GB2400178A

GB2400178A - A combustion sensor arrangement

Info

Publication number: GB2400178A
Application number: GB0307292A
Authority: GB
Inventors: Ian C D Care; Paul D Rees
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2003-03-29
Filing date: 2003-03-29
Publication date: 2004-10-06
Also published as: GB0307292D0

Abstract

A combustion sensor arrangement for an engine (1) is provided in which a thick film semi-conductor device (5) appropriately doped is utilised as a gas sensor. The semi-conductor device (5) is positioned at a gaseous location whereby through gas diffusion into the sensor variations in electrical conductivity are detected in order to provide indicator signals of varying gas constituents indicative of actual combustion or predictive combustion. The sensor (5) may be located within vents or other gaseous locations near engine air flows, gearbox vents or bearing chambers. Typically, the sensor is located where particulate and liquid matter will not become incident upon the sensor, in a housing with a gas diffuser.

Description

COMBUSTION SENSOR

The present invention relates to combustion sensors and more particularly to combustion sensors used with regard to fires which may not generate sufficient temperature elevation to be detected by previous sensors.

There is a clear requirement with regard to engines to detect as soon as possible actual fires and potential fires. Fires can occur in combustion areas of the engine as well as bearing compartments.

Traditionally, combustion sensors have required a fire to generate sufficient heat about a fire wire sensor to cause bridging of contacts in order to generate a sensor signal indicative of a fire. Unfortunately, such wire sensors do not detect so-called cold combustion or indicate a potential fire and are relatively slow to indicate an actual fire as it is generally necessary for the fire to generate sufficient heat to activate the fire sensor wire. There are also problems when the source of the fire is located some distance from the fire sensor wire. With regard to bearing compartments, there is so- called cold combustion where a volatile (hydrocarbon) is oxidised with little or no rise in general temperature. Such events can be very short lived. A flame front may not establish itself but self extinguish well before sufficient heat energy is created to activate a fire sensor wire. In such circumstances, the combustion of the volatiles is not detected using normal sensor instrumentation. Nevertheless, bearing combustion and in particular the lubricant used in to such bearings creates carbon particles which will degrade the engine lubrication system and prematurely block lubricating oil filters.

In short, it is desirable to detect fires and combustion as soon as possible so that remedial action can be taken but as with all sensor systems it is also necessary to ensure that the combustion sensing used does not impinge materially upon the normal performance of the engine or bearing compartment. - 2

In accordance with the present invention, there is provided a combustion sensor arrangement for an engine, the arrangement comprising a combustion sensor coupled to an indicator means whereby upon detecting in use combustion the combustion sensor provides an indicator signal to the indicator means and the indicator means provides an indication of combustion, the arrangement characterized in that the sensor is a thick film semi-conductor device mounted to remain in a gaseous location whereby in use variation in gas composition thereabouts is determined by gas diffusion into the device and the sensor thereby provides the indicator signal to the indicator means.

Typically, the thick film semi-conductor device is surface mounted. Alternatively, the semi-conductor device is entrenched within a cavity.

Possibly, the semi-conductor device is coupled to the indicator means by a wireless connection. Normally, the semi-conductor device is coupled to the indicator means by wire connections.

Normally, the semi-conductor device provides indicator signals dependent upon gaseous composition and the indicator means provides different indications dependent upon specific indicator signals received from the sensor. Furthermore, the indicator means provides specific indications indicative of actual combustion and/or predictive combustion.

Possibly, the arrangement includes a gas and/or a particulate filter in order to facilitate or selectively regulate gas diffusion into the sensor. Possibly, the particulate filter is a carbon filter.

Possibly, the arrangement includes stagnater baffles associated with the semi- conductor device in order to facilitate a still or stagnant gaseous location adjacent the semi-conductor device.

Typically, the sensor is located about an engine cowling or ducting.

Alternatively, a sensor is located in or adjacent a vent for a bearing compartment.

Typically, the thick film semi-conductor device is of a chromium/titanium oxide (CrTiO) type or a tungsten oxide (WO) type or a tin oxide (SnO) type semi- conductor device maintained at a constant temperature whereby variations in gas diffusion composition stimulate variations in the electrical resistance across the film of the semi- conductor device to provide the indicator signal.

Possibly, the thick film sensor can be double sided. Possibly each side of the sensor can sense a different gas component target molecule.

Typically, the semi-conductor device is arranged to detect nitrogen dioxide and/or carbon monoxide and/or carbon dioxide and relative levels therebetween indicative of actual combustion. Furthermore, the semiconductor device is arranged to determine hydrocarbon contents within the gas diffusion indicative of oil and/or fuel and/or hydraulic fluid predictive of combustion onset.

Possibly, the semi-conductor device is associated with means to purge the gaseous location at least adjacent the semi-conductor device for calibrative and/or re- interrogation purposes.

Also in accordance with the present invention there is provided an engine incorporating a combustion sensor arrangement as described above.

Further in accordance with the present invention there is provided a bearing compartment incorporating a combustion sensor arrangement as described above.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which; Fig. 1 is a schematic front view of an engine indicating location of a combustion sensor in accordance with the present invention; Fig. 2 is a schematic plan view of a gear box arrangement incorporating a combustion sensor in accordance with the present invention; Fig. 3 is a schematic front view of a bearing compartment incorporating a combustion sensor in accordance with the present invention; Fig. 4 is a schematic cross- section of a combustion sensor in accordance with the present invention; and Fig. 5 is a schematic illustration of a control arrangement for a thick film semiconductor device utilised in order to provide a combustion sensor in accordance with the present invention.

Figs 1 to 3 illustrate schematically positioning of a combustion sensor in accordance with the present invention. In Fig. 1 a turbine engine 1 is illustrated with cowlings 2, 3 arched about a pylon 4 as will be typical during maintenance.

Combustion sensors 5, 6 are positioned at locations A, B such that in use these combustion sensors 5, 6 are either side of a heat exchanger 7. The sensors 5, 6 will thereby detect escape of fumes from the engine. The sensors 5, 6 in accordance with the present invention will be of a thick semi-conductor device type whereby gaseous diffusion into the sensor alters the conductivity of the sensor and therefore provides an indication signal. This indication signal is forwarded to a controller 10 either through wire couplings 12 or through a radio frequency wireless connection (sensor 5). The sensors may be surface mounted to protrude beyond the cowling surface or mounted in a cavity so that they are flush with that cowling surface.

The sensors 5, 6 in use detect the level of fluids which exceeded their volatility point. Clearly, when a liquid such as fuel, oil or hydraulic fluid is heated beyond its volatility point that fluid vaporises to form a mist. This mist is mixed with the air about the sensors 5, 6 such that the combined gaseous volume diffuses into the sensors 5, 6 and an appropriate indicator signal provided. It will be understood that by the nature of the fluids which form the mist e.g. fuel, oil or hydraulic fluid there can be a potential for - 5 ignition and subsequent combustion and fire within and about the engine 1. The sensors 5, 6 thereby provide a prediction as to the onset of combustion and a fire within the engine 1. The controller 10 may itself provide signals to alter operation of the engine to eliminate the potential combustion situation or instruct a fire suppression device in the pylon 4 to take appropriate action but in any event will provide an indication through appropriate means e.g. an audible alarm and indicator light as to the potential fire and combustion situation.

A gearbox 8 is coupled to a heat exchanger 7 through pipes 9. Typically, lubricating oil used in the gearbox 8 will be cooled in the heat exchanger 7. The lubricating oil may leak from the gearbox 8, pipes 9 or heat exchanger 7 and may present, particularly as a vapour, a significant combination threat.

Fig. 2 is a schematic illustration of a gear box 20 in which an oil tank 21 acts as a reservoir for lubricating oil into the gear box 20 by an oil pump 22. The gear box 20 acts as part of the drive train for a drive shaft 23 and auxiliary apparatus such as a hydraulic pump 24, scavenging pump 25 and a starter motor 26. The gearbox 20 incorporates an oil breather system 27 which includes a vent 28. This breather system 27 is incorporated in order to avoid creation of over pressures within the gear box 20.

Thus, should the gear box operate above its accepted temperature, and in particular beyond the volatility point of the lubricating oil, vapour and fumes will escape through the vent 28. In accordance with the present invention a sensor 29 is located in the vent 28 in order to sense variations in the fumes vented through the vent 28. The sensor 29 again is a thick film semi-conductor device in which by gaseous diffusion changes in the vented fumes from the gear box 20 are detected and an indicator signal passed through a wire 30 to indication means (not shown) which in turn provides an indication of combustion or the possibility of combustion.

Possibly, where an oil system is vented through the centre of an engine, then a sensor in accordance with the present invention could be located in the vent. - 6

Fig. 3 is a schematic cross-section illustrating a bearing chamber 31 in which a bearing 32 is located. Oil 33 is projected towards the bearing 32 and air 34 passes in a jacket 35 about the bearing chamber 31 to provide cooling, some of which enters the bearing area through the rotary seals (not shown).

An air/oil mix 36 is vented or scavenged from the chamber 31. In accordance with the present invention a combustion sensor 38 is located in a part of the bearing chamber 31 where the sensor 38 remains in a gaseous location and so is not coated with lubricating oil 33. The sensor 38 includes a thick film semi-conductor device 37 in order to determine and sense changes in the gaseous content of the gaseous location.

In such circumstances, by using a thick film semi-conductor device 37 in accordance with the present invention and by gaseous diffusion into that sensor 38 variations in the gaseous content and in particular the presence of volatile constituents will enable a determination of the potential for combustion within the bearing chamber 31. Thus, the sensor 38 will be associated with appropriate indication means to show such combustion or the potential for combustion.

Operation of thick film semi-conductor devices as gas sensors is known. These thick film semi-conductor devices are principally used with respect to air-conditioning systems and particularly with respect to air quality. International Patent Application No. W0/93/08550 describes use of tin oxide sensors impregnated with noble metals to detect combustion gases, e. g. hydrogen, carbon monoxide, water vapour and temperature. The present invention utilises such thick film semi-conductor devices at such locations of stable gaseous presentation. Thus, the current gaseous composition presented to the sensor is analysed by the thick film semiconductor device. An appropriate variation in conductivity as a result of the gas diffusion into the device is utilised to provide an indication of the potential for combustion. It will be appreciated that a number of devices in accordance with thick film sensor technology may be optimised for different gaseous compositions or components. These respective sensors may all be incorporated upon the same semi-conductor substrate. Generally, a thick film semi-conductor device in accordance with known sensor technology takes the form of an element approximately the size of a typical eight pin dual in-line integrated circuit, and sensors for respective gases which are products of combustion (CO2, CO) as well as gases which are precursors to combustion (hydrocarbons, alkaloids, etc) are all incorporated in the same substrate. Each sensor is made by appropriate doping and etching in order to create the necessary response to respective gases diffused into the sensor.

By monitoring the relative differences between the gas compositions in the gaseous location within which the thick film semi-conductor device is located it is possible to predict occurrence of combustion at a far earlier stage in comparison with previous techniques. As indicated above, generally fire wire technology has previously been used but then sufficient heat energy is required to combust insulation between wires in order that there is electrical conductivity to indicate a fire. In situations where there is insufficient heat such as so-called cold combustion particularly prevalent with regard to bearing assemblies, such previous techniques are unacceptable. However, the present technique of analysing diffused gas adjacent a potential seat of combustion will detect such low energy combustion and with earlier predictability.

It is important that the thick film semi-conductor device providing the gas sensor in accordance with the present invention is located at a substantially gaseous position.

It will be understood that liquid and particles by their nature will not diffuse as readily and may effectively block consistent gas diffusion to the sensor for appropriate analysis and therefore combustion prediction. Furthermore, it is desirable to achieve the same environmental conditions about the sensor. It will be understood that varying gas pressures to the sensor will alter the rate of diffusion and therefore the response signals from the sensor and so the indication signal generated by the sensor determinant of combustion gas products or the onset of combustion by gaseous precursors.

Fig. 4 is a schematic illustration showing a thick film semi-conductor device 48 utilised in accordance with the present invention as a sensor for gas/vapour composition. Thus, the semi-conductor device 48 is located within a housing 40 which ensures a relatively stable gaseous location 41 whereby the gases within that location 41 can passively diffuse into the semi-conductor device 48 in order to provide - 8 appropriate indicator signals through connections 42. The housing 40 is secured to a wall 44 by appropriate fixings 45 for robust location. The device 48 is heated by electrical heaters coupled to connections 46 in order to achieve conventional semi- conductor gas sensor operation in terms of variations in the electrical conductivity between couplings 42 for diffusion gas both in terms of proportion and/or type.

Of particular concern with regard to ensuring a stable gaseous location within the chamber 41 is provision of a diffuser filter 47. This diffuser 47 allows infusion of gas into the chamber 41 but prevents access by particulate matter such as carbon particles.

Periodically, purge air flows will be presented through vents 43 in order to dislodge carbon, oil droplets and other particles caught by the filter 47. Similarly, the chamber 41 will be purged periodically in order to effectively "sniff" further gas about the housing in order to determine its gaseous composition and therefore onset or actual combustion through such gas sensor analysis.

Grooves in the filter 47 allow a gradual gas infusion into the chamber 41 such that the gas location about the thick film device 48 is relatively stable. It will be understood that if gas were projected or jetted towards the thick film device 48 such propulsion of the gas would create enhanced gas diffusion such that if the value of such gas jet pressure varied, so would the analytical accuracy of the thick film device 48.

Furthermore, baffle plates may be provided above the thick film device 48 to prevent direct jetting or flow of gas towards the thick film device 48. Such baffle plates will present an indirect path or labyrinth for gas flow whereby gas at a location above the sensor is stagnant or still and so diffusion controlled.

The device 48 as indicated previously is a semi-conductor device utilising thick film technology and gas diffusion in order to determine gas composition by variations in electrical conductivity. The device 48 may be single or double acting in the sense that it may detect combustion products, e.g carbon monoxide, carbon dioxide as a result of oil combustion, cold combustion and fires and/or ester aromatics indicative of hot oil and hydrocarbon breakdown as a precursor to combustion and/or alkaloids indicative of oil degradation due to elevated temperature and other stressed operation. - 9 -

Thick film semi-conductor sensor devices utilised as gas sensors in accordance with the present invention are more resistant to high temperatures and so can be located nearer to the combustion chamber of an engine or other potential seat of a fire.

In such circumstances, earlier indication of actual or prospective combustion can be achieved.

A semi-conductor device in accordance with the present invention may be an independent unit incorporating its own electrical supply through a battery and a radio transmitter for delivery of indicator signals as to combustion status. However, more normally, power supply will be provided to the thick film semi-conductor device through wires with a mineral heat insulating coating resistant to high temperatures. Similarly, indicator signals will be passed through appropriately protected cabling to a controller and an indicator device such as a display panel. Thus, in accordance with the present invention, it is simply necessary to secure the thick film semi-conductor device sensor through an appropriate adhesive or cement at a desired location and then bundle and secured the cabling as necessary in order to achieve a combustion sensor arrangement with little intrusion with regard to normal operation of an engine. The sensor may be surface mounted or retained within a cavity formed such that the sensor is flush with an engine or other surface. The sensor may be mounted flush to its housing (as shown) or end mounted (preferred if a double sided thick film sensor is used).

Typically, as indicated above a thick film semi-conductor sensor device in accordance with the present invention will provide individual indication signals dependent upon various gaseous constituents at the gaseous location of the sensor.

Thus, respective indicator signals for each gaseous composition will be presented to a controller in order to provide a consolidated indicator signal indicative of actual combustion or predictive combustion. The respective indicator signals may also present informative signals through a display panel of their particular gas constituent at the gaseous location. - 10

lt will be appreciated that there may be advantages with regard to calibrating the sensor periodically. Thus, the chamber 41 or gaseous location may be purged with a known inert gas such as nitrogen, argon or other such that a new cycle of gas diffusion is initiated for appropriate determination by the sensor and provision of indicator signals in order to allow the controller to determine current actual combustion or predictive combustion. On aircraft, to avoid a requirement for pressure vessels of purging gas, ducted air from the compressor and a comparator sensor may be used.

Fig. 5 is a schematic illustration of a control arrangement in accordance with the present invention. Thus, a sensor 51 is arranged as described previously at a gaseous location where gas diffusion into the sensor 51 presents indicator signals through connections 52 to a controller 53. These indicator signals are analysed by the controller 53 in order to provide a composite indicator signal through a connector 54 to stimulate an alarm 55 indicating actual combustion or potential onset of combustion.

The controller 53 also provides control signals to respective indicators 56 for different gas constituents at the gaseous location within which the sensor 51 is located.

The controller 53 also controls an electrical power supply 57 to ensure appropriate operation of the sensor 51 in terms of temperature and electrical current.

Furthermore, the controller 53 where required will periodically stimulate purge of the sensor 51 for recalibration and/or in order to dislodge particulate matter from a filter.

The control regime described with regard to Fig. 5 is clearly simplistic and highly schematic. In a practical installation a sensor incorporated within a combustion sensor arrangement in accordance with the present invention would be operated as part of a detailed engine management regime whereby detection of actual or predictive combustion will be utilised in order to alter engine performance and management to limit damage and/or prevent further combustion. It will also be understood that the indicator signals provided in accordance with the present combustion sensor arrangement will generally be logged and utilised with regard to engine servicing and predictive maintenance of the engine along with optimization of performance and reliability of that engine. - 11

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. - 12

Claims

1. A combustion sensor arrangement for an engine, the arrangement comprising a combustion sensor coupled to an indicator means (56) whereby upon detecting in use combustion the combustion sensor provides an indicator signal to the indicator means and the indicator means provides an indication of combustion, the arrangement characterized in that the sensor (5, 6, 29, 37, 48, 51) is a thick film semi-conductor device mounted to remain in a gaseous location (41) whereby in use variation in gas composition thereabouts is determined by gas diffusion into the device and the sensor thereby provides the indicator signal to the indicator means.

2. An arrangement as claimed in claim 1 wherein the thick film semiconductor device is surface mounted.

3. An arrangement as claimed in claim 1 wherein the thick film semiconductor device is mounted to protrude into the cavity.

4. An arrangement as claimed in claim 1 wherein the semi-conductor device is entrenched within a cavity.

5. An arrangement as claimed in any of claims 1, to 4 wherein the semiconductor device is coupled to the indicator means by a wireless connection.

6. An arrangement as claimed in any of claims 1 to 4 wherein the semiconductor device is coupled to the indicator means by wire connections (12, 30, 42, 52).

7. An arrangement as claimed in any preceding claim wherein the semiconductor device provides indicator signals dependent upon gaseous composition and the indicator means provides different indications dependent upon specific indicator signals received from the sensor. - 13

8. An arrangement as claimed in any preceding claim wherein the indicator means provides specific indications indicative of actual combustion and/or predictive combustion.

9. An arrangement as claimed in any preceding claim wherein the arrangement includes a gas diffuser and/or a particulate filter (47) in order to facilitate or selectively regulate gas diffusion into the sensor.

10. An arrangement as claimed in claim 9 wherein the particulate filter is a carbon filter, carbon foam, or carbon matrix.

11. An arrangement as claimed in any preceding claim wherein the arrangement includes stagnater baffles associated with the semi-conductor device in order to facilitate a still or stagnant gaseous location adjacent the semi-conductor device.

12. An arrangement as claimed in any preceding claim wherein the sensor is located about an engine cowling (2, 3) or ducting or adjacent a vent (28) for a bearing compartment or gearbox.

13. An arrangement as claimed in claim 11 wherein the sensor is mounted internal to an engine.

14. An arrangement as claimed in any preceding claim wherein the thick film semi- conductor device is of a chromium/titanium oxide (COO) type or a tungsten oxide (WO) type or a tin oxide type semi-conductor device maintained at a constant temperature whereby variations in gas diffusion composition stimulate variations in the electrical resistance across the film of the semi- conductor device to provide the indicator signal. - 14

15. An arrangement as claimed in any preceding claim wherein the semiconductor device is arranged to detect nitrogen dioxide and/or carbon monoxide and/or carbon dioxide and relative levels therebetween indicative of actual combustion.

16. An arrangement as claimed in any preceding claim wherein the semiconductor device is arranged to determine hydrocarbon contents within the gas diffusion indicative of oil and/or fuel and/or hydraulic fluid predictive of combustion onset.

17. An arrangement as claimed in any preceding claim wherein the semiconductor device is arranged to detect alkaloids to detect oil degradation.

18. An arrangement as claimed in any preceding claim wherein the semiconductor device is arranged to detect ester aromatics for too hot oil.

19. An arrangement as claimed in any preceding claim wherein the semiconductor device is associated with means to purge the gaseous location at least adjacent the semi-conductor device for calibrative and/or reinterrogation and/or regeneration purposes.

20. A combustion sensor arrangement substantially as hereinbefore described with reference to the accompanying drawings.

21. An engine incorporating a combustion sensor arrangement as claimed in any preceding claim.

22. A bearing compartment incorporating a combustion sensor arrangement as claimed in any of claims 1 to 16. -

23. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.