GB2552811A

GB2552811A - Method and system for reducing crystallisation of diesel exhaust fluid in an injector

Info

Publication number: GB2552811A
Application number: GB1613765.5A
Authority: GB
Inventors: Subhash Gharpure Siddharth; Michael Cole Brian
Original assignee: Perkins Engines Co Ltd
Current assignee: Perkins Engines Co Ltd
Priority date: 2016-08-10
Filing date: 2016-08-10
Publication date: 2018-02-14

Abstract

Method for reducing crystallisation of a urea-based water solution 25 in an injector 30 for an exhaust aftertreatment system 10 associated with an engine 11, by supplying the injector with the urea solution at an operating pressure during engine operation and maintaining pressure to the injector at engine shutdown. The system comprises a reservoir 36 fluidly connected to an injector by a conduit 33 comprising a pump 32 for supplying urea solution to the injector and a controller 65, configured to control the pump and maintain pressure to the injector at engine shutdown. The method may include determining if the system is above a first threshold temperature, upon which pressure is maintained after engine shutdown. The method may include maintaining pressure at or above a value, such that the boiling point is greater than an expected injector peak temperature. The pressure may be maintained for a predetermined time period after engine shutdown. Pressure may be maintained until a second threshold temperature is reached, which may be lower than urea atmospheric boiling point and may be between 20°C to 90°C. The injector may be purged after pressure maintenance has ceased. A secondary power source 64 (fig.4) may maintain pressure to injector.

Description

(54) Title of the Invention: Method and system for reducing crystallisation of diesel exhaust fluid in an injector Abstract Title: Reducing urea injector crystallisation by pressure maintenance at engine shutdown (57) Method for reducing crystallisation of a urea-based water solution 25 in an injector 30 for an exhaust aftertreatment system 10 associated with an engine 11, by supplying the injector with the urea solution at an operating pressure during engine operation and maintaining pressure to the injector at engine shutdown. The system comprises a reservoir 36 fluidly connected to an injector by a conduit 33 comprising a pump 32 for supplying urea solution to the injector and a controller 65, configured to control the pump and maintain pressure to the injector at engine shutdown. The method may include determining if the system is above a first threshold temperature, upon which pressure is maintained after engine shutdown. The method may include maintaining pressure at or above a value, such that the boiling point is greater than an expected injector peak temperature. The pressure may be maintained for a predetermined time period after engine shutdown. Pressure may be maintained until a second threshold temperature is reached, which may be lower than urea atmospheric boiling point and may be between 20°C to 90°C. The injector may be purged after pressure maintenance has ceased. A secondary power source 64 (fig.4) may maintain pressure to injector.

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FIG. 4

METHOD AND SYSTEM FOR REDUCING CRYSTALLISATION OF DIESEL EXHAUST FLUID IN AN INJECTOR

Technical Field

This disclosure is directed to a method and system for reducing crystallisation of a urea-based water solution in an injector, and in particular to a method and system for reducing crystallisation of a urea-based water solution in an injector in an exhaust aftertreatment system.

Background

Engines, for example internal combustion engines burning gasoline, diesel, or biofuel, output various substances which must be treated to meet current and future emissions legislation. Most commonly, such substances comprise hydrocarbons (HC), carbon monoxides (CO), mono-nitrogen oxides (NOx), and particulate matter such as carbon (C), a constituent of soot. Some of those substances may be reduced by careful control of the operating conditions of the engine, but usually it is necessary to provide an aftertreatment module downstream of the engine to treat at least some of the substances entrained in the exhaust gas.

Various apparatus for reducing and/or eliminating constituents in emissions are known. By these methods, engine emissions can be cleaned, meaning that a proportion of the substances which would otherwise be released into the atmosphere are instead converted to carbon dioxide (CO₂), nitrogen (N₂) and water (H₂O).

For example, it is known to provide an oxidation device, such as a diesel oxidation catalyst (DOC), to reduce or to eliminate hydrocarbons (HC) and/or carbon monoxide (CO). Oxidation devices generally include a catalyst to convert those substances into carbon dioxide and water.

As a further example, aftertreatment modules may include filtration devices to restrict the particulates present in the exhaust gas from being output to the atmosphere.

The soot collected in the filtration device must later be removed to maintain the efficiency of the filtration device. The methods by which soot may be removed from the filtration device are well known in the art and may generally be referred to as regeneration, which is carried out at elevated temperatures.

In addition, it is known to reduce or eliminate mono-nitrogen oxides (NOx) in diesel combustion emissions by selective catalytic reduction (SCR). In a typical SCR system, urea or a urea-based water solution is mixed with exhaust gas. In some applications, a urea solution is injected directly into an exhaust passage through a specialised injector device. The injected urea solution mixes with exhaust gas and breaks down to provide ammonia (NH₃) in the exhaust stream. The ammonia then reacts with nitrogen oxides (NOx) in the exhaust at a catalyst to provide nitrogen gas (N₂) and water (H₂O).

When a fluid reductant is used, such a fluid reductant is known as diesel exhaust fluid, or DEF. The use of DEF has become popular because of its fluid form, which is easy to store and handle, and it has been found that the use of DEF reduces the need to rely upon exhaust gas recirculation to meet modern emission requirements. However, various challenges are associated with the use of DEF.

During low temperature conditions, following engine shutdown, the DEF may freeze in the system, causing it to expand. This may damage some components, such as the supply lines and injector. To avoid such freezing issues, DEF that is present in supply lines and the injector is purged after engine shutdown.

Further problems are associated with hot engine shutdown, following a period of strenuous use. Under such conditions, the elevated temperature may result in crystallisation of urea at the injector. In the event crystallised urea is present within the injector, the crystallised urea solids may fluidly and/or mechanically block a valve member of the injector. In the case of mechanical blocking, an actuator force provided to actuate the injector may be insufficient to open the valve member when injection of DEF is desired. In the case of fluid blocking, successful opening of the valve member may not lead to a desired injection amount and/or timing if a sufficient flow of DEF cannot reach and pass through the valve member.

-3Summary

The present disclosure provides a method for reducing crystallisation of a ureabased water solution in an injector for an exhaust aftertreatment system associated with an engine, the method comprising the steps of: supplying the injector with a urea-based water solution at an operating pressure during operation of the engine; and maintaining pressure to the injector at shutdown of the engine.

The present disclosure further provides a system for reducing crystallisation of a urea-based water solution in an injector for an exhaust aftertreatment system in an engine, the system comprising: a reservoir fluidly connected to an injector by a conduit, the conduit comprising a pump for supplying the injector with a urea-based water solution at an operating pressure during operation of the engine; and a controller configured to control the pump such as to maintain pressure to the injector at shutdown of the engine.

By way of example only, embodiments of a method and system for reducing crystallisation of a urea-based water solution in an injector are now described with reference to, and as shown in, the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a block diagram of a typical exhaust aftertreatment system;

Figure 2 is a partially sectioned perspective view of the aftertreatment system of Figure 1;

Figure 3 is a perspective view of an example injector for use in the aftertreatment system of Figure 2; and

Figure 4 is a schematic diagram of a system for reducing crystallisation of a ureabased water solution in an injector according to the disclosure.

-4Detailed Description

Figure 1 illustrates a block diagram of a typical exhaust aftertreatment system 10 associated with the engine 11 of a machine (not shown). The term ‘machine’ is used generically to describe any machine driven by mechanical means by an engine through a transmission. The machine may be a work machine, such as a backhoe loader. The engine 11 may be an internal combustion engine, such as a diesel engine.

The aftertreatment system 10 may be modularly packaged as shown in the illustrated embodiment for retrofit onto existing engines or, alternatively, for installation on new engines. As shown in Figure 1, the aftertreatment system 10 may include a first module 12 that may be fluidly connected to an exhaust conduit 13 of the engine 11. The first module 12 may contain various exhaust gas treatment devices such as a diesel oxidation catalyst (DOC) 14 and a diesel particulate filter (DPF) 15, but other devices may be used.

A transfer conduit 20 may fluidly interconnect the first module 12 with a second module 21. The second module 21 may enclose an SCR catalyst 22 and an Ammonia Oxidation Catalyst (AMOX) 23. An exhaust outlet 24 may be fluidly connected to the second module 21 such that the exhaust gas that has passed through the second module 21 may be released into the atmosphere.

The SCR catalyst 22 and AMOX 23 may operate to treat exhaust gas from the engine 11 in the presence of ammonia. The ammonia may be provided through degradation of a urea-based water solution 25 (commonly known as diesel exhaust fluid, DEF) injected into the exhaust gas in the transfer conduit 20 by an injector 30. The DEF 25 may meet the ISO22241 standard and comprise from 31.8% to 33.2% urea by weight. A DEF system 29 may be provided, wherein the DEF 25 may be contained within a reservoir 31 and may be provided to the injector 30 by a pump 32, which may be located in a DEF conduit 33 fluidly connecting the reservoir 31 to the injector 30. The pump 32 may pressurise the DEF system 29 to an operating pressure. A typical operating pressure may be 5 bar or 9 bar, but other operating pressures may also be possible, for example less than 5 bar or greater than 9 bar. To promote mixing of DEF 25 with the exhaust gas in the transfer conduit 20, a mixer 34 may be disposed along the transfer conduit 20, downstream of the injector 30.

-5Figure 2 is a partially sectioned perspective view of the aftertreatment system 10. The first and second modules 12 and 21 may be disposed next to one another, with the transfer conduit 20 disposed between them. The injector 30 may be disposed on an upstream end of the transfer conduit 20 relative to a direction of exhaust gas flow 35. The aftertreatment system 10 may be packaged such that the position of the injector 30 is relatively external to the surrounding structures and thus may be exposed to a convective cooling air flow, both during operation of the engine 11 as well as post-shutdown.

A perspective view of an example of a suitable injector 30 is shown in Figure 3. The injector 30 may include a body portion 40 that may house an electrical actuator (not shown), which may receive command signals through an electrical connector 41 connected to the body portion 40. The actuator may be an electrically activated solenoid or the like. The actuator may be connected to, and configured to operate, a valve member 42, which may be movable between an open position and a closed position. The valve member 42 may comprise a needle (not shown). The valve member 42, when open, may permit a flow of DEF 25 out of the injector 30 and into the transfer conduit 20. DEF 25 may be supplied to the valve member 42 through a DEF inlet 51, which may be fluidly connected to the DEF conduit 33 (Figure 1).

A plurality of spacers 44 may be used to space apart the body portion 40 from a mounting flange 45, thus creating a gap 50 therebetween. This may serve to create a conductive heat transfer barrier between the body portion 40 of the injector 30 and the transfer conduit 20 to which the injector 30 is connected, which may protect electronic and other components within the injector 30 from elevated temperatures.

As can be appreciated, the location of the injector 30 on the transfer conduit 20 may expose the injector 30 to relatively high temperatures due to heating from exhaust gas during operation. Under certain operating conditions, the flow of DEF 25 through the injector 30 between the DEF inlet 51 and the valve member 42 may act to convectively cool the body portion 40 during operation. Optionally, additional convective cooling may further be provided by routing engine coolant or another cooling fluid through internal passages formed in the body portion 40. An internal passage (not shown) extending through the body portion 40 may be fluidly accessible through inlet and outlet coolant ports 52 and 53. Each coolant port 52 and 53 may be connected to a respective conduit (not shown), which may

-6be adapted to receive a flow of coolant therethrough for convectively controlling a temperature of the body portion 40.

One challenge that may arise with the DEF system 29 is preventing crystallisation of urea in the DEF 25, especially at the injector 30. Crystallisation may occur, for example, when the DEF 25 is depressurised during system purge following engine shutdown, in particular following hot engine shutdown. Hot engine shutdown may be defined as shutdown of the engine 11 when the aftertreatment system 10 is above a first threshold temperature, which may for example be 200°C or 500°C.

When the DEF system 29 is purged, the injector 30 and DEF conduit 33 may be emptied of DEF 25, to decrease the likelihood of damage to the DEF system 29, and in particular to the injector 30, due to freezing of the DEF 25 when the engine 11 is not in operation. During purge, pressure in the DEF system 29 may be reduced from the operating pressure to a pressure close to atmospheric pressure, or even a negative pressure. This decrease in pressure may lower the boiling point of the DEF 25. Given the relatively elevated temperature of the injector 30 following engine shutdown, and in particular following hot engine shutdown, water from the DEF 25 may boil and evaporate.

In certain conditions, the evaporated water may cause a super-saturated solution and/or solid urea crystals to form within the injector 30. Such crystallisation may obstruct normal injector operation, for example by causing a partial or full blockage of the injector 30 (and/or sticking of the needle), and thereby inhibit proper operation. The melting point of urea solids under typical precipitation conditions can be as high as 190°C, which may be higher than the maximum normal operating temperature of the injector 30. Therefore, once crystallisation has occurred the urea solids may not readily return to a liquid state under normal operating conditions of the aftertreatment system 10, and the injector 30 may remain blocked. This may result in a reduced performance of the injector 30.

Referring to Figure 4, a schematic diagram for a system 60 for reducing crystallisation of DEF 25 in an injector 30 is shown. As per Figure 2, the injector 30 may be fluidly connected to the reservoir 31 via the DEF conduit 33, which may be configured to be pressurised by the pump 32. The pump 32 may be configured to be powered by a machine electrical system 61, which may receive power from the engine 11.

-7A secondary power source 62 may be provided, which may comprise a power storage device 64, such as a battery array. The secondary power source 62 may optionally additionally comprise a power management module 65. The power management module 65 may include an electronic controller (not shown) in addition to other electrical components such as switches and relays. A temperature sensor 70 may be provided on, or in the locality of, the injector 30. For example, the temperature sensor 70 may be provided at the SCR inlet, or anywhere on the aftertreatment system 10, engine 11, or machine from where the temperature of the injector 30 can be inferred or predicted. The temperature sensor 70 may be configured to provide a temperature signal 71 to the power management module 65.

The secondary power source 62 may be configured to be charged with electrical power from the machine electrical system 61 during engine operation. The secondary power source 62 may be further configured to be isolated from the machine electrical system 61, for example when the engine 11 is not operating. The isolation of the secondary power source 62 from the machine electrical system 61 may be automatically effected upon shutdown of the engine 11. The secondary power source 62 may be connected to, and configured to operate, the pump 32 and, optionally, the injector 30 (not shown) when the secondary power source 62 is isolated from the machine electrical system 61. Thus the secondary power source 62 may retain power safely, even after engine shutdown.

The system 60 may be configured to activate when the engine 11 is shut down. In an alternative embodiment, a controller (not shown) may be configured to activate the system 60 only if the temperature of the aftertreatment system 10 is above the first threshold temperature at engine shutdown, which may signify hot engine shutdown. The temperature of the aftertreatment system 10 may be a temperature of the injector 30 detected by temperature sensor 70, a temperature detected at the SCR inlet, or any other temperature reading from the aftertreatment system 10, engine 11, or machine from which the temperature of the aftertreatment system 10 can be inferred or predicted.

Industrial Applicability

The method and system for reducing crystallisation of DEF in an injector for an exhaust aftertreatment system has industrial applicability in the field of internal combustion engines, and particularly in the field of diesel internal combustion engines.

-8In use, while the engine 11 is operating, the machine electrical system 61 may provide power to the pump 32 to supply DEF 25 to the injector 30 at the operating pressure. The machine electrical system 61 may additionally provide a trickle charge to the secondary power source 62, and in particular to the power storage device 64 of the secondary power source 62.

Following operation of the engine 11, the engine 11 may be shut down, at which time the rpm of the engine 11 may reduce to zero. When the engine 11 is shut down, which may deactivate the machine electrical system 61, the system 60 may be activated. In an alternative embodiment, the system 60 may be activated only if the temperature of the aftertreatment system 10 is above the first threshold temperature at engine shutdown, which may signify hot engine shutdown. The secondary power source 62 may be isolated from the machine electrical system 61 and may discharge to operate the pump 32 to maintain pressure in the injector 30, such that DEF crystallisation may be reduced and substantially prevented.

In one embodiment of the disclosure, the pressure in the injector 30 may be maintained at a value such that the boiling point of the DEF 25 may be elevated above a typical peak temperature of the injector 30. The typical peak temperature of the injector 30 may be determined from an injector temperature profile for a specific machine after shutdown of the engine 11.

In an alternative embodiment, pressure in the injector 30 may be maintained at a value such that the boiling point of the DEF 25 may be elevated above an actual temperature of the injector 30. The temperature of the injector 30 may be measured by the temperature sensor 70. Alternatively, an approximate temperature of the injector 30 may be inferred or predicted from a temperature detected at the SCR inlet, or any other temperature reading from the aftertreatment system 10, engine 11, or machine.

In a further alternative embodiment, pressure in the injector 30 may be maintained at the operating pressure. For example, at a typical operating pressure of 9 bars, the adjusted boiling point of water is approximately 180°C.

-9Pressure in the injector 30 may be maintained until the temperature of the injector 30 falls below a second threshold temperature. The second threshold temperature may lower than the atmospheric boiling point of the DEF 25.

In one embodiment of the disclosure, pressure in the injector 30 may be maintained for a predetermined period of time. The predetermined period of time for a particular machine may be the expected period of time for the temperature of the injector 30 to reach the second threshold temperature, based on the injector temperature profile for that machine after shutdown of the engine 11. The predetermined period of time may depend on the temperature of the injector 30, or more generally of the aftertreatment system 10, at engine shutdown.

In an alternative embodiment of the disclosure, the temperature sensor 70 may provide a temperature signal 71 to the power management module 65, such that pressure in the injector 30 may be maintained until the temperature signal 71 indicates that the second threshold temperature has been reached. Again, an approximate temperature of the injector 30 may be inferred or predicted from a temperature detected at the SCR inlet, or any other temperature reading from the aftertreatment system 10, engine 11, or machine.

After the predetermined period of time has elapsed and/or the second threshold temperature has been reached, the injector 30 may be purged. To effect the purge, the secondary power source 62 may activate the pump 32 in a reverse direction, to return DEF 25 contained within the injector 30 back to the reservoir 31. The secondary power source 62 may also open a valve of the injector 30.

During purge, the pressure in the DEF conduit 33 and injector 30 may become negative. This may lead to a significant drop in the boiling point of the DEF 25, and therefore some DEF crystallisation may occur. However, any crystals formed at this lower temperature will liquidate easily when a similar temperature is reached during a priming cycle when the engine 11 is next in operation. For this reason, the second threshold temperature may be selected to be significantly below the atmospheric boiling point of the DEF 25, for example 50°C. Alternatively, the second threshold temperature may be any value selected from a range of 20°C to 90°C, more preferably from a range of 40°C to 60°C. Alternatively, the second threshold temperature may be selected to be less than the

- 10boiling point of the DEF 25 at the lowest expected pressure during purge, such that DEF crystallisation may be substantially completely prevented.

By maintaining the temperature in the injector 30 below the boiling point of the DEF 5 25, DEF crystallisation can be reduced and substantially prevented. Therefore the system may avoid any decreases in operational capability of the injector 30 such that the cost and time otherwise required for repair or replacement of the injector 30 and other system components can be avoided.

Claims

CLAIMS:

1. A method for reducing crystallisation of a urea-based water solution in an injector for an exhaust aftertreatment system associated with an engine, the method comprising the steps of:

supplying the injector with a urea-based water solution at an operating pressure during operation of the engine; and maintaining pressure to the injector at shutdown of the engine.

2. A method according to claim 1, further comprising the step of determining whether the exhaust aftertreatment system is above a first threshold temperature, and only maintaining pressure to the injector at shutdown of the engine when the aftertreatment system is above the first threshold temperature.

3. A method according to claim 1 or claim 2, wherein, in the step of maintaining pressure, the pressure to the injector is maintained at or above a value such that the boiling point of the urea-based water solution is greater than an expected peak temperature of the injector.

4. A method according to claim 1 or claim 2, wherein, in the step of maintaining pressure, the pressure to the injector is maintained at or above a value such that the boiling point of the urea-based water solution is greater than an actual temperature of the injector.

5. A method according to claim 1 or claim 2, wherein, in the step of maintaining pressure, the pressure to the injector is maintained at the operating pressure.

6. A method according to any one of the preceding claims, wherein the operating pressure is substantially 9 bar.

7. A method according to any one of the preceding claims, further comprising the step of ceasing to maintain the pressure to the injector after a predetermined period of time has elapsed following shutdown of the engine.

- 12

8. A method according to claim 7, wherein the predetermined period of time is an expected period of time for a temperature of the injector to reduce to a second threshold temperature.

9. A method according to any one of claims 1 to 6, further comprising the step of ceasing to maintain pressure to the injector after a temperature of the injector has fallen to a second threshold temperature.

10. A method according to claim 8 or claim 9, wherein the second threshold temperature is lower than the boiling point of the urea-based water solution at atmospheric pressure.

11. A method according to claim 10, wherein the second threshold temperature is selected from a range of 20°C to 90°C.

12. A method according to any one of claims 7 to 11, further comprising the step of purging the injector after ceasing to maintain pressure to the injector.

13. A method according to any one of the preceding claims, wherein, in the step of maintaining pressure, pressure to the injector is maintained by a secondary power source isolated from a main electrical system of the engine.

14. A method according to claim 13, wherein the secondary power source receives power from the main electrical system during operation of the engine.

15. A system for reducing crystallisation of a urea-based water solution in an injector for an exhaust aftertreatment system in an engine, the system comprising:

a reservoir fluidly connected to an injector by a conduit, the conduit comprising a pump for supplying the injector with a urea-based water solution at an operating pressure during operation of the engine; and a controller configured to control the pump such as to maintain pressure to the injector at shutdown of the engine.

Intellectual

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Application No: Claims searched:

GB1613765.5

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