What is a rotary pulse jet engine?

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another_someone

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Re: What is a rotary pulse jet engine?
« Reply #50 on: 07/09/2007 14:51:11 »
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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Offline McQueen

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Re: What is a rotary pulse jet engine?
« Reply #51 on: 07/09/2007 16:09:54 »
Soul Surfer
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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.
« Last Edit: 07/09/2007 16:22:25 by McQueen »
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Offline McQueen

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Re: What is a rotary pulse jet engine?
« Reply #52 on: 07/09/2007 16:19:06 »
another someone
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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.
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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another_someone

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Re: What is a rotary pulse jet engine?
« Reply #53 on: 07/09/2007 18:33:52 »
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.
« Last Edit: 07/09/2007 19:16:19 by another_someone »

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Offline syhprum

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Re: What is a rotary pulse jet engine?
« Reply #54 on: 07/09/2007 22:11:50 »
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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Offline Soul Surfer

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Re: What is a rotary pulse jet engine?
« Reply #55 on: 07/09/2007 22:24:15 »
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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Offline McQueen

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Re: What is a rotary pulse jet engine?
« Reply #56 on: 08/09/2007 03:59:54 »
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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.
True! There should be two separate exhausts, but have been combined in to one, to make the animation easier. McQueen.
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Re: What is a rotary pulse jet engine?
« Reply #57 on: 08/09/2007 04:01:27 »
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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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another_someone

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Re: What is a rotary pulse jet engine?
« Reply #58 on: 08/09/2007 12:07:33 »
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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
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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.
« Last Edit: 08/09/2007 13:14:02 by another_someone »

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Offline McQueen

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Re: What is a rotary pulse jet engine?
« Reply #59 on: 08/09/2007 13:29:07 »
Another Someone
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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
« Last Edit: 08/09/2007 13:43:03 by McQueen »
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another_someone

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Re: What is a rotary pulse jet engine?
« Reply #60 on: 08/09/2007 18:25:33 »
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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Re: What is a rotary pulse jet engine?
« Reply #61 on: 09/09/2007 05:27:00 »
Another someone
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   After all, the Pelton turbine is able to achieve 92% efficiency without any seals.
Quote
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
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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)   
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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)   
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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)   
Quote
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


« Last Edit: 09/09/2007 05:31:50 by McQueen »
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Offline syhprum

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Re: What is a rotary pulse jet engine?
« Reply #62 on: 09/09/2007 19:40:06 »
"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.   
« Last Edit: 09/09/2007 19:45:10 by syhprum »
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Re: What is a rotary pulse jet engine?
« Reply #63 on: 09/09/2007 23:20:53 »
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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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lyner

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Re: What is a rotary pulse jet engine?
« Reply #64 on: 10/09/2007 13:28:08 »
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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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Re: What is a rotary pulse jet engine?
« Reply #65 on: 10/09/2007 23:43:14 »
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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.
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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
« Last Edit: 10/09/2007 23:46:50 by McQueen »
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another_someone

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Re: What is a rotary pulse jet engine?
« Reply #66 on: 11/09/2007 00:30:51 »
Rockets don't need a large mass to react against, that is precisely the point!

http://en.wikipedia.org/wiki/Rocket_engine#Performance
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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.)



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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Offline McQueen

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Re: What is a rotary pulse jet engine?
« Reply #67 on: 11/09/2007 02:21:03 »
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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.
« Last Edit: 11/09/2007 02:25:18 by McQueen »
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another_someone

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Re: What is a rotary pulse jet engine?
« Reply #68 on: 11/09/2007 02:43:55 »
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.
« Last Edit: 11/09/2007 02:51:40 by another_someone »

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another_someone

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Re: What is a rotary pulse jet engine?
« Reply #69 on: 11/09/2007 03:07:00 »
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.
« Last Edit: 11/09/2007 03:42:40 by another_someone »

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Offline McQueen

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Re: What is a rotary pulse jet engine?
« Reply #70 on: 11/09/2007 06:44:31 »
Another Someone
Quote
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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Re: What is a rotary pulse jet engine?
« Reply #71 on: 16/09/2007 10:13:32 »
Another someone
Quote
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
Quote
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
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…..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.
“Sometimes a concept is baffling not because it is profound but because it’s wrong.”

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Offline syhprum

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Re: What is a rotary pulse jet engine?
« Reply #72 on: 16/09/2007 10:59:59 »
May I suggest you put foward your idea for a 'pulse jet engine' on the CR4 engineering forum where many skilled engineering experts correspond.
syhprum

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Offline McQueen

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Re: What is a rotary pulse jet engine?
« Reply #73 on: 16/09/2007 23:25:51 »
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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
“Sometimes a concept is baffling not because it is profound but because it’s wrong.”

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Offline McQueen

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Re: What is a rotary pulse jet engine?
« Reply #74 on: 30/09/2007 12:03:37 »
The main problem that the Rotary Pulse Jet 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.
“Sometimes a concept is baffling not because it is profound but because it’s wrong.”

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Offline McQueen

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Re: What is a rotary pulse jet engine?
« Reply #75 on: 22/05/2008 11:10:00 »
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.
“Sometimes a concept is baffling not because it is profound but because it’s wrong.”

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lyner

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Re: What is a rotary pulse jet engine?
« Reply #76 on: 23/05/2008 21:12:19 »
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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lyner

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Re: What is a rotary pulse jet engine?
« Reply #77 on: 23/05/2008 22:04:31 »
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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Offline McQueen

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What is a rotary pulse jet engine?
« Reply #78 on: 24/05/2008 06:04:28 »
Hi. Sophiecentaur,
Quote
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.

“Sometimes a concept is baffling not because it is profound but because it’s wrong.”

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lyner

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What is a rotary pulse jet engine?
« Reply #79 on: 25/05/2008 12:08:35 »
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.
« Last Edit: 25/05/2008 12:35:08 by sophiecentaur »

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Offline McQueen

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What is a rotary pulse jet engine?
« Reply #80 on: 31/05/2008 11:09:17 »
Hi SophieCentaur, I may have a surprise for you from which you won't recover!!! Especially if you stick to your present stand!
“Sometimes a concept is baffling not because it is profound but because it’s wrong.”

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Offline McQueen

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What is a rotary pulse jet engine?
« Reply #81 on: 31/05/2008 11:13:34 »
Quote
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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lyner

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What is a rotary pulse jet engine?
« Reply #82 on: 01/06/2008 21:28:35 »
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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Offline McQueen

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What is a rotary pulse jet engine?
« Reply #83 on: 02/06/2008 14:39:58 »
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!!!
« Last Edit: 02/06/2008 14:42:21 by McQueen »
“Sometimes a concept is baffling not because it is profound but because it’s wrong.”

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lyner

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What is a rotary pulse jet engine?
« Reply #84 on: 02/06/2008 18:47:50 »
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.
« Last Edit: 02/06/2008 18:50:52 by sophiecentaur »