BACKGROUND OF THE INVENTION
[0001] This invention relates to oil burners and particularly to oil burner heads.
[0002] 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.
SUMMARY OF THE INVENTION
[0003] 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.
[0004] 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 tubular member to form a primary
air passage, and, in operation, 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 apprecia- . ble radial velocity component at the
exit plane of the burner head, 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, 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 longitudinal axis of the tubes being in a range of in the order
of 50° to 60°, 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,
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 extremities of said tubular members all
being substantially in said exit plane,
the arrangement being such that said flame is substantially a sun-flower shaped flame.
[0005] 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.
[0006] 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 deflector vanes to impart a swirling motion to the air passing
through said primary air passage with an axial and tangential velocity without any
a
ppre- ciable 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 externally 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 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] An embodiment of the present invention will now be described, by way of example,
with reference to the accompanying 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 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 EMBODIMENTS
[0008] Referring to the Figures and particularly to Figures l'and 2, the oil burner head
includes a nozzle 2 for spraying oil under pressure and a first nozzle-surrounding
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.
[0009] 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.
[0010] 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.
[0011] 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
restrictions in the two air passages, and this results in a cylindrical region of
shear between the two air flows causing significant turbulences. The air meeting the
oil in this region of turbulence combined with the rotational 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.
[0012] 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°.
[0013] 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.
[0014] 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 substantially reduce the formation of an air void downstream of the nozzle
outlet.
[0015] Around the circumference of the first tubular member 4, at region 21 (Figure 2),
four equi-spaced entrance slot openings (not shown) are provided through its circumferential
wall from the primary air passage 10 to permit air therefrom to enter the nozzle space
immediately 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.
[0016] 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 formation of an air void downstream of the nozzle outlet, the resulting
flame being a sun-flower shaped flame.
[0017] 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.
[0018] Whilst the perforations 30 have been shown as circular, it will be understood that
they might be of different 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 appear that the range in the required number of vanes is relatively
large.
[0019] The oil supply for the oil burner atomizing nozzle 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.
[0020] 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 (soot) 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 constructed head would operate with two different nozzle sizes
(0.5 U.S. gallons per hour, GPH, and 0.65 US GPH).
[0021] 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 air
flow input needed for good mixing. The electrodes are inserted through the head outside
the secondary tube and set to avoid impingement on them. The air blows the spark into
the oil-air.spray and keeps the electrodes to a reasonable temperature whilst in operation.
[0022] It will be understood that the two air flows produce a region where there are turbulences
of the proper distribution of size with the proper distribution of rotational velocities
(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.
[0023] 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 nozzle and also shields the
nozzle from the radiant heat of the fire
pot.
[0024] 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 least 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 burned that is transferred to either the air or the water that is circulated
through the building to be heated.
[0025] The electrode assembly is not located in the critical air flow path in the head and
downstream-of the head, but there is still enough room for the high voltage conductors
to be installed in the 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 that the spark is blown in the oil air mixture to ensure immediate ignition.
[0026] 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.
[0027] It will be realized that any combination of hole size, configuration or shape that
would produce those desired results would be acceptable.
[0028] 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.
[0029] Ignition of the air oil mixture should occur within a fraction of a second after
the oil spray has started.
[0030] 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.
[0031] The head illustrated produces a symmetrical sun-flower flame which contributes to
better mixing of oil with air.
[0032] 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.
1. A burner head for the combustion of oil with air to produce a flame comprising:
(i) a nozzle for spraying oil under pressure,
(iil 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 coaxially 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-surrounding 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 longitudinal 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 assembly,
(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 wherein 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-surrounding
tubular members and having therein a first set of annularly 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 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 externally 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 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.