>>12026268Anyone else want to take a stab at how hot the preburners run inside Raptor?
We know that Raptor has three sets of double-redundant electric torch igniters, two pairs for the preburners and one pair for the main combustion chamber. What we can take away from this is the fact that both gas streams leaving either preburner must not be hot enough to auto-ignite on contact with each other when they flow into the main combustion chamber. This puts a relatively firm upper temperature bound for those gasses at 600 celsius. However, given that Raptor has failed to ignite the main combustion chamber before, it's likely that the gasses are actually significantly below the 600 degree upper bound, and are sitting at something more like 300 celsius. The preburners themselves will be hotter than the gas flow downstream, because as the gasses flow out of the preburner and across the turbines they will expand and cool off. In either preburner, the peak temperature they need to run at is determined by the amount of work the turbines need to extract by expanding the gasses, and the amount of pressure required after that work is done in order to be able to blow into the main combustion chamber.
Remember, in order to achieve ~300 bar inside the main combustion chamber, the preburner pressure needs to be around 800 bar as per Elon's tweet, nearly three times higher.
With everything I've considered here, I'd say that the peak temperature any materials need to handle inside the preburners of Raptor are no greater than 900 celsius, and could be lower still. As per reusability, once you have alloys that can handle those high temperatures and high pressures, you're golden, because methane does not form coking deposits even when decomposed under extreme heat (instead it forms CH3, CH2, and CH species, all of which are volatile, and decrease in probability of formation as the number of hydrogens goes down).
