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Pulse Detonation Engines: The Future of Aviation
noah_fense writes "Popular Science is running an interesting article about the race to replace the jet turbine with a more efficient source of Mach-breaking airpower: the pulse-detonation engine. It works by detonating (instead of slow burning) fuel hundreds to thousands of times a second. PDE technology is poised to make supersonic passenger flights and space travel affordable. 'Pulse detonation is a hot topic in combustion research,' says Gabriel Roy of the Office of Naval Research. 'Compared with gas turbines, the PDE has a much simpler configuration. It has the capability of going from subsonic to supersonic using less fuel, and it's thermodynamically more efficient. But there are big engineering issues--thermal fatigue, noise. It's very challenging research.'"
Isn't this what the black helicopter people say the Aurora (fabled SR71 replacement) uses?
'Pulse detonation is a hot topic in combustion research,' says Gabriel Roy of the Office of Naval Research.
Sounds like they're strained for humor over there.
The coolest voice ever.
most of them probably won't make it across the english channel.
Would this system possibly be the type of propulsion that produced the infamous "doughnut on a rope" vapor trail? If so, then this technology has been in development for quite a while. </fox_mulder>
Overrated / Underrated : Moderation
"...But there are big engineering issues--thermal fatigue, noise..." ...Potential explosions...
If any research is beeing done into the bladeless (Tesla) turbine?
The bladeless turbine pump is hailed as the best thing to hit industrial pumps ever.
All you need to reverse the intake and exaust and it is an engine (was orignally designed as an engine)
Pulse detonation seems to be the best way to power these turbines. Tesla claims over 10 horsepower to the pound of engine weight.
With this horsepower to weight ratio, I wonder what could be acomplished using this instead of a conventional turbine.
More info on the tesla turbine here.
It's easier to fight for one's principles than to live up to them.
To quote from Wikipedia:
Nuclear pulse propulsion is a proposed method of spacecraft propulsion that uses nuclear explosions for thrust. It was briefly developed as Project Orion by ARPA. It was invented by Stanislaw Ulam in 1957, and is the invention of which he was most proud.
Calculations show that this form of rocket would combine both high thrust and a high specific impulse, a rarity in rocket design. Specific impulses from 2000 (easy, yet ten times chemical specific impulses) to 100,000 (requires specialized nuclear explosives and spacecraft design) are possible, with thrusts in the millions of tons.
Gentlemen! You can't fight in here, this is the War Room!
In America (the leading consumer of air travel) the FAA has limits on the noise level generated by an airport. From the article, this is such a big problem that the development of this engine in passenger aircraft may be halted because of the inability to dampen the noise output. Strictly speaking, this is going to be a rocket engine, not an passenger jet engine. It probably won't even be a military jet engine either, the military doesn't like their pilots deaf.
The FAA rules were never a big problem for me, though. The reindeer are fairly silent except for the actual landing part.
Like since 1941. (V1)
Yep, you should go RTFA. PDE is very explosive. The idea was first thought of in the 1930's. The article says that the Germans tried it on the V-1 rocket, but didn't succede. The article states that detonation is different from deflagration. I don't know what the internal combustion engine uses, but PDE is very complicated and has only recently been showing signs of success.
...interesting if true.
...we might finally get affordable supersonic jet transportation?
I can't stand flights of over an hour or two myself, and it would probably encourage even greater mobility then we have today if it's cheap enough. For example, transcontinental dating.
Yes, he is the guy of DIY cruise missile fame.
Still no anti-matter engine...
but until then this seems promising...
- Danny
from the article:
" Imagine a tube, closed at one end and filled with a mixture of fuel and air. A spark ignites the fuel at the closed end, and a combustion reaction propagates down the tube. In deflagration?even in "fast flame" situations ordinarily called explosions?that reaction moves at tens of meters per second at most. But in detonation, a supersonic shock wave slams down the tube at thousands of meters per second, close to Mach 5, compressing and igniting fuel and air almost instantaneously in a narrow, high-pressure, heat-release zone. "
from the article: "The first scientists to recognize that rapidly pulsed detonations might be used to create thrust were probably the Germans, who developed the V-1 "buzz bomb" in the 1930s. "The Germans attempted a detonation with the V-1 but never got it," says Chris Brophy, a propulsion research professor at the Naval Postgraduate School in Monterey, California. "The V-1 was a pulse-jet, more of a high-speed deflagration.""
You still have two centuries to go...
The first scientists to recognize that rapidly pulsed detonations might be used to create thrust were probably the Germans, who developed the V-1 "buzz bomb" in the 1930s. "The Germans attempted a detonation with the V-1 but never got it," says Chris Brophy, a propulsion research professor at the Naval Postgraduate School in Monterey, California. "The V-1 was a pulse-jet, more of a high-speed deflagration."
From page 2
What changed under Obama? Nothing Good
The internal combustion engine uses an air/fuel mixture sprayed into a small cylinder and then exploded. This part is identical to the PDE.
... blah blah blah ... which moves the tires. The PDE blasts all that power straight out the back so that instead of losing power to the moving parts, it is all (half, actually) used to propel the cylinder forward.
The difference is that the explosion in the internal combustion engine is used to move a piston which in turn moves a cam which moves
The key difference, then, is their definition of detonation. Apart from the fact that it is faster than the detonation of fuel in a standard IC engine (fast flame?), can anyone tell us exactly what a "detonation" is, in the sense used in the article?
http://www.wam.umd.edu/~ojenkins/words/donuts.html
I actually did my Master's Research on a Pulsed Detonation Engine (Rocket actually, since we were providing the oxygen). It is a more efficient form of propulsion (for thermo geeks, detonation can be modeled by a constant volume Humphrey thermo cycle, rather than the constant pressure Brayton cycle and a comparison of efficiencies results in a vast improvement for the pulsed detonation engine). It certainly isn't too new as far as the idea being thrown around, but it certainly is gaining momentum as being more and more plausible. Aside from the efficiency benefits, the engine itself results in a much simpler design and weight savings rather than relying on today's complex turbomachinery. Furthermore, pulsed detonation engines offer the potential for substantiative performance increases; finally bringing hypersonic flight to within a practical reach. A detonation is different than a deflagration in basically the speed at which combustion occurs. Deflagration occurs at relatively low flame speeds on the order of 1 or 2 m/sec.; whereas, detonation is a supersonic mode of combustion. Most forms of combustion that we are familiar with today utilize the deflagrative mode. The article was accurate in stating that this technology still has a few hurdles to overcome. Primarily, the pulsed detonation engine is an unsteady flow phenomenon that requires a periodic input to control fuel injection into the detonation chamber coupled with a very large energy input to ignite the fuel and reach a critical Chapman-Jouguet velocity. Such energy input has been accomplished so far using an arc igniter, but doing so on a reliable basis at frequencies of at least 100Hz, necessary for practical use have been somewhat of a challenge thus far.
I don't know if they are already doing so, but it seems a natural match to use something like this in conjunction with a pulsejet.
Have a look at HowStuffWorks for the Internal Combustion Engine. Then imagine if there wasn't all the piston/crankshaft crap in the way of letting the explosion run free out the bottom of the block.
Or think of a gas stove. The biggest release of energy you get is when you turn on the stove because it is 'exploding' from nothing into full flame. Once it has ignighted and the fuel is constantly coming, the flame becomes controlled and much less powerful than the initial burst. The largest amount of power generated by an explosion is at the moment of ignition as all the gases are suddenly expanded and expelled in all directions. If you could control the direction of the explosion, you could direct the container in any direction that was feasible. And if you could recreate the explosion multiple times instead of devolving to normal fuel burn, you could utilize the power of the explosion repeatedly.
I think that several such paradigm shift in several disciplines must occur in order to keep space exploration viable in the near future. I am always impressed by the near-wishful thinking that MUST occur before science leaps forward. Plus, they're competing for juicy government contracts, and that always greases the wheel.
Windows XP SP2 told me to install third-party software that prevents viruses and protects stability... I chose Ubuntu
Everyone knows all you need is some dilithium to stabilize the deuturium/anti-deuturium reactions.
...flying cars! Where the hell are my flying cars?
3D Printing Tips and Tricks at Zheng3.com
Yes, the V1 was a pulse jet. Also, if you ever saw ads for a jet powered helicopter in the back of Popular Mechanics magazine years ago, I think those were pulse jets too.
Mark Pauline of SRL built one of these & set it off in San Francisco's Mission district as a fiery noisemaker. Video here:
SRL Pulse Jet Demo
Now that's art!
Basically you're igniting the fuel air mixture in front of a set of one-way shutters that are closed by the detonating mixture. After the mixture detonates, there is a consequent vacuum created that sucks more air through the shutters to mix with the incoming fuel. Repeat very rapidly. Similar principle as the old pop-pop boat child's toy
You don't see them much because the noise is awful and the stresses on the materials are very high.
Assembly is the reverse of disassembly.
Us: OOP, patterns, Extreme Programming...
Them: fire, matches, detonation...
Engineering is the art of compromise.
At the Dayton Air Show. It was mounted on a small UAV-sized plane. It consisted of a standard block from a 4 cylinder car engine with the bottom half, including crankshaft and pistons, removed. Each cylinder had a four foot or so exhaust pipe welded to the bottom of it, pointing to the rear. It ran like a normal engine, but exhausted the explosions directly, instead of pushing on the pistons.
The weird part - a whole other engine was needed to run the valve cams.
They were pitching it as a cheap, reliable replacement for things like disposable UAVs and cruise missiles, in the short term.
It sure looked loud.
People who disagree with you are not automatically evil, greedy, or stupid.
Is this what they are talking about? Dr. Fun
The AirForce research guys demoed a pulsejet made out of automotive parts at Oshkosh this year. There's a link and a picture at Avweb
All you need to reverse the intake and exaust and it is an engine (was orignally designed as an engine)
Since the apparatus described in your link is axisymmetric: when you put air through it, which way do you expect it to turn?
The United States Air Force Research Lab Propulsion Directorate has a pulse detonation engine program as well. Pics and story here. Apparently their engine is made mostly of off-the-shelf automotive parts. It's powered by any type of general aviation fuel (Jet-A, JP-8), and even gasoline.
The article discusses using thrust pulses from combustible propellant, not the nuclear explosions of scifi lore.
If,
You were to go through your issues of PS you would find an incredible amount of "wonderful engineering" that never ever shows up anywhere.
It's seems like there is at least a once a year issue of PS that specifically describes a stupendous advance in airships that's gonna haul all of the world's heavy objects.
Usually some big white triangular airship. Seen any of those lately. You get my drift....
Caution: Contents under pressure
From what I understand of the article, this is using hydrogen as a fuel, not exactly practical. I would think even a very wll vaporized liquid fuel would present a very large problem for this technology. Gasses are just not compact enough to be used as general fuels.
I say that that this technology is a few decades off from real use, unless amazing jumps foward in using liquid fuels occur or somebody miraculously develops both a space-efficent way to store hydrogen and a cheap way to produce it.
They keep talking about how noisy it is, why would that matter if you are going supersonic above the ocean? You'd have to use some other sort of engine to take off and land, wouldn't you? My understanding is that this technology does not function below a certain airspeed.
"It sounds like this:
pbpbpbpbpbpbpbbpbpbbpbpbppbbppbpbpbpbpbpb "
Oops. I think my joke caused ppl to make the sound I was describing.
"Derp de derp."
I suspect that "blowing shit up" is another one of those big issues.
I've found that my posts don't format quite right w/o a sig.
Allowing it to burn fuel for localized (low) flight and explode it to explode for fast-acceleration/long-distance (high altitude) flight might perhaps solve this? Of course, I'm not sure how much work or overhead it would be to create a system that allows both methods to be used....
Is that like soap on a rope?
I've found that my posts don't format quite right w/o a sig.
If your car is detonating its not gonna last long. When a car engine detonates the shock wave produced often destroys the engines internals, or atleast causes some damage.
A cars combustion engine when working normally uses deflagation to produce power. Its easy smooth and works well. The octain or lead (1980) in petrol helps prevent detonation.
some peoples moderation does not include weed
Except that Tesla also thought we should 'beam' electrical power through the air by generating masive RF fields; you'd have a big RF generator in the center of town, and everyone would have magical antennas that harvested this magnetic energy. Instead of, say, just laying down some wire underground or on poles. It's a good thing he isn't around today, because the tin-foil-hat wearing anti-cell-phone-tower freaks would tear him apart.
If anything, some of the 'greatest' minds of our time have also had some of the 'greatest' moments of stupidity. For example, Edison(who strongly believed DC was much safer, outweighing transmission problems) was mostly responsible for death by electrocution; he figured the public would be shocked by how easily a man was killed by AC, and would fear it as a result...putting an end to Tesla, who was quickly taking Edison Electric to the cleaners, with more efficient generation and transmission.
It backfired, massively- it amounted to torture and the man was electrocuted repeatedly and at length before finally dying; it literally cooked him alive and at times they had to stop and put out the fires on his body. Those who witnessed it were indeed horrified beyond belief. Common view was that AC was NOT lethal, and Edison was responsible for the slow death, rather than the quick painless instant killer he had promised.
Please help metamoderate.
Following up on my post now that I've read the article. They're calling it a Pulse Detonation Engine (PDE) instead of a pulse jet. They claim they're detonating the air fuel mixture instead of just burning it, although the Nazis were supposedly hoping for detonation in the V1.
They're actually using an idea I've wondered about for pulse jets, calling it valveless operation (as in no moving parts) using the aerodynamics of the detonation chamber to direct the blast out the back.
Assembly is the reverse of disassembly.
I remember studying this in college back in the 80s. It was still mostly theoretical then. despite the amount of research that had gone into it. The main problem back then seemed to be fine control of fuel delivery, ignition and monitoring of the results. Computer control seems to have solved at least part of that. It looks like, from the article, that precision machining and hightemp materials might have solved some of he other ones problems.
;)
Hell, maybe I'll make it to space after all.
If they can really make this work, real-world, it might revolutionize high-altititude to orbit engines. It's probably at least a decade away from production use, but still....
Utterly cool. Cut off not their research funds!
realityshunt
Democracy is susceptible to being led astray by having scapegoats paraded in front of the electorate.
just a article on conspiracy and jet contrails
I don't know what this guy was smoking
..........FULL STOP.
Three things:
Heat expansion of metals.
Pipe-organs.
Fluidics.
I'll leave the rest to you.
This story sounds a little like this earlier slashdot story. Using combustion pulses to push steam out the back of this water jet engine.
Pretty cool even if its unrelated.
I notice in the pictures that the lady standing next to the engine on the second page has no head.
An engine that decapitates people is certainly very injurous to health.
Nope, I wasn't smoking anything at the time.
I originally wrote that paper for an Honors Seminar at the University of Maryland. It was called Science and Pseudoscience: An Investigative Approach. Pretty nifty class that helped you to look at things differently. I'm not sure what the conspiracy angle is that you're talking about aside from it discussing aircraft technologies that are still under wraps. As you can see from the bibliography section of the report I wrote, Popular Science and other news organizations have known about the existence of this technology for a while. More than a decade in fact.
Space craft take off using a continuous propulsion system in the form of gasses leaving the rocket. The force exerted by a pulse-detonation engine is more powerful than a continuous propulsion system when it comes to force exerted over a smaller amount of time. Also by having a series of detonations instead of a continuous burn, the craft doesn't have as many problem when it comes to ignitions back-tracking up the fuel supply lines to the main fuel storage area.
"Destroy science and religion. Science would re-emerge exactly the same; but not religion." - Penn Jillette, paraphrased
are old hat. There are even toys that work like that (Dynajet). Dynajets are so noisy that most towns and cities banned these toys, decades ago. The German buzz bombs used it in WW2.
Oh well, what the hell...
Actually the V-1 wasn't a rocket. It was a pulse jet powered cruise missile. A pulsejet is sort of like a ramjet with venetian blinds on the air intake, It fires in pulses rather than a continuous stream. Unlike a ramjets, pulsejets can be started while standing still.
It is cowardly, and a betrayal of whatever it means to be a Jew, to act as a white man
-James Baldwin
You're right, I wouldn't steal a car. But if it were possible, I sure as hell would download one!
OTOH, from general considerations (which may be wrong, I am not a rocket scientist) the scramjet should be more efficient. In it there is no obstacle to the air flow, the air only gets compressed. With the PDEs, as far as I got from the article, there is a wheel with holes perpendicular to the air flow that blocks (and unblocks) the air flow regularly.
Um, if the crankshaft and pistons were removed, how was air drawn into the combustion chamber? And did the exhaust valves still work, and if so then how did that affect performance?
And if "it ran like a normal engine" then how was the air compressed for an explosion?
Okay, I thought maybe you were on crack, but another poster linked to this which looks like what you described. My questions still stand, but I actually believe you now.
Unless you want to become extra-tasty, crispy.
8==8 Bones 8==8
looks more like a screwed up MPEG GOP (missing the I-Frame, of course)
Some funny guy with his f4 phantom broke the sonic wall in 35000feet altitude just above my hometown here in germany last week.
I lived near a military base in my childhood, and i dont even notice distant explosions ect anymore.
But that sound was LOUD.
I was standing near an open window and i could FEEL the shockwave entering the room.
Thats nothing you really want every day...
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
Squirting the fuel in and igniting it with high compression sounds a lot like a good old diesel. Can't get enough of diesel on the ground--put it in the sky too!
Seriously, diesels use so much more of the energy from fuel then gas cars--a similar improvement would be great in airplanes as well!
-m
http://www.invisik.com
In the UK this is done by catalytic reforming to produce benzene and other ring-shaped molecules. This certainly gets the octane rating up to 95 or 97 ("premium" and "super" unleaded respectively) but, from a health point of view, may actually be more harmful than a bit of lead bromide in the exhaust. The alleged link between lead in exhaust fumes and childhood development was always hard to prove, although lead itself is undeniably toxic in the wrong forms. Benzene is carcinogenic in any quantity. We may have swapped one problem for another.
As an aside, a friend of mine worked at a factory where they had a lot of bulk benzene available - all the managers were running their cars on a 50/50 mix of benzene and unleaded petrol. Naughty.
When I am king, you will be first against the wall.
I couldn't find anything that said what they are hoping for as far as gains i efficiency or power.
Does anyone have a clue how much potential efficiency there is to be gained?!
Any numbers would be appreciated.
I read that the Germans once tried to create a fighter based on the V1 pulsejet engine. It shook so badly it was intolerable for human pilots.
Have you seen the very weird picture of a woman with no head and a deformed right arm on page 2 of the article? I wonder if she stood too close when the engine was switched on.
-- Cheers!
...but when are we going to start developing replacements that avoid fossil fuels altogether? Yes, it would be nice to lower fuel consumption, but sometime it's going to have to go away completely and be replaced by something else.
this is quite nice, one 'little' drawback is that it burns earths low oil resources even more rapidly than engines before ...
class he-man extends man!
It looks to me like there are a lot of moving parts on that engine. wasn't the idea of a PDE that it has no moving parts?
From what I can judge from one picture, it is a small piston engine that provides the ignition pulses for the final detonation in the pipes. From the color of those shiny pipes, I'd say that this engine has not been run yet.
This space is intentionally staring blankly at you
Didn't Flying Toast Man from the Wren and Stimpy series do something rather similar? Flying Toast man was cooler. :P
Forget thrust, drag, lift and weight. Airplanes fly because of money.
Assuming for a moment that it's possible to get this technology to work, the question of noise has been raised as a show stopper with regards it's commercial use.
But two things spring to mind:
1) Stealth aircraft use noise damping technology, and some of this might be appropriate even for this weird engine.
2) Conventional engines will probably have to be used for take off and landing anyway. These can be commercial low-noise devices that just get the plane to/from off-shore locations where it can fire up it's PD engines.
Just make sure you've finished your complementary drink at that point or you'll be wearing it for the rest of the flight...
"Jet Fuel" is basically kerosene, and cheaper than Avgas. The price varies, but A1-jet fuel is usually about the same price as standard pump gasoline
Aviation piston engines use Avgas, aviation jet engines use jet fuel (duh!).
Lastly, the airlines purchase usually both jet fuel and avgas tax free due to international agreements IATA has negotiated, which means they often pay less for avgas than you will for standard unleaded.
Check http://www.iata.org/mgr/fuel/index and http://www.eia.doe.gov/oil_gas/petroleum/info_glan ce/prices.html for details.
Hydrogen is much more expensive than any of these fuels, even in commercial quantities, and it's easy to see why if you do a little mental exercise (which is more fun than google
Think of it this way: is milk cheaper to produce and transport than hydrogen? You put grass in a cow, suck milk out of the cow, boil the milk and transport it in a big stainless steel tube. Once you package it (in cheap plastic) you need to keep it moderately cool. If you have a large milk spilling accident, it smells bad, but causes no real issues.
Hydrogen is significantly more expensive to produce and transport than milk, requiring either lots of power or propane + power and catalysts, and it's more dangerous if spilled (and therefore more expensive to transport.
Go compare the price of a gallon of milk and a gallon of gasoline. Milk is cheaper than gas. Hydrogen is (obviously) a lot more expensive than milk. Therefore, hydrogen is much more expensive than gasoline.
Wasn't that fun. Or, you could just go look it up....
I don't think you'll *ever* see a PDE in use on a passenger jet -- mainly because of the noise and vibration problem.
When a PDE fires it doesn't just make a loud noise, it produces a train of supersonic shock waves that transfer vastly more energy than a regular acoustic (sound) wave.
Standing in reasonable proximity (10 yards or so) of a large (but conventional) pulsejet will give you a really bad headache even if you're wearing hearing protection -- because the amplitude of the acoustic wave generated is so great that it hammers your skull and your body.
It really surprises a lot of people when I demonstrate a very large pulsejet to them. They say that they feel it right to the core of their body and, despite using grade 5 hearing protection, their ears ring afterwards.
Now multiply that by an order of magnitude (as is the case with a PDE) and you find that anyone within spitting distance will suffer actual physical harm consisting (at worst) damage to internal organs and (at best) concussion and damage to the inner ear as the shockwaves bash on your skull like a ball-peen hammer.
I seem to recall the article mentioning that the shockwaves from the demo engine were still causing discomfort after passing through a concrete barrier?
And, to be quite honest, I have to say that I don't think the engine attached to the Long-EZ and shown running in the video was actually producing true detonations at all.
Now tell me how many airline passengers will pay good money to ride on a jackhammer, even if it is a supersonic jackhammer.
I believe the real market for PDEs is unmanned aerial vehicles (including missiles) and as the airbreathing stage of LEO vehicles used for scientific or military purposes.
You're assuming that it has to be treated as a liquid fuel like gasoline. There is no transporting Hydrogen; it can be produced on-site from water and electricity. There is a test system already setup at the Munich airport.
I'll admit that Hydrogen probably is more expensive than *whatever* fuel the airlines get tax free. I can't see how it would be that much more expensive, though, since it can basically be created from anything from natural gas to ethanol using relatively efficient processes. Besides, surely the airlines would pay a premium to use an engine like this that would operate at supersonic speeds?
I can honestly say I don't know how to respond to any of the rest of your post. Your milk analogy is completely incomprehensible.
"I assumed blithely that there were no elves out there in the darkness"
To demonstrate the difference between a deflagration (the slow combustion you get in your auto engine or a pulsejet) and detonation (the rapid combusiton that occurs in a PDE) I like to draw the following comparison.
:-).
1. Take a can of gasoline and pour a trail on the ground as you walk along. That trail might end up being 20-30 yards long.
Above that trail there is a stoichiometric mixture (ie: a mixture capable of burning) of gasoline vapor and air -- just as you'd find inside an engine.
Now light one end of the trail and watch how long it takes for the flame to travel along to the far end.
It actually takes several seconds. That's the speed of a flame-front during deflagration.
2. Now take a very long piece of cordite or some other "high explosive" and lay it along the ground for some distance.
Then place a detonator at one end, stand well back and energize it.
The entire length of the explosive will appear to explode at once. The shockwave that propogates the explosion down the length of explosive material will travel far to quickly for you to see. Instead of taking several seconds to travel just 20-30 yards, the detonation will travel over a mile per SECOND or faster.
That's the difference in speed between deflagration and detonation.
But there's one other very important difference:
If you pour a gallon of gasoline out onto the ground and light it it will go "woof" (just like a dog
You can safely stand within just a few yards of such a deflagration without fear of being harmed.
However, if you were to *detonate* (rather than deflagrate) that same amount of gasoline it would blow you right into the middle of next week and further.
With a detonation, all the available energy is released in a very tiny fraction of a second and this generates huge pressures (thus huge thrust).
With deflagration, the energy is released far more gradually so the pressures are lower.
What's more, because deflagration is such a slow process, when the fuel is burnt inside an engine, there's far more time for the heat of combustion to be transfered to the engine itself. That means the engine will require more cooling and a greater percentage of the fuel's energy will be wasted as radiated heat rather than in producing work.
I hope that clarifies the key differences between deflagration and detonation -- and goes some way to explaining why a PDE could provide greater efficiencies than an engine that simply "burns" its fuel through deflagration.
1. A gas turbine is an IC engine.
2. Various IC piston engines have successfully been converted to operate reliably with hydrogen decades ago.
3. Although H2 permits high compression ratios, it does not require them. The same applies to LPG.
4. The main obstacle is therefore not satisfactory engine operation, but the hydrogen infrastructure.
The problem is not a theoretical limit for thrust development, but a physical one. As the gas goes through a compressor and combustor, it gets very hot. So hot, in fact, that without the special current ceramic coatings the turbine would melt. If one could develop a way to make the turbine survive even hotter temperatures then turbojet/turbofan engines can produce even more power, at least subsonically.
The pulsejet in the V1 Missile certainly couldn't be started whilst standing still. It had to be accelerated down a launching track using steam generated by mixing hydrogen peroxide and potassium permangenate. This was one of the issues with the V1 design - it required permanent infrastructure to launch it, whereas there were mobile launch teams (in around 3 trucks) that could launch a V2 from pretty much anywhere.
Let me repeat: pulse jets are not pulse detonation jets. Unlike pulse detonation jets, pure pulse jet research efforts have been all but abandoned as they were concluded to be too inefficent and overall inferior to any other jet design.
Pulse jets are composed of a combustion section, a set of inlet shutters and an exhaust valve. Air enters the combustion chamber and the inlet shutters closes, forcing the combusting fuel-air mixture out through the exhaust valve, producing thrust. Pulse detonation jets have no such valves.
Yes. I did some research on these things a couple years ago, with the grand idea of making one. Never got around to it.
Its completely different from anything nuclear. The explosion sends the "pulse" down the tube, most of it excapes giving thrust. The sheer momentum of the air moving in that direction creates a low pressure zone in the tube, and some of the hot gasses shoot back up the tube, compressing as well as igniting the new fuel/air mixture which has in the meantime been put into the front of the engine.
I guess I don't know much about these "pulse" nuclear engines, but I can't see how a nuclear blast could use the momentum of itself to create a low pressure zone back inside the engine (lower pressure than the vaccuum of space outside?!), and then the backlash would have to create the huge amount of pressure to spontaneously create another nuclear blast. Nope, the same principal just doesn't seem possible to me.
The snow doesn't give a soft white damn whom it touches. -- ee cummings
http://www.aardvark.co.nz/pjet/gokart.htm
The German V1, which first flew in the late 1930's, used pulse detonation. At the time it was considered to be the future of aviation
an ill wind that blows no good
good points! noise==vibration
I think the engine you refer to was the Tesla disk tubine - which relied on couette (sp?) flow to spin the disk. It would totally work, but would be subject to the same thermodynamic efficiency limitations of conventional turbines. Also, he included a "reedless" valve design that, unfortunately won't work. Ironically, had the design have been workable, pulsejets would have been a lot easier to make.
I need to bring myself up to speed on research done on this new generation of pulse engines. I have a good idea of what the may be doing as I played with this myself for a while. However, I lack the time, experience, and resources to solve many of the problems. It's an intriguing problem though, because if you can make it work reliably and throughout a range of power, you should be able to achieve significantly higher efficiency.
Of course, it will still be noisy as hell, and that may make it difficult to operate out of a commercial airport.
A goal is a dream with a deadline
It relied on there being quite a number of parallel discs. Which would look like circular "fins" on the axle of the turbine.
retrorocket.o not found, launch anyway?
IIRC, Ethylene oxide and oxygen are the primary ingredients in the fuel-air bomb. So, yeah, I would expect the equivalent of an open-ended bomb to produce more thrust than a conventional jet engine. I'll be more impressed when they can do this without supplemental oxygen, bomb fuel, and a large compressor to "simulate mach 4 speeds".
Granted, it sounds promising, but as of yet they haven't managed to build a prototype which can run on conventional fuels (hydrocarbon based, ethyl alcohol, etc...). Furthermore, the article states that these engine may someday produce power from near standstill to hypersonic speeds, yet their prototype can't run at less than mach4, and requires supplemental O2 at that. Quite frankly, the ramjet designs of the 80's showed more promise than PDEs.
The society for a thought-free internet welcomes you.
At Oshkosh, there was somebody showing a VariEze with a Pulse Detonation Wave engine. I didn't catch whether it had actually flown with it. I took some pictures here.
Don't be fooled by the USAF markings on the plane - I didn't see any indication that it had any sort connection to the military.
The next Cmdr Taco duplicate will be ready soon, but subscribers can beat the rush and see it early!
Are you aware if these designs can operate over a range of power settings? I would envision that, in setting up a workable flow-field, you're going to have to make concessions for operational range.
Also, at it's core, a turbine engine is a pretty simple animal. What makes it complicated is the addition of fuel delivery and lubrication systems. While the core of a PDE engine is even simpler, I see significant engineering problems associated with reliable fuel delivery.
Did any of your (or your universities) research ever get into the noise issue?
Just curious really, if the design problems can be solved, then you've definately got something. Even if it only works for a limited power range, you can use it in a hybrid engine, such as a bleed-burn or hybrid turbojet.
A goal is a dream with a deadline
That would be Xcor Aerospace, which gets /. coverage pretty often. :)
Their rocket-powered Long-EZ is called the EZ-Rocket.
retrorocket.o not found, launch anyway?
Any slashdotters that have flown supersonic could maybe enlighten me, like when you fly above the speed of sound, can you no longer hear the engine?
As many others have stated, and you would know if you read the article, the pulse jet engine on the V1 is not the same technology as the pulse detonation engine. The difference, according to the article, is that that a pulse detonation engine creates an explosion which is channeled in one direction to create thrust, and another direction to compress the intake charge. The explosion is much faster than the combustion which occurs in a jet engine. Think blowtorch vesus bomb.
Go compare the price of a gallon of milk and a gallon of gasoline. Milk is cheaper than gas. Hydrogen is (obviously) a lot more expensive than milk. Therefore, hydrogen is much more expensive than gasoline.
M < G, M < H, therefor G < H?
Surely, I cannot pick the wine in front of you.
Our materials technology currently lags too far behind current levels of commercial flight tech. As long as "metal fatigue" can be used as an explanation or even part of an explanation for something going wrong in any field of human endeavour we should all be keeping our feet firmly on the ground.
kartune85 : Incapable of reason, observation or learning. A kind of dim, drab, flightless parrot.
...any moment now!"
Yes, in fact the Argus motor in the V1 could run while standing still. They used forward momentum to start the engines, but a simple blast of air would suffice to get the cyclical firing going. Once started the engine has no trouble operating in still air.
BTM
That was the turning point of my life--I went from negative zero to positive zero.
Having last year done the 24 hour flight from Sydney to London and having to go back at Christmas, I could handle a little noise if it cut the flight to 5 hours. 10 hours even. I am 6'4" so after a while planes just suck. I'm excited by this.
-- Karma Karma Karma Karma, Karma Chameleon - Boy George
I stared at that picture for five minutes and still can't figure out what the deal is. As far as I can tell, she has really large breasts, really short arms (well, arm) and no head. But she's qualified to operate the machinery. Hey, good for her! That's a real accomplishment!
I've found that my posts don't format quite right w/o a sig.
I think for your arguement, you mean "Milk is more expensive than gas", not "Milk is cheaper than gas."
so you get GMH.
"Operating machinery without head. Fine: $250"
Miko O'Sullivan
But there are big engineering issues--... noise.
"God is knocking. And He wants in. BAD!"
--Footfall
Baha!!
- jon
Ganymede, a GPL'ed metadirectory for UNIX
Somebody wrote, that it was a goatsexc link. I merely stated that it WASN'T a goatsecx link, and that the person who said it was a link to that site was wrong. I was not implying that the webpage on contrials was wrong or wacko.
Sorry about that.
..........FULL STOP.
Necessity transportation hydrogen, power necessary for electrolysis of significant amounts hydrogen nearly equal to energy potential of hydrogen separate, matter of chemistry that bond of element requires energy greater in application for separation, only energy of bond reclaimed in reaction. Expense hydrogen and necessity transportation relate in location free hydrogen and transportation to distribution centers.
Aah...thats for wimps
How bout a jet powered bike?
Not really, if you RTFA, you will see that even in an internal combustion engine, where there is a so called explosion, it is really a fast flame, or deflagration. The key to the PDE is to make this deflagration turn into a supersonic explosion, that moves the flame out of the end of the tube much faster than a fast flame.
From the article:
Imagine a tube, closed at one end and filled with a mixture of fuel and air. A spark ignites the fuel at the closed end, and a combustion reaction propagates down the tube. In deflagration--even in "fast flame" situations ordinarily called explosions--that reaction moves at tens of meters per second at most. But in detonation, a supersonic shock wave slams down the tube at thousands of meters per second, close to Mach 5, compressing and igniting fuel and air almost instantaneously in a narrow, high-pressure, heat-release zone.
The same problem that put a stop to the plan to use flywheels to make cars more efficient in stop-and-go traffic - above a given speed, any flywheel will destructively disintigrate. The pdwe doesn't have that particular problem. Therefore it is a better bet to get a vehicle to high altitude at a good speed, and then on-board LOX can replace the atmospheric 02 as oxidizer and get you into LEO. After that, though, you might want to use a naquada(TM) energy source for further travel (USAF is looking into quantum isomer batteries, often of halfnium, but other metals will also work) and as pinpoint gamma ray bombs. Energy yeild has been said to be 50 kilos to the gram, and 50 terawatts to the cubic meter.
The USAF kept saying "We have no idea what that is, it's not ours, etc". While Aviation Week kept publishing pictures of the things flying over Nevada and Utah, well away from the airline flight routes.
Best Slashdot Co
Very early diesel tractors used the same technique back in the steel-wheel days. I've seem them at antique engine shows. You put a cartridge on a special port on the engine, and then hit it with a hammer to start the tractor. Then you can go do your field work.
I was at the Oshkosh airshow recently and the Air Force had a pulse-detonation powered Long-EZ homebuilt aircraft on display. Doing a quick search on the 'net finds some links to it here: http://www.af.mil/stories/story.asp?storyID=123005 352
I spoke with one of the engineers for awhile. This engine only produces 200 lbs of thrust, which is barely enough to get the Long-EZ airborne (contrast this to the EZ-Rocket project, in which each of two engines produce 400lbs of thrust IIRC). It is built from low-cost autmotive parts -- imagine a 4cyl engine with ~4' exhaust tubes coming straight off the exhaust ports of the head. The exhaust reaches speeds of up to mach 5 IIRC.
They do not forsee commercial applications for their design, but rather for use as an efficient missile powerplant.
With the engine in the back and the plane going super-sonic (and with decent vibration issolation between the engine and the plane) the noise will be literally left behind.
You don't ride the jackhammer. The best application would be a really fast and cheap cruise missile. You don't even need to blow anything up, just fly in circles over them and the sound will have them puking on the ground from the sound.
Ok, I read the popular science article and found it lacking in the technical details. As one of my old professors said: "Engineering is done with numbers, anything else is just opinion" Both the article and you mention that the engine is more efficient than conventional jet engines. Can you give some figures on that? What kind of specific impulse are we talking about here? Conventional jet engines run from 3000-5000 seconds, how much better is a PDE? Or, since you were using a rocket form, how much better than a similarly sized rocket? (same thrust) How much lighter is it than a conventional rocket or jet engine, can you quantify it with more than just "its better" Quantify if at all possible, thanks.
Let's get something straight here- no airliner company or for-profit corporation or university/institute is going to research this alone. There isn't enough money or incentive. It takes the crazy whacky USA military industrial complex to get this done.
So when you are taking that three hour shuttlejet trip to catch the peace protest in Hiroshima, please remember where your life-enhancing toy came from before you whine.
________________________________________ History Must Not Fall Into The Wrong Hands ___________________________________
Okay, how small can you make a PDE? If it was small enough, could you cycle them so that the net shock wave effect canceled out, and the shock per pulse was tiny?
Correct Horse Battery Staple: 72 bits of entropy. Enter "Correct H" into google. When it generates the phrase, that's
Actually the concept of the nuclear pulse engine (NASA now calls it "External Pulsed Plasma Propulsion") was demonstrated to work back in the 50's using a scale model driven by high explosives. It worked because the blast wave bounced off a "pusher plate" and also vaporized part of the surface for propellant. The only real engineering problems had to do with limiting the acceleration on the crew to a reasonable level and recovering from a misfire. The project was killed for political reasons (The nuclear test ban treaty etc...), but NASA is now looking into again. Do a search on "Project Orion" for more information.
Problem is getting past that first detonation.... Come on baby. BOOM! Damn, vaporized again.
Ah, but if you could aim it, and gradually ramp up the sound level, what a great crowd control device!
The guided anti-ship weapon (Fritx-X) was commanded by radio waves, not by wire. It worked quite well (sank ROMA among others). They did develop a wire-guided anti-aircraft missile (ground-to-air) and a guided anti-tank missile.
Geniuses like Tesla are like gold mines. They produce as much crap as anybody else, it's just that their crap has nuggets of gold in it.
For all intensive purposes, "whom" is no longer a word. That begs the question, "who cares"?
Lol!
Sorry I missed that! Heheh
"Derp de derp."