AIRCRAFT ENGINE LUBRICANT CIRCULATION

Abstract

An aircraft engine circulation system comprises a conduit arranged in use to communicate a lubricant to and from one or more bearings of an engine. The conduits define a space which comprises a material that is selected to change phase at a predetermined temperature.

Claims

1.-33. (canceled)

34. An aircraft engine circulation system, comprising: a conduit arranged to communicate a lubricant to and from one or more bearings, said conduit comprising a central tube defining a passage for communicating lubricant and a peripheral tube surrounding the central tube and defining a space between the outer surface of the central tube and an inner surface of the peripheral tube, wherein the space includes a thermally induced phase changing material arranged to change phase when heated.

35. The system of claim 34, wherein the phase changing material is selected so as to change phase from a solid above a predetermined engine temperature.

36. The system of claim 35, wherein the phase changing material is selected to return to a solid phase below a predetermined engine temperature.

37. The system of claim 34, wherein the phase changing material is arranged to change or begin to change phase between 180 degrees C. and 250 degrees C.

38. The system of claim 34, wherein the phase changing material is arranged to change phase between 200 degrees C. and 250 degrees C.

39. The system of claim 34, wherein the phase changing material is arranged to change phase at 225 degrees C.

40. The system of claim 34, wherein the phase changing material is a salt selected from the group of organic or inorganic salts.

41. The system of claim 40, wherein the phase changing material is an H220 molten salt or an H105 salt.

42. The system of claim 34, wherein the phase changing material is a metal.

43. The system of claim 42, wherein the phase changing material is one of lithium, zinc, or lead, or an alloy of lithium, zinc, or lead.

44. The system of claim 43, wherein the phase changing material is an iron or iron containing alloy.

45. The system of claim 34, wherein the radial separation defined between the outer surface of the central tube and the inner surface of the peripheral tube is approximately constant.

46. The system of claim 45, wherein the radial separation of the outer surface of the central tube and the inner surface of the peripheral tube is between 0.5 millimeters and 1.5 millimeters.

47. The system of claim 34, wherein the radial separation of the outer surface of the central tube and the inner surface of the peripheral tube along the length of the conduit is non-uniform.

48. The system of claim 47, wherein the radial separation along the length of the conduit is selected according to a predetermined or predicted heating of the local region of the conduit.

49. The system of claim 48, wherein some regions of the conduit have a radial separation of zero millimeters.

50. The system of claim 34, wherein the tubes are at least one of (a) concentric and (b) having a same cross-sectional shape.

51. The system of claim 34, wherein the cross-sectional shape of the tubes is non-uniform along the length of the conduit.

52. The system of claim 34, wherein at least one of the radial spacing or concentricity of the central and peripheral tubes is selected according to a predicted or predetermined temperature of the tube in use along a specific length or the conduit during use.

53. The system of claim 34, further comprising a heat exchanger arranged to receive lubricant to and from the central tube.

Description

BRIEF SUMMARY OF THE DRAWINGS

[0081] Aspects of the disclosure will now be described, by way of example only, with reference to the accompanying figures in which:

[0082] FIG. 1 shows a simplified schematic of the principal components of an aero-engine bearing support and lubrication circuit;

[0083] FIGS. 2A, 2B and 2C show the progressive build-up of carbon or coking within an oil tube;

[0084] FIGS. 3A and 3B show a multi-layered pipe or tube according to an example;

[0085] FIGS. 4A and 4B show how the profile of the circuit tubes may modified to include tapering and or a stepped section;

[0086] FIG. 5 shows a central or inner tube which is not concentric with an outer tube;

[0087] FIG. 6 shows how the concept shown in FIG. 5 may be adjusted along the length of all or part of the circuit; and

[0088] FIG. 7 shows a graph illustrating temperature versus time after engine shut-down illustrating the advantageous effect of the present disclosure.

[0089] While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood however that the drawings and detailed description attached hereto are not intended to limit the invention to the particular form disclosed but rather the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the claimed invention.

[0090] It will be recognised that the features of the aspects of the invention(s) described herein can conveniently and interchangeably be used in any suitable combination.

DETAILED DESCRIPTION

[0091] FIG. 1 is a simplified schematic of the principal components of an aero-engine bearing support and lubrication circuit.

[0092] The engine 1 has an outer casing shown in dotted line. At the front of the engine (denoted by F for Front) a fan 2 is situated. The fan creates a proportion of the thrust which drives air towards the Aft (denoted by A) of the engine. As will be understood by the person skilled in the art of the operation of a gas turbine engine a central shaft 3 passes along the central axis of the engine 1. The shaft 3 couples the fan 2 to a turbine 4 located at the rear of the engine. In operation air is compressed by one or more compressors 5 and introduced into a combustor (not shown). The combustor ignites the compressed air with fuel which is directed to the turbine 4. Rotation of the turbine causes the fan to rotate which drives air towards the aft of the engine creating (in combination with the exhaust gas from the combustor) thrust to drive the aircraft forwards.

[0093] The central shaft 3 is rotationally mounted on a plurality of bearings 6A-6D which support the shaft and allow for rotational movement. The bearings operate at high speed and also high temperature owing to their position within the core of the engine which typically operate at 550° C. It is therefore necessary not only to provide a lubricant to the bearings to allow them to rotate but also to cool the lubricant.

[0094] A typical lubricant used in aircraft engines is an oil complying with SAE AS5780 manufactured by numerous oil manufacturers including BP, Exxon, Shell, Anderon and others.

[0095] The cooling circuit will now be described again with reference to the schematic shown in FIG. 1.

[0096] Each of the bearings 6A-6D is in fluid communication with a heat exchanger 7 by means of a supply conduit 8 and a return conduit 9. The flow paths shown in FIG. 1 are purely for illustration only and are shown merely to illustrate that each bearing is in fluid communication with the heat exchanger 7. The fluid is driven by a mechanical or electrical pump (not shown) which is driven either mechanically or electrically by the engine.

[0097] As described herein when the engine is switched off the circulation of the lubricant through the conduits 8, 9 stops and oil no longer moves through the heat exchanger which would ordinarily dissipate heat from the oil/lubricant. The oil then rapidly increases in temperature.

[0098] The coking problems discussed herein are caused by heating the oil lubricant to elevated temperatures which causes a chemical breakdown of the oil by oxidation and deposition of carbon on the hot surfaces of the inner wall of the conduits 8, 9. Specifically, the breakdown is a result of a chemical process with the influence of time, temperature, and presence of oxygen/air. For example, with the Arrhenius approach, the accumulated damage is the summed time at the damage exponential to the exposed temperature.

[0099] Referring to FIGS. 2A, 2B and 2C the progressive build-up of carbon or coking is illustrated. Over time (time extending between 2A to 2C) the coking builds up on the inner surface of the tube 9 slowly increasing in thickness and thus reducing the inner flow path 10 of the tube 9.

[0100] Conventionally this problem is solved by cleaning and/or replacement of the tubes during scheduled or emergency maintenance.

[0101] FIGS. 3A and 3B illustrate an example described herein.

[0102] Referring first to FIG. 3A a multi-layered pipe or tube 11 is shown that makes up all or part of the circulation path shown in FIG. 1. The pipe system comprising a central pipe 12 for communicating the oil. Surrounding the pipe 12 is a peripheral pipe 13 which in the example shown in FIG. 3A is concentric with the central pipe and spaced therefrom by a radial separation gap r.sub.s.

[0103] Each tube may be formed of any suitable material such as a steel alloy. The radial separation between the inner and outer (peripheral) tubes defines a space 14 which surrounds the inner tube 12. It has been established that by filling all or part of this space 14 with a material which changes phase at a predetermined temperature the inner tube 12 (and its oil content) can be thermally shielded or insulated.

[0104] Specifically, by introducing a thermally induced phase changing material into the space 14 exterior heat (which would normally be conducted through the pipe to the oil) can be absorbed. The heat is absorbed in changing the material from a solid state to a semi-solid or liquid phase.

[0105] Taking one example, the phase changing material may be selected as an inorganic salt selected from the table below. It may similarly be lead, lithium, zinc, amongst others.

[0106] Alloys of tin and lithium mixtures are also feasible as the Lead-Tin ASTM Sn50 or the Tin-Lead L13701 having a melting temperature approximately at 200° C.

[0107] FIG. 3B shows a cross-section of the system circuit with the central tube 12, peripheral tube 13 and phase changing material 15 filling the void between the two tubes.

[0108] FIGS. 4A and 4B illustrate how the profile of the circuit tubes may modified to include tapering and or stepped sections. The radial separation of the inner oil carrying tube can be spaced from the heated sides of the tube accordingly providing flexibility in design according to the specific heating of a given zone or region of an engine.

[0109] FIG. 5 shows a still further example arrangement. Here, the central or inner tube 12 is not concentric with the outer tube 13. This allows the amount of phase changing material between the oil carrying inner tube 12 and outer tube 13 to be controlled and adjusted. If for example the top of the pipe shown in FIG. 5 is particularly hot then moving the inner tube so as to be non-concentric with the outer tube increases the thickness of the phase changing material thereby increasing the amount of energy that it may absorb on the ‘hot’ side of the circuit.

[0110] FIG. 6 shows how the concept shown in FIG. 5 may be adjusted along the length of all or part of the circuit.

[0111] The combination of selecting the phase changing material and its thickness can advantageously be used to optimise the heat absorption capabilities of the system. Regions of excessive heat on engine shut-down can thus be provided with section of greater phase changing material thickness to absorb higher energy and prevent coking within the inner tube.

[0112] The conduit may be formed of a plurality of sections which maybe be manufactured in a conventional manner or formed using 3D additive manufacturing techniques.