WO2008053105A1

WO2008053105A1 - Exhaust line of a diesel engine and method of regenerating a particulate filter

Info

Publication number: WO2008053105A1
Application number: PCT/FR2007/051764
Authority: WO
Inventors: François Fresnet
Original assignee: Renault S.A.S
Priority date: 2006-10-31
Filing date: 2007-08-01
Publication date: 2008-05-08
Also published as: FR2907845A1; FR2907845B1

Abstract

A method of regenerating a PF (4a,4b) of an exhaust line of a diesel engine, intended to eliminate at least some of the soot particles trapped in said PF during the operation of said engine, comprises the following steps: producing ozone in an air stream using an ozonizer device (14); injecting said ozone-loaded air stream into the exhaust line at an injection point (5a,5b) situated downstream of the engine and upstream of the PF; bleeding the stream of exhaust gases from a bleed point (2) on the exhaust line situated upstream of said injection point (5a,5b); and continuing the injection of ozone into said PF in order to carry out said regeneration. The method is used in particular in an exhaust line comprising two PFs (4a,4b) mounted in parallel, a bypass system, (2) for distributing the stream of exhaust gases between the two PFs, an ozonizer (14), and a valve system (7) for distributing the ozone leaving the ozonizer (14) between two injection points (5a,5b) respectively arranged in parallel upstream of the first and second PFs and downstream of said bypass (2).

Description

fiËCiAËârtiçMteii

The present invention relates to an exhaust line of a diesel engine and a method of regeneration of a particulate filter integrated in this line, the method being intended to extract during operation of the engine at least a part of the fixed soot particles in the particle filter.

Gas purification systems are being installed more and more systematically in the exhaust line of diesel engines. Such purification systems may include catalyst systems, NOx traps and / or particulate filters, commonly referred to as FaP for short. This abbreviation will be used in the remainder of this text to designate a particulate filter. The use of these FaP is of great importance in diesel engines, known to emit much larger quantities of soot particles than gasoline engines _" engine emission regulations tending to become more and more severe,

The FaP are normally housed in a housing integrated in a section of the exhaust line of the engine, Hs consist of a monolithic or segmented filter element which is crossed by the exhaust gas to be filtered, The porosity of the FaP is chosen depending on the properties of the components to be separated and the conditions imposed by the technique of the loaded fluids. The soot particles are retained in the filter element which clogs gradually during use, which causes an increase in the pressure upstream in the exhaust line, which has the effect of generating a significant excess fuel consumption , even the engine stall. It is therefore necessary to carry out regular regeneration operations to remove soot accumulated in the FaP.

JS \ 2.R442.12FR.dpt A known method of regeneration, called thermal regeneration, consists in removing the soot particles by oxidation with the oxygen of the air contained in the exhaust gas under conditions of richness <1, at temperatures greater than 550 ^° C. C. These operating conditions, however, can only be achieved with specific strategies engine control _"that are intrusive vis-à-vis the operation of the engine and can cause fuel overconsumption and lubrication problems.

It has also been proposed to use NO2 to oxidize your soot. US Pat. No. 6,546,717 describes an exhaust gas treatment process in which the NOx are first oxidized to NO2 by injection of ozone into these gases. In a second step, carried out downstream, NO2 is reduced to N2 either by passing over a catalyst or by serving to oxidize the soot fixed in a FaP.

The application EP 1 026 373 describes an exhaust gas purification device comprising a source of ozone which releases ozone in these gases before they pass through a FaP, in order to regenerate the latter. The gases pass over an oxidation catalyst upstream of the ozone injection point in the exhaust line.

US Pat. No. 6,557,340 describes an exhaust gas treatment system in which ozone is produced by a plasma generator positioned in the exhaust line upstream of the FaP,

Ozone oxidizes exhaust NOx to NO2. The soot particles fixed in the FaP are oxidized by NO2, possibly by

03 according to the operating conditions of the engine. An oxidation of soot fixed in a FaP by NO2, as proposed by the processes mentioned above, requires to be

JS \ 2 R442! 2FR dpt effective high temperature and therefore a hot exhaust flow. But the ozone molecule becomes unstable when the temperature rises. This molecule tends to decompose at temperatures above 200 ° C. When ozone is produced in a stream of hot exhaust gas, some of this ozone is redecomposed and therefore lost. This phenomenon considerably limits the efficiency of these processes.

The patent application FR 2,859,240 describes a method for treating a FaP in which ozone is produced from atmospheric air and injected into the flow of exhaust gases when the temperature of the latter is less than 250 ° C and that the amount of NOx present in the gases is low, so that the amount of ozone produced is optimally used for the oxidation of soot. But these physico-chemical conditions of the exhaust gases are only encountered when the engine is idling or when the vehicle is traveling at low speed. The process can not be implemented when the engine runs for a long time at high speed.

The patent application FR 2 877 588 also describes a process of this type applied to an exhaust line comprising in series an oxidation catalyst, a NOx trap and a FaP, the use of the amount of ozone. product is optimized by injecting it, depending on the operating conditions of the engine, such as starting, idle, or accelerations, either upstream of the oxidation catalyst, or upstream of the NOx trap, or upstream of the FaP, relatively complex management of this process extends its range of use, but does not allow its implementation when the engine runs for a long time at high speed. The object of the invention is to propose a method for regenerating a FaP which does not exhibit the defects of the processes of the state of the

JS \ 2 R442 12FR dpt mentioned above. More particularly, the object of the invention is to propose a regeneration process that can be implemented independently of the momentary operating conditions of the engine, which does not require a modification of these conditions, and which optimizes the production of the engine. ozone

These goals are achieved by a method of regenerating a FaP of a diesel engine exhaust line, said method being intended to eliminate during operation of said engine at least a portion of the soot particles fixed in the so-called FaP, comprising the following steps:

-production of ozone in an air flow by an ozone device, -injection of said air flow loaded with ozone in the exhaust line at an injection point located downstream of the engine and upstream of the FaP, -derivating the flow of exhaust gases from a diversion point of the exhaust line located upstream of said injection point, and continuing the injection of ozone into said FaP to achieve the said regeneration.

The said air stream can be taken from the engine air supercharging circuit.

The said air flow can pass through an air pump activated if the boost pressure is lower than the gas pressure in the exhaust line and stopped if the boost pressure is greater than the gas pressure in the line exhaust.

Ozone can be produced by means selected from non-thermal plasmas, microwave discharges, high voltage electrical discharges and ultraviolet radiation.

JS'.2.R442,12FR, warehouse The airflow in Pozoneur and the electric power consumed by the ozonizer can be adjusted to produce the desired amount of ozone under conditions of minimum energy consumption of the ozonizer.

The periodicity of the regeneration process may be predetermined, either as a function of the engine operating time or as a function of a mileage traveled. The duration of the derivation step may be predetermined; the duration of the derivation step may in particular be between 10 seconds and 20 minutes.

Alternatively, the start of a regeneration process and the duration of the bypass step can be determined by a pressure measurement in the exhaust line upstream of the FaP, or by a soot estimator disposed in The FaP,

At the end of a stage of regeneration _"exhaust gases are redirected in Ie FaP and ozone production can be stopped.

The method according to the invention can be applied to the regeneration of an exhaust line comprising two FaPs connected in parallel, and a by-pass system making it possible to distribute the flow of the exhaust gases between your two FaPs, a system valves for distributing the ozone leaving the ozonizer between two injection points arranged in parallel respectively upstream of the first and second FaP and downstream of the bypass.

Each of the two FaPs may alternatively be in the loading phase and in the regeneration phase. A plurality of charging and bypassing steps can alternate in cycles, and the production of ozone is continuous during said cycles.

JS \ 2 R442 12FR dpt In another aspect, the invention provides an exhaust line of diesel engines comprising a FaP, a bypass device upstream of the FaP and a bypass line allowing the exhaust gas to bypass said FaP and to be reinjected downstream from said FaP, an ozonizer and an air duct passing through said ozonizer, said air duct opening into the exhaust gas duct downstream of the bypass device and upstream of the FaP, and a computer capable of driving a method according to the invention,

The exhaust line may include an air pump and a flow meter mounted on the air line supplying the ozonizer.

The invention proposes in particular an exhaust line comprising two FaPs connected in parallel, a by-pass system for distributing the flow of the exhaust gases between the two FaPs, an ozonizer, a valve system for distributing the fuel. ozone exiting the ozonizer between two injection points arranged in parallel respectively upstream of the first and second FaP, and downstream of said bypass.

Other features and advantages of the invention will become apparent to those skilled in the art from the description below of an embodiment and accompanying figures, in which:

FIG 1 is a schematic representation of an embodiment of the air + ozone supply circuit of an exhaust line, FIG 2 is a schematic representation of an embodiment of a exhaust line,

2 R442 12FR dpt Ozone can not be stored in a vehicle and must therefore be produced aboard it by an on board ozone, that is to say an ozone generating unit supplied with air. Ozone can be produced either by a microwave discharge, an electrical discharge by applying a high voltage between two electrodes, or by exposing the airflow to radiation produced by ultraviolet-emitting lamps. . The air can be taken in the ambient atmosphere or in an air supply from another part of the vehicle.

Figure 1 shows a device for producing the air + ozone mixture supplying the exhaust line of the engine. From top to bottom are schematically represented

-Ie supply circuit 11 of air motor, the air flow is symbolized by solid arrows, oriented left to right of Figure 1;

a part of the air is diverted in a pipe to a pump

12;

downstream of the pump 12 is disposed at a flow meter 13;

an ozonizer 14 with electric discharge; a pipe 6 at the exit of the ozonbeam feeds the exhaust line via a three-way valve system 7,

In the device shown in FIG. 1, the air is taken from the air supercharging circuit 11 of the engine, but without eliminating the air pump 12 dedicated to the ozonizer. The supercharging pressure, given by the vehicle computer, is compared with the pressure measured in the exhaust line, at the point of injection of ozone in this line. If the boost pressure is significantly greater than the pressure measured in the exhaust line _"the air pump 12 may be stopped and the air flow only controlled by the flow meter 13 Ia to limit energy consumption of the system. If the pressure of

JS \ 2.R442.I2FR.dpt supercharging is of the same order as or less than the pressure in the line, the pump is started.

The ozone flow is determined and controlled by the air flow in the ozonizer and the electrical power consumed by the ozonizer. In order to produce the desired amount of ozone with the lowest possible energy consumption of the ozonizer, it is advantageous to set the airflow and electrical power to unique values, to operate the ozonizer in an optimum energy condition. By way of nonlimiting example, the electrical consumption of the ozonizer is typically of the order of 100 W and the air flow rate is of the order of 1.5 l / s.

FIG. 2 diagrammatically illustrates one embodiment of a part of an exhaust line concerned by the invention. To the left of the figure is located the inlet pipe 1 for the exhaust gases issuing from the engine. By-pass device 2 directs exhaust gas either to line 3a or to line 3b. The pipe 3a opens into a FaP 4a and the pipe 3b into a second FaP 4b. The output ducts of the two FaP meet at a connection point 8 of the main line 9 exhaust. The valve system 7 directs the flow of air charged with ozone coming from the pipe 8 either in the pipe 5a or in the pipe 5b, which respectively open into the pipes 3a and 3b downstream of the bypass 2 and upstream respective PSAs 4a and 4b.

When the FaP 4a is to be regenerated, the exhaust gases are deflected by the bypass 2 to the branch 3b-8 of the line. The air + ozone mixture arriving via the pipe 6 is injected into the pipes 5a and 3a by means of the valve system 7 and passes into the FaP 4a. Ozone oxidizes the soot stored in FaP 4a by converting it into gaseous compounds entrained by the air stream to line 9. The skilled person

JS \ 2 R442 12FR dpt observe that because of the bypass of the exhaust gases by bypass 2, the ozone is not mixed with the NOx and is not consumed by these, and that after an initial cooling phase of the FaP by the air flow, it is at a temperature such that the ozone is no longer thermally decomposed. Those skilled in the art will also observe that the execution of the regeneration process does not involve any modification of the engine speed or the richness of the mixture which feeds it.

For the regeneration of the FaP 4a, the branch 3b-8 could be a simple bypass line, which would not include the FaP 4b, But then, the soot emitted by the engine during the regeneration process of the FaP 4a would momentarily enter the atmosphere _" which may be contrary to the regulations in force. The presence of the FaP 4b in the branch 3b-8 avoids this disadvantage When the FaP 4b is loaded in soot and in turn to regenerate, the exhaust gases are directed by the bypass 2 in the branch 3a-4a 8 of the exhaust line and the ozone is injected by the valve system 7 into the ducts 5b, 3b, and the FaP 4b it regenerates.

When the soot level in one of the FaPs 4a or 4b reaches a given threshold level, its regeneration is carried out. This threshold is detected either by a pressure measurement upstream of the FaP, or by a soot estimator stored in the FaP. Preferably, a low level _" typically 5g _" threshold is chosen to limit the back pressure in the line of exhaust and therefore the overconsumption of energy related to the loss of charge due to soot stored in the FaP,

The present invention provides a non-intrusive regeneration method vis-à-vis the engine _"while minimizing consumption of Ia

JS ^ι 2 R442 i2FR dpt fuel, the engine operating conditions, including the richness of the mixture fueling the diesel engine not being affected by the execution of the process steps outlined above. This method can be applied in particular to the regeneration of an exhaust line comprising 2 FaPs connected in parallel, alternately in the charging phase and in the regeneration phase, and this at any time and regardless of the operating speed of the engine. at the moment. A regeneration operation can be performed typically every 500 km traveled.

JS \ 2 R442 12FR dpt

Claims

1. A method for regenerating a FaP (4a, 4b) of an exhaust line of a diesel engine, said method being intended to eliminate during operation of said engine at least a portion of the soot particles fixed in said FaP, characterized by the following steps;

-production of ozone in an air flow by an ozonizer device (14), -injection of said air flow loaded with ozone into the exhaust line at a downstream injection point (5a, 5b) of the engine and upstream of the FaP ₁

-derivating the flow of exhaust gases from a diversion point (2) of the exhaust line upstream of said injection point (5a, 5b), and continuing the injection of ozone in the said FaP to achieve the said regeneration.

2. Method according to claim 1, characterized in that said air flow is taken from the circuit (11) supercharging the engine air.

3. Method according to claim 2, characterized in that said air flow passes through an air pump (12) put into operation if the boost pressure is lower than the gas pressure in the exhaust line and stopped if the boost pressure is greater than the gas pressure in the exhaust line.

4. Method according to one of the preceding claims _{"characterized} in that ozone is produced by a means selected from the non-thermal plasmas, microwave discharges, thy high-voltage electric shock and ultraviolet radiation.

JS \ 2 R442 12FR dpt

5. Method according to claim 4, characterized in that the air flow in the ozonizer (14) and the electrical power consumed by the ozonizer are adjusted to produce the desired amount of ozone under consumption conditions. minimal energy of the ozonizer.

6. Method according to one of the preceding claims, characterized in that the duration of the derivation step is predetermined, in particular that the duration of the derivation step is between 10 seconds and 20 minutes.

7. Method according to one of claims 1-5, characterized in that the duration of the bypass step is determined by a pressure measurement upstream of the FaP.

8. Method according to one of the preceding claims, characterized in that at the end of a said bypass step, the exhaust gas is redirected into the FaP (4a, 4b) and that the production of ozone is stopped ,

9. Application of a method according to one of claims 1-8 to the regeneration of an exhaust line comprising two faPs (4a, 4b) connected in parallel, and a bypass system (2) allowing distributing the flow of the exhaust gases between the two facades _" characterized by the use of a valve system (7) for distributing the ozone leaving the ozonizer (14) between two injection points (5a, 5b) arranged in parallel respectively upstream of the first and second FaP and downstream of the bypass (2).

JS \ 2 R442 12FR dpt

10. Application according to claim 9, characterized in that each of the two FaP (4a, 4b) is alternately in the loading phase and in the regeneration phase.

11, Application according to one of claims 9 or 10, characterized in that a plurality of loading and bypass stages alternate in cycles, and the production of ozone is continuous during said cycles.

12, Exhaust line for diesel engines having a FaP (4a, 4b), characterized by the presence of a bypass device (2) upstream of said FaP and a bypass line allowing the exhaust gases by-passing said FaP and being reinjected downstream (8) of said FaP, by the presence of an ozonizer (4) and an air duct passing through said ozoneur _" said pipe opening into the line d exhaust downstream of the bi-pass device and upstream of the FàP _" and by the presence of a computer capable of driving a method according to one of claims 1-8.

13. Exhaust line according to claim 12, characterized by the presence of an air pump (12) and a flowmeter (13) mounted on the air duct (6).

14. Exhaust line according to one of claims 12 or 13 for implementing a method according to one of claims 9-11, comprising two FaPs (4a, 4b) connected in parallel, a bypass system ( 2) for distributing the flow of exhaust gases between the two FaPs, characterized by the presence of an ozonizer

(14), a valve system (7) for distributing the ozone exiting the ozonizer (14) between two injection points (5a, 5b)

JS \ 2 R442 HFR dpt arranged in parallel respectively upstream of the first and second FaP and downstream of said bypass (2). 42 12FR φt