Patent Application
20100050616
This disclosure is related to exhaust aftertreatment systems for internal combustion engines operating lean of stoichiometry.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An internal combustion engine operating lean of stoichiometry can generate an exhaust gas feedstream including NOx emissions and particulate matter. There is a need for an exhaust aftertreatment system to manage the exhaust gas feedstream.
An apparatus for treating an exhaust gas feedstream from an internal combustion engine operating lean of stoichiometry comprises a particulate filter device comprising a porous substrate element having a hydrocarbon-selective catalytically reactive washcoat. The hydrocarbon-selective catalytically reactive washcoat comprises a silver-oxide catalytic material on an alumina-based washcoat. An injection device is operative to inject a hydrocarbon reductant upstream of the particulate filter device.
One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,
The exemplary engine 10 comprises a multi-cylinder internal combustion engine operative in a repetitive combustion cycle which can comprise intake, compression, power, and exhaust strokes. The engine 10 is selectively operative at an air/fuel ratio that is lean of stoichiometry. The engine 10 can be one of a compression-ignition engine and a spark-ignition engine that is operative lean of stoichiometry. The engine 10 can operate in one or more combustion modes including compression-ignition, spark-ignition, and controlled auto-ignition combustion modes. The engine 10 includes a plurality of reciprocating pistons attached to a crankshaft, which is operably attached to a transmission and a vehicle driveline to deliver tractive torque thereto, none of which are shown. The engine 10 generates an exhaust gas feedstream containing constituents that can be transformed by the aftertreatment system, including, e.g., hydrocarbons (hereafter ‘HC’), carbon monoxide (hereafter ‘CO’), nitrides of oxygen (hereafter ‘NOx’), and particulate matter (hereafter ‘PM’).
The exhaust aftertreatment system comprises an integrated system for converting the constituents of the exhaust gas feedstream to other forms in the presence of catalytically reactive materials through oxidation and reduction processes. An exhaust manifold (not separately labeled) entrains and directs exhaust gas flow to the exhaust aftertreatment system. The exhaust aftertreatment system of
One or more sensing devices can be adapted to monitor the exhaust gas feedstream. The exhaust gas feedstream can be monitored at various locations in the exhaust aftertreatment system, with the locations shown being monitored by various ones of sensors 12, 18, 22, 26 and 28. An application of the exhaust aftertreatment system can include one or more of the sensors 12, 18, 22, 26 and 28. The sensors 12, 18, 22, 26 and 28 monitor parameters of the exhaust gas feedstream that can be correlated to constituents and/or temperature of the exhaust gas feedstream, and generate signals that are transmitted to the control module 5. This may include sensor 12 which monitors the exhaust gas feedstream output from the engine 10, preferably including one of NOx concentration and air/fuel ratio. Sensor 26 may monitor the exhaust gas feedstream downstream from the catalytic device 14, preferably including a parameter corresponding to one of NOx concentration, air/fuel ratio, and temperature. A specific embodiment of the system that includes sensor 12 may not include sensor 26. Sensor 18 may monitor the exhaust gas feedstream output from the catalytic device 14 and downstream of the injection device 16, preferably including a parameter corresponding to one of NOx concentration and temperature. Sensor 22 may monitor the exhaust gas feedstream downstream from the particulate filter device 20, preferably including a parameter corresponding to one of NOx concentration, temperature, and ammonia (NH3). As shown in
The catalytic device 14 depicted in the embodiments shown in
The injection device 16 depicted in the embodiments shown in
The particulate filter device 20 comprises a filtering device that is coated with a hydrocarbon-selective catalytically reactive washcoat for NOx emission reduction. The filtering device traps particulate matter contained in the exhaust gas feedstream. There is a filter inlet 19 and a filter outlet 21. The particulate filter device 20 is constructed in a manner which causes the exhaust gas entering the filter inlet 19 to pass through a portion of the particulate filter device 20 to reach the filter outlet 21. By way of example, the particulate filter device 20 can include a multi-channel monolithic substrate element (not shown) constructed of a porous material. Each of the channels is either capped on an end proximal to the filter inlet 19 or capped on an end proximal to the filter outlet 21, with adjacent channels capped on alternate ends. By way of example, the porosity of the substrate element is about 40% to 55%, indicating that 40% to 55% of the volume of the substrate element comprises pores and not substrate material. The pores can have diameters that are less than about 3 microns on average. The porous material of the substrate element can be formed from ceramic material, e.g., cordierite that is extruded and sintered.
The porous material of the multi-channel substrate is coated with the hydrocarbon-selective catalytically reactive washcoat. The hydrocarbon-selective catalytically reactive washcoat, also referred to as an HC-SCR washcoat, includes a chemically reactive material that reacts with the injected hydrocarbon reductant to reduce NOx gases to N20. The hydrocarbon-selective catalytically reactive washcoat can comprise an alumina-based washcoat material with the chemically reactive material comprising a selective catalyst reduction catalyst. The selective catalyst reduction catalyst can comprise a silver alumina (hereafter “AgAl”) catalytic material, of a pre-selected weight percent of Ag2O supported on an alumina washcoat. One range for the selective catalyst reduction catalyst can be applied at a 1 to 4 wt. % Ag in AgAl, with a washcoat loading in a range 0.5 to 4 g/in3 supported on the multi-channel substrate. Alternatively, the selective catalyst reduction catalyst can comprise copper on a washcoat at a copper mass loading and applied onto a substrate device. The coated substrate of the particulate filter device 20 is assembled into a metallic structure that is a part of the exhaust aftertreatment system.
The second catalytic device 24 depicted in the embodiments shown in
The control module 5 is preferably an element of a distributed architecture comprising a plurality of control modules adapted to provide coordinated control of the engine 10 and other systems when the engine 10 and exhaust aftertreatment system are applied onto a vehicle (not shown). A user interface (‘UI’) 13 signally connects to a plurality of devices through which a vehicle operator controls and directs operation of the vehicle, including the engine 10. Exemplary devices through which the vehicle operator provides input to the user interface 13 include an accelerator pedal, a brake pedal, transmission gear selector, and vehicle speed cruise control, none of which are separately illustrated. The control module 5 preferably communicates with the user interface 13 via a local area network bus 6. The local area network bus 6 allows for structured communication of control parameters and commands between the various processors, control modules, and devices. The specific communication protocol utilized is application-specific.
The control module 5 comprises a general-purpose digital computer including a microprocessor or central processing unit, storage mediums comprising non-volatile memory including read only memory and electrically programmable read only memory, random access memory, a high speed clock, analog to digital and digital to analog circuitry, input/output circuitry, and devices and appropriate signal conditioning and buffer circuitry. The control module 5 has a set of control algorithms, comprising resident program instructions and calibrations stored in the non-volatile memory and executed to provide the respective functions for controlling the engine 10. The algorithms are preferably executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms are executed by the central processing unit and are operable to monitor inputs from the aforementioned sensing devices and execute control and diagnostic routines to control operation of actuators, using preset calibrations. Loop cycles are preferably executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.
During operation of the engine 10, the control module 5 monitors inputs from sensing devices, synthesizes information, and executes algorithms to control actuators to achieve control targets, including fuel economy, emissions, performance, driveability, and protection of hardware. The engine 10 is preferably operated lean of stoichiometry, generating a lean exhaust gas feedstream that passes through the exhaust aftertreatment system.
The control module 5 monitors engine speed and load and air/fuel ratio to determine a mass flow concentration of NOx emissions, and controls the injection device 16 to control timing and mass or quantity of the hydrocarbon reductant injected into the exhaust gas feedstream based upon the mass flow concentration of NOx emissions. The quantity of the injected hydrocarbon reductant is controlled to react with the NOx emissions and reduce to nitrogen in the presence of the selective catalyst reduction catalyst.
The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
