DE102017219508B4 - Method for enriching the exhaust gas of a direct-injection internal combustion engine with reducing agent - Google Patents

Abstract

A method for enriching the exhaust gas of a direct injection internal combustion engine, wherein each cylinder is equipped with an injector having a movable closure body, the positively controlled in the context of injection nozzle openings for introducing fuel into the cylinder with a fuel supply system connects and thus releases, wherein the Closure body separates the nozzle openings in a rest position from the fuel supply system and connects in a working position with the fuel supply system, in which at least one post-injection is carried out, wherein the introduced by Nacheinspritzen amount of _fuel .DELTA.m _{fuel enrich} enrichment enrichment is used.
An improved method for enrichment of exhaust gas is to be shown.
This is achieved with a method in which a plurality of post-injections are performed, which overlap and are therefore not hydraulically separated from each other, but form a cohesive common injection process, in such a way that
- The closure body is transferred to initiate the common injection process from the rest position to a working position,
- The closure body during the common injection process between different working positions repeatedly oscillates, and
- The closure body is transferred to the completion of the common injection process again in the rest position.

Description

The invention relates to a method for enriching the exhaust gas of a direct-injection internal combustion engine with a reducing agent, wherein the at least one cylinder comprehensive internal combustion engine Abgasabführsystem for discharging the exhaust gas and at least one arranged in this Abgasabführsystem exhaust aftertreatment system, which at least temporarily requires a supply of reducing agent, and Each cylinder of the internal combustion engine is equipped for direct introduction of fuel into a cylinder-associated combustion chamber with an injection nozzle, which positively controls in the context of an injection combustion chamber side nozzle openings of the injection nozzle for the purpose of introducing fuel into the combustion chamber with a fuel supply system and thus releases wherein the movable closure body separates the nozzle openings in a rest position from the fuel supply system and thus obstructed and connected in a working position with the fuel supply system, in which after the introduction of an intended combustion quantity of fuel .DELTA.m _{fuel, burn} at least one post-injection is made, wherein the injected _fuel injection amount Δm _{fuel, enrich is used} as a reducing agent for exhaust gas enrichment.

Internal combustion engines are used for example as motor vehicle drives. In the context of the present invention, the term internal combustion engine relates to diesel engines and gasoline engines, but also to hybrid internal combustion engines, i. Internal combustion engines, which are operated with a hybrid combustion method, and hybrid drives, which comprise at least one further torque source for driving a motor vehicle in addition to the internal combustion engine, for example a drive-connected to the engine or drive connected electric machine, which instead of the internal combustion engine or in addition to Internal combustion engine gives off power.

In the development of internal combustion engines, efforts are constantly being made to minimize fuel consumption and reduce pollutant emissions.

The problem is the fuel consumption, especially in gasoline engines. The reason for this is the principle of operation of the traditional gasoline engine, which is operated with a homogeneous fuel-air mixture, wherein the adjustment of the desired performance by changing the filling of the combustion chamber takes place, i. by quantity regulation. By adjusting a throttle valve provided in the intake tract, the pressure of the intake air downstream of the throttle valve can be more or less reduced. With a constant combustion chamber volume, the air mass, i. E. the quantity will be set. However, the quantity control by means of throttle valve has thermodynamic disadvantages due to the throttle losses in the partial load range.

One approach to dethrottling the Otto engine process is to develop hybrid combustion processes based on the adoption of technical features of the traditional diesel engine process, characterized by air compression, inhomogeneous mixing, auto-ignition and quality control. The low fuel consumption of the diesel engine results, among other things, from the quality control, in which the load is controlled by the injected fuel quantity.

The injection of fuel directly into the combustion chamber of the cylinder is regarded as a suitable measure for dethrottling the Otto engine operating method, with which the fuel consumption can be significantly reduced even in gasoline engines. In certain operating areas, then a quality control is used.

With the direct injection of the fuel into the combustion chamber can be realized in particular a stratified combustion chamber charge, which can contribute significantly to the dethrottling of the Otto engine operating method, since the internal combustion engine with the help of the stratified operation can be emaciated very far, which is particularly in part-load operation, i. In the lower and middle load range, when only small amounts of fuel are to be injected, it offers thermodynamic benefits.

The layer charge is characterized by a very inhomogeneous combustion chamber charge which can not be characterized by a uniform air ratio, but has both lean (λ> 1) mixture parts and rich (λ <1) mixture parts, wherein in the region of the ignition device an ignitable fuel air Mixture with comparatively high fuel concentration is present.

The inhomogeneity of the fuel-air mixture is also a reason that the known from the diesel engine process particle emissions in direct-injection gasoline engine are also relevant, whereas these emissions have almost no significance in traditional gasoline engine.

A direct injection internal combustion engine is also the subject of the present invention.

For the injection of the fuel, the mixture preparation in the combustion chamber, namely the mixing of air and fuel and the treatment including the evaporation, and the ignition of the treated mixture is comparatively little time available.

Since the direct injection of the fuel into the combustion chamber only little time for the preparation of an ignitable and combustible fuel-air mixture available direct injection internal combustion engines are much more sensitive to changes and deviations in the mixture formation, especially in the injection, as conventional internal combustion engines with manifold injection.

In principle, the aim is to distribute the fuel introduced into the cylinder within the scope of an injection as far as possible and evenly in the combustion chamber in the available time, and to homogenize the fuel-air mixture as far as possible before initiating the ignition. This advantageously affects the combustion and the formation of the pollutants, in particular the emissions of unburned hydrocarbons and soot, and also reduces fuel consumption.

In a direct injection gasoline engine, the mixture formation is further complicated by the fact that the initiation of the spark ignition an ignition device, such as a spark plug, is to be provided, and the injection nozzle is tuned to the ignition in the combustion chamber to arrange. Due to the very limited space available, the injector often becomes off-centered, i. spaced from the longitudinal axis of the cylinder arranged in the cylinder head.

To improve the mixture formation in direct-injection internal combustion engines further measures are required.

In the prior art, internal combustion engines are equipped with various exhaust aftertreatment systems to reduce pollutant emissions.

In gasoline engines, catalytic reactors are used which, using catalytic materials which increase the speed of certain reactions, ensure oxidation of HC and CO even at low temperatures. If, in addition, nitrogen oxides NO _x are to be reduced, this can be achieved by using a three-way catalytic converter, which, however, requires a narrow-flow stoichiometric operation (λ≈1) of the gasoline engine. In this case, the nitrogen oxides NO _x are reduced by means of the existing unoxidized exhaust gas components, namely the carbon monoxide CO and the unburned hydrocarbons HC, wherein at the same time these exhaust gas components are oxidized.

Usually and in the context of the present invention, the air ratio λ is defined as the ratio of the air mass actually supplied to the at least one cylinder of the internal combustion engine to the stoichiometric air mass which would be required to completely oxidize the fuel mass supplied to the at least one cylinder (λ _stöch = 1).

In internal combustion engines which are operated with an excess of air, for example direct injection diesel engines or direct injection gasoline engines, the nitrogen oxides NO _{x present} in the exhaust gas can in principle not be reduced due to the lack of reducing agents.

As a result, an exhaust aftertreatment system for reducing nitrogen oxides must be provided, for example, a storage catalyst, also referred to as LNT. The nitrogen oxides are first adsorbed in the catalyst during lean operation (λ> 1) of the internal combustion engine, i. collected and stored, to then be reduced during a regeneration phase, for example by means of a substoichiometric operation (λ <1) of the internal combustion engine with lack of oxygen, the unburned hydrocarbons HC and the carbon monoxide CO serving as reducing agent in the exhaust.

Further internal engine possibilities for enriching the exhaust gas with reducing agent, in particular with unburned hydrocarbons, provide the exhaust gas recirculation (EGR) and the throttling of the charge air in the intake system. Both measures reduce the guided through the internal combustion engine charge air mass or fresh air mass and thereby reduce the air ratio λ. It is enriched by reducing the air mass provided.

With respect to the stoichiometric operation (λ <1) of the internal combustion engine, i. enrichment, it must be borne in mind that the initiation and maintenance of sub-stoichiometric operation can not always or only with restrictions be realized. The reasons for this are manifold and vary depending on the instantaneous load with which the internal combustion engine is operated.

At low loads, stable combustion in rich operation can not be ensured, especially when using compression ignition. It can lead to misfires or incomplete combustion of the mixture. The result is an undesirably high pollutant emission, in particular unburned hydrocarbons HC. In the middle load range often a load change occurs. The transient operating conditions make it difficult to maintain a constant air ratio and make individual enrichment impossible. In the range of higher, higher and highest loads, a stoichiometric operation is usually regulated by the maximum permissible exhaust gas temperature, the exhaust gas temperature is often limited by provided in Abgasabführsystem components or their thermal capacity is limited, for example by the turbine of an exhaust gas turbocharger, an exhaust aftertreatment system or the exhaust gas recirculation. It should be noted in this context that the exhaust gas temperature usually increases when enriched.

An enrichment of the exhaust gas with unburned hydrocarbons, also called HC enrichment, can also be realized by means of post-injection of additional fuel into at least one cylinder of the internal combustion engine. In this case, the nacheingespritzte fuel should not be ignited in the combustion chamber by the still running main combustion or by - even after completion of the main combustion - high combustion gas temperatures, but are introduced unburned during the charge exchange in the Abgasabführsystem upstream of the catalyst.

A method for enriching the exhaust gas by means of post-injection is also an object of the present invention, wherein the introduced by Nacheinspritzen _fuel amount .DELTA.m _{fuel, enrich is used} as a reducing agent for exhaust gas enrichment.

Internal combustion engines utilizing post-injection are inherently susceptible to dilution or contamination of the oil by unburned hydrocarbons. Depending on the quantity of the nacheingespritzten fuel and the injection timing, passes a more or less large proportion of the nacheingespritzten fuel on the cylinder inner wall, where it mixes with the adhering oil film and thus contributes to the oil dilution.

In practice, attempts are made to avoid or reduce wall wetting and the associated oil dilution by reducing the penetration depth of the injection jets during post-injection. The penetration depth can be controlled via the fuel pressure in front of the injection valve, the so-called rail pressure, and reduced by reducing or restricting the fuel mass or the fuel mass flow, whereby the mass flow via the opened nozzle opening can be lowered by shortening the opening duration, ie the nozzle opening is closed again before the mass flow increases or increases too much (see also 1a and 1b) , It should be noted in this context that the injector regularly requires a certain minimum rail pressure for stable operation without malfunction so that the penetration depth can not be arbitrarily reduced by lowering the rail pressure.

The German patent application DE 10 2005 054 387 A1 describes a method for the regeneration of a particulate filter, in which an enrichment of the exhaust gas with fuel by means of post-injection is realized. The post-injection takes place at intervals in order to avoid or reduce oil dilution. That is, the HC enrichment of the exhaust gas takes place by means of several post-injections of fuel into the combustion chamber of the cylinder, wherein the post-injections spaced from each other, ie hydraulically separated from each other (see also 1b) , In the preceding combustion, fuel is burned which has been introduced into the combustion chamber as part of a pre-injection, a main injection and a post-injection.

1a shows a variant according to the prior art, in which the fuel is introduced for the purpose of exhaust gas enrichment by means of a single post-injection into the combustion chamber, the rapidly increasing large mass flow due to the large penetration depth has a significant wall wetting and a noticeable oil dilution result. According to the in 1b illustrated concept, an equal amount of fuel in four intervals, ie introduced into four smaller, spaced-apart post-injection, with much smaller mass flows and thus lower penetration depths can be realized.

That in the DE 10 2005 054 387 A1 revealed and in 1b illustrated concept of exhaust gas enrichment proves to be problematic when a relatively large injection of fuel in a relatively short injection window.

The German patent application DE 10 2015 117 826 A1 describes a method for post injection of fuel, in which the Penetration force of the fuel is increased in the context of post-injection against the penetration force of the fuel in the main injection, if the speed of the internal combustion engine is equal to or greater than a first predetermined speed, whereas the penetration force of the fuel in the post-injection compared to the penetration force of the fuel in the frame the main injection is reduced if the rotational speed of the internal combustion engine is lower than a second predetermined rotational speed. This procedure is intended to enable the use of the post-injection in a more effective manner, wherein in particular the charge movement generated by the post-injection in the combustion chamber is influenced in an advantageous manner and dependent on the rotational speed. The German patent application DE 10 2015 000 590 A1 describes a method in which a pilot injection and a post-injection is carried out in order to realize the most advantageous distribution of the fuel in the combustion chamber. The fuel introduced into the combustion chamber as part of the post-injection should not ignite until the associated piston has passed top dead center and is in the expansion phase, with the combustion of the fuel introduced into the combustion chamber as part of the pre-injection already initiated.

The German patent application DE 10 2010 014 824 A1 describes a method in which the injection depth of the injection jet of a direct injection internal combustion engine is adjusted or varied as needed, that is selectively reduced for selected injection events. This is achieved by adjusting the Injektornadelhubes in such a way that the injector is only partially opened. By this measure, a wetting of the combustion chamber inner wall during certain operating phases should be avoided or prevented.

The German patent application DE 10 2012 018 954 A1 The object of the invention is to inject fuel into at least one cylinder in order to support the regeneration of a particle filter arranged downstream of an oxidation catalytic converter in the exhaust gas tract. The control of the valve needle of the associated injection valve takes place in dependence on the temperature of the oxidation catalyst.

A storage catalyst is just one example of an exhaust aftertreatment system that requires, at least temporarily, a supply of reductant. Instead of a storage catalytic converter or in addition to a storage catalytic converter, a selective catalytic converter, which is also referred to as an SCR catalytic converter, can be provided to reduce the nitrogen oxides. With regard to the supply of reducing agent, what has been said for the storage catalytic converter applies. The reducing agents used in addition to unburned hydrocarbons and ammonia NH ₃ and urea to selectively reduce the nitrogen oxides. The latter reducing agents are introduced specifically into the exhaust gas, ie directly into the Abgasabführsystem. However, due to the toxicity of ammonia and the fact that not only nitrogen oxides but also ammonia enter the environment in the event of a malfunction of an SCR catalyst, it is more advantageous to use fuel as a reducing agent. An additional container for storing reducing agent is omitted when fuel is used for reduction.

Against the background of the above, it is the object of the present invention to provide an improved method for enriching the exhaust gas of a direct-injection internal combustion engine with a reducing agent according to the preamble of claim 1.

• - der bewegliche Verschlusskörper zur Einleitung des zusammenhängenden gemeinsamen Einspritzvorganges aus der Ruheposition in eine Arbeitsposition überführt wird,
• - der bewegliche Verschlusskörper während des zusammenhängenden gemeinsamen Einspritzvorganges zwischen unterschiedlichen Arbeitspositionen mehrfach oszilliert, und
• - der bewegliche Verschlusskörper zur Beendigung des zusammenhängenden gemeinsamen Einspritzvorganges wieder in die Ruheposition überführt wird.

This object is achieved by a method for enriching the exhaust gas of a direct-injection internal combustion engine with a reducing agent, wherein the at least one cylinder comprehensive internal combustion engine has a Abgasabführsystem for discharging the exhaust gas and at least one arranged in this Abgasabführsystem exhaust aftertreatment system, which at least temporarily requires a supply of reducing agent has and each cylinder of the internal combustion engine is equipped for directly introducing fuel into a cylinder-associated combustion chamber with an injection nozzle having a movable closure body which positively connects in the context of an injection combustion chamber side nozzle openings of the injection nozzle for introducing fuel into the combustion chamber with a fuel supply system and thus releases, wherein the movable closure body separates the nozzle openings in a rest position from the fuel supply system and thus blocked and connected in a working position with the fuel supply system, in which at least one post-injection is carried out after the introduction of an intended combustion amount of fuel .DELTA.m _{fuel, burn} , wherein the introduced by Nacheinspritzen amount of _fuel .DELTA.m _{fuel, enrich is used} as a reducing agent for exhaust gas enrichment, and characterized in that a plurality of post-injections are made, which overlap and are therefore not hydraulically separated from each other, but form a cohesive common injection process, in such a way that

• - The movable closure body is transferred to initiate the cohesive joint injection process from the rest position to a working position,
• - The movable closure body during the cohesive common injection process between different working positions repeatedly oscillates, and
• - The movable closure body is transferred to the completion of the coherent common injection process again in the rest position.

According to the method of the invention, several post-injections are made which overlap. The series of post-injections according to the invention forms a cohesive joint injection process, wherein the movable closure body is in the rest position only at the beginning and at the end of the cohesive joint injection process. During the coherent common injection process, the movable closure body assumes different working positions, between which the closure body oscillates several times. That is, the post-injections of the series according to the invention are not hydraulically separated from each other, but rather are hydraulically connected to each other. The fuel flow into the cylinder is increased and decreased during the post-injection, but never interrupted, ie lowered to zero.

With the method according to the invention for enrichment of the exhaust gas, a comparatively short fuel quantity can be introduced into a cylinder in a comparatively short injection window and this while the fuel mass flow is limited.

The oscillating closure body ensures that the mass flow is lowered via the released nozzle openings before it grows too much, i. gets too big. As a result, the penetration depth of the injection jets during post-injection can be reduced or limited. As a result, wall wetting and associated oil dilution is avoided or reduced, thereby significantly reducing emissions of unburned hydrocarbons as well.

The oscillating closure body results in a fluctuating mass flow, which in turn causes the fuel to enter the combustion chamber via the nozzle opening at a changing speed from the injection nozzle. Fuel masses or fuel droplets of different speed collide with each other in the combustion chamber, whereby the homogenization of the fuel-air mixture, in particular the atomization and the evaporation, driven forward, i. is supported.

With the method according to the invention, the object underlying the invention is achieved, namely an improved method for enriching the exhaust gas of a direct-injection internal combustion engine with a reducing agent according to the preamble of claim 1.

According to the invention, additional injection of additional fuel takes place in at least one cylinder of the internal combustion engine, preferably in each cylinder of the internal combustion engine.

The fuel supply system may include a pump, a storage container, i. a fuel storage, and / or a fuel line, for example, the common supply line of a common rail system include. That is based in the context of the present invention on the separation of the fuel supply system, is justified by the fact that to complete the injection process, the openings are not closed regularly in the strict sense, but often only separated from the fuel supply.

The closure body, for example the spherical tip of a nozzle needle, may be actuated electromagnetically, piezoelectrically or otherwise, i. moved and transferred from one position to another position, the closure body can take several working positions regularly. The closure body does not necessarily have to be translationally displaced. A different, for example non-linear displacement of the closure body is possible in individual cases.

Further advantageous embodiments of the method according to the invention are discussed in connection with the subclaims.

For enriching the exhaust gas of a direct injection internal combustion engine in which each cylinder is associated with a piston which oscillates between a top dead center OT and a bottom dead center UT, thereby rotating a crankshaft of the internal combustion engine, embodiments of the method are advantageous, which are characterized that the exhaust gas enrichment is carried out when the piston is in a crank angle window between 110 ° CA after TDC and 160 ° CA after TDC after initiation of combustion.

Advantageous in this connection are embodiments of the method in which the exhaust gas enrichment is carried out when the piston is located after the initiation of combustion in a crank angle window between 120 ° CA to TDC and 150 ° CA to TDC.

Advantageous embodiments of the method in which the exhaust gas enrichment is performed when the piston is after the initiation of combustion in a crank angle window between 120 ° CA to TDC and 140 ° CA to TDC or between 125 ° CA to TDC and 135 ° CA. located.

For enrichment of the exhaust gas of a direct-injection internal combustion engine in which each cylinder has at least one outlet opening for discharging the exhaust gases via Abgasabführsystem which is opened in the context of a charge exchange for an opening duration .DELTA.t _max , embodiments of the method are advantageous, which are characterized in that the exhaust gas enrichment is performed when the at least one outlet opening is closed.

Also advantageous in this connection are embodiments of the method in which the exhaust gas enrichment is initiated when the at least one outlet opening is closed.

For enrichment of the exhaust gas of a direct-injection internal combustion engine in which each cylinder has at least one outlet opening for discharging the exhaust gases via Abgasabführsystem which is opened in the context of a charge exchange for an opening duration .DELTA.t _max , embodiments of the method are advantageous, which are characterized in that the exhaust gas enrichment is performed when the at least one outlet opening is opened.

Advantageous embodiments of the method in which the movable closure body is controlled during the cohesive joint injection process in such a way that a predetermined maximum fuel mass flow (.DELTA.m _fuel / At) _{max is} not exceeded.

In this context, embodiments of the method are advantageous in which the maximum fuel mass flow (Δm _fuel / Δt) _max is determined taking into account a penetration depth of a fuel jet emerging from a nozzle opening and entering the combustion chamber.

Also advantageous in this context are embodiments of the method in which the fuel mass flow .DELTA.m _fuel / .DELTA.t is varied several times by means of oscillation of the movable closure body during the coherent common injection process, that is at least twice varied.

The stronger the variation in the fuel mass flow, the more pronounced or violent is the collision of the fuel particles or the fuel masses in the combustion chamber and the effect which is intended or intended to be achieved according to the invention.

In this connection, further advantageous embodiments of the method are those in which the fuel mass flow Δm _fuel / Δt is modeled in a predeterminable manner using the movable closure body during the coherent common injection process. According to this variant of the method, the course of the mass flow Δm _fuel / Δt over the time t or over the injection duration is arbitrarily, ie freely designed.

Embodiments of the method in which the movable closure body changes the direction of its movement at least five times during the cohesive common injection process and the oscillation are advantageous.

Embodiments of the method in which the movable closure body changes the direction of its movement at least seven times during the coherent joint injection process and the oscillation are advantageous.

Embodiments of the method in which the movable closure body changes the direction of its movement at least nine times during the cohesive common injection process and the oscillation are advantageous.

Embodiments of the method in which the movable closure body changes the direction of its movement at least eleven times or at least thirteen times during the cohesive common injection process and during the oscillation are advantageous.

Advantageous embodiments of the method in which the movable closure body is displaced translationally during the coherent common injection process and the oscillating.

In the case of an injection nozzle which opens inward, a nozzle needle is regularly displaced translationally in order to transfer a closure body arranged at the combustion chamber end of the nozzle needle from the rest position into a working position and vice versa. In the working position, the closure body often releases a blind hole and thus connects the outgoing of the blind hole channels of the nozzle openings with the fuel supply system of the internal combustion engine.

Also advantageous are embodiments of the method in which the injection nozzle is equipped with a displaceable in the direction of a longitudinal axis in a nozzle needle guide nozzle needle, wherein the nozzle needle is connected at a free end to the movable closure body.

Advantageous embodiments of the method, in which as the exhaust aftertreatment system for reducing the nitrogen oxides Storage catalyst is used. Reference is made to the statements already made.

During the regeneration phase, the nitrogen oxides (NO _x ) are released and essentially converted into nitrogen dioxide (N ₂ ), carbon dioxide (CO ₂ ) and water (H ₂ O). The temperature of the storage catalyst should preferably be in a temperature window between 200 ° C and 450 ° C, so that on the one hand a rapid reduction is ensured and on the other hand no desorption takes place without converting the re-released nitrogen oxides NO _x , which can be triggered by excessive temperatures.

One difficulty with the use of a storage catalyst results from the sulfur contained in the exhaust gas, which is also adsorbed and must be removed regularly in a so-called desulfurization. For this purpose, the storage catalytic converter must be heated to high temperatures, usually between 600 ° C. and 700 ° C., and supplied with a reducing agent, for example unburned hydrocarbons.

Embodiments of the method in which a selective catalyst is used as the exhaust aftertreatment system for reducing the nitrogen oxides are advantageous. Reference is made to the statements already made.

Embodiments of the method are advantageous in which a particulate filter arranged in the exhaust-gas removal system is used as the exhaust-gas aftertreatment system, which at least temporarily requires a supply of reducing agent. Reference is made to the statements already made.

In order to minimize the emission of soot particles, so-called regenerative particle filters can be used which filter out and store the soot particles from the exhaust gas, wherein these soot particles are intermittently burned as part of a regeneration of the filter. For this purpose, oxygen or an excess of air in the exhaust gas is required to oxidize the soot in the filter, which can be achieved for example by a superstoichiometric operation (λ> 1) of the internal combustion engine.

The high temperatures of about 550 ° C for regeneration of the particulate filter in the absence of catalytic support are achieved in operation only at high loads and high speeds. Therefore, additional measures must be used to ensure regeneration of the filter under all operating conditions.

The heating of the particulate filter can be done by post injection of additional fuel into the combustion chamber, wherein the nacheingespritzte fuel is not oxidized or burned in the combustion chamber, but rather in the Abgasabführsystem, so that the exhaust gas temperature is raised upstream of the particulate filter or in the particulate filter.

Embodiments in which the injection nozzle has at least five or at least six or at least seven or at least eight combustion chamber-side nozzle openings are advantageous. The more openings are provided, the more spacious the fuel can be distributed in the combustion chamber and the more effectively the fuel-air mixture can be homogenized.

The number of nozzle openings also depends on the amount of fuel that is to be introduced into a cylinder, but in particular also on the installation position of the injection nozzle in the cylinder and the geometry of the combustion chamber in the individual case.

Advantageous embodiments of the method in which the ignition of the fuel-air mixture is initiated by means of auto-ignition.

Embodiments of the method may also be advantageous in which the ignition of the fuel-air mixture is initiated by means of spark ignition.

• 1a in einem Diagramm den Massenstrom Δm_fuel/Δt über der Zeit t für ein Verfahren zur Anreicherung des Abgases mit Kraftstoff mittels Nacheinspritzen gemäß dem Stand der Technik,
• 1b in einem Diagramm den Massenstrom Δm_fuel/Δt über der Zeit t für ein Verfahren zur Anreicherung des Abgases mit Kraftstoff mittels Nacheinspritzen gemäß der DE 10 2005 054 387 A1 ,
• 2a in einem Diagramm den Massenstrom Δm_fuel/Δt über der Zeit t gemäß einer ersten Ausführungsform des erfindungsgemäßen Verfahrens zur Anreicherung des Abgases mit Kraftstoff mittels Nacheinspritzen,
• 2b in einem Diagramm den Massenstrom Δm_fuel/Δt über der Zeit t gemäß einer zweiten Ausführungsform des erfindungsgemäßen Verfahrens zur Anreicherung des Abgases mit Kraftstoff mittels Nacheinspritzen, und
• 2c in einem Diagramm den Massenstrom Δm_fuel/Δt über der Zeit t gemäß einer dritten Ausführungsform des erfindungsgemäßen Verfahrens zur Anreicherung des Abgases mit Kraftstoff mittels Nacheinspritzen.

In the following, the invention will be described with reference to three variants of the method according to the invention and according to FIGS 1a . 1b . 2a . 2 B and 2c described in more detail. Hereby shows:

• 1a in a diagram, the mass flow Δm _fuel / At over time t for a method for enriching the exhaust gas with fuel by means of post-injection according to the prior art,
• 1b in a diagram, the mass flow .DELTA.m _fuel / .DELTA.t over the time t for a method for enriching the exhaust gas with fuel by means of post-injection according to the DE 10 2005 054 387 A1 .
• 2a in a diagram the mass flow Δm _fuel / Δt over the time t according to a first embodiment of the method according to the invention for enriching the exhaust gas with fuel by means of post-injection,
• 2 B in a diagram, the mass flow .DELTA.m _fuel / .DELTA.t over time t according to a second embodiment of the inventive method for enriching the exhaust gas with fuel by means of post-injection, and
• 2c in a diagram, the mass flow Δm _fuel / At over time t according to a third embodiment of the method according to the invention for enriching the exhaust gas with fuel by means of post-injection.

The 1a and 1b have already been discussed in connection with the prior art, which is why reference is made at this point to the statements made at the outset. The fuel mass flow Δm _fuel / Δt over time t is shown in a diagram, the time t being plotted on the abscissa and the fuel mass flow Δm _fuel / Δt plotted on the ordinate.

In the preceding combustion, fuel is burned which has been introduced into the combustion chamber as part of a pre-injection, a main injection and a post-injection.

2a shows in a diagram the mass flow Δm _fuel / Δt over the time t according to a first embodiment of the method according to the invention for enriching the exhaust gas with fuel by means of post-injection. It should only be complementary to the 1a and 1b For this reason, reference is made to FIGS 1a and 1b as well as the corresponding description. Employee comparisons refer to the process variant according to 1b ,

According to the in 2a illustrated method variant four overlapping post-injections are made, which are hydraulically connected to each other and form a coherent common injection process.

The movable closure body of the injector used oscillates during the cohesive joint injection process and changes the direction of its movement seven times during oscillation.

By means of the four overlapping post-injections, an almost equal amount of fuel as with the in 1b injected concept presented. To introduce the fuel but much less time is needed. That is, the injection window can be significantly shortened without the mass flow and thus the penetration depth of the injection jets would have to be increased disadvantageously.

2 B shows in a diagram the mass flow Δm _fuel / Δt over the time t according to a second embodiment of the method according to the invention for enriching the exhaust gas with fuel by means of post-injection. It should only be complementary to the 1a and 1b For this reason, reference is made to FIGS 1a and 1b as well as the corresponding description. Employee comparisons refer to the process variant according to 1b ,

According to the in 2 B illustrated method variant ten overlapping post-injections are made, which are hydraulically connected to each other and form a coherent common injection process.

The movable closure body of the injector used oscillates during the cohesive common injection process and changes the direction of its movement twenty-one times during oscillation.

By means of the ten overlapping post-injections, a larger quantity of fuel is injected at the same time, ie in an equal-size injection window, than at the in 1b shown concept without the mass flow and thus the penetration depth of the injection jets would have to be increased.

2c shows in a diagram the mass flow Δm _fuel / Δt over the time t according to a third embodiment of the method according to the invention for enriching the exhaust gas with fuel by means of post-injection. It should only be complementary to the 1a and 1b For this reason, reference is made to FIGS 1a and 1b as well as the corresponding description. Employee comparisons refer to the process variant according to 1b ,

According to the in 2c shown method variant again ten overlapping post-injections are made, which are hydraulically connected to each other and form a coherent common injection process.

The movable closure body of the injector used oscillates during the cohesive common injection process and changes the direction of its movement twenty-one times during oscillation.

By means of the ten overlapping post-injections, an equal amount of fuel is injected at the same time, ie in an equal-size injection window, as in the case of FIG 1b illustrated concept, wherein the mass flow and thus the penetration depth of the injection jets is advantageously reduced.

LIST OF REFERENCE NUMBERS

° CA

Degree crank angle

Δm _{fuel, burn}

intended for the combustion amount of fuel

Δm _{fuel, enrich}

by fuel injection introduced amount of fuel for exhaust gas enrichment

Δm _fuel / Δt

Fuel mass flow

(Δm _fuel / Δt) _max

predefinable maximum fuel mass flow

Claims (17)

Method for enriching the exhaust gas of a direct-injection internal combustion engine with a reducing agent, wherein the internal combustion engine comprising at least one cylinder Abgasausführsystem for discharging the exhaust gas and at least one disposed in this Abgasabführsystem exhaust aftertreatment system which at least temporarily requires a supply of reducing agent comprises, and each cylinder of the internal combustion engine is provided for direct introduction of fuel into a cylinder-associated combustion chamber with an injection nozzle having a movable closure body positively connected in the context of injection combustion chamber side nozzle openings of the injector for introducing fuel into the combustion chamber with a fuel supply system and thus releases, wherein the movable Closing body, the nozzle openings in a rest position from the fuel supply system separates and thus locked and in an Arb eitsposition with the fuel supply system connects, in which after introducing an intended for the combustion amount of fuel .DELTA.m _{fuel, burn} at least one post-injection is made, wherein the introduced by Nacheinspritzen _fuel amount .DELTA.m _{fuel, enrich is used} as a reducing agent for exhaust gas enrichment, characterized in that a plurality of post-injection be made, which overlap and are therefore not hydraulically separated from each other, but form a cohesive common injection process, in such a way that - the movable closure body is transferred to initiate the cohesive joint injection process from the rest position to a working position, - the movable Closure body during the cohesive joint injection process between different working positions repeatedly oscillates, and - the movable closure body to terminate the zusammenhän ing common injection process is returned to the rest position. Method according to Claim 1 for enriching the exhaust gas of a direct injection internal combustion engine, wherein each cylinder is associated with a piston which oscillates between a top dead center TDC and a bottom dead center UT, thereby rotating a crankshaft of the internal combustion engine, characterized in that the exhaust gas enrichment is carried out when the Piston is located after the initiation of combustion in a crank angle window between 110 ° CA to TDC and 160 ° CA to TDC. Method according to Claim 2 , characterized in that the exhaust gas enrichment is carried out when the piston is after the initiation of combustion in a crank angle window between 120 ° CA to TDC and 150 ° CA to TDC. Method according to Claim 2 or 3 , characterized in that the exhaust gas enrichment is performed when the piston is after the initiation of combustion in a crank angle window between 120 ° CA to TDC and 140 ° CA to TDC. Method according to one of the preceding claims for enriching the exhaust gas of a direct-injection internal combustion engine, wherein each cylinder has at least one exhaust port for discharging the exhaust gases via Abgasabführsystem which is opened in the context of a charge exchange for an opening duration .DELTA.t _max , characterized in that the exhaust gas enrichment is performed when the at least one outlet opening is closed. Method according to one of Claims 1 to 4 for enriching the exhaust gas of a direct-injection internal combustion engine, wherein each cylinder has at least one outlet opening for discharging the exhaust gases via Abgasabführsystem which is opened in the context of a charge exchange for an opening duration .DELTA.t _max , characterized in that the exhaust gas enrichment is initiated when the at least one outlet opening closed is. Method according to one of Claims 1 to 4 for enriching the exhaust gas of a direct-injection internal combustion engine, wherein each cylinder has at least one exhaust port for discharging the exhaust gases via Abgasabführsystem which is opened in the context of a charge exchange for an opening duration .DELTA.t _max , characterized in that the exhaust gas enrichment is performed when the at least one exhaust port is open. Method according to one of the preceding claims, characterized in that the movable closure body is controlled during the cohesive joint injection process in such a way that a predeterminable maximum fuel mass flow (Δm _fuel / At) _{max is} not exceeded. Method according to Claim 8 , characterized in that the maximum fuel mass flow (Δm _fuel / Δt) _max is set taking into account a penetration depth of a fuel jet emerging from a nozzle opening and penetrating into the combustion chamber. Method according to Claim 8 or 9 , characterized in that the fuel mass flow Δm _fuel / Δt is varied several times by means of oscillation of the movable closure body during the coherent common injection process. Method according to one of Claims 8 to 10 , characterized in that the fuel mass flow Δm _fuel / Δt is modeled using the movable closure body during the cohesive joint injection process in a predetermined manner. Method according to one of the preceding claims, characterized in that the movable closure body changes the direction of its movement at least five times during the coherent joint injection process and the oscillation. Method according to one of the preceding claims, characterized in that the movable closure body during the cohesive joint injection process and the oscillating at least seven times changes the direction of its movement. Method according to one of the preceding claims, characterized in that the movable closure body during the cohesive joint injection process and the oscillating at least nine times changes the direction of its movement. Method according to one of the preceding claims, characterized in that the movable closure body during the cohesive joint injection process and the oscillating at least eleven changes the direction of its movement. Method according to one of the preceding claims, characterized in that the movable closure body is displaced translationally during the coherent common injection process and the oscillating. Method according to one of the preceding claims, characterized in that the injection nozzle is equipped with a displaceable in the direction of a longitudinal axis in a nozzle needle guide nozzle needle, wherein the nozzle needle is connected at a free end to the movable closure body.

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