Atomizing Devices For Liquid Fuel

Abstract

In the end portion of a fuel-atomization nozzle in which the fuel passage contains at its end pressure-atomization means as well as an end opening for atomization by ultrasonic vibration of the nozzle, the pressure-atomization means include a swirl plug having helical passages and, spaced from it by a swirl chamber, an orifice disc containing a final orifice of smaller diameter than the plug. Both the plug and the disc are secured in a larger-diameter counter-bore at the end of the fuel passage. They are secured in the counter-bore by electron-beam welding, the plug by radial spot welding through the wall, and the disc by a circumferential weld, which also forms seal closing the ends of the counter-bore.

Description

This invention relates to atomizing devices for liquid fuel and more particularly but not exclusively to liquid fuel burners for gas-turbine engines. Our co-pending British Patent specification No. 1,289,341 describes a gas-turbine engine having a fuel burner equipped with an injection device for liquid fuel wherein a passage for fuel under pressure terminates in an open orifice provided with a pressure-atomization nozzle, and an ultrasonic vibrator is so connected with the nozzle as to vibrate, when operative, the nozzle in the axial direction of the nozzle. The present invention has for an object to provide an improved nozzle arrangement terminating in an open orifice and it provides a pressure-atomization nozzle which is connected to such ultrasonic vibrator, for applying longitudinal vibrations to the nozzle, and wherein the nozzle is provided with helical swirl passages which produce circulation of the flow of fuel injected through a nozzle, and a more specific object of the invention is to provide an improved construction of such an arrangement, which will satisfactorily withstand for long periods the mechanical effect of the ultrasonic vibrations. The swirl passages of the swirl nozzle are preferably formed in a plug which is secured in a counter-bore at the end of the fuel passage of the nozzle.

The securing of this plug must withstand very considerable forces when the nozzle is subjected to ultrasonic vibrations, and according to a subsidiary feature of the invention, the necessary mechanical strength is obtained by spot-welding the plug in position through the wall of the passage, preferably by so-called electron-beam spot welding. This method of securing a plug provided with swirl passages in a longitudinal bore of a stepped-horn vibration transformer constitutes another aspect of the invention. The swirl passages are preferably formed as open grooves in the circumference of the plug, which co-operates with the wall surface of the counter-bore when the plug is inserted, and in order to facilitate manufacture, a number of spot-welds is preferably employed which differs from the number of the grooves so as to ensure that if one of the spot-welds faces one of the grooves and is therefore liable to block that particular groove, the other spot welds are positioned clear of the other grooves. In a typical case, four swirl grooves and three spot welds, all uniformly spaced round the circumference, may be employed.

The final orifice is preferably arranged in an orifice disc which is fitted into the end of the counter-bore and which is axially spaced from the outer end of the swirl plug so that the interposed part of the length of the counter-bore provides a swirl chamber between the end of the swirl plug and the disc containing the final orifice. The latter disc is preferably secured in the counter-bore by seam welding, preferably by electron-beam seam welding, with the electron beam applied in the axial direction so as to form a welded seam round the circumference of the orifice disc, thus ensuring sealing of the orifice disc in the counterbore as well as mechanically fixing it to the nozzle body.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawing, in which

FIG. 1 is an elevation showing the general construction of one form of atomizer nozzle according to the present invention, and

FIG. 2 is an elevation, drawn to a larger scale and partly in axial section, showing the end portion of the nozzle including the fuel passage, the swirl plug and the final-orifice disc.

Referring now to the drawings, the atomizing device illustrated comprises a stepped horn member 1 and a balance member 2, which are attached adhesively or by any other means to the opposite sides, respectively, of a piezoelectric-disc transducer 3, so that the latter will produce ultrasonic vibrations of the members 1 and 2 towards and away from each other when it is energised by the application of an alternating voltage of ultrasonic frequency to a pair of terminals 4, 5. The transducer 3 will transmit the ultrasonic vibrations on the one hand to the balance member 2 and on the other hand to the stepped horn member 1. The reduced-diameter horn portion 6 of the latter acts to increase the amplitude of the vibrations that appear at its outer end. A fuel passage 7 for the fuel to be ejected extends longitudinally through the horn portion 6 and leads the fuel to the opening 8a of an orifice disc 8, which the fuel reaches after passing through helical passages constituted by open grooves 9 in a cylindrical swirl plug 10. At its inlet end the passage 7 is joined by a radial passage 11, which is arranged in a plane central to the length of the transducer 3, and which serves for connection to an external fuel line 12; being arranged in the transverse plane of symmetry of the transducer 3, the radial passage 11 and the line 12 remain unaffected by the ultrasonic vibrations.

As will be seen more clearly, in FIG. 2, the outer end of the passage 7 is enlarged by the provision of a counter-bore 13, in which the swirl plug 10 provided with the grooves 9 forming the helical passages, and the orifice disc 8 which contains final orifice 8a, are secured in axially spaced relation so as to leave between them a swirl chamber 14. The plug 10 is also spaced from the bottom of the counter-bore 13 to provide, between the end of the small-diameter passage 7 proper and the larger-diameter plug 10, a distribution chamber 15 in which the flow of fuel from the passage 7 can spread in order to reach the helical grooves 9.

It is important that the swirl plug 10 and the disc 8 should each be firmly held in position because they have to withstand the action of ultrasonic vibration of the horn portion 6, and we have found that this can be achieved very satisfactorily by spot-welding the plug 10 to the wall of the counter-bore 13 with the help of electron beams applied radially to the outer surface of the horn portion 6 as indicated by the arrow Y. To ensure reliable operation of the swirler passages 9, it is necessary to ensure that at least the majority of these passages are not obstructed by the spot-welding operation, and while this could be achieved by a careful check on the angular position of the plug 10 about its axis in relation to the points at which spot welding is effected, we have found that such a check is generally unnecessary if the welds are uniformly spaced round the circumference and the number of welds employed differs in such manner from the number of swirl grooves 9 as to ensure that if one of the welds should be substantially in line with one of the swirl grooves 9, the other swirl grooves 9 will be clear of any welding spots. Thus it has been assumed in the illustrated example that three spot welds, uniformly distributed round the circumference of the horn portion 6, are used for securing a swirl plug 10 having four swirl grooves 9. The orifice disc 8, which contains the final orifice 8a, is also secured in position in the counter-bore 13 by electron-beam welding, but in this case the electron beam is applied in an axial direction at the circumference of the disc 8, as indicated by the arrow X. The weld produced extends continuously round the whole of the circumference of the disc 8 and thus ensures an effective seal between the circumference of the disc 8 and the wall of the counter-bore 13, as well as securing the disc 8 in position.

Claims

What we claim is:

1. An atomizing device for liquid fuel, comprising: an ultrasonic vibrator; a velocity-transformer body of the stepped-horn type having one end attached to the vibrator, said body having a bore extending along the axis thereof from the other end of said body and including a first portion, remote from said other end, and an adjoining second portion connecting said first portion to the said other end and being of larger diameter than said first portion; a swirl plug having a cylindrical external surface that is provided with helical grooves extending from one end to the other of said surface, said plug having substantially the same diameter as, and being coaxially accommodated in, said second portion of the bore with the end of the plug at a distance from the said other end of the transformer body, and being secured in position in said bore by a weld connecting at least some points on the circumference of the plug and the wall of the bore; and an end-wall member having a central orifice of a diameter substantially smaller than the diameter of said second portion of the bore, said end-wall member being sealingly secured to the transformer body by a weld, in a position in which said orifice is aligned with the bore, and in which the end member closes, apart from said orifice, the outer end of the bore and to face the adjacent end of the swirl plug at an axial distance therefrom.

2. A device as claimed in claim 1, wherein the swirl plug is secured in the bore by spot welds that join circumferentially spaced points on the plug to the wall of the bore.

3. A device as claimed in claim 2, wherein a plurality of helical grooves are uniformly spaced round the plug, and a number of spot welds are also uniformly spaced round the plug, the number of said spot welds being prime to the number of said grooves.

4. A device as claimed in claim 2, wherein said end-wall member is secured to the transformer body by an endless seam weld.

5. A device as claimed in claim 1, wherein said end-wall member is a disc fitting into the end of said bore adjacent to said other end of the velocity transformer and is secured to the wall of the bore by an endless seam weld.