Influence of launch parameters of liquid rocket engine on the balance of axial forces in the turbopump

In the process of launching a liquid rocket engine (LRE) and on the modes of its deep throttling of thrust, the prob- lem of balance of axial forces in the turbo-pump assembly (TPA) is the most important. The reason is the pumps and turbine work of the engine in non-nominal modes, and, consequently, the appearance of unbalanced excess of axial forces acting on the bearings of TPA. To reduce the axial loads in the TPA, an automatic discharge device (ADD) is used, the task of which is to reduce the axial impact on the bearings due to the action of hydrodynamic forces. In the process of working in the ADD, friction of the surfaces, which forms a hydraulic gap, is not allowed, otherwise it can lead to the local combustion. The object of influence is LRE RD-120 developed by “NPO Energomash named after academician V. P. Glushko” [1], working on liquid oxygen-kerosene components, with afterburning of the oxidizing gas-generating gas scheme. The pneumatic-hydraulic scheme of the engine, the TPA design, the working principle of automatic discharge device are presented. Using the example of the LRE RD-120, the effect of axial forces acting on the angular contact ball bear- ing located on the side of the turbine TPA is considered. When the engine was developed, it was established that under some launch conditions it is possible to contact sur- faces in the discharge device. In the article authors identify the conditions of contact in ADD and try to study the effect of the launch parameters of the LRE on the gap size of the working surfaces in the discharge device. For the theoretical analysis of the problem, a dynamic mathematical model of a liquid rocket engine is used. Mathematical modeling of engine start-up with nominal and early entry into operation of the combustion chamber was studied. The results show that with early starts of combustion chamber, there is a significant temperature rise in the gas generator, which can lead to the ignition of the nozzle or blades of the TPA turbine. Modeling the launch of the LRE with a change in the closing pressure of the oxidant supply valve to the pre-pump turbine booster, shows that this provides a longer operation of the oxidizer pump with a reduced hydraulic head, and allows changing the balance of axial forces during the engine launch and, as a result, prevent the full closure of the working gap in the ADD.