FLAME CONTROL IN THE MOMENTUM-DOMINATED FLUID DYNAMICS REGION

Abstract

A combustion system includes a fuel nozzle and first and second electrodes. An electric charge is applied to a flame supported by the nozzle via the first electrode. An electrical potential applied to an aerodynamic surface of the second electrode. The electrically charged flame reacts to the electrical potential according to the respective magnitudes and polarities of the charge applied to the flame and the electrical potential applied to the aerodynamic surface. Where the polarities are the same, the flame is repelled by the aerodynamic surface, and where the polarities are in opposition, the flame is pulled into contact with the aerodynamic surface by the electrodynamic attraction.

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority benefit from U.S. Provisional Patent Application No. 61/792,169, entitled “FLAME CONTROL IN THE MOMENTUM-DOMINATED FLUID DYNAMICS REGION”, filed Mar. 15, 2013; which, to the extent not inconsistent with the disclosure herein, is incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to combustion systems, and more particularly, to electrode arrangements that affect flame shape and position.

BACKGROUND

Combustion systems are employed in a vast number of applications, in industry and commerce, and in private homes. Tightening government regulations, increasing costs of fuel, and public opinion all contribute to a continual pressure to reduce emissions and improve efficiency of such combustion systems.

SUMMARY

Methods and apparatuses for stabilizing a flame within a combustion volume may operate in identifying specific zones of thermo-physical flame characteristics, i.e., a region with buoyancy-dominated fluid dynamics, a region with momentum-dominated fluid dynamics, or a flame holding region.

According to an embodiment, a combustion system is provided, which includes a fuel nozzle and first and second electrodes. An electric charge is applied to a flame supported by the nozzle via the first electrode. An electrical potential is applied to an aerodynamic surface of the second electrode. The electrically charged flame reacts to the electrical potential according to the respective magnitudes and polarities of the charge applied to the flame and the electrical potential applied to the aerodynamic surface. Where the polarities are the same, the flame is repelled by the aerodynamic surface, and where the polarities are in opposition, the flame is pulled into contact with the aerodynamic surface by the attraction between the opposite polarities.

According to an embodiment, a combustion system is provided, having a fuel nozzle, a voltage supply, and first and second electrodes. The first electrode is coupled to the voltage supply, and positioned and configured to apply an electric charge to a flame supported by the fuel nozzle. The second electrode includes an aerodynamic surface coupled to the voltage supply and positioned adjacent to the fuel nozzle. The aerodynamic surface has portions that vary in distance from a longitudinal axis of the fuel nozzle. The voltage supply is configured to apply the electric to the flame via the first electrode, and to apply electrical energy to the flame via the aerodynamic surface of the second electrode.

If a polarity of the electrical energy applied by the second electrode is the same as a polarity of the charge applied to the flame, the aerodynamic surface repels the flame, such that a lateral bias is applied to the flame away from the second electrode. Conversely, if the values have opposite polarities, the flame is attracted to the second electrode, such that the flame tends to be biased toward continuous contact with the second electrode along the length of the aerodynamic surface.

According to an embodiment, the fuel nozzle comprises the first electrode, such that the electric charge is applied to fuel as it exits the nozzle, and is subsequently passed to the flame as the fuel is combusted.

According to an embodiment, a third electrode is provided, preferably positioned opposite the second electrode, and coupled to the voltage supply.

The third electrode can include an additional aerodynamic surface, positioned so that movement of the flame toward the aerodynamic surface of the second electrode moves the flame away from the additional aerodynamic surface, and vice-versa. By selection of the polarities of a voltage applied to the second and third electrodes, relative to the polarity of the charge applied to the flame, the flame can be made to move toward one or the other aerodynamic surface, or, in some cases, to broaden to contact both surface or narrow to avoid both surfaces.

According to an embodiment, the second electrode is positioned and configured to generate vortices in the flame. Because the second electrode can be made to attract the flame, it can be smaller than conventional flame holders.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present disclosure are described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. Unless indicated as representing the background art, the figures represent aspects of the disclosure.

FIG. 1 illustrates regions that may be identified in a flame within a combustion volume, according to an embodiment of present disclosure.

FIGS. 2-4 show schematic views of combustion systems, according to respective embodiments.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, which are not necessarily to scale or proportion, similar reference characters typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description and drawings are not intended to limit the scope of the claims. Other embodiments and/or other changes can be made without departing from the spirit or scope of the present disclosure.

In many of the embodiments disclosed below, various electrodes are described as being configured to apply a charge, an electrical potential, or electrical energy to a flame. While these terms are not normally synonymous, they are often used interchangeably, as there is significant overlap in their respective meanings, and it is often difficult to distinguish between them, or to do one without doing the others. For the purposes of the present disclosure and claims, they can be construed as being synonymous, except where a term is more explicitly defined.

Various burner systems are disclosed herein as embodiments. Many elements are omitted from the embodiments described, particularly where such elements are not necessary for an understanding of the principles disclosed. In practice, these and other embodiments typically include more extensive combustion systems used in industry and commerce as parts of, for example, boilers, refineries, smelters, foundries, commercial and residential HVAC systems, etc.

FIG. 1 is a schematic diagram of a portion of a burner 100 including a burner nozzle 106 configured to emit a fuel stream 102 along a longitudinal axis A of the nozzle and to support a flame 104, according to various embodiments. Relative particle velocity within the flame 104 is represented by arrows V, of lengths corresponding to relative velocity. For the purposes of the present disclosure, a flame can be divided into three general regions or portions. The first region R₁, closest to the nozzle 106, is a flame-holding region. Adjacent to, and downstream from the flame holding region R₁ is the second region R₂, a momentum-dominated fluid dynamics region, and furthest downstream, the third region R₃ is a buoyancy-dominated fluid dynamics region.

The term flame particle refers primarily to gaseous atoms and/or molecules that comprise the fluid within a flame, as well as the small solid particles that may be entrained within the flame.

A flame front 108 of the flame is located in the flame holding region R₁. As fuel flows from the nozzle 106 in a downstream direction in the fuel stream 102 the flame front 108 is continually moving upstream. The velocity of the fuel stream 102 is a function of a number of factors, including the geometry of the nozzle 106 and the pressure of the fuel within the nozzle 106. Meanwhile, the flame propagation rate, i.e., the speed at which the flame front 108 moves upstream, depends upon factors that include the type of fuel, the amount of oxygen available, ambient temperature, etc. When the flame propagation rate and the fuel stream velocity are at equilibrium, the flame 104 remains substantially stationary relative to the nozzle 106, and the flame is said to be stable. There are a number of structures and methods known in the art by which a stable flame can be obtained under many conditions and across a wide range of fuel stream velocities. According to the embodiments disclosed hereafter, the flame 104 can be stabilized in accordance with any appropriate structure or method.

Within the momentum-dominated fluid dynamics region R₂ of the flame 104, the velocity and vector of flame particles within the flame 104 are substantially determined by the velocity and vector associated with the fuel stream 102. In this region, the velocity of the flame particles is sufficiently high that other common factors, including buoyancy, have little influence on their vectors. However, as the flame particles move downstream, they lose velocity, and the buoyancy of the flame 104, relative to the cooler and denser surrounding gases, tends to push the flame 104 upward. As the flame particles move further downstream and continue to lose velocity, the direction of movement is increasingly dominated by flame buoyancy.

The shape of the flame 104, and the relative dimensions of the three regions R₁-R₃, can vary significantly, according to many factors. For example, in some cases, the buoyancy-dominated fluid dynamics region R₃ is nonexistent, or very nearly so, as in, e.g., some welding torch flames. In these types of flames, the fuel is substantially consumed before the velocity has dropped to a level where buoyancy can exert a significant influence. In other cases, the momentum-dominated fluid dynamics region R₂ is substantially nonexistent, as in, for example, the case of a candle flame or other flame in which little or no velocity is imposed on the flame by the fuel, so that the velocity and vector of the flame particles are entirely controlled by other factors, including buoyancy.

As illustrated in the embodiments disclosed below, the inventors have recognized that application of electrical energy to the momentum-dominated fluid dynamics region R₂ of a flame can have a surprisingly strong affect on various flame characteristics such as shape, position, breadth, etc., even in cases where flame particle velocity is relatively high.

FIG. 2 shows a schematic view of a combustion system 200, according to an embodiment, including a first electrode 202, a second electrode 208, a voltage supply 204, and an actuator 206. The first electrode 202 includes an aerodynamic surface 210 adjacent to the nozzle 106 in a position corresponding to the second flame region R₂ of the flame 104. In the embodiment shown in FIG. 2, the aerodynamic surface 210 includes irregularities or convolutions. The voltage supply 204 is configured to apply a respective voltage potential to each of the first and second electrodes 202, 208.

According to an embodiment, the second electrode 208 applies an electrical charge to the flame 104, which then reacts to the electrical potential at the first electrode 202. For example, according to an embodiment, the second electrode 208 applies a charge having a positive polarity to the flame 104. The first electrode 202, including the aerodynamic surface 210, is also held at a positive voltage potential, which is repellent to the positively charged flame 104. The repelling effect of the voltage potential at the first electrode 202, or a combination of the aerodynamic effect and the electrical repulsion, applies a lateral bias to the flame 104 along the length of the portion of the aerodynamic surface 210 that faces the flame 104, in a direction away from the first electrode 202. This bias repels hot gases associated with the flame 104 from the aerodynamic surface 210, thereby keeping the aerodynamic surface cool. Because the strength of the repelling bias is a function of distance, the shape of the flame 104 tends to conform to the contours of the aerodynamic surface 210, as shown in FIG. 2, maintaining a relatively constant distance from the surface, in spite of the various contours.

Alternatively, the first electrode 202 is held at a negative voltage potential (or at ground potential), which is attractive to the positively charged flame 104. In this case, the electrical attraction, or a combination of the aerodynamic effect and the electrical attraction, applies a lateral bias toward the first electrode 202, drawing the flame 104 into or toward continuous contact with the aerodynamic surface 210. This serves to increase heat transfer from the flame 104 to the aerodynamic surface 210. Of course, in other embodiments, the polarities can be reversed from those described above.

In practice, the effect described can be employed in combustion systems in which the combustion volume is defined in part by irregular surfaces. The electrical energy and polarity applied to the flame 104 and the surfaces can be selected to either reduce or increase thermal coupling between the flame 104 and the surfaces in question, according to the requirements of the particular system. In conventional combustion systems, where a heat transfer surface includes convolutions or irregularities, a flame may transfer heat most efficiently at the high spots of the surface, i.e., those portions that are closest to the longitudinal axis A of the nozzle 106, while transferring relatively little heat at portions of the surface that are farthest from the longitudinal axis A. In contrast, by appropriate selection of voltage and polarity, the flame 104 can be made to transfer heat substantially continuously along a length of the surface, thereby reducing hot spots while increasing overall efficiency.

According to an alternate embodiment, the nozzle 106 (or a portion thereof) is electrically coupled to the voltage supply 204, as shown in phantom lines in FIG. 2, and is configured to act as a second electrode 212 in place of the second electrode 208. In this embodiment, an electric charge is applied to the fuel as it exits the nozzle 106, where after the flame 104 retains the charge and reacts with the first electrode 202 as previously described.

According to a further embodiment, the nozzle 106 is electrically coupled to the voltage supply 204 as a third electrode 212, and is configured to apply a charge to the flame 104, while the first and second electrodes 202, 208 are configured to be held at respective voltage potentials and polarities in order to interact with the charge applied via the nozzle 106. For example, the second electrode 208 can include a second aerodynamic surface, so that the flame 104 passes between two such surfaces. By selection of the voltage and polarity applied to each of the three electrodes 202, 208, 212, the flame 104 can be made to selectively couple with only one of the two surfaces, with both surfaces, or with neither surface.

Furthermore, according to an embodiment, a reactive moiety can be instantaneously withdrawn or supplied to the combustion reaction in the momentum-dominated fluid dynamics region R₂. Withdrawing of electrons from the combustion reaction may enable parsing of more sub-formations and may cause at least a temporary inability of reactants to react to completion within the combustion reaction. This may cause a temporary formation of soot within the flame 104, which in turn can increase radiation heat transfer from the flame 104 as soot particles are heated to become incandescent.

The aerodynamic surface 210 can be a single surface or a plurality of aerodynamic structures such as a turbine blade, a piece of refractory brick, or any type of bluff body, amongst others, which can operate in combination with the application of electrical energy in the proximity of the resulting aerodynamic effect. The aerodynamic structures can be made of high temperature-stable conductive materials, such as, e.g., very high melting point metal or metal alloy, such as titanium or one of a plurality of iron-nickel-cobalt super alloys, composite ceramic materials, etc., that is capable of sustaining high temperature flames without degradation or failure.

According to an embodiment, the aerodynamic surface 210 is a stationary structure, relative to the nozzle 106. According to another embodiment, the aerodynamic surface 210 is part of a structure that moves or rotates with respect to the longitudinal axis A of the nozzle 106. Movement of the aerodynamic surface 210 can be in any appropriate direction, such as, e.g., parallel to the longitudinal axis A, transverse to the axis A, or a combination of both. Movement of the aerodynamic surface 210, relative to the longitudinal axis A, can be in translation, in orientation or both. In embodiments in which the aerodynamic surface 210 is configured to move or rotate, appropriate mechanisms, such as the actuator 206, for example, are provided to enable the desired movement.

According to an embodiment, movement of the aerodynamic surface 210 is coordinated with a modulation of a voltage applied to one or more of the electrodes 202, 208, in order to create a spinning effect or other pattern in the flame 104.

The application of combined aerodynamic and electrical effects in momentum-dominated fluid dynamics region R₂ to increase or decrease heat transfer from the flame 104 to the aerodynamic surface 210 may affect the chemistry of the flame 104, such that, for example, the flame 104 is either transparent and non-incandescent, or incandescent yellow, in the form of hot black body radiator flames. This effect can be exploited to increase or decrease output of infrared energy, as radiated energy, to radiation collection surfaces of combustion systems.

FIG. 3 is a schematic view of a combustion system 300, according to an embodiment, including a rotating first electrode 302 having aerodynamic surfaces positioned adjacent to the momentum-dominated fluid dynamics region R₂ of flame 104. The rotating aerodynamic surfaces can be in contact or in proximity to the flame 104. The first electrode 302 is configured such that an aerodynamic effect causes the flame 104 to flow over the aerodynamic surfaces. Subsequently, a charge or an electric field can be applied via the voltage supply 204 and the first and second electrodes 302, 208 to the momentum-dominated fluid dynamics region R₂ to affect the flame 104. As previously described, an opposite polarity voltage or a circuit ground potential can be applied to the first electrode 302 to bring flame 104 into closer contact with the aerodynamic surfaces, in order to extract higher heat transfer from the flame. Conversely, application of a same-polarity potential to the first electrode 302 can be employed to reduce the degree of contact and the corresponding thermal coupling of the flame 104 with the aerodynamic surfaces.

FIG. 4 depicts an embodiment of a combustion system 400, including an electrode 208 and an aerodynamic surface 402 configured to operate in combination with the application of electrical energy in the momentum-dominated fluid dynamics region R₂. According to an embodiment, the aerodynamic surface 402 causes an interruption in the flame 104 thereby causing vortices 404 to form on the leeward side of the aerodynamic surface 402 to maintain ignition of flame 104. When the aerodynamic effect is combined with an electrical effect created by the application of an opposite-polarity voltage to the aerodynamic surface 402, a smaller aerodynamic structure can be used, thereby reducing the aerodynamic drag and maintaining lower back-pressure on flame 104, thus producing an improved response of flame 104.

The aerodynamic surface 402 may be comprised, in part, of a refractory brick which may be laterally introduced part way into the flame 104, as shown in FIG. 4, to form vortex 404 on the leeward side of the aerodynamic surface 402. A smaller aerodynamic surface 402, in combination with the application of electrical energy, as previously described, may be more effective in creating vortices 404 while controlling the level of aerodynamic drag.

According to an embodiment, the voltage supply 204 is configured to apply an electric charge having a first polarity to the flame 104 via, for example, the electrode 208. The voltage supply is further configured to apply a voltage potential having a second polarity opposite the first polarity at the leeward side of the aerodynamic surface 402, but not necessarily on the entire aerodynamic surface 402, in order to provide an attractive force to bring flame 104 into contact with the leeward side of the aerodynamic surface 402, increasing the tendency of the flame 104 and vortex 404 to remain intact. Therefore, by adding the electric potential to the aerodynamic surface 402, the size of the protuberance of the aerodynamic surface necessary to hold the flame 104 can be reduced. This combination, in turn, reduces aerodynamic drag, resulting in a lower back-pressure on flame 104. In contrast, controlling the flame 104 with a conventional aerodynamic surface 402, alone, typically requires larger aerodynamic pressures under conditions that can cause high aerodynamic drag and a larger back-pressure level on flame 104.

According to an embodiment, the aerodynamic surface 402 is positioned and configured such that if the voltage potential applied to the aerodynamic surface 402 has the same polarity as the charge applied to the flame 104, the flame will be repelled from the aerodynamic surface 402 such that the flame 104 flows smoothly past the aerodynamic surface 402 without obstruction. On the other hand, if the voltage potential applied to the aerodynamic surface 402 has the opposite polarity, the flame 104 is pulled into contact with the aerodynamic surface 402, and vortices 404 are generated. By selection and control of the relative magnitudes and polarities of the voltage potential applied to the aerodynamic surface 402 and the charge applied to the flame 104, the degree of contact between the flame 104 and the aerodynamic surface 402 can be regulated. This feature may be advantageous in systems in which factors that affect the velocity of the fuel stream 102, and/or the propagation rate of the flame front 108 vary during normal operation.

In another embodiment, the aerodynamic surface 402 includes an embedded electrode 410 to which an electric charge can be applied. The aerodynamic surface 402 and the embedded electrode 410 act on an upward flowing region of the flame 104 so that when a voltage having an opposite polarity (relative to the polarity of electric charges in the flame 104) is applied, flame 104 is attracted toward the electrode 410 further adding to the formation of vortices 404 in the momentum-dominated fluid dynamics region R₂ of flame 104.

In a further embodiment, a reactive moiety is withdrawn or supplied to the flame 104, in the momentum-dominated fluid dynamics region R₂. When electrons are withdrawn from the combustion reaction at periods within a range of about 5 msec, for example, more sub-formations are temporarily parsed causing temporary formation of soot that disrupts the ability of the reactants in the flame to react to completion. Subsequently, newly formed soot is heated to incandescence and thereby increases the radiation heat transfer from the flame 104.

The aerodynamic surface 402 can be a cooled surface or made from a high temperature stable material combined with the electrode 410. The electrode 410 can also be made from high temperature stable material. For relatively low adiabatic flame temperatures, metal alloy materials that do not degrade or fail under high temperature conditions can be employed. A high temperature flame 104 may exceed the softening point of a metal alloy. For these applications, ceramic materials can be used in spite of tensile strains that may be exhibited by composite ceramic.

Ordinal numbers, e.g., first, second, third, etc., are used in the claims according to conventional claim practice, i.e., for the purpose of clearly distinguishing between claimed elements or features thereof. The use of such numbers does not suggest any other relationship, e.g., order of operation or relative position of such elements. Furthermore, ordinal numbers used in the claims have no specific correspondence to those used in the specification to refer to elements of disclosed embodiments on which those claims read, nor to numbers used in unrelated claims to designate similar elements or features.

The abstract of the present disclosure is provided as a brief outline of some of the principles of the invention according to one embodiment, and is not intended as a complete or definitive description of any embodiment thereof, nor should it be relied upon to define terms used in the specification or claims. The abstract does not limit the scope of the claims.

While various aspects and embodiments have been disclosed, other aspects and embodiments may be contemplated. The various aspects and embodiments disclosed here are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

1. A combustion system, comprising:

a fuel nozzle;

a voltage supply;

a first electrode coupled to the voltage supply, positioned and configured to apply an electric charge to a flame supported by the fuel nozzle; and

an aerodynamic surface coupled to the voltage supply, positioned adjacent to the fuel nozzle and having portions that vary in distance from a longitudinal axis of the fuel nozzle.

2. The system of claim 1, wherein the fuel nozzle comprises the first electrode.

3. The system of claim 1, wherein the voltage supply is configured to apply the electric charge having a first value to the flame via the first electrode, and to apply electrical energy having a second value to the flame via the aerodynamic surface.

4. The system of claim 3, wherein the first value and the second value are at a same polarity.

5. The system of claim 3, wherein the first value and the second value are at opposite polarities.

6. The system of claim 3, wherein one of the first and second values is a ground potential.

7. The system of claim 3, wherein the voltage supply is configured to selectively control polarities of the first and second values.

8. The system of claim 3, comprising a second electrode coupled to the voltage supply, positioned and configured to apply electrical energy to the flame supported by the nozzle.

9. The system of claim 8, wherein the voltage supply is configured to apply electrical energy having a third value to the flame via the second electrode.

10. The system of claim 9, wherein the voltage supply is configured to apply the electric charge having the first value to the flame via the first electrode, and to selectively control polarities of the second and third values according to an intended effect on the flame.

11. The system of claim 8, wherein the second electrode includes an additional aerodynamic surface.

12. The system of claim 11, wherein the additional aerodynamic surface includes portions that vary in distance from the longitudinal axis of the fuel nozzle.

13. The system of claim 3, wherein the aerodynamic surface is positioned and configured such that when polarities of the first and second values are opposite each other, formation of vortices directly upstream from the aerodynamic surface increases, relative to formation of vortices when the polarities of the first and second values are not opposite each other.

14. The system of claim 1, wherein the aerodynamic surface comprises a plurality of convolutions that include the portions that vary in distance from the longitudinal axis of the fuel nozzle.

15. The system of claim 1, wherein the aerodynamic surface is movable relative to the longitudinal axis of the nozzle.

16. The system of claim 15, wherein the aerodynamic surface is translatable relative to the longitudinal axis of the nozzle.

17. The system of claim 15, wherein the aerodynamic surface is rotatable relative to the longitudinal axis of the nozzle.

18. The system of claim 15, wherein the aerodynamic surface is one of a plurality of aerodynamic surfaces that are mechanically and electrically coupled together and configured to rotate about a common axis.

19. A method for controlling a flame, comprising:

supporting a flame in a combustion volume;

applying an electrical charge to the flame;

applying a lateral bias to the flame along a length of an aerodynamic surface positioned adjacent to the flame by applying an electrical potential to the aerodynamic surface.

20. The method of claim 19, wherein the applying a lateral bias to the flame includes applying a lateral bias to the flame toward the aerodynamic surface by applying an electrical potential having an opposite polarity from a polarity of the electrical charge.

21. The method of claim 19, wherein the applying a lateral bias to the flame includes applying a lateral bias to the flame away from the aerodynamic surface by applying an electrical potential having a same polarity as a polarity of the electrical charge.

22. The method of claim 19, wherein the applying a lateral bias to the flame includes applying the lateral bias to the flame substantially within a momentum-dominated fluid dynamics region of the flame.

23. The method of claim 19, comprising varying a value of the electrical potential.

24. The method of claim 19, comprising varying a polarity of the electrical potential, relative to a polarity of the electrical charge.

25. The method of claim 19, wherein the applying an electrical potential comprises applying a ground potential to the aerodynamic surface.

26. The method of claim 19, comprising increasing formation of vortices downstream from the aerodynamic surface, wherein the increasing formation of vortices includes the applying a lateral bias to the flame.

27. The method of claim 19, wherein the supporting a flame includes emitting a fuel flow from a nozzle, the method further comprising moving the aerodynamic surface relative to a longitudinal axis of the nozzle.