JP3398558B2 - Internal combustion engine exhaust gas purification device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for purifying exhaust gas from an internal combustion engine, and more specifically to a hydrocarbon-based fuel from an external source upstream of a NOx catalyst installed in an exhaust pipe for treating exhaust gas from the internal combustion engine. When adding and introducing NOx reduction, the reaction tube provided in the exhaust pipe is filled with a granular cracking catalyst, the hydrocarbon fuel is brought into contact with the cracking catalyst, and then injected to the inlet of the NOx catalyst to reduce NOx. The present invention relates to an exhaust gas purification device having a markedly improved effect.

[0002]

Exhaust gas from an internal combustion engine, such as a diesel engine, is generally exhausted into the atmosphere after being purified by a NOx catalyst. As a means for improving the purification effect of the NOx catalyst, the upstream side of the NOx catalyst is used. A hydrocarbon fuel from an external source (sometimes called a reducing agent)
Has been proposed to introduce.

The hydrocarbon material thus introduced is N
Ox catalyst acts to partially oxidize to form active species and N
NO on the surface of the Ox catalyst reacts with NOx in the exhaust gas
It is believed that x is reduced.

Further progressing this, for example, Japanese Patent Laid-Open No. 5-5
In the specification of 9933, a reducing agent (hydrocarbon-based substance, for example, light oil) is passed through a reducing agent reforming reactor composed of a reaction tube installed in an outer wall surface heating type housing provided outside an exhaust pipe. NOx in the exhaust pipe
An exhaust gas purifying device of a type in which fuel is injected to the upstream side of a catalyst through a nozzle and related art are disclosed.

[0005]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The present inventor has conducted various studies and researches in order to put into practical use a NOx reduction technique of introducing a decomposition product (cracking product) of a hydrocarbon-based fuel into an exhaust pipe. Recognizing the need for downsizing, elimination of external heating equipment and heat sources for external heating, rapid response to various operating conditions, improvement of hydrocarbon fuel cracking efficiency, etc. We conducted a wide variety of experiments to solve various problems one by one, devised an exhaust gas purification device that was easy to put into practical use, and further hydrocarbon fuel (reducing agent)
It was also found that the quality of the introduction timing of the engine largely depends on the operating conditions of the internal combustion engine. Therefore, the three factors of the rotational speed of the internal combustion engine, the load of fuel on the internal combustion engine, and the exhaust gas temperature on the upstream side of the NOx catalyst in the exhaust pipe are constantly monitored, and these signals are input to the computer to optimize the hydrocarbon amount. It is important to send the system fuel (reducing agent) to the spiral cracking reaction tube in a timely manner.

Furthermore, by arranging the cracking reaction tube in the exhaust tube, the heat of the exhaust gas can be utilized for the cracking reaction, thereby eliminating the need for an external heat source and, in addition, making the apparatus itself compact. Achieved

[0007]

The present invention thus provides a NOx catalyst in the exhaust pipe between the exhaust manifold of the internal combustion engine and the muffler and the upstream side of the NOx catalyst when the exhaust gas temperature is 180 ° C to 450 ° C. A pump for adding and introducing a hydrocarbon fuel from an external source to the exhaust gas flow to cause a reaction,
And an exhaust gas purifying device comprising an external hydrocarbon fuel introduction system including a spiral reaction tube arranged in an exhaust pipe: a rotational speed of an internal combustion engine, a fuel load on the internal combustion engine, and N
A computer for sensing the exhaust gas temperature upstream of the Ox catalyst, inputting each of these signals and controlling the operation of the pump accordingly to deliver an optimum amount of external hydrocarbon fuel to the reaction tube, and An exhaust gas purifying apparatus for an internal combustion engine, characterized in that the spiral reaction tube is filled with a granular cracking catalyst.

For example, NOx catalysts used in the case of diesel engines are known and are the surface of ceramics, in particular refractory ceramics (eg cordierite, alumina) or other metal oxides, or the surface of metal supports. above, Pt-Al ₂ O ₃ based, Pd-Al ₂ O ₃ system,
Examples thereof include those carrying known catalyst substances such as Rh—Al ₂ O ₃ system and Ir—Al ₂ O ₃ system.

According to the findings of the present inventors, the suitable exhaust gas temperature for introducing the hydrocarbon fuel (reducing agent) is about 1.
The temperature is higher than 50 ° C., and the temperature may be preferably around 180 to 250 ° C. for the Pt—Al ₂ O ₃ based catalyst.

The hydrocarbon-based fuel used as the reducing agent in the present invention may be the same as the fuel supplied to the internal combustion engine. For example, in the case of a diesel engine, light oil (fuel) is used.
It is also convenient in terms of availability to use the above.

In the present invention, the cracking reaction tube arranged in the exhaust tube has a spiral shape in order to utilize the heat of the exhaust gas as a heat source for the cracking reaction of the reducing agent (hydrocarbon-based fuel). The material is preferably a metal having corrosion resistance and high thermal conductivity, typically stainless steel. Thus, the temperature in the reaction tube can follow the exhaust gas temperature well and quickly.

The inside of the spiral reaction tube is filled with a cracking catalyst (granular or granular) such as zeolite or alumina. Particle size is, for example, 3 to 15 m
It can be about m. When a hydrocarbon-based substance, for example, light oil, is flowed through the catalyst bed in the spiral reaction tube heated by such exhaust gas, the hydrocarbon chain is fragmented and unsaturated hydrocarbons having a short molecular chain are mainly produced, These are downstream N
It reaches the Ox catalyst in the form of spray and promotes and strengthens the NOx reduction action.

According to the results of experiments conducted by the present inventors, the cracking efficiency is improved by using alumina having high-temperature activity in the exhaust manifold side of the cracking reaction tube and zeolite having low-temperature activity in the muffler side. It has been proved that the NOx reduction effect is improved and the NOx reduction effect is significantly improved.

Further, according to the present invention, not only the NOx catalytic activity is improved, but the NOx catalytic activity temperature range is extended (for example, about 160 to 300 ° C.).

It is preferable that a concave groove is formed (or drawn) from the outside around the pipe wall near the injection port at the tip of the spiral cracking reaction tube to prevent catalyst particles from jumping out of the reaction tube. .

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further illustrated and described with reference to the schematic view of a specific example of the exhaust gas purifying apparatus of the present invention applied to the diesel engine shown in FIG.

A spiral cracking reaction tube 5 is arranged on the inner wall of an exhaust pipe 4 attached to a diesel engine 1 via a manifold, and a reducing agent (hydrocarbon decomposition product) is injected at the tip of the reaction tube. Nozzle 1 for
2 is provided. Spiral reaction tube 5 and nozzle 12
A temperature sensor 8 and a NOx catalyst 9 are arranged on the downstream side of
Further, a muffler muffler 10 is attached downstream. A rotation sensor 2 for detecting the rotation speed of the diesel engine and a load sensor 3 for detecting the fuel load on the diesel engine are attached. These sensors are connected so as to input their detection data (signals) to the computer 11.

A hydrocarbon fuel (reducing agent; light oil) is supplied to the spiral cracking reaction tube 5 from a tank 7 via a supply pump 6.

When the diesel engine 1 is started and operated, exhaust gas is concentrated in the manifold, passes through the exhaust pipe 4,
After being treated with the Ox catalyst 9, it is released into the atmosphere through the muffler 10. At this time, the cracking reaction tube 5 made of a material having a high thermal conductivity and the cracking catalyst filled therein are heated in the exhaust pipe. The hydrocarbon-based fuel supplied by the hydrocarbon-based fuel (reducing agent) supply pump 6 is decomposed (cracked) by coming into contact with a heated catalyst to generate unsaturated hydrocarbons having a shortened molecular chain, These are injected from the injection nozzle 12 toward the NOx catalyst 9. The supply of the hydrocarbon fuel is performed by the pump 6 whose operation is controlled by the computer 11 which receives signals from the exhaust gas temperature sensor 8, the rotation speed sensor 2 and the load sensor 3.

[0020]

EFFECT OF THE INVENTION Hydrocarbon fuel (reducing agent) injection type exhaust gas purifying apparatus is made compact, quick response, economical,
The practical value was increased by improving the NOx reduction effect and expanding the NOx catalyst activation temperature range.

To exemplify the NOx reduction effect according to the present invention, in the apparatus shown in FIG. 1, Pt—Al ₂ O ₃ -supporting honeycomb ceramics is used as the NOx catalyst 9 and the spiral cracking reaction tube 5 is provided with granular alumina.
NOx reduction rate (%; measured by an exhaust gas analyzer) data at various catalyst inlet temperatures (° C.) when the cracking catalyst is packed and installed (Example of the present invention), and JP-A-5-5.
The same data as in the case of using the cracking reaction tube arranged outside the exhaust pipe described in the specification of 9933 (comparative example) is shown below in comparison. The diesel engines in both cases were the same and had the same operating conditions.

NOx reduction rate (%) Catalyst inlet temperature (° C.) Example Comparative Example 150 4 2.5 175 7 4 200 16.5 10 225 28 20 20 250 13.5 10.5 275 8 4.5 300 4. 5 3 325 3.5 2

[Brief description of drawings]

FIG. 1 is a schematic view of a specific example in which an exhaust gas purification device according to the present invention is applied to a diesel engine.

FIG. 2 is an enlarged conceptual diagram of a reducing agent reaction tube and an injection nozzle.

[Explanation of symbols]

1 diesel engine 2 rotation sensor 3 load sensor 4 exhaust pipe 5 Spiral cracking reaction tube 6 (reducing agent) supply pump 7 (reducing agent) tank 8 Temperature sensor 9 NOx catalyst 10 muffler 11 computer 12 Reducing agent injection nozzle

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F01N 3/36 F01N 3/36 C 9/00 9/00 Z (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/08-3/36 B01J 23/40 F01N 9/00

Claims (4)

(57) [Claims] 1. A NOx catalyst and exhaust gas temperature in an exhaust pipe between an exhaust manifold of an internal combustion engine and a muffler muffler are 1
A pump for adding and introducing a hydrocarbon fuel from an external source to the exhaust gas flow on the upstream side of the NOx catalyst at a temperature of 80 ° C. to 450 ° C., and an external hydrocarbon fuel including a spiral reaction tube arranged in an exhaust pipe An exhaust gas purifying apparatus comprising an introduction system, which detects the number of revolutions of an internal combustion engine, the load of fuel on the internal combustion engine, and the exhaust gas temperature upstream of the NOx catalyst, inputs these signals, and outputs them. Equipped with a computer that controls the operation of the pump so as to send the optimum amount of external hydrocarbon fuel to the reaction tube, and for high temperature in the spiral reaction tube near the exhaust manifold.
Particulate cracking catalyst, and part close to NOx catalyst
An exhaust gas purifying device characterized in that a low temperature granular cracking catalyst is filled in. 2. The exhaust gas purifying apparatus according to claim 1 , wherein the high temperature catalyst comprises alumina and the low temperature catalyst comprises zeolite. 3. The claim 1, characterized in that externally to the tube wall around the vicinity of the injection port of the spiral reaction tube to form a concave groove are prevented from jumping out of the catalyst particle from the reaction tube
2 is an exhaust gas purification device. 4. The internal combustion engine is a diesel engine,
One of the exhaust gas purifying apparatus according to claim 1 to 3 an external source a hydrocarbon fuel is diesel fuel.