GB2474638A

GB2474638A - Anti-icing valve monitoring for gas turbine

Info

Publication number: GB2474638A
Application number: GB0918261A
Authority: GB
Inventors: Saurav Dutta
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2009-10-20
Filing date: 2009-10-20
Publication date: 2011-04-27
Also published as: GB0918261D0

Abstract

The present invention provides an arrangement and a method of confirming activation of a gas turbine engine anti-icing valve. The valve is commanded to activate and a compressor exit pressure is monitored for at least a predetermined time interval. A confirmation of activation is provided if the pressure exhibits a spike equalling or exceeding a predetermined threshold magnitude within the predetermined time interval. As bleeding of compressor air for warming fan blades (14 see fig 1) reduces the efficiency of a gas turbine, it is beneficial to provide actuation confirmation when the valve has been commanded to open or close. The present invention can be even be used when not in flight, for example in testing at the end of ground based maintenance, and it may be advantageous in terms of reliability and in not requiring additional components to be added to an engine.

Description

ANTI-ICING VALVE ACTIVATION

The present invention relates to a method and an arrangement for confirming activation of a gas turbine engine anti-icing valve. It may have particular application for use with an engine section stator anti-icing valve for a gas turbine engine.

A gas turbine engine for providing propulsive power to an aircraft is vulnerable to icing at high altitude, and in very cold conditions. Ice builds up on the fan blades and nose cone of the engine and is periodically shed into the engine, dislodged by vibration or shear weight. If the ice does not break up but is shed in a slab or sheet it can cause significant damage to the fan blades, engine section stator behind the fan and other components further into the engine. It is therefore preferable to prevent the ice from forming large sheets.

One way in which this is achieved is by heating the fan, engine section stator and the air around them so that the ice is discouraged from forming and melted if it does form.

Typically warm air is bled from a compressor in the engine and ducted to the forward components for anti-icing purposes. Since bleeding working fluid from the engine reduces its efficiency it is beneficial to bleed the air only when required for anti-icing and not at other times. Thus an anti-icing valve is used to control the bleed of warm compressor air to the engine section stator.

If the anti-icing valve does not open when commanded, ice can build up and be shed, causing damage as described above. If the anti-icing valve does not close when commanded, compressor air continues to be bled when not required and the engine operates inefficiently. Thus it is beneficial to periodically test the anti-icing valve response and to have feedback of its activation following a command to open or close.

It is particularly helpful to test the anti-icing valve activation after any maintenance activity has been performed on it.

One method of confirming activation of the anti-icing valve is to attach a differential pressure transducer (DPT) to the valve to monitor the change in pressure across it.

This is disadvantageous because it can only be performed, in flight, by comparing the measured pressure drop against known threshold values. The DPT is not used for any other purpose, so it is an additional component that adds to the weight and cost of the engine. Furthermore, it is usual for the DPT to be simplex, ie connected to a single channel of the duplex control system, so there is no system redundancy in the case of a loss of the signal. Similarly, if the control system channel is lost there may be an undetected failure of the anti-icing valve. Generally the anti-icing valve is commanded open for comparatively short periods of time so that if the anti-icing valve fails in the open configuration the DPT may be exposed to very high temperatures for a prolonged period, which may reduce its life and lead to increased maintenance requirements with consequent costs.

The present invention seeks to provide a method and arrangement for confirming activation of an anti-icing valve that seeks to address the aforementioned problems.

Accordingly the present invention provides a method of confirming activation of a gas turbine engine anti-icing valve comprising commanding activation of the valve; monitoring a compressor exit pressure for at least a predetermined time interval; and providing a confirmation of activation if the pressure exhibits a spike equalling or exceeding a predetermined threshold magnitude within the predetermined time interval.

This has the advantage that a short time interval of monitoring will enable confirmation that an anti-icing valve has activated. In general the anti-icing valve is commanded to activate at a time in use of the gas turbine engine when there is no other factor changing the compressor exit pressure.

The step of commanding activation of the valve may comprise commanding opening of the valve, closing of the valve or opening and then closing of the valve.

The step of commanding activation of the valve may occur during normal operation of the gas turbine engine or may comprise a test activation of the valve in addition to the normal operation of the gas turbine engine.

There may be a further step of aborting the method if the compressor exit pressure is changed by another action in the gas turbine engine.

The threshold magnitude may be defined at up to lOpsi/ms. This is an absolute value.

For example, it may be set at -t-8psi/ms for the positive spike and -8psi/ms for the negative spike. The threshold magnitude may be determined by empirical calculation for the specific application envisaged.

The predetermined time interval may be up to 10 milliseconds and may be determined by empirical calculation.

A second aspect of the present invention provides an arrangement for confirming activation of a gas turbine engine anti-icing valve comprising an anti-icing valve; an activation mechanism to activate the valve; and a monitoring sensor coupled to a compressor to monitor the exit pressure thereof; whereby the monitoring sensor provides a confirmation of activation if the exit pressure equals or exceeds a predetermined threshold magnitude within a predetermined time interval begun by activation of the valve.

The anti-icing valve may be coupled to an engine section stator of the gas turbine engine.

The activation mechanism may open the valve, close the valve or open and then close the valve.

The compressor may be a high pressure compressor.

For example, it may be set at +8psilms for the positive spike and -8psilms for the negative spike. The threshold magnitude may be determined by empirical calculation for the specific application envisaged.

The present invention also provides a gas turbine engine comprising the method as described above having any of the variations described, and a gas turbine engine comprising an arrangement as described above having any of the variations described.

The present invention will be more fully described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional side view of a gas turbine engine; Figure 2 is a plot of high pressure compressor exit pressure signature and anti-icing valve demand according to the present invention; and Figure 3 is a set of characteristic plots of high pressure compressor exit pressure signature and anti-icing valve demand according to the present invention.

A gas turbine engine 10 is shown in Figure 1 and comprises an air intake 12 and a propulsive fan 14 that generates two airtlows A and B. The gas turbine engine 10 comprises, in axial flow A, an engine section stator 34, an intermediate pressure compressor 16, a high pressure compressor 18, a combustor 20, a high pressure turbine 22, an intermediate pressure turbine 24, a low pressure turbine 26 and an exhaust nozzle 28. A nacelle 30 surrounds the gas turbine engine 10 and defines, in axial flow B, a bypass duct 32. The engine section stator 34 comprises an annular array of stator blades. Mounted upon at least one of these is one or more anti-icing valve 36. The anti-icing valve or valves 36 take air bled from a compressor, particularly the intermediate compressor 16, and direct it to warm forward areas of the engine 10 including the fan 14 and engine section stator 34.

An exemplary embodiment of the present invention is described with respect to Figure 2. The invention will be described with a single anti-icing valve 36 although it is to be understood that multiple anti-icing valves 36 may be used and, particularly with larger engines 10, it may be preferable to have an annular array of anti-icing valves 36.

The anti-icing valve 36 is coupled to the engine control system (not shown) from which is supplied an anti-icing valve demand signal that commands the anti-icing valve 36 to open or close dependent on the icing condition that is present or anticipated. A typical demand signal produces the line 38 as shown on the plot in Figure 2, with time on the x-axis. Thus the anti-icing valve 36 is initially commanded closed, section 38a, and at a time when anti-icing is required the valve 36 is commanded open, section 38b. Once anti-icing is no longer required, the anti-icing valve 36 is commanded to close again, section 38c. The demand signal is digital so that the line 38 resembles a square wave.

Surprisingly, it has been found that opening and closing the anti-icing valve 36 causes a distinct change in the signature of the exit pressure of the high pressure compressor 18, P30. As shown in Figure 2, line 40 is the P30 signature relating to the demand signal 38. Thus the first section 40a of the signature shows the comparatively noisy background signal level. Rapidly after the anti-icing valve 36 is commanded to open, there is a prominent spike 42 in the P30 signature 40. If the background signal level, seen in section 40a, is considered to be at zero, the spike 42 relating to the open command has a large negative magnitude. The spike 42 has an almost infinite gradient to a peak value, before the signal returns to the background level with a gentler gradient. Whilst the anti-icing value 36 is open the P30 signature has a second section 40b at the background signal level. When the anti-icing valve 36 is commanded to close again there is a second prominent spike 44 with a large positive magnitude. As with the first spike 42, the spike 44 has an almost infinite gradient to a peak value, followed by a gentler gradient to return to the background signal level for a third section 40c.

From Figure 2 it can be seen that the command to transition from closed to open causes a large negative magnitude spike 42 whereas the command to transition from open to closed causes a large positive magnitude spike 44 in the P30 signature 40. By monitoring the P30 signature 40 for at least a period of time around the activation of the anti-icing valve 36, it is possible to ascertain whether or not the valve 36 has correctly activated.

It is not necessary to know the exact peak value of the spikes 42, 44 in order to confirm activation of the anti-icing valve 36 since the spikes 42, 44 have a significantly greater magnitude than the noise in the background signal level. Therefore, beneficially a threshold magnitude is predetermined so that if the anti-icing valve 36 has successfully activated when commanded, the magnitude of the P30 signature 40 will equal or exceed the predetermined threshold magnitude. The threshold magnitude can be determined from experimental data, modelling or any other method apparent to the skilled reader.

Similarly, it may not be necessary to monitor P30 for the whole of a flight. Instead the P30 signature 40 may be monitored for at least a predetermined time interval around the activation command. Thus, if the P30 signature 40 exhibits a spike 42, 44 that equals or exceeds the predetermined threshold magnitude within the predetermined time interval, activation of the anti-icing valve 36 is confirmed. Otherwise, it is deemed to have failed. As for the threshold magnitude, the predetermined time interval may be determined from experimental data, modelling or by any other known method.

Since P30 is a noisy signal it is advantageous to filter the signal, as shown in Figure 3.

A characteristic anti-icing valve demand signal 38 is plotted at the top of the figure, aligned with the monitored P30 signature 40, the middle plot. As is clear from the plot of P30 signature 40, the difference between peak magnitudes of the spikes 42, 44 and the noise level on the background signal level 40a, 40b, 40c is relatively small.

Therefore, the P30 signature 40 is filtered using conventional filtering techniques, such as fast Fourier transforms or low pass filters to remove high frequency noise by differentiating the signal, to produce the filtered P30 signature 46 shown in the bottom plot of Figure 3. A gain may also be applied to enhance the differences in magnitude.

The filtered P30 signature 46 has first 46a, second 46b and third 46c sections that correspond to the first 40a, second 40b and third 40c sections of the monitored P30 signature 40. The filtering technique is chosen such that the spikes 48, 50, which correspond to the spikes 42, 44 respectively, have their magnitude increased proportionately more than the background noise of the P30 signature 40. Thus the filtered spikes 48, 50 are more prominent from the filtered P30 signature 46 than the spikes 42, 44 are from the background signal level of the P30 signature 40.

Dependent on the running mode of the engine 10 and the underlying environmental conditions, the P30 signature 40 may have a different profile for the background signal level 40a, 40b, 40c. Thus, in Figure 2 the background signal level, averaged for noise, is predominantly flat whereas in Figure 3 the background signal level decreases through time (left to right on the x-axis). Nevertheless, there will always be a negative magnitude spike 42 corresponding to the command to open the closed anti-icing valve 36 and a positive magnitude spike 44 corresponding to the command to close the opened anti-icing valve 36. Similarly, the recovery from the peak of a spike 42, 44 to the background signal level 40a, 40b, 40c may be quicker or slower than the exemplary plots in Figure 2 and Figure 3 depending on the underlying engine 10 and environmental conditions.

There are two options for testing the activation of the anti-icing valve 36, particularly following maintenance activity. Firstly, the activation can be checked when the anti-icing valve 36 is first commanded open and then closed during normal operation of the gas turbine engine 10 during a flight. Secondly, a test activation can be commanded which is additional to the normal operation of the gas turbine engine 10. The spike 42, 44 in P30 signature 40 occurs rapidly after the activation command transition, line 38, so a test activation can take the form of commanding the anti-icing valve 36 to open, monitoring the P30 signature 40 for a spike 42 equalling or exceeding the predetermined threshold magnitude within a predetermined time interval and then commanding the anti-icing valve 36 to close and repeating the monitoring.

A confirmation of the successful activation may be generated after each commanded activation is confirmed by the presence of a spike 42, 44 or the confirmation may only be generated after the pair of the commanded activations, open and close, has been confirmed. The confirmation may be passed to another engine 10 system, for example the engine control system, for further actions to be triggered or to be logged for later analysis. Similarly, a failure to activate should be passed to an appropriate control system for corrective action to occur, such as overriding the anti-icing demand signal or re-trying the commanded activation.

In some circumstances the P30 signature 40 will be disrupted by an event that is unconnected to the activation of the anti-icing valve 36, for example opening or closing of the handling bleed valves that regulate compressor 16, 18 behaviour and/or supply cooling air to hot parts of the engine 10. In this case, the method may include a step that enables the method to be aborted if P30 changes due to another action in the gas turbine engine 10. The activation can then be confirmed at a later point in the flight, either at the next activation during normal operation or by scheduling a test activation during a part of the flight during which disruption is not anticipated, such as during aircraft cruise.

The method and arrangement of the present invention has several advantages over the prior art. Firstly, P30 is monitored on both channels of the engine control system for other purposes so that there is built-in redundancy for the signal and increased reliability due to the reduced likelihood of failing to detect a failed anti-icing valve 36.

Secondly, there is no need for the additional differential pressure transducer to monitor activation of the anti-icing valve 36, reducing cost and weight. If a reliable P30 signature 40 can be detected whilst an aircraft is on the ground, it will be possible to use the method and arrangement of the present invention to confirm activation of the anti-icing valve 36 after maintenance whilst on the ground, or even before the engine is returned to the aircraft, so that the confirmation is provided before the aircraft powered by that engine 10 takes off.

Although the present invention has been described with respect to identifying the change in P30 in order to determine activation of the anti-icing valve 36, it can equally use the exit pressure of another compressor since they are all affected by the activation. For example, the exit pressure of the intermediate pressure compressor 16 could be used instead of the exit pressure of the high pressure compressor 18.

Although only one anti-icing valve 36 has been assumed for simplicity of explanation, there may be more than one anti-icing valve 36 activated independently or from a single activation command. The magnitude of the spikes 42, 44 may be demonstrably different depending on whether all or only some of a plurality of anti-icing valves 36 have activated, in which case there may be a requirement to monitor the exact pressure of the peak of the spikes 42, 44 or to have multiple threshold magnitudes to indicate how many anti-icing valves 36 have activated.

The exit pressures of more than one compressor 16, 18 may be monitored to provide redundancy of the method of confirmation or to each focus on the activation of different ones of a plurality of anti-icing valves 36.

Preferably the anti-icing valve 36 is coupled to the engine section stator 34.

Alternatively the anti-icing valve 36 is coupled to a different part of the engine 10 or there is a plurality of anti-icing valves 36 placed in a variety of locations on the engine 10 that are prone to icing.

Any conventional pressure sensor may be used as a monitoring sensor coupled to the compressor to monitor its exit pressure. Any conventional activation mechanism may be used to activate the anti-icing valve 36 when commanded to do so. The command to activate the anti-icing valve 36 may originate from the engine control system, a monitoring system or a dedicated anti-icing control system for the anti-icing valve.

Although the method of the present invention has been described with respect to an engine section stator anti-icing valve 36, it may be used with equal felicity with any pneumatic system in the engine 10 comprising a valve that is smaller than the compressor bleed valves and which can be tested at high power.

Claims

CLAIMS1 A method of confirming activation of a gas turbine engine anti-icing valve comprising: * commanding activation of the valve; * monitoring a compressor exit pressure for at least a predetermined time interval; and * providing a confirmation of activation if the pressure exhibits a spike equalling or exceeding a predetermined threshold magnitude within the predetermined time interval.
2 A method as claimed in claim 1 wherein the step of commanding activation of the valve comprises commanding opening of the valve.
3 A method as claimed in claim 1 wherein the step of commanding activation of the valve comprises commanding closing of the valve.
4 A method as claimed in claim 1 wherein the step of commanding activation of the valve comprises commanding opening and then closing of the valve.
A method as claimed in any of claims 1 to 4 wherein the step of commanding activation of the valve occurs during normal operation of the gas turbine engine.
6 A method as claimed in any of claims 1 to 4 wherein the step of commanding activation of the valve comprises a test activation of the valve additionally to normal operation of the gas turbine engine.
7 A method as claimed in any preceding claim further comprising a step of aborting the method if the compressor exit pressure is changed by another action in the gas turbine engine.
8 A method as claimed in any preceding claim wherein the threshold magnitude is defined at up to 10 psi/ms.
9 A method as claimed in claim 8 wherein the threshold magnitude is determined by empirical calculation.

A method as claimed in any preceding claim wherein the predetermined time interval is up to
10 milliseconds.
11 A method as claimed in claim 10 wherein the time interval is determined by empirical calculation.
12 A method substantially as hereinbefore described with reference to the accompanying figures.
13 An arrangement for confirming activation of a gas turbine engine anti-icing valve comprising: * an anti-icing valve; * an activation mechanism to activate the valve; and * a monitoring sensor coupled to a compressor to monitor the exit pressure thereof; whereby the monitoring sensor provides a confirmation of activation if the exit pressure equals or exceeds a predetermined threshold magnitude within a predetermined time interval begun by activation of the valve.
14 An arrangement as claimed in claim 13 wherein the anti-icing valve is coupled to an engine section stator of the gas turbine engine.
An arrangement as claimed in claim 13 or 14 wherein the activation mechanism opens the valve.
16 An arrangement as claimed in claim 13 or 14 wherein the activation mechanism closes the valve.
17 An arrangement as claimed in claim 13 or 14 wherein the activation mechanism opens and then closes the valve.
18 An arrangement as claimed in any of claims 13 to 17 wherein the compressor is a high pressure compressor.
19 An arrangement as claimed in any of claims 13 to 18 wherein the threshold magnitude is defined at up to 10 psi/ms.
An arrangement as claimed in claim 19 wherein the threshold magnitude is determined by empirical calculation.
21 An arrangement as claimed in any of claims 13 to 19 wherein the predetermined time interval is up to 10 milliseconds.
22 An arrangement as claimed in claim 21 wherein the time interval is determined by empirical calculation.
23 An arrangement substantially as hereinbefore described with reference to the accompanying figures.
24 A gas turbine engine comprising a method as claimed in any of claims 1 to 12.A gas turbine engine comprising an arrangement as claimed in any of claims 13 to 23.