WO2008081153A1

WO2008081153A1 - Exhaust apparatus

Info

Publication number: WO2008081153A1
Application number: PCT/GB2006/004942
Authority: WO
Inventors: Colin Laurence White
Original assignee: Perkins Engines Company Limited
Priority date: 2006-12-28
Filing date: 2006-12-28
Publication date: 2008-07-10

Abstract

Exhaust apparatus (100) is disclosed comprising an inlet (101) for receiving input exhaust gas; a heater (105) adapted to heat part of the input exhaust gas with the remaining input exhaust gas bypassing the heater; a first catalyst stage (106) adapted to oxidise exhaust gas heate by the heater (105); a second catalyst stage (109) adapted to oxidise a mixture of the input exhaust gas which bypassed the heater (105) and exhaust gas oxidised by the first catalyst stage (106); and a particulate trap (110) adapted to trap particulates in exhaust gas output from the second catalyst stage (106).

Description

DESCRIPTION

EXHAUST APPARATUS

Field of Invention

This invention relates to exhaust apparatus with a heater, a catalyst stage and a particulate trap for treating exhaust gases from an internal combustion engine or the like, and to a corresponding method of treating exhaust gas.

Background to Invention EP1253300A1 discloses an exhaust gas cleaning device for an internal combustion engine having a particulate filter means and method of regenerating the filter means. Specifically, the device comprising a catalyst filter system comprising a catalyst for converting nitric oxide (NO) to nitrogen dioxide (NO2) and a filter in which particulates are filtered from the exhaust gas and burned whilst converting NO2 to NO.

EP1253300A1 further discloses providing a heater for heating the exhaust gas entering the catalyst filter system and a control unit which activates the heater when the exhaust gas temperature in the catalyst-filter system is less than the required temperature to convert NO to NO2.

However, a disadvantage of the arrangement disclosed in EP1253300A1 is the large amount of electrical energy consumed by the heater in heating the exhaust gas entering the catalyst filter system so as to ensure light off.

The current disclosure is aimed at overcoming some or ail of the disadvantages associated with the prior art. Summary of Invention in accordance with a first aspect of the present invention, there is provided exhaust apparatus including an inlet for receiving input exhaust gas; a heater adapted to heat a first portion of the input exhaust gas with a second portion of the input exhaust gas bypassing the heater; a first catalyst stage adapted to oxidise exhaust gas heated by the heater; a second catalyst stage adapted to oxidise a mixture of the first and second portions of the input exhaust gas; and a particulate trap adapted to trap particulates in exhaust gas output from the second catalyst stage.

In accordance with a second aspect of the present invention there is provided an internal combustion engine comprising an exhaust apparatus in accordance with the first aspect of the invention.

In accordance with a third aspect of the present invention, there is provided a method of treating exhaust gas, comprising: receiving input exhaust gas; heating a first portion of the exhaust gas to a temperature sufficient to induce catalytic light off; oxidising the first portion of the input exhaust gas in a first catalyst stage; mixing the first oxidised portion of the exhaust gas with a second non-oxidised portion of the exhaust gas, wherein the temperature of the mixture is a temperature sufficient to induce catalytic light off; oxidising the mixture of the first and second portions of the input exhaust gas in a second catalyst stage; and trapping particulates in the exhaust gas oxidised in the second catalyst stage.

Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings Brief Description of Drawings

The present invention will now be described, by way of example only, with reference to the following figures in which:

Fig. 1 is a section through a first embodiment of an exhaust according to the present invention;

Fig. 2 is a section through a second embodiment of an exhaust according to the present invention; and

Fig. 3 is a section through a third embodiment of an exhaust according to the present invention

Detailed Description

Referring to figure 1 , a first embodiment of an exhaust 100 includes an inlet pipe 101. Downstream of the inlet pipe 101 are further components of the exhaust 100 including a divergent section 102 which leads into a heater section 103, a first catalyst section 104 and a mixing section 107. A portion of the heater section 103 is electrically heated with a grid heater 105, whilst the first catalyst section 104 contains an oxidation catalyst 106. A baffle 108 is provided in the mixing section 107 downstream of the oxidation catalyst 106.

A second catalyst section 109 is provided downstream of the mixing section 107. This second catalyst section 109 has a further oxidation catalyst area which is larger than that located in the first catalyst section 104. The final component of the exhaust 100 is a particulate trap 110 located downstream of the second catalyst section 109. The particulate trap may be a regenerating particulate trap, for example any particulate filter design which generally removes particulates from a gas flow by trapping the particulates on a surface, such as a ceramic surface. For example, filters may comprise ceramic fibre, foam, membrane, sheet or pad devices. The filter may comprise at least one tubular cell defined by a porous ceramic wall, and most preferably comprises a plurality of such cells. Adjacent cells have alternate ends blocked off, so that the ceramic walls act as a filter surface in a conventional manner.

A second embodiment of the exhaust, generally designated 200, is shown in Figure 2. The exhaust 200 has an inlet pipe 201 which fluidly communicates with a split duct downstream thereof. The split duct divides exhaust gas flow between an outer duct 202 and an inner duct 203 located within the outer duct 202. Downstream of the outer duct 202 is a bypass duct 204 which leads into a mixing section 207. Located within the bypass 204 is a heater section 205 having an electrical grid heater, and a first catalyst section 206, both of which are in flow communication with the inner duct 203. The first catalyst section 206 is also in flow communication with the mixing section 207 located downstream. The mixing section 207 includes a baffle 208.

Downstream of the mixing section 207 is a connecting pipe 209 which connects the mixing section 207 with a divergent section 210. A second catalyst section 211 , which is of a larger area than the first catalyst section 206, is located downstream of the divergent section 210. A particulate trap 212 is located downstream of the second catalyst section 211.

A third embodiment of the exhaust, generally designated 300, is shown in Figure 3. The third embodiment is identical to the second embodiment described above, with the addition of a second bypass duct 302. The second bypass duct 302 is fluidly connected at one end to the inlet pipe 201 and at the other end to the connecting pipe 209. A control valve 301 controls flow into the second bypass duct 302 from the inlet pipe 201. Other arrangements of bypass ducts are possible, in order to ensure a proportion of the exhaust gas enters the heater section 103, 205. Industrial Applicability

In the first embodiment shown in Figure 1 , exhaust gas from a diesel engine (not shown) is received through the inlet pipe 101 and channelled into the divergent section 102. After the divergent section 102, the exhaust gas is then passed through the heater section 103 and the first catalyst section 104.

When an engine is idling, exhaust temperature will be between 100 and 15O⁰C. However, catalytic induced light off of an exhaust gas typically occurs at around 250⁰C. The grid heater 105 within the heater section 103 causes approximately 20% of the exhaust gas passing through the heater section 103 to be heated to approximately 250⁰C, at which catalytic induced light off occurs. It is to be understood that the proportion of exhaust gas heated by the heater section 103 may be more or less than 20%, for example in the ranges 10% to 40% or 15% to 30%, provided that the energy input to the heater section is sufficient to heat the proportion of exhaust gas to the temperature at which catalytic induced light off occurs.

The oxidation catalyst 106 located in the adjacent first catalyst section 104 exposes the flow of exhaust gas heated in the heater section 103 to catalyst, thereby causing light off and exothermic oxidation of that portion of the exhaust gas, preferably heating it to a temperature somewhere in the range 550°C-650°C.

Further downstream in the mixing section 107, hot exhaust gases oxidised in the first catalyst section 104 and cooler exhaust gases not previously heated or oxidised in the exhaust are mixed. The baffle 108 is provided to cause turbulent mixing. The combined temperature of the mixture in the mixing section 107 is approximately 250⁰C. When the mixture reaches the second catalyst section 109 further downstream, further light off and oxidation of the exhaust gas occurs, with the temperature of the mixture again rising to somewhere in the range 550°C-650°C.

Thereafter, the exhaust gas is passed through the particulate trap 110 which because of the high temperature of the exhaust gas entering the trap 110 is able to both function and regenerate efficiently.

In the embodiment of Figure 2, the exhaust 200 receives the exhaust gas via the inlet pipe 201 , and the exhaust gas is then channelled into the outer and inner ducts 202, 203. The outer duct 202 channels approximately 80% of the exhaust gas via the bypass 204 to the mixing section 207 downstream. The inner duct 203 channels the remaining 20% of the exhaust gas through the heater section 205 occupying the whole cross section of the inner duct 203, wherein all the exhaust gas in the inner duct is heated to approximately 250⁰C, at which catalytic induced light off occurs. Thereafter, the exhaust gas of the inner duct 203 is passed through the first catalyst section 206 causing exothermic oxidation of that portion of the exhaust gas and the raising of the temperature of that portion of the exhaust gas to somewhere in the range 550°C-650°C.

Exhaust gases from both ducts 202,203 mix in the mixing section 207, encouraged by the baffle 208 located adjacent the confluence of the ducts 202,203. The combined temperature of the mixture is approximately 25O⁰C, such that when the mixture reaches the second catalyst section

211 further downstream, further light off and oxidation of that portion of the exhaust gas occurs.

Prior to reaching the second catalyst section 211 , the exhaust gases output from the mixing section 207 are transported through the connecting pipe 209 and divergent section 210. In the second catalyst section 211 , the exhaust gas is oxidised, reaching a temperature in the range 55O⁰C- 65O⁰C, and thereafter passed through the particulate trap 212.

The control valve 301 and bypass 302 of the third embodiment shown in Figure 3 allows the exhaust gas flow through the heater and first catalyst sections 205,206 to be controlled. For example, with the valve 301 closed, approximately 30 to 40% of the exhaust flow could pass through the heater/first catalyst sections 205,206. Partially opening the valve 301 would reduce the flow through the heater/first catalyst sections 205,206. Opening the valve 301 fully, when the exhaust is above 250⁰C and the heater 205 is not needed, would reduce the restriction to exhaust flow and improve fuel consumption.

In order for a particulate trap, especially a regenerating particulate trap, to operate satisfactorily, it may be necessary to heat the input exhaust gases to ensure light off (especially when the exhaust gases are relatively cool when the exhaust apparatus is lightly loaded); and also that heating of all input exhaust gas is not required if a two stage catalyst is employed. Rather, the present invention makes it possible to heat only a portion of the input exhaust gas to ensure satisfactory operation of a particulate trap and regeneration of the same. By avoiding having to heat all of the input exhaust gas, the invention also ensures a reduction in back-pressure within the exhaust.

In the context of a vehicle with such exhaust apparatus, such a heater would be typically powered by battery and/or an alternator and the present invention would reduce the load on such a battery and/or alternator. Whilst this embodiment uses electrical heating, it is conceivable that such heating could be done by burning additional fuel, requiring a fuel injector and/or igniter. The fuel may be injected prior to each of the first and second catalyst sections. Alternatively, the fuel may only be injected prior to the first catalyst section, with any remaining unburnt fuel continuing on to the second catalyst section.

In the mixing sections of the described embodiments, a bladed rotor or other mixing means may alternatively be used in place of a baffle.

In the second and third embodiments of the invention, the wall separating the inner and outer ducts may be formed from a temperature sensitive metal or a combination of such metals. As a result, the relative cross- sectional areas of the two ducts may vary depending on the temperature of the exhaust gases passing through.

Although the preferred embodiments of this disclosure have been described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.

Claims

CLAIMS:

1. Exhaust apparatus comprising: an inlet for receiving input exhaust gas; a heater adapted to heat a first portion of the input exhaust gas with a second portion of the input exhaust gas bypassing the heater; a first catalyst stage adapted to oxidise the first portion of exhaust gas heated by the heater; a second catalyst stage adapted to oxidise a mixture of the first and second portions of the input exhaust gas; and a particulate trap adapted to trap particulates in exhaust gas output from the second catalyst stage.

2. Exhaust apparatus according to claim 1 wherein the particulate trap is a regenerating particulate trap.

3. Exhaust apparatus according to claim 1 or claim 2 including a duct which is joined to the inlet and houses the heater; and wherein the heater occupies only part of the cross section of the duct.

4. Exhaust apparatus according to claim 1 or claim 2 including first and second ducts, each of which is joined to the inlet and receives part of the input exhaust gas; wherein the first duct houses the heater and the first catalyst stage; and wherein the second duct is joined to the first duct downstream of the heater and the first catalyst stage, and upstream of the second catalyst stage.

5. Exhaust apparatus according to claim 4 wherein one duct is located inside the other.

6. Exhaust apparatus according to claim 4 or claim 5 further comprising a baffle adjacent the confluence of the first and second ducts.

7. Exhaust apparatus according to any preceding claim wherein the heater is an electric heater.

8. Exhaust apparatus according to any of the preceding claims further comprising a control valve and a bypass duct for enabling at least some of the input exhaust gas to controllably bypass the heater and first catalyst stage.

9. An internal combustion engine comprising an exhaust apparatus according to any of the preceding claims.

10. A method of treating exhaust gas comprising the steps of: receiving input exhaust gas; heating a first portion of the exhaust gas to a temperature sufficient to induce catalytic light off; oxidising the first portion of the input exhaust gas in a first catalyst stage; mixing the first oxidised portion of the input exhaust gas with a second non-oxidised portion of input exhaust gas, wherein the temperature of the mixture is a temperature sufficient to induce catalytic light off; oxidising the mixture of the first and second portions of the input exhaust gas in a second catalyst stage; and trapping particulates in the exhaust gas oxidised in the second catalyst stage.

11. A method of treating exhaust gas according to claim 10 wherein between 10% and 40% of the input exhaust gas is heated and oxidised in the first catalyst stage.

12. A method of treating exhaust gas according to claim 11 wherein approximately 20% of the input exhaust gas is heated and oxidised in the first catalyst stage.

13. A method of treating exhaust gas according to any of claims 10 to 12 wherein the heating is electric heating.

14. A method of treating exhaust gas according to any of claims 10 to 13 wherein the input exhaust gas not previously oxidised in the first catalyst stage bypasses the first catalytic stage.