Engine cooling – why rocket engines don’t melt

https://everydayastronaut.com/engine-cooling-methodes/

by wolfram74 • 5 years ago

559 164 5 years ago

everydayastronaut.com

jamesmunns• 5 years ago

This is just a really clearly written introduction of a lot of rocket engine concepts.

It was a super good read.

opwieurposiu• 5 years ago

This thing I can not comprehend about rocket engines is how the turbopump manages to hold together.

A turbine blade in the SSME about the size of your thumb makes 600 horsepower.

https://www.enginehistory.org/Rockets/SSME/SSME6.pdf

bernulli5• 5 years ago

Also try to imagine the thermal stresses when you have cryogenic propellants on the pump side and hot exhaust gases (gas generator or staged combustion) on the turbine side!

avmich12• 5 years ago

With "fire wall" of the engine, over the distance of a millimeter you have full temperature of the chamber - that's thousands of Kelvins, not just gas generator temperatures which are lower because otherwise turbine blades will melt - and relatively low temperature of the coolant, and also mechanical stress of high pressure in the cooling channels and lower pressure in the thrust chamber.

jaywalk2• 5 years ago

Well, 63 blades together make 600 horsepower. But as that paper notes, each blade is subject to 50,000 psi which is wild.

TylerE• 5 years ago

It is wild, but not as wild as you might think.

The fuel rail in a modern diesel engine is operating at 25-30,000 psi all the time.

jhgb• 5 years ago

600 horsepower each. The whole turbine has tens of megawatts of mechanical power output.

HPsquared5• 5 years ago

I the power level of these engines is difficult to comprehend. The fuel pump has thousands of horsepower. Compare this to the fuel pump on a car engine, which is a tiny little electric thing. The combustion power must be in the gigawatt range.

Edit: the SSME high pressure fuel pump turbine produces 63000 hp (46 MW). There's also one for the oxygen, and a pair of low pressure pumps as well. Crazy...

Edit edit: the fuel pump transfers 155 lb/sec of liquid hydrogen. If fully combusted (142 MJ/kg), that would release 10.0 GW of heat per engine.

79522• 5 years ago

Saturn V at take off had an equivalent power of 166GW. If that was electricity it would be around 2x the total capacity of all the power stations in the UK.

post_break2• 5 years ago

Reminds me of fuel injectors of funny cars. Watch it go from just idling, to full throttle. Then remember there's 8 of them on the engine. https://www.youtube.com/watch?v=xGTbQuhhluY

skykooler• 5 years ago

This is why electric turbopumps (like those used on RocketLab's Electron rocket) don't scale up to larger rockets well - the power draw is just infeasible to support with current battery technology.

beerandt4• 5 years ago

And then on top of it all, throttling ability.

People don't grasp what an unbelievably complex engineering problem that is. It's at least an addition of difficulty at the same magnitude as building a steady-state 63000 hp turbine pump in the first place.

Mechanically implementing it in the inherently steady-state design rocket of most rocket cycles. Having variable controls able to work at those pressures. Testing structural dynamics for a range of harmonic conditions instead of one. And do all of that with materials that need to tolerate temperatures going from cryogenic to white hot, without allowing thermal expansion to affect the mechanical tolerances of parts running at thousands of RPMs. And now you have varying flow rates and negative pressures in the lines coming from the external tanks, so have to design such that cryogenic liquids (that normally would require immense positive pressure to keep liquid) don't spontaneously boil or cavitate or cause a shock-like wave (think water hammer turning off your bath faucet) under changing negative pressures.

It's really difficult even for seasoned engineers to grasp the scale of difficulty involved.

kragen4• 5 years ago

Yeah, it's pretty amazing. Doing this in a controlled fashion is the hard part; a largish wooden building on fire can also dissipate 10 GW.

A .22 LR rifle bullet might acquire 200 J in 2 ms, which means the firing gun is producing 100 kW mechanical, plus probably another 300 kW thermal. So another way of thinking of this is that an engine dissipating 10 GW is equivalent to something like 25000 handguns firing at once, without ever stopping.

throwawaylinux5• 5 years ago

The turbopumps on the Saturn V first stage make about the same power as an aircraft carrier, over 200MW. Civilian electric power plants that make this much power are called "medium sized" and can power about 100,000 homes.

That's not the power output of the rocket (which someone quoted below). That's the power required to move the fuel and oxidizer into the rocket engines. Pumping the same amount of liquid can move a 100,000 ton floating city across the ocean at 40mph.

dekhn• 5 years ago

It sounded incomprehensible to me too but as I did some more learning about the process of building rocket engines I learned some interesting details. First, remember that people have been making high strength metals through careful processing for thousands of years. Second, the parts of engines are not made as part of large-scale industrialized manufacturing. Almost all the parts are made as few-offs, with far more energy, time, and effort put into making sure that a single instance of something is extremely reliable. Third, we got damn good at materials science in the past 100 year, and metals can be absurdly resistant to deformation under heat.

dokem• 5 years ago

They also only run for a few minutes.

chasd002• 5 years ago

The alloy on the oxygen side pump in the Raptor engine is a work of magic and or art. An oxygen rich turbopump runs so hot it was thought impossible to create because the turbine would fail before the burn was over. SpaceX had to invent the alloy before the first Raptor full duration fire. That's a very low level, never done before, breakthrough required just to get to the real hard stuff.

edit: if you watch gas generator tests on youtube the gas coming out is dark because it's very fuel rich which keeps it cool (in a relative sense)

Gravityloss• 5 years ago

It's because of the liquid oxidizer.

A jet engine can't have such power density because it uses gaseous air which is about 1000 times less dense than liquid oxygen and only contains 20% oxygen.

Everything follows from that.

The pumps are not challenging temperature wise since they pump cold liquids.

The turbine is challenging, but the temperature can be limited by varying the ratio of propellants in the preburner (very lean or very rich means lower temperature). If you use lean, then it's a very oxidizing environment. If you go very rich, there's soot (if you use fuels with carbon).

And the chamber is not so challenging because there is so much cool liquid available for cooling.

You can boil water with a candle and a paper cup.

A high performance jet engine is a harder problem than a medium performance rocket engine.

throwaway0a5e• 5 years ago

Don't think of it as "making horsepower", think of it as "resisting the forces upon it".

A gear tooth the size of your thumb pulls a semi truck up a mountain.

VBprogrammer• 5 years ago

If that interests you then this series of videos is definitely worth watching. It details several parts of the German V2 missile, the grand father of all modern liquid propellant rockets. This one is about the turbopump which is one of the most interesting parts.

https://youtu.be/EgiMu8A3pi0

mikewarot• 5 years ago

I had no idea they individually manufactured those blades on the steam turbine... the number of parts that little factory had to crank out was astounding. I can see why the Russians simplified it to a bent piece of sheet instead.

Considering all the manufacturing, precision manufacturing involved the V2 effort, it's astounding they could do it at all.

kunai• 5 years ago

It is pretty mind-boggling. Makes the average turbofan's turbine assembly look like child's play, and those are also pretty ridiculous in terms of power-to-weight ratio.

HPsquared5• 5 years ago

It's mostly because the working fluid is at very high pressure (much denser than the air coming through an aero engine). The turbine side works with hot gas at 100+ bar, and the pump side is dealing with liquid. Therefore small parts can exert a lot of force (large pressure differences) and do a lot of work (high speeds).

The most similar technology is a boiler feed pump (used to feed the boilers in a steam turbine system, e.g. in a ship or power station) - these work in a similar way, high pressure steam is bled off from the system to drive a small turbine, which drives a high pressure pump to feed the boiler, which feeds the 'main' steam turbine. Similar pressure (>100 bar), but the turbine on the rocket engine needs to handle much higher temperatures (hot gas rather than steam).

avmich12• 5 years ago

Turbofans can be more complex than rocket engines - in the rocket engine thrust chamber you don't have moving parts, but with turbofans the whole engine is like a big turbopump, with air compressor instead of centrifugal pump.

chasd002• 5 years ago

The turbo pump is the main barrier to entry when making a large rocket engine. There's so much energy per unit volume that there is no failure mode that does not result in an explosion. Also keep in mind, you have very hot gas on one side and a few inches over cryogenic liquid oxygen. Liquid oxygen turns anything in to fuel so think about how to lubricate that shaft let alone seal it.

Another interesting thing to think about, it's the turbopump keeping the combustion from running back up the injectors. So, the turbopump has to outperform the combustion chamber in terms of pressure and flow rate.

avmich12• 5 years ago

Liquid oxygen turns anything in to fuel

Not quite literally, in e.g. Soviet engine designs some gas generators are oxygen-rich, they produce oxidized exhaust of high temperature, and the engine still doesn't burn (usually).

So, the turbopump has to outperform the combustion chamber in terms of pressure and flow rate.

Yes, the injector pressure drop can't be too small.

ncmncm3• 5 years ago

Robert Goddard had terrible difficulties with fuel/oxidizer pumps. It wasn't because he was not smart enough. Most of what was needed hadn't been invented yet.

mountainwalker• 5 years ago

Tim's videos are always so well done! Even if you're not a rocket enthusiast there's tons to get out of this video.

throwaway894345• 5 years ago

Agreed. Tim was an old friend of mine in university, but we lost touch over the years. He was always a good, quirky, creative, and talented guy. He bought an old cosmonaut suit on ebay on a lark and started doing funny/silly photo shoots with it and then photo shoots at rocket launches and then real educational stuff. It's been wild to see it take off (pun intended).

bernulli5• 5 years ago

Minor nitpick: fluids are not either liquids or gases, this is particularly true for rocket engines where many of the discussed processes (injection, compression, regenerative coolant flow) actually occur at super- or transcritical conditions.

Also, I don't think you can say the faceplate is heat sink-cooled. Remember that just behind it is the propellant manifold, so it's rather some form of regenerative cooling.

Dig1t3• 5 years ago

Everyday Astronaut is such an impressive dude, I don't understand why he doesn't just work for SpaceX at this point. He knows more about rocket engineering and can explain it 10x better than most aerospace new grads.

criley2• 5 years ago

SpaceX sounds pretty nasty to work for. Long hours, machismo/sexist culture, aggressive management, and certainly not the best pay you can find.

He's probably happy where he is.

sgtnoodle• 5 years ago

I worked there for a few years, on flight software. The culture depends quite a bit on what department you're in. I learned how to push back on schedule pressure and was able to strike a reasonable work-life balance, and the head of my department was very good at buffering us from management. My departure was uncommon in that I left on good terms while I was happy. There were other departments, though, that seemed to operate more like a fraternity, and plenty of burnt-out people.

geocrasher9• 5 years ago

He is definitely knowledgeable, but strikes me as too much of a fanboy to be taken seriously. I have a hard time taking his videos all that seriously. And it's not about his knowledge, it's about his presentation.

texasbigdata• 5 years ago

Take seriously? Ok let’s use his last Russian rocket program history piece….what exactly did you feel was factually inaccurate about it?

GuB-42• 5 years ago

I find he toned down the fanboy aspect a bit. A few years ago, he could have been part of SpaceX marketing department.

He still loves SpaceX, and to be fair, who doesn't. You may not like Elon Musk, his fanboys, the outrageous claims, and the way the company is run, but most of the exciting news in rocketry for the last decade are about SpaceX. But for the last few years, it is clear that he makes some efforts to be impartial and focus on the technical aspects.

And you should watch the videos he made with Elon Musk when he visited SpaceX. I expected little more than an ad for SpaceX, and it turned out surprisingly technical and hype-free.

mlindner3• 5 years ago

I completely agree, but the fanboy aspect isn't really my main sticking point, it's his tone that feels like he's teaching elementary schoolers something.

sebzim45002• 5 years ago

Classic SpaceX fanboys, always making 90 minute documentaries about the history of every Russian rocket engine.

thamer• 5 years ago

I've seen this kind of comment before about his presentation, and I don't really understand it. It's true that he's a fanboy and that's especially visible in his video interviews/visits with Elon Musk, but the style of those videos is markedly different from the more educational ones which are often trying to cover a topic with a lot of detail while remaining relatively accessible.

I watched the video version of the article linked here this morning, and don't recall any part that was fawning over anyone or anything in particular.

What is it about his presentation that puts you off?

lilyball• 5 years ago

too much of a fanboy to be taken seriously

I would be really interested to know why "caring too much" is a disqualification.

Dig1t3• 5 years ago

I guess some people's exuberance can turn people off, but honestly its great in my opinion. Why should someone's joyful exuberance for something make his educational content not worth watching? The guy is obviously just very passionate about spaceflight and people who are pushing the boundaries of science/technology. I think 99% percent of the people I talk to approach this kind of stuff with mundane indifference and cynicism, so I think seeing someone genuinely passionate and excited by it is a breath of fresh air.

rpmisms• 5 years ago

I understand the sentiment: he comes across as one of those "hype guys" who's always talking about get-rich-quick schemes, but he's honestly incredibly knowledgeable about rocketry. He toured Starbase with Elon and asked questions that belayed a deep understanding of the mechanics involved.

natch• 5 years ago

I take him seriously (although frankly there's no requirement that it all be serious) and enjoy some of his stuff but it's true that sometimes the screaming glee level and emotional outbursts are way beyond my comfort zone, landing somewhere between cringe and get me out of here.

Reminds me of the launches I have seen where I really wanted to soak in the thumping sound of the rocket engines, but the people nearby are just screaming at the top of their lungs… "America!!!" as if that's helping anything at all.

He's also friends with a previously Tesla-focused YouTuber (name redacted, but rhymes with "Ken Mullins") who imho sold out to affiliate and sponsorship deals to the point where I lost all respect for him (the friend) and can no longer trust a word he says. So I have a suspicious eye on Tim's fire hose of cash harvesting mechanisms, but he seems to be staying legit so far. And he does have fantastic content. Also I'm not saying he doesn't deserve the cash he's earning; he puts it to good use and has a growing staff, as I understand it.

guynamedloren• 5 years ago

Small pedantic note: this article is authored by Claire Percival, not Tim Dodd.

I'm not familiar with the working dynamic - Tim very well could been involved in authoring this piece - but, credit where credit is due.

Edit: I partially recant this. The article includes a video by Tim.

philipwhiuk2• 5 years ago

As I understand (as a Patreon), in general, Tim writes the video and then one of his team write an article that covers what the video says only with more text to substitute for the lack of visuals.

For Pre-Launch Previews they are written first by a team member.

mlindner3• 5 years ago

I don't actually think he's that impressive and I don't get people's praise for him. His videos have a lot of mistakes in them and while they're written in a way that dumbs down a topic well for an audience who doesn't understand the subject very well, that's his only major skill that's involved here. He's not especially smart or ingenious, he's just a good communicator. If he was to work somewhere it would be in a communications department, but he probably makes more from Youtube than such a job would provide.

That's why he doesn't work for somewhere in the industry, youtube makes him more. (He makes enough money to hire other people to write for him, as we can see in the linked article.)

HectorRamos• 5 years ago

Tim spends countless amount of time going through the scripts, read throughs, first recordings, and so on, with Patreons. I've been on many of these read throughs, usually with several engineers in the aerospace industry present, and it's meticulous how Tim makes sure any possible mistake is identified and rectified. Even then, once you upload, there's no editing of a video.

The goal is to bring the subject down to a level where everyday people can still follow. It's not meant to be a college course, so of course there will be some dumbing down.

colordrops• 5 years ago

He's probably making more money with his media that he would working there.

paxys• 5 years ago

Having a YouTube channel with 1M+ subscribers and videos that get 5M+ views each is a much more profitable and generally better gig than SpaceX employee #10,000+ working 60-80 hours a week in a high pressure culture.

kylecordes2• 5 years ago

Also... even aside from the $/year, having 1M+ fans (many quite enthusiastic) is a far stronger position to be in than having one boss whom you must keep happy at all times.

philipwhiuk2• 5 years ago

There's a big difference between researching a topic to a standard good enough for 'popular rocket science' and 'understanding the maths well enough to work in the field'.

kragen4• 5 years ago

Has he built prototype rocket engines like Integza, Ben Krasnow, or Tech Ingredients? They're still primarily divulgadores (there isn't a good word for this in English) but they have a certain amount of practical experience getting things to work.

OTOH at the point that you're EDM-drilling thousands of micron-scale holes in your combustion chamber for film cooling, you may start to need practical experience with different things.

gherkinnn• 5 years ago

There's a distinction between wanting to do something and being something.

Finding joy in cooking does not mean you'll be happy as a cook. And some people like being a cook where the cooking part is tedious.

Animats• 5 years ago

Making rocket engines by metal 3D printing has become popular. A rocket engine bell and combustion chamber has one big rigid part with lots of channels and voids inside. That's the ideal case for 3D printing. Much simpler than building the thing up by machining and welding together many individual parts.

m4rtink• 5 years ago

I remember reading in an article that without 3D printing they could simply not get the cooling channel geometry they needed on the Super Dracos on Dragon 2.

Without 3D printing the combustion chamber they would need to use other cooling channel geometry, makin ghr engine heavier, bigger and less efficient.

avmich12• 5 years ago

There are different problems with 3D printing than with classical subtractive manufacturing. E.g. you need to get the supporting powder out of long thin passages in the cooling chamber - you don't have such problem with milling machine approach.

pfdietz5• 5 years ago

An alternate scheme is to stack thin metal layers into which holes have been cut, then diffusion bond them together.

ncmncm3• 5 years ago

Maybe the main problem is that you want different materials in different parts of the structure?

E.g., the inner wall of the cooling channel in the bell is better made of something weaker but more heat-conductive, as noted in TFA. And, different materials in the chamber, throat, and bell.

I suppose you could have multiple feeders, on an additive system. But there are various reasons to want to use laser sintering of powdered metal, instead. And bonding the different metals is its own challenge. You could vary the mix of powder dropped at different levels, and rate of motion of the laser to match. But the combustion chamber probably wants concentric layers.

Plenty of hard choices and problems to solve. Engineers earn their keep.

ortusdux• 5 years ago

One of my favorite bits from Tim's videos was during a tour of Firefly Aerospace's facility when they talk about engine cooling. They discuss EDM machining small holes into the coolant channels just before the throat, which lets a small amount of cryogenic coolant out to cool the interior. The funny part is that you can purposefully undersize the holes and they will melt larger until they are big enough to adequately cool the engine. You basically pre-season the engine with a test-fire and let it choose how much internal cooling it needs.

https://youtu.be/ac-V8mO0lWo?t=2203

jpm_sd• 5 years ago

Ignorant question: are solid-fueled rockets at all interesting, anymore? Do they have any advantages (e.g. simplicity of design) over the fancy throttle-able liquid-fueled engines?

anarazel• 5 years ago

Depends on the purpose. E.g. for military uses like ICBMs they're quite important...

j8asic• 5 years ago

Not really. Gel propellants are a new direction.

evo• 5 years ago

I suspect their primary advantage remains shelf-stability at room temperatures, which will make them stay relevant for military applications, e.g. you don't want a cryogenics facility in your submarine or cruise missile launch platform.

Historically, I think they're cheaper than an equivalent disposable liquid fueled engine but don't hold up to the fully reusable designs of today, and from a reliability perspective there's not a lot of room between working-as-intended and "activate the flight termination system" at a total loss.

Terr_• 5 years ago

I suspect their primary advantage remains shelf-stability at room temperatures, which will make them stay relevant for military applications

I while ago I read--but barely understood--a book that went into a lot of this: "Ignition! An Informal History of Liquid Rocket Propellants" by John D. Clark.

_____________________

IIRC there were some cases where a fuel was not militarily-acceptable because you would need to warm/thaw the mobile missile prior to firing in a Russian winter, or other cases where a permanent missile-silo meant it was cost-effective to run heating/refrigeration all the time, etc.

[I]n applications which do not require a low freezing point, hydrazine itself is fused, either straight or mixed with one of its derivatives. The fuel of the Titan II ICBM doesn't have to have a low freezing point, since Titan II lives in a steam-heated hole in the ground, but it does need the highest possible performance, and hydrazine was the first candidate for the job.

_____________________

Another fuel-choice issue involves how badly it might self-destruct if anything unusual happened:

[I]n the summer of 1960, we tried to fire a 10,000-pound thrust Cavea B motor. [...] Well, through a combination of this and that, the motor blew on startup. We never discovered whether or not the [detonation] traps worked—we couldn't find enough fragments to find out.
The fragments from the injector just short-circuited the traps, smashed into the tank, and set off the 200 pounds of propellant in that. (Each pound of propellant had more available energy than two pounds of TNT.) I never saw such a mess. The walls of the test cell—two feet of concrete—went out, and the roof came in. The motor itself—a heavy, workhorse job of solid copper— went about 600 feet down range. And a six-foot square of armor plate sailed into the woods, cutting off a few trees at the root, smashing a granite boulder, bouncing into the air and slicing off a few treetops, and finally coming to rest some 1400 feet from where it started. The woods looked as though a stampeding herd of wild elephants had been through.
As may be imagined, this incident tended to give monopropellants something of a bad name. Even if you could fire them safely—and we soon saw what had gone wrong with the ignition process—how could you use them in the field?
Here you have a rocket set up on the launching stand, under battlefield conditions; and what happens if it gets hit by a piece of shrapnel? LRPL came up with the answer to that. You keep your monoprop in the missile in two compartments: one full of fuel-rich propellant made up to A. = 2.2 or 2.4, and the other containing enough acid to dilute it to X = 1.2. Just before you fire, a can-opener arrangement inside the missile slits open the barrier separating the two liquids, you allow a few seconds for them to mix, and then push the button.

jandrese• 5 years ago

They are useful when you need a rocket that can take off at a moments notice but sit idle for decades at a time. For typical rocket launches they don't make much sense.

I suspect the Space Shuttle SRBs were chosen because they were a handout to ICBM manufacturers.

dylan604• 5 years ago

Depends on your definition of "interesting". If you mean do people still use them for practical purposes, then yes they are. If you mean are people still researching them for use in exploring space, then probably not.

Robotbeat5• 5 years ago

Extremely simple (basically just one big rocket combustion chamber with the propellant already inside, no pumps or plumbing) and shelf storable and potentially extremely high thrust to weight ratio.

Useful for munitions and for one-time-use. I’d like to think we’re going to reusable rockets and not as much war, so I’d LIKE to think they have fewer uses, but…

numpad03• 5 years ago

Biggest drawback is Americans don’t like them built in volume and ITAR-free. They didn’t like it in free hands so much that they once did a civilian “military aid” to let an ally build a clone of then top of the line Delta II.

Looking back at history, maybe what goes on top actually do keep the peace in the world, so maybe we could safely go back to building solids at scale for peaceful space transportation. But not likely without an American nod, I would imagine.

magicalhippo• 5 years ago

Interesting enough to still be of use. Japan has a three-stage solid-fuel rocket[1] for example, with several launches planned.

[1] https://en.wikipedia.org/wiki/Epsilon_(rocket)

jcims2• 5 years ago

Two of them just helped get JWST into space.

WalterBright3• 5 years ago

The turbopump, regenerative cooling, and boundary layer cooling by drilling holes, were innovations from the V2.

avmich12• 5 years ago

All of that was greatly improved over time. Centrifugal pump was taken by von Braun from fire engines, boundary level cooling wasn't as good as transpirational cooling, and regenerative cooling was with little supports, which required thick and strong fire wall, so they only could use 70% ethanol.

Still - hats off to the pioneers. It's always pretty hard.

WalterBright3• 5 years ago

I would hope that it would have improved over the last 80 years :-/

The V2 had other foundational inventions - the ballistic missile shape, and the gyroscopic guidance system.

trhway• 5 years ago

a bit related - modern turbofan engines are running extremely hot and to avoid damage/melting to the turbine blades the blades are cooled from inside and with the boundary layer by the cooling air flowing out of the holes in the blade

https://www.researchgate.net/figure/Evolution-of-turbine-ent...

https://www.youtube.com/watch?v=4FqMLyo7fyU

soheil3• 5 years ago

Serious question: why is it bad to run your rocket engine-rich? If you know you're not going to use the engine and it's nearing its end of life why not get more power out of your fuel/oxidizer by hitting the stoichiometric point? Also, if engine is melting maybe allow it to continue to melt, but at a lower rate and rebuild it later.

pfdietz5• 5 years ago

The optimal (in the sense of maximum specific impulse) operating point of a liquid propellant rocket engine is typically fuel rich. This is because with stoichiometric fuel/oxidizer ratio, the temperature is so high that there's significant dissociation, which robs the gas of some of the heat of combustion. Going a bit fuel rich wins back some of this, enough that the reduction in average molecular weight of the gas from inclusion of more hydrogen atoms is a net win.

An exception to this is if your oxidizer is hydrogen peroxide. Peroxide/hydrocarbon engines typically optimize to stoichiometric, because the flame temperature is lower. If you look at photos of that British launch vehicle, the Black Arrow, that used peroxide, the rocket exhaust jet is radiating very little visible light, because most of the carbon has been oxidized.

https://ichef.bbci.co.uk/news/976/mcs/media/images/55155000/...

soheil3• 5 years ago

In fuel-rich engines can't the fuel be harvested after it does its function of cooling the chamber walls at the end of the nozzle. There are cases where fuel is boiling before it's ignited so I don't think the heat will be an issue. If it's not possible to have a pipe that transfers the fuel from the end of the nozzle back to the tip of the engine because of re-transfer of heat can't there be a secondary small engine near the end of the main engine that directly gets its fuel from the excess fuel used to cool the main engine?

pfdietz5• 5 years ago

All the fuel goes through the cooling channels before injection into the thrust chamber, typically. So what you're talking about there is standard practice.

soheil3• 5 years ago

Not in those type of engines. I meant the type of engine that creates a layer of fuel on the outside walls that gets pushed out with the exhaust gases.

shmeeed• 5 years ago

Anybody interested in this topic might want to read the NASA Saturn V Owners' Workshop Manual: 1967–1973 (Apollo 4 to Apollo 17 & Skylab) by David W. Woods. It's an incredible collection of information, tables, and drawings relating to the Saturn V's development and operations.

Engine cooling – why rocket engines don’t melt

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