JPS6081419A - Purifying method of exhaust - Google Patents

Abstract

PURPOSE:To improve purifying efficiency of exhaust, by setting the ratio of a time holding air-fuel ratio in its rich side to that in its lean side to 0.05-10, in the case of an internal-combustion engine equipping a ternary catalyst of palladium system. CONSTITUTION:In the case of an engine equipping a ternary catalyst of palladium system, if air-fuel ratio of an intake mixture is amplitude changed alternately to a lean side 11 and a rich side 12, the air-fuel ratio C being the center of amplitude change is determined by ratio (a) of a holding time (D, E) in the lean side to the time in the rich side and a width W of change. If the ratio (a) of the holding time, that is, a value of E/D is determined to a range of 0.05- 0.8 or 1.5-10, high efficiency of purifying exhaust gas can be maintained over all of NOx, CO, HC.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas purification method for highly efficiently purifying nitrogen oxides, carbon oxides, and hydrogen ash, which are harmful components in exhaust gas discharged from an internal combustion engine.

Various proposals have been made regarding methods for purifying the harmful components in the exhaust gas of internal combustion engines. and.

As one method for purifying the above three components at the same time.

The operation of an internal combustion engine is defined as a period in which the air-fuel ratio (depleted weight ratio to gasoline fed to the internal combustion engine, expressed as A, /F) is equal to the high air-fuel ratio side and the low air-fuel ratio side around the stoichiometric air-fuel ratio. How to vary (see below)

There is a method called the isotemporal variation method.

On the other hand, various types of exhaust purification catalysts have been proposed, among which palladium-based catalysts are considered promising for use as the catalyst in terms of resources and economy.

However, when the above-mentioned isochronous variation method is used for purification using the palladium-based catalyst, a high purification rate cannot be achieved as will be described later.

The present invention aims to overcome the drawbacks of such conventional methods and provide a method capable of purifying the 3W component with high efficiency.

That is, two aspects of the present invention are to eliminate nitrous oxide (hereinafter, NO
x), - a method for purifying carbon oxides (hereinafter referred to as CO) and hydrocarbons (hereinafter referred to as THC) using a catalyst, using a palladium-based catalyst as the catalyst,
In operation of the engine, the air-fuel ratio is varied between a high air-fuel ratio side and a low air-fuel ratio side, and the time ratio of maintaining the air-fuel ratio on the low air-fuel ratio side with respect to the high air-fuel ratio side is 0.05 to 0.8.
Alternatively, the air-fuel ratio is in the range of L5 to 10, and the average air-fuel ratio is near the stoichiometric air-fuel ratio.

@-g, THC can be purified with high efficiency. Furthermore, since the catalyst used in the present invention is a palladium-based catalyst, the purification method is advantageous in terms of resources and economy.

In the present invention, the vaadium-based catalyst is vaadium,
Refers to catalysts containing only palladium or containing palladium as a main component, such as palladium-platinum, palladium-lanthanum, palladium-ceria, and palladium-platinum-ceria.

Next, the operation of the internal combustion engine is as shown by the square wave in Figure 1.
1. This is done by alternating the amplitude of the air-fuel ratio to a high air-fuel ratio side 11 and a low air-fuel ratio side 12.

Therefore, the air-furnace ratio (center air-fuel ratio) C, which is the center of this amplitude fluctuation, is the ratio (a) of the high air-fuel ratio side and the low air-fuel ratio side at the time of holding rttj (D, E), as described later.

It is determined by the fluctuation range (W) and the stoichiometric air-fuel ratio.

The most important thing in the present invention is that the above-mentioned air-fuel ratio fluctuation is not caused to vary by #P time as in the conventional method, but by changing the holding time (D) of the high air-fuel ratio side 11 as shown by the rectangular wave in FIG. The retention time (E) on the low air-fuel ratio side 182 is varied, and the ratio is set within a predetermined range, and the average air-fuel ratio (T) resulting from the variation is near the stoichiometric air-fuel ratio.

In the above, the ratio (E/D) of the low air-fuel ratio side holding time (E) to the high air-fuel ratio side holding time CD).

That is, the retention time ratio (σ) is 0, o5 to o, 8. Or it needs to be in the range of 15 to 10. a is 0.05
If the air-fuel ratio is lower, the holding time on the low air-fuel ratio side will be shorter,
Furthermore, if a is too large than 0.8, the retention time ratios will be close to the same amount, making it impossible to obtain the effect of improving the purification efficiency of the present invention. In addition, when α is smaller than L5, the retention time ratio becomes close to the same amount, and when α is larger than 10, the retention time on the high air-fuel ratio side is shortened, and the effect of improving the purification efficiency of the present invention is reduced. I can't get it.

Next, when the internal combustion engine is operated under the above conditions, the average air-fuel ratio (T) is as shown in FIG.

Center air-fuel ratio (C), one-sided variation width (W) of the air-fuel ratio that changes the center air-fuel ratio (C) to higher and lower air-fuel ratios, holding time on the high air-fuel ratio side (D) and holding time on the low air-fuel ratio side (E) ,
Between the retention time ratio (E/D) = a and the unilateral flux transfer rate (W/C) = β.

The following relational expression holds true.

T=C(C+W)D+(C-W)iia/(D+E)=
(C(1+ρ)D+C(1-β)E]/(D+E)=
C((1+β)D+(1-β)E:)/(D+E) =C((1+β)D+(1-β)Dσ:)/(D+Dα
)=C((1+β)+(l-β)a)/(l+a) In the above, the average air-to-purple ratio (T) is the average air-fuel ratio per unit time when the air-fuel ratio is varied as described above. and
This value is set so that the areas of parts 2 and 3 shown by line 61 in FIG. 1 are equal.

If each of the above conditions is determined by specific numerical values, it is 1. For example, using gasoline with a stoichiometric air-fuel ratio of 144, the center air-fuel ratio is C = 1.
4.0, 9 one-sided fluctuation ta + w = o, q, that is, one-sided fluctuation transport index β - 0,7/ 14. If O=0.05 and the average air-fuel ratio fTl is rubbed by the same t as the stoichiometric air-fuel ratio, the high and low retention time ratio α can be determined by the following equation. That is.

14.4=14.0((1+0.05)+(1-0,
05)×a]/(1+a), it is possible to obtain the pU ratio σ=027. Therefore, if the fluctuation period is 1 hertz, the holding times on the high and low air-fuel ratio sides will be 079 seconds and 0.21 seconds, respectively.

In the above, the values of C and W are determined.

I calculated the value of a necessary for this, as mentioned above.

In the present invention, the above conditions can be arbitrarily determined as long as a is within the above range and the average air-to-minimal ratio (T, ) is close to the theoretical air-to-smoking ratio.

In addition, the average air-to-air ratio (T) should be close to the stoichiometric air-fuel ratio, but the value should be set to f(
It is preferable to employ an air-fuel ratio near the stoichiometric air-fuel ratio that represents α. Such a value usually exists within a range of 10% above and below the stoichiometric air-fuel ratio. The stoichiometric air-fuel ratio is the air-fuel ratio required to completely burn gasoline, and is usually within the range of 14 to 5.

Further, it is desirable that the deflection line (β) of the air-fuel ratio toward the high or low air-fuel ratio side be set at 0.02 to 0.1 1 below the center air-fuel ratio, centered on the center air-fuel ratio. In addition, the center air-fuel ratio can be determined by the relational expression in nfl,
It is preferable to set it in the range of 135 to 15.

Further, it is preferable that the frequency of the air-fuel ratio fluctuation is between C5 and 2 Hz; otherwise, it is difficult to obtain the effects of the present invention.

In addition, the operation control of the inner P engine as described above+, 1. This can be done using a well-known electronic combustion electronic combustion control device or the like.

Example L a-Alumina carrier 1 (palladium (Pd) at 1'
The palladium catalyst supported on the 5y axis is 9ψL7° [
194! Fill the converter with 2, OOOc
o placed in the exhaust path of a gasoline engine, and the purification rate f
f1ll determination was performed.

As shown in FIG. 1, the engine was operated at a rectangular wave air-fuel ratio on the high and low air-fuel ratio sides.

At this time, the average air-fuel ratio (T) was the stoichiometric air-fuel ratio of 144, and the operating frequency was 1 hertz. In addition.

The temperature of the exhaust gas flowing into the converter was approximately 350°C.

Table 1 shows the center air-drink ratio (C) and the lateral runout line (β).

The conditions for the retention time ratio (+zl) and the measurement results of the purification rate are shown.

In addition, as a comparative example, the same table also shows difficult C in the case of the conventional method where the retention time ratio is 10 (C1 to C3).

Table 1 As can be seen from Table 1, according to the present invention.

It can be seen that the purification rate can be significantly improved compared to the conventional method (proximity). In addition, the effect is particularly on NOx.

It can be seen that this method has a remarkable effect on purifying CO.

Example 2 Using the same catalyst as in Example 1, the NOx purification rate was measured in the same manner as in Example 1, with various retention time ratios.

The engine is operated with an average air-fuel ratio (T) of 14.4, and a swing coefficient (β) of air-fuel ratio fluctuations of 0.04 and 0.06.
The test was carried out for each case of 0.08°. Note that the fluctuating frequency was 1 hertz I.

The measurement results are calculated as 2.3 and p for each case where the transfer coefficient (β) is 0.04, 0.06 and 008
I have shown an A4 diagram.

As known from Figures 2 to 4, retention time ratio (a)
is around 10, and below 0.05 or above 10,
It can be seen that the purification rate is low.

Example 3 Pd was added at 0.05 f/ to a-a A/Mina carrier le.
, wonton (La) to 0. A catalyst supporting 1 mole was prepared, and the purification rate was measured in the same manner as in Example 1.

Table 2 shows the center air-fuel ratio (C) and the one-sided flux transfer coefficient (β).

The conditions for the retention time ratio (σ) and the measurement results for the purification rate are shown.

Table 2 According to the invention, as can be seen from Table 2.

It can be seen that the purification efficiency can be considerably improved compared to the conventional method (comparative example).

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the state of air-fuel ratio fluctuation in the exhaust gas purification method of the present invention, and FIGS. 2 to 4 are diagrams showing the relationship between the holding time ratio fffl and the NOx purification rate in Example 2.

Claims (1)

[Claims] (1) A method for purifying nitrogen oxides, -carbon oxides, and hydrocarbons in the exhaust gas by bringing exhaust gas from an internal combustion engine into contact with a catalyst, in which the catalyst uses a palladium-based catalyst, and In this operation, the air-fuel ratio is varied between a high air-fuel ratio side and a low air-fuel ratio side, and the time ratio of maintaining the air-fuel ratio on the low air-fuel ratio side with respect to the high air-fuel ratio side is set in the range of 0.05 to 08 or L5 to 1.0. and an average air-fuel ratio near the stoichiometric air-fuel ratio. +21 Palladium-based catalysts include bawodium, palladium-platinum, bawodium-lanthanum, palladium-ceria,
The exhaust gas purification method according to claim 1, which is vaodium-platinum-ceria. (8) The fluctuation in air fuel efficiency is 0.02 to 0. (4) The frequency of the air-fuel ratio fluctuation is 0.2 to 3 Peltz. Claim (11) Exhaust purification method described in.