INSIDE AN ENGINE;
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Thanks TurbineD, Mecaniquito84, DevX!
Well, I have to collect all the information given by everyone!
1)But in your photo, TurbineD, does the apu air bleed go bellow the compressor? Does the APU bleed air turn the fan??
2) But does the fan already start taking air inside? Or does it block something till we start the engine, if not, I imagine that apu bleed air is then only for packs for A/C.
3) If for example, we put thrust TOGA, will they put all the fuel required for TOGA thrust in the combuster or will it keep giving fuel till we reach TOGA thrust? (Well I think it will keep giving fuel, not the entire amount required!)
4) Ok, so the APU bleed air is normal air which goes inside a compressor and then travels inside pipes to finally arrive at the pneumatic engine starter, then the drive box, and turns the main engine rotor. What is the main engine rotor? The fan? So is it the inverse process? The fan turning the compressor and the turbine? So no mixing with fuel for apu bleed air in the combuster?
5) Could anyone show me on a photo, where is the pneumatic engine starter, drive box?
Well, I have to collect all the information given by everyone!
1)But in your photo, TurbineD, does the apu air bleed go bellow the compressor? Does the APU bleed air turn the fan??
2) But does the fan already start taking air inside? Or does it block something till we start the engine, if not, I imagine that apu bleed air is then only for packs for A/C.
3) If for example, we put thrust TOGA, will they put all the fuel required for TOGA thrust in the combuster or will it keep giving fuel till we reach TOGA thrust? (Well I think it will keep giving fuel, not the entire amount required!)
4) Ok, so the APU bleed air is normal air which goes inside a compressor and then travels inside pipes to finally arrive at the pneumatic engine starter, then the drive box, and turns the main engine rotor. What is the main engine rotor? The fan? So is it the inverse process? The fan turning the compressor and the turbine? So no mixing with fuel for apu bleed air in the combuster?
5) Could anyone show me on a photo, where is the pneumatic engine starter, drive box?
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Here's a Trent 700 starter motor, IDG, anti icing valve and external gearbox:
http://www.pprune.org/rumours-news/2...ml#post2944866
The starter motor is on the left of the picture, the IDG is the black lump with wires on the right of the picture, the anti icing valve is at the top of the picture and the external gearbox is in the middle.
Also, the biscuit coloured area above the starter is the multi layer Kevlar wrap which goes around the fan case to (hopefully) contain a fan blade, or parts of, from piercing the fuselage after a failure. The small piece of titanium plate above the starter is to prevent pieces of the starter turbine from damaging the Kevlar wrap in the event of a failure. When a motor does fail, usually due to lack of maintenance/oil, it goes off like a huge Catherine wheel!
The unit, extreme top right of the picture is the IDG cooler which uses fan air to cool the oil.
http://www.pprune.org/rumours-news/2...ml#post2944866
The starter motor is on the left of the picture, the IDG is the black lump with wires on the right of the picture, the anti icing valve is at the top of the picture and the external gearbox is in the middle.
Also, the biscuit coloured area above the starter is the multi layer Kevlar wrap which goes around the fan case to (hopefully) contain a fan blade, or parts of, from piercing the fuselage after a failure. The small piece of titanium plate above the starter is to prevent pieces of the starter turbine from damaging the Kevlar wrap in the event of a failure. When a motor does fail, usually due to lack of maintenance/oil, it goes off like a huge Catherine wheel!
The unit, extreme top right of the picture is the IDG cooler which uses fan air to cool the oil.
Last edited by DevX; 2nd Sep 2014 at 14:25. Reason: Additional info.
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AF330
Just wanted to welcome you and wish you the best of luck in the future. You have already gotten lots of help here and I hope to see you in an engineer's costume/pilot's uniform somewhere in the world some day!
Just wanted to welcome you and wish you the best of luck in the future. You have already gotten lots of help here and I hope to see you in an engineer's costume/pilot's uniform somewhere in the world some day!
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Hi
Engine rotor is the part that moves (rotates) in an Turbine engine. It consist in the Compressor (to the right in the img below) and the turbine in a one axle.
And again:
1. something external (air starter) makes the whole axle (compressor + turbine) rotate.
2. When axle is rotated, compressor start to compress intake air.
3. When the air has enough pressure it is mixed with fuel, ignited by spark plugs. Air + fuel ignited, (called gas from now on) had adquiered extra energy from combustion.
4 High energy gas impact the turbine and gas energy is transformed in a mechanical movement: gas turns the turbine. With turbine, whole axle is turned including compressor, who compress more aire and (go to 2.
)
http://nihrecord.nih.gov/newsletters...ter-balanc.jpg
Engine rotor is the part that moves (rotates) in an Turbine engine. It consist in the Compressor (to the right in the img below) and the turbine in a one axle.
And again:
1. something external (air starter) makes the whole axle (compressor + turbine) rotate.
2. When axle is rotated, compressor start to compress intake air.
3. When the air has enough pressure it is mixed with fuel, ignited by spark plugs. Air + fuel ignited, (called gas from now on) had adquiered extra energy from combustion.
4 High energy gas impact the turbine and gas energy is transformed in a mechanical movement: gas turns the turbine. With turbine, whole axle is turned including compressor, who compress more aire and (go to 2.
)http://nihrecord.nih.gov/newsletters...ter-balanc.jpg
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Hi AF330,
1. The APU bleed air goes only to the starter motor. The starter motor uses this air to turn a shaft that is connected to the compressor of the main engine. The fan is turned by the rotation speed of the Low Pressure Turbine at the rear of the engine.
2. The fan takes air in but keep in mind, most of that fan air goes around the engine, not through it.
3. Your question isn't clear enough to answer.
4. To answer this question I would suggest you go to this Rolls Royce learning site and go through each of the 4 presentation stages. It will help you to understand the different sections of a turbo-fan jet engine and how they relate to one another:
Journey through a jet engine
I hope you will enjoy this!
1. The APU bleed air goes only to the starter motor. The starter motor uses this air to turn a shaft that is connected to the compressor of the main engine. The fan is turned by the rotation speed of the Low Pressure Turbine at the rear of the engine.
2. The fan takes air in but keep in mind, most of that fan air goes around the engine, not through it.
3. Your question isn't clear enough to answer.
4. To answer this question I would suggest you go to this Rolls Royce learning site and go through each of the 4 presentation stages. It will help you to understand the different sections of a turbo-fan jet engine and how they relate to one another:
Journey through a jet engine
I hope you will enjoy this!
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This thread reminds me of some of my less successful tech reviews.
Hint: 13 year old french kid. Obviously bright but unfamiliar with any technical terms. May need description reduced to simplest form!
Suck, squeeze, bang, blow.
Hint: 13 year old french kid. Obviously bright but unfamiliar with any technical terms. May need description reduced to simplest form!
Suck, squeeze, bang, blow.
Let us look at a car engine; maybe this will clear things up a bit.
Such a piston engine cannot start to run on its own; it needs to have its crankshaft turned by some external power source in order to get the air/fuel mixture, ignition, oil system etc. in motion. As soon as there are the first one or two charges igniting in the cylinders and driving the pistons, the engine can run on its own and no assistance from outside is needed.
The external power source used for this is typically an electric motor that will turn the engine; its power normally comes from an accumulator.
In analogy to this: Neither can a jet engine get running on its own. Its shafts will need to be spun up to a certain speed by an external power source so the compressors feed the combustion chambers enough air. As soon as there is a steady flame in the combustion chambers (requiring a constant supply of air and fuel), the compressors are kept running by the power delivered by the turbines and no outside assistance is needed any more.
And also here: You need some means to get the compressors up to speed. An electric motor is definitely eligible but comes at some costs that makes it less than optimal in most cases. So a pneumatic motor is used instead. The place of the batteries is taken by the APU here.
As soon as the starter has done its job of accelerating the engine (be it piston or jet engine) to a self-sustaining speed, it is disengaged. The power needed to sustain the engine then comes from the power stroke (in case of a piston engine) or from the turbine section of the jet engine.
I would advise You to get a good understanding of gas turbine basics first. Many postings in this thread contain links that will help You a lot. And once You have a good grip of what happens in a steadily running gas turbine, it will be the time to look at how a gas turbine is started, governed and operated. For Your question 3, You will likely find this thread of interest.
EDIT: I found a cutaway picture of a pneumatic starter on this page.
The APU bleed air enters from the left, passes a row of stator vanes before working on the turbine and is then vented via the annular grille overboard. As such a turbine runs at rather high RPM, its speed is translated to a lower RPM and higher torque (remember, p=T*n*const.) in order to drive the engine shaft: this is why there is a planetary gearbox installed. Typically, such a starter also has a clutch that allows the starter to drive the engine but keeps the engine from driving the starter.
Such a piston engine cannot start to run on its own; it needs to have its crankshaft turned by some external power source in order to get the air/fuel mixture, ignition, oil system etc. in motion. As soon as there are the first one or two charges igniting in the cylinders and driving the pistons, the engine can run on its own and no assistance from outside is needed.
The external power source used for this is typically an electric motor that will turn the engine; its power normally comes from an accumulator.
In analogy to this: Neither can a jet engine get running on its own. Its shafts will need to be spun up to a certain speed by an external power source so the compressors feed the combustion chambers enough air. As soon as there is a steady flame in the combustion chambers (requiring a constant supply of air and fuel), the compressors are kept running by the power delivered by the turbines and no outside assistance is needed any more.
And also here: You need some means to get the compressors up to speed. An electric motor is definitely eligible but comes at some costs that makes it less than optimal in most cases. So a pneumatic motor is used instead. The place of the batteries is taken by the APU here.
As soon as the starter has done its job of accelerating the engine (be it piston or jet engine) to a self-sustaining speed, it is disengaged. The power needed to sustain the engine then comes from the power stroke (in case of a piston engine) or from the turbine section of the jet engine.
I would advise You to get a good understanding of gas turbine basics first. Many postings in this thread contain links that will help You a lot. And once You have a good grip of what happens in a steadily running gas turbine, it will be the time to look at how a gas turbine is started, governed and operated. For Your question 3, You will likely find this thread of interest.
EDIT: I found a cutaway picture of a pneumatic starter on this page.
The APU bleed air enters from the left, passes a row of stator vanes before working on the turbine and is then vented via the annular grille overboard. As such a turbine runs at rather high RPM, its speed is translated to a lower RPM and higher torque (remember, p=T*n*const.) in order to drive the engine shaft: this is why there is a planetary gearbox installed. Typically, such a starter also has a clutch that allows the starter to drive the engine but keeps the engine from driving the starter.
Last edited by Tu.114; 2nd Sep 2014 at 20:29.
Another way to think about is that if you burned fuel in the middle of an engine without the compressor turning, you'd just get flames coming out both ends of the engine.
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The physical link between starter and core rotor is two sets of bevel gears, one in the accessory gearbox (I'll call it AGB) and the other on the core shaft; these two are linked by a shaft called the radial driveshaft or quill shaft.
Go back to post #14 to see the AGB and quill shaft.
During starting the starter is turning the engine, along with fuel pump, oil pump, electrical generator etc. Once the starter drops out, the engine is turning those accessories.
Go back to post #14 to see the AGB and quill shaft.
During starting the starter is turning the engine, along with fuel pump, oil pump, electrical generator etc. Once the starter drops out, the engine is turning those accessories.
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Hi everyone,
Before confirming/asking what I have learnt, I would like to thank you all to help and support me in my passion!
"AF330
Just wanted to welcome you and wish you the best of luck in the future. You have already gotten lots of help here and I hope to see you in an engineer's costume/pilot's uniform somewhere in the world some day!"
Thanks a lot for your welcome! I really appreciate, and yes, I hope to wear a pilot's uniform! It is my biggest dream, fly the A330! Well, again, thanks a lot for your great welcome MrSnuggles!
"This thread reminds me of some of my less successful tech reviews.
Hint: 13 year old french kid. Obviously bright but unfamiliar with any technical terms. May need description reduced to simplest form!
Suck, squeeze, bang, blow."
Thanks for your compliment! I loved your hint! But, I really don't mind technical words, even If I don't understand them! I really love to learn about aviation. I have noticed that there is alway something new to learn, when you finish with SELCAL, you don't understand A/THR, when you understand that, you get confused with Alpha Floor! You are absolutely right, when you say that I am unfamiliar with technical terms, but when It talks about aviation, I am ALWAYS ready to learn it! Thanks a lot for your post Fe Hoppy!
"Of course there are differences, this is just a basic explanation. And sorry, I'm not an instructor
Keep asking!!!"
No, don't say that Mecaniquito84! You really have helped me a lot! Thanks for your help!
I also would really like to thank TurbineD, DevX, barit1, Tu.114, lomapaseo and many more for their great explanations and answers on my boring and, I am sure, not professional questions that you expect on this forum.
Thanks a lot to everyone!
Well, let's say that I have more or less got the concept, and here is a nice photo that I found: http://www.aviation-news.co.uk/archive/media/CFMd2.gif
The APU BLEED AIR goes inside a compressor, it travels in different pipes to the accessory drive section, which is outside the aircraft, and then enters inside the gear box, where it stops it's route and turns an impeller, which turns the horizontal drive shaft, then turns the radial drive shaft by the help of the transfer gearbox, am I right till here?
Thanks a lot to confirm and help!
Before confirming/asking what I have learnt, I would like to thank you all to help and support me in my passion!
"AF330
Just wanted to welcome you and wish you the best of luck in the future. You have already gotten lots of help here and I hope to see you in an engineer's costume/pilot's uniform somewhere in the world some day!"
Thanks a lot for your welcome! I really appreciate, and yes, I hope to wear a pilot's uniform! It is my biggest dream, fly the A330! Well, again, thanks a lot for your great welcome MrSnuggles!
"This thread reminds me of some of my less successful tech reviews.
Hint: 13 year old french kid. Obviously bright but unfamiliar with any technical terms. May need description reduced to simplest form!
Suck, squeeze, bang, blow."
Thanks for your compliment! I loved your hint! But, I really don't mind technical words, even If I don't understand them! I really love to learn about aviation. I have noticed that there is alway something new to learn, when you finish with SELCAL, you don't understand A/THR, when you understand that, you get confused with Alpha Floor! You are absolutely right, when you say that I am unfamiliar with technical terms, but when It talks about aviation, I am ALWAYS ready to learn it! Thanks a lot for your post Fe Hoppy!
"Of course there are differences, this is just a basic explanation. And sorry, I'm not an instructor
Keep asking!!!"
No, don't say that Mecaniquito84! You really have helped me a lot! Thanks for your help!
I also would really like to thank TurbineD, DevX, barit1, Tu.114, lomapaseo and many more for their great explanations and answers on my boring and, I am sure, not professional questions that you expect on this forum.
Thanks a lot to everyone!
Well, let's say that I have more or less got the concept, and here is a nice photo that I found: http://www.aviation-news.co.uk/archive/media/CFMd2.gif
The APU BLEED AIR goes inside a compressor, it travels in different pipes to the accessory drive section, which is outside the aircraft, and then enters inside the gear box, where it stops it's route and turns an impeller, which turns the horizontal drive shaft, then turns the radial drive shaft by the help of the transfer gearbox, am I right till here?
Thanks a lot to confirm and help!
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Pretty good.
With my instructor head on just for a second (I try not to bring it home with me), I would just say this:
Air is air. It only becomes "Bleed air" when it is taken from a compressor for some other use.
So our little Auxiliary Power Unit at the back of the aircraft normally has a valve on its compressor which when open allows air to "bleed" away from the APU along a network of pipes known as the pneumatic system where it can be used for many different tasks.
Examples might be:
Air conditioning,
Pressurisation of the cabin,
Pressurisation of the water systems,
Toilet flush!
Anti-ice systems (though not usually as the demand is too high)
and engine starting.
For engine starting, the air goes through a valve called the start valve to an air driven starter motor known often as an Air Turbine Starter motor. Because of course it is a motor which uses a turbine to convert pressure (of the bleed air) into mechanical rotation. This ATS is connected to the gearbox and therefore turns not only the gearbox and all the other pumps and things connected to the gearbox but also as you said the engine itself.
On your picture the yellow shaft is connected to the red "spool" or "rotor" and this will then rotate. When this spins the compressor on the front of that rotor starts to draw air through the engine from the inlet to the exhaust.
The picture you posted is a "twin spool" or "dual rotor" engine so the air entering the engine flows past the "Fan" and low pressure compressor shown in blue before passing through the high pressure compressor then through the combustion section, out through the high pressure turbine (which is doing no work at this stage) the low pressure turbine (which is extracting energy to help turn the fan) and out the back.
When the two rotors are turning fast enough (often this is dictated only by the speed of the red high pressure rotor) we can add fuel and a spark. The combustion of that fuel with a small % of the air going through the engine adds pressure at the two turbine sections, this makes the engine accelerate, as the engine accelerates the amount of air (mass) passing into the combustion section increases and we can add more fuel which in turn creates more pressure.
This continues until the energy from combustion alone is enough to keep the engine turning. This is known as "self sustaining" speed. At this point we no longer need the help of the ATS and the start valve can close.
But the yellow drive shaft is still connected so now the engine is providing the power to drive the gear box and all connected pumps and things. We don't need the ATM to turn anymore so some kind of clutch or freewheel device is incorporated to allow it to stop. This is important as the ATS is one of the fastest rotating devices on the aircraft. 50,000rpm on some models and we don't want them turning when not needed.
Hope that helps a bit. I would also suggest looking at many different engine types and aircraft too as you will find many variations in design and names for things but the general principal is roughly the same.
Bonne Chance young man!
With my instructor head on just for a second (I try not to bring it home with me), I would just say this:
Air is air. It only becomes "Bleed air" when it is taken from a compressor for some other use.
So our little Auxiliary Power Unit at the back of the aircraft normally has a valve on its compressor which when open allows air to "bleed" away from the APU along a network of pipes known as the pneumatic system where it can be used for many different tasks.
Examples might be:
Air conditioning,
Pressurisation of the cabin,
Pressurisation of the water systems,
Toilet flush!
Anti-ice systems (though not usually as the demand is too high)
and engine starting.
For engine starting, the air goes through a valve called the start valve to an air driven starter motor known often as an Air Turbine Starter motor. Because of course it is a motor which uses a turbine to convert pressure (of the bleed air) into mechanical rotation. This ATS is connected to the gearbox and therefore turns not only the gearbox and all the other pumps and things connected to the gearbox but also as you said the engine itself.
On your picture the yellow shaft is connected to the red "spool" or "rotor" and this will then rotate. When this spins the compressor on the front of that rotor starts to draw air through the engine from the inlet to the exhaust.
The picture you posted is a "twin spool" or "dual rotor" engine so the air entering the engine flows past the "Fan" and low pressure compressor shown in blue before passing through the high pressure compressor then through the combustion section, out through the high pressure turbine (which is doing no work at this stage) the low pressure turbine (which is extracting energy to help turn the fan) and out the back.
When the two rotors are turning fast enough (often this is dictated only by the speed of the red high pressure rotor) we can add fuel and a spark. The combustion of that fuel with a small % of the air going through the engine adds pressure at the two turbine sections, this makes the engine accelerate, as the engine accelerates the amount of air (mass) passing into the combustion section increases and we can add more fuel which in turn creates more pressure.
This continues until the energy from combustion alone is enough to keep the engine turning. This is known as "self sustaining" speed. At this point we no longer need the help of the ATS and the start valve can close.
But the yellow drive shaft is still connected so now the engine is providing the power to drive the gear box and all connected pumps and things. We don't need the ATM to turn anymore so some kind of clutch or freewheel device is incorporated to allow it to stop. This is important as the ATS is one of the fastest rotating devices on the aircraft. 50,000rpm on some models and we don't want them turning when not needed.
Hope that helps a bit. I would also suggest looking at many different engine types and aircraft too as you will find many variations in design and names for things but the general principal is roughly the same.
Bonne Chance young man!
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Nicely explained Hoppy, and then there are the engines fitted with an electric starter/generator, known as a VFSG, or Variable Frequency Starter Generator. The GenEx and Trent 1000 engines use these on the Dreamliner and have 2 units fitted per engine. They are quite complex pieces of kit (not to mention expensive!
) as once the units have started the engine, they convert into generators to supply the aircraft with electrical power.
See here: 787 Propulsion System
) as once the units have started the engine, they convert into generators to supply the aircraft with electrical power. See here: 787 Propulsion System
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Originally Posted by AF330
Thanks for your compliment! I loved your hint! But, I really don't mind technical words, even If I don't understand them! I really love to learn about aviation. I have noticed that there is alway something new to learn, when you finish with SELCAL, you don't understand A/THR, when you understand that, you get confused with Alpha Floor! You are absolutely right, when you say that I am unfamiliar with technical terms, but when It talks about aviation, I am ALWAYS ready to learn it!
How is your mechanical aptitude in general? Do you know, for example, how to replace a spark plug on a motorcycle (or even a lawnmower)? How about where the air filter is on your Dad's Citroen? I'm not asking you this to put you down, I'm only suggesting that many mechanical concepts translate from the small to the large, just the means of execution differ.
I'm sure there are plenty of books in French on engines in general, never mind turbofans. Starts small, then go big, the big isn't going anywhere.
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AF330,
Quote by Amadis of Gaul:
To add to the suggestion Amadis made, just outside Paris on the A6, Exit E50, are two jet engine companies. CFM International has their main engine assembly plant there. SNECMA, who are half owners of CFM International (the other half is owned by GE), have offices and engine assembly facilities there as well. SNECMA's Evry-Corbeil address is:
10 Allée du Brévent 91019 Courcouronnes
+33 1 69 87 09 00
snecma.com
I think if you contact them, they can provide you with information to help you. If you explain to them your age and your dedication to understand and learn about jet engines there could even be more opportunities besides written information.
Quote by Amadis of Gaul:
I'm sure there are plenty of books in French on engines in general, never mind turbofans. Starts small, then go big, the big isn't going anywhere.
10 Allée du Brévent 91019 Courcouronnes
+33 1 69 87 09 00
snecma.com
I think if you contact them, they can provide you with information to help you. If you explain to them your age and your dedication to understand and learn about jet engines there could even be more opportunities besides written information.
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Thanks a lot!
Just would like to confirm these for the apu bleed air route at the beginning:
So apu air bleed get's compressed and then travel's into pipes and then goes inside a start valve and the air turbine starter. It ends it's route there. The ATS spins the accesory drive box, so the gearbox, the impeller, which turns the horizontal drive shaft, then turns the
radial drive shaft with the help of the transfer gear box. Am I right here?
Thanks a lot to confirm!
PS: I am now in 3e- since 1 day! (9th grade, I think, but not sure at all) and I will have to do a small "formation" in any company I would like to for just 3 days. As I am 13 (going to be 14 in November), I thought that I would do one in Air France as I want to become a pilot (and my friend's father is a 777 captain) ! But I could really try your address! Thanks a lot!
Just would like to confirm these for the apu bleed air route at the beginning:
So apu air bleed get's compressed and then travel's into pipes and then goes inside a start valve and the air turbine starter. It ends it's route there. The ATS spins the accesory drive box, so the gearbox, the impeller, which turns the horizontal drive shaft, then turns the
radial drive shaft with the help of the transfer gear box. Am I right here?
Thanks a lot to confirm!
PS: I am now in 3e- since 1 day! (9th grade, I think, but not sure at all) and I will have to do a small "formation" in any company I would like to for just 3 days. As I am 13 (going to be 14 in November), I thought that I would do one in Air France as I want to become a pilot (and my friend's father is a 777 captain) ! But I could really try your address! Thanks a lot!
