Full flow / Dual staged expander cycle

[Skye]

Staged expander cycle, but there’s a pre burner for both fuel and oxidiser. Could it work? Should it be used?

[Roy_H]

I don't understand what you are proposing. What is different from SpaceX's Raptor?

[russianhalo117]

I was going to link NASA William D Greene's Constellation era blog series on researched and proposed expander cycle concepts  to achieve maximum efficiency but the blog series has been archived or deleted and displays error 404.
Some of its is here in NTRS:
https://ntrs.nasa.gov/citations/20090006594

Other reasearch:
https://ntrs.nasa.gov/api/citations/19910010893/downloads/19910010893.pdf

[DanClemmensen]

See:
   https://en.wikipedia.org/wiki/Staged_combustion_cycle#Full-flow_staged_combustion_cycle

[Ixokani]

Staged expander cycle, but there’s a pre burner for both fuel and oxidiser. Could it work? Should it be used?

The point of an expander cycle is to drive the pumps -without- needing a pre-burner. So you'll need to expound your idea into more detail if you want it to at least be comprehensible.

[Skye]

Oh I was just thinking staged expander but for both fuel and oxidiser

[Ixokani]

https://en.wikipedia.org/wiki/Expander_cycle#Dual_expander
https://en.wikipedia.org/wiki/BE-7

[Skye]

So why don’t people just use dual expander instead of FFSC? it provides the same fuel preheating, but doesn’t need preburners

[Gliderflyer]

So why don’t people just use dual expander instead of FFSC? it provides the same fuel preheating, but doesn’t need preburners

Because you don't get the same heating. The amount of chamber/nozzle wall available for heating per unit propellant decreases as the engines get bigger.

[sdsds]

So why don’t people just use dual expander instead of FFSC? it provides the same fuel preheating, but doesn’t need preburners

Because you don't get the same heating. The amount of chamber/nozzle wall available for heating per unit propellant decreases as the engines get bigger.

Reportedly the Vinci engine design addressed this by having a long cylindrical combustion chamber.

NASA once had a Liquid Rocket Engines blog that tried to explain some of this stuff. Back when, you know, NASA was involved in rocket engine design.
https://web.archive.org/web/20250404063927/https://blogs.nasa.gov/J2X/

https://blogs.nasa.gov/J2X/wp-content/uploads/sites/212/2014/03/closeddualexp.jpg
https://blogs.nasa.gov/J2X/wp-content/uploads/sites/212/2014/03/blog3.jpg

[Jim]

So why don’t people just use dual expander instead of FFSC? it provides the same fuel preheating, but doesn’t need preburners

It doesn't provide enough power for the pumps

[edzieba]

So why don’t people just use dual expander instead of FFSC? it provides the same fuel preheating, but doesn’t need preburners

Because you don't get the same heating. The amount of chamber/nozzle wall available for heating per unit propellant decreases as the engines get bigger.

Reportedly the Vinci engine design addressed this by having a long cylindrical combustion chamber.

NASA once had a Liquid Rocket Engines blog that tried to explain some of this stuff. Back when, you know, NASA was involved in rocket engine design.
https://web.archive.org/web/20250404063927/https://blogs.nasa.gov/J2X/

https://blogs.nasa.gov/J2X/wp-content/uploads/sites/212/2014/03/closeddualexp.jpg
https://blogs.nasa.gov/J2X/wp-content/uploads/sites/212/2014/03/blog3.jpg

You'll find long cylindrical combustion chambers for almost all expander cycle engines. e.g. LE-9 (& LE-5), RL-10, RD-0146, BE-3U (not BE-3, which is a different engine merely with a similar name), etc. It's generally buried inside the turbomachinery and support plumbing so not obvious unless the engine is disassembled. The aspect ratio reduces as TWR is reduced and if you can pull in more heating from bell cooling (the RL-10 does both, hence why its chamber is squatter than other expanders).


Note that you'll see long chambers on some very small engines and motors too, but this is for a different reason: to give enough distance (and thus travel time) between the injectors and throat for mixing and full combustion to occur. It can also aid in cooling for engines and motors that rely fully on radiative cooling.

[InterestedEngineer]

So why don’t people just use dual expander instead of FFSC? it provides the same fuel preheating, but doesn’t need preburners

Because you don't get the same heating. The amount of chamber/nozzle wall available for heating per unit propellant decreases as the engines get bigger.

Reportedly the Vinci engine design addressed this by having a long cylindrical combustion chamber.

NASA once had a Liquid Rocket Engines blog that tried to explain some of this stuff. Back when, you know, NASA was involved in rocket engine design.
https://web.archive.org/web/20250404063927/https://blogs.nasa.gov/J2X/

https://blogs.nasa.gov/J2X/wp-content/uploads/sites/212/2014/03/closeddualexp.jpg
https://blogs.nasa.gov/J2X/wp-content/uploads/sites/212/2014/03/blog3.jpg

You'll find long cylindrical combustion chambers for almost all expander cycle engines. e.g. LE-9 (& LE-5), RL-10, RD-0146, BE-3U (not BE-3, which is a different engine merely with a similar name), etc. It's generally buried inside the turbomachinery and support plumbing so not obvious unless the engine is disassembled. The aspect ratio reduces as TWR is reduced and if you can pull in more heating from bell cooling (the RL-10 does both, hence why its chamber is squatter than other expanders).


Note that you'll see long chambers on some very small engines and motors too, but this is for a different reason: to give enough distance (and thus travel time) between the injectors and throat for mixing and full combustion to occur. It can also aid in cooling for engines and motors that rely fully on radiative cooling.

My impression is that Raptor's combustion chamber is really small in relation to these designs.  Is that correct?

[Skye]

Because you don't get the same heating. The amount of chamber/nozzle wall available for heating per unit propellant decreases as the engines get bigger.

Cool you install those (I think they’re called) heat exchangers? (The things that inject oxidiser into the fuel and vice versa in the preburners in FFSC) somewhere in the line? Would that increase power, heat output, etc.?

[edzieba]

Because you don't get the same heating. The amount of chamber/nozzle wall available for heating per unit propellant decreases as the engines get bigger.

Cool you install those (I think they’re called) heat exchangers? (The things that inject oxidiser into the fuel and vice versa in the preburners in FFSC) somewhere in the line? Would that increase power, heat output, etc.?

Heat exchangers, as the name implies, need to exchange heat with something. The regenerative cooling channels around the combustion chamber are already a heat exchanger, you're not going to extract any more heat from the chamber without losing heat exchange surface you already have.

FFSC and Expander-cycle engines are two different things.

[Skye]

So they (edit for clarification: expanders, not heat exchangers) do similar things as the preburners in FFSC, but worse? Do I have that right?

[edzieba]

So they do similar things as the preburners in FFSC, but worse? Do I have that right?

No, preburners and heat exchanges are unrelated.

[Skye]

No, I meant expanders, sorry

[DanClemmensen]

So they do similar things as the preburners in FFSC, but worse? Do I have that right?

No. the term "heat exchanger" is generic, not just for rocket engines.
   https://en.wikipedia.org/wiki/Heat_exchanger

[Skye]

So they do similar things as the preburners in FFSC, but worse? Do I have that right?

No. the term "heat exchanger" is generic, not just for rocket engines.
   https://en.wikipedia.org/wiki/Heat_exchanger

Again, I meant expanders, not HEs, sorry for confusion