Electric field-based systems and methods for affecting a flame

Abstract

An apparatus for affecting a flame includes a combustion burner, a plurality of conductive elements, and positive and negative electrodes. The combustion burner outputs a flame and a gas flow from a face of the burner, and the conductive elements are positioned at the face of the burner. The electrodes are each coupled with a power source, with the positive electrode being electrically coupled with at least one conductive element and the negative electrode being electrically coupled with at least one different conductive element. The positive electrode and the negative electrode are configured to generate an electric field horizontally across the face of the burner between the different conductive elements and perpendicular to the gas flow path.

Description

70476-02 ELECTRIC FIELD-BASED SYSTEMS AND METHODS FOR AFFECTING A FLAME CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to and claims the priority benefit of U.S. Provisional Application No. 63 / 620,870, entitled “Electric Field-Based Systems and Methods for Affecting a Flame,” filed January 14, 2024, the contents of which are hereby incorporated by reference in their entirety into the present disclosure. TECHNICAL FIELD

[0002] The present disclosure in general relates to manipulating flames and, more particularly, to applying an electric field to a flame via electrodes to affect combustion. BACKGROUND

[0003] This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.

[0004] Fossil fuel combustion is currently the largest source of energy with the U.S., accounting for 79% of energy produced in 2021. Combustion processes are employed in many residential, commercial, and industrial systems for a wide range of purposes, such as, e.g., for environmental heating, power generation, smelting, refining, propulsion, etc. In response to global warming and air quality concerns, stricter legislation is being created worldwide to reduce the harmful emissions that are a product of combustion, including carbon monoxide (CO), carbon dioxide (CO2), nitrous oxides (NOX), sulfur oxides (SOX), and unburned hydrocarbons (UHC). These restrictions apply to all market sectors including power generation, residential, commercial, and industrial.

[0005] An effective method for reducing NOX emissions is to use extra air beyond what is needed for complete combustion, referred to as “burning leaner.” Burning leaner aims to lower the flame temperature and the formation of thermal NOX. However, these leaner conditions are often more prone to the combustion phenomenon70476-02 known as “thermoacoustic instabilities” and they severely limit the optimization of the combustor design. Thermoacoustic instabilities are a common combustion problem studied since the 1850’s and were a significant problem in the F1 engines during the Apollo program. The combustion community has long sought actuators which could affect the combustion process in real-time and suppress the instabilities. Several potential actuation methods have received considerable research attention including loudspeaker forcing and pulsed fuel injection, but none have been widely adopted due to their expense, lack of reliability, or inability to scale from laboratory to large scale thermal power. SUMMARY

[0006] Described herein are systems and methods related to the manipulation of flames and the area of combustion. The combustion process can be modified by applying an electrical potential to the combustion reaction to improve efficiency and reduce harmful emissions. To that end, the present disclosure includes aspects which can include a combustion burner, a plurality of conductive elements positioned at the face of the burner, and a positive electrode and a negative electrode each coupled with a power source. The combustion burner can be configured to output a flame and a gas flow from a face of the burner, and the gas flow can define a gas flow path in a direction away from the burner. The positive electrode can be electrically coupled with at least one conductive element and the negative electrode can be electrically coupled with at least one different conductive element. The positive electrode and the negative electrode can be configured to generate an electric field horizontally across the face of the burner between the at least one and the at least one different conductive elements and least a portion of the electric field can be oriented perpendicular to the gas flow path. In some aspects, the power source can selectively modify which conductive elements of the plurality of conductive elements couple with the positive and negative electrodes to therefore selectively increase or decrease a quantity of the at least one flame root.

[0007] The apparatus can further include various structural forms. In one aspect, the plurality of conductive elements positioned at the face of the burner can include a plurality of planar plates spanning across the face of the burner, and each planar plate can be arranged in parallel and oriented on a plane defined perpendicular to the face of70476-02 the burner. The positive electrode can be coupled with at least two planar plates and the negative electrode is coupled with at least one planar plate, and the planar plate coupled with the negative electrode can be positioned in between the planar plates coupled with the positive electrode.

[0008] In another aspect, the plurality of conductive elements positioned at the face of the burner can include a plurality of conductive wires spanning across the face of the burner, and each conductive wire can be arranged in parallel and oriented along a plane defined perpendicular to the face of the burner. The positive electrode can be coupled with at least two conductive wires and the negative electrode can be coupled with at least one conductive wire. The conductive wire coupled with the negative electrode can be positioned in between the conductive wires coupled with the positive electrode.

[0009] In another aspect, the plurality of conductive elements at the face of the burner can include a conductive element positioned around a perimeter of the face of the burner and a conductive element positioned across the face of the burner. The positive electrode can be coupled with the conductive element positioned around a perimeter of the face of the burner and the negative electrode can be coupled with the conductive element positioned across the face of the burner.

[0010] In another aspect, the plurality of conductive elements at the face of the burner can include a conductive element positioned around a perimeter of the face of the burner and a conductive pin element positioned inside the perimeter of the face of the burner. The positive electrode can be coupled with the conductive element positioned around a perimeter of the face of the burner and the negative electrode can be coupled with the conductive pin element positioned inside the perimeter of the face of the burner.

[0011] In another aspect, the plurality of conductive elements at the face of the burner can include a series of conductive plates affixed to an interior surface spanning around a perimeter defined by the face of the burner.

[0012] In another aspect, an insulative substrate can be included across the face of the burner. The plurality of conductive elements positioned at the face of the burner can be arranged across a surface of the insulative substrate.

[0013] The present disclosure further includes methods of operating a combustion70476-02 burner. The methods can include various acts such as generating a flame from the burner, generating an electric field between two conductive elements of the plurality of conductive elements, forming at least one electrohydrodynamic bluff-body via the two conductive elements based upon the electric field, generating a first flame root based upon the electrohydrodynamic bluff-body, and increasing a strength of the electric field to generate a second flame root based upon the electrohydrodynamic bluff-body.

[0014] This summary is provided to introduce a selection of the concepts that are described in further detail in the detailed description and drawings contained herein. This summary is not intended to identify any primary or essential features of the claimed subject matter. Some or all of the described features may be present in the corresponding independent or dependent claims, but should not be construed to be a limitation unless expressly recited in a particular claim. Each embodiment described herein does not necessarily address every object described herein, and each embodiment does not necessarily include each feature described. Other forms, embodiments, objects, advantages, benefits, features, and aspects of the present disclosure will become apparent to one of skill in the art from the detailed description and drawings contained herein. Moreover, the various apparatuses and methods described in this summary section, as well as elsewhere in this application, can be expressed as a large number of different combinations and subcombinations. All such useful, novel, and inventive combinations and subcombinations are contemplated herein, it being recognized that the explicit expression of each of these combinations is unnecessary. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] While the specification concludes with claims which particularly point out and distinctly claim this technology, it is believed this technology will be better understood from the following description of certain examples taken in conjunction with the accompanying drawings, in which like reference numerals identify the same elements and in which:

[0016] FIG.1A depicts a schematic of a jet burner having a ring annulus bluff-body;

[0017] FIG.1B depicts a conical flame structure created by the ring annulus bluff-body of FIG.2A;70476-02

[0018] FIG.1C depicts a conical flame structure upon inserting a bluff-body rod within the flame root, showing a resultant “V” in the flame shape that is formed by the creation of a new flame root on the backside of the bluff-body rod;

[0019] FIG.2 depicts a schematic representation of the modification of FIG.2C;

[0020] FIG. 3A depicts a schematic of a jet burner having a single copper wire positioned across the burner face, showing certain dimensions of the single copper wire according to one example embodiment;

[0021] FIG.3B depicts the flame shape of a jet burner according to the system of FIG. 4A, showing the flame shape while the electric field is disabled;

[0022] FIG.3C depicts the flame shape of a jet burner according to the system of FIG. 4A, showing the flame shape while the electric field is enabled;

[0023] FIG. 4 depicts a schematic representation of the resultant flame shape of FIG. 4C;

[0024] FIG.5 depicts a schematic diagram showing example interval volumes defined by the conical and “V” flame surfaces;

[0025] FIG. 6 depicts a schematic diagram showing a rate of energy into the control volume, the control volume defined by the flame surface, and a rate of energy out of the flame surface (commonly referred to as the flame heat-release);

[0026] FIG. 7 depicts a graphical chart showing the measured heat-release deviation obtained when applying a slowly varying ramp of electric field magnitude to a flame;

[0027] FIG. 8 depicts a graphical chart showing the single-wire cathode heat-release obtained while applying a ramp waveform in the applied electric field magnitude;

[0028] FIG. 9 depicts a graphical chart showing the control volume energy reduction as it relates to the electric field magnitude for the single-wire cathode, showing both axes being normalized;70476-02

[0029] FIG. 10 depicts a graphical chart showing one example of a desired linear relationship approximated by a quasilinear relationship by adding N cathode elements, showing N transitions of the flame geometry;

[0030] FIG. 11A depicts a schematic diagram showing one experimental burner utilizing an adjacent electrode configuration;

[0031] FIG.11B depicts a photograph showing an isometric view of a flame generated from the burner of FIG.11A before an electric field was applied to the electrodes;

[0032] FIG.11C depicts a photograph showing a front view of a flame generated from the burner of FIG.11A before an electric field was applied to the electrodes;

[0033] FIG.11D depicts a photograph showing a side view of a flame generated from the burner of FIG.11A before an electric field was applied to the electrodes;

[0034] FIG. 12A depicts an example EHD bluff body system having the standard electrode layout with the anode downstream in the hot exhaust gas and the cathode as a single fin electrode, showing the resultant “V”-shaped flame;

[0035] FIG. 12B depicts an example EHD bluff body system having the adjacent electrode layout having a cathode with two adjacent anodes wired to a positive DC voltage, showing a magnified inset of the electric fields formed;

[0036] FIG.13A depicts a schematic diagram of certain electric body components of a burner having the adjacent electrode configuration and how the electric field is localized, showing parallel plate electrodes creating a largely uniform electric field between the electrodes but curved electric field lines at the plate edges;

[0037] FIG.13B depicts a schematic diagram of the components of FIG.13A, showing chemical ionization creating a quasineutral plasma in a narrow region immediately around the reaction zone;

[0038] FIG.13C depicts a schematic diagram of the components of FIG.13A, showing a small region immediately downstream of the cathode which has both a high electric field magnitude and a high plasma density;70476-02

[0039] FIG.13D depicts a schematic diagram of the components of FIG.13A, showing how the electric body force is only of significant magnitude near the flame tip and is directed mostly against the bulk flow direction;

[0040] FIG.14A depicts a schematic diagram of a burner face showing a nominal case of uniform electric field created by parallel plate electrodes whereby the cations are accelerated directly towards the cathode and the flux is spread over a length of ^ at the cathode;

[0041] FIG.14B depicts a schematic diagram of a burner face showing the conductive layer effect whereby the same parallel plate electrodes see a highly non-uniform electric field due to the charge transport effect of the flame front;

[0042] FIG. 15A depicts a schematic diagram of a first example of an adjacent electrode configuration, showing one or more anode plates and one or more cathode plates arranged in parallel in an orientation perpendicular to the burner face;

[0001] FIG. 15B depicts a schematic diagram of a second example of an adjacent electrode configuration, showing one or more anode wires and one or more cathode wires arranged in parallel across the burner face;

[0002] FIG. 15C depicts a schematic diagram of a third example of an adjacent electrode configuration, showing one or more cathode wires across the burner face and one or more anode rings positioned around the edges of the burner face;

[0003] FIG. 15D depicts a schematic diagram of a fourth example of an adjacent electrode configuration, showing one or more cathode pins positioned in the burner face and one or more anode rings positioned around the edges of the burner face;

[0043] FIG. 15E depicts a schematic diagram of a fifth example of an adjacent electrode configuration, showing one or more anode plates and one or more cathode plates positioned around the edges of the burner face and in an alternating pattern;

[0044] FIG. 15F depicts a schematic diagram of a sixth example of an adjacent electrode configuration, showing an insulative substrate positioned across the burner face having anodes and cathodes arranged in alternating fashion across the insulative substrate;70476-02

[0004] FIG. 16A depicts a schematic diagram of a burner tube exemplifying the concept of controlling the flame location by enabling different electrode sets, showing moving the flame location along the longitudinal axis of a tube by engaging different sets of electrodes;

[0005] FIG.16B depicts a schematic diagram of a burner tube exemplifying the concept of controlling the flame location by enabling different electrode sets, showing moving the flame stabilization point laterally by setting which electrode is the cathode and making the rest the anodes;

[0006] FIG. 17 depicts a schematic diagram of a portion of a swirl stabilized burner incorporating one configuration of adjacent electrodes;

[0007] FIG. 18 depicts a schematic diagram of a portion of a swirl stabilized burner incorporating an alternative configuration of adjacent electrodes;

[0008] FIG.19 depicts a schematic diagram of a portion of a V-gutter flame stabilizers in an afterburner incorporating one configuration of adjacent electrodes;

[0009] FIG. 20A depicts a schematic diagram of a burner configured for varying the heat release by creating an EHD bluff body, showing the original flame shape encloses a volume, V;

[0010] FIG. 20B depicts a schematic diagram of the burner of FIG. 20A, showing the creation of an EHD bluff body with the electric field creates a “V” in the flame surface and reduces the total volume enclosed by the flame, V*, where the volume difference (∆V) is consumed during the transition from (A) to (B);

[0011] FIG.21A depicts a schematic diagram of a burner having an adjacent electrode configuration, showing zero EHD bluff bodies formed;

[0012] FIG.21B depicts a schematic diagram of a burner having an adjacent electrode configuration, showing one EHD bluff body formed;

[0013] FIG.21C depicts a schematic diagram of a burner having an adjacent electrode configuration, showing two EHD bluff bodies formed;

[0014] FIG.21D depicts a schematic diagram of a burner having an adjacent electrode70476-02 configuration, showing three EHD bluff bodies formed;

[0015] FIG. 22 depicts a series of images of the flame distortion with an increasing number of EHD bluff bodies, such as from the configurations depicted in FIGS. 21A- 21D, showing a progressively increasing number of EHD bluff bodies by switching more electrodes to a negative voltage;

[0016] FIG. 23 depicts a flowchart of one exemplary method of using an adjacent electrode configuration with a burner to modify the number of EHD bluff-bodies to change the flame shape, internal volume of the flame, and heat release of the burner.

[0017] The drawings are not intended to be limiting in any way, and it is contemplated that various embodiments of the technology may be carried out in a variety of other ways, including those not necessarily depicted in the drawings. The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present technology, and together with the description serve to explain the principles of the technology; it being understood, however, that this technology is not limited to the precise arrangements shown, or the precise experimental arrangements used to arrive at the various graphical results shown in the drawings. DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0018] The following description of certain examples of the technology should not be used to limit its scope. Other examples, features, aspects, embodiments, and advantages of the technology will become apparent to those skilled in the art from the following description, which is by way of illustration, one of the best modes contemplated for carrying out the technology. As will be realized, the technology described herein is capable of other different and obvious aspects, all without departing from the technology. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not restrictive.

[0019] It is further understood that any one or more of the teachings, expressions, embodiments, examples, etc. described herein may be combined with any one or more of the other teachings, expressions, embodiments, examples, etc. that are described herein. The following-described teachings, expressions, embodiments, examples, etc. should therefore not be viewed in isolation relative to each other. Various suitable ways70476-02 in which the teachings herein may be combined will be readily apparent to those of ordinary skill in the art in view of the teachings herein. Such modifications and variations are intended to be included within the scope of the claims.

[0020] Reference systems that may be used herein can refer generally to various directions (for example, upper, lower, forward and rearward), which are merely offered to assist the reader in understanding the various embodiments of the disclosure and are not to be interpreted as limiting. Other reference systems may be used to describe various embodiments, such as those where directions are referenced to the portions of the device, for example, toward or away from a particular element, or in relations to the structure generally (for example, inwardly or outwardly).

[0021] I. Overview

[0022] One potential solution to improve fossil fuel-based energy generation involves the use of electric fields to affect combustion. Many fuel-air chemistries produce charged particles during combustion. Applying an electric field to the flame accelerates these particles. Their resulting collisions with the bulk gas molecules create appreciable pressure and velocity effects, commonly referred to as the “ionic wind.”

[0023] Accordingly, described herein are systems and methods for significantly enhancing the electric field effect on a flame to modify the flow field, flame shape, and heat-release of the flame using the electric field. In some embodiments, heat- release modifications can be utilized to provide further improvements, such as suppressing thermoacoustic instabilities in the combustor. The systems and methods presented have no consumables or moving parts, is relatively inexpensive due to its use of simple materials and inexpensive electronics, and is efficient (e.g., in one example, the system only consumes a mere 40 mW of electrical power to control a 3 kW thermal power flame). Further, the systems and methods are applicable for gaseous fuel types and continuous combustion. Examples of gaseous fuels include natural gas, butane, methane, propane. Non-gaseous fuels are solid and liquid types, such as coal, gasoline, kerosene, and diesel. Continuous combustion is where the flame is constantly present, and examples include furnaces, stoves, and lighters. A non- continuous example is the automotive internal combustion engine. The most common70476-02 example of a gaseous fuel type is natural gas, which is the largest segment of U.S. energy consumption. Natural gas is used for electrical power generation, heating homes, cooking food, and many industrial activities.

[0024] II. Exemplary Systems and Methods for Affecting Flame Combustion

[0025] Described herein is an alternative electrode configuration used in conjunction with concepts from US Patent Application No. 18 / 521,164, titled “Systems and Methods for Flame Stabilization and Heat-Release Modulation, filed November 28, 2023 (“the ’164 Application”). The ‘164 Application describes certain physical structures (referred to herein as a “standard” configuration) and methods for creating an electric field-based actuator to affect a flame. The actuator from the ‘164 Application is also combined with a feedback controller to suppress the classic combustion problem of thermoacoustic instabilities. The electrode configuration described in the present disclosure performs a similar function but includes improvements. The following sub- section discusses the improved systems and methods that allow modulation of burner flame heat-release with an electric field and provides systems and methods for suppressing thermoacoustic instabilities.

[0026] A. Exemplary Systems and Methods for Electric Field Induced Flame Heat-Release Modulation

[0027] The systems and methods include creating an EHD bluff-body for affecting the heat-release and using multi-element anodes and / or cathodes to improve the effects on the flame. Each part will be discussed in greater detail below.

[0028] i. Creation of an EHD Bluff-Body

[0029] An EHD bluff-body acts similar to an aerodynamic bluff-body—a classic tool in combustion used to stabilize flames. It is a geometric shape placed in the flow of a fuel-air mixture that disrupts the flow, creating a wake region with low-velocity zones that aid in stabilizing flames. An example of an introduction of an aerodynamic bluff- body is shown in FIGS. 1A-1C. Particularly, FIG. 1A shows a burner (100) having a stabilization ring (102) around the circumference of the burner face. FIG.1B shows an initial flame shape before inserting an aerodynamic bluff-body across the burner face, and FIG. 1C shows the change in flame shape after inserting a bluff-body (104) at the70476-02 base of the flame on the burner face. In this example application, the bluff-body (104) is a 1.59-millimeter (mm) diameter metal rod. Its effect is to block the fluid flow and cause flow recirculation on the backside of the rod, as depicted in the diagram of FIG. 2. The flow recirculation reduces the velocity enough that a new flame root is created in this region, seen as a “V” in the flame surface. Flame geometries are largely defined by their flame roots and thus creating a new one causes a significant change in the flame shape, as seen when comparing FIG.1B and 1C.

[0030] One example process of creating an EHD bluff-body is shown in FIGS.3A-3C. The process starts at FIG. 3A by adding a small diameter copper wire (204) stretched across the face (202) of the burner (200). The 0.127 mm diameter of this wire is small enough that it causes minimal interference to the flow field and the flame. Thus, it does not act as an aerodynamic bluff-body. The image of the flame (see, FIG.3B) shows that it is has the original conical shape and no flame root or “V” is present.

[0031] The flame shape of FIG.3C is formed by creating an EHD bluff-body using the copper wire (204) along with an electric field. As depicted in the diagram of FIG.4, the electric field accelerates the positive ions present in the flow towards the wire (204). Their upstream movement causes collisions with the other gas molecules and creates a local reduction of the gas velocity near the wire (204). The gas velocity profile is depicted by the white line in the figure. Increasing the electric field magnitude causes a greater velocity reduction near the wire (204). This reduction can be great enough to reduce gas velocity all the way to the laminar flame speed of the gas mixture, ^U. If this occurs, a flame root forms just downstream of the wire resulting in the observed “V” shape. This flame structure is the same as that seen with the previous aerodynamic bluff-body. Thus, the electric field reduces the flow velocity near the wire (204) and the flame responds to this velocity reduction the same way it does when the flow is blocked with an aerodynamic bluff-body. Due to the similarity, this effect is referred to as an EHD bluff-body.

[0032] The primary benefit of the EHD bluff-body compared to a traditional aerodynamic one is the EHD version can be switched on and off very quickly with the electric field, much like turning a light on and off with a switch. This switching can be up to a few hundred cycles per second or more. Essentially, the flame shape is now electrically controlled.70476-02

[0033] ii. Heat-Release Change

[0034] A heat-release change occurs when the flame shape transitions. The conical and “V” flame surfaces have internal volumes, as illustrated in FIG.5. A key feature is that the internal volumes between the two shapes are different, with the volume of the conical flame being larger than the volume of the “V” flame. When the flame shape is changed with the electric field, the internal volume of the flame reduces. The volume reduces by the difference between the two internal volumes, ∆^. During the transition from the conical to “V” shape, this volume difference (∆^) is consumed by the flame and adds to the thermal power of the flame.

[0035] The thermal power is more commonly referred to as “heat-release,” ^(^). A control volume analysis, defined in FIG. 6, is used is derive the relationship between the flame heat-release and changing flame volume: ^(^) = ^^(^ ^^^^(^)^^ ) − ^^ ,(“Equation 1”) where ^^^^the control volume and ^^^(^) is the chemical potential energy associated with the control volume. These two terms can be expressed in terms of the reactant properties ^^^^(^) = ℎ^^^^(^),(“Equation 2”) and ^^^(^) = ℎ^^^(^),(“Equation 3”) where ℎ^is the heat of combustion of the mixture, ^ is the reactant mixture density, ^ is the burner outlet area, ^(^) is the gas velocity into the control volume, and ^(^) is the control volume. The heat-release with these substitutions is ^(^) = ℎ ^^^(^) − ℎ ^ ^^(^)^ ^ ^^ ,(“Equation 4”). To simplify this expression, a constant incoming gas velocity is assumed, ^(^) = ^. Additionally, the change in heat-release can be created by changingthe control volume, so the heat-release deviation can be viewed from the mean value, defined as70476-02 ^^(^) = ^(^) − ^^,(“Equation 5”). The heat-release deviation, ^^(^), in terms of Equation.4 is then ^^(^) = −ℎ ^^(^)^^ ^^ ,(“Equation 6”).

[0036] This equation shows that changing the control volume, ^(^), by the electric field will cause a deviation in the flame heat-release, ^(^). This mechanism constitutes an actuator which can be used to suppress the thermoacoustic instability. An experimental example of this effect is shown in FIG. 7, which shows the measured heat-release deviation when applying a slowly varying ramp waveform in electric field magnitude. The response shows there is a 12 to 14% brief increase in heat-release when the flame transitions from the conical to the “V”-shape. When the electric field is then decreased and the flame makes the reverse transition from the “V” back to the conical shape, there is a 5 to 7% decrease.

[0037] iii. Multi-Element Cathode

[0038] Adding more cathode elements can improve the actuator relationship. The single wire heat-release response of FIG. 7 shows that the electric field changes the heat-release by causing the flame to transition between shapes. However, the changes in heat-release were only brief impulses, which may not be ideal for an actuator. To better characterize this actuator, an alternative representation is used. If the heat-release deviation, q' (t), is integrated, it gives the energy reduction of the control volume, ∆Q. This is illustrated in FIG. 8, which shows the heat-release versus time, and FIG. 9, which shows the normalized control volume energy reduction (∆Q) versus electric field strength (E ̅). The control volume energy reduction is the area under the heat-release curve. Comparison of the two plots of FIGS. 8-9 shows that the positive heat-release impulse (see, FIG.8) corresponds to the step increase in ∆Q (see, FIG.9). This occurs when the flame shape transitions from the conical to the “V” shape (see, FIG. 9). Similarly, the negative heat-release impulse corresponds to the step decrease in ∆Q, occurring when the flame transitions back from the “V” to the conical shape (see, FIG. 9). The step-like shape of the ∆^ vs. ^ plot is characteristic of affecting the flame with an EHD bluff-body. With a goal of making an actuator of heat-release using the electric70476-02 field, the ideal relationship between the two instead would be linear and continuous, represented by the linear line in FIG. 9. To better approximate the linear relationship, more cathode elements can be added. For each cathode element added, an additional EHD bluff-body is therefore created and another step change occurs in the ∆^ vs. ^ profile. This concept is illustrated in FIG. 10, which shows the approximation if N cathode elements are added. Particularly, FIG. 10 shows that the desired linear relationship can be approximated by a quasilinear relationship by adding N cathode elements, creating N transitions of the flame geometry. Each flame transition between two shapes creates a step change in the control volume energy reduction.

[0039] B. Exemplary Adjacent Electrode Configurations for Electric Field Induced Flame Heat-Release Modulation

[0040] An improvement of the “adjacent” electrode configurations described herein as compared to the ‘164 Application is that all electrodes are removed from the downstream hot flame area. This can be important as some combustion applications will not allow electrodes in the flame due to durability and erosion concerns. An additional benefit of the adjacent electrode configurations is that they confine all the electrodes to a single manufacturable part, which is advantageous for manufacturing, retrofitting, and to quell safety concerns.

[0041] i. Introduction and One Example Burner Design

[0042] An experimental burner used to demonstrate the adjacent electrode configuration is shown in FIG. 11A, though it should be understood that this example is not intended to be limiting. As shown, the burner geometry includes a rectangular opening with a flow area of 12.7mm x 26.4 mm. The burner housing is constructed from machinable glass-mica ceramic to withstand the high flame temperatures but also be electrically insulating. Slots are cut into the ceramic to hold the metal electrodes. The electrodes are stainless steel strips, 0.254 mm in thickness and 6.4 mm tall. There are 12 electrodes in total and they were evenly spaced 2 mm apart. The flame geometry before the electric field was applied is shown by the images of FIGS. 11B-11D. A premixture of methane and air was used, with typical bulk flow velocities of 1.5 to 3.5 m / s, and equivalence ratios around stochiometric (ϕ=1.0).

[0043] A demonstration of creating an EHD bluff body by both the standard and70476-02 adjacent electrode configurations with this burner is shown in FIGS. 12A-12C. The standard electrode arrangement is shown in FIG. 12A whereby the anode is located within the flame and approximately 50 mm downstream from the burner exit plane. The cathode is a single fin electrode in the center of the array. All other electrodes were not wired to. Accordingly, as depicted in FIG. 12A, the standard electrode configuration creates an electric field that is largely in the vertical direction and oriented against the bulk flow direction. The use of the thin cathode strip (e.g., 0.254 mm thick) focuses the electric field and ion jet, creating the localized EHD bluff body. The result is a “V”- shape in the flame.

[0044] An adjacent electrode configuration is shown in FIG. 12B. The electrode was grounded while the two adjacent electrodes were electrically connected to a positive DC voltage (e.g., ~900V). All other electrodes of the array were not wired to. The electrodes oriented in parallel to one another resemble the classic electrode configuration of parallel plates and the electric field depicted in FIG. 12B is that for parallel plate electrodes. The electric field would be uniform in the space immediately between the plates but would curve on the top and bottom edges of the electrodes. This curvature results from the property that the electric field is perpendicular to the surface of a conductor. As shown in the magnified inset, the electric field approaching the top of the negative electrode would have a mostly vertical component, oriented downwards. This meets one condition needed to create an EHD bluff body, which is the electric field be oriented against the flow direction in the region immediately downstream of the cathode.

[0045] ii. Electrode Geometry to Localize the Electric Body Force

[0046] The adjacent electrode configuration and its distorted electric field is best understood through the electric body force. The electric body force (1) resulting from elastic collisions between charged particles and neutral molecules is: ^^⃑ = ^^⃑ (!" − !#)(“Equation 7”) where ^ is the unit charge (1.602e-19 C), ^⃑ is the electric field, and !",#are the ion densities. For lean methane-air flames, the dominant particle assumed responsible for collisional momentum transfer effects is the cation hydronium, H3O+.70476-02 Effects from anions are typically assumed negligible. The dominant negative charge carrier is the electron, but it transfers negligible momentum to the bulk gas flow field due to the large mass disparity between it and the neutral molecules that compose the bulk gas. Therefore, the electric body force can be simplified to only considering cation collisional effects: ^^⃑ = ^^⃑ !"(“Equation 8”). For the simple 1D case, the pressure due to the electric body force (1) is: %^(&) = ' ^^⃑(&)(&(“Equation 9”). In terms of thenumber density, the pressure is: %^(&) = ^ ' ^⃑ (&)!"(&)(&(“Equation 10”). Thedepends significantly on the distribution of the electric body force and the aerodynamics of the combustor (1). However, for incompressible and inviscid flow, the conservation of momentum gives the maximum velocity reduction: %^(&) 1 1' ' ^⃑(“Equation. electric field magnitude and a high number density will create a velocity reduction. All other regions can be ignored.

[0047] Error! Reference source not found. FIGS. 13A-13D show the components contributing to the electric body force for the adjacent electrode configuration. The electric field for parallel plate electrodes is shown in FIG. 13A. As discussed above, the parallel plate arrangement creates a uniform electric field between the plates (point A). The property that an electric field is perpendicular to the surface of a conductor causes the electric field lines at the top and bottom edges of the electrodes to be oriented in the vertical direction. This creates a vertical and downward oriented component on70476-02 the top of the cathode edge (point B).

[0048] Chemical ionization creates a region of relatively high plasma density immediately around the reaction front (flame), as shown in FIG. 13B. Outside of the ionization region, the plasma density can be considered negligible (!",+ = 0). Thenarrow width of the ionization region limits the areas where high electric body forces can be expected. This is depicted in FIG.13C, which shows the overlapping regions of both high plasma density and high electric field magnitude. The expected electric body force is depicted in FIG. 13D. The electric body force will be oriented parallel to the local electric field and with a magnitude dependent on the local electric field magnitude and local number density. As depicted in FIG.13D, there is a small region immediately downstream of the cathode that has a high electric body force. The electric body force will be weak everywhere else and will have negligible effects on the flow field (i.e., velocity reduction). This localization of electric field and ion number density creates the localized electric body force required for the EHD bluff-body.

[0049] iii. Flame Conductive Layer Transport to Localize the Electric Body Force

[0050] The reaction zone behaves as a quasi-neutral plasma, acting to efficiently transport charge along the reaction zone (referred to as a “conductive layer effect”). The difference this makes on the electric field and charge movement is illustrated in FIGS.14A-14B. The flame shape is the common “V”-shape and the electrodes are the standard parallel plates arrangement. In FIG. 14A, the conductive layer effect is ignored, so the resulting electric field given the parallel plate electrodes is uniform and oriented straight from the anode to the cathode. This results in the -. / "cations being accelerated directly upstream towards the cathode, and the electrons being accelerated directly downstream towards the anode. When the cations reach the cathode, they cover a width of 0.

[0051] The conductive layer effect is illustrated in FIG. 14B. The electric field lines are initially perpendicular at the electrode surfaces. As they approach the flame, the lines turn and run tangent to the flame surface. Due to the quasi-neutral assumption of the flame front, any external electric fields are perfectly shielded by charge redistribution within the flame front, thus the net electric field within the flame front is70476-02 zero. The charge redistribution creates a continuous current flow along the flame, as indicated by the new directions of the cations and electrons. While it’s common in plasma devices to use dielectric coatings at the electrodes to prevent loss of the plasma by recombination, the electrodes used here are conductive. There is continuous recombination at both electrodes and so there is a continuous current of cations to the cathode and electrons to the anode to replenish the lost charges and maintain the quasi- neutral condition. The primary effect is that even though a uniform electric field would be expected for the parallel plate electrodes, the electric field is highly non-uniform. This non-uniform electric field and charge transport along the flame front results in a focusing of the cations to the flame tip. There they exit the flame front and meet the cathode, but at a much narrower point than before (width is reduced to 0∗from 0). Thus, the conductive layer effect and flame shape act to focus the cations to a narrow point, largely independent of the externally applied electric field.

[0052] The conductive layer effect and it focusing the cation current has a compounding effect on the electric body force and ionic wind velocity reduction. As given in Equation 8, the electric body force is proportional to the local net charge density and electric field magnitude. The charge density at the flame tip has been shown to increase by approximately 65 times from the conductive layer effect. The local electric field was significantly increased by the space charge concentration, as given by Poisson’s Equation ^∇^ =4 (!" − !+)5(“Equation 12”).

[0053] The local electric field strength was measured and found to be increased by approximately 10 times compared to a flat flame condition. Combining these two, it was found the electric body force was increased by as much as 1250 times, from 10 N / m3for a flat flame to 12,500 N / m3for a “V” shaped flame. As previously stated, the relationship between the electric body force and the velocity reduction depends on the aerodynamics of the combustor. However, an increase in the electric body force of three orders of magnitude can be expected to significantly increase the velocity reduction as well.70476-02

[0054] The conductive layer effect can significantly alter all aspects of the EHD bluff-body problem. The shape of the “V”-flame naturally transports or guides cations to the flame tip, significantly increasing the charge density compared to what would be expected with a uniform electric field. A consequence of this is that the electric body force can be localized just by the flame shape.

[0055] The conductive layer transport effect does not have to be relied on to localize the electric body force. As demonstrated in the previous sections with the standard and alternative electrode configurations, the electrode geometries can be used to focus the electric field and in turn focus the cation current and localize the electric body force. The conductive layer transport effect would further focus the current, which is beneficial to creating the velocity reduction point and achieving a greater flow velocity reduction by ionic wind. It is worth mentioning that it would not be practical to solely rely on the charge transport effect to create the EHD bluff-body and flame stabilization point. There is no control where the stabilization point will occur, and multiple stabilization points are needed for incremental control of the flame and heat-release. The preferred combination is an electrode geometry that focuses the electric field to the cathode, and a resulting flame shape that assist in guiding charge to the stabilization point by the conductive layer effect.

[0056] iv. Exemplary Adjacent Electrode Configurations

[0057] Various example electrode configurations using this adjacent configuration are shown in FIGS. 15A-15F and hereinafter described. The common elements to all of these are that they each (a) include thin enough cathode elements so as to not act as an aerodynamic bluff-body and anchor the flame, (b) position no electrodes within the flame (i.e., downstream exhaust gas), and (c) the localized electric body force is created by the electrode geometry, but flame shape focusing through the conductive layer effect does exist too.

[0058] The configuration of FIG. 15A is the parallel plate configuration. The burner housing shown is round but could be other geometries, such as the rectangular profile presented above. The configuration of FIG.15B includes parallel wires and would have a similar electric field to the plates. For the configurations of FIGS. 15A-15B, more than three electrodes could be used, such as the burner shown in FIG. 11A, which has70476-02 12 electrodes. The configurations of FIGS. 15E-15D include a ring anode located around the burner perimeter. The configuration of FIG. 15C includes a wire cathode while the configuration of FIG. 15D includes a pin electrode. The change of cathode shapes between FIGS. 15C and 15D would create different velocity profiles and therefore flame shapes.

[0059] The configuration of FIG.15E includes a circular array of positive and negative electrodes located around the inner circumference of the burner. When the electric field is applied, the electrodes would create only small distortions of the flame surface around the circumference. However, based on the work discussed in the ‘164 Patent Application, a small distortion and the accompanying change in heat-release is sufficient to control a thermoacoustic instability. Lastly, the configuration of FIG.15F shows the concept of combining the positive and negative electrodes onto a single insulative substrate. The advantage of this configuration is easier assembly of the burner and electrodes. It could also enable more complex burner and electrode geometries for enhanced performance. While a variety of example adjacent electrode configures are shown and described, it should be understood that additional configurations have been contemplated and aspects of each variation may be interchangeable according to the particular application.

[0060] v. Electrode Locations

[0061] The adjacent electrode configuration allows new possibilities in terms of practical designs but also flame control. One possibility is having multiple electrode sets that can be used to move the base of the flame. An example of moving the flame location within a tube is shown in FIG.16A. Multiple electrode sets are mounted along the long axis of the tube. Each electrode location (e.g., 1, 2, 3, ...) has a single or multiple electrode pairs to create flame stabilization points. An electrode pair consists of the anode and cathode, in various geometries, coupled with a power source and a controller. These could be embedded into the tube wall or partially protruding from it. Engaging an electrode set, via the power source and controller, would cause the flame to stabilize at its location either through autonomous adjustment or manually. Specifically, sensors affiliated with the burner may be configured to measure an acoustic characteristic (e.g., an acoustic pressure) of the burner, compare the acoustic characteristic to a pre- determined acoustic characteristic, based upon the comparison, selectively modify the70476-02 electrode sets and therefore the electric field induced between the positive electrodes and the negative electrodes to modify a heat-release of the flame.

[0062] Alternatively, the flame stabilization point could be shifted laterally as shown in FIG.16B. The flame stabilization point occurs at the cathode, so one electrode is set as the cathode while all other electrodes become the anodes.

[0063] In an example application, the electric field stabilization method could be added to an existing combustion device to permit electrical adjustability of the flow field and flame. An example of a typical swirl–stabilized burner with added electrodes is depicted in FIG. 17. One example is adding the electrodes around the injector and swirler as shown. The negative electrode is incorporated into the swirler vanes while the positive electrode is incorporated into the body surrounding the swirler. The specific geometry of the electrodes would depend on the application but would be similar to the elementary shapes shown in FIGS.15A-15F. This would allow modifying the flow field with an electric field to affect the flame and its heat-release. An alternative version is shown in FIG. 18. where the electrodes have been incorporated as positive-negative pairs into the combustor housing (“dome”).

[0064] An example of adding electrodes to an afterburner is shown in FIG. 19. Here, the electrodes have been incorporated in the vapor gutter (“v-gutter”) flame stabilizers. The required positive and negative electrodes could be located around the v-gutter with a regular spacing or mounted in positive / negative electrode pairs. The specific geometry of the electrodes would depend on the application but would be similar to the elementary shapes shown in FIGS. 15A-15F. The addition of these electrodes would allow electrical adjustability of the flow field and subsequent flame stabilization in applications which currently have no adjustability.

[0065] vi. Varying the Heat-Release

[0066] The sections above discussed the mechanism of creating an EHD bluff-body and different electrode configurations to achieve it. A primary reason for creating an EHD bluff-body is to alter the flame heat-release. Being able to alter the flame heat-release by the electric field allows suppressing adverse combustion dynamics such as thermoacoustic instabilities. One example method for varying the heat-release is presented below.70476-02

[0067] As shown in FIG.20A, the flame surface encloses a certain volume, ^. Forming an EHD bluff-body with the electric field significantly alters the flame shape and reduces the volume enclosed by the flame surface, as shown in FIG. 20B. During the transition to the new flame shape, the volume difference between the two shapes is consumed, adding to the flame heat-release. In our previous disclosure, a control volume analysis was used to model this change, with the final relationship being: ^^(^) = −ℎ ^^(^)^^6 ^^(“Equation 13”) where ^^(^)from the mean value, ℎ^is the heat of combustion of the reactant mixture, ^6is the mixture density, and ^(^) is the time-varying volume enclosed by the flame surface. The heat-release deviation from the mean value is defined as: ^^(^) = ^(^) − ^^(“Equation 14”) where ^(^) is the instantaneous heat-release and ^^ is the time-averaged heat-release. Thus, if the control volume is reduced (^^^^ < 0), the heat-release brieflyincreases (^^(^) > 0). Alternatively, eliminating the EHD bluff-body to let the flamereturn to the shape of (A) will increase the control volume and cause a brief decrease of the heat-release.

[0068] Multiple EHD bluff bodies can be progressively engaged to incrementally reduce the flame volume, as depicted in FIG. 21 and shown implemented on the prototype burner images of FIG. 22. The number of EHD bluff bodies is increased by switching more electrodes to a negative voltage to become cathodes. An EHD bluff body forms over each negative electrode and a heat release event will occur with each flame shape transition. The use of multiple EHD points to incrementally reduce the control volume produces a better relationship between the applied electric field and heat release. The improved relationship will directly affect the ability to suppress thermoacoustic instabilities by forcing the flame heat release.

[0069] Accordingly, the concepts shown and described within the present disclosure advance the EHD bluff body concept by incorporating knowledge about the electric field and charge density to allow improved anode and cathode designs. A practical70476-02 benefit of the adjacent electrode configuration is the removal of any electrodes from the hot exhaust gases, where the electrode could erode away with use in some applications. The adjacent electrode configuration also has all of the electrodes moved to the same location (e.g., at the burner face), which would allow more compact electrode / burner designs and reduce the assembly cost and complexity. Reducing the total part count of the system also helps with making this method a retrofit for devices already in the field.

[0070] In addition to the hardware design improvements described, a method (300) is also provided in FIG. 23 for modulating the internal volume of the flame to modulate the flame heat release. This is a critical requirement for the application of thermoacoustic instability suppression. The method (300) for using the adjacent electrode configuration to stabilize the flame from one or multiple EHD bluff bodies includes various steps such as, at step (302), positioning a set of “adjacent” electrodes at the burner outlet as described in the present disclosure. At step (304), the method (300) includes setting at least one electrode to a negative voltage and at least one electrode, or all remaining electrodes, to a positive voltage. At step (306), which may optionally be carried out before step (304), the fuel of the burner can be ignited to generate a flame. At step (308), the method (300) includes accelerating the ions from the flame, via the electric field, to create EHD bluff-bodies at the negative electrode(s). Thereafter, at step (310), the flame is stabilized in the low-velocity regions created by the EHD bluff-bodies.

[0071] Optionally, at step (312) the number of EHD bluff-bodies may be modified or their positions modified by changing, via the controller (e.g., automatically or manually), which electrodes are provided a positive voltage and which are provided with a negative voltage. For example, to increase the number of EHD bluff-bodies, an additional electrode may be switched at the burner outlet from a positive to a negative voltage. For example, this step may include measuring an acoustic characteristic of the burner, comparing the acoustic characteristic to a pre-determined acoustic characteristic, based upon the comparison, selectively modifying which electrodes are provided a positive voltage and which are provided with a negative voltage to modify a heat-release of the flame.

[0072] While examples, one or more representative embodiments and specific forms of the disclosure have been illustrated and described in detail in the drawings and70476-02 foregoing description, the same is to be considered as illustrative and not restrictive or limiting. The description of particular features in one embodiment does not imply that those particular features are necessarily limited to that one embodiment. Some or all of the features of one embodiment can be used in combination with some or all of the features of other embodiments as would be understood by one of ordinary skill in the art, whether or not explicitly described as such. One or more exemplary embodiments have been shown and described, and all changes and modifications that come within the spirit of the disclosure are desired to be protected.

Claims

70476-02 CLAIMS I / we claim:

1. An apparatus, comprising: (a) a combustion burner configured to output a flame and a gas flow from a face of the burner, wherein the gas flow defines a gas flow path in a direction away from the burner; (b) a plurality of conductive elements positioned at the face of the burner; and (c) a positive electrode and a negative electrode each coupled with a power source, wherein the positive electrode is electrically coupled with at least one conductive element and the negative electrode is electrically coupled with at least one different conductive element, wherein the positive electrode and the negative electrode are configured to generate an electric field horizontally across the face of the burner between the at least one and the at least one different conductive elements, wherein at least a portion of the electric field is oriented perpendicular to the gas flow path; wherein the power source is configured to generate the electric field to form at least one flame root defined by the flame.

2. The apparatus of claim 1, wherein the power source is configured to selectively modify which conductive elements of the plurality of conductive elements couple with the positive and negative electrodes to therefore selectively increase or decrease a quantity of the at least one flame root.

3. The apparatus of claim 1, wherein the plurality of conductive elements positioned at the face of the burner includes a plurality of planar plates spanning across the face of the burner, wherein each planar plate is arranged in parallel and oriented on a plane defined perpendicular to the face of the burner.

4. The apparatus of claim 3, wherein the positive electrode is coupled with at least two planar plates and the negative electrode is coupled with at least one planar plate, wherein70476-02 the planar plate coupled with the negative electrode is positioned in between the planar plates coupled with the positive electrode.

5. The apparatus of claim 1, wherein the plurality of conductive elements positioned at the face of the burner includes a plurality of conductive wires spanning across the face of the burner, wherein each conductive wire is arranged in parallel and oriented along a plane defined perpendicular to the face of the burner.

6. The apparatus of claim 5, wherein the positive electrode is coupled with at least two conductive wires and the negative electrode is coupled with at least one conductive wire, wherein the conductive wire coupled with the negative electrode is positioned in between the conductive wires coupled with the positive electrode.

7. The apparatus of claim 1, wherein the plurality of conductive elements at the face of the burner includes a conductive element positioned around a perimeter of the face of the burner and a conductive element positioned across the face of the burner.

8. The apparatus of claim 7, wherein the positive electrode is coupled with the conductive element positioned around a perimeter of the face of the burner and the negative electrode is coupled with the conductive element positioned across the face of the burner.

9. The apparatus of claim 1, wherein the plurality of conductive elements at the face of the burner includes a conductive element positioned around a perimeter of the face of the burner and a conductive pin element positioned inside the perimeter of the face of the burner.

10. The apparatus of claim 9, wherein the positive electrode is coupled with the conductive element positioned around a perimeter of the face of the burner and the negative electrode is coupled with the conductive pin element positioned inside the perimeter of the face of the burner.

11. The apparatus of claim 1, wherein the plurality of conductive elements at the face of the burner includes a series of conductive plates affixed to an interior surface spanning70476-02 around a perimeter defined by the face of the burner.

12. The apparatus of claim 1, comprising an insulative substrate across the face of the burner, wherein the plurality of conductive elements positioned at the face of the burner are arranged across a surface of the insulative substrate.

13. A method of operating a combustion burner to affect a heat-release of the combustion burner, wherein the combustion burner is configured to output a flame and a gas flow from a face of the burner defining a gas flow path in a direction away from the burner, wherein a plurality of conductive elements are positioned at the face of the burner, a positive electrode is coupled with at least one conductive element, and a negative electrode is coupled with at least one conductive element, the method comprising: (a) generating a flame from the burner; (b) generating an electric field between two conductive elements of the plurality of conductive elements; (c) forming at least one electrohydrodynamic bluff-body via the two conductive elements based upon the electric field; (d) generating a first flame root based upon the electrohydrodynamic bluff- body; and (e) increasing a strength of the electric field to generate a second flame root based upon the electrohydrodynamic bluff-body.

14. The method of claim 13, wherein generating the electric field between the positive electrode and the negative electrode includes generating the electric field in an orientation perpendicular to the gas flow path.

15. The method of claim 13, comprising: (a) generating a second electric field between two different conductive elements of the plurality of conductive elements; and (b) forming a second electrohydrodynamic bluff-body via the two different conductive elements based upon the electric field.

16. A method of operating a combustion burner, wherein the combustion burner is70476-02 configured to output a flame and a gas flow from a face of the burner defining a gas flow path in a direction away from the burner, wherein a plurality of conductive elements are positioned adjacent to the face of the burner, a negative electrode is coupled with at least one conductive element and a positive electrode is coupled with the remaining conductive elements, the method comprising: (a) generating a flame from the burner; (b) applying a first electric field between a first and second conductive element of the plurality of conductive elements; (c) measuring an acoustic characteristic of the burner; (d) comparing the acoustic characteristic to a pre-determined acoustic characteristic; and (e) based upon the comparison, selectively modifying at least one conductive element from a positive voltage to a negative voltage to form a second electric field.

17. The method of claim 16, wherein applying the first electric field between the first and second conductive element includes: (a) forming a first electrohydrodynamic bluff-body; (b) generating a first flame root based upon the electrohydrodynamic bluff- body.

18. The method of claim 16, wherein selectively modifying the at least one conductive element from the positive voltage to the negative voltage to form the second electric field includes: (a) forming a second electrohydrodynamic bluff-body; (b) generating a second flame root based upon the second electrohydrodynamic bluff-body.

19. The method of claim 16, wherein the acoustic characteristic includes an acoustic pressure.

20. The method of claim 16, wherein the first electric field is oriented perpendicular70476-02 to the gas flow path.

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