FR3132326A1 - PARTICLE FILTRATION SYSTEM FOR A HEAT ENGINE WITH IMPROVED EFFICIENCY AND OPTIMIZED BACK PRESSURE - Google Patents

Abstract

The invention relates to a motor vehicle (10) comprising a heat engine (11) and an exhaust line (12) capable of evacuating and treating exhaust gases emitted by the heat engine (11), said exhaust line comprising: - a first particulate filter (14.1) arranged at the output of the internal combustion engine, and - a second particulate filter (14.2) arranged under a floor (15) of the vehicle, - the second particulate filter (14.2) arranged under the floor (15) of the vehicle having a greater filtration efficiency than the first particulate filter (14.1) arranged at the outlet of the combustion engine (11). Figure 2

Description

PARTICLE FILTRATION SYSTEM FOR A THERMAL ENGINE WITH IMPROVED EFFICIENCY AND OPTIMIZED BACK PRESSURE

The present invention relates to a particle filtration system for a heat engine with improved efficiency and optimized counter pressure. The invention finds a particularly advantageous, but not exclusive, application with conventional or hybrid thermal vehicles equipped with a gasoline thermal engine.

In a manner known per se, vehicles equipped with a gasoline type thermal engine include a depollution system formed by a catalyst, called "three ways" (or TWC for "Three Way catalytic Converter" in English) and a particle filter (or GPF for "Gasoline Particulate Filter" in English) allowing the storage of polluting particles contained in exhaust gases.

Such a particle filter can be made of cordierite but also of alumina titanate or silicon carbide. The filter provides mechanical filtration through porous walls.

To this end, as illustrated by the , filter 1 is composed of channels 2 open at the input and blocked at the output. Conversely, channels 3 blocked at the input are open at the output. The exhaust gases 4 loaded with particles therefore enter the filter through the channels 2 open at the inlet, the gases 4 passing through the walls to reach the channels 3 open at the outlet. The particles are stored in channels 2 open at the inlet because the porosity of the walls does not allow them to pass through them. Unlike particle filters used with diesel engines, this type of filter 1 is passive in that it does not require programmed regeneration, except in the event of a malfunction. In fact, the regeneration of stored particles occurs naturally by combustion of the latter in the presence of oxygen at high temperature, in particular between 550 and 600°C.

Due to its operating principle and its technical characteristics, a particle filter induces a significant additional exhaust back pressure (CPE) (from around fifty to several hundred millibars depending on the soot load of the GPF with a flow rate of 0.1m3/s, for example). This back pressure is representative of the resistance to the flow of exhaust gases. To improve filtration efficiency, it is possible to tighten the porosity of the filter walls and the average pore size or to cover it with a membrane made of alumina to simulate the creation of a bed of ashes.

Whatever the solution chosen, the exhaust back pressure will increase significantly. However, the operation of the gasoline engine is particularly sensitive to this exhaust back pressure.

There is therefore a need to be able to comply with new standards imposing very high levels of filtration, without this causing a crippling increase in exhaust back pressure impacting the operation of the heat engine, whether in terms of its performance. or its fuel consumption (and therefore its CO2 emissions). For example, the maximum particle number limit could be set in the case of the Euro7 emissions standard at 1.10 ¹¹ #/km for particle diameters greater than 10nm instead of 6.10 ¹¹ #/km currently for diameters of particles larger than 23nm. The new standard could thus correspond to a particle elimination rate of 99.9% depending on the level of engine output emissions.

The invention aims to effectively meet this need by proposing a motor vehicle comprising a heat engine and an exhaust line capable of evacuating and treating exhaust gases emitted by said heat engine, said exhaust line comprising:
- a first particle filter placed at the outlet of the heat engine, and
- a second particle filter placed under a floor of the vehicle,
- the second particle filter placed under the floor of the vehicle having a greater filtration efficiency than the first particle filter placed at the outlet of the heat engine.

The invention thus makes it possible to significantly improve filtration efficiency while limiting the exhaust back pressure generated by the pollution control device. Indeed, the second particle filter is located under the floor where the temperatures are lower than those observable at the outlet of the heat engine, so that the back pressure at the exhaust will be contained (because the higher the temperature of the gases the more the back pressure at the exhaust is important). Another advantage of this arrangement is that the particles which have managed to pass through the first particle filter whose porosity is less restricted will, despite their very small diameter, be stopped by the second filter with restricted porosity. The compromise between efficiency and exhaust back pressure is then optimal. The invention also makes it possible to limit particle reduction work at the source, that is to say in the combustion chamber of the heat engine.

According to one embodiment of the invention, the first particle filter is associated with a “three-way” catalyst.

According to one embodiment of the invention, the second particle filter is associated with a “three-way” catalyst.

According to one embodiment of the invention, the “three-way” catalyst is placed upstream of the particle filter.

According to one embodiment of the invention, the second particle filter is associated with a catalyst for eliminating residual ammonia emissions.

According to one embodiment of the invention, the second particle filter is associated with a selective reduction catalyst.

According to one embodiment of the invention, the exhaust line further comprises a hydrocarbon trap placed under the floor of the vehicle upstream or downstream of the second particle filter.

According to one embodiment of the invention, the first particle filter and/or the second particle filter are bare filters.

According to one embodiment of the invention, the first particle filter and/or the second particle filter are impregnated filters.

According to one embodiment of the invention, the heat engine is a gasoline engine.

The invention will be better understood on reading the following description and examining the accompanying figures. These figures are given for illustrative purposes only but in no way limit the invention.

There is a perspective view illustrating the operation of a particle filter;

There is a schematic representation of a first embodiment of the pollution control system according to the present invention;

There is a schematic representation of a second embodiment of the pollution control system according to the present invention;

There is a schematic representation of a third embodiment of the pollution control system according to the present invention;

There shows graphical representations of an accumulation of particles released into the atmosphere during the WLTC operating cycle respectively with and without the additional particle filter placed under the floor of the vehicle;

There shows graphical representations of the number of particles per kilometer emitted during the different phases of the WLTC operating cycle respectively with and without the additional particle filter placed under the floor of the vehicle.

Identical, similar, or analogous elements retain the same reference from one figure to another.

Furthermore, the terms such as "upstream" and "downstream" are understood by reference to the direction of flow of the exhaust gases emitted by the heat engine.

There shows a motor vehicle 10 comprising a heat engine 11 and an exhaust line 12 for the exhaust gases emitted by said heat engine 11. The exhaust line 12 is constituted by the conduit evacuating the exhaust gases towards the atmosphere as well as by the various exhaust gas treatment devices mounted along the conduit.

The heat engine 11 includes a combustion chamber in which fuel and oxidizer are mixed. The fuel can, for example, be gasoline, and be injected into the combustion chamber by an injector (not shown), in particular by a direct injection system. The oxidant can, for example, be air.

The combustion of the mixture in the combustion chamber drives a piston in translation, which makes it possible to transform the thermal energy of combustion into mechanical energy in order to drive the motor shaft in rotation. When burning the mixture, exhaust gases are formed. These exhaust gases are evacuated and treated by the exhaust line 12.

For this purpose, the exhaust line 12 comprises a first particle filter 14.1 disposed at the outlet of the heat engine 11, that is to say that the first particle filter 14.1 is coupled to the exhaust manifold of the engine either directly either downstream of a catalyst, as described in more detail below. Such a configuration of the particle filter 14.1 relative to the heat engine is called a "close-coupled" configuration in English which translates into French as "close-coupled" configuration. The first particle filter 14.1 is arranged inside the engine compartment.

A second particle filter 14.2 is arranged under a floor 15 of the vehicle, that is to say under the area of the vehicle body on which the vehicle seats are mounted. The second particle filter 14.2 is thus placed at a distance from the heat engine 11 in a zone where the temperatures of the exhaust gases are lower than those observable at the outlet of the heat engine 11 (between 100 and 200°C less). This limits the back pressure induced by the particle filter 14.2.

The second particle filter 14.2 disposed under the floor 15 has a greater filtration efficiency than the first particle filter 14.1 disposed at the outlet of the heat engine 11. The desired filtration efficiency is obtained by adapting the overall porosity and the size of the pores of the particle filter. According to a non-limiting exemplary embodiment, the pores of the second particle filter 14.2 are tighter, that is to say smaller, than the pores of the first particle filter 14.1.

The second particle filter 14.2 may for example have a filtration efficiency of between 95 and 98%; while the first particle filter 14.1 may have a filtration efficiency of between 75 and 85%.

In the embodiment of the , the first particle filter 14.1 is associated with a “three-way” catalyst 16.1, called TWC catalyst for “Three Way catalytic Converter” in English. The second particle filter 14.2 is placed alone under the floor 15 of the motor vehicle 10.

In the embodiment of the , the second particle filter 14.2 is also associated with a “three-way” catalyst 16.2. Each “three-way” particle filter-catalyst assembly can be placed inside a common envelope. Each “three-way” particle filter-catalyst assembly thus forms a one-piece device that can easily be integrated into the exhaust line 12.

The “three-way” catalyst 16.1, 16.2 is preferably placed upstream of the corresponding particle filter 14.1, 14.2. The underbody arrangement between the “three-way” catalyst 16.2 and the particle filter 14.2 can be reversed, but this is less effective for treating gaseous pollutants because the “three-way” catalyst 16.2 will then have less available. thermal energy to carry out the conversion reactions of the pollutants which require it.

In the embodiment of the , the second particle filter 14.2 is also associated with a catalyst 17 for eliminating residual ammonia emissions called "ASC" catalyst for "Ammonia Slip Catalyst" in English.

The “particle filter-“three-way” catalyst-ASC” assembly can be placed inside a common envelope. Each “particle filter – “three-way” catalyst-ASC” assembly thus forms a one-piece device that can easily be integrated into the exhaust line 12.

Alternatively, the ASC 17 catalyst can be replaced by a selective reduction catalyst, called SCR catalyst for "Selective Catalytic Reduction" in English.

The exhaust line 12 may also include a hydrocarbon trap 18 placed under the floor 15 of the vehicle upstream or downstream of the second particle filter 14.2.

In all embodiments, the particle filters 14.1, 14.2 may take the form of bare filters or impregnated filters. The impregnation layer can be made with precious metals of the same type as those used for “three-way” catalysts, namely Platinum (Pt), Palladium (Pd), or Rhodium (Rh). This makes it possible to add an additional function of eliminating gaseous pollutants in the case of a dimensionally constrained depollution architecture. The particle filter 14.1, 14.2 may also be covered with a membrane, in particular made of alumina, to simulate the creation of a bed of ashes and improve the performance of the particle filter.

There shows graphical representations of an accumulation of particles released into the atmosphere during the WLTC operating cycle (for "Worldwide harmonized Light vehicles Test Cycle" in English)

This operating cycle has a driving phase P1 at low speed, a driving phase P2 at medium speed, a driving phase P3 at high speed, as well as a driving phase P4 at very high speed. The vehicle speed curve as a function of time is referenced V_veh.

There highlights that the accumulation of polluting particles obtained for a configuration with double particle filters 14.1, 14.2 (see curve C_14.1+14.2) is much lower than the accumulation of polluting particles observable for a configuration with a single particle filter (see . curve C_14.1).

There shows graphical representations of a number of particles per kilometer traveled during the different phases of the WLTC operating cycle respectively with and without the additional particle filter 14.2 placed under the floor 15 of the vehicle. This figure highlights that the number of particles per kilometer rejected during the low-speed driving phase is much lower for the double particle filter configuration 14.1, 14.2 compared to the single particle filter configuration 14.1.

The invention could also be implemented with a diesel type thermal engine 11, even if the latter is less sensitive to exhaust back pressure.

Claims (10)

Motor vehicle (10) comprising a thermal engine (11) and an exhaust line capable of evacuating and treating exhaust gases emitted by said thermal engine (11),
characterized in that said exhaust line (12) comprises:
- a first particle filter (14.1) arranged at the outlet of the heat engine (11), and
- a second particle filter (14.2) arranged under a floor (15) of the vehicle,
- the second particle filter (14.2) disposed under the floor (15) of the vehicle having a greater filtration efficiency than the first particle filter (14.1) disposed at the outlet of the heat engine (11). Motor vehicle according to claim 1, characterized in that the first particle filter (14.1) is associated with a “three-way” catalyst (16.1). Motor vehicle according to claim 1 or 2, characterized in that the second particle filter (14.2) is associated with a “three-way” catalyst (16.2). Motor vehicle according to claim 2 or 3, characterized in that the “three-way” catalyst (16.1, 16.2) is arranged upstream of the particle filter (14.1, 14.2). Motor vehicle according to any one of claims 1 to 4, characterized in that the second particle filter (14.2) is associated with a catalyst (17) for eliminating residual ammonia emissions. Motor vehicle according to any one of claims 1 to 4, characterized in that the second particle filter (14.2) is associated with a selective reduction catalyst. Motor vehicle according to any one of claims 1 to 6, characterized in that the exhaust line (12) further comprises a hydrocarbon trap (18) disposed under the floor (15) of the vehicle upstream or downstream of the second particle filter (14.2). Motor vehicle according to any one of claims 1 to 7, characterized in that the first particle filter (14.1) and/or the second particle filter (14.2) are bare filters. Motor vehicle according to any one of claims 1 to 8, characterized in that the first particle filter (14.1) and/or the second particle filter (14.2) are impregnated filters. Motor vehicle according to any one of Claims 1 to 9, characterized in that the thermal engine (11) is a gasoline engine.