DE102009040111A1 - dosing - Google Patents

Abstract

The invention relates to a system for the selective catalytic reduction of nitrogen oxides in the exhaust gas of internal combustion engines (1) or the like by means of an SCR catalytic converter (2), a dissolved reducing agent, in particular a urea solution, being introduced into the exhaust gas stream by means of a metering device (6) The system has a delivery line (4) which can be connected or connected to a reducing agent tank (3), the system having a sensor arrangement (5) by means of which the volume and / or mass flow and at least one substance property of the conveyed reducing agent, in particular the urea solution , is detectable or is recorded.

Description

The invention relates to a system for selective catalytic reduction of nitrogen oxides in the exhaust gas of internal combustion engines or the like by means of an SCR catalyst, wherein a contribution of a dissolved reducing agent, in particular a urea solution, into the exhaust gas stream by means of a metering, wherein the system can be connected to a reducing agent tank or associated funding line.

Furthermore, the invention relates to a method for controlling the metering and introduction of a reducing agent, in particular urea solution, into the exhaust gas flow of an internal combustion engine or the like, for the selective catalytic reduction of nitrogen oxides in the exhaust gas by means of an SCR catalyst.

Such systems and methods for introducing a reducing agent in the form of a urea solution in the exhaust gas stream are known. Under reducing agent or urea solution in this sense, both ammonia or an ammonia solution and urea solution and in particular a urea solution according to DIN 70070 be understood.

Selective catalytic reduction (abbreviated SCR - English: selective catalytic reduction) refers to the technique of reducing nitrogen oxides in exhaust gases from diesel engines of commercial vehicles, but also from other combustion plants, waste incinerators, gas turbines and industrial plants. The chemical reaction on the SCR catalyst is selective, ie, the nitrogen oxides NOx are preferably reduced, while undesired reactions are largely suppressed. The reaction requires ammonia, which is added to the exhaust gas. This ammonia is in the form of a urea solution in particular according to DIN 70070 metered into the exhaust stream.

When using such systems for selective catalytic reduction in commercial vehicles, a so-called on-board diagnosis (OBD) of the function of the SCR catalyst system is required by law, which usually takes place with a NOx sensor arranged downstream of the SCR catalytic converter , The disadvantage of this approach is the very high cost of the NOx sensor and the high cost in the calibration of each system variant.

In order to prevent manipulation, it is sometimes demanded by the legislator that improper operation of the NOx emission facilities in the engine system must be detected by NOx concentration monitoring probes located in the exhaust gas flow. According to the legal requirements, these facilities must also have appropriate records and records of any errors.

The object of the invention is to develop a system for selective catalytic reduction of nitrogen oxides and a method for controlling the metering and introduction of a reducing agent into the exhaust stream for selective catalytic reduction such that a tamper-proof diagnosis of the dosage of the reducing agent and tamper-proof monitoring of the reducing agent quality is guaranteed.

This object is achieved by a system according to claim 1 and by a method according to claim 12. Advantageous developments of the invention are specified in the respective dependent claims.

Particularly advantageous in the system for the selective catalytic reduction of nitrogen oxides in the exhaust gas of internal combustion engines or the like by means of an SCR catalyst, wherein an introduction of a dissolved reducing agent, in particular a urea solution, in particular according to DIN 70070 , in the exhaust stream by means of a metering, wherein the system comprises a connectable to a reducing agent tank or connected conveyor line, it is that the system comprises a sensor arrangement by means of which the volume and / or mass flow and at least one material property of the subsidized reducing agent, in particular the urea solution, is detectable or detected.

The invention is thus based on the fact that the proper functioning of the SCR system over the lifetime can also be represented by means of a urea quality sensor. The amount of reducing agent is hereby monitored with suitable sensors in the metering system itself. By a urea quality sensor, by means of which at least one substance property of the conveyed reducing agent is detected, it can also be determined whether the correct reducing agent is injected.

Because the system has such a sensor arrangement, manipulation is impossible, ie it would not be possible to monitor the sensor by means of which the reducing agent quality is monitored, to supply urea, so that it emits a correct signal, while the dosage for reducing the operating costs suck in simple water. Since the sensor arrangement is integrated into the system and both the volume and mass flow and also at least one substance property monitored the subsidized reducing agent, a manipulation is excluded.

Preferably, the sensor arrangement is adapted to continuously and / or periodically perform the detection of the volume flow and / or the mass flow and the at least one material property of the delivered reducing agent, which is metered into the exhaust gas flow.

This makes it possible to monitor the quality and the funded amount of the reducing agent permanently or with a predetermined timing and to capture, in particular save.

The sensor arrangement preferably has a flow sensor. In particular, the system may further comprise means for calculating the mass flow and / or the volume flow of the delivered reducing agent, in particular the urea solution, for example on the basis of a pressure drop across a metering orifice. For the detection of the volume and / or mass flow can thus be made use of known flow measuring techniques, with a manipulation is excluded by the fact that the sensor assembly is integrated into the system, d. H. that such a measurement is not carried out at a bypass, but in or on the delivery line of the reducing agent itself.

The sensor arrangement preferably has a sensor for measuring the electrical conductivity of the conveyed reducing agent, in particular the urea solution.

In this case, the quality is monitored in such a way that the electrical property is measured and monitored as the substance property of the promoted reducing agent.

Alternatively or cumulatively, the sensor arrangement can have a sensor for measuring the speed of sound in the conveyed reducing agent, in particular the urea solution.

In this case, the quality monitoring takes place in that, as an alternative or cumulative measure of the electrical conductivity, the sound velocity in the conveyed reducing agent is measured and monitored as the substance property of the promoted reducing agent.

As a result, a reliable quality monitoring of the subsidized reducing agent is guaranteed and a manipulation excluded because quality deviations are detected immediately.

In this case, the system can be set up in such a way that limit values are predetermined for the at least one substance property of the conveyed reducing agent, which is detected by means of the sensor arrangement, an error message being generated and permanently stored when it is undershot or overshot.

In a particularly preferred embodiment, the sensor arrangement is integrated into the delivery line. With the term integrated is meant that it is installed in the delivery line and forcibly flows through or is associated with the delivery line, wherein such an arrangement takes place that a flow through the sensor assembly or an overflow of the sensor arrangement is mandatory to preclude a possibility of manipulation.

In a particularly preferred embodiment, at least one temperature sensor is arranged upstream and downstream of the catalyst in the flow direction.

This means that temperature sensors are arranged in front of and behind the catalyst, for example thermocouples or the like, by means of which the temperature is measured, in particular continuously and / or periodically measured and thus monitored.

In a preferred embodiment, the system has means for calculating the exhaust gas mass flow and / or at least one sensor for measuring the exhaust gas mass flow and / or a sensor for measuring the exhaust gas temperature.

Alternatively or cumulatively, the system receives a signal that correlates to the exhaust gas mass flow from the engine controller.

From the exhaust gas mass flow signal and / or from the exhaust gas temperature and / or the measured exhaust gas mass flow, it is possible to detect the operating parameters exhaust gas temperature or exhaust gas mass flow present in dependence on the respective engine operating point and to evaluate them via a corresponding control electronics of the dosing system, in order thus to control the dosage with regard to time control and quantity the metered reducing agent to the measured operating parameters to adjust and regulate.

The system preferably has a control unit by means of which the triggering of the metering of the reducing agent, in particular the volume flow and / or the duration of the metering, is controllable or controlled as a function of the measured values recorded, in particular as a function of at least one substance property of the reducing agent and / or or as a function of the exhaust gas temperature and / or as a function of Exhaust gas mass flow and / or depending on the temperatures in front of and behind the SCR catalyst.

In this case, the sensors are preferably set up to carry out the acquisition of the measured values continuously and / or periodically, so that an online diagnosis and / or a repeated diagnosis and monitoring can take place.

The system preferably has a memory for the permanent storage of the recorded measured values and / or control states of the metering and / or any error messages.

By such a memory ensures that, for example, in the context of an inspection of the commercial vehicle, a review of the metering can be done later, as well as any errors are permanently stored and readable by means of this memory.

In a preferred embodiment, the system has a reducing agent tank, in particular a urea solution tank, and / or a urea filter and / or a pump for conveying the reducing agent, in particular the urea solution.

By arranging such components, a compact system with all the components required for the metering of the reducing agent can be created.

The system preferably has a nozzle, in particular a two-component nozzle, by means of which the reducing agent, in particular the urea solution, is injected into the exhaust gas stream and / or atomized in the exhaust gas stream. Furthermore, the metering system can have an integrated compressed air supply, in particular a compressor, and / or can be coupled to an external compressed air supply, so that the atomization and injection of the reducing agent, in particular the urea solution, takes place by means of compressed air in order to obtain an optimum droplet size of the reducing agent in the exhaust gas flow to get into the SCR catalyst.

To ensure that the reducing agent is also introduced into the exhaust gas, a corresponding sensor can be introduced in the exhaust pipe. Suitable is, for example, a temperature sensor, which is acted upon by the reducing agent. When injecting the reducing agent, the temperature of the sensor is lowered by the cooling effect. As a result, reliable production can be detected that the subsidized reducing agent also enters the exhaust and not z. B. is collected in a sump.

Particularly advantageous in the inventive method for controlling the dosage and introduction of a reducing agent, in particular urea solution, in the exhaust gas stream of an internal combustion engine or the like for the selective catalytic reduction of nitrogen oxides in the exhaust gas by means of an SCR catalyst is that at least one material property, in particular the electrical Conductivity and / or the speed of sound, the subsidized reducing agent, in particular urea solution, is detected, and wherein at least the temperatures are measured before and after the SCR catalyst, wherein the dosage of the reducing agent, in particular the control of the volume flow and / or the time duration of the Dosing, depending on at least one detected material property of the reducing agent and in dependence on the measured before and after the SCR catalyst temperatures of the exhaust gas.

The method according to the invention is equivalent to the method required by the legislature.

It has been found that the fact whether an SCR catalytic converter is used in the exhaust system can be determined without any problems by an evaluation of the temperature signals before and after the SCR catalytic converter. The physical size here is the heat capacity of the catalyst support itself. Furthermore, it can be determined via the temperature sensors whether the SCR catalyst has been overheated. If this is not the case, the SCR catalyst has been proven to have an effect over the life of a vehicle. Thus, it is tamper-resistant to continue to determine whether the correct amount of the reducing agent has been supplied and whether the reducing agent the required quality, in particular according to DIN 70070 , in order to meet the legislator's requirements for the reduction of NOx emissions equivalent.

Preferably, in the method for controlling the metering and introducing a reducing agent, the detected measured values and control states are stored permanently in order to make them permanently and verifiably available for checking and monitoring the operation.

Preferably, the measured values recorded are checked for plausibility, the errors being displayed and stored when error limits are exceeded.

It is proposed to combine the urea quality sensor directly with a sensor for the flow of urea, preferably in a housing. As a result, it can be perfectly detected that the urea sucked in by the metering is also that which was measured by the quality sensor. With Quality sensor is meant that sensor of the sensor arrangement, by means of which at least one substance property of the reducing agent is monitored. Mass flow sensors, temperature sensors or pressure sensors can be used to record the flow. It is not necessary to detect the mass flow at the sensor itself very accurately. It is only necessary to detect that urea was sucked from the dosage when the dosage has received a corresponding signal from the electronics. This combination of quality and flow sensor, ie the entire sensor arrangement which is provided according to the invention, can be used in the suction or pressure line, ie before or after the metering.

The application of the system and the method is not limited to vehicles, in particular commercial vehicles, construction machines and the like, but rather is also used in other furnaces, waste incineration plants, gas turbines, industrial plants and stationary engines. The application in commercial vehicles, however, is a particularly preferred application of the system, since this particular can be designed very compact by the integration of all required system components.

An embodiment of the system according to the invention is in 1 and will be explained in more detail below. It shows:

1 a diagram of a system according to the invention for the selective catalytic reduction of nitrogen oxides in the exhaust gas of an internal combustion engine.

The exhaust gases of the internal combustion engine 1 be using the SCR catalyst 2 treated. This is done in the SCR catalyst 2 NOx by means of the nozzle 8th in the exhaust stream injected reducing agent in the form of a urea solution according to DIN 70070 reduced.

The reducing agent injected into the exhaust stream becomes the urea water solution tank 3 via a conveyor line 4 taken. In the promotion line 4 is a sensor arrangement 5 integrated. The sensor arrangement can also be arranged in the tank itself. The sensor arrangement 5 in the promotion line 4 on the one hand has a quality sensor and also a flow sensor. By means of the quality sensor, a substance property of the extracted urea water solution is detected and monitored. By means of the flow sensor, the delivered volume flow of the urea water solution is monitored.

Furthermore, the system has an electronics 7 , by means of which, taking into account currently measured values, the dosage 6 the system is controlled and by means of which the dosing and dosing through the nozzle 8th in the exhaust stream of the engine 1 discharged urea water solution is controlled. This dosage 6 has a pump, by means of which the urea solution from the tank 3 promoted and dosed.

In the flow direction of the exhaust gas before the SCR catalyst 2 is arranged a first temperature sensor 9 , In the flow direction behind the SCR catalyst 2 is arranged a second temperature sensor 10 , By means of temperature sensors 9 and 10 The temperatures are before and after the SCR catalyst 2 measured and the electronics 7 forwarded for evaluation. By evaluating the temperature signals of the sensor 9 before and of the sensor 10 after the SCR catalyst 2 can be determined if the SCR catalyst 2 used in the exhaust system and works properly. Furthermore, by means of the temperature sensors 9 . 10 monitors whether the SCR catalyst 2 was overheated during operation.

The Electronic 7 has a permanent memory which can be read and in which any error messages of the system or limit value exceed the sensor arrangement 5 or the temperature sensors 9 . 10 be stored permanently readable. When the SCR catalyst 2 at no time during engine operation 1 has been overheated, it is guaranteed that the SCR catalyst 2 its effect over the entire life of the vehicle and thus also of the internal combustion engine 1 fulfilled and works reliably.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• DIN 70070 [0003]
• DIN 70070 [0004]
• DIN 70070 [0009]
• DIN 70070 [0037]
• DIN 70070 [0044]

Claims (15)

System for the selective catalytic reduction of nitrogen oxides in the exhaust gas of internal combustion engines ( 1 ) or the like by means of an SCR catalyst ( 2 ), wherein an introduction of a dissolved reducing agent, in particular a urea solution, into the exhaust gas stream by means of a metering ( 6 ), the system having one with a reducing agent tank ( 3 ) connectable or linked delivery line ( 4 ), characterized in that the system comprises a sensor arrangement ( 5 ), by means of which the volume and / or mass flow and at least one substance property of the conveyed reducing agent, in particular the urea solution, can be detected or detected. System according to claim 1, characterized in that the sensor arrangement ( 5 ) has a flow sensor, in particular that the system further comprises means for calculating the mass flow and / or the volume flow of the subsidized reducing agent, in particular the urea solution. System according to claim 1 or 2, characterized in that the sensor arrangement ( 5 ) has a sensor for measuring the electrical conductivity of the promoted reducing agent, in particular the urea solution. System according to one of the preceding claims, characterized in that the sensor arrangement ( 5 ) has a sensor for measuring the speed of sound in the promoted reducing agent, in particular the urea solution. System according to one of the preceding claims, characterized in that the sensor arrangement ( 5 ) in the support line ( 4 ) is integrated. System according to one of the preceding claims, characterized in that in front of and behind the catalyst ( 2 ) at least one temperature sensor ( 9 . 10 ) is arranged. System according to one of the preceding claims, characterized in that it comprises means for calculating the exhaust gas mass flow and / or at least one sensor for measuring the exhaust gas mass flow and / or a sensor for measuring the exhaust gas temperature. System according to one of the preceding claims, characterized in that the reducing agent in the exhaust gas influences the temperature signal of a temperature sensor. System according to one of the preceding claims, characterized in that it is a control unit ( 7 ), by means of which the control of the dosage ( 6 ) of the reducing agent, in particular of the volumetric flow and / or the duration of the dosing, is controllable or controlled as a function of the detected measured values, in particular as a function of at least one substance property of the reducing agent and / or as a function of the exhaust gas temperature and / or as a function of the exhaust gas mass flow and / or depending on the temperatures in front of and behind the SCR catalyst ( 2 ). System according to one of the preceding claims, characterized in that it comprises a memory for the permanent storage of the detected measured values and / or control states of the dosage ( 6 ) having. System according to one of the preceding claims, characterized in that the system comprises a reducing agent tank ( 3 ), in particular a urea solution tank, and / or a urea filter and / or a pump for conveying the reducing agent, in particular the urea solution. System according to one of the preceding claims, characterized in that it has at least one nozzle ( 8th ), in particular a two-fluid nozzle, by means of which the reducing agent, in particular the urea solution, injected into the exhaust stream and / or atomized in the exhaust stream, and / or that the metering system has an integrated compressed air supply, in particular a compressor, and / or with an external Compressed air supply can be coupled, so that the atomization and injection of the reducing agent, in particular the urea solution, by means of compressed air. Method for controlling the metering and introduction of a reducing agent, in particular urea solution, into the exhaust gas flow of an internal combustion engine ( 1 ) or the like for the selective catalytic reduction of nitrogen oxides in the exhaust gas by means of an SCR catalyst ( 2 ), characterized in that at least one material property, in particular the electrical conductivity and / or the speed of sound, of the delivered reducing agent, in particular urea solution, is detected, and wherein at least the temperatures upstream and downstream of the SCR catalyst ( 2 ), wherein the metering of the reducing agent, in particular the control of the volume flow and / or the duration of the metering, depending on at least one detected material property of the reducing agent and depending on the upstream and downstream of the SCR catalyst ( 2 ) measured temperatures of the exhaust gas takes place. A method according to claim 13, characterized in that the detected measured values and control states are stored permanently. A method according to claim 13 or 14, characterized in that the detected measured values are checked for plausibility and the errors are displayed and stored when exceeding error limits.

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