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Title: Combustion driven ammonia generation strategies for passive ammonia SCR system

Abstract

A method for controlling ammonia generation in an exhaust gas feedstream output from an internal combustion engine equipped with an exhaust aftertreatment system including a first aftertreatment device includes executing an ammonia generation cycle to generate ammonia on the first aftertreatment device. A desired air-fuel ratio output from the engine and entering the exhaust aftertreatment system conducive for generating ammonia on the first aftertreatment device is determined. Operation of a selected combination of a plurality of cylinders of the engine is selectively altered to achieve the desired air-fuel ratio entering the exhaust aftertreatment system.

Inventors:
; ; ;
Publication Date:
Research Org.:
GM GLOBAL TECHNOLOGY OPERATIONS LLC, Detroit, MI (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1334661
Patent Number(s):
9,512,793
Application Number:
13/652,549
Assignee:
GM GLOBAL TECHNOLOGY OPERATIONS LLC (Detroit, MI) DOEEE
DOE Contract Number:
EE0003379
Resource Type:
Patent
Resource Relation:
Patent File Date: 2012 Oct 16
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 54 ENVIRONMENTAL SCIENCES

Citation Formats

Toner, Joel G., Narayanaswamy, Kushal, Szekely, Jr., Gerald A., and Najt, Paul M. Combustion driven ammonia generation strategies for passive ammonia SCR system. United States: N. p., 2016. Web.
Toner, Joel G., Narayanaswamy, Kushal, Szekely, Jr., Gerald A., & Najt, Paul M. Combustion driven ammonia generation strategies for passive ammonia SCR system. United States.
Toner, Joel G., Narayanaswamy, Kushal, Szekely, Jr., Gerald A., and Najt, Paul M. 2016. "Combustion driven ammonia generation strategies for passive ammonia SCR system". United States. doi:. https://www.osti.gov/servlets/purl/1334661.
@article{osti_1334661,
title = {Combustion driven ammonia generation strategies for passive ammonia SCR system},
author = {Toner, Joel G. and Narayanaswamy, Kushal and Szekely, Jr., Gerald A. and Najt, Paul M.},
abstractNote = {A method for controlling ammonia generation in an exhaust gas feedstream output from an internal combustion engine equipped with an exhaust aftertreatment system including a first aftertreatment device includes executing an ammonia generation cycle to generate ammonia on the first aftertreatment device. A desired air-fuel ratio output from the engine and entering the exhaust aftertreatment system conducive for generating ammonia on the first aftertreatment device is determined. Operation of a selected combination of a plurality of cylinders of the engine is selectively altered to achieve the desired air-fuel ratio entering the exhaust aftertreatment system.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month =
}

Patent:

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  • Often NOx selective catalysts that use ammonia to reduce NOx within exhaust to a harmless gas require on-board storage of ammonia which can be hazardous and inconvenient. In order to generate ammonia in exhaust, the present disclosure increases a NOx concentration in exhaust from at least one combustion chamber, at least in part, by injecting fuel in a predetermined increased NOx generation sequence that includes a first injection during non-auto ignition conditions and a second injection during auto ignition conditions. At least a portion of the NOx is converted to ammonia by passing at least a portion of the exhaustmore » with the increased NOx concentration over an ammonia-producing catalyst.« less
  • A system according to the principles of the present disclosure includes a rate determination module, a storage level determination module, and an air/fuel ratio control module. The rate determination module determines an ammonia generation rate in a three-way catalyst based on a reaction efficiency and a reactant level. The storage level determination module determines an ammonia storage level in a selective catalytic reduction (SCR) catalyst positioned downstream from the three-way catalyst based on the ammonia generation rate. The air/fuel ratio control module controls an air/fuel ratio of an engine based on the ammonia storage level.
  • Lean gasoline engines offer greater fuel economy than the common stoichiometric gasoline engine, but the current three-way catalyst (TWC) on stoichiometric engines is unable to control nitrogen oxide (NOX) emissions in the oxygen-rich exhaust. Thus, lean NOX emission control is required to meet existing Tier 2 and upcoming Tier 3 emission regulations set by the U.S. Environmental Protection Agency (EPA). While urea-based selective catalytic reduction (SCR) has proven effective in controlling NOX from diesel engines, the urea storage and delivery components can add significant size and cost. As such, onboard NH3 production via a passive SCR approach is of interest.more » In a passive SCR system, NH3 is generated over a close-coupled TWC during periodic slightly rich engine operation and subsequently stored on an underfloor SCR catalyst. Upon switching to lean operation, NOX passes through the TWC and is reduced by the stored NH3 on the SCR catalyst. In this work, a passive SCR system was evaluated on a 2.0-liter BMW lean burn gasoline direct injection engine to assess NH3 generation over a Pd-only TWC and utilization over a Cu-based SCR catalyst. System NOX reduction efficiency and fuel efficiency improvement compared to stoichiometric engine operation were measured. A feedback control strategy based on cumulative NH3 produced by the TWC during rich operation and NOX emissions during lean operation was implemented on the engine to control lean/rich cycle timing. 15% excess NH3 production over a 1:1 NH3:NOX ratio was required (via longer rich cycle timing) to achieve 99.7% NOX conversion at an SCR average inlet temperature of 350 C. Increasing NH3 generation further resulted in even higher NOX conversion; however, tailpipe NH3 emissions resulted. At higher temperatures, NH3 oxidation becomes important and limits NH3 availability for NOX reduction. At the engine conditions studied here, greater than 99% NOX conversion was achieved with passive SCR while delivering fuel efficiency benefits ranging between 6-11% compared with stoichiometric operation.« less
  • Lean gasoline engines offer greater fuel economy than the common stoichiometric gasoline engine, but the current three way catalyst (TWC) on stoichiometric engines is unable to control nitrogen oxide (NOX) emissions in oxidizing exhaust. For these lean gasoline engines, lean NOX emission control is required to meet existing Tier 2 and upcoming Tier 3 emission regulations set by the U.S. Environmental Protection Agency (EPA). While urea-based selective catalytic reduction (SCR) has proven effective in controlling NOX from diesel engines, the urea storage and delivery components can add significant size and cost. As such, onboard NH 3 production via a passivemore » SCR approach is of interest. In a passive SCR system, NH 3 is generated over a close-coupled TWC during periodic slightly rich engine operation and subsequently stored on an underfloor SCR catalyst. Upon switching to lean operation, NOX passes through the TWC and is reduced by the stored NH 3 on the SCR catalyst. In this work, a passive SCR system was evaluated on a 2.0-liter BMW lean burn gasoline direct injection engine to assess NH 3 generation over a Pd-only TWC and utilization over a Cu-based SCR catalyst. System NOX reduction efficiency and fuel efficiency improvement compared to stoichiometric engine operation were measured. A feedback control strategy based on cumulative NH 3 produced by the TWC during rich operation and NOX emissions during lean operation was implemented on the engine to control lean/rich cycle timing. At an SCR average inlet temperature of 350 °C, an NH 3:NOX ratio of 1.15:1 (achieved through longer rich cycle timing) resulted in 99.7 % NOX conversion. Increasing NH 3 generation further resulted in even higher NOX conversion; however, tailpipe NH 3 emissions resulted. At higher underfloor temperatures, NH 3 oxidation over the SCR limited NH 3 availability for NOX reduction. At the engine conditions studied, greater than 99 % NOX conversion was achieved with passive SCR while delivering fuel efficiency benefits ranging between 6-11 % compared with stoichiometric operation.« less
  • This patent describes an apparatus for reducing the emission of NO{sub x} in a boiler or furnace system having a primary combustion chamber from which combustion products are directed upwardly along a path leading to an exhaust stack. It comprises: the combination of first pulse combustor means for combusting a fuel with air in successive explosive pulses of hot combustion gases, means for entraining additional air with the pulses,means for injecting and mixing pulverized coal with the pulses and additional air, means for directing the mixture of coal, pulses and additional air into a first zone along the path formore » mixture with the combustion products, with fuel NO{sub x} in the combustion products being substantially reduced to molecular nitrogen by chemical reaction in the zone.« less