GB2465151A

GB2465151A - Engine exhaust treatment unit

Info

Publication number: GB2465151A
Application number: GB0820226A
Authority: GB
Inventors: Gabriel Menier
Original assignee: AGCO SA
Current assignee: AGCO SA
Priority date: 2008-11-05
Filing date: 2008-11-05
Publication date: 2010-05-12
Also published as: GB0820226D0

Abstract

An engine exhaust treatment unit (12) for an exhaust system is provided. The unit comprises a housing (18) which contains a particulate filter (26) and a treatment volume (30) both disposed in an exhaust gas stream defined between an inlet (21) and an outlet (34). A wall (31) of the treatment volume (30) is suitable for receiving an injector (32) which serves to inject a reducing agent (100) such as urea into the treatment volume (30). The exhaust treatment unit (12) further comprises a hydrolysis catalyst (28) for hydrolyzing the reducing agent (100). By housing the particulate filter (26) and the treatment volume (30) in a single module the space required by the engine exhaust treatment unit (12) is reduced.

Description

ENGINE EXHAUST TREATMENT UNIT

The invention relates to the cleaning of engine exhaust gases including the removal of particulate matter and a chemical treatment process to remove harmful gases from the stream.

In particular, but not exclusively, the invention relates to an engine exhaust after-treatment (EAT) unit which can be installed in an agricultural tractor.

Increasing demands on engine manufacturers to improve the quality of exhaust emissions has driven recent developments in the chemical treatment of exhaust streams. It is well known to provide a particulate filter in the exhaust stream of a diesel engine wherein diesel particulate matter, or soot, exhausted by the engine is removed. Such filters can regenerate continuously through the use of a catalyst or can be simply disposable. Today, particulate filters are commonly fitted to diesel-powered tractors and are positioned between the engine and an exhaust pipe which passes the filtered gases into the sunounding environment.

As well as particulate matter there is a continuing desire to reduce potentially harmful nitrogen oxides present in the exhaust of a diesel engine. Selective catalytic reduction (SCR) is a known means to convert nitrogen oxides into diatomic nitrogen (N2) and water.

Reference is invited to the website http:!/en.wikipedia.org/wiki/Seiective caraiytic reduction which provides a description of SCR and the chemical reactions involved. A liquid reducing agent which typically comprises a urea solution (or Diesel Exhaust Fluid (DEE)) is added to the exhaust gas stream so as to drive the reduction of nitrogen oxide in to the relatively less harmful form.

Such a reductant injection is typically carried out by means of an injector fitted to ducting of the exhaust gas stream upstream of a catalyst unit in which the reactions take place. The space available within an engine compartment is often at a premium, especially under the bonnet of an agricultural tractor.

It is thus an object of the invention to provide an engine exhaust treatment unit which occupies less space on the vehicle to which it is fitted.

According to the invention there is provided an engine exhaust gas after-treatment unit comprising a housing which contains particulate filter means and a treatment volume both disposed in an exhaust gas stream defined between an inlet and an outlet, a wall of the treatment volume being suitable for receiving an injector which can inject into the treatment volume an agent for reducing nitrogen oxides. By housing the particulate filter means and the treatment volume in a single module the space required by the engine exhaust treatment unit is reduced.

It should be understood that the "treatment volume" is the volume of space into which a reducing agent can be injected, for example in vapour form.

In a first preferred embodiment the particulate filter means is disposed upstream of the treatment volume thereby removing the particulate matter before adding the reductant to the exhaust gas stream. The particulate filter means may separate an inlet chamber disposed at one of the housing from the treatment volume which is disposed at the other end.

Downstream of the treatment volume the unit may further comprise an outlet duct which carries the exhaust gas stream to the outlet. The geometry of the outlet duct may be designed to encourage mixing of the reducing agent with the gas stream before being ejected from the treatment unit.

The housing is preferably substantially cylindrical and such an outlet duct and the particulate filter means are co-axial with respect to the cylindrical axis of the housing. Therefore, the majority of the exhaust gas stream path lay substantially parallel with the axis of the housing.

In a first direction the exhaust gas is filtered by the particulate filter means. In a second, opposite, direction the exhaust gas and reducing agent mixture is passed through the housing to the outlet. Advantageously this optimises the available space within the housing.

Preferably, the outlet duct intersects the particulate filter means along the cylindrical axis. In this way the particulate filter means (having an annular cross section) occupies the volume around the centrally disposed outlet duct.

The outlet duct may be located in one end wall of the cylindrical housing with the treatment volume (and injector) being located at the opposite end. This minimises the external projections from the side wall of the housing thereby streaming the canning and making it easier to fit into the available space.

In a second preferred embodiment the treatment volume separates a diesel oxidation catalyst (DOC) from a hydrolysis catalyst and filter. The wall which receives the injector may be arranged such that the treatment is projected onto the upstream surface of the hydrolysis catalyst.

In accordance with the invention there is also provided an engine exhaust system as described above connected upstream of a catalytic converter unit for reducing nitrogen oxide present in the exhaust stream.

Further advantages of the invention will be understood from the following description of specific embodiments with reference to the appended drawings in which:-Figure 1 is a perspective view of a tractor embodying an engine exhaust treatment unit in accordance with the invention; Figure 2 is a perspective view of an engine exhaust system for a tractor; Figure 3 is a perspective view of an engine exhaust treatment unit in accordance with a first embodiment of the invention; Figure 4 is a perspective cutaway view of the treatment unit of Figure 3; Figure 5 is a side sectional view of the treatment unit of Figure 3; and Figure 6 is a side sectional view of a engine exhaust treatment unit in accordance with a second embodiment of the invention.

With reference to the following description of specific embodiments of the invention, features common to more than one embodiment will, where appropriate, share the same reference numerals for ease of understanding.

With reference to Figure 1, a tractor 10 comprises a bonnet 11 which defines an engine compartment space. The exhaust stream from the engine (not shown) is conveyed to an engine exhaust system which comprises a treatment unit 12 connected to a catalytic converter unit 13 (Figure 2) by ducting 14. An upright exhaust pipe 15 is connected to the outlet of catalytic converter unit 13 and, in this example, is located to the side of the cab 16 in alignment with a front corner post 17 to maximize visibility for the driver.

Referring now to Figures 2 to 5, the engine exhaust treatment unit 12 comprises an insulated housing structure 18 formed of a double skin wall of aluminized steel and which defines the interior volume of the module. The exhaust gases from the engine (not shown) are conveyed to an exterior inlet pipe 20 which is connected to an inlet orifice 21 of the treatment unit 12.

The pipe 20 is connected to the orifice 21 by means of mounting plates 22 which are bolted together and are sealed by a gasket disposed therebetween.

It will be understood that the term "exhaust gas stream" used hereinafter is intended to mean the path by which the exhaust gases from the engine pass through the treatment unit 12 from the inlet to the outlet and onto the catalytic converter unit and exhaust pipe. Furthermore the tern! "upstream" will iiiean towards the source of the exhaust gases, that is the engine.

Conversely the term "downstream" is intended to mean towards the outlet of the system, that is away from the engine.

The exhaust gases, once conveyed through the inlet 21, pass through an inlet chamber 24 which is disposed at one end of the cylindrical housing 18. In reality the inlet chamber 24 is annular in section due to an outlet duct 25 passing through the centre which will be discussed in more detail below.

From the inlet chamber 24 the exhaust gases continue downstream into a pre-filter 26 which is, again, annular in shape and surrounds the outlet duct 25. The pre-filter 26 serves to trap particulates present in the exhaust gases.

The pre-filter 26 includes a diesel oxidation catalyst (DOC) which serves to oxidise nitric oxide (NO) gases into nitrogen dioxide (NO2). The reaction is exothermic thereby increasing the temperature of the exhaust gases. In turn, this facilitates the passive regeneration of the particulate filter (particulates are burnt into soot without fuel injection down-stream of the filter). Also, the presence of NO2 improves the NO reduction reaction in the SCR substrate.

Continuing downstream, the exhaust gases then pass through a filter 28 which is again annular in shape and surrounds the outlet duct 25.

At the end of the housing 18 remote the inlet end the exhaust gases are passed into a treatment volume 30 in which the direction of flow is steered through 180° into the outlet duct 25 which is disposed co-axially with the two filters 26, 28. The end wall 31 of the housing 18 is adapted to receive an injector 32. The injector 32 is fixed and sealed to the end wall 31 so as to inject a reducing agent into the treatment volume 30 as required.

Therefore, as the exhaust gases exit the particulate filter means 26. 28 urea 100 is injected into the stream so as to mix with the exhaust gases as they pass through the outlet duct 25. The shape of the treatment volume 30 is defined to optimize the gas flow from the filter outlet 28 to the outlet duct 25, to encourage mixing and to limit the exhaust back-pressure of the system.

The outlet duct 25 is formed of stainless steel pipe and runs along the cylindrical axis of the housing referenced at X as shown in Figure 5. By adopting such a co-axial arrangement of the outlet duct 25 and filter arrangement 26, 28 the use of available space within the housing is optilnised thus saving overall space consumed underneath the bonnet 11.

The exhaust gases exit the treatment unit 12 through an outlet 34 in the end of the outlet duct 25. It can be seen from Figure 4 that both the inlet and outlet orifices 21, 34 are disposed on the side wall of the housing 18 at one end thereof. This increases the design flexibility in locating the treatment unit 12 within the engine compartment.

With reference again to Figure 2. the exhaust gas stream continues through the ducting 14 and into the catalytic converter unit 13 in which the harmful nitrogen oxides present in the exhaust gases are reacted with the urea to produce less harmful water and nitrogen gas which are vented through the exhaust pipe 15 in a known manner.

A second embodiment of the invention is shown in Figure 6 in which the exhaust gas stream is treated with urea 100 in a treatment volume 30 which is disposed between the DOC 26 and filter 28. In this example, the filter 28 includes a hydrolysis catalyst. Unlike the previously described embodiment, the overall exhaust gas stream flows from an inlet 21 at one end of the housing 18 in a substantially linear direction exiting the housing at the other end through outlet 34.

In more detail, the exhaust gases from the engine enter the treatment unit 42 through inlet 21 into an inlet chamber 24. The gases are then passed through a DOC 26 which fills the circular section of the housing 18. Flowing downstream the catalysed exhaust gases pass into a treatment volume 30 before being passed through the filter and hydrolysis catalyst 28. In accordance with the invention, an injector 32 is mounted to the wall of the treatment volume at a hole located in the housing 18. Urea 100 is injected into the treatment volume 30 and is furthermore directed at the inlet face 43 of the hydrolysis catalyst 28.

The exhaust gas and urea mixture then pass through the hydrolysis filter 28 and exit into an outlet chamber 36 disposed at the end of the housing 18 remote the inlet chamber 24. The mixture then exits the treatment unit 42 through an outlet vent 34 before being conveyed to the catalytic converter unit 13 in a similar manner to the first described embodiment.

Although the above described embodiments employ urea as the reducing agent it should be appreciated that other suitable reducing agents (or diesel exhaust fluids) can instead used without deviating from the scope of the invention.

Furtheniiore, the particulate filter means above coiiiprise a DOC and a hydrolysis filter.

However, it is envisaged that various different arrangements of filter means can instead be employed. For example, in a more simplistic arrangement. a single filter can be fitted inside the housing together with the treatment volume without deviating from the scope of the invention. Alternatively, more than two filters may be arranged in the same module.

Although described in relation to a tractor, it will be appreciated that the engine exhaust treatment unit in accordance with the invention can be employed on any vehicle or machine having a diesel-powered internal combustion engine which can benefit from particulate filtration and reductant injection. For example this can include cars, lorries and boat engines to name but a few.

From reading the present disclosure, other modification will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the field of engine exhaust systems and component parts therefore and which may be used instead of or in addition to features already described herein.

Claims

CLAIMS1. An engine exhaust gas after-treatment unit comprising a housing which contains particulate filter means and a treatment volume both disposed in an exhaust gas stream defined between an inlet and an outlet, a wall of the treatment volume being suitable for receiving an injector which can inject into the treatment volume an agent for reducing nitrogen oxides.
2. An engine exhaust treatment unit according to Claim 1, further comprising a diesel oxidation catalyst (DOC).
3. An engine exhaust treatment unit according to Claim 2, wherein the DOC is upstream of a hydrolysis catalyst.
4. An engine exhaust treatment unit according to any preceding claim, wherein the particulate filter means is disposed upstream of the treatment volume.
5. An engine exhaust treatment unit according to Claim 4. wherein the particulate filter means separates an inlet chamber from the treatment volume.
6. An engine exhaust treatment unit according to Claim 4 or 5, wherein downstream of the treatment volume, an outlet duct carries the exhaust gas stream to the outlet.
7. An engine exhaust treatment unit according to Claim 6, wherein the housing is substantially cylindrical and the outlet duct and the particulate filter means are coaxial with respect to the cylindrical axis of the housing.
8. An engine exhaust treatment unit according to Claim 7, wherein the outlet duct carries the exhaust gas stream through the particulate filter means along the cylindrical axis.
9. An engine exhaust treatment unit according to Claim 8, wherein the outlet is located in an end wall of the cylindrical housing and the treatment volume is located at the opposite end of the housing.
10. An engine exhaust treatment unit according to any one of Claims 7 to 9, wherein said wall of the treatment volume being suitable for receiving an injector is an end wall of the cylindrical housing.
11. An engine exhaust treatment unit according to Claim 3, wherein the treatment volume separates the DOC from the hydrolysis catalyst.
12. An engine exhaust treatment unit according to Claim 3 or 11, wherein the wall receives the injector such that the treatment is projected onto a surface of the hydrolysis catalyst.
13. An engine exhaust treatment unit according to any preceding claim, further comprising the injector.
14. An engine exhaust system comprising a treatment unit according to any preceding claim connected upstream of a catalytic converter unit for reducing nitrogen oxides present in the exhaust stream.
15. A tractor comprising an engine exhaust system according to Claim 14.