What is regenerative cooling in a rocket engine?
Regenerative cooling runs the rocket’s own cold fuel through channels in the engine wall before burning it — cooling the engine and warming the fuel at the same time.
A rocket combustion chamber runs far hotter than the metal it is made of could survive unprotected. Something has to carry that heat away continuously.
The neat solution is to use the propellant already on board. Fuel is pumped through narrow passages built into the nozzle and chamber walls, picking up heat on the way to the injector.
Nothing is wasted, which is where the name comes from: the heat is recovered rather than dumped. A Merlin engine cools its nozzle this way with its own RP-1 kerosene.
See it happen
Meet a RocketEvery part, namedSource: Merlin rocket engine family