Note: Descriptions are shown in the official language in which they were submitted.
IMPROVEMENTS IN
LIpUID FUEL BURNERS
Description
Technical Field
As is well recognized in the industry,
there has been a need to develop and to pxovide a
fuel burning system which is capable of burning a
liquid fuel in a very efficient manner with little
or no smoke, and with minimal pollution to the atmos-
phere.
In the case of existing residential oil
burners, the burner must operate with low smoke e~ls-
sions to prevent sooting of the heat exchanger and
the objectionable pollution of residential neighbor-
hoods. The result is that large amounts of excessair must be introduced in the present residential
combustion process to assure that the burner operates
at acceptable smoke levels.
It is well known that the pexformance of
the high pressure oil burner that is used almost ex-
clusively in residential heating applications today
will vary dramatically from one furnace or boiler
design to the next. This is hecause ~he high pres-
sure nozzle does a poor job of atomizing the fuel.
These nozzles produce a substantial number of large
droplets which impinge upon the wal.l.s of the combus-
tion chamber and burn slowly. The speed at which
these particles finally vaporize and hurn depends
upon the size, shape, and residual heat within the
furnace or boi.ler's combustion chamber. It can be
said then that the combustion chamber within the.
furnace or boiler serves as a receptacle to capture
large droplets of fuel and as an after-burning de~ice
to burn these large droplets of fuel. Indeed, if the
existing high pressure oil burner were capable o~
atomizing fuel oil to a hi~h degree, the heat exchanger
could be coupled dixectly to the burner and there
would be no need for a hot combustion cha~beF or fixe-
box to complete the combustion process.
In many instances, the conventional oil
burner may be 2-3 times larger than is necessary t:o
provide adequate space heating. This is the case when
the same burner is required to provide heat for hot
water in addition to heat for home comfort. When out-
side temperatures are low, and hot water demands are
high, a high pressure burner in this type of system
must be able to satisfy both requirements. This
maximum heat load is what normally determines the
firing rate of the burner. ~owever, when the demand
for heat i5 low, as in the spring and fall months,
and hot water demands are at a minimum, as would be
the case at night, the burner will still operate at
the same firing rate as it does when heating and hot
water demands are high. The onl~ difference is th~t
when the. heating requirements are low, the burner will
stay on for ~ very short period of time. As is well
known, this mode of operation is very inefficient.
During the short "on" cycle, the burner cannot achieve
smokeless operation and reasonable efficiency before
the thermostat cuts it off. During the "off" cycle,
the residual heat in the furnace is dissipated to the
atmosphere and this contributes to increased heat loss.
During the off cycle, there is also a loss_of heat
within the house as the warm air escapes through the
furnace stack. From this description it can be ap-
preciated that the most economical domestic oil burner
~7~g
syste~ would be one in which the burner operatescontinuously with the a~ility to vary its output to
satisfy the fluctuating heat requirements within the
household. In this way, there can be no inefficiencies
associated with repeated startup and shutdown. A
quick calculation will show that the added electrical
cost for continuous burner operation is very minimal
compared with the fuel savings that can be realized.
Background Art
An innovative approach to fuel burners is
illustrated in U.S. Patent No. 3,425,058, issued
January 28, 1969, to Robert S. Babingtoll. The burner
therein disclosed represents an adaptation of the
liquid atomization principles disclosed in U.S.
Patents 3,421,699 and 3,421,692, issued Jan~ary
14, 1969, to the same named inventor and his co-
inventors in developing the apparatus and method shown
in these patents.
In brief, the principle involved in the a-
forementione~ patents is that of preparing a liquidfor spraying by causing it to spread out in a thin
film over the exterior surface of a hollow plenum
chamber which contains at least one orifice. When
gas is introduced into the in~erior of the plenum,
25 it escapes through the aperture and thereby creates
a very uniform spray of small liquid particles.
By varying the number of apertures, the
configuration of the apertures, the shape and charac-
teristics of the surface, the velocity and amount of
30 liquid supplied to the surface, and by controlling
the gas pressure within the plenum, the quantity and
quality of the resultant spray can be optimized to
suit the particular burner application.
~13~7~9
It is this basic principle, described above~
that was utilized in the develop~ent of the ~urner
disclosed in said Patent 3,425,058.
In the above mentioned patent, the burner is
S so simple that it might even be called a fuel atomizing
subsystem for a burner rather than a complete burner
Indeed, from this very simple burner or subassembly
evolved the more sophisticated and complete burner
described in the present invention. In the earlier
said Patent 3,425,058, the burner is comprised of a
simple atomizing chamber having a cover thereover,
the cover being provided with a spray discharge port
to discharge the atomiæed fuel in a generally vertical
direction. Disposed withln the atomizing chamber is
a hollow plenum type atomizer t:hat is in communication
with~an outside source of pressurized air. Liquid is
introduced into the atomizing chamber so as to $10w
over the exterior surface o~ the atomizing plenum.
Excess fuel that is not sprayed off flows downwardly
into a drain where it is recirculated via a pump
means to the liquid supply line. The atomizing
plenum is provided with a small aperture centrally
located beneath the opening in the cover, and the alr
exiting there~rom creates a fine mist ~hich is dis-
charged upwardly and out of the atomizing chamber Porcombustion external to the system. Means compri~ing
a series of regulatable apertures are also provided
in the atomizing chamber such that aspirated air can
be drawn into said chamber or burner and mingled with
the spray as it discharges from the opening in the
top cover.
From this very simple version of a fuel
burner was derived more sophisticated equipment, such
as that shown and discussed in an art:icle in the
113~719
January 1976 issue of Popular Science entitled "Clog-
Proof Super Spray Oil Burner". As noted in the article,
one development that evolved was the use of two atomiz-
ing plenums arranged to di.scharge the atomized liquids
towards each other to create a more stable flame and
a good place to initiate ignition.
Other arrangments of opposed spray heads
are also suggested in U.S. patents by Babington,
namely Patent 3,751,210 dated August 1973, and .
Patent 3,864,326 dated February 1975.
All of the above noted developmental work
based on the utilization o~ the "Babington' principle
proved conclusively that the system was perfectly
capable of use in a fuel burning system and that,
if properly designed, such a system has the potential
of evolving into a commercial, practical, highly
effi.cient fuel burner which can be used for domestic
heating furnaces.
Descri~tion of the Invention
The present invention deals with a novel
fuel burner, particularly adapted for use in practi-
cally every type of domestic heating furnace and, in
particular, as a retrofit burner for exis~i.ng heating
systems. Fuel oil can be burned close to the maxi-
mum theoretical efficiency and with smoke readings
which are zero at the instant the burner is ignited
and which remain at zero throughout the burner opera~
tion.
In the present invention, the inefficiencies
associated with many on-off burner cycles ~re elimi-
nated. By simply controlling the liquid film thick-
nesses over the atomizing surfaces as will be des-
cribed, the firing rate of the burner can be modulated
g
-6-
over a typical range of 5-1 This means that the
same burner, without changing atomizers, can be modu-
lated either manually or automatically to match the
heating and/or hot water loads in the house. For
example, during modestly cool spring and summer
evenings, the burner can be set to operate at a firing
rate of 0.2 gal./hr. and during cold winter days
when hot water is required, the same burner can be
adjusted to consume fuel at a rate of 1.0 gal./hr~
These ~djustments can be made manually by simply ad-
justing the fuel flow rate over the atomizing plenums
by means of a simple valve in the liquid combustion
air delivered to the flame tube. In the most sophis-
ticated version of the novel burner disclosed herein,
these adjustments can be made automatically with
suitable control techniques. Accordingly, an object
of the present invention is to produce an oil burner
whose firing rate can be simply modulated either
manually or automatically to suit the heating demand.
Another object of the invention is to pro-
duce a burner that performs with high efficiency
regardless of the combustion chamber that it is
placed into and therefore is ideally suited as a
retrofit or replacement burner for existing Eurnaces.
Another object of this invention is to pro-
duce an oil burner that will permit substantial re-
ductions in energy costs when retrofitted into exist-
ing furnaces.
Still another object of this invention is to
produce an oil burner with an exceptionally stable
flame front.
Still another object of the invention is to
produce a burner that is capable of operating at low
firing rates, as for example less than 0.5 gal./hr.
without clogging problems.
~33719
A further object of this invention is to pro-
duce an oil burner wherein combustion is essential~y
completed within the fla~e tube of the burner,
Still another object ~f this invention is to
produce an oil burner where combustion air is suppliea
in stages so as t~ control the burning rate and temper-
ature and hence objectionably high nitrous oxide emis-
sions.
The burner of this invention comprises a flame
tube haying an inlet end and outlet end; means f~r ad-
mittin~ air into the flame tube to cause said admitted
air to flow in a direction along and parallel to the
central axis of said tube; and a plurality of second
~eans for producing a corresponding plurality of
streams of atomized fuel which are angled toward said
outlet end and also toward the flame tube central axis
so as to intersect substantially at said central axis.
Brief Description of the Drawin~~
Reference is now made to the appended drawin~s
and the de.tailed description which follows, showing
two preferred modes of practicing the invention:
Figs. lA and lB are schematic views of a
typical heating furnace or irebox and showing the
utility o the present invention as compared to the
usual prior art apparatus;
Fig. 2 is a front end view of a fuel burner as-
sembly as utilized in the firebox referred to in Fi~. 1.
719
Fig. 3 is a vertical section view taken along the line
3-3 of Fig. 2 and showing details of one of the fuel atomizing
systems;
Fig. 4 is a sectional plan view taken along the line 4-4
of ~ig. 2 and showing details of one flame tube assembly;
Fig. 5 is a sectional plan view showing details of another
flame tube assembly in accordance with the present invention;
Fig. 6 is still another sectional view of a fuel atomizing
system in which an improved spray discharge horn is utilized.
Best Mode for Carrying Out the Invention
Deferring descriptions of Figs. lA and lB momentarily,
consideration will first be given to Figs. 2 and 4 which show
one mode of carrying out the improved fuel burning assembly of the
present invention. As shown in Fig. 4, an air tube 1, typically
with an outside diameter of about 4", which is essentially an
elon~ated open ended pipe, supports concentrically therein a flame
tube 3 which typically is about 3 to 3-3/4 inches in diameter on
a plurality of annular rings 5 and 7. The concentric relationship
between the air tube ancl the Elame tube deEines an annular air
passage 4 therebetween. Annular ring 7 is solid so as to close
off said annular air passaqe at the discharge end o~ the burner
assembly for the purpose oE dirccting second.lry combustion air as
will be discussed later. ~nnular rinc3 5 helps to conce~ntrically
support flame tube 3 and also contains a series of circumferential
holes 6. These holes create a
- 8 -
~13~7i9
slight pressure dxop in the airflow passin~ throu~h said
air passage 4, which i.n turn equalizes the flow of ai.r
through said passage. Hot or downstream end 9 of the
flame tube is nor~ally placed in the firebox of the fur-
5 nace or the like. The other end 11 of fl~me tube 3 isrelatively cool and connects to a foraminous fire wall
14, which is shown as being generally cone shaped, said
wall being provided with a relatively large central
aperture 16 passin~ through fire wall 14. Also affixed
to said fire wall are two fuel atomizing systems 30 and
30' which are defined by cuplike atomizin~ chambers 15,
15', Typically, the apertures in said fora3ninous fire
wall a~e ~bout 1/8" in diameter or less, and the large
central aperture 16 would be on the order of about~ 1/2"
to about 1-1/2" diameter.
Further upstream of the fuel atomizing systems
and not shown are provisivns for housing the burner
motor, air compressor, air blower, fuel recirculating
~ystem, and electronic burner combustion controls.
The hot end 9 of the flame tube 3 is provided
with a pair of cutouts 13,13', the function of which will
become apparent subsequently. Similarly, the flame tube
is proviaed with a further pair o~ apertures 12,12' loca-
ted approxi3~ately ~idway of its length. ~hese apertures
tl2,12') are disposed at 90 relative to the cutouts 13,
13'~ As shown in Fig. 2, cutouts 13' and 13 are loca-
ted at the twelve o'clock and six o'clock position, while
aperture 12' and 12 are located at the three o'clock and
nine o'clock position. However, tube 3 may be rotated 90
so as to reverse the relative positionin~ of cutouts 13'
and 13 with respect to those of apertures 12' and 12.
Such reversal will serve only to cause the~flame leaving
the burner to bush out in the twelve o'clock and six
o'clock posit~on, rather than in the thre~- orclock and
nine o'clock position as will be the case with the con-
figuration shown in Figs. 2 and 4. The function of these
1~3~719
-10--
cutouts and ~pertures will ~e discussed in ~ore detail later~
Projecting into the flame tube through the
central opening 16 of wall 14 and disposed midway
between the sprays emanating from atomizing systems
30,30' is a conventional spark ignitor 18 which in-
cludes a pair of discharge electrodes 19 and 21. The
ignitor may be supported by a suitable bracket (not
shown) and, of course, is energized from a source of
high voltage electricity. In addition, if desired,
the gap between electrodes 19 and 21 need not be
located midway between the fuel atomizing systems
30,30' but instead can be located adjacent the spray
plume from either atomizing system 30 and 30'
~s shown in Figs. 3 and 4, the atomizing
chambers 15 and 15', respectively, m~y be provided
with spray discharge ho~ns 17 and 17', the purpose
of which will be discussed later.
Fig. 3 shows that each atomizing chamber 15
is provided with a pair of conduits 23' and 25'
which are, in essence, elbows having one end projectin~
into the chamber along a generally vertical plane
passing immediately through the walls thereof. The
uppermost conduit 23' defines a fuel supply conduit
whose lower end 36' e~tends .into atomizing chamber 15'
where it is disposed generally over the high point of
atomizing plenum 26'. The upper end 37' of conduit 25'
is ~lush with the lower interior surface of atomizing
chamber 15.
Disposed directly below each fuel supply
conduit 23' and supported on the rear wall 31' of
atomizing chamber 15' is atomizing plenum 26' which is
shown in Fig. 3 in the form of a hollow sphere but
~hich may be in the form of any hollow plenum with a
smooth convex outer surface Gas under pressure is
supplied to atomizing plenum 26' ~hrough conduit 27',
113~7~9
which extends through the rear wall 31' of the atomizing
chamber 15'. The ato~izing plenum 26' is provided with
at least one small aperture 29', only one being shown
in Fig. 3, which is located so as to discharge fuel
5 spray particles directly toward and through discharge
horn 17'.
As clearly shown in Fig. 3, the rear wall 31'
of the atomizing chamber 15' is provided with a pair
of apertures 33~ whose function will be described in
10 detail hereinafter.
Though not shown, it is to be llnderstood that
each inlet conduit 23' is connected to a so-lrce of liquid
fuel by means of a pump whereby the fuel may be pumped
through these conduits and deposited on the convex
15 surface of plenum chamber 26'. Similarly, the drain
or discharge conduit 25' is connected to the fuel sup-
ply system so that the excess or run-off liquid which
is not atomized by ~ir escaping from orifice 29' in
atomizer 26' can be returned to the fuel system not
20 shown and recirculated therein. The description given
above with specific reference to fuel atomizing system
30'of Fig. 3 applies in identical fashion to fuel
atomizi.ng system 30 shown in Fig. 4,
Fig. 3 also shows one means whereby spray
25 discharge horn 17' may be affixed to atomizing chamber
15', Said horn 17' is shown in its pref~rred form as
a txuncated cone with its small opening facing the
flame tube, However~ in certain burner variations
discharge horn 17' may be a simple cylindrical section
30 or even a truncated cone diverging outwardly towards
the flame tube. The size and shape of spray discharge
horn 17 will depend upon the aerodynamic cQnditions
surrounding atomizing chamber 15', as dictated by the
u~stream blower` pre~sure and the (lownst)^eam static and
113~ 9
~12-
dynamic pressure within the flame tube, In any eyentt
the spray discharge hoxns are desi~ned to control the
size of the liquid fuel spray particles and/or to
prevent the flame ~ithin the flame tube ~rom propa~atin~
upstream into the atomizing chamber. These features
will be explained further in a subsequent discussion
of Fig. 6 which shows an improved discharge horn con-
figuration. In certain app:Lications of the present
invention where there is sufficient ai~flow and pres-
sure available from the auxiliary compressor and com-
bustion air blower, the upstream flame propagation
may be pxevented, and the liquid particle size opti-
miæed, without the need for spray discharge horn 17'.
This is done by controlling the conditions within
atomizing chamber 15' and involves the interrelation-
ship of variables such as the size and shape of atomizer
26'; the size and shape of discharge orifice 29';
the pressure supplied to the interior of atomizer
2~' via tube 27~; the interna]. diameter of feed tube
23'; the spacing and relative fore and aft positioning
of atomizer 26' with respect to lower end 36 of feed
tube 23'; the spacing between discharge orifice 29'
and the forward face 38' of atomizing chamber 15'; the
quantity of fuel suppli.ed through feed tuhe 23'; t.he
size of blower inlet ports 33', and the velocity and
~uantity o air enteri.ng atomiziny chamber 15' through
blower inlet ports ~3'. In cases where the spray dis-
charge horns 17 and 17' are not required, they are
simply removed with the result that the spray particles.
emanating from atomizers 26 and 26' are discharged
directly into flame tube 3 through openings 34 and 34'
in their respective atomizing chambers lS and 15'.
The following parameters represent some typi-
cal ~alues for a burner with a variab.le irin~ rat.e
. . ,
~13697~9
from about 0.2 to about 0.6 gal./hr. A typical atomizer is a
sphere or bullet shape between about 1/4" to about 1" outside
diameter. The cross-sectional area of the discharge orifice 29'
typically is about 0.0001 square inch to about 0.0003 square
inch. The pressure supplied to the interior of atomizer 26' via
tube 27' is typically about 2 psi to about 20 psi. The spacing
35' between discharge orifice 29' and the forward face 38' of
atomizing chamber 15' can be from 0 to about 1". The spacing
between lower end 36' of liquid feed tube 23' and the uppermost
surface of atomizer 26' is typically about 1/8" to about 3/8".
The typical dimensions for blower inlet ports 33' are about 1/8"-
3/8" diameter. Typical internal diameters of feed tube 23' are
about 1/16" to about 1/4". The length of spray dischargehorn 17'
when present can be up to about 1-1/2" and have an exit diameter
between about 3/8" and 1".
Figure 5 is a sectional plan view showing details of a fuel
burning assembly which includes a number of features which are
employed to minimize the problem of soot formation which can occur
along fire wall 14 and on the inside walls of the flame tube
especially at the hic3her firing rates.
As shown in Fic3. 5, the improvecl fuel burning assembly
consists of an air tube 1 which is essentially an elonc3ated open
ended pipe. nisposed within air tube 1 is flame tube 3 whieh is
maintained concentric with respect to the air tube so as to de-
fine an annular air passage therebetween. Flame tube 3 is main-
tained concentric to air tube 1 by positioning against a circum-
ferential shoulder 67 which can include set pins or screws ( not
shown). Other means can be used to maintain the flame tube con-
centrically within the air tube 1. The flame tube 3 is open atboth
- 13-
~7~
ends; one end 9 thereof, which may be ~ermed the hot
end, faces toward the interior of the firebox of the fur-
nace or the like. The other end which may be called the
cool end, is attached to atomizing chamber 52 by means
of a slip fit over the aforementioned shoulder 67.
Further upstream of atomizing chamber 52 and not shown,
provisions may also be made to house the auxiliary
burner equipment such as the drive motor, air atomizing
compressor, combustion air blower, fuel recircuiation
system and the electronic burner controls, if desired.
The open end 9 of the flame tube 3 is provided
with a pair of cutouts 13,13', the function of which
will become apparent subsequently. Similarly the flame
tube is provided with a further pair of à~ertures 12,
12' located approximately midway of its length. These
apertures (12,12') are disposed at 90 relative to
the cutouts 13,13' but as mentioned previously, flame
tube 3 may be rotated 90 to alter the flame pattern
leaving the burner.
In ad~ition, the flame tube of ~ig. 5 is pro-
vided with a plurality of centrifugal swirl shutters
or louvers 50. One convenient confic3uration employs
4 louvers, each bein~ spaced abou~ one-quarter of the
circumference of the flame tube ~rom the ~djacent louvers.
Other con~igurations and amounts of louvers can be em-
ployed if desir~d. The louvers arc placed upstream from
the apertures 12,12' and preferably axially about mid-
way b~tween apertures 12,12 t and fire wall 57. The lou-
vers provide for a curtain of swirlin~ air along the flame
tube wall. The swirling is confined as will be discussed
hereinbelow in view of the interrelationship of the lou-
vers with the apertures 12,12' and the cu~outs 13,13'.
Typic~lly the apertures 50, 12, 12', 13 and 13' are about
0 2-0 4 square inch in cross-sectional area ~r ~ typical
burner with a variable firing rate o from about 0 2 to
about 0.6 gal./hr.
113a~
~15-
The cylindric~l ~lame tube 3 is provided at
its opposite end 11 with a pair of spray discharge horns
17 and 17', opening into a common atomizing chamber 5~.
As was previously discussed, certain burner operating
conditions would not require the use of spray discharge
horns 17 and 17' and in such cases, a simple opening in
said atomizing chamber 52 would he provided instead.
Spray discharge horns 17 and 17' are supported
upon a solid wall 51 which is shown as being generally
straight and transverse to the flame tube. Also support~
ed upon the solid wall 51 is an air blast tube 53
located within and concentrically around the central
axis of the atomizing chamber 52. The air blast tube 53passes
throu~lfand isalso supported by the backwall`54 of ator~lizing
chamber 52. Tlle air blast tube 53 can include a
pai~ of apertures 56,56' (e.g. - typically having
a diameter between 1/8" to 1/2") 1eading to the
atomizing chamber 52. These apertures provide for a
portion of the blower air entering the central air
blast tube to be entrained into the atomizing chamber
52 where it commingles with the fuel spray and is dis-
charged into the flame tube through spray discharge
horns 17 and 17'. Should ap~rtures 56 and 56' be
insuffic~ent to provide chamber S2 with t.he needed air
to supply the aspiration needs of plenums 26 and 26~,
or if it is desired to further raise the static pres
sure within common chamber 52, then blower air inlet ports
66and 66' o~similar or sma~ler cross-sectional area to
56,56' may be provided in wal] 54. Consequently, by
sizing blower air inlet ports 66 and 66' in conjunction
with apertures 56 and 56', chamber 52 may be operated
at any desired pressure. The forward wall 51 of atomiz-
ing chamber 52 is provided with a relatively large
central aperture 55 passing through the wall 51. This
7~9
-.l6
aperture 55 is the same size as tne'inside diameter
of air blast tube 53 which is about 1/~:" to about
1-1/2" so that blower air can pass directly throug~
air ~last tube 53, and enter the flame tube via aper-
ture 55 in wall 51, Spaced slightly downstream such asabout 1/8" to about 1/2" from the forward wall 51 of
the atomizing chamber and parallel theretor'isa fora-
minous or perforated fire wall 57 which is shown as
being generally pl~nar and' containing apertures there-
in~ The perforated fire wall 57 is provided with arelatively large central aperture 59 passing through
the wall 57. The large central opening 59 in the perforat~
ed fire wall 57 ispxefer~bl~y sm~ller than the inside'.di.a-
meter of the central blast tube and hence the opening
55 in wall 51. As a result, a small amount of air
is forced out radially between the forward wall 51
of the 'atomizing chamber 52 and the perforated fire
wall. This air bleeds throuyh the perforated ~ire wall
and into the flame tube to keep the fire within the
flame tube:f~om impinying on the fire wall.
Projecting through rear wall 54 and front
wall 51 of the atomizing chamber and ful-ther extending
into the flame tube through a pai~ of openings .n fire
wall 57 lS a pair of electrodes 19 and 21. S~id elec--
trodes are encased in porcelain jackets 68 and 69to shie].d said eleatrodes from fuel spray as they pass
through atomizing chamber 52. The spark yap 70 be-
tween electrodes 19 and 21 is located within the flame
tube and on the outer periphery of the spray plume
issuing from atomizer 26.
~ s shown.in Fig. 5, the chamber 52 may be
provided with discharge cones 17 and 17' which discharge
atomized fuel inwardly into the flame tube 3.
Both of the atomizing plenum chambers 26,26'
are disposed within the same atomizing chamber 52~
.
113~719
~17-
Plenum 26' is supported on the rear wall 54 of chamber
52 and plenum 26 is interconnected via conduit 27' from
plenum 26'. Use of a common cham~er assures that the
static pressure surrounding atomizing plenum 26 is essen-
tially the same as that surrounding plenum 26', Plenums
26 and 26' are supplied with air under pressure through
conduits 27 and 27' respectively. As shown in Fig, 5,
the air is supplied to 27 and 27' from the same source
via conduits 60 and 61 respectively, Of course, separate
sources of air can be employed if desired.
The liquid fuel supply system for the atomizing
plenums is essentially the same as the fuel supply sys-
tem referred to with respect to Fig. 3 except that both
supply lines o~ conduits are in a common chamber. Also,
in the embodiment of Fig. 5, there need only be one
common drain located at the low point in atomizing cham-
ber 52. Each atomizing plenum 26 and 26' is provided
with at least one small aperture 29 and 29' as illustrated
in Fig. 3 which is located so as to discharge air and fuel
spray directly toward its associated discharge horn 17 and
17'.
As shown in Fig. 5, the rear wall 54 of the
atomizing chan~er 52 is provided with an aperture 61' to
admit air into the air blast tube 53.
A pair of fuel supply conduits 23 and 23' are pre-
ferably connected to a source of liquid fuel by rneans
of a pump, whereby the fuel may be pumped through these
conduits and deposited on the convex surfaces of atom-
izing plenums 26 and 26' respectively. Similarly, the
singular drain conduit 25' is connected to the fuel sup-
ply system so that liquid which is not atomized within
common atomizing chamber 52 can be returne~ to the fuel
system not shown and recirculated back to fuel supply
conduits 23 and 23',
Accordingly, the main differences between the
configuration of Fig. 5 as compared to Fig. 4 are a
1~30'7~9
-18-
single atomizinq ch~m~er instead of two such cham-
bers; a generall~ planar fo~w~xd wallor face instead of a
generally cone shaped fire wall; a perforated fire wall
spacea from the forward wall of the atomizing chamber;
and the presence of centrifugal swirl shutters or lou-
vers. If desired, the burner of Fig. 4 can ~e modified
by employing less than all of the modifications dis-
cussed hereina~ove for the embodiment of Fig. 5 by em-
ploying any one ox any combination of two or more of the
new features of the burnex illustrated by Fig. 5.
Directing attention now particularly to Figs. 3
and 4, the operation of the fuel atomizing and combus-
tion system is as follows.
Liquid fuel is introduced into the system by the
conduits 23,23'. The liquid uel flows over atomizing
plenums 26,26' and a portion thereof is atomized by air
under pressure which is introduced in~o each plenum
through conduits 27 and 27'. Liquid which is not atom-
ized flows to the bottom of the atomizing chambers 15,
15' and is withdrawn therefrom by drain con~u.its 25,25'
for recirculation in the fuel supply system.
As described above, tlle atomization process uti-
lizes the b~sic "Babington" p.rinc.iple disclosed in prior
mentioned Patents 3,421,699 and 3,421,692.
Due to the dischar~e of air from the atomizing
plenums through apertures 29 and 29' there is created a
low pressure region in the immediate vicinity of said
apextures~ This causes additional air to flow into
atomizing chambexs 15,15' through ports 33,33' to com-
~.ingle with the atomized fuel being discharged into flame
tube 3. Additional combustion ai~ is supplied throu~h
the aperture 16 in the foraminous fire wall_l4, 60 as to
~low axially alon~ flame tube 3 to intersect with the
fuel sprays emanating from atomizers 26 and 26' so as to
readily i~nite when the igniter 18 is energized to cause
a sp~rk between electrodes 19 and 21.
113~'719
--19--
In the preferred embodiments disclosed herein the
combustion air enters through the aperture 16. It is, how-
ever~ within the scope of the invention to supply such com-
bustion air by increasing the supply of air which enters
the atomizing chambers through the ports 33 and 33' in Fig.
4, or the ports 66,66' in Fig 5. This in turn will supply
more air to fla~e tube 3 through discharge horns 17 and 17'
The two streams of additional air thus provided intersect
substantially along the flame tube axis, a~d the resultant
of these two intersecting airstreams tends to flow general-
ly along the axis of the flame tube. Such an arrangement
may ~e satisfactory in certain instances, particularly
where the burner geomet~y ~ay make it difficult to provide
for the combustion air to be directed into the flame tube
from one end thereof, or in instances where the burner is
deslgned for a low firing rate in which event sufficient
co~bustion air is obtained by such an alter~ative arrangement.
Additional combustion air passes along the annular
passage 4 between flame tube 3 and blast tube 1 and is
staged into the interior of the flame tube 3 through the
staging ports 12,12' and the cutouts 13,13'. Fig. 4 also
shows one means whereby additional combustion air may be
provided at the juncture betweell tl~e flam~ tube and the
conical fire wall as, for ins~ance, a multiplicity ofports 8.
Tlle unique confi~urat.ion of the flame tube within
a blast tube provides a unique heat exchanger in which com-
bustion air for staging purposes passes through the anular
area between the flame tube and t.he bla~st tuhe. In traver-
sing this route, the combustion air picks up heat from the
inner hot walls of the flame tube. This hot air t as it is
delivered to the interior of the flame tube at the two a-
forementioned staging locations and throu~h ports 8, i~
desired helps to promote rapid vaporization of the atom-
ized fuel to complete the combustion process downstream
in the flame tube. The staging of combustion air in this
manner allows the temperature within the flame tube ~o be
maintained at the desired level to keep nitrous oxide
emissions to a mi.nimum.
1~3~ 9
.-~o--
Still another advantage of the manner in which
combustion air is staged is to produce a flame in which,
when emitted from the burner, is short and bushy. This is
achieved by introducing staged air in a nonsymmetrical
manner which is contrary to the fuel~air mixing technique
used in conventional residential type oil burners. For
example, at the first combustion air staging location,
downstream from the spray impingement site, two air
blasts 12,12' may be introduced per~endicular to the
long axis of the blast tube, at three o'clock and nine
o'clock locations. By subjecting the flame within the
flame tube to a nonsymmetrical air blast of this type~
the flame is c~used to s~uirt out and fill the flame
tube at the six o'clock and twelve o'clock positions, Fur-
thermore~ the low static pxessure within the air blastsat the three and nine o'clock positions causes the flame
to ~rap around the air blasts and thus produce a shorter
and more compact flame which fills the entire flame tube.
In the second combustion air stagin~ location, two
air blasts are introduced at the lip of the blast tube
hùt this time the air blasts are introduced at the twelve
o'clock and six o'clock positions. This causes the flame
to spread out in the three o'clock and nine o'clock posi-
tion as it leaves the burner blast tube and enters the
combustio:l chamber~
A short bushy flame of this type is ideal for a
retrofit or replacemellt burner, because i~ is suited for
use in any type of combustion chamber. This is in
contrast to a long thin flame which would impinge upon
the back side of many combustion chambers and cause ero-
sion of the combustion liner, At the same time, the
combustion air passing between the flame tube and the
blast tube serves to keep the outer blast tube cool,
thereby preventing heat erosion of the blast tube, In
the case of the present invention, the atomization sys-
tem is so efficient, and the subsequent fuel/air mixing
1~3(~7~
and vaporization is likewise carried out in such a
highly efficient manner, that the burner does not re-
quire a hot combustion chamber to achieve high combus-
tion perform~nce.
The present burner desiyn of Fig 4 has been
utilized in a wide variety of different combustio~-
chambers and has always been able to achieve smokeless
operation, and flue-gas CO2 levels between 14-141/2%,
when operating at a firing rate which is close to that
of the furnace rating. Even when the present burner
is set to operate at firing rates well helow the furnace
rating (e.g. burner operating at 0~ gal./hr, in ~ 1,0
gal./hr. furnace) CO2 levels with smokeless operation
will normally never fall below 13~.
The burner configuration illustrated in Fig
5 is somewhat bette- in performance than that illus-
trated in Fig. 4. For instance, flue-gas CO2 levels
of 15%, which areapproxim~tely the maximum level,
have been achieved at zero smoke. This value is just
below the theoretica].ly obtainable when ~he precise
amount of air is mixed with the hydrocarbon fuel. This
is in contrast to the average conventional home oil
burner that operates at CO2 levels of 8~ evcn when
the burner firing rate is matchcd to the furnace
capacitY
These characteristics o~ total independence
of furnace design and furnace temperature makes ~he
present invention ideal as a replacement or retrofit
burner. This non-dependence of furnace temperature
also means that the present burner will achieve smoke-
less operation the instant ignition occurs and before
the combustion chamber becomes hot. The typical con-
ventional high pressure burner takes several minutes for
the smoke level to drop to acceptable levels after
ignition has occurred.
1~30719
~22-
Another fact to be noted is that conventional
high pressure nozzles have difficulty oper~ting at
firing rates below approximately 0.7 gal.~hr. without
encountering a high incidence of clogging. In the
present burner, there is essentially no minimum
firing rate that can beatt~ined; a prototype burner has
been operated ata firing rate ofless thanO~l gal /hr, This
means that each individual atomizer is operating
at less th~n 0 05 gal./hr. Further, it is not neces-
sary, in the present burner, that both atomizers begenerating the same amount of fuel spray fox the bur-
n~r to operate efficiently. For example, one atomizer
may have a firing rate of 0 06 gal./hr~ while the
other has a firing rate of 0.04 gal /hr. A burner of
this type will operate just as efficiently as one
in which each atomizer is delivering a spray rate of
0 05 gal./hr. This low firing xate capability of the
present invention is very important in ]ight of the
present energy crisis because homes in the future will
20 be built with better insulation and the trend is
towards low Eiring burners that can provide high]y
efficiant operation.
It should be not~d that the perforations in
the fire wall 14 are so numbered and sized that a ver~
25 30~t flow of air passes through this wall. This soft
air flow tends to keep products of combustion from fil-
tering or rolling bac~ toward the fuel atomizing sys-
tems and the ignitor, thus inhibiting sooting of these
elements.
The included ang]e between the fuel atomizing
systems 30,30~ is sh~n in Fig. 4 as being approximately
90, This angle can be varied, however, a~d ~ay be
between 15 and 150, and pre~exably between 45 ~nd 150~,
Turning now to Figs. 1 and lA, it will he
noted that in the prior art the atomizing nozzles are
1~307~9
~23-
located at the end of the blast tube. Consequently~
the nozzle'is subjected to high temperaturesrand as
such is subject to varnish 'depositions ana clogging.
In contrast, utilizing applicant's improved fuel
burning system, the atomizing plenums are located well
upstream from the end of the blast tube and as such are
sheltered from the radiant~nd convective heat of the
firebox and the associated problems of fuel cracking
and varnishing.
Even though burners made in accordance with
~igs, 3 and 4 are very efficient and qui,te satisfac-
tory as discussed hereinabove, the operation of such
at the higher fuel rates can lead to some limited
amount of sooting on conical fire wall 14 and on
portions of the 1ame tube. The impxoved con~iguration
illu~trated by Flg. 5 eliminates all soot formation.
Only the basic differences between the operation of the
buxner illustrated by Fig. 5 and that of the burner il-
lustrated by Fig. 4 will be discussed hereinbelow, it
being understood that those aspects of the operation o~
the burner illustrated by Fig. 5 not discussed in any
detail are simil~r to those of the burncr of the type
shown by Fi~. 4.
The air blast ~ube 53 directs air along the cen-
tral axis of the single atomizing chamber 52 and alongthe central axis oE the flame tube 3. ~ portion of
the blower air entering the air blast tube 53 is pre-
ferably entrained or forced into the atomizing chamber
52 via openings 56 and 56' where it conmingles with the
fuel spray and is discharged into the ~lame tube 3 via
spray discharge horns 17 and 17'. The atomizers may
draw the air into the ch~mber 52 via apertures 56 and
56' by the low pressure area created at the orifices of
said atomizing plenums, or under certain operation con-
ditions pressurized air may also be forced into atomiæingchamber 52 through apertures 56 and 56'.
11307~9
~2~-
As st~ted earlier, common chamber 52 m~y also
be fitted with blower air pressurization ports 66 and
66' so that common ch'amber 52 r.lay be operated at still
a more elevated stattc pressure if so desired. Such
pressurization would more likely be employed at high
firing rates'and where it is desirous to mix as much
air with the atomized spray as possible before dis--
chargin~ the mixture into the fl~me tube.
The use of one common atomizing chamber to
contain the atomizing plenums instead of a plurality
of atomizing chambers assures that the ambient pres-
sure surrounding each ato~izing p~enum will be essen-
~ially the'same, 'With a common at:omizing chamber the
local air velocity around each atomizer is also reduce~
because of the larger volume inside common chamber 52.
Thus in chamber 52 it is further assured that high air
velocities will not disturb the film of liquid flowin~
over atomizers 26 and 26', The configuration of Fig. 5
is therefore less sensitive than thatshown in Fig. 4.
Since the large aentral opening in the per-
forated wall is smaller than the inside diameter of the
central air blast tube 53, a small amount of air is
directed or forced radially outwarflly between the for~lard
face of lhe a'omizin~ chamber and the perforated fire
wall. The perforations in the fire w~ re so num~ered
and sized that a very soft flow of air p~sses throu~h
this wall. This air bleeds througll the perforated'
fire wall and into the flame tube, thereby keeping
or holding the flame off the fire wall, and insulatin~
the relatively aool surface of the front face of the
atomizing chamber ~rom the hot environment: on the down-
stream side of the fire wall. Without the perfoxated
113~19
~25~-
fire wall the condition of relatively cool fuel on
the inside of the` atomizing chamber, and a hot fire
on the downstream side of the atomizing chamber would
predispose the forward wall of the atomizing chamber
to soot buildup on the flame tube side. In addition,
the use of generally straight walls instead of the
generally cone shaped fire wall of Fig. 4 ~inimizes
the tendency for soot buildup since in the configura-
tion of FigO 4, the number of corners involved makes
it difficult to provide sufficient air mixing to all
of the corners
The use of a substant.ially planar faced fire
wall removes the restriction on the minimum spray
angle as stated for the sprays in Fig. 4. The use of
the planar face fire wall permits the minimum included
angle where sprays meet to be reduced substantially.
The preferred minimum included angle is about 5.
Excellent results have been achieved with an angle of
about 27.
The centrifugal swirl shutters or louvers 50
promote rapid mixing of combustion air and fuel spray
to prevent soot buildup on the flame tube 3~ The air
which passes into the flame tube through the centri-
fugal swirl shutters provides a curtain of swirling air
along the flame tube wall. rrhis i.nsulates t:he flame tube
wall from direct ~lame impin~ementand prevents hot spots and
113~719
~26-
flame erosion problems. The curtain of swirling air
is heaviest in the upstream vicinity of the flame tube
where it enters through the louvers. When the
swirling air encounters the transverse air blasts
about midway along the flame tube from apertures
12,12', and again at the discharge lip ~f the flame
tube from cutouts 13,13', the swirling motion is sub-
stantially destroyed. This is important to assure
that the swirling air is mixed with the vaporized
and burning fuel before it exits flame tube 3.
It was discussed hereinabove with respect
to Fig. 3 that the spray discharge horn 17' served
two purposes. Horn 17' was designed to control the
mass median diameter of the spray entering flame tube
3 and also to prevent the flame within flame tube 3
from pxopagati.ng upstream and into atomizing chamber
15. The spray particle size can be optimized by ad-
justing the geometry of horn 17' with respect to its
length, exit diameter and conical angle. Said horn
can be sized such that the spray issuing forth from
ori~ice 29' i9 disch~r~ed into flame tube 3 unrestricted
by horn 17', or said horn may be designed to restxict
a portion of the spray emanatin~ from 29', In this
latter c~se, the inner walls of said horn serve to skim
off the lar~er spray particles on the outer periphery
of the spray plume, These captured fuel particles
simply flow back into atomizing chamber 15 along the
inclined inner walls of said spray discharge horn 17'.
This technique works ~ell when the skimming required is
minimal, and when the ~elocity of the commingled air
and fuel particles passing through said horn is low.
However, when it is desired to restrict a ~ubstantial
amount o~ the spray to further reduce particle size,
or when velocities within discharge ho~n 17' axe hi~h~
11307~9
the discharge horn assembly shown in Fig. 6 is more useful. This
high velocity discharqe horn assembly 20 is comprised of an inner
shroud 17' and an outer shroud 22. As shown in Fig. 6 the down-
stream ends of these shrouds are preferably in the same plane.
However, in some cases, depending upon the static pressure, com-
bustion air velocity, and local eddies within flame tube 3, outer
shroud 22 may be somewhat longer or shorter than inner shroud 17'
to promote better drainback and/or to eliminate soot buildup
between said shrouds or around the entire configuration 20'.
In operation the high velocity discharge horn assembly 20
shown in Fig. 6 skims off a portion of the fuel spray originating
from orifice 29'.
The relatively high velocity of the spray passing through
inner shroud 17' causes impinging fuel to run along the inner walls
of shroud 17' towards the flame tube. This raw fuel is prevented
from spilling over into the flame tube by means of the outer shroud
22. Said raw fuel upon reaching the discharge lip of the inner
shroud 17' runs back between said inner shroud and said outer
shroud 22, mostly along the outer surEace of thc inner shroud 17,
and back towards the forward wall 28 o~ the atomi~inc3 chamber 15.
This excess or run-off fue~1 then drains back into chamber 15 via
small drain tub~ 72. Durinc~ burner operation, drain tube 72 which
has an I.D. of appro~imately 1/16-1/8" becomes filled with fuel and
acts as a trap to prevent the back flow of combustion products into
the atomizing chamber.
The other purpose of high velocity discharge horn assembly
20 is to prevent burn back in the atomizing chamber. Essentially the
assembly acts as an ejector which is sized such that the fuel/air
velocity exiting from said inner shroud 17' is at least as
27 ~
~3~7~9
great as the flame speed of the fuel burning within
- 27a -
-2~-
flame tube 3, This means that the ~lame within the
flame tube cannot propagate upstream and into atomiziny
chamber 15'.
In cases where the velocity of commingled
liquid spray and air exiting from discharge horn
assembly 20' is very high so as to cause flame in-
stability or a fluctuating flame front within the flame
tube 3, then flame holder 71 may be provide~. Said
flame holder is in the form of a simple ring or
washer having a large central opening 63, said
opening being sized slightly larger than that of the
spr~y plume diameter at that point. 'rhis allows
the fuel spray to pass unimpeded through saia opening
63 without wetting the walls of said flame holder 71.
The turbulence and subsequent low static pressure that
is created around flame holder 71 when the spray passes
through it, causes the flame to seat or attach itself
to the downstream face of flame holder 71. In Fig. 6
said flame holder 71 is supported from outer shroud 22
~ two small rod like appendages 62. ~t i5 desir-
able that these rods 62 be small in cross-section so
that flame holder 71 takes on the appearance Qf be.ing
suspended in space approximately 1/8 - 1.-1/2" down-
stream of the exit oE inner shroud 17'. The exact loca-
tion of flame holder 71 will depend upon the relativevelocity between the flame speed and the fuel/air mi.x-
ture leaving shroud 17'.
Having described a pre~erred mode of practicing
the invention, it will be apparent to those ~killed in
the art that Various modifications and changes can be
made therein; which modification and changes fall within
the purview of the inventive concept defi~ed by the ap-
pended claims wherein what is claimed is:
