Supply voltage of a controlled ionization current

Abstract

A method of operating an internal combustion engine comprising a combustion chamber and an ion sensor fluidly connected thereto, the method comprising: Supplying the ion sensor with a low voltage during a combustion cycle of the internal combustion engine, the low voltage being adjusted to prevent premature ignition of fuel in the combustion chamber; after supplying the low voltage, supplying the ion sensor with a high voltage during the combustion cycle at a first time based on an angular position of a crankshaft of the internal combustion engine, wherein the high voltage exceeds the low voltage and is adjusted to increase an ion sensor current above a current threshold; and Disconnecting the high voltage supply to the ion sensor at a second time based on the angular position of the crankshaft during the combustion cycle; where the high voltage is proportional to a percentage of exhaust gas recirculation or to an air / fuel ratio of an air / fuel mixture in the combustion chamber.

Description

TECHNICAL FIELDThe present disclosure relates to an ionization sensor in an internal combustion engine and a method of using the ionization sensor.BACKGROUNDIonized particles can electrically conduct across an electrical gap formed between two contacts, thereby completing a circuit and permitting current to flow through the gap. If the two contacts forming the gap are positioned in or part of a combustion chamber, then the current provides information about the state of combustion in the combustion chamber. The current, or ionization signal, represents the balance between ion generation and ion recombination which change with a change in pressure, flame formation, and other factors. The ionization signal can be used to determine combustion characteristics.When the amount of exhaust gas re-supplied to the engine increases or the air-fuel mixture becomes lean, the ionization signal becomes weaker to a point where it may be difficult or impossible to use. Improved methods and apparatus for detecting ionization are desirable to obtain a useful ionization signal under various operating conditions of the engine.DE 101 62 253 A1 describes an ignition and ion current measuring device for a diesel engine. An ion current measurement voltage is applied to the glow plug as a function of a crankshaft angle position at the time of an expected ion current signal during the combustion process, while the remaining time is used for the energization of the glow and ion current measurement plug. The beginning of the ion current measurement phase coincides with the expected time of the ignition or of the combustion process. The glow and ion current measuring candle is designed such that its nominal voltage at which it reaches the required temperatures is 4 to 9 volts in vehicle electrical system systems with 14 volts.The object on which the invention is based is achieved with the features of the independent patent claims; advantageous refinements of the invention are the subject matter of the dependent claims.SUMMARY OF THE DISCLOSED EMBODIMENTSEmbodiments of an internal combustion engine, a method of operating the internal combustion engine, and a controller configured to implement the method are disclosed. In principle, the disclosed embodiments address the problems identified above. The method may be partially implemented by the controller and includes determining an angular position of a motor shaft and supplying an ion sensor fluidly connected to a combustion chamber of the motor with a low voltage at a beginning of a combustion cycle to generate an ion sensor current and a high voltage during an ionization voltage window based at least in part on the angular position of the shaft. Here, the low voltage is set to prevent premature ignition of fuel in the combustion chamber, and the high voltage is higher than the low voltage and is set to increase the ion sensor current beyond a current threshold. In some examples, the low voltage is zero volts.In some embodiments, a method is provided for operating an internal combustion engine that includes a combustion chamber and an ion sensor fluidly connected thereto. The method includes supplying the ion sensor with a high voltage at a first time of the combustion cycle based on a crank angle / angular position of a crankshaft of the internal combustion engine, and interrupting the supply of the ion sensor with the high voltage at a second time of the combustion cycle based on the angular position of the crankshaft. Here, the high voltage is more than 400 volts and is set to generate an ion sensor current that is higher than a current threshold.In some embodiments, a controller for an internal combustion engine includes control electronics configured to supply the ion sensor with a low voltage during a combustion cycle / power stroke of the internal combustion engine, the low voltage adjusted to prevent premature ignition of fuel in the combustion chamber; after the supply with the low voltage, supply the ion sensor with a high voltage at a first time during the combustion cycle based on an angular position of a crankshaft of the internal combustion engine; and interrupt the supply of the ion sensor with the high voltage at a second time of the combustion cycle based on the angular position of the crankshaft. Herein, the high voltage is higher than the low voltage and is set to increase an ion sensor current beyond a current threshold.BRIEF DESCRIPTION OF THE DRAWINGSThe features of this invention and the manner in which they are achieved will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, in which: FIG. 1 shows a block diagram of a portion of an embodiment of a motor; FIG. 2 is a diagram of an ionization signal based on an embodiment of a method of using an ion sensor in the engine of FIG. 1 ; FIG. 3 shows a schematic block diagram of a portion of another embodiment of an engine; and FIG. 4 shows a flow diagram of an embodiment of a method for using an ion sensor.Corresponding reference numerals throughout the several views refer to the same parts. While the drawings illustrate embodiments of the present invention, they are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the embodiments.DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTSThe following terms have the following meanings except where an opposite intention is expressly stated:"About" as used herein with respect to a measurable value such as an amount, time duration, and the like is intended to be inclusive of the exact numerical value as if set forth without the term "about.".The words of connection "comprises", "comprising" / "includes", "containing", "having" and the like mean "including", "including" and the like are inclusive or extensible terms and do not exclude other unspecified elements or method steps. In contrast, the connection term "consisting of" is a closed term that does not allow non-specified terms to be added.The terms "first," "second," "third," "fourth," and the like, if any, are used in the specification and claims to distinguish between similar elements, and not necessarily to describe a particular sequential or temporal order. It is understood that any terms so used are interchangeable under appropriate circumstances, such that the embodiments described herein are suitable for operation, for example, in sequences other than those illustrated or otherwise described herein. Similarly, when a method is described herein as including a series of steps, the order of these steps illustrated herein is not necessarily the only order in which these steps may be performed, and certain of the listed steps may be omitted, and / or certain other steps not described herein may be added to the method. Acts recited in the claims may be performed in any order, particularly in a different order than that depicted, unless an order is expressly or inherently claimed. The representations in the accompanying figures do not necessarily require a particular order.For clarity, terms are used in their singular form and are intended to include their plural form, except where an opposite intention is expressly stated.Where the terms "in one embodiment" or "in one aspect" occur herein, they do not necessarily all refer to the same embodiment or aspect.FIG. 1 is a block diagram of a portion of an engine 10. the engine 10 includes a combustion chamber 36 in an engine block 30, and a piston 34 that traverses a path length of the combustion chamber 36 in a reciprocating motion and thereby moves a connecting rod 16 to rotate a crankshaft 18 of the engine 10. A sensor 20 is positioned near the crankshaft 18 to determine its angle of rotation and communicate it to a controller 12 via a communication line 22. The communication line 22 transmits a signal which may be analog or digital and which represents a value for a rotation angle. The controller 12 includes control electronics configured to determine an instruction for a high voltage supply 40 and communicate via a communication line 14. The communication line 14 transmits a signal which may be analog or digital and which represents a value for the voltage of an ion sensor. The high voltage supply 40 includes an output 42 that provides a high voltage signal to an ion sensor 38 via a line 44, 48. a current meter 46 is connected in series between the high voltage supply 40 and the ion sensor 38 and measures the current flowing through the ion sensor 38 and shown in FIG. 2 as an ion sensor current 56. A magnitude of the ion sensor current 56 is provided to the controller 12 via a line 45. Controller 12 may use or communicate the signal to determine the mass fraction of fuel burned in the combustion chamber as a function of time relative to crank angle (angular position of a crankshaft), piston position in the combustion chamber, pressure in the combustion chamber, maximum cylinder pressure position, or any other combustion characteristics suitable for improving operation of engine 10. The ion sensor 38 may include one or more of: a spark plug, a glow plug, a pressure transducer, an injector, or a stand-alone transducer (PD). Here, an independent converter is referred to as a converter which only performs the function of providing a current path for the sensor current. In contrast, when operated as an ion sensor, the spark plug, glow plug, pressure transducer and injector perform this function and a primary function such as injecting fuel or generating spark.The engine 10 may be a four-stroke engine. A four-stroke engine includes an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The crankshaft makes two full revolutions so that the piston 34 moves twice into and out of the combustion chamber 36. As is well known, during the intake stroke, the piston 34 begins at top dead center (TDC) and moves downward until it reaches bottom dead center (BDC), increasing the volume of the combustion chamber 36 with the intake valves and the exhaust valves open while the combustion chamber 36 is supplied with a gas mixture / charge. During the compression stroke, the piston 34 moves from BDC to TDC and compresses the gas mixture with both intake and exhaust valves closed. At the end of the compression stroke and / or the beginning of the power stroke, while the piston 34 is near TDC, the compressed gas mixture is ignited. The resulting pressure from the combustion of the compressed gas mixture forces the piston back down toward the BDC. As used herein, upward means movement toward a position near the cylinder head / valve portion and downward means movement away from a position far from the cylinder head and toward the crankshaft 18.FIG. 2 is a diagram of an ionization signal 56 based on an embodiment of a method of using an ion sensor shown in FIG. 4. In contrast, the diagram also shows an ionization signal 58 resulting from previous methods of using the ion sensor. Additionally, the graph illustrates a combustion pressure signal 50 as a function of crankshaft angular position and an ion sensor voltage 52 applied to the ion sensor, where the ion sensor voltage 52 includes a low voltage 60 and a high voltage 54. The ionization signal 56 results from applying the ion sensor voltage 52 to the ion sensor, and the ionization signal 58 results from only the low ion sensor voltage being applied to the ion sensor. The graph illustrates that the additional high voltage 54 increases the highest ion current from about 135 microamps (at about 10-20 degrees) in the ionization signal 58 to about 265 microamps in the ionization signal 56. A value of ionization current of 135 microamperes is sensitive to noise and is difficult to distinguish therefrom. Such weak ionization signals may result from, for example, high exhaust gas recirculation (EGR) or rich or lean air / fuel mixing ratios (LKM). In some embodiments, the controller causes the high voltage supply to provide a voltage sufficient to exceed an ionization current threshold. In some examples, the ionization current threshold is 175 microamperes.In the present embodiment, a high voltage source electrically coupled to the ion sensor generates a voltage signal having a low value until the angular position of the crankshaft reaches a first angular position of the crankshaft, and then increases the voltage signal to a high value corresponding to the high voltage 54. The low voltage value is chosen to prevent ignition of the gas mixture and may be zero volts. At a second angular position of the crankshaft, the high voltage source lowers the voltage signal, for example to the low voltage 60. the first and second angular positions of the crankshaft, exemplified by angular positions 64, 65, define a high voltage window 73 configured to increase the ion current beyond a minimum current threshold 70, for example 175 microamperes. The high voltage window is smaller than an ionization window 74 defined by angular positions 64 and 66 during which ionization occurs in the combustion chamber. In the present example, the high voltage window is about 12 crank angles. Exemplary values for the low voltage include 30, 40, 50, 60, up to 400 volts, and any voltage therebetween. Exemplary values for the high voltage include 400, 500, 600, 750, 1000, 1500, up to 3000 volts, and any voltage therebetween. In one variation, the low voltage is selected to result in a maximum ion current of less than 145 microamperes and the high voltage is selected to result in a maximum ion current of more than 175 microamperes.FIG. 3 is a schematic block diagram of a portion of an engine 100. Components of the engine 100 that function in the same manner as components of the engine 10 are denoted by the same reference numerals. As disclosed with respect to FIG. 1, the motor 10 includes the controller 12 that includes control electronics configured to determine an instruction for the high voltage power supply 40 and communicate over the communication line 14. In the present embodiment, a high voltage supply 102 is provided that includes an inverter controller 106 coupled to a rectifier circuit 112. The inverter controller 106 switches power switches 120, 122 coupled to a (DC) DC voltage V IN to generate an (AC) AC voltage for a transformer 110. A secondary winding of the transformer 110 supplies the rectifying circuit 112 with a step-up AC voltage from which the voltage V becomes OUT after rectification with which the ion sensor is supplied. The inverter controller 106 also includes control electronics and may therefore be configured to cooperate with the controller 12. In one embodiment, controller 12 provides signals indicative of the angular position of the crankshaft to inverter controller 106, and inverter controller 106 is programmed to determine the angular positions indicative of the beginning and end of the high voltage window based on the type of engine (e.g., spark ignition or compression ignition), the type of fuel consumed by the engine, the EGR percentage, the LKM, and any other parameters. The control electronics in inverter controller 106 are programmed to increase V OUT from the low to the high voltage based on the parameters of the high voltage window. The control electronics in inverter controller 106 may also be programmed to provide V OUT based on the ion sensor current such that the current remains above a minimum current threshold. As is known in the art, V OUT may be adjusted by changing the duty cycle of the power switches 120, 122. Of course, any known switching power supply may be used. At least some of the tasks of the control device 12 and of the converter control device 106 can be distributed between these and further control devices.In another embodiment, the controller 12 provides signals indicative of the desired output voltage or current to the inverter controller 106, and the inverter controller 106 is programmed to determine the switching pattern of the power switches 120, 122 to generate the desired voltage or current. The signals may be generated dynamically based on current operating conditions of the engine. The controller 12 may determine the desired output voltage or current directly or indirectly from the position of the crankshaft.In certain embodiments, a controller includes one or more modules configured to functionally perform the operations of the controller. This description, including modules, emphasize the structural independence of certain aspects of the controller and illustrates a organization of the controller's operations and responsibilities. It should be understood that other arrangements that perform similar overall operations are within the scope of the present application. Modules may be embodied as hardware and / or as process instructions on a non-transitory computer readable storage medium. Modules may be distributed over various hardware or computer-based components. Example, non-limiting elements of a module implementation include sensors that provide any value as determined herein, sensors that determine any value that is a precursor to a value as determined herein, data link and / or network hardware including communication chips, crystal, communication links, cables, twisted pair cables, coaxial cables, shielded cables, transmitters, receivers, and / or transceivers, logic circuitry, hardwired logic circuitry, reconfigurable logic circuitry configured according to the module specification in a particular non-volatile state, any actuator including at least one electrical, hydraulic, or pneumatic actuator, a solenoid, an operational amplifier implemented as an integrated circuit, analog control elements (springs, filters, integrators, adders, dividers, amplifier elements), and / or digital control elements.Certain operations described herein include operations for evaluating and / or determining one or more parameters. Evaluation or determination as used herein includes receiving values by any method known in the art, including at least receiving values from a data connection or network communication, receiving an electronic signal indicative of the value (e.g., a voltage, a frequency, a current, or a pulse width modulated signal), receiving a computer generated parameter indicative of the value, reading the value from a storage location on a non-transitory machine readable storage medium, receiving the value as a run-time parameter in any way known in the art, and / or receiving a value from which the evaluated parameters may be calculated, and / or referencing a preset value interpreted as the parameter value.As used herein, the term "control electronics" includes software and / or firmware on one or more programmable processors, application specific integrated circuits, FPGAs, digital signal processors, hardwired logic, or combinations thereof. For example, in various embodiments, controllers 12 and 106 may include or have access to control electronics. Therefore, various logic in accordance with the embodiments may be implemented in any suitable manner and would remain in accordance with the embodiments disclosed herein. It may additionally be contemplated that a non-transitory machine-readable medium including control electronics may be included in any tangible form of computer-readable medium, such as solid-state memory, magnetic disk, and optical disk, that includes a suitable set of computer instructions and data structures that would cause a processor to perform the techniques described herein. A non-transitory machine-readable medium or memory may include random access memory (RAM), read only memory (ROM), erasable programmable read only memory (e.g., EPROM, EEPROM, or flash memory), electrically programmable read only memory (EPROM), magnetic disk memory, or any other medium that can be used to transfer or store process instructions and data structures and that can be accessed via a general purpose computer, special purpose computer, or other processing device.With the benefit of the disclosures set forth herein, one skilled in the art will recognize that controllers 12 and 106 are configured to perform operations that improve various technologies and provide improvements in various technical fields. Example non-limiting technology improvements include, without limitation, improvements in combustion performance of internal combustion engines, improvements in emissions performance, aftertreatment system regeneration, engine torque generation and torque control, engine fuel consumption, improved durability of components of the exhaust system of internal combustion engines, and improved engine noise and vibration control. Example, non-limiting technical fields that are improved include, without limitation, the technical fields of internal combustion engines, as well as their fuel system, aftertreatment system, air supply devices, and intake and exhaust system devices.An embodiment of a method for using an ion sensor will now be described with reference to a flow chart 300 shown in FIG. 4 The method may be implemented by controllers 12 and 106. The method begins at 302 with determining an angular position of the shaft. The angular position may be the angular position of a crankshaft and indicates the position of the piston in the combustion chamber.The method continues at 304 with determining whether the angular position of the shaft exceeds a first angular position. The first angular position corresponds to the beginning of the high-voltage window. If the angular position of the shaft is less than the first angular position, the method continues at 302. Otherwise, at 320, the method continues with determining whether the angular position of the shaft exceeds a second angular position. The second angular position corresponds to the end of the high voltage window. If the angular position of the shaft is less than the second angular position, the method continues at 306 with supplying a high voltage to the ion sensor and then sensing the ion sensor current at 308. Otherwise, the method continues at 322 by interrupting the supply of the high voltage to the ion sensor.In a variant of the present embodiment, the control electronics determine the duration of the high-voltage window on the basis of motor parameters, such as revolutions per minute, without determining the second angular position.In another variation of the present embodiment, the control electronics determine the beginning of the high voltage window based on a combustion state signal representing a state of combustion without measuring the first angular position. The combustion state signal may be, for example, a spark ignition signal. The combustion state signal may also be a signal indicative of the start of ignition in a compression ignition engine. The spark ignition signal and the ignition start signal may of course be based on the position of the crankshaft, such that the determination indirectly implies the first angular position.Certain features discussed in this specification in the context of various implementations may also be embodied in combination in a single implementation. Conversely, various features described in the context of a single implementation may also be embodied in multiple implementations separately or in any suitable sub-combination. Moreover, one or more features of a claimed combination may in some cases be removed from the combination, even though the features may be described above as acting in certain combinations and even originally claimed as such, and the claimed combination may be directed to a sub-combination or variant of a sub-combination.It should be noted that the term "example" as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples, illustrations, and / or illustrations of possible embodiments (and that such term is not intended to mean that such embodiments are necessarily exceptional or excellent examples). Thus, certain implementations of the invention have been described. Other implementations are within the scope of the following claims. In some instances, acts recited in the claims may be performed in a different order and still achieve desired results.

Claims

A method of operating an internal combustion engine comprising a combustion chamber and an ion sensor fluidly connected thereto, the method comprising: supplying the ion sensor with a low voltage during a combustion cycle of the internal combustion engine, the low voltage being adjusted to prevent premature ignition of fuel in the combustion chamber; after the supplying with the low voltage, supplying the ion sensor with a high voltage during the combustion cycle at a first time based on an angular position of a crankshaft of the internal combustion engine, the high voltage exceeding the low voltage and being adjusted to increase an ion sensor current beyond a current threshold; and interrupting the supply of the ion sensor with the high voltage at a second time based on the angular position of the crankshaft during the combustion cycle; wherein the high voltage is proportional to a percentage of exhaust gas recirculation or to an air / fuel ratio of an air / fuel mixture in the combustion chamber.The method of claim 1, wherein the low voltage comprises 0 volts.The method of any one of claims 1 or 2, wherein the high voltage is equal to or greater than 500 volts and less than 3000 volts.The method of claim 3, wherein the high voltage is equal to or greater than 1000 volts.The method of any of claims 1 or 2, wherein the first and second timings define a high voltage window and the supplying with a high voltage includes supplying with the high voltage during the high voltage window and not at other timings during the combustion cycle.The method of claim 5, wherein a duration of the high voltage window is greater than 8 degrees and less than 90 degrees.The method of claim 6, wherein the duration of the high voltage window is between 10 and 40 degrees.The method of claim 7, wherein the duration of the high voltage window is between 10 and 20 degrees.The method of any of claims 1 or 2, wherein the internal combustion engine is a compression-ignition engine and wherein the first time occurs at or after a start of ignition in the combustion chamber.The method of any of claims 1 or 2, wherein the high voltage is set to maintain the ion sensor current flowing through the ion sensor above the current threshold.The method of claim 10, wherein the current threshold is greater than 100 μA.The method of claim 11, wherein the current threshold is greater than 145 μA.An internal combustion engine comprising: a block including a combustion chamber; an ion sensor fluidly connected to the combustion chamber; a crankshaft; an output of a high voltage supply electrically connected to the ion sensor; and a controller including control electronics configured to: - provide a low voltage to the ion sensor during a combustion cycle of the internal combustion engine, the low voltage being set to prevent premature ignition of fuel in the combustion chamber; - after providing the low voltage, provide a high voltage to the ion sensor during the combustion cycle at a first time based on an angular position of a crankshaft of the internal combustion engine, the high voltage exceeding the low voltage and being set to increase an ion sensor current beyond a current threshold; and interrupts the provision of the high voltage to the ion sensor at a second time based on the angular position of the crankshaft during the combustion cycle; wherein the high voltage is proportional to a percentage of exhaust gas recirculation or to an air / fuel ratio of an air / fuel mixture in the combustion chamber.The internal combustion engine of claim 13, wherein the ion sensor includes an anode connected to the high voltage supply and a cathode electrically connected to the block of the internal combustion engine.The internal combustion engine of claim 14, wherein the ion sensor includes a spark plug, a glow plug, a pressure transducer, an injector, or a self-contained transducer.The internal combustion engine of claim 13, further comprising a high voltage supply including the output of the high voltage supply.The internal combustion engine of claim 16, wherein the high voltage supply includes a transformer having a primary coil connected to a power switch, the controller configured to cause the power switch to switch an input voltage at a duty cycle set to boost the input voltage to generate the high voltage.A controller for an internal combustion engine, the controller including control electronics configured to: - provide a low voltage to an ion sensor during an internal combustion cycle of the internal combustion engine, the low voltage being set to prevent premature ignition of fuel in the combustion chamber; - after providing the low voltage, provide a high voltage to the ion sensor during the combustion cycle at a first time based on an angular position of a crankshaft of the internal combustion engine, the high voltage exceeding the low voltage and being set to increase an ion sensor current beyond a current threshold; and - interrupt the provision of the high voltage to the ion sensor at a second time based on the angular position of the crankshaft during the combustion cycle; wherein the high voltage is proportional to a percentage of exhaust gas recirculation or to an air / fuel ratio of an air / fuel mixture in the combustion chamber.The controller of claim 18, wherein the low voltage comprises 0 volts.A method of operating an internal combustion engine comprising a combustion chamber and an ion sensor fluidly connected to the combustion chamber, the method comprising: supplying the ion sensor with high voltage during a combustion cycle at a first time based on an angular position of the crankshaft of the internal combustion engine, wherein the high voltage is greater than 400 volts and is set to generate an ion sensor current that is above a current threshold; and interrupting supply of the ion sensor with the high voltage at a second time based on the angular position of the crankshaft during the combustion cycle; wherein the high voltage is equal to or greater than 1000 volts.The method of claim 20, further comprising: supplying the ion sensor with a low voltage prior to supplying the high voltage, wherein the low voltage is adjusted to prevent premature ignition in the combustion chamber.The method of claim 20, wherein the high voltage is equal to or greater than 1000 volts and less than 3000 volts.The method of claim 20, wherein the first time and the second time define a high voltage window and supplying a high voltage includes supplying the high voltage during the high voltage window and not at other times during the combustion cycle.The method of claim 23, wherein the duration of the high voltage window is greater than 8 degrees and less than 90.The method of claim 24, wherein the duration of the high voltage window is between 10 and 40 degrees.A method of operating an internal combustion engine comprising a combustion chamber and an ion sensor fluidly connected thereto, the method comprising: supplying the ion sensor with a high voltage during the combustion cycle at a first time based on an angular position of the crankshaft of the internal combustion engine, the high voltage being greater than 400 volts and being set to generate an ion sensor current above a threshold value, and interrupting the supply of the high voltage to the ion sensor at a second time based on the angular position of the crankshaft during the combustion cycle; wherein the first time and the second time define a high voltage window and the supplying with a high voltage includes supplying the high voltage during the high voltage window and not at other times during the combustion cycle; and wherein the duration of the high voltage window is between 10 and 40 degrees.A method of operating an internal combustion engine comprising a combustion chamber and an ion sensor fluidly connected thereto, the method comprising: supplying the ion sensor with a high voltage during a combustion cycle at a first time based on an angular position of the crankshaft of the internal combustion engine, wherein the high voltage is greater than 400 volts and is set to generate a sensor current above a current threshold; and interrupting the supply of the ion sensor with the high voltage at a second time based on the angular position of the crankshaft during the combustion cycle; wherein the internal combustion engine is a compression-ignition engine, and wherein the first time occurs at or after a start of ignition in the combustion chamber.A method of operating an internal combustion engine comprising a combustion chamber and an ion sensor fluidly connected thereto, the method comprising: supplying the ion sensor with a high voltage during a combustion cycle at a first time based on an angular position of the crankshaft of the internal combustion engine, wherein the high voltage is greater than 400 volts and is set to generate a sensor current above a current threshold; and interrupting the supply of the ion sensor with the high voltage at a second time based on the angular position of the crankshaft during the combustion cycle; wherein the high voltage is set to maintain the ion sensor current flowing through the ion sensor above the current threshold; and wherein the current threshold is greater than 100 μA.The method of claim 28, wherein the current threshold is greater than 145 μA.

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