CA1167369A

CA1167369A - Oil burner head

Info

Publication number: CA1167369A
Application number: CA000395122A
Authority: CA
Inventors: Gordon W. Ellis; Horace C. Aubrey; Jacques R. Domey
Original assignee: National Research Council of Canada
Current assignee: National Research Council of Canada
Priority date: 1982-01-28
Filing date: 1982-01-28
Publication date: 1984-05-15
Also published as: EP0160134A1

Abstract

ABSTRACT OF THE DISCLOSURE
A burner head for the combustion of oil with air to produce a sun-flower shaped flame with the nozzle-surr-ounded by three tubular members to form a nozzle space, a primary air passage and a secondary passage, a perfor-ated annular disc at the downstream end of the nozzle space, a first set of deflector vanes in the primary air passage, a second set of deflector vanes in the secondary air passage, the lead angles of the vanes to the normal to the longitudinal axis of the burner being in the range of the order of 50° to 60°.

Description

1~i'73~9 , BACKGROUND OF THE INVENTION
Thi invention relates to oil burners and particu-larly to oil burner heads.
Many oil burners are used for heating homes and commercial or industrial buildings. In recent years the energy supply situation has caused the price of oil to increase dramatically so that considerable effort is being put forth to find a more efficient way to use oil as a heating medium.

SUMMP~RY OF THE INVENTION
From one aspect of the present invention it is an object to provide an oil burner head which will facilitate a more efficient use of oil as a fuel.
Accordingly the present invention provides a burner head for the combustion of oil with air to produce a flame comprising: a nozzle for spraying oil under pressure, a - first nozzle-surrounding, tubular member surrounding and coaxially spaced from the said nozzle and open at the downstream end, a second tubular member surrounding and coaxially spaced from said first nozzle-surrounding tubu-lar member to form a primary air passage, and, in opera-tion, to provide air to the open downstream end of the first nozzle_surrounding tubular member, a third tubular member surrounding and coaxially spaced from said second tubular member to form a secondary air passage, a first set of annularly arranged deflector vanes in said primary air passage to impart a swirling action to the air passing through said primary air passage, said air having an axial and tangential velocity without any appreciable radial velocity component at ~he exit plane of the burner head, a second set of annularly arranged deflector vanes 3f~

in said secondary air passage to impart a swirling action to the air passing through said secondary air passage, said air having an axial and tangential velocity without any appreciable radial velocity component at the exit plane of the burner head, means for causing air to enter said primary air passage and said secondary air passage substantially axially thereof, the lead angles of the first set of vanes and the second set of vanes to the normal to the longitud-. inal axis of the tubes being in a range of in the order of 50 to 60, a perforated, annular disc partially blockingand radially inwardly spaced from the downstream end of the first nozzle-surrounding member and providing, a) a central aperture for oil from the nozzle and air, b) a heat shield for the nozzle, c) air flow through perforations for substantially reducing the formation of an air void downstream of the nozzle outlet, an igniter assembly for initiating said flame and located externally of said air passages containing said deflector vanes whereby the air flow through said passages is substantially free of interruption by said igniter assembly, the exit from said nozzle and the outward extremi-ties of said tubular members all being substantially in said exit plane, the arrangement being such that said flame is sub-stantially a sun-flower shaped flame.
From another aspect of the present invention it is an object to provide a method of combusting oil which will facilitate a more efficient use of oil as a fuel.

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According to this aspect there is provided a method of combusting oil comprising forcing said oil through a nozzle, forcing combustion air through a primary air passage between first and second nozzle-surrounding tubular members and having therein a first set of annularly arranged de-flector vanes to impart a swirling motion to the air passing through said primary air passage with an axial and tangential velocity without any appreciable radial velocity component, forcing combustion air through a secondary air passage between said second and a third nozzle-surrounding tubular member and having therein a second set of annularly arranged deflector vanes to impart a swirling motion to the air passing through said secondary air passage with an axial and tangential velocity without any appreciable radial velocity component, arranging the lead angles of the first set of vanes and the second set of vanes to the normal to the longitudinal axis of the tubes to be in a range of in the order of 50 to 60, providing an igniter assembly ex-ternally of said air passages containing deflector vanes whereby the air flow through said passages is substantially free of interruption by said igniter assembly and arranging the exit from said nozzle and the outward extremities of said tubular members substantially in said exit plane, and forcing combus~ion air through said first nozzle-surrounding tubular member and through a per~orated, annular disc parti-ally blocking and radially inwardly spaced from the down-stream end of said first nozzle-surrounding member to provide a sun-flower shaped flame.
BRIEF DESCRIPTION OF THE DRA~INGS
.
An embodiment of the present invention will now be j described, by way of example, with reference to the accom-panying drawings in.which:-Figure 1 is a frontaL view of an oil burner head, Figure 2 is a cross-sectional view on the line II-II
of the oil burner head shown in Figure 1, Figure 3 is a front view of the radiation shield and some of the vanes in the nozzle of Figure 1, Figure 4 is a side view corresponding to Figure 3 to illustrate said vanes, and Figure 5 is a diagrammatic flat layout of the arrangement of Figure 4.

DESCRIPTION OF PREFERRED EMBODIMh'NTS
Referring to the Figures and particularly to Figures 1 ànd 2, the oil burner head includes a nozzle 2 for spraying oil under pressure and a first noz21e-surround-ing ,~;' ..
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tubular member 4 which surrounds and is coaxially spaced from the nozzle 2 to form a nozzle space. The tubular member 4 is open at the downstream end 6 thereof. A
second nozzle-surrounding tubular member 8 having a diameter larger than the tubular member 4 is provided coaxially located with respect of the tubular member 4 and the nozzle 2. A primary air passage 10 is thus formed between the first tubular member 4 and the second tubular member 8.
A third nozzle-surrounding tubular member 12 is provided of a larger diameter than the tubular member 8 and located coaxially therewith. Thus a secondary air passage 14 is provided between the second tubular member 8 and the third tubular member 12.
A first set of annularly arranged deflector vanes 16, sometimes called fins, is provided in the primary air passage 10 to impart a swirling action to air passing through the primary air passage whilst a second set of annularly arranged deflector vanes 18 is provided in the secondary air passage 14 to impart a swirling action in the same rotational direction to air passing through the secondary air passage.
The arrangement of the vanes, and the corresponding dimensions, is such that two hollow cylindrical volumes of air exit the primary and secondary air passages with a tangential velocity, due to the angle of the vanes in the respective passage. The velocity of the two air volumes is different, due to the different dimensions and restric-tions in the two air passages, and this results in a cylindrical region o shear between the two air flows causing significant turbulences. The air meeting the oil in this region of turbulence combined with the rotational ~_~tj~73~3 velocity of the air produces excellent mixing between the air and the oil from nozzle 2 and a radial movement of the oil droplets. This is due to the centrifugal force acting on the oil droplets and to the radial velocity of the air volume as a result of the lower pressure farther from the longitudinal axis 20 of the oil burner head.
Thus there is produced a hollow cone of oil which is well mixed with slightly more than the stoichiometric quantity of air and this produces clean combustion and excellent furnace efficiency.
The lead angles of the first and second sets of vanes, 16 and 18, to the normal to the longitudinal axis 20 is in the range of the order of 50 to 60.
As will be seen from Figures 1 and 2, a perforated annular disc 22 is provided and this partially blocks, and is radially inwardly spaced from, the downstream end of the first nozzle-surrounding member 4. As shown in Figures 1 and 3, the spacing is obtained by providing the disc 22 with three spacing tabs 24 which are used to weld the disc 22 to the first nozzle-surrounding tubular member 4. Thus a space 26 is formed between the disc 22 and the tubular member 4. In use, oil passes through a central aperture 28 whilst air is forced through surrounding perforations 30 in the annular disc 22.
The central aperture 28 has a diameter of 0.15 inches whilst the surrounding perforations 30 have a diameter of 0.024 inches. Thirty two surrounding perforations 30 are provided in the disc 22 and these are arranged in two concentric rings as shown in Figures 1 and 3 to substantial-ly reduce the formation of an air void downstream o the nozzle outlet.

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-Around the circumference of the first tubular member 4, at region 21 (Figure 2~, four equi-spaced entrance slot openings (not shownl are provided through - its circumferential wall from the primary air passage 10 to permit air therefrom to enter the nozzle space immedi-ately around nozzle 2 and behind disc 22. Thus, in use, some air flows through the primary air passage 10 and some air flows through disc 22 at the open downstream end of the first nozzle-surrounding member 4~ It will be understood that, in some cases, one slot opening will be adequate.
The disc 22 acts as a heat shield for the nozzle 2 protecting it from radiant heat reflected from the fire pot (not shown) whilst the air flow through perforations 30 and the gap between the disc and the inner surface of the first tubular member substantially reduces the forma-tion of an air void downstream of the nozzle outlet, the resulting flame being a sun-flower shaped flame.
In Figure 4 the shape of the vanes 16 can be clearly seen on the external surface of the first tubular member 4.
Figure 5 is a rolled-out or flat layout corresponding to Figure 4 to illustrate the vanes 16 having a 55 lead angle of fin, i.e. 55 to the normal to the longitudinal axis 20 of the oil burner nozzle in the illustrated practical embodiment .
Whilst the perforations 30 have been shown as circu-lar, it will be understood that they might be of di~ferent shapes, size or number, for example they may be rectangular slots. In different constructed embodiments the number of vanes has been 8 and 12 and it would thus appeax that the range in the required number of vanes is relatively large.

The oil supply for the oil burner atomizing nozzle ~ 73~;9

2 is fed along an oil feed line 23 whilst ignition electrodes 25 and 27 are connected to an electrical supply line by way of terminals such as 29 surrounded by a high voltage insulator 31.
Whilst a new oil burner may be manufactured with an oil burner head according to the present invention, it has been found that the oil burner head is particularly suitable as a retro-fit oil burner head for fitting in existing oil furnaces, and also this new burner or retrofitted oil burner can be installed in most existing furnaces without ~ requiring major modifications to the furnace itself. Most standard house burner can supply the required volume of combustion air at a barrel pressure in the range of 0.25 to 0.35 inches of water which is necessary to achieve the velocities required in the two air passages 10 and 14, so as to provide the turbulence downstream of the outlet of these air passages to obtain the required mixing. The illustrated head provides a twin air passage whereby air is combined with oil spray from a standard oil burner nozzle to produce a very low carbon tsoot) content (clean fire) and high carbon dioxide content flue gases. A
nozzle adapter with disc 22 may be placed in front of the nozzle with the appropriate perforations and aperture as discussed above. Thus the nozzle is maintained cool on its operation cycle and the disc acts as a radiation shield after burner shut-down. Air is metered in the rear of the nozzle adapter tube. It was found that one construc-ted head would operate with two different nozzle sizes (0.5 U.S. gallons per hour, GPH, and 0.65 US GPH).
To build a highly efficient burner head we have found that it is preferable not to have the electrodes in the air path in the blast tube as this changes the smooth -i'7~6~3 air flo~ inpu~ needed ~or yood mixing. The electrodes are insertedthrough the head outside the secondary tube and set to avoid impinyement on them. The air blows the spark into the oil-air spray and keeps the electrodes to a reasonable temperature whilst in operation.
It will be understood that the two air flows pro-duce a region where there are turbulences of the proper di tribution of size with the proper distribution of rotational ve~ocities (previously called "region of shear") so that when the atomized oil enters that region it mixes very well, on a very small scale, with the air.
The perforated disc supplies enough air in the centre to produce an over pressure in that central area to avoid an inflow of the air oil mixture and avoid combustion in that area which would raise the temperature of the no~zle and also shields the nozzle from the radiant heat of the firepot.
As during the combustion of the oil there is almost always enough oxygen, on a microscopic scale, near each molecule of oil, very little free carbon is produced. This is what is called clean combustion. High efficiency is a result of the fact that as the mixing between air and oil is excellent everywhere, where combustion occurs, very little excess air is required to ensure at 18ast stoichiometry everywhere where combustion occurs and as a result of that, very little heat is required from the combustion to heat up excess air that has the negative effect of increasing the velocity in the heat exchanger, reducing the time of heat transfer and reducing the total heat per unit of fuel burn-ed that is transferred to either the air or the water that is circulated through the building to be heated.

~tj~7~9 The electrode assembly is no$ located in the criti-cal air flow path in the head and downstream of the head, but there is still enough room ~or the high voltage cond-uctors to be installed in thé barrel of the oil burner and go through the face of the burner head outside of the air flow. Only the electrodes themselves are placed in the air flow so tha~ the spark is blown in the oil air mixture to ensure immediate ignition.
The perforations in the disc are there to:
1. allow the oil to be sprayed without impinging on the disc, and without allowing too much radiant heat to be incident on the nozzle;
2. produce a sufficiently uniform air flow in front of it so as not to create a low pressure area nor to be too turbulent so as to have detrimental effect on the oil spray.
It will be realized that any combination of hole size, configuration or shape that would produce those desired results would be acceptable.
A common problem with oil burner heads is the positioning electrodes without disturbing flow of combustion air and without requiring significant modifications to oil burners and furnaces which would make them uncompatible with existing furnaces.
Ignition of the air oil mixture should occur within a fraction of a second after the oil spray has started.
This embodiment clearly shows where the ignition electrode assembly can be positioned so as not to disturb the symmetry of flow of the combustion air hence permit a combustion-which is not perturbed by the electrodes, and the location of these is compatible with present oil burner housings.
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The head illustrated produces a s~mmetrical sun-flower flame which contributes to better mixing of oil with air.
It has been found that the described burner head can burn oil at very low oil flow rates using a standard nozzle and with all the advantages previously described -i.e.: efficiency, cleanliness, compatibility with most existing furnaces and oil burner housings. The nozzles that have been tried had flow rates between 0.4 and 0.65 US
GPH but it is expected that the embodiment will work with 0.3 U.S. GPH - the lowest flow rate which can be obtained with presently available commercial nozzles.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A burner head for the combustion of oil with air to produce a flame comprising:
(i) a nozzle for spraying oil under pressure, (ii) a first nozzle surrounding, tubular member surrounding and coaxially spaced from the said nozzle and open at the downstream end, (iii) a second tubular member surrounding and coaxial-ly spaced from said first nozzle surrounding tubular member to form a primary air passage, and, in operation, to provide air to the open downstream end of the first nozzle-surround-ing tubular member, (iv) a third tubular member surrounding and coaxially spaced from said second tubular member to form a secondary air passage, (v) a first set of annularly arranged deflector vanes in said primary air passage to impart a swirling action to the air passing through said primary air passage, said air having an axial and tangential velocity without any appreciable radial velocity component at the exit plane of the burner head, (vi) a second set of annularly arranged deflector vanes in said secondary air passage to impart a swirling action to the air passing through said secondary air passage, said air having an axial and tangential velocity without any appreciable radial velocity component at the exit plane of the burner head, (vii) means for causing air to enter said primary air passage and said secondary air passage substantially axially thereof, (viii) the lead angles of the first set of vanes and the second set of vanes to the normal to the longitudin-al axis of the tubes being in a range of in the order of 50° to 60°, (ix) a perforated, annular disc partially blocking and radially inwardly spaced from the downstream end of the first nozzle-surrounding member and providing, a) a central aperture for oil from the nozzle and air, b) a heat shield for the nozzle, c) air flow through perforations for substantially reducing the formation of an air void downstream of the nozzle outlet, (x) an igniter assembly for initiating said flame and located externally of said air passages containing said deflector vanes whereby the air flow through said passages is substantially free of interruption by said igniter assem-bly, (xi) the exit from said nozzle and the outward extremities of said tubular members all being substantially in said exit plane, (xii) the arrangement being such that said flame is substantially a sun-flower shaped flame.

2. A burner head according to claim 1 in which said central aperture and said perforations are circular.

3. A burner head according to claim 1 in which said perforations are rectangular.

4. A burner head according to claim 1, 2 or 3 where-in at least one opening is provided in the circumferential wall of said first tubular member to permit, in use, some of the air passing through said primary air passage to exit through said perforated annular disc.

5. A method of combusting oil comprising forcing said oil through a nozzle, forcing combustion air through a primary air passage between first and second nozzle-surround-ing tubular members and having therein a first set of annu-larly arranged deflector vanes to impart a swirling motion to the air passing through said primary air passage with an axial and tangential velocity without any appreciable radial velocity component, forcing combustion air through a secon-dary air passage between said second and a third nozzle-surrounding tubular member and having therein a second set of annularly arranged deflector vanes to impart a swirling motion to the air passing through said secondary air passage with an axial and tangential velocity without any apprecia-ble radial velocity component, arranging the lead angles of the first set of vanes and the second set of vanes to the normal to the longitudinal axis of the tubes to be in a range of in the order of 50° to 60°, providing an igniter assembly externally of said air passages containing deflector vanes whereby the air flow through said passages is sub-stantially free of interruption by said igniter assembly and arranging the exit from said nozzle and the outward extremities of said tubular members substantially in said exit plane, and forcing combustion air through said first nozzle-surrounding tubular member and through a perforated annular disc partially blocking and radially inwardly spaced from the downstream end of said first nozzle-surrounding member to provide a sun-flower shaped flame.

6. A method according to claim 5 wherein some of the air passing through said primary air passage is forced through at least one opening in the circumferential wall of said first nozzle-surrounding tubular member and through said perforated, annular disc.