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What Is A Turbomeca Astafan?  
User currently onlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Posted (4 years 10 months 1 week 22 hours ago) and read 13595 times:

Okay, well, here's this picture:


View Large View Medium
Click here for bigger photo!

Photo © Doug Green



Were the Turbomeca Astafans some sort of a ducted fan? Was this particular conversion very popular (or even successful)?

2H4, are you watching (I sense Doomsday Vault photos...)   


Celebrating the birth of KELPkidJR on August 5, 2009 :-)
34 replies: All unread, showing first 25:
 
User currently offlineBrenintw From Taiwan, joined Jul 2006, 1723 posts, RR: 1
Reply 1, posted (4 years 10 months 1 week 21 hours ago) and read 13604 times:

Wikipedia has some information on it (however accurate it may be).

http://en.wikipedia.org/wiki/Turbomeca_Astafan

The pic you have posted appears to be one of two test-bed aircraft for the engine. It never made it into production.



I'm tired of the A vs. B sniping. Neither make planes that shed wings randomly!
User currently offlinejetmech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 2, posted (4 years 10 months 6 days 21 hours ago) and read 13123 times:

Quoting KELPkid (Thread starter):

Interesting bit of kit. Geared fan with variable pitch blades, axial / centrifugal compressor, designed to operate at a constant RPM.

http://i94.photobucket.com/albums/l118/Jet-Mech/astafan.jpg

I wonder if a similar concept ( variable pitch fan with constant RPM operation ) would be beneficial for larger engines; provided such a design is technically feasible at such a scale?

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineLarshjort From Niue, joined Dec 2007, 1527 posts, RR: 0
Reply 3, posted (4 years 10 months 6 days 11 hours ago) and read 13025 times:

Quoting jetmech (Reply 2):
Interesting bit of kit. Geared fan with variable pitch blades, axial / centrifugal compressor, designed to operate at a constant RPM.

That does indeed look very interesting, it looks like an attemp to get turboprop like operation but avoiding the propeller
Hers a test flight article from 1978
http://www.flightglobal.com/pdfarchive/view/1978/1978%20-%202750.html

/Lars



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
User currently offline2H4 From United States of America, joined Oct 2004, 8956 posts, RR: 60
Reply 4, posted (4 years 10 months 6 days 11 hours ago) and read 13031 times:
AIRLINERS.NET CREW
DATABASE EDITOR

Quoting KELPkid (Thread starter):
2H4, are you watching (I sense Doomsday Vault photos...)

This one was new to me. It's certainly worthy of the Vault, but it's now too well-known to include in the next round of Identify This (which I really need to kick off soon).

Anyway, this Astafan testbed reminds me of G-FANS:


View Large View Medium
Click here for bigger photo!

Photo © Martin Stephen




Intentionally Left Blank
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 5, posted (4 years 10 months 6 days 10 hours ago) and read 12959 times:

Quoting KELPkid (Thread starter):
KELPkid

Aww you beat me to it. I was gonna start a thread on this contraption. At least I wasn't lazy and at least I bothered doing a google search to educate myself before hand     
Quoting jetmech (Reply 2):
provided such a design is technically feasible at such a scale?

Me thinks anything larger than this would see a significant increase in fuel consumption. Unless you had a ridiculous gearing reduction to use a relatively tiny engine core and a huge fan, but that would create a myriad of other problems.

I find it interesting that both the engine and the prop are governed.

Aren't there a few turboprops out there that have constant speed single shaft engines as well? I want to say the Garret TPE331 is one but not sure.

Quoting 2H4 (Reply 4):
This one was new to me.

  


User currently offlineLarshjort From Niue, joined Dec 2007, 1527 posts, RR: 0
Reply 6, posted (4 years 10 months 6 days 9 hours ago) and read 12939 times:

Quoting FLY2HMO (Reply 5):
Aren't there a few turboprops out there that have constant speed single shaft engines as well? I want to say the Garret TPE331 is one but not sure.

It is, as is the Allison T56

/Lars



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
User currently onlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 7, posted (4 years 10 months 6 days 9 hours ago) and read 12929 times:

Quoting FLY2HMO (Reply 5):
Aren't there a few turboprops out there that have constant speed single shaft engines as well? I want to say the Garret TPE331 is one but not sure.

Ahh, so THAT's why you can't turn MU-2 or Turbo Commander props on the ground by hand   When I was a lineboy, I always loved anything with a PT-6 in it, it was so cool to effortlessly spin the prop blades out of the way (because of the pT-6's free turbine design)   That and the sounds that PT-6's make are incredibly cool. TPE331's are just LOUD.



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 8, posted (4 years 10 months 6 days 9 hours ago) and read 12916 times:

Quoting Larshjort (Reply 6):
It is, as is the Allison T56

Ah yes another weird engine. I never understood the logic of having the gearbox so far forward in that thing.

So in these engines the prop basically acts as the engine's governor as well right?

Been a while since my turbines class, need to freshen up   

Quoting KELPkid (Reply 7):
Ahh, so THAT's why you can't turn MU-2 or Turbo Commander props on the ground by hand

Hmmm, so you actually can't or you just shouldn't?   

We had a display TPE331 in our turbines class and it spun freely, mind you, it didn't have any accessories connected at all, so I'd imagine it would be a bit tougher to move than a free wheeling PT6. But a fully assembled Garrett would not horribly hard to spin like a piston engine, or is it?   


And yes I'm feeling nerdy today 


User currently offlineA342 From Germany, joined Jul 2005, 4722 posts, RR: 3
Reply 9, posted (4 years 10 months 6 days 7 hours ago) and read 12888 times:

Quoting FLY2HMO (Reply 5):
Aren't there a few turboprops out there that have constant speed single shaft engines as well? I want to say the Garret TPE331 is one but not sure.

I think there is no constant speed single shaft engine. While torque could be adjusted by changing propeller pitch, the gas generator couln't adapt to it, since the compressor would also run at a constant speed and thus could only provide a fixed air flow. While you can change the fuel/air mixture for a set amount of air, it only works in a relatively narrow band.

In contrast, a free turbine engine like the PT6 can indeed have a fixed prop speed, since the gas generator is independent and can match output to the demand.

Or a I missing something?


A342



Exceptions confirm the rule.
User currently offlineLarshjort From Niue, joined Dec 2007, 1527 posts, RR: 0
Reply 10, posted (4 years 10 months 6 days 7 hours ago) and read 12872 times:

Quoting A342 (Reply 9):
I think there is no constant speed single shaft engine. While torque could be adjusted by changing propeller pitch, the gas generator couln't adapt to it, since the compressor would also run at a constant speed and thus could only provide a fixed air flow. While you can change the fuel/air mixture for a set amount of air, it only works in a relatively narrow band.

In contrast, a free turbine engine like the PT6 can indeed have a fixed prop speed, since the gas generator is independent and can match output to the demand.

Or a I missing something?

I know the TPE331 is capable of running from 71% idle up to 97 in beta mode and 100% in alpha mode if i remember correct, but when you are in the air you are always running 100% engine RPM. You have a speed lever ontrolling RPM and a power lever controlling the torque you want.

I just hope my teacher isn't reading this :p I'm doing Module 15 turbine engine, 16 piston engines and 17 propellors at the moment, and were mostly talking about the TPE331  

/Lars



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
User currently offlineA342 From Germany, joined Jul 2005, 4722 posts, RR: 3
Reply 11, posted (4 years 10 months 5 days 5 hours ago) and read 12756 times:

Quoting Larshjort (Reply 10):
but when you are in the air you are always running 100% engine RPM. You have a speed lever ontrolling RPM and a power lever controlling the torque you want.

Well, maybe other members could chime in and explain how the gas generator in the TPE331 varies power/torque if it works at a constant rpm? Because, at a fixed prop speed and with only a single shaft for the entire engine, rpm HAS to stay constant, right? Is it only by changing the fuel/air ratio?



Exceptions confirm the rule.
User currently offlinejetmech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 12, posted (4 years 10 months 5 days 4 hours ago) and read 12743 times:

Quoting A342 (Reply 11):

I don't know much about the TPE331, but from what I can find out, it does appear to have a constant RPM gas generator, if not a single shaft, overall design.

http://www.turbinedromader.com/New_images/TPE331-%20U.JPG

http://www51.honeywell.com/aero/comm..._brochures-documents/TPE331-14.pdf

http://en.wikipedia.org/wiki/Garrett_TPE331

Quoting A342 (Reply 9):
While torque could be adjusted by changing propeller pitch, the gas generator couln't adapt to it, since the compressor would also run at a constant speed and thus could only provide a fixed air flow. While you can change the fuel/air mixture for a set amount of air, it only works in a relatively narrow band.

I think the key to it all is the way a gas turbine mixes and combusts fuel with the working fluid.

In spark ignition ( petrol ) engines, the speed and power output of the engine is controlled by adjusting ( throttling ) the mass flow rate of air taken in. The carburettor or fuel injection system then adds the correct mass flow rate of fuel to burn completely in the air. This is usually somewhere around the stoichiometric ratio, but can be leaner or richer for specific conditions. However, the air / fuel ratio remains relatively fixed no matter the engine speed.

Compression ignition engines ( diesel ) and gas turbines are different, in that the engine speed and power output are controlled by the amount of fuel added. There is no means to control the amount of air taken in by these engines. Thus, the air / fuel ratio varies significantly with engine speed, being leanest at idle and richest at full power.

If we extrapolate this to the TPE331, we can imagine that the compressor is indeed supplying a fixed mass flow rate of air at a constant RPM. This mass flow rate of air would be sufficient for high power settings, and obviously, more than enough for low power settings.

Thus, at "low" power settings, the TPE331 would be adding a very small mass flow rate of fuel, and would thus be running very lean. At "high" power settings, the TPE would be adding a much greater mass flow rate of fuel, and would thus be running far richer. Although the RPM remains fixed, the power output varies due to the amount of torque being extracted by the turbine.

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineA342 From Germany, joined Jul 2005, 4722 posts, RR: 3
Reply 13, posted (4 years 10 months 4 days 17 hours ago) and read 12680 times:

Quoting jetmech (Reply 12):
Compression ignition engines ( diesel ) and gas turbines are different, in that the engine speed and power output are controlled by the amount of fuel added. There is no means to control the amount of air taken in by these engines. Thus, the air / fuel ratio varies significantly with engine speed, being leanest at idle and richest at full power.

Except if the diesel engine is turbocharged. Then you can control the amount of air by regulating the boost pressure. However, for a naturally aspirated diesel, you are correct. But I'd like to add that the maximum torque output from NA diesel engines is quite low, and thus the range in which you can regulate torque at a constant rpm is relatively small. In fact, this is what made me ask about the TPE331.

Quoting jetmech (Reply 12):
If we extrapolate this to the TPE331, we can imagine that the compressor is indeed supplying a fixed mass flow rate of air at a constant RPM. This mass flow rate of air would be sufficient for high power settings, and obviously, more than enough for low power settings.

Thus, at "low" power settings, the TPE331 would be adding a very small mass flow rate of fuel, and would thus be running very lean. At "high" power settings, the TPE would be adding a much greater mass flow rate of fuel, and would thus be running far richer. Although the RPM remains fixed, the power output varies due to the amount of torque being extracted by the turbine.

I think every flammable liquid and gas has a fuel/air mixture range where ignition is possible. When you're going either too lean or too rich, it just won't ignite any more.
Now two questions:
Is the ignition range for diesel or jet fuel wider than for gasoline? (I assume yes)
And might the TPE331 have another way of regulating airflow? Maybe a valve that blows off excess air after the last compressor stage?



Exceptions confirm the rule.
User currently offlineLarshjort From Niue, joined Dec 2007, 1527 posts, RR: 0
Reply 14, posted (4 years 10 months 4 days 5 hours ago) and read 12611 times:

Quoting A342 (Reply 13):
And might the TPE331 have another way of regulating airflow? Maybe a valve that blows off excess air after the last compressor stage?

I have some pages on the TPE331 at school , so I will post a reply later today.What I do remember is that ~25% of the air which enters the combustion chamber is used for burning, the rest is used to cool/keep the heat from the combustion chambers walls.

/Lars



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
User currently offlinetimz From United States of America, joined Sep 1999, 6903 posts, RR: 7
Reply 15, posted (4 years 10 months 4 days ago) and read 12563 times:

In any case, the T56 is single shaft? And constant speed?

User currently offlinefrancoflier From France, joined Oct 2001, 3849 posts, RR: 11
Reply 16, posted (4 years 10 months 3 days 4 hours ago) and read 12448 times:

Quoting FLY2HMO (Reply 8):
But a fully assembled Garrett would not horribly hard to spin like a piston engine, or is it?

No it's not. It takes more effort than a free turbine to turn it, but you certainly can.

As a matter of fact, it is recommended to spin it around a few times after shutdown to vent the gas turbine and prevent uneven cooling and possible early wear. It also helps lower the core temperature to allow for a faster restart and turnaround.

Quoting A342 (Reply 13):
And might the TPE331 have another way of regulating airflow? Maybe a valve that blows off excess air after the last compressor stage?

Not that I remember. It is a fairly simple engine design. The tricky bit, as with every single shaft constant speed TP, is the delicate and sensitive linkage between the fuel control unit and prop governor which needs to be properly rigged.

As Jetmech said, the amount of air going through the compressor is the same, the mass flow going out the back varies and thus the turbine temperature varies. Proper combustion chamber design is sufficient to ensure a flame at every temperature.

The governor maintains RPM by varying pitch as the power produced by the turbine varies according to the amount of fuel injected.



Looks like I picked the wrong week to quit posting...
User currently offlineSgtusmc96 From United States of America, joined Apr 2007, 47 posts, RR: 0
Reply 17, posted (4 years 10 months 3 days 3 hours ago) and read 12421 times:

Yes the T-56 is a single shaft turboprop. The torque shaft I directly conected from the reduction gear box to the front of the compressor. In there are two different idle modes. Ground and flight. I don't remember the rpm percent for ground but as soon as you put it in flight idle the motor spools up to 100% and never leaves 100%. If I remember right prop rpm was governed to 1013 rpm. At all flight parmeters the engine ran 100%. When you advanced the throttles you changed the fuel and in turn the prop would automatically adjust pitch to keep with in it's rpm limits. It was never fun changing a fuel control and cordinator on a kc-130t. I really hated rigging the cordinator and fuel control. Then adjusting settings on the prop was another story. Having a engine running and spinning a thirteen foot prop inches from your head was always fun and a bit cold in the winter.

User currently offlineJETMECH From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 18, posted (4 years 10 months 2 days 19 hours ago) and read 12339 times:

Quoting A342 (Reply 13):
Except if the diesel engine is turbocharged. Then you can control the amount of air by regulating the boost pressure.

Yes, but whether a diesel has a turbo or not, it will not have any throttling mechanism on the intake, and thus, there is still no way to actively regulate the amount of air entering the engine. The speed and power output of a turbo diesel is still controlled by the amount of fuel added (cut-off ratio), not by restricting (throttling) the amount of air taken in.

Quoting A342 (Reply 13):
the range in which you can regulate torque at a constant rpm is relatively small.

Sure. But you must remember that the quoted torque for a given RPM is a maximum value only. Just because the engine is spinning at that RPM does not mean that this torque value is being delivered. For example, Caterpillar quotes the C15 turbo diesel as capable of delivering a maximum torque of 2050 ft-lb’s at 1200 RPM.

http://ohe.cat.com/cda/layout?m=85523&x=7

If however, the transmission is in neutral, and you press the accelerator to achieve 1200 RPM, there would not be anywhere near 2050 ft-lb’s being delivered. There would just be enough torque to spin the rotating mass of the engine at 1200 RPM.

You can increase the load on the engine up to a maximum of 2050 ft-lb’s and you can maintain 1200 RPM by increasing the mass flow rate of fuel. This is true of any RPM, and is similar in concept to a constant speed turboprop as mentioned by previous posters.

Quoting francoflier (Reply 16):
The governor maintains RPM by varying pitch as the power produced by the turbine varies according to the amount of fuel injected.
Quoting francoflier (Reply 16):
The tricky bit, as with every single shaft constant speed TP, is the delicate and sensitive linkage between the fuel control unit and prop governor which needs to be properly rigged.
Quoting Sgtusmc96 (Reply 17):
When you advanced the throttles you changed the fuel and in turn the prop would automatically adjust pitch to keep with in it's rpm limits.
Quoting A342 (Reply 13):
Is the ignition range for diesel or jet fuel wider than for gasoline? (I assume yes)

According to Wikipedia, the flammability limits of diesel and gasoline are similar.

http://en.wikipedia.org/wiki/Flammability_limit

However, I suspect it is not too wise to assume the flammability limit of a fuel is related to the range of power outputs deliverable by a gas turbine. According to this link;

http://www.globalsecurity.org/milita...brary/policy/army/fm/1-506/ch3.htm

only 25% of the air entering the core engine is actually mixed with fuel to form the desired air / fuel ratio. The other 75% forms a cooling film around the combustion chamber and dilutes the products of combustion. Thus, the flammability limit is only important right within the combustion can itself.

I suspect that the range of power outputs deliverable by a gas turbine has a lot more to do with the maximum amount of air the compressor can deliver, and less to do with the flammability limits of the fuel.



Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlinefrancoflier From France, joined Oct 2001, 3849 posts, RR: 11
Reply 19, posted (4 years 10 months 2 days 17 hours ago) and read 12319 times:

Quoting JETMECH (Reply 18):
I suspect that the range of power outputs deliverable by a gas turbine has a lot more to do with the maximum amount of air the compressor can deliver

Exactly, and also the maximum temperature the hot section can withstand, as more power will be produced by burning more stuff hotter.


And by the way:

Quoting 2H4 (Reply 4):
This one was new to me.

  

...he IS human after all.



Looks like I picked the wrong week to quit posting...
User currently offlineDashTrash From United States of America, joined Aug 2006, 1565 posts, RR: 2
Reply 20, posted (4 years 10 months 2 days 13 hours ago) and read 12285 times:

Quoting FLY2HMO (Reply 8):
Hmmm, so you actually can't or you just shouldn't?
Quoting francoflier (Reply 16):
As a matter of fact, it is recommended to spin it around a few times after shutdown to vent the gas turbine and prevent uneven cooling and possible early wear. It also helps lower the core temperature to allow for a faster restart and turnaround.

It also prevents the shaft from sagging. We were required to spin the prop around a few times after shutdown and within a few minutes of it. You can bind up the innards if you don't.


User currently offlineA342 From Germany, joined Jul 2005, 4722 posts, RR: 3
Reply 21, posted (4 years 10 months 2 days 11 hours ago) and read 12268 times:

Quoting JETMECH (Reply 18):
The speed and power output of a turbo diesel is still controlled by the amount of fuel added (cut-off ratio), not by restricting (throttling) the amount of air taken in.

There is actually some throttling. To use your example of the Caterpillar engine, when you put it in neutral and increase rpm (say to 2000rpm), the turbo would actually be capable of delivering very high boost. But it is blown off by the so-called wastegate, because the load condition does not demand such a high airflow.
Other reasons to actively regulate boost pressure include emissions and engine durability.

Quoting JETMECH (Reply 18):
Sure. But you must remember that the quoted torque for a given RPM is a maximum value only. Just because the engine is spinning at that RPM does not mean that this torque value is being delivered. For example, Caterpillar quotes the C15 turbo diesel as capable of delivering a maximum torque of 2050 ft-lb’s at 1200 RPM.

http://ohe.cat.com/cda/layout?m=85523&x=7

If however, the transmission is in neutral, and you press the accelerator to achieve 1200 RPM, there would not be anywhere near 2050 ft-lb’s being delivered. There would just be enough torque to spin the rotating mass of the engine at 1200 RPM.

But now you're refering to a turbo engine. Let's assume for a moment that it would be naturally aspirated. Then the max. torque at 1200rpm would be somewhere along the lines of 600-700 ft-lbs.
So both engines are capable of delivering just enough torque to run the engine with no load at 1200rpm. But the maximum torque at 1200rpm is MUCH higher for the turbo engine, because intake airflow, and not just fuel delivery, is variable (at a given rpm high enough for the turbo to provide significant boost, the amount of air entering the engine is varied by adjusting boost pressure).
Let's assume that both engines are producing max. torque at 1200rpm. If you inject as much fuel in the N/A engine as in the turbo, all you'd get is an atrocious amount of soot.

So to use this analogy, the single-shaft, constant-speed TPE331 works like a naturally aspirated engine (constant intake airflow), while the PT6 with its independent gas generator (free power turbine) can adjust intake airflow at a given prop rpm by increasing gas generator rpm (of course, the principle is different than a turbo, but the result is the same).

That's what led me to my question about possible fuel/air mixture ratios.

Quoting JETMECH (Reply 18):
According to Wikipedia, the flammability limits of diesel and gasoline are similar.

From what I know, the numbers mean that diesel has a much better capability to operate at lean mixtures than gasoline. I'd say the range is wuite a bit wider (even if the numbers suggest otherwise at first sight).

Quoting JETMECH (Reply 18):
I suspect that the range of power outputs deliverable by a gas turbine has a lot more to do with the maximum amount of air the compressor can deliver, and less to do with the flammability limits of the fuel.

For a multi-spool or variable-speed single shaft engine, that's 100% correct. But I remain somewhat unsure about the constant airflow in the TPE331 (at a given density altitude, the compressor always delivers the same amount of air).


(Don't want to completely hijack this topic, but Mitsubishi is about to introduce a turbodiesel with variable valve control!    )



Exceptions confirm the rule.
User currently offline2H4 From United States of America, joined Oct 2004, 8956 posts, RR: 60
Reply 22, posted (4 years 10 months 2 days 3 hours ago) and read 12212 times:
AIRLINERS.NET CREW
DATABASE EDITOR

Quoting DashTrash (Reply 20):
It also prevents the shaft from sagging

I understand, however, that this problem is inevitable beyond a certain age.



Intentionally Left Blank
User currently offlineJetmech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 23, posted (4 years 10 months 1 day 22 hours ago) and read 12187 times:

Quoting A342 (Reply 21):
There is actually some throttling.

But the power output and RPM are still controlled by the amount of fuel injected, not variations in boost pressure. Throttling for a reciprocating engine generally refers to an actively controlled physical restriction in the inlet tract (throttling plate). I’m not sure boost pressure variation would fit this description.

Quoting A342 (Reply 21):
But now you're refering to a turbo engine

The analogy I put forth in my earlier reply holds for any engine; petrol, diesel, turbo or naturally aspirated. What I was trying to get at is that a motor will only deliver sufficient torque for the magnitude of the external load at that instant. The magnitude of the external load can vary markedly for a fixed RPM, thus, so can the torque output.

Quoting A342 (Reply 21):
So to use this analogy, the single-shaft, constant-speed TPE331 works like a naturally aspirated engine (constant intake airflow),
Quoting A342 (Reply 21):
But I remain somewhat unsure about the constant airflow in the TPE331 (at a given density altitude, the compressor always delivers the same amount of air).

I suspect that the key to this engine being able to deliver a range of power levels at a constant RPM is the fact that the RPM chosen for operation can supply sufficient air for the maximum power condition. At low power settings, there is a great excess of air.

Quoting A342 (Reply 21):
That's what led me to my question about possible fuel/air mixture ratios.

If you took a dish of kerosene outside in your garden, you could light it and cause combustion to occur. In theory, the air fuel ratio is infinitely low (close to zero), as you are mixing that small amount of kerosene with the Earth's entire atmosphere. However, a flame still appears, as within some small region above the dish of kerosene, the air / fuel mixture is within the flammability limit.

A similar analogy holds for a gas turbine combustion chamber. The flammability limit is only important right within the combustion chamber ( primary zone ) where the actual flame burns. The heat released in the primary zone heats all the air passing through the combustion section of the engine ( primary and secondary air ). I suspect that some of the secondary cooling air would be available to support combustion during high power operations.

http://www.users.zetnet.co.uk/gas/cutway1.jpg
http://www.users.zetnet.co.uk/gas/cutway2.jpg

Regards, JetMech

[Edited 2010-03-03 00:06:16 by jetmech]


JetMech split the back of his pants. He can feel the wind in his hair.
User currently onlineStarlionblue From Greenland, joined Feb 2004, 17187 posts, RR: 66
Reply 24, posted (4 years 10 months 1 day 20 hours ago) and read 12168 times:

Quoting francoflier (Reply 19):
And by the way:

Quoting 2H4 (Reply 4):
This one was new to me.



...he IS human after all.

Barely.  



"There are no stupid questions, but there are a lot of inquisitive idiots."
25 francoflier : You guys are digging way too deep into that turbine/reciprocating engine comparison. So I brought a shovel: Many GPUs actually have governed piston en
26 Post contains images A342 : Ah, think I got it now. Or, to use the kerosene dish analogy, right at the fuel nozzles. The gas generator turbine does, but the (free) power turbine
27 DH106 : Might be wrong but I think the Dart is constant speed
28 francoflier : Huh, not sure I'm following anymore, but I was merely separating the power producing elements of an engine vs the elements that receive and transform
29 Post contains links Larshjort : Yes and the PW100 series is a 3 spool engine, two spool gasgenerator. http://en.wikipedia.org/wiki/Pratt_&_Whitney_Canada_PW100
30 Post contains images PITingres : While technically I suppose you are correct, very simple usage and maintenance procedures will prevent any ill effects from shaft sagging - even at r
31 HercPPMX : The Torque shaft mates into the Air Inlet Housing at the front of the compressor section, and to the Safety Coupling on the aft side of the RGB. Beca
32 TwinCommander : we had a discution at work about this aircraft... it was a demonstrator to show that it could be done... however, the fuel burn sucked, and... it was
33 Post contains images KELPkid : Well, as a fomer lineboy, I could say that a good policy to keep one's job is not to turn a prop by hand that resists you unless the aicraft owner as
34 TwinCommander : rule of thumb : any rotating assembly is to be spun in its normal direction of rotation only if required to perform your task. when i was a line boy
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