Method for pretreating a particulate filter, particulate filter and engine arrangement

Abstract

Method for pretreating a particulate filter to be arranged in an exhaust stream of an internal combustion engine, comprising: - Applying a hydrocarbon-containing composition to a surface of the particle filter, wherein the hydrocarbon-containing composition is a synthetic resin, and - Formation of soot on the surface of the particle filter through incomplete oxidation of the hydrocarbon-containing composition.

Description

[0001] The present invention relates to a method for pretreating a particulate filter, a particulate filter and an engine arrangement with such a particulate filter.

[0002] Particulate filters are increasingly used in the exhaust systems of both diesel and gasoline engines to filter out particulate pollutants, especially soot particles, from the exhaust stream and thus reduce their emissions into the environment. At certain intervals, the particulate filter requires regeneration, during which the filtered particles are burned off at an increased temperature. However, this combustion is not residue-free, so ash deposits accumulate on the particulate filter surface over time.

[0003] US Regulation 2015 / 0000254 A1 describes how particulate filters with a certain soot load prevent hydrocarbon emissions during a cold engine start more effectively than unloaded particulate filters. Therefore, it is proposed to ensure a certain minimum soot load in the particulate filter to increase filter efficiency. This can be achieved by controlling particulate filter regeneration, ensuring that not all soot particles are burned during regeneration, but rather that a certain minimum load remains in the particulate filter.

[0004] However, with this method, the minimum soot load can only be achieved after a certain period of engine operation, since soot particles are only formed during engine operation. During initial engine start-up, the filter efficiency remains lower. Furthermore, the soot load creates strong exhaust back pressure, leading to increased fuel consumption and also increasing the likelihood of knocking in gasoline engines when operating under high load.

[0005] DE 10 2009 049 624 A1 discloses a process in which a new particulate filter undergoes a conditioning step in which a particle-containing gas is passed through the particulate filter. The particles can be composed of solids of one or more of the elements C, H, Al, Si, Ti, Fe, Cu, Pt, Pd, Ce, S, O, N, P, Zn, Ca, Na, Li, Ba, Cl, Rh, F. The conditioning step is carried out in such a way that the particle separation efficiency of the particulate filter is increased compared to the new condition.

[0006] DE 10 2016 103 735 A1 describes a process in which a layer of ash is applied as a filter cake to the surface of the channel wall of a new particulate filter to prevent deep filtration. Ca, Mg, P, and Zn can be used as ash formers.

[0007] Further prior art is disclosed in the documents US 2010 / 0 266 461 A1 and US 8 889 221 B2, which relate to the coating of a particle filter.

[0008] The object of the present invention is therefore to provide a means by which sufficient filter performance can be achieved even during the initial start-up of an engine. Furthermore, it would be desirable to reduce the build-up of exhaust back pressure and largely avoid the associated disadvantages.

[0009] This problem is solved by the subject matter of the independent claims. The dependent claims contain embodiments of these inventive solutions.

[0010] The invention is based on the inventors' finding that, particularly but not exclusively, when particulate filters are used in the exhaust system of gasoline engines, the filter efficiency—that is, the ratio of filtered-out particles to the total number of particles of a certain size present—increases significantly after a certain initial operating period (run-in phase), which, for example, corresponds to an approximate mileage of 3,000 km in gasoline engines. This is due to the formation of a soot layer or filter cake on the surface of the particulate filter, which is formed from the soot particles contained in the exhaust stream.

[0011] To ensure adequate filtering of particulate pollutants during initial operation of an engine with a particulate filter, a new particulate filter should currently have a very small pore size due to the lack of a soot layer at that time. However, this becomes disadvantageous after a certain period of operation, as the combination of small pore size and the developing soot layer further increases exhaust backpressure, exacerbating the associated adverse effects mentioned above.

[0012] Later on, i.e. after the break-in period, the pore size could be chosen to be significantly larger without significantly reducing the filter efficiency, since the layer containing soot and / or ash that has formed now also contributes to the filtration.

[0013] The basic idea of ​​the invention is therefore to manufacture and use a particle filter whose porosity is adapted to the conditions after the break-in period.

[0014] However, to ensure sufficient filter efficiency even during the break-in period, it is proposed to coat the surface of the unused particulate filter with a hydrocarbon-based composition, from which soot is subsequently formed through incomplete oxidation. For this purpose, the hydrocarbon-based composition can, for example, be incompletely combusted during the initial operation of the combustion engine. The soot formed contributes to the filtration process, thus increasing the filter efficiency.

[0015] A method according to the invention for pretreating a particulate filter comprises applying a hydrocarbon-containing composition to a surface of the particulate filter and subsequently forming soot on the surface of the particulate filter by incomplete oxidation of the hydrocarbon-containing composition. The incomplete oxidation refers to the carbon of the hydrocarbon-containing composition, i.e., the carbon of the hydrocarbon-containing composition is (partially) oxidized. The formation of soot on the surface of the particulate filter leads to soot loading of the particulate filter.

[0016] The particulate filter can be, for example, a wall-flow filter or a bypass filter. The particulate filter can have filter walls made of various porous materials, such as ceramics or metals, and is usually housed in a casing. The particulate filter can be equipped with a catalytic coating, such as a coating for selective catalytic reduction, for the oxidation of carbon monoxide and / or hydrocarbons, or for a three-way catalyst. The particulate filter can be used, for example, for the aftertreatment of exhaust gases from an internal combustion engine.

[0017] The particulate filter surface is defined as the area that comes into contact with the exhaust gas flow during the operation of the particulate filter in the exhaust system. This includes internal surfaces, such as the surface of the particulate filter's pores. Preferably, soot can form on a surface, i.e., at least on a portion of the total surface area.

[0018] Soot is understood to mean a composition that arises, for example, from incomplete oxidation, especially incomplete combustion, of the hydrocarbon-containing composition. Soot can, for example, contain carbon in a proportion between 80 and 99.5 wt.% and, in addition, sulfates, condensed hydrocarbons, and / or ash.

[0019] The formation of soot allows the use of a particulate filter with a larger pore size, resulting in low exhaust backpressure. This backpressure increases only minimally, if at all, over the course of the filter's service life, and is certainly lower than with a particulate filter with a smaller pore size. This, in turn, reduces fuel consumption and the tendency for engine knocking.

[0020] The soot formed increases the filter efficiency, so that a sufficient filtration effect is achieved even during the running-in phase of the combustion engine.

[0021] The method according to the invention is used for pretreating the particulate filter; that is, an unused particulate filter is treated, which has not yet been used as intended, i.e., for filtering out particulate components from an exhaust gas stream. In other words, the particulate filter is only used as intended after the hydrocarbon-containing composition has been applied.

[0022] For example, the hydrocarbon-containing composition can be applied to the exhaust system of an internal combustion engine before the particulate filter is used for the first time to filter out particles from the exhaust stream flowing in the exhaust system. Soot formation can also occur before or simultaneously with the start of intended use.

[0023] According to various design variants, incomplete oxidation, e.g., incomplete combustion, can occur after positioning the particulate filter in the exhaust system of an internal combustion engine.

[0024] This allows incomplete oxidation to be advantageously carried out using the exhaust system's equipment. For example, an oxidizing gas can be supplied to the particulate filter via the exhaust system, and gaseous reaction products can be removed via the exhaust system. Optionally, the hydrocarbon-containing composition can also be applied to a surface of the particulate filter after the particulate filter has been positioned in the exhaust system.

[0025] According to various embodiments, the hydrocarbon-containing composition can be incompletely oxidized by supplying an oxygen-containing gas stream. This results in the conversion of the hydrocarbon-containing composition to carbon and water, and possibly to by-products such as hydrocarbons and / or carbon monoxide.

[0026] For example, an oxygen-rich exhaust stream from an internal combustion engine can be supplied as an oxygen-rich gas stream. For this purpose, the combustion air-fuel ratio of the internal combustion engine can be adjusted so that there is a slight excess of oxygen, which is used for the incomplete oxidation of the hydrocarbon-containing compound. The amount of oxygen supplied must be adjusted so that the oxidation is incomplete, otherwise the carbon in the hydrocarbon-containing compound will be converted into carbon dioxide instead of soot.

[0027] For example, in a stoichiometrically or substoichiometrically operated internal combustion engine with an air / fuel ratio of λ ≤ 1, oxygen can be drawn through the exhaust system during overrun phases, which can be used for incomplete oxidation of the hydrocarbon-containing composition. Complete oxidation can be prevented by the enormous heat dissipation in the particulate filter. Furthermore, the oxygen supply during overrun can be limited so that only incomplete oxidation occurs.

[0028] In addition, it is possible, as part of a break-in calibration, to operate the combustion engine lean during an initial operation, e.g. during the first kilometers, i.e. with a combustion air ratio λ > 1, so that the incomplete oxidation of the hydrocarbon-containing composition is enabled or facilitated.

[0029] Advantageously, the incomplete oxidation can therefore be carried out when the particulate filter of the internal combustion engine is put into operation by feeding the exhaust gas flow of the internal combustion engine to the particulate filter previously provided with the hydrocarbon-containing composition.

[0030] According to further design variants, the hydrocarbon-containing composition can be applied before the particulate filter is positioned in the exhaust system of the combustion engine. This allows for greater flexibility in applying the hydrocarbon-containing composition. It can be applied, for example, during the manufacturing of the particulate filter or when it is housed in a casing.

[0031] According to various embodiments, the method can further include determining an optimal pore size and / or pore size distribution for the particulate filter for a point in time after the completion of a break-in phase of an internal combustion engine in whose exhaust stream the particulate filter is to be arranged, wherein the soot formation takes place in such a way that the soot-laden particulate filter has the optimal pore size and / or pore size distribution.

[0032] In other words, the first step is to determine, for example, through simulations known to those skilled in the art or corresponding tests with an identical particulate filter, which pore size and / or pore size distribution is most favorable for the specific particulate filter after the run-in phase, i.e., at which pore size and / or pore size distribution the filter efficiency is as high as possible without causing the exhaust backpressure to increase excessively. The tolerable exhaust backpressure depends heavily on the engine design, e.g., the number of cylinders, the combustion process used, etc.

[0033] Based on this optimal pore size and / or pore size distribution, the formation of soot on the particle filter surface is carried out in such a way that this optimal pore size and / or pore size distribution is already present before the first intended use, or before further intended use if the soot formation occurs simultaneously with the start of intended use. In other words, the pores of the particle filter are reduced in size by the formation of soot until the optimal pore size and / or pore size distribution is achieved. Depending on requirements, the amount of soot to be formed, the particle size of the soot, and / or the particle size distribution of the soot can be varied.

[0034] This ensures an optimal pore size and / or pore size distribution already during the running-in phase of the combustion engine, so that particulate pollutants can be effectively removed from the exhaust gas stream during this phase.

[0035] According to further design variations, hydrocarbon-containing compositions such as organic compounds that can be easily applied in thin layers can be used. One possible example is synthetic resins, which, in the form of dispersions such as those used for priming porous surfaces like masonry before painting, can be applied to the surface of the particle filter. Water, for example, can be used as a dispersing agent, resulting in an aqueous synthetic resin dispersion.

[0036] Such synthetic resin dispersions contain finely dispersed synthetic resin particles that, after removal of the dispersant, e.g., by drying, are deposited as a layer on the surface of the particle filter. The porosity of this layer can be adjusted by modifying the properties of the dispersion, e.g., solids content, particle size, and particle size distribution. The deposited synthetic resin particles are then at least partially converted into carbon black by incomplete oxidation. Synthetic resins are defined as resins produced synthetically by polymerization, polyaddition, or polycondensation reactions, e.g., alkyd or acrylic resins.

[0037] According to further embodiments, the particulate filter can be a diesel particulate filter or a gasoline particulate filter, e.g., a particulate filter for internal combustion engines powered by gasoline. Since the particulate emissions of gasoline engines are significantly lower compared to diesel engines, it takes considerably longer to build up a filter cake sufficient for adequate filtration. Therefore, the method according to the invention leads to a significant improvement in filter performance from the outset, particularly for gasoline particulate filters.

[0038] A particle filter according to the invention has a surface that at least partially has a hydrocarbon-containing composition.

[0039] The hydrocarbon-containing composition can be incompletely oxidized, for example, through incomplete combustion, forming soot. The resulting soot layer contributes to the filtration effect of the particulate filter and can increase its efficiency. Therefore, a larger pore size can be selected for the particulate filter, thus reducing exhaust backpressure and saving fuel.

[0040] The production of this particulate filter can be carried out, for example, as described above in the inventive method, by applying a hydrocarbon-containing composition to a surface of the particulate filter. Therefore, the above explanations of the inventive method also serve to describe the inventive particulate filter. The advantages of the inventive particulate filter correspond to those of the inventive method and its corresponding embodiments.

[0041] The particle filter according to the invention can, for example, be arranged in the exhaust stream of an internal combustion engine and be used for the aftertreatment of an exhaust stream generated by the internal combustion engine, i.e., for filtering out particulate components of the exhaust stream.

[0042] The hydrocarbon-containing composition on the surface of the particulate filter is designed and arranged in such a way that, after incomplete oxidation of the hydrocarbon-containing composition, the particulate filter has an optimal pore size and / or pore size distribution for a point in time after the completion of a break-in phase of an internal combustion engine in whose exhaust stream the particulate filter is to be arranged.

[0043] In other words, the first step is to determine, for example, through simulations known to those skilled in the art or corresponding tests with an identical particulate filter, which pore size and / or pore size distribution is most favorable for the specific particulate filter after the run-in phase, i.e., at which pore size and / or pore size distribution the filter efficiency is as high as possible without causing the exhaust backpressure to increase excessively. The tolerable exhaust backpressure depends heavily on the engine design, e.g., the number of cylinders, the combustion process used, etc.

[0044] Based on this optimal pore size and / or pore size distribution, the hydrocarbon-containing composition is designed and arranged on the particle filter surface in such a way that this optimal pore size and / or pore size distribution is achieved after incomplete oxidation of the hydrocarbon-containing composition. Depending on the requirements, the amount of the hydrocarbon-containing composition, its specific chemical composition, and the location on the particle filter surface where the hydrocarbon-containing composition is applied can be varied.

[0045] According to further design variants, the carbon-containing composition can be a synthetic resin.

[0046] According to further design variants, the particulate filter can be designed as a diesel particulate filter or a gasoline particulate filter.

[0047] An engine arrangement according to the invention comprises an internal combustion engine with an exhaust system for receiving an exhaust gas flow generated by the internal combustion engine, wherein a particulate filter is arranged in the exhaust system according to the preceding description.

[0048] The engine assembly can be located in a vehicle, where "vehicle" refers to any mobile means of transport, i.e., a land vehicle as well as a watercraft or aircraft, e.g., a passenger car. Since legal regulations regarding permissible emissions of air pollutants from vehicles with internal combustion engines are becoming increasingly stringent, i.e., the limit values ​​to be observed are being reduced, the invention is particularly advantageous in this area because, on the one hand, improved filtration of particulate components from the exhaust stream is enabled even during the break-in phase. On the other hand, the pore size and / or pore size distribution can be optimized for the situation after the break-in phase, thus minimizing problems caused by excessive exhaust back pressure, such as increased fuel consumption.

[0049] The invention is explained in more detail below with reference to the illustrations and the accompanying description. The illustrations show: Fig. 1. Exemplary pore size distributions of commercially available filters; Fig. 2 exemplary pore size distributions in new and used condition, Fig. 3. Number of particles released in consecutive tests.

[0050] In Fig. Figure 1 shows typical pore size distributions of commercially available particle filters. These distributions result from the production process and cannot be arbitrarily adjusted.

[0051] Fig. Figure 2 shows the changes in pore size distribution after intended use of the particle filter (aged) compared to its new condition. Using the particle filter reduces the frequency of large pores, which is the main cause of poor filtration efficiency.

[0052] In other words, the filtration efficiency of the aged filter is significantly better than when new. However, the pore size distribution of the aged particle filter cannot be directly adjusted during production.

[0053] The improvement in filter efficiency during the intended use of the particulate filter is also due to Fig. Figure 3 highlights the results of six consecutive tests in which the particulate filter in the exhaust system of a vehicle's internal combustion engine was used to filter particles from the exhaust stream flowing in the exhaust system. During each test, the vehicle speed was varied over time, and the cumulative number of particles that were not filtered out—that is, the number detectable downstream of the particulate filter in the exhaust system—was determined.

[0054] It can be seen that the cumulative number of released particles decreases from test to test, especially during the first tests. In order to enable sufficient filter performance during initial commissioning (corresponding to Test 1), according to the invention, a hydrocarbon-containing composition is applied to the surface of the particle filter before the first use of the particle filter, and soot is formed on the surface of the particle filter by incomplete oxidation of the hydrocarbon-containing composition. The soot is formed in such a way that the soot-laden particle filter has an optimal pore size distribution before first use, for example, the pore size distribution "aged" according to Fig. 2, which was previously determined.

Claims

[1] Method for pretreating a particulate filter to be arranged in an exhaust system of an internal combustion engine, comprising: - applying a hydrocarbon-containing composition to a surface of the particulate filter, wherein the hydrocarbon-containing composition is a synthetic resin, and - Formation of soot on the surface of the particulate filter due to incomplete oxidation of the hydrocarbon-containing composition. [2] Method according to claim 1, wherein the incomplete oxidation takes place after positioning of the particulate filter in the exhaust system of the internal combustion engine. [3] A process according to any one of the preceding claims, wherein the hydrocarbon-containing composition is incompletely oxidized by supplying an oxygen-containing gas stream. [4] Method according to one of the preceding claims, wherein the hydrocarbon-containing composition is applied before positioning the particulate filter in the exhaust system of the internal combustion engine. [5] Method according to one of the preceding claims, further comprising: - Determining an optimal pore size and / or pore size distribution for the particulate filter for a point in time after the end of a running-in phase of the internal combustion engine in whose exhaust system the particulate filter is to be arranged, wherein the soot formation takes place in such a way that the soot-laden particulate filter has the optimal pore size and / or pore size distribution. [6] Method according to one of the preceding claims, wherein the particulate filter is a diesel particulate filter or a gasoline particulate filter. [7] Particle filter for filtering out particles from an exhaust gas stream of an internal combustion engine, wherein a surface of the particle filter at least partially comprises a hydrocarbon-containing composition, wherein the hydrocarbon-containing composition is a synthetic resin and wherein the hydrocarbon-containing composition is formed and arranged on the surface of the particle filter in such a way that, after an incomplete oxidation of the hydrocarbon-containing composition, the particle filter has an optimal pore size and / or pore size distribution for a point in time after the end of a running-in phase of an internal combustion engine in whose exhaust system the particle filter is to be arranged. [8] Particle filter according to claim 7, wherein the particle filter is designed as a diesel particle filter or gasoline particle filter. [9] Engine arrangement, comprising an internal combustion engine with an exhaust system for receiving an exhaust gas flow generated by the internal combustion engine, wherein a particle filter according to one of claims 7 to 8 is arranged in the exhaust system.

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