Vibrating element for use on an ultrasonic injection nozzle
TECHNICAL FIELD 
     This invention relates generally to an ultrasonic injection nozzle, and particularly to a vibrating element for use with ultrasonic atomizing apparatus for atomizing liquid intermittently or continuously, such ultrasonic atomizing apparatus including (1) automobile fuel injection nozzles such as electronically controlled gasoline injection valves or electronically controlled diesel injection valves, (2) gas turbine fuel nozzles, (3) burners for use on industrial, commercial and domestic boilers, heating furnaces and stoves, (4) industrial liquid atomizers such as drying atomizers for drying liquid materials such as foods, medicines, agricultural chemicals, fertilizers and the like, spray heads for controlling temperature and humidity, atomizers for calcining powders (pelletizing ceramics), spray coaters and reaction promoting devices,and (5) liquid atomizers for user other than industrial, such as spreaders for agricultural chemicals and antiseptic solution. 
     BACKGROUND ART 
     Pressure atomizing burners or liquid spray heads have been heretofore used to atomize or spray liquid in the various fields of art as mentioned above. The term &#34;liquid&#34; herein used is intended to mean not only liquid but also various liquid materials such as solution, suspension and the like. Injection nozzles used with such spray burners or liquid atomizers relied for atomizing the liquid on the shearing action between the liquid as discharged through the nozzles and the ambient air (atmospheric air). Thus, increased pressure under which liquid was supplied was required to achieve atomization of the liquid, resulting in requiring complicated and large-sized liquid supplying means such as pumps and piping. 
     Furthermore, regulation of the flow rate of injection was effected either by varying the pressure under which to deliver supply liquid or by varying the area of the nozzle discharge opening. However, the former method provided poor atomization at a low flow rate (low pressure), as a remedy for which air or steam was additionally used on medium or large-sized boilers to aid in atomization of liquid, requiring more and more complicated and enlarged apparatus. On the other hand, the latter method required an extremely intricate construction of nozzle which was troublesome to control and maintain. 
     In order to overcome the drawbacks to such conventional injection nozzles, attempts have been made to impart ultrasonic waves to liquid material as it is injected out through the jet of the injection nozzle under pressure. 
     However, the conventional ultrasonic liquid injecting nozzle had so small capacity for spraying that it was unsuitable for use as such injection nozzle as described above which required a large amount of atomized liquid. 
     As a result of extensive researches and experiments conducted on the ultrasonic liquid atomizing mechansim and the configuration of the ultrasonic vibrating element in an attempt to accomplish atomization of a large amount of liquid, the present inventors have discovered that large quantity of liquid may be atomized by providing an ultrasonic vibrating element formed at its end with an edged portion along which liquid may be delivered in a film form, and have proposed an ultrasonic injection method and injection nozzle based on said concept as disclosed in Japanese Patent Application No. 59-77572. 
     The present invention relates to improvements on the ultrasonic injection nozzle of the type according to the invention of the aforesaid earlier patent application, and particularly to improvements on the vibrating element for use with such ultrasonic injection nozzle. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a vibrating element for use with an ultrasonic injection nozzle which is capable of delivering liquid intermittently or continuously. 
     It is another object of the invention to provide a vibrating element for an ultrasonic injection nozzle which is capable of delivering and atomizing or spraying a large quantity of liquid with an increased spray spread angle. 
     It is still another object of the invention to provide a vibrating element for an ultrasonic injection nozzle which is capable of accompishing consistent atomization in that there is no change in the conditions of atomization (flow rate and particle size) depending upon the properties, particularly the viscosity of the supply liquid. 
     It is yet another object of the invention to provide a vibrating element for an ultrasonic injection nozzle which provides for stable and sustantailly consistent atomization even at a low flow rate, and hence permits a very high turndown ratio. 
     The aforesaid objects may be accomplished by the vibrating element for an ultrasonic injection nozzle according to the present invention. 
     Briefly, this invention consists in a vibrating element for use on an ultrasonic injection nozzle, said vibrating element being formed around its outer periphery with a multi-stepped edged portion having one or more projecting steps each defining an edge, said edges having the same diameter, said edged portion being adapted to be supplied with liquid. 
     Specific embodiments of the present invention will now be described by way of example and not by way of limitation with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fractionary cross-sectional view of one embodiment of the vibrating element for an ultrasonic injection nozzle according to this invention; 
     FIG. 2 is a cross-sectional view of one embodiment of an ultrasonic injection nozzle incorporating a vibrating element according to this invention. 
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Referring to the accompanying drawings and first to FIG. 1, one embodiment of the vibrating element for use with an ultrasonic injection nozzle according to the present invention is illustrated. 
     According to this invention, the vibrating element 1 is formed around its forward end with an annular edged portion 2 including one or more concentric steps, three steps (A), (B) and (C) in the illustrated embodiment. Each step defines an edge, the edge of said steps having the same diameter. 
     The shape of the edged portion 2 as viewed in the direction indicated by the arrow (X) is not limited to a circle but may be triangular, square or any other polygonal shape. 
     The geometry such as the width (w) and height (h) of each of the grooves cooperating to define the edges or steps (A), (B), (C) is such that the edge of each step may act to render the liquid flow filmy and to dam the liquid flow. 
     Studies and experiments have shown that with the vibrating element according to this invention having the edges of generally the same outer diameter, liquid spray is spread over a wider angle as viewed in cross-section, as compared to the prior art spray nozzle or ultrasonic injection nozzle. 
     While the edged portion 2 is illustrated as comprising the projections (A), (B), (C) of the same triangular shape in cross-section, the projections need not necessarily be triangulr but may be of any other shape, provided that they define edges around their outer periphery. 
     With the construction as described above, as liquid, which is fuel in the illustrated embodiment, is fed to the edged portion 2, the stream of fuel is severed and atomized at each edge due to the vertical vibrations imparted to the vibrating element. More specifically, fuel is first partially atomized at the edge (A) of the first step, and the excess portion of the fuel which has not been handled at the first step (A) is fed further through the second step (B) and the third step (C) to be handled thereby. It is to be understood that at a higher flow rate of fuel a larger effective area is required for atomization, requiring a greater number of stepped edges. At a lower flow rate, however, a smaller number of steps are required before the atomization of fuel is completed. With the vibrating element 1 according to the present invention, the number of steps required will vary with changes in the flow rate so as to insure generally uniform conditions such as the thickness of liquid film at the location of each step where the atomization takes place, resulting in uniform particle size of the droplets being atomized. The vibrating element of this invention provides a full range of flow rates usually required for atomization, so that atomization of various types of liquid material may be accomplished, whether it may be on an intermittent basis or on a continuous basis. 
     An ultrasonic injection nozzle 10 in which the vibrating element 1 constructed according to this invention is incorporated will be described with reference to FIG. 2. While the present invention is suitably applicable to injection or spray nozzles for various uses as indicated hereinbefore, it will be described with reference to a fuel injection nozzle for a gas turbine. 
     Referring to FIG. 2, an injection nozzle which is a fuel nozzle 10 for a gas turbine in the illustrated embodiment includes a generally cylindrical elongated valve housing 8 having a central bore 6 extending through the center thereof. A vibrating element 1 according to this invention is disposed extending through the central bore 6 of the valve housing 8. The vibrating element 1 includes an upper body portion 1a, an elongated cylindrical vibrator shank 1b having a diameter smaller than that of the body portion 1a, and a transition portion 1c connecting the body portion 1a and the shank 1b. The body portion 1a has an enlarged diameter flange 1d which is attached to the valve housing 8 by a shoulder 12 formed in the upper end of the valve housing and an annular vibaration retainer 14 fastened to the upper end face of the valve housing by bolts (not shown). 
     The forward end of the vibrating element 1, that is, the forward end of the shank 1b is formed with an endged portion 2. The lower portion of the valve housing 8 has one or more supply passags 4 formed therethrough for feeding said edged portion 2. Communicating with the upper end of the supply passage 4 is a radial fuel inlet port 16 which is in turn connected with an external supply line (not shown) leading to a source of fuel (not shown). The flow and flow rate of fuel are controlled by a supply valve (not shown) disposed in the external supply line. 
     With the construction described above, the vibrating element 1 is continuously vibrated by an ultrasonic generator 100 operatively connected to the body portion 1a. Liquid fuel is thus fed through the external line, the supply valve and the supply passage 4 to the edged portion 2 where the fuel is atomized and discharged out. 
     An example of various parameters and dimensions applicable to the ultrasonic injection nozzle according to this invention is as follows: 
     Output of ultrasonic vibration generating means: 10 watts. 
     Amplitude of vibration of vibrating element: 30 μm 
     Frequency of vibration: 38 KHz 
     Geometry of edged portion of vibrating element 
     Crests (edges: 7 mm in diameter 
     Valleys: 4 mm in diameter 
     Height (h) of each step: 1 mm 
     Fuel--Type of oil: gas oil, kerosene, gasoline 
     Flow rate: 0-0.06 cm 3  per injection 
     Injection pressure: 1-70 Kg/cm 2   
     Temperature: normal temperature 
     Material for vibrating element: Titanium (or iron). 
     It is to be appreciated from the foregoing description that the vibrating element according to this invention is capable of spray-spreading liquid over a wider angle, atomizing a large amount of liquid, and accomplishing consistent atomization with no change in the conditions of atomization (flow rate and particle size) depending upon the properties, particularly the viscosity of the supply liquid, as compared to the conventional vibrating element used with spray nozzles or ultrasonic injection nozzles. Furthermore, the present vibrating element provides for stable and substantially consistent atomization even at a low flow rate, and hence permits a very high turndown ratio.