Method for controlling fuel flow to a gas turbine engine

#The present invention relates to a fuel supply and control system for gas turbine engines and, more particularly, to a system and method for controlling the flow of fuel to a gas turbine engine even under various postulated fuel supply and control system faults.

#Typical gas turbine engine fuel supply systems include a fuel source, such as a fuel tank, and one or more pumps that take a suction on the tank and deliver pressurized fuel to the fuel manifolds in the engine combustor via a main supply line. The main supply line may include one or more valves in flow series between the pumps and the fuel manifolds. These valves generally include at least a main metering valve and a pressurizing-and-shutoff valve downstream of the main metering valve. In addition to the main supply line, many fuel supply systems also include a bypass flow line connected upstream of the metering valve that bypasses a portion of the fuel flowing in the main supply line back to the inlet of the one or more pumps, via a bypass valve. The position of the bypass valve is controlled to maintain a substantially fixed differential pressure across the main metering valve.

#A redundant channel engine control system controls the operation of the engine and the fuel supply system. In particular, each of the redundant channels in the engine control system receives input parameters from the engine and aircraft and a thrust setting from the pilot. In response to these inputs, the engine control system modulates the position of the main metering valve to control the fuel flow rate to the engine fuel manifolds to maintain the desired thrust.

#FIG. 1 is a block diagram of fuel delivery and control system for a gas turbine engine according to an exemplary embodiment of the present invention; and

#FIG. 2 is a block diagram of an exemplary controller used in the fuel delivery and control system depicted in FIG. 1.

#A fuel delivery and control system for a gas turbine engine, such as a turbofan jet aircraft engine, according to one embodiment the present invention, is depicted in FIG. 1. The system 100 includes a fuel source 102, such as a tank, that stores the fuel supplied to a jet engine combustor 104. A supply line 106 is coupled to the fuel source 102 and, via various components, delivers the fuel to the combustor 104. It is noted that the supply line 106 is, for convenience, depicted and described with a single reference numeral. However, it will be appreciated that the system is implemented using separate sections of piping, though a single section is certainly not prohibited.

#One or more pumps are positioned in flow-series in the supply line 106 and take a suction on the fuel source 102. In the depicted embodiment, a booster pump 108, such as a relatively low horsepower centrifugal pump, and a high pressure pump 110, such as a positive displacement pump, are used. The booster pump 108 takes a suction directly on the fuel source 102 and provides sufficient suction head for the high pressure pump 110. The high pressure pump 110 then supplies the fuel, at a relatively high pressure, such as up to 1200 psig, to the remainder of the supply line 106.

#A metering valve 112 is positioned in flow-series in the supply line 104 downstream of the high pressure pump 110. The metering valve 112 includes a first variable area flow orifice 113 through which a portion of the fuel in the supply line 106 flows. A metering valve control device 114 is used to adjust the position of the metering valve 112, and thus the area of the first variable area flow orifice. In the depicted embodiment, the metering valve 112 is a hydraulically-operated valve and the metering valve control device 114 is an electro-hydraulic servo valve (EHSV) that supplies a metering valve control signal output 113. The control signal output 115 from the metering valve control device 114 is coupled to the metering valve 112 and is used to adjust the position of the metering valve 112 by controlling the flow of operational hydraulic fluid to the metering valve 112. It is to be appreciated that the metering valve 112 and its control device 114 just described are only exemplary of a particular preferred embodiment, and that each may be implemented using other types of components. For example, the metering valve 112 could be an electrically operated valve. In this case, it may not utilize a control device 114 such as an EHSV, or the control device 114 could be implemented as an independent controller. In any case, as will be described further below, fuel flow rate to the combustor 104 is, under normal circumstances, controlled by adjusting the position of the metering valve 112, and thus the area of the first variable area flow orifice 113, via the metering valve control device 114.