EP2199597A2 - Ignition device for a combustion engine, which supplies a corona discharge - Google Patents

Abstract

The ignition arrangement provides a corona discharge for ignition of a fuel/air mixture in the combustion chamber (24) of combustion machine. The ignition arrangement delivers basic voltage which is always different from zero for triggering and maintaining corona discharge for each ignition process. An independent claim is included for method of igniting fuel/air mixture in combustion chamber of combustion machine.

Description

The invention relates to an ignition device for an internal combustion engine, which provides a corona discharge for igniting a fuel / air mixture in the combustion chamber of the internal combustion engine. Furthermore, the invention relates to a method for igniting a fuel / air mixture preferably in the combustion chamber of an internal combustion engine by means of a corona discharge. Finally, the invention relates to an internal combustion engine and a stationary power plant with just such an ignition device.

Various technologies are used to ignite internal combustion engine driven engines. For the most part, the ignition takes place by means of so-called spark ignition systems. Due to increasing requirements for the optimization of combustion, other technologies, such as the diesel pilot, laser or corona ignition, have been developed in addition to this option and used in high-performance engines.

In Koronazündeinrichtungen the fuel / air mixture in the combustion chamber of the internal combustion engine is ignited by high electric field strengths, but without arc discharge. In contrast to spark ignition systems, corona ignition only permits one glow discharge, but not the formation of the arc discharge. Arc discharge is when a breakdown occurs with the formation of an electric spark between the electrodes. A corona discharge is thus a state in which partial discharges occur in the air gap between two electrodes, which manifests itself in short high-frequency current peaks. However, no permanent current flow is generated. Shortly before the breakthrough between the two electrodes, the partial discharges occur very frequently. In the breakthrough, a continuous current flow is generated between the two electrodes. In this case, ions act as charge carriers, which are generated by a plasma around at least one of the electrodes. Thus, a fluid is ionized, which surrounds an electrical conductor.

For a Koronazündeinrichtung is usually an electrode, which preferably as a tip or with several to generate the required field strengths Peaks is executed, used in the area of each cylinder head of the internal combustion engine. As a counterpole, the combustion chamber of the cylinder itself is usually used. The piston and the underside of the cylinder head form the ground electrode for such Koronazündeinrichtungen.

In the US 6,883,507 by Paul Douglas Freen has been described an ignition device for an internal combustion engine, which provides a corona discharge for igniting a fuel / air mixture in the combustion chamber of the internal combustion engine. An alternating voltage of 30 kHz to 3 MHz is provided. In the US 5,649,507 a generic ignition device is also provided. For the ignition process, a voltage is provided which consists only of the positive sine waves of an alternating voltage.

In order to optimize the working area of the corona discharge, the occurrence of the arc discharge must be prevented. The voltage range is therefore limited by a lower voltage, which must be high enough to excite the electrons and an upper voltage, which leads to the arc discharge. The arc discharge can be prevented by, on the one hand, this upper voltage limit is not exceeded or the time for the formation of the arc discharge is too short. When using AC voltage sources, there is a voltage or time limitation, since on the one hand the peak value of the voltage below the breakthrough must be kept to the arc discharge and on the other hand, the time of transhipment can not be used. To make matters worse, that the limit to the arc discharge and the formation of a corona discharge depends on the polarity.

The ignition devices used in the prior art have the disadvantage that the introduced to ignite the fuel / air mixture energy is not optimally utilized.

Object of the present invention is therefore to provide an ignition device of the type mentioned, in which these problems are reduced.

This object is achieved by an ignition device, preferably Koronazündeinrichtung, for an internal combustion engine, which for ignition of a Fuel / air mixture in the combustion chamber of the internal combustion engine provides a corona discharge, which is characterized in that the ignition device for triggering and maintaining the corona discharge for each ignition an always different from zero base voltage U _L supplies.

In tests, it has been shown that the optimum energy input is achieved if the voltage at the boundary is kept continuously shortly before the arc discharge. It is essential that for triggering and maintaining each individual corona discharge, the basic voltage provided is always different from zero. This means that, in contrast to an AC voltage, no zero crossing is provided or in contrast to the device according to FIG US 5,649,507 the voltage applied to the electrode never drops to zero over an extended period of time. In the prior art, there are on the one hand losses due to the reloading of the electrodes. Below the "Corona limit", the corona breaks down during the transhipment and must then be rebuilt when the corona boundary is reached again. On the other hand, when using a base voltage that is always different from 0, one can approach closer to the breakdown limit for the arc discharge, since polarity effects due to the polarity reversal at the electrodes no longer occur, so that the effectiveness of the energy input is increased. Therefore, it is preferably provided that the base voltage different from 0 is always kept above the corona boundary.

In a preferred embodiment, it is provided that the ignition device is characterized by a transformer, wherein on the primary side of the transformer, a voltage source is provided which provides AC or a varying DC voltage. As varying DC voltage is meant such a DC voltage that changes in height as a function of time. In the simplest case, a conventional AC power source is provided which generates a sinusoidal or rectangular voltage.

In order to be able to use a small voltage source on the primary side, it can be advantageously provided that a voltage multiplier is provided on the secondary side of the transformer.

In order to keep the voltage on the secondary side substantially constant, it can be provided that a voltage smoother is arranged on the secondary side of the transformer. In the simplest case, it can be provided that the stress smoother is a disposable smoother. For example, here offers a so-called smoothing capacitor. For more complex applications, it has proven to be advantageous if the tension smoother is a Mehrwegglätter.

For a particularly optimal corona discharge it can be provided that the control device and / or regulating device keeps the voltage U _L at the electrode in the combustion chamber substantially constant. Here, on the one hand, in the simplest case, a control device can be provided, with which the voltage is maintained at a substantially constant value. In order to take better account of disturbing influences, a control device can be provided which keeps the voltage on the secondary side of the transformer substantially constant. For this purpose, the voltage is ideally adjusted to a desired value, which is determined, for example, as a function of different engine parameters. It can be provided that the at least one engine parameter is selected from the group ignition timing, ignition duration or combinations thereof. The ignition device may be configured such that the control device and / or regulating device always keeps the basic voltage U _L below the breakdown voltage U _B for an arc discharge. Furthermore, the ignition device may be configured such that the control device and / or regulating device always maintains the basic voltage U _L above the corona boundary U _K.

In the simplest case, the ignition device is designed so that an electrode is provided on the secondary side, which extends into the combustion chamber of the internal combustion engine. At this electrode, the nonzero ground voltage is applied. The counter electrode can also extend into the combustion chamber. However, the counter electrode can also be formed by the combustion chamber itself, for example via the piston and / or bottom of the respective cylinder head.

In addition to the ignition device described above, the object initially set is of course also solved by a corresponding method. In such a method for igniting a fuel / air mixture, preferably in the combustion chamber an internal combustion engine by means of a corona discharge is provided that for triggering and maintaining the corona discharge a non-zero base voltage U _{L is} provided. The further embodiments of the method result essentially from the aforementioned ignition device or from the following description of the figures.

In a further aspect of the invention, an internal combustion engine with an ignition device of the aforementioned type is provided. Furthermore, a stationary power plant comprising a generator, an internal combustion engine and an ignition device of the aforementioned type is provided according to the invention. In the preferred case, the internal combustion engine is a stationary internal combustion engine, as used, for example, in stationary power plants. Stationary power plants usually have an internal combustion engine and an electric generator for electric power generation.

Furthermore, the internal combustion engine, preferably stationary, may be a gas engine, i. an internal combustion engine that burns a gaseous fuel such as methane. It is particularly preferably a mixed-charged gas engine. In mixed-supercharged gas engines is compressed as a fluid not pure air, but a fuel / air mixture in the compression devices. Gas engines are particularly suitable for ignition devices with corona discharge.

Fig. 1

das Schaltbild einer ersten erfindungsgemäßen Zündeinrichtung,

Fig. 2

eine zweite Ausführungsvariante einer erfindungsgemäßen Zündeinrichtung,

Fig. 3

eine dritte Ausführungsvariante einer erfindungsgemäßen Zündeinrichtung,

Fig. 4

ein Blockdiagramm eines Regelkreises für eine erfindungsgemäße Zündeinrichtung

Fig. 5

ein Diagramm, das den verbesserten Energieeintrag demonstriert und

Fig. 6

den Zeitverlauf verschiedener Spannungen und Stromstärken anhand des Beispiels der Zündeinrichtung gemäß Fig. 3.

Further advantages and details of the invention will be explained with reference to the following figures and description of the figures. It shows

Fig. 1

the circuit diagram of a first ignition device according to the invention,

Fig. 2

a second embodiment of an ignition device according to the invention,

Fig. 3

a third embodiment of an ignition device according to the invention,

Fig. 4

a block diagram of a control circuit for an ignition device according to the invention

Fig. 5

a diagram that demonstrates the improved energy input and

Fig. 6

the time course of different voltages and currents based on the example of the ignition device according to Fig. 3 ,

The Fig. 1 schematically shows an ignition device for an internal combustion engine according to the invention. In this case, a first electrode 1 is provided, which extends into the schematically (dashed) indicated combustion chamber of the internal combustion engine. The counter electrode 2 is at least partially formed by the combustion chamber 24 and the walls of the combustion chamber 24. Between electrode 1 and counter electrode 2, a corona discharge is provided within the combustion chamber 24. The ignition device initially supplies for triggering and then for maintaining the corona discharge within the combustion chamber for each ignition a non-zero base voltage U _L over the entire period of the corona discharge. For this purpose, a voltage source 5 is provided on the primary side 4 of the transformer 3. This has a DC voltage source 6 and a plurality of thyristors 7, 7 ', 7 ", 7"'. By means of a control device 8 from the DC voltage of the DC voltage source 6, a clocked AC voltage by switching the thyristors 7, 7 ', 7 ", 7"' generated. It is provided that the voltage generated is converted into an AC voltage with about 150 to 200 kHz frequency. As already indicated, the actual electrode 1 and the counterelectrode 2 are provided on the secondary side 5 of the transformer 3. By means of the diode 9 and the capacitor 10 to achieve a rectification of the voltage. The capacitor 10 and the diode 9 together form a disposable smoother, the capacitor 10 acts as a smoothing capacitor. The ignition device thus has a DC voltage source, for example a battery, with a voltage U ₀ . About the control device 8 and the thyristors 7, 7 ', 7 ", 7"', which form the voltage source 5 together with the DC voltage source 6 is generated from the DC voltage U _0, an AC voltage U ₁ . The transformed voltage U _{2 is produced} via the transformer 3 and the winding number ratio n ₁ / n ₂ of the primary coil 3 'and the secondary coil 3. The diode 9 and the capacitor 10 convert the alternating voltage U _{2 into} a DC voltage applied to the electrodes 1, 2 U _L a additionally provided control means 8. detected via the resistor 25 at the secondary side 5 of the transformer 3 to the secondary current I _2. at the same time, the controller 8 detects various engine parameters. Using a closed loop control can actuation of individual thyristors 7, 7 ', 7 ", 7 "', the primary voltage U ₁ are readjusted so that the secondary voltage U _{2 is} tracked to its desired value.

In the combustion chamber 24, a fuel / air mixture is admitted at the beginning of the ignition process and compressed via a piston stroke. For ignition, the voltage U _{L is} built up and maintained over the entire ignition process and readjusted with the control device 8. It forms a corona discharge with simultaneous current flow I _L. The corona discharge is maintained until a stable flame core has formed. Subsequently, the voltage U _{L is} turned off.

In contrast to the embodiment of Fig. 1 has the embodiment of Fig. 2 now not only a disposable smoother but a Mehrwegglätter on. By the two diodes 9, 9 'and the capacitor 10, this is designed as a center rectifier. A variant, not shown, could also be designed as a full-wave rectifier via a bridge rectifier.

Both in the embodiment of Fig. 1 as well as in the embodiment of Fig. 2 In addition, a control unit 8 is provided. However, this is only optional. With a known voltage characteristic U _L across the electrodes 1, 2 over the entire ignition process, a simple actuating operation can also be provided. The voltage U _L is simply kept only at a certain value. In the example of Fig. 2 is the voltage U _L additionally used as a size for the scheme.

While the voltage U ₂ on the secondary side 5 only results in the winding number of the respective coil 3 ', 3 "on the transformer 3, in the embodiment of the Fig. 3 on the secondary side 5 of the transformer 3 in addition a voltage multiplier 26 is used. For this purpose, a so-called high-voltage cascade is provided, which may have several stages. In the exemplary embodiment shown, it is a three-stage cascade with which the voltage on the secondary side 5 can theoretically be tripled. In practical embodiments, high-voltage cascades with 3 to 5 stages have proven to be advantageous. The other components as well as the regulation are based on the Fig. 1 and 2 held.

In practical examples, the following values were obtained: The primary voltage of the ignition coil U ₁ was between 100 and 500 V, the secondary voltage of the coil U ₂ was in the range between 5 and 100 kV, preferably between 5 and 30 kV. The AC voltage for feeding the cascade was in frequency ranges between 50 and 500 kHz. By amplifying and converting in the cascade circuit, the rectified ignition voltage U _{L reaches} values of 10 to 100 kV.

In Fig. 4 schematically the operation of the control device 8 is shown. Central component is the control device 8, which is supplied on the one hand with certain engine parameters 23, such as ignition parameters such as ignition timing and ignition duration. The control device also obtains information about the voltage measurement on the secondary side between electrodes 1 and 2 via a filter 22 from the corona path 20. The actual control is performed by manipulated variable tracking via the power circuit 21 on the primary side 4 of the transformer. 3

The Fig. 5 shows a diagram voltage U as a function of time t. Schematically, the voltage curve (as sinusoidal curve) applied to the electrode 1 in a corona ignition device designed according to the prior art is shown during a firing process. First, the voltage is built up until the corona boundary U _K. is reached, above which it comes to the formation of the corona discharge in the combustion chamber. (It should be noted here that the voltages always mean the amount of voltage, ie without the respective sign, when "above" or "below" is mentioned.) However, the maximum voltage must be below the breakdown limit for the Arc discharge U _{B + be} kept. Then the voltage drops again and falls below the corona limit U _{K +} , makes a 0-pass and continues until the lower corona boundary U _{K- is} reached, so it comes again to the formation of a corona. Again, the amount of breakdown voltage for the arc discharge U _{B- may} not be exceeded. Due to polarization effects, the amounts of the voltages U _{B +} or U _B- and U _K- or U _{K- are} different. This results in differently high corona windows F + and F- in which the corona discharge can take place. The actual energy input into the combustion chamber is proportional to the integral over the respective period t _K of a corona window in which a corona discharge takes place. The rest of the time there is no energy input and the polarity reversal of the electrodes remains in the range g between U _{K +} and U _{K -} unused. In addition, due to polarization effects, the distance between the extreme points of the sine curve to the respective breakdown voltage U _B for the Arc discharge U _{B +} or U _B- different, so that the amount of energy introduced can only be optimized for one polarity (plus or minus) (here: on the lower part of the sine wave voltage). For rectified voltages where only one half-wave of the voltage is "cut off", one would have to accept at least the losses between 0 and the corona limit U _{K +} or U _K- (depending on which half-wave is cut off). By keeping the fundamental voltage U ₀ always above the corona limit U _K (depending on the polarity), one can minimize the energy losses and optimally approach the limit for the breakdown voltage for the arc discharge U _B and always remain in the corona window F + or F-.

In the Fig. 6 are the time courses of the most important signals (voltages and currents) for the corona ignition device of the Fig. 3 shown. Here are the stacked Fig. 6a to 6f each associated values. The illustrated period is that for an ignition process. Such should be completed within about 2 ms, preferably within 500 μs and 1 ms, so that an optimal ignition of the fuel / air mixture takes place. In the Fig. 6a the AC voltage pulsed from the DC voltage source 6 via the thyristors 7 to 7 '' can be seen on the primary-side coil of the transformer 3. Due to the transformer effect, the result in the secondary side of the coil Fig. 6b illustrated AC voltage with the in Fig. 6c shown current I ₂ . Due to the high-voltage cascade and the rectifying effect on the secondary side, the voltage U _L on the electrode 1 according to Fig. 6d educated. This is steadily over the entire time course of the corona discharge and once the corona limit is exceeded, never again below the corona boundary U _K. In the Fig. 5f are the momentum currents from the Fig. 5e shown again, but after the filter 27 of Fig. 3 ,

Claims (16)

Ignition device for an internal combustion engine, which provides for the ignition of a fuel / air mixture in the combustion chamber (24) of the internal combustion engine, a corona discharge, characterized in that the ignition device for triggering and maintaining the corona discharge for each ignition an always different from zero base voltage U _L supplies. Ignition device according to claim 1, characterized by a transformer (3), wherein on the primary side (4) of the transformer (3) a voltage source (5) is provided, which supplies alternating current or a varying direct voltage. Ignition device according to claim 2, characterized in that a voltage multiplier is provided on the secondary side (5) of the transformer (3). Ignition device according to Claim 2 or Claim 3, characterized in that a voltage smoother is arranged on the secondary side (5) of the transformer (3). Ignition device according to claim 4, characterized in that the voltage smoother is a half-wave rectifier. Ignition device according to claim 4, characterized in that the voltage smoother is a multipath rectifier. Ignition device according to one of claims 1 to 6, characterized in that a control device and / or regulating device (8) is provided. Ignition device according to claim 7, characterized in that the control device and / or regulating device (8) keeps the voltage U _L on the secondary side (5) of the transformer (3) substantially constant. Ignition device according to claim 7, characterized in that the control device (8) adjusts the voltage U _L on the secondary side (5) of the transformer (3) to a desired value. Ignition device according to claim 9, characterized in that for controlling in addition to at least one motor parameter (23) is used. Ignition device according to claim 10, characterized in that the at least one engine parameter (23) is selected from the group ignition timing, ignition duration or combinations thereof. Ignition device according to one of claims 7 to 11, characterized in that the control device and / or control device (8) keeps the base voltage U _L always below the breakdown voltage U _B for an arc discharge. Ignition device according to one of Claims 7 to 12, characterized in that the control device and / or regulating device (8) always maintains the basic voltage U _L above the corona boundary U _K. A method for igniting a fuel / air mixture preferably in the combustion chamber (24) of an internal combustion engine by means of a corona discharge, characterized in that for triggering and maintaining the corona discharge a base voltage U _{L which} is always different from zero is provided. Internal combustion engine with an ignition device according to one of claims 1 to 13. Stationary power plant comprising a generator, an internal combustion engine and an ignition device according to one of claims 1 to 13.

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