AT525550A4 - 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. 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

Internal combustion engine system with an ammonia internal combustion engine and

emission control system connected thereto and operating procedures therefor

Ammonia (NHs) as a fuel for internal combustion engines has the advantage of not causing any CO2 emissions. However, the combustion of NH: produces nitrogen oxides (NOx). In addition, residues of unburned NH; be included. Both NOx and

NH; are pollutants that have to be removed from the exhaust gas at least to a large extent

is applicable.

It is known from US 2010/0019506 A1 to use an SCR catalytic converter for exhaust gas purification in an internal combustion engine operated with NHz3, which combines NOx contained in the exhaust gas with NH contained in the exhaust gas as a result of incomplete NHs combustion; (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 associated with an unfavorable increase in fuel consumption.

It is the object of the present invention 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 training is in the respective

Subclaims specified.

The internal combustion engine system according to the invention comprises an internal combustion engine operated at least predominantly with ammonia as the 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

Reduction of NOx contained in the exhaust gas on the first SCR catalyst

is upstream in terms of flow. 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 used in a car, a commercial vehicle, a

be installed in a tractor, a ship or in a locomotive.

The fuel NHz 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 fuel NH; is taken from a fuel tank in which it is at least predominantly in liquid form. To improve the NHs: ignition, the additional addition or injection of an ignition promoter such as diesel, ethanol, diethyl ether or another suitable substance to the internal combustion engine can be provided. However, the amount of the ignition promoter is comparatively small compared to the amount of the actual fuel NHs. preferred

wise it is less than 20% or less than 10% of the NHs amount.

Regarding the SCR catalysts, they are catalysts that are able to achieve a reduction of NOx to nitrogen (N2) using NH3 as a reducing agent.

onmittel to catalyze even in the presence of an excess of oxygen.

In an embodiment of the invention, the exhaust gas purification system has precisely one injector for adding NH 3 to the exhaust gas, the injector for adding NH 3 to the exhaust gas being designed on the inlet side of the first SCR catalytic converter. Said NH8s injector is therefore the only NHs 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 NHs in liquid form or gaseous form into the exhaust gas. Preferably it will

taken from the fuel tank. The second, located further upstream

The SCR catalytic converter receives the NOx reducing agent NH3 with the supplied exhaust gas, which contains it in the form of NHs slip from the internal combustion engine due to incomplete combustion. The second SCR catalytic converter can thus be referred to as a passive SCR catalytic converter, which has a NOx

Reduction effected without adding a reducing agent from the outside.

Typically, the amount of NH: present in the form of NHs slip in the exhaust gas 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 reduced at the downstream first SCR catalytic converter by means of NHs supplied from the outside. In this way, very low NOx tailpipe

emissions are achieved.

In a further embodiment of the invention, the exhaust gas purification 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 NH3 addition point formed by the NH3 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 and the second SCR catalyst amount.

In a further embodiment of the invention, the exhaust gas purification system has an oxidation catalytic converter which is arranged in terms of flow between the second SCR catalytic converter and the particle filter. The NO2 content of the NOx contained in the exhaust gas can be increased by the oxidation catalytic converter, whereby the NOx

Reduction in the first SCR catalyst is improved.

As an alternative to providing a separate oxidation catalytic converter between the second SCR catalytic converter and the particulate filter, a version of the particulate

filters can be provided 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. The internal combustion engine therefore does not need ignition means such as spark plugs to ignite the fuel in its combustion

clear.

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 removed at a first SCR catalytic converter by means of NH added to the exhaust gas through an injector; is reduced, with 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 NH 2 emitted by the internal combustion engine; 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 NHs component 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

compliance with the strictest limits for NOx and particle emissions. In a further embodiment of the method it is provided that the combustion

engine is operated at least predominantly with excess air. this makes possible

fuel combustion with high mechanical efficiency.

The invention is explained in more detail below with reference to 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 comprises an internal combustion engine 1 and an exhaust gas cleaning system 2 connected to it. The combustion air required for fuel combustion is supplied to the internal combustion engine 1 via an air supply line 3, which is fed into an intake manifold 4 of the internal combustion engine 1 downstream of a 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, NHs can also be fed directly to the intake manifold 4. Also possible is NH3s direct injection into the individual combustion chambers of internal combustion engine 1, which are also not shown separately here. To improve ignition of the NH3s 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 substance, can be used be provided flammable substance. Corresponding supply means are not shown for reasons of clarity. The amount of the ignition promoter used is relatively small compared to the amount of the actual fuel NHs 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 arranged in the exhaust pipe 9 turbocharger turbine is driven, which in turn via

a shaft, not shown, drives the turbocharger compressor 5 .

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

reduction catalyst.

The catalytic converters 11, 12 and 14 are preferably in the form of, in particular, 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, for example, be a zeolite exchanged with iron and/or copper as the catalytically active substance. The catalytically active substances enable a selective reduction of NOx contained in the exhaust gas with the NH3 used here as a reducing agent, even under oxidizing conditions.

ments.

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 in the form of a honeycomb body through which air flows through the wall and is closed alternately on the inlet and outlet sides, in parallel

running channels formed.

As far as the second SCR catalytic converter 11 is concerned, this is designed according to the invention as a so-called passive SCR catalytic converter. 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, NHs3 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 NH 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 the combustion engine 1.

Depending on the ratio of NHs 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 NHs may 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 (NO2) with the oxygen contained in the exhaust gas of lean-burn internal combustion engine 1. The aim here is an NO/NO2 ratio of around 1 :1, which improves or facilitates the catalytic NOx reduction in the first SCR catalytic converter 14 arranged further downstream. If there is a residual amount of NH: in the exhaust gas, this NH: 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 further downstream

arranged first SCR catalyst 14 is at least largely reduced.

Before exhaust gas flowing through the exhaust 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 NHs 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 is supplied with NH3 at least predominantly in gaseous form. This ensures an even NHs distribution in the exhaust gas, which is why a mixer is not required. 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 emission control system 2. The injector 7 is therefore the only NOx reduction

Agent adding device of the emission control system 2.

A needs-based control of the addition of NHs to the exhaust gas by the injector 15 for the desired complete reduction of NOx contained in the exhaust gas takes place by means of NOx sensors 17, 18 provided signals, 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 NOx content of the exhaust gas flowing into the first SCR catalytic converter 14 to be determined. 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 oxidation catalytic converter 12 and particle filter 13 are combined to form an integral common component, then 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 NH3 can be adjusted

become.

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/NH3 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 may improve the accuracy of NHs dosing.

Overall, the internal combustion engine system according to the invention enables an extremely environmentally friendly operation of a corresponding vehicle. Not only emissions of climate-damaging CO2 are at least largely avoided, but also at least largely emissions of hydrocarbons NOx, NHz3 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, characterized in that the exhaust gas purification system (2) further comprises a second SCR catalytic converter (11) for reducing nitrogen oxides contained in the exhaust gas, the first SCR catalytic converter (14) is connected upstream in terms of flow. 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 to the second SCR catalyst (11) is arranged. 4. Internal combustion engine system according to claim 3, characterized in that the exhaust gas purification system (2) has an oxidation catalyst (12) which is fluidically between the second SCR catalyst (11) and the Particulate filter (13) is arranged. 5. Internal combustion engine system according to one of claims 1 to 4, characterized in that the internal combustion engine (1) as a compression-ignited internal combustion engine is trained. 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, 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). be reduced. 7. Operating method according to claim 6, characterized in that particles contained in the exhaust gas are separated by means of a fluidic between the first SCR catalytic converter (14) and the second SCR catalytic converter (11) arranged particle filter (13) are filtered out of the exhaust gas. 8. Operating method according to claim 6 or 7, characterized in that the internal combustion engine (1) at least predominantly with excess air is operated.