Expander bleed cycle

Expander bleed cycle

The expander bleed cycle (also known as the expander open cycle and coolant tap-off) is a modification of the standard expander cycle in which only a portion of the heated propellant is routed through the turbine and then vented overboard instead of entering the combustion chamber. The remaining propellant is injected into the combustion chamber. Bleeding the turbine exhaust can increase turbopump efficiency by reducing backpressure and increasing the pressure drop across the turbine. Compared with a standard expander cycle, the trade-off is higher engine thrust at the expense of efficiency because part of the propellant is discarded after passing through the turbine.