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For the little I know about turbine engines, I know that these run at enormous high temperatures and thus, need nickel based superalloys.

From what I know, jet engines use a smart use of air flow throughout the parts of the engine (such as the combustion chamber) in order to make an air layer of protection between the metal walls and the flames.

... But you have to keep a balance between air cooling with the energy used to compress the air in order to increase efficiency.


Well, in the scenario that one wouldn't use such superalloy because of its high price, if someone were to inject water with the combustion jet ejecting the combustion chambers directly to the turbine, would the water avoid the material melting?

... Or it would just make unnecessary steam?

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    $\begingroup$ A water droplet hitting a blade turning at 180000rpm - what do you think? Cavitatuon may be a word to check out. Is this a 3 or 4 beer question?? $\endgroup$
    – Solar Mike
    Apr 6, 2023 at 15:18
  • $\begingroup$ @SolarMike Dunno about the beer, but yeah, I didn't think about the droplets, could you post an answer involving the subject? $\endgroup$
    – Fulano
    Apr 6, 2023 at 15:37
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    $\begingroup$ Water injection In aircraft turbines is definitely a thing: en.wikipedia.org/wiki/Water_injection_(engine)?wprov=sfti1 $\endgroup$
    – Eric S
    Apr 6, 2023 at 17:10
  • $\begingroup$ @EricS yes, but the link you provide clearly states after the compressor or into the afterburner so nowhere near the blades. $\endgroup$
    – Solar Mike
    Apr 6, 2023 at 17:29
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    $\begingroup$ This is old school. We outgrew it - mostly. There's still a few around on some STOL and VTOL ships. Don't worry about the droplets too much - planes can fly in the rain. They even fly through clouds. $\endgroup$
    – Phil Sweet
    Apr 7, 2023 at 0:41

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Injecting water into the airstream in front of a turbine spinning at speeds in excess of 180000rpm will destroy the blades in short order.

Even propellors in water can easily suffer cavitation and it is to do with vapor pressure. The droplets of water will eat away the metal edges and surface.

Will adding water be effective when incoming air to a jet engine at 30000 feet is cool anyway.

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    $\begingroup$ I don’t disagree with your conclusion, but the RPM you cite is not typical of aircraft engines. Multiple sources suggest 10,000 to 25,000 RPM as typical. $\endgroup$
    – Eric S
    Apr 6, 2023 at 17:07
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    $\begingroup$ Also, cavitation is when there is a vapor cavity in otherwise 100% liquid that forms due to a local drop in fluid pressure to a value below the local vapor pressure of the fluid. Droplets entrained in vaporous fluids isn't anything like cavitation. Both can cause metal erosion, but the mechanics are very different. As others have mentioned, water injection take-off assist was pretty common for a while. youtube.com/watch?v=xfTdRF66QPo $\endgroup$
    – Phil Sweet
    Apr 7, 2023 at 0:14
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    $\begingroup$ code7700.com/water_injection.htm#section3 That's what happens when you think you have water injection and don't. $\endgroup$
    – Phil Sweet
    Apr 7, 2023 at 0:20
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    $\begingroup$ jet engines do run in the rain $\endgroup$
    – Tiger Guy
    Apr 7, 2023 at 1:37
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Airplanes with turbojet engines have been designed to fly in rain, snow, and thunderstorms for long periods of time.

So the imapct of water at high speeds is no problem.

If adding or spraying water was practical, they would do it. It's a new system to maintain, new water tanks, etc.

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Water injection for the sake of cooling down the combustion gas would miss the point. An air engine is designed to have the highest temperature possible at the first stage of the turbine. The higher the temperature the higher the fuel efficiency of the air engine. The temperature is limited by several factors, e.g. emissions or materials.

The cooling air used for the blades in the hot section provides a very thin layer of reduced temperature to the surface of the blades. The cooling air acts as a local (!) cushion to keep the hot combustion gas away from the blade surface. It has not the purpose to cool down the overall combustion gas temperature in the hot section, because that would effectively decrease the overall turbine efficiency.

If you would inject water upstream of the turbine to cool down the combustion gas, you would cool down the overall temperature of the gas, which you don't want to keep the temperature as high as possible. Not to mention the extra equipment which needs to be carried by the plane.

BTW: cavitation wouldn't be the limiting factor. The combustion chamber operates at temperatures far beyond 1000°C, so the water droplets would evaporate before they hit the blades, if the injection is properly designed. In fact there are new concepts of water enhanced air engines, which inject steam to the combustion chamber to increase the efficiency. Though the purpose of the steam is not to cool down the temperature, but to increase the mass flow through the turbine.

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