Combustion Pressure: Jet Engine Mistakes 1 

Yes! I was thinking he could give a workshop or classes. I know if I were to sign up for one, he’d never get through his lesson plan, because my hand would be up all the time to ask a question.😉

I'm a very slowly progressing Stratocaster operator. I am guilty of focusing too much on gear, and not enough on practice. I want to built the Mojotone 5E3 kit, but it's way pricey, and I know my sound would improve more with just a bit more practice. I did build my own speaker cab. Of course with a JBL E-130. Having one of the most powerful lead guitar speakers ever made resulted in my little Bassbreaker sounding louder, but not better. Toys are great, eh?

Valve amps are also a hobby of mine. Although I build hi-fi grade. It's nice to know I'm not the only one "jets and thermonic valves" life's good 😉

As Dave used to say: "F'n A one Bubba!"

I am one of those people and for some reason it makes understanding turbines somewhat hard! Lol Because in a piston engine, despite the valves and near-sonic intake flows, there is flow reversal. Or, can be in some situations.

@@hordboy In piston engines there is flow reversal back out the intake valves that occurs when the piston is near the bottom of the intake stroke. This is called backflow. It occurs primarily at higher engine RPM's and limits the amount of power the engine can produce. This is why many engines now use variable valve timing (VVT). This technique causes the intake valves to close earlier as the engine RPM's go up, which limits backflow. Then as a side benefit the intake valves also open earlier when the piston is near the top of the exhaust stroke. This allows some of the exhaust gas to flow out through the open intake valves and into the intake manifold, which eliminates the need for an external EGR valve along with its associate plumbing and control system.

@Mark Grudt When I was in the Air Force in the Strategic Air Command (SAC) we used to say, "A suck for SAC is a blow for freedom".

@@joevignolor4u949 This assumes of course a 4-stroke Otto cycle engine with valves instead of a 2-stroke Otto cycle engine without valves and with something to pressurize the incoming air stream or with a misstuned exhaust pipe.

Remember that, although there is a slight pressure loss throughout the combustor, it starts at compressor discharge pressure, which in this engine is 75 psi. Modern airliner engines have CDP of over 600 psi.

@@AgentJayZ I know almost nothing about jet engines. So I had to look up schematics a bit to understand. If I'm reading your comment right I believe you're saying that this engine's compressor side compresses air to 75 psi. That goes into the combustor where pressure drops a bit and it remains at a higher pressure around the combustor where you showed in this video it leaks in? Is that pressure drop in the combustor from going from a small narrow 75psi opening to the larger diameter combustor?

The cooling air surrounding the liner is at a couple of psi higher than the air inside the combustor, so it leaks in through the holes in the liner. It mixes with the very hot flame, and as the mixture leaves the combustor and starts to enter the turbine section, the temperature has been brought down to about 1200F, which almost the upper limit of what the turbine can handle.

@@AgentJayZ awesome. I just learned a bit today about jet engines. Thank you!

That's the engine I trained on.

Dam it!

Wow, thank you!

Yes, thank you. It was a surprise, and very generous of you!

Obvious to people like you, sure... But this video is a result of being asked on a daily basis: "Why don't the gases flow forward through the compressor and come out the front?" You might think it's common sense, but it ain't that common, Joey!

@@AgentJayZ A lot of your subscribers must be down here in the United States. As has been recently demonstrated Americans do seem to have a lot less common sense that people in other countries such as Canada for example.

It's obvious that it doesn't happen but the question is generally why.

@@hannahranga Why it doesn't happen is obviously because the discharge pressure at the outlet of the compressor is higher than the working pressure inside the combustion chambers. Also, the same thing is true for the fuel delivery system. The fuel pump also maintains a higher pressure at the fuel nozzles inside the combustion chambers so that fuel flow into the chambers is maintained. This causes fuel to be continually sprayed into the chambers where is mixes with the air coming from the compressor to support the combustion.

Freddy... One more stupid comment, and that's it buddy.

Well, you just couldn't help yourself... Good riddance.

Be careful here - there is pressure from the compressor on the air and a reaction force from the air back onto the compressor. On the other end the gas is pretty much free to flow out the back, so there's no opposing force there. That difference times the area of the back of the compressor is the thrust. So while the thrust doesn't come from an increase in pressure post-compressor, it does equal a pressure times area SOMEWHERE (i.e., the output of the compressor).

@@sbreheny force = mass X velocity squared. This is to say the thrust is how fast and how much stuff you are throwing out the back ,it works for air or bowling balls just the same. The pressure calculation is jus a different whay of calculating the same thing because difertual pressure creates a velocity.

@@Bri_bees > force = mass X velocity squared. Ummm, no. Force is the time rate of change of momentum (i.e. F = d(mv)/dt) where mass can be treated as a constant so long as relativity doesn't apply, meaning that force is a mass times an acceleration applied to the mass (i.e. F = ma). I think you are confusing "(kinetic) energy" (or "work") with "force". The kinetic energy of an object is one-half of the object's mass times the square of its velocity (i.e. KE = (mass X velocity squared)/2). This applies to either a mass of air or a mass of a bullet. It is this kinetic energy equation that shows why jets are so inefficient compared to aircraft with propellers at subsonic speeds. F = ma means that you can get a given amount of force by either accelerating a small mass to a very high speed or by accelerating a much larger mass to a much slower speed. But accelerating a mass to a very high speed means that that air mass has a much larger amount of kinetic energy than a much larger mass of air accelerated to a much slower speed. That difference in kinetic energy has to come from somewhere and it comes from the stored chemical energy of the fuel being turned into a massive amount of heat.

@@lewiscole5193 yes I was referring to the kinetic energy of the air leaving the jet.

If you were referring to kinetic energy, why was your equation Force equals blah...? Your credibility is gone. You are not helping anyone. We, the nation of Jet City, are not interested in your further blatherings. Thank you for realizing that.

In some respects radically different and in some respects exactly the same. EG air in and compressed, fuel burned to heat and expand, exhaust gas out. OK a jet has all of that going on simultaneously and a two stroke diesel for example does not, but it's the same basic physics just applied differently as far as the thermodynamics is concerned.

That's the bottom of the engine, and those two symmetrical lines are the drains, through which any fuel flows after shutting down the engine. That open flange connects to an overboard drain on the aircraft.

@@AgentJayZ ahh damn... you mentioned that a few times...

I have mentioned it in an earlier video, but every time he says the same. Maybe he don’t know Bernoulli.?

I think it would be useful ahead of time to wave your arms at why you think this would be "helpful". FWIW, static pressure is the pressure of volume of gas that isn't moving. Total pressure that comes from bringing a moving volume of air to a standstill. Dynamic pressure is the difference between the total pressure and the static pressure and oddly enough, the equation describing it looks a lot like the equation for kinetic energy if you squint your eyes closed enough. In the case of a turbojet, using the engine as your frame of reference, the incoming air stream comes in at some velocity and pressure and is effectively reduced to zero speed (a standstill) and a much higher pressure at the start of the combustor stage by the compressor. So the air before it hits the engine is at some static pressure, it has some additional dynamic pressure thanks the movement of the air relative to hitting the jet, and all of that is turned into a total pressure at the face of the combustor. None of these seems especially useful to me in terms of the subject of this video and so that's why I think you need to do some more arm waving.

@@stevenss8070 I suspect he knows Bernoulli well enough to get his job done. If you really want to know the gory details of physics that goes on in a jet, may I suggest Randall Manteufel's channel. Search through his video list for Brayton cyclc and/or jets.

@@lewiscole5193 Your explanation is inaccurate.

@@fascistpedant758 > Your explanation is inaccurate. And your comment is useless. Feel free to expand on it when you get a clue.

This is a non question. Thrust is a force, and pressure is a force divided by an area. I don't mean to be picky, those are two different things. I can't turn one into another. Used conversationally those two words mean the same thing. Add to that energy, power, strength, determination and certainty. In order to actually explain how things work, we need to use technical language, where all of those terms have different definitions. Thanks for the nice words, though.

@@AgentJayZ The fact that you finally correctly explained that in the chamber the pressure drops, but the volume and speed increases is the only correct thing, my question was a little unclear, I will correct myself. Since we are talking about the chambers, I wonder if the thrust acts on the front wall of the chamber in the direction of the plane's movement, given that the rear wall is open? Like an inflated balloon, it flies into the air because the back wall is open and the front is closed. Since you really understand things and are one of the few who explain them correctly, one question arises: if we could achieve that the gases in the chamber are formed in a new way, in some way swirl before they go towards the blades of the turbine, would this increase the exhaust power on the blades? Well, we all know that the narrowed exhaust chamber at the end of the engine accelerates the speed of the exhaust gases, if this is an action, then which part of the engine is the reaction, which rear part of the engine is the thrust applied to? Regarding the new swirl chamber, I could also send a picture.

You want me to remake my Engine Shipping Containers video?

@@AgentJayZ remakes and sequels are real popular these days

The correct spelling is "Canadia" ;-)

You need a constrictor with a rocket motor which on a firework is usually made of clay. The nozzle is for making it more efficient and actually not strictly needed if you don't care about efficiency. The "bell" for maximum efficiency needs to enlarge to the size where pressure is dropped to ambient pressure which is why some rocket motors have different bells for the same combustion chamber. The combustion chamber in a solid fuel motor is usually the hole down the middle of the grain.

@@gordonlawrence1448 Interesting, the cheap little ones i have seen landed in the garden just looked hollow. Is this on all rockets? Wikipedia doesn't mention as much detail as you do in en.wikipedia.org/wiki/Skyrocket#Construction . Perhaps you could add to the wikipedia article :) On a separate vein; One of the things as regards jet engines that has puzzled me lately is is exactly which parts of the metals of a turbojet actually get the reaction force of accelerating all that air and thus transmit force to the plane, hmmmm....

Just go do it, it will only open more and more doors, to pursue your interests.

There are pros and cons to both designs. Good idea...

compromises ... the more bits you put in the way of the exit gases the less thrust you get .... but the less thrust used to keep things working reduces efficiency ... so you have to decide when enough turbine blades are enough and still have enough thrust left over to fly ... . just like how many compressor sections you have also depends on how much compression you want and how many turbine blades can turn them at the speeds you need them to turn from the thrust you get from the combustor with the compressed air you made in the compressor from the turbine blades in the exhaust path that is trying to push you forward ...

Yes, the volume increases greatly due to expansion. And not being contained, this expansion makes the gases move faster, out to the turbine. Pressure does not increase with the heat of combustion, because it does not take place in a chamber, but in a section. That section is open at the front to higher pressure air, and it is open at the rear to the turbine section.

@@AgentJayZ When you said the gas leaves the turbine nozzle at near sonic velocity, would not the velocity be much faster than the stated 700mph, as the air is greatly heated?

Sort of. Bernoulli assumes the energy stays constant. With burning of fuel, energy is added to the airstream so although it speeds up a great deal, there is no large pressure drop.

@Jake Bullet I believe AgentJayZ had a video a few years back in which he said something like "there's also 30,000 hp compressor pushing it towards a hole in the back". It's not going out the front.

All compression is done by the compressor. The name sort of indicates function, eh?

I see what you are getting at. The compressor is somewhat analogous to the intake valves in a piston engine in that it prevents backflow out through front intake of the engine. But it does this by providing a constant output pressure and there are of course no mechanical intake valves in a jet engine so the analogy ends there.

Dear Bob... ... ... did I not show the inlet and the outlet of the combustor in this video? Is that not what you are asking here? Is it me who is missing something here, or is it you who have not watched the video? I do this without all the math and equations to hopefully help with an intuitive explanation of things. Have I failed here? Or... ?

@@AgentJayZ When I said nozzles I meant the annual rings with vanes immediately after the compressor and immediately before the turbine, I would expect it is something you take and pick up a with your hand and show them, the final compressor stage blades and the first turbine blades are much different in size and I think that is quite significant. although this is a dynamic situation there still are physical static forces and I would just like you know where they're at. There appears to be a gap between the jet pipe and variable nozzle turkey feathers does this create a vacuum in that Gap. I'm not trying to be confrontational I'm just trying to understand things. I used to work for a machine shop and they had a large air hose to bow the chips off and for safety purposes they had a little extension on the end of the nozzle that was larger than the exit of the nozzle and It had holes in the sides, if you plug up the holes in the sides it would have a lot less thrust and not blowing very well. I think it would be interesting if you had some kind of a smoke machine or cigarette and have it around the engine while it's running and see where the air is moving on the outside of the engine and in the shop, does a Shop create Venturi effect. I'm sorry if I ask too many questions I just think it's very interesting

What you did ask for, was shown in this video. The fact that you meant something else is unfortunate. The proper use of the names of things is critical. What you meant to ask for has been covered in quite a few videos on my channel. The fact that I did not know what you meant to ask for, but used the wrong names for things... is not a thing.

@@bobschultz2895 > When I said nozzles I meant the annual > rings with vanes immediately after the > compressor and immediately before the > turbine, [...] I'm not a jet designer or jet mechanic and I don't play one on TV, but I think I have at least a passing familiarity with turbojets, at the 50,000 foot level and I have no idea what you are talking about. Between the end of the compressor stage and the start of the turbines is the combustion chamber(s), be they cans or donuts. IF you are talking about a gas turbojet with a centrifugal compressor (AKA an centrifugal impeller), then there is a section before the compressor manifold that can sometimes have vanes which is called the diffuser which converts the speed of imparted to the input airstream into a slower moving high pressure mass of air that's dumped into the combustion chambers. I don't know that you would be able to see that looking "upstream" from the combustion chamber of any working turbojet. More over, since the jet @AgentJayZ is supposedly dealing with is a J-47, or its Orenda equivalent, you wouldn't see anything since they have an axial flow compressor rather than a centrifugal one. > I would expect it is something you take > and pick up a with your hand and show > them, the final compressor stage blades > and the first turbine blades are much > different in size and I think that is > quite significant. > although this is a dynamic situation > there still are physical static forces > and I would just like you know where > they're at. Ummm ... okay, so what forces are you talking about here? Since you're apparently interested in differences in area, we're presumably not talking about forces but rather pressures (AKA force applied to an area). Assuming that what you're really interested in is pressures at various points in a turbojet, then may I humbly suggest that you look at the graph that @FlyNAA gave earlier. His graph shows how the pressures change over the length of a turbojet. > There appears to be a gap between the > jet pipe and variable nozzle turkey > feathers does this create a vacuum > in that Gap. Ummm, yeah. @AgentJayZ waved his arms at how this gap basically creates the equivalent of a convergent/divergent exhaust nozzle in one of his earlier videos. I'm too lazy to look for the particular one at the moment, but IIRC, it was one of the videos he did on afterburners. > I'm not trying to be confrontational > I'm just trying to understand things. > I used to work for a machine shop and > they had a large air hose to bow the > chips off and for safety purposes they > had a little extension on the end of > the nozzle that was larger than the > exit of the nozzle and It had holes > in the sides, if you plug up the holes > in the sides it would have a lot less > thrust and not blowing very well. I suspect that the extension used the venturi effect to increase the mass of air moved out the end of the nozzle at the expense of speed of the higher pressure air stream blown into the nozzle. > I think it would be interesting if you > had some kind of a smoke machine or > cigarette and have it around the engine > while it's running and see where the > air is moving on the outside of the > engine and in the shop, does a Shop > create Venturi effect. I'm sure there are any number of things @AgentJayZ could do, but he does have a day job and trying to hook up a smoke machine to show how the air moves around in the shop isn't terribly useful when they're trying to test out an engine on the stand. I mean, if you're just interested in whether or not air is entrained by a moving airstream, you could find that out with a smoke generater or cigarette and your compressed air hose. > I'm sorry if I ask too many questions > I just think it's very interesting

Suggestions in the description

​@@AgentJayZ Sir, I want to know, when the compressed air bleeds through mixing air holes into combustion area, it is the low pressure area ,does the compressed gas looses it's compression before burning??

Simple short answer: no.

I'm not @AgentJayZ and I don't play him on TV, but you're correct as to why a turbofan is more fuel efficient compared to a turbojet. Congratulations on working this out for yourself. Many don't.

Whew! OK, I don't think you actually have a question, but I do have a comment. The efficiency of an aircraft travelling through the air is higher if the jet exhaust velocity of the engines is closer to the flight speed of the aircraft. If you need to go 1500 mph, then a pure turbojet is your most efficient solution, because only rockets can also cover that speed range, and they are thirsty! If you want to travel at Mach 0.85 in the most efficient way, a high bypass turbofan is best, because it takes a much larger mass of airflow, and accelerates it to about that speed. If you can get by with going Mach 0.5 or so, a turboprop accelerates an even greater mass of air to about that speed. All of these examples would be of engines of the same overall power output. The confusion starts when we realize that turboprops are typically under 10Khp. and turbojets are in the 10 - 40Khp range, low bypass turbofans are in the 30 - 50Khp range, and high bypass airliner engines are in the 40 - 100Khp range. Anyway my comment is almost as wordy as yours...

@@AgentJayZ thank you, sir! The context of airspeed had quite eluded me. I was thinking of turbofans vs. turbojets purely in terms of turning fuel into impulse under the conditions that commercial aviation favors, .8 Mach or so. I did have a question in there, which @Lewis Cole kindly answered for me. Specifically, my question was whether my understanding of the relative effects of mass flow, kinetic energy, and fan diameter, is correct.

@@lewiscole5193 , thank you, that business regarding supersonic blade/prop speeds fascinates me. As for the limits of fan diameters, I had assumed a major limiting factor would also be the tensile strength of available and suitable materials. [EDIT: I just realized that I need an integral to do the back-of-an-envelope-estimate for the centrifugal acceleration acting on the blades, and if I could calculus, I wouldn't have flunked out of the engineering program at uni. But the acceleration acting on those blades would increase geometrically with increasing diameter, as would the blades' mass, wouldn't they?] The Ge9X uses carbon composite blades, apparently “fourth generation” thereof. I can’t help but wonder if, should larger turbofans ever come into demand, before even considering tip speed, the limitations of materials will make gearing turbofans a necessity.

The pressure only increases if the expanding gas has nowhere to go. In a jet engine the expanding gas is free to leave, so no pressure develops. Instead the energy that would cause an increase pressure if the gas were contained becomes an increase in velocity. Less simpler: Combustion in jet engines is an isobaric process. More simpler: No pressure because the gas is allowed to expand. Hope that helps!

@@fletcherreder6091 Thanks for the explanation!

I used to live in Surrey... The compressor gets better at its job as the rpm increases. At starting rpm it is supplying air at about 3 or 4 psi... just enough to get things happening. At full rpm it is supplying 75 psi in the Orenda.

@@AgentJayZ Thanks for the great explination. It's not a bad thing to think of yourself from Surrey. It just designate you as Canadian. Great job Sir. As an FYI I always wanted to get into the airplane industry as a maintenance worker. But they didn't think that I was worth their time. I have dysgraphia and it screws up me trying to relay what I really can do and my abilities.

What? No Fire Tetrahedron (chemical chain reaction)?

@@perrydiddle3698 yeah, sure! Indeed, you need the reaction as well, good call.

In the Saturn V F-1 first stage engines the chamber pressures ran at about 1,000 psi at the injector plate. As such the oxidizer and fuel pumps discharge pressures had to run at about 1,200 psi to maintain a positive inflow. This allowed the F-1 turbopump to deliver the propellants into the thrust chamber at the rate of about 1,500 lbs per second, which permitted the engine to produce 1.5 million lbs of thrust.

I read a book about liquid fuel rocket engine development. The author said that the hardware and components are under about ten times the stress experienced by jet engines, so when things go wrong, there is often no surviving evidence of the cause.

@@jordmosselman3403 I’m just being difficult. Lol As you said, the triangle is the budding block of combustion. Oh, no. Now my mind is racing again, the obvious things (to me) to break the chain for combustion are to remove O2 and fuel. Let’s say you were in the back yard grilling some burgers on a propane bbq. Now, the weather turned and it’s starting to snow. It’s getting colder. Just how cold does it have to be to extinguish the fire? You still have fuel. You still have oxygen. I guess, the chain of reaction creates combustion and the heat. But, removing the heat (or ignition source) stops the fire, right. Then the chain reaction stirs. The O2 and fuel remain. If you fed O2 and fuel and ignition to get fire, I suppose at some point, it would get cold enough to stop it. I don’t know now. I’m thinking the combustion is the self sustaining heat source. Rocket engines sill burn in the cold of outer space. I thought I understood fire science until they tossed in the tetrahedron. Let’s say I have a chamber in which I continuously provide O2. I continuously provide the propane. I have a heating element to which I crank up the temperature to the flashpoint of the fuel. Fire! Now, without changing any of those 3 elements, how can I eliminate the chemical chain reaction only and extinguished the fire. Unless it is some agent (nitrogen, CO2, dry chemical...) that creates a barrier between the fuel and the O2. Bet, even that is just removing the O2 at an intimate level. Tylenol time.

Well, the compressor delivers pressure and velocity, and the turbine receives velocity and pressure, so I dunno...

@@AgentJayZ well I mean there is more pressure than velocity in the compressor section. And there is more velocity than pressure in the turbine section. Is that not true?

Your teachers explanation seems vague. It demands further explanation.

I would not describe it that way, so to answer your direct question, that is not true.

Restored but engineless? I do not believe that. Perhaps you meant retired, or even scrapped.

@@AgentJayZ I can certainly understand your skepticism about something found on the Internet. FWIW, the Web page in question says, "In 2011, there was a restored, albeit engineless, F-104 for sale in the UK for £25,000." which can be found here: < yeahmotor.com/aero/aircraft-for-sale/ > Just for giggles, I looked around for anyone else mentioning an F-104 for sale dirt cheap and ran across something roughly similar on another Web page which says, "If you want one with a working engine and parts, you'll need $325,000, but if you desire one as the ultimate decoration piece, an engine-less example was listed for 25,000 British pounds back in 2016" which can be found here: < www.hotcars.com/10-actual-fighter-jets-you-can-buy-for-less-money-than-a-new-ferrari/ > Obviously, the dates aren't a matched, but assuming that the two F-104s are roughly comparable, this would suggest that a J-79 costs roughly $285K ... which I have idea if it's in the ballpark or not, hence my question to you.

Well, there's your opportunity! A flight worthy dash 11 J79? We are testing four of them right now. How much would it cost to get all of that together and have a qualified pilot take it for a spin? The pieces won't cost as much as the putting together of all those pieces.

@@AgentJayZ A dash 11? Well, if I'm going to dream, then I might as well dream for a dash 19. Seriously, I may be ignorant, but I'm completely clueless. I'm well aware of the fact that Bernoulli has very little to do with getting an aircraft into the air. Instead, it's about having enough money to stack under the wings so that you can lift the aircraft off of the ground. So when I see the sort of thing I mentioned before, I'm almost certain that it's wrong/very misleading, but I have no idea by how much. OBTW, you folks loaned out a J-79 to the wingless American Eagle race car didn't you? Did you ever get it back? And if so, if it isn't being too nosy, what ever happened to it?

So... I guess you're not aware that Jesse Coombs lost her life in that car?

Indubitably.

People forget that the back end of a turbine engine is open. The illustration of the bucket is a good one.

Yes I should. It's the Sabre Jet, and it's my company logo. I should have a nice big model of one in my shop. I'll get on that.

@@AgentJayZ You do realize that "Real Soon Now", you're going to be inundated with model F-86s from some of your devoted fans. Well, if you feel like getting rid of some of the excess, I might be willing to take any 1:48 scale F-86Gs you get.

F-84F would be secondary to a Canadair Sabre 6... just like it is in real life. Yes it is.

@@AgentJayZ Do I detect a little bit of Canadian pride? I suppose this means that you want your F-86 models to be in Snowbird livery as well. ;-) Well, in any case, I still might be interested in taking any excess F-86G models you get your hands. (OBTW, the G was an unbuilt variation of the F-86D, not a variant of the F-86A, F-86C, or any of the billions of F-86F variants.)

Maybe, but I recognize it was an American design. North American Aviation sure had a string of hits there, eh? The Mustang, Sabre, and the only aircraft to be way faster, higher, cooler, and better looking than the SR-71, the mighty winged spaceship that was the X-15. "So... your SR-71 goes so fast that it heats up to the point where you need to make the skin out of titanium alloy? Interesting. Of course you are aware that for the same reason, our little rocket glider is skinned in Inconel? It is less practical, but also better looking. Funny how that always seems to happen, eh?"

I'm not @AgentJayZ and I don't play him on TV, but let me take a swack at this until the Big Guy gets around to answering. (I assume that he's more than a little tired of saying the same old thing and won't mind if someone else tries to say the same old thing in a slightly different way that hopefully might click with you.) If you simply compress the air in front of the compressor and then some how release it that compressed air through the turbine, then ideally, the speed of the air flowing into the engine would be the same as the speed of the air flowing out of the engine. Since we live in the real world where it take energy to overcome friction and the like, the engine would spin down and eventually stop as their is nothing to keep it going: any work done by the out flowing air would exactly match the work done to compress the in flowing air in the first place. In a real jet, fuel is burned in the combustion stage and so heat is added to the air which causes it to expand. Expansion doesn't cause a change in mass of the air in the combustion stage. Instead, since combustion stage isn't sealed, there's no reason for the expanded air to cause an increase in pressure since it can simply flow out of combustion stage into the turbine. But since the expanded air wants to occupy more space (i.e. volume) and there isn't any, it moves out of the combustion state at a higher speed than the compressed air coming in from the compressor (i.e. it is accelerated). And by definition whenever you accelerate a mass of anything, you've done so through the application of a force. Apply Newton's Third Law and you've got jet that wants to move in the opposite direction of the mass of air flowing out the exhaust. So to answer your question specifically, (1) "can you argue that the mass increases in compression", no, you can't because it doesn't and (2) "the velocity of air increases in the decompression", yes, because the air has been heated and so wants to expand, not simply because it was compressed in the first place.

Woah, colonel... Mass never will increase. As for the rest of what you said... Cheers for Lewis for trying, but I'm going to say it makes no sense. Take the advice in this very video, and you will agree.

@@lewiscole5193 Thanks for the reply .The knowledge of the combustor not being sealed is an eye opener and for sure mass doesn't change, matter only expands to occupy more space but the amount of substance remains the same . Cheers man my perspective on the jet engine has changed.

Yes. This video is about combustor pressure. Turbofan combustors are exactly the same. ...And calling it a fan jet was hip back in 1965.

@@AgentJayZ Didn't mean to offend! Was a machinist on gas turbines for Westinghouse back in the day! Also built combusters for said turbines! At 78 yrs old,I still miss that job,as it was very interesting.

Like most things in life, it varies greatly but the fan in a modern turbo fan engine can account for about 80 % of the total thrust.

@@skunkjobb Yep!About right! My favorite jet engine is in the SR 71! At a certain speed, the intake bypasses the compressor, and heads straight to the combustors,making it a ramjet Kelly Johnson was always ahead of the game! With your handle, I'm wondering if you worked in the Skunkworks!! 😆

@@skunkjobb so turbo fans are just turbo props with attitude?

Actually, that's close, but a better way of describing it is that the compressor outlet pressure falls below what it was supplying to the combustors. It does so because the compressor airfoils experience aerodynamic stall, like a wing at too high an angle of attack for the speed it is going. This is why the name of the phenomenon is compressor stall. Have look at my video explaining exactly what goes on during a compressor stall. It's called Compressor Stall.

@@AgentJayZ sorry, I worded that poorly. I meant to say that's what happens after a compressor stall occurs, not that it is the cause of a compressor stall. Effect from the cause, not cause of the effect sorta thing

No. If you overload a single shaft turboshaft, the engine will lose rpm and eventually quit working. If you overload a free power turbine turboshaft, the PT will lose rpm, while the GG will be screaming away at its temp limit. Neither engine will stall, but both aircraft will crash, unless the overload is remedied.

@@AgentJayZ Thanks for the response, appreciate your efforts to educate the uneducated

Your name is the best.

@@AgentJayZ Well thank you kind Sir. You are the Oracle to all things exciting & potentially dangerous. I do like the smell of jet fuel in the morning. Please never stop making your videos.

It all depends on the daily price of cooked bacon, divided by the average westerly component of the velocity of all trucks delivering uncooked bacon to all non-franchised cafes that serve bacon, in the country of origin of the manufacture, not the design, of the combustors. This quotient is then multiplied by the Bacon compensation factor, which changes daily, depending on Kevin's mood. So the short answer would be: anywhere between .0047 and .000106. I hope this helps in your calculations. If not, maybe you should add more bacon.

@@AgentJayZ haha..sorry had to ask the question. Who knew that fucking bacon could increase combustion. Do jets run on bacon grease 🐖???

JayZ, explained perfectly in fluent Canadian 🇨🇦. Well, let's explain my Sunday. I have a Prevost that needs some attention on my weekend. Sitting with my Saint Bernard, he says it's ok as long as we have bacon and pancakes. Of course, with real maple syrup. None of that communist corn syrup crap, eh? Bob

@@aaronyork3995 They probably could if you get the bacon bits out and had the appropriate fuel nozzles.

@@AgentJayZ That reminds me, I bought bacon last week but haven't had time for a decent breakfast in 2 months. I think I'll have bacon and eggs for dinner tonight.

Brayton cycle...

@@milantrcka121 yes, baryton. Was hurrying when typing

The channel page lists the business email.

@@AgentJayZ Found a shop street address but no business email?

Ooh! You just made me check, and there is a huge button that says Email address. Jeez! Can you push it? please.

My first car was a Mazda R100. Rotary engines are awesome. Nothing to do with turbine engines.

@@AgentJayZ I know. I’m just throwing fuel on the fire, to muddy the waters so to say. Although those rotary 16 cylinder airplane engines crankshafts are quite interesting, as I recall. All I had was the plastic model Wankel engine. I did drive a Mazda 808 (sort of a cross between the VW Squareback and a mini station wagon.). It was a straight 4 cylinder.

@@AgentJayZ I almost bought an RX 7, but, I had no experience working on them. That, and I’m 6’2”. So, there’s that.😉

They were 9s 14s,18s, and 28s, but I don't know of any 16s. I worked with a guy who had an 808 when I had my R100. We had a drag race one day, because he figured 1600cc of piston power would beat 900cc of rotary screaming fury. When I shifted into second, he was two little lights in my mirror. Some piston engines do feel a lot like rotaries, but they are all in motorcycles.

@@AgentJayZ I’ll have to look up some rotary action. I did get a pretty good idea with my acrylic model, but, outdated love to hear one and see one running.

/elasticity

The compressor does cause the pressure to rise. Combustion doesn't.

@@AgentJayZ alright, that makes more sense. I like the analogy of the bucket, makes it a lot easier to understand

On the contrary, you can thank all of the people who are unaware of Bernoulli for this.

I disagree. Most people have no idea how a rocket engine works. I think the misunderstanding is caused by attempting to understand jet engines from a rattlebox (piston engine) point of view.

Rockets the pressure in the combustion chamber is less than the pressure the fuel is injected at, because all of the now very hot gas is leaving via the throat. Jet the same, you made a lot of hot gas and it leaves via the rear. Going out the front you have a compressor stall. The pressure drops, especially after the turbine, as that is extracting a lot of the energy from the hot gas. Still plenty enough to provide thrust, the energy you remove is used to compress the incoming cool air to the operating pressure. Any extra turbine stages are extracting more energy, either to drive a turbofan, or to drive an output shaft to provide power to an external load, either a generator set or a main gearbox for a helicopter.

Nice troll. A little too obvious.

@@AgentJayZ Not so much trolling as poking fun at those who ask such questions. I've been watching your videos since 2013 so I've heard your 6 or 7 explanations to "why isn't the fan spinning" in the time frame and after a while it got humorous. At some point in one of your Questions videos you expressed your frustration with having to answer a question over and over again and I was thinking to myself... it's the fan question isn't it... then you finally confirmed it and I laughed out loud at 1AM watching the video and woke up the family. Maybe I find it more funny than others because I have to deal with a similar thing as a lightning researcher. For us the equivalent of the fan question is people assuming that positive cloud-to-ground lightning always comes from the top of a storm and is ridiculously powerful, both of which are not true. This idea came from back in the day when we thought lightning strikes were just giant sparks and now we have to reprogram the masses. The problem is that even the media refuses to look at new findings so they spread this lie and funnel all of the general public our way to repeat those claims.

Oh, ok now I understand better. Humor is difficult to get accross in text form. I do feel a common bond. Even the aviation experts working for the big networks make multiple mistakes every time they try to explain anything about jet engines. Point me to any news clip about the subject, and I'll find at least two misunderstandings. I'll bet you could find three in any lightning clip!

@@AgentJayZ Part of the issue as far as I can tell is that the "aviation experts" (especially the ones doing news reports) have less knowledge than me, and I'm no expert.

@@thelightninghunter23 I remember watching a documentary about thunderstorms and all their fascinating complexity once. A few things still stick in my brain from that, and I'm writing this wondering how many of them are wrong, because documentaries surely get things wrong sometimes too, though hopefully less frequently than "news" programs do. So all that follows take with a bit of a pinch of salt, because I'm hoping you might correct anything which isn't true. Anyway, the first was the existence of "positive streamers" which strike upwards from the ground, or from other things connected to the ground, like lightning conductors on tall buildings. The documentary in question had even managed to capture some footage of these, from storm chasing photographers who got lucky and captured them on video or in photographs. Apparently there are several positive streamers striking upwards for each individual cloud-to-ground strike, with the latter happening when at least one positive streamer intersects with the ionized channels generated by the cloud, completing the "circuit" and allowing the built up charge to drain to earth. So allegedly the cloud is negatively charged (or parts of it are, at least) and the ground is positively charged? The second was the apparent reason why a thunderstorm cloud adopts that "anvil" shape - that somehow the cloud cannot penetrate any higher than the ionosphere (though it might have been a lower level than that, I'm not 100% sure), giving it an upper altitude limit, which forces it to spread out laterally once it gets that high. If this is true, what is the reason for this limit - why can the cloud not spread above whatever the level is? Now here's the really odd bits: They had footage taken from flights above a thunderstorm, which seemed to show what they called "sprites", which were short, extensively branched lightning strikes emanating from the top of the cloud, shooting upwards. Are these for real, and if so, what causes them? Finally, the existence of "ball lightning", which was "controversial" at the time, and for all I know may still be. The part I remember most was an interview they conducted with a researcher who claimed to be able to make his own "ball lightning" in his own lab. Which he did by basically shorting out a massive bank of old submarine batteries, using a long metal pole as one electrode and a big metal tray full of water as the other electrode. He would make a brief contact between the pole and the edge of the tray, creating showers of sparks and occasionally what seemed to be floating orbs which hovered above the water for a few seconds before disappearing. No idea if this was in any way legitimate, or if any of it was true, but what do you think?

Flag size has been discussed before. The very first one up was the US flag. It, Canada, and AUS are about the right size. The Jet City council has come to the conclusion that the size of the flag is inversely proportional to one's confidence in one's place in the World Order. It takes a big man to ride a small motorcycle...

@@AgentJayZ I forgive you. Love your work, by the way.

Forgive me? You realize that the flags are sent to me by friendly people, right?

@@AgentJayZ Yep, I forgive you for not asking for bigger ones. Cheers!

Reading your first two sentences I would have to conclude that your skull isn't as thick as you say it is. Note that in jet engines there is a partial restriction created by nozzles that are located at the outlets of the individual combustion chambers (not to be confused with the one big nozzle located at the rear of the engine). The restriction created by these nozzles maintains some pressure inside the chambers, although the chamber pressure always has to stay below the outlet discharge pressure of the compressor. The nozzles are there to convert some of the pressure present in the chambers into kinetic energy, which means the hot gas speeds up going out through the nozzles. This increases the velocity of the hot gas, which along with the mass of the gas is what creates the force that turns the turbine.

It be.