Detail of the inside of the nozzle extension, interface between the engine and
the extension, and the fuel return manifold. Note the lugs welded
to the inside wall of the fuel return manifold; these were used for
attaching a piece of equipment when testing for leaks.
Note the channels where the turbine exhaust is vented around the circumference
of the extension. The gas generator burns a fuel-rich mixture, resulting in
lower combustion temperatures. This relatively cool exhaust flows down the
wall of nozzle extension, protecting it from the exhaust gas from the
combustion chamber. According to the F-1
Engine Familiarization Training Manual (R-3896-1) [direct link
to 16.8M PDF file], the combustion chamber exhaust is 5,970°F, while
the turbine exhaust is a relatively balmy 1,138°F.
Picture 2 of 3.