WO2022002948A1

WO2022002948A1 - Device and method for the treatment of flue gases from a turbocharged internal combustion engine on board a motor vehicle

Info

Publication number: WO2022002948A1
Application number: PCT/EP2021/067865
Authority: WO
Inventors: Joel Op De Beeck; Sébastien DECAMP; Frédéric PEUCAT
Original assignee: Plastic Omnium Advanced Innovation And Research
Priority date: 2020-06-30
Filing date: 2021-06-29
Publication date: 2022-01-06
Also published as: BE1028445B1; BE1028445A1; EP4172475A1

Abstract

The invention relates to the treatment of flue gases from a turbocharged internal combusiton engine, comprising: • determining a first pressure, P₁, in a flue gas exhaust system (3) upstream of at least one turbocharger (30); • determining a second pressure, P₂, in an injection line (22) for injecting a reducing agent; • controlling the pressurisation of the injection line when a pressure difference, P₂ - P₁, is less than a first reference value; • injecting the reducing agent upstream of a selective catalytic reduction catalyst (31) arranged upstream of the at least one turbocharger (30) in the exhaust system (3) only when the pressure difference, P₂ - P₁, is greater than or equal to a second reference value.

Description

Device and method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle

The invention relates to the field of motor vehicles with internal combustion heat engines such as cars for example. The invention relates more particularly to a method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation and to a device implementing said method.

The invention is intended for use in particular in the field of injecting a reducing agent of the ammonia precursor solution type, such as an aqueous urea solution, into the exhaust system of an engine. turbocharged internal combustion engine on board a motor vehicle in operation. The fuel burned in such a vehicle can be gasoline, diesel, alcohol, or even a gas (LPG, ¾, etc.). In the case of the injection of a reducing agent, this reducing agent mixes with the exhaust gases and makes it possible to reduce the emissions of pollutants called NO _x . The expression “in operation” means that the heat engine of the motor vehicle is not stopped.

Various techniques have already been proposed for reducing the emissions of polluting elements discharged into the atmosphere with the exhaust gases of motor vehicles fitted with a thermal internal combustion engine. This is particularly the case for emissions of nitrogen oxides NO _x which are treated by catalytic reduction. To this end, one technique is to mix a reducing agent, in particular gaseous ammonia, with the exhaust gases and to pass the mixture into or over a catalyst placed in the exhaust system. This technique is known by the abbreviation RCS (for Selective Catalytic Reduction) or the English abbreviation SCR (for Selective Catalytic Reduction). It is therefore necessary to have in the system exhaust an ammonia gas injector and a catalyst. The catalyst may have been deposited, for example by impregnation, on the walls of the channels of a ceramic block composed of a multitude of channels substantially parallel to the direction of flow of the exhaust gases. The reducing agent converts nitrogen oxides into nitrogen and water. When the reducing agent is ammonia NH3 a chemical reaction is as follows:

4 NO + 4 NH ₃ + O2 - _► 4 N ₂ + 6H2O (I)

According to another embodiment of this technique, an aqueous solution of urea (and therefore a liquid) is injected, which is transformed into gaseous ammonia under the effect of the heat of the exhaust gases. The aqueous urea solution is injected into the exhaust line at a relatively high pressure (about 5 bar or 0.5 MPa) compared to the pressure in the exhaust line. Since the solution is a liquid and therefore incompressible, the flow rate of the injected aqueous urea solution is relatively insensitive to small fluctuations in the pressure of the exhaust gases downstream of a turbocharger. In other words, the flow rate of the injected aqueous urea solution is practically independent of the pressure in the exhaust line downstream of a turbocharger.

A problem with these methods of treating nitrogen oxides present in the exhaust gases of an internal combustion engine on board a motor vehicle is the temperature which the selective catalytic reduction catalyst must reach in order to catalyze the NO (I) reduction reaction efficiently. It is generally considered that said temperature should ideally be around 250 ° C, in this case one speaks of standard SCR conditions. At lower temperatures, of at least 160 ° C, preferably of at least 180 ° C, a reduction of nitrogen oxides can also be carried out according to reaction (II), we will then speak of fast SCR:

In all cases, it is therefore observed that it is essential to reach a certain temperature in order to be able to carry out the reduction of nitrogen oxides.

The object of the invention is in particular to overcome these drawbacks of the prior art.

More precisely, an objective of the invention, in at least one of its embodiments, is to implement a method for treating the exhaust gases from a turbocharged internal combustion heat engine on board a motor vehicle. having an optimized yield. Another objective of the invention, in at least one of its embodiments, is to provide a device for treating the exhaust gases of a turbocharged internal combustion heat engine on board a motor vehicle.

Another objective of the invention, in at least one of its embodiments, is to provide a motor vehicle comprising a device for treating the burnt gases of a turbocharged internal combustion heat engine according to the invention.

In accordance with a particular embodiment, the invention relates to a method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation,

According to the invention, such a method comprises:

• a step of determining a first pressure, Pi, in a burnt gas exhaust system upstream of at least one turbocharger; • a step of determining a second pressure, P2, in a line for injecting a reducing agent of the ammonia precursor solution type;

• a control step of a means of pressurizing the injection line when the pressure difference, P2 - Pi, is less than a first reference value;

• a step of injecting the reducing agent upstream of a selective catalytic reduction catalyst arranged upstream of the at least one turbocharger in a flue gas exhaust system by opening and closing a first injector, said step injection being performed only when the pressure difference, P2 - Pi, is greater than or equal to a second reference value.

The general principle of the invention is based on the injection of a reducing agent upstream of at least one turbocharger (commonly called a “turbo”) into a flue gas exhaust system of a turbocharged internal combustion engine. . Preferably, the flue gas exhaust system includes a flue gas exhaust line. By "exhaust line" is meant a duct placed at the outlet of the turbocharged internal combustion engine of the motor vehicle which allows the exhaust gases from the internal combustion of the engine to be evacuated.

Thus, the invention is based on a completely new and inventive approach for injecting a reducing agent of the ammonia precursor solution type, upstream of a selective catalytic reduction catalyst (commonly called a “catalyst”) arranged upstream of at least one turbo in a flue gas exhaust system of a turbocharged internal combustion engine. This injection allows the treatment of gases burnt at a higher temperature compared to an injection carried out downstream of the at least one turbo. In order to obtain good treatment of the burnt gases, it is necessary for this injection via the first injector to be carried out with a sufficient pressure differential between the exhaust system and the injection line. A sufficient pressure differential is a pressure differential which makes it possible to obtain an optimum size of droplets of ammonia precursor solution at the outlet of the first injector. An optimal droplet size is a size that allows the droplets sprayed by the first injector to be all (or nearly all) evaporated and converted to gaseous ammonia before entering the selective catalytic reduction catalyst. In fact, it is sought to prevent the reducing agent from entering the catalyst in liquid form. Taking into account the fact that very little space is available in the exhaust line between the outlet of the first injector and the inlet of the catalyst, it is important to be able to rapidly evaporate the liquid reducing agent on pain of allowing the catalyst to enter the catalyst. reducing agent in liquid form. The optimal droplet size is linked, among other things, to the characteristics of the first injector, in particular, the diameter of the injection port (s), the injection pressure, the orientation and the location of the first injector in the injection port. exhaust line. Thus, a given exhaust system corresponds to an optimal droplet size. The size of a droplet can be defined by its Sauter Mean Diameter (SMD). In a given example of an exhaust system, the optimum SMD is in a range between 50 µm and 500 µm.

It is understood that the means of pressurizing the injection line is a means other than that used for the injection of the reducing agent. The pressurizing means makes it possible to cause a large and rapid pressure variation allowing, at any time, to adjust the pressure difference, P2 - Pi to the first reference value.

The first reference value is a target pressure value which, until it is reached, prevents the execution of the agent injection step. reducer. The target pressure value is the minimum pressure necessary to guarantee a good quality of nebulization of the reducing agent, for a given exhaust system. In fact, an injection of the reducing agent at a pressure lower than the target pressure would not make it possible to obtain an optimal size of droplets, the droplets would be too large. The larger the droplets, the greater the risk of forming unwanted residual deposits on the walls of the exhaust system, which can lead to clogging or clogging of the exhaust system. The first reference value is approximately at least equal to or greater than 5 bar, more preferably is approximately less than or equal to 8 bar, more preferably approximately less than or equal to 7 bar. The second reference value is a threshold pressure value from which the reducing agent can be injected. This makes it possible to create droplets of the optimum size before injecting them. The second reference value is approximately at least equal to or greater than 5 bar, more preferably is approximately less than or equal to 8 bar, more preferably approximately less than or equal to 7 bar. Preferably, the second reference value is equal to the first reference value. Such values of first and second reference values thus make it possible to obtain at any time a pressure differential P2 - Pi sufficient to obtain good nebulization of the reducing agent in the exhaust system upstream of a reduction catalyst. selective catalytic converter arranged upstream of the at least one turbo but also to prevent the formation of deposits on the walls of the exhaust system when the pressure differential is too high. In fact, the injection carried out with a high pressure differential causes the projection of the droplets formed by nebulization on the walls of the exhaust system and the formation of undesirable residual deposits.

By the expressions “approximately at least equal to or greater than”, “approximately less than or equal to”; it is intended to denote the fact that a tolerance is applied to this pressure value, said tolerance being of the order of 0.5 bar. The pressure values are relative values expressed with respect to atmospheric pressure. Atmospheric pressure can be measured using a third sensor located outside the exhaust system or located in the muffler. In the case of a third pressure sensor located in the muffler, the measured value can be corrected by calculation using vehicle data.

Advantageously, the method of treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation according to the invention is such that it comprises a step of controlling a pressure reduction means in the injection line when the pressure difference, P2 - Pi, is greater than the second reference value. Said second reference value is approximately less than or equal to 8 bar, more preferably approximately less than or equal to 7 bar. In one example, when the pressure in the exhaust line drops, for example due to a decrease in speed of the turbo, the pressure difference, P2- Pi, can increase rapidly, which should be avoided by reducing the pressure in the turbo. the injection line.

Thus, such a step of controlling a means of reducing pressure in the injection line of the reducing agent makes it possible to guarantee the maintenance of a good quality of nebulization of the reducing agent.

According to a preferred embodiment or in accordance with the invention, the method of treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that the step of injecting the fuel. reducing agent upstream of the selective catalytic reduction catalyst arranged upstream of the turbo is carried out when the pressure difference, P2 - Pi, is equal to a third reference value, said third reference value being preferably equal to 80% of the difference in pressure, i.e. 0.8 c (P2 - Pi). Said third reference value being between 5 and 7 bar expressed as a relative pressure value. Thus, a step of injecting the reducing agent carried out at this pressure difference still makes it possible to guarantee a good quality of nebulization of the optimum reducing agent while still guaranteeing a sufficiently fine droplet size.

According to an advantageous implementation or variant of the invention, the method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that the step of determining the first pressure , Pi, in a flue gas exhaust system is carried out upstream of the selective catalytic reduction catalyst.

According to an advantageous implementation or variant of the invention, the method of treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that the step of determining the second pressure , P ₂ , in the injection line of a reducing agent is carried out by measuring said second pressure, P ₂ , by a first pressure sensor.

According to an advantageous implementation or variant of the invention, the method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that the step of determining the first pressure , Pi, in the exhaust gas exhaust system upstream of the turbo is carried out by measuring the pressure by a second pressure sensor or is calculated on the basis of the exhaust gas temperature, the intake temperature and of the intake pressure, also called "turbo pressure" because the intake pressure is regulated by the flow of the turbo. Preferably, the step of determining the first pressure, Pi, in the exhaust system of the burnt gases upstream of the turbo is carried out by measuring the pressure by a second pressure sensor. The use of a second pressure sensor makes it possible to have a more precise pressure value than that obtained by calculation. More preferably, the second pressure sensor is located on the first injector. Such an arrangement makes it possible to obtain a more precise pressure value and thus ensure better control of the nebulization.

According to an advantageous implementation or variant of the invention, the method of treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that the reducing agent is ammonia. or an ammonia precursor such as urea, preferably the reducing agent is ammonia.

According to an advantageous implementation or variant of the invention, the method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that the means for pressurizing the line injection is a gear pump. The use of a gear pump allows better regulation of the pressure in the injection line.

According to an advantageous implementation or variant of the invention, the method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that the pressure reduction means in the line injection of the reducing agent is a gear pump.

Advantageously, the gear pump of the injection line pressurizing means is a reversible pump and the pressure reducing means in the injection line is said reversible pump.

According to an advantageous implementation or variant of the invention, the method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that the first reference value is greater than or equal to 5 bar, preferably greater than or equal to 6 bar. According to an advantageous implementation or variant of the invention, the method of treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that the second reference value is greater than or equal to 5 bar, preferably greater than or equal to 6 bar.

According to an advantageous implementation or variant of the invention, the method of treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation is such that it comprises an injection step of the reducing agent downstream of the turbo in the exhaust gas exhaust system by opening and closing a second injector.

Thus, such an injection step downstream of the turbo into the exhaust gas exhaust system by opening and closing a second injector makes it possible to optimize the injection of reducing agent into the exhaust gas exhaust system. .

The invention also relates to a device for treating the burnt gases of a turbocharged internal combustion engine on board a motor vehicle capable of implementing the method for treating the burnt gases of a turbocharged thermal engine according to the invention. , said processing device comprising:

• a reducing agent reservoir connected to at least a first injector via an injection line, said at least one first injector of the injection line being located upstream of a selective catalytic reduction catalyst arranged upstream of the injection line. at least one turbo in the flue gas exhaust system,

• a first pressure sensor able to measure the pressure in the injection line • a gear pump fluidly connected to the injection line, said pump being able to inject the reducing agent contained in the reservoir into the injection line,

A second pressure sensor located in the exhaust gas exhaust system upstream of the at least one turbo, preferably said second sensor is located on the head of at least one first injector, said second sensor being able to measure the pressure in the exhaust gas exhaust system, a first control unit controlling the starting or stopping of the gear pump as well as its speed as a function of the pressures measured by the first and the second pressure sensor.

Finally, the invention also relates to a motor vehicle comprising a device for treating the burnt gases of a turbocharged heat engine according to the invention.

Other characteristics and advantages of the invention will emerge more clearly on reading the following description of a preferred embodiment, given by way of simple illustrative and non-limiting example, and the accompanying drawings, among which:

• Figure 1 shows a block diagram of an implementation of a process for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle in operation according to the invention.

FIG. 2 illustrates an embodiment of a device for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle according to the invention. In relation to FIG. 1, an embodiment of a method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle (1) in operation according to the invention is presented. . Said method for treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle (1) in operation comprises:

• a step of determining a first pressure, Pi, in a flue gas exhaust system upstream of at least one turbo (10);

• a step of determining a second pressure, P2, in a line for injecting a reducing agent (11) of the ammonia precursor solution type;

• a control step of a means of pressurizing the injection line when the pressure difference, P2 - Pi, is less than a first reference value (12);

• a step of injecting the reducing agent upstream of the at least one turbo into a burnt gas exhaust system by opening and closing a first injector, said injection step being performed only when the pressure difference , P2 - Pi, is greater than or equal to a second reference value (13).

The first reference value is approximately at least equal to or greater than 5 bar, more preferably is approximately less than or equal to 8 bar, more preferably approximately less than or equal to 7 bar. The second reference value is approximately at least equal to or greater than 5 bar, more preferably is approximately less than or equal to 8 bar, more preferably approximately less than or equal to 7 bar. Such values of first and second reference values make it possible to obtain at all times a pressure differential sufficient to obtain a good nebulization of the reducing agent in the exhaust system upstream of the at least one turbo but also to avoid a deposit on the walls of the exhaust system when the pressure differential is too high. The injection carried out with a high pressure differential causes the projection of the droplets formed by nebulization on the walls of the exhaust system and the formation of deposits.

FIG. 2 illustrates an embodiment of a device for treating the flue gases of a turbocharged internal combustion heat engine on board a motor vehicle according to the invention. The device for treating the burnt gases of a turbocharged internal combustion engine on board a motor vehicle (2) comprises:

• a reducing agent reservoir (20) connected to at least a first injector (21) via an injection line (22), said at least a first injector (21) of the injection line (22) being located upstream of a selective catalytic reduction catalyst arranged upstream of the turbo (30) in the flue gas exhaust system (3),

• a first pressure sensor able to measure the pressure in the injection line (22),

• a gear pump fluidly connected to the injection line (22), said pump being able to inject the reducing agent contained in the reservoir (20) into the injection line (22), the gear pump being located in a module (23),

• a second pressure sensor located in the flue gas exhaust system (3) upstream of the at least one turbo (30), preferably said second sensor is located on the head of at least one first injector (21), said second sensor being able to measure the pressure in the exhaust gas system (3),

• a first control unit (24) controlling the starting or stopping of the gear pump as well as its speed according to the pressures measured by the first and the second pressure sensor. Preferably, the first control unit (24) records system data including in particular the pressures measured by the first and second pressure sensors and controls a second control unit (25) which controls the gear pump. This arrangement makes it possible to optimize the control of the various components present in the module (23) such as the gear pump or the drivers (26). The first control unit (24) can also be connected to a NOx / NFL sensor (28) attached to or near the outlet of the exhaust system (3).

• The injection line (22) can also include a second injector (27) located downstream of the at least one turbo (30).

• The exhaust system (3) comprises a so-called SCRF unit (31) located upstream of the at least one turbo (30) and an SCR UF unit (32) coupled with an ASC unit (33). Said SCRF unit (31) is located between the at least one turbo (30) and the at least one first injector, said SCR UF (32) and ASC (33) units being located downstream of the second injector (27). The SCRF unit (31) (or “Selective Catalytic Reduction on Filter”) is a particulate filter which incorporates a selective catalytic reduction (SCR) catalyst, which makes it possible to fulfill both the function of soot and NO _x reduction. The SCR UF (or “SCR Under-Floor”) and ASC (or “Ammonia Slip Catalyst”) units are respectively a selective catalytic reduction unit for NO _x and a unit containing a catalyst to treat leaks. ammonia.

Claims

1. A method of treating the burnt gases of a turbocharged internal combustion heat engine on board a motor vehicle (1) in operation, said method (1) comprising:

• a step of determining a first pressure, Pi, in a flue gas exhaust system upstream of at least one turbocharger (10);

• a step of determining a second pressure, P2, in a line for injecting a reducing agent (11) of the ammonia precursor solution type; A step of controlling a means of pressurizing the injection line when the pressure difference, P2 - Pi, is less than a first reference value (12);

• a step of injecting the reducing agent upstream of a selective catalytic reduction catalyst arranged upstream of the at least one turbocharger in a flue gas exhaust system by opening and closing a first injector, said step injection being performed only when the pressure difference, P2 - Pi, is greater than or equal to a second reference value (13).

2. Method according to claim 1, such that it comprises a step of controlling a pressure reduction means in the injection line when the pressure difference, P2 - Pi, is greater than the second reference value (12 ).

3. Method according to any one of the preceding claims, such as the step of injecting the reducing agent upstream of the selective catalytic reduction catalyst arranged upstream of the turbo in a flue gas exhaust system (13) is carried out when the pressure difference P2 - Pi is equal to a third reference value, said third reference value preferably being equal to 80 % of the pressure difference, i.e. 0.8 x (P2 - P1).

4. Method according to claim 1, such that the step of determining the second pressure, P2, in the injection line of a reducing agent (11) is carried out by measuring said second pressure, P2, by a first. Pressure sensor.

5. Method according to any one of the preceding claims, such that the step of determining the first pressure, Pi, in the exhaust system of the burnt gases upstream of the turbo (10) is carried out by measuring the pressure by a second pressure sensor or is calculated on the basis of the exhaust gas temperature, the intake temperature and the intake pressure.

6. Method according to claim 5, such that the step of determining the first pressure, Pi, in the exhaust system of the burnt gases upstream of the turbo (10) is carried out by measuring the pressure by the second pressure sensor. pressure.

7. The method of claim 6, such that the second pressure sensor is located on the first injector.

8. Method according to any one of the preceding claims, such that the reducing agent is ammonia or an ammonia precursor such as urea, preferably the reducing agent is ammonia.

9. Method according to any one of the preceding claims, such that the means for pressurizing the injection line is a gear pump.

10. Method according to any one of the preceding claims, such that the first reference value is greater than or equal to 5 bar, preferably greater than or equal to 6 bar.

11. Method according to any one of the preceding claims, such that the second reference value is greater than or equal to 5 bar, preferably greater than or equal to 6 bar.

12. Method according to any one of the preceding claims, such that it comprises a step of injecting the reducing agent downstream of the turbo into the exhaust gas system by opening and closing a second injector.

13. Device for treating the burnt gases of a turbocharged internal combustion engine on board a motor vehicle (2) capable of implementing the method for treating the burnt gases of a turbocharged thermal engine (1) according to l any of claims 1 to 12, said processing device comprising:

• a reducing agent reservoir (20) connected to at least a first injector (21) via an injection line (22), said at least a first injector (21) of the injection line (22) being located upstream of a selective catalytic reduction catalyst arranged upstream of at least one turbocharger (30) in the flue gas exhaust system (3),

• a first pressure sensor able to measure the pressure in the injection line,

• a gear pump fluidly connected to the injection line, said pump being able to inject the reducing agent contained in the reservoir into the injection line, a second pressure sensor located in the system exhaust of the burnt gases upstream of the at least one turbocharger (30), preferably said second sensor is located on the head of the at least one first injector,

• a first control unit (23) controlling the starting or stopping of the gear pump as well as its speed according to the pressures measured by the first and second pressure sensors.

14. Motor vehicle comprising a device for treating the burnt gases of a turbocharged heat engine according to claim 13.