DE102020212898A1 - Method and device for operating a system for injecting water into an intake manifold of an internal combustion engine - Google Patents

Abstract

The invention relates to a method and a device for operating a system for injecting water into an intake manifold (11) of an internal combustion engine. In a normal operating phase, the system injects a specified quantity of water in synchronism with a combustion process of the internal combustion engine, depending on the operating state of the internal combustion engine. In a special operating phase, the specified quantity is increased compared to the normal operating phase.

Description

State of the art

The invention is based on a method and a device according to the species of the independent patent claims. It is already known that the properties of the combustion taking place in the combustion chamber are improved by injecting water into a combustion chamber of an internal combustion engine. In this case, water can be injected into an intake manifold of the internal combustion engine and the injected water is introduced into the combustion chamber by the air flow in the intake manifold.

Advantages of the Invention

In contrast, the method according to the invention and the device according to the invention have the advantage that an increased injection quantity of water is permissible in a special operating phase. This increased injection quantity can be used in particular to optimize the water injection system. Improved operation of the system for injecting water into an intake manifold of an internal combustion engine can thus be implemented.

Further advantages and improvements result from the measures in the dependent patent claims. By limiting the increased quantity for a specified number of combustion processes, it can be ensured that the combustion in the combustion chamber is not impaired. Alternatively, this can also be realized by an alternating operation, in which the quantity is alternately increased for a first combustion process and the quantity of the normal operating phase is used again in an immediately subsequent combustion process. The deposit of the water on the wall of the suction pipe (wall film) is taken into account in particular when determining the increased quantity. An increased quantity can thus be selected which does not cause any deterioration in the combustion process. The increased quantity is determined in a particularly simple manner by determining an influence of the increased quantity on a torque generated during combustion and comparing it with an expected torque. It can thus be ensured that, despite the increased quantity, the operation of the internal combustion engine is not impaired. The engine operating point (speed, load, ignition point) and the engine temperature are particularly important when determining the permissible increased quantity. Determining the wall film that has actually accumulated also depends on the operating point, as well as on the medium and intake manifold temperature.

The special operating phase during filling of an empty system with water is particularly useful. Due to the increased quantity, the system can be filled with water particularly quickly and safely. Furthermore, the special operating phase can be used to diagnose the system. Due to the increased quantity, an improved diagnosis of the system for injecting water can be implemented, in particular in the case of a diagnosis by evaluating a pressure curve or a differential pressure caused by an injection.

character list

• 1 ein System zur Einspritzung von Wasser in ein Saugrohr einer Brennkraftmaschine,
• 2 Verfahrensschritte bei der Befüllung eines Systems zur Einspritzung von Wasser in ein Saugrohr einer Brennkraftmaschine, und
• 3 Verfahrensschritte bei einer Diagnose eines Systems zur Einspritzung von Wasser in ein Saugrohr einer Brennkraftmaschine.

Embodiments of the invention are shown in the drawings and explained in more detail in the following description. Show it:

• 1 a system for injecting water into an intake manifold of an internal combustion engine,
• 2 Process steps for filling a system for injecting water into an intake manifold of an internal combustion engine, and
• 3 Process steps in a diagnosis of a system for injecting water into an intake manifold of an internal combustion engine.

description

In the 1 an engine, ie an internal combustion engine, having a cylinder 10 is shown schematically. A combustion chamber 101 is defined in the cylinder 10 by a piston 100 . The cylinder 10 or the combustion chamber 101 is supplied with air for combustion through an intake manifold 11 and fuel for combustion in the cylinder 10 through a fuel injector 13 . The resulting exhaust gases are conducted away from the cylinder 10 through the exhaust pipe 12 .

It is a conventional Otto engine or diesel engine in the 1 is shown only schematically. In particular, other control elements such as air intake and exhaust gas outlet valves, means for influencing the air flow through the intake manifold 11 (such as a throttle valve), a spark plug or a glow plug and other elements of conventional Otto engines and diesel engines are not shown, since they are are not relevant to the understanding of the invention.

Furthermore, in the 1 a water injection into the intake manifold 11 is shown. The water injection consists of a water tank 2 which is connected to an electric pump 1 by a connecting line 5 . Through the connecting line 5 water can flow from the tank 2 to the electric pump 1 or from be sucked out of the tank by the electric pump 1. The side of the electric pump 1 that is connected to the water tank 2 via the connecting line 5 is referred to below as the inlet. Furthermore, the electric pump 1 has a high-pressure outlet, which is connected to a water rail 3 via the connecting line 5 . The water rail 3 is a pressure accumulator that can be filled with water from the electric pump and is pressurized. During the injection into the intake manifold, the pressure is relatively low, so that the water rail 3 can also be designed as a simple hose or as a hose distributor. The water rail 3 is then connected via a further connecting line 5 to a water injector 4 which opens into the suction pipe 11 . The water in the tank 2 is thus supplied via the inlet to the electric pump 1 and is made available at the high-pressure outlet of the pump 1 at increased pressure. This water is then temporarily stored in the water rail 3 until it is injected through a corresponding opening in the water injector 4 into the intake manifold 11 .

A multiplicity of water injectors 4 can also be connected to the water rail 3, which water injectors supply a multiplicity of cylinders 10 with water. In particular in the case of multi-cylinder engines, such as are common today in motor vehicles, this is a configuration with which each cylinder can be supplied individually with a quantity of water tailored to it.

By injecting water into the intake manifold 11, a mixture of air, fuel and water is generated in the combustion chamber 101 of the cylinder 10, together with the fuel injected by the fuel injector 13. The fuel-air mixture is then burned in the combustion chamber of cylinder 10 by appropriate ignition, either by a spark plug or by a self-ignition process in a diesel engine. The water contained in this air-fuel mixture effectively cools combustion chamber 101 in the Cylinder 10, which reduces the combustion temperature and, when used in the Otto engine, reduces the tendency to knock. This enables an optimized ignition timing, which has a positive effect on the efficiency and fuel consumption of the gasoline engine. In the case of petrol and diesel engines, the formation of harmful exhaust gases can also be reduced. The introduction of water into a combustion chamber is therefore a measure with which the quality of the combustion in the combustion chamber of a cylinder 10 can be positively influenced. This measure can positively influence both the quality of the exhaust gas and the thermal load on the cylinder 10, the performance and also the fuel requirement.

When water is injected into the intake manifold 11, water is deposited on the wall of the intake manifold 11 (wall film formation), particularly at lower temperatures. A similar effect is already known for the injection of fuel into the intake manifold 11, the effect of the injection of water in the intake manifold 11 being more pronounced due to the poorer evaporation of water. When water is injected into intake manifold 11 for the first time or once, not all of the injected water will therefore be immediately available for the next combustion process in combustion chamber 101 . Typically, the injection of water into the intake manifold 11 takes place immediately before a combustion, so that the air flow for the combustion in question also contains a desired amount of water for the combustion. Because of the condensation on the wall of the intake manifold 11, however, this cannot be ensured when water is injected into the intake manifold for the first time or once. The amount of water actually introduced into combustion chamber 101 is correspondingly distorted by this condensation effect, which must be taken into account in particular in the case of dynamic operating states. During normal operation of the internal combustion engine, these effects must therefore be taken into account empirically, particularly in the case of dynamic operating states.

However, the condensation of water on the wall of the intake manifold 11 can also be used positively in special operating states, which are referred to below as the special operating phases.

In the 2 method steps are shown in which a first-time filling of the system for injecting water into an intake manifold of an internal combustion engine is described as a special operating phase. When the engine is turned off, the water injection system should be drained. In particular when the internal combustion engine is operated in a motor vehicle, temperatures can occur which are lower than the freezing point of water. If there is still water in the system at such temperatures, this water can freeze and, due to the increase in volume of frozen water, lead to an impermissibly high pressure in the connecting lines 5 or in the water rail 3 or the water injectors 4.

When the vehicle or the internal combustion engine is put into operation again, the lines 5 and the water rail must be filled 3 take place. Any air bubbles contained must be emptied through the water injector 4 into the intake manifold 11 . Since this process does not ensure whether water is injected into the intake manifold 11 or whether only air is emptied, this should be done in an operating phase of the internal combustion engine in which a certain amount of water does not impair combustion and at the same time no water is absolutely necessary to protect the internal combustion engine from overload. This is typically the case when the internal combustion engine is subjected to low loads, but when only small amounts of water are injected during normal operation of the internal combustion engine.

Depending on the system configuration and the geometry of the water-carrying system (line routing, diameter, cross-sectional jumps, etc.), such small amounts of water may not lead to reliable removal of water from the system for injecting water into a suction pipe. In order to reliably remove air bubbles from the system, longer injection times and larger amounts of water are required. Sufficient flow velocity must probably first develop in the system for injecting water in order to reliably remove air bubbles that collect at high points in the system or adhere to surfaces from the system. A single injection, with a larger amount of water, removes air bubbles more reliably than several small injections, the accumulated amount of which corresponds to the larger amount. In order not to introduce too much water into the combustion chamber, the number of injection processes should therefore remain limited to a predetermined number of combustion processes in this special operating phase.

Alternatively, the injections with an increased quantity can also take place alternately with injections with a normal quantity (which can also be 0). In such an operation, after a first combustion process with an increased injected quantity, a normal quantity (which can also be 0) would be injected immediately thereafter.

Furthermore, the increased amounts for the injection can also be determined as a function of the condensation on the wall of the intake manifold 11 or as a function of a deterioration in the combustion processes. In order to assess deterioration in combustion processes, the torque actually generated in the combustion process is compared with an expected torque. If the difference is too great, the amount of water selected was too high. The corresponding amounts can be determined empirically on the internal combustion engine. A dependency on a temperature of intake manifold 11 can be taken into account.

In the 2 it is determined in a first step 201 whether the system for injecting water into an intake manifold of an internal combustion engine is being filled with water. This is always the case, for example, when the internal combustion engine has been restarted after a long break in operation. If this is not the case, step 201 is followed by step 205, with which the method ends.

If a filling of the system is detected, step 201 is followed by step 202, in which the normal amount of water that is permissible in the current operating state of the internal combustion engine is determined. Step 202 is followed by step 203, in which the amount of water that condenses on the wall of the intake manifold 11 during injection into the intake manifold 11 is determined. It is taken into account whether previous injections with an increased quantity have already taken place or whether injections with an increased quantity or with a normal quantity have taken place alternately. Furthermore, the temperature of the intake manifold 11 and other operating parameters of the internal combustion engine are taken into account. In the subsequent step 204, water is then injected into the intake manifold 11 with the sum of the quantities determined in steps 202 and 203. In the subsequent step 205, the method ends.

Furthermore, the special operating phase can also be used to diagnose the system for injecting water into an intake manifold of an internal combustion engine. A pressure profile in the system during the injection of water can be evaluated in particular for diagnosing the system. In this case, a change in pressure is typically evaluated by injecting water, in particular if the pump 1 does not subsequently deliver water into the water rail 3 . An increased quantity of the injection causes a correspondingly higher pressure drop or greater drop in pressure due to the injection. Such a higher pressure drop improves the measurability of deviations and thus also the quality of the diagnosis.

In the 3 Method steps of a special operating phase, in which a diagnosis of the system for injecting water takes place, are shown. In a first step 301, it is determined whether a diagnosis of the system for injecting water into an intake manifold of an internal combustion engine using water is carried out. This is triggered, for example, as a function of the operating states of the internal combustion engine. If not so Step 301 is followed by step 305, with which the method ends. If a diagnosis of the system is detected, step 301 is followed by step 302 in which the normal amount of water that is allowable at the current operating condition of the engine is determined. Step 302 is followed by step 303, in which the amount of water that condenses on the wall of the intake manifold 11 during injection into the intake manifold 11 is determined. In this case, it is taken into account whether previous injections with an increased quantity have already taken place or whether injections with an increased quantity or with a normal quantity have taken place alternately. Furthermore, the temperature of the intake manifold 11 and other operating parameters of the internal combustion engine are taken into account. In the subsequent step 304, water is then injected into the intake manifold 11 with the sum of the quantities determined in steps 302 and 303. Furthermore, an evaluation then takes place as to whether the pressure drop triggered thereby corresponds to an expected pressure drop, or the pressure drops of several injection processes are determined and compared for diagnostic purposes. Depending on the deviation determined, a corresponding result of the diagnosis is then recorded as "OK" or "Not OK". In the subsequent step 305, the method ends.

Claims (9)

Method for operating a system for injecting water into an intake manifold (11) of an internal combustion engine, the system in a normal operating phase with little or no engine requirement for water injection depending on the operating state of the internal combustion engine synchronous to a combustion process of the internal combustion engine Injects water, characterized in that in a special operating phase, the set amount is increased compared to the normal operating phase. procedure after claim 1 , characterized in that in the special operating phase the amount is increased only for a predetermined number of combustion processes. procedure after claim 1 , characterized in that the quantity for a first combustion process is increased in the special operating phase and the quantity of the normal operating phase is used again in the immediately following combustion process. Method according to one of the preceding claims, characterized in that the increased quantity is measured in such a way that the increased quantity, reduced by a proportion which is deposited on the wall of the intake manifold (11), does not lead to a worsening of the combustion process. procedure after claim 4 , characterized in that the deterioration is detected by comparing a generated torque with an expected combustion torque. Method according to one of the preceding claims, characterized in that the increased quantity is determined taking into account the engine operating point and the temperature of the intake manifold (11) and the medium. Method according to one of the preceding claims, characterized in that an empty system is filled with water in the special operating phase. Method according to one of the preceding claims, characterized in that in the special operating phase the system is diagnosed by evaluating a pressure curve when water is injected. Device for operating a system for injecting water into an intake manifold (11) of an internal combustion engine, which in a normal operating phase depending on an operating state of the internal combustion engine synchronously with a combustion process of the internal combustion engine controls an injection of a specified quantity of water, characterized in that it in a special operating phase, the specified quantity is increased compared to the normal operating phase.

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