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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?
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
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.
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.
Considering his inventions (AC power, 3 phase power, the transformer, modern radio,electromagnetic motors, fluorescent lighting etc etc etc), I think he was a pretty smart guy. I wouldnt dismiss out of hand the things that he's talked about just because you dont understand how it works.
Not only that, it is very easy to build a tesla turbine, and pictures exist with witness comments on the one that tesla built getting almost 10hp per pound.
That, and the tesla turbine only has 1 moving part. The disks spinning inside the housing. Sounds like it makes for a pretty reliable engine to me.
It's easier to fight for one's principles than to live up to them.
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.
That reminds me of the quote from Colonel Albert Pope in the 1890s (owner of one of the first electric car companies): Internal combustion engines will never take off because "people won't want to sit on top of an explosion".
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 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.