WO2005066471A1

WO2005066471A1 - Arrangement for supply of reducing agent

Info

Publication number: WO2005066471A1
Application number: PCT/SE2004/001964
Authority: WO
Inventors: Roger HÄLLEBERG
Original assignee: Scania Cv Ab (Publ)
Priority date: 2004-01-08
Filing date: 2004-12-21
Publication date: 2005-07-21
Also published as: SE525601C2; SE0400008D0; SE0400008L; DE112004002530T5

Abstract

An arrangement for supply of reducing agent to an exhaust line from a combustion engine, comprising an injection device (11) for injecting reducing agent into the exhaust line, a reducing agent tank (15), a reducing agent pump (16), and heating means (30) for heating of reducing agent. The reducing agent tank is divided into at least a first chamber (15a) and a second chamber (15b) which have flow connection with one another, whereby the first chamber comprises an outlet (40) for feeding reducing agent from the reducing agent tank to the injection device, and that the return line comprises a first return line portion (31a) arranged in heat-transferring relationship with the first chamber in order to heat reducing agent present in the first chamber by heat transfer from return fuel in the first return line portion to reducing agent present in the first chamber.

Description

Arrangement for supply of reducing agent

FIELD OF THE INVENTION, AND STATE OF THE ART

The present invention relates to an arrangement according to the preamble of claim 1 for supply of reducing agent to an exhaust line from a combustion engine.

To meet prevailing exhaust cleaning requirements, today's motor vehicles are usually provided with a catalyst in the exhaust line in order to effect catalytic conversion of environmentally harmful components of exhaust gases to environmentally less harmful substances.

One type of catalyst which has been developed and brought into use is based on so-called SCR (Selective Catalytic Reduction) technology. This type of catalyst is hereinafter called SCR catalyst. An SCR catalyst selectively reduces NO_x in exhaust gases but not the oxygen in exhaust gases. In an SCR catalyst, NO_x present in exhaust gases, together with ammonia, is brought into contact with the catalytic substance in the catalyst and is converted to nitrogen and water. Ammonia is a toxic and malodorous substance and it is therefore not appropriate to store ammonia in a vehicle. What is therefore commonly used instead of ammonia in a vehicle equipped with an SCR catalyst is a reducing agent in the form of urea, which does not have the aforesaid disadvantages associated with ammonia. The urea is stored in a special reducing agent tank in the vehicle and is injected via an injection device into the exhaust gases upstream from the SCR catalyst. Injecting urea into exhaust gases results in the formation of ammonia which, as mentioned above, assists catalytic conversion in the SCR catalyst.

A disadvantage associated with urea is that its freezing point is about -6 to -10° Celsius, with consequent risk of urea in the reducing agent tank and in the lines between the reducing agent tank and the injection device freezing when a vehicle equipped with an SCR catalyst is exposed to severe cold. A solution proposed to this problem in US patent specification 5 884 475 A is heating of the reducing agent by the combustion engine's cooling medium being led through the reducing agent tank and along the lines between the reducing agent tank and the injection device. The cooling medium flowing from a combustion engine is often at a very high temperature. To prevent the reducing agent being heated by said cooling medium to such a high temperature as to risk being vaporised, US 5 884 475 A proposes the use of a device for monitoring and controlling the temperature of the reducing agent, e.g. comprising temperature sensors for temperature monitoring and an adjustable valve for regulating the flow of cooling medium which provides the desired heating. A system designed in accordance with the solution proposed in US 5 884 475 A thus may well be complex and expensive.

OBJECT OF THE INVENTION

The object of the present invention is to provide an arrangement which enables easy and cost-effective heating of reducing agent in an arrangement of the type described above for supplying reducing agent from a reducing agent tank to an exhaust line from a combustion engine.

SUMMARY OF THE INVENTION

According to the invention, said object is achieved by an arrangement comprising the features of claim 1.

The solution according to the invention is based on return fuel from a combustion engine being used for heating of reducing agent, whereby the heating of the reducing agent is effected by heat transfer from return fuel which is led through a return line from the combustion engine to a fuel tank. Surplus fuel which in the combustion engine's fuel system bypasses the engine without being injected into the engine cylinders receives from the engine a temperature rise amounting in normal cases to 20-30°

Celsius. In cases where the ambient temperature is not below the reducing agent's freezing point by too great a margin, i.e. when the degree of cold temperature is severe but not extremely severe, this fuel temperature increase is sufficient to enable the return fuel to be used as a heat source for heating the reducing agent to a temperature just above its freezing point. As the fuel bypassing the combustion engine is subjected to a relatively low temperature increase, there is in practice no risk of return fuel heating the reducing agent so powerfully that the latter might reach a temperature close to or exceeding its vaporising point. Thus there is no need of equipment for monitoring and controlling the temperature of the reducing agent, which means that implementing the solution according to the invention is particularly easy and cost-effective. On a vehicle equipped with an SCR catalyst, the reducing agent tank is also normally situated in the immediate vicinity of the fuel tank and the solution according to the invention therefore involves only minor adaptation of the existing fuel return line. This likewise helps to make implementing the solution according to the invention easy and cost-effective. The reducing agent tank is divided into at least a first chamber and a second chamber which have flow connection between them, whereby the first chamber comprises an outlet for supplying reducing agent from the reducing agent tank to the injection device, and part of the return line for return fuel is arranged in a heat-transferring relationship with the first chamber in order to heat the reducing agent in the first chamber by heat transfer from return fuel in that portion of the return line to reducing agent present in the first chamber. Thus a limited volume of the reducing agent present in the reducing agent tank can be heated at an initial stage, thereby considerably hastening the thawing of a first amount of reducing agent. It should be appreciated that the volume of the first chamber needs to be such that the first chamber can accommodate a sufficiently small amount of reducing agent to enable relatively rapid thawing of the latter, and at the same time a sufficiently large amount of reducing agent to enable reducing agent injection as necessary into the exhaust gases for a period of time which is normally long enough for the reducing agent in the second chamber to thaw before the reducing agent initially accommodated in the first chamber is used up.

In this description and the attached claims, the definition "return fuel which is led through a return line from the combustion engine to a fuel tank" is intended to comprise return fuel which has passed through a line which extends directly through the combustion engine or extends along and in direct contact with the combustion engine, and is also intended to comprise return fuel which has passed through a line which extends at a distance from the combustion engine but is situated in a heat-transferring relationship with the combustion engine, so that the return fuel passing through said line can receive an addition of heat from the combustion engine. Thus the definition here concerned denotes fuel which is returned to a fuel tank after having first passed the combustion engine in a heat-transferring relationship with the latter, with the result that said return fuel has been able to receive an addition of heat from the combustion engine and has thus been able to acquire a temperature increase after passing through or close to the combustion engine.

Embodiments of the arrangement are indicated by the dependent claims and the description set out below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail below on the basis of examples of embodiments with reference to the attached drawings, in which:

Fig. 1a is a schematic diagram of a combustion engine with relating fuel system and SCR catalyst, illustrating a first embodiment of the arrangement according to the invention,

Fig. 1b is a schematic diagram of a combustion engine with relating fuel system and SCR catalyst, illustrating a second embodiment of the arrangement according to the invention, and

Fig. 2 is a schematic illustration in more detail of parts of the arrangement according to Fig. 1a and Fig. 1b.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1a depicts schematically a combustion engine provided with an arrangement 10 according to the invention for supply of reducing agent to an exhaust line from the combustion engine. The combustion engine is schematically depicted and is denoted by ref. 1. Exhaust gases leaving the combustion engine 1 pass through an exhaust line 2 and reach the environment via an exhaust outlet 3. An SCR catalyst 4 is arranged in the exhaust line 2. Exhaust gases from the combustion engine 1 are thus caused to pass through this SCR catalyst 4 before they reach the environment via the exhaust outlet 3.

The combustion engine 1 illustrated in Fig. 1a is provided with a fuel system 20 comprising a fuel tank 21 for storage of fuel and an injection device 22 for injecting desired amounts of fuel into the engine cylinders of the combustion engine. Said injection device 22 comprises inter alia an injection pump and injectors. The fuel system 20 further comprises a fuel pump 23 for supplying fuel from the fuel tank 21 to the injection device 22. A first feed line 24 extends between the fuel tank 21 and the fuel pump 23, and a second feed line 25 extends between the fuel pump and the injection device 22. A return line 26 via which surplus fuel from the fuel pump can be returned to the fuel tank 21 extends from the fuel pump 23. The return line 26 is connected to a return line 27 which extends from the injection device 22 and via which surplus fuel from the injection device 22 can be led back to the fuel tank 21. The fuel pump 23 is arranged to feed fuel to the injection device 22 at a relatively low first pressure, while the injection pump of the injection device 22 is arranged to increase the pressure of the fuel for its injection into the engine cylinders at a second pressure substantially higher than said first pressure. The surplus fuel leaving the injection device 22 via the return line 27, the so-called spillage, is pressurised by the injection pump to a high pressure. The surplus fuel from the fuel pump 23 and the injection device 22 is led towards the fuel tank 21 via a common return line 28 which is connected to the return line 26 and the return line 27.

An injection point for reducing agent is situated in the exhaust line 2 upstream from the SCR catalyst 4. The injection of reducing agent is via an injection device 11 comprising one or more injection means 12 arranged in the exhaust line in the form of injection nozzles or the like. This injection device further comprises a proportioning unit 13 which itself comprises a proportioning arrangement and a regulating means, e.g. a control valve or the like, arranged to regulate the supply of reducing agent to said injection means 12, and a control means 14 connected to the proportioning unit 13. The proportioning unit 13 is controlled by said control means 14, which determines the amount of reducing agent to be injected into the exhaust gases on the basis of the prevailing operating conditions of the combustion engine 1 and the SCR catalyst 4.

The arrangement 10 further comprises a reducing agent tank 15, connected to the injection device 11 , for storage of reducing agent, and a reducing agent pump 16, e.g. in the form of a gear pump or piston pump, for feeding reducing agent from the reducing agent tank 15 to the injection device 11. The reducing agent tank 15 and the reducing agent pump 16 have a first reducing agent feed line 17 extending between them via which reducing agent can be fed from the reducing agent tank 15 to the reducing agent pump 16, and a feedback line 18 via which reducing agent can be led back from the reducing agent pump 16 to the reducing agent tank 15. The reducing agent pump 16 and the injection device 11 have a second reducing agent feed line 19 extending between them via which reducing agent can be fed from the reducing agent pump 16 to the injection device 11.

The arrangement 10 also comprises a heating means 30 for heating of reducing agent present in the reducing agent tank 15 and/or in the lines 17, 18, 19 between the reducing agent tank 15 and the injection device 11. According to the invention, this heating means 30 comprises a return line 31 arranged to lead return fuel from the combustion engine 1 to the fuel tank 21 , which return line 31 is arranged in a heat-transferring relationship with at least one part, containing reducing agent, of the arrangement 10 for heating of reducing agent present in said part by heat transfer from return fuel in the return line 31 to reducing agent present in said part. This return line 31 carries the so-called spillage from the combustion engine's fuel injection device 22 and/or surplus fuel from the fuel pump 23 arranged in the fuel system 20 which passes through or close to the combustion engine and thereby receives from the latter an addition of heat. The spillage from the injection device 22 acquires a temperature increase partly by being pressurised by the injection pump and may also receive an addition of heat by heat transfer from the combustion engine. In the embodiment illustrated in Fig. 1a the return line 31 entering the heating means has its upstream end connected at a junction point 33 to the return line 28 which is common to the injection device 22 and the fuel pump 23. In the embodiment illustrated, said return line 31 comprises:

- a first return line portion 31a, denoted by a broken line in Fig. 1a, which is arranged in a heat-transferring relationship with the reducing agent tank 15 in order to heat reducing agent present in the reducing agent tank by heat transfer from return fuel in the first return line portion 31a to reducing agent present in the reducing agent tank,

- a second return line portion 31b arranged in heat-transferring relationship with the feed line 17 between the reducing agent tank 15 and the reducing agent pump 16 in order to heat reducing agent present in this feed line by heat transfer from return fuel in the second return line portion 31b to reducing agent present in this feed line 17,

- a third return line portion 31c arranged in heat-transferring relationship with the feedback line 18 between the reducing agent pump 16 and the reducing agent tank 15 in order to heat reducing agent present in this feedback line by heat transfer from return fuel in the third return line portion 31c to reducing agent present in this feedback line 18, and

- a fourth return line portion 31 d arranged in heat-transferring relationship with the feed line 19 between the reducing agent pump 16 and the injection device 11 in order to heat reducing agent present in this feed line by heat transfer from return fuel in the fourth return line portion 31 d to reducing agent present in this feed line 19.

In the embodiment illustrated, the return fuel in the return line 31 is arranged to pass successively through the fourth return line portion 31 d, the second return line portion 31b, the first return line portion 31a and the third return line portion 31c, although the mutual sequence between the various return line portions may of course vary from case to case depending on what is found advantageous. In the embodiment illustrated, the return line 31 has its downstream end connected to the common return line 28 at a connection point 34, although this return line 31 might of course instead be arranged to lead directly into the fuel tank 21.

The first return line portion 31a extends with advantage in a loop through the reducing agent tank 15 in contact with reducing agent present in the reducing agent tank. In the embodiment illustrated, a first control valve 32 is arranged in the return line 31 , and a second control valve 29 is arranged in the return line 28, downstream from the junction point 33 and upstream from the connection point 34. These control valves 29, 32 make it possible to lead return fuel to the fuel tank 21 via the return line 31 or directly to the fuel tank via the return line 28, depending on the extent to which heating of reducing agent is required or not.

The respective return line portions 31b, 31c and 31 d may be arranged to extend alongside the adjacent reducing agent lines 17, 18, 19, either in direct contact with them or at a distance from them which is short enough to allow what will, in the context, be sufficiently effective heat transfer between return fuel in the respective return line portion and adjacent reducing agent line. Said distance is preferably less than 5 cm. The respective return line portions 31b, 31c and 31 d are with advantage arranged coaxially with the adjacent reducing agent lines 17, 18, 19, in which case each of the reducing agent lines 17, 18, 19 will be arranged to extend inside the pertinent return line portions 31b, 31c, 31 d.

Fig. 1b illustrates an alternative embodiment of the arrangement according to the invention whereby in all operating situations the return fuel is led to the fuel tank 21 via a return line 31 which is in heat- transferring relationship with the parts of the arrangement 10 which contain reducing agent. In this case the arrangement 10 lacks a line via which return fuel might be led directly to the fuel tank 21 , but instead the return fuel passes through the return line 31 which is in heat-transferring relationship with the parts of the arrangement according to the invention which contain reducing agent. In the embodiment according to Fig. 1 b there is therefore no need to arrange any control valve in the return line 31 which leads return fuel from the combustion engine 1 to the fuel tank 21. The arrangement according to Fig. 1b otherwise coincides with the arrangement illustrated in Fig. 1a and described above.

Fig. 2 depicts in more detail parts of the arrangement 10 illustrated in Fig. 1a and Fig. 1 b and the return line 31 entering the heating means 30. The reducing agent tank 15 is here depicted in partly cutaway sideview. In the embodiment here illustrated, the reducing agent tank 15 is divided into a first chamber 15a and a second chamber 15b, with flow connection between them. The first chamber 15a has a smaller volume than the second chamber 15b. The first chamber 15a comprises an outlet 40 for feeding reducing agent from the reducing agent tank 15 to the injection device 11 via the reducing agent pump 16. The feedback line 18 from the reducing agent pump 16 is with advantage arranged to end at an outlet 41 arranged in the first chamber 15a. Said first return line portion 31a is arranged in heat-transferring relationship with the first chamber 15a in order to heat reducing agent present in the first chamber by heat transfer from return fuel in the first return line portion 31a to reducing agent present in the first chamber 15a. The first return line portion 31a extends with advantage in a loop through the first chamber 15a.

The first chamber 15a is separated from the second chamber 15b by separating walls 42a, 42b, preferably made of metal, which have good thermal conductivity for enabling heat propagation via the separating walls from the reducing agent in the first chamber 15a to the reducing agent in the second chamber 15b. The heating means 30 is in this case arranged to heat reducing agent present in the second chamber 15b by transfer via said separating walls 42a, 42b of heat from return fuel in the first return line portion 31a to reducing agent present in the second chamber 15b. In the embodiment illustrated, apertures 43 are arranged at the lower parts of the separating walls 42a, 42b to enable reducing agent to flow between the second chamber 15b and the first chamber 15a.

The outer walls 44a, 44b, 44c, 44d of the reducing agent tank 15 are with advantage thermally insulated to counteract freezing of reducing agent in the reducing agent tank when the ambient temperature falls.

The reducing agent preferably takes the form of urea (CO(NH₂)₂) but may also take the form of some other suitable substance, depending on the catalytic material of the SCR catalyst.

The invention is in no way limited to the embodiments described above, since a multiplicity of possibilities for modifications thereof are likely to be obvious to a specialist in the field without thereby having to depart from the basic concept of the invention as it is defined in the attached claims.

Claims

1. An arrangement for supply of reducing agent to an exhaust line from a combustion engine, comprising an injection device (11 ) for injecting reducing agent into the exhaust line, a reducing agent tank (15) connected to the injection device, a reducing agent pump (16) for feeding reducing agent from the reducing agent tank to the injection device, and heating means (30) for heating of reducing agent, where the heating means (30) comprises a return line (31 ) arranged for leading return fuel from the combustion engine to a fuel tank, which return line (31 ) is arranged in heat-transferring relationship with at least one part, which contains reducing agent, of the arrangement in order to heat reducing agent present in said part by heat transfer from return fuel in the return line (31 ) to reducing agent present in said part, characterised in that - the reducing agent tank (15) is divided into at least a first chamber (15a) and a second chamber (15b) which have flow connection with one another, whereby the first chamber (15a) comprises an outlet (40) for feeding reducing agent from the reducing agent tank (15) to the injection device (11 ), and that - the return line (31 ) comprises a first return line portion (31a) arranged in heat-transferring relationship with the first chamber in order to heat reducing agent present in the first chamber by heat transfer from return fuel in the first return line portion (31a) to reducing agent present in the first chamber (15a).

2. An arrangement according to claim 1 , characterised in that the first return line portion (31a) extends in a loop through the first chamber (15a).

3. An arrangement according to claim 1 or 2, characterised in that the first chamber (15a) is separated from the second chamber (15b) by one or more separating walls (42a, 42b) which have good thermal conductivity, whereby the heating means (30) is arranged to heat reducing agent present in the second chamber (15b) by transfer, via said one or more separating walls (42a, 42b), of heat from return fuel in the first return line portion (31a) to reducing agent present in the second chamber (15b).

4. An arrangement according to any one of the preceding claims, characterised in that the first chamber (15a) has a smaller volume than the second chamber (15b).

5. An arrangement according to any one of the preceding claims, characterised in that the return line (31) comprises a second return line portion (31b) arranged in heat-transferring relationship with a first feed line (17) extending between the reducing agent tank (15) and the reducing agent pump (16), in order to heat reducing agent present in the first feed line by heat transfer from return fuel in the second return line portion (31 b) to reducing agent present in the first feed line (17).

6. An arrangement according to any one of the preceding claims, characterised in that the return line (31 ) comprises a third return line portion (31c) arranged in heat-transferring relationship with a feedback line (18) extending between the reducing agent pump (16), and the reducing agent tank (15), in order to heat reducing agent present in the feedback line by heat transfer from return fuel in the third return line portion (31c) to reducing agent present in the feedback line (18).

7. An arrangement according to any one of the preceding claims, characterised in that the return line (31 ) comprises a fourth return line portion (31 d) arranged in heat-transferring relationship with a second feed line (19) which extends between the reducing agent pump (16) and the injection device (11 ), in order to heat reducing agent present in the second feed line by heat transfer from return fuel in the fourth return line portion (31 d) to reducing agent present in the second feed line (19).