CN101316994A - Apparatus for treating nitrogen oxides from motor vehicle exhaust - Google Patents

Abstract

The invention relates to a power system, in particular for a motor vehicle, comprising an internal combustion engine (1), a catalytic converter (5) for reducing nitrogen oxides NOx contained in the exhaust gas of said engine (1), provided An additional fuel injector (4) upstream of the catalytic converter (5) and means (6, 3) for determining the amount of nitrogen oxides NOx emitted from the engine (1), characterized in that the powertrain comprises a means (6, 10) for determining the amount of fuel required to achieve a ratio below or substantially equal to the stoichiometric ratio with respect to the amount of nitrogen oxides NOx, and for determining when said required amount is related to the amount of nitrogen oxides NOx Means (6) for triggering injection of said required quantity when the ratio of quantities is below a trigger threshold.

Description

Apparatus for treating nitrogen oxides from motor vehicle exhaust

technical field

The invention relates to the field of powertrains, in particular for motor vehicles. The invention relates in particular to the field of devices and methods for the catalytic treatment of nitrogen oxides (NOx) in the exhaust gases of internal combustion engines.

Background technique

Nitrogen oxides are known to cause respiratory infections and allergies, and affect the formation of smoke and acid rain. Most countries already enforce standards limiting nitrogen oxide emissions from vehicles. These standards generally specify different thresholds for private vehicles, commercial vehicles and industrial engines. In fact, each of these categories covers a wide range of engines. For example, private vehicles include vehicles with gasoline engines and vehicles with diesel engines. Private vehicles include small city vehicles and four-wheel drive vehicles. Achieving the same pollutant emission threshold for a high power engine requires enhanced treatment of nitrogen oxides NOx compared to achieving the same pollutant emission threshold for a small engine. In addition, there is greater economic pressure to provide inexpensive devices for treating nitrogen oxides in small urban vehicles than in luxury vehicles.

Several technologies have been developed to reduce emissions of nitrogen oxides NOx. In particular, a distinction is made between passive methods using catalytic converters through which the exhaust gas passes and active methods using complex processes such as electrochemical catalysis or photocatalytic methods. Passive catalytic methods are commonly used in gasoline engine vehicles. Three-way catalytic converters are used to simultaneously treat nitrogen oxides, carbon oxides and unburned hydrocarbons. Exhaust gas from a combustion chamber of a gasoline engine is generally rich in reducing components such as hydrocarbons and carbon monoxide, so exhausted nitrogen oxides (NOx) are reduced to nitrogen by using a three-way catalyst. These three-way catalytic converters have the advantage of being cheap.

The combustion chamber of a diesel engine is fed with a mixture containing excess air. The exhaust gas from the engine is thus starved of reductant. Since the reduction efficiency of these catalysts decreases rapidly in the presence of oxygen, three-way catalysts cannot be used.

In the absence of reducing agents in the exhaust, NOx traps have been proposed to treat nitrogen oxides. 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 driving of the vehicle, the exhaust gas passes through the NOx trap, where the catalytic converter generally contains alkaline or alkaline-earth elements and a storage mixture (adsorbent mixture). These catalysts facilitate the oxidation of nitrogen monoxide NO to nitrogen dioxide NO ₂ and the conversion of nitrogen dioxide NO ₂ to nitrates, which are deposited as a whole. During normal use of the engine, NOx is absorbed by the NOx trap. The stored NOx is released periodically. During this release phase, the proportion of exhaust reducing agent is higher than the stoichiometric proportion (the mixture is said to be rich). Controlling this NOx treatment is a complex process in which release phases must be detected and the amount of injected hydrocarbons must be increased. Storage mixtures for NOx traps are particularly sensitive to sulfur. Parallel to the NOx storage process, it was necessary to develop a desulfurization step at regular (time) intervals.

Patent application WO 02/31325 (Corning Inc.) describes a method for reducing nitrogen oxides in diesel engine exhaust. This method involves continuously injecting fuel into the exhaust and passing the mixture of fuel and exhaust through a catalyst so that the NOx in the exhaust is reduced to nitrogen. This procedure has the disadvantage of causing additional fuel consumption.

Patent application US 2004/0083722 (Ford) describes an improved (method of) conversion of NOx by using a catalytic converter, wherein the quantity of fuel injected upstream of the catalytic converter is corrected with reference to the quantity injected under steady-state operating conditions of the engine, The engine acceleration and deceleration phases are thus taken into account. The catalyst is of the ALNC or SCR type, which continuously reduces NOx emissions by active injection of reducing agents (hydrocarbons or urea). Despite the improvements, in the example described, the ratio of reductant to NOx injected under steady state conditions is 10 times that of NOx. Despite the improvements, such systems consume a considerable amount of fuel.

Contents of the invention

The present invention provides a power system (particularly for use in motor vehicles) and a method for treating power system exhaust gas, said system and method ameliorating said disadvantages, in particular, said system and method provide low-cost Nitrogen oxide NOx treatment reduces additional fuel consumption.

According to one embodiment of the invention, the power system, in particular for a motor vehicle, comprises an internal combustion engine, a catalytic converter for reducing nitrogen oxides NOx contained in the exhaust gas of the engine, an additional fuel injector arranged upstream of the catalytic converter, Means for determining the amount of nitrogen oxides NOx emitted from an engine, means for determining the amount of fuel required to achieve a ratio lower than or substantially equal to the stoichiometric/stoichiométrique ratio relative to the amount of nitrogen oxides NOx , and means for triggering the injection of said required amount when the ratio of said required amount to the amount of nitrogen oxides NOx is less than a trigger threshold.

It will be appreciated that such a power system comprising a NOx reduction catalyst for the passage of a substantially stoichiometric mixture may utilize an inexpensive catalyst such as a three-way catalyst type known for gasoline engine vehicles. In addition, additional fuel consumption can be avoided as long as the ratio of the quantity to be injected to the quantity of NOx is below a trigger threshold. In other words, when the amount of NOx present in the exhaust gas does not reach a permissible (regulated) limit, for example a limit permissible by a standard, no additional injection takes place. In the case of small urban vehicles, this limit is generally exceeded only during certain operating phases of the vehicle, such as those with a cold engine, high acceleration or high engine load. Said fuel quantity is limited due to the (used) means for adjusting the injected fuel quantity to a stoichiometric ratio. In fact, engine operating phases with higher NOx emissions also correspond to phases in which the exhaust gas is richer in unburned hydrocarbons and reducing agents than under steady-state conditions. (At this time) the amount of diesel fuel that needs to be injected to achieve the stoichiometric ratio is even lower.

Advantageously, the exhaust gas upstream of the additional injector is devoid of reducing agent. The engine may be of diesel type and the fuel injected by the additional injector may be diesel fuel.

According to another embodiment, the means for determining the amount of NOx comprise a computer adapted to receive data on engine speed and data on injection into the combustion chamber of the engine and to compare these data with stored data. Advantageously, the device comprises means for measuring the exhaust fuel-air ratio downstream of the engine and upstream of the additional injector.

According to another embodiment, the power system comprises a particle filter upstream or downstream of the catalyst, or in combination with the catalyst. Additional injectors may be positioned upstream of the particulate filter and may be activated to regenerate the particulate filter.

Advantageously, the power system comprises a second instrument for measuring the concentration of reductant downstream of the additional injector and upstream of the catalyst. The second instrument may comprise a temperature sensor 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 power method, in particular for motor vehicles, comprises a step in which the exhaust gas from the internal combustion engine is treated by injecting hydrocarbons into the exhaust line upstream of the NOx reduction catalyst, and determine the amount of NOx present in the exhaust gas upstream of the injector, trigger hydrocarbon injection when a threshold value for the amount of NOx is reached, adjust the injection amount so that the amount of reducing agent relative to the amount of NOx present in the exhaust gas is lower than Or basically equal to the theoretical ratio.

Description of drawings

Other characteristics and advantages of the invention will emerge from reading the detailed description of a number of non-limiting exemplary embodiments shown in the accompanying drawing, the only drawing showing a number of schematic diagrams of a power system according to the invention .

Detailed ways

As shown in the figure, the motor vehicle power system includes a diesel-type internal combustion engine 1 and an exhaust pipe 2, which includes a first part 2a immediately downstream of the internal combustion engine 1 and a second part immediately downstream of the first part 2a. Two part 2b.

As schematically indicated by dashed lines, the figure shows four embodiments which differ from each other with respect to the second part 2 b of the exhaust gas line 2 .

In a first embodiment, the first part 2a of the exhaust gas line 2 includes a fuel-air ratio sensor 3 of the lambda (λ) type, or an oxygen sensor sensitive to the proportion of oxygen in the exhaust gas from the internal combustion engine 1 . An additional injector 4 is inserted downstream of the fuel-air ratio sensor 3 in the first part 2 a. The second part 2 b of the exhaust line 2 of the first embodiment includes a catalytic converter 5 . The power system also includes a computer 6 .

The operation of the first embodiment will now be described. The diesel internal combustion engine is equipped with a crankshaft speed sensor 7 (not shown), a sensor 8 for detecting the injection condition of the main injection of the engine 1 . For example, the sensor may be an accelerator position sensor or a sensor in the main injection control loop. Optionally, the engine is equipped with a combustion chamber temperature sensor. The data from these sensors are passed to the computer 6 . Likewise, data on the type of fuel used can be entered and communicated to the computer 6 . A complete map of the operating speed of the different engines in relation to the properties of the fuel used is stored in the computer 6 . This enables the computer to determine the engine speed and, in real time, the proportion of nitrogen oxides escaping from the combustion chamber of the engine 1 and the amount of unburned hydrocarbons or reducing components escaping from the combustion chamber of the engine 1 . The computer 6 can then determine the amount of reducing component that needs to be injected by the additional injector 4 so that the ratio between the amount of oxidizing component and the amount of reducing component of the gas mixture thus corrected is a stoichiometric ratio.

When the computer 6 activates the additional injector 4 and triggers the injection of said required quantity, the mixture passing through the catalyst 5 has the desired stoichiometric ratio. The conditions triggering diesel injection into the exhaust line (the amount of NOx expelled by the engine and the fuel-to-air ratio of the gas mixture in the combustion chamber) can be modified to accommodate, for example, changes in the regulations in force. This condition corresponds to the proportion of NOx that is reduced by the action of the catalytic converter 5 before being discharged from the exhaust gas line 2 . The desired stoichiometric ratio can also correspond to the maximum amount of NOx that is not reduced by the catalytic converter 5 . When the computer 6 does not actuate the additional injector 4, all the NOx emitted from the internal combustion engine 1 passes through the catalyst 5, the reduction efficiency of the catalyst 5 being significantly reduced due to the low content of reducing agent in the mixture.

In a variant, the desired stoichiometric ratio is equal to “1” so that all the NOx present in the exhaust gas can be treated by the catalytic converter 5 . In another variant, the ratio is less than "1", which helps to save the additional fuel consumed when treating the fraction of NOx present in the exhaust gas to meet current standards.

The computer also stores injector trigger thresholds. The computer receives real-time data on engine speed and also calculates in real time the amount of NOx present in the exhaust from the engine and the amount of fuel required to achieve the desired stoichiometric ratio. The computer actuates additional injectors when the ratio of required fuel quantity to nitrogen oxides is below a trigger threshold, and does not command additional injections when the ratio is above the threshold. A ratio above the trigger threshold corresponds to an amount of NOx emitted from the engine 1 which would require very much additional fuel for treatment at the catalyst.

According to another embodiment of the invention, the fuel-air ratio of the exhaust gas leaving the engine is not determined by comparing the manufacturer's data with engine speed measurements, but is measured directly by the fuel-air ratio sensor 3 . The computer 6 calculates the amount of fuel required to achieve the desired stoichiometric ratio, compares the ratio of the required amount to the estimated NOx amount, and triggers additional injection if the ratio is below a trigger threshold. This embodiment is used to better estimate the required amount to be injected by combining real-time measurement data and calculation data. This is also used to compare calculated predetermined quantities with measured quantities to detect any anomalies in the sensors or computing system.

The reducing agent injected by the auxiliary injector 4 does not have to be the same fuel as the fuel used by the internal combustion engine 1 . However, the use of the same fuel avoids the need for additional fuel tanks. The internal combustion engine is preferably a diesel engine, the fuel injected by the additional injector being diesel fuel. In a diesel engine, the intake arrangement in the combustion chamber and the injection arrangement in the combustion chamber are usually arranged such that the combustion chamber is filled with oxygen. Exhaust gases from diesel engines are therefore generally oxidizing.

Diesel engines operating with a combustion type called homogeneous charge combustion have a high concentration of reducing agents in the exhaust and limited NOx emissions, so that the amount of additional fuel to be injected is kept low.

The power method and system of the present invention are compatible with gasoline-powered internal combustion engines where the exhaust gas is devoid of reducing components. For example, in a stratified charge combustion engine, the method of the present invention can be used to combine the advantages of a three-way catalyst with the advantages of very low fuel consumption despite lower combustion temperatures reducing the amount of NOx produced by the engine.

The injector 4 is attached in such a way that the injector 4 is dedicated and attached to a main injector (not shown) of the internal combustion engine 1 . The injector 4 may be arranged in close proximity to the inlet of the catalyst canister 5 . The injector 4 can also be formed by a main injector, in which case the injector 4 is added in such a way that the injection sequence referred to by the triggering device of the invention is in addition to the usual injection cycle of the engine 1 . This additional injection may occur as gases begin to be expelled from the combustion chamber.

A particularly advantageous combination of the use of a particle filter with such a power system is now described.

According to the second embodiment as shown in the figure, the second part 2b of the exhaust gas line includes along the direction of gas flow: a second fuel-air ratio sensor 10, a catalytic converter 5, an upstream temperature and pressure sensor 11, a particulate filter 12 and Downstream temperature and pressure sensor 13. The particulate filter 12 serves to trap soot and unburned particulates exhausted from the engine 1 . The particulate filter 12 may be catalyzed or non-catalyzed. During normal operation of the engine 1, a second fuel-air ratio sensor 10 downstream of the additional injector 4 is used to control the calculation of the quantity to be injected to achieve stoichiometric conditions. The additional injector 4, the second lambda-type sensor 10 and the temperature sensors 11 and 13 are also used to regenerate the particle filter. An exothermic reaction occurs in the catalyst 5 to heat the exhaust gas entering the particulate filter at a temperature sufficient to combust the soot and filtered particles. With catalyzed particulate filters, the exhaust gas temperature required to achieve regeneration is lower than with non-catalyzed particulate filters.

In the third embodiment shown in the figure, the second part 2b of the exhaust pipeline 2 includes along the gas flow direction: an upstream temperature and/or pressure sensor 11, a particle filter 12, a downstream temperature and/or pressure sensor 13, The second fuel-air ratio sensor 10 and the catalytic converter 5 .

In the fourth embodiment shown in the figure, the second part 2b of the exhaust pipe 2 includes along the gas flow direction: a second fuel-air ratio sensor 10, an upstream sensor 11, and a catalytic converter 5 combined with a particle filter 12 and downstream sensor 13. The fourth embodiment has an advantage of reducing the number of components mounted on the exhaust line 2 . However, the second and third embodiments offer greater flexibility in the arrangement of the different components.

Each of the three embodiments described includes a particulate filter 12, which may comprise corundum, cordierite, or any other ceramic or metal structure for filtering particulates.

The means for determining the amount of nitrogen oxides being emitted from the engine 1 may be a computer 6 which compares real-time engine speed measurements with a map stored in the computer for this predetermined operation.

The means for determining the amount of fuel required to achieve the stoichiometric ratio can also be a computing means which compares real-time measurements with predetermined maps, or it can also be the second fuel-to-air ratio sensor 10 .

The present invention is used to achieve desired NOx treatment efficiencies at lower powertrain development costs than NOx trap-type systems, at a cost of controlled extra consumption.

The flexibility of this method is particularly advantageous for power systems used on construction sites, where the main criterion is not additional consumption, but priority is given to the complete treatment of nitrogen oxides. To adapt the power system to a construction site, only the trigger threshold needs to be modified.

Claims (12)

1. A power system, in particular for a motor vehicle, comprising an internal combustion engine (1), a catalytic converter (5) for reducing nitrogen oxides NOx contained in the exhaust gas of said engine (1), An additional fuel injector (4) arranged upstream of the catalytic converter (5) and means (6, 3) for determining the amount of nitrogen oxides NOx emitted from the engine (1), characterized in that the power system comprises a means (6, 10) for determining the amount of fuel required to achieve a ratio lower than or substantially equal to the stoichiometric ratio relative to the amount of nitrogen oxides NOx, and for determining when said required amount is related to nitrogen oxides NOx The means (6) for triggering the injection of said required quantity when the ratio of the quantities falls below a trigger threshold. 2. The power system according to claim 1, characterized in that the engine (1) is a diesel internal combustion engine, and the fuel injected by the additional injector (4) is diesel fuel. 3. The power system according to claim 1 or 2, characterized in that the means for determining the amount of NOx comprises a computer (6) adapted to receive rotational speed data of the engine (1) and send the engine (1) Data of injections in the combustion chamber, and suitable for comparing said data with stored data. 4. The power system according to any one of the preceding claims, characterized in that the means for determining the amount of NOx comprise a system for measuring the exhaust gas Air ratio instrument (3). 5. A power system according to any one of the preceding claims, characterized in that it comprises a particle filter (12) upstream or downstream of the catalytic converter (5). 6. A power system according to any one of claims 1 to 4, characterized in that the system comprises a particle filter (12) in combination with a catalytic converter (5). 7. Power system according to claim 5 or 6, characterized in that said additional injector (4) is placed upstream of the particulate filter (12), which is activated to regenerate Particle filter (12). 8. The power system according to any one of claims 5 to 7, characterized in that the system comprises a second sensor for measuring the reducing agent concentration downstream of the additional injector (4) and upstream of the catalytic converter (5). Instruments (10). 9. The power system according to any one of claims 5 to 8, characterized in that the system comprises a temperature sensor upstream (11) or downstream (13) of the particulate filter (12), and/or Pressure sensor upstream (11) or downstream (13) of filter (12). 10. A use of the power system according to any one of the preceding claims, wherein the means (6, 3) for determining the amount of nitrogen determine the nitrogen oxides escaping from the combustion chamber of the engine (1) proportion. 11. Use of a power system according to claim 10, characterized in that the exhaust gas upstream of the additional injector (4) is devoid of reducing agent. 12. A power method, in particular for a motor vehicle, in which the gas from an internal combustion engine (1) is treated by injecting hydrocarbons into the exhaust line (2a) upstream of a NOx reduction catalyst (5). ), characterized in that the method comprises a step in which the amount of NOx present in the exhaust gas upstream of the injector is determined, the injection of hydrocarbons is triggered when a threshold value of the amount of NOx is reached, the The injection quantity is adjusted such that the quantity of reducing agent relative to the quantity of NOx present in the exhaust gas is lower than or substantially equal to the stoichiometric ratio.

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