Method for operating a direct-injection gas internal combustion engine, in particular a hydrogen engine

Abstract

The invention relates to a method for operating a direct-injection gas internal combustion engine (2), in particular a hydrogen engine, wherein a post-injection process (202) is intended to take place in a first working cycle (A1) at a first point in time (t1) and a main injection process (201) is intended to take place in a second working cycle (A2), immediately following the first working cycle, at a second point in time (t2). The method has the steps of determining the lag (tA) between a third point in time (t3), which is defined by the end of the combustion during the post-injection process (202), and the second point in time (t2), comparing the determined lag (tA) with a lower lag threshold value if the determined lag (tA) does not fall below the lower lag threshold value, carrying out the post-injection process (202) in the first working cycle (A1) at the first point in time (t1) and carrying out the main injection (201) in the second working cycle (A2), immediately following the first working cycle, at the second point in time (t2), and if the determined lag (tA) falls below the lower lag threshold value, increasing the lag (tA) between the third point in time (t3) and the second point in time (t2).

Description

[0001] R.414521

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for operating a direct-injection gas combustion engine, in particular a hydrogen engine

[0006] The present invention relates to a method for operating a direct-injection gas combustion engine, in particular a hydrogen engine, as well as a computing unit and a computer program for carrying it out.

[0007] Background of the invention

[0008] To ensure combustion stability in hydrogen engines while simultaneously limiting nitrogen oxide emissions, injection timing can be selected based on the operating point. In engines equipped with a direct injection system into the combustion chamber, hydrogen can be injected during the open intake valve (open valve injection - abbreviated OVI) or during the closed intake valve (closed valve injection - abbreviated CVI). Furthermore, post-injection (i.e., after ignition) can be used to improve the response of the exhaust gas turbocharger. The timing of post-injection is crucial for achieving optimal turbocharger performance. Post-injection is therefore primarily used during transient operation.

[0009] However, when using a secondary injection, an undesirable pre-ignition of the next main injection can occur. The probability of this happening can be significantly increased under certain boundary conditions. The point in time of premature ignition of injected hydrogen when using a secondary injection is always identical to the main injection process (i.e., the relevant moment-effective injection process before R.414521).

[0010] - 2 -

[0011] Ignition) of the subsequent combustion cycle. This means that combustion begins as soon as the main injection starts. Under certain conditions, the injected hydrogen can ignite directly at the outlet of the injection valve. This type of premature ignition can cause significant mechanical damage both inside the engine and to the engine's peripheral components (e.g., the air system) and should therefore be strictly avoided.

[0012] One boundary condition known to promote this premature ignition is increased seat leakage of the injection valve. Preventing this pre-ignition is typically achieved by minimizing seat leakage. However, seat leakage can increase with extended injector runtime and exceed a critical value, necessitating additional measures.

[0013] Disclosure of the invention

[0014] According to the invention, a method for operating a direct-injection gas combustion engine, in particular a hydrogen engine, as well as a computing unit and a computer program for carrying it out, with the features of the independent claims, are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0015] This invention presents a way to avoid pre-ignition of a subsequent main injection when using a post-injection by selectively controlling the post-injection and / or the next main injection.

[0016] The invention employs the measure of providing a minimum distance, which must be maintained and in particular also verified, between the post-injection of the preceding combustion cycle and the main injection of the following combustion cycle in order to prevent pre-ignition at the time of the main injection. This distance, or lower R.414521

[0017] - 3 -

[0018] The minimum distance threshold can be determined for a specific gas combustion engine on an engine test bench and stored in an executing control unit. A suitable minimum distance could, for example, be 180° crank angle.

[0019] The mechanism that leads to premature ignition at the time of the main injection depends on numerous boundary conditions. These include, in addition to seat leakage at the injection valve, pressure, temperature, residual oxygen content, and the time interval between the end of one combustion cycle and the subsequent main injection of the next.

[0020] The end of combustion is defined by the complete or near-complete energy conversion of the injected hydrogen. Therefore, the end of combustion can be significantly delayed by using a secondary injection, as a further quantity of hydrogen is introduced into the combustion chamber for subsequent combustion. Consequently, the time interval between the end of combustion and the subsequent main injection can be considerably reduced.

[0021] When determining the end of the post-injection combustion (hereinafter also referred to as the third point in time), the end of the post-injection injection can be used as an approximation, since combustion in this case takes place close to the injector and with very little ignition delay. During the main injection, the start of the injection (hereinafter also referred to as the second point in time) is defined by the actual needle movement, which results from the start of the current flow and the opening delay (time between the start of the current flow and the actual needle movement). All parameters can be easily determined and are known in the executing control unit.

[0022] This invention now addresses the influence of the time interval between the end of combustion using a post-injection and the start of the subsequent main injection. In order to achieve sufficient purging or residual gas dilution in the injector area, and R.414521

[0023] - 4 - To avoid favorable conditions for pre-ignition, sufficient time is necessary during the charge exchange. This means that during the period of exhausting the burnt cylinder charge and drawing in fresh air, the residual gas charge in the cylinder is diluted. Only when this process is sufficiently complete is there no longer an increased risk of premature ignition at the time of the main injection. This means that a defined minimum time interval must be maintained between the end of combustion in one cycle and the time of the main injection in the following cycle, or a lower threshold interval must not be undercut, in order to prevent premature ignition during the main injection.

[0024] In the inventive method, in which a secondary injection is to take place at a first time point in a first working cycle and a primary injection is to take place at a second time point in a second, immediately subsequent working cycle, a distance between the first and second times point in time is determined. This determined distance is then compared with a lower distance threshold, and if the determined distance does not fall below the lower distance threshold, the secondary injection is carried out at the first time point in the first working cycle and the primary injection is carried out at the second time point in the second, immediately subsequent working cycle. If, however, the determined distance falls below the lower distance threshold, the distance between the first and second times point in time is increased.

[0025] The invention can be advantageously used in direct-injection hydrogen combustion engines to avoid the risk of premature ignition.

[0026] According to one embodiment, increasing the interval between the first and second time points includes bringing forward the first time point to an earlier first time point, and / or delaying the second time point to a later second time point. In particular, the activation or unlocking of the post-injection can only occur when R.414521

[0027] - 5 -

[0028] The main injection was stopped at a sufficiently late time and / or the timing of the secondary injection was adjusted sufficiently forward. This avoids the risk of premature ignition.

[0029] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0030] Implementing a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this incurs particularly low costs, especially if an executing control unit is already available for other tasks. Finally, a machine-readable storage medium is provided with a computer program stored on it as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical storage media, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0031] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0032] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0033] Brief description of the drawings

[0034] Figure 1 shows a schematic, block-based representation of a hydrogen engine. R.414521

[0035] - 6 -

[0036] Figure 2 schematically shows in a diagram the curves of injections, inlet pressure and cylinder pressure with and without pre-ignition of a main injection.

[0037] Figure 3 schematically shows in a diagram a course of injections according to an embodiment of the invention.

[0038] Figure 4 shows an embodiment of the invention in a block diagram.

[0039] embodiment(s) of the invention

[0040] Figure 1 shows a hydrogen engine 2 with several cylinders 6 into which gaseous hydrogen is injected through injection valves or injectors 5, and in which an air-hydrogen mixture is ignited by spark plugs 4. It is therefore a direct-injection engine. The hydrogen engine has an air inlet 8 and a hydrogen inlet 10. The air inlet 8 is connected to each cylinder 6 via corresponding inlet valves (not shown). The combusted air-hydrogen mixture is expelled from the cylinders into an exhaust system via corresponding exhaust valves (not shown).

[0041] A turbocharger 12 is provided, through which exhaust gas flows, which then exits through an exhaust outlet 14. The turbocharger 12 is coupled to a compressor 13, which compresses air and supplies it to the air inlet 8. The illustration here is very schematic and can be supplemented by conventional pipe and valve arrangements.

[0042] A control unit 16 is coupled to the hydrogen engine 2 and can, among other things, initiate the injection of hydrogen into the cylinders 6 of the hydrogen engine 2 and the ignition of the spark plugs 4, both of which are generally correlated with a rotational angle of an engine shaft or crankshaft (not shown). R.414521

[0043] - 7 -

[0044] Several sensors are provided, which are not shown here, and which enable the control unit 16 to detect the current operating state of the hydrogen engine 2. These could be, for example, temperature, pressure, and mass flow sensors, which can be arranged at different locations within the hydrogen engine 2.

[0045] The control unit 16 is configured to carry out a method for operating a direct-injection gas combustion engine according to embodiments of the invention, exemplary embodiments being described below with reference to Figures 2 and 3.

[0046] Figure 2 schematically shows in a diagram the curves of injections 200, inlet pressure 300 and cylinder pressure 400 with and without pre-ignition of a main injection over a crank angle (p.

[0047] The injection sequence 200 shows a main injection 201 and a subsequent injection 200.

[0048] During regular combustion of the main injection 201 and the post-injection 200, no increase or peak is discernible in the intake pressure curve 301. However, an increase or peak is discernible in the cylinder pressure curve 401 due to the combustion of the main injection 201.

[0049] In the event of irregular combustion or pre-ignition of the main injection 201, an increase or peak 303 is visible in an intake pressure curve 302 immediately at the end of the main injection 201. In a cylinder pressure curve 402, only a slight increase or peak due to the combustion of the main injection 201 is still visible.

[0050] Figure 3 schematically shows in a diagram a curve of 500 injections over a crank angle (p) according to an embodiment of the invention. Figure 4 shows in a block diagram an embodiment of a method according to the invention, which is carried out in particular by the control unit 16. Figures 3 and 4 are described together below. R.414521

[0051] - 8 -

[0052] The x-axis shows individual strokes T1, T2, T4 of an exemplary four-stroke engine, where T1 is the intake stroke, T2 the compression stroke, T3 the power stroke, and T4 the exhaust stroke. Bottom dead center (BDC) is marked BDC, and top dead center (TDC), with a distinction made between charge exchange TDC (LWOT) and ignition TDC (ZOT).

[0053] Each subsequent injection 202 begins at time h and ends at time ts, while each main injection 201 begins at time t2. Here, t1 denotes the first time at which a subsequent injection 202 is to occur in a first operating cycle A1, t2 the second time at which a main injection 201 is to occur in a second, immediately following operating cycle A2, and t3 a third time, defined by the end of the combustion of the subsequent injection 202. The time interval between the third time ta and the second time t2 is denoted by U.

[0054] In embodiments of the invention, in step 601 the distance U between the third time ta and the second time t2 is determined.

[0055] In step 602, the determined distance U is compared with a lower distance threshold value, which may be stored in the control unit 16.

[0056] If the specified distance U does not fall below the lower distance threshold, branch "0", the subsequent injection 202 is carried out in step 603 in the first work cycle A1 at the first time h and the main injection 201 in the second, immediately following work cycle at the second time t2.

[0057] If the specified distance U falls below the lower distance threshold, branch 1, the distance U between the third time ta and the second time t2 is increased in step 604. R.414521

[0058] - 9 -

[0059] Increasing the distance between the third time ta and the second time t2 can involve bringing forward the first time h to an earlier first time and / or delaying the second time t2 to a later second time.

[0060] However, if the specified distance U falls below the lower distance threshold, but it is not possible to increase the distance U between the third time ta and the second time t2 to a value above the lower distance threshold, the subsequent injection 202 will be omitted or suspended.

[0061] The invention makes it possible to avoid pre-ignition of a main injection by selectively controlling the main injection and / or subsequent injection.

Claims

R.414521 - 10 - Claims 1. Method for operating a direct-injection gas combustion engine (2), in particular a hydrogen engine, wherein in a first operating cycle (A1) a post-injection (202) is to take place at a first time (h) and in a second, immediately following operating cycle (A2) a main injection (201) is to take place at a second time (ta), the method comprising the following steps: determining (601) a distance (tA) between a third time (ts), defined by an end of the combustion of the post-injection (202), and the second time (ta), Comparing (602) the determined distance (tA) with a lower distance threshold if the determined distance (tA) does not fall below the lower distance threshold, performing (603) the post-injection (202) in the first work cycle (A1) at the first time (h) and performing the main injection (201) in the second, immediately following work cycle (A2) at the second time (ta), and if the determined distance (tA) falls below the lower distance threshold, increasing (604) the distance (tA) between the third time (ta) and the second time (ta).

2. The method of claim 1, wherein increasing (601) the distance (tA) between the third time (ta) and the second time (ta) comprises: bringing forward the first time (h) to an earlier first time.

3. Method according to claim 1 or 2, wherein increasing (601) the distance ^A) between the third time (ta) and the second time (ta) comprises: Delaying the second time point (ta) to a later second time point. R.414521 - 11 - 4. Method according to one of the preceding claims, further comprising: if the specified distance (tA) falls below the lower distance threshold, omission (605) of subsequent injection (202) if it is not possible to increase the distance (tA) between the third time (t3) and the second time (ta) to a value above the lower distance threshold.

5. Method according to one of the preceding claims, wherein the lower distance threshold value is determined on an engine test bench and stored in a memory.

6. Method according to one of the preceding claims, wherein the lower distance threshold is at least 180° KW.

7. Computing unit (16) configured to perform all process steps of a process according to any of the preceding claims.

8. Injection system of a direct-injection gas combustion engine (2), in particular a hydrogen engine, comprising at least one injector (4) for injecting gas into a cylinder (6) of the gas combustion engine (2) and the computing unit (16) according to claim 7.

9. Computer program that causes a computing unit (16), in particular a blowing system according to claim 8, to perform all process steps of a method according to any one of claims 1 to 6 when executed on the computing unit.

10. Machine-readable storage medium with a computer program stored thereon according to claim 9.

Images