Method and device for operating internal combustion engine with hydrogen

Abstract

The invention relates to a method and a device for operating an internal combustion engine (10) with hydrogen, in which hydrogen is blown directly into a combustion chamber (5) of the internal combustion engine. After an air inlet valve (6) of the internal combustion engine is closed, hydrogen is blown in in an angular range which is later than a 40-degree crankshaft angle.

Description

Technical Field

[0001] This invention relates to a method and apparatus for operating an internal combustion engine using hydrogen. Background Technology

[0002] A method and apparatus for operating an internal combustion engine using hydrogen are known, wherein the hydrogen is directly blown into the combustion chamber of the internal combustion engine. The corresponding internal combustion engine and the valve for directly blowing hydrogen into the combustion chamber of the internal combustion engine are known from DE 10 2023 206 011. Summary of the Invention

[0003] Advantages of the present invention In contrast, the method and apparatus according to the invention, which have the features of the independent claims, have the advantage of enabling improved operation of the internal combustion engine. In particular, combustion knocking in the internal combustion engine is avoided, thereby enabling more efficient operation of the internal combustion engine.

[0004] Further advantages and improvements are derived from the measures in the dependent claims. By selecting the latest possible injection angle range, the operation of the internal combustion engine, particularly its knock tendency, is improved. The optimal injection angle range is optimized by taking into account the pressure in the combustion chamber caused by compression. For this optimization, the amount of hydrogen injected and the center of gravity of combustion are also advantageously considered. In particular, the center of gravity of combustion can be influenced by selecting a suitable ignition angle. The aforementioned measures thus optimize the knock tendency of the internal combustion engine. Attached Figure Description

[0005] Embodiments of the present invention are shown in the accompanying drawings and explained in more detail in the following description.

[0006] in: Figure 1 A schematic diagram of an internal combustion engine is shown, and Figure 2 The family of characteristic curves showing the tendency to detonate is shown relative to the angle of hydrogen injection. Detailed Implementation

[0007] exist Figure 1 The diagram schematically illustrates an internal combustion engine 10 powered by hydrogen, which has a cylinder 3 in which a piston 4 is arranged. Above the piston 4, the cylinder 3 forms a combustion chamber 5, into which a mixture of hydrogen and air is introduced and burned. The combustion of the hydrogen-air mixture in the combustion chamber 5 increases the pressure within the combustion chamber 5, and this pressure is converted into mechanical work by the movement of the piston 4 within the cylinder 3 via a connecting rod and crankshaft (not shown here). Therefore, this relates to the generally known gasoline internal combustion engine.

[0008] An intake pipe 2 is provided to supply air to the combustion chamber 5, and the amount of air supplied is controlled by a throttle plate 1 within this intake pipe. The amount of air introduced into the combustion chamber 5 is controlled by opening and closing the throttle plate 1. Additionally, a blow-in valve 9 is provided, through which hydrogen is directly blown into the combustion chamber 5. The ignition of the hydrogen-air mixture in the combustion chamber 5 is achieved by a spark plug (not shown in the attached drawings). An exhaust pipe 8 is provided to remove exhaust gases after combustion, through which the combusted exhaust gases are discharged from the combustion chamber 5. Furthermore, in Figure 1 The diagram also schematically shows an air inlet valve 6 and an exhaust outlet valve 7. By opening and closing the air inlet valve 6 and the exhaust outlet valve 7, the combustion chamber 5 is connected to the intake manifold 2 or the exhaust manifold 8 depending on the operating stage of the internal combustion engine 10. A control device 11 is also shown for controlling the internal combustion engine 10, which generates signals for manipulating the throttle plate 1 or the blow-in valve 9.

[0009] Such an internal combustion engine 10 typically operates in a four-stroke manner. Here, in the first intake stroke, fresh air is drawn into the combustion chamber 5 by opening the air inlet valve 6 and moving the piston 4 from top dead center to bottom dead center. The piston's movement creates a negative pressure in the combustion chamber, which draws air in through the intake manifold 2. The amount of air introduced into the combustion chamber 5 is controlled by opening the throttle plate 1. Then, the compression stroke occurs, in which the piston 4 moves back from bottom dead center to top dead center, thus compressing the gas in the combustion chamber 5. During this compression stroke, hydrogen is also directly injected into the combustion chamber 5 through the blow-in valve 9. Following the compression stroke is the combustion stroke, in which the hydrogen and air mixture is ignited and burned in the combustion chamber 5 by an ignition spark. Through this combustion, the pressure in the combustion chamber 5 increases dramatically, and this pressure is converted into mechanical work by the movement of the piston 4 from top dead center to bottom dead center. During the combustion stroke, not only the air inlet valve 6 but also the exhaust valve 7 is closed. Then, the exhaust stroke is performed, during which the exhaust outlet valve 7 is opened, and the exhaust gas, i.e. the combustion byproducts, is discharged from the combustion chamber 5 through the exhaust pipe 8 by the movement of the piston 4 from the bottom dead center to the top dead center.

[0010] The operation of the internal combustion engine 10 should proceed in such a way that the largest possible share of the energy released through combustion is converted into mechanical work. During hydrogen combustion inside the engine, important, load-limiting aspects are knock combustion and premature ignition of hydrogen before the actual ignition point of the spark plug. A significant cause of knock combustion or premature ignition of hydrogen is the high temperature during combustion (knock) or shortly before combustion (pre-ignition). During knock combustion, various undesirable flame fronts are formed, which can damage the flame front originating from the spark plug and cause undesirable pressure oscillations in the combustion chamber. This can lead to drastically excessive cylinder pressure and damage to the engine. In the case of premature ignition of hydrogen before the ignition point, fuel energy conversion occurs at a very early stage. This means that only a very small combustion chamber volume is available for combustion, resulting in very steep pressure and temperature gradients. Consequently, pressure and temperature increase very rapidly during combustion, which is why knock combustion is often observed as an accompanying phenomenon when pre-ignition occurs.

[0011] A feasible approach to lower combustion temperature to avoid knocking or premature ignition is to introduce the hydrogen required for combustion into the combustion chamber as late as possible. The "correct" timing of hydrogen injection largely depends on the closure of the inlet valve. The closure of the inlet valve determines the start of compression of fresh air in the cylinder.

[0012] exist Figure 2 The effect of the timing of hydrogen injection into combustion chamber 5 and the effect of the ignition angle on the operation of hydrogen-powered internal combustion engines, particularly in terms of knock occurrence, are shown below. As will be shown in more detail later, in Figure 2 As can be seen, a significant potential for reducing knock combustion is achieved when hydrogen is introduced starting from a 40° crankshaft angle after one or more air inlet valves 6 are closed. This potential continues to increase at later points in the hydrogen introduction process. The latest feasible time for introducing hydrogen is reached if complete hydrogen introduction is no longer possible due to increased cylinder back pressure at the end of the introduction process.

[0013] The reduced tendency to detonate is primarily due to the lower final compression temperature resulting from the later introduction of hydrogen. By introducing hydrogen later during compression with inlet valve 6 closed, the compression work done by the piston on the entire gas mixture can be reduced. This is achieved by compressing the fresh air in the cylinder first with the inlet valve closed, and then, subsequently or once hydrogen is introduced, compressing it along with the piston through upward movement. This causes the temperature of the hydrogen-air mixture to decrease at the end of compression or shortly before ignition. Consequently, the combustion temperature also decreases. Because less undesirable flame front is formed, the lower combustion temperature results in increased resistance to detonation combustion.

[0014] The proposed operating strategy for internal combustion engines powered by hydrogen stipulates that, under high load conditions, the later injection of hydrogen is used to reduce the probability of knock combustion and premature ignition of hydrogen.

[0015] To prevent undesirable and slow closure of the blow-in valve 9 due to increased cylinder back pressure during later blow-in, a flow-optimized beam-forming cap on the blow-in valve 9 is preferred. This beam-forming cap design allows for minimally lossless internal flow within the closed sleeve, thereby reducing back pressure below the nozzle needle and simultaneously directing the beam into the combustion chamber. Such a blow-in valve 9 is known from DE 10 2023 206 011.

[0016] exist Figure 2 The diagram illustrates the effect of the timing of hydrogen injection into combustion chamber 5 and the center of gravity of combustion on the knock tendency of an internal combustion engine running on hydrogen. The x-axis shows the crankshaft angle range of -190° to -70° before the top dead center (TDC) of piston 4, where combustion takes place. The TDC where combustion occurs is commonly referred to as ignition OT. This TDC is located at angle 0. The ignition spark is triggered shortly before angle 0, i.e., ignition OT, initiating combustion of the hydrogen-air mixture in combustion chamber 5. However, because complete combustion requires a certain time offset, the center of gravity of combustion and therefore the maximum pressure increase caused by combustion are only realized after ignition OT. Because the timing of the ignition spark has a significant impact on the knock tendency of an internal combustion engine, Figure 2 The center of gravity of combustion is also shown on the Y-axis. The Y-axis shows the combustion center of gravity in an angle range of 5° to 11° after ignition (OT). The combustion center of gravity here is at the angle at which 50% of the hydrogen introduced is burned.

[0017] The X-axis blow-in moment is represented by the moment the blow-in begins. Typically, hydrogen is blown in at pressures of several tens of bar, such as 40 bar. Under high load conditions on internal combustion engines, such as at very low speeds and when the user of the internal combustion engine has high demands for power or torque, a large amount of hydrogen is blown in, and this blow-in can be sustained over an angle range of several tens of degrees, such as 50 degrees of crankshaft angle. Figure 2 The angle at which hydrogen gas was first introduced is shown in the diagram.

[0018] exist Figure 2The diagram illustrates different ranges for knock tendency. Range 21 exhibits very severe knocking in the internal combustion engine, which can directly damage the engine, thus disallowing its use. Range 22 also results in very severe knocking and should therefore be avoided; in this range, the combustion center of gravity is blown in at approximately 10° to 6° within a crankshaft angle range of -170° to -130°. Range 23 also shows a large knock tendency and should be avoided as much as possible; this range has a moderate combustion center of gravity between 10° and 8° when blown in earlier than -130°, or an even earlier combustion center of gravity between 8° and 5° when blown in earlier than -90°. Range 25 shows a very low knock tendency between approximately 10° and 9° when blown in later than -130°. Between ranges 23 and 25 lies range 24, which has a moderate knock tendency and is also suitable for continuous operation of the internal combustion engine. Range 26 has a combustion center angle later than 11°, which reliably eliminates knocking, but has the disadvantage of reduced internal combustion engine efficiency, and therefore should only be used when knocking of the internal combustion engine should be reliably avoided.

[0019] exist Figure 2 Lines 31, 32, and 33 are marked, representing three different angular ranges of crankshaft angle. Line 31, at a crankshaft angle of -170°, represents the moment the air inlet valve closes, meaning no injection into combustion chamber 5 occurs before this moment. Following the closing of the injection valve is a crankshaft angle range of approximately 40°, within which it is very difficult to achieve knock-free operation of the internal combustion engine. Therefore, it is advantageous to blow fuel in a range later than 40°. Thus, the usable range for blowing hydrogen is to the right of line 32, at a crankshaft angle later than 40° after the inlet valve closes, that is, at -130°. The problem with very late blowing, especially when the amount of hydrogen to be introduced is that further blowing is no longer possible due to the increased pressure in the combustion chamber caused by compression during the compression phase, as the inlet valve is compressed, i.e., closed, by the pressure in the combustion chamber. This limit for the start of blowing is indicated by line 33 at approximately -90° crankshaft angle. The precise location of line 33 should be understood exemplarily here, as the precise location of limit 33 also depends on the amount of hydrogen used for blowing. In the case of a very small amount, the duration of blowing is very short, so that such blowing can be terminated before the pressure in combustion chamber 5 reaches a critical value.

[0020] Therefore, the following angle range should now be used for hydrogen injection, which is later than 40° crankshaft angle after the air inlet valve 6 is closed. It is advantageous to choose the latest possible angle range, as this allows for efficient operation of the internal combustion engine without knocking. The pressure in the combustion chamber due to compression after the air inlet valve 6 is closed must be considered when selecting the angle used to initiate the injection or the angle range used for the injection.

[0021] Furthermore, the amount of hydrogen blown in should also be considered when determining the range of blowing angles. Depending on the amount of hydrogen blown in, it can be meaningful to shift the direction of the blowing start towards an earlier or later blowing direction.

[0022] Furthermore, combustion can be influenced by selecting the corresponding center of gravity for combustion. In particular, the center of gravity for combustion can be influenced by selecting the corresponding ignition angle.

[0023] All of these measures are designed to enable efficient operation of the internal combustion engine while simultaneously preventing knocking.

Claims

1. A method for operating an internal combustion engine (10) with hydrogen gas, wherein the hydrogen gas is directly blown into the combustion chamber (5) of the internal combustion engine, characterized in that, Hydrogen is blown in at an angle range later than 40° crankshaft angle after the air inlet valve (6) of the internal combustion engine is closed.

2. The method according to claim 1, characterized in that, Choose the angle range for the blow-in as late as possible.

3. The method according to claim 2, characterized in that, For the selection of the angle range, the pressure in the combustion chamber (5) caused by compression after the air inlet valve (6) is closed is taken into account.

4. The method according to claim 2 or 3, characterized in that, When selecting the angle range, the amount of hydrogen gas blown in is taken into account.

5. The method according to claims 2 to 4, characterized in that, When selecting the angle range, the center of gravity of the hydrogen combustion is taken into account.

6. The method according to claim 5, characterized in that, The center of gravity of the combustion is influenced by selecting the ignition angle of the combustion.

7. The method according to any one of the preceding claims, characterized in that, When selecting the angle range, the tendency of combustion to detonate is taken into account.

8. An apparatus for operating an internal combustion engine (10) with hydrogen gas, wherein the hydrogen gas is directly blown into the combustion chamber (5) of the internal combustion engine (10), characterized in that, The device causes the hydrogen to be blown in at an angle range later than 40° crankshaft angle after the air inlet valve (6) of the internal combustion engine is closed.

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