JPH05141229A - Method for purifying exhaust gas of automobile engine - Google Patents

Abstract

(57) [Summary] [Purpose] To purify exhaust gas with a high HC concentration, which is discharged in the low-temperature starting region from the start of the automobile engine to the warm-up operation. [Structure] Catalytic converter 2 in exhaust passage from engine 1
In the exhaust gas purifying apparatus for an automobile engine in which is installed oxygen or oxygen-enriched air produced by the oxygen-enriched air producing apparatus 3 via the supply amount control valve 6 on the exhaust gas introduction side of the catalytic converter 2. Supply. [Effect] The combustion reaction of HC is promoted by supplying a shortage of oxygen to the exhaust gas. By using oxygen or oxygen-enriched air as an oxygen source, the space velocity at the exhaust gas introduction portion of the catalyst is suppressed, and HC combustion is started at a lower temperature to promote the combustion reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to unburned components of fuel discharged from automobile engines and HC and C which are combustion products of fuel.
Exhaust gas purification method including O and NOx, particularly purification of exhaust gas with high concentration of unburned fuel and HC and CO, which are combustion products of fuel, discharged in a low temperature starting region from engine start to warm-up operation Regarding the method.

[0002]

Exhaust gas from an automobile engine is composed of unburned fuel, HC, CO, and NO which are combustion products of fuel.
x, etc. are included. When released into the atmosphere, they cause the generation of photochemical smog and acid rain, which have a great adverse effect on humans and the ecosystem. Beginning in the 1970s, exhaust gas regulations were set, and methods for removing harmful substances in exhaust gas were eagerly studied by automobile manufacturers to develop a noble metal three-way catalyst that simultaneously treats HC, CO, and NOx. It has been done.

However, in recent years, environmental problems on a global scale such as ozone layer depletion, global warming, and acid rain have been closed up, and automobile exhaust gas regulation values have been further strengthened.
Among the harmful substances of HC, CO, and NOx, especially HC
As for the above, since it greatly contributes to the destruction of the ozone layer, the regulation becomes stricter than that of other substances.

Approximately 70% of the total amount of HC released from the automobile into the atmosphere is exhausted within about 2 minutes after the start of engine activation of the automobile. This is because the exhaust gas temperature is low and the three-way catalyst does not work when the engine is started up and does not reach steady operation.

Therefore, in addition to the improvement of the engine combustor and the combustion state, two exhaust gas purifying catalysts, a low temperature catalyst at the time of starting and a high temperature catalyst at the time of steady operation, are installed in parallel (Japanese Patent Laid-Open No. 61). -200316), a bypass passage is provided in the exhaust pipe from the engine outlet to the exhaust gas purifying catalyst, and an adsorbent for adsorbing the exhaust gas at the time of start is installed therein (JP-A-63-63).
-68713), the secondary air is supplied to the exhaust gas introduction part of the three-way catalyst during the period from the engine start to the warmed state to cause the combustion reaction on the three-way catalyst (JP-A-1-227815).
Etc. methods have been proposed.

[0006]

SUMMARY OF THE INVENTION In order to meet the strict requirement for reduction of HC emissions, the present invention aims to meet the strict requirements for reduction of HC emissions, that is, unburned components of fuel and HC, CO which are combustion products of fuel, And an NOx-containing exhaust gas purification method, in particular, unburned components of fuel discharged in a low temperature starting region from engine start to warm-up operation, and H which is a combustion product of fuel
In an exhaust gas purification method having a high C and CO concentration, a technique for efficiently burning and purifying these exhaust gases on an exhaust gas purification catalyst is provided.

[0007]

The above-mentioned problems are solved by supplying oxygen or oxygen-enriched air to the exhaust gas in an oxygen-deficient state at engine startup at the exhaust gas introduction side of the exhaust gas purification catalyst. , CO, etc. can be achieved by promoting the combustion reaction of unburned components. The method for purifying exhaust gas of an automobile engine is to use oxygen or oxygen on the exhaust gas introduction side of the catalyst for purifying exhaust gas in an exhaust gas purifying apparatus for automobile engines in which a catalyst for purifying exhaust gas is installed in the exhaust passage of the automobile engine. It is characterized in that the combustion reaction of unburned components such as HC and CO is promoted in the catalyst by supplying the enriched air.

The oxygen or oxygen-enriched air supplied is
Atmosphere, that is, a film method of passing air through an oxygen permeable membrane, atmosphere,
That is, an adsorption method (P to obtain an oxygen-rich gas by sending air to an adsorption tower filled with molecular sieves to adsorb nitrogen) (P
SA method) and an electrolysis method of electrolyzing water into oxygen and hydrogen. The oxygen permeable membrane used in the membrane method includes an inorganic membrane and an organic membrane. The organic film is advantageous in use at low temperatures because the operating temperature is room temperature. On the other hand, an inorganic membrane such as a solid electrolyte needs to be operated at a high temperature of 300 to 1000 ° C., but it can be used by utilizing the waste heat of the engine, exhaust gas and catalyst during steady running. Adsorbent molecular sieves used in the adsorption method of
Zeolites are commonly used. The hydrogen produced simultaneously with oxygen in the electrolysis method can be used as an auxiliary fuel added for promoting combustion as described later. In either method, if the production capacity of oxygen or oxygen-enriched air per unit time is inferior to the supply rate, a tank is installed and oxygen or oxygen-enriched air is produced during steady running without supply. Just keep it.

The supply amount of oxygen or oxygen-enriched air is adjusted by detecting the oxygen concentration in the exhaust gas at the engine outlet and the air-fuel ratio in the engine combustor with a sensor. Further, by detecting the catalyst temperature of the exhaust gas purifying catalyst or the catalyst inlet gas temperature, the supply timing of oxygen or oxygen-enriched air is set in the low temperature starting region from engine start with a large amount of HC emissions to warm-up operation. Adjust.

A technique for supplying oxygen or oxygen-enriched air on the exhaust gas introduction side of the exhaust gas purifying catalyst to efficiently burn and purify exhaust gas such as HC on the exhaust gas purifying catalyst is
It works effectively in a conventional exhaust gas purification device that uses a three-way catalyst. Furthermore, this technology can be used more effectively in a dual converter system in which a low-temperature catalyst for burning unburned components such as HC and CO is installed before the conventional three-way catalyst. That is, a combustion catalyst for unburned components such as HC and CO is installed immediately after the engine outlet of the exhaust passage of an automobile engine, a three-way catalyst is installed behind this, and oxygen or oxygen-enriched air is introduced on the exhaust gas introduction side of the catalyst. To supply. By installing the low temperature combustion catalyst, the HC combustion reaction starts at a temperature lower than that of the three-way catalyst alone, the temperature of the exhaust gas introduced into the three-way catalyst rises, and the purification capacity improves.

A system developed from this, that is, a system in which oxygen or oxygen-enriched air is simultaneously added with the auxiliary fuel for combustion at the supply position, is a catalyst and three The temperature rise of the original catalyst is accelerated, and the catalyst can be rapidly activated. As the auxiliary fuel, gasoline, methanol, propane for an automobile engine, or hydrogen produced by electrolysis is used.

In this system, in order to further shorten the combustion start time of the auxiliary fuel and accelerate the activation of the catalyst, an ignition source is installed at a position for supplying oxygen or oxygen-enriched air and auxiliary fuel for combustion. After the combustion by the ignition source is started, the combustion is continued by the heat of the combustion reaction of the catalyst.

[0013]

The operation of the present invention will be described below.

HC, CO, and NOx in exhaust gas
Purifies by performing the following reactions on a three-way catalyst for purifying automobile exhaust gas.

CmHn + (m + 0.5n) O ₂ → mCO ₂ + 0.5nH ₂ O (1) CO + 0.5O ₂ → CO ₂ … (2) NO + CO → CO ₂ + 0.5N ₂ … (3) HC and CO The oxidation reaction is carried out as in the above formulas (1) and (2). Under oxygen-deficient exhaust gas conditions, the oxidation reaction of all HC and CO in the exhaust gas does not proceed, so excess HC
And CO act as a reducing agent, and the NO purification reaction proceeds as shown in equation (3). When the engine is started, the amount of NO generated is small due to the relationship between the air-fuel ratio and the temperature inside the combustor. Therefore, a large amount of HC is generated at the time of start-up as compared with the time of steady running. This HC
In order to remove the above, it is sufficient to supply the lacking oxygen into the exhaust gas and burn all the HC and CO on the catalyst. The oxygen supplied is generally added to the exhaust gas as secondary air. However, when air is supplied as the oxygen source, the supply amount becomes 10% or more of the exhaust gas amount. Therefore, the amount of treatment per unit time on the exhaust gas purifying catalyst, that is, the space velocity (SV) increases, which has a negative effect on the catalyst purifying performance. On the other hand, in the system for directly supplying oxygen or oxygen-enriched air into the exhaust gas as in the present invention, since the supply amount is reduced from one half to one fifth in the case of air, the space velocity (SV ) Can be supplied without causing a large fluctuation in Furthermore, in a dual converter system in which a low-temperature catalyst for burning unburned components such as HC and CO is installed before the conventional three-way catalyst, the space velocity (SV) of the exhaust gas introduction part of the low-temperature catalyst is increased. By suppressing the increase, it acts to start HC combustion at a lower temperature and promote the combustion reaction.

When oxygen or oxygen-enriched air is supplied to the exhaust gas and an auxiliary fuel is added at the same time, the temperature of the low temperature catalyst rapidly rises due to the combustion heat of the auxiliary fuel on the low temperature catalyst, and the combustion of HC and The purification performance is improved, and at the same time, the latter three-way catalyst is heated to act rapidly.
When an ignition source is installed in this, the auxiliary fuel is ignited by the ignition source, and the combustion of the auxiliary fuel after ignition is continued by its own heat of combustion on the low temperature catalyst.

[0017]

The present invention will be described in detail below with reference to specific examples.

<Embodiment 1> FIG. 1 is an embodiment of the present invention and is a flow chart of an exhaust gas purifying apparatus of a method for supplying oxygen or oxygen-enriched air on the exhaust gas introduction side of an exhaust gas purifying catalyst.

In an exhaust gas purifying apparatus for an automobile engine in which a catalytic converter 2 is installed in an exhaust passage from an engine 1, oxygen produced by an oxygen-enriched air producing apparatus 3 or oxygen-enriched air is produced by the catalytic converter 2. It is supplied through the supply amount control valve 6 on the exhaust gas introduction side of. By supplying oxygen or oxygen-enriched air to the exhaust gas of the engine 1 that is in an oxygen-deficient state, as shown in equations (1) and (2),
The combustion reaction (oxidation reaction) of unburned components such as C and CO is promoted, and the exhaust gas purification performance is improved.

Oxygen or oxygen-enriched air is produced by the oxygen-enriched air producing device 3 when the engine is started up or when the engine is running at a constant speed. The shortage of is supplemented from the tank 4. Manufacturing with the oxygen-enriched air manufacturing device 3 is performed with
Is controlled by the control device 5 based on the remaining amount and the supply amount described later.

Oxygen or oxygen-enriched air in the oxygen-enriched air producing apparatus 3 and the tank 4 is supplied to the tank outlet cock 41,
The flow path is adjusted by the flow path switching valve 42 and supplied through the supply amount adjustment valve 6. The supply through the supply amount control valve 6 is controlled by the control device 5. The engine speed, accelerator, cooling water, air-fuel ratio sensor 51, and engine exhaust gas air-fuel ratio sensor (oxygen sensor) 52 determine the amount of oxygen supplied. The catalyst is heated up to a set temperature and reaches a steady state, which is controlled by a catalyst temperature sensor 53 installed in the catalytic converter 2.

<Embodiment 2> FIG. 2 is an embodiment of a method for producing oxygen or oxygen-enriched air according to the present invention, which is a schematic diagram of an oxygen-enriched air producing apparatus by a membrane method.

The air introduced into the oxygen-enriched air producing apparatus 3 through the air inlet 37 is dust-removed by the filter 31 and then introduced into the membrane module 32. Membrane module 32
Oxygen-enriched air comes out to the low pressure side by decompressing the outlet side of the with the vacuum pump 33. This is the vacuum pump 3
It is introduced into the next dehumidifier 34 by utilizing the pressurizing side of No. 3, and after dehumidification, is introduced from the oxygen-enriched air outlet 35 into the tank 4 or the supply amount control valve 6. The oxygen-depleted air remaining on the high-pressure side of the membrane module 32 is exhausted from the oxygen-depleted air outlet 36. An organic membrane is generally used as the oxygen permeable membrane of the membrane module 32. In this case, the membrane module 32 can operate at room temperature. When using an inorganic membrane for the oxygen permeable membrane,
The membrane module 32 is heated by waste heat such as exhaust gas or a heater.

<Third Embodiment> FIG. 3 shows a dual converter system in which a catalytic converter 7 which is a low temperature catalyst and a catalytic converter 2 which is a three-way catalyst are installed in an exhaust passage from an engine 1. This is a device flow in which oxygen or oxygen-enriched air and auxiliary fuel for combustion are supplied on the side and an ignition source is installed. By installing the catalytic converter 7 which is a low temperature catalyst in front of the catalytic converter 2 of the three-way catalyst, the combustion reaction of HC starts at a lower temperature than in the first embodiment, and the catalytic converter 2 is heated by the combustion heat of the catalytic converter 7. Activates faster. By supplying the auxiliary fuel for combustion by the auxiliary fuel supply amount adjusting valve 8 to the position of the supply amount adjusting valve 6, the combustion heat of the catalytic converter 7 can be increased and the activation of the catalyst can be further accelerated. In order to easily ignite and burn the auxiliary fuel by the catalyst, the ignition source 9 ignites and thereafter the catalyst continues to burn the auxiliary fuel. The supply amount and the supply timing of oxygen or oxygen-enriched air by the supply amount control valve 6 are controlled by the controller 5 as in the first embodiment. The supply amount and supply timing of the auxiliary fuel and the operation of the ignition source 9 are also controlled by the control device 5.

[0025]

According to the present invention, the unburned components of the fuel discharged in the low temperature starting region from the engine start of the automobile to the warm-up operation and the exhaust gas having a high concentration of HC and CO, which are combustion products of the fuel, can be efficiently used. Can be purified to.

[Brief description of drawings]

FIG. 1 is a system diagram of an exhaust gas purification device showing an embodiment of the present invention.

FIG. 2 is a block diagram of an oxygen-enriched air production apparatus by a membrane method.

FIG. 3 is a system diagram of an exhaust gas purifying apparatus according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine, 3 ... Oxygen-enriched air manufacturing device, 4 ... Tank, 5 ... Control device, 6 ... Supply amount control valve, 35 ... Oxygen-enriched air intake port, 41 ... Tank outlet cock, 42 ... Flow path switching valve , 51 ... rpm, accelerator, cooling water, air-fuel ratio sensor,
52 ... Air-fuel ratio sensor (oxygen sensor), 53 ... Catalyst temperature sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Yamashita 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitate Manufacturing Co., Ltd., Hitachi Research Institute (72) Hiroshi Miyadera 4026 Kuji Town, Hitachi City, Hitachi City, Ibaraki Prefecture Nitate Factory Hitachi Research Laboratory

Claims (8)

[Claims] 1. An exhaust gas purifying apparatus for an automobile engine, wherein an exhaust gas purifying catalyst is installed in an exhaust passage of an automobile engine, wherein oxygen or oxygen-enriched air is introduced at an exhaust gas introducing side of the exhaust gas purifying catalyst. Is supplied to accelerate the combustion reaction of unburned components in the catalyst. 2. A method for purifying exhaust gas of an automobile engine according to claim 1, wherein oxygen or oxygen-enriched air is manufactured and supplied by passing air through an oxygen permeable membrane. 3. A method for purifying exhaust gas of an automobile engine according to claim 1, wherein oxygen or oxygen-enriched air is produced and supplied by an adsorption method using a molecular sieve. 4. A method for purifying exhaust gas of an automobile engine according to claim 1, wherein oxygen or oxygen-enriched air is produced and supplied from oxygen generated by electrolyzing water. 5. The exhaust gas according to claim 1, wherein the amount of oxygen or oxygen-enriched air supplied is adjusted by detecting the oxygen concentration of the exhaust gas at the outlet of the automobile engine and the air-fuel ratio in the engine combustor. An exhaust gas purification method for an automobile engine, which adjusts the supply timing of oxygen or oxygen-enriched air in a low temperature starting region from engine start to warm-up operation by detecting the catalyst temperature of a gas purifying catalyst or the catalyst inlet gas temperature. 6. The combustion catalyst according to claim 1, wherein a combustion catalyst for an unburned portion is installed immediately after an engine outlet of an exhaust passage of the automobile engine, and a three-way catalyst is installed behind the combustion catalyst. A method for purifying exhaust gas of an automobile engine, which supplies oxygen or oxygen-enriched air at the exhaust gas introduction side. 7. A method for purifying exhaust gas of an automobile engine according to claim 1 or 6, wherein auxiliary combustion fuel is added at the same position where oxygen or oxygen-enriched air is supplied. 8. A method for purifying exhaust gas of an automobile engine according to claim 7, wherein an ignition source is installed at a position for supplying oxygen or oxygen-enriched air and auxiliary fuel for combustion.