The F1 engines of the Saturn V 1st. stage used a rich-mixture gas generator to drive the turbopump, but its exhaust was fed into the engine's nozzle about halfw

The F1 engines of the Saturn V 1st. stage used a rich-mixture gas generator to drive the turbopump, but its exhaust was fed into the engine's nozzle about halfway down, through an annular manifold [1]. Up to that point, the combustion chamber and nozzle were cooled by circulating fuel through them, but beyond that point, the cooler turbopump exhaust layer protected the nozzle extension. In pictures of launches [2], you can make out the brown smoky annulus of the turbopump exhaust, for a distance about equal to the length of the nozzle extension, until it either mixes with the hot exhaust, or with ambient air and then burns, at which point the smoke particles become incandescent. [1] https://history.msfc.nasa.gov/saturn_apollo/documents/F-1_Engine.pdf https://history.msfc.nasa.gov/saturn_apollo/documents/F-1_En... [2] https://images.nasa.gov/details-ksc-69pc-442.html https://images.nasa.gov/details-ksc-69pc-442.html