Heat in turbines has always represented the majority of engineering headaches. Any increase in temperature effects the very basic proprieties of any metal. In the case of a rocket turbine pump the most important are: resistance, fatigue, tolerances, chemical stability, abrasion.Maui wrote:I guess I would be curious to know comparatively how much of a problem heat is in the turbines vs the combustion chamber.
Modern metallurgical knowledge enables us to design with quite an high degree of confidence metals that can withstand at least 2 of these conditions for a rocket turbine pump application, but not all the 5 of them. Hence reducing even of a small amount the temperature into the turbine chamber makes quite a big difference in the turbine assembly complexity and reliability.
The combustion chamber on the other hand is static, so even if the temperature is higher than in the turbine pump assembly we can use other ways to improve reliability and/or limit heat influence, like boundary layer flow control, regenerative cooling, or the Vortex concept idea.
I would say that with today metallurgical knowledge, 95% of all heat related problems in a rocket engine are focused on the turbo pump side, so any improvement there brings lot of benefits everywhere else, and that's the reason why SpaceX is going for the the full flow/staged combustion/regenerative cooling Raptor Engine.
Just consider that the actual Merlin engine turbo pump section is running at 1350 'C, while the Raptor has a projected mean combustion temperature of around 500 'C in the 2 turbo pumps assembly. It's a huge thermal difference.
They are running cool enough to allow them to increase the pressure to the turbine head up to an incedible 650 Bar, which in turn will allow them to reach the expected 300 Bar in the combustion chamber.
They will need for sure some time to characterize the turbines behavior and their life evolution before they reach that target, but there is no real engineering issue to prevent them from reaching it, and that's why most people are so excited about the Raptor.