JPH08303228A - Particulate type for diesel engine - Google Patents

Abstract

PURPOSE: To efficiently burn particulates collected in a filter by means of oxygen supply by natural convection during a stop of an engine so as to accomplish a high filter regenerative ratio with less heater electric energy in a shorter regenerating time. CONSTITUTION: In an outer case 5 storing a filter element 10, an air introducing port 6, through which outside air is introduced to the outside of an outer cylinder filter 2 by means of natural convection, and a discharging port 7, from which air used for combustion is discharged to the outside of the case 5, are arranged. In addition, an outside air introducing pipe 8 introducing outside air to the inside of an inner cylinder filter 1 is arranged. In this way, inflow outside air is spread over respective parts in the filter element 10, so that collected particulates can be burnt by means of a heater 3 with less electric energy in a shorter time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particulate trap for collecting and removing fine particles (particulates) such as carbon contained in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art Exhaust gas from an automobile is one of the major causes of air pollution, and a technique for removing harmful components contained in the exhaust gas is extremely important.

Particularly in diesel engine vehicles, the removal of particulates mainly composed of NOx and carbon is an important issue.

In order to remove these harmful components, it has been proposed to install an exhaust trap in the exhaust passage, collect particulates by the trap, and remove them by post-treatment. In addition, EGR (exhaust gas recirculation) is applied, the fuel injection system is improved, and efforts are being made on the engine side, but there is no fundamental deciding factor, and up to now, the above-mentioned trap treatment method has been adopted. Is considered to be the most practical and is being studied.

This trap is constructed by mounting a filter element in an outer case installed in the middle of the exhaust system.

The post-treatment of the collected particulates is best burned for repeated use of the trap. As a method of regenerating the particulate trap by the combustion, particulate incineration using a light oil burner is also considered, but from the viewpoint of safety and ease of control, combustion regeneration by an electric heater is the most promising at present. A particulate trap that actually employs the electric heater is (1) JP-A-5-22290, (2) JP-A-6-257422, (3) The same as JP-A-6-26472.
It is proposed in Japanese Patent Publication No. 2 and the like.

In all of these traps, filters are arranged in parallel. For such traps,
While the engine is operating, the amount of exhaust gas flowing into the filter is adjusted by a valve having a control means, etc. without significantly reducing the thermal efficiency of the heater, and the amount of oxygen required for combustion of soot (particulate) is also adjusted. Exhaust gas purification devices have been developed to ensure sufficient combustion regeneration (for example,
JP-A-6-101449).

However, in the case of the system for controlling the engine displacement, considering that delicate control is required and that a control device that withstands the high temperature of exhaust gas is required, the device is complicated and expensive. It is obvious that

Therefore, a relatively simple exhaust gas purifying apparatus has been proposed in which the trapped particulates are burned while the engine is stopped to regenerate the filter. Some of these systems supply oxygen required for trapped particulate combustion during regeneration by an external air source or an electric fan, but recently, the external case that houses the filter has been modified to make it more natural. It is considered that an external device or an auxiliary device that supplies necessary oxygen by convection is unnecessary.

[0010]

FIG. 2 shows an example in which a natural convection type oxygen supply mechanism is applied to a particulate trap employing a multi-cylindrical filter.

The filter element 10 used in the illustrated particulate trap is a cylindrical filter having different diameters, that is, the inner cylinder filter 1 and the outer cylinder filter 2 are combined in a concentric arrangement, and the inner cylinder filter 1 on the exhaust gas inflow side is combined. Of the inner and outer cylinder filters 1, and the gaps between the end openings of the inner and outer cylinder filters on the exhaust gas outflow side are closed by the end plates 4.
The exhaust gas introduced from the inlet side into the gap between the two flows through the filtering portion of each cylindrical filter into the exhaust gas derivation space generated inside the inner cylinder filter 1 and outside the outer cylinder filter 2.

The particulate trap employing the multi-cylindrical filter element 10 can secure a wide filtration area, and a planar electric heater 3 is inserted between the opposing filtration surfaces as shown in FIG. There is an advantage that the entire filtration surface can be uniformly and efficiently heated during combustion regeneration, and the overall size can be reduced and the power consumption of the heater can be reduced.

However, as shown in the figure, when the conventional outer case 5 for a single cylindrical filter provided with an air inlet 6 and an air outlet 7 by natural convection is used for a multi-cylindrical filter, from the outside of the case at the time of filter regeneration. The introduced outside air does not sufficiently reach between the inner and outer cylinder filters and inside the inner cylinder filter.Therefore, oxygen is deficient in those parts, and particulate combustion does not proceed smoothly, which is the case when using a single cylinder filter. In comparison, the amount of electric power for reproduction increases and the reproduction time also increases. In extreme cases, the reproduction itself will be insufficient.

It is an object of the present invention to provide a particulate trap which eliminates such a problem and makes full use of the advantages of the multi-cylindrical filter.

[0015]

In order to solve the above-mentioned problems, in the present invention, a particulate trap for a diesel engine, wherein a filter for collecting particulates in exhaust gas has a double or more multiple structure, In the external case for storing the filter that is installed in the middle of the exhaust system,
This is because a natural convection type outside air introduction path is provided from the outside of the case to the inside of the multiple cylindrical filter housed in the case.

[0016]

When the outside air is introduced into the inside of the multiplex cylindrical filter, there is no part where the oxygen supply is extremely deteriorated, and the combustion of the particulates trapped in the entire area of the filtration part proceeds efficiently. Further, because of this, the absolute amount of introduced outside air can be reduced, and the heat of the heater taken by the outside air is also reduced.

As a result, it is possible to reduce the heater power and the regeneration time, and the regeneration rate of the filter is improved.

[0018]

1 shows an example of a particulate trap for a diesel engine of the present invention. In this particulate trap, a filter material made of a metal having good heat resistance is processed into a tubular shape to form an inner tubular filter 1 and an outer tubular filter 2, and the outer tubular filters 1 and 2 are shown in FIG. As shown in the drawing, the electric heaters 3 are arranged concentrically with each other and the electric heater 3 is arranged between them, and the filter element 10 with the heater thus formed is mounted in the outer case 5 shown in FIG. FIG. 1C is a cross-sectional view of the filter element with a heater 10 used here. The exhaust gas is introduced into the space between the inner cylinder filter 1 and the outer cylinder filter 2, passes through the inner cylinder and the outer cylinder filter, and flows to the inside of the inner cylinder filter 1 and the outside of the outer cylinder filter 2. In order to create this gas flow, the opening on the gas inflow side of the inner cylinder filter 1 and the opening in the space between the inner and outer cylinder filters on the gas outflow side are closed by the end plates 4 fixed to the inner and outer cylinder filters.

The outer case 5 is provided with the above-mentioned air introduction port 6 and air discharge port 7 through which outside air flows into the outside of the filter element 10 by utilizing natural convection generated by the heat of the heater.

The removable lid 5a is provided with an outside air introduction pipe 8 extending from the outside of the case to the inside of the inner cylindrical filter 1. The outside air introducing pipe 8 has a hole 9 in the end plate 4 that closes the end opening of the inner cylinder filter 1, and the hole 9 is formed when the lid 5a is attached.
It has a structure in which the inner end of the pipe is inserted and fitted.

If this outside air introduction pipe 8 is provided on the exhaust gas outflow side, the flow of the filtered gas that has flowed inside the inner cylinder filter 1 becomes poor, so that as shown in the figure, it is provided on the exhaust gas outflow side. It is good to provide. Further, it is preferable that the inlet of the pipe 8 is located lower than the outlet so that air can be smoothly introduced by natural convection.

The electric heater 3 punches an Inconel thin plate into a shape in which the heat generating circuit is alternately folded back at one end and the other end, adjusts the resistance and processes it into a tubular shape, and energizes this to directly generate heat. It is preferable to use a cylinder made of punching metal, expanded metal, wire mesh, porous metal or the like as a heat medium, and a sheath heater wound around the cylinder.

This is because such a heater can efficiently heat by facing the entire area of the filtration surface facing each other.

The filter element to be used may be one in which two or more cylindrical filters having different diameters are concentrically arranged.

A more detailed embodiment will be described below.

FIG. 3 shows an experimental apparatus used for performance evaluation of the prototype. This device comprises a 3400 CC, 4-cylinder direct injection diesel engine vehicle and a chassis dynamometer, and the particulate trap 11 to be evaluated is connected to the exhaust pipe as shown in the figure.

A Ni-Cr three-dimensional network structure porous body (trade name: Celmet) manufactured by Sumitomo Electric Industries, Ltd. is made into Ni-Cr to form an outer cylinder filter, and the inner cylinder filter is combined with the outer cylinder filter. A filter element 10 having a double cylinder structure shown in FIG. 1 was produced. As the heater 3, a heater was used in which a thin Inconel plate was punched and the resistance of which was adjusted, processed into a tubular shape, and directly heated to generate heat.

Then, the filter element with a heater 10 was housed in the outer case 5 of FIG. 1 (a) to obtain a particulate trap of the embodiment (invention). Also,
The same filter element 10 was housed in the external case 5 for a single filter shown in FIG. 2 to obtain a particulate trap for comparison.

Next, each of the prototypes was mounted on the experimental apparatus shown in FIG. 3, and the amount of particulates deposited (collection amount) on the filter element became 1.5 g under the operating conditions of 1800 rpm and 1/4 load. Exhaust gas was filtered.

After that, the engine was stopped, and the heater 3 was energized by a constant voltage power source to burn the trapped particulates under the condition where natural convection of air occurs due to heating. The heater power and regeneration time at this time were as shown in Table 1, and thereafter, the regeneration condition of the filter was evaluated. The evaluation was performed by obtaining the differential pressure recovery rate (regeneration rate) defined by the following equation.

Differential pressure recovery rate = {1-A / B} × 100 (%) A = (filter differential pressure after regeneration) − (filter differential pressure before collection) B = (filter differential pressure after collection) )-(Filter differential pressure before collection) The results are also shown in Table 1.

[0032]

[Table 1]

From the results of this experiment, the invention product has a higher regeneration rate than the comparative product even if the heater power and the regeneration time are both halved. In addition, the regeneration rate at a heater power of 300 W and a regeneration time of 7 minutes is 5% in Comparative Example 4, whereas
In Example 3, the ratio is 82%, and practical filter regeneration is possible even if the vehicle-mounted battery has a small capacity.

[0034]

As described above, in the particulate trap of the present invention, the introduction path for introducing the outside air by natural convection is provided inside the cylindrical filter in the outer case for accommodating the multiple cylindrical filter. Combustion of trapped particulates can be promoted throughout the filtration section, and at the same time, the absolute amount of outside air introduced can be reduced to reduce the escape of heater heat, reducing the heater power consumption and shortening the regeneration time. , The regeneration rate can be improved.

[Brief description of drawings]

FIG. 1A is a sectional view showing an example of a particulate trap of the present invention. FIG. 1B is a perspective view of a filter element used in the trap described above. FIG. 1C is a sectional view of a filter element used in the trap described above.

FIG. 2 is a sectional view of a particulate trap before the device of the present invention is added.

[Explanation of symbols]

 1 Inner Cylinder Filter 2 Outer Cylinder Filter 3 Electric Heater 4 End Plate 5 Outer Case 6 Air Inlet 7 Air Outlet 9 Hole 10 Filter Element 11 Particulate Trap

Claims (1)

[Claims] 1. In a particulate trap for a diesel engine, wherein a filter for collecting particulates in exhaust gas has a double or more multiple structure, an external case for storing a filter is installed in the middle of an exhaust system from the outside of the case. A particulate trap for a diesel engine, which is provided with a natural convection type outside air introduction path leading to the inside of the multiple cylindrical filter housed in the case.