The amount of wasted flow decreases in the order of Gas Generator → Staged Combustion → Full-Flow
Gas Generator
Burn a portion and discard it
Part of fuel/oxidizer → Gas generator → Drive turbine → Exhaust to atmosphere
Remainder → Main combustion chamber
Ex: Nuri 75-ton engine, Merlin
Staged Combustion
Burn only one side rich
1 fuel-rich or oxidizer-rich preburner → Drive turbine → Re-inject into main combustion chamber
The other propellant flows directly into the main combustion chamber
Ex: SSME (fuel-rich), RD-263 (oxidizer-rich)
Full-Flow
Complete combustion on both sides
Fuel-rich preburner → Drive fuel turbine
Oxidizer-rich preburner → Drive oxidizer turbine
Both exhaust gases are re-injected into the main combustion chamber, no wasted flow
Ex: RD-270, IPD, Raptor