DE102017218655A1 - Process for the regeneration of a particulate filter - Google Patents

Abstract

The present invention relates to an exhaust aftertreatment system for a gasoline engine and a method for regenerating a particulate filter in an exhaust aftertreatment system for a gasoline engine, which reduces the emission of nitrogen oxides during the regeneration of the particulate filter.

Description

The present invention relates to an exhaust aftertreatment system for a gasoline engine and a method for regenerating a particulate filter in an exhaust aftertreatment system for a gasoline engine, which reduces the emission of nitrogen oxides during the regeneration of the particulate filter.

In order to be able to comply with stricter limits for particulate emissions, motor vehicles with gasoline engines are also increasingly being equipped with a particulate filter. As a rule, this is followed by a three-way catalytic converter for the exhaust gas purification.

If a high exhaust backpressure hinders the exhaust emissions too much due to the particle loading, a regeneration of the particulate filter becomes necessary. The regeneration of the filter takes place by combustion of the stored particles. As with any chemical reaction, a certain temperature is needed to burn the accumulated particles. The necessary exhaust gas temperature for a regeneration is at least 500-550 ° C. During the regeneration of the particulate filter, therefore, the engine is operated with a rich mixture, i. the ratio of air and fuel is a maximum of 1. Due to the incomplete combustion of the fuel, reducing conditions prevail in the three-way catalyst ("rich operation"). Under these conditions, ammonia is formed in the three-way catalyst of nitrogen oxides and hydrogen. The more nitrogen oxide is in the raw exhaust gas, the more ammonia is formed in the three-way catalyst.

During the regeneration of the particulate filter, ambient air is introduced into the exhaust system upstream of the particulate filter in order to provide additional oxygen for the combustion of the soot particles deposited in the particulate filter. In the particulate filter, the exhaust gas therefore has an excess of oxygen ("lean operation"). Ammonia is oxidized in the particle filter under these conditions again to nitrogen oxides.

Against this background, the present invention has the object to provide an exhaust gas aftertreatment system for a gasoline engine and a method for regenerating a particulate filter in an exhaust aftertreatment system for a gasoline engine, with which the production of nitrogen oxides during the regeneration of the particulate filter can be reduced.

The DE 10 2011 101 079 A1 discloses a process for the regeneration of nitrogen oxide storage catalysts and a suitably adapted exhaust gas purification system for lean burn engines. Therein, during a regeneration operation of the nitrogen oxide storage catalytic converter, exhaust gas recirculation is completely opened and an exhaust gas recirculation rate is increased.

The DE 199 59 610 A1 discloses a method for heating an exhaust gas catalyst, in particular during idling operation of a runnable internal combustion engine of a vehicle. The heating is preferably carried out after a regeneration phase of the catalyst by switching to a stoichiometric combustion in idle mode, optionally with retarded ignition.

From the EP 1 942 263 B1 goes out a control method for an emission control system. The regeneration method for a diesel particulate filter uses multiple injection to initiate regeneration of the diesel particulate filter.

According to the invention the object is achieved by a method having the features of claim 1 and an apparatus having the features of claim 6. Embodiments of the method and the apparatus emerge from the dependent claims.

The invention relates to a method for regenerating a particulate filter in an exhaust aftertreatment system of a gasoline engine, which comprises a three-way catalytic converter and a particle filter arranged downstream thereof. In the method according to the invention ambient air is introduced into the exhaust aftertreatment system during regeneration before the particulate filter and reduces the formation of nitrogen oxides in the combustion chamber of the gasoline engine by reducing the maximum pressure in the combustion chamber and / or reducing the combustion temperature in the combustion chamber.

By reducing the maximum pressure in the combustion chamber operated during regeneration with a rich mixture and / or reducing the combustion temperature, the formation of nitrogen oxides in the combustion chamber is minimized. As a result, less ammonia is produced in the three-way catalytic converter, which is operated in fat during the regeneration of the particle filter, and less nitrogen oxides are produced in the following lean-burned particulate filter.

During the regeneration of the particulate filter operating points are approached, which minimize the formation of nitrogen oxides in the combustion chamber, so get less nitrogen oxides in the precatalyst.

In one embodiment of the method, the maximum pressure in the combustion chamber of Petrol engine reduced. In one embodiment, the focus of combustion, ie the point in time at which 50% of the fuel mass used is burned, is shifted backwards ("spark retard"). A shift in the focal point of combustion leads to a reduction in the peak pressure in the combustion chamber and thus to a reduction in the formation of nitrogen oxides. In another embodiment, the maximum pressure in the combustion chamber of the gasoline engine is reduced by multiple injection of the fuel or direct injection with a qualitative control (stratified charge method). In another embodiment, the load point of the gasoline engine is shifted, for example by selecting a gear ratio (gear selection), which leads to a higher speed. As a result, the torque requirement is reduced, which also leads to a reduction in the maximum combustion chamber pressure.

In another embodiment of the method, the combustion temperature in the combustion chamber of the gasoline engine is reduced. In one embodiment, this is done by maximizing exhaust gas recirculation (EGR) into the combustion chamber. In one embodiment, the gasoline engine is a direct injection gasoline engine and the maximum exhaust gas recirculation rate is 50%. In another embodiment, the gasoline engine is an intake manifold gasoline engine and the maximum exhaust gas recirculation rate is 20%.

If the air supplied to the combustion chamber admixed with exhaust gas, the oxygen concentration of the mixture decreases. To completely burn the amount of fuel used, less fuel is injected because of the lower oxygen concentration. Accordingly, the calorific value of the mixture and thereby also the reaction rate and the combustion temperature decrease. This effect is supported by the higher heat capacity of the main components of the exhaust gas carbon dioxide and water. This reduces nitrogen oxide production. Cooling the recirculated exhaust gas enhances this effect.

In one embodiment, an external exhaust gas recirculation is used. The exhaust gas is removed from the exhaust tract and fed via a line, a radiator and an exhaust gas recirculation valve to the intake. In one embodiment, the removal of the exhaust gas takes place in front of the turbocharger turbine and the exhaust aftertreatment, the introduction to the intercooler and the throttle valve (high-pressure EGR). In another embodiment, the removal of the exhaust gas takes place after the exhaust aftertreatment, the introduction before the turbocompressor (low-pressure EGR). This eliminates two disadvantages of high pressure EGR. On the one hand, the intake air is not heated by hot exhaust gas and thus reduces the filling, on the other hand, the exhaust gas mass flow is not reduced before the turbine of the exhaust gas turbocharger (ATL), which allows maintaining the high exhaust enthalpy, so that the ATL responds better and a better gas exchange process is possible. In a further embodiment, the recirculated exhaust gas is selectively distributed inhomogeneously in the combustion chamber in order to have a lower proportion of exhaust gas in the core region of the combustion (stratified EGR).

In another embodiment, an internal exhaust gas recirculation is used. In this case, the exhaust gas is sucked in a controlled manner during the intake stroke by an open exhaust valve again.

The invention also provides an exhaust aftertreatment system for a gasoline engine, comprising a three-way catalytic converter and a particle filter arranged downstream thereof, means for controlled supply of ambient air into the exhaust aftertreatment system between three-way catalytic converter and particulate filter, means for controlled exhaust gas recirculation into the combustion chamber the Otto engine, and a control device which is adapted, during regeneration of the particulate filter, the supply of ambient air into the exhaust aftertreatment system and the exhaust gas recirculation into the combustion chamber of the gasoline engine, and / or the fuel injection into the combustion chamber, and / or the ignition timing in the combustion chamber and / or to regulate the load point of the gasoline engine.

The particulate filter may be a wall-flooded ceramic module, for example a honeycomb module with parallel channels whose channel ends are mutually closed, so that the exhaust gas flow from the inflow side through the channel walls of the closed at the rear end channels in the closed at the front end channels and on to Outflow side flows, or a sintered metal filter having closed and folded pockets of porous sintered metal, or be a side-stream deep bed filter, which deposits the soot particles by targeted flow deflections from the exhaust stream.

If appropriate, an oxidation catalytic converter can be arranged in front of the particle filter, ie between the three-way catalytic converter and the particle filter, in order to increase the exhaust gas temperature. In order to achieve a significant increase in the temperature of the exhaust gas on the oxidation catalyst, a sufficient residual oxygen content is necessary in addition to a high concentration of hydrocarbons and carbon monoxide. The hydrocarbon concentration can be greatly increased, for example, by in-engine post-injection or fuel injection into the exhaust gas line through a metering valve arranged upstream of the oxidation catalytic converter. The fuel burns in the oxidation catalyst and can the Raise the exhaust gas temperature so that it is sufficient to ignite the soot deposits in the following particle filter.

In one embodiment, the particulate filter may also be a so-called four-way catalyst. This consists of a provided with a catalytic coating honeycomb wall-flooded ceramic module whose channels are closed at one end. Particles are retained in the channels and catalytically oxidized.

The exhaust aftertreatment system according to the invention comprises means for the controlled supply of ambient air into the exhaust aftertreatment system between three-way catalyst and particulate filter. The means include, for example, a suction device, a control valve and a secondary air supply in the exhaust line upstream of the particulate filter.

The exhaust aftertreatment system according to the invention comprises means for controlled exhaust gas recirculation into the combustion chamber of the gasoline engine. In one embodiment, the means comprise an external exhaust gas recirculation with a removal connection in the exhaust tract, an exhaust gas recirculation line, an exhaust gas cooler, an exhaust gas recirculation valve and an exhaust gas inlet in the intake tract. In one embodiment, the exhaust port is located in front of the turbine of the turbocharger and the exhaust aftertreatment, the exhaust gas inlet to the intercooler and the throttle. In another embodiment, the extraction connection is after the exhaust aftertreatment, the exhaust gas inlet in front of the turbocompressor.

The exhaust aftertreatment system according to the invention comprises a control device which is adapted, during a regeneration of the particulate filter, the supply of ambient air into the exhaust aftertreatment system and the exhaust gas recirculation into the combustion chamber of the gasoline engine, and / or the fuel injection into the combustion chamber, and / or the ignition timing in the combustion chamber and / or to regulate the load point of the gasoline engine.

During the regeneration of the particulate filter, the control device regulates the supply of ambient air into the exhaust gas line in front of the particulate filter, for example via the control of a control valve in the intake tract. The control device thus controls the secondary air supply in the particulate filter. In one embodiment, during the regeneration of the particulate filter, the control device regulates the exhaust gas recirculation into the combustion chamber of the gasoline engine, for example via the control of an exhaust gas recirculation valve in an exhaust gas recirculation line. In another embodiment, the control device regulates the intake of exhaust gas during the intake stroke through an open exhaust valve of the gasoline engine in an internal exhaust gas recirculation. In one embodiment, the control device is configured to set the exhaust gas recirculation rate to a maximum value during a regeneration of the particulate filter, for example 20% for an intake manifold gasoline engine or 50% for a gasoline engine with direct injection.

In one embodiment, the control device is configured to intervene in the engine control of the gasoline engine during a regeneration of the particulate filter, for example to shift the ignition point or the combustion center in the combustion chamber rearward and / or to control a multiple injection of fuel into the combustion chamber and / or the load point of the gasoline engine.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 102011101079 A1 [0006]
• DE 19959610 A1 [0007]
• EP 1942263 B1 [0008]

Claims (10)

A method for regenerating a particulate filter in an exhaust aftertreatment system of a gasoline engine, comprising a three-way catalyst and a downstream arranged particulate filter, wherein ambient air is introduced into the exhaust aftertreatment system during the regeneration before the particulate filter and a formation of nitrogen oxides in a combustion chamber of the gasoline engine through a reduction in the maximum pressure in the combustion chamber and / or a reduction in the combustion temperature in the combustion chamber is reduced Method according to Claim 1 , wherein the reduction of the maximum pressure in the combustion chamber is effected by shifting the combustion center. Method according to Claim 1 or 2 wherein the reduction of the maximum pressure in the combustion chamber is effected by multiple injection of the fuel. Method according to one of Claims 1 to 3 , wherein the reduction of the maximum pressure in the combustion chamber is effected by displacement of the load point of the gasoline engine. Method according to one of Claims 1 to 4 wherein the reduction in the combustion temperature is accomplished by maximizing exhaust gas recirculation into the combustion chamber. Exhaust gas aftertreatment system for a gasoline engine, comprising a three-way catalyst and a downstream arranged particulate filter, means for controlled supply of ambient air in the exhaust aftertreatment system between three-way catalyst and particulate filter, means for controlled exhaust gas recirculation into a combustion chamber of the gasoline engine, and a control device , which is adapted, during a regeneration of the particulate filter, the supply of ambient air into the exhaust aftertreatment system and the exhaust gas recirculation into the combustion chamber of the gasoline engine, and / or a fuel injection into the combustion chamber, and / or the ignition timing in the combustion chamber and / or the load point of the gasoline engine to regulate. Exhaust after-treatment system according to Claim 6 in which the control device is adapted to set an exhaust gas recirculation rate to a maximum value during a regeneration of the particulate filter. Exhaust after-treatment system according to Claim 6 or 7 in which the control device is set up to shift the center of combustion in the combustion chamber to the rear during a regeneration of the particulate filter. Exhaust after-treatment system according to one of Claims 6 to 8th in which the control device is adapted to shift the load point of the gasoline engine during a regeneration of the particulate filter. Exhaust after-treatment system according to one of Claims 6 to 9 in which the control device is adapted to regulate a multiple injection of fuel into the combustion chamber during a regeneration of the particulate filter.