FR3100839A1 - Set comprising an internal combustion engine with an electric compressor and a heating element - Google Patents

Abstract

This relates to an assembly comprising an internal combustion engine (1), - an air intake line (2) connected to the engine (1), an exhaust line (3) comprising an upstream end connected to the engine ( 1) and a downstream end opening to the ambient air, this line carrying at least one depollution element (4, 6, 7, 8, 9) of a pollutant present in the gases passing through the exhaust line (3) , an electric compressor (11), a heating element (10) for the gases passing through the exhaust line (3), characterized in that the heating element (10) is arranged in the exhaust line (3), in upstream of the pollution control element closest to the upstream end of the exhaust line (3), or integrated into an upstream portion of this pollution control element and in that the electric compressor (11) is arranged upstream of the heating element (10). Figure 1

Description

Assembly comprising an internal combustion engine with an electric compressor and a heating element

The present invention relates to the field of the control of polluting emissions and more specifically the control of emissions from compression ignition engines, in particular a diesel engine or one operating on diesel fuel, but the present invention can also be applied to a controlled ignition heat engine, in particular a gasoline fuel engine or a mixture containing gasoline. More particularly, the subject of the invention is an assembly comprising an electric compressor and a heating element upstream of the depollution element closest to the upstream end of the exhaust line.

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 measurement of pollutants as well as emission measurements in real driving known under the name of RDE. This new test procedure requires car manufacturers to clean up engines over the entire engine field.

In particular, taking the non-limiting example of nitrogen oxide depollution for 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.

In particular, the gradual implementation of the Euro6 standard for Europe or equivalent standards in other countries has led manufacturers to choose between different options.

The first option is the reduction of NOx at the source via technologies of the type "exhaust gas recirculation in the engine", in particular a system of recirculation of exhaust gases at the intake of the high and low pressure engine known as the acronym for EGR system. The second option is the reduction of NOx via a sequential treatment technology called "NOx-trap" which will be detailed later. The third option is the reduction of NOx via a continuous treatment technology called "selective catalytic reduction" and known by the acronym of SCR system, specifically dedicated to a compression ignition engine. It is also possible to combine these three options.

If these options make it possible to satisfy the standards in force, they are not necessarily capable of satisfying one or more future stages which promise to be even more stringent. These future standards will include more and more cycles in real driving, which is unfavorable to the pollution control of exhaust gases.

To respond in particular to the risks of NOx emissions in these cycles in real driving, various technological solutions and architectures can be envisaged. They each have their advantages and disadvantages. For a compression ignition engine, it is advisable to focus on the most efficient nitrogen oxide treatment technology on the market, namely the selective catalytic reduction carried out by a system hereinafter referred to as SCR for selective catalytic reduction using as an agent reducing agent a urea-based solution, with the chemical formula CO(NH ₂ ) ₂ , to treat nitrogen oxides, NOx.

Document WO2017198601 A1 proposes the use of a heating element in the pollution control line but upstream of an SCR system and downstream of a diesel oxidation catalyst and a particulate filter. The document also proposes injecting air into the exhaust line by means of an electric compressor, upstream of the SCR system, and downstream of the Diesel oxidation catalyst and the particulate filter, which passing through the heating element allows the SCR system heating. The disadvantage of this proposal is that it does not benefit from this electric heating for all the depollution elements, namely in the present case the Diesel oxidation catalyst, this depollution element placed upstream of the heating element being able to play an essential role in the activation of the depollution of the line.

The problem underlying the present invention is, for an exhaust line comprising at least one depollution element, to ensure the temperature rise of this depollution element so that it reaches its minimum operating temperature allowing effective depollution of the specific pollutant treated.

To achieve this objective, an assembly is provided according to the invention comprising:
- an internal combustion engine,
- an air intake line connected to the engine,
- an exhaust line comprising an upstream end connected to the engine and a downstream end leading to the ambient air, this line carrying at least one element for depolluting a pollutant present in the gases passing through the exhaust line,
- an electric compressor,
- a gas heating element passing through the exhaust line,
characterized in that the heating element is arranged in the exhaust line, upstream of the depollution element closest to the upstream end of the exhaust line, or integrated in an upstream portion of this element of depollution and in that the electric compressor is arranged upstream of the heating element.

The technical effect is to use a heating element coupled to an electric compressor placed upstream of the most upstream depollution element in the exhaust line so as to heat this depollution element and minimize the time of priming of the depollution element or elements in a cold environment.

Various additional features may be provided, alone or in combination:

According to one embodiment, the heating element is an electric heating element.

According to one embodiment, the electric compressor is arranged in the exhaust line or in the air intake line.

According to one embodiment, the most upstream depollution element is an oxidation catalyst which incorporates an active NOx trap and/or a passive NOx trap.

According to one embodiment, the exhaust line comprises, from upstream to downstream, a reducing agent injector, a mixer, a first catalyst for the selective reduction of nitrogen oxides, a second catalyst for the selective reduction of nitrogen oxides, a particulate filter, a catalyst for converting ammonia discharges, these aforementioned elements being arranged downstream of the most upstream depollution element.

According to one embodiment, the second catalyst for the selective reduction of nitrogen oxides and the particulate filter are in the form of a particulate filter impregnated with an active phase for the catalytic reduction of nitrogen oxides.

According to one embodiment, this assembly comprises means for controlling the electric compressor and the heating element allowing their activation when the engine is stopped.

The invention also relates to a method for heating an element for depolluting a pollutant present in the gases passing through the exhaust line of a vehicle comprising an assembly according to one of the previously described variants, the electric compressor being arranged in the air intake line, this assembly further comprising an exhaust gas recirculation line, the internal combustion engine being stopped, characterized in that the air coming from the electric compressor is sent to the element heater via the exhaust gas recirculation line.

The invention also relates to a method for heating an element for depolluting a pollutant present in the gases passing through the exhaust line of a vehicle comprising an assembly according to one of the previously described variants, the internal combustion engine being stopped, characterized in that the decision to activate the electric compressor and the heating element comprises the detection of an action of unlocking the vehicle, or the detection of the driver of the vehicle in his seat, or the detection of the hands of the driver of the vehicle on the steering wheel.

Other features and advantages will appear on reading the description below of a particular, non-limiting embodiment of the invention, made with reference to the figures in which:

represents a first embodiment of the invention comprising an engine connected to an air intake line and to an exhaust line comprising several depollution elements.

represents another embodiment of the invention.

represents another embodiment of the invention.

In the rest of this thesis, the upstream and the downstream are to be understood with regard to the direction of flow of the fluids circulating in the intake or exhaust lines connected to the internal combustion engine.

Figure 1 shows a first embodiment of the invention. Figure 1 shows an internal combustion engine 1 connected on the one hand to an air intake line 2 and on the other hand to an exhaust line 3 of the exhaust gases passing through this exhaust line 3. The internal combustion engine 1 can for example equip a motor vehicle for its propulsion. This assembly may include a turbocharger 12, the compressor part 12a of which is placed in the air intake line 2 while the expansion part 12b is placed in the exhaust line 3. This assembly may also include an exhaust gas recirculation line 13 connecting the exhaust line 3 to the intake line 2. This exhaust gas recirculation line 13 can be equipped with a recirculated gas flow control valve 13a as well as a cooler 13b for these recirculated gases. This line 13 can be used to send the fresh gases compressed by the electric compressor 11 to the heating element 10 during phases with the heat engine stopped, in particular before the engine is started.

A valve 14 for metering the admitted air is arranged in line 2 of admission. In the case of an engine 1 equipped with the turbocharger 12, a charge air cooler 15 is also provided. This cooler 15 is arranged in the intake line 2 between the compressor part 12 and the valve 14 for air metering.

The exhaust line 3 comprises an upstream end connected to the engine 1 and a downstream end leading to the ambient air and carries at least one pollution control element 4, 6, 7, 8, 9 of a pollutant present in the passing gases line 3 exhaust.

The exhaust line 3 also comprises a gas heating element 10 passing through this line 3. This heating element 10 is arranged in the exhaust line 3, upstream of the depollution element 4 closest to the upstream end of exhaust line 3. As a variant, not shown, the heating element 10 can be integrated in an upstream portion of this depollution element 4 closest to the upstream end of the exhaust line 3. The heating element 10 can in fact be housed in this depollution element 4 closest to the upstream end of the exhaust line 3.

It follows that the heating element 10 is the first element located downstream of the engine 1 with no other depollution element located upstream of this heating element 10, contrary to what had been described in the document WO2017198601 A1 for which an oxidation catalyst trap and a particulate filter were located upstream of the heating element in the exhaust line.

The heating element 10 can be an electric heating element, which allows rapid auxiliary heating without waiting for the internal combustion engine 1 to warm up.

Provision is also made to dispose, upstream of the heating element 10, an electric compressor 11. This electric compressor 11, when it is activated, makes it possible to supply a flow of gas which, with the heating element 10, makes it possible to heat the elements depollution without waiting for the internal combustion engine 1 to warm up.

Control means (not shown) of the electric compressor 11 and of the heating element 10 allowing their activation when the engine 1 is stopped are also provided. These control means can be integrated into an engine control unit.

Thus the activation of the electric compressor 11 and of the heating element 10 can be done as soon as possible, before starting the engine, in order to reduce the heating time of the pollution control elements to their nominal or priming temperature. Advantageously, this decision to activate the electric compressor 11 and the heating element 10 can comprise the detection of an unlocking action of the vehicle, or the detection of the driver of the vehicle on his seat, or the detection of the hands of the driver of the vehicle on the steering wheel, which allows the start of the heating of the pollution control elements to be anticipated in relation to that of the internal combustion engine.

This electric compressor 11 is in this embodiment arranged in the intake line 3, between the compressor part 12a of the turbocharger 12 and the air cooler 15. The fact of arranging the electric compressor 11 in the intake line 2 makes it possible to use this compressor also for the air supercharging of the engine 1. A circuit 16 equipped with a valve 17 of control can also be provided allowing the air admitted to bypass not to pass through the electric compressor 11.

In this embodiment, the depollution element 4 closest to the upstream end of the exhaust line 3 is an oxidation catalyst. This oxidation catalyst oxidizes carbon monoxide, CO, and unburnt hydrocarbons, HC. The reactions that oxidation catalyst 4 promotes are:
CO + ½ O ₂ => CO ₂ , for the carbon monoxide oxidation reaction,
C _x H _y + x+Y/4 O ₂ => x CO ₂ + y/2 H ₂ O, for the oxidation reaction of unburned hydrocarbons.

The oxidation catalyst 4 also incorporates a NOx trap, of the lean richness adsorption nitrogen oxide trap type known by the abbreviation of LNT and/or a passive nitrogen oxide trap known by the abbreviation of PNA. These traps allow the retention of NOx under engine 1 operating conditions which are not favorable for depollution, these NOx traps being able to release the nitrogen oxides trapped under other conditions more favorable to their destruction. For example, a passive NOx trap as a NOx adsorber can be used in conjunction with an SCR system. This makes it possible to increase the removal efficiency of nitrogen oxides by adsorption of nitrogen oxides at low temperature and desorption of oxides once the SCR catalyst is active.

For the other type of NOx trap, the low richness NOx adsorber trap, this retains on sites provided in its interior the nitrogen oxides by chemical reaction for so-called poor richness conditions. Once the trap is filled with reacted nitrogen oxides, it can be proceeded by a strategy of injecting a surplus of fuel, therefore sending an excess of CO and hydrocarbons or HC through the exhaust line 3 hence a higher fuel richness and greater than one. These hydrocarbons and these CO react with the NOx, then in the form of NO ₂ then released and transformed mainly into nitrogen.

The major advantage of an absorption NOx trap is that it does not require the presence of a reductant tank, a heated reductant line, a reductant injector, etc. Nitrogen oxide scavenging material can be integrated into the oxidation catalyst 4 to reduce size, mass and cost.

A NOx trap of the LNT or lean richness type has the incidental disadvantage of involving greater fuel consumption and also of increasing the CO ₂ emissions sequentially for the elimination of the NOx.

The exhaust gases leaving the oxidation catalyst 4 then pass through a box 5 of the reducing agent mixture. This mixing box 5 contains a reducing agent injector, this reducing agent being used for the catalytic reduction of nitrogen oxides, as well as a mixing device making it possible to mix the exhaust gases with the injected reducing agent.

The reducing agent is an aqueous solution of 32.5% urea and water. This reducing agent forms the reducing agent NH3 from the following reactions:
(NH ₂ ) ₂ CO => NH ₃ + HNCO, thermolysis of urea, then
HNCO + H ₂ O => NH ₃ + CO _2, the hydrolysis of isocyanic acid.
These two reaction steps, and especially the first, require temperatures of at least 180 - 200° C., hence the advantage of having the mixing box 5 in a position close to the engine 1.

The reducing agent injector is itself fed by a gauge-pump module which draws urea in aqueous solution from a tank of approximately 20 liters, ensures a mixture between the drops of urea and the sufficient exhaust for the thermolysis reaction to take place completely and for the hydrolysis reaction to take place in part before being “finished” on the next catalyst that we are now detailing.

The exhaust gases leaving the mixing box 5 then enter a first catalyst 6 for reducing nitrogen oxides. In this first catalyst 6 for reducing nitrogen oxides and its SCR active phase, the following equations take place:
4 NO + O ₂ + 4 NH ₃ => 4 N ₂ + 6 H ₂ O , as a standard reaction,
NO + NO ₂ + 2 NH ₃ => 2 N ₂ + 3 H ₂ O , as a fast-kinetic reaction,
6 NO ₂ + 8 NH ₃ => 7 N ₂ + 12 H ₂ O , as a reaction at high temperature,

Several reactions can take place but the optimal and desired conversion of NOx is obtained thanks to the second reaction with the fastest kinetics but whose stoichiometry imposes a NO ₂ /NOx ratio close to 0.5 especially at low temperatures, for example lower at 250°C. However, the combustion of fuel produces a large excess of nitric oxide compared to nitrogen dioxide.

There are two types of SCR active phase. The first type concerns active phases based on zeolites, β, ferrierite, ZMS5, etc., exchanged with iron or Fe. These active phases can also contain oxides of Cerium, Zirconium, or even Nobium, Tungsten and Titanium.

The second type concerns active phases based on zeolites, chabazite, β, ferrite, ZMS5, etc., exchanged with copper. These active phases can also contain oxides of Cerium, Zirconium, or even Nobium, Tungsten and Titanium.

The active phases based on zeolites exchanged with iron are known to exhibit initiation at a lower temperature than those based on zeolites exchanged with copper, once the NO ₂ /NOx ratio is close to 0.5. If this condition is satisfied, an active phase based on zeolites exchanged with iron will convert NOx from 150°C. Conversely, the active phases based on zeolites exchanged with copper are almost insensitive to the NO ₂ /NOx ratio. These last active phases nevertheless have the disadvantage of converting the NOx at a higher temperature than the active phases based on zeolites exchanged with iron.

Furthermore, the active phases based on zeolites exchanged with copper are known for their ability to store more NH ₃ than the active phases based on zeolites exchanged with iron.

For this first catalyst 6 for reducing nitrogen oxides, an active phase based on iron-exchanged zeolites is particularly suitable, for the reasons set out above.

The exhaust gases leaving this first catalyst 6 for reducing nitrogen oxides then enter a second catalyst 7 for reducing nitrogen oxides which will complete the reduction of NOx, then a filter 8 for particles. The SCR active phase of this second catalyst 7 for reducing nitrogen oxides can be of the same type as that of the first catalyst 6 for reducing nitrogen oxides. The particulate filter 8 is made up of a substrate which has alternately blocked channels at the inlet and at the outlet and which offers precise characteristics in terms of porosity, allowing the gases to pass through its walls while retaining the solid phase, namely soot particles. The porosity of the walls is thus made, being between 15 and 25 microns, that it lets the gases pass without generating too much counter-pressure while retaining the soot particles.

This accumulation phase, which lasts approximately 300 to 1,000 km, is neither dependent on the operating conditions of engine 1, cold, hot or full load, etc., nor dependent on the size of the particles. Coarse particles as well as ultrafine particles are retained. However, the back pressure increases continuously during this phase while the particulate filter 8 fills with soot and when different physical criteria are met, such as the soot loading rate of the particulate filter 8, the thermal of the exhaust line 3, etc., the engine control initiates a regeneration phase. This phase generally consists of an increase in the temperature of exhaust line 3 via a specific adjustment of engine 1, with post-fuel injections and oxidation of HC in large excess in oxidation catalyst 4 generating exotherms.

Once the combustion temperature of the soot has been reached in the particulate filter 8, namely between 550 and 700° C. depending on whether or not a regeneration aid additive is used, the particles will be eliminated and transformed into vapor. water and CO ₂ . This regeneration done, the particle filter 8 is cleaned of its soot and a new accumulation cycle can start.

In a variant presented in FIG. 2, the second selective reduction catalyst is integrated into the particulate filter. In other words, the particulate filter is impregnated with an SCR active phase. This filter, designated SCRF, is referenced 8' in Figure 2.

The active phases used for particulate filters are identical to those of a SCR slice catalyst. They are nevertheless required to have a high thermal resistance in order to withstand the conditions encountered during the combustion of the soot during a regeneration phase. It was observed that an active phase based on zeolites exchanged with copper Cu was particularly suitable for the impregnated 8' particulate filter, for the following reasons.

Such an active phase has better thermal resistance than an active phase based on iron-exchanged zeolites. Such an active phase has a higher NH ₃ storage capacity than an active phase based on iron-exchanged zeolites.

In addition, the combustion of soot by NO ₂ at temperatures close to 350°C tends to reduce the NO ₂ /NOx ratio. However, the active phases based on zeolites exchanged with iron are more sensitive to this NO ₂ /NOx ratio. The active phases based on zeolites exchanged with copper therefore seem more suitable.

As mentioned previously, an active phase based on copper-exchanged zeolites is better able to store NH ₃ than an active phase based on iron-exchanged zeolites. A small volume of the SCR catalyst can be the cause of significant NH ₃ leaks. The latter will be more easily captured in the particulate filter 8′ impregnated with an active phase based on zeolites exchanged with copper than with an active phase based on zeolites exchanged with iron.

The exhaust gases leaving the particulate filter 8 (FIG. 1) or the impregnated particulate filter 8' (FIG. 2) then enter a catalyst 9 for converting ammonia emissions, NH ₃ , making it possible to oxidize the NH ₃ residual in N ₂ .

Provision may be made to position a NOx sensor upstream of the oxidation catalyst 4 integrating the active and/or passive NOx trap and a NOx sensor downstream of the second catalyst 7 for catalytic reduction or, where appropriate, of the impregnated particulate filter 8' . The first NOx sensor can be replaced by an estimation model.

Finally, it is possible to implement an even more expensive configuration with a third NOx sensor positioned downstream of the catalyst 9 for converting the NH ₃ discharges to properly verify that all the NH ₃ discharges have been treated.

Figure 3 shows another embodiment. This exemplary embodiment differs from that presented in FIG. 1 in that the electric compressor 11 is arranged in the exhaust line 3, upstream of the depollution element 4 closest to the upstream end of line 3 exhaust. In the case of a turbocharged engine, the electric compressor 11 is arranged between the turbine part 12b and the pollution control element 4 closest to the upstream end of the exhaust line 3.

Various layouts of the elements of the exhaust line 3 of the assemblies previously described in the vehicles can be provided. Indeed, some of these elements can be installed in a space under the bonnet of the vehicle, this space housing the internal combustion engine 1 or in a space under the body of the vehicle.

According to a first possible distribution, the heating element 10 and the oxidation catalyst 4 are housed in the space under the bonnet while the following elements of the exhaust line 3 are placed under the body of the vehicle.

According to a second possible distribution, the heating element 10, the oxidation catalyst 4, the mixing box 5 and the first selective reduction catalyst 6 are housed in the space under the hood, while the following elements of line 3 d exhaust are placed under the body of the vehicle.

According to a second possible distribution, all the elements of the exhaust line 3 are housed in the space under the hood, while the catalyst 9 for converting ammonia, NH ₃ emissions, is placed under the body of the vehicle.

The invention allows an advance heating time saving compared to starting the engine, therefore operation with optimized efficiency over a very wide temperature range which covers both slow urban driving and “aggressive” driving.

This makes it possible to ensure the elimination of gaseous pollutants including NOx, the elimination of particulate pollutants and to optimize the regeneration of the impregnated particulate filter in an urban environment thanks to the heating of the heating element. Such a line architecture will make it possible to meet the very strict requirements of future standards in real driving without risk of excess NOx emissions or NH ₃ emissions, including on "extreme cold" driving below an outside temperature of minus 7°C.

It is also provided with a gain in fuel consumption. Such an architecture is effective in reducing NOx and makes it possible, unlike other technological solutions, to dispense with or reduce the specific combustion modes for heating the exhaust line, which are very costly in CO ₂ , as well as to orient the CO ₂ / NOx always leads to more NOx and therefore less CO ₂ , the reduction in CO ₂ emissions meaning a reduction in the fuel consumption of the engine. Finally, the present invention makes it possible to greatly reduce or even completely eliminate the residual emissions of NH ₃ at the outlet of the exhaust line.

Claims (9)

Set including:
- an internal combustion engine (1),
- an air intake line (2) connected to the engine (1),
- an exhaust line (3) comprising an upstream end connected to the engine (1) and a downstream end leading to the ambient air, this line carrying at least one pollution control element (4, 6, 7, 8, 9) a pollutant present in the gases passing through the exhaust line (3),
- an electric compressor (11),
- a heating element (10) for the gases passing through the exhaust line (3),
characterized in that the heating element (10) is arranged in the exhaust line (3), upstream of the depollution element closest to the upstream end of the exhaust line (3), or integrated in an upstream portion of this depollution element and in that the electric compressor (11) is arranged upstream of the heating element (10). Assembly according to claim 1, characterized in that the heating element (10) is an electric heating element. Assembly according to Claim 1 or Claim 2, characterized in that the electric compressor (11) is arranged in the exhaust line (3) or in the air intake line (2). Assembly according to one of the preceding claims, characterized in that the most upstream depollution element (4) is an oxidation catalyst which incorporates an active NOx trap and/or a passive NOx trap. Assembly according to one of the preceding claims, characterized in that the exhaust line (3) comprises, from upstream to downstream, a reducing agent injector, a mixer, a first catalyst (6) for the selective reduction of oxides of nitrogen, a second catalyst (7) for the selective reduction of nitrogen oxides, a particulate filter (8), a catalyst (9) for converting ammonia discharges, these aforementioned elements being arranged downstream of the element pollution control (4) furthest upstream. Assembly according to the preceding claim, characterized in that the second catalyst for the selective reduction of nitrogen oxides and the particulate filter are in the form of a particulate filter (8') impregnated with an active catalytic reduction phase. nitrogen oxides. Assembly according to one of the preceding claims, characterized in that it comprises means for controlling the electric compressor (11) and the heating element (10) allowing their activation when the engine (1) is stopped. Method for heating an element (4, 6, 7, 8, 9) for depolluting a pollutant present in the gases passing through the exhaust line (3) of a vehicle comprising an assembly according to the preceding claim, the electric compressor (11) being disposed in the air intake line (2), this assembly further comprising an exhaust gas recirculation line (13), the internal combustion engine (1) being stopped, characterized in that the air from the electric compressor is sent to the heating element via the exhaust gas recirculation line (13). Method for heating an element (4, 6, 7, 8, 9) for depolluting a pollutant present in the gases passing through the exhaust line (3) of a vehicle comprising an assembly according to claim 7, the internal combustion engine (1) being stopped, characterized in that the decision to activate the electric compressor (11) and the heating element (10) comprises the detection of an action of unlocking the vehicle, or the detection of the driver of the vehicle in his seat, or the detection of the hands of the driver of the vehicle on the steering wheel.