Method for operating a spark-ignited reciprocating engine, control system and motor vehicle

Abstract

The invention relates to a method for operating a spark-ignited reciprocating engine (2) with a crankcase (5) and with at least one cylinder (3) in which a piston (4) is movable back and forth when a supplied fuel-air mixture (12) is ignited in a combustion chamber (7), and with a water injection (8), wherein overflow gases (9) from the combustion chamber (7) enter the crankcase (5). To improve the operation of a spark-ignition reciprocating engine (2), the fuel-air mixture (12) is corrected as part of a mixture correction (11) depending on a transfer gas mass flow from the combustion chamber (7) into the crankcase (5), wherein the transfer gases (9) are, at least partially, discharged from the crankcase (5) and directed into the intake manifold (6) at a transfer gas inlet point (13), wherein the mixture correction (11) is carried out depending on the amount of water injected.

Description

[0001] The invention relates to a method for operating a spark-ignition reciprocating engine with a crankcase and at least one cylinder in which a piston is reciprocally movable when a supplied fuel-air mixture is ignited in a combustion chamber, and with water injection, wherein overflow gases from the combustion chamber enter the crankcase. The invention further relates to a control system for an internal combustion engine and a motor vehicle.

[0002] European patent application EP 4 265 900 A1 discloses a control system for an internal combustion engine comprising a cylinder with an intake port into which water is injected. German patent application DE 10 2017 006 263 A1 discloses a method for operating a spark-ignition internal combustion engine of a motor vehicle, in which air and fuel are introduced into at least one combustion chamber of the engine, and in which a cooling medium different from the fuel is introduced into the at least one combustion chamber by means of a metering device.German patent application DE 10 2016 118 220 A1 discloses a method for determining a lambda value, wherein a quantity of water is selectively supplied to a combustion chamber of an internal combustion engine, wherein a lambda value is measured in the exhaust gas on an exhaust side of the internal combustion engine by means of a lambda probe, and wherein the selectively supplied quantity of water is taken into account when determining a corrected lambda value.

[0003] The object of the invention is to improve the operation of a spark-ignited reciprocating engine with a crankcase and with at least one cylinder in which a piston can be moved back and forth when a fuel-air mixture supplied via an intake manifold is ignited in a combustion chamber, and with water injection, wherein overflow gases from the combustion chamber enter the crankcase.

[0004] The problem is solved in a method for operating a spark-ignition reciprocating engine with a crankcase and at least one cylinder in which a piston is reciprocating when a fuel-air mixture, supplied, for example, via an intake manifold, is ignited in a combustion chamber, and with water injection, whereby overflow gases from the combustion chamber enter the crankcase, by correcting the fuel-air mixture as a function of the overflow gas mass flow from the combustion chamber into the crankcase, wherein the overflow gases are, at least partially, and in particular in a controlled manner, discharged from the crankcase and directed into an intake manifold at an overflow gas inlet point, wherein the mixture correction is carried out as a function of the injected amount of water. The overflow gases are also referred to as blow-by gases.Blow-by gases consist partly of an inert gas that does not participate in combustion in the combustion chamber. The corresponding amount must be subtracted from the calculated air charge for the combustion chamber to prevent undesirable mixture deviations. This proportion is significantly increased with water injection. The claimed method advantageously corrects the fuel-air mixture depending on the dynamics of gas exchange. By taking into account the mass flow of blow-by gases returned from the crankcase to the intake manifold, increased mixture deviations during the operation of the reciprocating engine can be effectively prevented.

[0005] A preferred embodiment of the method is characterized in that the water injection takes place downstream of the overflow gas inlet into the intake manifold. In combination with a suitable throttle, a so-called Venturi effect can be utilized when the overflow gas mass flow from the crankcase is returned to the intake manifold. The throttle is advantageously designed such that neither too much nor too little overflow gas is returned from the crankcase to the intake manifold.

[0006] Another preferred embodiment of the method is characterized in that the crankcase pressure is detected at a given operating point and stored in a characteristic map or measured with a sensor. The crankcase pressure is detected, for example, with a crankcase pressure sensor. However, the crankcase pressure can also be detected or determined by other means. Depending on the amount of water injected, the overflow gas mass flow or blow-by volume flow increases significantly, as the introduced water evaporates and occupies a correspondingly larger volume in its gaseous state. During operation of the reciprocating engine, it can be operated with or without water injection at the same operating point, depending on the current exhaust gas temperature. Due to the associated dynamics, different pulsation levels occur in the intake manifold, which affect the current fuel-air mixture.The applied mixture correction specifically takes the influence of water into account to prevent increased mixture deviations. Using the recorded and stored crankcase pressure and appropriate diagnostics, the influence of water injection during engine operation can be effectively measured.

[0007] Another preferred embodiment of the method is characterized in that the mixture correction is performed during gas exchanges when water injection is detected at a current operating point. In this way, the claimed mixture correction can be implemented using simple means.

[0008] Another preferred embodiment of the method is characterized in that the mixture correction is supplemented by a water influence when water injection takes place. Within the scope of the claimed mixture correction, the fuel-air mixture supplied to the combustion chamber is corrected in the fuel path via the fuel metering.

[0009] Another preferred embodiment of the method is characterized in that a fuel injection quantity is varied by a controller depending on the exhaust gas temperature. During operation of the reciprocating engine in combination with such a controller, the spread between the different pressure levels in the crankcase increases. Depending on the injected water quantity, the pressure level or pulsation in the crankcase changes. This is detected, for example, by the crankcase pressure sensor and effectively taken into account in the mixture correction.

[0010] Another preferred embodiment of the method is characterized in that the overflow gases from the crankcase are returned to the overflow gas inlet via an oil separator. Undesirable components are separated from the returned overflow gas mass flow via the oil separator.

[0011] The problem stated above is also solved by a control system for an internal combustion engine comprising at least one cylinder, one piston, a crankcase, in particular a crankcase pressure sensor, and an intake manifold, wherein the control system is configured to execute a previously described method. The control system is advantageously implemented in an engine control unit of a motor vehicle equipped with the reciprocating piston engine.

[0012] The invention further relates to a machine-readable storage medium on which a computer program is stored that is configured to execute a previously described method.

[0013] The invention also relates to a motor vehicle with a control system configured to carry out a previously described method.

[0014] Further advantages, features and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawing.

[0015] The only accompanying figure shows a schematic sectional view of an internal combustion engine with water injection and mixture correction depending on the water injection.

[0016] In Fig. Figure 1 is a cylinder 3 of a reciprocating piston engine 2 of an internal combustion engine 1, schematically depicted in a longitudinal section during operation. A piston 4 is located in the cylinder 3. Fig. 1. Movable up and down.

[0017] One in Fig. 1. A crankshaft assembly in a crankcase 5 is assigned to the lower end of the piston 4. A Fig. 1 The upper end of the piston 4 defines a combustion chamber 7 in the cylinder 3. A fuel-air mixture 12 is supplied to the combustion chamber 7 via an intake manifold 6. An arrow indicates water injection 8 into the intake manifold 6.

[0018] When the fuel-air mixture 12 is ignited in the combustion chamber 7, overflow gases 9, also known as blow-by gases, flow from the combustion chamber 7 past the piston 4 into the crankcase 5. These overflow gases or blow-by gases 9 consist partly of an inert gas that does not participate in combustion. The water injection 8 increases the proportion of inert gas in the overflow gases 9.

[0019] Arrows 16 and 17 indicate in Fig. Figure 1 indicates that the overflow gases 9 are partially returned to the combustion chamber 7 via an oil separator 15 and the intake manifold 6. The returned overflow gases 9, 16, 17 are introduced into the intake manifold 6 at an overflow gas inlet point 13.

[0020] A control unit 10, indicated by a rectangle, is used to perform a mixture correction 11. As part of the mixture correction 11, a crankcase pressure sensor 14 detects whether water injection 8 takes place at an operating point in which the reciprocating piston engine 2 of the internal combustion engine 1 is operating.

[0021] The water injection 8 causes the pressure in the crankcase 5 to increase at the operating point. A larger mass flow of overflow gas must then be routed from the crankcase 5 back into the intake manifold 6 via the oil separator 15.

[0022] This larger overflow gas mass flow is then taken into account in the mixture correction 11 in the control unit 10 when metering fuel in the fuel path of the internal combustion engine 1. This prevents undesirable mixture deviations during the operation of the reciprocating engine 2. Reference sign 1 Internal combustion engine 2 reciprocating piston engines 3 cylinders 4 pistons 5 Crankcase 6 Intake manifold 7 Combustion chamber 8 Water injection 9 Overflow gas 10 Control 11 Mixture correction 12 Fuel-air mixture 13 Overflow gas inlet 14 Crankcase pressure sensor 15 oil separators 16 Arrow 17 Arrow

Claims

[1] Method for operating a spark-ignited reciprocating engine (2) with a crankcase (5), with at least one cylinder (3) in which a piston (4) is movable back and forth when a supplied fuel-air mixture (12) is ignited in a combustion chamber (7), and with a water injection system (8), wherein overflow gases (9) from the combustion chamber (7) enter the crankcase (5), characterized by , that the fuel-air mixture (12) is corrected as part of a mixture correction (11) depending on a flow rate of overflow gases from the combustion chamber (7) into the crankcase (5), wherein the overflow gases (9) are, at least partially, discharged from the crankcase (5) and directed into an intake manifold (6) at an overflow gas inlet (13), wherein the mixture correction (11) is carried out depending on the amount of water injected. [2] Method according to claim 1, characterized by, that the water injection (8) takes place downstream of the overflow gas inlet (13) into the intake manifold (6). [3] Method according to any one of the preceding claims, characterized by , that a crankcase pressure in the crankcase (5) is recorded at a respective operating point and stored in a characteristic map or measured with a sensor. [4] Method according to claim 3, characterized by , that the mixture correction (11) is performed during gas exchanges when it is detected at a current operating point that water injection (8) is taking place. [5] Method according to any one of the preceding claims, characterized by , that the mixture correction (11) is supplemented by a water influence when water injection (8) takes place. [6] Method according to any one of the preceding claims, characterized by , that a fuel injection quantity is varied by a controller depending on an exhaust gas temperature. [7] Method according to any one of the preceding claims, characterized by , that the overflow gases (9) from the crankcase (5) are returned to the overflow gas inlet point (13) via an oil separator (15). [8] Control (10) for an internal combustion engine (1) comprising at least one cylinder (3), one piston (4), one crankcase (5) and one intake manifold (6), wherein the control (10) is configured to execute a method according to any of the preceding claims. [9] Machine-readable storage medium on which a computer program is stored which is configured to execute a method according to any one of claims 1 to 7. [10] Motor vehicle with a control system (10) configured to perform a method according to any one of claims 1 to 7.

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