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
  • F01N3/2066—Selective catalytic reduction [SCR]
  • F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• • 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
  • 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
• • 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]
• • 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
  • 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
  • F01N2590/00—Exhaust or silencing apparatus adapted to particular use, e.g. for military applications, airplanes, submarines
  • F01N2590/08—Exhaust or silencing apparatus adapted to particular use, e.g. for military applications, airplanes, submarines for heavy duty applications, e.g. trucks, buses, tractors, locomotives
• • 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
• • 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 disclosure relates to an apparatus and method for exhaust gas after treatment.
• Exhaust gases generated by, for example, a boiler or an internal combustion engine, such as a diesel engine may contain gases that are preferably reduced or removed from the gas stream before it is released into the atmosphere.
• the exhaust gases may contain nitrous oxides (NOx) , which may be converted into less harmful emissions, such as nitrogen and water, by a Selective Catalytic
• SCR SCR Reduction
• SCR systems may comprise a catalyst that facilitates a reaction between the NOx, which may be present in an exhaust gas stream passing through the SCR system, and a reductant to substantially remove the NOx from the exhaust gas.
• the reductant may be added to the gas stream and absorbed onto the catalyst before it reacts with the NOx in the gas stream passing through the SCR system.
• the reductant is ammonia
• it may be added to the gas stream as, for example, anhydrous ammonia, aqueous ammonia or urea, the last of which may thermally decompose into ammonia within the SCR system before being absorbed onto the catalyst.
• the storage state of the catalyst may depend upon the temperature of the catalyst. At low temperatures, the catalyst may not absorb any of the reductant, meaning that the SCR system may not remove NOx from the exhaust gas stream.
• the SCR system may not be dosed with reductant until the catalyst has reached a temperature at which it may absorb the reductant, which may then react with NOx in the gas stream passing through the SCR system. If, however, the catalyst of an SCR device is dosed whilst it is very hot, the metals of the catalyst may be damaged.
• SCR devices may have an operating temperature range, outside of which they may not be dosed and cannot, therefore, remove NOx from the exhaust gas stream.
• Techniques may be used to adjust the engine operating parameters in order to increase or decrease exhaust gas temperatures for some operating conditions of the engine in order to maintain the SCR device within its operating temperature range for longer.
• these techniques result in a decrease in engine efficiency and may therefore be undesirable.
• DPF Diesel Particulate Filter
• SCR device may then reduce or remove NOx from the exhaust gas stream before the exhaust gas is released into the atmosphere.
• operation of the SCR device will be limited by its operating temperature range. This means that NOx may at times be released untreated into the atmosphere during normal engine operation, for example during idling or low-loading conditions for an SCR device with a high operating temperature range, or during high-load or roading conditions for an SCR device with a low operating temperature range.
• the disclosure provides: a method of dosing an exhaust gas after treatment device comprising a first selective
• SCR catalytic reduction
• DPF diesel particulate filter
• the method comprising the steps of: allowing dosing of the first SCR device with reductant when a temperature of the first SCR device is within the operating temperature range of the first SCR device, and preventing dosing of the first SCR device with reductant when the temperature of the first SCR device is outside the operating temperature range of the first SCR device; and allowing dosing of the second SCR device with reductant when a temperature of the second SCR device is within the operating temperature range of the second SCR device, and preventing dosing of the second SCR device with reductant when the temperature of the second SCR device is outside the operating temperature range of the second SCR device; and reducing the level of dosing of the first SCR device when regeneration of the DPF is required.
• the disclosure also provides: a controller to control the dosing of an exhaust gas after treatment device comprising a first selective catalytic reduction (SCR) device, a second SCR device downstream of the first SCR device and a diesel particulate filter (DPF) located between the first SCR device and the second SCR device, wherein an operating temperature range of the first SCR device is different to an operating temperature range of the second SCR device, the controller being configured to: allow dosing of the first SCR device with reductant when a temperature of the first SCR device is within the operating temperature range of the first SCR device, and prevent dosing of the first SCR device with reductant when the temperature of the first SCR device is outside the operating temperature range of the first SCR device; and allow dosing of the second SCR device with reductant when a temperature of the second SCR device is within the operating temperature range of the second SCR device, and prevent dosing of the second SCR device with reductant when the temperature of the second SCR device is outside the operating temperature range of the second SCR device; and
• an exhaust gas after treatment device comprising: a first selective catalytic reduction (SCR) device dosable by a first reductant injector upstream of the first SCR device; a second SCR device downstream of the first SCR device, the second SCR device being dosable by a second reductant injector; and a diesel particulate filter (DPF) located between the first and second SCR devices;
• SCR selective catalytic reduction
• DPF diesel particulate filter
• the second reductant injector is located between the DPF and the second SCR device; and an operating
• temperature range of the first SCR device is different to an operating temperature range of the second SCR device.
• Figures Figure 1 shows a schematic drawing of an engine unit
• Figure 2 shows a schematic drawing of an engine unit
• Figure 3 shows a graphical representation of how the dosing of the SCR devices shown in Figures 1 and 2 may be
• Figure 4 shows a graphical representation of how the dosing of the SCR devices shown in Figure 2 may be controlled
• Figure 5 shows an example vehicle within which the engine units shown in Figures 1 and 2 may be used.
• a Selective Catalytic Reduction (SCR) device may be used for a variety of applications where a reduction in NOx levels in an exhaust gas stream is desired.
• Such applications may include, but are not exclusive to, boilers, gas turbines and internal combustion engines, for example diesel engines.
• Figure 1 shows an internal combustion engine 10 with a first SCR device 20 in the exhaust gas stream of the internal combustion engine 10 and a second SCR device 40 downstream of the first SCR device 20. According to this arrangement, exhaust gases expelled from the internal combustion engine 10 pass through the first SCR device 20 and then pass through the second SCR device 40 before being released into the atmosphere or before passing through other downstream components .
• Each of the SCR devices may be independently dosed with reductant.
• the first SCR device 20 may be dosed with urea by a first injector 14, which may spray urea into the exhaust gas stream upstream of the first SCR device 20, and the second SCR device 40 may be dosed with urea by a second injector 34, which may spray urea into the exhaust gas stream upstream of the second SCR device 40.
• a first temperature sensor 12 may be located upstream of the first SCR device 20 and a second temperature sensor 32 may be located upstream of the second SCR device. Readings from these sensors may be used by a controller 50 to determine the temperature of the first 20 and second 40 SCR devices and control the first 14 and second 34 injectors
• the injected urea may be stored on the catalyst as ammonia.
• ammonia When ammonia is stored on the catalyst, it may react with NOx in the exhaust gas passing through the SCR device and remove the NOx in the exhaust gas.
• the SCR device may not be dosed and may not operate to remove NOx from the exhaust gas stream.
• the first SCR device 20 may be optimised to operate at low temperatures; for example, it may have an operating
• the second SCR device 40 may be optimised to operate at high temperatures; for example, it may have an operating temperature range of 300°C-600°C. This may be achieved, for example, by using a catalyst comprising an iron zeolite (FeZe) .
• One of the primary factors that determines the temperature of the catalyst in each of the first 20 and second 40 SCR devices may be the exhaust gas temperature.
• the first SCR device 20 may operate at low exhaust gas temperatures, for example, soon after the internal
• combustion engine 10 has been started from cold, or during idling of the internal combustion engine 10 or low-load conditions. This may result in good low temperature NOx conversion.
• the second SCR device 40 may operate at higher exhaust gas temperatures, for example during high-load conditions or roading. This may result in good high
• the operating temperature ranges of the first SCR device 20 and the second SCR device 40 may overlap such that at times both are being dosed.
• the upper bound of the operating temperature range of the first SCR device 20 may be greater than the lower bound of the operating temperature range of the second SCR device 40 and lower than the upper bound of the operating temperature range of the second SCR device 40.
• the upstream exhaust gas temperatures may be higher than the downstream exhaust gas temperatures, as each component that the exhaust gas stream passes through may reduce the
• the first SCR device 20 By making the first SCR device 20 low temperature optimised, it may enter its operating temperature range more readily after a cold start or during engine idling. If the operating temperature ranges of the two SCR devices are set to overlap, as the exhaust gas temperatures rise, the temperature of the first SCR device 20 may approach the upper bound of its operating temperature range at about the time that the temperature of the second SCR device 40 exceeds the lower bound of its operating temperature range.
• the first SCR device 20 may be optimised to have a high temperature operation range and the second SCR device 40 may be optimised to have a low temperature
• the first 20 and second 40 SCR devices could be arranged to operate in parallel to each other, with a valve that directs the exhaust gas flow to either or both of the first 20 or second 40 SCR devices according to the exhaust gas
• first 20 and second 40 SCR devices may be dosed with any other suitable dosing agent, for example anhydrous or aqueous ammonia.
• the dosing agent may be added to each of the first 20 and second 40 SCR devices using any suitable technique well known to the skilled person.
• the dosing agent and application technique may be different for each of the first 20 and second 40 SCR devices.
• Figure 2 shows an engine unit that is similar to that shown in Figure 1, but further includes a Diesel Particulate
• DPF Filter
• the DPF 30 may reduce or remove diesel particles or soot from the exhaust gas stream passing through it.
• the DPF 30 may be arranged to be downstream of the first SCR device 20 and upstream of the second SCR device 40 (as shown in Figure 2), or may be upstream of both the first 20 and second 40 SCR devices, or may be downstream of both the first 20 and second 40 SCR devices.
• the DPF 30 may function most effectively when it is at a relatively high temperature, so it may be preferable to locate it as far upstream as possible so that the
• the first SCR device 20 may be optimised for low temperature operation and be located as far upstream as possible.
• the DPF 30 may be located downstream of the low temperature optimised first SCR device 20 and upstream of the high temperature optimised second SCR device 40 (as shown in Figure 2), in order to strike a balance between the first SCR device 20 needing to be located where the exhaust gas temperatures are at their highest, and the DPF 30 needing to run at relatively high temperatures.
• the DPF 30 is a passive regeneration DPF (i.e., it is regenerated by NOx in the exhaust gas stream that may react with, and remove, soot from the DPF), it can be regenerated by controlling the dosing of the upstream SCR device (s) .
• the first SCR device 20 When regeneration of the DPF 30 is required, dosing of the first SCR device 20 is reduced or stopped in order to allow some NOx particles in the exhaust gas stream to pass through the first SCR device 20 and into the DPF 30 and regenerate the DPF 30. Any remaining NOx particles which exit the DPF 30 may be removed by the second SCR device 40, provided the second SCR device 40 is within its operating temperature range.
• the operating temperature range of the first SCR device 20 may be arranged to be below the temperature range at which the DPF 30 may passively regenerate. This means that when the temperature of the catalyst of the first SCR device 20 exceeds its operating temperature range, dosing of the first SCR device 20 stops and the first SCR device 20 stops operating. NOx may then pass through the first SCR device 20 un-reacted on to the DPF 30, where it may passively regenerate the DPF 30 as the DPF 30 enters its passive regeneration temperature range. If the operating
• temperature range of the second SCR device 40 has been set such that as the temperature of the first SCR device 20 reaches and exceeds the upper bound of its operating
• the second SCR device 40 is already within its operating temperature range, any remaining NOx particles output from the DPF 30 may be removed by the second SCR device 40.
• DPF 30 is an active regeneration DPF (i.e., it is regenerated by an elevated DPF temperature that causes oxidation and removal of soot from the DPF)
• dosing of the first 20 and second 40 SCR devices may continue as normal, taking account of the temperatures of the first 20 and second 40 SCR devices.
• an ammonia slip catalyst may also be arranged downstream of one or both of the first 20 and second 40 SCR devices in order to prevent ammonia slip.
• a single ammonia slip catalyst may be located
• FIG. 3 shows the method steps that might be undertaken by the controller 50 in order to determine when the first 20 or second 40 SCR devices may be dosed with reductant.
• the temperatures of the catalysts in the first 20 and second 40 SCR devices may be determined from the exhaust gas temperature measured upstream of the first SCR device 20.
• the catalyst temperatures may also be determined from the exhaust gas temperature measured downstream of the first SCR device 20 and upstream of the second SCR device 40, or the exhaust gas temperature measured downstream of the second SCR device 40, or from some combination of measurements taken at at least two of those locations.
• the temperature of the catalysts may alternatively be obtained from a temperature sensor within at least one of the catalysts; for example, a temperature sensor may be located within the catalyst of the first SCR device 20, the measurement of which might also be used to estimate the temperature of the catalyst in the second SCR device 40.
• the temperature of the catalysts of the first 20 and second 40 SCR devices may be estimated from measured internal combustion engine parameters, such as at least one of engine speed, fuel injection quantity, altitude and ambient temperature.
• the temperatures of the catalyst may alternatively be obtained from any other direct or indirect temperature measurement or estimation technique that would be known to the skilled person.
• Step S320 it may be determined whether or not the first SCR device 20 is within its operating temperature range.
• the first SCR device 20 may be optimised to operate at catalyst temperatures of between 180°C-350°C. If the temperature of the first SCR device 20, as determined in Step S310, is below that range, it may not be able to absorb ammonia onto its catalyst and may not, therefore, be dosed. Thus, the control method progresses to Step S330, where dosing of the first SCR device 20 is prevented. If the temperature of the first SCR device 20, as determined in Step S310, is above the operating temperature range, it may not be dosed because operation of the device may result in damage to the catalyst. Thus, the control method progresses to Step S330, where dosing of the first SCR device 20 is prevented .
• Step S310 If, however, the temperature of the first SCR device 20, as determined in Step S310, is within the operating temperature range, it may be dosed so that it may operate to reduce or remove NOx from the exhaust gas stream.
• the control method progresses to Step S340, where dosing of the first SCR device 20 is allowed.
• the level of dosing that may be applied may be dependent upon a number of factors, which may include, but are not exclusive to, at least one of: catalyst temperature, exhaust gas flow rate, NOx concentration, type of catalyst and estimated ammonia storage state on the catalyst .
• Step S350 it may be determined whether or not the second SCR device 40 is within its operating temperature range, for example, 300°C-600°C. This step is analogous to Step S320.
• Step S360 dosing of the second SCR device 40 is prevented.
• Step S370 dosing of the second SCR device 40 is allowed.
• the level of dosing applied to the second SCR device 40 may be set by considering a number of different factors, as explained earlier in respect of the first SCR device .
• Figure 4 shows further method steps undertaken by the controller 50 in order to determine when the first 20 or second 40 SCR devices may be dosed in the arrangement shown in Figure 2.
• Steps S310-S370 are the same as those shown in Figure 3.
• the control method proceeds to Step S410, where it is determined whether or not DPF regeneration should take place. Whether or not DPF regeneration should take place may be determined by any suitable means, for example the controller 50 may consider the status of a flag that is set when the operator demands DPF regeneration, or when measurement of soot content in the DPF 30 has
• Step S310 If it is determined that regeneration should not take place, the control method proceeds back to Step S310. If it is determined that regeneration should take place, the control proceed proceeds to Step S420 where the level of dosing of the first SCR device 20 is reduced, for example by a
• the DPF 30 may have a minimum temperature for regeneration and the DPF 30 and first SCR device 20 may be configured such that the minimum temperature for regeneration is greater than the upper bound of the first SCR device 20 operation temperature range. In this way, when it is determined that the DPF 30 should be regenerated, when the DPF 30 has reached its minimum temperature for regeneration the first SCR device 20 will already have ceased to be dosed with reductant, in which case reduction of the dosing level in Step S420 will maintain reductant dosing at a zero level.
• the minimum temperature for regeneration may be less than the upper bound of the first SCR device 20.
• Step S420 it may be arranged that the level of dosing of the first SCR device 20 is only reduced when regeneration of the DPF 30 is desired and the DPF temperature is above its minimum regeneration temperature. If the DPF temperature is below its minimum regeneration temperature, the reductant dosing level may not be reduced for DPF regeneration until the DPF temperature has risen above its minimum regeneration temperature.
• the temperature of the DPF 30 may be determined by any suitable means, for example using a temperature sensor (s) located upstream, within and/or downstream of the DPF 30, and/or using at least one of the temperature sensors 12 and 32, and/or may be estimated from measured internal
• combustion engine parameters such as at least one of engine speed, fuel injection quantity, altitude and ambient
• the temperature of the DPF 30 may be any temperature.
• Steps S410 and S420 are shown in Figure 4 as taking place after Steps S310-S370, they may in fact take place at any time during the control method shown in Figure 4.
• Steps S410 and S420 may take place before Step S310 and determine whether or not to apply a reduction to the current first SCR device 20 dosing level or the first SCR device 20 dosing level that will be set in Step S330 or S340.
• Steps S410 and S420 may take place after Step S330/S340 and before Step S350.
• FIGS. 1 and 2 show a controller 50 in accordance with an embodiment of the present disclosure.
• the controller 50 may be configured to carry out the method steps described in the present disclosure.
• the controller 50 may have a number of inputs and outputs that may be used to control the dosing of the first 20 and second 40 SCR devices.
• the inputs might include, but are not exclusive to: a measurement from the temperature sensor 12 upstream of the first SCR device 20 and a measurement from the temperature sensor 32 upstream of the second SCR device 40.
• the controller 50 may also have a number of outputs, including, but not exclusive to, a dosing level control signal for the first injector 14 and a dosing level control signal for the second injector 34.
• the controller 50 may be implemented in an engine control unit, for example the Caterpillar® A4:E4 or A5:E2, or as a standalone control unit.
• Figures 1 and 2 also show an engine unit comprising the first 20 and second 40 SCR devices.
• Figure 4 shows a vehicle within which the engine unit shown in Figures 1 and 2 could be used.
• an exhaust gas after treatment device comprising: a first selective catalytic reduction (SCR) device; and a second SCR device; wherein, an operating temperature range of the first SCR device is different to an operating temperature range of the second SCR device.
• SCR selective catalytic reduction
• a method of dosing an exhaust gas after treatment device comprising a first selective catalytic reduction (SCR) device and a second SCR device, wherein an operating temperature range of the first SCR device is different to an operating temperature range of the second SCR device, the method comprising the steps of: allowing dosing of the first SCR device with reductant when a temperature of the first SCR device is within the
• controller to control the dosing of an exhaust gas after treatment device
• SCR selective catalytic reduction
• temperature range of the first SCR device is different to an operating temperature range of the second SCR device, the controller being configured to: allow dosing of the first SCR device with reductant when a temperature of the first
• SCR device is within the operating temperature range of the first SCR device, and prevent dosing of the first SCR device with reductant when the temperature of the first SCR device is outside the operating temperature range of the first SCR device; and allow dosing of the second SCR device with reductant when a temperature of the second SCR device is within the operating temperature range of the second SCR device, and prevent dosing of the second SCR device with reductant when the temperature of the second SCR device is outside the operating temperature range of the second SCR device .
• the present disclosure finds application in converting NOx within an exhaust gas stream into less harmful products across a greater range of operating temperatures.
• a first, upstream SCR device may have a lower operating temperature range than a second, downstream SCR device.
• the upstream SCR device may reach its operating temperature more quickly after engine start-up by virtue of its low operating temperature range and close proximity to the engine exhaust output and begin NOx conversion quickly.
• NOx emissions may also be reduced or eliminated over a greater range of engine operating conditions by having a first SCR device with a low operating temperature range and a second SCR device with a high operating temperature range, for example from engine idling through to high-speed/high- load conditions, without having to adjust the engine
• temperature range may be greater than the lower bound of the second SCR device temperature range, such that the two operating temperature ranges overlap.
• the second SCR device may already be within its operating temperature range so that unbroken NOx conversion may take place over a wide range of temperatures.
• DPF diesel particulate filter
• the minimum regeneration temperature of the DPF is greater than the upper bound of the first SCR device operating temperature range, such that when the DPF is at regeneration temperature, dosing of the first SCR device will already have stopped and a reduction of dosing for regeneration of the DPF may simply be maintenance of dosing at a zero level.

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• Engineering & Computer Science (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Exhaust Gas After Treatment (AREA)

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• 2012
  • 2012-07-27 GB GBGB1213443.3A patent/GB201213443D0/en not_active Ceased
• 2013
  • 2013-07-26 CN CN201380039697.7A patent/CN104718356A/zh active Pending
  • 2013-07-26 WO PCT/GB2013/052013 patent/WO2014016616A1/en active Application Filing
  • 2013-07-26 US US14/416,861 patent/US20150204226A1/en not_active Abandoned
  • 2013-07-26 EP EP13742726.6A patent/EP2888458A1/en not_active Withdrawn

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