EP0152177A2

EP0152177A2 - Liquid fuel sprayers

Info

Publication number: EP0152177A2
Application number: EP85300255A
Authority: EP
Inventors: John Frederick Stratton
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1984-01-21
Filing date: 1985-01-15
Publication date: 1985-08-21
Also published as: EP0152177A3

Abstract

In order to obtain efficient atomisation of fuel at low air pressures of theorder of 1 inch of water (249 Pa), a fuel , sprayer which is designed to produce a flat fan-shaped spray of fuel from a discharge slot (14) is provided with a plurality of discrete air outlets (19 or 124,125) which are inclined so as to produce discrete air jets which are directed at different portions of the flat fan-shaped spray so as to disturb said portions.

Description

This invention relates to a liquid fuel sprayer and is more particularly, though not exclusively, concerned with liquid fuel sprayers for gas turbine engines.
For optimum efficiency of combustion, it is advantageous to obtain efficient atomisation of liquid fuel even at low fuel and air pressures. In gas turbine engines, very low fuel and air pressures occur during engine start-up. For example, gauge air pressures as low as 0.036 psig(l''H₂0 or 249 Pa) are obtained from the compressor and liquid fuel pressures as low as 5 to 6 psig (34.6 to 41.5KPa) are available from the fuel pump at engine start-up. Liquid fuel sprayers which produce a flat-fan shaped spray are known from, for example, GB 1269123, 1269214 and 1269215. Such flat fan-shaped spray patterns are obtained by discharging fuel through a slot intermediate the ends of a tube which is fed from both ends with fuel and by arranging such a slot to discharge into one side of an air passage having a larger slot in its opposite side so that the two slots are mutually aligned. The larger discharge slot is provided intermediate the ends of the air passage which is fed with air under pressure from both ends. Such a device gives effective atomisation at 5 to 6 psig (34.6 to 41.5 KPa)fuel pressure and at an air pressure of 2 to 2¹/₂ inches of water (498 - 622 Pa). However, at very low gauge air pressures of the order of 1 inch of water (249 Pa) referred to above, the above described flat, fan-shaped spray pattern does not give effective atomisation.
It is per se known to provide a conical discharge pattern by discharging liquid fuel through an axial bore and to expand the cone angle by discharging the liquid into a swirling air pattern downstream of the fuel outlet. However, even at air pressures at 2 to 2¹/2 inches of water (498 - 622 Pa), such a conical spray pattern does not give effective fuel atomisation as a large amount of energy is dissipated in imparting the swirl and is not transferred to the fuel which therefore tends to be discharged in large drops rather than fine atomised droplets.
It is an object of the present invention to provide an improved liquid fuel sprayer which enables efficient atomisation even at very low air pressures.
According to the present invention, there is provided a liquid fuel sprayer comprising a fuel passage, a discharge slot arranged to discharge fuel from said fuel passage so that the fuel is discharged as a flat fan-shaped spray, an air passage externally of said slot, and a plurality of discrete air outlets fed from said air passage, said discrete air outlets being inclined so that, in use, a discrete jet of air is discharged from eacb air outlet in the direction of the flat fan-shaped spray so as to disturb a respective portion of said spray and thereby promote more effective atomisation of the fuel, said discrete air outlets being positioned so as to act on different portions of the flat fan-shaped spray issuing from said slot in use.
In one embodiment, a pair of said discrete air outlets is provided, the air passage surrounds said fuel discharge slot and an air swirler device is provided in said air passage so as to impart a swirl to air which does not pass through said discrete air outlets, said discrete air outlets being disposed between said air swirler device and said fuel discharge slot and being positioned on opposite sides of the latter so as to deflect the respective edges of the flat fan-shaped spray, in use, in the direction of swirl of air passing through the air swirler device.
In said one embodiment, it is preferred for the air swirler device to be disposed downstream of said discrete air outlets relative to the general direction of flow of air in said air passage.
In certain cases, it may desirable to provide an extended length of passage between said air swirler device and a final discharge outlet of the sprayer.
In another embodiment, said discrete air outlets are arranged in sets which are disposed above and below the slot, the outlets in the sets being mutually staggered.
Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Fig. 1 is an axial section through a downstream end of a liquid fuel sprayer according to one aspect of the present invention,
Fig. 2 is an end view of the sprayer of Fig. 1,
Fig. 3 is an axial section through the downstream end of another liquid fuel air sprayer according to the present invention and
Fig. 4 is a section on the line A-A of Fig. 3.

Referring now to Figs. 1 and 2, the liquid fuel sprayer illustrated therein comprises a fan sprayer which, in this embodiment, is of the general type illustrated in Figs. 1 to 5 of British Patent No. 1269215.
Briefly, such a fan sprayer comprises a liquid fuel tube (not shown) which is provided with a fuel discharge slot 10 cut across a hypodermic tube -11 intermediate the closed ends of the latter. Slots (not shown) adjacent the ends of the tube 11 provides communication between the fuel tube and the hypodermic tube 11 so that liquid fuel passing under pressure from the liquid fuel tube enters each end of the hypodermic tube 11 to emerge from the fuel discharge slot 10 as a flat fan-shaped spray. The liquid fuel tube is disposed in a casing 12 having a configurated end wall 13 which defines a passage extending transversely of the casing 12. The transverse passage has an intermediate fuel/air discharge slot 14 tnerein aligned with the outlet slot 10. The fuel discharge outlet slot 10 is smaller in area than the discharge slot 14 and is disposed on the opposite side of the transverse passage to the slot 14. This construction causes a horizontal, flat fan-shaped spray of liquid fuel to be discharged from the discharge slot 14.
The above-described fan sprayer is mounted axially in a cylindrical air casing 15 so that an outer, annular air passage 16 is defined between the casings 12 and 15. Adjacent its downstream end, the casing 12 is rigidly secured to an annular support 17 which is itself rigidly connected to the casing through the intermediary of a multiplicity of mutually inclined air swirler blades 18 which are orientated relative to the direction of flow of air to the passage 16 so as to impart an anti-clockwise swirl (as viewed in Fig. 2) to air passing between the blades 18. The majority of the air from the air passage 16 passes between the blades 18. However a small proportion of the air passes through a pair of small diameter, discrete bores 19 which are drilled through the annular support 17. These bores 19 are arranged to discharge onto diametrically opposed sides of the fan sprayer. As can be seen from Figs. 1 and 2, each bore 19 has radial and axial components in its direction of extent and is so arranged that it extends forwardly and inwardly to terminate adjacent to but behind the end wall 13 of the casing 12. As can be seen from Fig. 2, the bores 19 discharge adjacent to but on opposite sides of the horizontal plane 20 of discharge of fuel from the slot 14. The angle of inclination of the bores 19 in the axial direction is approximately 45°.
Downstream of the fan sprayer, the air casing 15 curves inwardly at 21 in the region of the outer peripheries of the blades 18 and is provided with an inwardly directed annular lip 22 defining a final discharge opening 23 of circular shape which is centred on the coincident axes of the casings 12 and 15. As can be seen from Fig. 2, the bores 19 are arranged to discharge just inwardly of the periphery of the discharge opening 23.
In use, the flat fan-shaped spray pattern of fuel which issues from the slot 14 towards the final discharge opening 23 is modified in shape by the air which passes through the discrete bores 19. The bores 19 are so positioned that, as viewed in Fig. 2, the left hand bore 19 deflects the left hand edge of the fan-shaped spray downwardly whilst the right hand bore 19 deflects the right hand edge of the fan-shaped spray upwardly.
Thus, the edge portions of the fan-shaped spray are deflected in an anti-clockwise direction as viewed in
Fig. 2, i.e. corresponding to the direction of swirl of the air from the passage 16 which passes between the air swirler blades 18. This action assists in ensuring that good mixing of the fuel and swirling air occurs and the net result is that an intimate mixture of air and fuel is discharged from the final discharge opening 23 as a conical spray pattern. It is found that by adoption of the above described combination of bores 19 and swirler, an effective atomisation of liquid fuel is obtained even at very low air pressures of the order of 1 inch of water (249 Pa) which exist during engine start-up.
In the above described embodiment, the bores 19 are arranged to discharge in the region of the configurated end wall 13 of the casing 12 and the swirler blades 18 have portions which are disposed forwardly and rearwardly of the configurated end wall 13. However, in a modification (not shown), the casing 15 projects to a much greater extent forwardly of the end wall 13 than is shown in Fig. 1 and the blades 18 and bores 19 are disposed in the extended portion of the casing 15 so that such parts are disposed downstream of the configurated end wall 13. In such a construction, the wall of the casing 15 may extend forwardly of the forward edge of the blades 18 to a considerable extent before turning inwardly to define the inwardly directed lip 22.
Referring now to Figs. 3 and 4, the liquid fuel sprayer illustrated therein incorporates the same fan-shaped liquid fuel sprayer as illustrated and described in Figs. 1 and 2. Accordingly, the same parts are accorded the same reference numerals. In this embodiment, the casing 12 is carried by a support 117 axially of a cylindrical air casing 115 so that an annular air passage 116 is defined between the casings 12 and 115. The casing 115 includes an inwardly curved end portion 121 disposed forwardly of the configurated end wall 13 of the casing 12. Such end portion 121 curves forwardly and inwardly away from the cylindrical part of the casing 115 before curving inwardly and rearwardly to define a pair of curved lips 122 which are spaced apart to define a slot 123. The end portion 121 is provided with a set of upper discharge orifices 124 and a set of lower discharge orifices 125 disposed above and below the slot 123. The orifices 124 and 125 of each set are disposed in respective horizontal planes. Each orifice 124, 125 is directed towards the plane of discharge of the fan-shaped liquid fuel spray at an acute angle (about 45°) relative to the axis of the casing 115 as viewed in Fig. 3. There are five orifices in each set. The orifices in each set are arranged in a similar manner and the arrangement of the orifices 125 is illustrated in Fig. 4. As shown in Fig. 4, the axis of the centre orifice 125 of the set has an axial component of direction whilst the pair of intermediate orifices 125 of the set are inclined with respect to the axis within the plane in which the axes of such orifices 125 lie. The outermost pair of orifices 125 are inclined at an even greater angle with respect to the axis of the centre orifice 125. As will be apparent from the fact that the orifice 124 illustrated in Fig. 3 is shown in dotted line whereas the orifice 125 in Fig. 3 is shown in full line, the sets of orifices 124 and 125 are mutually staggered. It will be appreciated from the above that some of the air which passes through the air passage 116 will pass through the sets of orifices 124 and 125 as discrete jets which will deflect the portions of the fan-shaped liquid spray produced by the fan sprayer. Because the orifices 124 and 125 are mutually staggered, the jets of air issuing therefrom will act on different portions of the flat fan-shaped spray so as, effectively, to deflect portions thereof alternately upwardly and downwardly with respect to the horizontal plane of discharge of the fan-shaped spray. This action enhances atomisation of the spray. It will be appreciated that the majority of the air passing through the passage 116 will be discharged with the fan-shaped liquid spray through the slot 123. This embodiment of air sprayer is also capable of producing effective atomisation of liquid fuel at very low air pressures of the order of 1 inch of water gauge (249 Pa).

Claims

1. A liquid fuel sprayer comprising a fuel passage, a discharge slot (14) arranged to discharge fuel from said fuel passage so that the fuel is discharged as a flat fan-shaped spray, and an air passage 16, 116) externally of said slot, characterized in that a plurality of discrete air outlets (19 or 124, 125) fed from said air passage (16, 116), said discrete air outlets (19 or 124, 125) being inclined so that, in use, a discrete jet of air is discharged from each air outlet (19, 124 or 125) in the direction of the flat fan-shaped spray so as to disturb a respective portion of said spray and thereby promote more effective atomisation of the fuel, said discrete air outlets (19 or 124, 125) being positioned so as to act on different portions of the flat fan-shaped spray issuing from said slot in use.

2. A liquid fuel sprayer as claimed in claim, wherein a pair of said discrete air outlets (19) is provided, the air passage (16) surrounds said fuel discharge slot (14) and an air swirler device (18) is provided in said air passage (16) so as to impart a swirl to air which does not pass through said discrete air outlets (19), said discrete air outlets (19) being disposed between said air swirler device (18) and said fuel discharge slot and being positioned on opposite sides of the latter so as to deflect the respective edges of the flat fan-shaped spray, in use, in the direction of swirl of air passing through the air swirler device (18).

3. A liquid fuel sprayer as claimed in claim 2, wherein the air swirler device to be disposed downstream of said discrete air outlets relative to the general direction of flow of air in said air passage.

4. A liquid fuel sprayer as claimed in claim 2 or 3, wherein an extended length of passage is provided between the air swirler device (18) and a final discharge outlet (23) of the sprayer.

5. A liquid fuel sprayer as claimed in claim 1, wherein said discrete air outlets (124, 125) are arranged in an upper set (124) and a lower set (125) which are respectively disposed above and below the slot (14), and said outlets (124) in the lower set are mutually staggered relative to said outlets (125) in the upper set.