WO2016140681A1

WO2016140681A1 - APPLICATION OF ELECTRIC FIELDS TO CONTROL CO AND NOx GENERATION IN A COMBUSTION REACTION

Info

Publication number: WO2016140681A1
Application number: PCT/US2015/019019
Authority: WO
Inventors: Joseph Colannino; David B. Goodson; Thomas S. Hartwick
Original assignee: Clearsign Combustion Corp
Current assignee: Clearsign Technologies Corp
Priority date: 2015-03-05
Filing date: 2015-03-05
Publication date: 2016-09-09
Anticipated expiration: 2017-09-05

Abstract

An apparatus comprises a reaction volume, a reactant or fuel nozzle, an oxidizer introducer, a sensor, a controller, and electrodes. The controller may comprise a power controller, a microcontroller, a sensor interface, a waveform generator, and amplifiers connected to the electrodes. The controller may control an electric current to the electrodes and produce an electric field proximate to a combustion boundary. The electric field may influence the movement of charged species in the reaction volume. The sensors may provide information to the controller, which information the controller may use to change parameters such as the rate of introduction of the reactant and/or oxidizer and/or of parameters of the electric current and electric field, such as the waveform of the electric current, the voltage of the electric current, the location of the electric field within the reaction volume. Reduction in undesirable reaction products may thereby be achieved.

Description

APPLICATION OF ELECTRIC FIELDS TO

CONTROL CO AND NOx GENERATION IN A

COMBUSTION REACTION

BACKGROUND

In an oxidation reaction such as a combustion reaction, diffusion mass transfer limitations that characterize laminar and/or conventional turbulent flow may give rise to reactant and oxidizer concentration gradients within a reaction volume. The concentration gradients may, in turn, cause temperature gradients in the reaction. One or more alternative reactions may be favored or disfavored as a function of temperature and/or concentration. For example, oxides of nitrogen (NOx) may tend to form in high temperature combustion (oxidation) reactions. In another example, a combustion reaction may tend to output carbon monoxide (CO) in regions that are cool and/or that are characterized by low oxygen concentration arising from poor mixing.

Moreover, naturally occurring collision frequencies between reactants, oxidizers, and reaction intermediates may, under conventional reaction conditions, result in relatively narrow concentration ranges under which a reaction is self-sustaining.

FIG. 1 is a diagram of an oxidation reaction 101 including a conventional diffusion flame 102, which is a familiar example of a mass transfer-limited oxidation reaction under laminar flow conditions. Similar considerations may apply under turbulent flow conditions. Similar considerations may apply in premixed reactants and/or premixed reactant/oxidizer combinations. In the reaction 101 , the flame 102 may be surrounded by air 104. Fuels in various forms, such as gaseous (hydrogen, natural gas, methane, ethane, propane, butane), liquids (fuel oils), or solids (coal, biomass, vaporized hydrocarbons and waxes) may typically be fed into the base of the flame and may form an oxygen- poor region 106 near the center of the flame 102. A peripheral region 107 of the flame 102 adjacent to the surrounding air 104 may tend to exhibit the highest reaction rate, and hence may tend to be at a higher temperature than other regions of the flame 102.

FIG. 2 is a graphical depiction of certain effects described herein. An illustrative temperature distribution of a conventional diffusion flame (or other mass transfer-limited oxidation reaction) is shown as curve 201 . The

temperature distribution is plotted as a number N as moles or differential volumes of reactants on the Y-axis vs. local temperature T on the X-axis. Various distributions may be contemplated. Model Boltzmann distributions are shown in FIG. 2 as representative of possible temperature distributions.

Generally, an area 204 under the high temperature tail of the distribution 201 corresponding to a temperature higher than T_Nox may have a relatively high probability of producing NOx, and may be responsible for the vast majority of all NOx produced by the combustion reaction.

The reason for this may be envisioned by reference to FIG. 3, which shows a concentration of oxides of nitrogen ([NOx]) produced in a combustion reaction in air as a function of temperature T. As may be seen, very little NOx may be produced below the temperature T_Nox, while a relatively high

concentration of NOx may be produced above the temperature T_Nox-

With respect to NOx, three primary mechanisms are important to evolution as a combustion product. The Zeldovich NOx mechanism is exponentially related to temperature such that, ceteris paribus, higher temperatures produce exponentially more NOx. The Fenimore mechanism occurs in fuel rich regions and is dependent on various species concentrations. The fuel-bound mechanism requires nitrogen incorporated as part of the fuel structure. The ultimate conversion of NOx in this latter mechanism depends on the availability of oxygen to react with nitrogenous species. In all cases, species concentrations and/or temperatures play an important role. Therefore, any strategy that alters time- concentration relations in the combustion reaction can potentially affect NOx.

Referring to CO oxidation, CO is oxidized most immediately by the presence of OH. Therefore, increasing the contact of CO and OH increases the oxidation and destruction of CO to CO2. NOx and CO are considered criteria pollutants by the Environmental Protection Agency.

Complete combustion is generally effected by causing sufficient mixing of fuel and oxidizer at sufficient temperatures. Practically speaking, sufficient mixing requires an excess of combustion air as indicated by some amount of oxygen above 0% in the flue gas termed "excess oxygen." For gaseous fuels, 3% excess oxygen is common, while liquid fuels generally require 3-5% excess oxygen, and solid fuels such as coal, require >5% excess oxygen. Thus, any method that increases mixing of the fuel and air has the potential to reduce excess oxygen requirements or improve combustion efficiency at a given excess oxygen concentration. A reduced excess oxygen requirement also lowers parasitic load requirements for air handling equipment such as fans and blowers. Excess oxygen also represents additional heat rejected into the environment as the mass flow of the flue gas products is reduced when excess oxygen is reduced.

In the case of sulfur, SO2 is the normal product of combustion. However other species such as SO3 can be more easily removed by post combustion processes. The actual oxidation state of the sulfur is affected by contact and degree of mixing with oxygen.

There is a need for an apparatus and method for controlling reaction products and byproducts evolved by an oxidation reaction.

SUMMARY

According to an embodiment, an apparatus includes a reaction volume, reactant or fuel nozzle, an oxidizer introducer, a sensor, a controller, and electrodes. The controller may include a power controller, a microcontroller, a sensor interface, a waveform generator, and amplifiers connected to the electrodes. The controller may control an electric current or electrical voltage delivered to the electrodes. The electrodes, in turn, produce an electric field proximate to a reaction boundary within the reaction volume, such as a combustion boundary. The electric field may influence the movement of charged species in the reactant, the oxidizer, and/or reaction intermediates. The sensors may provide information to the controller that the controller may use to practice a method to change parameters such as the rate of introduction of the reactant and/or oxidizer and/or of parameters of the electric current and electric field, such as the waveform of the electric current, the voltage of the electric current, the location(s) at which the electric field is introduced within the reaction volume, and location and/or movement of the electric field within the reaction volume. The method may be practiced to change the production of undesirable species in the reaction product, such as CO, SOx, and NOx, among others.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an oxidation reaction including a conventional diffusion flame, according to the prior art.

FIG. 2 is a diagram of a temperature distribution in the diffusion flame of

FIG. 1 , compared to corresponding temperature distributions influenced by embodiments described herein.

FIG. 3 is a diagram showing production of oxides of nitrogen (NOx) as a function of temperature, according to an embodiment.

FIG. 4A is a block diagram of an apparatus for supporting a combustion reaction and controlling output of combustion products by a combustion reaction, according to an embodiment.

FIG. 4B is a block diagram of an apparatus for supporting a combustion reaction and controlling output of combustion products by a combustion reaction, according to another embodiment. FIG. 5 is a flow chart showing a method for selecting a product mixture in a gas phase oxidation reaction, according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the

accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.

FIG. 2 is a diagram 200 of a temperature distribution 201 in the diffusion flame of FIG. 1 , compared to corresponding temperature distributions 203 influenced by embodiments described herein. As may be appreciated, enhanced mixing in the oxidation reaction may tend to reduce hot spots {e.g., 204) and cold spots in the reaction. Instead, electric fields may be used to mix moieties in a combustion volume and create a more uniform temperature distribution, conceptually illustrated by curve 203.

FIG. 3 is an illustrative diagram showing a concentration of oxides of nitrogen (NOx) evolved from a combustion reaction as a function of temperature. As may be seen, NOx is typically formed at higher temperatures. The higher temperatures under which NOx is formed may tend to occur at regions of greatest temperature in a non-homogenized flame. Even a small reduction in the volume or portion of a flame that is at higher than average temperatures, may result in significant decreases in NOx production.

FIG. 4A is a schematic diagram of a combustion system 400 configured to support a combustion and/or oxidation reaction in a reaction volume 401 , according to an embodiment. The system 400 includes a fuel source 405 configured to introduce at least one reactant into the volume 401 . The reactant may be a fuel which may be solid, liquid, gas, powder and/or other molecular species volatilized, vaporized, sublimated, or otherwise obtained from a gaseous, liquid or solid fuel. Fuel examples include, without limitation, hydrogen, coal, coal dust, propane, ethane, natural gas, butane, gasoline, diesel, bunker oil, jet fuel, or other petrochemical, hydrocarbon, or analogous compounds. Reactants such as bunker oil or coal may contain sulfur. The reactant may be introduced into the reaction volume by a fuel nozzle or grate 405. The fuel nozzle or grate 405 may be connected to a fuel delivery system (not shown).

An oxidizer may be introduced in proximity to the reactant. The oxidizer may be provided by oxygen in the air and/or from an oxidizer introduction channel (not shown). The reactant and oxidizer may be premixed. The reactant, oxidizer, reaction intermediates, and reaction products (also called "exhaust") may comprise charged particles, molecules, and/or atoms. The reactant, oxidizer, and reaction may be configured to impart a mass flow along a reaction axis (generally upward in the example shown in FIG. 4A).

The system 400 may have a refractory or cooled wall 406, for example in the shape of a cylinder, a Venturi tube, or another shape, that defines the volume 401 ; with an air inlet 408 and an air and exhaust outlet 410. The air inlet and/or oxidizer introduction channel and/or fuel nozzle 405 may be variable, to vary the introduction of reactant and oxidizer to the reaction. The reaction volume 401 may be and/or may be part of a combustion chamber for a furnace, a turbine engine, or for another context in which a combustion chamber is utilized. A flame holder (not shown) may be disposed in the reaction volume 401 and configured to hold the reaction at one or more locations in the reaction volume. The combustion system 400 may further include a reaction initiator (not shown), such as a spark generator, a pilot light, a flare, a glow plug, or similar. The reaction initiator may be utilized to initiate the reaction. The nozzle, grate, fuel delivery system, air inlet, and/or oxidizer introduction channel 405 may be utilized to vary the rate of introduction of the reactant and the oxidizer to the reaction. The rate of introduction of the reactant and the oxidizer may be varied separately. A controller 412 may be configured to control a fuel valve, a blower, dampers or another component to vary the introduction rates of reactant and oxidizer.

As shown in FIG. 4A, electrodes 414 are present in, or in proximity to, the reaction volume 401 . The electrodes 414 may be arranged in one or more pairs and/or may be arranged in a matrix wherein pairing is determined by the controller 412. Spacing of the electrodes 414 relative to other electrodes 414 may be determined by the driving voltage, conductivity of the reactants, reaction intermediates, and products, and by the desired electric field and amount of mixing desired. The electrodes 414 may be located on or in the refractory wall 406. The electrodes 414 may be located adjacent to the reaction volume. The electrodes 414 may be located in or proximate to a flame anchor. The electrodes 414 may be reversible and driven by an alternating current, producing a periodic or modulated electric field, or may comprise dedicated anode and cathode electrodes driven by a direct current. In an embodiment, one electrode may be coupled to a voltage driver 416, and another electrode may be continuously coupled to voltage ground. The voltage driver 416 and electrode(s) 414 can cooperate to produce a periodic electric field formed between the electrodes 414. More than one electrode 414 may be utilized, with the active electrodes being varied. Two or more electrodes may form an electric field at least partly between the two or more electrodes. A conductive structure such as the fuel source 405 can optionally be grounded to form a counter-electrode relative to the driven electrode 414. Alternatively, a structure such as the fuel source 405 can be electrically insulated or isolated from voltage ground, and can be driven by the voltage driver 416 to act as the electrode 414. A counter electrode 414 or other grounded structure in the system 400 (acting as a counter electrode) can cooperate with the driven structure 405 to create the electric field.

FIG. 4B is a block diagram of an apparatus 402 configured to support a combustion reaction and control the output of combustion products from the combustion reaction according to another embodiment. As shown in FIG. 4B, a charge electrode 404 is configured to impart a voltage onto the combustion reaction. The charge electrode 404 can be immersed in, and therefore in electrical continuity with the flame. Alternatively, the charge electrode 404 can be in the form of an ionizer configured to deliver a stream of charged particles to the flame without being in actual electrical continuity with the flame. In the case of apparatuses 402 that include a charge electrode, the flame itself can be electrically insulated or isolated from voltage ground. By so doing, the flame forms an electrical potential relative to another electrode 414 and thus forms an electric field therebetween.

Other aspects of the embodiments 400 and 402 of FIGS. 4A and 4B can operate similarly to one another as described herein.

As shown in FIGS. 4A and 4B, a controller 412 may control a voltage driving the electrodes 414. The controller 412 is depicted as including a microcontroller 418, a data interface 420, a sensor interface 422, a waveform generator 424, and one or more voltage drivers 416. The waveform generator 424 may generate a modulated and/or periodic signal, which may comprise one or more modulated voltage waveforms that may be converted and/or amplified by the voltage drivers 416 into a modulated voltage signal. A modulated voltage signal may be output or emitted by the electrodes 403 as an electric field. The waveform generator 424 may include a state machine configured to output the modulated voltage waveforms responsive to waveform data. The waveform data may be provided by the controller 412. The waveform generator 424 may include a field programmable gate array ("FPGA"). The waveform generator 424 may include a sine, a cosine, or a sine and cosine synthesizer or other waveforms such as square, triangular, sawtooth, or complex composite waveforms. The waveform generator 424 may include one or more resistive- capacitive ("RC") circuits (not shown) configured to apply slew to the one or more voltage waveforms. The waveform output by the waveform generator 424 may be analog or digital.

The microcontroller 418 may control the waveform generator 424 and/or the voltage drivers 416. The microcontroller 418 may control the waveform generator 424 by selecting or loading the one or more modulated voltage waveforms generated by the waveform generator 424. The microcontroller 418 may control the voltage drivers 416 by selecting gain of the one or more voltage drivers 416 and/or by selecting a number of amplifier stages applied to amplify the modulated voltage waveform(s) to form the modulated voltage signal(s).

The microcontroller 418 may communicate with the one or more sensors 426 via one or more sensor interfaces 422. The sensors 426 may sense a characteristic of the reaction and/or reaction volume 401 , such as a temperature, luminosity, acoustic response, concentration of NOx, concentration of CO, concentration of SOx, humidity, electrical resistance, magnetic field, and/or electric field strength. Information received from the sensor(s) 426 may be used by the microcontroller 418 as the microcontroller selects one or more

characteristics or parameters of the modulated voltage signal, thus providing a feedback loop. Alternatively, the microcontroller 418 may cooperate with the sensor(s) 426 to provide a feed-forward control loop. Control may be performed according to fuzzy logic, Boolean logic, Bayesian logic, proportional-integral- differential (PID) control, other approaches, or combinations thereof. The modulated electric field produced by or at the electrodes 414 may be an AC voltage of about 1 to 1 ,000,000 volts per meter between electrodes adjacent to or within the reaction volume 401 at a frequency of about 1 to 100 KHz. According to an embodiment, the AC voltage may be about 75,000 volts per meter at about 15 KHz, and may be varied in frequency and duty cycle. The modulated electric field may be produced by applying an AC voltage to the electrodes 414 along at least one axis different than the reaction axis. The at least one axis different than the reaction axis may be substantially orthogonal to the reaction axis. The microcontroller 418 may control which electrode(s) 414 emit an electric field, optionally as a function of time. More than one electrode 414 may be arranged along a reaction axis.

The electric field produced by the electrodes 414 influences the movement of charged species in particles, molecules, and atoms in the reactants, reaction intermediates, and/or reaction product. Modulating the electric field may thereby promote mixing of the reactants, oxidizer(s), intermediates, and/or reaction products. Optionally, the electric field may slow or speed motion of charged species (and via momentum transfer, uncharged species) through all or part of the reaction volume 401 . The reduction in one or more of output of NOx, CO, or SOx by the combustion reaction may be caused at least in part by increasing collisions between reactants and/or intermediates that react to output carbon dioxide (CO₂), by reducing differences in temperature within the reaction volume 401 , and/or by homogenizing concentrations of reactants within the reaction volume 401 .

An example of a reaction that produces NOx is as follows:

Ο· + N₂ -> NO + Ν· + energy

2Ν· + O₂ -> 2NO + energy

N₂ + O₂ -» 2NO + energy

A rate of reaction formula is as follows:

d[NOx]/dt = A e^{"b T} [N₂][O₂]^{1 2}

The modulating electric field may be selected to smooth the temperature distribution across the reaction volume 401 , reduce the peak temperature across the reaction volume 401 , increase the minimum temperature across the reaction volume 401 , decrease the number of moles of reactant and/or reactant intermediates which traverse the reaction volume 401 at a lower temperature, and/or reduce a rate of reaction that occurs at one or more extremes of temperature.

Oxygen radicals, which may convert CO or other carbon-containing species to CO₂ and convert NO and NOx to N₂ and O₂, may be formed by oxidation of hydrocarbons and may be present in reaction intermediates.

The modulated electric field may thereby be selected to reduce the production of NOx, CO, and other charged species, reduce a rate of reaction that occurs at one or more extremes of temperature, reduce temperature differences within the oxidation reaction to cause one or more of i) a decrease in output of oxides of nitrogen (NOx), ii) a decrease in output of carbon monoxide (CO), iii) a decrease in output of oxides of sulfur (SOx). After the reaction is initiated and a modulated electric field applied, a concentration of a reactant and/or an oxidizer may be changed to a concentration outside a range that would sustain the reaction without applying the modulated electric field. The modulated electric field may be selected to substantially eliminate the presence of a visible reaction boundary and/or a visible flame.

As shown in FIG. 5, the systems shown in FIGS. 4A and 4B may initiate a reaction and practice a method wherein a waveform and voltage may be established in step 501 . At step 503 the microcontroller and/or waveform generator may then drive the electrodes to homogenize the flame or reaction temperature. At step 505 the sensors may then sense a characteristic within the reaction volume and communicate this to the microcontroller. At step 507 the microcontroller may make a determination regarding whether to change a characteristic or parameter of the waveform and/or the electric field output by the electrodes. If the microcontroller determines that no change is to be made, the method may return to step 503. If the microcontroller determines that a change is to be made, the method may return to step 501 and implement parameters of the changed waveform and voltage.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein 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

CLAIMS What is claimed is:

1 . A method for selecting a product mixture in a gas-phase oxidation reaction, comprising:

providing a first reactant to a reaction volume;

providing an oxidizer to the reaction volume;

supporting an oxidation reaction between the first reactant and the oxidizer in the reaction volume to produce charged reaction intermediates; and applying a modulated electric field to the reaction volume and the charged reaction intermediates, the modulated electric field being selected to promote at least first reactant and oxidizer mixing;

wherein the mixing causes one or more of a reduction in temperature differences within the oxidation reaction, a change in species concentration differences within the oxidation reaction, or a reduction in excess oxygen requirement, compared to not applying the modulated electric field.

2. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein providing the first reactant includes providing at least one fuel.

3. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein providing the first reactant includes providing a solid fuel.

4. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein providing the first reactant includes providing a liquid fuel.

5. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein providing the oxidizer includes providing air including oxygen.

6. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein the oxidation reaction is a combustion reaction.

7. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , further comprising:

initiating the oxidation reaction.

8. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 7, further comprising:

after initiating the oxidation reaction, changing a concentration of the first reactant to a concentration outside a range of first reactant concentrations that would sustain the oxidation reaction without applying the modulated electric field.

9. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 7, further comprising:

after initiating the oxidation reaction, changing a concentration of the oxidizer to a concentration outside a range of oxidizer concentrations that would sustain the oxidation reaction without applying the modulated electric field.

10. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , further comprising:

providing at least one flame holder to anchor the oxidation reaction at one or more locations in the reaction volume.

1 1 . The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein in applying a modulated electric field to the reaction volume and the charged reaction intermediates, the modulated electric field is also selected to substantially eliminate the presence of a visible reaction boundary.

12. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein the oxidation reaction includes a combustion reaction; and

wherein in applying a modulated electric field to the reaction volume and the charged reaction intermediates, the modulated electric field is also selected to substantially eliminate the presence of a visible flame.

13. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein the reduction in temperature differences within the oxidation reaction includes reducing a rate of reaction that occurs at one or more extremes of temperature.

14. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein the reduction in temperature differences within the oxidation reaction includes reducing peak temperature.

15. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein the reaction volume includes nitrogen; and

wherein the reduction in temperature differences within the oxidation reaction causes a decrease in output of oxides of nitrogen (NOx).

16. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein the reduction in temperature differences within the oxidation reaction causes a decrease in output of carbon monoxide (CO).

17. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , applying a modulated electric field to the reaction volume and the charged reaction intermediates, the modulated electric field being selected to promote at least first reactant and oxidizer mixing causes a decrease in output of carbon monoxide (CO).

18. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein the reaction volume includes sulfur; and

wherein applying a modulated electric field to the reaction volume and the charged reaction intermediates, the modulated electric field being selected to promote at least first reactant and oxidizer mixing causes a decrease in output of oxides of sulfur (SOx).

19. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein providing the first reactant and providing the oxidizer includes imparting a mass flow along a reaction axis; and

wherein applying the modulated electric field includes applying an AC voltage along at least one axis different than the reaction axis.

20. The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein providing the first reactant and providing the oxidizer includes imparting a mass flow along a reaction axis; and

wherein applying the modulated electric field includes applying an AC voltage along at least one axis substantially orthogonal to the reaction axis.

21 . The method for selecting a product mixture in a gas-phase oxidation reaction of claim 1 , wherein applying the modulated electric field includes applying an AC voltage of about 75,000 volts per meter between electrodes adjacent to the reaction volume at a frequency of about 15 KHz.

22. An apparatus for controlling output of combustion products by a

combustion reaction, comprising:

a controller configured to output one or more modulated voltage signals; and

one or more electrodes operatively coupled to the controller and configured to apply a modulated electric field corresponding to the one or more modulated voltage signals within a reaction volume; wherein the one or more modulated voltage signals and the modulated electric field are selected to cause periodic movement of charged species within the reaction volume;

wherein the periodic movement of the charged species is selected to cause mixing of combustion reactants; and

wherein the mixing of the combustion reactants is selected to reduce one or more of output of oxides of nitrogen (NOx), output of carbon monoxide (CO), or output of oxides of sulfur (SOx) by the combustion reaction.

23. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, wherein the one or more electrodes includes one electrode and the periodic electric field is formed between the one electrode and image charges formed responsive to a voltage carried by the one electrode.

24. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, wherein the one or more electrodes includes two or more electrodes and the electric field is formed at least partly between the two or more electrodes.

25. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, wherein the one or more electrodes are located within the reaction volume.

26. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, wherein the one or more electrodes are located adjacent to the reaction volume.

27. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, wherein the reduction in one or more of output of NOx, output of CO, or output of SOx by the combustion reaction is caused at least in part by increasing collisions between at least one of reactants, reaction intermediates, or reactants and reaction intermediates that react to output carbon dioxide (CO₂).

28. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, wherein the reduction in one or more of output of NOx, output of CO, or output of SOx by the combustion reaction is caused at least in part by reducing differences in temperature within the reaction volume.

29. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, wherein the reduction in one or more of output of NOx, output of CO, or output of SOx by the combustion reaction is caused at least in part by homogenizing concentrations of reactants within the reaction volume.

30. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, further comprising:

a refractory wall defining the reaction volume.

31 . The apparatus for controlling output of combustion products by a combustion reaction of claim 22, further comprising:

a fuel nozzle or grate configured to provide fuel to the combustion reaction

32. The apparatus for controlling output of combustion products by a combustion reaction of claim 31 , further comprising:

a fuel delivery system configured to supply fuel to the fuel nozzle or grate.

33. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, wherein the controller further comprises:

a waveform generator configured to generate one or more modulated voltage waveforms; and one or more amplifiers configured to amplify the one or more modulated voltage waveforms to form the one or more modulated voltage signals.

34. The apparatus for controlling output of combustion products by a combustion reaction of claim 33, wherein the controller further comprises:

a microcontroller configured to select or load the one or more modulated voltage waveforms generated by the waveform generator.

35. The apparatus for controlling output of combustion products by a combustion reaction of claim 33, wherein the controller further comprises:

a microcontroller configured to select gain of the one or more amplifiers.

36. The apparatus for controlling output of combustion products by a combustion reaction of claim 33, wherein the controller further comprises:

a microcontroller configured to select a number of amplifier stages applied to amplify the at least one modulated voltage waveform to form the at least one modulated voltage signal.

37. The apparatus for controlling output of combustion products by a combustion reaction of claim 33, wherein the controller further comprises:

a data interface operatively coupled to the microcontroller and configured to receive commands to cause the microcontroller to select one or more modulated voltage signal parameters or characteristics.

38. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, further comprising:

a sensor configured to sense a characteristic of the combustion reaction; wherein the controller further comprises a microcontroller operatively coupled to the sensor and configured to select one or more parameters or characteristics of the modulated voltage signal responsive to the sensed characteristic.

39. The apparatus for controlling output of combustion products by a combustion reaction of claim 38, wherein the sensor is configured to measure one or more of combustion temperature, combustion luminosity, concentration of NOx, concentration of CO, and concentration of SOx.

40. The apparatus for controlling output of combustion products by a combustion reaction of claim 22, wherein the modulated electric field includes an AC voltage between 1 and 1 ,000,000 volts per meter between electrodes adjacent to or within the reaction volume at a frequency between about 1 and 100 KHz.

41 . The apparatus for controlling output of combustion products by a combustion reaction of claim 40, wherein the modulated electric field includes an AC voltage of about 75,000 volts per meter between electrodes adjacent to or within the reaction volume at a frequency of about 15 KHz.