US3255804A - Ultrasonic vaporizing oil burner - Google Patents

Description

June 14, 1966 R. J. LANG 3,255,804

ULTRASONIC VAPORIZING OIL BURNER Filed Aug. 15, 1963 2 Sheets-Sheet l Robert J. Long Inventor a w. M By Potent Arrornev June 14, 1966 R. J. LANG 3,255,804

ULTRASONIC VAPORIZING OIL BURNER Filed Aug. 15, 1963 2 Sheets-Sheet 2 FIGURE- 2 w w 90 i l u o FEED RATE H 0656 H J g 10 p LU o 60 u; so M|n|r;::n.P0wer EBG L Atomlzohon p 0 4O 3 so 2- 2o FLUID ATOMIZED a: 2 HEATING on. 0. IO m I 1 l DRIVER POWER,WATTS FIGURE-4 Robert J. Long lnvenror By 4 M Potent Ahornev United States Patent 3,255,804 ULTRASONIC VAPORIZING OIL BURNER Robert J. Lang, Watchung, NJ, assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Aug. 15, 1963, Ser. No. 302,251 Claims. (Cl. 158-76) The present invention relates to a liquid fuel burner and more particularly, it relates to a vaporizing blueflame type burner which employs a mechanism for atomizing the liquid fuel.

In recent years, need has developed in the oil burner industry for a burner which operates at a low firing rate (e.g., less than 0.6 gallon per hour). Such burners would make a more compact furnace package possible and would be applicable for use in domestic hot water heaters; Conventional liquid fuel burners which use high pressure nozzles are unreliable at rates below 0.6 g.p.h.-, because the tiny swirl slots needed to obtain low rates are prone to plugging. With return-flow nozzles, firing rates of 0.4 g.p.h. are possible, but this is still too large for many applications.

Accordingly, it is an object of the present invention to provide a self-controlling, vaporizing, blue-flame type oil burner which embodies the unique characteristic of an ultrasonic atomizer and wherein the vaporizing func tion is activated automatically after start up. It is also an object of the present invention to provide a vaporizing blue-flame oil burner, essentially as described above, equipped with means for providing radiant type heating. It is a further object of the present invention to provide an oil burner of the aforementioned type which will operate without plugging at low feed rates. In accordance with the objects of the present invention, there is provided a liquid fuel burner comprising, in combination, an-

ultrasonic atomizer, vaporizing means for vaporizing atomized fuel, temperature sensing means appended to the vaporizing means, a flame holder and a radiator.

The exact nature, substance and objects of this invention will be more clearly perceived and fully understood by referring to the following description and claims taken in connection with the accompanying drawings in which:

FIGURE 1 represents a side elevation view, partly in section, of an ultrasonic transducer disposed horizontally in a conventional blast tube which has been designed to incorporate a flame holder, a vaporizing plate and a re fractory ceramic bowl;

FIGURE 2 represents a cross-sectional view taken at section 22 of FIGURE 1;

FIGURE 3 represents a cross-sectional view taken at section 3-3 of FIGURE 1; and

FIGURE 4 represents a plot of spray angles achieved at steady feed rates when atomizing power is varied.

It should be here noted that the design represented by FIGURE 1 is only one of many which could be depicted. It is not intended that this particular design be construed so as to limit the invention.

Referring now to the drawings and especially FIG- URE 1, the numeral 12 designates a controller. Any conventional controller such as a General Electric CR 7865 A101A master controller can be used in this invention. A suitable motor 10, connected to the controller 12 by leads 74 and 75, drives oil pump 11 and blower 13. The oil pump 11 transfers fuel oil from a suitable source, not shown, through feed line 15 and by-pass feed line 16 to a radial hole 28 in the atomizer. The atomizer, which is to be described below, is situated Within a conventional blast tube 14. Since the ultrasonic atomizer does not require a high pressure oil supply, a simple low torque pump, such as a centrifugal pump, may be used in conjunction witha cheap shaded pole motor. Solenoidcontrolled blocking valve 17 prevents oil flow to the atomizer when the motor is off. Alternatively, a high torque pump, such as a gear pump, can be used. However, in that case, it is necessary to employ a larger motor to drive the pump. Some gear pumps have spring-loaded valves on the outlet line whichopen only when the pump is operating and building up pressure. With this type of pump, valve 17 can be eliminated from the system. A standard needle valve 20 in feed line 15 is preset to deliver 21 low oil flow rate. A similar valve 19 is placed in the parallel feed line 16 to regulate the feed rate therein.

A blower or fan 13 supplies ambient air through the space between the atomizer assembly and the conventional blast tube 14. The blower can be of the squirrel cage or cylinder type as shown; or any other suitable type. between the tip of the stepped horn 23 and the vaporizing plate 58. The mixture is expelled through the orifice 70 in the vaporizing plate and the orifices 57 in the flameholder 56 by the air pressure supplied by the blower. Most of the air-fuel mixture is expelled through the orifices in the flameholder. Only 1020% of the admixture is ejected through the orifice in the vaporizing plate because that area is proportionately smaller than the total area of the orifices in the flameholder. In addition, the air has a swirling motion imparted to it by turbulator vane 44, 45, 46, 47, 48 and 49, shown in FIGURE 3, which causes the air to flow preferentially out through the flameholder. The rate of air flow through all the orifices is maintained at a value higher than the flame propagation value in order to prevent flame flashback.

The ultrasonic atomizer is essentially the device described in the copending application of John C. Young, Robert I. Lang and James A. Wilson, Serial No. 199,788, filed June 4, 1962 and now Patent No. 3,200,873. It is particularly suited for use in a burner like that of the present invention for the reasons that it permits a low feed rate, the particle size of atomized oil decreases with decreasing feed rate and the spray angle of atomized oil may be controlled with atomizer power and/ or feed rate. Essentially, the atomizer comprises two stepped horns 23 and'25 placed in a base-to-base relationship with a piezoelectric crystal disc 26 between them. The disc is made of a ceramic material, such as a ferroelectric ceramic barium titanate, or lead-zirconium titanate. The particular material of disc 26 is not critical for the present invention. The stepped horns are constructed of a suitable electrically conductive material such as aluminum, brass and stainless steel. For this particular transducer, aluminum was utilized.

The stepped horns 23 and 25 are held in compression against the piezoelectric disc 26 by mechanical clamping means comprising front and rear flanges 21 and 22 and studs connecting such flanges. The studs 29 and 32 are shown in FIGURES 2 and 3. The studs enter the rear flange 22 and are screwed into the front flange 21.

As depicted in FIGURE 1, the front flange 21 and the rear flange 22 contact respectively the first stepped horn 23 and the second stepped horn 25 at the periphery of the shoulders of the stepped horns in order to minimize damping of the ultrasonic atomizer. In the particular design shown, it is necessary that a sheet of a suitable insulating material, such as polyethylene terephthalate polyester, e.g. Mylar, be placed between the rear flange and the second stepped horn.

An axial hole 27 in the tip of the first stepped horn 23 extends back to a radial hole 28 which is located essen tially at a vibrational node of the horn. The radial hole is positioned in this manner so that the feed line 15 can be attached to the side of the horn without damping the atomizer. The tip of stepped horn 23 is filleted for reinforcement purposes at 34 so that it can withstand high stresses. A groove 30 is formed around the Air and vaporized oil are admixed in the space tip of the first stepped horn to prevent oil from creeping back along the horn and accumulating in the space 31. Such an accumulation could dampen the oscillation of the atomizer or render it entirely inoperable.

In order to protect the piezoelectric material from heat, a portion of the aluminum stepped horn 23 is replaced by a disc of stainless steel 24. Stainless steel is used in this instance because it has a thermal conductivity of about one-tenth that of aluminum but has reasonably similar sonic properties. To protect the atomizer from radiant heat, a heat shield 33 is attached to the front flange.

Downstream from the tip of stepped horn 23 is the vaporizing plate 58. It is circular in shape and contains a 0.5 to 1.0 diameter orifice 70 which is located at the center of the plate and opposite to the tip of stepped horn 23. Afiixed to the inside of the vaporizing plate are narrow rectangular metal slabs 59 which are inclined vertically away from the horizontal. They supply the extensive surface area needed to vaporize the fuel oil. When atomized oil from the tip of the transducer is sprayed against the hot vaporizing plate, the fine droplets of oil are retained upon the rectangular metal slabs and consequently vaporized. The oil vapor is admixed with the combustion air from blower 13, expelled mainly through the orifices 57 in the burner head 56 and thereafter burned.

At start up, the vaporizing plate is not hot enough to vaporize atomized oil striking its surface. Atomizing power and feed rate are therefore initially kept at a level low enough to send a fine cylindrical stream of atomized oil through the orifice 70. When the vaporizing plate plate reaches a predetermined temperature, atomizing power and feed rate are automatically increased in accordance with the present invention to allow atomized oil to impinge on the upstream side of plate 58. Operating the burner without this delay results in liquid oil collecting on the vaporizing plate. Accordingly, the vaporizing plate 58 is equipped with a thermal sensitive switch 51 such as a bimetallic strip. The switch is integrated into the rest of the system by a number of leads and switches. Lead 88 from the thermal switch runs to the coil of the relay switch 68 and then continues to the solenoid 87. Return lead 86 from the solenoid is connected in parallel to lead 75 which is connected to controller 12. To complete the circuit, lead 85 from the thermal switch 51 is connected in parallel to lead 74. When plate 58 reaches the predetermined temperature, the thermal switch closes and permits current to flow through the coil of the relay switch 68 and the solenoid 87. The relay switch closes, thereby sending additional power to the atomizer, and solenoid 87 opens valve 18 which permits additional fuel to enter feed line 15. As a consequence, the spray angle of atomized fuel increases to permit impingement against vaporizing plate 58.

Fitted to the end of the blast tube 14 are the flame holder 56, perforated with orifices 57, and four semicircular shaped fins of which only three 52, 54 and 55 are shown. The flame holder and the fins are preferably constructed of a heat resistant alloy such as Inconel or Hastelloy X. The purpose of the flameholder is to prevent the flame which surrounds its outside surface from blowing away or flashing back into the space between the vaporizing plate 58 and the tip of the first stepped horn 23. The semicircular fins are employed, so that heat from the burner flame may be easily conducted to the vaporizing plate 58. The fins are not critical to the invention and can be eliminated.

In a'preferred embodiment of the invention, a refractory ceramic bowl 95 is placed immediately behind the flame holder. It provides a means of furnishing radiant type heating and helps to maintain the flame surrounding the flameholder.

Ignition of the fuel-air admixture is accomplished by an are formed between two electrodes. The positions of the electrodes, 35 and 37, are best observed in FIGURES 2 and 3. The electrodes are fastened to the rear flange 22 by means of a fiber clamp 40. As shown in FIGURE 1, electrode 35 is inserted through the heat shield 33 and is fitted into an electrode guide 39 which is drive fitted into the front flange 21. Electrode 37, not shown in FIGURE 1, is mounted in like manner. The electrodes are insulated with a suitable material, for example, porcelain. Ignition is accomplished by an are formed across the electrode tips 36 and 38, shown in FIGURE 3.

The ignition electrodes 35 and 37 are connected to the ignition transformer by leads 76 and 78. Lead 78 is connected with electrode 35, as shown in FIGURE 1, and lead 76 is connected with electrode 37, as shown in FIG- URE 2.

The ignition transformer 77 steps up the line voltage of volts to a voltage, e.g., 10,000 volts, suflicient to cause an arc across electrode tips 36 and 38.

The atomizer is equipped with a flame sensing device 50 which is mounted on the front flange 21 and extends through the heat shield. A flame detector, such as a cadmium sulfide photoresistor, e.g. White Rodgers 956 Kwik Sensor, can be used in this system. The flame detector upon sensing the flame sends a signal via leads 72 and 73 to the controller 12 which breaks the circuit to the ignition transformer 77. If no flame is established,

the controller will shut down the burner, repeat the cycle and then lock the system out.

The atomizer unit is fitted into a turbulator tube 43 which has vanes 44, 45, 46, 47, 48 and 49, shown in FIGURE 3, around its periphery. These vanes are tacked to the blast tube 14. The atomizer unit need not be attached to the turbulator tube. In fact, it is preferred that it merely fit snugly in said tube. This allows the convenient removal of the atomizer unit for maintenance. The horizontal axis of the atomizer unit is maintained parallel to the horizontal axis of the blast tube 14 by support 97. For the purposes of this invention, it is highly desirable that the front flange 21 blocks otf the air flow so that all the combustion air is forced to flow in the annular space between the turbulator tube and the blast tube.

The atomizer is supplied with power by an electronic driver or oscillator 65 which is connected with electric mains 60 and 61 by leads 63 and 64. The driver is connected with the atomizer by lead 66 and line 67 which is composed of leads 67a and 67b. Interposed in line 67 are a resistor 69 and a relay switch 68. The input lead 66 is connected with a post 41 which is imbedded in the fiber clamp 40. In order to prevent short circuiting the oscillator, it is necessary that the post 41 does not extend through the fiber clamp and make contact with the rear flange 22. The post 41 is connected with the second stepped horn 25 by lead 71. As shown in FIG- URE 2, return lead 67b is connected to post 42 which extends through the fiber clamp and is screwed into the rear flange.

The driver is essentially the device described in copending application Serial No. 59,335, filed September 29, 1960 by James A. Wilson and now Patent No. 3,121,534. It is an electronic oscillator and power generator which operates in class C and is stabilized by current feedback. It supplies power at a frequency which concurs with the natural resonance of the atomizer or with one of the major harmonics thereof. The frequency will depend upon the particular design of the sonic atomizer, but will usually be within the range of from 20,000 to 230,000 cycles per second. It is preferred that the atomizer be designed to have a resonant frequency within the range of from 50,000 to 100,000 cycles per second.

In order to integrate the driver 65 into the-rest of the control circuit and to ensure that oil cannot be injected into the atomizer before the driver and transducer are operating suitably, a coil 82 is inductively coupled with the plate inductance 84 of the driver. The coil is connected to the heater resistance of a thermal delay switch 83, and the switch is connected in series with one of the thermostat terminals 80 of the conventional controller 12.

When alternating voltage of relatively high frequency is impressed across disc 26, the piezoelectric material expands and contracts in sympathy with the pulsating voltage. These vibrations are transmitted through stepped horn 23-and are concentrated at it tip as a result of the decrease in area. When a drop of liquid, such as home heating oil, is applied to the horn tip, sonic energy will flow into the drop and atomize the oil into particles having a mass median particle diameter of 125 microns or less.

Power input to a transducer and oil flow rate are important variables affecting atomization. A minimum amount of power is necessary just to overcome frictional losses within the transducer so that it vibrates strongly enough to cause atomization. At the minimum power, the atomized oil has essentially a cylindrical shape. However, with a higher power input, the atomized spray becomes conical in shape. Excess power over the minimum necessary just to support atomization is therefore an effective way of controlling the spray angle. For a given feed rate, the angle of the cone increases with power up to a point and then levels-off at a maximum value. Spray angles up to 85 are obtainable at 0.65 g.p.h., but at 0.2 g.p.h. the upper limit is 65. FIGURE 4 illustrates the relationship between spray angle and power at given feed ratesf In operating this burner, thermostat 62, upon receiving the desired stimulus, completes the circuit which is supplied with 115 volt alternating current by electric mains 60 and 61. The electronic driver 65 transmits power to the atomizer via leads 66, 67a, 67b and resistor 69 at the resonant frequency of the atomizer. The resistor 69 reduces the amount of power delivered to the atomizer so that only the minimum amount of power necessary to cause cylindrical atomization is received.

As the driver warms up, current is transmitted to the normally open thermal delay switch 83. The switch closes, completing the controller circuit which is supplied with 115 volt alternating current by electric mains 80 and 81.

The controller supplies the ignition transformer 77 with voltage via leads 76 and 78. The transformer steps up the voltage to anamount sufficient to cause an arc to form across the electrode tips 36 and 38. Current is supplied to the solenoid 79 via leads 89 and 90. The solenoid opens valve 17 to permit the passage of fuel. At the same time, motor receives power through leads 74 and 75. The motor drives oil pump 11 which transmits oil through feed line 15, at a rate of from 0.1 to 0.2 gallon per hour. The flow of oil through feed line 16 is blocked by the solenoid controlled valve 18. Valve 20 in feed line restricts the feed rate to that amount which corresponds to the power delivered to the atomizer so that cylindrical atomization occurs.

The motor also drives fan 13 which upplies combustion air at a rate of from 6 to 30 cubic feet per minute and higher, depending upon the oil rate. The flow of air is adjusted by a manual control valve, not shown. The oil passes into the radial hole 28, through the axial hole 27, is atomized by the vibration of the stepped horn, and emerges from the tip of the first stepped horn 23 to be admixed with the combustion air. The air-oil admixture is expelled through plate 58 and ignited by the arc formed across the electrode tips 36 and 38.

The flame sensing device or photocell 50 sees the flame and sends a signal to the controller 12 which breaks the circuit to the transformer and turns off the arc.

Vaporizing plate 58 and vaporizing surfaces 59 become hot by radiant heating from the flame and by conduction through the semicircular fins. When these surfaces attain a temperature which is sufiicient to vaporize the fuel oil, thermal switch 51 closes and permits current to flow through the coil of relay-switch 68 and solenoid 87. Relay switch 68 closes permitting full power to be delivered to the atomizer, and solenoid 87 opens valve 18 permitting an increase in feed rate. At these new conditions, conical atomization occurs and thereby causes the oil spray to impinge against plate 58 and vaporizing surfaces 59. The metal slabs 59 retain the fine oil droplets until vaporization occurs. The vaporized oil admixes with the combustion air, is expelled through the flameholder and is burned.

The advantage of this type of oil burner over those of the prior art is that oil vapor is burned instead of a fine oil spray. Consequently more complete combustion is attained. Instead of the smoky luminous yellow flame of conventional burners, the present burner gives a blue flame which is quieter and much cleaner. Experiments have shown that there is no coking of the vaporizing plate or surface.

The invention has been described with a certain degree of particularity. It will be obvious that other modifications may be made consistent with the invention by those skilled in the art. It is intended by the following claims to cover such modifications and variations as are properly a part of this invention so far as permitted by the prior art.

What is claimed is:

1. A liquid fuel burner comprising, in combination, a fuel atomizing device capable of converting a liquid fuel into a first divergent spray pattern and a second divergent spray pattern, vaporizing means for said liquid fuel spray, said vaporizing means being so constructed so as to permit the substantially unimpaired passage thereby of said first selected spray pattern and to obstruct the passage of at least a part of said second selected spray pattern, temperature sensing means associated with said vaporizing means, and control means for varying the spray pattern of said atomizing device from said first divergent spray pattern to said second divergent spray pattern in response to temperature changes in said vaporizing means detected by said temperature sensing means so that atomized fuel is only caused to impinge upon said vaporizing means after said vaporizing means has attained a temperature sufficient to vaporize the atomized fuel.

2. A liquid fuel burner according to claim 1 which comprises further, a flameholder and flash back arrester adjacent to said vaporizing means.

3. A liquid fuel burner according to claim 2 which comprises further, radiator means adjacent to said flameholder and flash back arrester.

4. A liquid fuel burner according to claim 1 wherein the vaporizing means comprises a plate having an orifice at the center of sufficient size to permit the unimpaired passage of cylindrically atomized fuel.

5. A liquid fuel burner according to claim 4 wherein the plate has affixed to it on the upstream side, means for retaining the atomized fuel for vaporization.

6. A liquid fuel burner according to claim 5 wherein the means for retaining the atomized fuel comprises parallel rows of narrow slabs inclined away from the horizontal.

7. A liquid fuel burner according to claim 3 wherein the radiator means comprises a refractory bowl.

8. A liquid fuel burner comprising, in combination, a fuel atomizing device capable of converting a liquid into variant and divergent spray patterns, vaporizing means for said liquid fuel spray, said vaporizing means being so constructed so as to permit the substantially unimpaired passage thereby of a first selected spray pattern and to obstruct the passage of at least a portion of a second selected spray pattern, temperature sensing means associated with said vaporizing means, means for supplying fuel under pressure to said atomizing device, control means for regulating the flow of said fuel, means supplying combustion air for admixture with said fuel, power driving means for said atomizing device, and control means electrically interconnecting said temperature sensing means, said fuel regulating means and said power driving means for varying said atomized fuel spray pattern to said second selected spray pattern to permit impingement of said atomized fuel on said vaporizing means after said vaporizing means has attained a predetermined elevated temperature sufiicient to vaporize atomized fuels sprayed thereagainst.

9. A liquid fuel burner comprising, in combination, an ultrasonic fuel atomizing device capable of converting a liquid fuel into variant spray patterns, a circular, metal, vaporizing plate adjacent to said atomizing device and so positioned that conical spray patterns of atomized fuel will impinge thereon, said vaporizing plate having an orifice at its center of suificient size to permit the unimpaired passage of cylindrically atomized fuel, said plate having afiixed thereto parallel rows of narrow, metal slabs, inclined away from the horizontal for retaining the atomized fuel until vaporization occurs, a thermal sensitive switch appended to said vaporizing plate, a pump for supplying fuel to said atomizing device, valve means for regulating the flow of said fuel, a blower for supplying combustion air for admixture with said fuel, an electronic oscillator for driving said atomizing device, electronic control means connected electrically to said thermal sensitive switch, said fuel valve means and said electronic oscillator, for varying the said fuel spray pattern from a cylindrical to a conical pattern, ignition means for initiating combustion of said fuel-air admixture, a flameholder and flash back arrester for stabilizing the resulting flame, and a refractory ceramic bowl adjacent to said flash back arrester for providing a source of radiant energy.

10. A liquid fuel burner according to claim 9 which comprises further, heat conduction means annexed to said vaporizing plate for conducting heat from the resulting flame to the vaporizing plate.

References Cited by the Examiner UNITED STATES PATENTS 824,361 6/1906 Hudson l5899' 2,073,552 3/1937 Curioni 15877 X 2,267,451 12/1941 Eweryd et al l5828 FREDERICK L. MATTESON, 1a., Primary Examiner.

E. G. FAVORS, Assistant Examiner.

Claims (1)

1. A LIQUID FUEL BURNER COMPRISING, IN COMBINATION, A FUEL ATOMIZING DEVICE CAPABLE OF CONVERTING A LIQUID FUEL INTO A FIRST DIVERGENT SPRAY PATTERN AND A SECOND DIVERGENT SPRAY PATTERN, VAPORIZING MEANS FOR SAID LIQUID FUEL SPRAY, SAID VAPORIZING MEANS BEING SO CONSTRUCTED SO AS TO PERMIT THE SUBSTANTIALLY UNIMPAIRED PASSAGE THEREBY OF SAID FIRST SELECTED SPRAY PATTERN AND TO OBSTRUCT THE PASSAGE OF AT LEAST A PART OF SAID SECOND SELECTED SPRAY PATTERN, TEMPERATURE SENSING MEANS ASSOCIATED WITH SAID VAPORIZING MEANS, AND CONTROL MEANS FOR VARYING THE SPRAY PATTERN OF SAID ATOMIZING DEVICE FROM SAID FIRST DIVERGENT SPRAY PATTERN TO SAID SECOND DIVERGENT SPRAY PATTERN IN RESPONSE TO TEMPERATURE CHANGES IN SAID VAPORIZING MEANS DETECTED BY SAID TEMPERATURE SENSING MEANS SO THAT ATOMIZED FUEL IS ONLY CAUSED TO IMPINGE UPON SAID VAPORIZING MEANS AFTER SAID VAPORIZING MEANS HAS ATTAINED A TEMPERATURE SUFFICIENT TO VAPORIZE THE ATOMIZED FUEL.

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