WO2010139876A1

WO2010139876A1 - Internal combustion engine and operation method associated with such an engine

Info

Publication number: WO2010139876A1
Application number: PCT/FR2010/050908
Authority: WO
Inventors: Anne-Sophie Quiney
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2009-06-04
Filing date: 2010-05-11
Publication date: 2010-12-09
Also published as: FR2946390A1; FR2946390B1

Abstract

The invention relates to an internal combustion engine (1) with at least two cylinders (2, 3, 4, 5) including air intake means (6), fuel supply means (12), means (23) for exhausting the combustion gases generated by the cylinders (2, 3, 4, 5), said engine comprising a first cylinder (2) capable of operating using a rich mixture in order to generate hydrogen-laden combustion gases, the supply means (12) being provided for supplying at least the first cylinder (2) with a secondary fuel containing a hydrocarbon or hydrocarbon mixture having 1 to 4 carbon atoms, and for supplying the other cylinders (3, 4, 5) with a primary fuel different from the secondary fuel. The engine of the invention comprises means (29) for treating NOx built into the gas exhaust line.

Description

Internal combustion engine and method of operation associated with such an engine

The present invention claims the priority of the French application 0953676 filed June 4, 2009 whose content (text, drawings and claims) is here incorporated by reference.

The present invention relates to the field of automotive, and more particularly the field of internal combustion engines comprising a pollutant treatment system such as a NOx trap storage / retrieval integrated into a line of exhaust of such an engine.

[0003] Poor and incomplete combustion leads to the production of NOx which are sent to the exhaust. NOx are pollutants that are particularly harmful for both health and the environment, in particular:

- are irritating to the respiratory tract, - promote the formation of ozone in the lower layers of the atmosphere,

- participate in the formation of acidic deposition and eutrophication of soils.

[ooo4] In addition, the constraints due to the standards, for example the European standards called Euro (euro 5, euro 6, euro 7 ... etc.), relating to the levels of polluting emissions generated by the operation of combustion engines internal, become more and more severe, particularly with regard to these nitrogen oxides (NOx) emitted and released to the exhaust.

[ooo5] In diesel engines with direct injection, among the means implemented to clean up the exhaust gases, the reduction of NOx emissions by a NOx trap storage / destocking is a technical solution.

Thus, one can consider using a NOx trap consisting for example of barium sulfate for absorbing NOx during the standard operation of a diesel engine. When the trap is saturated, a transient destocking phase is triggered by temporarily switching the motor from this standard operating mode to a rich mixing regeneration mode to produce reducing agents such as HC and CO, which reduces NOx. who are then desorbed from the trap. Such a regeneration system of a NOx trap integrated in an exhaust line of a diesel engine of vehicles is described in particular in FR 2 846 370.

[0007] Another way to reduce NOx is to use selective catalytic reduction (SCR). In the SCR system, ammonia is used as a selective reducing agent, in the presence of excess oxygen, to convert more

70% (up to 95%) NOx (NO and NO ₂ ) in N ₂ thanks to a suitable catalytic system. Different ammonia precursors can be used and most often an aqueous solution of urea is precisely dosed from a separate reservoir and vaporized in the exhaust system upstream of the SCR catalyst, where it is hydrolyzed to ammonia. However, the problem then arises of the management of a complementary fluid, especially with regard to its storage in the vehicle.

[OooD] DE 103 32 047 describes a process for the selective catalytic reduction of NOx in the exhaust gas of a vehicle comprising a combustion engine operating with hydrogen. The NOx, especially during operation of the engine with an air-fuel ratio of about 1, is removed by forming ammonia (NH ₃ ) by reaction of NOx with hydrogen from the fuel tank and this on an NH ₃ synthesis catalyst. The ammonia formed is then used on an SCR catalyst to reduce excess NOx that is not captured by the ammonia synthesis. It is therefore proposed here using a hydrogen engine to synthesize "on board" ammonia for selective catalytic reduction. However, this implies operation of the engine with hydrogen.

To overcome these drawbacks, the present invention therefore aims to provide an internal combustion engine with at least two cylinders whose operation allows to meet the current standards of pollutant emissions. In particular, the present invention aims to provide an engine with at least two internal combustion cylinders operating in lean mixture, and wherein at least one cylinder of said engine is arranged to operate in a rich mixture to produce in addition to usual combustion products such as that HC, CO, CO ₂ , NOx,

O ₂ and N ₂ , H ₂ can be used for post-treatment of NOx. The invention main advantage of proposing an engine whose mode of operation is dedicated to ultra-low NOx emissions.

For this purpose, the invention is an internal combustion engine that can treat the NOx present in the exhaust and which have been trapped on a NOx trap by proposing to purge said NOx trap by producing H ₂ , either to directly reduce the destocked NOx or to convert it to usable ammonia for selective catalytic reduction.

The invention therefore relates to an internal combustion engine with at least two cylinders comprising air intake means, fuel supply means, exhaust means of the combustion gases produced by the cylinders, said engine having a first cylinder operable in a rich mixture to generate hydrogen-laden combustion gases, the supply means being adapted to supply at least the first cylinder with a secondary fuel based on a hydrocarbon, or a mixture of hydrocarbons having from 1 to 4 carbon atoms and at least one or the other cylinders with a primary fuel different from the secondary fuel, characterized in that it comprises NOx treatment means integrated in the fuel circuit; exhaust gas.

Indeed, the lower the number of carbon atoms of a hydrocarbon, the higher the ratio between the number of hydrogen atoms and the number of carbon atoms, and the greater the excess of fuel will, after combustion, result in a significant presence of hydrogen in the combustion products.

Advantageously, the hydrogen produced is usable for the post-treatment of NOx.

According to a first embodiment, the NOx processing means integrated into the exhaust circuit of the engine according to the invention consist of a NOx trap in which the NOx are reduced and stored, the operating mode rich of said at least a first cylinder triggering the purging of the NOx trap using I 'H ₂ from the cylinder. Thus, advantageously, the nominal operation of said first cylinder is in lean mode like the other cylinders of the engine according to the invention and as soon as it goes into a rich operating mode, the production of reducers such as H ₂ but also HC, CO cause the purge of said NOx trap and their conversion in the form of N ₂ . This production of H ₂ advantageously promotes a faster and complete reduction reaction, with a better conversion efficiency than if only HC and CO were produced.

According to a second embodiment, the NOx treatment means integrated in the exhaust circuit consist of a NOx trap followed downstream of a SCR catalyst, the operation in rich mode of said at least a first one. cylinder triggering the purging of the NOx trap, the NOx trap being of the type capable of releasing NOx in the form of NO ₂ which are converted using I 'H ₂ resulting from this NH ₃ cylinder captured by the catalyst SCR . Thus, the NOx trap during the passages in the rich operating mode of said first cylinder is purged, the nitrogen oxides being destocked in the form of unreduced NO ₂ and being converted by means of the H ₂ present, ammonia stored thereafter on an SCR catalyst to be so active to reduce NOx exhaust, especially those not trapped on the NOx trap.

[0017] Preferably, the secondary fuel is based on methane. Indeed, as a hydrocarbon, methane is able to provide the largest amount of hydrogen in the context of the invention because it represents the best hydrogen / carbon ratio.

In addition, the engine is of the compression ignition type. In fact, compression ignition engines have the best combustion efficiency. The first cylinder is fed with a mixture of primary fuel and secondary fuel, to obtain a rich mixture whose products of combustion will be, thanks to the formulation of the secondary fuel loaded with hydrogen. Advantageously, the primary fuel is based on diesel or biodiesel.

Furthermore, the subject of the invention is also a method of operating an internal combustion engine according to the invention, characterized in that the first cylinder is fed at least periodically with a rich mixture, combustion charged with hydrogen produced by the first cylinder being sent into the exhaust circuit at least to purge a NOx trap.

The invention also relates to a motor vehicle comprising an engine according to the invention and such a vehicle further comprising an electric motor.

Other features and advantages will appear on reading the description below of a particular embodiment, not limiting of the invention, with reference to the figures in which:

- Figure 1 is a schematic representation of a first embodiment of the engine according to the invention.

- Figure 2 is a schematic representation of a NOx trap in lean burn operation.

FIG. 3 is a schematic representation of the NOx trap in rich mixture operation. In Figure 1 is presented an internal combustion engine 1 according to a preferred embodiment of the invention.

The engine 1 is a multicylinder engine, preferably of the compression ignition type, such as a diesel engine. The engine 1 comprises four cylinders 2, 3, 4 and 5. The cylinders 2, 3, 4 and 5 are supplied with air by intake means 6. The intake means 6 comprise a main air duct 7 connected to intake ducts or ducts 8, 9, 10, 1 1. The intake ducts 8, 9, 10, 11 distribute the air of duct 7 respectively in cylinders 2, 3, 4 and 5.

The cylinders 2, 3, 4 and 5 are supplied with fuel by supply means 12.

The supply means 12 comprise a first supply circuit 13 connected to injectors 15, 16, 17, 18 implanted so as to directly inject said fuel respectively into the cylinders 2, 3, 4 and 5. Preferably the primary fuel is based on diesel or biodiesel. While diesel is a petroleum product, here is meant by biodiesel, a biofuel capable of operating a diesel engine obtained from vegetable or animal oil, transformed by a chemical process such as transesterification into reacting this oil with an alcohol or hydrogenation. Biodiesel can be used alone in the engine or mixed with diesel fuel.

The supply means 12 also comprise a second supply circuit 14 of a secondary fuel connected to the injectors 19, 20, 21, 22. The injectors 19, 20, 21, 22 are implanted in their tubing. respective intake 8, 9, 10, 11 so as to inject indirectly said secondary fuel in the corresponding cylinders 2, 3, 4 and 5. It could also be envisaged that the injectors 19, 20, 21, 22 are implanted so as to inject directly the secondary fuel in the corresponding cylinders.

Preferably, the secondary fuel is based on a hydrocarbon or a mixture of hydrocarbons having 1 to 4 carbon atoms and the secondary fuel is different from the primary fuel. More preferably, the secondary fuel is based on methane. In practice, a natural gas, such as town gas is therefore very suitable.

Moreover, the engine 1 comprises exhaust means 23 of the gases produced by the combustion of the mixture of air and fuel introduced into the cylinders. The exhaust means comprise an exhaust line 24 connected to exhaust pipes 25, 26, 27, 28. The exhaust pipes 25, 26, 27, 28 collect the exhaust gases for transmission to the means. 23, the latter having downstream a NOx trap 29 according to a first embodiment.

This NOx trap 29 is shown in Figure 2a where in the normal operating mode or lean operating mode whose richness is less than 1, the NOx are trapped according to the mechanism and visible reactions in the figure 2.

In a conventional manner, the NOx trap is provided with a catalytic coating containing platinum and / or palladium, Rhodium and at least one selected compound. among alkalis and / or alkaline earths such as barium. The function of platinum and / or palladium is to catalyze the oxidation of HC hydrocarbons, carbon monoxide CO and nitric oxide NO, while rhodium is intended to catalyze the NOx reduction reaction to N N ₂ while barium is used to adsorb NOx in the form of nitrates.

Such a trap 29 which stores the NOx must be regularly purged to continue to be effective and NOx released must be converted to N ₂ , especially in the presence of reducing agents such as HC, CO and H ₂ (see Figure 3). .

In this embodiment, the production of favored H ₂ allows a faster and more complete reduction reaction of the NOx removed from the NOx trap, the conversion efficiency of NOx into N ₂ being better with H ₂ as an agent. reduction only with HC or CO.

Thus, to promote the reduction of NOx pollutants (NO, NO ₂ ) which are present in the exhaust, the NOx trap is periodically purged with periodic engine operating points for which it is required that exhaust are enriched in hydrogen, and thus the first cylinder 2 is fed with a rich mixture of first richness Φi greater than 1, the other cylinders 3, 4 and 5 with a poor mixture of second richness Φ ₂ less than 1.

In a motor 1 as shown in Figure 1, the first cylinder is fed preferably with a mixture of primary fuel and secondary fuel. More specifically, the first wealth Φ-i is obtained by admitting in the first cylinder 2 a mixture of air from the tubing 8 and natural gas injected by the gas injector 19 in the required proportions. The mixture is then compressed and an injection of diesel fuel through the injector 15 makes it possible to ignite the rich mixture. This injection of diesel can be reduced to just necessary to ensure ignition of the mixture, which is favorable to the CO ₂ emission balance of the first cylinder 2 and thus the engine.

In general, the excess fuel is translated after combustion by the significant presence in the combustion products of carbon monoxide (CO), and hydrogen (H ₂ ). The combustion equation of a hydrocarbon of formula general C _n H _m , with n and m, respectively the number of carbon atoms and the number of hydrogen atoms in the hydrocarbon molecule is as follows:

^• (O ₂ + 3.78N ₂ ) → OC ₁ ^• CO ₂ + OC ₂ ^• H ₂ O + oc ₃ ^• CO + oc ₄ ^• H ₂ + oc ₅ ^• N ₂ (1)

with α-i at α ₅ the mole fractions of the products of combustion, and Φ the richness of the mixture determined by the relationship, known per se, as follows:

The invention, according to this first embodiment, allows the use of natural gas to produce a larger molar amount of hydrogen (H ₂ ). Indeed, the advantage of generating hydrogen from natural gas is as follows:

Natural gas is conventionally made up of more than 90% methane (CH ₄ ). The CH ₄ molecule has an H / C ratio between the number of hydrogen atoms (H) and the number of carbon atoms (C) of 4, which is higher than any other hydrocarbon fuel. . As an indication, the H / C ratio of a gasoline is typically between 1.7 and 1.9. Methane is therefore the most favorable compound for the greatest production of molar amounts of H ₂ .

The presence of hydrogen from the exhaust of the first cylinder 2 promotes the destocking NOx trapped in a NOx trap.

For engine operating points for which hydrogen-enriched exhaust gas is not required, the four cylinders 2, 3, 4, 5 operating at the same richness.

The second embodiment of the engine according to the invention differs from the first embodiment in that it further comprises in the exhaust line a SCR catalyst downstream of the NOx trap, the latter being able to destock nitrogen oxides in the form of NO ₂ .

Thus, to allow the purging of the NOx trap as in the first embodiment, engine operating points are required for which the exhaust gases are enriched in hydrogen, the first cylinder 2 being fed with a rich mixture. of first richness Φi greater than 1, the other cylinders 3, 4 and

5 being fed with a lean mixture of second richness Φ ₂ less than 1. The NOx trap is able to destock nitrogen oxides in the form of NO ₂ . The

NO ₂ destocked from the NOx trap without being reduced, reacts in the presence of hydrogen according to the following reaction:

2NO ₂ + 3H ₂ ^ 2 NH ₃ + 2 O ₂ .

The NH ₃ product is then stored on the SCR catalyst which is thus active to reduce NOx exhaust that would not have been trapped by the NOx trap.

According to a variant, the engine 1 may be of the gasoline controlled ignition type. The primary fuel is then a gasoline or any other fuel suitable for spark ignition engines such as for example mixtures comprising ethanol as LΕ85.

According to another variant of the invention, the supply means 12 comprise a second secondary fuel supply circuit 14, such as natural gas, connected to injectors 19, 20, 21, 22. alternatively, each of the injectors 19, 20, 21, 22 is implanted in its corresponding cylinder 2, 3, 4 and 5 so as to inject said fuel directly.

According to another variant, the supply means 12 comprise a second secondary fuel supply circuit 14, such as natural gas, connected only to the first cylinder 2. Thus all the cylinders are fed with primary fuel and only the first cylinder 2 is supplied with secondary fuel. This variant is more economical because it only requires a single gas injector, however the CO ₂ assessment is less interesting. According to another variant, the natural gas may be replaced by LPG. Indeed this fuel allows a greater capacity of storage but as it consists of hydrocarbons more loaded with carbon than the methane of natural gas, the balance of hydrogen and CO ₂ are less interesting.

The main advantage of the invention is to propose an engine whose mode of operation is dedicated to ultra-low NOx emissions and to allow the combustion of homogeneous poor mixtures close to the flammability limit, which allows to achieve a significant gain in CO ₂ emissions while effectively cleaning up NOx emissions at the source.

Claims

1. Internal combustion engine (1) with at least two cylinders (2, 3, 4, 5) comprising air intake means (6), fuel supply means (12), fuel injection means exhaust (23) of the combustion gases produced by the cylinders (2, 3,

4, 5), said motor comprising a first cylinder (2) capable of operating in rich mixture in order to generate hydrogen-laden combustion gases, the supply means (12) being provided for supplying at least the first cylinder (2 ) with a hydrocarbon-based secondary fuel, or a mixture of hydrocarbons, having 1 to 4 carbon atoms and at least one or more of the other cylinders (3, 4, 5) with a primary fuel other than secondary fuel, characterized in that it comprises NOx processing means (29) integrated in the exhaust gas circuit.

2. Engine according to claim 1, characterized in that the NOx processing means integrated in the exhaust circuit consist of a NOx trap (29) in which the NOx are reduced and stored, the operation in rich mode said at least one first cylinder (2) triggering the purging of the NOx trap (29) using I 'H ₂ from this cylinder (2).

3. Engine according to claim 1, characterized in that the NOx treatment means integrated in the exhaust circuit consist of a NOx trap (29) followed downstream of a catalyst SCR, operation in rich mode said at least one first cylinder (2) triggering the purging of the NOx trap, the latter being of the type capable of releasing NOx in the form of NO ₂ which are converted using I 'H ₂ resulting from this cylinder into NH ₃ captured by the SCR catalyst.

4. Internal combustion engine according to any one of claims 1 to 3, characterized in that the secondary fuel is based on methane.

5. Internal combustion engine according to claim 4, characterized in that said engine is of the compression ignition type.

6. Internal combustion engine according to claim 5, characterized in that the first cylinder (2) is fed with a mixture of primary fuel and secondary fuel.

7. Internal combustion engine according to claim 5 or claim 6, characterized in that the primary fuel is based on diesel or biodiesel.

8. Operating method of an internal combustion engine according to one of claims 1 to 7, characterized in that is supplied at least periodically the first cylinder (2) rich mixture, the combustion gases loaded with hydrogen produced by the first cylinder (2) being sent into the exhaust circuit at least to purge a NOx trap.

9. Motor vehicle characterized in that it comprises a motor according to one of claims 1 to 7.