FR2933445A1 - Nitrogen oxide trap desulphurizing method for post processing of exhaust gas emitted by diesel engine of motor vehicle, involves desulphurizing trap after beginning and before ending of regeneration of filter - Google Patents

Abstract

The method involves estimating a combined realization effectiveness of desulphurization of a nitrogen oxide trap, during regeneration of particle filter. The trap is desulphurized, after beginning of the regeneration of the particle filter and before ending of the regeneration of the filter, so that the desulphurization of the trap and the regeneration of particles (MP) are carried out simultaneously in partial manner, if the combined realization effectiveness is positive. An independent claim is included for a power train of a motor vehicle comprising an engine.

Description

The invention relates to a process for the desulphurisation of a NOx-Trap, an aftertreatment device for exhaust gas emitted by an internal engine of a motor vehicle. It also relates to a power train equipped with a NOx-Trap and a motor vehicle as such implementing such a desulfurization process. The invention is particularly suitable for motor vehicles equipped with a diesel engine.

Internal combustion engines, and more particularly diesel-type engines, discharge into the atmosphere polluting elements such as polluting particles, nitrogen oxides, sulfur, carbon monoxide and unburned hydrocarbons. To reduce the emission of these pollutants, after-treatment devices are arranged on the exhaust line and their function is to trap these elements. A first after-treatment device is a nitrogen oxide trap, generally known by its Anglo-Saxon NOx-Trap name: this device chemically retains the nitrogen oxides (NO and NO2) produced by the engine. A second post-treatment device is a particulate filter, the function of which is to mechanically trap polluting particles such as soot leaving the combustion chamber.

Conventionally, these post-processing devices operate periodically, in two phases. During a first phase, they store pollutants emitted by the engine, and during a second so-called regeneration phase, these pollutants are eliminated. The regeneration of a NOx-Trap consists in reducing the nitrogen oxides to nitrogen N2 and carbon dioxide 002, when a predetermined threshold of NOx loading is reached. Similarly, the regeneration of the particulate filter consists in burning the stored particles as soon as the mass of particles in the filter becomes too large. For this, a specific fuel injection strategy makes it possible to raise the temperature in the particulate filter to a high value at about 600 ° C, thus making it possible to burn the stored particles. The regeneration phases take place when the engine is running, without the driver of the vehicle being aware of it.

These regeneration phases are necessary because when the after-treatment devices reach a certain load, they no longer fulfill their function. In addition, particles accumulated in the particulate filter eventually result in significant backpressure to the engine exhaust, as well as an increase in differential pressure across the particulate filter, significantly reducing engine performance. .

On the other hand, sulfur in the exhaust also alters the NOx-Trap's operation over time. Indeed, during operation of the engine, the sulfur initially present in the fuel and the oil is found in the exhaust gas in the form of SO2 sulfur dioxide, which is then adsorbed by the NOx-Trap on the sites of adsorption expected for nitrogen oxides NOx, thus decreasing the storage capacity of NOx. In addition, the adsorbed sulfur is not destocked during the NOx purges of the NOx-Trap regeneration phases. As a result, the efficiency of a NOx trap decreases with the accumulation of sulfur. Thus, a phase of desulfurization of NOx-Trap is also periodically implemented to purge sulfur products, in addition to the regeneration of NOx-Trap previously explained.

The desulphurization requires a very high thermal level within the NOx-30 Trap, ie a temperature generally greater than 650 ° C., and a REN100FR / PJ8795 - rich DA 3 (excess of reducing agents) medium for a duration that may range from several seconds to several tens of seconds. To comply with these purge conditions, specific fuel injection strategies are put in place.

In the two regeneration phases of the particulate filter and NOx-Trap desulphurization, a large increase of the exhaust gas temperature is necessary, obtained by a specific injection strategy such as a delayed fuel injection in the chambers. engine combustion. In particular, it is possible to inject fuel just after the top dead center during the expansion phase, which has the effect of increasing the temperature of the exhaust gases. Alternatively, it is also possible to provide one or more late injections, that is to say clearly after the top dead center or a fuel introduction directly into the exhaust line via the use of a fifth injector or a vaporizer in the exhaust. The fuel thus injected does not burn in the combustion chamber of the engine, but, for example, in a catalytic device also provided in the exhaust line, thus increasing the temperature of the gases then passing through the particulate filter.

This induces an increase in fuel consumption. On the other hand, there is also a phenomenon of fuel dilution in the engine oil. Thus, it is advantageous to limit as best as possible the number and duration of these phases at high temperature.

The current solution of the state of the art is to trigger the regeneration of the particle filter and the desulphurization of NOx-Trap independently, depending on the mass of stored particles on the one hand and the amount of sulfur stored in 'somewhere else. If by REN100FR / PJ8795 - deposit DA 4 chance the two phases are necessary simultaneously, then the regeneration of the particulate filter is done in priority, the desulphurization coming then, after the end of the regeneration.

To improve this solution, the document US20050050884 proposes a solution consisting in carrying out a desulfurization immediately after the end of the regeneration of the particulate filter when possible, in order to take advantage of the already high temperature of the exhaust gases and to reduce the necessary time. for the desulfurization phase. However, the overall duration to achieve these two consecutive purges remains too important.

According to another solution described in WO200641545, the desulfurization and regeneration of the particulate filter are carried out simultaneously. This solution has the disadvantage of being very risky because the desulfurization causes a sharp rise in temperature which may cause overheating and runaway combustion of the particulate filter, which may deteriorate.

These solutions are therefore unsatisfactory and there is a need for another improved solution for managing regeneration and desulphurization.

Thus, a general object of the invention is to propose another solution for managing the desulfurization and / or regeneration of an aftertreatment device for the exhaust gas of a motor vehicle.

For this purpose, the invention is based on a process for the desulphurisation of a NOx-Trap for the aftertreatment of exhaust gases emitted by an internal engine of a motor vehicle, characterized in that it comprises a stage to estimate the efficiency of a combined realization of the REN100FR / PJ8795 - NOx-Trap desulfurization DA deposition during the regeneration of a particulate filter, then a step of NOx-Trap desulfurization which is initiated during the regeneration of the particulate filter, after the beginning of the regeneration of the particulate filter and before the end of this regeneration, so that the desulphurization of the NOx-Trap and the regeneration of the particulate filter are carried out partially simultaneously, if the estimation of the effectiveness of this combination performed at the estimation stage is considered positive.

The estimation step may include taking into account parameters selected from the sulfur loading of the NOx-Trap and / or the soot loading of the particulate filter and / or the operating point of the engine and / or the recognition of rolling profile.

The desulphurization of NOx-Trap may only be initiated during the regeneration of the particulate filter after verification that the remaining mass of particles in the particulate filter is below a predefined threshold which limits the risk of reaching an unbearable temperature within the particulate filter after initiation of the desulfurization.

The verification step may include other physical condition checks, including verifying that the temperature before entering the turbine is low enough not to damage the turbine, and / or verifying that the temperatures within the NOx- Trap and particulate filter are low enough not to damage the catalysts, and / or verification that the operating point of the engine makes it possible to ensure the feasibility of the necessary conditions for desulfurization, and / or verification of the compatibility of the ratio of gearbox engaged. The de-sulphurization process may comprise a preliminary step of verifying that the mass of particles stored in the particulate filter is below a predefined threshold value or that the mass of sulfur in the NOx-Trap exceeds a predefined threshold value before launching the step of estimating the efficiency of a realization. NOx-Trap desulfurization was combined during the regeneration of a particulate filter.

The desulfurization process may comprise a regeneration phase of the particulate filter carried out until the inlet temperature of the particulate filter reaches a stabilized value, then initiation of NOx-Trap desulfurization during regeneration and simultaneous realization of the particulate filter and NOx-Trap desulphurization so that the NOx-Trap internal temperature oscillates between a minimum value defined by the poor periods of desulphurization and a maximum value defined by the rich periods of desulfurization, so that this maximum internal temperature of NOx-Trap does not cause the maximum permissible temperature to be exceeded by the particulate filter.

Further, the desulphurization process may comprise a step of performing desulphurization or regeneration independently if the step of estimating the efficiency of a combined realization of NOx-Trap desulfurization during regeneration of a particulate filter comes to the conclusion of non-effectiveness of the combined embodiment.

The invention also relates to a powertrain for a motor vehicle, comprising a motor and an exhaust pipe for conducting the exhaust gases to a NOx-Trap and a particulate filter, characterized in that it comprises a unit of electronic control REN100FR / PJ8795 - DA 7 ECU depot which automatically implements the desulfurization process as described above.

The invention also relates to a motor vehicle characterized in that it comprises a powertrain according to the preceding claim.

These objects, features and advantages of the present invention will be set forth in detail in the following description of a particular non-limiting embodiment in connection with the accompanying figures among which:

FIG. 1 schematically represents a power unit according to the invention; FIG. 2 diagrammatically represents the method implemented according to one embodiment of the invention; FIG. 3 diagrammatically represents the variation of the maximum temperature allowed by a particle filter as a function of its particle charge; FIG. 4 represents the variation of the internal temperature of NOx-Trap 20 as a function of time during the implementation of the method according to the embodiment of the invention.

Figure 1 schematically illustrates a powertrain according to the invention. This device comprises a diesel engine 1, supplied with air 25 arriving via an intake pipe 2 and with fuel via an injection system 6. At the outlet of the engine, the exhaust gases are driven by an exhaust pipe 3 and pass successively a NOx-Trap 4 and then a particulate filter 5.

The device further comprises an electronic control unit (ECU) 10, composed of hardware elements (harware) and / or software (software), which is generally in the form of a computer of edge. This ECU unit receives data from different sensors, not shown, such as for example a temperature sensor for measuring the temperature of the exhaust gas, an oxygen sensor which measures the amount of oxygen in the exhaust gas, a sensor of temperature arranged at the inlet of the particulate filter so as to measure the temperature of the exhaust gas at this filter, a differential pressure sensor mounted at the terminals of the particulate filter. On the basis of these data and / or memorized models, the ECU unit implements a powertrain management method and in particular the management of the desulfurization and the regeneration of the post-processing devices 4, 5. For this purpose, it controls for example the various valves and injectors of the device. This process is explained later.

The concept of the invention is to achieve maximum NOx-Trap desulfurization combined with regeneration of the particulate filter by allowing the triggering of a desulphurization during a regeneration of the particulate filter, from the moment when certain physical conditions are met. Thus, during such a combination of these two types of purge, the overlap between the desulfurization and the regeneration takes place after a first regeneration phase alone.

Thus, the method of the invention, implemented by an automaton, as illustrated in FIG. 2, comprises a first step El consisting of determining whether there is a need to purge a post-processing device, more precisely, either a regeneration of the particulate filter or a desulfurization. For this, the method essentially verifies that the mass of PM particles stored in the particulate filter exceeds a predefined threshold value SMP or that the mass of sulfur MS in the NOx-Trap exceeds a predefined threshold value SMS .

In case of detection of a need for a purge in step E1, the method implements a second step E2 consisting of evaluating the feasibility of a combined purge consisting in partially achieving regeneration and desulphurization. This step therefore consists in evaluating the effectiveness of a combination of these two purges and the appropriate time to launch such a combined purge. For example, the utility of triggering a combined purge can be determined by a mass of sulfur stored in the NOx-Trap above a threshold and a mass of soot stored in the particulate filter above another threshold, which thresholds may depend on of the current rolling profile. For example, the soot combustion and desulphurization efficiencies can be calculated over a rolling time window of the last 5 to 10 minutes and compared with predetermined thresholds to judge the utility of performing a combined purge. This calculation makes it possible to estimate whether the current operating conditions are adapted to a combined purge.

The utility or effectiveness of performing a combined purge is therefore determined from various estimates including: - the total cost in dilution (related to injection strategies) - the total duration of the combination of purges These estimates depend on of several selected parameters among which: - the sulfur loading of the NOx-Trap, - the soot loading of the particle filter, - the operating point of the engine, - the rolling profile recognition.

When step E2 concludes that the conditions are met to initiate the combined regeneration of the particulate filter with the desulphurization, then the regeneration of the particulate filter is performed in step E3. In addition, in parallel with this regeneration of step E3, a condition is checked periodically at step E4 to determine when it is possible to trigger the desulfurization during regeneration.

Step E4 may consist in verifying whether certain physical conditions are met, the essential condition of which is that the mass of particles PM present in the particulate filter has fallen below a predefined SE runaway threshold.

Indeed, desulfurization consists of the alternation of rich niches and poor niches. The desulphurization begins with a rich niche, in which a large excess of reducers is present in the exhaust gas, allowing in particular to consume the residual oxygen of the exhaust gas. In a rich niche, the inlet temperature of the particulate filter 5 is very high, above 100 to 150 C of that normally expected for its regeneration phase. The curve of FIG. 3 illustrates the maximum temperature allowed by the particulate filter, which strongly depends on the mass of particles present in the filter. Beyond this maximum temperature, combustion within the particulate filter becomes uncontrolled and ends up damaging or even destroying the particulate filter. This explains why the method is based on the definition of a runaway threshold, which corresponds to a choice of remaining mass of particles SE in the particulate filter, which also corresponds to a maximum temperature allowed by the filter, before eventually starting. a desulfurization. This runaway threshold therefore represents a compromise between the desire to initiate the most rapid REN50FR / PJ8795 - deposition DA 11 possible desulfurization during the regeneration of the particulate filter to reduce the total time of regeneration phases and desulfurization and on the other hand the elimination of the risk of runaway regeneration which may damage the particulate filter.

According to alternative embodiments, other physical conditions can be verified during this step E4 among which: - Verification that the temperatures in the NOx-Trap and the particulate filter are low enough not to damage the catalysts; - Verification that the operating point makes it possible to ensure the feasibility of the desired conditions (desulfurization zone) Checking the gearbox ratio engaged.

After validation in step E4, the desulfurization is performed in step E5. It begins with the implementation of a rich niche, according to the previous explanations. The end of the following poor slot, whose setting is similar to that of the regeneration phase of the particulate filter, is then determined either by a temperature criterion or by a predefined maximum duration. This alternation of rich and poor periods is repeated until the end of the desulfurization. FIG. 4 illustrates the variation of the internal temperature of NOx-Trap during the implementation of the method according to the invention. In a first period t1, only the regeneration is carried out and the internal temperature of the NOx-Trap 25 increases progressively until reaching a temperature close to Ti, resulting in an inlet temperature of the particle filter of the order of 600 t. At time t2, the desulfurization is initiated, while the regeneration is still in progress. Desulphurization thus benefits from favorable conditions for its beginning since the temperature of the exhaust gas is already very high because of the regeneration. For example, the time t2 will correspond to a progress of the regeneration of the particulate filter between 0 and 60%. The mass of soot to trigger a regeneration (SMP) will typically be between 6 and 10g / L. The maximum soot threshold for triggering rich slots will be included, depending on the temperature between 4 and 6 g / L. During the period t3, the regeneration and the desulphurization are carried out simultaneously: the internal temperature of the NOx-Trap then oscillates between a maximum temperature T3 and a minimum temperature T2, according to rise periods 12 corresponding to so-called rich periods of the desulfurization and periods of descent 13, corresponding to so-called poor periods. The triggering threshold for desulphurisation has been set such that the internal temperature of NOx-Trap T3 does not cause the permissible maximum inlet temperature of the particulate filter defined in Figure 3 to be exceeded.

In parallel with the process described above, the control automaton for the desulfurization can also lead to the conclusion in step E2 that the combination of the regeneration and the desulphurization is not effective for the device and then decide to initiate regeneration or desulfurization independently, as in conventional solutions of the state of the art. This part of the process is not shown in Figure 2 for reasons of simplification.

Finally, the invention has the following advantages: the escape route undergoes a total time of reduced heating periods, which greatly reduces the dilution of gas oil in the oil; the total time of regeneration and desulphurization can be greatly reduced since these two purges are carried out partly simultaneously. According to the invention, this time can be divided by two approximately. This therefore reduces the heating period of REN100FR / PJ8795 - deposit DA 13 the exhaust line; - the dilution of oil and the consumption of the motor vehicle are greatly reduced. REN100FR! PJ8795 - DA 14 deposit

Claims (9)

Revendications1. Process for desulfurizing a NOx trap (4) for the CLAIMS1. Process for the desulphurization of a NOx trap (4) for the aftertreatment of exhaust gases emitted by an internal engine of a motor vehicle, characterized in that it comprises a step (E2) for estimating the efficiency of a combined realization of the desulphurization of the NOx trap (4) during the regeneration of a particulate filter (5), then a step (E5) of desulfurization of the NOx trap which is initiated during the regeneration (E3 ) of the particulate filter (5), after the beginning of the regeneration of the particulate filter (5) and before the end of this regeneration, so that the desulphurization of the NOx trap (4) and the regeneration of the particulate filter ( 5) are performed partially simultaneously, if the estimation of the effectiveness of this combination performed in the estimation step (E2) is considered positive. 2. Desulfurization process according to claim 1, characterized in that the estimation step (E2) comprises taking into account parameters chosen from the sulfur loading of the NOx trap and / or the soot loading of the filter. particles and / or the operating point of the engine and / or the rolling profile recognition. 3. Desulfurization process according to claim 1 or 2, characterized in that the desulphurization of the NOx trap (4) is initiated during the regeneration of the particulate filter (5) after verification (E4) that the remaining mass of particles (MP) in the particulate filter (5) is below a predefined threshold (SE) which makes it possible to limit the risk of reaching an unsupportable temperature within the particulate filter after initiation of the desulphurisation.RENI 00GB I PJ8795 - DA filing 15 4. Desulfurization process according to claim 3, characterized in that the verification step (E4) comprises other checks of physical conditions among which the verification that the temperature before entry into the turbine is low enough not to damage the turbine, and / or verify that the temperatures within the NOx trap and the particulate filter are low enough not to damage the catalysts, and / or verify that the operating point of the engine makes it possible to ensure the feasibility of the necessary conditions for desulphurisation, and / or verification of the compatibility of the gearbox ratio engaged. 5. Desulfurization process according to one of the preceding claims, characterized in that it comprises a preliminary step (El) verification that the mass of particles (MP) stored in the particulate filter is less than a predefined threshold value ( SMP) or that the mass of sulfur (MS) in the NOx trap exceeds a predefined threshold value (SMS) before launching the estimation step (E2) of the efficiency of a combined realization of trap desulfurization to NOx (4) during the regeneration of a particulate filter (5). 6. Desulfurization process according to one of the preceding claims, characterized in that it comprises a phase (t1) for regeneration of the particulate filter (5) carried out until the inlet temperature of the particulate filter reaches a stabilized value (T1), then initiation of the desulphurization of the NOx trap during regeneration and simultaneous realization of the regeneration of the particulate filter (5) and the desulfurization of the NOx trap (t3) so that the internal temperature of the trap to NOx oscillates between a minimum value (T2) defined by the poor periods of desulphurization and a maximum value (T3) defined by the rich periods of desulphurisation, so that this temperature is the maximum internal depot DA 16 of the trap. NOx (T3) does not cause the maximum permissible temperature to be exceeded by the particulate filter (5). 7. Desulfurization process according to one of the preceding claims, characterized in that it comprises a step of performing a desulphurization or regeneration independently if the step (E2) for estimating the efficiency of a combined realization of the desulphurization of the NOx trap (4) during the regeneration of a particulate filter (5) reaches the conclusion of non-effectiveness of the combined embodiment. 10 Motor vehicle power train, comprising a motor (1) and an exhaust pipe (3) for conducting the exhaust gases to a NOx trap (4) and a particulate filter (5), characterized in that it comprises an ECU electronic control unit (10) which automatically implements the desulfurization process according to one of the preceding claims. 9. Motor vehicle characterized in that it comprises a powertrain according to the preceding claim. 20