Method for determining the fuel type of fuel injected into an internal combustion engine

Abstract

The problem to be solved is to determine the fuel type of the fuel injected into an internal combustion engine without applying additional fuel sensors to the injection system. [Solution] The method includes the steps of measuring a drive current of a fuel injector (5) by a current sensor (20a), determining an opening delay of the fuel injector (5) by a control device (20) based on the measured drive current, determining a fuel type of fuel to be injected into the internal combustion engine by the control device (20) based on the determined opening delay, and setting control parameters of the injection system (100) by the control device (20) in response to the determined fuel type.

Description

[Technical Field]

[0001] The present subject matter relates to a method and control device for determining the fuel type of fuel injected into an internal combustion engine using a drive current for a fuel injector, an injection system including the control device, and an internal combustion engine including the injection system. [Background technology]

[0002] To slow global climate change, significant reductions in CO2 emissions from industry and transport are necessary. In addition to the increasing use of electric drives, there is still a need for internal combustion engines in vehicles to be able to cover longer distances.

[0003] To achieve the required CO2 reductions, biofuels and so-called electrofuels (E-fuels) for internal combustion engines could play an important role in the near future. E-fuels are synthetic fuels produced by reacting hydrogen from renewable energy with carbon dioxide. This process, commonly known as "power-to-x," offers the opportunity to convert and conserve energy from renewable resources in chemical form for long-term storage and use. The "x" represents any gaseous or liquid fuel that can be used in internal combustion engines. Examples of liquid E-fuels that can be used in gasoline engines are methanol, methyl formate (MeFo), and dimethyl carbonate (DMC). It is expected that these synthetic fuels will be supplied to filling stations in the future both in pure form and blended with conventional fuels.

[0004] However, synthetic fuels have different fuel properties compared to traditional fossil fuels such as gasoline. For example, DMC requires a higher injection rate than gasoline due to its lower net heating value. Therefore, the control parameters of the injection system used in an internal combustion engine, such as injection timing and injection pressure, must be adapted to each fuel / fuel composition. To provide accurate control parameters, it is necessary to know exactly which type of fuel is currently included in the injection system / injected into the internal combustion engine. One possibility for detecting the currently used fuel type would be the application of a dedicated fuel sensor in the injection system. However, this would lead to increased costs and implementation effort. Therefore, there is a need for a "virtual" fuel sensor based on fuel injector feedback. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 6,237,572 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 describes a method and apparatus for determining fuel injection delay for a fuel injector located within an engine during engine operation. The fuel injector includes a solenoid electrically connected to a controller. The method includes generating an injection command signal, determining a time for generating the injection command signal, and detecting a start of injection. The start of injection is detected dynamically during engine operation.

[0007] The subject matter described herein addresses the technical objective of determining the fuel type of fuel injected into an internal combustion engine without the need for an additional fuel sensor. This objective is achieved by the subject matter of the accompanying claims. Also, the term "fuel type" may encompass compositions of different types of fuel. The compositions of different types of fuel may preferably include a mixture of a conventional fuel, such as gasoline, and an E-fuel, such as DMC. [Means for solving the problem]

[0008] According to the subject matter of the appended claims, a method is proposed for determining a fuel type of fuel to be injected into an internal combustion engine via an injection system. The internal combustion engine may preferably be a gasoline engine, and the injection system may preferably be a system for gasoline port fuel injection. The injection system includes at least one fuel injector for injecting fuel into the internal combustion engine, a current sensor, and a control device. Preferably, the at least one fuel injector may inject fuel into an intake port of the internal combustion engine.

[0009] At least one fuel injector may have a valve housing in which an axially movable valve needle may be disposed. The valve housing may include a valve seat against which the valve needle is pressed when the fuel injector is closed, for example, by a spring and fuel pressure acting on the fuel injector. The valve needle may be connected to a magnetic armature and include a cavity through which fuel introduced into the fuel injector can flow to the valve seat. The fuel injector may further include a coil to which a field current (drive current) can be applied. When the drive current flows through the coil, a magnetic field is generated in a magnetic circuit surrounding the coil, thereby attracting the magnetic armature. This allows the valve needle to lift from the valve seat so that fuel can exit the fuel injector.

[0010] The current sensor may preferably be included in a control device of the injection system or in an electronic control unit (ECU) of the internal combustion engine. It is also possible for the current sensor to be a stand-alone sensor that may be located remotely from the control device or ECU.

[0011] The control device of the injection system may preferably be included in an ECU or may itself be an ECU. It is also conceivable to have several control devices that may control subgroups of the injection system. If several control devices are present, these may be interconnected with each other hierarchically or otherwise.

[0012] The fuel type is determined by the control device by measuring a drive current of at least one fuel injector with a current sensor and determining an opening delay of the at least one fuel injector based on the measured drive current, where the opening delay is then used to determine the fuel type. The term "drive current" also includes a drive current curve as a function of time. It is also possible that drive current curves of two or more fuel injectors are measured based on which opening delays of the two or more fuel injectors are determined.

[0013] In other words, the opening delay determined by the control device from the measured drive current may be correlated to a specific fuel type and / or specific compositions of different fuels. The correlation between the opening delay of a fuel injector and the type of injected fuel is based on the different fluid forces that different fuel types exert on the fuel injector. For example, the bulk modulus of a gasoline-DMC composition increases with increasing DMC fraction because the bulk modulus of DMC is higher than that of gasoline. This results in a greater hydraulic force acting on the valve needle, which must be overcome by a magnetic force when the injector opens. Therefore, the opening delay of a gasoline-DMC composition increases with increasing DMC fraction. Furthermore, the bulk modulus, viscosity, and density of different fuel types may be correlated with the opening delay of a fuel injector. The correlation between a specific fuel type and the opening delay of a fuel injector may be stored in the control unit, for example, as a characteristic curve at a given fuel temperature. It is also possible to store different correlations for different characteristic curves based on different fuel properties, thereby improving the accuracy of the determination.

[0014] Once the fuel type is determined, control parameters of the injection system are set by the control device according to the determined fuel type. The control parameters of the injection system may include, for example, parameters for controlling injection timing (start, duration, and end of injection) and injection pressure. These parameters may be determined based on additional fuel properties of the determined fuel type, such as net heating value, boiling point section, density, and viscosity.

[0015] The subject matter described herein allows for reliable detection of changes in fuel composition after refueling without the need for additional fuel sensors. Because the fuel decision is based on the fuel injector opening delay, the fuel type of the fuel currently being injected is determined, which allows for feedback control within the same operating cycle of the internal combustion engine.

[0016] According to one example, a first time at which energization of the at least one fuel injector begins and a second time at which the at least one fuel injector reaches a full open state for the first time after energization may be detected by the control device based on the measured drive current. The fuel injector may reach its full open state when a valve needle of the fuel injector reaches its full lift. In other words, the determined opening delay of the fuel injector may be the period from energization to the time at which a valve needle of the fuel injector reaches its full lift for the first time after energization.

[0017] Initially, when the fuel injector begins to energize, the drive current begins to increase from zero to a predetermined holding current. This means that the start of energization causes an inflection in the drive current curve, which can be detected by the control device by analyzing the measured drive current. When the fuel injector valve needle reaches its full lift, a further inflection in the drive current curve occurs due to a change in coil resistance caused by the now stationary needle. This second inflection can also be determined by analyzing the measured drive current. After detecting the aforementioned points in time (first and second times), the first time may be subtracted from the second time to determine the opening delay of the fuel injector.

[0018] According to one example, the first time period may be detected by the control device by low pass filtering the drive current of the at least one fuel injector, and the second time period may be detected by high pass filtering the drive current. Details regarding how the first and second times may be detected are described below in conjunction with Figures 3a and 3b.

[0019] According to one example, the fuel temperature may be determined by the control device based on the slope of the drive current between a first time and a second time. The opening delay, which is the period from the first time when the power supply starts to the second time when the valve needle reaches maximum lift, includes a first period during which the magnetic circuit is established and the valve needle is not yet moving, and a second period during which the valve needle moves from the valve seat to its maximum lift. The second period is much shorter than the first period. Because the valve needle is stationary during the first period, changes in temperature only affect the resistance of the coil (higher fuel temperature results in higher resistance) and cause a change in the slope of the drive current during the first period (higher fuel temperature results in a lower drive current slope). Because the first period is larger than the second period, the fuel temperature can be easily derived from the slope of the drive current between the first and second times. For example, the slope may be determined at different times between the first and second times, or a single slope may be determined between two predetermined times between the first and second times. The slope determined in the described manner can then be correlated with fuel temperature, and the corresponding correlation may be predetermined, for example, by measuring the resistance / drive current of the fuel injector coil at a defined temperature on a test bench.

[0020] According to one example, the determined opening delay may be adjusted by the control device in response to the determined fuel temperature. Because fuel properties such as bulk modulus, density, and viscosity change with fuel temperature, the fluid forces acting on the fuel injector, and therefore the opening delay, also change. To further improve the accuracy of the fuel type determination, the opening delay determined from the drive current may be adjusted in response to the fuel temperature. For example, a characteristic curve representing the dependence of each fuel property on temperature may be stored in the control device. The opening delay determined from the drive current may then be multiplied by, for example, a value from the temperature characteristic curve, or a value from the temperature characteristic curve may be subtracted from, or added to, the opening delay determined from the drive current.

[0021] According to one example, the opening delay of at least one fuel injector may be determined by the control device when the determined fuel temperature is within a predetermined temperature range. This means that the internal combustion engine can be operated under specified operating conditions (engine temperature, engine load, engine speed) to ensure that the fuel temperature, and therefore the fluid force on the fuel injector, is equivalent each time the opening delay of the fuel injector is determined. This reduces the need to adjust the opening delay depending on temperature, further improving the accuracy of the fuel type determination.

[0022] According to one example, the determined opening delay of at least one fuel injector may be adjusted by the control device based on the fuel pressure of the fuel in the injection system. As the fuel pressure increases, the fluid force acting on the fuel injector increases, and the opening delay also increases. To take this effect into account, the opening delay determined from the drive current may be adjusted depending on the fuel pressure. For example, a characteristic curve representing the dependence of each fuel characteristic on fuel pressure may be stored in the control device. The opening delay determined from the drive current may then be multiplied, for example, by a value from the fuel pressure characteristic curve, or a value from the fuel pressure characteristic curve may be subtracted from the opening delay determined from the drive current, or a value from the fuel pressure characteristic curve may be added to the opening delay determined from the drive current. The fuel pressure may be measured by a fuel pressure sensor included in the injection system. For example, the fuel pressure sensor may be located upstream of the fuel injector to measure the fuel pressure acting on the fuel injector.

[0023] According to one example, the determined opening delay of at least one fuel injector may be adjusted by the control device based on the intake pressure of the internal combustion engine. The higher the intake pressure, the smaller the pressure difference between the fuel pressure and the intake pressure. Therefore, the opening delay of the fuel injector may be reduced as the intake pressure increases. To take this effect into account, the opening delay determined from the drive current may be adjusted depending on the intake pressure. For example, a characteristic curve representing the dependence of the opening delay on the intake pressure may be stored in the control device. Then, for example, the opening delay determined from the drive current may be multiplied by a value from the intake pressure characteristic curve, or a value from the intake pressure characteristic curve may be subtracted from the opening delay determined from the drive current, or a value from the intake pressure characteristic curve may be added to the opening delay determined from the drive current. The intake pressure may be measured by an intake pressure sensor included in the injection system. For example, the intake pressure sensor may be located in an intake port of the internal combustion engine.

[0024] According to one example, the opening delay of at least one fuel injector may be determined by the control device after a predetermined time after refueling the internal combustion engine. This means that the opening delay of the fuel injection valves can be determined after a specified waiting time after engine start to eliminate the influence of possible air bubbles in the fuel system. Alternatively or additionally, a predetermined flushing process of the injection system can be performed before the opening delay is determined.

[0025] Further provided is a computer program product storable in a memory and comprising instructions which, when executed by a computer, cause the computer to perform the method described above. [Effects of the Invention]

[0026] In summary, the disclosed subject matter enables reliable detection of changes in fuel composition after refueling without the need for additional fuel sensors. Because the fuel determination is based on the fuel injector opening delay, the fuel type of the currently injected fuel is determined, which enables feedback control within the same operating cycle of the internal combustion engine. Furthermore, by taking into account fuel temperature, fuel pressure, and intake pressure when determining the fuel type, changes in fuel composition can be detected regardless of the operating point of the internal combustion engine. [Brief explanation of the drawings]

[0027] The claimed subject matter will now be further described based on at least one preferred example with reference to the accompanying drawings. [Figure 1] 1 shows a schematic representation of an injection system and cylinder of an internal combustion engine according to a preferred embodiment of the present subject matter; [Figure 2] 1 shows a graph exemplarily depicting fuel injector opening delay as a function of bulk modulus for gasoline-DMC fuel blends with increasing DMC fraction. [Figure 3] a, b Exemplary fuel injector drive currents are shown that can determine the opening delay of the fuel injector. [Figure 4] a Schematic showing the resistance of a coil used in a fuel injector versus temperature and the bulk modulus of a given fuel versus temperature, b Schematic showing the drive current curve and valve needle lift resulting from the drive current applied to the fuel injector. [Figure 5] A flow chart is used to illustrate a preferred example of the method disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0028] FIG. 1 illustrates, in schematic form, an example of an injection system 100 and cylinder 200 of an otherwise unspecified internal combustion engine according to a preferred embodiment of the present subject matter.

[0029] The internal combustion engine (or simply "combustion engine" or "engine") may preferably be a gasoline engine and may include a plurality of cylinders 200. For example, the internal combustion engine may have 2, 3, 4, 6, 8 or fewer / more cylinders 200. The cylinder 200 shown in Figure 1 comprises a combustion chamber 9 in which a piston 12 is disposed, having a connecting rod 13 so that the piston 12 can move. The connecting rod 13 is connected to a crankshaft (not shown), which may be any known crankshaft.

[0030] A spark plug 8 is attached to the cylinder 200 to ignite the air-fuel mixture drawn into the combustion chamber 9 and initiate combustion. The spark plug 8, or at least a portion thereof, is connected to the interior of the combustion chamber 9 so as to be able to introduce a spark into the combustion chamber 9.

[0031] An intake port 6 provided with an intake valve 7 and an exhaust port 11 provided with an exhaust valve 10 are connected to the combustion chamber 9. A fuel injector 5 is disposed in the intake port 6, and the intake port 6 is capable of injecting fuel. Ambient air can be drawn into the intake port 6 and mixed with the fuel injected by the fuel injector 5. In other words, the air-fuel mixture may be generated outside the combustion chamber 9 in the intake port 6.

[0032] During the intake stroke of an internal combustion engine, the air-fuel mixture may enter combustion chamber 9 through open intake valve 7, where it may be ignited by spark plug 8. After combustion has taken place, exhaust gases may exit combustion chamber 9 through exhaust valve 10 and exhaust port 11 during the exhaust stroke of the engine.

[0033] The injection system 100 may preferably be a system for gasoline port fuel injection. The illustrated exemplary injection system 100 includes a tank 1, a fuel pump 2, a fuel rail 3 having a fuel pressure sensor 3a, a pressure regulator 4, a fuel injector 5, and a control device 20 having a current sensor 20a.

[0034] A fuel pump 2 may deliver fuel from the tank 1 to a fuel rail 3 at a predetermined fuel pressure. The tank may be filled with different types of fuel, in particular different types of E-fuel, or a mixture of conventional fuel and E-fuel. Preferably, the tank may be filled with a mixture of gasoline and DMC.

[0035] The predetermined fuel pressure may be in the range of 2 bar to 20 bar, preferably in the range of 3 bar to 12 bar. In the illustrated example, a fuel pressure sensor 3a for measuring the fuel pressure is arranged in the fuel rail 3, and a pressure regulator 4 for adjusting / regulating the fuel pressure is arranged in the return flow. However, non-return flow type injection systems are also possible, for example, where the fuel pump 2 adjusts the fuel pressure in the fuel rail 3. Furthermore, the fuel pressure sensor 3a may be arranged outside the fuel rail, for example, in a pipe between the fuel pump 2 and the fuel rail 3 and / or in a pipe between the fuel rail 3 and the fuel injector 5. The fuel injector 5 is hydraulically connected to the fuel rail 3 and injects fuel into the intake port 6. A control device 20 for controlling the injection system 100 shown in FIG. 1 is electrically connected to the fuel pump 2, the fuel regulator 4, and the fuel injector 5. Multiple further actors may be electrically connected to the control device 20 and controlled by the control device.

[0036] The illustrated control device 20 further includes a current sensor 20a for measuring the drive current of the fuel injector 5. The current sensor 20a may be a separate sensor unit separate from the control device 20. The current sensor 20a may measure the drive current of the fuel injector 5, and the opening delay of the fuel injector 5 may be determined based thereon. To determine the opening delay, the control device 20 may detect a first time when the fuel injector 5 is energized and a second time when the fuel injector 5 reaches its full open state for the first time after the energization. The fuel injector 5 can reach its full open state when the valve needle of the fuel injector 5 reaches its full lift. That is, the opening delay of the fuel injector 5 determined by the control device 20 may be the period from the energization to the time when the valve needle of the fuel injector 5 reaches its full lift for the first time after the energization.

[0037] Here, the control device 20 may detect the first time by low-pass filtering the drive current of the fuel injector 5, and the second time by high-pass filtering the drive current. Details on how the first and second times may be detected by the control device 20 will be described below in relation to Figures 3a and 3b.

[0038] The determined opening delay correlates with the fuel type because different fuel types induce different fluid forces acting on the fuel injector when it is closed. For example, the bulk modulus of DMC is higher than that of gasoline, so the bulk modulus of a gasoline-DMC composition increases with increasing DMC fraction. This results in a greater hydraulic force acting on the fuel injector valve needle, which must be overcome by magnetic forces when the fuel injector opens. Therefore, the opening delay of a gasoline-DMC composition increases with increasing DMC fraction.

[0039] In addition to bulk modulus, the viscosity and density of different fuel types can be correlated with the opening delay of the fuel injector. The correlation between a particular fuel type and the opening delay of the fuel injector may be stored in the control unit, for example, as a characteristic curve at a given fuel temperature. It is also conceivable to store different correlations for different characteristic curves based on different fuel properties, which can improve the accuracy of the determination.

[0040] The accuracy of the fuel type determination can be further improved by taking fuel temperature into consideration. Fuel properties such as bulk modulus, density, and viscosity change with fuel temperature, so the fluid forces acting on the fuel injector, and therefore the opening delay, also change. This can be taken into account, for example, by storing characteristic curves in the control device that represent the dependence of each fuel property on temperature.

[0041] The fuel temperature can be determined based on the slope of the drive current between a first time and a second time. The opening delay determined from the drive current includes a first period during which the magnetic circuit is established and the valve needle is not yet moving, and a second period during which the valve needle moves from the valve seat to its maximum lift. The second period is much shorter than the first period. Because the valve needle is stationary during the first period, changes in temperature only affect the resistance of the coil, resulting in a change in the slope of the drive current during the first period. Because the first period is larger than the second period, it is easy to derive the fuel temperature from the slope of the drive current. For example, the slope can be determined at different times during the opening delay, or a single slope can be determined between two predetermined times during the opening delay.

[0042] The control device 20 may receive sensor signals from at least the fuel pressure sensor 3a and the intake air pressure sensor 6a. By taking these sensor signals into account, the opening delay determined from the drive current can be adapted to the different forces acting on the fuel injector when the fuel pressure and / or intake air pressure changes. This further improves the accuracy of the fuel type determination. Multiple additional sensor signals may also be received by the control device 20. For example, the control device 20 may be included in an engine control unit (ECU) or may itself be the engine control unit (ECU).

[0043] The control device 20 may also be any other control unit, and the signal line connections between the control device 20 and the controlled units may differ from the example of Fig. 1. For example, there may be multiple control devices 20 that can control subgroups of controlled actors, e.g., one control device 20-1 may control only the fuel injectors 5, another control device 20-2 may control only the fuel pump 2, etc. Furthermore, when multiple control devices 20 are present, these control devices 20 may be interconnected hierarchically or in other ways.

[0044] 2 shows an exemplary graph of fuel injector opening delay as a function of bulk modulus for gasoline-DMC fuel blends with increasing DMC fraction. From the curves shown in FIG. 2, the opening delay Δt VO It can be seen that increases almost linearly with increasing bulk modulus K. The increase in bulk modulus is due to the increase in the DMC fraction in the gasoline-DMC composition. If the density of the fuel is changed (not shown), a similar behavior of the release delay can be observed. This also applies when a larger amount of DMC is included in the gasoline-DMC composition.

[0045] 3a and 3b show an exemplary drive current curve 30 of a fuel injector 5 plotted over time t, based on which the opening delay Δt of the fuel injector 5 can be calculated. VO3a, it can be seen that the drive current curve 30 increases from an initial value to a holding current used to maintain the valve needle opening. When energization begins, an inflection occurs in the drive current curve 30, which can be detected by the control device 20 by analyzing the measured drive current 30. To close the fuel injector 5, the drive current 30 is switched off and decreases to its initial value. During the valve needle opening period, two key points can be recognized in the drive current curve 30: the initiation of energization 310 (first time) and the time when the valve needle reaches its full lift for the first time after energization 320 (second time). The initiation of energization causes an inflection in the drive current curve 30, which can be detected by the control device 20. To determine the initiation of energization 310, the drive current curve 30 is filtered by a low-pass filter, resulting in a low-pass filtered drive current curve 31, also shown in FIG. 3a. The initiation of energization can be reliably detected by detecting the first positive peak 310 in the low-pass filtered drive current curve 31. The low-pass filtered drive current curve 31 also allows the end of energization to be detected by detecting a large negative peak 311 when the drive current is switched off. For example, the end of energization may be detected when the low-pass filtered drive current falls below a predetermined value. The positive peak of the low-pass filtered drive current curve at the start of energization is less pronounced than the negative peak at the end of energization. Therefore, for example, the start of energization may be determined by taking into account not only the positive peak but also the time range in which the positive peak occurs. For example, the start of energization may be detected when the low-pass filtered drive current exceeds a predetermined value for a predetermined period before the end of energization. In this case, the start of energization can be detected by first detecting the end of energization.

[0046] When the valve needle of the fuel injector 5 reaches its full lift, a further inflection in the drive current curve 30 occurs due to the change in coil resistance caused by the now-stationary needle. This second inflection can be determined by filtering the drive current curve 30 with a high-pass filter to obtain a high-pass filtered drive current curve 32, as shown in FIG. 3b. FIG. 3b shows that the time at which the valve needle reaches its full lift can be determined by detecting the respective peak 320 in the high-pass filtered drive current curve 32. It can be seen that the low-pass filtered drive current curve 31 also has a positive peak at this point (FIG. 3a), but it is less pronounced than the peak 320 occurring in the high-pass filtered drive current curve 32. Conversely, the high-pass filtered drive current curve of FIG. 3b also exhibits a peak at the onset of energization, and this peak has a similar amplitude to the peak 320 occurring when the valve needle reaches its full lift. Due to the similar amplitudes, it is more difficult to distinguish between the two peaks, and therefore, a more reliable detection of the onset of energization can be achieved by determining it from the low-pass filtered drive current curve 31 (FIG. 3a). If the start of energization has already been determined from the low-pass filtered drive current curve 31, the time at which the valve needle reaches full lift can be detected when the high-pass filtered drive current 32 exceeds a predetermined value within a predetermined period from the start of energization. VO can be calculated by subtracting the time when the current begins to flow from the time when the valve needle reaches full lift.

[0047] 4a and 4b show, by way of example, the effect of fuel temperature on the determination of the opening delay as shown in FIGS. 3a and 3b.

[0048] Figure 4a shows the resistance R of the coil used in fuel injector 5 over temperature T. i and the bulk modulus K of any fuel over temperature T. iIt can be seen that increases linearly with temperature, and the bulk modulus K decreases linearly with temperature. i The temperature dependence of Δt can be used to determine the fuel temperature from the drive current curve 30 of the fuel injector 5, as will be described below in connection with Figure 4b. The temperature determined from the drive current curve 30 can then be used to calculate the opening delay Δt of the fuel injector 5, which is a function of the bulk modulus K, to enable the fuel type in question to be determined with greater accuracy. VO can be used to adjust the

[0049] Figure 4b shows the drive current curve 30 and valve needle lift 40 resulting from the drive current 30 applied to the fuel injector 5. In Figure 4b, the opening delay Δt covers the period from the start of energisation until the valve needle reaches its full lift. VO It can be seen that includes two periods τ1 and τ2. During the first period τ1, the valve needle is stationary, so changes in temperature only affect the coil resistance, resulting in a change in the slope of the drive current during the first period τ1 (indicated by the thick arrow marked with a "T"). During this period τ1, the fuel temperature can be easily derived from the slope of the drive current curve 30. For example, the slope may be determined at different times during period τ1, or a single slope may be determined between two predetermined times that fall into the first period τ1. The slope determined in the described manner can then be correlated with the fuel temperature. The corresponding correlation may be predetermined, for example, by measuring the fuel injector coil resistance / drive current at a defined temperature on a test bench.

[0050] During the second period τ2, the valve needle moves from its initial position to its maximum lift. This duration / slope of this movement depends on the fuel properties of the injected fuel, such as bulk modulus, which affect, among other things, the hydraulic force acting against the opening force of the magnetic circuit established by the drive current. As a result, the second period τ2 changes when the type of fuel injected changes.

[0051] In other words, the opening delay Δt derived from the drive current curve 30 of the fuel injector 5 VO The first period τ1 corresponds to the fuel temperature, and the opening delay Δt VO The second period τ2 corresponds to the fuel type (see also Fig. 4a).

[0052] FIG. 5 illustrates a preferred example of the method disclosed herein using a flow chart. After starting the method, in step S500, the drive current curve I(t) of at least one fuel injector of the injection system 100 is measured by the current sensor 20a. It is also possible to measure and analyze the drive current curves I(t) of two or more fuel injectors 5 to improve the accuracy of the fuel determination. In subsequent steps S501 and S502, a first time t(SOE) at which the fuel injector 5 begins to be energized and a second time t(h) at which the valve needle reaches full lift are determined from the measured drive current curve I(t). v In the next step S503, the second time t(h v ) to calculate the fuel injector opening delay Δt VO Next, in step S504, the fuel temperature T and the fuel pressure p fuel , and intake pressure p in Depending on the opening delay Δt VO is adjusted, and the adjusted opening delay Δt VO_adj The adjusted opening delay Δt VO_adj Based on this, the fuel type of the fuel to be injected into the internal combustion engine is determined in the next step S505.

[0053] In other words, the fuel type of the fuel injected into the internal combustion engine is determined by measuring the drive current I(t) of at least one fuel injector 5 and calculating the opening delay Δt of said fuel injector 5 from the measured drive current I(t). VO and determining the fuel type based on the determined opening delay. In order to improve the accuracy of the fuel determination, the determined opening delay Δt VO is the fuel temperature T, fuel pressure p fuel , and intake pressure p inand the adjusted opening delay Δt VO_adj Then, the adjusted opening delay Δt VO_adj Based on this, the fuel type of the fuel injected into the internal combustion engine is determined by the control device 20.

[0054] Finally, the control parameters of the injection system 100, such as the injection timing and injection pressure, are set by the control unit 20 in accordance with the detected type of fuel (S506), and the method ends.

[0055] In summary again, the disclosed subject matter allows for reliable detection of changes in fuel composition after refueling without the need for additional fuel sensors. Because the fuel decision is based on the fuel injector opening delay, the fuel type of the currently injected fuel is determined, which allows for feedback control within the same operating cycle of the internal combustion engine. Also, by taking into account fuel temperature, fuel pressure, and intake pressure when determining the fuel type, changes in fuel composition can be detected regardless of the operating point of the internal combustion engine. [Explanation of symbols]

[0056] 3a fuel pressure sensor 5 fuel injector 6a Intake pressure sensor 20 Control Device 20a current sensor 100 Injection System

Claims

1. 1. A method for determining a fuel type of a fuel to be injected into an internal combustion engine via an injection system, the injection system having at least one fuel injector for injecting fuel into the internal combustion engine, a current sensor, and a control device, the method comprising: measuring a drive current of the at least one fuel injector with the current sensor; determining, by the control device, an opening delay for the fuel injector based on the measured drive current; determining a fuel type of fuel to be injected into the internal combustion engine based on the determined opening delay by the control device; setting the control parameters of the injection system according to the determined fuel type by the control device; A method comprising:

2. 2. The method of claim 1, wherein determining the opening delay for the at least one fuel injector comprises: detecting, based on the measured drive current, a first time when energization of the at least one fuel injector begins and a second time when the at least one fuel injector reaches a fully open state for the first time.

3. 3. The method of claim 2, wherein the first time period is detected by filtering the drive current of the at least one fuel injector with a low pass filter and the second time period is detected by filtering the drive current with a high pass filter.

4. The method of claim 2 , wherein the control device determines a fuel temperature based on a slope of the drive current between the first time and the second time.

5. The method of claim 4 , wherein the determined opening delay is adjusted by the control device in response to the determined fuel temperature.

6. The method of claim 4 , wherein the opening delay of the at least one fuel injector is determined by the control device when the determined fuel temperature is within a predetermined temperature range.

7. 2. The method of claim 1, wherein the injection system further includes a fuel pressure sensor, and the determined opening delay of the at least one fuel injector is adjusted by the control device based on a fuel pressure of the fuel in the injection system.

8. 2. The method of claim 1, wherein the injection system further includes an intake air pressure sensor, and the determined opening delay of the at least one fuel injector is adjusted by the control device based on intake air pressure of the internal combustion engine.

9. The method of claim 1 , wherein the opening delay of the at least one fuel injector is determined by the control device after a predetermined time after refueling the internal combustion engine.

10. A control device configured to perform the method of claim 1.

11. An injection system comprising at least one fuel injector for injecting fuel into the internal combustion engine, a current sensor, and a control device according to claim 10.

12. An internal combustion engine comprising an injection system according to claim 11.

13. A computer program product storable in a memory comprising instructions which, when executed by a computer, cause said computer to perform the method of claim 1.

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