MODELLING AND REDUCING FUEL FLOW PULSATION OF A FUEL-METERING SYSTEM BY IMPROVING RESPONSE OF THE PRESSURE CONTROL VALVE DURING PUMP MODE SWITCHING IN A TURBOFAN ENGINE

摘要

In an aircraft turbo/an engine, a fuel metering unit meters and supplies the required fuel to the engine according to the flight situation. When a centrifugal fuel pump (CFP) is used as the fuel pump, the ratio of hydraulic power per weight can be increased by raising the rated rotational speed, so the weight of the fuel pump can be decreased compared to when using a gear pump (GFP). There is an advantage that it can be reduced significantly. However, since the operating range of the fuel pump is wide, it is not effective to use CFP in an extremely low flow rate region because the fuel temperature rises due to its PQ characteristics and a large loss. Therefore, it is considered effective to combine CFP and GFP as pressure sources, and to use GFP in the low flow region and CFP in the high flow region. For that purpose, it is necessary to have a pump mode switching mechanism. The disadvantage in this case is that changing the pump mode causes a large pressure change of the fuel pressure source, which in turn causes fuel flow pulsations. There are three possible ways to solve this problem. The first method is to keep the differential pressure control valve (DPCV) unit response constant, which keeps the metering valve differential pressure constant in FMS. A second method is to remove high frequency components that the DPCV cannot follow pressure changes in the fuel control system. A third method is to keep the pressure difference between the two fuel sources small and to reduce the amplitude of the applied disturbance. In this paper, the first method, which makes DPCV response high response, is verified by modeling and simulation, and its effectiveness is confirmed.