脉冲喷气发动机

1 Inside the pulsejet engine Report 1.0 Written by Fredrik Westberg This report would not exist without Dave Brill who inspired me from the begining, thanks for all help. Also a great thanks to those who have contributed with all kinds of information. This report is a private study on the pulsejet engine. You can contact me by e-mail, “fredrik_wg@hotmail.com” My homepage address. “http://www.geocities.com/Area51/Rampart/9722/welcome.htm”. This document is free available on my homepage. 2 Summary This document describes how to build/design a pulsejet engine, and how to put all parts together. I have also included some F.A.Q with answers. I have put some effort into the V1 chapter which describes the No: 1 Pulsejet engine, the Argus AS-014. There are also a short briefing on the pulsejet theories, this chapter is the one I’am most uncertain about. Finally I have added some blue-prints on different pulsejet engines, including my own design. Fredrik Westberg, 25 April 2000 3 List of contents Page 1. Introduction. 4 1.1 Who I am 4 1.2 Revision history 5 1.3 The first pulsejets. 5 1.4 For what use. 5 1.5 Pulsejets in this report 6 2. Pulsejet theory. 7 2.1 How it works. 7 2.2 Equations. 11 2.2.1 Pulsejet operation equations 11 2.2.2 Valve flow area 12 2.2.3 Exhaust pipe lenght 15 2.2.4 Thrust (Output power) 16 2.3 Argus pulsejet (V1) 17 3. Building your own pulsejet 20 3.1 Some ideas. (F.A.Q) 20 3.2 My pulsejets 27 3.2.1 Building description 28 3.3 Future project 31 3.4 Pulsejet plans. 33 4. Conclusion. 37 5. Glossary 38 6. Sources 38 7. Index 39 Pictures No. 1 My ice yacht No. 14 Angled valve design No. 2 Heinz Ollarius plane, 90 mm pulsejet No. 15 Pulsejet engine design No. 3 Static pressure wave No. 16 Pulsejet assambly No. 4 Microwave antenna No. 17 Start attempt on my second engine No. 5 Valve flow area table No. 18 Two pulsejets No. 6 Air flow speed No. 19 Valve plate deformation No. 7 Tube shape No. 20 Fuel injector No. 8 Exhaust pipe lenght table No. 21 Large pulsejet engine design No. 9 Argus pulsejet engine No. 22 Ice yacht No. 10 Fieseler Fi 103 (V1) No. 23 Brauner drawings No. 11 Flower valve shape No. 24 Alpha drawings No. 12 Argus valve design No. 25 My own drawing No. 13 My own valve design No. 26 Argus drawings 4 1. Introduction 1.1 Who I am My name is Fredrik Westberg, and I’m born in April 1973, in Sweden. I am (right now) a bachelor or engineer in computer and electronic science, but my interest’s lies more into the mechanic science area, like pulsejet engines and other physical things. Anyway, I do have an ordinary jobb, right now as a test engineer. My job is to make test equipment for printed circuit boards and for large systems. My employer is Solectron. Well, I have been interested in designing, building my own things, like different kind of vehicles. The first project was a propeller driven machine, ice yacht. I used it in the winter, riding on the ice covered lakes. Maximum speed of 25-30 Km/h with a 150 cm^3 engine, se picutre below. Another project was a boat driven by a pushing propeller. This boat was 3x4 meter big, it had two pontoons, and an 45-50 hp engine. With my badly homemade propeller, it was no success. Pic No. 1 My ice yacht Why am I writing a paper called “Inside the pulsejet engine”? There are several things. One is my interest in pulsejet engines, I have build two engines already with a lot of experience as outcome. None of them worked well, but I think I know what I have to do with them to get them work. Second is one of my bad habits. I always want to understand everything, in detail. Third, I will learn to write better English, at least I hope so. This document has been writen during a period of 10 month. 5 1.2 Revision history Revision Note P 1.0 First Release (preliminary state) R 1.0 New chapter 1.5 Chapter 1.4 updated Chapter 2.1 updated Chapter 2.2.2 updated Chapter 2.2.4 updated Chapter 3.1, question 3. New valve design added 1.3 The first pulsejets The word “pulse” and “engine” can be recorded back to somewhere around 1880-1890. And in the early 1900 a man in France build a pulsejet engine, but he didn’t get it into a reconance, only single explosions. Almost everybody has heard something about the “Buzz bomb”, they know where it was used, and how terrible it was. That is true. Their sound spread horror across southern England during the Second World War. This “thing” was the Fieseler Fi 103 powered with an Argus AS-014 pulsejet engine. This aircraft was an unmanned bomb, steered by a gyro. When the fuel ran out, it just dropped down from the sky and explodes on the ground. But it was something wrong with the design, the engine was never supposed to die out before impact. Because this was a warning signal, when the “Buzz bomb” stopped, soon there would be an explosion. But the Englishmen could defend them self from this weapon. It wasn’t fast enough for thier fastest aircrafts, so it was possible to hunt it and and shoot it down. It was also possible to shoot it down with anti-aircraftgun. I will go into detail on this Argus pulsejet engine later when I discuss pulsejet theory in chapter 2. 1.4 For what use Why do we need pulsejet engines? We have operational jet engines, big and small and they run longer and more efficient that any pulsejet engine. That’s true, but you can’t build a lightweight jet engine that’s deliver 3-10 kg thrust easily in you garage. But with a pulsejet, you can. So what do we use them for? Small engines are mainly used to give thrust to model aircrafts. I got a mail from Gilberto Giardini Weber, he said he had worked in a factory where they produced towplanes (drones). They where also producing a model 6 aeroplane powerd with a 17 cc engine, with a top speed of 250 Km/h. These planes where used as targets for the anti-aircraft artillery. At that time a project was initiated to develop a pulsejet engine on 50 lbs thrust for these planes. Gilberto said he left the company before anything happens. He later heard that the project was closed because the Brazilian army didn´t give the funds needed to the research. But he do know that some preliminary drawings and specifications where made, anyone heard of a 50 lbs pulsejet engine? Please, e- mail me about it. 1.5 Pulsejets in this report In this report I will use a few pulsejet engine designes in my investigation. Those are, Argus AS-014, Team Helmonds P90 and my own engine design. Teams Helmonds P90 have originaly been desigen by Heinz Ollarius, His design are approx. 20 years old. You will find this engine described on different places. Pic No. 2 Heinz Ollarius plane, 90 mm pulsejet. Picture to the left is Heinz Ollarius model airplane, it´s completly build from fiberglass and honeycom and it´s very strong and super light. The engine is a 90 mm pulsejet with 80 N thrust. Heinz worked with a injection pressure of 8 bar. Picture to the right is a starting attempt, Heinz (to the left in the picture) are managing the fuel and air pressure. Remko Klaassens (to the right) is igniting the engine. Unfortunately Heinz passed away a few years ago, he is by many seen as the “number 1” pulsejet engine designer. Remko Klaassens is now building these engines after Jean Quadvlieg gave all his tools and equipment to him. Jean was a close friend of Heinz, he build even more engines than Heinz based on the 90 mm pulsejet engine. Jean Quadvlieg also made an engine for the Pulsejet team Helmond (AMTjets) and he is now building micro turbines with high thrust. Remko also mention that the jet aeroplanes need a good pilot, and one of the best is Bennie v/d Goor. He has a spectacular show and his motto is “Go low and fast” but always with the safty in first place. That’s what makes him the best. Pictures and story comes from Remko Klaassens. 7 2. Pulsejet Theory 2.1 How it works When you look at the material details you will think, “This must be a simple engine” but infact, it's a rather complex engine. It’s also difficult to understand the operation sequence. So where do we begin? The first guy to understand the theories was the German Paul Schmidt. He was active from 1928 to later after the Second World War with his pulsejet ideas. Infact, he did not build the famous V1 engine, he just lead the Argus Company on the right track when they desiged the engine. He had a better and more efficent construction. But he didn’t reviel his secerets because he thought that he could make a profit out of his ideas after the war. But the turbine jet engine was at its dawn and the pulsejet engine never became the commercial succes that Paul once thought. Below is my personal thought about the pulsejet engine operation sequence. Fact, my experience A pulsejet engine deliver thrust, gasses of burned fuel/air comes out of the exhaust pipe with such a speed that a force is created in the opposite direction. A pulsejet engine can run without any outside help. The pulsejet engine repeats its puls sequence at a given frequence. The reconance frequence is among others depending on the lenght of the pulsejet engine. Conclution, my experience Okey, here comes the hard part. First of all, pulsejet engine is now also related to the word “tube”. We begin with the fact that the tube is approx. 15-20% filled with fuel/air mixture (*), some how it detonates and the high pressure makes the gasses to be pushed out through the exhaust pipe in a high speed, propobly not above speed of sound. By reading documents and talking to other people my experience is that the peak speed may by speed of sound but not above. I have found that there are at least two different circumstances why a pulsejet engine operates in a resonance sequence. Simply, why the pulsejet engine run. · The pulsejet engine has a lengt of a half wavelength of the resonance frequenze. This means that when detonation occurs a shockwave is travelling from “valves” to the end of the pipe. Then the shockwave turns 8 and go back (reflection). This pressure resonance is what I call the static pressure. If we compare audio resonance theory with electrical resonance theory we will find that they are pretty good adapteble. Resonance behavior is the same. Electricity is also my subject field. If we look at the resonance in an electrical cable, we look at open, close and adapted termination. Adapted termination will return none reflection. Open and close termination will return 100% but in different phase. And in this case it´s the open termination that is comparable to the pulsejet engine. In a cable, 100% are reflected back, but in a pulsejet engine this is not the case. Imagine putting a loudspeaker where the valves are placed and tune it into the resonance frequence, should be something like X*2*f=340, where X = pulsejet lenght in meter. f is the resonance frequence. Ofcourse will you here the resonance sound at the open end, so this will decrease the reflected shockwave, how much is hard to tell, lets say 50-60%. If we look at the picture below we will see 3 curves, Black color is the shockwave traveling to the end, green is the reflected wave and red are the summurize of the two curves. Green curve has the smallest amplititude, in this picture, color is more dark green. Pic No. 3 Static pressure wave PJ equals to the pulsejet engine, “tube”. + indicates high static pressure. Sequence is run from pos 1 to pos 8, then begins with pos 1 again. Explosion occurs when the static pressure goes high in pos 1. In this picture 9 the reflected wave are 50% of the forward wave. The forward wave is a constant sinus wave. In a pulsejet engine the situation are a little more different. I belive that the pressure in the forward wave won´t rise above atmospheric pressure after it have fall. If we summurize the two curves (red curve) we will se that static pressure will change more at the tube ends than in middle, so peak pressure will be higher at the valves and at the end than in the middle. If we had 100% reflection static pressure in the middle would be 0. · As I said, high pressure makes the gasses to be pushed out of the exhaust pipe in a high speed. Due to the gasses inertia there will finally be a low pressure inside the tube, just like pulling your finger out of a bottle and you will hear a “plopp”. The pulsejet works exactly the same way. This low pressure will cooperate with the static pressure resonance wave because the low pressures apper at the same time. The reflected pressure wave is at this time positive, but the summaries of the forward and the reflected static wave are negative. This pressure is what I call the dynamic pressure. Let’s go back to the pulsejet sequence. After the explosion, the static and the dynamic pressure will fall. This will finally open the valves and let new fuel/air mixture enter the pulsejet engine. Next thing that happens is that the resonance shockwave will raise the pressure and trigg the ignition, and a new sequence will begin. This is the basic princip behind the pulsejet engine operation. The static pressure gives us the resonance and the dynamic pressure gives us the thrust. I think that it is this that makes the pulsejet engine so hard to overcome. The static and the dynamic pressure must synchronize to achieve a perfect resonance. If we summurize this discussion we will see that the shape of the pipe will affect the reflected shockwave. If we compare to microwave theory an adapted antenna look somthing like this. Pic No. 4 Microwave antenna Black arrow is the forward signal, green arrows and the black arrow has the same energy. The reflected wave is very small compared to the forward signal. 10 If we make a pulsejet engine that looks like this the reflected shockwave will decrease even more, and the engine will have serious trouble to run properly. So if you would like to design a new type of pulsejet rear end you have to have this phenomenon in your head. Another thing thats matter is also the relation between wavelenght and resonance pipe diameter. Equals to the pulsejet lenght contra diameter. Those model pulsejet engines I have seen, have a Lenght/Diameter L/D ratio of 15 to 17. Argus (V1) has a L/D of 8.7. I have not paid attention to the largment after the valves. The lower L/D ratio you have the more reduced reflected shockwave you will get. My guess is that the model pulsejets have a higher L/D ratio to secure a stable resonance and to lower the resonance frequence. I belive that there are more circumstance why a pulsejet is running, but they are today beyond my knowledge. Shockwave speed The Argus pulsejet engine had a stable resonance frequence of 43 Hz (**). The shockwave travels with the speed of sound through the tube, speed of sound can then be calculated to 3.49*2*43=300.14 m/s. I dont have the knowledge to culculate speed of sound in a pulsejet engine with it’s high pressure and high temperature. But if this is true, we could have some use for this information. To find the reconance frequence to calculate the shockwave speed se chapter 3.1 question 8. My first pulsejet had a frequece around 170 Hz and a lenght of 590 mm. Shockwave speed must then have be 0.59*2*170/sek => 200 m/s. I think my engine did not run properly, the ignition did not occur by the shockwave. That’s why 200 m/s is not equal to 300 m/s. My engine also change frequence depending on fuel consumption. The P90 has a frequence of 150 Hz, it’s lenght is 86 cm, this gives us a shockwave speed of 150*2*0.86= 258 m/s. The following conclusion is just a guess from my point of view. If you obtain a higher “shockwave” speed, the clearer or more effective the engine will run. Shockwave speed is the wrong word to use but it´s also the easiast word to use. It´s not the shockwave speed that´s increases. I think that it is the dead time between the reflected shockwave and the ignition that gets shorter, therefor “shockwave speed” increases. As you se I´m not talking about Combustion chambers and resonance pipes any more. Paul Smidth once said, “as long as the valve opening area, and the other conditins of resonance sequence are met, tube shape has little effect on the operation of the engine.” The importent thing is the exhaust pipe area contra the valve flow area. So when you hear people talk about combustion chamber in a pulsejet engine thay are wrong, even myself thought that once. 11 (*) 15-20% is a value calculated (or estimated) by Paul Schmidt (**) According to Dave Brill 2.2 Equations In this chapter I will give some clues about culculating with pulsejet engines. These equations are far away from finished, but it may be a good start to understand something. There are also some equations from practical examples. I know that there exist several different blueprints on fully operational pulsejet engines. The equations come from these engines. 2.2.1 Pulsejet operation equations First some basic facts, I have found that the Air/Fuel ratio is something about 12-13, this means that you need 12-13 kg of air to burn 1 kg fuel at ground level. I found this information in two different reports, I think that this is correct for most kind of fuel types. 1 litre of air is approx. with 1 gram. Another fact I use is that the gas exit velocity never goes above speed of sound, right or wrong? I have approximated explosive air (air/fuel mixture) with just air, because to simplyfy it. They have almost the same weight. Let’s begin with some variables V = tube volume (dm^3 = litre.) f = pulsejet engine operation frequence. (Hz) va = gas exit average velocity. (m/s) F = force, thrust (N, Newton) fc = fuel consumption (gram/second) m = mass in kg t = time in second. Equation (1){ m*va=F*t } Here follows some practical examples. V1 fuel consumption V= 511 litre, f= 43 Hz. Se chapter 3.4 pulsejet plans pic 26. 20% (*) of 511 litre is 102.1. 102 litre of explosive fuel/air mixture = 0.102 kg. To burn this amount of air we need approx. 0.102/12.5 = 0.00816 kg of fuel/explosion. 0.00816*43= 0.351 kg fuel/sek. fc = 351. We know that the V1 had around 450 litre of fuel in it´s tank. 450 litre is approx 380 kg. With this fuel amount it could then fly for 380/(0.351*60)= 18 minutes. Which is the flying time between the coast of France to London. 12 P90 studies To find blueprint of this engine, check web address at chapter 3.4 pulsejet plans. V = 2.9 litre fc = 6.7 gram/sec f = 150 Hz va = 258 m/s F = 85 Newton “fc” is based on information from the P90 homepage 1.2 kg of fuel over 3 minutes. This number might be incorrect, because maybe not all fuel was used or burned correctly in the tube. “f” was measured from a sound file at their homepage, se chapter 3.1 Some ideas (F.A.Q) question 8, “va” are approximated to it’s shockwave speed, right or wrong? From equation (1) m = F*t/va = 85/258= 0.329 kg/second. This gives us 0.329/150= 2.2 gram gas/explosion. At least 2.2 are less than 2.9 because the tube contains only 2.9 gram of air. I have read that the pressure during the intake cycle is the same as in ambient medium. That’s why there can’t be any more air than 2.9 gram in the tube. If we check the fuel consumption instead, 6.7 gram of fuel needs 6.7*12.5= 84 gram of air/second. 84/150 = 0.56 gram of air/explosion. By an “incident” 0.56 gram is exactly 20% of the tube volume which Paul Schmidt said it should be. Conclution might be that, of totaly 2.9 gram air. 2.2 gram is pushed out by 0.56 gram air/fuel mixture in an average speed of 258 m/s. And it is a BIG might, I have not calculated with any energy, nor temperature, nor pressure, nor efficient, so please correct me if I’am wrong. (*) 15-20% is a value calculated (or estimated) by Paul Schmidt 2.2.2 Valve flow area Brauner, Alpha, Sov faa, B-12, Aerojet, PAM, Silnik. Is it possible that they have something in common. I have choosen these engines because they have almos