Naked Science Forum
Non Life Sciences => Technology => Topic started by: McQueen on 01/09/2007 16:37:57
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Right! Well you all know that there has been a lot of talk of late on global warming, carbon emission and so on! Well just have a look at this site and tell me what you think!
http://www.geocities.com/rotarypulsejet (http://www.geocities.com/rotarypulsejet) Mcqueen
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The problem with all rotary engines is that in principle they seem simple (this is certainly true regarding the Wankel engine), but heavily dependent on the quality of the seals - and it is often the breakdown of all the seals that gives the biggest headache.
I would have thought the other problem with this engine is that so little of the energy generated by the drive is actually used. The exhaust gasses from the engine will be travelling at high speed, and be very hot - that is a lot of energy in that heat and exhaust gas speed that has not been put to use by the engine. Conventional IC engines still have some significant residual heat (the catalytic converters, it is now very difficult to reuse that heat because the catalytic converters need that heat to function), but they no not have very much exhaust velocity since they rely on pressure rather than impulse derived from the exhaust velocity to derive their energy.
From what I have read, I cannot see actual efficiency figures for the engine they are describing (or how they would compare with other rotary engines, such as the wankel engine, of gas turbine engines).
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anothersomeone
From what I have read, I cannot see actual efficiency figures for the engine they are describing (or how they would compare with other rotary engines, such as the wankel engine, of gas turbine engines).
Well, all I can say is that you have not gone through the web-site. A Wankel Engine for your information is just a glorified version of the Rotary vacuum pump, that has been around for more than a hundred years, while the rotary vacuum pump is extremely efficient, since it runs in an oil bath for effective sealing, the Wankel engine, dealing with much higher pressures, tries to do the smae thing in reverse in air! It is a huge scam, on which a lot of money has been spent. Let's take another look at this site, right! McQueen
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And another thing, in an effective CDN de laval nozzle, the very thing is to extract heat and energy from that initially high temperature, high velocity gas flow. You do agree I hope that rockets are the most powerful form of engine known to man? Imagine trying to go to the moon in a souped up IC piston engine, or even a jet engine. Still have doubts about the energy of high velocity gases? Let me know McQueen
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Rockets are not necessarily the most powerful engines known to man, but they are engines designed for a particular purpose.
Nuclear power plants generate far more power than rockets (usually thought the medium of steam turbine engines), but they would not work (at least in the way they are designed for electric power generation) to take a vehicle to the moon.
The advantage of a rocket engine is that the high exhaust gas speed allows the vehicle to be propelled at high speed. Rocket engines can propel vehicles at high speed, but not necessarily with the highest power (a little like the top gear in a motor car - you use that to travel very fast, but it is useless for carrying a very heavy load up a steep hill - it all depends on what you need to do with that power).
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The normal IC engine achieves its reasonable thermal efficiency due to the high temperature of combustion compared to exhaust, Wankel engines have an additional problem apart from seals which is the shape of the combustion chamber which makes it hard to achieve a good expansion ratio (commonly called compression ratio) without pre-ignition.
There are many things to consider in an automobile engine besides thermal efficiency primarily the spurious gases in the exhaust.
Aircraft gas turbines achieve good thermal efficiency by the use of expensive alloys to allow a high combustion temperature and a high expansion rayio but are very expensive and inflexable.
The engine described in the URL given is just a bad joke!
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The efficiency of a rocket is connected to the mass that it is throwing out of the back. the force you get from throwing something out is proportional to the mass times the velocity where as the energy you use is the mass x velosity2 so the more mass you throw out the back the slower it needs to go so the less energy you need to have the same effect.
A conventional IC engine is essentially pushing the whole weight of the car which is very efficient, where as the engine you draw is only throwing out the gasses from the explosion which will come out very fast but very inefficiently.
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daveshorts
The efficiency of a rocket is connected to the mass that it is throwing out of the back. the force you get from throwing something out is proportional to the mass times the velocity where as the energy you use is the mass x velosity2 so the more mass you throw out the back the slower it needs to go so the less energy you need to have the same effect.
Exactly the p9oint. Let's look at it another way.
For example, take an open ended cylinder of a certain diameter, equipped with a piston and a cork pushed tightly into one end, and call this cylinder A. When the piston is pushed up the cylinder it reaches a compression ratio of 3 : 1, or 44 psi approx. before the cork is pushed out of the cylinder. OK< take another cylinder, of exactly the same dimensions as cylinder A and call it cylinder B, it also has a cork stuck into one end. However, instead of a piston, it is equipped with a venturi at one end, the venturi is equipped with a valve. Cylinder B is then filled with compressed air throughj a compressor until its internal pressure reaches 43 psi (i.e., a pressure just a little less than that needed to blow the cork out of the hole, in cylinder.} The valve to the venturi is opened? What happens ? will the cork fly out of the end of cylinder B. If so how far will it go? My guess is that they will travel the same distance or that B will travel further because it has more compressed air behind it. In order to be exactly equal, when cylinder B is filled with compressed air, its size should also change correspondingly, so that it is the size that remains of cylinder A after the piston has compressed the air to 44 psi.
OK, take another scenario, now cylinder A is fully sealed at both ends, this time it is fitted with piston rings that enable it to be placed in an air-tight manner down a long barrel. The barrel is equipped with an air-tight piston that allows the air behind the cylinder to be compressed in a ratio of 3 : 1 or to 44psi. When the piston is depressed cylinder A flies out of the barrel. Cylinder B has exactly the same dimensions as Cylinder A, however instead of piston rings it has a venturi equipped with a valve. Cylinder B is filled with compressed air to a pressure of 44 psi and the venturi is opened. Which cylinder would go further, my guess is cylinder B, because it retains the pressure for longer.McQueen
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The normal IC engine achieves its reasonable thermal efficiency due to the high temperature of combustion compared to exhaust, Wankel engines have an additional problem apart from seals which is the shape of the combustion chamber which makes it hard to achieve a good expansion ratio (commonly called compression ratio) without pre-ignition.
shyprum, I have only one question for you. Do you consider the Wankel to be a good engine. Anything at all about it? If yu think the rotary pulse jet is a bad joke, I don't know what you would think of as a good joke! McQueen.
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anothersomeone
Well, all I can say is that you have not gone through the web-site.
I did look at the entire site, but I don't say I could not have overlooked something - I was merely skimming over what I was reading.
A Wankel Engine for your information is just a glorified version of the Rotary vacuum pump, that has been around for more than a hundred years, while the rotary vacuum pump is extremely efficient, since it runs in an oil bath for effective sealing, the Wankel engine, dealing with much higher pressures, tries to do the smae thing in reverse in air! It is a huge scam, on which a lot of money has been spent.
Tell that to all the people who seem to love the performance of the Mazda RX7.
The Wankel engine has many problems with it, but it has a good power to weight ratio, and very smooth power curve, and very quiet in comparison to a piston engine. Aside from the RX-7, it is very suitable for motorcycles and microlight aircraft - anywhere where you need a compact light weight engine.
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For some niche applications where light weight overides fuel efficiency and emission standards (like the two stroke)the Wankel has its uses, even the the pulse jet found application in WWII in a successfully missile system but as an automobile engine no way.
The Wankel achieved success in a Nissen car at Le Mans about twenty years ago but the present regulation favours Diesels
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Syhprum, you seem to be interested in engines, so I suggest that you go through the site (http://www.geocities.com/rotarypulsejet) I had suggested, it is a quite extraordinary design. The compressed air is supplied to the combustion chambers at a pressure of 125 psi ( compression ratio equivalent to 9: 1) from the air tank, through throtary union and via a poppet valve into the combustion chamber in a completely hermetically sealed environment. Fuel is similarly introduced through the rotarty union, so the fuel and compressed air are kept separate until they enter the passage in the rotor leadi\ng to the combustion chambers. The poppet valve is closed and the fuel/air mixture is ignited. Simultaneously with this or a little later, a gate valve in the CDN (Convergent divergent nozzle) opens and the hot gases of combustion escape at velocity thrusting the rotor in the opposite direction. Much, much more efficient than either the Wankel or an IC Piston engine. McQueen
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Tell that to all the people who seem to love the performance of the Mazda RX7.
That's just what gets me, granted it is a highly desirable emngine design if it can be sealed. Have you claculated the area that has to be sealed ? An eccentric rotary vacuum pump, runs on exactly the same principle, but runs in an oil bath to achieve proper sealing. No doubt, engineers diud manage to do the almost impossible with the Wankel, but only at hell of a cost! And even then it never sealed perfectly which is why it has never caught on, leave alone the high precision engineering required! McQueen
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I find it difficult to make any serious criticism of the so called pulse jet engine, compressed air provided by a separate compresser! (I guess a turbo charger could be used), poppet valves operating at 2000°C the exhaust valves in an IC engine have a hard enough time coping with the exhaust gases after they have cooled by expansion.
How are inlet and exhaust valves to be operated (if they could be built) on these moving conbustion chambers?, I think the request for funds to develop it says it all!
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I find it difficult to make any serious criticism of the so called pulse jet engine, compressed air provided by a separate compresser! (I guess a turbo charger could be used), poppet valves operating at 2000°C the exhaust valves in an IC engine have a hard enough time coping with the exhaust gases after they have cooled by expansion.
How are inlet and exhaust valves to be operated (if they could be built) on these moving conbustion chambers?, I think the request for funds to develop it says it all!
I can understand the cynicism, but then again, if you don't mind me saying so, you haven't really gone through the site at all. These questions have all been answered in some detail! The poppet valves are used only for the inlet port, because they provide such excellent sealing, the valve to the CDN (exhaust port) is a sliding gate valve. Now if we take the final pressure in the combustion chamber (after ignition) to be 500psi, then the pressure on the gatevalve, since it sealing a hole about a quarted inch in diameter would be about 1/20th that area so the pressure it has to cope with is just 25 psi, right. Commercially available belt run compressorsd are available that deliver 125 pf psi at a flow rate of 8 cu ft/min! The size of this compressor is *' in length and a diameter of just 5". This compressor would be used to replenish the main air tank, with the small amount of air (16 cu in) used for each combustioon cycle. What is so impossible about that! Anyway one man's meat............ as the saying goes. McQueen
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Soory that should be the compressor length is 8" and its diameter 5"!
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Belt driven compressers on IC engines have been obsolete for thirty years superseded by ceramic turbos.
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Belt driven compressers on IC engines have been obsolete for thirty years superseded by ceramic turbos.
We are obviously talking about two different things, I am referring to an air-compressor to supply compressed air to a tank, while you are referring to a turbo that is used to supply extra air to the engine!!!!!McQueen
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Rocket engines may be very powerful and the only way to achieve thrust in space but they are not thermodynamically efficient and that is the most important figure when it comes to fuel consumption in terrestrial vehicles.
To properly calculate the true thermodynamic efficiency of an internal combustion engine one needs to calculate the temperature and pressure of the high pressure gases and temperature and pressure of the exaust gases and the efficiency with which the expansion of these gases have been converted into useful work.
Think of a normal car the velocity of the exhaust gases do provide in theory a useful thrust out of the back of the car but this is miniscule in proprtion to the much more effective thrust via the expanding gases pushing the cylinder down inside the engine.
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Think also of modern aircraft engines. they are all high bypass ratio turbofans in which most of the energy in the gas turbine is used to suck air from the front of the aircraft and push it out the back and the jet thrust is only about ten pecent of the total thrust of the engine.
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Rocket engines may be very powerful and the only way to achieve thrust in space but they are not thermodynamically efficient and that is the most important figure when it comes to fuel consumption in terrestrial vehicles.
To properly calculate the true thermodynamic efficiency of an internal combustion engine one needs to calculate the temperature and pressure of the high pressure gases and temperature and pressure of the exaust gases and the efficiency with which the expansion of these gases have been converted into useful work.
Think of a normal car the velocity of the exhaust gases do provide in theory a useful thrust out of the back of the car but this is miniscule in proprtion to the much more effective thrust via the expanding gases pushing the cylinder down inside the engine.
Have you read my post at http://www.thenakedscientists.com/forum/index.php?topic=9816.msg120599#msg120599
?Think also of modern aircraft engines. they are all high bypass ratio turbofans in which most of the energy in the gas turbine is used to suck air from the front of the aircraft and push it out the back and the jet thrust is only about ten pecent of the total thrust of the engine.
This is not a jet engine, but functions more on the principles of a rocket engine. McQueen
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What you are describing in that thought experiment has nothing to do with calculating the true thermodaynamic efficency of converting heat energy into useful work and contains several unfair and invalid assumptions.
The jet engine example was just to show that the high bypss turbojet engine can create much more thrust by using the heat enrgy to move more air than just using the heat energy to create thrust in its own right like a rocket.
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The jet engine example was just to show that the high bypss turbojet engine can create much more thrust by using the heat enrgy to move more air than just using the heat energy to create thrust in its own right like a rocket.
I entirely agree with you soulsurfer, you are perfectly right. A bypass turbjet does infact create most of its thrust from the extra air it pulls in with its turbine, the jet component is comparably small. What I am trying to demonstrate is the equivalency between an IC Piston engine and the thrust that is produced by the Rotary Pulse Jet Engine. In fact there is a practical demonstration of this in the form of recoilless guns. There is a good article on the subject in Wikipedia. McQueen
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So you agree that your rotary pulse jet engine cannot be a thermodynamically efficient way of turning the heat energy of burning fuel into useful work for driving a car along a road. Presumably you just find the rotary pulse jet emgine to be an interesting engine like the first steam engine designed by the ancient greek Hero which by using opposed steam jets similar to your propsed design created a fast rotary motion but could produce very little useful work.
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McQueen wrote
while the rotary vacuum pump is extremely efficient, since it runs in an oil bath for effective sealing,
The 'efficiency' of a vacuum pump is not a relevant thermodynamic concept. It is not a 'heat engine' in the conventional meaning of the term - you don't get mechanical work from internal energy.
However good your seals etc, are, you maximum efficiency is defined by the range of temperatures in the gases involved.
Hero (the greek not the member) used steam at a bit over 400K in his rotary jet so the engine wuld not have been very efficient. The jet engine - operating at 2000K (?) would be more thermodynamically efficient than Hero's engine but there's much more involved if you actually want to realise anything near that efficiency.
I cannot (carnot?) find any reference to the overall efficiency of the pulse jet engine in the article. This would be absolutely critical before it would be worth while considering it as an alternative to the internal combustion engine, with its well known range of efficiencies.
As others have pointed out, jet engines are only used in certain applications and NOT because of their efficiency. As soon as you can 'push' against something solid - e.g. with tyres against a road , you do much better than a jet engine (a reaction engine) can hope to. This is basically because, the MOMENTUM given to the Earth is equal (and opposite) to the MOMENTUM given to the vehicle. The Kinetic Energy - which is proportional to velocity squared - is hogged, almost exclusively by the vehicle; the Earth's velocity change is virtually zero , so no KE wasted. The energy, necessarily, given to the very fast exhaust gases of a jet engine is a huge proportion of the available energy and means LOW efficiency. You only use them when there is no alternative. Think of the wasted energy in getting a Space Shuttle the first 10m off its launch pad!
As this engine would use conventional fuels, I wonder why, if it's so good, Ford haven't tried it in their new models. They are always after good ideas and it wouldn't upset any vested interests.
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Otto got it right first time, he did have the experience of 50 years of steam locomotives to draw on.
Wankel engines have been around for about 100 years but have only caught on for niche applications, about every 10 years an eccentric rotary design is published but none ever get built.
Just after WWII a few specialist cars were built with true pulse jet engines of the type used on the V1 missile (not very practical!)
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Otto got it right first time, he did have the experience of 50 years of steam locomotives to draw on.
Wankel engines have been around for about 100 years but have only caught on for niche applications
The point is that every engine design serves a particular functionality.
I do not doubt that Wankel engines would not be suitable to drive a heavy goods vehicle; but equally, most electricity generation is now done using steam or gas turbines, and not using the Otto cycle either. It is very much about horses for courses.
True, our own personal experience of power generation is for medium to heavy road transport, and in this context, the Otto cycle engines tend to predominate; but that is not a reflection of all oil based power generators (from aeroplanes, to gas powered electricity generating plants).
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I wonder if and when nanotechnology will ever give us an internal combustion engine.
You could imaging all sorts of advantages (and problems, of course) with a distributed engine with, in effect, thousands of tiny reciprocating parts, all working independently and thinking for themselves (well you know what I mean). No vibration, easy cooling and easy replacement of parts. Sounds a bit like muscles.
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I wonder if and when nanotechnology will ever give us an internal combustion engine.
You could imaging all sorts of advantages (and problems, of course) with a distributed engine with, in effect, thousands of tiny reciprocating parts, all working independently and thinking for themselves (well you know what I mean). No vibration, easy cooling and easy replacement of parts. Sounds a bit like muscles.
Micro sized internal combustion - maybe; but nano sized, I would rather wonder if we could even fit a single molecule of heavy fuel oil into such an engine (not a problem for methane, but certainly not a diesel engine). Would also wonder how you could guarantee proper air flow for each engine, and proper separation of intake and outflow.
I would have actually thought it probably easier to have nano sized fuel cells, generating electricity, rather than generating mechanical power (it would be easier to channel electrical power out of the system than to channel mechanical power out of such a system).
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Good points another someone.
It would have to operate in some sort of Wave mode; adjacent cells would have to be inletting or exhausting at similar times - some sort of circulation system (capillaries? spiracles?) would have to deliver the fuel and air. With the big surface area / volume ratio, catalysts would be effective. Sounds more and more like muscles. The engines need not be reciprocating, of course. The Wankel idea could be taken further and developed into a peristaltic system., rather than a rotary system.
I must get that patent written before someone else takes it on.
Think how quiet it would be.
The snag is that most IC engines are better as they get bigger.
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syphrum
Otto got it right first time, he did have the experience of 50 years of steam locomotives to draw on.
Wankel engines have been around for about 100 years but have only caught on for niche applications, about every 10 years an eccentric rotary design is published but none ever get built.
You know I've been thinking about this! 150 years of the IC piston engine , based on the one Otto built, and hundreds of 'improvements, including overhead cams, double overhead, cams, multiple valves, MPFI and still the efficiency remains about 20% under actual road conditions ( although diesels are reputedly more efficient). My point is whatever can be done using piston technology has already been done, one cannot even imagine the money spent on trying to improve its performance or the number of people involved. So, a breakthrough, if one is going to come, would have to involve some new type of technology, such as that suggested in the Rotary Pulse Jet Engine. McQueen.
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The thing that I find impressive about the Rotary Pulse Jet Engine is that it provides equivalent power to that of a piston engine. In effect what the Rotary Pulse Jet Engine does is to take only the combustion chamber volume of the IC piston engine and discards the rest, cylinder, pistons, piston rings etc., It then supplies compressed air to this combustion chamber (rocket pods) at 125 psi from an external tank, the compressed air supplied to the combustion chambers by the external tank( a very small volume 18 cu ins) is constantly replenished by a commercially available belt driven air compressor that can deliver 8.5 cu ft min at 125 psi ! The thing that makes the rotary Jet Engine possible is the use of rotary union, this makes possible the introduction of fuel and compressed air to the rotor even though the rotor is rotating at high speed! Otherwise imagine the situation, here is the rotor spinning at several thousand rpm and you are trying to introduce fuel and air into it ! Sounds ridiculous and it is the rotary union that makes it possible. The rest is simple, the compressed air fuel mixture is fed into the combustion chambers through a poppet valve, (125 psi works out to a compression ratio of 9:). The poppet valve is closed, sealing the combustion chamber and the fuel/air mixture is ignited using a piezo electric spark plug. A Valve to the CDN (Convergent divergent nozzle ) is opened and the hot gases of expansion escape at velocity driving the rotor forward through reactive forces. McQueen
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May I draw your attention to this URL
http://www.antonine-education.co.uk/physics_a2/options/Module_7/Topic_4/answer_7_4_6.htm
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The problem, McQueen, is still that you are ignoring the efficiency issue. All those hot gases you are sending out somewhere have a lot of KE. That had to be transferred from the fuel energy and can't be used for useful work. Bang goes your efficiency. The exhaust gases from an IC engine have nothing like the same amount of KE -so the efficiency is not significantly affected.
All your practical details about how it will operate can't help with that basic problem.
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What is the difference between your belt driven compressor and a supercharger?, it would absorb a large proportion of the output power and would be much better replaced by an exhaust driven turbine.
If your engine was to produce the same power as a conventional 3 litre engine running at 5000 rpm it would require 140 cubic feet per minute of air.
wracking my brains I seem to recall that an engine of this type using a hypoglopic fuel mixture was used to drive the fuel pumps on the the Saturn 5 rockets but I cannot quote chapter and verse, of course thermal efficiency does not figure very largely in this application!
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Syhprum
It might surprise you to know that I, at one time thought as you did, that there could not possibly be much energy in reactive forces. Looking at some of the posts by other members in this thread, this seems to be a widely held view. What changed my mind, and set me thinking was an article on the Recoilless Gun (http://en.wikipedia.org/wiki/Recoilless_gun)
The Recoilles rifle (gun) was originally invented by an American naval Commander by the name of John Cleland Davis, his purpose was to design a gun that would eliminate the forces of recoil, which necessitated a bulky gun carriage and heavy weight to overcome the forces of recoil. Originally he deigned a twin barreled gun, with the two barrels pointing in opposite directions. In one of the barrels he placed the shell and in the other an equivalent weight of grease, in the center was the charge (propellant). When the charge was ignited it exerted equal force in both barrels sending the shell out of one barrel and the grease out of the other with equal force. Eventually Cleland came to the conclusion that since mass1 x velocity1 = mass2 x velocity2 it would be possible to eliminate the grease in the second barrel and to replace it with gases escaping at high velocity! Thus was born the recoilless gun in 1866 as it happens this was also the year in which Nicholaus Otto invented the IC piston engine! Now as you can see from the article the recoilless gun propels the same caliber shell as an ordinary cannon, to aprrox. The same distance. However one very important point is that in the recoilless gun, the gases are left to exit freely through the Venturii (CDN) without interruption. If one thinks about it this makes sense. If one did try to impede the exit of the gases, as say by the placing of a valve in the venturi, the purpose of the gun would be defeated and the forces of recoil would be present. In the Rotary Pulse Jet Engine, since we are not concerned with the forces of recoil a valve is present in the venturi (CDN). Therefore the power of the gases escaping at velocity from the combustion chamber should yield an equivalent power to that of a similar sized IC piston engine. In this way the recoilless gun was the fore runner of the modern grenade launcher and all other rocket based type of armaments, including missiles. Forgive the long winded post, but I hope you see where I am coming from. McQueen.
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You cannot compare a gun to an engine of this type.
The purpose of a gun is to fire a projectile at a given velocity, and the power output is incidental; whereas for what you are trying to create, power is all, and it is velocity that is incidental.
In order to drive a projectile at a given velocity, it is a prerequisite that the exhaust gasses behind the projectile are travelling at the same velocity as the desired projectile at the point where the projectile leaves the muzzle of the gun. If you wish to fire a projectile at Mach 2, then the gasses behind it must be travelling at Mach 2, and that is a prerequisite, from which all else will follow.
In order to maximise the efficiency of the engine you desire, the requirement is to maximise impulse power, and the only requisite minimum velocity that constrains you is that the gasses should leave the combustion chamber should be only slightly faster than the movement of the combustion chamber itself (i.e. that the exhaust velocity should be as close to zero when compared to the stationary parts of the engine as it is possible to be, with just enough energy left to force the gasses through the exhaust pipes). Since you have no intention of blasting projectiles for several kilometres out of the nozzle of the combustion chambers, any excess velocity is simply waste.
In any event, guns are anything but the epitome of energy efficiency - they have other standards by which they are judged (when was the last time you ever saw energy efficiency of a gun of any kind being quoted as a pertinent statistic?).
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You cannot compare a gun to an engine of this type.
Let's have a poll ! Does the IC Piston engine resermble a gun, or are you blind? McQueen.
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But a recoiless rifle needs several times more propellant, and therefore several times more energy, than a conventional gun of the same design. This is why recoiless weapons are restricted mostly to infantry weapons that are not fired very often so the lighter weight of barrel is more of an advantage than the much heavier ammunition that you need to fire in it. If you are going to fire a lot of rounds it rapidly becomes easier to transport a heavier gun and lighter ammunition.
I don't see how your design of internal combustion engine would be much lighter than a normal one and it would definitely need far more fuel in order to accelerate the exhaust gasses to the immense speeds you would need to get any useful power out of it.
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And have you an answer about the efficiency, yet, McQueen?
It is, after all, quite a relevant question.
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And McQueen why your insistence on a power hungry belt driven compressor when a high velocity exhaust stream is available that could drive a readilly available turbine.
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Daveshorts
But a recoiless rifle needs several times more propellant, and therefore several times more energy, than a conventional gun of the same design. This is why recoiless weapons are restricted mostly to infantry weapons that are not fired very often so the lighter weight of barrel is more of an advantage than the much heavier ammunition that you need to fire in it. If you are going to fire a lot of rounds it rapidly becomes easier to transport a heavier gun and lighter ammunition.
When you say "several times the propelant" exactly how many "times" more are you talking about ? I have researched the subject and can tell you that at most a recpoilless gun uses about 2/3 more propellant than a normal cannon to achieve the same performance as that of an ordinary gun. Also consider, what I have been saying, the gases of combustion in a recoilles gun cannont be restricted in any way, as for instance by a valve because the moment the gases of combustion are restricted,the forces of recoil come into play. If it were possible to restrict the gases of combustion before release then the pressure would build up and the amount of propellant needed would be less, while the performanace would be the same as that of a normal gun.. McQueen
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sophiecentaur
....and have you an answer about the efficiency yet..?
I don't have the exact figures but the efficiency of a rotary pulse jet should be far greater than that of an IC Piston engine, it stands to reason. In an IC piston engine the fuel/air is ignited and the piston moves down with great force for a distance of a bout 3 ins. before being brought to a halt and being hauled up again by the fly=wheel or crankshaft. It can't be all that efficient! McQueen
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May I suggest for your reading
The high-speed internal-combustion engine
by Harry Ralph Ricardo
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Syhprum
....May I suggest for your reading....
The efficiency of the gasoline IC Piston engine is only about 20%, you can look it uip wherever you want on the net, by comparison a rocket or jet engine has an efficiency of over 70%. McQueen
P.S I get the idea of using the exhaust to run a turbine, at the moment what is being checked out is the feasability of the RPJ.
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http://en.wikipedia.org/wiki/Jet_engine
The problem was that rockets are simply too inefficient at low speeds to be useful for general aviation.
http://en.wikipedia.org/wiki/Turbojet
Turbojets are quite inefficient (if flown below about Mach 2) and very noisy. Most modern aircraft use turbofans instead.
http://en.wikipedia.org/wiki/Turbofans
Depending on specific thrust (i.e. net thrust/intake airflow), ducted fans operate best from about 400 to 2000 km/h (250 to 1300 mph), which is why turbofans are the most common type of engine for aviation use today in airliners, as well as subsonic/supersonic military fighter and trainer aircraft. It should be noted, however, that turbofans use extensive ducting to force incoming air to subsonic velocities (thus reducing shockwaves throughout the engine).
Not sure where and in what contexts you regard jet and rocket engines have an efficiency of 70%, but like all efficiency issues, it depends on context.
IC piston engines can gain efficiencies significantly higher 20%, but this may be applicable to large IC engines that run higher internal temperatures and pressures (and pre-cool the air coming into the cylinder), but these are not practical within the constraints of a small motor vehicle. It should also be remembered that rockets use unusual fuels (energy efficiency when burning cryogenic hydrogen and oxygen, and ignoring the energy costs involved in creating those fuels, can appear to be far higher than burning petrol in natural air that is not cryogenicly cooled).
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Quote
The problem was that rockets are simply too inefficient at low speeds to be useful for general aviation.
Well the most obvious reason for that inefficiency, as I have been trying to point out, is that most rockets are simply not equipped with a valve, they burn fuel continuosly at tremendous pressures and temperatures and have hitherto been impractical. If the tremendous power of a rocket design can be harnessed in the manner that is described for the Rotary Pulse Jet Engine, it would definitely be a great improvement over present technology such as the IC piston engine. here's what wikipedia has to say:
en.wikipedia.org/wiki/Pulse_detonation_engine (http://en.wikipedia.org/wiki/Pulse_detonation_engine)
quote:In theory the design can produce an engine with an efficiency far surpassing more complex gas turbine Brayton cycle engines, but with almost no moving parts.
Consider the idea as it stands, namely ignition of fuel resulting in increase in pressure and then release of that pressure to turn the potential energy of the pressure into kinetic energy of the escaping gases, producing thrust through reactive forces. McQueen
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What is interesting is that you earlier quote jet engines as having 30% efficiency, whereas the Wikipedia article you quote refers to conventional jets having only 30% efficiency, and the pulse jets (when someone actually succeeds in making one) having a theoretical limit of 50% (still short of your 70%).
But it seems very unlikely that what you are referring to in your design is a true pulsed detonation engine. The reason I say this is three fold:
Firstly, although there are development projects to develop pulsed detonation engines, the peculiar complexities of the required supersonic flame front required for these engines means that none have yet been commercially produced. I do not recollect anything in your documentation that suggests you have made any particular breakthrough in this problem.
Secondly, since the flame front, and exhaust gasses, are supersonic, it therefore follows that maximum efficiency (the quoted 50% efficiency) will only be attained when driving supersonic aircraft (the Wikipedia article suggests it might be used to drive an aircraft at Mach 5). There is nothing in that you have said that has lead me to believe that you intended to propel your combustion chambers at supersonic speeds.
Finally, the benefit of the pulsed detonation design is that it obviates the need for a compressor (which inevitably absorbs much of the energy of the jet); yet your design clearly does require a compressor.
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If you are interested in pulse detonation (as described in the Wikipedia article), one of the links off from the Wikipedia article is to a radio interview on pulse detonation undertaken by a New Zeeland radio station (it does make clear that you would not use pulse detonation direction for subsonic flight, although you could fit a pulse detonation combustion chamber inside a turbofan engine).
http://www.publicaddress.net/assets/upload/13073/224975781/PAS_PulseDetonationEngines.mp3
There are also issues raised about noise levels associated with pulse detonation engines.
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The only way that I could envisage the rotary pulse jet engine becoming efficient is to use what is effectively a very lean burn having a small volume near the ignitor exploding violently with most of the air simply being used as mass to be ejected from the cylinder. The big problem is the energy needed to compress the gas to provide the air for the combustion chamber. The range of revs it will operate efficiently may be small because of the assymmetry between the two combustion chambers in the illustrated design.
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I am still not at all sure why you require the combustion chambers within the rotating part of the mechanism. Since action = reaction, so extracting energy from the exhaust gasses (e.g. by use of a turbine) should be as effective as relying on the reaction force imparted to the combustion chamber, and it would be mechanically far simpler to implement. Ofcourse, what you then have is simply a novel gas turbine engine.
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Soul Surfer
The range of revs it will operate efficiently may be small because of the assymmetry between the two combustion chambers in the illustrated design.
Look the graphics are not very good, and if there is someone who can help out with that, it would be good. Both combustion chambers are supposed to be symmetric both in shape and as regards position. The word on pulse jets is that they create quite a bit of vibration, so by having two combustion chambers (rocket pods) on opposite side of the rotor firing synchronously, the output should be extremely smooth. Ok as regards the efficiency let's for a moment look at the efficiency of the piston engine. Let's say you have a 4" x 3" cylinder. When the fuel is ignited in the combustion chamber the temperature rises to about 2000 deg C and the pressure to 500 psi. This means that the total pressure on the piston head works out to 6280 lbs. Quite a bit of force! But because it is linked to a connecting rod and through this to the crankshaft very little of this power in the form of torque actually reaches the engine, about 160 ft lbs! Now take a flywheel 2ft in diameter, here even a force of 1lb wt applied to turn the flywheel results in a force of 1 ft lb force at the axle. 1lb wt = 1/32 of a ft lb. So you see the RPJ can deliver a lot of torque! It is the same principle that led Archimedes to state: Give me a lever that is long enough and I will move the earth, or words to that effect. Now since the recoilless gun requires 2/3 more fuel than an IC piston engine and still taking the same example as above (4” x 3” ) the presence of two combustion chambers firing simultaneously adequately fulfils this requirement. Furthermore in a rotor 12” in diameter, each pound weight of force applied by the combustion chambers (rocket pods) translates almost exactly into one foot pound of force. OK you say this engine is still using two thirds more fuel than an IC Piston engine of similar capacity. But that’s just the point, with so much torque available, a flywheel can be connected at a gearing of 3:1 or even 4 : 1, once accelerated the RPJ is switched off, (disconnected) and the flywheel carries the load, as it loses energy the RPJ again kicks in. This solves all problems of cooling, fuel efficiency etc.,and it achieves this with (relatively) low flywheel rpm! McQueen.
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another someone
I am still not at all sure why you require the combustion chambers within the rotating part of the mechanism. Since action = reaction, so extracting energy from the exhaust gasses (e.g. by use of a turbine) should be as effective as relying on the reaction force imparted to the combustion chamber, and it would be mechanically far simpler to implement. Ofcourse, what you then have is simply a novel gas turbine engine.
It is not as simple as that! For one thing a turbine depends for its efficiency on conintuous combustion, this would defeat the very purpose of the RPJ which is to have an extremely fuuel efficient engine. For another, you cannot stop and start a turbine, it is simply not practical. McQueen
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It is not as simple as that! For one thing a turbine depends for its efficiency on conintuous combustion, this would defeat the very purpose of the RPJ which is to have an extremely fuuel efficient engine.
That would rather depend on the design of the turbine.
In terms of axial flow turbines, I would agree with you, it would be difficult to adapt it to a pulsed drive load, but I would have thought that a tangential turbine (which is in essence closer to what you seem to be trying to design, even if you have inverted the design) would be amenable to pulsed pressure load.
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I have been trawling the internet without success to try and find the picture but I have a distinct recollection of a copy of the 'Dandy' (D C Thompson comic) that had 'Desperate Dan riding in a soap box cart propelled by 'Catherine reels' attached to the wheels.
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The combustion chambers may be symmetrical but the exhaust system illustrated is definitely not. Instead of two identical stub exhausts, the exhaust of the first chamber sends its gas round to the exhaust of the second chamber which then exhausts to the air. Depending on the timing of the exhaust pressure waves from the first chamber at the second chamber this could either interfere with or help the exhaust from the second chamber.
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Reply with quote
The combustion chambers may be symmetrical but the exhaust system illustrated is definitely not. Instead of two identical stub exhausts, the exhaust of the first chamber sends its gas round to the exhaust of the second chamber which then exhausts to the air. Depending on the timing of the exhaust pressure waves from the first chamber at the second chamber this could either interfere with or help the exhaust from the second chamber.
True! There should be two separate exhausts, but have been combined in to one, to make the animation easier. McQueen.
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In terms of axial flow turbines, I would agree with you, it would be difficult to adapt it to a pulsed drive load, but I would have thought that a tangential turbine (which is in essence closer to what you seem to be trying to design, even if you have inverted the design) would be amenable to pulsed pressure load.
A pelton wheel type turbine, of the type you suggest would be far less efficient! McQueen
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In terms of axial flow turbines, I would agree with you, it would be difficult to adapt it to a pulsed drive load, but I would have thought that a tangential turbine (which is in essence closer to what you seem to be trying to design, even if you have inverted the design) would be amenable to pulsed pressure load.
A pelton wheel type turbine, of the type you suggest would be far less efficient! McQueen
http://en.wikipedia.org/wiki/Water_turbines
This is the modern form of the Pelton turbine which today achieves up to 92% efficiency.
You have not actually quoted what you believe the efficiency of the turbine part of your mechanism is (excluding the efficiency, or otherwise, of combustion).
Granted, that the efficiency of the Pelton wheel quoted is for use with water, not with use with hot exhaust gases, and for higher pressure but lower speed flows; so by all means if you wish to recalculate what the efficiency would be for hot gas exhausts.
There are ofcourse other designs of tangental flow turbines which are all fairly efficient, although the Pelton wheel is quoted as the most efficient as a water turbine, it may be that calculations for hot gasses might prove one of the other designs more suitable.
For pulsed applications, you might even be able to get something as simple as the Savonius turbine to work efficiently (the lack of efficiency is because it only extracts energy from part of its cycle, when the cup is facing into the mass flow - but in an intermittent design, you can switch off the mass flow at the times when the cup is not facing into the flow).
Alternatively, if you think it more suitable to your purposes, a Banki turbine, or even try and design a hybrid between a Banki and a Savonius that takes advantage of the pulsed nature of the flow through the turbine.
The point is that in each case, the efficiency of a turbine can quickly be estimated by looking at the velocity drop in the working fluid as it passes through the turbine (the greater the velocity drop, the greater the amount of energy must have been extracted). The recurring concern about your design is the apparently very high velocities of the exhaust gasses, that indicate that relatively little energy has been extracted from it.
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Another Someone
For pulsed applications, you might even be able to get something as simple as the Savonius turbine to work efficiently (the lack of efficiency is because it only extracts energy from part of its cycle, when the cup is facing into the mass flow - but in an intermittent design, you can switch off the mass flow at the times when the cup is not facing into the flow).
What in effect would happen is that there would be no sealing, the flow of hot gases would impact on the cup and might turn it, but not efficiently.As for the efficency part of the engine, the point is that I think, and this is reasoned thinking, that the efficiency of the actual power produced by the RPJ through reactive forces should be equivalent with that got by expansion forces in an IC piston engine. That, said, because of the pure rotary output, the power developed by the RPJ should be far superior to that of the IC piston engine. Look, all kinds of units have been used to power cars, from batteries, to electric motors powered by solar cells, to fuel cells, to turbines, to rockets. All of them have worked, but none as efficiently viz a viz fuel consumption, as the IC piston engine. The Rotary Pulse Jet, just might change all that. McQueen
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What in effect would happen is that there would be no sealing,
One needs to seal gas to prevent leakage of pressure, but is irrelevant to flow velocity (if the gas is moving sideways, then it must have already lost its forward velocity, and so all the energy has already been extracted from that velocity).
Unlike a piston engine, you are not talking about a pressure motivated engine, but a velocity motivated engine, so sealing is not particularly important. After all, the Pelton turbine is able to achieve 92% efficiency without any seals.
the flow of hot gases would impact on the cup and might turn it, but not efficiently.
I would guess that this would depend on the torque extracted from the turbine. If the turbine is spinning fast, then a lot of energy would be wasted (although the Banki turbine, or something similar, might be better in such circumstances), but if there is a lot of torque, and so the cups are moving slowly, then you could extract a very large about of energy from the gas flow (particularly if you combine the cups with aerodynamic devices to further slow down the gas flow).
As for the efficency part of the engine, the point is that I think, and this is reasoned thinking, that the efficiency of the actual power produced by the RPJ through reactive forces should be equivalent with that got by expansion forces in an IC piston engine.
The point about those reactive forces is that they will only be efficient when the forward velocity of the combustion chambers are close to the velocity of the exhaust gasses. In pulse detonation engines, the exhaust velocities are normally supersonic, which means that either you have to find a way of slowing down the gas flow (and increasing the mas of the gas flowing at that speed) at the exhaust, or you have to have your device spinning at supersonic speeds.
This is what was clearly shown in the interview that I posted the link to - for subsonic use, a pulse detonation engine has to be fitted within a turbofan in order that the turbofan reduce the exhaust velocity but increase the mass of gas flowing at the exhaust.
That, said, because of the pure rotary output, the power developed by the RPJ should be far superior to that of the IC piston engine.
Actually, no difference.
If you look at the way your device works, it is simply a crankshaft embedded inside a flywheel. The force of the combustion chambers are still linear, not rotary; but they are converted into a rotary force by the flywheel they are embedded in translating that linear force into a rotary force (just as a crankshaft does). You might argue that you have fewer bearings (although the complex rotary unions that you have to use to feed the fuel/air into the combustion chambers are themselves a form of bearing, although not load bearing); but yu will still have lots of bearing to deliver that power to the wheels in any cars (and if you have to massively step down the speed because you have a supersonic flywheel - that will lose energy there also).
Also, outside of the issue of efficiency, you may have to concern yourself with whether such a massive (for the combustion chambers and the flywheel they are embedded in must be massive) structure rotating at very high velocity might not cause undesirable gyroscopic effects within a vehicle (at very least, you may require two of them contra-rotating in order to minimise the gyroscopic effects).
Incidentally, not all applications actually require rotating power - even electrical generation can in theory be extracted as well from linear power and from rotating power.
Look, all kinds of units have been used to power cars, from batteries, to electric motors powered by solar cells, to fuel cells, to turbines, to rockets. All of them have worked, but none as efficiently viz a viz fuel consumption, as the IC piston engine. The Rotary Pulse Jet, just might change all that.
Electric motors are actually very efficient - but the production, delivery, and storage, of electricity ware what let it down.
You have not at all convinced me that the design you suggest would be efficient for the task you propose (pulsed detonation is considered efficient for other functions, but it is about matching the power unit to the task, and at the low velocities of land vehicles, it is simply not suitable).
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Another someone
After all, the Pelton turbine is able to achieve 92% efficiency without any seals.
The point about those reactive forces is that they will only be efficient when the forward velocity of the combustion chambers are close to the velocity of the exhaust gasses
If you look at the way your device works, it is simply a crankshaft embedded inside a flywheel. The force of the combustion chambers are still linear, not rotary; but they are converted into a rotary force by the flywheel they are embedded in translating that linear force into a rotary force (just as a crankshaft does).
I am sorry to have to say that I find your answers are becoming increasingly, rhetorical, wandering, and downright misleading. Take a look at the above quotes. Now I am asking you to take a real look those quotes !. OK:
1) the pelton wheel has a 92% efficiency !
Yes in water maybe, because water is an incompressible liquid and therefore acts as its own sealant. Please, please design and show me a pelton wheel that works at 92% efficiency in air!
2) The point about those reactive forces is that they will only be efficient when the forward velocity of the combustion chambers are close to the velocity of the exhaust gasses.
all I can say is that this statement has been made by some kind of a scientific genius !! Talk about Newton’s third law, you have got it down pat man!!
3) If you look at the way your device works, it is simply a crankshaft embedded inside a flywheel. The force of the combustion chambers are still linear, not rotary; but they are converted into a rotary force by the flywheel they are embedded in translating that linear force into a rotary force (just as a crankshaft does)
Ah! A Daniel come to justice! Indeed such discrimination, such knowledge, even though he has never heard of Archimedes! Or that the IC piston engine requires linear to rotary conversion!!
McQueen
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"Incidentally, not all applications actually require rotating power - even electrical generation can in theory be extracted as well from linear power and from rotating power".
Indeed not I have been reading an interesting article on a space qualified linear power generator
http://esto.nasa.gov/conferences/nstc2007/papers/Richardson_Rebecca_D2P2_NSTC-07-0155.pdf
fueled by P238 that has been designed as a replacement for the peltier effect generators used on deep space missions.
this machine has a heat to power conversion of about 25% enabling less P238 to be used.
on a more mundane level I can purchase for about £2.0 a flashlight with a linear generator that you actuate by shaking.
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I can purchase for about £2.0 a flashlight with a linear generator that you actuate by shaking.
That's interesting, I have one where you press and release a handle to recharge the battery.
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(if the gas is moving sideways, then it must have already lost its forward velocity, and so all the energy has already been extracted from that velocity).
I can't agree there - what ever direction it is going in, if it has KE then it is lost energy. Remember KE is a scalar quantity and does not have a direction.
This thread is really getting bogged down with red herrings and irrelevant details.
There are some important fundamental things which have been mentioned - like the necessity of a large mass to 'react against' and possible thermodynamical efficiencies but some of the points made, relating to forces, seals and reciprocating parts being inherent mechanisms for energy loss are all a bit dodgy.
If the fundamental objections are valid then no amount of design detail can make the RPJ a superior engine.
The basic problem seems to be the enormous velocity of the exhaust gases - all wasted KE. If these gases are to be used to turn a turbine in order to reclaim the energy - why not just have a good old gas turbine?
I think the Desperate Dan idea is best.
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The basic problem seems to be the enormous velocity of the exhaust gases - all wasted KE
The KE is not wasted it is used to turn the rotor, providing motivating power. If it is necessary to further use the KE in the gas it might be possible to put in a small turbine in the exhaust as Syhprum had suggested. Don't forget it is the enormous velocity of the escaping gases that provide the motivating power for rockets in the first place.
like the necessity of a large mass to 'react against'
Rockets don't need a large mass to react against, that is precisely the point!
McQueen
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Rockets don't need a large mass to react against, that is precisely the point!
http://en.wikipedia.org/wiki/Rocket_engine#Performance
Rocket engine nozzles are surprisingly efficient heat engines for generating a high speed jet, as a consequence of the high combustion temperature and high compression ratio in accordance with the carnot cycle. For a vehicle employing a rocket engine the energetic efficiency is very good if the vehicle speed approaches or somewhat exceeds the exhaust velocity (relative to launch); but at low speeds the efficiency asymptotically approaches 0% at zero speed (as with all jet propulsion.)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fen%2F1%2F1c%2FPropulsiveEfficiency.GIF&hash=324f27f63119fb28a69ec1d971d8da13)
So please stop blithely suggesting that rockets are highly efficient. As I have repeatedly said, rockets are efficient only when the speed of the rocket approaches the speed of the exhaust gasses (at low speed, the efficiency gets very low indeed). So, unless you are suggesting that the flywheel within which the combustion chambers are embedded are travelling at a speed comparable to the exhaust velocity of the gasses generated (which, for a pulse detonation engine, will mean that the rim of the flywheel must be travelling at supersonic speeds), then you do not have anything like the efficiency you are claiming.
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For a vehicle employing a rocket engine the energetic efficiency is very good if the vehicle speed approaches or somewhat exceeds the exhaust velocity
I protest that common sense tells us that the above statement cannot be true and request that the moderators at Nakedscientist to take it up with the editors at Wikipedia.
According to Newton’s third law m1 x v1 = m2 x v2. Since in this case m2 (i.e the rocket carrying the fuel, and remember that the fuel although occupying a large space in the rocket is still a fraction of the weight of the rocket itself.) has got to have more mass than the fuel being expended, it follows that the statement that maximum efficiency is achieved only when the rocket reaches or exceeds the same velocity as the hot gases propelling it can never, in practice, be true, doesn't make sense and is axiomatically wrong! For instance while the Apollo space craft had a gross weight of about 108,000 lbs, the fuel it carried weighed only 40,000 lbs. How can the statement that the kinetic velocity of the gases equal the velocity of the rocket be true. Further the statement that the KE is wasted does not make sense if Newton’s Laws are valid. Obviously if you have a certain amount of kinetic energy going out of the back, it must exert an equal and opposite force in the opposite direction i.e., on the rocket! It might as well be another way of saying that a rocket can never, under any circumstances, be inefficent! McQueen.
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and request that the moderators at Nakedscientist to take it up with the editors at Wikipedia.
I would suggest that the moderators here have no more weight with the editors (administrators) of Wikipedia than you have.
Wikipedia is a community project, and although there are some Wikipedia administrators who have special authority and responsibility, for the most part it is up to anybody who thinks they have a correction to make, to make that correction.
You are free to make your own changes to Wikipedia (if the Wikipedia administrators are happy with your changes, they will leave it in place - if they feel it has not been adequately researched, they will quickly stamp on your changes).
Being a moderator of the Naked Scientist makes us no different to you, or anybody else, as far as Wikipedia are concerned.
There are also discussion pages assocaited with every Wikipedia page (http://en.wikipedia.org/wiki/Talk:Rocket_engine in the case of the relevant page in this case) where you might wish to discuss your changes before diving in.
To edit the Wikipedia page, you can go to http://en.wikipedia.org/w/index.php?title=Talk:Rocket_engine&action=edit
If you feel you have a correction to make to Wikipedia, the matter is in your hands - if you end up pissing off the Wikipedia administrators, that is up to you to judge.
That having been said, although I agree with the general gist of the argument, there are a few details that I will agree do not quite work for me either (the notion that a rocket motor that is stationary has zero efficiency does not make sense, although it is reasonable in my view to argue a stationary rocket engine is far less efficient than a rocket that is in flight, but it does sound unbelievable to say it has zero efficiency).
The efficienncy argument comes not merely from Newton's third law, but its relation to E = mV2, which ofcourse means that the higher the exhaust velocity, the greater the energy it carries away, and its energy is (unlike the momentum equation) not linear but proportional to the square of the velocity. This it does not take much imagination to say if the exhaust velocity exceeds a threshold, the energy usage will rise faster than the increase in thrust you will obtain from the momentum equations.
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Since in this case m2 (i.e the rocket carrying the fuel, and remember that the fuel although occupying a large space in the rocket is still a fraction of the weight of the rocket itself.) has got to have more mass than the fuel being expended, it follows that the statement that maximum efficiency is achieved only when the rocket reaches or exceeds the same velocity as the hot gases propelling it can never, in practice, be true, doesn't make sense and is axiomatically wrong! For instance while the Apollo space craft had a gross weight of about 108,000 lbs, the fuel it carried weighed only 40,000 lbs. How can the statement that the kinetic velocity of the gases equal the velocity of the rocket be true. Further the statement that the KE is wasted does not make sense if Newton’s Laws are valid. Obviously if you have a certain amount of kinetic energy going out of the back, it must exert an equal and opposite force in the opposite direction i.e., on the rocket! It might as well be another way of saying that a rocket can never, under any circumstances, be inefficent!
You are confusing efficiency with functionality. There are many aspects of functionality (and even system efficiency) that go beyond the efficiency of a particular component. It may well be that the Saturn V operates in a region of its performance envelope that is outside the optimum energy efficiency of the motors (after all, if one drives a car at its top speed, you don't expect it to be as efficient as driving the car at 56mph, but sometimes you have reasons for pushing the envelope further for other reasons).
You also have to be careful not to confuse system efficiency with component efficiency. Again looking at the motor car, I would guess that the peak efficiency of the engine would be around the point where it produces peek power (about 4000 to 6000 rpm for most car engines) - this is efficiency measured as the amount of energy provided by the engine for a given amount of fuel. On the other hand, the system efficiency of the overall car has to take into account rolling resistance, aerodynamic drag, and all sorts of factors that are very different from the efficiency of the motor alone. Taking all these into account, the peek efficiency of the system is usually found at the lowest revs that can be sustained in the highest gear - usually around 45 to 50 mph, possibly with the engine running at around 1000 to 2000 rpm. The engine is producing less than its peek power, but less of that energy is being wasted in other parts of the system. Thus, simply looking at where the peek efficiency of the rocket motor itself may lie does not necessarily tell you where the peek efficiency of the overall system lies.
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Another Someone
Being a moderator of the Naked Scientist makes us no different to you, or anybody else, as far as Wikipedia are concerned.
I should have posted this apology before. Ihad no idea that you were (when you quoted from Wikipedia in your post http://www.thenakedscientists.com/forum/index.php?action=post;quote=122434;topic=9816.50;num_replies=69;sesc=9a1f0417bca648a8c6222229a45b19e3
that you were quoting from a referrable source. My first impression was that the post was misleading, hence my rather acerbic reply. Thankyou, for the information on how to get redressal/confirmation from the Wikipedia site, for which I am much indebted. McQueen
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Another someone
I am still not at all sure why you require the combustion chambers within the rotating part of the mechanism. Since action = reaction, so extracting energy from the exhaust gasses (e.g. by use of a turbine) should be as effective as relying on the reaction force imparted to the combustion chamber, and it would be mechanically far simpler to implement. Ofcourse, what you then have is simply a novel gas turbine engine.
Sophiecentaur
If the fundamental objections are valid then no amount of design detail can make the RPJ a superior engine.
The basic problem seems to be the enormous velocity of the exhaust gases - all wasted KE. If these gases are to be used to turn a turbine in order to reclaim the energy - why not just have a good old gas turbine?
I think the Desperate Dan idea is best.
Syhprum
…..wracking my brains I seem to recall that an engine of this type using a hypoglopic fuel mixture was used to drive the fuel pumps on the the Saturn 5 rockets but I cannot quote chapter and verse, of course thermal efficiency does not figure very largely in this application!
I have just been going through this thread once more, and I find a lot of scepticsim, where there should, in fact, only be guarded optimism. This is especially true of the persisting delusion that a turbine would be a more efficient unit than a rocket. So here it is again. I am once again stating that weight for weight the rocket is the most powerful engine that has yet been devised, and I am willing to prove this argument by using common place easy to understand arguments. Any takers? Also that the Rotary Pulse Jet would therefore be far more fuel efficient, powerful and clean than any engine that has as yet been designed for use in road transport. (except maybe the air engine, but then again that has a lot of fatal design flaws.). McQueen.
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May I suggest you put foward your idea for a 'pulse jet engine' on the CR4 engineering forum where many skilled engineering experts correspond.
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May I suggest you put foward your idea for a 'pulse jet engine' on the CR4 engineering forum where many skilled engineering experts correspond.
I posted at the site suggested, let's see how things work out. I thought you guys were doing pretty well, myself ! McQueen
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The main problem that the Rotary Pulse Jet (http://www.geocities.com) is likely to face is that of cooling the exhaust. In turbines that were designed for use in cars, such as the "Firebired" manufactured as a prototype by General Motors, the problem had been effectively solved. Rover motors in the UK had also managed to solve the problem of cooling down the exhaust from their turbine engine cars to acceptable levels. There is no reason to think that the Rotary Pulse Jet cannot solve the problem with equal ease. In designing a new car engine, the main criteria, is 'does it have the power?' followed by 'is it fuel efficient?' If these two criteria are met, solving other incidental problems is routine.
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The CR4 engineering site were stumped, I can tell you that I had received about 400 e-mails from the forum while the subject was hot!!! Unfortunately the most positive aspect of the discussion was that they wanted me to build a working proto-type!! Well you all know how expensive that is!!! Apart from that opinions were divided. One great plus point is that they even offered to pass around the hat , so that I could build a prototype.
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Have you actually received any money from them yet, tho'?
If you have then I must remember to include them in my list of possible investors in my perpetual motion machine design.
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On the topic of efficiency of a reaction engine.
The Momentum formula : m1v1 = m2v2 is correct, of course; the mass of ejected gas being much less (per second) than the mass of the vehicle.. What is more relevant, however, is the actual POWER / ENERGY transfer.
The KE is mvsquared/2.
So the share of energy imparted to the vehicle is, actually, VANISHINGLY SMALL when its velocity is low; most of the energy going to the propellant gases (the 'square' factor making all the difference in this matter). As the vehicle gets faster, the share of the Energy it gets (the efficiency) goes up.
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Hi. Sophiecentaur,
So the share of energy imparted to the vehicle is, actually, VANISHINGLY SMALL when its velocity is low; most of the energy going to the propellant gases (the 'square' factor making all the difference in this matter). As the vehicle gets faster, the share of the Energy it gets (the efficiency) goes up.
I don’t blame you for doubting my conclusions, however you might perhaps think twice about conclusions drawn by Robert Goddard, namely that not only would a rocket generate the same type of impulse power as a piston engine but that it would do so more efficiently. In drawing these conclusions Goddard had made use of the same type of experiments that I myself have been carrying out. Here is what he has to say: “If, however, successive charges were fired from the same chamber, much as in a rapid-fire gun, most of the mass of the rocket could consist of propellant, and the superiority over the ordinary rocket could thereby be increased enormously. Such reloading mechanisms are the subject of all the above patents except the first, which is chiefly concerned with the nozzle, and what I have termed a "primary and secondary" rocket principle. I have not made a working model of a reloading device, as it is the one feature of the method that is self-evidently operative.” I think that you will be struck by the similarity in this idea and that of the Rotary Pulse Jet Engine. More information on Robert Goddard including the above passage can be found at: http://siarchives.si.edu/history/exhibits/documents/goddardsept1916.htm
Unfortunately ofcourse Goddard was never able to implement his ideas in a practical way and so didn’t receive a patent for his idea, he did however go on to make his mark with liquid fuelled rockets.
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MQ
Goddard was a conventional engineer who was clever and very successful. None of his views needed to violate the conventions of Mechanics and Dynamics. I think there could be a problem with your interpretation of what he had to say.
btw, I can't find any reference tp pulse jets in his paper.
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Hi SophieCentaur, I may have a surprise for you from which you won't recover!!! Especially if you stick to your present stand!
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The Momentum formula : m1v1 = m2v2 is correct, of course; the mass of ejected gas being much less (per second) than the mass of the vehicle.. What is more relevant, however, is the actual POWER / ENERGY transfer.
This is the veriest bullshit! And I can tell you this based on my experiments. The RPJ builds up tremendous pressure before exiting the gases, during which velocities are out of sight. In my next post I will quote from an Encyclopaedia Brittancia article!
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That particular bull must have been a particularly learned one. If you think that it is force and pressure that count when you are trying to transfer energy to do 'work' then you will also believe in perpetual motion machines. There is no hope for you, my friend.
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OK Sophiecentaur
I am sorry for the S word in the last post. But if you look at the encyclopaedia under ballistics, I think you will find that explosives just after ignition travel at something like a 100,000 km hour, so even taking your moth eaten mv formula, the RPJ would win by a wide margin!! Lets face it the piston engine is hemmed in by its short stroke and the complete end to power of its stroke therein!!!
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The two engines are very different, of course. But the reaction engine is, essentially a momentum transfer mechanism - the relative shares of the energy between propellant and rocket are determined by relative masses and speeds. Momentum is conserved so, for low rocket speeds, the efficiency just has to be poor. That doesn't necessarily matter but you could at least acknowledge it.
The piston engine transfers its energy as a gas moves a piston load under pressure over its stroke. It has several shortcomings - theoretical and where thermodynamics meets engineering reality. It performs reasonably at relatively low revs, which is a particular advantage in that the gear ratios need not be too great. So it is not possible to compare their operation step by step. You need to look at the bottom line figures of power and efficiency of two practical, working systems.
A number of people have pointed out aspects in which your RPJ throws energy away. You have to address that, either by a demonstration or reasoned argument with proper use of terms and calculations (the more likely way in the case of your proposal).
It is best compared with a gas turbine (another high revving engine) but that has really been a non starter for ground transport (when did you last see one driving round town?).
We can have a sensible conversation (on any number of threads) as long as you use the correct terms and don't suddenly take off on expressions like "tremendous force" which, taken on its own, means nothing.
My learned bull didn't take offence, btw.
Also, Britannica is very limited in its technical content in several directions. There were a large number of 'howlers' when I last looked at the details of Television signals and coding.