System Control Means to Preheat Waste Oil for Combustion

1. Field of the Invention

This invention generally relates to an apparatus and method for controlling the temperature and preheat of waste oil in coperation with a waste oil burner. More particularly, the invention relates to such an apparatus and method comprised of a system control means, a temperature control means, a heat transfer assembly for preheating the oil, and a pressure relief means to eliminate nozzle drip.

2. Description of the Prior Art

For many years, various methods and apparatus have been employed to attempt to preheat oil and other combustibles to obtain proper atomization of the oil for burning. Conventional oil burners frequently use the pressure atomizing principle and waste oil burners typically preheat the oil in order to reduce the viscosity and to make pressure atomization possible.

The application of such systems and methods to heavy oil and used oil of varying types, "waste oil", has created several problems which, up until now, have not been sufficiently overcome.

The problems with prior art can best be explained in light of the properties of waste oil in general. Because waste oil has already been in use, its viscosity is generally much higher than regular and unused heavy oil and it also has a substantially higher particle and dirt content. Additionally, with today's automobile oil being predominantly multi-viscosity and containing additives and polymers to achieve multi-viscosity properties, the problems are magnified. The characteristics and properties of a medium or heavy oil are substantially changed by the additives that are introduced to render the oil multi-viscosity. As an example, the temperature at which multi-viscosity oil experiences the formation of solid carbonaceous residue, i.e. coking, is substantially reduced.

The characteristics and properties, including the viscosity, of medium and heavy oils are also substantially affected by the typical use of the oil in an automobile or other engine. The typical use of oil in engines not only breaks down and thereby increases the viscosity of the oil, but also adds a significant amount of foreign particles to the oil, such as dirt and grime.

The effect on medium and heavy oils of the multi-viscosity additives, continued high-temperature use and the addition of dirt and grime, alter the properties of the oil to such an extent that the efficient, effective, and maintenance free preheating and combustion of waste oil has until now, not been sufficiently achieved.

The temperature at which waste oil forms a solid carbonaceous residue, i.e. coking, is drastically reduced as compared to clean heavy oil prior to its use. At the same time, because of the increased viscosity from use and from the introduction of additives, dirt and grime, the waste oil must be heated to a higher temperature to obtain proper atomization. The result is that there is a very narrow temperature range which must be reached and maintained in order to obtain a sufficient viscosity to achieve proper atomization, while avoiding coking and other problems which require substantial maintenance of the system and adversely affect the performance of the burner. The high temperature limitations must be maintained not only at the nozzle, but throughout the preheater and oil feed system.

The oil burner systems represented by prior art and in the industry are designed and configured such that if or when used for waste oil, they experience coking and other maintenance problems on the heat transfer surface and along the oil path, as well as inefficient and inconsistent atomization. The solid residue not only eventually covers and corrodes the heat transfer surface of the preheat means, but also clogs the oil passageway and requires the unit to frequently be disassembled to undergo maintenance, including cleaning and replacement of parts. The solid residue formed in the coking process will also periodically partially break or flake off, and flow with the oil to the nozzle filter, which it then blocks.

The prior art and systems employed in the industry require frequent maintenance for several reasons. The first is that the actual heater element is typically positioned too remote from the nozzle, resulting in excessive heat loss in passage to the nozzle. Because of this heat loss and the target oil temperature at the nozzle, waste oil must be heated to too high of a temperature at the heater. This results in coking on the heating element as well as in the passageway.

Secondly, to obtain a high enough temperature to compensate for the heat loss of the oil in passage to the nozzle, conventional heating means transfer an excessive amount of energy per area of heat transfer surface between the heater and the waste oil. This is referred to as watt density or watts per square inch for the heat transfer area. The allowable watt density for waste oil is generally substantially lower than that for regular medium and heavy oil and is approximately eleven to thirteen watts per square inch.

Exceeding the allowable watt density for waste oil causes coking on the heat transfer surface, which gradually impinges and reduces the heat transfer to the oil and the ability to sufficiently raise the temperature of the oil. Coking is a condition which causes the need for a substantial amount of maintenance, not just on the transfer surface and in the oil passageway, but also at the nozzle.

The prior art has heretofore been unable to sufficiently reduce the coking and maintenance problems for waste oil systems. The waste oil heaters and burners in the market today have also been unable to achieve sufficient temperature control of the oil atomized at the nozzle. Insufficient or inaccurate temperature control results in insufficient atomization and incomplete combustion. The prior art utilizes unresponsive, remote and inaccurate temperature sensing devices to obtain and maintain the preferred oil temperature at the nozzle.

The failure of the prior art to maintain sufficient temperature control of the waste oil being atomized at the nozzle has led to several problems with the performance of the waste oil burner and the maintenance of the unit. First of all, if the temperature of the waste oil at the nozzle is too high, coking occurs at and around the nozzle. This substantially reduces the ability of the nozzle to properly atomize the waste oil and obtain complete combustion. The coking resulting from too high a temperature at the nozzle will corrode and clog the nozzle and require frequent maintenance and/or replacement of it. If the oil temperature upstream from the nozzle is allowed to exceed the coking temperature, then coking occurs upstream. The residue formed by coking will partially breakup during operation, causing flakes and particles to flow with the oil through the oil passageway and cover and clog the nozzle filter, which requires additional maintenance.

The inefficient and inconsistent atomization and resultant combustion greatly reduces the ability of the heater to maintain a constant, controllable and predictable heat output. This causes unacceptable temperature variation in the space heated.

If the waste oil passing through the nozzle is not at a sufficiently high temperature, it will not properly atomize or fully combust. This results in the formation of clinkers or solid carbonaceous formations in the combustion chamber, substantial wearing and destruction of the nozzle, and consequently, higher maintenance.

The industry and prior art typically utilize what is referred to as a "bi-metal snap disc thermal switch control" temperature sensor/control to monitor and control the temperature of the waste oil. These snap disc thermal switch controls typically have a 20.degree. F. control variation. The temperature variations when bi-metal discs are used is too large for an efficient waste oil system and results in what is commonly referred to as overshoot and droop. The snap discs are generally configured to activate and turn the heater off when the oil temperature reaches 10.degree. above the target temperature. However, because the temperature rise does not immediately stop, the oil coming through the passage will rise to as high as 15.degree.-20.degree. F. above the target temperature. This is commonly referred to as "overshoot", and overshoot causes coking and the many other problems discussed herein.

The typical waste oil burner in the industry today, utilizing the bi-metal snap disc thermal control, does not operate again until the oil temperature drops approximately twenty degrees below the set point temperature. The snap disc thermal control will then activate and turn the heating element on when the oil temperature drops 20.degree. below the target temperature. The temperature of the waste oil continues to drop for a period of time until the heating element has a chance to stop the temperature from decreasing and then to heat the temperaute back up to the set point temperature. The actual temperature of the oil can drop as much as fifteen or twenty degrees below the target temperature. This is referred to as "droop". Droop results in incomplete combustion, clinker buildup in the combustion chamber, excessive wear and corrosion on the nozzle and other problems discussed herein.

Another objective which must be achieved in order to greatly reduce the maintenance and increase the efficiency of a waste oil feed apparatus and preheat method is to prevent the flow of oil through the nozzle when at too low a temperature to properly atomize.

Prior art has attempted to reduce this problem by placing an inlet to complicated valve arrangements adjacent to the nozzle, including some type of structure or means for closing off the oil supply line from the nozzle. A different method disclosed by prior art for preventing the standing cold oil from discharging through the nozzle is by use of a purge line with a second pump means and a time delay valve control means to close the purge line valve on startup after a predetermined time interval. See Bears, et al. U.S. Pat. No. 4,392,810.

The problems in the industry and in prior art caused by reaching too high a temperature are greatly reduced by our new heat transfer assembly by the placement of the heat transfer assembly, controlling its receipt and distribution of heat from the heating element and its distribution thereof throughout the assembly and the resultant transfer of heat to the oil passing through the helical passageway. This has also been accomplished through the use of the temperature and system control means described in this specification.

Our invention has greatly reduced or eliminated the problem of exceeding the allowable watt density of waste oil during preheat by utilization of a helical oil passageway through an aluminum heat transfer assembly, which surrounds a cylindrical cartridge type electrical resistance heater. The distribution and transfer of heat through our heat transfer assembly and to the oil in the passageway has effectively redistributed the transfer of the heat, reduced the watt density for transfer of heat to the waste oil, and greatly reduced the coking, carbonization and consequent maintenance problems that occur in prior art and other systems.

Our invention has substantially reduced the coking and maintenance required on the waste oil feed systems, burners, and nozzles to an extent the prior art and the industry have heretofore been unable to achieve.

Our invention utilizes an anticipatory function and a rate proportional band function in its temperature controls to greatly reduce or eliminate both overshoot and droop and the problems associated therewith. Our invention also greatly reduces the temperature variation from the target temperature during the normal operating cycle, or to approximately plus or minus one degree.

Our invention is distinguished from prior art because it utilizes a simple and inexpensive control system that, upon cold startup, does not turn the fuel pump, the electrodes, or the heater fan on until the heat transfer assembly has reached a predetermined temperature, the set point temperature. During this cold startup period and before the fuel pump is energized, the standing cold oil in the heat transfer assembly is heated, which causes it to expand within the heat transfer assembly. In order to prevent this expanding oil from flowing through the nozzle, our invention includes an expansion pressure relief means which creates less resistance to the flow of the expanding oil than the nozzle and, therefore, receives the flow of expanded oil. This allows the nozzle to remain continually open while providing a pressure expansion relief means. Our invention discloses a simple, inexpensive means to prevent oil from being discharged through the nozzle on cold startup.

Our invention is distinguished from prior waste oil burners and systems individually or any combination of it by providing a method and apparatus which eliminates the problems relating to all prior art as discussed more fully herein.

Our invention generally provides an apparatus and method for controlling the temperature of, and preheat system for, waste oil, in cooperation with a typical waste oil burner and which can be used for both an oil pressure driven atomization and an air pressure driven atomization system.

An object of our invention is to greatly reduce coking at the heat transfer surface, in the waste oil passageway and at the nozzle, by reducing the high temperature heating requirement and by maintaining the energy transfer rate per area, watt density, below the maximum for waste oil. In carrying out this object, the invention is comprised of the combination of an anticipatory proportional band temperature control system, a heat transfer assembly placed adjacent to the nozzle and a heat monitering thermocouple at the nozzle chamber.

This forenamed combination also accomplishes a further object of the invention, namely to greatly reduce the flame impingement, inefficient burning and incomplete combustion occurring in the waste oil burner industry.

A further object of our invention is to provide a temperature and process control system accurate and responsive enough to obtain and maintain the target temperature of the waste oil at the nozzle with a sufficiently low variation. This object is carried out through the combination of use of an anticipatory proportional band temperature control system, our heat transfer assembly and a heat monitering thermocouple at the nozzle chamber in the heat transfer assembly.

A further object of our invention is to prevent waste oil at too low of a temperature from being forced through the nozzle and to do so in a simple, effective and inexpensive manner. To carry out this objective during cold startup of the waste oil burner, a pressure expansion relief means adaptable to both the air and the oil driven systems is utilized. To carry out this objective during the normal operating cycle of the burner, our invention utilizes a process control method which maintains the temperature in the heat transfer assembly during the time the burner is not providing heat to the space and does not cause or allow the oil pump to operate during that time. Therefore, there is no oil flow or expansion during this period in the operational stage.

Other and further objects of our invention will appear from the specifications and accompanying drawings which form a part hereof. In carrying out the objects of our invention, it is to be understood that its essential features are susceptible to change in design and structural arrangement with only one practical and preferred embodiment being illustrated in the accompanying drawings as is required.

In the accompanying drawings which form a part hereof and wherein like numbers of reference refer to similar parts throughout:

FIG. 1 is a schematic view showing the important components of the air pressure driven atomization application of the oil burner feed system according to this invention;

FIG. 2 is a schematic view showing the important components of the oil pressure driven atomization application of the oil burner feed system according to this invention;

FIG. 3 is a plan view showing the heat transfer assembly with the electrodes configured in place according to the invention;

FIG. 4 is a longitudinal cross-section view of the heat transfer assembly according to the invention;

FIG. 5 is a longitudinal view of the conventional type of air syphon nozzle that can be used in the air pressure driven atomization application according to this invention;

FIG. 6 is a longitudinal view of the conventional type of nozzle that can be used in the oil pressure driven atomization application according to this invention;

FIG. 7 is a cross-sectional view from Section A--A in FIG. 4.

FIG. 8 is a cross-sectional view from Section B--B in FIG. 4.

FIG. 9 is a cross-sectional view from Section C--C in FIG. 4.

FIG. 10 is a cross-sectional view from Section D--D in FIG. 4.

FIG. 11 is a cross-sectional view from Section E-E in FIG. 4.

Our invention generally provides an apparatus and method for the system control and preheat of waste oil in a waste oil feed system and burner, which can be used in cooperation with a conventional space heater.

Many of the fastening means, connection means and piping means utilized in the invention are generally widely known in the field of the invention described and their exact nature or type is not necessary for an understanding and use of the invention by a person skilled in the art and they will not therefore be discussed in detail.

FIG. 1 shows the air pressure atomization application of the waste oil burner system according to the invention. The oil supply line 2 is emersed at one end in the waste oil fuel in the oil storage tank 1 and connected at the other end by common means to the oil filter 3. The oulet side of the oil filter 3 is connected to the oil supply line 2a which is connected at the other end to a tee pipe junction 4, where the outlet 5a from the flow control bypass line 5 reenters the oil supply line at the tee 4a. The third part 4b of the tee 4 is connected to the inlet to the positive displacement type fuel pump 6.

The oulet 7 to the fuel pump 6 is connected to the oil flow inlet to a second tee junction 8, where the excess oil flow is diverted into the inlet 5b to the oil flow control bypass line 5. The inolet 5b to the flow control bypass line 5 is connected to a flow control needle valve 9 by conventional means. The flow control needle valve 9 is connected by conventional means to the tee junction 4 in the oil supply line 2 just upstream from the fuel pump 6.

The tee junction 8 just downstream from the fuel pump 6 is conventionally connected and acts as the inlet to the fuel valve 10. A part of the fuel valve 10 and conventionally connected thereto is the back-pressure fuel gauge 10a. The fuel valve 10 outlet is conventionally connected to the oil supply line 2b, which is connected on its other end to the inlet means 11 to the heat transfer assembly 12. The inlet means of the heat transfer assembly 12 consists of a cylindrical plug 13, axially drilled and internally threaded to accept the externally threaded oil supply line inlet connection 11. The plug 13 is heli-arc welded 14 to the heat transfer assembly 12 to affix it and further comprise the connection means.

The oil entering the heat transfer assembly 12 then passes through the helical passageway 15 and into the nozzle filter chamber 16 by a passageway means 17 that will be discussed later.

FIGS. 1, 3 and 4 show the pressurized air inlet means 18 to the nozzle filter chamber 20 for the air pressure driven atomization application of the invention. To accomodate the pressurized air inlet 19 to the nozzle filter chamber 20, a hole 19 is bored and internally threaded to mate with the inlet elbow 18. The elbow 18 is conventionally connected to the air supply line 21, which, at its other end, is conventionally connected to a second elbow junction 22 as shown in FIG. 3. The air supply line 21 beyond the second elbow junction 22 is conventionally connected to a normally closed air solenoid valve 23, which is conventionally connected by the air supply line 21 to the air regulator 24. The air regulator 24 has an air pressure gauge 25 tapped into the air supply. The other outlet side 26 of the air regulator 24 is conventionally connected to the air proving switch 27. The air proving switch 27 is wired by conventional means to the fuel valve 10 and if the air pressure falls below an acceptable level, the air proving switch 27 causes the fuel valve 10 to close. This effectively prevents fuel from passing through the nozzle without pressure sufficient to atomize it.

The air regulator 24 is conventionally connected to the integral air pump 28, by means of a continuation of the air supply line and conventional means.

In the oil pressure driven atomization application of our invention as shown in FIG. 2, there is no longer the need for the air supply equipment, such as the air regulator, the air pump, the air proving switch, etc. The need for and use of the flow control bypass line 5, the flow control needle valve 9 and the norally closed fuel valve 10 has also been eliminated.

The oil pressure driven atomization application as shown in FIG. 2 does require an expansion pressure relief line 29 as discussed more fully herein. The expansion pressure line 29 uses the same means as the air supply line 21 up until the air solenoid valve 23 is reached on the air driven system. The expansion pressure relief line 29 uses the same inlet means 18 and 19 at the nozzle filter chamber 20, the same piping means 21 and elbow part 22. From elbow 22, the expansion pressure relief line 29 is conventionally connected to an expansion pressure relief solenoid valve 30. The pressure relief solenoid valve 30 is then conventionally connected to the piping means 31 and facilitates the expansion of the oil back into the oil supply tank 1.

According to our invention, the waste oil is pumped by means of a positive displacement type oil pump 6 through a conventional oil filter 3 to reduce the particulate content of the fuel. The waste oil pump is a commonly used waste oil "Mini-pump," which can be obtained from Suntec, and is rated at approximately thirteen to fifteen gallons per hour. The fuel is drawn through the filter by the vacuum created by the oil fuel pump 6 and then travels through the pump itself 6. In the oil pressure driven atomization application of our invention as shown in FIG. 2, the target back-pressure needed to be achieved by the fuel pump 6 in order to properly atomize the oil fuel is approximately one hundred pounds per square inch. In the air driven atomization application as shown in FIG. 1, the target back-pressure is approximately ten pounds per square inch and merely functions to provide a supply fuel to the nozzle filter chamber 16. The back-pressure is achieved by means of an adjustment feature on the flow control needle valve 9.

The fuel pump 6 then moves the fuel to the inlet side to the fuel valve 10. At this point, in addition to the fuel line entering the fuel valve 10, there is a fuel control bypass line 5 which diverts whatever portion of the fuel it is adjusted to intercept to control and regulate the flow rate of fuel to the heat transfer assembly 12 and the required back-pressure to drive the fuel oil through the system. A portion of the oil flow enters the flow control line 5 and passes through a typical flow control needle valve 9. The fuel passing through the needle valve is then transported to the inlet side to the fuel pump 6, where it re-enters the fuel line at elbow junction 4 and again flows through the fuel pump 6. The desired flow rate for the preferred embodiment of the invention is one and one-half gallons per hour and since the pump we use is rated at approximately thirteen to fifteen gallons per hour, approximately twelve gallons of oil per hour continually pass through the flow control bypass line 5 in the air driven atomization application as shown in FIG. 1.

The approximate one and one-half gallons of fuel oil per hour which are to be pumped into the heat transfer assembly 12 is pumped into the fuel valve 10. The fuel valve 10 is a conventional type fuel valve and can be obtained from Suntec Company. The fuel valve 10 is normally open when electrically energized and closes when the electrical current is shut off. The fuel valve is electrically wired by conventional means to the air proving switch 27, which will cause it to close if the air pressure drops too low.

From the fuel valve 10 the fuel is transported through conventional piping to the inlet 11 of the heat transfer assembly 12, where it enters the inlet cylindrical plug 13 to the heat transfer assembly 12, as shown in FIG. 3. The inlet means to the heat transfer assembly 12 consists of a cylindrical plug 13, axially drilled and internally threaded to accept the externally threaded oil supply line connective means. The plug 13 is heliarc welded to the heat transfer assembly 12 to affix the connection means.

After the fuel passes through the inlet means of the heat transfer assembly, it enters the helical path 15 through the heat transfer assembly 12, where it is pre-heated for efficient atomization and combustion. The special design, passageway 15 configuration and means for transfering heat to the fuel in the heat transfer assembly 12 results in the fuel exiting the passageway 15 in the assembly and into the drilled hole 17, which serves as a passageway connectives means in combination with the radially drilled hole 32 to pass the fuel oil to the nozzle filter chamber 20. Once the radially drilled hole 32 is made, it is partialy plug-welded to seal the passageway configuration.

In the oil pressure driven atomization application of our invention as shown in FIG. 2, the oil in the nozzle filter chamber 20 is then either forced through the nozzle filter and then atomized for combustion by the nozzle, or it passes into the inlet of the cold start pressure relief line 29. In the air pressure driven system applicatin of our invention shown in FIG. 2, the oil in the nozzle filter chamber 20 is drawn through the siphon air nozzle 33 by the incoming air at approximately ten pounds per square inch, partially mixed with the air and then atomized through the air siphon nozzle 33 for combustion.

In the oil driven atomization application as shown in FIGS. 2 and 3, there is a pressure relief line 29 to absorb the ambient standing oil which is in the system on a cold startup and which undergoes substantial expansion during the heatup phase of the pre-heater on a cold startup. The expanding oil on cold startup inlets the pressure relief line 29 in the nozzle filter chamber 20. The core component 34 of the heat transfer assembly 12 has an internally threaded entry to the nozzle filter chamber 20 for connection of the pressure relief line 29 to heat transfer assembly 12.

The exanding oil passing through the pressure relief line 29 is controlled by means of an electronically controlled, normally open solenoid valve 30. The valve is normally open and allows the expanding oil to flow through it and back to the oil storage tank 1 with nominal resistance. On a cold startup, the temperature of the heat transfer assembly 12 is raised to the set point for the system, which approximately ten degrees below the target operating temperature for the proper atomization of the fuel, which is 210 HVF. For the air driven application of this invention, the set point is one hundred and seventy degrees farenheit and for the oil pressure driven applicaiton, the set point temperature is two hundred degrees farenheit. During this expansion phase of cold startup, the resistance presented by the oil pressure atomized nozzle 35 is sufficiently greater than that of the open pressure relief line 29, that the oil flows through the pressure relief expansion line 29.

During the cold startup phase, the control system of our invention is targeted to the set point temperature, and when the heat transfer assembly 12 reaches this temperature, the normally open solenoid valve 30 in the pressure relief line is energized and closed. The closure of the pressure relief line via the solenoid valve 30 allows sufficient pressure to accumulate in the nozzle filter chamber 20 to then force the oil through the nozzle at a temperature and pressure sufficient to properly atomize and efficiently combust the fuel oil.

The application of this invention which utilizes air as the driving force for atomization of the oil fuel as shown in FIGS. 1 and 3 utilizes air under pressure of approximately ten pounds per square inch to force the oil through the air syphon nozzle 33 and which is shown in FIG. 5. As shown in FIGS. 1 and 3, the air is pumped and pressurized by an integral type air pump 28, which forces the air to the inlet side of the air regulator 24. The air regulator 24 is a conventional regulator in the industry and which is available as a Watts brand mini-regulator. The air pressure regulator 24 serves to convert the source pressure of the air from whatever source the user can utilize to the ten pounds per square inch pressure required by our invention.

The air pressure regulator 24 has two exits, the first leading to the air proving switch 27 and the second leading to the air line solenoid valve 23. The air proving switch 27 is a common switch of this type in the industry and one that can be utilized for such a use is a "Tridelta" type switch. The air proving switch functions to moniter the pressure of the air exiting the air regulator 24, and is internally set to send current to the fuel valve 10 to close the fuel valve 10 if a sufficient loss of air pressure is incurred. This is a safety feature of our control system to avoid pumping air and consequently oil through the air siphon nozzle 33 if there is insufficient air pressure to properly atomize the oil.

The air exiting the air regulator 24 is conventionally piped through an air solenoid valve 23. The air solenoid valve 23 is normally closed and is opened when the system thermostat monitering the heating space ambieint air temperature senses a need for additional heat and as part of the heating cycle. The air passing through the air solenoid valve 23 is then piped to the nozzle filter chamber 20 in the heat transfer assembly 12. The air siphon nozzle 33 is shaped differently than that for the oil pressure driven system, in that it extends through the nozzle filter chamber 20 and into the extended section of the filter chamber 16 and as shown in FIG. 4. The air siphon nozzle 33 oil inlet is in the extended section 16 of the filter chamber 20 and this section is sealed from the main nozzle filter chamber by means of a rubber "O" ring 36 around the circumference of the extended portion of the air siphon nozzle 33.

The air driven atomization application of our invention uses the same piping means for the air supply that the oil pressure atomization application uses for the pressure relief line. The air driven system relieves the pressure from cold startup oil expansion by means of the configuration of the heat transfer assembly 12 designed to cooperate with the conventional configuration of air siphon nozzles in such a way as to provide a chamber 20 that can absorb the expanding oil. In the air pressure atomization system, the pressurized air siphons the oil and mixes with it at the nozzle. On cold startup, the pressure and excess oil created by the oil expansion in the heat transfer assembly 12 is absorbed and relieved by allowing the oil to flow and expand back through the air inlet channels 37 in the air nozzle 33 before the oil passes through the nozzle. The air siphon atomization nozzle is a well-known and widely used nozzle in the field of the art, and can be obtained through Delavan, Inc., of West DesMoine, Iowa. Persons skilled in the field of the art commonly referred to the nozzle as a "Siphon Type SNA Air Atomizing Nozzle". The aperture of the atomization nozzle 33 presents a sufficient resistance to the flow of the expanding oil and associated pressure, in comparison to the nominal pressure through the air inlet channels 37 and the air supply line and inlet on cold startup, that the expanding oil does not flow through the nozzle outlet, but instead flows through the air inlet channels 37, into the nozzle filter chamber 20, the air supply inlet 18 and the air supply line 32. The oil then collects in the main nozzle filter chamber 20 of the heat transfer assembly 12. This heated fuel oil remains in the nozzle filter chamber 20 until the set point temperature is reached, which activates the air pump, at which time the pressurized air forces the expanded oil back through the channels 37 in the air nozzle 33, where it is then atomized.

The fuel oil is atomized by the nozzle and ignited upon exit from the nozzle by the use of two electrodes 38, as shown in FIG. 3. FIG. 3 shows a pair of electrodes 38 configured in a conventional manner. The tips 39 of the electrodes create a spark across the gap 40 for igniting the atomized oil spray emanating from the nozzle 41.

FIGS. 3 and 4 show the heat transfer assembly 12 of our invention, which is a machined aluminum assembly. The first part of the assembly is the cylindrical cartridge heating element 42, the second a cylindrical center bored aluminum core component 34, and the third an outer sleeve 43 component which is shrink fit to surround the core component 34. The heat transfer assembly 12 receives heat from the heating element 42, distributes it throughout its configuration and then transfers the heat to the oil in the internal helical passageway 15.

The heating element 42 in the heat transfer assembly 12 is a conventional cartridge type heating element 42, such as one sold by Watlow Electric Manufacturing Company under the Trademark "Firerod". The heating element is located in the central cylindrical cavity 44 bored in the core component 34 of the heat transfer assembly 12, which is drilled to a length of seven and three-quarter inches into the assembly.

The heating element 42 is tightly fit into the central cavity 44 so that heat is easily transferred radially into the core component 34 of the assembly 12. The core component 34 in turn efficiently distributes the heat throughout the assembly, including to the outer sleeve component 43 and the assembly configuration transfers the heat to the oil in the helical passageway 15. The redistribution of the heat received from the heating element 42 and the heat transfer to the oil in the passageway 15 has achieved a sufficiently low watt density to eliminate the coking problems heretofore experienced throughout the industry.

The core component 34 of the heat transfer assembly 12 is machined aluminum cylindrically shaped component, nine and five hundred and sixty-two one thousands inches in length, with an outer diameter of one and one-quarter inches. A seven and thirteen-sixteenths inch long, one-half inch diameter cylindrical shaped cavity 44 is bored out of the center of the core component 34 and along its axis. This cavity 44 houses the electric cartridge heater 42. The heating element 42 is tightly fit into the cavity 44 so that heat is easily transferred to the core component 34 for redistribution throughout the heat transfer assembly 12.

Machined into the outer diameter of the core component 34 are approximately twenty to twenty-one turns of a helically configured groove 45, or three and one-half threads per inch. The machined groove 45 is approximately one-eighth of an inch wide in the axial direction. The groove 45 constitutes the boundary of the oil passageway 15 and is machined one-eighth of an inch deep in the radial direction.

The outer sleeve component 43 of the assembly is a cylindrically shaped and mechanically extruded component 43, with a wall thickness of one-eighth of an inch, an inner diameter of one and one-quarter inchyes, an outer diameter of one and one-half inches and seven and three-quarter inches in length.

The core component 34 is shrunk fit into the outer sleeve 43 of the heat transfer assembly 12, which portion which contains the oil passageway. To obtain a tight fit and seal, the core component 34 is chilled and the outer sleeve component 43 is heated and the core component 34 is then shrink fit into the outer sleeve 43. The sudden reduction in diameter caused where the core component 34 extends beyond the outer sleeve 43 is welded 47 to further affix and seal the two components of the heat transfer assembly together.

The core component 34 extends beyond the outer sleeve 43 by approximately two inches. This extended portion of the core component 34a contains a passageway 17 and 32 that transfers the oil from the helical passageway 15 to the nozzle filter chamber 20, and houses and receives the male-threaded nozzle, and houses and receives 48 the male-threaded thermocouple heat sensor 48. This portion of the core component also houses and receives the male-threaded inlet line to the cold startup pressure relief line for the oil pressure system and the air inlet for the air driven system. The extended portion of the core component 34a also contains the extended portion 16 of the nozzle filter chamber 20, a one-eighths of an inch diameter holed drilled along the axis at a length of one and one-eighth inches.

As shown in FIG. 3, the heat transfer assembly 12 also includes two convention threaded screws 49 that screw into the assembly and are use to position the nozzle within the flame cone of the conventional burner housing. The heat transfer assembly 12 is further insulated by means of a one-quarter of an inch thick neoprene insulation layer 46.

The system control means according to this invention uses conventional wiring means and devices which are generally widely known in the field of the invention described and their exact nature or type is not necessary for an understanding and use of the invention by a person skilled in the art and they will not therefore be discussed in detail. The cold startup of the heater unit is accomplished by turning the mode switch to the heavy oil position, which energizes only the heat transfer assembly 12.

The system control means 50 provides the control function on cold startup to energize only the heating element 42, until the heat transfer assembly adjacent to the atomization nozzle attains a temperature of a pre-selected value. Once the pre-selected temperature value is reached, then the system control means 50 energizes the fuel oil pump 6, energizes the electrodes for igniting the atomized fuel oil exiting the aperture of the atomization nozzle 33, energizes the air solenoid valve 23, and energizes the air pump 28. Once the heat transfer assembly 12 reaches set point temperature, and assuming the room thermostat points are closed and communicating the need for heat output, the control system energizes and turns on the main unit motor, the oil fuel pump 6, the electrodes 39 and energizes and therefore closes the normally open expansion oil pressure relief solenoid valve 30.

Once the heat transfer assembly 12 reaches set point temperature, the burner unit goes into its operational cycle, responding to the thermostat. If the thermostat requires no more heat output, the points will open and current will be discontinued to all components except the heat transfer assembly 12, which will remain at set point temperature for quick starting in the operational cycle.

The system control means also includes a conventional wiring connection from the air proving switch 27 to the fuel valve 10 in the air driven atomization application, which will deenergize the valve 10 and close it if the air proving switch 27 detects insufficient air pressure.

The system control means according to this invention also provides a safety and efficiency shutoff means so that if the temperature measured in the extended portion 34a of the core component 34 of the heat transfer assembly drops ten degrees below the target temperature, the controls will shut the entire system off.

The temperature monitoring and control means 51 includes the location of the receiving means for the thermocouple 48 adjacent to the atomization nozzle 33 and within the extended portion of the core component 34a of the heat transfer assembly 12. The temperature monitoring and control means 51 may also utilize an anticipatory and a rate proportional band function to accomplish the temperature control and monitoring of the fuel oil. This can be accomplished by utilizing a widely-known thermal control system, such as one manufactured and sold by Whatlow Company, St. Louis, Mo.

The temperature monitoring and control means 51 according to this invention uses conventional wiring means and devices which are generally and widely-known in the field of the invention described and their exact nature or type is not necessary for an understanding and use of the invention by a pserson skilled in the art and they will not therfore be discussed in detail.

The temperature monitoring and control means is operatively connected by conventional wiring means and devices to the temperature monitoring thermocouple received in the extended portion of the core component 34a of the heat transfer assembly 12 and operatively connected to the heating element 42.