Systems and methods for filling a fuel manifold of a gas turbine engine

Systems and method for filling a fuel manifold comprising at least a primary and a second manifold of a gas turbine engine are described. The method comprises providing fuel flow to the secondary manifold of the gas turbine engine, the secondary manifold being partly or completely empty; monitoring at least one engine operational parameter of the gas turbine engine as fuel fills the secondary manifold; and accelerating the engine when a transition threshold is reached, the transition threshold being associated with the engine operational parameter and indicative that fuel has reached the combustor.

TECHNICAL FIELD

The present disclosure relates generally to gas turbine engines, and more particularly to methods and systems of filling a manifold of a gas turbine engine in order to bring the engine to a given power level.

BACKGROUND OF THE ART

Starting a gas turbine engine, either on the ground or in-flight, requires filling of a gas manifold and nozzle before fuel reaches the combustor and starts to combust. If fuel is injected into the manifold too quickly, an over fuel spike into the combustor may cause the engine compressor to surge. However, it may be desired to fill the manifold quickly in order to bring the engine into a fully operational mode quickly.

SUMMARY

In accordance with a broad aspect, there is provided a method for filling a fuel manifold comprising at least a primary and a second manifold of a gas turbine engine. The method comprises providing fuel flow to the secondary manifold of the gas turbine engine, the secondary manifold being partly or completely empty; monitoring at least one engine operational parameter of the gas turbine engine as fuel fills the secondary manifold; and accelerating the engine when a transition threshold is reached, the transition threshold being associated with the engine operational parameter and indicative that fuel has reached the combustor.

In accordance with another broad aspect, there is provided a system for filling a fuel manifold of a gas turbine engine. The system comprises a processing unit, and a non-transitory computer-readable medium having stored thereon program instructions executable by the processing unit. The program instructions are executable for providing fuel flow to a secondary manifold of the gas turbine engine, the secondary manifold being partly or completely empty; monitoring at least one engine operational parameter of the gas turbine engine as fuel fills the secondary manifold; and accelerating the engine when a transition threshold is reached, the transition threshold being associated with the engine operational parameter and indicative that fuel has reached the combustor.

Features of the systems, devices, and methods described herein may be used in various combinations, in accordance with the embodiments described herein.

DETAILED DESCRIPTION

There are described herein methods and systems for filling a fuel manifold of a gas turbine engine. In some embodiments, the gas turbine engine is part of a multi-engine aircraft and is operating in a standby mode, as described in more detail below. When operating in the standby mode, the engine may be running at low speed and hence, low fuel. Fuel in a secondary manifold of the gas turbine engine may be purged or emptied through gravity while the engine operates in the standby mode, for example to reduce fuel nozzle coking. When transitioning the engine from the standby mode to a non-standby mode, which may be an active mode or a regular operating mode, the secondary manifold of the gas turbine engine is refilled in accordance with a refilling scheme as described in the present disclosure.

In some embodiments, the refiling scheme for filling a fuel manifold of a gas turbine engine is applied upon engine start-up (on the ground or inflight), or during any other suitable operating mode of the aircraft, such as at high altitude idling and high altitude autorotation. Although described with reference to dual manifold systems, the manifold refilling scheme is also applicable to engine systems having more than two manifolds, such as three, four, or any other suitable number.

FIG.1Adepicts an exemplary multi-engine rotorcraft100, which in this case is a helicopter. The rotorcraft100includes at least two gas turbine engines102,104. These two engines102,104may be interconnected to a transmission clutch system (TCS)105, as shown inFIG.1B, to drive a main rotor108.

Turning toFIG.1B, illustrated is an exemplary multi-engine system. The multi-engine system may include two or more gas turbine engines102,104. In the case of a helicopter application, these gas turbine engines102,104will be turboshaft engines. Control of the multi-engine system is effected by one or more controller(s)210, which may be FADEC(s), electronic engine controller(s) (EEC(s)), or the like, that are programmed to manage the operation of the engines102,104to reduce an overall fuel burn, particularly during sustained cruise operating regimes, wherein the aircraft is operated at a sustained (steady-state) cruising speed and altitude. The cruise operating regime is typically associated with the operation of prior art engines at equivalent part-power, such that each engine contributes approximately equally to the output power of the system. Other phases of a typical helicopter mission include transient phases like take-off, climb, stationary flight (hovering), approach and landing. Cruise may occur at higher altitudes and higher speeds, or at lower altitudes and speeds, such as during a search phase of a search-and-rescue mission.

In some embodiments, while the aircraft conditions (cruise speed and altitude) are substantially stable, the engines102,104of the system may be operated asymmetrically, with one engine operated in a high-power “active” mode and the other engine operated in a lower-power (which could be no power, in some cases) “standby” mode. Doing so may provide fuel saving opportunities to the aircraft, however there may be other suitable reasons why the engines are desired to be operated asymmetrically. This operation management may therefore be referred to as an “asymmetric mode” or an “asymmetric operating regime”, wherein one of the two engines is operated in a lower-power (which could be no power, in some cases) “standby mode” while the other engine is operated in a high-power “active” mode. The asymmetric operating regime may be engaged for a cruise phase of flight (continuous, steady-state flight which is typically at a given commanded constant aircraft cruising speed and altitude). The multi-engine system may be used in an aircraft, such as a helicopter, but also has applications in suitable marine and/or industrial applications or other ground operations.

Referring still toFIG.1B, the multi-engine system is driving in this example a helicopter (H) which may be operated in the asymmetric operating regime, in which a first of the engines (say,102) may be operated at high power in an active mode and the second of the engines (104in this example) may be operated in a lower-power (which could be no power, in some cases) standby mode. In one example, the first engine102may be controlled by the controller(s)210to run at full (or near-full) power conditions in the active mode, to supply substantially all or all of a required power and/or speed demand of a common load170. The second engine104may be controlled by the controller(s)210to operate at lower-power or no-output-power conditions to supply substantially none or none of a required power and/or speed demand of the common load170. A clutch may be provided to declutch the low-power engine.

Controller(s)210may control the engine's governing on power according to an appropriate schedule or control regime. The controller(s)210may comprise a first controller for controlling the first engine102and a second controller for controlling the second engine104. The first controller and the second controller may be in communication with each other in order to implement the operations described herein. In some embodiments, a single controller210may be used for controlling the first engine102and the second engine104.

In another example, an asymmetric operating regime of the engines may be achieved through the one or more controller's210differential control of fuel flow to the engines, as described in pending application Ser. No. 16/535,256, the entire contents of which are incorporated herein by reference. Low fuel flow may also include zero fuel flow in some examples.

Although various differential control between the engines of the multi-engine system are possible, in one particular embodiment the controller(s)210may correspondingly control fuel flow rate to each engine102,104accordingly. In the case of the standby engine, a fuel flow (and/or a fuel flow rate) provided to the standby engine may be controlled to be between 70% and 99.5% less than the fuel flow (and/or the fuel flow rate) provided to the active engine. In the asymmetric operating regime, the standby engine may be maintained between 70% and 99.5% less than the fuel flow to the active engine. In some embodiments, the fuel flow rate difference between the active and standby engines may be controlled to be in a range of 70% and 90% of each other, with fuel flow to the standby engine being 70% to 90% less than the active engine. In some embodiments, the fuel flow rate difference may be controlled to be in a range of 80% and 90%, with fuel flow to the standby engine being 80% to 90% less than the active engine.

In another embodiment, the controller210may operate one engine (say104) of the multi-engine system in a standby mode at a power substantially lower than a rated cruise power level of the engine, and in some embodiments at substantially zero output power and in other embodiments less than 10% output power relative to a reference power (provided at a reference fuel flow). Alternately still, in some embodiments, the controller(s)210may control the standby engine to operate at a power in a range of 0% to 1% of a rated full-power of the standby engine (i.e. the power output of the second engine to the common gearbox remains between 0% to 1% of a rated full-power of the second engine when the second engine is operating in the standby mode).

In another example, the multi-engine system ofFIG.1Bmay be operated in an asymmetric operating regime by control of the relative speed of the engines using controller(s)210, that is, the standby engine is controlled to a target low speed and the active engine is controlled to a target high speed. Such a low speed operation of the standby engine may include, for example, a rotational speed that is less than a typical ground idle speed of the engine (i.e. a “sub-idle” engine speed). Still other control regimes may be available for operating the engines in the asymmetric operating regime, such as control based on a target pressure ratio, or other suitable control parameters.

Although the examples described herein illustrate two engines, the asymmetric operating regime is applicable to more than two engines, whereby at least one of the multiple engines is operated in a low-power standby mode while the remaining engines are operated in the active mode to supply all or substantially all of a required power and/or speed demand of a common load.

In use, the first engine (say102) may operate in the active mode while the other engine (say104) may operate in the standby mode, as described above. During the asymmetric operating regime, if the helicopter (H) needs a power increase (expected or otherwise), the second engine104may be required to provide more power relative to the low power conditions of the standby mode, and possibly return immediately to a non-standby mode (i.e. a high- or full-power condition). This may occur, for example, in an emergency condition of the multi-engine system powering the helicopter, wherein the “active” engine loses power, and the power recovery from the lower power to the high power may take some time. Even absent an emergency, it will be desirable to repower the standby engine to exit the asymmetric operating regime.

In some embodiments, the standby engine may be de-clutched from the TCS105of the rotorcraft. As illustrated inFIG.1B, first and second engines102,104each having a respective transmission152are interconnected by a common output gearbox150to drive a common load170. In one embodiment, the common load170may comprise a rotary wing of a rotary-wing aircraft. For example, the common load170may be a main rotor108of the aircraft100. Depending on the type of the common load170and on the operating speed thereof, each of engines102,104may be drivingly coupled to the common load170via the output gearbox150, which may be of the speed-reduction type.

For example, the gearbox150may have a plurality of transmission shafts156to receive mechanical energy from respective output shafts154of respective engines102,104. The gearbox150may be configured to direct at least some of the combined mechanical energy from the plurality of gas turbine engines102,104toward a common output shaft158for driving the common load170at a suitable operating (e.g., rotational) speed. It is understood that the TCS105may also be configured, for example, to drive accessories and/or other elements of an associated aircraft. The gearbox150may be configured to permit the common load170to be driven by either of the gas turbine engines102,104or by a combination of both engines102,104together.

With reference toFIG.2, the gas turbine engines102,104can be embodied as turboshaft engines. Although the foregoing discussion relates to engine102, it should be understood that engine104can be substantively similar to engine102. In this example, the engine102is a turboshaft engine generally comprising in serial flow communication a low pressure (LP) compressor section12and a high pressure (HP) compressor section14for pressurizing air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, a high pressure turbine section18for extracting energy from the combustion gases and driving the high pressure compressor section14, and a lower pressure turbine section20for further extracting energy from the combustion gases and driving at least the low pressure compressor section12.

The low pressure compressor section12may independently rotate from the high pressure compressor section14. The low pressure compressor section12may include one or more compression stages and the high pressure compressor section14may include one or more compressor stages. The low pressure compressor section12may include one or more variable guide vanes at its inlet or inter stage. The high pressure compressor section14may include one or more variable guide vanes at its inlet or inter stage. A compressor stage may include a compressor rotor, or a combination of the compressor rotor and a compressor stator assembly. In a multistage compressor configuration, the compressor stator assemblies may direct the air from one compressor rotor to the next.

The engine102has multiple, i.e. two or more, spools which may perform the compression to pressurize the air received through an air inlet22, and which extract energy from the combustion gases before they exit via an exhaust outlet24. In the illustrated embodiment, the engine102includes a low pressure spool26and a high pressure spool28mounted for rotation about an engine axis30. The low pressure and high pressure spools26,28are independently rotatable relative to each other about the axis30. The term “spool” is herein intended to broadly refer to drivingly connected turbine and compressor rotors.

The low pressure spool26includes a low pressure shaft32interconnecting the low pressure turbine section20with the low pressure compressor section12to drive rotors of the low pressure compressor section12. In other words, the low pressure compressor section12may include at least one low pressure compressor rotor directly drivingly engaged to the low pressure shaft32and the low pressure turbine section20may include at least one low pressure turbine rotor directly drivingly engaged to the low pressure shaft32so as to rotate the low pressure compressor section12at a same speed as the low pressure turbine section20. The high pressure spool28includes a high pressure shaft34interconnecting the high pressure turbine section18with the high pressure compressor section14to drive rotors of the high pressure compressor section14. In other words, the high pressure compressor section14may include at least one high pressure compressor rotor directly drivingly engaged to the high pressure shaft34and the high pressure turbine section18may include at least one high pressure turbine rotor directly drivingly engaged to the high pressure shaft34so as to rotate the high pressure compressor section14at a same speed as the high pressure turbine section18. In some embodiments, the high pressure shaft34may be hollow and the low pressure shaft32extends therethrough. The two shafts32,34are free to rotate independently from one another.

The engine102may include a transmission38driven by the low pressure shaft32and driving a rotatable output shaft40. The transmission38may vary a ratio between rotational speeds of the low pressure shaft32and the output shaft40.

One or more sensors202,204are coupled to the engine102for acquiring data about one or more operating parameters of the engine102. The sensors202,204, may be any suitable type of sensor used to measure operating parameters, such as but not limited to, speed sensors, acceleration sensors, pressure sensors, temperature sensors, altitude sensors, and the like. The sensors202,204, can be coupled to the engine controller210in any suitable fashion, including any suitable wired and/or wireless coupling techniques. In the example illustrated inFIG.2, sensor202is a pressure sensor positioned to measure “P3” pressure, at an outlet of the high pressure compressor section14, sensor204is a speed sensor positioned to measure the engine core spool speed (Ng), as represented by the rotational speed of the high pressure shaft34. Note that in some embodiments, Ng is measured through the rotational speed an accessory coupled to the high pressure shaft34, in some cases through an accessory gearbox, such as a starter/generator, a fuel control unit, an oil pump, or any other suitable accessory. Parameters such as P3 and Ng may be used in the manifold refilling scheme, as explained in more detail below.

Referring toFIG.3, there is illustrated a fuel supply system300for supplying fuel to the combustor14of the gas turbine engine102. In the embodiment illustrated, a first set of nozzles301of at least one first (or primary) manifold311supplies fuel to the combustor14, and a second set of fuel nozzles302of at least one second (or secondary) manifold312supplies fuel to the combustor14. An electronic controller340, which may be controller210or a different controller, controls a fuel pump342to supply fuel from a reservoir346to the manifolds311,312through one or more fuel lines. The fuel pump342provides the fuel to a fuel flow divider348, which is operably connected to the manifolds311,312.

The primary manifold311, secondary manifold312, or both manifolds311,312may be used to supply fuel to the combustor14depending on the operating mode of the engine102. For example, at higher fuel flow (e.g. in active mode), the majority of fuel may be supplied via the secondary manifold312. At low fuel flow (e.g. in standby mode), all of the fuel may be supplied via the primary manifold311. In order to avoid coking of the stagnant residual fuel in the secondary manifold312, the fuel in the secondary manifold312may be purged into the combustor, siphoned back into an accumulator device, or naturally emptied through gravity. There may also be other reasons for which it is desirable to purge or empty a fuel manifold when fuel is supplied through a different manifold.

When the engine exits the standby mode, the secondary manifold312may be filled using a controlled refilling scheme. In particular, one or more engine operational parameters are monitored as the manifold is filled in order to prevent engine surge. An example method for filling the fuel manifold in accordance with the refilling scheme is illustrated inFIG.4.

With reference toFIG.4, at step402, fuel flow to the secondary manifold is increased. It will be understood that if the engine is operating in a mode whereby fuel is provided to the combustor through the secondary manifold and it is the primary manifold that is empty (in whole or in part), then step402will consist in increasing fuel flow to a primary manifold.

At step404, one or more engine operational parameters are monitored as fuel fills the secondary manifold (or the previously substantially empty or completely empty manifold). At step406, the engine is accelerated when a transition threshold is reached. The transition threshold is indicative that fuel has reached the combustor, i.e. that the manifold and nozzles are filled and that fuel has pushed through the nozzles and into the combustor. The nature of the transition threshold depends on the operational parameter being monitored.

The method400will be explained in more detail using specific and non-limiting examples with reference toFIGS.5A-5F. Referring toFIG.5A, a first embodiment for the manifold refilling scheme is illustrated. The monitored engine operational parameter is the rate of change of pressure at the outlet of the compressor of the engine, i.e. the rate of change of P3. Curve502illustrates fuel flow to the engine over time. Prior to time T1, there is no fuel provided to the engine through the secondary manifold. Curve504illustrates P3 concurrently with fuel flow. The rate of change of P3 may be derived from P3 as measured, for example using sensor202.

At time T1, fuel flow is provided to the empty (in whole or in part) manifold. In this example, fuel is initially provided to the manifold using an open-loop fuel flow control scheme at a predefined rate. Prior to T1, the engine may be in a standby mode or another operating mode whereby substantially no power is provided to the aircraft and at least one manifold of the engine is empty in part or in whole. P3 remains substantially constant until time T2, where it starts to increase. Curve506illustrates the rate of change of P3, as compared to a transition threshold508. In this example, the transition threshold508is a maximum limit for the rate of change of P3. At time T2, the rate of change of P3 begins to increase with the increase of P3. At time T3, the rate of change of P3 reaches the transition threshold508, which triggers acceleration of the engine. The open-loop fuel flow control scheme is transitioned to a closed-loop fuel flow control scheme for engine acceleration. The transition may comprise resetting the fuel flow command to a lower value, such as the value of fuel flow at time T1when the open-loop fuel flow control scheme was initiated, and applying a closed-loop fuel flow schedule from that value.

The embodiment ofFIG.5Aillustrates the “manifold effect”, which refers to an engine operational parameter that does not vary (or varies insignificantly) until the fuel has filled the manifold, pushed through the nozzles, and entered into the combustor. The combustion increasing causes the engine operational parameter to vary. The fill rate of the manifold may be reduced quickly when the engine operational parameter begins to change, as demonstrated at time T3. The manifold effect may be observed using various parameters, as demonstrated in the other embodiments illustrated inFIGS.5B-5F.

Another embodiment for the manifold refilling scheme is illustrated inFIG.5B. The monitored engine operational parameter is a rate of change of engine core spool speed, i.e. the rate of change of Ng (or Ngdot). Ng may be used to observe the manifold effect due to the correlation between Ng and P3. Curve522illustrates fuel flow to the engine over time. Curve524illustrates Ng concurrently with fuel flow. Ngdot526may be derived from Ng524as measured, for example using sensor204. Alternatively, Ngdot526may be measured directly with an accelerometer or another sensor suitable for measuring acceleration.

As can be seen fromFIGS.5A,5B, the difference between the two embodiments is the operational engine parameter monitored as fuel fills the manifold. An open loop fuel flow control scheme is used prior to the operational engine parameter reaching the transition threshold528, and a closed-loop fuel flow control scheme is used after having reached the transition threshold528. The transition threshold528, which in this case is a maximum core spool acceleration, acts as a trigger to begin acceleration of the engine once the fuel has reached the combustor and combustion has started.

FIG.5Cillustrates another embodiment for the manifold refilling scheme. The monitored engine operational parameter is the rate of change of engine core spool speed (Ngdot). Curve532illustrates fuel flow to the engine over time, curve534illustrates Ng concurrently with fuel flow. Ngdot536may be derived from Ng534as measured, for example using sensor204. Alternatively, Ngdot536may be measured directly with an accelerometer or another sensor suitable for measuring acceleration.

In contrast to the example ofFIG.5B, fuel flow is provided to the manifold in a closed-loop fuel control scheme at time T1in the embodiment ofFIG.5C, i.e. when the manifold begins to receive fuel. An Ngdot limit538, used in the closed-loop fuel control scheme, is modulated in order to prevent the fuel flow controller, such as controller340, from commanding an over-fuel. For example, the Ngdot limit538is set to a lower value than nominal at time T1. The lower Ngdot limit538is maintained until Ngdot536is within a predefined tracking error of Ngdot limit538. The tracking error thus acts as the transition threshold, indicative of fuel having reached the combustor of the engine. Core spool speed534is shown to begin to increase at time T2. The tracking error reaches the transition threshold at time T3, after which the Ngdot limit538is ramped back up to a nominal setting at a predefined rate.

In yet another embodiment, illustrated inFIG.5D, the monitored engine operational parameter is the pressure P3. Curve542is the fuel flow to the engine over time, curve544is P3 concurrently with fuel flow. Fuel flow is provided to the manifold at time T1using a closed-loop fuel control scheme, and P3 is monitored as the manifold fills. P3 is compared to a P3 limit546, which is modulated to a lower value during the manifold filling phase, and a tracking error between the sensed P3544and the P3 limit546acts as the transition threshold. The lowered P3 limit may be an offset of an initially sensed P3 value, before it starts to increase. The engine is accelerated at time T3, when the transition threshold has been met.

InFIG.5E, the monitored engine operational parameter is a ratio of commanded fuel flow (Wf) to P3, also referred to as a ratio unit (RU). Curve552is fuel flow to the engine over time, curve554is RU concurrently with fuel flow. Fuel flow is provided to the manifold at time T1using a closed-loop fuel control scheme, and RU is monitored as the manifold fills. RU is compared to an RU limit556, which is modulated to a lower value during the manifold filling phase, and a tracking error between the sensed RU554and the RU limit556acts as the transition threshold. The lowered RU limit may be an offset of an initially sensed RU value, before it starts to increase. The engine is accelerated at time T3, when the transition threshold has been met.

Referring toFIG.5F, there is illustrated yet another embodiment for the manifold refilling scheme. The monitored engine operational parameter corresponds to the pressure at the outlet of the compressor (P3), but could be any other one of the engine operational parameters mentioned herein, such as rate of change of P3, Ng, Ngdot, RU, and the like. The sensed P3 is compared to a synthesized P3, generated using an engine model. The manifold effect, i.e. the delay in P3 increasing due to the fuel not having reached the combustor, is not present in the engine model. Thus, when the sensed P3 and the synthesized P3 are compared, there is a discrepancy during the manifold filling phase. This discrepancy decreases once the manifold is full, fuel enters the combustor, and combustion is started.

Curve562illustrates fuel flow, curve564illustrates the synthesized P3, and curve566illustrates the sensed P3. Curve568illustrates the difference between the synthesized P3564and the sensed P3566. Curve570is a rate of change of the difference between the synthesized P3564and the sensed P3566. The rate of change570is compared to a transition threshold572, which is a lower limit for the rate of change. When the rate of change570reaches the transition threshold572, this implies the manifold is full and the fuel has reached the combustor. The sensed P3566and the synthesized P3564have converged to a common value. This convergence is used to transition the fuel flow control scheme from an open loop fuel flow control to a closed-loop fuel flow control, and to accelerate the engine using the closed-loop fuel flow control scheme.

It will be understood from the embodiments illustrated inFIGS.5A-5Fthat many variants are possible for the method400ofFIG.4. For example, in the embodiment ofFIG.5A, P3 can be compared to a transition threshold corresponding to an upper limit for P3, instead of comparing the rate of change of P3 to a transition threshold corresponding to an upper limit for the rate of change for P3. Similarly with the embodiments ofFIGS.5B and5C, the core spool speed may be compared to a transition threshold corresponding to an upper limit for core spool speed instead of comparing the rate of change of the core spool speed to an upper limit for the rate of change of the core spool speed. In yet another embodiment, a pressure sensor may be provided in the manifold and monitored as fuel fills the manifold. The fuel pressure in the manifold will not increase significantly until the manifold is completely filled, at which point fuel will get pushed through the nozzles instead of air. This will result in a signification pressure spike, indicative that the manifold is full. P3 in the embodiments ofFIGS.5A,5D, and5Fcan therefore be replaced with P_manifold. Other variants may also apply.

The method400of filling a fuel manifold of a gas turbine engine may be implemented using a controller dedicated to fuel flow, such as controller340, or using an engine controller210, configured for operating one or more of the engines102,104in the aircraft100. With reference toFIG.6, the method400may be implemented by a computing device600, which can embody part or all of the engine controller210and/or the fuel controller340. The computing device600comprises a processing unit602and a memory604which has stored therein computer-executable instructions606. The processing unit602may comprise any suitable devices configured to implement the functionality described in the method400, such that instructions606, when executed by the computing device600or other programmable apparatus, may cause the functions/acts/steps performed by a controller210,340and/or described in the method400as provided herein to be executed. The processing unit602may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a central processing unit (CPU), an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, custom-designed analog and/or digital circuits, or any combination thereof.

The methods and systems for filling a fuel manifold of a gas turbine engine as described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device600. Alternatively, the methods and systems described herein may be implemented in assembly or machine language. The language may be a compiled or interpreted language.

Embodiments of the methods and systems described herein may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processing unit602of the computing device600, to operate in a specific and predefined manner to perform the functions described herein, for example those described in the method400.