New Concept Engine Design: Get Feedback Now

[django]

Hi! I have designed a new concept engine and hope that I can get some useful feedback.
http://www.geocities.com/rotarypulsejet . The design is quite radical and I would appreciate any comments that you might have. django

 

[FredGarvin]

Link does not work.

 

[Danger]

Welcome to PF, Django.
It's impossible to tell from your picture just how much planning you've put into both the basic design and the necessary subsystems. The most obvious deficits are that you don't indicate how you'll deal with either ignition timing or air/fuel intake.
I can foresee a lot of problems with this idea, but further discussion is warranted.

edit: Hi, Fred. It worked fine for me the first time; now it's giving some sort of overload notice. The design basically involves a pair of tip-jets built into a rotating disk inside some sort of housing with 2 opposed exhaust ports.

 

[AlephZero]

After two or three pages I got the message "The GeoCities website you were trying to view has temporarily exceeded its data transfer limit. Please try again later."

Actually, I got bored waiting for the BMP on the front page to download and started viewing the other pages, so I never got to see the image on the front page. You might want to replace the BMP with a smaller JPG file, or something.

It's not fair to comment on it before seeing all your descrption, so I won't - except to say the basic idea makes sense, though there may be some practical problems with it.

 

[FredGarvin]

edit: Hi, Fred. It worked fine for me the first time; now it's giving some sort of overload notice. The design basically involves a pair of tip-jets built into a rotating disk inside some sort of housing with 2 opposed exhaust ports.

Cool. Thanks Danger.

I can tell you that I have experience dealing with this concept with one exception. The designs I have worked with were continuous burners, not pulse jets. However, I can tell you that there are indeed many pitfalls to this idea and depending on some of the constraints, i.e. rotational velocity and fuel flow, the basics in the design become very difficult.

Like Aleph, I will await to see a cross section though before getting too much into it.

 

[brewnog]

Looks like a Catherine Wheel to me.

How do you fuel it? How do you provide combustion air? How do you control it?

 

[Danger]

I have a bit of an idea of how the thing might actually work, but I wouldn't go so far as to call it a 'pulse jet'. It's more like a Wankel with the combustion chambers built into the rotor. In the design as shown, timing would be absolutely critical and the thing would be able to run at only one constant rpm value.

 

[django]

Danger's comment:

I have a bit of an idea of how the thing might actually work, but I wouldn't go so far as to call it a 'pulse jet'. It's more like a Wankel with the combustion chambers built into the rotor. In the design as shown, timing would be absolutely critical and the thing would be able to run at only one constant rpm value.

Interesting comment Danger, but look at the differences, a Wankel has to seal a huge area over the whole of its cycle and do so while performing an eccentric rotation! In actual fact the Wankel is nothing more than a glorified eccentric rotary vacuum pump working in reverse, the Rotary vacuump pump has been around for eighty years or more. While the rotary vacuum pump works very efficiently because it is normal running in an oil bath in order to provide sealing, the Wankel tries to perform the same work in air! django

 

[Danger]

You're right about the Wankel, Django. I was just trying to help the others visualize it (I didn't realize at the time that your link was working again).
What I meant about the timing is that you have a very narrow window of time/angle when combustion can take place. That means that the rpm's have to be set so that each 'jet' fires exactly twice per revolution, when it's lined up with one of the exhaust ports, and it has to be a fast burn. I defer to Fred's expertise in the matter, but I think that it would be very difficult if not impossible to tune the pulse frequency that precisely. Pulse-jets ordinarily have a much higher 'duty-cycle'.

 

[django]

Hi! Danger, in practice the timing is not a problem at all, think about it, this engine is running in a perfect circle, not the extremely complicated lienar up and down motion of the IC piston engine, therefore grooves and cams placed on the inner surface of the rotor housing in which the rotor runs can interact with spring activated valve stems to open them at exactly the right moment. The calculations needed to do this accurately are simple. It is the ignition timing that is a little more complicated, if maximum power is to be extracted from the system, but with todays technology this can easily be solved.

I think that it would be very difficult if not impossible to tune the pulse frequency that precisely. Pulse-jets ordinarily have a much higher 'duty-cycle'.

When I called this design a "pulse jet" I did not mean that it worked on the physical principles of the pulse jet but that it exhibited the same characteristics, it is an engine that works on pulsed or intermittent firing of the jet, there the resemablance ceases. A real pulse jet engine is just a chamber and a tube with a bend in it. Fuel is injected into the chamber through reed valves and ignited, causing it to expand and leave the tube at force, when this happens a vacuum is left in the chamber and air rushes into take its place resulting in a slight compression of the air in the combustion chamber and the whole cycle is repeated. The disadvantage of the system is that air is compressed at very low ratios prior to ignition, about 2:1, so it is not very efficient. The maximum frequency of a pulse jet is, as you had pointed out, low about 60 rpm, if that's the correct word fot it. django
I almost forgot, I have been meaning to do this for my last two posts but kept forgetting:

The design basically involves a pair of tip-jets built into a rotating disk inside some sort of housing with 2 opposed exhaust ports.

The above quote is by Danger and is by far the most succint, insightful and accurate description of how the RPJ works, and should explain to anyone who is interested the basic concept behind the engine. Thanks Danger. django
__________________

 

[Danger]

Okay, I'm getting a better idea of what you have in mind now. I just got hung up on the term 'pulse-jet' and thought that you're trying to harness a couple that work on the normal principle. Thinking of them more as 'on-demand jets' eliminates most of my objections. My main problem was simply that a regular pulse-jet spends just about equal amounts of time inhaling and exhaling, whereas yours will be 'coasting' for most of the cycle. It seems to me that you could get a much longer and more efficient burn time if you were to mill exhaust grooves around a lot more of the circumference rather than just have those two little ports.
You might also eliminate any other mechanical complications such as the cams and valves that you mentioned by simply drilling holes from the face rather than the rim of the rotor into the combustion chambers that will cyclically match up to intake ports in the case. The rotor would then in effect become its own rotary valve. It would be a lot simpler, and shouldn't have much different sealing issues than anything else.
One issue which might cause an efficiency loss is the manner in which a pulse-jet (and maybe your design) breathes. The old buzz-bomb units, at least, were discovered to actually suck something like 80% of the fresh intake charge through the tailpipe rather than the valvebox. Your 'tailpipes' are sealed except for when they're lined up with the exhaust ports.

 

[django]

Comment by Danger

You might also eliminate any other mechanical complications such as the cams and valves that you mentioned by simply drilling holes from the face rather than the rim of the rotor into the combustion chambers that will cyclically match up to intake ports in the case. The rotor would then in effect become its own rotary valve. It would be a lot simpler, and shouldn't have much different sealing issues than anything else.

Thank you Danger your comments are appreciated. May I take a few moments to elucidate the reasons for my undertaking to design a new type of engine. (a) I wanted an engine that was cleaner (b) I wanted an engine that was more fuel efficient (c) I wanted an engine that would be trouble free easy to maintenance and have a service life comparable with that of the IC piston engine. If, in my opinion, a new engine design did not fulfill all of these criteria it was simply not worth building.
Kindly note the combustion chambers are equal in volume to the combustion chambers of an ordinary IC Piston engine, so what I have in effect done is take only the combustion chamber volume of an IC piston engine and used them as the jet pods (combustion chambers} of my design, the rest, the cylinder, pistons etc., have been discarded . Next these combustion chambers are supplied with compressed air at a pressure of 125 psi, in a fully sealed environment. That is from the compressed air tank, through the rotary union, through the passages in the rotor, where fuel is added ( again through a separate pipe in the rotary union) to the combustion chambers in an absolutely air-tight and pneumatically sealed environment, this compressed air/fuel mixture is then fed to the combustion chambers via an inlet poppet valve, which is one of the best air-tight seals going. A pressure of 125 psi works out to a compression ratio of 9:1. The inlet poppet valve is closed and the fuel ignited by a piezoelectric spark plug. The fuel/air mixture combusts and the volume and temperature rise accordingly, almost simultaneously a gate valve to the Convergent/Divergent (CDN) De Laval nozzle is opened and these hot gases escape at velocity providing the power for the engine in the same way that a rocket provides power. Notice that the engine is designed for efficiency, with only two pods there is no problem with cooling.
Comment by Danger

. It seems to me that you could get a much longer and more efficient burn time if you were to mill exhaust grooves around a lot more of the circumference rather than just have those two little ports.

As I had pointed out this particular design has been designed for maximum efficiency, fuel economy and power output. I have of course considered the use of multiple pods and even made an animation to illustrate their use. Sorry for the length of this post but I felt that I had to clear up any misconceptions. django

 

[Danger]

I have of course taken into account that multiple pods might be used, but the design on the site is for an engine that can be used on the road.

I don't immediately see a conflict between the 2 concepts, but I'll give it some more thought. Not tonight, unfortunately; it's almost 12:30 am, I have a 30-hour day ahead of me (starting in 7 hours), and a wife who doesn't like me staying up even this late.
Your post has given me much more to consider, since you've obviously looked into this a lot more thoroughly than your picture and initial description indicated. To start with, your combustion chambers are far bigger than was apparent, and there was no indication of a specific nozzle design in the illustration.
Goodnight for now.

 

[FredGarvin]

I finally got to see the link. I didn't get a chance to read all of the presentation though. It's a sound concept. Of course, the devil is in the details. Have you got one of these running yet?

I have a few questions:

- What is the expected operational angular velocity?
- Do you have any data to back up the zero emissions claim?
- In your section regarding the materials, you seem to concentrate on the melting point of steel. Are you aware of the rapid degradation of yield point as a function of elevated temperatures?
- What fuel are you running on or plan on running on?

 

[django]

Thanks Fred a great post,

- What is the expected operational angular velocity?
- Do you have any data to back up the zero emissions claim?
- In your section regarding the materials, you seem to concentrate on the melting point of steel. Are you aware of the rapid degradation of yield point as a function of elevated temperatures?
- What fuel are you running on or plan on running on?

I’ll take your questions one at a time:

What is the expected operational angular velocity?

Angular velocity may be expressed either in radians or as rpm. The most efficient rpm for the RPJ, taking into account, complete combustion of fuel, adequate air etc., would be at a working speed of between 1500 rpm to 3000 rpm. Ok now the diameter of the rotor should be between 10” – 12” , if we take the rotor diameter as being 12” then the circumference of the rotor would be equal to 2 x pi x r = 75.4” approx. At 3000 rpm, this would work out to 50 rotations per second. Which works out to an angular velocity of 50 x 2 x pi = 314.5 rads/sec. At this speed there is sufficient time to fully load the combustion chambers, ignite the fuel and activate the jets.

Do you have any data to back up your zero emission claim?

Mostly it is just common sense. Look at the IC piston engine, it is full of half burnt combustion products that are constantly being ejected into the atmosphere. An RPJ fully combusts the fuel and so has to be cleaner. At least to my way of thinking.

In your section regarding the materials, you seem to concentrate on the melting point of steel. Are you aware of the rapid degradation of yield point as a function of elevated temperatures?

Look I’m not trying to take the mickey or anything, it is after all one of the most important questions on whether this engine design will work and as it happens I do have all the answers, but if you forgive me saying so your question needs to be answered by a question. Are you aware that the melting point of aluminium is something like 800 degrees centigrade and that is far moiré susceptible to structural degradation at elevated temperatures. Yet even diesels use aluminum pistons. I have tried to explain in the section on cooling how this is possible.

What fuel are you running on or planning on running on?

At the moment gasoline. That is why a compression ratio of 9:1 has been chosen so that it doesn’t pre-ignite or anything. Further it lends itself to the simplest most aesthetic design. I did do a study on a compression ignition model but it was bulky and comparably unattractive. I hope that I have answered your questions as honestly as I could and that I have not given you offense in anyway. Your ideas seem to be sound. I apologise again for the length of this post. Django.

 

[Danger]

Well, this is embarrassing.
Fred's comment about the 'presentation' prompted me to revisit the link. My monitor is fairly small, so I have to scroll around to see the whole picture. I had not, however, scrolled down far enough to see that there was more to it. Everything that I've said has been based purely upon the initial drawing.
Now that I've discovered the textual part and started reading it, things are falling into place very nicely. Unfortunately, I might not have time to get into it very much today, and will be away for the weekend. I'm really looking forward to studying it in detail.

 

[django]

Hi Danger! I thought that you'd be gone for the next 72 hours. I am just posting to say that , now that I've explained most of my views I think I'd like to sit back and see what others have to say, good or bad. I feel like I' hogging the whole thread, comment- reply, comment-reply, which is not pleasant for anyone. So if you don't mind, from now on I'll just try and listen, if that's OK. django

 

[Danger]

Sure it's okay, but I don't think that anyone can be accused of 'hogging' his own thread.
As for my availability, it depends. I'm getting ready for work, which is a 10 1/2-hour shift. I never know whether or not I'll be able to log on from there, since we have only 1 computer with net access and it's not in my work area. From work, I have a 6-hour drive to my brother-in-law's birthday party. There's no net there at all, although I'm taking my iBook. I'll be back some time Monday.

 

[FredGarvin]

...complete combustion of fuel, adequate air etc., would be at a working speed of between 1500 rpm to 3000 rpm.

OK. This is very low speed.

Mostly it is just common sense. Look at the IC piston engine, it is full of half burnt combustion products that are constantly being ejected into the atmosphere. An RPJ fully combusts the fuel and so has to be cleaner. At least to my way of thinking.

Not necessarily. Depending on your fuel to air ratios and actual combustion temps, you can still dump a ton of NOx into the atmosphere amongst other things.

Look I’m not trying to take the mickey or anything, it is after all one of the most important questions on whether this engine design will work and as it happens I do have all the answers, but if you forgive me saying so your question needs to be answered by a question. Are you aware that the melting point of aluminium is something like 800 degrees centigrade and that is far moiré susceptible to structural degradation at elevated temperatures. Yet even diesels use aluminum pistons. I have tried to explain in the section on cooling how this is possible.

I won't touch this one then. I was just curious why you mention melting point instead of yield. That's all. I will say that a piston is hardly a combustion chamber.

At the moment gasoline. That is why a compression ratio of 9:1 has been chosen so that it doesn’t pre-ignite or anything.

I don't have any real combustion experience with gasoline. I was wondering if you would be using a kerosene based like JET-A.

 

[django]

Look guys,
take it as granted that cooling has been solved, ignition has been solved... will this engine deliver power, power is the main factor! If power is available, everything else is available,right! We have a totally pneumatically sealed system for delivering fuel/air, we have an efficient cooling system, right ! Is there enough power in the thrust. Physicsforums are mythbusters man! What kind of pussyfooted respone is this!~ django

 

[brewnog]

You can work out that the beast is going to be sufficiently cooled, lubricated, fuelled and controlled, yet not that it will create power?

 

[django]

You can work out that the beast is going to be sufficiently cooled, lubricated, fuelled and controlled, yet not that it will create power?

It might surprise you to know that I, at one time thought as you did, that there could not possibly be much energy in reactive forces. Looking at some of the posts by other members in this thread, this seems to be a widely held view. What changed my mind, and set me thinking was an article on the Recoilless Gun

The Recoilles rifle (gun) was originally invented by an American naval Commander by the name of John Cleland Davis, his purpose was to design a gun that would eliminate the forces of recoil, which necessitated a bulky gun carriage and heavy weight to overcome the forces of recoil. Originally he deigned a twin barreled gun, with the two barrels pointing in opposite directions. In one of the barrels he placed the shell and in the other an equivalent weight of grease, in the center was the charge (propellant). When the charge was ignited it exerted equal force in both barrels sending the shell out of one barrel and the grease out of the other with equal force. Eventually Cleland came to the conclusion that since mass1 x velocity1 = mass2 x velocity2 it would be possible to eliminate the grease in the second barrel and to replace it with gases escaping at high velocity! Thus was born the recoilless gun in 1866 as it happens this was also the year in which Nicholaus Otto invented the IC piston engine! Now as you can see from the article the recoilless gun propels the same caliber shell as an ordinary cannon, to aprrox. The same distance. However one very important point is that in the recoilless gun, the gases are left to exit freely through the Venturii (CDN) without interruption. If one thinks about it this makes sense. If one did try to impede the exit of the gases, as say by the placing of a valve in the venturi, the purpose of the gun would be defeated and the forces of recoil would be present. In the Rotary Pulse Jet Engine, since we are not concerned with the forces of recoil a valve is present in the venturi (CDN). Therefore the power of the gases escaping at velocity from the combustion chamber should yield an equivalent power to that of a similar sized IC piston engine. In this way the recoilless gun was the fore runner of the modern grenade launcher and all other rocket based type of armaments, including missiles. Forgive the long winded post, but I hope you see where I am coming from. django