JP2008069663A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily control exhaust gas in the desired temperature and the air-fuel ratio, even when using fuel different in an oxygen including quantity. <P>SOLUTION: This exhaust emission control device of an internal combustion engine has a storage-reduction type NOx catalyst 41 arranged in an exhaust system 40 of an engine 1 and a reducing agent adding valve 17 injecting and adding a part of using fuel into the exhaust gas, and purifies the exhaust gas by controlling a fuel adding quantity of the reducing agent adding valve 17, and also has a fuel oxygen concentration sensor 19 detecting the oxygen concentration of the using fuel and an injection rate calculating means for calculating an injection rate of the using fuel becoming an equal calorific value when using predetermined standard fuel (gas oil) as a reference or an injection rate of the using fuel required to be set as the stoichiometric air-fuel ratio, in response to the oxygen concentration of the using fuel. A fuel adding quantity of the reducing agent adding valve 17 is corrected based on the injection rate calculated by this injection rate calculating means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that supplies a reducing agent upstream of a NOx catalyst provided in the exhaust system of the lean combustion internal combustion engine and promotes purification of harmful components in the exhaust gas. More particularly, the present invention relates to an exhaust gas purification apparatus for an internal combustion engine that can easily control exhaust gas to a desired temperature and air-fuel ratio even when fuels having different oxygen contents are used.

  In recent years, internal combustion engines mounted on automobiles and the like have been required to improve exhaust emission. That is, before releasing the exhaust gas from the internal combustion engine to the atmosphere, gas components such as carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx) contained in the exhaust gas are purified or removed. It is requested that.

  In a diesel engine or a gasoline engine capable of lean combustion, an operation region in which an engine operation is performed by using a high air-fuel ratio (lean atmosphere) mixture for combustion occupies most of the entire operation region. In this type of engine, the exhaust system is generally provided with a NOx catalyst that can absorb NOx in a lean atmosphere.

  The NOx catalyst has a characteristic of absorbing NOx when the reducing component concentration in the exhaust gas is low and releasing NOx when the reducing component concentration in the exhaust gas is high. The NOx released into the exhaust reacts quickly with the reducing components such as HC and CO in the exhaust and is reduced to nitrogen.

  Further, there is a limit amount (saturation amount) in the amount of NOx that can be stored by the NOx catalyst, and when the catalyst stores NOx exceeding the saturation amount, the concentration of the reducing component in the exhaust gas becomes low. Even if it exists, it no longer absorbs NOx.

  Therefore, the conventional exhaust gas purification apparatus for an internal combustion engine includes an addition valve for supplying a reducing agent to the exhaust system of the internal combustion engine, and before the NOx occlusion amount of the NOx catalyst reaches a predetermined amount, the NOx Control is performed in which the reducing agent is repeatedly added to the exhaust gas flowing into the catalyst at predetermined intervals.

  Thus, when the reducing agent is supplied to the exhaust system through the addition valve, the reducing agent increases the concentration of the reducing component in the exhaust, releases and reduces the NOx stored in the NOx catalyst, and reduces the NOx of the NOx catalyst. Restores absorption capacity.

  Therefore, the amount of reducing components in the exhaust gas flowing into the NOx catalyst can be increased at a desired time, and the exhaust gas purification efficiency of the NOx catalyst can always be kept high.

  In addition, in a compression ignition type diesel engine using light oil as fuel, soot contained in exhaust gas, particulate matter such as SOF (Solbule Organic Fraction), etc. (PM) in addition to CO, HC, NOx, etc. ) Is required to be purified or removed.

  As described above, various conventional techniques are provided to improve exhaust emission. As another example, for example, the following conventional technique is known. In other words, in order to obtain a high NOx conversion rate regardless of the nature of the fuel given as the reducing agent, a reducing agent supply means has a catalyst for purifying exhaust gas in the exhaust passage of the internal combustion engine and supplies the reducing agent to this catalyst. In the exhaust gas processing apparatus, the operation state detection means for detecting the operation state of the internal combustion engine and the property detection means for detecting the property of the reducing agent supplied to the catalyst, the detected operation state and the reducing agent A technique for controlling the amount of reducing agent supplied to the catalyst according to the properties has been proposed (see, for example, Patent Document 1).

  Further, the following prior art is known in order to always suppress the amount of sulfate produced regardless of the amount of oxygen component contained in the fuel, and to achieve both exhaust gas purification and reduction of the amount of sulfate produced. That is, in an exhaust gas purification apparatus for an internal combustion engine including a catalyst having an oxidizing ability in an exhaust pipe of the internal combustion engine, and a bypass passage and a switching valve for preventing exhaust gas from flowing into the catalyst side, oxygen is contained in the fuel. Oxygen detection means for detecting whether or not it is included, and switching valve control for causing exhaust gas to flow only into the bypass passage by the switching valve when it is determined by the oxygen content detection means that the amount of oxygen contained in the fuel is large A technique provided with a means has been proposed (for example, see Patent Document 2).

JP 2000-179335 A Japanese Patent Laid-Open No. 11-350943

  When purifying exhaust gas containing CO, HC, NOx, etc., it is important to control the temperature and air-fuel ratio of the catalyst to predetermined values. However, in the conventional exhaust gas purification apparatus for an internal combustion engine, if oxygen is present in the fuel, the calorific value and the theoretical air-fuel ratio with respect to the injection amount are different from those of a standard fuel (for example, gasoline or light oil). Since feedback control by the air-fuel ratio sensor is not performed in all operating states (for example, NOx reduction, PM regeneration, S regeneration, etc.), there is a problem that the exhaust gas cannot be controlled to a desired temperature and air-fuel ratio.

  In recent years, alcohol and oxygen-containing fuels such as so-called biofuels have attracted attention as alternative fuels to standard fuels such as gasoline and light oil from the viewpoint of energy and environmental measures, and these fuels can be used. Development of an internal combustion engine is also required. Even in this case, the presence of oxygen in the fuel may cause a problem that the exhaust gas cannot be controlled to a desired temperature and air-fuel ratio for the same reason as described above.

  Therefore, it has been desired to provide a means for easily controlling the exhaust gas to a desired temperature and air-fuel ratio even when fuels having different oxygen contents are used.

  The present invention has been made in view of the above, and is an exhaust purification device for an internal combustion engine that can easily control exhaust gas to a desired temperature and air-fuel ratio even when fuels having different oxygen contents are used. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust system of an internal combustion engine, and performs a NOx reduction reaction when the concentration of reducing components in the exhaust gas increases. And a fuel addition means for injecting and adding a part of the used fuel as a reducing agent into the exhaust gas flowing into the NOx catalyst through the exhaust system, and a fuel for the fuel addition means In an exhaust gas purification apparatus for an internal combustion engine that purifies the exhaust gas by controlling the amount of addition, a fuel oxygen concentration detecting means for detecting the oxygen concentration of the fuel used, and an equal calorific value when a predetermined standard fuel is used as a reference And an injection ratio calculation means for calculating an injection ratio of the used fuel necessary for setting the used fuel injection ratio or the stoichiometric air-fuel ratio according to the oxygen concentration of the used fuel. And it is characterized in that for correcting the fuel amount of the fuel addition means on the basis of the fuel injection ratio calculated by the injection ratio calculation unit.

  According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, even when fuels having different oxygen contents are used, the exhaust gas is easily controlled to a desired temperature and air-fuel ratio as in the case of standard fuel. can do.

  An example in which an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine system will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a schematic configuration diagram showing a diesel engine system to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied. As shown in FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 1 is an in-line four-cylinder diesel engine having a fuel supply system 10, a combustion chamber 20, an intake system 30, an exhaust system 40, and the like as main parts. System.

  The fuel supply system 10 includes a fuel tank 18, a main fuel passage P0, a supply pump 11, a common rail 12, a fuel injection valve 13, a cutoff valve 14, a reducing agent addition valve (fuel addition means) 17, an engine fuel passage P1, and an addition fuel passage. (Fuel adding means) P2 and the like are provided. The fuel tank 18 is provided with a fuel oxygen concentration sensor (fuel oxygen concentration detecting means) 19 for detecting the oxygen concentration of the fuel.

  The supply pump 11 increases the pressure of the fuel pumped from the fuel tank 18 via the main fuel passage P0 and supplies it to the common rail 12 via the engine fuel passage P1. The common rail 12 accumulates the high-pressure fuel supplied from the supply pump 11 at a predetermined pressure and distributes it to each fuel injection valve 13. A fuel injection valve 13 that is an electromagnetic valve injects and supplies fuel into the combustion chamber 20.

  Further, the supply pump 11 supplies a part of the fuel pumped from the fuel tank 18 to the reducing agent addition valve 17 through the addition fuel passage P2. The shut-off valve 14 shuts off the fuel supply P2 when necessary and stops the fuel supply.

  A metering valve (not shown) is also provided in the added fuel passage P2. This metering valve controls the pressure (fuel pressure) of the fuel supplied to the reducing agent addition valve 17. The reducing agent addition valve 17 which is an electromagnetic valve adds and supplies the fuel functioning as a reducing agent to the upstream of the NOx storage reduction catalyst (NOx catalyst) 41 in the exhaust system 40 at an appropriate amount and at an appropriate timing.

  Further, the intake system 30 forms a passage (intake passage) for intake air supplied into each combustion chamber 20. The exhaust system 40 forms a passage (exhaust passage) for exhaust gas discharged from each combustion chamber 20.

  Further, the engine 1 includes a turbocharger 50 that supercharges intake air by the exhaust gas. The intercooler 31 provided in the turbocharger 50 forcibly cools the intake air whose temperature has been increased by supercharging. The throttle valve 32 provided downstream of the intercooler 31 is a so-called electronic throttle, and adjusts the amount of intake air supplied.

  Further, the engine 1 is provided with an EGR passage 60 that bypasses the intake system 30 and the exhaust system 40 and returns a part of the exhaust to the intake system 30. The EGR passage 60 is provided with an EGR valve 61 that adjusts the exhaust gas flow rate and an EGR cooler 62 that cools the exhaust gas.

  Further, the exhaust system 40 includes an NOx storage reduction catalyst 41 and an oxidation catalyst 42 provided downstream thereof. The NOx storage reduction catalyst 41 stores NOx when the air-fuel ratio of the exhaust gas is lean, and lowers the oxygen concentration in the exhaust gas and releases and reduces NOx stored in the reducing atmosphere.

  In addition, when the temperature of the NOx storage reduction catalyst 41 is relatively low, the fuel added by the reducing agent addition valve 17 may slip through the NOx storage reduction catalyst 41. The oxidation catalyst 42 ensures this. Can be oxidized to.

  An air flow meter 72 that detects the intake air amount, an air-fuel ratio sensor 73 that detects the oxygen concentration in the exhaust, and exhaust temperatures on the upstream and downstream sides of the NOx storage reduction catalyst 41 are detected in each part of the engine 1. Exhaust temperature sensors 74a and 74b and a pressure sensor 75 for detecting a pressure difference between the upstream side and the downstream side of the NOx storage reduction catalyst 41 are provided.

  Although not shown, each part of the engine 1 includes a temperature sensor and a pressure sensor for detecting the temperature and pressure of the fuel in the common rail 12, a crank position sensor for detecting the crankshaft rotation of the engine 1, and an intake air temperature. Intake temperature sensor for detecting, intake pressure sensor for detecting intake pressure, accelerator position sensor for detecting accelerator pedal depression amount (accelerator position), throttle position sensor for detecting position of throttle valve 32, and cooling of engine 1 A water temperature sensor or the like for detecting the water temperature is provided.

  The ECU, which is an electronic control unit (not shown), inputs detection signals from the various sensors via an external input circuit, and controls the operation of the engine 1 such as opening / closing control of the fuel injection valve 13 and the reducing agent addition valve 17 based on these signals. Implement various controls related to the state. The ECU functions as a means for calculating an injection ratio, which will be described later, and also functions as a means for correcting the fuel addition amount of the reducing agent addition valve 17 based on the injection ratio.

  Next, a control method according to the present embodiment will be described based on FIG. 4 with reference to FIGS. Here, FIG. 4 is a flowchart showing a control method. Since the basic control for exhaust gas purification is almost the same as that of the known technology, the duplicated explanation is omitted and the differences will be explained.

  FIG. 2 is a graph showing the relationship between the oxygen concentration of the fuel and the ratio of the calorific value. The injection ratio of the used fuel that has an equal calorific value when using light oil (predetermined standard fuel) as a reference is shown in FIG. It is the map computed according to oxygen content (oxygen concentration). The graph also shows biofuels, organic fuels, and alcohol fuels in addition to the standard fuel gas oil.

  FIG. 3 is a graph showing the relationship between the oxygen concentration of the fuel and the stoichiometric air-fuel ratio. The injection ratio of the used fuel necessary to obtain the stoichiometric air-fuel ratio based on light oil is used as the oxygen content of the used fuel. It is the map computed according to quantity (oxygen concentration). In the graph, alcohol fuel is shown in addition to light oil, which is a standard fuel.

  2 and 3, a, b, c, d, and e on the vertical axis indicate predetermined numerical values (ratio) when light oil is 1 (reference value). Moreover, wt1, wt2, and wt3 on the horizontal axis are predetermined numerical values indicating the oxygen content (weight percent). As can be seen by comparing FIG. 2 and FIG. 3, the graph of the change in the injection ratio due to the difference in the equal calorific value (FIG. 2) and the graph of the change in the injection ratio due to the difference in the theoretical air-fuel ratio (FIG. 3) are almost It is the same.

  That is, as can be seen from FIG. 2 and FIG. 3, when the oxygen content of the fuel used increases, the injection ratio of the fuel used equal to calorific value with the light oil also increases, and the fuel used necessary to achieve the stoichiometric air-fuel ratio. The injection ratio of the gas also increases along almost the same curve.

  Therefore, if the oxygen content of the fuel used is known, the reducing agent addition valve 17 is based on the injection ratio corresponding to the oxygen content by using one of these maps (FIG. 2 or FIG. 3). The amount of fuel added from can be easily corrected (injection rate increased).

  That is, the control method according to the present embodiment is executed by the ECU, and as shown in FIG. 4, the oxygen content of the used fuel is detected by the fuel oxygen concentration sensor 19 of the fuel tank 18 (step S10).

  Next, the injection ratio corresponding to this oxygen content is obtained from, for example, the map shown in FIG. 2, and this injection ratio is multiplied by the fuel addition amount in the case of the light oil as a reference. The amount of fuel added can be corrected (step S20).

  Then, the corrected fuel addition amount is injected from the reducing agent addition valve 17 (step S30). As a result, even when fuels with different oxygen contents are used, or even when the oxygen content of the fuel has changed, a calorific value (catalyst temperature) equivalent to that of light oil can be obtained, and rich gas is occluded. The reduced NOx catalyst 41 can be supplied.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine according to this embodiment, even when fuels having different oxygen contents are used, the exhaust gas is desired to have a desired temperature and air temperature as in the case of light oil. The fuel ratio can be easily controlled.

  In the above embodiment, the present invention is applied to a diesel engine system and the standard fuel is assumed to be light oil. However, the present invention is not limited to this. For example, the invention may be applied to a gasoline engine and the standard fuel may be gasoline. Good. In this case, if the oxygen content of gasoline is detected, the exhaust gas can be easily controlled to a desired temperature and air-fuel ratio, so that complicated feedback control by a catalyst temperature sensor or an air-fuel ratio sensor is not required. it can.

  As described above, the exhaust gas purification apparatus for an internal combustion engine according to the present invention supplies the reducing agent to the upstream side of the NOx catalyst provided in the exhaust system of the lean combustion internal combustion engine and provided in the exhaust system. It is useful for promoting the purification of harmful components, particularly in an internal combustion engine that aims to easily control the exhaust gas to a desired temperature and air-fuel ratio even when using fuels having different oxygen contents. Is suitable.

1 is a schematic configuration diagram showing a diesel engine system to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied. It is a graph which shows the relationship between the oxygen concentration of a fuel, and the emitted-heat amount ratio. It is a graph which shows the relationship between the oxygen concentration of a fuel, and a theoretical air fuel ratio. It is a flowchart which shows a control method.

Explanation of symbols

1 engine (internal combustion engine)
10 Fuel supply system 17 Reducing agent addition valve (fuel addition means)
18 Fuel tank 19 Fuel oxygen concentration sensor (fuel oxygen concentration detection means)
20 Combustion chamber 30 Intake system 40 Exhaust system 41 NOx storage reduction catalyst (NOx catalyst)
73 Air-fuel ratio sensor 74a, 74b Exhaust temperature sensor P0 Main fuel passage P1 Engine fuel passage P2 Addition fuel passage (fuel addition means)

Claims (1)

A NOx catalyst that is provided in an exhaust system of an internal combustion engine and has a characteristic that promotes a reduction reaction of NOx when the concentration of a reducing component in the exhaust gas increases;
Fuel addition means for injecting and adding a part of the used fuel as a reducing agent into the exhaust gas flowing into the NOx catalyst through the exhaust system;
An exhaust gas purification apparatus for an internal combustion engine that purifies the exhaust gas by controlling a fuel addition amount of the fuel addition means,
Fuel oxygen concentration detection means for detecting the oxygen concentration of the fuel used;
Injection that calculates an injection ratio of the used fuel that is equal in calorific value when a predetermined standard fuel is used as a reference or an injection ratio of the used fuel that is necessary to obtain a stoichiometric air-fuel ratio according to the oxygen concentration of the used fuel A ratio calculation means;
Further comprising
An exhaust emission control device for an internal combustion engine, wherein the fuel addition amount of the fuel addition means is corrected based on the injection ratio calculated by the injection ratio calculation means.

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