Sir, may I congratulate you on your great experience of jet engines, your vast practical and theoretical knowledge, and the elegant and accurate vocabulary you use to describe the details of the procedures and the actions involved. When you speak about any working part of the engine, it is as if you are part of it and feeling and experiencing the action yourself. You seem to feel the pains and the glory of all parts of the jet engine which you seem to love so much and you treat them as if they were part of your family. You want them to work, but not suffer. At the moment I am working on a very small jet engine to show my grandson the working principles of the engine. I am using tinned milk containers to make compressors and turbines and combustion chambers and rather than building up pressure with the compressor, I am using the small engine in a vertical manner and so high speed convection currents will help to rotate the turbine which in turn rotates the compressor below it with the flame in between. I found that the combustion chamber part needs to be longer to permit the air to gain a higher velocity due to convection and not the pressure after the compression, which I can never obtain. Even with such a small flame working vertically to get the best convection currents, the combustion chamber has to cooled down and even the first part of the flame has to be in a slow air stream and mixing with other air must be at a later stage. Using convection currents, these are powerful enough to give an idea of the true working principles of a jet engine to anyone. Using this "toyish" engine, I have got it to rotate at about 2500 rpm. I find no difficulty with shaping the compressor blade/ disc and the turbine blade/disc, but the combustion chamber working vertically to obtain high speed convection currents, seem to be the most difficult. Congratulations for all your videos, you should be invited at Universities to transfer your vast knowledge to students who tend to miss out on the practical side. Prosit.
Thank you for saying those nice things. Feel free to retract them after I regretfully inform you that you have not at all illustrated the true working principles of a jet engine. If I wasn't honest I would be in the wrong. Please upload a video of your creation for those of us who are interested in finding out more about it.
Agent JayZ, I've been enjoying your videos for a long time. All of them, the more technical the better. But, like most people, I love the J-79 tests with afterburners. For some reason, I recently stumbled upon videos of the B-58 Hustler, which used four afterburning J-79s, mounted under the wings, airliner style. FOUR J-79 engines with afterburner per aircraft!! The B-58 set all sorts of speed records in its day, and was known to fly over the USA at supersonic speeds. Sonic booms for everyone! I can only imagine what it might have been like to be on the flightline near one of these during takeoff. Thanks for all the vids, man. There's a whole generation of people who actually understand turbine engine fundamentals because of your efforts. Keep up the good work!
john90430 I must confess I'm one of those who only started to effectively understand turbine engines after watching some of his videos (even though I still feel more comfortable dealing with piston engines)
john90430 I must confess I'm one of those who only started to effectively understand turbine engines after watching some of his videos (even though I still feel more comfortable dealing with piston engines)
I don't know jets, but I remain fascinated by the human ingenuity and inventiveness that brought us jet engines, and that's why I find your videos fascinating. I'm reading (Sir) Stanley Hooker's book "Not much of an Engineer" (1985) and it's exciting to see the technology he discusses in the 'flesh' in your videos. Power on!
stoichiometric Kerosene/Air mix: ~ 2093°C or 3800°F Fancy steel alloys melt: ~ 1400°C or 2600°F ... so, that means roughly half of the air flow through the compressor is used for cooling the hot flame down to a usable temperature... and, that half of the compressed air now isn't available for increased power by heating to stoicheometric temperature. PS: thanks JZ
Think about this people, for all the air going in the front of the engine only 30% or so is used to burn the fuel, the rest is used for cooling and in the case of a turbofan, thrust. Thanks JayZ for giving us all a lesson in turbine engines. And for the question of flames out the front in a compressor stall, I worked on F-14's with TF-30 engines, they would blow flame almost past the cockpit when in the hush house, can you say BOOM.
Designing a combustion chamber is an art in itself. And getting it spot on is a miracle. I am looking everywhere to find any guide so I can design one for an experimental 400 foot-pound jet turbine. The other parts can be made on a CNC but not combustion chamber. Thank you for the excellent videos you post. I learnt a lot.
so funny, how questions keep coming in, that have been ansewered a 1000 times before :D :D :D :D I follow this channel since 2010 and there is no question left to ask about turbine engines ;-)
I think the explanation at 6:39 is why you get a hot start unless you let the speed reach ~15% before applying fuel so that adequate airflow prevents the flame from touching.
Sir I just want say thank you very very much, I learn so much from you, so awesome how you actually show the actual things, I want to become a pilot 1 day & I love learning about planes. Once again thank you
You might be interested to know that Inconel and Hastelloy alloys have been used in the high heat and corrosive environment of the Molten Salt Nuclear Reactor. The Reactors use a flouride molten salt above 600 degrees to transport and contain the reactants in a convective flow around a reactive barrier of solid graphite. Inconel , even tough it can melt is still tough stuff!
Interesting. I've been challenging myself to design a jet engine for a little while, and while I was close, I had no idea the combustion chambers rely on active cooling to work. And to think I was gonna talk to the guys at Northrop Grumman about this. Thanks, you've spared me a little embarrassment :)
Thanks for you're patience and replying to questions that have been answered before, not everyone has the time to watch ALL of you're past videos. They don't know what they are missing!
I love your videos. Will look into the raffle. I wanted to know if there has been any progress on the Orenda Iroquois engine you showed a few years ago... cant wait for that one. Also, can you show the accessory drive of a commercial jet engine?
thought it was the kekistani glag at first lol.. Iv been wondering this too but I figured out a few things on my own from experimenting. still very glad you made this video. thank you.
As you say that there is no detonation happening in combustion chambers , you once replied to me that is nothing such as "sucking" of air by the large fan in a turbofan engine, Why ?
There is no such thing as suction. Air will always move from a location of higher pressure to a location of lower pressure. Air can be pushed but it can not be pulled. Check with your physics teacher. Suction is an imaginary force that we use for convenience.
@@AgentJayZ I see what you're saying, but air can be pulled, it may not be listed as a force, but the suction our lungs and the combustion engine create to force air intake are the primary element behind the designs functionality.
even the lungs don't "suck" air @@burtpanzer . The rib cage is made of internal and external intercostal muscles that contract and relax in a rhythm set by the medulla oblongata. By contraction of External intercoastal muscles and relaxation of internal intercostal muscles, the rib cage increases in volume and thus lowering pressure concurrently. this pressure is lower as compared to that of the atmosphere, or what is termed as " ambient pressure". This ambient pressure creates a gradient with which a continuous air mass migrates. the reason is simple. our atmosphere is not void. it is made up of particles that are closely stacked, and the force gets bigger as you advance further down the layer. this force keeps pushing any particle below it. it's this that forces air- our particles, into any space that is created with energy as expenditure, thus, since space, or void that is created within us, with us or for us, is almost a deficit, it should be filled with particles. what you can regulate is how fast this void can get filled(flow rates), whether or not we even want to have it filled(on/off valves). we don't "pull", we don't "push". we create conditions that make us feel like we are pulling, or pushing air masses, and the condition is...pressure gradient.
This was a cool demonstration! It is very interesting how important it is to blanket the ultra high temp. flames with compressed air to keep the surrounding metals from melting in the hot section... I heard that special measures have been taken with the turbine blades (buckets) to keep them from melting as well...
I'm one of those idiots who has built a jet engine out of a turbocharger, and I can tell you that you can melt a burner can quite easily! Keeping the metal cool and the flame hot is quite a job.
Well if you design it properly and use liquid fuel rather than propane then it should work without melting. What you do is get it glowing then add more fuel until it glows a lot less. The evaporating fuel will remove a lot of heat. You kind of need to see inside but you could do it with an EGT probe and gauge. You have to reconcile, most of what comes out the rear will be fresh air. This is an awful pumping loss and terribly inneficient but it is a turbocharger jet not a dedicated jet engine and it doesn't have to do any work so who cares? Even real jets have large pumping losses so don't despair. This air is needed. Running the air fuel mixture well rich of peak exhaust gas temperature should help a lot. Thing is the combustor is the most complex part and getting it right difficult which no doubt you know. I have seen a guy on TH-cam build a combustor can and he did a very good job of it but it took many goes but it worked well, started easily, idled and spooled up beautifully without so much as a hiccup. I'm sure you've seen the vids. I'm offering support so don't think I'm lecturing. If you want to do it I'm sure you can.
Yeah, nah... don't listen to thePaulwhatever, because he's full of shit. The most important part that every home made jet engine project seems to ignore is the combustor liner. I have a series of videos on them. Absolutely critical. You might say they are the secret to making a jet engine work. Carry on, Kenny!
Maybe the guy that mentioned detonation was referring instead to a compressor surge/stall. Makes a heck of a bang at full throttle. The ITT rises and damage can be done depending on the cause. Still not a detonation but can sure spill the pilots coffee and ruin the passengers day when the pilot ends up having to go back to the airport for inspection/ repair.
That's really interesting. I wonder though -- how does the cooling work in rocket engine thrust chambers and nozzle walls? There's no air stream there that keeps the exhaust gases off the walls, afaik there's just yet-unburned liquid fuel that streams through pipes in the nozzle walls to cool it. So how is this enough to keep the wall from melting, even though (I assume) the gas touches the wall directly. Is it just cooler that jet engine exhaust gas?
I don't work on rocket engines, but I have done some reading. It's much like what you said. Rocket fuel is vaporized around a liner to create an insulating layer that keeps the actual flame from touching the chamber walls. The liner was very difficult to develop, and is extremely expensive to make.
Wannabe rocket scientist here. Rocket engine bells/nozzles can be coated in ablative materials that 'burn' away, protecting the bell itself (Like a heat shield). Or, cryogenic fuel can be pumped through channels in the nozzle and back into the combustion chamber for nozzle cooling. The Shuttle engines actually worked like this. The combustion chambers themselves are more complicated. I believe they are made of extreme temperature resistant materials and use a blanket of excess fuel or oxidizer surrounding the combustion area for protection. Don't quote me on that though, I might be wrong.
There are several ways too cool the bell of a rocket engine, many are listed here by others who responded to the question. For a detailed examination of rocket engines from someone who is as knowledgeable as Agent Jay Z is on jet engines, check out Scott Manly and his TH-cam channel. He does a great job teaching one about how rocket engines work, just as Jay does with jet engines.
I worked for a Pratt & Whitney vendor, and was trained in GTAW at Pratt, to go back and weld Flaps and Seals. Rowboats, Adams and Eves. I also did some Electron Beam welding, connecting the machined ends to the honeycomb portions. I started out in resistance welding, assembling Turkey Feathers for the braze ovens.
Have you ever happened to work on any forein jet engine? USSR or Chinese jets? If yes whats your opinion(design, quality, tolerances, etc) thanks man I love your vids.
Hi Agent Jay Z! Awesome video, thank you! Speaking of heat, metals expand under heat, so a few questions on the topic: 1.Do jet engines account for that and how? 2. Are there parts that are you have to assemble with some freedom of movement or some such? 3. In your testing, do you have to run engines long enough to experience thermal expansion? Thanks a bunch! Yakov
New to your channel. Love the videos and thank you for your time, patience, and passing on information that no one else is talking about. Cool and interesting to say the least.
Hello Sir, The amount of knowlegde you have, I think that now you should be making your own engines. Have you ever had designed any? wish to work with you as a researcher.
As far as I'm aware, he isn't an engineer, so designing one would be out of his field of knowledge. Rebuilding engines though? Yeah he can obviously do that.
Maybe I’ll have liquid nitrogen pumped around the core and afterburner of my jet engine. Idk how to center the fuel stream in such a way that it never actually touches the core, and I suck at math!
1- unnecessary. 2- The videos I have on cooling air explain it. 3- Many books, including the ones I recommend in my called Books, explain with diagrams how to protect metal parts from the flame.
Ok Jay, I have a mother question that may be rudimentary to you but new to me. During a compressor stall/surge, does the flame front from the combusters move forward into the compressor blades? Is this what can cause the damage to the compressor blades? Does the flame front ever move forward of the combusters? Please let me know if there is a video I should watch that would explain this better. Once again cheers from the Yukon. Keep up the good work
Here's a quote from a Boeing training video on the subject of engine surge, as near as I can remember it: "Usually, there are flames visible from both ends of the engine." In the video, there are a couple of shots of the intake of a 'Dependable Engine' with visible flame projecting forwards through the fan. Frequently, this is propelled rearwards by the fan and down the by-pass duct. I actually saw this happen on a Russian aircraft at the Farnborough Air Show some years ago. You might like to check out a clip on TH-cam of a birdstrike event at Manchester Airport (UK). The right-hand engine of a B.757 ingests a bird on take-off and suffers multiple surges, with flames and smoke pulsating from the engine efflux, before it is shut down. The engine has a full-length cowling, so it is not possible positively to identify that any flame is coming down the by-pass duct, but it certainly looks that way to me. In this case, the engine surged because the compressor blades and vanes were damaged by the passage of the sliced-up remains of the bird and their aerodynamic efficiency was degraded. However, undamaged compressors can surge for various reasons, but brief exposure to a surge event should not result in damage to a properly designed compressor. In particular, the very brief exposure to the flame should not cause any damage whatsoever to the blading. All engine manufacturers will have design rules for dealing with surge, which dictate the need for adequate axial clearances between blades and vanes. During a surge event, the blading will experience extreme deflections, because of the rapid change(s) in pressure and flow reversal. The degree of dynamic deflection will typically be so great that, if it was imposed statically, the aerofoils would be permanently deformed. However, if you want an explanation of this phenomenon, which is well known, you will need a specialist in materials science.
Detonation, as described by many credible resources, is an ultrasonic combustion or oxidization of fuel, in such a manner that the flame front expansion speed exceeds the speed of sound in that medium, while combustion is a rapid but infrasonic chemical reaction which produces heat. Detonation, generally speaking, is considered negative in Thermodynamic applications, as it introduces the system to ultra high pressure shock waves and uncontrollable reactions.
The first jets had separate outer combustor cases, or "cans", each with their own liners. The next step forward was a single outer case enclosing a circle of "can type" liners... this was known as a "can annular" arrangement. Since the 1970s, the most advanced way do do it is to have a single annular combustor liner indide a single outer combustor case. This is called an annular combustor, and it is the most efficient way to combust the fuel.
It is easier to contain the pressure. Cans match the compressor vanes and injectors. You may try to avoid the stator before the turbine. But Ignition needs a torus.
Hi JayZ. I thoroughly enjoy your programmes, ty for making them. What makes a low-smoke fuel nozzle low smoke? I'm guessing it must mix the reactants more efficiently or at a higher temperature but have no training or experience in jet engines so wondered if you knew. As a knock on question is the low-smoke property what was being sought when these nozzles were designed or is being smokeless a secondary bonus of just trying to make a more efficient engine? Many thx.
Never been a huge jet fan, but love these videos. Always thought I was born too late and wished I was a radial tech in the 40,s. Qualified for anything the military had asked for jets in 1983 was told there was a year waiting list. Should have waited. I could be where you are.
Rocket engines do not have inlet air. The nozzle is cooled by a liquid, usually the fuel flowing through and around it in complex patterns I can't explain. Solid fuel rockets I am not able to comment on.
@@AgentJayZ i mean is that what happen to the flame inside a rocket? I can imagine that The flame also does not touch the metal surfaces inside a rocket engine ....... Thank you for your response sir, your explanation answer a lot of question in my head
Rocket engines use different kinds of cooling methods. Some pump the fuel through the nozzle walls to cool it, before it is injected into the combustion chamber (regenerative cooling). Some engines inject a fuel-rich mixture right next to the walls of the chamber, to keep a lower temperature there, and have some unburnt fuel that can cool the walls (curtain cooling). Others use the exhaust from the turbine used to drive the fuel pumps instead of a fuel-rich mixture. Some engines have an ablative material coating on the inside walls, which takes the abuse instead of the nozzle itself (ablative cooling), that doesn't work for engines that need to fire for long periods of time or to be reused often of course. These methods are probably also combined in many engines.
@@luarbiasawaras8700 Rocket engine cooling can be very impressive, there are many RS-25 engine testing video on youtube, and you can see inside the nozzle it's the manifesto of hell, a blue-hued, near translucent flame blazing at a whooping 3300 °C, hot enough to boil iron, but outside the nozzle is warm to the touch, if you are really that ballsy to touch it.
AmdusiasSix Six the labyrinth seal keeps the oil mist from flowing into the air stream. This is achieved because the pressure in the bearing compartment is slightly higher then atmospheric. Your questions 33 has more information
Essentially, a labyrinth seal works by creating successive restrictions to the flow of air from a higher pressure region to a lower pressure region. The restrictions are formed by a series of small fins, typically on a rotating component, running with a very close clearance in a static housing. However, labyrinth seals can be used between two rotating components in a two- (or three-) shaft engine and their use is not restricted to the sealing of bearing housings.
dieselscience that was my guess, and it makes sense, but how does it do it? Just higher pressures? Different nozzle geometry? That's what I'm curious about.
Combination of mostly nozzle improvement with some fuel formulation changes through the years. My experience is with diesel engine injectors. Nozzle improvements alone have been a big help in reducing smoke particulates.
You mention no flame touching metal. What happens during a "torch" on startup where there is flame running through the turbines? Is that definitely causing damage or since the turbine is rotating it has time to cool off since the flame is probably only at a certain point along the circumference of the combustor?
There is insufficient oxygen exposure, or an incomplete burn of the fuel, which means the flame temperature is insufficient to cause damage over a short term.
As discussed before in videos about hot starts, it's all about exposure time. The temps involved at starting are definitely enough to destroy the engine... if they are experience for more than a few seconds. It's exactly like your hand and a flame. Put your hand fully into a fire, for one quarter of a second... everything is exciting and fine. Put your hand fully into a fire, for one quarter of a minute... uh, oh... I think we wrecked it.
they went to fort ticonderoga...... *_WAIT A SECOND_* you _could_ kill someone with a pencil... but you don't, why, because its too impractical and schools let you use them, there could be mass murderers at a school and would have a full supply of "weaponry". never thought of that now did ya? thats why im the edgyest kid at my highschool.
Nope ..... er, no, I'm a Brit and we've been here several times before on this channel. It's called a mid-span shroud in N America, or a clapper, if you work at R-R Derby, or a snubber, if you work at R-R Bristol. It has no aerodynamic function: it is essentially a friction damping and vibration modifying device for the blade aerofoil. It works by coming into contact with the mid-span shrouds of the blades on either side of it, effectively forming a ring.
When looking at the air right as it exits the compressor, about what percent of it is working air? Also, the percentages used to feed the flame, cool the blades, etc.? Very nice explanation by the way.
How small is small? If you want to build a functioning model aircraft sized jet engine, the answer is, yes, you can! Try looking for books by Thomas Kamps and Kurt Schreckling. Or you can buy one ready made from a UK company called Wren (other model gas turbine engines are available). It will cost you around USD3,000.
Yeah, they are right. It is like thousands of dollars for a proper working model plane jet engine. That being said, you could do it yourself in about 10 years & $25,000. It really depends on how much fancy metals are going to cost you. Also if it breaks, ur fukt.
There are several smaller planes and helicopters that have switched to turbine engines due to their reliability. The PT6 is a good example found in smaller planes like the TBM 850
Hi ! I just discovered your collection of videos. Being a pilot, i find them highly interesting. Thank you so much for the job, keep it up. I also have a question relating to the fan blade you showed at the end of this video. I have a few of them that I would like to clean up and put on stands. Any trick on how to make them shiny ? Thanks a million !! Seb
Depending on how beat up they are, and how shiny you want: Wet sanding by hand with 320, 400, 600 grit sandpaper (about an hour or more on these steps). Cleaning with soap and water until a white cloth stays white. Metal polish, with hand rubbing. Loads of elbow grease required if you want that mirror finish.
Great stuff Jay, and thanks for your support of the Special Olympics. Could you comment on the air/flame/heat flow at the flame holders in the afterburner? Why don't they melt, where is the actual flame, how are they cooled? Thanks much, I love your stuff.
The burning happens just downstream of the flame holder, so it's not in the flame, but it does glow red hot, as you can see in many of my test run videos.
I wonder if HarryT was meant to say conflagration as apposed to detonation. Two very different things some people confuse. Burning of fuel as opposed to a chemical chain reaction. (made a spelling typo)
nndorconnetnz As far as I learned the burning of fuel is also a chemical chain reaction. The difference between conflagration and detonation only lies in the speed of the reaction front vs. the local speed of sound.
In the mid 1980's I was assigned to the power plants division of a Naval Air Reserve A-7B squadron. During that time, Bell and Howell defense came up with an engine monitoring system that was supposed to help extend engine life. The theory went that engines operated at mostly low power settings should last longer than those flown at high settings. So, with sensors and a means to record them, projected life till overhaul could be predicted. If something went wrong, that was recorded as well. Almost immediately, the system was recording impossibly high turbine inlet temperatures of 5000 degrees for 2 hours flight time. Even so, the powers that be (chiefs/officers) would have us (mechs) check out the airplane even when told 5,000 degrees C would literally melt the engine. The system also recorded flights that lasted 100+ hours. I always thing back to those days whenever a Bell and Howell commercial comes on. : D
The earliest maintenance monitoring system I recall was on the C-5A galaxy. It didn't work too well either. However eventually these systems did prevail, and engine and systems lifespan improved dramatically. This had a major positive impact to extend TSO, and time change intervals saving the aviation industry Billions annually.
@@scootergeorge9576 What does that have to do with the overall aircraft maintenance monitoring systems in modern aircraft? These systems evolved rather than just showing up one day. The point I was addressing is we are where we are today because of the many efforts by everyone's effort. Including your own. Even if you didn't recognize it at the time.
@@Dave-ty2qp - Before Bell and Howell techs showed up at Pt Mugu California, I had been an aircraft mechanic in the Navy for 13 years and had never heard of anything like this. Another unit operating the A-7 was notified BY AIMD, NOT to turn in another engine based simply upon data from this monitoring system. This was 1984 or 1985. I'm sure the technology has progressed quite a bit over the years but back in the eighties it was worthless.
Hi AgentJayZ, great video as always, could you explain a little more about the smoke less fuel injectors? how are they different? only the injector makes the difference or there is also a special smoke less cobustion casing?
Some time ago I read somewhere (I don't recall where) that one of the problems Frank Whittle encountered developing the engine was maintaining flame stability. The issue (if I recall correctly) was the velocity of the air fed to the fuel flame front. A figure of something like 15mph was the don't exceed number that a flame (reliable?) could be maintained. A lot of the development was how to slow down the air stream to/in the combustion chamber. Can you tell us if that was the case, if so is it still a consideration in engine design? Has the increasing effective compression ratios of the newer engines changed this limitation (if the basis of my query is was true)? I think you might've alluded to this in the past without mentioning the velocity.
The air is really slowed down in the diffuser, then slowed even more inside the combustor liner. The speed limits for combustion have stayed the same. We would be lucky to hear from our friendly neighborhood Jet Engine Design Engineer on this subject. He's much more qualified to answer you.
Greetings from Singapore, where the Air Force was tearing up the sky with its F-15s earlier, and thanks for the invitation to respond, AgentJayZ. As a matter of courtesy to you, I refrained from answering on this topic earlier. Thanks, too, for blowing a well-deserved raspberry at a certain individual: 'detonation' does NOT occur in any current jet engine, despite previous contributions from some smartarses (-asses if you want N American spelling). The very fact that we are discussing a low flame propagation rate goes a long way towards proving this. However, I was never a specialist combustion engineer, but I had heated discussions with them on several occasions, over issues that arose during the design of various combustion chambers. In essence, the flame propagation rate in a jet engine combustor is not very much different from that which occurs in ambient conditions and, from memory, I've seen a figure of 20 to 30 ft/sec quoted somewhere. It might be a bit faster in the elevated pressure (and temperature) conditions of the combustor, because the Oxygen molecules are closer together and more energetic, and I've seen a figure of 50 ft/sec for the non-detonation flame velocity in a petrol/gasoline engine. It would be interesting to have a real expert to comment. I was going to suggest that if you've ever seen an oxy-acetylene torch lit up, with a 'rich' smoky yellow flame and then promptly be extinguished when the Oxygen was turned on too quickly, then that might be a demonstration of the flame being 'blown out' with too high a velocity. I'm having second thoughts, though, because it could well be that it results from a sudden excess of Oxygen and too weak a mixture. Nevertheless, the 'trick' in a jet engine combustion chamber is to create a swirling recirculatory flow in the primary zone of the combustor, in which the flame is stabilised. The same essentially goes for an afterburner (I did so want to say'reheat'), which usually has 'gutters', either radial or circumferential, to create swirling low velocity regions in the flow immediately downstream.
Hi, i love your videos. can you make a video that explain -why the heated gas in the combustion chamber (which is at highest pressure in the system)- does not goes back to the compressor? what make it flow to toward the turbine and not back to the compressor (through the combuster liner holes)?
i could not find the video, would you include a link? in the combustion chamber, the pressure is higher than the compressor because of the combustion of fuel, so why the what does not goes back to the compressor? what make the gas flow to toward the turbine and not back to the compressor (through the combuster liner holes)?
Doron Koren The path of least resistance is through the turbine blades. The air would have to reverse direction, then fight all the incoming air and the blades of the compressor (just not possible). The turbine blades are already spinning the correct direction for the airflow of the engine when the fuel is introduced, so the hot expanding gas follows the path of least resistance back to atmospheric pressure, which will always be out the back of the engine(by design).
Hi Andy, Question: in the combustion chamber, the pressure is higher than the compressor because of the combustion of fuel, so how come new air comes into the combustion chamber ?, is it air pulse? one way valve? thanks for interesting videos.
Who's Andy? You are incorrect sir. I will not spoon feed you, but will remind you that a gas pressure profile graph is shown in all of the books I recommend in my video called books. Also, we review just such a diagram for this very engine in one of my videos in the Diagrams series. I suggest you enjoy them all.
this is what i found in the web, seems that the velocity of the compressed air is going up in the combustion liner. so according to Bernoulli law the pressure is going down but stay almost the same due to the heat of the flame (i hope that I understand it correctly) i really hope you would make a video on this. thanks for interesting and fascinating stuff.
I already have. The videos I suggested to you will explain. We are not debating some question. I am trying to let you discover on your own what is really happening. Please proceed.
@@doronkoren7040 As the air leaves the compressor it goes threw the diffuser case. The air velocity decreases, as it enters the diffuser and as a result the air pressure increases because it has more volume in the combustion area. The flame of the combustion is centered by the air being squeezed threw the many little holes in the combustion chamber. The only escape of the hot exhaust gasses then is threw the transition liner and is directed to the the turbine nozzles. Does that help?
Watching a video on F-86 when they entered service in Korea it was mentioned engine had a 60 hour service life. Thought it would be the cans but not sure. Maybe bearing surfaces?
AgentJayZ you have covered the igniters,what about the power source for the igniters. Is there a battery in the aircraft? I think modern airlines are 48volts 400hz what is the voltage feed for the J79. When mounted in the test cell or in an electricity generating plant is the J79 “plugged into the mains”or does it have a battery?
As you know, the igniters are only used to light the flame, and are then turned off. On the J79, there are two power sources and three separate individual ignition circuits. One 440Hz 120VAC, and two 28VDC. There were also some 120VAC 60Hz boxes produced. An industrial application will have any of these systems, and and appropriate power supply to run it. The engine is designed in such a way that, once running, it is a net producer of electricity, and does not need any to run. In an industrial setting, all the sensors and equipment that might need electricity are powered by the facility and are not really considered part of the engine. A bit like an old timey diesel, no electric power is required for an old-school turbojet to function.
If air from the compressor stage can flow into the combustion liner to cool it, does that mean the pressure of the hot gas in the combustor is lower than that in the compressor stage?
Yes it does. In one of my turbine engine diagrams videos, we follow the air through a turbojet measuring it's pressure along the way. The heat of combustion does not cause a rise in pressure in the combustors. Always remember, these are not piston engines, and do not behave according to the Otto cycle...
First I want to thank you for sharing this knowleadge with us. Now a question, Its posible to build a mini or micro Jet engine and also build a mini or micro rocket engenie? For aeromodelism or amateur proyects ? Thank for the time.
In respect of a model aircraft sized jet engine, I've already answered this question for another subscriber. If you want to build a functioning model aircraft sized jet engine, the answer is, yes, you can! Try looking for books by Thomas Kamps and Kurt Schreckling. Or you can buy one ready made from a UK company called Wren (other model gas turbine engines are available). It will cost you around USD3,000. Alternatively, you can buy the engine as a kit and assemble it yourself. If you wanted to try building a liquid-fuelled rocket engine, I believe that would be an altogether more risky proposition.
Many years ago, I did actually work on rocket engines - briefly - before having a career lifetime designing gas turbine engines. With safety in mind, my advice would be to stick to trying to make a small turbojet engine. Nevertheless, I have done some research for you, but I take absolutely no responsibility if you ever tried to make a rocket engine of any description. You would do so entirely at your own risk. Back in 1967, a book was published, entitled, ' How to Design, Build and Test Small, Liquid-Fuel Rocket Engines', by L J Krzycki. It's out of print now, but it can be downloaded from the internet. The first sentence of its foreword reads, "The rocket engine is a relatively simple device ....." . Yes, it might be relatively simple, but it's potentially very dangerous. Please note also that the book doesn't tell you how to fly a liquid-fuel rocket engine. It assumes ground testing only, using gaseous Oxygen and a hydrocarbon liquid fuel, such as gasoline or methyl alcohol. A conventional Oxygen cylinder, even a small one, would be far too heavy to fly and to make a lightweight cylinder would be high-end aerospace technology. As you will have seen, if you have watched satellite launches, handling liquid Oxygen would be extremely risky for an amateur and, in any case, no responsible supplier would sell it to you. The same goes for concentrated Hydrogen Peroxide (HTP), which is another possible liquid oxidiser. It's extremely unstable and, again, I would hope that no responsible supplier would sell it to you. I once witnessed a rocket engine test where there was a severe leak of HTP. I was glad to have been behind armoured glass. You could try making a solid-fuel rocket, using Sodium Nitrate and sugar: you will find information on the internet. Yet again, however, there are real dangers: you would be trying to mix a fast-burning fuel that is potentially explosive. If you did want to fly small rockets, check out 'Estes' rocket motors. They are commercially available and relatively safe, if properly handled: I am trained in their use for rocket-powered model cars. Note for AgentJayZ: I have given due warning of the potential dangers, but if you saw fit to delete this, I would have no problem with your decision.
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Why don't jet engines melt? Because they're so COOL!
🙄
😁
Sir, may I congratulate you on your great experience of jet engines, your vast practical and theoretical knowledge, and the elegant and accurate vocabulary you use to describe the details of the procedures and the actions involved. When you speak about any working part of the engine, it is as if you are part of it and feeling and experiencing the action yourself. You seem to feel the pains and the glory of all parts of the jet engine which you seem to love so much and you treat them as if they were part of your family. You want them to work, but not suffer. At the moment I am working on a very small jet engine to show my grandson the working principles of the engine. I am using tinned milk containers to make compressors and turbines and combustion chambers and rather than building up pressure with the compressor, I am using the small engine in a vertical manner and so high speed convection currents will help to rotate the turbine which in turn rotates the compressor below it with the flame in between. I found that the combustion chamber part needs to be longer to permit the air to gain a higher velocity due to convection and not the pressure after the compression, which I can never obtain. Even with such a small flame working vertically to get the best convection currents, the combustion chamber has to cooled down and even the first part of the flame has to be in a slow air stream and mixing with other air must be at a later stage. Using convection currents, these are powerful enough to give an idea of the true working principles of a jet engine to anyone. Using this "toyish" engine, I have got it to rotate at about 2500 rpm. I find no difficulty with shaping the compressor blade/ disc and the turbine blade/disc, but the combustion chamber working vertically to obtain high speed convection currents, seem to be the most difficult.
Congratulations for all your videos, you should be invited at Universities to transfer your vast knowledge to students who tend to miss out on the practical side. Prosit.
Thank you for saying those nice things. Feel free to retract them after I regretfully inform you that you have not at all illustrated the true working principles of a jet engine.
If I wasn't honest I would be in the wrong.
Please upload a video of your creation for those of us who are interested in finding out more about it.
Agent JayZ, I've been enjoying your videos for a long time. All of them, the more technical the better. But, like most people, I love the J-79 tests with afterburners. For some reason, I recently stumbled upon videos of the B-58 Hustler, which used four afterburning J-79s, mounted under the wings, airliner style.
FOUR J-79 engines with afterburner per aircraft!! The B-58 set all sorts of speed records in its day, and was known to fly over the USA at supersonic speeds. Sonic booms for everyone! I can only imagine what it might have been like to be on the flightline near one of these during takeoff.
Thanks for all the vids, man. There's a whole generation of people who actually understand turbine engine fundamentals because of your efforts. Keep up the good work!
john90430 I must confess I'm one of those who only started to effectively understand turbine engines after watching some of his videos (even though I still feel more comfortable dealing with piston engines)
john90430 I must confess I'm one of those who only started to effectively understand turbine engines after watching some of his videos (even though I still feel more comfortable dealing with piston engines)
I was an AD (jet mechanic) in the USN 89-94 F404-400, TF-30 and J-52... loved working on them
I don't know jets, but I remain fascinated by the human ingenuity and inventiveness that brought us jet engines, and that's why I find your videos fascinating. I'm reading (Sir) Stanley Hooker's book "Not much of an Engineer" (1985) and it's exciting to see the technology he discusses in the 'flesh' in your videos. Power on!
Also recommended: Herman the German, the autobiography of renowned GE engineer Gerhard Neumann.
stoichiometric Kerosene/Air mix:
~ 2093°C or 3800°F
Fancy steel alloys melt:
~ 1400°C or 2600°F
... so, that means roughly half of the air flow through the compressor is used for cooling the hot flame down to a usable temperature... and, that half of the compressed air now isn't available for increased power by heating to stoicheometric temperature.
PS: thanks JZ
Two thirds. you might want to watch my latest vid called Heat upon HEAT, and also an old one called cooling air.
Think about this people, for all the air going in the front of the engine only 30% or so is used to burn the fuel, the rest is used for cooling and in the case of a turbofan, thrust. Thanks JayZ for giving us all a lesson in turbine engines. And for the question of flames out the front in a compressor stall, I worked on F-14's with TF-30 engines, they would blow flame almost past the cockpit when in the hush house, can you say BOOM.
Designing a combustion chamber is an art in itself. And getting it spot on is a miracle. I am looking everywhere to find any guide so I can design one for an experimental 400 foot-pound jet turbine. The other parts can be made on a CNC but not combustion chamber. Thank you for the excellent videos you post. I learnt a lot.
I worked at Roll Royce combustion systems Derby UK. 'Film Cooling' is the term for directed air that protects the metal surfaces.
so funny, how questions keep coming in, that have been ansewered a 1000 times before :D :D :D :D I follow this channel since 2010 and there is no question left to ask about turbine engines ;-)
That was a piece of information searching for my lifetime
I think the explanation at 6:39 is why you get a hot start unless you let the speed reach ~15% before applying fuel so that adequate airflow prevents the flame from touching.
Carlos Pulpo similar thought came to my mind too :)
Sir I just want say thank you very very much, I learn so much from you, so awesome how you actually show the actual things, I want to become a pilot 1 day & I love learning about planes. Once again thank you
You might be interested to know that Inconel and Hastelloy alloys have been used in the high heat and corrosive environment of the Molten Salt Nuclear Reactor. The Reactors use a flouride molten salt above 600 degrees to transport and contain the reactants in a convective flow around a reactive barrier of solid graphite. Inconel , even tough it can melt is still tough stuff!
Thankyou for sharing the wealth of experience you have with jet engines that are a modern marvel, keep up the great work 🇬🇧 👍
Interesting. I've been challenging myself to design a jet engine for a little while, and while I was close, I had no idea the combustion chambers rely on active cooling to work. And to think I was gonna talk to the guys at Northrop Grumman about this. Thanks, you've spared me a little embarrassment :)
Matt Brody after you're done designing the jet engine, maybe consider designing a new cpu?
.
Thanks for you're patience and replying to questions that have been answered before, not everyone has the time to watch ALL of you're past videos.
They don't know what they are missing!
Thank you for helping special olympics. My son is a special person and I help and he participates in the Texas Special Olympics.
I love your videos. Will look into the raffle. I wanted to know if there has been any progress on the Orenda Iroquois engine you showed a few years ago... cant wait for that one. Also, can you show the accessory drive of a commercial jet engine?
Thank you sir, you just helped me in my modules.
Love your Vids man, thanks for sharing your wealth on knowledge with us, your probably the best source on TH-cam,
thought it was the kekistani glag at first lol.. Iv been wondering this too but I figured out a few things on my own from experimenting. still very glad you made this video. thank you.
love the things you teach us jay. a question, please.
why soviet jets make so much smoke?
because they are inefficient crap, the whole internet debate that they are more powerful is an utter bs
They run Rich. Aka Too much Fuel being fed into the Combustion Chamber
I just have to say that is the coolest thing, helping out the special olympics like that good for you
Have you entered? There are not as many entries as I expected, so your chances of winning are pretty good!
I like your channel, taught me A LOT. Thanks. Keep it going you are doing fantastic
They are made of unmeltium.
And in cooling down the combustion chamber and flame, the cooling air heats up and expands, and in expanding is able to do work. M
Thanks man. All kinds of knowledge here. I appreciate you. ,,,,,,,,,,, Jeremy in Alabama.
As you say that there is no detonation happening in combustion chambers , you once replied to me that is nothing such as "sucking" of air by the large fan in a turbofan engine, Why ?
There is no such thing as suction. Air will always move from a location of higher pressure to a location of lower pressure. Air can be pushed but it can not be pulled.
Check with your physics teacher. Suction is an imaginary force that we use for convenience.
@@AgentJayZ thanks alot for your explanation .
@@AgentJayZ Maybe he intended the backfire, I don't know thou.
@@AgentJayZ I see what you're saying, but air can be pulled, it may not be listed as a force, but the suction our lungs and the combustion engine create to force air intake are the primary element behind the designs functionality.
even the lungs don't "suck" air @@burtpanzer . The rib cage is made of internal and external intercostal muscles that contract and relax in a rhythm set by the medulla oblongata. By contraction of External intercoastal muscles and relaxation of internal intercostal muscles, the rib cage increases in volume and thus lowering pressure concurrently. this pressure is lower as compared to that of the atmosphere, or what is termed as " ambient pressure". This ambient pressure creates a gradient with which a continuous air mass migrates. the reason is simple. our atmosphere is not void. it is made up of particles that are closely stacked, and the force gets bigger as you advance further down the layer. this force keeps pushing any particle below it. it's this that forces air- our particles, into any space that is created with energy as expenditure, thus, since space, or void that is created within us, with us or for us, is almost a deficit, it should be filled with particles. what you can regulate is how fast this void can get filled(flow rates), whether or not we even want to have it filled(on/off valves). we don't "pull", we don't "push". we create conditions that make us feel like we are pulling, or pushing air masses, and the condition is...pressure gradient.
Cool to see the four flags together.
Lotta flags. Can't fit all of them in one shot.
This was a cool demonstration! It is very interesting how important it is to blanket the ultra high temp. flames with compressed air to keep the surrounding metals from melting in the hot section... I heard that special measures have been taken with the turbine blades (buckets) to keep them from melting as well...
That was a great a competition with a very worthy cause, I really hate that I missed it.
Totally agree about the detonation thing. Get fed up of hearing people talk about explosions or detonation, when they mean Combustion!!
I'm one of those idiots who has built a jet engine out of a turbocharger, and I can tell you that you can melt a burner can quite easily! Keeping the metal cool and the flame hot is quite a job.
Well if you design it properly and use liquid fuel rather than propane then it should work without melting. What you do is get it glowing then add more fuel until it glows a lot less. The evaporating fuel will remove a lot of heat. You kind of need to see inside but you could do it with an EGT probe and gauge.
You have to reconcile, most of what comes out the rear will be fresh air. This is an awful pumping loss and terribly inneficient but it is a turbocharger jet not a dedicated jet engine and it doesn't have to do any work so who cares? Even real jets have large pumping losses so don't despair. This air is needed.
Running the air fuel mixture well rich of peak exhaust gas temperature should help a lot.
Thing is the combustor is the most complex part and getting it right difficult which no doubt you know. I have seen a guy on TH-cam build a combustor can and he did a very good job of it but it took many goes but it worked well, started easily, idled and spooled up beautifully without so much as a hiccup. I'm sure you've seen the vids. I'm offering support so don't think I'm lecturing. If you want to do it I'm sure you can.
Yeah, nah... don't listen to thePaulwhatever, because he's full of shit. The most important part that every home made jet engine project seems to ignore is the combustor liner. I have a series of videos on them. Absolutely critical. You might say they are the secret to making a jet engine work.
Carry on, Kenny!
@@AgentJayZ i mentioned what you mentioned. WTFs your problem?
Ignore the stupid responses here. I like your videos. Love turbines, some of the concepts are simple, but that’s cool too.
Maybe the guy that mentioned detonation was referring instead to a compressor surge/stall. Makes a heck of a bang at full throttle. The ITT rises and damage can be done depending on the cause. Still not a detonation but can sure spill the pilots coffee and ruin the passengers day when the pilot ends up having to go back to the airport for inspection/ repair.
Maybe, but the point is, we do not use vague and inaccurate terms in this occupation.
Get it right, or get it wrong...
If you had a chance to design a new engine what would you change from the ones currently in use today?
That's really interesting. I wonder though -- how does the cooling work in rocket engine thrust chambers and nozzle walls? There's no air stream there that keeps the exhaust gases off the walls, afaik there's just yet-unburned liquid fuel that streams through pipes in the nozzle walls to cool it. So how is this enough to keep the wall from melting, even though (I assume) the gas touches the wall directly. Is it just cooler that jet engine exhaust gas?
I don't work on rocket engines, but I have done some reading. It's much like what you said. Rocket fuel is vaporized around a liner to create an insulating layer that keeps the actual flame from touching the chamber walls. The liner was very difficult to develop, and is extremely expensive to make.
Wannabe rocket scientist here. Rocket engine bells/nozzles can be coated in ablative materials that 'burn' away, protecting the bell itself (Like a heat shield).
Or, cryogenic fuel can be pumped through channels in the nozzle and back into the combustion chamber for nozzle cooling. The Shuttle engines actually worked like this.
The combustion chambers themselves are more complicated. I believe they are made of extreme temperature resistant materials and use a blanket of excess fuel or oxidizer surrounding the combustion area for protection. Don't quote me on that though, I might be wrong.
There are several ways too cool the bell of a rocket engine, many are listed here by others who responded to the question. For a detailed examination of rocket engines from someone who is as knowledgeable as Agent Jay Z is on jet engines, check out Scott Manly and his TH-cam channel. He does a great job teaching one about how rocket engines work, just as Jay does with jet engines.
Hello
I am in Montreal right now
Can I get an appointment to visit the workshop....
Bcz I am a jet engine lover
Ft. St. John, BC.
I worked for a Pratt & Whitney vendor, and was trained in GTAW at Pratt, to go back and weld Flaps and Seals. Rowboats, Adams and Eves. I also did some Electron Beam welding, connecting the machined ends to the honeycomb portions.
I started out in resistance welding, assembling Turkey Feathers for the braze ovens.
Have you ever happened to work on any forein jet engine? USSR or Chinese jets? If yes whats your opinion(design, quality, tolerances, etc) thanks man I love your vids.
Hi Agent Jay Z!
Awesome video, thank you!
Speaking of heat, metals expand under heat, so a few questions on the topic:
1.Do jet engines account for that and how?
2. Are there parts that are you have to assemble with some freedom of movement or some such?
3. In your testing, do you have to run engines long enough to experience thermal expansion?
Thanks a bunch!
Yakov
yes, yes, yes. Maybe have a look at Twin Shaft Turbine Engine Bearings
Thanks a lot!
New to your channel. Love the videos and thank you for your time, patience, and passing on information that no one else is talking about. Cool and interesting to say the least.
Hello Sir,
The amount of knowlegde you have, I think that now you should be making your own engines. Have you ever had designed any? wish to work with you as a researcher.
As far as I'm aware, he isn't an engineer, so designing one would be out of his field of knowledge. Rebuilding engines though? Yeah he can obviously do that.
Maybe I’ll have liquid nitrogen pumped around the core and afterburner of my jet engine. Idk how to center the fuel stream in such a way that it never actually touches the core, and I suck at math!
1- unnecessary.
2- The videos I have on cooling air explain it.
3- Many books, including the ones I recommend in my called Books, explain with diagrams how to protect metal parts from the flame.
Now it all makes sense.
You have the ultimate snowblower at your disposal ......you need to test an engine during a blizzard...
We've done that a couple times. Videos are up. Your mission, if you choose to accept it, is to find them and enjoy.
@@AgentJayZ sir you have a deal....blow some snow...
Awesome explanation Sir. I didn't know that. Thanks for sharing. Regards from Brazil.
Even the RC turbine engine I have cost $4000.00. Putting out 45lbs thrust @ 110,000rpm idles @ 33,000rpm. I can only imagine what the big boys cost! 😆
good video. could you show us the amount of snow you have ?
Your humour kills me lol
Great video. Thanks for the insights.
Ok Jay, I have a mother question that may be rudimentary to you but new to me. During a compressor stall/surge, does the flame front from the combusters move forward into the compressor blades? Is this what can cause the damage to the compressor blades? Does the flame front ever move forward of the combusters? Please let me know if there is a video I should watch that would explain this better. Once again cheers from the Yukon. Keep up the good work
Here's a quote from a Boeing training video on the subject of engine surge, as near as I can remember it: "Usually, there are flames visible from both ends of the engine." In the video, there are a couple of shots of the intake of a 'Dependable Engine' with visible flame projecting forwards through the fan. Frequently, this is propelled rearwards by the fan and down the by-pass duct. I actually saw this happen on a Russian aircraft at the Farnborough Air Show some years ago.
You might like to check out a clip on TH-cam of a birdstrike event at Manchester Airport (UK). The right-hand engine of a B.757 ingests a bird on take-off and suffers multiple surges, with flames and smoke pulsating from the engine efflux, before it is shut down. The engine has a full-length cowling, so it is not possible positively to identify that any flame is coming down the by-pass duct, but it certainly looks that way to me.
In this case, the engine surged because the compressor blades and vanes were damaged by the passage of the sliced-up remains of the bird and their aerodynamic efficiency was degraded. However, undamaged compressors can surge for various reasons, but brief exposure to a surge event should not result in damage to a properly designed compressor. In particular, the very brief exposure to the flame should not cause any damage whatsoever to the blading.
All engine manufacturers will have design rules for dealing with surge, which dictate the need for adequate axial clearances between blades and vanes. During a surge event, the blading will experience extreme deflections, because of the rapid change(s) in pressure and flow reversal. The degree of dynamic deflection will typically be so great that, if it was imposed statically, the aerofoils would be permanently deformed. However, if you want an explanation of this phenomenon, which is well known, you will need a specialist in materials science.
Fun with flags, Dr Sheldon Cooper :D
Detonation, as described by many credible resources, is an ultrasonic combustion or oxidization of fuel, in such a manner that the flame front expansion speed exceeds the speed of sound in that medium, while combustion is a rapid but infrasonic chemical reaction which produces heat. Detonation, generally speaking, is considered negative in Thermodynamic applications, as it introduces the system to ultra high pressure shock waves and uncontrollable reactions.
This video assumes the viewer already knows that, and I think they do.
@@AgentJayZ I added that clarification for anybody who is not familiar with the technical definition.Great content anyways! Thanks.
That combustor works a lot like an oil furnace.
This is cool I'm from Vermont and work at GE Aviation and make jet engine blades.
This is pure gold ✨️
Same principle you have with flame containment as the magnetic bottle containing the antimatter for the enterprise
so why do they have separate combustors instead of one continuous combustors?
The first jets had separate outer combustor cases, or "cans", each with their own liners.
The next step forward was a single outer case enclosing a circle of "can type" liners... this was known as a "can annular" arrangement.
Since the 1970s, the most advanced way do do it is to have a single annular combustor liner indide a single outer combustor case. This is called an annular combustor, and it is the most efficient way to combust the fuel.
It is easier to contain the pressure. Cans match the compressor vanes and injectors. You may try to avoid the stator before the turbine. But Ignition needs a torus.
Hay Jay you give us loads of great info !!!!!!!!
Hi JayZ. I thoroughly enjoy your programmes, ty for making them. What makes a low-smoke fuel nozzle low smoke? I'm guessing it must mix the reactants more efficiently or at a higher temperature but have no training or experience in jet engines so wondered if you knew. As a knock on question is the low-smoke property what was being sought when these nozzles were designed or is being smokeless a secondary bonus of just trying to make a more efficient engine? Many thx.
Never been a huge jet fan, but love these videos. Always thought I was born too late and wished I was a radial tech in the 40,s. Qualified for anything the military had asked for jets in 1983 was told there was a year waiting list. Should have waited. I could be where you are.
is that also what happen inside rocket engine?
Rocket engines do not have inlet air. The nozzle is cooled by a liquid, usually the fuel flowing through and around it in complex patterns I can't explain.
Solid fuel rockets I am not able to comment on.
@@AgentJayZ i mean is that what happen to the flame inside a rocket? I can imagine that The flame also does not touch the metal surfaces inside a rocket engine ....... Thank you for your response sir, your explanation answer a lot of question in my head
Rocket engines use different kinds of cooling methods. Some pump the fuel through the nozzle walls to cool it, before it is injected into the combustion chamber (regenerative cooling). Some engines inject a fuel-rich mixture right next to the walls of the chamber, to keep a lower temperature there, and have some unburnt fuel that can cool the walls (curtain cooling). Others use the exhaust from the turbine used to drive the fuel pumps instead of a fuel-rich mixture. Some engines have an ablative material coating on the inside walls, which takes the abuse instead of the nozzle itself (ablative cooling), that doesn't work for engines that need to fire for long periods of time or to be reused often of course. These methods are probably also combined in many engines.
@@MeepMu thank you for the explanation
@@luarbiasawaras8700 Rocket engine cooling can be very impressive, there are many RS-25 engine testing video on youtube, and you can see inside the nozzle it's the manifesto of hell, a blue-hued, near translucent flame blazing at a whooping 3300 °C, hot enough to boil iron, but outside the nozzle is warm to the touch, if you are really that ballsy to touch it.
Is it possible for you to make a video explaining how labyrinth seals work?
AmdusiasSix Six the labyrinth seal keeps the oil mist from flowing into the air stream. This is achieved because the pressure in the bearing compartment is slightly higher then atmospheric. Your questions 33 has more information
Essentially, a labyrinth seal works by creating successive restrictions to the flow of air from a higher pressure region to a lower pressure region. The restrictions are formed by a series of small fins, typically on a rotating component, running with a very close clearance in a static housing. However, labyrinth seals can be used between two rotating components in a two- (or three-) shaft engine and their use is not restricted to the sealing of bearing housings.
My son might be there with you some day
I think dumping entry tickets in a jet blast is the greatest idea ever
My little engine schooling explained it burns. Just real really fast.
What makes the low smoke nozzle different than the old ones?
In a word ... atomization. The new ones have a better, finer spray and that contributes to more thorough combustion.
dieselscience that was my guess, and it makes sense, but how does it do it? Just higher pressures? Different nozzle geometry? That's what I'm curious about.
Combination of mostly nozzle improvement with some fuel formulation changes through the years. My experience is with diesel engine injectors. Nozzle improvements alone have been a big help in reducing smoke particulates.
Canadians are awesome mechanics
This is excellent, thank you.
You mention no flame touching metal. What happens during a "torch" on startup where there is flame running through the turbines? Is that definitely causing damage or since the turbine is rotating it has time to cool off since the flame is probably only at a certain point along the circumference of the combustor?
There is insufficient oxygen exposure, or an incomplete burn of the fuel, which means the flame temperature is insufficient to cause damage over a short term.
As discussed before in videos about hot starts, it's all about exposure time.
The temps involved at starting are definitely enough to destroy the engine... if they are experience for more than a few seconds.
It's exactly like your hand and a flame.
Put your hand fully into a fire, for one quarter of a second... everything is exciting and fine.
Put your hand fully into a fire, for one quarter of a minute... uh, oh... I think we wrecked it.
I want a jet engine to effectively swirl My coffee... spoons are overrated, and dangerous. Someone could gouge your eyes out
they went to fort ticonderoga...... *_WAIT A SECOND_*
you _could_ kill someone with a pencil... but you don't, why, because its too impractical and schools let you use them, there could be mass murderers at a school and would have a full supply of "weaponry". never thought of that now did ya? thats why im the edgyest kid at my highschool.
Why is there a fin on the fan blade?
I'm taking a guess, to stop pressure building up and channel the air
Nope ..... er, no, I'm a Brit and we've been here several times before on this channel. It's called a mid-span shroud in N America, or a clapper, if you work at R-R Derby, or a snubber, if you work at R-R Bristol. It has no aerodynamic function: it is essentially a friction damping and vibration modifying device for the blade aerofoil. It works by coming into contact with the mid-span shrouds of the blades on either side of it, effectively forming a ring.
I've always wondered about this topic.
Thanks for your excellent explanation !!!
Interested to see what you make for a display stand. I've got one of those blades that I've been meaning to make something to display it.
You got a CF6-6 blade? Or something similar?
CF6
When looking at the air right as it exits the compressor, about what percent of it is working air? Also, the percentages used to feed the flame, cool the blades, etc.?
Very nice explanation by the way.
Check my channel search bar: cooling air.
Is it possible to built a small sized jet engine .
How small is small? If you want to build a functioning model aircraft sized jet engine, the answer is, yes, you can! Try looking for books by Thomas Kamps and Kurt Schreckling.
Or you can buy one ready made from a UK company called Wren (other model gas turbine engines are available). It will cost you around USD3,000.
Yeah, they are right. It is like thousands of dollars for a proper working model plane jet engine. That being said, you could do it yourself in about 10 years & $25,000. It really depends on how much fancy metals are going to cost you. Also if it breaks, ur fukt.
Define small and purpose. There is no shortage of R/C size jet engines. They were looking at making turbines for fuel cells in laptops.
There are several smaller planes and helicopters that have switched to turbine engines due to their reliability. The PT6 is a good example found in smaller planes like the TBM 850
Hi ! I just discovered your collection of videos. Being a pilot, i find them highly interesting. Thank you so much for the job, keep it up. I also have a question relating to the fan blade you showed at the end of this video. I have a few of them that I would like to clean up and put on stands. Any trick on how to make them shiny ? Thanks a million !! Seb
Depending on how beat up they are, and how shiny you want:
Wet sanding by hand with 320, 400, 600 grit sandpaper (about an hour or more on these steps).
Cleaning with soap and water until a white cloth stays white.
Metal polish, with hand rubbing.
Loads of elbow grease required if you want that mirror finish.
AgentJayZ Thanks a lot. Did you ever try it yourself ? Seb
thanks bud, always a pleasure.
Nice!!!! Never imaginated
Great stuff Jay, and thanks for your support of the Special Olympics.
Could you comment on the air/flame/heat flow at the flame holders in the afterburner? Why don't they melt, where is the actual flame, how are they cooled?
Thanks much, I love your stuff.
The burning happens just downstream of the flame holder, so it's not in the flame, but it does glow red hot, as you can see in many of my test run videos.
I wonder if HarryT was meant to say conflagration as apposed to detonation. Two very different things some people confuse. Burning of fuel as opposed to a chemical chain reaction. (made a spelling typo)
nndorconnetnz As far as I learned the burning of fuel is also a chemical chain reaction. The difference between conflagration and detonation only lies in the speed of the reaction front vs. the local speed of sound.
Cool.
Way to go :-)
Great info, presentation and video.
Good job.
2/3 of the compressor gas flow is used for combuster & turbine cooling , how much energy as percentage of output is used
in cooling roles ??
In the mid 1980's I was assigned to the power plants division of a Naval Air Reserve A-7B squadron. During that time, Bell and Howell defense came up with an engine monitoring system that was supposed to help extend engine life. The theory went that engines operated at mostly low power settings should last longer than those flown at high settings. So, with sensors and a means to record them, projected life till overhaul could be predicted. If something went wrong, that was recorded as well. Almost immediately, the system was recording impossibly high turbine inlet temperatures of 5000 degrees for 2 hours flight time. Even so, the powers that be (chiefs/officers) would have us (mechs) check out the airplane even when told 5,000 degrees C would literally melt the engine. The system also recorded flights that lasted 100+ hours. I always thing back to those days whenever a Bell and Howell commercial comes on. : D
@I COME FROM SUN The point was that the system was WORTHLESS. It also recorded flight times of 100 hours or more. For an individual flight!
The earliest maintenance monitoring system I recall was on the C-5A galaxy. It didn't work too well either. However eventually these systems did prevail, and engine and systems lifespan improved dramatically. This had a major positive impact to extend TSO, and time change intervals saving the aviation industry Billions annually.
@@Dave-ty2qp - Never saw any improvement because in a year or less the squadron transitioned to the F/A-18A and retired the A-7B.
@@scootergeorge9576 What does that have to do with the overall aircraft maintenance monitoring systems in modern aircraft? These systems evolved rather than just showing up one day. The point I was addressing is we are where we are today because of the many efforts by everyone's effort. Including your own. Even if you didn't recognize it at the time.
@@Dave-ty2qp - Before Bell and Howell techs showed up at Pt Mugu California, I had been an aircraft mechanic in the Navy for 13 years and had never heard of anything like this. Another unit operating the A-7 was notified BY AIMD, NOT to turn in another engine based simply upon data from this monitoring system. This was 1984 or 1985. I'm sure the technology has progressed quite a bit over the years but back in the eighties it was worthless.
Hi AgentJayZ, great video as always, could you explain a little more about the smoke less fuel injectors? how are they different? only the injector makes the difference or there is also a special smoke less cobustion casing?
In one of the combustor liner videos i mention in this video, I compare the shapes or the original "standard" liners and the newer "lo-smoke" liners.
Some time ago I read somewhere (I don't recall where) that one of the problems Frank Whittle encountered developing the engine was maintaining flame stability. The issue (if I recall correctly) was the velocity of the air fed to the fuel flame front. A figure of something like 15mph was the don't exceed number that a flame (reliable?) could be maintained. A lot of the development was how to slow down the air stream to/in the combustion chamber. Can you tell us if that was the case, if so is it still a consideration in engine design? Has the increasing effective compression ratios of the newer engines changed this limitation (if the basis of my query is was true)? I think you might've alluded to this in the past without mentioning the velocity.
The air is really slowed down in the diffuser, then slowed even more inside the combustor liner. The speed limits for combustion have stayed the same.
We would be lucky to hear from our friendly neighborhood Jet Engine Design Engineer on this subject.
He's much more qualified to answer you.
Greetings from Singapore, where the Air Force was tearing up the sky with its F-15s earlier, and thanks for the invitation to respond, AgentJayZ. As a matter of courtesy to you, I refrained from answering on this topic earlier.
Thanks, too, for blowing a well-deserved raspberry at a certain individual: 'detonation' does NOT occur in any current jet engine, despite previous contributions from some smartarses (-asses if you want N American spelling). The very fact that we are discussing a low flame propagation rate goes a long way towards proving this. However, I was never a specialist combustion engineer, but I had heated discussions with them on several occasions, over issues that arose during the design of various combustion chambers.
In essence, the flame propagation rate in a jet engine combustor is not very much different from that which occurs in ambient conditions and, from memory, I've seen a figure of 20 to 30 ft/sec quoted somewhere. It might be a bit faster in the elevated pressure (and temperature) conditions of the combustor, because the Oxygen molecules are closer together and more energetic, and I've seen a figure of 50 ft/sec for the non-detonation flame velocity in a petrol/gasoline engine. It would be interesting to have a real expert to comment.
I was going to suggest that if you've ever seen an oxy-acetylene torch lit up, with a 'rich' smoky yellow flame and then promptly be extinguished when the Oxygen was turned on too quickly, then that might be a demonstration of the flame being 'blown out' with too high a velocity. I'm having second thoughts, though, because it could well be that it results from a sudden excess of Oxygen and too weak a mixture.
Nevertheless, the 'trick' in a jet engine combustion chamber is to create a swirling recirculatory flow in the primary zone of the combustor, in which the flame is stabilised. The same essentially goes for an afterburner (I did so want to say'reheat'), which usually has 'gutters', either radial or circumferential, to create swirling low velocity regions in the flow immediately downstream.
Hi, i love your videos. can you make a video that explain -why the heated gas in the combustion chamber (which is at highest pressure in the system)- does not goes back to the compressor? what make it flow to toward the turbine and not back to the compressor (through the combuster liner holes)?
This question has been addressed and answered many times. Enjoy my playlist called Your Questions Answered.
i could not find the video, would you include a link? in the combustion chamber, the pressure is higher than the compressor because of the combustion of fuel, so why the what does not goes back to the compressor? what make the gas flow to toward the turbine and not back to the compressor (through the combuster liner holes)?
Doron Koren The path of least resistance is through the turbine blades. The air would have to reverse direction, then fight all the incoming air and the blades of the compressor (just not possible). The turbine blades are already spinning the correct direction for the airflow of the engine when the fuel is introduced, so the hot expanding gas follows the path of least resistance back to atmospheric pressure, which will always be out the back of the engine(by design).
Hi Andy, Question: in the combustion chamber, the pressure is higher than the compressor because of the combustion of fuel, so how come new air comes into the combustion chamber ?, is it air pulse? one way valve? thanks for interesting videos.
Who's Andy?
You are incorrect sir. I will not spoon feed you, but will remind you that a gas pressure profile graph is shown in all of the books I recommend in my video called books.
Also, we review just such a diagram for this very engine in one of my videos in the Diagrams series. I suggest you enjoy them all.
this is what i found in the web, seems that the velocity of the compressed air is going up in the combustion liner. so according to Bernoulli law the pressure is going down but stay almost the same due to the heat of the flame (i hope that I understand it correctly) i really hope you would make a video on this. thanks for interesting and fascinating stuff.
I already have. The videos I suggested to you will explain.
We are not debating some question. I am trying to let you discover on your own what is really happening.
Please proceed.
Oof
@@doronkoren7040 As the air leaves the compressor it goes threw the diffuser case. The air velocity decreases, as it enters the diffuser and as a result the air pressure increases because it has more volume in the combustion area. The flame of the combustion is centered by the air being squeezed threw the many little holes in the combustion chamber. The only escape of the hot exhaust gasses then is threw the transition liner and is directed to the the turbine nozzles. Does that help?
Watching a video on F-86 when they entered service in Korea it was mentioned engine had a 60 hour service life. Thought it would be the cans but not sure. Maybe bearing surfaces?
AgentJayZ you have covered the igniters,what about the power source for the igniters. Is there a battery in the aircraft? I think modern airlines are 48volts 400hz what is the voltage feed for the J79. When mounted in the test cell or in an electricity generating plant is the J79 “plugged into the mains”or does it have a battery?
As you know, the igniters are only used to light the flame, and are then turned off. On the J79, there are two power sources and three separate individual ignition circuits. One 440Hz 120VAC, and two 28VDC.
There were also some 120VAC 60Hz boxes produced. An industrial application will have any of these systems, and and appropriate power supply to run it.
The engine is designed in such a way that, once running, it is a net producer of electricity, and does not need any to run.
In an industrial setting, all the sensors and equipment that might need electricity are powered by the facility and are not really considered part of the engine.
A bit like an old timey diesel, no electric power is required for an old-school turbojet to function.
Crack!! We love you!! Keep doing this!!
If air from the compressor stage can flow into the combustion liner to cool it, does that mean the pressure of the hot gas in the combustor is lower than that in the compressor stage?
Yes it does. In one of my turbine engine diagrams videos, we follow the air through a turbojet measuring it's pressure along the way.
The heat of combustion does not cause a rise in pressure in the combustors.
Always remember, these are not piston engines, and do not behave according to the Otto cycle...
03:12 - 03:30
Reminds me why i love this guy and this channel :-D
Can't wait to see the raffle selection.
Thanks again! Great video!
First I want to thank you for sharing this knowleadge with us. Now a question, Its posible to build a mini or micro Jet engine and also build a mini or micro rocket engenie? For aeromodelism or amateur proyects ? Thank for the time.
In respect of a model aircraft sized jet engine, I've already answered this question for another subscriber. If you want to build a functioning model aircraft sized jet engine, the answer is, yes, you can! Try looking for books by Thomas Kamps and Kurt Schreckling.
Or you can buy one ready made from a UK company called Wren (other model gas turbine engines are available). It will cost you around USD3,000. Alternatively, you can buy the engine as a kit and assemble it yourself.
If you wanted to try building a liquid-fuelled rocket engine, I believe that would be an altogether more risky proposition.
Many years ago, I did actually work on rocket engines - briefly - before having a career lifetime designing gas turbine engines. With safety in mind, my advice would be to stick to trying to make a small turbojet engine. Nevertheless, I have done some research for you, but I take absolutely no responsibility if you ever tried to make a rocket engine of any description. You would do so entirely at your own risk.
Back in 1967, a book was published, entitled, ' How to Design, Build and Test Small, Liquid-Fuel Rocket Engines', by L J Krzycki. It's out of print now, but it can be downloaded from the internet. The first sentence of its foreword reads, "The rocket engine is a relatively simple device ....." . Yes, it might be relatively simple, but it's potentially very dangerous. Please note also that the book doesn't tell you how to fly a liquid-fuel rocket engine. It assumes ground testing only, using gaseous Oxygen and a hydrocarbon liquid fuel, such as gasoline or methyl alcohol.
A conventional Oxygen cylinder, even a small one, would be far too heavy to fly and to make a lightweight cylinder would be high-end aerospace technology. As you will have seen, if you have watched satellite launches, handling liquid Oxygen would be extremely risky for an amateur and, in any case, no responsible supplier would sell it to you. The same goes for concentrated Hydrogen Peroxide (HTP), which is another possible liquid oxidiser. It's extremely unstable and, again, I would hope that no responsible supplier would sell it to you. I once witnessed a rocket engine test where there was a severe leak of HTP. I was glad to have been behind armoured glass.
You could try making a solid-fuel rocket, using Sodium Nitrate and sugar: you will find information on the internet. Yet again, however, there are real dangers: you would be trying to mix a fast-burning fuel that is potentially explosive. If you did want to fly small rockets, check out 'Estes' rocket motors. They are commercially available and relatively safe, if properly handled: I am trained in their use for rocket-powered model cars.
Note for AgentJayZ: I have given due warning of the potential dangers, but if you saw fit to delete this, I would have no problem with your decision.
Thank You for sharing Your Knowledge
Hey how's the ORENDA IROQUOIS COMING??