US2119007A - Oil burning apparatus - Google Patents

Description

May 31, 1938. DALEN OIL BURNING APPARATUS 3 Sheets-Sheet 1 Filed July 13, 1935 /H Ill loo u .0 I Q Q Q O O 1/ o a a 0 I WI 3 a 0 u l l 2 A 4' 6. I v i1 I w I /N I INVENTOR. W 49.44.,

ilk ATTORNEY.

Patented May 31, 1938 PATENT OFFICE OIL BURNING APPARATUS Gustaf, Daln,

Lidinga. Sweden,

assignor to Svenska Aktiebolaget Gasaccumulator, Stockholm, Sweden, a corporation of Sweden Application July 13, 1935, Serial No. 31,196

In Sweden July 20,1934

21 Claims.

The present invention relates to oil burning apparatus and has particular reference to oil burners for burning hydro-carbon fuel vapor produced from relatively heavy hydro-carbon fuels. Still more particularly the invention relates to oil burners of the kind in which one or more perforated walls, usually in the form 'of cylindrical tubes, separate air and fuel vapor chambers and in which. the air passes through the perforations of the walls to form a combustible gas mixture in the fuel chamber.

In burners of this kind, combustion occurs in the form of a series of independent flames each localized at one of the perforations in the wall structure and heretofore such burners have been subject to unsatisfactory operation because of a number of factors among which the following are important. Hydro-carbon oil vapors break down by cracking at a temperature of around 1,000 C. When this occurs, free carbon is formed which usually occurs as soot and the flame becomes incandescent. Such operation should be avoided and combustion should therefore take place at a temperature below 1,000" C.

The temperature of combustion is however among other things dependent upon the velocity of the air entering the mass of oil vapor. The higher the velocity of the air, the higher the temperature of combustion tends to become and the greater the tendency to form free carbon. From experiment it has been found that air velocities up toabout thirty centimeters per second are most suitable for the combustion of pure oil vapor formed from ordinary crude or fuel oil. In order to accelerate the entering air to this maximum velocity requires a pressure differential corresponding to about five millimeters of air. Additional pressure corresponding to possibly a fraction of a millimeter may be required to overcome friction in the air inlet orifices but this is so small that it may for practical purposes be neglected. In order to secure the best results, the pressure differential should also be substantially constant over the entire height of the burner.

As burners of the character under consideration have heretofore been constructed, this is however not the case. In the first place, the comparatively cold oil vapor in the lower portion of a vapor chamber is much more dense than the air, while the combustion products in the upper portion of the burner, which products may be rich in water vapor, are of less density than the air. In the second place, because of the high temperature of the products of combustion which as a rule approaches the temperature of combustion in the upper portions of the burner, the variation of the specific weight of the gases is even more pronounced on the oil' vapor side of the burner wall. In addition to this, the drop in pressure due to the work of acceleration expended on the combustion gases, for which there is no corresponding amount of work on the air side of the burner wall, tends to produce a still larger variation in the pressure differential.

With previous types of burners it has therefore proved to be impossible to keep the pressure. difference constant over the entire height of the burner. If the pressure differential is normal for proper combustion at the center of the height of the burner wall, then the flames formed in the upper part of the burner become incandescent and soot forming because of too high air velocity. while in the lower part of the burner the pressure of the air may not exceed the pressure of the fuel vapor and may even be less, in which event there may be flow of fuel vapor into the air chamber which is exactly thereverse of what is desired. The last mentioned phenomena are more pronounced the higher the rate of fuel consumption is in a given burner. In burners where the oil vapor is produced by vaporization caused by some of the heat that is produced by the burner, the vaporizing surface or surfaces are usually in the lower part of the burner and receive most of the heat from the flame or flames produced in this part of the burner. The more fuel there is supplied to the burner, the more heat must be supplied to the vaporizing surfaces from the lower flames of the burner. However, for reasons pointed out above, the conditions obtaining at high burner capacity are likelyto cause the flames in the lower part of the burner to diminish or even go out, just at the time when they are most required. Such action leads to incomplete vaporization and to the formation of coke in the vaporizing apparatus to such an extent as to render continued operation of the .burner impossible.

It is the general object of the present invention to improve upon burner constructions of the character under discussion so as to provide for proper combustion over the entire active area of the burner, regardless of they variations in the rate at which fuel is supplied to the burner. A further object is to provide improved burner structure of the character described which will insure adequate combustion and an adequate" vaporizing temperature. It is a further object of the invention to provide improved burner structure whereby the rates of combustion at different places or in different zones along the. height of the burner may be controlled in a predetermined manner so as to produce the desired relative amounts of heat in the different zones.

The foregoing objects and other and more detailed objects which will appear as this description proceeds are obtained by constructing the burner apparatus in accordance with the following general principles. The difference in pressure between the gases in the combustion zone of the burner and the surrounding air is many times greater than is required for forcing, the air into the combustion chamber at the maximum rate desirable. Heretofore the air for combustion has been'regulated by throttling the conduit between the outside air and the air chamber of the burner in order to decrease the pressure in the air chamber to a suitable value. In ac-v cordance with the present invention, the air supply is throttled individually for the various parts or sections of the burner in accordance with the character of the pressure differential ordinarily existing in the parts of the burner. Such throttling is however not effected by reducing the area of the burner perforations or orifices where such orifices communicate with the vapor or combustion chamber as this would result either in a deflciency of air for combustion or to a penetrative velocity of the air which would exceed the permissible maximum.

Accordingly the burner is divided into several sections each of which ordinarily includes a relatively large number of individual perforations but which, insofar as the principle of the invention is concerned, may comprise as few as a single perforation per section. In order to obtain the desired control of the air the arrangement is made such that the air for each section must flow serially first through a series. of throttling orifices which determine the quantity of air supplied and then through a second series of orifices the combined area of which is sufficiently larger than the combined area of the first series of orifices so that the desired maximum velocity of the air entering the combustion space is not exceeded. Preferably the latter series of orifices are the perforations in the burner wall at which combustion takes place. 7

For a better understanding of the details of the nature of the invention and the advantages to be derived from its use, reference may best be had to the ensuing description of embodiments of apparatus suitable for carrying the invention into effect, and illustrated in the accompanying drawings forming a part of this specification.

In the drawings:

Fig. 1 is a more or less diagrammatic vertical section, partly in elevation, of a domestic hot water heater equipped with a burner embodying the invention;

Fig. 2 is a view partly in section and partly in elevation and on a larger scale of part of the burner apparatus shown in Fig. 1;

Fig. 3 is a view partly in section and partly in elevation of the outer burner wall structure shown in Fig. 2;

Fig. 4 is an elevation, partly in section, showing a slightly different form of burner construction; and

Fig. 5 is a sectional view showing still another form of burner-wall construction.

Referring now to Fig. 1, the burner indicated generally at A is provided with a lower base member Hi having a burner portion I 2 of generally circular cross section providing a recess I4 from the bottom of which there extends upwardly a short circular flange l6. Adjacent the burner portion of the base member an extension is provided which forms a vaporizer l8 consisting of a vaporizing chamber 20 and a vaporizing surface 22, the chamber 20 being in communication with the recess l4 by way of passage 24.

Extending upwardly from the base member is a plurality of burner tubes which will be described more in detail later. Above the burner tubes there is located the heat receiving member 26 adapted to be heated by the gases of combustion produced in the burner. In the form shown, this member is a hollow casting providing a combustion gas space 28 and water heating spaces 30, the space 28 being in communication with a flue opening 32 and water being admitted to and withdrawnfrom the spaces 30 by means of pipes 34 and 36 respectively.

Liquid fuel is supplied to the vaporizer at a suitably controlled rate in known manner fromfuel supply means indicated generally at 38, the fuel flowing through passage 40 and dropping to the vaporizing surface from the. feeding member 42. Advantageously a restricted quantity of air, insuflicient to form a combustible gas mixture in the vaporizing chamber, is supplied through pipe 44.

The upper portion of the burner structure and the heat receiving member 26 are preferably surrounded by a mass of insulating material indi-' with chamber 50 and the air inlet 52.

Turning now more particularly to Figs. 2 and 3 of the drawings, the burner wall structure comprises two sets of perforated tubes, one set of which forms an inner burner wall indicated generally at B and the other set of which forms an outer burner wall C. The space inside the inner burner wall B is in communication at its lower end with the air inlet pipe 53 and constitutes an air space for supplying air to the fuel vapor space 54 which is also the combustion space of the burner. The space 48 provides a second air space for supplying air to the combustion space 54 through the outer wall of the burner.

The inner burner wall B is formed inthe present embodiment by an inner perforated tube 56 and an outer perforated tube 58, the latter tube resting at its lower end on the base flange I6.

The two tubes are concentric and spaced apart and the construction is such that the burner wall formed by the tubes is divided into a plurality of separate sections along the height of the wall. In the present embodiment, the division of the burner wall into sections is accomplished by inwardly extending ridges 60 pressed at intervals into the outer tube 58 and contacting the inner tube 56. Obviously the outer tube may be made cylindrical and the ridges pressed outwardly from the surface of the inner tube to obtain the same effect.

spaced inwardly projecting ridges 86 pressed from the outer tube. I

Assuming the burner to be in operation, the combustion action is as follows:

Substantially pure fuel vapor unmixed with sufiicient air to support combustion flows under the influence of the draft from the vaporizing chamber 20 through the passage 24 to the annular space provided in the recess 14 of the base member which is outside of .the inner burner wall and which is in effect a continuation of the combustion space formed by the passage 54 between the bumer walls. Air, which is drawn in by the draft through the perforations in the tubes in the inner burn'er wall mixes with the fuel vapor and forms an ignitible mixture which burns in a series of separate flames in the orifices or perforations in the burner tube 58. The heat generated by the flames in the lower part of the If the burner is being operated at minimum capacity, the quantity of fuel vapor will'be mixed with air and burned by the time a level is reached which should be approximately that of the lower end of the outer burner wall C. The gases of combustion thus formed will flow upwardly through the combustion chamber space, being mixed'in their passage with additional excess air which enters through the perforations lying above those where active combustion takes place. If the quantity of fuel fed to the burner is increased, the level of the active flame front rises in the combustion space as unburned fuel vapor progressively reaches higher and higher levels in the burner and is there mixed with the air necessary for combustion at the perforations in both the inner and the outer burner walls. At maximum capacity, the flame front should be at the top of the burner.

With an arrangement such as this, there should be combustion at substantially constant rate in the lower portion of the burner, thus insuring delivery of suificient heat to the vaporizer to maintain it at proper vaporizing temperature under all conditions.

Constant and proper combustion in the various parts of the burner might be easily obtained if the pressure conditions governing the flow of combustion air to the several partsof the burner remained-constant under different burner operating conditions. This, however, is not the case and as previously explained I overcome the difliculties due to the conditions normally arising by dividing the burner walls into different sections to which the combustion air is admitted in different man-- the burner will be seriously diminished and in extreme cases combustion may even cease in this part of the burner.

In order to. overcome this condition, I provide different areas for flow of air in different portions of the burner wall structure so that in each section of the burner the air is throttled to the degree required to provide proper combustion,

while at the same time excessive velocity of the air entering the combustion space due to such throttling is avoided. To this end, in'the embodiment illustrated, the inner tube 56 of the inher wall B and the outer tube 54 of the outer wall C are constructed as throttling tubes the perforations in which govern the amount of air passing through the walls, while the outer tube 58 of the ,in the burner tubes per unit area of these tubes is constant, it will .be evident that the area of the perforations in the throttling tubes must be less Moreover to.

per unit area of the latter tubes. obtain a fixed inlet velocity of the entering air over the height of the burner, the ratio of the area of the perforations per unit area in the burner tubes to the area of the perforations per unit area in the throttling tubes should be constant over the height of the burner, whereas the total area of perforations per section of the burner wall should be less the greater the pressure difference. existing at the section.

A fixed inlet velocity over the entire height of the burner is however not always desirable. On account of the combustion taking place in the lower portion of the burner, the unburned oil vapor in the upper portion of the burner is diluted by combustion gases and is consequently less dense than in the lower portion. As previously noted, the maximum entering air velocity 'desirable for air mixing with pure fuel vapor is about 1 30 centimeters per second; A somewhat higher velocity is required for the entering air mixing with diluted vapor in order to obtain a constant combustion temperature. In the top part of a burner of the kind herein disclosed the entering air velocity may be as high as 50 centimeters per second. Therefore where higher velocity is desired at the upper part of the burner the constant relationship of the area of the burner tube perforations to the area of the throttling tube perforations may be altered to provide proportionately smaller areaof perforations in the burner tubes or a larger proportional area of perforations in the throttling tubes.

Also in some cases, it may be desirable to control the combustion over the height of the burner in a pre-determined manner so that at maximum capacity combustion takes place at ahigher rate in both the lower and upper portions of the burner than at the middle portion of the burner. In a construction such as that illustrated this may be desirable in order to provide suflicient heat at the lower part of the burner to insure proper operation of the vaporizing apparatus and to provide the generation of the greater portion of the heat for the heat requiring parts at a place as closely-adjacent to such parts as possible. The reason for the latter is that the loss of heat by convection to the surroundings of the burner is less, the nearer the place of combustion to the place of heat utilization. In this sort of arrangement the total area of perforations per section of burner wall should be less at the center of the burner than at the upper and lower ends thereof.

In order to illustrate the foregoing, I will give the characteristic features of an actual example of practical burner construction built in accordance with the invention.

Referring now more particularly to Figs. 2 and 3, the throttling tube 56 of the inner burner wall has a diameter of 44 mm. and a height of 329 mm. The burner tube 58 of the inner burner wall has a diameter of 49 mm. and a height of 342 mm. The burner tube is'provided with burner perforations or orifices 68 which are uniformly spaced from top to bottom of the tube. The perforations 68 are 2.2 mm. in diameter arranged in rows spaced vertically 8 mm. apart, with the perforations in each row spaced 6 mm. apart peripherally.

The ridges 60 in the inner burner tube 58 divide the space between the two tubes of the wall into a series of separate sections a, b, c,'d, e, j, g, h and z. Sections a to d inclusive each include two rows of burner holes, section e includes four rows, sections 1', g and-h each include eight rows and section i includes five rows.

The throttling tube 56 of the inner burner wall is provided with throttling orifices or perforations 10, also 2.2 mm. in diameter and arranged in rows so that one row communicates with each of the sections a to d inclusive. The perforations in these rows are spaced peripherally 7.4 mm. apart. Two rows of throttling perforations l communicate with the section e, perforations in one row being placed peripherally 7.4 mm. and the perforations in the remaining row being spaced peripherally 19.3 mm. Sections 1, a and h each have communicating therewith three rows of throttling perforations spaced peripherally 19.3 mm. and section 2 has two rows of throttling perforations of this latter spacing.

It will be evident that in this embodiment the area for flow of air through the burner tube is constant per unit area over the height of the burner. The desired balancing of air flow through the burner wall-at different heights in the burner is accomplished by variations in the spacing of the throttling perforations. It will be evident that in this instance we have a construction where the throttling tube controls the rate of air flowat different heights by providing fewer throttling perforations, and consequently greater throttling effect, for the upper sections than for the lower sections. The least throttling is effected for the sections a to d inclusive which sections may be said to represent the zone of combustion providing vaporizing heat as distinguished from the zone represented by sections such as g and h, which provide heat for external use.

The outer burner wall construction is generally similar to the inner construction. In this wall the burner tube 62 is 71 mm. in diameter and 270 mm. in height. The ridges iiii in the throttling tube 64 are spaced to divide the wall structure into separate Sections :i, k, l, m and n. The burner tube 62 is provided with perforations l2 uniformly spaced through the height of the burner.

These perforations are 2.2 mm. in diameter, the vertical and peripheral spacing of the perforations being the same as for the inner burner tube 56. Each of the lower sections :i and It has four rows of burner perforations l2 communicating therewith while the three upper sections Z, m and 11. each have eight rows of burner perforations. In

the outer throttling tube 04, two rows of throttling perforations ll with perforations 2.2 mm. in diameter, spaced peripherally 14.8 mm. communicate with each of the lower sections 1 and k.- .Threerows of throttling orifices communicate with each of sections 1, m and n, the perforations in these latter rows being spaced peripherally 18 mm. It will therefore be evident that, as in the inner burner wall construction, the burner tube provides a constant area for flow of air per unit height of the burner while the compensation required for difference in pressure is provided by'a greater degree of throttling per unit area of the burner wall at the upper portion of the burner than at the lower portion.

As previously noted, it may be desirable to distribute the combustion occurring at maximum capacity so that more heat is generated at the top and bottom of the burner than in the middle. This result may be obtained by a burner construction as illustrated in Fig. 4 in which for example in sections f and g of the inner burner wall there are fewer perforations per unit area of the sections, both in the burner tube and the throttling tube, then in the sections h and i above. The same relationship also is advantageously employed with respect to the total number of perforations in the sections 1' and m of the outer burner wall as compared with section n.

It is not essential in order to carry the invention into effect to make the burner walls hollow as in the embodiments previously described. If a solid burner wall of relatively heavy cross section of wall thickness is employed, the same general effect may be obtained by utilizing conical or similar air passages of increasing cross section area from the air side of the burner wall to the combustion chamber side of the wall. Such a construction is illustrated more or less diagrammatically in Fig. 5 in which the channels 1'6 in the inner burner wall B provide throttling perforations of relatively small diameter communicating with burner perforations 68' of relatively large diameter. The outer burner wall C is similarly constructed with channels 18 providing small throttling perforations H on the air side of the wall and larger burner perforations 12' on the combustion chamber side of the wall.

As in the embodiments previously described, the throttling effect desired in order to compensate for different pressure differences at different heights in the burner is obtained by varying the distribution of the throttling perforations over the height of the burner in accordance with the principles previously discused.

From the foregoing it will be evident that the broad concept of the invention may be carried out in a variety of diiferent specific embodiments of apparatus and invention is accordingly to be considered as embracing all forms of apparatus falling within the scope of the appended claims.

I claim:

' 1. In a fuel burner of the kind in which a perforated partition wall separates a combustion space, to the lower portionpf which fuel vapor is admitted, from an air space from which combus-' sections one above the other, each of said plates having a plurality of perforations therein and the total area of the perforations for each section of the plate on the c6mbustion space side of the wall being greater than the total area of the perforations for each section of the remaining plate.

2. In a fuel burner, a hollow partition wall separating the combustion space of the burner from the source of air supply having a series of separate sections one above another, a series of perforations for flow of air from the interior of the several sections to the combustion space of the burner, and a series of perforations for flow of air from the source of air supply to the interior of the several sections of the wall, the. last mentioned series of perforations having a less total area for each section than the first mentioned series.

spaces comprising two spaced burner tubes and means dividing the space between the tubes into a plurality of separate wall sections one above another, each of said tubes being perforated and the perforations communicating with said air space being of less total area than the total area of the perforations communicating with said combustion space.

4. In a fuel burner having a combustion space and an air space, a burner wall separating said spaces comprising two spaced burner tubes and means dividing the space between the tubes into a plurality of separate wall sections one above another, each of said tubes being perforated, the

totalarea of the perforations providing communication between said air space and each wall section being less than the total area of the perforations providing communication between the same wall section and said combustion space.

5. In a fuel burner, two spaced and concentric burner walls, each of said walls comprising spaced inner and outer burner tubes and means for dividing the space between the tubes of each wall into a plurality of separate wall sections one above another, each of said tubes being perforated, and the total area of perforations per section in one of the tubes of each wall being different from the total area of the perforations in the same section of the other tube of the same wall.

6. In a fuel burner, an inner tubular burner wall, an outer tubular burner wall concentric with and spaced from said inner wall to provide a combustion space between the two walls, means for admitting fuel vapor to the lower portion of said combustion space, means for admitting cornbustion air to the space surrounding said outer wall and to the space surrounded by said inner wall, each of said walls comprising spaced inner and outer perforated burner tubes, the perforations in the outer tube of the outer wall and the inner tube of the inner wall having less total area for flow of air therethrough than the perforations in the inner tube of the outer wall and the outer tube of the inner wall.

7. In a fuel burner, a perforated partition wall for separating a combustion space from an air space, said wall having a series of channels ex,- tending through the material of the wall, said channels increasing in cross sectional area from the air space side of the wall to the combustion chamber side of the wall to provide perforations having a total area for flow of air from the air space less than total area of the perforations to flow of air to the combustion space.

8. In a fuel burner, a perforated partition wall for separating an air space from a combustion space, said partition wall having a series of generally conical channels extending therethrough providing perforations having a smaller total area in communication with the air space than the total area of the perforations in communication with the combustion space and said channels being distributed to provide a greater total area for flow of air through the wall per unit area of the wall in the lower portion of the burner than in the upper portion of the burner.

9. In a fuel burner, spaced upwardly extending inner and outer burner wall structures providing therebetween an annular combustion space, there being air spaces for combustion air outside the outer wall structure and inside the inner wall structure, means for causing a column of gaseous fuel having insumcient oxygen to be combustible to flow upwardly in said combustion space, said wall structures being perforated to provide paths for flow of combustion airfrom the air spaces to the combustion space and the total area of the outlets of said paths for flow of air into said combustion space from said wall structure being greater than the total area available for flow of air from one of said air spaces through said paths to said outlets.

10. In a fuel burner, an upwardly extending burner wall separating a combustion space on one side of the wall from an air space on the opposite side of the wall and means for causing a body of gaseous fuel having insufficient oxygen to support combustion to flow upwardly in said combustion space adjacent to one-face of the wall,'said wall being perforated to provide paths for flow of air through the wall from said air space to said combustion space, the total area of the outlets of said paths for flow of air into said combustion space from said wall being greater than the total area available for flow of air from said air space through said paths to said outlets and the relation between the values of said areas per unit area of the wall being different at different levels to compensate for the difference between the pressure of the air in said air space and of the gases in the combustion space at such different levels.

11. In a fuel burner, an upwardly extending hollow burner wall separating a combustion space on one side of the wall from an air space on the opposite side of the wall and means for causing a body of gaseous fuel having insuflicient oxygen to support combustion to flow upwardly in said combustion space adjacent one face of said wall, the' interior space of said hollow wall being divided into a plurality of separated sections one above another and said wall being perforated for flow of air from the air space to the combustion space through said sections, the total area of the perforations in communication with the air space being less than the total area of the perforations in communication with the combustion space and the relation of the total area of the first mentionedperforations to the total areacf the second mentioned perforations in different sections beingdifierent to compensate for the difference between the pressures in the air space and in the combustion space at the levels of different sections. 1

12. In a fuel burner, a perforated burner wall structure separating an air space from a combustion space to the lower portion of which fuel vapor is admitted, said wall structure being divided into a plurality of sections, one above another and providing paths therethrough for flow of air from said air space to said combustion space, the outlet area of said paths for flow of air from said wall structure into said combustion space being different in different sections and such outlet area in each section being greater than the area for flow of air from said air space through said paths to the outlets in the same section.

13. In a fuel burner, a perforated burner wall structure separating an air space from a combustion space to the lower portion of which fuel vapor is admitted, said wall structure being divided into a plurality of sections, one above another and providing paths therethrough for flow of air from said air space to said combustion space, the relative area of the outlet area for flow of air from said wall structure into said combustion space with respect to the area for flow of air from said air space through said paths to the outlets thereof being different in different sections and said outlet area being relatively greater for a section where the pressure difference between said air space and said combustion space is relatively greater than for a section where such pressure difference is less.

14. 'In a fuel burner, a perforated burner wall structure separating an air space from a combustion space to the lower portion of which fuel vapor is admitted, said wall structure being divided into a plurality of sections, one above another and providing paths therethrough for flow of air from said air space to said'combustion space, the outlet area of said paths for fiow of air from said wall structure into said combustion space being greater per unit area of the wall structure in the lower and upper portions of the wall than in the middle portion thereof, and the outlet area of said paths for flow of air from said wall structure into said combustion space in a lower one of said sections being greater than the area for flow of air from said air space through said paths to the outlets in the last mentioned section.

15. In a fuel-burner a vaporizer for vaporizing liquid fuel to produce fuel vapor, a perforated burner wall separating an air space from a combustion space to the lower portion of which fuel vapor is admitted from said vaporizer, said vaporizer being in good heat conducting relation with the combustion space adjacent to the lower portion of said wall structure, said wall structure providing paths for flow of air therethrough from said air space to said combustion space, the area for such flow per unit area of said wall structure being greater in the lower wall portion of the wall structure than above such lower portion, and the outlet area of said paths for flow of air from said wall structure into said combustion space being greater than the area for flow of air from said air space through said paths to the outlets thereof in the lower portion of the burner.

16. In a fuel burner of the kind in which a perforated partition wall separates a combustion space, to the lower portion of which fuel is ad.- mitted, from an air space from which combustion air flows to the combustion space through the perforations in the wall, an upwardly extending partition wall construction comprising two spaced plates, each of said plates having a plurality of perforations therein and the combined area of the perforations in the lower por-.

tion of the plate on the combustion space side of the wall beinggreater than the combined area of the perforations in the corresponding portion of the remaining plate.

17. In a fuel burner of the kind in which a perforated partition wall separates a combustion space, to the lower portion of which fuel is admit- I ted, from an air space from which combustion air flows to the combustion space through the one above another, each of said in the plate on the combustion space side of the wall being greater than the combined area in such .section of the perforations in the remaining plate.

18. In a fuel burner having a combustion space and an air space, a burner wall separating said spaces comprising two spaced burner tubes and means dividing the space between the tubes into a plurality of separate wall sections one above another, each of said tubes being perforated and the perforations providing communication between the interior of at least one of the sections in the lower portion of the burner and said air space being of less total area than the total area of the perforations providing communication between the interior of the last mentioned section and said combustion space.

'19. In a fuel burner, a perforated burner wall structure separating an air space from a combustion space to which fuel vapor is admitted, said wall structure providing paths therethrough for flow of air from said air space to said combustion space, and the total area of the outlets of said paths for flow of air into said combustion space from said wall structure being greater than the total area available for flow of air from said air space through said paths to said outlets.

20. In a fuel burner, a perforated burner wall structure separating an air space from a combustion space to the lower portion of which fuel vapor. is admitted, said wall structure providing paths therethrough for flow of air from said air space to said combustion space and the total area of the outlets of said paths for flow of air into said combustion space from said wall structure in the lower portion of the burner being greater than the total area available for flow of air from-said air space through said paths to said outlets in said lower portion of the burner.

21. In a fuel burner, a perforated burner wall structure separating an air space from a combustion space to the lower portion of which fuel vapor is admitted, said wall structure being divided into a plurality of sections, one above another and providing paths therethrough for flow of' air from said air space to said combustion space, the total area of theoutlets of said paths for flow of air into said combustion space from at least one of said sections in the lower portion of the burner being greater than the total area available for flow of air from said air space through the paths of flow communicating with the outlets in the same section.

GUSTAF DALEN.

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