Method for controlling internal combustion engine

Abstract

The invention relates to a method for controlling an internal combustion engine, in which gaseous fuel is blown directly into a combustion chamber in a compression phase of the internal combustion engine after an air inlet valve is closed. The pressure rise caused by the blowing of the gaseous fuel is determined as a function of the air-fuel ratio of the combustion with respect to the pressure without the blowing of the gaseous fuel, and is used to control the combustion in the internal combustion engine.

Description

Technical Field

[0001] The present invention relates to a method for controlling an internal combustion engine having the general features of claim 1, wherein gaseous fuel is blown directly into the combustion chamber. Background Technology

[0002] An internal combustion engine is known from DE 10321795 A1, in which gaseous fuel is blown in during the compression phase, that is, after the air inlet valve is closed. Summary of the Invention

[0003] Advantages of the present invention.

[0004] In contrast, the method according to the invention, with the features of the independent claims, has the advantage of making it particularly easy to obtain the pressure ratio during the compression phase, and especially at the end of the compression phase. Thus, it is particularly easy to determine the effect of the injection on the operation of the internal combustion engine. In particular, the effect of a later injection close to the ignition timing can be taken into account. If the pressure ratio can be obtained quickly and easily in the combustion chamber, the amount of fuel injected can also be adjusted later, for example, even after the air inlet valve has closed, through the injection during the compression phase. This simplifies and improves the control of the internal combustion engine.

[0005] Further advantages arise from the features of the dependent claims. The effects of combustion chamber volume changes can be ignored by rapid injection, thus facilitating the acquisition of pressure ratios. Furthermore, various influences are advantageously considered to optimize the timing of injection. The pressure rise during the compression phase is much more dramatic compared to injecting liquid fuel, and this must be taken into account when operating the valve for injecting gaseous fuel. The compression values ​​of air and gaseous fuel in the combustion chamber are considered to obtain the optimal injection timing. The pressure rise thus obtained can be taken into account under various combustion parameters, particularly in obtaining the optimal air-fuel mixture, the residual oxygen content in the exhaust gas, the combustion process, and the untreated emissions of the internal combustion engine. Attached Figure Description

[0006] Embodiments of the present invention are shown in the accompanying drawings and explained in more detail in the specification. Wherein:

[0007] Figure 1 An internal combustion engine with blast-in fuel is shown, and

[0008] Figure 2 The relationship between λ and the relative pressure increase compared to compression without fuel injection is shown. Detailed Implementation

[0009] Figure 1An internal combustion engine 1 with cylinder 2 is schematically shown, in which piston 3 is arranged. A combustion chamber 4 is formed in the space above piston 3 within cylinder 2. Air for combustion is introduced into the combustion chamber 4 via an air supply unit 5. The exhaust gases from the combustion in the combustion chamber 4 are discharged into the surrounding environment through an exhaust pipe 6. Specifically, through… Figure 1 The air supply is controlled by an air inlet valve (not shown). Figure 1 An exhaust outlet valve (not shown) controls the discharge of exhaust gases. Additionally, a blow-in valve 7 is provided, through which gaseous fuel is blown into the combustion chamber 4. A spark plug (not shown) can also be present to ignite the air-fuel mixture in the combustion chamber.

[0010] The internal combustion engine 1 is therefore a common gasoline internal combustion engine, which operates using gaseous fuels, such as hydrogen or natural gas (CNG) or other gases, such as LNG. If the air inlet valve is still open when gaseous fuel is introduced and therefore there is a connection to the air supply 5, a corresponding amount of air will be discharged from the combustion chamber 4 or will not be able to enter the combustion chamber 4. Therefore, it is advantageous to blow in gaseous fuel when the inlet valve is closed. After the air inlet valve is closed, a predetermined amount of air is confined in the combustion chamber 4, and blowing in the gas does not discharge or reduce the amount of air in the combustion chamber 4.

[0011] Gaseous fuel is injected at a pressure higher than the corresponding current pressure in combustion chamber 4, for example, 30 to 40 bar. Because the pressure in combustion chamber 4 increases due to the increasing compression during the compression phase of the internal combustion engine 1, the amount of fuel injected depends not only on the opening duration of the injection valve and the pressure of the gaseous fuel, but also on the timing of the injection during the compression phase. Besides the opening duration, the pressure difference between the injected gaseous fuel and combustion chamber 4 is crucial to the amount of fuel injected. Here, especially near the end of the compression phase, there can be a pressure in combustion chamber 4 that prevents further injection of gaseous fuel. Therefore, the timing of injection and the length of the injection valve's opening duration must take into account the pressure ratio in the combustion chamber caused by the injection and subsequent compression during the compression phase.

[0012] Compared to internal combustion engines that operate on liquid fuels, the amount of fuel in the combustion chamber and the resulting pressure ratio must be considered more precisely based on the amount of fuel injected. Furthermore, since the final determination of the amount of gaseous fuel to be injected is made, for example, after the air inlet valve is closed, this calculation should be as straightforward as possible. This approach enables a very rapid response to changing operating conditions of the internal combustion engine.

[0013] According to the present invention, a very simple calculation method is proposed that enables the calculation of the pressure ratio based on the air-fuel ratio (i.e., the λ value). Since the amount of air in the combustion chamber is determined after the air inlet valve closes, from that moment on, combustion can only be affected by changing the amount of fuel injected. Because the time for such intervention is limited, a simple method for obtaining the resulting pressure ratio during the compression phase is advantageous.

[0014] In the closed combustion chamber 4, the following relationship applies between air and fuel, where λ_St_Fu represents the stoichiometric mass ratio of air to fuel, and λ represents an additional coefficient used to describe the excess air condition. This results in the following relationship between air mass m_Air and fuel mass m_Fu:

[0015]

[0016] Thus, after the injection, a total mass m_tot is generated, which can also be described solely by the mass of air due to the prescribed stoichiometric ratio λ_St_Fu between fuel and air:

[0017]

[0018] Mass can be converted into state parameters using the first law of thermodynamics, where the state of air relates to "before" it is blown in, and the state "tot" relates to "after" it is blown in.

[0019]

[0020] As a further simplification, we now assume that the blow-in occurs so rapidly that changes in cylinder volume can be ignored.

[0021]

[0022] The desired pressure ratio can then be described by changes in gas composition and temperature:

[0023]

[0024] Ignoring temperature changes, the gas mixture constant is calculated as follows:

[0025]

[0026] Thus, the following pressure ratio is obtained between before and after the blowing:

[0027]

[0028] A coefficient was obtained that, under the given fuel conditions, depends only on the air / fuel mixture λ, thereby keeping the calculated costs very low.

[0029] exist Figure 2 In the figure, the pressure rise at top dead center of the compression stage with injection is shown as a coefficient relative to the value of λ, compared to the compression stage without injection, i.e., only air is compressed. Curve 21 is shown for the injection of hydrogen and curve 22 for the injection of CNG (i.e., natural gas). For comparison, curve 23 is also shown for the pressure rise when liquid fuel is injected. When λ is 1, the pressure rise at the end of the compression stage is more than about 40% in the case of hydrogen, about 10% in the case of natural gas, and less than about 5% in the case of liquid fuel. Since the proportion of the injected fuel relative to the total mass in the combustion chamber decreases, the pressure rise decreases as λ increases.

[0030] With the air inlet valve closed, the quality of air introduced into combustion chamber 4 is fixed and can no longer be changed. However, the amount of gaseous fuel can still be influenced and thus can respond very quickly to changes in the operating conditions of the internal combustion engine. In particular, it can also affect changes in the driver's desired output or other changes in the power output of the internal combustion engine. This is especially feasible for hydrogen, as hydrogen combustion is feasible over a wide λ range, that is, over a very wide range of hydrogen-to-air ratios. The necessary control parameters can be calculated particularly easily using a convenient method for determining the pressure ratio by blowing in the fuel. Therefore, the necessary control parameters can be calculated very quickly, either immediately before or after the air inlet valve closes.

Claims

1. A method for controlling an internal combustion engine (1), wherein Blowing gaseous fuel into or at least partially into a combustion chamber (4) of the internal combustion engine directly after the air inlet valve has closed during the compression phase of the internal combustion engine, characterized in that the pressure increase caused by the blowing of the gaseous fuel is taken into account for controlling the combustion in the internal combustion engine (1) in terms of the air-fuel ratio of the combustion.

2. The method of claim 1, wherein, The blowing is carried out so quickly that the volume change of the combustion chamber (4) can be neglected.

3. The method according to any of the preceding claims, characterized in that, The pressure increase caused by the blowing and the pressure increase caused by compressing air and gaseous fuel in the combustion chamber (4) during the compression phase of the internal combustion engine are taken into account for determining the actuation duration of the blowing (= energization duration of the valve).

4. The method according to any of the preceding claims, characterized in that, The pressure increase caused by the blowing and the pressure increase caused by compressing air and gaseous fuel in the combustion chamber (4) during the compression phase of the internal combustion engine are taken into account for determining the time of the blowing.

5. The method of claim 4, wherein, The work for compressing air and gaseous fuel in the combustion chamber (4) is taken into account for determining the time of the blowing of the fuel.

6. The method according to any of the preceding claims, characterized in that, The pressure increase is taken into account for determining the air-fuel mixture in the combustion.

7. The method according to any of the preceding claims, characterized in that, The pressure increase is taken into account for determining the untreated emissions of the combustion.

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