Why do (real) engines not overheat?

[snsmac]

My question is: "Why do engines not overheat if they are out of the atmosphere?", because in space there is no air or so that could cool them by heat conduction. So why do the engines not get hotter and hotter?

thanks snsmac

[SilentHunter7]

Because engineers. They (obviously) have to find ways to deal with the cooling issue, which you can do by using less energetic fuels so that simple passive cooling is enough, or using some kind of active cooling system.

Good read:

http://en.wikipedia.org/wiki/Regenerative_cooling_(rocket)

[AngelLestat]

They still can radiate the heat with more efficiency than here at earth.

[sal_vager]

Also, many engines use ablative nozzles, excess heat causes the material of the nozzle to burn away, taking heat away with the lost material.

These engines are of course only capable of limited use, but this is factored into the design and intended use of the engine.

[TheDataMiner]

Also, if you look at a rocket nozzle carefully, you'll see little tubes wrapping around it. They are there for two purposes.

1. To heat up the liquid hydrogen for combustion

2. To cool down the nozzle...with liquid hydrogen

It's simple heat transfer, folks.

[PakledHostage]

@TheDataMiner: I think that was the gist of SilentHunter7's post, above.

[snsmac]

Thanks for you answers

[cantab]

One other thing to note is the most powerful engines tend to be first stage ones, operating in dense atmosphere. Upper stage engines are generally less powerful so presumably generate less heat.

[Tommygun]

Aren't the engine bells usually, made out of titanium?

It would take a great deal of heat to damage one of those.

Also infrared heat radiation can leave an object in the vacuum of space.

It leaves as invisible light (invisible to the human eye) it just takes a lot longer.

You just make an engine (usually smaller ones) that can take the heat and let it cool off over hours or days.

[TheShadow1138]

If I remember correctly the F-1 injected the turbopump exhaust gases into the nozzle extension to create a "film" of cooler gases to keep the extension from melting, but I may be wrong about that.

[Moss]

Most spacecraft are cooled by radiation rather than convection.

[Seret]

Most spacecraft are cooled by radiation rather than convection.

"Most"? The OP specifically mentions vacuum.

[softweir]

"Most"? The OP specifically mentions vacuum.

There are other cooling techniques. The Apollo CSM collected waste water from the crew cabin and from the fuel cells and used evaporation into the vacuum as a coolant system. Many engines, when thrusting, use regenerative cooling - they preheat the fuel using the excess heat from the engine, which improves efficiency.