SE539643C2

SE539643C2 - Silencer with a vaporization chamber for a combustion engine

Info

Publication number: SE539643C2
Application number: SE1451429A
Authority: SE
Inventors: Klasson Martin; Öfverholm Carolina; Johansson Lars
Original assignee: Scania Cv Ab
Priority date: 2014-11-26
Filing date: 2014-11-26
Publication date: 2017-10-24
Also published as: DE102015014198B4; DE102015014198A1; SE1451429A1

Abstract

23 ABSTRACT The present invention relates to a silencer for a combustion engine to an exhaust gassystem comprising the silencer, to a Vehicle comprising the exhaust gas system and toa method for exhaust gas purification by means of the silencer. The silencer (12)comprises a casing (44), With at least one inlet (20) and at least one outlet (40), aVaporisation chamber (42), Wherein the Vaporisation chamber (42) is situated inside thecasing (44). A duct (46) is provided between the Vaporisation chamber (42) and thecasing (44). The exhaust gases (22) inside the Vaporisation chamber (42) are arrangedto flow in a direction (100) from a first end (48) to a second end (50) of theVaporisation chamber (42). The silencer (l2) further comprises a selective catalyticreduction (SCR) purification system (34) Which comprises an arrangement (28) foradding a reducing agent (30) to the exhaust gas ﬂoW (22) exhaust gas ﬂoW arrangedupstream of the Vaporisation chamber (42). The silencer (l2) comprises a Variable ﬂoWguide (52) for directing the ﬂoW of exhaust gases (22) and reducing agent (30) insidethe Vaporisation chamber (42) and Which Variable ﬂoW guide (52) is arranged upstream of the second end (50) of the Vaporisation chamber (42). (Fig. 5)

Description

Silencer With a vanorisation chamber for a combustion engine TECHNICAL FIELD The present invention relates to a silencer for a combustion engine, an eXhaust systemprovided with the silencer, a vehicle provided with the eXhaust system and a method for eXhaust gas purification by means of the silencer.

BACKGROUND TO THE INVENTION AND PRIOR ART Diesel engines are provided with eXhaust purification devices with the object ofreducing discharges of particles and harmful gases which occur in diesel engineeXhaust gases. To regulate emissions from vehicles there are various standards andlegal requirements which govem permissible levels for eXhaust discharges. Vehiclesare consequently provided with various purification devices for eXhaust gases in order to meet legal requirements.

Silencers are used in combustion engines to damp engine noise and reduce emissionsand are usually situated in the engine's exhaust system. The noise may be damped byproviding one or more filters in a casing through which the sound waves pass, and/orby reducing the velocity of the exhaust gases through the silencer, e. g. by changes ofdirection of the eXhaust gas flow in the silencer. The velocity of the eXhaust gases and the sound waves is thus reduced.

Combustion engines provided with a silencer may be used in various differentapplications, e. g. in heavy vehicles such as trucks or buses. The vehicle mayaltematively be a passenger car. Motorboats, steamers, ferries or ships, industrialengines and/or engine-powered industrial robots, power plants, e. g. an electric powerplant provided with a diesel generator, locomotives or other applications may havecombustion engines with silencers. Particle emissions from these combustion engines,particularly in the case of diesel-powered heavy vehicles, may be reduced by means of particle filters.

Another known practice to reduce particle emissions from combustion engines is touse a so called SCR (selective catalytic reduction) system which comprises a reducingagent and a Catalyst with an SCR-substrate for purification of nitrogen dioXides (NOX)from exhaust gases. To reduce the nitro gen dioXide content and also to be able toconvert the nitrogen dioxides to less harmful gases, the eXhaust gases are treated with areducing agent, e. g. a miXture of 32.5 % urea and water. Injecting the liquid and miXingit with the eXhaust gases results in a chemical reaction whereby nitro gen gas and water are formed across the SCR catalyst.

Urea solutions may be supplied by means of an injection system which eXtends intothe eXhaust gas line. The injection system has one or more outlet apertures via whichthe urea solution is injected into the exhaust gas line. During much of diesel engineoperation the eXhaust gases are at a high enough temperature to vaporise the ureasolution so that ammonia is formed, but it is difficult to prevent that a part of the ureasolution does not vaporise and comes into contact with and becomes attached to theinside wall surface of the eXhaust gas line in an unvaporised state as urea lumps or ureacrystals. The urea lumps or the urea crystals may over time block the eXhaust gas line and disrupt the eXhaust gas ﬂow by causing a high backpressure in the eXhaust system.

It is previously known how to improve the vaporisation of the urea solution byarranging a vaporisation chamber inside the casing of the silencer, such that a duct isprovided between the vaporisation chamber and the casing. The vaporisation chamberis provided with a first end and a second end. The first end of the vaporisation chamberis connected to the inlet of the casing and the second end of the vaporisation chamberis connected to the outlet of the casing, such that eXhaust gases inside the vaporisationchamber are caused to ﬂow in a direction from the first end to the second end of thevaporisation chamber and such that eXhaust gases in the duct are caused to flow in thesame direction. This makes it possible for the eXhaust gas ﬂow to warm thevaporisation chamber and for the temperature of the vaporisation chamber to be kept ata stable level. Thereby the vaporisation of the urea solution is improved and the formation of urea lumps and urea crystals is thus reduced.

Patent application US 20060153748 Al discloses an eXhaust gas aftertreatmentsystem, especially for a diesel engine. The eXhaust gas aftertreatment systemcomprises a silencer with a collection manifold. The collection manifold works as avaporisation chamber, but a problem with this vaporisation chamber and also otherknown vaporisation chambers is that the degree of formation of urea lumps and urea crystals is not sufficiently low.

There is thus a need to improve existing silencers in order to reduce or eliminate the abovementioned disadvantage.

There is also a great need for a high degree of eXhaust purification of combustion engines.

SUMMARY OF THE INVENTION It is an object of the present invention to increase the vaporisation of the urea solutionand thus reduce the problem of formation of urea lumps and urea crystals in the eXhaust gas line.

Another object of the present invention is to achieve a high degree of eXhaust gas purification of combustion engines.

The above objects are achieved with a silencer for a combustion engine according tothe present invention defined in the appended claims. The silencer comprises a casin gwith at least one inlet for leading a flow of eXhaust gases into the casing and at leastone outlet for leading the eXhaust gas ﬂow out from the casing. The silencer furthercomprises a vaporisation chamber provided with a first end and a second end. Thevaporisation chamber is arranged inside the casing, such that a duct is providedbetween the vaporisation chamber and the casing. The first end of the vaporisationchamber is in ﬂuid connection with the inlet of the casing and the second end of thevaporisation chamber is in ﬂuid connection with the outlet of the casing and eXhaust gases inside the vaporisation chamber are arranged to ﬂow in a direction from the first end to the second end of the vaporisation chamber. Preferably, the eXhaust gases in theduct are also arranged to ﬂoW in the same direction. The silencer also comprises aselective catalytic reduction (SCR) purification system Which comprises a SCR-substrate arranged doWnstream the vaporisation chamber and an arrangement foradding a reducing agent to the eXhaust gas ﬂoW in order to reduce NOX contents of the eXhaust gas ﬂoW, and Which is arranged upstream of the vaporisation chamber.

The silencer according to the present invention comprises a variable ﬂoW guide fordirecting the ﬂoW of exhaust gases and reducing agent inside the vaporisation chamberand is arranged upstream of the second end of the vaporisation chamber. The variableﬂoW guide makes it possible to direct the eXhaust gas ﬂoW such that the eXhaust gasescan utilize the heat of the Walls in the vaporisation chamber and thus it is possible toincrease the vaporisation of the urea solution and decrease the formation of urea lumps and urea crystals.

The above object is also achieved With a method for eXhaust gas purification by meansof a silencer as above. The method comprises the steps of leading the eXhaust gases tothe inlet of the casing of the silencer, the inlet comprising an arrangement for adding areducing agent, then leading the eXhaust gases from the inlet of the casing of thesilencer to the first end of the vaporisation chamber and to the duct. The methodfurther comprises leading the eXhaust gases in the vaporisation chamber to the secondend of the vaporisation chamber, then leading the eXhaust gases from the second end ofthe vaporisation chamber and from the duct to the outlet of the casing of the silencer.The method further comprises arranging a variable ﬂoW guide upstream of the secondend of the vaporisation chamber for directing the ﬂoW of eXhaust gases and reducing agent inside the vaporisation chamber.

The present invention also relates to an eXhaust gas system for a combustion engineprovided With a silencer according to the invention. The exhaust gas system may for example be part of a motor vehicle Which may be for example a truck, bus or a car.

The present invention further relates a vehicle provided with an eXhaust system according to the invention.

Further objects, advantages and feature of the invention are evident from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. l Fig. 2 Figs. 3a-b Fig. 4 Fig. 5 Fig. 6 Figs. 7a-e is a schematic side view of a vehicle comprising a silencer according to the present invention. is a schematic drawing showing path of the eXhaust gas ﬂow through a silencer. are a schematic cross-section views of silencers comprising a vaporisation chamber according to prior art. is a schematic cross-section view of a silencer comprising a vaporisationchamber with a variable ﬂow guide according to one embodiment of the present invention. is a schematic perspective view of a silencer comprising a vaporisationchamber with a variable ﬂow guide generating several complete heliX turns according to one embodiment of the present invention is a perspective view of a silencer comprising a vaporisation chamberwith a variable flow guide not generating a complete heliX turn according to one embodiment of the present invention. are schematic drawings of a silencer comprising a variable flow guide according to the present invention.

Fig. 8 is a ﬂow chart showing schematically the steps of a method for exhaust gas purification by means of the silencer.

DETAILED DESCRIPTION OF THE INVENTION Combustion engines are used in various types of applications and vehicles today, e. g.in heavy vehicles such as trucks or buses, in cars, motorboats, steamers, ferries orships. They may also be used in industrial engines and/or engine-powered industrialrobots, power plants, e. g. electric power plants provided with a diesel generator, and inlocomotives. The silencer according to the present invention is intended for a combustion engine and may be employed preferably in a vehicle, e. g. in a truck or bus.

According to the present invention a vehicle is provided with a combustion engine andFig. l depicts the vehicle l in a schematic side view and provided with a combustionengine 2 which powers the vehicle's tractive wheels 4 via a gearbox 6 and a propellershaft 8. The engine 2 is provided with an exhaust system l0 in which a silencer l2according to the present invention is fitted. The engine 2 is powered by fuel l4 supplied to it via a fuel system l6 which comprises a fuel tank 18.

According to the present invention the silencer comprises an inlet for leading anexhaust gas flow into the silencer. The silencer may comprise several inlets. A dieseloxidation catalyst (DOC) may be arranged downstream of the inlet. A DOC is a unitdesigned to oxidize carbon monoxide, gas phase hydrocarbons and soluble organicfraction (SOF) of diesel particulate matter to C02 and H20. A diesel particulate filter(DPF) may be arranged downstream of the DOC. A DPF is a unit designed to removediesel particulate matter or soot from the exhaust gas flow. The DPF can for example be a catalysed soot filter (CSF).

A reducing agent arrangement for adding a reducing agent to the exhaust gas flow inorder to reduce NOX contents of the exhaust gas ﬂow is arranged downstream of the DPF. The reducing agent may be for example a n1ixture of water and urea, e. g. a product with the trade name AdBlue®. A mixing and vaporisation arrangement, Whichcomprises a vaporisation chamber, for mixing of the exhaust gas ﬂow and reducingagent and for vaporization the reducin g agent is arranged downstream of the reducingagent arrangement. Further, a selective catalytic reduction (SCR) purification system isarranged downstream of the mixing and vaporisation arrangement. The SCRpurification system comprises a SCR-substrate which may comprise a vanadium, ironor copper based catalyst, which reduces NOX to water Vapour and nitrogen. Anammonia slip catalyst (ASC), which is designed to convert the NH3 slip to Ng and H20,may be arranged downstream of the SCR purification system. An outlet for leading theexhaust gas ﬂow out from the silencer is arranged downstream of the ASC. The silencer may comprise several outlets.

The silencer does not necessarily need to comprise a DOC and/or a DPF and/or anASC. In case the silencer does not comprise a DOC and a DPF, the exhaust gas ﬂow isarranged to ﬂow from the inlet to the reducing agent arrangement. If the silencercomprises a DOC but not a DPF, the exhaust gas flow is arranged to flow from theinlet to the DOC and then to the reducing agent arrangement. The exhaust gas isarranged to flow from the inlet to the DPF and then to the reducing agent arrangementif the silencer comprises a DPF and not a DOC. If the silencer does not comprise anASC the exhaust gas is arranged to flow from the SCR purification system to the outlet.

Fig. 2 shows schematically examples of the possible ways the flow of exhaust gasescan flow through a silencer l2 according to the present invention. The arrows in Fig. 2illustrate the flow of exhaust gases 22, but the reference number 22 is only attached toone of the arrows. The silencer l2 comprises an inlet 20 for leading an exhaust gasflow 22 into the silencer l2 and a diesel oxidation catalyst (DOC) 24 is arrangeddownstream of the inlet 20. A diesel particulate filter (DPF) 26 is arrangeddownstream of the DOC 24 and the DPF 26 can for example be a catalysed soot filter(CSF).

A reducing agent arrangement 28 is arranged downstream the DPF 26 for adding areducing agent 30 (shown in Figs. 3-6) to the eXhaust gas ﬂow 22 in order to reduceNOX contents of the eXhaust gas ﬂow 22. A miXing and vaporisation arrangement 32including a vaporisation chamber for miXing of the eXhaust gas ﬂow 22 and thereducing agent 30, and for vaporisation of the reducing agent 30, is arrangeddownstream of the reducing agent arrangement 28. A se1ective cata1ytic reduction(SCR) purification system 34 comprising a SCR-substrate is arranged downstream themiXing and vaporisation arrangement 32. An ammonia s1ip cata1yst (ASC) 38 isarranged downstream of the SCR-purification system 34 and an out1et 40 for 1eading the eXhaust gas ﬂow 22 out from the si1encer 12 is arranged downstream the ASC 38.

In case the si1encer 12 does not comprise a DOC 24 and/or a DPF 26 and/or an ASC38, the eXhaust gas ﬂow 22 is arranged to ﬂow from the in1et 20 to the reducing agentarrangement 28. If the si1encer 12 comprises a DOC 24 and not a DPF 26 the eXhaustgas ﬂow 22 is arranged to ﬂow from the in1et 20 to the DOC 24 and then to thereducing agent arrangement 28. The exhaust gas ﬂow 22 is arranged to ﬂow from thein1et 20 to the DPF 26 and then to the reducing agent arrangement 28 if the si1encer 12comprises a DPF 26 and not a DOC 24. If the si1encer 12 does not comprise an ASC38 the eXhaust gas ﬂow 22 is arranged to ﬂow from the SCR purification system 34 tothe out1et 40.

A type of si1encer usefu1 in the present invention is shown in Fig. 3a which depictsschematica11y a cross-section view of a prior art si1encer 12. The si1encer 12 comprisesa casing 44 with an in1et 20 for 1eading an eXhaust gas ﬂow 22 into the casing 44 andan out1et 40 for 1eading the exhaust gas ﬂow 22 out from the casing 44. The arrows inFig. 3a i11ustrate the ﬂow of exhaust gases 22, but the reference number 22 is on1yattached to one of the arrows. Fig. 3a does not show the DOC 24, the DPF 26 and theASC 38. The si1encer 12 further comprises a miXing and vaporisation arrangement 32which comprises a vaporisation chamber 42. The vaporisation chamber 42 is arrangedinside the casing 44, such that a duct 46 is provided between the vaporisation chamber42 and the casing 44. The vaporisation chamber 42 is provided with a first end 48 and a second end 50. The first end 48 of the vaporisation chamber 42 is in ﬂuid connection with the inlet 20 of the Casing 44 and the second end 50 of the Vaporisation Chamber42 is in ﬂuid ConneCtion with the outlet 40 of the Casing 44, and eXhaust gases 22inside the Vaporisation Chamber 42 are arranged to flow in a direction 100 from thefirst end 48 to the second end 50 of the Vaporisation Chamber 42. Also exhaust gases22 in the duCt 46 are arranged to ﬂow in the same direCtion 100. ln this way it ispossible for the eXhaust gas ﬂow 22 to heat the Vaporisation Chamber 42 and the temperature of the Vaporisation Chamber 42 to be kept at a stable leVel.

HoweVer, in other embodiments the eXhaust gas ﬂow Could be arranged to reverseﬂow direCtion inside the silenCer. For example the exhaust gas ﬂow Could be arrangedto ﬂow through more than one Channel inside the silenCer and thus turn the ﬂowdireCtion aCCordingly. SuCh a silenCer is presented in Fig. 3b. In this embodiment, theeXhaust gas ﬂow is lead into the inlet 22, through the duCt 46, preferably in a swirlingﬂow, thereby Warming the wall of the Vaporisation Chamber 42, before the eXhaust gasﬂow is turned 180° and led through the Vaporisation Chamber 42 in the other direCtion towards the outlet 40 of the Casing 44.

The silenCers 12 in Figs 3a and 3b further Comprises a reduCing agent arrangement 28for adding a reduCing agent 30 to the eXhaust gas ﬂow 22 in order to reduCe NOXContents of the eXhaust gas ﬂow 22. The reduCing agent arrangement 28 is arrangedupstream of the Vaporisation Chamber 42. The reduCing agent 30 is mixed with theeXhaust gas ﬂow 22 inside the Vaporisation Chamber 42. The silenCer 12 alsoComprises a SCR-purifiCation system 34 whiCh Comprises a SCR-substrate 36 (shownin Fig. 2). The SCR-purifiCation system 34 is arranged downstream of the Vaporisation Chamber 42.

The silenCer aCCording to the present inVention Comprises a Variable ﬂow guide fordireCting the ﬂow of eXhaust gases and the reduCing agent inside the VaporisationChamber. The Variable ﬂow guide aCCording to the inVention is arranged upstream ofthe seCond end of the Vaporisation Chamber suCh that it Can direCt the ﬂow inside theVaporisation Chamber. The Variable ﬂow guide Can be arranged inside the Vaporisation Chamber. The Variable ﬂow guide extends at an angle ot relatiVe to an inside wall of the vaporisation chamber. The ﬂow guide is variable meaning that the angle ot may beadjusted e. g. to optimize the utilization grade of the heat provided by the inside wall ofthe vaporisation chamber for the need while for example back pressure created by the guide can be taken into account.

The vaporisation chamber can be substantially circular cylindrical and has a centre lineand the inside wall is substantially parallel to the centre line. In this way a simplestructure can be provided, but the vaporisation chamber may have also another shape,for example a substantially elliptical cylindrical shape or an asymmetric shape.

The variable flow guide may be attached to the inside wall of the vaporisation chamberby an attachment means. The attachment means may be resilient and/or the variableflow guide may be resilient and comprise for example a resilient material, such as asoft metal or an alloy. ln this way the angle ot of the variable ﬂow guide can bemechanically controllable, e. g. by forces created by the exhaust gas ﬂow, and thus beself-adjusted. The greater the ﬂow is, the smaller the angle ot is, and vice versa, i.e. thelower the ﬂow is, the greater the angle ot is. The angle ot may also be manuallycontrollable. The variable flow guide may be installed in many ways and the exhaustgas ﬂow can control the position and angle of inclination of the variable ﬂow guide inrespect of the extension of the vaporisation chamber. The ﬂow guide may be inclinedin respect of the extension of the vaporisation chamber both in the same direction asthe exhaust gas ﬂow or in the direction which is opposite to the direction of the exhaust gas ﬂow.

It is also possible to regulate the angle ot in other ways. The inlet may comprise a ﬂowmeasuring means for measuring the exhaust gas ﬂow in the inlet and providing anoutput signal for the exhaust gas ﬂow to a communication bus, such as a CAN bus. Itis also possible to use a ﬂow calculating means for calculating the exhaust gas ﬂow inthe inlet and providing an output signal for the exhaust gas ﬂow to the communicationbus, such as the CAN bus. The inlet may also comprise a temperature measuringmeans for measuring or calculating the temperature of the exhaust gases in the inletand providing an output signal for the temperature of the exhaust gases to the communication bus. The variable ﬂow guide may be controlled by a control unit that 11 receiVes the output signal for the exhaust gas ﬂoW and the output signal for thetemperature of the exhaust from the communication bus and regulates the angle ot. Byarranging an automatic control of the angle, the angle of the Variable ﬂoW guide maybe further optimized and other parameters in the exhaust gas system and/or fuel systemmay be taken into account When deciding the angle ot for the Variable ﬂoW guide. Thus, for example fuel consumption may be controlled in an accurate Way.

The angle ot is preferably in the range of from about 0° to about 90°, in respect to theextension of the inner Wall of the Vaporisation chamber. The direction of the VariableﬂoW guide can be regulated in the direction of the centre line and a direction transVersely to the centre line.

The Variable ﬂoW guide generates an exhaust gas ﬂoW With a helically shaped ﬂoWpath inside the Vaporisation chamber. Thus, the ﬂoW path inside the Vaporisationchamber has the form of a helix Which is a curVe in a three-dimensional space. Thepitch of the helix is the Width of one complete helix tum, measured parallel to the axisof the helix. The axis of the helix substantially coincides With the centre line of theVaporisation chamber, and the axis of the helix is about the same as the centre line ofthe Vaporisation chamber. The greater the angle is, the smaller the pitch is. The pitch issmallest When the angle is about 90° and the pitch is largest When the angle is close to0°. When the angle is exactly 0° the Variable ﬂoW guide Will not generate an exhaustgas ﬂoW With a helically shaped ﬂoW path inside the Vaporisation chamber because theVariable ﬂoW guide Will be parallel With the inside Wall of the Vaporisation chamber.Thus, according to one embodiment laminar ﬂoW may be obtained, Whereby for example the back pressure in the exhaust gas system may be decreased.

The exhaust gas ﬂoW With a helically shaped ﬂoW path Will ﬂoW along the inside Wallof the Vaporisation chamber and Will generate a sWirl effect inside the Vaporisationchamber. The greater the angle ot is, the greater is the area of the inside Wall that theexhaust gas ﬂoW Will follow by means of the helically shaped ﬂoW path. Thus, Whenthe angle is about 90° the exhaust gas ﬂoW Will ﬂoW along almost the Whole length of the inside Wall of the Vaporisation chamber, and thus the ﬂoW Will be in contact With 12 the inside Wall along a large area of the inside wall. ln this way the heat of the wallsmay be utilized maXimally. The smaller the angle ot is, the smaller the area of theinside wall is that the flow path will follow. ln this way, back pressure in the systemmay be decreased, for example in situations when the eXhaust gas flow is sufficiently hot and the flow rate of the eXhaust gas is stable and relatively high.

The eXhaust gas flow with a helically shaped flow path may attain one or severalcomplete heliX tums inside the vaporisation chamber. It is also possible that theeXhaust gas ﬂow will not attain a complete heliX tum inside the vaporisation chamber.It is both the above mentioned angle ot and the length of the vaporisation that deterrnines the number of complete heliX turns.

The greater the area of the inside wall that the ﬂow path will follow is, the greater thevaporisation of the reducing agent is. The smaller the area of the inside wall that theﬂow path will follow is, the smaller the vaporisation of the reducing agent is. Thus, thevariable ﬂow guide makes it possible to adjust the vaporisation degree of the reducingagent. Thus, it is possible to increase the vaporisation of urea solution and thereby it ispossible to decrease the formation of urea lumps or urea crystals. The variable ﬂowguide makes it also possible to adjust where the reducing agent will hit the inside wallof the vaporisation chamber. It is thereby possible to alter where the reducing agentwill hit the inside wall of the vaporisation chamber and to prevent that the ureasolution will encounter substantially the same region of the vaporisation chamberthroughout the period of time. Thereby, it is possible to reduce coatings formed by theurea solution on the inside wall of the vaporisation pipe. Thus, it is possible to reduce backpressure and to increase the lifetime of the vaporisation chamber.

When the revolutions of the engine are at an almost constant level during a relativelong time period, for example during light haulage on an almost ﬂat and straight roador during generator operation, the gas ﬂow can be regulated such that it will initiallyhit the inside wall of the vaporisation chamber at a specific spot near the first end ofthe vaporisation chamber to enable as great area of the inside wall as possible to be in contact with the gas ﬂow. 13 It Would be an advantage to be able to regulate the angle ot of the variable ﬂow guidesuch that the exhaust gas ﬂow with a helically shaped ﬂow path will initially hit theinside wall of the vaporisation chamber close to the same spot independent of the rateof the exhaust gas ﬂow. For example the exhaust gas flow may have a relatively lowﬂow rate, e. g. below about 400 kg/h or the exhaust gas flow may have a relatively highﬂow rate, e. g. at least about 3000 kg/h, and these ﬂows need to be differently regulatedand directed by the variable flow guide so that the gas ﬂow can hit the inside wall ofthe vaporisation chamber at nearly the same initial hit spot. Different regulation of thevariable ﬂow guide provides nearly the same utilization of the vaporisation chamberand thus optimized vaporisation degree for the reducing agent during both low andhigh exhaust gas ﬂow rates. Thereby the utilization of the inside wall of the vaporisation chamber can be optimized for many different ﬂows.

For example, when the exhaust gas ﬂow in the inlet of the casing has a relative highrate, e. g. about 3000 kg/h, and/or a temperature of e. g. about 500°C, the angle ot ispreferably about 0°. Thereby the variable ﬂow guide will be positioned parallel withthe inside wall of the vaporisation chamber and will not create swirl in the exhaust gasﬂow. In this way the variable ﬂow guide will not disrupt the exhaust gas ﬂow andcause for example a high back pressure in the exhaust system. Hence the fuel consumption can be reduced.

On the other hand, when the exhaust gas ﬂow rate in the inlet of the casing is low, e. g.about 400 kg/h and/or the temperature of the exhaust gases in the inlet of the casing arelow, e. g. below about 300°C, the angle can be 90°. In this way, the gas ﬂow will attaina helix shaped ﬂow path and thus follow the inside wall of the vaporisation chamber,whereby maximum heating of the exhaust gas and/or the reducing agent inside the vaporisation chamber can be obtained.

An example of a silencer according to the present invention will be further describedwith reference to Fig. 4, 5 and 6. Fig. 4 depicts a cross-section view of a silencer 12 according to one embodiment of the present invention. The silencer in Fig. 4 is similar 14 to the silencer in Fig. 3a, except that the silencer in Fig. 4 shows a Variable ﬂow guide52 for directing the ﬂow of exhaust gases 22 and the reducing agent 30 inside theVaporisation chamber 42. Fig. 5 depicts a perspective View of the Vaporisation chamberaccording to the same embodiment of the present inVention that Fig. 4 shows. Fig. 6shows similar Vaporisation chamber as Fig. 5, except that in Fig. 6 an exhaust gas ﬂow 22 has a different helically shaped ﬂow path inside the Vaporisation chamber 42.

The Variable flow guide 52 is arranged upstream of the second end 50 of theVaporisation chamber 42, and directs the flow of exhaust gases 22 and the reducingagent 30 inside the Vaporisation chamber 42. The Variable flow guide 52 is arrangedinside the Vaporisation chamber 42 and the extension of the Variable flow guide 52 hasan angle ot relatiVe to an extension of the inside wall 54 of the Vaporisation chamber42. The Vaporisation chamber 52 is substantially circular cylindrical and has a centreline CL, which is shown in Fig. 5 and 6. Thus, the inside wall 54 is substantially parallel to the centre line CL.

Fig. 4 shows a ﬂow measuring means 56, a CAN (controller area network) bus 58, atemperature measuring means 60 and a control unit 62. The inlet 20 comprises a flowmeasuring means 56 for measuring the exhaust gas ﬂow 22 in the inlet 20 and forproViding an output signal regarding the quantity of the exhaust gas ﬂow 22 to theCAN bus 58. The inlet 20 also comprises a temperature measuring means 60 formeasuring the temperature of the exhaust gases 22 in the inlet 20 and proVides anoutput signal regarding the temperature of the exhaust gases 22 to the CAN bus 58.The Variable ﬂow guide 52 can be controlled by a control unit 62 that receiVes theoutput signal regarding the exhaust gas ﬂow 22 and the output signal regarding thetemperature of the exhaust 22 from the CAN bus 58 and regulates the angle ot according to predeterrnined Values.

The Variable ﬂow guide 52 is attached to the inside wall 54 of the Vaporisationchamber 42 by an attachment means 64 and the attachment means 64 is resilient tocontrol the angle ot by means of the ﬂow of the exhaust gas 22 or manually. As explained also aboVe, the higher the ﬂow 22, the smaller the angle ot is and the lower the ﬂow 22, the greater the angle ot is. The Variable ﬂow guide 52 is installed by meansof the attachment means 64 so that the exhaust gas flow 22 can control the position ofthe Variable ﬂow guide 52 in respect of the extension of the Vaporisation Chamber 42and thus the angle ot of the Variable flow guide 52 in respect of the extension of the Vaporisation chamber 42.

The angle ot can be in the range of from about 0° to about 90° in respect to the insidewall of the Vaporisation chamber and can be inclined in the same or opposite directionof the exhaust gas flow. Thus, the Variable flow guide 52 can be regulated in thedirection of the centre line CL and a direction transVersely to the centre line CL. It mayalso possible to regulate the Variable flow guide 52 in a direction transVersely a planedefined by the direction of the centre line CL and the direction transVersely to the centre line CL.

The Variable flow guide 52 generates an exhaust gas flow 22 with a helically shapedflow path inside the Vaporisation chamber 42. The arrows in Pig. 4 illustrate the flowof exhaust gases 22, but the reference number 22 is only attached to two of the arrows.Thus, the flow path inside the Vaporisation chamber 42 has the form of a helix. Thepitch P of the helix that is shown in Pig. 5 is the width of one complete helix turn,measured parallel to the axis of the helix. The axis of the helix coincides essentiallywith the centre line CL of the Vaporisation chamber 42. Thus, the axis of the helix isessentially the same as the centre line CL. The pitch P is smallest when the angle ot isabout 90° and the pitch P is largest when the angle ot is close to 0°. When the angle ot isexactly 0° the Variable flow guide 52 will not necessarily generate an exhaust gas flow22 with a helically shaped flow path inside the Vaporisation chamber 42, but insteadthe flow path inside the Vaporisation chamber 42 is almost straight or laminar (asshown in Pig. 3a). When the angle is about 90° the exhaust gas flow 22 will flow alongalmost the whole length of the inside wall 54 of the Vaporisation chamber 42, and thusthe flow will be in contact with a large portion the inside wall 54 and the residencetime of the flow in the Vaporisation chamber is long. In this way the heat of the wallsmay be utilized maximally. The smaller the angle ot is, the smaller the area of the inside wall 54 is that the flow 22 follows. In this way, back pressure in the system may 16 be deCreased, for example in situations When the eXhaust gas ﬂow 22 is suffiCiently hot and the ﬂow rate of the eXhaust gas is stable and relatively high.

As shown in Fig. 4, 5 and 6, the eXhaust gas ﬂow 22 with a heliCally shaped ﬂow pathwill ﬂow along the inside wall 54 of the vaporisation Chamber 42 and will generate aswivel or swirl effect inside the vaporisation Chamber 42. The greater the angle ot is,the greater is the area of the inside wall 54 that the exhaust gas ﬂow 22 will follow.Thus, when the angle ot is about 90° the eXhaust gas ﬂow 22 will follow the inside wall54 of the vaporisation Chamber 42 nearly along the whole length of the vaporisationChamber 42. The smaller the angle ot is, the smaller is the area of the inside wall 54 that the exhaust gas ﬂow 22 will follow.

The eXhaust gas ﬂow 22 may attain one or several Complete heliX tums inside thevaporisation Chamber 42. Several Complete heliX tums are illustrated in Fig. 4 and Fi g.5. The eXhaust gas ﬂow 22 may have a heliCally shaped ﬂow path but not reaCh aComplete heliX tum inside the vaporisation Chamber 42, as shown in Fig. 6. It is boththe angle ot and a length L, whiCh is shown in Fig. 6, of the vaporisation Chamber 42 that determines the number of Complete heliX turns.

In Fig. 4-6 the variable ﬂow guide 52 is arranged inside the vaporisation Chamber 42.However, the variable ﬂow guide 52 may be arranged at other loCations in the silenCerl2. There Can also be several variable ﬂow guides plaCed in the silenCer at differentloCations, as long as the ﬂow of the eXhaust gases inside the vaporisation Chamber Canbe direCted at a desirable direCtion. It is important that the eXhaust gas ﬂow Can bedireCted suCh that the exhaust gases Can utilize the heat of the walls in the vaporisationChamber, e. g. by generating a heliCally shaped ﬂow path inside the vaporisationChamber. It is possible to arrange the variable ﬂow guide upstream of the DOC. It isalso possible to arrange the variable ﬂow guide upstream of the DPF. The variableﬂow guide may also be arranged upstream of the reduCing agent arrangement. It is alsopossible to arrange the variable ﬂow guide upstream of the miXing and vaporisationarrangement. As mentioned above, it is possible that the silenCer does not Comprise a DOC and/or a DPF. Preferably, the variable ﬂow guide is arranged as Close to the first 17 end of the Vaporisation chamber as possible so as to enable an easy direction of theexhaust gas ﬂow. The Variable ﬂow guide may be placed at the desired location in theeXhaust gas line leading the gases through the silencer in a sirnilar manner as in theVaporisation chamber explained above, and the inclination of the Variable flow guide ismade in respect of the extension of the eXhaust gas line, but it is important that ahelically shaped flow path inside the Vaporisation chamber can be obtained. Examplesof different possible locations of the Variable flow guide 52 will be described withreference to Fig. 7a-7e which schematically show a silencer l2 comprising the Variableflow guide 52 for directing the flow of eXhaust gases 22 and the reducing agent 30 inside the Vaporisation chamber 42 according to the present inVention.

Fig. 7a shows that the Variable ﬂow guide 52 is arranged upstream of the DOC 24. It isalso possible to arrange the Variable ﬂow guide 52 upstream of the DPF 26, as shownin Fig. 7b. The Variable ﬂow guide 52 may also be arranged upstream of the reducingagent arrangement 28. This is shown in Fig. 7c. It is also possible to arrange theVariable ﬂow guide 52 upstream of the miXing and Vaporisation arrangement 32, asshown in Fig. 7d. As described in Fig. 4, the Variable ﬂow guide 52 may also be arranged inside the miXing and Vaporisation arrangement 32. This is shown in Fig. 7e.

As mentioned aboVe, the silencer l2 needs not to comprise a DOC 24 and/or a DPF 26.

Preferably, the Variable ﬂow guide 52 is arranged as close to the first end 48 of the Vaporisation chamber 42 as possible.

The inVention as presented aboVe in relation to Figs. 4-6 can also be included in a silencer of the type presented in Fig 3b.

The present inVention also relates to a method for eXhaust gas purification by means ofthe silencer according to the present inVention and Fig. 8 shows in a ﬂow chart thesteps of the method according to the present inVention. The method comprises thefollowing steps: a) leading the eXhaust gases 22 to the inlet 20 of the casing 44 of the silencer l2, the inlet 20 comprising an arrangement 28 for adding a reducing agent 30; 18 b) leading the exhaust gases 22 from the inlet 20 of the casing 44 of the silencer 12 tothe first end 48 of the Vaporisation chamber 42 and to the duct 46; c) leading the eXhaust gases 22 in the Vaporisation chamber 42 to the second end 50 ofthe Vaporisation chamber 42; d) leading the eXhaust gases 22 from the second end 50 of the Vaporisation chamber 42and from the duct 46 to the outlet 40 of the casing 44 of the silencer l2; e) arranging the Variable ﬂoW guide 52 upstream of the second end 50 of theVaporisation chamber 42 for directing the ﬂoW of eXhaust gases 22 and reducing agent inside the Vaporisation chamber 42.

The present description of the preferred embodiments of the present invention isprovided With the object of illustrating and describing the invention. The embodimentsdescribed are not intended to be exhaustive or to limit the invention, as it is limited by the scope of the attached claims.

Claims

19 Claims

1. A silencer (12) for a combustion engine (2), which silencer (12) comprises a casing(44) with at least one inlet (20) for leading a ﬂow of eXhaust gases (22) into the casing(44) and at least one outlet (40) for leading the flow of eXhaust gases (22) out from thecasing (44), a Vaporisation chamber (42) provided with a first end (48) and a secondend (50), wherein the Vaporisation chamber (42) is situated inside the casing (44) suchthat a duct (46) is provided between the Vaporisation chamber (42) and the casing (44),wherein the first end (48) of the Vaporisation chamber (42) is in ﬂuid connection withthe inlet (20) of the casing (44) and the second end (50) of the Vaporisation chamber(42) is in ﬂuid connection with the outlet (40) of the casing (44) and eXhaust gases (22)inside the Vaporisation chamber (42) are arranged to ﬂow in a direction (100) from thefirst end (48) to the second end (50) of the Vaporisation chamber (42), which silencer(12) further comprises a selectiVe catalytic reduction (SCR) purification system (34)which comprises a SCR-substrate (36) arranged downstream of the Vaporisationchamber (42) and an arrangement (28) for adding a reducing agent (30) to the eXhaustgas flow (22) arranged upstream of the Vaporisation chamber (42), characterized inthat the silencer (12) comprises a Variable flow guide (52) for directing the flow ofeXhaust gases (22) and reducing agent (30) inside the Vaporisation chamber (42) andwhich Variable flow guide (52) is arranged upstream of the second end (50) of theVaporisation chamber (42), which Variable ﬂow guide (52) is arranged to generate aneXhaust gas ﬂow (22) with a helically shaped ﬂow path inside the Vaporisationchamber (42).

2. A silencer according to claim 1, characterized in that the Variable ﬂow guide (52)is arranged inside the Vaporisation chamber (42) and eXtends at an angle ot relatiVe to an inside wall (54) of the Vaporisation chamber (42).

3. A silencer according to claim 2, characterized in that the angle ot of the Variable ﬂow guide (52) is mechanically controllable.

4. A silencer according to any one of claims 2 or 3, characterized in that the angle ot of the Variable ﬂoW guide (52) is manually controllable.

5. A silencer according to claim 2, characterized in that the inlet (20) comprises aﬂoW measuring means (56) for measuring or calculating the eXhaust gas ﬂoW (22) inthe inlet (20) and providing an output signal for the eXhaust gas ﬂoW (22) to acommunication bus (58), and a temperature measuring means (60) for measuring orcalculating the temperature of the eXhaust gases (22) in the inlet and providing anoutput signal for the temperature of the eXhaust gases (22) to the communication bus(58), and Wherein the Variable ﬂoW guide (52) is controlled by a control unit (62) thatreceiVes the output signal for the exhaust gas ﬂoW (22) and the output signal for thetemperature of the eXhaust gas (22) from the communication bus (58), and regulates the angle ot.

6. A silencer according to any one of claims 2-5, characterized in that the VariableﬂoW guide (52) comprises an attachment means (64) Which attachment means (64) and/or the Variable ﬂoW guide (52) is resilient.

7. A silencer according to any one of claims 2-6, characterized in that the angle ot isin the range of from about 0° to about 90°, in respect to the extension of the inner Wall of the Vaporisation chamber (48).

8. A silencer according to any one of the preceding claims, characterized in that the Vaporisation chamber (42) is substantially circular cylindrical.

9. A silencer according to any one of the preceding claims, characterized in that the Vaporisation chamber (42) is substantially elliptical cylindrical.

10. A silencer according to claims_l, characterized in thatthe Variable ﬂoW guide (52) is arranged upstream of the first end (48) of the Vaporisation chamber (42) and that the extension of the Variable ﬂoW guide (52) has an angle ot relatiVe to an inside Wall (54) of the Vaporisation chamber (42). 21

11. A silencer according to claimsﬂ, characterized in thatthe Variable ﬂoW guide (52) is arranged upstream of the arrangement (28) for adding a thireducing agent (30) to the exhaust gas ﬂoW (22).

12. An eXhaust system for a combustion engine, characterized in that the eXhaust system (10) comprises a silencer (12) according to any one of claims 1-11.

13. A vehicle (1), characterized in that the vehicle (1) comprises an eXhaust system (10) according to claim 12.

14. A method for eXhaust gas purification by means of a silencer (12) according to anyof claims 1-11, Which method comprises the following steps: a) leading the eXhaust gases (22) via an exhaust gas line (47) into the inlet (20) of thecasing (44) of the silencer (12), the inlet (20) comprising an arrangement (28) foradding a reducing agent (30); b) leading the exhaust gases (22) from the inlet (20) of the casing (44) of the silencer(12) to the first end (48) of the vaporisation chamber (44) and to the duct (46); c) leading the eXhaust gases (22) in the vaporisation chamber (42) to the second end(50) of the vaporisation chamber (42); d) leading the exhaust gases (22) from the second end (50) of the vaporisation chamber(42) and from the duct (46) to the outlet (40) of the casing (44) of the silencer (12); e) arranging a Variable ﬂoW guide (52) upstream of the second end (50) of thevaporisation chamber (42) for directing the ﬂoW of exhaust gases (22) and reducing agent (30) With a helically shaped ﬂoW path inside the vaporisation chamber (42).