JP2501542Y2 - Exhaust gas purification system for diesel engines - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to an exhaust gas purification apparatus for a cylinder injection type internal combustion engine that performs lean combustion, in which an exhaust system is provided with a zeolite catalyst supporting a noble metal or a transition metal. Regarding

[Conventional technology]

A catalyst (hereinafter referred to as a lean NOx catalyst) in which a precious metal or a transition metal is supported on a zeolite-based carrier, which has an NOx purification capacity in a lean air-fuel ratio region, is known (for example, JP-A-63-283727). .

On the other hand, the in-cylinder injection engine that performs lean combustion represented by a diesel engine is burned in a lean range (A / F22 to 24) far more than stoichiometric (theoretical air-fuel ratio, A / F13 to 14).
Although fuel consumption is improved by lean combustion, in the lean region, there is almost no NOx purification capacity with a three-way catalyst, so conventional exhaust gas purification with a three-way catalyst cannot be used, and NOx purification becomes a problem. Lean NOx catalyst is lean
Since it has a NOx purification capability, it is effective to reduce the NOx by providing a lean NOx catalyst in the exhaust system of such an engine.

(Problems to be solved by the device) However, according to the test studies of the inventor and the like, the following conditions are necessary to promote the NOx purification action by the lean NOx catalyst.

(B) The concentration of HC (end-burning hydrocarbon) in the exhaust gas is high. The exhaust gas of a cylinder injection type internal combustion engine that performs lean combustion is
Due to lean combustion, it is in an atmosphere with excess oxygen, and most of the fuel HC is oxidized, and it is in a state of HC shortage, but lean NOx
For effective NOx purification by catalyst, HC must still remain in the exhaust gas at the required concentration.

(B) The residual HC has a small number of carbon atoms in its molecule. For example, the diesel engine fuel is light oil, so the residual HC in the exhaust gas that remains after combustion in the engine is a relatively high molecular weight molecule (a molecule with a large number of carbon atoms).
In order for NOx reduction by the x catalyst to work effectively, it is desirable that it is a low-grade (small number of molecules) HC molecule.

The present invention, in an exhaust gas purification device for a direct injection internal combustion engine that performs lean combustion with a lean NOx catalyst in the exhaust system, increases the HC concentration in the exhaust gas flowing to the lean NOx catalyst and further reduces the HC to a low molecular state. The purpose is to be able to supply to the lean NOx catalyst at.

[Means for solving the problem]

According to the present invention, the above object is achieved by the following exhaust gas purification apparatus for an internal combustion engine. That is, an in-cylinder injection internal combustion engine that has fuel injection means for injecting fuel into the cylinder during the intake or compression stroke and that is operated in a lean air-fuel ratio region, and NOx in exhaust gas with excess oxygen provided in its exhaust passage In a device for purifying exhaust gas of an internal combustion engine, which comprises a lean NOx catalyst for reducing and purifying fuel, fuel injection means for injecting fuel in the intake or compression stroke injects part of the fuel into the cylinder in the expansion or exhaust stroke. An exhaust gas purification device for an internal combustion engine, characterized in that the cylinder is used as a reformer for decomposing fuel injected into a cylinder in expansion or exhaust stroke with heat in the cylinder to lower HC. .

[Action]

In the exhaust gas purifying apparatus for an internal combustion engine of the present invention, in addition to the normal fuel injection that is performed in the intake or compression stroke, fuel is also injected into the cylinder in the expansion stroke or exhaust stroke where combustion has ended. The fuel injected in this expansion or exhaust stroke is pyrolyzed by the residual heat in the cylinder without meeting the combustion stroke, breaking the chain bonds of higher molecules, and as a so-called lower molecule HC molecule having a small carbon content. Emitted from the cylinder. Therefore, the HC of the exhaust gas flowing to the lean NOx catalyst
The concentration is increasing, and HC is in a lower molecular state.

The NOx purification mechanism in the lean NOx catalyst by HC is estimated as follows.

That is, most of the unburned HC in the exhaust gas is oxidized to CO ₂ and H ₂ O, but part of it is partially oxidized and becomes the active species CO 2.
^- to become. Part of this active species is NO with the help of lean NOx catalysts.
reacts with x to reduce NOx to N ₂ and CO ₂ to make it harmless,
The rest is oxidized to CO and further oxidized to CO ₂ . In this case, as the HC concentration in the exhaust gas increases, the amount of active species also increases, and NOx purification is promoted. In addition, the lower the HC molecule, the greater the amount of active species produced. This is the reason why, in the present invention, fuel is injected into the cylinder in the expansion or exhaust stroke to increase the number of lower HC molecules.

〔Example〕

Hereinafter, a preferred embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings.

FIG. 1 shows an exhaust emission control device according to an embodiment of the present invention.
In FIG. 1, 1 is a fuel injection pump of a cylinder injection type internal combustion engine (for example, diesel engine, the same applies hereinafter) that performs lean combustion, 2 is fuel injection nozzles 2 and 3 provided in each cylinder of the diesel engine, and fuel injection is performed. Fuel supply passages for guiding the light oil fuel from the pump 1 to the respective fuel injection nozzles # 1, # 2, #
3 and # 4 indicate the cylinder numbers in the case of four cylinders, for example. There are as many fuel injection nozzles 2 and fuel supply passages 3 as there are cylinders.

FIG. 2 shows a cross section taken along line II-II of FIG. 1 in a state enlarged from that of FIG. In FIG. 2, # 1, # 2, # 3, #
Reference numeral 4 denotes the fuel supply passages 3 corresponding to the # 1 cylinder, # 2 cylinder, # 3 cylinder, and # 4 cylinder, respectively. In the middle of the fuel supply passage 3, there is provided a communication passage 5 that connects the fuel supply passage 3 to the cylinder in the fuel injection period and the fuel supply passage 3 to the cylinder in the initial stage of the exhaust stroke at the same time. ing. Then, in each communication passage 5, when the pressure of the fuel supply passage 3 to the cylinder in the fuel injection period exceeds a certain value, a part of the fuel in the fuel supply passage 3 to the cylinder in the fuel injection period A relief valve 4 is provided to relieve the fuel supply passage 3 to the cylinder in the exhaust stroke. For example, in an engine having an ignition order of # 1, # 3, # 4, # 2, the relief of fuel is # 3 → # 1, # 1 → # 2, # 2 → # 4, # 4.
→ It becomes # 3.

FIG. 3 shows a relief valve 4 provided for the fuel supply passage 3 of the # 3 cylinder, for example. Relief valve 4
Is urged by the spring 6 from the fuel supply passage 3 connected to the # 1 cylinder toward the fuel supply passage 3 connected to the # 3 cylinder. # 3 When the cylinder is in the intake stroke, # 3
When the fuel pressure in the fuel supply passage 3 connected to the cylinder exceeds a certain value determined by the urging force of the spring 6, the relief valve 4 opens and the fine fuel is relieved in the fuel supply passage 3 connected to the # 1 cylinder. , Through the fuel injection nozzle 2 of the # 1 cylinder into the # 1 cylinder at the beginning of the exhaust stroke. The valve opening pressure of the relief valve 4 is determined so that the amount of HC supplied to the lean NOx catalyst described later is appropriate.

FIG. 4 shows a diesel engine and its intake and exhaust systems. Reference numeral 7 is a diesel engine, 8 is an intake manifold, 9 is an exhaust manifold, and 11 is a reformer provided as necessary. A catalytic converter including the lean NOx catalyst 10 is provided in the exhaust system, and downstream of the reformer 11 when provided. The reformer 11 is a device for thermally decomposing high-molecular-weight molecules of light oil fuel having a high carbon number into lower-molecular-weight molecules having a low carbon number. The lean NOx catalyst 10 is composed of a zeolite-based catalyst supporting a noble metal or a transition metal, and the catalyst has a NOx reducing ability in a lean air-fuel ratio region. However, the NOx purification capacity requires the presence of HC, especially the presence of lower HC, as described above.

 Next, the operation will be described.

When one cylinder, for example, the # 3 cylinder is in the fuel injection period, another cylinder, that is, the # 1 cylinder is in the early stage of the exhaust stroke. The fuel injected into the # 3 cylinder passes through the combustion stroke, works as a heat engine, and is then discharged to the exhaust system. in this case
Since NOx is produced, it is emitted together with NOx. # 3
Since the pressure of the fuel supply passage 3 of the cylinder exceeds a certain value, a part of the pressure is relieved to the fuel supply passage 3 of the # 1 cylinder through the relief valve 4 and the communication passage 5, and the fuel is injected through the fuel injection nozzle 2 of the # 1 cylinder to # 1. It is injected into the cylinder. The small amount of fuel injected into the # 1 cylinder is discharged without being burned because the # 1 cylinder is in the exhaust stroke. Before being discharged from the # 1 cylinder, HC is thermally decomposed by the heat remaining in the combustion gas of the # 1 cylinder, and lower molecules, for example, C, become three propylene. The exhaust gas containing NOx from the # 3 cylinder and the exhaust gas containing low-grade HC from the # 1 cylinder are combined at the confluence of the exhaust manifold 9 to reach the lean NOx catalyst. With the help of the lean NOx catalyst 10, NOx is reduced and rendered harmless to N ₂ and CO ₂ according to the mechanism described above. This reduction is sufficiently performed by the required amount of low-grade HC which is reliefed in the # 1 cylinder and thermally decomposed in the # 1 cylinder. Therefore, the NOx contained in the exhaust gas discharged to the atmosphere through the lean NOx catalyst 10 is sufficiently reduced.

In the above exhaust gas purification device, the communication passage 5 and the relief valve 4 need only be added to the conventional device, and a special fuel pressure feeding device,
No special control device need be provided. For example, the relief valve 4 automatically opens when the biasing force of the spring 6 is exceeded, and no special timing control device for supplying HC is required. For this reason, there is almost no increase in cost, and since the structure is simple, the operation and durability are high.

[Effect of device]

The lean NOx catalyst requires HC, especially low-grade HC, to accelerate NOx purification.
Fuel is injected into the cylinder in the exhaust stroke, and the fuel is thermally decomposed by the residual heat in the cylinder to become low-grade HC and exhausted, so the lean NOx catalyst can be supplied with a sufficient amount of low-grade HC. The NOx purification rate is improved.

Further, since the same means as the fuel injection means for injecting fuel in the intake or compression stroke is used as the means for injecting fuel into the cylinder in the expansion or exhaust stroke, it is not necessary to newly provide the HC supply means. Further, it is used as a reformer that reforms the fuel injected into the cylinder during the expansion or exhaust stroke of the cylinder by the heat in the cylinder to reform it to lower HC that is effective in reducing NOx and supplies it to the lean NOx catalyst. Therefore, it is not necessary to add a dedicated fuel reformer or the like. That is, since only a slight improvement is required, the cost is not increased significantly, and the reliability of the device is not significantly lowered.

[Brief description of drawings]

FIG. 1 is a schematic system diagram of an exhaust purification system for an internal combustion engine according to the present invention, FIG. 2 is a sectional view taken along the line II-II in FIG. 1, and FIG. 3 is an enlarged sectional view in the vicinity of the relief valve in FIG. FIG. 4 is a schematic plan view of an internal combustion engine that performs lean combustion and its intake and exhaust systems. 1 ... Fuel injection pump 2 ... Fuel injection nozzle 3 ... Fuel supply passage 4 ... Relief valve 5 ... Communication passage 6 ... Spring 7 ... Internal combustion engine performing lean combustion, for example, diesel engine 9 ... Exhaust manifold 10: lean NOx catalyst

Claims (1)

(57) [Scope of utility model registration request] 1. An in-cylinder injection type internal combustion engine having fuel injection means for injecting fuel into a cylinder during an intake or compression stroke and operated in a lean air-fuel ratio region, and an excess oxygen exhaust gas provided in an exhaust passage thereof. In an exhaust gas purification device for an internal combustion engine, which comprises a lean NOx catalyst that reduces and purifies NOx, a part of the fuel in the cylinder in which the fuel injection means that injects fuel in the intake or compression stroke is in the expansion or exhaust stroke Of the internal combustion engine, wherein the cylinder is used as a reformer that decomposes the fuel injected into the cylinder in the expansion or exhaust stroke with heat in the cylinder to lower HC. Exhaust purification device.