Reductant injection system

Abstract

The present disclosure provides a reductant injection system for an SCR catalyst of an internal combustion engine, the reductant injection system comprising at least one injector, a first storage container for storing liquid reductant and a pump for pumping reductant from the first storage container to the injector for injection into an exhaust gas stream, wherein the injector is cooled by reductant. The reductant injection system may comprise a second storage container for storing liquid reductant and is configured such that the injector can be cooled by reductant from the second storage container.

Claims

1. A reductant injection system for an SCR catalyst of an internal combustion engine, the reductant injection system comprising: at least one injector; a first storage container for storing liquid reductant; a pump for pumping reductant from the first storage container to the injector for injection into an exhaust gas stream, wherein the injector is cooled by reductant; and a second storage container for storing liquid reductant that is configured such that the at least one injector is cooled by reductant from the second storage container, wherein the reductant injection system is configured such that the injector is cooled by reductant from the first storage container and by reductant from the second storage container, wherein the reductant injection system comprises a controller having at least an injection mode and a cooling mode, and wherein at least one of the following applies: in the injection mode, reductant from the first storage container is used both for injection into the exhaust gas stream and for cooling of the injector, and in the cooling mode, reductant from the second storage container is used for cooling of the injector.

2. The system of claim 1, wherein the first storage container has a larger storage capacity than the second storage container.

3. The system of claim 1, wherein the first and the second container are formed by a first and a second section of a reductant tank.

4. The system of claim 1, wherein at least one of the following applies: in the injection mode, a part of the reductant pumped by the pump to the injector for cooling is used for injection, while the remaining reductant is flowing back from the injector, and in the cooling mode, reductant is only circulated through the injector and no reductant is injected.

5. The system of claim 1, wherein the first and the second container each have a suction module for sucking out reductant from the respective container, wherein each suction module has at least one heating arrangement.

6. The system of claim 1, wherein the pump is configured for pumping reductant from the first storage container and from the second storage container to the injector.

7. The system of claim 1, wherein at least one of the following applies: the second storage container has a fluid connection connecting it to the first storage container for reductant to flow from the second storage container to the first storage container, wherein the fluid connection is an overflow, such that reductant will only flow from the second storage container to the first storage container if the second storage container is full, and the fluid connection is connected to a top part of the first storage container such that in case that the reductant in the first storage container is frozen, reductant from the second storage container will flow on top of the frozen reductant in the first storage container.

8. The system of claim 1, wherein the system comprises a reductant fluid line for allowing reductant to flow back from the injector to the second storage container, wherein the system is configured such that the reductant will always flow back to the second storage container.

9. The system of claim 1, wherein the system comprises a filling orifice for refilling of reductant, wherein the refilling orifice is at least one of connected with the second storage container and arranged at the second storage container, wherein the first storage container is filled via the second storage container.

10. The system of claim 1, wherein the second storage container has a storage capacity of at least 10 liters.

11. A reductant storage system for a reductant injection system according to claim 1, the reductant storage system comprising at least the first and the second container.

12. An exhaust gas aftertreatment system comprising an SCR-catalyst and a reductant injection system according to claim 1, wherein the at least one injector is directly connected to an exhaust gas duct of the exhaust gas aftertreatment system upstream of the SCR-catalyst.

13. An internal combustion engine comprising at least one out of: a) an exhaust gas aftertreatment system according to claim 12, and b) a reductant injection system comprising: at least one injector; a first storage container for storing liquid reductant; a pump for pumping reductant from the first storage container to the injector for injection into an exhaust gas stream, wherein the injector is cooled by reductant; and a second storage container for storing liquid reductant that is configured such that the at least one injector is cooled by reductant from the second storage container, wherein the reductant injection system is configured such that the injector is cooled by reductant from the first storage container and by reductant from the second storage container, wherein the reductant injection system comprises a controller having at least an injection mode and a cooling mode, wherein at least one of the following applies: in the injection mode, reductant from the first storage container is used both for injection into the exhaust gas stream and for cooling of the injector, and in the cooling mode, reductant from the second storage container is used for cooling of the injector.

14. A working machine comprising an engine according to claim 13, wherein the working machine is a mobile machine, wherein the engine is used for driving a propulsion of the working machine, wherein the working machine is at least one out of an earth moving machine, a transport machine and a load handling machine.

15. The system of claim 2, wherein the storage capacity of the first storage container is at least 3 times larger than the storage capacity of the second storage container.

16. The system of claim 5, wherein the at least one heating arrangement includes at least one out of a heat exchanger to be connected to an engine cooling system, an electric heater, and a temperature sensor.

17. The system of claim 16, further comprising a valve arrangement for separately connecting an inlet of the pump with at least one out of the first and the second container, wherein the valve system is controlled to connect the first storage container or the second storage container to the pump, such that the first and the second storage container are never connected to the pump at the same time.

18. The exhaust gas aftertreatment system of claim 12, wherein the at least one injector is directly in front of the SCR-catalyst.

19. The working machine of claim 14, wherein the working machine is a dumper truck or a crane.

20. The system of claim 1, wherein the first and the second container are formed by separate reductant tanks.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The present invention will now be described on the basis of preferred embodiments and using drawings.

(2) The drawings show in

(3) FIG. 1: a first embodiment of an inventive system comprising a reductant tank having a first and a second section and in

(4) FIG. 2: a second embodiment of an inventive system comprising a first and second reductant tank.

(5) FIG. 3: a block diagram of a working machine according to at least one example of the present disclosure.

DETAILED DESCRIPTION

(6) The embodiments of the present invention are reductant storage systems for delivering urea solution to a urea dosing system having one or more injectors (7). Each urea injector (7) comprises a valve that is controlled in order to control the amount of urea injected into the exhaust gas stream. Because the urea injector is located directly at the catalyst, it has to be cooled.

(7) In the present invention, this is done by the urea that is used for injection. The urea is pumped from a storage container to the injector, circulates in the injector for cooling purposes, and flows back to the storage container. If the injection valve is opened, a part of the urea supplied by the pump and flowing through the injector is injected into the exhaust gas stream. In such system the urea solution is used to reduce the NOx emissions and to control the temperature of the injectors mounted on the exhaust pipe.

(8) The present invention provides a urea storage system having a first urea storage container (10, 10′) and a second urea storage container (11, 11′). In the first embodiment shown in FIG. 1, the first and the second urea storage container are provided by a first and second section (10, 11) of a tank (14). In the second embodiment shown in FIG. 2, the first and the second urea storage container are provided by a first and a second tank (10′, 11′). In the latter design, the second tank (11′) could be retrofitted to an existing urea injection system using urea solution to cool the injectors.

(9) The first urea storage container has a larger storage capacity than the second urea storage container, and is therefore provided by a larger section or larger tank. The first container is the dosing or primary tank and the second container is the cooling or secondary tank. The tank or tank section may be insulated to prevent freezing of the urea solution as much as possible.

(10) The containers are connected to the pump (1) in such a way that urea from each of the containers (10, 10′, 11, 11′) can be pumped to the injector (7). For this purpose, the containers are connected in parallel via line (13) to the pump, which in turn is connected to the injector (7) by line (8). A return line (9) for the urea connects the injector (7) at least with the second container (11, 11′). In the embodiments, the return line (9) is only connected to the second container (11, 11′), such that reductant flowing back from the injector (7) will always flow into the second container first.

(11) The first container (10, 10′) is connected to the second container (11, 11′) by a fluid connection (12, 12′) via which urea can flow from the second container to the first container. The fluid connection is formed by an overflow, such that urea will only flow from the second container to the first container if the second container is full. This makes sure that there is always urea in the second container for cooling the injector.

(12) It has to be noted that the return flow from the urea injection system is only linked to the second container, i.e. the cooling tank or tank section. Thus even when the urea is fed from the first container, i.e. the dosing tank or tank section to the injector, the return flow is always going back to the second container, i.e. the cooling tank or tank section.

(13) It is important that the second container, i.e. the cooling tank or tank section is always full and thus the return urea flow always enters inside it and the urea filling is made through this tank. The second container, i.e. the cooling tank or tank section, is therefore equipped with a filling cap or orifice (6). Having the urea filling orifice on the second container, i.e. the cooling tank or tank section helps keeping it always full in order to always be able to cool down the injector (7).

(14) At least one suction module (2 and 3) is provided in each container, i.e. in each tank or tank section. The suction modules has a suction line for sucking urea from the container, and at least one heating element 15, formed e. g. by a heat exchanger or a heater. The suction modules are preferably heated up using engine coolant but in order to have a fast defrosting of the urea, at least one of the suction modules could use an electrical heater. The electrical heater is preferably provided for the second container (11, 11′). There can be more than one suction module inside each container, i.e. tank or tank section.

(15) If the second container is heated up, the return flow from the urea injector will also help to defrost the urea solution in the first container or prevent having it frozen.

(16) The suction modules are equipped with urea quality, level and temperature sensors, (e.g., temperature sensor 16), however the suction module of the second container, i.e. the cooling tank or tank section could be simplified in order to include only a heater as the urea from the cooling tank is not intended to be used for emission reduction.

(17) The invention also comprises two valves (4 and 5) which allow the selection between the two containers, i.e. the two tanks or tank sections. The two valves cannot be opened or closed at the same time during engine operation. Thus when the injector cooling is needed while no emission reduction is required, the valve (5) is opened and the valve (4) is closed. This selection is made by the engine controller or the urea injection system controller.

(18) The invention works using two separate modes:

(19) The cooling mode: in this mode, the urea injection is stopped and the urea is only used to cool down/protect the injectors from overheating. The valve 4 is closed and the valve 5 is opened.

(20) The dosing mode: in this mode, the urea injection is started and the urea is used to reduce the NOx emissions as well as to cool down the urea injectors. The valve 5 is closed and the valve 4 is opened. If the urea pressure inside the system cannot be increased to the working pressure, the mode is switched back to the cooling mode.

(21) There may further be an idling mode where there is neither cooling nor injection. In this mode, pump (1) is not operated.

(22) If the urea storage system in frozen at start-up of the engine, the urea solution will first have to be defrosted before SCR catalytic reaction can be taken up.

(23) There is preferably provided an electric heater for the pipes (8, 9, 13) connecting the urea storage containers, the pump and the injector. The pump can be heated electrically and/or via the engine cooling system.

(24) At least the first urea storage container (10, 10′) is defrosted by a heat exchanger connected to the engine cooling system. This heat exchanger is part of the suction module (2). In order to defrost the urea solution, it is therefore necessary to provide enough engine heat. This is usually done by running the engine in idle mode.

(25) There is a requirement that after start of the engine, the engine may run for 20 minutes in idle mode, and then for another 50 minutes using a higher speed, before the SCR has to be operational. During the first 20 minutes in idle mode, no urea solution is injected and no cooling may be required. For the following operation at a higher speed, cooling is however required.

(26) The second container provides sufficient urea for the cooling purpose already after the idling phase, because it is defrosted more quickly than the first container. This is because it has a smaller storage capacity. Further, there may be an electric heater for the second storage container. Alternatively or in addition, the engine cooling system my be controlled such that more heat is transferred to the second container after start-up with a frozen storage system and defrosting of the first container is only started once the second container has been defrosted.

(27) Preferably, the controller of the engine or of the urea injection system will automatically control the urea injection system such that the engine is first run, after start-up with a frozen urea storage system, in an idling mode and/or the cooling mode until a sufficient quantity of urea in the first tank is defrosted to start the dosing mode.

(28) In particular, the controller of the engine or of the urea injection system may automatically control the urea injection system such that the engine is first run, after start-up with a frozen urea storage system, in an idling mode and/or an electric heating is performed for the second storage container until a sufficient quantity of urea is melted in the second storage container to start the cooling mode. The engine is then run in the cooling mode with a higher engine speed than in the idling mode, in order to create more heat, which will speed up the melting of the urea in the first container.

(29) The controller of the engine or of the urea injection system may detect a frozen state of the urea storage system, e.g. by using the signals form the temperature sensors of the suction modules (2) and/or (3).

(30) Further, the heating of the urea containers can be controlled by the temperature sensors of the suction modules. For example, there can be a valve in the engine coolant circle, by which the flow of engine coolant through the suction modules is controlled depending on the temperature of the urea in the first and second container.

(31) To increase the cooling efficiency, it is possible to add a heat exchanger on the urea solution lines located between the valve 4 and 5.

(32) The controller can be further configured in such a way that during normal operation of the engine, if all the melted urea has been used up by injection, the engine is operated in a low NOx mode, and the urea injection system is operated in the cooling mode, i.e. with the urea injector cooled by the coolant from the second container, with switched-off urea injection.

(33) The first urea container may e. g. comprise about 1,000 l of urea solution. This corresponds to about 10% of the fuel storage fuel capacity of the fuel tank. The requirement is that the refilling of fuel and refilling of urea can be done at the same time, i.e., that the respective containers have a capacity that corresponds to the same working time. The second urea container may e.g. have a capacity of about 50 to 1001. It does not have to be scaled with the first container, because it is only used for cooling purposes.

(34) The embodiments have been described with respect to urea as the reductant. The embodiments could however also be used with any other kind of fluid reductant.

(35) The invention could in particular be applied to all off-road machines and/or all our excavators, trucks, etc. equipped with SCR systems and urea cooled injectors.