[0001] This invention relates to a blue flame burner for liquid fuels.
[0002] Known in the art are blue flame burners for liquid fuels which, while being much
more efficient than traditional white flame burners, require the provision of two
discrete combustion air feed paths to the burner combustion chamber. The two paths
are conventionally designated primary air path and secondary air path, respectively.
The provision of such dual path involves, in addition to designing and construction
problems, also the solution of complex problems connected with the volume and velocity
metering of the air flown therethrough, as well as of mutual correlation and interdependence.
[0003] Thus the task of this invention is to provide a blue flame burner for liquid fuels
which, additionally to substantially removing the cited problems and shortcomings
affecting prior burners, can afford a definitely superior performance level.
[0004] Within this task it is an object of the invention to provide a burner as indicated,-which
affords,to all practical effects, a complete combustion, leaving no unburned portions
of the fuel, by ensuring that the combustion can take place in a stoichiometric ratio
of fuel to combustion air, or a ratio very close to the theoretical stoichiometric
values. This means that the excess air flowing through the burner is nil or close
to zero, for a higher thermal efficiency of the burner.
[0005] A further object of this invention is to provide a burner as indicated, which has
a very simple construction, comprises a minimum of components, can be readily and
conveniently assembled and disassembled, and can be manufactured at a highly competitive
cost.
[0006] These and other objects, such as will be apparent hereinafter, are achieved by a
blue flame burner for liquid fuels, characterized in that it comprises an externally
cooled combustion chamber, a pre-heating chamber for combustion air from a source
of pressurized air, a calibrated neck wherethrough said pre-heating chamber is communicated
to said combustion chamber, an atomizing injector cantilever mounted inside said calibrated
neck and being adapted to scatter atomized fuel toward said combustion chamber, and
a pressurized fuel intake conduit arranged within said air pre-heating chamber in
heat exchange relationship therewith and being connected to a source of pressurized
fuel.
[0007] Further aspects and advantages will become apparent after considering the following
detailed description of a preferred embodiment of this invention, given herein by
way of example and not of limitation, in conjunction with the accompanying illustrative
drawings, where:
Figure 1 is a schematic view, in elevation and longitudinal section, of a burner according
to the invention;
Figure 2 is a schematic elevation view of the burner of Figure 1, as placed at the
inlet end of a refractory material lined chamber; and
Figure 3 is a C02 vs. 02 percent graph.
[0008] With reference to Figures 1 and 2, where similar parts have been designated with
the same reference numerals, this burner 1 has an elongate hollow body 2, a calibrated
nosepiece 3 removably attached to one end of the hollow body 2, and an end cap 4,
removably attached to the other end of the hollow body. The latter is formed, at an
intermediate region thereof, with an annular increased-thickness portion, whereat
a restriction or neck 5 is defined internally. The annular thickened portion in the
hollow body 4 acts as a partition member separating two internal cavities in the body
4, namely a front cavity 6 and rear cavity 7. The front cavity 6 is, thus, delimited
on the front by the nosepiece 3 and constitutes the burner combustion chamber, which
is cooled externally by a fluid circulated at 6a, while the rear cavity 7 is closed
by the end cap 4 and constitutes a combustion air pre-heating chamber, as will be
explained hereinafter. The chambers 6 and 7, and the neck 5, are all aligned together
along the longitudinal axis x-x.
[0009] At the neck 5, there is arranged, in a removable manner, a bushing 8, which abuts
externally and peripherally against the inner wall of the neck 5, and has an inner
bore 9 convergent toward its calibrated end 10 facing the chamber 6.
[0010] The end cap 4, and accordingly the chamber 7, is communicated, through a hole 11
formed through a lug 12 whereto is secured one end of a preferably flexible hose line
13, to the delivery end of a blower or compressor 15 of the two-stage type which is
arranged to deliver pressurized air into the chamber 7. Through the end cap 4, a hole
16 is also formed which extends coaxial with the axis x-x, and is connected to a a
pressurized liquid fuel (e.g. Diesel oil) supply conduit 17. nore specifically, the
hole 16 is formed through an inside lug 18 which,from the rear wall of the end cap
4
t extends in cantilever relationship along the axis x-x over the entire length of the
end cap. At the free end of the lug 18, there is secured one end of a conduit or line
19, which enters the bushing 8 cantilever-fashion. The free end of the conduit 19
accommodates, mounted therein, an atomizing injector device 20, which barely clears
with its spray nozzle 21 the calibrated end 10 of the bushing 8.
[0011] On that section of the line 19 which extends outside of the bushing 8, there is slidably
mounted, and adjustably fastened, a disk or diaphragm 22 which functions as a restrictor
element for the air coming from the passage 11 and directed to the combustion chamber.
[0012] Laterally to the restriction 5, at the thickened region of the hollow body 2, there
are formed holes intended to accommodate flame ignition and control metal electrodes
24, which protrude into the combustion chamber 6.
[0013] The pressurized fuel supply line 17 is in turn connected, with the interposition
of a control solenoid valve 25, to a suitable fuel pump 26.
[0014] At the intake mouth 27 of the blower 15, a conduit 28 is provided which can be shut
off by means of a movable shutter 29 driven by a solenoid valve 30. Upstream of the
shutter 29 is located a metering device 31 arranged to control the flow rate of the
combustion air directed to the burner.
[0015] Preferably, the metering device 31 can be adjusted by means of a micrometric adjustment
pin screw.
[0016] The burner described hereinabove operates in a very simple manner. After starting
the blower 15 and actuating the pump 26, the shutter 29 will be in its air shut-off
position; however, thanks to a central hole 32 provided therein, a sufficient amount
of air can still be admitted to the combustion chamber 6 to cause ignition. Once the
fuel has been so ignited, the solenoid valve 30 will be controlled, by an electronic
control unit not shown in the drawings, to open, so that pressurized combustion air
can be delivered into the chamber 7 at a pressure and volume consistent with the amount
of fuel issueing from the atomizing injector 20, and in all cases in stoichiometric
proportion for burning the particular fuel being used.
[0017] In operation, the hollow body 2 will be heated at the combustion chamber 3, and transfer
part of its heat by conduction to both the air within the chamber 7 and fuel flowing
through the lug 18. By convection, the air contained in the chamber 7 will in turn
aasist in the transfer of heat from the inner walls of the chamber 7 to the conduit
19, thereby the oncoming fuel to the atomizing injector device 20 is adequately pre-heated.
[0018] The air contained in the chamber 7 initially undergoes expansion in flowing from
the hole 11 to that portion of the chamber 7 which is located upstream of the diaphragm
22. The diaphragm 22 will instead force the air to flow peripherally past it and then
sweep the inner wall of the tubular body 2, thereby its velocity is increased. Between
the diaphragm 22 and bushing 8, the air is subjected to further expansion, and by
virtue of the bushing 8 being configured to protrude in part, cantilever-fashion,
toward the interior of the chamber 7 from the restriction or neck 5, it undergoes
a mixing and thermal stabilization process prior to flowing through the bore 9 in
the bushing 8. Through the bore 9, the air-is uniformly distributed along and around
the atomizing injector device 20, and upon reaching the calibrated end 10 of the bushing
8, it is directed concentrically toward the interior of the chamber 9, to encircle
the jet(s) of atomized fuel issueing from the nozzle 21. It is important that the
atomized fuel spray be focussed on the area of highest turbulence of the combustion
air being fed into the combustion chamber.
[0019] With burners constructed as described hereinabove and operating as herein detailed,
efficiency rates have been achieved on a regular basis which equal or exceed 99 percent,
as against maximum rated efficiencies of 82-85 percent of comparable white flame burners
of conventional design and construction.
[0020] Moreover, besides the very high thermal efficiency afforded by a burner according
to this invention, several other advantages can be secured, among which:
- complete combustion of the fuel with total absence of unburned residue;
- high temperature of the resulting flame emerging from the combustion chamber 6;
- issue of polluting gases in negligible amounts; and
- very low maintenance costs, largely on account of the absence of unburned products.
[0021] Tests have been carried out on a burner as described above, having its nosepiece
3 located at the inlet end of a chamber 33 lined with tiles 34 of a refractory material,
as shown in Figure 2. The . refractory material lining, upon becoming red-hot, will
issue light in the white-red bands with a high emissivity. Thus, inside the chamber
33 temperatures in excess of 1,500°C are to be achieved within few minutes (3 to 5
minutes) from burner ignition.
[0022] with a burner 1 and chamber 33 as shown in Figure 2, but associated with a small-size
boiler (having outside dimensions of 45 x 88 x 58 cm) surrounded by a water jacket,
actual tests have provided the following values:

[0023] As may be appreciated from the graph of Figure 3 (Ostwald triangle), for a content
of carbon dioxide of 14.5 percent, there only occurs a both theoretical and practical
excess of air of 1.3. Moreover, the virtual absence of carbon monoxide from the combustion
products along with the high percentage of carbon dioxide is a sure indication, to
all practical effects, of all the fuel being burned completely.
[0024] Actual tests have also shown that the sizing of this burner to meet varying power
requirements in different applications will depend on the varying and mutual correlation
of but a few structural elements. These are the inlet port size of the metering device
31 (T), the port size (U) of the calibrated end 10 of the nozzle 8, the maximum inside
diameter (C) of the combustion chamber, the length (L) of the combustion chamber,
and the diameter (B) of the nosepiece 3.
[0025] The following exemplary correlations of the above- specified values T,U,C,L and B
have shown to be advantageous in practicing the invention:

[0026] The above-tabulated results relate to a fuel delivery pressure of 18
kg/c
m2.
[0027] The invention as described is susceptible to many modifications and variations without
departing from the scope and spirit of the instant inventive concept.
[0028] The materials and dimensions used may vary to suit individual applicational requirements.
1. A blue flame burner for liquid fuels, characterized in that it comprises an externally
cooled combustion chamber (6), a pre-heating chamber (7) for combustion air from a
source of pressurized air, a calibrated neck (5) wherethrough said pre-heating chamber
(7) is communicated to said combustion chamber (6), an atomizing injector (20) cantilever
mounted inside said calibrated neck (5) and being adapted to scatter atomized fuel
toward said combustion chamber (6), and a pressurized fuel intake conduit (16) arranged
within said air pre-heating chamber (7) in heat exchange relationship therewith and
being connected to a source of pressurized fuel.
2. A burner according to Claim 1, characterized in that said neck (5) accommodates
a calibrated passage bushing (8) adjacent said combustion chamber (6).
3. A burner according to either Claim 1 or 2, characterized in that said combustion
and pre-heating chambers (6,7) are formed within an internally restricted hollow body
(2) closed at one end by a calibrated nosepiece (3) adapted to confine said combustion
chamber (6), and at the other end by an end cap (4) adapted to confine said pre-heating
chamber (7).
4. A burner according to Claim 3, characterized in that said end cap (4) has a bored
lug (18) connected to said pressurized fuel supply source and adapted to feed and
cantilever carry said atomizing injector 20.
5. A burner according to Claim 4, characterized in that said combustion chamber (6),
calibrated restriction or neck (5), pre-heating chamber (7), and end cap bored lug
(18) are all aligned together along a common axis.
6. A burner according to any of the preceding claims, characterized in that it further
comprises a velocity regulator for the airflow entering said pre-heating chamber (7).
7. A burner according to Claim 6, characterized in that said regulator comprises a
disk-like diaphragm (22) the position whereof is adjustable.
8. A burner according to any of the preceding claims, characterized in that said pressurized
air source includes a two-stage blower (15) comprising a metering-shutter device (29,31)
located at the intake end thereof (27).
9. A burner according to Claim 8, characterized in that said shutter device (29) is
controlled by means of a solenoid valve (30), while said metering device (31) includes
a micrometric adjustment pin screw.
10. A blue flame burner for liquid fuels, substantially as herein described and illustrated.