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The Rotary Pulse Jet Engine: New Concept in engines.

09/16/2007 9:44 AM

I have been looking into alternative engines for cars for some time now and I found that the MDI Aircar http://www.theaircar.com posed an audacious and ingenious challenge to IC piston engine technology. There is little doubt that the idea of a car that runs solely on compressed air is highly intriguing and desirable. Unfortunately, the idea is far from viable. 300 litres of compressed air at a pressure of 4500 psi, (300 bars) corresponds to an energy equivalent of 1.5 litre of petrol (0.3 US Gallons) this would give a very short running time, and need an air-compressor running at 500 KW to re-charge in 2-3 minutes, plus special cooling equipment would have to be put in place while the tank was being filled. If the air is compressed on-board the car itself it will take anything from 3 – 4 hrs. Given the short range and the limited time for which the compressed air lasts, the idea is not viable at present. An engine design that seems to fulfil all of the gaps in the MDI air car technology, is the Rotary Pulse Jet Engine. For those of you who are still hoping for a breakthrough in IC piston technology, all I can say is that it seems unlikely. Think of all the money, and time spent over the past 150 years or so and the efficiency of the IC piston car, even with double overhead cams, MPFI and multiple valves remains at the same disappointing 15% - 20%! Think of it 80% of the energy in the fuel is wasted. Like the MDI aircar, The Rotary Pulse Jet Engine also uses a tank of pre-compressed air but the pressure in this tank is only 125 psi or about 9 bars. The idea in using a pre-compressed air tank is (a) to reduce the size of the engine and (b) to reduce any cushioning effect that a piston and cylinder might provide, thus maximizing the power of the engine. The Rotary Pulse Jet Engine consists basically of a rotor, with fully sealable combustion chambers (rocket pods) at its periphery. Compressed air at a pressure of 125 psi is fed into the combustion chambers through a rotary union, through which fuel is also added via a separate line connected to an electronic fuel injector. Compressed air at 125 psi works out to a compression ratio of 9 : 1. The fuel air mixture is fed into the combustion chambers through a poppet valve, once the combustion chambers have been filled, which happens almost instantaneously, the poppet valve is closed and the fuel/air mixture is ignited, raising the temperature in the combustion chamber to 2000 deg. C and the pressure to 500 psi (35 bar). A valve leading to a CDN (Convergent divergent nozzle) is opened and the gases of combustion escape through the CDN at high velocities, spinning the rotor forward in the manner of a Catherine wheel. Because there are two rocket pods (combustion chambers)igniting at the same time and in the same direction, the power output is extremely smooth and powerful, although the engine will run with even a single combustion chamber if necessary. This then is basically the Rotary Pulse Jet engine, it is a zero pollution, high torque engine that is capable of harnessing fly-wheel storage at relatively low rpm to increase fuel economy. The compressed air is replaced as it is used by a commercially available belt driven air-compressor that is capable of supplying 8 cu ft min at 125 psi. Thus the RPJ (Rotary Pulse Jet Engine ) can run almost indefinitely for as long as it has fuel in the tank, at power and speed comparable to or exceeding that of an IC engine, while delivering much better fuel economy and zero air pollution. The whole idea of the RPJ is since the piston cylinder, crankshaft, cam shaft etc., have all been discarded, only the combustion chamber, (i.e., the small part of the cylinder in the IC engine cylinder, where the fuel is stored after compression) has been utilized. This means that a relatively tiny portion of compressed air has to be replaced after each combustion cycle , only 18 cu ins ( taking a two combustion chamber rotor) one cu ft of air is 1728 cu in. Rocket engines are far more efficient than IC piston engines, which have an efficiency of only about 15% - 20 %, rocket engines can reach 60% - 70%, efficiency and are far cleaner, this in itself is a tremendous saving in fuel. DDjames

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#1

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/16/2007 2:20 PM

Hi DDjames. I do not consider this as a new technology, what you are describing is a gas or oil burning turbine. They were first tested in motor cars in the 1950s by the rover motor company in the UK. The problem with them is the high exhaust heat that they generate, if you point the exhaust towards the ground or side of the road you burn enything that gets in it's way. If you point the exhaust upwards anyone who passes behind the car while it is waiting at the traffic lights is going to get burned. Another thing with turbines in motor cars is that they are not fuel efficient because of the high rpm of the turbine to produce a high enough torque. Spencer.

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#2
In reply to #1

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/16/2007 6:18 PM
[quote]

They were first tested in motor cars in the 1950s by the rover motor company in the UK. The problem with them is the high exhaust heat that they generate, if you point the exhaust towards the ground or side of the road you burn enything that gets in it's way.

[quote]

Hi Scapolie, No this is not a turbine, at least not in the sense of the turbine that you are talking about, it may be a turbine like Hero of Alexander's aeropile, invented more than 2500 years ago. Yes the original turbines did have a lot of exhaust heat, Fiat, int Italy, dropped the whole project becuase of the heat. But both Chrysler in the US and Rover in GB, solved the problem and had production models on the road, unfortunately because they are continuous combustion engines, they use about 8 times the fuel of a normal car, and so had to be abandoned. The engine described here utilises rocket pods situated on the edges of the rotor to spin the rotor. That is compressed air and fuel is introduced to a fully sealed combustion chamber, ignited to raise the temp. and pressure and then vented to create a high speed jet, the rotor turns in an equal and opposite reaction in the opposite direction, in accordance with Newto's Third Law. DDjames

p.s. The Rotary Pulse Jet Engine turns at relatively low rpm , with a maximum of between 3000rpm and 5000 rpm

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#3
In reply to #2

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/16/2007 7:13 PM

The energy that it takes to compress its own air to be self suffient would be a challange enough, but then have enough to power to power any type of drive train.

These would be unlikely.

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#4

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/16/2007 9:38 PM

Lack of paragraphs make this a little hard to read, but I don't quite understand the statement of zero pollution from burning a fuel in a compressed fuel air mixture (my first big question). The second one being, I don't see how the engine efficiency can be increased that much by making the engine smaller, especially when you will need to INCREASE the overall weight of the system when you also include the air compression and storage stage(s).

The fact that it is called an invention, and that the statement "zero pollution " is used, when clearly it is not, leads me to conclude that this (backyard inventor) does not really know what he is talking about.

As for any statement regarding onboard air compression when air is the primary fuel component, forget it!

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#10
In reply to #4

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/17/2007 9:01 PM

Jack of all trades

[quote]

Lack of paragraphs make this a little hard to read,

[quote]

Sorry, I can't seem to get the text to wrap around, so it is a little difficult to format. By zero pollution I mean by current polltuion standards, it is not a zero pollution engine in the sense that the aircar is ! As regards efficiency, rocket power, which is basically what is used in the RPJ (Rotary Pulse Jet) is , weight for weight, the most powerful engine there is, far more efficient than the IC piston engine. In fact the engine has so much torque that it can be linked to a flywheel storage system that runs at low rpm, in much the same way that toy cars use a fly-wheel ! So fuel economy is also present. As for compressed air, remember, in the RPJ, we are not replacing a cylinder full of air, only the relatively tiny volume occupied by the cmobustion chamber, commercially available belt driven compressors, can easily fulfil this criteria.

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#12
In reply to #10

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 12:06 AM

Firstly, just use the old enter key to help break up the blocks of text into easy to read sections like so.

Secondly, I have covered the air car in a previous thread (and it is certainly NOT zero pollution. In fact its overall system pollution is much greater than a standard petrol engine).

Smoke and mirrors. Have a close look at how it is supposed to work and how it gets its fuel (I will give you a clue, would you buy a standard petrol-powered car with its own onboard oil refinery), also its ability to convert petrol into air, etc. The more you read the more you shake your head.

Sad really, but sometimes people cannot see the wood for the trees.

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#5

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/17/2007 2:37 AM

Jet engines, at 0-10,000 feet, are hideously inefficient, and generate loads of pollution, as compared to ordinary modern cars.

A jet large enough to move a car is a very large thing, and the two tiny ones pictured inside this engine are too small by a factor of 100 or so. A jet engine works on the reaction principle: It throws a huge mass of air rearward, and the airplane (or jet car) moves forward. The pictured jets are far too small to move large masses of air. Any mechanism interposed between the jets and the wheels will reduce efficiency: the most efficient mounting of a jet is just as it is on an airplane: facing backwards and parallel to the intended direction of travel. So this engine would be more efficient it these two tiny jets were simply mounted on the back of the car facing rearward, rather that mounted pinwheel fashion, to turn a shaft, and a transmission, and a differential, etc. (But they'd be far too tiny to push a car.)

Nowhere on the site referenced is there any explanation of how one would move hundreds of pounds of air through these tiny jets to produce any meaningful horsepower. With a rotor of 10- 12" diameter, as the referenced site says, each nozzle would be, at best, 5" from center. So, for 125 lb ft torque (very small car engine) each jet would have to produce 150 lb thrust. You can buy 150 lb thrust jets for $32,000 each, and you'd need two. They are much much larger than the tiny jet combustion chambers pictured in the inventors site, and burn 50 oz of fuel per minute (3 lb/minute, or roughly 1/2 gallon per minute: 20-30 gallons per hour per engine.) To be optimistic, let's say 40 gph at full power (110mph in a small car) so on the order of three miles per gallon.

Of course a key problem, aside from the horrible fuel efficiency, it the fact the these $32,000 engines are many times too large (more than 100 times the volume) to fit in the tiny space the inventor has drawn.

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#7
In reply to #5

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/17/2007 3:32 AM

Turbines are smaller than their piston crank equivalent.

The jet engines of jet planes are so big due to the propulsion fan. Indeed they propel the plane by throwing enromous amounts of air backwards. This fan is driven by the turbine inside the system.

But the turbine that drives helicopters and tanks is way smaller and in many cases of the radial type. The energy output is on a shaft and the speed is reduced to a usable level (with gears) In helicopters it is driving the rotors and in tanks it drives hydraulic pumps which generates high pressure oil, used to distribute the energy over the tank. (propulsion and other systems)

In airplanes there is always a turbine that no-one sees: the generator which make sthe planes electricity, a direct coupled generator to a turbine, resulting in a system at 400 hz. Mostly this turbine is in the tail section.

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#9
In reply to #7

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/17/2007 11:40 AM

Turbines are smaller than their piston crank equivalent.

Sure, (at least lighter) but a turbine or pulse jet of a size that can make 150 lb thrust, (required to create adequate torque if built into a rotor of only 10 - 12 inches diameter) is about 100 times the volume of that shown in the inventor's drawings. The inventor claims 9 cu in (150 cc) per combustion chamber (in other words, per "jet"), whereas real jets of that thrust are about 1000 cu in physical volume. Squirting compressed air into a tiny combustion chamber does not make a jet -- the mass airflow accelerated is simply far far too small.

This thing is not a turbine engine. It is, according to the inventor, two jets rotating a disc to produce torque. The jets, (which I've replaced by real jets in my thought experiment, to illustrate) are simply far too small, and from his description (per the linked reference) they would not work in any way remotely as described. The inventor's understanding of the pressures created is completely off base, as is his understanding of pressure and flow, in general, and math. For example:

  • If the rotor has a diameter of 10" then its circumference is 62.8.
  • If there is a half inch pipe leading out of a tank with a pressure of 125 psi, it follows that the pressure in the pipe will be 25 psi (i.e 1/2 2 = 1/4)

(The pressure in the pipe would also be 125 psi -- at least until we analyze flow, which the inventor does not do.)

Using the force against the back of a combustion chamber as equivalent to the thrust of the jet is utterly and completely wrong. A jet or rocket's thrust is based only on reaction: with F=MA, as always. The inventor calculates the force against the back of the combustion chamber:

  • The power developed by a Rotary Pulse Jet Engine with a cylindrical combustion chamber (rocket pod) having a volume of 9" and a back wall diameter of 2.5" is ideally 1.252 x 3.14 x 500 = 2453lbsf, since both combustion chambers fire at the same time, the total power available during a single power stroke should be 2453 x2 or 4906 lbsf approximately.

(We'll ignore the fact that 4906 lbsf is not "The power developed..." [power is not measured in units of force]). But the inventor apparently fails to realize that pressure acts in all directions, so the the force on the "front wall" (if we accept his term "back wall" for the other wall) is a similar amount, although a little lower because of the small hole in the front wall (the nozzle). Thus, the only valid measure of thrust (which is all the can push the rotor around) is from the standard calculations of the mass of air accelerated, and for any meaningful mass transfer, you need a very large nozzle: the people who design jet engines are not nitwits, and 4906 lb thrust jets are HUGE, and even the 150 lb version I mentioned above is 100 times the volume of the inventor's dream combustion chamber size.

So, this has nothing in common with a turbine engine, other than both create heat from burning fuel. .

In airplanes there is always a turbine that no-one sees:

While that is true, it has little to do with the inventor's claims. His "engine" is nothing like a turbine, and moves orders of magnitude less air. The APU is primarily intended to make the plane's electricity when the plane is on the ground, and is usually shut off when the plane in in the air, and often before (right after lighting the main engines). For some aircraft, though, the APU is left running during takeoff in hot and high conditions, to offload services that would otherwise consume engine power. The APU can also provide limited air conditioning, bleed air for main engine starting, hydraulic system backup, etc. On some aircraft, the APU is rarely used, with a ground APU used instead. Many APUs cannot (and/or are not allowed to be) started in the air. The 747 APU is like that, and it has 1450 shaft HP, and although lighter than a 1450hp petrol engine, it is close to the same size, as installed. The Fokker F28 had (or has, although most have been replaced by Fokker 100s by now, I'd think) a 28 hp APU, and there may be even smaller ones. Back when I was doing work for Fokker, I though it would be fun to have a couple of these to use in powering a tiny airplane with turboprops. (I had a kit airplane at the time that required only 40 hp.)

But all this has nothing to do with the subject engine which would produce tiny amounts of torque, because it could not move anything remotely close to the required mass of air: The nozzles would need to be on the order of 100 mm, and they are shown as perhaps 10 mm (1/100 the area).

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#16
In reply to #9

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 3:11 AM

Ken,

You went quite deep into this "new" idea.

I saw from the first lines that this has nothing to do with a working application and did not spend more time in it. As always those inventors have nice drawings and on such a drawing everything can work. I can even prove that a "turbine" will turn backwards.

As you explained quite well: they even don't have a clue on pressure and are already driving 1000 miles on one liter of fuel. Next stop free energy?

Gwen

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#6

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/17/2007 3:24 AM

A smooth power output?

It is as un-smooth as possible: every rotation you have one enormous peak, the thing should have three combustion chambers, and two outlets, resulting in 6 peaks, only half the size and resulting in 50% more output and way less fatigue problems.

This proves that the inventor is not really an engineer (perhaps in communication or financial science)

extra: Why are rockets so efficient? Due the high dT they have. (they don't use Hydrogen and Oxygen just because is it so f** dangerous)

Why does a car have such a limited range with only 1.5 liter of fuel? Breaking, mass and the overall efficiency of the ICE. only 15 to 20% is really used to propel the car (that is less than 1.5 liter / 100 km)

The aircar uses regenerative breaking and it is no Carnot cycle, you just have to compare it with a battery.

The compression rate is also not sufficient as the mixture is to cold: compare it with the expansion of compressed air. the fuel will not vaporise (this uses extra heat) nor ignite or you have to use very low octane fuels. The burning rate will be to slow, resulting in unburned fuel in the exhaust. In an ICE the compression also heats up the mixture, bringing it in the zone just below self ignition. The combination of heat and pressure induces a high speed flame which uses all the fuel before the exhaust opens.

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#8

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/17/2007 7:57 AM

If this is a viable solution you will get whacked. It happened to Diesel, Mallove, and a slew of others, you'll be next. Don't upset the status quo.

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#11
In reply to #8

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/17/2007 9:17 PM

This is with regard to all of the comments that have been made regarding the size of the jet pods (i.e., combustion chambers) and the probable power. Remember that when we consider the RPJ (Rotary Pulse Jet) we are referring to an engine that gives an equivavlent power to that of a IC piston engine. OK, now the myth, that expansion power as used in the IC piston engine or in the barrel of a canon is much more effective that reaction forces as used by rockets, seems to be an inbuilt prejudice, of most engineers and physicists. Let me remind you of the super gun, invented by Gerald Bull. I'm doing this of the top pf my head, so I hope that, the facts are right. The super gun, was 510 ft long, weighed 2,100 tons, fired explosive in stages as the projectile travelled up the barrel, and was still not able to put a 600 Kg payload into orbit! At the most it could push the shell out to 1000 kms. By contrast, a rocket, just twenty to thiry feet in length, using the same amount of fuel, (or less ) than the super gun, could easily place a 600 Kg payload into orbit. What makes you think that expansion is more powerful than reaction ? There are so many replies to my post, that I am having a bit of trouble keeping up. But I will get around to answering in detail, why the size of the combustion chamber does nto matter, providing that it is similar in size to that of an IC piston engine of similar size.

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#14
In reply to #11

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 12:52 AM

What makes you think that expansion is more powerful than reaction ?

I don't think anyone has said that expansion is more powerful than reaction. That is a bit like saying that leverage is more powerful than a pulley system. They are two different ways of getting kinetic energy out of a heat engine.

Rocket scientists admit that their engines are not as efficient as jet engines, so your claim that a rocket is the most efficient engine seems very strange. Is that what you are intending to say?

Here is an excerpt from a Wikipedia article that aligns pretty well with my own understanding:

An air-breathing engine typically has a much larger specific impulse than a rocket: a jet engine may have a specific impulse of 2000−3000 seconds or more at sea level. Note also that it is more efficient; mainly due to the actual exhaust speed being lower, particularly for turbofan jets, and thus the jet engine uses far less energy to generate thrust. While the actual is lower, the effective exhaust velocity is very high for jet engines. This is because the effective exhaust velocity calculation essentially assumes that the propellant is providing all the thrust, and hence is not physically meaningful for air-breathing engines; nevertheless it is useful for comparison.

In some ways, comparing specific impulse seems unfair in the case of jet engines and rockets. However in rocket or jet powered aircraft, specific impulse is approximately proportional to range, and suborbital rockets do indeed perform much worse than jets in that regard.

Are you saying this writer is wrong? In this wikipedia article there is a chart that shows rockets at rock bottom, and turbofans near the top in efficiency for thrust engines. Piston engine driven propellers are more efficient yet that turbofan engines. Is that counter to your understanding?

By efficiency I mean the caloric input vs the mechanical output, or in automotive terms, the equivalent of miles per gallon. As a test of efficiency, you could take two identical cars, one with a standard engine, one with an experimental engine, weight them identically, and then run them over the same course at the same speed. The one using less fuel per mile is the more efficient. Is that your understanding?

The description does not include any mention of the mass flow rate of these tiny jets. How many kilograms of air per second will these move? What is the velocity of the gas through your nozzle? Given that the mass of the fuel is 1/15 the mass of the air, If you simply measure the amount of air that can move through the engine, you can get a good approximation of the thrust. The compressor would need to supply that entire mass.

What HP output are you getting from your prototype, and what is the specific fuel consumption? In other words, at the engine's torque peak, how many pounds of fuel are burned per hour per hp?

BTW, I am assuming you are the inventor. Is that correct?

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#13

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 12:47 AM

DDjames; I have read what the nasayer have had to say,and of your description of the RPJ design. To that end the only comment I can make will be, BUILD the thing and make it work as you suggest. You must be onto something or you wouldn't have generated that much negative opinnion. If someone/anyone could make the engineers/scientists look beyond the ends of their collective noses(instead of down them) maybe we as a life form might have a chance of surviveing. GO FOR IT AND MAKE IT WORK.

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#25
In reply to #13

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 12:51 PM

Although you may not like it, engineering and science are the fields that come into play in inventing and developing ideas such as new engines. (This particular idea is anything but new, and was demonstrated by Hero about 2000 years ago, using steam as the working fluid.)

We've had visitors to this site who have spent thousands of dollars on perpetual motion machines (named free energy, over unity, magnetic motors, etc) only to realize, that once the science is described, they've wasted time and money. One of these people, having come to that realization, immediately jumped to another perpetual motion machine project -- the engineers and scientist had hoped he would pursue something in which he had some training, where he might make a positive contribution.

So one approach to all these ideas which are unsupported by science is yours: go ahead and built it. That's not a bad approach, although many have lost money and relationships from taking that path.

This is an engineering and science site, and people here speak the language of engineering and science, and many of us have some education in physics, the basis for all the sciences and engineering. In speaking or writing about the way things work, you cannot have a meaningful dialog if you use the terms "power" to mean "force"... or "pressure" to mean "force"... or "acceleration" to mean "speed"... etc., etc., etc.

So, if the inventor is to sell anyone with and engineering or science education on his idea (and selling seems to be what he is doing), he will have to describe it by using the engineering terms he has used in ways that make sense. He does not do that. So it is impossible to make sense of the description. What he seems to be claiming is that these tiny jets produce a force of 4900 lb. They cannot, for many reasons you can prove to yourself by reading about physics and jet propulsion. There are many paragraphs in the description in which there is not a single sentence that makes sense from a basic physics point of view. So scientific types cannot help but be naysayers. We are saying: this will not work as described. (Unfortunately, we can't make sense of the description, because it is effectively in a foreign language.) We could simply say, as you have: go ahead and build it... but then we have contributed nothing. We could say to a kid, sure go ahead and eat the lead paint... but would that be responsible.

The power developed by a Rotary Pulse Jet Engine with a cylindrical combustion chamber (rocket pod) having a volume of 9" and a back wall diameter of 2.5" is ideally 1.252 x 3.14 x 500 = 2453lbsf, since both combustion chambers fire at the same time, the total power available during a single power stroke should be 2453 x2 or 4906 lbsf approximately.

The sentence says, in essence: "The power developed is ...(many words) ... 4960 lbsf approximately. Power is not equivalent to a force. Power is a rate of doing work. So, for example, one horsePOWER is 33,000 ft lb per second. It has a unit of force, a unit of distance, and a unit of time. So the sentence is utter nonsense.

The third sentence reads:

When I had first proposed this idea, many critics had suggested that the combustion chamber would simply explode under the combined pressure of 500 psi and a temperature of 20000 Centigrade.

No critic with a high school understanding of engines would suggest such a thing. 500 psi is about 1/3 the peak pressure a typical aluminum piston endures in a typical run-of-the-mill engine. Aluminium is weaker than steel, and the top of a piston is fairly thin. Gas at far higher that 500 psi is routinely contained in tanks with relatively thin walls. So this statement seems like a (perhaps deliberate?) lie.

Just a little further down it say this:

If the rotor has a diameter of 10" then its circumference is 62.8 inches

Again, nonsense.

A little further down:

Torque is everything in a car engine, it represents the amount of power available for turning the main shaft.

Torque is not power. Torque is a measure twisting force. Power can be measured in terms of torque and rpm. The are "high" torque engines with "low" power, and there are "low" torque engines with "high" power. And no, torque is not everything in a car engine. It is one of perhaps one hundred technical terms that have specific meanings when talking about ICEs.

Here's another excerpt from a typical sentence on another page:

combustion rush out of the convergent divergent de laval nozzle at speeds in excess of 5,000 ft/sec 2

5,000 ft/sec 2 is an acceleration, not a speed. The exponent would have to be deliberate, because it takes extra effort to put in the superscript. If we assume that he'd intended to write 5000 ft/sec, that number alone is outlandish. In engines, a reasonable optimal flow rate around valves, etc is about 300 ft/sec. It would be silly to design for 5000 ft/sec flows (several times the speed of sound), because doing so would require tiny little nozzles, and therefore very low mass transfer.

I could go on, and on and on. I would guess that there are fifty significant misstatements of this type in the description. Much (such as the distracting info on rotary unions) seems intended to be fraudulent. In other words the writer seems to be suggesting that new rotary unions enable the engine to work. But, in fact there have been rotary unions available for many many years that can easily handle the flows and pressures involved. It seems the writing is intended to convince someone that this engine will work, when in fact it will not. One can only assume the person(s) to be convinced are investors.

We are not naysayers at all. We are saying yes to physics and yes to sound engineering. We are saying yes, get an education. And we are saying yes, describe things truthfully. And we are saying yes, if your implulse is to think that you are being "sold" on magic, you're right.

Gotta go.

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#15

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 12:54 AM

A believe you (or the inventor) said the pressure after combustion would be about 500 psi. I didn't see any where where the flow through the nozzle was calculated, however. Just as a guess, I'd say the thrust from a 1/8 inch air nozzle at 125 psi is about 1 pound: e.g., a large bore air gun at 125 psi is easy to hold onto, with thrust just detectable. At 500 psi thrust would be on the order of 4 times this, or about 4 lbs. Therefore I'd guess that your engine might produce about 3 lb ft or so of torque. Does that sound about right? At 5252 rpm, that would be 3 hp, which would probably not be sufficient to drive a compressor to supply the air requirements of the engine. Sound reasonable?

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#17
In reply to #15

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 3:20 AM

OK 3 lb ft of torque, for how long? 10° of rotation? which is 1/36 of a full rotation.

I don't think that he reaches 1 hp.

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#18
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 4:20 AM

Hi Gwen, I agree with you there. Spencer.

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#19
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 5:21 AM

To all those jet turbine fans! Let me fill you in on the facts, let me tell you that a turbine engine, is very similar to a normal propeller powered engine, the only thing is that to create all those fantastic statistics, (50 bar compression and above) you have to (a) create a contained environment and (b) expend a lot of fuel ! Yes, in order to draw the air in, you need combustion to turn the fan, this requires a lot of fuel and is the reason, that you have never seen a model plane powered by a jet turbine engine ! Even a pulse jet, with a 2:1 compression ratio (approx, it might be lower) works on a model plane, but a jet turbine never! Using the amount of fuel that a RPJ (rotary pulse jet) does, you might get slightly better heating for your car, but a motivating unit never! Friends! The turbine just does not compare to a rocket. Also remember that an RPJ uses a 9:1 compression or greater, so you can get some idea of the efficiency.

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#26
In reply to #19

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 1:10 PM

Even a pulse jet, with a 2:1 compression ratio (approx, it might be lower) works on a model plane, but a jet turbine never!

More lies.

The link below is to a site where you can buy microturbines for use in radio-controlled models.

http://usamt.com/Mel/comm/comm_Specs.html

Further, your statement that high pressure ratios "expend a lot of fuel" seems to be implying that such engines would be less efficient than lower pressure ratio engines. That is flat wrong. High pressure ratio engines are more efficient, using less fuel per pound of thrust.

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#27
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 1:56 PM

Yes! I'm sorry, wrong and misleading statement, in fact did know about it, just slipped my mind, but not too unexpected since, a turbine does in fact resemble a prop engine.

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#20
In reply to #18

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 5:34 AM

Gwen Southuysen

[quote]

OK 3 lb ft of torque, for how long? 10° of rotation? which is 1/36 of a full rotation. I don't think that he reaches 1 hp.

[quote]

You don't get it do you? All that the RPJ has to do is to achieve an equivalent power to that of an IC piston engine, which it does. Torque, takes care of the rest. The presence of a crankshaft and the need for linear to rotary conversion is what makes the IC piston engine so inefficient. If you don't believe me. Look at all the 'improvements' in recent years: Double over head cams, multiple valves, MPFI, etc., I am sick of seeing a piston and cylinder as motivating power, lets try something different!

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#21
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 9:18 AM

Oh Kr@p it's thermodynamics, ever heard of them??

Let me out!!!!!

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#22
In reply to #20

Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 9:53 AM

I am sick of seeing a piston and cylinder as motivating power, lets try something different!

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#24
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 11:00 AM

Could this be the' gas plant' often referred to by a French engineer friend. (Dont know what Babel fish would make of it but my translation is talking shop).

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#23
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 10:48 AM

I don't think that he reaches 1 hp.

I agree completely. I was going overboard to give him the benefit of the doubt. If he would agree that the output might be as much as 3 hp, then it is easy to show that the the hp required to drive a compressor to fill his 9 cubic inch (150cc) combustion chambers to 125 psi, while the engine is running at 5252 rpm, exceeds the output of the engine. So, if it could operate, it would operate at a net loss, in terms of mechanical output. It's a complicated furnace.

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#28
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 2:05 PM

Blink You have made several extremely, perceptive and incisive statements, that unfortunately I have not been able to immediately address. Take the pressure calculations on the backplate. This actually is valid when considering a cylinder , in fact there are only two stresses that are calculated the hoop stress and the end plate stress. And of course a rocket can be thought of as working by the reaction of gases leaving the combustion chamber and also as the result of the uneven pressure distribution that remains in the combustion chamber. Like your image of Hero of Alexander's aeropile. A more sophisticated version of which probably supplies the power you are using to run your computer right now. So what does it signify.

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#29
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/18/2007 2:45 PM

Blink Tried to add to my post and was time barred! Ok coming back to the Rotary Pulse Jet Engine. You keep harping on the fact that those tiny jets, could not possibly provide as much power as an IC piston engine. That seems to be your main concern right. Let me explain. A 4in x 3in cylinder in an IC piston engine has a combustion chamber with a volume of 6.3 cu ins. OK, the Rotary Pulse Jet has combustion chambers with a volume of 8 cu ins - 9 cu ins. So how can these tiny combustion chambers produce a power equivalent to that of an IC piston engine. The principle on which the RPJ works is that of the Recoiless Gun . As you can see from the article the recoilless gun has a performance similar to that of a conventional gun. But remember that the breech (nozzle) of the Recoilless gun, remains open throughout. If an attempt were made to close the breech (nozzle) the whole purpose of the design would be defeated and the forces of recoil would be present. Ok, now take a hypothetical situation, in which it were possible to close the breech (nozzle) allowing the gases of combustion to build up pressure before release, then the power of the recoilless gun would be equivalent with if not better than that of a conventional gun. This is why I say the Rotary Pulse Jet would have the same power output as an IC piston engine with similar size combustion chambers! Hold your horses. How does a piston engine resemble a gun. Take the cylinder as the barrel, the piston as the projectile and the air/fuel mixture as the propellant. What happens when the propellant is ignited, the piston travels down the barrel (cylinder) for 3 ins. and comes to a dead halt before its direction is reversed. How can you say that the piston engine is more efficient than the Rotary Pulse Jet, which after all delivers pure rotary motion. This is why , i hope, the tiny combustion chambers will give an equivalent output to that of a conventional piston engine.

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#30
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/21/2007 5:59 PM

DDJAMES - PLEASE READ/VISIT THIS LINK. I IMPLORE YOU.

Seriously. You have a lot of great info, but it is so hard to follow.

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#31
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

09/24/2007 2:45 AM

Hi C Rummel ( Guru )

Thanks for your support and encouragement. I was directed to this forum from another forum The Naked Scientist on the grounds that CR4 was the best engineering forum on the net, and that the advice and opinions that I would receive at this forum would be the most reliable on offer anywhere. I hope I have posted in the right place, would the engineering section have been better?

The piston engine is not a very efficient engine, even though it is astonishingly dependable and durable. The world just cannot afford to squander precious fossil fuel reserves on an engine that is twenty percent efficient at most. Yes, it is true that there are some marine diesels with an astonishing efficiency of 50 per cent! But if you look at the design closely you will notice that the stroke in these engines is about 3 x the bore of the piston, normally a square cylinder ( where the length of the stroke is equal to the bore) is considered near ideal. A longer piston stroke means that the rpm is dramatically reduced, affecting both the speed and performance of the engine. It is very clear that any improvements in engine design will have to come from a source other than the IC piston engine. All the improvements in recent years, such as MPFI, multiple valves, double overhead cams etc., have not made a jot of difference, the IC piston engine performance remains at 20 per cent under ideal conditions and considerably lower under actual on the road conditions!

So what are the alternatives? The electric car is probably the most desirable, offering a clean, smooth and efficient power output, but until battery design and performance have increased by a factor of 10 or more, they are woefully inadequate and the disposal of used batteries poses a worse long time environmental hazard than the fumes emitted by present day piston engines. The fuel cell, with its 90 per cent efficiency offers another ideal solution, the only problem is that fields of hydrogen, comparable to oil fields or natural gas fields, do not exist, and cannot exist, because even a tiny hole will mean that the hydrogen will escape into the atmosphere. Until a fuel cell is invented that can work on natural gas or LPG, the fuel cell is out of the running, at least for the moment. The only other alternative and practical means of obtaining hydrogen, at the moment, is from the breakdown of existing fossil fuels, which is both environmentally harmful and wasteful of potential fuel content.

The idea for the Rotary Pulse Jet originally came from the recoilless gun, clearly if the recoilless gun had a similar performance to a normal canon even when the breech (nozzle) of the gun was left open throughout the combustion process, then a design in which the combustion process could be completely sealed offered a good alternative design to the IC piston engine. The basic theory was borne out by the fact that the super gun cannot really compete with a rocket in terms of the pay-load lifted and the distance it can be carried. A solution as to how, fuel and compressed air could be introduced into a rotor (disc) that was rotating at several thousands of rpm, was the second problem. The answer came in the form of the Rotary Union, commercially available and capable of sealing several thousands of PSI at 20,000 rpm. Even though the manufacturers state that some leakage would always take place, the manner in which the design has been implemented in the Rotary Pulse Jet guarantees that no leakage will take place even under high rpm. From there it was simple, all that had to be done was to design a combustion chamber based on the same, or slightly larger, combustion chamber volume as an equivalent IC piston engine, ensure that the combustion chamber (rocket pod)was fully sealable and then to introduce a way to ignite the fuel and to devise a leakproof valve to release the products of combustion through a CDN. (Convergent Divergent Nozzle). This has been done. The next thing was to eliminate the piston, crankshaft, camshaft etc., because the RPJ is basically an impulse engine, any use of a piston to compress the air would have a cushioning effect reducing the efficiency of the engine, therefore precompressed air at a pressure of 125 psi (or compression ratio of 9:1) is supplied to the combustions chambers from a tank. The compressed air in the tank is constantly re-supplied by a commercially available compressor capable of delivering 8 cu ft/min at 125 psi. The compressor would use about 8 per cent of the total engine output. The engine is air cooled, since the whole engine is rotating, fins could be designed so that the flow of air effectively cooled the engine. In addition, it was thought that since the RPJ runs only intermittently (much of the load being carried by a flywheel at low rpm), a few cycles could be run dry, (i.e., without fuel) the sudden release and expansion of compressed air results in considerable cooling, this should serve to keep the exhaust system fairly cool. This is the basic design of the Rotary Pulse Jet engine, it remains only for a working model to be built and tested. I have already made a beginning by building a complete exact size replica of the combustion chamber in industrial nylon which can be worked on a lathe. However, to build a model out of steel and cast iron and to carry out testing of the engine would require more money than I have at the moment.

What is there to be gained by implementing the RPJ. Well for one thing it offers pure rotary output, even the Wankel engine, with its eccentric rotary output and inefficient sealing, performed better than an IC piston engine, so this is a big plus point, the second offshoot of this is that with a pure rotary output, it is possible to use storage devices such as the fly-wheel that would be impossible to implement using an IC piston engine, again because the fuel is burnt completely in an oxygen rich environment, the RPJ is relatively pollution free.. Lastly the simplicity and compact size of the engine would result in lowered manufacturing costs. DDjames.

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#32

Re: The Rotary Pulse Jet Engine: New Concept in engines.

10/27/2007 6:11 PM

20,000 tons (the weight of the supergun) is also the weight of the fully fuelled Soyuz space craft! If anyone is interested.

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#33
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

10/29/2007 3:44 AM

???

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#34
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

10/29/2007 8:45 AM

Sorry, I did try to edit the post but timed out. The actual weight of the Soyuz was about 2500 metric tons and the total weight of the apollo mission about 2750 metric tons.

Stil that's just one tenth the wieght of the super gun right!

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#35
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Re: The Rotary Pulse Jet Engine: New Concept in engines.

10/29/2007 9:20 AM

Do you mention the supergun of Gerhard Bull?

How do you calculate the weigth of such a device? What amount of the mountain do you take into account?

And what has this to do with your rotary puls engine?

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