[0001] This invention relates to oil fuel atomisers for use in oil burners.
[0002] A common practice in oil burners for large boilers is to use atomisers of the Y-jet
type in which a number of ports are arranged at an angle to the burner axis to produce
a hollow conical spray. Each exit port has a co-axial atomising fluid port for injection
of the atomising fluid (which may be steam or air) and also has an oil port entering
at an angle. A degree of mixing between the atomising fluid and oil takes place in
the exit port and the two phase mixture then expands out of the exit port to form
a spray. One of the problems with this type of atomiser is that the jet of oil from
the oil port tends to impinge on the opposite side of the exit port where it forms
a thick film. This thick film can persist through the exit port to the end thereof
and hence lead to the formation of relatively large oil droplets.
[0003] In British Patent Specification No 1470671 there is described an atomiser in which
the oil is introduced into the exit ports either axisymmetrically (that is symmetrical
with regard to the axis of the exit port) through an annular port or symmetrically
through a number of discrete oil ports. This arrangement prevents the formation of
a thick asymmetric oil film. In the construction described in the aforementioned specification
the ports are formed as a number of inserts which are mounted in a unitary body. This
construction gives a significant improvement in performance over a Y-jet but there
can be problems in the cleaning of this type of atomiser.
[0004] In accordance with the present invention a multi-jet atomiser for an oil burner comprises
a body having a plurality of exit ports leading outwardly from an annular mixing chamber
to form a conical spray, means for injecting oil through oil inlet ports into the
mixing chamber, the oil being injected at each inlet port in a direction to produce
a toroidal recirculation in the annular mixing chamber with the injected oil from
each inlet port passing close to an exit port at approximately right angles to the
axis of that exit port and means for injecting an atomising fluid into the mixing
chamber at a plurality of positions in a wall of the mixing chamber.
[0005] With this construction, the atomising fluid is injected into a turbulent recirculating
flow region through ports in the wall of the mixing chamber opposite the exit ports.
The atomising fluid thus becomes well mixed with the oil and carries part of the recirculating
mixture into the exit ports in the appropriate directions to pass through these ports
and to expand outwardly therefrom as a fine spray.
[0006] Conveniently there is provided a plenum chamber or a plurality of plenum chambers
through which the oil is fed into the aforementioned oil inlet ports.
[0007] The aforementioned annular mixing chamber preferably has a curved surface opposite
each oil injection port shaped to direct the impinging oil around a curved path towards
the axis of the burner assembly and hence to promote the toroidal recirculation.
[0008] The aforesaid means for injecting an atomising fluid into the mixing chamber may
be at a plurality of positions in a wall of the mixing chamber opposite the exit ports.
[0009] The mixing chamber may have walls shaped to guide the injected oil in a direction
across the exit ports and thence around in a recirculatory path over the wall opposite
the exit ports.
[0010] Conveniently the annular mixing chamber and, if provided, the plenum chamber or chambers
are constituted by regions between the end of a main burner body element containing
a central atomising fluid passage extending axially through the body element to atomising
fluid injection ports in the end thereof and a cap which is secured, e.g. threaded,
onto the main burner body element and which has the aforesaid exit ports.
[0011] Alternatively the main burner body element may contain a central oil passage extending
axially through the body element to said oil inlet ports.
[0012] In this case the atomising fluid is passed through passages around the central oil
passage.
[0013] The following is a description of a number of embodiments of the invention, reference
being made to the accompanying drawings in which:-
Figure 1 is a front elevation of an atomiser for an oil burner;
Figure 2 is a section along the line 2-2 of Figure 1 through the front part of the
burner, showing the atomiser; and
Figures 3, 4 and 5 are sections, similar to Figure 2, through the front parts of burners
forming further embodiments of the invention.
[0014] Referring to Figures 1 and 2, the atomiser has a main elongate body member 10 with
a central passage 11 extending axially through the member 10 towards the end thereof
to carry an atomising fluid, either steam or air. This passage 11 terminates in a
frusto- conical face 12 from which a number of ports 13 extend, these ports leading
into an annular mixing chamber 15. This mixing chamber has a plurality of exit ports
14 as seen most clearly in Figure 1. These ports 14 are formed in cap member 16, internally
threaded at 17, which fits over the end of the body member 10. In the particular embodiment,
the ports 13 and the ports 14 are at angles of about 45
o to the axis of the assembly. These ports 13 and 14 need not necessarily be at the
same angle to the axis of the assembly. The angles for the exit ports 14 would depend
on the desired cone angle of the spray. In some cases it may be preferred to make
the inlet ports 13 parallel to the axis of the assembly.
[0015] Oil from an annular region 20 around the outside of the body member 10 passes through
a plurality of oil ducts 21 in the cap member 16, into an annular plenum chamber 22.
From the plenum chamber, the oil is injected into a mixing chamber 15 through a ring
of ports 23 through an upstanding part 24 in the body member 10. The injection from
the ports 23 into the mixing chamber is in a direction such as to produce a toroidal
circulation of the oil in the mixing chamber 15. The oil ports 23 are arranged to
produce oil jets which pass close to the exit ports 14 at approximately right angles
to the axis of the exit ports. These oil jets are directed towards a curved surface
25 of the mixing chamber, this surface being shaped so that the oil is diverted around
a curved path inwardly towards the axis of the burner assembly. This shaping facilitates
the recirculation of the injected oil. It will be seen that the atomising fluid is
injected through the ports 13 into the mixing chamber at an angle to the direction
of injection of the oil through ports 23. In the mixing chamber, the atomising fluid
becomes well mixed with the oil. In the particular example illustrated two rows of
ports 13 are provided for injection of the atomising fluid. The oil is injected at
ports 23 in the form of oil jets. A proportion of the recirculating mixture will emerge
from the mixing chamber 15 through the interstices between these oil jets and will
pass out through the exit ports 14 as a two-phase mixture which expands out of these
ports to form a fine spray.
[0016] The plenum chamber 22 and mixing chamber 15 are formed as gaps between the cap member
16 and the main body member 10. The shaping of these members 10, 16 is such that,
when the cap member is screwed in position on the body member, the gaps between the
cap member and body member form the mixing chamber and plenum chamber. By providing
a plenum chamber 22, there need not be equal numbers of ducts 21 and ports 23 and
they do not have to be accurately aligned on assembly.
[0017] The exit ports 14 have their axes defining a cone, the axis of this cone being aligned
with the longitudinal axis of the burner and the apex of the cone being on that longitudinal
axis. The oil spray from the plurality of exit ports 14 thus is in the general form
of a hollow cone. In the mixing chamber 15 the atomising fluid is injected through
ports on the opposite wall of the chamber, that is the wall facing the exit ports.
This wall is conical. It is not necessary in this construction however that the cap
member 16 is angularly aligned with respect to the body element 10. Alignment of the
injection ports and exit ports is not critical and, in the particular embodiment illustrated,
there are two rows of injection ports 13 and one row of exit ports 14. The fluid entering
the exit ports is well mixed in the mixing chamber and is forced into the exit ports.
This construction gives good atomisation.
[0018] The simple construction having a cap 16 screwed onto the body member 10 enables the
atomiser to be easily cleaned after these parts are separated.
[0019] In the above-described embodiment, the exit ports 14 are evenly spaced with their
axes lying on the same cone. In some cases, however, it may be advantageous to have
these exit ports on more than one cone. The ports 14 need not necessarily be evenly
spaced; they may be irregularly spaced or grouped.
[0020] In Figures 1 and 2, the atomising fluid ports are directly opposite and pointing
towards the exit ports. Figure 3 illustrates a modification of that construction and
the same reference characters are used to indicate corresponding components. In Figure
3 the atomising fluid inlets to the mixing chamber, as shown at 30, produce atomising
fluid jets which tend to counter the toroidal circulation produced by the oil jets
23. This may be advantageous in some cases to enhance mixing with the oil. In this
construction, because the inlets to the atomising fluid ports 30 are at a greater
distance from the atomiser axis than in the arrangement of Figures 1 and 2, it is
easier to provide the requisite number of ports.
[0021] In the constructions of Figures 1, 2 and 3, the atomising fluid is fed axially through
a central passage 11 in the main burner body 10. In some cases, as shown in Figures
4 and 5, it may be preferred to reverse the position of the oil and atomising fluid
feeds, the oil feed being axially through a passage 41 and the atomising fluid being
from an annular region 42 around the outside of the body member 10. This arrangement
makes the incorporation of sufficient atomising fluid port area much easier by locating
these ports as far as possible from the atomiser axis. The fact that the oil ports
shown at 43 in Figure 4 are now much closer to the axis is not too much of an imposition
because the total oil port area is generally significantly less than the total atomising
fluid port area.
[0022] Figure 5 illustrates a modification of Figure 4 in which the oil ports, shown at
50, are approximately parallel to the atomiser axis. The mixing chamber wall is shaped
to direct the oil jets across the approach region to the exit ports. This arrangement
may simplify manufacture.
1. A multi-jet atomiser for an oil burner comprising a body having a plurality of
exit ports leading outwardly from an annular mixing chamber to form a conical spray,
means for injecting oil through oil inlet ports into the mixing chamber, the oil being
injected at each oil inlet port in a direction to produce a toroidal recirculation
in the annular mixing chamber with the injected oil from each inlet port passing close
to an exit port at approximately right angles to the axis of the exit port and means
for injecting an atomising fluid into the mixing chamber at a plurality of positions
in a wall of the mixing chamber.
2. A multi-jet atomiser as claimed in claim I wherein said means for injecting an
atomising fluid into the mixing chamber are at a plurality of positions in a wall
of the mixing chamber opposite the exit ports.
3. A multi-jet atomiser as claimed in claim 1 wherein the mixing chamber has walls
shaped to guide the injected oil in a direction across the exit ports and thence around
in a recirculatory path over the wall opposite the exit ports.
4. A multi-jet atomiser for an oil burner as claimed in any of the preceding claims
and having a plenum chamber or a plurality of plenum chambers through which the oil
is fed into said oil inlet ports.
5. A multi-jet atomiser for an oil burner as claimed in any of the preceding claims
wherein the annular mixing chamber is constituted by regions between the end of a
main burner body element containing a central atomising fluid passage extending axially
through the body element to atomising fluid injection ports in the end thereof and
a cap which is secured onto the main burner body element and which has the said exit
ports.
6. A multi-jet atomiser for an oil burner as claimed in any of claims 1 to 3 and having
a plenum chamber or a plurality of plenum chambers through which the atomising fluid
is fed into the mixing chamber.
7. A multi-jet-atomiser for an oil burner as claimed in any of claims 1 to 4 or 6
wherein the annular mixing chamber is constituted by regions between the end of a
main burner body element containing a central oil passage extending axially through
the body element to said oil inlet ports and a cap which is secured onto the main
burner body element and which has said exit ports.
8. A multi-jet atomiser as claimed in claim 5 as appendant to claim 6 wherein said
cap and said main burner body element have co-operating surfaces defining said plenum
chamber or chambers.
9. A multi-jet atomiser for an oil burner as claimed in any of the preceding claims
wherein said annular mixing chamber has a curved surface opposite each oil inlet port
shaped to direct the impinging oil around a curved path towards the axis of the burner
assembly and hence to promote the toroidal recirculation.
10. A multi-jet atomiser as claimed in any of the preceding claims wherein said exit
ports comprise a plurality of ports evenly spaced around the longitudinal axis of
the burner, the axes of the ports defining a conical surface symmetrically around
and with its apex on said longitudinal axis.