JP2011122471A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system promptly raising temperature of an exhaust emission control device provided in an exhaust system. <P>SOLUTION: The exhaust emission control system sets an OC ratio based on the temperature of the exhaust emission control device in the exhaust system and controls a fuel reformer based on the set value of the OC ratio. Operation modes of the fuel reformer are classified, according to the set value of the OC ration, into three or more of a reform stoichiometric mode in which a proportion of hydrogen and carbon monoxide in reformed gas produced is large as compared with other operation modes, a reform rich mode in which a proportion of light hydrocarbon in reformed gas produced is large as compared with other operation modes, and a reform lean mode in which a proportion of oxygen in materials supplied to a reforming catalyst is large as compared with other operation mode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

  In recent years, various environmental pollutants discharged into the atmosphere from internal combustion engines such as generators and automobiles have been regarded as problems. Environmental pollutants cause acid rain and photochemical smog as well as damage to human health, and there is a movement to regulate their emissions worldwide. In particular, in an internal combustion engine such as a diesel engine or a gasoline lean burn engine, lean combustion is performed, and therefore, for example, a large amount of nitrogen oxide (NOx) and particulate matter (Particulate Matter (PM)) are discharged. In recent years, various techniques for efficiently purifying exhaust containing NOx and PM have been proposed.

  For example, in Patent Documents 1 and 2 and Non-Patent Document 1, a NOx occlusion reduction catalyst is provided in the exhaust system, and during the lean operation in which the exhaust gas is excessive in oxygen, the exhaust gas is passed through an oxidation catalyst active species to convert NOx into an alkali metal or alkali. An exhaust purification system that reduces the stored NOx during a rich operation where the oxygen concentration of the exhaust gas is reduced by reacting with an earth metal or the like to reduce the oxygen concentration of the exhaust gas is shown. In this exhaust purification system, NOx occlusion and NOx reduction can be performed periodically by repeating the lean operation and the rich operation.

  Patent Documents 3 and 4 show an exhaust purification system using urea water. In this system, NOx in the exhaust is adsorbed by a selective reduction catalyst provided in the exhaust system, and ammonia is generated by hydrolysis from urea water sprayed from the upstream side of the catalyst, and this ammonia is adsorbed as a reducing agent. Is decomposed into nitrogen and water to purify the exhaust.

  Patent Documents 5 and 6 show an exhaust gas purification system in which an exhaust gas purification filter (hereinafter referred to as “DPF (Diesel Particulate Filter)”) is provided in an exhaust system and PM contained in the exhaust gas is collected by this filter. ing. Since the DPF has a limit in the amount of PM that can be collected, it is necessary to periodically perform a regeneration process for burning the accumulated PM. In Patent Document 5, an oxidation catalyst is provided upstream of the DPF, and in the regeneration process of the DPF, unburned fuel is injected upstream of the oxidation catalyst in the exhaust system (hereinafter referred to as “exhaust injection”). There is shown a technique in which the PM accumulated in the DPF is burned by raising the exhaust gas temperature by burning fuel with an oxidation catalyst. Further, in Patent Document 6, in the DPF regeneration process, fuel is burned by an oxidation catalyst upstream of the DPF by performing fuel injection (hereinafter referred to as “post-injection”) during the cylinder exhaust process, unlike the above-described exhaust injection. Technology to raise the exhaust temperature is shown.

Japanese Patent No. 2,586,738 Japanese Patent No. 2600492 Japanese Patent No. 3051142 Japanese Unexamined Patent Publication No. 1-447427 Japanese Patent No. 3835241 Japanese Patent Laid-Open No. 8-43436

“Development of NOx storage-reduction type three-way catalyst system” Automobile Engineering Society Proceedings Vol. 26, no. 4, October, 1995

  In the NOx storage-reduction catalysts of Patent Documents 1 and 2 and Non-Patent Document 1, alkali metal or alkaline earth metal is used to store NOx during lean operation, oxidation of HC, CO, NOx during lean operation, and In addition, a noble metal such as platinum is used for NOx reduction during the rich operation. Since the alkali metal or alkaline earth metal is a strongly basic substance, the activity of the noble metal tends to decrease. Therefore, in order to maintain the NOx purification performance high, it is necessary to increase the catalyst temperature. In this case, although the exhaust gas temperature can be raised and the catalyst temperature can be raised by retarding the fuel injection timing or reducing the intake throttle, the fuel consumption may be deteriorated.

  Even in the exhaust purification system using the selective reduction catalyst of Patent Documents 3 and 4, there is a problem that NOx in the exhaust cannot be sufficiently purified unless the catalyst temperature is raised to about 150 ° C. or higher.

When the DPF is regenerated by performing exhaust injection as in the exhaust purification system of Patent Document 5, unburned fuel may directly adhere to the DPF or other catalytic converters. Then, there is a possibility that only the portion where the fuel adheres becomes locally hot and heat deterioration occurs, or the temperature is locally lowered due to the latent heat of vaporization of the fuel and coking is generated.
Further, as in the exhaust gas purification system of Patent Document 6, when the DPF is regenerated by performing post injection, fuel is injected during the exhaust process of the cylinder, so that part of the injected fuel adheres to the cylinder wall surface, and the engine There is a risk of contamination in oil. Therefore, as a result, there is a possibility that fuel efficiency may deteriorate due to fuel loss or oil dilution may occur.
In both exhaust injection and post-injection, the hydrocarbon oxidation reaction occupies most of the energy that contributes to the temperature increase of the DPF. For this reason, it is necessary to maintain the oxidation catalyst at a temperature at which hydrocarbons can undergo an oxidation reaction. Therefore, if the low load operation is continued, the temperature of the oxidation catalyst is lowered, and the DPF may not be regenerated.

  The present invention has been made in consideration of the above-described points, and an object thereof is to provide an exhaust purification system capable of quickly raising the temperature of an exhaust purification device provided in an exhaust system.

  To achieve the above object, the present invention generates a reformed gas by supplying a raw material containing fuel and air to a reforming catalyst (for example, a reforming catalyst 41 described later), and the generated reformed gas is used as an internal combustion engine. Provided is an exhaust purification system (for example, an exhaust purification system 1 to be described later) provided with a fuel reformer (for example, an after-mentioned fuel reformer 4) to be supplied to an engine exhaust system (for example, an exhaust pipe 2 to be described later). . The exhaust purification system is based on exhaust temperature acquisition means (for example, exhaust temperature sensor 61 and ECU 5 described later) for acquiring the temperature of the exhaust system and the temperature of the exhaust system acquired by the exhaust temperature acquisition means. Parameter setting means (for example, ECU 5 described later and means for executing the reformer control process in FIG. 4) for setting a parameter (for example, OC ratio described later) having a correlation with the ratio of oxygen and carbon of the raw material; , And reformer control means (for example, ECU 5 described later and means for executing reformer control processing in FIG. 4) for controlling the fuel reformer based on the set value of the parameter.

According to the present invention, a fuel reformer is provided in which a reformed gas is generated by supplying a raw material containing fuel and air to a reforming catalyst, and the generated reformed gas is supplied to an exhaust system of an internal combustion engine. The reformed gas generated by the reforming catalyst contains light hydrocarbons and the like in addition to hydrogen and carbon monoxide that can be combusted at low temperatures. Therefore, by supplying such a reformed gas to the exhaust system and combusting the reformed gas, it is possible to raise the temperature of the exhaust system or an exhaust purification device provided in the exhaust system.
In addition, since the temperature of the exhaust system is raised with the reformed gas, there is no need to retard the fuel injection timing, throttle the intake throttle, or perform post injection as in the prior art. For this reason, the internal combustion engine can be continuously operated under optimum conditions while raising the temperature of the exhaust system, so that the exhaust discharged from the internal combustion engine can be cleaned and the fuel consumption can be improved. In addition, unlike the above-described exhaust injection that supplies unburned fuel, the exhaust system is heated with the reformed gas in a gas state generated by the reforming catalyst, and therefore the exhaust purification device provided in the exhaust system is unburned. Since the fuel does not adhere, there is no local high temperature and thermal degradation, and no local temperature decrease and coking.
Since hydrogen and carbon monoxide contained in the reformed gas have characteristics of burning from low temperatures compared to hydrocarbons, the temperature of the low-temperature exhaust system is increased by burning hydrogen and carbon monoxide in the reformed gas. can do. On the other hand, hydrocarbons have a characteristic that the heat of combustion is larger than that of hydrogen or carbon monoxide, so that the exhaust system can be quickly heated by burning hydrocarbons in the reformed gas. Therefore, according to the present invention, a parameter having a correlation with the ratio of oxygen and carbon is set based on the temperature of the exhaust system, and the temperature of the exhaust system is controlled by controlling the fuel reformer based on the set value of this parameter. Therefore, the exhaust gas can be efficiently heated.
In addition, by controlling the fuel reformer based on a parameter setting value that correlates with the ratio of raw material oxygen to carbon, it is possible to prevent thermal runaway of the fuel reformer and excessive coke accumulation. .

From the above, for example, when a DPF is provided in the exhaust system, PM deposited on the DPF can be combusted by supplying a reformed gas having a composition ratio suitable for the temperature of the DPF. Therefore, there is no need to perform post injection or exhaust injection in order to perform the DPF regeneration process, so that occurrence of oil dilution and deterioration of fuel consumption can be suppressed.
Further, since the molecular diameter of hydrogen and carbon monoxide is smaller than that of hydrocarbon, even when PM is thickly deposited on the DPF, it can reach the deep part of this PM layer. Therefore, when a catalyst is applied to the surface of the DPF, it can be efficiently burned even when PM is thickly deposited.
For example, when a NOx purification catalyst that captures NOx in exhaust under an oxidizing atmosphere and reduces the captured NOx under a reducing atmosphere, such as the above-described NOx storage reduction catalyst, is provided in the exhaust system. By supplying the reformed gas having a composition ratio suitable for the temperature of the catalyst, it is possible to raise the temperature of the NOx purification catalyst or reduce the trapped NOx.

  In this case, the operation mode of the fuel reformer is a reforming stoichiometry in which the proportion of hydrogen and carbon monoxide in the generated reformed gas is larger than that in the other operation modes in accordance with the set value of the parameter. Mode, a reformed rich mode in which the proportion of light hydrocarbons in the generated reformed gas is larger than that in other operating modes, and the proportion of oxygen in the raw material supplied to the reforming catalyst in other operations It is preferable to divide into three or more of the reformed lean mode which is larger than the mode.

According to the present invention, for example, when the internal combustion engine is started at a low temperature, the fuel reformer is operated in the reformed stoichiometric mode so that the reformed gas containing a large amount of hydrogen and carbon monoxide combusted from a low temperature is supplied to the exhaust system. Therefore, the temperature of the low-temperature exhaust system can be raised quickly. For example, when the temperature of the exhaust system rises to such an extent that hydrocarbons can be combusted, the fuel reformer is operated in the reformed rich mode, so that reforming containing a large amount of light hydrocarbons with large combustion heat is performed. Since the gas can be supplied to the exhaust system, the temperature of the exhaust system can be raised more rapidly. Therefore, when a DPF is provided in the exhaust system, the fuel reformer is operated in an operation mode suitable for the temperature of the DPF. Even DPF regeneration can be performed.
By the way, when the fuel is continuously supplied to the reforming catalyst, coke is deposited on the reforming catalyst and the performance of the catalyst may be deteriorated. In this case, the fuel reformer is operated in the reforming lean mode, and the raw material containing a large amount of oxygen is supplied to the reforming catalyst, so that the coke deposited on the reforming catalyst is removed by combustion, and the reforming catalyst Performance can be restored.

  In this case, the parameter setting means sets the parameter setting value to the reforming stoichiometric mode side when the acquired exhaust system temperature is lower than the determination temperature, and the acquired exhaust system temperature is equal to or higher than the determination temperature. In this case, it is preferable to set the parameter setting value to the modified rich mode side.

  According to the present invention, when the temperature of the exhaust system is lower than the judgment temperature, the exhaust gas can be exhausted with the reformed gas containing a large amount of hydrogen and carbon monoxide by setting the parameter setting value to the reformed stoichiometric mode side. Can be quickly heated. In addition, when the exhaust system temperature is equal to or higher than the judgment temperature, the parameter set value is set to the reformed rich mode side, so that the exhaust system can be further rapidly raised with the reformed gas containing a large amount of light hydrocarbons. Can be warmed.

  In this case, when the predetermined lean transition condition is satisfied, the parameter setting means sets the parameter setting value to the reformed lean mode side, and the lean transition condition is determined by the amount of coke deposited on the reforming catalyst. It is preferable to include at least one of exceeding the deposition upper limit and exceeding the operation upper limit time when the fuel reformer is operated in the reformed rich mode.

  According to this invention, the amount of coke deposited on the reforming catalyst exceeds at least the upper limit of deposition, and at least one of the time when the fuel reformer is operated in the reformed rich mode exceeds the upper limit of operation. When the lean transition condition is satisfied, the parameter set value is set to the reforming lean mode, and the fuel reformer is operated in the reforming lean mode. As a result, the raw material containing a large amount of oxygen is supplied to the reforming catalyst, and the coke deposited when the fuel reformer is operated in the reforming rich mode can be removed by combustion. Can be prevented. Further, when the lean transition condition is satisfied, the fuel reformer is operated in the reforming lean mode to prevent the reforming catalyst from being deteriorated by heat due to unnecessary operation in the reforming lean mode. be able to. Further, since it is not necessary to directly detect a decrease in the performance of the reforming catalyst in determining the lean transition condition, the configuration of the exhaust purification system can be simplified.

  In this case, the parameter setting unit sets the parameter setting value to the reforming rich mode side or the reforming mode when a predetermined lean end condition is satisfied after the parameter setting value is set to the reforming lean mode side. The lean end condition is that the amount of coke deposited on the reforming catalyst is below the lower limit of deposition, and the time during which the fuel reformer has been operating in the reforming lean mode is the upper limit of operation. It is preferable to include at least one of exceeding.

  According to the present invention, after the fuel reformer is operated in the reforming lean mode, the amount of coke deposited on the reforming catalyst is below the lower limit of deposition, and the fuel reformer is operated in the reforming lean mode. When the lean end condition including at least one of the running time exceeding the operation upper limit value is satisfied, the parameter setting value is set to the reforming rich mode side or the reforming stoichiometric side. As a result, the time for operating the fuel reformer in the reforming lean mode can be kept to a minimum, so that the reforming catalyst can be prevented from being exposed to a high temperature for a long time. Therefore, it is possible to prevent the noble metal contained in the reforming catalyst from being sintered and the performance of the reforming catalyst from being deteriorated.

  In this case, when the operation mode of the fuel reformer is shifted to the reforming lean mode, the parameter setting unit is configured so that the temperature of the highest temperature portion of the reforming catalyst does not exceed the upper limit temperature. It is preferable to change the set value of the parameter stepwise up to a predetermined target value on the reformed lean mode side.

According to the present invention, when the operation mode of the fuel reformer is shifted to the reforming lean mode, the parameter setting value is changed so that the temperature of the highest temperature portion of the reforming catalyst does not exceed the upper limit temperature. The quality is gradually changed to a predetermined target value on the lean side.
When the operation mode of the fuel reformer is suddenly shifted from the reforming rich mode or the reforming stoichiometric mode to the reforming lean mode, the oxygen concentration of the raw material supplied to the reforming catalyst may suddenly increase. At this time, coke and unreacted hydrocarbon components deposited on the reforming catalyst may burn violently, and the catalyst temperature may rise rapidly and deteriorate. According to the present invention, as described above, the temperature of the reforming catalyst can be prevented from increasing rapidly by gradually changing the parameter setting values and gradually shifting to the reforming lean mode.

  In this case, when the operation mode of the fuel reformer is shifted to the reforming rich mode, the parameter setting unit is configured so that the temperature of the lowest temperature portion of the reforming catalyst does not fall below a lower limit temperature. It is preferable that the parameter setting value be changed stepwise up to a predetermined target value on the reformed rich mode side.

According to the present invention, when the operation mode of the fuel reformer is shifted to the reforming rich mode, the parameter setting values are changed so that the temperature of the lowest temperature portion of the reforming catalyst does not fall below the lower limit temperature. It is changed stepwise up to a predetermined target value on the quality rich mode side.
When the operation mode of the fuel reformer is rapidly changed from the reforming lean mode or the reforming stoichiometric mode to the reforming rich mode, the amount of fuel supplied to the reforming catalyst may increase rapidly. At this time, the heat of the reforming catalyst is lost due to the vaporization of the fuel, and the temperature of the reforming catalyst is drastically lowered, and there is a risk of misfire. According to the present invention, as described above, the temperature of the reforming catalyst can be prevented from suddenly lowering by changing the parameter setting values in stages and gently shifting to the reforming rich mode.

  In this case, the reforming catalyst includes at least one metal catalyst component selected from the group consisting of platinum, palladium, rhodium, ruthenium, nickel, iron, and cobalt, ceria, alumina, zirconia, titania, magnesia, and zeolite. It is preferable to include at least one oxide selected from the group consisting of the above or a composite oxide having this as a basic composition.

  According to the present invention, by using the reforming catalyst including the metal catalyst component and the composite oxide as described above, the thermal oxidation with respect to the high use temperature is reduced while increasing the partial oxidation reaction activity in the reforming catalyst. be able to.

  In this case, it is preferable that the fuel reformer is provided separately from the exhaust system.

  According to the present invention, the reformed gas can always be efficiently generated without being affected by the exhaust component in the exhaust system, the exhaust temperature, the exhaust flow velocity, the coexisting gas, the oxygen concentration, the water vapor concentration, and the like. Therefore, the amount of catalyst used as the whole exhaust gas purification system can be reduced, and the cost can be reduced.

It is a mimetic diagram showing composition of an engine exhaust purification system concerning one embodiment of the present invention. It is a figure which shows the composition ratio of the reformed gas at the time of operating a fuel reformer in each operation mode which concerns on the said embodiment. It is a figure which compares the emitted-heat amount on the exhaust gas purification device of a reformed gas at the time of drive | operating by the reforming stoichiometric mode and reforming rich mode which concern on the said embodiment. It is a flowchart which shows the procedure of the reformer control process which concerns on the said embodiment. It is a figure which shows the relationship between the reformed gas flow volume and OC ratio which concern on the said embodiment, and the amount of coke deposits per unit time. It is a time chart which shows an example of the reformer control process which concerns on the said embodiment. It is a figure which shows the exhaust gas temperature of the upstream of the exhaust gas purification device which concerns on the said embodiment, and the exhaust gas temperature of downstream. It is a schematic diagram which shows the structure of the exhaust gas purification system which concerns on the modification of the said embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration of an exhaust purification system 1 of an internal combustion engine (hereinafter referred to as “engine”) according to the present embodiment.

  An exhaust purification system 1 includes an exhaust purification device 3 provided in an exhaust pipe 2 of an engine, a fuel reformer 4 connected to the exhaust pipe 2, and an electronic control unit (hereinafter referred to as "ECU") 5. Consists of including.

  The exhaust gas purification device 3 includes a catalytic converter, a filter, a filter coated with a catalyst, and the like, and purifies the exhaust gas by passing the exhaust discharged from the engine.

The fuel reformer 4 includes a casing 42 that houses the reforming catalyst 41 and a raw material supply device 43 that supplies the raw material to the reforming catalyst 41. In the fuel reformer 4 having the above-described configuration, the fuel is reformed by the action of the reforming catalyst 41, and a reducing gas containing hydrogen (H ₂ ), carbon monoxide (CO), and light hydrocarbons (HC). The reformed gas is generated and supplied to the upstream side of the exhaust purification device 3 in the exhaust pipe 2 through the reformed gas passage 45. The reformed gas supplied from the fuel reformer 4 is used for raising the temperature of the exhaust purification device 3 and reducing the exhaust gas in the exhaust purification device 3.

  The raw material supply device 43 mixes fuel stored in a fuel tank (not shown) and air supplied by a compressor (not shown) at a predetermined ratio to produce a raw material, and the raw material is supplied to the reforming catalyst 41 in the casing 42. To supply. More specifically, the raw material supply device 43 includes an air valve that controls the amount of air supplied to the reforming catalyst 41, a fuel valve that controls the amount of fuel supplied to the reforming catalyst 41, and the air and fuel. And an injector for injecting the mixture into the reforming catalyst 41. These actuators that open and close the air valve and the fuel valve are connected to the ECU 5, and the air amount and fuel amount of the raw material supplied to the reforming catalyst 41 are controlled by the ECU 5.

  The reforming catalyst 41 is selected from the group consisting of at least one metal catalyst component selected from the group consisting of platinum, palladium, rhodium, ruthenium, iron, and cobalt, and ceria, alumina, zirconia, titania, magnesia, and zeolite. And at least one kind of oxide or a composite oxide having these as a basic composition. The reforming catalyst 41 reforms the raw material supplied from the raw material supply device 43 and generates a reformed gas containing light hydrocarbons in addition to hydrogen and carbon monoxide. More specifically, the reforming catalyst 41 generates the reformed gas by a partial oxidation reaction between a hydrocarbon constituting the raw material and oxygen.

  The method for preparing the reforming catalyst 41 is not particularly limited, and is prepared by a conventionally known impregnation method. For example, a slurry is prepared by putting ceria and rhodium powders blended to a predetermined mass ratio into a ball mill together with a binder and an aqueous medium and stirring and mixing them. Next, the prepared slurry is wash-coated on a cordierite honeycomb carrier, dried and fired under predetermined conditions, whereby the reforming catalyst 41 is obtained.

The fuel reformer 4 includes a heater (not shown) such as a glow plug or a spark plug, and can heat the reforming catalyst 41 when the fuel reformer 4 is started.
The fuel reformer 4 is provided separately from the exhaust pipe 2, and the raw material supply device 43 and the reforming catalyst 41 of the fuel reformer 4 are not provided in the exhaust pipe 2. That is, the fuel reformer 4 is provided in the exhaust pipe 2 and does not reform the fuel component contained in the exhaust gas in the exhaust pipe 2, but reforms the fuel gas supplied directly from the fuel tank. Therefore, a large amount of reformed gas can be generated and the generated amount can be controlled.

Next, the operation mode of the fuel reformer will be described with reference to FIGS. 2 and 3.
The operation mode of the fuel reformer 4 is selected from the reforming stoichiometric mode, the reforming rich mode, and the reforming lean mode according to parameters correlated with the ratio of the raw material oxygen and carbon supplied to the reforming catalyst 41. And can be divided into three types. In the present embodiment, as a parameter having a correlation with the ratio of oxygen to carbon of the raw material, the OC ratio (by the ratio of the number of moles of carbon in the fuel to the number of moles of oxygen in the air supplied to the reforming catalyst 41 ( The number of moles of oxygen / the number of moles of carbon) is defined, and the operation mode of the fuel reformer 4 is classified according to the OC ratio.

FIG. 2 is a diagram showing the composition ratio of the reformed gas when the fuel reformer 4 is operated in each operation mode.
Hereinafter, setting the OC ratio of the raw material within a predetermined width centered on “1.0” is referred to as operating the fuel reformer in the reformed stoichiometric mode. On the other hand, setting the OC ratio of the raw material to a value smaller than the set value of the reforming stoichiometric mode is called operating the fuel reformer in the reforming rich mode, and reforming the OC ratio of the raw material. Setting a value larger than the stoichiometric mode setting value means operating the fuel reformer in the reforming lean mode.

  In FIG. 2, the setting values of the OC ratio of the raw materials are “1.15”, “1.1” (above, reformed lean mode), “1.0” (above, reformed stoichiometric mode), “0”. The composition ratio of the reformed gas when .9 ”and“ 0.8 ”(reform rich mode) is shown. Further, FIG. 2 shows only composition ratios of hydrogen, carbon monoxide, and light hydrocarbons as main components of the reformed gas. For light hydrocarbons, in FIG. 2, the carbon number “1” is C1, the carbon number “2” is C2, the carbon number “3” is C3, "4" is C4. Note that the heat of combustion of each component, that is, the amount of heat generated upon combustion is shown in parentheses. FIG. 2 shows the combustion heat of the reformed gas generated when the fuel reformer is operated in each operation mode in addition to the composition ratio.

As shown in FIG. 2, when the fuel reformer is operated in the reformed stoichiometric mode, the ratio of hydrogen and carbon monoxide in the generated reformed gas is compared with that in the other operating modes. large.
When the fuel reformer is operated in the reformed rich mode, the ratio of hydrogen and carbon monoxide is smaller than that in the reformed stoichiometric mode, compared with the case where the fuel reformer is operated in the reformed stoichiometric mode. The proportion of light hydrocarbons is greater than when operating in other operating modes.
In addition, when the fuel reformer is operated in the reformed lean mode, the ratio of hydrogen and carbon monoxide is smaller than when the fuel reformer is operated in the reformed stoichiometric mode, compared with the case where the fuel reformer is operated in the reformed stoichiometric mode. The proportion of light hydrocarbons is smaller than when operating in the reformed rich mode. In addition, since the OC ratio setting value is set to be larger than the reforming stoichiometric mode setting value, when operating in the reforming lean mode, the ratio of the raw material oxygen flowing into the reforming catalyst is determined in other operating modes. Bigger than the case.
Further, as the OC ratio of the raw material is reduced, the combustion heat of the entire reformed gas produced tends to increase.

  FIG. 3 is a diagram for comparing the calorific value of the reformed gas on the exhaust purification device when operated in the reformed stoichiometric mode and the reformed rich mode. In FIG. 3, the left side shows a comparison of the heat generation amount when the exhaust purification device is at a low temperature, and the right side shows a comparison of the heat generation amount of the reformed gas when the exhaust purification device is at a high temperature.

As described above, when the fuel reformer is operated in the reforming rich mode, the ratio of hydrogen and carbon monoxide in the generated reformed gas is smaller than that in the reforming stoichiometric mode operation, but the carbonization with a large combustion heat is performed. A lot of hydrogen is produced. For this reason, the total calorific value of the reformed gas is larger during the reformed rich mode operation than during the reformed stoichiometric mode operation.
However, hydrocarbons have a characteristic that they are difficult to burn at low temperatures compared to hydrogen and carbon monoxide. Therefore, as shown on the left side in FIG. 3, hydrocarbons do not burn on the low-temperature exhaust purification device, and as a result, the calorific value of the reformed gas is higher than that in the reformed rich mode operation. Time becomes bigger. On the other hand, as shown on the right side in FIG. 3, hydrocarbons burn on the high-temperature exhaust purification device. As a result, the amount of heat generated by the reformed gas is higher than that during reformed stoichiometric mode operation. It becomes larger during mode operation.

Returning to FIG. 1, various sensors such as an exhaust temperature sensor 61 and a catalyst temperature sensor 62 are connected to the ECU 5.
The exhaust gas temperature sensor 61 detects the temperature of the exhaust gas downstream of the exhaust gas purification device 3 in the exhaust pipe 2 and transmits a signal substantially proportional to the detected value to the ECU 5. The temperature of the exhaust purification device 3 is calculated by the ECU 5 based on the output of the exhaust temperature sensor 61.
The catalyst temperature sensor 62 detects the temperature of the reforming catalyst 41 of the fuel reformer 4 and transmits a signal substantially proportional to the detected value to the ECU 5.

  The ECU 5 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter, “ CPU ”). In addition, the ECU 5 includes a storage circuit that stores various calculation programs and calculation results executed by the CPU, and an output circuit that outputs a control signal to the injector 22 and the like. With the hardware configuration as described above, the ECU 5 is configured with a module that executes the reformer control process described below.

  FIG. 4 is a flowchart showing the procedure of the reformer control process. This process is a process for controlling the fuel reformer in an appropriate operation mode in accordance with the temperature of the exhaust purification device, and in response to a request for the supply of reformed gas, such as when the exhaust purification device is heated. And executed by the ECU.

  In step S1, the temperature of the exhaust purification device is acquired based on the output of the exhaust temperature sensor, and it is determined whether or not the temperature of the exhaust purification device is higher than a predetermined determination temperature. This determination temperature is set, for example, in the vicinity of the combustion temperature of light hydrocarbons produced by the reformed gas.

  As described above, when the temperature of the exhaust purification device is lower than the combustion temperature of light hydrocarbons, operating the fuel reformer in the reformed stoichiometric mode rather than operating in the reformed rich mode The combustion heat of the reformed gas in the exhaust purification device is large (see FIG. 3). Therefore, if the determination in step S1 is NO and the temperature of the exhaust purification device is lower than the determination temperature, the process proceeds to step S2, and the reformed gas containing a large amount of hydrogen and carbon monoxide that burns from a low temperature is more efficient. In order to raise the temperature of the exhaust purification device, the fuel reformer is operated in the reformed stoichiometric mode. A more specific procedure for operating the fuel reformer in the reforming stoichiometric mode in step S2 will be described in detail later. On the other hand, if the determination in step S1 is YES and the temperature of the exhaust purification device is equal to or higher than the determination temperature, the process proceeds to step S3 to operate the fuel reformer in the reforming rich mode or the reforming lean mode.

  In step S3, it is determined whether or not a lean mode flag F_lean is “1”. The lean mode flag F_lean is a flag requesting to operate the fuel reformer in the reforming lean mode, and is sequentially updated by a process not shown. If the determination in step S3 is NO, the process proceeds to step S4 to efficiently raise the temperature of the exhaust purification device with the reformed gas containing a large amount of light hydrocarbons having a large calorific value in addition to hydrogen and carbon monoxide. The fuel reformer is operated in the reformed rich mode. On the other hand, when the determination in step S3 is YES, the process proceeds to step S5, and the fuel reformer is operated in the reforming lean mode.

Here, a procedure for updating the lean mode flag F_lean will be described.
In the reformed rich mode, the OC ratio is set to a value smaller than that in the reformed stoichiometric mode, so that the ratio of carbon of the raw material is large and coke tends to deposit on the reforming catalyst. On the other hand, in the reformed lean mode, since the OC ratio is set to a larger value than in the reformed stoichiometric mode, the ratio of the raw material oxygen is large, and the coke deposited on the reforming catalyst can be removed by combustion. As described above, when the fuel reformer is operated in the reforming rich mode, coke is deposited on the reforming catalyst, and when the fuel reformer is operated in the reforming lean mode, the deposited coke can be removed by combustion. Then, the lean mode flag F_lean is updated at an appropriate time so that excessive coke does not accumulate on the reforming catalyst and the reforming catalyst is not continuously exposed to an excessively high temperature.

  In this embodiment, the condition for setting the lean mode flag F_lean from “0” to “1”, that is, the lean mode transition condition for shifting the operation mode of the fuel reformer from the reformed rich mode to the reformed lean mode is used. At least one of the following two conditions (A) and (B) is used.

(A) The amount of coke deposited on the reforming catalyst is estimated, and the amount of coke deposited ΣCk exceeds the upper limit of deposition.
The coke deposition amount Ck per unit time can be estimated by searching a predetermined map based on, for example, the flow rate of the reformed gas and the OC ratio.
FIG. 5 is a diagram showing a relationship between the reformed gas flow rate and the OC ratio and the coke deposition amount Ck per unit time, and is a diagram showing an example of the map. According to the map shown in FIG. 5, the coke deposition amount Ck per unit time increases as the reformed gas flow rate decreases and the OC ratio decreases. While operating the fuel reformer in the reforming rich mode, the coke deposition amount ΣCk can be estimated by integrating the coke deposition amount Ck calculated in this way.
In the above example, the coke deposition amount ΣCk is calculated based on the two parameters of the reformed gas flow rate and the OC ratio. In addition, the consumption of fuel supplied to the reformed gas, the operation time of the fuel reformer, The coke deposition amount ΣCk may be calculated based on parameters such as the oxygen concentration and carbon concentration of the reforming catalyst, the differential pressure between the upstream side and the downstream side of the reforming catalyst, and the temperature of the reforming catalyst.

(B) The time during which the fuel reformer is operated in the reforming rich mode is timed, and the rich mode operating time exceeds the operation upper limit time.
As described above, since coke accumulates on the reforming catalyst when the fuel reformer is operated in the reforming rich mode, it is possible to determine an appropriate time to shift to the reforming lean mode even in the rich mode operating time. it can.

  There are two types of conditions for resetting the lean mode flag F_lean from “1” to “0”, that is, the lean mode end conditions for shifting the operation mode of the fuel reformer from the reforming lean mode to the reforming rich mode. At least one of the conditions (C) and (D) is used.

(C) The amount of coke deposition ΣCk is below the lower limit of deposition.
When the fuel reformer is operated in the reforming lean mode, the coke deposited on the reforming catalyst is gradually burned and removed. At this time, the amount of coke removed -Ck per unit time is It can be estimated based on parameters such as the oxygen concentration and the temperature of the reforming catalyst. While operating the fuel reformer in the reforming lean mode, the coke deposition amount ΣCk can be estimated by integrating the coke removal amount -Ck calculated in this way.

(D) The time during which the fuel reformer is operated in the reforming lean mode is timed, and the lean mode operating time exceeds the operation upper limit value.
As described above, by operating the fuel reformer in the reforming lean mode, the coke accumulated on the reforming catalyst is burned and removed, so that the reforming lean mode is ended even in the lean mode operating time. The right time can be determined.

  Returning to FIG. 4, in the reformed stoichiometric mode operation in step S <b> 2, the actual OC ratio is calculated from the amount of air and the amount of fuel supplied to the reforming catalyst. Then, the set value of the OC ratio is set to “1.0”, and the amount of air and the amount of fuel supplied to the reforming catalyst are adjusted so that the actual OC ratio matches this set value. At this time, the temperature of the reforming catalyst is controlled within a predetermined range (for example, about 800 ° C. to about 1200 ° C.).

In the reformed rich mode in step S4, the actual OC ratio is calculated from the amount of air and fuel supplied to the reforming catalyst. Then, the OC ratio set value is gradually reduced to “0.8” which is the target value in the reformed rich mode operation, and the OC ratio is set so that the actual OC ratio matches the set value. Adjust the amount of air and fuel supplied to the catalyst. At this time, the set value of the OC ratio is decreased stepwise over a predetermined time so that the temperature of the lowest temperature portion of the reforming catalyst does not fall below the lower limit temperature. Here, the lower limit temperature of the reforming catalyst is set to a temperature (for example, about 800 ° C.) at which the reforming catalyst can maintain a stable reforming reaction. In addition, the amount of decrease when the OC ratio setting value is decreased stepwise is set, for example, between “0.01” and “0.05”.
As described above, when it is determined that the temperature of the reforming catalyst is lower than the lower limit temperature while the set value of the OC ratio is decreased stepwise, the temperature of the reforming catalyst can be maintained above the lower limit temperature. Then, the target value is reset within the range of “0.8” to “1.0”.

In the reformed lean mode in step S5, the actual OC ratio is calculated from the amount of air and fuel supplied to the reforming catalyst. Then, the OC ratio setting value is increased stepwise up to the target value “1.2” during the reforming lean mode operation, and the OC ratio setting value is adjusted to match the actual OC ratio. Adjust the amount of air and fuel supplied to the catalyst. At this time, the set value of the OC ratio is increased stepwise over a predetermined time so that the temperature of the highest temperature portion of the reforming catalyst does not exceed the predetermined upper limit temperature. Here, the upper limit temperature of the reforming catalyst is set to a temperature (for example, about 1200 ° C.) at which the degradation of the reforming catalyst becomes significant. Further, the increment when the OC ratio setting value is increased stepwise is set, for example, between “0.01” and “0.05”.
As described above, when it is determined that the temperature of the reforming catalyst exceeds the upper limit temperature while the set value of the OC ratio is increased stepwise, the temperature of the reforming catalyst can be maintained below the upper limit temperature. Then, the target value is reset within the range of “1.0” to “1.2”.

FIG. 6 is a time chart showing an example of the reformer control process.
Control of the fuel reformer is started at time t0. At this time, the fuel reformer is operated in the reforming stoichiometric mode when it is determined that the temperature of the exhaust purification device is equal to or lower than the determination temperature (see steps S1 and S2 in FIG. 4).
At time t1, the operation mode of the fuel reformer is shifted from the reforming stoichiometric mode to the reforming rich mode in response to determining that the temperature of the exhaust purification device is higher than the above-described determination temperature (step of FIG. 4). S1, S4 reference). At this time, the set value of the OC ratio is decreased stepwise so that the temperature of the reforming catalyst does not fall below the lower limit temperature.

At time t2, the lean mode flag F_lean is set to “1” in order to burn and remove the coke deposited on the reforming catalyst. As a result, the operation mode of the fuel reformer is shifted from the reformed rich mode to the reformed lean mode (steps S3 and S5 in FIG. 4). At this time, the set value of the OC ratio is increased stepwise so that the temperature of the reforming catalyst does not exceed the upper limit temperature.
At time t3, the lean mode flag F_lean is reset to “0” in response to the completion of the combustion removal of the coke deposited on the reforming catalyst. Thereby, the operation mode of the fuel reformer is shifted from the reformed lean mode to the reformed rich mode (steps S3 and S4 in FIG. 4).

According to this embodiment, the following effects can be obtained.
(1) According to the present embodiment, a reformed gas containing light hydrocarbons and the like in addition to hydrogen and carbon monoxide is supplied to the exhaust pipe 2, and the reformed gas is combusted so that the exhaust pipe 2 The temperature of the provided exhaust purification device 3 can be raised.
FIG. 7 is a diagram showing the exhaust temperature on the upstream side and the exhaust temperature on the downstream side of the exhaust purification device 3. In FIG. 7, the broken line indicates the exhaust temperature upstream of the exhaust purification device 3, and the solid line indicates the exhaust temperature downstream of the exhaust purification device 3. As shown in FIG. 7, until the reformed gas generated by the fuel reformer is supplied, the exhaust temperature on the downstream side of the exhaust purification device 3 is lower than the exhaust temperature on the upstream side. From the start to the stop, the exhaust temperature on the downstream side of the exhaust purification device 3 is higher than the exhaust temperature on the upstream side. This is considered to be because components such as hydrogen, carbon monoxide, and light hydrocarbons contained in the reformed gas generated by the fuel reformer 4 burned in the exhaust purification device.

Further, since the temperature of the exhaust purification device 3 is raised with the reformed gas generated by the reforming catalyst 41, the engine can be continuously operated under the optimum conditions while raising the temperature of the exhaust purification device 3, so that the exhaust gas is discharged from the engine. It is possible to purify exhausted air and improve fuel efficiency. In addition, since the temperature of the exhaust purification device 3 is raised with the reformed gas in the state of gas generated by the reforming catalyst 41, unburned fuel does not adhere to the exhaust purification device 3, so the temperature becomes locally high and heat Deterioration does not occur, and there is no local temperature drop and coking.
Since hydrogen and carbon monoxide contained in the reformed gas have characteristics of burning from low temperatures compared to hydrocarbons, the temperature of the low-temperature exhaust system is increased by burning hydrogen and carbon monoxide in the reformed gas. can do. On the other hand, hydrocarbons have a characteristic that the heat of combustion is larger than that of hydrogen or carbon monoxide, so that the exhaust system can be quickly heated by burning hydrocarbons in the reformed gas. According to the present embodiment, the ratio (OC ratio) of the number of moles of carbon in the fuel to the number of moles of oxygen in the air is set based on the temperature of the exhaust purification device 3, and based on the set value of this OC ratio. By controlling the fuel reformer 4, a reformed gas having a composition ratio suitable for the temperature of the exhaust purification device 3 can be supplied, so that the exhaust purification device 3 can be efficiently heated. Further, by controlling the fuel reformer 4 based on the set value of the OC ratio, it is possible to prevent thermal runaway of the fuel reformer 4 and excessive coke accumulation.

(2) According to the present embodiment, when the engine is started at a low temperature, the fuel reformer 4 is operated in the reformed stoichiometric mode so that the reformed gas containing a large amount of hydrogen and carbon monoxide combusted from a low temperature is exhausted and purified. Since it can supply to the device 3, the temperature of the low-temperature exhaust purification device 3 can be quickly raised. Further, for example, when the temperature of the exhaust purification device 3 rises to such an extent that hydrocarbons can be combusted, the fuel reformer 4 is operated in the reforming rich mode, thereby containing a large amount of light hydrocarbons having a large combustion heat. Since the reformed gas can be supplied to the exhaust gas purification device 3, the temperature of the exhaust gas purification device 3 can be further increased.
When coke is deposited on the reforming catalyst 41 and the performance of the catalyst is deteriorated, the fuel reformer 4 is operated in the reforming lean mode, and a raw material containing a large amount of oxygen is supplied to the reforming catalyst 41. Thus, the coke deposited on the reforming catalyst 41 can be burned and removed, and its performance can be recovered.

  (3) According to the present embodiment, when the temperature of the exhaust purification device is lower than the determination temperature, a large amount of hydrogen and carbon monoxide is contained by setting the OC ratio setting value to the reforming stoichiometric mode side. The exhaust gas purification device 3 can be quickly heated with the reformed gas. Further, when the temperature of the exhaust purification device 3 is equal to or higher than the determination temperature, the exhaust purification device 3 is formed with a reformed gas containing a large amount of light hydrocarbons by setting the OC ratio setting value to the reformed rich mode side. The temperature can be raised more rapidly.

  (4) According to the present embodiment, the lean transition condition includes at least one of the coke accumulation amount ΣCk exceeding the accumulation upper limit value and the rich mode operation time of the fuel reformer 4 exceeding the operation upper limit time. Is satisfied, the OC ratio set value is set to the reforming lean mode, and the fuel reformer 4 is operated in the reforming lean mode. As a result, the raw material containing a large amount of oxygen is supplied to the reforming catalyst 41, and the deposited coke can be removed by combustion. Further, when the lean transition condition is satisfied, the fuel reformer 4 is operated in the reforming lean mode to prevent the reforming catalyst from being deteriorated by heat due to unnecessary operation in the reforming lean mode. can do. Further, since it is not necessary to directly detect a decrease in the performance of the reforming catalyst 41 when determining the lean transition condition, the configuration of the exhaust purification system 1 can be simplified.

  (5) According to the present embodiment, after the fuel reformer 4 is operated in the reforming lean mode, the coke accumulation amount ΣCk is less than the accumulation lower limit value, and the lean mode operation time exceeds the operation upper limit value. When the lean end condition including at least one of the above is satisfied, the OC ratio set value is set to the reformed rich mode side or the reformed stoichiometric side. As a result, the time during which the fuel reformer 4 is operated in the reforming lean mode can be kept to a minimum, so that the reforming catalyst 41 can be prevented from being exposed to a high temperature for a long time. . Therefore, it is possible to prevent the noble metal contained in the reforming catalyst 41 from being sintered and the performance of the reforming catalyst 41 from being deteriorated.

  (6) According to this embodiment, when the operation mode of the fuel reformer 4 is shifted to the reforming lean mode, the OC is controlled so that the temperature of the highest temperature portion of the reforming catalyst does not exceed the upper limit temperature. The ratio set value is changed stepwise to a predetermined target value on the reformed lean mode side. Thereby, the rapid temperature increase of the reforming catalyst 41 can be prevented.

  (7) According to the present embodiment, when the operation mode of the fuel reformer 4 is shifted to the reforming rich mode, the temperature of the portion of the reforming catalyst 41 having the lowest temperature does not fall below the lower limit temperature. The set value of the OC ratio is changed stepwise up to a predetermined target value on the reformed rich mode side. Thereby, a rapid temperature drop of the reforming catalyst 41 can be prevented.

  (8) According to the present embodiment, by using the reforming catalyst including the metal catalyst component and the composite oxide as described above, the partial oxidation reaction activity in the reforming catalyst 41 is increased, and the use temperature is increased. Thermal degradation can be reduced.

  (9) According to this embodiment, by providing the fuel reformer 4 separately from the exhaust pipe 2, the exhaust component, exhaust temperature, exhaust flow velocity, coexisting gas, oxygen concentration, water vapor concentration, etc. in the exhaust pipe 2 can be obtained. The reformed gas can always be generated efficiently without being affected. Therefore, the amount of catalyst used in the exhaust purification system 1 as a whole can be reduced, and the cost can be reduced.

<Example 1>
Example 1 of the above embodiment will be described.
In the first embodiment, a case where a DPF is provided as an exhaust purification device will be described.
In this case, the reformer control process shown in FIG. 4 described above is executed in response to the accumulation of a predetermined amount of PM in the DPF and the time to execute the DPF regeneration process. At this time, it is preferable to set the determination temperature in step S1 described above to about 100 ° C.
That is, when the DPF is regenerated, if the temperature of the DPF is lower than 100 ° C., the fuel reformer is operated in the reforming stoichiometric mode, and the fuel reformer is changed in response to the DPF temperature exceeding 100 ° C. Are operated in the reformed rich mode or the reformed lean mode. Thereby, PM deposited on the DPF can be removed by combustion.

  According to the present embodiment, PM deposited on the DPF can be combusted by supplying a reformed gas having a composition ratio suitable for the temperature of the DPF. Therefore, there is no need to perform post injection or exhaust injection in order to perform the DPF regeneration process, so that occurrence of oil dilution and deterioration of fuel consumption can be suppressed. Further, by operating the fuel reformer in an operation mode suitable for the temperature of the DPF, it is possible to perform DPF regeneration even immediately after starting the engine or during low-load operation, which was not easy in the prior art. Further, since the molecular diameter of hydrogen and carbon monoxide is smaller than that of hydrocarbon, even when PM is thickly deposited on the DPF, it can reach the deep part of this PM layer. Therefore, when a catalyst is applied to the surface of the DPF, it can be efficiently burned even when PM is thickly deposited.

<Example 2>
Example 2 of the above embodiment will be described.
In Example 2, a case will be described in which an NOx purification catalyst that captures NOx in exhaust under an oxidizing atmosphere and reduces the captured NOx under a reducing atmosphere is provided as an exhaust purification device.
The reformed gas generated by the fuel reformer can be used not only when raising the temperature of the NOx purification catalyst as in the DPF of Example 1, but also when reducing NOx trapped by the NOx purification catalyst.
That is, the reformer control process shown in FIG. 4 described above is executed in response to the time for reducing the NOx stored in the NOx purification catalyst. At this time, it is preferable to set the determination temperature in step S1 described above to about 200 ° C.
That is, when NOx trapped by the NOx purification catalyst is reduced, when the temperature of the NOx purification catalyst is 200 ° C. or lower, the fuel reformer is operated in the reforming stoichiometric mode, and the temperature of the NOx purification catalyst exceeds 200 ° C. Accordingly, the fuel reformer is operated in the reformed rich mode or the reformed lean mode. Thereby, NOx can be reduced and the NOx purification catalyst can be regenerated.
As with the DPF of Example 1, the reformed gas generated by the fuel reformer can also be used when raising the temperature of the NOx purification catalyst.

  According to this embodiment, by supplying a reformed gas having a composition ratio suitable for the temperature of the NOx purification catalyst, it is possible to raise the temperature of the NOx purification catalyst or reduce the trapped NOx.

The present invention is not limited to the embodiment described above, and various modifications can be made.
In the above-described embodiment, the operation mode of the fuel reformer is divided into the reforming stoichiometric mode, the reforming rich mode, and the reforming lean mode, but is not limited thereto. The number of operation modes may be divided into four or more according to the set value of the OC ratio.

FIG. 8 is a schematic diagram showing a configuration of an exhaust purification system 1A according to a modification of the embodiment.
The exhaust pipe 2 is provided with a first exhaust purification device 3A and a second exhaust purification device 3B in order from the upstream side to the downstream side.
The casing 42 and the exhaust pipe 2 of the fuel reformer 4A are connected to the first reformed gas passage 45A connected to the upstream side of the first exhaust purification device 3A and the upstream side of the second exhaust purification device 3B. 2 is connected via a passage switching device 46A for switching between the reformed gas passage 45B.
The ECU 5A is provided with a first exhaust temperature sensor 61A and a second exhaust temperature sensor 61B for detecting the temperature of the exhaust on the downstream side of each of the exhaust purification devices 3A and 3B, and based on the outputs of the exhaust temperature sensors 61A and 61B. The fuel reformer 4A and the passage switching device 46A are controlled.
As described above, when a plurality of exhaust purification devices are provided in the exhaust pipe 2, the reformed gas generated by the fuel reformer may be supplied to the upstream side of each of the exhaust purification devices.

1, 1A ... exhaust purification system 2 ... exhaust pipe (exhaust system)
3, 3A, 3B ... Exhaust purification device (exhaust system)
4, 4A ... Fuel reformer 41 ... Reforming catalyst 5, 5A ... ECU (exhaust temperature acquisition means, parameter setting means, reformer control means)
61, 61A, 61B ... exhaust temperature sensor (exhaust temperature acquisition means)

Claims (9)

An exhaust purification system including a fuel reformer that generates a reformed gas by supplying a raw material including fuel and air to a reforming catalyst, and supplies the generated reformed gas to an exhaust system of an internal combustion engine. ,
Exhaust temperature acquisition means for acquiring the temperature of the exhaust system;
Parameter setting means for setting a parameter having a correlation with the ratio of oxygen to carbon of the raw material supplied to the reforming catalyst based on the temperature of the exhaust system acquired by the exhaust temperature acquisition means;
An exhaust purification system comprising: reformer control means for controlling the fuel reformer based on a set value of the parameter. The operation mode of the fuel reformer depends on the set value of the parameter,
A reformed stoichiometric mode in which the proportion of hydrogen and carbon monoxide in the generated reformed gas is large compared to other operation modes;
A reformed rich mode in which the proportion of light hydrocarbons in the generated reformed gas is large compared to other operation modes,
2. The exhaust gas purification according to claim 1, wherein the raw material supplied to the reforming catalyst is divided into three or more of a reforming lean mode in which a proportion of oxygen is large compared to other operation modes. system. The parameter setting means includes
When the acquired exhaust system temperature is lower than the judgment temperature, the parameter setting value is set to the reforming stoichiometric mode side,
The exhaust purification system according to claim 2, wherein when the acquired exhaust system temperature is equal to or higher than the determination temperature, the parameter setting value is set to the reforming rich mode side. When the predetermined lean transition condition is satisfied, the parameter setting means sets the parameter setting value to the reforming lean mode side,
The lean transition condition is at least one of the amount of coke deposited on the reforming catalyst exceeding a deposition upper limit value, and the time when the fuel reformer is operated in the reforming rich mode exceeds the operation upper limit time. The exhaust gas purification system according to claim 2 or 3, characterized by comprising: The parameter setting means sets the parameter setting value to the reforming lean mode side, and if the predetermined lean end condition is satisfied, sets the parameter setting value to the reforming rich mode side or the reforming stoichiometric mode side. West,
The lean end condition is at least that the amount of coke deposited on the reforming catalyst is below the lower limit of accumulation, and that the time during which the fuel reformer has been operated in the reformed lean mode exceeds the upper limit of operation. The exhaust gas purification system according to any one of claims 2 to 4, characterized in that any one of them is included. When shifting the operation mode of the fuel reformer to the reforming lean mode,
The parameter setting means changes the parameter setting value stepwise to a predetermined target value on the reforming lean mode side so that the temperature of the highest temperature portion of the reforming catalyst does not exceed the upper limit temperature. An exhaust purification system according to any one of claims 2 to 5, wherein When shifting the operation mode of the fuel reformer to the reforming rich mode,
The parameter setting means changes the parameter setting value stepwise to a predetermined target value on the reforming rich mode side so that the temperature of the lowest temperature portion of the reforming catalyst does not fall below a lower limit temperature. The exhaust gas purification system according to any one of claims 2 to 6, wherein The reforming catalyst is
At least one metal catalyst component selected from the group consisting of platinum, palladium, rhodium, ruthenium, nickel, iron, and cobalt;
8. At least one oxide selected from the group consisting of ceria, alumina, zirconia, titania, magnesia, and zeolite, or a composite oxide based on the oxide, or any one of claims 1 to 7 The exhaust gas purification system according to the above.   The exhaust gas purification system according to any one of claims 1 to 8, wherein the fuel reformer is provided separately from the exhaust system.

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