JPH05231134A - Engine exhaust emission control system - Google Patents

Abstract

PURPOSE:To obtain an engine exhaust emission control system which can improve the adsorption performance of an adsorbent for adsorbing the uncombusted hydrocarbon which is exhausted by a large quantity on the engine start and permits the long period maintenance of the initial performance. CONSTITUTION:In an adsorbent chamber 3, a moisture adsorbing material is arranged at the edge parts upstream and downstream from an adsorbent for adsorbing the uncombusted hydrocarbon, and at the high temperature which is sufficient for the combustion of the carbon adhering on the adsorbent due to coaking, air is supplied into the adsorbent chamber 3 from an air feeding device 5. Accordingly, the purification rate for the hydrocarbon is improved, and the repetitive use for a long period is permitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust gas purification system, and in particular, an exhaust gas purification catalyst and an adsorbent are provided in an exhaust passage of an automobile engine to temporarily discharge a large amount of unburned hydrocarbons immediately after starting the engine. In an engine exhaust gas purification system that reduces the amount of unburned hydrocarbons released to the atmosphere at the time of engine startup by adsorbing the adsorbent, the adsorption performance of the adsorbent is prevented from deteriorating at the time of engine startup, and The present invention relates to an engine exhaust purification system capable of maintaining its initial performance for a long period of time.

[0002]

2. Description of the Related Art In order to purify exhaust gas of an automobile engine, a catalyst is usually provided in the exhaust passage. However, many catalysts used today do not operate effectively unless the temperature reaches about 300 ° C. or higher. Therefore, when the exhaust gas temperature is low immediately after the engine is started, the exhaust gas cannot be sufficiently purified by the catalyst alone. It will be. That is, immediately after the engine is started, the engine temperature is low and a large amount of unburned hydrocarbons are discharged. Therefore, by interposing an adsorbent in the exhaust passage, the unburned hydrocarbon is once adsorbed by the adsorbent,
A method has been disclosed in which, after the exhaust gas temperature rises and the catalyst reaches its operating temperature, unburned hydrocarbons are desorbed from the adsorbent and purified by the catalyst (JP-A-2-7532, JP-A-2-7532). -135126 publication).

Further, for the purpose of improving the catalyst temperature in a shorter time, an auxiliary oxidation catalyst having a lower reaction start temperature than the three-way catalyst is arranged in the bypass passage downstream of the adsorbent, and
An outside air introduction passage is connected to a bypass passage between the adsorbent and the auxiliary oxidation catalyst, the unburned gas is first oxidized by the auxiliary catalyst, and the temperature of the exhaust gas flowing to the three-way catalyst rises faster due to this oxidation action. Such a structure is also known (Japanese Patent Laid-Open No. 63-68713).

For the purpose of quickly and satisfactorily desorbing the gas from the adsorbent, outside air is used as a cooling source to maintain the temperature of the adsorbent at about 400 ° C. which is the optimum temperature for the desorption. There is also known one which is introduced in Japanese Patent Laid-Open No. 3-194113.

[0005]

The known engine exhaust gas purification system as described above effectively functions as a system suitable for purifying exhaust gas when the engine is started. The present inventors have earnestly studied the adsorbent capacity of the unburned coal-hydrogen of the adsorbent that has been conventionally used to develop a more efficient engine exhaust purification system. As a result, it was found that most of the adsorbents had a significantly reduced amount of adsorbed hydrocarbons when water was already adsorbed, as compared with when they were in a dry state.

Further, it has been found that if the adsorption and desorption of unburned hydrocarbons are repeated only by using the exhaust gas of the engine, the adsorption performance of the adsorbent gradually decreases and the initial performance cannot be maintained. .. This is because most of the adsorbed unburned hydrocarbons are desorbed when the exhaust temperature is high, but some of them remain in the adsorbent as carbon due to coking.
It is also understood that the other cause is that soot (carbon) contained in the exhaust adheres to the adsorbent. Therefore, in order to efficiently adsorb unburned hydrocarbons discharged at a low temperature immediately after engine startup for a long period of time, it is necessary to completely remove the attached carbon by the next adsorption.

[0007] However, none of the conventionally known engine exhaust gas purification systems give special consideration to the above technical problems, and the adsorption efficiency of the adsorbent at engine startup and the length of the adsorbent itself are long. It was found that there is a problem to be improved from the viewpoint of life extension. For example, the one disclosed in Japanese Patent Laid-Open No. 63-68713 aims at improving the efficiency and speeding up of the exhaust gas purification system by introducing the outside air, which is a technical means for the catalyst. However, no special consideration is given to the above technical problems of the adsorbent. In addition, Japanese Patent Laid-Open No. 3-1
The device described in Japanese Patent No. 94113 takes a means for supplying outside air to the adsorbent itself in order to quickly and satisfactorily desorb the unburned coal hydrogen gas from the adsorbent. Outside air is introduced into the adsorbent as a cooling source in order to maintain the optimum temperature of about 400 ° C for desorption, and no special consideration is given to the combustion removal of "carbon" adhering to the adsorbent. ..

Therefore, an object of the present invention is to provide an engine exhaust gas purification system in which moisture is not adsorbed on an adsorbent before adsorbing unburned hydrocarbons, thereby further improving the adsorption efficiency at the time of starting the adsorbent. Especially. Another object of the present invention is to provide an engine exhaust purification system capable of improving the removal rate of carbon adhering to the adsorbent and thereby maintaining the initial performance of the adsorbent.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems and achieve the object, the present invention has a catalyst and an adsorbent disposed in an exhaust passage of an engine, and unburned carbonization discharged when the engine is started. Once adsorbing hydrogen on the adsorbent,
In an engine exhaust gas purification system for reducing the amount of unburned hydrocarbons released from the engine to the atmosphere, a means for suppressing adsorption of moisture to the adsorbent when the engine is stopped is provided. Disclose. In a particularly preferred embodiment, the means for suppressing the adsorption of water is a water absorbent or an adsorbent (hereinafter referred to as an absorbent) located on at least one of the upstream side and the downstream side of the adsorbent, preferably on both sides. is there.

Further, in the engine exhaust gas purification system as described above, the adsorbed unburned hydrocarbons remain in the adsorbent as carbon due to partial coking when the exhaust gas temperature is high, and the soot in the exhaust gas acts as the adsorbent. By attaching,
In order to prevent deterioration of the adsorption performance and deterioration of the adsorbent, external air is supplied to and passed through the adsorbent at high temperature of the adsorbent to burn and remove carbon adhering to the adsorbent to regenerate the adsorbent. Also disclosed is an engine exhaust purification system having an air supply means capable of performing the above. The supply of air is not particularly limited, but it may be performed for a predetermined time when the engine is stopped, preferably immediately after the engine is stopped. External air is heated and supplied to the adsorbent and then passed through the adsorbent after the engine is operated. You may do it. As the temperature raising means, a flow path from the air supply device is provided in contact with or wound around the engine and the exhaust passage, and external air is caused to flow through the flow path to generate air by engine exhaust heat while passing through the flow path. May be performed by raising the temperature. Further, a tank for compressed air may be positioned in the air flow path, the compressed air may be stored in the tank during engine startup, and the compressed air may be supplied after the engine is stopped.

The above inventions can be carried out independently of each other, or can be carried out in combination.

[0012]

As described above, if water is adsorbed on the adsorbent before the adsorption of hydrocarbons, the amount of adsorbed hydrocarbons will be greatly reduced, which must be suppressed. Normally, the water content, when the exhaust pipe is cold when the engine starts,
It reaches the adsorbent as liquid water and reduces the hydrocarbon adsorption capacity. If the vehicle is left unattended after the engine is stopped, moist air diffuses from the exhaust pipe outlet and reaches the adsorbent, which similarly reduces the hydrocarbon adsorption capacity. In the present invention, means for suppressing the adsorption of water to the adsorbent when the engine is stopped,
More specifically, by disposing the water absorbing material before and after the adsorbent, it becomes possible to remove the liquid water present in the exhaust gas at the time of engine startup by the water absorbing material, and when the engine is stopped. It is also possible to prevent the adsorbent from being exposed to an atmosphere containing water.

Further, the carbon remaining in the adsorbent due to coking and the soot in the exhaust adhering to the adsorbent, when the adsorbent is at a high temperature (preferably 400 ° C. or higher), the adsorbent is exposed to external air. By introducing it, it becomes possible to increase the oxygen concentration and efficiently burn carbon. Furthermore, when the adsorbent reaches the high temperature state as described above by exhaust gas and then introduces air into the exhaust passage, desorption and combustion of hydrocarbons simultaneously proceed, and coking is suppressed, and It is possible to accelerate the rise of the catalyst temperature in the wake.

[0014]

The present invention will be described in more detail based on the following examples. FIG. 1 is an overall system diagram showing an embodiment of an engine exhaust gas purification system according to the present invention. The exhaust passage 2 of the engine body 1 is provided with an adsorbent chamber 3 in an upstream position and a catalyst chamber 4 in a downstream position in series. As shown in FIG. 2, the adsorbent chamber 3 has, for example, a charcoal-hydrogen adsorbent 31 containing mordenite powder as a main component in the center thereof, and the charcoal-hydrogen adsorbent 31 has upstream and downstream ends thereof. Is filled with moisture absorbing materials 33, 33 via porous partition walls 32, 32. The catalyst chamber 4 is provided with a three-way catalyst that is usually used in automobiles as an exhaust gas purification catalyst.

On the upstream side of the adsorbent chamber 3 in the exhaust passage 2 and in the vicinity of the engine exhaust chamber, an air flow path 6 is provided from an air supply device 5 composed of, for example, a reciprocating pump or the like via a variable flow control valve 8. Are connected. Further, the adsorbent chamber 3 and the catalyst chamber 4 each have a temperature sensor.
21 and 21 are attached, and an oxygen sensor is provided in a communication passage between the adsorbent chamber 3 and the catalyst chamber 4.
22 is attached. The signals from the respective sensors are taken into the control unit 20, and based on these signals, the control unit 20 gives signals to the air supply device 5 and the variable flow rate control valve 8 to control the supply air amount.

For example, when the temperature of the adsorbent 31 reaches a temperature at which the adsorbed hydrocarbons can be desorbed after the engine is started, the control unit 20 supplies a predetermined flow rate of air from the air supply device 5 into the adsorbent chamber 3. Control is performed to stop the air supply when the desorption end temperature is reached.
As a result, the unburned carbon-hydrogen adsorbed on the adsorbent at a low temperature when the engine is started is desorbed from the adsorbent and flows into the catalyst chamber 4 located further downstream. At that point, the catalyst has reached operating temperature and emission of charcoal hydrogen to the atmosphere is blocked.

Further, when the engine is in a steady operation and the exhaust gas temperature rises, the temperature of the adsorbent becomes higher, and even after the engine is stopped, the high temperature state continues for a while. In this high temperature state, a predetermined amount of air is supplied from the air supply device 5 to the adsorbent according to an instruction from the control unit 20. As a result, the carbon adhering to the adsorbent can be efficiently burned by the soot or coking adhering to the adsorbent, and the adsorbent can be returned to the initial adsorption performance state. The air supply time is appropriately set according to the amount of carbon deposited and the carbon burning rate.

Further, as shown in FIG. 2, since the water absorbing material 33 is arranged at the inflow upstream end side and the downstream end side of the adsorbent 31, the liquid water which tends to be present in the exhaust gas at the time of starting the engine. Is absorbed by the moisture absorber 33 on the upstream side,
While the entry into the adsorbent 31 is prevented, the moisture in the outside air, which tends to enter through the outlet of the exhaust pipe 2 when the engine is stopped, is absorbed by the moisture absorber 33 on the downstream side, and the adsorbent 31 is also absorbed.
Entry into the area is prevented. Therefore, the adsorbent 31 can always be maintained in a dry state, and it is possible to reliably prevent the adsorption performance of the adsorbent from being deteriorated when the engine is started.

FIG. 3 shows a modification of the embodiment shown in FIG. In this structure, a branch pipe 7 is provided downstream of the air flow path 6 from the air supply device 5 for supplying air into the adsorbent chamber 3 arranged in the engine exhaust passage 2. Is different from that of the embodiment shown in FIG. 1 only in that it is connected to an exhaust chamber near the engine to supply air, and the other points are similar to those of the first embodiment. The same members are designated by the same reference numerals and detailed description thereof will be omitted.

In the case of the system of this modified example, there is an effect that the temperature of the supply air is raised and the desorption / regeneration is promoted. FIG. 4 shows a further modification of the embodiment shown in FIG. In this structure, a portion 6a in which an air supply path for supplying air into the adsorbent chamber 3 arranged in the engine exhaust passage 2 is provided in contact with an engine outer wall is provided with an air flow path 6 for supplying air from the air supply device 5. And the portion 6b wound around the passage 2 connected thereto, which is different from that of the embodiment shown in FIG. Similar to that of. The same members are designated by the same reference numerals and detailed description thereof will be omitted.

In this modification, the air is heated and supplied into the adsorbent chamber 3 while passing through the flow paths 6a and 6b. As a result, the temperature of the supply air rises and desorption / regeneration is promoted. FIG. 5 shows another modification of the embodiment shown in FIG. In this case, the engine exhaust passage 2
For supplying air into the adsorbent chamber 3 disposed in the compressed air tank 10, the compressed air tank 10 provided in the air flow path 6 from the air supply device 5, the air flow rate adjusting valve 8 provided downstream of the compressed air tank 10, and It differs from the embodiment shown in FIG. 1 only in that a branch pipe 7 is provided, and the branch pipe 7 is connected to an exhaust chamber 9 near the engine to supply air into the adsorbent chamber 3. The others are the same as those in the first embodiment. The same members are designated by the same reference numerals and detailed description thereof will be omitted.

In this embodiment, air is stored in the compressed air tank 10 in a compressed state by the air supply device 5 during engine operation, and the stored compressed air is supplied into the adsorbent chamber 3 after the engine is stopped. To do. As a result, it is possible to perform the detachment regeneration after the engine is stopped. . FIG. 6 shows still another embodiment of the engine exhaust purification system according to the present invention. In this embodiment, the exhaust passage 2 is provided with a bypass 12 bypassing the adsorbent chamber 3 between the adsorbent chamber 3 and the catalyst chamber 4 from the upstream of the adsorbent chamber 3, and the upstream side branch of the bypass 12 is provided. The structure is different from that of the embodiment of FIG. 1 in that a flow path switching valve 23 is interposed in a part, and the other structure is the same as that of FIG. The same members are designated by the same reference numerals and detailed description thereof will be omitted.

The bypass 12 is the upstream branch passage portion 1
1, a bypass main body portion 12a, and a downstream side branch passage portion 13, and a passage switching valve 23 is provided at a branch portion between the exhaust passage 2 and the upstream side branch passage portion 11, and an exhaust gas is generated by a signal from the control unit 20. The flow path between the passage 2 side and the upstream side branch passage portion 11 can be partially or completely switched.

In this embodiment, the passage switching valve 23 is set to the position for closing the bypass 12a when the engine is started. When the adsorbent 31 reaches the desorption temperature, the passage switching valve 23 is switched and the exhaust gas is bypassed by the bypass 1.
It flows to the 2 side. The air flow path 6 is connected to the upstream side of the adsorbent chamber 3 as in the other embodiments, and the air is supplied into the adsorbent chamber 3 even while exhaust gas is flowing on the bypass side. You can

When the exhaust temperature rises, the switching valve 23
Open a little to allow a small amount of hot exhaust to adsorbent chamber 3
At the same time, the external air is introduced through the air flow path 6 by the air supply device 5 to perform desorption and regeneration of the adsorbent. When the desorption of hydrocarbons is completed, the switching valve 23
By adjusting again so that most of the exhaust gas passes through the inside of the adsorbent chamber 3, it becomes possible to raise the temperature of the adsorbent to a temperature at which the adhering carbon burns.

Immediately before the engine is stopped, the switching valve 23 is controlled so that the exhaust gas flows through the bypass 12 side, and when the temperature of the adsorbent is high after the engine is stopped, the air is supplied from the air supply device 5 by the instruction of the control unit 20. By supplying a predetermined amount of carbon, it becomes possible to completely burn the carbon adhering to the adsorbent. FIG. 7 shows another embodiment of the switching valve mechanism in the embodiment shown in FIG. In this example, the switching valve 23a is made of a material that is deformed by a change in temperature, and the valve seat 2
It is deformed so as to block the bypass entrance together with 4. FIG. 8 is a view of A-A of FIG.
Shows that it is blocked. When the temperature of the adsorbent 31 reaches the desorption temperature of hydrocarbons over time, the switching valve 23a is thermally deformed to open the bypass inlet and the valve seat 24a.
At the same time, close the main passage side. As a result, the flow of exhaust changes from the bypass 12a side to the adsorbent chamfer 3 side.

The switching valve 23a is used when the engine temperature is high.
May not be configured to completely close the adsorbent inlet, but may be configured to provide a predetermined gap. As a result, a small amount of high temperature exhaust gas can flow to the adsorbent chamber 3 side, and the temperature rise of the adsorbent can be promoted. It will be readily understood that this embodiment could operate similarly to that shown in FIG.

FIG. 9 shows still another embodiment of the switching valve mechanism in the embodiment shown in FIG. In this example, the passage switching valve 23 provided in the branch portion between the exhaust passage 2 and the upstream branch passage portion 11 is composed of a valve 27 movable by an electromagnet. The movable valve 27, which is set to a position where the bypass 12 side is closed at the time of start-up, is moved by energizing the electromagnet 26 by a signal from the control unit 20 when the adsorbent becomes at the desorption temperature or higher, and moves. So that the exhaust gas flows to the bypass 12 side. Also in this case, as in the case shown in FIG.
It will be easily understood that the switching valve 27 may be configured not to completely close the adsorbent inlet side but to have a predetermined gap. The specific configuration of this solenoid valve is arbitrary, and many other modified examples can exist.

[0029] In the above, the purification is equipped with both a means for suppressing the adsorption of moisture to the adsorbent and an air supply means for regenerating the adsorbent by burning and removing the carbon adhering to the adsorbent. Although the system has been described, it is clear that it is not essential in the present invention that both means are always present in the same system, and a system including only one of them can be implemented. Thus, it will be readily understood that it is encompassed by the present invention. As a specific embodiment, for example, an exhaust purification system having only a configuration in which an adsorbent is located in a bypass exhaust passage provided in parallel to the upstream side of the catalyst, a circulation bypass passage from the downstream side of the catalyst Even in the case of an exhaust gas purification system having only a structure in which the adsorbent is located, the present invention is implemented there, that is, the water absorbent is located upstream and downstream of the adsorbent used therein. It is also obvious that the objectives of the present invention can be fully achieved.

Further, in any of the purification systems having one means or both means, the water absorbent cannot be located integrally with the adsorbent in the adsorbent chamber as described in the above embodiment. It is not always necessary, but in the pipe system where the adsorbent, through which the exhaust gas from the engine flows down, is located in the chamber on the upstream side and the downstream side of the adsorbent that is different from or separate from the adsorbent chamber. It will also be readily appreciated that the objectives can be achieved even when the is positioned.

Furthermore, it is not always essential to position the water absorbent on both the upstream side and the downstream side of the adsorbent, and it may be positioned on only one side in relation to the overall structure of the device. It is a good thing.

[0032]

COMPARATIVE EXAMPLE For each of the embodiments of the engine exhaust gas purification system according to the present invention described above, a cold start test was conducted by an engine bench in order to compare the exhaust gas purification performance. That is, using an engine left for at least 12 hours after stopping, the engine was started, idled, accelerated, and run at 60 km / h, and the unburned hydrocarbons emitted were analyzed. The exhaust purification performance of the engine exhaust purification system was evaluated by comparing the total unburned hydrocarbons emitted during the test.

FIG. 10 summarizes the experimental results of the repeated test. The vertical axis of the figure is the hydrocarbon emission amount when the first hydrocarbon emission amount is 1. For comparison, the hydrocarbon purification performance in the comparative example system shown in the figure is also shown. In this case, no moisture absorbent is used and no air supply device is connected. In the comparative example, the purification performance gradually decreases, but according to this method, the performance degradation of the adsorbent can be suppressed, so that the hydrocarbon purification performance is less degraded.

The curve a shows the test results in the form shown in FIG. 1, and the curve b shows the results in FIGS.
, The curve c has the form shown in FIG.
And curve d represent the types shown in FIGS. 6, 7, and 8, respectively.

[0035]

According to the engine exhaust gas purification system of the present invention, the conventional purification system is equipped with a simple device to prevent the adsorption performance from being deteriorated due to the adsorption of moisture by the adsorbent and to be eliminated so far. Unnecessary carbon deposits can be removed, the regeneration of the adsorbent can be further improved, and the initial adsorption performance can be maintained, so that the automobile exhaust purification performance is further improved.

[Brief description of drawings]

FIG. 1 is an overall system diagram showing an embodiment of an engine exhaust gas purification system according to the present invention.

FIG. 2 is a cross-sectional view showing an adsorbent chamber according to the present invention.

FIG. 3 is a diagram showing a modification of the embodiment shown in FIG.

FIG. 4 is a diagram showing another modification of the embodiment shown in FIG.

FIG. 5 is a diagram showing still another modification of the embodiment shown in FIG.

FIG. 6 is an overall system diagram showing another embodiment of the engine exhaust gas purification system according to the present invention.

FIG. 7 is an enlarged partial sectional view showing another embodiment of the switching valve in the embodiment shown in FIG.

8 is a cross-sectional view taken along the line AA in FIG.

9 is an enlarged partial sectional view showing still another embodiment of the switching valve in the embodiment shown in FIG.

FIG. 10 is a diagram showing purification characteristics of some embodiments of the engine exhaust purification system according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Exhaust passage, 3 ... Adsorbent, 4 ... Exhaust purification catalyst, 5 ... Air supply device, 6 ... Air supply passage, 7 ...
Air branch pipe, 8 ... Air flow control valve, 9 ... Engine exhaust chamber, 10 ... Compressed air tank, 11 ... Upstream branch passage, 1
2 ... Bypass, 13 ... Downstream branch passage, 20 ... Control unit, 21 ... Temperature sensor-, 22 ... Oxygen sensor-, 23
... Switching valve, 24 ... Stopper-, 25 ... Exhaust, 26 ...
Electromagnet, 27 ... Movable valve, 31 ... Hydrocarbon adsorbent, 32 ...
Partition wall, 33 ... Water absorbing material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Kuroda 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitate Manufacturing Co., Ltd.Hitachi Laboratory Ltd. Inside Hitachi Research Laboratory (72) Hiroshi Miyadera 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Co., Ltd.Hitachi Research Center Inside (72) Inventor Takeshi Atago 2520 Takaba, Katsuta City, Ibaraki Hitachi, Ltd. Automotive Equipment Business Department

Claims (13)

[Claims] 1. A catalyst and an adsorbent are disposed in an exhaust passage of an engine, and unburned hydrocarbons discharged at the time of starting the engine are once adsorbed by the adsorbent and then released from the engine to the atmosphere. An engine exhaust purification system for reducing the amount of hydrocarbons, comprising means for suppressing adsorption of moisture to the adsorbent. 2. The means for suppressing the adsorption of water is a water absorbent or an adsorbent positioned on at least one of the upstream side and the downstream side of the adsorbent,
The engine exhaust purification system according to claim 1. 3. A catalyst and an adsorbent are arranged in an exhaust passage of an engine, and unburned hydrocarbons discharged at the time of starting the engine are once adsorbed by the adsorbent and released from the engine to the atmosphere. In an engine exhaust purification system that reduces the amount of hydrocarbons, an air supply that can regenerate the adsorbent by supplying and passing external air to the adsorbent at the time of high temperature of the adsorbent to burn and remove carbon adhering to the adsorbent. An engine exhaust gas purification system, characterized in that it has means. 4. Further comprising means for suppressing adsorption of moisture to the adsorbent when the engine is stopped.
The engine exhaust purification system according to claim 3. 5. The engine exhaust gas purification system according to claim 3, wherein the air supply means is operated for a predetermined time immediately after the engine is stopped. 6. The engine exhaust purification according to claim 3, wherein the air supply unit has an air supply device and an air flow path capable of supplying external air to an exhaust chamber near the engine. system. 7. The engine exhaust gas purification system according to claim 6, wherein the air flow path further includes a branch pipe connecting the air supply device to each exhaust chamber near the engine. 8. The engine exhaust gas purification system according to claim 3, wherein the temperature of the external air is raised and then supplied to and passed through the adsorbent. 9. A flow path from the air supply device is provided in the vicinity of the engine and in contact with or around the exhaust passage, or external air is flown through the flow path to generate air by engine exhaust heat while passing through the flow path. The engine exhaust purification system according to claim 8, wherein the temperature of the external air is raised by raising the temperature. 10. The engine according to claim 5, wherein a tank for compressed air is located in the air flow passage, and the compressed air is stored in the tank during engine startup. Exhaust purification system. 11. A bypass, which bypasses the adsorbent, is provided between the upstream position of the adsorbent and the catalyst and the adsorbent, and an exhaust flow path switching section is arranged at a bypass connection section upstream of the adsorbent. 4. When desorbing unburned hydrocarbons from the adsorbent, the exhaust gas is switched to flow to the bypass, while air is supplied to and passed through the adsorbent for desorption regeneration. Engine exhaust purification system. 12. The engine exhaust gas purification system according to claim 11, wherein the exhaust gas switching portion is made of a material that is displaced and deformed by a change in temperature. 13. The engine exhaust gas purification system according to claim 11, wherein the exhaust gas switching unit includes an electromagnet and a partition member, and the partition member is operated by the electromagnet.