US20040118109A1 - Enhanced ammonia feed control for selective catalytic reduction - Google Patents
Enhanced ammonia feed control for selective catalytic reduction Download PDFInfo
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- US20040118109A1 US20040118109A1 US10/325,319 US32531902A US2004118109A1 US 20040118109 A1 US20040118109 A1 US 20040118109A1 US 32531902 A US32531902 A US 32531902A US 2004118109 A1 US2004118109 A1 US 2004118109A1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
- F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
- F01N13/0093—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are of the same type
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
- F01N13/0097—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are arranged in a single housing
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/008—Mounting or arrangement of exhaust sensors in or on exhaust apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
- F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
- F01N2560/021—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting ammonia NH3
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
- F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
- F01N2560/026—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting NOx
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
- F01N2570/14—Nitrogen oxides
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2610/00—Adding substances to exhaust gases
- F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2610/00—Adding substances to exhaust gases
- F01N2610/08—Adding substances to exhaust gases with prior mixing of the substances with a gas, e.g. air
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2610/00—Adding substances to exhaust gases
- F01N2610/14—Arrangements for the supply of substances, e.g. conduits
- F01N2610/1453—Sprayers or atomisers; Arrangement thereof in the exhaust apparatus
- F01N2610/146—Control thereof, e.g. control of injectors or injection valves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/08—Parameters used for exhaust control or diagnosing said parameters being related to the engine
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
Definitions
- the present invention relates generally to emissions control systems for reciprocating engines, and more particularly to an emissions control system for increasing selective catalytic reduction (SCR) efficiency through enhanced reactant feed control.
- SCR selective catalytic reduction
- Combustion engines including compression ignition and spark ignition reciprocating engines and gas turbines provide efficient power sources requiring low operating personnel requirements.
- Combustion engines produce and emit NO x (nitrogen oxides). Control methods to reduce the NO x often increase the fuel consumption of the engines and require large increase in the operating personnel required.
- Compression ignition engines such as diesel engines, provide advantages in fuel economy, but produce and emit both NO x and particulates during normal operation.
- primary measures actions that affect the combustion process itself, such as exhaust gas recirculation and engine timing adjustments
- combustion conditions selected to reduce pollution from particulates and obtain good fuel economy tend to increase the output of NO x .
- Current and proposed regulations and legislation present significant challenges to manufacturers to achieve good fuel economy while at the same time reducing the emission levels of particulates and NO x .
- SCR selective catalytic reduction
- the SCR method consists of injecting gaseous ammonia (NH 3 ), ammonia in aqueous solution or aqueous urea, or ammonia supplied from an ammonia generator using a solid source of ammonia such as ammonia carbamate or ammonia carbonate, into the exhaust gas system of the compression ignition engine as a reduction agent.
- gaseous ammonia NH 3
- ammonia supplied from an ammonia generator using a solid source of ammonia such as ammonia carbamate or ammonia carbonate
- the reduction agent undergoes a hydrolysis process and is decomposed into ammonia and CO 2 .
- the gaseous ammonia reacts with the NO x to reduce the NO x to molecular nitrogen. This reduces or limits the NO x emissions from the compression ignition engine.
- the amount of ammonia required at any given time varies as operating conditions of the engine change, and the exhaust gas content includes more or less NO x . It is important that a sufficient amount of ammonia be supplied to treat NO x present in the exhaust gas stream, so that NO x emission standards are achieved. On the other hand, it is wasteful and inefficient to supply ammonia in excess of the amount required to treat the NO x present in the exhaust gas stream.
- the present invention is directed to overcoming one or more of the problems as set forth above.
- an emissions control system for treating an exhaust gas stream with a reduction agent in an exhaust system of an engine is provided with a first sensor for determining at least one operating condition of the engine; and a control unit connected to the sensor for determining a calculated amount of the reduction agent needed to treat the exhaust gas stream.
- a reduction agent supply source has a first metering means for supplying a first dose of the reduction agent to the exhaust stream in an amount less than the calculated amount of the reduction agent.
- a reactor has an inlet receiving the exhaust gas stream with the first dose of reduction agent.
- a second metering means supplies a second dose of the reduction agent to the exhaust stream.
- an engine is provided with a combustion section including a plurality of combustion chambers; a combustion air system supplying combustion air to the combustion chambers, and an exhaust system receiving exhaust gases from the combustion chambers.
- the exhaust system includes an exhaust manifold and an exhaust conduit for conducting the exhaust gases in an exhaust gas stream from the engine.
- An emissions control system includes a reduction agent supply source and a reactor having first and second reacting beds in fluid flow communication with the exhaust conduit.
- a first sensor and a control unit connected to the first sensor determine a calculated amount of the reduction agent needed for treatment of the exhaust gas stream.
- a first metering means supplies to the exhaust stream a first dose of reduction agent less than the calculated amount of the reduction agent.
- a second metering means between the reacting beds supplies a second dose of the reduction agent to the exhaust stream.
- a second sensor determines a characteristic of the exhaust stream, and the control unit is connected to the second sensor for determining the amount of the second dose of reduction agent.
- a method for increasing the efficiency of an emissions control system for a compression ignition engine capable of producing an exhaust gas stream to be treated by a reduction agent which is mixed with the exhaust gas stream to convert the exhaust gas is provided with steps of: determining a needed amount of the reduction agent to treat the exhaust gas stream; supplying a first dose of the reduction agent to the exhaust gas stream; reacting the exhaust gas stream with the first dose of reduction agent; supplying a second dose of reduction agent to the exhaust gas stream after reacting the exhaust gas stream with the first dose of reduction agent; and reacting the exhaust gas stream with the second dose of reduction agent.
- FIG. 1 is a schematic illustration of an engine having enhanced ammonia feed control for selective catalytic reduction, in accordance with the present invention.
- FIG. 1 illustrates an emissions control system 10 constructed and operated according to the present invention.
- Emissions control system 10 is used to control the emissions from a compression ignition engine 12 , such as a diesel engine.
- Engine 12 includes an exhaust system 14 in which an exhaust gas stream, indicated by arrows 16 , is conducted.
- Exhaust system 14 includes one or more exhaust manifolds 18 and an exhaust conduit 20 .
- Emissions control system 10 is particularly advantageous in use for diesel engines, but can be used advantageously in all types of reciprocating engines including spark ignited engines, diesel engines, compression ignition and pilot ignition engines.
- engine 12 shown and described herein is a diesel engine, it should be understood that the term “engine” is intended to apply to all types of reciprocating engines, and not limited to diesel engines only.
- System 10 also can be adapted for use in gas turbines.
- Engine 12 further includes a main combustion section 30 which includes, among other elements, an engine block and a cylinder head forming a plurality of combustion chambers 32 therein.
- a fuel injector, cylinder liner, at least one intake port and corresponding intake valves, at least one exhaust port and corresponding exhaust valves and a reciprocating piston movable within each chamber 32 are provided or associated with each chamber 32 .
- a combustion air system 34 including a combustion air conduit 36 and an intake manifold 38 provide a combustion air stream, indicated by arrows 40 , to each combustion chamber 32 .
- While the present emissions control system 10 is shown and described for use on a heavy duty six cylinder in-line four stroke direct injection diesel engine, numerous other engine types may be used, including two stroke engines.
- the engine configurations may include in-line and/or v-type engines, as well as various modifications in the number of combustion chambers 32 .
- Emissions control system 10 includes a reduction agent supply source 50 , such as a source for ammonia, urea, or other acceptable reduction agent for processing exhaust gas stream 16 .
- Source 50 may include an ammonia generator system, storage tanks, pumps, valves, piping and controls, as those skilled in the art will understand readily.
- Supply pipes 52 and 54 from source 50 provide reduction agent to exhaust gas stream 16 in a first dose indicated by arrows 56 , and a second dose indicated by arrows 58 .
- First and second doses 56 and 58 are supplied to exhaust gas stream 16 in individually controllable amounts by a first metering means 60 and a second metering means 62 , respectively.
- First metering means 60 and second metering means 62 can be any suitable flow control device, for reliably controlling the rate at which reduction agent in the forms of first dose 56 and second dose 58 , respectively, are provided to exhaust gas stream 16 .
- suitable devices that can be used for first metering means 60 and second metering means 62 are a controllable valve or other orifice, a nozzle, a pump or the like.
- a reactor 70 is provided in flow communication with exhaust conduit 20 , and includes a first reacting bed 72 and a second reacting bed 74 .
- First dose 56 of reduction agent is provided to exhaust gas stream 16 in advance of first reacting bed 72
- second dose 58 is supplied to exhaust gas stream 16 between first and second reacting beds 72 and 74 .
- Reactor 70 includes an inlet 76 receiving exhaust gas stream 16 , together with first dose 56 , and an outlet 78 through which the reacted exhaust gas stream, indicated by arrows 80 , passes from reactor 70 .
- An intermediate zone 82 is provided in reactor 70 , between first reacting bed 72 and second reacting bed 74 .
- Emissions control system 10 further includes an electronic control unit 90 that is used to control and monitor various operations and functions of emissions control system 10 and engine 12 .
- Electronic control unit 90 is capable of monitoring various functions of engine 12 , by use of one or more sensors 92 that are associated with engine 12 .
- Sensors 92 are connected to electronic control unit 40 via a signal connection 94 , which may be an electrically conductive wire.
- Examples of sensors 92 that may be employed at various locations in engine 12 are an engine speed sensor, an intake manifold air temperature sensor, an intake manifold pressure sensor, various other load, boost and speed sensors, all of which are known to those skilled in the art.
- Sensor or sensors 92 monitor the operating status of engine 12 , providing data signals with regard thereto to control unit 90 .
- Several such sensors 92 can be used to concurrently monitor a number of operating conditions of engine 12 , and the various systems associated therewith.
- At least one sensor 96 connected to controller 90 by a signal connection 98 is used to determine a condition of exhaust gas stream 16 at some point after first reacting bed 72 .
- Sensor 96 can be one to sense NO x present in exhaust gas stream 16 , or sensor 96 can be one to determine the presence of ammonia in exhaust gas stream 16 .
- Sensor 96 can be positioned in outlet 78 of reactor 70 , to provide a signal indicative of the level of ammonia or NO x remaining in reacted exhaust gas stream 80 , after treatment in reactor 70 .
- Sensor 96 also can be positioned in reactor 70 , between first and second reacting beds 72 and 74 , to determine the presence of ammonia or NO x between reacting beds 72 and 74 .
- FIG. 1 illustrates two sensors 96 , one in each of the aforementioned positions; however, it is not necessary that one sensor 96 be used in each position.
- a single sensor 96 in either position shown, is adequate in many applications for emission control system 10 .
- different sensors 96 can be used in each position.
- an ammonia sensor 96 between first reacting bed 72 and second reacting bed 74 , can be sued to determine the amount of ammonia still available for reacting with exhaust gas stream 16 ; and an NO x sensor 96 can be used associated with outlet 78 , to determine the effectiveness of the overall treatment in reactor 70 .
- Electronic control unit 90 also is connected to first metering means 60 by a control signal connection 100 , and to second metering means 62 by a control signal connection 102 , to control the operations of first and second metering means 60 and 62 .
- Electronic control unit 90 further is connected to reduction agent supply source 50 by an electrical connection or connections 104 , to control the operation of the various valves, pumps and the like associated with reduction agent supply source 50 .
- Electronic control unit 90 also known as a control module or a controller, and may take many forms, including a computer based system, a microprocessor based system including a microprocessor, a micro-controller, or any other control type circuit or system.
- Electronic control unit 90 may include memory for storage of a control program for operating and controlling the emissions control system 10 of the present invention, and other memory for temporary storage of information.
- the operation of the emissions control system 10 is based on electronic control unit 90 monitoring the status of the engine 12 and the effectiveness of the performance of emissions control system 10 , and controlling the supply of reduction agent to exhaust gas stream 16 based thereon.
- Combustion air stream 40 in combustion air system 34 is provided to intake manifold 38 from combustion air conduit 36 .
- Fuel and combustion air from intake manifold 38 are provided to each combustion chamber 32 of engine 12 , and are combusted therein in known manner.
- the combustion gases remaining after the combustion stroke in chambers 32 are expelled from chambers 32 to exhaust system 14 , first entering exhaust manifold 18 .
- Exhaust gas stream 16 is formed as the combustion gases flow from exhaust manifold 18 to and through exhaust conduit 20 .
- Exhaust gas stream 16 will contain differing amounts of NO x , depending on the operating conditions of engine 12 , therefore requiring different amounts of reduction agent for the proper treatment of NO x contained in exhaust gas stream 16 .
- control unit 90 uses data from one or more of engine operating condition sensors 92 to determine a calculated amount of the reduction agent, such as ammonia or urea, that will be need to treat exhaust gas stream 16 .
- Control unit 90 sends a signal to first metering means 60 and to reduction agent supply source 50 , whereby first dose 56 of reduction agent is transported from reduction agent supply source 50 to exhaust gas stream 16 , via supply pipe 52 and first metering means 60 .
- First dose 56 includes an amount of the reduction agent which is less than the calculated amount needed to treat exhaust gas stream 16 .
- a statistical approach can be used for calculating first dose 56 .
- One such approach includes determining the accuracy of the NO x emissions calculation from the parameters monitored, and determining the accuracy of the dosing metering equipment.
- first dose 56 may be an amount of approximately ninety percent (90%) of the calculated amount.
- Other statistical approaches to calculating first dose 56 also can be used.
- First dose 56 is supplied to exhaust gas stream 16 , and travels therewith to first reacting bed 72 in reactor 70 .
- the reduction agent of first dose 56 and first reacting bed 72 cause chemical reactions to occur, decreasing the amount of NO x present in exhaust gas stream 16 .
- first dose 56 includes an amount less than the calculated amount of reduction agent required to treat the NO x present in exhaust gas stream 16 , it is necessary to supply additional reduction agent to complete the treatment of exhaust gas stream 16 .
- Control unit 90 sends a signal to second metering means 62 and to reduction agent supply source 50 , whereby second dose 58 of reduction agent is transported from reduction agent supply source 50 to exhaust gas stream 16 , via supply pipe 54 and second metering means 62 .
- Second dose 58 includes a remaining amount of the reduction agent necessary to complete the treatment of exhaust gas stream 16 .
- Second dose 58 can be the balance of the calculated amount needed to treat exhaust gas stream 16 , not supplied in first dose 56 .
- first dose 56 included an amount of approximately ninety percent (90%) of the calculated amount
- second dose 58 can include an amount of approximately ten percent (10%) of the calculated amount.
- first and second doses 56 and 58 make up one hundred percent (100%) of the calculated amount.
- the amount of reduction agent supplied in second dose 58 can be separately determined and varied, to thereby supply an adequate amount of reduction agent, but not an excessive amount of reduction agent for treating exhaust gas stream 16 .
- control unit 90 determines an amount of reduction agent to be supplied in second dose 58 to complete the treatment of exhaust gas stream 16 .
- the effectiveness of the treatment with first dose 56 in first reacting bed 72 is considered, and if sensor 96 is provided downstream of second reacting bed 74 , feedback on the overall effectiveness of the treatment in both reacting beds 72 and 74 is provided.
- control unit 90 may determine an amount for second dose 58 such that the combined amount of first dose 56 and second dose 58 is more, or less, than the original calculated amount.
- Second dose 58 is supplied to exhaust gas stream 16 between first reacting bed 72 and second reacting bed 74 , as exhaust gas stream 16 flows through intermediate zone 82 . Exhaust gas stream 16 then flows to second reacting bed 74 , together with second dose 58 and any residual amounts of first dose 56 . The treatment of NO x in exhaust gas stream 16 is continued in second reacting bed 74 , so that the NO x levels of reacted exhaust gas stream 80 leaving reactor 70 are at acceptable limits.
- a single reactor 70 with split reacting beds 72 and 74 is believed to be advantageous in its simplicity and reduced space requirements compared to using separate reactors.
- the present invention provides a selective catalytic reduction emissions control system for treating an exhaust gas stream from an engine, which has closed feedback control, so that an adequate amount, but not an excessive amount of the reduction agent is provided. Reduction agent is not wasted, and the exhaust gas stream is treated adequately. The efficiency of the process is thereby improved.
Abstract
A selective catalytic reduction emissions control system of a compression ignition engine is provided with enhanced ammonia feed control for improved emissions control performance. The reduction agent is provided in two doses, and the reactor is provided with two reacting beds. The second dose of reactant is provided between the first and second reacting beds.
Description
- The present invention relates generally to emissions control systems for reciprocating engines, and more particularly to an emissions control system for increasing selective catalytic reduction (SCR) efficiency through enhanced reactant feed control.
- Combustion engines including compression ignition and spark ignition reciprocating engines and gas turbines provide efficient power sources requiring low operating personnel requirements. Combustion engines produce and emit NOx (nitrogen oxides). Control methods to reduce the NOx often increase the fuel consumption of the engines and require large increase in the operating personnel required.
- Compression ignition engines, such as diesel engines, provide advantages in fuel economy, but produce and emit both NOx and particulates during normal operation. When primary measures (actions that affect the combustion process itself, such as exhaust gas recirculation and engine timing adjustments) are taken to reduce one, often the other is increased. Thus, combustion conditions selected to reduce pollution from particulates and obtain good fuel economy tend to increase the output of NOx. Current and proposed regulations and legislation present significant challenges to manufacturers to achieve good fuel economy while at the same time reducing the emission levels of particulates and NOx.
- In order to meet such requirements or restrictions, a method known as SCR (selective catalytic reduction) has been used for reducing the emission of NOx. The SCR method consists of injecting gaseous ammonia (NH3), ammonia in aqueous solution or aqueous urea, or ammonia supplied from an ammonia generator using a solid source of ammonia such as ammonia carbamate or ammonia carbonate, into the exhaust gas system of the compression ignition engine as a reduction agent. When the temperature of the exhaust gas stream is above a reaction temperature, for example a temperature above 160° C. for aqueous urea, the reduction agent undergoes a hydrolysis process and is decomposed into ammonia and CO2. As the exhaust gas stream is passed through the SCR catalyst, the gaseous ammonia reacts with the NOx to reduce the NOx to molecular nitrogen. This reduces or limits the NOx emissions from the compression ignition engine.
- The amount of ammonia required at any given time varies as operating conditions of the engine change, and the exhaust gas content includes more or less NOx. It is important that a sufficient amount of ammonia be supplied to treat NOx present in the exhaust gas stream, so that NOx emission standards are achieved. On the other hand, it is wasteful and inefficient to supply ammonia in excess of the amount required to treat the NOx present in the exhaust gas stream.
- U.S. Pat. No. 4,403,473 entitled “Ammonia/Fuel Ratio Control System For Reducing Nitrogen Oxide Emissions”, issued Sep. 13, 1983, teaches a method and apparatus for efficiently reducing NOx emissions from an engine. Ammonia is metered to the exhaust gas conduit in a pre-selected proportion to the fuel mass flow rate, but only in response to the temperature of the exhaust gas stream in the reactor being within a pre-selected temperature range.
- While the aforementioned U.S. Pat. No. 4,403,473 provides a reasonably reliable method and apparatus for reducing NOx emissions, the method and apparatus do not provide feedback control based on the actual effectiveness of the process. It would be advantageous to control ammonia addition to the exhaust gas stream based on the actual effectiveness of the treatment process.
- The present invention is directed to overcoming one or more of the problems as set forth above.
- In one aspect of the present invention, an emissions control system for treating an exhaust gas stream with a reduction agent in an exhaust system of an engine is provided with a first sensor for determining at least one operating condition of the engine; and a control unit connected to the sensor for determining a calculated amount of the reduction agent needed to treat the exhaust gas stream. A reduction agent supply source has a first metering means for supplying a first dose of the reduction agent to the exhaust stream in an amount less than the calculated amount of the reduction agent. A reactor has an inlet receiving the exhaust gas stream with the first dose of reduction agent. A second metering means supplies a second dose of the reduction agent to the exhaust stream.
- In another aspect of the invention, an engine is provided with a combustion section including a plurality of combustion chambers; a combustion air system supplying combustion air to the combustion chambers, and an exhaust system receiving exhaust gases from the combustion chambers. The exhaust system includes an exhaust manifold and an exhaust conduit for conducting the exhaust gases in an exhaust gas stream from the engine. An emissions control system includes a reduction agent supply source and a reactor having first and second reacting beds in fluid flow communication with the exhaust conduit. A first sensor and a control unit connected to the first sensor determine a calculated amount of the reduction agent needed for treatment of the exhaust gas stream. A first metering means supplies to the exhaust stream a first dose of reduction agent less than the calculated amount of the reduction agent. A second metering means between the reacting beds supplies a second dose of the reduction agent to the exhaust stream. A second sensor determines a characteristic of the exhaust stream, and the control unit is connected to the second sensor for determining the amount of the second dose of reduction agent.
- In still another aspect of the invention, a method for increasing the efficiency of an emissions control system for a compression ignition engine capable of producing an exhaust gas stream to be treated by a reduction agent which is mixed with the exhaust gas stream to convert the exhaust gas, is provided with steps of: determining a needed amount of the reduction agent to treat the exhaust gas stream; supplying a first dose of the reduction agent to the exhaust gas stream; reacting the exhaust gas stream with the first dose of reduction agent; supplying a second dose of reduction agent to the exhaust gas stream after reacting the exhaust gas stream with the first dose of reduction agent; and reacting the exhaust gas stream with the second dose of reduction agent.
- Other aspects and advantages of the present invention will be apparent to those skilled in the art upon reading the following detailed description in connection with the drawing and appended claims.
- The invention will be better understood and its advantages more apparent from the following detailed description, especially when read in light of the accompanying drawing, wherein:
- FIG. 1 is a schematic illustration of an engine having enhanced ammonia feed control for selective catalytic reduction, in accordance with the present invention.
- Referring now to the drawing, FIG. 1 illustrates an
emissions control system 10 constructed and operated according to the present invention.Emissions control system 10 is used to control the emissions from acompression ignition engine 12, such as a diesel engine.Engine 12 includes anexhaust system 14 in which an exhaust gas stream, indicated byarrows 16, is conducted.Exhaust system 14 includes one ormore exhaust manifolds 18 and anexhaust conduit 20. -
Emissions control system 10 is particularly advantageous in use for diesel engines, but can be used advantageously in all types of reciprocating engines including spark ignited engines, diesel engines, compression ignition and pilot ignition engines. Althoughengine 12 shown and described herein is a diesel engine, it should be understood that the term “engine” is intended to apply to all types of reciprocating engines, and not limited to diesel engines only.System 10 also can be adapted for use in gas turbines. -
Engine 12 further includes amain combustion section 30 which includes, among other elements, an engine block and a cylinder head forming a plurality ofcombustion chambers 32 therein. A fuel injector, cylinder liner, at least one intake port and corresponding intake valves, at least one exhaust port and corresponding exhaust valves and a reciprocating piston movable within eachchamber 32 are provided or associated with eachchamber 32. Acombustion air system 34, including acombustion air conduit 36 and anintake manifold 38 provide a combustion air stream, indicated byarrows 40, to eachcombustion chamber 32. - While the present
emissions control system 10 is shown and described for use on a heavy duty six cylinder in-line four stroke direct injection diesel engine, numerous other engine types may be used, including two stroke engines. The engine configurations may include in-line and/or v-type engines, as well as various modifications in the number ofcombustion chambers 32. -
Emissions control system 10 includes a reductionagent supply source 50, such as a source for ammonia, urea, or other acceptable reduction agent for processingexhaust gas stream 16.Source 50 may include an ammonia generator system, storage tanks, pumps, valves, piping and controls, as those skilled in the art will understand readily.Supply pipes source 50 provide reduction agent toexhaust gas stream 16 in a first dose indicated byarrows 56, and a second dose indicated byarrows 58. First andsecond doses exhaust gas stream 16 in individually controllable amounts by a first metering means 60 and a second metering means 62, respectively. First metering means 60 and second metering means 62 can be any suitable flow control device, for reliably controlling the rate at which reduction agent in the forms offirst dose 56 andsecond dose 58, respectively, are provided toexhaust gas stream 16. Some examples of suitable devices that can be used for first metering means 60 and second metering means 62 are a controllable valve or other orifice, a nozzle, a pump or the like. - A
reactor 70 is provided in flow communication withexhaust conduit 20, and includes a first reactingbed 72 and a second reactingbed 74.First dose 56 of reduction agent is provided toexhaust gas stream 16 in advance of first reactingbed 72, andsecond dose 58 is supplied toexhaust gas stream 16 between first andsecond reacting beds Reactor 70 includes aninlet 76 receivingexhaust gas stream 16, together withfirst dose 56, and anoutlet 78 through which the reacted exhaust gas stream, indicated byarrows 80, passes fromreactor 70. Anintermediate zone 82 is provided inreactor 70, between first reactingbed 72 and second reactingbed 74. -
Emissions control system 10 further includes anelectronic control unit 90 that is used to control and monitor various operations and functions of emissions controlsystem 10 andengine 12.Electronic control unit 90 is capable of monitoring various functions ofengine 12, by use of one ormore sensors 92 that are associated withengine 12.Sensors 92 are connected toelectronic control unit 40 via asignal connection 94, which may be an electrically conductive wire. Examples ofsensors 92 that may be employed at various locations inengine 12 are an engine speed sensor, an intake manifold air temperature sensor, an intake manifold pressure sensor, various other load, boost and speed sensors, all of which are known to those skilled in the art. Sensor orsensors 92 monitor the operating status ofengine 12, providing data signals with regard thereto to controlunit 90. Severalsuch sensors 92 can be used to concurrently monitor a number of operating conditions ofengine 12, and the various systems associated therewith. - At least one
sensor 96 connected tocontroller 90 by asignal connection 98 is used to determine a condition ofexhaust gas stream 16 at some point after first reactingbed 72.Sensor 96 can be one to sense NOx present inexhaust gas stream 16, orsensor 96 can be one to determine the presence of ammonia inexhaust gas stream 16.Sensor 96 can be positioned inoutlet 78 ofreactor 70, to provide a signal indicative of the level of ammonia or NOx remaining in reactedexhaust gas stream 80, after treatment inreactor 70.Sensor 96 also can be positioned inreactor 70, between first and second reactingbeds beds sensors 96, one in each of the aforementioned positions; however, it is not necessary that onesensor 96 be used in each position. Asingle sensor 96, in either position shown, is adequate in many applications foremission control system 10. Alternatively,different sensors 96 can be used in each position. For example, anammonia sensor 96, between first reactingbed 72 and second reactingbed 74, can be sued to determine the amount of ammonia still available for reacting withexhaust gas stream 16; and an NOx sensor 96 can be used associated withoutlet 78, to determine the effectiveness of the overall treatment inreactor 70. -
Electronic control unit 90 also is connected to first metering means 60 by acontrol signal connection 100, and to second metering means 62 by acontrol signal connection 102, to control the operations of first and second metering means 60 and 62.Electronic control unit 90 further is connected to reductionagent supply source 50 by an electrical connection orconnections 104, to control the operation of the various valves, pumps and the like associated with reductionagent supply source 50. -
Electronic control unit 90, also known as a control module or a controller, and may take many forms, including a computer based system, a microprocessor based system including a microprocessor, a micro-controller, or any other control type circuit or system.Electronic control unit 90 may include memory for storage of a control program for operating and controlling theemissions control system 10 of the present invention, and other memory for temporary storage of information. - The operation of the
emissions control system 10 is based onelectronic control unit 90 monitoring the status of theengine 12 and the effectiveness of the performance of emissions controlsystem 10, and controlling the supply of reduction agent to exhaustgas stream 16 based thereon. -
Combustion air stream 40 incombustion air system 34 is provided tointake manifold 38 fromcombustion air conduit 36. Fuel and combustion air fromintake manifold 38 are provided to eachcombustion chamber 32 ofengine 12, and are combusted therein in known manner. The combustion gases remaining after the combustion stroke inchambers 32 are expelled fromchambers 32 toexhaust system 14, first enteringexhaust manifold 18.Exhaust gas stream 16 is formed as the combustion gases flow fromexhaust manifold 18 to and throughexhaust conduit 20.Exhaust gas stream 16 will contain differing amounts of NOx, depending on the operating conditions ofengine 12, therefore requiring different amounts of reduction agent for the proper treatment of NOx contained inexhaust gas stream 16. - Using data from one or more of engine
operating condition sensors 92,electronic control unit 90 determines a calculated amount of the reduction agent, such as ammonia or urea, that will be need to treatexhaust gas stream 16.Control unit 90 sends a signal to first metering means 60 and to reductionagent supply source 50, wherebyfirst dose 56 of reduction agent is transported from reductionagent supply source 50 to exhaustgas stream 16, viasupply pipe 52 and first metering means 60.First dose 56 includes an amount of the reduction agent which is less than the calculated amount needed to treatexhaust gas stream 16. A statistical approach can be used for calculatingfirst dose 56. One such approach includes determining the accuracy of the NOx emissions calculation from the parameters monitored, and determining the accuracy of the dosing metering equipment. For example, if the NOx emission calculation is accurate within seven percent (7%) and the dosage metering equipment has a three percent (3%) accuracy,first dose 56 may be an amount of approximately ninety percent (90%) of the calculated amount. Other statistical approaches to calculatingfirst dose 56 also can be used. -
First dose 56 is supplied to exhaustgas stream 16, and travels therewith to first reactingbed 72 inreactor 70. In known manner, the reduction agent offirst dose 56 and first reactingbed 72 cause chemical reactions to occur, decreasing the amount of NOx present inexhaust gas stream 16. - Since
first dose 56 includes an amount less than the calculated amount of reduction agent required to treat the NOx present inexhaust gas stream 16, it is necessary to supply additional reduction agent to complete the treatment ofexhaust gas stream 16.Control unit 90 sends a signal to second metering means 62 and to reductionagent supply source 50, wherebysecond dose 58 of reduction agent is transported from reductionagent supply source 50 to exhaustgas stream 16, viasupply pipe 54 and second metering means 62.Second dose 58 includes a remaining amount of the reduction agent necessary to complete the treatment ofexhaust gas stream 16.Second dose 58 can be the balance of the calculated amount needed to treatexhaust gas stream 16, not supplied infirst dose 56. For example, iffirst dose 56 included an amount of approximately ninety percent (90%) of the calculated amount,second dose 58 can include an amount of approximately ten percent (10%) of the calculated amount. Thus, together first andsecond doses - Advantageously, in emissions control
system 10 of the present invention, the amount of reduction agent supplied insecond dose 58 can be separately determined and varied, to thereby supply an adequate amount of reduction agent, but not an excessive amount of reduction agent for treatingexhaust gas stream 16. Processing a signal or signals from one ormore sensors 96,control unit 90 determines an amount of reduction agent to be supplied insecond dose 58 to complete the treatment ofexhaust gas stream 16. By so calculating the amount ofsecond dose 58, the effectiveness of the treatment withfirst dose 56 in first reactingbed 72 is considered, and ifsensor 96 is provided downstream of second reactingbed 74, feedback on the overall effectiveness of the treatment in both reactingbeds sensors 96,control unit 90 may determine an amount forsecond dose 58 such that the combined amount offirst dose 56 andsecond dose 58 is more, or less, than the original calculated amount. -
Second dose 58 is supplied to exhaustgas stream 16 between first reactingbed 72 and second reactingbed 74, asexhaust gas stream 16 flows throughintermediate zone 82.Exhaust gas stream 16 then flows to second reactingbed 74, together withsecond dose 58 and any residual amounts offirst dose 56. The treatment of NOx inexhaust gas stream 16 is continued in second reactingbed 74, so that the NOx levels of reactedexhaust gas stream 80 leavingreactor 70 are at acceptable limits. - Rather than having a
single reactor 70 with first reactingbed 72 and second reactingbed 74 therein, two separate reactors, each having a single reacting bed, also could be used. Asingle reactor 70 withsplit reacting beds - The present invention provides a selective catalytic reduction emissions control system for treating an exhaust gas stream from an engine, which has closed feedback control, so that an adequate amount, but not an excessive amount of the reduction agent is provided. Reduction agent is not wasted, and the exhaust gas stream is treated adequately. The efficiency of the process is thereby improved.
- Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.
Claims (20)
1. An emissions control system for treating an exhaust gas stream with a reduction agent in an exhaust system of an engine, the emissions control system comprising:
a first sensor for determining at least one operating condition of the engine;
a control unit connected to the sensor for determining a calculated amount of the reduction agent needed to treat the exhaust gas stream;
a reduction agent supply source;
a first metering means for supplying a first dose of the reduction agent to the exhaust stream, said first dose of reduction agent being less than the calculated amount of the reduction agent needed to treat the exhaust gas stream;
a reactor having an inlet receiving the exhaust gas stream with the first dose of reduction agent; and
a second metering means for supplying a second dose of the reduction agent to the exhaust stream downstream from the reactor inlet.
2. The emissions control system of claim 1 , including a second sensor for determining a characteristic of the exhaust gas stream, and said control unit connected to said second sensor for determining the amount of said second dose of reduction agent.
3. The emissions control system of claim 2 , said reactor including a first reacting bed and a second reacting bed, and said second sensor and said second metering means disposed between said first and second reacting beds.
4. The emissions control system of claim 3 , said first metering means being a flow control device to dispense said first dose in an amount of approximately ninety percent (90%) of said calculated amount of said reduction agent.
5. The emissions control system of claim 1 , said reactor having an outlet, and a second sensor associated with said outlet for sensing the level of NOx emissions emitted by the reactor, said sensor being connected to said control unit for determining the amount of reduction agent in said second dose.
6. The emissions control system of claim 1 , said first sensor being adapted for sensing one of engine speed, fuel consumption rate, boost and load.
7. The emissions control system of claim 1 , said reactor including a first reacting bed and a second reacting bed, and said second metering means disposed between said first reacting bed and said second reacting bed.
8. The emissions control system of claim 1 , said first dose being approximately ninety percent (90%) of said calculated needed amount of said reduction agent.
9. An engine producing an exhaust gas stream to be treated by a reduction agent which is mixed with the exhaust gas stream to convert the exhaust gas stream, the engine comprising:
a combustion section including a plurality of combustion chambers;
a combustion air system supplying combustion air to said combustion chambers, said combustion air system including an intake air manifold and a combustion air conduit for supplying combustion air to said intake manifold,
an exhaust system receiving exhaust gases from said combustion chambers, said exhaust system including an exhaust manifold and an exhaust conduit for conducting the exhaust gases in an exhaust gas stream from the engine; and
an emissions control system, including:
a reduction agent supply source;
a reactor having first and second reacting beds in fluid flow communication with said exhaust conduit;
a first sensor and a control unit connected to said first sensor for determining a calculated amount of the reduction agent needed for treatment of the exhaust gas stream;
a first metering means for supplying to the exhaust stream a first dose of reduction agent less than the calculated amount of the reduction agent;
a second metering means between said reacting beds for supplying a second dose of the reduction agent to the exhaust stream; and
a second sensor for determining a characteristic of the exhaust stream, and said control unit connected to said second sensor for determining the amount of said second dose of reduction agent.
10. The engine of claim 9 , said first metering means being a flow control device controlled for supplying said first dose in an amount of approximately ninety percent (90%) of said calculated amount.
11. The engine of claim 9 , said second sensor disposed between said first and second reacting beds.
12. The engine of claim 9 , said second sensor disposed downstream from said second reacting bed.
13. The engine of claim 9 , said second sensor being an NOx sensor.
14. A method for increasing the efficiency of an emissions control system for a compression ignition engine capable of producing an exhaust gas stream to be treated by a reduction agent which is mixed with the exhaust gas stream to convert the exhaust gas, the method comprising steps of:
determining a needed amount of the reduction agent to treat the exhaust gas stream;
supplying a first dose of the reduction agent to the exhaust gas stream, said first dose being less than the needed amount;
reacting the exhaust gas stream with the first dose of reduction agent;
supplying a second dose of reduction agent to the exhaust gas stream after reacting the exhaust gas stream with the first dose of reduction agent; and
reacting the exhaust gas stream with the second dose of reduction agent.
15. The method of claim 14 , including a step of determining an amount of the second dose based on effectiveness of said step of reacting the exhaust gas stream with the first dose.
16. The method of claim 14 , including supplying said first dose of the reduction agent in an amount of approximately ninety percent (90%) of the needed amount from said step of determining the needed amount.
17. The method of claim 16 , including a step of determining an amount of the second dose based on effectiveness of said step of reacting the exhaust gas stream with the first dose.
18. The method of claim 17 , including determining the NOx content of the exhaust gas stream after said step of reacting the exhaust gas stream with the second dose of reduction agent, and determining the amount of the second dose in response to said determining the NOx content.
19. The method of claim 17 , including determining the NOx content of the exhaust gas stream between said step of reacting the exhaust gas stream with the first dose of reduction agent and said step of reacting the exhaust gas stream with the second dose of reduction agent, and determining the amount of the second dose in response to said determining the NOx content.
20. The method of claim 14 , said step of determining the needed amount including sensing at least one engine operating condition from the group of engine operating conditions including boost pressure, fuel consumption rate, engine speed and engine load.
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JP2003420109A JP4471643B2 (en) | 2002-12-19 | 2003-12-17 | Advanced ammonia supply control for selective catalyst reduction |
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Also Published As
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JP2004197746A (en) | 2004-07-15 |
US6761025B1 (en) | 2004-07-13 |
DE10354843A1 (en) | 2004-07-01 |
JP4471643B2 (en) | 2010-06-02 |
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