Cold-start exhaust-gas emission control

Abstract

The invention relates to a method and a device for removing NOx from the exhaust gas of an internal combustion engine during cold starting.

Description

[0001] The invention relates to a method and a device for removing NO x from the exhaust gas of an internal combustion engine during cold start.

[0002] The combustion process of hydrocarbons (fuels) provides heat energy for propulsion and generates emissions such as CO2 and NOx. While the CO2 problem has not yet been technically solved, there are various commercial solutions for NOx (e.g., three-way catalysts, urea addition), all of which only function above a certain operating temperature of approximately 200°C. During the so-called cold-start phase, shortly after engine ignition, both gasoline and diesel vehicles generate substantial NOx emissions, which have not yet been reduced with current technical approaches.

[0003] From WO 2019 / 072 973 A1 a method for reducing the nitrogen oxide content and / or the CO content in an exhaust gas of a vehicle, which comprises water vapor and one or more nitrogen oxides and / or CO, is known, in which a particulate hydrophobic aluminosilicate zeolite is brought into contact with the exhaust gas at a temperature of at least 20°C and adsorbs at least a portion of the nitrogen oxides and / or the CO from the exhaust gas on its surface and / or in its pores.

[0004] DE 60 130 406 T2 discloses a system for purifying exhaust gases from diesel or gasoline engines that contain an average excess of oxygen, wherein the engine's mixing ratio is periodically adjusted from a lean mixing ratio to a stoichiometric or rich mixing ratio with a λ value below 1.2. The system comprises a combination of an oxidation catalyst effective to accelerate the oxidation of at least NO to NO 2 , a particulate separator, and a NO x adsorption catalyst. The order of this combination of the three operating units in the exhaust gas flow direction is as follows: a NO x adsorption catalyst, a particulate separator, and an oxidation catalyst. The NO x adsorption catalyst and the particulate separator are arranged in the same structure.The system reduces the amounts of hydrocarbons, carbon monoxide, nitrogen oxides and particulates present in the exhaust gas.

[0005] DE 10 2016 219 301 A1 relates to a method for purifying exhaust gas generated by an internal combustion engine. The exhaust gas generated by the internal combustion engine is passed through an exhaust path in which at least one adsorption element is arranged, on which pollutants contained in the exhaust gas, in particular carbon dioxide, are at least partially bound. The at least one adsorption element is regenerated by at least partial desorption of the bound pollutants. Pollutants desorbed from the at least one adsorption element during desorption are stored in at least one reservoir. The adsorption element has an adsorption layer made of aluminum oxide and / or aluminum silicate. Further absorption elements are known from US5771684A and DE69618357T.

[0006] Against this background, the object of the invention is to provide devices and methods with which the high NO x emission rates during the cold start phase of an internal combustion engine can be reduced.

[0007] The object is achieved according to the invention by a method having the features of claim 1 and a device having the features of claim 6.

[0008] Embodiments and developments of the invention emerge from the dependent claims, the description and the illustrations.

[0009] The exhaust gas composition of modern combustion engines is high in NO, with a very low NO2 content. While a wide range of materials can remove NO2, the adsorptive removal of NO2 is much more difficult to achieve. The invention succeeds in reducing NOx emissions during the cold start phase, even in high-powered vehicles, by selectively metering oxygen or air into the exhaust stream. By introducing oxygen or air into the exhaust system, the reaction equilibrium shifts from NO to NO2, which facilitates the absorption of NOx in an adsorbent material, since NO2 is bound much more easily than NO.

[0010] The invention relates to a process for removing NO and / or NO x from an exhaust gas stream of an internal combustion engine during the cold start phase, i.e., preferably in the first 120 to 180 seconds after engine start-up. In this process, the exhaust gas stream and an oxygen-containing gas stream are simultaneously passed through an adsorber module containing aluminosilicate particles, and NO and / or NO x are oxidized by the oxygen and adsorbed on the aluminosilicate particles. The aluminosilicate particles are regenerable by heating, i.e., they release the adsorbed nitrogen oxides and can adsorb nitrogen oxides again after cooling.

[0011] In one embodiment, the process according to the invention is carried out in a temperature range from -40°C to 40°C outside temperature and at a flow rate of at least 60 m 3 / h of exhaust gas, and the process according to the invention has a space-time yield of at least 30,000 h -1 . In one embodiment, the total volume of the aluminosilicate particles contained in the adsorber module is 1 to 4 L, e.g., 1 to 3 L, in particular 2 to 2.5 L, for example, 2.2 L. In one embodiment, the ratio of the flow rates of exhaust gas to oxygen-containing gas is from 10:1 to 1:1, for example, from 5:1 to 3:1.

[0012] According to the invention, aluminosilicate particles are used as adsorbent material. Examples of suitable aluminosilicates are feldspars and zeolites, such as zeolite A, zeolite Y, or zeolite ZSM-5. In one embodiment, the zeolite particles have a Si:Al molar ratio in the range of 500:1 to 5:1, for example, from 40:1 to 10:1. According to the invention, aluminosilicate particles are used that do not contain metals as promoters.

[0013] In one embodiment, the aluminosilicate particles have a bulk density of 650 to 750 kg / m 3 . According to the invention, the aluminosilicate particles have an average diameter in the range of 0.1 to 0.7 mm, for example 0.15 to 0.6 mm.

[0014] One of the advantages of the process according to the invention is that the aluminosilicate particles can be regenerated by heating to release the adsorbed nitrogen oxides and restore their original adsorption capacity. This allows the aluminosilicate particles to be used over a longer period of time and across many cold-start phases of the internal combustion engine. In one embodiment of the process, the aluminosilicate particles are regenerated by passing a hot exhaust gas stream through the adsorber module. During regeneration, no additional oxygen is supplied to the adsorber module.

[0015] In one embodiment of the method according to the invention, the exhaust gas stream leaving the adsorber module is fed to an SCR module. The SCR module performs selective catalytic reduction (SCR) of the nitrogen oxides contained in the exhaust gas stream. In one embodiment of the method, the exhaust gas stream is intermittently passed through the adsorber module during the cold-start phase and / or to regenerate the aluminosilicate particles from time to time. In another embodiment of the method, the exhaust gas stream is continuously passed through the adsorber module and the SCR module, but only during the cold-start phase is an oxygen-containing gas stream additionally passed through the adsorber module. After the combustion engine has reached its operating temperature, the hot exhaust gas stream desorbs the nitrogen oxides adsorbed in the adsorber module, which are then reduced to nitrogen in the downstream SCR module.This means that the full adsorption capacity of the adsorber module is available again for a subsequent cold start.

[0016] The invention also relates to a device suitable for carrying out the method according to the invention, which is defined in independent claim 6.

[0017] The adsorber module is positioned in the exhaust system of the combustion engine in such a way that the exhaust gas flow flows through the adsorber module at least during the cold start phase.

[0018] In In one embodiment, the exhaust gas module is arranged in a bypass line of an exhaust gas purification device (e.g. three-way catalyst, oxidation catalyst, reduction catalyst (SCR)) connected downstream of the internal combustion engine, and means (e.g. electronically controlled valves) are provided which direct the exhaust gas through the adsorber module according to the invention only during the cold start phase.

[0019] In another embodiment, the adsorber module is located upstream of the SCR module in the exhaust system. In a further embodiment, the exhaust system comprises means for selectively directing an exhaust gas flow through or past the adsorber module, for example, a bypass line equipped with valve flaps.

[0020] In another embodiment, the adsorber module is arranged upstream of the exhaust gas purification device in such a way that the exhaust gas stream continuously flows through the adsorber module according to the invention. Once the exhaust gas purification device has reached its operating temperature after the cold start phase, it removes the nitrogen oxides from the exhaust gas stream.

[0021] No heating device is provided for targeted heating of the adsorber module. The adsorber module is not heated; the operating temperature is the climatically determined ambient temperature. Due to the high reactivity of the oxygen and the aluminosilicate particles, the adsorber module according to the invention is capable of removing nitrogen oxides from the exhaust stream in a temperature range from -40°C to 40°C outside temperature without external heat input.

[0022] In one embodiment of the adsorber module, the aluminosilicate particles are arranged in a replaceable cartridge. A replaceable cartridge filled with aluminosilicate particles makes replacement considerably easier. Over time, the adsorption capacity of the aluminosilicate particles can decrease, for example, due to the deposition of contaminants contained in the exhaust gas, to such an extent that even regeneration cannot adequately restore it. If the adsorption capacity of the aluminosilicate particles in the cartridge is permanently exhausted, it is simply replaced with a new cartridge.

[0023] In one embodiment, the cartridge has a volume in the range of 25 mL to 4,000 L, for example from 2 L to 4 L. This small volume allows for miniaturization or compact design of the cold-start adsorber module.

[0024] In one embodiment, the cartridge is made of metal. In another embodiment, the cartridge is a plastic cartridge. The cartridge can have various shapes. In one embodiment, the cartridge is cylindrical and has a circular cross-section. In another embodiment, the cartridge has an elliptical cross-section. In yet another embodiment, the cartridge has the shape of a prism, for example, a square, pentagonal, hexagonal, or octagonal prism.

[0025] In one embodiment, the cartridge has a perforated base and / or lid. This facilitates the flow of exhaust gas through the cartridge and also retains the aluminosilicate particles within the cartridge. The perforation can consist of holes or slots, for example. It is important that the diameter of the holes or the width of the slots is smaller than the diameter of the aluminosilicate particles to effectively retain them within the cartridge.

[0026] The device according to the invention comprises means for metering an oxygen-containing additional gas into the adsorber module. In one embodiment, these means comprise a metering line opening into the adsorber module and means for gas metering, such as valves, reducing valves, or compressors. In another embodiment, these means comprise a metering line opening into the exhaust system at the inlet of the adsorber module and means for gas metering.

[0027] In one embodiment, the oxygen-containing supplementary gas is pure oxygen. In another embodiment, the oxygen-containing supplementary gas is compressed air. In another embodiment, the oxygen-containing supplementary gas is ambient air, optionally in compressed form.

[0028] Implementation in the vehicle can be achieved as follows, for example: The adsorber module is positioned in the exhaust stream upstream of the SCR module. The cold exhaust gas (at restart) is passed through the adsorber module for a few seconds, while at the same time an oxygen-containing gas stream (pure oxygen, compressed air, or ambient air) is passed through the adsorber module until the temperatures in the existing exhaust gas catalyst system are sufficient for it to function. A flap control can be used to direct the exhaust stream so that only cold exhaust gas is passed through the adsorber module. Regeneration of the loaded material on-board can be achieved by passing sufficient hot exhaust gas through the adsorber module. This stream should be cleaned by the SCR system. The adsorber material can be loaded and unloaded very frequently.

[0029] Alternatively, a replaceable cartridge can be used, which can be replaced during the service interval if necessary. The nitrogen oxides adsorbed on the aluminosilicate particles can be desorbed and recycled, for example, as a raw material for the production of nitro compounds.

[0030] The inventive solution enables the reduction of NO x emissions from internal combustion engines during cold starts under extreme flow conditions with space-time yields of at least 30,000 h -1 < under real conditions (RDE, real drive emissions). With only 2.2 L of adsorber material, at least 60 m 3 < / h of exhaust gas can be effectively cleaned in a low temperature range (- 40 to 40°C outside temperature). High NO x absorption rates of approximately 50% can be achieved even with an exhaust stream in which NO accounts for > 99% of the nitrogen oxides, even with an unfavorable combination of high exhaust flows under real cold start conditions and without external heat input. The nitrogen oxide content in the exhaust stream during the cold start phase is reduced by up to 67%.

[0031] This makes it possible to substantially reduce NO x emissions even in high-powered vehicles. The NO x absorption rates are reproducibly high, while the pressure loss caused by the high flow through the adsorber module can be kept low due to the large particle diameters of the aluminosilicate particles. Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0032] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0033] The invention is illustrated by way of example in the following examples and the accompanying drawings, and will be further described with reference to the drawings. It shows: Figure 1 shows an example diagram of the nitrogen oxide and oxygen contents in an exhaust gas stream leaving an exhaust gas module according to the invention over time; Figure 2 shows an example diagram of the nitrogen oxide and oxygen contents in an exhaust gas stream at the inlet and outlet of an exhaust gas module according to the invention over time. Example 1

[0034] In a laboratory test, 25 mL of zeolite particles (bulk density 700 kg / m 3 < ) were placed in a cylindrical plastic cartridge (diameter 1.6 cm). After setting a volume flow of 4.7 L / min of an N 2 stream containing 1,500 ppm NO through the cartridge, an additional oxygen gas flow of 1.3 L / min O 2 (99% purity) was metered into the cartridge, resulting in a total volume flow of 6 L / min through the cartridge. Using a testo 340 flue gas analyzer (Testo SE & Co. KGaA, 79822 Titisee-Neustadt), the course of the NO, NO 2 , NO x and oxygen levels in the flue gas stream at the outlet of the cartridge was recorded and documented over a period of 900 s.

[0035] Figure 1 shows the measurement results. A maximum NO x uptake rate of 67% was determined; this corresponds to a space-time yield of 14,400 h -1 . Without the addition of oxygen, virtually no NO is adsorbed. Example 2

[0036] An embodiment of the exhaust module according to the invention was tested in a field trial with a high-powered (>350 hp) passenger car under realistic conditions. For this purpose, 2.2 L of the adsorbent material from Example 1 were placed in a cylindrical cartridge (16 cm diameter) and covered with 1.5 L of silica gel as a moisture barrier. The raw exhaust gas from the car's ICE was bundled via two tapers on the dual exhaust and introduced via two inlets into the upper segment of the cartridge, which was perforated at the bottom. In addition, 50–100 L / min of pure oxygen from a compressed gas cylinder were continuously introduced during the cold-start phase (0 s to 120 s after engine start). The course of temperature, NO and NO 2 as well as NO x at the inlet and outlet of the cartridge were recorded and documented using a testo 340 flue gas analyzer (Testo SE & Co. KGaA, 79822 Titisee-Neustadt).The cold start was performed after calibrating the sensors, and the measured values ​​were recorded under mobile cold-start conditions. This simulated real-world conditions, also known as RDE ("real drive emissions").

[0037] Figure 2 shows the NO x content of the exhaust stream and at the outlet of the exhaust module according to the invention over time during the cold start phase (0 s to 130 s after engine start). Despite high engine power (> 350 hp) and high volume emissions of at least 60 m 3 / h, the NO x uptake rates are approximately 48%, and the space-time yields are high, in the range of at least 30,000 h -1 .

Claims

1. Method for removing NO and / or NOx from an exhaust gas stream of an internal combustion engine during the cold start phase, wherein the exhaust gas stream and a gas stream containing oxygen are simultaneously passed through an adsorber module containing aluminosilicate particles, and NO is oxidized by the oxygen and adsorbed on the aluminosilicate particles, wherein the aluminosilicate particles contain no metals as promoters and the average particle diameter of the aluminosilicate particles is in the range of 0.1 mm to 0.7 mm, and wherein the method is carried out in an outside temperature range of -40°C to 40°C and at a flow rate of at least 60 m3 / h of exhaust gas and has a space-time yield of at least 30,000 h-1.

2. Method according to claim 1, wherein the bulk volume of the aluminosilicate particles contained in the adsorber module is 1 to 3 L.

3. Method according to claim 1 or 2, wherein the bulk density of the aluminosilicate particles is in the range of 650 kg / m3 to 750 kg / m3.

4. Method according to any one of the preceding claims, wherein the aluminosilicate particles are regenerated by passing a hot exhaust gas stream through the adsorber module.

5. Method according to any one of the preceding claims, wherein the exhaust gas stream leaving the adsorber module is fed to an SCR module.

6. Device for removing NO and / or NOx from an exhaust gas stream of an internal combustion engine during the cold start phase, comprising a) an adsorber module arranged in an exhaust gas system of the internal combustion engine containing aluminosilicate particles, which contain no metals as promoters and the average particle diameter of which is in the range of 0.1 mm to 0.7 mm, b) a module arranged in the exhaust gas system of the internal combustion engine for selective catalytic reduction of nitrogen oxides, which is connected downstream of the adsorber module, and c) means for metering an additional gas containing oxygen into the adsorber module.

7. Device according to claim 6, wherein the exhaust gas system comprises means, which guide an exhaust gas stream either through or past the adsorber module.

8. Device according to claim 7, wherein the means, which guide an exhaust gas stream either though or past the adsorber module, comprise a bypass line equipped with valve flaps.

9. Device according to any one of claims 6 to 8, wherein the means for metering an additional gas containing oxygen into the adsorber module comprise, at the entrance to the adsorber module, a metering line leading into the exhaust gas system and means for gas metering.

10. Device according to claim 9, wherein the means for gas metering comprise valves, reduction valves or compressors.

11. Device according to any one of claims 6 to 10, wherein the aluminosilicate particles are arranged in a replaceable cartridge.

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