Expander cycle

In this cycle, the fuel is used to cool the engine's combustion chamber, picking up heat and changing phase.

In the bleed (or open) cycle, instead of routing all of the heated propellant through the turbine and sending it back to be combusted, only a small portion of the heated propellant is used to drive the turbine and is then bled off, being vented overboard without going through the combustion chamber.

Compared with a standard expander cycle, this allows higher engine thrust at the cost of efficiency by dumping the turbine exhaust.

[6] Blue Origin chose the expander bleed cycle for the BE-3U engine used on the upper stage of its New Glenn launch vehicle.

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.

Expander rocket cycle. Expander rocket engine (closed cycle). Heat from the nozzle and combustion chamber powers the fuel and oxidizer pumps.
Expander bleed cycle. Expander open cycle (Also named coolant tap-off).