JPH11229851A - Exhaust gas purifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of NOx emissions in exhaust gas as well as to prevent a reduction in fuel consumption efficiency. SOLUTION: A NOx reduction catalyst 12 is installed inside of an exhaust pipe 4 through which exhaust gas flows from an engine body 1. A gas sampling pipe 14 connects the inside of the exhaust pipe 4 upstream of the NOx reduction catalyst 12 with an upper space 2a in a fuel tank 2. A pump 16 (feed supply means) which is provided in the gas sampling pipe 14 appropriately supplies fuel vapor F' which is generated in the fuel tank 2 to the inside of the exhaust pipe 4 upstream of the NOx reduction catalyst 12 according to the temperature of the exhaust gas. Further, HC storage material is preferably attached to the NOx reduction catalyst 12 on the upstream side thereof.

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 applied to an internal combustion engine such as a diesel engine, and more particularly, to an exhaust gas purifying apparatus that effectively utilizes fuel vapor of liquid fuel generated in a fuel tank. Nitrogen oxides (N
This is to reduce the emission concentration of Ox) and to prevent a decrease in fuel efficiency.

[0002]

2. Description of the Related Art Conventionally, in an exhaust gas purifying apparatus for an internal combustion engine of this type, for example, a diesel engine, as shown in FIG. A NOx reduction catalyst e built in the casing d, and a communication pipe g connects between the exhaust pipe b upstream of the NOx reduction catalyst e and the fuel tank f. through the injection nozzle h provided in g to inject (light oil containing HC mainly C ₇ -C ₂₄₎ liquid fuel F in the fuel tank f by the drive of the pump i to NOx reduction catalyst e upstream of the exhaust pipe b There is something like that.

[0003] The NOx reduction catalyst e used in such a conventional exhaust gas purification apparatus is, for example, alumina (A
l ₂ O ₃ ) as a carrier and, for example, platinum (P
t), rhodium (Rh), iridium (Ir), silver (A
g), a form in which at least one selected from copper (Cu), cobalt (Co), iron (Fe) and the like is supported, and a liquid fuel (light oil) F supplied from the fuel tank f
The hydrocarbon (HC) contained therein is used as a reducing agent to chemically react with NOx in the exhaust gas to reduce the NOx emission concentration.

[0004] Further, the supply control of the liquid fuel F is performed by estimating the NOx emission amount of the exhaust gas by using a rotation sensor j for detecting the engine speed of the engine body a and a load sensor k for detecting the engine load. The exhaust gas temperature is detected by the temperature sensor 1 installed on the upstream side of the NOx reduction catalyst e, and the information is input to the electronic control unit m, whereby the NOx is reduced.
When the reduction catalyst e has reached an active state (200 to 550 ° C.), the pump i is driven based on the NOx emission amount of the exhaust gas estimated by the rotation sensor j and the load sensor k,
The injection amount of the liquid fuel F, that is, the supply amount of the hydrocarbon (HC) is controlled.

[0005]

However, in the above-mentioned conventional exhaust gas purifying apparatus, the excess fuel vapor F 'of the liquid fuel F generated in the fuel tank f is supplied to the check valve n.
, And the liquid fuel F is injected into the exhaust pipe b by the drive control of the pump i via the communication pipe g and the injection nozzle h to be supplied, so that the fuel efficiency is improved. There was a problem of lowering.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to reduce the NOx emission concentration in exhaust gas and to reduce the fuel vapor of liquid fuel generated in a fuel tank. About 1 to 1 as gas in
Low boiling hydrocarbons (C ₂ to
By effectively utilizing the HC) of C ₇ as a reducing agent for NOx, it is to provide an exhaust purification apparatus that can prevent a decrease in fuel efficiency.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a NOx reduction catalyst is provided in an exhaust passage through which exhaust gas from an internal combustion engine flows, and an exhaust passage upstream of the NOx reduction catalyst and a fuel tank. The upper space of the NOx reduction catalyst is connected in communication with a gas sampling pipe, and fuel vapor generated in the fuel tank is appropriately discharged according to exhaust gas temperature by a feeding means provided in the gas sampling pipe. The present invention relates to an exhaust gas purification device characterized in that it can be supplied to a system path.

That is, according to the present invention, by employing the above structure, the fuel vapor of the liquid fuel generated in the fuel tank is supplied to the NOx reduction catalyst appropriately disposed in the exhaust system according to the exhaust gas temperature. Since it is sent to the upstream side, low-boiling hydrocarbons contained in the fuel vapor can be effectively used as a reducing agent of the NOx reduction catalyst.

In the present invention, it is preferable that a hydrocarbon occluding material (hereinafter, referred to as an HC occluding material) is provided upstream of the NOx reduction catalyst. If the supply is set to the storage temperature of the low-boiling hydrocarbons by the HC storage material, the low-boiling hydrocarbons contained in the fuel vapor fed into the exhaust pipe are stored in the HC storage material. The low-boiling hydrocarbons can be concentrated in an inert state, and the concentrated low-boiling hydrocarbons can be largely removed from the HC storage material when the temperature of the exhaust gas rises.

[0010]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described in detail with reference to the drawings shown in FIG.
FIG. 1 shows a first embodiment of an exhaust gas purification apparatus according to the present invention,
In the figure, reference numeral 1 denotes an engine body which is a diesel engine, 2 denotes a fuel tank for supplying a liquid fuel F (light oil) to the engine body 1, and 3 denotes an excess fuel vapor F 'of the liquid fuel F generated in the fuel tank 2. Check valve that can release air into the atmosphere, 4
Reference numeral 5 denotes an exhaust pipe connected to the exhaust manifold 1a of the engine body 1 through which exhaust gas flows, and reference numeral 5 denotes a muffler connected to the exhaust pipe 4.

An exhaust gas purification device 10 is installed in the exhaust pipe 4, and the exhaust gas purification device 10 is provided in a casing 11 connected to the exhaust pipe 4 on the upstream side of the muffler 5. And a gas sampling pipe 14 for communicating between an upstream side of the casing 11 and an upper space 2a in the fuel tank 2. The gas sampling pipe 14 is The fuel vapor F ′ of the liquid fuel F generated in the fuel tank 2 is exposed to the exhaust pipe 4 through a stop valve 15, and the casing 1 is driven by a pump 16 as a feeding means.
1 upstream.

A rotation sensor 1 for detecting the engine speed of the engine body 1 as in the conventional apparatus shown in FIG.
9 and a load sensor 20 for detecting the engine load, the exhaust gas emission amount is estimated.
The exhaust gas temperature is detected by a temperature sensor 17 installed on the upstream side, and the information is input to an electronic control unit 18 to activate the NOx reduction catalyst 12 (200 to 550 ° C.).
The rotation sensor 19 and the load sensor 2
Pump 1 based on the exhaust gas emissions estimated at 0
6, the amount of fuel vapor F ′ generated in the fuel tank 2 can be controlled.

According to this embodiment, the fuel vapor F ′ generated in the fuel tank 2 is sent to the upstream side of the NOx reduction catalyst 12 disposed in the exhaust pipe 4 according to the temperature of the exhaust gas. Thus, the low-boiling hydrocarbons (C _{2 to} C ₇ HC) in the fuel vapor F ′ can be effectively used as a reducing agent of the NOx reduction catalyst 12.

FIG. 2 shows a second embodiment of the exhaust gas purifying apparatus according to the present invention.
1, an HC storage material 13 is provided on the upstream side of the NOx reduction catalyst 12, and a gas sampling pipe 14 is connected to a casing 1 immediately before the HC storage material 13 via a check valve 15.
1

By the way, the HC occluding material 13 has, for example, a Cayban ratio (SiO ₂ / Al ₂ O ₃ ) of 10 to 1000.
(Molar ratio) zeolite, a slurry mixed with water through a binder (silica sol, alumina sol), adhered to the honeycomb material, dried and fired, and coated at 100 to 300 g / l to form a honeycomb structure. When the exhaust gas temperature is 200 ° C. or less, about 1 to 1
It absorbs low-boiling hydrocarbons (C _{2 to} C ₇ HC) present as a gas at a concentration of about 0 ppm, and has such characteristics that the adsorbed low-boiling hydrocarbons can be desorbed at 200 ° C. or more. .

A temperature sensor 17 is provided in the exhaust pipe 4 on the upstream side of the casing 11. The temperature sensor 17 is connected to the exhaust pipe 4 on the upstream side of the HC storage material 13.
The pump 16 is driven and controlled by detecting the temperature of the exhaust gas in the inside and inputting the information to the electronic control unit 18. The detected temperature is 100 to 200 ° C. within the set temperature. When the pump 16 is driven, the fuel vapor F ′ of the liquid fuel F generated in the fuel tank 2 is fed into the exhaust pipe 4. It is controlled so that the supply of F 'is stopped.

Therefore, according to the present embodiment, by providing the HC storage material 13 on the upstream side of the NOx reduction catalyst 12, the supply by the pump 16 controlled by the exhaust gas temperature can be controlled by the storage temperature of the HC storage material 13. (200 ° C. or less, preferably 100 to 200 ° C.), the HC storage material 13
The low-boiling hydrocarbons in the fuel vapor F ′ fed into the casing 11 immediately before the NOx reduction catalyst 12 are stored in the HC storage material 13 so that the NOx reduction catalyst 12 is in an inactive state (200 ° C. or lower).
, The low-boiling hydrocarbon becomes high in concentration, and the low-boiling hydrocarbon desorbs in large quantities from the HC storage material 13 at or above the set temperature (200 ° C.) of the exhaust gas.
NOx reduction by the Ox reduction catalyst 12 can be promoted.

FIG. 3 shows the overall NOx reduction rate (%) of the exhaust gas purifying apparatus according to the first and second embodiments of the present invention. A1 denotes NOx reduction in which fuel vapor F 'is not supplied. The NOx reduction rate (5%) by the catalyst alone, A2 is the N2 reduction by the NOx reduction catalyst 12 to which the fuel vapor F 'of the present invention is fed.
O3 reduction rate (10%) and A3 indicate the NOx reduction rate (15%) by the NOx reduction catalyst 12 provided with the HC storage material 13 together with the supply of the fuel vapor F 'of the present invention, and A1
As a result, the NOx reduction rate is better in the first embodiment of A2 than in the case of A2, and further, the NOx reduction rate is better in the second embodiment of A3 than in the first embodiment of A2. Obtained.

Although not shown, the method using excess fuel vapor according to the present invention has a result that the fuel efficiency is improved by 1 to 2% as compared with the method using fuel (liquid) shown in FIG. .

FIG. 4 shows the relationship between the exhaust gas temperature (° C.) and the NOx reduction rate (%) under predetermined operating conditions in the exhaust gas purifying devices of the first and second embodiments according to the present invention. B1 is a NOx reduction rate by the NOx reduction catalyst 12,
B2 is a NOx reduction catalyst 12 provided with an HC storage material 13
According to this, the addition of the HC storage material 13 makes it possible to shift the reduction of NOx to the low-temperature region side, and obtains a result that the NOx reduction rate is improved by 5%. Was done.

It should be noted that the exhaust gas purifying apparatus of the present invention is not limited to the above-described embodiment, but may be variously modified without departing from the gist of the present invention.

[0022]

As is apparent from the above description, the exhaust purifying apparatus according to the present invention has the following various excellent effects.

(I) According to the first aspect of the present invention, the fuel vapor generated in the fuel tank is provided upstream of the NOx reduction catalyst appropriately disposed in the exhaust pipe according to the exhaust gas temperature. Since the fuel is supplied, the low-boiling hydrocarbons contained in the fuel vapor can be effectively used as a reducing agent of the NOx reduction catalyst, so that the NOx emission concentration can be reduced and the fuel efficiency as in the related art can be reduced. A decrease in efficiency can be prevented.

(II) According to the second aspect of the present invention, the low-boiling hydrocarbons in the fuel vapor fed into the exhaust pipe are occluded by the HC storage material, and the low-boiling hydrocarbons are highly concentrated. And a large amount of this high-concentration low-boiling hydrocarbon can be desorbed from the HC storage material when the temperature of the exhaust gas rises, so that the reduction of NOx by the active NOx reduction catalyst is promoted. Accordingly, it is possible to further promote the reduction of the NOx emission concentration.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first embodiment of the present invention.

FIG. 2 is a schematic view showing a second embodiment for implementing the present invention.

FIG. 3 is a graph showing a reduction rate of NOx in comparison with a conventional device.

FIG. 4 is a graph showing the relationship between the temperature of exhaust gas and the reduction rate of NOx.

FIG. 5 is a schematic view showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body (internal combustion engine) 2 Fuel tank 2a Upper space 4 Exhaust pipe 10 Exhaust purification device 12 NOx reduction catalyst 13 HC storage material 14 Gas sampling pipe 16 Pump (feeding means) F 'Fuel vapor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 25/08 301 F02M 25/08 301U

Claims (2)

[Claims] An NOx reduction catalyst is provided in an exhaust passage through which exhaust gas from an internal combustion engine flows, and
x An exhaust passage upstream of the reduction catalyst and an upper space in the fuel tank are connected and communicated with each other by a gas sampling pipe, and fuel vapor generated in the fuel tank is supplied to the exhaust gas by feeding means provided in the gas sampling pipe. The N
An exhaust gas purification apparatus characterized in that it can be supplied to an exhaust system upstream of an Ox reduction catalyst. 2. The exhaust gas purification apparatus according to claim 1, wherein a hydrocarbon storage material is provided upstream of the NOx reduction catalyst.