EP2935817A1

EP2935817A1 - Arrangement to insert a liquid medium into exhausts from a combustion engine

Info

Publication number: EP2935817A1
Application number: EP13864833.2A
Authority: EP
Inventors: Fredrik HOLMBERG; Henrik BIRGERSSON; Hans Göransson; Tommy Eriksson; Morgan Colling; Eric FURBO; Niklas NORDIN
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2012-12-21
Filing date: 2013-12-05
Publication date: 2015-10-28
Also published as: RU2015129689A; SE536832C2; WO2014098728A1; KR20150092337A; RU2609009C2; SE1251488A1; BR112015014580A2; EP2935817A4

Abstract

Arrangement (1) to introduce a liquid medium, for example urea, into exhausts from a combustion engine, which arrangement comprises: - a mixing chamber (2) intended to be perfused by exhausts, wherein the mixing chamber is delimited in a radial direction outwards by a tubular metal wall (6), and - an injection element (10) for injection of the liquid medium as a spray (11) into the mixing chamber. Said tubular wall has a variable wall thickness seen in the mixing chamber's longitudinal direction, so that the section (6a) of the tubular wall which is intended to be impacted by said spray of a liquid medium from the injection element has a wall thickness which is greater than the wall thickness of those sections (6b) of the tubular wall l which are adjacent to this wall section.

Description

Arrangement to insert a liquid medium into exhausts from a combustion engine

FIELD OF TH E I NVENTION AN D PR IOR ART

The present invention relates to an arrangement to insert a liquid medium , for example urea, into exhausts from a combustion engine, according to the preamble of patent claim 1 . In order to meet current requirements regardi ng exhaust purification, today's motor vehicles are usually equipped with a catalytic converter in the exhaust pipe in order to achieve a catalytic conversion of environmentally harmful exhaust components into less environmentally harmful substances. One method used to achieve an effective catalytic conversion is based on injecting a reduction agent into the exhausts upstream of the catalytic converter. A reduction substance included in or created by the reduction agent is introduced into the catalytic converter by the exhausts where it is absorbed in active sites in the catalytic converter, which causes an accum ulation of the reduction agent in the catalytic converter. The accumulated reduction agent may then react with an exhaust substance for the conversion of this exhaust substance into a substance with less environmental impact. Such a catalytic reduction converter may for example be of SC R-type (SC R = Selective Catalytic Reduction). This type of catalytic converter is referred to hereafter as an SC R-catalyst. An SC R-catalyst reduces NO_x in the exhausts. In an SC R-catalyst a reduction agent in the form of urea is usually i njected into the exhausts upstream of the catalytic converter. When urea is injected into the exhausts, am monia is formed , and it is this ammonia which constitutes the reduction agent contributing to the catalytic conversion in the SC R-catalyst. The ammonia is accumulated in the catalytic converter by being absorbed in active sites in the catalytic converter and NO_x present in the exhausts is converted into nitrogen and water when brought into contact with accumulated am monia at the active sites in the catalytic converter. When urea is used as a reduction agent, it is injected into the exhaust pipe in the form of a liquid urea solution with the help of an injection element. The injection element comprises a nozzle via which the urea solution is injected into the exhaust pipe under pressure, in atomised form as a spray. During long periods of a diesel engine's operation, the exhausts have a sufficiently high temperature to be able to vaporize the urea solution so that am monia is formed . However, it is difficult to avoid that a part of the added urea solution comes into contact with and sticks to the exhaust pipe's internal wall surface in an unevaporated state. When a combustion engine is operated in a consistent manner for a period of time, i.e. during a stationary operating condition, there are no substantial variations in the gas flow, and the urea solution injected into the exhausts will therefore hit essentially the same area of the exhaust pipe during this entire period of time. Under the impact of the relatively cool urea solution the temperature in this area of the exhaust pipe may be reduced locally to a temperature lower than 1 00 °C, which in turn may lead to the formation of a film of urea solution in this area, which is then pulled along with the exhaust flow. Once this film has been moved a certain distance in the exhaust pipe, the water in the urea solution will boil off due to the hot exhausts. There remains solid urea, slowly evaporating by the heat in the exhaust pipe. If the supply of solid urea is greater than the evaporation , solid urea accumulates inside the exhaust pipe. If the layer of urea becomes sufficiently thick, the urea and its decomposition products will react with each other to form urea-based primitive polymers, so called urea lumps. Such urea lumps may, over time, block an exhaust pipe. OBJ ECTIVE OF TH E INVENTION

The objective of the present invention is to achieve an arrangement of the type mentioned above which creates improved possibilities of ensuring a good vaporisation of the injected reduction agent.

SU MMARY OF TH E I NVENTION

According to the present invention, the above-mentioned objective is achieved with the help of an arrangement having the features defined in patent claim 1 .

The arrangement according to the invention comprises:

- a m ixing chamber intended to be perfused by exhausts, wherein mixing chamber is delimited in a radial direction outwards by a tubular metal wall , and

- an injection element for injection of the liquid medium as a spray into the mixing chamber.

Said tubular wall has a variable wall thickness seen in the mixing chamber's longitudinal di rection , so that the section of the tubular wal l which is intended to be impacted by said spray of a liquid medium from the injection element has a wall thickness which is greater than the wall thickness of those sections of the tubular wal l which are adjacent to this wall section .

Because of the increased wall thickness of the section of the tubular wall which is impacted by the spray from the injection element, this wall section becomes capable of taking up and storing a greater amount of heat from the passing exhausts compared to the other, thinner wall sections. Thus, the thickened wal l section acquires an improved ability to counteract the cooling down caused by the injected medium impacting this section of the wal l. The stored heat also contributes to an increased vaporisation of the injected medium impacting the relevant wall section . Because of its increased wall thickness, the relevant wall section also acquires an improved heat conducting ability, which means that the cooling action which is caused by the injected medium impacting the wall section is spread over a larger area. This spreading of the injected medium's cooling action leads to a reduced cooling down in the area impacted by the spray from the injection element. The solution according to the invention does not require the use of any heating fins or any other heat transfer elements and is thus exceedingly simple and advantageous. One embodiment of the invention is characterised by:

- the arrangement comprising an exhaust channel adjacent to the mixing cham ber, which is intended to be perfused by exhausts and extends along the outside of said tubular wall , wherein the exhaust channel is delimited from the mixing chamber by the tubular wall , and - the exhaust channel being delimited in a radial direction outwards by another tubular wall , which is designed to guide the exhausts flowing through the exhaust channel to pass on the outside of said wall section .

Thus the thickened wall section is heated from its back by the exhausts flowing through said exhaust channel .

According to another embodiment of the invention a throttle is arranged in the section of the exhaust channel located on the outside of said wall section, in order to achieve an acceleration in the exhausts flowing through the exhaust channel in this exhaust channel section, so that these flow with an increased speed over the outside of said wall section . The heat transfer coefficient with respect to the heat transfer from a flowing gas to a surface increases with increased flow rate of the gas. As the exhausts in the exhaust pipe are brought to flow over the thickened wall section with increased speed , an increased heat transfer is thus achieved from the exhausts to this wall section is achieved, contributing to an effective heating of the relevant wall section .

Other favourable features of the arrangement according to the invention are set out in the non-independent patent claims and the description below.

BR IEF DESCR IPTION OF THE D RAW ING

The invention is described below with the help of exam ple em bodiments, with reference to the enclosed drawing . Shown in : Fig 1 is a schematic longitudinal section through arrangement according to one embodiment of present invention , and

Fig 2 is a section according to the line II-II in Fig 1 .

DETAILED DESC R I PTION OF EM BODI M ENTS ACCO RD I NG TO TH E INVENTION In Fig 1 -2 an arrangement 1 according to one embodiment of the present invention to introduce a liquid medium into exhausts from a combustion engine is illustrated . The arrangement may for example be arranged inside an exhaust pipe upstream of an SC R-catalyst to i ntroduce a liquid reduction agent in the form of urea or ammonia into the exhaust pipe upstream of the SC R- catalyst, or be arranged inside an exhaust after-treatment device to introduce a liquid reduction agent in the form of urea or am monia upstream of an exhaust after-treatment device included in an SC R-catalyst.

The arrangement 1 comprises a mixing chamber 2 intended to receive exhausts from a combustion engine and to lead these exhausts further in a direction toward an exhaust after-treatment device, for example in the form of an SC R-catalyst. The mixing chamber 2 is thus intended to be perfused by exhausts. The mixing chamber 2 has an upstream end 4 and a downstream end 5. The mixing chamber 2 is delimited in a radial direction outwards by a tubular metal wall 6, extending between the mixing chamber's upstream end 4 and its downstream end 5. The mixing chamber 2 has an inlet 7 for receipt of exhausts at its upstream end and an outlet 8 for emission of exhausts at its downstream end . The inlet 7 is suitably annular and arranged to extend around the mixing cham ber's central shaft 9. The mixing chamber 2 preferably has a circular cross sectional form , as illustrated in Fig 2.

An injection element 1 0 for injection of the liquid medium is arranged in the centre of the mixing chamber's upstream end 4, to inject the liquid medium in a direction toward the mixing chamber's downstream end 5. The injection element 1 0, which may for example comprise an injection nozzle, is arranged to inject the liquid medium into the m ixing chamber 2 under pressure, in an atomised form as a spray 1 1 . The tubular wall 6 has a variable wall thickness seen in the mixing chamber's longitudinal direction , so that the section 6a of the tubular wall , which is intended to be impacted by said spray 1 1 of a liquid medium from the injection element 1 0, has a wall thickness which is greater than the wall thickness of the sections 6b of the tubular wall that are adjacent to this wall section 6a.

At its thickest section , the thickened wall section 6a preferably has a thickness which is at least 30% greater, and preferably 1 .5-3 times greater than the thickness of the wall's thinner section 6b. The wall's thinner section 6b may for example have a thickness of around 0.5-2 mm .

In the illustrated embodiment, the arrangement 1 com prises an exhaust channel 1 2 with an annular cross section, adjacent to the mixing chamber 2 and intended to be perfused by exhausts and extending along the exterior of the tubular wall 6. The exhaust channel 1 2 encloses the mixing cham ber 2 and is concentric with the latter, as illustrated in Fig 2. The exhaust channel 1 2 and the mixing chamber 2 are delim ited from each other by the tubular wall 6. The exhaust channel 1 2 is delimited in a radial di rection inwards by the tubular wall 6 and in a radial direction outwards by another tubular wall 1 3, designed to guide the exhausts flowing through the exhaust channel 1 2 so that they pass on the outside of the thickened wall section 6a.

A throttle 1 4 is arranged in the section 1 2a of the exhaust channel located on the outside of the thickened wall section 6a, in order to achieve an acceleration of the exhausts flowing through the exhaust channel 1 2 i n this exhaust channel section 1 2a, so that these flow with an increased speed over the outside of said wall section 6a. At the throttle 1 4, the exhaust channel 1 2 has a cross sectional area which is smaller than the cross sectional area of the section of the exhaust channel which is located upstream of the throttle.

In the illustrated example the exhaust channel 1 2 is arranged downstream of the mixing cham ber 2 and connected to the mixing chamber 2 via a flow reversal element 1 5, arranged to reverse the flow direction of the exhausts flowi ng from the mixing chamber 2, so that these are brought to flow through the exhaust channel 1 2 in a flow direction which is opposite to the flow direction of the exhausts in the mixing chamber 2. In the illustrated embodiment the flow reversal element 1 5 is arranged opposite the mixing chamber's outlet 8 and equipped with a middle section 1 5a and an annular edge section 1 5b surrounding the middle section 1 5a. Said middle section 1 5a, facing the mixing chamber 2, preferably has a convex shape, as illustrated in Fig 1 . The side of said edge section 1 5b, facing the mixing chamber 2, forms a guide surface 1 6 which is rounded in order to - during the reversal of the flow di rection of these exhausts - direct the exhausts flowing toward the flow reversal element 1 5 into a flow directed toward the exhaust channel's annular inlet 1 7. The spray 1 1 of a liquid medium which is injected into the mixing chamber 2 via the injection element 1 0 comes into contact with exhausts, flowing into the mixing chamber via the mixing chamber's inlet 7 in an essentially symmetric flow around this spray 1 1 . The exhausts flowing into the mixing chamber 2 bring along the liquid medium downstream in the mixing chamber. While moving downstream in the mixing chamber 2, the liquid medium spreads into the exhausts and evaporates due to the exhaust heat. Liquid medium which is not evaporated impacts the thickened section 6a of the tubular wall 6. The liquid medi um which impacts this thickened wall section 6a will be evaporated due to the hot wall surface and the hot exhausts. From the mixing chamber 2, the exhausts are led further to the exhaust channel 1 2. During their passage through the throttle 1 4 in the exhaust channel 1 2, the exhausts are accelerated and flow with an increased speed along the outside of the thickened wall section 6a while delivering heat to the same.

The arrangement according to the invention is intended to be used in a heavy goods vehicle, such as a bus, a towing vehicle or a truck. The invention is not li mited in any way to the embodiments described above, but numerous possible modifications thereof should be obvious to a person skilled in the art, without such person departing from the spirit of the invention as defined by the appended patent claims.

Claims

1 . Arrangement to introduce a liquid medium , for example urea, into exhausts from a combustion engine, which arrangement ( 1 ) comprises:

- a mixing chamber (2) intended to be perfused by exhausts, wherein the mixing chamber (2) is delimited in a radial direction outwards by a tubular metal wall (6), and

- an i njection element (1 0) for injection of the liquid medium as a spray (1 1 ) into the m ixing chamber (2),

characterised by said tubular wall (6) having a variable wall thickness seen in the mixing chamber's longitudinal direction , so that the section (6a) of the tubular wall (6) intended to be impacted by said spray ( 1 1 ) of a liquid medium from the injection element ( 1 0) has a wall thickness which is greater than the wall thickness of the sections of the tubular wal l (6) which are adjacent to this wall section (6a) .

2. Arrangement according to claim 1 , characterised by :

- arrangement (1 ) comprising an exhaust channel (1 2) adjacent to the mixing chamber (2), intended to be perfused by exhausts and extending along the outside of the said tubular wall (6), so that the exhaust channel (1 2) is delimited from the m ixing chamber (2) by the tubular wall (6), and

- the exhaust channel ( 1 2) being delimited in a radial direction outwards by another tubular wall ( 1 3), which is designed to guide the exhausts flowing through the exhaust channel (1 2) so that they pass on the outside of said wal l section (6a). Arrangement according to claim 2, characterised by a throttle (1 4) being arranged in the section (1 2a) of the exhaust channel which is located on the outside of said wall section (6a), in order to achieve an acceleration of the exhausts flowi ng through the exhaust channel (1 2) in the exhaust channel section (1 2a), so that these flow with an increased speed over the outside of said wall section (6a) .

Arrangement according to clai m 2 or 3, characterised by said exhaust channel ( 1 2) being arranged downstream of the mixing chamber (2) and connected to the mixing chamber (2) via a flow reversal element (1 5), which is arranged to reverse the flow direction of the exhausts flowing from the mixing chamber (2) , so that these are brought to flow through the exhaust channel (1 2) in a flow direction which is opposite that of the exhaust flow direction in the mixing chamber (2).

Arrangement according to any of claims 2-4, characterised by the exhaust channel (1 2) and the mixing chamber (2) being concentric.

Arrangement according to any of the claims 1 -5, characterised by the injection element (1 0) being arranged in the centre of the mixing chamber's upstream end (4) and arranged to inject the liquid medium in a direction toward the mixing chamber's downstream end (5).