2013 Volume 56 Issue 1 Pages 49-60
Throttled operation of turbopumps of liquid rocket engines is studied analytically. Two types of pressure drops in the propellant injector are examined, that is, the drop of gas injection and that of liquid injection. Circulation is examined in relation to throttling to operate the pump in the vicinity of the design condition. An enthalpy increase at the pump entrance is derived analytically in the circulation system. With the derived analytical relationships, throttled operating conditions are examined for imaginary LH2 and LOX turbopumps with a LH2/LOX property calculation code. The circulation causes gasification at the entrance of the high-pressure LH2 pump. This does not occur in the mid-pressure LH2 pump or the LOX pump. In the liquid propellant injection system, the unstable region becomes narrower than in the gas propellant injection. The ratio of the turbine flow rate to the pump flow rate decreases in line with throttling. Throttling does not degrade the engine specific impulse from the viewpoint of the turbine bleed ratio.