Expander Cycle (rocket) - Expander Bleed Cycle (open Cycle)

Expander Bleed Cycle (open Cycle)

This operational cycle is a modification of the traditional expander cycle. In the bleed (or open) cycle, instead of routing heated propellant through the turbine and sending it back to be combusted, only a small portion of the propellant is heated and used to drive the turbine and is then bled off, being vented overboard without going through the combustion chamber. Bleeding off the turbine exhaust allows for a higher turbopump output by decreasing backpressure and maximizing the pressure drop through the turbine. Compared with a standard expander cycle, this leads to higher engine thrust at the cost of sacrificing some efficiency due to essentially wasting the bled propellant by not combusting it. However, in some cases, such as the Japanese LE-5A/B, the thrust performance gains can take precedence over absolute efficiency.