JP5006776B2 - Fuel reformer - Google Patents

Description

  The present invention relates to a fuel reformer, and more particularly to a fuel reformer that purifies exhaust gas by reforming hydrocarbon fuel to generate reformed gas and supplying the reformed gas to an exhaust passage of an internal combustion engine. .

  Hydrogen energy is clean energy and is expected to expand its use in the future as an energy source for fuel cells and internal combustion engines. Regarding internal combustion engines, research has been conducted on hydrogen engines, hydrogenated engines, NOx purification devices using hydrogen as a reducing agent, and auxiliary power sources using fuel cells. In addition, research and development have been actively conducted on stationary hydrogen production apparatuses as hydrogen supply sources in fuel cell vehicles and household fuel cell generators.

Conventionally, as such an apparatus for producing hydrogen, a fuel reformer having a reforming catalyst for producing hydrogen by reforming a hydrocarbon fuel (hereinafter simply referred to as “fuel”) has been proposed. . As a reforming reaction in the reforming catalyst, for example, a reaction for producing a gas containing hydrogen and carbon monoxide by a partial oxidation reaction of hydrocarbon as shown in the following formula is known.
_{C n H m + 1 / 2nO} 2 → nCO + 1 / 2mH 2

This partial oxidation reaction is an exothermic reaction using fuel and oxygen, and the reaction proceeds spontaneously. For this reason, once the reaction starts, it is possible to continue producing hydrogen without supplying heat from the outside. Further, in such a partial oxidation reaction, when fuel and oxygen coexist at a high temperature, a combustion reaction as shown in the following equation also proceeds in the reforming catalyst.
_{C n H m + (n +} 1 / 4m) O 2 → nCO 2 + 1 / 2mH 2 O

As a reforming reaction, in addition to a partial oxidation reaction, a steam reforming reaction represented by the following formula is also known.
_{C n H m + nH 2 O} → nCO + (n + 1 / 2m) H 2
This steam reforming reaction is an endothermic reaction using fuel and steam, and is not a reaction that proceeds spontaneously. For this reason, the steam reforming reaction is easily controlled with respect to the partial oxidation reaction described above.

  By the way, when the fuel for automobiles such as gasoline and light oil is used as the fuel, and the catalyst supporting the noble metal such as rhodium is used as the reforming catalyst, the hydrogen yield is reduced when performing the partial oxidation reaction or the steam reforming reaction as described above. In order to increase the emission amount of white smoke, that is, unreacted hydrocarbons, it is necessary to raise the temperature of the reforming catalyst to an activation temperature of 800 ° C. to 1000 ° C. This is because as the carbon value increases, the molecular size increases and more energy is required to decompose the hydrocarbon.

  In particular, immediately after starting the fuel reformer, even if the reforming catalyst is heated by an overheating device such as a glow plug or a spark plug, it is difficult to raise the temperature of the reforming catalyst to the activation temperature as described above. It is. Thus, the following techniques have been proposed for the purpose of preventing unreacted hydrocarbons from being discharged even immediately after startup.

  For example, Patent Document 1 discloses a fuel reformer that includes an oxidation catalyst in addition to the above-described reforming catalyst, and further locally heats the oxidation catalyst immediately after startup. According to the fuel reformer of Patent Document 1, the temperature raising performance of the reforming catalyst is improved by promoting the oxidation of hydrocarbons by the oxidation catalyst. Further, by locally heating the oxidation catalyst immediately after startup, the temperature of the reforming catalyst can be quickly raised to the activation temperature, albeit locally.

Further, for example, in Patent Document 2 and Patent Document 3, a reforming catalyst as a hydrogen enriching means, a NOx purification catalyst, and an HC trap catalyst for adsorbing hydrocarbons are provided in order from the upstream side in the exhaust passage of the internal combustion engine. Exhaust gas purification systems have been proposed. According to this system, exhaust gas containing hydrogen is allowed to flow into the NOx purification catalyst as a reducing agent, so that NOx can be efficiently purified even at low temperatures. In addition, even when the temperature of the reforming catalyst or NOx purification catalyst is low immediately after the system is started, adsorption by the HC trap catalyst suppresses discharge of unreacted hydrocarbons to the atmosphere. can do.
JP 2001-106512 A JP 2007-132355 A Japanese Patent No. 3642273

  However, the fuel reformer disclosed in Patent Document 1 and the exhaust gas purification system disclosed in Patent Documents 2 and 3 have the following problems.

In the fuel reformer of Patent Document 1, although the time for raising the temperature of the reforming catalyst to the activation temperature can be shortened, unreacted hydrocarbons may be discharged before the reforming catalyst reaches the activation temperature. There is.
The fuel reformer also includes a flap valve that controls the flow of warm air gas for heating the oxidation catalyst. In this fuel reformer, it is necessary to synchronize the opening degree of the flap valve and the reforming reaction in the reforming catalyst in order to improve the hydrogen yield or prevent excessive reforming of the reforming catalyst. is there. However, the reforming reaction is fast, and in order to synchronize the reforming reaction and the opening of the flap valve, it is necessary to control the flap valve at high speed and with high accuracy. Therefore, the structure of the fuel reformer may be complicated.

  In the exhaust gas purification systems of Patent Document 2 and Patent Document 3, the reforming catalyst is provided in the exhaust passage of the internal combustion engine. For this reason, carbon may be deposited (coking) or melted down, and the reforming catalyst may be deteriorated. Further, in order to improve the hydrogen yield in the reforming catalyst, it is necessary to accurately adjust the mixing ratio of hydrocarbon and oxygen, but in this exhaust gas purification system, the reforming catalyst is discharged from the internal combustion engine. Therefore, it is difficult to improve the hydrogen yield stably.

  The present invention has been made in view of the above-described points, and is a fuel reformer that reforms fuel to produce reformed gas and supplies the reformed gas to an exhaust passage of an internal combustion engine. An object of the present invention is to provide a fuel reformer that can prevent unreacted hydrocarbons from being discharged into the exhaust passage immediately after starting.

In order to achieve the above object, the invention described in claim 1 is characterized in that a reformed fuel gas is produced to produce a reformed gas, and the reformed gas is passed through an exhaust passage (4, 4) through which exhaust gas discharged from an internal combustion engine flows. In the fuel reformer (50) to be supplied to 5), a gas passage (51) whose one end is connected to the exhaust passage, and a fuel gas supply means (52) for supplying fuel gas from the other end of the gas passage ), A fuel reforming catalyst (53) provided in the gas passage, and an HC adsorbent (54) provided downstream of the fuel reforming catalyst in the gas passage, The passage includes a passage (513) that passes through the HC adsorbent and a passage that does not pass through the HC adsorbent on the downstream side of the fuel reforming catalyst, and the temperature (T ₁ ) of the fuel reforming catalyst is If the predetermined judgment temperature (T _R) is lower than, the When the reformed gas discharged from the fuel reforming catalyst is circulated through a passage passing through the HC adsorbent, and the temperature (T ₁ ) of the fuel reforming catalyst is equal to or higher than the determination temperature (T _R ) The gas passage switching means (40, 514) for allowing the reformed gas discharged from the fuel reforming catalyst to flow through a passage not passing through the HC adsorbent is provided.

  According to a second aspect of the present invention, in the fuel reformer of the first aspect, the reformer discharged from the fuel reforming catalyst from the downstream side of the HC adsorbent in a passage passing through the HC adsorbent. It further comprises desorption treatment means (40, 514, 516) for desorbing hydrocarbons adsorbed on the HC adsorbent by supplying gas.

  According to a third aspect of the present invention, in the fuel reformer of the second aspect, the upstream side of the HC adsorbent in the passage passing through the HC adsorbent and the fuel reforming catalyst in the gas passage. The desorption processing means supplies a part of the reformed gas discharged from the fuel reforming catalyst from the downstream side of the HC adsorbent. The hydrocarbon desorbed from the HC adsorbent is caused to flow into the fuel reforming catalyst through the reflux passage.

  According to a fourth aspect of the present invention, in the fuel reformer according to the third aspect, the desorption treatment means is a carbonization desorbed from the HC adsorbent using a negative pressure generated in the reflux passage. Hydrogen is allowed to flow into the fuel reforming catalyst.

  According to a fifth aspect of the present invention, in the fuel reformer of the fourth aspect, the time from when the fuel reformer is started until the fuel reforming catalyst reaches the activation temperature is reached. The time from when the fuel reformer is started until the HC adsorbent reaches the desorption temperature is defined as the desorption temperature arrival time, and the desorption temperature arrival time is equal to or greater than the activation temperature arrival time. It is characterized by being.

  The invention according to claim 6 is the fuel reformer according to any one of claims 1 to 5, wherein the fuel reforming catalyst is at least selected from the group consisting of rhodium, platinum, palladium, nickel, and cobalt. It includes a metal component containing one kind and an oxide or composite oxide containing at least one kind selected from the group consisting of ceria, zirconia, alumina, and titania.

  The invention according to claim 7 is the fuel reformer according to any one of claims 1 to 6, wherein the HC adsorbent is selected from the group consisting of mordenite type, ZSM-5 type, β type, and Y type. A hydrogen-type zeolite containing at least one selected from the above, or a hydrogen-type zeolite obtained by ion-exchange of silver, an alkali metal or an alkaline earth metal.

  According to the first aspect of the present invention, when the temperature of the fuel reforming catalyst is lower than the predetermined determination temperature, the reformed gas discharged from the fuel reforming catalyst is exhausted through the HC adsorbent. When the temperature of the fuel reforming catalyst is equal to or higher than a predetermined determination temperature, the reformed gas is supplied to the exhaust passage without passing through the HC adsorbent. Here, for example, the determination temperature is set to the activation temperature of the fuel reforming catalyst. As a result, even when the temperature of the fuel reforming catalyst is lower than the activation temperature and unreacted hydrocarbons are included in the reformed gas, the hydrocarbons are adsorbed with the HC adsorbent to enter the exhaust passage. It is possible to prevent hydrocarbons from being discharged. Therefore, the reformed gas containing no unreacted hydrocarbon can be supplied to the exhaust passage of the internal combustion engine regardless of the temperature of the fuel reforming catalyst.

  Further, for example, when the NOx purification device is provided in the exhaust passage, the NOx purification device using the reformed gas not containing unreacted hydrocarbons as the reducing gas regardless of the temperature of the fuel reforming catalyst as described above. It becomes possible to supply to. Thereby, even immediately after the start of the internal combustion engine, NOx contained in the exhaust gas can be efficiently purified.

Further, by providing the fuel reforming catalyst in a gas passage different from the exhaust passage, it is possible to prevent the fuel reforming catalyst from deteriorating due to carbon deposition or melting.
Further, the fuel reforming catalyst is provided in a gas passage different from the exhaust passage, and further, the fuel gas is supplied from the other end side of the gas passage by the fuel gas supply means, so that the fuel gas supplied to the fuel reforming catalyst is reduced. It becomes easy to accurately adjust the fuel / air mixing ratio. Thereby, it becomes easy to stably improve the hydrogen yield in the fuel reforming catalyst.

According to the invention of claim 2, when adsorbing hydrocarbons on the HC adsorbent, the reformed gas flows through the HC adsorbent from the upstream side to the downstream side, while the adsorbed hydrocarbon is removed. When desorbing from the HC adsorbent, the reformed gas flows through the HC adsorbent from the downstream side toward the upstream side.
By the way, the HC adsorbent is heated in order from the upstream side to the downstream side by the heat of adsorption when adsorbing hydrocarbons. Therefore, as described above, by allowing the reformed gas to flow from the downstream side toward the upstream side, the hydrocarbon adsorbed on the upstream side can be quickly desorbed.

  According to the invention described in claim 3, the unreacted hydrocarbon desorbed from the HC adsorbent is recirculated to the fuel reforming catalyst through the recirculation passage together with the reformed gas supplied from the downstream side. Thereby, the unreacted hydrocarbon adsorbed by the HC adsorbent can be reused as fuel.

  Here, when desorbing hydrocarbons from the HC adsorbent, part of the reformed gas discharged from the fuel reforming catalyst is used. That is, by supplying a reformed gas containing almost no oxygen to the HC adsorbent and desorbing hydrocarbons, when the hydrocarbons are desorbed, unreacted This prevents the hydrocarbons from burning and becoming unusable as fuel.

  According to the fourth aspect of the present invention, the hydrocarbon desorbed from the HC adsorbent is caused to flow into the fuel reforming catalyst due to the negative pressure generated in the reflux passage. By flowing hydrocarbons using negative pressure in this way, for example, energy consumption can be suppressed as compared to the case where pressurized hydrocarbons are pumped using a pressure pump. .

  According to the invention described in claim 5, after the temperature of the fuel reforming catalyst reaches the activation temperature, the temperature of the HC adsorbent reaches the desorption temperature. That is, when the temperature of the HC adsorbent reaches the desorption temperature and the adsorbed hydrocarbon is desorbed, the temperature of the fuel reforming catalyst always reaches the activation temperature. As a result, it is possible to continue supplying the reformed gas to the exhaust passage even while desorbing the HC adsorbent.

According to the sixth aspect of the present invention, the fuel reforming catalyst is excellent in heat resistance, and thereby the reformed gas can be generated efficiently. That is, in order to efficiently perform the partial oxidation reaction, it is necessary to raise the temperature of the fuel reforming catalyst, but by including the above-mentioned oxide, the fuel reforming catalyst can be heated to about 1000 ° C. Further, even if H ₂ O, H ₂ and CO ₂ generated during the reaction are present, the reforming performance is not impaired.

  According to the seventh aspect of the present invention, unreacted hydrocarbons can be adsorbed efficiently even immediately after the start of the fuel reformer. By the way, in order to adsorb hydrocarbons having a high carbon number, it is preferable to use zeolite having a pore diameter of 0.5 nm or more. According to the invention described in claim 7, since zeolite satisfying such conditions is used for the HC adsorbent, unreacted hydrocarbons containing a large amount of high carbon number hydrocarbons are discharged particularly immediately after starting. Even in this case, it can be efficiently adsorbed.

Further, by using hydrogen-type zeolite, the acid strength can be improved and the chemical adsorption ability of the HC adsorbent can be improved. Thereby, the temperature at which hydrocarbons can be adsorbed and retained in the HC adsorbent can be further increased.
Moreover, the chemical adsorption ability of the HC adsorbent can be further improved by using hydrogen-type zeolite obtained by ion exchange of silver, alkali metal, or alkaline earth metal. Thereby, the temperature at which hydrocarbons can be adsorbed and retained in the HC adsorbent can be further increased.

  FIG. 1 is a diagram showing a configuration of an internal combustion engine and an exhaust purification device thereof according to an embodiment of the present invention. An internal combustion engine (hereinafter referred to as “engine”) 1 is a diesel engine that directly injects fuel into each cylinder 7, and each cylinder 7 is provided with a fuel injection valve (not shown). These fuel injection valves are electrically connected by an electronic control unit (hereinafter referred to as “ECU”) 40, and the valve opening time and valve closing time of the fuel injection valve are controlled by the ECU 40.

  The engine 1 includes an intake pipe 2 through which intake air circulates, an exhaust pipe 4 through which exhaust gas circulates, an exhaust gas recirculation passage 6 that recirculates part of the exhaust gas in the exhaust pipe 4 to the intake pipe 2, and intake air into the intake pipe 2. And a supercharger 8 for pressure-feeding.

  The intake pipe 2 is connected to the intake port of each cylinder 7 of the engine 1 through a plurality of branch portions of the intake manifold 3. The exhaust pipe 4 is connected to the exhaust port of each cylinder 7 of the engine 1 through a plurality of branch portions of the exhaust manifold 5. The exhaust gas recirculation passage 6 branches from the exhaust manifold 5 and reaches the intake manifold 3.

  The supercharger 8 includes a turbine (not shown) provided in the exhaust pipe 4 and a compressor (not shown) provided in the intake pipe 2. The turbine is driven by the kinetic energy of the exhaust flowing through the exhaust pipe 4. The compressor is rotationally driven by the turbine, pressurizes the intake air, and pumps it into the intake pipe 2. The turbine includes a plurality of variable vanes (not shown), and is configured to change the turbine rotation speed (rotational speed) by changing the opening of the variable vanes. The vane opening degree of the turbine is electromagnetically controlled by the ECU 40.

  An intercooler 11 for cooling the pressurized air and a throttle valve 12 for controlling the amount of intake air are provided downstream of the supercharger 8 in the intake pipe 2. The throttle valve 12 is connected to the ECU 40 via an actuator, and its opening degree is electromagnetically controlled by the ECU 40.

  The exhaust gas recirculation passage 6 connects the exhaust manifold 5 and the intake manifold 3 and recirculates part of the exhaust discharged from the engine 1. The exhaust gas recirculation passage 6 is provided with an EGR cooler 21 that cools the exhaust gas that is recirculated and an EGR valve 20 that controls the flow rate of the recirculated exhaust gas. The EGR valve 20 is connected to the ECU 40 via an actuator (not shown), and the valve opening degree is electromagnetically controlled by the ECU 40.

  The exhaust pipe 4 is provided with an exhaust converter that purifies the exhaust. The exhaust converter includes a catalytic converter 31, a particulate matter collection device (hereinafter referred to as “DPF” (Diesel Particulate Filter)) 32, and a NOx purification device 33, and is connected to the exhaust pipe 4 from the upstream side. The catalytic converter 31, the DPF 32, and the NOx purification device 33 are provided in this order.

The catalytic converter 31 incorporates an oxidation catalyst, purifies the exhaust by a reaction between the catalyst and the exhaust, and raises the temperature of the exhaust. More specifically, the catalytic converter 31 is, for example, a zeolite excellent in hydrocarbon (HC) adsorption action on platinum (Pt) acting as a catalyst supported on an alumina (Al ₂ O ₃ ) support. And an oxidation catalyst containing rhodium (Rh), which is excellent in the steam reforming action of HC.

  When the exhaust gas passes through fine holes in the filter wall, the DPF 32 deposits soot as particulates mainly composed of carbon in the exhaust gas on the surface of the filter wall and the holes in the filter wall. Collect. As a constituent material of the filter wall, for example, ceramics such as silicon carbide (SiC) or a porous metal body is used.

The NOx purification device 33 acts as a catalyst supported on a support of alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), and a composite oxide of cerium and rare earth (hereinafter referred to as “ceria-based composite oxide”). Platinum (Pt), a ceria or ceria-based composite oxide having NOx adsorption capability, and a zeolite having a function of holding ammonia (NH ₃ ) in the exhaust as ammonium ions (NH ₄ ⁺ ).

  When the amount of adsorbed ammonia in the NOx purifying device 33 decreases, the NOx purifying ability decreases. Therefore, in order to appropriately reduce NOx, a reducing agent is supplied to the NOx purifying device 33 (hereinafter referred to as “reduction”). . In this reduction, the reducing agent is reduced by making the air-fuel ratio of the air-fuel mixture in the combustion chamber richer than the stoichiometric air-fuel ratio by increasing the amount of fuel injected from the fuel injection valve and decreasing the amount of intake air by the throttle valve. The NOx purification device 33 is supplied. That is, by enriching the air-fuel ratio, the reducing agent concentration in the exhaust gas flowing into the NOx purification device 33 becomes higher than the oxygen concentration, and reduction is executed.

The NOx purification in the NOx purification device 33 will be described.
First, when the air-fuel ratio of the air-fuel mixture combusted in the engine 1 is set to be leaner than the stoichiometric air-fuel ratio, so-called lean burn operation is performed, the reducing agent concentration in the exhaust gas flowing into the NOx purification device 33 is lower than the oxygen concentration. Become. As a result, nitrogen monoxide (NO) and oxygen (O ₂ ) in the exhaust gas react with each other by the action of the catalyst, and are adsorbed as NO ₂ on the ceria or ceria-based composite oxide. In addition, carbon monoxide (CO) that has not reacted with oxygen is also adsorbed to ceria or ceria-based composite oxide.

Next, when reduction is performed to make the reducing agent concentration in the exhaust gas higher than the oxygen concentration, carbon monoxide (CO) in the exhaust gas reacts with water (H ₂ O), and carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) is generated, and the hydrocarbon (HC) in the exhaust gas reacts with water to generate hydrogen together with carbon monoxide (CO) and carbon dioxide (CO ₂ ). Furthermore, NOx contained in the exhaust gas, NOx (NO, NO ₂ ) adsorbed on ceria or ceria-based complex oxide (and platinum), and the produced hydrogen react with each other by the action of the catalyst, and ammonia (NH ₃ ) and water are produced. Further, the ammonia generated here is adsorbed on the zeolite in the form of ammonium ions (NH ₄ ⁺ ).

Next, when lean burn operation is performed in which the air-fuel ratio is set to be leaner than the stoichiometric air-fuel ratio, and the reducing agent concentration in the exhaust gas flowing into the NOx purification device 33 is set to be lower than the oxygen concentration, the ceria or ceria-based composite NOx is adsorbed on the oxide. Further, when ammonium ions are adsorbed on the zeolite, NOx and oxygen in the exhaust gas react with ammonia to generate nitrogen (N ₂ ) and water.

  Thus, according to the NOx purification device 33, ammonia generated during the supply of the reducing agent is adsorbed by the zeolite, and the ammonia adsorbed during the lean burn operation reacts with NOx, so that the NOx purification can be performed efficiently. Can do.

Further, between the DPF 32 and the NOx purification device 33 in the exhaust pipe 4, the fuel gas is reformed to produce a reformed gas containing hydrogen (H ₂ ) and carbon monoxide (CO). A fuel reformer 50 is connected to supply the quality gas as the reducing gas to the exhaust pipe 4.

FIG. 2 is a block diagram showing the configuration of the fuel reformer 50.
The fuel reformer 50 includes a gas passage 51 having one end connected to the exhaust pipe 4, a fuel gas supply device 52 as a fuel gas supply means for supplying fuel gas from the other end of the gas passage 51, a gas A reforming catalyst 53 as a fuel reforming catalyst provided in the passage 51 and an HC adsorbent 54 provided on the downstream side of the reforming catalyst 53 in the gas passage 51 are configured.

  The fuel gas supply device 52 mixes fuel stored in the fuel tank and air supplied by the compressor at a predetermined ratio to produce fuel gas, and supplies the fuel gas to the gas passage 51. The fuel gas supply device 52 is connected to the ECU 40, and the fuel gas supply amount and the mixing ratio thereof are controlled by the ECU 40.

  Of the gas passage 51, the upstream side of the reforming catalyst 53 is a fuel gas passage 511 through which the fuel gas supplied from the fuel gas supply device 52 flows, and the downstream side of the reforming catalyst 53 is the reforming catalyst. Thus, the reformed gas passage 512 through which the reformed gas produced in 53 is circulated.

  The reformed gas passage 512 is provided with an adsorption passage 513 that connects the upstream side and the downstream side of the reformed gas passage 512. An HC adsorbent 54 is provided in the adsorption passage 513.

  In addition, the upstream side of the adsorption passage 513 and the reformed gas passage 512 has a passage through which the reformed gas discharged from the reforming catalyst 53 flows, an adsorption passage 513 that passes through the HC adsorbent 54, and A three-way valve 514 that switches between the reformed gas passage 512 that does not pass through the HC adsorbent 54 is provided. The three-way valve 514 is connected to the ECU 40 via an actuator (not shown), and the opening degree is electromagnetically controlled by the ECU 40.

  The gas passage 51 is provided with a reflux passage 515 that connects the upstream side of the HC adsorbent 54 in the adsorption passage 513 and the upstream side of the reforming catalyst 53 in the fuel gas passage 511. The reflux passage 515 is provided with a negative pressure control valve 516 that opens and closes the reflux passage 515. That is, when the fuel gas is supplied to the fuel gas passage 511 by the fuel gas supply device 52, a negative pressure is generated in the recirculation passage 515, and in the recirculation passage 515, from the adsorption passage 513 side to the fuel gas passage 511 side. Gas circulates. The negative pressure control valve 516 adjusts the flow rate of the gas that flows through the generation of such a negative pressure. The negative pressure control valve 516 is connected to the ECU 40 via an actuator (not shown), and the opening degree is controlled by the ECU 40.

  The reforming catalyst 53 is a catalyst that reforms the fuel gas supplied from the fuel gas supply device 52 to produce a reformed gas containing hydrogen and carbon monoxide. More specifically, the reforming catalyst 53 includes a metal component containing at least one selected from the group consisting of rhodium, platinum, palladium, nickel, and cobalt, and a group consisting of ceria, zirconia, alumina, and titania. And an oxide or composite oxide containing at least one selected.

  In the present embodiment, as the reforming catalyst 53, ceria and rhodium powder are weighed so that the mass ratio of rhodium to ceria is 1%, and this powder is put into a ball mill together with an aqueous medium and stirred and mixed. Thus, a slurry prepared by coating a slurry of cordierite on a support made of cordierite, and then drying and firing at 600 ° C. for 2 hours is used.

  The reforming catalyst 53 is connected to a heater (not shown) configured to include a glow plug, a spark plug, and the like, so that the reforming catalyst 53 can be heated when the fuel reformer 50 is started. It is possible.

  The HC adsorbent 54 adsorbs unreacted hydrocarbons contained in the reformed gas produced by the reforming catalyst 53. More specifically, the HC adsorbent 54 is a hydrogen-type zeolite containing at least one selected from the group consisting of mordenite type, ZSM-5 type, β-type, and Y-type, or silver particles in these hydrogen-type zeolites. And those obtained by ion exchange of alkali metals or alkaline earth metals.

In the present embodiment, as the HC adsorbent 54, a ZSM-5 type hydrogen zeolite (SiO ₂ / Al ₂ O ₃ = 40) powder is added to a 20 mass% silica sol aqueous solution to 50 mass% with respect to the zeolite mass. The slurry was added to a ball mill with an aqueous medium and stirred and mixed to prepare a slurry. After coating the slurry on a cordierite carrier, this was applied at 500 ° C. for 2 hours. Use one prepared by drying and firing.

In the fuel reformer 50 as described above, the configuration and arrangement of the reforming catalyst 53, the HC adsorbent 54, and the like are designed such that the desorption temperature arrival time is equal to or greater than the activation temperature arrival time. Here, the activation temperature attainment time is the time after starting the fuel reformer 50 to the reforming catalyst 53 reaches the activation temperature T _R, desorption temperature arrival time, fuel reformer 50 Is the time from when the HC adsorbent 54 reaches the desorption temperature _THC .

  In the fuel reformer 50 as described above, the fuel gas supplied from the fuel gas supply device 52 is controlled while the three-way valve 514 and the negative pressure control valve 516 are controlled, so that the reformer manufactured by the reforming catalyst 53 is improved. The flow path of the quality gas can be switched in a plurality of modes.

  FIG. 3 is a block diagram showing the configuration of the fuel reformer 50, and shows the flow path of the reformed gas. In FIG. 3, among the gas passages 51 of the fuel reformer 50, a passage through which the reformed gas mainly circulates is indicated by a solid line, and a passage through which the reformed gas does not circulate or hardly circulates is indicated by a broken line. As shown in FIGS. 3A, 3 </ b> B, and 3 </ b> C, in the fuel reformer 50, the reformed gas flow path can be formed mainly in three different modes.

FIG. 3A shows a flow path where the reformed gas reaches the exhaust pipe 4 without passing through the HC adsorbent 54. The flow path shown in FIG. 3A controls the three-way valve 514 so that the reformed gas discharged from the reforming catalyst 53 flows into a reformed gas path 512 that does not pass through the HC adsorbent 54. It is formed by doing. The reformed gas flow path shown in FIG. 3A is hereinafter referred to as a reforming line.
When such a reforming line is formed, the negative pressure control valve 516 is controlled so that the reflux passage 515 is basically closed.

FIG. 3B shows a flow path through which the reformed gas passes through the HC adsorbent 54 and reaches the exhaust pipe 4. The flow path shown in FIG. 3B controls the three-way valve 514 so that the passage through which the reformed gas discharged from the reforming catalyst 53 flows becomes an adsorption passage 513 that passes through the HC adsorbent 54. Formed with. The reformed gas flow path shown in FIG. 3B is hereinafter referred to as an adsorption line.
When such an adsorption line is formed, the negative pressure control valve 516 is controlled so that the reflux passage 515 is basically closed.

  FIG. 3C shows a flow path through which the reformed gas recirculates through the HC adsorbent 54. The flow path shown in FIG. 3C controls the three-way valve 514 to change the passage through which the reformed gas discharged from the reforming catalyst 53 flows into the reformed gas passage 512, and a negative pressure control valve. It is formed by controlling 516 and opening the reflux passage 515.

  More specifically, when the fuel gas is supplied to the fuel gas passage 511 by the fuel gas supply device 52, a negative pressure is generated in the recirculation passage 515. Therefore, by controlling the negative pressure control valve 516 and opening the reflux passage 515, a reformed gas flow path as shown in FIG. 3C is formed.

  Thereby, a part of the reformed gas discharged from the reforming catalyst 53 reaches the exhaust pipe 4 via the reformed gas passage 512. Further, the remaining reformed gas passes through the HC adsorbent 54 from the downstream side of the adsorption passage 513 (exhaust pipe 4 side) and enters the fuel gas passage 511 (upstream side of the reforming catalyst 53) via the reflux passage 515. Refluxed. The reformed gas flow path shown in FIG. 3C is hereinafter referred to as a reflux line.

Returning to FIG. 1, the ECU 40 is connected with a reforming catalyst temperature sensor 531 for detecting the temperature T ₁ of the reforming catalyst 53 and an adsorbent temperature sensor 541 for detecting the temperature T ₂ of the HC adsorbent 54. The detection signals of these sensors are supplied to the ECU 40.

  The ECU 40 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 40 includes a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, an output circuit that outputs control signals to the fuel gas supply device 52, the three-way valve 514, the negative pressure control valve 516, and the like. Is provided.

  FIG. 4 is a flowchart showing a control procedure of the fuel reformer by the ECU. The control of the fuel reformer shown in this flowchart is started based on the ignition being turned on. In the flowchart shown in FIG. 4, only the procedure from when the ignition is turned on until the desorption process for desorbing the hydrocarbons adsorbed on the HC adsorbent is shown.

In step S1, the heater is turned on to start heating the reforming catalyst, and the process proceeds to step S2. In step S2, and it acquires the reforming catalyst temperature T ₁ of based on the output from the reforming catalyst temperature sensor, the flow proceeds to step S3. In step S3, the reforming catalyst temperature T ₁ is determined whether a predetermined combustion initiation temperature T ₀ or more of the reforming catalyst. If this determination is YES, the process proceeds to step S4, and if NO, the process proceeds to step S2.

In step S4, in response to the reforming catalyst temperature T ₁ is now the combustion start temperature T ₀ or more, to start the supply of the fuel gas, the flow proceeds to step S5. In step S5, the three-way valve is controlled so that the flow path of the reformed gas discharged from the reforming catalyst becomes an adsorption line (see (b) of FIG. 3 described above), and the process proceeds to step S6. As a result, the reformed gas discharged from the reforming catalyst is supplied to the exhaust pipe via the HC adsorbent.

In step S6, it obtains the reforming catalyst temperature T ₁ of based on the output from the reforming catalyst temperature sensor, the flow proceeds to step S7. In step S7, the reforming catalyst temperature T ₁ is determined whether a predetermined activation temperature T _R above reforming catalyst. If this determination is YES, the process proceeds to step S8, and if NO, the process proceeds to step S6.

In step S8, in response to the reforming catalyst temperature T ₁ is equal to or larger than the activation temperature T _R, and controls the three-way valve, the flow path of the reformed gas discharged from the reforming catalyst and the reforming line (See (a) of FIG. 3 described above), the process proceeds to step S9. Thereby, the reformed gas discharged from the reforming catalyst is supplied to the exhaust pipe without passing through the HC adsorbent.

In step S9, it obtains the HC adsorbent temperature T ₂ on the basis of the output from the adsorbent temperature sensor, the flow proceeds to step S10. In step S10, the HC absorbent temperature _{T 2} is determined whether a predetermined HC desorption temperature _{T HC} or more HC adsorbent. If this determination is YES, the process proceeds to step S11, and if NO, the process proceeds to step S9.

In step S11, in response to the HC adsorbent temperature _{T 2} is equal to or larger than HC desorption temperature _{T HC,} starts HC desorption processing of the HC adsorbent. More specifically, the three-way valve and the negative pressure control valve are controlled so that the flow path of the reformed gas discharged from the reforming catalyst becomes a recirculation line (see (c) in FIG. 3 above), and the reformed gas A part of is supplied from the downstream side of the HC adsorbent. As a result, hydrocarbons desorbed from the HC adsorbent flow into the reforming catalyst via the reflux passage and are reused as fuel in the reforming catalyst.

  In the present embodiment, the three-way valve 514 and the ECU 40 that controls the three-way valve 514 constitute a gas passage switching means. Further, the three-way valve 514 and the negative pressure control valve 516 and the ECU 40 that controls the three-way valve 514 and the negative pressure control valve 516 constitute a desorption processing means. Specifically, the means according to steps S5 to S8 in FIG. 4 corresponds to the gas passage switching means, and the means according to step S11 in FIG. 4 corresponds to the desorption processing means.

As described above in detail, according to this embodiment, when the temperature T ₁ of the reforming catalyst 53 is lower than a predetermined activation temperature T _R is the reformed gas discharged from the reforming catalyst 53, it is supplied to the exhaust pipe 4 through the HC adsorbent 54, when the temperature T ₁ of the reforming catalyst 53 is the predetermined activation temperature T _R above, reformed gas, without passing through the HC adsorbent 54 It is supplied to the exhaust pipe 4. It Thereby, the temperature T ₁ of the reforming catalyst 53 is lower than the activation temperature T _R, even if it contains unreacted hydrocarbon in the reformed gas, which adsorbs the hydrocarbons in the HC absorbent 54 Thus, hydrocarbons can be prevented from being discharged into the exhaust pipe 4. Therefore, regardless of the temperature T ₁ of the reforming catalyst 53, a reformed gas that does not contain unreacted hydrocarbons can be supplied to the exhaust pipe 4.

Further, the NOx purification device 33 is provided in the exhaust pipe 4. Therefore, regardless of the temperature T ₁ of the reforming catalyst 53 as described above, it is possible to supply the reformed gas not containing unreacted hydrocarbons to the NOx purification device 33 as a reducing gas. As a result, even immediately after the engine 1 is started, NOx contained in the exhaust can be efficiently purified.

Further, by providing the reforming catalyst 53 in the gas passage 51 different from the exhaust pipe 4, it is possible to prevent the reforming catalyst 53 from deteriorating due to carbon deposition or melting.
Further, the reforming catalyst 53 is provided in the gas passage 51 different from the exhaust pipe 4, and the fuel gas is supplied from the other end side of the gas passage 51 by the fuel gas supply device 52, thereby supplying the reforming catalyst 53. It becomes easy to accurately adjust the fuel / air mixing ratio of the fuel gas. Thereby, it becomes easy to improve the hydrogen yield in the reforming catalyst 53 stably.

Further, according to the present embodiment, when adsorbing hydrocarbons on the HC adsorbent 54, the reformed gas flows through the HC adsorbent 54 from the upstream side to the downstream side, while the adsorbed hydrocarbon is removed. When desorbing from the HC adsorbent 54, the reformed gas flows through the HC adsorbent 54 from the downstream side toward the upstream side. That is, the direction in which the gas flowing through the HC adsorbent 54 flows is opposite between the time of adsorption and the time of desorption.
By the way, the HC adsorbent 54 is heated in order from the upstream side to the downstream side by the heat of adsorption when adsorbing hydrocarbons. Therefore, as described above, by allowing the reformed gas to flow from the downstream side toward the upstream side, the hydrocarbon adsorbed on the upstream side can be quickly desorbed.

  Here, as in this embodiment, the advantage of reversing the flow direction of the gas flowing through the HC adsorbent 54 during adsorption and desorption is compared with the fuel reformer 50 according to this embodiment. The fuel reforming apparatus according to the example will be compared and described in detail.

  FIG. 5 is a block diagram showing a configuration of a fuel reformer 50A according to a comparative example. About the structure of this fuel reformer 50A, the same code | symbol is attached | subjected about the same structure as the fuel reformer 50 of this embodiment, and the description is abbreviate | omitted.

This fuel reformer 50A is configured so that the gas flowing through the HC adsorbent 54A flows in the same direction during adsorption and desorption.
More specifically, in this fuel reformer 50A, the recirculation passage 515A connects the downstream side of the HC adsorbent 54A in the adsorption passage 513A and the upstream side of the reforming catalyst 53 in the fuel gas passage 511. . Further, at the time of desorption, the hydrocarbon desorbed from the HC adsorbent 54 is recirculated through the recirculation passage 515A, so that a control valve that opens and closes the adsorption passage 513 on the downstream side of the HC adsorbent 54A in the adsorption passage 513. 517A is provided.

  Here, when the fuel reformer 50 (see FIG. 2) of the present embodiment and the fuel reformer 50A (see FIG. 5) of the comparative example are compared, the fuel reformer 50A shows a broken line 519 in FIG. As shown, the length of the reflux passage 515A needs to be increased according to the total length of the HC adsorbent 54A. In addition to this, in the fuel reformer 50A, it is necessary to provide an extra control valve 517A, which complicates the configuration of the passage.

  Further, according to the present embodiment, the unreacted hydrocarbon desorbed from the HC adsorbent 54 is refluxed to the reforming catalyst 53 via the reflux passage 515 together with the reformed gas. Thereby, the unreacted hydrocarbon adsorbed by the HC adsorbent 54 can be reused as fuel.

  Here, when desorbing hydrocarbons from the HC adsorbent 54, a part of the reformed gas discharged from the reforming catalyst 53 is used. Therefore, the reformed gas contains almost no oxygen. By supplying such a reformed gas containing almost no oxygen to the HC adsorbent 54 and desorbing hydrocarbons, when the hydrocarbons are desorbed, unreacted in the HC adsorbent 54 that has reached a high temperature. It is possible to prevent the hydrocarbons from burning and becoming unusable as fuel.

  Further, according to the present embodiment, the hydrocarbon desorbed from the HC adsorbent 54 is caused to flow into the reforming catalyst 53 due to the negative pressure generated in the reflux passage 515. By flowing hydrocarbons using negative pressure in this way, for example, energy consumption can be suppressed as compared to the case where pressurized hydrocarbons are pumped using a pressure pump. .

Further, according to this embodiment, after the temperature _{T 1} of the reforming catalyst 53 has reached the activation temperature _{T R,} the temperature _{T 2} of the HC adsorbent 54 reaches a desorption temperature _{T HC.} That is, the temperature T ₂ of the HC adsorbent 54 has reached the desorption temperature T _HC, when desorbs hydrocarbons once adsorbed, the temperature T ₁ of the reforming catalyst 53 is always reached the activation temperature T _R. As a result, it is possible to continue supplying the reformed gas to the exhaust pipe 4 while desorbing the HC adsorbent 54.

  In addition, according to the present embodiment, unreacted hydrocarbons can be adsorbed efficiently even immediately after the fuel reformer 50 is started. By the way, in order to adsorb hydrocarbons having a high carbon number, it is preferable to use zeolite having a pore diameter of 0.5 nm or more. According to the present embodiment, since zeolite satisfying such conditions is used for the HC adsorbent 54, particularly when unreacted hydrocarbons containing a large amount of hydrocarbons having a high carbon number are discharged immediately after startup. Even so, it can be efficiently adsorbed.

Further, by using hydrogen-type zeolite, the acid strength can be improved and the chemical adsorption ability of the HC adsorbent can be improved. Thereby, the temperature at which hydrocarbons can be adsorbed and held in the HC adsorbent 54 can be further increased.
Further, for example, when a hydrogen-type zeolite obtained by ion exchange of silver, an alkali metal, or an alkaline earth metal is used, the chemical adsorption ability of the HC adsorbent can be further improved. Thereby, the temperature at which hydrocarbons can be adsorbed and retained in the HC adsorbent can be further increased.

  The present invention is not limited to the embodiment described above, and various modifications can be made. For example, in the above-described embodiment, the negative pressure control valve 516 that opens and closes the reflux passage 515 is provided, but the present invention is not limited thereto. For example, a negative pressure pump that reduces the pressure in the reflux passage may be provided.

  The present invention can also be applied to a fuel reformer such as a marine vessel propulsion engine such as an outboard motor having a vertical crankshaft.

1 is a diagram illustrating a configuration of an internal combustion engine and an exhaust purification device thereof according to an embodiment of the present invention. It is a block diagram which shows the structure of the fuel reformer which concerns on the said embodiment. It is a block diagram which shows the structure of the fuel reforming apparatus which concerns on the said embodiment, and is a figure which shows the flow path of reformed gas. It is a flowchart which shows the procedure of control of the fuel reformer by ECU which concerns on the said embodiment. It is a block diagram which shows the structure of the fuel reforming apparatus which concerns on a comparative example.

Explanation of symbols

1 engine (internal combustion engine)
4 Exhaust pipe (exhaust passage)
5 Exhaust manifold (exhaust passage)
40 ECU (gas passage switching means, desorption processing means)
50 Fuel reformer 51 Gas passage 511 Fuel gas passage 512 Reformed gas passage 513 Adsorption passage 514 Three-way valve (gas passage switching means)
515 Reflux passage 516 Negative pressure control valve (desorption processing means)
52 Fuel gas supply device (fuel gas supply means)
53 Reforming catalyst (fuel reforming catalyst)
54 HC adsorbent

Claims (6)

In a fuel reformer that reforms a fuel gas to produce a reformed gas and supplies the reformed gas to an exhaust passage through which exhaust discharged from an internal combustion engine flows.
A gas passage whose one end is connected to the exhaust passage;
Fuel gas supply means for supplying fuel gas from the other end of the gas passage;
A fuel reforming catalyst provided in the gas passage;
HC adsorbent provided downstream of the fuel reforming catalyst in the gas passage,
The gas passage includes, on the downstream side of the fuel reforming catalyst, a passage that passes through the HC adsorbent and a passage that does not pass through the HC adsorbent,
When the temperature of the fuel reforming catalyst is lower than a predetermined determination temperature, the reformed gas discharged from the fuel reforming catalyst is circulated through a passage passing through the HC adsorbent, and the fuel reforming catalyst Gas passage switching means for causing the reformed gas discharged from the fuel reforming catalyst to flow through a passage that does not pass through the HC adsorbent when the temperature of the fuel is not less than the determination temperature ;
By supplying the reformed gas discharged from the fuel reforming catalyst from the downstream side of the HC adsorbent in the passage passing through the HC adsorbent, the hydrocarbon adsorbed on the HC adsorbent is moved upstream thereof. A fuel reforming apparatus comprising: a desorption treatment means for desorption . A recirculation passage connecting the upstream side of the HC adsorbent in the passage passing through the HC adsorbent and the upstream side of the fuel reforming catalyst in the gas passage;
The desorption processing means supplies a part of the reformed gas discharged from the fuel reforming catalyst from the downstream side of the HC adsorbent, and removes hydrocarbons desorbed from the HC adsorbent in the reflux passage. The fuel reformer according to claim 1 , wherein the fuel reformer is caused to flow through the fuel reforming catalyst. The desorption processing means, by using the negative pressure generated in said reflux passage, according hydrocarbons desorbed from the HC adsorbent to claim 2, characterized in that to flow into the fuel reforming catalyst Fuel reformer. The time from when the fuel reformer is started until the fuel reforming catalyst reaches the activation temperature is defined as the activation temperature arrival time,
The time from when the fuel reformer is started until the HC adsorbent reaches the desorption temperature is the desorption temperature arrival time,
The fuel reformer according to claim 3 , wherein the desorption temperature arrival time is equal to or longer than the activation temperature arrival time. The fuel reforming catalyst is
A metal component containing at least one selected from the group consisting of rhodium, platinum, palladium, nickel, and cobalt;
Ceria, zirconia, alumina, and a fuel reforming apparatus according to any one of claims 1 to 4, characterized in that it comprises an oxide or a composite oxide containing at least one selected from the group consisting of titania. The HC adsorbent is
Hydrogen type zeolite containing at least one selected from the group consisting of mordenite type, ZSM-5 type, β type, and Y type, or those obtained by ion exchange of silver, alkali metal or alkaline earth metal to these hydrogen type zeolites the fuel reforming apparatus according to any one of claims 1 to 5, characterized in that it comprises a.

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