DE102009048169A1 - Method for operating exhaust gas after treatment system of direct injection 4-cycle-diesel engine of vehicle, involves oxidizing combustible components in gas simultaneously and partially by releasing heat quantity to precatalytic converter - Google Patents

Abstract

The method involves providing adding fuel to exhaust gas in an operating mode by a fuel adding device (9) that is arranged between a precatalytic converter (5) and a primary catalytic converter (7). The fuel is oxidized by releasing heat quantity to the catalytic converter and injected into a combustion chamber of an internal combustion engine i.e. diesel engine (1), such that the gas with combustible components is delivered from the engine with excess oxygen. The components in the gas are simultaneously and partially oxidized by releasing another heat quantity to the precatalytic converter. An independent claim is also included for an internal-combustion engine comprising a supercharger.

Description

The invention relates to a method for operating an exhaust gas aftertreatment system connected to an internal combustion engine according to the preamble of claim 1 and to an internal combustion engine having an exhaust gas aftertreatment system according to the preamble of claim 14.

From the DE 10 2006 051 790 A1 an exhaust aftertreatment system is known, which has two successively arranged oxidation catalysts. This is followed by a particle filter. By means of a fuel adding device, a fuel can be added to the exhaust gas between the first and the second oxidation catalyst. By exothermic oxidation of the added fuel on the second oxidation catalyst, the particulate filter can be heated to a temperature required for thermal regeneration by Rußabbrand temperature.

The object of the invention is to provide a method or an internal combustion engine with an exhaust aftertreatment system, which allow a further improved Abgasaufheizung.

This object is achieved by a method having the features of claim 1 and by an internal combustion engine having an exhaust gas aftertreatment system having the features of claim 14.

The method according to the invention is characterized in that, in a first operating mode for heating the exhaust gas, a late injection of fuel into at least one combustion chamber of the internal combustion engine is carried out such that an exhaust gas rich in combustible constituents is released by the internal combustion engine with an excess of oxygen and that the exhaust gas present in the exhaust gas combustible components are at least partially oxidized on the primary catalyst under heat release. Since the fuel added at the same time by the fuel addition device between the precatalyst and the main catalyst is oxidized at least partially and also with heat release at the main catalytic converter, a two-stage exhaust gas heating takes place, which even under unfavorable conditions, for example at outside temperatures below freezing point and / or within a short time interval a cold start of the engine causes an effective Abgasaufheizung. The main catalytic converter downstream exhaust purification units can thus be heated rapidly to its operating temperature or to an optionally required for regeneration elevated temperature. A ratio of the first quantity of heat released as a result of oxidation of fuel at the main catalytic converter and the second quantity of heat released as a result of oxidation of late-injected fuel at the primary catalytic converter can be adjusted within a wide range. By adjusting the fuel addition rate and / or the injection quantity as a function of the temperatures of the primary catalytic converter and main catalytic converter or the exhaust gas temperatures determined before and / or after them, a ratio of the heat quantities optimally adapted to the respective heating state and the respective catalyst activity can be set. The inventive method thus proves to be particularly flexible and effective. The inventive method is mainly for predominantly lean-burn internal combustion engines, in particular for trained as a diesel engine engines advantageous because these, at least at partial load, usually give off a relatively low heated exhaust.

The enrichment of the exhaust gas with combustible constituents upstream of the precatalyst is preferably performed in a normal traction of the internal combustion engine at least approximately by a fuel post injection, whereas a fuel injected by a time from the post-injection and previously performed main injection fuel quantity at least approximately completely effective torque in the least one combustion chamber burns. In the braking operation of the internal combustion engine, typically a torque-generating main fuel injection is omitted. Irrespective of this, a late injection takes place in a manner analogous to post-injection, with which an enrichment of combustible components in the exhaust gas takes place. In any case, an excess of oxygen remains in the exhaust gas, such that this total lean, d. H. is oxidizing. The internal combustion engine is accordingly operated with a lean engine lambda value of greater than 1.0.

In an embodiment of the method, it is provided that the late injection of fuel comprises a noninflamming fuel injection designed in particular as post-injection. In train operation with main fuel injection, a post-injection takes place in time from the main fuel injection in the same work cycle as this. Here, by not co-firing is meant a (post-) injection in which the injected fuel does not or only to a limited extent participate in combustion in the combustion chamber. Typically, 60% to 95%, preferably 70% to 90%, of the calorific value is retained. In the combustion chamber can quite run off cracking processes, which cause a shortening of the chain length in chain-shaped hydrocarbons in the fuel. It can also be a splitting off of hydrogen and a partial oxidation, such that the exhaust gas with hydrogen and / or Carbon monoxide is enriched. As a result, a run off of post-oxidation reactions at the precatalyst is improved. A possible reduction in the activity of the precatalyst by surface coating with long-chain hydrocarbons is avoided. Typically, the late injection takes place at the earliest in the decaying combustion of a main fuel injection. When a main fuel injection is performed, the late injection starts after the completion of the combustion of the fuel injected with the main injection. Preferably, the late injection, with which the exhaust gas is enriched with combustible components, at crank angles of 30 ° to 120 °, more preferably between 40 ° and 90 ° after top dead center in the power stroke. However, it may also be provided an injection in Ausschiebetakt. It is preferred to specify the start of injection in dependence on the speed. In particular when a main fuel injection is carried out, the start of injection of the late injection is shifted with increasing speed to increasing degrees of crank angle. In addition to the non-burning late injection, it is also possible to provide one or more pilot injections and an early post-injection, which is attached in particular to the main injection.

Although the fuel adding device may be configured to add a gaseous fuel such as methane, hydrogen, or a reformate provided by a reformer to be preferably separately provided, in another aspect of the invention fuel is used as the liquid fuel used to operate the engine. This is added by means of an injector or a nozzle preferably quantitatively and timed adjustable to the exhaust gas. This eliminates a supply or generation of another fuel. In particular, it is provided in a further embodiment of the invention that is used as fuel for the operation of the internal combustion engine used liquid fuel. Since the invention is preferably used in engine designed as a diesel engine, it is provided in particular that the fuel adding device diesel fuel is finely distributed to the exhaust gas is added. Although a partial treatment of the liquid fuel, for example by pre-evaporation, may be provided before the addition to the exhaust, it is preferred if the liquid fuel is added to the exhaust gas at least approximately completely unchanged in its original liquid state.

In a further embodiment of the method according to the invention, it is provided that at least partial evaporation of the liquid fuel added to the exhaust gas by the fuel adding device takes place before entry into the main catalytic converter. The at least partial evaporation of the fuel added in liquid form to the exhaust gas can be intensified by a mixing device in the exhaust gas line and / or by a sufficiently long residence time of the added fuel in the exhaust gas. Preferably, the fuel adding device and the downstream part of the exhaust system are designed so that at least 50%, preferably more than 70% of the fuel added in liquid form to the exhaust gas evaporates before entering the main catalyst in the exhaust gas.

In a further embodiment of the method, it is provided that the second quantity of heat released at the primary catalytic converter corresponds at least approximately to the quantity of heat required for the at least partial evaporation of the liquid fuel added to the exhaust gas by the fuel adding device. This ensures that the at least partial evaporation of the added liquid fuel in the exhaust gas has no or at least no significant exhaust gas temperature reduction result.

It is preferred that the second amount of heat released at the primary catalytic converter overcompensate for the amount of heat required for the at least partial evaporation of the liquid fuel added to the exhaust gas by the fuel adding device. In particular, it is provided in a further embodiment of the invention that the second amount of heat sufficient to increase the exhaust gas temperature on the outlet side of the primary catalytic converter by at least 50 K compared to the exhaust gas temperature inlet side of the primary catalytic converter. In this case, it is particularly preferred if an exhaust gas temperature increase of at least 50 K in comparison to the exhaust gas temperature on the inlet side of the primary catalytic converter is also present on the inlet side of the main catalytic converter. This allows a particularly rapid onset of the catalytic oxidation effect of the main catalyst.

In a further embodiment of the method, it is provided that the first amount of heat is sufficient to increase the exhaust gas temperature on the outlet side of the main catalytic converter by at least 200 K compared to the exhaust gas temperature on the inlet side of the main catalytic converter. For this purpose, a sufficiently large amount of fuel between the pre-catalyst and the main catalyst is added to the exhaust gas. In particular, it is provided in a further embodiment that the first and / or the second amount of heat sufficient to heat the exhaust gas outlet side of the main catalyst to the extent that regeneration of the particulate filter can be done by thermal Rußabbrand. Typically, a temperature increase to about 600 ° C is sufficient for this purpose.

In a further refinement of the method, provision is made for the fuel addition and the fuel injection to be carried out in such a way that a specifiable ratio of the first and second heat quantities, which is dependent on the outside temperature and / or the load point of the internal combustion engine, results. As a result, the current temperature conditions in the exhaust system can be taken into account in a particularly advantageous manner. In the case of a pre-catalyst that has already been sufficiently warmed up, for example, the fuel addition in relation to the late injection quantity and thus the first quantity of heat can be increased in relation to the second quantity of heat, thereby enabling a more effective heating of a particle filter arranged downstream of the main catalytic converter. If, as a result of a comparatively large engine load, the internal combustion engine delivers a comparatively strongly heated exhaust gas anyway, the late injection quantity and thus the second quantity of heat can likewise be reduced. At particularly low outside temperatures, for example, less than minus 10 ° C, however, it is preferred to first select a higher late injection quantity and thus to increase the ratio of the second amount of heat to the first amount of heat.

In a further embodiment of the method, it is provided that the amount of fuel injected in a working cycle of the internal combustion engine with the late injection is chosen to be less than 10 mg per liter of displacement of the internal combustion engine. As a result, a risk of a lubricating oil dilution can be avoided or at least reduced, which is given at higher late injection quantities.

In a further embodiment of the method, it is provided that in a present request for exhaust gas heating and the presence of a predeterminable first threshold below exhaust gas temperature on the inlet side and / or outlet side of the primary catalytic converter, the fuel injection is activated and is activated by the start of the fuel addition of the first operating mode when the exhaust gas temperature inlet and / or the outlet side of the main catalyst exceeds a predetermined second threshold. This ensures that the first mode of operation with late injection and simultaneous addition of fuel between the primary catalyst and the catalyst does not prematurely, d. H. takes place before reaching the light-off temperature of the main catalyst. Accordingly, the second threshold value, which is preferably slightly higher than the first threshold value, is preferably predefined such that it approximately corresponds to the light-off temperature of the main catalytic converter. In this case, an adaptation to the aging state of the main catalytic converter can be provided during the operating time.

In a further embodiment of the method, it is provided that when the first operating mode is active when a predeterminable third threshold value for the exhaust gas temperature on the inlet side and / or outlet side of the primary catalytic converter ends at the end of the late injection, switching from the first operating mode to a second operating mode takes place, wherein in the second operating mode the fuel addition is continued into the exhaust gas through the fuel adding device. The first operating mode with simultaneous late injection and fuel addition is thus maintained only until the exhaust gas temperature on the inlet side and / or outlet side of the precatalyst has exceeded the third threshold. Thus, a further exhaust gas heating is performed by post-oxidation only by the main catalyst. This prevents a thermal overload of the precatalyst and advantageously takes advantage of the efficiency of the main catalyst which is more efficient with respect to the generation of exothermic energy.

In a further embodiment of the method, the internal combustion engine is predominantly operated such that the exhaust gas emitted by the internal combustion engine has a NOx / PM ratio of more than 20, in particular more than 40. A NOx / PM ratio is understood as meaning a mass ratio of the NOx emitted by the internal combustion engine, calculated as NO, to the emitted particulate matter (PM). The adjustment according to the invention of the NOx / PM ratio of more than 20 or 40 is carried out in particular during normal operation, ie when the exhaust gas heating is inactive. Due to the NOx-rich engine operation, the frequency of particulate filter regeneration due to thermal soot burnup is reduced because NO emitted from the engine is oxidized to NO ₂ at the primary catalyst and / or at the main catalyst and this allows soot oxidation at relatively low temperatures.

The object underlying the invention is also achieved by an internal combustion engine having an exhaust gas aftertreatment system, which comprises a precatalyst arranged as an oxidation catalyst, a main catalyst downstream of the precatalyst in the exhaust gas flow direction and designed as an oxidation catalyst, a particle filter downstream of the main catalyst in the exhaust gas flow direction, and a fuel adding device for adding a fuel into the exhaust gas between the pre-catalyst and the main catalyst, wherein the fuel adding device is adapted to discharge a spray of liquid fuel droplets having an average diameter smaller than 0.2 mm. It is particularly preferred if the fuel adding device liquid droplets with an average diameter of less than 0.1 mm can deliver. As a result of this embodiment, effective vaporization of diesel fuel, in particular added by the fuel adding device in the form of a spray, is enabled before it reaches the main catalyst. This allows effective oxidation of the diesel fuel at the main catalyst with appropriate heat release and effective heating of the downstream particulate filter. The greatest possible evaporation of diesel fuel added by the fuel adding device also avoids surface occupancy and optionally downstream carbon fouling of the main catalyst.

For the internal combustion engine according to the invention it is provided that no further cleaning-effective exhaust gas treatment element is arranged in the exhaust aftertreatment system between the primary catalyst and catalyst. It is further provided that the internal combustion engine is capable of carrying out multiple injections, in particular fuel injection. Furthermore, in an embodiment of the invention for the internal combustion engine, an exhaust gas turbocharger with a turbine drivable by the exhaust gas is provided and the precatalyst is arranged near the turbine downstream of the turbine. This embodiment with a small distance of the pre-catalyst to the turbine allows a rapid warming of the precatalyst. Preferably, the distance of the precatalyst to the turbine is less than 400 mm, more preferably less than 200 mm.

In a further embodiment of the invention, the main catalyst has a noble metal loading, which is less than 40 g / ft ³ and the precatalyst has a contrast to at least 50% higher noble metal loading. Preferably, the coating of at least the precatalyst is designed as a coating with low or negligible oxygen storage capacity. The noble metal loading is preferably formed by the platinum metals platinum (Pt), palladium (Pd) and / or rhodium (Rh). The noble metal loading, in particular of the precatalyst, may also be free of rhodium. Preferably, for the precatalyst and / or the main catalyst is a noble metal loading with a Pt / Pd ratio of 10: 1 to 1: 1. Particularly preferred is a ratio of about 3: 1. Preferably, the precatalyst is designed relatively small in relation to the main catalyst. It is sufficient if the volume of the precatalyst is 30% to 10% of the main catalyst volume. In this way, effective heating of the particulate filter even at low outside temperatures can be achieved with an overall comparatively low use of precious metals. In this case, the embodiment according to the invention enables a two-stage exhaust gas heating, in which a first exhaust gas temperature increase can take place by post-oxidation of late-injected fuel at the primary catalytic converter. A second, further increase in exhaust gas temperature takes place by oxidation of the fuel added by the fuel adding device to the main catalytic converter.

Advantageous embodiments of the invention are illustrated in the drawings and described below. In this case, the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination of features, but also in other combinations or alone, without departing from the scope of the present invention.

The single FIGURE shows a schematic representation of an advantageous embodiment of a system of internal combustion engine and exhaust aftertreatment system for performing the method according to the invention,

The internal combustion engine 1 in the figure is preferably designed as a direct injection 4-stroke diesel engine. An associated not shown fuel injection system is preferably designed as a so-called common rail system with adjustable rail pressure or fuel injection pressure or in the form of an injection system according to the pump-nozzle or pump-line-nozzle principle.

The cylinders of the diesel engine 1 are each associated with a combustion chamber with one or two inlet and outlet valves, a glow plug and a fuel injector and one or more inlet channels for the combustion air, which is not shown in detail. The fuel injectors are capable of performing multiple injections.

The diesel engine 1 receives its combustion air via an air supply line 3 in which an unillustrated air mass meter is arranged. The combustion air is by means of an exhaust gas turbocharger 15 compressed and a charge air cooler 16 supplied for cooling. The exhaust gas turbocharger is preferably designed as a so-called VTG loader or as a wastegate loader with adjustable boost pressure.

In the combustion chambers of the cylinders of the diesel engine 1 generated exhaust gas is via an exhaust pipe 4 derived. In this case, the combustion air via an exhaust gas recirculation line 13 Adds exhaust gas and thus to the diesel engine 1 to be led back. The proportion of recirculated exhaust gas (EGR rate) can via an EGR valve 14 be set. Preferably, for the intercooler 16 and / or the EGR cooler each provided a switchable bypass line, which in 1 not shown. This is advantageous an influence on the temperature of the diesel engine 1 supplied combustion air allows. The preferably provided bypass EGR cooler makes it possible to mix the combustion air optionally cooled or hot exhaust gas. A bypass of the intercooler 16 and / or the EGR cooler improves a Abgasaufheizung provided for example in connection with a cold start or warm-up or a particulate filter regeneration.

A preferred embodiment of the diesel engine 1 associated exhaust aftertreatment system 2 includes in the flow direction of the exhaust gas seen in this order designed as an oxidation catalyst precatalyst 5 , a main catalyst designed as an oxidation catalyst 7 , a particle filter 6 , and an SCR catalyst 8th , main catalyst 7 and particle filters 6 are preferably arranged as shown with a small distance from each other in a common housing.

As a particle filter 6 For example, a so-called wallflow filter based on SiC-cordierite or aluminum titanate is preferably used. The particle filter 6 However, it can also be designed as a sintered metal filter or as a filter unit with an open filter structure. Preferably, for the particulate filter 6 an oxidation catalytic and / or a Rußabbrand promotional coating provided. For a high absorption capacity of carbon black and ash particles, the largest possible volume of about 1.5 times the engine displacement is advantageous. Because the upstream catalysts 5 . 7 already cause a certain back pressure, is an optimized with regard to the exhaust back pressure interpretation of the particulate filter 6 prefers. Porosity and size are preferably determined so that at a soot loading of about 5 g / l in the vast operating range of the internal combustion engine, a back pressure of about 100 mbar is exceeded. In this case, a round design with a ratio of length to diameter (L / D ratio) in the range of 0.8 to 2.0 is preferred. With an L / D ratio of 1.0 to 1.3, a particularly uncritical and even temperature distribution during thermal regeneration can be achieved.

The SCR catalyst 8th is preferably a catalyst suitable for carrying out a selective catalytic NOx reduction reaction by means of ammonia. It may, for example, be a V2O5-WO3-based full catalyst or a layered catalyst based on iron or copper zeolite or a coated catalyst with a noble metal-containing coating.

The precatalyst 5 is preferably relatively small with a volume of less than 10% of the stroke volume of the diesel engine 1 and preferably has a length-to-diameter ratio of LID <1.0 and a low cell density of preferably about 50 cpsi. The coating of the precatalyst 5 is designed so that a conversion of hydrocarbons already takes place at about 200 ° C to a considerable extent (light-off temperature). An oxidation of CO or H ₂ is typically carried out already from about 180 ° C to a significant extent. A washcoat with little or no oxygen storage capacity and with a platinum-palladium content of about 90 g / ft ³ based on the catalyst volume and a Pt / Pd ratio of 10: 1 has proven to be particularly suitable for this purpose.

The main catalyst 7 is preferably designed for high activity with respect to oxidation of NO and HC. On the one hand, this results in a low hydrocarbon slip in a thermal particle filter regeneration. On the other hand, under normal operating conditions, a high NO ₂ production rate and thus a high continuous soot degradation rate in the downstream particulate filter 6 achieved. A design for high aging and temperature stability is for the main catalyst 7 also preferred. An optimized design with respect to the mentioned criteria provides an L / D ratio of about 1.5 to 2.25, a cell density of 300 cpsi to 400 cpsi and a volume which is about 1.1 to 2.2 times the Stroke volume of the diesel engine 1 is, before. In this case, a coating is analogous to the coating of the precatalyst 5 , but provided with a reduced precious metal loading. A washcoat with a noble metal content of 40 g / ft ³ or less based on the catalyst volume and a Pt / Pd ratio of 3: 1 has proven to be sufficient. As a result, a significant saving of precious metal is achieved, which brings corresponding cost advantages. A light-off temperature with respect to hydrocarbons or fuel, which is thereby increased to about 250 ° C., does not represent a disadvantage, since preheating by the precatalyst 5 can be done. This is a turnover of the main catalyst 7 improved. An oxygen storage capacity, for example, by a cerium oxide content in the washcoat can for the main catalyst 7 be provided.

On the output side of the precatalyst 5 is a fuel adding device 9 provided, for example, via which diesel fuel can be supplied as fuel to the exhaust gas. As a result of exothermic oxidation of the exhaust gas supplied as needed is a targeted and effective heating of the exhaust gas at the main catalyst 7 allows. Not completely at the main catalyst 7 converted fuel can also be in the downstream particulate filter 6 be oxidized. The fuel supply device is actuated 9 predominantly in connection with an active one Regeneration of the particle filter 6 by thermal Rußabbrand or for heating a downstream exhaust gas purification component. For the addition of ammonia or another preferably for the release of ammonia-capable reducing agent for NOx reduction is the input side of the SCR catalyst 8th a reductant addition unit 11 intended. Preferably, aqueous urea solution is used as the reducing agent. The fuel adding device 9 and the reducing agent addition unit 11 are preferably connected to dosing systems not shown in detail.

In the exhaust aftertreatment system 2 Various temperature and exhaust gas sensors are provided to detect exhaust gas and component temperatures as well as concentrations of important exhaust gas constituents. Exemplary are the input side of the main catalyst 7 a temperature sensor 10 and on the output side of the SCR catalyst 8th a sensitive to NOx and / or NH ₃ gas sensor 12 intended. By means of these and possibly other sensors, the operating state of the exhaust aftertreatment system 2 be determined.

For controlling or detecting the engine operation is an electronic engine control unit 17 intended. The engine control unit 17 receives on the one hand information about significant state variables such. As speed, temperatures, pressures from the corresponding sensors or sensors and on the other hand, control signals as adjustment variables to actuators such. B. to the EGR valve 14 or to the turbocharger 15 output. This relates to state variables on the gas supply side as well as on the fuel supply side. In particular, the engine control unit 17 being able to control the fuel injectors to perform multiple injections and optionally adjust the fuel injection pressure as needed. For this purpose, the engine control unit 17 resort to stored maps or calculation routines.

In an analogous manner is for the detection and adjustment of operating and state variables of the exhaust aftertreatment system 2 a second controller 18 intended. The engine control unit 17 and the second controller 18 are by means of a bidirectional data line 19 connected with each other. In this way, a mutual exchange of data available to a particular control device is made possible.

The following is on advantageous settings and procedures in the operation of the diesel engine 1 and the connected exhaust aftertreatment system 2 received in connection with a Abgasaufheizung. Without limiting the generality, it is assumed that an exhaust gas heating for initiating and carrying out a thermal regeneration of the particulate filter 6 he follows. Due to its intended function of retaining soot particles, increasing carbon black loading of the particulate filter results with increasing operating time 6 and a concomitant disturbing increase in its flow resistance. Although soot deposited under normal operating conditions is contained in the exhaust gas, in particular by the precatalyst 5 and the main catalyst 7 Oxidation-produced NO _{2 can be} continuously oxidized and removed from the carbon black, resulting in more or less regular intervals a need for particle filter regeneration by thermal Rußabbrand. Since the required high temperatures of 550 ° C to 650 ° C are usually not achieved in normal driving, this is a corresponding increase in the exhaust gas temperature by oxidation of by means of late engine injection and / or by the Brennstoffzugabevorrichtung 9 If necessary, the fuel or fuel discharged into the exhaust gas is caused.

The loading of the particle filter 6 With soot or particles is continuously determined or estimated, which by determining a differential pressure over a particulate filter 6 containing exhaust line and / or can be done via a loading model. Preferably, there are provided summation values for specific operating parameters governing particulate emission, such as engine operating time and / or vehicle travel distance and / or fuel consumption, with respect to a resulting soot load of the particulate filter 6 to rate. If a predeterminable loading value or a predetermined, typically empirically determined and applied limit value of one of the decisive operating parameters is exceeded, then this becomes an inadmissibly increased soot loading of the particulate filter 6 rated and thermal regeneration, typically with Abgasaufheizung, requested.

In a setting referred to below as the first operating mode, a two-stage exhaust gas heating is carried out. The first mode of operation becomes advantageous especially at low outside temperatures and thus typically associated relatively low temperatures in the exhaust aftertreatment system 2 set. In the first operating mode, the exhaust gas temperature is raised at the primary catalytic converter 5 by a first temperature level and an increase in the exhaust gas temperature at the main catalyst 7 at a second temperature level. Overall, the exhaust gas temperature to about 600 ° C or more input side of the particulate filter 6 raised, allowing a regeneration of the particulate filter 6 can be done by thermal Rußabbrand.

To realize the exhaust gas temperature increase by the first temperature level at the primary catalytic converter 5 is a late injection of fuel into at least one combustion chamber of the diesel engine 1 intended. All cylinders of the diesel engine are preferred 1 operated with late injection. The fuel injectors are controlled so that in the train operation of the diesel engine 1 deducted to a provided for generating a main injection main injection is a post-injection of fuel. For this late injection, an injection quantity of less than 10 ml per liter displacement of the diesel engine is set, wherein the injection quantity is set so that a temperature increase of at least 50 K at the primary catalytic converter 5 is possible.

To realize the exhaust gas temperature increase by the second temperature stage at the main catalytic converter 5 it is envisaged that from the fuel adding device 9 present diesel fuel is added as fuel to the exhaust finely divided in the form of droplets. For a fine distribution, it is advantageous to use the fuel adding device 9 as a Mehrlochinjektor, which can deliver a spray of diesel droplets with an average diameter of 0.2 mm or less. For this purpose, it is advantageous if the injector is supplied with an under an increased pressure of preferably 5 bar to about 100 bar standing diesel fuel. Together with the exhaust gas temperature increase of the first stage at the primary catalytic converter 5 is achieved so that the added substantially in liquid form diesel fuel along its way in the exhaust pipe 4 at least partially, preferably mostly volatilized, before reaching the main catalyst.

The injector or the fuel adding device 9 The amount of fuel delivered is adjusted to result in a temperature increase due to oxidation of the fuel at the main catalytic converter, which is sufficient to initiate a particulate filter regeneration. In any case, it is provided that an excess of oxygen on the input side of the particulate filter 6 is available. Preferably, an exhaust gas temperature of about 600 ° C inlet side of the particulate filter 6 regulated. Typically, the height of the second temperature stage is 200 ° C to 300 ° C. For a needs-based volume control, it is provided to operate the fuel injector clocked. The corresponding opening ratio and thus the amount of fuel delivered per unit time are preferably dependent on the signal of an output side of the main catalyst 7 arranged temperature sensor set.

A particularly advantageous procedure envisages an adjustment of the late injection quantity and the fuel quantity delivered by the injector in such a way that initially a ramp-shaped increase of the main catalyst outlet temperature to a target value for the particle filter regeneration in the range between 525 ° C. and 625 ° C. Preferably, a temperature rise rate of more than 1 K / min is set. Particularly preferred is a temperature rise rate of about 75 K / min. In this way, the risk of rapid onset and uncontrollable running, avalanche Rußabbrandreaktion with locally inadmissibly excessive peak temperatures and resulting damage to the particulate filter 5 avoided.

In this context, it is advantageous to divide a combustion phase subsequent to the ramp-shaped heating phase into two, preferably approximately six phases with different rates of Rußabbrandgeschwindigkeiten or different main catalyst outlet temperatures. In a first Rußabbrandphase the regeneration is started after increase of the main catalyst outlet temperature to a first target value of about 525 ° C. Preferably, the temperature is increased in predetermined or predeterminable steps after the expiration of a respectively specifiable steady time to a final target value of preferably about 600 ° C to 625 ° C. The temperature target values and steady-state times of the respective temperature stages are preferably chosen taking into account the oxygen content of the exhaust gas, the exhaust gas mass flow and optionally further parameters influencing the soot combustion rate such that no uncontrollable reaction can take place, but nevertheless the best possible burnup takes place. Depending on the size and type of filter, soot burning rates are set corresponding to a decrease in soot loading of 1 g per liter of filter volume in about 0.5 to 4 minutes. It is advantageous to carry out the changeover from one phase to the next in a time-controlled manner after the lapse of a predefined or predefinable period taking into account the aforementioned influencing factors. Switching is accomplished by adjusting late injection amount and / or fuel addition amount to result in an increase in the main catalyst exit temperature to the respective temperature target value. Regarding the result of oxidation of the late injection amount and the fuel addition amount of the precatalyst 5 or main catalyst 7 released amounts of heat is adjusted such that the at the primary catalytic converter 5 amount of heat released, at least sufficient to compensate for the heat of vaporization, which for evaporation of the fuel adding device 9 added diesel fuel is needed. This ensures that the main catalytic converter Inlet temperature corresponds at least to the pre-catalyst outlet temperature.

A two-stage exhaust gas heating is provided in the present case in the case of a low exhaust gas temperature. With sufficiently high exhaust gas temperatures in the area of the fuel adding device 9 or the main catalyst 7 can be dispensed with a late injection. The particle filter 6 is then heated only by Exothermierzeugung due to oxidation of fuel supplied by the fuel adding device to the exhaust gas to the temperature required for Rußabbrand temperature. It is therefore intended to activate the late injection only when inlet side and / or outlet side of the primary catalytic converter 5 a lying below a predetermined first threshold exhaust gas temperature is detected. Typically, a temperature in the range between 300 ° C and 350 ° C is set as the first threshold value.

It is also contemplated to allow the late injection only in certain areas of the load-speed map of the diesel engine. In the present case, a release of the late injection is provided for exhaust gas heating in a map area, which is given by a speed range from idle speed to 90% of the rated speed. With respect to the load range, the map area downwards is preferably limited by the maximum negative torque during coasting or braking operation. To the top of the approved for a late injection map area is preferably limited by a straight line which runs from a mean pressure of about 8 bar at idle speed to 0 bar at 90% value of the rated speed.

For the release of a parallel to the late injection fuel addition by the fuel adding device 9 and thus activation of the first operating mode is in this case the exceeding of a second threshold value for the exhaust gas temperature on the inlet side and / or outlet side of the main catalyst 7 queried. Depending on the light-off temperature of the main catalyst 7 and thus also dependent on its noble metal loading or its aging state, a second threshold value of about 300 ° C. is typically specified. Before a release of the fuel addition, it may also be provided to make a comparison of the main catalyst inlet temperature and the main catalyst outlet temperature. When the main catalyst exit temperature is more than about 20 ° C below the main catalyst inlet temperature, the main catalyst becomes 4 is judged insufficiently warmed and does not give release for fuel addition even if the main catalyst inlet temperature is above the light-off temperature of the main catalyst 7 lies.

As with sufficiently high exhaust gas temperatures in the fuel adding device 9 or the main catalyst 7 an exhaust gas temperature increase at the primary catalytic converter 5 is not required, it is intended to terminate the active first mode of operation by deactivating the late injection when inlet side and / or outlet side of the primary catalytic converter 5 a lying above a predetermined third threshold exhaust gas temperature is detected. This results in a transition to a second operating mode for exhaust gas heating, or particulate filter regeneration with only one-stage heating of the main catalyst 7 , This is done by continuing the fuel addition by the fuel adding device 9 achieved.

In case of regeneration of the particulate filter 6 the exhaust gas heating is stopped when a predetermined end criterion is met. The end criterion may be due to the soot loading of the particulate filter 6 estimating loading model or a differential pressure measurement over the particulate filter 6 be determined. In the simplest case, the regeneration is terminated after a predetermined or predefinable period of typically about 25 minutes, and the fuel adding device 9 put out of order.

Overall, the present invention provides a method or an internal combustion engine with which a particularly effective exhaust gas heating is also possible and especially at very low outside temperatures. Due to the two-stage exhaust gas heating according to the invention, for example, a particulate filter regeneration is enabled by Rußabbrand in wide map areas both at low loads and in thrust or braking operation.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102006051790 A1 [0002]

Claims (16)

Method for operating an internal combustion engine ( 1 ) connected exhaust aftertreatment system ( 2 ), comprising - a precatalyst carried out as an oxidation catalyst ( 5 ), - a precatalyst ( 5 ) downstream in the exhaust gas flow direction and designed as an oxidation catalyst main catalyst ( 7 ), and - a particulate filter downstream of the main catalytic converter in the exhaust gas flow direction ( 6 ), wherein in a first operating mode for exhaust gas heating, a fuel from a fuel adding device ( 9 ) between the precatalyst ( 5 ) and the main catalyst ( 7 ) is added to the exhaust gas and that of the fuel adding device ( 9 ) added to the exhaust gas at least partially at the main catalyst ( 7 ) is oxidized with release of a first amount of heat, characterized in that a late injection of fuel into at least one combustion chamber of the internal combustion engine ( 1 ) is performed such that of the internal combustion engine ( 1 ) an exhaust gas enriched with combustible constituents is released with an excess of oxygen and that the combustible constituents present in the exhaust gas are at least partially present at the primary catalytic converter ( 5 ) are oxidized to release a second amount of heat. A method according to claim 1, characterized in that the late injection of fuel comprises a formed in particular as a post injection, non-burning fuel injection. A method according to claim 1 or 2, characterized in that as fuel in particular for the operation of the internal combustion engine ( 1 ) used liquid fuel is used. A method according to claim 3, characterized in that at least partial evaporation of the fuel feed device ( 9 ) added to the exhaust gas before entering the main catalyst ( 7 ) he follows. A method according to claim 4, characterized in that the pre-catalyst ( 5 ) is at least approximately equal to the amount of heat released for at least partial evaporation of the fuel adding device ( 9 ) the exhaust gas added liquid fuel is needed. Method according to one of claims 1 to 5, characterized in that the second amount of heat is sufficient to the exhaust gas temperature on the outlet side of the precatalyst ( 5 ) by at least 50 K compared to the exhaust gas temperature inlet side of the primary catalytic converter ( 5 ) increase. Method according to one of claims 1 to 6, characterized in that the first amount of heat sufficient to exhaust gas temperature on the outlet side of the main catalyst ( 7 ) by at least 200 K compared to the exhaust gas temperature on the inlet side of the main catalytic converter ( 7 ) increase. Method according to one of claims 1 to 7, characterized in that the first and / or the second amount of heat sufficient to the exhaust gas on the outlet side of the main catalyst ( 7 ) to heat up so far that a regeneration of the particulate filter ( 6 ) Can be done by thermal Rußabbrand. Method according to one of claims 1 to 8, characterized in that the fuel addition and the late injection are performed such that a specifiable and the outside temperature and / or the load point of the internal combustion engine ( 1 ) dependent ratio of first and second amount of heat results. Method according to one of claims 1 to 9, characterized in that in a working cycle of the internal combustion engine ( 1 ) injected with the late injection amount of fuel less than 10 mg per liter displacement of the internal combustion engine ( 1 ) is selected. Method according to one of claims 1 to 10, characterized in that in a present request for exhaust gas heating and the presence of a predeterminable first threshold below exhaust gas temperature on the inlet side and / or outlet side of the primary catalyst ( 5 ) the fuel post injection is activated and the first operating mode is activated by the start of the fuel addition when the exhaust gas temperature on the inlet side and / or outlet side of the main catalytic converter ( 7 ) exceeds a predefinable second threshold. Method according to one of claims 1 to 11, characterized in that when the first operating mode is active when a predefinable third threshold value for the exhaust gas temperature on the inlet side and / or outlet side of the primary catalytic converter ( 7 ) is carried out with termination of the late injection switching from the first operating mode to a second operating mode, wherein in the second operating mode, the fuel addition to the exhaust gas by the fuel adding device ( 9 ) is continued. Method according to one of claims 1 to 12, characterized in that the internal combustion engine ( 1 ) is operated predominantly in such a way that the from the internal combustion engine ( 1 ) discharged exhaust has a NOx / PM ratio of more than 20, in particular more than 40. Internal combustion engine ( 1 ) with exhaust aftertreatment system ( 2 ) for carrying out a method according to any one of claims 1 to 13, wherein the exhaust aftertreatment system - a precatalyst carried out as an oxidation catalyst ( 5 ), - a precatalyst ( 5 ) downstream in the exhaust gas flow direction and designed as an oxidation catalyst main catalyst ( 7 ), - a particle filter downstream of the main catalyst in the exhaust gas flow direction ( 6 ), and - a fuel adding device ( 9 ) for adding a fuel into the exhaust gas between the precatalyst ( 5 ) and the main catalyst ( 7 ) characterized in that the fuel adding device ( 9 ) is designed for dispensing a spray of liquid fuel droplets, which have on average a smaller diameter than 0.2 mm. Internal combustion engine ( 1 ) with exhaust aftertreatment system ( 2 ) according to claim 14, characterized in that an exhaust gas turbocharger ( 15 ) is provided with a turbine drivable by the exhaust gas and the precatalyst ( 5 ) is arranged downstream of the turbine downstream of the turbine. Internal combustion engine with exhaust aftertreatment system ( 2 ) according to claim 14 or 15, characterized in that the main catalyst ( 7 ) has a noble metal loading which is less than 40 g / ft ³ and the precatalyst ( 5 ) has a contrast of at least 50% higher noble metal loading.

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