Turboshaft Racecar?

[CH3NO2]

Maybe this will work. A copy and paste from Excel. The Turbonetics data
SAE Compressor Map Data
Compressor Wheel Exducer Dia: 141 mm, Trim: 56

(RPM) PR kg/s EtaC
26888 1.27 0.156 58%
27029 1.27 0.227 66%
26906 1.26 0.290 70%
27133 1.26 0.341 72%
27032 1.23 0.403 71%
27053 1.20 0.466 67%
27085 1.16 0.531 58%
36279 1.51 0.230 60%
36281 1.51 0.307 66%
36541 1.52 0.389 72%
36510 1.49 0.475 73%
36370 1.44 0.559 73%
36425 1.39 0.654 69%
36330 1.30 0.739 60%
46046 1.85 0.290 58%
45978 1.87 0.395 64%
45989 1.87 0.514 71%
45897 1.84 0.627 73%
45973 1.77 0.741 73%
45966 1.67 0.858 70%
46048 1.51 0.988 59%
55112 2.32 0.473 63%
55105 2.33 0.600 67%
55153 2.33 0.720 70%
55317 2.27 0.845 72%
55048 2.15 0.984 72%
55256 2.04 1.096 69%
55365 1.80 1.232 59%
63806 2.82 0.593 60%
63991 2.86 0.731 64%
64135 2.89 0.858 67%
63982 2.79 1.007 70%
64090 2.67 1.159 70%
63988 2.57 1.306 69%
64177 2.12 1.455 56%
74061 3.45 1.191 64%
73924 3.53 1.321 68%
73897 3.47 1.432 67%
73966 2.45 1.568 52%
80866 4.00 1.311 62%
80974 4.08 1.375 63%
80857 3.97 1.476 63%
81009 2.70 1.595 49%

It's a lower pressure, lower efficiency compressor but it's centered where it needs to be.

[CH3NO2]

And then there is this one by Turbonetics.

[CH3NO2]

And this is the Turbonetics Turbine map.

[racket]

Hi Tony

Those 141 mm comp wheels at 56 Trim are very similar to the Garrett GT6041 maps

The 129.5mm turb is what Anders and I use , the 1.50 A/R scroll is their biggest that suits the G Trim turb wheel .

I don't know if you'll be able to run the engine at only 10 psi P2 and still extract 50 lbs/min of air , its a big percentage , a lot will depend on turbine efficiency at such low pressures and rpm , I'd have to work some numbers to see if its possible , leave it with me .

Cheers
John

[racket]

Numbers aren't looking good at low PRs :-( the Corrected Flow of that turb stage at 85 lbs/min is the problem , I've gotta run high temps to get sufficient horsepower development and its "over flowing" the stage .

I'll do some more number tomorrow , don't think too well at night

[CH3NO2]

Found some good news, the GTX 5533R is available with a range of different compressors.


85mm Inducer




88mm Inducer




91mm Inducer




98mm Inducer



If you look closely when flipping between the above plots, it appears the 85 and 88 maps are scaled from the same data set.


The maps for 91 and 98 are also from another data set.  Apparently, the same data is being rescaled via an extrapolation or interpolation.

[racket]

Hi

If we use the low pressure 141 mm comp at 2:1 PR and setup for a max flow of 0.9kgs/sec-2 lbs/sec-120 lbs/min , effic is 80% so a 79 deg rise in compression, requiring a ~68 degree drop thru the turb , but because of the "inbalance" between comp flow and turb flow we'll be needing , 68 X 120 div 70 = 117 deg C

With a ~5% pressure drop through the combustor theres a 1.9 PR going into the turb stage of the G Trim wheel which can accommodate a Corrected Flow of ~75 lbs/min .

As theres only 70 lbs of actual flow , 50 lbs/min of bleed, we'll calculate for 70 lbs/min at 900 C - 1652 F , it comes out at 74.3 lbs/min Corrected Flow , .......Just right. :-)

But we need to make sure we can get a 117 C degree drop thru the turb from the temps and pressures used at the turb effic of say 75% , my calcs give a required PR of 1.77 , that still leaves a bit of PR for the the exhaust velocity which can be aided by having a diffusing exhaust cone.

All looking OK

Cheers
John

[CH3NO2]

That is awesome. You make it look easy.

I wish I started studying turbines 20 years ago. I have so much to study and learn on the subject.
I've been doing blow down rocket propulsion systems for so long it's easy. A lot of the rocket propulsion science transfers over but Turbines are a whole new world of engineering to explore and become familiar with.

I will start a build with this Turbonetics unit and share my progress/results here on JATO.
This will be fun.

Thanks John!
Tony

[racket]

Hi Tony

Only too happy to help :-)

I'm not too sure whats going to happen when you don't need the bleed air , theoretically it should run cooler , but theres a large turb stage that needs "filling" , you may need to lower the PR .

Theres "tradeoffs" that can be made to juggle parameters to achieve outcomes especially when you aren't after the optimum power or fuel burn rate , you're attempting a large bleed rate as a percentage of flow so some compromises will need to be made .

LOL..........I started with this hobby >25 years ago and still don't know enough , and never will :-(

Looking forward to your creation

Cheers
John

[CH3NO2]

Hi John,

I placed the order for the turbo charger with 141mm 56trim... only to find it is out of stock.
Unfortunately, it wont be available for some time.

It's back to square one in the search for an appropriate combo.

Would you happen to know of an existing turbo charger that would work?

Also, what is the method you use to determine proper suitability between the compressor/turbine stage?
If I knew how to recognize a good combo I can spend days and days digging through the net.

Thank you for all your help.
Tony

[CH3NO2]

A possible second option is to simply buy an RC jet engine, weld a flange onto the exit nozzle and bolt it to the turbine section of another turbo charger. ... but I'm a bit wary of arbitrarily putting back pressure on a finely tuned RC jet engine. It would likely throw off all the tune. If it worked, that would be fantastic, but something tells me it would be a long shot.

[racket]

Hi Tony

The similar Precision turbo www.precisionturbo.net/Street-and-Race/ss/2-000--HP/details/Street-and-Race-Turbocharger---PT106/327 would probably do the same job, the more expensive Garrett GT6041 which I've had dealings with jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart would also be a very good candidate, though they are getting hard to source with the large turb scroll needed .

Generally as long as the turbine wheels exducer area is ~20% larger in area than the comp inducer the turbo should work as a GT , using the 106 mm inducered comps at 8825 sq mms , if we apply the 20% increase would require an exducer of ~10,590 sq mms or 116 mm dia, the G trim turb wheels are ~111mm , so close enough ............there are a heap of variable which need to be taken into account if we want to refine the exercise , too many to go into here .

Using a RC jet engine isn't the best idea , you'd be needing a pretty big one as your horsepower needs to compress 2 lbs/sec to a 2:1 PR is ~100 HP , this would need a 100 lb thrust engine, expensive :-( then you'd still need the large turbo for compressing your air , so more expense :-(((

Cheers
John

[CH3NO2]

20% area ratio between comp inducer to turb exducer? That's simple enough.

I checked the comp inducer to turb exducer area ratios on the PT106 and it has a 12% difference. Is 12% adequate?

Then there is the turbine housing A/R. Options range from 1 to 1.5. Are there general ratios to look for in Turbine applications?
The nice thing about the housing is it can be swapped out for another in the tuning process.

[racket]

Hi Tony

12% should be adequate , its the same sizes as the Turbonetics rotative , so go with the same 1.5 A/R .

Changing the turbine scroll A/R is a useful tuning aid , better to start with the largest and work backwards towards the smaller sizes , less chance of doing damage as long as one keeps an eye on the turbine temperatures , but you're barely getting past our normal idling power settings , so the turbo will be "over engineered" and able to take a bit of unintentional abuse if need be.

Thinking back on my previous email concerning using a RC turbine to drive a turbo to produce your 50 lbs/min a 10 psi , I've overstated the RC turbine size and turbo sizes on reflection , I took the quick way and extrapolated from our previous needs instead of taking the time to think this through a bit more .

It'd only take ~30 HP to compress your required 50 lbs/min at 10 psi ,so a turbo of around GT45 size , still a fairly decent sized unit so not cheap to buy as well as your RC engine , I still feel your best bet is the DIY turbojet with bleed .

What do you need the compressed air for ??

Cheers
John

[CH3NO2]

I need to build a flow bench for manifold pressure drop testing. And I just want to build a jet engine for the fun of it.
There are industrial compressors that can pump 50lbm/min@10psi all day long, but the high power electric motor requires at least 3 phase 208V. I only have access to single phase 220V.

Besides, I have always had a love of chemistry and combustion systems. Building a jet engine would be awesome and it's time I learned it anyways. I studied and worked the heck out of rocket and ramjet propulsion when I worked at Boeing and Marquardt... but never turbines. I was intimidated by the complexity of turbine systems so I never really went there... but this has changed due to necessity. I would love to do all kinds of things with rocket propulsion but the chemicals required for rocket propulsion are all under strict scrutiny due to terrorism and national security. Unless it is for a government contract at a major aerospace company, most everything solid rocket propellant or storable hypergolic propellant, is restricted in the US. Even if there were no regulations, some of the chemicals are too costly or way too dangerous for casual use.
Hydrazine is too toxic.
Nitrogen tetroxide is too toxic.
Hydrogen Peroxide is too unstable and scarce.
Nitromethane (when pure) is too susceptible to detonation.
Lox isn't storable.
Ammonium nitrate and Ammonium perchlorate are restricted.
Potassium nitrate is too weak.
35% Hydrogen peroxide is too weak.
WFNA is restricted and way too nasty.
Nitrous oxide is restricted.
I could go on and on. I researched every nook and crany of chemical propellants trying to find a viable solution.
As much as I love rocket propulsion, there are too many road blocks to do anything practical with it.

At least we still have diesel fuel and air as safe, cheap and legal propellants. It's time to cross over to jet propulsion.