KR102391708B1 - Method and device for operating an internal combustion engine - Google Patents

Abstract

The present invention relates to a method and apparatus for operating an internal combustion engine comprising an injection device for injecting a cooling fluid into a combustion chamber (101) of the internal combustion engine, wherein the risk of knocking during current combustion in the combustion chamber (101) is reduced. It is determined, and when the knock risk exceeds the threshold, injection of the cooling fluid into the combustion chamber 101 is performed during the current combustion.

Description

METHOD AND DEVICE FOR OPERATING AN INTERNAL COMBUSTION ENGINE

The present invention relates to a method and apparatus for operating an internal combustion engine comprising an injection device for injecting a cooling fluid into a combustion chamber of the internal combustion engine according to the categories of the independent patent claims.

A method and a device for injecting a cooling fluid (water) into the combustion chamber of an internal combustion engine are already known from DE 39 28 611, respectively.

On the other hand, the method according to the invention or the device according to the invention for operating an internal combustion engine comprising an injection device for injecting a cooling fluid into the combustion chamber of the internal combustion engine, the direct knock risk of the current combustion is determined, the Then, there is an advantage that knock can be continuously prevented through the injection during combustion, which is currently being carried out, or at least the damaging action of knock on the engine can be weakened. In this way, knock reduction is achieved during the current combustion. In particular, the occurrence of knock can be generally prevented through the above measures. Therefore, knock-on combustion can be prevented before knock-on combustion occurs, and knock-on combustion can continue to be hindered or reduced during occurrence of knock-on combustion. In this way, the stress of the engine is also reduced by the knock-on combustion. This enables continuous operation closer to the knock limit, since otherwise inevitable and always recurring knock events are avoided. Thereby, internal combustion engines operated according to the method according to the invention can be operated closer to the knock limit and thus more effectively. Compared to conventional water injection devices, a significantly reduced cooling fluid consumption can be achieved, thereby reducing the need for charging, for example in automobiles equipped with an internal combustion engine of this type.

Further advantages and improvements are achieved through the measures of the patent dependent claims. Currently, the detection of the knock risk during combustion is carried out particularly reliably through an assessment of the pressure in the combustion chamber. Said pressure can be measured directly via a combustion chamber pressure sensor with great accuracy. Alternative measurement methods use structural sound sensors or ion current sensors, which are obviously more economical than combustion chamber pressure sensors. For the assessment of the knock risk, the pressure in the combustion chamber is compared with an expected value. The expected value includes not only the pressure but also the point at which the pressure occurs after the start of combustion, or the angle position of the internal combustion engine is taken into account. In addition to the absolute level of pressure, the point in time or angular position at which that pressure occurs within the combustion chamber is also important for determining whether a knock hazard exists. In this way, the detection of the knock risk can be performed very reliably. The expected values used for this purpose can be deterministically preset for the internal combustion engine, eg for a specific engine type, from the outset. In addition, it is possible to learn typical expected values for current combustion by continuously evaluating combustion processes during operation of the internal combustion engine. Then, if a strong deviation of the current combustion compared to previous combustions occurs, this may be a clear indication of an increased risk of knocking. If, on the basis of this evaluation, an increased knock risk is identified, an injection of cooling fluid can likewise be carried out for a predetermined number of subsequent combustions. In short, as the knock risk identified during combustion indicates an overall increased knock tendency of the internal combustion engine, it is premised in that case that an injection of the cooling fluid must be performed for a predetermined number of subsequent combustions. Alternatively, upon detection of a knock hazard, it is possible to activate the cooling fluid injection and then maintain the cooling fluid injection until a predetermined change in operating conditions of the internal combustion engine occurs. A change in operating conditions may be defined, for example, by a change in rotational speed, engine load or other operating parameters.

1 is a schematic diagram of an internal combustion engine comprising a cylinder;

1 schematically shows an engine comprising a cylinder 10 , ie an internal combustion engine. In the cylinder 10 , the combustion chamber 101 is delimited via the piston 100 . Air for combustion is supplied to the cylinder 10 or the combustion chamber 101 through the intake pipe 11 , and fuel for combustion in the cylinder 10 is supplied through the fuel injector 13 . At this time, the generated exhaust gas is discharged from the cylinder 10 through the exhaust pipe 12 . In this case, a conventional Otto engine or a diesel engine, shown only schematically in FIG. 1 , is concerned. In particular intake valves, exhaust valves, means (such as a throttle valve) for regulating the flow rate of air flowing through the intake pipe 11 , spark plugs or glow plugs and other components of ordinary Otto engines and diesel engines; Such additional control elements are not shown, since they are not very important for understanding the present invention.

Also shown in FIG. 1 is an injector, in particular a water injector, for injecting a cooling fluid into the combustion chamber 101 . Hereinafter, although always a water jetting device is described, this water jetting device is representative of any cooling fluid jetting device. Besides water, mixtures of water and alcohols, or mixtures of other liquids and water are also conceivable. The key here is that the cooling fluid requires a high amount of heat during vaporization and thus contributes to the cooling of the combustion chamber. Direct injection of water into the combustion chamber of cylinder 10 requires significant pressure. Since the injection of the cylinder 10 into the combustion chamber can be carried out when the intake valve is already closed in the direction of the intake pipe 11 and the cylinder is in the compression stage, for injection of water into the combustion chamber it is up to 200 bar magnitude. Obviously higher pressures are required. Therefore, in the water rail 3 , water must be supplied at high pressure to enable direct injection of the cylinder 10 into the combustion chamber. The water spraying device is formed of a water tank 2 connected to an electric pump 1 via a connection line 5 . Via the connecting line 5 water can flow from the tank 2 towards the electric pump 1 , or it can be sucked in by the electric pump 1 from the tank. The side of the electric pump 1 connected to the water tank 2 through the connection line 5 is hereinafter referred to as a supply unit. The electric pump 1 also has a high-pressure outlet which is connected to the high-pressure pump 6 via a connection line 5 . The supply of the high-pressure pump 6 is connected with the high-pressure outlet of the electric pump 1 via a connection line 5 . The high-pressure outlet of the high-pressure pump 6 is connected to the water rail 3 via a connection line 5 .

The water rail 3 is then connected via a further connecting line 5 with a water injector 4 leading into the combustion chamber 101 . Accordingly, the water in the tank 2 is supplied to the electric pump 1 via the supply and is supplied to the high-pressure pump 6 at an increased pressure at the high-pressure outlet of the pump 1 . The water thus subjected to a high pressure of about 200 bar by means of the high-pressure pump 6 is then temporarily stored in the waterrail 3 until it is injected into the combustion chamber 101 through the corresponding opening of the water injector 4 . do. In this way, an arrangement is provided in which a sufficiently high pressure is generated to enable direct water injection directly into the combustion chamber of the engine.

A plurality of water injectors 4 for supplying water to the plurality of cylinders 10 may also be connected to the water rail 3 . In particular, in the case of a multi-cylinder engine that is common in recent automobiles, it is a configuration that allows water to be supplied in an amount matched to each cylinder for each cylinder.

Through the water injection, in the combustion chamber 101 of the cylinder 10 , a mixture of air, fuel, and water is generated together with the fuel injected through the fuel injector 13 . The combustion of the fuel/air mixture is then carried out in the combustion chamber of the cylinder 10 , either via a spark plug or, in the case of a diesel engine, via a corresponding ignition via a self-ignition process. Through the water contained in the air/fuel mixture, effective cooling of the combustion chamber 101 in the cylinder 10 is effected, thereby lowering the combustion temperature and reducing the tendency to knock when applied to an Otto engine. This allows for an optimized ignition timing that positively affects the efficiency or consumption of the Otto engine. In addition, in the case of an auto engine and a diesel engine, generation of harmful exhaust gas may be reduced. Therefore, the introduction of water into the combustion chamber is a measure that can positively affect the quality of combustion in the combustion chamber of the cylinder 10 . Through this measure, it is possible to positively affect not only the quality of the exhaust gas, but also the thermal load of the cylinder 10 , the power output and the fuel demand.

FIG. 1 also shows a combustion chamber pressure sensor 20 which projects into the combustion chamber 101 and directly measures the pressure in the combustion chamber. Thus, the pressure ratio in the combustion chamber 101 is always known by means of a pressure sensor of this type, and in particular through this direct pressure measurement in the combustion chamber, the combustion in progress and the pressure that occurs at this time are directly monitored. In particular, by means of a direct pressure measurement of this type, it is possible to determine whether a knock will occur in the continuation of combustion, already in the first half-cycle of combustion. In this type of knock-on combustion, in addition to the actual ignition by the spark, the ignition of the gas/air mixture is carried out spontaneously at a number of other locations in the combustion chamber, and a number of flame fronts at different locations of occurrence combustion that takes place During this type of knock-on combustion, very high pressures and pressure gradients are formed which allow damage to the internal combustion engine, in particular to the piston 100 , to occur. In another aspect, the operation of the internal combustion engine near the knock-on operating point is particularly effective, since the energy generated through combustion at the knock-on operating point is particularly effectively converted into mechanical motion. Therefore, it is desirable to operate the internal combustion engine as close as possible to the knock-on actuation point, but to avoid knocking. Now, according to the present invention, it is determined whether knock will occur when the progress of combustion is continued through evaluation of the current combustion in progress, and when it is determined that knock will occur, the cooling of the current combustion is continuously implemented by injecting water during the current combustion immediately It is proposed to keep knocking while the current combustion proceeds. This measure allows the internal combustion engine to operate very close to the knock limit, while knocking is not occurring.

As an alternative to the combustion chamber pressure sensor 20 , other sensors may also be used that allow a determination of the combustion in progress. A knock sensor is mounted on the outside of the cylinder 10 and measures the combustion noise, which is also a measure of the pressure generated in the combustion chamber 101 . Knock sensors of this type are typically structured sound sensors or vibration sensors which are designed as piezoelectric sensors or acceleration sensors. Another possibility is the use of an ion current sensor in which a voltage is applied between the electrodes in the combustion chamber and the current flow between the two electrodes flowing through the gas mixture in the combustion chamber is evaluated. In this case, since the conductivity largely depends on the pressure in the combustion chamber, the sensors also supply information on the pressure ratio in the combustion chamber. However, the use of a combustion chamber pressure sensor is preferred because of the possibility of direct evaluation.

It has been found that, through evaluation of the pressure profile of the first half cycle of combustion, it is possible to determine relatively well whether knocking will occur in the second half cycle of combustion. In this case, through the injection of a cooling fluid, in particular water, it is possible to influence the temperature of the second half cycle of combustion so that the knock is suppressed or the knock intensity is obviously reduced. Even though the operation of the internal combustion engine near the knock limit is thus made possible, the knock also does not occur. In this case, the determination of whether or not knock will occur during the current combustion is performed by evaluating the knock risk based on the pressure in the combustion chamber. For this purpose, the pressure is compared to an expected value, which includes not only the level of pressure but also the starting point or angular position of the pressure. During combustion in an internal combustion engine, the maximum pressure is sought to be carried out after top dead center of the piston 100 in the cylinder 10 . A knock hazard is detected when a pressure value that is too increased occurs prematurely, ie at a very fast angular position. In this case, the expected value, ie the combination of the pressure value and the angular position or time point after the start of combustion, can be determined personally, or the operation of the internal combustion engine can be learned in progress. If the values are predetermined, it is determined for a particular type of internal combustion engine which expected value must be exceeded in order to detect a knock hazard for the continuation of the progression of combustion during the design phase or the application phase. In this case, the determination may depend on the operating conditions of the internal combustion engine, for example the load or the rotational speed. Alternatively, the expected values may be learned. In this case, a standard pressure profile may be stored as the operation of the internal combustion engine proceeds, for example by means of an average value calculation. In this case, if the pressure profile during combustion shows a significant deviation from the learned standard pressure profile, in particular if it exceeds the learned standard pressure profile, a knock risk is detected and the injection according to the invention is triggered during further progress of combustion do. In this case, the learning can also depend on operating parameters of the internal combustion engine, for example load or rotational speed.

Once a knock hazard has been detected during the current combustion, it must be determined whether the injection of the cooling fluid is to be performed only for said combustion, or whether subsequent combustions are also performed together with the injection of the cooling fluid. In short, the presence of a knock hazard once implies that the internal combustion engine is in an operating state immediately prone to knock and therefore measures must be taken to prevent further knock events as well. Of course, since injecting the cooling fluid in advance at the start of combustion is a more suitable measure to reduce the occurrence of knock, it is preferable to perform additional cooling through injection of the cooling fluid as a preventive measure when the risk of knocking is detected once . Once a knock hazard has been detected, it is possible to simply execute an injection of cooling fluid for a preset number of subsequent burns. This is done irrespective of whether the knock hazard will be detected again. In this mode, the knock hazard can no longer be detected in the first half cycle of combustion, since the injection of the cooling fluid is already carried out at the start of combustion. Then, only after the injection of the cooling fluid has been performed for a preset number of combustions, it switches back to a process in which injection of the cooling fluid is not performed from the beginning, but only when a knock hazard is identified during the current combustion. Alternatively, if a knock hazard is detected after an injection during an ongoing knock hazard combustion, injection of the cooling fluid as a whole may be activated for all subsequent combustions. This injection of cooling fluid may be maintained until an apparent fluctuation in operating conditions of the internal combustion engine occurs. In this case, in particular, the deactivation of the injection of the cooling fluid can be carried out only when the operating conditions of the internal combustion engine are changed in the direction in which the knock tendency is reduced, for example by an apparent reduction of the load or the rotational speed.

In figure 2 the individual steps of the method according to the invention are shown schematically once more. In a first step 21, it is checked whether the method according to the invention can be implemented. The prerequisites for this are that the cooling fluid for injection is present, or that there is no error message to the combustion chamber pressure sensor 20 , or that the warm-up mode of the internal combustion engine has been terminated, or that other prerequisites have been met. can be In a subsequent step 22, a pressure assessment of the ongoing combustion is performed for the determination of the knock risk. For this purpose, in particular the pressure is compared to a threshold or a sequence of thresholds, the thresholds taking into account not only the level of pressure but also the pressure generation over time. This hourly occurrence may be defined, for example, as a time point after the start of combustion or before piston top dead center, or it may be defined as an angular value of an internal combustion engine. If the knock hazard exceeds the threshold, an injection of cooling fluid is triggered during the ongoing combustion. In general, knock-on combustion is carried out in the second half cycle of combustion. Accordingly, a knock hazard is detected in the first half cycle of combustion, which is normally started to be carried out, in order to carry out the injection of the cooling fluid in the second half cycle of combustion. If no knock risk is detected in step 22, step 21 is performed again following step 22. If a knock hazard is detected in step 22, step 22 is followed by step 23, in which injection of a cooling fluid is performed during the current combustion. Through this measure, knock occurrence is suppressed, or at least the knock strength is reduced. Then, following step 23, step 21 is performed again.

Claims (8)

A method for operating an internal combustion engine comprising an injector for injecting a cooling fluid into a combustion chamber (101) of the internal combustion engine, the method comprising:
A method of operating an internal combustion engine, characterized in that a knock risk is determined during current combustion in the combustion chamber, and injection of a cooling fluid into the combustion chamber ( 101 ) is performed during the current combustion if the knock risk exceeds a threshold value. Method according to claim 1 , characterized in that the pressure in the combustion chamber ( 101 ) is evaluated for the assessment of the knock risk. Method according to claim 2 , characterized in that the pressure in the combustion chamber ( 101 ) is measured directly via a combustion chamber pressure sensor ( 20 ) or indirectly via a structure transmission sound sensor or an ion current sensor. Method according to claim 2 or 3, characterized in that the pressure as a threshold value is compared with at least one expected value, the expected value corresponding to the pressure at a specific point in time after the start of combustion or at an angular position of the internal combustion engine. . 5. A method according to claim 4, characterized in that the expected value is predetermined for the internal combustion engine or is learned during operation of the internal combustion engine. 4. The method according to any one of claims 1 to 3, wherein if the knock risk exceeds the threshold value during the current combustion, for a preset number of subsequent combustions, irrespective of whether the knock risk again exceeds the threshold value or not. A method of operating an internal combustion engine, characterized in that the injection of cooling fluid is carried out. 4. The cooling fluid according to any one of claims 1 to 3, wherein if the knock risk exceeds a threshold value during the current combustion, for subsequent combustions again, irrespective of whether the knock risk exceeds the threshold value or not. A method of operating an internal combustion engine, characterized in that the injection is carried out and the injection of the cooling fluid is stopped again only when a predetermined change of operating conditions of the internal combustion engine occurs. An apparatus for operating an internal combustion engine comprising an injector for injecting a cooling fluid into a combustion chamber (101) of the internal combustion engine, the apparatus comprising:
Means are provided for determining a knock risk during a current combustion in the combustion chamber and causing an injection of a cooling fluid into the combustion chamber during the current combustion if the knock risk exceeds a threshold value, internal combustion engine operating device.

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