US2397988A - Liquid fuel burner - Google Patents

Description

2 SheetsPSheet l ll; lil' im. I 11||I MII i ,111i H INVENTOR April 9, 1946. E. J. SENNINGER LIQUID FUEL BURNER Filed Jan. 27, 1942 April 9, 1946 E. J. SENNINGER 2,397,988

LIQUID FUEL BURNER Filed Jan. 27, '1942 2 Sheets-Sheet 2 INVENT OR.

Afm/s Patented Apr. 9, 1946 LIQUID FUEL BURNER Earl Joseph Senninger, Chicago, Ill., assigner to Sanmyer Corporation, a corporation o! Illinois Application January 27, 1942, Serial No. 428,392

4c1aims.

This invention relates to liquid fuel burners,

"especially adapted for heavy oils such as No. 5

fuel oil. It has for its principal object to provide suiiicient preheating of the oil as it approaches the burner to insure proper atomizing while preventing carbonizing.

Generally speaking, this is accomplished by feeding the oil directly from a pump to the burner, preferably a positive displacement; pump, and surrounding a suitable length of the oil supply pipe adjacent to the burner nozzle with a heating element whose wattage after starting drops below, and remains below, the capacity required to produce carbonizing temperatures in the oil.

Further objects and advantages of the invention will appear as the disclosure proceeds and the description is read in connection with the accompanying drawings in which Fig. l is a vertical section through a commercial embodiment of the new oil burner;

Fig, 2 is a view, partly in longitudinal'section and partly in side elevation, of a rearward portion of the preheaterl incorporated in the burner; and

Fig. 3 is a similar view of the forward portion of the preheater.

But these specific illustrations and the corresponding description are used for the purpose of disclosure only and are not intended to impose unnecessary limitations on the claims, or confine the patented invention to a particular use.

General description In Fig. 1 a main housing, having a base 12, provides a tank or reservoir II for lubricating oil, a chamber I2 for Primary or atomizing air above the oil tank, a suitable filter or cleaner and oil separator I3, and a secondary fan or blower casing I5, communicating with a horizontally directed draft tube I6, passing out through the chamber I2.

Within the draft tube I6 are a primary air line I'I, a burner nozzle I8. an oil line I9 with its asso'- ciated heater 20 for delivering heated oil to the nozzle I8, and a pair of electrodes 2I associated with the nozzle for igniting the mixture of oil and air when the burner is started. Only one of the electrodes is shown in Fig. 1.

The main housing also forms a support for a motor drivensecondary air fan or blower 23, which delivers secondary air through the draft tube I6 around the mixture of oil and air discharged from the nozzle IB. A suitable primary or atomizing air pump (not shown) forces air filter is charged with bronze wool. In the chamber I2 the primary air passes over the supply of lubricating oi1 3|. The primary air is led from the chamber I2 through a pipe 32 'to the air line I1. the pipe 32 may be considered as forming a single air line with a storage or pressure chamber in an intermediate position which insures an even flow to the nozzle and forms pressure for several other purposes.

An arrangement (not shown) for circulating lubricant continuously delivers air and oil foam to the .iilter I3, whereby the bronze wool in the filter is made to serve as an oil separator and an air cleaner, and the lubricating oil collected there drops down over the outside of the draft tube I6 and returns to the tank II.

When-a room thermostat or boiler control, or

equivalent means, in the burner control system through the chamber I2 and the filter I3, which 55 calls for heat, an electric circuit is closed automatically to allow current to flow to the oil heater 20. After a delayed action, for example, twenty# five seconds, a motor circuit will close to start the Asecondary air fan or blower 23, the primary or atomizing air pump for forcing air through the primary air line I1, and the oil pump for forcing air into the burner oil line I9. As the mixture of air and atomized heated oil is discharged from the nozzle I8, sparks from the electrodes 2I ignite it and the flame is further fed by thesupply of secondary air delivered by the fan or blower 23 through the draft tube I6. The resistance of the heater element 20 increases with the rise in temperature and the wattage drops to the selected limit for the particular design. It l will be understood that various automatic control systems may be used.

It is contemplated that the oil pump employed to force oil through the oil line I9 will have a positive displacement, and continuous delivery, the pump output for a given adjustment and speed being constant for all practical purposes. For that reason when it is used as a metering pump the apparatus can operate successfully on No. 5 oil.

The draft tube I6 intersects the main housing somewhat below the mid portion, and the lower wall BI of the draft tube extends across the main housing above the lubricating oil tank II and, in eiect, forms the upper portion of the chamber for primary or atomlzing air.

The sides of the main housing are bulged to form passages upwardly around the draft tube and leading to the space for the iilter I3, which In fact, the air line i1, the chamber I2 and space is closed at the top by a cap plate 85, secured in place by bolts and carrying an air pres-- sure gauge 85. The bronze wool, which really forms the filtering and oil separating element of the filter I3, is in the space above the draft tube under the cap 84. Removing that cap permits access for cleaning the bronze wool, which should be done at suitable periods by removal and washing in kerosene or some similar solvent.

The upper portion of the draft tube I6 at the left in Fig. 1 opens into the secondary air fan or blower casing I5, which is generally eccentric with respect to the fan or blower 23 but affords direct and proper communication for air from the blower into and through the draft tube I6.

Just below the fan casing I5, and opposite to the draft tube, the main housing has an opening closed by a cap 86, into which the air tube I1 is fitted at the end opposite to that connected with the nozzle I8. The cap also carries an appropriate nipple, etc., 81, for connection with the air pipe 32, thus establishing the complete air line from the primary or atomizing an` pump to the nozzle.

At each side of the nipple 8l, and slightly above, are open insulated fittings 88 to admit wires 89, the inner ends of which are secured to the electrodes 2| by nuts 9U.

Beneath the nipple 81 the cap 86 has an open ing 9| to admit the heater tube 92 which surrounds the heater 2U and the oil line I9 leading to the nozzle I8. Suitable mounting for the electrical connections and the end of the oil pipe I9 are provided by a. large cast fitting 93, secured to the cap 86.

Forked pedestals 94, formed with legs |00, have openings 95 and 96 to receive the air pipe I1 and the heater tube 92, respectively, and carry clamps 91 to receive the insulating tubes 98 for the electrodes 2|. By removing the fastenings for the cap 86 this assembly (called in practice the drawer assembly) may be withdrawn as a unit from the draft tube. The delivery end of the dr'aft tube is equipped with a suitable converging fitting to direct the secondary air against the mixture of oil and primary air discharged from the nozzle |8. The detailed construction of the nozzle, its connection with the primary air pipe I1, the oil pipe I9 and its operation in use, will be sufficiently clear without specific description.

The size of the orifice, the spray angle, and

. such like will vary with conditions and personal preference.

The prcheater The large cast fitting 93, shown in Figs. l and 2, may well be called the base of the preheater, for it and associated parts form a unit that may be inserted and removed from the cap 86 of the drawer assembly. This base is made hollow to provide a chamber |10, the outer wall I'II of which has an opening wherein one end of the oil pipe I9 is fitted. The opposite Wall has a larger opening |13 through which the pipe I9 projects with clearance and into which the inner end of the heater tube 92 is fitted. The otherwise free end of the oil pipe I9 is connected with the nozzle I8 by the elbow |14. Adjacent to the elbow the pipe I has a brass collar |15 pressed on it which is received in the adjacentend of the heater tube 92 and secured to it by crimping |16. The electrical resistance element 28 is wound upon a mica tube |11 fitted over the oil pipe I9, and, in turn, is enclosed within a second mica tube |18. Insulated lead wires |19 and are brought into the chamber |10 through fiexible hose connected to the base 93 by a nipple IBI, One lead |19 is electrically connected with one end of the resistance element 20 by havingT a stripped portion |82 intertwined with it and made fast by a clamp |83. The other lead |86 passes along between the outer mica tube |18 and the heater tube 92, and has a stripped portion |84 intertwined with the opposite end of the resistance element 2| and made fast by a clamp |85.

By way of a specific example that has been found satisfactory in heavy oil burnersfor No. 5 fuel oil consuming from one-quarter of a gallon an hour to seven gallons an hour, the following details are added.

The oil pipe I9 is steel tubing onequartcr inch outside diameter and approximately threcsixteenths inch inside diameter. The resistanceI element is composed of No. 35 pure nickel wire, fourteen (14) turns per inch, for approximately nineteen 19) inches of the length of the tube IEI. It has approximately 4i) ohms resistance cold; that is, at a room temperature of around 70': and it draws 300 watts on volts A. C., but, duc to the peculiarities of the metal, the wattage drops to when the heating element is hot, i. e., at normal operating temperatures.

Of course, other materials can be used. Nickel wire containing a small proportion ol' chromium, cobalt, or other metals will approximate the same results.

Preferably the control system turns on the heater as soon. as there is a call for heat and approximately one-half minute before the air flow and oil flow are started. During this interval the preheater will condition the oil remaining in the oil tube I9 after the last stop. This insures that the oil pipe I9, with its contained oil and associated parts, will be appropriately warmed up by the time oil fiow starts to the burner. ForI the values of resistance given, and using a half minute time delay, the relationship is such that the oil in the fuel line immediately adjacent to the nozzle is heated to a temperature of around D F., which is not far below the flash point of the oil and hence provides for quick ignition. As soon as the fuel valve is opened so that there is a fiow of oil through the pipe I9 to the nozzle, the temperature of the heater drops because of the more rapid heat transfer and the wattage input settles to a value of approximately 150 watts, fifty per cent less than the wattage input when the heater is cold. With oil flowing through the pipe I9 and the heater operating at 150 watts, the oil is heated to a temperature of around 105 F., which is well below the temperature at which oil carbonizing will take place but which is sufficiently high. to give the oil proper viscosity characteristics for atomlzation of fuel at the nozzle. As the temperature rises the resistance in the coil 20 will rise and the wattage will drop accordingly.

The considerable length of oil pipe i9 enclosed within the preheater insures appropriate preheatingy and the close proximity of the end of the coil to the nozzle insures the delivery of properly conditioned oil to the orifice.

By this arrangement the appropriate preheating is accomplished with very small current consumption as compared with prior devices. The

automatic drop in wattage as the resistance increases eliminates the necessity or even expedlency for including a make and break Lliermostat. The temperature at which the heating coil or resistance element 20 tends to hover under any given operating conditions involves an equilibrium of several factors, among which are the i nickel as the resistance material is that it pro-A vides a particular combination of resistivity and temperature coefiicient of resistance that causes the equilibrium to occur and to vary in a manner essential to proper functioning of the burner. In other words, the properties of pure nickel cause a certain inherent automatic regulation of the Aoil-heating coil, regulation that would ordinarily require auxiliary automatic controls.

One aspect of thevautomatic regulation is the above mentioned drop from an initial 300 watts heat input to a normal heat input of 150 watts as normal oil flow is establisher'i, the normal level of heat input attributable to peculiar properties of nickel being moderate enough to be continued indefinitely without overheating the oil.

Another aspect of the automatic regulation is that any tendency of the heating coil to be cooled is offset by the relatively large increase in wattage brought about by any drop in temperature of the resistance. In other words, pure nickel minimizes the drop in temperature of the heating coil that occurs whenever the oil flow is increased above normal to meet an increased demand for fuel consumption.

Both of these aspects obviously are intimately i related to the temperature coefficient of resistance, since both aspects vary directly with the temperature coefficient. 'I'he temperature coeillcient of pure nickel is approximately .005 per degree-C. If this temperature coeflicient is used as a basis for calculations, it is found that the resistanceof the heating coils doubles when it is heated from room temperature to a value on the order of 400 F.; therefore the heating coil in the described .apparatus normally is at this temperature-when the heat input is at the normal rate of 150 watts.

In the preliminary heating period before oil flow exists to keep the heating coil cool, the heating coil reaches temporarily an exceedingly high temperature, as high; for example, as approximately 1000 F. with corresponding increase in resistance'and drop in wattage. The input of the heating coil starts with 300 watts with the coil at room temperature, then drops to a minlmum of, say, approximately 80 watts with the heating coll at around 1000 F., and finally climbs to the normal 150 watts after oil flow begins.

In considering the suitability of other metals or alloys as substitutes for pure nickel, two questionsarise. First, is the resistivity of the proposed substitute close enough to the resistivity of pure nickel to make the dimensions of the substitute coil practical for the present purpose? As .an extreme example. copper has a high temperature coeillcient but has such low resistivity..

- that itwould be inconceivable to employ a coil big enough to give the required ohmic resistance. Second, is the temperature coefficient large enough to provide the automaticl regulation 'to an extent adequate for the present purpose? It is believed that any satisfactory substitute for pure nickel must have a temperature coemcient of resistance on the order of .003 per degree C., or higher, to introduce the required degree of inherent regulation into the described burner combination. Very few resistance materials meet 3 both requirements of high resistivity and high coefficient o f resistance. Resistance materials commonly used for elements to heat flowing oil,

to the nozzle and characterized by having a sumv ciently rapid rise in resistancewith rising temperature to result in a wattage input at room temperature of F. that is at least` substantially twise as high as it is when the heater has reached its normal operating temperature, said latter temperature being such as to insure against carbonizing of the fuel.

2. In an oil burner of the type including a nozzle with fuel and primary air lines leading to the nozzle, the combination therewith of an electric heater for the fuel line vlocated closely adjacent to the nozzle and characterized by having a resistance element having a temperature coeflicient of resistivityv on the order of .003 per degree C. or higher over the range of temperatures that it operates whereby the heater will heat rapidly but will automatically reduce the wattage input to a substantially lower value, said resistance element also being characterized by havinga normal operatingtemperature when a minimum amount of fuel'is being delivered to the nozzle for burner operation, that is low enough to insure against carbonizing of the fuel. l

3. In an oil burner of the type including a nozzle with fuel and primary air lines leading to l the nozzle, the combination therewith of an electric heater for the fuel line located closely adjacent to the nozzle andcharacterized by having a resistance element composed of wire having a sufficiently high nickel content to result in a temperature coefficient of resistivity on the order Vof .003 per degree C. or higher whereby the heater will heat rapidly but will automatically reduce the vwattage input to a substantially lower value, said resistance element also being characterized by having'a normal operating temperature when a minimum amount of fuel is being delivered to the nozzle for burner operation, that is low enough to insure against carbonizing'of the fuel.

4. In an'oil burnerofthe type including a nozzle with fuel and primary air lines leading to the nozzle, the combination therewith of an electric heater for 'the fuel line located closely adjacent to the nozzle and comprising an insulating tube telescoped over the fuel line, anelectrical resistance element wound on the 'insulating tube, and a second insulating tube telescoped over the resistance element. said resistance element .being characterized by having a temperature coeillcient of resistivity onthe ordervof .003 per degree C. or higher and having a wattage input having a normal operating temperature .when a minimumamount of fuel is being deliveredto s the nozzle for burner operation. that is low enough to insure against carbonizing of the fuel,

- EARL JOSEPH SEN'NINGER.

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