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A
pulse detonation engine, or "PDE", is a type of
Air propulsion system that has the potential to be both light and powerful and can operate from a standstill up to supersonic speeds. To date no practical PDE engine has been put into production, but several testbed engines have been built, proving the basic concept to some extent at least. In theory the design can produce an engine with an efficiency far surpassing more complex gas turbine Brayton cycle engines, but with almost no moving parts.
Concept
All regular jet engines and most rocket engines operate on the
deflagration of fuel, that is, the rapid but subsonic combustion of
fuel. The pulse detonation engine is a concept currently in active development to create a jet engine that operates on the supersonic
detonation of fuel.
The basic operation of the PDE is similar to that of the pulse jet engine; 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 Pulse Detonation Engines (interview) An interview with Dr John Hoke, the head researcher from the United States Air Force Research Laboratory's pulse detonation engine program (broadcast on New Zealand radio, 14th April 2007), 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 with careful tuning of the inlet to force the air to travel in one direction only through the engine.
The main difference between a PDE and a traditional pulsejet is that the mixture does not undergo subsonic combustion but instead, supersonic detonation. In the PDE, the
oxygen and
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, the shutters are even removed because the process can be controlled by timing on the periodic sudden pressure drops that occur after each shock wave when the "combustion" products have been ejected in one shot.
The main side effect of the change in cycle is that the PDE is considerably more efficient. In the pulsejet 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), and even while inside the engine the mixture's volume is continually changing, 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. The maximum energy efficiency of most types of jet engines is around 30%, a PDE can attain an efficiency theoretically near 50%.
Another side effect, not yet demonstrated in practical use, is the cycle time. A traditional pulsejet tops out at about 250 pulses per second, but the aim of the PDE is thousands of pulses per second, so fast that it is basically continual 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 ones 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). DDTs occur far more readily if there are obstacles in the tube. The most widely used is the "
Shchelkin spiral", 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 a regular DDT in.
National Aeronautics and Space Administration maintains a research program on the PDE, which is aimed at high-speed, about
Mach number, 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 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. (See
Aurora aircraft)
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 and
General Electric 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; reducing the noise (often described as sounding like a jackhammer); and damping the severe vibration caused by the operation of the engine.
In science fiction
- In the movie Stealth (film) (2005), the advanced fighters use pulse detonation engines with scramjet boosters. Incidentally, the Fictional military aircrafts changed their wing shape from forward swept wings to delta wings for hypersonic flight.
- In the drama television series JAG, the List of JAG episodes episode "The One That Got Away" (original air date October 17, 2003) features the Aurora aircraft — which, in the show is a super-secret hypersonic aircraft under development by the CIA, that uses a pulse detonation engine.
- The PDE has been used as a story point in a number of modern novels such as Dan Brown's thriller, Deception Point and Victor Koman's science fiction polemic, Kings of the High Frontier.
Notes
See also
Nuclear_pulse_propulsion
External links
- Pulse Detonation Engines
- Popular Science
- 1952 Pulse Detonation Jet Propulsion Patent by William Bollay
A
pulse detonation engine, or "PDE", is a type of Air propulsion system that has the potential to be both light and powerful and can operate from a standstill up to
supersonic speeds. To date no practical PDE engine has been put into production, but several testbed engines have been built, proving the basic concept to some extent at least. In theory the design can produce an engine with an
efficiency far surpassing more complex
gas turbine Brayton cycle engines, but with almost no moving parts.
Concept
All regular jet engines and most rocket engines operate on the
deflagration of fuel, that is, the rapid but subsonic
combustion of fuel. The pulse detonation engine is a concept currently in active development to create a jet engine that operates on the supersonic
detonation of fuel.
The basic operation of the PDE is similar to that of the
pulse jet engine; 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 Pulse Detonation Engines (interview) An interview with Dr John Hoke, the head researcher from the United States Air Force Research Laboratory's pulse detonation engine program (broadcast on New Zealand radio, 14th April 2007), 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 with careful tuning of the inlet to force the air to travel in one direction only through the engine.
The main difference between a PDE and a traditional pulsejet is that the mixture does not undergo subsonic combustion but instead, supersonic detonation. In the PDE, the
oxygen and
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, the shutters are even removed because the process can be controlled by timing on the periodic sudden pressure drops that occur after each shock wave when the "combustion" products have been ejected in one shot.
The main side effect of the change in cycle is that the PDE is considerably more efficient. In the pulsejet 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), and even while inside the engine the mixture's volume is continually changing, 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. The maximum energy efficiency of most types of jet engines is around 30%, a PDE can attain an efficiency theoretically near 50%.
Another side effect, not yet demonstrated in practical use, is the cycle time. A traditional pulsejet tops out at about 250 pulses per second, but the aim of the PDE is thousands of pulses per second, so fast that it is basically continual 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 ones 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). DDTs occur far more readily if there are obstacles in the tube. The most widely used is the "Shchelkin spiral", 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 a regular DDT in.
National Aeronautics and Space Administration maintains a research program on the PDE, which is aimed at high-speed, about
Mach number, 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 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. (See Aurora aircraft)
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 and General Electric 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; reducing the noise (often described as sounding like a jackhammer); and damping the severe vibration caused by the operation of the engine.
In science fiction
- In the movie Stealth (film) (2005), the advanced fighters use pulse detonation engines with scramjet boosters. Incidentally, the Fictional military aircrafts changed their wing shape from forward swept wings to delta wings for hypersonic flight.
- In the drama television series JAG, the List of JAG episodes episode "The One That Got Away" (original air date October 17, 2003) features the Aurora aircraft — which, in the show is a super-secret hypersonic aircraft under development by the CIA, that uses a pulse detonation engine.
- The PDE has been used as a story point in a number of modern novels such as Dan Brown's thriller, Deception Point and Victor Koman's science fiction polemic, Kings of the High Frontier.
Notes
See also
Nuclear_pulse_propulsion
External links
- Pulse Detonation Engines
- Popular Science
- 1952 Pulse Detonation Jet Propulsion Patent by William Bollay
Pulse detonation engine - Wikipedia, the free encyclopedia
A pulse-detonation engine, or "PDE", is a type of propulsion system that can operate from subsonic up to hypersonic speeds. In theory the PDE design can produce an engine with a ...
UCLA Energy & Propulsion Research Laboratory :: Research Projects ...
Aerospace Propulsion: Transverse Jet Control. Propulsion: Pulse Detonation Wave Engine Simulation
Pulse Detonation Engine
What is a Pulse Detonation Engine and how does it work? ... Jet engine technologies for interested amateurs Last Updated: 6 April, 2002
www.pulse-jets.com • View forum - Pulse detonation engine forum
Topics Replies Views Last post; Just playing around! by Chadly33 on Sun Oct 19, 2008 3:58 am 0 Replies 60 Views Last post by Chadly33 on Sun Oct 19, 2008 3:58 am
YouTube - Turbine Truck Engines' Hydrogen Powered Pulse Detonation ...
The World's First HYDROGEN POWERED Pulse Detonation Turbine Engine. Turbine Truck Engines, Inc. Detonation Cycle Gas Turbine Engine 5th Generation Prototype September, 2008 Hydrogen ...
www.pulse-jets.com • View topic - Development of a Gas-Fed Pulse ...
In the latter case, the device is referred to as a pulse detonation rocket engine (PDRE). Generally speaking, PDEs operate on an intermittent cycle by filling a chamber with ...
Pulse jet engine - Wikipedia, the free encyclopedia
The pulse detonation engine (PDE) marks a new approach towards non-continuous jet engines and promises higher fuel efficiency compared even to turbofan jet engines. Pratt & Whitney ...
PDWE
Acronym Finder: PDWE stands for Pulse Detonation Wave Engine ... Suggest new definition. This definition appears very rarely and is found in the following Acronym Finder categories ...
PDRE
Acronym Finder: PDRE stands for Pulse Detonation Rocket Engine ... Suggest new definition. This definition appears very rarely and is found in the following Acronym Finder ...
Pulse Detonation Rocket Engine - What does PDRE stand for? Acronyms ...
Acronym Definition; PDRE: Pulse Detonation Rocket Engine
