GB2310457A

GB2310457A - Rotary fuel atomiser

Info

Publication number: GB2310457A
Application number: GB9615992A
Authority: GB
Inventors: Leslie George Abberton
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-02-22
Filing date: 1996-07-30
Publication date: 1997-08-27
Anticipated expiration: 2016-07-30
Also published as: GB2310457B; GB9603786D0; GB9615992D0

Abstract

A spray of fuel is produced by a rotor which resembles a miniature paddle-wheel having radial vanes 4 which are provided with atomising points 7 in the form of wire, glass, carbon or thermoplastics fibres 7 located in slots (6,fig.4) at the outer ends of the vanes 4. Drops of fuel are discharged by centrifugal force from the end points of the fibres 7 into air drawn by rotation of the rotor past the outer ends of the vanes 4. The rotor may rotate at 5350 rpm to produce droplets of 75 microns diameter from points 7 having diameters in the range 0.025 to 0.075 mm. An electric motor (21,fig.2) drives the rotor on a central stationary hub having nozzles (17) spraying fuel on to the inner ends of the vanes 4. One or more rotors may be mounted in an engine intake manifold.

Description

A ROTARY FUEL ATOMIZER Technical Field 1. The technical field is the problem of developing fuel atomizers capable of reducing every drop of fuel delivered to an IC petrol engine down to particles small enough to be completely and efficiently consumed during an engine's firing strokes.

2. Rotary atomizers are described in the McGraw-Hill Encyclopedia of Science and Technology Vol.2 (1987), and an earlier paper "The Atomization of Liquids by means of Rotating Cups" by J.O. Hinze and H. Milborne was published in J.Appl.Mech., 17, 145-153 (1950). A great deal of important additional work on this subject was described by A.R. Frost in an article published in J. Agric. Engng.

Res., 26, 63-78 (1981) under the title "Rotary Atomization in the Ligament Formation Mode". A number of illustrations from this article are shown, with Mr. Frost's permission, in this application as Figs. 5 to 8 inclusive.

3. When liquid is fed to the centre of a spinning disk, fine liquid 'ligaments' or jets of the type shown in Fig. 7 may develop on the edge of the rotor. Small droplets are emitted from the points of these jets and the resulting spray of fine particles forms an excellent fine cloud which would be useful for a number of purposes if this mode of droplet production could be maintained. However, variations in the liquid feed-rate or the angular velocity of the disk, or vibration, can cause these liquid jets or 'ligaments' to disintegrate and the droplet-production mode then changes to one similar to those shown in Figs. 5, 6 & 8 which are much less satisfactory. But if very fine, closely-spaced solid filaments or fibers referred to as atomizing points were employed to replace the ligaments or jets, then good atomization could be obtained without fear of the disintegration of these synthetic components. A liquid drop is detached from each atomizing point when the centrifugal force applied to the droplet is greater than the surface tension holding the drop to the fine point. If the diameter of an atomizing point is, say, 0.005 cm (0.002 inch) and the liquid (lead-free petrol in this example) has a surface tension of 25 dynes/cm then the total force holding the drop to the point is 0.393 dynes. The angular velocity required to remove a drop can be obtained by solving the following equation: Surface tension = centrifugal force i.e. 0.395 dynes = m.r.w2 (1) and if m = the mass of a 75 micron diameter droplet of fuel which is 0. 157x10-6 gramme of density = 0.7 and r = the distance of the atomizing point from the centre of rotation which is 8 centimetres in this example, w = angular velocity in radians/sec then, substituting these values into equation(l) and solving for w gives a value of 560 radians/sec (5350 rpm) for droplets of 75 microns dia.

Smaller drops can be produced by increasing the angular velocity, or the radius r or reducing the surface tension by employing atomizing points of smaller diameter.

Summary of the Invention 4. The object of the invention is the development of a liquid atomizer capable of reducing every drop of fuel fed to the device into particles small enough to be completely consumed during an engine's firing strokes. Liquid will be supplied to all the atomizing points continuously and when a droplet is dislodged the next quickly grows to the same size and mass as its predecessor and then it, too, is removed. Because the droplets are so small this occurs in an extremely small fraction of a second and a stream of droplets is produced from each atomizing point. Therefore, if a large number of atomizing points are employed a sufficient number of droplets can be produced to feed a petrol engine or for an agricultural spray. However, the complete reduction of only a single millilitre of liquid down to the size required necessitates the production of millions of droplets and a special rotor capable of supporting a large number of atomizing points is therefore required. A rotor shaped like a miniature paddle wheel, for use in air not water, is therefore employed since the number of vanes, 4, can be increased to enable it to hold the required number of atomizing points, 7, as seen in Figs 1, 2 & 3.

This device can therefore be constructed so as to enable ALL the liquid to be reduced to fine droplets, these all being identical if the atomizing points have the same dimensions. Modern methods of constructing lengths of fine wire or fibers are such that it would be difficult to detect any difference in diameter throughout the total length. Therefore the short lengths used for each point are almost identical and all the droplets produced form a spray with an extremely narrow drop-size spectrum.

Brief Description of the drawings 5. The present invention may be more fully understood by reference to the description when it is read in conjunction with the attached drawings, wherein: Fig 1 is a plan view of a section of a preferred embodiment of the invention.

Fig 2 is an elevation of a section through the device shown in Fig 1.

Fig 3 is a perspective view of the rotor vanes, 4, and the atomizing points, 7, on those vanes.

Fig 4 shows a strip of atomizing points as described in paragraph 6 fixed into a slot, 6, on a vane, 4. Also shown is the strip of points before they are fixed into the slot, 6.

Detailed Description of the Invention (Figs 1, 2, 3, 4) 6. The main component of the fuel Atomizer, the rotor (FIGS 2 & 3), is connected by the keyway, to the motor shaft, 2, which drives the rotor bottom plate, 3. This is connected to a plurality of items, 4, the vanes, which are joined to the rotor top plate, 5, thus forming a very rigid component. Each vane, 4, is provided with a slot, 6, (Fig. 1) into which the atomizing points, 7, are fitted as described in paragraph 7. The slots, 6, extend along the edges of the vanes, 4, the full distance between items 3 and 5. Each vane, 4, has a wedge-shaped end, 8, (Fig. 1) at the opposite end to the slot, 7. The sharp wedge-shaped end, 8, enables the liquid to be sprayed more easily on to both sides of the vanes, 4, than would be the case if this end, 8, were blunt. The stationary liquid distributor, 9, is supported between two bearings, 10 and 11, and is held stationary by the cover plate, 12, and the screw, 15, whichjoins 9 and 12. When the rotor is spinning item 12 is connected, (beforehand), to a stationary component. The liquid passes through tube, 14, into the connector, 13, and passes through the narrow channel, 16, to the nozzles, 17. The nozzles, 17, spray the liquid on to the wedge-shaped ends, 8, of the rotating vanes, 4, and the liquid then flows over the vanes under centrifugal force to the atomizing points from each of which it is emitted as a stream of individual droplets. Alternatively the delivery tube, 14, may be supplied with compressed air into which the liquid can be injected, and then, entrained in the compressed air, delivered to connector 13. It then passes on to the vanes as described above. If it were decided to deliver atomized fuel to an engine at a rate of one milliliter per second (3.6 litres/hour) the atomizer could be designed so that the rotor contained 60 vanes, 4; each with a slot, 6, into which a doubleedged flexible strip of atomizing points (see paragraph 7) may be located. Each strip if six cm long could hold sixty atomizing points on each edge at one millimetre intervals, ie. a total of 7,200 atomizing points per atomizer. If the atomizing points were very fine, say 0.025 mm diameter, they could be located at only 0.5 mm intervals, ie. at 14,400 atomizing points per atomizer. The number, 18, on Fig 2 represents the liquid spray from the nozzles and the liquid flow over the vanes is represented by the number 20. Item 23 on Fig 2 is a circular flexible seal covering bearing number, 11, to prevent air passing through the bearing. It is desirable that the engine's requirement for an intimate mixture of air and fuel should be provided by the atomizer. Taking the present case where the required air:fuel ratio is 15:1 and that one milliliter (0.7 gramme) of lead-free petrol is to be atomized each second, then 10.5 grammes (8564 milliliters) of air per second must be mixed with the fuel. This volume of air will be delivered via item 14 as shown on FIG 2. (It should be noted now, that the engine is to be provided with this quantity of fuel and air continuously, as discussed in paragraph 9). The air, (8564 ml), will pass through an area of 300 cm2 where the atomizing points are located, and the air velocity will therefore be 28.5 cm/second. The surface tension force holding the fuel droplets to the atomizing points is 0.393 dynes (see para 3) and it is now necessary to estimate the effect of this low-velocity airflow on the droplets. In this example the atomizing points and the droplets are 0.005 cm diameter and 0.0075 cm diameter respectively, and as a result only a small part of the cross-sectional area of the droplet comes under the influence of the airflow (see FIG 4b). The aerodynamic drag on the droplet is therefore much reduced as an area of only #/4 x 31 x 104 cm2 of the droplet is subjected to the airflow instead of the full cross-sectional area which is 4 x 56 x 104 cm2. An estimate of the aerodynamic force on each droplet can therefore be made:

Aerod dynamic drag # = Cd x # x V x Cross sectional area of drop ... ... (2) 2 where CD = 2 for a drop partly protected from the airflow V = air velocity of 28.5 cm/second

cross sectional area of drop 4 xl306 cm2 p = 123 x 10-5 gramme/cm3 Substituting these values into equation (2) the aerodynamic force is found to be 0.243 x 104 dynes which is negligible compared with the surface tension holding the drops on the atomizing points, and indicates that the use of air as described is not employed to dislodge drops from the atomizing points, but only to provide the necessary quantity of air in relation to the fuel.

Best Mode for Carrying Out the Invention 7. The best mode for carrying out the invention is as follows: the rotor, less the rotor end-plate, 5, can be made in one piece using an aluminum alloy by the impact-extrusion system or by moulding in a suitable material. The second endplate can then be connected to the main part. All the remaining components except the atomizing points, 7, can be made in accordance with normal engineering practice.

The atomizing points, 7, are made in groups to fit exactly into the slots, 6 (Fig.

1), at the end of each vane, 4. Each group of atomizing points, 7, will be made in the form of a flexible strip the same length as the slots, 6, and the width will be equal to the curved surface of the slot so as to leave a fringe of atomizing points projecting outward from both edges of the slot in a radial direction from the centre of the atomizer as shown in Figs 1, 2 and 3. The atomizing points, 7, may be constructed from fine wire or glass, carbon or thermoplastic fibers depending upon the requirement. The diameter of the atomizing points, 7, may be 0.025 mm to 0.075 mm if the selected material is sufficiently stiff. Larger or smaller diameter atomizing points can be used if required. These points should be separated from their neighbours to ensure that the drops on the points do not touch and coalesce. If they are spaced at 10 points/cm, that is at one millimetre intervals, that should be satisfactory for many purposes but any desired spacing is acceptable. The length of the atomizing points should be one or more millimetres and the strips should be permanently fixed in the slots. The atomizing points would be laid on to their flexible base by a manufacturer with the necessary specialist equipment required for locating them parallel to each other and the desired distance apart and then fixing them in position. The flexible base could be a mesh (10 mesh/cm or any other desired mesh), the mesh being constructed from fine wire or fine fibres. The atomizing points could be held between two pieces of very fine mesh if desired. No. 22 is the mesh, Fig 4a.

Industrial Applicability 8. Use as a crop sprayer A number of these atomizers can be fitted below a wide supporting boom behind a tractor. They would be particularly advantageous where an atomizer capable of delivering a spray of very fine droplets with an extremely narrow drop-size spectrum is required and/or where a uniform covering of very small droplets is necessary.

9. Use as a fuel atomizer for lean-burn engines The efficiency of I.C. petrol engines could be much improved by employing this atomizer. A small engine using this device could be set to run continuously at its most efficient "on-load" speed to charge a battery-operated system which would act as power reservoir to supply sudden bursts of energy without affecting the efficiency of the petrol engine. One or more of these atomising devices could be installed inside an enlarged inlet manifold and simple arrangements made to provide the exact air-fuel ratio for lean-burn conditions when running at a constant speed. But there might be some reluctance to use larger manifolds in this way.

However, as it has become normal to use large silencers to reduce excessive noise, it could also become acceptable to employ large manifolds to contain devices capable of helping to reduce atmospheric pollution and of improving engine efficiency. A pressure release valve could be installed in the inlet manifold designed to open rapidly if the internal pressure rose above a certain value.

Although the rotary atomizer as described can be designed to provide a high standard of atomization, modern high-speed engines with their short firing strokes make it difficult to ensure that the fuel will all be completely and efficiently consumed in the short time available. But a long-stroke, slow-speed engine used in conjunction with an atomizing system as described could assist towards the development of a good hybrid system.

Claims

What I claim as my invention is: 1. A rotary fuel atomizer capable of producing a spray of fine droplets with an extremely narrow drop-size spectrum, every millilitre of petrol, or similar fuel, being reduced into millions of particles completely free of large drops, this being achieved with the aid of a rotor holding a plurality of fibrils or atomizing points from each of which the fuel is dislodged as a stream of discrete particles as shown in Fig. 7, so that when sufficient atomizing points are employed finely atomized fuel can be provided in the required quantity for environmentallyfriendly engines.
2. A rotor as claimed in Claim 1 constructed in the form of a miniature paddle wheel for use in air, not water, provided with a number of vanes, like paddles, radiating outwards from the central area, each vane holding a plurality of fibrils or atomizing points, means being provided to ensure that fuel can be delivered to the spinning vanes and which then flows to all the atomizing points, from each of which it is dislodged by centrifugal force as a stream of discrete particles, and since each atomizing point is separated from its neighbours droplets forming on the points do not touch and coalesce.
3. A rotor as claimed in Claims 1 and 2 wherein each vane is provided with a slot which extends along each vane between components 3 and 5 as shown in Figs. 3 and 4, a plurality of fine atomizing points being positioned 0.5mm, or more, apart, to form a fringe along both sides of the slot, with each atomizing point extending beyond the edge of the slot a distance of 1.0mum, or more, each pointing radially outward from the centre of rotation as shown in Fig. 3.
4. A rotor as described in the previous claims which, instead of being fitted with atomizing points of near-identical diameters is instead, provided with wires or fibres with a variety of different diameters each in the required number to ensure that the resultant spray consists of drops with a WIDE particle-size spectrum designed for a particular requirement.

4. A rotor as claimed in Claims 2 and 3 wherein each fringe of atomizing points consists of parallel lengths of fine (0.025mm diameter, or more) stiff wire or fibers constructed from glass, carbon or thermoplastic materials these being held between two pieces of fine mesh or net which exactly fit the surface area of the slot as shown in Figs. 4 and 4a, said mesh or net being attached to the surface of the slot with solder, adhesive, spot welding or with screws and washers depending upon the materials employed.

5. A rotor as described in the previous claims which, instead of being fitted with atomizing points of near-identical diameters is instead, provided with wires or fibres with a variety of different diameters each in the required number to ensure that the resultant spray consists of drops with a WIDE particle-size spectrum designed for a particular requirement.

Amendments to the claims have been tlled as follows What I claim as my invention is:

1. A rotary fuel atomizer which employs a rotor with a plurality of fibrils on its external circumference each fibril operating in its own space and, under centrifugal force each producing a stream of fine particles as illustrated in FIG 7, one example of this system, as shown in FIGS 1, 2 and 3 being a device with a rotor constructed in the form of a miniature paddle wheel with a plurality of paddles or vanes 4 and a plurality of atomizing points 7 located on the outer edge of each vane, a two-stage atomizing system being employed, the fuel firstly being injected into a compressed air line and then, entrained in the compressed air; delivered to one or more small spray nozzles (see FIG 2) from which it is sprayed on both sides of the spinning vanes 4, and then dislodged by centrifugal force from each of the many atomizing points 7 such as those shown on the typical array in FIG 3, each point being located in its own operating space which ensures that particles on two or more points cannot touch and coalesce, this being essential where an extremely narrow drop-size spectrum is required - as in this case; a further important requirement demands that all the atomizing points must have near-identical dimensions as discussed in paragraph 4 of the patent application, the above features all assisting toward the provision of a cloud of very fine particles which is also mixed with air to give the desired air: fuel ratio; also, because centrifugal force is proportional to the square of angular velocity (see equation 1) one or more small - diameter atomizers, running at a higher speed than required by a large device, may be installed inside the inlet manifold to deliver finely-atomized fuel at the correct air : fuel ratio and at the required flow rate close to the engine's inlet valves.

2. A rotor as claimed in Claim 1 wherein each vane 4 is provided with a slot which extends along each vane between components 3 and 5 as shown in Figs. 3 and 4, a plurality of fine atomizing points being positioned 0.25mm, or more, apart, to form a fringe along both sides of the slot, with each atomizing point extending beyond the edge of the slot a distance of 0.5mm, or more, each pointing radially outward from the centre of rotation as shown in Fig. 3.

3. A rotor as claimed in Claims 1 and 2 wherein each fringe of atomizing points consists of parallel lengths of fine (0.l5mm or more diameter) stiff wire or fibers constructed from glass, carbon or thermoplastic materials these being held between one or two pieces of fine mesh or net which exactly fit the surface area of the slot as shown in Figs. 4 and 4a, said mesh or net being attached to the surface of the slot with solder, adhesive, spot welding or with screws and washers depending upon the materials employed.