JPH11125113A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rationalize the temperature of an exhaust emission control vessel of catalyst or the like by a simple constitution. SOLUTION: In the halfway of an exhaust manifold 18, an NOx catalyst 19 reduction purifying NOx in an exhaust is arranged. In a periphery of an upstream part of the NOx catalyst 19 and its periphery of the exhaust manifold 18, respectively a heat accumulator 24, 25 is provided. In each heat accumulator 24, 25, a fusion latent heat type accumulating material 26 is sealed in a good heat conductive closed case 24a, 25a. In this fusion latent heat type accumulating material 26, use of a fusion latent heat type accumulating material with a phase change generating temperature (fusing temperature) in s purifying temperature range of the NOx catalyst 19 is only required, and more preferably a fusion latent heat type accumulating material with a fusing temperature in almost the center of a purifying temperature range of the NOx catalyst 19 may be used. For instance, in the case that the almost center of the purifying temperature range of the NOx catalyst 19 is about 250 deg.C, as a fusion latent heat type accumulating material 26, NaF-SnF2 of 253 deg.C fusing temperature may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine for purifying exhaust gas discharged from an internal combustion engine.

[0002]

2. Description of the Related Art In order to purify nitrogen oxides (hereinafter referred to as "NOx") in exhaust gas discharged from an internal combustion engine in which combustion is performed at a lean air-fuel ratio such as a diesel engine, a NOx catalyst is provided in an exhaust pipe. There has been proposed a technique for selectively purifying NOx using a hydrocarbon as a reducing agent under an excess of oxygen. However, since this NOx catalyst can purify NOx only in a specific purification temperature range (for example, 200 to 300 ° C.), it is effective to control the temperature of the NOx catalyst to increase the NOx purification rate.

From this viewpoint, for example, Japanese Patent Laid-Open No. Hei 5-144
In Japanese Patent No. 45, a water-cooled heat exchanger is installed upstream of the catalyst, and the flow rate of cooling water flowing through the heat exchanger is adjusted in accordance with the catalyst temperature, thereby reducing the temperature of exhaust gas flowing into the catalyst. I try to adjust it. Also, Japanese Patent Application Laid-Open No.
In Patent Document 3, a heat storage material is provided inside the catalyst, and the catalyst is activated by the heat storage material even when the engine is stopped, so that the catalyst is activated early after the engine is started.

[0004]

However, the former (Japanese Patent Application Laid-Open No. Hei 5-144445) requires a heat exchanger and a mechanism for adjusting the flow rate of the cooling water in accordance with the catalyst temperature. Increases cost. In addition, there is a disadvantage that when the exhaust gas temperature is lowered, the temperature of the catalyst cannot be increased.

On the other hand, in the latter case (JP-A-6-254403), the catalyst can be kept warm by the heat capacity of the heat storage material provided inside the catalyst, so that the catalyst can be prevented from being excessively high or low temperature. Since the temperature of the heat storage material also changes with a change in the exhaust gas temperature, the temperature of the catalyst cannot be kept within a relatively narrow purification temperature range, and the effect of improving the exhaust gas purification rate is small.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and therefore has as its object to maintain the temperature of an exhaust purifier such as a catalyst within a relatively narrow purification temperature range with a simple configuration. It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine that can achieve both improved exhaust gas purifying performance and cost performance.

[0007]

According to a first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine, wherein an exhaust gas purifying efficiency of an exhaust gas purifier is increased within a specific purifying temperature range. The heat storage device is configured using a latent heat type heat storage material that causes a phase change within the purification temperature range, and the exhaust gas purifier is kept warm by the heat storage device. here,
The latent heat type heat storage material is a heat storage material that efficiently stores heat using the latent heat associated with the phase change between the solid phase and the liquid phase. A large amount of heat can be stored or dissipated while maintaining the temperature at a constant temperature. For this reason, even if the exhaust gas temperature changes greatly, the temperature of the exhaust gas purifier can be made close to the melting temperature of the latent heat storage material by heat storage or heat radiation of the latent heat storage material.
Therefore, if the melting temperature of the latent heat type heat storage material is set within a specific purification temperature range where the exhaust gas purification rate is high, the temperature of the exhaust gas purifier can be kept within the purification temperature range, and high purification performance can be obtained. Can be.

In this case, the exhaust gas purifier may be a NOx adsorbent that adsorbs NOx in a specific purification temperature range or a NOx catalyst that reduces and purifies NOx using hydrocarbon as a reducing agent. . These NOx adsorbents and N
Since the purification temperature range of the Ox catalyst is relatively narrow, high purification performance can be obtained by combining it with the latent heat type heat storage material.

It is desirable that the melting temperature of the latent heat type heat storage material is substantially at the center of a specific purification temperature range. For example, the NOx catalyst can purify NOx in a specific relatively narrow purification temperature range, but the NOx purification rate becomes highest approximately in the center of the purification temperature range. Therefore, the highest purification performance can be obtained by setting the melting temperature of the latent heat type heat storage material to approximately the center of the purification temperature range.

[0010] When the latent heat storage material is completely melted and liquefied, the temperature rises due to the specific heat of the liquid. In this temperature range, the above-described advantage (that is, heat storage or heat radiation at a constant temperature) unique to the above-described latent heat storage material cannot be obtained.

Therefore, a regenerator is constructed by combining a plurality of types of latent heat type heat storage materials having different melting temperatures, so that the latent heat type heat storage material having a low melting temperature falls within a specific purification temperature range. A phase change may be caused. With this configuration, after the melting latent heat type heat storage material having a low melting temperature is completely melted, heat can be stored with the latent heat of the melting latent heat type heat storage material having a higher melting temperature, and the melting latent heat having a lower melting temperature can be obtained. Excessive temperature rise of the mold heat storage material, and thus excessive temperature rise of the exhaust gas purifier, can be prevented, so that a reduction in purification performance and deterioration of the heat storage material can be prevented.

The exhaust passage may include a main exhaust passage through which the exhaust gas passes through the regenerator and flows into the exhaust purifier, and a bypass that bypasses the regenerator and flows into the exhaust purifier. It is also possible to adopt a configuration in which a flow path switching unit that branches to the flow path and switches the flow path according to the temperature is provided at a branch portion of both flow paths. For example, if the internal combustion engine is started with the exhaust purifier or regenerator cold, the exhaust heat or heat of the exhaust purifier or regenerator rises, but the temperature rise of the exhaust purifier is delayed by the heat capacity of the regenerator. In this case, the purification performance may be reduced. As a countermeasure, when the temperature is low, the exhaust gas passage is switched to a bypass flow path, and the exhaust gas is caused to flow into the exhaust gas purifier by bypassing the regenerator, so that the temperature of the exhaust gas purifier is raised at an early stage. Reduce emissions. When the temperature is medium, the exhaust gas is caused to flow through the main exhaust passage to raise the temperature of the regenerator and the exhaust gas purifier to an appropriate temperature by the exhaust heat, thereby increasing the exhaust gas purification rate. In addition, when the temperature is high, the flow of the exhaust gas is switched to the bypass flow path, and the exhaust gas is bypassed to the regenerator, thereby preventing the regenerator from deteriorating at a high temperature.

Here, the melting latent heat type heat storage material used in the heat storage device has a characteristic that the volume changes when the phase changes from a solid to a liquid. Focusing on this point, the channel switching means may use the volume change accompanying the phase change of the latent heat type heat storage material as the temperature detection unit or the drive unit. With this configuration, even without a temperature sensor or an actuator, the exhaust passage can be appropriately switched by the phase change of the latent heat type heat storage material.

[0014]

[Embodiment (1)] An embodiment (1) in which the present invention is applied to a diesel engine will be described below with reference to FIGS.

First, the configuration of the entire engine control system will be described with reference to FIG. To each cylinder of the diesel engine 10 which is an internal combustion engine, intake air taken in through an intake pipe 11 is taken in through an intake manifold 13. An electromagnetic valve type fuel injection valve 14 is attached to each cylinder of the diesel engine 10, and fuel stored at a high pressure from a high pressure fuel pump 15 is distributed to each fuel injection valve 14 through a common rail 16.

The fuel injection valve 14 performs a main injection for generating an engine output near the compression top dead center, and performs a pilot injection to inject a small amount of fuel prior to the main injection, and this fuel is ignited. Once in the state,
By performing the main injection, the premixed combustion in the initial stage of the combustion is reduced, and the NOx emission is reduced. Further, the fuel injection valve 1
4 executes post-injection in the latter half of the expansion stroke in which the temperature in the cylinder decreases and fuel does not burn, and a NOx catalyst 19 described later.
Is supplied with a hydrocarbon as a reducing agent.

Exhaust gas exhausted from each cylinder of the diesel engine 10 is exhausted through an exhaust manifold 17 to one collective exhaust pipe 18 (exhaust passage). , NO in exhaust
A NOx catalyst 19 for reducing and purifying x is provided. The NOx catalyst 19 is made of Pt (platinum) / zeolite, and uses a hydrocarbon (fuel such as light oil) supplied by post-injection as a reducing agent to selectively select NO under an excess of oxygen.
x is reduced and purified.

As shown in FIG. 2, this NOx catalyst 19 does not purify NOx below about 200 ° C.
Purifies NOx only in the temperature range from 300 to 300 ° C, about 250 ° C
NOx purification rate is highest at about 300 ° C or higher.
NOx cannot be purified very much. Therefore, the purification temperature range of the NOx catalyst 19 is about 200 to 300 ° C.

An exhaust temperature sensor 20 is provided downstream of the NOx catalyst 19. The output signal of the exhaust gas temperature sensor 20 is input to an engine electronic control circuit (hereinafter referred to as “ECU”) 21. The ECU 21 mainly includes a microcomputer, reads signals output from an accelerator sensor 22, an engine speed sensor 23, and the like, detects an operating state of the diesel engine 10, and performs pilot injection, main injection, and post injection described above. Control of the injection amount and the injection timing.

Heat accumulators 24 and 25 are provided on the outer periphery of the upstream portion of the NOx catalyst 19 and the outer periphery of the NOx catalyst 19 in the collective exhaust pipe 18, respectively. Each regenerator 24, 2
5 is a sealed case 2 made of a heat conductor such as stainless steel.
4a and 25a are formed by enclosing a latent heat type heat storage material 26 therein. As the melting latent heat type heat storage material 26, a melting latent temperature type heat storage material having a temperature at which a phase change occurs (melting temperature) within the purification temperature range of the NOx catalyst 19 may be used. More preferably, the melting temperature of the NOx catalyst 19 is reduced. It is preferable to use a latent heat type heat storage material substantially at the center of the temperature range. In the present embodiment (1), since the approximate center of the purification temperature range of the NOx catalyst 19 is about 250 ° C.,
NaF—SnF ₂ having a melting temperature of 253 ° C. is used.

The regenerator 24 upstream of the NOx catalyst 19
When the exhaust temperature is higher than the melting temperature of the latent heat storage material 26, heat is taken from the exhaust gas to lower the exhaust temperature, and when the exhaust temperature is lower than the melting temperature, heat is applied to the exhaust gas to increase the exhaust temperature. . When the temperature of the NOx catalyst 19 is higher than the melting temperature, the regenerator 25 on the outer periphery of the NOx catalyst 19 removes heat from the NOx catalyst 19 to lower the temperature of the NOx catalyst 19, and the temperature of the NOx catalyst 19 becomes lower than the melting temperature. When the temperature is lower, heat is applied to the NOx catalyst 19 so that the NOx catalyst 19
Raise the temperature of. As a result, the temperature of the NOx catalyst 19 is kept substantially within the purification temperature range (about 200 to 300 ° C.).

Here, the characteristics of the heat storage characteristics of the latent heat type heat storage material 26 will be described with reference to FIG. FIG. 2 shows the relationship between the temperature of the latent heat type heat storage material 26 and the amount of heat storage on the basis of 100 ° C. (heat storage = 0). The melting latent heat type heat storage material 26 is solid from 100 ° C. to about 250 ° C., and the specific heat of the solid is about 2 kJ / kg. Therefore, the heat storage amount increases at a rate of about 2 kJ / kg · ° C. as the temperature rises. , 250
Approximately 300 kJ / kg of heat is stored at ℃. The melting latent heat type heat storage material 26 melts at about 250 ° C. (a phase change from a solid to a liquid), and the temperature remains constant at about 250 ° C. until it becomes completely liquid. This latent heat type heat storage material 2
Since the latent heat of fusion of No. 6 is about 300 kJ / kg, the amount of heat stored when completely liquefied is about 600 kJ / kg. The specific heat of the latent heat type heat storage material 26 after completely liquefied is about 2 k.
J / kg, so the amount of heat stored increases with the temperature
/ Kg ・ ℃, and increase at 400 ℃, about 900kJ
/ Kg of heat. Thus, the NOx catalyst 19
At about 250 ° C., at which the NOx purification rate of
NO.4 and 25 store or dissipate a large amount of heat.
The temperature of the x catalyst 19 can be automatically adjusted so as to maintain a state in which the NOx purification rate is the highest, that is, a temperature substantially at the center of the purification temperature range (about 250 ° C.).

Next, the temperature change of the latent heat storage material 26 when the temperature of the exhaust gas flowing into the heat accumulators 24 and 25 rises and falls will be described with reference to FIG. The heat storage material that does not change phase also raises the temperature of the heat storage material to a high temperature as the inflow gas temperature increases. Therefore, the temperature of the heat accumulators 24 and 25 becomes N
The temperature range of the inflow gas temperature falling within the purification temperature range of the Ox catalyst 19 (about 200 to 300 ° C.) is narrow, and the heat accumulators 24 and 2
5, the temperature of the NOx catalyst 19 easily falls outside the purification temperature range.

On the other hand, when the inflow gas temperature rises from 100 ° C., the temperature of the molten latent heat type heat storage material 26 gradually rises as it is in a solid state. When the temperature reaches about 250, the melting latent heat type heat storage material 26 starts melting.
It is constant at 0 ° C. At this time, the melting latent heat type heat storage material 2
Reference numeral 6 denotes a state in which the solid and the liquid are mixed, and the heat storage amount is increased by increasing the ratio of the liquid as the inflow gas temperature increases. Thereafter, at the point B, the latent heat type heat storage material 26 is melted.
Is completely melted into only liquid, the temperature of the molten latent heat type heat storage material 26 rises with the rise of the temperature of the inflow gas.

Thereafter, when the temperature of the inflow gas starts to decrease,
The temperature of the molten latent heat type heat storage material 26 drops in a liquid state, and C
At this point, when the temperature of the latent heat type heat storage material 26 reaches about 250 ° C., the latent heat type heat storage material 26 begins to solidify (phase change from liquid to solid), and the temperature of the heat storage material becomes approximately 2 °
It is constant at 50 ° C. At this time, the molten latent heat type heat storage material 26 is in a state where the solid and the liquid are mixed, and the heat storage amount is reduced by increasing the ratio of the solid as the inflow gas temperature decreases. At the point D, the latent heat type heat storage material 2
When 6 solidifies completely and becomes only a solid, the temperature of the heat storage material decreases as the temperature of the inflowing gas decreases.

Next, with reference to FIG. 4, a description will be given of a temperature change of the latent heat type heat storage material 26 and a temperature change of the NOx catalyst 19 when the temperature of the inflowing gas rises and falls at a constant speed. In the state where the melting latent heat type heat storage material 26 is only a solid or only a liquid, the temperature of the melting latent heat type heat storage material 26 and the NOx catalyst 19 also increase and decrease in accordance with the rise and fall of the inflow gas temperature. When the heat storage material 26 is in a mixed state of a solid and a liquid, even if the temperature of the inflow gas rises or falls, the melting latent heat type heat storage material 26 only changes the mixing ratio of the solid and the liquid, and the molten latent heat type heat storage material 26 The NOx catalyst 19 is kept at a substantially constant temperature. For this reason, the latent heat type heat storage material
6 and the temperature change of the NOx catalyst 19 are small, and the NOx catalyst 1
The temperature of No. 9 comes to substantially fall within the NOx purification temperature range, and the NOx purification rate often reaches the highest of about 250 ° C. Thereby, high NOx purification performance can be obtained, and the demand for low emission can be satisfied.
In addition, since it is only necessary to provide the heat accumulators 24 and 25, the configuration is simple and the demand for cost reduction can be satisfied.

In this embodiment (1), as the latent heat type heat storage material 26, NaF—SnF ₂ whose melting temperature is substantially at the center of the purification temperature range of the NOx catalyst 19 (melting temperature: 253 ° C.)
However, a latent heat type heat storage material having a melting temperature within the purification temperature range of the NOx catalyst 19 may be used.
H-NaNO ₂ (melting temperature 237 ° C.), NaOH-Na
NO ₃ (melting temperature 257 ° C.), LiNO ₃ (melting temperature 2
64 ° C.), NaOH—NaNO ₂ (melting temperature 237)
° C), SnF ₂ (melting temperature 213 ° C), NaNO ₂ (melting temperature 282 ° C), or the like.

In this embodiment (1), Pt (platinum) / zeolite is used as the NOx catalyst 19.
Cu (copper) / zeolite (purification temperature range: about 350-5
00 ° C.). In this case, LiOH (melting temperature 462 ° C.), NaCl—
MgCl ₂ (melting temperature 450 ° C) or KF-LiF-Mg
F ₂ -NaF (weight composition 55: 27: 6: 12, melting temperature 449 ° C.), KF-LiF-NaF (weight composition 59:
29:12, a melting temperature of 454 ° C.) and the like. In particular, fluoride eutectic salts have the advantage of low corrosiveness and toxicity.

In this embodiment (1), the NOx catalyst 1
Although the heat storage devices 24 and 25 are provided on the outer periphery of the upstream portion of the NOx catalyst 9 and the outer periphery of the NOx catalyst 19, either one of the heat storage devices may be omitted. Heat exchange fins for promoting heat transfer with the gas may be provided. Further, the NOx catalyst 19 may use a metal carrier. In this case, since the metal carrier has better heat conductivity than the ceramic honeycomb carrier, there is an advantage that the heat exchange performance between the regenerator 25, the NOx catalyst 19, and the exhaust gas can be increased. Further, the heat accumulators 24 and 25 may be arranged inside the collective exhaust pipe 18. Further, in the present embodiment (1), hydrocarbons are supplied to the NOx catalyst 19 by post injection, but an injector for spraying hydrocarbons such as fuel may be provided upstream of the NOx catalyst 19.

In this embodiment (1), the NOx catalyst 19 is used as the exhaust gas purifier.
An adsorbent may be used. The adsorption and desorption characteristics of the NOx adsorbent will be described with reference to FIG. Mn as NOx adsorbent
When (manganese) -Zr oxide (zirconia) is used, NOx is not adsorbed at about 150 ° C. or less, and about 150 ° C.
NOx is adsorbed between 350 ° C and 350 ° C, and N
Ox is desorbed. On the other hand, when Pt (platinum) -Ba (barium) is used, NOx is not adsorbed at about 250 ° C. or less, and NOx is adsorbed at about 250 ° C. to 550 ° C.
Above about 550 ° C., NOx is desorbed. Therefore, since the NOx adsorbent also has a temperature range in which NOx can be adsorbed, the NOx adsorption performance can be improved by combining the NOx adsorbent with a latent heat type heat storage material.

When Mn (manganese) -Zr oxide (zirconia) is used, Na is used as a latent heat type heat storage material.
It is preferable to use F-SnF ₂ (melting temperature: 253 ° C.). When Pt (platinum) -Ba (barium) is used, Li ₂ CO ₃ -Na ₂ C is used as a latent heat type heat storage material.
O ₃ -K ₂ CO ₃ (weight composition 43.5: 31.5: 2
5, a melting temperature of 397 ° C.).

Also, an oxidation catalyst for diesel (a catalyst for oxidizing and purifying HC and SOF in exhaust gas with O ₂ in exhaust gas) may be used as the exhaust gas purifier. As shown in FIG.
The oxidation catalyst does not purify HC and SOF at about 200 ° C. or lower, but starts purifying at about 200 ° C. or higher, and the purification rate increases as the temperature increases. On the other hand, the purification characteristics of sulfate (SO ₂ → SO ₃ ⁻ → H ₂ SO ₄ ) indicate that sulfate is not generated at about 350 ° C. or lower, and sulfate starts to be generated at about 350 ° C. or higher, and the generation rate increases as the temperature increases. Will be higher. Sulfate is a part of particulates, which is an emission control substance, so its production must be suppressed. Therefore, if the temperature of the oxidation catalyst is maintained at, for example, 280 ° C. to 400 ° C. by the latent heat type heat storage material, high HC,
It is possible to achieve both a purification rate of SOF and a low production rate of sulfate. In this case, as the latent heat type heat storage material,
For example, KNO ₃ (melting temperature: 337 ° C.) may be used.

[Embodiment (2)] Next, an embodiment (2) of the present invention will be described with reference to FIGS. In this embodiment (2), the latent heat storage material 3 having a different melting temperature is used.
Two types of regenerators 30 and 31 using 2 and 33 are combined. Each of the heat accumulators 30 and 31 is a cylindrical closed case 3 made of a heat conductor such as stainless steel.
0a and 31a are filled with a latent heat type heat storage material 32 and 33, respectively. The heat storage unit 30 on the inner peripheral side is provided with the NOx catalyst 19.
The heat storage device 31 is fitted so as to be in close contact with the outer periphery of the heat storage device 30. Both regenerators 30 and 31 are installed inside the collective exhaust pipe 18. In this case, as the melting latent heat type heat storage material 32 of the heat storage device 30 on the inner peripheral side, a material having a melting temperature within the purification temperature range of the NOx catalyst 19, more preferably substantially at the center of the purification temperature range, is used. The latent heat type heat storage material 33 of the heat storage device 31 is:
A material having a melting temperature higher than the melting latent heat type heat storage material 32 on the inner peripheral side is used. Other configurations are the same as those in the embodiment (1).

Here, the heat storage characteristics of the latent heat storage material 32 on the inner periphery and the latent heat storage material 33 on the outer periphery will be described with reference to FIG. FIG. 8 is based on a temperature of 100 ° C. (heat storage amount = 0)
Shows the relationship between the heat storage amount and the heat storage material temperature. In the present embodiment (2), NaF—SnF ₂ (melting temperature: 253 ° C.) used in the embodiment (1) as the heat storage material 32 on the inner peripheral side.
And KF-LiF-Na as the heat storage material 33 on the outer peripheral side.
F (weight composition 59:29:12, melting temperature 455 ° C.). The heat storage characteristics of the heat storage material 32 on the inner peripheral side are the same as the contents described in FIG. 2 of the embodiment (1).

On the other hand, the heat storage material 33 on the outer peripheral side is solid from 100 ° C. to about 450 ° C., and has a specific heat of about 2.6 kJ /
kg, the amount of heat stored increases with the temperature rise to about 2.6 kJ.
/ Kg · ° C, about 900 kJ at 450 ° C
/ Kg of heat. The heat storage material 33 on the outer peripheral side is about 4
At 50 ° C., melting (solid to liquid phase change) occurs and the temperature remains at about 450 ° C. until it is completely liquid.
Since the latent heat of fusion of the heat storage material 33 on the outer peripheral side is about 400 kJ / kg, the heat storage amount when the heat storage material 33 on the outer peripheral side is completely liquefied is about 1300 kJ / kg. Since the specific heat of the heat storage material 33 on the outer peripheral side after being completely liquefied is about 2.4 kJ / kg, the heat storage amount increases with the temperature rise to about 2.4 kJ / kg ·.
The heat amount is increased at a rate of 500 ° C. and about 1420 kJ / kg is stored at 500 ° C.

Next, referring to FIG. 9, the inflow gas temperature is increased,
A description will be given of a temperature change of the heat storage material 32 on the inner peripheral side when the temperature is lowered. When the temperature of the inflow gas rises from 100 ° C., the temperature of the heat storage materials 32 and 33 on the inner and outer circumferences gradually rises in a solid state. When the temperature reaches 250 ° C., the heat storage material 32 on the inner circumference side starts melting, and the temperature of the heat storage material on the inner circumference side remains constant at about 250 ° C. even if the temperature of the inflow gas rises. Thereafter, when the heat storage material 32 on the inner circumference side is completely melted at the point F and becomes only liquid, the temperature of the heat storage material 32 on the inner circumference side increases with the rise of the inflow gas temperature. After this,
When the temperature of the heat storage material 33 on the outer peripheral side reaches about 450 ° C. at the point I, the heat storage material 33 on the outer peripheral side starts to melt, and even if the temperature of the inflow gas rises, the heat storage materials 32 and 33 on the inner and outer peripheral sides are melted. The temperature is about 45
It remains at 0 ° C. Then, at point H, the heat storage material 33 on the outer peripheral side
The temperature of the heat storage materials 32 and 33 on the inner peripheral side and the outer peripheral side remains at about 450 ° C. until is completely melted into only liquid.

Thereafter, when the temperature of the inflow gas starts to decrease,
Until the heat storage material 33 on the outer circumference side is completely solidified at the point I and becomes only a solid, the temperature of the heat storage materials 32 and 33 on the inner circumference side and the outer circumference side remains at about 450 ° C. even if the temperature of the inflow gas is lowered. is there. When the temperature of the inflow gas further decreases, the temperatures of the heat storage materials 32 and 33 on the inner circumference and the outer circumference also decrease, and the heat storage material 32 on the inner circumference at the point J is reduced by about 2%.
When the temperature reaches 50 ° C., the heat storage material 32 on the inner circumference side starts to solidify (phase change from liquid to solid), and the temperature of the heat storage material on the inner circumference side remains at about 250 ° C. even if the temperature of the inflow gas further decreases. And
At the point K, when the heat storage material 32 on the inner circumference side is completely solidified and becomes only solid, the temperature of the inflow gas temperature decreases and the heat storage material 3 on the inner circumference side decreases.
2 also cools down. From the above, the inflow gas temperature was 6
Even if the temperature is raised to 00 ° C, the heat storage material 32 on the inner peripheral side is 450 ° C.
The heat storage material 32 on the inner peripheral side can be prevented from deteriorating at a high temperature.

In this embodiment (2), two kinds of latent heat type heat storage materials 32 and 33 having different melting temperatures are combined, but three or more kinds of latent heat type heat storage materials may be combined. Also, a plurality of types of latent heat type heat storage materials may be sealed in the same closed case (provided that a plurality of types of latent heat type storage materials do not chemically react with each other).

[Embodiment (3)] Next, an embodiment (3) of the present invention will be described with reference to FIGS. FIG.
0 shows the state of the heat storage device 41 at the time of low temperature, FIG. 11 shows the state of the heat storage device 41 at the time of medium temperature, FIG. 12 shows the state of the heat storage device 41 at the time of high temperature, and FIG. It is sectional drawing shown along a line. In FIGS. 10 and 11,
The diesel engine is located on the left and NOx on the right
An exhaust purifier such as a catalyst is located.

A housing 42 of the heat storage device 41 is provided in the middle of the collective exhaust pipe 18. Inside the housing 42, a honeycomb structure 43 made of a good heat conductor such as a metal is provided.
Are assembled via a plurality of support members 44.
The honeycomb structure 43 has a large number of flow paths penetrating left and right. The leading end of the pipe 18a of the collective exhaust pipe 18 contacts the left end face of the honeycomb structure 43, and the pipe 18a
Openings 45 and 46 through which exhaust gas passes are formed in a. At the center of the honeycomb structure 43, a columnar first
Is disposed so as to protrude into the pipeline 18a, and the outer peripheral portion of the honeycomb structure 43 has a cylindrical second
Is disposed so as to be located outside the pipeline 18a.

The first heat accumulator 47 is constructed by enclosing a melting latent heat type heat storage material 49 in a cylindrical closed case 47a, and has a bellows portion 47b which can expand and contract in the left-right direction at its left end. Is provided. This bellows part 47b
At the left end of the pipe 1 according to the expansion and contraction of the bellows part 47b.
A flow path switching member 51 (flow path switching means) that slides in the left and right direction inside 8a is provided, and the flow path switching member 51 has an opening 52 through which exhaust gas passes.

The second regenerator 48 is constructed by enclosing a melting latent heat type heat storage material 50 in a cylindrical closed case 48a, and has a bellows portion 48b which can expand and contract in the left-right direction at its left end. Is provided. This bellows part 48b
At the left end of the pipe 1 according to the expansion and contraction of the bellows portion 48b.
A channel switching member 53 (channel switching means) that slides in the left-right direction along the outer peripheral surface of 8a is provided, and the channel switching member 53 has an opening 54 through which exhaust gas passes.

The latent heat type heat storage material 49 of the first heat storage unit 47 located on the inner peripheral side has a melting temperature within a purification temperature range, more preferably a material substantially at the center of the purification temperature range, for example, NaF-SnF. ₂ (melting temperature 253 ° C) is used. On the other hand, the melting latent heat type heat storage material 50 of the second heat storage unit 48 located on the outer peripheral side has a melting temperature higher than the melting latent heat type heat storage material 49 on the inner peripheral side, for example, KF-LiF-NaF.
(Weight composition 59:29:12, melting temperature 455 ° C.).

Next, the operation of the heat storage device 41 will be described with reference to FIGS. When the temperatures of the first and second regenerators 47 and 48 are low, such as when the engine is started, the latent heat storage materials 49 and 50 of the two regenerators 47 and 48 are melted.
Are in a solid state, the bellows portions 47b and 48b are both contracted as shown in FIG. 10, and the flow path switching member 53 on the outer peripheral side closes the opening 46 on the right side of the conduit 18a. . In this state, the exhaust gas flowing through the collective exhaust pipe 18 flows through the outer periphery of the second regenerator 48 through the opening 45 on the left side of the pipe 18a as indicated by an arrow in FIG. It becomes a bypass flow path referred to in the claims). At this time, a part of the exhaust gas passes through the opening 52 of the flow path switching member 51 on the inner peripheral side and also flows into the internal flow path of the honeycomb structure 43. However, the internal flow path of the honeycomb structure 43 Due to the high resistance, most of the exhaust gas flows around the outer periphery of the second regenerator 48 and is supplied to the downstream NOx catalyst.
Thereby, the heat of the exhaust gas is transferred to the first and second regenerators 4.
It is supplied to the NOx catalyst without being deprived by 7,48,
The temperature of the NOx catalyst can be raised early.

Thereafter, when the temperature of the exhaust gas rises and the latent heat type heat storage material 49 of the first heat storage unit 47 reaches about 250 ° C., it starts to melt and becomes liquid. This latent heat storage material 49 has a volume of about 2 when the phase changes from a solid to a liquid.
Since it increases by 0%, the bellows portion 47b extends to the left as shown in FIG. 11, and the flow path switching member 51 on the inner peripheral side closes the left opening 45 of the conduit 18a. At this time, since the melting latent heat type heat storage material 50 of the second heat storage unit 48 has a melting temperature or lower, it is in a solid state, and the bellows portion 48
b is maintained in a contracted state as shown in FIG. For this reason, the flow path switching member 53 on the outer peripheral side is
The opening 46 on the right side of FIG.

Therefore, all the exhaust gas flowing through the collective exhaust pipe 18 passes through the opening 52 of the flow path switching member 51 on the inner peripheral side as shown by the arrow in FIG. And is supplied to the downstream NOx catalyst (this flow path becomes the main exhaust flow path in the claims). At this time, the exhaust gas loses heat while passing through the internal flow path of the honeycomb structure 43 and is stored in the first heat storage 47. Thereby, even if the exhaust gas becomes high temperature, the temperature of the exhaust gas is lowered by the heat storage action of the first heat storage device 47,
The temperature of the exhaust gas flowing into the NOx catalyst is approximately 250 ° C., which is approximately at the center of the purification temperature range, and a high NOx purification rate can be obtained.

Thereafter, the exhaust gas temperature further rises,
The melting latent heat type heat storage material 50 of the second heat storage 48 is approximately 450 ° C.
When it becomes, it begins to melt and become liquid. Since the volume of the molten latent heat type heat storage material 50 increases by about 20% when the phase changes from solid to liquid, the bellows portion 48b extends leftward as shown in FIG.
Open the opening 46 on the right side of the conduit 18a. At this time, the latent heat type heat storage material 49 of the first heat storage 47 is used.
Is a liquid state, and since the bellows portion 47b is maintained in an extended state as shown in FIG. 12, the flow path switching member 51 on the inner peripheral side closes the left opening 45 of the conduit 18a. It is still.

Therefore, the exhaust gas flows from the opening 52 of the flow path switching member 51 on the inner peripheral side to the pipe line 1 as shown by the arrow in FIG.
The outer circumference of the second regenerator 48 flows through the path from the opening 46 on the right side of 8a to the opening 54 of the flow path switching member 53 on the outer peripheral side (this flow path also becomes a bypass flow path in the claims). ,
It is supplied to the downstream NOx catalyst. Accordingly, when the exhaust gas has a high temperature, the exhaust gas flows by bypassing the first regenerator 47, so that the first regenerator 47 does not overheat,
High temperature deterioration of the first heat storage 47 can be prevented.

According to the embodiment (3) described above, the volume change accompanying the phase change of the latent heat type heat storage material 49, 50 is used as the temperature detecting unit or the driving unit, so that a special temperature sensor or actuator is not used. However, it is possible to raise the temperature of the NOx catalyst early after the engine is started, maintain the temperature of the exhaust gas flowing into the NOx catalyst at an appropriate temperature, and prevent high-temperature deterioration of the latent heat type heat storage material.

In this embodiment (3), the NOx catalyst (exhaust gas purifier) is disposed downstream of the heat storage device 41, but the honeycomb structure 43 may carry the NOx catalyst. In addition, the present invention is not limited to a diesel engine but can be applied to a gasoline engine.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an entire engine control system showing an embodiment (1) of the present invention.

FIG. 2 is a diagram showing NOx purification characteristics and heat storage characteristics of a latent heat type heat storage material.

FIG. 3 is a diagram showing a change characteristic of a heat storage material temperature with respect to an inflow gas temperature.

FIG. 4 is a diagram showing changes in the heat storage material temperature and the NOx catalyst temperature when the inflow gas temperature is raised and lowered at a constant speed.

FIG. 5 shows a Mn—Zr oxide used as a NOx adsorbent,
The figure which shows the temperature change characteristic of NOx adsorption rate of Pt-Ba

FIG. 6 is a purification characteristic diagram of an oxidation catalyst.

FIG. 7 is a longitudinal sectional view showing an arrangement structure of a heat storage device according to an embodiment (2) of the present invention.

FIG. 8 is a diagram showing heat storage characteristics of a heat storage material on the inner circumference side and a heat storage material on the outer circumference side.

FIG. 9 is a diagram showing a change characteristic of a temperature of a heat storage material on an inner peripheral side with respect to an inflow gas temperature.

FIG. 10 is a longitudinal sectional view showing a state at a low temperature of a heat storage device according to an embodiment (3) of the present invention.

FIG. 11 is a longitudinal sectional view showing a state at a medium temperature of the heat storage device.

FIG. 12 is a longitudinal sectional view showing a state of the heat storage device at a high temperature.

FIG. 13 is a sectional view taken along the line AA in FIG. 12;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Diesel engine (internal combustion engine), 14 ... Fuel injection valve, 18 ... Combined exhaust pipe (exhaust passage), 19 ... NOx catalyst (exhaust gas purifier), 24, 25 ... Heat storage device, 26 ... 30, 31 ... heat storage device, 32, 33 ... melting latent heat type heat storage material, 41 ... heat storage device, 43 ... honeycomb structure,
45, 46 ... opening, 47 ... first regenerator, 47b ... bellows part, 48 ... second regenerator, 48b ... bellows part,
49, 50: a latent heat type heat storage material; 51, a flow path switching member (flow path switching means); 52, an opening; 53, a flow path switching member (flow path switching means);

Claims (6)

[Claims] 1. An exhaust purifier provided in an exhaust passage of an internal combustion engine, and a heat accumulator for keeping the exhaust purifier warm, wherein the heat accumulator has a high exhaust gas purification rate of the exhaust purifier. An exhaust gas purifying apparatus for an internal combustion engine, characterized by using a latent heat type heat storage material that undergoes a phase change within the purifying temperature range. 2. The exhaust gas purifier according to claim 1, wherein the exhaust gas purifier includes a NOx adsorbent that adsorbs nitrogen oxides (hereinafter, referred to as “NOx”) in the exhaust gas in the specific purification temperature range, or a NOx adsorbent using a hydrocarbon as a reducing agent. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus is configured using a NOx catalyst that performs reduction purification. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the melting latent heat type heat storage material has a melting temperature substantially at the center of the specific purification temperature range. 4. The heat storage device is configured by combining a plurality of types of latent heat type heat storage materials having different melting temperatures, and the phase change occurs in the latent heat storage material having a low melting temperature within the specific purification temperature range. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein: 5. The exhaust passage includes a main exhaust passage through which exhaust gas passes through the regenerator and flows into the exhaust purifier, and a bypass passage that bypasses the regenerator and flows into the exhaust purifier. 5. An exhaust purification system for an internal combustion engine according to claim 1, wherein a flow path switching means for switching the flow path in accordance with the temperature is provided at a branch portion of both flow paths. apparatus. 6. The exhaust gas purification of an internal combustion engine according to claim 5, wherein the flow path switching means uses a volume change accompanying a phase change of the latent heat storage material as a temperature detecting unit or a driving unit. apparatus.