Claims:
What we claim is
1. An arrangement for injecting liquid fuel into combustion air for an internal combustion engine comprising: a nozzle body having an end face, a nozzle inlet in said body, a fuel passage for feeding liquid fuel to said nozzle inlet, a nozzle outlet in said end face, vibrator means which when energized apply ultrasonic vibrations to said nozzle body, energization control means for said vibrator means responsive to engine operating data to energize said vibrator means during engine operation to produce periods of vibration varying in duration according to the momentary fuel requirement of the engine, and a normally closed valve in said fuel passage which valve is open only when said ultrasonic vibrations are applied to said nozzle body thereby to atomize fuel from said end face.
2. An arrangement as claimed in claim 1 wherein said valve is a solenoid valve.
3. An arrangement as claimed in claim 1, wherein the valve is movable in the nozzle body in the longitudinal direction of the nozzle so that the valve is opened by its inertia when the nozzle is longitudinally vibrated.
4. An arrangement as claimed in claim 3, wherein solenoid-actuating means, and means for energizing these actuating means to open the valve for the period of each vibration pulse, are additionally provided.
5. An arrangement as claimed in claim 3, wherein a valve seat is provided at the inlet to the nozzle passage and the valve is arranged to co-operate with said seat so as to be urged on to the seat by the pressure of the fuel fed to the nozzle.
6. An arrangement as claimed in claim 5, wherein the nozzle body is provided with a swirl chamber of a diameter substantially greater than the seat diameter, the valve seat being arranged at the transition from the swirl chamber to the nozzle, and an annular-section inlet passage being arranged coaxially with the nozzle and its swirl chamber, said passage being so constructed as to form helical ducts through which the fuel supplied passes into the swirl chamber.
7. An arrangement as claimed in claim 1, wherein said valve is a ball valve.
8. An arrangement as claimed in claim 7, wherein said ball valve is spring biassed to the normally closed position.
Description:
This invention relates to fuel injection devices and has for an object to provide improved nozzle arrangements for the injection of liquid fuel into a gaseous medium and may be applied to the injection of liquid fuel into the combustion air of a turbo-jet engine or other gas turbine or internal combustion engine.
In order to ensure effective atomization of liquid fuel during its injection into combustion air, for example into the combustion air supplied to the burners of a gas-turbine engine, within a wide range of fuel-supply rates, an injection-nozzle arrangement has been proposed which will hereinafter be referred-to as of the kind specified, and in which the fuel-injection nozzle is arranged to be subjected to vibrations, generally at ultrasonic or similar frequencies hereinafter called ultrasonic vibrations, the amount of fuel injected within a given period, for example within a revolution of the engine, being arranged to be controlled by varying the length of time in which the ultrasonic vibrations are applied, and thereby varying the length of time of injection, in each such period. In order to make this control effective, and also to avoid the injection of inadequately atomized fuel, it is necessary in this case to avoid as far as possible the injection of any fuel during the periods at which no vibrations are applied, and for this purpose it has been proposed in British patent specification No. 1,138,536 to maintain the fuel pressure at the nozzle inlet just below the value at which fuel would pass from the nozzle into the gas stream in the absence of vibrations and in U.S. Pat. No. 3,613,649 it has been proposed, as an alternative solution to this problem, to inject the fuel through the nozzle in such a manner as to form, in the absence of vibration, a solid jet which extends across the flow of combustion air and is intercepted by a collector orifice, from which it is returned to the fuel system without reaching the combustion chamber, while when vibrations are applied to the nozzle, the jet is broken-up by the vibrations into small droplets which are conveyed by the flow of combustion air to the combustion chamber.
The present invention has for a more specific object to provide an arrangement of improved efficiency for effecting metered injection of liquid fuel into a flow of combustion air for a combustion engine with the help of a nozzle subjected to pulses of ultrasonic longitudinal vibrations, in which variation of the length of the pulses of vibration is utilized to vary the amount of fuel injected during each revolution of the engine.
According to the present invention the nozzle of an injection-nozzle arrangement of the kind specified is equipped at its inlet side with a valve, preferably a ball valve, which is arranged to normally close the inlet to the nozzle passage and thus to prevent the transfer of fuel to the combustion air but to be automatically operated to permit flow of fuel through the nozzle passage into the combustion air during the periods in which atomization is intended to be effective. In a preferred arrangement, in which periods in which the nozzle is vibrated in its longitudinal direction to render atomization effective, are separated by periods in which there is no such vibration, and the valve is arranged to be normally held on its seat by fuel pressure, which may be assisted by spring action, although the valve could, if desired, be alternatively so arranged that the fuel pressure tends to open the valve, which is normally held closed in this case by the opposite action of spring pressure. Inertia forces will effect, during the times in which longitudinal vibrations are applied to the nozzle, opening of the non-return valve to permit the flow of fuel. Alternatively the opening of the valve may be arranged to be effected by magnetic action upon the valve element, for example with the help of a solenoid coil which is energized to permit injection, during the periods of vibration of the nozzle, and if desired such an arrangement may also be used to assist the above-mentioned inertia operation. If magnetic operation is required, the valve element is made wholly or partly of magnetic material and is so arranged as to be urged in a direction away from its seat by the magnetic action of the energized solenoid.
In order that the invention may be more readily understood, reference will now be made to the accompanying drawing, in which:
FIG. 1 is a somewhat diagrammatic axial section of one embodiment of an injection nozzle arrangement according to the present invention, and
FIG. 2 is a fragmentary section illustrating a modification thereof.
Referring now first to FIG. 1, 1 indicates a passage, which may be the induction line of an internal-combustion engine, or, for example, a passage leading from the air-compressor unit to the burners of a turbojet engine or other gas-turbine E. In order to inject liquid fuel into the combustion air, which may be assumed to pass through the line 1 in the direction of the arrow A, a cylindrical nozzle portion 2 of an atomizer 3 is arranged to project with its end 2a through an aperture 4 in the wall of the passage 1 in such a manner as to provide substantially sealing co-operation while permitting mutual movement in the longitudinal direction of the portion 2. The cylindrical portion 2 forms a so-called horn at one side of the large-diameter portion 5 of a resonant stepped vibration amplifier which is attached at the opposite surface of the portion 5 to one side of a piezoelectric transducer element 6. A balancing body 7 is similarly attached to the opposite side of the transducer element 6, the arrangement being such that when an a.c. voltage of a given ultrasonic frequency is applied to the piezoelectric element 6 by means of wires 9 and 10, resonant ultrasonic vibrations in the longitudinal direction of the cylindrical horn portion 2 are applied to the large-diameter portion 5 of the vibration amplifier. The amplitude of the vibrations is magnified in horn portion 2, which is so dimensioned that maximum amplitude of oscillations is generated near the outer end 2a of the horn, which projects into the duct 1. Arranged coaxially in cylindrical horn portion 2 is a fuel passage 11, and in order to provide a spray nozzle, this passage 11 is formed, near the end 2a of the horn portion 2, with a restricted throat portion 12 which terminates in an outwardly flared cone portion 13, and the fuel passage 11 is formed at the opposite end of the throat portion with a conical valve-seat surface 14. The latter co-operates with a ball-valve element 15, which is normally held in contact with the seat 14 by a light spring 16. Liquid fuel under suitable pressure is admitted to the passage 11 by a transverse bore 17 formed in the portion 5 of the vibration-amplifier body, in which it is located near the nodal zone of oscillation.
With the arrangement as so far described, it will be readily appreciated that the co-operation of the ball-valve element 15 with its seat 14 will normally prevent any fuel from leaving the passage 11 through the nozzle 12 and thus being injected into the flow of combustion air in the duct 1. When, however, an alternating voltage of the appropriate ultrasonic frequency is applied to the piezoelectric transducer element 6 by the wires 9 and 10, the resultant resonant vibration of the end portion 2a of the cylindrical horn 2 of the resonant vibration amplifier will produce dynamic forces upon the ball-valve element 15 which lift the latter off its seat, thus permitting fuel from the passage 11 to pass through the nozzle passage 12 into the duct 1 and to produce there, while the ultrasonic vibrations take place, a spray of fuel, which is atomized by these vibrations to become intimately mixed with the flow of combustion air in the duct 1 and thus to produce the desired fuel-and-air mixture as long as the ultrasonic-frequency voltage is applied to the piezoelectric transducer element 6. As soon as the application of this ultrasonic-frequency voltage ceases, the ball valve 15 will return on to its seat 14 under the combined action of the fuel pressure in line 17, 11 and of its return spring 16, and will thus prevent the escape of fuel into the air stream in the duct 1 during the intervals between the pulses of ultrasonic vibration of the nozzle.
The means for producing the required pulses of energization for the transducer element 6 may be substantially as described in the above-mentioned British Patent Specification No. 1,138,536. They are schematically indicated in FIG. 1 as a pulse generator P mechanically coupled to the engine E and having in addition a control input C. An oscillatory voltage of the frequency of the desired ultrasonic vibrations is produced by an oscillator O energized with current from a battery B, a pulse generator P geing operative to apply this oscillatory voltage to the wires 9 and 10 in the form of the requisite pulses.
The illustrated embodiment also shows other means by which the ball valve 15 can be lifted off its seat 14 during the periods in which injection is desired, and which do not rely on the dynamic action of ultrasonic vibration of the cylindrical horn member 2. Although these means can be used independently, they are used in the illustrated embodiment to increase the rate of flow permitted by the ball valve above the rate achieved when inertia action during the vibration is exclusively relied-upon. They comprise a solenoid winding 18 arranged round the cylindrical horn portion 2 at a suitable axial position. This cylindrical horn portion 2 is made of non-magnetic material, while the ball valve element 15 consists of magnetizable steel or other ferromagnetic material. The winding 18 is so positioned that the valve element 15 will be lifted off its seat 14 by magnetic action when the solenoid winding 18 is energized. The energizing current is preferably direct current; otherwise the cylindrical portion 2 should be made of a material having sufficiently low electric conductivity to avoid undue screening action by induced currents. Suitable means are provided for timing the energizing current pulses for the winding 18 so as to coincide with pulses of ultrasonic-frequency current applied to the piezoelectric element 6. In the illustrated embodiment this is achieved by connecting the winding, via a rectifier arrangement 19, 20 across the wires 9, 10, as shown by chain-dotted connecting lines 9a, 10a. It will be readily appreciated by a person skilled in the art that the described solenoid arrangement may be modified in various ways, for example by combining a non-magnetic valve element with a magnetic armature connected to it for common movement, and that, on the other hand the function of the ball-valve arrangement in an ultrasonically vibratable nozzle is independent of any particular means applied for producing the ultrasonic vibrations.
It has been found that while the atomization of the fuel achieved by the application of ultrasonic vibrations to the nozzle is highly effective at low and medium rates of fuel supply, it tends to become inadequate beyond a certain flow rate for any given nozzle arrangement, and FIG. 2 illustrates a further development of the invention which in experiments has been found to improve considerably the effectiveness of atomization at such high rates of fuel supply while retaining the advantages of ultrasonic atomization at lower rates. In this arrangement, in which the same references as in FIG. 1 are used as in FIG. 1, and in which the parts not shown may be as shown in FIG. 1, the stem 2 is formed with a stepped bore having two parts 11a, 11b, the latter being in the form of a counterbore, in which a valve-seat member 14a forming the valve seat 14 and the nozzle passage 12, and a plug 21, which at its circumference is provided with helical grooves 22, are secured in axially spaced positions so as to leave between the plug 21 and the valve seat 14 a swirl chamber 23, in which the ball valve 15 is movable. This valve is normally held on its seat 14 by the pressure of the liquid fuel in the chamber 23, no spring having been found necessary in the tests carried out.
When during the application to the nozzle of longitudinal vibrations, liquid fuel passes through the nozzle at a relatively high rate, the rate of swirl produced at the circumference of the chamber by the flow through the helical passage 22 increases as the cross-section of the flow is constricted to pass through the small-diameter passage 12, thereby introducing effective swirl atomization action, and it has been found that such an effect can be achieved without the use of additional valve-operating means such as a solenoid arrangement.