Patent Description:
According to one aspect, there is provided a system for simultaneously pumping and measuring fuel density of an aircraft fuel as defined by claim <NUM>.

According to another aspect, there is provided a method for simultaneously pumping and measuring fuel density of aircraft fuel as defined by claim <NUM>.

System and associated method relate to simultaneously pumping and measuring density of an aircraft fuel. The aircraft fuel is pumped by a centrifugal pump having an impeller. A rotational frequency of the impeller is determined while the centrifugal pump is pumping the aircraft fuel. Flow rate of the aircraft fuel through the centrifugal pump is sensed. Pressure of the aircraft fuel is measured at two different points within or across the centrifugal pump or a differential pressure is measured between the two different points while the centrifugal pump is pumping the aircraft fuel. Density of the aircraft fuel is determined based on a head-curve relation characterizing the centrifugal pump. The head-curve relation relates the fuel density to the rotational frequency, the flow rate, and pressures at the two different points or the differential pressure between the two different points.

<FIG> is a schematic view of an aircraft engine configured to be supplied with aircraft fuel by a fuel system not according to the claimed invention. In <FIG>, aircraft engine <NUM> includes fuel system <NUM>. Fuel system <NUM> includes fuel pump <NUM>, fuel metering unit <NUM>, Fuel densimeter <NUM>, and fuel control module <NUM>.

Fuel pump <NUM> receives fuel from a fuel inlet port connected to a fuel line and pumps the received fuel to an outlet port. Fuel densimeter <NUM> receives the fuel from the outlet port of fuel pump <NUM>, measures the density of the fuel, and provides fuel control module <NUM> a signal indicative of the measured density of the fuel. Fuel control module <NUM> controls the fuel metering unit <NUM>, based at least in part on the measured density of the fuel. Fuel metering unit <NUM> then meters the fuel provided to aircraft engine <NUM> as controlled by fuel control module <NUM>. Fuel densimeter includes a centrifugal pump and pressure sensors configured to measure fluid pressure at various radial distances from an impeller axis.

<FIG> shows cross-sectional views of a densimeter not according to the claimed invention. that measures density of aircraft fuel. In <FIG>, densimeter <NUM> includes centrifugal pump <NUM>, first and second pressure sensors <NUM> and <NUM>, and fuel density calculator <NUM>. Centrifugal pump <NUM> has pump casing <NUM> in which resides impeller <NUM>. Pump casing <NUM> has fuel inlet <NUM> through which the aircraft fuel is drawn. In some embodiments, pump casing <NUM> has a fuel outlet through which the aircraft fuel is pumped. The fuel outlet can be used to facilitate circulation of fuel through pump casing <NUM>. Impeller <NUM> is configured to rotate about impeller axis <NUM>. Impeller <NUM> has a plurality of blades 32A-32D. Impeller <NUM>, when rotated, causes the aircraft fuel to be circularly rotated within pump casing <NUM>, thereby creating a pressure differential between fuel located near impeller axis <NUM> and fuel located at a radial periphery of pump casing <NUM>. Impeller <NUM>, when rotated, causes a pressure difference between a first fuel pressure at a first radial distance from the impeller axis <NUM> and a second fuel pressure at a second radial distance from the impeller axis <NUM>.

First pressure sensor <NUM> is configured to measure the first fuel pressure, and second pressure sensor <NUM> is configured to measure the second fuel pressure. Second pressure sensor <NUM> is further configured to measure second fuel pressure in a radial direction at the pump casing. Density calculator <NUM> configured to calculate density of the aircraft fuel based on the first and second fuel pressures as measured by first and second pressure sensors <NUM> and <NUM>.

Densimeter is also depicted in <FIG> as having motor and speed sensor <NUM>. In some embodiments, motor and speed sensor <NUM> can be electrically coupled to densimeter calculator <NUM>, so that densimeter calculator <NUM> can control the rotational speed of impeller <NUM>.

Centrifugal pump <NUM> has pump casing <NUM> in which resides impeller <NUM>. Pump casing <NUM> has fuel inlet <NUM> through which the aircraft fuel is drawn and, in some embodiments, a fuel outlet through which the aircraft fuel is pumped. In the depicted embodiment, fuel inlet <NUM> is aligned near or along impeller axis <NUM>. The fuel outlet, if present, is at a radially distal location of pump casing <NUM> as measured from impeller axis <NUM>. Impeller <NUM> is configured to rotate about impeller axis <NUM>. Impeller <NUM> has a plurality of blades 32A-32D. Impeller <NUM>, when rotated, causes the aircraft fuel to be drawn from fuel inlet <NUM> and to be expelled through the fuel outlet, if so equipped. Impeller <NUM>, when rotated, also causes a pressure difference between first fuel pressure P<NUM> at a first radial distance r<NUM> from the impeller axis <NUM> and second fuel pressure P<NUM> at a second radial distance r<NUM> from the impeller axis <NUM>.

As the impeller is rotated, a centrifugal pump imparts a rotational or circumferential component R to flow of the aircraft fuel being pumped. Because of this rotational component, a radial pressure gradient of the pumped fuel is produced. This radial pressure gradient varies for aircraft fuels of different densities. Therefore, such a pressure gradient can be indicative of the density of the aircraft fuel. For systems in which the first fuel pressure is measured along impeller axis <NUM> (i. e, the radial distance of first pressure sensor <NUM> from impeller axis <NUM> is zero: r<NUM> = <NUM>), such a relation between density D and measured pressures can be given by: <MAT> Here, P<NUM> is the first fuel pressure, P<NUM> is the second fuel pressure, r<NUM> is the radial distance of second pressure sensor <NUM> from impeller axis <NUM>, and ω is the rotation frequency of aircraft fuel. The rotational frequency of the aircraft fuel can measured and/or calculated based on a rotational frequency of the impeller as measured by motor and speed sensor <NUM>. In some embodiments, a relation between the rotational frequency of the impeller and the rotational frequency of the aircraft fuel can be based on aircraft fuel dynamics. In some embodiments, the aircraft fuel dynamics of the system are such that the rotational frequency of the impeller and the rotational frequency of the aircraft fuel are substantially equal to one another.

Various embodiments have first and second pressure sensors <NUM> and <NUM> located at various radial distances r<NUM> and r<NUM> from impeller axis <NUM>. For example a ratio of the distance r<NUM> to distance r<NUM> can be less than <NUM>. <NUM>, <NUM>, or it can be <NUM> when first pressure sensor <NUM> is aligned along impeller axis <NUM>.

In the embodiment in <FIG>, centrifugal pump <NUM> is a zero flow pump, having no fuel outlet. For such a zero flow pump, the impeller can be designed to direct the fluid in purely circumferential directions about impeller axis <NUM>. Such circumferential directed impellers can also be used for pumps designed for small flow rates - flow rates that corresponding to operation near zero flow rate as described above. The impeller of such a zero flow pump can have substantial axial mirror symmetry, thereby having to axial direction that is preferential.

In the embodiment depicted in <FIG>, impeller <NUM> is an open vane impeller. An open vane impeller has blades, such as blades 32A-32D extending from a central hub. In some embodiments, impeller <NUM> can be a semi-open vane impeller. A semi-open vane impeller has a plate, which in some embodiments can be substantially circular, affixed to one axial side of impeller blades 32A-32D. In some embodiments, impeller <NUM> can be a closed vane impeller, which has plates on both axial sides of impeller blades 32A-32D.

First pressure sensor <NUM> is configured to measure the first fuel pressure, and second pressure sensor <NUM> is configured to measure the second fuel pressure. Second pressure sensor <NUM> is further configured to measure second fuel pressure in a radial direction at the pump casing. Such a radial directive sensor can have a sensing membrane that has a normal vector aligned with a radial direction from the impeller axis. For example, the radial directive sensor can have a sensing membrane that is substantially conformal with an inside surface of pump casing <NUM>. Such a sensing membrane can deflect, in response to aircraft fuel pressure, in the radial direction that is parallel to the normal vector of the membrane. Fuel control module <NUM> can be configured to calculate density of the aircraft fuel based on the first and second fuel pressures as measured by first and second pressure sensors <NUM> and <NUM>.

In some embodiments, instead of first and second pressure sensors <NUM> and <NUM>, a differential pressure sensor measure a differential pressure between two different radial locations r<NUM> and r<NUM> from impeller axis <NUM>. For example, instead of pressures sensors <NUM> and <NUM> at the radial locations r<NUM> and r<NUM> from impeller axis <NUM>, a differential pressure sensor can be in fluid communication with ports located where pressures sensors <NUM> and <NUM> are depicted in <FIG>.

<FIG> is a graph depicting a relation between normalized differential pressure and fluid flow and pump speed of a normalized head-curve according to the invention. In <FIG>, graph <NUM> includes horizontal axis <NUM>, vertical axis <NUM> and relations 46A, 46B, and 46C. Horizontal axis <NUM> is indicative of volumetric flow of a fluid being pumped by a centrifugal pump, such as centrifugal pump <NUM> depicted in <FIG>. Vertical axis <NUM> is indicative of normalized differential pressure of the fluid being pumped by the centrifugal pump (for a given fluid density). Normalized differential pressure is a ratio of the sensed differential pressure to the fluid density. Relations 46A-46Care indicative of relationships between the normalized differential pressure and the volumetric flow of the pumped fluid for different rotational speeds of the pump impeller, such as impeller <NUM> depicted in <FIG>.

As depicted in <FIG>, for a given rotational speed, the measured pressure differential is not constant, even for a fluid with constant density. For embodiments in which no fluid flow is caused by rotation of impeller <NUM> (e.g., embodiments having no outlet port), such variable relations are not problematic. In such no-flow embodiments, the only operable point in the relation between measured density and volumetric flow is at the vertical axis where volumetric flow is zero. For embodiments that provide fluid flow via an outlet port, however, rate of fluid flow must be either measured (or otherwise be known), or must be controlled to within a certain range about a target operating point. For example, the flow rate can be maintained near zero by providing a small flowrate, as controlled, for example, by a pinhole orifice in the fuel outlet path. Such a low flow rate can facilitate fuel circulation, while maintaining fluid flow near the target operating point (e.g., near zero). Such a rate of fluid flow can be, for example, a flow rate corresponding to a measured differential pressure being within <NUM>%, <NUM>%, <NUM>%, or <NUM>% of the differential pressure measured for a zero fluid flow rate, for example.

In some embodiments, such as those which will be disclosed below with reference to <FIG> according to the invention, a measured flow rate is used in the determination of density of the aircraft fuel. For example, using a known relation between differential pressure and fluid flow and pump speed, accurate determination of aircraft fuel density can be determined based on impeller speed, measured flow rate, and measured differential pressure. Various ways of determining such accurate determinations of aircraft fuel density can be performed using such measured metrics, as will be described below.

<FIG> is a block diagram of a portion of a system according to the invention. In <FIG>, fuel system <NUM> includes centrifugal pump <NUM>, first and second pressure sensors <NUM> and <NUM>, and fuel density calculator <NUM>. Fuel density calculator includes processor(s) <NUM>, aircraft interface <NUM>, and storage device(s) <NUM>, and sensor interface <NUM>. Processor(s) <NUM> can receive program instructions 54P from storage device(s) <NUM>. Processor(s) <NUM> can be configured to calculate fuel density, based on received pressure sensor signals and on program instructions 54P. For example, processor(s) <NUM> can be configured to receive pressure sensor signals, via sensor interface <NUM>, indicative of measured fuel pressures P<NUM> and P<NUM>. Processor(s) <NUM> can calculate fuel density based on the received pressure sensor signals and provide the calculated density to other aircraft systems via aircraft interface <NUM>.

As illustrated in <FIG>, fuel density calculator <NUM> includes processor(s) <NUM>, aircraft interface <NUM>, storage device(s) <NUM>, and sensor interface <NUM>. However, in certain examples, fuel density calculator <NUM> and/or fuel system <NUM> can include more or fewer components. For instance, in some embodiments, fuel system <NUM> can include a tachometer configured to measure a rotational velocity of the impeller and/or a rotational flow measurement sensor. The rotational velocity of the impeller as measured by a tachometer, can be indicative of the rotational frequency of the aircraft fuel. In some embodiments, fuel density calculator can include a flow regulator configured to regulate, based at least in part on the calculated fuel density, fuel flow of the aircraft fuel. In some examples, fuel density calculator <NUM> can be performed in one of various aircraft computational systems, such as, for example, an existing Full Authority Digital Engine Controller (FADEC) of the aircraft.

Processor(s) <NUM>, in one example, is configured to implement functionality and/or process instructions for execution within fuel density calculator <NUM>. For instance, processor(s) <NUM> can be capable of processing instructions stored in storage device(s) <NUM>. Examples of processor(s) <NUM> can include any one or more of a microprocessor, a controller, a digital signal processor(s) (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other equivalent discrete or integrated logic circuitry. Processor(s) <NUM> can be configured to perform fuel density calculations.

Storage device(s) <NUM> can be configured to store information within fuel density calculator <NUM> during operation. Storage device(s) <NUM>, in some examples, is described as computer-readable storage media. In some examples, a computer-readable storage medium can include a non-transitory medium. The term "non-transitory" can indicate that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium can store data that can, over time, change (e.g., in RAM or cache). In some examples, storage device(s) <NUM> is a temporary memory, meaning that a primary purpose of storage device(s) <NUM> is not long-term storage. Storage device(s) <NUM>, in some examples, is described as volatile memory, meaning that storage device(s) <NUM> do not maintain stored contents when power to Fuel density calculator <NUM> is turned off. Examples of volatile memories can include random access memories (RAM), dynamic random access memories (DRAM), static random access memories (SRAM), and other forms of volatile memories. In some examples, storage device(s) <NUM> is used to store program instructions for execution by processor(s) <NUM>. Storage device(s) <NUM>, in one example, is used by software or applications running on fuel density calculator <NUM> (e.g., a software program implementing fuel density calculation).

Storage device(s) <NUM>, in some examples, can also include one or more computer-readable storage media. Storage device(s) <NUM> can be configured to store larger amounts of information than volatile memory. Storage device(s) <NUM> can further be configured for long-term storage of information. In some examples, storage device(s) <NUM> include non-volatile storage elements. Examples of such non-volatile storage elements can include magnetic hard discs, optical discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories.

Aircraft interface <NUM> can be used to communicate information between fuel density calculator <NUM> and an aircraft. In some embodiments, such information can include aircraft conditions, flying conditions, and/or atmospheric conditions. In some embodiments, such information can include data processed by fuel density calculator <NUM>, such as, for example, alert signals. Aircraft interface <NUM> can also include a communications module. Aircraft interface <NUM>, in one example, utilizes the communications module to communicate with external devices via one or more networks, such as one or more wireless or wired networks or both. The communications module can be a network interface card, such as an Ethernet card, an optical transceiver, a radio frequency transceiver, or any other type of device that can send and receive information. Other examples of such network interfaces can include Bluetooth, <NUM>, <NUM>, and Wi-Fi radio computing devices as well as Universal Serial Bus (USB). In some embodiments, communication with the aircraft can be performed via a communications bus, such as, for example, an Aeronautical Radio, Incorporated (ARINC) standard communications protocol. In an exemplary embodiment, aircraft communication with the aircraft can be performed via a communications bus, such as, for example, a Controller Area Network (CAN) bus.

<FIG> is a schematic diagram of a fuel system <NUM> according to the invention that simultaneously pumps fuel and measures fuel density based on a normalized head curve. In <FIG>, fuel system <NUM> includes centrifugal pump <NUM>, speed sensing arrangement <NUM>, flow-rate sensing arrangement <NUM>, pressure sensing arrangement <NUM>, and processor <NUM>. Centrifugal pump <NUM> includes an impeller (not depicted) configured to pump the aircraft fuel. Speed sensing arrangement <NUM> is configured to determine a rotational frequency of the impeller while the centrifugal pump is pumping the aircraft fuel. Flow-rate sensing arrangement <NUM> is configured to measure flow rate of the aircraft fuel through centrifugal pump <NUM>. Pressure sensing arrangement <NUM> is configured to measure pressure at two different points within or across centrifugal pump <NUM> or a differential pressure between the two different points while centrifugal pump <NUM> is pumping the aircraft fuel. Processor <NUM> configured to calculate a density of the aircraft fuel based on the normalized head curve. The normalized head curve relates a normalized differential pressure to the rotational frequency and the flow rate. The normalized differential pressure is the differential pressure divided by the fluid density. Using this normalized head curve along with the differential pressure, the rotational frequency, and the flow rate, the fluid density is determined.

Claim 1:
A system (<NUM>) for simultaneously pumping and measuring a fuel density of an aircraft fuel, the system comprising:
a centrifugal pump (<NUM>) including an impeller configured to pump the aircraft fuel;
a speed sensing arrangement (<NUM>) configured to determine a rotational frequency of the impeller while the centrifugal pump is pumping the aircraft fuel;
a flow-rate sensing arrangement (<NUM>)) configured to measure flow rate of the aircraft fuel through the centrifugal pump;
a pressure sensing arrangement (<NUM>) configured to measure pressure at two different points within or across the centrifugal pump or a differential pressure between the two different points while the centrifugal pump is pumping the aircraft fuel;
computer-readable memory containing data indicative of a normalized head-curve relation (<NUM>) corresponding to the centrifugal pump, the normalized head-curve relation relating to a normalized differential pressure to the rotational frequency and the flow rate, the normalized differential pressure being the differential pressure divided by the fuel density; and
a processor (<NUM>) configured to calculate the fuel density of the aircraft fuel based on the normalized head-curve relation, the rotational frequency, the flow rate, and either the pressures of the two different points or the differential pressure between the two different points.