WO2019170225A1

WO2019170225A1 - Multi doser scr system

Info

Publication number: WO2019170225A1
Application number: PCT/EP2018/055516
Authority: WO
Inventors: Andrew R. CRAIG; Martin A. SYKES
Original assignee: Delphi Technologies Ip Limited; Delphi France Sas
Priority date: 2018-03-06
Filing date: 2018-03-06
Publication date: 2019-09-12

Abstract

A Selective Catalytic Reduction system (10) (SCR system) comprising a tank (12), a pump (14), a first doser (16), a last doser (30) for injecting, in an exhaust pipe, reagent (R) stored in the tank (12) and delivered by the pump (14) to the dosers; the pump and said dosers being arranged in-line, the last doser (30) having just an inlet and being a purging type doser.

Description

Multi Doser SCR system TECHNICAL FIELD

The present invention relates to a multi-doser SCR system having an in line architecture adapted to purging the system.

BACKGROUND OF THE INVENTION

Multi-doser Selective Catalytic Reduction (SCR) systems are adapted to spray reagent in the exhaust gases of an internal combustion engine. Said systems have a tank filled with reagent and a pump flowing said reagent to a plurality of dosers. The dosers of said system are hydraulically connected in parallel to the outlet of the pump or to a common manifold, or via“T” or“Y” junction elements, said systems comprising multiple parallel branches ending with a doser. Such complex and expensive system architecture are typically provided for engines having several bank of cylinders, V6 type for instance, or requiring spray upstream and downstream the exhaust pipe. When the engine stops, a SCR system provided with purging dosers performs a purging cycle to remove the reagent from all the branches, emptying the dosers and avoiding damages due to freezing of the reagent. During said purging cycle, the pump reverses and the dosers open so the reagent remaining in a branch flows back to the tank. To the contrary, a SCR system having non-purging dosers cannot purge the entire system. Non purging dosers are for instance high pressure dosers disclosed in patent

EP1878920B1.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a Selective Catalytic Reduction system (SCR system) comprising a tank, a pump, a first doser, a last doser for injecting, in an exhaust pipe, reagent stored in the tank and delivered by the pump to the dosers. The pump and said dosers are arranged in-line, the first doser being provided with an inlet for receiving reagent from the pump and with an outlet for delivering reagent to the last doser and wherein the last doser is a purging type doser.

Typically, the first doser is a non-purging type doser. Also, the SCR system comprises a plurality of dosers arranged in-line, one after the other, the first doser in the line being the only doser to receive the reagent from the pump, all the other dosers from the second to the last receiving reagent from the previous doser in the line. All the dosers from the first to the last but one are non-purging type dosers.

The invention further extends to a method to purge a SCR system provided with a pump a plurality of dosers arranged in-line, only the first doser being connected to the pump all the other dosers from the second to the last doser being connected to the previous doser in the line, the last doser being a purging- type doser; the method comprising the step of:

a) open the last doser in the SCR line;

b) close all dosers intermediate the pump and said last doser ; c) reverse the pumping direction so that is created an aspiration in the SCR line, sucking back toward the tank the reagent R remaining in the last doser.

During said aspiration step c) flow is created in all the dosers and in the feed pipes, thus sucking back toward the tank the reagent remaining in all the dosers and all the feed pipes.

The invention further extends to an Electronic command unit (ECU) adapted to pilot a SCR system purging method as previously described.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying figure 1 which sketches a SCR system as per the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A powertrain system comprises an internal combustion engine expelling gases in an exhaust pipe wherein said exhaust gases are filtered and chemically treated to remove pollutants prior to exiting the tailpipe. The powertrain system further comprises a selective catalytic reduction system 10, hereafter SCR system 10, adapted to spray a reagent R, such as urea fluid, at an injection point of the pipe. Engines having two or more banks of cylinders, such as V6 engines, have several exhaust pipes and thus several reagent injection points. It is also common to have reagent injection in the hot part of the exhaust pipe upstream a particulate filter and also, in the cold part of the pipe downstream said filter.

More in details in reference to figure 1, the SCR system 10 comprises a tank 12 storing the reagent R, a pump 14 immersed in the reagent R is arranged to suck said reagent R and to deliver it to a first doser 16 adapted to open spraying the reagent R at a first injection point Pl of the exhaust pipe and, to close preventing such spray. To flow the reagent from the pump 14 to said first doser 16, a first feed pipe 18 extends from the pump outlet 20 to the inlet 22 of the first doser. Said first doser 16 is also provided with an outlet 24 connected to another feed pipe, which in the example shown is a last feed pipe 26, extending to the inlet 28 of a last doser 30 adapted to spray the reagent R at a last injection point P30 of the exhaust pipe. In the first doser 16, the inlet 22 and the outlet 24 both join a common internal portion 31 wherefrom the reagent flow divides in a portion flowing to a nozzle wherefrom it is sprayed and, another portion exiting the first doser 16 and flowing toward the last doser 30.

An electronic control unit 32, ECU, electrically connected to the dosers 16, 30 delivers opening and closing command signals to said dosers urging them to open and spray the reagent or to close and prevent said spray. Furthermore, the dosers of the SCR system can be liquid cooled, as the first doser 16 shown, or air cooled as the last doser 30 is. Also, the pump 14 represented immersed in the tank may be arranged outside the tank with a suction line from its inlet into the reagent R.

The reagent R being an aqueous liquid such as urea, it freezes whenever the ambient temperature falls below -1 l°C or, if the urea concentration differs, below another threshold temperature. When the engine stops the SCR system 10 performs a purging cycle to prevent reagent remaining in the dosers, or in the feed pipes, to freeze and damage said system. To perform such purging cycle, the dosers open, the pump reverses direction and, a reverse pressure allows gas to flow backward pushing the reagent R toward the tank 12 purging the doser. The SCR system 10 advantageously has an in-line organisation of the dosers. The last doser 30 receives reagent R from the first doser 16 rather than directly from the pump. The fluid connection is done by the first doser 16 that is provided with inlet 22 and outlet 24 in fluid communication with said common internal portion 31. This in-line architecture advantageously simplifies the purging process and frees the system 10 from any flow dividing elements such as connection blocks, T-junction elements, manifold, distributors arranged in the middle of a feed pipe between dosers.

Furthermore, the first doser 16 is a non-purging type injector and, the last injector 30 is a purging type injector. Generally, a non-purging doser is not adapted to open at engine shut-down in order to enable backflow of gas and, a purging type doser is adapted to open and to enable such purging backflow of gas. After completion of a purging cycle of a prior art SCR system, reagent remains in the non-purging dosers and in the branches of the system where are said non purging dosers. To evacuate said remaining reagent, said non-purging dosers can be operated in the normal way and expel said remaining reagent in the exhaust pipe.

When at engine shut-down, the SCR system 10 performs a purging cycle, the ECU 32 sends an opening command signal to the last doser 30, the first doser 16 remains closed and, the pump 14 receives a reverse pumping command signal. Aspired by the pump 14, a purging backflow of gas enters the last doser 30, then flows into the last feed pipe 26, then it gets to the first doser 16 where is purged said internal portion 31 then, the purging gas flow gets to the first feed pipe 18.

Such an in-line architecture can be extended to a SCR systems 10, not shown, provided with three dosers. In this case a second doser 36 is inserted in the line between the first doser 16 and the last doser 30. The first doser receives reagent R from the pump 14, the second doser 36 receives reagent R from the first doser 16 and, the last doser 30 receives reagent R from the second doser 36. Said second doser 36 is a non-purging doser provided, similarly to the first doser 16, with and inlet 22 and with an outlet 24 opening in an internal portion 31.

For purging said three-doser-SCR system, the ECU 32 closes the first and the second dosers, it opens the last doser 30 and it reverses the pump 14 flow direction. More generally, an SCR system 10 having one pump 14,“n” dosers arranged in-line comprises“n” feed pipes, as many as injectors. The first feed pipe 18 is arranged between the pump 14 and the first doser 16 and, the other n-l feed pipes are arranged between the dosers. In such in-line SCR system architecture, all the dosers from the first doser to the last but one are all non-purging type dosers provided with an inlet 22 and with an outlet 24 in fluid communication with an internal portion 31. The nth doser 30, last in the line, connected to said last but one doser has just an inlet 28 and is a purging type doser.

Similarly, for purging said n-dosers in-line SCR system, the ECU 32 executes a method 100 wherein the pump 14 is reversed, the last doser 30 is opened and all the other dosers from the first to the last but one are closed so enabling a gas back flow to purge the system.

LIST OF REFERENCES:

R reagent

P 1 first inj ection point

P30 last inj ection point

10 SCR system

12 tank

14 pump

16 first doser

18 first feed pipe

20 pump outlet

22 first doser inlet

24 first doser outlet

26 last feed pipe

28 inlet of the last doser

30 last doser

31 internal portion

32 ECU

36 second doser

100 purging method

Claims

CLAIMS:

1. Selective Catalytic Reduction system (10) (SCR system) comprising a tank (12), a pump (14), a first doser (16), a last doser (30) for injecting, in an exhaust pipe, reagent (R) stored in the tank (12) and delivered by the pump (14) to the dosers; the pump and said dosers being arranged in-line, the first doser (16) being provided with an inlet (22) for receiving reagent (R) from the pump (14) and with an outlet (24) for delivering reagent (R) to the last doser (30) and wherein the last doser has just an inlet (28) and is a purging type doser.

2. SCR system (10) as claimed in the preceding claim wherein the first doser (16) is a non-purging type doser.

3. SCR system (10) as claimed in claim 2 comprising a plurality of dosers (16, 36, 30) arranged in-line one after the other, the first doser (16) in the line being the only doser to receive the reagent (R) from the pump (14), all the other dosers from the second (36) to the last (30) receiving reagent (R) from the previous doser in the line; all the dosers from the first to the last but one being non-purging type dosers.

4. Method (100) to purge a SCR system (10) as claimed in any one of the preceding claims, said SCR system (10) being provided with a pump (14), a plurality of dosers arranged in-line, only the first doser (16) being connected to the pump (14) all the other dosers from the second (36) to the last (30) doser being connected to the previous doser in the line, the last doser (30) being a purging- type doser; the method comprising the step of:

a) open the last doser (30) in the SCR line;

b) close all dosers intermediate the pump (14) and said last doser (30); c) reverse the pumping direction so that is created an aspiration in the SCR line, sucking back toward a tank (12) reagent (R) remaining in the last doser

(30).

5. Method (100) as claimed in claim 4 wherein during step c), aspiration flow is created in all the dosers and in the feed pipes, thus sucking back toward the tank (12) the reagent (R) remaining in all the dosers and all the feed pipes. 6. Electronic command unit (ECU 32) adapted to pilot a SCR system (10) purging method (100) as claimed in the claims 4 or 5.