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Turbine Inlet Temperature


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15 hours ago, GeeBee said:

The turbo is an exhaust driven turbine, it is attached to a compressor.

Bernoulli’s principle would suggest differently. The fact that there is a turbine restricting the flow of air raises the pressure, which increases the temperature. 
To be fair, and perhaps what you meant in your comment is that given the temps we are talking about, the increase is probably negligible, but it most certainly, is not neutral or cooling. 
The turbo concentrates heat simply based on its purpose, location and function. It most certainly creates heat as well, simply by the compression and increased pressure, but these are again, negligible compared to exhaust gasses. 
I guess it’s fair to say that the combustion/exhaust cycle is the origin of the heat, but it is focused and intensified in the turbo by receiving all cylinders cycles. 
I’m not sure we aren’t all saying the same thing….

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What I was trying to say is a "turbo" is consists of two different components, a turbine, and a compressor. While they are attached, they each have different work principles. One absorbs energy the other creates potential energy. While the turbine portion absorbs energy, the exhaust of a turbine is cooler than the intake. If this were not true, the air cycle machine, AKA "the packs" on a jet aircraft would never work. You can also see this in the EGT's on jet engines. Despite the same fuel and thrust the probes behind the turbine are cooler than those in front. 

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14 hours ago, A64Pilot said:

Yes but, there is always a but, the source of the kinetic energy is heat.

Just like the aircraft in flight, it has kinetic energy from airspeed, and potential from altitude, both came from heat from burning fuel.

 

Kinetic energy requires mass — “heat” has no mass.

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2 hours ago, GeeBee said:

What I was trying to say is a "turbo" is consists of two different components, a turbine, and a compressor. While they are attached, they each have different work principles. One absorbs energy the other creates potential energy. While the turbine portion absorbs energy, the exhaust of a turbine is cooler than the intake. If this were not true, the air cycle machine, AKA "the packs" on a jet aircraft would never work. You can also see this in the EGT's on jet engines. Despite the same fuel and thrust the probes behind the turbine are cooler than those in front. 

Air Cycle Machines cool air by expanding it, basically PV=nRT run the other way, by starting with air at much higher pressure.    They consume energy to do it (and therefore create more heat), but the excess heat gets dumped elsewhere, usually an air-air heat exchanger to outside air.    The turbo exhaust temp and pressure go down compared to the input because the energy was used to do work elsewhere, specifically compress the intake charge.

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A turbo does raise temps by restricting airflow, this raises pressure and therefore the temp, but as the pressure increase is so small, it likely not measurable.

You raise the temp of the air in a balloon when you blow it up, but again as the pressure increase is so small the balloon doesn’t get hot, it’s temp increase is miniscule.

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22 hours ago, Will.iam said:

Torrey 380 is your cylinder head temperature (cht) your exhaust gas temperature (egt) is closer to 1400 to 1500 and is the same exhaust gas that flows down to the turbo cooling somewhat but then rises a little when it gets compressed to the turbo fins to spin the turbo. And reads higher than the individual probes because the tit probe is exposed to all 6 cylinders exhaust gases not just one and gives the tit probe a higher temp because of this.  

Yep, I am a dummy. The post was comparing EGT, not cylinder head temperature! I sometimes just open my mouth to change shoes!

Thanks for setting me straight, Will........ I hope MS doesn’t have a dummy of the day award!:(:lol:

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10 minutes ago, T. Peterson said:

Yep, I am a dummy. The post was comparing EGT, not cylinder head temperature! I sometimes just open my mouth to change shoes!

Thanks for setting me straight, Will........ I hope MS doesn’t have a dummy of the day award!:(:lol:

No problem we all make mistakes, Or reference the wrong things. I just didn’t want you to think your turbo was 3 x your egt temps that would be a head scratcher. 

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58 minutes ago, GeeBee said:

Two things are happening. One air is rapidly expanding and two it is being relieved of energy by doing work, turning the turbine.

Same as the air cycle AC, except I don’t think the pressure drop is all that much in a turbo as I don’t think there is that much back pressure on the engine

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About 20 years ago we did a research project on a F-250 diesel turbo. We mounted pyrometers both before the turbine and after the turbine as well as pressure sensing of the compressor itself. Our goal was to determine the amount of "cool down" and "spin down" required for some high performance ball bearing turbo units. What was surprising is at power, after 10 minutes run time at power, how much heat was removed by the turbine itself. About 350-400 degrees difference between the "TIT" probe and the nearest exit probe. What was equally surprising was the ball bearing turbo while having excellent acceleration required more cool down time that the stock unit because it being a billet machined compressor wheel vs the lighter cast unit and having ball bearing maintained a higher RPM longer creating a greater heat of compression. Generally the stock unit after 1 minute of idle was ready for shut down whereas the ball bearing unit was about 2.5 minutes

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10 minutes ago, GeeBee said:

About 20 years ago we did a research project on a F-250 diesel turbo. We mounted pyrometers both before the turbine and after the turbine as well as pressure sensing of the compressor itself. Our goal was to determine the amount of "cool down" and "spin down" required for some high performance ball bearing turbo units. What was surprising is at power, after 10 minutes run time at power, how much heat was removed by the turbine itself. About 350-400 degrees difference between the "TIT" probe and the nearest exit probe. What was equally surprising was the ball bearing turbo while having excellent acceleration required more cool down time that the stock unit because it being a billet machined compressor wheel vs the lighter cast unit and having ball bearing maintained a higher RPM longer creating a greater heat of compression. Generally the stock unit after 1 minute of idle was ready for shut down whereas the ball bearing unit was about 2.5 minutes

Did you measure how much energy was being moved to the compressor side?   The pressure and temp drop across the turbine will be due to a few things, the big effect in a turbocharger is that the energy is being extracted to do work elsewhere, so the more efficient that is the more the temperature and pressure will drop across the turbine.   You might have seen different results with different boost levels at the output, particularly high boost vs completely vented to atmosphere.  In the Air Cycle Machine the purpose of the device is to provide cold air, so the efficiency of the expansion at the outlet is more important than doing work elsewhere, so the optimizations will be different.   The physics is similar but the optimizations of what is happening and where the energy is going is a bit different.

But generally, yeah, when input pressure and temperature is used to do work somewhere there will be less energy in the output, and when pressure is dropped quickly the temperature goes down.  A turbocharger does work elsewhere, and an ACM chills air.   It's kind of cool that they're very similar in many ways.

My understanding is that the most modern turbine engines lose too much efficiency if bleed air is drawn out, so many newer airplanes use vapor cycle air conditioners instead of ACMs these days.

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The newer Turbo Diesels are water cooled center sections I believe and you can get away with no cool down.

My little Mazda Speed turbo is surprisingly a ball bearing turbo, personally I like the BB turbos, more tolerant of short oil pressure losses and seem to last longer, but there is more mass and mass retains heat. Tanstasfl. I had a pyrometer on my Dmax, and the tuner box I had allowed me to set an EGT limit where it would drop to stock fueling, I set it to 1400 F and would hit it every now and again.

It was interesting to me to see that Diesel EGT ran so much lower than spark ignition motors, I believe that’s because Diesels operate super LOP. If memory is right normal driving it never exceeded 1000 F

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27 minutes ago, EricJ said:

My understanding is that the most modern turbine engines lose too much efficiency if bleed air is drawn out, so many newer airplanes use vapor cycle air conditioners instead of ACMs these days.

That’s one consideration, A model Apache had an air cycle AC, but we ran it off of a shaft driven compressor, essentially a big turbo that was driven off of the transmission, we didn’t use bleed air for anything.

Air cycle units work really well in humid air partially because when humid air is cooled the water drops  out, this water was taken and sprayed onto the heat exchanger greatly improving its function, thing worked so well it would blow ice pieces out of the AC ducts in Alabama

So go to the desert, no humidity so it didn’t cool for squat, I’m sure the heat had a lot to do with it, but we flew whole missions with the temp warning for the black boxes on the whole time, we had never seen that light before, even in Texas.

When the Longbow was built it had dual 7.25 ton Vapor cycle units, for a total of 14.5 tons of AC, average house is maybe 3 tons. You should see the aircraft in humid environments the whole thing just about was wet and dripped water like an iced drink glass.

But they were heavier than the air cycle unit and used a bunch of electrical power, but we had dual 60KVA AC generators though so we had power to burn.

But the takeaway is vapor cycle units (AKA airconditioners) just work so much better, especially in hot weather

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3 hours ago, EricJ said:

Did you measure how much energy was being moved to the compressor side?   The pressure and temp drop across the turbine will be due to a few things, the big effect in a turbocharger is that the energy is being extracted to do work elsewhere, so the more efficient that is the more the temperature and pressure will drop across the turbine.   You might have seen different results with different boost levels at the output, particularly high boost vs completely vented to atmosphere.  In the Air Cycle Machine the purpose of the device is to provide cold air, so the efficiency of the expansion at the outlet is more important than doing work elsewhere, so the optimizations will be different.   The physics is similar but the optimizations of what is happening and where the energy is going is a bit different.

But generally, yeah, when input pressure and temperature is used to do work somewhere there will be less energy in the output, and when pressure is dropped quickly the temperature goes down.  A turbocharger does work elsewhere, and an ACM chills air.   It's kind of cool that they're very similar in many ways.

My understanding is that the most modern turbine engines lose too much efficiency if bleed air is drawn out, so many newer airplanes use vapor cycle air conditioners instead of ACMs these days.

Well the 787 tried going with electric driven compressor with just air expansion, it was insufficient. Had to add refridgeration evaporator to the system, still more efficient than bleed air. However it is "back to the future" as the 707 had freon backup too, an FAA requirement based on the distrust at the time of ACMs.

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From an efficiency perspective not much more efficient than a heat pump, which is nothing more than a reversible AC.

The newer Tesla’s have heat pumps because in cold weather resistance heating ate up huge amounts of power, as much as 40% of the batteries power was used to heat the car, however in real cold weather the Tesla heat pump is no more efficient, with a COP of 1.

I should imagine an airliner just like the Longbow, uses bleed air for heat, it’s easy to heat with an essentially unlimited amount of 400F air under pressure.

I would also image the cooling is really only needed on the ground, up at 30,000 ft surely your heating

An air cycle cooler is I believe terribly inefficient by comparison 

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6 minutes ago, GeeBee said:

However it is "back to the future" as the 707 had freon backup too, an FAA requirement based on the distrust at the time of ACMs.

That's a little weird since ACMs are far more historically mature than vapor cycle refrigeration.    ACMs were invented not long after steam power came along and allowed power distribution via compressed air.   There were steam ships with ACM refrigerated holds for shipping perishables long distances in the 1800s.   It was a big shipping innovation at the time.

Lear Jets, at least the early ones, used vapor cycle refrigeration as well.   It's kind of interesting to see the mix in turbine powered airplanes of which use vapor cycle and which use ACM.   I initially thought that ACMs were kind of a slam dunk since they provide both pressurization and AC at the same time, but the tradeoffs are apparently more complex on smaller aircraft.

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On 11/23/2022 at 10:15 AM, LANCECASPER said:

This subject has been asked and answered many times on Mooneyspace. Since on every turbo-charged airplane I've owned, the TIT has always been higher than the highest EGT, I just accept that's the way it is. Although the answers I've read over the years seem to make sense, while I don't fully understand it, the reality is that the TIT is always higher than the hottest single EGT reading, so I go with it. 

@Brandt after two pages of posts trying to explain it, you now see why I just accept it. :D

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