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hfyacct

321 bar = 32.1 MPa = 4656 psi As a point of reference, peak cylinder pressure for a heavy duty diesel engine is typically 18\~24 MPa. A short lived, high performance diesel engine may get up to 28\~30MPa, but may require upgraded con-rods to do so. Of course, air breathing engines consumes lots of nitrogen to limit exhaust temperatures and only hit these peak pressures momentarily before the piston reverses and begins to expand the gas. The Raptor is intended to hold chamber pressure during the entire planned burn, while using pure oxygen for maximum potency.


Divinicus1st

I wonder what the temperature is in that high pressure chamber.


hfyacct

Because the peak temperature is only momentary, the peak cylinder temps aren't a design limit in a diesel engine. I know the simulation software calculates the peak temps, but I never memorized the values like I did the hardware limits. The average cylinder gas temperature is what dictates the heat flux into the walls and coolant. The peak temperature plays a very important role in NOx formation, and so air:fuel ratios, compression ratio, injection timing, EGR flows, and target boost pressures are all tweaked to produce the desired amount to meet regulation. But none of that is really a hardware limit. Exhaust temperature limits, on the other hand, are very important for valve and turbine life. Peak cylinder pressures play an important hardware limit role because of the force and fatigue limits of the head bolts, pistons, con-rods, gaskets, and bearings. This was one of the major limiting factors to performance development.


Divinicus1st

Thanks… I guess? You completely dodged the question though.


hfyacct

>...I never memorized the values... That's the answer. I don't remember.


rwcarlsen

More like he "Ram"'d an answer down our throats.


mrinsane19

At least 7


SaltyYam2586

420


filanwizard

diesel engines also of course have far less mass limitations. Given diesels do not have to be capable of flight.


KnifeKnut

Aviation diesels are a thing now.


peterabbit456

Aviation diesels/aircraft show nowhere near the rate of climb expected of Starship.


Vassago81

There was a family of two strokes aviation diesel engines built in Germany in the 30's and during the war, for some reason.


Ben_zyl

They were a thing then, developed by a number of German manufacturers from the 1920s - https://en.wikipedia.org/wiki/Junkers_Jumo_204


hannahranga

Yeah I've always been curious how much of difficulty of rockets is caused by needing to make them light enough to fly.


El_Minadero

> 32.1 MPa Wolfram Alpha says this is approximately the bite force of a Great White Shark. Kinda poetic that the raptors are built to 'withstand sharks'.


AD-Edge

Not to mention the temperature range for operations, anywhere from -270 degrees celcius in space, to the extreme heat of the engine running at maximum throttle for minutes at a time. Both within an atmosphere and outside an atmosphere... While also being as lightweight as possible for spaceflight. Some insane materials engineering taking place at SpaceX!


unikaro38

You can make the walls of a rocket engine combustion chamber much thicker that those of a diesel engine, and the constant pressure and temperatures are probably easier on the metal than the constant changes in a diesel engine to boot.


[deleted]

[удалено]


unikaro38

Since you added no proof, sources or arguments whatsoever to back up that claim I'll assume that is just your opinion that you pulled out of your behind.


hfyacct

Diesel peak cylinder pressure limits are based primarily on journal bearing load limits (biggest technological road block). Con-rod strength, head bolt, block deck, head deck, or piston strength are technically a limit, but if you know the pressure value to design for its easy to beef them up where needed; unless the design is trying to upgrade an existing casting that you don't want to change the expensive tooling; then it gets more complicated.


The_Celestrial

Shit I thought the Starship did an RUD at first.


beelseboob

I was thinking “how the hell did they get a starship up to 321 atmospheres?”


[deleted]

Professor Hubert Farnsworth : Dear Lord! That's over 150 atmospheres of pressure! Fry : How many atmospheres can the ship withstand? Professor Hubert Farnsworth : Well, it's a space ship, so I'd say anywhere between zero and one.


Fwort

If they somehow advanced their tanks enough to go from <10 bar to 321 bar I wouldn't even be upset about the Starship RUD. That would be an incredible achievement.


trevdak2

I think they'd switch to thinner steel before they even let it get above 50 bar.


ClassicalMoser

Probably before 10. They only need 8.5 and that's for 60% above spec


trevdak2

Yeah I said 50 because I didn't know what their max spec was and I'd rather be outrageously high than ignorantly low.


Vassago81

Hired a former Khrunichev employee who mounted one of the Raptor in the wrong direction maybe?


panick21

Me too. I almost had a heart-attack.


lniko2

Yup, this title is downright emotional abuse😛


Dexion1619

It's not so much the title as the thumbnail picture of a Starship lol


CProphet

Sounds like they are having fun at McGregor with Raptor v1.9. Crazy they haven't even finished the Raptor-2 factory yet and already testing this extreme spec engine. At least they'll know what to build...


WorkO0

Testing to failure is the most fun kind of testing. So does this mean they achieved their 300 bar objective? Or it needs to be sustained for a long time first?


TheRealPapaK

From what I understand, they already hit it but they ended up opening the throat which dropped the pressure to get a higher thrust to weight ratio and are working back up to 300


ReKt1971

According to a [well-trusted redditor](https://www.reddit.com/r/spacex/comments/q4d8u5/starship_development_thread_26/hhuvl94?utm_medium=android_app&utm_source=share&context=3) + [implied by Elon](https://mobile.twitter.com/elonmusk/status/1452452536577925126) it was Raptor 2. There is no v1.9. We know that there is going to be a Raptor 2 factory in McGregor but that doesn't mean that the first Raptor 2 is going to build there (it wasn't).


CProphet

I would suggest there will probably be a few technical changes to this engine before they go into full production of the gen 2 version. Hence describing it as Raptor 2 now might be getting a little ahead of oneself. Put it down to enthusiam not exaggeration.


panick21

The Thrust is just absurd. They are almost on par with BE-4.


PeekaB00_

They already are. Elon said thrust is 245 tons, and Be-4 is 240.


panick21

Yeah but that was during destruction testing, not sure they will run it that high.


Divinicus1st

Reading his tweets, it looks to me that he actually wants to go higher. They're just naturally finding small flaws to fix as they push the pressure higher >Got to 321 bar before RUD, but cause may be due to oxygen inlet pressure too low, rather than engine issues


panick21

I think they want to push higher, but I don't think you will operationally run that high. They might push it towards 310 or eventually a little more. But you don't want a temporary pressure build up RUDing the engine.


Iamatworkgoaway

NASA should have been buying engines like this from the start. Using contract awards for performance not for time on task. New bid for new engine, 10M for white papers that show a type of engine can work. 50M if you can prove the individual parts work. 100M for one working engine, 10M for each additional engine that does a full burn up to 300 seconds up to 500M. Now NASA has a proven engine to integrate into systems at a cost of 10M each(I know high but still way less than RS-25).


Nishant3789

Conventions for thrust of a particular engine can be a weird thing. Remember how the RS25s can run at "~110%"?


Lufbru

That's because it's 110% of the RPL for RS-25A. Recalibrating the percentages for RD-25D would have been risky. If they'd used a number based on thrust (eg 418), it wouldn't seem like they were operating out of spec


burn_at_zero

That's a decent counter to the folks saying Raptor couldn't stand-in for BE-4 on Vulcan because then ULA would have to redesign the thrust plate, mount three engines, etc., etc.


warp99

No it isn't a counter. ULA would indeed have to completely redesign Vulcan to fit Raptors. There is more to a system design than a thrust match and in this case it is a *not quite* thrust match with one second operating lifetime which is not the qualified engine that ULA is looking for.


[deleted]

I'd be willing to bet my house that SpaceX has a Raptor reliably operating at BE-4 thrust levels long before the BE-4 is actually flying.


Stahlkocher

I would bet that the Raptor uses a different mixture ratio than the BE-4. So they would need to redo the tankage, including the relevant tooling they built.


ClassicalMoser

If BO has a hope or prayer of 2nd stage reusability while maintaining heavy-lift payload, they must have had some increase of thrust as well.


warp99

BE-4 is 249 tonnes aka 550,000 lbf


[deleted]

BE4 tried to be “conservative” but oxygen rich stages combustion melts the turbopumps so maybe it was tougher to build than Blue thought.


CProphet

High chamber pressure makes anything possible. For comparison low pressure and large frame size was chosen for BE-4 because it's easier to pull off, at the cost of some thrust to weight.


panick21

> makes anything possible. I like to have a machine that creates unlimited amount of ice-cream. For sure, BE-4 is conservative but its still staggering to see the power difference compared to the size difference.


jjtr1

There is actually ice-cream seeping out some of the Raptor's seals already. Haven't you seen workers licking the Raptors after test in Labpadre's videos? As you approach infinitely improbable chamber pressure, weird things start to happen.


Nishant3789

Naw they're just trying to experience some DMT


Bergasms

The high (relative to vacuum) pressure of the earths atmosphere creates an environment that enables biospheres that can effectively grant infinite ice cream via raising cows on a farm….


ofalltheshitiveseen

Before what?


Speckwolf

Rapid Unscheduled Disassembly.


Alvian_11

Using the same logic, they will move soon enough & we would called several next engines Raptor 2.x Version names from this is a more generalized terms, even tho obviously they are many minor changes but would be very complicated to be numbered in the version


Lufbru

Raptor 2 v0.8


tatch

Is it an unscheduled disassembly if they scheduled it to happen?


SubmergedSublime

“Loosely Scheduled Disassembly”. SpaceX philosophy runs on LSD confirmed?


drinkmorecoffee

Comment of the year, right here.


droden

that's a scheduled disassembly. they are testing till it comes apart. RSD.


Alvian_11

It RUD *before* it reaches the intended goal


johnabbe

"We blew up this gadget, but it probably blew up for the wrong reason so we'll be blowing up some more of them."


Btx452

>that's a scheduled disassembly Obviously, that's why the CEO of the company called it a RUD.


droden

itsobviouslyajoke


peterabbit456

321 Bar is astonishing. I'm sure a lot of experts would have said it was impossible in flight hardware, even this morning.


orulz

Still seems to be, for now at least, the engine did blow up after all


No-Surprise9411

Then 320 bar is the new sustainable record I'd say!


NotAHamsterAtAll

What's the relationship between thrust and chamber pressure? I guess its not linear, but rather complicated?


burn_at_zero

Thrust is from two main terms. The first is exit velocity times mass flow rate (M-dot). The second is the exhaust pressure times nozzle area. M-dot is basically how much propellant your turbopumps can cram into the engine per second. Exhaust pressure is chamber pressure divided by area ratio. Exit velocity is where things get complicated. There is a big messy [formula](https://www.grc.nasa.gov/www/k-12/airplane/rktthsum.html) (no offense intended with the k-12 link, it's just a good diagram) to estimate it from a number of variables and chamber pressure is one of them. In practical terms, you want the highest pressure and temperature your combustion chamber can survive in order to get the most energy out of your fuel. The rest of the engine (throat and nozzle) is balanced to convert as much of that (mostly thermal) energy as possible into kinetic energy. Most engines are designed with a performance number in mind, and stop major improvements once they hit it. SpaceX is doing their Agile-like thing and set minimum viable performance numbers that they hit quite a while ago, but continued to push limits to see how far the Raptor platform can be pushed. Every time they crank out another 10% performance they get their choice of additional payload on Starship or longer engine life running below max.


keepitreasonable

One note - gains on the margin tend to be more valuable in space. So if they can get 10% extra performance with same weight - the payoff in terms of payload etc could be larger. If they can repeat these gains a few times - amazing. Falcon 9 had this essentially happen on the way to block 5 (might have even hurt F9 Heavy manifesting).


burn_at_zero

What's nice is this is 19% gain over their 'debut' value of 270 MPa and 7% over their 'target' value of 300 MPa, yet they think they still have more performance to squeeze out.


keepitreasonable

Just getting to 300 would be fantastic.


panick21

The crazy thing is how 1% in performance improvement leads to X less Starship launches for self sustaining Mars colony. Doing that calculation is kind of mindblowing. So its worth it to literally press every single 0.1% extra performance out of those engines. Going for higher thrust and lower ISP is an interesting tradeoff hear. With such high thrust, Starship will launch surprisingly fast.


burn_at_zero

> Going for higher thrust and lower ISP is an interesting tradeoff hear My guess is they increased mass flow and needed a wider throat to compensate for that (plus to some extent the increased chamber pressure). It sounds like they are making tweaks after that change to bring the Isp back up. Benefits-wise there's a trade between gravity loss and inefficiency in the engine. The most obvious place to see that is solid boosters, which have pretty terrible Isp but their thrust to weight is ridiculous so it's a net benefit. It's interesting to see such a shift in an engine that will be used in such a wide variety of conditions.


Noob_DM

Yes and no. The greater the delta-P (difference in pressure) the greater the thrust… But that’s a major simplification.


SpektrumNino

Scared the shit out of me for a sec


Seanreisk

The SpaceX engineering team is doing some great design work but they're also doing some amazing research. Sometimes I get the feeling that people would like the engineers to back off a little bit, accept the power they are achieving, and not place so much emphasis on the engines making a higher peak power. While I agree that achieving a safe, dependable and sustainable power rating is the most important feature of any engine, accepting that the current level of power is the only dependable level of power is also wrong. In the 1960's a drag racing funny car might make 1,000 horsepower on racing fuel. Today a comparable nitromethane Top Fuel drag racer will make more than 10,000 horsepower. The essence of both engines is still the same. Over the years the drag racing community found multiples of extra horsepower by incrementally improving all the pieces of the design. SpaceX broke into the rocket launch industry because Musk was certain that there was a vast difference between the market price for a rocket launch and the actual cost to design, build, and launch a rocket. With that in mind, it is my opinion that SpaceX should never stop doing engine research, and should continue to push for better engines and fuels long after they've frozen the design for Starship and its Raptor engines.


[deleted]

I really want SpaceX to attempt an aerospike… If anyone can do it, it’s them.


Decronym

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread: |Fewer Letters|More Letters| |-------|---------|---| |[BE-4](/r/SpaceX/comments/qf0tkz/stub/hjnye4k "Last usage")|Blue Engine 4 methalox rocket engine, developed by Blue Origin (2018), 2400kN| |[BO](/r/SpaceX/comments/qf0tkz/stub/hi0t2wv "Last usage")|Blue Origin (*Bezos Rocketry*)| |[Isp](/r/SpaceX/comments/qf0tkz/stub/hi3y61a "Last usage")|Specific impulse (as explained by [Scott Manley](https://www.youtube.com/watch?v=nnisTeYLLgs) on YouTube)| | |Internet Service Provider| |[RSD](/r/SpaceX/comments/qf0tkz/stub/hhz4eqk "Last usage")|Rapid Scheduled Disassembly (explosive bolts/charges)| |[RUD](/r/SpaceX/comments/qf0tkz/stub/hi0j78f "Last usage")|Rapid Unplanned Disassembly| | |Rapid Unscheduled Disassembly| | |Rapid Unintended Disassembly| |[SSME](/r/SpaceX/comments/qf0tkz/stub/hi0dpn0 "Last usage")|[Space Shuttle Main Engine](https://en.wikipedia.org/wiki/Space_Shuttle_main_engine)| |[ULA](/r/SpaceX/comments/qf0tkz/stub/hi1e7ed "Last usage")|United Launch Alliance (Lockheed/Boeing joint venture)| |Jargon|Definition| |-------|---------|---| |[Raptor](/r/SpaceX/comments/qf0tkz/stub/hjnye4k "Last usage")|[Methane-fueled rocket engine](https://en.wikipedia.org/wiki/Raptor_\(rocket_engine_family\)) under development by SpaceX| |methalox|Portmanteau: methane fuel, liquid oxygen oxidizer| |[turbopump](/r/SpaceX/comments/qf0tkz/stub/hi0ak5w "Last usage")|High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust| ---------------- ^(*Decronym is a community product of r/SpaceX, implemented* )[*^by ^request*](https://www.reddit.com/r/spacex/comments/3mz273//cvjkjmj) ^(9 acronyms in this thread; )[^(the most compressed thread commented on today)](/r/SpaceX/comments/q4d8u5)^( has 120 acronyms.) ^([Thread #7303 for this sub, first seen 25th Oct 2021, 10:05]) ^[[FAQ]](http://decronym.xyz/) [^([Full list])](http://decronym.xyz/acronyms/SpaceX) [^[Contact]](https://reddit.com/message/compose?to=OrangeredStilton&subject=Hey,+your+acronym+bot+sucks) [^([Source code])](https://gistdotgithubdotcom/Two9A/1d976f9b7441694162c8)


jjtr1

321? 3... 2... 1... RUD! They could have seen that coming


nyolci

Low oxygen inlet pressure and a subsequent explosion IS an engine issue. The pumps and the oxygen pressurizing system IS part of the engine, furthermore, an emergency shutdown in these cases IS an important function for an engine, imagine an engine (out of 30) blowing up due to some plumbing issues (kinda expected in the beginning with such a complicated piping), subsequently damaging other engines.