• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to a method for the targeted generation of NH3 during the regeneration process of an in an exhaust system of an internal combustion engine (1) arranged NOX storage catalyst (LNT), wherein the regeneration by setting a reducing exhaust gas atmosphere before the NOX storage catalyst (LNT) is triggered and the temporal History of at least during the regeneration phase upstream and downstream of the NOX storage catalytic converter (LNT) determined lambda values (λ1, λ2) in the exhaust gas upstream and downstream of the NOx storage catalyst (LNT) is determined. The following steps are carried out: a) Searching for a crossover point (K) at which the determined lambda values (λ1, λ2) have the same value upstream and downstream of the NOx storage catalytic converter (LNT); b) determining a differential area (D) spanned from the point of intersection (K) up to a reference time (TB) by the temporal profiles of the lambda values (λ1, λ2) upstream and downstream of the NOX storage catalytic converter (LNT); c) determining an amount of NH3 in the exhaust gas downstream of the NOX storage catalyst (LNT) based on the differential area (D); d) termination of the regeneration process, when the determined amount of NH3 in the exhaust downstream of the NOx storage catalyst (LNT) exceeds a defined limit.
    公开号:AT516469A1
    申请号:T50814/2014
    申请日:2014-11-07
    公开日:2016-05-15
    发明作者:Albert Dipl Ing Dr Beichtbuchner；Bernhard Dipl Ing Breitegger
    申请人:Avl List Gmbh；
    IPC主号:
    专利说明:

    The invention relates to a method for the targeted generation of NH3 during the regeneration process of an arranged in an exhaust system of an internal combustion engine NOx storage catalyst, the regeneration is triggered by adjusting a reducing exhaust gas atmosphere upstream of the NOx storage catalyst and the time course of at least during the regeneration phase upstream and downstream of the NOx storage catalytic converter determined lambda values in the exhaust gas upstream and downstream of the NOx storage catalytic converter is determined.
    For the fulfillment of current and future emission limit values, there are various possibilities in the operation of the initially mentioned internal combustion engines. A NOx storage catalyst, also known as LNT ("Lean NOx Trap"), may be combined with an SCR catalyst that requires NH3 to operate, which may be formed in the LNT by prolonged rich operation. This internal generation of NH3 during prolonged LNT regeneration in combination with a downstream SCR is referred to as passive SCR. Alternatively or additionally, an active NH3 dosage can be provided from the outside. Usually, the end of the regeneration of a ΝΟχ storage catalytic converter, which is also known as LNT (Lean NOx Trap), is detected on the basis of a characteristic decrease in the lambda value of a lambda sensor arranged after the ΝΟχ storage catalytic converter, see WO 00/19075 A1. Alternatively, the point of intersection (lambda crossing) of the temporal courses of the lambda values upstream and downstream of the ΝΟχ storage catalytic converter is used to detect the end of the regeneration (DE 10 2010 001 202 A1). Furthermore, it is known from DE 10 355 037 B4 to use a characteristic increase and subsequent drop of a NOx value of a NOx sensor which is arranged downstream of the ΝΟχ storage catalytic converter.
    However, known methods have the disadvantage that they are relatively inaccurate and / or that additional and expensive measuring sensors (for example at least one NOx probe, currently costing approximately three times the value of simple lambda probes) are required for the measurement.
    It is the object of the invention to avoid these disadvantages and to propose a method which requires no additional expensive sensors and enables high-quality statements.
    According to the invention, this is achieved by carrying out the following steps: a) Searching for an intersection point at which the determined lambda values upstream and downstream of the NOx storage catalytic converter have the same value, b) determining from the time of intersection to a reference time point through the time profiles the lambda values upstream and downstream of the ΝΟχ-storage catalyst spanned difference area; c) determining an amount of NH3 in the exhaust gas downstream of the ΝΟχ storage catalyst based on the differential area; d) terminating the regeneration process when the determined amount of NH3 in the exhaust gas downstream of the ΝΟχ storage catalyst exceeds a defined limit.
    The method according to the invention allows a deliberate NH3 generation by defined extension of the regeneration process. The NH3 may then be used in the exhaust aftertreatment system, e.g. a downstream SCR catalyst, are stored. The determination of the lambda values can be implemented with any probes that can measure lambda values - for example, dedicated lambda probes or probes that measure 02 values, but also probes that determine the lambda value as an intermediate value. For the NH3 determination, therefore, no expensive NOx probes with the corresponding NH3 cross sensitivity are necessary.
    The crossing time in a) is the time from or after which the lambda value downstream of the NOx storage catalytic converter is lower than the upstream lambda value. Before this crossing time, the downstream lambda value is greater than upstream.
    The reference time in b) is the time of the end of regeneration, where the downstream lambda value rises again, in particular over the value at the crossing time or above. This reference time is also characterized by the change of the upstream lambda value back to the normal operating value outside the regeneration mode.
    The limit in d) is defined in particular by the amount of NH3 required in the downstream exhaust system, in particular to be stored in a downstream SCR catalyst.
    In a first variant of the invention, the amount of NH3 in c) is determined on the basis of an empirically determined relationship between the differential area and the NH3 amount. The relationship is established in a known manner by an empirical formula or a corresponding map. Among others, the following parameters can be considered: temperature of the exhaust gas and the catalyst (or LNT); Exhaust gas mass flow; Engine operating points such as engine speed and load. The respective differences of the upstream and downstream lambda values are weighted with empirically determined factors and the weighted differences are integrated into the differential area. Thus, at any time using lambda difference value on the empirically determined relationship and the exhaust gas mass flow on a NH3 amount inferred, which is integrated into a total NH3 amount. In step d), the regeneration is stopped when a certain amount of NH3 is reached.
    Thus, a higher-level SCR coordination ensures that sufficient NH3 is present in the exhaust system or stored in an SCR catalytic converter in order to ensure a desired NOx conversion.
    According to a second variant, a particularly simple determination of the amount of NH 3 in the exhaust gas results in c) if an H 2 concentration in the exhaust gas downstream of the NOx storage catalytic converter is determined on the basis of the differential area and the amount of NH 3 in the exhaust gas downstream of the ΝΟχ storage catalytic converter is determined on the basis of the determined H2 concentration. After the crossing time stored 02 is consumed and H2 formation occurs, which can be detected accordingly. This means that lambda values should be the same upstream and downstream when all 02 is consumed. The H2 formation takes place, for example, by splitting water molecules into H2 and
    Vi 02 in the SCR catalyst. Because of the greater cross sensitivity of the sensor used to detect lambda values, particularly e.g. For a lambda probe-for H2 than for 02, the ratio of H2 to O2 concentrations in the probe is greater than in the exhaust gas in the catalyst, and therefore the lambda value is smaller.
    The determined amount of NH3 can be supplied as an input variable to a NH3 loading model for a downstream of the NOx storage catalytic converter exhaust gas flowed through the SCR catalytic converter (SCR = Selective Catalytic Reduction).
    According to the invention, the NH3 is balanced on the basis of the, for the period after regeneration end, spanned surface of the lambda values before and after the ΝΟχ-storage catalyst and used in a NH3 loading model for a subsequent SCR catalyst.
    The invention is based on the property of &quot; empty &quot; ΝΟχ storage catalytic converter to produce ammonia (NH3) with continued subchemic engine operation (rich operation, lambda value <1). At a ΝΟχ-storage catalyst, the so-called &quot; water gas shift &quot; Reaction H2 from CO but also using "steam reforming" made of HC. This H2 is used to reduce NOx desorbed from the plätzen storage catalyst storage locations. As soon as NOx is no longer stored, or in some cases before, NH3 and H2 are formed.
    The invention is based on the fact that after the end of the regeneration of the ΝΟχ-storage catalytic converter - which is determined by means of the so-called lambda crossing - the lambda probe is used downstream of the ΝΟχ-storage catalytic converter quasi as H2 sensor by on the basis of the spanned difference surface of the lambda values or O2 signals of the lambda probes upstream and downstream of the ΝΟχ storage catalytic converter, the H2 concentration is calculated.
    Among other things, the invention makes use of the observation that the H2 concentration is proportional to the differential area D spanned by the temporal courses of the lambda values upstream and downstream of the ΝΟχ storage catalytic converter: D = Kl H2.
    The amount of NH3 formed is in turn proportional to the amount of H2 present: H2 = K2 NH3.
    Kl and K2 are each proportionality factors. In addition, it is taken into account that the 02 signals of the lambda probes have a higher sensitivity with regard to H2 than to CO and HC and 02.
    The invention will be explained in more detail with reference to a non-limiting embodiment in the figures.
    Show it
    1 shows a schematic arrangement of an internal combustion engine for carrying out the method according to the invention,
    2 shows the time profiles of the lambda value, the H2 concentration and the NH3 amount in the exhaust gas downstream of the NOx storage catalytic converter.
    1 schematically shows an internal combustion engine 1 with an exhaust system 2, in which an N0X storage catalytic converter LNT (LNT = Lean NOxTrap), a particle filter cDPF and an SCR catalytic converter SCR are arranged to comply with the statutory emission regulations. In the exemplary embodiment, the NOX storage catalytic converter and the particulate filter cDPF are designed as a structural unit. Reference numeral 3 designates the intake line and reference numeral 4 designates an exhaust gas recirculation system branching off from the exhaust system 2 between the particulate filter cDPF and the SCR catalytic converter and entering the intake system 3. However, the invention can be applied not only in the illustrated low-pressure exhaust gas recirculation (removal of the exhaust gas upstream of an exhaust gas turbocharger), but also in high-pressure exhaust gas recirculation (removal of the exhaust gas upstream of an exhaust gas turbocharger).
    Upstream of the NOx storage catalytic converter LNT, a first lambda sensor LI and downstream of the NOx storage catalytic converter LNT, a second lambda sensor L2 is arranged. Basically, any sensors can be used with which a lambda value can be determined - lambda probes according to the described embodiment are one of several possibilities. The
    Lambda sensors (lambda sensors) LI, L2 measure the residual oxygen content 02 in the exhaust gas, which results after combustion of all previously unburned fuel components (for example HC, CO) in order to be able to set the ratio (lambda value) λ of combustion air to fuel. If there is too little oxygen for this oxidation, it is pumped in the opposite direction from the exhaust gas via an oxygen pump integrated in the lambda probe. This negative oxygen pumping current is calculated as negative oxygen concentration and subsequently as lambda smaller than 1. The lambda value serves as a control sensor for a lambda control circuit (not shown).
    The ΝΟχ-storage catalytic converter LNT is used for temporary storage of nitrogen oxides (NOx) contained in the exhaust gas. For intermediate storage of the nitrogen oxides, the ΝΟχ-storage catalyst LNT on suitable supports on a noble metal catalyst such as platinum and a NOx storage component, such as barium on. In the lean, that is oxygen-rich, atmosphere, the nitrogen oxides are oxidized under the action of the noble metal catalyst, absorbed to form nitrates such as barium nitrate in the catalyst and thus removed from the exhaust gas stream. Through a regular short-term &quot; enrich &quot; of the exhaust gas mixture, ie lowering the lambda value λ- run these reactions in the opposite direction, whereby the NOx molecules are released back into the exhaust stream and by the existing in the rich atmosphere reducing components such as CmHn -Incompletely burned hydrocarbons - and / or CO on be reduced.
    If the absorption capacity of the NOx storage catalytic converter LNT is exhausted, the engine electronics briefly set a rich, reducing exhaust gas mixture for a few seconds (about two to ten seconds). In this short, fat cycle, the nitrogen oxides NOx temporarily stored in the catalytic converter are reduced to nitrogen N2, thus preparing the ΝΟχ storage catalytic converter for the next storage cycle. In order to keep the engine operation as short as possible in the rich cycle, it is essential in classic LNT operation that the reduction end be recognized as accurately as possible.
    In the downstream SCR catalytic converter, with passive SCR, NOx molecules are reduced to N2 by NH3 for further nitrogen oxide reduction. An SCR catalyst model is used to determine the amount of NH3 to be supplied.
    2 shows the curves of the lambda value λι upstream of the NOx storage catalytic converter LNT, the lambda value λ2 downstream of the NOx storage catalytic converter LNT, the course of the nitrogen oxide NOx downstream of the ΝΟχ storage catalytic converter LNT, the profile of the hydrogen H2 downstream of the NOx The course of the proportions of carbon monoxide CO downstream of the ΝΟχ-storage catalytic converter LNT and the course of the shares of unburned hydrocarbons HC downstream of the ΝΟχ-storage catalyst LNT, in particular during a regeneration phase REG of the ΝΟχ-storage catalyst LNT applied over the time t. During the regeneration phase REG, the internal combustion engine 1 is operated stoichiometrically, as can be seen from the operating mode indicating line M. Where &quot; 1 &quot; for rich operation and &quot; 2 &quot; for lean operation. At the point marked RI, the shift from lean to rich engine operation is made.
    The regeneration phase REG is divided into two time periods. The first period A is characterized in that the lambda value λι upstream of the ΝΟχ-storage catalytic converter LNT is smaller than the lambda value λ2 downstream of the ΝΟχ-storage catalytic converter LNT. In the second period of time, however, the lambda value λι upstream of the ΝΟχ storage catalytic converter LNT is greater than the lambda value λ2 downstream of the ΝΟχ storage catalytic converter LNT. At the time of intersection K of the curves of the two lambda values λ 1 λ 2, the lambda values λ 1, λ 2 determined by means of the lambda sensors L 1, L 2 have the same value upstream and downstream of the NOx catalyst. Surprisingly, it was found that there is a relationship between the differential area D between the curves of the lambda values λ lf λ 2, starting with the crossing point K and ending with the reference time TB, and the NH 3 generated during the regeneration process. In a first variant of the invention, therefore, an empirically determined relationship is used, which is produced by an empirical formula or a corresponding characteristic field. Among others, the following parameters may be taken into account: temperature of exhaust and / or catalyst (e.g., LNT); Exhaust gas mass flow; Engine operating parameters such as engine speed and load.
    The lambda differences are weighted with empirically determined factors and the weighted differences are integrated into the differential area D. After reaching a desired NH3 amount downstream, the regeneration is stopped.
    A further variant of the invention is as follows: as soon as all the cached nitrogen oxides reduce NOx to nitrogen N2 and the NOx storage catalyst LNT thus reduces "empty". is produced in this hydrogen H2, indicated by reference R2. The proportion of hydrogen H2 is usually more than ten times as large as the proportion of carbon monoxide CO, which is again more than zehmals as large as the proportion of unburned hydrogen HC (Comparison R3 and R4). Hardly any H2 is found upstream of the NOx storage catalytic converter LNT (or it is oxidized immediately with the residual oxygen or O2 stored in the LNT). Investigations have shown that the hydrogen concentration H2 produced in the second period B of the regeneration phase REG is proportional to the differential area D between the curves of the two lambda values λ1-λ2 beginning with the point of intersection K and ending with the reference point TB-.
    Since the differences of the lambda values are thus determined primarily by the hydrogen H2, the lambda sensor LI, L2 can be used as a hydrogen sensor. In addition, different sensitivities of the lambda probe to carbon monoxide CO and hydrocarbons HC are also known.
    The concentration of hydrogen H2 can thus be set as proportional to the differential area D: D = Kl H2, where Kl represents a first proportionality factor.
    The production of hydrogen is mainly due to the so-called &quot; water gas shift &quot; Reaction H2 from CO
    but also on &quot; steam reforming &quot; from HC:
    This H2 is used to reduce NOx desorbed from the storage locations of the NOx storage catalyst. As soon as NOx is no longer stored, or in some cases already before, NH3 is formed from H2 and NO:
    The amount of NH3 formed is in turn proportional to the amount of H2 present:
    where K2 represents a second proportionality factor.
    The amount of NH3 determined in this way can be fed as input quantity to a known NH3 loading model for an SCR catalytic converter SCR through which exhaust gas flows downstream of the NOx storage catalytic converter.
    权利要求:
    Claims (6)
    [1]
    1. A method for the targeted generation of NH3 during the regeneration process of a NOx storage catalytic converter (LNT) arranged in an exhaust system of an internal combustion engine (1), the regeneration being triggered by setting a reducing exhaust gas atmosphere in front of the NOx storage catalytic converter (LNT) and temporal course of at least during the regeneration phase upstream and downstream of the ΝΟχ-storage catalyst (LNT) determined lambda values (λι, λ2) in the exhaust upstream and downstream of the ΝΟχ-storage catalyst (LNT) is determined, characterized in that the following steps are carried out: a Finding a crossing time point (K) at which the determined lambda values (λι, λ2) have the same value upstream and downstream of the ΝΟχ storage catalytic converter (LNT); b) determining a differential area (D) spanned from the point of intersection (K) up to a reference time (TB) by the temporal courses of the lambda values (λι, λ2) upstream and downstream of the ΝΟχ-storage catalytic converter (LNT); c) determining an amount of NH3 in the exhaust gas downstream of the ΝΟχ-storage catalyst (LNT) based on the differential area (D); d) termination of the regeneration process when the determined NH3 amount in the exhaust gas downstream of the ΝΟχ-storage catalyst (LNT) exceeds a defined limit.
    [2]
    2. The method according to claim 1, characterized in that in step c) the NH3 amount is determined based on an empirically determined relationship between the differential area (D) and the amount of NH3.
    [3]
    3. The method according to claim 1, characterized in that in step c) determines an H2 concentration in the exhaust gas downstream of the ΝΟχ-storage catalyst (LNT) on the basis of the differential area (D) and the NH3 amount in the exhaust gas downstream of the NOx storage catalyst (LNT) is determined on the basis of the determined H2 concentration.
    [4]
    4. The method according to claim 3, characterized in that the H2 concentration in the exhaust gas downstream of the ΝΟχ-storage catalyst (LNT) is assumed to be proportional to the differential area (D):

    where Kl is a first proportionality factor.
    [5]
    5. The method according to claim 3 or 4, characterized in that the NH3 amount in the exhaust gas downstream of the ΝΟχ-storage catalyst (LNT) is assumed to be proportional to the hydrogen concentration H2:

    where K2 is a second proportionality factor.
    [6]
    6. The method according to any one of claims 1 to 5, characterized in that the determined NH3 amount is supplied as an input NH3 loading model for a downstream of the ΝΟχ-storage catalyst (LNT) from the exhaust gas flowed SCR catalyst (SCR). 2014 11 07 Fu
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    引用文献:
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    法律状态:
    优先权:
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    DE102015119249.7A| DE102015119249B4|2014-11-07|2015-11-09|Method for the targeted generation of NH3 during the regeneration process of a NOx storage catalyst|
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