Patent Description:
An effective Thermal Management Systems (TMS) for an aircraft jet turbine is dependent on a high degree of integration and interdependency among many systems. These systems often behave symbiotically whereas one system is made less efficient to benefit another (parasitism) or one system's inherent inefficiency benefits the other at no further cost (mutualism). The former is a detriment to overall aircraft efficiency and is often the focus of architecture advancement for future programs.

Fuel system designs can utilize positive displacement pumps which are sized for low N2 start. N2 is a term used for the rotational speed of the high pressure spool of turbine engines expressed as a percentage of the maximum normal operating RPM. This generally results in waste heat created at higher N2. This waste heat created by the fuel system is rejected to other points on the engine for thermal management, such as oil heating or fuel ice melting. The most efficient pumping system creates only the needed pressure/flow for all N2 speeds and is the ultimate goal for fuel system design. When this goal is attained, waste heat is reduced and alternate means of performing legacy heating tasks through a TMS are needed.

The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved fuel system bleed valves. This disclosure provides a solution for this need. <CIT> relates to a fuel delivery system for a gas turbine engine. <CIT> relates to a fuel control valve for an aircraft gas turbine engine. <CIT> relates to a control and protection system for an aircraft jet engine.

A fuel system includes a fuel metering unit having a fuel inlet and a fuel outlet defining a flow path therebetween. The fuel system includes a bleed valve in fluid communication with the flow path of the fuel metering unit. The fuel system includes a controller in communication with the fuel metering unit and the bleed valve to send data thereto and/or receive data therefrom. The bleed valve is configured and adapted to open or close depending on a command from the controller. The flow path is configured and adapted to be in selective fluid communication with a fuel system interstage through the bleed valve.

According to the invention, the fuel outlet is in fluid communication with an engine. The fuel metering unit can include a first main stage pump and a second main stage pump upstream from the engine. The bleed valve can be downstream from the first and second main stage pumps. The fuel metering unit can include a fuel metering valve between the first and second main stage pumps and the engine. The bleed valve can be positioned between the first and second main stage pumps and the engine. The fuel metering unit can include a temperature sensor positioned between the bleed valve and the engine.

In some embodiments, the controller is in communication with an N2 sensor to receive an input from the N2 sensor and determine whether a speed of the engine is at or above an idle state or below the idle state According to the invention the controller is in communication with the bleed valve to send a shut-off command to the bleed valve when the engine is below the idle state. The controller can be configured and adapted to be in communication with the fuel system interstage to receive a TMS bleed demand input therefrom. The fuel metering unit can include a temperature sensor positioned between the bleed valve and the engine. The controller can be in communication with the temperature sensor to receive a fuel temperature measurement therefrom. The controller can be in communication with the bleed valve to send a turn-on command to the bleed valve when the TMS demand input is positive and when the fuel temperature measurement is greater than a hysteresis band limit. The controller can be in communication with a second main stage pump. The controller is configured and adapted to send a flood command to the second main stage pump when the fuel temperature measurement is less than or equal to a hysteresis band limit.

These and other features of the systems of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a schematic view of an exemplary embodiment of the fuel system in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments of the fuel system in accordance with the disclosure, or aspects thereof, are provided in <FIG> as will be described. The systems and methods described herein can be used to allow fuel systems to become more efficient, e.g. by implementing a two-stage fuel pump design, while also providing the heating needed by other systems, such as a thermal management system (TMS) of a fuel system interstage <NUM> which typically relies on the fuel pump waste heat. This allows other systems to avoid taking on weight and complexity of other thermal control devices to handle thermal control typically handled by coupling to the fuel system.

As shown in <FIG>, a fuel system <NUM> includes a fuel metering unit (FMU) <NUM> having a fuel inlet <NUM> and a fuel outlet <NUM> with a FMU fuel discharge pressure (POUT). A flow path <NUM> is defined between the fuel inlet <NUM> and the fuel outlet <NUM>. The fuel inlet <NUM> is in fluid communication with a boost stage pump <NUM> and a fuel tank <NUM>. A boost wash screen is downstream from boost stage pump <NUM> and splits flow between flow path <NUM> and an electric start pump. Flow path <NUM> is configured and adapted to be in selective fluid communication with a TMS of a fuel system interstage <NUM>. The fuel system interstage <NUM> is within the fuel oil manifold (FOM), which is the interface between the fuel system <NUM> and a gear box. Fuel system <NUM> includes a TMS bleed valve <NUM> in fluid communication with the flow path <NUM> at a TMS bleed port <NUM>. A flow regulating orifice <NUM> is downstream from valve <NUM>. In the fuel system interstage <NUM>, the fuel enters a number of heat exchangers (fuel-oil, generator heat exchangers, etc) and the main fuel filter before returning to the fuel control and entering the main pump stage. The purpose of the TMS bleed valve <NUM> and port <NUM> is to increase the fuel flow through the interstage <NUM> when engine <NUM> is at low burn flow. For example, engine <NUM> may be at a ground-idle condition with <NUM>/h (<NUM> pph) of fuel low, but the oil in the fuel oil control unit of the interstage <NUM> needs fuel flow rates of <NUM>-<NUM>/h (<NUM>-<NUM> pph) to prevent overheating the engine oil. So the TMS bleed port <NUM> is opened to return the delta fuel required (above burn flow) to interstage <NUM>, in order to satisfy the heat exchangers of the TMS of the interstage <NUM>.

Conversely, there are conditions where the fuel can be too cold and there are concerns of ice build-up in the fuel system (during descent conditions after hours of cruising at altitude). In this situation, the delta temperature between the oil and the fuel is too high and the fuel-oil heat exchangers are not able to adequately transfer enough heat to raise fuel above freezing temperatures, so the TMS bleed valve <NUM> is opened to increase fuel flow through the heat exchangers of the TMS of the interstage <NUM>, using a combination of heat from the heat exchangers and the additional waste heat from a second main stage pump <NUM> to increase the fuel temperature. The fuel system <NUM> includes a controller <NUM> in communication with the interstage <NUM>, one or more elements in the fuel metering unit <NUM> and TMS bleed valve <NUM> to send data thereto and/or receive data therefrom. Bleed valve <NUM> controls flow through TMS bleed port <NUM> taken after a pump selector valve <NUM>. Bleed valve <NUM> is configured and adapted to selectively open or close depending on a command from controller <NUM>. Controller <NUM> can be the Full Authority Digital Engine Control (FADEC). Controller <NUM> is configured and adapted to be in communication with fuel system interstage <NUM>.

With continued reference to <FIG>, fuel outlet <NUM> is in fluid communication with an engine <NUM>, such as a turbine engine. The fuel metering unit <NUM> includes a first main stage pump <NUM> and a second main stage pump <NUM> upstream from engine <NUM>. TMS bleed port <NUM> and TMS bleed valve <NUM> are downstream from the first and second main stage pumps <NUM> and <NUM>, respectively. TMS bleed port <NUM> is downstream from a pump selector valve, which switches between an electric start pump (at start pump discharge pressure PSSP) and or more of the main stage pumps <NUM> and <NUM>. The fuel metering unit <NUM> includes a fuel metering valve <NUM> between the first and second main stage pumps <NUM> and <NUM>, respectively, and engine <NUM>. TMS bleed port <NUM> and bleed valve <NUM> are positioned between the first and second main stage pumps <NUM> and <NUM>, respectively, and engine <NUM>. TMS bleed port <NUM> and bleed valve <NUM> are upstream from fuel metering valve <NUM>. An inline pressure regulating valve (PRV) is downstream from the metering valve <NUM> and upstream from the fuel outlet <NUM>.

As shown in <FIG>, fuel metering unit <NUM> includes a fuel temperature sensor <NUM>, e.g. a resistive thermal device (RTD) <NUM>, positioned between bleed valve <NUM> and engine <NUM>. Those skilled in the art will readily appreciate that the temperature sensor can be a RTD, or a variety of other suitable temperature sensors. Engine <NUM> includes an N2 sensor <NUM> to sense the rotational speed of the high pressure turbine of the engine <NUM>. Controller <NUM> is in communication with N2 sensor <NUM> to receive an input from N2 sensor <NUM> and determine whether a speed of engine <NUM> is in an idle state or above, or below an idle state. If engine <NUM> is at a speed below idle state, controller <NUM> is in communication with bleed valve <NUM> to send a shut-off command to bleed valve <NUM>. Controller <NUM> is in communication with interstage <NUM> (fuel-oil, generator heat exchangers, oil temperature sensors, etc).

With continued reference to <FIG>, controller <NUM> is in communication with fuel system interstage <NUM> to receive a TMS bleed demand input therefrom. If the speed of engine <NUM> is at or above idle state, controller <NUM> receives a TMS bleed demand input. If the TMS bleed demand input is negative (F), controller <NUM> sends shut-off command to bleed valve <NUM>. If the TMS bleed demand input is positive (T), controller <NUM> is in communication with RTD <NUM> to receive a fuel temperature measurement therefrom. In accordance with the embodiment shown in <FIG>, the TMS bleed demand input is positive (T) if the difference in temperature between the fuel downstream from second main stage pump <NUM> and engine oil running through fuel system interstage <NUM> is greater than a oil-fuel temperature delta threshold, or if the fuel or oil temps are above or below a normal operating band. Those skilled in the art will readily appreciate that the oil temperature in the interstage can be measured using at least one oil temperature sensor <NUM>.

With continued reference to <FIG>, controller <NUM> is in communication with bleed valve <NUM> to send an "on" command to bleed valve <NUM> when the TMS demand input is positive and when the fuel temperature measurement is greater than a hysteresis band limit. Controller <NUM> is in communication with second main stage pump <NUM>. Controller <NUM> is configured and adapted to send a flood command to second main stage pump <NUM> when the TMS demand input is positive and the fuel temperature measurement is less than or equal to a hysteresis band limit. This flood command to second main stage pump <NUM> allows for the bleed valve <NUM> fluid flow to meet the TMS demand input in a two-stage centrifugal main fuel pump, where the second main stage pump <NUM> may not be running. While there are inefficiencies associated with flooding the second main stage pump <NUM>, there is a benefit to providing the needed fluid flow to the fuel system interstage <NUM>.

As shown in <FIG>, a method <NUM>, not belonging to the claimed subject matter, for controlling a bleed valve, e.g. bleed valve <NUM>, in a fuel system, e.g. fuel system <NUM>, includes receiving a data input with a controller, e.g. controller <NUM>, from an N2 sensor, e.g. N2 sensor <NUM>, of a turbine engine, e.g. engine <NUM>, as shown schematically by box <NUM>. The method includes determining whether a speed of the engine is at or above an idle state or below the idle state based on the data input from the N2 sensor, as shown schematically by box <NUM>. The method includes switching a bleed valve, e.g. bleed valve <NUM>, ON or OFF depending on whether the speed of the engine is below the idle state OR at or above the idle state. If the speed of the engine is below the idle state, the method includes switching the bleed valve OFF, as shown schematically by box <NUM>.

With continued reference to <FIG>, if the speed of the engine is at or above the idle state, the method includes determining if the TMS demand (T) is positive or negative (F), as schematically shown by boxes <NUM>, <NUM>. If negative, the method includes switching the bleed valve OFF, as shown schematically by box <NUM>. If TMS demand is positive, the method includes measuring a fuel temperature with a temperature sensor, e.g. RTD <NUM>, and receiving a fuel temperature measurement in the controller, as shown schematically by box <NUM>.

With continued reference to <FIG>, if the TMS demand is positive, and the fuel temperature measurement is greater than a hysteresis band limit (F), as shown schematically by boxes <NUM> and <NUM>, the method includes switching the bleed valve ON, as shown schematically by box <NUM>. Those skilled in the art will readily appreciate that the TMS demand input can come from application code hosted in the FADEC, in the aircraft common computing resource, or in the TMS controller. If the TMS demand is positive and the fuel temperature measurement is less than or equal to the hysteresis band limit (T), as shown by boxes <NUM> and <NUM>, the method includes flooding a second stage pump of fuel system, as shown schematically by box <NUM>, and then the method includes switching the bleed valve ON, as shown schematically by box <NUM>.

The methods and systems of the present disclosure, as described above and shown in the drawings, provide for fuel systems with superior properties including allowing fuel systems to become more efficient, e.g. by implementing a two-stage fuel pump design, while also providing the heating needed by other systems, such as a thermal management system which typically rely on the fuel pump waste heat. The systems of the present invention can apply to gas turbine engines in aircraft, power generation, or the like. While the apparatus of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.

As will be appreciated by those skilled in the art, aspects of the present embodiments may be embodied as a system, method or computer program product. Accordingly, aspects of the present embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit," "module," "component" or "system. " Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

More specific examples (a nonexhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Aspects of the present disclosure are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the embodiments.

Claim 1:
A fuel system (<NUM>) for a turbine engine of an aircraft, the fuel system comprising:
a fuel system interstage (<NUM>), the fuel system interstage comprising:
a number of heat exchangers; and
a main fuel filter;
wherein the fuel system further comprises:
a fuel metering unit (<NUM>) including a fuel inlet (<NUM>) and a fuel outlet (<NUM>) defining a flow path therebetween;
a bleed valve (<NUM>) in fluid communication with the flow path of the fuel metering unit (<NUM>); and
a controller (<NUM>) in communication with the fuel metering unit (<NUM>) and the bleed valve (<NUM>) to send data thereto and/or receive data therefrom, wherein the bleed valve (<NUM>) is configured and adapted to open or close depending on a command from the controller (<NUM>), wherein the flow path is configured and adapted to be in selective fluid communication with the fuel system interstage (<NUM>) through the bleed valve (<NUM>);
wherein the fuel outlet (<NUM>), when the fuel system is installed, is in fluid communication with the turbine engine; and
wherein the controller (<NUM>) is in communication with the bleed valve to send a shut-off command to the bleed valve when the turbine engine is below an idle state.