FR2892766A1 - Propulsion system for motor vehicle e.g. commercial vehicle, has logic controller triggering injection of required quantity when ratio between required quantity and nitrogen oxide quantity is less than triggering threshold - Google Patents

Abstract

The system has a logic controller (6) calculating fuel quantity required for attaining a proportion equal to stoichiometric proportion with respect to the nitrogen oxide quantity. The controller triggers the injection of a required quantity when the ratio between the required quantity and the nitrogen oxide quantity is less than a triggering threshold. The controller receives information about the speed of a diesel type thermal engine (1) and injection in the combustion chambers of the engine. An independent claim is also included for a propulsion method.

Description

1 Nitrogen oxides treatment device for exhaust gas from

motor vehicle.

  The invention relates to the field of motorization systems, especially motor vehicles. The invention particularly relates to the field of devices and methods for the catalytic treatment of nitrogen oxides (NOx) in the exhaust gases of combustion engines. In a known manner, nitrogen oxides cause respiratory infections and allergies and play a role in influencing the formation of fumes and acid rain. Most countries have imposed standards limiting the emission of nitrogen oxides in vehicles. These standards generally specify a different threshold for passenger cars, for commercial vehicles, and for industrial engines. Each of these categories covers a wide variety of engines. For example, in private vehicles, there are gasoline-powered vehicles and diesel-powered vehicles. There are small urban vehicles and four-wheel drive vehicles. Obtaining the same threshold of pollutant emissions by a high-power engine requires treatment NOx nitrogen oxides more advanced than obtaining the same threshold of polluting emissions by a small engine. In addition, the economic pressure to offer inexpensive nitrogen oxide treatment devices is more severe on small urban vehicles than on luxury vehicles. Several technologies have been developed to reduce nitrogen oxides NOx emissions. Passive methods including catalysts on which the exhaust gases are passed and active methods using

  2 complex processes, such as electrochemical catalysts or photocatalytic approaches. Passive catalytic methods are commonly used for gasoline vehicles. A three-way catalyst can treat both oxides of nitrogen, carbon, and unburned hydrocarbons. The exhaust gases from the combustion chambers of gasoline engines are generally rich in reducing elements, such as hydrocarbons and carbon monoxide, so that, thanks to the three-way catalyst, the nitrogen oxides (NOx) emitted are reduced. in gaseous nitrogen. These three-way catalysts have the advantage of being cheap. Diesel type engines have combustion chambers fed with excess air mixture. The exhaust gases from the engine are therefore poor in reducing agents. The use of three-way catalysts is not possible because the reduction efficiency of these catalysts decreases rapidly in the presence of oxygen. It has been proposed NOx traps for the treatment of nitrogen oxides in the case of exhaust gases low in reducing agents. Such NOx traps are described in particular in patent applications EP 0 573 672 A1 (TOYOTA) and EP 1 079 084 A2 (TOYOTA).

  During normal vehicle operation, exhaust gases pass through the NOx trap where catalysts generally comprise alkaline or alkaline earth elements and storage compounds. These catalysts promote the oxidation of nitric oxide NO to nitrogen dioxide NO2 and the conversion of nitrogen dioxide NO2 to nitrate depositing on a monolith. During normal engine operation, NOx is absorbed by the NOX trap. Periodically, stored NOx are destocked. During this destocking phase, the proportion of exhaust gas reducers is greater than the stoichiometric proportion (so-called rich mixture). Control of such a NOx treatment is a complex process, in which the destocking phase must be detected and the amount of hydrocarbons injected must be increased. In particular, the storage components of the NOx trap are particularly sensitive to sulfur. It was necessary to develop in parallel the NOx storage process, desulfation steps at regular intervals. The patent application WO 02/31325 (CORNING Inc.) describes a method for reducing nitrogen oxides in the exhaust gases of diesel type engines. This method involves continuously injecting fuel into the exhaust gas and passing the mixture of fuel and exhaust gas through a catalyst to reduce the NOx of the exhaust gas to nitrogen gas. The disadvantage of such a process is to cause additional fuel consumption. Patent Application US 2004/0083722 (FORD) describes an improvement in the conversion of NOx by a catalyst in which the amount of fuel injected upstream of the catalyst is corrected with respect to a quantity injected when the engine is in steady state to take into account phases of acceleration and deceleration of the engine. The catalysts mentioned are of the ALNC or SCR type which continuously reduce NOx emissions by means of an active injection of reducing agents (hydrocarbons or urea). Despite the improvement, the proportion injected in the steady state is in the example represented by ten times more reductant than NOx. Despite an improvement, such a system remains very fuel-efficient. The invention proposes a motorization system, especially for a motor vehicle, and a process for treating the exhaust gases of the motorization system, which remedy these

  4 disadvantages and in particular that offer a cheap treatment of nitrogen oxides NOx, reducing the overconsumption of fuel. According to one embodiment of the invention, the motorization system, in particular for a motor vehicle, comprises a heat engine, a catalyst for reducing the nitrogen oxides NOx of the exhaust gases of the engine, an additional fuel injector located in upstream of the catalyst, a means for determining the amount of nitrogen oxides NOx from the engine, a means for determining the amount of fuel required to reach a proportion less than or substantially equal to the stoichiometric proportion relative to the amount of NOx nitrogen oxides, and means for triggering the injection of said necessary amount when the ratio between said amount required on the amount of NOx nitrogen oxides is less than a trigger threshold.

  It is conceivable that such a motorization system, comprising a NOx reduction catalyst traversed by a substantially stoichiometric mixture, can use a cheap catalyst, for example of the three-way catalyst type known for gasoline vehicles. In addition, the additional fuel consumption is suppressed as long as the ratio between the quantity to be injected and the amount of NOx is less than a triggering threshold. In other words, the additional injection is stopped when the amount of NOx present in the exhaust gas has not reached the authorized limit, for example by standards. In the case of small urban vehicles, this limit is generally exceeded only during certain phases of the vehicle's operation, such as a cold engine, a phase of strong acceleration or a heavy load of the engine. By means of adjusting the amount of fuel injected to obtain the stoichiometric proportion, this amount of fuel is limited. In fact, the operating phases of the engine with high NOx emission also correspond to phases in which the exhaust gases are richer than in the established regime for unburned hydrocarbons and reducing agents. The amount of diesel necessary to inject to reach stoichiometry is even lower. Advantageously, the exhaust gases upstream of the additional injector are poor in reducing agents. The engine may be of diesel type and the fuel injected by the additional injector of the gas oil type. According to another embodiment, the means for determining the amount of NOx comprises a computer able to receive engine speed and engine speed information. injection into the combustion chambers of the engine and compare this information to data stored in a memory. Advantageously, this means comprises, downstream of the engine and upstream of the additional injector, a device for measuring the richness of the exhaust gases. According to another embodiment, the motorization system comprises a particle filter upstream or downstream of the catalyst or integrating the catalyst. The additional injector may be placed upstream of the particulate filter and operated to regenerate the particulate filter. Advantageously, the motorization system comprises a second device for measuring the richness of reducers downstream of the additional injector and upstream of the catalyst. It may comprise a temperature probe upstream or downstream of the particulate filter, and / or a pressure sensor upstream or downstream of the particulate filter. According to another embodiment of the invention, the motorization method, in particular of a motor vehicle, comprises a stage in which the exhaust gases of a heat engine are treated.

  6 injecting hydrocarbons into the exhaust line upstream of a NOx reduction catalyst, the amount of NOx present in the exhaust gas is determined, the injection of the hydrocarbons is triggered when a NOx quantity threshold is reached and the amount injected is adjusted so that the amount of reducing agents is substantially stoichiometric with respect to the amount of NOx present in the exhaust gas. Other features and advantages of the invention will become apparent on reading the detailed description of some embodiments taken as non-limiting examples and illustrated by the accompanying drawing, in which the single figure is a schematic representation of the components of FIG. a motorization system according to the invention. As illustrated in the figure, the engine system of a motor vehicle comprises a diesel engine 1 and an exhaust line 2 comprising a first section 2a immediately downstream of the engine 1 and a second section 2b immediately downstream of the first section 2a. The figure illustrates four embodiments differing from each other by their second section 2b of exhaust line 2, as shown schematically by the dashed line. In the first embodiment, the first section 2a of the exhaust line 2 comprises a richness probe 3 of the lambda type, or oxygen sensor, sensitive to the proportion of oxygen inside the exhaust gases from of the heat engine 1. An additional injector 4 is inserted in the first section 2a downstream of the richness sensor 3. The second section 2b of the exhaust line 2 of the first embodiment comprises a catalyst 5. The motorization system also includes a calculator 6.

  The operation of this first embodiment will now be described. The diesel engine type is equipped with a speed sensor 7 of the crankshaft not shown, a sensor 8 of the injection conditions of the main injectors of the engine 1. This sensor may be for example a sensor of the position of the engine. accelerator or a sensor of the control circuits of the main injectors. Optionally, the engine is equipped with a temperature sensor of the combustion chambers. The information coming from these different sensors is sent to the computer 6. Similarly, information on the type of fuel in use can be entered and sent to the computer 6. A complete map of the various operating speeds of the engine according to the characteristics of the fuel in use, is stored in the computer 6. This allows the computer to determine the operating speed of the engine and to deduce, in real time, the proportion of nitrogen oxides escaping from the engines. combustion chambers of the engine 1 as well as the amount of unburned hydrocarbons or reducing components escaping from the combustion chambers of the engine. The computer 6 can then determine the amount of reducing elements necessary to be injected by the additional injector 4 so that the gaseous mixture thus modified has a stoichiometric proportion between the amount of oxidizing elements and the amount of reducing elements. When the computer 6 actuates the additional injector 4, and triggers the injection of said necessary amount, the mixture passing through the catalyst 5 has the desired proportion of stoichiometry. The conditions under which the injection of diesel fuel into the exhaust line is triggered (amount of NOx emitted by the engine and the richness of the gas mixture in the combustion chamber) can

  8 to be modified to adapt, for example, to changes in the legislation in force. It corresponds to the proportion of NOx that will be reduced by the action of the catalyst 5 before escaping from the exhaust line 2. The proportion of desired stoichiometry may also correspond to a maximum amount of NOx that will not be reduced by the catalyst 5. When the computer 6 does not actuate the additional injector 4, all of the NOx from the heat engine 1 passes through the catalyst 5, and it has a very reduced reduction efficiency due to poverty reducer mixture.

  In a variant, the desired stoichiometric proportion is equal to unity, so that all the NOx present in the exhaust gas can be treated by the catalyst 5. In another variant, this proportion is less than unit, which saves additional fuel consumed while treating some of the NOx present in the exhaust gas so as to comply with the standards in force. The computer also has in memory a trigger threshold of the injector. The computer receives in real time the engine speed data and calculates in real time both the amount of NOx present in the exhaust gas from the engine and the amount of fuel that achieves the desired stoichiometric proportion. When the ratio between the necessary quantity of fuel and the quantity of nitrogen oxides is less than the triggering threshold, the computer actuates the additional injector, and when the ratio is greater than the threshold, the additional injection is not controlled. A ratio greater than the trigger threshold corresponds to a quantity of NOx coming from engine 1 which would require too much additional fuel to be treated on the catalyst.

  According to another embodiment of the invention, the richness of the exhaust gas at the engine output is not evaluated by comparing manufacturer data with engine speed measurements, but is directly measured by the wealth probe. The calculator 6 calculates the quantity of fuel required to reach the desired stoichiometric proportion and compares the ratio of the quantity required to the estimated amount of NOx and triggers the additional injection if this ratio is below the triggering threshold. This embodiment makes it possible, by combining measured data and calculated data in real time, to have a better evaluation of the quantity necessary to be injected. It can also be used to compare calculated predictions and measured quantities so as to detect any anomalies in the sensor or calculation system. The reducer injected by the additional injector 4 is not necessarily identical to the fuel used by the heat engine 1. Nevertheless, the fact of using the same fuel makes it possible to dispense with an additional reservoir. The heat engine is preferably a diesel-type engine and the fuel injected by the additional diesel-type injector. In diesel type engines, it is common that the gas admission devices in the combustion chambers and the injection devices in the combustion chambers are adjusted so that the combustion chambers are saturated with oxygen. Thus, the exhaust gases from the diesel engine are generally oxidizing.

  Diesel engines, operating with a type of combustion known as homogeneous combustion, have exhaust gases with a high reductant content and limited NOx emissions, so that the quantity of additional fuel to be injected remains low.

  The method and motorization system of the invention may be compatible with an internal combustion engine using gasoline whose exhaust gases are low in reducing compounds. For example, in stratified charge engines, although the amount of NOx produced by the engine has been reduced by a lowered combustion temperature, the process of the invention nevertheless makes it possible to combine the advantages of a three-way catalyst and a very low fuel consumption. The injector 4 is additional in the sense that it is specific and is added to the unrepresented main injectors of the heat engine 1, it can be located directly at the inlet of the catalytic converter 5. The injector 4 can also be made by the main injectors, it is then additional in the sense that the injection sequence concerned by the triggering means of the invention is additional to the normal injection cycle of the engine 1. This additional injection can take place at the beginning of the expulsion of the gases from the combustion chamber. We will now describe the particularly advantageous combination of such a motorization system with the use of particulate filters. According to the second embodiment illustrated in the figure, the second section 2b of the exhaust line comprises, in the direction of the gas flow: a second richness probe 10, the catalyst 5, an upstream temperature sensor 11 and pressure, a particulate filter 12 and a downstream sensor 13 of temperature and pressure. The particulate filter 12 is responsible for retaining the soot and unburned particles emitted by the engine 1. The particulate filter 12 may be catalyzed or not. The second wealth probe 10 downstream of the injector

  11 additional 4 allows controlling the calculation of the amount to be injected to achieve stoichiometric conditions during normal operation of the engine 1. The additional injector 4, the second lambda probe 10 and the temperature sensors 11 and 13 are also used for the regeneration of the particulate filter. An exothermic reaction is obtained in the catalyst 5 to heat the exhaust gas entering the particulate filter at a temperature to burn soot and filtered particles. With a catalyzed particulate filter, the temperature of the exhaust gas necessary to achieve regeneration is lower than with an uncatalyzed particulate filter. In the third embodiment illustrated in the figure, the second section 2b of the exhaust line 2 comprises, in the gas flow direction, the upstream temperature and / or pressure sensor 11, the particulate filter 12, the downstream sensor 13 of temperature and / or pressure, the second richness probe 10 and the catalyst 5. In the fourth embodiment illustrated in the figure, the second section 2b of the exhaust line 2 comprises in the direction of the flow of the gases, the second richness probe 10, the upstream sensor 11, a catalyst 5 integrated in the particulate filter 12 and the downstream sensor 13. The fourth embodiment has the advantage of reducing the number of components to be installed on On the other hand, the second and third embodiments allow more flexibility in the implementation of the various components.

  In each of the three particulate filter embodiments 12, it may be made of silicon carbide, cordierite or any other ceramic or metal structure for filtering the particles.

  The means for determining the amount of nitrogen oxides from the engine 1 may be a calculator 6 comparing the real-time engine speed measurements with a map of this operation pre-stored in memory.

  The means for determining the amount of fuel necessary to reach a stoichiometric proportion may also be a calculation comparing real-time measurements with a prerecorded cartography or be the second wealth probe 10. The invention makes it possible to achieve, at the expense of controlled overconsumption, the targeted NOx treatment efficiency with a lower development cost and development of the motorization system than for NOx trap systems. The flexibility of the process is particularly advantageous for motorization systems used on construction sites, where overconsumption is not the key criterion and where the priority is to completely treat the nitrogen oxides. To adapt the motorization system to site applications, simply modify the trip threshold.

Claims (11)

  1-Motorization system, especially for a motor vehicle, comprising a heat engine (1), a catalyst (5) for reducing the nitrogen oxides NOx of the exhaust gases of the engine (1), an additional injector (4) of fuel located upstream of the catalyst (5) and means (6, 3) for determining the amount of nitrogen oxides NOx from the engine (1), characterized in that it comprises a means (6, 10) ) determining the amount of fuel necessary to reach a proportion less than or substantially equal to the stoichiometric proportion relative to the amount of NOx nitrogen oxides, and means (6) for triggering the injection of the said necessary quantity when the ratio between said amount required on the amount of NOx nitrogen oxides is less than a trigger threshold.   2-motorization system according to claim 1, wherein the exhaust gas upstream of the additional injector (4) are poor in reducing agents.   3-motorization system according to claim 1 or 2, wherein the engine (1) is a diesel-type internal combustion engine and the fuel injected by the additional injector (4) is of the diesel type.   4-motorization system according to any one of the preceding claims, wherein the means for determining the amount of NOx comprises a computer (6) adapted to receive engine speed information (1) and injection into the chambers of combustion of the engine (1) and to compare this information with data stored in a memory.   5-motorization system according to one of the preceding claims, wherein the means for determining the amount of 14 NOx comprises, downstream of the engine (1) and upstream of the additional injector (4), a device (3 ) to measure the richness of the exhaust gases.   6-motorization system according to any one of the preceding claims, comprising a particle filter (12) upstream or downstream of the catalyst (5).   7-motorization system according to any one of claims 1 to 5, comprising a particulate filter (12) incorporating the catalyst (5).   8-motorization system according to claim 6 or 7, wherein the additional injector (4) is placed upstream of the particulate filter (12) and operated to regenerate the particulate filter (12).   9-motorization system according to any one of claims 6 to 8, comprising a second device (10) for measuring the richness of reducing agents downstream of the additional injector (4) and upstream of the catalyst (5).   10-motorization system according to any one of claims 6 to 9, comprising an upstream temperature sensor (11) or downstream (13) of the particulate filter (12), and / or an upstream pressure sensor ( 11) or downstream (13) of the particulate filter (12).   11-Motorization process, in particular of a motor vehicle, in which the exhaust gases of a heat engine (1) are treated by injecting hydrocarbons into the exhaust line (2a) upstream of a catalyst ( 5) NOx reduction, characterized in that it comprises a step where the amount of NOx present in the exhaust gas is determined, the injection of hydrocarbons is triggered when a NOx quantity threshold is reached and the amount injected is adjusted so that the amount of reducing agents is substantially stoichiometric with respect to the amount of NOx present in the exhaust gas.