Science Abuse Posted August 15, 2005 Report Share Posted August 15, 2005 I'm trying to find info on these, and I'm finding the intarweb a bit dry. I want to know how they work, down to every part, and if you can control throttle. Anyone know any good resources? Pulse-jet.com showed promise, but all the links there seem to be dead. Quote Link to comment Share on other sites More sharing options...
Lustalbert Posted August 15, 2005 Report Share Posted August 15, 2005 I may be wrong, but wasnt the pule jet the jet that was used by germany on the "buzz bombs"? Named buzz bombs because of the buzzing made by the rapid pulseing of the jet motor. http://www.airtoi.com/pulse.htm http://www.aardvark.co.nz/pjet/gokart.htm http://conceptengine.tripod.com/conceptengine/id2.html http://www.aardvark.co.nz/pjet/ Quote Link to comment Share on other sites More sharing options...
Mowgli1647545497 Posted August 15, 2005 Report Share Posted August 15, 2005 http://en.wikipedia.org/wiki/Pulsejet Heed the last line: "However, despite this advantage, pulsejets are seldom considered to be practical power plant due to their high fuel consumption, low efficiency, noise, and significant vibration levels. Today, they survive as a powerplant for model aeroplanes." If it "was" and "isn't anymore", then, in engineering at least, there's a reason. Nobody throws away good engineering. As opposed to fashion and religion.... Good for models and dorks in gokarts in New Zealand though. Whatcha building? Quote Link to comment Share on other sites More sharing options...
MrMeanGreen Posted August 15, 2005 Report Share Posted August 15, 2005 http://www.abovetopsecret.com/pages/pdwe.html Pulse Detonation Wave Engines, do a search. Supposedly used in the SR-75 Aurora. Quote Link to comment Share on other sites More sharing options...
Mowgli1647545497 Posted August 15, 2005 Report Share Posted August 15, 2005 I can pretty much guarantee you pulse technology is not used in the Aurora or any other operational Black Program aircraft. And I won't say why not, so there. SCRAMjet tech, maybe... That site, erm...whoa mm-ok. This little gem has got to be the most Fred Sanford I've seen since my grad student days, made me spit up my Diet coke: "Liquid methane or liquid hydrogen is ejected onto the fuselage, where the fuel mist is ignited, possibly by surface heating. The PDWE works by creating a liquid hydrogen detonation inside a specially designed chamber when the aircraft is traveling beyond the speed of sound. When traveling at such speeds, a thrust wall (the aircraft is traveling so fast that molecules in the air are rapidly pushed aside near the nose of the aircraft which in essence becomes a wall) is created in front of the aircraft. When the detonation takes place, the airplane's thrust wall is pushed forward. This process is continually repeated to propel the aircraft. From the ground the jet stream looks like "donuts-on-a-rope." I think one of my profs just rolled over in his grave. Ugh. Meanwhile, work progresses on my leprachaun-powered sled. Looking for investors. Updates next Tuesday. Quote Link to comment Share on other sites More sharing options...
Science Abuse Posted August 15, 2005 Author Report Share Posted August 15, 2005 Good for models and dorks in gokarts in New Zealand though. Whatcha building? A dorky model. I'm considering attempting an RC X-43. I built an 8" glider version to start off with, but it flies like a roller pigeion. I'll probably end up using the X43-B, the canards will help keep the nose up and give me another control surface. I managed to find a pdf of some 50's-60's text book exerpt. As I was reading it, I was saying to myself "this actualy works?" Still haven't realy found a means to control throttle, though. A SCRAMjet would be cool, but I'm not sure about the Mach5 stall out speed, seems unsafe for an RC plane. Having no moving parts and being extremely laight makes them intriguing, though. I read about PDWE's a while back, they were billed as "external combustion jets"....and they dont make sense. It's far too inefficient to have the explosion happen without a chamber. Did anyone consider the fact that maybe what they heard and saw were just jets with problems? Imagine, for a second, that it does work. You have combustion capable of propelling an air craft beond hypersonic...thats alot of thrust. Imagine that hitting you in the ass in a pulse, you'd hemorage. Quote Link to comment Share on other sites More sharing options...
Science Abuse Posted August 31, 2005 Author Report Share Posted August 31, 2005 update, now that the board lives. In the time past I have picked up a pair of FD3S turbos and done a good bit of reading. I beleive I have a good setup planned, and have even begun making an annular combustor for it, as apposed to the single can combustors most use. I've got a plan for a proper jet engine based on a turbo cartridge, but I'll get this one done and running first. I've got them in autocad if some one can host the stuff. Quote Link to comment Share on other sites More sharing options...
Renner Posted August 31, 2005 Report Share Posted August 31, 2005 I'm bored this morning... I can pretty much guarantee you pulse technology is not used in the Aurora or any other operational Black Program aircraft. And I won't say why not, so there. SCRAMjet tech, maybe... Actually, this isn't correct. Every big aerospace firm is dumping cubic dollars into PDEs right now. At my last job, my project was designing/building/tuning/testing pulse detonation engines. Not surprisingly, today's pulse detonation engines (PDEs) they are nothing like the old buzz bombs or the ones used in model planes. Building a low speed PDE (less then 50hz) is actually not that hard at all if you have the right combustion background and a good test facility. Here is a picture of an initial test firing of our “baby” version: http://www.streetneeds.com/uploads/twinturbonet/pde_firing_1.JPG I have some pretty good movies of test runs too, but I cant’ exactly post those. Current technology is able to match thrust numbers from turbine engines, but the PDE does it at 1/3 the fuel consumption. These are multi-tube PDE's firing at over 120hz. They are still pretty loud, but they are not as bad as they used to be since the multi-tube PDE’s are using frequency cancellation to control noise. Still very fun to play with though. Quote Link to comment Share on other sites More sharing options...
Science Abuse Posted August 31, 2005 Author Report Share Posted August 31, 2005 I'd be very interested in seeing the guts of those, at least what is behind the black box. The only actual PDE plans I've been able to come by pre-date sputnik. Quote Link to comment Share on other sites More sharing options...
Renner Posted August 31, 2005 Report Share Posted August 31, 2005 Sorry, can’t do that. For a low speed PDE engine the hardware is relatively cheap and easy come up with, the cycle is very similar to an IC engine. Air/fuel in, spark, purge exhaust out, repeat. It's the microprocessor controller that you need to control the events, the testing/monitoring equipment, and of course the proper test facility (so you don't kill yourself if it doesn't run right), that start to drive the costs up. You also need to have the right internal geometry for the DDT (Deflagration to Detonation Transition) to take place. And that of course changes based on what you are using for fuel. There are all sorts of academia publications out there about this stuff, start searching through some of those. By the way, you really shouldn’t be messing with these things on any sort of scale anyway. Several people have died and lost limbs over the years from getting in the way of these things when they fire. Notice that remote camera behind the bulletproof lexan in the top right corner of the photo? That’s because being within 10 feet of that tube exit in just about any direction causes some serious damage. As in, open-air sonic boom peak impact pressure intensity x 100. Quote Link to comment Share on other sites More sharing options...
Science Abuse Posted August 31, 2005 Author Report Share Posted August 31, 2005 Keeping it safe shouldn't be a problem. Testing is my profession, afterall. By no means wil this be done inside anything. My co conspirator has access to land equipped with a firing range. Keeping the test stand 30ft away and on the other side of 1/4" lexan should do just fine. I dont think I'm going to play with homade pulsjets untill I have more machine shop access. Right now we're just playing with the gas turbine. I've never set up a burn like this, so I'm trying to find some good models or data on how to set up my deisel burn. I'm using probane to get the ball rolling, then plan to shoot deisel to get the trust pumping, but I'm at a loss for where the best place to spray it is. In the head of the diffuser, the primary, the dillusion area, or just spray the cone aft of the whole thing? I could experiment, but it'd be nice to have some reading material to go off of. It'd at least save me the gas of driving 40mins to "the site". With these wee hitachi turbos, I doubt we'll be pushing enough gas to exeed the speed of sound. I'd consider us fortunate to get 20lbs out of one. Quote Link to comment Share on other sites More sharing options...
Mowgli1647545497 Posted August 31, 2005 Report Share Posted August 31, 2005 Hmm, I can tell you at least Lockheed and Boeing are not putting money into PDEs, unless someone is lieing to my face. Wright Patt's last sponsored PDE research RFP was more than 15 years ago for drones, at least according to my GSA search. Who's spending money on PDEs for super or hypersonic propulsion use? Last I heard the money du jour was in laser sheet ignition for supersonic combustion. So if some skunkworks group has scored corporate cash to do research on pulse jets under the guise of new transport or other vehicle applications, I need to talk to their venture lead. My leprechaun sled needs funding bad, and I figure they'd be the person to get me my dough. +1 on Renner's warning about being careful with this stuff. If you ever get a chance to hit Bolz Hall over on campus check out the compressor on display (at least it used to be on display what ten years ago). Shows what happens when you get a shock wave formed in the area of the outer lip of the compressor blades. Kerplowee. Shockwaves and carelessness = bad. BTW - I did that to it, my claim to fame (infamy). P.S. - combustion without a chamber is in common use, we call it an afterburner. Quote Link to comment Share on other sites More sharing options...
Renner Posted August 31, 2005 Report Share Posted August 31, 2005 Pratt & Whitney contacted us (my old employer) for some consulting work in this endeavor, and then turned out to be our main competition of course. We had competition in this area from the other big two as well, I suppose it’s possible they have dropped it since then, but IMO that is highly unlikely considering the history and involvement they had at the time. And we had several consultants from Wright Patt sit in on our design reviews, as they were currently researching/testing 120+hz multi tube PDE’s, and it was indeed funded work. This was in early 2004, so I probably shouldn’t name any names since the work is ongoing. They were not making claims of hypersonic operation though, they just stated that they had easily matched thrust capabilities of any conventional turbine engine in use today, and that with the fuel consumption savings at those levels (along with the mechanical simplicity) that this was not just a research exercise. They of course did not disclose anything regarding future airframes, they just discussed modified current airframes for test drudgery. They also had a flight scale for a high speed missile application, which was already airborne and being shaken down. Once again, their definition of “high speed” was intentionally foggy. Quote Link to comment Share on other sites More sharing options...
Science Abuse Posted August 31, 2005 Author Report Share Posted August 31, 2005 P.S. - combustion without a chamber is in common use, we call it an afterburner. Why have one when you can have both. The project is a larf, a hobbie, but I have imposed some goals. I'd like to keep it somewhat efficient. What alot of guys seem to be doing is, essentialy, building a single can ala'can-annular, and blasting fuel through it. It makes noise, makes fire, but burns alot of fuel. They also have large dillusion areas as a result. I'd like to have a nice constant temp, relatively cool, so i can make the actuialy combustion chamber assembly small, and still be able to run it for a 10 minutes at a time without anything melting. Apart from the turbo, everything else will be 304 stainless. I'm not expecting much more then 1400 deg from the deisel burn, so EGTs should be slightly lower, well within everything elses operational limits. The turbos appear to be both water and oil cooled...I'm wondering if putting water through 1000 deg iron channels would be a bad idea. Quote Link to comment Share on other sites More sharing options...
Mowgli1647545497 Posted September 1, 2005 Report Share Posted September 1, 2005 Renner, thats very interesting stuff. I'm going to stick my nose in a few places and bug my brother-in-law about who's doing what (he's still contracting at Wright Patt). So these guys said they beat the efficiency of a turbofan or turbojet engine with a pulsejet? Not surprised by your comment about Pratt&Whitney, I've got little good to say about P&W, some sleazy individuals over there... Quote Link to comment Share on other sites More sharing options...
Renner Posted September 1, 2005 Report Share Posted September 1, 2005 Renner, thats very interesting stuff. I'm going to stick my nose in a few places and bug my brother-in-law about who's doing what (he's still contracting at Wright Patt). So these guys said they beat the efficiency of a turbofan or turbojet engine with a pulsejet? Not surprised by your comment about Pratt&Whitney, I've got little good to say about P&W, some sleazy individuals over there... Actually, both P&W and the Wright Patt people talked about their thrust to fuel efficiency advantage. This is one of the key reasons why my company was so interested. On our system the fuel consumption levels were very reasonable. Funny thing about P&W, when they realized that we really were going to move forward on our own without just handing everything over to them a few feathers got ruffled. So to try and discourage our progress (since they had of course decided to pursue this direction themselves after meeting with us) they said that it would take us 7 years and about 5 mil to go from ground zero to a working installable prototype, because that’s what it took them initially. ~9 months and ~$250K total project budget later I was destroying piezo impact pressure targets with our “medium” sized prototype without even trying. I probably shouldn’t post any more details about this stuff online. I’d be happy to chit chat over a beer sometime though if you are interested. Quote Link to comment Share on other sites More sharing options...
Science Abuse Posted September 1, 2005 Author Report Share Posted September 1, 2005 so, since this is obviously the place to ask, back to my origional question: how do you control the throttle of a pulsejet, simple fuel metering? I'd think there would only be a very narrow window in which you could play....? Quote Link to comment Share on other sites More sharing options...
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