ENGINE OUT NOx REDUCTION USING ENHANCED DEF

Abstract

Unenhanced DEF and anhydrous solid reductant capable of forming ammonia are mixed to create enhanced DEF which is injected into an engine exhaust aftertreatment system which performs selective catalytic reduction (SCR) of engine-out exhaust.

Claims

1. A motor vehicle propelled by a diesel engine comprising an exhaust aftertreatment system forming an exhaust flow path having an entrance through which engine-out diesel exhaust enters and an exit through which treated diesel exhaust exits, the exhaust flow path containing: 1) a diesel oxidation catalyst (DOC) for treating engine-out exhaust, 2) a diesel particulate filter (DPF) for treating exhaust flow from the DOC, and 3) a main SCR catalyst having surfaces containing catalytic material across which exhaust flow from the DPF passes; a diesel exhaust fluid (DEF) storage tank which holds unenhanced DEF; a secondary reductant store which holds anhydrous solid reductant capable of forming ammonia; a mixing zone in which anhydrous solid reductant and unenhanced DEF are mixed to create enhanced DEF; and a DEF injector for injecting enhanced DEF to entrain with exhaust flow from the DPF for enabling catalytic reduction of some NOx in exhaust flow across the catalytic material of the main SCR catalyst.

2. A motor vehicle as set forth in claim 1 in which the mixing zone is within a delivery conduit through which a DEF supply module delivers DEF from the DEF storage tank to the DEF injector.

3. A motor vehicle as set forth in claim 2 in which the anhydrous solid reductant comprises prills and a screw augur conveyor conveys prills from the secondary reductant store to the delivery conduit.

4. A motor vehicle as set forth in claim 1 in which the mixing zone comprises an interior of a mixing chamber which is external to a delivery conduit through which a DEF supply module delivers DEF from the DEF storage tank to the DEF injector.

5. A motor vehicle as set forth in claim 4 in which the anhydrous solid reductant comprises prills, and a screw augur conveyor conveys prills from the secondary reductant store to the interior of the mixing chamber.

6. A motor vehicle as set forth in claim 5 including at least one heater for heating prills after they have left the secondary reactant store.

7. A motor vehicle as set forth in claim 6 in which the at least one heater comprises a first heater for heating prills being conveyed by the screw augur conveyor and a second heater for heating prills as they are mixing with DEF within the interior of the mixing chamber.

8. A motor vehicle as set forth in claim 4 in which the anhydrous solid reductant comprises prills and the mixing zone comprises an interior of a mixing chamber within which an agitator is disposed to agitate prills as they are mixing with DEF.

9. A motor vehicle as set forth in claim 8 in which a screw augur conveyor conveys prills from the secondary reductant store to the interior of the mixing chamber, and least one heater heats the prills.

10. A motor vehicle as set forth in claim 9 in which the at least one heater comprises a first heater for heating prills being conveyed by the screw augur conveyor and a second heater for heating prills as they are mixing with DEF within the interior of the mixing chamber.

11. A motor vehicle as set forth in claim 4 including valves which are selectively operable to a first condition which diverts unenhanced DEF from the DEF supply module to the interior of the mixing chamber for mixing with anhydrous solid reductant to create enhanced DEF and allows enhanced DEF to be delivered from the mixing chamber to the DEF injector while simultaneously preventing unenhanced DEF from being delivered to the DEF injector, and to a second condition which prevents unenhanced DEF from the DEF supply module from being diverted to the interior of the mixing chamber and allows unenhanced DEF to be delivered from the DEF supply module to the DEF injector while simultaneously preventing enhanced DEF in the mixing chamber from being delivered to the DEF injector.

12. A motor vehicle as set forth in claim 4 including valves which are selectively operable to a first condition which allows only unenhanced DEF to be delivered to the DEF injector, to a second condition which allow only enhanced DEF from the mixing chamber to be delivered to the DEF injector, and to a third condition which mixes unenhanced DEF and enhanced DEF from the mixing chamber to create blended enhanced DEF which is delivered to the DEF injector.

13. A diesel engine exhaust aftertreatment system comprising an exhaust flow path having an entrance through which engine-out diesel exhaust enters and an exit through which treated diesel exhaust exits, the aftertreatment system comprising: 1) a diesel oxidation catalyst (DOC) for treating engine-out exhaust, 2) a diesel particulate filter (DPF) for treating exhaust flow from the DOC, and 3) a main SCR catalyst having surfaces containing catalytic material across which exhaust flow from the DPF passes; a diesel exhaust fluid (DEF) storage tank which holds unenhanced DEF; a secondary reductant store which holds anhydrous solid reductant capable of forming ammonia; a mixing zone in which anhydrous solid reductant and unenhanced DEF mix to create enhanced DEF; and a DEF injector for injecting enhanced DEF to entrain with exhaust flow from the DPF for enabling catalytic reduction of some NOx in exhaust flow across the catalytic material of the main SCR catalyst.

14. A diesel engine exhaust aftertreatment system as set forth in claim 13 in which the mixing zone is within a delivery conduit through which a DEF supply module delivers DEF from the DEF storage tank to the DEF injector.

15. A diesel engine exhaust aftertreatment system as set forth in claim 14 in which the anhydrous solid reductant comprises prills and a screw augur conveyor conveys prills from the secondary reductant store to the delivery conduit.

16. A diesel engine exhaust aftertreatment system as set forth in claim 13 in which the mixing zone comprises an interior of a mixing chamber which is external to a delivery conduit through which a DEF supply module delivers DEF from the DEF storage tank to the DEF injector.

17. A diesel engine exhaust aftertreatment system as set forth in claim 16 in which the anhydrous solid reductant comprises prills, and a screw augur conveyor conveys prills from the secondary reductant store to the interior of the mixing chamber.

18. A method for aftertreatment of engine-out exhaust from an internal combustion engine flowing through an exhaust flow path having an entrance through which untreated engine-out exhaust enters and an exit through which treated exhaust exits, the method comprising: in a mixing zone, mixing anhydrous solid reductant capable of forming ammonia and unenhanced DEF to create enhanced DEF; injecting enhanced DEF upstream of a main SCR catalyst to entrain with exhaust flow for enabling catalytic reduction of some NOx in exhaust flow across the catalytic material of the main SCR catalyst.

19. A method as set forth in claim 18 further comprising using a diesel oxidation catalyst (DOC) in the flow path upstream of the main SCR catalyst to treat engine-out exhaust and using a diesel particulate filter (DPF) downstream of the DOC and upstream of the main SCR catalyst to treat exhaust coming from the DOC.

20. A method as set forth in claim 18 further comprising blending enhanced DEF from the mixing zone and unenhanced DEF to create blended enhanced DEF and injecting blended enhanced DEF upstream of the main SCR catalyst.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 shows a motor vehicle which is propelled by an internal combustion engine.

[0019] FIG. 2 is a general schematic diagram of the engine showing detail of its exhaust aftertreatment system.

[0020] FIG. 3 is a schematic diagram illustrating a first embodiment of a portion of the exhaust aftertreatment system.

[0021] FIG. 4 is a schematic diagram illustrating a second embodiment of a portion of the exhaust aftertreatment system.

[0022] FIG. 5 is a schematic diagram illustrating a third embodiment of a portion of the exhaust aftertreatment system.

[0023] FIG. 6 is a schematic diagram illustrating a fourth embodiment of a portion of the exhaust aftertreatment system.

[0024] FIG. 7 is a schematic diagram illustrating a fifth embodiment of a portion of the exhaust aftertreatment system.

[0025] FIG. 8 is a schematic diagram illustrating a sixth embodiment of a portion of the exhaust aftertreatment system.

[0026] FIG. 9 is a schematic diagram illustrating a sixth embodiment of a portion of the exhaust aftertreatment system.

DETAILED DESCRIPTION

[0027] FIG. 1 shows a truck vehicle 10, such as a highway tractor for example, having a chassis 12 and a cab body 14 supported on a frame of chassis 12 which also supports a fuel-consuming engine 16 of a powertrain 18. Engine 16 operates through a drivetrain of powertrain 18 to drive wheels 20 which propel the truck vehicle on land.

[0028] FIG. 2 shows engine 16 having an engine intake system 22 for conveying air to engine cylinders 24 into which fuel is injected and within which injected fuel is combusted to operate the engine. An engine exhaust system 26 conveys exhaust resulting from combustion of fuel in cylinders 24 to surrounding atmosphere. Exhaust system 26 includes an aftertreatment system 28 for treating engine out exhaust before exhaust passes into surrounding atmosphere through a tailpipe 30.

[0029] Engine 16 is representative of a turbocharged diesel engine which comprises a turbocharger 32 having a turbine 34 operated by engine out exhaust before exhaust enters aftertreatment system 28. Turbine 34 operates a compressor 36 to create charge air entering cylinders 24 from intake system 22. Other components associated with this type of engine, such as a charge air cooler for example, are not shown in the drawing.

[0030] An engine controller comprises a processor-based engine control unit (ECU) 38 which controls various aspects of engine operation, such as injection of fuel into engine cylinders 24. Control of fuel injection and other functions is accomplished by processing various input data to develop control data for controlling those functions.

[0031] Exhaust aftertreatment system 28 is shown in FIG. 2 to comprise structure through which exhaust is constrained to pass before exiting exhaust system 26. It should be understood that various components of the illustrated structure are shown schematically rather than as actual components, many of which are well-known in aftertreatment systems. Aftertreatment system 28 comprises an enclosure 40 providing an exhaust flow path between an exhaust entrance 42 at an upstream end, and an exhaust exit 44 at a downstream end. Arrows 46 indicate a direction of exhaust flow into, through, and out of the interior of enclosure 40. The exhaust flow is constrained to pass in succession across surfaces of a diesel oxidation catalyst (DOC) 48, through a diesel particulate filter (DPF) 50, across surfaces of a main SCR catalyst 52 and surfaces of an ammonia slip (AMOX) catalyst 54.

[0032] DOC 48 treats engine exhaust by removing certain entrained matter, such as the soluble organic fraction of diesel particulate matter. DPF 50 removes entrained soot from the exhaust. If exhaust temperature needs elevation for burning off trapped soot (i.e. regeneration), combustible hydrocarbons, available as diesel fuel from a vehicle's fuel tank, may be introduced into the exhaust ahead of DOC 48 via a fuel injector (not shown). Main SCR catalyst 52 treats engine exhaust by reducing NOx according to chemical reactions mentioned above. While any catalytic material which can withstand whatever DPF regeneration temperatures main SCR catalyst may be subjected to during DPF regenerations may be used, iron zeolite and copper zeolite are examples of catalyst materials suitable for main SCR catalyst 52. Ammonia slip catalyst 54 is placed after main SCR catalyst 52 to convert any ammonia leaving the latter into nitrogen and water vapor.

[0033] Between DPF 50 and SCR 52, exhaust flow is constrained to pass through a mixing zone comprising a mixer 56 which promotes mixing of exhaust with DEF which is injected via a DEF injector 58 to entrain and mix with exhaust flow before the flow reaches main SCR catalyst 52. An example of mixer 56 is a static mixer which is placed between DEF injector 58 and main SCR catalyst 52 and which promotes wide distribution of DEF within the exhaust flow before the flow reaches main SCR catalyst 52. Thermal energy in the exhaust flow vaporizes the DEF water component and decomposes the DEF urea component to create free ammonia molecules which attach to catalytic surface sites of main SCR catalyst 52 when a metal-exchanged zeolite is used.

[0034] Enclosure 40 may be mounted on a frame rail of chassis 12 or alternately the various components of aftertreatment system 28 may be housed within individual enclosures connected by pipes.

[0035] Standard DEF is stored in a DEF storage tank 60 which is typically mounted on truck vehicle 10 at a location exposed to ambient temperatures which if low enough will freeze DEF in the DEF storage tank. When not frozen, standard DEF is drawn from DEF storage tank 60 by a pump 62 through a supply conduit 64 and delivered to a DEF supply module 66 which, under control of ECU 38, delivers a controlled quantity of DEF to DEF injector 58 through a delivery conduit 68. Pumped DEF which is in excess of DEF delivered to DEF injector 58 returns from DEF supply module 66 to DEF storage tank 60 through a return conduit 70. A secondary reductant store 72 holds solid, anhydrous urea or a similar anhydrous solid reductant capable of forming ammonia (e.g. ammonium carbamate). Solid reductant material from store 72 is mixed with standard DEF from DEF storage tank 60 (represented generically by mixer 73) to create enhanced DEF.

[0036] ECU 38 monitors operation of engine 16 and controls proportions of secondary reactant solid and DEF being mixed to create a desired urea concentration for enhanced DEF appropriate for how engine 16 is operating to enable tailpipe out NOx to comply with applicable tailpipe out NOx emission criteria while mitigating both formation of deposits on surfaces of aftertreatment system 28 and occurrences of ammonia slip. ECU 38 controls both timing and quantity of secondary reductant which is mixed with standard DEF and may at times limit quantity of secondary reductant added to assure that all secondary reductant will be dissolved in enhanced DEF which is being injected.

[0037] Control of the injection of unenhanced DEF may be performed using known strategies, such as by processing measurements from NOx sensors (not shown) to calculate NOx reduction quantity and using those measurements to control quantity of unenhanced DEF as it is being injected so that calculated NOx reduction quantity meets a NOx reduction quantity target which provides compliance with applicable NOx emission criteria.

[0038] Control of the injection of enhanced DEF may also be performed using known strategies, such as by processing measurements from NOx sensors (not shown) to calculate NOx reduction quantity and using those measurements to control both the urea concentration of enhanced DEF to be injected and the quantity of enhanced DEF as it is injected so that calculated NOx reduction quantity meets a NOx reduction quantity target which provides compliance with applicable NOx emission criteria.

[0039] FIG. 3 shows a first embodiment of mixing equipment 74 for creating enhanced DEF. Mixing equipment 74 comprises a secondary reactant store 72 containing a multitude of prills 78 of secondary reactant and a mixing zone 80 where prills 78 and standard DEF mix to create enhanced DEF. A prill comprises a urea sphere having a diameter of approximately 1.65 mm. Although other forms of solid urea may be used, the use of prills of known size provides a convenient way to accurately measure quantity of urea being mixed with unenhanced DEF to create enhanced DEF.

[0040] Mixing zone 80 comprises an interior of a mixing chamber. Prills 78 are conveyed from store 76 into the interior of the mixing chamber by a screw augur conveyor 82 operated by an electric motor 84. Speed at which conveyor 82 operates determines the rate at which prills 78 are being added to unenhanced DEF, and hence control of conveyor speed is one factor in controlling urea concentration of enhanced DEF. Quantity of unenhanced DEF entering the interior of the mixing chamber is another factor.

[0041] Entry of unenhanced DEF into the mixing chamber is controlled by a first three-way valve 86, and flow of enhanced DEF from the interior of the mixing chamber is controlled by a second three-way valve 88. Valves 86, 88 are selectively operable to a first condition and a second condition. ECU 38 controls whether enhanced or unenhanced DEF is delivered to DEF injector 58 by controlling valves 86 and 88.

[0042] The first condition diverts unenhanced DEF from DEF supply module 66 to the interior of the mixing chamber for mixing with prills 78 to create enhanced DEF and allows enhanced DEF to be delivered from the mixing chamber to DEF injector 58 while simultaneously preventing unenhanced DEF from being delivered to the DEF injector. The second condition prevents unenhanced DEF from DEF supply module 66 from being diverted to the interior of the mixing chamber and allows unenhanced DEF to be delivered from the DEF supply module to DEF injector 58 while simultaneously preventing enhanced DEF in the mixing chamber from being delivered to the DEF injector.

[0043] When valves 86, 88 are allowing enhanced DEF to be delivered to DEF injector 58, its urea concentration is controlled by speed of conveyor 82 and quantity of unenhanced DEF being supplied to mixing zone 80 from DEF supply module 66.

[0044] When valve 86 is allowing unenhanced DEF to continue flowing through delivery conduit 68 to valve 88 while disallowing flow of unenhanced DEF into mixing zone 80, and valve 88 is disallowing flow of enhanced DEF out of mixing zone 80 while allowing flow of unenhanced DEF from valve 86 to continue flowing through to DEF injector 58, DEF injector 58 injects unenhanced DEF. Screw augur conveyor 82 is also stopped.

[0045] FIG. 4 shows a second embodiment of mixing equipment 90 for creating enhanced DEF. In all material respects of construction and operation, mixing equipment 90 is like mixing equipment 74, but further comprises a first heater 92 and a second heater 94, each of which is electrically operated. First heater 92 is disposed to begin heating prills 78 as they approach mixing zone 80 while second heater heats prills 78 and DEF within mixing zone 80. Each heater is independently controlled by ECU 38 to operate at its own selected temperature for its own selected length of time. Heating of prills at a location remote from the location at which prills enter conveyor 82 assures accuracy in quantity of urea being mixed with unenhanced DEF.

[0046] FIG. 5 shows a third embodiment of mixing equipment 96 for creating enhanced DEF. In all material respects of construction and operation, mixing equipment 90 is like mixing equipment 74, but further comprises an agitator 98 for agitating mixture of prills and unenhanced DEF within mixing zone 80. Agitator 98 is operated by an electric motor 100 controlled by ECU 38.

[0047] FIG. 6 shows a fourth embodiment of mixing equipment 102 for creating enhanced DEF. In all material respects of construction and operation, mixing equipment 102 is like mixing equipment 74, but combines the heaters 92, 94 of the second embodiment with the agitator 98 and motor 100 of the third embodiment.

[0048] FIG. 7 shows a fifth embodiment for mixing unenhanced DEF and anhydrous solid reductant to create enhanced DEF. Prills 78 are conveyed from store 76 by screw augur conveyor 82 directly into delivery conduit 68 to mix with unenhanced DEF from DEF supply module 66 flowing toward DEF injector 58. Hence, the mixing zone is within delivery conduit 68 rather than in a distinct mixing zone external to delivery conduit 68. Heater 92 is disposed to heat prills 78 before they enter delivery conduit 68.

[0049] FIG. 8 shows a sixth embodiment of mixing equipment 104 which is like mixing equipment 74 except for the valve arrangement. A shut-off valve 106 and a two-way directional control valve 108 are controlled by ECU 38. FIG. 8 shows the second condition, as described earlier for FIGS. 3-6, but now with shut-off valve 106 preventing flow of unenhanced DEF into mixing zone 80 while directional valve 108 allows flow of unenhanced DEF from DEF supply module 66 to DEF injector 58. When ECU 38 operates the valves to the first condition, which was described earlier for FIGS. 3-6, shut-off valve 106 allows flow of unenhanced DEF into mixing zone 80 while directional valve 108 disallows flow of unenhanced DEF from DEF supply module 66 to DEF injector 58 and allows flow of enhanced DEF from mixing chamber 80 to DEF injector 58.

[0050] FIG. 9 shows a seventh embodiment of mixing equipment 110 which is like mixing equipment 74 except for the valve arrangement. An apportioning valve 112 is controlled by ECU 38 to selectively allow 1) only unenhanced DEF to be delivered to DEF injector 58, 2) only enhanced DEF to be delivered to DEF injector 58, or 3) a blend of unenhanced DEF and enhanced DEF to create blended enhanced DEF which is delivered to DEF injector 58.

[0051] Although not shown, each embodiment of mixing equipment 104, 110 may have agitators and/or heaters as described for prior embodiments.

[0052] If urea in other than the form of prills is used, it may be mechanically processed to provide sizes suitable for mixing, and other ways of measuring quantity may be employed.

[0053] While the diesel engine which has been described is one example of an internal combustion engine, enhanced DEF and the disclosed method of creating it may be used in any internal combustion engine which runs lean of stoichiometric (i.e. any lean burn engine).