Fuel combustion device

Abstract

The invention relates to a fuel combustion device (1) for the combustion of fuels in an exothermic chemical reaction, comprising a device (2) for supplying the fuels, a combustion chamber for combustion of the supplied fuels in a flame (10) and at least two electrodes (5, 9) through which an electrical field (E) is applied to the flame (10) with the purpose of producing a reaction plasma in said flame (10), wherein the reaction plasma produced has a high degree of ionization.

Description

The invention relates to a fuel combustion apparatus for combustion of fuels in an exothermic chemical reaction.

The combustion is a chemical reaction (oxidation) of fuels with oxygen from the air, with heat being released. Hydrocarbons react to form carbon dioxide CO₂, and water vapor H₂O. The combustion of solid fuels is initiated by heating to an ignition temperature, while the combustion of liquid fuels is brought about by intermediate gassing by the ignition limit being instantaneously exceeded by means of an ignition spark. In the case of gaseous fuels, the combustion is induced by means of an ignition spark by the ignition limit instantaneously being exceeded. The combustion process results in exhaust gases. The quality of the combustion can be assessed from the composition of the exhaust gases. In the conventional sense, combustion is an exothermic redox reaction which has a plasma appearance and takes place with electromagnetic radiation being emitted, such as light and thermal radiation. In chemistry, oxidation is a chemical process in which a particle emits electrons. The emitted electrons are absorbed by other particles, for example oxygen and chlorine atoms. This process is referred to as reduction. Every oxidation process is coupled to a reduction process. The reactions on which an electron transfer such as this are based are referred to as redox reactions. Energy is involved in all chemical reactions. Relatively high-energy systems change to relatively low-energy systems with energy being released. Conversely, relatively low-energy systems are changed into relatively high-energy systems with energy being consumed. If thermal energy is released during a reaction, then this is referred to as an exothermic reaction. Conversely, if energy is absorbed, then this is an endothermic reaction. While some substances, for example charcoal, only glow during combustion, other fuels, such as wood, gasoline or gas, form a flame.

A candle flame has three brightness zones. Internally, the flame contains a dark core which is surrounded by a luminous yellow envelope. The luminous yellow envelope is generally surrounded by a blue flame band. The relatively cool core contains the unburnt vapors from the solid substance. A vapor is generally the gas phase of a substance which is solid or liquid at room temperature. These vapors are decomposed in the flame envelope to form burnt gases and fine carbon particles which glow brightly and emit light. These carbon particles burn only when air enters the outermost flame band, without any impediment. The flame band forms the hottest part of the flame. A flame is thus a burning gas flow, with the brightness of the flame being caused by glowing solid particles. Flames thus burn all combustible gases as well as those liquids and solids which develop combustible vapors or gaseous decomposition products above the ignition temperature. Flames have a different electrical resistance at the flame envelope than the surrounding gas. The flame envelope is able to transport electrical charges. A conventional flame is a thermal ionization phenomenon which can be derived from Brownian molecular motion.

The capability of flames to transport electrical charges is used for flame monitoring in so-called flame ionization detectors (FID). Ionization flame monitoring is based on the effect that the hot flame gases can change electrically charged atoms, molecules or ions which conduct electric current.

FIG. 1 shows a flame ionization detector (FID) according to the prior art. The flame ionization detector (FID) has a ring electrode R and a point electrode S. The flame, which comprises the flame core K and the flame envelope M, is supplied with fuel. An electrical alternating field is formed between the ring electrode R that surrounds the flame core K and the point electrode S by applying an AC voltage from a voltage source between the two electrodes. The application of the AC voltage to the point electrode S that enters the flame allows a current measurement device to measure a current. Despite the applied AC voltage, the measured current is not alternating current, but is a direct current. The ammeter can be used to determine whether a flame is burning. The rectifier effect of the flame also means that the presence of a flame cannot be detected inadvertently even if there is a short circuit between the electrodes. Flame ionization detectors (FID) can also be used to measure the concentration of hydrocarbons in the exhaust air and surrounding air. In this case, the ionization of organically bonded carbon atoms in a hydrogen flame is used as the measurement effect. The ion current which occurs in the electrical field is electrically amplified and indicated. The ion current is proportional to the number of organically bonded carbon atoms in the air sample. The total carbon concentration is thus obtained in PPM. The verification limit is in this case 0.1-0.2 PPM.

FIG. 2a shows a plasma jet reactor according to the prior art. In the illustrated reactor, a gas mixture composed of N₂ and O₂ flows through a tube and enters a microwave field. A generator produces microwaves, which are fed into a waveguide and are reflected at the other end of the waveguide. This results in the input wave and the output wave being superimposed. The plasma jet reactor is used as an exhaust gas catalyzer. The time for which the gas mixture composed of O₂ and N₂ flowing through the remains in the superimposition field of the microwaves results in a thermal plasma being formed, with peak temperatures of up to 10 000 Kelvin. If the microwave is pulsed in this case, this results in a cold plasma at a temperature of 1000-2000 Kelvin. The plasma that is introduced into the reaction chamber reduces the concentration of hazardous substances contained in the exhaust gas.

In general, a plasma is an ionized gas or gas mixture. If energy is supplied continuously to these gases, for example in the form of electric current, then they change to a state in which neutral gas molecules are stimulated and, if more energy is supplied, positively charged ions and negatively charged electrons are frequently produced. This mixture of neutral, positively and negatively charged particles is referred to as a plasma.

A further possible way to reduce the concentration of hazardous substances is to convert an easily ionizable noble gas, such as argon, as a carrier gas to plasma, by an electrical field by means of microwaves.

FIG. 2b shows an arrangement according to the prior art for destruction of hazardous substances. A microwave generator produces an electromagnetic field. The microwaves that are produced are reflected on a reflector and produce a plasma which acts via an opening on the hazardous substance to be destroyed. The hazardous substance is, for example, a dioxin. This greatly increases the Brownian molecular motion of the dioxin molecules. The argon plasma leads to destruction of the dioxin molecules owing to the high temperature in a chemical reaction. One disadvantage of the arrangement illustrated in FIG. 2b is that the generator for production of the microwaves consumes a very large amount of energy, with a power level of 1-0 kW typically being required. In the arrangement illustrated in FIG. 2b, a plasma is generated first of all, and the generated plasma is then brought into contact with the hazardous substance to be destroyed, in a separate reaction chamber. The combustion flame and the plasma field which is formed by the reflector are locally separated from one another. The efficiency of the arrangement illustrated in FIG. 2b for destruction of hazardous substances is very low, owing to the large amount of energy required.

The object of the present invention is thus to provide a fuel combustion apparatus for combustion of fuels, in which the proportion of the hazardous substances which are created by the combustion is minimized with little energy being consumed.

According to the invention, the object is achieved by producing an AC voltage which forms a potential difference, that is to say a voltage field in a flame whose voltage form allows a charge to flow from the cathode to the anode, for example a pulsed DC voltage or an AC voltage superimposed on a DC voltage. A pure AC voltage is not functional, and a pure DC voltage is only inadequately functional to satisfactorily achieve the object according to the invention.

Together with the AC voltage which forms a potential difference, the flame forms a dispersion spectrum with a flame resistance which varies over the frequency range.

According to the invention, this object is achieved by a full combustion apparatus having the features specified in patent claim 1.

The invention provides a fuel combustion apparatus for combustion of fuels in an exothermic chemical reaction

having

a device for supplying the fuels,

a combustion chamber for combustion of the fuels that

are supplied in a flame, and having at least two electrodes by means of which an electrical field is applied to the flame in order to produce a reaction plasma in the flame, with the reaction plasma that is produced having a high ionization degree.

In the fuel combustion apparatus according to the invention, an electrical field is superimposed on the flame. The electrical field in this case produces a reaction plasma within the flame. This reaction plasma results in the fuel that is supplied being burnt efficiently, so that the concentrations of the hazardous substances which are created during the combustion process are minimal.

The fuel combustion apparatus according to the invention is distinguished by a power consumption which is less than 100 watts for a 10 kW burner, that is to say the electrical energy that is introduced is only 0.1% of the total chemical energy that is introduced.

The fuels that are supplied are virtually 100% burned, with undesirable byproducts being emitted in the exhaust gas, such as nitrogen oxides (NO_x) in only very low concentrations.

When hydrocarbons are burned as the fuel, the fuel combustion apparatus according to the invention results in the proportion of the unburnt hydrocarbons, which likewise represent hazardous substances, in the exhaust gas likewise being reduced to a proportion of virtually zero.

The formation of a reaction plasma within the flame results in a considerable improvement in the energy yield in comparison to conventional combustion devices. The environmentally hazardous toxic substances, such as dioxins and furanes, are virtually completely destroyed by the fuel combustion apparatus according to the invention.

The reaction plasma which is produced in the flame increases the reaction rates within the flame and thus the combustion temperatures. The energy which is obtained from the combustion reaction that takes place, the so-called reaction enthalpy depends on the reaction rate. For example, hydrocarbon molecules (C_xH_y) are supplied as fuel to the fuel combustion apparatus. The energy which is produced by the fuel combustion apparatus thus becomes greater the greater the number of hydrocarbon molecules that react with oxygen (O₂) per unit time. The production of the plasma increases the combustion temperature, and thus the reaction rate. However, this does not significantly increase the energy yield, because the increase in energy from the combustion process is only the thermal content of the combustion gases whose residue can be oxidized by the effect. The hazardous substance emissions are greatly reduced by the fuel combustion apparatus according to the invention. The fuel combustion apparatus according to the invention allows the energy yield to be increased by 1-3%, depending on the fuel.

The fuel combustion apparatus according to the invention essentially has the following advantages:

the energy yield is increased in comparison to

conventional fuel combustion apparatuses;

the proportion of hazardous substances. in the emitted exhaust gases is minimized. These hazardous substances may, for example, be nitrogen oxides or unburnt hydrocarbons.

Components of the fuel combustion apparatus may be physically small for the same power.

In addition, the noise emission can be reduced by about 10 decibels.

A further advantage of the fuel combustion apparatus according to the invention is that the form of the flame can be influenced by the applied electrical field. This makes it possible for the combustion flame that is produced to fill the entire combustion chamber or, alternatively, for the flame to reach only specific chamber sections of the combustion chamber.

The fuel combustion apparatus according to the invention may be used in all appliances in which an open fire or an open flame occurs. These are, in particular:

• • plants for production of steam and process heat in industry;
  • heating systems;
  • gas turbines;
  • waste incineration plant;
  • jet engines;
  • high-temperature furnaces; and
  • internal combustion engines.

The essence of the invention is that an electrical field is applied to the combustion flame in order to produce a reaction plasma in the flame. In this case, the electrical field is applied to the flame by means of at least two electrodes.

In one preferred embodiment of the fuel combustion apparatus according to the invention, the electrodes are connected to a voltage generator.

In this case, the voltage generator preferably produces an AC voltage.

In one preferred embodiment, a transformer is provided for step-up transformation of the AC voltage that is produced by the voltage generator, with charge displacement taking place, statistically on average, in only one charge transport direction.

The applied AC voltage may have different signal forms.

In a first embodiment, the AC voltage that is produced is virtually sinusoidal, with the positive half-cycles having a greater amplitude than the negative half-cycles, or vice versa.

In an alternative embodiment, the AC voltage that is produced is pulsed, with there likewise being a discrepancy between half-cycles, in the area of the voltage function between the positive and the negative half function.

In one preferred embodiment, the voltage generator produces not only the AC voltage but also a DC voltage. In this case, the AC voltage may be a pure sinusoidal AC voltage.

In this case, an electrical DC field is additionally superimposed on the electrical alternating field in the combustion chamber.

The field strength of the electrical field which is applied to the flame is preferably between 0.1 and 10 kV/cm.

In one preferred embodiment, the frequency of the electrical field which is applied to the flame is between 50 Hz and 2 GHz.

The combustion chamber may be open or closed.

The combustion chamber may also contain a combustion medium in which the flame is formed, for example a catalytic burner body or a pore burner body.

In a first embodiment of the fuel combustion apparatus according to the invention, the combustion chamber is an open chamber.

In an alternative embodiment, the combustion chamber is a closed combustion chamber.

In principle, the fuel that is supplied may be any desired fuel.

In one preferred embodiment, the fuel that is supplied is a gas mixture.

In one particularly preferred embodiment, the fuel gas mixture that is supplied is a hydrocarbon mixture. An electrical field is applied via at least two electrodes to the flame, in order to produce a reaction plasma.

An electrical field is applied to the flame via at least two electrodes, between which at least one grid electrode is located (in order to influence the oscillations) in one possible embodiment, in order to produce a reaction plasma.

An electrical DC field is applied by means of the two electrodes, and an electrical alternating field is applied by the grid electrodes. This arrangement is equivalent to a tube arrangement, for example a triode or a pentode.

The grid electrodes in this case control the charge flow within the flame combustion.

In this case, a pure DC voltage may be present between the anode and the cathode when changing-frequency control currents flow at the grid electrodes.

In this case, at least one electrode preferably has an electrode tip in order to increase the field strength of the electrical field.

The other electrode is preferably a ring electrode.

In one particularly preferred embodiment, the two electrodes together with the flame form a capacitor, which is connected in an electrical resonant circuit, with the flame itself forming an RC element.

In one preferred embodiment, waste substances, for example refuse, are incinerated by the flame in the closed combustion chamber of the fuel combustion apparatus.

The waste substances form the fuel that is supplied.

In one preferred embodiment of the fuel combustion apparatus according to the invention, the form of the flame in the combustion chamber can be varied by changing the field strength and the frequency of the electrical field E which is applied to the flame.

This offers the particular advantage that the flame can deliberately reach specific areas within the combustion chamber. The flame can thus be matched to the physical dimensions of the combustion chamber, and the field strength and frequency of the applied electrical field can preferably be set such that the combustion chamber is completely filled.

In one preferred embodiment, the fuel combustion apparatus according to the invention has a mixing device for premixing of the fuels that are supplied.

In the fuel combustion apparatus according to the invention, ignition preferably takes place by application of the electrical field.

In an alternative embodiment of the fuel combustion device according to the invention, an ignition device is also provided, in order to ignite the fuels that are supplied. By way of example, this ignition device produces an ignition spark in order to initiate the combustion.

In one particularly preferred embodiment of the fuel combustion apparatus according to the invention, at least one of the two electrodes is composed of a catalytically active material.

This catalytically active material is preferably platinum.

In a further preferred embodiment of the fuel combustion apparatus according to the invention, one of the two electrodes is in the form of an injector electrode, through which the fuels are sprayed, or are atomized by means of ultrasound oscillations, into the combustion chamber.

In a further preferred embodiment of the fuel combustion apparatus according to the invention, one of the two electrodes is in the form of a corona-discharge electrode.

The flame is preferably electrostatically charged by the corona-discharge electrode.

An electromagnetic alternating field can be coupled into the flame via an antenna system which is formed by the ring electrode.

The invention also provides a method for combustion of fuels by means of a flame in an exothermic chemical reaction comprising the following steps, namely: the fuels are supplied into a combustion chamber in order to produce the flame, an electrical field is applied to the flame in order to produce a reaction plasma with a high ionization degree within the flame.

In this case, an electrical alternating field is preferably applied to the flame.

The electrical alternating field can also be coupled into the flame via a waveguide.

The electrical alternating field may in this case be generated by a microwave generator.

In addition to the electrical alternating field, an electrical DC field is applied to the flame in one alternative embodiment of the method according to the invention.

The field strengths of the electrical field are preferably between 0.1 kV/cm and 10 kV/cm.

In the method according to the invention, the electrical field is applied to the flame by means of at least two electrodes.

The field strength of the electrical alternating field which is superimposed on the DC voltage field has a sinusoidal waveform, in a first embodiment.

In an alternative embodiment of the method according to the invention, the field strength of the electrical alternating field has a pulsed waveform.

The nature of the pulsing of a DC voltage is just as important as its pulse curve profile. The frequency and the waveform of an AC voltage which is superimposed on a DC voltage are also important.

If the pulse width with the corresponding pulse flank rise of from 1 kV/ns falls below 500 ms or less, solid fuels within the flame body will be further pulverized. The pulse flank rise and the pulse width are a measure of the particular decomposition of solid fuels, such as coal dust.

In the case of refuse incineration, this avoids a large amount of dust being developed, and avoids adhesion of unburnt hydrocarbons.

A radio-frequency combustion reaction caused by a high voltage is highly desirable, since a number of plasma flame phenomena which are created for a short time and intensity are formed, and lead to short-term, intensive discharging within the flame. However, an equilibrium can be calculated for the energy introduced via the flame resistance.

In one particularly advantageous development of the apparatus according to the invention, the radio-frequency field is operated in such a manner that the plasma which is formed in the fuel/air mixture in the combustion chamber is in thermal equilibrium, even though the energy that is introduced can also only be pulsed.

The radio-frequency field of an electrically pulsed DC voltage field or a DC voltage field which is superimposed on an alternating field is regulated according to the invention by forming steady-state plasma combustion and thus a uniform high-intensity plasma discharge, with only a minor discharge inclination. Instead of this, a high frequency according to the invention means that short-term, high-impedance plasma discharges are formed within the flame, in the form of plasma flashes, which result in energy intensively, for radicalization of the hydrocarbon/air mixture. These plasma discharges admittedly act for only a short time, but they are particularly intensive owing to the number of them in the area adjacent to the electrode when high potential differences are present. This explains the small amount of energy introduced into the flame.

In one particularly advantageous refinement, the radio-frequency field is operated at a frequency in the MHz band. A frequency as high as this contributes to the formation of homogenously steady-state plasma combustion in thermal equilibrium, in which equalization processes take place by virtue of discharges in the form of high-impedance plasma discharges, thus resulting in an intensive flame reaction.

It is particularly advantageous for the plasma to be produced by a radio-frequency field with a pulsed waveform with steep edges, in which, in a further refinement, the pulsed waveform with steep edges is limited to values of less than or equal to about 500 V/us. Voltage waveforms such as these assist the formation of high-impedance plasma discharges, which burn for only a short time, within the flame.

In another development, the radio-frequency field is regulated to have an essentially sinusoidal waveform, which may have a steep-edged waveform in the area of the flanks of the sine-wave function.

It is particularly advantageous for the plasma discharge to be formed from corona-discharges and/or streamer discharges on the electrode, in order to produce a reliable flame contact and to reduce the electrode wear. In this case, in one development, the plasma threads can propagate in the form of a divergent beam from the electrode to the flame.

In one advantageous refinement, the discharges are formed between a single electrode on the flame in the combustion chamber.

This has the advantage that the geometry of the at least one electrode causes field strength peaks in the radio-frequency field, which lead to the formation of short-time plasma discharges into the flame. A concentration of the effects of the radio-frequency field on the flame such as this not only allows the flame to be ignited reliably, but also allows it to be operated reliably.

By way of example, it is worthwhile providing an electrode in the center of the reaction area of the technical flame, which initiates a point ignition discharge by means of a Tesla transformer arrangement, at the start of the reaction.

The wear capacity is a dynamic flame control factor and can be used as a dynamic flame control optimization constant.

Flames are caused to oscillate at their natural frequency, at specific frequencies. The oscillation of the flame can be frequency-controlled.

Based on the superposition principle, application of two AC voltages to the flame results in a difference between the frequencies of the two AC voltages, and this makes a significant contribution to the avoidance of flame separations, and to the suppression of dynamic overshoots of the flames.

The frequency of the electrical alternating field is preferably between 50 Hz and 2 GHz.

In one preferred embodiment of the method according to the invention, the fuels that are supplied are ignited by the application of an electrical field, with the exothermic chemical reaction being initiated.

In one alternative embodiment of the method according to the invention, an ignition device is additionally provided, by means of which the fuels that are supplied are ignited.

In one particularly preferred embodiment of the method according to the invention, the fuels are first of all stoichiometrically mixed by means of a mixing device, and are then supplied to the combustion chamber.

The fuels are preferably sprayed into the combustion chamber.

The invention also provides an internal combustion engine with little hazardous substance emission, having:

a fuel supply device for supplying fuel,

at least one combustion chamber for combustion of the

supplied fuel in an explosion flame, with each combustion chamber in each case having at least two electrodes, by means of which an electrical field can be applied into the explosion flame in order to produce a reaction plasma.

The combustion chamber is preferably formed by an engine cylinder and an engine piston, which can move in it, in order to transmit power.

The first electrode of the internal combustion engine according to the invention is preferably a point electrode.

The second electrode of the internal combustion engine according to the invention is preferably formed by the grounded engine cylinder.

In one preferred embodiment of the internal combustion engine according to the invention, the first electrode is connected to a DC voltage source.

This DC voltage source is preferably connected in series with a resonant circuit, which is formed from a capacitor with a resonant circuit coil.

A pulsed signal is preferably coupled into this resonant circuit coil via a further coil.

The oscillation frequency of the resonant circuit is in this case preferably between 50 Hz and 2 GHz.

In a first embodiment of the internal combustion engine according to the invention, the internal combustion engine is an Otto-cycle engine.

In an alternative embodiment of the internal combustion engine according to the invention, the internal combustion engine is a diesel engine.

In one preferred embodiment of the internal combustion engine according to the invention, the fuel that is supplied is ignited by the applied electrical field in order to produce an explosion flame.

The invention also provides a refuse incineration apparatus for combustion of waste substances having a combustion chamber for combustion of the waste substances located in it, in a flame, and having at least two electrodes by means of which an electrical field is applied to the flame, in order to produce a reaction plasma.

In a first embodiment of the refuse incineration apparatus according to the invention, the combustion chamber is a rotating drum furnace.

In this case, the first electrode is preferably formed by a point electrode, and the second electrode is preferably formed by a furnace casing electrode.

In a further embodiment of the refuse incineration apparatus according to the invention, the first electrode is formed by a needle electrode grid, and the second electrode is formed by a grate burner grid.

In the preferred embodiment of the refuse incineration apparatus according to the invention, the combustion chamber has a first opening for supplying inlet air, and a second opening for carrying exhaust air away.

The invention furthermore creates a heating furnace for combustion of fuels in an exothermic chemical reaction with a device for supplying the fuels, a combustion chamber for combustion of the supplied fuels in a flame, and with at least two electrodes by means of which an electrical field can be applied to the flame in order to produce a reaction plasma with a high ionization degree, with a medium being heated by the flame.

The medium is preferably the surrounding air.

The heated medium is preferably supplied to a heat exchanger.

Preferred embodiments of the fuel combustion apparatus according to the invention, of the method according to the invention for combustion of fuels, of the internal combustion engine according to the invention, of the refuse incineration apparatus according to the invention and of the heating furnace according to the invention will be described in the following text with reference to the attached figures, in order to explain the features according to the invention.

In the Figures:

FIG. 1 shows a flame ionization detector according to the prior art;

FIG. 2a shows a plasma jet generator according to the prior art;

FIG. 2b shows a hazardous substance catalyser according to the prior art;

FIG. 3 shows a first embodiment of the fuel apparatus according to the invention;

FIG. 4a shows a first embodiment of the point electrode which is used in the fuel combustion apparatus according to the invention;

FIG. 4b shows a second embodiment of the point electrode which is used in the fuel combustion apparatus according to the invention;

FIG. 5 shows a second embodiment of the fuel combustion apparatus according to the invention;

FIG. 6a shows a third embodiment of the fuel combustion apparatus according to the invention;

FIG. 6b shows the third embodiment, as illustrated in FIG. 6a, of the fuel combustion apparatus according to the invention in a control loop;

FIG. 7 shows a fourth embodiment of the fuel combustion apparatus according to the invention;

FIG. 8 shows an AC voltage, which is applied to the electrodes, according to one embodiment of the fuel combustion apparatus according to the invention;

FIG. 9 shows a further AC voltage signal, which is applied to the electrodes, according to a further embodiment of the fuel combustion apparatus according to the invention;

FIG. 10 shows a further voltage signal, which is applied to the electrodes, according to a further embodiment of the fuel apparatus according to the invention;

FIG. 11 shows a further AC voltage signal, which is applied to the electrodes of the fuel combustion apparatus according to the invention, according to a further embodiment;

FIG. 12 shows the arrangement of the fuel combustion apparatus according to the invention in a resonant circuit;

FIG. 13 shows an equivalent circuit of the resonant circuit illustrated in FIG. 12;

FIG. 14 shows an internal combustion engine with little hazardous substance emission according to the invention;

FIG. 15a shows a pulsed signal which is coupled into the resonant circuit of the internal combustion engine according to the invention as shown in FIG. 14;

FIG. 15b shows an AC voltage signal which is applied to the point electrode of the internal combustion engine according to the invention, according to one preferred embodiment of the internal combustion engine according to the invention as shown in FIG. 14;

FIG. 16 shows a first embodiment of the refuse incineration apparatus according to the invention;

FIG. 17 shows a second embodiment of the refuse incineration apparatus according to the invention;

FIG. 3 shows the basic arrangement of the combustion apparatus 1 according to the invention. The fuel combustion apparatus 1 is used for combustion of fuels in an exothermic chemical reaction. The fuel combustion apparatus 1 has a device 2 for supplying fuels. The embodiment illustrated in FIG. 3 uses a gas mixture for the fuels. In this case, the gases to be burned are supplied to a mixing device 3, which premixes the gases to be burned stoichiometrically, and emits the fuel mixture via a gas line 2. The gas line 2 has an outlet opening 4 through which the gas mixture flows out. A ring electrode 5 is arranged in an annular shape around the outlet opening 4, and is connected via a cable 6 to a voltage generator 7. The voltage generator 7 is connected to a point electrode 9 via a cable 8. An electrical field E is produced in the open combustion chamber between the electrodes 5, 9 by application of an electrical voltage U between the ring electrode 5 and the point electrode 9.

The electrical field E ignites the gas mixture flowing out, which burns in a combustion flame 10. The flame 10 has a flame core 10a and a flame envelope 10b. The flame 10 burns in a combustion chamber. In the embodiment illustrated in FIG. 3, the combustion chamber is open. In an alternative embodiment, the combustion chamber is a closed combustion chamber. The electrical field E which is applied to the flame 10 results in a reaction plasma being produced in the flame 10, with the reaction plasma having a high ionization degree. The AC voltage which is applied to the two electrodes 9, 5 is preferably at a frequency f between 50 Hz and 2 GHz. In this case, the AC voltage may be sinusoidal or pulsed. In addition, the voltage generator 7 preferably additionally produces a DC voltage, so that an electrical DC field is also applied to the flame 10, in addition to the electrical alternating field. The field strength of the applied electrical field E is in this case preferably 0.1-10 kV/cm.

A charge-accelerated exothermic reaction takes place in the flame 10. The applied electrical field E, which comprises an electrical DC field and an electrical alternating field, results in ions and electrons being produced in the flame.

The most important reaction phases within the combustion process of redox-reactive exothermic reactions are the thermal radicalization, the cracking and redox-reactive burning-away reaction. The thermal radicalization and the plasma formation are reinforced by the applied electrical field E. The radicals that are formed maintain their energy state until a redox reaction partner initiates the chemical redox reaction. The reaction time of the redox reaction decreases as the radicalization degree of the redox reaction partners increases. This means that the exothermic temperature gradient rises. The temperature within the flame 10 and thus the combustion efficiency n thus likewise increase.

The fuel molecules that are supplied are thermally cracked. The applied electrical field E accelerates the combination of the radicalized and ionized redox reaction partners, so that the reaction rate increases sharply. The electrical field E shifts the electrochemical equilibrium of the combustion reaction. The steady-state, electrodynamic and combustion-kinetic parameters are changed. The burning-away times are shortened. The reaction plasma of the flame has a very high ionization degree I. The flame resistance R of the plasma that is produced is lower than the electrical resistance of a conventional flame. The ionization degree I which occurs in this case within the plasma depends on the frequency, the edge gradient and the duty ratio of the applied electrical AC voltage U.

The electrical alternating field is formed, with respect to the field strength and the frequency, in such a way that the ionization degree I within the flame is optimal. As the ionization degree I increases, the proportion of hazardous substances decreases, since the combustion substances burn away completely. The ionization degree I must not however, be increased too sharply, in order to avoid too much of the electrical energy that is supplied being lost as heat. The setting of the fuel strength and of the frequency of the applied electrical field E makes it possible to influence the ratio of the products of the chemical redox reaction with respect to one another. If, for example, two substances A, B react to form products C, D, the ratio of the products C, D can be influenced by the frequency f and the field strength of the electrical field E which is applied to the flame 10. The fuel apparatus 1 according to the invention thus allows the proportion of hazardous fuel products to be deliberately reduced.

FIGS. 4a, 4b show various embodiments of the point electrode 9 within the fuel apparatus 1 according to the invention. The point electrodes 9a and 9b result in compression of the lines of force, and thus in a local increase in the field strength. In the embodiment of the point electrode 9a illustrated in FIG. 4a, a wire 11a with a diameter of 1/10 to 1/100 mm is accommodated in a casing 12a. The sheath 12a is composed of an insulation material or a ceramic, such as quartz. This wire 11a is connected via the cable 8 to the voltage generator 7. A ball 13a, whose diameter is larger than the diameter of the wire 11a, is located at the end of the supply line wire 11a. The wire 11a is conventionally composed of a tungsten/steel alloy. The ball 13a is likewise composed of a tungsten/steel alloy before ignition. After ignition, a layer of tungsten carbide is formed in the ball 13a, and this is resistant to high temperatures.

FIG. 4b shows an alternative embodiment of the point electrode 9. In the embodiment illustrated in FIG. 4b, the point electrode 9b has a spherical point 13b. Since the point 13b ends in a conical shape, this results in a particularly higher field strength density.

FIG. 5 shows a further embodiment of the fuel combustion apparatus 1 according to the invention. The embodiment illustrated in FIG. 5 also has a transformer 14, which contains a first coil 14a and a second coil 14b. The transformer 14 steps up the AC voltage that is produced by the voltage source 7 in accordance with the transformation ratio of the two coils 14a, 14b. The stepped-up AC voltage is applied via the cables 6, 8 to the two electrodes 5, 9 in order to produce an electrical alternating field. The embodiment illustrated in FIG. 5 allows particularly high electrical field strengths to be achieved.

FIG. 6a shows a third embodiment of the fuel combustion apparatus 1 according to the invention. In the embodiment illustrated in FIG. 6a, the opposing electrode 9 is not formed by a point electrode but by an opposing electrode 9 which surrounds a glass cylinder that is composed of insulation material. The cylinder 15 which is composed of insulating material is coated with the opposing electrode 9. The interior of the cylinder 15 forms the combustion chamber for the flame 10. The cylinder 15 is preferably a quartz tube. The flame 10 absorbs electrical charge via the quartz 15, so that a capacitive reactive current can flow as a result of the electrical alternating field. If the voltage generator 7 additionally applies a DC voltage to the electrodes 5 and 9, a small direct current flows as well.

FIG. 6b shows the third embodiment (which is illustrated in FIG. 6a) of the fuel combustion apparatus 1 according to the invention in a control loop. The flame 10 burns the supplied gas mixture and emits exhaust gases upwards to an exhaust gas detector 16. The exhaust gas detector 16 detects the chemical composition of the exhaust gas, and determines the proportion of hazardous substances, for example the proportion of nitrogen oxide within the exhaust gas. The exhaust gas detector 16 provides data via a data line 17 to a controller 18, with the data that is supplied indicating the proportion of the hazardous substances to be destroyed in the exhaust gas. The controller 18 uses control lines 19 to control the amplitude (U) and the frequency f of the voltage U that is produced by the voltage generator 7. In this way, the amplitude |U| and the frequency f of the electrical field E that is supplied to the flame 10 are set. The arrangement that is illustrated in FIG. 6b represent a control loop 20 by means of which the proportion of hazardous substances in the exhaust gases that are produced by the burning flame 10 can be minimized. For this purpose, the controller 8 varies the frequency and the amplitude of the voltage until the exhaust gas detector 16 detects the minimum proportion of hazardous substances. The control system illustrated in FIG. 6b allows particularly environmentally friendly heating furnaces to be produced. The production of the plasma within the flame 10 minimizes the proportion of hazardous substances. In this case, the frequency f and the amplitude of the applied electrical field E are controlled such that the concentration of the emitted hazardous substances is minimal.

In one preferred embodiment, the controller 18 can be programmed for different fuel/gas mixtures supplied by the mixer 3.

FIG. 7 shows a fourth embodiment of the fuel combustion apparatus 1 according to the invention. In the embodiment illustrated in FIG. 7, the opposing electrode is formed by ground or the chassis. The advantage of the embodiment illustrated in FIG. 7 is that there is no need to provide an opposing electrode or point electrode.

FIGS. 8 to 11 show various signal waveforms of the voltage U that is applied to the electrodes 5, 9. The voltage waveform that is illustrated in FIG. 8 is a sinusoidal AC voltage, on which a DC voltage U₀ is superimposed. In this case, the ratio of the amplitude of the AC voltage |{overscore (U)}| to the DC voltage U₀ is preferably approximately unity, as illustrated in FIG. 9.

FIG. 10 shows a further possible signal waveform of the applied AC voltage signal, with the rising signal flank being steeper than the falling signal flank. The applied AC voltage signal is pulsed. The rising signal flank has a flank grading, for example, of 2 kV/ms. This allows a particularly high ionization gradient to be achieved within the flame.

FIG. 11 shows a further variant of an AC voltage signal applied to the electrodes 5, 9. The AC voltage signal illustrated in FIG. 11 is pulsed. The duty ratio, that is to say the ratio between the duration of the pulse Δt_pulse and the pulse repetition time Δt_pause, is preferably about ⅓. As the duration of the applied voltage pulses increases, the resistance R of the flame falls asymptotically to a resistance R₀. The flank gradient of the voltage pulses is, for example, 2 kV/ms. Typical amplitudes of the voltage pulses are around 8 kV. The flame oscillates harmonically as a result of the application of the pulsed AC voltage.

FIG. 12 shows the third embodiment of the fuel combustion apparatus 1 according to the invention, as illustrated in FIG. 6a, in a resonant circuit. The voltage U which is produced by the voltage generator 7 is applied to the secondary circuit via capacitor 21 and a transformer 22, which comprises two coupled coils 22a, 22b. The ring electrode 5 is connected to the secondary coil 22b via a cable 23. The opposing electrode 9 is connected to a DC voltage source 25 via a cable 24. The flame envelope 10b of the flame 10 forms an opposing electrode for the cylindrical electrode 9. The flame envelope 10b forms a capacitor surface. Energy is injected via the resonant circuit. The secondary resonant circuit comprises the coupling inductance 22b and a capacitor. This capacitor is formed by the opposing electrode casing 9, the flame envelope 10b and the air dielectric.

FIG. 13 shows the equivalent circuit of the resonant circuit that is illustrated in FIG. 12. The electrode 9 and the flame envelope 10b form a capacitor 26, with the flame resistance 27 connected in parallel with it. A DC bias voltage of 1 to 10 kV is applied by means of the DC voltage source 25. The resonant circuit stabilizes the shape of the flame, and the way in which it burns the fuel. The secondary resonant circuit is an RCL resonant circuit. The resonant circuit has a resonant frequency f_R. The flame may act as a half-open resonant circuit or as a closed resonant circuit. The flame 10 acts as an open resonant circuit or as an antenna, with the flame body itself acting as an energy absorber.

FIG. 14 shows one preferred embodiment of an internal combustion engine according to the invention, with little hazardous substance emission. The internal combustion engine has a fuel supply device (which is not illustrated) for supplying fuel. The fuel is supplied in a closed combustion chamber 28, as the combustion chamber. The combustion chamber 28 is formed by an engine cylinder 29 and by an engine piston 20 which can move in it and is intended to transmit power. A point electrode 9 projects into the combustion chamber 28. Preferred embodiments of a point electrode 9 such as this are illustrated in FIGS. 4a, 4b. The piston 30 can move as far as a top dead center point OT within the engine cylinder 29. The point electrode 9 extends into the combustion chamber 28 for a distance L1. The distance between the upper face of the combustion chamber and the top dead center point OT is L2. In one preferred embodiment, the distance L1 is greater than the difference between L2 and L1. As soon as the piston 30 has reached the top dead center point OT, a voltage pulse is injected into the resonant circuit coil 31b via a transformer 31, which has two coils 31a, 31b. A capacitor 32 is connected in parallel with the resonant circuit coil 31b. A DC voltage source 32 is connected in series between the point electrode 9 and the resonant circuit coil 31b. The opposing electrode for the point electrode 9 is preferably formed by the grounded engine cylinder 29.

The voltage signal illustrated in FIG. 15b is applied to the point electrode 9. The transformer 31 couples the voltage U1 into the resonant circuit coil 31b, so that the resonant circuit which is formed from the capacitor 32 and the coil 31 starts to oscillate. The resultant oscillation is damped, so that its amplitude decreases. The amplitude of the pulsed voltage which is produced by the voltage generator is, for example, 2 kV. The distances between the various voltage pulses of the voltage pulse U1 are determined by the speed of revolution of the engine. An oscillating, decaying sinusoidal AC voltage signal is applied to the point electrode 9 by the resonant circuit 31b, 32, with a DC voltage U₀ superimposed on it. The voltage signal formed in this way is illustrated in FIG. 15b. The first pulse of a voltage pulse sequence ignites the fuel mixture which has been supplied to the combustion chamber. The subsequent voltage pulses in the pulse sequence maintain the plasma that is formed in the explosion flame. Ignition preferably takes place shortly before the piston 30 has reached the top dead center point OT. The internal combustion engine according to the invention, as is illustrated in FIG. 14, does not require its own ignition device. This can optionally be provided in addition. The internal combustion engine according to the invention is an Otto-cycle engine or a diesel engine. The frequency f of the voltage pulses which are produced by the resonant circuit 31b, 32 may be in a range between 50 Hz and 2 GHz. The internal combustion engine that is illustrated in FIG. 14, according to the invention, is distinguished by a particularly simple design. There is no need for a conventional spark plug for ignition. The ignition is provided by the point electrode 9. As a result of the production of the plasma within the explosion flame, the combustion within the combustion chamber 28 takes place particularly effectively, with high efficiency. The proportion of the hazardous substances that are formed in this case is particularly low, owing to the plasma that is formed in the explosion flame.

FIG. 16 shows a first embodiment of a refuse incineration apparatus 33 according to the invention. The refuse incineration apparatus 33, as is illustrated in FIG. 16, has a combustion chamber 34, which is a rotating drum furnace 34 in the embodiment illustrated in FIG. 16. The rotating drum furnace 34 is rotated continuously by roller drivers 36, 37. The refuse substance 38 to be incinerated is located at the bottom of the rotating drum furnace 34. The refuse substance 38 is introduced within the rotating drum 34 through an opening. A point electrode 9 projects into the rotating drum furnace 34. The point electrode 9 is connected to the voltage generator 7 via a cable 8. The voltage generator 7 produces an AC voltage and a DC voltage. The voltage that is produced is applied to a furnace casing electrode 39 via a cable 6. The voltage U that is generated for refuse incineration is, for example, between 30 and 45 kV. This results in such a strong electrical field E being produced within the combustion chamber 34 that the waste substance 38 contained in it starts to burn. The refuse substance 38 burns away in a flame 10, which contains a reaction plasma. Typical combustion chambers are 800° C. to 900° C.

FIG. 17 shows an alternative embodiment of a refuse incineration apparatus 33. In this embodiment, the first electrode is formed by a needle electrode grid 40, and the second electrode is formed by a grate burner grid, that is to say by an insulated network strip 41. The combustion chamber 34 has a first opening 42 for supplying input air, and a second opening 43 for carrying away the exhaust air.

The combustion apparatus 1 according to the invention, as it is illustrated in FIG. 3, is also suitable for the construction of heating furnaces. In this case, the flame 10 heats the surrounding air as the energy transmission medium. The surrounding air is then supplied to a heat exchanger.

Figure Captions:

• 1. Fuel
• 2. Prior art
• 3. Gas mixture
• 4. Plasma jet
• 5. Exhaust gas
• 6. Microwave
• 7. Reactor
• 8. Plasma jet generator
• 9. Reflector
• 10. Hazardous substance (dioxin)
• 11. MW generator
• 12. Fuel gases
• 13. Mixer
• 14. Transformer
• 15. Exhaust gas detector
• 16. Controller
• 17. Pulse
• 18. Ground

Claims

1-55. (canceled)

56. A fuel combustion apparatus for the combustion of fuels in an exothermic chemical reaction having:

(a) a device for supplying the fuels;

(b) a combustion chamber for combustion of the supplied fuels in a flame; and

(c) with the flame and a coil forming a resonant circuit, and with energy being coupled into the flame via a resonant coupling with a further resonant circuit.

57. The fuel combustion apparatus as claimed in claim 56, wherein the secondary resonant circuit forms an open resonant circuit, a half-open resonant circuit or a closed resonant circuit.

58. The fuel combustion apparatus as claimed in claim 56, wherein the energy is coupled into the flame in the secondary resonant circuit through a waveguide, with a DC field or direct current being superimposed on the resonant circuit.

59. The fuel combustion apparatus as claimed in claim 56, wherein at least one electrode and one opposing electrode are provided, by which an electric current with a DC component and an AC component is applied through the flame in order to produce a reaction plasma in the flame with the reaction plasma that is produced having a high ionization degree.

60. The fuel combustion apparatus as claimed in claim 59, wherein the opposing electrode and a flame envelope of the flame form a capacitor which is connected to the coil of a transformer to form the resonant circuit, into which energy is coupled via a further coil on the transformer from the primary resonant circuit in order to stabilize the flame.

61. The fuel combustion apparatus as claimed in claim 60, wherein the primary resonant circuit has a capacitor and the first coil of the transformer.

62. The fuel combustion apparatus as claimed in claim 56, wherein the secondary resonant circuit has the capacitor and the second coupling coil of the transformer, with the flame resistance connecting the flame in parallel with the capacitor.

63. The fuel combustion apparatus as claimed in claim 56, wherein a voltage generator is connected to the primary resonant circuit.

64. The fuel combustion apparatus as claimed in claim 60, wherein a DC voltage source is connected to the opposing electrode.

65. The fuel combustion apparatus as claimed in claim 60, wherein the transformer is a Tesla transformer.

66. The fuel combustion apparatus as claimed in claim 60, wherein one of the two electrodes is a grid electrode.

67. The fuel combustion apparatus as claimed in claim 63, wherein the voltage generator produces AC voltage.

68. The fuel combustion apparatus as claimed in claim 67, wherein the transformer is intended for step-up transformation of the AC voltage which is produced by the voltage generator.

69. The fuel combustion apparatus as claimed in claim 68, wherein the AC voltage which is produced is virtually sinusoidal, with there being a difference in the area of the voltage function between the positive and the negative half-cycle.

70. The fuel combustion apparatus as claimed in claim 68, wherein the AC voltage which is produced is pulsed.

71. The fuel combustion apparatus as claimed in claim 59, wherein the field strength of the electrical field which is applied to the flame is between 0.1 and 10 kV/cm.

72. The fuel combustion apparatus as claimed in claim 59, wherein the frequency of the electrical field which is applied to the flame is between 50 Hz and 2 GHz.

73. The fuel combustion apparatus as claimed in claim 56, wherein the combustion chamber is a closed combustion chamber.

74. The fuel combustion apparatus as claimed in claim 56, wherein the combustion chamber is an open chamber.

75. The fuel combustion apparatus as claimed in claim 56, wherein the fuel that is supplied is a gas mixture.

76. The fuel combustion apparatus as claimed in claim 75, wherein the fuels which are supplied are a hydrocarbon mixture.

77. The fuel combustion apparatus as claimed in claim 56, wherein the opposing electrode has an electrode tip in order to increase the field strength of the electrical field.

78. The fuel combustion apparatus as claimed in claim 56, wherein the electrode is a ring electrode.

79. The fuel combustion apparatus as claimed in claim 73, wherein waste substances are burnt by the flame in the closed combustion chamber.

80. The fuel combustion apparatus as claimed in claim 56, wherein the shape of the flame in the combustion chamber can be adjusted by variation of the field strength and the frequency of the electrical field which is applied to the flame.

81. The fuel combustion apparatus as claimed in claim 56, wherein a mixing device is provided for premixing of the fuels which are supplied.

82. The fuel combustion apparatus as claimed in claim 56, wherein an ignition device is provided for ignition of the fuels which are supplied.

83. The fuel combustion apparatus as claimed in claim 56, wherein at least one of the electrodes is composed of a catalytically active material.

84. The fuel combustion apparatus as claimed in claim 83, wherein the catalytically active material is platinum.

85. The fuel combustion apparatus as claimed in claim 56, wherein one of the electrodes is a corona-discharge electrode, through which the fuels can be sprayed into the combustion chamber.

86. The fuel combustion apparatus as claimed in claim 85, wherein the flame can be electrostatically charged by the corona-discharge electrode.

87. A method for combustion of fuels by a flame in an exothermic chemical reaction comprising:

(a) the fuels are supplied in a combustion chamber in order to produce the flame, which has a flame core and a flame envelope;

(b) an AC voltage, which forms a potential difference, is applied to an electrode and to an opposing electrode in order to produce an electrical DC field and an electrical alternating field at the flame, so that a reaction plasma with a high ionization degree is produced in the flame;

(c) with the opposing electrode and the flame envelope of the flame forming a capacitor which is connected to a coupling coil of a transformer to form a secondary resonant circuit; and

(d) energy is coupled into the secondary resonant circuit via a first coupling coil on the transformer from a primary resonant circuit, in order to stabilize the flame.

88. The method as claimed in claim 87, wherein the field strength of the electrical field is between 0.1 kV/cm and 10 kV/cm.

89. The method as claimed in claim 87, wherein the field strength of the electrical alternating field has a sinusoidal waveform.

90. The method as claimed in claim 87, wherein the field strength of the electrical alternating field has a pulsed waveform.

91. The method as claimed in claim 87, wherein the frequency (f) of the electrical alternating field is between 50 Hz and 2 GHz.

92. The method as claimed in claim 87, wherein the fuels that are supplied are ignited by application of the electrical field which is pulsed or is in the form of AC superimposed on a DC voltage, with the exothermic chemical reaction being initiated.

93. The method as claimed in claim 87, wherein the fuels that are supplied are ignited by an ignition device that is provided.

94. The method as claimed in claim 87, wherein the fuels are stoichiometrically mixed by a mixing device, and are then supplied to the combustion chamber.

95. The method as claimed in claim 87, wherein the fuels are sprayed into the combustion chamber.

96. A fuel combustion apparatus for combustion of fuels in an exothermic chemical reaction, having:

(a) a device for supplying the fuels;

(b) a combustion chamber for combustion of the fuels that are supplied, in a flame which has a flame core and a flame envelope;

(c) at least one electrode and one opposing electrode; and

(d) with the opposing electrode and the flame envelope forming a capacitor which is connected to a second coupling coil on a transformer to form a secondary resonant circuit, into which energy is coupled via a first coupling coil on the transformer from a primary resonant circuit in order to stabilize the flame.

97. A fuel combustion apparatus for combustion of fuels in an exothermic chemical reaction, comprising:

(a) a device for supplying the fuels;

(b) a combustion chamber for combustion of the fuels that are supplied, in a flame which has a flame core and a flame envelope;

(c) at least one electrode and one opposing electrode, by which an electric current with a DC component and an AC component is applied by the flame in order to produce a reaction plasma in the flame, with the reaction plasma that is produced having a high ionization degree; and

(d) with the opposing electrode and the flame envelope forming a capacitor which is connected to a second coupling coil on a transformer to form a secondary resonant circuit, into which energy is coupled via a first coupling coil on the transformer from a primary resonant circuit in order to stabilize the flame.