US3852022A - Liquid fuel burner head - Google Patents

Abstract

An improved fuel burner head comprising a fuel atomizing nozzle and a structure coaxial to said nozzle that forms two coaxially located chambers for feeding the comburent air from a known air blower to a zone wherein said air is mixed with the fuel for forming and maintaining a flame. Said comburent air is suitably subdivided between said chambers in order to have a first inner flow in an amount smaller than that stoichiometrically required for the combustion, and respectively a second outer flow in an amount at least complemental to the stoichiometric amount and in the form of a cone-shaped laminar flow converging toward a point located on the nozzle axis and behind said nozzle.

Description

ite States Medeot et al. Dec. 3, 1974 LIQUID FUEL BURNER HEAD 3,051,228 8/1962 Peoples et al 431/265 x 3, 6,384 41971 P l 431 3 3 [75] Inventors: Renzo Medeot, Padova; Francesco 57 eczeu et a l 5 C' f L V a, b th g gnago emu Q Primary ExaminerEdward G. Favors Attorney, Agent, or Firm-McGlew and Tuttle [73] Assignee: 0.F.R. Officine Fratelli Riello S. .A., Le 0, Ver It 1 p gnag (ma 3 y 57ABSTRACT 22 Filed: on. 1, 1973 An improved fuel burner head comprising a fuel atompp Noel 402,374 izing nozzle and a structure coaxial to said nozzle that forms two coaxially located chambers for feeding the [30] Foreign Application Priority Data comburent air from a known air blower to a zone 0 6 1972 I l 30178 72 wherein said air is mixed with the fuel for forming and ct. ta y maintaining a flame.

[52] s Cl 431/186, 239/420, 239/424, Said comburent air is suitably subdivided between said 431/115, 431/265 chambers in order to have a first inner flow in an [51] int. Cl.F23c 5/06 amount Smaller than that stoichiometricany required 58 Field of Search 431/265, 264, 115, 187, for the Combustion, and respectively a second Outer 431/186, 239/423, 424, 420 flow in an amount at least complemental to the I stoichiometric amount and in the form of a [56] References Cited cone-shaped laminar flow converging toward a point UNITED STATES PATENTS located on the nozzle axis and behind said nozzle.

2,5 85,081 2/1952 Bernhard 431/265 8 Claims, 4 Drawing Figures LIQUID FUEL BURNER HEAD BACKGROUND This invention relates to a liquid fuel burner head,

particularly suitable for gas oil burners that are designed to operate within a well limited environment, as e.g. the furnace (usually having an elongated cylindric shape) of boilers for domestic-heating applications or the like.

In the current technical terminology of the specific field, the term burner head means an assembly adapted to start and maintain the combustion, usually in the form of an elongated flame, said assembly comprising a nozzle that is fed with a pressure liquid fuel and delivers an atomized fuel jet, as well as a system of chambers, passages and outlet openings, suitably connected with a fan or blower in order to meteredly deliver one or more air streams, having pre-set flow rate, pressure and distribution conditions and adapted to thoroughly mix with said atomized fuel to start and maintain the flame formation.

Such burner heads should desirably ensure a complete oxidation of all carbon present in the fuel, as well as a steady and efficient flame, in order to attain the highest yield of the heat source. Accordingly, the combustion phenomenon should be established by presetting a combustible/comburent ratio such that the oxigen amount in the air fed by the blower be in a suitable, but not too high excess over the oxigen amount as stoichiometrically required for the complete carbon oxidation. Moreover, the combustion process should be carried-out, as far as possible, with the fuel in a gaseous condition, i.e., after the liquid droplets delivered by the nozzle have been gasified. Additionally, it is highly desirable that no smoke (revealing the presence of unburnt carbon particles) be discharged from the furnace, and that no carbon scales be formed on the furnace walls and/or head components.

Moreover, in the field wherein the considered burners are prevailingly used, it is desirable that rather low temperatures are reached by the flame in order to decrease the formation of polluting compounds as S and NO As well known by those skilled in the art, a distinctive indication of a burner regular and profitable operation is given by a bluish and low-brightness flame that'indicates the absence of incandescent carbon particles and then a complete combustion. Also well known is that such a flame can be more or less completely attained when the mixture of fuel and oxigen of the fed air is suitably diluted in an inert gas stream, typically formed by the same combustion products. However, to comply with such conditions leads to conflicting requirements, in particular when considering thata steady and uniform flame should be obtained and that said burner should be adapted to orderly operate at different rates and under different regulation conditions as well as easily and readily started in such a manner as properly overcome ignition and starting transitory conditions.

When considering that a complete combustion, in particular with an air excess suitably kept within narrow limits (in the current production burners the air excess is limited by the impossibility of obtaining a sootless combustion and its value is an inverse function of the attainable CO value) depends on the fact that each (liquid or gasified) fuel particle should find the presence of oxigen under combustion conditions, the actual technical trends are based on the belief that it is desirable --if not indispensable to set up a strong turbulence condition in the mixing zone. In general, a compromise is sought between a prompt and quick mixing and the dilution of the mixture, in order to attain a desirable low brightness flame. However, such a desirable flame generally leads to an instability thereof and to further operating troubles, both during its normal run ning and in the transient steps.

SUMMARY According to this invention, as it was recognized and experimentally proved, a low brightness bluish flame with a practically complete absence of soot formation can be obtained in a burner of the type and for the applications referred to, by means of a suitably fed, improved burner head, wherein the fuel and the comburent air are gradually mixed in different zones of the limited furnace environment.

More detailedly, one object of this invention is to provide an improved liquid fuel burner head comprising a system of passages and outlet openings for. the comburent air, that is subdivided into two flows, namely a flow for the initial combustion of atomized liquid fuel (that may be even incorrectly defined as primary air") and a flow for the final combustion of gasified fuel and the dilution of combustion products by means of induced streams within the furnace.

Another object of this invention is to provide an improved burner head comprising separate outlet passages for said flows, said passages being suitably directed and complying with given geometric parameters in order to ensure that said sequential distribution of combustion steps completely occur outside the burner head, thus practically avoiding any formation of carbon deposits on the furnace walls or at any rate on the head components, as well as ensuring a long useful life of burner head and decreasing the periodic servicing requirements thereof.

A further object of this invention is to provide an improved burner head having an unusually simple design and that can be adjusted in many different ways for complying with different specific application and operation requirements.

According to this invention, the improved burner head is essentially characterized in that it comprises in a structural assembly surrounding a nozzle and coaxial thereto two coaxially located chambers both connected, through passages having a free cross-sectional area adapted to quantitatively separate the fed air, with an already known blower, each of said chambers having a single or multiple outlet port,"namely a first port directly adjacent to nozzle outlet orifice (for feeding the primary air flow) and respectively a second port at a pre-established radial distance from the nozzle axis, said second (single or multiple) outlet port comprising at least one essentially truncated-cone shaped wall that is directed in such a manner as to form an essentially laminar air flow (or crown of flows) converging toward the nozzle axis in a point beyond the outlet orifice thereof, and forming a gaseous barrier or curtain that circumscribes an essentially conical space wherein the ignition and initial combustion of atomized fuel occur,

and the gasification of unburnt fractions is practically completed, while outside the same space a dilution of burning mixture is performed by recycled flows of gaseous combustion products that are induced by the direction and speed of said gaseous curtain, as defined by a localized and directionally settled blowing, into said space inner zone, of a controlled excess, over the stoichiometrically required amount, of the secundary air for the completion of combustion.

DRAWINGS FIG. 1 is a sectional view of a preferred embodiment of this invention taken along a symmetry plane extending across the nozzle axis and comprising a few inner components shown in side view.

FIG. 2 is a fragmentary enlarged view of the same improved head, as seen from the plane and in the direction indicated by IIII in FIG. 1.

FIG. 3 is a fragmentary sectional view showing detail of primary air outlet opening taken along the cylindric plane IIIIII in FIG. 2.

FIG. 4 is a diagrammatic view of the burner head as operatively mounted within an essentially cylindric shaped furnace, along with an approximate indication of space zones outside the same head, wherein the complete combustion process is controllably distributed in order to obtain a low brightness bluish flame.

PREFERRED EMBODIMENT As shown in FIG. 1, the burner head is structurally and operatively associated with the outlet section of a preferably centrifugal blower of an already known type, that delivers comburent air in a required excess (from 3 to 45 percent over the stoichiometric amount) and under a required pressure, e.g., 40 50 mms. H 0. The head assembly includes a composite structure, whose main components are concentri-cally fitted about the axis of afuel conveying rod 12, carrying an atomizingnozzle 14 at one end and a pipe fitting 16 for a meteredly fuel feeding duct at the other end thereof. Said fuel conveying rod may be supported by abracket 18 that is in turn supported by arod 20 secured, e.g., to awall 22 of burner body. Saidrod 12 is preferably threaded in order to allow an adjustment of the axial position thereof, together with all components structurally associated therewith.

Said components comprise an essentially tubularinner body 24 that defines aninner chamber 26 having afront diaphragm 28, wherein a primaryair outlet orifice 30 is provided in front of the atomizingnozzle 14. The details of said orifice will be disclosed later on.

The front end of said inner body shows a smooth truncated-cone shapedsurface 32, having a geometric vertex V lying on the nozzle axis and a vertex angle A preferably in the range of 65 50, said truncatedcone shapedsurface 32 showing an endsharp corner 34 at its minor base to ensure the displacement of a laminar air flow that licks said surface at a high speed.

The shown head also comprises a substantially cylindricouter body 36 that is fastened to the burner structure, namely to theblower delivery section 10, and defines anouter chamber 38 directly communicating with said blower delivery section and wherein an air pressure as resulting from the blower flow and the free cross-sections of outlet passages is established.

Saidinner chamber 26 communicates with theouter chamber 38 through a crown ofpassages 40, whose free sections can be adjustably restricted, e.g., by

means of a threadedring nut 42, that is screwed on the rear end ofinner body 24 and can be brought more or less near to inlets ofpassages 40. By such adjustment (or obviously by any other equivalent means), the ratio of primary air that is fed to theinner chamber 26, to secondary air that flows toward the fore end of thechamber 38, can be accurately established.

The fore end ofouter body 36, that is preferably kept coaxial with theinner body 24 by a crown oflongitudinal fins 44, shows a truncated-cone shapednarrowing section 46, ending with alip 48 circumscribing the truncated-cone shapedsurface 32 and defining, together with said latter surface, an outlet annular passage for the secondary air. The free cross-section of said annular passage can be adjusted with the highest accuracy by axially shifting theinner body 24 in respect of theouter body 36. It is to be pointed out that said annular passage, that is continuous in the considered example, may be subdivided into neighbouring sectors, without prejudicing the operation and advantages of improved head. For instance, said outlet annular passage may be subdivided into sectors by radially extending fins or baffles, adapted to ensure an accurate coaxiality betweensurface 32 andlip 48, respectively defining the inner and outer contours of said outlet passage.

The above described component structure definin said annular passage ensures that an essentially laminar air flow is formed by the air fed to thechamber 38 and leaving the head outside, said laminar flow being in the form of a cone-shaped jet that displaces from thesharp corner 34 and flows toward the vertex V of a cone partly formed bysaid surface 32.

The burner head obviously comprises all usual fittings, as eg aphotosensitive element 50 for a burner thermal control,ignition electrodes 52, and so on.

The primary air outlet opening 30 should also be able to ensure a ready mixing of said primary air with the atomized fuel flowing fromnozzle 14, as well as a suitable distribution of the initially burning mixture within the cone-shaped space, as defined by said vertex V and saidcorner basis 34. Therefore said opening is preferably formed by a suitably thinned inner portion 54 (see FIGS. 2 and 3) ofdiaphragm 28, having an axial bore 56 (see FIG. 2) wherefrom a plurality of suitably slanting radially directedslits 58 extend in order to induce at least a part of primary air flow to form a vortex and thereby to expand within said cone-shaped space.

A burner as previously described can be suitably adjusted (e.g. by acting on the ring nut 42) to preferably maintain the ratio of secondary or annularly delivered air to primary or axially delivered air, in a range of 0.4 3.5, said burner being fed with an air pressure value such that the secondary air flow speed along the truncated-cone shapedsurface 32 be in the range of 24-30 m/sec. However, said values can obviously undergo to wide changes, according to the head capacity and sizes, as well as to the angle of cone-shaped surface 32 and the like.

Moreover the communication between thechambers 38 and 26 should preferably include a portion (e.g., between thering nut 42 and the inlets of passages 40) having a free cross-section smaller than that ofprimary air outlet 30, in order to allow said primary air to flowout at a speed much smaller than that of secondary air, or at any rate in order to avoid any prejudice to the laminarity and directional regularity of secondary air,

at least in the starting portion of its conically converging path.

An improved burner head T of the type referred to and as diagrammatically shown in FIG. 4, when operates in a limited environment S of an already known furnace F, essentially causes the hereinafter stated phenomena, all occurring outside the same head and out of contact with the components thereof.

The essentially laminar flow of secondary (or annular) air defines an inner zone 2 wherein the combustion is stated under conditions of comburent deficiency and obviously with a local formation of a small, intensely colored flame, due to unburnt or only partially burnt incandescent particles; however, the gasification of unburnt fraction of liquid fuel is practically completed within said zone.

The secondary air converging laminar flow L operates in different ways. First of all, the flow inner limit layer exerts an intensive induction on the fuel-primary air mixture, and mixes with the same to complete the combustion and reach the stoichiometric value. Further the flow outer limit layer induces recycling flows C within the furnace, in order to progressively dilute the burning mixture with the same combustion products.

As it can be seen, though with a given approximation, between said recycling flows C and said secondary air laminar flow L an outer zone Z is formed, wherein a low brightness bluish flame extends in a direction D, essentially coincident with the burner axis, till to a complete exhaustion of wholly gasified and diluted fuel, and without any soot formation and other undesirable phenomena.

The above stated desirable burner operation regularly occurs when the furnace inside environment S shows a minimum volume, obviously proportional to the burner capacity. As minimum volume it may be assumed that indicated in the table DIN 4,787 for the maximum sizes of test chambers for gas oil burners.

We claim:

1. An improved liquid fuel burner head comprising coaxial components, a nozzle for delivering a jet of atomized fuel in a direction coincident with the axis of said components and means to deliver flows of comburent air all around said fuel jet, wherein coaxial chambers are formed within said components, to which pressure air is fed in an amount smaller than the stoichiometrically required amount, for the formation of primary air or initial combustion flow, and respectively in an amount at least complemental to attain said stoichiometric amount, for the formation of a secondary air flow adapted to complete the combustion, said chambers comprising systems of axial andrespectively annular openings and passages coaxial with said component axis, said annular system delivering said secondary air flow comprising means for quidedly delivering pressure air in the form of a converging, essentially laminar flow that encompasses an inner space wherein an initial combustion with comburent air deficiency occurs, and surrounds an outer space wherein said combustion is completed and the burning mixture is diluted by circulating flows, as induced by the speed of said essentially laminar flow said outlet system from the inner chamber of said coaxial chambers comprising a central orifice in front of said nozzle, as well as essentially radially directed slits that are slanting in respect of a plane perpendicular to nozzle axis, in order to induce at least a part of the air flowing from said system to form a vor-. tex that ensures the mixture of said air and atomized fuel to expand within a space as defined by said convergent laminar flow delivered from the outer chamber, outlet systems.

2. An improved head according to claim 1, wherein the outer chamber of said coaxial chambers comprises an air delivering system including a passage defined between a truncated-cone shaped surface having an imaginary vertex coincident with said axis, and an outer component having an edge surrounding said truncatedcone shaped surface and acting to force the air delivered between said surface and component to assume an essentially laminar form, licking said cone-shaped surface and then continuing toward said vertex.

3. An improved head according to claim 2, wherein said truncated-cone shaped surface has an outer minor basis ending with a sharp corner for displacement of said laminar air flow.

4. An improved head according to claim 3, wherein said outer chamber outlet system comprises guide means to form a cone-shaped laminar flow, having a vertex angle in the range of 65 5. An improved head according to claim 2, wherein an inner essentially tubular body comprises an outer portion forming said truncated-cone shaped surface and surrounding said nozzle, near the plane perpendicular to said axis and extending across said nozzle, and wherein an outer tubular body comprises an end portion surrounding said truncated-cone shaped surface and converging toward the inside, said portion comprising in turn said end sharp edge.

6. An improved head according toclaim 5, wherein said inner and outer bodies are supported in such a manner as to allow their relative axial position to be changed for the adjustment of the radial spacing between said truncated-cone shaped surface and said edge.

7. An improved head according toclaim 5, wherein an inner space of said outer body freely communicates with a delivery side of an comburent air blower, as well as with an inner space of said inner body, through passages having a free cross section adapted to subdivide said comburent air between said outlet systems of said inner and outer chambers.

8. An improved head according to claim 7 and comprising means for adjusting said free cross-section of said passages between said outer and inner chambers.

Claims (8)

1. An improved liquid fuel burner head comprising coaxial components, a nozzle for delivering a jet of atomized fuel in a direction coincident with the axis of said components and means to deliver flows of comburent air all around said fuel jet, wherein coaxial chambers are formed within said components, to which pressure air is fed in an amount smaller than the stoichiometrically required amount, for the formation of primary air or initial combustion flow, and respectively in an amount at least complemental to attain said stoichiometric amount, for the formation of a secondary air flow adapted to complete the combustion, said chambers comprising systems of axial and respectively annular openings and passages coaxial with said component axis, said annular system delivering said secondary air flow comprising means for quidedly delivering pressure air in the form of a converging, essentially laminar flow that encompasses an inner space wherein an initial combustion with comburent air deficiency occurs, and surrounds an outer space wherein said combustion is completed and the burning mixture is diluted by circulating flows, as induced by the speed of said essentially laminar flow said outlet system from the inner chamber of said coaxial chambers comprising a central orifice in front of said nozzle, as well as essentially radially directed slits that are slanting in respect of a plane perpendicular to nozzle axis, in order to induce at least a part of the air flowing from said system to form a vortex that ensures the mixture of said air and atomized fuel to expand within a space as defined by said convergent laminar flow delivered from the outer chamber outlet systems.

2. An improved head according to claim 1, wherein the outer chamber of said coaxial chambers comprises an air delivering system including a passage defined between a truncated-cone shaped surface having an imaginary vertex coincident with said axis, and an outer component having an edge surrounding said truncated-cone shaped surface and acting to force the air delivered between said surface and component, to assume an essentially laminar form, licking said cone-shaped surface and then continuing toward said vertex.

3. An improved head according to claim 2, wherein said truncated-cone shaped surface has an outer minor basis ending with a sharp corner for displacement of said laminar air flow.

4. An improved head according to claim 3, wherein said outer chamber outlet system comprises guide means to form a cone-shaped laminar flow, having a vertex angle in the range of 65* - 75*.

5. An improved head according to claim 2, wherein an inner essentially tubular body comprises an outer portion forming said truncated-cone shaped surface and surrounding said nozzle, near the plane perpendicular to said axis and extending across said nozzle, and wherein an outer tubular body comprises an end portion surrounding said truncated-cone shaped surface and converging toward the inside, said portion comprising in turn said end sharp edge.

6. An improved head according to claim 5, wherein said inner and outer bodies are supported in such a manner as to allow their relative axial position to be changed for the adjustment of the radial spacing between said truncated-cone shaped surface and said edge.

7. An improved head according to claim 5, wherein an inner space of said outer body freely communicates with a delivery side of an comburent air blower, as well as with an inner space of said inner body, through passages having a free cross section adapted to subdivide said comburent air between said outlet systems of said inner and outer chambers.

8. An improved head according to claim 7 and comprising means for adjusting said free cross-section of said passages between said outer and inner chambers.

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