Jet Engine Evolution - From Turbojets to Turbofans
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- Опубліковано 10 тра 2024
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In our last video on jet engines, we have learned that just like piston engines jet engines do intake, compression, combustion, and exhaust but the big difference is that in piston engines these events occur one after the other in every cylinder whereas in a jet engine, these events occur continuously, all the time and they occur simultaneously with each other.
In this video, we will explore how jet engines have evolved to become much more powerful and much more efficient. Now this engine is called a turbojet and by modern standards, this is very much obsolete. This right here is a turbofan, or more specifically a low by-pass turbofan, and an engine like this is nowadays most commonly found on fighter jets and other military aircraft. As you can see, even upon first glance, the engine is pretty different from our turbojet.
Now the first, and most important difference is that in a turbojet, all the thrust generated by the engine comes from the exhaust stream, or the jet of expanding gasses coming out of the back. In other words, all the air that comes through the front of the engine ends up inside the core which houses all the key mechanical components of the engine.
But in a turbofan, this is not the case. Not all the air ends up in the core, some of the air is bypassed around the core and never contacts the internal parts of the engine. So why would we bypass some of the air around the engine?
Well to understand that we must remember that jet engines are also called reaction engines. Essentially they move incredible masses of air. This movement creates a force. And as we know for every force there is a reaction force in the opposite direction. This reaction force moves the engine and because the engine is attached to the aircraft the entire aircraft moves.
This tells us that to travel faster and/or to move a larger heavier aircraft we must move greater masses of air. To move a greater mass of air we can either move more air or we can move the air faster.
A turbofan engine exploits the first concept and that is to move more air. Now we have two kinds of turbofans, a high bypass and a low by-pass turbofan. When a civilian like you or me flies in a commercial aircraft we are propelled through the sky by a high by-pass turbofan. A high bypass turbofan takes the concept of moving more air to the extreme because at the very front of the engine, we will find a giant fan. This is where the name comes from, turbofan. We have a giant fan and gas turbines at the back which harness the energy of the combustion and thus power the fan. Now because the fan is so large it is capable of moving absolutely incredible amounts of air and about 80% of the thrust of the engine actually comes from the fan and only around 20% comes from the exhaust jet coming out of the back of the engine.
Because most of the thrust comes from the fan it means that we don’t have to burn ridiculous amounts of fuel to move the aircraft. Modern fans are designed to be extremely efficient at cruising speeds and altitudes of commercial aircraft. The added benefit of the is that the bypassed air creates a sheath of air around the exhaust jet and this greatly reduces the noise pollution created by modern commercial aircraft.
But unfortunately moving more air has its limits. You can’t make infinitely large fans because the greater the size of the fan the greater the difference in speed between the blade root and the blade tip, because the tip covers a much greater distance than the root. In other words, an overly large fan will inevitably achieve supersonic speeds at the blade tips and this leads to inadequate and inefficient operation.
This is where low bypass turbofan engines like this one come in. Their bypass ratio is around 0.5 to 1 compared to the bypass ratio of commercial turbofans which is usually 9:1 and above. A bypass ratio of 9:1 tells us that for every kilogram of air going through the engine core 9 kilograms of air go around it.
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00:00 Moving More Air or Moving it Faster
02:36 High Bypass vs Low Bypass
07:56 More Shafts More Efficiency
11:14 Gyros and Ducatis - Авто та транспорт
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Turbojet model from the video: www.enginediy.com/products/1-3-turbojet-engine-model-kit-build-your-own-turbojet-engine-that-works-wp-85-turbojet-diy-aircraft-engine-model-100-pcs?ref=d4a
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0:20 So the jet engine would be a true 1 stroke motor, right?
Looking for a jet powered Ducati 🏍️
No, it's a zero-stroke motor, because there are no strokes,@@gustavmeyrink_2.0.
modified bypass and combust chamber shape, what will happen?
@@jdwdfw
Sorry, all the jet-powered Ducatis are located at the bottom of that cliff over there:
Flying 4 Answers!!! I'm here for it :D
@d4a you should do a video on some driving turbines 😎 Some of cars that have used turbine engines and some future concepts like that turbine hybrid garbage truck
😮 I want 🚀 4 Answers 🎉
Also riding for answers
But the Answers flew over my head
@@ddd.777- Y2K Baby!!! Man I want one so frickin bad.
A financial improbably at this point, but not impossible.
The best description of how a jet fan works that I have ever heard
You are not subscribed to Agent JayZ?
Indeed... very compressed desciption. I loved it.
@@meleardil excuse the pun?
D4a is a phenomenal teacher lol I find my self thinking this with every one of his videos
Excellent.
As an aeronautical engineer I affirm that this material is of good quality. super recommended for all audiences.
About the only thing he didn't mention was the average exhaust velocity which has to be higher than vehicle speed and is why low bypass jet engines are used for fighter jets and not high bypass and why Concorde used turbojets.
@@BooBaddyBigI think that was sort of implied in other words by some of the other related things he said.
@@johnstudd4245 I don't think it was. He said that low bypass jets were used by fighters, and he said that they were less efficient, but gave higher thrust, but he never really said why they were chosen, and in fact pretty much implied it was just a weight thing.
and u didnt noticed blades of them jet models are all wrong?? & The turbine is in wrong direction in first jet at the start.
@@BooBaddyBig Yea, the key word would have been specific thrust. They certainly don't produce higher thrust in general. Just compare the F135 of the F35 to the GE9X on the B777X.
I worked for Rolls-Royce for 32 years and have experience on a whole range of engines from Speys (A 'leaky-turbojet' more than a turbofan) to BR-700's. I think you did a marvelous job explaining the basics. Obviously it is far more complicated when it comes to practical applications!
Nice. RB engine Trent engine XWB
I love the trent 900 from RR engine❤
Would you mind sharing some recommended sources for learning about turbo engines? I'd greatly appreciate any suggestions you may have.
I just love the way you describe things in such a logical manner
Thoroughly understands and teaches. Thank you!
Every video of yours where I “know” the topic, I come away realizing there’s so much more to learn.
Yes! And even when I watch them again, I still learn some more.
Of course, my memory’s short and I don’t have a long one, I get distracted easily, and if/when I go an look for more info to clarify something, I’ll end up in another six-hour rabbit hole - kinda how I ended up here in the first place!
As an aviation guy who watches your channel because cars are cool, I love to see you tackling stuff about aircraft.
You have an incredible talent for explaining things my dogg.
As you said, turbofan engines of higher and higher bypass ratios have been developed to improve efficiency and reduce noise. To add a bit of engineering and physics to the discussion I offer the following:
Noise - A significant source of jet engine noise is the shearing/mixing of high speed flow from the core with the lower speed flow surrounding it. In a turbojet engine, all the high speed core flow is interacting with the low speed flow around the outside of the engine, creating one very strong shear/mixing zone. With a turbofan engine the high speed core flow is mixing with the slower fan flow (still much faster than the overall flow over the engine) and the fan flow is mixing with the slower overall flow creating two less intense shear zones and therefore spreading out the mixing zone resulting in a gentler energy exchange and less noise.
Fuel Efficiency - The job of the engine is to produce thrust. When thrust exceeds drag the aircraft accelerates. At cruise, thrust = drag. Thrust comes from increasing the momentum (mass flow rate X change in velocity) of the air flow. Fuel requirements are driven by energy considerations however, not momentum. Jet fuel is a storage medium for energy and is about 43Mj/Kg. Kinetic energy of the flow is (1/2 X mass flow X velocity squared).
So, if we want an engine that produces say 1000 units of thrust, we can chose a low air flow rate/high airflow speed change solution (turbojet) or a high airflow rate/low airflow speed change solution (turbofan). But in either case, the fuel flow will be proportional to the kinetic energy change of the flow. So, suppose we want 1,000 units of thrust.
We could choose a turbojet engine that processes 250 units of air flow and accelerates it 4 units of speed. Multiplying those parameters for momentum change/thrust we get 250 x 4 = 1,000 units of thrust and for kinetic energy change we get 2,000 units (0.5 X 250 X 4 X 4).
Now we choose a turbofan engine that can process 500 units of air flow and accelerate it 2 units of speed. Multiplying again for momentum/thrust we have 500 X 2 = 1,000 units of thrust. However, the kinetic energy change required is now 0.5 X 500 X 2 X 2 = 1,000 units of kinetic energy...half of what the turbojet would require for the same thrust. In practice we can't get all that improvement and the resulting turbofan engine will be more complex, heavier and more expensive, but you can easily see why engineers pursue them!
This is a good, insightful description.
that is speed/velocity efficiency
Very good explanation. I haven't thought in terms of momentum vs. kinetic energy before but it makes perfect sense now.
Thank you for this clarification. I have another question that I didn't understand from the video. The author of the video mentioned that we can't have the bypass air (or end of the tips) exceed the speed of sound, but how come there are low-byepass supersonic airplanes? This confused me quite a bit...
@@tijljappens7953 on any kind of jet engine, only place where gas is faster than speed of sound is exhaust, but because that gas is hot, it has high speed of sound so maybe on some aircraft , at supersonic flight, hot gas does not need to be on supersonic speed because of itself hot temperature it still is more faster than true airspeed of ac(for ex Ma1 for air at 15C deg is 1200km/h but for gas at 800C deg it is at 2370km/h) sa exhaust gas at 800C deg, can flow through nozzle at 2300km/h and it is still below Ma 1
Now i know edactly what i should swap in my Vw Golf
Haha, do it!
I’ve taken my Scirocco down the Guildford bypass and it works!
Your ability to explain complex ideas is unsurpassed sir.
Better yet, you also add a little humor but not so much it becomes a distraction.
You are an inspiration.
Never change.
…and also as you speak you do not wake up your roommates…!
Absolutely fantastic, I work for an aircraft engine manufacturer and this has a far better explanation than any of the courses or literature the company has to offer. Thank you
This guy is amazing. From maybe three videos on turbine engines, he's (re)taught me 90% of the layman's understanding of turbines that it took me a decade to glean from AgentJayZ videos. No knock on AgentJayZ whatsoever, he just goes into way, way, way more depth. It takes more time to process. The high level view presented here condenses the core principles wonderfully.
AgentJayZ is for the technical minded.
And for those tolerant of his personality. Although he seems to have reeled it in after YT and viewers yanked his chain. His misplaced criticism of Bill Sweetman and Bill Gunston were particular sore spots for me, for example.
In fairness, his deep dives motivated me towards adding a jet cert to my A&P, and doing a lot of reading and research.
I used to be a Harrier mechanic. I’m impressed that you know this about our Rolls Royce engine! Additionally, the Harrier uses 4 nozzles with a single engine. The two “cold” nozzles come from the Low pressure compressor and the “hot” nozzles from the high pressure compressor, combustion chamber and all the turbines. You can walk up to a running Harrier and put your hand in front of the LP cold nozzle and the air was only slightly warmer than ambient. But even at idle it is a LOT of volume of air at a pretty high speed. You wouldn’t want to put your face in front of it!
I’m 24 and have worked on automobiles for about 6.5 years now, restoring my own collection of older trucks. I’ve always figured airplanes and their technology were out of my reach so I never gave them much thought. Until about mid December (‘23) I watched one recommended YT video of a C17 Globemaster III accidentally lane at the wrong airport that happened to be much smaller and it reversed back and still took off to the shock of the crew behind the camera. Ever since, I’ve done so much research of what kind of aircraft the US military and others have around the world and their capabilities and support roles. Now I’m going thru the process of enlisting in the Air Force and by watching this one video I’ve realized that their engines aren’t too complicated and that I can pretty easily comprehend how they function, just like how I learns how automotive engines work. I will forever help my future children in understanding that they can achieve anything in this world and that nothing is out of their reach as long as they have some kind of interest in it. Passion can really be incredible.
I just can't get enough of your videos! Looking back at my days in school, wishing I had teacher like you.
In the mid 1960s I was a jet engine mechanic in the Navy. Your video was well done.
I’m a 30+ year aircraft technician, this is a very good video! One guy I knew who worked on aircraft from the 1950s to the 1990s told me those old turbojets were “designed to do two things: eat gas and haul ass!” He added fuel efficiency was just something that was not thought of back then.
As a person who loves internal combustion engines in both cars and planes, the fact that you started taking up jet engines too because I finished watching all of your car engine related videos long back is a HUGE win for me! Please continue making videos not just about car engines but also about jet engines. I feel like you dont get as much information in youtube about them as you get in car engines.
This is one of the absolute best explanations of how and why the components of these engines work the way they do that I've ever come across. As someone who has zero background in mechanical engineering, this was readily understandable and a joy to watch!
12:50 The Losi dirtbike R/C and its 2 counter spinning internal flywheels make it dang near impossible to tip over.
This part of the video reminded me of it and similarities to how the engine + wheels affect the bike.
I had an RC motorbike as a kid with an internal flywheel. It makes a HUGE difference to model bikes, otherwise you have to maintain very high speeds to keep the gyroscopic except of the wheels high enough... Not something that's easy to do with a model bike, without the gyro you'd need a massive perfectly flat parking lot to run it and take long sweeping turns. With the gyro it was possible to turn it on a 2 lane street with ease.
@@volvo09 yea they used to come with training wheels.. hah thats the kind we had.. very slow, with training wheels, but it was an R/C motorcycle!! Sewper Kewl! Not.
@@umakemerandy3669 yeah I remember taking them off. Gave up on the body real quick. The riders foot was all worn away from crashing and sliding when I finally stopped using it.
Ok, now we need a vídeo about the chrysler turbine car!
Wow that was a thing?
@@user-qo3yy9nv1u yeah, a concept back in the mid 60's if I remember correctly. Turbine engine ran an auto transmission through a gear reduction. Goal of the car was to have a car that could run on multiple fuels.
It wasn't fuel efficient, wasn't exactly quiet (but wasn't too loud either) so it never made it past a handful of test cars. The testers loved it though.
@@volvo09 a turbine on a CVT would probably work really well.
Even with a CVT a turbine is garbage,@@user-qo3yy9nv1u, because response to power changes is poor and low-load efficiency is even worse than the low efficiency at ideal load. A turbine engine is only close to viable for a modern road vehicle in a series hybrid configuration.
The US Army M1 Abrams tank is turbine-powered, with an ordinary mechanical transmission. The engine is the Honeywell AGT1500. It works well, except that it consumes far too much fuel. There are lots of web pages and UA-cam videos about it.
@@user-qo3yy9nv1u well, check out the "Marine Turbine" MOTORCYCLE too :) Based on an Helicopter modified turbine.
Absolutely brilliant coverage of the topic!
i cannot thank you enough D4A, i can attribute your videos mostly into pushing me to become a car mechanic, which has been my dream career since...pretty much ever, i just didn't know it beforehand :P, this next march i will begin my course to become a Car Mechanics engineer, and i will definitely remember everything you have taught us here
Happy to hear, I wish you the best of luck 💪🔧
@@d4a I remember reading somewhere that Pratt & Whitney were now using a gear-box so that the fan would turn slower than the jet engine that it was connected to & that this would mitigate the problem of the fan blade tips going supersonic.
This guy is one of the best teachers I've seen in the last 20 years.
You're the best "explainer" in the biz! Thanks for this excellent vid!
Love your channel. Always clear and concise explanations!
Great knowledge and wonderful delivery. Thank you so much!
Just told myself I want to learn how jet engine works days ago and here it come, from a automotive UA-camr I like❤
Absolutely amazing explanation. It was so clear and so engaging.
Great topic selection King. Loved it.
Excellent video, with clear explanations of gas turbine (jet engine) operating fundamentals, & basic differences between turbojet & turbofan engine design & operation. The model turbojet & turbofan engines are outstanding in their detail & functionality, & greatly aided your explanations with a visual reference!
Superior presentation!
We had this discussion last week and your timing and video is impeccable
Thank you very much
ABSOLUTLY fascinating! GREAT video!
If someone can explain a very complex topic in a easy way it means that that's a professional who knows what he's talking about. Thanx for sharing.
Many thanks for this brilliant elucidation of the operation of jet engines and the factors involved their design. The brief snippet about motorcycle engines and the gyro effect was a nice homely touch. Great stuff!
Bloody effin excellent video! Knew practically everything but I've never seen it explained so well. Not a word too many nor too little, the models are effin great and the presentation fantastic. That's all the compliments you'll get from me, I don't want to overdo it.
Great overview of this topic, you explained it very well as usual!
Brilliant. Was trying to explain to a colleague how the evolution of engine diameter & ground clearance had impacted the 737 against the A320 & the disastrous results.
Another fantastic video! Works perfectly with the previous one. Thanks again D4A!
Very well explained. Thank you! I've been watching some channels about aviation where countless times the terms turbofan, turbojet and high/low bypass ratio came across and you managed to answer all the questions I had in only 13 minute video.
Every one of your videos , I learn something new. I actually take notes, so I don’t forget. You have a natural skill in teaching.
Longtime subscriber.
Keep up the great work!
Excellent explanation! I’m studying AGK for ATPL and this video helps me a lot to clarify other few minor but important aspects of turbofan.
Thanks
So much information in every single video. Your channel is a real gem. 🙂
Most informative video I’ve seen in a while good job explaining it
Solid explanation. The best I have come across!
Me trying to get my other automotive enthusiasts friends into war thunder:
*it's just a bigger spooly boi*
😂😂
I started in your channel last year with a general interest in car piston engines. Now I begin my position in aircraft engines and I’d never forget how you light up my passion toward the engines 😊 a great thanks to you for landing my dream career.
Succinct, packed with information, and no fluff. Excellent explanation!
I would personally love if you got into depth about the few cars that applied turbine engines, like the Chrysler Turbine Car and the Jaguar CX-75 concept, which although it was a concept, an engineer friend of mine from school told me once JLR were exploring jet engines to power their cars at a point in late 2000s, early 10s.
the problem with a turbine engine in a car is that they are hopelessly inefficient at anything but near full power and making them small makes it even worse
@@fuzzy1dk from what I recall from my friend, and it was what was shown on the cx-75 concept was for the turbine to be a generator than a engine for the power. So maybe there was something in there that just made it cost prohibitive back then.
Well, while turbines are theoretically low maintenance compared to piston engines, the manufacturing of turbine blades is much more expensive. If you don't want air leaking out of the compressor section, you need extremely fine tolerances, and extreme heat tolerance to handle the constant burning exhaust. This cost is understandable for building an aircraft, not really for consumer vehicles.
That's a series hybrid configuration,@@hf7188, and it's the only possibly viable way to use a gas turbine engine in a modern vehicle. Many have tried this, and none have been successful, because the engine is too expensive, too inefficient, too loud, not clean enough, and not even very small or light once you add the regenerator required to help boost the efficiency from horrendous to just really bad.
I have been wanting to know/searching for this exact information for 25 years. I cannot thank you enough so here it goes ... thank you!
Such a great explanation! Exactly what I was looking for!
Fantastic job explaining complicated stuff in simple terms. Thank you.
Went to school for two years to learn to fix planes and want you said made so much more since than what some of my professors were saying lol keep up the good work.
I was looking forward to this follow up and it didn't disappoint.
Brilliant explanation. Thanks for putting this together
This was very informative. Great work!
That was an incredible and fascinating explanation of the differences and similarities between the two engine types. Thank you!
Brilliant description of jet engine operation! Thank you.
Wow what a great explanation and I love those models!! Thanks!
Loved it buddy! U explained the technical stuff also in a simple language and format.❤
A model of clarity, literally! A thoroughly enjoyable and informative video.
Could you also cover turboshafts and turboprops? I'm loving this series so far
EPIC explanation and vid in general. Loved it n I was able to follow up so easily
This is a fantastic piece of content. Job well done.
Thank you for such a clearcut explanation! Superb work! Subbed.
Thank you. I've been looking for this exact explanation.
One of your best explanatory videos, thank you.
Thanks for this excellent video! You answered many questions I've had for years regarding jet engines, and you answered many other questions I didn't even think to ask yet! Way to go! 😃👍
woaaa well done, the blades look like they should at last
Yes! Thanks for noticing. Enginediy sent me new blades and fixed it for future models
Great video! You have a real skill explaining complex things in simple terms. Well done. Subscribed with notifications on! :)
Great follow up video to the previous one on turbojets!
Another excellent video - well done! You manage to get across all of the important concepts in a beautifully simple way - the hallmarks of a good teacher!
Amazing job explaining this subject!
Great Explanation! 👍
Nothing like the feeling of being pushed back into your seat after they release the brakes during takeoff! 😁🥰
After more than 50 years of flying, I Still enjoy it every single time! 🛫
Mike in San Diego. 🌞🎸🚀🖖
I was not expecting this but i loved it !! Awesome !! 🔥🔥🔥
Thanks for the great video, Excellent job.
I've watched a lot of videos on turbofans but this one pulled everything together wonderfully.
Fantastic job!
this video was soo complex yet soo simple to understand. Thank you for the explanation.
These videos are why I love this channel. Such intricate and interesting topics explained so well.
Never really thought much about jet engines and until now thought that turbo jets were the "never" ones, because turbo fan didn't make "sense" to be better.
Now I know better and understand why. And the example with the Ducati was interesting too.
Thanks for this, lovely video better then I could possibly imagine!
This was an outstanding lesson on jet engines! I always wondered why military jet engines were so different from those on commercial planes. Now I know. Thank you!
This is very informative, well explained, and narrated.
Awesome video man, love it!
Amazingly easy to understand explanations! Thank you very much!
Thanks very much. Great breakdown. Good explanation. 👍
Wonderful explanation as allways, thank you so much my friend 🎉
*THE BEST DAY OF MY LIFE* was a private tour of the Rolls Royce Airo engine plant - they GROW the turbine blades as a single titanium crystal
they were the first to think outside the box, until then only solid fan blades were used, which brought into question the increase in fan diameter due to the large centrifugal forces due to the large mass of the blades
yes and no. The turbine blades are cast in a 'Nickel superalloy' of undisclosed recipe - not Titanium. It's the extremely carefully controlled (and secretly controlled!) solidification that results in the inherently flawless single crystal turbine blades. It's a true marvel of engineering for sure! The fan blades have long been made in Titanium, for it's superior strength to weight ratio.
@@crazyg74 - Yes that is a more accurate way of saying it. I was lacking the language to describe it. it is a casting process that results in the entire casting being a single crystal
@@makantahi3731They gave me one of the fan blades to hold, they are giant and next to weightless. This channel should see if he can get a tour fo the factory.
First video on your channel I have seen. Loved every second of it. You "dumb down" the explanations enough so a simpleton like myself can understand it, using just enough techno-speak. The graphics (with the assist to Animagraffs on this one) are simple and easy to follow. Thumbs up, and I am now subscribed!
That was a truly excellent description of how these jets engines work.
I've looked into this stuff before, and kinda understood it, but this presentation really drove it home for me. Thanks!
I'm in awe of the fact that you made me understand this complex topic so easily. You've earned my subscription!
this video is truly testament to your quality of content. i honestly have very little interest in planes and their engines [no offence Aerospace Enthusiasts] but i loved watching this video and found it super interesting [as with all your others :D]. gotta be one of the best [mostly] Automotive Channels out there, if not THE best 👍🏻
Phenomenal video. Thank you!
Beautiful vid! about as clear as it can get to explain what a jet engin is!!
What a fantastic presentation ... the best I have ever seen on jet engines. Well done!
Bloody brilliant mate.
ASMR sound, quite understandable English and a fantastic technic explanation. This video is a gem.
Amazing way to explain complicated things in an easy-to-understand manner... Kudos!
Great video, I love the engine cutaways :)