GB2035538A - Oil-atomisation burner - Google Patents

Abstract

A burner comprises an oil-atomisation nozzle (12) and a cup- shaped combustion chamber (13) whose wall (15) is provided with holes (30) for the feeding of preheated combustion air. A tangential flow component of the air is introduced into a first, inner portion (31) of the combustion chamber where it forms a vortex which is constricted to form an axial potential vortex flow by a tangential flow component of the combustion air which is introduced into a second portion (32) of the combustion chamber, so that there ensues in this portion a rotary flow which is superimposed on the potential vortex flow thereby resulting in complete combination of even the smallest quantities of fuel. <IMAGE>

Description

SPECIFICATION Oil atomisation burner The invention relates to an oil-atomisation burner. Such a burner is already known (USA Patent Specification No. 2,469.272) in which a proportion, forming the primary air, of the total quantity of combustion air, or a predomi nantly axial component thereof, is introduced axially into the combustion chamber, whilst the other portion, forming the secondary air, of the quantity of combustion air enters the combustion chamber radially through the wall thereof. This results in a substantially axial flow in the combustion chamber, which flow is confined around the longitudinal axis of the combustion chamber by the radially fed secondary air.These burners operate satisfactorily when, with a view to the low performance required, the fuel is still injected into the combustion chamber at so high a pressure that the fuel is finely distributed in the cone shaped atomisation volume from the atomisation nozzle employed. However, if the burner has to be designed for even lower performances, a substantially axial flow of the fue I/air mixture in the combustion chamber is no longer sufficient to prepare the mixture such that residue-free combustion takes place in the combustion chamber.

There is provided by the present invention an oil-atomisation burner of the type having an oil-atomisation nozzle and a cup-shaped combustion chamber whose bottom, provided with a central opening, faces the nozzle and whose casing is provided with holes for feeding pre-heated combustion air, wherein a tangential flow component of the combustion air enters at least an inner portion of the combustion chamber where it forms a vortex, and that a restrictor is provided at the outlet of the combustion chamber to constrict the vortex in the first portion to form an axial potential vortex.

In contrast to the known burner the burner in accordance with the invention has the advantage that even minimum quantities of fuel can be burnt in the combustion chamber in a soot-free manner. Even when a restriction is formed by a vortex of combustion air produced by introducing air tangentially in the region of a second axial portion of the combustion chamber, a rotational flow is superimposed on the potential vortex formed in the first portion of the combustion chamber, so that complete combustion can be obtained with a very small excess of air.

The burner of the present invention is therefore especially suitable for a low grade heating appliance such as used for domestic heating.

It is particularly advantageous when the rotational flow of the quantity of combustion air fed into the second portion of the combustion chamber opposes the flow of the potential vortex in the first portion, and when the total quantity of combustion air is distributed to the two portions of the combustion chamber such that, with substantial vapourisation of the injected fuel, a stable flame is formed in the first portion and fully burns out the fuel in the second portion under intimate mixing with the porportion of the combustion air which is introduced into the second portion and which acts as secondary air.

The combustion air can be heated without an additional source of heat in a known manner by conducting the air through an annular chamber which directly surrounds the combustion chamber. By virtue of the fact that the openings in the wall of the combustion chamber are formed by slots between fins of the jacket which are pressed correspondingly obliquely inwardly, a tangential flow component can be imparted in a simple manner to the air flowing into the interior of the combustion chamber through the jacket thereof. As a result of this, particles of fuel which are not yet completely vapourised or gasified can be prevented from flowing outwardly through the openings in the jacket of the combustion chamber where they would form residues.

It is particularly advantageous when an axial component of the combustion air directed in the opposite direction to the nozzle enters the interior of the combustion chamber at least in the first portion of the combustion chamber. Larger, unburnt particles of fuel are thereby forced back to the bottom of the combustion chamber until they are completely vapourised or gasified and burnt. The axial flow component, directed in the opposite direction to the nozzle, of the fuel can be produced in a simple manner by introducing the flow of combustion air into the annular chamber, surrounding the combustion chamber, in the direction towards the nozzle.

The desired intimate mixing of the fuel with the combustion air is further promoted when the oil-atomising nozzle is in the form of a turbulence nozzle whose direction of turbulence is opposed to the potential vortex in the first portion of the combustion chamber.

An embodiment of the invention is illustrated in the accompanying drawings: Figure 1 is a longitudinal section through the burner, Figure 2 is an end elevation of the burner, Figure 3 is a section through the combustion chamber of Fig. 1, taken on the line Ill-Ill, and Figure 4 is a section through the combustion chamber of Fig. 1, taken on the line lV-lV.

Preferring to the drawings, the housing of the burner comprises a cup-shaped casing 1 drawn from sheet metal, a cylinder 2, and a cover 3 which are inter-connected in a conventional manner. A motor 5 is secured in the cylinder 2 by means of a bracket 4 and drives a fan blade 6 and an oil pump 7 to which the oil flows by way of a line 8. The fan blade 6 draws in combustion air by way of an opening 9 in the cover 3 and forces the combustion air into the casing 1 by way of an annular gap 10 between the motor 5 and the cylinder 2, the motor 5 thus being cooled. An oil-atomising nozzle 1 2 is secured to that end face of the oil pump 7 which is remote from the motor 5, the injection orifice of which nozzle opens into a combustion chamber 1 3 whose basic shape is that of a cup having a bottom 14 and a slightly diverging skirt 15.The end edge of the combustion chamber 1 3 is secured to the rim of a hole 1 7 in the bottom 1 8 of the casing 1, a sealing and heatinsulating ring 1 9 being interposed therebetween. A hood 20 is secured to the bottom 14 of the combustion chamber 1 3 and its peripheral wall 21 separates two annular chambers 22 and 23 in the housing from one another. A deflection chamber 24 is formed at the end edge of the hood 20 and interconnects the two annular chambers 22 and 23.The gap between the nozzle 12 and an opening 25 in the bottom 14 of the combustion chamber 1 3 is covered by a sealing member 26 which presses against a conical outer surface of the nozzle body 1 2 and abuts against the bottom of the hood 20 by way of a sealing and heat-insulating ring 27.

The entire surface of the combustion chamber 1 3 is provided with slots 30 through which the combustion air, flowing through the annular chamber 22 into the deflection chamber 24 and the annular chamber 23, can enter the interior of the combustion chamber 1 3. The slots 30 are combined to form two groups which are associated with a first, inner portion 31 of the combustion chamber, and a second, outer portion 32 of the combustion chamber. The two groups of slots 30 differ from one another by virtue of the fact that they open into the interior of the combustion chamber 1 3 in opposite tangential directions and impart oppositely directed spins to the combustion air in the two portions 31 and 32 of the combustion chamber.The boundary between the two portions 31 and 32 of the combustion chamber is indicates symbolically by the dash-dot line 33. Each slot 30 is formed between obliquely inwardly pressed fins 34 and 35 in the casing 1 5 of the combustion chamber (Figs. 3 and 4). As is shown in Figs 3 and 4, the differing radial inflow components of the combustion air in the portions 32 and 31 are produced by appropriate alignment of the fins 34 and 35. The slots 30 continue into the bottom 1 4 of the combustion chamber 1 3.

An incandescant coiled filament 40 is mounted,by means of a clip 41 supported on the hood 21, at a location which is just reached by the atomisation cone 38 of the nozzle 12, the filament 40 being connected to an electrical iead 42 which also supplies the motor 5 with current. Three resilient retaining plates 43 for the open end of the hood 21 are distributed within, and around, the circumference of the annular chamber 23 of the housing, as is also indicated by dash-dot lines in Fig. 2.

The fuel is ignited at the filament 40 when the burner is put into operation, the combustion air entering the combustion chamber 30 still being cold, and incomplete combustion results for a short period of time. The combustion air is forced with a slight over-pressure of 5 to 10 mm WS through the annular chamber 22 and the deflection chamber 24 into the annular chamber 23. A portion of the air, acting as primary air, flows through the slots 30 into the inner portion 31 of the combustion chamber 1 3 where it forms a vortex. This vortex initially mixes the fuel with the primary air. The air soon commences to be heated up, so that the mixing of the fuel with the primary air is increasingly improved.When combustion is fully established, the air vortex becomes so hot that a substantial portion of the fuel in the portion 31 of the chamber is vapourised or gasified and burns up.

The combustion air entering the portion 32 of the combustion chamber acts as secondary air to ensure that the particles of fuel which have not yet been vapourised or gasified and burnt out in the inner portion 31, or which have only been incompletely vapourised or gasified and burnt therein, are fully burnt or at least fully gasified before they leave the combustion chamber. Furthermore, the secondary air in the outer protion 32 of the combustion chamber 1 3 has a further important function.Owing to the fact that it is introduced tangentially into the combustion chamber, this air forms a rotary flow which acts like a restrictor for the vortex in the inner region 31 and constricts the core region of the vortex to form a potential flow which enters, with a high circumferential velocity, the oppositely directed rotational flow in the outer portion 32 where it is superimposed by the said rotational flow. The dwell time of the gas in the inner portion 31 of the combustion chamber is thereby also prolonged, with the result that excellent mixing and residual vapourisation or gasification in the outer portion 32 is achieved which ensures complete combustion even when, as a result of the low performance of the burner, fine atomisation of the fuel in the nozzle 1 2 is no longer possible for technical reasons. As a result of the preheating of the combustion air and the associated cooling of the combustion chamber 13, the hot flame is maintained stable in the combustion chamber without touching the walls, and the walls of the combustion chamber are not subjected to excessive thermal stress despite the high concentration of energy in the centre of the combustion chamber.

In addition to flowing into the combustion chamber 1 3 with a tangential flow component, the combustion air flowing axially through the annular chamber 23 also enters the combustion chamber 1 3 with a small axial flow component which is directed towards the bottom 14 of the combustion chamber. Thus, heavier particles of fuel, which are not yet vapourised or gasified, are forced back towards the bottom 14 of the combustion chamber until vapourisation or gasification has been effected. The fins 34 shield the slots 30 such that particles of fuel forced outwardly by centrifugal force do not pass through the casing 1 5 of the combustion chamber and cannot form residuces in the annular chamber 23. The air flowing through the slots 30 in the bottom 14 of the combustion chamber 1 3 additionally acts to cool the nozzle 12, so that fuel residues also cannot form at the nozzle 12.

Claims (11)

1. An oil-atomisation burner of the type having an oil-atomisation nozzle and a cupshaped combustion chamber whose bottom, provided with a central opening, faces the nozzle and whose casing is provided with holes for feeding pre-heated combustion air, wherein a tangential flow component of the combustion air enters at least an inner portion of the combustion chamber where it forms a vortex, and that a restrictor is provided at the outlet of the combustion chamber to constrict the vortex in the first portion to form an axial potential vortex.

2. A burner as claimed in claim 1, wherein the restrictor is formed by a tangential flow component of combustion air which is introduced into a second portion of the combustion chamber and which forms therein a rotary flow which is superimposed on the potential vortex flow.

3. A burner as claimed in claim 2, wherein the rotary flow in the second portion of the combustion chamber is directed in the opposite direction to the potential vortex flow.

4. A burner as claimed in claim 2 or 3, wherein the entire quantity of combustion air is distributed to the two portions of the combustion chamber such that a stable flame is formed in the first portion with substantial vapourisation and gasification of the injected fuel, which flame fully burns up the fuel in the second portion under intimate mixing of the fuel with the combustion air, acting as secondary air, introduced into the second portion.

5. A burner as claimed in any of the preceding claims, wherein the combustion air is heated up by conducting it axially through an annular chamber surrounding the combustion chamber.

6. A burner as claimed in claim 5, wherein the openings in the casing of the combustion chamber are formed by slots between obliquely inwardly pressed fins of the casing.

7. A burner as claimed in any of the preceding claims, wherein a flow component, axially directed towards the nozzle or the bottom of the combustion chamber of the combustion air enters the interior of the combustion chamber at least in the first portion thereof.

8. A burner as claimed in any of the preceding claims, wherein a turbulence nozzle, having a direction of swirl opposed to the potential vortex in the first portion of the combustion chamber, is provided as the oilatomising nozzle.

9. A burner as claimed in any of the preceding claims, wherein the bottom of the combustion chamber is also provided with openings for the passage of the combustion air.

10. A burner as claimed in any of the preceding claims, wherein an incandescant coiled filament is provided for igniting the burner and is secured to the wall of the combustion chamber at a location which is just reached by the atomisation cone of the fuel.

11. An oil-atomisation burner, substantially as hereinbefore described with reference to the accompanying drawings.