DE102011118766A1 - Spark-ignition engine has purification system for lean exhaust gas, which is arranged in exhaust line of outlet pressure wave supercharger - Google Patents

Abstract

The spark-ignition engine (1) has a pressure wave supercharger (2) and a regulated three-way catalyst (3), where the three-way catalyst is arranged in an exhaust line (4) between the engine exhaust and intake pressure wave supercharger. A purification system for lean exhaust gas is arranged in the exhaust line of an outlet pressure wave supercharger. The lean exhaust gas purification system is a system for selective catalytic reduction (5). An independent claim is included for a method for controlling an exhaust gas temperature in a spark-ignition engine.

Description

The invention describes a gasoline engine in combination with a pressure wave supercharger and a controlled three-way catalytic converter, wherein the three-way catalytic converter is arranged in the exhaust gas line between the engine outlet and the pressure wave supercharger inlet.

From the EP 0 885 352 B1 It is known to provide a gasoline engine in combination with a pressure wave supercharger and a controlled three-way catalyst, wherein the three-way catalyst is arranged between the engine outlet and the pressure wave supercharger inlet and after the pressure wave supercharger follows an oxidation catalyst in the exhaust system. Here are used to control the catalysts, a lambda probe, a temperature sensor and a wastegate flap. This is an Otto engine to be specified, which has both a much higher specific power and a much lower pollutant emissions.

From the EP 0 899 436 B1 is a gasoline engine in combination with a pressure wave machine and a three-way catalyst known, the three-way catalyst is disposed in the outlet of the gasoline engine between the gasoline engine and the exhaust inlet of the pressure wave machine and after the pressure wave machine, an oxidation catalyst is arranged. According to 2 The three-way catalyst may also be divided into two, with a heating device between the two parts. In addition, a diesel engine in combination with a pressure wave machine, a heater and a catalyst is disclosed, wherein the heater acts on the exhaust inlet of the pressure wave machine. The catalyst is an oxidation catalyst. It is located in the outlet of the diesel engine between the diesel engine and the exhaust inlet of the pressure wave machine.

From the DE 101 02 376 B4 there is known a turbocharged direct injection type stratified gasoline engine which is supercharged by means of a turbocharger of variable turbine geometry. In addition, it is disclosed that the variable geometry turbocharger provides additional flexibility that can be used to control NOx emission schedules through improved EGR delivery and exhaust temperature control. At air / fuel ratios beyond stoichiometry, the NOx conversion efficiency of a three way catalyst is greatly reduced. As a result, in lean burn engines, it is often necessary to utilize a lean burn NOx trap or a lean burn NOx catalyst. These devices are most effective within a small temperature window, thus requiring temperature management for the implementation of any lean-mix engine technology. With a variable geometry turbocharger, the temperature of the exhaust gas entering the aftertreatment device can be electronically controlled. In addition, lean NOx traps have a limited capacity and must be periodically purged by homogeneous operation with a rich mixture. In order to minimize the amount of time spent in the purge mode, and thus the increase in fuel consumption, the NOx output of the engine must be reduced as much as possible. A conventional approach to NOx reduction is the use of exhaust gas recirculation. During lean operation, the recirculated exhaust gas consists of air and also burnt gas. As a result, higher exhaust gas recirculation levels must be set to achieve the same amounts of burned gas in the cylinder. When a turbocharger is used, the pressure in the exhaust manifold increases, allowing adequate EGR levels at some operating points. In addition, the document discloses that the engine can also be charged by a pressure wave charger.

Shock wave machines for supercharging engines are well known in the art. In this case, the maximum representable boost pressure of the pressure wave machine is determined by the exhaust gas inlet temperature in the pressure wave supercharger. The higher the inlet temperature, the higher the pressure on the side of the exhaust gas inlet into the cell rotor and thus the resulting boost pressure. At low exhaust gas temperatures, the pressure wave process becomes more and more problematic, and in extreme cases this process can come to a complete standstill.

On the other hand, the rinsing process of the pressure wave machine is limited by the pressure gradient between the exhaust gas outlet and fresh air inlet of the pressure wave machine. It is therefore important that the exhaust gas outlet has the lowest possible counterpressure. Consequently, an exhaust gas purification system should be positioned before the pressure wave load inlet in the exhaust line, if possible, so that the back pressure at the exhaust gas outlet from the pressure wave supercharger is not increased by the exhaust gas purification system. If the exhaust gas purification system is located before the pressure wave input, it heats up better due to the higher exhaust gas temperature. At the same time, however, the exhaust gas purification system now represents a thermal inertia for the pressure wave supercharger and leads to a delay of a temperature increase in front of the pressure wave supercharger. In a load jump, so an engine operation change from part load to full load, as a result, the boost pressure buildup in the pressure wave supercharger is limited by the delayed increase in temperature of the exhaust gas temperature. In addition, the emission levels of a gasoline engine must be controlled even when charging with a pressure wave supercharger, wherein the Exhaust emission standards have already been tightened several times and will also intensify in the future.

It is therefore an object of the present invention to further improve the exhaust gas purification concept of a gasoline engine in combination with a pressure wave supercharger. In particular, it is necessary to design an exhaust gas purification concept adapted to the system-specific requirements of the pressure wave supercharger so as to fall short of the future most stringent exhaust emission limit values (Europe EU6 and / or USA LEV III).

This object is achieved by the invention with the features of claim 1. Accordingly, in a gasoline engine in combination with a pressure wave supercharger and a controlled three-way catalyst, the three-way catalyst in the exhaust line between the engine outlet and pressure wave inlet. According to the invention, a lean exhaust gas cleaning system is arranged downstream of the pressure wave supercharger outlet in the exhaust gas line.

The positioning of the three-way catalyst between the exhaust of the engine and the inlet of the pressure wave supercharger causes the thermal mass to be heated in front of the pressure wave supercharger to draw controllably low catalyst heating requirements. Due to the fact that the lean exhaust gas purification system in the exhaust line is downstream of the pressure wave supercharger outlet, only the three-way catalyst upstream of the pressure wave supercharger needs to contain a high proportion of noble metal for aging protection. Due to the possibility of supplying small quantities of residual gas via the pressure wave charger to the gasoline engine, only small nitrogen oxide emissions occur. The inventively downstream of the pressure wave supercharger system for cleaning lean exhaust gas allows compliance with exhaust limits, even with a lean engine operation. The lean engine operation leads to a desirable consumption reduction. However, the counterpressure by the downstream system for the purification of lean exhaust gas limits the maximum charge air quantity of the pressure wave supercharger.

In a preferred embodiment, the lean exhaust gas purification system is a selective catalytic reduction system. The term Selective Catalytic Reduction (SCR) refers to a technique for the reduction of nitrogen oxides in exhaust gases of, inter alia, engines. The chemical reaction on the SCR catalyst is selective, that is, it is preferable that the nitrogen oxides (NO, NO ₂ ) are reduced, while undesirable side reactions (such as the oxidation of sulfur dioxide to sulfur trioxide) are largely suppressed.

As a rule, ammonia (NH ₃ ), which is admixed with the exhaust gas, is required for the reaction to proceed. The products of the reaction are water (H ₂ O) and nitrogen (N ₂ ). In vehicle technology, the SCR process is used to reduce nitrogen oxide emissions in diesel vehicles. According to the invention, the method is also suitable for the exhaust gas purification of a direct-injection gasoline engine charged with a pressure wave supercharger. The ammonia required for the SCR reaction is not used directly, ie in pure form, but, for example, in the form of an aqueous urea solution, uniformly designated by the industry as AdBlue. This aqueous solution is placed in front of the SCR catalyst in the exhaust line, z. B. by means of metering pump or injector injected. From the urea-water solution caused by a hydrolysis reaction ammonia and CO ₂ . The ammonia thus produced can then react in a special SCR catalyst at the appropriate temperature with the nitrogen oxides in the exhaust gas.

However, it is necessary to control the proper operation of all catalysts in the exhaust system. For monitoring the three-way catalytic converter, an on-board diagnostic concept with 2 probes is already present in the vehicle anyway. If, according to the invention, a lean exhaust gas cleaning system is arranged downstream of the pressure wave supercharger outlet, a further probe for on-board diagnosis is necessary in front of and behind this system, thereby increasing the number of probes to 4. In particular, controlling and monitoring the SCR catalytic converter consuming. However, this must then be accepted to meet the strict emission standards.

In an alternative preferred embodiment, the lean exhaust gas purification system is a nitrogen oxide storage catalyst. The storage catalyst stores in lean driving on the storage component nitrogen oxides. If the storage catalytic converter has reached its permissible filling quantity, the stored nitrogen oxides are desorbed again during a brief, fat driving operation. These nitrogen oxides are then reduced to the coating according to the known 3-way principle. The working range for this memory function is approximately between 200 ° C. and 500 ° C exhaust gas temperature. This work area thus determines the maximum lean driving range of the vehicle. Above this exhaust gas temperature, the storage catalytic converter operates like a 3-way catalytic converter. Its maximum operating temperature is ~ 800 ° C.

In another preferred embodiment, either both a nitrogen oxide storage catalyst and a selective catalytic reduction system may be connected in series or The nitrogen oxide storage catalyst is additionally equipped with an SCR functionality.

Particularly preferably, the pressure wave supercharger arrangement according to the invention can also be used for a control method in which the pressure wave supercharger is controlled so that the pressure wave supercharger enriches the exhaust gas after the pressure wave supercharger outlet with oxygen by purging the exhaust gas with air. As a result, the exhaust gas temperature can be influenced by the Druckwellenladerauslass in terms of thermal management.

In a rich exhaust gas composition, unburned fuel is contained in the exhaust, which may burn by reaction with oxygen. If oxygen is supplied to the rich exhaust gas mixture by flushing with air via the pressure wave supercharger, then the exhaust gas temperature can be increased via an afterburner effect downstream of the pressure wave supercharger outlet. Thus, the pressure wave supercharger can be used to implement a secondary air function to reduce the time to light-off, ie until the start temperature of the located after the pressure wave supercharger lean exhaust system. In particular, the blast loader is controlled so that the blast exhaust gas enriches the exhaust gas for exhaust gas outlet with oxygen when the flue gas temperature in rich exhaust gas composition is lower than that for functioning of the purge system minimum temperature required for lean exhaust gas. This ensures a reliable cleaning operation. Advantageously, can be dispensed with a separate heating or Sekundärluftzuführeinrichtung.

Alternatively, the exhaust gas temperature after the pressure wave supercharger can be lowered by flushing with fresh air to a desired lower temperature. In accordance with the invention, this makes it possible to keep the lean exhaust gas cleaning system located downstream of the pressure wave supercharger within an optimum operating temperature range, in particular, exceeding a predetermined maximum temperature can thus be prevented. According to the invention, a method for controlling an exhaust gas temperature is disclosed in the gasoline engine, wherein the pressure wave supercharger by flushing the exhaust gas with air then enriches the exhaust gas after the Druckwellenladerauslass with oxygen, if in a stoichiometric or lean exhaust gas mixture, the exhaust gas temperature after Druckwellenladerauslass a predetermined temperature range for Cleaning system for lean exhaust exceeds. In the case of a stoichiometric or lean exhaust gas mixture, there is no longer any surplus fuel in the exhaust gas which could still burn. By supplying relatively cold fresh air, the exhaust gas temperature is lowered above the cooler mass flow. The lean exhaust gas cleaning system can thus be operated in its preferred temperature window for a maximum period of time.

The invention is described in more detail below with reference to the figures. Showing:

1 an exhaust system ( 4 ) with a three-way catalyst ( 3 ) in front of a pressure wave loader ( 2 ) and a selective catalytic reduction system ( 5 ) after the pressure wave loader,

2 the exhaust system ( 4 ) with the three-way catalyst ( 3 ) in front of the pressure wave loader ( 2 ) and a nitrogen oxide storage catalyst ( 6 ) after the pressure wave loader ( 2 )

3 an exhaust system ( 4 ) with the three-way catalyst ( 3 ) in front of the pressure wave loader ( 2 ) and the selective catalytic reduction system ( 5 ) as well as the nitrogen oxide storage catalyst ( 6 ) after the pressure wave loader ( 2 ).

1 schematically shows a gasoline engine ( 1 ), at the outlet of which an exhaust gas line ( 4 ). Close to the outlet of the gasoline engine ( 1 ) sits a three-way catalyst ( 3 ). Supercharged gasoline engines currently on the market are only charged in multiple stages with exhaust gas turbochargers, mechanically driven compressors or a combination of both. The close-to-the-engine placement of the three-way catalytic converter ( 3 ) by the pressure wave loader ( 2 ). An energy exchange from a hot gas side ( 21 ), which in the exhaust system ( 4 ) and in the exhaust gas in the direction of arrow from the exhaust line ( 4 ) and the hot gas side ( 21 ) in the direction of the arrow in the exhaust line ( 4 ) leaves again, to a cold gas side ( 20 ), which is flown in the direction of arrow of the ambient air and the cold gas side ( 20 ) in the direction of a charge air line not shown in detail to the gasoline engine ( 1 ) leaves again, takes place at the speed of sound. This results in a response to a turbocharger significantly better, so that a filling of the pressure wave supercharger ( 2 ) does not play such a critical role as in a turbocharger. Consequently, the three-way catalyst ( 3 ) in front of the pressure wave loader ( 2 ) in the exhaust line ( 4 ) to sit. Due to the possibility of extremely close-to-motor connection of the three-way catalyst ( 3 ), the operating temperature of the cleaning system ( 3 ) reached earlier. The three-way catalyst ( 3 ) in front of the pressure wave loader ( 2 ) represents a thermal mass that is based on the exhaust gas temperature before the pressure wave loader ( 2 ), because it always has to be heated first, but this can be countered by means of a heating strategy. To the pressure wave loader ( 2 ) closes according to the invention, a lean exhaust gas purification system ( 5 ), in this case a selective catalytic reduction system. This is also in a modern with a pressure wave loader ( 2 ) supercharged, direct injection gasoline engine ( 1 ) ensures that not only the desired engine performance is provided, but also the legal emission limits are met. Should the exhaust gas temperature after the pressure wave loader ( 2 ) are not sufficient to the so-called light-off temperature, ie the starting temperature of the lean exhaust gas purification system ( 5 ), the exhaust gas temperature can be increased by an afterburn effect by purging the exhaust gas in the pressure wave supercharger ( 2 ) with air from the cold gas side ( 20 ) are increased to enrich the exhaust gas with oxygen.

2 also shows the gasoline engine ( 1 ) with subsequent exhaust gas line ( 4 ) and the pressure wave loader ( 2 ) with hot gas side ( 21 ) and cold gas side ( 20 ). In front of the pressure wave loader ( 2 ) sits the three-way catalyst ( 3 ). The lean exhaust gas purifying function is controlled by a nitrogen oxide storage catalyst ( 6 ) behind the blast loader ( 2 ) in the exhaust line ( 4 ) sits.

In 3 follows the system for selective catalytic reduction ( 5 ) nor the nitrogen oxide storage catalyst ( 6 ) at. Through the three-way catalyst ( 3 ), the selective catalytic reduction system ( 5 ) and the nitrogen oxide storage catalyst ( 6 ), that of the gasoline engine ( 1 ) exhaust gas cleaned while it through the pressure wave loader ( 2 ) about the energy exchange between hot gas side ( 21 ) and cold gas side ( 22 ) is used to compress the charge air.

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

• EP 0885352 B1 [0002]
• EP 0899436 B1 [0003]
• DE 10102376 B4 [0004]

Claims (7)

Gasoline engine ( 1 ) in combination with a pressure wave charger ( 2 ) and a controlled three-way catalyst ( 3 ), wherein the three-way catalyst ( 3 ) in the exhaust line ( 4 ) is arranged between the engine outlet and the pressure wave load inlet, characterized in that after the pressure wave loader outlet in the exhaust gas line ( 4 ) a cleaning system ( 5 . 6 ) is arranged for lean exhaust gas. Gasoline engine ( 1 ) according to claim 1, characterized in that the lean exhaust gas purification system comprises a selective catalytic reduction system ( 5 ). Gasoline engine ( 1 ) according to claim 1, characterized in that the lean exhaust gas purification system comprises a nitrogen oxide storage catalyst ( 6 ). Gasoline engine ( 1 ) according to any one of the preceding claims, characterized in that the lean exhaust gas purification system comprises a nitrogen oxide storage catalyst ( 6 ) in combination with a selective catalytic reduction ( 5 ). Method for controlling an exhaust gas temperature in the gasoline engine ( 1 ) according to one of the preceding claims, characterized in that the pressure wave loader ( 2 ) is controlled so that the pressure wave loader ( 2 ) is enriched with oxygen by purging the exhaust gas with air, the exhaust gas to the Druckwellenladerauslass, whereby the exhaust gas temperature is influenced after the Druckwellenladerauslass. Method for controlling the exhaust gas temperature in the gasoline engine ( 1 ) according to claim 5, characterized in that the pressure wave loader ( 2 ) is enriched by flushing the exhaust gas with air, the exhaust gas after the Druckwellenladerauslass with oxygen when, in a rich exhaust gas composition, the exhaust gas temperature in the arranged after the Druckwellenladerauslass cleaning system ( 5 . 6 ) for lean exhaust gas is lower than that for functioning of the cleaning system ( 5 . 6 ) required for lean exhaust gas minimum temperature. Method for controlling the exhaust gas temperature in the gasoline engine ( 1 ) according to claim 5, characterized in that the pressure wave loader ( 2 ) is enriched by flushing the exhaust gas with air, the exhaust gas to the Druckwellenladerauslass with oxygen when, for a stoichiometric or lean exhaust gas mixture, the exhaust gas temperature after the Druckwellenladerauslass a predetermined temperature range for the arranged after the Druckwellenladerauslass cleaning system ( 5 . 6 ) for lean exhaust gas.

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