GB1578418A

GB1578418A - Fuel injectors

Info

Publication number: GB1578418A
Application number: GB2252678A
Authority: GB
Original assignee: Garrett Corp
Current assignee: Garrett Corp
Priority date: 1977-11-25
Filing date: 1978-05-25
Publication date: 1980-11-05

Description

(54) IMPROVEMENTS IN OR RELATING TO FUEL INJECTORS (71) We, THE GARRETT CORPORATION, a Corporation organised under the laws of the State of California, United States of America, of 9851-9951 Sepulveda Boulevard, P.O. Box 92248, Los Angeles, California 90009, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to fuel injectors.

One of the main functions of a fuel injector is to break up the injected fuel into small droplets; this is commonly known as atomisation. Various methods of achieving this result have previously been proposed.

According to one aspect of the present invention, a fuel injector comprises a hollow body whose interior space has an axis of symmetry, the interior space having the general shape of a body of revolution about the said axis of symmetry, and the injector also has a conduit projecting into the interior of the body, generally along the said axis, for the supply of fuel to the injector, and a first group of gas inflow passages spaced about the fuel supply conduit, and leading into the interior of the body and converging with the said axis, and a second group of gas inflow passages spaced around the body and leading into the interior of the body in directions tangential to the interior space of the body, and the body also has a relatively large exit opening opposite the fuel supply conduit.

In operation, gas is supplied to the first and second groups of gas inflow passages, and fuel is supplied through the fuel supply conduit. The gas streams flowing through the passages of the first group intersect with and break up and atomise the fuel stream, while the gas streams flowing through the passages of the second group produce further breaking up and atomisation of the fuel stream, the combined effects of the gas streams passing through the two groups of passages creating a substantially atomised fuel fog which leaves the exit opening with axial and circumferential components of velocity. This result is achieved without the need to supply the fuel to the injector at a high pressure, and without using a particularly fine jet to deliver the fuel at the injector. The danger of clogging of the fuel passage is therefore reduced.In many cases, the two groups of gas supply passages may be supplied with air from the main supply of combustion air, so that no auxiliary gas supply is needed to atomise the fuel.

One possible application for the invention is in gas turbine engines. In such engines, it may be desirable to use an annular combustor with a plurality of fuel injectors spaced around the combustor. With a small engine such as an auxiliary power unit for an aircraft, the total fuel flow is not particularly large, and therefore, if an injector design were used which requires a fine jet, it would probably not be practicable to divide the total fuel flow between a number of injectors, since this would require a further reduction in the jet size. The inven- tion may make it possible to subdivide the fuel flow in such a case between a number of injectors, without using small jets which are prone to clogging.

The invention may be carried into practice in various ways, but one specific embodiment will now be described by way of example, with reference to the accompanying drawings of which: Fig. 1 is a section through a gas turbine engine having fuel injectors embodying the present invention; Fig. 2 is an enlarged fragmentary vertical section of a combustor and the fuel injector forming part of the engine of Fig. 1; and Fig. 3 is an enlarged vertical section taken on the line 3-3 of Fig. 2.

The fuel injector 10 of this invention is shown generally in Fig. 1 in conjunction with an annular-type combustor 12 of a turbine engine 14. As shown, the engine 14 comprises a housing 15 forming an air intake 16 through which air is drawn and compressed by a first compressor 18. The compressed charge air is delivered through a crossover duct 20 to a second compressor 22 for additional compression, and then to a turbine plenum chamber 24 for supply to the combustor 12 having an annular shape.

More specifically, the compressed air flows into the combustor 12 primarily through a series of flow openings 28 for admixture and combustion with fuel supplied by a plurality of peripherally disposed "run" fuel injectors 11. The products of combustion enter a power turbine section 30 which is shown including three power turbines 32.

The energy in the exhaust gases is transferred to the turbines 32 to cause rotation of a power shaft 34 via which suitable work may be performed.

The combustor 12 is shown in detail in Figs. 1 and 2. As shown, the combustor 12 comprises a cylindrical canister 36 having radially inner and outer walls 38 and 40, respectively, forming an annular combustion chamber 42. Air compressed by the dual compressors 18 and 22 is supplied to the turbine plenum chamber 24 which surrounds the combustor 12, and enters the combustion chamber primarily through the series of flow openings 28 formed along the length of the combustor inner and outer walls 38 and 40. Products of combustion within the combustion chamber 42 exit the combustor 12 via a downstream exit passage 44 for supply to the power turbine section 30 of the engine. The products of combustion drive the turbines 32 in the power turbine section 30 which, in turn, drives the compressors 18 and 22 and the output shaft 34, all in a well known manner.

The upstream end 46 of the combustor 12 includes an annular wall 48 joining the radially inner and outer walls 38 and 40 of the combustor 12. This annular end wall 48 includes a plurality of central openings 50 formed about its circumference, and these central openings provide mounting positions for a plurality of fuel injectors 10 and 11 for injecting fuel into the combustion chamber. In normal operation of a turbine engine of the type shown in the drawings, one or more of these fuel injectors comprises a socalled "start" nozzle 11 for use during startup. These start nozzles inject and atomize relatively high pressure fuel into the combustion chamber to provide ignition and engine acceleration during start-up.These start nozzles are combined with suitable ignition means such as a spark electrode (not shown) for obtaining flame propagation within the combustion chamber 42 to accelerate the engine to idle speed. The fuel supply to the start nozzzles may be cut off when idle speed is achieved and the fuel injectors 10 of this invention are supplied with fuel to maintain normal engine operation.

One of the fuel injections 10 of this invention is shown in detail in Figs. 2 and 3, and comprises a relatively low pressure injectoratomizer for maintaining the engine in a running condition. As shown, the injector 10 comprises a generally cylindrical or cupshaped hollow nozzle 52 formed from a suitable temperature resistant material such as ceramic or stainless steel, and received partially through one of the combustor end wall openings 50. The nozzle 52 includes a peripheral, outwardly extending flange 53 which is suitably retained with respect to the annular combustor end wall 48 as by welding or brazing, or by clips (not shown) to account for differences in thermal expansion of the combustor and engine housing materials.The nozzle 52 is formed to have an entrance end wall 54 or base through which fuel is received, and an exit end 56 opening into the combustion chamber 42 of the combustor.

Fuel is supplied to the nozzle 52 via a fuel line 58. More specifically, the fuel line 58 supplies fuel from a fuel supply and pumping means (not shown) through the engine housing 15 and turbine plenum chamber 24 to the interior of the nozzle. The fuel line 58 is received through and supported within a central passage 59 in the entrance end wall 54 of the nozzle 52 whereby a continuous stream of fuel is supplied to the nozzle interior generally along the longitudinal axis of the nozzle. Importantly, this stream of fuel is supplied to the nozzle in a manner to provide a relatively low pressure drop across the nozzle, say on the order of up to about 50 psi. Conveniently, if desired, the fuel line terminates slightly beyond the nozzle end wall 54 within the nozzle interior, for reasons which will become more apparent.

A portion of the compressed charge air within the turbine plenum chamber 24 flows into the nozzle interior through a plurality of angularly disposed air impingement openings 60. These air impingement openings are formed in the nozzle entrance end wall 54 in an equiangular arrangement about the fuel line 58. The impingement openings 60 extend generally axially with respect to the longitudinal axis of the nozzle, and anle inwardly toward said nozzle axis. In this manner, the impingement openings direct a series of air jets comprising a portion of the combustor air flow angularly inwardly to intersect at the fuel stream to break up and shear said fuel stream into finely atomized droplets, and to help carry the fuel axially toward the combustion chamber 42 largely independent of the nozzle pressure drop.

Conveniently, as shown, the termination point of the fuel line 58 is slightly upstream of the point of intersection of the air passing through the impingement openings so that the fuel exiting the fuel line 58 is immediately picked up by the impingement air This configuration is particularly advan tageous at relatively low fuel flows in that possible dripping of fuel down the nozzle end wall 54 is prevented.

The fuel injector 10 of this invention also includes a series of tangentially oriented air swirl openings 62 formed in the nozzle downstream of the impingement openings 60.

More specifically, the tangential swirl openings are generally equiangularly arranged about the nozzle and generally radially displaced of the point of intersection of air passing through the impingement openings.

The swirl openings 62 allow passage of a series of swirl air jets comprising another portion of the combustor charge air into the nozzle interior with a velocity generally tangential to the nozzle inner diameter and normal to the longitudinal nozzle axis. This secondary swirl air picks up the fuel fog and droplets along with the impingement air, and imparts a swirling circumferential velocity to this air-fuel mixture. Further, the swirl air prevents the fuel from collecting or condensing on the inner surfaces of the nozzle to assure uniform fuel distribution and to help minimize combustor smoke and carbon formation. The result is a finely atomized cloud of air and fuel which is carried into the combustion chamber 42 for combustion as a generally conical, substantially evenly distributed and expanding cloud.This expanding conical shape is enhanced by an outward conical taper 64 of increasing inner diameter at the exit end 56 of the nozzle. If required, an outward taper could, of course, be provided along a much greater part of the length of the nozzle.

In operation, one the engine is accelerated to idle speed by means of the ''start" nozzles 11, continued engine operation is sustained by the atomized fuel flow from the air blast type "run" nozzles 10 of this invention.

These nozzles 10 operate at a comparatively Jow fuel pressure drop to finely atomize the fuel supplied to the combustor through the use of combustor air flow only. Accordingly, expensive high pressure fuel pumping elements and auxiliary air supplies and equipment are avoided. Moreover, the compact, integral nozzle construction minimizes the nozzle mass for retaining heat upon combustor shut-down, and thereby also minimizes the risk of gumming or coking of the fuel line.

A variety of modifications of the fuel injector of this invention are believed to be possible within the scope of this application.

For example, the angular positions and sizes of the impingement openings, and the sizes of the tangential swirl openings and the fuel line may be varied as desired to suit a given application. Moreover, the end of the fuel line within the nozzle may be tapered to correspond with the shape of the intersecting impingement air jets to allow the fuel line to terminate as close as possble to the air jet intersection point without interfering with the air flow. The material forming the injector nozzle may be selected from a wide våriety of materials according to the fuel used and the temperature levels encountered, and à wide variety of contaminated and/or highly viscous fuels may be successfully used. These and other modifications are believed to be contemplated by the descrip- tion herein and encompassed by the ap

Claims

pended claims.

WHAT WE CLAIM IS:- 1 A fuel injector comprising a hollow body whose interior space has an axis of symmetry, the interior space having the general shape of a body of revolution about the said axis of symmetry, and the injector also having a conduit projecting into the interior of the body, generally along the said axis, for the supply of fuel to the injector, and a first group of gas inflow passages spaced about the fuel supply conduit, and leading into the interior of the body and converging with the said axis, and a second group of gas inflow passages spaced around the body and leading into the interior of the body in directions tangential to the interior space of the body, and the body also having a relatively large exit opening opposite the fuel supply conduit.
2. An injector as claimed in Claim 1 in which the interior space of the body increases in diameter towards the exit opening, at least in the zone adjacent the exit opening.
3. An injector as claimed in Claim 1 or Claim 2 in which the fuel supply conduit and the first group of gas inflow passages enter the interior space through a generally flat wall portion of the body.
4. An injector as claimed in Claim 1 or Claim 2 or Claim 3 in which the gas inflow passages of the first group are generally equiangularly spaced about the said axis.
5. An injector as claimed in any of the preceding Claims in which the gas inflow passages of the first group converge towards a common point which lies on the said axis of the interior space.
6. An injector as claimed in Claim 5, in which the gas inflow passages of the second group lie in or close to a plane normal to the said axis of the interior space and passing through the said common point.
7. An injector as claimed in Claim 5 or Claim 6 in which the fuel supply conduit terminates slightly upstream of the said common point.
8. An injector as claimed in any of the preceding Claims, in which the first group of gas inflow passages comprises at least three passages.
9. An injector as claimed in any of the preceding Claims, in which the second group of gas inflow passages comprises at least three passages.
10. An injector as claimed in any of the preceding Claims, in which the gas inflow passages of the second group are generally equiangularly spaced around the interior space.
11. An injector as claimed in any of the preceding Claims, which includes a common source of gas arranged to supply gas to the inflow passages of both the first and second groups.
12. A fuel injector comprising a hollow body whose interior space is generally cupshaped, having an open end, and a base which extends generally at right angles to an axis of symmetry of the interior space, and the injector also having a conduit projecting through the base into the interior of the body, generally along the said axis, for the supply of fuel to the injector, and a first group of gas inflow openings spaced about the fuel supply conduit and leading into the interior of the body and converging with the said axis towards the open end of the body, for passage of a plurality of combustionsupporting gas streams into the body to break up and atomise the fuel stream, and a second group of gas inflow openings spaced around the body and leading into the interior of the body in directions tangential to the interior space of the body, for passage of another plurality of combustion-supporting gas streams into the body for further breaking up and atomising the fuel stream, the combined effects of the gas streams passing through the two groups of openings creating a substantially atomised fuel fog exiting the open end of the body with axial and circumferential components of velocity.
13. A fuel injector substantially as herein described, with reference to Figs. 2 and 3 of the accompanying drawings.
14. A combustion arrangement comprising a combustor providing a combustion chamber, a fuel injector as claimed in any of the preceding Claims arranged to inject fuel into the combustion chamber, and means arranged to supply air to the combustion chamber.
15. A combustion arrangement as claimed in Claim 14 when appendant to Claim 11 in which the air supplying means constitutes the said common source of gas.
16. A combination comprising a combustion arrangement as claimed in Claim 14 or Claim 15, and means arranged to be operated by exhaust gases from the combustor to activate the air supplying means, the fuel injector being arranged to be supplied with fuel when the air supplying means has been activated, and the combination also including a starting fuel injector arranged to inject atomised fuel into the combustion chamber, and means arranged to ignite such atomised fuel to initiate operation of the air supplying means.
17. A combination as claimed in Claim 16, in which the combustor is annular in shape, and is provided with a plurality of fuel injectors as claimed in any of Claims 1 to 13, spaced around the combustor, and in which the starting fuel injector comprises a fuel injector nozzle connected to means arranged to supply fuel at a comparatively high pressure.
18. A combination as claimed in Claim 16 or Claim 17, which constitutes a gas turbine engine.
19. A method of injecting fuel into a combustor having a combustion chamber comprising the steps of forming a generally cylindrical fuel nozzle having a wall at a fuel entrance end and a relatively open exit end opening into the combustion chamber; passing a stream of fuel through a conduit extending through the wall and projecting into the nozzle generally along the ]ongitudinal axis thereof; passing a plurality of combustion-supporting gas streams through gas impingement openings opening into the nozzle axially along and angularly inwardly toward the fuel stream to break up and atomise the fuel stream; passing another plurality of combustion-supporting gas streams through tangentially oriented swirl openings into the nozzle downstream of the impingement openings to further break up and atomise the fuel stream, whereby the combined effects of the gas streams creates a substantially atomised fuel fog supplied to the combustion chamber with axial and circumferential components of velocity.