GB2383120A

GB2383120A - Lamp with a conical diffraction grating for emitting a disc of light

Info

Publication number: GB2383120A
Application number: GB0130042A
Authority: GB
Inventors: John David Black
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2001-12-15
Filing date: 2001-12-15
Publication date: 2003-06-18
Also published as: GB0130042D0

Abstract

A lamp for illuminating the interior of structures comprises a rod 38 of transparent material with a conical end 40 on which is formed a diffraction grating. This end of the rod is placed in the interior to be illuminated, whilst the other end remains outside the interior and is exposed to a light source. Light travels along the length of the rod and is diffracted by the grating so that it is emitted as a disc of light to illuminate the interior surface. Preferably, the light is deflected through 90{ so that the disc of light is perpendicular to the rod. For light with a wavelength of 532 nm, a 10 mm diameter rod is used in conjunction with a diffraction grating of pitch 1717.4 lines / mm and the angle at the apex of the cone is 168.58{. The rod may be enclosed by a light trapping cover 42. The lamp may be used to inspect interiors or to provide illumination for photography during testing of fuel-air mixing in a combustion chamber 10.

Description

STRUCTURE INTERIOR ILLUMINATOR The present invention relates to a means with which the interior of a hollow structure may be illuminated. The invention has particular efficacy where a hollow structure, in an operative state, has a fluid and/or gaseous flow passing therethrough, which flow should not be diverted or distorted by an illuminating means being utilised within the hollow structure, so as to enable observation of the actual flow pattern obtained during the operative state.

The present invention also has efficacy where the internal surfaces hollow structure need to be illuminated for the purpose of discovering faults of any kind therein.

According to the present invention a structure interior illuminator comprises a rod of transparent material supportable for movement into the interior of a said structure along the axis thereof, that end extremity of said rod which in use enters said structure being conical, and has a diffraction grating formed thereon. The other end of said rod exterior to said structure being exposable to a light source and on said exposure said rod, via its length, guides said light to said diffraction grating which diffracts said light through an angle so as to cause it to radiate onto the interior surface of said structure in the form of a disc of light.

The invention will now be described by way of example and with reference to the accompanying drawings.

Fig 1 is a diagrammatic axial cross section part view of a combustion chamber including a transparent rod in accordance with an aspect of the present invention.

Fig 2 is an enlarged view of the conical end portion of the transparent rod of fig 1.

Referring to fig 1 a can type combustion chamber 10 has a frustum like end member 12, which terminates in a

tubular portion 13 containing a ring of swirl vanes 14. Swirl vanes 14 in turn support a fuel injection 16. A further frustum 18 is fixed to and in spaced relationship with the inner surface of frustum 12 via struts 20. A truly conical member 22 is fixed to and in space relationship with frustum 18 by struts 24.

A cylindrical member 26 has an expanded and crimped end portion 28 in know manner and is fixed thereby in overlapping manner to the end of a cylindrical portion 30 of member 12.

Combustion chamber 10 is the kind used in a gas turbine engine and its operation, though well known per se, is now explained so as to enable introduction of the present invention. During operation of combustion chamber 10, air from a compressor (not shown) is forced into and through the swirl vanes 14, and exit therefrom, into passages 32 and 34 defined between members 12 and 18 and members 18 and 22 respectively. At the same time fuel is injected from ejector 16 on to cone 22, and thence by deflection along passage 34 mixing with air therein as it does so. Finally all flows meet in the primary mixing zone 36 and mix together.

It is essential that the fuel and air mixes in the primary zone 36 in such a manner as to ensure efficient burning and so achieve a desired specific fuel consumption by an associated gas turbine (not shown), having regard to whatever engine thrust control lever setting is selected by the operator thereof. Further it is desirable that the designed mixing criteria is met before manufacturing the combustion chamber 10 in quantity and fitting the combustion chambers 10 so produced in an operating environment. To this end a combustion chamber 10 having been made is fitted in a test rig (not shown) which includes connecting the fuel injector to a fuel supply (not

shown) and connecting swirl vanes 14 to a compressed air supply. The rate of fuel and air flows are adjusted so that they should mix as desired in primary mixing zone 36, and if the mix were ignited a pre calculated gas flow at a pre determined velocity and temperature would result at the exit end (not shown) of a combustion chamber 10.

When the fuel and air supplies have been connected and switched on as described immediately hereinbefore, a transparent rod 38 which is capable of passing light through its length within loss laterally thereof, is inserted in the exit end (not shown) of combustion chamber 10, and caused to traverse its interior length. The rod 38 is round in a plane normal to its longitudinal axis, and its diameter is very small relative to the corresponding dimensions of the interior of combustion chamber 10.

Therefore the presence of rod 38 at the very centre of the mixed fuel and air flow will minimise in distortion or diversion of the mixed flow.

As rod 38 transverses the interior length of combustion chamber 10 driven by any suitable means (not shown), a light source (not shown) directs onto that rod end which does not enter combustion chamber 10. The light traverses the interior of rod 38 and radiates from its interior end in the form of a disk, ie in mean directions normal to the longitudinal axis of rod 38, thus illuminating the mixed fuel/air flow which immediately surrounds it. A camera (not shown) is appropriately positioned so as to enable the obtaining of a photographic record or electronically stored image of the mixing achieved.

Clearly as rod 38 traverses the interior of combustion chamber 10, any number of photographs may be taken, provided that the light source (not shown) is continuously activated.

Referring now to fig 2, turning of the light as it exits rod 38 is achieved by forming the exit end 40 into a cone, applying a photo resist on the cone and then producing a diffraction grating on the photo resist by known techniques. An example of one such arrangement is as follows: a 10 mm diameter transparent rod 38 encased in a light trapping cover 42 and terminating in a cone, the apex angle of which is 168. 58 , will transport a collimated beam of 532 nm light to its exit end and via a diffraction grating the pitch of which is 1717.4 lines/mm, will produce a first order diffraction thereof at 90 to the original beam direction.

Whilst the present invention was conceived when the applicant for a patent therefor was endeavouring to find ways of improving known illuminating means having flow interference problems, it is clear that the rod 38 as described can also be used for simply illuminating an interior surface for the purpose of exposing faults such as cracks or failed welds or the like.

Claims

CLAIMS 1. A structure interior illuminator comprising a rod of transparent material supportable for movement into the interior of a said structure along the axis thereof, that end extremity of said rod which in use enters said structure being conical and has a diffraction grating formed thereon, the other end of said rod exterior to said structure being exposable to a light source, and on exposure, said rod via its length, guides said light to said diffraction grating which diffracts said light through angle so as to cause it to radiate onto the interior surface of said structure in the form of a disk of light.
2. A structure interior illuminator as claimed in claim 1 wherein said diffraction grating diffracts said light through an angle of 90 .
3. A structure interior illuminator as claimed in claim 1 wherein said rod is round in planes normal to its axial length.
4. A structure interior as claimed in claim 3 wherein said rod has a diameter of 10 mm, the apex of said cone is 168. 580 and the pitch of the diffraction grating is 1717.4 lines/mm.
5. A structure interior substantially as described in this specification and with reference to the accompanying drawings.