Method and device for detecting charged particles in a gas flow

Abstract: The detection of charged debris in the gas flow path of an engine without the need to provide additional sensors intruding into the flow path is made possible by an integrated sensor. The integrated sensor is made by selecting from within the engine an existing sensor associated with the gas flow path and electrically isolating a portion of the sensor from the engine. This enables the isolated portion to be used in detecting charged particles in the gas flow path. In a preferred embodiment the existing sensor includes a housing which is isolated to form the charged particle detector. The integrated sensor can be connected to signal conditioning apparatus to produce signals indicative of the passage of charged particles in the vicinity of the sensor.

Description: IMPROVEMENTS RELATING TO CHARGE SENSORS The present invention relates to a charged particle sensor, to a method of integrating a charged particle sensor into a gas turbine engine or the like, and to a method of detecting charged particles in the gas flow path of a gas turbine engine or the like. The detection of debris in the various gas flow paths of a gas turbine engine is an area of research which we have been investigating in recent years inter alia as a means of providing an early warning of engine malfunction or damage so that remedial action can be taken before engine failure occurs. We have found that debris in a gas flow path may be detected by sensing electrostatic charge carried by the debris and this technique promises to be very effective. However charge sensors suitable for this purpose are not incorporated into the original designs of gas turbine engines and we have found that engine manufacturers and operators are extremely reluctant to countenance modification of engines for enabling the charged particles which constitute the debris in the gas flow path to be detected. Hitherto known charge sensors have, so far as we are aware, all been of a form which results in some degree of intrusion into the gas flow path of the engine and/or requires some modification of the engine for mounting of the sensor and neither of these aspects will have featured in the original design of the engine. Therefore such sensors are prima facie unacceptable as add-on components to an existing engine design. Thus for example one kind of charge sensor that we have utilized in our research comprises a sensing member mounted in and insulated from a housing which is adapted to be secured to the outside of the engine casing with the sensing member arranged to operate through an aperture in the casing and to be substantially flush with the inner surface of the casing. This particular kind of sensor is designed to minimise intrusion into the gas flow path of the engine but is such that substantial modifications in the form of sensor viewing apertures and securing bolt receiving holes have to be made to the engine casing. When it is considered that a fully monitored engine would include a plurality of such sensors, possibly ten or more, at various engine locations, it will be understood that the fitting of the sensors would require relatively major structural modifications to be made to the engine which were not envisaged in the original engine design and that engine operators and manufacturers would be reluctant to accept them. US-A-4591794 discloses an electrostatic probe adapted to be mounted in a borescope access hole in a gas turbine engine. EP-A-256846 describes a sensor assembly for inclusion in the gas path of a gas turbine engine. Both of the aforementioned documents were cited against this specification by the European Patent Office during examination. It is moreover the case that the environment within a gas turbine engine is generally hostile and extreme stress can be imposed on sensors in the gas flow path. Hitherto known sensors therefore have had to be carefully designed to minimise the risk of their disintegration, which could result in damage to the engine, and in consequence have generally been expensive to manufacture and/or install in the engine. Accordingly, it would be desirable to be able to detect electrostatically charged debris in the gas flow path of a gas turbine engine for example without the need to provide additional sensors which intrude into the engine gas flow paths and/or require substantial modifications to the engine which were not envisaged in the original engine design. We have realised that the detection of charged debris in the gas flow path of an engine may be effected by utilization of existing parts or components of the engine as charge sensors. By electrically insulating existing portions of the engine, such portions can be used as a means by which charged particles constituting debris in the gas flow path can be detected. In one aspect the invention provides a method of integrating a charged particle sensor into a gas turbine engine or the like having a gas flow path, the method comprising the steps of selecting from within the engine an existing part or component designed to perform a function associated with the gas flow path of the engine, electrically isolating at least a portion of the selected part from the engine such that the selected part can continue to perform its designed function, and providing an electrical connection to the isolated portion to enable the portion to output a signal representative of charged particles in the gas flow path in the vicinity of the part or component, the portion thereby serving as a charged particle sensor. In another aspect the invention provides a method of detecting charged particles in a gas flow path of a gas turbine engine or the like, the method comprising the steps of electrically isolating at least a portion of an existing part of component of the engine which part or component is designed to perform a function associated with the gas flow path of the engine such that the part or component can continue to perform its designed function, providing an electrical connection to the isolated portion to enable the portion to output a signal representative of charged particles in the vicinity of the part or component, the portion thereby serving as a charged particle sensor and inputting the signal from the isolated portion to signal conditioning apparatus for producing conditioned signals representative of the passage of charged particles in the vicinity of the selected part or component. In a further aspect the invention provides a gas turbine engine in which a charged particle sensor in integrated into the engine for sensing charged particles in the gas flow path thereof, the sensor being formed by electrically isolating at least a portion of an existing part or component of the engine from the engine, which part or component is designed to perform a function associated with the gas flow path of the engine, such that the component can continue to perform its designed function, and by providing an electrical connection to the isolated portion to enable the portion to output a signal representative of charged particles in a gas flow path in the vicinity of the part or component. It is common practice that a gas turbine engine for example should incorporate various sensors in the gas flow paths of the engine for monitoring parameters such as temperature, gas flow velocity etc. For example, it is common practice to provide an array of thermocouple devices downstream of the turbine to enable measurement of the temperature of gas exhausted from the combustion chamber. The original engine design takes into account the presence of these sensors. It is thus a preferred feature of the present invention to modify existing sensors, as appropriate, to enable them additionally to be used as charge sensors. In a preferred embodiment of the invention, to be described in greater detail hereinafter, the body of an existing thermocouple provided in the engine is electrically isolated from the engine so that it can be used as a charge sensor and an electrical connection is made to the thus isolated body to provide a means by which signal conditioning apparatus or the like can be connected to the isolated body. The invention thus offers to the engine manufacturer or operator the significant advantage of new technology, namely the sensing of electrostatically charged debris particles within the engine, without need for significant modification of existing engine designs. In order that the invention may be well understood, an embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a thermocouple typical of thermocouples found in gas turbine engines; Figure 2 is a schematic view of the thermocouple of Figure 1 modified in accordance with the present invention. Referring now to Figure 1 there is shown a typical thermocouple assembly 10 bolted to a portion 12 of a body of a gas turbine engine. As has already been mentioned it is not uncommon for gas turbine engines to be designed to incorporate a number of sensors such as the thermocouple 10 shown at desired locations within the engine. A number of thermocouple assemblies 10 may for example be provided in an array downstream of the turbine to enable the temperature of gasses exhausted from the combustion chamber and through the turbine to be measured to detect hot or cold spots in the engine. The thermocouple assembly 10 comprises an elongate tubular housing 14 which extends through an aperture 16 in the engine body 12 and a securing flange 18 which is secured to the engine body by way of securing bolts 20 to hold the assembly 10 in position. A pair of thermocouple wires 22,24 are provided in the housing and are joined at one end to form a thermocouple bead 26. The wires 22,24 extend from the bead 26 along the length of the housing 14 to connect with corresponding wires 28,30 in an armoured cable 32 which wires 28,30 are in turn connected to signal conditioning circuitry (not shown) at another location. The armoured cable 32 may for example comprise a casing 34 of for example stainless steel connected electrically to the tubular housing 14 and an insulating powder 36 which isolates the conducting wires 28,30 from each other and the casing 34 whilst allowing the cable to be bent. An aperture 38 is provided at the end of the housing 14 to enable gas from the engine to come into contact with the thermocouple bead 26. In Figure 1 the direction of gas flow is indicated by arrow F and normally the aperture 38 is oriented to face downstream in relation to the gas flow to protect the thermocouple bead 26 against damage from the high velocity gases. The thermocouple assembly 10 shown in Figure 1 can be modified in accordance with the present invention to provide an integrated sensor for detecting the presence of charged debris particles in the gas stream in addition to the temperature sensing function already provided and such a modification is shown in Figure 2. As may be seen from Figure 2, the thermocouple assembly is electrically isolated from the engine body 12 by way of insulating washers 40,42 which respectively isolate the flange 18 from the bolt 20 and the engine body 12. The armour of the armoured cable 32 is normally electrically connected at one end to the thermocouple assembly and at the other end (not shown) to a reference potential which may be at the same potential as the engine body and in order to isolate the thermocouple from this reference potential the armour of the cable is cut to form to cable portions 32a, 32b which are held together by way of an isolating clamp 44 which is shown in section in Figure 2. An insulating sheath 46 is placed around each of the end portions of the cable portions 32a,32b to isolate the end portions from the clamp 44 and the clamp is arranged to hold the end portions in spaced relation to electrically isolate the cable portions 32a,32b from one another. The conducting wires 28,30 extend across the space between the clamped end portions to provide an electrical path for signals from the thermocouple to signal conditioning apparatus (not shown). The thus described thermocouple assembly is electrically isolated from the engine body 12 and any other reference potential and can be used in the detection of charged particles in the gas flow path. In order to detect signals sensed by the isolated thermocouple housing, the housing is arranged to be connectable to signal conditioning apparatus and the like by way of an insulated wire 48 electrically connected to any suitable part of the isolated assembly such as for example the associated portion 32a of armoured cable. An embodiment of the invention having been described it should be apparent that many modifications are possible. For example it is envisaged that the housing of any suitable sensor, and not just a thermocouple housing, in a gas turbine engine could be modified to enable charged particles to be detected. Thus, pressure rakes for example, which are commonly incorporated by design into gas turbine engines, could be modified to provide an integrated sensor for detecting the presence of charged particles as well as the pressure of gas in the gas flow path. Indeed it is not intended that the present invention should be limited to the adaptation of existing sensors since it is possible, at least in theory, to modify any suitable part of the engine to be electrically isolated from the rest of the engine. For example, stator blade could be modified in this way, although this might prove to be undesirable in practice on the ground of cost. Furthermore, while the embodiment of the invention has been described by reference to gas turbine engines, it is to be appreciated that it may be applicable also to other installations.

Claims: A method of integrating a charged particle sensor into a gas turbine engine or the like having a gas flow path, the method comprising the steps of selecting from within the engine an existing part or component (10) designed to perform a function associated with the gas flow path of the engine, electrically isolating at least a portion (14) of the selected part from the engine such that the selected part can continue to perform its designed function, and providing an electrical connection (48) to the isolated portion to enable the portion to output a signal representative of charged particles in the gas flow path in the vicinity of the part or component, the portion thereby serving as a charged particle sensor. A method as claimed in claim 1, wherein the selected part or component comprises a sensor (10) having a housing (14), and a portion of the housing is electrically isolated from the sensor to form the said isolated portion. A method as claimed in claim 2, wherein the electrically isolated portion of the housing comprises a portion of the housing that extends into the gas flow path. A method of detecting charged particles in a gas flow path of a gas turbine engine or the like, the method comprising the steps of electrically isolating at least a portion (14) of an existing part or component (10) of the engine which part or component is designed to perform a function associated with the gas flow path of the engine such that the part or component can continue to perform its designed function, providing an electrical connection (48) to the isolated portion to enable the portion to output a signal representative of charged particles in the vicinity of the part or component, the portion thereby serving as a charged particle sensor, and inputting the signal from the isolated portion to signal conditioning apparatus for producing conditioned signals representative of the passage of charged particles in the vicinity of the selected part or component. A method as claimed in claim 4, wherein the selected part or component comprises a sensor (10) having a housing (14) and a portion of the housing is electrically isolated from the sensor to form the said isolated portion. A method as claimed in claim 6 wherein the electrically isolated portion of the housing comprises a portion of the housing which extends into the gas flow path. A gas turbine engine in which a charged particle sensor is integrated into the engine for sensing charged particles in the gas flow path thereof, the sensor being formed by electrically isolating at least a portion (14) of an existing part or component (10) of the engine from the engine (12), which part or component is designed to perform a function associated with the gas flow path of the engine, such that the component can continue to perform its designed function, and by providing an electrical connection (48) to the isolated portion (14) to enable the portion (14) to output a signal representative of charged particles in a gas flow path in the vicinity of the part or component, the portion thereby serving as a charged particle sensor. An engine as claimed in claim 7, wherein the selected part of component comprises a sensor (10) having a housing (14), and a portion of the housing is electrically isolated from the sensor to form the said isolated portion. An engine as claimed in claim 8, wherein the electrically isolated portion of the housing comprises a portion of the housing that extends into the gas flow path. An engine as claimed in claim 7 or 8 or 9, wherein the electrical connection is arranged to enable the output signal to be input to signal conditioning apparatus for producing signals representative of the passage of charged particles in the vicinity of the sensor.

Inventors: FISHER CELIA ELIZABETH, FORFITT ROY, FISHER, CELIA ELIZABETH, FORFITT, ROY
Applicants: STEWART HUGHES LTD, STEWART HUGHES LIMITED
Application year: 1990
Main classification: G01N27
IPC codes: G01N27, F01D21