DE102021113161A1 - Cold start emission control - Google Patents

Abstract

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

Description

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.

The combustion process of hydrocarbons (fuels) provides thermal energy for propulsion and generates emissions such as CO ₂ and NO _x . While the CO ₂ problem has not yet been technically solved, there are various commercial solutions for NO _x (e.g. three-way catalytic converter, addition of urea), all of which only work above a certain working temperature of around 200°C. In the so-called cold-start phase, shortly after the engine is ignited, both petrol and diesel vehicles produce substantial NO _x emissions, which current technical approaches have not yet been able to reduce.

WO 2019/072 973 A1 discloses 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, 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 part of the nitrogen oxides and/or the CO from the exhaust gas on its surface and/or in its pores.

the DE 60 130 406 T2 discloses a system for purifying exhaust gases from diesel or gasoline engines containing an excess of oxygen on average, in which system a mixture ratio of the engine periodically changes from a lean mixture ratio to a stoichiometric or rich mixture ratio with a λ value below 1.2 is set. 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 operational units in the flow direction of the exhaust gas being as follows: a NO _x adsorption catalyst, a particulate separator and an oxidation catalyst, and the NO _x adsorption catalyst and the particulate separator are arranged in the same structure. The system reduces the levels of hydrocarbons, carbon monoxide, nitrogen oxides and particulates present in the exhaust.

the DE 10 2016 219 301 A1 relates to a method for cleaning exhaust gas generated by an internal combustion engine, in which the exhaust gas generated by the internal combustion engine is routed through an exhaust gas 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, and in which the at least one adsorption element is regenerated by at least partial desorption of the bound pollutants, and in which pollutants desorbed from the at least one adsorption element are stored in at least one reservoir during the desorption. The adsorption element has an adsorption layer made of aluminum oxide and/or aluminum silicate.

Against this background, the invention has set itself the task of providing devices and methods with which the high NO _x emission rates during the cold start phase of an internal combustion engine can be reduced.

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 8. Configurations and developments of the invention result from the dependent claims, the description and the figures.

The exhaust gas composition of modern internal combustion engines is NO-heavy, the NO ₂ content is very low. While a plethora of materials can remove NO ₂ , adsorptive removal of NO is far more difficult to accomplish. According to the invention, the targeted metering of oxygen or air into the exhaust gas stream makes it possible to reduce NO _x emissions during the cold start phase, even in vehicles with high engines. The introduction of oxygen or air into the exhaust line shifts the reaction equilibrium from NO to NO ₂ , which facilitates the absorption of NO _x in an adsorber material, since NO ₂ is bound much more easily than NO.

The subject matter of the invention is a method for removing NO and/or NO _x from an exhaust gas flow of an internal combustion engine during the cold start phase, ie preferably in the first 120 to 180 seconds after engine start, in which the exhaust gas flow and an oxygen-containing gas flow are simultaneously passed through an aluminosilicate particle containing adsorber module is passed, and NO and / or NO _x are oxidized by the oxygen and adsorbed on the aluminosilicate particles. The aluminosilicate particles can be regenerated by heating, ie they release the adsorbed nitrogen oxides again and can adsorb nitrogen oxides again after cooling.

In one embodiment, the inventive method in a temperature range from -40 ° C to 40 ° C outside temperature and at a flow rate of at least 60 m ³ / h 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. B. 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 and oxygen-containing gas is from 10:1 to 1:1, for example from 5:1 to 3 :1.

According to the invention, aluminosilicate particles are used as the adsorber 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 from 500:1 to 5:1, for example from 40:1 to 10:1. According to the invention, aluminosilicate particles are used which contain no metals as promoters.

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

One of the advantages of the method according to the invention is that the aluminosilicate particles can be regenerated by heating in order to release the adsorbed nitrogen oxides and restore the original adsorption capacity. As a result, the aluminosilicate particles can be used over a longer period of time and over many cold start phases of the combustion engine. In one embodiment of the method, the aluminosilicate particles are regenerated by passing a hot exhaust gas flow through the adsorber module. No additional oxygen is supplied to the adsorber module during regeneration.

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 carries out a selective catalytic reduction (SCR) of the nitrogen oxides contained in the exhaust gas flow. In one embodiment of the method, the exhaust gas flow is passed through the adsorber module intermittently during the cold start phase and/or in order to regenerate the aluminosilicate particles from time to time. In another embodiment of the method, the exhaust gas stream is permanently 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 subsequent SCR module. The full adsorption capacity of the adsorber module is then available again for a subsequent cold start.

The invention also relates to a device suitable for carrying out the method according to the invention, which comprises an adsorber module containing aluminosilicate particles arranged in an exhaust system of an internal combustion engine and a module for the selective catalytic reduction of nitrogen oxides (SCR module). Furthermore, the device comprises means for metering an additional gas containing oxygen into the adsorber module.

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

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

In another embodiment, the adsorber module is connected upstream of the SCR module in the exhaust line. In a further embodiment, the exhaust line comprises means for directing an exhaust gas flow selectively through the adsorber module or past it, for example a bypass line provided with valve flaps.

In another embodiment, the adsorber module is connected upstream of the exhaust gas cleaning device in such a way that the exhaust gas stream flows permanently through the adsorber module according to the invention. When the exhaust gas cleaning device has reached its operating temperature after the cold start phase, it removes the nitrogen oxides from the exhaust gas flow.

There is no heating device for targeted heating of the adsorber module. The adsorber module is not heated, the working temperature is the climatic ambient temperature. Due to the high reactivity of the oxygen and the aluminosilicate particles, the adsorber module according to the invention is able to remove nitrogen oxides from the exhaust gas flow in a temperature range from -40° C. to 40° C. outside temperature without external heat supply.

In one embodiment of the adsorber module, the aluminosilicate particles are arranged in an exchangeable cartridge. One with aluminosilicate exchangeable cartridge filled with particles makes the change considerably easier. Over time, the adsorption capacity of the aluminosilicate particles can decrease to such an extent, for example due to the deposit of impurities contained in the exhaust gas, that it cannot be adequately restored even through regeneration. If the adsorption capacity of the aluminosilicate particles in the cartridge is permanently exhausted, it is simply exchanged for a new cartridge.

In one embodiment, the cartridge has a volume in the range from 25 mL to 4000 L, for example from 2 L to 4 L. This small volume allows the cold-start adsorber module to be miniaturized or compact.

In one embodiment, the cartridge is made of metal. In another embodiment, the cartridge is a plastic cartridge. The cartridge can have different 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 is in the form of a prism, such as a quadrangular, pentagonal, hexagonal, or octagonal prism.

In one embodiment, the cartridge has a perforated base and/or lid. On the one hand, this facilitates the flow of exhaust gas through the cartridge and, on the other hand, the aluminosilicate particles are retained in 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 in order to effectively retain them in the cartridge.

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

In one embodiment, the oxygen-containing makeup gas is pure oxygen. In another embodiment, the oxygen-containing supplemental gas is compressed air. In another embodiment, the oxygen-containing supplemental gas is ambient air, optionally in compressed form.

The implementation in the vehicle can take place, for example, as follows: The adsorber module is positioned in the exhaust gas flow in front of the SCR module. The cold exhaust gas (when restarting) is passed through the adsorber module for a few seconds and 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 catalytic converter system are sufficient for it to function can exercise. The exhaust jet can be directed accordingly via a flap control so that only cold exhaust gas is routed through the adsorber module. The loaded material can be regenerated on-board by passing sufficiently hot exhaust gas through the adsorber module. This stream should be cleaned via the SCR system. The adsorber material can be loaded and unloaded very frequently.

Alternatively, a replacement cartridge can be used, which may need to be replaced during the service interval. The nitrogen oxides adsorbed on the aluminosilicate particles can be desorbed and recycled and z. B. be used as a raw material for the production of nitro compounds.

The solution according to the invention makes it possible to reduce 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 approx. 50% can also be achieved with an exhaust gas stream in which NO makes up >99% of the nitrogen oxides, even with an unfavorable combination of high exhaust gas flows under real cold start conditions and without external heat supply. The nitrogen oxide content in the exhaust gas flow during the cold start phase is reduced by up to 67%.

In this way, it is possible to substantially reduce NO _x emissions even in high-powered vehicles. The NO _x absorption rates are reproducibly high, while the pressure loss that occurs due to the high flow rate across the adsorber module can be kept low due to the large particle diameter of the aluminosilicate particles. Further advantages and refinements of the invention result from the description and the accompanying drawings.

It goes without saying that the features mentioned above and those to be explained below not only in the combination specified in each case, but also in other combinations NEN or can be used alone without departing from the scope of the present invention.

• 1 ein Beispieldiagramm der Gehalte an Stickoxiden und Sauerstoff in einem ein erfindungsgemäßes Abgasmodul verlassenden Abgasstrom über die Zeit;
• 2 ein Beispieldiagramm der Gehalte an Stickoxiden und Sauerstoff in einem Abgasstrom am Eingang und am Ausgang eines erfindungsgemäßen Abgasmoduls über die Zeit.

The invention is exemplified by means of embodiments in the following examples and the accompanying drawings and is further described with reference to the drawings. It shows:

• 1 an example diagram of the contents of nitrogen oxides and oxygen in an exhaust gas flow leaving an exhaust gas module according to the invention over time;
• 2 an example diagram of the contents of nitrogen oxides and oxygen in an exhaust gas flow at the inlet and at the outlet of an exhaust gas module according to the invention over time.

example 1

In a laboratory test, 25 mL 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 flow containing 1,500 ppm NO through the cartridge, an oxygen gas flow of 1.3 L/min O ₂ (99% purity) was additionally metered into the cartridge, so that overall resulted in a flow rate 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 content in the flue gas flow at the outlet of the cartridge was recorded and recorded over a period of 900 s.

1 shows the results of the measurement. A maximum NO _x uptake rate of 67% was determined; this corresponds to a space-time yield of 14,400 h ^-1 . Virtually no NO is adsorbed without the addition of oxygen.

example 2

One embodiment of the exhaust gas module according to the invention was tested under real conditions in a field test with a high-powered (engine power >350 hp) passenger car. For this purpose, 2.2 L of the adsorber material from Example 1 were placed in a cylindrical cartridge (16 cm in diameter) and covered with 1.5 L of silica gel to protect against moisture. The raw emission gas of the car's ICE was bundled via 2 tapers on the double exhaust and introduced via 2 inlets into the upper segment of the cartridge, which was perforated at the bottom. In addition, during the cold start phase (0 s to 120 s after engine start), 50-100 L/min of pure oxygen from a compressed gas cylinder were continuously introduced. Using a testo 340 flue gas analyzer (Testo SE & Co. KGaA, 79822 Titisee-Neustadt), the course of temperature, NO and NO ₂ as well as NO _x at the inlet and outlet of the cartridge was recorded and recorded. The cold start took place after the sensors were calibrated, the measured values were recorded under mobile cold start conditions. This simulated real conditions, one can also speak of RDE ("real drive emissions").

2 shows the NO _x content of the exhaust gas stream and at the outlet of the exhaust gas module according to the invention over time during the cold start phase (0 s to 130 s after engine start). The NO _x absorption rates are about 48% despite high motorization (> 350 hp) and high volume emissions of at least 60 m ³ /h, the space-time yields are high and are in the range of at least 30,000 h ^-1 .

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was 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.

Patent Literature Cited

• DE 60130406 T2 [0004]
• DE 102016219301 A1 [0005]

Claims (10)

A method for removing NO and/or NO _x from an exhaust gas flow of an internal combustion engine during the cold start phase, in which the exhaust gas flow and an oxygen-containing gas flow are passed simultaneously through an adsorber module containing aluminosilicate particles, and NO and/or NO _x is oxidized by the oxygen and on be adsorbed on the aluminosilicate particles. procedure after claim 1 , which is carried out in a temperature range of -40°C to 40°C outside temperature and at a flow rate of at least 60 m ³ /h exhaust gas and has a space-time yield of at least 30,000 h ^-1 . procedure after claim 1 or 2 , in which the bulk volume of the aluminosilicate particles contained in the adsorber module is from 1 to 3 L. Procedure according to one of Claims 1 until 3 , in which the bulk density of the aluminosilicate particles is in the range from 650 kg/m ³ to 750 kg/m ³ Method according to one of the preceding claims, in which the mean particle diameter of the aluminosilicate particles is in the range from 0.1 mm to 0.7 mm. Method according to one of the preceding claims, in which the aluminosilicate particles are regenerated by passing a hot exhaust gas stream through the adsorber module. Method according to one of the preceding claims, in which the exhaust gas flow leaving the adsorber module is fed to an SCR module. Device for removing NO and/or NO _x from an exhaust gas stream of an internal combustion engine during the cold start phase, comprising a) an adsorber module containing aluminosilicate particles which is arranged in an exhaust gas system of the internal combustion engine; b) a module for the selective catalytic reduction of nitrogen oxides (SCR module); and c) means for metering an oxygen-containing additional gas into the adsorber module. device after claim 8 , wherein the adsorber module is connected upstream of the SCR module in the exhaust line. device after claim 8 or 9 , wherein the exhaust system comprises means that guide an exhaust gas flow either through the adsorber module or past it.

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