EP2007976A1

EP2007976A1 - Method and device for monitoring the regeneration of a pollution-removal system

Info

Publication number: EP2007976A1
Application number: EP07731851A
Authority: EP
Inventors: Jean-Marc Duclos; Frédéric LIPPENS; Mohammed Ouazzani-Chahdi
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2006-04-14
Filing date: 2007-03-30
Publication date: 2008-12-31
Also published as: WO2007119015A1; CN101443534B; CN101443534A; FR2899932A1; RU2008144967A; JP2009533597A; RU2435043C2; US20100132334A1

Abstract

Method for monitoring the regeneration of a pollution-removal system (8), relying on the introduction of fuel into the exhaust gases by delayed injections of fuel into certain combustion chambers of the engine and/or direct injections into the exhaust system upstream of the filter depending on the inlet temperature of the system, characterized in that the fuel delivery (Q<SUB>red</SUB>) introduced is assigned to direct injections into the exhaust system and/or to delayed injections into the combustion chamber according to the value of the wall temperature (T<SUB>paroi</SUB>) of the exhaust system.

Description

METHOD AND CONTROL OF THE REGENERATION OF A

DEPOLLUTI ON SYSTEM

The present invention is in the field of internal combustion engines and more particularly diesel type engines, since they reject particles. Indeed, this invention relates in particular to the management of f ilt res except icules or FAP.

It applies in particular to any vehicle equipped with a particulate filter, but also in the case of the use of an additional injector for nitrogen oxide trap (NOxTrap) purge strategies, or its obsolete atat ion.

In contrast to a traditional oxidation catalyst, these systems operate discontinuously or alternatively, that is, in normal operation they trap the pollutants, to treat them only during regeneration phases. To be regenerated, these filters, or traps, require specific combustion modes, in order to guarantee the necessary thermal and / or richness levels.

To regenerate the particulate filters, it is possible to carry out one or more delayed injections in the combustion chambers of the engine, after the top dead center (WFH), during the expansion phase, these injections having the effect of increasing the temperature exhaust gases. The diesel fuel injected long after the PMH, does not burn in the combustion chamber, but in the catalytic part of the exhaust line. Always in order to reduce the pollutant emissions, it is indeed possible to have in addition to the FAP, either an oxidation catalyst (DOC) in the exhaust line, upstream of the FAP, or directly a catalytic material (such as platinum) within the FAP. It is on these catalytic sites that the HC and CO of the late injections oxidize, increasing the temperature of the gases. Finally, by increasing the flow rate of a remote post injection, it causes high emissions of HC and CXD at the output of the engine. These reducing agents react in the oxidation catalyst with the oxygen present in the exhaust gas, producing heat, which contributes to increasing the temperature of the exhaust gas at the inlet of the particulate filter.

Thus, the regeneration of a particulate filter can use the heat produced by an oxidation catalyst generally placed upstream of the particulate filter, and that of the catalytic phase which is coated with the catalytic particle filter. The latter performs the oxidation function of hydrocarbons and carbon monoxide untreated by the oxidation catalyst. It can also use the heat produced by the oxidation phase of the catalytic particle filter, when there is no oxidation catalyst upstream thereof.

The activation of the various regeneration aid means is generally controlled by the engine control computer, which determines, as a function of several parameters, including the soot loading of the particulate filter, the instant of the regeneration, as well as its duration and injection parameters during this phase.

However, to improve the efficiency of the regeneration, it is necessary to produce a temperature internal to the filter, favorable to the oxidation of soot

(570-650 ⁰ C), higher than the normal temperature of the exhaust, regardless of the point of operation of the engine. Similarly, to optimize the treatment of all pollutants, it is necessary to best manage the storage and regeneration phases of these traps. These operations therefore require controlling the inlet temperature of the particulate filter, at the time of the regeneration phases, and the dilution due to the post injection.

Currently, the heat required for the regeneration of the particle storage elements is generated by means of additional injections, either during the expansion phase of the cylinder, either directly in the exhaust line. The adjustment of the injection is generally carried out by a loop on the temperature at the outlet of the oxidation catalyst T _SD ocau by a Pl D (Proportional, Integrator, Derivator), which applies a correction calculated to regulate this temperature .

The two actuators available to achieve the expected exotherm in the catalytic phase of the exhaust line, are not equal before the fuel dilution criterion in the lubricating oil.

The use of a post-injection in the cylinder creates a significant extra cost in terms of dilution, while the use of direct injection in the exhaust, can allow to ease the development of the system on this aspect.

The object of the present invention is to maximize the regeneration performance of the particulate filter, by favoring the injection of reducers into the exhaust line at the post-injection, in order to limit the dilution cost associated with the use of the post-injection.

For this purpose, it proposes that the fuel flow introduced, be assigned to direct injections into the exhaust line and / or delayed injections in the combustion chambers, depending on the value of the wall temperature.

Preferably, the injection of fuel into the exhaust line is limited to a zone of the lowest loads, and to a zone of the highest loads of the engine, and the fuel flow injected into the exhaust line is limited to a maximum flow, beyond which the fuel injected would not be completely oxidized therein.

The invention also proposes a device comprising a first temperature sensor upstream of the turbine, an oxidation catalyst, a second temperature sensor measuring the inlet temperature of a heating system. depollution, the pollution control system, and means for determining the wall temperature of the exhaust line.

Other characteristics and advantages of the invention will become clear from reading the following description of a non-limiting embodiment thereof, with reference to the drawings, in which:

FIG. 1 shows an example of application of the invention,

FIG. 2 shows the distribution of the injections as a function of exhaust conditions,

FIG. 3 presents the method for determining the wall temperature,

FIG. 4 is a block diagram of the command, and

FIG. 5 shows saturation traces of the quantity of fuel injected into the exhaust line (fifth injector) for three times per hour. Figure 1 illustrates in a non-limiting manner the application of the invention to a vehicle engine. It reveals a four-cylinder engine 1, the turbine 2 and the compressor 3 of a turbocharger, as well as an EGR loop and its cooler 4. In the exhaust line, there is an oxidation catalyst 7 ( DOC), followed by a particulate filter 8 (FAP). An exhaust fuel injector 9, called the fifth injector, is placed upstream of the catalyst 7. The various associated sensors are a front turbine temperature sensor (T _avt ) 11, a filter inlet temperature sensor. particles (T _efap ) 13, a particle filter output temperature sensor (Tes _f a _p ) 14, an oxygen sensor 16, and a differential pressure sensor 17, or relative pressure sensor, between the upstream end of the filter and atmosphere. Finally, the diagram mentions the throttle valve of the engine 8, the EGR valve 19, and the means for isolating the exhaust line 21. The associated engine control unit 22 receives and processes the signals emitted by the sensors mentioned. as well as other information from electrical consumers 23, motorcycle fan assembly 25, a controlled thermostat 26, and temperature and atmospheric pressure sensors 27, 28.

In the context of the invention, the additional inj ector positioned in the exhaust line, or fifth inj ector 9, can however be placed, either upstream or downstream of the turbine, without this location having any incidence. on the proposed strategy. The device concerned by the invention therefore comprises the following elements: an injector at the exhaust 9, a first temperature sensor 11 upstream of the turbine, an oxidation catalyst 8, a second temperature sensor 12 measuring the temperature

T _EFAP input of a pollution control system, the pollution control system 8, and means for determining wall temperature T _parol, of the exhaust line. According to the invention, the wall temperature means may be a calculation model integrated in the computer, or a wall temperature sensor (not shown). Finally, the pollution control system 8 may be either a particulate filter or another system such as a nitrogen oxide trap, and the exhaust nozzle 9 may be positioned upstream or downstream. , of the turbine.

As indicated above, the invention provides for distributing the quantity of fuel Q _re d, making it possible to reach the desired temperature at the inlet of the particle filter, between an additional injector implanted in the passage of the exhaust gases, and the post-injection.

Specifically, the quantity of gear reducers Q _red controlled by the input filter temperature control strategy of the particulate filter will be assigned to the additional injector, Q ₅ ,,, first and / or to the post injection Q _p0 , , according to the instantaneous value of the temperature of the wall T _par0 ι, of the exhaust line. The invention assumes that the exhaust injector can not be used over the entire operating range of the engine. Indeed, the area characterized by a low exhaust gas flow rate and a low wall temperature, does not allow a satisfactory vaporization of the fuel injected. For safety, it may also be preferable not to use the exhaust injector in areas characterized by high exhaust gas flow and high wall temperature, due to the residence time of the reducers. in the oxidation catalyst too weak, to allow oxidation of all reductants. According to FIG. 2, the injection of fuel into the exhaust line is therefore used only in certain operating ranges of the engine, and limited for example to a zone of the lowest loads, and to a zone of the highest loads of the engine. engine.

The wall thickness can be determined either by a sensor or by a model integrated in the engine computer, according to different parameters. In order to determine the temperature of the wall T _par0 ι, it is indeed possible to use a sensor or a calculation model, integrated for example in the engine control computer, which makes it possible to give an instantaneous value of T _parol . This temperature is a function of various parameters mentioned in FIG. 3, including the temperature of the exhaust gases before the turbine of a turbocharger T _avt , the water temperature T _water of the engine, the flow of the exhaust gases Q _eCh , and Q _alr airflow

(measured for example at admission). The model can use all or only some of these parameters depending on the engine operating point.

The quantity of fuel to be injected Q _red depends on the temperature of the wall, the temperature at the outlet of the oxidation catalyst DOC or the inlet temperature of the FAP T _efap , and the operating point of the engine. (exhaust gas flow). The quantity of fuel Q _re d is calculated by means of a module integrated in the engine control computer. This module, illustrated in FIG. 4, is composed of a basic setting of the injector gearing rate (assumed to be independent of the actuator), mapping by operating point governed by the motor torque, and a correction generated by a corrector of PID type (Proportional Integrator Derivator) dependent on the deviation of the input temperature measurement of the particulate filter at the set temperature T _cons .

The conversion capacity of the DOC, which depends on the temperature of the wall and the flow rate of the gases passing therethrough, defines a maximum flow rate for the fifth injector, beyond which part of the reducers injected into the exhaust will not be oxidized. To take account of this constraint, the invention provides that the flow rate of fuel Q _5mj injected into the exhaust line is limited to a maximum flow Qι _nJ max, beyond which the injected fuel would not be completely oxidized therein . Precisely, the fuel is injected in priority in the exhaust line, as long as the injected flow rate Q _mj is lower than the maximum flow oxidizable completely in it Q _{lnJ max-}

FIG. 5 illustrates the principle of high throughput saturation of the fifth injector, for different wall temperatures T _parol i, T _parol 2,

T _P a _r oi3- In both zones where the injector can not be used, the post-injection is permitted, if the temperature control strategy at the entrance of the DPF requires the production of an exotherm in the DOC.

When the use of the fifth injector is allowed, it is saturated first, so as to favor its use until saturation, by postponing the surplus ordered on the post-injection:

- if Qred <05mj max, then Q _51n ] = Qred and Q _po n = O - if Q _r ed max, then Q _5lnJ ≈Qsmj max and Q _pol1 = Q _red - Q _5lnJ max.

Thus, the excess fuel Q _p0 , relative to the oxidizable flow rate in the exhaust line Q _mjm a _x , is introduced by delayed injections into the combustion chambers of the engine. Preferably, the computer 22 of the motor controls the fuel flow Q _re d in the dedicated injector of the exhaust line 9, to a saturation level of the oxidation catalyst 7, before transferring the surplus controlled by the regeneration of the filter 8 on delayed fuel injections into the combustion chambers of the engine. In the event of simultaneous activation of the injection at the exhaust and the post injection, it is preferable that the latot ality of the injected fuel follows a progression ramp, to reach the setpoint, so as to avoid that a part injected fuel passes through the catalyst without reacting. With such an injection profile, the reducers passing through the catalyst, in the event of high exhaust gas flow and high wall temperature, are more likely to oxidize.

In order to improve the dynamics of the system, the present invention proposes to vary firstly the flow rate of the injector to the exhaust in response to a variation of the overall flow rate. In this way, the post - injection is insensitive to the variation of the set point. However, since it is preferable to minimize the dilution due to the post-injection, the invention provides for restoring equilibrium (that is to say, to have the maximum flow of possible reducers to the exhaust and the minimum in the combustion chambers of the engine) by progressively increasing the flow of exhaust reducers.

The strategy model of injection of reducers in the exhaust line is integrated into the vehicle ECU. The main steps of the strategy are: • the model first determines an additional quantity of fuel to be injected (Q _red ) for the operating point under consideration, based on a map.

• the temperature measurement at the output of the DOC (or at the inlet of the FAP) makes it possible to correct this quantity of gearbox, in order to get as close as possible to the desired temperature (setpoint temperature) in contact with the FAP (T _SD oc = T _EF AP) -

• the control then manages the distribution of the additional fuel between the fifth injector (Q _51n ) and the post injection (Q _po n) according to the characteristics of the exhaust gases (T _parol and Q _E C _H ) - It is possible that only the fifth injector, or only the late injection, does not work.

Finally, it should be noted that the accuracy of the wall temperature calculation model may limit the use of the proposed strategy. Indeed, it is important to be able to use the additional injector over the highest possible load speed range, but it is also important not to use it when the wall temperature is too low. The margin taken on the value of the parcel, will directly impact the field regime / load accessible.

Claims

A method of controlling the regeneration of a pollution control system comprising an oxidation catalyst and a filter (8), based on the introduction of fuel into the exhaust gas by delayed fuel injections in certain chambers of combustion of the engine and / or by direct injections in the exhaust line upstream of the filter through a dedicated injector (9) of the exhaust line, depending on the temperature at the inlet of the system, characterized in that the flow The amount of fuel (Q _r ed) introduced is assigned to direct injections into the exhaust line and / or delayed injections into certain combustion chambers according to the value of the wall temperature (T _parol ) of the exhaust line.

2. Control method according to claim 1, characterized in that the fuel injection in the exhaust line is used only in certain operating ranges of the engine.

3. Control method according to claim 1, characterized in that the fuel injection in the exhaust line is limited to a zone of the lowest loads and a zone of the highest loads of the engine.

4. Control method according to claim 1, 2 or 3, characterized in that the temperature of the wall is determined by a sensor.

5. Control method according to claim 1, 2 or 3, characterized in that the wall temperature (T _parol ) is determined by a model integrated in the engine computer, according to parameters including the temperature of the exhaust gas. before the turbine of a turbocharger (T ₃ Vt), the water temperature (T _water ), the flow of the exhaust gases (Q _eC h), and the air flow (Q _a ι _r ) -

6. Control method according to one of the preceding claims, characterized in that the fuel flow (Q _lnJ ) injected into the line exhaust is limited to a maximum flow rate (Q _lnj max) beyond which the injected fuel is not completely oxidized therein by the oxidation catalyst.

7. Control method according to one of the preceding claims, characterized in that the fuel is injected in priority in the exhaust line as the injected flow rate (Q _mj ) is less than the maximum flow completely oxidizable in it (Qmjmax ) -

8. Control method according to claim 7, characterized in that the excess fuel (Q _pol ) relative to the oxidizable flow rate in the exhaust line (Q _lnJ max) is introduced by delayed injections into the combustion chambers of the engine.

9. Control method according to one of the preceding claims, characterized in that the total fuel flow (Q _red ) is corrected on each operating point of the engine by a factor depending on the difference between the inlet temperature of the engine. filter (T _efap ) and the regeneration setpoint temperature (T _con s) -

10. Control method according to one of the preceding claims, characterized in that the computer (22) of the engine controls the fuel flow (Q _re ) in dedicated injector of the exhaust line (9) to a saturation level of an oxidation catalyst (7), before transferring the surplus controlled by the regeneration of the filter (8) to delayed fuel injections into the combustion chambers of the engine.

11. Control method according to claim 10, characterized in that the flow of the inj ector to the exhaust varies in priority in response to a change in the global flow setpoint.

12. Control method according to one of the preceding claims, characterized in that the pollution control system (8) is a particulate filter.

13. Apparatus for implementing a method according to one of the preceding claims, characterized in that it comprises an injector dedicated to the exhaust (9), a first temperature sensor (11) upstream of a turbocharger turbine, an oxidation catalyst (8), a second temperature sensor (12) measuring the temperature (T _efap ) at the inlet of the pollution control system, the pollution control system (8), and a means for determining wall temperature (T _par0 ι) of the exhaust line.

14. Control device according to claim 13, characterized in that the wall temperature means is a calculation model integrated in a computer (22).

15. Control device according to claim 13 or 14, characterized in that the fuel injector (9) is arranged upstream of a turbocharger turbine (2).

16. Control device according to claim 13 or 14, characterized in that the fuel injector (9) is disposed downstream of a turbo compressor turbine (2).

17. Control device according to one of claims 13 to 16, characterized in that the first temperature sensor (11) is disposed upstream of a turbo compressor turbine (2).

18. Control device according to one of claims 13 to 17, characterized in that it comprises a fourth temperature sensor (14) at the outlet of the pollution control system (T _sfap ).

19. Control device according to one of claims 13 to 17, characterized in that the pollution control system (8) is a particulate filter.

20. Control device according to one of claims 13 to 17, characterized in that the pollution control system (8) is a trap nitrogen oxides.