4 ms·

In my mind a rocket engine would be much more tolerant of debris since you just pipe the fuel into a giant fireball (yes I can practically see the eyes rolling,

In my mind a rocket engine would be much more tolerant of debris since you just pipe the fuel into a giant fireball (yes I can practically see the eyes rolling, sorry! :-). For ICEs I can understand clogging tiny injectors or carbs would be a problem, do rocket engines also have injectors or other narrow parts susceptible to clogs?

bilsbie 3y ago
The problem is that that fuel gets routed through a thin tube around the engine bell and then goes through a turbo pump before going into the engine. Both of those would have tight tolerances.
CarVac 3y ago
Yes, rocket engines have many small orifices to atomize and mix the propellant. It's like a showerhead, except if the fuel side clogs, the oxidizer might eat your chamber wall.
- pantalaimon 3y ago
  > if the fuel side clogs, the oxidizer might eat your chamber wall Ah, good old 'engine rich combustion'
  - inglor_cz 3y ago
    I still remember the exhaust plume of one of the experimental Starships turning green. "Whoa, it is eating itself!" And verily it was.
    - chasd00 3y ago
      yeah copper burns green and is commonly used in liners and other components. If it starts to burn, which it's not suppose to, you see green. You'll see a green flash when the merlin engines startup but that's because of the hypergolic fluids used to get the pumps running and ignition started, not copper burning. During Falcon night launches you can really see the green glow of the starter fluid on ignition.
Ajedi32 3y ago
> do rocket engines also have injectors Yes[1]. You want the fuel and oxidizer mixed as well as possible to achieve efficient combustion. There are also other small channels fuel has to flow through, like the ones used for regenerative cooling[2]. And not sure how well most turbopumps[3] would tolerate debris either, though that probably depends on the exact design. There are some really simple rocket designs out there that I could imagine tolerating debris (like solid motors[4] or pressure fed hyperbolic engines[5]) but Raptor definitely doesn't fall into those categories. [1]: https://en.wikipedia.org/wiki/Liquid-propellant_rocket#Injectors https://en.wikipedia.org/wiki/Liquid-propellant_rocket#Injec... [2]: https://en.wikipedia.org/wiki/Regenerative_cooling_(rocketry) https://en.wikipedia.org/wiki/Regenerative_cooling_(rocketry... [3]: https://en.wikipedia.org/wiki/Turbopump https://en.wikipedia.org/wiki/Turbopump [4]: https://en.wikipedia.org/wiki/Solid-propellant_rocket https://en.wikipedia.org/wiki/Solid-propellant_rocket [5]: https://en.wikipedia.org/wiki/Hypergolic_propellant#Characteristics https://en.wikipedia.org/wiki/Hypergolic_propellant#Characte...
- s1artibartfast 3y ago
  I posted upthread, but another concern is that stray particulate is an ignition source. Rocket fuel pumps are ~100,000 hp, and that energy is put into kinetic energy of the fluid flow. A stray particulate can cause the metal pump and fuel lines to burn in the presence of O2 at 300 atmospheres.
  - foobarian 3y ago
    > Rocket fuel pumps are ~100,000 hp That is wild. I need to learn more about rocket fuel pumps :-) Thank you all for these comments.
    - s1artibartfast 3y ago
      They also arent as big as you might think. Much of the engine size you see in pictures is the Nozzle https://www.teslarati.com/wp-content/uploads/2018/08/Block-5-Merlin-1D-work-SpaceX-1-1-1024x569.jpg https://www.teslarati.com/wp-content/uploads/2018/08/Block-5...
db48x 3y ago
Yes, they do. All of the fuel and oxidizer goes through injectors to atomize it as it is sprayed into the combustion chamber. For a Merlin 1D, that’s about 340 pounds of propellant going through the injector plate every second. Rocket Fuel Injectors - Things Kerbal Space Program Doesn't Teach https://www.youtube.com/watch?v=aa4ATJGRqA0 https://www.youtube.com/watch?v=aa4ATJGRqA0
chasd00 3y ago
The thing is the energy density, flow rate/volume, and heat flux in a raptor is just so extreme. For example, there's two turbopumps operating at around 100k HP each in a volume not much bigger than the propane tank on your grill.. and those are basically just fuel pumps, not even where the real party is (pre-burners and combustion). Anything not going according to plan like a very small piece of debris in a filter causing turbulence or a change in flow rate is almost always catastrophic.

bilsbie 3y ago

The problem is that that fuel gets routed through a thin tube around the engine bell and then goes through a turbo pump before going into the engine. Both of those would have tight tolerances.

CarVac 3y ago

Yes, rocket engines have many small orifices to atomize and mix the propellant. It's like a showerhead, except if the fuel side clogs, the oxidizer might eat your chamber wall.

pantalaimon 3y ago
> if the fuel side clogs, the oxidizer might eat your chamber wall Ah, good old 'engine rich combustion'
- inglor_cz 3y ago
  I still remember the exhaust plume of one of the experimental Starships turning green. "Whoa, it is eating itself!" And verily it was.
  - chasd00 3y ago
    yeah copper burns green and is commonly used in liners and other components. If it starts to burn, which it's not suppose to, you see green. You'll see a green flash when the merlin engines startup but that's because of the hypergolic fluids used to get the pumps running and ignition started, not copper burning. During Falcon night launches you can really see the green glow of the starter fluid on ignition.

Ajedi32 3y ago

> do rocket engines also have injectors Yes[1]. You want the fuel and oxidizer mixed as well as possible to achieve efficient combustion. There are also other small channels fuel has to flow through, like the ones used for regenerative cooling[2]. And not sure how well most turbopumps[3] would tolerate debris either, though that probably depends on the exact design. There are some really simple rocket designs out there that I could imagine tolerating debris (like solid motors[4] or pressure fed hyperbolic engines[5]) but Raptor definitely doesn't fall into those categories. [1]: https://en.wikipedia.org/wiki/Liquid-propellant_rocket#Injectors https://en.wikipedia.org/wiki/Liquid-propellant_rocket#Injec... [2]: https://en.wikipedia.org/wiki/Regenerative_cooling_(rocketry) https://en.wikipedia.org/wiki/Regenerative_cooling_(rocketry... [3]: https://en.wikipedia.org/wiki/Turbopump https://en.wikipedia.org/wiki/Turbopump [4]: https://en.wikipedia.org/wiki/Solid-propellant_rocket https://en.wikipedia.org/wiki/Solid-propellant_rocket [5]: https://en.wikipedia.org/wiki/Hypergolic_propellant#Characteristics https://en.wikipedia.org/wiki/Hypergolic_propellant#Characte...

s1artibartfast 3y ago
I posted upthread, but another concern is that stray particulate is an ignition source. Rocket fuel pumps are ~100,000 hp, and that energy is put into kinetic energy of the fluid flow. A stray particulate can cause the metal pump and fuel lines to burn in the presence of O2 at 300 atmospheres.
- foobarian 3y ago
  > Rocket fuel pumps are ~100,000 hp That is wild. I need to learn more about rocket fuel pumps :-) Thank you all for these comments.
  - s1artibartfast 3y ago
    They also arent as big as you might think. Much of the engine size you see in pictures is the Nozzle https://www.teslarati.com/wp-content/uploads/2018/08/Block-5-Merlin-1D-work-SpaceX-1-1-1024x569.jpg https://www.teslarati.com/wp-content/uploads/2018/08/Block-5...

db48x 3y ago

Yes, they do. All of the fuel and oxidizer goes through injectors to atomize it as it is sprayed into the combustion chamber. For a Merlin 1D, that’s about 340 pounds of propellant going through the injector plate every second. Rocket Fuel Injectors - Things Kerbal Space Program Doesn't Teach https://www.youtube.com/watch?v=aa4ATJGRqA0 https://www.youtube.com/watch?v=aa4ATJGRqA0

chasd00 3y ago

The thing is the energy density, flow rate/volume, and heat flux in a raptor is just so extreme. For example, there's two turbopumps operating at around 100k HP each in a volume not much bigger than the propane tank on your grill.. and those are basically just fuel pumps, not even where the real party is (pre-burners and combustion). Anything not going according to plan like a very small piece of debris in a filter causing turbulence or a change in flow rate is almost always catastrophic.