Editing Expander cycle (section)

== Dual expander ==
In a similar way that the [[Staged combustion cycle (rocket)|staged combustion]] can be implemented separately on the oxidizer and fuel on the [[Full flow staged combustion cycle|full flow cycle]], the expander cycle can be implemented on two separate paths as the '''dual expander cycle'''. The use of hot gases of the same chemistry as the liquid for the turbine and pump side of the turbopumps eliminates the need for purges and some failure modes. Additionally, when the density of the fuel and oxidizer is significantly different, as it is in the [[Hydrogen|H<sub>2</sub>]]/[[LOX]] case, the optimal turbopump speeds differ so much that they need a gearbox between the fuel and oxidizer pumps.<ref name=sutton-rpe7edp221p227 /><ref name=ustpo-patent7418814 /> The use of dual expander cycle, with separate turbines, eliminates this failure-prone piece of equipment.<ref name=ustpo-patent7418814 />

Dual expander cycle can be implemented by either using separated sections on the [[Regenerative cooling (rocket)|regenerative cooling system]] for the fuel and the oxidizer, or by using a single fluid for cooling and a [[heat exchanger]] to boil the second fluid. In the first case, for example, you could use the fuel to cool the [[Rocket engine#Combustion chamber|combustion chamber]], and the oxidizer to cool the [[Rocket engine nozzle|nozzle]]. In the second case, you could use the fuel to cool the whole engine and a heat exchanger to boil the oxidizer.<ref name=ustpo-patent7418814 />