DE102018124761B4 - Device and method for igniting a fuel mixture in the combustion chamber of an internal combustion engine - Google Patents

Abstract

The invention relates to a device for igniting a fuel mixture in the combustion chamber (3) of an internal combustion engine, comprising at least one microwave generator (1) with at least one microwave transmitter, by means of which the ignition of the fuel mixture is supported and/or initiated by microwave irradiation of the fuel mixture. It is essential that the device (4) comprises a variable and/or controlled matching network (2) for impedance matching of the microwave radiation to the impedance of the combustion chamber that changes over time at a constant microwave frequency. The invention also relates to a method for igniting a fuel mixture in the combustion chamber (3) of an internal combustion engine by subjecting it to microwave radiation.

Description

The invention relates to a device for igniting a fuel mixture in the combustion chamber of an internal combustion engine according to the preamble of claim 1 and a method for igniting a fuel mixture in the combustion chamber of an internal combustion engine according to the preamble of claim 10.

In connection with internal combustion engines, such as for internal combustion engines, reciprocating engines or gas turbines, the reduction in fuel consumption and compliance with the limits for pollutant emissions are the focus of current development. The ignition of the fuel mixture in the combustion chamber of the internal combustion engine has a significant influence here. Traditional ignition concepts envisage ignition of the fuel mixture, usually a fuel-air mixture, with the aid of a sparkover (ignition spark). The ignition process usually spreads through multi-spark ignition in the combustion chamber.

The disadvantage of these methods, which are already known from the prior art, is that the ignition spark also ionizes the atmospheric nitrogen and unwanted nitrogen compounds that are harmful to the environment are easily formed. In addition, complete combustion of the fuel mixture is not achieved. As a result, the pollutant emissions increase and there is higher consumption without any significant power being generated in this ignition phase.

Alternatively, it is known to use microwaves to ignite the fuel mixture. In this process, the absorption capacity of long-chain hydrocarbons for pulsed microwave radiation is usually used, which leads to the break-up of the long-chain hydrocarbons and, via the radicals formed, triggers a radical chain reaction and thus a combustion process. These ignition methods are also known as plasma ignition.

For example, from the DE19914941C1 a method for the combustion of a fuel mixture in the combustion chamber of an internal combustion engine is known, in which the combustion is supported by microwave radiation into the combustion chamber. Next it is from the DE 10 2006 005 792 A1 known to support the ignition with a high-frequency signal in the range of 50 GHz.

Next is from the pamphlet DE 10 243 271 A1 an ignition device with a coaxial waveguide is known into which microwaves are coupled. Also the CN 2020 215411 U relates to a coupling device for microwaves in a combustion chamber.

Despite certain improvements compared to the traditional ignition with spark plugs, microwave ignitions still have an exhaust gas composition that needs improvement and, in particular, a nitrogen oxide content that needs to be reduced.

The present invention is therefore based on the object of proposing a device and a method for igniting a fuel mixture which has a reduced pollutant load, in particular nitrogen oxide load, in the exhaust gases. This object is achieved by a device according to claim 1 and by a method according to claim 10. Advantageous configurations of the device according to the invention can be found in claims 2 to 9. Advantageous configurations of the method according to the invention can be found in claims 11 to 14 all claims explicitly included by reference in the description.

The device according to the invention for igniting a fuel mixture in the combustion chamber of an internal combustion engine comprises, as is known, a microwave generator with at least one microwave transmitter, by means of which the ignition of the fuel mixture is supported and/or initiated by microwave irradiation of the fuel mixture.

It is essential that the device comprises a variable and/or controlled matching network for impedance matching of the microwave transmitter with the impedance of the combustion chamber, which changes over time, at a constant microwave frequency.

The device thus includes a variable and/or controlled matching network for impedance matching of the microwave transmitter to the impedance of the combustion chamber of the internal combustion engine, which changes over time, and thereby also a corresponding matching of the impedance of the microwave radiation.

It is within the scope of the invention that the ignition of the fuel mixture in the combustion chamber is triggered in the form of a space ignition by the microwave irradiation of the fuel mixture. It is also possible that only a plasma is generated by the microwave irradiation, which is ignited by the use of a spark plug, ie the ignition is only supported by the microwave irradiation. This configuration has the advantage that the previous microwave excitation of the fuel-air mixture significantly less energy is required for actual ignition. The plasma is created from the fuel mixture in the combustion chamber, which is excited by the microwave radiation.

A field distribution that is as homogeneous as possible is advantageously achieved by the microwave irradiation. This can be done with either pulsed or continuous microwave radiation.

• Im Gegensatz zu den aus dem Stand der Technik vorbekannten Vorrichtungen, weist die Vorrichtung ein variables, gesteuertes Anpassnetzwerk zur Impedanzanpassung des Mikrowellensenders mit dem zeitlich sich verändernden Brennraum auf. Im Gegensatz zum Stand der Technik bleibt hier die Mikrowellenfrequenz konstant, so dass positiven Aspekte der Absorption in vorbestimmbaren Molekülen erhalten bleiben, während aufgrund der Impedanzanpassung ein hoher Leistungseintrag erreicht wird. Dadurch wird eine bestmögliche Einkopplung der Mikrowellenstrahlung gewährleistet.

The device according to the invention thus differs from previously known devices in essential aspects:

• In contrast to the devices already known from the prior art, the device has a variable, controlled matching network for impedance matching of the microwave transmitter with the combustion chamber that changes over time. In contrast to the prior art, the microwave frequency remains constant here, so that positive aspects of the absorption in predeterminable molecules are retained, while a high power input is achieved due to the impedance matching. This ensures the best possible coupling of the microwave radiation.

In combination, fuel consumption, the proportion of nitrogen oxides and the number of soot particles decrease.

A non-equilibrium plasma is preferably generated in the combustion chamber. In contrast to a thermal plasma, a non-equilibrium plasma contains a high proportion of activated and high-energy molecules or atoms. In particular, in a non-equilibrium plasma, radicals are formed which can start and/or maintain a radical chain reaction. This enables reliable ignition of lean mixtures.

Preferably the fuel mixture is a mixture of fuel and air. Optionally, water can be added. In this embodiment, the microwave transmitter preferably also specifically radiates frequencies in the range of the absorption frequencies of water vapor into the combustion chamber. The ignition of lean mixtures is within the scope of the invention.

In a preferred embodiment of the invention, the microwave radiation has a microwave frequency in the range of the absorption frequency of oxygen, about 60 GHz and/or about 118 GHz, and/or the absorption frequency of ozone, at about 166 GHz and/or 184 GHz and/or 196 GHz , and/or another absorption frequency of a component in the fuel mixture.

Advantageously, the oxygen molecules and/or ozone molecules are excited by using a microwave frequency in the absorption range of oxygen and/or ozone. As a result, oxygen molecules and/or ozone molecules are dissociated in a targeted manner. This results in the advantage that, due to the ratio of dissociated oxygen compounds to nitrogen compounds, significantly less nitrogen is excited than with plasma ignitions of a different frequency, so that fewer nitrogen oxides are produced during combustion. In addition, due to the high power density of the high-frequency electromagnetic fields of the microwave radiation in the combustion chamber, more complete combustion of the fuel mixture can be achieved.

In an advantageous embodiment of the invention, the matching network for impedance matching of the microwave radiation is designed in such a way that, at a constant microwave frequency, an impedance matching of the microwave radiation is matched to an impedance of the combustion chamber that changes over time. This has the advantage that the microwave radiation, which is adapted to the impedance of the combustion chamber that changes over time, enables the best possible coupling of the power of the microwaves or millimeter waves.

The impedance of the combustion chamber changes over time as a function of parameters such as the volume of the combustion chamber, the composition of the fuel mixture, the prevailing temperature and the prevailing pressure, the radiated frequency and similar factors. The impedance of the combustion chamber can therefore be described as a function of the parameters mentioned (combustion chamber parameters). In this case, for example, the volume can be determined by the angle of rotation of the piston. The composition of the fuel mixture changes due to soot particles from ignition processes and the supply of new fuel. Pressure and temperature will vary with engine run time etc.

For optimal microwave power adjustment, the impedance of the microwave transmitter and the microwave load, here the combustion chamber, should preferably be complex conjugate to each other. The impedance of the microwave transmitter is given by Equation 1. $${\text{Z}}_{\text{S}}={\text{R}}_{\text{S}}+{\text{j X}}_{\text{S}}$$

In Equation 1, Zs is the impedance of the microwave transmitter whose real part is Rs and imaginary part is Xs. The impedance of the combustion chamber (microwave load) is described by Equation 2. $${\text{Z}}_{\text{B}}={\text{R}}_{\text{B}}+{\text{j X}}_{\text{B}}$$

$${\text{X}}_{\text{B}}={\text{X}}_{\text{B}}\left({\text{f}}_{\text{i}},\text{t},\text{T},\text{G},\dots \right)$$

In Equation 2, Z _B is the impedance of the combustion chamber, the real part of which is R _B and the imaginary part of which is X _B . The real and imaginary parts of the combustion chamber depend on the combustion chamber parameters, such as the combustion chamber geometry that changes over time, the temperature T and the pressure p, as well as the gas composition and other parameters such as the transmitter frequencies f _i as described in Equations 3 and 4. $${\text{R}}_{\text{B}}={\text{R}}_{\text{B}}\left({\text{f}}_{\text{i}},\text{t},\text{T},\text{G},...\right)$$

$${\text{X}}_{\text{B}}={\text{X}}_{\text{B}}\left({\text{f}}_{\text{i}},\text{t},\text{T},\text{G},...\right)$$

$${\text{X}}_{\text{B}}=-{\text{X}}_{\text{S}}$$

The optimal high-frequency power matching between the microwave transmitter and the combustion chamber takes place when the microwave transmitter and the combustion chamber are adapted in a complex conjugate manner, ie Equations 5 and 6 are satisfied. $${\text{R}}_{\text{B}}={\text{R}}_{\text{S}}$$

$${\text{X}}_{\text{B}}=-{\text{X}}_{\text{S}}$$

Zs is the transmitter's variable matching network and Z _B is the impedance of the combustion chamber that changes over time (see description for 1 ). The optimal values of Zs are preferably read out from a characteristic map that ensures that an optimal adjustment is guaranteed at every operating time.

In a preferred development of the invention, the matching network is designed as a controlled pot circuit or cavity resonator. Alternatively, the matching network can be implemented as an electronically controlled high-frequency power semiconductor circuit, preferably implemented using GaN technology.

The microwave generator is preferably designed to emit high-power, high-frequency pulses to ignite the fuel mixture. Additionally or alternatively, the microwave generator is designed to continuously emit microwave radiation at a constant microwave frequency for plasma excitation of the fuel mixture. You can alternatively choose between different types of ignition.

In an alternative embodiment of the invention, the device has at least one spark plug for igniting the excited plasma of the fuel mixture.

As described above, a non-equilibrium plasma can be generated by microwave irradiation of the fuel mixture in the combustion chamber. This non-equilibrium plasma can be burned off by ignition using a spark plug. The advantage of excitation of the plasma beforehand is that significantly less energy is consumed and fewer pollutants remain.

An advantageous development of the device includes a combustion chamber window made of diamond for coupling the microwave radiation into the combustion chamber. A diamond window is microwave-transparent, inert, has good thermal conductivity and withstands high temperatures and pressures. This means that the entire volume of the combustion chamber can be irradiated with high power. This enables the high pressure in the combustion chamber to be decoupled from the waveguide of the microwave generator. In addition, the high temperatures can be released to the material surrounding the combustion chamber or the environment due to the good thermal conductivity of diamond. The coupling through a diamond window enables a high power density of the high-frequency electromagnetic field in a large area of the combustion chamber, so that the fuel mixture can be burned more completely.

In a further advantageous embodiment of the invention, the device is designed with a control unit which is arranged and designed to interact with the matching network to control the microwave impedance. The control unit records combustion chamber parameters such as pressure, volume, temperature, gas composition and/or plasma composition and other engine condition parameters. These are preferably used in the control of the matching network for impedance matching for the microwave radiation in accordance with Equations 1 to 6 described above.

The periodically changing impedance of the combustion chamber during the operation of the internal combustion engine is known at each operating point from data that was determined by measurement and/or simulation. For optimal power adjustment, the millimeter wave transmitter of the microwave generator should therefore have an output impedance which is advantageously complex conjugate to the combustion chamber impedance. This is achieved by an electronic controller that determines the optimal setting for the matching network from the data: crankshaft angle, speed, temperature, pressure, gas composition and fuel quantity.

Preferably, the device comprises a detector unit, the combustion chamber parameters such as Pressure, volume, temperature, gas composition and / or plasma composition detected.

Alternatively or additionally, data of the combustion chamber are stored in a characteristic map and the impedance adjustment is controlled on the basis of the data from the characteristic map.

In a further advantageous embodiment of the invention, the microwave generator also has microwave radiation with a microwave frequency in the range of the absorption frequency of other components of the fuel mixture, such as hydrocarbons.

By stimulating the other components of the fuel mixture, such as hydrocarbons, in addition to stimulating oxygen, combustion can be further optimized and pollution levels reduced. The microwave radiation with a frequency in the range of the absorption frequency of hydrocarbons is additionally absorbed in the hydrocarbon molecules, so that overall a higher energy input takes place.

The object described above is also achieved by the method according to the invention and/or a preferred embodiment of the method according to the invention.

The method according to the invention is preferably designed to be carried out by means of the device according to the invention and/or an advantageous embodiment thereof. The device according to the invention is preferably designed to carry out the method according to the invention and/or an advantageous embodiment of the method.

• A Einleiten des Brennstoffgemischs in den Brennraum der Brennkraftmaschine;
• B Bestrahlen des Brennstoffgemisches in dem Brennraum mit Mikrowellenstrahlung mittels des Mikrowellengenerators;
• C Zündung des Brennstoffgemisches;

The method according to the invention for igniting a fuel in the combustion chamber of an internal combustion engine is carried out using a microwave generator and comprises the following method steps:

• A introducing the fuel mixture into the combustion chamber of the internal combustion engine;
• B irradiating the fuel mixture in the combustion chamber with microwave radiation using the microwave generator;
• C ignition of the fuel mixture;

What is essential is that, given at least one constant microwave frequency, an impedance of the microwave radiation is adapted to an impedance of the combustion chamber that changes over time.

The method according to the invention also has the above-mentioned possible variations and corresponding advantages of the device according to the invention.

The fuel mixture is advantageously irradiated with microwaves in the range of the absorption frequency of oxygen, preferably at 60 GHz and/or approximately 118 GHz, and/or the absorption frequency of ozone, approximately 166 GHz and/or 184 GHz and/or 196 GHz. Excitation of water absorption lines at frequencies around 180 GHz and 325 GHz can also be useful because of the water vapor content in the intake air or by deliberately adding water to the fuel mixture.

In an advantageous development of the method according to the invention, the microwave irradiation takes place in the form of high-power high-frequency pulses and leads to the ignition of the fuel mixture. The high power radio frequency pulses create a non-equilibrium plasma by initiating a radical chain reaction that results in ignition of the fuel mixture throughout the volume of the combustion chamber.

In an alternative embodiment of the method according to the invention, the microwave irradiation takes place continuously with a constant microwave frequency. This creates a non-equilibrium plasma, which can be ignited by means of a spark plug, ie by an ignition spark. Starting from the ignition spark, the ignition spreads comparatively quickly throughout the entire volume of the combustion chamber.

In an advantageous embodiment of the invention, additives are added to the fuel mixture. The microwave generator is advantageously adapted in such a way that additional microwave radiation is generated with a microwave frequency in the range of the absorption frequency of the added additives.

Further preferred features and embodiments of the method according to the invention and the device according to the invention are explained below with reference to exemplary embodiments and the figures.

• 1 eine schematische Darstellung des Mikrowellensenders, der variablen Anpassimpedanz des Senders Zs und der sich während des Betriebs verändernden Impedanz Z_B des Brennraums.
• 2 eine schematische Darstellung einer Hubkolbenmotors mit einer Mikrowellen-Einspeisung;
• 3 eine schematische Darstellung einer Steuereinheit.

It shows:

• 1 a schematic representation of the microwave transmitter, the variable matching impedance of the transmitter Zs and the changing impedance Z _B of the combustion chamber during operation.
• 2 a schematic representation of a reciprocating engine with a microwave feed;
• 3 a schematic representation of a control unit.

1 shows a schematic representation of a circuit diagram of a device 4 for igniting a fuel mixture in the combustion chamber of an internal combustion engine. The device consists of a microwave transmitter 1 and a variable matching impedance 2. Zs is the variable matching network of the transmitter. The changing impedance 3 describes the cavity impedance Z _B of the combustion chamber 3 that changes over time.

The matching impedance 2 can also be designed as a matching network that is changed by a control unit (not shown). The control unit can make the settings using a map. Alternatively or additionally, a detector unit (not shown) is provided, which detects the operating parameters, pressure, temperature, crankshaft position, gas composition, and other parameters and forwards this data to the control unit.

The control unit 12 and the microwave generator 1 are arranged and designed to interact with the impedance matching network 2 in such a way that the impedance of the microwave radiation is matched to the impedance 3 of the combustion chamber, which changes over time. The frequencies of the microwave radiation are kept constant. The frequency of the microwave radiation is in the range of the absorption frequency of oxygen, in the present case approximately in the range of 60 GHz and 118 GHz.

The impedance of the combustion chamber 3 is dependent on parameters such as pressure, temperature, volume, gas composition and the like in the combustion chamber 3. The impedance of the microwave radiation is adapted to the impedance of the combustion chamber 3 by means of the matching network 2 as a function of these parameters that change over time.

The connection between the device 4 and the combustion chamber is established via an impedance line 5 (cf. 2 ), which in this case is designed using waveguide technology.

2 shows schematically a reciprocating engine with a crankshaft 10, a connecting rod 9, a piston 8, a cylinder 6 and (optionally) a spark plug 7. The combustion chamber 3 forms a combustion chamber impedance 3 ( 1 ) out. The microwave or millimeter wave is conducted into the combustion chamber 3 via a waveguide 5 through a diamond window 11 .

The combustion chamber 3 is delimited by the piston 8 moving up and down and by the cylinder 6. The combustion chamber 3 in 2 is the geometric description of the combustion chamber impedance 3, which is given in 1 shown as a circuit symbol Z _B and includes the operating conditions such as gas composition, pressure and temperature.

In cooperation with the microwave generator 1, the device 4 comprises a variable and controlled matching network 2 for impedance matching of the microwave radiation (cf. 1 ). In addition, a control unit and a detection unit (not shown) are provided.

In the present case, the matching network is designed as a controlled pot circle.

The control unit and the microwave generator 1 with the impedance matching network 2 are arranged and designed to work together in such a way that the impedance of the microwave radiation is matched to the impedance 3 of the combustion chamber, which changes over time. The frequencies of the microwave radiation are kept constant. The frequency of the microwave radiation is in the range of the absorption frequencies of oxygen, in the present case approximately in the range of 60 GHz and 118 GHz. Optionally, other absorption frequencies of the components involved in the gas mixture can also be excited.

The impedance of the combustion chamber 3 is dependent on parameters such as pressure, temperature, volume, gas composition and the like in the combustion chamber 3. The impedance of the microwave radiation is adapted to the impedance of the combustion chamber 3 by means of the matching network 2 as a function of these parameters that change over time.

• Die sich periodisch ändernde Impedanz des Brennraums wird während des Betriebs des Verbrennungsmotors kann durch Messung und/oder Simulation der Brennraum-Parameter zu jedem Betriebspunkt ermittelt. Der Millimeterwellensender des Mikrowellengenerators 1 weist eine Ausgangsimpedanz konjugiert komplex zu der Brennraumimpedanz auf. Dies wird durch eine elektronische Steuerung erreicht, die beispielsweise aus den Daten: Kurbelwellenwinkel, Drehzahl, Temperatur, Druck, Gaszusammensetzung und Kraftstoffmenge die optimale Einstellung für das Anpassnetzwerk ermittelt.

For example, this can be done using the combustion chamber parameters such as crankshaft angle, speed, pressure, volume, temperature, gas composition and/or plasma composition:

• The periodically changing impedance of the combustion chamber is determined during operation of the internal combustion engine by measuring and/or simulating the combustion chamber parameters at each operating point. The millimeter wave transmitter of the microwave generator 1 has an output impedance that is the complex conjugate of the combustion chamber impedance. This is achieved by an electronic controller that determines the optimal setting for the matching network from the data: crankshaft angle, speed, temperature, pressure, gas composition and fuel quantity.

The connection between the device 4 and the combustion chamber takes place via an impedance line 5, which in the present case is designed using waveguide technology. The microwave radiation with the matched impedance is coupled into the combustion chamber via the impedance line.

A diamond window 11 is provided in the outer wall of the cylinder 6 of the combustion chamber 3 . The inner volume of the combustion chamber 3 is acted upon by microwave radiation by the microwave generator 4 through the impedance line 5 via the diamond window 11 . The diamond window 11 is arranged on the cylinder wall of the combustion chamber 3 in such a way that the energy density distribution of the microwave radiation in the combustion chamber 3 is as homogeneous as possible.

The diamond window 11 is microwave-transparent, inert, has good thermal conductivity and withstands high temperatures and high pressures. This enables the high pressure in the combustion chamber 3 to be decoupled from the coupling-in waveguide 5.

This allows maximum coupling of the power of the microwaves into the fuel mixture in the combustion chamber, resulting in efficient and low-residue combustion.

The fuel mixture in the combustion chamber is ignited in the form of space ignition by the microwave irradiation of the fuel mixture. As described, a spark plug can optionally be provided. Ignition can also take place without a spark plug 7 by means of a pulse of the millimeter wave power fed in via the waveguide 5 . In another embodiment, in which the millimeter wave power only excites the gas mixture, ignition takes place via the ignition spark of the spark plug 7. In this case, a plasma is generated by the microwave irradiation. The plasma is created from the fuel mixture in the combustion chamber, which is excited by the microwave radiation. This plasma is ignited by the use of the spark plug. The ignition is only supported by the microwave radiation.

3 12 shows a control unit 12 which controls the impedance of the millimeter wave transmitter 2. FIG. The control unit processes the information from a detector unit 13 which, for example, reads in the values of a temperature sensor T, a pressure sensor P and/or the angular position of the crankshaft φ, which describe the state of the combustion chamber 3 .

reference list

1

Microwave generator, microwave transmitter

2

Matching impedance, impedance matching network

3

combustion chamber impedance, combustion chamber

4

contraption

5

waveguide, impedance line

6

cylinder

7

spark plug

8th

Pistons

9

connecting rod

10

crankshaft

11

diamond window

12

control unit

13

detector unit

Claims (13)

Device for igniting a fuel mixture in the combustion chamber (3) of an internal combustion engine, comprising at least one microwave generator (1) with at least one microwave transmitter, by means of which the ignition of the fuel mixture is supported and/or initiated by microwave irradiation of the fuel mixture, characterized in that the device (4 ) comprises a variable and/or controlled matching network (2) for impedance matching of the microwave radiation to the impedance of the combustion chamber (3) that changes over time, the matching network (2) for impedance matching of the microwave radiation being designed in such a way that an impedance of the microwave radiation is matched to a time-changing impedance of the combustion chamber (3) is adjusted at a constant microwave frequency. device after claim 1 , characterized in that the microwave radiation has a microwave frequency in the range of the absorption frequency of oxygen, approximately 60 GHz and/or approximately 118 GHz, and/or the absorption frequency of ozone, approximately 166 GHz and/or 184 GHz and/or 196 GHz. Device according to one of the preceding claims, characterized in that the microwave generator (1) is designed to emit high-power high-frequency pulses for igniting the fuel mixture and/or that the microwave generator (1) for the continuous emission of microwave radiation min at least one constant microwave frequency is configured for plasma excitation of the fuel mixture. Device according to one of the preceding claims, characterized in that the device (4) has at least one spark plug (7) for igniting a non-equilibrium plasma of the fuel mixture. Device according to one of the preceding claims, characterized in that the device (4) comprises a combustion chamber window (11) made of diamond for coupling in the microwave radiation. Device according to one of the preceding claims, characterized in that the device (4) comprises a control unit (12) which is arranged and configured to interact with the matching network (2) so that the control unit can monitor combustion chamber parameters such as pressure, volume, temperature, gas composition and/or plasma composition when controlling the matching network (2) for impedance matching for the microwave radiation. Device according to one of the preceding claims, characterized in that the device (4) comprises a detector unit (13) which detects combustion chamber parameters such as pressure, volume, temperature, gas composition and/or plasma composition. Device according to one of the preceding claims, characterized in that the microwave generator (1) is designed in such a way that microwave radiation is additionally generated with a microwave frequency in the range of the absorption frequency of other components of the fuel mixture, preferably in the range of the absorption frequency of hydrocarbons and/or in the range of Absorption frequency of added additives. Method for igniting a fuel mixture in the combustion chamber (3) of an internal combustion engine, the ignition of the fuel mixture being supported and/or initiated by microwave irradiation of the fuel mixture, characterized in that at least one constant microwave frequency causes an impedance of the microwave radiation to an impedance of the combustion chamber that changes over time (3) is adjusted. procedure after claim 9 , characterized in that the microwave irradiation occurs at at least one microwave frequency in the range of the absorption frequency of oxygen, in particular approximately 60 GHz and/or approximately 118 GHz, and/or the absorption frequency of ozone, approximately 166 GHz and/or 184 GHz and/or 196 GHz , or/and a different absorption frequency of the gas mixture. procedure after claim 9 or 10 , characterized in that the combustion chamber parameters such as pressure, volume, temperature, gas composition and/or plasma composition are detected in a detection unit (13) and transmitted to a control unit (12) in order to optimally adapt the impedance of the microwave transmitter to to achieve the combustion chamber impedance changing over time. Procedure according to one of claims 9 until 11 , characterized in that the impedance adjustment of the microwave irradiation takes place on the basis of the combustion chamber parameters, such as pressure, volume, temperature, gas composition and/or plasma composition, preferably that the combustion chamber parameters are described by a characteristic map which is stored in the control unit (12) is saved. Procedure according to one of claims 9 until 12 , characterized in that additives are added to the fuel mixture and the microwave generator (1) additionally generates microwave radiation with a microwave frequency in the range of the absorption frequency of the added additives.

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