JP2016079872A - Ozone supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress excess and deficiency in amount of produced ozone.SOLUTION: There is provided an ozone supply device for oxidizing NO contained in the exhaust gas into NOby supplying ozone to an upstream side of NOx removal device 12 in the exhaust gas passage 10ex of an internal combustion engine 10. This ozone supply device comprises: an ozonizer 30 for generating ozone through electrical discharge; taking means 41a and a control means 41b to be described as follows. The taking means 41a takes as NO reduction correlation values, some physical quantities related to a cause for reducing NOinto NO in a portion upstream of the NOx removal device 12, of the exhaust passage 10ex or within the NOx removal device. The control means 41b controls ozone production amount by the ozonizer 30 in accordance with NO reduction correlation value got by the taking means 41a.SELECTED DRAWING: Figure 1

Description

The present invention relates to an ozone supply device that changes NO in exhaust gas to NO ₂ by supplying ozone to an upstream side of a NOx purification device in an exhaust passage of an internal combustion engine.

One system that purifies NOx (nitrogen oxide) in exhaust gas is one that stores and purifies NOx (nitrogen oxide) in exhaust gas. In such NOx occlusion reaction, NO ₂ (nitrogen dioxide) is more active than NO (nitrogen monoxide). Therefore, as described in Patent Document 1, if the oxidation of NO with ozone is supplied to the exhaust passage to the NO ₂ by ozone supply device, it is possible to improve the storage efficiency.

As another NOx purification system, there is a system in which NOx is reduced and reduced by a reducing agent on a reduction catalyst. In the case of this type of system, there is a system in which urea water is supplied to the exhaust passage and ammonia is supplied to the reduction catalyst as a reducing agent, and a hydrocarbon is supplied to the exhaust passage as a reducing agent. In the case of these systems, it is known that the NOx purification rate is improved by optimizing the ratio of NO and NO _{2 in} the exhaust gas. Therefore, the NO and supplying ozone to the exhaust passage by oxidizing to NO ₂ by ozone supply device, it is desirable to improve the NOx purification rate by the optimum value the ratio of NO and NO _2.

JP 2008-163887 A

  Now, ozone is generally generated by discharge, but it is required to reduce the amount of ozone generated and to reduce power consumption in discharge. Therefore, in the conventional ozone supply device used in the various NOx purification systems described above, ozone is generated in an amount corresponding to the NO amount in the exhaust gas and supplied to the exhaust passage.

However, based on the knowledge that NO ₂ generated from NO by ozone supply may be reduced to return to NO in the upstream portion of the NOx purification device or inside the NOx purification device in the exhaust passage. The inventors obtained. When such a phenomenon occurs, the less the actual NO ₂ content than the desired NO ₂ amount, there is a concern that leads to deterioration of the NOx purification efficiency.

  This invention is made | formed in view of the said problem, The objective is to provide the ozone supply apparatus aiming at suppression of excess and deficiency of the amount of ozone production.

  The invention disclosed herein employs the following technical means to achieve the above object. Note that the reference numerals in parentheses described in the claims and in this section indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the invention. .

One of the disclosed inventions is provided in a combustion system that is disposed in an exhaust passage (10ex) of an internal combustion engine (10) and includes a NOx purification device (12, 12A) that purifies NOx in exhaust gas. Among them, in the ozone supply device that oxidizes NO in the exhaust to NO ₂ by supplying ozone to the upstream side of the NOx purification device, the ozonizer (30) that generates ozone by discharge, and the NOx purification device in the exhaust passage Acquisition means (41a) that acquires, as the NO reduction correlation value, a physical quantity that correlates with a factor that reduces NO ₂ to NO in the upstream portion or inside the NOx purification device, and NO reduction correlation acquired by the acquisition means And a control means (41b) for controlling the amount of ozone generated by the ozonizer according to the value.

According to the present invention, the ozone generation amount is controlled according to the physical quantity (NO reduction correlation value) correlated with the factor that reduces NO ₂ to NO. Therefore, the reaction of increasing the amount of ozone generated and oxidizing NO to NO ₂ can be promoted according to the factor that reduces NO ₂ to NO. Therefore, since the ozone generation amount can be adjusted in consideration of the reduction factor to NO, it is possible to suppress the excess or deficiency in the ozone generation amount due to the above phenomenon.

The schematic diagram which shows the reducing system which has a function as an ozone supply apparatus which concerns on 1st Embodiment of this invention, and the combustion system to which this apparatus is applied. The graph explaining that an oxidation reaction arises in two steps, a cold flame reaction and a hot flame reaction. The figure explaining the reaction course of a cold flame reaction. The figure which shows the range which two-step oxidation reaction produces of atmospheric temperature and equivalent ratio. The flowchart explaining the process sequence of control based on the reducing agent supply apparatus shown in FIG. The flowchart which shows the procedure of the subroutine process regarding the strong oxidation control shown in FIG. The flowchart which shows the procedure of the subroutine process based on the ozone supply control shown in FIG. The map which shows the relationship between the coefficient which correct | amends the ozone supply amount used in the process of FIG. 7, and HC density | concentration. The map which shows the relationship between the coefficient which correct | amends the ozone supply amount used by the process of FIG. 7, and CO density | concentration. The map which shows the relationship between the coefficient which correct | amends the ozone supply amount used in the process of FIG. 7, and exhaust temperature. FIG. 8 is a map showing a relationship between a coefficient for correcting an ozone supply amount and a catalyst temperature used in the process of FIG. 7, taking into consideration a reaction rate on a reduction catalyst. FIG. 8 is a map showing a relationship between a coefficient for correcting an ozone supply amount and a catalyst temperature used in the process of FIG. The test result which shows the relationship between CO density | concentration and NOx adsorption rate. The test result which shows the relationship between HC density | concentration and NOx adsorption rate. Test results showing that the NOx adsorption rate, which decreases due to CO, can be improved by ozone. Test results showing that the NOx adsorption rate, which decreases due to HC, can be improved by ozone. The schematic diagram which shows the ozone supply apparatus which concerns on 2nd Embodiment of this invention, and the combustion system to which this apparatus is applied.

  Hereinafter, a plurality of modes for carrying out the invention will be described with reference to the drawings. In each embodiment, portions corresponding to the matters described in the preceding embodiment may be denoted by the same reference numerals and redundant description may be omitted. In each embodiment, when only a part of the configuration is described, the other configurations described above can be applied to other portions of the configuration.

(First embodiment)
The combustion system shown in FIG. 1 includes an internal combustion engine 10, a supercharger 11, a NOx purification device 12, a particulate collection device (DPF 13), and a reducing agent addition device, which will be described in detail below. The combustion system is mounted on a vehicle, and the vehicle travels using the output of the internal combustion engine 10 as a drive source. The internal combustion engine 10 is a compression self-ignition type diesel engine, and light oil which is a hydrocarbon compound is used as a fuel used for combustion. The internal combustion engine 10 basically operates to burn in a lean state. That is, combustion is performed (lean combustion) in a state where the air-fuel ratio, which is the ratio between the fuel injected into the combustion chamber and the air sucked into the combustion chamber, is set to an excess of air.

  The supercharger 11 includes a turbine 11a, a rotating shaft 11b, and a compressor 11c. The turbine 11a is disposed in the exhaust passage 10ex of the internal combustion engine 10 and rotates by the kinetic energy of the exhaust. The rotating shaft 11b couples the impellers of the turbine 11a and the compressor 11c to transmit the rotational force of the turbine 11a to the compressor 11c. The compressor 11c is disposed in the intake passage 10in of the internal combustion engine 10, compresses the intake air, and supercharges the internal combustion engine 10.

  A cooler (not shown) for cooling the intake air (pressurized air) compressed by the compressor 11c is disposed on the downstream side of the compressor 11c in the intake passage 10in. The compressed intake air cooled by the cooler is adjusted in flow rate by a throttle valve (not shown) and distributed to a plurality of combustion chambers of the internal combustion engine 10. A NOx purification device 12 is disposed downstream of the turbine 11a in the exhaust passage 10ex, and a DPF 13 (Diesel Particulate Filter) is disposed further downstream. The DPF 13 collects fine particles contained in the exhaust.

  A supply pipe 23 of the reducing agent addition device is connected to the exhaust passage 10ex on the upstream side of the NOx purification device 12. The reformed fuel generated by the reducing agent addition device is added as a reducing agent from the supply pipe 23 to the exhaust passage 10ex. The reformed fuel is obtained by partially oxidizing a hydrocarbon compound (fuel) used as a reducing agent and reforming it into a partially oxidized hydrocarbon such as an aldehyde, which will be described in detail later with reference to FIG. Further, the reducing agent addition device has a function of supplying ozone from the supply pipe 23 to the exhaust passage 10ex, and provides an ozone supply device.

The NOx purification device 12 is configured by accommodating a honeycomb-shaped carrier in a housing. A coating material is provided on the surface of the carrier, and a reduction catalyst is supported on the coating material. The NOx purification device 12 purifies NOx contained in the exhaust by reacting NOx in the exhaust with the reformed fuel on the reduction catalyst and reducing it to N ₂ . The exhaust gas contains O ₂ (oxygen) in addition to NOx, but the reformed fuel reacts selectively with NOx in the presence of O ₂ .

  A reduction catalyst having a function of adsorbing NOx is used. Specifically, when the catalyst temperature is lower than the activation temperature at which the reduction reaction is possible, the reduction catalyst exhibits a function of adsorbing NOx in the exhaust. For example, the NOx purification device 12 having a NOx adsorption function is provided by a reduction catalyst made of silver alumina supported on a carrier. Specifically, it is a structure in which silver as a reduction catalyst is supported on alumina coated on the support surface. The adsorbed NOx is desorbed from the reduction catalyst when the catalyst temperature is equal to or higher than the activation temperature. The desorbed NOx is reduced and purified by the reformed fuel.

  Next, a reducing agent addition device that generates reformed fuel and adds it to the exhaust passage 10ex from the supply pipe 23 will be described. The reducing agent addition apparatus includes a reaction vessel 20, a heater 21, an injection valve 22, an ozonizer 30, and an air pump 30p described in detail below. Further, the reducing agent adding device includes a supply pipe 23 and a blower pipe 26 which will be described in detail below, and further includes an electronic control unit (ECU 40).

  The ozonizer 30 includes a housing 32 that forms a flow passage 32a therein, and a plurality of electrodes 31 are disposed in the flow passage 32a. These electrodes 31 have a flat plate shape arranged so as to face each other in parallel, and electrodes to which a high voltage is applied and electrodes having a ground voltage are alternately arranged. The voltage application to the electrode 31 is controlled by a microcomputer (microcomputer 41) provided in the ECU 40.

  The air blown by the air pump 30p flows into the housing 32 of the ozonizer 30. The air pump 30p is a centrifugal air pump, and is configured by housing an impeller driven by an electric motor in a case. This electric motor is controlled by the microcomputer 41. The air pump 30p sucks and pressurizes the air from the suction port 30in formed in the case, and blows air to the ozonizer 30. The air blown to the ozonizer 30 flows into the flow passage 32 a in the housing 32 and flows through the interelectrode passage 31 a that is a passage between the electrodes 31.

  The ozonizer 30 is connected to the reaction vessel 20 through the blower pipe 26. An electromagnetically driven check valve 26v is attached to the blower pipe 26. The microcomputer 41 controls the opening / closing drive of the check valve 26v. Specifically, the valve body of the check valve 26v is controlled to be switched between a fully open position and a fully closed position. Therefore, when the air pump 30p is driven to open the check valve 26v, the air that has flowed through the interelectrode passage 31a flows through the blower pipe 26, the reaction vessel 20, and the supply pipe 23 in order and flows into the exhaust passage 10ex. Will be. That is, the supply pipe 23 and the blower pipe 26 provide a blower pipe that guides the air blown by the air pump 30p to the exhaust passage 10ex.

  A heater 21 and an injection valve 22 are attached to the reaction vessel 20, and a reaction chamber 20a communicating with the inflow port 20in and the outflow port 20out is formed inside the reaction vessel 20. The heater 21 has a heat generating portion that generates heat when energized, and power supply to the heat generating portion is controlled by the microcomputer 41. Specifically, the amount of heat generated is controlled by the microcomputer 41 performing duty control on the amount of power supplied to the heat generating unit. The heat generating portion is disposed in the reaction chamber 20a and heats the fuel injected from the injection valve 22 to the reaction chamber 20a. The temperature of the reaction chamber 20 a is detected by a reaction chamber temperature sensor 27. The reaction chamber temperature sensor 27 outputs the detected temperature information (reaction chamber temperature Th) to the ECU 40.

  The injection valve 22 has a body in which an injection hole is formed, an electric actuator, and a valve body. When the electric actuator is energized, the valve body opens and fuel is injected from the nozzle hole into the reaction chamber 20a. When the electric actuator is turned off, the valve body closes and fuel injection is stopped. The microcomputer 41 controls the amount of fuel injected per unit time into the reaction chamber 20a by controlling energization to the electric actuator. Liquid fuel in a fuel tank (not shown) is supplied to the injection valve 22 by a fuel pump (not shown). The fuel in the fuel tank is also used as the fuel for combustion described above, and the fuel used for combustion of the internal combustion engine 10 and the fuel used as the reducing agent are shared.

  The fuel injected from the injection valve 22 into the reaction chamber 20a collides with the heat generating portion and is heated and vaporized. The vaporized fuel is mixed with the air flowing into the reaction chamber 20a from the inflow port 20in. As a result, the gaseous fuel is partially oxidized by oxygen in the air and reformed into partially oxidized hydrocarbons such as aldehydes. The reformed gaseous fuel (reformed fuel) flows into the exhaust passage 10ex through the supply pipe 23.

  When the electrode 31 of the ozonizer 30 is energized, electrons emitted from the electrode 31 collide with oxygen molecules contained in the air in the interelectrode passage 31a. Then, ozone is generated from oxygen molecules. That is, the ozonizer 30 generates oxygen as active oxygen by bringing oxygen molecules into a plasma state by discharge. Therefore, ozone is contained in the air flowing through the blower pipe 26 when the ozonizer 30 is energized.

  In the reaction chamber 20a, a cold flame reaction described in detail below occurs. This cold flame reaction is a reaction in which gaseous fuel is partially oxidized by oxygen in the air flowing in from the inlet 20in. Specific examples of such partially oxidized fuel (reformed fuel) include partial oxides (for example, aldehydes) in which a part of the fuel (hydrocarbon compound) is oxidized to aldehyde groups (CHO). It is done.

  Here, the cold flame reaction will be described in detail with reference to FIGS.

  FIG. 2 is a simulation result simulating a phenomenon in which fuel (hexadecane) is sprayed on the heater 21 to be vaporized, and the vaporized fuel stays in the vicinity of the heater 21 and is reformed. Specifically, it shows changes in various physical quantities with respect to the elapsed time from the start of exposure when gaseous fuel (hexadecane) is exposed to 430 ° C. That is, (a) in the figure shows the change in ambient temperature. (B) shows the change in the molar concentration of fuel (hexadecane). (C) shows the change in the molar concentration of each of oxygen molecules consumed by oxidation, water molecules generated by oxidation, and carbon dioxide molecules. (D) shows the change in the molar concentration of acetaldehyde and propionaldehyde, which are reformed fuels produced by the cold flame reaction. Initial conditions at the start of fuel injection are 1 atm, hexadecane concentration 2200 ppm, oxygen concentration 20%, carbon dioxide concentration 9%, and water concentration 2%.

  As shown in FIG. 2, as soon as fuel is injected, the ambient temperature increases, the molar concentration of the fuel decreases, and the molar concentration of the reformed fuel increases. This phenomenon means that the fuel is oxidized to oxygen and generates heat, and reformed fuel is generated from the fuel. That is, a cold flame reaction is occurring. However, such a temperature rise and changes in various molar concentrations are temporary, and during the period of about 4 seconds from the start of fuel injection, no temperature rise and no change in molar concentration appear.

  When about 4 seconds elapse, the atmospheric temperature further rises, the reformed fuel molar concentration decreases, and the amount of carbon dioxide and water produced and the amount of oxygen consumed increase. This phenomenon means that the reformed fuel is oxidized to oxygen and generates heat, and the reformed fuel is completely burned to generate carbon dioxide and water. That is, a hot flame reaction is occurring. In addition, the temperature rise amount by a cold flame reaction is smaller than the temperature rise amount by a hot flame reaction. Moreover, the oxygen consumption by a cold flame reaction is less than the oxygen consumption by a hot flame reaction.

  When the oxidation reaction occurs in two stages, the reformed fuel appears as an intermediate product during the period from the start of the cold flame reaction to the start of the hot flame reaction. Specific examples of the intermediate product include various hydrocarbon compounds such as aldehydes and ketones. FIG. 3 shows an example of a main reaction route through which aldehyde is generated.

  First, as shown in (1) in the figure, hydrocarbon (light oil) reacts with oxygen molecules to generate hydrocarbon peroxy radicals. This hydrocarbon peroxy radical is decomposed into an aldehyde and a hydrocarbon radical (see (2)). This hydrocarbon radical reacts with oxygen molecules to generate another hydrocarbon peroxy radical (see (3)). This hydrocarbon peroxy radical is decomposed into an aldehyde and a hydrocarbon radical (see (4)). This hydrocarbon radical reacts with oxygen molecules to generate another hydrocarbon peroxy radical (see (5)). In this way, hydrocarbon peroxy radicals are repeatedly generated while reducing the number of carbon atoms, and aldehydes are generated each time the carbon peroxy radical is generated. In the hot flame reaction, the fuel is completely burned to generate carbon dioxide and water, and no intermediate product appears. That is, the intermediate product produced by the cold flame reaction is oxidized to carbon dioxide and water.

  In the simulation shown in FIG. 2, the exposure temperature was 430 ° C. On the other hand, the present inventors further conducted analysis by simulation with different exposure temperatures. As a result, when the exposure temperature is 530 ° C., there is almost no period of staying in the cold flame reaction, and the oxidation reaction is completed in one stage. When the exposure temperature is set to 330 ° C., the start time of the cold flame reaction is delayed as compared with the case where the exposure temperature is set to 430 ° C. When the exposure temperature is 230 ° C. or lower, neither a cold flame reaction nor a hot flame reaction occurs, and no oxidation reaction occurs.

  In the simulation shown in FIG. 2, the equivalence ratio, which is the ratio between the injected fuel and the supplied air, is 0.23. On the other hand, the present inventors further performed analysis by simulation with different equivalence ratios. If the equivalence ratio is strictly defined, it is a value obtained by dividing "the weight of fuel contained in the actual air-fuel mixture" by "the weight of fuel capable of complete combustion". When the equivalence ratio is 1.0, there is almost no period of staying in the cold flame reaction, and the oxidation reaction is completed in one stage. In addition, when the equivalent ratio is 0.37, the start time of the cold flame reaction is earlier than when the equivalent ratio is 0.23. In addition, the cold flame reaction rate is increased and the cold flame reaction period is shortened. In addition, the atmospheric temperature at the time when the cold flame reaction ends is increased.

  FIG. 4 summarizes these analysis results. That is, the relationship between the exposure temperature (atmosphere temperature) and the equivalence ratio and the presence / absence of the occurrence of a cold flame reaction is shown. The horizontal axis in FIG. A region with dots in the figure represents a region where a two-stage oxidation reaction occurs. As shown in the figure, in the region where the ambient temperature is lower than the lower limit value, it becomes a non-reactive region where no oxidation reaction occurs. Even if the atmospheric temperature is higher than the lower limit, if the equivalent ratio is in the region of 1.0 or more, it becomes a one-step oxidation reaction region where the oxidation reaction is completed in one step.

  Further, the boundary line between the two-stage oxidation reaction region and the first-stage oxidation reaction region varies depending on the ambient temperature and the equivalence ratio. That is, a two-stage oxidation reaction occurs when the ambient temperature is in a predetermined temperature range and the equivalent ratio is in a predetermined equivalent ratio range. These temperature range and equivalent ratio range correspond to the range of the region with dots in FIG. When the atmospheric temperature is adjusted to an optimum temperature (for example, 370 ° C.) within a predetermined temperature range, the equivalent ratio at the boundary line becomes the maximum value (for example, 1.0). Therefore, in order to cause the cold flame reaction at an early stage, the heater temperature is adjusted to the optimum temperature and the equivalence ratio is set to 1.0. However, since the cold flame reaction does not occur when the equivalent ratio exceeds 1.0, it is desirable to adjust the equivalent ratio to a value smaller than the margin by 1.0.

  In the simulation shown in FIG. 2, the ozone concentration in the air is zero. On the other hand, the present inventors further performed an analysis by simulation with different ozone concentrations in the air. The initial conditions in this simulation are 1 atm, hexadecane concentration 2200 ppm, and ambient temperature 330 ° C. As a result, it was confirmed that the start time of the cold flame reaction was earlier as the ozone concentration was higher. Such a phenomenon caused by ozone occurs for the following reason. That is, in (1), (3), and (5) in FIG. 3, hydrocarbon radicals and oxygen molecules react, but when ozone is contained in the air, this reaction is promoted, and aldehyde Will be generated in a short time.

  The microcomputer 41 provided in the ECU 40 includes a storage device that stores a program, and a central processing unit that executes arithmetic processing according to the stored program. The ECU 40 controls the operation of the internal combustion engine 10 based on various detected values such as an accelerator pedal depression amount (engine load), an engine speed (engine speed), an intake pressure, an exhaust pressure, and the like.

  Further, the ECU 40 controls the operation of the reducing agent addition device based on the physical quantity detected by the reaction chamber temperature sensor 27 and the catalyst temperature sensor 42 in addition to the detected value of the operating state of the internal combustion engine 10 such as the engine load and the engine speed. To do. The catalyst temperature sensor 42 is attached to the NOx purification device 12 and detects the atmospheric temperature (catalyst temperature) of the reduction catalyst.

  In general, the ECU 40 controls the operation of the reducing agent adding device as follows. That is, based on the reaction chamber temperature Th, switching is performed between a reducing agent supply control for supplying a reducing agent to the exhaust passage 10ex and an ozone supply control for supplying ozone. Further, when carrying out the reducing agent addition control, strong oxidation control, weak oxidation control, and oxidation stop control are switched based on the reaction chamber temperature Th.

  Specifically, the microcomputer 41 repeatedly executes the program of the procedure shown in FIG. 5 at a predetermined cycle, thereby controlling the operation of the reducing agent adding device. First, in step S10 of FIG. 5, it is determined whether or not the internal combustion engine 10 is in operation. If it is determined that the engine is not in operation, it is assumed that NOx to be purified does not exist in the exhaust passage 10ex, and in step S18, full stop control is performed to stop the operation of the reducing agent addition device. The total stop control is control for stopping supply of the ozone and the reducing agent to the exhaust passage 10ex. That is, the air pump 30p, the ozonizer 30, the heater 21, and the injection valve 22 are all stopped, and the check valve 26v is closed.

  On the other hand, if it is determined in step S10 that the internal combustion engine 10 is in operation, it is determined in step S11 whether or not the catalyst temperature is higher than a predetermined temperature T1. When it is determined that the temperature is lower than the predetermined temperature T1, it is determined in subsequent step S12 whether or not the catalyst temperature is higher than the second predetermined temperature T2. When it is determined that the temperature is lower than the second predetermined temperature, it is determined in subsequent step S13 whether or not the catalyst temperature is higher than the activation temperature T3.

  The predetermined temperature T1 and the second predetermined temperature T2 are set to be higher than the activation temperature T3. The predetermined temperature T1 is set to be higher than the second predetermined temperature T2. For example, when the activation temperature T3 is 200 ° C., the second predetermined temperature T2 is set to 350 ° C., and the predetermined temperature T1 is set to 400 ° C. Here, the activation temperature T3 of the reduction catalyst is the lowest temperature at which NOx can be reduced and purified on the reduction catalyst.

  If it is determined in steps S11, S12, and S13 that the catalyst temperature is lower than the activation temperature T3, ozone supply control is performed in step S14. When it is determined that the catalyst temperature is higher than the activation temperature T3 and lower than the second predetermined temperature T2, strong oxidation control is performed in step S15. When it is determined that the catalyst temperature is higher than the second predetermined temperature T2 and lower than the predetermined temperature T1, weak oxidation control is performed in step S16. When it is determined that the catalyst temperature is higher than the predetermined temperature T1, oxidation stop control is performed in step S17.

  In the strong oxidation control according to step S15 in FIG. 5, a subroutine process shown in FIG. 6 is performed. First, in step S20 of FIG. 6, a detection value (reaction chamber temperature Th) by the reaction chamber temperature sensor 27 is acquired. In subsequent step S21, the heater 21 is feedback-controlled so that the obtained reaction chamber temperature Th matches the preset target temperature Ttrg. The target temperature Ttrg is set to an atmospheric temperature (for example, 370 ° C.) at which the equivalence ratio is maximum in the two-stage oxidation reaction region shown in FIG.

  In subsequent step S22, when all the NOx flowing into the NOx purification device 12 is reduced, a reducing agent addition amount for supplying the NOx purification device 12 without excess or deficiency is set as a target fuel amount Ftrg. The target fuel amount Ftrg is the mass of fuel supplied to the NOx purification device 12 per unit time.

  Specifically, the target fuel amount Ftrg is set based on the NOx inflow amount and the catalyst temperature described below. The NOx inflow amount is the mass of NOx flowing into the NOx purification device 12 per unit time. For example, the NOx inflow amount can be estimated based on the operating state of the internal combustion engine 10. The target fuel amount Ftrg is increased as the NOx inflow amount increases. Further, since the amount (reducing power) in which NOx is reduced on the reduction catalyst varies depending on the catalyst temperature, the target fuel amount Ftrg is set according to the difference in the reducing power depending on the catalyst temperature.

  In the subsequent step S23, fuel injection is performed by controlling the operation of the injection valve 22 based on the target fuel amount Ftrg set in step S22. Specifically, the valve opening time of the injection valve 22 is lengthened as the target fuel amount Ftrg increases. Alternatively, the interval from the end of the current injection to the start of the next injection is shortened.

  In the subsequent step S24, the target equivalent ratio φtrg is calculated so as to cause a cold flame reaction based on the reaction chamber temperature Th. Specifically, a maximum value of the equivalent ratio in the two-stage oxidation reaction region, which is a maximum value of the equivalent ratio corresponding to the ambient temperature, or a value obtained by subtracting a predetermined margin from the maximum value is a target equivalent ratio φtrg. As a map and stored in the microcomputer 41. A target equivalent ratio φtrg corresponding to the detected reaction chamber temperature Th is calculated with reference to the map. By setting the target equivalent ratio φtrg in consideration of the margin as described above, even if the actual equivalent ratio becomes larger than the target equivalent ratio φtrg, the possibility of exceeding the maximum value of the equivalent ratio can be reduced. The risk of reaching a hot flame reaction can be reduced.

  In the subsequent step S25, the target air amount Atrg is calculated based on the target equivalent ratio φtrg set in step S24 and the target fuel amount Ftrg set in step S22. Specifically, the target air amount Atrg is calculated so that φtrg = Ftrg / Atrg. In the following step S26, the operation of the air pump 30p is controlled based on the target air amount Atrg calculated in step S25. Specifically, the duty ratio for energizing the air pump 30p is increased as the target air amount Atrg is larger.

  As described above, the target air amount Atrg is set according to the target fuel amount Ftrg and the target temperature Ttrg is set, and the air pump 30p and the heater 21 are controlled, whereby the reaction chamber temperature Th and the equivalence ratio are set to the two-stage oxidation reaction. Adjusted to the area. Therefore, the above-described reformed fuel is generated by causing a cold flame reaction. The lower limit of the temperature range in which the reaction chamber temperature Th is adjusted is 260 ° C. serving as a boundary line between the first-stage oxidation region and the second-stage oxidation region and the non-reaction region. The upper limit of the temperature range is the maximum temperature on the boundary line between the first stage oxidation region and the second stage oxidation region. The upper limit of the range in which the equivalence ratio is adjusted is the maximum value of the boundary lines between the first stage oxidation region and the second stage oxidation region, and is an equivalent ratio corresponding to 370 ° C.

  In the subsequent step S27, the power supplied to the ozonizer 30 is controlled in accordance with the fuel concentration in the reaction vessel 20. Specifically, the target ozone amount Otrg is calculated based on the target fuel amount Ftrg. Specifically, the target ozone amount Otrg is calculated so that the ratio of the ozone concentration to the fuel concentration in the vaporizing chamber 25a becomes a predetermined value (for example, 0.2). For example, the ratio is set so that the cold flame reaction is completed within a predetermined time (for example, 0.02 seconds). Also, the target ozone amount Otrg is set to increase as the temperature of the reduction catalyst decreases.

  Then, based on the target air amount Atrg and the target ozone amount Otrg, a target energization amount Ptrg to the ozonizer 30 is calculated. Specifically, as the target air amount Atrg is larger, the residence time of air in the interelectrode passage 31a is shortened, so the target energization amount Ptrg is increased. Further, the target energization amount Ptrg is increased as the target ozone amount Otrg is increased. Next, the energization amount to the ozonizer 30 is controlled based on the target energization amount Ptrg. Specifically, as the target energization amount Ptrg is larger, the energization duty ratio to the ozonizer 30 is increased. Alternatively, the interval from the end of current energization to the start of next energization is shortened.

  By executing the process in step S27, ozone is generated and supplied to the reaction vessel 20, so that the start timing of the cool flame reaction is advanced and the cool flame reaction time is shortened. It is done. Therefore, even if the reaction vessel 20 is downsized so that the residence time of the fuel in the reaction vessel 20 is shortened, the cold flame reaction can be completed within the residence time. Therefore, the reaction vessel 20 can be downsized. In the subsequent step S28, the check valve 26v is controlled to open.

  As described above, according to the strong oxidation control of FIG. 6, the ozone generated by the ozonizer 30, the oxygen in the air, and the fuel vaporized by the heater 21 are mixed, and the fuel is partially oxidized in an environment where ozone exists. Is done. On the other hand, in the weak oxidation control in step S16 of FIG. 5, the fuel is partially oxidized in an environment where ozone is not present by stopping the ozonizer 30 and stopping ozone generation. Further, in the oxidation stop control in step S17, the ozonizer 30 and the heater 21 are stopped to stop the ozone generation and the fuel heating, so that the fuel that is not partially oxidized without being oxidized by oxygen or ozone is obtained. It is added to the exhaust passage 10ex. The fuel added in this way is exposed to high-temperature exhaust gas in the exhaust passage 10ex or the NOx purification device 12 and partially oxidized.

  More specifically, in the weak oxidation control, the process of step S27 is abolished while performing the same process as steps S20 to S26 shown in FIG. That is, the heater control, fuel injection control, air pump control, valve opening control in steps S21, S23, S26, and S28, and the target fuel amount Ftrg, target equivalent ratio φtrg, and target air amount Atrg in steps S22, S24, and S25 are set. carry out. However, the discharge control in step S27 is not performed, and energization to the ozonizer 30 is stopped to stop ozone generation.

  Further, in the oxidation stop control, the processes in steps S21 and S27 in FIG. 6 are abolished while the processes similar to S20 and S22 to S26 shown in FIG. 6 are performed. That is, fuel injection control, air pump control, valve opening control in steps S23, S26, and S28, and setting of the target fuel amount Ftrg, target equivalent ratio φtrg, and target air amount Atrg in steps S22, S24, and S25 are performed. However, the discharge control in step S27 is not performed, and energization to the ozonizer 30 is stopped to stop ozone generation. Further, the heater control in step S21 is not performed, and the energization to the heater 21 is stopped to stop the heating of the fuel.

In the ozone supply control according to step S14 in FIG. 5, the ozone generator 30 generally generates ozone in a state where the energization to the heater 21 is stopped and the energization to the injection valve 22 is stopped to stop the fuel injection. . The generated ozone is supplied to the exhaust passage 10ex through the blower pipe 26 and the supply pipe 23. As a result, when the reduction catalyst of the NOx purification device 12 is not activated, NO in the exhaust is oxidized to NO ₂ by ozone, and the amount of NOx adsorbed on the reduction catalyst increases.

However, HC and CO contained in the exhaust gas react with NO ₂ (inhibition reaction) and reduce NO ₂ to NO. The inhibition reaction occurs on the upstream side of the NOx purification device 12 in the exhaust passage 10ex, or on the reduction catalyst. Specifically, when the HC is reacted with NO _2, partial oxide of HC (HC-O) and NO occurs. CO is NO and CO ₂ occurs upon reaction with NO _2.

In addition, since HC reacts with ozone (inhibition reaction) and becomes an oxide such as aldehyde, the amount of ozone used to oxidize NO to NO ₂ by the amount of ozone that has been inhibited by HC in the supplied ozone. Decrease. Therefore, when these inhibition reactions occur, the NO ₂ concentration decreases and the amount of NOx adsorbed on the reduction catalyst decreases. Furthermore, the higher the exhaust gas temperature Tex and the catalyst temperature Tcat, the faster the reaction rate of the inhibition reaction described above, and the more the NOx adsorption amount decreases due to the NO ₂ concentration decrease.

Therefore, the inhibition reaction is promoted as the HC concentration and the CO concentration are higher and as the exhaust temperature Tex and the catalyst temperature Tcat are higher. That is, it can be said that the HC concentration, the CO concentration, the exhaust temperature Tex, and the catalyst temperature Tcat are physical quantities (NO reduction correlation values) correlated with factors that reduce NO ₂ to NO. As measures against these inhibition reactions, if the ozone supply amount is increased, the NOx adsorption amount can be suppressed as follows.

That is, excess ozone used to oxidize NO to NO ₂ reacts with CO, which is an inhibitory reaction factor, in the exhaust gas and on the reduction catalyst, and is oxidized to CO ₂ . The surplus ozone reacts with HC, which is an inhibitory reaction factor, and is oxidized to aldehyde or the like. As a result of such oxidation, the concentration of CO and HC, which are inhibitory reaction factors, decreases, so that the inhibitory reaction is suppressed.

The higher the catalyst temperature Tcat, the higher the activity and the faster the reaction rate, so that the inhibition reaction is promoted as described above. On the other hand, even when the catalyst temperature Tcat is low, the adsorptive power of NO _{2 to} the catalyst is weakened, so that the adsorbed NO ₂ is easily inhibited by CO and HC. As a countermeasure against the inhibition reaction due to such a decrease in the adsorption power, if the ozone supply amount is increased, the NOx adsorption amount can be suppressed as follows.

That is, the excess ozone used to oxidize NO to NO ₂ further oxidizes NO ₂ and changes it to N ₂ O ₅ (dinitrogen pentoxide) and HNO ₃ (nitric acid). N ₂ O ₅ and HNO ₃ have stronger adsorption power to the catalyst than NO ₂ . Thus, the excess of ozone increases the suction force to NO _2, NO ₂ adsorption state can be prevented to inhibit the reaction with CO and HC.

  In view of these points, the microcomputer 41 controls the ozone supply amount according to the NO reduction correlation value. That is, as the HC concentration is higher, the CO concentration is higher, and the exhaust temperature Tex is higher, the ozone generation amount by the ozonizer 30 is increased and the ozone supply amount is increased. Regarding the catalyst temperature Tcat, the ozone generation amount is changed in consideration of both the influence of the reaction rate and the influence of the adsorption force.

  Hereinafter, the subroutine of the ozone supply control will be described with reference to FIG. First, in step S30, the NO concentration, HC concentration, and CO concentration in the exhaust are acquired. Specifically, these concentrations are estimated based on the operating state of the internal combustion engine 10. In the subsequent step S31, the catalyst temperature Tcat and the exhaust temperature Tex are acquired. The catalyst temperature Tcat is detected and acquired by the catalyst temperature sensor 42. The exhaust temperature Tex is estimated based on the operating state of the internal combustion engine 10. Note that the microcomputer 41 when acquiring the HC concentration, the CO concentration, the catalyst temperature Tcat, and the exhaust temperature Tex as described above acquires the physical quantity (NO reduction correlation value) correlated with the factor of the inhibition reaction described above. Means 41a (see FIG. 1) is provided.

In subsequent step S32, a base ozone amount Obase is calculated based on the NO concentration acquired in step S30. Specifically, the exhaust flow rate is estimated based on the operating state of the internal combustion engine 10, and the NO amount flowing into the NOx purification device 12 per unit time is estimated based on the flow rate and the NO concentration. The amount of ozone necessary to oxidize all of this NO amount to NO ₂ is the base ozone amount Obase.

  In subsequent step S33, a correction coefficient K1 for the base ozone amount Obase is calculated based on the HC concentration acquired in step S30. The correction coefficient K1 is a real number equal to or greater than 1. The larger the value of the correction coefficient K1, the larger the correction amount that increases the base ozone amount Obase. For example, the optimum value of the correction coefficient K1 corresponding to the HC concentration is obtained by testing in advance, and the optimum value is stored in the ECU 40 in the map format shown in FIG. Then, referring to the map, the correction coefficient K1 is determined based on the acquired HC concentration.

  In subsequent step S34, a correction coefficient K2 for the base ozone amount Obase is calculated based on the CO concentration acquired in step S30. The correction coefficient K2 is a real number equal to or greater than 1. The larger the value of the correction coefficient K2, the larger the correction amount that increases the base ozone amount Obase. For example, the optimum value of the correction coefficient K2 corresponding to the CO concentration is obtained by testing in advance, and the optimum value is stored in the ECU 40 in the map format shown in FIG. Then, referring to the map, the correction coefficient K2 is determined based on the acquired CO concentration.

  Here, if the ozone increase amount is increased as the HC concentration or the CO concentration is higher, the ozone supply amount can be reduced with less excess or deficiency in consideration of the suppression of the inhibition reaction described above. However, in the region where the HC concentration or CO concentration is equal to or higher than the predetermined concentration, the inhibitory reaction suppression effect due to the increase in ozone cannot be expected. In view of this point, if the HC concentration and the CO concentration are regions of a predetermined concentration or more, the correction coefficients K1 and K2 are set to the maximum values K1a and K2a regardless of the difference in the HC concentration and the CO concentration (see FIGS. 8 and 9). ).

  In subsequent step S35, a correction coefficient K3 for the base ozone amount Obase is calculated based on the exhaust temperature Tex acquired in step S31. The correction coefficient K3 is a real number equal to or greater than 1. The larger the value of the correction coefficient K3, the larger the correction amount that increases the base ozone amount Obase. For example, the optimum value of the correction coefficient K3 corresponding to the exhaust temperature Tex is obtained by testing in advance, and the optimum value is stored in the ECU 40 in the form of a map shown in FIG. Then, referring to the map, the correction coefficient K3 is determined based on the acquired exhaust gas temperature Tex.

  In the example shown in FIG. 10, the correction coefficient K3 is set so that the ozone increase amount increases as the exhaust gas temperature Tex increases. However, the characteristic line shown in FIG. 10 varies depending on various conditions such as the type of the reduction catalyst. Different. For example, when the exhaust gas temperature Tex is higher, the ozone increase amount is decreased, the characteristic line is a convex curve on the upper side of FIG. 10, or the lower curve is a convex curve, depending on various conditions.

  In subsequent step S36, a correction coefficient K4 for the base ozone amount Obase is calculated based on the catalyst temperature Tcat acquired in step S31. The larger the value of the correction coefficient K4, the larger the correction amount that increases the base ozone amount Obase. The correction coefficient K4 is set based on two types of correction coefficients K4a and K4b described below.

That is, the higher the catalyst temperature Tcat, the faster the reaction rate of the inhibition reaction that occurs on the reduction catalyst, while the lower the catalyst temperature Tcat, the weaker the NO ₂ adsorption force on the reduction catalyst, as described above. It is. Therefore, considering the reaction rate, it is desirable to set the correction coefficient K4a as shown in FIG. 11 so that the ozone amount increases as the temperature increases. On the other hand, considering the adsorption force, it is desirable to set the correction coefficient K4b as shown in FIG. 12 so that the ozone amount increases as the temperature decreases.

  For example, the optimum values of the correction coefficients K4a and K4b corresponding to the catalyst temperature Tcat are obtained by testing in advance, and the optimum values are stored in the ECU 40 in the map format shown in FIGS. Then, with reference to the map, correction coefficients K4a and K4b are calculated based on the acquired catalyst temperature Tcat to determine the correction coefficient K4. Therefore, the correction coefficient K4 based on the catalyst temperature Tcat may increase the ozone as the temperature is higher depending on the temperature range, and decrease the ozone as the temperature is higher depending on the temperature range.

  In subsequent step S37, the base ozone amount Obase calculated in step S32 is corrected based on the correction coefficients K1, K2, K3, and K4 calculated in steps S33 to S36. For example, the corrected target ozone amount Otrg is calculated by multiplying the base ozone amount Obase by each of the correction coefficients K1, K2, K3, and K4. In short, the target ozone amount Otrg is set by increasing the correction amount for increasing the base ozone amount Obase as the environment is more susceptible to an inhibition reaction. The target ozone amount Otrg is a target value of the ozone amount supplied to the exhaust passage 10ex per unit time.

  In subsequent step S38, discharge control for the ozonizer 30 is performed based on the target ozone amount Otrg calculated in step S37. Specifically, the amount of power supplied to the electrode 31 is increased as the target ozone amount Otrg is increased. In the subsequent step S39, the operation of the air pump 30p is controlled based on the target ozone amount Otrg. Specifically, as the target ozone amount Otrg increases, the amount of power supplied to the electric motor of the air pump 30p is increased to increase the amount of air blown by the air pump 30p.

  In the subsequent step S40, the check valve 26v is controlled to open. In the subsequent step S41, energization to the heater 21 is stopped, and energization to the injection valve 22 is stopped to stop fuel injection. When the heater 21 is energized contrary to this embodiment, ozone is heated and collapses. Moreover, if fuel injection is implemented, ozone will react with fuel. In view of these points, since heating by the heater 21 is stopped and fuel injection is stopped in step S40, it is possible to avoid ozone reacting with the fuel and heating collapse. Therefore, the generated ozone is added to the exhaust passage 10ex as it is.

As described above, according to the present embodiment, the acquisition unit 41a that acquires a physical quantity (NO reduction correlation value) correlated with the factor that reduces NO ₂ to NO, and the ozone generation amount is controlled based on the acquired NO reduction correlation value. Control means 41b. Therefore, the reaction of increasing the amount of ozone generated and oxidizing NO to NO ₂ can be promoted according to factors that reduce NO ₂ to NO, that is, the HC concentration, the CO concentration, the exhaust temperature Tex, and the catalyst temperature Tcat. Therefore, since the ozone generation amount can be adjusted in consideration of the reduction factor to NO, it is possible to suppress the excess or deficiency in the ozone generation amount due to the inhibition reaction.

The present inventors have obtained the following findings. That is, as described above, the higher the HC concentration and the CO concentration, the higher the concern about the NO ₂ concentration decrease due to the inhibition reaction. On the other hand, since the degree to which HC and CO are oxidized to ozone increases if the ozone supply amount is increased, the concern can be suppressed. Further, if the ozone supply amount is increased, NO ₂ is further oxidized and the adsorption power is increased. In the present embodiment in view of these findings, the NO reduction correlation value acquired by the acquisition unit 41a includes the HC concentration and the CO concentration in the exhaust, and the control unit 41b The higher the CO concentration, the greater the ozone generation amount. Therefore, it can suppress that excess and deficiency arises in the amount of ozone production.

The present inventors have confirmed the effect of increasing the ozone generation amount as described above based on the test results shown in FIGS. The reduction catalyst shown in FIG. 1 selectively reacts the reducing agent with NOx in the presence of O ₂ , whereas the catalyst used in this test is NOx in a lean environment in the presence of O _2. And the reducing agent reacts with NOx in a rich environment.

The test conditions in FIG. 13 are an NO concentration of 100 ppm, an ozone concentration of 100 ppm, an HC concentration of zero, and a catalyst temperature of 180 ° C., and the NOx adsorption rate is measured by changing the CO concentration. The test results shown in FIG. 13 indicate that the NOx adsorption rate decreases as the CO concentration increases. The test conditions in FIG. 14 are an NO concentration of 100 ppm, an ozone concentration of 100 ppm, a CO concentration of zero, and a catalyst temperature of 180 ° C., and the NO x adsorption rate is measured by changing the C ₃ H ₆ concentration. The test results shown in FIG. 14 indicate that the NOx adsorption rate decreases as the C ₃ H ₆ concentration increases.

  The test conditions of FIG. 15 are NO concentration 100 ppm, CO concentration 300 ppm, HC concentration zero, catalyst temperature 180 ° C., and the NOx adsorption rate is measured by changing the ozone concentration. The test results shown in FIG. 15 indicate that the NOx adsorption rate is almost zero when the ozone concentration is zero in an environment with a CO concentration of 300 ppm, whereas the NOx adsorption rate can be significantly improved by increasing the ozone concentration.

The test conditions in FIG. 16 are an NO concentration of 100 ppm, a C ₃ H ₆ concentration of 300 ppm, a CO concentration of zero, and a catalyst temperature of 180 ° C., and the NOx adsorption rate is measured by changing the ozone concentration. The test results shown in FIG. 16 show that the NOx adsorption rate is almost zero when the ozone concentration is zero in an environment with a C ₃ H ₆ concentration of 300 ppm, whereas the NOx adsorption rate can be greatly improved by increasing the ozone concentration. Represents. From the above, according to the test results of FIGS. 13 to 16, it has been clarified that the decrease in the NOx adsorption rate caused by HC and CO is improved by supplying ozone.

  Furthermore, the present inventors obtained the following knowledge. That is, as described above with reference to FIGS. 8 and 9, in the region where the HC concentration or the CO concentration is equal to or higher than the predetermined concentration, the effect of suppressing the inhibition reaction due to the increase in ozone cannot be expected. In the present embodiment in view of this knowledge, the control unit 41b sets the correction coefficients K1 and K2 regardless of the difference in the HC concentration or the CO concentration as long as the acquired HC concentration or the CO concentration is in the region of the predetermined concentration or more. Fix and set the amount of ozone generated. Therefore, it is possible to avoid unnecessarily increasing the ozone generation amount.

Furthermore, the present inventors obtained the following knowledge. That is, as described above, the higher the exhaust gas temperature Tex, the more the inhibition reaction is promoted, and the fear of the NO ₂ concentration decrease increases. On the other hand, since the degree to which HC and CO are oxidized to ozone increases if the ozone supply amount is increased, the concern can be suppressed. In the present embodiment in view of this knowledge, the NO reduction correlation value acquired by the acquisition unit 41a includes the exhaust gas temperature Tex, and the ozone generation amount is controlled according to the exhaust gas temperature Tex. The shortage can be suppressed.

Furthermore, the present inventors obtained the following knowledge. That is, as described above, the lower the catalyst temperature Tcat, the lower the NO ₂ adsorbing power, so that the NO ₂ concentration decreases due to the inhibition reaction reduced to NO. On the other hand, if the ozone supply amount is increased, NO ₂ is further oxidized and changed to nitric acid having a strong adsorptive power. In the present embodiment in view of this knowledge, the NO reduction correlation value acquired by the acquisition unit 41a includes the catalyst temperature Tcat, and the ozone generation amount is controlled according to the catalyst temperature Tcat. The shortage can be suppressed.

  Now, during steady operation of the internal combustion engine 10, the exhaust gas temperature Tex and the catalyst temperature Tcat are almost the same value. However, during a transient operation in which the load suddenly increases in the internal combustion engine 10, the catalyst temperature Tcat rises behind the rise in the exhaust gas temperature Tex, so that there is a difference between the two temperatures. In this embodiment in view of this point, the exhaust temperature Tex and the catalyst temperature Tcat are acquired, and the correction coefficients K3 and K4 are set according to each temperature. Therefore, even when there is a difference between the exhaust temperature Tex and the catalyst temperature Tcat as described above, it is possible to control the generation of ozone without excess or deficiency.

  Furthermore, according to this embodiment, the reduction catalyst is a substance containing at least silver. Specifically, a silver catalyst is supported on alumina coated on a carrier. By employing a silver catalyst in this way, the partial oxidation reaction of FIG. 3 is more likely to occur than when a platinum catalyst is employed, for example. Therefore, according to this embodiment that employs a silver catalyst, the NOx purification rate can be improved as compared with the case where a platinum catalyst is employed. In particular, the effect of improving the NOx purification rate is remarkably exhibited in the low temperature region of the temperature region where the catalyst temperature Tcat is activated.

  Furthermore, in this embodiment, the reducing agent heated to a predetermined temperature or higher by the heater 21 is partially oxidized by oxygen contained in the air to be reformed. According to this, partial oxidation of the fuel can be easily realized, and reforming of the reducing agent can be easily realized. Further, by heating the fuel with the heater 21, cracking that causes the fuel to decompose into a hydrocarbon compound having a small number of carbon atoms occurs. And since the boiling point of the hydrocarbon whose carbon number decreased by cracking becomes low, it is suppressed that the vaporized fuel returns to a liquid.

  Furthermore, in the present embodiment, ozone generated by the ozonizer 30 is supplied when a cold flame reaction is caused by strong oxidation control. Therefore, it is possible to accelerate the start time of the cold flame reaction and shorten the cold flame reaction time. Therefore, even if the reaction vessel 20 is downsized so that the residence time of the fuel in the reaction chamber 20a is shortened, the cold flame reaction can be completed within the residence time. Therefore, the reaction vessel 20 can be downsized.

(Second Embodiment)
In the first embodiment, the reducing agent addition device having a function of supplying ozone provides the ozone supply device according to the present invention. On the other hand, in the present embodiment, the ozone supply device shown in FIG. 17 is provided, which is a device in which the reaction vessel 20, the heater 21, and the injection valve 22 shown in FIG. 1 are eliminated. The ozone supply device includes an ozonizer 30, an air pump 30p, a blower pipe 26, a supply pipe 23, a check valve 26v, and an ECU 40.

Further, the NOx purification device 12 shown in FIG. 1 employs a reduction catalyst that selectively reacts the reducing agent with NOx in the presence of O ₂ . In contrast, the NOx purification device 12A according to the present embodiment employs a reduction catalyst that stores NOx in a lean environment in the presence of O ₂ and reacts a reducing agent with NOx in a rich environment.

  In the control according to the present embodiment, the processing contents shown in FIGS. 5 and 6 are changed as follows. That is, the determinations in steps S11 and S12 shown in FIG. 5 are abolished, and the reducing agent supply control in steps S15, S16, and S17 is abolished. When it is determined in step S13 that the catalyst temperature is higher than T3, the full stop control in step S18 is performed.

  Further, the processing of steps S20, S21, S22, and S25 shown in FIG. 6 is abolished. The target air amount Atrg used for the air pump control in step S26 is set according to the NO concentration in the exhaust. In step S27, the power supplied to the ozonizer 30 is controlled according to the NO concentration in the exhaust gas. In short, the higher the NO concentration in the exhaust, the greater the amount of ozone supplied.

  The processing of FIG. 7 is performed in the present embodiment as well as in the first embodiment. That is, the ozone generation amount is controlled based on the NO reduction correlation value. Therefore, according to the present embodiment as well, it is possible to suppress an excess or deficiency in the ozone generation amount due to the inhibition reaction in the same manner as in the first embodiment.

(Other embodiments)
The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made as illustrated below. Not only combinations of parts that clearly show that combinations are possible in each embodiment, but also combinations of embodiments even if they are not explicitly stated, unless there is a problem with the combination. Is also possible.

The present inventors have obtained the following findings. That is, the exhaust contains sulfur components, which can be adsorbed by the catalyst. The adsorbed sulfur component is less likely to be desorbed from the catalyst than NO ₂ and is likely to accumulate in the catalyst, so that the amount of sulfur adsorbed on the catalyst increases and eventually the NO ₂ adsorption amount decreases. is there. When the sulfur poisoning progresses, the suction force to NO ₂ in the catalyst is weakened. As a result, the adsorbed NO ₂ is liable to inhibit the CO and HC. Therefore, the greater the sulfur adsorption amount (the poisoning amount), the lower the NO ₂ adsorption power. That is, it can be said that the sulfur adsorption amount is a physical quantity (capture force correlation value) correlated with the NO ₂ capture force. In view of this point, the acquisition unit 41a may acquire the sulfur adsorption amount, and the control unit 41b may control the ozone generation amount based on the acquired sulfur adsorption amount.

  The characteristic lines illustrated in FIGS. 10 and 11 may be different depending on the ratio between the HC concentration and the CO concentration. In view of this point, the ozone supply amount correction coefficients K3 and K4 according to the catalyst temperature Tcat or the exhaust temperature Tex may be variably set according to the ratio. Further, a function representing the relationship between a plurality of types of NO reduction correlation values such as HC concentration, CO concentration, exhaust gas temperature Tex, catalyst temperature Tcat and the like and the total correction coefficient is stored in the microcomputer 41 in advance. Then, the total correction coefficient may be calculated by substituting the obtained plural types of NO reduction correlation values into the above function, and the target ozone amount Otrg may be calculated by multiplying the base ozone amount Obase by the total correction coefficient.

  In each of the above embodiments, the HC concentration, the CO concentration, the exhaust gas temperature Tex, and the catalyst temperature Tcat are used as the NO reduction correlation value in controlling the ozone supply amount according to the NO reduction correlation value. In contrast, the present invention is not limited to acquiring all these NO reduction correlation values and controlling the ozone supply amount. For example, at least one of all these NO reduction correlation values is acquired. Then, the ozone supply amount may be controlled.

  In each of the above embodiments, the catalyst temperature sensor 42 attached to the NOx purification device 12 is provided, and the atmospheric temperature (catalyst temperature) of the reduction catalyst is directly detected. On the other hand, the catalyst temperature sensor 42 may be eliminated, and the catalyst temperature may be estimated based on, for example, the operating state of the internal combustion engine 10.

  In step S30 in FIG. 7, the NO concentration, HC concentration, and CO concentration in the exhaust gas are estimated based on the operating state of the internal combustion engine 10, but these concentrations may be directly detected by a sensor. In step S31 of FIG. 7, the catalyst temperature Tcat is detected by the catalyst temperature sensor 42. However, the catalyst temperature Tcat may be estimated based on the operating state of the internal combustion engine 10 and the detected value of the exhaust temperature sensor. In step S31 of FIG. 7, the exhaust gas temperature Tex is estimated based on the operating state of the internal combustion engine 10, but an exhaust gas temperature sensor may be provided to directly detect the exhaust gas temperature Tex.

  In the first embodiment, a catalyst containing silver is used as the reduction catalyst. However, the present invention is not limited to such a silver catalyst. For example, a catalyst containing copper or iron is used as the reduction catalyst. May be. In the first embodiment, a reduction catalyst that physically captures (that is, adsorbs) NOx is employed. However, the combustion system employs a reduction catalyst that captures (or stores) NOx by chemical bonding. A reducing agent addition device may be applied. Specific examples of the reduction catalyst that occludes in this way include a catalyst in which an alkaline earth metal such as barium or an alkali metal such as lithium is combined with platinum.

  When the internal combustion engine 10 is burning in a state leaner than the stoichiometric air-fuel ratio, the reducing agent addition device is applied to a combustion system in which the NOx purification device 12 adsorbs NOx and reduces NOx in other than lean combustion. Also good. In this case, ozone may be generated during lean combustion, and reformed fuel may be generated at times other than lean combustion. As a specific example of the catalyst that captures NOx during lean combustion in this way, an occlusion reduction catalyst using platinum and barium supported on a carrier can be cited. Moreover, in the said 1st Embodiment, although the fuel is used for the reducing agent added to the exhaust passage 10ex, the ozone supply apparatus which concerns on this invention is added to the combustion system which added urea water and used ammonia as a reducing agent. May be applied.

  Although the electromagnetically driven check valve 26v is employed in the first embodiment, a mechanical check valve may be employed. In the first embodiment, the air pump 30p is disposed on the upstream side of the ozonizer 30, but may be disposed on the downstream side of the ozonizer 30. In each of the above embodiments, the DPF 13 is disposed on the downstream side of the NOx purification device 12 in the exhaust passage 10ex, but may be disposed on the upstream side of the NOx purification device 12.

  In the reforming according to the first embodiment, when the reducing agent supply control is performed, the reforming is performed so that the ratio of the aldehyde contained in the reducing agent is a predetermined ratio (for example, 10%). On the other hand, according to the amount of NOx flowing into the NOx purification device 12 and the catalyst temperature, the aldehyde ratio may be variably set for reforming. Further, the modified reducing agent according to the present invention is not limited to containing an aldehyde. For example, a reducing agent addition apparatus using alcohol, acetate, carbon monoxide, or hydrogen as a partial oxide may be used.

  In the embodiment shown in FIG. 1, a reducing agent addition device is applied to a combustion system mounted on a vehicle. On the other hand, a reducing agent addition device may be applied to a stationary combustion system. In the embodiment shown in FIG. 1, a reducing agent addition device is applied to a compression self-ignition diesel engine, and light oil used as a fuel for combustion is used as a reducing agent. On the other hand, gasoline used as a fuel for combustion may be used as a reducing agent by applying a reducing agent addition device to an ignition ignition type gasoline engine.

  Means and / or functions provided by the ECU 40 (control device) can be provided by software recorded in a substantial storage medium and a computer that executes the software, only software, only hardware, or a combination thereof. For example, if the controller is provided by a circuit that is hardware, it can be provided by a digital circuit including a number of logic circuits, or an analog circuit.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 10ex ... Exhaust passage, 12, 12A ... NOx purification apparatus, 30 ... Ozonizer, 41a ... Acquisition means, 41b ... Control means.

Claims (5)

An exhaust passage (10ex) of the internal combustion engine (10) is provided in a combustion system provided with a NOx purification device (12, 12A) for purifying NOx in the exhaust, and upstream of the NOx purification device in the exhaust passage. In the ozone supply device that oxidizes NO in the exhaust to NO ₂ by supplying ozone to the side,
An ozonizer (30) for generating ozone by electric discharge;
Acquisition means (41a) for acquiring, as a NO reduction correlation value, a physical quantity correlated with a factor that reduces NO ₂ to NO in a portion of the exhaust passage upstream of the NOx purification device or inside the NOx purification device. When,
Control means (41b) for controlling the amount of ozone generated by the ozonizer according to the NO reduction correlation value obtained by the obtaining means;
An ozone supply device comprising: The NO reduction correlation value acquired by the acquisition means includes at least one of HC concentration and CO concentration in exhaust gas,
2. The ozone supply device according to claim 1, wherein the control unit increases the ozone generation amount as the HC concentration or the CO concentration acquired by the acquisition unit is higher.   The control means sets the ozone generation amount regardless of the difference in the HC concentration or the CO concentration if the HC concentration or the CO concentration obtained by the obtaining means is in a region of a predetermined concentration or more. The ozone supply device according to claim 2.   The ozone supply device according to any one of claims 1 to 3, wherein the NO reduction correlation value acquired by the acquisition means includes an exhaust gas temperature. The NOx purification device has a function of capturing NO ₂ in the exhaust,
The ozone supply device according to any one of claims 1 to 4, wherein the NO reduction correlation value acquired by the acquisition means includes a temperature of the NOx purification device.

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