JP2008232061A - Diesel engine exhaust system - Google Patents

Abstract

An exhaust device for a diesel engine capable of combusting combustible gas even when the exhaust temperature is low is provided.
In an exhaust system of a diesel engine, an oxidation catalyst 12 is disposed upstream of a filter in an exhaust path 1, and a combustible gas 7 heated by an exothermic reaction in a gas generator 3 is contained in the oxidation catalyst 12. In order to promote the combustion of the combustible gas 7 by accelerating the combustion of the combustible gas 7, the combustible gas outlet 9 is provided in the exhaust passage peripheral wall 1 a surrounding the oxidation catalyst 12, and the exhaust introduction nozzle 71 is provided on the exhaust upstream side of the oxidation catalyst 12. This exhaust introduction nozzle 71 is provided with a cylindrical nozzle peripheral wall 71a, the nozzle peripheral wall 71a is surrounded by the oxidation catalyst 12, a plurality of exhaust inlets 71b are provided in the nozzle peripheral wall 71a, and the exhaust catalyst downstream of the oxidation catalyst 12 is provided. An exhaust outlet 12a was provided.
[Selection] Figure 2

Description

  The present invention relates to an exhaust device for a diesel engine, and more particularly to an exhaust device for a diesel engine that can reliably burn combustible gas even when the exhaust temperature is low.

As in the present invention, as a conventional diesel engine exhaust system, liquid fuel is supplied from a liquid fuel supply source to a gas generator, and the liquid fuel is made into a combustible gas by the gas generator, and the combustible gas of the gas generator is used. An outlet is provided in the exhaust path upstream of the diesel particulate filter, the combustible gas flowing out from the combustible gas outlet is burned with oxygen in the exhaust, and the exhaust heated by the combustion heat is accumulated in the filter. There are some that can burn the exhaust particulates.
This type of exhaust system has the advantage that even during light load operation where the exhaust temperature is low, the temperature of the exhaust flowing into the filter can be increased by the combustion heat of the combustible gas, the exhaust particulates can be burned, and the filter can be regenerated. Has been.

  However, the conventional exhaust device has a problem because there is no means for promoting the combustion of the combustible gas.

The above prior art has the following problems.
<< Problem >> When the exhaust temperature is low, the combustible gas cannot be reliably burned.
Since there is no means for promoting the combustion of the combustible gas, the combustible gas cannot be reliably burned when the exhaust temperature is low.

  An object of the present invention is to provide an exhaust device for a diesel engine that can solve the above problems, that is, an exhaust device for a diesel engine that can reliably burn combustible gas even when the exhaust temperature is low. And

Invention specific matters of the invention according to claim 1 are as follows.
As illustrated in FIG. 1, the liquid fuel (6) is supplied from the liquid fuel supply source (5) to the gas generator (3), and the liquid fuel (6) is supplied to the combustible gas (3) by the gas generator (3). 7), and the combustible gas outlet (9) of the gas generator (3) is provided in the exhaust passage (1) upstream of the diesel particulate filter (2), and the combustible gas outlet (9) The combustible gas (7) flowing out of the exhaust gas (10) can be burned with oxygen in the exhaust gas (10), and the exhaust gas (10) heated by the combustion heat can burn the exhaust particulate accumulated in the filter (2). In the exhaust system of a diesel engine,
An oxidation catalyst (12) is disposed upstream of the filter (2) in the exhaust path (1), and the combustible gas (7) heated by an exothermic reaction in the gas generator (3) is converted into an oxidation catalyst ( 12) In merging with the exhaust (10) and promoting the combustion of the combustible gas (7),
As illustrated in FIG. 2, a combustible gas outlet (9) is provided in the exhaust path peripheral wall (1 a) surrounding the oxidation catalyst (12), and an exhaust introduction nozzle (71) is provided on the exhaust upstream side of the oxidation catalyst (12). The exhaust nozzle (71) is provided with a cylindrical nozzle peripheral wall (71a), the nozzle peripheral wall (71a) is surrounded by an oxidation catalyst (12), and a plurality of exhaust inlets (71b) are provided in the nozzle peripheral wall (71a). ), And an exhaust outlet (12a) is provided on the exhaust downstream side of the oxidation catalyst (12).

<Effect> Even when the exhaust temperature is low, the combustible gas can be reliably burned.
As illustrated in FIG. 1, an oxidation catalyst (12) is disposed upstream of the inlet (2a) of the filter (2) in the exhaust path (1) and heated by an exothermic reaction in the gas generator (3). The combustible gas (7) is combined with the exhaust (10) in the oxidation catalyst (12) to promote the combustion of the combustible gas (7), so that even if the temperature of the exhaust (10) is low, combustible Gas (7) can be burned reliably.

<Effect> Even when the exhaust temperature is low, the combustible gas can be reliably burned.
As illustrated in FIG. 2, a combustible gas outlet (9) is provided in the exhaust path peripheral wall (1 a) surrounding the oxidation catalyst (12), and an exhaust introduction nozzle (71) is provided on the exhaust upstream side of the oxidation catalyst (12). The exhaust nozzle (71) is provided with a cylindrical nozzle peripheral wall (71a), the nozzle peripheral wall (71a) is surrounded by an oxidation catalyst (12), and a plurality of exhaust inlets (71b) are provided in the nozzle peripheral wall (71a). ) And the exhaust outlet (12a) is provided on the exhaust downstream side of the oxidation catalyst (12). Therefore, the exhaust per unit area of the exhaust inlet (71b) can be increased to the extent that the total opening area of the exhaust inlet (71b) can be increased. The amount of inflow can be reduced. For this reason, even when the temperature of the exhaust (10) is low, the mixture of the combustible gas (7) and the exhaust (10) passes through the oxidation catalyst (12) while maintaining a relatively high temperature. For this reason, the activation temperature of the oxidation catalyst (12) is ensured, and even when the temperature of the exhaust (10) is low, the combustible gas (7) can be reliably burned.

(Invention according to Claim 2)
In addition to the effect of the invention according to claim 1, the following effect is achieved.
<Effect> It is possible to reduce the exhaust passage resistance in the oxidation catalyst.
As illustrated in FIG. 2, when the exhaust inlet (71b) is arranged side by side on the nozzle peripheral wall (71a) from the exhaust upstream end of the nozzle peripheral wall (71a) toward the exhaust downstream end, the oxidation catalyst (12 ) Is gradually widened from the exhaust upstream side toward the exhaust downstream side, so that the oxidation catalyst (12) increases in accordance with the exhaust passage amount that increases as it approaches the exhaust downstream side from the exhaust upstream side of the oxidation catalyst (12). The passage sectional area of 12) can be gradually increased, and the passage resistance of the exhaust (10) in the oxidation catalyst (12) can be reduced.

(Invention according to claim 3)
In addition to the effect of the invention according to claim 1 or claim 2, the following effect is achieved.
<Effect> Burnout of the oxidation catalyst can be prevented.
As the oxidation catalyst (12), a metal carrier having a three-dimensional network structure on which a catalyst component is supported is used. Therefore, flame combustion in the oxidation catalyst (12) is suppressed by the flame extinguishing function of the carrier, and the oxidation catalyst. Burnout can be prevented.

(Invention of Claim 4)
In addition to the effects of the invention according to any one of claims 1 to 3, the following effects are provided.
<Effect> Even when the exhaust gas temperature is low, the combustible gas can be burned.
As illustrated in FIG. 2, the oxidation catalyst (12) is disposed in the exhaust pipe (1b), and the exhaust pipe (1b) is surrounded by the cylindrical gas generator (3) from the periphery thereof. Even when the activation temperature of 12) is ensured and the exhaust temperature is low, the combustible gas (7) can be combusted.

<Effect> The oxidation catalyst is hardly damaged.
As illustrated in FIG. 2, the oxidation catalyst (12) is disposed in the exhaust pipe (1b), and the exhaust pipe (1b) is surrounded by the cylindrical gas generator (3) from the periphery thereof. 12) is double protected by the exhaust pipe (1b) and the gas generator (3), and the oxidation catalyst (12) is hardly damaged.

<Effect> The exhaust device can be made compact.
As illustrated in FIG. 2, the oxidation catalyst (12) is disposed in the exhaust pipe (1b), and the exhaust pipe (1b) is surrounded by a cylindrical gas generator (3) from the periphery thereof. It can be made compact.

(Invention according to claim 5)
In addition to the effect of the invention according to claim 4, the following effect is achieved.
<< Effect >> Overheating of the gas generator (3) can be suppressed.
As illustrated in FIG. 1, since the gas generator (3) is surrounded by a cylindrical air introduction passage (72) from its periphery, the gas generator (3) can be air-cooled from its periphery, Overheating of the vessel (3) can be suppressed.

<Effect> The gas generator is hardly damaged.
As illustrated in FIG. 2, since the gas generator (3) is surrounded by a cylindrical air introduction passage (72) from the periphery thereof, the gas generator (3) is protected by the cylindrical air introduction passage (72). Therefore, the gas generator (3) is hardly damaged.

<Effect> The exhaust device can be made compact.
As illustrated in FIG. 2, since the gas generator (3) is surrounded by the cylindrical air introduction passage (72) from its periphery, the exhaust device can be made compact.

(Invention of Claim 6)
In addition to the effects of the invention according to any one of claims 1 to 5, the following effects are provided.
<Effect> Can be manufactured at low cost.
As illustrated in FIG. 1, when the fuel from the fuel tank (5a) of the diesel engine is used as the liquid fuel (6) and air (44) is mixed into the liquid fuel (6), excess air is used as the air (44). Since the air from the charger (39) is used, the fuel tank (5a) of the diesel engine with a supercharger and the supercharger (39) are connected to the fuel supply source and the air supply source of the gas generator (3). And can be manufactured at low cost.

(Invention of Claim 7)
In addition to the effects of the invention according to any one of claims 1 to 6, the following effects are provided.
<Effect> The combustion heat of the combustible gas can be stably obtained.
By vaporizing the liquid fuel (6) with the gas generator (3), this liquid fuel (6) is made into a combustible gas (7). Compared to reactions such as partial oxidation, combustible gas There is little fluctuation in the component ratio of (7), and the combustion heat of the combustible gas (7) can be obtained stably.

(Invention of Claim 8)
In addition to the effects of the invention according to any one of claims 1 to 6, the following effects are provided.
<Effect> Even when the exhaust gas temperature is low, the combustible gas can be burned.
Since the liquid fuel (6) is partially oxidized by the gas generator (3), the liquid fuel (6) is reformed into a combustible gas (7) containing carbon monoxide and hydrogen. Even when the gas (7) is ignited at a relatively low temperature and the temperature of the exhaust (10) is low, the combustible gas (7) can be combusted.

  Embodiments of the present invention will be described with reference to the drawings. 1 and 2 are diagrams illustrating an exhaust device for a diesel engine according to an embodiment of the present invention.

The outline of the embodiment of the present invention is as follows.
As shown in FIG. 1, the liquid fuel (6) is supplied from the liquid fuel supply source (5) to the gas generator (3), and the liquid fuel (6) is supplied to the combustible gas (7) by the gas generator (3). The combustible gas outlet (9) of the gas generator (3) is provided in the exhaust passage (1) upstream of the diesel particulate filter (2), and is connected to the combustible gas outlet (9). The combustible gas (7) that has flowed out is burned with oxygen in the exhaust (10), and the exhaust (10) heated by the combustion heat can be used to burn the exhaust particulate accumulated in the filter (2). I have to. This exhaust system is connected to the exhaust outlet (36) of the exhaust manifold of the diesel engine. The diesel particulate filter (2) is generally called a DPF and is a ceramic honeycomb structure. The diesel particulate filter (2) carries an oxidation catalyst. The filter (2) may be supported on the NO _X storing catalyst.

  As shown in FIG. 1, an oxidation catalyst (12) is disposed upstream of the inlet (2a) of the filter (2) in the exhaust path (1) and heated by an exothermic reaction in the gas generator (3). When the combustible gas (7) is combined with the exhaust gas (10) in the oxidation catalyst (12) and the combustion of the combustible gas (7) is promoted, the oxidation catalyst (12) is used as shown in FIG. A combustible gas outlet (9) is provided on the surrounding exhaust path peripheral wall (1a), an exhaust introduction nozzle (71) is disposed upstream of the oxidation catalyst (12), and a cylindrical shape is formed on the exhaust introduction nozzle (71). A nozzle peripheral wall (71a) is provided, the nozzle peripheral wall (71a) is surrounded by the oxidation catalyst (12), a plurality of exhaust inlets (71b) are provided in the nozzle peripheral wall (71a), and the exhaust catalyst downstream of the oxidation catalyst (12) is provided. An exhaust outlet (12a) is provided.

  As shown in FIG. 2, when the exhaust inlet (71b) is arranged side by side on the nozzle peripheral wall (71a) from the exhaust upstream end of the nozzle peripheral wall (71a) to the exhaust downstream end, the nozzle peripheral wall (71a) By gradually reducing the diameter of the nozzle peripheral wall (71a) from the exhaust upstream end to the exhaust downstream end, the cross-sectional area of the oxidation catalyst (12) gradually increases from the exhaust upstream to the exhaust downstream. It is trying to spread. The exhaust downstream end of the exhaust introduction nozzle (71) is closed, and the exhaust introduction nozzle (71) has a shape in which the cup is turned down. A plurality of combustible gas outlets (9) are formed at predetermined intervals in the circumferential direction of the exhaust passage peripheral wall (1a). A plurality of exhaust inlets (71b) are also formed at predetermined intervals in the circumferential direction of the cylindrical peripheral wall (71a) of the truncated cone. Such annular rows of the exhaust inlets (71a) are arranged in a plurality of rows from the exhaust upstream end of the nozzle peripheral wall (71a) toward the exhaust downstream end.

The configuration of the oxidation catalyst is as follows.
As the oxidation catalyst (12), a catalyst in which a catalyst component is supported on a metal carrier having a three-dimensional network structure is used. Specifically, foam metal (Metal Form) is used for the carrier of the oxidation catalyst (12). The foam metal is a porous metal body having the same three-dimensional network structure as a resin foam represented by sponge. A foam metal is obtained by a well-known manufacturing method. For example, it can be obtained by using a polyurethane foam having a three-dimensional network skeleton as a base material, subjecting the base material to electroconductivity, applying electroplating, removing the base material by thermal decomposition, and leaving a metal three-dimensional network skeleton. . The catalyst (12) carrier may be made of stainless steel and generally called a wire mesh.

The configuration of the gas generator (3) is as follows.
As shown in FIG. 2, the gas generator (3) is composed of an upper mixer (73) and a lower catalyst chamber (51). The mixer (73) generates liquid fuel (6) and air (44). The gap (74) is supplied, the liquid fuel (6) and the air (44) are mixed in the gap (74), and the air-fuel mixture is supplied from the gap (74) to the catalyst chamber (51). Fuel from the fuel tank (5a) of the diesel engine is used as the liquid fuel (6), and air (44) from the supercharger (39) is used as the air (44). An oxidation catalyst (12) is arranged in the exhaust pipe (1b), the exhaust pipe (1b) is surrounded by a cylindrical gas generator (3) from the periphery thereof, and the gas generator (3) is formed in a cylindrical shape from the periphery thereof. It is surrounded by an air introduction passage (72). An electric heater (75) is disposed in the air introduction passage (72) so that the air (44) can be heated.

The structure for supplying fuel or the like to the gas generator is as follows.
As shown in FIG. 1, a liquid fuel valve (40) is provided in the liquid fuel supply passage (46), an air valve (41) is provided in the air supply passage (38), and each valve (40) (41) is connected to a controller ( 42) through the back pressure sensor (43). When exhaust particulates accumulate in the filter (2), the back pressure rises. Based on the detection by the back pressure sensor (43), the controller (42) connects the liquid fuel valve (40) and the air. By opening the valve (41), supplying liquid fuel (6) and air (44) to the gas generator (3), and vaporizing the liquid fuel (6) with the gas generator (3), The liquid fuel (6) is used as a combustible gas (7), and the combustible gas (7) is supplied into the exhaust path (1).

  The catalyst (51a) in the catalyst chamber (51) is an oxidation catalyst, which oxidizes a part of the liquid fuel (6) and vaporizes the remaining liquid fuel (6) with its oxidation heat. As the catalyst (51a), a metal carrier having a three-dimensional network structure and a platinum catalyst component supported thereon is used. Specifically, a foam metal (Metal Form) is used for the support of the catalyst (51a). Metal pellets such as alumina pellets may be used as the carrier for the catalyst (51a). The mixing ratio of the air (44) and the liquid fuel (6), that is, the air-fuel ratio O / C is set in the range of 0.4 to 0.8, which is around 0.6. When the catalyst (51a) is a carrier having a flame extinguishing function, such as a metal carrier having a three-dimensional network structure, burning of the catalyst (51a) can be prevented.

  In this embodiment, the liquid fuel (6) is made into a combustible gas (7) by vaporizing the liquid fuel (6) with the gas generator (3). The liquid fuel (6) may be reformed into a combustible gas (7) containing carbon monoxide and hydrogen by partially oxidizing 6). In this case, a partial oxidation catalyst is used instead of the oxidation catalyst as the catalyst (51a) in the catalyst chamber (51). As the carrier for the partial oxidation catalyst, a metal carrier having a three-dimensional network structure on which a catalyst component made of palladium or rhodium is supported may be used. In addition, metal pellets such as alumina pellets may be used. The mixing ratio of the air (44) and the liquid fuel (6), that is, the air-fuel ratio O / C is set to a range of 1.0 to 1.6, which is around 1.3.

The specific configuration of the filter housing case is as follows.
As shown in FIG. 1, a cylindrical filter storage case (11) provided with end walls (17) and (18) at both ends is used, and the axial length direction of the filter storage case (11) is defined as the front-rear direction. 2) The front side of the inlet (2a) and the rear side of the outlet (2b) are the rear, and the exhaust inlet chamber (19) is placed in front of the filter (2) in the filter housing case (11), and the rear of the filter (2). An exhaust outlet chamber (20) is provided, and an exhaust inlet pipe (21) is connected to the exhaust inlet chamber (19), and an exhaust outlet pipe (22) is connected to the exhaust outlet chamber (20).
The exhaust inlet pipe (21) is inserted into the exhaust inlet chamber (19) along the radial direction of the filter housing case (11), and the exhaust inlet pipe (21) and the exhaust outlet (36) of the exhaust manifold are connected. An exhaust pipe (1b) is provided therebetween, and the oxidation catalyst (12) is accommodated in the exhaust pipe (1b).

  An exhaust muffler (28) is used as the filter housing case (11), the exhaust inlet chamber (19) is constituted by the first expansion chamber (29), and the exhaust outlet chamber (20) is constituted by the final expansion chamber (30). The exhaust inlet pipe (21) is constituted by the exhaust introduction pipe (31) of the first expansion chamber (29), and the exhaust outlet pipe (22) is constituted by the exhaust outlet pipe (32) of the final expansion chamber (30). .

The generation and function of the combustible gas is as follows.
As shown in FIG. 2, when the liquid fuel (6) and the air (44) are supplied to the gas generator (3), the liquid fuel (6) is mixed with the air (44) in the gap (74). The liquid fuel (6) is atomized and flows into the catalyst chamber (51) from the gap (74). A part of the liquid fuel (6) is oxidized (catalytic combustion) in the catalyst chamber (51), and the remaining liquid fuel (6) is vaporized by the oxidation heat (combustion), and the high-temperature combustible gas (7). It becomes. Hot combustible gas (7) is supplied into the oxidation catalyst (12) from the combustible gas outlet (9). On the other hand, the exhaust gas (10) passing through the exhaust path (1) flows into the oxidation catalyst (12) from the exhaust inlet (71b), and is mixed with the high temperature combustible gas (7). Pass through. The combustible gas (7) is oxidized (combusted) by oxygen in the mixed exhaust (10), and the mixed exhaust (10) is heated by the oxidation heat (combustion heat).

  As shown in FIG. 1, the exhaust (10) flows out from the oxidation catalyst (12) as indicated by an arrow (60), and further flows out from the outlet hole (47) of the exhaust introduction pipe (31), and the first expansion chamber. After flowing into (29), it flows into the filter (2) from its inlet (2a) as shown by the arrow (62) and passes through the filter (2). Exhaust gas that has passed through the filter (2) flows into the final expansion chamber (30) from the outlet (2b) of the filter (2) as indicated by an arrow (63), and then enters the inlet hole ( 48) flows into the exhaust introduction pipe (32) and flows out from the exhaust outlet pipe (32) as indicated by an arrow (64).

1 is a longitudinal sectional view of an exhaust device for a diesel engine according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view of an oxidation catalyst of the exhaust device of FIG. 1 and its surroundings.

Explanation of symbols

(1) Exhaust route
(1a) Exhaust path wall
(1b) Exhaust pipe
(2) Diesel particulate filter
(3) Gas generator
(5) Liquid fuel supply source
(5a) Fuel tank
(6) Liquid fuel
(7) Combustible gas
(9) Combustible gas outlet
(10) Exhaust
(12) Oxidation catalyst
(12a) Exhaust outlet
(44) Air
(71) Exhaust introduction nozzle
(71a) Nozzle wall
(71b) Exhaust inlet
(72) Air introduction path

Claims (8)

The liquid fuel (6) is supplied from the liquid fuel supply source (5) to the gas generator (3). The gas generator (3) converts the liquid fuel (6) into a combustible gas (7). The combustible gas outlet (9) of (3) is provided in the exhaust passage (1) upstream of the diesel particulate filter (2), and the combustible gas (7) flowing out of the combustible gas outlet (9) ) Is combusted with oxygen in the exhaust gas (10), and exhaust gas accumulated in the filter (2) can be combusted by the exhaust gas (10) heated by the combustion heat. In the device
An oxidation catalyst (12) is disposed upstream of the filter (2) in the exhaust path (1), and the combustible gas (7) heated by an exothermic reaction in the gas generator (3) is converted into an oxidation catalyst ( 12) In merging with the exhaust (10) and promoting the combustion of the combustible gas (7),
A combustible gas outlet (9) is provided on the exhaust passage peripheral wall (1a) surrounding the oxidation catalyst (12), and an exhaust introduction nozzle (71) is disposed upstream of the oxidation catalyst (12), and the exhaust introduction nozzle ( 71) is provided with a cylindrical nozzle peripheral wall (71a), the nozzle peripheral wall (71a) is surrounded by an oxidation catalyst (12), a plurality of exhaust inlets (71b) are provided in the nozzle peripheral wall (71a), and an oxidation catalyst (12 An exhaust system for a diesel engine, characterized in that an exhaust outlet (12a) is provided downstream of the exhaust gas. The exhaust system for a diesel engine according to claim 1,
In arranging the exhaust inlet (71b) side by side on the nozzle peripheral wall (71a) from the exhaust upstream end of the nozzle peripheral wall (71a) to the exhaust downstream end,
By gradually decreasing the diameter of the nozzle peripheral wall (71a) from the exhaust upstream end of the nozzle peripheral wall (71a) to the exhaust downstream end, the cross-sectional area of the oxidation catalyst (12) is reduced from the exhaust upstream side to the exhaust downstream side. An exhaust system for a diesel engine, characterized in that it gradually expands as it approaches the side. The exhaust system for a diesel engine according to claim 1 or 2,
An exhaust device for a diesel engine, characterized in that a catalyst component is supported on a metal carrier having a three-dimensional network structure as the oxidation catalyst (12). In the exhaust device of the diesel engine according to any one of claims 1 to 3,
An exhaust system for a diesel engine, characterized in that an oxidation catalyst (12) is disposed in an exhaust pipe (1b), and the exhaust pipe (1b) is surrounded by a cylindrical gas generator (3) from its periphery. The exhaust system for a diesel engine according to claim 4,
In mixing air (44) into liquid fuel (6),
An exhaust system for a diesel engine, characterized in that the gas generator (3) is surrounded by a cylindrical air introduction passage (72) from its periphery. The exhaust system for a diesel engine according to any one of claims 1 to 5,
In using the fuel from the fuel tank (5a) of the diesel engine as the liquid fuel (6) and mixing the air (44) into the liquid fuel (6),
An exhaust system for a diesel engine, characterized in that air (44) from a supercharger (35) is used as the air (44). The exhaust system for a diesel engine according to any one of claims 1 to 6,
An exhaust system for a diesel engine, characterized in that the liquid fuel (6) is made into a combustible gas (7) by vaporizing the liquid fuel (6) with the gas generator (3). The exhaust system for a diesel engine according to any one of claims 1 to 6,
By partially oxidizing the liquid fuel (6) with the gas generator (3), the liquid fuel (6) is reformed into a combustible gas (7) containing carbon monoxide and hydrogen. Diesel engine exhaust system characterized.

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