Rocket nozzle thermal protection

[Jiec]

TL;DR

Information on materials used in multilayer walls of rocket nozzles

Hello, I'm looking for information on materials used in the nozzle thermal protection.
In particular I'm interested in a protection made by different layers, an inner/outer lining, a conductive and an insulating layer, whitout rigenerative/film cooling.
I would like to know typical mateials used in the walls of real rockets and some examples if available

 

[berkeman]

Welcome to PF.

What have you found so far with your Google searching? Can you post some links to your reading? Thanks.

 

[Flyboy]

So, you’re looking at ablative nozzles? Pretty straightforward technology, if a little tricky to manufacture at smaller scales.

 

[Jiec]

Welcome to PF.

What have you found so far with your Google searching? Can you post some links to your reading? Thanks.

Thanks :)
I found some information, but it is not clear regarding the specific implementation in the thermal protection design. For the inner lining an ablative material like carbon phenolic or silica phenolic can be used; for the conductive layer is often chosen copper or inconel; for insulation typical material are ceramic/silicon fiber, but it is not clear if they are used in the nozzle walls; the outer lining is usually a steel layer.

I'm looking for some non ablative materials that can be used in the inner lining and more information about the insulating materials...I couldn't find information about a nozzle with this specific configuration.

 

[Jiec]

So, you’re looking at ablative nozzles? Pretty straightforward technology, if a little tricky to manufacture at smaller scales.

No, not necessarily, other types of nozzles as well :)

 

[Flyboy]

I'm looking for some non ablative materials that can be used in the inner lining and more information about the insulating materials...I couldn't find information about a nozzle with this specific configuration.

I’ve never heard of a nozzle built with insulation as an internal component. Wrapped around the outside to protect it from radiant heat from nearby engines and the backflow of hot gasses as you climb, sure, but never on the inside. You want to remove the heat from the inside of the chamber and nozzle if you can, or at least minimize the direct contact of superheated gases on the chamber and nozzle.

The type of propellant being used, and the choice of propellants if it’s liquid bipropellant, dictates the best approach. If it’s solid fuel, you basically have to use ablative nozzles. There’s no other practical way.

Liquid bipropellant gets more interesting. The most common option is regenerative cooling, but there’s a couple well documented examples of thin-film or boundary layer cooling. I know the F-1 engine used the fuel-rich exhaust from the turbopump gas generator to provide a cooling boundary layer for the last portion of the nozzle. That’s what the big duct running down and wrapping around the nozzle is for, and what caused that distinctive blackened exhaust plume just downstream of the nozzle mouth. I seem to recall an earlier Ariane first stage engine using boundary layer film cooling on the main combustion chamber to reduce the heat load for the regenerative cooling by placing a ring of fuel-only injectors which sprayed down the walls of the chamber rather than impinging on another jet.

 

[Astronuc]

TL;DR Summary: Information on materials used in multilayer walls of rocket nozzles

Hello, I'm looking for information on materials used in the nozzle thermal protection.
In particular I'm interested in a protection made by different layers, an inner/outer lining, a conductive and an insulating layer, whitout rigenerative/film cooling.
I would like to know typical mateials used in the walls of real rockets and some examples if available

What kind of propellant? LOx + RP-1 (type of kerosene) or H₂, or straight H₂, or N₂O₂ + N₂H₂.

Alloy C-103 is commonly used for rocket nozzles
https://ntrs.nasa.gov/citations/19940018579

https://www.materion.com/en/products/performance-materials/high-performance-alloys/niobium-alloy
https://www.hcstarcksolutions.com/w...03-Alloy-for-Space-Exploration-102020-Web.pdf


Some historical background -
EXPERIMENTAL EVALUATION OF THROAT INSERTS IN A STORABLE-PROPELLANT ROCKET ENGINE
https://apps.dtic.mil/sti/tr/pdf/ADA307817.pdf

More recent considerations
https://yang.gatech.edu/publications/Journal/JPP (2009, Thakre).pdf
and
https://ultramet.com/propulsion-system-components/solid-rocket-engines/

Thermal protection layers have to be chemically compatible with the nozzle wall alloy and propellant. Refractory alloys cool by radiant heat, otherwise, one can run cooler propellant down the inside surface of the nozzle.

 

[Jiec]

I’ve never heard of a nozzle built with insulation as an internal component. Wrapped around the outside to protect it from radiant heat from nearby engines and the backflow of hot gasses as you climb, sure, but never on the inside. You want to remove the heat from the inside of the chamber and nozzle if you can, or at least minimize the direct contact of superheated gases on the chamber and nozzle.

The type of propellant being used, and the choice of propellants if it’s liquid bipropellant, dictates the best approach. If it’s solid fuel, you basically have to use ablative nozzles. There’s no other practical way.

Liquid bipropellant gets more interesting. The most common option is regenerative cooling, but there’s a couple well documented examples of thin-film or boundary layer cooling. I know the F-1 engine used the fuel-rich exhaust from the turbopump gas generator to provide a cooling boundary layer for the last portion of the nozzle. That’s what the big duct running down and wrapping around the nozzle is for, and what caused that distinctive blackened exhaust plume just downstream of the nozzle mouth. I seem to recall an earlier Ariane first stage engine using boundary layer film cooling on the main combustion chamber to reduce the heat load for the regenerative cooling by placing a ring of fuel-only injectors which sprayed down the walls of the chamber rather than impinging on another jet.

Thanks for the information, i start to have a much clear idea.
Yes the insulating layer tends to overheated the internal part of the nozzle and seems not the best thing to do...but considering a conductive layer not resistant to direct exposure to the space envinronment and an outer coating (to protect it) not resistant to high temperatures, maybe a thin insulating layer between them could be added.
Regarding the external insulation from the nearby engines/hot gasses backflow, what are the typical materials? Is there an external coating or they are directly exposed?

 

[berkeman]

Maybe try this Google search and click into some of the many good links that it returns. That should give you a better background into the current designs:

 

[Jiec]

What kind of propellant? LOx + RP-1 (type of kerosene) or H₂, or straight H₂, or N₂O₂ + N₂H₂.

Alloy C-103 is commonly used for rocket nozzles
https://ntrs.nasa.gov/citations/19940018579

https://www.materion.com/en/products/performance-materials/high-performance-alloys/niobium-alloy
https://www.hcstarcksolutions.com/w...03-Alloy-for-Space-Exploration-102020-Web.pdf


Some historical background -
EXPERIMENTAL EVALUATION OF THROAT INSERTS IN A STORABLE-PROPELLANT ROCKET ENGINE
https://apps.dtic.mil/sti/tr/pdf/ADA307817.pdf

More recent considerations
https://yang.gatech.edu/publications/Journal/JPP (2009, Thakre).pdf
and
https://ultramet.com/propulsion-system-components/solid-rocket-engines/

Thermal protection layers have to be chemically compatible with the nozzle wall alloy and propellant. Refractory alloys cool by radiant heat, otherwise, one can run cooler propellant down the inside surface of the nozzle.

Thanks for the useful sources.
I'm interested in general engines, so for all types of propellants, so a double based solid propellant or maybe N2O4+hydrazine or LOX+RP1

 

[Jiec]

Maybe try this Google search and click into some of the many good links that it returns. That should give you a better background into the current designs:

View attachment 348164

Yes, I have searched for similar documents, but I often found general materials used in engines without an explanation of the nozzle layers configuration or a specific nozzle design. Anyway, I keep searching :)

 

[Flyboy]

Yes the insulating layer tends to overheated the internal part of the nozzle and seems not the best thing to do...but considering a conductive layer not resistant to direct exposure to the space envinronment and an outer coating (to protect it) not resistant to high temperatures, maybe a thin insulating layer between them could be added.

Let me make sure I’m understanding this correctly… you’re proposing a thermally conductive material that is able to withstand the 1000°+ (units not needed) gases of the engine, but somehow not able to survive exposure to space? And a material that’s the other way around to protect it from space?

Surviving the space environment is the easy bit. It’s the exhaust temperatures that are the challenge. Anything that can withstand that can survive in space.

Regarding the external insulation from the nearby engines/hot gasses backflow, what are the typical materials? Is there an external coating or they are directly exposed?

It’s usually specific to the design/application/situation. For the F-1 engines on the first stage of the Saturn V, it was a mix of a reflective outer layer of metal foil, can’t remember off the top of my head what metal, and an insulator layer might have been involved. It was mostly a radiant heat barrier.

Other designs like the Delta IV Heavy (may it rest in pieces ) used a fiberglass cloth type material to seal the gap between engine nozzle and the structural shroud around the engine. I suspect that similar choices are fairly common for first/booster stage engines that need to gimbal.

 

[Jiec]

Let me make sure I’m understanding this correctly… you’re proposing a thermally conductive material that is able to withstand the 1000°+ (units not needed) gases of the engine, but somehow not able to survive exposure to space? And a material that’s the other way around to protect it from space?

Yes, that was the idea; I thought that for some specific application (maybe long-term) or to have some advantage in terms of cost/weight this might be a possible configuration.

It’s usually specific to the design/application/situation. For the F-1 engines on the first stage of the Saturn V, it was a mix of a reflective outer layer of metal foil, can’t remember off the top of my head what metal, and an insulator layer might have been involved. It was mostly a radiant heat barrier.

Other designs like the Delta IV Heavy (may it rest in pieces ) used a fiberglass cloth type material to seal the gap between engine nozzle and the structural shroud around the engine. I suspect that similar choices are fairly common for first/booster stage engines that need to gimbal.

Ok, thank you I see that cork is also widely used, from Space Shuttle to SLS, but I think that its function is as an ablative layer to protect the engine when the latter is off, right?
Could an insulating layer of fiberglass/silicon fiber covered by aluminum/steel or a foam layer cover by steel be a possibility?

 

[Flyboy]

Yes, that was the idea; I thought that for some specific application (maybe long-term) or to have some advantage in terms of cost/weight this might be a possible configuration.

Not really. You’re adding complexity to the structure and to the assembly process. It’s better to use a single material that can handle the heat loads, whether through active cooling, film/boundary layer cooling, and/or radiant cooling (only applicable to upper stages and thrusters).

Ok, thank you I see that cork is also widely used, from Space Shuttle to SLS, but I think that its function is as an ablative layer to protect the engine when the latter is off, right?
Could an insulating layer of fiberglass/silicon fiber covered by aluminum/steel or a foam layer cover by steel be a possibility?

It’s used as an ablative for areas where they get high temperature gas impingement on the structure, whether from exhaust plumes or aerodynamic heating on ascent.

The use of a high-temperature shell paired with a high-performance insulator is well proven. The shuttle’s heat shield tiles are a wonderful example of that, though they use a refractory material like ceramic or carbon to shrug off the worst of the heat first.

Aluminum is a poor choice for rocket engines for a few reasons, despite its excellent thermal conductivity. Chief among them is the reactivity. Aluminum is, in fact, a potent rocket fuel, at least in solid rocket motors. Running aluminum anywhere near liquid oxygen makes me nervous as all it would take is a decent hit from a small piece of debris and all of a sudden your engine is in fire in places where it really shouldn’t be. I don’t recall what they made the turbopump housings on the Soviet NK-33 engines but I do know more than a few of them got eaten from the inside during test firings because of a turbopump impeller striking the wall of the housing, and the engine promptly turned into a fireball. Might work with the right protective coatings, but still kinda “ehhhh”.

Steel is a common choice for engines, despite being heavier and less thermally conductive than, say, aluminum or copper, mainly due to strength and ease of manufacturing.

 

[Jiec]

Not really. You’re adding complexity to the structure and to the assembly process. It’s better to use a single material that can handle the heat loads, whether through active cooling, film/boundary layer cooling, and/or radiant cooling (only applicable to upper stages and thrusters).

Ok, got it :)

Aluminum is a poor choice for rocket engines for a few reasons, despite its excellent thermal conductivity. Chief among them is the reactivity. Aluminum is, in fact, a potent rocket fuel...

Yes it is the typical fuel in solid propellants to enhance performance (micro/nano aluminum powder), I thought it might be good with some coating also due to its corrosion resistance, but probably there are better materials ahah.

Here i put a summary to see if I catched the main points of the topic.
For solid propellants probably the only cooling method is ablative cooling. The nozzle is made usally by carbon-carbon composite and the inner part is a layer of ablative material (carbon phenolic, silica phenolic).
For liquid propellants all the cooling methods can be implemented.
Considering upper stages/small rockets, it is possible to use radiative cooling. The nozzle is often made by niobium alloy (C-103) film cooled to help controlling the temperature.
In the case of regenerative/film cooling, nozzles are made by nickel-base superalloys (inconel, hastelloy) or copper alloys (inner lining of copper alloy and then a layer of inconel for example).
For the external insulation a ceramic/glass/silicon fiber can be used, sometimes with a metal coating (steel).