Авіаційно-космічна техніка та технологія (Nov 2018)
DETERMINATION OF THE EFFICIENCY OF TWO-COMPONENT PNEUMO-PUMP UNIT FOR A SPACECRAFT
Abstract
Research has been carried out to determine the efficiency of the piston pneumatic pump unit (PPU) of two-way action for the fuel supply system of a spacecraft operating on propellants of AT and MMH (UDMH). The PPU relates to volumetric pumps, therefore, the efficiency is defined as the ratio of effective work performed by the PPU to the expended gas work. The range of total propellants flow rates from 100 to 240 g/s through the PPU is determined by the operating modes of main engine and steering thrusters. As a result of performed researches, the PPU efficiency and main factors influencing on its value were theoretically determined, namely: gas losses for filling "parasitic" volumes including the volumes that do not participate in the process of fluid displacement from hydraulic pumps (volumes associated with incomplete fit of the pneumatic pistons to the bottoms of the pneumatic cylinders, the volume of control and supply channels), but are ejected into the environment at each operation of the PPU pneumatic distributor together with the volume of gas that performed effective work; gas ejections through the drainage seats into the environment at pneumatic distributors switchings, since at pneumatic distributors switchings some cavities are connected with the power supply source by control pressure, and other ones - with environment by poppet moving from the feed seat to the drainage seat; inlet air (helium) pressure losses due to the resistance of gas channels of the pneumatic distributors; friction of seals with fluoroplastic collars of the piston blocks; resistance of the hydraulic channels which components are: pressure losses of non-return valves and hydraulic channels; displaced fluid volume decreasing by hydraulic pumps due to leakage of non-return valves, piston collars and hydraulic pumps rods. The bipropellant PPU efficiency was theoretically and experimentally determined at different operating modes. The calculated value of the efficiency is well confirmed by experiments at that the divergence does not exceed 4%. The results of this research will allow us to determine the necessary gas reserves on board of spacecraft at the stage of designing.
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