Method for operating a hydrogen combustion engine

Abstract

The present invention relates to a method for operating a hydrogen internal combustion engine, comprising the steps of: initiating the injection of hydrogen by means of a hydrogen injector, detecting early pre-ignition before a target ignition time of the hydrogen and, if early pre-ignition has been detected, immediately stopping the injection of hydrogen by the hydrogen injector.

Description

State of the art

[0001] The present invention relates to a method for operating a hydrogen (H2) internal combustion engine and to an engine control unit for carrying out the method according to the invention.

[0002] Hydrogen-powered internal combustion engines represent an important technological pathway towards emission-free mobility. Familiar internal combustion engines, typically operating on the Otto cycle, can serve as the basis for implementation. This involves the external ignition of a generally homogeneous hydrogen-air mixture. The gaseous fuel required to operate the hydrogen engine is supplied to the cylinder either indirectly (port injection) or directly (direct injection). In both cases, the stochastic distribution of residual gas, which consists of remnants from the combustion of a previous combustion phase, can lead to spontaneous ignition of the freshly supplied hydrogen. Due to hydrogen's high flammability, even small quantities are sufficient to ignite upon contact with the hot residual gas.

[0003] Fig. Figure 2 shows an example of a regular operating cycle of a hydrogen combustion engine with retarded ignition. Several curves are plotted against a crankshaft angle. Curve A represents the cylinder pressure P, curve B shows the control of an injection injector, curve C shows the heat release process, curve D shows the control of a spark plug, and time Z indicates the ignition point. As in Fig. As can be seen in Figure 2, a heat release process of heat Q begins after the regular ignition Z.

[0004] Fig. Figure 3 shows a combustion cycle in which early pre-ignition occurs. A clear increase in cylinder pressure (curve A) is visible at a crankshaft angle of approximately -315° to cylinder pressure P1. During the further course of the combustion cycle, the already combusted mixture is compressed further. The regularly initiated later ignition Z (crankshaft angle approximately 15°) does not result in any further heat release Q (curve C). The subsequent combustion cycle is in Fig. Figure 4 shows that early pre-ignition can be followed by late pre-ignition. This can be seen because the heat release Q (curve C) begins significantly earlier than the ignition initiation Z. This leads to a very sharp increase in cylinder pressure P (curve A), resulting in a very high mechanical load on the internal combustion engine.

[0005] The occurrence of early and / or late pre-ignition is unpredictable due to its stochastic nature. In conventional gasoline engines, the standard response of engine control units is such that retarding the ignition timing, as is standard practice in the case of knocking combustion cycles, has no effect because the hydrogen combustion has already occurred. The consequence of pre-ignition in hydrogen engines is therefore a very high mechanical stress. Disclosure of the invention

[0006] The inventive method for operating a hydrogen combustion engine with the features of claim 1 has the advantage that mechanical stress on components of the combustion engine can be prevented in the event of premature pre-ignition. While the inventive method cannot prevent pre-ignition itself, its associated effects on the hydrogen combustion engine are significantly reduced. This is achieved in the inventive method by detecting, after the commencement of hydrogen injection via a hydrogen injector, whether or not undesired premature pre-ignition of the hydrogen occurs. Pre-ignition is defined as ignition before the target ignition point of the hydrogen-air mixture in the cylinder. If premature pre-ignition is detected, further injection of hydrogen is stopped immediately, i.e., without any time delay.By shutting off the injection, the further supply of hydrogen is stopped, thus limiting heat release. This significantly reduces the probability of late pre-ignition occurring in the next operating cycle. Consequently, mechanical stress on the internal combustion engine caused by pre-ignition can be considerably reduced.

[0007] The dependent claims describe preferred embodiments of the invention.

[0008] Preferably, early pre-ignition is detected based on a change in the rotational speed of the crankshaft of the hydrogen combustion engine. The rotational speed is preferably measured by means of a speed sensor. The speed sensor can preferably detect whether early pre-ignition is occurring or not by comparing the current rotational speed with a predetermined target rotational speed.

[0009] Alternatively or additionally, a torque curve at the crankshaft can be monitored, and early pre-ignition can be detected if there is a deviation of the current torque from a target torque.

[0010] Alternatively or additionally, early pre-ignition can be detected by measuring a change in the current draw of a hydrogen injector. The early pressure increase during early pre-ignition, for example, increases the back pressure against which the hydrogen injector must work if it is an outward-opening injector. This leads to an increased current draw. Therefore, early pre-ignition can also be detected by comparing the measured current draw with the injector's target current draw.

[0011] Preferably, if pre-ignition occurs, a crank angle is determined and compared with the target crank angle before the target injection end. If the determined crank angle is before the target injection end crank angle, the hydrogen injection is stopped.

[0012] The detection of early pre-ignition is particularly preferably carried out in an engine control unit of the hydrogen combustion engine.

[0013] Preferably, to stop the hydrogen injection, the hydrogen injector is controlled in such a way that it is immediately activated to close. This allows further hydrogen injection to be prevented immediately after the early pre-ignition is detected.

[0014] Particularly preferred is the inventive method for operating the hydrogen combustion engine integrated into a regular injection process for injecting the hydrogen.

[0015] The method is further preferably used in a hydrogen combustion engine in which hydrogen is blown directly into a cylinder and / or in which hydrogen is blown into an intake manifold.

[0016] Furthermore, the present invention relates to an engine control unit of a hydrogen internal combustion engine, which is configured to carry out the method according to the invention. Brief description of the drawings

[0017] A preferred embodiment of the invention is described in detail below with reference to the accompanying drawing. The drawing shows: Fig. 1 a schematic flowchart of a method according to the invention for operating a hydrogen combustion engine, Fig. 2 a schematic diagram showing various operating curves and states of the hydrogen combustion engine during a working cycle without pre-ignition, Fig. 3 a diagram accordingly Fig. 2 with early pre-ignition and Fig. 4 a diagram accordingly Fig. 2 in the case of late pre-ignition. Preferred embodiments of the invention

[0018] The following refers to the Fig. 1, Fig. 2, Fig. 3 to Fig. 4 a method according to the invention for operating a hydrogen combustion engine is described in detail.

[0019] Assuming normal operation of the hydrogen combustion engine, which is in Fig. The following section, which is shown in section 2, refers to the Fig. 3 and Fig. 4 clarifies the occurrence of pre-ignition in detail.

[0020] In the Fig. 2, Fig. 3 to Fig. Figure 4 shows different curves and states of the hydrogen combustion engine as a function of the crank angle of two complete revolutions of a crankshaft: Curve A shows a pressure profile of a pressure P in the cylinder. Curve B shows a current profile for controlling a hydrogen injector that injects the hydrogen. Curve C shows the course of heat release Q in the cylinder. Curve D shows the control of an ignition device such as a spark plug. Point Z is the regular ignition timing at approximately +15° crank angle.

[0021] In the Fig. In the normal operating scenario shown in Figure 2, hydrogen is injected by controlling the hydrogen injector at a crankshaft angle of approximately -315°. As the crankshaft angle moves towards top dead center (crankshaft angle 0°), the pressure P increases (curve A). Ignition Z occurs at a crankshaft angle of +15°, resulting in the release of a large portion of the heat Q (curve C).

[0022] In Fig. Figure 3 shows an early pre-ignition, represented by curve A, which indicates a pressure increase P in the cylinder to the value P1. During early pre-ignition, after the hydrogen injection begins, some of the hydrogen ignites from hot residual gas from the previous operating cycle. Due to hydrogen's high flammability, even very small amounts of hydrogen are sufficient to ignite from the hot residual gas.

[0023] This increased pressure P1 can be detected, for example, by a pressure sensor in the cylinder or by injector current measurement and / or speed and / or torque measurement at the crankshaft. If such a pressure increase is detected at point P1, the engine control unit will immediately stop further hydrogen injection by activating the hydrogen injector. This then, as described in Fig. 3 shown, no more heat is released (curve C in Fig. 3) What's next? Fig. As can be seen in Figure 3, the pressure in the cylinder does not increase excessively. Therefore, this procedure leads to a loss of torque contribution from this cylinder, which may result in a noticeable deceleration of the internal combustion engine, although this would happen anyway if early pre-ignition occurs.

[0024] The probability of mechanical damage to the internal combustion engine due to the subsequent late pre-ignition, as in Fig. The effect shown in section 4 is reduced by this intervention. Fig. Figure 4 shows the next operating cycle after an early pre-ignition, in which a very high pressure P2 of a late pre-ignition can occur and lead to mechanical damage to the internal combustion engine. This results, as shown in Fig. Figure 4 shows that even before the ignition point Z, there is an early heat release Q (curve C) significantly before the ignition point Z. This can cause excessive pressure in the cylinder and lead to very high loads on the internal combustion engine.

[0025] Fig. Figure 1 schematically illustrates the process sequence according to the invention. In the first step S1, hydrogen is injected using a hydrogen injector. The injection can take place directly into a cylinder and / or an intake manifold.

[0026] In the next step, S2, a check is performed to detect undesired early pre-ignition. As described above, various parameters such as cylinder pressure, injector current consumption, crankshaft speed, and / or torque can be recorded. The recorded parameters are then compared with corresponding target values, and if there is a deviation (J (yes) in Fig. 1) The procedure proceeds to step S3.

[0027] In step S3, the injection of further hydrogen is immediately stopped, unless the injection has already been completed due to the cycle. Therefore, the comparison of the measured parameter with the target parameters should ideally only take an extremely short time.

[0028] If no early pre-ignition is detected in the comparison (N (no) in step 2 in Fig.1) The process continues from step S2 to step S4 and the injection of hydrogen is carried out as planned.

[0029] Thus, although the present invention cannot prevent the occurrence of pre-ignitions, it can prevent excessive damage to components of the internal combustion engine due to pre-ignitions.

Claims

[1] Method for operating a hydrogen internal combustion engine, comprising the steps of: - Start of hydrogen injection using a hydrogen injector, - Detection of early pre-ignition before the target ignition time of the hydrogen and - if early pre-ignition is detected, immediately stop the injection of hydrogen by the hydrogen injector. [2] Method according to claim 1, wherein the early pre-ignition is detected due to a change in the rotational speed of a crankshaft of the hydrogen internal combustion engine. [3] Method according to one of the preceding claims, wherein the early pre-ignition is detected due to a change in the torque of the crankshaft. [4] Method according to one of the preceding claims, wherein the early pre-ignition is detected due to a change in the current input of the hydrogen injector. [5] Method according to one of the preceding claims, wherein, in the event of early pre-ignition, an actual crank angle is determined and the actual crank angle is compared with a target crank angle, wherein the target crank angle is a crank angle at the target end of the hydrogen injection process. [6] Method according to one of the preceding claims, wherein the detection of early pre-ignition takes place in an engine control unit of the hydrogen internal combustion engine. [7] Method according to one of the preceding claims, wherein the hydrogen injector is controlled to stop the injection of hydrogen. [8] Method according to one of the preceding claims, wherein the method is integrated into a regular injection process for injecting the hydrogen. [9] Method according to one of the preceding claims, wherein the hydrogen is injected directly into a cylinder of the hydrogen internal combustion engine and / or into an intake manifold. [10] Engine control unit of a hydrogen internal combustion engine, which is configured to carry out a method according to one of the preceding claims.

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