Patent Application
20070163245
1. Field of the Invention
The present invention relates to exhaust aftertreatment systems for use in internal combustion engines, and, more particularly, to such exhaust aftertreatment systems using selective catalytic reduction.
2. Description of the Related Art
Increasingly stringent emissions control standards necessitate continually improved emissions from internal combustion (IC) engines used as motive power for vehicles. At present, the most significant of these emissions are sulfur dioxide (SO2), oxides of nitrogen (NOx), and airborne particulate.
NOx refers to the cumulative emissions of nitric oxide (NO), nitrogen dioxide (NO2) and trace quantities of other species generated during combustion. NOx emissions are minimized using low NOx combustion technology and postcombustion techniques. If combustion modifications alone are insufficient, postcombustion techniques such as selective catalytic reduction (SCR) systems may be employed. In SCR systems, NOx is reduced to nitrogen (N2) and water (H2O) through a series of reactions with a chemical reactive agent (reagent) injected into the exhaust gas. Ammonia and urea are the most commonly used chemical reagents with SCR systems.
In 2007, it is estimated that engine out NOx emissions will on average be approximately 1.2 g/hp-hr (gallons/horse power-hour). In order to meet the 2010 NOx standard of 0.2 g/hp-hr, an SCR system (using ammonia) can be used. For about 1 g/hp-hr NOx reduction the amount of ammonia (NH3) required is not very large. Since anhydrous ammonia is a toxic substance, another likely reagent is an aqueous solution of 32.5% urea and 67.5% water, although the exact reagent formulation can vary from one application to another. To achieve the desired 1 g/hp-hr NOx reduction, the amount of the proposed reagent required is approximately 1.3% of the diesel fuel burned, on average.
Since the urea mixture is a depletable supply, one contemplated supply solution is to provide a bulk tank at fueling stations with a supply hose and nozzle used for refilling a holding tank on the vehicle. This urea mixture supply solution may have logistics difficulties, however, with inadvertent spillage from the nozzle, the need to dedicate or retrofit a supply hose and nozzle at each fueling island, etc.
What is needed in the art is a quick, convenient and relatively safe system and method for refilling a reagent for use in an SCR exhaust aftertreatment system.
The present invention provides a reagent refill and supply system and method including a reagent holding tank permanently onboard the vehicle, and a portable and selectively couplable reagent supply canister for refilling the reagent holding tank.
The invention comprises, in one form thereof, an internal combustion engine including an exhaust manifold; and a selective catalytic reduction exhaust aftertreatment system. The selective catalytic reduction exhaust aftertreatment system includes a reduction catalytic converter in communication with the exhaust manifold; a reagent holding tank in fluid communication with the reduction catalytic converter; and a reagent supply canister selectively and removably couplable with the reagent holding tank.
The invention comprises, in another form thereof, a method of operating an internal combustion engine, including the steps of: treating exhaust gas with a selective catalytic reduction system including a reduction catalytic converter; supplying a reagent to the reduction catalytic converter from a reagent holding tank; coupling a reagent supply canister with a refill head on the reagent holding tank; and refilling the reagent holding tank with reagent from the reagent supply canister.
An advantage of the present invention is that the reagent can be quickly and easily replenished in a motor vehicle at periodic intervals as it is depleted from the reagent holding tank.
Another advantage is that the periodic interval can be a predetermined interval or can be a varying interval based upon a sensed reagent level in the holding tank.
Yet another advantage is that the reagent supply canister is sealed to the ambient environment and automatically opened upon coupling with the reagent holding tank to allow reagent refilling.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
Cylinder block 14 is shown as including six combustion cylinders, but may also include a different number of combustion cylinders, such as eight, ten or twelve combustion cylinders.
Intake manifold 18 and exhaust manifold 20 are each in fluid communication with the plurality of combustion cylinders 16, and may be of single part design, as shown, or of multiple part design.
Exhaust manifold 20 discharges exhaust gas to turbine 24 of turbocharger 22. Turbine 24 may be of a fixed geometry as shown, or may be an adjustable turbine such as a variable geometry turbine (VGT). Exhaust gas from exhaust manifold 20 rotatably drives turbine 24, and is then discharged to SCR exhaust aftertreatment system 12, as will be described in more detail hereinafter.
Turbine 24 rotatably drives compressor 26 via a shaft 28, as indicated by arrow 30. Compressor 26 receives air from the ambient environment, compresses the air and provides compressed charge air to intake manifold 18.
SCR exhaust aftertreatment system 12 generally includes a reduction catalytic converter 32, doser 34, reagent holding tank 36 and reagent supply canister 38. Reduction catalytic converter 32 may be of conventional design for an SCR exhaust aftertreatment system. Doser 34 provides a predetermined amount of reagent which is mixed with the exhaust gas discharged from turbine 24. The reagent is preferably mixed with the exhaust gas upstream from reduction catalytic converter 32 for sufficient mixing prior to entering reduction catalytic converter 32. Doser 34 may also be of any suitable configuration, and is thus not discussed further.
Reagent holding tank 36 and reagent supply canister 38 together define a reagent refill and supply system 40, shown in more detail in
Reagent holding tank 36 includes a refill head 42 which is sized and configured to couple in a sealed manner with reagent supply canister 38. More particularly, reagent supply canister 38 includes a nozzle 44 having an outside diameter which is slightly smaller than the inside diameter of refill head 42. Refill head 42 includes an annular groove (not numbered) at the inside diameter thereof which receives an O-ring seal 46. O-ring seal 46 fluidly seals between nozzle 44 and refill head 42 when reagent supply canister 38 is coupled with reagent holding tank 36 (
Refill head 42 includes a first latch 48 and nozzle 44 includes a second latch 50 which mate together when reagent supply canister 38 is coupled with reagent holding tank 36. In the embodiment shown, latches 48 and 50 are bayonet latches, but may be differently configured depending upon the application. Latch 48 is a female-type bayonet latch and latch 50 is a male-type bayonet latch.
Positioned within nozzle 44 is a spring biased valve 52 which opens and closes to substantially seal reagent supply canister 38 from the ambient environment when in a closed position, and allow transfer of the reagent from reagent supply canister 38 to reagent holding tank 36 when in an open position. In the embodiment shown, valve 52 is in the form of a valve disk which is biased to the closed position by a compression spring 54. Valve 52 is shown in the closed position in
To bias valve 52 to an open position shown in
Reagent holding tank 36 may also include an optional heater 58 therein for heating the reagent during cold weather. In the embodiment shown, heater 58 is in the form of a single resistance heater wire configured as a heater coil extending into a sump 60 in the bottom of reagent holding tank 36. A suction line 62 in communication with doser 34 has an inlet 64 for receiving reagent near the bottom of sump 60. Heater 58 receives electrical power at electrical leads 66 from an on-board power supply (such as one or more vehicle batteries) through controllable actuation using onboard controller 68.
To provide an operator with an indication of the level of reagent within reagent holding tank 36, one or more reagent level sensors 70 are positioned at respective heights within reagent holding tank 36. In the embodiment shown, a pair of reagent level sensors 70 are in communication with controller 68 via respective leads 72. Controller 68 receives a signal from one or more reagent level sensors 70 and provides an output signal to visual indicator 74 providing an operator with a real time indication of the reagent level within reagent holding tank 36 and/or the need to refill reagent holding tank 36.
SCR exhaust aftertreatment system 12 may also optionally include a reagent quality sensor 76 providing an output signal to controller 68 indicative of the quality of reagent within reagent holding tank 36. Additionally, an optional NOx sensor 78 (
Referring now to
Reagent refill and supply system 80 also includes an optional housing 96 in which reagent holding tank 82, reagent supply canister 84A and reserve reagent supply canister 84B are positioned. Of course, it is also possible to enclose reagent refill and supply system 40 shown in
During operation, when the level of the urea solution reaches the upper reagent level sensor 70, a light in the instrument panel indicates that at the next diesel fueling the urea solution needs to be replenish with one canister of urea. In the case that the driver, for some reason, fully refueled the diesel tank(s) just before the upper reagent level sensor 70 sent the signal, there is enough urea solution between the upper reagent level sensor 70 and the lower reagent level sensor 70 for an uninterrupted trip achievable with full tanks of the diesel fuel. In the case of 200 gallons of diesel fuel, that would be about 2.6 gallons of urea solution. If for some reason, the driver would again fail to refill the urea, then during the next trip when the level of the reagent reaches the lower reagent level sensor 70, a red light on the instrument panel indicates that the reagent must be refilled soon. The volume of the urea below the lower reagent level sensor 70 (approximately 0.4 gallons) is sufficient for approximately 240 miles of travel. At that time reagent holding tank 36 must be filled with 6 gallons of urea (two reagent supply canisters 38).
During a regular diesel refueling, the operator purchases one reagent supply canister 38 (or two if required). After an optional cap (not shown)is removed, reagent supply canister 38 is placed on refill head 42. O-ring seal 46 engages with nozzle 44, and after lowering of reagent supply canister 38, bayonet type latches 48 and 50 are latched together by turning reagent supply canister 38 through approximately ninety degrees. Valve opener pin 56 pushes valve disk 52 into an open position and reagent flows from reagent supply canister 38 into reagent holding tank 36. After several seconds, reagent supply canister 38 empties, is removed, and the cap is replaced. The empty reagent supply canister 38 is returned to the fueling station.
In the event of ambient air below approximately −11° C., heater 58 may be actuated to heat reagent within reagent holding tank 36. However, since reagent holding tank 36 is small it can also be attached to the heated cab sleeper and thus would not require electricity during the vehicle trip. However, if the vehicle is parked for an extended period in the sub −11° C. weather, the urea solution could freeze and therefore a freeze tolerant tank design and a heater is required. In situations where the solution freezes during vehicle inactivity, the heating system within reagent holding tank 36 is activated at the start of the truck engine. The heating system would be designed such that adequate urea solution for operation would melt by the time the exhaust components (mainly catalyst) would reach the operating temperature.
If a reagent quality sensor 76 is used (e.g., an aqueous urea quality sensor), the engine power can be reduced to a limp home mode if adequate urea solution is not available. This may be important since a lack of adequate urea solution would result in tail pipe NOx emissions exceeding the emissions standard. In addition, optional NOx sensor 78 can be used to reduce engine power if any of the emissions control devices fail, such as an insufficient supply of urea in reagent holding tank 36
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
