FR2920030A3 - Particle filter regenerating method for oil engine of vehicle, involves injecting fuel-rich mixture in one cylinder and injecting fuel-poor mixture in another cylinder to obtain oxygen content of exhaust gas reaching particle filter - Google Patents

Abstract

The method involves injecting a fuel-rich mixture in one of a set of cylinders (21-24) and injecting a fuel-poor mixture in another cylinder to obtain temperature and oxygen content of an exhaust gas (13) reaching a particle filter (7) and adapted to combustion of particles. Fuel contents of the fuel-rich mixture and the fuel-poor mixture are respectively higher and lower than a stoichiometric mixture. The injection of the fuel-rich mixture is carried out by post injection of fuel in the respective cylinder when a respective piston is near a top dead center. An independent claim is also included for an oil engine comprising cylinders.

Description

B07 / 1621EN AXC / JK

  Société par Actions Simplifiée known as: RENAULT s.a.s. System and method of regeneration of particulate filter of a combustion engine. 1 Invention of: Pascal BARBIER System and method of particle filter regeneration of a combustion engine.

  The invention relates to the field of diesel depollution, and more particularly, the regeneration steps of a particulate filter. Internal combustion engines produce exhaust gases that include polluting substances, such as nitrogen oxides, unburnt hydrocarbons, carbon monoxide, soot particles. The accepted release rates of these different pollutants are strictly regulated and subject to periodic downward revisions.

  Diesel-type engines in particular emit pollutant particles into the atmosphere, the quantity of which must be reduced. These particles, which consist of soot produced during imperfect combustion in the engine, can be trapped in the exhaust gas by the implementation of a particulate filter in the exhaust line, downstream of the exhaust chambers. combustion of the engine. This particulate filter is generally mounted downstream of an oxidation catalyst, a catalyst that completes the oxidation of carbon monoxide and unburned hydrocarbons. Such a filter is made of porous ceramic material so as to retain particles in the exhaust gas passing through the filter. As the engine is used, the particles accumulate in the filter and eventually result in significant backpressure to the engine exhaust, which significantly reduces its performance. 3 Regeneration of the particulate filter must be done periodically during regeneration steps, as soon as the amount of particles in the filter becomes too great, which usually occurs after the vehicle has traveled a distance of the order from the hundred kilometers. The excess of accumulated particles is generally estimated from differential pressure measurements between the inlet and the outlet of the particulate filter. The regeneration steps take place when the engine is running, without the driver of the vehicle being aware of it. A particulate filter therefore operates periodically, in two stages. In a first step, it stores particles emitted by the engine, and in a second step, the stored particles are burned to regenerate the filter. In order to restore the performance of the engine, it is known to practice a regeneration of the filter by combustion of the particles that have accumulated therein. This combustion operation requires an increase in the internal temperature of the particulate filter, and the provision of an adequate amount of oxidizing gases or oxygen. To do this, it is necessary to reach thermal levels in the exhaust line at the inlet of the particle filter 600 C to 700 C, and preferably an operating temperature of around 620 C. The temperature of the exhaust gas being substantially lower than these values in the normal engine operating mode, various strategies are used to raise this temperature during the regeneration steps of the filter. One of these strategies is to introduce additional reducing gases into the exhaust gas to allow additional exothermic reactions. These exothermic reactions take place either by combustion of the reducing agents in the exhaust line or by their catalytic oxidation in the oxidation catalyst. Additional reducers are the fuel or fractionated hydrocarbons obtained therefrom.

  The fuel required for the preheating exotherm is introduced either directly into the exhaust line via a specific injector or into the combustion chambers of the engine by post-injection and / or delayed injection. In particular, it is possible to inject fuel just after the top dead center, by so-called near injection, carried out when the crankshaft has traveled at an angle of substantially less than 90 above the top dead center. The post-injection is said to be close when the fuel participates in the combustion in the chamber. It is also possible to provide a so-called late post-injection, performed when the crankshaft has traveled at an angle of substantially more than 90 beyond the top dead center of the piston, the fuel not participating in the combustion chamber. The injection of fuel into the cylinder at the time of the expansion step can lead to a significant dilution of fuel in the oil, even more so in the case of a late post injection.

  In addition, when the engine operates in lean mixture, that is to say with a surplus of oxygen, the additional fuel introduced by close post injection is, under the effect of the engine temperature, prematurely oxidized in the cylinder by the available oxygen. The heat thus released is partly dissipated before the exhaust gases reach the catalyst. The injection of fuel directly into the exhaust line is limited by the flow and temperature of the gases in this line. As gas oil is relatively difficult to vaporize, a mixture of inhomogeneous gas is obtained, resulting in an incomplete reaction in the catalyst and the final emission of residual polluting species. The areas of operation of the engine where this type of injection can be practiced are reduced, which is a constraint in the choice of times when the regeneration steps can be carried out. An effective regeneration strategy must ensure the arrival of sufficiently hot and sufficiently reducing gases for a wide range of engine operation, avoiding dilutions of fuel in the engine oil. Since the regeneration temperature of the particulate filter is substantially higher than that of the exhaust line in the normal operating mode of the engine, the regeneration strategy must provide for a temperature rise mode in the catalyst. In addition, the presence of a minimum amount of oxygen is necessary in the gas sent to the particulate filter, to feed the combustion reaction of the particles. JP200603817 (Toyota Motor Corp.) describes an exhaust gas recirculation combustion engine, which reinjects at least a portion of the exhaust gas after passing them into a reformer. The engine comprises two groups of cylinders fed one rich mixture of fuel, gas, and air, the other lean mixture. The reformer is supplied with heat by the general exhaust manifold and is supplied with gas by a specific connection of the gases from the group of cylinders operating with a rich mixture of fuel. An additional feed of the reformer into fuel allows the manufacture of reformed gas which is injected into the feed mixtures of the different cylinders. The strategy described is only intended to ensure a feed reformer rich exhaust reducing species. FR2798703 (Renault) discloses a method of heating a gasoline direct injection engine catalyst. In order to accelerate the temperature rise of the catalyst during engine start-up, and to prevent too many polluting species from being discharged during the period when the catalyst has not reached its operating temperature, two groups of cylinders are temporarily supplied with mixtures of different richness. The exhaust of the cylinders thus returns in the exhaust line, on the one hand reducing gases, and on the other hand oxidizing gases, which supply exothermic reactions in the exhaust line or in the catalyst. The described strategy makes it possible to obtain a rapid heating (in a few minutes at most) of the catalyst, to bring it to operating temperatures of 300 C-400 C by strongly exothermic reactions. The pollutant species emitted during the short preheating period are neglected in this process before the catalyst is at its optimum operating temperature. The document WO 03/048533 (DELPHI Technologies INC) describes a system for deactivating at least one cylinder of a combustion engine, deactivation which is accompanied by increasing the richness of the mixture injected into at least one of the cylinders remaining, in order to raise the temperature of the exhaust gas reaching a post-treatment system, and allow this post-processing system to perform a regeneration operation. The post-treatment system may include a particulate filter. The strategy described increases the temperature of the exhaust line by degrading the operating conditions of the cylinders remained active. This strategy does not optimize the arrival of oxygen necessary for the particulate filter. In addition, it imbalances the operation of the engine. The subject of the present invention is a method of regeneration of a particulate filter which makes it possible, on the one hand, to increase the temperature of the exhaust line, and on the other hand, to continue with a combustion step of particles ensured by the efficiency of maintaining temperature and the respect of a minimum rate of oxygen in the exhaust gas arriving at the filter. These two steps are optimized to limit overconsumption of fuel, the emission of polluting species and the dilution of fuel in the oil. According to an embodiment of the invention, a method allows the regeneration of a particulate filter for a diesel engine with several cylinders, said particulate filter being mounted in an exhaust line of the engine as a result of a oxidation catalyst. According to this method, a richer fuel mixture is injected than the stoichiometric mixture into at least one of the cylinders, and a lighter fuel mixture is injected simultaneously than the stoichiometric mixture into the other cylinders, so as to obtain a temperature and a oxygen content of the gases reaching the filter, adapted to the combustion of the particles. In a preferred embodiment, before the regeneration of the particulate filter, the exhaust gases are preheated to a predetermined activation temperature of the oxidation catalyst by reducing the amount of air admitted in the cylinders and post fuel injection in all the cylinders when each of the pistons is still close to the top dead center. Advantageously, during the regeneration, the fuel-rich mixture is injected by a fuel injection in the combustion chamber of the cylinder or cylinders concerned when the piston is still close to the top dead center. The exhaust gases are thus fed with unburnt fractionated hydrocarbons without unduly degrading the air / fuel proportions at the time of the explosion. In one embodiment, different intake air flow rates and / or different admission gas compositions are imposed on at least two groups of cylinders during regeneration of the filter. This regulation makes it possible to increase the air flow rate with respect to the normal operation of the engine for the group of cylinders fed with lean mixture, and to reduce the air flow rate for the group of cylinders fed with rich mixture.

  According to an advantageous embodiment of the process, during the regeneration of the particulate filter, the oxygen level in the gases entering the filter is regulated at a rate that is substantially between 4% and 8% by weight, and the temperature gases entering the filter substantially between 600 C and 650 C.

  In another aspect, it is also proposed a diesel engine with several cylinders equipped with a regeneration system for particulate filter, said system comprising an air intake pipe with flow control of the gases admitted to the cylinders, a fuel injection system in the different cylinders adjustable in fuel quantity injected and injection time, an exhaust line provided with a particulate filter mounted downstream of an oxidation catalyst, and a unit of control capable of controlling air intake and fuel injection. The control unit is capable of intermittently triggering a regeneration step of the particle filter by injecting a richer fuel mixture than the stoichiometric mixture into at least one of the cylinders, and simultaneously by injecting a mixture more lean fuel than the stoichiometric mixture in the other cylinders. According to a preferred embodiment, the control unit is furthermore capable of controlling, before the regeneration step, preheating of the exhaust gases to a determined activation temperature of the oxidation catalyst, by reduction of the quantity of air admitted into the cylinders and by post-injection of fuel in all the cylinders when each of the pistons is still close to the top dead center. Advantageously, the engine is equipped with a system of air intake valves in the cylinders, controllable by the control unit so as to impose different air flow rates to at least two groups of cylinders. Advantageously, the motor is equipped with a means for determining the differential pressure between the inlet and the outlet of the particulate filter, a means for determining the inlet temperature of the particulate filter, a determination means the inlet temperature of the catalyst, a means for determining the oxygen content in the gases entering the particulate filter, the control unit being able, from the data supplied by these determination means, to decide launching a regeneration step and adapting the quantities and moments of fuel injection in each cylinder.

  The invention will be better understood from the study of an embodiment taken by way of nonlimiting example and illustrated in Figure 1 attached, which shows schematically the main elements of intake and exhaust of a motor to internal combustion equipped with a catalyst and a particulate filter in the exhaust line. As illustrated in FIG. 1, a combustion engine 1, which here is a diesel engine, comprises an intake manifold 2 and an exhaust manifold 3. A turbocharger 4 comprises a turbine 4a and a compressor 4b mounted on a shaft. common. The intake manifold 2 is supplied via a line 8 through the compressor 4b by the air 12 coming from an air filter 9 connected to an air inlet 10. A flow meter 11 makes it possible to measure the air flow rate. entering the pipe 8. The exhaust gases 13 which pass through the turbine 4a are conveyed by an exhaust line 5 to a catalyst 6 and then to a particulate filter 7 mounted downstream of the catalyst 6. Temperature probes 17, 18 are arranged in the exhaust line respectively upstream of the catalyst 6 and between the catalyst 6 and the particulate filter 7. An oxygen sensor 19 is placed in the exhaust line 5 between the catalyst 6 and the particulate filter 7. A differential pressure sensor 20 is connected between the inlet of the particulate filter 7 and its outlet. The differential pressure sensor 20 may optionally be replaced by a simple pressure sensor mounted upstream of the particulate filter, to measure the overpressure generated by the accumulation of particles.

  The temperature sensors 17, 18 and the oxygen sensor 19 may possibly be omitted, and the corresponding values of temperature and oxygen content may be obtained by calculation from the other operating parameters of the engine. A bypass line 14 is also directly connected to the exhaust manifold 3, so as to recycle a portion of the exhaust gas to the inlet of the intake manifold 2, into which the end of the pipe opens In the pipe 14, is mounted a cooling exchanger 15 for cooling the recycled exhaust gas 11 or EGR, and a recirculation valve 16 to regulate the proportion of reinjected gases in proportion to the fresh air Incoming 12. The engine 1 comprises four cylinders 21, 22, 23, 24 fed by the manifold 2 through 4 intake valves 21a, 22a, 23a, 24a, for regulating the flow of gaseous mixture entering each cylinder from an electronic control unit 25 by means of electrical signals passing through control connections 30. The individual admission valves 21a, 22a, 23a, 24a can also be replaced by two valves. are of collective admissions independent of each other, but each controlling a group of cylinders, which can be easily achieved in the case where the cylinders of the engine are arranged in V. Each cylinder 21, 22, 23, 24 is also equipped with a fuel injector not shown in the figure, each injector being individually controlled by the control unit 25 both in fuel quantity, and in terms of moments when the injection (or injections) of fuel occurs at each engine cycle. The electronic control unit 25 receives different information from the engine 1, as well as the measurement of the flow of air from the flowmeter 11, the signals of the temperature probes 17 and 18, the oxygen sensor 19, and the differential pressure measurement 20, the signals being conveyed by the connections 11a, 17a, 18a, 19a, and 20a respectively. The control unit 25 comprises a calculation module 26 capable, from the power supply data of the engine 1 such as the intake air flow rate, the recycled gas flow rate, the quantity of fuel injected into each cylinder, and the When the fuel injections are made, evaluate the temperatures and compositions of the exhaust gases 13 12 reaching the catalyst 6, then the particulate filter 7 after additional oxidation reaction in the catalyst. When the differential pressure sensor 20 returns to the control unit 25 differential pressure values above a threshold programmed in advance, the control unit 25 initiates a regeneration step of the particulate filter 7. On average, the mileage traveled by the vehicle between two stages of regeneration of the particle filter represents one or several hundred kilometers.

  At the moment when the control unit 25 initiates the regeneration step of the particle filter 7, the vehicle may be running at low load in the city, with a temperature of the gases 13 in the exhaust line 5 in the vicinity of 150 C at 200 C. The vehicle may also run at high highway load, with temperatures in the exhaust line reaching 600 C to 700 C. The vehicle may still be in intermediate taxiing configurations with a line temperature at the stage of regeneration of the particulate filter 7, the particles are burned in the particulate filter 7 by the arrival of sufficiently hot gases and containing a minimum proportion of oxygen for allow the combustion of particles. This combustion may be preceded by a step of preheating the flow of exhaust gas 13 to an activation temperature of the oxidation catalyst substantially around 300 C. The control unit 25 triggers a preheating step as follows: it sends to the gas admission valves 21a, 22a, 23a, 24a a reduction order of the air intake, so that the combustion in the cylinders is made from a mixture proportionally enriched with fuel . Meanwhile, the fuel injectors of the cylinders 21, 22, 23, 24 receive from the control unit 25, a signal to perform, in addition to fuel injection for the engine cycle, a close post injection. The exhaust gases are hotter than normal due to the reduced amount of air admitted. The heat released then contributes to an increase in the temperature of the exhaust gas, measurable by the temperature sensor 17, and therefore the catalyst.

  Once the temperature measured by the sensor 18 has reached the activation temperature of the catalyst, either as a result of the preheating step described above, or because of the engine speed at the start of the regeneration step, the control unit 25 sends the signals triggering the particle regeneration step. For this purpose, the inlet valves of a part of the cylinders, for example the valves 23a and 24a and the injectors of the cylinders 23 and 24 corresponding, are regulated so that the resulting fuel mixture is leaner in fuel than the stoichiometric mixture, or even become even leaner in fuel than the mixture at normal engine speed. At the same time, the inlet valves of the remaining cylinders, in our example the valves 21a and 22a and the injectors of the corresponding cylinders 21 and 22, are regulated so that the resulting fuel mixture is richer in fuel than the stoichiometric mixture. This increase in the richness of the mixture injected into the cylinders 21 and 22 may be accentuated by a reduction in the admission of air by the valves 21a and 22a. Thus, the exhaust gases from the poor cylinders 23 and 24 contain residual oxygen, and the exhaust gases from the rich cylinders 21 and 22 contain fractionated but unoxidized hydrocarbons. The deficit of each gas stream is either reducing or oxidizing, prevents combustion in the cylinders. These two gas flows are then combined in the exhaust line 5, and the passage through the catalyst 6 makes it possible to trigger the oxidation of the residual hydrocarbons. The exothermic energy of the reaction is therefore used for heating or maintaining the temperature of the only catalyst 6 and the exhaust gas downstream of the catalyst, instead of dissipating in the heating of the line of Exhaust 5 upstream of the catalyst 6. In order that the operation of the rich cylinders 21 and 22 is not unduly degraded, the injection of the additional fuel is carried out by close post injection. This combines the advantages of the presence of a leaner than stoichiometric mixture in the cylinder at the moment of the explosion, the feeding of the exhaust gases to fractionated hydrocarbons, and the low post combustion of these hydrocarbons in the cylinder. the cylinder because of the richness, on average on the cycle, of the injected mixture, and the low dilution of fuel in the engine oil.

  It should be noted that in this embodiment, the proportion of recycled gases returned to the air intake of the cylinders is identical for all the cylinders. It is also possible to envisage a selective recirculation of these exhaust gases, to contribute to the difference in the richness of the mixtures injected into the two groups of cylinders, for example by returning a part of the exhaust gases from the lean-burn cylinders to the admittance of the rich mixture cylinders. The regulation of the amount of air admitted into the poor cylinders 23 and 24 allows the control unit 25, thanks to the calculations made by the module 26, to impose the residual oxygen level reaching the catalyst 6 in a first time, and then after oxidation of excess hydrocarbons, the particulate filter 7. In this embodiment, an identical number of cylinders is fed rich mixture and lean mixture. It is also conceivable to vary the number of cylinders of each group, or even to vary them during the same regeneration cycle in order to further adapt the delivered proportions of fractionated hydrocarbons and residual oxygen to the needs of the reactor. particle filter 7 as detected by the control unit 25. The signals returned by the temperature sensors 17 and 18 to the control unit 25 allow it to check the effectiveness of the afterburner taking place in the catalyst. The data of the temperature sensors 17, 18 and of the oxygen sensor 19 enable the control unit 25 to check when the optimum temperature and oxygen content conditions are reached at the inlet. particulate filter 7, and secondly refine the control of the injectors and intake valves. In fact, from the air intake flow rates and the quantities of fuel injected into each cylinder, the calculation module 26 integrated in the control unit 25 models the combustion reactions in each cylinder, then the combustion or combustion reactions. The module 26 thus estimates the temperatures and the compositions of the exhaust gases between the output of the engine cylinders and their arrival at the particulate filter 7. The temperature measurements are carried out in the exhaust line 5 and in the catalyst 6. returned by the temperature sensors 17, 18 and the oxygen sensor 19 allow to consolidate these calculations, and to adapt the control of the air intake valves 21a, 22a, 23a, 24a, the control of the valve 16 of EGR recirculation, as well as the piloting 16 of the fuel injectors of the cylinders 21, 22, 23, 24, in order initially to obtain a temperature of the exhaust gas, measured at the level of the temperature sensor. 18, superior re or equal to the reference temperature Tl, then maintain, during the pyrolysis regeneration step, the temperature measured by the sensor 18 and the oxygen content measured by the sensor 19, in predefined ranges. It is also possible to envisage a variant embodiment in which all or some of the sensors 17, 18, 19 would be omitted, the corresponding measurements being evaluated by the only calculation module 26 from the other engine operating data such as the air flow rates. the recirculated EGR rate, the quantities of fuel injected into each cylinder. To ensure an efficient reaction of pyrolysis of the particles, the temperature measured by the sensor 18 at the inlet of the particulate filter 25 is advantageously maintained in an operating range between 600 C and 650 C, ideally in the vicinity of 620 C. In parallel, the measurable oxygen level at the oxygen probe 19 is advantageously controlled in a range of 4% to 8%, preferably in the vicinity of 6%. Thanks to the invention, the regeneration steps of the particulate filter can be carried out in a wide range of rotational speeds of the engine, as soon as the pressure drop between the inlet and the outlet of the filter reaches a critical value, without dilution. accidental fuel in the engine oil, and optimizing the additional amount of fuel consumed for regeneration. The reactions that take place in the catalyst from the fractionated hydrocarbons from the rich mixture cylinders are more efficient than those from the reducing compounds 17 from the simple post-late injection or an injector mounted in the exhaust line. . This regeneration process is therefore particularly advantageous for vehicles equipped with catalysts of reduced volume, which can thus more easily generate the exothermic reactions and the amount of heat necessary for the pyrolysis of the particles.

Claims (9)

  Process for the regeneration of a particulate filter (7) for a multi-cylinder diesel engine (1) (21, 22, 23, 24), said particulate filter being mounted in an exhaust line (5) of the engine downstream of an oxidation catalyst (6), characterized in that a richer fuel mixture is injected than the stoichiometric mixture into at least one of the cylinders, and a lighter fuel mixture is injected simultaneously than the mixture stoichiometric in the other cylinders, so as to obtain a temperature and an oxygen content of the gases arriving at the filter (7), adapted to the combustion of the particles.   2. The process according to claim 1, wherein before the regeneration of the particulate filter (7), the exhaust gases (13) are preheated to an activation temperature of the oxidation catalyst by reduction. the amount of air admitted into all the cylinders (21, 22, 23, 24) and post fuel injection in these cylinders when each of the pistons is still close to the top dead center.   3. A method according to claim 1 or 2, wherein the injection of fuel-rich mixture is by a post-injection of fuel into the combustion chamber of the cylinder or cylinders concerned when the piston is still close to the top dead center.   4. Method according to one of the preceding claims, wherein one imposes different inlet air flow rates and / or different admission gas compositions to at least two groups of cylinders during the regeneration of the filter (7).   5. Method according to one of the preceding claims, wherein is regulated during the regeneration of the filter (7), the oxygen level in the gas inlet filter at a rate substantially between 4% and 8% by weight, and the temperature of the gas entering the filter substantially between 600 C and 650 C.   6. Diesel engine (1) with several cylinders (21, 22, 23, 24) equipped with a regeneration system for particulate filter (7), said system comprising an air intake pipe (8) with regulation (21a, 22a, 23a, 24a) the flow rate of the gases admitted to the cylinders, a fuel injection system in the different cylinders adjustable in the amount of fuel injected and the moment of injection, an exhaust line (5) equipped with a particulate filter (7) mounted downstream of an oxidation catalyst (6), and a control unit (25) capable of controlling the air intake and the fuel injection, characterized in the control unit (25) is capable of intermittently triggering a regeneration step of the particulate filter (7) by injecting a richer fuel mixture than the stoichiometric mixture into at least one of the cylinders, and simultaneously by injecting a leaner fuel mixture than the stoichi metric in the other cylinders.   7. Motor according to claim 6, wherein the control unit (25) is furthermore capable of controlling, before the regeneration step, a preheating of the exhaust gases (13) up to an activation temperature. of the oxidation catalyst, by reducing the quantity of air admitted into all the cylinders (21, 22, 23, 24) and by post-injection of fuel into these cylinders when each of the pistons is still close to the top dead center .   8. Motor according to claim 6 or 7, comprising an air intake valve system (21a, 22a, 23a, 24a) in the cylinders (21, 22, 23, 24), controllable by the control unit. (25) so as to impose different air flow rates to at least two groups of cylinders.   9. Motor according to one of claims 6 to 8, equipped with means for determining (20) the differential pressure between the inlet and the outlet of the particulate filter (7), a means (18) for determining the inlet temperature of the particulate filter (7), a means (16) for determining the inlet temperature of the catalyst (6), a means (19) for determining the oxygen content in the gases entering in the particle filter (7), the control unit (25) being able, from the data provided by these determination means, to decide to launch a regeneration step and to adapt the quantities and the moments injecting fuel into each cylinder (21, 22, 23, 24).