Those rocket motors are fascinating. The combustion nozzles are lined with cooling tubes so they wont overheat. The space shuttle almost lost a motor on a launch due to a number of them failing, if 3 more failed (IIRC it was 17) the motor would have shut down and the shuttle would have had to abort and land in Africa.
The DeltaIV RS-68 engine is a fine piece. Been up close to them working in the boattail of the rocket. Insider info: The DeltaIV heavy carries so much liquid hydrogen that just prior to launch, they bleed off the excess (to reduce weight) and when the ROFI's (big sparklers whose job it is to burn off excess fuel) ignite it makes that huge black fuel rich fireball. At least that's what the real rocket scientists (prop engineers) told me.