He is the owner of the publishing house ....

's science fiction polemic, Kings of the High Frontier
Kings of the High Frontier
Kings of the High Frontier is a hard science fiction novel by Victor Koman, first published in 1996.-Summary:The story is a polemic about NASA. The thesis is that NASA, far from helping space exploration, actually prevents it from going forth...

.
In X-COM
X-COM
X-COM is a series of strategy games created by Julian Gollop. In 2010 2K Marin announced the official reboot of the series, entitled simply XCOM. The original game has a cult following.- Original series :...

, the Interceptor is equipped with a PDE, however even this huge propulsion force is inferior compared to the alien Gravity Wave Engines.
In the SyFy
Syfy
Syfy , formerly known as the Sci-Fi Channel and SCI FI, is an American cable television channel featuring science fiction, supernatural, fantasy, reality, paranormal, wrestling, and horror programming. Launched on September 24, 1992, it is part of the entertainment conglomerate NBCUniversal, a...

television series, Eureka
Eureka (TV series)
Eureka is an American science fiction television series that premiered on Syfy on July 18, 2006. Since then four seasons have aired, and a fifth is currently being filmed. The second half of season 4 began on SyFy on July 11, 2011 and ended on September 19, 2011...

, season 4 episode 10 features a flying sleigh described as being powered by a PDE.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.