Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2002-11-27
2004-10-12
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S274000, C060S295000, C060S311000
Reexamination Certificate
active
06802180
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purification system and a method for controlling a regeneration thereof using a filter which is called a diesel particulate filters (DPF: Diesel Particulate Filter: called a DPF hereinbelow) to collect particulate matters: (PM: particulate matters: called a PM hereinbelow) in an exhaust gas of a diesel engine.
2. Related Art
The exhaust volume control of the PM exhausted from a diesel engine, together with that of Nox, CO, HC, and the like, has been strengthened with the years and a technique for collecting the PM by the DPF in order to reduce the PM volume to be exhausted out has been developed.
For the DPF to directly collect the PM, there are a monolith honeycomb-shaped wall flow type filter made of ceramics, a fiber-shaped type filter having a fiber made of ceramics or metals. An exhaust gas purification device using these DPF is disposed on the way of an exhaust pipe of the engine to purify the exhaust gas generated in the engine.
In such DPF, however, a filter is clogging up during collecting the PM to cause a raise of an exhaust gas pressure (exhaust pressure), so that some methods and systems have been developed for the necessity of removing the PM from the DPF.
Among the methods and systems aforementioned, there are systems to burn and remove the PM by heating the filter by an electric heater or a burner and to reverse-clean the PM by ventilating air in the reverse direction. However, since the PM is burned by a heating energy supplied from exterior, in such systems there are problems to cause a deterioration of fuel efficiency and a difficulty of controlling the regeneration.
Furthermore if these systems are applied, two systems of exhaust passages equipped with a filter are acquired and there are many cases to repeat the collection of the PM and the regeneration of the filter alternately, so that the system tends to becomes large and be expensive.
To overcome these problems, as illustrated in FIG.
3
and
FIG. 4
, a continuous regeneration type DPF system is proposed to combine a catalyst with a wall flow type filter in order to reduce the regeneration temperature of the DPF and to regenerate the DPF by using an exhaust heat from the engine.
The wall flow type filter
10
includes a plurality of exhaust gas passages (cells)
11
a
,
11
b
of which a periphery is formed with a porous wall surface
12
, and an inlet side
15
and an outlet side
16
of the exhaust gas passages
11
a
,
11
b
are respectively formed to seal in a staggered way
13
.
In a continuous regeneration type DPF system, the regeneration of the DPF and the collection of the PM are practiced continuously to become a further compact single system, so that the control of the regeneration may be also simple.
In
FIG. 5
, a continuous regeneration type DPF system (NO
2
regeneration type DPF system)
1
A by nitrogen dioxide comprises an oxidation catalyst
3
Aa in the upper flow side and a wall flow type filter
3
Ab in the lower flow side. Nitrogen monoxide in the exhaust gas is oxidized by an oxidation catalyst
3
Aa such as platinum in the upper flow side, the PM collected in the filter
3
Ab in the lower flow side is oxidized by generated nitrogen dioxide into carbon dioxide and the PM is removed.
As compared with the oxidation of the PM by oxide, the oxidation of the PM by nitrogen dioxide is practiced in a low temperature due to low energy barrier. Therefore since the energy supply from exterior can be reduced, by using heat energy in the exhaust gas, the filter regeneration can be achieved by oxidizing to remove the PM while collecting the PM continuously.
Furthermore in
FIG. 6
, a continuous regeneration type DPF system (an integrated type NO
2
regeneration DPF system)
1
B which the system
1
A illustrated by
FIG. 5
is improved is shown. In the system
1
B. The oxidation catalyst
32
A is coated on a wall surface of a wall flow type filter
3
B equipped with the catalyst and on the wall surface, nitrogen monoxide in the exhaust gas is oxidized and the PM is oxidized by nitrogen dioxide. The system can be made simple by this structure. In order to coat the catalyst on the wall surface of the wall flow filter, however, a earlier pressure damage of the early filter tends to be increased.
Moreover in a continuous regeneration type DPF system
1
C (DPF system equipped with the PM oxidation catalyst) illustrated by
FIG. 7
, a rare metal oxidation catalyst
32
A such as platinum and a PM oxidation catalyst
32
B are coated on the wall surface of the wall flow type filter
3
C equipped with the PM oxidation catalyst in order to achieve the oxidation of the PM on the wall surface by the lower temperature.
The PM oxidation catalyst
32
B is a catalyst to directly oxidize the PM by an oxide in the exhaust gas and is made of cerium dioxide.
Moreover for the continuous regeneration type DPF system
1
C, in a low temperature oxidation area (about 350° C. to 450° C.), the PM is oxidized by nitrogen dioxide in using a reaction of oxidizing nitrogen monoxide of the oxidation catalyst
32
A into nitrogen dioxide. Furthermore in a medium temperature oxidation area (about 400° C. to 600° C.), the PM is oxidized in using a reaction of directly oxidizing the PM by activating oxide in the exhaust gas with the PM oxidation catalyst
32
B. Then in a higher temperature oxidation area (600° C. or more) than the temperature in which the PM is burned by oxide in the exhaust gas, the PM is oxidized by oxide in the exhaust gas.
In continuous regeneration type DPF system, by using the catalyst and the oxidation of the PM by nitrogen dioxide, the temperature capable of oxidizing the PM is lowered and the PM is oxidized and removed while collecting the PM.
In these continuous regeneration type DPF systems, however, it is also necessary to raise the exhaust gas temperature to be about 350° C. Therefore under an operation condition of the engine such as an idling or a low load, due to lack of the exhaust gas temperature, the temperature of the catalyst lowers and the activation thereof is deteriorated, thus the necessary reaction described hereinbefore is not caused, and the DPF cannot be regenerated by oxidizing the PM.
Therefore if such operating manner is continued, the DPF cannot be regenerated as it is, the DPF clogs up due to the accumulation of the PM, the system results in problems that the exhaust pressure raises and the deterioration of fuel efficiency or the like is caused.
Therefore in the continuous regeneration type DPF system, an accumulation volume of the PM accumulated on the DPF is calculated from the engine operation condition, the control operation of regenerating the DPF is practiced in comparison with the predetermined DPF regeneration condition set from the relation of the PM accumulation volume and the DPF pressure drop, and the accumulated PM is burned to remove.
Under the condition of the engine operation such as the idling condition with a low exhaust gas temperature and the low load, the filter regeneration is so controlled by using an electronic control type fuel injection system such as a common rail that the exhaust temperature is raised by an injection time delay, by a multiple injection and the like, or for an oxidation catalyst in the former step of the DPF, the fuel is supplied by a post injection and by an injection within an exhaust pipe and burned to raise the exhaust gas temperature more than the PM reburning temperature.
In the regeneration control of such DPF, however, at the time of starting the PM reburning in a medium engine speed area where the exhaust gas is comparatively much exhausted, in the early step of burning PM, if the engine speed is rapidly changed to the operating condition of the low flow rate of the exhaust gas such as the idling, the exhaust gas flow rate which brings out the heat caused by oxidation of the PM in the DPF is reduced. Then a heat quantity brought out of the DPF exhaust gas is also reduced.
Therefore an interior of the DPF is heated to a high tempe
Gabe Masashi
Imai Takehito
Ochi Naofumi
Denion Thomas
Isuzu Motors Limited
Staas & Halsey , LLP
Tran Diem
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