AT525550B1 - Internal combustion engine system with an ammonia internal combustion engine and exhaust gas purification system connected thereto and operating method therefor - Google Patents

Abstract

The invention relates to an internal combustion engine (1) which is at least predominantly operated with ammonia as fuel and has an exhaust gas cleaning system (2) connected thereto for cleaning an exhaust gas emitted by the internal combustion engine (1), the exhaust gas cleaning system (2) having a first SCR catalytic converter (14) for Has reduction of nitrogen oxides contained in the exhaust gas. According to the invention, the exhaust gas cleaning system (2) also has a second SCR catalytic converter (11) for reducing nitrogen oxides contained in the exhaust gas, which is upstream of the first SCR catalytic converter (14) in terms of flow, the second SCR catalytic converter (11) as a passive SCR Catalyst is formed, which causes a reduction of nitrogen oxides contained in the exhaust gas by means of the internal combustion engine (1) emitted ammonia and without adding a reducing agent from the outside. For the operating method according to the invention for the internal combustion engine system, it is provided that exhaust gas, which is cleaned by an internal combustion engine (1) that is at least predominantly operated with ammonia as the fuel, nitrogen oxides contained in the exhaust gas being transported to a first SCR catalytic converter (14) by means of the exhaust gas through an injector (15) added ammonia are reduced, with nitrogen oxides contained in the exhaust gas additionally being reduced at a second SCR catalytic converter (11) upstream of the first SCR catalytic converter (14) by means of ammonia emitted by the internal combustion engine (1).

Description

Description

INTERNAL COMBUSTION ENGINE SYSTEM WITH AN AMMONIA INTERNAL COMBUSTION ENGINE AND CONNECTED EMISSION CONTROL SYSTEM AND OPERATING METHOD THEREOF

Ammonia (NH) as a fuel for internal combustion engines has the advantage of not causing any CO>»emissions. However, the combustion of NH; Nitrogen oxides (NOx). In addition, in the exhaust gas with NH; operated internal combustion engines may contain residues of unburned NHs. Both NOx and NHz3 are pollutants that have to be removed from the exhaust gas at least to a large extent.

From US 2010/0019506 A1 it is known to use an SCR catalyst for exhaust gas purification in an internal combustion engine operated with NHz3, the NOx contained in the exhaust gas with NH contained in the exhaust gas due to incomplete NHs combustion NH; (NHs slip) can reduce. For this purpose, the internal combustion engine is operated in such a way that a sufficiently high NHs slip occurs. However, on the one hand it can be difficult to adjust the NHs slip appropriately to avoid both NOx and NHs emissions. On the other hand, the intentional generation of an NHs slip is associated with an unfavorable increase in fuel consumption.

Other internal combustion engine systems with an ammonia internal combustion engine are known, for example, from US 2011264355 A1, US 2021079826 A1, CN 110219718 A and CN 111255560 A.

The object of the present invention is to provide an internal combustion engine system with an ammonia internal combustion engine and an exhaust gas cleaning system connected thereto and an operating method for this, by means of which improved exhaust gas cleaning is made possible. This object is achieved by an internal combustion engine system having the features of claim 1 and an operating method having the features of claim 6. Advantageous developments are specified in the respective dependent claims.

The internal combustion engine system according to the invention comprises an internal combustion engine operated at least predominantly with ammonia as fuel and an exhaust gas cleaning system connected to the internal combustion engine for cleaning the exhaust gas emitted by the internal combustion engine. The exhaust gas purification system has a first SCR catalytic converter for reducing NOx contained in the exhaust gas and, according to the invention, a further, second SCR catalytic converter for reducing NOx contained in the exhaust gas, which is upstream of the first SCR catalytic converter in terms of flow, the second SCR Catalyst is designed as a passive SCR catalyst, which causes a reduction of nitrogen oxides contained in the exhaust gas by means of ammonia emitted by the internal combustion engine and without adding a reducing agent from the outside. The fact that two SCR catalytic converters arranged separately from one another are provided means that NOx can be removed from the exhaust gas in an improved manner. As a result of a naturally occurring temperature gradient along the exhaust gas flow path, the second SCR catalytic converter, which is preferably installed close to the engine, is quickly ready for operation. If the catalytic effectiveness drops as a result of excessive heating, the first SCR catalytic converter, which is preferably arranged in the underbody area of the corresponding motor vehicle, can take over the NOx removal as a result of its meanwhile starting to heat up. The internal combustion engine system can be installed in a car, a commercial vehicle, a tractor, a ship or in a locomotive.

The fuel NHs predominantly used to operate the internal combustion engine can be mixed with the combustion air in an intake manifold or injected directly into a combustion chamber in liquid or gaseous form. The NH3 fuel is taken from a fuel tank in which it is at least predominantly in liquid form. To improve the NH: ignition, the additional addition or injection of an ignition promoter such as diesel, ethanol, diethyl ether or another suitable substance for combustion

voltage engine be provided. However, the amount of the ignition promoter is comparatively small compared to the amount of the actual NH fuel. Preferably it is less than 20% or less than 10% of the NHs amount.

[0007] As regards the SCR catalytic converters, they are to be understood as meaning catalytic converters which are able to catalyze a reduction of NOx to nitrogen (N2) using NH3 as the reducing agent even in the presence of an excess of oxygen.

In an embodiment of the invention, the emission control system has exactly one injector for adding NH; to the exhaust gas, the injector for adding NHs to the exhaust gas being designed on the input side of the first SCR catalytic converter. Said NHs injector is thus the only NH8s injector in the emission control system. It is preferably arranged directly in front of the exhaust gas inlet side of the first SCR catalytic converter in the exhaust gas cleaning system. The injector can inject the NOx reducing agent NH3 in liquid or gaseous form into the exhaust gas. It is preferably taken from the fuel tank. The second SCR catalytic converter arranged further upstream receives the NOx reducing agent NH3 with the supplied exhaust gas, in which it is contained in the form of NH3 slip from the internal combustion engine due to incomplete combustion. The second SCR catalytic converter is thus designed as a passive SCR catalytic converter, which brings about a reduction in NOx without the addition of a reducing agent from the outside.

Typically, the amount of NHs present in the exhaust gas in the form of NHs slip is less than the amount of NOx emitted by the engine. Downstream of the second SCR catalytic converter, the exhaust gas therefore still contains more or less high levels of NOx. These are then at the downstream first SCR catalytic converter by means of externally supplied NH; reduced. In this way, very low NOx tailpipe emissions can be achieved.

In a further embodiment of the invention, the emission control system has a particle filter for filtering out particles contained in the exhaust gas, the particle filter being arranged upstream of the first SCR catalytic converter and downstream of the second SCR catalytic converter. The particle filter is preferably arranged upstream of the NHs3 addition point formed by the NHs injector in the exhaust system. Although no soot particles are produced by the NH3 combustion in the engine, particle emissions caused by engine oil additives or the combustion of an ignition promoter can occur. The corresponding particles can be removed from the exhaust gas by the particle filter. Since particle emissions are typically relatively low, the particle filter can be comparatively small. The volume of the particle filter can therefore be less than 70%, less than 50% or even less than 30% of the volume of the first or second SCR catalytic converter.

In a further embodiment of the invention, the emission control system has an oxidation catalyst which is arranged in terms of flow between the second SCR catalyst and the particle filter. The NO » proportion of the NOx contained in the exhaust gas can be increased by the oxidation catalytic converter, as a result of which the NOx reduction in the first SCR catalytic converter is improved.

As an alternative to providing a separate oxidation catalytic converter between the second SCR catalytic converter and the particle filter, the particle filter can also be designed with an oxidation-catalytic coating.

In a further embodiment of the invention, the internal combustion engine is designed as a compression-ignited internal combustion engine. Therefore, ignition means such as spark plugs for igniting the fuel in its combustion chambers are omitted for the internal combustion engine.

For the operating method according to the invention for operating an internal combustion engine system, in which exhaust gas emitted by an internal combustion engine operated at least predominantly with ammonia as fuel is cleaned, it is provided that NOx contained in the exhaust gas is added to a first SCR catalytic converter by means of the exhaust gas through an injector NH; is reduced, with the NOx contained in the exhaust gas additionally being converted to a second SCR catalytic converter upstream of the first SCR catalytic converter by means of a

NH emitted by internal combustion engines; is reduced. There is thus a two-stage NOx reduction. The second SCR catalytic converter acts as the first NOx cleaning stage, in which the NOx contained in the exhaust gas is reduced by means of the NH: content in the exhaust gas, which is present in the form of an NHs slip and is provided by the internal combustion engine. The second NOx purification stage is formed by the downstream first SCR catalyst. In this, the NOx remaining in the exhaust gas is reduced by NH added to the exhaust gas from outside by means of an injector.

In an embodiment of the method according to the invention, particles contained in the exhaust gas are filtered out of the exhaust gas by means of a particle filter arranged in terms of flow between the first SCR catalytic converter and the second SCR catalytic converter. There is thus a comprehensive cleaning of the exhaust gas, which enables compliance with the strictest limit values for NOx and particle emissions.

In a further embodiment of the method it is provided that the internal combustion engine is at least predominantly operated with excess air. This enables fuel combustion with high mechanical efficiency.

The invention is explained in more detail using a drawing and associated examples. The only figure shows an advantageous embodiment of the internal combustion engine system according to the invention.

The internal combustion engine system shown only as an example and schematically in the figure includes an internal combustion engine 1 and an exhaust gas cleaning system 2 connected to it the air supply line 3 arranged turbocharger compressor 5 opens. The internal combustion engine 1 is designed as an internal combustion engine operated predominantly with excess air according to the diesel principle, ie as a compression igniter of the reciprocating piston type. NH3 is used as the fuel, which in the present case is taken from a tank 7 and is supplied to the combustion air on the inlet side of the intake manifold 4 via a first NHs supply line 6 . A feed pump used for this purpose and a control valve for controlling the amount of NHs supplied are not shown separately. Of course, NH3 can also be fed directly to the intake manifold 4 . Also possible is NHs direct injection into the individual combustion chambers of the internal combustion engine 1, which are also not shown separately here. To improve ignition of the NH3 fuel, a pilot or pre-injection of a substance that acts as an ignition promoter, such as diesel fuel, ethanol, dimethyl ether, acetone or another, can be used be provided flammable substance. Corresponding supply means are not shown for reasons of clarity. The amount of ignition promoter used is relatively small compared to the amount of the actual fuel NH3 and is preferably less than 10%, less than 5% or less than 2%.

Exhaust gas produced during fuel combustion is discharged from the internal combustion engine 1 via an exhaust manifold 8 and an exhaust pipe 9 connected thereto and fed to the exhaust gas cleaning system 2 . In this case, a turbocharger turbine arranged in the exhaust gas line 9 is driven, which in turn drives the turbocharger compressor 5 via a shaft (not shown).

The exhaust gas cleaning system 2 in the present case has the following active cleaning components, seen in the direction of the exhaust gas flow, arranged one behind the other in the exhaust pipe 9 . A nitrogen oxide reduction catalytic converter, referred to here as the second SCR catalytic converter 11 , an oxidation catalytic converter 12 , a particulate filter 13 and a further nitrogen oxide reduction catalytic converter, referred to here as the first SCR catalytic converter 14 .

The catalysts 11, 12 and 14 are preferably designed in particular as ceramic honeycomb bodies with continuous, parallel channels. The duct walls that come into contact with the exhaust gas are coated with the respective specific catalytically active substance. The SCR catalytic converters 11, 14 can be, for example, one

act with iron and / or copper-exchanged zeolite as a catalytically active substance. The catalytically active substances enable a selective reduction of NOx contained in the exhaust gas with the NHs used here as a reducing agent, even under oxidizing conditions.

The catalytically active substance of the oxidation catalyst can be a finely dispersed metal from the platinum group such as platinum, palladium and/or rhodium. The particle filter 13 is preferably designed as a honeycomb body through which air flows through the wall, with parallel channels that are alternately closed on the inlet and outlet sides.

As far as the second SCR catalyst 11 is concerned, this is designed according to the invention as a so-called passive SCR catalyst. This means that the reducing agent NH3 required for NOx reduction is not supplied to the second SCR catalytic converter 11 from outside by a separate supply device. Instead, NHs: emitted by the internal combustion engine 1 serves as a reducing agent for selective NOx reduction. This so-called NHs slip of internal combustion engine 1 is the result of incomplete combustion of the fuel NHs in internal combustion engine 1. The source of the reducing agent NH3 for selective catalytic NOx reduction in the second SCR catalytic converter is therefore exclusively the NHs slip of internal combustion engine 1.

Depending on the ratio of NH3 slip and NOx content in the exhaust gas, or also depending on the conversion capacity of the second SCR catalytic converter 11, residual amounts of NOx or NHes can be present in the exhaust gas flowing out of the second SCR catalytic converter 11. These are introduced into the downstream oxidation catalytic converter 12 with the exhaust gas flow. If there are residual amounts of NOx in the exhaust gas, the NOx component nitrogen monoxide (NO) is at least partially oxidized there to form nitrogen dioxide (NO») with the oxygen contained in the exhaust gas of lean-burn internal combustion engine 1. The aim here is an NO/NO2 ratio of about 1:1, which improves or facilitates the catalytic NOx reduction in the further downstream arranged first SCR catalyst 14 . If there is a residual amount of NH3 in the exhaust gas, this NH3 is at least partially oxidized to NO or NO». In any case, it can be assumed that the exhaust gas flowing out of the oxidation catalytic converter 12 contains NOx, which is at least largely reduced in the first SCR catalytic converter 14 arranged further downstream.

Before the exhaust gas flowing through the exhaust gas line 9 reaches the first SCR catalytic converter 14 , it is at least largely freed from particles by being filtered out in the particle filter 13 . The first SCR catalytic converter 14 receives the reducing agent NH3 required for selective NOx reduction by adding it via an upstream injector 15. This is connected to the tank 7 via a second NHs supply line 16. A feed pump that is preferably provided is not shown separately. NH3 can be taken from the tank 7 in liquid form or in gaseous form and injected into the exhaust gas by the injector 15 on the inlet side of the first SCR catalytic converter 14 . When liquid NH3 is added, it evaporates in the hot exhaust gas, which is why the SCR catalytic converter 14 NHs is supplied at least predominantly in gaseous form in any case. This ensures an even NH3 distribution in the exhaust gas, which is why a mixer can be dispensed with. Since, in contrast to the first SCR catalytic converter 14, the second SCR catalytic converter 11 does not cover its NOx reducing agent requirement by adding it to the exhaust gas through an injector, but rather by NHs slip from the internal combustion engine 1, no further NOx reducing agent adding device is required in addition to the injector 15 for the exhaust gas cleaning system 2. The injector 7 is therefore the only NOx reducing agent addition device of the exhaust gas cleaning system 2.

Needs-based control of the addition of NH3 to the exhaust gas by the injector 15 for the desired complete reduction of NOx contained in the exhaust gas is carried out using signals provided by NOx sensors 17, 18, which are evaluated accordingly by a control unit, not shown. A first NOx sensor 17 for detecting the NOx content in the exhaust gas is provided on the outlet side of the oxidation catalytic converter 12 or between the oxidation catalytic converter 12 and the particle filter 13 . This enables the determination of

NOx content of the exhaust gas flowing into the first SCR catalytic converter 14 . The NH3 requirement for reducing NOx contained in the exhaust gas in the first SCR catalytic converter 14 can in turn be determined from the determined NOx content of the exhaust gas and the injector 15 can be activated accordingly. If the oxidation catalytic converter 12 and particle filter 13 are combined to form an integral common component, the first NOx sensor 17 is preferably arranged on the output side of this component.

A second NOx sensor 18 is arranged on the output side of the first SCR catalytic converter 14 and makes it possible to determine any NOx that may have slipped through the first SCR catalytic converter 14 . In this case, the enrichment of the exhaust gas caused by the injector 15 with the reducing agent NHs can be adjusted.

It should be noted that one or both of the sensors 17, 18 referred to here as NOx sensors can also be designed as combined NOx/NHs sensors. As a result, in addition to the NOx contents in the exhaust gas upstream and downstream of the first SCR catalytic converter 14, the corresponding NH: contents can also be determined, which can improve the accuracy of the NHs dosing if necessary.

Overall, an extremely environmentally friendly operation of a corresponding vehicle is made possible by the internal combustion engine system according to the invention. Not only emissions of climate-damaging CO are at least largely avoided, but also at least largely the emissions of hydrocarbons NOx, NHs and particles.

REFERENCE LIST

1 combustion engine

2 Exhaust aftertreatment system 3 Air supply line

4 intake manifold

5 turbocharger compressors

6 First NH3 supply line 7 Tank

8 exhaust manifold

9 exhaust pipe

10 turbocharger turbine

11 Second SCR catalyst 12 Oxidation catalyst

13 particle filter

14 First SCR catalytic converter 15 injector

16 Second NH3 supply line 17 First NOx sensor

18 Second NOx sensor

Claims (8)

patent claims 1. Internal combustion engine system comprising an internal combustion engine (1) that is at least predominantly operated with ammonia as the fuel and has an exhaust gas cleaning system (2) connected thereto for cleaning an exhaust gas emitted by the internal combustion engine (1), the exhaust gas cleaning system (2) having a first SCR catalytic converter (14) for reduction of nitrogen oxides contained in the exhaust gas, wherein the exhaust gas purification system (2) also has a second SCR catalytic converter (11) for reducing nitrogen oxides contained in the exhaust gas, which is upstream of the first SCR catalytic converter (14), characterized in that the second SCR catalytic converter (11) is designed as a passive SCR catalytic converter, which causes a reduction of nitrogen oxides contained in the exhaust gas by means of the internal combustion engine (1) emitted ammonia and without adding a reducing agent from the outside. 2. Internal combustion engine system according to claim 1, characterized in that the exhaust gas purification system (2) has precisely one injector (15) for adding ammonia to the exhaust gas, the injector (15) for adding ammonia to the exhaust gas being on the input side of the first SCR catalytic converter (14 ) is trained. 3. Internal combustion engine system according to claim 1 or 2, characterized in that the exhaust gas cleaning system (2) has a particle filter (13) for filtering out particles contained in the exhaust gas, the particle filter (13) being fluidically upstream of the first SCR catalytic converter (14) and behind the second SCR catalytic converter (11) is arranged. 4. Internal combustion engine system according to claim 3, characterized in that the exhaust gas cleaning system (2) has an oxidation catalytic converter (12) which is arranged in terms of flow between the second SCR catalytic converter (11) and the particle filter (13). 5. Internal combustion engine system according to one of claims 1 to 4, characterized in that the internal combustion engine (1) is designed as a compression-ignited internal combustion engine. 6. Operating method for operating an internal combustion engine system, in which exhaust gas emitted by an internal combustion engine (1) that is at least predominantly operated with ammonia as fuel is cleaned, with nitrogen oxides contained in the exhaust gas being removed at a first SCR catalytic converter (14) by means of the exhaust gas through an injector (15 ) added ammonia are reduced, and nitrogen oxides contained in the exhaust gas are additionally reduced at a second SCR catalytic converter (11) upstream of the first SCR catalytic converter (14) by means of ammonia emitted by the internal combustion engine (1). 7. Operating method according to claim 6, characterized in that particles contained in the exhaust gas are filtered out of the exhaust gas by means of a particle filter (13) arranged in terms of flow between the first SCR catalytic converter (14) and the second SCR catalytic converter (11). 8. Operating method according to claim 6 or 7, characterized in that the internal combustion engine (1) is at least predominantly operated with excess air. 1 sheet of drawings