JP2009513868A - Device for treating nitric oxide in automobile exhaust gas - Google Patents

Abstract

In particular, in an automobile propulsion system, an internal combustion engine (1), a catalyst (5) for reducing nitric oxide NOx contained in the exhaust surface of the internal combustion engine (1), and an additional arranged upstream of the catalyst (5) A fuel injector (4) and means (6, 3) for determining the amount of NOx received from the internal combustion engine (1) are provided. The propulsion system of the present invention comprises means (6, 10) for determining the amount of fuel necessary to obtain a ratio below the stoichiometric ratio to the amount of nitric oxide NOx, and the ratio and the amount of nitric oxide NOx. Means (6) for starting the injection of the required amount when the is below the start threshold.

Description

  The invention relates in particular to the field of propulsion systems for motor vehicles. In particular, the present invention relates to the field of devices and methods for catalytic treatment of nitric oxide (NOx) in exhaust gases of internal combustion engines.

  As is obvious, nitric oxide causes respiratory infections and allergies, and is a leading cause of soot and acid rain production. Most countries impose standards that limit the emission of nitric oxide from vehicles. This standard generally defines different thresholds for private vehicles, utility vehicles and general purpose engines. In fact, each of these classifications spans a wide variety of engines. For example, private vehicles include vehicles equipped with gasoline engines and vehicles equipped with diesel engines. These include small urban vehicles and four-wheel drive vehicles. In order to obtain the same pollutant emission threshold for a high-power engine, it is necessary to enhance the treatment of nitric oxide NOx compared to obtaining the same pollutant emission threshold for a small engine. Furthermore, the economic pressure of providing inexpensive equipment for the treatment of nitric oxide is more severe in small urban cars than in luxury cars.

Several techniques have been developed to reduce NOx emissions. Such techniques are distinguished between passive methods using a catalyst that allows exhaust gas to pass through and active methods that utilize a complex process such as an electrochemical or photocatalytic method. Passive catalytic methods are usually used for gasoline vehicles. Three-way catalysts are used to treat nitrogen and carbon oxides and unburned hydrocarbons simultaneously. The exhaust gas discharged from the combustion chamber of a gasoline engine generally contains abundant reducing components such as hydrocarbons and carbon monoxide. Therefore, by using a three-way catalyst, the nitrogen oxide (NOx) discharged is nitrogen gas. Reduced to Three-way catalysts have the advantage of being inexpensive.
The diesel engine has a combustion chamber to which a mixture containing excess air is supplied. Therefore, the concentration of the reducing agent in the exhaust gas discharged from the engine is low. This catalyst is not practical because the reduction efficiency of the three-way catalyst decreases rapidly in the presence of oxygen.

NOx traps have been proposed to treat nitric oxide when the concentration of reducing agent in the exhaust gas is low. This NOx trap is described in particular in EP-A-0573672 (Toyota) and EP-A-1079084 (Toyota). During normal operation of the vehicle, the exhaust gas generally passes through a NOx trap where the catalyst contains an alkaline or alkaline earth element and a storage compound. The catalyst, the oxidation of nitrogen dioxide NO ₂ of nitric oxide NO, the conversion of nitrate nitrogen dioxide NO ₂ promotes, the nitrate is deposited on the monolith. During normal engine operation, NOx is absorbed by the NOx trap. The stored NOx is periodically desorbed. The ratio of exhaust gas reductant during this desorption period is higher than the stoichiometric ratio (the mixture is called rich). Such control of NOx treatment is a complicated process, and it is necessary to detect the desorption period and increase the injection amount of hydrocarbons. The storage component of the NOx trap is particularly sensitive to sulfur. In parallel with the NOx storage process, it was necessary to periodically perform a desulfurization step.

WO 02/31325 (Corning Inc.) describes a method for reducing nitric oxide in the exhaust gas of a diesel engine. In this method, fuel is continuously injected into exhaust gas, a mixture of fuel and exhaust gas is passed through a catalyst, and NOx in the exhaust gas is reduced to nitrogen gas. This process has the disadvantage that additional fuel consumption occurs.
U.S. Patent Application Publication No. 2004/0083722 (Ford) describes an improvement in the conversion of NOx through the use of a catalyst, whereby the engine is stationary in consideration of the engine acceleration and deceleration periods. The amount of fuel injected upstream of the catalyst is corrected for the amount injected under conditions operating in the state. The catalyst is of the ALNC or SCR type that continuously reduces NOx emissions by active injection of a reducing agent (hydrocarbon or urea). Although improved, the ratio of reducing agent injected under steady-state conditions in the described embodiment is 10 times greater than NOx. Even with improvements, such systems consume large amounts of fuel.

  The present invention proposes a propulsion system, in particular for motor vehicles, and a method for treating the exhaust gas of this propulsion system. The system and method according to the invention proposes an inexpensive treatment of nitric oxide NOx which overcomes the above-mentioned drawbacks and in particular reduces the excess fuel consumption.

According to one embodiment of the invention, the propulsion system, particularly for automobiles, comprises an internal combustion engine, a catalyst for reducing NOx contained in engine exhaust gas, an additional fuel injector disposed upstream of the catalyst, Means for determining the amount of nitric oxide NOx discharged from the engine, means for determining the amount of fuel required for the ratio to the amount of nitric oxide NOx to be less than or equal to the stoichiometric ratio, and the nitric oxide Means are provided for injecting the required amount when the ratio of the required amount to the amount of NOx is below a starting threshold.
It can be seen that such a propulsion system comprising a NOx reduction catalyst through which a substantially stoichiometric mixture passes can utilize an inexpensive catalyst of the three-way catalyst type known for example for gasoline vehicles. Furthermore, no additional fuel consumption occurs if the ratio of the injected amount to the NOx amount is below the starting threshold. In other words, the additional injection is stopped when the amount of NOx present in the exhaust gas does not reach the limit value allowed by the standards, for example. In the case of small cars for cities, this limit is generally exceeded only during certain driving periods of the vehicle, for example in the case of cold engines, during periods of high acceleration or high loads of the engine. The amount of fuel is limited by means of adjusting the amount of fuel injected to obtain the stoichiometric ratio. In fact, the engine operation period in which the amount of NOx emission is large corresponds to a period when the concentrations of unburned hydrocarbons and the reducing agent are higher than when the exhaust gas is in a steady state condition. Correspondingly, the amount of diesel required for the injection to reach stoichiometry (ratio) is reduced.

  Advantageously, the concentration of reducing agent in the exhaust gas upstream of the additional injector is low. The engine can be diesel and the fuel injected by the additional injector can be diesel fuel.

  According to another embodiment, the means for determining the amount of NOx comprises a computer suitable for receiving data relating to engine speed and injection into the engine combustion chamber and comparing these data with stored data. I have. Advantageously, this means comprises a device for measuring the air / fuel mixture ratio of the exhaust gas downstream of the engine and upstream of the additional injector.

According to another embodiment, the propulsion system comprises a particle filter upstream or downstream of the catalyst or the propulsion system incorporates a catalyst. An additional injector can be placed upstream of the particle filter and can be activated to regenerate the particle filter.
Advantageously, the propulsion system comprises a second device for measuring the concentration of the reducing agent downstream of the additional injector and upstream of the catalyst. The system can include a temperature probe upstream or downstream of the particle filter and / or a pressure probe upstream or downstream of the particle filter.

  According to another embodiment, the invention relates in particular to a vehicle propulsion method, which treats exhaust gas from an internal combustion engine by N-injecting hydrocarbons into the exhaust line upstream of the Ox reduction catalyst. The amount of NOx present in the exhaust gas is determined upstream of the injector, and when the NOx amount threshold is reached, the injection of hydrocarbons is started, and the amount of reducing agent is greater than the amount of NOx present in the exhaust gas. Adjusting the amount to be injected so that it is less than or equal to the stoichiometric ratio.

  Other features and advantages of the present invention will become apparent upon reading the detailed description of a plurality of non-limiting exemplary embodiments shown in the accompanying drawings. The drawing is only one and schematically shows the components of the propulsion system according to the invention.

As shown in the drawings, the automobile propulsion system includes a diesel-type internal combustion engine 1 and an exhaust line 2, and the exhaust line 2 includes a first section 2 a adjacent to the downstream side of the internal combustion engine 1, and a first section 2 a. And a second section 2b adjacent to the upstream side of the first section 2a.
The drawing shows four embodiments in which the second section 2b of the exhaust line 2 is different from one another, which is schematically indicated by a dotted line.

In the first embodiment, the first section 2 a of the exhaust line 2 includes a λ air fuel ratio probe 3 or an oxygen probe that senses the ratio of oxygen in the exhaust gas from the internal combustion engine 1. An additional injector 4 is inserted downstream of the air fuel ratio probe 3 in the first section 2a. The second section 2 b of the exhaust line 2 of the first embodiment includes a catalyst 5. The propulsion system also includes a computer 6.
The operation of the first embodiment will be described below. The diesel internal combustion engine is provided with a crankshaft speed sensor 7 (not shown) and a sensor 8 that senses the injection conditions of the main injection of the engine 1. This sensor may be, for example, an accelerator position sensor or a sensor of a main injector control circuit. Optionally, the engine is equipped with a combustion chamber temperature sensor. Data obtained from these sensors is transmitted to the computer 6. Similarly, data regarding the type of fuel used can be entered and transmitted to the computer 6. A complete mapping of the various engine operating speeds depending on the characteristics of the fuel used is stored in the computer 6. This allows the computer to determine the engine speed and, in real time, the ratio of nitric oxide discharged from the combustion chamber of the engine 1 to the amount of unburned hydrocarbons or reducing components discharged from the engine combustion chamber. Can be determined. Next, the computer 6 determines the required amount of reducing component to be injected by the additional injector 4 so that the ratio of the amount of oxidizing component to the amount of reducing component of the gas mixture changed by the injection of the reducing element becomes the stoichiometric ratio. Can be determined.

  When the computer 6 activates the additional injector 4 and starts the required amount of injection, the mixture passing through the catalyst 5 has the desired stoichiometric ratio. The conditions under which diesel injection into the exhaust line is initiated (the amount of NOx emitted by the engine and the air / fuel ratio of the gas mixture in the combustion chamber) can be modified, for example, in response to changes in law in force. The desired stoichiometric ratio corresponds to the ratio of NOx reduced by the action of the catalyst 5 before being discharged from the exhaust line 2. The desired stoichiometric ratio may correspond to the maximum amount of NOx that is not reduced by the catalyst 5. When the computer 6 does not operate the additional injector 4, all NOx discharged from the internal combustion engine 1 passes through the catalyst 5, and in this case, the reduction efficiency of the catalyst 5 is reduced due to the low content of the reducing agent in the mixture. Substantially reduced.

In another embodiment, the desired stoichiometric ratio is equal to 1, so that all NOx present in the exhaust gas can be treated by the catalyst 5. In yet another embodiment, this ratio is less than 1, thereby saving additional fuel consumed while processing some of the NOx present in the exhaust gas to comply with enforced standards. The
The computer also stores the injector start threshold. The computer receives real-time data about the engine speed and again determines in real time both the amount of NOx present in the exhaust gas exhausted from the engine and the amount of fuel needed to reach the desired stoichiometric ratio. calculate. If the ratio of the required amount of fuel to the amount of nitric oxide is below the starting threshold, the computer activates the additional injector, and if the ratio is above the threshold, the additional injector is not commanded. A ratio that is greater than the start threshold corresponds to the NOx emissions of the engine 1 that need to handle excess additional fuel on the catalyst.

According to another embodiment of the present invention, the air / fuel ratio of the exhaust gas exhausted from the engine is not directly evaluated by comparing the manufacturer's data with engine speed measurements, but directly by the air / fuel ratio probe 3. Measured. The computer 6 calculates the required amount of fuel to reach the desired stoichiometric ratio, compares the ratio of the required amount to the estimated amount of NOx, and if the ratio is below the starting threshold, additional injections are made. To start. This embodiment improves the assessment of the infused requirement by combining measured data with calculated data in real time. This embodiment also helps to compare the expected value calculated to detect any irregularities in the sensor or computing system with the measured quantity.
The reducing agent injected by the additional injector 4 need not be the same as the fuel used by the internal combustion engine 1. However, if the same fuel is used, there is no need to provide an additional tank. The internal combustion engine is preferably a diesel engine, and the fuel injected by the additional injector is diesel fuel. In a diesel engine, the combustion chamber gas suction device and the combustion chamber injection device are usually arranged so that the combustion chamber is saturated with oxygen. Therefore, the exhaust gas discharged from the diesel engine is generally oxidized.

The exhaust gas of a diesel engine that operates in a combustion system called premixed combustion has a high concentration of reducing agent and NOx emission is restricted. Thus, the amount of additional fuel injected is kept small.
The propulsion method and system of the present invention can be adapted to an internal combustion engine using gasoline in which the concentration of reducing components in the exhaust gas is small. For example, in a stratified charge internal combustion engine, the amount of NOx produced by the engine is already reduced due to the low combustion temperature, but the advantages of the three-way catalyst and low fuel consumption are still achieved by the method of the present invention. Are combined.

  The injector 4 is additional in the sense that it is added to the main injector (not shown) of the internal combustion engine 1 and is unique. The injector 4 may be disposed directly at the inlet of the catalyst pot 5. The injector 4 may be provided by a main injector, in which case the injection sequence involving the starting means of the present invention is additional in the sense that it is additional compared to the normal injection cycle of the engine 1. This additional injection can take place at the start of the discharge of gas from the combustion chamber.

A particularly advantageous combination of such a propulsion system and the use of a particle filter will now be described.
According to the second embodiment shown in the drawing, the second section 2b of the exhaust line 2 comprises a second air fuel ratio probe 10, a catalyst 5, an upstream temperature and pressure sensor along the direction of gas flow. 11, a particle filter 12, and a downstream temperature and pressure sensor 13. The particle filter 12 holds soot and unburned particles discharged by the engine 1. The particle filter 12 may or may not be catalyzed. A second air fuel ratio probe 10 provided downstream of the additional injector 4 controls the calculation of the injection amount to reach stoichiometric conditions during normal operation of the engine 1. The additional injector 4, the second λ probe 10 and the temperature sensors 11 and 13 are also used for regeneration of the particle filter. By obtaining an exothermic reaction with the catalyst 5, the exhaust gas that has entered the particle filter is heated to a temperature sufficient to burn the soot and the remaining particles that have been filtered. With a catalyzed particle filter, the temperature of the exhaust gas required to reach regeneration is lower than with an uncatalyzed particle filter.

In the third embodiment shown in the drawing, the second section 2b of the exhaust line 2 has an upstream temperature and / or pressure sensor 11, a particle filter 12, a downstream temperature and / or along the direction of gas flow. A pressure sensor 13, a second air fuel ratio probe 10 and a catalyst 5 are provided.
In the fourth embodiment shown in the drawing, the second section 2b of the exhaust line 2 is incorporated into the second air fuel ratio probe 10, the optional sensor 11, and the particle filter 12 along the direction of gas flow. The catalyst 5 and the downstream sensor 13 are provided. The fourth embodiment has an advantage that the number of components attached to the exhaust line 2 is small. However, in the layout of various components, the second and third embodiments are more flexible.

In three embodiments including the particle filter 12, the filter can be composed of silicon carbide, cordierite, or any other ceramic or metal structure that has the function of filtering particles.
The means for determining the amount of nitric oxide discharged from the engine 1 can be a computer 6 that compares the measured engine speed in real time with a pre-recorded mapping of this operation stored in the computer.

The means for determining the amount of fuel required to reach the stoichiometric ratio can also be an operation that compares real-time measurements with pre-recorded mappings. Alternatively, the means may be the second air fuel ratio probe 10.
The present invention is useful for obtaining the desired NOx treatment efficiency at a lower cost for propulsion system development than NOx trap type systems at the expense of additional controlled consumption.

  The flexibility of the method is particularly advantageous in propulsion systems used at construction sites where additional consumption is not an important criterion and prioritizes complete treatment of nitric oxide. In order to adapt the propulsion system to construction site applications, it is sufficient to change the starting threshold.

1 is a schematic view of members of a propulsion system according to the invention.

Claims (12)

  In particular, a propulsion system for an automobile, which is an internal combustion engine (1), a catalyst (5) for reducing NOx contained in exhaust gas of the engine (1), and an additional fuel disposed upstream of the catalyst (5). An injector (4) and means (6, 3) for determining the amount of NOx discharged from the engine (1) are provided, and the ratio of the fuel amount to the NOx amount is equal to or less than the stoichiometric ratio. Means (6, 10) for determining the amount of fuel required to reduce the amount of fuel, and means (6) for injecting the required amount when the ratio of the required amount to the amount of NOx is below a starting threshold Propulsion system characterized by having.   The propulsion system according to claim 1, wherein the engine (1) is a diesel internal combustion engine and the fuel injected by the additional injector (4) is diesel fuel.   The means for determining the amount of NOx comprises a computer (6) suitable for receiving data relating to engine speed (1) and injection of the engine (1) into the combustion chamber and comparing these data with stored data. The propulsion system according to claim 1 or 2.   The means for determining the amount of NOx comprises a device (3) for measuring the air-fuel ratio of the exhaust gas downstream of the engine (1) and upstream of the additional injector (4). The propulsion system according to claim 1.   The propulsion system according to any one of claims 1 to 4, comprising a particle filter (12) upstream or downstream of the catalyst (5).   The propulsion system according to any one of the preceding claims, comprising a particle filter (12) incorporating a catalyst (5).   The propulsion system according to claim 5 or 6, wherein the additional injector (4) is arranged upstream of the particle filter (12) and is activated to regenerate the particle filter (12).   The propulsion system according to any one of claims 5 to 7, comprising a second device (10) for measuring the concentration of the reducing agent downstream of the additional injector (4) and upstream of the catalyst (5).   A temperature probe (11) provided upstream of the particle filter (12) or a temperature probe (13) provided downstream and / or a pressure probe (11) or downstream provided upstream of the particle filter (12) The propulsion system according to any one of claims 5 to 8, further comprising a pressure probe (13) provided on the vehicle.   The propulsion system according to any one of the preceding claims, wherein the means (6, 3) for determining the amount of NOx NOx determine the proportion of nitric oxide discharged from the combustion chamber of the engine (1). .   The propulsion system according to claim 10, wherein the concentration of the reducing agent in the exhaust gas upstream of the additional injector (4) is low.   In particular, a propulsion method for an automobile, in which exhaust gas discharged from an internal combustion engine (1) is processed by injecting hydrocarbons into an exhaust line (2a) upstream of a NOx reduction catalyst (5), The amount of NOx present in the exhaust gas upstream of the injector is determined, and when the NOx amount threshold is reached, hydrocarbon injection is started, and the amount of reducing agent relative to the amount of NOx present in the exhaust gas Adjusting the injection volume so that is less than or equal to the stoichiometric ratio.

Images