FR2873160A1 - METHOD FOR MANAGING THE REGENERATION OF A PARTICLE FILTER - Google Patents

Abstract

Process for managing the regeneration of an exhaust line particle filter (1) provided with a catalytic element, by regulating the inlet temperature (TeFAP) of the filter (1), characterized in that it imposes a limitation of the inlet temperature (TeFAP) if the temperature gradient across the terminals (E) of the catalytic member exceeds a threshold (F) presenting a risk of degradation therefor.

Description

METHOD FOR MANAGING THE REGENERATION OF A FILTER

PARTICLE

  The invention relates to the depollution of diesel engines.

  More specifically, it relates to the management of the regeneration of a particulate filter, or FAP, exhaust line provided with a catalytic member, by regulating the temperature at the inlet of the filter.

  Regeneration of the particulate filter by combustion of soot pollutants, or particles, contained therein, is generally performed through delayed injections (after the top dead center) of fuel. These have the effect of increasing the temperature of the exhaust gases.

  When there is also in the exhaust line a catalytic member (either in the form of an oxidation catalyst upstream of the filter, or in the form of a catalytic material disposed within the filter), for oxidizing the reducing elements (HC, CO, H2), the fuel injected late, which did not burn in the combustion chamber, burns in the catalytic part of the exhaust line.

  These oxidation reactions of HC and CO on the catalytic sites, in the presence of oxygen, increase the catalyst inlet / outlet temperature gradient, to the point of being able to deteriorate it.

  According to the known prior art illustrated in particular by the publication FR 2 804 168, the regeneration of the filter is managed by regulating its inlet temperature. That is to say that the quantity and / or the delay of the gas oil injections is modified, so as to have a temperature at the input of the FAP as close as possible (equal in absolute terms) to a temperature setpoint allowing the regeneration of the FAP, while protecting the latter from possible deteriorations due to the runaway of soot combustion reactions.

  This technique therefore makes it possible to control the thermal inputs upstream of the FAP, but without taking into account the contributions of HC and CO upstream of the catalyst. However, in the presence of oxygen and catalytic materials, and at high temperature, HC and CO oxidize by releasing heat and increasing the temperature of the inlet / outlet temperature of the catalyst. The increase in temperature is thus likely to damage the regulator, without having been detected and avoided.

  In general, the known strategies for controlling the regeneration of a particulate filter do not ensure the protection of the catalytic members implanted upstream of the filter.

  The present invention aims to overcome this major disadvantage, and to prevent the risk of temperature runaway within the catalytic body.

  For this purpose, it proposes to limit the temperature gradient across the catalytic body, when this limitation is necessary to preserve the catalytic body from deterioration related to the oxidation of reducing elements in the presence of oxygen and materials. catalyst.

  According to a preferred embodiment of the invention, the limitation of the temperature gradient across the catalytic member is imposed if the latter exceeds a threshold presenting a risk of degradation for the catalytic member.

  Preferably, the gradient is limited by reducing the amount of fuel injected late after the top dead center (PHM) because it creates little heat input of the particulate filter, but brings a lot of HC and CO, responsible for the temperature gradient at the terminals of the catalytic organ.

  Other characteristics and advantages of the invention will become clear from a reading of the following description of a non-limiting embodiment thereof, with reference to the accompanying drawings, in which: FIG. 1 is a diagram of FIG. FIG. 1 shows a catalytic particle filter 1, ie containing catalytic materials (not shown), for example platinum, for oxidizing HC and CO mainly from late injections. Upstream of the filter 1 is placed a temperature sensor 2, measuring the temperature at the inlet of the TeFAP filter. On the other hand, no output temperature sensor has been shown because the downstream temperature of the filter can advantageously be calculated on the basis of a conventional statistical model. In the case presented, the engine has a turbo 3 and an EGR 4 (Exhaust Gas Recirculation) circuit.

  The diagram also shows a cylinder 6 of the engine with its fuel injector 7, its intake duct 8 and its exhaust duct 9. These two ducts are connected by the EGR circuit 4, with its EGR valve 4a. The intake duct 8 has a flowmeter 8a, a collector pressure sensor 8b and an intake flap 8c. It opens into an intake manifold 9. Finally, the circuit comprises a turbo-compressor 3, arranged between the intake and exhaust ducts 8, 9. In the diagram, no catalyst has been shown. oxidation, because it is assumed that a large amount of catalytic material is disposed directly inside the filter (it is therefore a catalytic particle filter). But the invention applies under the same conditions, if the catalyst is juxtaposed upstream of the filter.

  In order to regenerate the filter 1, at least one delayed injection is made in the combustion chambers of the engine, which has the effect of increasing the temperature of the exhaust gases. The main injection is eventually followed by one or more late injections. The late-injected gas oil does not burn in the combustion chamber, but in the catalytic part of the exhaust line, where HC and CO oxidize by increasing the temperature of the gases. The late injection also has the effect of increasing the input / output temperature gradient of the catalyst.

  The process of the invention illustrated in FIG. 2 proposes to control this temperature gradient during the regeneration phases. Specifically, it is planned to regulate the amount of gasoil injected late, preferably after the top dead center, so as to maintain between the inlet and the outlet of the catalytic member, a permissible temperature gradient although there is no In some cases, the temperature of the regeneration temperature FAP is reached, this arrangement makes it possible to preserve the catalyst from cracks due to an excessive temperature gradient.

  The proposed solution has the advantage of taking into account the effect of the contributions of HC, CO in the management of the regeneration of the FAP. Thus, knowing by direct measurement, or modeling, the inlet and outlet temperatures of the catalytic member and controlling the corresponding gradient, it is ensured not to damage this body.

  As shown in Figure 1, the vehicle engine may be equipped with an EGR system, a turbocharger and / or an intake flap.

  Within the scope of the invention, the engine can also have a common high pressure inlet manifold or a direct injection system. However, the invention applies under the same conditions in the absence of one or more of these elements.

  According to the invention, the management of the regeneration of the FAP is ensured by a regulation of the temperature at the inlet of the TeFAP filter.

  That is to say that the quantity and / or the delay of the injections of gas oil is modified, so as to have an inlet temperature of FAP TeFAP, as close as possible (equal in absolute terms) to a set temperature given, allowing the regeneration of the FAP while protecting, as much as possible, a deterioration by runaway reaction.

  As shown in FIG. 2, the difference (C) between the setpoint (A) and the measured temperature value (B) of the TeFAP filter (t) is continuously calculated. The engine calculator deduces a first injection pattern (b). At the same time, the occurrence of the input / output temperature gradient (E) of the catalytic element is monitored at each occurrence of the computer. If this gradient exceeds a certain threshold (F), difference (G) (E) (F) <0, the computer imposes a second injection pattern of its own to limit the amount of gas oil injected late to maintain the gradient (E ) below the threshold (F). The threshold (F) depends on the materials used in the catalyst. Furthermore, the inlet and outlet temperatures of the catalytic member can be indifferently determined by means of sensors, or by physical or statistical modeling (for example by neural networks).

  This method has very large advantages for managing the regeneration of a FAP, because it provides in a simple way the protection of the catalytic member of the exhaust line, minimizing the impact of protection on the course of the regeneration.

  However, its implementation requires some precautions, since the catalytic member generally has a high thermal inertia, so that the modifications of the fuel injection exert their influence on the temperature gradient after a certain lapse of time. time. The thermal inertia of the catalytic element must be taken into account in the control loop to avoid any risk of deterioration. Another safety margin will have to be introduced to take into account that on a part of the operating field of the engine (especially at low loads), it is practically impossible to cancel the temperature gradient, even by stopping any late injection. because after stopping the late injection, the outlet temperature of the catalytic member may remain a few tens of degrees higher than the inlet temperature. By integrating these constraints in the control system of the invention, the protection of the catalytic member can be provided with the greatest safety and the least possible effects on the regeneration.

Claims (5)

  Method for managing the regeneration of an exhaust line particle filter (1) provided with a catalytic element by regulating the inlet temperature (TeFAP) of the filter (1), characterized in that a limitation of the inlet temperature (TeFAP) is imposed if the temperature gradient across the terminals (E) of the catalytic member exceeds a threshold (F) presenting a risk of degradation therefor.   2. The management method according to claim 1, characterized in that the filter inlet temperature (TeFAP) is limited by reducing the fuel quantities injected late after the top dead center.   3. Management process according to claim 1 or 2, characterized in that the inlet temperature (TeFAP) is limited when the limitation is necessary to preserve the catalytic body deterioration related to the oxidation of reducing elements in the presence of oxygen and catalytic materials.   4. Management method according to one of claims 1, 2 or 3, characterized in that limits the inlet temperature of the filter (TeFAP), changing the fuel injection delay.   5. Management method according to one of the preceding claims, characterized in that the inlet temperature of the filter (TeFAP), is maintained as close as possible to a set temperature ensuring the optimization of the regeneration.