DE102019004384A1 - Device and method for cleaning exhaust gases - Google Patents

Abstract

The invention relates to a device for cleaning exhaust gases of an internal combustion engine (1) with an exhaust pipe (2) and at least one exhaust gas cleaning device (3) in the exhaust pipe (2). The device according to the invention is characterized in that a cooling device for the exhaust gas is arranged upstream of the at least one exhaust gas purification device (3) in the flow direction of the exhaust gas.

Description

The invention relates to a device for cleaning exhaust gases from an internal combustion engine according to the type defined in more detail in the preamble of claim 1. In addition, the invention relates to a method for cleaning exhaust gases from an internal combustion engine according to the type defined in more detail in the preamble of claim 7.

The cleaning of exhaust gases from internal combustion engines is so far known from the prior art. Typically, exhaust gas purification devices are used in the exhaust gas lines or exhaust gas lines of the internal combustion engines in order to subsequently oxidize or otherwise convert undesired substances, so as to reduce harmful emissions to the environment. A typical example of such an exhaust gas purification device, without restricting it in the sense of the invention, would be, for example, a so-called SCR catalytic converter, ie a catalytic converter for selective catalytic reduction. Such catalysts can be used, for example, to reduce nitrogen oxide in the exhaust gases by adding urea. Another example would be a particle filter, in particular a diesel particle filter, which filters out predominant soot particles and is “burned free” from time to time.

Frequently, in addition to the exhaust gas cleaning device, burners are arranged in the exhaust systems in order to regenerate the exhaust gas cleaning device or to heat it up to a certain temperature or to keep it at a certain temperature level. In this context, the DE 10 2008 032 600 A1 are pointed out, in which a burner is provided, which comprises its own fresh gas supply for the combustion. The DE 10 2016 014 254 A1 describes keeping a catalytic converter warm via an electrically heated air flow in a hybrid vehicle if not enough exhaust gas with a correspondingly high temperature arrives at the exhaust gas cleaning device.

It is also known from the general prior art that exhaust gas purification devices, in particular catalysts for selective catalytic reduction, only work ideally in certain temperature windows. For example, with an SCR catalytic converter, a temperature window with temperatures of up to 450 ° C is ideal, because then an optimal conversion of the nitrogen oxide takes place. If the exhaust gas temperature becomes higher with a higher load and rises to 600 ° C, for example, the rates of the reacted substances decrease to approx. 60%, in each case based on the temperature upstream of the SCR catalytic converter.

The object of the present invention is to provide an improved device and an improved method for cleaning exhaust gases from an internal combustion engine.

According to the invention, this object is achieved by a device with the features in claim 1 and a method with the features in claim 7. Advantageous refinements and developments of the device result from the dependent claims 2 to 6, with respect to the method from the dependent claims 8 to 10.

The device according to the invention for cleaning exhaust gases of an internal combustion engine with an exhaust pipe and at least one exhaust gas cleaning device in the exhaust pipe provides, according to the invention, that a cooling device for the exhaust gas is arranged upstream of the at least one exhaust gas cleaning device in the flow direction of the exhaust gas. This makes it possible to cool the exhaust gas accordingly if it has been heated up due to a relatively high engine output of the internal combustion engine at temperatures above a predetermined temperature limit, which in the example of the SCR catalytic converter is approximately 450 ° C. The exhaust gas can then be cooled accordingly by the cooling device, so that the conversion rate in the exhaust gas cleaning device can also be significantly improved for this type of operation. An alternative application can be the cooling of the exhaust gas for a particle filter, in particular a diesel particle filter. It is the case that one is regenerated from time to time. Accumulated particles are burned off in a controlled manner. At exhaust gas temperatures of more than 600 ° C and almost full particle filter, however, uncontrolled soot burn-off can also occur, which can also lead to component damage. This can also be avoided via the cooling device according to the invention.

According to a very advantageous development of the device according to the invention, the cooling device is switchable in terms of its cooling capacity. The cooling device, which can be, for example, a heat exchanger or, in particular, a device for supplying fresh gas into the exhaust gas stream, is designed to be switchable in order to provide the required cooling capacity and the temperature, for example at an exhaust gas temperature of 550 ° C. in front of an SCR catalytic converter, as an exhaust gas cleaning device, to be reduced to approx. 400 to 450 ° C. On the one hand, a further reduction is not necessary, and a very strong reduction, for example to less than 250 ° C., would also adversely affect sales. For a particle filter, the exemplary temperatures would be higher, for example at 700 ° C and with a reduction to approx. 580 ° C due to the cooling. As already mentioned, the cooling device can be designed, for example, as a heat exchanger or the like. According to In a very advantageous development of the idea, the cooling device is designed in particular as a device for supplying fresh gas. Such a device for supplying fresh gas thus supplies fresh gas, which is therefore not exhaust gas from the internal combustion engine. This fresh gas then cools the exhaust gas accordingly. According to a very advantageous development, the device for supplying fresh gas can be implemented as a fresh gas pump, for example as a passive or active electrically controlled fresh gas pump, and / or can comprise a switchable bypass of compressed air around the internal combustion engine. Pre-compressed air, which is compressed, for example, via a turbocharger, can thus get into the exhaust gas flow around the internal combustion engine in the bypass, for example via an inversely used high-pressure exhaust gas recirculation, in order to reduce the temperature of the exhaust gas accordingly and to cool it accordingly before it flows into the exhaust gas cleaning device ,

A very advantageous further development of the idea also provides that an existing burner, which is designed, for example, as a flame burner or catalytic burner and serves to regenerate components of the exhaust gas cleaning device, can be used as a device for supplying fresh gas. Instead of the pure supply of the freely controllable fresh gas flow to the burner during the combustion, this is used in non-burning operation as a device for supplying fresh gas, in order to supply a regulated amount of fresh gas in order to achieve the desired temperature of the exhaust gas via the regulation which is already present for the burner in the area in front of the exhaust gas purification device and thus ultimately in the exhaust gas purification device itself.

The method according to the invention for cleaning exhaust gases of an internal combustion engine with an exhaust gas cleaning device arranged in the exhaust gas stream downstream of the internal combustion engine accordingly provides that the exhaust gases flowing to the exhaust gas cleaning device are cooled in the flow direction upstream of the exhaust gas cleaning device, specifically if their temperature exceeds a predetermined temperature limit. The cooling is therefore temperature-controlled, in particular by using measured temperatures, preferably directly in front of the exhaust gas cleaning device, to influence the cooling, be it cooling in a heat exchanger or cooling by supplying fresh gas, in order to ensure the desired temperatures ,

According to a very advantageous development of the method according to the invention, it is provided that the temperature limit for a catalyst for selective catalytic reduction is set by the catalyst at approximately 450 ° C. This temperature limit ensures that the catalytic converter achieves an optimal conversion rate for exhaust gases just below this temperature limit. In the case of a particle filter, the temperature limit would be around 600 ° C in order to prevent uncontrolled burn-up, especially when the particle filter is almost full.

As already mentioned in the construction according to the device, the active cooling can take place by supplying fresh gas, which is preferably temperature-controlled. The fresh gas can be supplied by the internal combustion engine itself or in the bypass around it. An alternative would be an active or passive fresh gas pump, which is arranged in the flow direction between the internal combustion engine and the exhaust gas cleaning device and supplies the fresh gas there accordingly. An active fresh gas pump could be an electric pump, for example, which doses the fresh gas into the exhaust gas directly or via a burner that is not operated, specifically by means of a corresponding temperature control, in order to supply a corresponding amount of fresh gas depending on the measured temperature. An alternative could also be a passive fresh gas pump, which draws in fresh gas automatically, for example, by narrowing the exhaust line in the manner of a Venturi tube. In order to regulate the amount of fresh gas accordingly, a valve device or the like that is controllable with respect to its cross-section would be necessary in order to be able to regulate the fresh gas supply accordingly and to be able to set the desired temperature upstream of the exhaust gas cleaning device.

Further advantageous refinements of the device according to the invention and of the method according to the invention also result from the remaining dependent subclaims and are clear from the exemplary embodiments which are described in more detail below with reference to the figures.

• 1 eine schematische Darstellung eines Verbrennungsmotors mit Zuluftseite und Abgasseite mit der erfindungsgemäßen Vorrichtung in einer denkbaren Ausführungsform;
• 2 eine schematische Darstellung einer passiven Frischgaspumpe; und
• 3 eine Darstellung einer weiteren Ausführungsform der erfindungsgemäßen Vorrichtung.

Show:

• 1 a schematic representation of an internal combustion engine with supply air and exhaust side with the device according to the invention in a conceivable embodiment;
• 2 a schematic representation of a passive fresh gas pump; and
• 3 a representation of a further embodiment of the device according to the invention.

In the representation of the 1 is a schematically indicated internal combustion engine 1 to recognize how he, for example, to complete or partial drive of a vehicle, for example a rail-less or rail-bound land vehicle or an aircraft or water vehicle. From the internal combustion engine 1 leads an exhaust pipe 2 the exhaust gas of the internal combustion engine 1 to an exhaust gas cleaning device 3 and from there to the surrounding area. In the exhaust pipe 2 is also purely exemplary and optionally an exhaust gas turbine 4 arranged. This stands with a compressor 5 via a shaft in connection as well as with an optionally indicated electric motor 6 , This makes it possible to use the turbine to generate electrical energy 4 , with generator operation of the electric motor 6 to recover and / or via the turbine 4 Energy to drive the compressor 5 provide. It can also use the engine 6 additional energy to drive the compressor 5 be provided if this is necessary and a corresponding electrical energy storage device in the vehicle for the electrical supply of the electric motor 6 is available. About the compressor 5 , which is also only one conceivable option on the supply air side, supply air is conveyed and via a fresh gas line 7 to the internal combustion engine 1 promoted. The intake air, which is also called fresh gas, is then drawn into the internal combustion engine 1 appropriately implemented with a suitable fuel, for example gasoline or diesel, in order to generate the desired mechanical output. The exhaust gas from the combustion taking place in the internal combustion engine 1 then, as already mentioned, reaches the exhaust pipe 2 , the optional turbine 4 and the exhaust gas purification device 3 in the nearby areas.

As a first example, without restricting it, the exhaust gas purification device 3 a catalyst for selective catalytic reduction, which is also referred to as an SCR catalyst. Its optimal operating temperature is below a temperature limit of approx. 450 ° C. With a correspondingly high performance of the internal combustion engine 1 is the temperature of the exhaust gas even after relaxing in the optional turbine 4 are typically above this temperature of 450 ° C., for example in the order of 600 ° C. An SCR catalytic converter heated to 600 ° C. as an exhaust gas cleaning device 3 However, it has a much worse conversion rate than an SCR catalytic converter working below the temperature limit of 450 ° C. For this reason, it is provided that the temperature of the exhaust gas in the exhaust pipe 2 before reaching the exhaust gas cleaning device 3 is cooled accordingly. In principle, heat exchangers of any kind would be conceivable for this. However, cooling is preferably carried out by supplying fresh gas. This fresh gas can now be in various ways down to the area of the exhaust pipe 2 and in particular in the area of the exhaust gas purification device 3 be promoted. A first possible way is that more fresh gas than is actually necessary through the fresh gas line 7 the internal combustion engine 1 fed and passed through this. This cools the exhaust gas in the exhaust pipe 2 and ultimately the exhaust gas purification device 3 from. As an alternative to this implementation of the additional fresh gas for cooling the exhaust gas in the exhaust pipe 2 through the internal combustion engine 1 can bypass the internal combustion engine 1 be performed. The fresh gas flows through a bypass line 8th with a bypass valve 9 around the internal combustion engine 1 around directly from the fresh gas line 7 into the exhaust pipe 2 , In particular, an already existing exhaust gas recirculation, in particular the high-pressure exhaust gas recirculation, can be used for this in inverse operation.

Another in the representation of the 1 The option shown is the supply of fresh gas from the environment or, as shown here, from the fresh gas line 7 via a fresh gas pump 10 , The in the representation of the 1 indicated fresh gas pump 10 is as an electric fresh gas pump 10 executed. Via a control unit 11 it can be controlled accordingly, in order to increase the fresh gas rate and ultimately the fresh gas volume fed into the exhaust gas in the exhaust pipe 2 to control. This allows the temperature of the exhaust gas in the flow direction in front of the exhaust gas cleaning device 3 to adjust. The control is now in particular temperature-controlled by the temperature of the exhaust gas or the mixture of exhaust gas and fresh gas via a temperature sensor 12 in the flow direction in front of the exhaust gas cleaning device 3 is recorded accordingly. Via the control unit 11 can then the fresh gas pump 10 are controlled so that the amount of fresh gas is supplied which is required to keep the temperature of the exhaust gas below the predetermined temperature limit of, for example, 450 ° C. for the SCR catalytic converter as an exhaust gas cleaning device 3 to lower. The control unit 11 can also the valve device 9 Activate accordingly in the bypass line in order to use this type to determine the amount of fresh gas that the exhaust line 2 reached, adjust accordingly. Another control option relates to the optional electric motor 6 , which can also be controlled so that the compressor 5 , if it is available, the correspondingly larger amount of fresh gas than for combustion in the internal combustion engine 1 is necessary.

In addition to the options described, it is now also conceivable that the fresh gas pump as a passive fresh gas pump 13 is trained. Such a passive fresh gas pump 13 instead of in 1 Fresh gas pump described 10 is in the representation of the 2 indicated in principle. You can, for example, from a narrowing of the Cross section of the exhaust pipe 2 be constructed. This narrowing of the cross-section is shown in the 2 designated with 14. This is due to this narrowing of the cross-section 14 flowing exhaust gas in the exhaust pipe 2 will increase its speed and create a vacuum, according to the well-known Venturi effect. Via a supply line 15 with a valve device 16 , which is also from the control unit 11 can be controlled, then the cross section of the supply line 15 control accordingly so that a suitable amount of air is sucked in so that it is in the area of the temperature sensor 12 which indirectly controls the cross-section, sets the desired temperature.

Another possibility for supplying fresh gas for cooling the exhaust gas is in 3 indicated. 3 shows a conventional burner known per se 17 in the exhaust pipe 2 in the flow direction in front of the exhaust gas cleaning device 3 , That burner 17 is, for example, a fresh gas pump 10 Fresh gas independent of the internal combustion engine 1 supplied in order to be able to control the burner accordingly and to be able to operate it with the desired lambda value. In addition to that via the fresh gas pump 10 Fresh gas supplied is also fed to the burner via a line denoted by 18. In certain situations, for example for the regeneration of catalysts and / or to burn off particle filters, such a burner 17 used. Is such a burner 17 then this can be in a situation where there is no fuel on the line 18 is fed to the burner 17 So does not burn, can be used to supply fresh gas via the fresh gas pump that is already available for the burner and thus again temperature-controlled, as shown in the illustration of the 1 was already explained to lower the temperature of the mixture of exhaust gas and fresh gas supplied below the predetermined temperature limit.

As another example, also without restricting it, the exhaust gas purification device 3 a particle filter, in particular a diesel particle filter. The structure can also be realized here as shown in the figures. If such a diesel particle filter is full, it is burned in a controlled manner according to the prior art by changing the combustion process. Controlled means that the temperatures in front of the diesel particulate filter are controlled in order to keep the soot burn-up under control. With a full diesel particle filter, for example, it is cleaned with lower exhaust gas temperatures of approx. 550-600 ° C. The emptier the diesel particulate filter, the higher the inlet temperature, e.g. 600-700 ° C, the exhaust gas temperature is regulated in order to clean the diesel particulate filter faster. If you were to go into the diesel particulate filter with a full diesel particulate filter with exhaust gas temperatures too high of more than 600 ° C, uncontrolled soot burn-off could occur through various chain reactions, which could also lead to component damage. In order to avoid this, a regeneration combustion process in the internal combustion engine is specifically used for the regeneration of the diesel particle filter 1 controlled to allow the soot to burn off in a controlled manner.

However, in engine operation at full load and in areas close to the full load, the exhaust gas can develop temperatures> 600 ° C upstream of the diesel particulate filter. Without a regeneration is desired and therefore without a regeneration combustion process in the internal combustion engine 1 is controlled, the soot in the diesel particulate filter can ignite in an uncontrolled manner.

The above as part of the SCR catalytic converter as an exhaust gas purification device 3 Cooling of the exhaust gas described can now for the particle filter as an exhaust gas purification device 3 be used to advantage. This allows the temperatures upstream of the exhaust gas cleaning device 3 to cool down here as the diesel particulate filter to less than 600 ° C, so that there is no risk of uncontrolled soot burn-off and the resulting unwanted exotherm in the diesel particulate filter. This ensures that the diesel particulate filter is only regenerated if the regeneration combustion process in the internal combustion engine is targeted 1 is controlled.

Furthermore, one can imagine that the regulated supply of cold fresh gas regulates the exhaust gas temperatures upstream of the diesel particle filter to temperatures that correspond to the exhaust gas temperatures during a specific regeneration of the diesel particle filter. Thus, one could use the already existing “high” exhaust gas temperatures in order to clean the diesel particle filter in a controlled and temperature-controlled manner, even outside of the conditions in which the regeneration combustion process is active.

All in all, this results in a very simple and efficiently functioning structure, with a high cleaning rate via the safe operation of the exhaust gas cleaning device 3 can also be achieved when the temperatures of the exhaust gases from the internal combustion engine 1 would actually be too high for this. This can significantly reduce undesirably high emissions in high-performance driving conditions of the vehicle. The design effort can be kept small, since in some of the exemplary embodiments it is possible to rely on components which are present anyway and which are only provided by a new type of temperature control for the purpose of the invention Device or the inventive method must be used or controlled.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• DE 102008032600 A1 [0003]
• DE 102016014254 A1 [0003]

Claims (10)

Device for cleaning exhaust gases of an internal combustion engine (1) with an exhaust gas line (2) and at least one exhaust gas cleaning device (3) in the exhaust gas line (2), characterized in that in the flow direction of the exhaust gas in front of the at least one exhaust gas cleaning device (3) a cooling device for the Exhaust gas is arranged. Device after Claim 1 , characterized in that the cooling device is designed to be switchable with regard to its cooling capacity. Device after Claim 1 or 2 , characterized in that the cooling device is designed as a device for supplying fresh gas. Device after Claim 3 , characterized in that the device for supplying fresh gas comprises a fresh gas pump (10, 13) and / or a switchable bypass (8) of compressed air around the internal combustion engine (1). Device after Claim 3 , characterized in that an existing burner (17) with freely controllable fresh gas supply in non-burning operation serves as the device for supplying fresh gas. Device according to one of the Claims 1 to 5 , characterized in that the exhaust gas purification device (3) comprises at least one catalytic converter for selective catalytic reduction (SCR) and / or a particle filter. Method for cleaning exhaust gases of an internal combustion engine (1) with an exhaust gas cleaning device (3) arranged in the exhaust gas stream after the internal combustion engine (1), characterized in that the exhaust gases flowing to the exhaust gas cleaning device (3) are cooled in the flow direction in front of the exhaust gas cleaning device (3) if their temperature exceeds a predetermined temperature limit. Procedure according to Claim 7 , characterized in that the temperature limit for a catalytic converter for selective catalytic reduction (SCR) is set at approx. 450 ° C and / or for a particle filter at approx. 600 ° C in front of the exhaust gas cleaning device (3). Procedure according to Claim 7 or 8th , characterized in that the cooling takes place as active cooling by a temperature-controlled supply of fresh gas by the internal combustion engine (1) or in a bypass (8) around the internal combustion engine (1): Procedure according to Claim 7 or 8th , characterized in that the cooling takes place by an active temperature-controlled supply of fresh gas via an active or passive fresh gas pump (10, 13) in the flow direction between the internal combustion engine (1) and the exhaust gas cleaning device (3).

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