GB2120772A - Fuel burner device - Google Patents

Abstract

A fuel burner device (1) comprises a nozzle (3) which terminates at its discharge end in a slit-like discharge orifice (5), so as to produce a wide, but thin, flame. In order to improve combustion efficiency, in particular when using the nozzle as an oil-fired burner, air pipes or passages (8) are provided in the wall of the nozzle. Owing to the high velocity of combustible mixture travelling through the nozzle, a suction effect is set up in the pipes (8) which draws in additional air from the atmosphere (Fig. 1). <IMAGE>

Description

SPECIFICATION Fuel burner device This invention relates to a fuel burner device, and in particular, although not exclusively, to an oil burner device.

Conventional burners, whether gas burners, oil-fired or using pulverised coal, for example, generally have an aperture through which the combustible fuel mixture is discharged which is circular in shape, and this produces a flame of generally circular cross-section along its length. However, when it is required to heat a flat surface, it is generally preferable to produce a flattened flame for this purpose.

Where an area of uneven road surface is to be softened and flattened or fresh screed is to be compacted and resurfaced using a road surfacing machine having a heated metal plate, the use of burners which produce flames of circular cross-section to produce a series of flames directed horizontally across the metal plate is very wasteful of heat because, due to the shape of the flame, a significant part of it, especially the upper part, does not come into contact with the metal plate and instead can end up heating and damaging other parts.

A much more efficient transfer to heat to the metal plate can be obtained by producing a wide, flat, flame which is so directed that its plane is parallel to, and just above, the plate.

A flame of this shape can easily be produced with a gas burner by simply using a muffler or nozzle which terminates at its discharge end in an elongated slit. However, this arrangement is not generally suitable in an oil-fired burner where it has been found to reduce burner efficiency.

The present invention seeks to provide a fuel burner device which can produce a wide but thin flame even when burning oil, but with good burning efficiency.

According to the invention from one aspect there is provided a fuel burner device comprising a nozzle which terminates at its discharge end in a slit-like discharge orifice for producing a jet of combustible mixture, there being at least one passage in the wall of the nozzle providing communication between the inside of the nozzle and a region containing combustion supporting medium, the combustible mixture velocity through the nozzle producing a suction effect within the passage.

According to the invention from another aspect there is provided a fuel burner device comprising a nozzle which terminates at its discharge end in a slit-like discharge orifice for producing a jet of air/fuel mixture, there being at least one air pipe extending through the wall of the nozzle to provide communication between the ambient atmosphere and the inside of the nozzle, the or each pipe slanting generally backwardly away from the discharge orifice.

The inventor has recognised that with either arrangement, any tendency to coalescence of oil droplets within the nozzle occurring in a burner not employing suction passages or air pipes, which leads to incomplete combustion, is mitigated or avoided, resulting in improved combustion efficiency. The reasons for the improvement are not fully understood but the following considerations, alone or in combination, are offered as possible explanations for the reduction or avoidance of coalescence of oil droplets in the nozzle: (1) The induced suction effect produced in the passages of air pipes draws in additional combustion supporting medium (air) to the flow of combustible mixture within the nozzle.

This effect is greatest at higher firing rates.

(2) Reduction in the size of eddies in the flow boundary layer in the nozzle around the mouths of the suction passages or air pipes.

(3) Turbulence produced in the main flow in the nozzle in the region of the mouths of the suction passages or air pipes.

Additionally, the increase in width of the nozzle due to the transformation from the nozzle upstream end to the elongated shape of the discharge slit widens the proximity of the oil droplets in the nozzle from one another and this is believed to assist in minimising oil droplet coalescence.

Preferably, the angle of slant of the or each air pipe is between 25 and 65 to the axis of the nozzle, so as to obtain the best results.

Suitably, the nozzle has upper and lower wall portions of relatively large surface area, there being a plurality of such air supply pipes extending through each of said upper and lower wall portions. By arranging the pipes of the upper wall portion and the pipes of the lower wall portion, in each case symmetrically relative to the axis of the fuel burner device, a symmetrical flame can be produced. The air supply pipes of each of the upper and lower wall portions may open into the inside space of the nozzle at locations arranged side-byside.

Advantageously, the nozzle has an internal cross-sectional shape which progressively widens and flattens towards its outlet end. This helps to control the shape of the flame. If the jet velocity produced by the discharge orifice is too high, the flame may be blown off. On the other hand, with jet velocities that are too small, flashback and flame flicker occurs. Preferably therefore, for good flame stability, the area of the discharge orifice is greater than (but not significantly greater than ) the crosssectional area of the nozzle at its upstream end.

In a preferred embodiment, the nozzle has a skirt at its inlet end for fitting the fuel burner device onto another fuel burner. In this way, the former can be fitted as a muffler onto an existing oil-fired fuel burner, so as to adapt the flame shape to a wide thin one. The discharge orifice can be in the form of a straight slit, to produce a wide flat flame, or it can alternatively be curved.

For a better understanding of the invention and to show how the flame may be carried into effect, reference will now be made, by way of example, to the accompanying draw ings, in which: Figure 1 is a horizontal sectional view, taken along the line I-I of Fig. 2, showing one form of oil-fired burner in accordance with the invention fitted onto a conventional oil fired burner for producing a thin, wide flame, Figure 2 is a horizontal sectional view taken along the line ll-ll of Fig. 1, and Figure 3 is an end view of the burner taken in the direction of Ill in Fig. 1.

Referring to Figs. 1 to 3, there is shown a fuel burner attachment 1 fitted onto a conventional oil-fired burner 2 with lateral air inlet ports 9, for adapting the flame to a wide, flat shape. The fuel burner attachment comprises a nozzle 3 which has a skirt portion 4 at its inlet end fitted around, and conforming to the shape of, the oil-fired burner 2. The skirt can be a force fit around the burner 2 or secured in any other suitable way, for example with a screw threaded connection.As clearly shown in the Figures, the height of the passage within the nozzle for carrying the combustible mixture progressively reduces along the length of the nozzle (Fig. 1) whereas the width increases, as shown in Fig. 2..The noule terminates at its discharge end in a slit-like discharge orifice 5 for producing a high-velo city jet of atomised oil and air. The area of the orifice 5 is such as to provide a suitable exit velocity for the combustible mixture from the nozzle. As indicated in Fig. 3, the area of the discharge orifice is greater than the cross sectional area of the discharge slit 5, but not significantly. In this way, the right jet velocity can be produced for good flame stability.

It will be seen that the nozzle has upper and lower wall portions 6, 7 of relatively large surface area, through which air supply pipes or passages 8 extend to provide communi cation between the ambient atmosphere out side the nozzle and the passage within the nozzle. Each pipe 8 slants generally away from the discharge orifice 5, as shown in Fig.

1. Fig. 2 shows that the pipes 8 extending through the lower wall portion of the nozzle open into the inside of the nozzle at locations arranged side-by-side. Similarly, the air supply pipes 8 in the upper wall portion terminate at the same axial position at side-by-side locations. Additionaily, the pipes 8 of the lower wall portion and the pipes 8 of the upper wall portion are in each case symmetrically ar ranged relative to the axis of the burner. This helps to produce a symmetrical flame shape.

In operation, the oil-fired burner discharges atomising oil droplets and air into the passage within the nozzle and this combustible mixture travels at high velocity past the ends of the air supply pipes 8. These pipes draw in additional air from the atmosphere due to a suction effect produced by the high velocity of the combustible mixture past the ends of the pipes. This serves to reduce or avoid any tendency of the atomising oil droplets in the nozzle 3 to coalesce, which in turn improves combustion efficiency.

The use of the rearwardly slanting air supply pipes enables the suction effect to be utilised to draw in the required additional combustion air, and this arrangement is both simple to make and effective to use. Preferably the angle between the axes of the pipes and the axis of the nozzle is between 25 and 65'.

The nozzle is suitably made of stainless steel. The air supply pipes can be made of any suitable metal and held in place in the wall of the noule using suitable means, for example welded connections.

The illustrated embodiment is a burner attachment fitted onto an existing oil-fired burner. It will be appreciated, however, that the air supply pipes could alternatively be incorporated in the design of a purpose-built burner, rather than in a burner attachment.

In the disclosed embodiment, the discharge orifice is in the form of a straight slit. However, in appropriate applications, the slit could be curved so as to produce a thin, wide flame that is suitably curved in cross-section.

The disclosed burner is also suitable for burning gas or pulverised coal.

Claims (11)

1. A fuel burner device comprising a nozzle which terminates at its discharge end in a slit-like discharge orifice for producing a jet of combustible mixture, there being at least one passage in the wall of the nozzle providing communication between the inside of the nozzle and a region containing combustion supporting medium, the combustible mixture velocity through the nozzle producing a suction effect within the passage.

2. A fuel device device comprising a nozzle which terminates at its discharge end in a slit-like discharge orifice for producing a jet of air/fuel mixture, there being at least one air pipe extending through the wall of the nozzle to provide communication between the ambient atmosphere and the inside of the nozzle, the or each pipe slanting generally backwardly from the discharge orifice.

3. A fuel burner device according to claim 2, wherein the angle of slant of the or each air pipe is between 25 and 65 to the axis of the nozzle.

4. A fuel burner device according to claim 2 or 3, wherein the nozzle has upper and lower wall portions of relatively large surface area, there being a plurality of such air supply pipes extending through each of said upper and lower wall portions.

5. A fuel burner device according to claim 4, wherein the pipes of the upper wall portion and the pipes of the lower wall portion are arranged in each case symmetrically relative to the axis of the fuel burner device.

6. A fuel burner device according to claim 4 or 5, wherein the air pipes of each of said upper and lower wall portions open into the inside space of the nozzle at locations arranged side-by-side.

7. A fuel burner device according to any preceding claim, wherein the nozzle has an internal cross-sectional shape which progressively widens and flattens towards its outlet end.

8. A fuel burner device according to any preceding claim, wherein the area of the discharge orifice is greater than (but not significantly greater than) the cross-sectional area of the nozzle at its upstream end.

9. A fuel burner device according to any preceding claim, wherein the nozzle has a skirt at its inlet end for fitting the fuel burner device onto another fuel burner.

10. A fuel burner device according to any preceding claim, wherein the discharge orifice is in the form of a straight slit.

11. A fuel burner device substantially as hereinbefore described with reference to Figs.

1 to 3 of the accompanying drawings.