WO2008006815A1

WO2008006815A1 - Storage system for ammonia precursor

Info

Publication number: WO2008006815A1
Application number: PCT/EP2007/057003
Authority: WO
Inventors: Francois Dougnier; Joel Op De Beeck; Vincent Potier; Jules-Joseph Van Schaftingen
Original assignee: Inergy Automotive Systems Research (Société Anonyme)
Priority date: 2006-07-12
Filing date: 2007-07-10
Publication date: 2008-01-17
Also published as: FR2903727B1; FR2903727A1

Abstract

System for storing an ammonia precursor for injection into an exhaust line (4) of an internal combustion engine, the said system comprising a tank (1) equipped with a ventilation line (10) comprising a canister (3) for absorbing the ammonia vapours generated in the tank, this canister being connected to a purge line (13) mountable on the exhaust line of the engine.

Description

Storage system for ammonia precursor

The present application relates to a system for storing an ammonia precursor (in particular, an aqueous urea solution) to be injected into the exhaust line of an internal combustion engine.

Laws governing passenger and utility vehicle emissions require, inter alia, a reduction of the nitrogen oxide NO_x releases into the atmosphere. This goal is known to be achieved by the SCR (Selective Catalytic Reduction) process, which serves to reduce the nitrogen oxides by injecting a reducing agent, generally ammonia, into the exhaust line. This ammonia may be produced by the thermolytic decomposition of a solution of an ammonia precursor whereof the concentration may be that of the eutectic. Such an ammonia precursor is generally a urea solution.

With the SCR process, the high NO_x releases produced in the engine during combustion at optimized efficiency are treated at the engine outlet in a catalyst. This treatment requires the use of the reducing agent in a precise concentration and in an extreme quality. The solution is thus accurately metered and injected into the exhaust gas stream, where it is hydrolysed, before converting the nitrogen oxide (NO_x) to nitrogen (N₂) and water (H₂O). For this purpose, it is necessary to equip the vehicles with a tank containing an aqueous urea solution, and with a device for metering and injecting the desired quantity of additive into the exhaust line.

Several urea solution storage and feed systems have been provided in the prior art. Some of these systems have even been designed to inhibit the effects associated with the decomposition of the onboard urea solution, which, under the action of heat, leads to the liberation of ammonia and carbon dioxide, which is in proportion to the temperature to which the solution is raised. The ammonia releases could in fact promote corrosion and be the source of olfactory pollution, due to the irritating property of this gas, whereof the detection threshold is between 0.5 and 37 mg/m³ of air.

Thus, application JP 2003-314252 describes a urea storage system comprising a tank and a canister for adsorbing the ammonia vapours generated in the tank before releasing to the atmosphere the pressurized gases generated above the urea solution in the closed tank. Application US 2006/0051276 discloses a system for adsorbing these vapours comprising a scrubbing cylinder containing water, and a safety valve.

Both of these documents propose the regular replacement of the canister and cylinder respectively, in order to guarantee the satisfactory long-term operation of the system. This procedure implies action by the user which is unpleasant (due to the olfactory problem discussed above). In the case of the canister, it is also costly.

It is the object of the present application to solve these problems by providing a storage system for urea solutions which allows automatic and controlled regeneration of the canister.

For this purpose, the present invention relates to a system for storing an aqueous urea solution for injection into an exhaust line of an internal combustion engine, the said system comprising a tank equipped with a ventilation line comprising a canister for adsorbing the ammonia vapours generated in the tank, this canister being connected to a purge line mountable on the exhaust line of the engine.

The present invention therefore relates to a storage system for aqueous urea solutions. In accordance with the above, in the context of the present invention, "aqueous urea solution" means any ammonia precursor to which the present invention can be applied. Eutectic urea solutions (comprising 32.5 % by weight of urea in water) are suitable in the context of the invention.

These solutions are intended to be injected into the exhaust gases of any internal combustion engine liable to generate NO_x in its exhaust gases. It may be an engine with or without fuel return line (that is, a line returning the surplus fuel not consumed by the engine to the fuel tank). It is advantageously applied to diesel engines and, in particular, to vehicle diesel engines and, most preferably, to heavy duty vehicle diesel engines.

The inventive system comprises at least one tank for storing the urea solution. This tank may be made from any material, preferably having chemical resistance to the additive concerned. It is generally made from metal or plastic. Polyolefin resins, particularly polyethylene (and more particularly, HDPE or high density polyethylene), are preferred materials.

According to the invention, the tank is equipped with a ventilation line which generally terminates in its upper wall (in fact, in the head of the filler pipe) and through which the pressurized gases above the stored solution are discharged. Preferably, this line comprises at least one valve calibrated to ventilate the tank (that is, to remove the pressurized gases by sending them to the canister) only above a certain pressure (generally equal to or higher than 200 mbar, or even 400 mbar, but preferably lower than or equal to 800 mbar, or even 600 mbar). This arrangement serves to limit the gas release. For this purpose, it is possible to use a pressure/vacuum safety valve fitted with two spring valves, one limiting the overpressure in the tank, and the second allowing air intake in case of vacuum.

This check valve may be positioned between the canister and its connection to the atmosphere, or between the tank and the canister. The latter alternative is preferred, because it limits the quantity of vapours to be adsorbed. In this case, the valve in question is preferably located near the place where the ventilation line terminates in the tank. According to a particularly preferred alternative of the invention, this place is located in the head of the filler pipe and the calibrated valve is integrated to the obturator (cap) thereof. It is thereby removed or retracted when the tank is filled.

According to a particularly preferred alternative of the invention which is the subject matter of a co-pending application in the name of the applicant, the inventive system also comprises (in addition to the abovementioned pressurizing valve) a device for sending the vapours present in the tank to the canister just before its filling, regardless of the pressure therein. In a particularly preferred manner, the system according to this alternative of the invention also comprises a device for sending the vapours present in the tank to the canister during its filling. According to the invention, the ventilation line comprises a canister or box comprising a substance capable of adsorbing the ammonia vapours. The material therein preferably consists of porous solids with high specific surface area (modified activated carbons, zeolites, molecular sieves, metal oxides, vanadium, titanium, and also alumino silicates). Such a canister is generally connected, on the one hand, to the ventilation line and, on the other, to the atmosphere.

According to the invention, this canister is also connected to the engine exhaust line by a purge line. In the context of the present invention, "purge line" means a line for conveying the releases from the canister during its regeneration, into the exhaust gases. - A -

The inventive system is preferably equipped with a device for aspirating a purge gas. A device offering good results is a Venturi and, considering the application, this Venturi is advantageously activated by the exhaust gases.

According to a first alternative, which is preferred, the purge gas precisely consists of exhaust gas which is forced to pass through the canister to regenerate (purge) it. In practice, this can be done by a branch on the exhaust line (upstream of the urea solution injector), through aspiration by a Venturi type device via the purge line. In this alternative, during ventilation, the ammonia is adsorbed on the canister, and the purified air can be injected into the exhaust gases via the purge line.

According to a second alternative, the purge line comprises a device which is capable of aspirating air through the canister to regenerate (purge) it, and of sending the gases resulting from regeneration to the exhaust gases. Such a device may be a Venturi placed at its end, which is preferably activated by the passage of the exhaust gases. The air is aspirated via a simple nipple connected to the canister, which is advantageously the same as the one for ventilating the tank. In fact, in this alternative, during ventilation, the ammonia is adsorbed on the canister, and the purified air is discharged to the atmosphere via a nipple.

The purge using the exhaust gases is preferred, because the effectiveness of the purge is enhanced by the high temperature of the gases. However, purging with air avoids an additional branch on the exhaust line.

Preferably, the inventive system also comprises at least one valve for isolating certain parts of the system in ventilation or in purge respectively. Solenoid valves controllable by an onboard computer (which manages the operation of the engine (ECU or Engine Control Unit) for example, that which manages the fuel system (FSCU or Fuel System Control Unit) or any other control unit yield good results. In the case in which the calibrated ventilation valve is placed between the tank and the canister, this valve may perform both functions (ventilation in case of overpressure, closure of the tank/canister connection in case of purge). This is feasible by using a pressure/vacuum safety valve as described previously.

When the exhaust gases are used as purge gas, this valve is preferably positioned on the ventilation line, at the place of the upstream branch. It serves respectively to open the branch and to close the connection to the tank (during the purge) or to close the branch and open the connection to the tank (during ventilation). When the purge gas is air, this valve is preferably positioned on the purge line and respectively opens the said line during the purge, and closes it during ventilation.

The present invention further relates to a motor vehicle equipped with a system as described above. In other words, it relates to a vehicle equipped with an internal combustion engine having an exhaust line and comprising a tank equipped with a ventilation line comprising a canister capable of adsorbing the ammonia vapours generated in the tank, the canister being connected to a purge line mounted on the engine exhaust line.

In this vehicle, the purge cycles are preferably managed automatically by a computer which may be specific to the management of the urea storage and injection system. It may also be entrusted to a computer already mounted on board the vehicle such as the onboard computer managing the running of the engine (ECU or Engine Control Unit), or the computer managing the fuel system (FSCU or Fuel System Control Unit). In this case, preferably, the ECU or FSCU manages the entire SCR function.

The present invention is illustrated in a non-limiting manner by Figures 1 to 3. Figure 1 shows a urea storage system incorporating certain alternatives described above, and whereof the purge is obtained using the exhaust gases, and Figure 2, such a system in which the purge is carried out with air. These two figures illustrate the same alternative device for ventilation just before filling. Figure 3 shows in detail the device for ventilation just before the filling of the systems shown in Figures 1 and 2, requiring an intermediate ring-shaped part.

In these figures, identical numbers denote identical or similar elements.

The figures show a tank (1) equipped with ventilation line (10) which terminates in the top of the filling manifold, and a valve (2) calibrated at 500 mbar for maintaining an overpressure in the tank (1). This valve (2) is integrated in a cap (12) and it comprises a first orifice (9) communicating with the tank (1) (via its filling manifold) and a second orifice (7) communicating with the inlet of the ventilation line (10) when the plug is closed. Under the effect of a pressure at least equal to 500 mbar, a mobile element in the valve (or the valve itself) lifts and makes the tank communicate with the ventilation line. A gas stream is then driven through the orifice (9) in the valve (2) and via the ventilation line (10), to a canister (3) in which the ammonia is adsorbed.

The outlet of this canister is connected to the exhaust line (4) of the engine by a purge line (13), and the inlet of the canister is connected either to the exhaust line by a line (6), through a valve (11) (Figure 1), or to the atmosphere via a nipple (6) (Figure 2).

In the system in Figure 1, the valve (11) is provided in the ventilation line (10) to isolate the tank (1) during the purge of the canister (3). During the adsorption process (both in operation and during filling), the valve (11) opens the ventilation line.

In this system, the canister (3) is regenerated by flushing with the exhaust gases. The valve (11) is then in a position in which it closes the ventilation line (10). A fraction of the exhaust gases is then aspirated through the canister via the branch line (6) by a Venturi type device (5) installed in the exhaust line (4).

In the system in Figure 2, the canister is regenerated by flushing with air and the valve (11) is placed on the purge line (13). During the purge, the valve (11) is in the open position; air enters the filter via the nipple (6), being aspirated through the canister (3) and the purge line (13) by a Venturi type device (5) installed in the exhaust line.

The two systems (the one in Figure 1 and the one in Figure 2) are designed to ventilate just before filling regardless of the pressure in the tank (1). The ammonia escaping via the line (10) is also adsorbed on the canister (3) on completion of this operation.

For this purpose, during the opening of the cap (12) for filling, any overpressure in the tank is released when a third orifice (14) of the check valve (2) coincides with the opening of a ring (8) connected with the head of the filler pipe, during the rotational movement (for example a quarter turn) of the cap (12) actuating the valve (2). The interior of the tank communicates with the ventilation line as indicated in Figure 3a, via a hollow chamber (15). The tank (when the cap is inserted) is ventilated as indicated by the arrow in Figure 3b.

Claims

C L A I M S

1 - System for storing an ammonia precursor for injection into an exhaust line of an internal combustion engine, the said system comprising a tank equipped with a ventilation line comprising a canister for adsorbing the ammonia vapours generated in the tank, characterized in that the canister is connected to a purge line mountable on the exhaust line of the engine.

2 - Storage system according to the preceding claim, characterized in that the ventilation line comprises a check valve calibrated to ventilate the tank only at a pressure equal to or higher than 200 mbar.

3 - Storage system according to the preceding claim, characterized in that it comprises a device for sending the vapours present in the tank to the canister just before its filling.

4 - Storage system according to the preceding claim, characterized in that it comprises a device for sending the vapours present in the tank to the canister during its filling.

5 - Storage system according to any one of the preceding claims, characterized in that it comprises a Venturi for aspirating a purge gas.

6 - Storage system according to the preceding claim, characterized in that the purge gas consists of exhaust gas which is forced to pass through the canister via a branch on the exhaust line and aspiration by the Venturi via the purge line.

7 - Storage system according to the preceding claim, characterized in that a valve placed on the ventilation line, at the branch point, is used respectively to open the branch and to close the connection to the tank (during a purge), and to close the branch and to open the connection to the tank (during ventilation).

8 - Storage system according to Claim 5, characterized in that the purge gas is air and in that the Venturi is placed on the purge line and aspirates the air through a nipple present on the canister. 9 - Storage system according to the preceding claim, characterized in that a valve placed on the purge line is used respectively to open the said line (during a purge) and to close it (during ventilation).

10 - Vehicle equipped with a storage system according to any one of the preceding claims.