EP1507964A1 - Moteur a explosion possedant un catalyseur a trois voies avec composant de stockage d'oxyde d'azote - Google Patents

Moteur a explosion possedant un catalyseur a trois voies avec composant de stockage d'oxyde d'azote

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Publication number
EP1507964A1
EP1507964A1 EP03725426A EP03725426A EP1507964A1 EP 1507964 A1 EP1507964 A1 EP 1507964A1 EP 03725426 A EP03725426 A EP 03725426A EP 03725426 A EP03725426 A EP 03725426A EP 1507964 A1 EP1507964 A1 EP 1507964A1
Authority
EP
European Patent Office
Prior art keywords
engine
twc
nox
engine according
nox storage
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP03725426A
Other languages
German (de)
English (en)
Inventor
Robert James Brisley
Daniel Swallow
Martyn Vincent Twigg
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Johnson Matthey PLC
Original Assignee
Johnson Matthey PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Johnson Matthey PLC filed Critical Johnson Matthey PLC
Publication of EP1507964A1 publication Critical patent/EP1507964A1/fr
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9495—Controlling the catalytic process
    • 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
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
    • 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
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • 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
    • F01N2570/16—Oxygen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/02—Input parameters for engine control the parameters being related to the engine
    • F02D2200/08—Exhaust gas treatment apparatus parameters
    • F02D2200/0806—NOx storage amount, i.e. amount of NOx stored on NOx trap
    • 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
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • 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 to a spark ignition engine comprising an exhaust system comprising a catalyst and an engine control unit programmed to control the air- to-fuel ratio of the engine to run at the stoichiometric air-to-fuel ratio during normal running conditions and to run lean of the stoichiometric air-to-fuel ratio during a defined portion of an engine speed/load map.
  • the present invention relates to such an engine wherein the catalyst is a three-way catalyst (TWC) including a NOx storage component.
  • TWC three-way catalyst
  • a heterogeneous catalyst capable of simultaneous conversion of nitrogen oxides (NOx), carbon monoxide (CO) and unburnt hydrocarbons (HC) in exhaust gas from a stoichiometrically operated, spark-ignited combustion engine is known as a three-way catalyst (TWC).
  • NOx reduction readily occurs over the TWC when the air-to-fuel ratio is rich of stoichiometric, whereas CO and HC reactions are hindered by insufficient oxygen (O 2 ).
  • O 2 oxygen
  • the CO and HC conversions are high, but NOx reduction is difficult because of the excess of oxidising species. Accordingly, effective three-way conversion occurs in a relatively narrow air-to-fuel ratio window.
  • an oxygen sensor is used to detect the lambda composition of the exhaust gas upstream of the TWC and to adjust the air-to-fuel ratio accordingly to equilibrate the exhaust gas.
  • a typical TWC comprises platinum (Pt) and/or palladium (Pd) as an oxidation catalyst and rhodium (Rh) as a reduction catalyst on a suitable high surface area oxide support, such as alumina (Al O 3 ), and an oxygen storage component (OSC), e.g. a ceria- zirconia mixed oxide.
  • a suitable high surface area oxide support such as alumina (Al O 3 )
  • an oxygen storage component e.g. a ceria- zirconia mixed oxide.
  • Various minor amounts of base metal catalyst promoters, stabilisers and hydrogen sulphide suppressers can be included. For further details, see WO 98/03251 (incorporated herein by reference).
  • a typical NOx trap composition comprises Pt and Rh on a high surface area oxide support, such as Al 2 O 3 , and a NOx storage component such as barium oxide (BaO (see, e.g. EP 0758713, incorporated herein by reference)).
  • a NOx storage component such as barium oxide (BaO (see, e.g. EP 0758713, incorporated herein by reference)).
  • loadings of NOx storage components in NOx trap washcoats can be up to 50wt% or even higher
  • NOx trap technology requires very careful and complicated control of the engine in order to provide for rich regeneration of the NOx storage component.
  • a number of feedback sensors are used to control the function of the NOx trap NOx storage capacity, e.g. sensors to estimate cumulative engine-out NOx production utilising stored engine maps and NOx trap temperature sensors, because the efficiency of the NOx storage component to absorb NOx is temperature dependent.
  • Base metal catalyst promoters such as barium (Ba), cerium, lanthanum, magnesium, calcium and strontium can also be used (see WO 98/03251, mentioned above).
  • the catalytic converter for a lean burn internal combustion engine, such as a direct injection gasoline engine, comprising a catalyst component capable of storing NOx.
  • the catalytic converter comprises a supported layered catalyst having a first, inner layer containing a first platinum group metal (PGM), e.g. Pt, and a NOx storage component, e.g. Ba, and a second, outer layer containing a second different PGM, such as Rh supported on a non-Al 2 O 3 support, and optionally an OSC such as a mixed oxide of ceria and zirconia.
  • PGM platinum group metal
  • Japanese Unexamined Patent Publication (KOKAI) No. 5-317,652 (incorporated herein by reference) describes a catalyst comprising a substrate, and an alkaline-earth metal compound and Pt loaded on the substrate.
  • the gasoline engine is run on the fuel lean side, such as an air-to-fuel ratio of up to 23:1 (wt./wt.).
  • the catalyst is designed to adsorb (or absorb) NOx on the alkaline-earth metal during lean rurming conditions and to use the natural fluctuation of the air-to-fuel ratio to the rich side to enable stored NOx to be released and reduced, thus regenerating the NOx storage capacity of the alkaline-earth metal compound.
  • 5-317,652 is poisoned by sulfate.
  • a catalyst comprising Pt or Pd and alkali metals, alkaline-earth metals and rare-earth elements including lanthanum (La) supported on lithium-stabilised Al 2 O 3 .
  • La lanthanum
  • spark ignition engine such as a port fuel injection gasoline engine, which engine comprising a
  • TWC including a NOx storage component, in such a way as to benefit from the increased fuel economy available during lean running conditions whilst avoiding the requirement for expensive and complicated control systems.
  • the invention provides A spark ignition engine comprising an exhaust system comprising a catalyst and an engine control unit programmed to control the air-to-fuel ratio of the engine to run at the stoichiometric air-to-fuel ratio during normal running conditions and to run lean of the stoichiometric air-to-fiiel ratio during a defined portion of an engine speed/load map, which catalyst comprising a three-way catalyst (TWC) including a NOx storage component, characterised in that the engine control unit is further programmed to determine the amount of NOx contacting the TWC during lean running operation in response to data input from sensor means, thereby to determine the remaining NOx storage capacity of the TWC and to return the air-to-fuel ratio to stoichiometry when the remaining NOx storage capacity is below a pre-determined value, the arrangement being such as to substantially prevent passing more NOx to atmosphere during an engine cycle compared with a spark ignition engine run continuously in stoichiometric mode.
  • TWC three-way catalyst
  • engine cycle herein we mean the period between key on and key off.
  • the present invention takes advantage of the natural fluctuation in the composition of an exhaust gas of a spark ignition engine operated at the stoichiometric air-to-fuel ratio to rich lambda values, e.g. during acceleration, to regenerate the NOx storage component.
  • a catalyst that facilitates the regeneration of a NOx storage component in a TWC, which catalyst is used in a preferred embodiment according to the invention.
  • the present invention provides a number of very substantial advantages.
  • One such advantage is that it enables a vehicle powered by a spark ignition engine to be run at a fuel saving over a similar vehicle operated continuously at substantially stoichiometric conditions. Such increased efficiency can result in lower CO 2 emissions in a legislative test cycle for a vehicle. Lower CO 2 emissions in a legislative test cycle translates to lower CO 2 emissions in "real world" driving conditions. Accordingly, a vehicle according to the invention can be more "environmentally friendly”. Furthermore, in countries where vehicles are taxed depending on the amount of CO 2 they emit (a so-called "green tax”), such as the UK, it can reduce the tax burden to the consumer.
  • a second such advantage is that it can allow existing vehicles including spark ignition engines to receive the benefit of the invention by retrofitting certain components. This can be done by simply replacing the existing TWC with a TWC including sufficient NOx storage component and the engine control unit for one programmed: (i) to run the engine lean of the stoichiometric air-to-fuel ratio during a defined portion of an engine speed/load map; and (ii) to determine the amount of NOx contacting the TWC during lean running operation in response to data input from sensor means, thereby to determine the remaining NOx storage capacity of the TWC and to return the air-to-fuel ratio to stoichiometry when the remaining NOx storage capacity is below a pre-determined value, thereby substantially to prevent passing more NOx to atmosphere during an engine cycle compared with a spark ignition engine run continuously in stoichiometric mode.
  • the defined portion of the engine speed/load map is engine idle.
  • the defined portion of the engine speed/load map can comprise low speed driving wherein the level of NOx emitted by the engine is up to ten times more, such as five times or twice more, than at engine idle.
  • a very substantial advantage of this preferred arrangement is that it avoids the requirement for complicated and expensive sensors and controls in order to meet emission legislation that presently burdens the adoption of NOx traps.
  • a number of means for inputting data to the engine control unit to determine the amount of NOx contacting the TWC, and hence the remaining NOx storage capacity of the NOx storage component, can be used either singly or in any mechanically/electronically viable combination.
  • Many of the sensor means required to collect this information are already included in the engine and/or vehicle fitted with the engine and are used by the engine control unit for controlling other functions of the engine and/or vehicle. This is one reason why it is possible to adopt the invention by retrofitting the vehicle engine control unit, together with a TWC including a NOx storage component.
  • Such detected data that can be used to monitor remaining NOx storage capacity in the TWC of the invention include: predetermined or predicted time elapsed from the start of lean running operation, by sensing the status of a suitable clock means; airflow over the TWC or manifold vacuum; ignition timing; engine speed; throttle position; exhaust gas redox composition, for example using a lambda sensor, preferably a linear lambda sensor; quantity of fuel injected in the engine; where the vehicle includes an exhaust gas recirculation (EGR) circuit, the position of the EGR valve and thereby the detected amount of EGR; engine coolant temperature; and where the exhaust system includes a NOx sensor, the amount of NOx detected upstream and/or downstream of the TWC.
  • EGR exhaust gas recirculation
  • the spark ignition engine can be any capable of operating during normal running conditions at the stoichiometric air-to-fuel ratio.
  • the engine can be powered by gasoline and the engine can be of the port fuel injection or direct injection type.
  • the engine can be fuelled using an alternative fuel such as liquid petroleum gas (LPG), natural gas (NG), methanol, hydrocarbon mixtures including ethanol or hydrogen gas.
  • LPG liquid petroleum gas
  • NG natural gas
  • methanol methanol
  • hydrocarbon mixtures including ethanol or hydrogen gas hydrocarbon mixtures including ethanol or hydrogen gas.
  • the invention can be used on all grades of sulfur-containing fuel, but with particular efficiency with grades containing less that 50 ppm by weight of sulfur, and most preferably less than 10 ppm by weight of sulfur.
  • the present invention can utilise any known TWC composition provided that sufficient NOx storage component is included in order to perform the desired function.
  • a typical TWC composition comprises at least one PGM, and can be selected from the group consisting of Pt, Pd, Rh, ruthenium, osmium and iridium and any combination of two or more thereof.
  • NOx storage components are disclosed in the prior art, and any can be utilised in the present invention.
  • Typical NOx storage components comprise alkali metals, such as potassium or caesium, alkaline-earth metals, e.g. magnesium, calcium, strontium or Ba, rare-earth metals lanthanide group metal, preferably La, or any viable combination, e.g. a mixed oxide, of any two or more thereof.
  • a common component of state-of-the-art TWCs is the OSC and these too can be included in the TWC, with utility, according to the present invention.
  • OSC an OSC assists in the combustion of HC at the stoichiometric point and slightly rich thereof.
  • This property runs counter to the requirement of a system including a NOx trap composition which is to regenerate the NOx storage component using reducing species, such as HCs in the exhaust, resulting from air-to-fuel ratio modulation. Accordingly, the presence of an OSC in a NOx trap composition would cause increased fuel consumption for the same amount of NOx storage component regeneration relative to an OSC-free NOx trap composition.
  • OSC include optionally stabilised ceria, perovskites, NiO, MnO , manganese-based compounds supported on Al 2 O 3 -containing mixed oxides (see PCT/GBO 1/05124, incorporated herein by reference) a mixed oxide of manganese and zirconium (see WO 99/34904, incorporated herein by reference), Pr 2 O 3 or a combination of any two or more thereof.
  • the ceria stabiliser can be zirconium, lanthanum, aluminium, yttrium, praseodymium or neodymium.
  • a preferred TWC for use in the present invention comprises a first PGM, preferably Pt, and the NOx storage component in a first, inner layer and an OSC and a second PGM, preferably Rh, in a second, outer layer.
  • Rh/OSC component is active for NOx reduction and other reactions while the Pt component is active for oxidation reactions.
  • the Rh is relatively inactive, the Pt is active for NO, HC and CO oxidation while the NO 2 produced is stored in the adsorber as nitrate.
  • the OSC component in the second layer prevents the stored NOx "seeing" reducing gas so that the NOx remains stored as nitrate.
  • the Rh is active for NOx reduction by CO and the Pt is active for oxidation of HC and CO.
  • the invention provides a vehicle comprising an engine according to the present invention.
  • TWC are generally placed in one or both of two positions in a vehicle according to the intended purpose: the close-coupled position, in which the TWC is disposed as close to the exhaust manifold as possible; and the underfloor position.
  • the reason for placing a TWC in the close-coupled position is to control emissions immediately following cold start, as much of the controlled emissions are emitted during the legislative test cycle immediately following cold-start.
  • the catalyst By positioning a TWC close to the engine, the catalyst is contacted by hot exhaust gases immediately after key on and accordingly reaches the light-off temperature for CO and HC oxidation sooner than a TWC in the cooler, underfloor location.
  • the underfloor catalyst shoulders much of the burden of treating the exhaust gas.
  • close-coupled TWC is exposed to very high temperatures e.g. up to 1000°C.
  • catalyst bed temperatures e.g. 970°C and up to 1010°C.
  • catalysts can lose activity as materials lose their surface area through sintering events, migration of active species into pores and component interactions. Accordingly, a TWC in the close-coupled position can be expected to lose some of its activity compared with a fresh catalyst.
  • the NOx storage component can also lose NOx storage capacity through this high temperature ageing by loss of surface area.
  • the fresh TWC includes sufficient of the NOx storage component to retain sufficient NOx storage capacity after high temperature ageing, for example in the close-coupled position.
  • the invention provides An engine control unit for a spark ignition engine comprising an exhaust system comprising a TWC including a NOx storage component, which engine control unit is programmed to control the air-to-fuel ratio of the engine to run at the stoichiometric air-to-fuel ratio during normal running conditions and to run lean of stoichiometry during a defined portion of an engine speed load map and to determine the amount of NOx contacting the TWC during lean running operation in response to data input from sensor means, thereby to determine the remaining NOx storage capacity of the TWC and to return the air-to-fuel ratio to stoichiometry when the remaining NOx storage capacity is below a pre-determined value, the arrangement being such as to substantially prevent passing more NOx to atmosphere during an engine cycle compared with a spark ignition engine run continuously in stoichiometric mode.
  • the invention provides A method of treating exhaust gas of a spark ignition engine run at the stoichiometric air-to-fuel ratio during normal nuining conditions, which engine comprising an exhaust system comprising a TWC including a NOx storage component, which method comprising the steps of controlling the engine air-to-fuel ratio to run lean of stoichiometry during a defined portion of an engine speed/load map and determining the amount of NOx contacting the TWC during lean ranning operation in response to data input from sensor means, thereby to determine the remaining NOx storage capacity of the TWC and to return the air-to- fuel ratio to stoichiometry when the remaining NOx storage capacity is below a predetermined value, the arrangement being such as to substantially prevent passing more NOx to atmosphere during an engine cycle compared with a spark ignition engine run continuously in stoichiometric mode.
  • Figure 1 is a graph showing HC conversion against temperature after ageing of a TWC including a NOx storage component according to the invention, a state-of-the-art TWC and a NOx trap;
  • Figures 2, 3 and 4 are graphs showing % conversion of CO, HC and NOx against lambda for a TWC including a NOx storage component according to the invention, a state-of-the-art TWC and a NOx trap formulation respectively.
  • Comparative catalyst A is a state- of-the art Pt/Rh TWC on a thermally stable, high surface area support at a ratio of 5Pt:lRh and a total precious metal loading of at 60 g ft "3 .
  • Catalyst B is a TWC including a NOx storage component according to the present invention supported on an identical substrate. It comprised a first, inner layer of a high surface area Al 2 O 3 impregnated with Pt and a NOx storage component, such as
  • Comparative catalyst C is a NOx trap composition comprising a high surface area Al 2 O 3 -based mixed oxide support impregnated with Pt, Rh and a NOx storage component.
  • the ratio of Pt:Rh was 6:1 and the total precious metal loading was 70 g ft "3 .
  • Each washcoat was coated on a 4.66 x 6 inch (11.9 x 15.2 cm) ceramic substrate of 400 cells per square inch ((cpsi) 62 cells cm “2 ) of 0.15 mm wall thickness and the resulting coated substrate was hydrothermally aged at 800°C for 5 hours under 10% O 2 /10% H 2 O/balance nitrogen.
  • the catalysts were fitted to the exhaust of a four cylinder 2.0 litre Port Fuel
  • Injection bench mounted engine controlled by a Bosch ME7 control system The catalyst temperature was increased by adjustment of a heat exchanger fitted to the exhaust line before the catalyst.
  • the temperature ramp rate was 14 °C/minute.
  • Example 2 In a bench test cell, a 4 cylinder, 1.8 litre, 1997 model year, Mitsubishi direct injection engine from a vehicle calibrated for the Japanese market was installed with a direct current dynamometer. A catalyst substrate prepared according to Example 1 was fitted in the close-coupled position approximately 30 cm from the engine exhaust manifold. The substrate volume represented of 22% engine swept volume (ESV). Concentrations of NOx, HC, CO 2 , CO and O 2 were measured using a dual bank of MEXA (Motor Exhaust Gas Analyser) 9500 sensors to allow continuous measurement of gas concentrations upstream and downstream of the catalyst. The catalyst inlet temperature was measured by thermocouple.
  • MEXA Motor Exhaust Gas Analyser
  • the engine was operated from one of two sets of maps: one for the homogeneous mode and the other for the lean, stratified mode.
  • Basic maps for ignition and injection timing and duration were generated by firstly logging data from the ECU of a vehicle including the same model of engine as the one used for the bench test and then basing the maps on this information by reverse engineering.
  • the lean, stratified mode was mapped by matching the torque achieved in homogeneous mode at the same speed and load demand.
  • the engine Prior to testing, the engine was thoroughly warmed up in idling condition. In homogeneous mode, the engine was then run so that the inlet temperature to the close- coupled catalyst was 300 °C. It was then switched to lean, stratified operation and the EGR valve position was adjusted until the engine-out NOx was 300 ppm. The EGR valve position was recorded and was referred to as the lean set point. The engine was switched back to homogeneous mode, and the EGR valve was closed. A rich set point was obtained by increasing the fuel injector pulse width to obtain lambda 0.80. A series of lean/rich cycles were run as follows. In the lean mode, the EGR valve was at the lean set-point position until the NOx efficiency of the system had dropped below 75%.
  • Table 1 shows the NOx storage efficiency with which each of comparative catalysts A and C and catalyst B store NOx, and in particular, how the efficiency with which each catalyst stores 30, 40, 50 and 60 mg of NOx.
  • NOx trap comparative catalyst C
  • TWC comparative catalyst A
  • Example 1 The results of Examples 1, 2 and 3 show that the TWC including a NOx storage component maintains TWC performance despite including a NOx storage component, and that NOx storage capacity is several times higher than a state-of-the-art TWC composition.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Analytical Chemistry (AREA)
  • Environmental & Geological Engineering (AREA)
  • Biomedical Technology (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Health & Medical Sciences (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)

Abstract

Ce moteur à explosion possède un échappement équipé d'un catalyseur à trois voies (TWC), pourvu d'un composant de stockage d'oxyde d'azote (NOx), et une unité de commande programmée pour agir sur le rapport air/carburant du moteur afin que celui-ci tourne selon un rapport stoechiométrique air/carburant en conditions normales et qu'il tourne à faible régime en dessous du rapport stoechiométrique air/carburant durant une période déterminée d'un régime et/ou d'une charge du moteur, et pour déterminer la quantité de Nox entrant en contact avec le TWC lors du fonctionnement à faible régime, en réaction aux entrées de données provenant du capteur, de façon à déterminer la capacité restante de stockage de Nox par le TWC et de revenir à un rapport stoechiométrique air/carburant lorsque cette capacité de stockage est inférieure à une valeur prédéterminée. Ce mécanisme permet d'éviter sensiblement le passage d'une plus grande quantité de Nox dans l'atmosphère durant un cycle de moteur en comparaison de ce qu'il advient avec un moteur à explosion tournant continuellement en mode stoechiométrique.
EP03725426A 2002-05-24 2003-05-21 Moteur a explosion possedant un catalyseur a trois voies avec composant de stockage d'oxyde d'azote Ceased EP1507964A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GBGB0211971.7A GB0211971D0 (en) 2002-05-24 2002-05-24 Spark ignition engine including three-way catalyst
GB0211971 2002-05-24
PCT/GB2003/002200 WO2003100228A1 (fr) 2002-05-24 2003-05-21 Moteur a explosion possedant un catalyseur a trois voies avec composant de stockage d'oxyde d'azote

Publications (1)

Publication Number Publication Date
EP1507964A1 true EP1507964A1 (fr) 2005-02-23

Family

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Application Number Title Priority Date Filing Date
EP03725426A Ceased EP1507964A1 (fr) 2002-05-24 2003-05-21 Moteur a explosion possedant un catalyseur a trois voies avec composant de stockage d'oxyde d'azote

Country Status (6)

Country Link
US (1) US20060075740A1 (fr)
EP (1) EP1507964A1 (fr)
JP (1) JP4494201B2 (fr)
KR (1) KR20050013996A (fr)
GB (1) GB0211971D0 (fr)
WO (1) WO2003100228A1 (fr)

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DE102007019460A1 (de) * 2007-04-25 2008-11-06 Man Nutzfahrzeuge Ag Abgasnachbehandlungssystem
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Also Published As

Publication number Publication date
JP4494201B2 (ja) 2010-06-30
GB0211971D0 (en) 2002-07-03
KR20050013996A (ko) 2005-02-05
JP2005534841A (ja) 2005-11-17
WO2003100228A1 (fr) 2003-12-04
US20060075740A1 (en) 2006-04-13

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