Cheap Ebay turbo for a first attempt - opinions on this one?

[turboron]

wannabebuilder, your described turbo would be a good cheep systems learning unit. However, you could not pull much power from it due to the need to restrict pressure ratio about 2.5 and Turbine inlet temperature to 1350 to 1400 degrees F. Another limiting factor is the area of the turbine exducer is almost the same as the compressor inducer. We would prefer that the turbine exducer area would be at least 25% greater than the compressor inducer area for a good DIY gas turbine.

Thanks, Ron

[racket]

Hi

Yep , I agree with Ron , it'll be OK as a learning tool, and not to much of an outlay if things go wrong , keep the pressures and temperatures at modest levels and you'll be OK.

DO NOT fit a jetnozzle onto the engine until you've run it several times and are certain about those temperatures .

All the best

Cheers
John

[wannabebuilderuk]

Thanks for your replies, is there any sort of turbo that I'd want to keep my eyes open for which is a good starter setup that's not too expensive new or 2nd hand which could produce a small amount of thust? (say 5-15lbs for a first attempt or whatever you think is a good amount)

Thanks

[turboron]

wanna, in my opinion you will not get far with this hobby unless you learn to make your own numbers. Get a gas turbines text and figure how much mass flow you need to achieve your desired thrust levels assuming an atmospheric suction pressure, 3.0/1 pressure ratio and a 1450 degree F turbine inlet temperature. Once you have determined the mass flow you need we can suggest some turbocharger options.

Thanks, Ron

[wannabebuilderuk]

Sorry I don't mean to annoy you by seeming like some kid that thinks it's an easy project, I'm genuinely interested in all of this just need some slight direction on where to start as not exactly a project where there's lots of information that's easy to find.

So my best bet is to try and read some hobbyist books on diy gas turbines where I'll find the equations for all calculations etc?

Thanks.

[turboron]

wanna, I am not annoyed. Kurt Schreckling's and Thomas Kamps's books are good. However, they have been priced out of reach for most people. Perhaps you can find a copy for loan at your library. Otherwise, text books from the 1930's to the 1950's are good for the basics.

Thanks, Ron

[racket]

LOL...........we're a tolerant lot here , it'll take a lot to get us annoyed , keep asking away , we're here to help :-)


jetandturbineowners.proboards.com/thread/680/diy-turbines just click on the icons

www.ebay.co.uk/itm/Model-Jet-Engines-3rd-Edition-Book-by-Thomas-Kamps/182992802331?hash=item2a9b38921b:g:pB0AAOSw6zheFftf

www.ebay.co.uk/itm/Acceptable-Gas-Turbine-Theory-H-Cohen-and-G-F-C-Rogers-1954-01-01-The-hinges/401750692717?hash=item5d8a35136d:g:kZAAAOSwNndctedu

[racket]

Hi

Further to my last email...............if we look at the GT3582 turb map www.garrettmotion.com/wp-content/uploads/2018/05/Turbine-Flow-GT35.jpg we see that a 0.63 A/R turb scroll can only flow ~23 lbs/min Correct Flow , the compressor map at a 2.5:1 Pressure Ratio will flow ~48 lbs/min Corrected Flow at a very good 79% efficiency www.garrettmotion.com/wp-content/uploads/2018/05/Comp-Map-GT-3582R.jpg.

If we do the calculations for the turb stage to find Actual Flow capacity we find that temps will need to be kept relatively low at say 550C for the TIT and maybe 450C TOT to allow an actual flow of ~30 lbs/min , which if we checkout the comp map will find us over near the surge line at a very poor 68% effic , this poor efficiency will require virtually all of the potential turb power to drive it.

The engine will most likely run , but there won't be scope for adding a jet nozzle .

If you can find a similar unit on Ebay but with the larger 1.06 A/R turb scroll which will increase the mass flow , you'll have some chance of making usable thrust.

Cheers
John

[wannabebuilderuk]

Thank you john, you've explained it perfectly so I now understand with what you've said plus the icon links the basis of calculating it all. I'm assuming you got the 2.5:1 from it being the highest number on the top "island" in relation to the flow rate?

So I want a turbo with a slightly larger turbine than compressor wheel and a high a/r ratio (that on both comp and turbine or just one side in general).

Thanks.

[racket]

Hi

Just the turbine side exducer needs to be bigger , as Ron mentioned , the turbine exducer area needs to be ~25% bigger in area than the comp wheel inducer ( bigger hole out than hole in ) and the turb scroll A/R needs to be a 1point something rather than 0 point something size.

The 2.5 PR limit is recommended when using the "inexpensive" chinese turbos to be on the safe side , "we gets what we pays for ".............same with keeping temperatures on the modest side as the turbine wheel material might not cope with high temps and high rpm/P2

All the best with your Ebay search

Cheers
John

[wannabebuilderuk]

If the compressor scroll is 0.7 would that still be useable if turbine scroll is <1.0 or are both scrolls the same a/r usually.

And yes I see, you don't know the makeup of the chinesium metal so for all you know it might catastrophically fail at high temp so best to stick to 2.5:1 and 650°c outlet.

Many thanks and I'll enjoy some light reading if I can get a copy of the books whilst not browsing the endless pages of ebay haha.

Ben

[racket]

Hi Ben

Comp scroll A/Rs need to be smaller than turb scroll A/Rs , probably ~50% bigger for the turb scroll , so if a 0.7 A/R on the comp , a 1.05 A/R on the turb

The Garrett GT6041 turbo I used on my kart build jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart had a 1.05 A/R on the comp and a 1.47 A/R on the turb .

There are slight variations each way , but aim for ~50% bigger A/R on the turb scroll and you won't be too far off especially if the turb exducer is ~25% bigger area than the comp inducer

Cheers
John