US3504994A

US3504994A - Burner for use with fluid fuels

Info

Publication number: US3504994A
Application number: US694319A
Authority: US
Inventors: Denis Henry Desty; David Montagu Whitehead
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1967-01-10
Filing date: 1967-12-28
Publication date: 1970-04-07
Anticipated expiration: 1987-04-07
Also published as: SE337878B; NL154588B; BE709159A; DE1551767A1; AT289344B; NL6800344A; NO121352B; DE1551767C3; FR1582020A; CH476261A; DE1551767B2

Description

April 7, 1970 D. HLDESTY ET AL 3,504,994

7 BURNER FOR USE WITH FLUID FUELS Filed Dec. 28. 1967 5 Sheets-Sheet 1 FIG. 7. 71

INVENTORS,

DEN/s HENRY 0557') DIV/D MONTAGU wH/n'HEAp WRGAN, F/NNEGAN, Dl/k/IAM a PM:

Arm/wars April 7', 1970- H, DEs-r ET AL 3,504,994

BURNER FOR USE WITH FLUID FUELS Filed Dc. 28, 1967 s Sheets-Sheet 2 FIG. 6. 33 32 3 5 INVENTORS,

DEN/S HENRY 0557) DAVID MONTAGU WHITE/LEAD MOAGA/V, FINA/EGAN, DURHAM f PINE ATTORNE rs April 7, "1970 b. H, DES-TY ETTAL 3,504,994v

BURNER FOR USE WIT FLUID FUELS 3 Sheets-Sheet 5 Filed Dec. 28, 19s? IN VE NTORS,

DEN/5 HENRY DESTY DAV/D MONTAGU WHITE/454D Mam/w, FIN/VEGA N, DURHAM PINE rromvsxs United States Patent 3,504,994 BURNER FOR USE WITH FLUID FUELS Denis Henry Desty, Sunbury-on-Thames, and David Montagu Whitehead, Camberley, England, assignors to The British Petroleum Company Limited, London,

England, a corporation of England Filed Dec. 28, 1967, Ser. No. 694,319 Claims priority, application Great Britain, Jan. 10, 1967, 1,247/ 67; Sept. 29, 1967, 44,376/ 67 Int. Cl. F23c 5/00 US. Cl. 431-174 23 Claims ABSTRACT OF THE DISCLOSURE A burner for fluid fiuels which comprises a plurality of combustion air tubes which pass through a fuel chamber having fuel outlet passages. The combustion air tubes convey air and the fuel outlet passages convey fuel to a combustion zone.

Preferably the cross sectional area of the bore of each combustion air tube is 0.01-1.0 cm. where it opens into the combustion zone and the bores of the combustion air tubes account for at least 25% of the surface area of the burner adjacent to the combustion zone.

This invention relates to a burner for use with fluid fuels, i.e. to a burner suitable for use with liquid and gaseous fuels.

It would be convenient for the manufacturers of appliances which incorporate burners to have available a type of burner which enables a wide range of fuels to be burnt in burners of similar construction, size and with similar heat outputs. In particular it would be convenient to have available a gas burner which, without modification, can burn both high and low speed gases, e.g. methane and hydrogen.

According to the invention a burner for fluid fuels comprises a plurality of combustion air tubes which pass through a fuel chamber having fuel outlet passages, the parts being arranged so that, in the use of the burner, the combustion air tubes convey air and the fuel outlet passages convey fuel to a combustion zone so as to maintain a diffusion flame.

In a diffusion flame the initial reaction takes place by a diffusion process which mixes air and fuel and it is necessary that the diffusion paths be sufiiciently small. In order to achieve this it is necessary to have a sufficiently large number of tubes, i.e. that the bores of the tubes shall account for a sufficiently large proportion of the surface area of the burner adjacent to the combustion zone and that the cross sectional area of each tube shall be suffi'ciently small. We have found that satisfactory combustion takes place when the bore of each tube has a cross sectional area of 1.0 cm} or less where it opens into the combustion zone and the bores of the tubes account for at least 25 preferably at least 50%, of the surfacearea of the burner adjacent to the combustion'zone.

The burners according to the invention are particularly suitable for use with natural draught because the combustion air tubes offer a low resistance to air flow. For this reason the cross sectional area of the combustion air tubes should not be too small, for example the bore of each tube should'have a cross sectional area of 0.01 cm. or higher where it opens into the combustion zone, preferably over its whole length.

Thus the invention includes a burner for fluid fuels which comprises a plurality of combustion air tubes which pass through a fuel chamber having fuel outlet passages, the parts being arranged so that, in the use of the burner, the combustion air tubes convey air and the fuel outlet lot:

passages convey fuel to a combustion zone so as to maintain combustion, the bore of each combustion air tube having a cross sectional area of 0.01-4.0 cm.'- where flie tube opens into the combustion zone and the bores of the combustion air tubes accounting for at least 25% preferably at least 50% of the surface area of the burner adjacent to the combustion zone.

Preferably the combustion air tubes are arranged with their axes parallel to one another. Cylindrical tubes, or cylindrical tubes modified at one or both ends as described below, are particularly suitable as the combustion air tubes.

In the burner described above the combustion air tubes provide a low resistance passage for combustion air and their interstitial space provides a low resistance passage for the fuel; in particular the interstitial space provides a low resistance to the flow of fuel across the cross-section of the fuel chamber thereby encouraging an even fuel distribution.

The burners according to the invention can, operate over a wide range of excess air conditions. Thus they can operate under stoichiometric conditions so as to generate a high temperature in the exit gas or with a large excess of air for applications where warm air is required. Furthermore under suitable conditions they can aspirate all the air, both combustion and excess, through the combustion air tubes although a blower may be needed if a sufficiently large quantity of excess air is required.

In the case of a burner for gaseous fuels narrow fuel outlet passages are desirable since these provide an out et resistance which is high in camparison with the internal resistance to flow across the fuel chamber. This encourages uniform supply of gas to the combustion zone. In the case of a burner designed to run on liquid fuel the supply of fuel into the combustion zone is controlled by the rate at which liquid in the fuel chamber vaporises. In these circumstances it is unnecessary to provide a high outlet fuel resistance and it is usually more convenient to use a construction which provides wider fuel outlet passages.

Conveniently the combustion air tubes terminate at one segment of the wall of the fuel chamber, this segment will hereinafter be called the outlet zone. The following constructions are particularly suitable for the outlet zone:

CONSTRUCTION l The combustion air tubes are secured into holes in an outlet zone plate which forms one wall of the fuel chamher and which is provided with fuel ports which, in the use of the burner, provide gas jets whose motion assists in the aspiration of the burner.

CONSTRUCTION 2 The combustion air tubes engage with holes in an outlet zone plate which forms one Wall of the fuel chamber; the holes being of such size that fuel outlet passages are formed by the co-operation of the holes and the walls of V the combustion air tubes. Preferably the outlet zone plate tion 1 and Construction 2 may be incorporated.)

CONSTRUCTION 3 The/Walls of the combustion air tubes co-operateto forin the fuel outlet passages. For low resistance fuel outlet passages (i.e. liquid fuel burners) combustion air tubes having the same cross-sectional area in the outlet zone as in the interior of the fuel chamber are preferred. For high. resistance fuel outlet passages (i.e. gaseous fuel burners) combustion air tubes whose cross-sectional areaexpands in the outlet zone so as to form narrow fuel outlet passages are preferred. Conformable polygons, e.g. equilatera1 triangles, squares or regular hexagons are particular suitable cross-sectional shapes for forming high resistance fuel outlet passages.

The flow of fuel from a burner which incorporates Construction 3 tends to be aligned with the flow of air from the combustion air tubes. This gives satisfactory combustion but where very high fuel flow rates are required better combustion may be achieved if the fuel flow is deflected into the combustion air flowing out of the combustion air tubes. Where this is required the burner may comprise a battle positioned over the fuel passages or, alternatively, a baflle positioned over the combustion air tubes.

Conveniently the combustion air tubes commence on another segment of the wall of the fuel chamber; this segment will hereinafter be called the air inlet zone. Two constructions are particularly suitable:

CONSTRUCTION A The combustion air tubes are secured in fluid tight manner into holes in an air inlet zone plate which forms one 'wall of the fuel chamber.

CONSTRUCTION B The cross-section of the combustion air tubes expands in the outlet zone so that their walls contact in fluid tight manner. Conformable polygons, e.g. equilateral triangles, squares or regular hexagons, are particularly suitable cross-sectional shapes.

The preferred burners incorporate Construction 3 and Construction A. This makes it convenient to use uniform cylindrical tubes as the combustion air tubes for liquid fuel burners and uniform cylindrical tubes except in the outlet zone in the case of gaseous fuels.

During use heat is conducted by the walls of the combustion air tubes into the fuel chamber and this heat is usefully employed to pre-heat combustion air and fuel, preferably to vaporisation point in the case of a liquid fuel. In the design of the burner this heat feed-back can be controlled by the selection of the material from which the tubes are made (i.e. a choice of the co-eflicient of thermal conductivity) and by the thickness of the wall of the tube. Materials of very low thermal conductivity, e.g. ceramic (including glass), have been found convenient for use with liquid fuels.

If desired additional high resistance zones can be incorporated in the interior of the fuel chamber; these high resistance zones can be formed in a manner analogous to Constructions 1, 2 and 3 of the outlet zone. This modification provides a sequence of low and high pressure zonesin the direction of fuel flow and helps to encourage a more even distribution of fuel. We have found that in most cases sufliciently even fuel distribution can be achieved with one high resistance zone, namely the outlet zone.

The burners described above burn with a distinctive compact diffusion flame which follows the configuration of the fuel outlet passages. The height of the flame is usually less than 10 mm. and often less than mm. even at high thermal outputs.

The invention includes a combustion appliance which incorporates a burner as described above which is mounted in a combustion chamber adapted to be connected to a flue. In the case of a combustion device intended for heating a fluid, e.g. a central heating boiler, the combustion appliance also comprises a heat exchanger positioned so as to receive hot gases generated by the burner when it is alight.

Combustion devices intended to run on liquid fuel may also comprise a constant flow or constant level device for controlling the heat output. Additionally, or as an alternative, the heat output may be controlled by means of a shutter which makes variable engagement with the outlet zone so as to block a variable portion of the air and fuel flow.

The invention also includes a warm air heater which comprises a blow for taking cold air (more than is required for combustion) from a suitable source and delivering it via a burner as described above to a desired destination.

The invention will now be described, by way of example, with reference to the drawings in which:

FIGURE 1 is a diagrammatic perspective view, with part cut away, of a burner according to the invention,

FIGURE 2 is a vertical cross-section through a gas burner,

FIGURE 3 is a vertical cross-section through a kerosine burner,

FIGURE 4 is a perspective, part cutaway, view of a prototype laboratory burner,

FIGURE 5 is a diagrammatic cross-sectional view of a burner as illustrated in FIGURE 1 installed in a water heater,

FIGURE 6 is a diagrammatic view of a warm air heater which incorporates a burner according to the invention,

FIGURE 7 is a diagrammatic top plan view of a burner incorporating an outlet zone plate which co-operates with the combustion air tubes to form fuel outlet passages,

FIGURE 8 is a cross-section on the line 8-8 of FIG- URE 7, and

FIGURE 9 is a diagrammatic top plan view of a burner incorporating an outlet Zone plate which has fuel outlet ports.

FIGURE 1 illustrates a burner, which, as shown, embodies Construction 3 in both high (i.e. gas burner) and low (i.e. liquid fuel burner) resistance forms and Construction B. (An operable burner would not normally utilise both forms and these are shown in the same figure for convenience.)

The burner comprises a fuel chamber 10 through which a plurality of combustion air tubes 11 pass from an air inlet zone at the bottom to an outlet zone at the top. The fuel is supplied to the fuel chamber 10 by the supply line 12 and the fuel is contained in the chamber in the interstices 13 between the combustion air tubes 11.

In the case of a gas burner, as represented by the lefthand of the portion FIG. 1 the combustion air tubes 11 have hexagonal openings 14 at the outlet zone. This arrangement provides narrow slit-like fuel exit passages 15 which provide a high exit resistance which is desirable for a gaseous fuel.

In the case of a burner intended for use with a liquid fuel, e.g. kerosine, as is represented by the right-hand portion of FIG. 1, the combustion air tubes 11 have circular openings 16 at the outlet zone. The interstices 13 between the combustion air tubes 11 provide passages 17 through which kerosine vapour (produced by the vaporisation of liquid kerosine within the fuel chamber 10) can pass into the combustion space. This arrangement is convenient where there is no need to provide a high exit resistance.

The arrangement of a gas burner embodying Construction 3 and Construction B, represented by the left-hand of FIG. 1, is further illustrated in FIGURE 2 from which it can be seen that the combustion air tubes 11 have a smaller cross-sectional area in the centre than at the extremities thereby providing sufliciently large interstices 13 to provide a low resistance to the movement of fuel within the fuel chamber. The figure also shows that the arrangement at the inlet zone is similar to the outlet zone except that the walls of the tubes are soldered together to prevent leakage of the fuel.

FIGURE 3 is the equivalent of FIGURE 2 but showing Construction 3 and Construction A, represented by the right-hand portion of FIG. 1, embodied in a liquid fuel burner. In this case the fuel outlet passages 17 at the outlet zone are of such dimensions that it is possible to use tubes of uniform cross-section and the interstices 13 are still of sufficient magnitude to permit sufliciently even distribution of the fuel so that kerosine vapour is supplied to all regions of the combustion zone. The combustion tubes 11 are soldered into holes in an air inlet zone plate 18 so as to form a fluid tight inlet zone. (If desired the inlet zones of FIGURES 2 and 3 may be interchanged; these arrangemenas will not be illustrated by means of separate drawings.)

throughout the outlet zone so that the bores 16 of the combustion air tubes account for 64% of the surface area of the burner adjacent to the combustion zone.

Both of these burners were operated under laboratory conditions under natural draught using a cylindrical glass A burner of the type illustrated in FIGURE 1 having 5 chimney 30 cm. high and 5 cm. internal diameter. Forced the dimensions 8 inches by 10 inches by 3 /2 inches deep draught (i.e. air was blown through the combustion air would provide a heating capacity of 100,000 B.t.u./hr. tubes from a laboratory supply) was used to simulate with a draught of 0.005 inch of water. chimneys of other lengths.

In the case of a burner operating on liquid fuel, e.g. 10 Experimental results are quoted in the following table kerosme, the burner is constructed so that the fuel 18 in which the kerosine was burnt in the kerosine burner vaporised within the fuel chamber 10 by means of heat and the methane in the gas burner.

TABLE Fuel Kerosine Methane Tgrfirlrnlail Pressure A K 1 Thetrmtzl Pressure A If 1 r0 Draught B.t.tL/hL/in. ins.wate t ra tib B.t.ujliiji fi ins. wa tgi' ra t i?) Forced:

Max 1,850 0.008 2.0 3,400 0.01 1.0 Min 720 0.002 4.5 600 0.001 1.2 Natural:

Max 1, 200 0. 003 3.0 1, 450 0. 003 1.06 Mm 600 0.001 1.2

transferred from the flames. A large proportion of this In the above table: heat is transferred by conduction down the walls of the The air fuel ratio gives the quantities of air measured tubes 11 and it will be apparent that the lower the level in terms of the stoichiometric quantity. of liquid kerosine in the fuel chamber the less the heat Max. indicates the largest heat output which could transfer to the liquid kerosine and therefore the less the be achieved under the conditions specified.

quantity of kerosine volatilised. This mechanism therefore provides the basis for control of the heat output and it may be utilised either by an'adjustable constant level device or an adjustable constant flow device. (Combustion air tubes of low thermal conductivity, e.g. ceramic, tend to give a higher thermal gradient which can facilitate this control.)

In the case of a constant level device the lower the levelthe less the heat transferred to the kerosine and therefore the less the vaporisation and the less the heat output.

In the case of a constant flow device the flow is adjusted to the heat requirement (within the capacity of the burner) and, if the flow rate exceeds the vaporisation rate, the level will rise thereby increasing the vaporisation rate until a'balance is achieved.

A prototype laboratory kerosine burner embodying Construction 3 and Construction B is illustrated in FIG- URE 4.A laboratory prototype gas burner similar to FIGURE 4 but with an arrangement of regular hexagons at the outlet zone was also made; this burner had com bustion air tubes arranged as shown in FIGURE .2. Further constructional details of these burners were as follows.-

Both burners consisted of a hexagonal fuel chamber 10 having fuel supply line 12 and, in the chamber, a hexagonal-arrangement of 19 cupro nickel tubes which were expanded into a hexagonal close fitting arrangement at the inlet zoneswhere the tube walls were soldered together and to the chamber 10 to give a fluid tight end face. The cylindrical portion of each tube had an internal diameter of 4.8 millimetres and an external diameter of 5.3 millimetres; the total cross-section of each burner was about 5.4 crn'.

The gas burner was 7 centimetres deep and the tubes 11 were expanded into a hexagonal pattern at the outlet zone to provide gas outlet passages approximately 0.5 millimetre wide extending about 7 millimetres down from the outlet zone face. The bores of the combustion air tubes 11 account for 79% of the surface area of the burner adjacent to the combustion zone.

In the case of the kerosine burner, the burner was 3.5 centimetres deep and the combustion air tubes 11 were of uniform cross-section from the centre zone and Min. indicates the smallest heat output which could be achieved without the burner going out.

Only one heat output, neither Max. nor Min., was available for kerosine under natural draught.

FIGURE 5 illustrates a gas fired water heater, suitable for use as a central heating appliance, which incorporates a gas burner 20.

The burner 20, constructed as shown in the left-hand portion of FIGURE 1 is situated at the base of a combustion space 21 which also contains a heat exchanger 23. The heat control system (not shown in the drawing) is conventional for gas appliances. It comprises a thermostat in the water output line 24 which operates a gas cut-off valve as necessary. A pilot jet provides re-ignition.

During use the burner 20 is connected to a fuel gas supply via a constant pressure device 26 and the combustion space 21 is connected to a flue via its outlet 29. The burner obtains its combustion air from an air space 22 and the hot gases produced by the combustion heat water circulated through the

pipes

24 and 25.

An appliance as described (burner dimensions 27 cm. by 4 cm. by 7 cm. deep) was tested using methane and town gas as the fuel. (Town gas has a variable composition but it always contains a high proportion, usually over 50% by volume, of hydrogen. Because of its high hydrogen content town gas has a high flame speed; methane has a low flame speed but about twice the calorific value of hydrogen.)

The appliance was run (at different times) on both methane and town gas at a steady pressure of 5 cm. water. The same burner and constant pressure device, without any readjustment to either, were used for both fuels. To accommodate the different calorific values an orifice plate (not shown in the drawing) was fitted between the pressure device 26 and the burner 20 and this was changed from a large orifice during the use of town gas to an orifice one-half the area of cross-section when methane was in use. Apart from this trivial alteration the burner operated equally well on both fuels giving a heat output of about 40,000 B.t.u./hr. about 30,000 of which were transferred to the water. This experiment illustrates the fact that the same burner will operate equally effectively on both gaseous fuels having a high flame speed and those having a low flame speed.

In both cases the burner was silent during the operation.

A modified heat control, suitable for use with liquid fuels, comprises a shutter 27 which can slide over the top of the burner 2 and extinguish part of the supply of air and fuel thereby reducing the heat output. This shutter is operated automatically by means of a retractor 28 which senses the temperature of the water in the output line 24. Control of rate of liquid fuel supply or the level of liquid fuel in the fuel chamber also provide control of heat output by the mechanism described above.

A warm air heating device incorporating a burner according to the invention is shown in FIGURE 6 in which cold air is drawn by electrically operated fan 30 from a flexible tube 31 and supplied to a heating unit 32. The heating unit 32 comprises a burner 33 which is of the type described previously. This burner is positioned so that the air stream provided by the fan 30 passes through the combustion air tubes of the heater 33. The fuel chamber of the heater 33 is connected to a supply of fuel gas, i.e. the bottle of propane 34, and as the gas emerges from the fuel passages it is burnt in the air supply. In this application a large quantity of excess air is used so that the result of combustion is a supply of Warm air which is delivered to its desired destination via the flexible tube 35. Liquid fuel burners may also be used in this application provided that the axes of the combustion air tubes are maintained vertical.

A burner as shown in FIGURE 1 was also tested in a radiant heat appliance (not shown in any drawing). This was constructed according to the conventional manner in which the burner is positioned below ceramic elements which are heated to redness during use. The burner according to the invention gave satisfactory performance with both town gas and methane.

The gas burner shown in FIGURES 7 and 8 (which are on a larger scale than the other drawings) incorporates Construction 2 and Construction A. Its structure is similar to the kerosine burner of FIGURE 3 (i.e. cylindrical combustion air tubes 11 of uniform cross-section secured into holes of an air inlet zone plate 18) with the addition of an outlet zone plate 40 which co-operates with the combustion air tubes 11 to form annular fuel outlet passages 41 which direct the flow of fuel into the air stream. As can be seen from FIGURE 7 the outlet zone plate 40 contains holes of similar size and arranged in the same pattern as the opening of the combustion air tubes 11.

A baflle plate, similar to the outlet zone plate 40, may be used in conjunction with the hexagonal arrangement illustrated in FIGURE 2 (the holes in the plate being hexagonal instead of circular). Although the two constructions are similar there is an important difference between the function of the outlet zone plate 40 and the baflle plate. The outlet zone plate 40 of FIGS. 7 and 8 co-operates with the cylindrical combustion air tubes 11 to define the annular fuel outlet passages 41 and the dimensions of these passages control the rate of flow of fuel and the pressure drop. In the case of the baflle plate the fuel outlet passages 15 are defined by the co-operation of the walls of the combustion tubes and it is their dimensions that control the pressure drop and rate of flow of the fuel. The baflie plate has no substantial effect upon these flow parameters and merely serves to deflect the flow of fuel so that it mixes with the air issuing from the combustion tubes.

The burner shown in FIGURE 9 embodies Construction 1 and Construction A. It comprises an outlet zone plate 40 into which the combustion air tubes 11 are sealed in fluid tight manner (i.e. the construction at the outlet zone is similar to the construction at the air inlet zone). The fuel outlet passages take the form of ducts 42 which are small holes drilled in the outlet zone plate and arranged in a hexagonal pattern between the combustion air tubes. In the use of the burner relatively fast jets of fuel issue from the ports 42 and this motion tends to 8 cause the gas in the combustion zone to move away from the burner thereby assisting in the aspiration.

A laboratory prototype burner of the type described in FIGURE 9 was tested under a 5 inch chinmey using methane and town gas as the fuel in two separate experiments. The burner consisted of 38 uniform cylindrical tubes having an internal diameter of 4.5 mm, and an external diameter of 5.0 mm. The tubes were arranged in alternate rows of 8 and 7 to give a rectangular burner 26 mm. by 45 mm. and 19 mm. deep. The outlet zone plate was drilled with 60 holes each having a diameter of 0.5 mm. which were arranged in a hexagonal pattern between the combustion air tubes as shown in FIGURE 9. Under a 13 cm. chimney the burner gave its maximum thermal output with a pressure drop of 0.05 mm. water gauge across the combustion air tubes. For methane the maximum heat output was 1700 B.t.u./hr./sq. in.; for town gas the maximum Was 2000.

The burners described in this specification are compact, i.e. they provide good heat output per unit area, they operate with a low air pressure drop across the burner and they are capable of operating with a wide range of fuels and excess air conditions. Furthermore they can be made in a wide variety of shapes.

We'claim.

1. A burner for fluid fuels which comprises an assembly of combustion air tubes; and wall means enclosing said assembly and forming a fuel chamber with said tubes, said fuel chamber being substantially co-extensive with said assembly axially of said combustion air tubes and said tubes being substantially uniformly distributed over the cross-sectional area of the fuel chamber, the wall of said fuel chamber having fuel outlet passages, an air inlet zone and an outlet zone, said outlet zone providing a surface area of the burner adjacent to the burner combustion zone, said combustion air tubes and said fuel outlet passages terminating at said surface area and opening over said surface area into said combustion zone and said combustion air tubes providing a low resistance passage for combustion air through said fuel chambers from said air inlet zone to said combustion zone, the interstitial space of said tubes in said fuel chamber providing a low resistance to the flow of fuel across the cross-section of said fuel chamber and the cross-sectional area of each tube being sufficiently small where the tube opens into the combustion zone and the bores of the tubes accounting for a sufliciently large proportion of said surface area that, in the use of the burner, the combustion air tubes convey air and the fuel outlet passages convey fuel to the combustion zone and distribute the air and fuel in said combustion zone with diflfusion paths sufiiciently small to maintain a diffusion flame over said surface area.

2. A burner according to claim 1, in which at least the central portion of each combustion air tube is cylindrical.

3. A burner according to claim 2, in which the combustion air tubes are arranged with their axes parallel to one another.

4. A burner for gaseous fuels according to claim 1 which also comprises an outlet zone plate which forms one wall of the fuel chamber and provides said surface area of the burner,

5. A burner for gaseous fuels according to claim 4, said plate overlying said combustion air tubes and having holes, the combustion air tubes engaging with said holes and the holes being of such a size that the fuel outlet passages are formed by the co-operation of the holes and the walls of the combustion air tubes.

6. A burner according to claim 5, in which the outlet zone plate is arranged so that, during the use of the burner, it directs the outflow of fuel into the combustion air emerging from the combustion air tubes.

7. A burner according to claim 4, in which the outlet zone plate has holes in which the combustion air tubes are secured and is also provided with fuel ports arranged between the combustion air tubes, which ports, in the use of the burner, provide gas jets whose motion assists the aspiration of the burner.

8. A burner according to claim 1, in which the walls of the combustion air tubes co-operate to form the fuel outlet passages.

9. A burner for gaseous fuels according to claim 8, in which the cross sectional area of each combustion air tube expands in the outlet zone so as to form narrow fuel outlet passages.

10. A burner according to claim 9, in which the crosssectional shape of the combustion air tubes in the outlet zone is that of conformable polygons.

11. A burner according to claim 10, in which the polygons are equilateral triangles, squares or regular hexagons.

12. A liquid fuel burner according to claim 8, in which the combustion air tubes have the same cross-sectional area in the outlet zone as in the interior of the fuel chamber.

13. A liquid fuel burner according to claim 12, in which the combustion air tubes are uniform cylinders and the burner also comprises an air inlet zone plate which forms one wall of the fuel chamber; the combustion air tubes being secured in fluid tight manner into said air inlet zone plate,

14. A burner according to claim 1 which also comprises an air inlet zone plate which forms one wall of the fuel chamber and the combustion air tubes are secured in fluid tight manner into said air inlet zone plate.

15. A burner according to claim 1, in which the crosssection of each combustion air tube expands in the air inlet zone so that their walls contact in fluid tight manner.

16. A burner according to claim 9, in which the burner comprises a baflie plate positioned over the fuel outlet passages and adapted to deflect the flow of fuel into the flow of combustion air.

17. A burner according to claim 9, in which the burner comprises a baflle plate positioned over the combustion air tubes and adapted to deflect the flow of combustion air into the flow of fuel.

18. A burner according to claim 1, in which the bores of the combustion air tubes account for at least 25% of the surface area of the burner adjacent to the combustion zone.

19. A burner according to claim 18 in which the bores of the combustion air tubes account for at least 50% of the surface area of the burner adjacent to the combustion zone.

20. A burner according to claim 1, in which the bore of each combustion air tube has a cross-sectional area of at the most 1.0 cm. where it opens into the combustion zone,

21. A burner according to claim 1, in which the bore of each combustion air tube has a cross-sectional area of at least 0.01 cm? where it opens into the combustion zone.

22. A liquid fuel burner according to claim 1, in which the combustion air tubes are made of ceramic material.

23. A burner for fluid fuels which comprises an assembly of combustion air tubes; and, Wall means enclosing said assembly and forming a fuel chamber with said tubes, said fuel chamber being substantially co-extensive with said assembly axially of said combustion air tubes and said tubes being substantially uniformly distributed over the cross-sectional area of the fuel chamber, the wall of said fuel chamber having fuel outlet passages, an air inlet zone and an outlet zone, said outlet zone providing a surface area of the burner adjacent to the burner combustion zone, said combustion air tubes and said fuel outlet passages terminating at said surface area and opening over said surface area into said combustion zone, and said combustion air tubes providing a low resistance passage for combustion air through said fuel chamber from said air inlet zone to said combustion zone, the interstitial space of said tubes in said fuel chamber providing a low resistance to the flow of fuel across the cross-section of said fuel chamber and the cross-sectional area of each tube being sufliciently small Where the tube opens into the combustion zone and the bores of the tubes accounting for a sufficiently large proportion of said surface area that, in the use of the burner, the combustion air tubes convey air and the fuel outlet passages convey fuel to the combustion zone and distribute the air and fuel in said combustion zone with difiusion paths sufliciently small to maintain a diffusion flame over said surface area, the bore of each combustion air tube having a cross sectional area of 0.01-1.0 cm. where it opens into the combustion zone and the bores of the combustion air tubes accounting for at least 25 of the surface area of the burner adjacent to the combustion zone.

References Cited UNITED STATES PATENTS 408,073 7/1889 Bell 431179 904,243 11/1908 Bennett 431-174 2,755,750 7/1956 Escher 431-178 2,880,717 4/1959 Tilmann 126-85 EDWARD G. FAVORS, Primary Examiner U.S. Cl. X.R. 26319;431-181 gzgg M UNITED sums PA'IENT omits CERTIFICATE OF CORRECTION Patent: No. 3,504,994 Datcd Affil- 7, 1;97Q

Invmuoz-(a) Denis Henry Desty and David Montagu Whitehead It in certified that error appeal in tho show-identified patent and that aid Lattara Patent are hnraby con-lead u lhonm balm:

Colman 5, line 4 for "arrangs" read "arrange-ants";

Column 5, line 56 for "tubes which" read "tubes 11 which";

calm 8, line 27 for "and well" read "and, wall"; and

Column 8, line 13 for "20:16 and" read "zone, and".

mm? 1!- mm x. .112. Am; Offi er Ooflniasiom of Patents