JPH06229274A - Exhaust emission control device for alcohol engine - Google Patents

Abstract

PURPOSE:To take a lean shift countermeasures to an oxygen sensor in an engine using alcohol as the fuel without applying a large change to an exhaust system. CONSTITUTION:In an alcohol engine, in which an oxygen sensor 9 is fitted to an exhaust manifold 3, the periphery of a part of the oxygen sensor 9, which projects inside of the exhaust manifold 3, is covered with a metal carrier catalyst 14. Since the H2 component is eliminated by the metal carrier catalyst 14, the lean shift countermeasures to the oxygen sensor can be taken even at a low exhaust temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust purification device for an alcohol engine, which is applied to an engine that uses alcohol as a fuel.

[0002]

BACKGROUND OF THE INVENTION engine, when using a three-way catalyst for the purpose of performing an exhaust purification, when the air-fuel ratio is near the stoichiometric air-fuel ratio, HC, to exhibit CO and NO _X are both very high purification rate known That is. Therefore, an oxygen sensor (O ₂ sensor or _two -sensor) is used as a means for bringing the air-fuel ratio close to this theoretical air-fuel ratio. By using this oxygen sensor, it is possible to detect from the oxygen component in the exhaust gas that it is close to the stoichiometric air-fuel ratio.

FIG. 7 schematically shows an engine exhaust system. In this figure, 1 is an engine, 2 is an intake manifold, 3 is an exhaust manifold, 4 is an exhaust pipe, and 5 is a catalyst (three-way catalyst). The exhaust manifold 3 and the exhaust pipe 4 are connected by a flange 6, and an oxygen sensor 7 is mounted slightly upstream of this connecting portion.

In this system, when the exhaust gas discharged from the combustion chamber of the engine 1 is purified by the catalyst 5, the oxygen sensor 7 detects the oxygen component in the exhaust gas, and the control circuit (not shown) controls the combustion. Will be done.

On the other hand, at present, it is conceivable that other components may be used as fuel instead of gasoline, which is the conventional fuel. Experiments have been conducted and some of them have been put to practical use. Alcohol (methyl alcohol, ethyl alcohol) is the first alternative fuel. When alcohol is used as a fuel for an automobile engine, there are cases where only alcohol is used as a fuel and cases where alcohol is mixed in gasoline at a constant ratio.

Even in an engine using alcohol as a fuel, a three-way catalyst is sometimes used to purify exhaust gas, and an oxygen sensor is used in connection therewith.
However, when the oxygen sensor is used when alcohol is used as a fuel, a problem that does not occur when gasoline is used as a fuel occurs.

That is, in an automobile using methanol as a fuel among alcohols, when the H ₂ concentration in the exhaust gas increases, it becomes difficult for oxygen components to reach the oxygen sensor, and as a result, the electromotive force change point is leaner. It shifts. It is considered that this is because the H ₂ concentration in the exhaust gas becomes high when the exhaust gas temperature is low, which makes it difficult for oxygen components to reach the oxygen sensor.

As disclosed in Japanese Patent Laid-Open No. 4-128529 as a prior art, as shown in FIG. 8, as a measure against lean shift, a catalyst 8 is provided inside an exhaust manifold 3 upstream of an oxygen sensor 7. It is installed. Although the intended purpose can be achieved by the purifying action of the catalyst 8, in order to do so, it is necessary to change the structure of the exhaust system to mount the catalyst 8 and the response of the oxygen sensor. It is conceivable that the property deteriorates and the durability of the catalyst 8 becomes a problem.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of this point, and a catalyst for lean shift countermeasures can be attached to an oxygen sensor without making a large change to the exhaust system. It is intended to provide an exhaust emission control device for an alcohol engine.

[0010]

Means for Solving the Problems As a means for solving the above problems, the present invention provides an alcohol engine in which an oxygen sensor is attached to an exhaust manifold, wherein an outer periphery of a portion of the oxygen sensor projecting into the exhaust manifold is The structure is covered with a metal carrier catalyst.

[0011]

With this structure, the portion of the oxygen sensor that projects into the exhaust manifold is covered with the metal-supported catalyst, so that the H ₂ concentration in the exhaust increases when the exhaust temperature is low. When the oxygen component becomes difficult to reach the oxygen sensor, this H ₂ component will be removed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an oxygen sensor 9 according to the present invention. The oxygen sensor 9 has a mounting flange 10 and a screw 11 in the central portion, a portion ahead of the screw 11 is a sensing portion 12, and a portion after the flange 10 is a main body portion 13. The portion of the oxygen sensor 9 that projects into the exhaust manifold 3, that is, the outer periphery of the sensing portion 12 is covered with a metal-supported catalyst 14 having a honeycomb structure. As shown in FIG. 2, the oxygen sensor 9 is attached by screwing a screw 11 on the upstream side of the connection portion of the exhaust manifold 3 with the exhaust pipe 4.

FIGS. 3 and 4 show an example of a method for producing the metal-supported catalyst 14. First, what is shown in FIG. 3 is a net 15 made of stainless steel. This net 15 is wound into a cylindrical shape as shown in FIG. 2 and its seam is welded or brazed to be fixed. A disc-shaped net 16 made of the same material is placed on the upper side, and the periphery is welded or brazed for attachment. This creates a basket with a bottom. When this cage-like object carries a catalyst and the sensing portion 12 of the oxygen sensor 9 is inserted and welded or brazed to the portion of the screw 11 to stop, the one as shown in FIG. 1 is obtained.

5 and 6 show a method of manufacturing the metal carrier catalyst 14 using a punching plate. In this case, the net 15 in FIGS. 3 and 4
Instead of punching plate 17 made of stainless steel
Using the disc 18 made of the same material as the above, the metal carrier catalyst 14 is manufactured by the same manufacturing method as in the case of the net 15.

According to the oxygen sensor 9 in which the sensing portion 12 is covered with the metal carrier catalyst 14 thus constructed, the oxygen sensor 9 is mounted around the oxygen sensor 9 even if the exhaust temperature is low and the H ₂ concentration in the exhaust is high. The metal-supported catalyst 14 can reduce the H ₂ concentration. As a result, the lean shift of the oxygen sensor 9 can be easily reduced, and accurate emission control can be performed.

[0016]

Since the present invention is the exhaust gas purification apparatus for an alcohol engine constructed as described above, it is possible to take a lean shift countermeasure of the oxygen sensor without making a great change in the exhaust system. . Since there are few changes, the cost can be kept low. As a result, lean shift is reduced, so that the accuracy of emission control is improved and exhaust gas purification is promoted.

[Brief description of drawings]

FIG. 1 is a side view of an oxygen sensor according to the present invention.

2 is a cross-sectional view showing a state where the oxygen sensor of FIG. 1 is attached to an exhaust manifold.

FIG. 3 is a front view showing an example of a method for producing a metal-supported catalyst.

FIG. 4 is a perspective view showing an example of a method for producing a metal-supported catalyst.

FIG. 5 is a front view showing another example of a method for producing a metal-supported catalyst.

FIG. 6 is a perspective view showing another example of a method for producing a metal-supported catalyst.

FIG. 7 is a system diagram showing an outline of an engine exhaust system.

FIG. 8 is a cross-sectional view showing a main part of the prior art.

[Explanation of symbols]

 1 engine 3 exhaust manifold 4 exhaust pipe 5 catalyst 9 oxygen sensor 12 detector 14 metal carrier catalyst

Claims (1)

[Claims] 1. An exhaust gas purifying apparatus for an alcohol engine, comprising: an alcohol engine having an oxygen sensor attached to an exhaust manifold, wherein an outer periphery of a portion of the oxygen sensor protruding into the exhaust manifold is covered with a metal carrier catalyst. .