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Just wondering whether the spacecraft engines/drives, or their booster rockets accumulate carbon the way car/truck engines do. What about ion/methane drives?

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Not typically. In fact, the opposite generally occurs. The high temperatures and velocities in the rocket motor tend to cause erosion (ablation) along the nozzle. There is considerable research into the ablation of the nozzles because it changes the shape and thus the thrust characteristics. See for example this paper, and a simple search will reveal many more.

It's also important to note that many spacecraft engines don't use carbon-based fuels. Solid rocket motors typically do, the binder material is usually a carbon-based material. But some liquid rocket engines are hydrogen and oxygen, so no carbon is involved.

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Nice answer, +1, but many rockets use LOX/RP-1 in their first stages. – mmc Oct 18 '12 at 17:14
These reference rockets heading from Earth's surface upwards. Any idea about drives for manouvering in space itself? For instance, the rockets on the Apollo modules. – Everyone Oct 18 '12 at 17:28
Apollo command modules and both the ascent and descent stages of the lunar modules ran on Aerozine 50 (N$_2$H$_2$/H$_2$NN(CH$_3$)$_2$) and nitrogen tetroxide (N$_2$O$_4$), which are not really hydrocarbons. They're also hypergolic: they react without a spark. – Emilio Pisanty Oct 18 '12 at 18:06
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  • If the LOX/Kerosene rockets would produce some soot, that would not stick to the combustion chamber, the velocities of the gases is just too high.
  • In fact all that engines since the V2 up to Saturn V use an excess of oxygen or alcohol in general, but especially close to the walls. This excess component vapor layer protects the walls, which otherwise would melt away immediatly in a stoichiometric oxygen-kerosene flame.
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This is simply wrong. LOX/RP-1 rockets almost always run fuel-rich, as a high temperature oxidizing environment would be hard on the engine components. The RD-180 seems to be the only rocket that actually runs oxidizer-rich, and it took careful design to handle the resulting high temperature, high pressure oxidizing environment. (Lumping oxygen and alcohol together doesn't make any sense either...alcohol's a fuel, like kerosene.) – Christopher James Huff Dec 30 '12 at 17:57
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Actually, it is a factor in some systems. RP-1 is a grade of kerosene specifically intended for use as rocket propellant, engineered specifically for reduced breakdown and coking at high temperatures which can otherwise cause problems for regenerative cooling channels, turbopumps, etc.

Also see page 115-116 in The Rocket Company.

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