GB2502364A

GB2502364A - Method of reactivating a Passive NOx Adsorber

Info

Publication number: GB2502364A
Application number: GB1209332.4A
Authority: GB
Inventors: Andrea De Filippo
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-05-25
Filing date: 2012-05-25
Publication date: 2013-11-27
Also published as: GB201209332D0

Abstract

The invention provides a method of reactivating a Passive NOx Adsorber (PNA) 280 in an exhaust line 275 of an Internal Combustion Engine 110, the exhaust line comprising a Diesel Particulate Filter 285, the method comprising the steps of subjecting the Diesel Particulate Filter (DPF) to a regeneration, and performing a rich combustion mode event after the end of the Diesel Particulate Filter regeneration. The passive NOx adsorber is adversely affected by the diesel particulate filter regeneration, and the platinum in the passive NOx adsorber can become platinum oxide which reduces the catalytic performance level. However by subjecting the platinum oxide to a fuel rich exhaust flow the ability of the passive NOx adsorbers to oxidise hydrocarbons and carbon monoxide into carbon dioxide and water is restored.

Description

METHOD CF REACTIVATION OFA PASSIVE NO,, ADSORBER

TECHNICAL FIELD

The present disclosure relates to a method of reactivation of a Passive N0, Adsorber.

BACKGROUND

Internal combustion engines, in particular Diesel engines, are generally equipped with exhaust gas after-treatment systems in order to reduce pollution due to engine emissions.

Such after-treatment systems may comprise a plurality of aftertreatrnent devices located in the exhaust line, for degrading and/or removing pollutants from the exhaust gas before discharging it into the environment.

In greater details, a conventional aftertreatment system generally comprises a Diesel Oxidation Catalyst (DOC), for oxidizing hydrocarbon (HC) and carbon monoxides (00) into carbon dioxide (C02) and water (H20), and a Diesel Particulate Filter (DPF), located in the exhaust line downstream the DOC, for removing diesel particulate matter or soot from the exhaust gas.

Furthermore, downstream of the DPF, another after-treatment device, namely an SCR (Selective Catalytic Reduction) may be provided.

An 5CR (Selective Catalytic Reduction) is a catalytic device in which the nitrogen oxides (NO) contained in the exhaust gas are reduced into diatonic nitrogen (N2) and water (H20), with the aid of a gaseous reducing agent, typically ammonia (NH3) that can be obtained by urea (CH4N2O) thermo-hydrolysis and that is absorbed inside catalyst.

Typically, urea is injected in the exhaust line and mixed with the exhaust gas upstream the 5CR. Other fluids can be used in a an 5CR in lieu of urea and are generally referred to as Diesel Exhaust Fluids (DEF).

During use of the vehicle, the Electronic Control Unit that manages the automotive system may start periodic regenerations of the DPF. A DPF regeneration phase is performed by operating the engine in special combustion mode, through which a certain amount of fuel is discharged unburned from the engine cylinders into the exhaust line.

This may be realized, for example, by means of so-called fuel after-injections which are fuel injections in a cylinder of the engine that occur after the Top Dead Center (TDC) of the piston.

The unburned fuel injected by these fuel injections bums inside the DOC, thereby producing hot exhaust gas that heats the DPF. As the temperature of the DPF reaches about 600°C-700°C, the soot matter trapped inside the DPF is burned off.

A new generation of Diesel Oxidant Catalyst (DOC) is under development and is known as Passive NO Adsorber (PNA), which identifies a technology that is characterized by the following features.

These catalyst have a HG/CO conversion efficiency like a conventional Diesel Oxidation Catalyst (DOG).

They can store NO at low temperature and can release NO as a function of temperature increase to combine with the functions of the downstream SCR.

Furthermore they might have significant sulphur tolerance and long term durability.

The interest in this new technology is related to the possibility to improve the low temperature behavior in those aftertreatment systems that include an urea injection based SCR in the exhaust line.

In fact, these newly developed Diesel Oxidation Catalysts are capable to store NO at low exhaust temperatures (typical of urban driving conditions) when SCR efficiency is low (because it is not possible to inject urea), and to release the stored NO at higher temperatures (i.e. during extra-urban driving conditions) where the urea injected into the SCR is effectively forming ammonia for the subsequent NQconversion.

However, the differences in the coating, namely in the Platinum Group Metal (PGM) characteristics, of this new catalysts require a different management with respect to a standard diesel oxidant catalyst.

In particular, the standard regeneration of the Diesel Particulate Filter, namely the exposure of the coating and of the Platinum Group Metals (PGM) to high temperature in a lean combustion mode, might have a negative impact on the catalyst performances of the PNA because it will produce a oxidic PGM, thus reducing its catalytic activation.

More specifically the Platinum contained in the PNA catalyst may react with Oxygen forming Platinum Oxides Pt02, therefore reducing catalyst's performance.

The purpose of this invention is to propose a simple strategy to reactivate the performances of such catalysts after it has been exposed to the effects due to a Diesel Particulate Filter (DPF) regeneration.

Another object is to provide a reactivation strategy for new generation Passive NO Adsorber catalysts that may be implemented without using dedicated devices and by taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle.

Another object of the present disclosure is to meet these goals by means of a simple, rational and inexpensive solution, These objects are achieved by a method, by an engine, by an apparatus, by an automotive system, by a computer program and a computer program product, and by an electromagnetic signal having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the invention provides a method of reactivating a Passive NOx Adsorber in an exhaust line of an Internal Combustion Engine, the exhaust line comprising a Diesel Particulate Filter, the methpd comprising the steps of: -subjecting the Diesel Particulate Filter to a regeneration, -performing a rich combustion mode event alter the end of the Diesel Particulate Filter regeneration.

An advantage of this embodiment is that it can be applied to all catalysts involving Platinum and Rhodium as noble metals after an oxidic PGM has been generated due to specific combustion conditions such as, for example, exposure at high temperature conditions in lean mode which reduce catalytic activation.

Therefore it must be considered that also Lean NO Traps (LNT) or No storage catalysts in general may benefit from this strategy.

According to another embodiment of the invention, the step of performing a rich combustion mode is executed for a predetermined length of time.

A rich combustion mode may be defined as a combustion' in which the air to fuel ratio, expressed in terms of lambda namely the ratio of the actual air to fuel ratio to stoichiometric air to fuel ratio, is less than 1. In a lean combustion mode, on the contrary, lambda is greater than 1, An advantage of this embodiment is that by performing rich combustion mode events after a DPF regeneration, CO conversion efficiency of the Diesel Oxidant Catalyst improves and stabilizes, According to a further embodiment of the invention, the step of performing a rich combustion mode is repeated for a predetermined number of times.

An advantage of this embodiment is that by performing a number of rich combustion modes HC conversion efficiency of the Diesel Oxidant Catalyst improves and stabilizes.

According, to another embodiment of the invention, the rich combustion modes are performed using a predetermined lambda target.

According to another embodiment of the invention, the rich combustion event is performed by energizing a fuel injector in order to inject fuel after injections in a cylinder of the Internal Combustion Engine.

An advantage of this embodiment is that existing software used for managing LNT regeneration events can be adapted to perform this embodiment of the method.

Another embodiment of the invention provides an apparatus for reactivating a Passive NOx adsorber in an exhaust line of an Internal Combustion Engine, the exhaust line comprising a Diesel Particulate Filter, the apparatus comprising: -means for subjecting the Diesel Particulate Filter to a regeneration, -means for performing a rich combustion mode event after the end of the Diesel Particulate Filter regeneration.

Another embodiment of the invention provides an automotive system having a Passive NOx Adsorber in an exhaust line of an Internal Combustion Engine, the exhaust line comprising a Diesel Particulate Filter, the automotive system being managed by an electronic control unit configured to: -subject the Diesel Particulate Filter to a regeneration, -perform a rich combustion mode event after the end of the Diesel Particulate Filter regeneration.

These last two embodiments have substantially the same advantages of the various embodiments of the method of the invention.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program product can be embodied as a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier 30, associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, wherein like numerals denote like elements, and in which: Figure 1 shows an automotive system; Figure 2 is a cross-section of an intemal combustion engine belonging to the automotive system of figure 1; Figure 3 represents schematically a portion of an aftertreatment system of the automotive system of figures 1-2; Figure 4 is a schematic representation of some steps that can be employed in an embodiment of the method of the invention; Figure 5 is a flowchart representing an embodiment of the method of the invention.

DETAILED DESCRIPTION

Exemplary embodiments will now be described with reference to the enclosed drawings without intent to limit application and uses.

Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to defjne a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190. Each of the cylinders has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

* The air may be distributed to the air intake port(s) 210 through an intake manifold 200. An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

*The exhaust system 270 may include an exhaust line 275 having one or more exhaust aftertreatment devices. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean N10 traps, hydrocarbon adsorbers, selective catalytic reduction (3CR) systems, and particulate filters.

More specifically, as also better detailed in Figure 3, the exhaust line 275 is equipped with a Passive NO Adsorber (PNA) 280, for oxidizing hydrocarbon (HC) and carbon monoxides (CO) into carbon dioxide (002) and water (H20), and a Diesel Particulate Filter (DPF) 285, located in the exhaust line downstream the Passive NO Adsorber 280, for removing diesel particulate matter or soot from the exhaust gas.

Furthermore, downstream of the DPF 285, a 5CR Selective Catalytic Reduction device (SCR) 287 is provided.

Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110.

The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and 13 the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system, or data carrier46o, and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carry out the steps of such methods and control the ICE 110.

More specifically, Figure 3 shows a schematic illustration of a portion of an aftertreatment system of the automotive system of figures 1-2.

As seen in Fig. 3, the exhaust line 275 of the Internal Combustion engine 110 is equipped with a Passive NO Adsorber (PNA) 280, and with a Diesel Particulate Filter (DPF) 285, located in the exhaust line downstream the PNA 280. Furthermore, downstream of the DPF 285, a 5CR Selective Catalytic Reduction device (SCR) 287 is provided.

The SCR catalyst 287 can be fed with a Diesel Exhaust Fluid (DEF), for example urea, that is stored in a DEF tank 720, in order to reduce the nitrogen oxides (NOr) contained in the exhaust into diatonic nitrogen (N2) and water (Fl20). The DEF is provided to a DEF injector 700 by means of a DEF pump 710 that receives the DEF from the DEF tank 720. The DEF injector 700 can be controlled by the ECU 450 of the automotive system 100.

A lambda sensor 500, also known as Universal Exhaust Gas Oxygen (UEGO) sensor, and a temperature sensor 510 are provided upstream of PNA 280. Moreover, a lambda sensor 520 and a temperature sensor 530 are provided downstream of PNA. All these sensors are connected to the ECU 450.

Figure 4 is a schematic representation of some steps that can be employed in an embodiment of the method of the invention.

In particular, according to the various embodiments of the invention, after the end of a Diesel Particulate Filter 285 regeneration1 one or more rich combustion mode events are performed, each event being performed for a predetermined length of time, ln.order to perform a rich combustion event, a possibility is to inject so-called fuel after injections into one or more of the cylinders 125 of the engine 110 by means of the corresponding fuel injectors 160. As is known, fuel after injections are performed after the Top Dead Center (TOC) of the corresponding piston 140 and leave a portion of the injected fuel unburned.

This portion of fuel bums in the exhaust line, raising the temperatures thereof.

The timing of the fuel after injections and the energizing times of the injectors 160 may be calculated by the ECU 450 accordingly.

Figure 5 is a flowchart representing an embodiment of the method of the invention.

In the illustrated embodiment, until a DPF regeneration is not active, no operations of the method are performed (block 600). If a DPF regeneration is active, namely if the ECU 450 that manages the Intemal Combustion Engine enables the DPF regeneration activation criteria, a DPF regeneration is performed (block 610).

The DPF regeneration is then continued until it is completed (block 620) and then engine is operated in a normal mode of operation (block 630), namely in a mode that does not entail a DPF regeneration.

After a calibratable amount of time (block 640), a rich combustion mode event of the internalcombustion engine is performed for a predetermined length of time (block 650), for example by employing after injections.

The predetermined length of time of the rich combustion mode event can be calibrated for the specific automotive system.

Finally, a check (block 660) is made to determine if other rich combustion mode event should be performed according a calibrated number of rich events and, in the affirmative, another rich combustion mode event is performed. In the negative, the procedure is ended.

The number of times that the step of performing a rich combustion mode event is repeated can be calibrated for the specific automotive system and in particular taking into account the specific Passive NOAdsorberto be regenerated.

Furthermore, the rich combustion mode events are performed using a predetermined air to fuel ratio, or lambda, target.

The lambda target can also be calibrated for the specific automotive system and in particular taking into account the specific Passive NO Adsorber to be regenerated.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

automotive system internal combustion engine (ICE) engine block 125 cylinder cylinder head camshaft piston crankshaft 150 combustion chamber cam phaser fuel injector fuel rail fuel pump 190 fuel source intake manifold 205 air intake duct 210 intake air port 215 valves of the cylinder 220 exhaust gas port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 intercooler 270 exhaust system 275 exhaust line 280 Passive NOx Adsorber (PNA) 285 DPF 287 SCR 290 VGT actuator 300 EGR system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensor 445 accelerator pedal position sensor 450 electronic control unit (ECU) 460 data carrier 500 lambda sensor upstream of PNA 510 temperature sensor upstream of PNA 520 lambda sensor downstream of PNA 530 temperature sensor downstream of PNA 600 block 610 block 620 block 630 block 640 block 650 block 660 block 11*

Claims

CLAIMSl.A method of reactivating a Passive NO Adsorber (280) in an exhaust line (275) of an Internal Combustion Engine (110), the exhaust line (275) comprising a Diesel Particulate Filter (285), the method comprising the steps of: -subjecting the Diesel Particulate Filter (285) to a regeneration, -performing a rich combustion mode event after the end of the Diesel Particulate Filter (285) regeneration.
2. A method according to claim 1, in which the rich combustion mode event lasts for a predetermined length of time.
3. A method according to claim 1 or 2, in which the step of performing a rich combustion mode event is repeated for a predetermined number of times after the end of the Diesel Particulate Filter (285) regeneration.
4. A method according to any of the preceding claims, in which the rich combustion mode events are performed using a predetermined lambda target.
5. A method according to claim 1, in which.the rich combustion event is performed by energizing a fuel injector (160) in order to inject fuel after injections in a cylinder (125) of the Internal Combustion Engine (110).
6. An Internal Combustion Engine (110), in particular a Diesel engine, the Internal Combustion Engine (110), in an exhaust line (275) thereof, being equipped with a Passive NOAdsorber (280) and a Diesel Particulate Filter (285), the engine (110) being managed by an Electronic Control Unit (ECU) configured for carrying out the method according to any of the preceding claims.
7. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-5.
8. Computer program product on which the computer program according to claim 7 is stored.
9. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (460) associated to the Electronic Control Unit (450) and a computer program according to claim 7 stored in the data carrier (460).
10. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 7.