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A/R
Jan 18, 2022 18:17:49 GMT -5
Post by racket on Jan 18, 2022 18:17:49 GMT -5
Thats a very strange combination of comp/turb , with a 2.35" hole "in" and a 3.4" hole "out " , theres a 1:2 ratio of areas , a very large turbine , your comp is probably flowing well into the choke region of its map at very poor efficiencies .
I'd remove the jet nozzle and check for changes in temperature
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rickw
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Posts: 73
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A/R
Jan 18, 2022 20:32:10 GMT -5
Post by rickw on Jan 18, 2022 20:32:10 GMT -5
I did that and not much difference. its a Garrett T1224 variant from a Cat diesel.
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rickw
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Posts: 73
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A/R
Jan 18, 2022 20:33:24 GMT -5
Post by rickw on Jan 18, 2022 20:33:24 GMT -5
Does my combustor look ok? Fuel nozzle location?
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A/R
Jan 18, 2022 23:35:10 GMT -5
Post by racket on Jan 18, 2022 23:35:10 GMT -5
Hi Rick
Could you please have all your "contributions" about your engine on the one Build Thread please , I have problems answering as I need to go looking for your earlier components of the build thread .
From what I can gather , your turbine stage is grossly oversized for the comp stage thats feeding it , this allows the comp to flow in the low efficiency choke region of its map requiring high temps to "fill" that large turb scroll and produce the necessary gas speeds to produce enough horsepower to drive the comp .
Its a missmatch of components :-( a very low boost turbo setup with a large turb stage to minimise backpressure on the diesel engine .
What you can do is provide a fine spray of water that can be turned into steam in the combustor to help fill the oversized turb stage , it'll increase thrust as well
Cheers John
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rickw
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Posts: 73
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A/R
Jan 19, 2022 11:18:51 GMT -5
Post by rickw on Jan 19, 2022 11:18:51 GMT -5
Thx. John
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rickw
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Posts: 73
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A/R
Jan 19, 2022 13:12:38 GMT -5
Post by rickw on Jan 19, 2022 13:12:38 GMT -5
One last question. what kind of pressure should I have at the compressor outlet or combustion chamber say at full throttle?
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A/R
Jan 19, 2022 14:39:47 GMT -5
Post by racket on Jan 19, 2022 14:39:47 GMT -5
With your flow being in the choke region , you could very easily over rev the engine at quite modest P2 pressures from the comp , I wouldn't recommend any more than 15 psi until you can get a tach and check the RPM and workout a rpm that equates to a max tip speed of 1450 ft/sec of the biggest wheel .
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rickw
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A/R
Jan 19, 2022 15:40:51 GMT -5
Post by rickw on Jan 19, 2022 15:40:51 GMT -5
Thx John
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A/R
Jan 22, 2022 21:40:47 GMT -5
racket likes this
Post by finiteparts on Jan 22, 2022 21:40:47 GMT -5
I did some searching on the Cat T1224 turbos and all I am finding is that they are offered with Comp inducers = 58.46 mm (2.302 inch), with turbine exducers = 77.7mm (3.059 inch)...and two different turbine housing A/Rs, 1.34 and 1.54. Are you certain on your measurements? I might have missed something, but I have a pretty good source of info. At the above measurements, it puts you at and exit area = 1.77 x comp inducer area, which is a bit high, but I have experience with my T04B based engine which was sitting at a touch over 1.6 x comp inducer area, and it ran like a champ!
I also want to stress that the turbine exducer area does not set the turbine flow unless you at at extreme expansion ratios or you have oversized your turbine nozzle. The turbine system swallowing capacity is set by the scroll housing throat, which ironically is actually termed the tongue. Turbine housing A/R gives a good indication of the housing throat area.
If we had two similar turbos, except that one had a small A/R housing and the other had a larger A/R housing, for a given mass flow, the larger A/R housing would cause the turbine to produce less turbine power for a given mass flow, because it produces a lower swirl velocity at the turbine entrance.
Now if we were comparing those turbos at a similar expansion ratio, the one with a larger A/R will give you a larger corrected flow capacity and a higher turbine power.
The real trick is to estimate how both the expansion ratio and the mass flow will change for a single turbocharger if you ran it with two different A/R housings. The system will balance out and find it's happy place, but sometimes that happy place really isn't that happy. ha!
Since the power produced by the turbine stage is due to the change in the angular momentum of the gas as it passes through, the idea is to get as much angular momentum into the flow before it enters the turbine. You want to have as high a swirl as possible when entering the turbine and so, we generally take the largest portion of the pressure drop through the turbine nozzle. This means that the turbine nozzle is the controlling area and it will set the flow capacity of the engine. The only time the exducer sets the flow capacity of the engine is when the turbine nozzle is oversized or you are going above expansion ratios larger than approximately 3.57 (because you have to choke first in the turbine nozzle and then in the exducer).
Ok, so with all that in mind, I am not sure that you are running into the choked region of the compressor map. From what I can find, these turbos a commonly used on off highway 3306T's, which are designed to be efficient over a very narrow operating range, thus the odd sizing. The free flowing turbine side suggests that they are not wanting to have the compressor function as the scavenging device for the cylinders, and thus the flows should be fairly well matched between the compressor and the turbine. It also suggests that this turbo is likely designed to produce a low PR at the design point, so it may be that the turbo operates very off design if you are trying to take it to higher PRs. The large turbine would produce less available power to the compressor and thus they may have needed to reduce the size of the compressor wheel just to match the lower shaft power (because compressor power demand goes up roughly as the square of the tip diameter).
There are a lot of things that can cause a gas turbine to run hot. Without compressor and turbine maps or accurate measurements of the gas properties at key stations, it is very challenging to know what the root cause is. Can you provide any pictures of you combustor, fuel injector and other hardware? Do you have any air leaks? What does you lubrication system look like? etc...
Good luck,
Chris
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A/R
Jan 23, 2022 21:50:45 GMT -5
Post by racket on Jan 23, 2022 21:50:45 GMT -5
Hi Chris
One thing I've found can be a problem with running a choked NGV with its large energy transfer from the high speed gases is we need to restrict the "deflection" in the exducer otherwise the turb wheel becomes overpowerful.
Because the gases are "artificially" slowed down we end up requiring more flow area at times , its a bit of a juggling act with any wheel thats a bit marginal in the exducer flow area, having the overall pressure drop more evenly divided seems to help the flow "numbers"
When I was developing the TV84 I initially ran the largest scroll A/R a 1.84 , but soon found that temps got a bit hot even though thrust was high , a change to a 1.60 A/R improved things , but I then decided to radically clip the "choked" exducer which changed everything , I tried a 1.39 A/R and temps were still too high , the smallest scroll a 1.23 A/R choked the flow and all was well even though mass flow was probably down a tad on ideal.
In hindsight I feel the 1.39 with the standard exducer would have provided the best outcome .............LOL, hindsight is such a wonderful thing :-(
Thankfully with turbine maps sorta becoming more available we can make some reasonable guesstimates that save a lotta trial and error work .
Cheers John
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rickw
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A/R
Apr 26, 2022 17:53:21 GMT -5
Post by rickw on Apr 26, 2022 17:53:21 GMT -5
Chris, you are correct the turbine is 3.059 inches. My mistake. Sorry for the late reply. Been up to my neck in alligators lately.
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