JP2018193905A - Exhaust emission control system and exhaust emission control method - Google Patents

Abstract

To provide an exhaust emission control system and exhaust emission control method, capable of suppressing generation of a white product, and also improving a purification rate of a nitrogen oxide.SOLUTION: An exhaust emission control system is configured to, based on a cumulative use time tx of a selective reduction catalyst device 25 acquired by a cumulative use time acquisition device 31, set an injection permission temperature Ta by a controller 30, and when an exhaust gas temperature Tx acquired as a temperature of the selective reduction catalyst device 25 by a temperature acquisition device 32 exceeds the set injection permission temperature Ta, inject urine water U1 from a reductant injection valve 24.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an exhaust gas purification system and an exhaust gas purification method, and more particularly to an exhaust gas purification system and an exhaust gas purification method that improve the purification rate of nitrogen oxides.

  As a system for reducing and purifying nitrogen oxides of exhaust gas discharged from an engine, a system in which an exhaust passage is provided with a reducing agent injection valve and a selective reduction catalyst device has been proposed (see, for example, Patent Document 1). . This exhaust gas purification system causes urea water to be injected from the reducing agent injection valve when the temperature of the selective reduction catalyst device (SCR catalyst device) becomes equal to or higher than a preset injection permission temperature (for example, 200 ° C.). ing.

JP 2008-163919 A

  However, the exhaust gas purification system has a problem that when the exhaust gas temperature is low, a crystallized white product derived from urea water is generated in the selective reduction catalyst device. In this regard, in the system described in Patent Document 1, the generation of the white product is suppressed by setting the injection permission temperature to a temperature at which the white product is difficult to generate.

  However, in the system described in Patent Document 1, urea water is not injected from the reducing agent injection valve when the temperature of the selective reduction catalyst device does not reach the set injection permission temperature. Therefore, there has been a new problem that the purification rate of nitrogen oxides in a state where the temperature is lower than the injection permission temperature is lowered.

  An object of the present invention is to provide an exhaust gas purification system and an exhaust gas purification method capable of improving the purification rate of nitrogen oxides while suppressing the production of a white product.

  The exhaust gas purification system of the present invention that achieves the above object is a reducing agent injection that is disposed in an exhaust passage of an engine and injects urea water into the exhaust gas in order from the upstream side to the downstream side with respect to the flow of the exhaust gas. In an exhaust gas purification system comprising a valve and a selective reduction catalyst device that reduces nitrogen oxides contained in exhaust gas using urea water as a reducing agent, the cumulative use time of the selective reduction catalyst device is acquired An accumulated usage time acquisition device; a temperature acquisition device for acquiring the temperature of the selective reduction catalyst device; the reducing agent injection valve; the cumulative usage time acquisition device; and a control device connected to the temperature acquisition device. An injection permission temperature is set by the control device based on the cumulative use time of the selective reduction catalyst device acquired by the cumulative use time acquisition device, and the temperature acquisition device takes When the temperature was exceeding its injection enabling temperature set, characterized in that a configuration of the control for injecting the urea water from the reducing agent injection valve.

In addition, the exhaust gas purification method of the present invention that achieves the above-described object causes the urea water to be injected from the reducing agent injection valve disposed in the exhaust passage of the engine, and the downstream of the exhaust gas flow from the reducing agent injection valve. In the exhaust gas purification method for reducing nitrogen oxides contained in the exhaust gas using the urea water as a reducing agent in the selective reduction catalyst device arranged on the side, the cumulative use time of the selective reduction catalyst device, The selective reduction catalyst device temperature is acquired, an injection permission temperature is set based on the acquired cumulative use time of the selective reduction catalyst device, and the acquired injection reduction temperature is set by the acquired temperature of the selective reduction catalyst device When the pressure exceeds, urea water is injected from the reducing agent injection valve.

  According to the present invention, the selective reduction catalyst device pays attention to the fact that the purification performance in the selective reduction catalyst device is reduced in accordance with the cumulative use time, so that a white product derived from urea water is easily generated. The injection permission temperature is set based on the accumulated usage time. Therefore, the injection permission temperature can be set to a stepwise high temperature in order to complement the purification performance that gradually deteriorates according to the cumulative use time of the selective reduction catalyst device.

  That is, when the cumulative use time of the selective reduction catalyst device is short, the production of white products is suppressed due to the high purification performance of the selective reduction catalyst device, so the injection permission temperature can be set to a low temperature. it can. Accordingly, when the exhaust gas temperature is low, it is advantageous for injecting urea water from the reducing agent injection valve, and the purification rate of nitrogen oxides can be improved.

  Moreover, when the cumulative use time of the selective reduction catalyst device is long, the injection permission temperature can be set to a high temperature. As a result, in a state where the selective reduction catalyst device has deteriorated, it is advantageous to prohibit the injection of urea water from the reducing agent injection valve when the exhaust gas temperature is low, and suppress the production of white products. can do.

1 is a configuration diagram illustrating an embodiment of an exhaust gas purification system of the present invention. It is a block diagram which illustrates the control apparatus of FIG. 1 is a first flowchart illustrating an embodiment of an exhaust gas purification method of the present invention. It is a 2nd flowchart which illustrates embodiment of the exhaust-gas purification method of this invention. It is a progress diagram which illustrates the relationship between the accumulation use time of a selective reduction catalyst apparatus, injection permission temperature, and the deterioration progress of a selective reduction catalyst apparatus.

  Embodiments of an exhaust gas purification system and an exhaust gas purification method of the present invention will be described below. In the figure, the arrow indicated by G1 indicates the flow of exhaust gas, the arrow indicated by F1 indicates the flow of unburned fuel, and the arrow indicated by U1 indicates the flow of urea water.

  As illustrated in FIG. 1, the exhaust gas purification system 20 according to the embodiment purifies exhaust gas G1 discharged from an engine 10 mounted on a vehicle. The engine 10 includes a cylinder 11, a cylinder injection valve 12, an exhaust valve 13, an exhaust passage 14, and a crankshaft 15.

  The plurality of cylinders 11 are arranged in series with the engine body, and housed therein are pistons (not shown) that reciprocate in the cylinder axis direction of the cylinders 11. The plurality of cylinder injection valves 12 are arranged for each cylinder 11 and inject fuel into the cylinder 11. The exhaust valve 13 is arranged for each cylinder 11, and exhausts the exhaust gas G <b> 1 generated by the combustion of fuel injected into the cylinder 11 from the cylinder injection valve 12 by opening in the exhaust stroke from the cylinder 11. ing. The exhaust passage 14 is connected to the exhaust manifold 16 through which the exhaust gas G1 that has been exhausted passes. The crankshaft 15 transmits driving force to driving wheels via a power transmission device such as a clutch or a transmission (not shown).

The exhaust gas purification system 20 is arranged in the exhaust passage 14 and arranged in order from the upstream side to the downstream side with respect to the flow of the exhaust gas G1 in the exhaust passage 14, the piping injection valve 21, the oxidation catalyst device 22, the trapping device. A collection filter 23, a reducing agent injection valve 24, a selective reduction catalyst device 25, and an ammonia catalyst device 26 are provided.

  The pipe injection valve 21 is inserted in the middle of the exhaust passage 14 interposed between the exhaust manifold 16 and the oxidation catalyst device 22 with the injection port directed in the flow direction of the exhaust gas G1. The piping injection valve 21 is supplied with the same fuel as the fuel injected from the cylinder injection valve 12 to the cylinder 11 from the fuel supply system including the fuel tank 27a and the fuel pump 27b, and is not directed toward the exhaust gas G1. It functions as a device for injecting and supplying the fuel F1.

  The oxidation catalyst device 22 is a cylindrical porous structure, and is partitioned by a porous partition made of ceramics. The oxidation catalyst device 22 penetrates from the inlet through which the exhaust gas G1 flows into the outlet through which the exhaust gas G1 flows. A plurality of ventilation holes (cells) serving as paths are formed. The oxidation catalyst device 22 carries an oxidation catalyst for oxidizing hydrocarbons, carbon monoxide, and nitrogen monoxide contained in the exhaust gas G1 in its porous partition wall. Examples of the oxidation catalyst include noble metals such as platinum (Pt), rhodium (Rh) and palladium (Pd).

  The collection filter 23 is a cylindrical porous structure, and a plurality of ventilation holes are formed by porous partition walls made of ceramics as in the oxidation catalyst device 22. Unlike the oxidation catalyst device 22, the collection filter 23 has a vent hole that is closed at either the inlet or the outlet by a sealing member, and the inlet and outlet of the collection filter 23 are adjacent to each other. The pores are alternately blocked.

  The reducing agent injection valve 24 is inserted in the middle of the exhaust passage 14 interposed between the collection filter 23 and the selective reduction catalyst device 25 with the injection port directed in the flow direction of the exhaust gas G1. The reducing agent injection valve 24 is supplied with urea water from a urea water supply system including a urea water tank 28a and a urea water pump 28b, and adds urea water U1 as a reducing agent to the exhaust gas G1. The urea water supply system is provided with a cooling water pipe through which the cooling water after cooling the engine 10 flows. The urea water tank 28a and a pipe through which the urea water flows are heated by the cooling water.

  The selective reduction catalyst device 25 is a cylindrical porous structure, and a plurality of ventilation holes are formed by porous partition walls made of ceramics as in the oxidation catalyst device 22. Unlike the oxidation catalyst device 22, the selective reduction catalyst device 25 carries a selective reduction catalyst that reduces nitrogen oxides contained in the exhaust gas G <b> 1 on its porous partition wall. Examples of the selective reduction catalyst include vanadium and zeolite.

  The ammonia catalyst device 26 is a device that removes ammonia contained in the exhaust gas G1 after passing through the selective reduction catalyst device 25, and has a function of oxidizing and decomposing ammonia or a function of adsorbing ammonia.

  The control device 30 is hardware including a CPU that performs various types of information processing, an internal storage device that can read and write programs and information processing results used to perform the various types of information processing, and various interfaces. The control device 30 is electrically connected to the reducing agent injection valve 24 and the various acquisition devices 31 to 34 via a signal line indicated by a one-dot chain line.

The accumulated use time acquisition device 31 is configured by a odometer that detects the number of rotations of the crankshaft 15 and acquires the travel distance of the vehicle on which the engine 10 is mounted as the accumulated use time tx. The cumulative usage time acquisition device 31 only needs to acquire the cumulative usage time tx of the selective reduction catalyst device 25. In addition to the odometer, the accumulated use time acquisition device 31 accumulates based on the timer that counts the time during which the engine 10 is driven as the accumulated use time tx, and the amount of fuel injected from the cylinder injection valve 12. Examples include a program for calculating the usage time tx.
In addition, as the cumulative use time tx, the state where the selective reduction catalyst device 25 is new may be zero.

  The temperature acquisition device 32 is arranged at the inlet of the selective reduction catalyst device 25, and is configured by a temperature sensor that acquires the exhaust gas temperature Tx of the exhaust gas G1 passing through the inlet as the temperature of the selective reduction catalyst device 25. Yes. Instead of the temperature sensor, the temperature acquisition device 32 is based on the rotational speed of the engine 10 and the amount of fuel injected from the cylinder injection valve 12 and combusted inside the cylinder 11. An apparatus that models and predicts the exhaust gas temperature may be used.

  The nitrogen oxide concentration acquisition device 33 is disposed downstream of the selective reduction catalyst device 25 in the exhaust passage 14 with respect to the flow of the exhaust gas G1, and is contained in the exhaust gas G1 after passing through the selective reduction catalyst device 25. It is composed of a NOx sensor that acquires the concentration of nitrogen oxides.

  The ammonia concentration acquisition device 34 is arranged downstream of the ammonia catalyst device 26 in the exhaust passage 14 with respect to the flow of the exhaust gas G1, and the ammonia concentration acquisition device 34 contains ammonia contained in the exhaust gas G1 after passing through the ammonia catalyst device 26. It consists of an ammonia sensor that acquires the concentration.

  In the exhaust gas purification system 20 described above, the components to be purified contained in the exhaust gas G1 generated by the combustion of the fuel injected from the cylinder injection valve 12 inside the cylinder 11 are the devices (22, 23, 25, It is purified by passing through (26). Specifically, the oxidation catalyst device 22 oxidizes hydrocarbons, carbon oxides, and nitrogen oxides contained in the exhaust gas G1. Next, particulate matter (soluble organic matter (SOF) and soot) contained in the exhaust gas G1 is collected by the collection filter 23. Next, nitrogen oxides contained in the exhaust gas G1 are reduced by the selective reduction catalyst device 25 by a reduction reaction by ammonia generated by hydrolysis of urea water injected from the reducing agent injection valve 24. Next, ammonia contained in the exhaust gas G1 is removed by the ammonia catalyst device 26.

  As illustrated in FIG. 2, the control device 30 includes a temperature setting unit 35, an injection determination unit 36, and an injection adjustment unit 37 as functional elements. Each functional element is stored in the internal storage device as a program and is executed by the CPU in a timely manner. In addition to the program, each functional element may be a device that functions independently.

  The temperature setting unit 35 is a functional element that sets the injection permission temperature Ta based on the cumulative use time tx of the selective reduction catalyst device 25. The injection determination unit 36 is a functional element that determines whether to perform control for injection based on the temperature of the selective reduction catalyst device 25. The injection adjusting unit 37 is a functional element that adjusts the injection amount of the urea water U1 injected from the reducing agent injection valve 24 in the control for injection based on the nitrogen oxide concentration and the ammonia concentration.

  As illustrated in FIG. 3, in the exhaust gas purification method of the present invention, the cumulative use time tx is periodically monitored, and the injection permission temperature Ta is set between the lowest temperature Tl and the highest temperature Th according to the cumulative use time tx. It is a method of setting the temperature. It is assumed that the injection permission temperature Ta at the start is set to the minimum temperature Tl.

  The minimum temperature Tl is a temperature at which the selective reduction catalyst device 25 in a substantially new state (a state where the cumulative use time tx is zero) can reduce and remove nitrogen oxides using ammonia as a reducing agent without causing ammonia slip. Examples of the minimum temperature Tl include 150 ° C. to 170 ° C.

The maximum temperature Th can reduce and remove nitrogen oxides using ammonia as a reducing agent without causing the ammonia reduction slip in the selective reduction catalyst device 25 in a state where replacement is necessary (the cumulative use time tx is equal to or longer than the replacement time ta). Temperature. Examples of the maximum temperature Th include 180 ° C. to 200 ° C.

  The cumulative usage time acquisition device 31 acquires the cumulative usage time tx of the selective reduction catalyst device 25 (S110). Next, the temperature setting unit 35 determines whether or not the acquired accumulated usage time tx is less than a preset replacement time ta (S120).

  The replacement time ta is set to a time during which it is possible to determine a state in which the selective reduction catalyst device 25 is deteriorated and needs to be replaced.

  In this step, when it is determined that the accumulated usage time tx has become equal to or longer than the replacement time ta (S120: NO), the temperature setting unit 35 uses a warning device (not shown) to selectively reduce the catalytic converter 25 to the vehicle driver. Is warned (S130).

  On the other hand, when it is determined that the accumulated usage time tx is less than the replacement time ta (S120: YES), the temperature setting unit 35 determines whether or not the fixed time tb has elapsed based on the accumulated usage time tx ( S140).

  The fixed time tb is set to a time during which it can be determined that the deterioration of the selective reduction catalyst device 25 has progressed one step. For example, when the cumulative usage time acquisition device 31 is configured by an odometer, the fixed time tb is exemplified by 10,000 km.

  If it is determined in this step that the predetermined time tb has not elapsed (S140: NO), the process returns to the start.

  On the other hand, when it is determined that the predetermined time tb has elapsed (S140: YES), the temperature setting unit 35 determines whether or not the injection permission temperature Ta currently set has reached the maximum temperature Th (S150). ).

  In this step, when it is determined that the injection permission temperature Ta set at the present time has reached the maximum temperature Th (S150: NO), the process returns to the start.

  On the other hand, when it is determined that the injection permission temperature Ta set at the present time has not reached the maximum temperature Th (S150: YES), the temperature setting unit 35 sets the injection permission temperature Ta as the injection set at the current time. The temperature is set to a temperature that is a certain temperature Tb higher than the permitted temperature Ta (S160).

  The constant temperature Tb is set to a temperature at which the purification ability of the selective reduction catalyst device 25 in a state where the deterioration has progressed by one stage can be supplemented by increasing the injection permission temperature Ta by the constant temperature Tb. For example, “1 ° C.” is exemplified as the constant temperature Tb.

  When the injection permission temperature Ta corresponding to the cumulative use time tx is set, the process returns to the start and the above flow is repeated. Until the selective reduction catalyst device 25 is newly replaced, the cumulative use time tx becomes longer and the injection permission temperature Ta becomes higher.

  As illustrated in FIG. 4, the exhaust gas purification method of the present invention periodically monitors the exhaust gas temperature Tx as the temperature of the selective reduction catalyst device 25 in parallel with the flow of FIG. In this method, urea water is injected from the reducing agent injection valve 24 when the temperature Tx exceeds the injection permission temperature Ta.

  The temperature acquisition device 32 acquires the exhaust gas temperature Tx passing through the inlet of the selective reduction catalyst device 25 (S210). Next, the injection determination unit 36 determines whether or not the acquired exhaust gas temperature Tx exceeds the injection permission temperature Ta set above (S220).

  In this step, when it is determined that the exhaust gas temperature Tx has not reached the injection permission temperature Ta (S220: NO), the process returns to the start.

  On the other hand, when it is determined that the exhaust gas temperature Tx has reached the injection permission temperature Ta (S220: YES), the injection determination unit 36 gives an injection permission to the injection adjustment unit 38, and the injection adjustment unit 38 performs the reducing agent injection. Control is performed to inject urea water from the valve 24 (S230).

  As illustrated in FIG. 5, when the cumulative use time tx is zero, the selective reduction catalyst device 25 is substantially new and has not deteriorated, and the minimum temperature Tl is set as the injection permission temperature Ta. Until the cumulative use time t1, the injection permission temperature Ta is set to a stepwise high temperature step by step every time the constant time tb elapses.

  When the cumulative usage time t1 is reached, the injection permission temperature Ta reaches the maximum temperature Th. Therefore, after the cumulative use time t1, the injection permission temperature Ta is maintained at the maximum temperature Th even if the fixed time tb has elapsed.

  When the cumulative usage time t2 is reached and the replacement time ta is exceeded, a warning is issued to urge the driver to replace the selective reduction catalyst device 25. When the selective reduction catalyst device 25 is replaced by this warning, the cumulative use time tx is reset to zero, and the injection permission temperature Ta is reset to the minimum temperature Tl.

  As described above, the exhaust gas purification system 20 sets the injection permission temperature Ta according to the cumulative use time tx of the selective reduction catalyst device 25. Therefore, in order to complement the purification performance that deteriorates stepwise according to the cumulative use time tx of the selective reduction catalyst device 25, the injection permission temperature Ta is increased stepwise from the lowest temperature Tl to the highest temperature Th. Can be set to

  Specifically, the exhaust gas purification system 20 suppresses the generation of a white product due to the high purification performance of the selective reduction catalyst device 25 when the cumulative use time tx of the selective reduction catalyst device 25 is short. The injection permission temperature Ta can be set to a low temperature. This is advantageous for injecting urea water from the reducing agent injection valve 24 in a state where the exhaust gas temperature Tx is low when the selective reduction catalyst device 25 has not deteriorated, and the exhaust gas temperature Tx is The purification rate of nitrogen oxides in a low state can be improved.

  Further, the exhaust gas purification system 20 can set the injection permission temperature Ta to a high temperature when the cumulative use time tx of the selective reduction catalyst device 25 is long. This is advantageous for prohibiting the injection of urea water from the reducing agent injection valve 24 in a state where the exhaust gas temperature Tx is low when the selective reduction catalyst device 25 is deteriorating. The production of objects can be suppressed.

  In the exhaust gas purification system 20 described above, it is preferable to set the injection permission temperature Ta to a higher temperature as the cumulative use time tx becomes longer, and the injection permission temperature Ta is set to a predetermined time tb based on the cumulative use time tx. It is more preferable that the temperature is increased stepwise by a certain temperature Tb each time. In this way, the white product that is likely to occur with the passage of the cumulative use time tx by complementing the deterioration in the purification performance of the selective reduction catalyst device 25 that progresses stepwise according to the cumulative use time tx by the temperature increase. It is advantageous to reliably suppress the production of.

  In this embodiment, the injection permission temperature Ta is increased stepwise by the fixed temperature Tb every time the fixed time tb elapses. However, the fixed time tb is increased stepwise in accordance with the accumulated use time tx, and is constant. The temperature Tb may be increased stepwise. That is, the injection permission temperature Ta is preferably increased in accordance with the deterioration degree of the purification performance that progresses as the cumulative use time tx of the selective reduction catalyst device 25 elapses.

  The exhaust gas purification system 20 of the above-described embodiment has a configuration in which unburned fuel is injected by post injection of the cylinder injection valve 12 instead of the configuration in which the unburned fuel F1 is injected from the piping injection valve 21. Good. Further, in the exhaust gas purification system 20 of the above-described embodiment, the reducing agent injection valve 24 is used when the temperature of the pipe through which the urea water tank 28a, the urea water pump 28b, or the urea water U1 flows becomes equal to or higher than a predetermined temperature. It is good to make it the structure which injects urea water U1. This predetermined temperature is set to a temperature at which it can be determined that the urea water U1 has been thawed.

DESCRIPTION OF SYMBOLS 10 Engine 14 Exhaust passage 20 Exhaust gas purification system 24 Reductant injection valve 25 Selective reduction catalyst apparatus 30 Control apparatus 31 Cumulative use time acquisition apparatus 32 Temperature acquisition apparatus G1 Exhaust gas U1 Urea water tx Cumulative use time Ta Injection permission temperature Tx selection Of catalytic reduction catalyst device (exhaust gas temperature)

Claims (5)

A reducing agent injection valve that is disposed in the exhaust passage of the engine and injects urea water into the exhaust gas in order from the upstream side to the downstream side with respect to the flow of the exhaust gas, and is included in the exhaust gas using urea water as a reducing agent In an exhaust gas purification system comprising a selective reduction catalyst device for reducing nitrogen oxides,
Cumulative usage time acquisition device for acquiring the cumulative usage time of the selective reduction catalyst device, temperature acquisition device for acquiring the exhaust gas temperature at the inlet of the selective reduction catalyst device, the reducing agent injection valve, and the cumulative usage time An acquisition device, and a control device connected to the temperature acquisition device,
Based on the cumulative usage time of the selective reduction catalyst device acquired by the cumulative usage time acquisition device, an injection permission temperature is set by the control device, and the inlet of the selective reduction catalyst device acquired by the temperature acquisition device. The exhaust gas purification system is configured to control to inject urea water from the reducing agent injection valve when the exhaust gas temperature of the exhaust gas exceeds the set injection permission temperature.   The exhaust gas purification system according to claim 1, wherein the injection permission temperature becomes higher as the cumulative use time becomes longer.   2. The exhaust gas purification system according to claim 1, wherein the injection permission temperature is increased stepwise by a preset constant temperature every time a preset preset time has elapsed based on the cumulative use time.   The injection permission temperature becomes a preset minimum temperature when the cumulative use time is zero, and reaches a preset maximum temperature before the cumulative use time reaches the replacement time of the selective reduction catalyst device. The exhaust gas purification system according to any one of claims 1 to 3. The urea water is injected from the reducing agent injection valve arranged in the exhaust passage of the engine, and the urea water is reduced by the selective reduction catalyst device arranged downstream of the reducing agent injection valve with respect to the exhaust gas flow. In an exhaust gas purification method for reducing nitrogen oxides contained in exhaust gas using as
Obtaining the cumulative usage time of the selective reduction catalyst device and the exhaust gas temperature at the inlet of the selective reduction catalyst device;
Based on the acquired cumulative use time of the selective reduction catalyst device, the injection permission temperature is set,
An exhaust gas purification method comprising injecting urea water from the reducing agent injection valve when the acquired exhaust gas temperature at the inlet of the selective reduction catalyst device exceeds the set injection permission temperature.