FR2944056A1 - INTERNAL COMBUSTION ENGINE AND METHOD OF OPERATION ASSOCIATED WITH SUCH A MOTOR - Google Patents

Abstract

The invention relates to a multi-cylinder internal combustion engine comprising air intake means (6), fuel supply means (12), exhaust means (23) for the combustion gases produced by the cylinders. (2, 3, 4, 5), said motor comprising a first cylinder (2) capable of operating in a rich mixture in order to generate hydrogen-laden combustion gases and a circuit (29) for the recirculation of the combustion gases of the first cylinder (2) to the air intake means (6), characterized in that the supply means (12) are provided for feeding at least the first cylinder (2) with a secondary fuel based on a hydrocarbon, or a mixture of hydrocarbons, having 1 to 4 carbon atoms and at least the other cylinders (3, 4, 5) with a primary fuel different from the secondary fuel. The invention also relates to a method of operating an engine according to the invention.

Description

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

TECHNICAL FIELD OF THE INVENTION The present invention relates to the field of the automobile, and more particularly to the field of internal combustion engines comprising an exhaust gas recirculation circuit.

BACKGROUND OF THE INVENTION The constraints due to standards, for example the Euro V standards, relating to the pollutant emission levels generated by the operation of internal combustion engines, are becoming more and more severe, particularly as regards nitrogen oxides (NOx).

Among the means used to clean up exhaust gases, exhaust gas recirculation (EGR, for the initials of Exhaust Gas Recirculation) constitutes, for both gasoline engines and diesel engines, excellent method of reducing NOx emissions. The principle of the EGR lies in the introduction of a given amount of exhaust gas to replace some of the fresh air at the intake of the engines. The fact of reintroducing exhaust gases into the combustion chamber of the engine makes it possible, by reducing the oxygen concentration and the combustion temperature, to limit NOx formation reactions during combustion.

From a physico-chemical point of view, it can be seen that the flame speed decreases sharply with the presence of an EGR system. Even resorting to an increase in turbulence can not overcome this speed deficit that can be described as chemical.

It has also been found that the enrichment of the EGR system with hydrogen makes it possible to significantly increase the flame speed and thus to counterbalance the kinetic effect of the dilution due to the EGR system.

It is known, as described in document FR2880657, to produce hydrogen by a physico-chemical reforming operation, by reacting fuel molecules with a portion of the water vapor contained in the exhaust gases. to produce hydrogen. However, it is necessary to conduct the reforming chemical reactions at high temperature, which requires the provision of auxiliary heating systems energy consumers.

The document US4131095 describes a multi-cylinder internal combustion engine of which one of the cylinders is dedicated to be powered according to the engine load conditions either by a stoichiometric mixture of air and gasoline, or by a very rich mixture of air and fuel. essence (the richness being between 2.5 to 3.3). The very rich mixture is produced for low engine load conditions and the cylinder then produces combustion gases whose composition is similar to reforming gases, that is to say containing in particular carbon monoxide (CO). , unburned hydrocarbons (HC) and hydrogen (H2).

Said dedicated cylinder comprises two exhaust valves and the combustion gases of the air / fuel mixture of this cylinder can be re-routed to the intake by means of an exhaust gas recirculation circuit extending from one first of the two exhaust valves to an intake duct specific to the other cylinders or can join the exhaust manifold with a pipe extending from the second exhaust valve to the exhaust manifold.

Thus, in a first mode of operation, with low load, the dedicated cylinder is fed by the very rich air / gasoline mixture, the second valve is closed, the combustion gases from said cylinder are reinjected into the intake duct of the others cylinders and are mixed in substitution of gasoline with intake air to feed the other cylinders.

In a second mode of operation, with a high load, the dedicated cylinder like the other cylinders is fed by the stoichiometric air / fuel mixture, the first valve is closed to prevent the recirculation of gas and the combustion gases are evacuated towards the gas line. exhaust via the second valve. The transition between the two operating modes is straightforward, that is, the motor switches from the first operating mode to the second operating mode from a predetermined demand load threshold.

However, such a device has many drawbacks: it is unsuitable for current standards relating to pollutant emission levels, it is not intended to control the amount of flue gas to be recirculated from the dedicated cylinder to the other cylinders. The combustion of the very rich air / gasoline mixture does not make it possible to generate a large quantity of hydrogen, the device involves for the selection of the mode of operation valves of the selected cylinder an expensive and complex system of control by camshaft driven in translation . The object of the invention is to overcome the drawbacks of the combustion engine according to the prior art by proposing a new combustion engine capable of meeting the current standards relating to pollutant emission levels, which can produce in a cylinder a larger quantity of fuel. 'hydrogen. The invention therefore relates to a multi-cylinder internal combustion engine comprising air intake means, fuel supply means, means for exhausting the combustion gases produced by the cylinders, said engine comprising a first cylinder capable of operating in a rich mixture in order to generate hydrogen-laden combustion gases and a circuit for recirculating the combustion gases from the first cylinder to the air intake means, characterized in that the supply means are provided for supplying at least the first cylinder with a secondary fuel based on a hydrocarbon, or a mixture of hydrocarbons, having 1 to 4 carbon atoms and at least the other cylinders with a primary fuel different from the fuel secondary.

In fact, the lower the number of carbon atoms in a hydrocarbon, the higher the ratio between the number of hydrogen atoms and the number of carbon atoms, and the higher the excess fuel will result. after combustion, by a large presence of hydrogen in the combustion products.

In addition, the invention may include one or more of the following features:

- The engine further comprising a turbocharger provided with a compressor 30 communicating with the air intake means and a turbine communicating with the exhaust means, the recirculation circuit extends exhaust means downstream of the turbine to the intake means upstream of the compressor. There is thus more space to implement the recirculation circuit.

The exhaust means comprising exhaust manifolds and the intake means comprising air intake manifolds connected to their corresponding cylinder, the recirculation circuit extends from the first cylinder exhaust manifold; to the air intake manifolds of the other cylinders. There is thus a short and efficient recirculation circuit in which the combustion products of the first cylinder charged with hydrogen are taken at the source and readmitted to the cylinders whose combustion is to be improved. the recirculation circuit comprises a valve for regulating the quantity of gas to be recirculated. There is thus a means of regulating the amount of recirculated gas that is reliable and economical.

The secondary fuel is based on methane. Indeed, as 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

the engine is of the compression ignition type. Indeed, compression ignition engines have the best combustion efficiencies.

- 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. - the primary fuel is based on diesel or biodiesel.

Moreover, 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 supplied with a rich mixture and the other cylinders with a lean mixture, one part of the hydrogen-laden combustion gases produced by the first cylinder being readmitted to promote combustion in the other cylinders.

The method of the invention may comprise the following characteristic:

it comprises the steps of admitting a rich mixture of air and secondary fuel, compression of the rich mixture and injection of primary fuel to ignite the rich mixture. Thus the amount of primary fuel is limited to the amount necessary to start the combustion, which is favorable to the CO2 balance. BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages will appear on reading the following description of a particular embodiment, not limiting of the invention, with reference to the figures in which: FIG. 1 is a schematic representation of a first embodiment of the engine according to the invention. - Figure 2 is a schematic representation of a second preferred embodiment of the engine according to the invention. - Figure 3 is a schematic representation of a third embodiment of the engine according to the invention.

DETAILED DESCRIPTION FIG. 1 shows an internal combustion engine 1 according to a first 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, 11. The intake ducts 8, 9, 10, 11 distribute the air of the duct 7 respectively in the 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 fuel is a petroleum product, here we mean by biodiesel, a biofuel capable of operating a diesel engine obtained from vegetable or animal oil, transformed by a chemical process such as transesterification by 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 injectors 19, 20, 21, 22. The injectors 19, 20, 21, 22 are located in their respective intake manifold. 8, 9, 10, 11 so as to indirectly inject said secondary fuel into the corresponding cylinders 2, 3, 4 and 5. Preferably, the secondary fuel is based on a hydrocarbon or a mixture of hydrocarbons having between 1 and 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.

Furthermore, 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 to transmit them to the exhaust system. exhaust line 23.

The engine 1 according to the invention comprises a circuit 29 for recirculating the exhaust gases. The exhaust gas recirculation circuit 29 (or EGR circuit corresponding to the acronym for Exhaust Gas Recirculation) preferably comprises a valve 30 for regulating the amount of exhaust gas to be recirculated. The EGR circuit 29 is implanted in such a way that it takes the combustion gases coming from the first cylinder 2 to transmit them to the other cylinders 3, 4, 5. For this purpose, the EGR circuit 29 is connected, on the exhaust side, to the exhaust manifold 25 of the first cylinder 2 and admission side to the intake manifolds 9, 10, 11 of the other cylinders 3, 4, 5. In this embodiment, the EGR circuit 29 is advantageously connected upstream of the manifolds. intake 9, 10, 11 of the other cylinders 3, 4, 5, downstream of a separation 32 with the intake manifold 8, in order to avoid or at least limit as much as possible to reinject gas from recirculated exhaust in the first cylinder 2.

The valve 30 is advantageously an EGR valve capable of modulating the flow rate of the exhaust gas passing through it such that the automobile industry uses it, because it represents a technical solution which is inexpensive and technically reliable to ensure the function of regulating the gas flow rate. exhaust from the first cylinder 2.

Thus, in this embodiment, for the engine operating points for which hydrogen-enriched EGR is required, the first cylinder 2 is fed with a rich mixture of first richness O1 greater than 1, the other cylinders 3, 4 and 5 with a lean blend of second richness 02 less than 1 and the EGR valve 30 is fully or partially opened to allow the readmission of a portion of the hydrogen-laden combustion gases produced by the first cylinder 2 by the circuit 29 EGR to the intake manifolds 9, 10, 11 to promote combustion in the other cylinders 3, 4, 5. The valve 30 ensures, according to its opening, a distribution between the amount of gas recirculated by the circuit 29 EGR and the quantity of exhaust gas sent to the exhaust line 24.

In a motor 1 as represented in FIG. 1, comprising four cylinders, the combustions follow one another: the first cylinder 2 burns its mixture then successively the others. When the valve 30 is open, such an EGR valve having in itself insufficient response time to open and close at the rate of the cycles of the first cylinder 2, it remains open during the exhaust phases of the other cylinders 3, 4, 5. A fraction of the exhaust gases of the other cylinders 3, 4, 5 can thus recirculate towards the intake means 6 by this valve 30. However, the mass of hydrogen recirculated towards the other cylinders 3, 4, 5 remains generally the same and this does not pose a problem on the operation of the engine according to the invention.

Preferably, the first cylinder is fed with a mixture of primary fuel and secondary fuel. More specifically, the first richness 01 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 via the injector 15 makes it possible to ignite the rich mixture. This injection of diesel fuel can be reduced to just necessary to ensure the ignition of the mixture, which is favorable to the CO2 emission budget of the first cylinder 2 and therefore 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 (H2). The combustion equation of a hydrocarbon of general formula CnHm, with n and m, respectively the number of carbon atoms and the number of hydrogen atoms in the hydrocarbon molecule is as follows: n + CnHm +. (02 + 3.78N2) a, - CO2 + a2 • H2O + a3 • CO + a4. H2 + a5. N2 (1) With a, to a5 the mole fractions of the products of combustion, and cD the richness of the mixture determined by the relation, known per se, as follows: 30 / MCARBURANT _ MAIR REEL The invention, according to this first embodiment , thanks to the use of natural gas, to produce a larger molar amount of hydrogen (H2). Indeed, the advantage of generating hydrogen from natural gas is as follows:

Natural gas is typically made up of more than 90% methane (CH4). The CH4 molecule has an H / C ratio of the number of hydrogen atoms (H) to 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 largest production of molar amounts of H2.

The presence of hydrogen from the exhaust gases of the first cylinder 2 promotes the combustion of poor mixtures (second richness 02 less than 1) in the other cylinders 3, 4, 5, because it allows a substantially faster combustion. The engine 1 thus has an increased EGR tolerance, and, therefore, allows the reduction of NOx emissions without degradation of other polluting emissions (CO and HC).

For the engine operating points for which hydrogen-enriched EGR is not required, the four cylinders 2, 3, 4, 5 operate at the same richness and the valve 30 is closed so as to prohibit the recirculation of the exhaust gases. exhaust of the first cylinder 2 by the EGR circuit 29. The valve 30 further allows the passage of the exhaust gases from the first cylinder 2 to the exhaust line 24.

These modes of operation are not limiting. Indeed, it can for example also provide to operate the engine 1 with EGR without hydrogen enrichment. In this case the four cylinders 2, 3, 4, 5 operate at the same richness and the valve 30 is open so as to allow the recirculation of at least a portion of the exhaust gas from the first cylinder to the other cylinders. It is also possible to operate the four cylinders 2, 3, 4, 5 of the engine 1 only by diesel fuel injection. FIG. 2 presents a second embodiment of the engine according to the invention. Identical elements have the same references. This second embodiment differs from the first embodiment in that it further comprises in its architecture a turbocharger 31. The turbocharger 31 comprises a compressor C rotatably connected to a turbine T. The compressor C is disposed in the path of the intake air in the main inlet duct 7 of the intake means 6 while the turbine T is disposed in the path of the exhaust gas passing through the exhaust line 24. The passage of the exhaust gas in the turbine T rotates the latter which in turn drives the compressor C. Thus, the intake air is sent compressed downstream of the compressor C to the cylinders 2, 3, 4, 5.

In this second embodiment, preferably the recirculation circuit 29 is of the high pressure type that is to say that it extends the exhaust means 23, upstream of the turbine T, the means of 6, downstream of the compressor C. The upstream and downstream direction is relative to the direction of fluid flow in the exhaust means 23 and amission 6. More precisely and preferably, the recirculation circuit 29 extends from the exhaust pipe 25 of the first cylinder 2 to the air intake pipes 9, 10, 11 of the other cylinders 3, 4, 5. In this embodiment, the EGR circuit 29 is advantageously connected to the pipes of FIG. admission of the other cylinders 3, 4, 5 downstream of the partition 32 with the intake manifold 8, so as to avoid or at least as much as possible to reinject the recirculated exhaust gases into the first cylinder 2. This second embodiment also allows the same modes of operation its for the first embodiment, namely, operation with EGR enriched in hydrogen, without EGR, or with EGR not enriched in hydrogen, or in injection of diesel fuel only.

Figure 3 shows a third embodiment of the engine according to the invention. Identical elements have the same references. In this third embodiment, the engine comprises the same way as for the second embodiment a turbocharger 31 and preferably, the recirculation circuit 29 is of the low pressure type that is to say that it extends exhaust means 23 downstream of the turbine T to the intake means 6 upstream of the compressor C. In this third embodiment, the exhaust pipe 25 of the first cylinder 2 is connected to the exhaust pipes 26, 27, 28 of the other cylinders 3, 4, 5.

Thus, for the engine operating points for which hydrogen enriched EGR is required, the first cylinder 2 is fed with a rich mixture of first richness O1 greater than 1, the other cylinders 3, 4 and 5 are fed with a poor mixture of second richness 02 less than 1, the EGR valve 30 placed downstream of the turbine T is open to allow the readmission of a portion of the exhaust gas containing hydrogen from the exhaust line 24 to the main intake pipe 7, upstream of the compressor C through the circuit 29 EGR. The hydrogen enriched EGR gases mix with the intake air, pass through the compressor and are distributed in each of the cylinders 2, 3, 4, 5 of the engine 1 by the corresponding intake manifolds 8, 9, 10, 11.

This third embodiment is advantageous in the sense that it provides more space to implement the EGR circuit 29 and the EGR valve in the environment of the engine 1. This third embodiment is also advantageous because it allows the production of hydrogen indifferently on one of the cylinders 2, 3, 4, 5 of the engine 1. It can thus be chosen to distribute the operating time in rich mode for the production of hydrogen on each of the cylinders 2 , 3, 4, 5, in order for example to homogenize the operating conditions of said cylinders. However, this embodiment is slightly less effective because the hydrogen produced is more diluted and its quantity can even decrease because of the thermodynamic equilibrium which varies with temperature.

The invention is not limited to the embodiments described in Figures 1 to 3.

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 such as E85.

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. In this variant, each injectors 19, 20, 21, 22 are 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 CO2 balance is less interesting. According to another variant, the natural gas can 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 CO2 are less interesting. According to another variant, the engine 1 being without turbocharger 31, the recirculation circuit 29 comprising the EGR valve 30 extends from the exhaust line 23 downstream of the exhaust pipes 25, 26, 27, 28, 7 main intake air duct. This variant has, as for the third embodiment shown in FIG. 3, the advantage of allowing the production of hydrogen indifferently on one of the cylinders 2, 3, 4, 5 of the engine 1. However, this variant is also slightly less effective in the sense that the hydrogen produced is more diluted and its quantity can even decrease because thermodynamic equilibria that vary with temperature.

The main advantage of the invention is to increase the engine's EGR tolerance and to allow the combustion of homogeneous poor mixtures close to the flammability limit, which enables us to achieve a notable gain in CO2 emission while also cleaning up effectively at the source NOx.5 emissions

Claims (10)

Revendications1. Multi-cylinder internal combustion engine comprising air intake means (6), fuel supply means (12), exhaust means (23) for the combustion gases produced by the cylinders (2, 3, 4, 5), said motor comprising a first cylinder (2) operable in rich mixture to generate hydrogen-laden combustion gases and a circuit (29) for recirculating the combustion gases from the first cylinder (2) to the air intake means (6), characterized in that the supply means (12) are provided for supplying at least the first cylinder (2) with a secondary fuel based on a hydrocarbon, or a mixture of hydrocarbons having 1 to 4 carbon atoms and at least the other cylinders (3, 4, 5) with a primary fuel different from the secondary fuel. 2. An internal combustion engine according to claim 1, further comprising a turbocharger (31) provided with a compressor (C) communicating with the air intake means (6) and a turbine (T) communicating with the combustion medium. exhaust (23), characterized in that the recirculation circuit (29) extends from the exhaust means (23) downstream of the turbine (T) to the intake means (6) upstream of the compressor (C) ). 3. Internal combustion engine according to claim 1, the exhaust means (24) comprising exhaust pipes (25, 26, 27, 28) and the intake means (6) comprising intake manifolds ( 8, 9, 10, 11) connected to their corresponding cylinder (2, 3, 4, 5), characterized in that the recirculation circuit (29) extends from the exhaust pipe (25) of the first cylinder (2) to the air intake pipes (9, 10, 11) of the other cylinders (3, 4, 5). 4. Internal combustion engine according to any one of claims 1 to 3, characterized in that the recirculation circuit (29) comprises a valve (30) for regulating the amount of gas to be recirculated. 5. Internal combustion engine according to any one of claims 1 to 4, characterized in that the secondary fuel is based on methane. 6. Internal combustion engine according to claim 4 or claim 5, characterized in that said engine is of the compression ignition type. 7. Internal combustion engine according to claim 6, characterized in that the first cylinder (2) is fed with a mixture of primary fuel and secondary fuel. 8. Internal combustion engine according to claim 6 or claim 7, characterized in that the primary fuel is based on diesel or biodiesel. 9. Operating method of an internal combustion engine according to any one of the preceding claims, characterized in that the first cylinder (2) is fed with a rich mixture and the other cylinders (3, 4, 5) with lean mixture, part of the hydrogen-laden combustion gases produced by the first cylinder (2) being readmitted to promote combustion in the other cylinders (3, 4, 5). 10. Operating method according to claim 9, characterized in that it comprises the steps of admitting a rich mixture of air and secondary fuel, rich mixture compression and primary fuel injection to ignite the fuel. rich mixture.