dieselguy86
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Post by dieselguy86 on Oct 14, 2021 20:31:48 GMT -5
Hi everyone,
Turbine and ngv have arrived. After getting scammed for $350, then multiple dead ends in China, I finally ponied up and bought the 85mm setup from jetmax. I am very impressed with the quality, and it came with documentation of the alloy % and xray certified. It was double the price, but I'm glad I went that way. The size of it has me second guessing using a 7" case. The micro pwm valve driver will be in soon, getting parts has been painfully slow. But atleast now I can calculate the shaft diameter needed and make sure the bearings I have will be sufficient. -Joe
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dieselguy86
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Post by dieselguy86 on Oct 8, 2021 5:20:32 GMT -5
It's also worth noting that your diffuser has 12 wedges, which matches up with the compressors 12 blades. I've always been told this is a no-no.
-Joe
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dieselguy86
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Post by dieselguy86 on Oct 7, 2021 20:03:46 GMT -5
The diffuser is definitely crappy. The point next to the compressor wheel should be a sharp point, the pics I seen on their site shows a very blunt point. Also in your video, do you have any oil going to your bearings?
-Joe
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dieselguy86
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Post by dieselguy86 on Oct 3, 2021 14:21:45 GMT -5
Hi Chris,
My rotor will probably be ~30% of the gt55's weight, so direct copying isn't possible.
My thought was to basically float the shaft tunnel/ bearing cartridge in another shaft tunnel, with only about .002"-.0025" diametric clearance. Basically treat it like a semi-float journal bearing. The gt55 cartridge has some deep grooves in it that I assume act as an "accumulator?" of sorts and probably handle the actual dampening forces. My GMN 61900 bearings are custom made with direct lube, where small holes were edm'd through the outer races to the non thrust side of the balls. I could position a groove directly over the bearing and use it as a reservoir of sorts to supply oil to the bearings.
This brings up another question, is the heat the bearings receive mostly from operation? Or do they get a large portion from the radiant heat from the cc, or soakback from the turbine, or both? Having the bearings isolated from a radiant heat source would have to help them live.
-Joe
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dieselguy86
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Post by dieselguy86 on Oct 2, 2021 18:56:31 GMT -5
Hi again guys,
I was looking at the ball bearing cartridge out of a Garrett gt55 turbo. They did something neat with it, where the cartridge floats on a film of oil for dampening.
While I was working on designing the shaft tunnel for my engine I was wondering if I could do something similar. Where my bearings are in their respective "shaft tunnel" or cartridge, and that is inside an outer "tunnel". An anti rotation pin will have to be utilized, but im curious if this could work? I know dampening is a big issue, and there's way smarter people than me in here. I'm trying to design this engine for as long of a service life as possible. The regular 25-50hr maintenance interval of the rc turbine will not cut it.
I've seen some use o rings, but I'm worried about how long those would survive on the turbine end.
-Joe
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dieselguy86
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Post by dieselguy86 on Sept 30, 2021 13:02:39 GMT -5
John, Chris,
I'm curious about total pressure, it's the added affect of gas speed correct? What role does it play in the calcs on the turbine side? Using previous example of a pr drop of 2 for a turbine, is the total pressure "added on" to the static? So that 2 pr drop is still 2 but static pressure wise it looks to be less because a portion of that is from the gas speed?
I'm trying to not make a long post, but my idea is this... currently figured of a 5.6pr in the manifold, which is static. Let's say total pressure is 6pr. Is the pr drop through the turbo still 2 but say only 1.5 of it is static while the other 1.3 is total. So it would look like (5.6 static/ 1.5 static = 3.7)
Or is it with total pressure the pr drop is higher. I'm just making sure these expansion ratios im figuring are realistic.
-Joe
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dieselguy86
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Post by dieselguy86 on Sept 26, 2021 19:07:08 GMT -5
Hi Chris,
As always, your answer is very thorough and well explained.
The moment the light bulb went off in my head is when John said that the lp turbo must be twice the size if the expansion ratio is to be equal to the hp. One of those aha, "I feel like an idiot".
Then once he explained how to correct flow, I was able to quickly follow along.
I felt like I had a pretty good understanding of things, then you and John come along and blow me out of the water.
I love this place lol
-Joe
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dieselguy86
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Post by dieselguy86 on Sept 25, 2021 19:24:54 GMT -5
Hi John,
How did you figure out what pr was needed in the manifold to squeeze 165lb/min through the hp turb? Only way I can think of is to use the continuity equation in Thomas Kamps book, assuming gas speed would be mach (choked) and rearranging it to solve for pressure. Is there a simpler way?
As I was playing with all the numbers today on another system (for myself) I worked out a crazy gas velocity of 1,922ft/sec thru a turbine. Knowing that was well above mach, I was curious what mach would be at 1,400°, and some online calculators all said 1,820ft/sec, which seems crazy. They also said pressure doesn't matter, but I always thought pressure did change speed of sound, any of that make sense?
-Joe
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dieselguy86
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Post by dieselguy86 on Sept 25, 2021 7:53:25 GMT -5
Hi John,
No we don't, just in the manifold. I would like to add more though, especially when we get the inter-stage cooler installed. I bet if we would of had 2 drive pressure gauges we would of noticed the gt55 being too small.
-Joe
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dieselguy86
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Post by dieselguy86 on Sept 24, 2021 23:43:18 GMT -5
Hi John,
Don't forget, and this might muddy things up some, but we have wastegates on both turbos. So we can dump the excess, with the hp stage im limited to the factory gate, which I think is around 25mm. The lp currently has a 38mm gate, but I can upsize that to 44mm if needed. Wouldn't the addition of "fresh" exhaust out the hp gate raise the gt60 itt, helping to keep the pr down "some"?
Plus, we can live with some drive pressure, acceptable would be ~1.2:1, maybe 1.5 at the very high end.
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dieselguy86
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Post by dieselguy86 on Sept 24, 2021 20:28:28 GMT -5
Hi John, You may remember, but I just happen to have a brand new gt6041 in my shop. Other thing to do would be to add a second gt55, but that's quite a bit of plumbing work. This is the info I'm missing out on. Would there be any way you could break it down into steps on how you figured all that out? It doesn't even need to be all in one go, even one step a day/ couple days so I could post process it. I've known that if I could calculate things in the manifold, then I could figure out the rest, but how do you know what speeds the gasses are flowing? How do you calculate the flow potential through the housings when you don't know the area of the throat? How do you correct the flow? The hp turbo is using a wastegated housing, so does that help the ~10% extra were trying to shove through it? I already know what your going to say, it's in Rodgers and Cohen's book lol, it's been m.i.a since June/ July when we packed up for the move. Wife handled the house, which is where all my books were at. I know you're busy doing your build, as well as advising everyone else, so I get it if you don't have the time to do a break down. Don't feel bad to say no -Joe
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dieselguy86
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Post by dieselguy86 on Sept 24, 2021 9:01:40 GMT -5
Hi John,
You are correct, 2.25 x 2.25pr is the goal. Right now the engine is basically not using the hp turbo. Wouldn't a properly working hp turbo lower the energy density going to the lp, somewhat acting like a larger a/r housing?
Currently the high pressure is a factory stock Garrett gt47, 74mm x 102mm compressor, 92mm x 83 turbine. Right now we're using a 1.42ar housing on it, with option of 1.27 housing.
The low pressure is a gt55, 112/102 turbine, 94mm x 123mm compressor, currently running a 1.24a/r open housing. Next a/r housing up is a 1.4, which I've been thinking about.
Airflow should be around 165lb/min, 2.75lb/sec. But will probably be close to 3lb/sec once we can get the hp turbo to start doing more and raise overall boost to 70psi. The egts can run hot at the high end, which tells me boost and airflow aren't where they need to be yet. My designed itt is 1200°f.
No inter-stage cooler yet, has it but I need to go back down to install it for him. The numbers showed something like a .4 increase in expansion ratio required to compress the hot air vs cooled, which is a big deal when there is another turbo downstream requiring its own exp ratio.
Truck runs good, it's making ~1500hp @ 60psi at 1:1, but its internally eating at me that the turbos aren't doing their equal share. I feel I need to understand why so I can work out future systems.
I have another garrett hp comp from John Deere and guess what, it's 43 trim. My plan now is to trim a billet 74 x 115 comp to 72mm, which raised my question of if I need a low trim turbine to power a low trim comp. I'm going machine out the map width enhancement groove in the housing and insert a solid chunk and taper the inlet to the inducer. I'm wondering if the map groove is helping to shove so much air into the wheel that the turb needs an excessive pressure drop to power it. Also going to make up a flow straightener, I think the gt55s compressor flow is spiraling against the gt47s rotation.
There's alot going on and I'm 1,500 miles away from the problem.
-Joe
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dieselguy86
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Post by dieselguy86 on Sept 23, 2021 16:49:05 GMT -5
Hi all,
This is a question for the experts, or guys that are/were in the design field. If I'm wrong someone correct me, please. We all know compressor trim affects the compressors pr capability at any given shaft speed. My question is, does turbine wheel trim correspond with the expansion ratio it is capable of?
I've been working with a guy who has twin turbos on his semi truck (that I built for him, I added a turbo over the factory gt47 turbo). I'm aware that with compounds turbos, the pr "load" should be equally split between both stages. In this case both should be doing 2.25pr each, but he's found its been working better with the low pressure doing 3.3 and the hp 1.5. Trying to make the hp do more immediately makes the exhaust drive pressure climb really high, really quick. With the 3.3/1.5 split drive pressure is close to 1/1 most of the way until the end of the revs where it starts to exceed boost, which I think is to be expected.
I've since gotten ahold of a factory compound turbo and found that their hp compressor has a really low trim of .43, the one were trying to use currently is ~55. So I ordered a billet wheel that I'm going to re profile to achieve the same trim. The same is true for the factory hp turbine wheel, it's a 76 trim, where all the other "normal" gt42 turbines are 84 trim. So will it be necessary to re profile the gt47 turbine we are using to a lower trim in order to drive the low trim compressor? I'm just wondering what all turbine wheel trim affects, I really don't want to have to re profile turbine wheels.
-Joe
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dieselguy86
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Post by dieselguy86 on Sept 21, 2021 21:22:50 GMT -5
Dang John, build quality so nice it would make GE jealous.
-Joe
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dieselguy86
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Post by dieselguy86 on Sept 7, 2021 21:49:54 GMT -5
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