JPH0713446B2 - Exhaust gas purification device for engine - Google Patents

Description

The present invention relates to an exhaust gas purifying apparatus for an engine, and more particularly to an exhaust gas purifying apparatus that collects and burns particulates (black smoke particles) discharged from the engine.

(Prior Art) Provide a particulate filter in the exhaust system of the engine,
An exhaust gas purifying apparatus for an engine, which is provided with a nozzle for injecting a catalyst solution for promoting combustion of particulates in an exhaust passage upstream thereof, has already been proposed by the applicant of this application (Japanese Patent Application No. 59-64627).

In this apparatus, the catalyst solution is supplied from the nozzle to burn and remove the particulates collected by the particulate filter.

(Problems to be Solved by the Invention) In the above conventional exhaust gas purifying apparatus, since the ignition temperature of particulates is slightly higher than the exhaust gas temperature range (usually 300 ° C. or less) under normal engine operating conditions, There is a problem that the particulates cannot be burned and removed.

Moreover, since sufficient oxygen is not supplied to the particulates adhering to the surface of the particulate filter, it is difficult to accelerate the oxidation reaction of these particulates.

(Means for Solving Problems) An exhaust gas purifying apparatus for an engine according to the present invention is an exhaust gas purifying apparatus for an engine, which comprises a particulate filter for collecting combustible particles and the like in an exhaust system. An injector for injecting a base metal catalyst solution is provided upstream, and a porous coating layer carrying a rare earth catalyst component is formed on the particulate filter.

(Operation) The operation of the exhaust gas purifying apparatus for an engine according to the present invention will be described. The particulates in the exhaust gas discharged from the engine are collected by the particulate filter.

When the base metal catalyst solution is injected from the injector, the catalyst solution adheres to the collected particulates, and the catalytic action of the catalyst component in the catalyst solution accelerates the oxidation reaction of the particulates. At this time, active oxygen is generated by the catalytic action of the catalyst component of the coating layer, the oxidation reaction of particulates is further promoted, and the particulates ignite and burn at a low temperature.

In addition, since the base metal catalyst is separated from the rare earth catalyst in advance, both catalysts do not react and deteriorate before exhibiting the catalytic effect.

(Effect of the Invention) According to the exhaust gas purifying apparatus for an engine of the present invention, the following is provided because the injector for injecting the catalyst solution is provided and the porous coating layer carrying the rare earth catalyst component is formed as described above. The effect is obtained.

(A) The particulates can be sufficiently combusted even in a normal operating region of a diesel engine or the like having a low exhaust gas temperature, and the particulates can be reliably removed.

(B) Since the base metal catalyst component and the rare earth catalyst component are used, the catalytic effect is promoted and the oxidation performance is improved.
This improves the purification performance of hydrocarbons and carbon monoxide and also improves the combustibility of carbon.

(C) Since the rare earth catalyst component is carried on the coating layer of the surface layer of the particulate filter, active oxygen is generated on the surface layer of the filter by its catalytic action, and the combustion of the particulates adhering to the surface layer portion of the filter is promoted. It

(D) Since both catalyst components are separated in advance and not mixed and supported, mutual reaction between the rare earth catalyst component and the base metal catalyst component is suppressed, and the durability of both catalyst components is improved.

(E) since the NO-H ₂ and NO-CO reaction is accelerated by the catalytic component of the rare earth, purification of NO ₂ is promoted.

(F) Since the rare earth catalyst component is supported on the porous coating layer, the catalyst component is hardly consumed, which is advantageous in terms of cost.

(Example) Hereinafter, the Example of this invention is described based on drawing.

In FIG. 1 showing the case where the present invention is applied to a four-cylinder diesel engine, an engine 1 is provided with an intake passage 2 for supplying intake air to the engine 1, and an exhaust passage for discharging exhaust gas from the engine 1. 3 are connected. Further, a particulate filter 4 is provided in the middle of the exhaust passage 3. An injector 5 is arranged upstream of the particulate filter 4.

The injector 5 includes a tank 6 that stores the aqueous catalyst solution, an injector 7 that is arranged upstream of the particulate filter 4 so as to face the ejection port, and a connecting pipe 8 that connects the tank 6 and the injector 7. The pump 9 provided on the communication pipe 8 and the pump 9 (not shown) detects that the back pressure of the engine 1 has reached a predetermined value which adversely affects the operating performance of the engine 1. And a sensor for operating the. With this, the injector 5 is
When the back pressure of the tank becomes a predetermined value or more, the pump 9 sucks up the aqueous catalyst solution in the tank 6 through the communication pipe 8, and the injector 7
To a predetermined amount (for example, 10 to 100 cc) to the upstream of the particulate filter 4. The above catalyst solution, for example, 1 to 10% by weight of one or more base metals _{(V, C u, C r} , F e, N i, M o, C a, B a) from a water-soluble salt of It contains the following catalyst components.

The particulate filter 4 is a so-called plugged monolith type. As shown in FIG. 2, the particulate filter 4 has a large number of passages 21 partitioned by partition walls 20, and one end of each passage 21 is plugged so that the upstream side and the downstream side are staggered. Closed by 22. The partition wall 20 is made of porous ceramics (for example, cordierite) and collects particulates in the exhaust gas when the exhaust gas passes through the partition wall 20 as shown by the arrow in FIG. .

The partition wall 20 is coated with a porous alumina layer (not shown) as a coating layer. In the alumina layer,
5-90% by weight of ceria (C _e O _2), or 1 to 5% by weight of L _a,
Nd is supported.

Further, a throttle valve 10 which receives a detection signal from the sensor and is substantially half-closed and throttle-adjusts an intake amount is arranged in the collecting portion of the intake passage 2.

Next, the operation of the above embodiment will be described.

With the operation of the engine 1, exhaust gas is discharged from the engine 1 through the exhaust passage 3. When the exhaust gas passes through the partition wall 20 of the particulate filter 4 as shown in FIG. 2, the particulates in the exhaust gas are collected on the partition wall 20.

When the back pressure of the engine 1 reaches a predetermined value or more due to clogging of the particulate filter 4, the control device operates the pump 9 of the injector 5 based on a signal from a sensor that detects the back pressure. As a result, the aqueous catalyst solution is injected from the injector 7 into the exhaust passage 3 upstream of the particulate filter 4. Then, the catalyst components premixed in the catalyst aqueous solution are uniformly deposited on the surface of the particulates collected in the particulate filter 4, and the catalyst components catalytically react with the particulates.

On the other hand, the ceria carried on the alumina layer coating the partition wall 20 of the particulate filter 4 has a property of adsorbing oxygen and donating active oxygen. The ceria causes the catalytic reaction by the catalyst component of the catalyst aqueous solution by injection to start at a lower temperature. The catalytic action of ceria can be obtained by adding ceria to the fuel. However, in that case, the ceria reacts with other compounds at a high temperature, and a sufficient catalytic reaction promoting action cannot be obtained. On the other hand, in the present embodiment, the deterioration of ceria is suppressed, and the ignition temperature of particulates can be significantly reduced. Further, since ceria can supply active oxygen, combustion is promoted even on the surface of the partition wall 20 where the oxygen concentration is low and combustion is not easy. In addition, since the partition wall 20 is coated with the alumina layer, the particulate collection rate is high.

In the combustion of particulates due to the above catalytic reaction, the ignition temperature of particulates will be significantly reduced,
Even in the normal operating range of the diesel engine 1 having a low exhaust gas temperature (for example, 300 ° C. or lower), the particulates can be burned well, and the particulates can be reliably removed.

Further, at the same time when the pump 9 is operated, the throttle valve 10 is substantially half closed. As a result, the amount of intake air is throttled, the air in the combustion chamber becomes insufficient, and the exhaust gas temperature rises, so that combustion of particulates can be promoted and promoted. Further, this can reduce the injection amount of the catalyst aqueous solution,
The operating cost of the engine can be reduced by saving the consumption of expensive catalyst components. Further, by reducing the consumption amount, secondary clogging of the particulate filter 6 due to the catalyst component can be prevented in advance. Further, since the exhaust gas flow velocity decreases due to the intake throttle, the catalyst component adheres to the vicinity of the upstream side of the particulate filter 6 and gradually spreads to the downstream side, so that the catalyst component can be used more effectively.

In the above embodiment, the back pressure of the engine 1 is detected by the sensor and the pump 9 is operated when the back pressure reaches a predetermined value. However, the operating time of the engine 1 reaches a predetermined time. The pump 9 may be activated at times.
Further, it goes without saying that the pump 9 may not be automatically operated by using the sensor or the like, but may be manually operated at any time.

Next, more specific examples will be described.

<Experimental Example 1> A cordierite / honeycomb carrier (100 cell, 12 mil), which is a constituent member of the particulate filter 4, is immersed in alumina slurry and pulled up, and then excess slurry is removed by high-pressure air blow, and at 130 ° C, 1 After drying for 1 hour at 550 ℃
Burned for hours. The alumina slurry used was obtained by mixing and stirring 160 g of γ-alumina, 160 g of boehmite, 500 cc of water and 4 cc of concentrated nitric acid with a homomixer for 10 hours.

After firing, it was immersed in 1.0 l of a 1.0 mol / l aqueous solution of ceric nitrate for 10 minutes and dried at 150 ° C. for 3 hours. Then, every other cell opening at both ends of the honeycomb carrier was plugged with water glass and fired at 550 ° C. for 1 hour.

As a result, a plugged monolith-type particulate filter 4 having 5% by weight of C _e O ₂ supported on the alumina layer was obtained. The amount of the alumina layer adhered was 13 with respect to the honeycomb carrier.
% By weight.

<Experimental Example 2> γ-alumina 235 g, boehmite 240 g, cerium oxide 25
In an alumina slurry consisting of g, water 500cc, concentrated nitric acid 3cc,
The same carrier as in Experimental Example 1 was dipped, excess slurry was removed by high pressure air blowing, dried at 130 ° C for 1 hour, and then calcined at 550 ° C for 1 hour.

Next, water glass was plugged and fired in the same manner as in Experimental Example 1 above.

As a result, a particulate filter 4 having 5% by weight of C _e O ₂ supported on the alumina layer was obtained. The amount of the alumina layer attached was 12.5% by weight with respect to the honeycomb carrier.

<Experimental Example 3> The foam type carrier (mesh 10) was treated in the same manner as in Experimental Example 1 above to obtain a foam type particulate filter in which 5% by weight of C _e O ₂ was supported on the alumina layer. The amount of the alumina layer attached was 12.0% by weight based on the carrier.

Here, the foam-type carrier means a carrier made of cordierite having a large number of sponge-like mesh-shaped pores.

<Experimental Example 4> form type carrier (mesh 10) were treated in the same manner as Experimental Example 2, to obtain a particulate filter of the form type C _e O ₂ is 5 wt% supported on alumina layer. The amount of the alumina layer attached was 12.0% by weight based on the carrier.

<Conventional Example> As the particulate filter, a plugged monolith type without any coating was used. Moreover, cerium nitrate was not added to the injected catalyst liquid.

<Comparative Example> As the particulate filter, a plugged monolith type filter not coated with an alumina layer was used.
However, in this comparative example, cerium nitrate was added to the catalyst liquid of the injector 5.

FIG. 3 shows a comparison of the degree of exhaust gas purification in the above-mentioned 4 examples, the comparative example and the conventional example not using rare earth. However, the test conditions are engine displacement = 2000cc, rotation speed 3000rp
m, P _e = 3.5 kg / cm ² . Further, the composition of the aqueous solution in the tank 6, 4 experimental examples and the conventional example C _u Cl ₂ (1.0g)
+ H ₂ O (10cc) + (CH ₃ ) ₂ CHOH (3cc)
_{C u Cl 2 (1.0g) +} H 2 O (10cc) + (CH 3) 2 CHOH (3cc) + C
_{It is e} (NO ₃ ) ₃ (1cc). As shown in FIG. 1, the regeneration temperature (the temperature of the exhaust gas supplied at the start of particulate combustion) is fitted with temperature sensors 11 and 12 inside the particulate filter 4 and upstream thereof, respectively, and The temperature measured by the temperature sensor 12 when there is a difference in the measured temperature between the sensors 11 and 12 due to the start of combustion is adopted.

As is apparent from FIG. 3, in the change of the conventional example (broken line A) which does not use a rare earth catalyst component such as cerium (broken line A), the change of the comparative example (solid line B) and the change of the experimental example (solid line group C), In each case, the regeneration temperature decreases as the number of regenerations (catalyst solution injection number) increases. However, in the conventional example and the comparative example, the regeneration temperature is 300 ° C. or higher even if the number of regeneration is increased, whereas according to the above experimental example, the regeneration temperature is 300 ° C. or less after the number of regeneration is about 4 to 6 times. That is, according to the above experimental example, the combustion of the patetilate in the normal operating region of the engine is favorably performed with the number of regeneration times of 4 to 6. On the other hand, between the above experimental examples, as is clear from FIG. 3, the reproduction temperature was decreased from the above experimental example 1 to the experimental example 2, the experimental example 3, and the experimental example 4, and in that order, a better effect was obtained. Is obtained.

Next, Table 1 shows the results of measuring the back pressure on the upstream side of the particulate filter 4.

Here, if the rate of increase in back pressure increases, the amount of unburned particulates in the particulate filter 4 is large (there are many cloggings). According to the results in Table 1,
In each experimental example, while the increase is 15% or less,
In the comparative example, it increased by about 20%. The back pressure at the initial stage of operation was relatively high in the experimental example because the alumina layer was coated. Further, in the experimental example, since the particulates burned well, the difference in back pressure between the experimental example and the comparative example disappeared after the seventh regeneration.

[Brief description of drawings]

The drawings show an embodiment of the present invention. Fig. 1 is a schematic overall configuration diagram of an exhaust gas purifying apparatus for an engine, Fig. 2 is a vertical sectional partial view of an example of a particulate filter, and Fig. 3 is obtained experimentally. It is a diagram which shows the relationship between the number of reproduction | regeneration and the reproduction | regeneration temperature which were obtained. 4 ... Particulate filter, 5 ... Injector.

Claims (1)

[Claims] 1. An exhaust gas purifying apparatus for an engine comprising a particulate filter for collecting combustible particles and the like in an exhaust system, wherein an injector for injecting a base metal catalyst liquid is provided upstream of the particulate filter, and the particulate filter is provided. An exhaust gas purifying apparatus for an engine, characterized in that a porous coating layer carrying a rare earth catalyst component is formed thereon.