US3385527A - Oil burner head - Google Patents

Description

y 8, 1968 M. K. DREWRY 3,385,527

OIL BURNER HEAD Filed Dec. 15; 1965 FROM BURNER FAN 1N VEN TOR. Mwwos: fiesmz y United States Patent 3,385,527 OIL BURNER HEAD Montrose K. Drcwry, 3019 S. Shore Drive, Milwaukee, Wis. 53207 Filed Dec. 15, 1965, Ser. No. 514,074 5 Claims. (Cl. 239-424) ABSTRACT OF THE DISCLOSURE An oil burner having a firing tube with a front nose cone, there being on oil nozzle spaced inwardly from said nose cone which is of a type to discharge an oil spray in a diverging hollow conical pattern through said nose cone, and a guiding cone supported to be within said diverging conical spray pattern and in said nose cone, with the margin of the nose cone opening surrounding the guiding cone intermediate the depth of the latter and spaced from the surface of the guiding cone to provide a restricted annular flow area therearound.

This invention relates to improvements in mixing heads and more particularly to an improved head which is specially useful in a gun-type domestic oil burner.

Ideal combustion of oil (total combustion without excess air) would require that every molecule of the oil be united with every molecule of oxygen in the air. However, it is practically impossible to obtain the perfect mixing which is necessary to achieve such a perfect union. In practice, substantially more air than the theoretical requirement is necessary for acceptable combustion. To obtain a low percentage of excess air, such as in a gun-type domestic oil burner is very difficult. As a result, the excess air in the majority of gun-type domestic oil burners presently in use is in the neighborhood of 50%.

To achieve as near perfect combustion as is practical requires:

Item 1.That the air and oil streams be thoroughly and intimately mixed into one homogeneous stream as soon as possible after discharge of the oil from the nozzle.

Item 2.that the air and oil streams be mixed in a condition of relatively low furnace temperature.

Item 3.That there be no subsequent separation of the oil and air before molecular union takes place.

Item 4.That total vaporization occur as early as possible.

Item 5.That adequate relative motion of air and oil vapor occur in the combustion zone for complete molecular union.

Item 1 above is an obvious requirement when it is realized that complete combustion must occur in about 5 second. Thus no time can be lost by delayed mixing. A further advantage of early mixing is the approximately four-fold increase of gaseous volumes when being heated to furnace temperatures, which further isolates the two components unless they are mixed close to the oil nozzle.

Referring to Item 2 above, if the mixing of oil and air does not take place in a region of relatively low furnace temperature, then the oil vapor, in the absence of air, will crack at the furnace temperature, causing the formation of elemental carbon, and this carbon is then not readily mixed with air and burned. Furthermore, in addition to the direct thermal loss, the carbon coats heating surfaces and indirectly causes additional heat loss, besides interfering with the functioning of control apparatus. Any unburned hydrocarbons which accompany the formation of soot also cause appreciable heat loss. Thus all burners of liquid and gaseous fuels benefit by conditions of minimum excess air, low unburned gases and minimum soot.

Referring to Item 3, oil is in the neighborhood of six hundred times as heavy as air and is usually impelled into the furnace at some five thousand times the force which impels the air. Thus it is desirable to have air so directed that it will accurately follow the path of the oil, in proper molecular proportions. Air is capable of altering the path of only the extremely fine oil droplets, and is powerless to change the course of the larger drops which are discharged by all nozzles. Thus, as different size oil drops take different paths from the nozzle, the proportional quantity of air requirement should accompany each drop. However, to obtain such proportioning is practically impossible. Attempts to remix in the furnace the isolated aggregations of oil and air have produced only mediocre benefits. No amount of swirling, impacting or other special action can result in all of the required molecules getting together in the proper proportions which are required for maximum efficiency. For this reason excess air has heretofore been necessary. Excess air, however, increases not only the weight of the heating gases but their temperatures as well, thus doubly increasing the fuel cost.

Referring to Item 4, although liquid oil drops may appear to burn directly from the liquid phase, nevertheless heating and evaporation of their surfaces is a prerequisite. Thus, any design that facilitates early evaporation is favorable to better combustion.

With reference to Item 5, because the molecules are so minute, their chemical union requires effective relative motion of the air and oil vapors to bring about complete union. Diffusion must be supplemented by turbulence to complete the molecular union in the small fraction of a second before the oil and air become cooled below temperatures at which they will unite.

Domestic oil burners as used in the past have discharged the air in a generally cylindrical, spiralling pattern of relatively large cross-sectional area. With such an arrangement the proximity and proportioning of the oil and air is not favorable for good mixing. This Was one of the reasons why 50% excess air has in the past been necessary to minimize the amount of soot and unburned gases.

More recently improved designs have arranged for the air to be discharged from the nozzle in the form of a hollow cone in an attempt to follow the pattern of the oil from the so-called hollow cone nozzles in common use. With this arrangement, improved combustion resulted and the requirements for excess air were reduced to 20-30%. However, with these designs, since oil and air flow are initiated at different locations, the two streams are made to intersect, which, of course, means that the trajectories are not coincident before and after intersection. Thus, mixing and evaporation do not occur at an early stage, and some separation after mixing occurs, in violation of Items 1-4 above. There is also doubt with these known designs as tothe effectiveness of final mixing because the hollow cone air flow patterns seems to have limited eddy currents that are necessary for molecular union.

It is a general object of the present invention to provide an improved burner head of the class described which will make it possible to carry out the requirements of Items 1-5 above and to efiiciently operate the burner with a low amount of excess air, in the neighborhood of 5%, thereby increasing the efficiency of the heating system.

A further object of the invention is to provide an improved oil burner head which provides for thorough and intimate mixing of the air and oil streams as soon as possible after the oil is discharged from the nozzle to thereby provide for mixing at relatively low furnace temperatures; to provide a construction which causes total vaporization to occur as early as possible; and to provide a burner head which provides for proper relative motion of air and oil vapor in the combustion zone so as to produce relatively complete molecular union.

A more specific object of the invention is to provide a mixing head wherein there is a guiding cone supported with its apex near the nozzle discharge hole for one fluid, with the axis of the cone parallel to that of the nozzle, there being additional means for jetting another fluid into the spray of the first fluid from said nozzle at a location approximately midway of the depth of the cone, resulting ing the two fluids travelling in identical paths but with relative motions.

With the above and other objects in view, the invention consists of the improved mixing head, and all of its parts and combinations, as set forth in the claims, and all equivalents thereof.

In the accompanying drawing, illustrating one complete embodiment of the preferred form of the invention, the figure is a longitudinal sectional view through an oil burner head, showing the new invention applied thereto, the firing tube being broken away so that only its forward end is illustrated.

Referring more particularly to the drawing, the numeral designates the usual firing tube of a conventional gun-type domestic oil burner, said tube having the usual nose cone 11 with a front discharge opening 12. Supported on a lower portion of the firing tube, as at 13, is the usual holder 14, which holder has a disc portion 15 through which the two insulators 16 with their two lighting electrodes 17 extend, as well as the oil tube 18 leading to the nozzle 19. In addition, the disc 15 has passageways 20 for scavenging air, as is customary.

The nozzle 19 is a conventional nozzle of the hollow cone type to give an oil spray of hollow conical form such as the spray S shown in the drawing. One satisfactory nozzle is the hollow cone type nozzle manufactured by Delavan Mfg. Co. of W. Des Moines, Iowa. Conventionally the spray angle is between 80 and 90, although such nozzles are available to provide hollow cone angles of between and 90. Low angles are usually considered preferable for furnaces that are long in the direction of the flame, whereas high angles are used when the furnace is short in this direction. The use of the so-called semihollow cone nozzle is not satisfactory with the present invention, as the semi-hollow cone nozzle has more nearly a solid cone spray.

Supported on the periphery of the disc 15 is an air jetting cylinder 21 having a front 22 with an opening 23 which exposes the nozzle 19 and electrodes 17. The cylinder extends forwardly to such a distance as to terminate short of the firing tube nose cone 11 and to provide an annular flow area A of restricted width between the annular front corner 30 of the cylinder and the inner surface of the nose cone about midway of the length of the latter.

In the forward portion of a conventional firing tube there are usually spiralling vanes so positioned as to cause a turbulence in the air flow. These vanes or any equivalent elements for effecting the turbulence of the air as customarily used are omitted in the present invention, and the air is allowed to flow undisturbed through the cylindrical passageway between the firing tube and the cylinder 21. This air is fed into the firing tube in the customary manner by the usual blower having a capacity which such blowers usually have in the conventional gun-type domestic oil burner, the amount of air being adjustable in the usual manner.

An important feature of novelty of the present invention resides in the use of a special guiding cone 26 suitably supported, as by one or more arms 27, from the nose cone of the firing tube. This cone 26 is preferably, but not necessarily, hollow, and is supported with its apex aligned with the axis of the nozzle and relatively close thereto. In practice the apex is preferably at least one-eighth of an inch from the hole of the nozzle 19. The cone 26 is preferably made of relatively thin stainless steel or other alloy suitable for operation at a temperature of approximately 15 00 F. Ceramics may also be used. Thinness, for low heat capacity, is desirable to minimize oil drops to the furnace floor when starting cold.

It is important that the guiding cone be centrally positioned with respect to the opening 12 of the nose cone so as to provide an annular flow area B of uniform width surrounding the cone 26, approximately midway of the height of the cone. It is desirable that the width of the flow area B be approximately twice the width of the flow area A. It is also important that the axis of the cone be coincident with the axis of the nozzle 19, and it is important that the supports 27 be such as to prevent displacement of the cone during use, as this cone angle must be maintained constant, and the width of the annular flow area B must be maintained constant throughout its circumference. The angle of the cone 26 should be substantially the same as the angle of the hollow cone spray S from the nozzle being used, but, preferably, the cone angle should be slightly greater than the angle of the hollow spray S to a degree just enough to limit to practical values the tendency of oil to drip from the cone, especially during the start-up period.

In operation the hollow cone oil spray S from the nozzle 19 envelopes the sides of the directing cone 26, since the latter has generally the same included angle. In other words, a guiding cone is used which has an angle about the same as the included angle of the hollow spray S of the nozzle being used. In most instances this angle will be about As before mentioned, the angle of the guiding cone 26 may exceed the angle of the spray S somewhat, as illustrated, just enough to limit to a practical value the tendency of oil to drip from the cone 26. In any event, the angle of the guiding cone 26 should not be substantially less than the angle of the spray S.

Air is being propelled through the firing tube, as indicated by the arrows, there being the usual blower having a capacity which is usual in the conventional guntype domestic oil burner. By use of the novel cylinder 21, with its front annular corner 30 arranged to produce the restricted flow area A, the air is directed at high velocity along the inner face of the nose cone 11 toward the opening 12, with all of the air being directed therealong at the angle of the nose cone. In the preferred embodiment, this is substantially at right angles to the angle of the guiding cone 26. The high velocity air, therefore, is forced to turn at approximately a right angle when it hits the guiding cone 26 to proceed in the same direction as the oil spray S. Eddy currents resulting from the sharp turn of the air stream cause violent intermixing of the air and oil as these two ingredients flow outwardly in the conical pattern into the furnace, and combustion is completed in a short flame in spite of the use of unusually low excess air. Because of the efficient action of the improved head, the air intake can be adjusted to supply as little as 5% excess air. With this arrangement very little cracking of the oil to soot occurs, which is proved by the fact that soot measurements show a soot formation as low as No. 1 on the Bacharach-Shell scale. This low a reading is considered excellent by recognized authorities.

While the best results with the present invention are obtained by the use of the cylinder 21 in conjunction with the guiding cone, nevertheless, for certain less-demanding requirements, the cylinder 21 may be omitted or the width of the flow area A may be increased over that shown, as in either case a large percentage of the air will still follow the angle of the nose cone toward the discharge opening 12 to impinge against the guiding cone 26 in a manner which requires it to turn at an angle sufficiently sharp to cause eddy currents which in turn will cause a violent mixing of the air and the oil. While the 90 impingement of the air against the cone is desirable, other angles may be effective in particular circumstances. As before mentioned, the angle of the directing cone 26 must be close to the angle of the hollow conical spray S from the nozzle.

While it is entirely practical to use a closed-base cone 26, the use of an open-base hollow cone is preferred. With a hollow cone the open base is open to the furnace so that there is radiant heating of the interior of the cone as well as of the exterior. This improves the evaporation of the oil that contacts the surface of the cone.

By use of the preferred embodiment illustrated, all of the requirements of Item 1 of the introduction of this specification are metbecause an early, intimate, and thorough mixing of the oil occurs. Initial union of the air and oil streams occurs within about one inch of the oil nozzle, and this is about the closest distance that is practical. The sharp angle turning of the high velocity air stream at flow area B results in high initial and continuing turbulence. Intimacy of mixture results from the small space occupied by all of the air and oil during this period of high turbulence. Thus the important rules for effective mixing are met. If unmixed oil and air should escape past the cone, they are still traveling at substantially the same angle and are, therefore, never far apart from each other, nor out of reach of the eddy currents that are capable of continuing the mixing action throughout the combustion chamber. Unlike many conventional designs, there is no problem of mixing remote accumulations of air and oil in the furnace. With the present invention the final mixing is close to ideal.

The construction of the present invention also meets all of the requirements of Item 2 of the introduction, because it prevents formation of any substantial amount of soot or unburned products. This is partly due to the early mixing referred to above and is also due to the fact that the temperature in the zone of the cone is relatively low because of the absorption of heat by the cone and because of the fact that the cone shields the oil spray from too early contact with the heat. Thus little cracking into soot occurs.

The design of the present invention also meets the requirements of Item 3 of the introduction because the cone 21 causes the air and oil to travel in the same path. No need exists for larger oil droplets to be redirected by the air stream as in conventional designs.

The requirements of Item 4 of the introduction are also fulfilled because the cone assists the evaporation of the oil very close to its source. With all of the oil traveling at about 40 mph only about 1/300 of a second is available in conventional burners for evaporation while the oil spray is free-flowing a distance about equal to the length of the cone 26, and not much more time than that is available in the furnace. With the present invention, however, upon contacting the cone there is a resistance to flow of the oil along the cone which greatly increases the time available for early evaporation. Early evaporation, therefore, is greatly assisted by the presence of the guiding cone 26.

The requirements of Item 5 of the introduction are met with the present design because of the intense turbulence caused by the high velocity and sharp-angled turning of the air as it joins the oil stream at flow area B. This turbulence is also aided by the wide difference in velocity of the air and oil as they progress along the cone. Local eddy currents will cause the air to cross the combined air-oil stream, and the oil drops may move relative to the air, but always in the same general direction.

For best performance, flow area A should be about half as Wide as flow area B. Exactness of air velocity is not critical as long as the air velocity is relatively high. However, too high an air velocity may wet the cone excessively during start-up, causing liquid oil to drop to the furnace bottom and thus resulting in excess initial air and subsequently in an air deficiency when the accumulated oil burns. The optimum air velocity is such that the blower customarily used in a conventional gun-type domestic oil burner can supply the required static pressure. The guiding cone 26 should be sized adequately to insure that the air and oil streams flow along the cone a suflicient distance to become coincident. Using a 90 guiding cone and a 90 nose cone 1-1 is preferred in order to take advantage of the conventional hollow cone nozzles 19 which are readily available and which afford desirably srn-a'll droplets and which usually have a spray angle of to however, the optimum included angle of the spray is obviously also dependent upon the thickness or thinness of the spray pattern.

The guiding cone apex must be at least one-eighth inch forwardly of the nozzle hole to allow for variable in practice. This dimension obviously influences the amount of spray that contacts the cone. With the present invention it is desirable to stop up most of the holes in the disc 15 which are customarily used to admit scavenging air such as indicated at 20'. This limits the formation of minor eddy currents which might tend to form near the head of the cylinder 21 to entrain some of the very fine oil droplets from the spray. By having low scavenging air the possibility of premature combustion of any fine droplets is minimized to keep the temperaturelow in the region of the cone and thereby avoid soot formation,

The cone is sized adequately from the base to the apex to insure that the air and oil streams flow parallel. In practice the diameter of the base portion of the cone should be about equal to the nose cone opening 12. A desirable size is about one and one-quarter times the diameter of the opening. A larger cone than this is normally unnecessary to provide proper performance.

Both the cylinder 21 and the cone 26 shield the nozzle 19 from heat and thus reduce its gradual clogging tendency. This is true because the cylinder and cone shield the nozzle from the radiant heat of the burner flame. In conventional oil burners there is relatively high radiant heat encircling the nozzle. Upon shut-down of the burner, the cone and cylinder, being of relatively thin metal, have little heat capacity. Thus when there is no air or oil flowing to cool the nozzle as in operation, the cylinder 21 and cone 26 act as barriers to radiant heat from the refractory material in the furnace, which refractory material remains hot for quite a period after shut-down of the burner.

Although the design is especially applicable to a guntype domestic oil burner, it is also applicable in other places where liquid and gaseous fluids or fuels are employed and may be useful for the mixing of gases and liquids without subsequent combustion. Evaporation of liquid may be attained if the gas temperature is adequate.

It is to be noted that with the design of the present invention air at relatively high velocity scrubs the inner surface of the nose cone 11 between the flow areas A and B. This serves to limit the temperature of the nose cone and thus reduces radiation of heat from the nose cone to the nozzle.

Various other changes and modifications may be made without departing from the spirit of the invention, and all of such changes are contemplated as may come within the scope of the claims.

What I claim is:

1. In an oil burner having a firing tube for receiving a flow of combustion air from the burner fan and having a front nose cone with a circular opening, and having at least a portion of the combustion zone located upstream of said circular opening, there being an oil nozzle spaced inwardly from said nose cone opening which is of a type to discharge an oil spray in a diverging hollow conical pattern through said nose cone opening, with said opening being of sufficient diameter to permit said oil passage, a guiding cone supported to be within said diverging conical spray pattern and in said nose cone opening, with the margin of said nose cone opening surrounding the guiding cone intermediate the depth of the latter and spaced from the surface of the guiding cone to provide a restricted annular flow area therearound through which substantially all of the required air for combustion is discharged together with the oil spray, said guiding cone having its apex spaced forwardly from and being coaxial with the axis of the nozzle to be forwardly of the apex of the conical spray pattern of the nozzle whereby the air, in following the angle of the firing tube nose cone toward said annular fiow area, is caused by the guiding cone to abruptly change its direction as it meets the diverging hollow conical spray of oil and with the latter is caused to pass outwardly along the side of the guiding cone, said guiding cone having a constant cone angle throughout its length whereby after the air contacts the cone and changes its direction it will be directed by the constant cone angle in substantially the same direction as the oil.

2. An oil burner head as claimed in claim 1 in which there is a cylinder in the firing tube surrounding the nozzle and having a front circular corner close to the nose cone to provide a restricted annular air flow area of approximately one-half the width of the annular flow area between the cone and the margin of the nose cone opening so that all of said air is directed toward the nose cone opening at the angle of the nose cone at an appreciable velocity.

3. An oil burner head as claimed in claim 1 in which the angle of the guiding cone is about the same as the angle of the hollow spray pattern from the oil nozzle.

4. An oil burner head as claimed in claim 3 in which said angles are generally about right angles.

5. An oil burner head as claimed in claim 3 in which the angle of the spray pattern is about a right angle and in which the front nose cone wall is approximately perpendicular to the angle of the oil spray pattern.

References Cited UNITED STATES PATENTS 733,579 7/1903 Fitton 239-426 X 744,220 11/ 1903 Neu 239-515 X 814,396 3/ 1906 Russell 239-432 1,039,365 9/1912 Coulter 239-515 X 1,071,381 8/1913 Anthony 239-432 X 1,464,909 8/1923 Kimberlin 239-424 X 1,901,806 3/1933 Fulton 239-432 2,486,137 10/ 1949 Evans 239-515 X 2,670,032 2/1954 Vignere 158-4 2,676,649 4/1954 Diehl et al. 158-76 3,225,813 12/1965 Walsh 158-76 M. HENSON WOOD, 111., Primary Examiner.

V. C. WILKS, Assistant Examiner.

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