FR2941015A1 - Exhaust gas recirculation device for internal combustion engine e.g. petrol engine, of motor vehicle, has adjustment device adjusting air proportion in air and fuel mixture according to oxygen quantity in exhaust gas for enrichment of gas - Google Patents

Abstract

The device has a recirculation circuit (26) in which a part of exhaust gas is derived and is recirculated in an intake manifold (14) of a combustion chamber (10) of an internal combustion engine. A hydrogen reformer (32) enriches the recirculated exhaust gas by hydrogen. An adjustment device (38) adjusts air proportion (A) in an air and fuel mixture provided in an inlet of the combustion chamber according to a desired oxygen quantity in recirculated exhaust gas for enrichment of the recirculated exhaust gas. A cooler (30) is arranged in the recirculation circuit. An independent claim is also included for an exhaust gas recirculation method for an internal combustion engine.

Description

The present invention relates to an exhaust gas recirculation device and method for a hydrogen reformer internal combustion engine. BACKGROUND OF THE INVENTION It also relates to an engine assembly provided with such a device.

In an internal combustion engine, the four stages of the thermodynamic cycle, comprising (1) the admission of a gaseous mixture comprising combustible gas and air, (2) the compression of the gaseous mixture, (3) the expansion due to the explosion of the mixture and (4) the exhaust, successively take place in a combustion chamber of the engine. The gases introduced into this combustion chamber consist on the one hand of air and on the other hand of fuel, in proportions proportionally dosed according to the engines and ignition systems used. The gas mixture is then ignited in the combustion chamber.

[0003] It is known for spark ignition and compression ignition engines to recirculate at least a portion of the exhaust gas to the combustion chamber air intake to reduce oxide emissions. nitrogen (NOx) and fuel consumption. The invention therefore applies in particular to internal combustion engines gasoline or diesel for motor vehicles with an exhaust gas recirculation circuit in which a portion of the exhaust gas is derived from a collector exhaust and is returned to an intake manifold of the combustion chamber of the engine. This part of the exhaust gas derived in the recirculation circuit is said to be recirculated.

This type of engine has been introduced to reduce the nitrogen oxide emissions formed when the temperature in the combustion chamber becomes too high. Above 1300 ° C, the nitrogen and oxygen atoms can combine with each other in the combustion chamber to form nitrogen oxide molecules which, combined with hydrocarbon molecules (HCx) in the presence of sun, produce a polluting mist.

The amount of nitrogen oxide can be reduced by reducing the combustion temperature, in particular by recirculating exhaust gas into the combustion chamber. Indeed, the exhaust gases have already burned and are rich in di-nitrogen (N2) and carbon dioxide (CO2). The recycled exhaust gases therefore dilute the fuel load, which leads to a slowing and cooling of the combustion.

However, the recirculation of exhaust gas produces a degradation of combustion by an increase in emissions of carbonaceous products, such as unburned hydrocarbons (HC) and carbon monoxide (CO). It also produces a degradation of the stability of the engine. From a physico-chemical point of view, the flame speed decreases sharply with the presence of recycled gases and even an increase in turbulence can not overcome this lack of flame speed.

The gains made by this exhaust gas recirculation are therefore limited by the maximum amount of exhaust gas permissible by the engine.

To solve this problem, it has been shown that an addition of hydrogen-rich gas (H2) in the intake manifold of the combustion chamber, during a recirculation of the exhaust gas, makes it possible to not degrade combustion, increase engine performance without degradation of emissions of unburned hydrocarbons (HC), carbon monoxide (CO) and soot by an increase in flame speed. Since the exhaust gases are hot and loaded with water vapor, it is then possible to envisage producing hydrogen by reforming, autothermal or even endothermic, fuel. The French patent application published under number FR 2 880 657 therefore proposes an internal combustion engine comprising an exhaust gas recirculation circuit and a hydrogen reformer designed to enrich the recycled exhaust gas with hydrogen. by catalytic reforming of fuel. Thanks to this hydrogen enrichment of the recirculated gases, their quantity can be increased without damaging the operation of the engine. The efficiency of the engine is thus improved while limiting the emissions of carbon products. [ooi o] Catalytic reforming of fuel is obtained by reacting fuel molecules (of CxHy composition) with water (H 2 O) and / or air (O 2 + 3.76N 2), all products being in vapor form, to produce hydrogen according to, principally, the following three chemical reactions: - partial oxidation of the fuel: (1) CxHy + x / 2 (02 + 3.76 N2) x x CO + y / 2 H2 + x / 2 3.76 N2 - fuel vapor reforming: (2) CxHy + x H2W x x CO + (x + y / 2) H2 - gas reaction to water: (3) CO + xH20uCO2 + H2 The preferred path for the production of hydrogen remains that of the reactions (2) and (3) because these two reactions are endothermic while the reaction (1) is exothermic. Indeed, the reactions (2) and (3) do not induce a penalty of overconsumption of fuel in the process of obtaining hydrogen. In addition, the reaction (2) is particularly favored by high temperatures and an excess of water vapor. So we try at least to balance the energy consumption of the partial oxidation of the fuel with the other two reactions to achieve autothermal operation.

The hydrogen reformer described in document FR 2 880 657 comprises a device for injecting fuel and water into the reforming circuit. It does not provide air injection, assuming that air is already present in the exhaust. However, this air is not always sufficient and an addition of air may be necessary during phases of low temperature operation, regeneration or priming.

In these situations, it may therefore be useful to provide an additional injection of air into the injection device of the hydrogen reformer. However, the use of this additional injection of air is quite problematic in terms of cost and implantation.

In order to better take advantage of the advantages in terms of depollution that a hydrogen reformer exhaust gas recirculation device provides, it may be desirable to provide a device which makes it possible to overcome the abovementioned problems and constraints.

The invention therefore relates to an exhaust gas recirculation device for an internal combustion engine, comprising a recirculation circuit in which a portion of the exhaust gas is derived and returned to an intake manifold. a combustion chamber of the engine, and a hydrogen reformer designed to enrich the recirculated exhaust gas with hydrogen, characterized in that it comprises a device for adjusting the proportion of air of a mixture of air and fuel supplied at the inlet of the combustion chamber according to a desired amount of oxygen in the recirculated exhaust gas for enrichment by the hydrogen reformer.

Thus, without requiring the addition of an additional injection of air in the hydrogen reformer, a device according to the invention can adjust the amount of air present in the exhaust gas recycled for optimization. catalytic reforming of fuel, enriching or depleting the mixture of air and fuel supplied as input to the combustion chamber of the engine. Indeed, it will be noted for example that a richness of 0.9 of the mixture of air and fuel supplied at the inlet of the combustion chamber does not penalize combustion but already induces about 3% of oxygen in the gases of exhaust, which is a significant amount for a good operation of the hydrogen reformer.

Optionally, an exhaust gas recirculation device according to the invention may comprise a device for detecting a quantity of air present in the exhaust gas, and the device for adjusting the proportion of the exhaust gas. The air can be controlled according to the amount of air measured by the detection device. Also optionally, the detection device is a lambda probe placed in an exhaust line of the engine between the exhaust manifold and an exhaust catalyst capable of treating the exhaust gases before their expulsion to the engine. 'outside.

Also optionally, the hydrogen reformer comprises a fuel injection device and a catalyst capable of causing a partial oxidation reaction of the injected fuel, a steam reforming reaction of the injected fuel and a reaction of gas to the water.

Also optionally, the hydrogen reformer is disposed in the recirculation circuit. Also optionally, a control valve of the amount of recirculated exhaust gas is disposed in the recirculation circuit downstream of the hydrogen reformer in the direction of gas flow.

Also optionally, a cooling device is disposed in the recirculation circuit. Also optionally, the cooling device is disposed downstream of the hydrogen reformer in the direction of gas flow.

The invention also relates to an internal combustion engine assembly comprising a combustion chamber, an intake manifold of the combustion chamber, an exhaust manifold of the combustion chamber, and a recirculation device of exhaust gas as defined above.

Finally, the invention also relates to an exhaust gas recirculation process for an internal combustion engine, comprising a bypass step, using a recirculation circuit, of a part of the gases. exhaust system from an exhaust manifold to an intake manifold of a combustion chamber of the engine, and a stage of hydrogen enrichment of the recirculated exhaust gas, characterized in that it comprises in in addition to a step of adjusting the proportion of air of a mixture of air and fuel supplied at the inlet of the combustion chamber as a function of a desired amount of oxygen in the recirculated exhaust gas for their enrichment in hydrogen. The invention will be better understood from the description which follows, given solely by way of example and with reference to the accompanying drawing in which Figure 1 is a schematic representation of a gas recirculation engine assembly. exhaust according to one embodiment of the invention. The internal combustion engine assembly shown in Figure 1 comprises an internal combustion engine comprising a combustion chamber 10 with four cylinders 121, 122, 123, 124. This engine is for example a gasoline engine, but the The invention also applies to a diesel engine. This engine further comprises an intake manifold 14 and an exhaust manifold 16 providing exhaust gas to an exhaust line 18 of the engine.

The exhaust line 18 comprises an exhaust catalyst 20 adapted to treat the exhaust gases before their expulsion to the outside atmosphere, in known manner. It may also comprise, upstream of the exhaust catalyst 20 in the direction of gas flow, a device 22 for detecting an amount of air present in the exhaust gas. This detection device 22 is for example an exhaust probe, generally referred to as a lambda probe.

The intake manifold 14 is supplied with combustion gas by a line 24 for supplying fresh air A from outside, generally called the intake line. A fuel injection is also introduced into the combustion chamber 10, generally by an injection nozzle (not shown).

The engine assembly of Figure 1 further comprises a recirculation circuit 26 in which a portion of the exhaust gas is derived from the exhaust manifold 16 of the combustion chamber 10 and is returned to the collector of admission 14. It may further comprise a supercharging device comprising a turbocharger not shown in this schematic representation and the recirculation circuit 26 may be at high temperature and high pressure or low temperature and low pressure depending on where it connects to collectors exhaust system 16 and intake 14. The gases recycled by the recirculation circuit 26 are mixed with the fresh air A entering the intake manifold 14.

It will be noted that the lambda probe 22 is disposed downstream of the recirculation circuit 26 in the direction of flow of the exhaust gas.

In a conventional manner, the flow rate of the gases flowing in this recirculation circuit 26, and therefore the composition of the fresh air / recycled gas mixture, is regulated by a valve 28 disposed in the recirculation circuit 26. It is the effect of precisely controlling the flow rate of the recycled exhaust gas: a too high flow rate causes a loss of engine power, while too low a flow rate leads to over-emission of nitrogen oxides.

The recirculation circuit 26 may also include a cooler 30 such as a heat exchanger tube exchanging heat with the engine coolant, so as not to introduce too hot recycled gas in the combustion chamber 10 , which would result in a loss of volumetric efficiency.

Finally, the recirculation circuit 26 comprises a hydrogen reformer 32 designed to enrich hydrogen recycled exhaust gas.

More specifically, this hydrogen reformer 32 comprises a fuel injection device 34 and a catalyst 36 capable of causing a partial oxidation reaction of the injected fuel C (equation 1), a fuel vapor reforming reaction. injected C (equation 2) and a gas reaction to water (equation 3).

To inject the fuel C into the gaseous state in the recirculation circuit 26, the injection device 34 further comprises a device, including an electrical device, for heating T of this fuel C. The catalyst 36 is conventional type and will not be detailed: it may include in particular one or two catalysis modules to cause the above three reactions. Optionally not shown, the injection device 34 could be adapted for the additional injection of steam if it was not always sufficient in the recycled gas.

The hydrogen reformer 32 is disposed in the recirculation circuit 26, upstream of the cooler 30. Indeed, it is advantageous to keep the temperature of the exhaust gas in the catalyst 36 as much as possible. for the same reason disposed upstream of the regulating valve 28, in order to avoid any relaxation of the gases penalizing the temperature even more.

To optimize the partial oxidation reaction of the injected fuel C in the catalyst 36, the amount of oxygen present in the recycled gas is regulated by an adjustment of the richness of the mixture of air and fuel supplied at the inlet of the the combustion chamber 10.

To this end, the motor assembly shown in Figure 1 comprises a device 38 for adjusting the proportion of air of the mixture of air and fuel supplied at the entrance of the combustion chamber. This device 38 is more particularly a device for adjusting the quantity of air A admitted into the supply line 24. It is therefore controlled according to the quantity of oxygen desired in the recirculation circuit 26 for a hydrogen enrichment. optimal.

Optionally, this adjustment device 38 is connected to the lambda probe 22 for an adjustment of the amount of air A to be admitted depending on the amount of air measured in the exhaust gas by the lambda probe. 22.

An exhaust gas recirculation method implemented by the motor assembly described above therefore comprises the following steps: derivation El, using the recirculation circuit 26, a part of the exhaust gas from the exhaust manifold 16 to the intake manifold 14 of the combustion chamber 10 of the engine, hydrogen enrichment E2 of the recycled exhaust gas in the catalytic fuel reformer 32 of the recirculation circuit 26, and setting E3 of the proportion of air of the mixture of air and fuel supplied at the inlet of the combustion chamber 10 as a function of the quantity of oxygen desired in the recycled exhaust gases for their enrichment in hydrogen by the reformer 32.

It is clear that the recirculation device described above optimizes the hydrogen enrichment of the recycled gas in all phases of engine operation, without the need to add an additional injection of air in the reformer hydrogen. This therefore allows without additional complication to significantly increase the proportion of recycled gas in the combustion chamber 10 for an optimization of fuel consumption and thus an optimization of the CO2 emission, and a reduction of pollutant NOx emissions. These polluting emissions are so reduced that we can do without a specific system for the cleanup of NOx, even with a lean mixture supplied at the entrance of the combustion chamber.

In addition, the adjustment of the amount of oxygen added to the exhaust gas and therefore in the recycled portion via a mixture of the richness of the mixture supplied at the inlet of the engine combustion chamber is not only simple and little expensive to implement, but is also easy to control. This control is for example achieved by a control of the amount of fresh air and fuel mass injected, without the need to measure anything at the recirculation circuit 26 and the inlet of the reformer 32. 0044] Note also that the invention is not limited to the embodiment described above. It will be apparent to those skilled in the art that various modifications can be made to the embodiment described above, in the light of the teaching that has just been disclosed. In the following claims, the terms used are not to be construed as limiting the claims to the embodiment set forth in this description, but must be interpreted to include all the equivalents that the claims are intended to cover by reason of their formulation and whose prediction is within the reach of those skilled in the art by applying his general knowledge to the implementation of the teaching which has just been disclosed to him.

Claims (10)

REVENDICATIONS1. An exhaust gas recirculation device for an internal combustion engine, comprising: a recirculation circuit (22) in which part of the exhaust gas is diverted and returned to an intake manifold (14) of a combustion chamber; combustion (10) of the engine; a hydrogen reformer (32) designed to enrich in hydrogen the recirculated exhaust gas, characterized in that it comprises a device (38) for adjusting the proportion of air (A) of an air mixture and fuel supplied at the inlet of the combustion chamber (10) as a function of a desired amount of oxygen in the recirculated exhaust gas for enrichment by the hydrogen reformer (32). Exhaust gas recirculation device according to claim 1, comprising a device (22) for detecting a quantity of air present in the exhaust gas and wherein the device (38) for adjusting the proportion of air is controlled according to the amount of air measured by the detection device (22). The exhaust gas recirculation device according to claim 2, wherein the detection device (22) is a lambda probe placed in an exhaust line (18) of the engine between an exhaust manifold (16) of the engine and an exhaust catalyst (20) adapted to treat the exhaust gases before their expulsion to the outside. An exhaust gas recirculation device according to any one of claims 1 to 3, wherein the hydrogen reformer (32) comprises a fuel injection device (34) (34) and a catalyst (36). ) capable of causing a partial oxidation reaction of the injected fuel (C), a steam reforming reaction of the injected fuel (C) and a gas reaction with water. 5. Exhaust gas recirculation device according to any one of claims 1 to 4, wherein the hydrogen reformer (32) is disposed in the recirculation circuit (26). The exhaust gas recirculation device according to claim 5, wherein a circulating exhaust gas control valve (28) is disposed in the recirculation circuit (26) downstream of the hydrogen reformer ( 32) in the direction of gas flow. 7. Exhaust gas recirculation device according to any one of claims 1 to 6, wherein a cooling device (30) is disposed in the recirculation circuit (26). 8. exhaust gas recirculation device according to claims 5 and 7, wherein the cooling device (30) is disposed downstream of the hydrogen reformer (32) in the direction of flow of gas. 9. Internal combustion engine assembly comprising a combustion chamber (10), an intake manifold (14) of the combustion chamber, an exhaust manifold (16) of the combustion chamber, and a recirculation device of exhaust gas according to one of claims 1 to 8. 10. Process for the recirculation of exhaust gas for an internal combustion engine, comprising a step (E1) of bypassing, with the aid of a recirculation circuit (26), a part of the exhaust gases from an exhaust manifold (16) to an intake manifold (14) of a combustion chamber (10) of the engine, and a step (E2) for hydrogen enrichment of the recirculated exhaust gas, characterized in that it further comprises a step (E3) for adjusting the proportion of air of a mixture of air and fuel supplied at the inlet of the combustion chamber (10) according to a quantity of desired oxygen in the recirculated exhaust gas for hydrogen enrichment.