FR3106618A1 - THERMAL ENGINE EXHAUST LINE INCLUDING A DEPOLLUTION SYSTEM AND A PREHEATING SYSTEM OF THE SAID DEPOLLUTION SYSTEM - Google Patents

Abstract

The invention relates to a gas exhaust line for a heat engine, comprising a pollution control system (2) successively presenting at least one catalyst (22) and a particulate filter (23), characterized in that it comprises a preheating system for the depollution system (2), configured to be actuated before starting the heat engine, said system comprising a bypass line (3) comprising a tapping (31) for the gases provided downstream of the gas removal system. pollution control (2) and an injection nozzle (32) arranged upstream of the pollution control system (2), an air pump (4), a valve (5) provided in the bypass line (3) as well as means for heating the gases circulating in the bypass line (3). Figure 1

Description

THERMAL ENGINE EXHAUST LINE COMPRISING A DEPOLLUTION SYSTEM AND A SYSTEM FOR PREHEATING THE SAID DEPOLLUTION SYSTEM

The present invention relates to an exhaust line for a combustion engine, gasoline or diesel, conventional or hybrid, comprising a depollution system having in particular a heating element upstream of depollution elements, the upstream being taken as reference with respect to the combustion engine and the flow of exhaust gases in the line, as well as a system allowing preheating of said pollution control system.

The field concerned by the present invention is the field of the control of polluting emissions and more specifically the control of emissions from gasoline or mixture combustion engines containing gasoline, or Diesel or operating on diesel fuel, the pollution control elements present in the exhaust line which may not be the same and may be specifically adapted to the engine.

Thus, the pollution control system varies according to the engine but in all cases the catalysts are the basis of these systems. For gasoline engines, depollution is carried out by a so-called 3-way catalyst known by the Anglo-Saxon acronym TWC (Three Way catalytic Converter) and a particulate filter (FAP) also known by the Anglo-Saxon acronym GPF ( Gasoline Particulate Filter). For diesel vehicles, depollution is carried out by a series of catalysts, an example is an oxidation catalyst known by the English acronym DOC (Diesel Oxidation Catalyst), followed by a selective reduction catalyst known by the acronym SCR and by a particulate filter (DPF).

These catalysts need to be at a certain temperature to be effective. This rise in temperature is generated by the temperature of the exhaust gases or by external equipment such as electric heating, and is more or less rapid depending on the technology chosen for the catalyst substrate or the external equipment.

Nowadays, the limits of authorized polluting emissions are more and more severe. A harmonized worldwide test procedure for passenger cars and light commercial vehicles has been put in place and includes a set of test procedures, comprising automobile driving cycles known as WLTC with new procedures for measuring pollutants as well as real-driving emission measurements known as RDE. This new test procedure requires car manufacturers to clean up engines over the entire engine field.

Thus, taking the non-limiting example of nitrogen oxide depollution as an illustration, the lowering of nitrogen oxide discharge thresholds, hereinafter also referred to by their chemical formula of NOx, in urban areas after cold start requires solutions for heating the NOx depollution system very quickly in order to reduce the start-up time.

It has therefore been proposed in FR-A-3081921 an exhaust line in which a heating element makes it possible to heat the gases entering the exhaust line upstream of the pollution control device provided in said line. It is thus possible to heat the elements constituting the depollution device as soon as possible even when the internal combustion engine cannot yet activate the specific heating combustion mode in order to minimize the priming time of the depollution device in a cold and therefore urban environment.
In FR-A-3028286, a motor vehicle exhaust gas treatment device has been proposed, comprising an exhaust line, a nitrogen oxide reduction catalyst arranged on the exhaust line, then a SCR catalyst for a diesel engine and a particulate filter and a line diverting at least part of the exhaust gases from the exhaust line. This bypass line comprises two tappings on the exhaust line, including an exhaust gas sampling tapping downstream of the particulate filter and an exhaust gas return tapping downstream of the oxide reduction catalyst. nitrogen and upstream of the SCR catalyst. This bypass line comprises a device for decomposing the reducing agent of nitrogen oxides into ammonia, the extracted exhaust gases are mixed with urea injected into the decomposition device, the temperature of these gases making it possible to heat the catalyst of the decomposition device which is also heated using an electric heater allowing the catalyst to be quickly brought to its operating temperature as quickly as possible when the vehicle is started.

However, this only applies when the engine has already started to improve the temperature rise of the pollution control device and still requires a more or less rapid implementation time after starting the engine.

Similarly, in EP 0460542, an exhaust line is proposed having two successive converters and a bypass line allows the gases to pass back into the first converter after passing through the second as long as the latter has not reached a effective processing temperature. This prevents gases from being expelled outside while the second converter is not sufficiently efficient in their treatment.

As already mentioned, catalysts must become more and more efficient to meet emission standards which are becoming very strict. A main objective of the invention is to propose an exhaust line in which one contributes to the reduction of polluting emissions on engine start-up corresponding to the heating phase of the elements of the depollution device while reducing fuel consumption with respect to the classic preheating system with air pump.

The object of the present invention is therefore to propose an exhaust line in which the time necessary for the temperature rise of the catalysts is further reduced.

To this end, the subject of the invention is a gas exhaust line for a heat engine, comprising:
a depollution system having successively
-at least one catalyst and
- a particulate filter,
characterized in that it further comprises a system for preheating the pollution control system, and more particularly the catalyst, configured to be actuated before starting the heat engine, said system comprising a bypass line comprising a gas sampling tap provided downstream of the depollution system and an injection tap provided upstream of the depollution system, an air pump, a valve provided in the bypass line as well as means for heating the gases flowing in the bypass line.

The invention therefore proposes an architecture which makes it possible to inject gases, more generally air, which will have been taken downstream of the pollution control system upstream of the pollution control system, and to recycle it in order to have a more rapid increase in the temperature of the catalyst of the depollution system and this, before the start of the thermal engine thanks to the heating means of the preheating system which are activated before starting. Thus, advantageously, the air taken from the exhaust line, which is less cold than the outside air, therefore has a faster temperature rise which then makes it possible to heat the pollution control system into which the air or the gases are reinjected. , which also makes it possible to raise the temperature of the catalyst, even though the internal combustion engine has not yet started.

Preheating the catalytic converter significantly reduces polluting emissions when starting the internal combustion engine and priming the pollution control system, the catalytic converter being ready or almost ready to operate optimally. The catalyst thus becomes more efficient more quickly.

According to an advantageous embodiment of the invention, the pollution control system comprises a heating element and the heating means of the preheating system consist of said heating element of this pollution control system.

We thus propose an exhaust line allowing an efficient and more economical preheating of the catalyst by using the heating element which is already present in the pollution control system.

It is also possible to provide heating means present in the bypass line of the preheating system.

Advantageously, the bypass line associated with the depollution system makes it possible to set up a closed circulation loop for the gases, these taken downstream are brought back upstream of the depollution system and pass through the heating element. of the depollution system which is activated, heat up and then pass through the catalytic converter which they also heat up. This rises in temperature so that when the engine starts the catalyst can perform its function more quickly and efficiently, thus limiting pollution.

The invention also relates to an assembly of a heat engine of the Diesel or Diesel hybrid type and an exhaust line according to the invention, in which the pollution control system comprises an oxidation catalyst (DOC) and a gasoline hybrid selective reduction (SCR), followed by a particulate filter (DPF).

The invention also relates to an assembly of a combustion engine of the gasoline or gasoline hybrid type and an exhaust line according to the invention, in which the pollution control system comprises a so-called three-way catalyst (TWC) followed by a particulate filter (DPF).

The invention also relates to a motor vehicle comprising an exhaust line or an assembly of a combustion engine and an exhaust line according to the invention.

The present invention also relates to a process for depolluting the exhaust gases of a thermal engine, implemented on an exhaust line for a thermal engine, comprising a depollution system successively having at least one catalyst and one filter. with particles, characterized in that the depollution process comprises a step of preheating the depollution system, in particular the catalyst, consisting, before starting the engine, in taking gases downstream of the depollution system in order to circulate them in a line of bypass which then opens upstream of said depollution system to inject them, heating means being actuated to heat said injected gases which then heat the catalyst.

Advantageously, it is thus possible to considerably reduce the time necessary for the rise in efficiency of the depollution system once the engine has started and therefore the risks of emanation of polluting substances. Preheating can take place just before starting a vehicle following a prolonged stop and/or even when restarting as part of an engine standby system commonly called "Stop and Start".

Other characteristics and advantages of the present invention will appear more clearly on reading the description illustrated by the appended drawings, in which the figures represent:

a side perspective view of an exhaust line according to a first embodiment of the invention; And

a side perspective view of an exhaust line according to a second embodiment of the invention;

In Figure 1 is shown an exhaust line 1 for a gasoline combustion engine M which includes a pollution control device 2.

This depollution device 2 has, preferably integrated in a casing, successively from upstream to downstream in the gas exhaust direction, a heating element such as an electrical resistor 21 called a catalyst. electric, a three-way catalytic converter 22 and a particulate filter 23.

The exhaust line 1 also comprises a bypass line 3 of the gases which has a gas or air tapping 31 in the exhaust line 1 and which is formed downstream of the pollution control device 2. The line diversion 3 is connected to the exhaust line 1 by a second tapping 32 allowing the injection of gas or air and provided upstream of the pollution control device 2.

The bypass line 3 further comprises an air pump 4 which makes it possible to draw air from the exhaust line 1 and to reinject it, imposing circulation from downstream of the pollution control system to upstream. A first valve 5 is provided in the bypass line, preferably between the air pump 4 and the injection tapping 32. A second valve 6 can also be provided between the air pump 4 and the sampling tapping 31 ( see figure 2).

This air pump 4 takes air downstream from the pollution control device 2 and reinjects it upstream before the pollution control device 2. The preheating system therefore comprises this bypass line, the air pump and the valves and present in besides heating means. Preferably, the heating means consist of the heating element of the depollution system or electric catalyst 21.

Thus, before the engine is started, the air pump 4 is actuated, for example 10 seconds before, to take the air from the exhaust line 1 and reinject it upstream of the pollution control device 2. The electric catalyst 21 is activated at the same time and heats the air which passes through to then be conveyed into the catalyst 22.

The electric catalyst 21 is therefore active, preferably with a heating power between 2 and 4 KW during these 10 seconds in order to heat the gases and the air drawn off. The air then circulates in a closed loop and in this way heats the three-way catalyst 22. The duration depends on the target temperature of the 3-way catalyst and its volume, for example 300°C.

When starting the internal combustion engine, the valve(s) close(s) to force the exhaust gases to pass through the three-way catalytic converter. The electric catalytic converter may or may not remain active for a few seconds.

Air recirculation allows air to pass through the electric catalyst several times (closed loop) allowing the temperature of the three-way catalyst to be increased more quickly.

The start of the preheating system is triggered for example 10 seconds before the start of the heat engine, and depends on the intended application. For example, for hybrid engine applications, heating using the electric heating element is triggered depending on the state of charge called SOC (state of charge) of the low voltage (48V) or high voltage battery. (100V). For conventional vehicles, that is to say (100% thermal), the strategy is similar to that of starting diesel vehicles: once the ignition is on, the preheating system is triggered and a warning light then indicates the moment to start.

This invention makes it possible to:
- reduce polluting emissions from petrol vehicles;
- reduce fuel consumption.

Claims (9)

Gas exhaust line for a heat engine, comprising:
- a depollution system (2) having successively
at least one catalyst (22) and
a particle filter (23),
characterized in that it comprises a system for preheating the depollution system (2), configured to be actuated before starting the heat engine, said system comprising a branch line (3) comprising a tapping tapping (31) for the gases provided downstream of the pollution control system (2) and an injection tapping (32) provided upstream of the pollution control system (2), an air pump (4), a valve (5) provided in the bypass line ( 3) as well as means for heating the gases flowing in the bypass line (3). Exhaust line according to Claim 1, characterized in that the depollution system (2) comprises a heating element (21) arranged upstream of a catalyst (22), the heating means of the preheating system being constituted by said heating element (21) of the depollution system. Exhaust line according to Claim 2, characterized in that the heating element (21) consists of an electrical resistor. Exhaust line according to Claim 3, characterized in that the electrical resistor (21) has a heating power between 2 and 4 KW for 10 seconds. Line according to one of Claims 1 to 3, characterized in that the bypass line (3) comprises a second valve (6) between the sampling tapping and the air pump. Assembly of a heat engine of the Diesel or Diesel hybrid type and of an exhaust line, characterized in that the exhaust line is an exhaust line according to one of Claims 1 to 5, in which the system pollution control comprises an oxidation catalyst (DOC) and a hybrid gasoline selective reduction catalyst (SCR), followed by a particulate filter (DPF). Assembly of a combustion engine of the gasoline or gasoline hybrid type and of an exhaust line characterized in that the exhaust line is an exhaust line according to one of claims 1 to 5, in which the system of pollution control includes a so-called three-way catalyst (TWC) followed by a particulate filter (DPF). Motor vehicle with combustion engine comprising an exhaust line according to one of Claims 1 to 5 or an assembly according to Claim 6 or 7. Process for depolluting the exhaust gases of a thermal engine, implemented on an exhaust line for a thermal engine, according to one of Claims 1 to 5, comprising a depollution system successively having a heating, at least one catalyst and one particulate filter, characterized in that the depollution process comprises a step of preheating the depollution system, in particular the catalyst, consisting, before starting the engine, in taking gases downstream of the depollution to make them circulate in a bypass line which then opens upstream of said depollution system to inject them, heating means being actuated to heat said injected gases which then preheat the catalyst.