Author Topic: A Simple Turbocharger.  (Read 5678 times)

Offline Danny M2Z

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A Simple Turbocharger.
« on: September 08, 2013, 03:06:07 PM »
G'day. Here is my exhaust driven turbocharger build so far.

It was originally intended to fit it to a side exhaust O.S. 45 FSR, hence the manifold adaptor, but I was not happy about the inlet plumbing so have decided to fit it vertically to an MVVS 40 that I acquired. This has a rear exhaust and a rear disk valve induction directly below it. This should simplify the carburettor installation and let me fit a tuned pipe exhaust.

The 16 segment rotor was the trickiest part as the vanes are angled at 3░ to the axis to encourage them to fling fuel (lube) into the centre bearing.

Whether it will work or not is going to be interesting, but I want to know. If it does work my friend wants one for his hydroplane, but then he wants it watercooled  :thinking:

Anyway I thought that maybe somebody might be interested.

Regards * Danny M *
« Last Edit: September 08, 2013, 03:13:19 PM by Danny M2Z »
Measure twice - cut once. You can't put it back!

Offline Mosey

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Re: A Simple Turbocharger.
« Reply #1 on: September 08, 2013, 03:09:44 PM »
Interested, and would like to see those angled vanes being machined. :thinking:
Mosey

Offline ths

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Re: A Simple Turbocharger.
« Reply #2 on: September 08, 2013, 10:57:54 PM »
That is interesting. Got a shot with a matchbox in it?

Hugh.

Offline Danny M2Z

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Re: A Simple Turbocharger.
« Reply #3 on: September 09, 2013, 12:19:07 AM »
That is interesting. Got a shot with a matchbox in it?

Hugh.

G'day. The body is 2.75" x 1" x 1". The bearings are 0.75" x 0.25".

Here is a photo with the modern equivalent of a match box. I am machining a new body with the exhaust and intake directly above each other. The new ports will be circular to simplify fitting the carby and pipe. That way the manifold adaptors may be redundant.

Regards * Danny M *

Measure twice - cut once. You can't put it back!

Offline gadabout

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Re: A Simple Turbocharger.
« Reply #4 on: September 09, 2013, 01:06:49 AM »
Mmmm reminds me of one published in "Flying Models" last century, made one myself from those plans but it was useless, still have it somewhere i reckon
Mark

Offline Danny M2Z

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Re: A Simple Turbocharger.
« Reply #5 on: September 09, 2013, 05:36:08 AM »
Mmmm reminds me of one published in "Flying Models" last century, made one myself from those plans but it was useless, still have it somewhere i reckon
Mark

G'day Mark. So that was where the plans came from! My hydroplane running mate gave them to me but they had been scanned and there were no build instructions. I should be interested to hear what problems you had. My mate is great at fibreglass casting, but would not know an end mill from a flour mill. That's why he picked on me.

Actually, one problem that I am having is trying to devise a method of pinning the rotors to the shaft.

I don't want to use Loctite as I want to be be able to disassemble the beastie to try different rotor configurations.

What I have dreamed up so far is to either;

      1. Mill a tiny keyway in the shaft and rotors and use a square key.
      2. Drill a keyway in the shaft and rotors at the seam and use a round piano wire key to lock them together.
      3. Cross drill the shaft, slot the end of the rotors and use a driving dog pin.

I would really like to hear input on these options or maybe a better one.

The MVVS is currently on the test stand in it's original configuration, my neighbours are all working so some rpm numbers are being documented for comparison reasons for when the blower is attached.

Surely the inlet rotor must be doing something wicked to the fuel atomisation?

Regards * Danny M *

 
 
« Last Edit: September 09, 2013, 06:09:19 AM by Danny M2Z »
Measure twice - cut once. You can't put it back!

Offline Admiral_dk

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Re: A Simple Turbocharger.
« Reply #6 on: September 09, 2013, 12:22:43 PM »
Hi Danny

I can't see a turbo with loose vanes ever working - only CNC milled turbine and compressor wheels .... it will have to rev to at least 50,000 rpm for it to really add boost and at that speed you'll loose a vane or two => creating total havoc.

You can't add a resonance camber / racing exhaust after the turbo - it will not work - a resonance chamber first pull the spend gasses out of the cylinder + fresh gas from the crankcase and the pushes the fresh gas back into the cylinder after transferports are closed.

If you look at snowmobiles with turbo - they are connected after the stinger on the resonance chamber, where you would put the noise damper. Your design will heat the fresh gas and that's not what you want (unless you fly at high altitudes).

That's not to say that you shouldn't build it anyway - but do not expect any real performance improvements  ;)

Offline lohring

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Re: A Simple Turbocharger.
« Reply #7 on: December 23, 2013, 05:02:54 PM »
Turbochargers and two strokes were made for each other.  The first serious, but ultimately unsuccessful efforts were the Rolls Royce Crecy (http://en.wikipedia.org/wiki/Rolls-Royce_Crecy) and the Napier Nomad (http://en.wikipedia.org/wiki/Napier_Nomad).  These days the best high power turbocharged two strokes are marine diesels (
) at the big end and turbocharged snowmobiles (
) at the small end.  All work on the principle of raising the exhaust back pressure along with the intake pressure to prevent blowing the new mixture out the exhaust.

The problem with turbocharging small engines is that turbomachinery gets seriously inefficient as the size goes down.  Also two strokes need a some way to run a pump at start up.  My favorite small turbocharger experiments are the Eco Motors electrically boosted turbocharged engines (http://www.ecomotors.com/technology) and some 50 cc scooter engine experiments (
). 

So far small engine turbochargers can't beat the simplest "turbocharger" of all, the tuned pipe.  It drops the cylinder pressure at bottom dead center to "suck" mixture in from the crankcase then adds as much as two atmospheres of boost just before the exhaust port closes.  The most powerful example of a tuned pipe two stroke I know of is the 54 hp Aprilia 125 cc motorcycle race engine.

Dental air driven handpieces use turbines that free run up to 500,000 rpm or maybe 200,000 rpm under load.  Their design might be a basis for the turbine.  Good luck on building a compressor that gives any serious boost with a tiny turbine.

Lohring Miller

Offline Admiral_dk

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Re: A Simple Turbocharger.
« Reply #8 on: December 23, 2013, 08:19:21 PM »
Hi Lohring

I'm sorry but the Roll Royce isn't a turbo charged engine. The Napier version II admittedly is, but with a twist. Although the big marine engines are interesting they can't be compared either and to my big astonishment I must admit to your description of the snowmobiles - I can't find the Pictures showing how the good stuff is done (only found it running - a 1200cc Suzuki snowmobile. So the best illustration is your link to the Swedish 50cc moped engine and it doesn't produce more power than could be done without.

So my conclusion doesn't match yours - on small engines it is not worth the effort. This doesn't mean that people shouldn't have fun trying and I'm sorry that I apparently has been a spoil spot in this thread.

Offline lohring

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Re: A Simple Turbocharger.
« Reply #9 on: December 24, 2013, 05:12:38 PM »
The 12 cylinder Crecy Had mechanical problems so the full size engine never reached the desired power levels and never had turbochargers fitted.  Single cylinder test engines had simulated turbocharging applied and reached very high power levels.  The book on the Crecy (http://www.amazon.com/Rolls-Royce-Crecy-Historical-Andrew-Nahum/dp/1872922058/ref=sr_1_1?s=books&ie=UTF8&qid=1387904133&sr=1-1&keywords=rolls+royce+crecy) as well as Ricardo's "The High Speed Internal Combustion Engine" (http://www.amazon.com/High-Speed-Internal-Combustion-Engine-Ricardo-F-R-S/dp/0216890268/ref=sr_1_2?s=books&ie=UTF8&qid=1387903215&sr=1-2&keywords=ricardo+high+speed+internal+combustion+engine) describes these efforts.

Below is a picture of a turbocharged snow mobile engine.  It developed over 800 hp with the help of nitrous oxide.  The problem with the turbocharger described above is that the design is too inefficient to develop significant boost.  I've been thinking about turbocharging small engines for over 50 years.  The small gas turbines have finally developed turbines and adapted small turbocharger compressors that are efficient enough to produce thrust.  (http://www.wrenturbines.co.uk/mw54-turbo-jet-and-turbo-prop-second-stage-plans)  This is the same system the 50 cc scooter engine experimenters are using.

Compressor and turbine design is not trivial if you expect to actually improve an engines performance.  A lot of people have worked on that.  The commercially available turbochargers are still too large for really small engines.   The only turbines even close are used in dental handpieces.  The Midwest style could easily be built by amateurs and runs on 30 psi air.  See the cutaway below.  A scaled up version might work, but would need some engineering.  The calculations are described in "gas Turbines for Model Aircraft" (http://www.amazon.com/Gas-Turbine-Engines-Model-Aircraft/dp/0951058916/ref=sr_1_fkmr0_1?s=books&ie=UTF8&qid=1387904509&sr=1-1-fkmr0&keywords=shrekling+model+gas+turbines) as well as some simple construction methods.

Lohring Miller


Offline lohring

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Re: A Simple Turbocharger.
« Reply #10 on: December 27, 2013, 05:52:31 PM »
If you are seriously interested in turbomachinery design, there is an online lecture series. (http://www.youtube.com/playlist?list=PLC1E9E61F956C56D0)  At the 47 minute point in the radial turbine lecture, Lecture 37, (
)  there is a description of a 21 mm diameter gas turbine.  The basic compressor and turbine designs could be the basis of a small turbocharger.  I would still be surprised if it would give better performance than a tuned pipe.

Lohring Miller

Offline Admiral_dk

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Re: A Simple Turbocharger.
« Reply #11 on: December 27, 2013, 07:06:02 PM »
Hi Lohring

My conclusions came from the Wiki link you provided and on that the Cresy had a compressor that ran of the crank and a turbine that should extract some of the lost energy from the exhaust - fine, but to me at turbo is a stand alone object (I'm aware of the lubrication coming from another unit, like the engine) with a single shaft with the turbine at one end and the compressor at the other !!!!..... and the Cresy simply doesn't fit that bill - the second Napier does to a point, because of the freewheeling clutch.

Thanks for the Pictures I couldn't find (though not 100% what I had in mind - no sharing of chambers between cylinders) and apparently it's not considered worth the effort to have the exhaust valves installed (there's Space for them), so I can't help thinking that this sled is made for dragracing.

Quote
I would still be surprised if it would give better performance than a tuned pipe.

I can see that you end up with the same conclusion as me and that's the reason why it to me isn't worth the effort. The Pipe is a lowtech (not the calculations or experiments, but the form and mechanical result) and therefore very reliable + low weight.
But as said before - that doesn't mean that I would tell other not to do the experiments.

Offline lohring

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Re: A Simple Turbocharger.
« Reply #12 on: December 28, 2013, 03:57:52 PM »
I'm sorry that I sounded so discouraging, but I've seen several manufacturers try to sell "superchargers" for model engines that are worthless.  I keep hoping that turbocharging could work, but despite a lot of research and work by others, it hasn't happened for small engines.  The two stroke simulation program I use just added a turbocharger section.  However, it needs maps from real turbos, and the smallest available probably isn't even suitable for 50 cc engines.  That means you need to design the unit and that's not a trivial job according to my friend who works for Eco Motors.  They buy the compressor and turbine for their electrically boosted turbochargers.  Again, take a look at the tiny gas turbine in the video.  It's very cute and might be a starting point.

Lohring Miller