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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?
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
Don't start a 'flame' war ...
Don't go to a brothel if you want to buy broth
"...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.
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.
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. "
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.
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.
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.
A pulse jet and a pulse detonation engine is not the same thing.
Pulse jet's was what the germans used in their "buzz-bombs" during WWII.
As far as I've been able to conclude the greatest difference is in the burnrate of the fuel.
In a pulse jet you have a series of "slow" burns or explotions at a fairly low rate.
In a pulse detonation engine you've got insanely fast burns (hence "detonation") at serveral hundred detonations per second.
One of the greatest enginering tasks was apparently to be able to not only achieve a detonation instead of a burn or explosion, but to also do this continously at a high rate.
/.Mattsson - My native language is not English, so please don't whine over linguistic errors. (That's lame anyway...)
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.
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.
Metal Hydrides can store Hydrogen at densities greater than even solid Hydrogen. Of course, the hydride weighs 10x the amount of Hydrogen it can store, so I don't know if it would be practical for use on airplanes, but it's definitely space-efficient and safe.
I don't know why people think creating Hydrogen is expensive, either. Electrolyzers can be made anywhere from 80 to 90% efficient. Of course, electricity isn't as cheap as gasoline, but Hydrogen could be produced during off-peak times. I'm sure it would be comparable to or cheaper than highly-refined jet fuel.
"I assumed blithely that there were no elves out there in the darkness"
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
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
Google for German Pulse Jet Fighters...
...and he grinned, like a fox eating shit out of a wire brush.
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.
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.