Patent Publication Number: US-11384667-B2

Title: Exhaust aftertreatment system with heated dosing control

Description:
BACKGROUND 
     The present disclosure relates to exhaust aftertreatment systems for automotive applications, and particularly to mixing devices included in exhaust aftertreatment systems. More particularly, the present disclosure relates to injectors for injecting reducing agents, such as urea solutions, into exhaust streams to mix with the exhaust stream so that chemical reaction between the reducing agent and exhaust gases reduces Nitrous Oxides (NOx) in the exhaust gas. 
     SUMMARY 
     An over-the-road vehicle in accordance with the present disclosure including an internal combustion engine that produces exhaust gases and an exhaust aftertreatment system configured to treat the exhaust gases before releasing them into the atmosphere. The exhaust aftertreatment system can include a number of components such as, for example, a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), one or more selective catalytic reduction units (SCRs), and one or more reducing agent mixers. 
     The reducing agent mixers can each include a mixing can defining at least a portion of an exhaust passageway for receiving a flow of exhaust gases therein and a doser for injecting reducing agent/reagent into the flow of exhaust gases. The dosers may be configured to selectively heat the reducing agent ahead of injection. Heating the reducing agent can encourage reaction with the flow of exhaust gases to reduce unwanted nitrous oxides (NOx) when system conditions might not otherwise support the reaction. 
     Dosers configured for selectively heating reducing agent ahead of injection may be part of heated doser units including dedicated heaters and doser controllers. These doser controllers may be configured to operate the heated doser units in heated and unheaded modes. Heating can be applied at various levels and can be applied based on a variety of inputs related to the over-the-road vehicle, the combustion engine, the exhaust gas aftertreatement system, and other factors as discussed in this disclosure. 
     Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of illustrative embodiments described in this paper. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       The detailed description particularly refers to the accompanying figures in which: 
         FIG. 1  is perspective view of an over-the-road automotive vehicle including an internal combustion engine and an exhaust aftertreatment system with an upstream reducing agent mixer located within an engine compartment of the vehicle having a heated doser for injecting a reagent into an exhaust stream and a downstream reducing agent mixer having a doser for adding additional reagent to the exhaust stream so as to chemically react unwanted materials (nitrous oxides/NOx) out of the exhaust gas before the exhaust stream is discharged into the atmosphere; 
         FIG. 2  is a side elevation view of a portion of the exhaust aftertreatment system from  FIG. 1  showing heated doser included in the upstream reducing agent mixer and a second doser included the downstream reducing agent mixer; and 
         FIG. 3  is a diagrammatic view of various components and devices that may be included in the vehicle of  FIG. 1  an exhaust aftertreatment system including a reducing agent tank, a reducing agent pump, the heated doser included in the upstream reducing agent mixer, and a control system for operating the reducing agent mixer based on various inputs so as to provide heated dosing control. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative over-the-road vehicle  10  includes an engine  12  an exhaust aftertreatment system  14  in accordance with the present disclosure as shown, for example, in  FIG. 1 . The engine  12  is, illustratively, an internal combustion engine configured to combust fuel and discharge exhaust gases that are carried through an exhaust passageway  16  defined by an exhaust conduit  17 , treated by the exhaust aftertreatment system  14 , and then released into the atmosphere. The exhaust aftertreatment system  14  is configured to reduce various effluents in the exhaust gases, such as, for example, nitrogen oxides (NOx), before the exhaust gases are released to the atmosphere. 
     In the illustrative embodiment, the exhaust aftertreatment system  14  includes a plurality of exhaust aftertreatment devices such as, for example, a diesel oxidation catalyst (DOC)  18 , a diesel particulate filter (DPF)  20 , and a selective catalytic reduction unit (SCR)  22 , and a reducing agent mixer  24 . Additional exhaust aftertreatment devices included in the system  14  include a light-off selective catalytic reduction unit (LO-SCR)  23  and a light off reducing agent mixer  25 . The LO-SCR  23  and the light off reducing agent mixer  25  are illustratively mounted in the engine compartment, upstream of other components, and can be specifically used at startup of the engine  12 . 
     The exhaust gases pass through or by each of the aftertreatment devices to remove or reduce different effluents. The reducing agent mixers  24 ,  25  are mounted upstream of associated SCRs  22 ,  23  and are configured to inject a reducing agent, into exhaust gases. Chemical reaction of the reducing agent with the exhaust gases occurs in the SCRs  22 ,  23  to reduce NO x  before the exhaust gases are released in the atmosphere. 
     The reducing agent mixer  24  includes a mixing can  261  and a doser unit  281  as shown in  FIGS. 2 and 3 . The light off reducing agent mixer  25  includes a mixing can  262  and a heated doser unit  282 . The mixing cans  261 ,  262  are coupled fluidly with the exhaust passageway  16  to receive the exhaust gases flowing therethrough. The doser unit  281  is configured to inject reducing agent (sometimes called reagent, urea solution, DEF, or AdBlue) into the mixing can  261  to mix with exhaust gases, and in some instances, may be heated like heated doser unit  282 . The heated doser unit  282  is configured to inject unheated or actively heated reagent into the mixing can  262  to mix with exhaust gases. 
     The reducing agent is stored on the vehicle  10  in a reducing agent tank  30  and is conducted to the doser units  281 ,  282  prior to being discharged into the mixing cans  261 ,  262 . In illustrative embodiments, the reducing agent is a urea solution (trade name AdBlue). A pump  32  is provided for supplying reagent to the doser units  281 ,  282 . Also, the reducing agent tank  30  may be coupled via a controlled valve  35  to an engine coolant supply  34  so as to be used as a heat sink for the engine coolant supply  34  as suggested in  FIG. 3 . 
     The heated doser unit  282  illustratively includes a reagent doser  40 , a heater  42 , and a doser controller  44  as shown, diagrammatically, in  FIG. 3 . The reagent doser  40  pressurizes and controls injection of reagent into a flow of exhaust gas via inlet/outlet valves  51 , 52  as well as an overpressure valve  55 . The heater  42  is coupled to, or integrated with, an outlet chamber  54  of the reagent doser  40  to selectively heat reagent in the doser  40  before discharge into the flow of exhaust gases. The doser controller  44  is coupled to the heater  42 , valves  51 ,  52 , and various sensors T, P, etc. so as to direct operation of the heated doser unit  282 . 
     The doser controller  44  is configured to operate the heated doser unit  282  in an unheated mode and a heated mode. In the unheated mode, reagent is injected by the reagent doser  40  without the addition of heat by the heater  42 . In heated mode reagent is injected by the reagent doser  40  with the addition of heat by the heater  42 . 
     The heated mode may have one or more levels of operation. For example, at a flash-boil level, the heater  44  may heat the reagent to 160 C before injection. At this temperature the reagent is at the saturated vapor pressure making reaction with NOx in exhaust gases more likely. At a warm-up level, the heater  44  may heat the reagent to less than 160 C before injection. At these temperatures, the regent may be more easily reacted with exhaust gases and/or better distributed through flows of exhaust gas. 
     In the illustrative embodiment, the doser controller  44  is in communication with sensors measuring temperatures T, pressures P, flow rates Q, fill levels L and the like within the heated doser unit  282  and throughout the vehicle  10  as suggested in  FIG. 3 . In some instances, the doser controller  44  may be linked to sensors and other systems in/around the vehicle  10  via a master engine control unit (ECU)  60 . In other embodiments, controller modules may be combined or separated to provide functionality of a doser controller  44 /ECU  60  as would be appreciated in the art. 
     In illustrative embodiments, the doser controller  44  is configured to determine an energy availability ratio based on various inputs. The energy availability ratio is associated with an amount of energy in the exhaust gas divided by the amount of energy needed to vaporize the urea in the flow of exhaust gases. In the illustrative embodiment, the controller calculates the energy availability ratio based on a temperature of the flow of exhaust gases, a flowrate of the flow of exhaust gases, a demanded flow rate of the reagent, and ambient temperature. In other embodiments, other inputs may be used to calculate or estimate the energy availability ratio so as to determine the ratio for purposes of heated doser unit  282  control. For example, the energy availability ratio can be calculated using the above noted inputs along with exhaust pressure, ambient pressure, etc. or can be estimated using only exhaust temperature. Accordingly, the particular set of inputs considered to determine energy availability ratio is flexible and may include one or more relevant factors. 
     The exemplary doser controller  44  is configured to operate the heated doser unit  282  in unheated mode when the energy availability ratio is at or above a predetermined reaction threshold. The doser controller is further configured to operate the heated doser unit  282  in heated mode, more specifically at the flash-boil level, when the energy availability ratio is at or below the predetermined reaction threshold. Accordingly, energy is only used to heat reagent when desired to reduce NOx in the exhaust gases at the expense of overall carbon creation by the engine  12  or use of energy in a battery  62 . 
     In the illustrated embodiment, the doser controller  44  may be configured to make exceptions and operation in unheated/heated mode in opposition to the energy availability ratio determined based on various inputs. By doing this, operation can be refined and optimized for the associated vehicle  10  and it&#39;s expected operation. As specific examples, the doser controller  44  may make exceptions to operation in view of energy availability ratio in view of: exhaust aftertreatment system information, vehicle information, engine information, accessory information, and/or exhaust gas chemistry information. These examples are not exhaustive and other inputs may be considered. 
     Exhaust aftertreatement system information that may be considered by the doser controller  44  to drive an exception and operation in opposition to the energy availability ratio determined. In particular, exhaust aftertreatement system information may include one or more of status of a diesel particulate filter regeneration event, status of an exhaust aftertreatement system catalyst de-sulphation event, reagent deposit detection, and time since last switch from one mode to another. A diesel particulate filter regeneration event may indicate heat added to the exhaust aftertreatment system  14  such that heating of the doser may not be required in spite of energy availability ratio determined. A system catalyst de-sulfation event may indicate high (or low) efficacy of the LO-SCR/SCR  23 ,  22  such that heating may needed (or not) in opposition to energy availability ratio determined. Reagent deposit detection may be determined via pressures or other inputs and may indicate desirability of heating (or not) in opposition to energy availability ratio determined. Of course other inputs associated with the exhaust aftertreatement system  14  (temperatures, pressures, etc) may also be considered to drive exception operation. 
     Vehicle information that may be considered by the doser controller  44  to drive an exception and operation in opposition to the energy availability ratio determined. In particular, vehicle information may include one or more of vehicle speed, key-switch status, vehicle gear selection, exhaust gas recirculation percentage, and diagnostic fault detection and activation status. These and other pieces of vehicle information can anticipate or indicate the desirability of heater  42  operation in opposition to energy availability ratio determined by the doser controller  44  so as to meet or exceed regulations related to NOx and/or to manage power consumption by the heated doser unit  282  in view of other vehicle  10  systems. In the illustrative embodiment, vehicle information is provided to the doser controller  44  by the master ECU  60 . 
     Engine information that may be considered by the doser controller  44  to drive an exception and operation in opposition to the energy availability ratio determined. In particular, engine information may include one or more of cylinder de-activation, engine/exhaust brake state, engine coolant temperature, engine speed, engine torque, intake manifold pressure, and intake manifold temperature, and engine fuel flowrate. These and other pieces of engine information can anticipate or indicate the desirability of heater  42  operation in opposition to energy availability ratio determined by the doser controller  44 . In the illustrative embodiment, engine information is provided to the doser controller  44  by the master ECU  60 . 
     Accessory information that may be considered by the doser controller  44  to drive an exception and operation in opposition to the energy availability ratio determined. In particular, accessory information may include one or more of power take off (PTO) system status, and external scan tool status. These and other pieces of accessory information can anticipate or indicate the desirability of heater  42  operation in opposition to energy availability ratio determined by the doser controller  44 . For example, upon PTO engagement, power may need to be diverted from heated doser unit  282  (change to unheated mode) or additional exhaust creation anticipated (change to heated mode). External scan tool status may drive automatic heated mode operation so as to confirm heated doser unit  282  suitability for normal operation. In the illustrative embodiment, accessory information is provided to the doser controller  44  by the master ECU  60 . 
     Exhaust gas chemistry information that may be considered by the doser controller  44  to drive an exception and operation in opposition to the energy availability ratio determined. In particular, exhaust gas chemistry information may include one or more of nitrous oxide concentration in an exhaust line, ammonia concentration in the exhaust line, and oxygen concentration in the exhaust line. These and other pieces of chemistry information can anticipate or indicate the desirability of heater  42  operation in opposition to energy availability ratio determined by the doser controller  44 . In the illustrative embodiment, chemistry information is provided to the doser controller  44  by the master ECU  60 . 
     In some embodiments, the doser controller  44  may be configured to make exception and to operate in heated/unheated mode in opposition to the determined energy availability ratio based upon a mixing uniformity factor. The mixing uniformity factor is associated with uniformity of reagent distribution within the flow of exhaust gases ahead of and/or upon interaction with a catalyst included in the LO-SCR  23  of the exhaust gas aftertreatment system  14 . The mixing uniformity factor may be determined (calculated, estimated, looked up) based on flowrate of the flow of exhaust gases, the demanded flow rate of the reagent, and/or other factors. 
     In some embodiments, the doser controller  44  may be configured to operate the heated doser unit in heated/unheated mode based on the mixing uniformity factor without determination of or regard for energy availability ratio. More specifically the doser controller  44  may operate the heated doser unit  282  in unheated mode when the mixing uniformity factor is at or above a predetermined uniformity threshold. Further, the doser controller  44  may operate the heated doser unit  282  in heated mode (specifically warm-up mode) when the mixing uniformity factor is below the predetermined uniformity threshold. 
     Heated doser unit  282  can control the urea state inside the heated chamber  54  of a doser  40  by using the parameters measured on engine and aftertreatment to switch between heated and non-heated mode. Some doser units are only capable of running in the non-heated mode. Such dosers are limited by the exhaust gas temperature parameter (among other things) to not dose below typically 180 Degrees C. This is because they could form significant urea deposits leading to potential blockage of the aftertreatment system, and could result in a lack of conversion of the urea to the ammonia needed for the NOx reduction catalytic reaction due to lack of exhaust temperature (or other factors). 
     The heated doser unit  282  in the present disclosure provides small droplets in heated mode to enable enhanced generation of ammonia below 180 Deg C exhaust gas temperature. It can accordingly be effective to much lower exhaust temperatures (e.g. 130 or 150 Degrees C.). While running in this heated mode, a small power consumption may be required to power the urea heater  42  incorporated in the doser. It may be advantageous to be able to turn off the power to the heater to run in non-heated mode when it is not needed at higher exhaust temperatures (eg 180 degrees plus) this saves power consumption. 
     In addition in the heated mode the flow rate can be limited by the power available in the heater  42  and flow rates required at high engine power (and consequently high exhaust temperatures) may not be achieved in heated mode. Operating in the non-heated mode can overcome this potential limitation of the heated doser unit  282 . 
     The effect of operation in two modes, controlled by aftertreatment and/or other parameters is that it changes the operating mode of the doser and the state of the urea within the doser  40 . Low exhaust temperature—urea heated mode—urea may be a superheated fluid vapor mix, and may be injected in a mode which promotes instant boiling of some of the fluid when it is ejected through the outlet nozzle. High exhaust temperature—non heated mode—urea is at ambient temperature, below its boiling point and injected as a normal fluid. 
     The present disclosure provides, among other things, methods and logic for determining when to switch between heated and non-heated mode of dosing. The controller  44  can use various data from the vehicle  10  and the environment to determine when to switch from one mode to the other. Doser controller  44  can provide optimized performance, minimize deposit formation, optimize for spray characteristics (droplet size, spray angle, velocity, vapor fraction) when needed, and manage power usage. 
     Software inside the controller  44  and/or ECU  60  may be programmed with logic, control laws, and calibration parameters that will determine when to switch from heated dosing mode to non-heated dosing mode. The inputs into that software may include, but are not limited to, the following: exhaust temperature, exhaust flow rate, exhaust pressure, ambient temperature, ambient pressure, UWS dosing flowrate demand, status of DPF regeneration event, status of SCR de-sulphation event, vehicle speed, engine speed, engine torque, intake manifold pressure, intake manifold temperature, time since the last switch from one mode to another, diagnostic fault detection and activation status, communication with an external scan tool, UWS pump pressure, UWS temperature at the inlet of the doser, vehicle gear selection, exhaust gas recirculation percentage, cylinder de-activation, engine/exhaust brake state, engine coolant temperature, Nox concentration in the exhaust line, NH3 concentration in the exhaust line, oxygen concentration in the exhaust line, UWS flowrate demand to other doser(s) in the exhaust line, PTO status, key-switch status, or engine fuel flowrate. 
     The following numbered clauses include embodiments that are contemplated and non-limiting: 
     Clause 1. An exhaust aftertreatment system for an over-the-road vehicle, the system comprising 
     a mixing can defining at least a portion of an exhaust passageway for receiving a flow of exhaust gases therein, and 
     a heated doser unit including a reagent doser configured to inject reagent into the flow of exhaust gases in the mixing can, a heater coupled to the reagent doser to heat reagent in the reagent doser, and a doser controller configured to control injection of the reagent by the reagent doser and heating of the reagent by the heater, 
     wherein the heated doser unit is configured to operate in (1) an unheated mode, in which reagent is injected by the reagent doser without the addition of heat by the heater, and (2) a heated mode, in which reagent is injected by the reagent doser with the addition of heat by the heater. 
     Clause 2. The system of clause 1, any other suitable clause, or combination of clauses, wherein the doser controller is configured to determine an energy availability ratio associated with an amount of energy in the flow of exhaust gases divided by the amount of energy needed to vaporize the urea, the doser controller is configured to operate the heated doser unit in unheated mode when the energy availability ratio is at or above a predetermined reaction threshold, and the doser controller is configured to operate the heated doser unit in heated mode when the energy availability ratio is below the predetermined reaction threshold. 
     Clause 3. The system of clause 2, any other suitable clause, or combination of clauses, wherein the doser controller calculates the energy availability ratio based on a temperature of the flow of exhaust gases, a flowrate of the flow of exhaust gases, a demanded flow rate of the reagent, and ambient temperature. 
     Clause 4. The system of clause 2, any other suitable clause, or combination of clauses, wherein the doser controller is configured to make exception and to operate in heated mode when the energy availability ratio is below the predetermined reaction threshold or to operate in unheated mode when the energy availability ratio is above the predetermined reaction threshold based upon exhaust aftertreatment system information including at least one of: status of a diesel particulate filter regeneration event, status of an exhaust aftertreatement system catalyst de-sulphation event, and time since last switch from one mode to another. 
     Clause 5. The system of clause 2, any other suitable clause, or combination of clauses, wherein the doser controller is configured to make exception and to operate in heated mode when the energy availability ratio is below the predetermined reaction threshold or to operate in unheated mode when the energy availability ratio is above the predetermined reaction threshold based upon vehicle information including at least one of: vehicle speed, key-switch status, vehicle gear selection, exhaust gas recirculation percentage, and diagnostic fault detection and activation status. 
     Clause 6. The system of clause 2, any other suitable clause, or combination of clauses, wherein the doser controller is configured to make exception and to operate in heated mode when the energy availability ratio is below the predetermined reaction threshold or to operate in unheated mode when the energy availability ratio is above the predetermined reaction threshold based upon engine information including at least one of: cylinder de-activation, engine/exhaust brake state, engine coolant temperature, engine speed, engine torque, intake manifold pressure, intake manifold temperature, and engine fuel flowrate. 
     Clause 7. The system of clause 2, any other suitable clause, or combination of clauses, wherein the doser controller is configured to make exception and to operate in heated mode when the energy availability ratio is below the predetermined reaction threshold or to operate in unheated mode when the energy availability ratio is above the predetermined reaction threshold based upon accessory information including at least one of: power take off system status, and external scan tool status. 
     Clause 8. The system of clause 2, any other suitable clause, or combination of clauses, wherein the doser controller is configured to make exception and to operate in heated mode when the energy availability ratio is below the predetermined reaction threshold or to operate in unheated mode when the energy availability ratio is above the predetermined reaction threshold based upon exhaust gas chemistry information including at least one of: nitrous oxide concentration in an exhaust line, ammonia concentration in the exhaust line, and oxygen concentration in the exhaust line. 
     Clause 9. The system of clause 2, any other suitable clause, or combination of clauses, wherein the doser controller is configured to make exception and to operate in heated mode when the energy availability ratio is below the predetermined reaction threshold based upon a mixing uniformity factor associated with uniformity of reagent distribution within the flow of exhaust gases upon interaction with a catalyst included in the exhaust gas aftertreatment system. 
     Clause 10. The system of clause 9, any other suitable clause, or combination of clauses, wherein the mixing uniformity factor is determined based on at least one of flowrate of the flow of exhaust gases and the demanded flow rate of the reagent. 
     Clause 11. The system of clause 1, any other suitable clause, or combination of clauses, wherein the doser controller is configured to determine a mixing uniformity factor associated with uniformity of reagent distribution within the flow of exhaust gases upon interaction with a catalyst included in the exhaust gas aftertreatment system, the doser controller is configured to operate the heated doser unit in unheated mode when the mixing uniformity factor is at or above a predetermined uniformity threshold, and the doser controller is configured to operate the heated doser unit in heated mode when the mixing uniformity factor is below the predetermined uniformity threshold. 
     Clause 12. The system of clause 11, any other suitable clause, or combination of clauses, wherein the mixing uniformity factor is determined based on at least one of flowrate of the flow of exhaust gases and the demanded flow rate of the reagent. 
     13. An over the road vehicle, the vehicle comprising 
     an internal combustion engine configured to produce a flow of exhaust gases that are conducted through an exhaust passageway defined by an exhaust conduit, and 
     an exhaust aftertreatment system according to any one of clauses 1-12 (including suitable combinations thereof) fluidly coupled to the internal combustion engine.