JP4941284B2 - Exhaust gas treatment system for internal combustion engine - Google Patents

Description

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

Devices such as internal combustion engines and boilers, along with their combustion, produce fine carbides (PM), hydrocarbons (HC), sulfur oxides (SOX: SO, SO ₂ ), nitrogen oxides (NOX: NO, NO ₂ , N ₂ O), carbon oxides (COX: CO, CO ₂ ) and the like are released into the atmosphere. In recent years, these exhaust gas components have become stricter regulations especially from the environmental aspect (such as global warming), and establishment of exhaust gas purification technology is regarded as important. In particular, for mobiles such as automobiles, there are many restrictions on size, weight, cost, efficiency, maintainability, etc., but a rapid increase in demand is expected, so the development of an efficient exhaust gas treatment device is urgently needed. is there.

In gasoline engines for automobiles, oxygen, etc. are used to control the engine so that combustion becomes the stoichiometric air-fuel ratio. By using an oxidation-reduction catalyst device (three-way catalyst) using platinum or the like, PM, HC, NOX are converted. Removed from the exhaust gas.
On the other hand, diesel engines have good fuel efficiency, and emit 20 to 30% less carbon oxides such as CO ₂ than gasoline engines. However, exhaust gas contains a lot of excess oxygen, and it is difficult to use a reduction catalyst. For this reason, the exhaust gas is circulated to reduce NOX (EGR), and the PM generated by this is removed by a filter (DPF), the urea is injected into the exhaust gas to reduce NOX (urea SCR), and NOX A method (DPNR) for temporarily adsorbing and reducing NOx adsorbed with fuel or the like at an appropriate timing has been put into practical use.

  However, EGR and DPF have a low NOX reduction effect and restrict the driving performance of the automobile. In the urea SCR, mounting of a urea tank and urea replenishment are problems, and in the DPNR, there is a problem that it is necessary to periodically inject extra fuel, resulting in deterioration of fuel consumption. In addition, these exhaust gas purification systems need to be linked to the combustion state of the engine, which complicates engine control, enlarges engine development, lengthens the development period, and increases costs. . Further, in any case, a noble metal such as platinum is required as a catalyst, and there is a problem from the viewpoint of cost or securing resources.

In order to solve these problems, Patent Document 1 describes an engine that reforms NOX using electric discharge. This engine has a structure in which corona discharge needles are arranged on the outer periphery of a cylinder in a dissociation cylinder (reformer) directly connected to the exhaust pipe of the engine, and oxygen atoms (oxygen) constituting NOX discharged and decomposed in the dissociation cylinder Radicals) are combined with carbon monoxide contained in the exhaust gas to form carbon dioxide, and the remaining nitrogen atoms constituting NOX are combined to form nitrogen (N ₂ ), thereby reducing NOx.

JP 61-31615 A

  However, since the NOX concentration in the exhaust gas is lean, there has been a problem that the reduction of NOX by discharge is inefficient.

  The present invention has been made to solve such problems, and an object thereof is to provide an exhaust gas treatment system for an internal combustion engine with improved NOx reduction efficiency.

An exhaust gas treatment system for an internal combustion engine according to the present invention includes two electrode plates provided at intervals in an exhaust pipe through which exhaust gas generated in the internal combustion engine flows, and a high frequency connected to one of the two electrode plates. A plasma generator having a power source and a NOX occlusion material provided between the two electrode plates is provided , and a plurality of plasma generators are provided in series in the exhaust pipe, and between the two electrode plates in each plasma generator. The discharge is performed at different timings, and the discharge energy of each plasma generator decomposes NOX adsorbed on each of the NOX storage materials . In the plasma generator, the NOX storage material adsorbs NOX in the exhaust gas, and the NOX adsorbed by the NOX storage material is decomposed by the plasma generated between the electrode plates .
A control device for detecting a load of the pre-SL engine, the control device, based on the load, may change the number of plasma generator operating.
The energy of discharge between the two electrode plates may be 642 to 942 kJ / mol .

  According to this invention, it has two electrode plates provided at intervals in the exhaust pipe, a high-frequency power source connected to one of the two electrode plates, and a NOX occlusion material provided between the two electrode plates. By providing the plasma generator, in the plasma generator, the NOX storage material adsorbs NOX in the exhaust gas, and the NOX absorbed and concentrated by the NOX storage material is decomposed by the plasma generated between the electrode plates. , NOX reduction efficiency can be improved.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 shows a configuration of a diesel engine provided with the exhaust gas treatment system according to the first embodiment. The cylinder block 2 of the diesel engine 1 is provided with combustion chambers 2a, 2b, 2c, 2d in four cylinders, and an intake manifold 3 and an exhaust manifold 4 so as to communicate with these. An intake pipe 5 through which air flows is connected to the intake manifold 3, and an exhaust pipe 6 through which exhaust gas generated in the combustion chambers 2 a, 2 b, 2 c, 2 d circulates is connected to the exhaust manifold 4. The exhaust pipe 6 is provided with two plasma generators 12 and 22 in series. Moreover, the diesel engine 1 is provided with ECU10 which is a control apparatus.

The plasma generator 12 includes a high frequency power supply 16 electrically connected to the ECU 10, an electrode plate 13 provided in the exhaust pipe 6 and connected to the high frequency power supply 16, and an electrode plate provided in the exhaust pipe 6 and grounded. 14 and a NOX occlusion material 15 carrying NOX occlusion particles made of BaO on a porous body made of conductive Al ₂ O ₃ provided between the electrode plates 13 and 14. Each of the electrode plates 13 and 14 is covered with a dielectric, and is provided in parallel in the exhaust pipe 6 with a gap therebetween. The plasma generator 22 has the same configuration as the plasma generator 12, and includes two electrode plates 23 and 24, a high-frequency power source 26, and a NOX occlusion material 25 provided between the electrode plates 23 and 24.

Next, operation | movement of the diesel engine provided with the exhaust gas processing system which concerns on this Embodiment 1 is demonstrated based on FIG.
When the diesel engine 1 is started, the air flowing through the intake pipe 5 is sucked into the combustion chambers 2 a to 2 d via the intake manifold 3. The air sucked into the combustion chambers 2a to 2d is compressed by a piston (not shown), and then fuel is injected into the combustion chambers 2a to 2d from an injection nozzle (not shown) to burn and become exhaust gas. The exhaust manifold 4 is discharged from ˜2d.

  When the exhaust gas in the exhaust manifold 4 flows through the exhaust pipe 6, the NOx in the exhaust gas is adsorbed by the NOX storage particles of the NOX storage material 15 as the exhaust gas passes through the NOX storage material 15 of the plasma generator 12. . Thereby, when the exhaust gas passes through the plasma generator 12, the NOX concentration in the exhaust gas is reduced. However, there is a limit to the amount of NOX that can be adsorbed by the NOX storage material 15, and if it exceeds that, the NOX concentration in the exhaust gas will not be reduced even if it passes through the plasma generator 12. In this case, the exhaust gas passes through the inside of the NOX storage material 25 of the plasma generator 22, so that NOX in the exhaust gas is adsorbed by the NOX storage particles of the NOX storage material 25. Thereby, when the exhaust gas passes through the plasma generator 22, the NOX concentration in the exhaust gas is reduced.

When a certain amount of NOX in the exhaust gas is adsorbed by the NOX occlusion material 15 of the plasma generator 12, the ECU 10 operates the high frequency power supply 16 to cause discharge between the electrode plates 13 and 14 (plasma is generated). Here, the energy of discharge is set in a range of 642 to 942 kJ / mol. This range corresponds to a range larger than the energy capable of decomposing NOx into N and O and smaller than the energy capable of decomposing N ₂ . As a result, the NOX adsorbed on the NOX storage material 15 is decomposed into N ₂ and O ₂ at a certain ratio, released from the NOX storage material 15, and when it becomes NOX again, the NOX storage material 15 or The NOx adsorbed again by the NOx 25 and finally adsorbed by the NOx occlusion material 15 is all released. The energy of the discharge by less than the energy that can decompose N _2, N ₂ is prevented from being regenerated NOX is decomposed again. Further, while the plasma generator 12 is being discharged, the NOX storage material 25 of the plasma generator 22 is adsorbing NOX.

Eventually, the plasma generator 22 also exceeds the limit of the amount of NOX that can be adsorbed by the NOX storage material 25, but the NOX adsorbed by the NOX storage material 15 is decomposed by the discharge between the electrode plates 13 and 14, and N _Since it becomes ₂ and O ₂ and is released from the NOX storage material 15, NOX in the exhaust gas passes through the NOX storage material 15 again and is adsorbed by the NOX storage particles of the NOX storage material 15. During this time, similarly to the plasma generator 12, in the plasma generator 22, by generating plasma between the electrode plates 23 and 24, NOX adsorbed on the NOX storage material 25 is decomposed and N ₂ and O ₂ are decomposed. As the NOX storage material 25.

  By repeating the above operation, NOx in the exhaust gas is reduced. Although the timing of generating plasma in each of the plasma generators 12 and 22 is shifted, the plasma may be generated in each of the plasma generators 12 and 22 in a preset time, or the ECU 10 may be diesel engine. The amount of exhaust gas may be estimated based on the operating state such as the rotational speed of the engine 1, and the timing for generating plasma in each of the plasma generators 12 and 22 may be determined based on this.

  As described above, the two electrode plates 13 and 14 provided in the exhaust pipe 6 with a space therebetween, the high-frequency power source 16 connected to one electrode plate 13, and the two electrode plates 13 and 14 are provided. By providing the plasma generator 12 having the NOX storage material 15 and the plasma generator 22 having the same configuration in series, in one plasma generator, the NOX storage material adsorbs NOX in the exhaust gas, and the other In this plasma generating apparatus, NOX adsorbed by the NOX storage material is decomposed by the plasma generated between the electrode plates, so that the NOX reduction efficiency can be improved. Further, by decomposing NOX adsorbed on the NOX occlusion material with plasma, the NOX reduction efficiency can be improved as compared with the case where NOX in the exhaust gas is decomposed with plasma.

In the first embodiment, two plasma generators are provided, but the number is not limited to two. Even with three or more plasma generators, the same effect can be obtained. Moreover, although the discharge energy in each plasma generator is limited to the range of 642-942 kJ / mol, it is not limited to this range. If it is greater than 942 kJ / mol, the produced N ₂ may be decomposed again to regenerate NOX. However, the regenerated NOX is again produced as NOX occlusion particles because of the reaction in the NOx occlusion material. NOx is not released from the NOX occlusion material. Accordingly, it is sufficient that the discharge energy is at least 642 kJ / mol or more.

In the first embodiment, the NOX storage material 15 is configured by supporting NOX storage particles made of BaO on a porous body made of conductive Al ₂ O _3, but is not limited to this form. It needs to include the adsorption material capable NOX. Examples of such materials include alkali metals such as Na, K and Li, alkaline earth metals such as Ba, Mg and Ca, lanthanoids such as La and Ce, oxides such as MgO, NaCl, and the like. Examples thereof include composites composed of these elements and other elements, and composite oxides containing these elements such as BaSO ₄ .

Embodiment 2. FIG.
Next, an exhaust gas treatment system according to Embodiment 2 of the present invention will be described. In the following embodiments, the same reference numerals as those in FIG. 1 are the same or similar components, and detailed description thereof will be omitted.
The exhaust gas treatment system according to Embodiment 2 of the present invention is different from Embodiment 1 in that the number of plasma generators is changed.

  In the diesel engine 31 shown in FIG. 2, six plasma generators 12, 22, 32, 42, 52, 62 are provided in series in the exhaust pipe 6. These six plasma generators have high frequency power supplies 16, 26, 36, 46, 56, 66, respectively, and each high frequency power supply is electrically connected to the ECU 10. The plasma generators 22, 32, 42, 52, 62 have two electrode plates 23, 24, 33, 34, 43, 44, 53, 54, 63, 64, respectively. It has NOX storage materials 25, 35, 45, 55, 65 provided between the two electrode plates, respectively, and has the same configuration as the plasma generator 12. Other configurations are the same as those of the first embodiment.

Next, operation | movement of the diesel engine provided with the exhaust gas processing system which concerns on this Embodiment 2 is demonstrated based on FIG.
After starting the diesel engine 31, the ECU 10 detects the operating state of the diesel engine 31. When it is determined that the load on the diesel engine 31 is small, the ECU 10 operates the high-frequency power sources 16 and 26 alternately at different timings as in the first embodiment. As a result, in one plasma generator, NOX is adsorbed by the NOX occlusion material, and in the other plasma generator, NOX adsorbed by the NOX occlusion material is decomposed by the plasma, and NOx in the exhaust gas is reduced. The

  When the load of the diesel engine 31 increases, the ECU 10 operates the high-frequency power sources 16, 26, 36, and 46 at different timings. When the load on the diesel engine 31 further increases, the ECU 10 shifts the timing to operate the high-frequency power sources 16, 26, 36, 46, 56, 66. As the load on the diesel engine 31 increases, the amount of NOx in the exhaust gas increases. Therefore, by increasing the number of plasma generators that operate, that is, the number of plasma generators that operate based on the load on the diesel engine 31. By changing, it is possible to appropriately cope with a change in the amount of NOX in the exhaust gas, and it is possible to improve the NOX reduction efficiency.

  In the second embodiment, the timing for operating each high-frequency power source has not been specifically described, but any one of the high-frequency power sources may be operated with a different timing from the other high-frequency power sources. For example, the high-frequency power sources 16, 26, 36, 46, 56, 66 are operated one by one in this order, or the high-frequency power source 16 and the high-frequency power source 36 (and 56) are simultaneously operated, and the high-frequency power source 26 is operated. And the high frequency power supply 46 (and 66) may be operated simultaneously.

  In the first and second embodiments, a plurality of plasma generators are provided, but only one plasma generator may be provided. In this case, while the NOX adsorbed on the NOX storage material 15 is decomposed by plasma, NOX in the exhaust gas cannot be reduced, but the NOX adsorbed on the NOX storage material 15 is reliably decomposed. Compared with the case where the discharge is simply performed in the exhaust gas, the NOx reduction efficiency can be improved comprehensively.

  In Embodiments 1 and 2, the exhaust gas treatment system is employed in a diesel engine, but the internal combustion engine is not limited to a diesel engine. You may employ | adopt for a gasoline engine, a boiler, etc.

1 is a schematic diagram of a diesel engine equipped with an exhaust gas treatment system according to Embodiment 1 of the present invention. 3 is a schematic diagram of a diesel engine provided with an exhaust gas treatment system according to Embodiment 2. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,31 Diesel engine (internal combustion engine), 6 exhaust pipe, 10 ECU (control apparatus), 12, 22, 32, 42, 52, 62 Plasma generator, 13, 14, 23, 24, 33, 34, 43, 44, 53, 54, 63, 64 Electrode plate, 15, 25, 35, 45, 55, 65 NOX storage material, 16, 26, 36, 46, 56, 66 High frequency power supply.

Claims (3)

Two electrode plates provided at intervals in an exhaust pipe through which exhaust gas generated in an internal combustion engine flows;
A high-frequency power source connected to one of the two electrode plates;
A plurality of plasma generators having a NOX occlusion material provided between the two electrode plates ;
The exhaust pipe is provided with the plurality of plasma generators in series,
The discharge between the two electrode plates in each plasma generator is performed at different timings, and the discharge energy of each plasma generator is an exhaust gas treatment of an internal combustion engine that decomposes NOX adsorbed on each of the NOX storage materials. system. A control device for detecting a load of the internal combustion engine;
The control device, based on the load, changes the number of plasma generator operating, exhaust gas treatment system for an internal combustion engine according to claim 1. The exhaust gas treatment system for an internal combustion engine according to claim 1 or 2 , wherein energy of discharge between the two electrode plates is 642 to 942 kJ / mol.