FR2933447A1 - Nitrogen oxide trap desulfurizing method for post processing of exhaust gas emitted by internal engine of motor vehicle, involves initiating desulfurization of trap during regeneration of particle filter - Google Patents

Abstract

The method involves desulfurizing a nitrogen oxide trap after beginning of regeneration of particle filter and before ending of filter regeneration so that trap desulfurization and filter regeneration are carried out simultaneously in partial manner. The trap desulfurization is initiated during regeneration of the filter as soon as two verifications are processed, where one of the verifications is made when a remaining mass of particles (MP) in the filter is below a predefined threshold (SE), and other verification is made when sulfur mass in the trap is sufficient for desulfurization. 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 exhaust gas post-treatment device 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 of reducing nitrogen oxides to N2 and CO2 carbon dioxide, 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 REN098FR - deposit DA 2 in the filter becomes too large. For this purpose, a specific fuel injection strategy makes it possible to raise the temperature in the particulate filter to a high value at about 600 t, 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 within the NOx-30 Trap, that is a temperature generally greater than 650 ° C, and a medium REN098FR - deposit DA 3 rich (excess of reductants) for a duration that can go 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 REN098FR - 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 desulphurization 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 desulphurization of a NOx-Trap for the aftertreatment of exhaust gas emitted by an internal engine of a motor vehicle, comprising a step of regenerating a filter characterized in that it comprises a step of REN098FR - NOx-Trap desulfurization deposition DA which is initiated during the regeneration of the particulate filter, after the commencement of the regeneration of the particulate filter and before the end of this regeneration, so that NOx-Trap desulphurization and particulate filter regeneration are carried out partially simultaneously, NOx-Trap desulphurization being initiated during the regeneration of the particulate filter as soon as the two conditions treated in the next two steps are verified : -checking that the remaining mass of particles in the particulate filter is below a predefined threshold which makes it possible to limit the risk e to reach an unbearable temperature within the particulate filter after initiation of the desulfurization; verification that the mass of sulfur present in the NOx-Trap is sufficient for a desulfurization to be useful.

The first verification step may include other physical condition checks including verifying that the temperatures within the NOx-Trap and the particulate filter are low enough not to damage the catalysts, and / or verification that the point The operation of the engine makes it possible to ensure the feasibility of the conditions necessary for the desulfurization, and / or verification of the compatibility of the gear ratio engaged.

The second verification step may include further verifications of the utility of initiating desulphurization during regeneration from parameters selected from NOx-Trap sulfur loading and / or soot loading of the particulate filter and / or the operating point of the engine and / or the rolling profile recognition in order to estimate the efficiency and the gain of the cumulation of the regeneration and the desulphurization, the desulfurization being engaged only beyond a predefined minimum gain. The process may comprise a preliminary step of verifying that the mass of particles stored in the particulate filter is less than a predefined threshold value before starting the regeneration of the particulate filter.

In addition, the desulphurization 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 realization. simultaneous regeneration of the particulate filter and the desulphurization of NOx-Trap so that the internal temperature of the NOx-Trap oscillates between a minimum value defined by the poor periods of desulfurization and a maximum value defined by the rich periods of the desulfurization, so that this internal temperature of the maximum NOx-Trap does not cause the maximum permissible temperature to be exceeded by the particulate filter.

The desulfurization process may further comprise a step of performing independent desulphurization if there is a need for desulfurization out of a need for regeneration.

The invention also relates to a power unit 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 electronic control unit ECU which automatically implements the desulfurization process as described above.

The invention also relates to a motor vehicle characterized in that it comprises such a powertrain.

These objects, features and advantages of the present invention will be described in detail in the following description of a particular embodiment made in a non-limiting manner in relation to the appended 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 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 20 arriving via an intake pipe 2 and with fuel via an injection system 6. At the outlet of the engine, the exhaust gases are conducted via 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 (harware) and / or software (software) elements, which is generally in the form of an on-board computer. 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 REN098FR - deposit DA 8 measures the amount of oxygen in the gases. exhaust, a temperature sensor disposed 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 allow the triggering of a desulfurization during a regeneration of the particulate filter, from the moment when both certain physical conditions and certain conditions of utility are met. Thus, the overlap between the desulphurization 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 in determining whether the conditions are met to start the regeneration of the particulate filter. For this, the mass of PM particles stored in the particulate filter is evaluated according to a known method of the state of the art, and if it exceeds a predefined threshold SMP then the regeneration of the particulate filter can be carried out at the stage E2. In addition, in parallel with this regeneration of step E2, two conditions are checked periodically at steps E3 and E3 'to determine whether to trigger the desulfurization during the regeneration.

The first condition, treated in step E3, consists 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 one 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 cc 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 desulphurization as quickly as possible during the regeneration of the particulate filter to reduce the total time of the regeneration and desulfurization phases and, on the other hand, the eliminating the risk of runaway regeneration which may damage the particulate filter.

According to alternative embodiments, other physical conditions can be verified during this first step E3 among which: - Verification that the temperatures in the NOx-Trap and the particulate filter are low enough not to damage the catalysts; REN098FR - DA 10 deposit - Verification that the operating point makes it possible to ensure the feasibility of the desired conditions (desulfurization zone) - Verification of the gearbox ratio engaged.

In parallel with step E3, the method processes a second condition verified in step E3 ', which determines the utility of triggering a desulfurization. For this, it implements a method of estimating the efficiency or utility of the cumulative desulphurization and regeneration. For example, the utility of triggering the desulphurization can be determined by a sulfur mass stored in the NOx-Trap above a threshold, this threshold being able to depend on the current rolling profile. We can also, for example, calculate the theoretical desulphurization efficiency that we would have had on a sliding window of the last 5 to 10 minutes, if we then triggered slots with wealth greater than 1. This calculation makes it possible to estimate if the current operating conditions are suitable for desulfurization.

Optionally, it can also estimate the total cost in dilution, related to the injection strategies. As previously, for example, it is possible to calculate the theoretically introduced dilution over the last 5 to 10 minutes, if it had then triggered slots with a richness greater than 1. This calculation makes it possible to estimate whether the current operating conditions are not not too expensive in dilution in the desulfurization mode.

The utility is therefore determined from selected parameters among which the sulfur loading of the NOx-trap, the soot loading of the particulate filter, the point of operation of the engine, the recognition of the rolling profile. REN098EN These conditions of utility allow to estimate if it is interesting to trigger a desulfurization, in terms of efficiency of desulphurization and / or cost of dilution.

Thus, the physical conditions correspond to the conditions for which it is possible to achieve a wealth niche greater than 1 without damaging the system; the utility conditions correspond to the conditions for which an algorithm estimates the moment when it is opportune to launch a niche with wealth greater than 1.

When the two conditions verified in steps E3 and E3 'are satisfied, the desulfurization is performed in step E4. 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 gradually increases until a temperature close to Ti is reached, resulting in a temperature at the inlet of the particle filter of the order of 600 ° C. . 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 soot threshold REN098FR - deposit DA 12 maximum to trigger 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 desulphurization control automaton also verifies the need for desulfurization out of any regeneration of the particulate filter, for example by verifying that the accumulated sulfur mass exceeds a predefined threshold, and then performs desulphurisation independently if this need is verified and desulphurization possible. 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 is 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 the exhaust line; the dilution of oil and the consumption of the motor vehicle are greatly reduced.

Claims (8)

Revendications1. Process for desulphurizing a NOx trap (4) for the aftertreatment of exhaust gas emitted by an internal engine of a motor vehicle, comprising a step (E2) for regenerating a particulate filter (5) , characterized in that it comprises a step (E4) of desulfurization of the NOx trap which is initiated during the regeneration of the particulate filter (5), after the commencement 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 carried out partially simultaneously, the desulfurization of the NOx trap (4) being initiated during the regeneration of the particulate filter ( 5) as soon as the two conditions treated in the two following steps (E3, E3 ') are satisfied: -check (E3) that the remaining mass of particles (PM) in the particulate filter (5) is below a threshold predefined (SE) that allows and to limit the risk of reaching an unbearable temperature within the particulate filter after initiation of the desulfurization; verifying (E3 ') that the mass of sulfur present in the 20 NOx trap (4) is sufficient for desulphurization to be useful. The desulphurization process according to claim 1, characterized in that the first verification step (E3) comprises further physical condition verifications including verification that the temperatures within the NOx trap and the 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 conditions necessary for the desulfurization, and / or verification of the compatibility of the gearbox ratio engaged. 30REN098EN - DA filing 14 3. Desulfurization process according to claim 1 or 2, characterized in that the second verification step (E3 ') comprises other checks of the utility of initiating the desulfurization during regeneration from selected parameters among the loading sulfur content of the NOx trap and / or the soot loading of the particulate filter and / or the operating point of the engine and / or the rolling profile recognition in order to estimate the efficiency and the gain of the accumulation of the regeneration and desulphurization, the desulphurization being engaged only beyond a predefined minimum gain. 4. Desulfurization process according to one of the preceding claims, characterized in that it comprises a preliminary step (E1) of verification that the mass of particles (MP) stored in the particulate filter is less than a predefined threshold value ( SMP) before starting the regeneration (E2) of the particulate filter. 5. Desulfurization process according to one of the preceding claims, characterized in that it comprises a phase (t1) of 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 desulfurization and a maximum value (T3) defined by the rich periods of desulphurisation, so that this internal temperature of the maximum NOx trap (T3) does not does not cause the maximum permissible temperature to be exceeded by the particulate filter (5) .REN098EN - DA 15 6. Desulfurization process according to one of the preceding claims, characterized in that it comprises a step of performing an independent desulphurization if there is a need for desulfurization out of a need for regeneration. 7. Power train for a motor vehicle, 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 electronic control unit 10 ECU (10) which automatically implements the desulfurization process according to one of the preceding claims. 8. Motor vehicle characterized in that it comprises a powertrain according to the preceding claim. 15