US20070289289A1

US20070289289A1 - Exhaust emission purifier with additive feeder unit and pressurized air introducer unit

Info

Publication number: US20070289289A1
Application number: US11/797,959
Authority: US
Inventors: Akikazu Kojima; Syoichi Yokoyama
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2006-06-16
Filing date: 2007-05-09
Publication date: 2007-12-20
Also published as: JP2007332901A; DE102007000333B4; FR2902456B1; JP4280934B2; FR2902456A1; DE102007000333A1

Abstract

An exhaust emission purifier includes a purification unit provided in an exhaust system of an engine for purifying exhaust gases. The exhaust emission purifier also includes an additive feeder unit operatively coupled to the exhaust system at a position between the internal combustion engine and the purification unit for providing an additive to the exhaust gases. Furthermore, the exhaust emission purifier includes a pressurized air introducer unit for receiving air pressurized by an air compressor unit, which is driven by the exhaust gases flowing in the exhaust system and compresses intake air flowing in an intake system of the internal combustion engine. The pressurized air introducer unit is operatively coupled to the additive feeder unit for providing the air pressurized by the air compressor unit to the additive feeder unit.

Description

CROSS REFERENCE TO RELATED APPLICATION

The following is based on and claims priority to Japanese Patent Application No. 2006-167126, filed Jun. 16, 2006, which is hereby incorporated reference in its entirety.

FIELD

The following relates generally to an exhaust emission purifier and, more specifically, to an exhaust emission purifier with an additive feeder unit and a pressurized air introducer unit.

BACKGROUND

It is known to provide an internal combustion engine such as a diesel engine with a purification unit such as a diesel particulate filter (hereinafter referred to as “DPF”) and a NOx reduction catalyst. For example, the purification unit feeds fuel, urea, or the like as an additive in order to regenerate the purification unit or to trigger a catalytic oxidation-reduction reaction. Examples of this purification device are disclosed in JP-2004-011463A and JP-2004-308526A. The additive is ejected into the exhaust gases flowing in the exhaust system to be delivered to the purification unit. The additive is fed in a fine spray form for promotion of the regeneration and the reaction in the purification unit. For this purpose, the additive is fed using high-pressure air from the additive feeder so that the atomization of the additive is promoted.
Typically, larger vehicles such as trucks include a high-pressure air supply source such as a mechanical compressor which is structured independently of the internal combustion engine. However, for smaller vehicles such as a passenger car, there may not be enough space to accommodate the high-pressure air supply source.
In view of the above, there exists a need for an exhaust emission purifier with an additive feeder and a pressurized air introducer unit for an internal combustion engine which overcome the above mentioned problems in the conventional art. The following addresses this need as well as other needs as will become apparent to those skilled in the art from this disclosure.

SUMMARY

An exhaust emission purifier is disclosed that includes a purification unit provided in an exhaust system of an internal combustion engine for purifying exhaust gases flowing in the exhaust system. The exhaust emission purifier also includes an additive feeder unit operatively coupled to the exhaust system at a position between the internal combustion engine and the purification unit for providing an additive to the exhaust gases flowing in the exhaust system. Furthermore, the exhaust emission purifier includes a pressurized air introducer unit for receiving air pressurized by an air compressor unit, which is driven by the exhaust gases flowing in the exhaust system and compresses intake air flowing in an intake system of the internal combustion engine. The pressurized air introducer unit is operatively coupled to the additive feeder unit for providing the air pressurized by the air compressor unit to the additive feeder unit.
An additive feeder is disclosed for providing an additive to a purification unit of an exhaust system of an internal combustion engine. The additive feeder included an additive injection valve operatively coupled to the exhaust system at a position between the internal combustion engine and the purification unit. The additive injection valve injects the additive into exhaust gases flowing in the exhaust system. A pressurized air introducer unit is further included for receiving air pressurized by an air compressor unit, which is driven by the exhaust gases flowing in the exhaust system and compresses intake air flowing in an intake system of the internal combustion engine. The pressurized air introducer unit is operatively coupled to the additive injection valve for providing the air pressurized by the air compressor unit to the additive injection valve.
An exhaust purification system is disclosed for an internal combustion engine that includes a purification unit provided in an exhaust system of an internal combustion engine for purifying exhaust gases flowing in the exhaust system. The exhaust purification system also includes an additive feeder unit operatively coupled to the exhaust system at a position between the internal combustion engine and the purification unit for providing an additive to the exhaust gases flowing in the exhaust system. Furthermore, an air compressor unit is included with a turbine provided in the exhaust system and driven by the exhaust gases flowing in the exhaust system. The air compressor unit further includes a compressor provided in an intake system of the internal combustion engine and driven by the turbine. The compressor pressurizes intake air flowing in the intake system. Moreover, the exhaust purification system includes a pressurized air introducer unit for receiving air pressurized by the air compressor unit and is operatively coupled to the additive feeder unit for providing the air pressurized by the air compressor unit to the additive feeder unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a schematic diagram illustrating an exhaust purification system according to a first embodiment;

FIG. 2 is a graph showing the relationship between the pressure of air supplied to an additive injection valve and the drop-diameter of a droplet of the injected additive;

FIG. 3 is a schematic diagram illustrating an exhaust purification system according to a second embodiment;

FIG. 4 is a graph illustrating the relationship between the boost pressure, and the engine rotational speed and output torque;

FIG. 5A is a graph showing the change in the amount of absorption of NOx absorbed in the NOx reduction catalyst during the engine operation period;

FIG. 5B is a graph showing the change in boost pressure during the engine operation period and the change in supply pressure of the air supplied to the additive injection valve;

FIG. 6 is a schematic diagram illustrating an exhaust purification system according to a third embodiment; and

FIG. 7 is a schematic diagram illustrating an exhaust purification system according to a fourth embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments according to the present disclosure will be described below with reference to the accompanying drawings. In these embodiments, structural components that are substantially the same are designated by the same reference numerals and repetitive description is omitted.

First Embodiment

FIG. 1 is an exhaust purification system for an internal combustion engine to which an exhaust emission purifier according to a first embodiment is applied. As illustrated in FIG. 1, the exhaust purification system 10 of the first embodiment purifies the exhaust gases emitted from a diesel engine 11 (hereinafter referred to as “engine”) serving as an internal combustion engine. The exhaust purification system 10 is equipped with a purification unit 20, an additive feeder unit (32), an air compressor unit (e.g., a turbocharger 40), and a pressurized air introducer unit 50. The engine 11 includes an exhaust system 60 and an intake system 70.
The exhaust system 60 guides exhaust gases from the engine 11 to an area outside of the engine 11. The exhaust system 60 has an exhaust pipe 61 that forms an exhaust passage 62. The exhaust gases emitted from the engine 11 flow through the exhaust passage 62 to the outside. The exhaust passage 62 defined by the exhaust pipe 61 is fluidly coupled to the engine 11 and an exhaust port 63. The purification unit 20 provided in the exhaust system and is operatively coupled to the exhaust pipe 61. Specifically, the purification unit 20 is disposed between the engine 11 and the exhaust port 63 in the exhaust system 60.
The intake system 70 supplies intake air to the engine 11 from an area outside the engine 11. The intake system 70 has an intake pipe 71 that defines an intake passage 72. The intake air introduced from an intake port 73 flows through an intake passage 72 into the engine 11. The intake passage 72 defined by the intake pipe 71 is fluidly coupled to the intake port 73 and the engine 11. A throttle 74 is disposed in the intake passage 72 for adjusting a flow rate of the intake air.
The purification unit 20 is disposed in the exhaust system 60. In the embodiment shown, the purification unit 20 has a DPE 21, a NOx reduction catalyst 22 and an oxidation catalyst 23. The DPE 21 collects particulate matter (PM) included in the exhaust gases. The NOx reduction catalyst 22 reduces NOx included in the exhaust gases in cooperation with, for example, fuel, such as light oil, and urea as the additive. As a result, the NOx included in the exhaust gases is reduced to N₂, CO₂, and H₂O which are less harmful. The oxidation catalyst 23 oxidizes PM included in the exhaust gases. The first embodiment describes an example of the purification unit 20 provided with the DPF 21, the NOx reduction catalyst 22 and the oxidation catalyst 23. However, it will be appreciated that any suitable purification unit 20 may be provided. For instance, in one embodiment, the NOx reduction catalyst 22 and either the DPF 21 or the oxidation catalyst 23 is provided. In another embodiment, the purification unit 20 is provided with a filter and a catalyst in place of the DPF 21, the NOx reduction catalyst 22, or the oxidation catalyst 23 which are exemplified above.
The additive feeder unit 32 is operatively coupled to the exhaust system 60 at a position between the engine 11 and the purification unit 20 for providing an additive to the exhaust gases flowing in the exhaust system 60. In the embodiment shown, the additive feeder unit 32 includes an additive injection valve 30 that is in fluid communication with the exhaust system 60 between the engine 11 and the purification unit 20. In other words, the injection valve 30 is closer to the engine 11 than the distance between the purification unit 20 and the engine 11.
As will be described below, air from the pressurized air introducer unit 50 allows the injection valve 30 to feed additive into the exhaust system 60. The additive injection valve 30 injects the additive into the exhaust gases flowing in the exhaust passage 62. The additive comprises substances performing the functions of the DPF 21, the NOx reduction catalyst 22 and the oxidation catalyst 23 of the purification unit 20.
For example, the DPF 21 collects the PM included in the exhaust gases. Therefore, when the DPF 21 collects more than a predetermined amount of PM, the DPF 21 can become clogged, resulting in a reduction in function of the DPF 21. To avoid this, the additive injection valve 30 injects, for example, fuel such as light oil as the additive, to burn off the PM collected by the DPF 21. As a result, the clogging of the DPF 21 is reduced, so that the DPF 21 is regenerated.
Also, the NOx reduction catalyst 22 absorbs the NOx included in the exhaust gases. Therefore, when the NOx reduction catalyst 22 absorbs more than a predetermined amount of NOx, the absorption capacity is saturated, resulting in a reduction in function of the NOx reduction catalyst 22. To avoid this, the additive injection valve 30 injects, for example, fuel such as light oil or urea which is an additive serving as a reducer, to thereby reduce the NOx absorbed in the NOx reduction catalyst 22. As a result, the NOx reduction catalyst 22 is regenerated.
Moreover, the oxidation catalyst 23 burns off the PM included in the exhaust gases. Therefore, fuel is required to burn off the PM. For this purpose, the additive injection valve 30 injects, for example, fuel such as light oil as the additive, so that the PM is burned off in the oxidation catalyst 23. As a result, the PM included in the exhaust gases burns, resulting in a reduction in exhaust emission to the outside.
In this manner, by feeding the additive from the additive injection valve 30 to the purification unit 20, the DPF 21, the NOx reduction catalyst 22 and the oxidation catalyst 23 constituting the purification unit 20 perform their functions.
The additive injection vale 30 injects light oil which is the fuel for the engine 11, urea and/or the like as the additive as described above into the exhaust gases flowing in the exhaust passage 62. For this purpose, the additive injection valve 30 is connected to an additive tank 31 such as a fuel tank. The additive is supplied from the additive tank 31 to the additive injection valve 30.
The turbocharger 40 has a turbine 41 disposed in the exhaust system 60, and a compressor 42 disposed in the intake system 70. The turbine 41 is disposed in the exhaust passage 62 between the engine 11 and the additive injection valve 30. In other words, the turbine 41 is closer to the engine 11 than the distance between the injection valve 30 and the engine 11. The compressor 42 is disposed in the intake passage 72 between the intake port 73 and the throttle 74. In other words, the compressor 42 is closer to the intake port 73 than the distance between the intake port 73 and the throttle 74.
The turbine 41 is rotatably driven by the high-pressure exhaust gases flowing in the exhaust passage 62. The turbine 41 and the compressor 42 are rotatably coupled to each other by a shaft 43. For this reason, when the turbine 41 is driven by the flow of the exhaust gases, the compressor 42 is rotated together with the turbine 41. This allows the compressor 42 to pressurize and transport the air flowing in the intake passage 72 toward the engine 11. As a result, the intake air is compressed and sent to the engine 11.
The pressurized air introducer 50 is fluidly and operatively coupled to the intake system 70 and the additive injection valve 30. One end of the pressurized air introducer 50 is fluidly coupled to the intake system 70 at a position between the engine 11 and the compressor 42. In other words, this end of the pressurized air introducer 50 is closer to the engine 11 than the distance between the compressor 42 and the engine 11. The other end of the pressurized air introducer 50 is fluidly coupled to the additive injection valve 30, which injects the additive into the exhaust passage 62. As such, the compressor 42 pressurizes air in the intake passage 72, the pressurized air introducer 50 receives at least a portion of the air pressurized by the compressor 42, and the pressurized air introducer 50 delivers the pressurized air to the additive injection valve 30. Then, the additive injection valve 30 injects the additive into the exhaust system 50 along with the high-pressure air introduced from the pressurized air introducer 50. As a result, the additive ejected from the additive injection valve 30 is formed into a fine spray at least partly due to injection of the high-pressure air introduced from the pressurized air introducer 50.
The additive ejected from the additive injection valve 30 has preferably a smaller drop-diameter, in order for the additive to promote the regeneration of and the burning in the purification unit 20 so that the purification unit 20 can perform its function. As shown in FIG. 2, the additive ejected from the additive injection valve 30, after forming into the fine spray, has droplets which become smaller in drop-diameter with the increase in the pressure of the air injected together with the additive from the additive injection valve 30. In other words, when the additive is ejected from the additive injection valve 30, the ejection of the additive along with the high-pressure air decreases the drop-diameter of the droplets of the ejected additive. As a result, the regeneration of and the burning in the purification unit 20 is promoted to enable the purification unit 20 to perform its function more effectively.
In this manner, in the first embodiment, highly pressurized air is introduced to the additive injection valve 30 from a position between the compressor 42 of the turbocharger 40. Thereby, when the additive is ejected from the additive injection valve 30, the high-pressure air is ejected along with the additive. This decreases the drop-diameter of the droplets of the additive ejected from the additive injection valve 30 to promote the formation into a fine spray and the reduction in drop-diameter of the additive. As a consequence, it is possible to exert the function of the purification unit 20 with high effectiveness and precision, and therefore to reduce the substances, such as PM and NOx, included in the exhaust gases.
Furthermore, in the case of the engine 11 equipped with the turbocharger 40, the high-pressure air can be provided to the injection valve 30 even without an additional high-pressure air supply source, such as a mechanical compressor, for example. Thus, a large sized high-pressure air supply source is not required, resulting in reduction of the spatial constraints of the system.

Second Embodiment

FIG. 3 illustrates an exhaust purification system according to a second embodiment. In the second embodiment shown in FIG. 3, the pressurized air introducer 50 of the exhaust purification system 10 has a check valve 51. In the embodiment shown, the check valve 51 is disposed at the end of the pressurized air introducer 50 adjacent to the intake system 70. The check valve 51 permits the flow of air through the pressurized air introducer 50 from the intake passage 72 to the additive injection valve 30. Also, the check valve 51 blocks the flow of air through the pressurized air introducer 50 from the additive injection valve 30 generally toward the intake passage 72. That is, the check valve 51 opens when the pressure in the intake passage 72 exceeds the pressure in the pressurized air introducer 50 adjacent the additive injection valve 30 and closes when the pressure in the intake passage 72 is lower than the pressure in the pressurized air introducer 50 adjacent the additive injection valve 30. By providing the check valve 51, the most highly pressurized air produced in the intake passage 72 is stored in the pressurized air introducer 50 from a point when the check valve 51 closes to a point when the additive injection valve 30 injects the additive. The check valve 51 is preferably disposed closer to a boost-pressure inlet port of the piping connecting between the additive injection valve 30 and the intake passage 72. In other words, the check valve 51 is provided in a position as close as possible to the intake passage 72, so as to increase the volume for storing the high-pressure air as much as possible.
As illustrated in FIG. 4, the boost pressure produced by the turbocharger 40 is varied by the rotational speed and the output torque of the engine 11. Specifically, the higher the rotational speed of the engine 11 and the greater the output torque, the higher the boost pressure produced by the turbocharger 40. However, the operation conditions of the engine 11, that is, the rotational speed and the output torque, vary every moment. Because of this, as shown in FIG. 5B, the boost pressure also varies every moment in accordance with the operation conditions of the engine 11.
On the other hand, for example, the regeneration of the NOx reduction catalyst 22 is started at the time when the amount of stored NOx, which increases with increased operation time of the engine 11, reaches a predetermined upper limit value M as shown in FIG. 5A. At this point, if the boost pressure is reduced by the operation conditions of the engine 11 as shown by the broken line in FIG. 5B, the pressure of the air which is to be ejected together with the additive from the additive injection valve 30 may be possibly reduced.
To avoid this, the check valve 51 is provided. As a result, even when the boost pressure varies as shown by the broken line in FIG. 5B, the pressure in the pressurized air introducer 50, that is, the pressure supplied to the additive injection valve 30, is at the maximum value of the boost pressure as shown by the solid line in FIG. 5B. In other words, the maximum boost pressure which is produced from the time of the last injection of the additive to the time of the current injection of the additive is maintained as the supply pressure of the pressurized air in the pressurized air introducer 50. For this reason, when the regeneration of the NOx reduction catalyst 22 is required, even if a low boost pressure is produced by the turbocharger 40 in accordance with the operation conditions of the engine 11, the air maintained at the high-pressure in the pressurized air introducer 50 promotes the spray formation of the additive ejected from the additive injection valve 30.
In the second embodiment, by providing the check valve 51, the pressure of the air supplied from the pressurized air introducer 50 to the additive injection valve 30 is maintained at the maximum value produced in the intake passage 72 until the injection of the additive. This makes possible the constant supply of the high-pressure air to the additive injection valve 30 irrespective of the operation conditions of the engine 11, thus promoting the spray formation of the additive injected.
The check valve 51 may be placed in any position in the pressurized air between the intake passage 72 and the additive injection valve 30. However, if the check valve 51 is disposed at the end of the pressurize air introducer 50 adjoining the intake passage 72, the volume of the pressurized air introducer 50 is increased, thus increasing the capacity of the high-pressure air. In addition, the second embodiment has described the case when the NOx reduction catalyst 22 is regenerated, as an example, but likewise, the DPF 21 is regenerated when the amount of PM collected reaches a predetermined amount.

Third Embodiment

FIG. 6 illustrates an exhaust purification system according to a third embodiment. In the case of the third embodiment shown in FIG. 6, the pressurized air introducer 50 of the purification system 10 includes a reservoir 52. The reservoir 52 is disposed between the intake system 70 and the additive injection valve 30. More specifically, the reservoir 52 is disposed between the check valve 51 and the additive injection valve 30. The reservoir 52 has a greater axial cross sectional area than the other portions of the pressurized air introducer 50. Thus, the reservoir 52 is an air capacity portion for storing the air introduced into the pressurized air introducer 50. That is, the reservoir 52 stores the high-pressure air introduced into the pressurized air introducer 50.
When the high-pressure air is ejected along with the additive from the additive injection valve 30 for exerting the function of the purification unit 20, it is preferable that the high-pressure air is supplied continuously in accordance with the additive injection period. For this purpose, in the third embodiment, the reservoir 52 is provided for increasing the volume of the pressurized air introducer 50. Thus, the high-pressure air introduced from the intake passage 72 is stored in the reservoir 52 in addition to the pressurized air introducer 50. As a consequence, in the third embodiment, the high-pressure air stored in the reservoir 52 is supplied when the additive is ejected, to thereby continuously promote the atomization of the additive irrespective of the operation conditions of the engine 11.

Fourth Embodiment

FIG. 7 illustrates an exhaust purification system according to a fourth embodiment.
In the case of the fourth embodiment shown in FIG. 7, the pressurized air introducer 50 of the exhaust purification system 10 has a flow-rate control unit 53. The flow-rate control unit 53 blocks flow from the intake system 70 to the additive injection valve 30 when the rate of flow in the pressurized air introducer 50 exceeds a predetermined value. In other words, the flow-rate control unit 53 blocks introduction of the high-pressure air into the pressurized air introducer 50 when the flow rate of air supplied from the intake passage 72 to the pressurized air introducer 50 exceeds a predetermined value. Thus, the flow-rate control unit 53 is a flow limiter for controlling the flow rate of intake air from the intake passage 72 to the pressurized air introducer 50.
For example, if the pressurized air introducer 50 is damaged and an air leak occurs in the pressurized air introducer 50, the air introduced from the intake passage 72 is emitted from the pressurized air introducer 50 to the outside. For this reason, the intake air pressurized by the turbocharger 40 is not supplied to the engine 11, resulting in a reduction in boost pressure of the turbocharger 40. As a result, the engine 11 is unlikely to achieve a predetermined output.
To avoid this condition, in the fourth embodiment, when the flow rate of intake air introduced from the intake passage 72 to the pressurized air introducer 50 becomes excessively high, the air introduction is blocked. Thus, a reduction in boost pressure produced by the turbocharger 40 is less likely and the output of the engine 11 can be stably sustained.
While only the selected example embodiments have been chosen to illustrate the present disclosure, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made therein without departing from the scope of the disclosure as defined in the appended claims. Furthermore, the foregoing description of the example embodiments according to the present disclosure is provided for illustration only, and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents.

Claims

1. An exhaust emission purifier, comprising:

a purification unit provided in an exhaust system of an internal combustion engine for purifying exhaust gases flowing in the exhaust system;

an additive feeder unit operatively coupled to the exhaust system at a position between the internal combustion engine and the purification unit for providing an additive to the exhaust gases flowing in the exhaust system; and

a pressurized air introducer unit for receiving air pressurized by an air compressor unit, which is driven by the exhaust gases flowing in the exhaust system and compresses intake air flowing in an intake system of the internal combustion engine, wherein the pressurized air introducer unit is operatively coupled to the additive feeder unit for providing the air pressurized by the air compressor unit to the additive feeder unit.

2. An exhaust emission purifier according to claim 1, further comprising a check valve that permits flow through the pressurized air introducer unit from the intake system and blocks flow through the pressurized air introducer unit from the additive feeder unit generally toward the intake system.

3. An exhaust emission purifier according to claim 1, wherein the pressurized air introducer unit includes a reservoir provided between the intake system and the additive feeder unit for storing the air pressurized by the air compressor unit.

4. An exhaust emission purifier according to claim 1, wherein the pressurized air introducer unit includes a flow-rate control unit that blocks flow from the intake system to the additive feeder unit when a rate of flow in the pressurized air introducer unit exceeds a predetermined value.

5. An exhaust emission purifier according to claim 1, wherein the air compressor unit is a turbocharger.

6. An additive feeder for providing an additive to a purification unit of an exhaust system of an internal combustion engine, the additive feeder comprising:

an additive injection valve operatively coupled to the exhaust system at a position between the internal combustion engine and the purification unit, wherein the additive injection valve injects the additive into exhaust gases flowing in the exhaust system; and

a pressurized air introducer unit for receiving air pressurized by an air compressor unit, which is driven by the exhaust gases flowing in the exhaust system and compresses intake air flowing in an intake system of the internal combustion engine, wherein the pressurized air introducer unit is operatively coupled to the additive injection valve for providing the air pressurized by the air compressor unit to the additive injection valve.

7. An additive feeder according to claim 6, further comprising a check valve that permits flow through the pressurized air introducer unit from the intake system and blocks flow through the pressurized air introducer unit from the additive feeder valve generally toward the intake system.

8. An additive feeder according to claim 6, wherein the pressurized air introducer unit includes a reservoir provided between the intake system and the additive injection valve for storing the air pressurized by the air compressor unit.

9. An additive feeder according to claim 6, wherein the pressurized air introducer unit includes a flow-rate control unit that blocks flow from the intake system to the additive injection valve when a rate of flow in the pressurized air introducer unit exceeds a predetermined value.

10. An additive feeder according to claim 6, wherein the air compressor unit is a turbocharger.

11. An exhaust purification system for an internal combustion engine, comprising:

an additive feeder unit operatively coupled to the exhaust system at a position between the internal combustion engine and the purification unit for providing an additive to the exhaust gases flowing in the exhaust system;

an air compressor unit that includes a turbine provided in the exhaust system and driven by the exhaust gases flowing in the exhaust system, the air compressor unit further including a compressor provided in an intake system of the internal combustion engine and driven by the turbine, wherein the compressor pressurizes intake air flowing in the intake system; and

a pressurized air introducer unit for receiving air pressurized by the air compressor unit and is operatively coupled to the additive feeder unit for providing the air pressurized by the air compressor unit to the additive feeder unit.

12. An exhaust purification system for an internal combustion engine according to claim 11, further comprising a check valve that permits flow through the pressurized air introducer unit from the intake system and blocks flow through the pressurized air introducer unit from the additive feeder unit generally toward the intake system.

13. An exhaust purification system for an internal combustion engine according to claim 11, wherein the pressurized air introducer unit includes a reservoir provided between the intake system and the additive feeder unit for storing the air pressurized by the air compressor unit.

14. An exhaust purification system for an internal combustion engine according to claim 11, wherein the pressurized air introducer unit includes a flow-rate control unit that blocks flow from the intake system to the additive feeder unit when a rate of flow in the pressurized air introducer unit exceeds a predetermined value.

15. An exhaust purification system according to claim 11, wherein the air compressor unit is a turbocharger.