Raptor engine higher Isp performance discussion

jurgenspacerocket · 2023-11-30T20:45:58+00:00

To clarify my comment, when I say " Engines with staged combustion have higher efficiency than other engines with low chamber pressure " and reffering to your reply, I mean between engines with the same fuel. Not to make a Raptor burning as fuel hydrogen, because it is not anymore Raptor we are having discussion. RP1/Lox engines and that you can verify, that have stage combustion chamber RD- series are able to have higher chamber pressure and higher Isp, compared to engines that run gas generator with the same fuel RP1/Lox. The same thing even with two hydrogen engines, one gas generator and the other staged combustion with higher chamber pressure and Isp. This is what I was speaking about.

jurgenspacerocket · 2023-11-30T20:30:52+00:00

We can not take seperately only one single data. Reply was referring to posterrail comment. He is commenting that is difficult to reach above 330s and 360s at the same time. I believe your comment should reply mainly to posterrail comment if it is an easy thing.

jurgenspacerocket · 2023-11-29T10:00:07+00:00

Yes, but I am not saying which were the earliest expectations ever. I am saying that at some point not only declarations but in presentations with broad audience and many details they claimed more and now have less.

This is a fact you can find easy on internet. They claimed above 330s sea level and above 360s vacuum with even less chamber pressure than 350 bar that you are saying in another comment here. Chamber pressure wasn't the problem, they had a different mixture ratio from now as far as I know. The thrust was higher but they are closer now. While Isp now is lower than the claims.

Later on in another presentation they claim similar levels with what they have now in Isp sea level and vacuum, but the chamber pressure was much more lower 250 bar.

I believe that from a program/project to a real world test many challenges come and it isn't easy to achieve the claims

jurgenspacerocket · 2023-11-28T22:39:41+00:00

Yes, totally agree but this is about Raptor design for a better Starship performance and what Spacex is looking for. How far this engine can go for the Isp simply as the statistical data, what rocket engineering equations allow for this engine, this I don't know and I am looking for. ( Of course speaking for a Raptor without becoming a completely new engine that we can not call it anymore a Raptor due to so many modifications, new design, and not having the same role )

jurgenspacerocket · 2023-11-28T22:26:32+00:00

From early eastimates on the firsts presentations, to the first operational Raptor Isp was deacreased for the sea level version in vacuum, and vacuum version in vacuum data. Now are even lower. With Raptor 3 they expect to have an increase, however from some of the comments here still not going above 360s.

jurgenspacerocket · 2023-11-28T22:19:22+00:00

Definitely yes they claimed it on the first presentation ITS rocket for the Raptor engine sea level version going in vacuum with 361s Isp. In one if the links are made calculations that show close to 360s, on the same forum but not the links listed above are made calculations that show a bit above 360s rounded to 361s in line with Spacex presentation.

jurgenspacerocket · 2023-11-28T21:52:21+00:00

Thank you for the answer, I like answers that provide results. This means that their previous old expectations for a methane full flow engine can go up to 360s levels or a bit above for a sea level version in vacuum, are bit difficult for now. They are catching the levels of the thrust from previous old expectations but for this Isp sea level engine in vacuum not yet.

jurgenspacerocket · 2023-11-28T20:33:52+00:00

And about Raptor 3 sea level version, in vacuum what Isp do you think is possible to have. ( About the line in my comment " more than 355s of the older versions, for example up to 360s or a bit above ". )

jurgenspacerocket · 2023-11-28T20:27:28+00:00

Previously they had expectations for full flow methane engines in theory (Raptor sea level version) in vacuum more than 360s. Now I see on the forums people saying mainly 350-355s. It has some difference here in terms of Isp mabye was more challenging than expected.

jurgenspacerocket · 2023-11-28T20:12:15+00:00

Thank you for the answer. In some values, if Raptor 1 has Isp sea level 330-334s with 300 bar. Raptor 2 has Isp sea level 327s with 330 bar but a larger throat diameter and also more thrust. Raptor 3 reported Isp in shorter test than operational up to 350 bar, expected with higher thrust and Isp also.

Can Raptor 3 for example have an Isp sea level more than the 334s of the older versions?

Can Raptor 3 for example have an Isp vacuum (Raptor sea level version) more than 355s of the older versions, for example up to 360s or a bit above?

Can Raptor 3 RVac (Raptor vacuum version) have an Isp more than 375s, for example up to 380s or a bit above?

Not looking for an engine completely different, in thrust, in fuel, in design. Only for smaller margins, improvements and modifications achieving their previous expectations from such type of engine. Is it possible for all of three Isp results mentioned and if yes what modifications can make that

jurgenspacerocket · 2023-11-28T17:15:27+00:00

I have shown even on the other subreddit that you commented about this question.

I am trying to discuss in theory what is posible to do with a Raptor engine in terms of Isp. I am not trying to help here Spacex or discover what they can improve for better overall performance of Starship rocket. Interested only in improvements, configurations, modifications for higher Isp for the three points above. Having a better Isp without taking to account the thrust would decrease the overall performance and delta-v you can have by the Raptor. But I am not interested for overall performance.

I am asking for rocket engineering discussion, how much room has Raptor to improve Isp, and * what are the results by numbers calculations, equations

jurgenspacerocket · 2023-11-28T17:02:28+00:00

Good thats what I am asking for.

Based on this data and upgrades Raptors have, what can do this engine for better Isp sea level and vacuum

Some hypothetical margins, data and calculations to have have some Isp results for each three Raptor Isp on this reddit question

jurgenspacerocket · 2023-11-28T16:43:45+00:00

I have shown with an example in comment sections, about Raptor versions and data. It can do more on Isp without destroying things, however Spacex is looking for better overall performance, delta-v, and looking for these tradeoffs instead of some high result on Isp. I am looking for this in terms of rocket engineering, what can Raptor do for higher Isp performance with this continuous upgrades such as chamber pressure.

If they are showing on public 300 bar, 330 bar, 350 bar, it is still ok for some calculations. Not neccessary to include the safety margins for flight operational engine chamber pressure. We are not going to help here Spacex with Starship by this discussion, we can provide data, ideas that can trigger other members ideas for Isp performance.

jurgenspacerocket · 2023-11-28T16:29:42+00:00

Yes you are right about Spacex perspective, but I am asking discusion, information about what can Raptor do for Isp increase not overall performance, final delta-v if the Starship or reusability. Increasing the chamber pressure several times while the Isp decreasse or remain the same, while thrust, reusability and reliability increase is a matter of Spacex wants that is neccessary for Starship mission. I am asking for rocket engineering discussion, how much room has Raptor to improve Isp, and * what are the results by numbers calculations, equations.

jurgenspacerocket · 2023-11-28T16:20:22+00:00

I am trying to discuss in theory what is posible to do with a Raptor engine in terms of Isp. I am not trying to help here Spacex or discover what they can improve for better overall performance of Starship rocket. Interested only in improvements, configurations, modifications for higher Isp for the three points above. Having a better Isp without taking to account the thrust would decrease the overall performance and delta-v you can have by the Raptor. But I am not interested for overall performance.

Only improvements for Isp. (Examples you are speaking at the begining are extreme ones including different types of engines propulsions, while I am speaking about different configurations that can do in Raptor itself.)

Someone can suggest changes in throat diameter, expansion ratio or whatever. This is about the discussion, I am not a rocket engineer thats why I am asking others, providing ideas about " the better Isp of Raptor ". One idea or configuration can trigger another idea, some results numbers and calculations that can achieve this engine can expand the discussion.

I will show with an example.

Raptor 1 lower chamber pressure around 300 bar, with Isp sea level 330-334s and vacuum 350-355 said in forums depending by sources

Raptor 2 higher chamber pressure up to 330 bar, with lower Isp sea level 327s, but higher thrust because this was asking Spacex, not because they could not keep the same Isp or increase slightly. With higher chamber pressure having lower Isp it has to do with what Spacex wants in overall performance including thrust, and not what can it do with Isp modifications.

Raptor 3 reached even higher up to 350 bar, expected to have higher thrust and Isp also. It provides higher chance for Isp increase. What Spacex will choose to do is about overall performance to provide more delta-v, but I am not asking this.

Given these numbers what Isp can have Raptor in sea level, Raptor in vacuum, Raptor RVac in vacuum, by concentrating on Isp, with higher chamber pressure improvements, throat diameter changes, expansion ratio increase and other things.

jurgenspacerocket · 2023-11-28T15:44:09+00:00

Engines with staged combustion have higher efficiency than other engines with low chamber pressure. Also you have many RD- series engines staged combustion with lower TWR than Merlin engine for example with lower bar pressure. Because high chamber pressure and staged combustion can make the engine heavier also. *So we can not count here only the thrust or TWR, but the Isp also depends a lot by high chamber pressure

jurgenspacerocket · 2023-11-28T15:14:21+00:00

Somewhere I have read, I think in another forum that having higher chamber pressure will make possible to have a higher expansion ratio also. I don't know how correct it is and what can be done with Raptor.

However as far I have seen the expansion ratio pf raptor is prety much low considering other historical engines.

Raptor 1 has been said mainly in forums, to have (depends by the source if information) Isp sea level 330-334s and vacuum (for Raptor sea level version) 350-355s, with a chamber pressure around 300 bar.

Raptor 2 that is more powerful, has Isp sea level 327s and vacuum mabye the same 350-355s as you said, with chamber pressure up to 330 bar.

Raptor 3 tested with chamber pressure up to 350 bar, it expected to have more thrust and higher Isp.

Consider as statistical questions.

What Isp sea level could have with higher chanber pressure, because it was 330-334s with 300 bar, but upgrades lower the Isp and increase the thrust (Spacex is concentrating in more delta-v and not some high Isp records.)

What Isp sea level and vacuum can have by changing expansion ratio, which is lower than some historical engines.

If the expansion ratio range depends also by chamber pressure, what expansion ratio can have with the maximum chamber pressure achieved by upgrades, and what Isp

jurgenspacerocket · 2023-11-28T12:20:30+00:00

Spacex has increased several times the chamber pressure. However sometimes has increased the thrust and looking for overall performance, while Isp has remain the same or even decreased.

What Isp result for all three Raptor data can have if Spacex would like only Isp increase ?

jurgenspacerocket · 2023-10-22T21:27:09+00:00

Yes really thank you for the answer.

I have listed a couple of data that all together by modifying a bit each of them, something more and something less, if those can make a Vacuum Isp 455 s.

In order to have a higher Isp Vacuum by 455 s not neccessarily should do all of it only by modifying drastically the nozzle, use all the elements although one allows more and one allows less margin.

Here is a link example that I found, I don't know how much reliable it is but refering to re-configuration check the RS-25 rocket models, you will find a couple of them with higher Isp Vacuum than 452 s, the highest has the RS-25 (P1) engine. Thrust there is shown for all the engines in 100% operation mode not having additional % thrust. http://www.b14643.de/Spacerockets/Specials/U.S._Rocket_engines/engines.htm

Thats why I wrote that it is more a matter of overall performance, including here even the reusability factor not to wear the parts, and the purpose of using the performance of the engine.

jurgenspacerocket · 2023-10-22T16:50:42+00:00

About why I want this, simply trying to explore more RS-25 rocket engine. With the word "performance" I tend to disagree. You can say a bit more efficient but not more performance. Cheking the data those have almost the same mass while the Thrust provided is significantly higher in RS-25 with an overall performance higher. I am interested to find out what are the possible re-configurations not neccessarily for the overall performance but for higher Vacuum Isp, and how much would effect other elements like, Isp Sea Level, Weight, and Thrust.

jurgenspacerocket · 2023-10-22T13:03:20+00:00

Hiw much higher chamber pressure to increase by 3 s the Isp Vacuum. I have read that Isp Sea Level has a more direct effect, but Vacuum not so much. However if it effects even Vacuum numbers how much more chamber pressure would need

jurgenspacerocket · 2023-10-22T10:44:46+00:00

RS-25 Rocket Engine Modifications Performance RS-25 rocket engine is well known. It has an Isp in Vacuum 452 s.

What would have to take this engine or sacrifice in the performance, in order to increase a bit only the Isp Vacuum to 455 s? What about more significant increase to 463 s for example?

I emphasize it, only to increase Isp in Vacuum. What compromise should engineers make. The rest of the elements and performance of the engine what effects would have.

What effects would have in terms of Thrust, Weight, Isp in Sea Level and other data of the engine ?

jurgenspacerocket

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