The present invention relates to a device for oil burners, comprising a nozzle connected with a pump to pro¬ duce a finely divided oil stream, a tube surrounding the nozzle, along which tube the air required for the combustion is supplied, a blower for the combustion air and means for regulation of the amount of air.

In general the oil burners available on the market include some type of stationary means to provide proper speed and pressure drop where the air meets the oil mist. Pressure-jet oil burners of free-burning type have, for instance, a brake disc placed immediately before or after the oil nozzle. All pressure air burners and rotary burners of the free-burning type have ingenious systems of guide vanes which create the desired speed, rotation and pressure drop. Common to all these means is that they must be dimen¬ sioned for a maximum capacity and that any choice of lower capacity would gradually deteriorate the combustion result since the superfluous air is throttled away by means of throttle valves on the suction or pressure side of the burner before the stationary means. This means that pressure drop, speed and rotation of the combustion air over the stationary means decrease with reduced capacity. This is a difficult problem especially in burners with large regulation areas or large capacity ranges. This invention intends to solve the problems that arise when an oil burner designed for a predetermined maxi¬ mum capacity is to work at a lower capacity. With lower capacity the combustion air will have a lower pressure drop and speed and a deteriorated rotation since the superfluous air- is throttled away before it reaches the front end of the combustion pipe.

The essential characteristic of the device according to the invention is that in addition to said first tube, there is a second tube disposed coaxially with and at some distance from the first tube, the space between the tubes

being in communication with the pressure side of the blower, that the second tube is displaceable relative to the first tube, that the tubes join each other at their ends adjacent the nozzle through preferably bent-over, overlapping portion and that, at the overlapping portions of each tube, there are provided corresponding air throughflow openings the area of which is variable by displacement of one tube relative to the other.

The device of the invention gives, int.alia, the follo- wing advantages.

When the capacity of the burner is reduced, the pressur drop, the air velocity and the rotation can be adjusted and be maintained at an appropriate level. Various flame shapes can be obtained by the adjustable regulation means being given a straight or conical shape. It is easy to apply ignition electrodes and photo resistances or the like. The principal angle of incidence of air relative to the oil mist can be made practically optimal in relation to the angle of diffusion of the oil mist. The entire device may be easily withdrawn from behind for inspection and service. The invention will be described in greater detail hereinafter with reference to the accompanying drawings . In the drawings, Fig 1 is a schematic, partially sectional, diagonal front view of the front portion of the device according to a preferred embodiment of the invention. Fig 2 is a sectional side elevation on a reduced scale, showing the device as mounted to an oil burner assembly. Fig 3 shows the assembly according to Fig 2 seen in a back view. Fig 4 is a sectional side elevation on an enlarged scale, showing the front portion of the assembly according to Fig 2. Fig 5 is a partially sectional front elevation of the front portion shown in Fig 4. Figs 6 and 7 show in analogy with Figs 4 and 5, the front poβrtion of the device according to a modified embodiment, and Figs 8 and 9 show broken-out, developed portions, as seen from the inside of the front end of the outer and inner tubes in the assemblies of Figs 1-5 and 6-7 respectively, including some examples of possible embodiments of the openings arranged therein.

Details having similar function will be designated by like reference numerals while minor differences will be marked, with indices.

The oil burner assembly includes some parts which are of a generally conventional design. A blower F is arranged on a frame S. Connected to an oil pump (not shown) is a pressure tube T, and there are also a nozzle M and ignition electrodes E and lines L therefor.

The device of the invention will be described below. An outer tube 1 is fitted and fixed in a seat X in the frame S. Inside said outer tube 1 there is an inner tube 2 which extends throughout the outer tube and through the lower part of the frame S where it projects from the rear portion thereof. The inner tube is rotatably mounted in the outer tube

1 and in an opening Y in the frame and is closed at its rear end where passages 3 and 4 are provided for the pressure tube T and the lines L, respectively, as well as lines for photocells or the like. The rear end of the inner tube is provided with a handle 5 and an index 6 corresponding with a scale 7. The inner tube 2 has an outer diameter which is essentially smaller than the inner diameter of the outer tube 1 so that an annular space 8 is formed between these tubes. The space 8 is in communication with the blower casing and the pressure side of the blower so that air from the blower has to pass into said space.

In the embodiment according to Figs 1-5 the outer tube 1 has, at its front end extending into the heart , a bent-over end portion which is formed of a radial wall por¬ tion 9 and a collar 10 disposed in parallel with the tube 1. Provided in the collar 10 is a number of openings 11 which are adapted to cooperate with an equal number of openings 12 in the front end 2' of the inner tube 2. The collar 10 extends some distance into the inner tube 2 and forms a bearing for the inner end thereof.

As appears from Fig 8, the form of the openings 11 and 12 may vary. Common to the openings shown in Figs 8 a

that their geometrical form is substantially maintained independently of the positions of rotation of the tubes 1 and 2.

In the embodiment of Figs 6 and 7 the outer tube 1 terminates in an inwardly inclined cone-shaped part 10' which merges with a cylindrical flange 13, while the inner tube 2 terminates in an outwardly inclined cone- shaped part 14. Openings 11 and 12 are provided in the portions 10' and 14, respectively, as in the embodiment of Figs 1-5.

Examples of possible opening shapes are shown in Fig 9.

In order to facilitate ignition of the oil burner, an air tube 15 , as indicated by broken lines in Figs 4 and 6 , which suitably is adapted to be shut off by means of a magnetic valve, should extend from the space 8 towards the ignition electrodes E. Alternatively, in the inner tube 2 , on a level with the electrodes , an opening may be provided which is closable by means of a sliding valve or the like, in order to produce the required current of air past the electrodes during the ignition moment.

During operation the air delivered by the blower F will be carried from the interior of the frame S through the space 8 up to the openings 11, 12 where the air flows out towards the mist of fuel leaving the nozzle. By turning of the inner tube 2 relative to the frame and the outer tube 1 the size of the throughflow openings may be varied so that an amount of air exactly adjusted to the delivered amount of fuel is supplied. With the device according to the invention the entire amount of air required for the combustion can be exactly regulated just as it meets the fuel.

There is another possibility of regulation, i.e. adjusting the throughflow of air on the suction, side of the blower F in a conventional manner. However, such an adjust¬ ment is required onlywhen it is a question of radically changing the capacity of the burner.

During operation all the combustion air passes throug

the space 8 between the outer and inner tubes 1 and 2. Air passes through the previously mentioned tube 15 past the electrodes only during the ignition phase.

After the conduit between the pump and the pressure tube T and the lines of the ignition electrodes and the photo-cell have been disconnected, the inner tube 2 can be pulled out rearwardly as a unit, which facilitates attendance to electrodes and nozzle.

It is obvious that the variation of size of the through- flow openings may also take place in another way. The openings 11 and 12 may, for instance, be orientated in another direc¬ tion and the inner tube may be made axially displaceable with the position of rotation unchanged. However, from a constructional point of view the embodiment shown and described would seem to be the simpliest one.

The invention should not be considered limited to that described above and shown in the drawings but may be modi¬ fied in various ways within the spirit and scope of the appendant claims.