WO2023233888A1

WO2023233888A1 - Method for determining the fuel type of a fuel injected into an internal combustion engine

Info

Publication number: WO2023233888A1
Application number: PCT/JP2023/016712
Authority: WO
Inventors: Henning SAUERLAND; Akiyasu Miyamoto; Yoshihito Yasukawa; Masayuki Saruwatari
Original assignee: Hitachi Astemo, Ltd.
Priority date: 2022-05-31
Filing date: 2023-04-27
Publication date: 2023-12-07
Also published as: DE102022205533A1

Abstract

The present subject matter particularly relates to a method and a control device (20) for determining a fuel type of a fuel to be injected into an internal combustion engine using a drive current of a fuel injector (5). The problem to be solved is to determine a fuel type of a fuel injected into an internal combustion engine without the application of an additional fuel sensor in the injection system. The method comprises the steps of measuring a drive current of the fuel injector (5) by a current sensor (20a), determining an opening delay of the fuel injector (5) based on the measured drive current by the control device (20), determining a fuel type of the fuel injected into the internal combustion based on the determined opening delay by the control device (20); and setting the control parameters of an injection system (100) according to the determined fuel type by the control device (20).

Description

METHOD FOR DETERMINING THE FUEL TYPE OF A FUEL INJECTED INTO AN INTERNAL COMBUSTION ENGINE

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

In order to slow down the global climate change, a massive reduction in CO₂emissions in industry and transport is necessary. In addition to the increased use of electric drives, there is still a need for internal combustion engines in vehicles, in order to be able to cover longer distances.

To achieve the required CO₂ reduction, biofuels and so-called electric fuels (E-fuels) for internal combustion engines will play an important role in the near future. E-fuels are synthetic fuels that are produced by reacting hydrogen from renewable energies with carbon dioxide. This process is commonly known as “power-to-x” and offers the opportunity to transform and save energy from renewable resources in a chemical form for long term storage and use. The “x” stands for arbitrary gaseous and liquid fuels that can be used in internal combustion engines. Examples for liquid E-fuels usable in gasoline engines are methanol, methyl formate (MeFo) and dimethyl carbonate (DMC). It is expected that these synthetic fuels will in future be provided at filling stations both in pure form and mixed with conventional fuels.

However, synthetic fuels have different fuel properties compared to conventional fossil fuels such as gasoline. DMC for example, has a lower net calorific value and therefore requires a higher injection rate than gasoline. Therefore, control parameters of an injection system used in an internal combustion engine, such as injection timing and injection pressure, must be adapted to the respective fuel/fuel composition. To provide the correct control parameters, it must be known exactly which type of fuel is currently included in the injection system/injected into the internal combustion engine. One possibility to detect the currently used fuel type may be the application of a dedicated fuel sensor in the injection system. However, this would lead to increasing costs as well as increasing implementation effort. Therefore, there is the need to have a “virtual” fuel sensor based on a feedback of the fuel injector.

Patent Literature 1: US 6237572 B1

Patent Literature 1 describes a method and apparatus for determining a fuel injection delay of a fuel injector located within an engine, during the operation of the engine. The fuel injector includes a solenoid that is electrically connected to a controller. The method includes the steps of generating an injection command signal, determining a time of said injection command signal generation, and sensing a start of injection. The start of injection is dynamically sensed during the operation of the engine.

The herein described subject matter addresses the technical object of determining a fuel type of a fuel injected into an internal combustion engine without the need of an additional fuel sensor. This object is achieved by the subject matter of the appended claims. The term “fuel type” may also encompass compositions of different types of fuel. A composition of different types of fuel may preferably include a mixture of a conventional fuel, such as gasoline, and an E-fuel, such as DMC.

According to the subject matter set forth in the appended claims, there is proposed a method for determining a fuel type of a 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, which injects 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.

The at least one fuel injector may have a valve housing in which an axially movable valve needle may be arranged. The valve housing may include a valve seat onto which the valve needle is pressed in a closed state of the fuel injector, e.g., 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 may flow to the valve seat. The fuel injector may further comprise a coil to which a field current (drive current) may be applied. When the drive current flows through the coil, a magnetic field is generated in a magnetic circuit surrounding the coil, which attracts the magnetic armature. This allows the valve needle to be lifted off the valve seat so that fuel can emerge from the fuel injector.

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

The control device of the injection system may preferably be included in the ECU or may itself be the ECU. It is also possible to have a plurality of control devices which may control subgroups of the injection system. If there is a plurality of control devices, these control devices may be interconnected with each other hierarchically or in another way.

The fuel type is determined by the control device by measuring a drive current of the at least one fuel injector by the current sensor and determining an opening delay of the at least one fuel injector based on the measured drive current, which is then used to determine the fuel type. The term “drive current” shall also include a drive current curve as a function of time. It is also possible that drive current curves of more than one fuel injector are measured based on which opening delays of more than one fuel injector are determined.

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 to a specific composition of different fuels. The correlation between the opening delay of the fuel injector and the type of fuel injected is based on the different fluid forces with which different fuel types act on the fuel injector. For example, the bulk modulus of DMC is higher than that of gasoline, so that the bulk modulus of a gasoline-DMC composition increases with increasing DMC fraction. This results in a larger hydraulic force acting on the valve needle, which must be overcome by the magnetic force when the injector opens. Thus, the opening delay of a gasoline-DMC composition becomes larger with increasing DMC fraction. Besides the bulk modulus 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 predetermined fuel temperature. It is also possible to store different correlations in different characteristic curves based on different fuel properties. This may improve the accuracy of the determination.

When the fuel type is determined, the 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, e.g., 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 calorific value, boiling section, density and viscosity

The subject matter described herein enables reliable detection of changes in fuel composition after refuelling without the need for an additional fuel sensor. Since the fuel determination is based on the opening delay of the fuel injector, the fuel type of the fuel currently injected is determined, which enables feedback control within the same operating cycle of the internal combustion engine.

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

At the first time, when the fuel injector starts to be energized, the drive current starts to increase from zero to a predetermined holding current. This means that the start of energization causes a bend in the drive current curve, which can be detected by the control device by analysing the measured drive current. When the valve needle of the fuel injector reaches its full lift, a further bend in the drive current curve occurs due to the change in coil resistance caused by the now static needle. This second bend can be also determined by analysing the measured drive current. After detecting the above-described time points (first and second time), the first time may be subtracted from the second time to determine the opening delay of the fuel injector.

According to an example, the first time may be detected by the control device by filtering the drive current of the at least one fuel injector with a low pass filter and the second time may be detected by filtering the drive current with a high pass filter. The details as to how the first and second time can be detected will be described later in connection with the Figures 3a and 3b.

According to an example, a fuel temperature may be determined by the control device based on a gradient of the drive current between the first and the second time. The opening delay being the time period from the first time at which the energization starts to the second time at which the valve needle reaches its maximum lift includes a first time period during which the magnetic circuit is established, and the valve needle does not yet move, and a second time period during which the valve needle moves from the valve seat to its maximum lift. The second time period is much shorter than the first time period. As the valve needle is at rest during the first time period, a change in temperature only affects the resistance of the coil (higher fuel temperature leads to higher resistance), resulting in a change in the gradient of the drive current during the first time period (higher fuel temperature leads to lower drive current gradient). Since the first time period is large compared to the second time period, the fuel temperature can be easily derived from a gradient of the drive current between the first and the second time. For example, the gradient may be determined at different time points between the first and second time or a single gradient may be determined between two predetermined time points that fall between the first and second time. The gradient determined in the described way can then be correlated with a fuel temperature. The corresponding correlation may be determined in advance, for example, by measuring the resistance/drive current of the fuel injector coil at defined temperatures on a test bench.

According to an example, the determined opening delay may be adjusted by the control device depending on the determined fuel temperature. Since the fuel properties such as bulk modulus, density and viscosity vary as a function of fuel temperature, the fluid force acting on the fuel injector and thus the opening delay also varies. To further improve the accuracy of the fuel type determination, the opening delay determined from the drive current may be adjusted depending on the fuel temperature. For example, a characteristic curve may be stored in the control device representing the dependence of the respective fuel properties on the temperature. The opening delay determined from the drive current may then be multiplied by the value from the temperature characteristic curve, for example, or the value from the temperature characteristic curve can be subtracted from or added to the opening delay determined from the drive current.

According to an example, the opening delay of the at least one fuel injector may be determined by the control device when the determined fuel temperature is in a predetermined temperature range. This means that the internal combustion engine may be operated at defined operation conditions (engine temperature, engine load, engine speed) to assure that the fuel temperature and thus the fluid forces on the fuel injector are comparable each time the opening delay of the fuel injector is determined. This can reduce the need to adjust the opening delay as a function of temperature and further increase the accuracy of the fuel type determination.

According to an example, the determined opening delay of the at least one fuel injector may be adjusted by the control device based on a fuel pressure of the fuel being in the injection system. As the fuel pressure increases, the fluid force acting on the fuel injector increases and so does the opening delay. To take this effect into account, the opening delay determined from the drive current can be adjusted as a function of the fuel pressure. For example, a characteristic curve may be stored in the control device representing the dependence of the respective fuel properties on the fuel pressure. The opening delay determined from the drive current may then be multiplied by the value from the fuel pressure characteristic curve, for example, or the value from the fuel pressure characteristic curve can be subtracted from or 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 can be positioned upstream of the fuel injector to measure the fuel pressure acting on the latter.

According to an example, the determined opening delay of the at least one fuel injector may be adjusted by the control device based on an intake pressure of the internal combustion engine. As the intake pressure increases, the pressure difference between the fuel pressure and the intake pressure decreases. Thus, the opening delay of the fuel injector may be reduced with increasing intake pressure. To take this effect into account, the opening delay determined from the drive current can be adjusted as a function of the intake pressure. For example, a characteristic curve may be stored in the control device representing the dependence of the opening delay on the intake pressure. The opening delay determined from the drive current may then be multiplied by the value from the intake pressure characteristic curve, for example, or the value from the intake pressure characteristic curve can be subtracted from or added to the opening delay determined from the drive current. The intake pressure may be measured by in intake pressure sensor included in the injection system. For example, the intake pressure sensor can be positioned in the intake port of the internal combustion engine.

According to an example, the opening delay of the at least one fuel injector may be determined by the control device after a predetermined time after refuelling of the internal combustion engine. This means that the opening delay of the fuel injection valve can be determined after a defined waiting time after engine start, in order to exclude influences due to possible air bubbles in the fuel system. Alternatively or additionally, a defined flushing process of the injection system can be carried out before the opening delay is determined.

Furthermore, a computer program product is provided that is storable in a memory and comprises instructions which, when carried out by a computer, cause the computer to perform the method as described above.

Summarizing, the disclosed subject matter allows for a reliable detection of changes in fuel composition after refuelling without the need for an additional fuel sensor. Since the fuel determination is based on the opening delay of the fuel injector, the fuel type of the fuel currently injected is determined, which enables feedback control within the same operating cycle of the internal combustion engine. In addition, changes in fuel composition can be detected irrespective of the operating point of the internal combustion engine, as the fuel temperature, the fuel pressure and the intake pressure is taken into account when determining the fuel type.

In the following the claimed subject matter will be further explained based on at least one preferential example with reference to the attached drawings, wherein:
[Fig. 1] Figure 1 shows schematically an injection system and a cylinder of an internal combustion engine according to a preferred example of the present subject matter;
[Fig. 2] Figure 2 shows a graph depicting exemplarily an opening delay of a fuel injector as a function of the bulk modulus of a gasoline-DMC fuel mixture with increasing DMC fraction;
[Fig. 3a] Figure 3a shows exemplarily a drive current of a fuel injector based on which an opening delay of the fuel injector can be determined;
[Fig. 3b] Figure 3b shows exemplarily a drive current of a fuel injector based on which an opening delay of the fuel injector can be determined;
[Fig. 4a] Figure 4a shows schematically a resistance of a coil used in a fuel injector over a temperature and a bulk modulus of an arbitrary fuel over the temperature;
[Fig. 4b] Figure 4b shows schematically the drive current curve and the valve needle lift resulting from the drive current applied to the fuel injector;
[Fig. 5] Figure 5 shows a preferred example of the method disclosed herein using a flow chart.

Figure 1 shows schematically an example of an injection system 100 and a cylinder 200 of an otherwise unspecified internal combustion engine according to according to a preferred example of the present subject matter.

The internal combustion engine (or briefly: “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 two, three, four, six, eight or less/more cylinders 200. The cylinder 200 shown in Figure 1 comprises a combustion chamber 9 in which a piston 12 with a connecting rod 13 is disposed allowing the piston 12 to travel.
The connecting rod 13 is connected to a crankshaft (not depicted) that can be a crankshaft as known.

A spark plug 8 is attached to the cylinder 200 for igniting an air-fuel mixture drawn into the combustion chamber 9 to initiate combustion. The spark plug 8, or at least parts thereof, is connected to the inside of the combustion chamber 9, so that a spark can be introduced into the combustion chamber 9.

The intake port 6 with an intake valve 7 as well as an exhaust port 11 with an exhaust valve 10 are connected to the combustion chamber 9. A fuel injector 5 is arranged in the intake port 6, which may inject fuel therein. Ambient air may 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 of the combustion chamber 9 in the intake port 6.

During an intake stroke of the internal combustion engine, the air-fuel mixture may flow through the open intake valve 7 into the combustion chamber 9, in which it may be ignited by the spark plug 8. After the combustion has taken place, during an exhaust stroke of the engine, exhaust gases may be discharged from the combustion chamber 9 via the exhaust valve 10 and the exhaust port 11.

The injection system 100 may preferably be a system for gasoline port fuel injection. The exemplary injection system 100 shown comprises a tank 1, a fuel pump 2, a fuel rail 3 with a fuel pressure sensor 3a, a pressure regulator 4, a fuel injector 5 and a control device 20 with a current sensor 20a.

The fuel pump 2 may deliver fuel at a predetermined fuel pressure from the tank 1 to the fuel rail 3. The tank may be filled with different types of fuel, especially different types of E-fuels or mixtures of conventional and E-fuels. Preferably, the tank may be filled with a mixture of gasoline and DMC.

The predetermined fuel pressure may be in the range of 2 bar to 20 bar, preferably in the range of 3 to 12 bar. In the depicted example, the fuel pressure sensor 3a for measuring the fuel pressure is disposed in the fuel rail 3, and the pressure regulator 4 for regulating/adjusting the fuel pressure is arranged in the return flow. However, a returnless flow type injection system is also possible, in which, e.g., the fuel pump 2 regulates the fuel pressure in the fuel rail 3. Further, the fuel pressure sensor 3a may also be arranged outside the fuel rail, e.g., 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, to inject fuel into the intake port 6. The control device 20 for controlling the injection system 100 depicted in Figure 1 is electrically connected to the fuel pump 2, the fuel regulator 4 and the fuel injector 5. A plurality of further actors may be electrically connected to and controlled by the control device 20.

The control device 20 shown further includes the current sensor 20a for measuring the drive current of the fuel injector 5. It is also possible for the current sensor 20a to be a separate sensor unit remote from the control device 20. The current sensor 20a may measure the drive current of the fuel injector 5 based on which an opening delay of the latter may be determined. To determining the opening delay, the control device 20 may detect a first time at which the energization of the fuel injector 5 starts and a second time at which the fuel injector 5 reaches a fully open state for the first time after start of energization. The fuel injector 5 may reach its fully open state when a valve needle of the fuel injector 5 reaches its full lift. In other words, the opening delay of the fuel injector 5 determined by the control device 20 may be the time period from start of energization until a time at which the valve needle of the fuel injector 5 reaches its full lift for the first time after start of energization.

In this context, the control device 20 may detect the first time by filtering the drive current of the fuel injector 5 with a low pass filter and the second time by filtering the drive current with a high pass filter. The details as to how the first and second time can be detected by the control device 20 will be described later in connection with the Figures 3a and 3b.

The determined opening delay correlates to a fuel type since different fuel types causes different fluid forces which act on the fuel injector in a closed state of the latter. For example, the bulk modulus of DMC is higher than that of gasoline, so that the bulk modulus of a gasoline-DMC composition increases with increasing DMC fraction. This results in a larger hydraulic force acting on the valve needle of the fuel injector, which must be overcome by the magnetic force when the fuel injector opens. Thus, the opening delay of a gasoline-DMC composition becomes larger with increasing DMC fraction.

Besides the bulk modulus, 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 predetermined fuel temperature. It is also possible to store different correlations in different characteristic curves based on different fuel properties. This may improve the accuracy of the determination.

The accuracy of the fuel type determination can be further improved by considering the fuel temperature. Since the fuel properties such as bulk modulus, density and viscosity vary as a function of fuel temperature, the fluid force acting on the fuel injector and thus the opening delay also varies. This can be taken into account, for example, by storing a characteristic curve in the control device representing the dependence of the respective fuel properties on the temperature.

The fuel temperature may be determined based on a gradient of the drive current between the first and the second time. The opening delay determined from the drive current includes a first time period during which the magnetic circuit is established, and the valve needle does not yet move, and a second time period during which the valve needle moves from the valve seat to its maximum lift. The second time period is much shorter than the first time period. As the valve needle is at rest during the first time period, a change in temperature only affects the resistance of the coil, resulting in a change in the gradient of the drive current during the first time period. Since the first time period is large compared to the second time period, the fuel temperature can be easily derived from a gradient of the drive current. For example, the gradient may be determined at different time points during the opening delay, or a single gradient may be determined between two predetermined time points that fall into the opening delay.

The control device 20 may at least receive the sensor signals of the fuel pressure sensor 3a and an intake pressure sensor 6a. By taking into account these sensor signals 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 the intake pressure vary. This even further improves the accuracy of the fuel type determination. A plurality of further 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).

The control device 20 may also be any other control unit, and signal line connections between the control device 20 and the controlled units may differ from the example of Figure 1. For example, there may be a plurality of control devices 20 which may control subgroups of the controlled actors, e.g., one control device 20-1 may only control the fuel injector 5, another control device 20-2 may only control the fuel pump 2 and so on. Even further, if there is a plurality of control devices 20, these control devices 20 may be interconnected with each other hierarchically or in another way.

Figure 2 shows a graph depicting exemplarily an opening delay of a fuel injector as a function of the bulk modulus of a gasoline-DMC fuel mixture with increasing DMC fraction. From the curve shown in Figure 2, it can be seen that the opening delay Δt_VO increases almost linearly with increasing bulk modulus K. The increasing bulk modulus results from an increasing DMC fraction in a gasoline-DMC composition. A similar behaviour of the opening delay can be observed when the density of the fuel is changed (not depicted). This is also the case when a higher amount of DMC is included in the gasoline-DMC composition.

Figures 3a and 3b show exemplarily a drive current curve 30 of a fuel injector 5 depicted over time t, based on which an opening delay Δt_VO of the fuel injector 5 can be determined. It can be seen in Figure 3a that the drive current curve 30 increases from an initial value to a holding current, which is used to maintain the opening of the valve needle. The start of energization causes a bend in the drive current curve 30, which can be detected by the control device 20 by analysing the measured drive current 30. To close the fuel injector 5, the drive current 30 is switched off and drops to its initial value. During the opening period of the valve needle two significant points in the drive current curve 30 can be recognized, namely the start of energization 310 (first time) and the time at which the valve needle reaches its full lift for the first time after start of energization 320 (second time). The start of energization causes a bend in the drive current curve 30, which can be detected by the control device 20. To determine the start of energization 310, the drive current curve 30 is filtered by a low pass filter resulting in the low pass filtered drive current curve 31 also shown in Figure 3a. By detecting the first positive peak 310 in the low pass filtered drive current curve 31, the start of energization can be reliably detected. The low pass filtered drive current curve 31 also allows for detecting the end of energization by detecting the 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 in 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, the start of energization may be determined, for example by considering not only the positive peak but also the time range at 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 during a predetermined period of time before the end of energization. In this case, in order to detect the start of energization, the end of energization should be detected first.

When the valve needle of the fuel injector 5 reaches its full lift, a further bend in the drive current curve 30 occurs due to the change in coil resistance caused by the now static needle. This second bend can be determined by filtering the drive current curve 30 with a high pass filter resulting in a high pass filtered drive current curve 32 as depicted in Figure 3b. Figure 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 (Figure 3a), but it is less pronounced than the peak 320 that occurs in the high-pass filtered drive current curve 32. Vice versa, the high pass filtered drive current curve in Figure 3b also shows a peak at the beginning of the energization, which has a similar amplitude to peak 320 that occurs when the valve needle reaches its full lift. Because of the similar amplitude, it is more difficult to distinguish between the two peaks, so more reliable detection of the start of energization can be achieved by determining it from the low pass filtered drive current curve 31 (Figure 3a). When the start of energization is already determined from the low pass filtered drive current curve 31, the time at which the valve needle reaches its full lift can be detected when the high pass filtered drive current 32 exceeds a predetermined value during a predetermined time period after start of energization. The opening delay Δt_VO of the fuel injector 5 can then be determined by subtracting the time at the start of energization from the time at which the valve needle reaches its full lift.

Figures 4a and 4b show exemplarily an influence of a fuel temperature on the determination of the opening delay as depicted in Figures 3a and 3b.

Figure 4a depicts exemplarily a resistance R_iof a coil used in a fuel injector 5 over a temperature T and a bulk modulus K of an arbitrary fuel over the temperature T. It can be seen that the coil resistance R_i increases linearly with the temperature and that the bulk modulus K decreases linearly with the temperature. The temperature dependence of the coil resistance R_i can be used to determine the fuel temperature from the drive current curve 30 of the fuel injector 5 as will be described hereinafter in connection with Fig. 4b. The temperature determined from the drive current curve 30 can in turn used to adjust the opening delay Δt_VO of the fuel injector 5, which is a function of the bulk modulus K, in order to be able to determine the fuel type in question with higher accuracy.

Figure 4b shows the drive current curve 30 and the valve needle lift 40 resulting from the drive current 30 applied to the fuel injector 5. One can see in Figure 4b that the opening delay Δt_VO, which covers the period from the start of energization to the time when the valve needle reaches its full lift, includes two time periods τ₁ and τ₂. During the first time period τ₁ the valve needle is at rest, so that a change in temperature only affects the resistance of the coil, resulting in a change in the gradient of the drive current during the first time period τ₁ (illustrated by the bold arrow marked with “T”). During this time period τ₁the fuel temperature can be easily derived from a gradient of the drive current curve 30. For example, the gradient may be determined at different time points during the time period τ₁ or a single gradient may be determined between two predetermined time points that fall in the first time period τ₁. The gradient determined in the described way can then be correlated with a fuel temperature. The corresponding correlation may be determined in advance, for example, by measuring the resistance/drive current of the fuel injector coil at defined temperatures on a test bench.

During the second time period τ₂, the valve needle moves from its initial position to its maximum lift. This duration/gradient of this movement depends in particular on the fuel properties of the fuel to be injected, such as the bulk modulus, which influence the hydraulic force acting against the opening force of the magnetic circuit built up by the drive current. As a result the second time period τ₂varies when the type of fuel to be injected changes.

In other words, the first time period τ₁of the opening delay Δt_VO derived from the drive current curve 30 of the fuel injector 5 corresponds the fuel temperature and the second time period τ₂ of the opening delay Δt_VO corresponds to the fuel type (see also Figure 4a).

Figure 5 shows a preferred example of the method disclosed herein using a flow chart.
It can be seen that after starting the method, in the step S500, a drive current curve I(t) of at least one fuel injector of an injection system 100 is measured by a current sensor 20a. It is also possible that drive current curves I(t) of more than one fuel injector 5 are measured and analysed to improve the accuracy of the fuel determination. In the subsequent steps S501 and S502 a first time t(SOE), at which the energization of the fuel injector 5 starts, and a second time t(h_v), at which the valve needle reaches its full lift, are obtained from the measured drive current curve(s) I(t). In the next step S503 the opening delay Δt_VO of the fuel injector is calculated by subtracting the first time t(SOE) from the second time t(h_v). Then the opening delay Δt_VO is adjusted in step S504 depending on the fuel temperature T, the fuel pressure p_fuel and the intake pressure p_in resulting in the adjusted opening delay Δt_{VO_adj}. Based on the adjusted opening delay Δt_{VO_adj} the fuel type of the fuel to be injected into the internal combustion engine is determined in the following step S505.

In other words, a fuel type of a fuel to be injected into an internal combustion engine is determined by measuring the drive current I(t) of at least one fuel injector 5, determining an opening delay Δt_VOof said fuel injector 5 from the measured drive current I(t) and determining a 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 adjusted to the operating conditions of the injection system 100, such as fuel temperature T, fuel pressure p_fuel and intake pressure p_in resulting in an adjusted opening delay Δt_{VO_adj}. A fuel type of the fuel injected into the internal combustion is then determined by the control device 20 based on the adjusted opening delay Δt_{VO_adj}.

Finally, the control parameters of the injection system 100, such as injection timing and injection pressure are set by the control unit 20 (S506) according to the detected fuel type and then the method is terminated.

Again summarizing, the disclosed subject matter allows for a reliable detection of changes in fuel composition after refuelling without the need for an additional fuel sensor. Since the fuel determination is based on the opening delay of the fuel injector, the fuel type of the fuel currently injected is determined, which enables feedback control within the same operating cycle of the internal combustion engine. In addition, changes in fuel composition can be detected irrespective of the operating point of the internal combustion engine, as the fuel temperature, the fuel pressure and the intake pressure is taken into account when determining the fuel type.

3a fuel pressure sensor
5 fuel injector
6a intake pressure sensor
20 control device
20a current sensor
100 injection system

Claims

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 the steps
measuring a drive current of the at least one fuel injector by the current sensor;
determining an opening delay of the fuel injector based on the measured drive current by the control device;
determining a fuel type of the fuel injected into the internal combustion based on the determined opening delay by the control device; and
setting the control parameters of the injection system according to the determined fuel type by the control device.
The method according to claim 1, wherein determining the opening delay of the at least one fuel injector comprises the steps of
detecting, based on the measured drive current, a first time at which the energization of the at least one fuel injector starts and a second time at which the at least one fuel injector reaches a fully open state for the first time after start of energization; and
subtracting the first time from the second time.
The method according to claim 2, wherein the first time is detected by filtering the drive current of the at least one fuel injector with a low pass filter and the second time is detected by filtering the drive current with a high pass filter.
The method according to claim 2, wherein a fuel temperature is determined by the control device based on a gradient of the drive current between the first and the second time.
The method according claim 4, wherein the determined opening delay is adjusted by the control device depending on the determined fuel temperature.
The method according to 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 in a predetermined temperature range.
The method according to claim 1, wherein the injection system further includes a fuel pressure sensor, and wherein 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 being in the injection system.
The method according to claim 1, wherein the injection system further includes an intake pressure sensor, and the determined opening delay of the at least one fuel injector is adjusted by the control device based on an intake pressure of the internal combustion engine.
The method according to claim 1, wherein the opening delay of the at least one fuel injector is determined by the control device after a predetermined time after refuelling of the internal combustion engine.
Control device configured to perform the method according to claim 1.
Injection system including at least one fuel injector injecting fuel into the internal combustion engine, a current sensor and the control device according to claim 10.
Internal combustion engine including the injection system according to claim 11.
Computer program product storable in a memory comprising instructions which, when carried out by a computer, cause the computer to perform the method according to claim 1.