hosedup
Junior Member
Joined: October 2019
Posts: 68
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Post by hosedup on Oct 27, 2019 18:49:39 GMT -5
So I started here jetandturbineowners.proboards.com/thread/680/diy-turbines and learned I learned quite a bit, but I still have a few questions. My engine build is going to be based on a T3T4 turbo and I plan on using propane in the beginning. At some point I may go with kerosene or even add an after burner or both, but for now, just propane. My main questions are in regards to the combuster. Im pretty sure the answer is no, but is there a reference design or a known good design that is out there for a small unit like a T3T4? I would lie with known good before I modify. Baby steps and such. Ive played with jetspecs a bit, inducer dia as 50mm, it suggests primary holes 6mm x 21, secondary 10mm x 5 and tertiary 16mm x 5. One thing I cant figure out is position such as number of holes per row, number of rows and row position. For diameter, 150mm was suggested but I would like to go with 115mm because I already have a bunch of stainless pipe this size. Length of 300mm. I would appreciate any insight from the veterans of this hobby.
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Post by racket on Oct 27, 2019 21:01:16 GMT -5
Hi
Is your turbo a hybrid with large compressor and smaller turbine ??
What size is turbine wheel exducer ??
If you have a look through the various build threads you'll probably find something similar to get ideas from
Cheers John
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hosedup
Junior Member
Joined: October 2019
Posts: 68
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Post by hosedup on Oct 28, 2019 7:16:56 GMT -5
Hi Is your turbo a hybrid with large compressor and smaller turbine ?? What size is turbine wheel exducer ?? If you have a look through the various build threads you'll probably find something similar to get ideas from Cheers John Hi John. It appears to be a hybrid, compressor is bigger. The exducer is 57mm. Edit: According to the castings, compressor AR is .5 and .58 for turbine. I'm noticing 2 basic differences in combustor design. One where the air comes in on the side of one end and exhaust out the other end and the other design, the air comes in on the same end as the exhaust. Is one better than the other or is the choice based on material availability and size constraints?
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Post by racket on Oct 28, 2019 15:33:52 GMT -5
Hi
Those A/R sizes aren't filling me with confidence that this is a suitable turbo to use .
I'm also not certain about that turb wheel exducer dia of 57mm , the turb wheel exducer is the "outlet hole" , unlike the comp wheel , what are the turb wheel dimensions , in , out and inlet "axial" tip height .
As for combustors , keep the delivery tube well away from the Primary Zone end to avoid combustion "problems"
Cheers John
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hosedup
Junior Member
Joined: October 2019
Posts: 68
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Post by hosedup on Oct 29, 2019 6:18:53 GMT -5
Hi Those A/R sizes aren't filling me with confidence that this is a suitable turbo to use . I'm also not certain about that turb wheel exducer dia of 57mm , the turb wheel exducer is the "outlet hole" , unlike the comp wheel , what are the turb wheel dimensions , in , out and inlet "axial" tip height . As for combustors , keep the delivery tube well away from the Primary Zone end to avoid combustion "problems" Cheers John I just remeasured the inducer and exducer. Exducer hole is 57mm with ~0.5mm gap to housing. Inducer opening is 65mm, necks down to 51mm, blades are 50mm. Not sure what exactly you are asking for on the turbo wheel dimensions, but this is what I measured. The largest diameter of the wheel (inside the housing) is 65.5mm, height is 25mm. From what I'm gathering, it sounds like this turbo may be less than ideal and thus, less forgiving. I know this will sound very lazy and newb like, but can you suggest a combustor design that has a good chance of working? It is the only part of the project that I'm really unsure about. I either own or have access to drill press, mill, welder (stick mig tig) plasma cutter, rolling mill, shear, etc. My ultimate goal is to make an engine I can play. I don't have any thrust goals or plans to power a go cart. I may try kerosene at some point but for now I'm going to run propane.
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Post by turboron on Oct 29, 2019 13:11:19 GMT -5
hosedup, what John is saying, based on our experience, is that the turbine exducer outlet area needs to be larger than the compressor impeller inlet area for a successful DIY Gas Turbine. Preferably, the turbine exducer outlet area will be 25% larger than the compressor inducer inlet area. The air flows in the compressor inducer (small diameter) and out the exducer (larger diameter). The turbine nomenclature is the opposite to that of the compressor. The hot gas flows into the turbine inducer (large diameter) and out the exducer (small diameter). A little Googleing on Turbochargers will help you.
Thanks, Ron
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Post by racket on Oct 29, 2019 16:31:37 GMT -5
Hi
Try and keep temperatures low (500-550 deg C .....900 -1,000 F ) by not adding a jet nozzle downstream of the turbo , just a short length of "exhaust" that a thermocouple can be fitted to .
Cheers John
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hosedup
Junior Member
Joined: October 2019
Posts: 68
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Post by hosedup on Oct 29, 2019 20:16:46 GMT -5
hosedup, what John is saying, based on our experience, is that the turbine exducer outlet area needs to be larger than the compressor impeller inlet area for a successful DIY Gas Turbine. Preferably, the turbine exducer outlet area will be 25% larger than the compressor inducer inlet area. The air flows in the compressor inducer (small diameter) and out the exducer (larger diameter). The turbine nomenclature is the opposite to that of the compressor. The hot gas flows into the turbine inducer (large diameter) and out the exducer (small diameter). A little Googleing on Turbochargers will help you. Thanks, Ron Ron, unless I'm doing math wrong (and is highly likely dude being late) inducer opening is 50mm and exducer opening is 57mm which comes to 14% larger. Do you think this is still workable?
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Post by racket on Oct 29, 2019 22:53:10 GMT -5
Hi
Your turb scroll A/R is rather small at 0.58 when matched with a 0.5 comp scroll , the turb scroll will probably choke pretty easily and mean the exducer will be OK at that size, but your compressor is more inclined to surge .
Remember that a turbine engine can"t force gases through a small turbine stage like a piston engine can , our turb stage needs to swallow it voluntarily , it can't generate "higher exhaust pressures" like the pistons can , where exhaust manifold pressures can be considerably higher than inlet manifold ( boost) pressures , our turbine stage inlet pressures are always lower than comp outlet pressures.
Cheers John
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Post by turboron on Oct 30, 2019 7:21:05 GMT -5
hosedup, I have a T4/T3 which means it has a Garrett type T4 compressor and a T3 turbine. Their supposed advantage is more airflow at the lower rpms and lower polar moment of inertia for quicker spin up to speed for drag racers. The dimensions of mine are:
Inducer Compressor 55 mm Turbine 65.5 mm Exducer Compressor 76 mm Turbine 55.9 mm
I have not used this as a DIY gas turbine. I bought it primarily to get some cheap parts.
It might create a marginal DIY gas turbine in that it would run a idle without an exhaust restriction. However, it you tried to pull some power it would fall on its face.
You would be better off buying a used Garrett T3 on eBay or at a junk yard with better numbers.
Thanks, Ron
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Post by turboron on Oct 30, 2019 8:01:06 GMT -5
John, what is your method or "rule of thumb" on compressor and turbine A/R ratios. All I know is the more area at a given radius the more top end flow before the turbine scroll chokes (reaches sonic velocity). On the compressor side I am sure that the scroll backpressure on the impeller due to restricted area can cause surge at some point. However, you seem to have observed some relationship between compressor scroll A/R and turbine scroll A/R. Please share this insight.
Thanks, Ron
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Post by racket on Oct 30, 2019 16:47:21 GMT -5
Hi Ron An A/R of ~50% bigger for the turb stage scroll is probably a reasonable figure , though there are a lot of variables with that assumption . If we take the Garrett G25 www.garrettmotion.com/racing-and-performance/performance-catalog/turbo/g-series-g25-550/ comp 48/60 mm turb 54/49 mm , comp A/R 0.7 , turb A/Rs 0.49 0.72 and 0.92 , flowing a corrected 15 , 20 and 24 lbs/min at 2.5 PR across the stage , with the comp at say 40 lbs corrected at 3.3 PR . If we had a 5% drop across the flametube there'd be a 3.13 PR going into the turb , if we Correct for a 1,500 deg F TIT , then that 40 lbs/min from the comp becomes ~24.8 lbs Corrected going into the turb stage , the only scroll to use would be the 0.92 A/R scroll, which is a ~31% greater "size" than the comps 0.7 A/R If the 0.49 A/R scroll was used with only 15 lbs/min Corrected , then the comp flow would need to be reduced to ~60% of the 40 lbs , so only 24 lbs/min , which for this compressor wheel is still possible due to its extremely wide map , but any thrust we got from this engine would be severely reduced , not only from only 60% mass flow , but the low efficiency of the comp at that flow would require more pressure drop across the turb stage leaving virtually no pressure for expansion in a nozzle. If the turbo was an older style with a "normal??" map width of ~2:1 , then surge of the comp would be a distinct possibility, also if more than 1,500 F was being used for the TIT , say 1,650 , then Corrected flow into the turb would increase by ~4% , which for the G25 would mean that even their biggest scroll A/R would be "undersized" . Cheers John
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Post by racket on Oct 30, 2019 19:21:01 GMT -5
Hi Ron At the other end of the scale www.garrettmotion.com/racing-and-performance/performance-catalog/turbo/gtx5544r-gen-ii/ 200 lbs/min at 4:1 PR and a 0.96 A/R , a very nice high flowing wheel . The turb stage has a range of scrolls on a 112/102mm wheel , from a 1.00 A/R up to a 1.78 A/R www.garrettmotion.com/wp-content/uploads/2018/11/Turbine-Flow-GT55.jpg with Corrected flows from 57 to 69 lbs/min on the 1.40 scroll , max efficiency a lowly 74% though . Lets use our 1650 F TIT for this high performance turbo , a 3.8 PR into the scroll and a 2.5 PR across the stage , a Corrected Flow of 69 lbs/min becomes an Actual Flow of 130 lbs/min ...........mmmmmm, thats a bit shy of the comps 200 lbs/min , and will be out in the surge region despite the turb scroll being 46% bigger ( 1.4 vs 0.96) .................this turbo needs a bigger 130/119mm GT6041 turbine wheel and scroll for it to be a proposition for us to use . This beautiful GEN 11 turbo is useless for us , an old 1980's vintage GT6041 turbo will produce more thrust, even our TV94 units would be competative . Unfortunately Garrett is now going down the "performance path " , beautiful high flowing and efficient compressors sadly "complemented ??" by turbine stages meant for performance IC engine use , great for a racetrack but not for making a turbine engine from . Some of the smaller GEN 11 turbos have slighly better combinations of comp/turb sizing , but most need the next bigger size of turb stage to be useful for us. My current feeling is that the Holset/Cummins range of large turbos meant for heavy duty use is a better place to look for rotating bits , a "standard" HX82 turb wheel will have 129/112mm dimensions and is probably the reason why the tractor pulling guys are using them ..................unfortunately theres not many maps available , especially turbine maps , but we can extrapolate some info by using the Garrett ones for a similar sized wheel . Cheers John
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Post by turboron on Oct 30, 2019 20:05:26 GMT -5
John, very helpful information. Thinking out loud it seems that the turbine analysis is clear. What is not clear to me is the compressor part. Your observation is based on the stated compressor scroll a/R of .7 which is the scroll used to create the map. What happens if we replace the .7 compressor a/R scroll with a .90 a/R compressor scroll and repeat the test. We probably reduced the possibility of surge at a given flow and pressure ratio due to reduced backpressure. I am not sure what would happen to the rest of them map. Do you have any data on what happens to the map as the scroll a/R is increased?
Thanks, Ron
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Post by racket on Oct 30, 2019 20:48:14 GMT -5
Hi Ron
Generally theres no replacement comp scrolls available , only for the turbine stage , comp wheel and its scroll A/R are a "matched pair" , probably there'll be a loss of efficiency with a change of A/R or simply a shift in the operating line as when a comp's diffuser vanes are changed .
Cheers JOhn
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