What factors can change the mixture ratio of propellant? I think they can be changed to control the thrust of a rocket.Stay safe. EDIT:What about considering only one stage? Do they change or can they be altered?
The second stage would switch from 5.5:1 (oxidizer mass to fuel mass) for higher thrust, to 4.5:1 for higher fuel efficiency partway through the ascent.
The third stage would normally start at 4.5:1 and switch to 5:1 partway through the burn, if the trans-lunar injection maneuver was executed at the first opportunity. It was possible to delay it by one orbit, during which time some hydrogen fuel would boil off and be lost; in that case the entire burn would be done at 5:1, which would ensure that a minimum of oxidizer was left unburned when the fuel ran out.
The thrust was about 35% higher at 5.5:1 than at 4.5:1 and the specific impulse (fuel efficiency) was only a couple of percent lower.
Similar mix ratio controls appear on some other engines (RL10, RD-180), but I'm not sure how universal they are. Their main use is to balance usage of fuel and oxidizer so you don't end up with a dead-weight surplus of one component or the other at the end of a burn.