The invention relates to a burner to combust oil in a combustion chamber. The burner is of the kind that comprises a burner casing; an atomizer cup mounted in the burner casing and arranged to supply oil to be burned to the combustion chamber and designed with a base and a tubular wall having a peripheral edge; an oil pump for metering the oil during operation to the interior of the atomizer cup; a shaft rotatably journaled in the burner casing and firmly connected to the base of the atomizer cup; a motor for rotating the shaft during operation at such high rates that the centrifugal force will make the oil in the atomizer cup leave its peripheral edge in a mist of fine oil particles; and a blower for supplying air to the combustion chamber for burning of the oil particles.

Oil is largely used as fuel in e.g. boilers for production of heat energy. However, the oil does not burn readily in the combustion chamber of such a boiler as long as it is in its original liquid state. Normally the oil is therefore atomized to fine oil particles that burn far better and purer in the combustion chamber.

Because of the relatively high cost of the oil, the environment, and the state of the combustion chamber, it is however important that the combustion takes place as completely as possible, that is without or with a minimum content of unburned elements such as e.g. carbon hydrides, carbon monoxides, and carbon in the gaseous effluents.

In attempts to solve this problem oil burners have therefore been developed in the course of time that are based on rather different atomization techniques. One particular technique can therefore be best suited for one particular combination of oil grade and boiler size but not for another.

A widely used atomization technique consists in the oil being forced into the combustion chamber at a relatively high pressure via a nozzle and is atomized on discharge from the nozzle outlet where the pressure drops suddenly. To avoid the nozzle clogging more or less, a not too heavy a fuel must be used in this case which also is of a high and uniform quality. These demands will normally be met by oil which is used for heating private residences where the boilers are relatively small.

This technique is especially suited for small boilers as the flame easily can be modulated to a small size fitting the relatively small combustion chambers of the boilers at the same time as the flame is kept at such a great distance from the nozzle that this nozzle is not damaged by the heat from the flame.

Heavy oils of varying grade are normally less expensive than the above oils and are therefore readily used if possible. These oils can especially be used as fuel in relatively large boilers where they are atomized by means of rotary burners with rapidly rotating atomizer cups which are not likely to clog as nozzles are.

From EP Patent No. 0026426 is known a rotary burner of this type. This known rotary burner has a hollow shaft which is driven by a motor with high shaft speed and which at the end is firmly connected to an atomizer cup. Via the hollow shaft, the oil is metered during operation by means of an oil pump at relatively low pressure onto the inside face of the rotating cup where the oil under the influence of the centrifugal force forms a very thin oil layer which concurrently with the metering of the oil is moving towards the peripheral edge of the cup from which the oil layer is ultimately thrown out into the combustion chamber in form of a fine oil mist.

Rotary burners of this type are well suited for, as mentioned above, relatively large boilers with correspondingly large combustion chambers that allow the flame to spread freely.

The reason that a relatively large flame is formed on application of this technique is that the oil must necessarily be thrown out of the combustion chamber at such a high rate and force that the oil particles formed are sufficiently fine to be able to burn at the required speed and purity.

However these known rotary burners are not suited for relatively small boilers with small combustion chambers as it is not possible under these circumstances to control the flame sufficiently to keep it at the necessary distance from the chamber wall and atomizer cup.

This may result in the combustion being incomplete at the wall and in the atomizer cup being damaged by the heat from the flame. If the damages are unevenly spread, the atomizer cup will easily be thrown off balance. In this state the atomizer cup will then be able to make the entire boiler vibrate and shake in a damaging manner during its rapid rotation.

From US Patent Nr. 1,490,861 and GB 620.596 is known oil burners for combusting oil in a combustion chamber. None of those oil burners are however equipped with means for effectively cooling the air passing the burner which therefore is in danger of being damaged from the heat from the flame.

In a first aspect according to the invention a burner of the kind mentioned in the opening paragraph is provided, which is arranged to be used in relatively small boilers.

In a second aspect according to the invention a burner of the kind mentioned in the opening paragraph is provided, which is provided with an atomizer cup which, during operation, is rotating at greater speeds than hitherto known.

In a third aspect according to the invention a burner of the kind mentioned in the opening paragraph is provided, which is arranged in such a way that the atomizer cup is not damaged by the heat stress from the flame.

In a fourth aspect according to the invention a burner of the kind mentioned in the opening paragraph is provided, which is arranged to burn heavy oils of varying grade, for example vegetable oils.

In a fifth aspect according to the invention a burner of the kind mentioned in the opening paragraph is provided, which is provided with an automatic suction atomizer cup.

In a sixth aspect according to the invention a burner of the kind mentioned in the opening paragraph is provided, which has a simple and reliable construction.

According to the invention the burner comprises an inlet cup facing in opposite direction from the atomizer cup and designed with a tubular wall with a peripheral edge and a base joint with the base of the atomizer cup; at least one guide channel extending obliquely through this base at a shorter distance from the rotational axis on the side of the inlet cup than on the side of the atomizer cup; and at least one oil duct connected to the at least one oil pump and opening into an area between the shaft and the inside of the wall of the inlet cup.

Such a burner can function with a relatively small cup and correspondingly very high rotational speed in a relatively small combustion chamber of the type found in boilers for heating of e.g. private residences.

The oil is supplied to the inlet cup in an area outside the shaft and led from there to the atomizer cup via the guide channels, after which it is thrown in finely atomized state out of the peripheral edge of the atomizer cup under the influence of the centrifugal force.

As the oil now is not led through a hollow shaft during operation as conventionally, the conventional gaskets for keeping the joint between the shaft and the oil inlet sealed are advantageously avoided. Such a gasket would not last in the long run at the very high rotational speeds with which the shaft necessarily has to rotate to be able to make a relatively small cup atomize the oil with the required degree of fineness.

In an advantageous embodiment the burner casing can be designed with an air chamber receiving combustion air from the blower of the burner and defined in the burner casing by a first partition at the atomizer cup and a second one at the atomizer cup.

A slit for primary air can furthermore be made in the second partition at the peripheral edge of the atomizer cup and a number of apertures or a slit for secondary air can be made near the periphery of the burner casing.

During operation the oil is led into the inlet cup and from there further onto the atomizer cup via the guide channels in the joint base. Thereby the supplied oil is momentarily taken to the same high rotational speed as the cup whereby it is affected by a very high centrifugal force.

As the guide channels are inclined in the base, this base functions as a centrifugal pump which furthermore affects the oil with a significant force in the direction of the channels. The combination of this force and the centrifugal force causes the oil to settle on the inside of the atomizer cup in an extremely thin oil film.

According to the invention the inside face of the atomizer cup is cone-shaped. Therefore the centrifugal force has a component directed towards the peripheral edge of the atomizer cup. Under the influence of this component of force the oil film travels on the interior wall of the atomizer cup continuously towards its peripheral edge where the extremely thin oil film now is successively broken into extremely fine oil particles that are spread in the combustion chamber as a mist.

The extremely fine oil particles burn far quicker than conventionally, resulting in a relatively small flame being able to develop just as much heat as a larger one but burning slower than a conventional flame. The burner according to the invention is therefore suitable for use in relatively small boilers with relatively small combustion chambers.

The inlet cup communicates with the air chamber via a relatively narrow slit between the first partition and the peripheral edge of the atomizer cup.

As mentioned the base between the inlet cup and the atomizer cup functions as a centrifugal pump pumping oil from the inlet cup to the atomizer cup. At the same time the centrifugal pump is however pumping air from the inlet cup to the atomizer cup whereby a negative pressure is created in the inlet cup that drives an airflow through the narrow slit.

Thereby the air expands and its temperature lowered so that the air now will act as cooling air to the inlet cup, the joint base and the atomizer cup which thereby continuously can stand the heat from the flame without being damaged.

The invention will be explained in greater details below, describing only exemplary embodiments with reference to the drawing, in which

• Fig. 1 is an axial view of an oil burner according to the invention, and fig. 2 shows on a larger scale a detail of the oil burner in fig. 1.

The oil burner shown comprises a burner 1 with a motor 2. The burner supplies a combustion chamber 3 in a boiler 4 with finely atomized oil which is spread in a mist of extremely fine oil particles burning in a flame 5.

A shaft 8 is rotatably journaled in a burner casing 6 by means of ball bearings 7, the shaft being rotated by the motor 2 during operation at very high shaft speed, for example 25,000 n/min.

On the shaft a blade wheel 9 is furthermore mounted that together with a blower chamber 10 made in the burner casing between a back wall 11 and a partition 12 form a blower.

The blower draws air into the blower chamber via a number of intake apertures 13 made in the wall of the burner casing and blows the drawn-in air out via a number of blow-off apertures 14 made in the partition 12.

Together with a second partition 15 the partition 12 defines an air chamber 16 which is provided with air from the pump chamber via the blow-off apertures 14. The second partition 15 increases outwards in the firing direction in a configuration that mainly follows the back of the flame 5 at an appropriate distance. Therefore there is no unfavourable space between the second partition and the flame, in which turbulent flows could be generated that would disturb the flame so that this flame would not be able to burn properly and purely.

On a cone 17 at the end of the shaft 8 a base 18 is firmly mounted with an atomizer cup 19 facing its opening in towards the combustion chamber 3 and an inlet cup 20 facing its opening in towards the partition 12 in the burner casing 6.

In a second partition 15 a slit 21 is made near the atomizer cup and a number of apertures or a slit 22 is made near the periphery of the burner casing.

The second partition 15 is extending inwards towards the first partition 12 in a funnel 23 surrounding the outer face 24 of the inlet and atomizer cup 20, 19 and together with this outer face defining an annular air nozzle 25 opening into the slit 21.

As seen best in fig. 2, the atomizer cup 19 has a first tubular wall 26 with a first conical inside face 27 and a first peripheral edge 28. The inlet cup 20 has a second tubular wall 29 with a second conical inside face 30 and a second peripheral edge 31. Both inside faces 27 and 30 are located on a conical surface with peak in the rotational axis 32 and in the case shown, on the.same conical surface.

It has been found that the flame formation is controlled the best at the same time as the formed oil particles obtain the desired extremely small size if the conical surface forms an angle with the rotational axis 32 of between 6° and 10°, especially between 7° and 9° in combination with the peripheral edge of the atomizer cup 19 having a diameter of between 20 mm and 100 mm, preferably between 20 mm and 50 mm, and especially 30 mm, and the rotational speed being between 10,000 n/min. and 40,000 n/min., preferably between 20,000 n/min. and 30,000 n/min., and especially 25,000 n/min.

The joint base 18 of the cups is furthermore designed with a number of guide channels 33 that open at a shorter distance from the rotational axis 32 on side of the inlet cup than on the side of the atomizer cup.

The first partition 12 is designed with a projection 34 extending into the inlet cup 20 at a short distance from the base 18 and near the peripheral edge 31 of the inlet cup which furthermore is near the partition 12. As it appears, a narrow slit 35 is thereby formed between the inlet cup 20 on the one hand and the partition 12 with its projection 34 on the other hand.

A pump (not shown) serves for pumping the oil to be burned into the inlet cup 20 via an oil duct 36 made in the first partition 12 and in through the projection 34 of this partition to near the base 18 of the cup and at least essentially within the circle of outlets of the guide channels 33 in the inlet cup.

The burner is furthermore provided with an air distributor shell 37 extending in continuation of the burner casing 6 a distance into the combustion chamber 3 and also with an igniter 38 located near the distributor shell and connected to an ignition unit (not shown) via an electric line 39.

The burner is furthermore provided with a control box, not shown, with among other things monitoring automatics and flame monitor.

When the burner is in operation, the inlet cup 20 receives oil from the oil pump via the oil duct 36 in the first partition 12. The inclined guide channels 33 function as the blades in a centrifugal pump which effectively pumps air from the air chamber 16 to the atomizer cup 19 via the narrow slit 35 between the inlet cup 20 and the partition 12 with its projection 34.

In the inlet cup a negative pressure is thereby created that supplies the inlet cup with an automatic suction power. The pump can therefore, at least essentially, be unpressurized and mainly only function as metering pump to meter the amount of oil that is continuously used for producing the desired heating effect.

As mentioned above, the outlet of the oil duct 36 is near the base 18 of the inlet cup 20 and at least partly within the outlet of the guide channels 33 in the inlet cup. The oil therefore settles in a thin oil layer on the base. Under the influence of the centrifugal force this oil layer travels continuously outwards in direction towards the conic inside face 30 of the tubular wall 29 of the inlet cup 20.

At the outlet of the guide channels on the side of the inlet cup the oil layer undergoes a severe splitting resulting in at least a part of the oil layer being transformed into oil particles that are mixed with the cooling airflow. The centrifugal force makes the rest of the oil layer flow through the guide channels in liquid state along the area that is farthest from the rotational axis 32.

At the outlet of the guide channels in the atomizer cup the pressure built-up in the cooling air during its passage in the guide channels drops suddenly. Thereby the oil particles are separated which, together with the liquid oil flowing out of the outlet of the guide channels, settle as an extremely thin oil film on the conic inside face 27 of the tubular wall 26 of the atomizer cup 19 under the influence of the very great centrifugal force produced due to the very fast rotational speed of the cup.

The oil film continuously travels towards the peripheral edge 28 of the atomizer cup where it is split up into extremely small oil particles that leave the edge as a flat mist.

The blower draws fresh air into the blower chamber 10 via the intake apertures 13 and blows the drawn-in air into the air chamber 16 via the blow-off apertures 14.

In the air chamber the air is now divided into three airflows, namely a primary airflow, a secondary airflow, and a cooling airflow that all finally will form part of the combustion air for the combustion process.

The primary air constituting a smaller part of the total amount of air is blown at appropriate rate out through the air nozzle 25. This primary airflow serves to, via the air distributor shell, draw the flat oil mist leaving the peripheral edge of the atomizer cup out into the combustion chamber of the boiler so that it will not burn so close to the atomizer cup that this cup is damaged by the heat from the flame. It has proven that the peripheral edge of the atomizer cup and the flame can be spaced between 10 mm and 40 mm.

The secondary air is blown out through the apertures or slit 22 of the second partition 15 near the air distributor shell 37 where it modulates the flame and keeps it free of the inside face of the shell. The secondary air contributes with the chief part of the required combustion air.

At start-up the mixture of combustion air and extremely fine oil particles is ignited by means of the igniter 38 so that a flame is produced. The combustion process is now in progress.

Especially the atomizer cup is located at a position in which it inevitably will receive a significant amount of radiation heat from the flame and its surroundings. It is important that the cup is not damaged during this so that it is thrown off balance and shakes the burner to pieces during its rapid rotation.

The cooling air flowing out through the aperture of the atomizer cup acts to some extent as a shield shielding the cup against the heat stress, the cooling air absorbing heat concurrently with it getting nearer the flame.

This air is in itself cooled when it is drawn via the narrow slit 35 between the inlet cup 20 and the partition 12 with its projection 34 into the atomizer cup 19 from the air chamber 16 of the joint base 18 of the cups, the base functioning, due to the presence of the guide channels 33, as a centrifugal pump which is very effective because the cooling air passing the guide channels is mixed with oil particles that are much heavier than the air.

The sharp pressure drop produced over the narrow slit 35 causes the air to expand and thereby its temperature to drop drastically.

The now cold air or the cooling air subsequently flows through the inlet cup, the guide channels, and the atomizer cup. Thereby the entire cup is cooled so effectively that it can be made of a material such as e.g. aluminium which in conventional burners would be destroyed by the great heat impact from the burning flame.

The application of such a well heat-conducting material as aluminium furthermore has the significant advantage in that the atomizer cup which is affected the most by the heat quickly conducts the absorbed heat on to the inlet cup which is cooled the best.

The burner according to the invention is well suited for heavy oils of varying grade such as e.g. vegetable oils. Thereby a perspective of global significance is opened.

Combustion of the vast amounts of oil brought up from the subsoil will gradually create more carbon dioxide than the forests and green areas on the planet will be able to assimilate.

However just as much of the atmosphere content of carbon dioxide is used for production of vegetable oils as is later released on combustion. Heating with vegetable oils is therefore neutral with respect to the atmosphere content of carbon dioxide.

A boiler is burned with 2 kg rape oil per hour by means of a rotary oil burner according to the invention.

The rape oil is of the following quality: Ash 0.068 w% Coke remainder 0.51 w% Density at 15°C 0.9209 g/ml Flash point. >140 °C Upper calorific value 44.35 MJ/kg Lower calorific value 41.78 MJ/kg Pour point -24 °C Sediments at extraction 0.02 w% Sulphur <0.05 w% Viscosity at 40°C 34.7 cSt Water 1480 ppm by weight

The atomizer cup of the burner had a diameter at the peripheral edge of 30 mm and a depth, of 10 mm whereas its inlet cup had a diameter at the peripheral edge of 20 mm and a depth of 10 mm. The joint base of the two cups had a thickness of 10 mm and their conicity was 8° measured as the angle between a generator and the rotational axis.

The entire cup was made of aluminium and was mounted on a shaft which was rotated at a rotational speed of 25,000 rpm by means of a direct-driven motor of 0.25 kW.

In the joint base six guide channels were arranged with axes forming an angle of 8° with the rotational axis. The diameter of the guide channels was 3 mm and during their rapid rotation a strong airflow was generated from the inlet cup to the atomizer cup.

The air was drawn in from an air chamber with an air temperature of 40 °C via a narrow slit with a width of 0.1 mm and length of about 11 mm whereby the air temperature dropped to minus 12 °C.

The cold air kept the atomizer cup temperature at about 115 °C. After 100 operating hours there were no signs of the atomizer cup being damaged by the heat from the flame.

The flame burned continuously purely. The content of carbon monoxide was 15 ppm and total unburnt was 22 ppm.