The working title was "Compressors 2" Watch the original "Compressors" here: • Compressors - Turbine ... Also, the compressor stall video is here: • Jet Tech: Compressor S... and the follow up Q&A video is here: • Compressor Stall Q&A
I’m an aerospace engineer that works on designing some of this stuff and I just wanted to thank you for this amazing description and explanation. We learn this stuff in textbooks and on the computer all the time, but it’s truly something special to see the people who work on this stuff explain it in a way that really explains what’s going on, so massive kudos and thank you for sharing your experience with a bunch of randos online!
Thanks! Your opinion means a lot around here. Although I don't know if the citizens of Jet City really think of themselves as randos... Anyway, input from professionals like you is very much appreciated!
@@danielmarquez8060 sorry Daniel, just now saw your message! I think books are a funny topic because it really does depend on what you’re doing and works for you, hence why 10 different engineers will swear by 3 different books, and of those 3, each will appear to be good at its own little niche, be it theory, numerics, lessons learned, etc. Also, none of these books are going to work from the basic math and physics, so one does have to work to understand the concepts and nomenclature. That said, I did pick up a copy of “Principles of Turbomachinery” by Korpela which I have found to be a pretty decent book to have around for me. However, I do have friends who swear by Sultanian too. Moral of the story, there is no perfect book so just grab one and take what it gives you till you can’t take from it anymore. Then grab another.
@@AgentJayZ I have a friend from high school (son of my Mom's BFF), and I keep asking him how his steam turbine plant works, but he won't tell me anything or even give me a tour. Rude! (Joking, he's a Master Chief Nuc on the new USS G. R. Ford) (But I still ask his mom every time she gets back from a Tiger Cruise, "Ooh, did you get any pictures of him at work?" which amuses her and does not amuse her son.)
I'm not into jet engines, but the way this guy describes stuff - you can clearly see his passion about his job. I don't know why - but i watching his videos completely 😆
Another way of describing piston engine static CR is "Swept volume/Combustion chamber volume". Thanks for all the years of great content, sure has gone by fast!
That’s the scary part we all watch you age but we all think we look the same from years ago. I’ve gathered more gray in the beard and some wrinkles in the face. Life of a industrial chiller mechanic
"Not much of an engineer" by Sir Stanley Hooker is an autobiography of his life. He worked at RR on the development of the jet engine along side Sir Frank Whittle the inventor of the jet engine. Well worth anyone's time.
Thank you Jay. Takes me back to the good old days of you teaching us the practical concepts of gas turbine engines with your excitement & charisma. Be well sir
The first axial compressor you counted the stages of, if you calculate using the equations you give on your blackboard, gives 1.23 pressure rise, average, across each stage, or 23%. That's more than twice the "10%" you suggested. Anyway, thanks much for your interesting video. It might be of interest to show the geometry of the stators and explain how the increasing area of flow converts kinetic energy to potential energy (pressure).
As a software engineer working in aerospace customer training, your channel has provided great insight into the workings of the type of engines I work on everyday. Thanks!!
The way he explained how compression ratio in a piston engine made me yell at the screen. Completely wrong. Compression ratio in a piston engine is a simple math equation. What he's describing is how to measure cylinder pressure. What he's trying to explain is the difference between static and dynamic compression ratios.
BE: Blah! I do not care about your theoretical, geometric, cartoon imaginary compression. I am talking about how much the compressor raises the pressure ( or density) of the air going into it. You know, the actual compression of the inlet air. Real, not imaginary, sales brochure, wannabe crap. What's the CR of a "12.5 to 1" piston slapper, if it has no rings? Not 12.5 to 1, Johnny, er.. Benny You comment made me yell at my screen.
I just bought the Aircraft Gas Turbine Powerplants book on your recommendation. As a private pilot flying Cessnas who's working my way to airline pilot, this should give me a big head start in the required learning of these engines. Thanks for suggesting it.
Apparently Axial compressors fall under the helicopter explanation: It beats air into submission. 16X! Centrifugal just makes it real dizzy to comply. Aerodynamics in a nutshell...
Thank You, that was very interesting. When I was in the US Navy, I was a TF30-P-414/A, jet engine mechanic at the Intermediate level. We were able to tear down the engine, (HSI) except the compressor. Did the majority of my work at NAS Oceana AIMD, and also on board a few aircraft carriers. The F-14 was just switching over to the new GE F110 engine when I left Oceana.
At one point in my life I serviced most of the LM25s West of Texas and South of Oregon. When they hit the DRMO sites and then out to the natural gas sites, pretty much any former military with turbine experience could work on them. One of the saddest months of my life was retrofitting an old destroyer LM25 with an updated emissions kit in Flagstaff AZ. I can still hear the old girl screaming "help! I can't breathe!!" in my sleep 🥲
I suppose it’s like compounding interest in that you’re multiplying the product of the previous stage. Works well for pensions and turbines! You have a gift for imparting this stuff and I hope that you are part of the STEM education process in Canada. Your enthusiasm is infectious and could inspire a whole new generation. 👍👏
I guess my effort is right here. I worked as a guest instructor at a nearby aircraft maintenance school, but I'm sure there were some politics involved. I was kept busy doing other things besides speaking about engines, even though one of the classes was just starting their turbine engine module. Interesting...
A really interesting video as always, I would add that the engineers also had fifteen years of improvements in materials science to help them build the components they wanted to.
Still one of the best sources of info. Greetings my friend, been very hectic at work, and once it’s public, I will let you know some more but anyway, wanted to say hi 😻
Hi AgentJayZ, Thanks for the mention: however, I’ve been slow in commenting, because I’ve been busy with STEM activities, DIY tasks and (name dropping) an e-mail conversation with Ian Whittle. As a matter of courtesy, I sent him the text of an article that I wrote for the latest issue of the Journal of the R-R Heritage Trust. The theme of the article was a rebuttal of the mythology that seems to surround the German axial flow engines, which saw service at the end of WWII. Compared even to Frank Whittle’s first flight engine, the W.1A of 1941, they were inferior in terms of performance, SFC, power-to-weight ratio, life, reliability and handling. Compared to the centrifugal British engines of 1944-45, they were grossly inferior. Moving on to the subject of your video, I think you’ve done a good job in explaining stage pressure rise to your subscribers. Although I was responsible for compressor design during my career, I was a mechanical designer relying on the compressor aerodynamicists to specify the blade and vane aerofoil forms. In fact, I am not aware that I was ever told what the stage-by-stage pressure rise was for any of the compressors I/we worked on. However, I would expect the stage pressure rise to be similar through each stage of a given compressor, because the same level of aerodynamic technology would have been applied to all the stages during the design process. Having said this, it might tend to increase across a multi-stage HP compressor with a constant annulus outer diameter. My reasoning is that the mean blade speed (in ft/sec or m/sec) increases front to rear, meaning that the stages can do progressively more work on the air. Conversely, the stage pressure rise across a fan booster with a falling annulus line might progressively reduce because of reducing blade speed. Are there any compressor aerodynamicists out there who can comment with authority? One of the last engines I worked on had an overall pressure ratio of 25:1 across 8 stages (3 stage fan, 5 stage HPC), which works out at a stage pressure rise of around 1.5:1. However, I would expect the stage pressure rise across the HPC to be relatively more than across the fan. Finally, having gone to Wikipedia (the fount of all knowledge?) for information, the overall pressure ratios quoted for the PW120, PW127 and PW150 are 12.14:1, 15.77:1 and 17.97:1 respectively. This means that the stage pressure rise of the centrifugal stages of these engines is, at best, comparable to the pressure ratio of the dear old Nene.
Great video content. Interesting to hear about the LM 2500 compressor ratio. I just checked the stats for the GE9X engine (powering the new 777X): 61:1 compressor ratio...900+ PSI air delivery at end of compressor section. The compressor section sealing must be an engineering marvel. It also explains why airborn emergency windmilling engine starts have such specific high energy requirements, EG airspeed of 300+ knots at altitudes below ~25,000' (apparently need the denser, lower-altitude air to provide rotational energy to achieve engine RPM to start and maintain engine ignition). Related, I had thought the Pratt & Whitney geared turbofan series would offer comparable compressor rations, but they don't. Their advantage is the gearing allowing the fan, compressors, and turbine to operate at optimal RPM. Made me think back a few years to when Rolls Royce's "Ultra Fan" design studies included a pitchable front fan, the efficiency advantages of which could be enormous, including not needing heavy thrust reversers in the engine because the fan pitch could be reversed enough to provide braking. However, a British turbine engineer with RR who regularly commented on this channel (Graham?) stated RR had shelved that design study, reasons unknown. Anyway, the point I'm coming to is that some manufacturer, some day, may yet tie all of these promising features into a single turbo-fan engine: enormous compressor ratios; gearing for optimal operation speeds of the fan, compressor, and turbine sections; and a pitchable fan out front for optimum performance from a standing start to high altitude cruise. That would be some engine.
@@AgentJayZ I am a subscriber and just a private pilot. I’m a pretty good shade tree piston engine mechanic, but have been fascinated by gas turbines. Is there a video that shows what N1 and N2 are, and their relationship between them? Also, what is the difference between compressors and stators? In general, I’d like to see how all stages of the engine work together, especially the “turbine” side.I realize that you are not my personal turbine guru and don’t have the time to explain all of this. I will go through your library of videos to see what I can learn and what I might still need help with. Again, your teaching style resonances with this dyslexic dude!
All of those topics have been the subject of videos. Try the search box on my channel page, and maybe my platlist called Your Questions Answered. There used to be an index, but RU-vid destroyed in with an update.
Hats off to the Engineers.I've done 14,000 hours on jets and turboprops- from PT6 to the new Pratt GTF engine on the Embraer 190 E2. Not a shutdown, not a surge, nothing.
Just wanted to thank you, Agent JZ, for your fascinating videos that I’ve enjoyed the last few years. I appreciate your expertise and experience. It pissed me off to see a couple of smartazz comments here.
I stuck my nose into a cut up GE404-variant and was surprised by how few compressor stages there were after seeing your videos with engines with 17 stages. It had 3 fan-stages and 7 compressor stages, the compressor looked absolutely tiny and so did the combustion section. With 10 stages in total and a pressure ratio of 27 each stage should give about a 40% increase in pressure.
The engineers do an amazing job, year in and year out. From 1951 to1975 or whatever... if you had a ten percent improvement in compressor performance each year, and it works like compound interest... that's definitely a massive increase...
@@LanaaAmor "The Jet Engine" by Rolls Royce " (fourth edition, 1986). There is a fifth edition, it is available on Amazon: www.amazon.com/gp/product/1119065992/ref=ppx_yo_dt_b_asin_image_o00_s00?ie=UTF8&psc=1
Has there been any hints in the future for the Orenda Iroquois Motor assembly? I'm sure it would be a great undertaking to assemble and aquire all the parts, and get it into working condition!! All the best from Surrey
Great your back. I was just thinking I was in need of some over my head jet engine rhetoric. But it's getting drilled in and maybe someday someone will ask me a jet engine question and I will know the answer.
@8:36 Compressions ratio in piston engines is even simpler then that @AgentJayZ. Compression ratio is the difference between the volume of the engine cylinder with the piston at the bottom of it's stroke, to the volume at the top of it's stroke. So a cylinder that has a volume of 1L (1000mL) at the bottom of the stroke and has a volume of 100mL at the top of the stroke has a 1000:100 (10:1) compression ratio.
Recovering engineer here. I put myself through engineering school working as an operator at a cogen plant with a 2500. Then I mostly worked on steam turbines, and then a few startups before I decided engineering wasn’t for me. I actually loved the startups, but it wasn’t a sustainable way to make a living. Anyhow, this video reminded me of why I fell in love with the field to begin with, and I’d like to thank you for that. P.S. There are calculator apps that are available for your phone that use RPN. PCalc is the one for iOS, and RealCalc for android. Both are about ten bucks the last time I looked, but it’s worth it to me not to have to dumb myself down to use the standard calculator apps.
I worked in a Siemens building doing some commercial electric work and I noticed that they had a bunch of fan blades coming out of an oven that were an aqua green color.. The blades were a weird shape and had dot's and lines carved in them :/ They wouldnt tell me what they were for but I guess it was some type of newer turbine :) It was pretty cool...
@@JohnnyWishbone85 They were individual blades johnny they were about a foot long each im pretty sure they were ge90 turbo fan blades, they had a serious twist in them... or the molds for them.. :) It was hush, hush around there... 8-10 years ago..
PS I'm going to be mildly critical of the use of the term 'compressor ratio'. The term that I learned as a student in the 1960s was 'pressure ratio'. as used in my text book of the time, 'Gas Turbine Theory', first published in 1951. During my career, the term 'overall pressure ratio' came into use, to cover engines with more than one spool. And, of course, use of the term 'compression ratio' in relation to a gas turbine engine is quite wrong.
Oticed s difference between the 1500 & the 2500. The blades - the 1500 has more or less straight blades( from inner to outer). They look like the walls of a straight cylinder. the 2500 those blades also have a twist from inner to outer. When i say inner to outer thst is from the center of rotation of the engine to the outer skin.
As we worked out here, the LM2500 uses over 500 psi of boost at full output of over 35 thousand Hp. It can do that for over ten thousand hours before needing an overhaul. I find it amazing to see diesel trucks outperforming gasoline powered race cars at the drags.
A cylinder compression ratio is not a pressure test standard, it's a design. Cylinder total volume at bottom center vs. Remaining combustion chamber volume when the piston is at TDC.
Maybe you should review the procedure for doing a "compression test" on a piston engine. My racebike was 10.8 to 1. I'm sure you understand what that means.
@@AgentJayZ I'v been a tech for over 20 years, I've done many compression tests. You could look at it either way, but if you have a car with a known design you can publish the compression ratio in a service manual, and they do, even though they have no idea what the tested pressure is. It's a ratio, not a PSI. only a test can reveal how close the pressure might come to the design expectation. But does a compression ratio relate linearly to a pressure ratio? I mean if the CR is 10:1 does that mean the pressure will be 10 bar or 147 psi? If given only one stroke of the piston it will be rather disappointing. And every 4th stroke of the piston is only one stroke, not seven strokes to build max pressure which is my standard for a test. Even a perfectly sealed piston cannot produce 10 bar on a single stroke. Still the engineer assigned it a 10:1 ratio. Only a test of accumulated strokes can come close because of the extreme compressibility of air.
@@blackbirdpie217 "But does a compression ratio relate linearly to a pressure ratio? I mean if the CR is 10:1 does that mean the pressure will be 10 bar or 147 psi?" - in a nutshell, yes you're correct. This is called Boyles law, or the ideal gas law. In reality the gas heats up when it's compressed and so the law is not 100% true. Boyles law states that, given constant temperature, a change in volume will cause an inversely proportional change in pressure. So 10:1 volume change will cause 1:10 pressure change.
Wiki says 8 LP and 7 Hp, with the first two stages of the LP being enlarged to create a 2 stg fan. I haven't worked on the engine, and i don't have access to the parts catalog.
great vid i actually came up with a question after seeing this, does the aircraft speed contribute to the cdp? thinking that at altitude with lower density and pressure the forward speed (inlet velocity) may be part of what maintains that cdp in lower density environment by increasing intake volume
Another great video,as someone who designs and fabricates perf. turbosystems and fuel management systems for automotive and motorcycles for 30 plus years, I can relate to many terms used in the turbine engine industry, pressure ratios,compressor stall etc. I have always been fascinated by them and wished to own one at some point for use in a perf alu jet boat.but still need to learn much more about them. Similar to what you mentioned about advances in technology in the efficiently of turbines, the same has applied to today's turbochargers in compressor and turbine design. Some of the higher level gas engines are able to achieve boost pressures above 80 psi+ on single stage compressors . As far as turbine compressor stages being of different sizes, would you think that it may be done that way to compensate for changes in air temp and density as the air is compressed through each stage? Also ,I would assume somewhere there are compressor maps for the stages of turbine engine compressors? (that are most likely locked away for only the most special to see.. ha) Keep up great wk. I'm def going to invest in the books you mentioned. 👍
One of the factors that limits a plane's maximum altitude [its 'ceiling'] is how much pressure the engine can achieve in rarefied atmosphere. This was the first thing people started to notice when they tried flying high to avoid the Germans in WW2 so it was pretty much known by the time jet aircraft were first made, but they had to [sort of] 're-learn' it for high speed flight, as a few other factors changed how much air one was having to compress, and how the plane managed it.
Airplane ceiling limits were noted in WW1 when German Zeppelins avoided British fighter planes by flying at high altitudes. The British countered by fitting their planes with superchargers which lead to a technical arms race that had the Zeppelins flying and bombing from 30,000 ft and both sides flying with oxygen.
I'm also very sceptical about the 2.5 per stage. That would mean that a modern engine with 60:1 overall ratio would need only 5 stages. That doesn't seem right. 1.5 is more like it, that fits with a reasonable number of stages to get to 60:1.
Excellent video, Thanks! Question sir-- Do you consider the addition of fuel and combustion to be an additional stage of compression or pressure increase? I have watched your videos about the Bernoulli effect and that it is more velocity, not pressure, that we're after at the backend. I'd be interested on your perspective of the role of compression all throughout the engine.
I am very interested in learning more about jet propulsion units. Can you recommend a few more books other than the 2 mentioned in this video? Or someone in the comments. Thank you for the informative videos you do, I really do appreciate the knowledge you share for free.
I just put Jet Propulsion in the Google search bar. The results were impressive. NASA is free. If you are interested in learning about the subject, There's a lot of great, free info out there. From there on, it's up to you.
Most automotive engines can handle around 15lbs boost, built engines get up to 30-45. Most diesels will hold 45 from the factory, and upwards of 80 some as high as 100psi in built form
Im assuming the combustor cans contribute to efficiency as well? Modern high performance engines have an anular combustor housing which i assume allows better burn and better flow.
Hey Jay :) I have a question. how often do you see "MacGyver style" fixes in the engines when you stripping them for overhaul? As a car mechanic sometimes I cant believe in what I see, been wondering if same thing might apply to gas turbines? Cheers. Greets from Ireland.
That's one of the things that I like most about working on jets. All examples of each model are identical. It's obvious when even one fastener is non standard, or one clamp is missing. If such an irregularity is found, the question becomes " how deep does this poor decision making go?" The owner is notified, and everything is reconfigured to the way it should be.
Schuesselmensch. The pressure itself depends on the flight altitude and flight speed, which determines the pressure inlet pressure, the compressor exit pressure is this inlet pressure times the 'compressor pressure ratio' running at design rpm (100%). Important to determine fuel consumption, for given design turbine inlet temperature. An efficient compressor has, for given pressure ratio, the lowest compressor exit temperature. All this becomes understandable if the 'temperature-entropy' diagram is used.
That would have an effect on mass airflow, which is one of the primary factors determining total power. Gas path area is something determined by the engineers designing the engine.
I've always wanted to build a model jet engine for an RC jet with an axial flow. All commercially available RC jet engines are centrifugal flow. I just wonder if it's possible. I have seen a few projects take shape but ultimately fizzle out or disappear. I would think that today with the availability of 3D printing, it would have been done. What say you AgentJayZ, is it possible to miniaturize an axial flow jet engine for RC, the thrust it would need to create would be about 50lbs?
Please see my video "so you want to design a jet engine". Also, Williams makes small axial flow turbojets and turbofans for missiles, starting at about 200Lbs thrust. Check out their designs, and see if you can get a price.
@@AgentJayZ I am not looking to design and build an engine all on my own, as you state in your video, and rightly so, it would take a team of people to do so. I guess it sounds outlandish when I say "I want to build" when what I really mean is to want to build an RC aircraft with an axial flow engine and purchase the design and parts for said engine in said model. The problem is, there does not seem to be anything available. I have written William in the past and no surprise I did not receive a reply. The F121, which is the smallest William engine I can find reference to, weighs 50 pounds, which is too heavy for an RC aircraft. It's also 8 in diameter which is also probably too large. The largest RC centrifugal flow engine is about 96 lbs of thrust, and weighs about 8 lbs, is 5 3/4 inches in diameter. It would seem there is no axial flow RC engine in existence, nor a working design that can be assembled. I'm sure Williams of Pratt has something sitting in a digital file somewhere. From what I have seen, and I have been peeking into the space for about 20 years, it is relatively easy to home kit a centrifugal flow model jet engine from commercially available parts, usually lifted from a car turbocharger, the burn can is also fairly easy to make and there are many designs readily downloadable, all that said, it is not the same for the axial flow. I am not looking to build a better mouse trap and get rich, far from it. An RC model is a hole into which you throw money. I just want the most accurate model that can be built by human hands.
Even though my day job involves the largest "blades and vanes" flying, I still love this channel. Is that a valve cover from the ill-fated Orenda recip? It was supposed to replace small turbines for greater efficiency.
Yes. That valve cover is from the Orenda 8. It was sent by a friend of Jet City. It's main feature was not efficiency, but up front cost. Is was/is less than half the price of a PT6.
I know you said that you are a technician and not a designer, but I was wondering if you could help me or point me towards a resource for a question I have. So when doing some research on commercial jet engines using this book called, "Turbofan and turbojet engines : database handbook", I noticed that they tend to have a higher pressure ratio when they are at cursing altitude and speed then when they are at a static max thrust at sea level. I was wondering why this was the case, for example the CFM56-2C1 on the DC-8 has a overall pressure ratio of 24.7 at max power, and a pressure ratio of 31.2 at cruise. I was thinking it could be ram pressure but could it really be that much of a impact? Or is it because of something like variable stators and guild vanes? I would appriciate any help you can give me. Also completely unrelated but I really enjoyed the part at 27:30
Well, if the throttle setting was the same, the only differences are ambient air pressure, being higher at standard test conditions ( sea level), and air speed, being zero at standard test conditions. At cruise, throttle setting is lower, ambient pressure is lower, and airspeed is higher, compared to test conditions. I would expect pressure ratio to be lower, but ram effect can really make a big difference. If the two conditions were both flying, max power vs cruise power at the same altitude, I would expect pressure ratio to increase as power setting increases. There is a very inexpensive manual out there for the DC-8 super 70 ( I think it's called that), That has a section on The CFM56 engines. I found mine at eflightmanuals.com
Does the quantity of compressor sections and/or compression ratio affect response rate of the engine? Is that even a concern to operation of the aircraft which it's powering?
Amazing to realize that something that small can generate the equivalent power of 40,000 horses. Pre industrial civilizations relying only on animal and human muscle power could not begin to imagine generating power like that. And rocket engines can generate the equivalent power of millions of horses!
Each stage of compression in an axial flow compressor consists of a rotating set of blades pushing air into a set of stators. For example, the Lm2500 has a single shaft, or single spool compressor, made up of 14 stages of compression, which all turn at the same speed.
We overhaul Turbine engines. If we scrap stuff, it goes to metal recycling. The idea of selling any parts of any kind was long ago proven to be a never-again nightmare. There are many people selling aerospace garbage on Ebay. Check out my video Ebay blades for some pointers...
great video. One question. Does inlet pressure change when an aircraft is traveling at, say, mach 0.5? And does that affect CDP? I realize altitude will affect things but I am curious about inlet pressure at speed in an aircraft application. Obviously a stationary application is not questioned -it is constant atmospheric inlet pressure as the unit is not in motion
Most airliner engine nacelle inlet ducts are designed as diffusers. As the aircraft moves through the air, the duct helps to increase the air pressure in front of the engine, "at the face of the compressor". Because the compressor is consuming huge quantities of air, the air pressure in front of it is lowered below what it is 10 feet or more in front of it. The diffusion of the airstream moving into the duct, raising the pressure is called ram recovery. After about Mach 0.5, the pressure at the face of the compressor is actually greater than ambient. You could say that ram recovery becomes ram boosting.
@@AgentJayZ That's why the SR-71 had the moveable spikes in the intakes to maintain that balance/kill the shockwaves and basically make sure the ram pressure was enough to make it run like a bat out of hell but not blow out the fire, right? Also re: ram boosting: the "ram-air "scoops on the hoods of old musclecars that sealed around the air filter .. didn't really do anything below 200mph. And even then, you could throw a blower from a two-stroke diesel (or an exhaust-driven power turbine) on the intake and actually pressurize the intake.
Great video ... plus thanks for the info on the books (an electronic .PDF is OK sometimes but being able to make notes in an actual paper book can be very helpful). (comment) I'm an old guy and I think in English units and then convert to Metric when needed. (question) I've read that modern 3D printing is allowing the development of cleaner burning jet engine fuel nozzle spray patterns. Is there any reason that more efficient (cleaner burning) fuel nozzles couldn't be retrofitted to existing engines so long as the fuel flow rate of the new nozzle design is in the same range that the old engine runs at ?
The efficiency of the combustion is a result of airflow management by the combustor liner, and interaction with the fuel nozzle. Everything is optimized, so redesigning a fuel nozzle won't help, unless the liner is also changed.
