Method and device for monitoring a combustion process in an internal combustion engine

1. A method for monitoring a combustion process in an internal combustion engine comprising the step of igniting a fuel-air mixture with a high-frequency plasma, wherein a high-frequency signal is applied to a resonator with a capacity which is so low that no electric arcing-over forms on the electrodes, wherein at least one high-frequency current and at least one high-frequency voltage are measured, wherein a quality of the resonator is determined based at least on the at least one high-frequency current and the at least one high-frequency voltage, and wherein an impedance of the ignited mixture is determined based at least on the determined quality of the resonator, and wherein the combustion process is evaluated by means of the impedance.

2. The method according to claim 1 , wherein the impedance of the ignited mixture is determined on each of the cylinders provided in the internal combustion engine.

3. The method according to claim 1 , wherein the combustion process over the course of time is determined from the impedance.

4. The method according to claim 1 , wherein an adaptation for an ignition process following the combustion process is determined from the impedance.

5. The method according to claim 3 , wherein from the combustion process over a course of time at least one of a plasma duration and a plasma capacity is adapted to an ignition process following the combustion process.

6. The method according to claim 1 , wherein from the determined impedance a conclusion is drawn as to whether firing-up has not materialized and in this case, a post-ignition for the same combustion process is initiated.

7. The method according to claim 1 , wherein from the determined impedance a conclusion is drawn as to whether firing-up has not materialized and in this case exhaust gas re-treatment or re-combustion is initiated.

8. The method according to claim 1 , wherein a high frequency which changes over time is applied to the resonator and the high-frequency voltage and the high-frequency current are measured at several frequencies and the quality of the resonator is determined from a phase shift of the high-frequency voltage and the high-frequency current.

9. The method according to claim 1 , wherein the impedance is determined in that a DC voltage is applied to the input of the resonator and with a DC voltage measurement of an ion current a resistance forming between the electrodes is measured.

10. A method for monitoring a combustion process in an internal combustion engine wherein a fuel-air mixture is ignited with a high-frequency plasma, the method comprising the steps of:

determining a quality of a resonator,

determining an impedance of the ignited mixture based at least on the determined quality of the resonator, and

evaluating the combustion process by means of the impedance,

wherein from the impedance a course over time of the combustion process is determined, and

wherein from the course over time of the combustion process at least one of a plasma duration and a plasma capacity are adapted for an ignition process following the combustion process.

11. The method according to claim 10 , wherein the impedance of the ignited mixture is determined on each of the cylinders provided in the internal combustion engine.

12. The method according to claim 10 , wherein an adaptation for an ignition process following the combustion process is determined from the impedance.

13. The method according to claim 10 , wherein from the determined impedance a conclusion can be drawn as to whether firing-up has not materialized and in this case, post-ignition for the same combustion process is initiated.

14. The method according to claim 10 , wherein from the determined impedance a conclusion is drawn as to whether firing-up has not materialized and in this case exhaust gas re-treatment or re-combustion is initiated.

15. The method according to claim 10 , wherein the impedance is determined in that a high-frequency signal is applied to the resonator with a capacity which is so low that no electric arcing-over forms on the electrodes and a high-frequency current and a high-frequency voltage are measured.

16. The method according to claim 10 , wherein a high frequency which changes over time is applied to the resonator and a high-frequency voltage and a high-frequency current are measured at several frequencies and the quality of the resonator is determined from a phase shift of the high-frequency voltage and the high-frequency current.

17. The method according to claim 10 , wherein the impedance is determined in that a DC voltage is applied to the input of the resonator and with a DC voltage measurement of an ion current a resistance forming between the electrodes is measured.

18. A method for monitoring a combustion process in an internal combustion engine comprising the step of igniting a fuel-air mixture with a high-frequency plasma, comprising:

applying a high-frequency signal is applied to a resonator with a capacity which is so low that no electric arcing-over forms on the electrodes,

measuring a high-frequency current and a high-frequency voltage,

determining an impedance of the ignited mixture from the high-frequency current and the high-frequency voltage,

determining both a temperature change and a pressure change based on the determined impedance, and

evaluating the combustion process based on the determined temperature change and pressure change.

19. The method according to claim 18 , evaluating the combustion process based on the determined whether or not firing-up has materialized based at least on the determined temperature change and pressure change.