Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
1995-09-05
2002-06-25
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S172000, C422S177000, C060S289000, C060S297000
Reexamination Certificate
active
06409973
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purification device for an engine. More specifically, the present invention relates to a device that is capable of effectively removing an NO
x
component from exhaust gas.
2. Description of the Related Art
An exhaust gas purification device capable of removing an NO
x
component from engine exhaust gas is, for example, disclosed in the Japanese Unexamined Patent Publication (Kokai) No. 62-117620. The device disclosed in JPP '620 is used for removing NO
x
components from the exhaust gas of a lean burn engine, i.e., an engine operated at an air-fuel ratio higher than a stoichiometric air-fuel ratio. In the device disclosed in JPP '620, an exhaust passage of the engine is diverged into two branch exhaust passages, and a NO
x
absorbent is disposed in each of the branch exhaust passages, namely, two NO
x
absorbents are disposed in the exhaust gas passage in parallel. The NO
x
absorbent is capable of absorbing an NO
x
component in the exhaust gas in the presence of oxygen. Since the engine is operated on a lean air-fuel ratio, the exhaust gas from the engine contains relatively high concentration of oxygen, therefore, NO
x
components contained in the exhaust gas are absorbed by the NO
x
absorbents.
When the NO
x
absorbent absorbs a certain amount of NO
x
, the ability of the NO
x
absorbent to absorb NO
x
in the exhaust gas is reduced. To regain the absorption ability, the absorbed NO
x
in the absorbent must be discharged and reduced periodically. For example, by supplying a reducing agent to the NO
x
absorbent, the NO
x
absorbents are regenerated to regain the initial NO
x
absorption ability. In the device in JPP '620, two NO
x
absorbents are disposed in parallel in the exhaust passage in order to enable regeneration of the NO
x
absorbent without stopping the purification of the exhaust gas. In JPP '620, two NO
x
absorbents are used alternately during normal engine operation, i.e., only one of the NO
x
absorbents is used for absorbing the NO
x
in the exhaust gas. Namely, in the normal operation, one of the branch exhaust passage is closed, and the exhaust gas from the engine is directed to the other branch exhaust passage where the NO
x
in the exhaust gas is absorbed by the NO
x
absorbent disposed in that exhaust branch passage. While absorbing NO
x
in the exhaust gas by one NO
x
absorbent, the other NO
x
absorbent disposed on the closed exhaust branch passage is regenerated by supplying a reducing agent, such as hydrogen gas.
According to the device disclosed in JPP '620, by using two NO
x
absorbents disposed in the exhaust passage in parallel, the NO
x
absorbents can be regenerated alternately while continuing to remove the NO
x
component from the exhaust gas.
However, a disadvantage of the device disclosed in JPP '620 has is that the reducing agent must be supplied to both exhaust branch passages. This requires two injection nozzles, one in each of the exhaust branch passages, and associated piping connecting the nozzles to the supply source of the reducing agent, and a three-way flow control valve for switching the supply of the reducing agent between the two nozzles. Further, elaborate control of the three-way flow control valve is required to enable the appropriate regeneration of the NO
x
absorbents.
SUMMARY OF THE INVENTION
In view of the problems in the prior art set forth above, the object of the present invention is to provide an exhaust gas purification device for an internal combustion engine which is capable of removing NO
x
components from the exhaust gas without requiring complicated devices and controls.
The above object is achieved by the present invention, an exhaust gas purification device, for an internal combustion engine. The engine is operated with an air-fuel ratio higher than a stoichiometric air-fuel ratio. The device comprises (a) first and second NO
x
absorbents disposed in the exhaust passage of the engine and connected in series by an exhaust connecting passage, each of the NO
x
absorbents absorbs NO
x
components in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the NO
x
absorbents is lean, and releases the absorbed NO
x
when the oxygen concentration in the exhaust gas becomes lower; (b) a reducing agent supply means for supplying a reducing agent to the exhaust gas in the exhaust connecting passage between the first and the second NO
x
absorbents; (c) a switching means for switching the direction of the exhaust gas flow between a first direction in which the exhaust gas flows through the first NO
x
absorbent, the exhaust connecting passage and the second NO
x
absorbent in this order, and a second direction in which the exhaust gas flows through the second NO
x
absorbent, the exhaust connecting passage and the first NO
x
absorbent in this order; (d) and a control means for controlling the switching means so that the direction of the exhaust gas flow is switched between the first and the second direction each time when a predetermined condition is satisfied.
When the flow direction of exhaust gas is switched to the first direction, the lean air-fuel ratio exhaust gas from the engine first flows into the first NO
x
absorbent and NO
x
components in the exhaust gas are absorbed by the first NO
x
absorbent. After passing through the first NO
x
absorbent, a reducing agent is supplied to the exhaust gas in the exhaust connecting passage before flowing into the second NO
x
absorbent. Therefore, the air-fuel ratio of the exhaust gas flowing into the second NO
x
absorbent becomes rich due to the reducing agent. Thus, in the second NO
x
absorbent, the absorbed NO
x
is released and reduced to nitrogen by the reducing agent. Namely, when the exhaust gas flow is switched to the first direction, NO
x
components in the exhaust gas are absorbed by the first NO
x
absorbent and removed from the exhaust gas, and the NO
x
in the second NO
x
absorbent is released and reduced to nitrogen.
On the other hand, when the exhaust gas flow is switched to the second direction, the lean exhaust gas from the engine first flows into the second NO
x
absorbent and NO
x
components in the exhaust gas are absorbed by the second NO
x
absorbent. Then, the reducing agent is supplied to the exhaust gas in the exhaust connecting passage before flowing into the first NO
x
absorbent. Therefore, the rich exhaust gas flows into the first NO
x
absorbent, and absorbed NO
x
is released from the first NO
x
absorbent and reduced to nitrogen by the reducing agent. Therefore, by switching the direction of the exhaust gas flow each time when the predetermined condition is satisfied, for example, each time an amount of NO
x
absorbed in the NO
x
absorbent reaches a predetermined value, absorption of NO
x
in the exhaust gas and releasing and reducing of the absorbed NO
x
is performed in each NO
x
absorbent alternatively without stopping the absorption of NO
x
in the exhaust gas as a whole.
According to another aspect of the present invention, there is provided an exhaust gas purification device for an internal combustion engine having an exhaust passage. The engine is operated at an air-fuel ratio equal to, or lower than, a stoichiometric air-fuel ratio. The device comprises (a), first and second NO
x
absorbents disposed in the exhaust passage of the engine and connected each other in series by an exhaust connecting passage, each of the NO
x
absorbents absorbs NO
x
components in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the NO
x
absorbents is lean, and releases the absorbed NO
x
when the oxygen concentration in the exhaust gas becomes; (b) a secondary air supply means for supplying secondary air to the exhaust gas in the exhaust connecting passage between the first and the second NO
x
absorbents; (c) a switching means for switching the direction of the exhaust gas flow between a first direction in which the exhaust gas flows through the first NO
x
absorbe
Igarashi Kouhei
Itou Takaaki
Kinugasa Yukio
Takaoka Toshifumi
Kenyon & Kenyon
Tran Hien
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