WO2013093266A1 - Exhaust line for a multiple supercharged engine with single injection of a reducing agent and method for injecting a reducing agent for such a line - Google Patents

Abstract

The present invention relates to an exhaust line for a multiple supercharged engine with single injection of a decontamination agent and a method for injecting a decontamination agent for such a line. The exhaust line is characterised in that the injection module (7) is arranged in only one (3a) of the exhaust branches (3a, 3b). The invention is suitable for use in the remediation of motor vehicles.

Description

 EXHAUST LINE FOR MULTIPLE-POWERED ENGINE WITH SINGLE INJECTION OF A REDUCING AGENT AND METHOD OF INJECTING A REDUCTION AGENT FOR

 Such a line

5

[Oooi] The present invention claims the priorities of the French applications 1162016 and 1162015 filed December 20, 2011 whose contents (texts, drawings and claims) are here incorporated by reference.

The present invention generally relates to an exhaust line 10 for a supercharging engine with a single injection of a depollution agent and a method of injecting a depollution agent for such a line. Multiple supercharging is frequently a double turbocharging using two specific turbochargers.

[Ooo3] On the one hand, it is known to inject a depollution agent in the exhaust line of an internal combustion engine. In what follows, a selective catalytic reduction process, otherwise known as SCR, will be taken as an example of a pollution control process, this reduction process operating by injection into the exhaust line of a so-called SCR reducing agent. This is however not limiting and the present invention applies for any method of depollution of the exhaust line of a vehicle requiring the injection of a quantity of depollution agent during operation of the engine of said vehicle.

[ooo4] Levels of pollutants emitted by vehicles are subject to regulation. Among these pollutants, nitrogen oxides NO _x are more particularly regulated with more and more stringent emission standards.

[ooo5] In order to reduce the level of emission of nitrogen oxides, these can be processed at the output of the engine via post-treatment systems. Thus, the engine exhaust aftertreatment system can include selective catalytic reduction using a reducing agent, preferably urea. On the other hand, it is known to equip a motor of a supercharging system comprising at least one turbocharger. This allows in particular to enhance the performance of an engine compared to its engine capacity. Indeed, in compliance with the new anti-pollution standards, the trend of car manufacturers is to reduce the engine capacity of a combustion engine for the same type of vehicle to help reduce pollutants emitted by the vehicle, to obtain a gain in fuel consumption and reduce the volume of space and the mass of said engine. [Ooo7] To compensate for this loss of displacement, the reduced displacement engine therefore advantageously comprises a supercharging system with at least one turbocharger using the energy contained in the exhaust gas to drive a compressor, the latter then providing energy. air at a higher pressure at the engine intake. [Ooo8] As a turbocharger has a favorable efficiency over a limited operating range, in order to ensure satisfactory overfeeding over the entire operating range of the engine, it is also known to use at least two turbochargers operating in parallel. , each of the turbochargers having a specific operating range.

[0oo9] Thus, as shown in Figures 1 and 2 which illustrate the state of the art, a multiple supercharging line can be double and include a first turbocharger 1 said small turbocharger, said turbocharger 1 is engaged at low speed to promote the engine revving. The line also includes a second turbocharger 2, said large turbocharger, operating on a range at higher speeds, this with or without disengagement of the small turbocharger 1. The two turbochargers 1, 2 advantageously operate in parallel, each having an exhaust branch 3a, 3b, each exhaust branch 3a, 3b being able to incorporate an auxiliary depollution device 4a, 4b, for example an oxidation catalyst, in particular but not only in the case of a diesel engine. The respective exhaust legs 3a, 3b of the two turbochargers 1, 2 are then connected together at the connection point P to form a grouped exhaust line 3c, the two branches 3a, 3b and the single line 3c forming The combined exhaust line 3c after connection advantageously comprises a particulate filter 5 in addition to a depollution device 6 by prior injection of a depollution agent. A first upstream portion of this line 3c extends in a hood area Za followed by a second portion extending in a box Zb zone of the vehicle, the separation between the two zones Za and Zb being illustrated by the dashed line and the gas flow direction being indicated by the arrow Fg in this figure.

[Ooi i] In a first embodiment according to the state of the art, this mode being shown in Figure 1, for the establishment of a depollution device 6 with prior injection of a depollution agent, for example a SCR agent, a single injection module 7 is located in the underbody area Zb after connection of the two exhaust branches 3a and 3b then forming a grouped exhaust line 3c. Said line 3c then passes through the depollution device 6 after a sufficient mixing distance of the depollution agent, in order to water the pollution control device 6 in a homogeneous manner.

[Ooi2] This embodiment has the disadvantage of not exploiting the injection potential very early in the clean-up cycle due to the retracted position of the injection module 7. This penalizes the cleanup balance and therefore the CO2 balance. Another disadvantage is the large space requirement in the box Zb area because of the distances required between the depollution device and the injection module 7, which can possibly lead to a decomposition of the depollution agent in the case of an injection of said agent in the liquid state. Finally, the optimal control of the injection, because of the mixture of compositions of the exhaust gases from the two branches 3a and 3b with gases from different sources, is made difficult.

A second embodiment according to the state of the art, shown in FIG. 2, has an exhaust line configuration. similar to Figure 1. This mode provides the implementation of a respective injection module 7a or 7b, preferably in the gaseous state, on each exhaust leg 3a or 3b in the hood area Za. This makes it possible to obtain a sufficient mixing zone incorporating the connection of the two branches 3a, 3b, while having control independence between each injection module 7a, 7b. This second embodiment has the disadvantage of requiring the implantation of two injection modules 7a and 7b.

[Ooi 4] The problem underlying the present invention is to design an exhaust system comprising a depollution device with pre-injection of a depollution agent which allows a satisfactory mixture of the depollution agent with the gases in the exhaust line while being simple in design, including not requiring many elements for its operation. To achieve this objective, it is provided, according to the invention, an exhaust line of a thermal combustion engine adapted to be connected to a supercharging system having at least two turbochargers, the exhaust line having exhaust branches, each of the branches being respectively connected to a turbocharger, said branches meeting at a connection point to form a grouped exhaust line, the exhaust line being provided with a depollution device for the elimination of at least one pollutant in the exhaust gases by prior injection of a depollution agent by an injection module carried by said line, characterized in that the injection module is disposed in only one of exhaust branches.

The technical effect obtained is the economy of an injection module with respect to the second embodiment of the state of the art while ensuring a better mixture of the depollution agent in the line of exhaust than the first embodiment of the state of the art. With an injector disposed only in one of the branches of the line, it performs a homogeneous premix between exhaust gas and pollution control agent, for example urea, in a first branch. The global mixing is then carried out in the grouped exhaust line after connecting the two branches.

In an extreme variant of implantation of the injector at the connection point, that is to say at the point where there is the most turbulence in the exhaust line due to the connection of the two branches, it s it carries out a mixing of the exhaust gases from the two branches which allows a homogeneous mixture between the exhaust gas and the depollution agent.

The exhaust line according to the invention may further optionally at least have any of the following characteristics:

• the injection module is located on the longest exhaust branch.

Each branch is provided with an auxiliary device for decontamination of the oxidation catalyst type. "The injection module is located on its exhaust branch between the auxiliary depollution device and the point of connection of the branches.

The line comprises two temperature probes in each of the exhaust branches as well as an emission measurement probe for the said pollutant to be eliminated, this measurement probe being disposed in the grouped exhaust line.

The two temperature probes in each of the exhaust branches are disposed on either side of the auxiliary device for the depollution of said branch and, in the exhaust branch carrying the injection module, the temperature probe, in the flow direction of the exhaust gas is disposed after the auxiliary pollution control device and before said module.

• the injection depollution device is located on the grouped exhaust line. The line comprises two exhaust branches, the connection of the two exhaust branches and the exhausted exhaust line having a Y shape, the two exhaust branches forming the upper part of the Y. the two branches form between them an angle greater than 45 °.

The invention also relates to a supercharging system having at least two turbochargers with different operating ranges, characterized in that it comprises such an exhaust line.

The invention also relates to a method of injecting a depollution agent into an exhaust line of such a supercharging system, said method comprising the step of measuring the instantaneous concentration of at least one pollutant to be eliminated by injection of said agent and the step of measuring a parameter in each of the branches, this parameter being representative of the instantaneous operating conditions of the respective turbocharger, the step of calculating the amount of depollution agent to injecting according to said measurements and the step of injecting the calculated amount of depollution agent into the exhaust branch carrying the injection module.

Other features, objects and advantages of the present invention will appear on reading the detailed description which follows and with reference to the accompanying drawings given by way of non-limiting examples and in which:

FIG. 1 is a diagrammatic representation of an exhaust line according to a first embodiment according to the state of the art, FIG. 2 a schematic representation of an exhaust line according to a second embodiment. according to the state of the art,

• Figure 3 is a schematic representation of an exhaust line according to the present invention, this line having a single injector in one of the branches of the line, each branch being connected to a respective turbocharger. Figures 1 and 2 have already been described in introductory part of the present patent application.

Figure 3 substantially shows the exhaust line shown in Figures 1 and 2 with an exhaust leg 3a or 3b respectively connected to a first 1 or a second turbocharger 2, branches 3a or 3b may extend from first parallel and then meeting at the connection point P to form a grouped exhaust line 3c.

Each of the exhaust branches 3a or 3b may incorporate an auxiliary depollution device 4a, 4b, preferably an oxidation catalyst, while the grouped exhaust line 3c carries the depollution device 6, for example a device SCR. The auxiliary depollution devices 4a, 4b are advantageously each in the form of an oxidation catalyst. The oxidation catalysts in a respective branch 3a or 3b may have different geometric and / or functional characteristics, being connected to a respective turbocharger 1 or 2, the turbochargers 1, 2 having different operating ranges . Indeed, advantageously, the first turbocharger 1 is operated alone at low speed. At around 3,000 revolutions / min of rotation speed of the heat engine, the opening of a valve allows the transfer of the exhaust gas at the inlet of the turbine of the second turbocharger 2, which makes said second turbocharger 2 in operation. Advantageously, the first turbocharger 1 continues to rotate, the second turbocharger 2 reinforcing the first thereby increasing the air pressure admitted into each cylinder of the engine.

The connection point P branches 3a and 3b is in the hood area Za and the grouped line 3c has a first portion at the output of the connection having a Y shape. The first portion extends into said zone Za and is followed by a second portion extending into the underbody zone Zb. This is the second portion of the grouped line 3c which advantageously carries the depollution device 6 by prior injection of an agent. Optionally, a pollution control system such as a particulate filter, which can be incorporated in the depollution device 6 by injection, can also be provided in this second portion, a possible position of the particulate filter having been shown. in Figure 1 under the reference 5.

Note that in the case of Figure 1, the particulate filter is positioned in the box Zb zone but it can also be located in the Za under hood area. It is also possible to place the particulate filter behind the depollution device 6, the only excluded configuration therefore being a positioning of the particulate filter between the injection module and the depollution device. According to the present invention, for the prior injection of the depollution agent in the exhaust line, this injection is made only in one of the branches 3a of said line connected to a turbocharger 1 by incorporation of a single injection module 7 on this branch 3a. The other branch 3b, connected to another turbocharger 2 than the first branch 3a, therefore does not have an injection module. The injection module 7 is advantageously disposed after the auxiliary depollution device 4a of the branch 3a in the gas flow direction according to the arrow Fg.

The injection module 7 is also preferably arranged before the connection of the two exhaust branches 3a, 3b and away from the connection point P sufficient for a pre-mixture of exhaust gas and agent of pollution is carried out sufficiently in this branch 3a.

Thus, compared to the first embodiment of the state of the art, the position of the injection module 7 is raised from the box Zb area in the Za under hood area. This reduces the underbody space having reassembled the injection position of a downstream position at the connection point P of the two exhaust branches 3a, 3b to a position upstream of said point P. The injection is therefore at most early in the depollution cycle with a possibility of optimal mixing of the depollution agent with the gases by providing a premix in the branch 3a carrying the injection module 7.

It is advantageous to incorporate the injection module 7 to the longest branch, this branch being the branch referenced 3a in Figure 3. Thus, a homogeneous premix of exhaust gas and depollution agent , for example urea for an SCR depollution device, is carried out in the longest branch. For example, in the case of a liquid injection of a depollution agent, this makes it possible to optimize the premixing by an improved decomposition of the depollution agent in a gaseous state.

Advantageously, the longest branch 3a is associated with the first turbocharger 1, said small turbocharger which can operate alone or in combination with the second turbocharger 2.

The overall mixture of the exhaust gas and the depollution agent is then performed in the exhaust line grouped 3c after connecting the two exhaust branches 3a and 3b. At the point of connection P of the two branches 3a and 3b and after this point P, it is advantageous to create turbulence in the grouped exhaust line 3c which promote the final mixture of the exhaust gas and the pollution control agent.

[Oooi] In a variant in which the injection module is disposed at the connection point (P) of the two exhaust branches (3a, 3b), the connection zone below the connection point in the grouped line 3c is naturally generating disturbance flux lines symbolized respectively by the references gb and ga for the exhaust branch 3a or 3b, which has the effect of creating areas of local turbulence. The position of the injection module 7 at the connection point therefore makes it possible to take advantage of these disturbances in order to improve the mixture of the depollution agent injected by the injection module 7 with the exhaust gas.

[ooo2] In addition, locally at the connection, the temperature conditions prevailing at this connection can limit the fouling of the injection module 7 for both liquid and gaseous injection, due to an advantageous mixing between the exhaust gas and the depollution agent.

[ooo3] There is also better mixing between the exhaust lines for a large angle between the branches 3a and 3b at the connection point.

The turbulence can be created in particular according to the shape given to the Y formed by the exhaust branches 3a, 3b and the grouped exhaust line 3c or shapes present inside these branches 3a, 3b and / or or the grouped line 3c, these turbulences may increase the mixing of the exhaust gases from the two branches 3a, 3b. For example, branches 3a, 3b having between them a high separation angle, advantageously greater than 45 °, can create more turbulence in the line. This turbulence leads to a better mixture of exhaust gases leaving the two branches 3a, 3b and therefore to a better distribution of the pollution control agent in the exhaust gas in the grouped line 3c.

In addition, an injection made according to the object of the invention makes it possible to take advantage of the still high temperature of the exhaust gases, this compared to an injection according to the state of the art according to FIG. go further downstream in the grouped line 3c. This injection at high temperature makes it possible to prevent fouling of the injection module 7.

According to the present invention, a method of injecting a depollution agent into an exhaust line of a supercharging system with at least two turbochargers comprises the step of measuring the instantaneous concentration of at least one pollutant to be eliminated by injection of said agent. The method then comprises the step of measuring a parameter in each branch, this parameter being representative of the instantaneous operating conditions of the respective turbocharger and the step of calculating the amount of depollution agent to be injected as a function of said measurements. The method finally comprises the step of injecting the calculated amount of depollution agent into the exhaust branch carrying the injection module.

The step of measuring the instantaneous concentration of at least one pollutant to be eliminated by injection of said agent is made by an emission measurement probe 8 of said pollutant, for example an NO _x probe, the pollutant being frequently a or nitrogen oxides. This probe 8 is advantageously disposed at the outlet of the depollution device 6.

The step of measuring a parameter in each of the branches 3a, 3b, this parameter being representative of the instantaneous operating conditions of the respective turbocharger 1 or 2, is advantageously the temperature measured at the inlet and the outlet of the auxiliary device 4a, 4b of each exhaust branch 3a, 3b, the calculation of the temperature difference at the outlet and at the inlet being made for each branch 3a, 3b, in order to calculate the quantity of depollution agent to be injected.

In accordance with the process for injecting a depollution agent into one of the branches 3 a of the exhaust line, the injection module 7 is then driven according to the operating conditions of the two turbochargers 1 and 2 as well as according to the concentration of pollutants at the outlet of the pollution control device 6, for example NO _x , which allows an optimal depollution.

This takes into account the specific characteristics of turbochargers 1 and 2 which can operate independently and / or in groups.

For example, the first turbocharger 1 said small turbocharger can be biased at a relatively low speed, for example, allowing a motor torque of 1 500 to 2500 rpm because of its reduced inertia. Then, the second turbocharger 2, called big turbocharger, can take over with or without operation of the small turbocharger 1, this over a speed range of 2,000 to 4,500 rpm. Advantageously, the two turbochargers 1 and 2 work together in this speed range.

It follows that the physical parameters of the exhaust gas are not the same in each branch 3a or 3b. The first turbocharger 1, said small turbocharger being advantageously still in action, the incorporation of the injection module 7 in the branch 3a of said small turbocharger makes it possible to take full advantage of the pollution control potential of the depollution device 6 with prior injection of an agent. depollution, including an SCR agent.

It is necessary to take into account the operating conditions of each of the two turbochargers 1 and 2 to determine the amount of depollution agent that will be injected into the branch 3a of one of the two turbochargers 1 or 2. [0046] For this purpose, it is advantageously provided for at least four temperature probes 9a, 9b, 10a, 10b in addition to at least one measuring probe 8 for emission of a pollutant of the NO _x type at the outlet of the depollution device 6, hence in the grouped exhaust line 3c. For each of the branches 3a, 3b, a temperature probe 9a, 9b is placed before the auxiliary depollution device 4a, 4b specific to one of the branches 3a, 3b and a temperature probe 10a, 10b is placed after the auxiliary depollution device 4a , 4b, advantageously before the injection module 7 for the branch 3a which carries the single module 7.

By taking the example of pollutants in the form of nitrogen oxides NO _x and a depollution agent in the form of urea, via the injection module 7, a first quantity of urea is injected when the temperature difference between the probes 10a and 9a exceeds a first threshold value and the concentration of NO _x exceeds the instantaneous concentration value of NOx calculated according to the flow rate of the gases. Initially, the instantaneous concentration value calculated corresponds to a stabilized operation at low speed with a single turbocharger 1 operating, that is to say the first turbocharger 1. A second quantity of additional urea is injected when the temperature difference between the probes 10a and 9a exceeds a second threshold value and the concentration of NO _x exceeds the instantaneous concentration value of NO _x calculated according to the gas flow rate. . This concentration value may, for example, correspond to a low-speed acceleration phase of the motor vehicle, with the only first turbocharger 1 operating.

A third quantity of additional urea is injected when the temperature difference between the probes 10a and 9a and the temperature difference between the probes 10b and 9b exceed a respective threshold value and the concentration of NO _x exceeds the value of instantaneous concentration of NO _x calculated according to the gas flow. This concentration value of NO _x may, for example, correspond to a stabilized phase at full power, the two turbochargers 1 and 2 being then actuated. The instantaneous concentration value of NO _x is thus calculated so that it is more or less depolluted according to the objective to achieve grams of NO _x eliminated per kilometer.

It is also possible to implement a so-called "buffer" strategy to refrain from injecting the de-polluting agent when the depollution device filled with depollution agent following a lifting of the driver's foot. accelerator at the time of the injection of the depollution agent. This saves the depollution agent.

Thus, the depollution agent injection is adjustable on a case by case basis according to the emissions of the engine, this for each of the branches 3a, 3b of a turbocharger 1, 2 as well as according to the needs in depollution.

If the present invention has been described in association with a supercharging system comprising two turbochargers, the line and the method according to the invention can also be applied to a higher number of turbochargers, so to any supercharging multiple. It is also possible to provide an injection module on each branch, a single injection module operating, the choice of this injection module dependent operating conditions of the engine. This could be practiced when, for example, the first turbocharger does not always work in conjunction with the second turbocharger.

The advantages of the present invention relate to the injection at the earliest in the pollution control cycle of the depollution agent, to the mixture of the exhaust gas with the homogenized and extended depollution agent, according to the variant of the invention in question, with a premix of exhaust gas from a turbocharger with a depollution agent and an optimized injection control strategy. Another advantage is an economic gain thanks to a single injection module for two turbochargers. This economic gain is supplemented by a gain in reliability by reducing the number of parts devoted to the depollution as well as a gain of implantation and mass by reducing the number of parts devoted to the depollution.

Claims

1. Exhaust line of a thermal combustion engine capable of being connected to a supercharging system having at least two turbochargers (1, 2), the exhaust line having exhaust branches (3a, 3b), each of the branches (3a, 3b) being respectively connected to a turbocharger (1, 2), said legs (3a, 3b) joining at a connection point (P) to form a grouped exhaust line (3c), the exhaust line being provided with a depollution device (6) for the removal of at least one pollutant in the exhaust gas by prior injection of a depollution agent by an injection module (7). ) carried by said line, characterized in that the injection module (7) is disposed in one (3a) of the branches (3a, 3b) exhaust. 2. Exhaust line according to the preceding claim, wherein the injection module (7) is on the branch (3a) the longest exhaust. 3. Exhaust line according to any one of the preceding claims, wherein each branch (3a, 3b) is provided with an auxiliary pollution control device (4a, 4b) of the oxidation catalyst type. 4. Exhaust line according to the preceding claim, wherein the injection module (7) is on its exhaust branch (3a) between the auxiliary depollution device (4a) and the connection point (P) of the branches (3a, 3b). 5. Exhaust line according to any one of the preceding claims, which comprises two temperature probes (9a, 10a, 9b, 10b) in each of the exhaust branches (3a, 3b) and a measurement probe ( 8) of emission of said pollutant to be eliminated, this measurement probe (8) being arranged in the grouped exhaust line (3c). 6. Exhaust line according to claims 4 and 5, wherein the two temperature probes (9a, 10a, 9b, 10b) in each of the branches (3a, 3b) exhaust are arranged on either side of the auxiliary device for the depollution (4a, 4b) of said branch (3a, 3b) and for which, in the exhaust branch (3a) carrying the injection module (7), the temperature probe (10a), in the flow direction of the exhaust gas, is disposed after the auxiliary pollution control device (4a, 4b) and before said module (7). 7. Exhaust line according to any one of the preceding claims, wherein the depollution device (6) by injection is on the grouped line (3c) exhaust. 8. Exhaust line according to any one of the preceding claims, which comprises two exhaust branches (3a, 3b), the connection of the two branches (3a, 3b) exhaust and the grouped line (3c) d exhaust having a Y-shape, the two exhaust branches (3a, 3b) forming the upper part of the Y. Boosting system having at least two turbochargers (1, 2) with different operating ranges, characterized in that it comprises an exhaust line according to any one of the preceding claims. A method of injecting a depollution agent into an exhaust line of a supercharging system according to the preceding claim, said method comprising the step of measuring the instantaneous concentration of at least one pollutant to be eliminated by injection of said agent and the step of measuring a parameter in each of the branches (3a, 3b), this parameter being representative of the instantaneous operating conditions of the respective turbocharger (1, 2), the step of calculating the quantity of depollution agent to be injected according to said measurements and the step of injecting the calculated amount of depollution agent into the branch (3a) of the exhaust bearing the injection module (7).