Classifications

• • 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
• • 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
  • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
• • 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
  • F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
  • F01N11/002—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus
• • 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
• • 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
  • F01N3/0821—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with particulate filters
• • 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
  • 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
• • 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
  • F01N9/00—Electrical control of exhaust gas treating apparatus
• • 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
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
• • 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
  • F01N2550/00—Monitoring or diagnosing the deterioration of exhaust systems
  • F01N2550/03—Monitoring or diagnosing the deterioration of exhaust systems of sorbing activity of adsorbents or absorbents
• • 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
  • Y02T10/40—Engine management systems

Definitions

• the present invention relates to an exhaust system for a lean-burn internal combustion engine comprising a NO x -absorbent and, in particular, to a method of controlling reductant addition into the exhaust system for the purpose of regenerating the NO x -absorbent and reducing NO x to N 2 .
• An exhaust system for a lean-burn internal combustion engine such as a diesel engine or a lean-burn gasoline engine comprising a NO x -absorbent is known from, for example, EP 0560991.
• NO x -trap is a catalyst comprising a NO x -absorbent and a catalyst for oxidising NO to NO 2 .
• NO x -traps are also known as “lean NO x traps" or "LNC”.
• a typical NO x -trap formulation includes a catalytic oxidation component, such as Pt, a NO x -absorbent, such as compounds of alkali metals e.g. potassium and/or caesium; compounds of alkaline earth metals, such as barium or strontium; or compounds of rare- earth metals, typically lanthanum and/or yttrium; and a reduction catalyst, e.g. rhodium.
• a catalytic oxidation component such as Pt
• a NO x -absorbent such as compounds of alkali metals e.g. potassium and/or caesium
• compounds of alkaline earth metals such as barium or strontium
• rare- earth metals typically lanthanum and/or yttrium
• a reduction catalyst e.g. rhodium
• the inorganic NO x -storage component is typically present as an oxide, it is understood that in the presence of air or exhaust gas containing CO 2 and H 2 O it may also be in the form of the carbonate or possibly the hydroxide.
• the nitrate species become thermodynamically unstable and decompose, producing NO or NO 2 .
• these NO x species are reduced by carbon monoxide, hydrogen and hydrocarbons to N , which can take place over the reduction catalyst.
• An object of an exhaust system comprising a NO x -trap is to improve the economy of the engine whilst meeting the relevant emissions standard, e.g. Euro IV.
• EP-B-0341832 (incorporated herein by reference) describes a process for combusting particulate matter (PM) in diesel exhaust gas, which method comprising oxidising NO in the exhaust gas to NO 2 on a catalyst, filtering the PM from the exhaust gas and combusting the filtered PM in the NO 2 at up to 400°C.
• PM particulate matter
• an exhaust system for a vehicular lean-burn internal combustion engine comprising a NO x -absorbent, a reductant injector disposed upstream of the NO x -absorbent and means, when in use, for controlling reductant addition, wherein the reductant addition control means supplies reductant to the NO x -absorbent at all vehicle speeds in a duty cycle at a rate which is predetermined to correlate with a desired NO x conversion at the average duty cycle speed of the vehicle.
• the invention of the first aspect has particular application to the retrofit market for vehicles of a limited duty cycle such as buses or refuse trucks.
• the idea is to determine what rate of reductant injection is required to reduce a chosen quantity of NO x , e.g. 90%, in a NO x -absorbent at the average duty cycle speed.
• the system controller can be arranged, when in use, to generate a continuous tempo and quantity of hydrocarbon (HC) fuel injection e.g. injection at 2 seconds every minute.
• HC hydrocarbon
• the system controller can also be arranged to provide occasional relatively long rich HC fuel pulses to ensure that the NO x -trap is substantially completely regenerated, followed by the more frequent sequence of shorter enrichment pulses to maintain the storing capability of the NO x -trap.
• the exact detail of the injection strategy depends on the vehicle and its duty cycle. At speeds higher than the average duty cycle speed, there would be more NO x and a greater mass airflow and so NO x conversion overall would fall off, because there would be insufficient reductant. However, because higher speed would be less likely e.g.
• the system can meet NO x emission standards over an entire drive cycle without increasing fuel penalty; equally where the vehicle speed drops below the average duty cycle speed, HC can be emitted, but on average over a duty cycle the system can meet the emission standard for HC.
• the correlation of the rate of HC injection to average duty cycle speed can be tailored to the particular application, e.g. buses in Manchester (UK) city centre would be expected to encounter different duty cycles to those in London (UK) city centre.
• an oxidation catalyst is disposed between the reductant injector and the NO x -absorbent for increasing the temperature of the NO x -trap for regeneration and/or to remove oxygen from the exhaust gas to ensure a rich exhaust gas for regeneration of the NO x -absorbent.
• the NO x -trap and systems for delivering reductant described herein are disposed downstream of the arrangement described in
• EP-B-0341832 mentioned hereinabove. That is, a catalyst for oxidising NO to NO 2 is followed by an optionally catalysed filter then a reductant injector followed by the NO x -absorbent.
• the NO x -absorbent for use in the invention is a component of a NO x -trap.
• the catalysts for use in the present invention are coated on high surface area substrate monoliths made from metal or ceramic or silicon carbide, e.g. cordierite, materials.
• a common arrangement is a honeycomb, flow- through monolith structure of from 100-600 cells per square inch (cpsi) such as 300-400 cpsi (15.5-93.0 cells cm “2 , e.g. 46.5-62.0 cells cm "2 ).
• the internal combustion engine can be a diesel or lean-burn gasoline engine, such as a gasoline direct injection engine.
• the diesel engine can be a light-duty engine or a heavy-duty engine, as defined by the relevant legislation.
• a method of reducing NO x in the exhaust gas of a vehicular lean-burn internal combustion engine comprises absorbing NO x from the exhaust gas in a NO x absorbent, contacting the NO x absorbent with a reductant to regenerate the NO x -absorbent at all vehicle speeds in a duty cycle, and reducing NO x to N 2 , wherein a rate of reductant injection correlates with a desired NO x conversion at the average duty cycle speed.
• Figure 1 shows a schematic system according to the first aspect of the invention
• Figure 2 is a schematic graph plotting quantity of fuel against time showing a fuel injection strategy for use in the system of Figure 1 ;
• Figure 3 is a schematic of a working embodiment of the invention.
• Figure 4 is a graph showing the upstream Air/Fuel Ratio (AFR) as a function of road speed in the embodiment of Figure 3;
• Figure 5 is a graph showing NO x measurements at the idle condition for the embodiment of Figure 3;
• Figure 6 is a graph showing the corresponding system temperatures at the idle condition for the trace shown in Figure 5;
• Figure 7 is a graph showing NO x measurements at 40mph for the embodiment of Figure 3;
• Figure 8 is a graph showing the corresponding temperature measurements at 40mph for the trace shown in Figure 7; and Figure 9 is a graph showing the NO x conversion as a function of road speed for the system of Figure 3.
• 52 is a conditional system controller (CSC)
• 54 is a master switch
• 56 is an alternator
• 58 is a blocking capacitor
• 60 is a thermocouple
• 62 is an injection controller (ICU)
• 64 is a fuel pump
• 66 is a valve
• 68 is a fuel injector
• 70 is a positive power line.
• the CSC 52 is a switch providing power to the ICU 62 if the master power switch 54 is on, the engine is running as determined by an AC ripple from the alternator 56 present after a DC blocking capacitor 58 and the output of a suitably placed thermocouple 60 to detect the exhaust system is above a minimum pre-determined temperature for reduction of NO x on a suitable NO x -trap.
• the master switch 54 need not be connected to the key-on position.
• the CSC 52 is designed to generate a continuous tempo and quantity of HC injection when all three features (master switch position, detection of alternator ripple and exhaust gas temperature above a pre-determined minimum) coincide.
• power is supplied to the injection pump 64 and the ICU 62 that operates a solenoid valve 66 to produce a series of pulses to enrich the exhaust gas before it passes over an oxidation catalyst upstream of the NO x absorbing components.
• the injection controller will provide occasional relatively very long rich pulses to ensure that the NO x -trap is substantially completely empty and this is followed by a more frequent sequence of shorter enrichment pulses, e.g. injection at 2 seconds every minute, to maintain the storing capability of the NO x -trap (see Figure 2).
• This fuel injection rate is correlated to a chosen NO x conversion e.g. 90% at the average duty cycle speed.
• the exact detail of the injection strategy depends on the vehicle and its duty cycle.
• the systems employing NO x -traps described herein have been developed to provide simple control mechanisms to predict when NO x -trap regeneration should be done, with particular application to retrofit, many vehicles already include a range of sensors to input data to the ECU for controlling other aspects of vehicular operation. By suitable re-programming of the ECU it is possible to adopt one or more of such existing sensor inputs for the purposes of predicting remaining NO x -trap capacity.
• ⁇ include, but are not limited to, predetermined or predicted time elapsed from key-on or previous regeneration, 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 NO x sensor, the amount of NO x detected upstream and/or downstream of the NO x -trap.
• EGR exhaust gas recirculation
• NO x the amount of NO x detected upstream and/or downstream of the NO x -trap.
• the predicted time can be subsequently adjusted in response to data input.
• the exhaust system (10) (shown in Figure 3) of a single deck bus fitted with a 6 litre rurbocharged engine and comprising engine turbo (12), type approved to European Stage 1 emission limits, was modified to incorporate a three-way splitter (14) for diverting the exhaust gas into one of three parallel legs (16), the exhaust gas flow in each leg being of equal velocity flow.
• Each leg (16) comprised a chamber (18) containing an oxidation catalyst (20) followed by a NO x -trap (22).
• the gas flows were then combined downstream of the NO x -traps and the total exhaust gas flow was passed through a "clean up" oxidation catalyst (24) to remove any unburned hydrocarbons (HC) exiting the NOx- traps before the exhaust gas was passed directly to the atmosphere.
• a fuel injector (26) comprising a fuel solenoid (28) was sited in front of each oxidation catalyst (20), a NO x sensor (29) in front of the exhaust splitter (14), combined NO x /air fuel ratio sensors (30) behind the NO x -traps and thermocouples (Tl, T2, T3, T4) measuring temperatures in front of and behind the oxidation catalysts (20) and at the exit of the reactors.
• the oxidation catalysts (20) and the NO x traps (22) were each coated on ceramic flow- through monoliths at 400 cells in "2 (62 cells cm “2 ) and 0.06 in (0.15mm) wall thickness.
• the oxidation catalysts (20) were 5.66 in (144mm) diameter x 3 in (76mm) and volume 75.5 in 3 (1.24 litre), the NO x -traps (22) were the same diameter but 6 in (152mm) long and the "clean up" catalyst (24) 10.5 in (267mm) diameter x 3 in (76mm) long and volume 260 in 3 (4.26 litres).
• the experiments described here were conducted using one leg of the split exhaust only.
• the vehicle was operated using diesel fuel containing 50ppm sulphur and run at steady speeds of idle, 10, 20, 30 and 40 mph for periods of time; fuel was injected at each of these points and the air fuel ratio during injection determined as shown in Figure 4.
• the combination of time and duration (2 seconds injection, one per minute per leg) was selected empirically as it gave the best combination of exhaust gas temperatures (to maintain the NO x -trap within an active temperature window) and NO x conversion. Simultaneously the NO x emissions pre- and post- the system together with the temperature profiles were measured.
• Figure 5 shows the NO x emissions (ppm) from the engine and after the NO x -trap for the idle condition together with the air fuel ratio measured after the NO x - trap.
• Figure 6 shows the temperature traces for the same period. From Figure 5 it is seen that when fuel is injected at the start of the idle period, the air fuel ratio drops from lean to rich as expected from the predictions in Figure 3 and, after the initial NO x breakthrough, good NO x conversion is seen. With time, the air fuel ratio remains lean throughout the injection event but good NO x conversion is still maintained.
• the exotherm (T2) generated over the oxidation catalyst helps maintain the temperature of the NO x -trap within its operating window of 220-550°C.
• Figure 9 presents the trend in calculated average NO x conversion efficiency, as a function of speed, for the system.
• Figure 3 indicates rich exhaust gas conditions do not occur above about 6 mph but good NO x conversions were obtained under lean conditions across a wider speed range. This is especially relevant in the range from idle to 30mph which is the most common operating range for an urban city bus.

Priority Applications (5)

Applications Claiming Priority (4)

Publications (1)

Family

ID=34971502

Family Applications (1)

Country Status (4)

Cited By (1)

Citations (4)

• 2005
  • 2005-06-16 KR KR1020077001075A patent/KR20070020138A/ko not_active Application Discontinuation
  • 2005-06-16 EP EP05756418A patent/EP1766201A1/en not_active Withdrawn
  • 2005-06-16 JP JP2007516039A patent/JP2008502843A/ja active Pending
  • 2005-06-16 WO PCT/GB2005/002373 patent/WO2005124114A1/en active Application Filing

Patent Citations (4)

Also Published As

Similar Documents

Legal Events