FR2941499A1 - Internal combustion engine i.e. diesel engine, for motor vehicle, has electrolyser connected to cooler for producing hydrogen from water contained in exhaust gas, where produced hydrogen is reinjected to intake and exhaust ducts - Google Patents

Abstract

The engine (1) has a condenser i.e. exhaust gas recirculation cooler (15), for cooling a part of water contained in exhaust gas at vapor state. A hydrogen production unit i.e. electrolyser (20), is connected to the condenser for producing hydrogen from the water contained in the exhaust gas. An exhaust gas recirculation circuit (10) connects an exhaust duct (9) to an intake duct (12), where the produced hydrogen is reinjected to the intake duct and the exhaust duct. The cooler has a lower part with an evacuation outlet for evacuating condensed water by gravity.

Description

Internal combustion engine having means for producing hydrogen

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.

There are mainly two architectures of exhaust gas recirculation circuit.

According to a first architecture, the exhaust gas recirculation circuit is of the High Pressure (HP) type when, for an internal combustion engine equipped with a turbocharger, the exhaust gases are taken upstream of the turbine of the turbocharger to be reinjected downstream of the turbocharger compressor.

According to a second architecture, the exhaust gas recirculation circuit is of the Low Pressure (LP) type when, for an internal combustion engine equipped with a turbocharger, the exhaust gases are taken downstream of the turbocharger turbine. to be reinjected upstream of the compressor of the turbocharger.

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 (H2) makes it possible to significantly increase the flame speed and thus to counterbalance the kinetic effect of the dilution due to the EGR system. However, from a practical point of view, it seems difficult to operate an engine with two separate fuels, which would require two tanks and two separate fuel distribution systems.

It is well known also that the exhaust gases are hot and charged with water vapor. It can be deduced that this water vapor can be a source of hydrogen.

It is known, as described in document FR2880657, to produce hydrogen (H2) by a physico-chemical reforming operation, by reacting fuel molecules with a portion of the water vapor contained in the gases of exhaust to produce hydrogen. However, for an optimal efficiency of the reforming of the fuel in hydrogen, it is necessary to conduct the reforming chemical reactions at high temperature, which conditions a positioning of the reforming system closer to the engine outlet to take advantage of a high exhaust gas temperature or provide auxiliary heating systems to maintain the reformer at temperature. These auxiliary heating systems are energy consumers which has an upward impact on the fuel consumption of a vehicle comprising such a reforming device. Moreover, in the case of a supercharged engine, this device, because of the high temperature required of the exhaust gas is mainly compatible with an HP EGR architecture and can not operate on a BP EGR architecture.

The object of the invention is to overcome the disadvantage of the prior art by proposing an internal combustion engine comprising an exhaust gas recirculation circuit and a means for producing hydrogen that does not require a high operating temperature. The invention therefore relates to an internal combustion engine comprising means for producing hydrogen from water contained in exhaust gases, characterized in that it comprises a condenser for condensing at least part of the water contained in the vapor state in the exhaust gas and that the means for producing hydrogen is an electrolyzer connected to the condenser to produce hydrogen from the condensed water. The invention has the additional advantage of producing hydrogen without additional fuel and water injection as is the case for reforming.

Moreover, the invention may include one or more of the following features: the engine further comprising an exhaust gas recirculation circuit connecting an exhaust duct to an intake duct, the condenser is a recirculating exhaust gas cooler. This takes advantage of a heat exchanger usually existing in an exhaust gas recirculation circuit to achieve the condensation of the water vapor contained in the exhaust gas taken for the purpose of being recirculated. - The exhaust pipe comprising a particulate filter, the recirculation circuit is connected to the exhaust pipe downstream of said particulate filter. Indeed, it ensures a recycling of particulate free gases. The cooler comprises a discharge outlet at the bottom of said cooler for gravity discharging the condensed water. There is thus a simple and economical way of recovering condensates. - A pump is upstream of the electrolyser, to discharge the condensed water by the cooler. There is thus the water supply of the electrolyser. A reservoir is included between the pump and the cooler to temporarily store the condensed water. the electrolyser comprises a U-shaped structure with separate oxygen and hydrogen evacuation outlets. Indeed, the gases rising above their electrolysis electrode by the buoyancy of Archimedes are thus kept separate and harmless. the hydrogen produced is reinjected at the intake and / or the exhaust. In fact, by adding hydrogen to the inlet, the combustion rate can be boosted and exhaust can be improved. The invention may advantageously comprise a hydrogen sensor or a proportional oxygen probe for measuring the quantity of hydrogen injected.

The subject of the invention is also a vehicle comprising an engine according to the invention. Brief description of the drawings Other features and advantages will become apparent on reading the following description of a particular embodiment, which is not limiting to the invention. invention, with reference to the figures in which:

- Figure 1 is a schematic representation of an embodiment of an internal combustion engine according to the invention. FIG. 2 is a partial schematic representation of the exhaust gas cooler of the recirculation circuit. - Figure 3 is a schematic representation of an embodiment of the electrolyser.

DETAILED DESCRIPTION FIG. 1 schematically illustrates an internal combustion engine 1 equipped with a turbocharger 2. The engine 1 comprises, in the illustrated example, four cylinders 3 receiving compressed air via a collector. intake 4, the exhaust gases being conveyed by an exhaust manifold 5.

In the example illustrated, the exhaust gas is treated by passing successively by an oxidation catalyst 6, by a catalyst of NOx 7, then by a particulate filter 8 disposed on the exhaust line 9. The catalyst of Oxidation 6 allows the elimination of HC unburned hydrocarbons, carbon monoxide CO and the oxidation of a portion of the nitrogen oxides NO to NO2. The NOx 7 catalyst allows the reduction of NOX nitrogen oxides present in the exhaust gas. The particulate filter 8 retains the soot particles contained in the exhaust gas.

The presence of the oxidation catalyst 6 and the NOx 7 catalyst is not essential for the realization of the invention. Similarly, other depollution devices not shown in FIG. 1, such as a second oxidation catalyst or an SCR catalyst making it possible to reduce the NOX nitrogen oxides present in the exhaust gases, by selective catalytic reaction between the NOX and a reducing agent can supplement the exhaust line, to improve the emission control of the exhaust gases.

In the illustrated example, which relates for example to a diesel engine, it is intended to recycle a portion of the exhaust gas by means of an exhaust gas recirculation circuit 10 said low pressure.

The recirculation circuit 10 draws exhaust gas from the exhaust line 9 of the engine 1, downstream of the turbine 11 of the turbocharger 2, more precisely downstream of the particulate filter 8 to ensure particle-free gas recirculation. . The exhaust gases taken by the recirculation circuit supply an intake duct 12 of an air / exhaust gas mixture upstream of the compressor 13 of the turbocharger 2. This recirculation circuit 10 comprises a regulating valve 14 for regulating the flow of the recycled exhaust gases at the engine inlet 1.

The recirculation circuit 10 also comprises a cooler 15 such as a tube heat exchanger, arranged upstream of the regulating valve 14, exchanging calories with the cooling circuit liquid to cool the exhaust gases so as not to not introduce too hot gases in the cylinders 3, which would result in a loss of volumetric efficiency. A reverse assembly, that is to say with the cooler 15 downstream of the recirculated gas flow control valve 14 is also possible.

As illustrated in FIG. 2, the cooler 15 comprises tubes 16 in which the exhaust gases circulate (arrow A). The hot exhaust gases taken by the recirculation circuit 10 are charged with steam. Depending on the mode of operation of the engine, the amount of water will vary substantially linearly depending on the richness of the mixture to reach about 7.5% by mass stoichiometry.

Advantageously, the cooler 15 of the recirculation circuit 10 is used in the invention for its additional function as a condenser. Indeed, as it passes through the cooler 15, the temperature of the exhaust gas decreases and the excess of water that the gases can no longer contain condenses. The condensed water flows and accumulates by gravity at the bottom of said cooler 15 (arrow B).

According to the invention, the cooler 15 comprises a discharge outlet 17 at the bottom of said cooler to allow evacuation and gravity recovery of the water contained in the exhaust gas.

The evacuation outlet 17 is connected to a reservoir 18 (FIG. 1) in which the condensed water is harvested and stored. The reservoir 18 is connected to a pump 19, such as an electric pump, itself connected to an electrolyzer 20.

The pump 19 has the function of discharging water from the tank 18 to the electrolyser 20. The tank 18 can be used to store the condensed water from the cooler 15 at a time when the electrolysis is not required, or still to send to the electrolyser 20 a higher water flow than can produce at the same time the cooler 15.

The electrolyser is electrically powered by an electric source 21. The electrical source 21 may be a battery not shown here or again, so as not to penalize the energy balance of the engine, an energy recovery device as an indication, the engine being embedded in a vehicle, a deceleration energy recovery device or an exhaust energy recovery device not explained here.

Indeed, a reaction report from a generic formulation of a commercial fuel, diesel or gasoline, gives us: CnH, 8n + 5,48n (02 + 3,773N2) - nCO2 + 0,9nH2O + 3,773 - 54n N2 (1) With n = 8 for a gasoline and n = 12 for a diesel.

This assessment allows us to deduce that we can have at best about 10% by volume of water vapor in the exhaust gas, potentially 10% by volume of hydrogen. Taking into account the calorific value of fuel (about 44 kJ / kg) and that of hydrogen (approximately 120 kJ / kg), we therefore have approximately 15% of energy from hydrogen when the engine uses a fuel rate. 35% recirculation gas.

The electrical efficiency of an electrolyser is about 50% with respect to the recoverable energy in the form of hydrogen. Therefore the maximum electrical cost would be 30% of the energy introduced by the fuel, so the order of magnitude of energy losses in the exhaust or energy losses by the cooling fluid of a current internal combustion engine. This estimate is a maximum and in practice the hydrogen requirements are lower. It is thus shown that it is possible and realistic to find the energy necessary for carrying out the invention by setting up an energy recovery system.

The decomposition of the water by electrolysis of the water in the electrolyser 20 is carried out according to the following known chemical reactions:

Oxidation at the anode (connected to the positive pole of the generator): 2 H2O (liquid) - 02 (gas) + 4H + (aqueous) + 4th - Reduction at the cathode (connected to the negative pole of the generator): 4 H2O (liquid) + 4e- - 2H2 (gas) + 4OH- (aqueous) With, overall: 2 H2O (liquid) - 2H2 (gas) + O2 (gas) The electrolytic system therefore produces hydrogen (H2) and hydrogen. oxygen (02) gas using condensed exhaust gas water.

FIG. 3 presents a schematic diagram of an embodiment of the electrolyser 20.

The electrolyzer 20 comprises an anode 27 connected to the positive pole of the electric source 21 and a cathode 28 connected to the negative pole of the electric source 21. The oxygen is produced at the anode 27 while the hydrogen is produced at the cathode 28. In the illustrated example, the collection of oxygen and hydrogen is separated to prevent the production of a gaseous mixture of hydrogen and explosive oxygen. Thus, the oxygen is directed to a first outlet 29. This first outlet 29 may be vented to the open air or used in an application outside the scope of this invention. Hydrogen is directed to a second output for engine applications. The electrolyser 20 has a water inlet 31 connected to the pump 19 (FIG. 1). The electrolyser 20 forms a generally U-shaped structure with a first branch intended for the collection and delivery of oxygen to the first outlet 29 and a second branch intended for the collection and delivery of hydrogen to the second exit 30.

It is thus possible to operate engine components powered by this production of hydrogen obtained by electrolytic reaction.

For this purpose, as illustrated in FIG. 1, a first sampling system 22 for the gas generated by the electrolyser 20 connected to the second outlet 30 is provided for directing the hydrogen towards the intake duct 12 as well as a means injection 23, such as a gas injector. The implantation of the injection means 23 can also be made at the intake manifold 3. The precise implantation of the injection means 23 is to be determined by the skilled person so as to obtain a good distribution cylinder to cylinder 3 of (2) (3) (4) mixture admitted for combustion, that is to say that the hydrogen from the electrolyser 20 is as intimately mixed possible with the intake air.

Thus, the introduction of the gaseous hydrogen obtained by electrolytic reaction at the inlet makes it possible in particular to operate the engine with high levels of EGR while reducing nitrogen oxide emissions and maintaining relatively low levels of emissions of carbon (CO, HC) and particulate matter.

A second sampling system 25 connected to the second outlet 30 of the gas generated by the electrolyser 20 is provided for directing the hydrogen gas towards the exhaust line 9 as well as injection means 26, such as an injector gas.

The implantation of the injection means 26 can be made upstream of the depollution devices 6, 7, 8. It is thus possible to improve the operation of the engine 1 depollution devices, by this electrolytic production of hydrogen as per example, their heating to bring them to a nominal temperature before starting the engine 1. It is also possible to operate the pollution control members to regenerate, such as for example the particulate filter 9, by injecting this mixture upstream of the catalyst Oxidation 6. The hydrogen is oxidized in the oxidation catalyst 6. The exothermic oxidation reaction of the mixture makes it possible to regenerate the particulate filter 9.

A control unit, not shown, is provided. This control unit is generally connected to a control unit of the operation of the engine 1. The control unit controls the power supply 21 of the electrolyser 20, the pump 19 to supply water to the electrolyzer 20 and the means In this way, the steps of production and distribution of hydrogen gas obtained by electrolysis are controlled.

Advantageously, there is provided a hydrogen sensor (H2) 24 (or a proportional oxygen sensor 02) for measuring the quantity of hydrogen injected disposed downstream of the electrolyser 20, for example on the first sampling system 22 and The sensors, connected to the control unit, are advantageously used in addition to the conventional sensors, present on recently designed engines, to better adjust the control strategies of the electrolysis.

Thus, during the operation of the engine 1, the exhaust gases produced flow from the exhaust manifold 5 to the exhaust line 9 by successively passing through the turbine 11 of the turbocharger 2 and the abatement units 6, 7, 8. part of the heat of these exhaust gases is lost at the same time by heat exchange. Following the passage of the exhaust gas in the particulate filter 8, the recirculation circuit 10 takes a part. The exhaust gas portion taken through the cooler cooled by the engine coolant. The decrease in the temperature of the exhaust gases in the cooler 15 results in the condensation of the water vapor contained in these gases. The condensed water trickles and escapes through the discharge outlet 17 to accumulate in the reservoir 18. The pump 19, controlled by the control unit loads the electrolyser 20 in condensed water. Powered by the electrical source 21, the electrolysis is performed at the terminals of the electrodes 27, 28. The hydrogen produced is discharged through the second outlet 30 to the sampling means 22, 25 to be reinjected at the inlet 12 and / or at the exhaust 9.

By choosing to withdraw the recirculation exhaust gas downstream from at least one of the pollution control members, this embodiment has the advantage of being able to benefit from an exhaust gas temperature reduced by the thermal losses sustained in the exhaust line 9 between the engine output and the sample. Thus the condensation at the cooler 15 is easier.

This embodiment described in FIG. 1 is in no way limiting. According to a variant without turbocharger 2, because it is not mandatory for the embodiment of the invention, the recirculation exhaust gas is taken downstream of the pollution control members disposed on the exhaust line, preferably in downstream of the particulate filter 8 and then reinserted in the intake duct 12 or in the intake manifold 4.

In addition, the invention is not limited to a diesel type engine. The invention can also be applied to gasoline engines, turbocharged or not, for which the recirculation exhaust gas is taken downstream of at least one of the pollution control organs disposed on the exhaust line. Indeed, it takes advantage of an exhaust gas temperature lower than that seen at the engine outlet, which facilitates the condensation of water vapor at the cooler 15.

In addition, according to one variant, the injection means 23 for the hydrogen gas can be implanted in the recirculation circuit 10, downstream of the cooler 15, however this embodiment limits the use of the invention to the points of engine operation with exhaust gas recirculation.

The invention has the advantage of using an already existing water source in the vehicle, previously unused and without impact on the environment. In the case of more than one stand-alone water supply system, there is no need to fill a tank.

The invention has the additional advantage of allowing the elimination of condensed water generated by heat exchangers whose accumulation can constitute in itself a technical problem.

Claims (10)

Revendications1. Internal combustion engine comprising a means for producing hydrogen from water contained in exhaust gases, characterized in that it comprises a condenser for condensing at least part of the water contained in the state of vapor in the exhaust gas and that the means for producing hydrogen is an electrolyzer (20) connected to the condenser for producing hydrogen from the condensed water. 2. Motor according to claim 1, comprising an exhaust gas recirculation circuit (10) connecting an exhaust duct (9) to an intake duct (12), characterized in that the condenser is a cooler ( 15) of recirculation exhaust gas. 3. Engine according to claim 2, the exhaust pipe (9) comprising a particulate filter (8), characterized in that the recirculation circuit (10) is connected to the exhaust pipe (9) downstream of said particulate filter (8). 4. Motor according to claim 2 or claim 3, characterized in that the cooler (15) comprises a discharge outlet (17) at the bottom of said cooler (15) for discharging by gravity condensed water. 5. Engine according to any one of claims 2 to 4, characterized in that it comprises upstream of the electrolyser (20), a pump (19) for discharging the condensed water by the cooler (15) to said electrolyzer. 6. Engine according to claim 5, characterized in that it comprises between the pump (19) and the cooler (15) a reservoir (18) for temporarily storing the condensed water. 7. Internal combustion engine according to any one of the preceding claims, characterized in that the electrolyser (20) comprises a U-shaped structure with outlets (29, 30) for the evacuation of oxygen and hydrogen. distinct products. 8. Engine according to any one of the preceding claims, characterized in that the hydrogen produced is reinjected at the inlet (12) and / or the exhaust (9). 9. Motor according to any one of the preceding claims, characterized in that it comprises a hydrogen sensor or a proportional oxygen sensor (24) for measuring the amount of hydrogen injected. 10. Motor vehicle comprising an engine according to any one of claims 1 to 9.