In situ valuation of auto-ignition quality of fuel in compression ignition engines

1. A system for an engine to determine in situ under specified conditions an auto-ignition quality of fuel used in a compression ignition engine, the system comprising:

an ion current sensor accessing an engine cylinder for obtaining ion current data from an ion current signal;

a control unit in communication with the ion current sensor for receiving the ion current data, the control unit being configured to determine the auto-ignition quality of the fuel based on features of the ion current data, wherein the auto-ignition quality includes a cetane number or a derived cetane number of the fuel; and

wherein the control unit determines the auto-ignition quality of the fuel based on a slope of the ion current data including a rate of second peak rise and a rate of second peak decay.

2. The system of claim 1 , wherein the specified conditions include steady state operation at a certain engine speed and load.

3. The system of claim 1 , wherein the control unit determines the auto-ignition quality of the fuel based on an ion current delay of the ion current data.

4. The system of claim 1 , wherein the control unit determines the auto-ignition quality of the fuel based on a location of a second peak of the ion current data.

5. The system of claim 1 , wherein the control unit determines the auto-ignition quality of the fuel based on a location of a peak of a derivative of the ion current signal leading to at least one of a first peak and a second peak of the ion current data.

6. The system of claim 1 , wherein the control unit determines the auto-ignition quality of the fuel based on a distance between a first peak and a second peak of the ion current data.

7. The system of claim 1 , wherein the control unit determines the auto-ignition quality of the fuel based on location of a start of the ion current data.

8. The system of claim 1 , wherein the control unit determines the auto-ignition quality of the fuel based on a location of a first peak of the ion current data.

9. The system of claim 1 , wherein the slope of the ion current data further includes a rate of ion current rise and a rate of ion current delay.

10. The system of claim 1 , wherein the control unit determines the auto-ignition quality of the fuel based on an area under a curve of the ion current data.

11. The system of claim 1 , wherein the control unit determines the auto-ignition quality of the fuel based on an amplitude of one or more peaks of the ion current data.

12. The system of claim 1 , wherein the control unit determines the auto-ignition quality of the fuel based on a sum of multiple functions of one or more of a start of the ion current signal and/or the slope of the ion current signal and/or an area under a curve of the ion current signal and/or an ion current amplitude and/or an ion current delay.

13. The system of claim 1 , further comprising a glow plug including the ion current sensor, wherein the glow plug is electrically insulated from an engine block by a dielectric isolation material and provides a measurement output to the control unit.

14. The system of claim 12 , wherein each function is weighted prior to summing.

15. A system for determining in situ under specified conditions an auto-ignition quality of a fuel used in a compression ignition engine, the system comprising:

an ion current sensor accessing an engine cylinder for obtaining ion current data of an ion current signal;

a control unit in communication with the ion current sensor for receiving the ion current data, the control unit being configured to determine the auto-ignition quality of the fuel based on a slope of the ion current signal and one or more of a start of the ion current signal and/or an area under a curve of the ion current signal and/or ion current amplitude and/or ion current delay and/or a function of any combination of the above or related parameters, wherein the slope of the ion current signal includes a rate of second peak rise and a rate of second peak decay; and

wherein the auto-ignition quality includes a cetane number or a derived cetane number of the fuel.

16. The system of claim 15 , wherein the control unit is configured to determine the auto-ignition quality of the fuel based on a sum of multiple functions of one or a combination of multiple ion current signal features.

17. The system of claim 15 , wherein the ion current sensor is integrated into an isolated in-cylinder engine part including a glow plug, an engine gasket, a fuel injector, or any electrically insulated probe, and wherein the isolated in-cylinder engine part is electrically insulated from an engine block by a dielectric isolation material.

18. A system for determining in situ under specified conditions an auto-ignition quality of fuel used in a compression ignition engine, the system comprising:

an ion current sensor integrated into a glow plug of an engine cylinder for obtaining ion current data of an ion current signal, the glow plug being electrically insulated from the engine cylinder by a dielectric isolation material; and

a control unit in communication with the ion current sensor for receiving the ion current data, the control unit being configured to determine the auto-ignition quality of the fuel based on at least one ion current parameter from a list of ion current parameters consisting of: a start of the ion current signal, a slope of the ion current signal, an area under a curve of the ion current signal, an ion current amplitude, an ion current delay, wherein the slope of the ion current signal includes a rate of second peak rise and a rate of second peak decay; and

wherein the auto-ignition quality includes a cetane number or a derived cetane number of the fuel.

19. The system of claim 18 , wherein the control unit is configured to determine the auto-ignition quality of the fuel based on a sum of multiple functions or a combination of multiple ion current signal features.

20. The system of claim 18 , wherein the control unit is configured to determine the auto-ignition quality of the fuel based on a sum of multiple functions or a combination of multiple ion current signal parameters, wherein each function is weighted prior to summing.