Hymee

iTrader: (1)

Good answer RG

Cheers,
Hymee.

zoom44

because then you would have something called by several on here "the jet engine". i invented that concept 14 pages ago and the rest of these folk took to naming it. why they get to name it when it was my idea i dont understand. i told them "jet engine" was a name already taken but they would not listen to me. but i'm forging ahead with the patent anyway


that's been done before here's some google results to get you started. what? you thought richard just started with these things at the begining of this thread?

Hymee

iTrader: (1)

Richard showed me a magazine article where he did install one of his axial flow units on a 350 Chev. It was installed in his 928 Porshe He also has extensive test results on this combo (350 chev / axial flow)

One interesting difference - those earlier units did not seem to use the planetary gearset for the step up ratio, just a big honking drive pully, and a rather small driven pulley

Cheers,
Hymee.

Cheers,
Mark.

rotarygod

It wouldn't be a jet engine. The just engine has combustion inside of it. The air entering the jet engine is compressed, ignited, and the exhaust spins the reas so that the front can suck more in. If we had an axial flow turbo, the air would flow into the turbo, get compressed, enter the engine, get further compressed where combustion takes place and then exhausted out the back spinning the exhaust wheel. This is no different than a current turbocharged engine and they aren't jets. An axial turbocharger would be pretty cool.

zoom44

hey im not argueing with you. you're argueing with richard and hymee and one or two others. i said "why cant we run this of a turbine from the exhaust instead of a belt and have an axial flow turbocharger" and they said "conrats you just invented the jet engine" and then a had a jolly good laugh at my expense i didnt say it was a jet engine i said they had told me i invented "the jet engine". :D

zoom44

reading thru some of the search results before i found the same belt/pulley info. i also found several comments from people who were looking for info and mentioned that they had got some real good answers from one richard paul the last post of one thread i read mentioned waiting for some technical paper sort of post that richard was going to write.

bureau13

But wouldn't it be inferior to a centrifugal-type turbocharger for the reasons I mentioned above? When the compressor is belt-driven and dependent on engine rpm, the nature of the centrifugal compressor's boost pattern means you get your maximum power only at maximum rpm, which for cars isn't so hot as we don't get to tool around at a consistently high rpm most of the time. However, for a turbo, you can hold the thing at max boost based on exhaust flow over a wide range of engine rpms. It seems that an axial flow compressor in this case would not reach max boost as quickly, and so would be at a disadvantage.

I know this is a bit of a tangent but globi asked why turbo makers didn't use this design and it seems logical to me...but I'm not 100% sure I'm not missing something obvious.

jds

rotarygod

The boost curve of a turbocharger will give us much more low end than the axial flow supercharger. They reach max desired boost pretty fast and then we can just hold it there. A turbo is ultimately the way to go in the race for max power. It will also do it over a wide rpm range.

I am a fan of turbos. I have one. Just not on an RX-8. When it comes to supercharging, I am more of a fan of positive displacement superchargers for the same early full boost reasons as a turbo. I am just intrigued by the axial design and have always has a fascination for jet engines. I believe that every product has it's place in the market. This system has a faster boost rise than the centrifugal but not as fast as positive displacement. It does have greater efficiency than both though and this translates into more power at the same boost level. It also takes less power to turn. At cruise speeds, the blower is hardly any drag on the engine at all.

The one thing a supercharger will always have over a turbo is reliability. They don't spin near as fast. The faster it spins, the less reliable it gets. Some turbo's such as the pathetic 3rd gen RX-7 turbos, could get up to 150,000 rpm!!! Turbo's need special care to make them last long. Many people only run oil cooled bearings and these run hotter than water and oil turbos. If run hard they need a turbo timer to prevent coking on shut down. On water cooled turbos, when you aren't on boost and just cruising, you still have hot coolant and oil circulating through the turbo heating it up. Some of this heat will transfer into the intake air. Many superchargers don't have this issue. Even when you are not under boost, you still have an exhaust restriction. So much for good scavenging from the exhaust. This effects mileage. Remember that we need a free flowing exhaust to make lots of power. People assumes this means after the turbo. While this too is important, the turbo itself is the first restiction. For a reliable street machine that wants a power boost but isn't trying to set any records, this supercharger is a great alternative.

For all out no holds barred max power, a properly sized turbo is the way to go. If that's what you are implying then you are correct. It would be neat to see an axial turbocharger. It would be more efficent than the centrifugal turbo.

Aoshi Shinomori

150,000 rpm?!?!
Damn, I thought when Richard mentioned 45,000 rpm on the axial flow that that was about as fast as anything would spin on a street car. Guess I was wrong. This may be a stupid question, but since you mentioned a centrifugal turbocharger, is that what the average turbocharger is? Or do companies produce positive displacement turbos? Do they even exist? I'm not entirely sure I understand.

bobclevenger

As far as I know all turbine-driven superchargers (read: "turbochargers") use a centrifugal turbine and a centrifugal compressor (the supercharger part). For one thing it's impractical to use a different type of turbine and compressor since they must operate at the same rpm. The rpm of a turbine at power would be far too high to run a positive-displacement blower, and I think it would also be too high for an axial-flow blower. Turbines suffer from lack of low-speed torque even more that rotaries do! They make up for it by running at very high rpms.

I suppose you could use a gear reduction scheme between the turbine and the blower, but that would cause more complexity, more moving parts, more power loss, and more failures. An axial-flow turbine could work, but it would be costly and difficult to plumb in the engine compartment of a practical automobile.

Centrifugal-centrifugal seems to be the best way to turbocharge. Axial-axial has proven to be the best way to build jet engines. Positive-displacement blowers work best at about the same rpm range as internal-combustion engines (not surprisingly, since IC engines are just a special kind of PD pump). The axial-flow blower seems like a good bet for the rotary because it likes high rpms, but not a lot higher than the rotary does, so a simple gear and/or belt drive system works.

Hey, I may be all wrong here, but that's what I have picked up over the years. Richard, please correct me where I'm wrong and we'll all learn.

globi

As I can understand why turbo manufacturers for cars don't bother to build turbochargers with axial flow compressors, I just don't see why companies that build turbochargers for ship diesel engines with 100000 HP don't use axial flow compressors on their turbochargers since all what they really care about is efficiency. (After all an ocean carrier doesn't go on a drag strip or something.)

http://www.abb.ch/Global/SEAPR/SEAPR035.NSF/viewunid/B82E4EA9415D0C09C1256AA8003DA74A/$file/Range+030415.pdf

As I mentioned before ABB builds gas turbines, so they would definitely have the expertise to build a turbocharger with an axial flow compressor and if you look at the pictures they are actually using axial flow turbines on their turbochargers.

http://www.bath.ac.uk/~ccsshb/12cyl/

globi

A turbocharger can easily be transformed into a jet engine (has nothing to do with axial or radial flow):

http://www.nickhaddock.co.uk/jetgallery.htm

bureau13

Actually, I thought I had a good idea why turbos themselves usually use a centrifugal compressor rather than an axial compressor...however I think I was mistaken...for the same max boost, the axial is actually getting closer soon, as you stated below. So never mind! :D

John Corbitt

Axial flow have a lot of rotational mass. "turbo Lag" would far greater with an axial flow compressor as opposed to a centrifugal compressor. Therefor an axial flow compressor in a car needs to be mechanically driven. Look at the spoolup time on a large axial flow jet engine. Interesting enough, the axial flow jet engines are more fuel efficient.

John

rotarygod

Look at the spool time on anything as large as a jet engine.

globi

which wouldn't really be an issue in a ship diesel, since they are driven at the same rpm for several weeks. So why are they not implementing it?

Exactly, and this rotational mass would also hurt the responsiveness of the engine even if it is mechanically connected to the engine (keyword: Flywheel).
It'd be a different story if it was electrically driven. But you'd need a car that generates and stores enough electric energy to run it. (If a hybrid car would use the electric energy to run a supercharger it would produce much more power overall than if it would just use the electric energy to help driving the flywheel.)

bobclevenger

The very fact that marine diesels run at a constant rpm makes the choice of supercharger type moot; you can use a drive which will run your blower at its peak efficiency whatever kind it is. So you use the one that is most cost-efficient. You design a system that produces x psi boost at y rpm using the cheapest parts available (consistent with durability, of course).


Just one acronym here: TANSTAAFL. There Ain't No Such Thing As A Free Lunch.

You can't get more power out of a motor than you put into it; you can't even get as much out as you put in. Every time you convert energy to a different form you have a loss. Mechanical to electrical to mechanical is only two conversions and that's what hybrids have. Mechanical to chemical to mechanical is what directly driven blowers and turbine driven blowers have -- again, two conversions.

An electrically driven blower would have a mechanical to electrical (generating the electricity from the engine's output shaft) conversion, then an electrical to mechanical conversion to run the blower motor, then a mechanical to chemical energy conversion (from blower motor motion to compression of the fuel/air mixture) and finally a chemical to mechanical energy conversion in the engine. That's four conversions.

And then there is the weight of the extra batteries you'd need to carry. Yeah, your engine would put out more hp than it would N/A, but the electrical load would use a lot of that extra power up -- more than a simple mechanical or turbine drive would. And you wouldn't have to increase the weight of your vehicle significantly.

Oh, the increased rotational mass of the engine (the blower's moving parts) is more than made up for by the increased power output of the blown engine.

Photic

Lets just slap a friggin scramjet on the RX8, mach 7 anyone?

globi

Well fact is the most efficient ship diesel engines are turbocharged 2 stroke diesel engines and they don't use axial compressors in their turbochargers and I just raised the question why they are not doing it if it was more efficient. Have you had a chance to look at the links?

There might be no free lunch but there's definitely free braking energy. That's why I was mentioning the Hybrid car. This concept, would only make sense in combination with recycling braking energy (flywheel motor/generator). The batteries might add weight but they can also lower the cg and they can be placed anywhere (better weight distribution). Also you generate more power out of a smaller engine. So you end up saving some weight on this end.

If you run the compressor with your recycled braking energy, the car will be more fuel efficient. And not only that: Since you're not taking any power from the crank you can generate more power at the same boost level than you could with a mechanical supercharger (no parasitic loss and no increased backpressure). Besides you have 100% flexibility, you have total control over the rpm of the supercharger. So for instance you could generate more boost at low rpms and less at high without having to blow it off (wasted energy).

Anyway still better than an electric supercharger would be a turbocharger with an electric motor/generator, but that's another story.

globi

I think I found one reason (there might be many others) why gas turbines with axial compressors are more efficient than gas turbines with centrifugal (or radial) compressors: In a gas turbine with centrifugal compressor the gas flow needs to be redirected (friction loss) and in a gas turbine with an axial compressor it does not (it can flow straight through).

However this issue does not apply to an engine with a turbocharger.

rotarygod

globi what are you trying to prove and why are you so against the axial flow?

You need to clarify your last post. The comment about it not applying to an engine with a turbo makes absolutely no sense.

I can give you a VERY big list of problems with turbos. I can also make arguments against any other type of forced induction. Every product has disadvatages. No form of power adder is free and regenerative braking can't power forced induction. At least not for any usable sustained period of time.

Turbos aren't necessarily all that everyone thinks they are. A very large majority of turbo systems out there (every factory turbo system) are very inefficient but people think they aren't because "turbos are efficient". They are just CHEAPEST. That is the ONLY reason you see centrifugal compressors everywhere. Price matters more than efficiency. This isn't the case with jet engines where efficiency comes first.

Any argument you give as to why we don't see axial units more all comes down to price. That's it.

Aoshi Shinomori

Did I miss something, I think he was stating why an axial flow turbine would be more efficient? From what I see he wants to see more axial flow units on vehicles like big ships and stuff. About the not applying to a turbocharged engine, I'm at a loss.

globi

I'm not against the axial flow compressor at all. I just believe that people shouldn't blindly support a new product, since that doesn't really help the ultimate application and I'm not saying that this is the case either. I'm just questioning. Asking questions is not necessarily criticizing it. (What's wrong with questioning things - after all there are enough people that don't.)
Maybe it is indeed just the price, but I was just thinking that if a ocean carrier can get an engine with just 1% higher efficiency that would save them a lot of costs per year. (These turbochargers might cost several $100k so price might play less of a role).

Clarification:
In a gas turbine the compressor the combustion chamber and the turbine is all in one line. The basic mass flow doesn't change directions. If you substitute the axial compressor with a centrifugal (radial) compressor it's not in one line. The compressed air moves sideways and needs to be redirected towards the combustion chamber and the turbine.

Here's a picture of a gas turbine with a centrifugal compressor:
http://www.users.globalnet.co.uk/~spurr/sec.htm
The mass flow is not in one line.

Now on a turbocharger the air has to move radially away from it anyway, so an axial compressor wouldn't really benefit in that case. This might be another explanation why it doesn't make sense to use axial compressors on turbochargers.

rotarygod

I'm fine with questions. No problem. I also agree that people shouldn't just blindly accept new technologies. On the other hand people should be more open to the possibilities of them though. Just as there are too many people that blindly accept things that don't work, there are an equal number of people that pass up the opportunity to use something very good. I apparently misinterpretted you by thinking you were criticizing it. I was just getting the distinct impression that you were only pro turbo and against everything else. If this is wrong then I apologize. Strong proponets of turbo use will argue their benefit until they are blue in the face and discount the possibility that anything else could possibly be as good regardless of situation. The RX-7 forum is a prime example of this.

I get what you mean on the direction change now. Now that I see it, I'm not sure how I misread it. While the air doesn't have to get directed sideways out of the axial unit, it does change directions every time it hits a new fan stage or stator. You are basing the efficiency advantage on the fact that the air is not having to turn 90 degrees out the side. This is one area that I disagree.

Don't take my comments as hostile towards you. They aren't. I'm just making sure we have open minded questions rather than close minded criticisms. Believe me, I don't hate turbos in any way. I have one.

Richard Paul

iTrader: (5)

Wow my server goes down for two days and I get all this action on my thread.
It's overwelming and I can't remember all the things I might coment on. No problem as it seems others have answered for me, thanks.

Except you zoom44, Yes, yes indeed you did invent the jet engine. The only thing the forum helped was we added the combustion section. You alone invented the rest. Don't let the sour grapes get to you.
Also what link did you find that I am expected to provide a paper for. I don'trecall owing anybody a tech paper. If I do then it should be addressed and I will do so if I only knew about it. Prey tell.

A comment on the large engine topic. The only place I know of where an axial flow supercharger is used by the OEM is on railroad engines I think built by Allison.
And on top of that, they drive the generator which then runs the electric motors for rail traction.

This system is also used in ocean going tugs belonging to the Navy.

Again if I forgot anyone Please let me know. I'm back on line and after 3 weeks my e mail works. I have 429 e mails backed up. If one of them is you now you know why.