Mitigation of diesel exhaust fluid (DEF) deposits in exhaust systems for engines

Abstract

An exhaust system for an engine includes an exhaust manifold, a selective catalytic reduction (SCR) device in the exhaust manifold, and a diesel exhaust fluid (DEF) system. The DEF delivery system includes a DEF delivery controller configured to: receive a status signal indicating a risk of DEF deposition in the exhaust system; and command an increase in the thermal output of a preheater to preheat the DEF to be permitted to enter the exhaust manifold, such that the temperature of the DEF increases to a deposition-mitigation temperature. Related methods and control logic are also disclosed.

Description

Technical Field

[0001] This disclosure generally relates to an exhaust system for an internal combustion engine, and more specifically to a diesel engine exhaust fluid system for preheating diesel engine exhaust fluid to mitigate the risk of forming solid deposits. Background Technology

[0002] In recent years, the use of exhaust aftertreatment devices in internal combustion engines has become almost ubiquitous. Combustion of a fuel-air mixture in the engine's combustion cylinders produces exhaust containing various components, and it is desirable to limit its emission into the atmosphere. In recent years, regulations have been implemented regarding the permitted emissions of nitrogen oxides, or "NOx," and particulate matter, which have spurred manufacturers to develop a wide range of technologies for capturing or chemically converting such materials in engine exhaust.

[0003] A common exhaust aftertreatment technology uses catalysis to reduce NOx to molecular nitrogen and water. A widely accepted and commercially successful system is called Selective Catalytic Reduction, or "SCR" unit. Proper operation of an SCR unit requires the introduction of a reductant into the exhaust stream to be treated. The reductant is typically provided in liquid form and is selectively injected directly into the exhaust stream upstream of the SCR unit. The proliferation of commercially available diesel exhaust fluids, or "DEF," is familiar to many.

[0004] Common DEF formulations are water-based, and in some cases, especially when the engine is operating under conditions of low ambient temperatures, onboard DEF can freeze into a solid. Various strategies have been proposed to heat DEF directly in the onboard tank or in the supply line connected to the exhaust system. This heating of the DEF allows the exhaust system to begin or continue injecting DEF, which would otherwise cause problems due to ambient conditions caused by the DEF freezing into a solid.

[0005] Another example of heating DEF in an exhaust system is described in U.S. Patent Application Publication No. 2007 / 0119153 by Pierz et al. Pierz proposed a urea SCR system for enhanced aftertreatment applications. In Pierz et al.'s patent application, the SCR system has a conduit connecting a delivery pump to an injection nozzle for urea, wherein a heating element is located downstream of the pump to preheat the aqueous urea to a superheated state before it is injected into the exhaust stream. Clearly, the superheated aqueous urea rapidly vaporizes instantaneously upon injection into the relatively cool exhaust stream. While Pierz et al. address certain challenges, there remains room for alternative strategies and different end goals in pursuing temperature manipulation of diesel engine exhaust fluids. Summary of the Invention

[0006] In one aspect, an exhaust system for an engine includes an exhaust manifold extending between an upstream end and a downstream end configured to receive exhaust gases produced by the engine. The exhaust system also includes a selective catalytic reduction (SCR) device and a diesel exhaust fluid (DEF) system located within the exhaust manifold. The DEF system includes a DEF inlet valve, a preheater, a condition sensor, and a DEF delivery controller connected upstream of the SCR to the exhaust manifold. The DEF delivery controller is coupled to the preheater and the condition sensor and is configured to: receive a condition signal generated by the condition sensor indicating a risk of DEF deposition in the exhaust system; and, based on the condition signal, command an increase in the thermal output of the preheater such that the temperature of the DEF to be permitted to enter the exhaust manifold increases to a deposition-mitigation temperature.

[0007] In another aspect, a diesel exhaust fluid (DEF) system includes: a DEF delivery controller configured to be coupled to a preheater for preheating DEF for delivery into an exhaust manifold in the exhaust system, and coupled to a condition sensor for monitoring DEF deposition risk conditions in the exhaust system. The DEF delivery controller is further configured to: receive from the condition sensor a condition signal indicating a DEF deposition risk condition in the exhaust system; and determine, based on the condition signal, a deposition-mitigation temperature at which DEF is permitted to enter the exhaust manifold in the exhaust system. The DEF delivery controller is also configured to command an increase in the thermal output of the preheater such that the temperature of the DEF to be permitted to enter the exhaust manifold increases to the deposition-mitigation temperature.

[0008] In another aspect, a method of operating an exhaust system of an internal combustion engine includes: generating a condition signal indicating a risk of diesel exhaust fluid (DEF) deposition in the exhaust system; and increasing the heat output of a preheater for the DEF in the DEF system of the exhaust system based on the condition signal. The method further includes: increasing the temperature of the DEF in the DEF system to a deposition-mitigation temperature based on the increased heat output; and commanding the DEF, whose temperature has increased to the deposition-mitigation temperature, to enter an exhaust manifold in the exhaust system. Attached Figure Description

[0009] Figure 1 This is a schematic side view of a machine according to one embodiment;

[0010] Figure 2 This is a schematic view of an exhaust system according to one embodiment;

[0011] Figure 3 This is a functional diagram of a DEF delivery controller according to one embodiment;

[0012] Figure 4 This is a calculation block diagram according to one embodiment; and

[0013] Figure 5 This is a flowchart illustrating an exemplary method and control logic flow according to one embodiment. Detailed Implementation

[0014] refer to Figure 1 The image illustrates a machine 10 according to one embodiment, which includes a frame 12, a ground-engaging propulsion element 14 supporting the frame 12, an implement system 16, and an operator's cab 18. An internal combustion engine system 20 is supported on the frame 12 and includes an internal combustion engine 22. The machine 10 is shown in the context of a wheel loader; however, the machine 10 may include any of a variety of other off-highway machines, such as tractors, trucks, automatic graders, scrapers, or other machines. The machine 10 may also be a road machine or a stationary machine, for example, a pump, compressor, or generator set, among other examples. The internal combustion engine 20 may include a compression-ignition multi-cylinder engine that operates using any of a variety of suitable fuels (e.g., diesel distillate fuels, mixtures of hydrocarbon fuels, or others). The internal combustion engine system 20 also includes an exhaust system 24 configured to feed exhaust gas from the internal combustion engine 22 to an outlet, such as an exhaust duct 31, a tailpipe, etc. As will become further apparent from the following description, exhaust system 24 is uniquely configured to reduce emissions of certain exhaust components that are not feasible or infeasible under various conditions.

[0015] Still referencing Figure 2 The exhaust system 24 includes an exhaust duct 26 extending between an upstream end 28 and a downstream end 30, the upstream end being configured to receive exhaust gas produced by the internal combustion engine 22. The exhaust system 24 also includes a selective catalytic reduction (SCR) device 32 located within the exhaust duct 26. Various other exhaust aftertreatment devices include, but are not limited to, a diesel particulate filter or “DPF,” a diesel oxidation catalyst or “DOC,” or other devices fluidly positioned within the exhaust system 24, between the SCR device 32 and the internal combustion engine 22, or between the SCR device 32 and the exhaust duct 31.

[0016] DEF system 34 includes a DEF inlet valve 36, such as a DEF injection valve, connected upstream of SCR unit 32 to exhaust pipe 26. DEF system 34 also includes a DEF reservoir 38, a DEF supply line 40 extending between DEF reservoir 38 and DEF inlet valve 36, and a DEF booster pump 45. DEF supply line 40 may include a lower pressure delivery line 41 extending into DEF reservoir 38 and fluidly connected to pump 45, and a booster line 43 extending between pump 45 and DEF inlet valve 36. Figure 2 The diagram also shows a radiator or other heat exchanger 54 associated with the cooling system of the internal combustion engine 22. In a practical embodiment, engine coolant can circulate between the heat exchanger 54 and the DEF reservoir 38, for example, to thaw the DEF stored in the DEF reservoir 38 in a generally known manner. In some embodiments, a separate heater, such as a resistive heater, may be positioned in the DEF reservoir 38 for a similar purpose.

[0017] DEF system 34 also includes a first preheater 42 and a second preheater 44. The first preheater 42 may be positioned in heat transfer contact with pressurization line 43, and the second preheater 44 may be positioned in heat transfer contact with delivery line 41. In some embodiments, only a single preheater may be used and associated with one of delivery line 41 or pressurization line 43. In a practical implementation, DEF system 34 includes at least one preheater configured to heat DEF relatively close to DEF inlet valve 36 and thus in contact with pressurization line 43. As described above, the heater or preheater may also be attached to DEF tank 38, immersed in DEF tank, or otherwise associated with DEF tank. Suitable preheaters may include resistive preheaters deployed as hot tape, hot packaging material, radiant heaters, hot air blowers, or other arrangements that are in direct physical contact with or otherwise positioned to provide heat directly to a portion of DEF supply line 40.

[0018] As discussed above, some exhaust system strategies employ heaters to increase the temperature of DEF in order to prevent freezing or promote thawing in DEF reservoirs or DEF supply lines, where frozen solid DEF would prevent or delay the availability of SCR units for exhaust treatment. Various preheaters considered herein can be used for such purposes. This disclosure also reflects the insight that preheaters can be used for other purposes, namely, to increase the temperature of DEF to be permitted entry into exhaust manifold 26 when the internal combustion engine system 22 and exhaust system 24 are operating in a manner that may additionally result in the formation and deposition of solid materials derived from DEF.

[0019] To this end, the DEF system 34 also includes condition sensors, and typically includes multiple condition sensors 46, 48, 50, and 52, one or more of which are configured to generate condition signals indicating a risk of DEF deposition in the exhaust system 24. Condition sensors may include: an exhaust temperature sensor 48 configured to generate an exhaust temperature signal; an exhaust mass flow sensor 46 configured to generate an exhaust mass flow signal; a DEF temperature sensor 52 configured to generate a DEF temperature signal indicating the temperature of DEF, for example, stored in a DEF tank 38 or elsewhere in the DEF system 34; and an ambient temperature sensor 50 configured to generate an ambient temperature signal. As further discussed herein, the DEF controller 60 may receive and interpret signals from each of the condition sensors 46, 48, 50, 52, and / or additional or alternative sensors, and controllably heat the DEF to be permitted to enter the exhaust duct 26 in liquid form to mitigate the risk of DEF material deposition, such as solid urea.

[0020] Figure 2 The diagram also shows an actuator 58 for the DEF inlet valve 36. A DEF delivery controller 60 may be configured to operate the actuator 58 to inject DEF into the exhaust pipe 26 for evaporation in the exhaust stream directed toward and entering the SCR unit 32; the actuator may include an electronically operated solenoid actuator. Therefore, the DEF delivery controller 60 is coupled to one or both of the first preheater 42 and the second preheater 44 and to one or more of the condition sensors 46, 48, 50, 52, and is configured to: receive a condition signal generated by the one or more condition sensors indicating a risk of DEF deposition in the exhaust system 26; and, based on the condition signal, command an increase in the thermal output of the first preheater 42 and / or the second preheater 44, such that the temperature of the DEF in the DEF supply line 40, which is to be permitted to enter the exhaust pipe 26, increases to the deposition-relief temperature.

[0021] In one implementation, the status signal includes, for example, an exhaust temperature signal indicating a decrease in exhaust temperature generated by exhaust temperature sensor 48. It has been observed that while exhaust temperatures may be relatively high during operation of exhaust system 24, the risk of DEF deposition may be relatively low or nonexistent. DEF controller 60 may periodically or more frequently receive signals from or query exhaust temperature sensor 48 to monitor exhaust temperature in exhaust conduit 26. The exhaust temperature signal generated by exhaust temperature signal 48 may indicate, for example, a decrease in exhaust temperature associated with a DEF deposition risk condition, relative to previous exhaust temperature signals. In one example, a decrease in exhaust temperature from a higher temperature to approximately 200°C or less may indicate the occurrence of a DEF deposition risk condition.

[0022] Those skilled in the art will understand that many exhaust systems shut off DEF delivery during relatively low exhaust temperature conditions and are subject to associated NOx penalties. According to this disclosure, DEF preheating can be achieved so that the SCR unit 32 can operate at relatively low exhaust temperatures and reduce or eliminate NOx penalties. Therefore, even at relatively low exhaust temperatures, such as from about 150°C to about 200°C, the DEF delivery controller 60 can still command the actuation of the DEF inlet valve 36 to allow DEF, with its temperature increased to the deposition-relief temperature, to enter the exhaust pipe 26 for continuous operation of the SCR unit 32.

[0023] It should be understood that although various sensors are discussed herein and may be part of the DEF system 34, some or all of these sensors may be replaced by virtual or alternative sensors. For example, instead of directly sensing the exhaust mass flow rate using the exhaust mass flow rate sensor 46, an estimate of the exhaust mass flow rate can be obtained by monitoring the operation of the internal combustion engine system 20, for example, by monitoring boost pressure, fuel quantity, engine load, engine speed, or other potential factors. Exhaust temperature can also be determined, inferred, or estimated by means other than directly sensing the exhaust temperature, for example, by sensing the intake air temperature, cylinder temperature, or other factors that will be obvious to those skilled in the art. It should also be understood that the term “about” herein should be understood to mean “generally” or “approximately”, or otherwise consistent with the understanding of those skilled in the art. For example, “about 200°C” does not simply mean exactly 200°C within measurement error, but considers temperatures above or below 200°C, at which SCR operation typically becomes impractical, as understood by those familiar with engine aftertreatment technology.

[0024] Still referencing Figure 3 Additional details of the DEF delivery controller 60 are shown. The DEF delivery controller 60 may include a single dedicated control unit for the DEF system 34, or multiple separate control units with distributed functionality. In the illustrated embodiment, the DEF controller 60 includes a processor 62 (e.g., a microprocessor or microcontroller) coupled to a computer-readable storage 64 (e.g., ROM, SDRAM, Flash, EPMOM, hard disk drive, or others). The storage 64 stores a DEF temperature map 68 and a DEF injection map 70, and may include additional maps and operating software suitable for controlling one or more of the functions described herein for the DEF system 34 or a general internal combustion engine system 10. The DEF delivery controller 60 also includes an input / output or I / O interface 66. Multiple inputs received by or determined on the processor 62 are shown, including an exhaust temperature input 72 (T... exh ), exhaust mass flow rate input 74 (m³) exhDEF temperature input 76 (T) DEF DEF dose input 78 (m DEF ) and ambient temperature input 80 (T amb ). Figure 3 Outputs generated by the DEF delivery controller 60 are also depicted, including: DEF injector commands 82, such as current commands for actuator 58; and preheater commands 84, such as current or voltage commands, on-time commands, temperature commands, turn-on commands, or others for the first preheater 42. As discussed above, the condition sensor in the DEF system 34 may be one of a plurality of condition sensors configured to generate a plurality of condition signals, which may be represented by inputs 72-80. As further discussed herein, the DEF delivery controller 60 may also be configured to determine the deposition-mitigation temperature based on the plurality of condition signals.

[0025] Still referencing Figure 4 A calculation block diagram 100 according to one embodiment is shown. The DEF delivery controller 60 can also be configured to locate the deposition-relief temperature in a graph having exhaust temperature coordinates, exhaust flow rate coordinates, and DEF dose (amount) coordinates. Figure 4 In section 110, the determination of the deposition-mitigation temperature is included. In some cases, a relatively low exhaust temperature can indicate a relatively high deposition-mitigation temperature, and vice versa. A relatively high exhaust mass flow rate can indicate a relatively low deposition-mitigation temperature, and vice versa. Exhaust temperature, exhaust mass flow rate, and DEF dosage are factors with respect to DEF deposition risk that can be cross-coupled and non-linearly related, and may vary depending on the exhaust system.

[0026] The DEF delivery controller 60 can locate the desired deposition-relief temperature on the DEF temperature graph 68. Alternatively, the DEF delivery controller 60 can determine the deposition-relief temperature through calculation. Box 120 shows the DEF tank temperature input, and box 130 shows the calculation of the desired DEF temperature change, or ΔDEF. Box 140 shows the DEF delivery controller 60 calculating the energy required to heat the DEF to be permitted entry. Box 140 can be understood as calculating the energy required to heat the DEF based on, for example, the specific heat of the DEF multiplied by the flow rate of the DEF multiplied by the desired ΔDEF. Box 150 shows the ambient temperature input, and box 160 shows the calculation of ambient heat loss. Box 170 shows the calculation of the total energy input to the DEF, and box 180 shows the preheater command. The DEF delivery controller 60 can also be understood as being configured to calculate the preheater control value based on the difference between the current DEF temperature and the deposition-relief temperature. The preheater control values ​​may include digital values ​​that serve as the basis for preheater command 84, for example, determined by calculations performed at box 130, box 140, or box 170. The preheater control values ​​may also be calculated based on expected ambient heat loss, including based on the ambient temperature input at box 150.

[0027] Industrial applicability

[0028] Generally referencing the diagrams, but now also referring to... Figure 5 Flowchart 200 is shown, illustrating an exemplary method and control logic flow according to this disclosure. At block 210, the internal combustion engine system 20 is operated to operate the internal combustion engine 22 and the exhaust system 24. At block 220, exhaust gas produced by the internal combustion engine 22 is fed through exhaust pipe 26. From block 220, flowchart 200 proceeds to block 230 to receive status signals, including exhaust temperature signals, DEF temperature signals, and ambient temperature signals as discussed herein.

[0029] From box 230, flowchart 200 can proceed to box 240 to determine the deposition-mitigation temperature as discussed herein. From box 240, flowchart 200 proceeds to box 250 to command an increase in the thermal output of a preheater (e.g., one of preheaters 42, 44). For example, commanding an increase in thermal output may include commanding the activation of one or both of preheaters 42, 44. From box 250, flowchart 200 proceeds to box 260 to command permission for DEF to enter exhaust manifold 26. In some embodiments, the process and control logic of flowchart 200 may cycle backward and repeat more or less continuously as the internal combustion engine system 20 operates with DEF heating occurring to a greater or lesser degree to optimally control the DEF temperature based on the current conditions. In other cases, the control logic may be triggered only under certain conditions, such as when the exhaust temperature is observed or inferred to have dropped below a threshold. This threshold can be fixed, for example, at about 200°C as discussed herein, or it can be varied taking into account several (or many) different factors inside or outside the internal combustion engine system 20.

[0030] This specification is for illustrative purposes only and should not be construed as limiting the scope of this disclosure in any way. Therefore, those skilled in the art will recognize that various modifications can be made to the embodiments disclosed herein without departing from the full and reasonable scope and spirit of this disclosure. Other aspects, features, and advantages will become apparent from the accompanying drawings and claims. As used herein, the articles “a” and “an” are intended to include one or more articles and are interchangeable with “one or more”. The term “one” or similar language is used when it is desired to indicate that there is only one article. Furthermore, as used herein, the terms “has,” “have,” “having,” etc., are intended to be open-ended terms. Additionally, the phrase “based on” is intended to mean “at least partially based on” unless otherwise expressly stated.

Claims

1. An exhaust system for an engine, the exhaust system comprising: An exhaust pipe extending between an upstream end and a downstream end configured to receive exhaust gas generated by the engine; The selective catalytic reduction device is located in the exhaust pipe; A diesel engine exhaust fluid system, the diesel engine exhaust fluid system comprising a diesel engine exhaust fluid inlet valve, a preheater, a condition sensor and a diesel engine exhaust fluid delivery controller connected to the exhaust pipe at a location upstream of the selective catalytic reduction device; The diesel engine exhaust fluid delivery controller is connected to the preheater and the condition sensor, and is configured such that: Receive a status signal generated by the status sensor indicating a risk of diesel engine exhaust fluid deposition in the exhaust system; Based on the condition signal, the preheater's heat output is increased, causing the temperature of the diesel exhaust fluid awaiting entry into the exhaust pipe to rise to the deposition-relief temperature. The deposition-mitigation temperature is determined based on exhaust temperature, exhaust mass flow rate, and diesel engine exhaust fluid dosage.

2. The exhaust system according to claim 1, wherein: The status signals include an exhaust temperature signal indicating a decrease in exhaust temperature; The diesel engine exhaust fluid delivery controller is also configured to determine the deposition-mitigation temperature; The diesel exhaust fluid delivery controller is also configured to command and actuate the diesel exhaust fluid inlet valve to allow diesel exhaust fluid with a temperature increased to the deposition-relief temperature to enter the exhaust manifold.

3. The exhaust system according to claim 2, wherein: The condition sensor is one of a plurality of condition sensors configured to generate a plurality of condition signals; The diesel engine exhaust fluid delivery controller is also configured to: The deposition-mitigation temperature is determined based on the multiple condition signals; The preheater control value is calculated based on the difference between the current diesel engine exhaust fluid temperature and the deposition-relief temperature; The heat output of the preheater is increased based on the preheater control value command. as well as Locate the deposition-relief temperature in a graph with exhaust temperature coordinates, exhaust flow rate coordinates, and diesel engine exhaust fluid dosage coordinates.

4. The exhaust system of claim 2, wherein the diesel engine exhaust fluid delivery controller is further configured to calculate preheater control values ​​based on expected ambient heat loss.

5. A diesel engine exhaust fluid system, comprising: A diesel exhaust fluid delivery controller is configured to be connected to a preheater for preheating diesel exhaust fluid for delivery to an exhaust manifold in an exhaust system, and to be connected to a condition sensor for monitoring the risk of diesel exhaust fluid deposition in the exhaust system. The diesel engine exhaust fluid delivery controller is also configured to: Receive a status signal from the status sensor indicating a risk of diesel engine exhaust fluid deposition in the exhaust system; The deposition-relief temperature of the diesel exhaust fluid in the exhaust pipe to be permitted to enter the exhaust system is determined based on the condition signal, exhaust temperature, exhaust mass flow rate, and diesel exhaust fluid dosage. as well as The command increases the heat output of the preheater, causing the temperature of the diesel exhaust fluid to be allowed to enter the exhaust pipe to increase to the deposition-relief temperature.

6. The diesel engine exhaust fluid system according to claim 5, wherein: The deposition risk conditions include reduced exhaust temperature conditions; The diesel engine exhaust fluid system includes the condition sensor, wherein the condition sensor is an exhaust temperature sensor, and the condition signal is an exhaust temperature signal.

7. The diesel engine exhaust fluid system according to claim 5 or 6, wherein the diesel engine exhaust fluid delivery controller is further configured to: The preheater control value is calculated based on the difference between the current diesel engine exhaust fluid temperature and the deposition-relief temperature; The heat output of the preheater is increased based on the preheater control value command. The diesel engine exhaust fluid delivery controller is also configured to locate the deposition-relief temperature in a graph having exhaust temperature coordinates, exhaust flow rate coordinates, and diesel engine exhaust fluid dosage coordinates.

8. The diesel engine exhaust fluid system according to claim 7, further comprising: A diesel engine exhaust fluid storage tank temperature status sensor, the diesel engine exhaust fluid storage tank temperature status sensor being configured to generate a diesel engine exhaust fluid storage tank temperature signal; An ambient temperature sensor is configured to generate an ambient temperature signal; and The diesel engine exhaust fluid delivery controller is also configured to calculate the preheater control value based on the exhaust temperature signal, the diesel engine exhaust fluid storage tank temperature signal, and the ambient temperature signal.

9. A method of operating an exhaust system for an internal combustion engine, the method comprising: Generates a condition signal indicating the risk of diesel exhaust fluid deposition in the exhaust system; Based on the condition signal, increase the heat energy output of the preheater for diesel engine exhaust fluid in the diesel engine exhaust fluid system of the exhaust system; Deposition-mitigation temperature is determined based on exhaust temperature, exhaust mass flow rate, and diesel engine exhaust fluid dosage. Based on the increased heat output, the temperature of the diesel engine exhaust fluid in the diesel engine exhaust fluid system is increased to the deposition-mitigation temperature; as well as The command allows diesel exhaust fluid with a temperature increased to the deposition-relief temperature to enter the exhaust pipe of the exhaust system.

10. The method according to claim 9, wherein: The generation of status signals includes generating an exhaust temperature signal indicating a decrease in exhaust temperature; The method further includes: The preheater control value is calculated based on the difference between the current diesel engine exhaust fluid temperature and the deposition-relief temperature; and / or The preheater control values ​​are calculated based on the expected environmental heat loss.

Images