Method for determining a water rate for water injection

Abstract

The present invention relates to a method for determining a water rate W for water injection of a gas internal combustion engine (1), comprising the steps of: simultaneously determining a first water rate W1 for a critical operating condition of the gas internal combustion engine (1) based on a first characteristic map KF1 as a function of a load M and a rotational speed n of the gas internal combustion engine (1), and determining a second water rate W2 for a non-critical operating condition of the gas internal combustion engine (1) based on a second characteristic map KF2 as a function of the load M and the rotational speed n of the gas internal combustion engine (1), determining an interpolation factor I which lies in a range of 0 ≤ I ≤ 1, and calculating a base water rate W0 based on the first water rate W1, the second water rate W2, and the interpolation factor I, wherein the interpolation factor is used to continuously interpolate between the first and second water rates.

Description

State of the art

[0001] The present invention relates to a method for determining a water rate for water injection in a gas internal combustion engine, in particular a hydrogen-powered gas internal combustion engine, and to a device for carrying out the method.

[0002] Water injection systems are known from conventional internal combustion engines, which in particular use gasoline, in order to increase the power and / or efficiency of the internal combustion engine. However, such known systems cannot be used directly in gas internal combustion engines. In particular, the combustion of hydrogen is much more prone to pre-ignition than, for example, gasoline. Furthermore, hydrogen is very prone to uncontrolled combustion during a compression stroke of the gas internal combustion engine, well before the ignition point. This can result in peak combustion pressures that can be greater than twice the normal combustion pressures. Due to the greater tendency towards pre-ignition in hydrogen-powered gas internal combustion engines, water injection also results in greater consumption of water, which is used for water injection. Since water resources are limited during operation, e.g.are limited due to a given volume of a water tank, a water injection rate should be selected as optimally as possible in order to optimise water consumption during operation. Disclosure of the invention

[0003] The method according to the invention for determining a water rate W for water injection in a gas internal combustion engine with the features of claim 1 has the advantage that optimized water injection is possible depending on the actual pre-ignition in the combustion chamber of the internal combustion engine. This makes it possible to increase the performance and / or efficiency of the gas internal combustion engine. Furthermore, it can be avoided that too much water is injected, so that the amount of water stored in a water tank in a vehicle is used optimally. This results in, in particular, longer refill intervals for the water tank. It can also be avoided that the gas internal combustion engine is damaged by an excessively high water injection rate.In particular, excessive water ingress can lead to a tearing of the oil wall film on the cylinder liner of the combustion chamber or to leakage via a piston seal into other areas of the gas internal combustion engine.

[0004] This is achieved according to the invention in that the method comprises the following steps: - first, a water rate is determined, in particular simultaneously, for a critical operating condition of the gas internal combustion engine and a non-critical operating condition of the gas internal combustion engine. In a critical operating condition, a first water rate W1 is determined based on a load M and a speed n of the gas internal combustion engine as well as a first characteristic map KF1. In a non-critical operating condition of the gas internal combustion engine, a second water rate W2 is determined based on the load M and the speed n of the gas internal combustion engine as well as a second characteristic map KF2. A critical operating condition is in particular pre-ignition or a tendency of the gas internal combustion engine towards pre-ignition. Subsequently, an interpolation factor I is determined, which lies in a range of 0 ≤ I ≤ 1.Then, based on the first water rate W1 and the second water rate W2 and the interpolation factor I, a base water rate W0 is calculated for a water quantity to be injected. Thus, according to the invention, the base water rate W0 can be easily determined, in particular based on the first and second characteristic maps KF1 and KF2, as well as a load and a speed, using the interpolation factor. The base water rate W0 can then be used as the water rate W.

[0005] Water is preferably injected directly into a combustion chamber and / or into an intake area of ​​the internal combustion engine.

[0006] The subclaims show preferred developments of the invention.

[0007] Preferably, when the interpolation factor I is zero, the base water rate W0 is set to the second water rate W2.

[0008] Further preferably, if the interpolation factor I is equal to 1, the base water rate W0 is set to the value of the first water rate W1.

[0009] The interpolation factor I is preferably calculated from a third characteristic map KF3 based on various variables, in particular the load M of the gas internal combustion engine and / or the speed n and / or a target or actual torque of the internal combustion engine and / or an air mass and / or a fuel mass and / or a relative air charge and / or a relative fuel quantity and / or a power output of the gas internal combustion engine. The interpolation factor I is preferably determined as an indicator of a history of various variables of the gas internal combustion engine. In this case, a weighting factor, which depends on the various variables, is determined from the third characteristic map KF3 and integrated. The weighting factor can also be constructed from the addition or multiplication of characteristic curves of the aforementioned variables.

[0010] Since the weighting factor (KF) can assume negative and positive values, the output of the integral is limited to the range 0 ≤ I ≤ 1. This allows, in particular, a first interpolation factor I1 to be determined.

[0011] Further preferably, a second interpolation factor I2 can additionally be determined in parallel or separately based on a fourth characteristic map KF4 as a function of the rotational speed n of the gas internal combustion engine and a combustion chamber temperature T1 and / or a piston temperature T2 or the maximum of the two temperatures.

[0012] Preferably, the interpolation factor I is determined as the largest value selected from the first interpolation value I1 based on the third characteristic map KF3, in particular as a function of the load M and the speed n of the gas internal combustion engine, and the second interpolation value I2 based on the fourth characteristic map KF4 as a function of the speed of the gas internal combustion engine and the combustion chamber temperature T1 and / or a piston temperature T2 or the maximum of the two temperatures.

[0013] According to a further preferred embodiment of the invention, for a more precise determination of the water rate, the base water rate W0 is multiplied by a first factor F1 based on a cooling water temperature T3 and / or an intake air temperature T4. The factor F1 is preferably determined from a fifth characteristic map KF5.

[0014] Further preferably, the base water rate W0 is multiplied by a second factor F2 based on a hydrogen temperature. This is particularly advantageous for accurately determining a water rate W, since the temperature range of the injected hydrogen during operation and regardless of the ambient temperature can usually be in a range from -40 °C to 70 °C and is thus much larger than, for example, a temperature range of gasoline. Furthermore, the temperature of the hydrogen is not correlated with the ambient temperature, as is the case with gasoline. Hydrogen cools continuously in a hydrogen tank upon withdrawal or is relatively warm, for example, after a refueling operation due to the compression process. Thus, a combination of relatively cool hydrogen and a relatively high intake air temperature can occur during operation, whereby in such a scenario the tendency towards pre-ignition increases significantly as the hydrogen temperature rises.

[0015] The hydrogen temperature T5 is preferably measured in a hydrogen pipeline system, in particular in a hydrogen rail located in the pipeline system near injection devices. Alternatively or additionally, the hydrogen temperature T5 is measured in a hydrogen tank.

[0016] If the gas internal combustion engine comprises at least two cylinder banks, the method according to the invention is preferably carried out individually for each cylinder bank.

[0017] Furthermore, the present invention relates to a device which is configured to carry out the method according to the invention. Short description of the drawing

[0018] A preferred embodiment of the invention will be described in detail below with reference to the accompanying drawings. In the drawing: Fig. 1 a schematic representation of a device for carrying out the method for determining a water rate during water injection of a gas internal combustion engine. Preferred embodiments of the invention

[0019] The following is based on reference to Fig. 1 a method according to the invention and a device according to the invention are described in detail.

[0020] To reduce the pre-ignition tendency in a gas-fired internal combustion engine 1, water is injected in addition to the injected gaseous fuel. The gaseous fuel is preferably hydrogen. Since hydrogen combustion has a significantly greater tendency toward pre-ignition, selecting an optimal water rate W for water injection is particularly important.

[0021] The water is preferably injected into an intake port of the gas internal combustion engine 1 and / or a combustion chamber.

[0022] According to the present invention, a method is carried out, e.g., in a control unit 2, in which a water rate W for water injection is determined, which depends on available influencing variables. For this purpose, a first water rate W1 and a second water rate W2 are determined simultaneously or separately.

[0023] The first water rate W1 is determined for a critical operating condition based on a first characteristic map KF1 as a function of a load M and a speed n of the gas internal combustion engine 1. The second water rate W2 is determined for a non-critical operating condition of the gas internal combustion engine 1 based on a second characteristic map KF2 as a function of the load M and the speed n of the gas internal combustion engine 1. The critical operating condition is the presence of pre-ignition or an existing tendency for pre-ignition. As further shown in Fig. 1, an interpolation factor I is additionally determined, which lies in a range of 0 ≤ I ≤ 1. Based on the base water rate W0, which is based on the first and second water rates W1, W2, and the interpolation factor I, a base water rate W0 is calculated in a computer 3.

[0024] The base water rate W0 could already be used as a value for determining the amount of water injected. However, to determine the optimal water quantity, it is advantageous to consider additional factors.

[0025] The interpolation factor I is used to continuously interpolate between the first characteristic map KF1 and the second characteristic map KF2. Preferably, if the interpolation factor is zero, the base water rate W0 is set to the value for the second water rate W2. Further preferably, if the interpolation factor is 1, the base water rate W0 is set to the first water rate W1.

[0026] The interpolation factor I can be determined using different methods, which can also be combined with each other as desired.

[0027] Firstly, the interpolation factor I can be calculated from a third characteristic map KF3 based on various variables X1, X2, in particular on the load M and / or the speed n of the gas internal combustion engine 1 and / or a target or actual torque of the internal combustion engine and / or an air mass and / or a fuel mass and / or a relative air charge and / or a relative fuel quantity and / or a power. Preferably, the value determined from the third characteristic map KF3 is subsequently integrated in a computer 4 so that a first interpolation factor I1 is determined. Since a weighting here can assume negative or positive values, the first interpolation factor I1 is limited to a range of 0 ≤ I1 ≤ 1. The first interpolation factor I1 is thereby relatively large, i.e.approaches 1 when the gas internal combustion engine 1 is in an operating range for a predetermined time in which the probability of pre-ignition increases. The first interpolation factor I1 approaches 0 when the gas internal combustion engine 1 is operated in a range that is non-critical for pre-ignition. In . Fig. 1, two quantities X1, X2 are shown as input variables for the third characteristic map KF3, but any number and combination of input variables can be used.

[0028] Further preferably, in addition to the first interpolation factor I1, a second interpolation factor I2 is calculated based on a fourth characteristic map KF4 as a function of the rotational speed n of the gas internal combustion engine 1 and a combustion chamber temperature T1 and / or a piston temperature T2, or the maximum of the two temperatures. The second interpolation factor I2 is also in a range of 0 ≤ I2 ≤ 1.

[0029] If both the first and second interpolation factors I1 and I2 are determined, a computer 5 additionally performs a query to determine which of the two interpolation factors I1 and I2 is the largest. The largest value is then used as interpolation factor I and applied to determine the base water rate W0.

[0030] How to continue Fig. As can be seen in Figure 1, in a further step, a first factor F1 is calculated based on a fifth characteristic map KF5 as a function of a cooling water temperature T3 and / or an intake air temperature T4. The first factor F1 is multiplied by the base water flow rate W0 (calculator 6).

[0031] In addition, a second factor F2 can be determined based on a sixth characteristic map KF6 as a function of a hydrogen temperature T5 and multiplied by the base water rate W0 (calculator 7).

[0032] As in Fig.As shown in Figure 1, in the illustrated embodiment, the base water rate W0 is multiplied by both the first factor F1 and the second factor F2. The result is then the water rate W that is injected into the gas combustion engine 1.

[0033] In particular, by using the first factor F1 and the second factor F2, which takes the hydrogen temperature into account, an optimal water rate W for water injection can be determined.

[0034] However, the water rate W can also be determined simply by multiplying the base water rate W0 by the first factor F1 or the second factor F2.

Claims

[1] Method for determining a water rate W for water injection of a gas internal combustion engine (1) comprising the steps: - Determining a first water rate W1 for a critical operating condition of the gas internal combustion engine (1) based on a first characteristic map KF1 as a function of a load M and a speed n of the gas internal combustion engine (1) and determining a second water rate W2 for a non-critical operating condition of the gas internal combustion engine (1) based on a second characteristic map KF2 as a function of the load M and the speed n of the gas internal combustion engine (1), - Determining an interpolation factor I which lies in a range of 0 ≤ I ≤ 1, and - Calculating a base water rate W0 based on the first water rate W1, the second water rate W2 and the interpolation factor I, wherein a continuous interpolation between the first and second water rates W1, W2 is carried out by means of the interpolation factor. [2] Method according to claim 1, wherein when the interpolation factor I is zero, the base water rate W0 is selected as the second water rate W2. [3] The method according to claim 1, wherein when the interpolation factor I is equal to 1, the base water rate W0 is selected as the first water rate W1. [4] Method according to one of the preceding claims, wherein the interpolation factor I is calculated based on a third characteristic map KF3 as a function of the load M and / or the rotational speed n and / or a desired or actual torque of the internal combustion engine and / or an air mass and / or a fuel mass and / or a relative air charge and / or a relative fuel quantity and / or a power of the gas internal combustion engine (1). [5] Method according to claim 4, wherein the interpolation factor I is determined by integrating the values ​​determined from the third characteristic map KF3 based on a history of variables, in particular a load history of the gas internal combustion engine (1), and a value limited to 0 to 1 is then used as the interpolation factor I. [6] Method according to one of the preceding claims, wherein the interpolation factor I is determined based on a fourth characteristic map KF4 as a function of the rotational speed n of the gas internal combustion engine (1) and a combustion chamber temperature T1 and / or a piston temperature T2 or the maximum of the two temperatures. [7] Method according to one of claims 1 to 3, wherein the interpolation factor I is determined as the largest value selected from a first interpolation value I1 based on the third characteristic map KF3 as a function of the load M and the rotational speed n of the gas internal combustion engine (1) and a second interpolation value I2 based on the fourth characteristic map KF4 as a function of the rotational speed n of the gas internal combustion engine (1) and the combustion chamber temperature T1 and / or the piston temperature T2. [8] Method according to one of the preceding claims, wherein the base water rate W0 is multiplied by a first factor F1 based on a fifth characteristic map KF5 as a function of a cooling water temperature T3 and / or an intake air temperature T4. [9] Method according to one of the preceding claims, wherein the base water rate W0 is multiplied by a second factor F2 based on a sixth characteristic map KF6 as a function of a hydrogen temperature T5, in particular a hydrogen temperature in a rail. [10] Method according to one of the preceding claims, wherein the gas internal combustion engine (1) comprises at least two cylinder banks and the method is carried out individually for each cylinder bank. [11] Device arranged to carry out a method according to one of the preceding claims.

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