GB2508802A

GB2508802A - Estimating sulphur release in desulphation process of NOx trap

Info

Publication number: GB2508802A
Application number: GB1219093.0A
Authority: GB
Inventors: Roberto Argolini; Andrea Dutto; Angela Vitiello; Sergio Valguarnera
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-10-24
Filing date: 2012-10-24
Publication date: 2014-06-18
Also published as: GB201219093D0; CN103775181A

Abstract

A method of estimating the sulphur release during a desulphation process of a lean NOx trap based on a space velocity 10, a catalyst temperature 11, an air/fuel ratio 12 and a DeSOx rich time duration 13. A plurality of regression coefficients 21 are provided, a line segment 23 is modelled, and a sulphur release quantity 26 is calculated in percentage. The line segment may be obtained by a linear interpolation between a sulphur release model at a time point i, and a sulphur release model at a time point i+1. The method may be repeated twice for a fresh lean NOx trap and for an aged lean NOx trap. The method may include interpolating a sulphur release quantity in percentage for a fresh lean NOx trap and for an aged lean NOx trap using a callibratable ageing factor, thus providing a sulphur release quantity in percentage, also determined by the lean NOx trap ageing status.

Description

METHOD OF ESTIMATING DESULPHATION FROM A LEAN NOx TRAP

CF AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of estimating the desuiphation from a Lean NOx Trap (LNT) of an internal combustion engine. In particular, the method estimates the sulphur release during the regeneration (DeSOx) of the LNT, located in the exhaust system of the internal combustion engine.

BACKGROUND

It is known that the exhaust gas after-treatment systems of a Diesel engine can be provided, among other devices, with a Lean NO Trap (hereafter1 also LNT).

A LNT is provided for trapping nitrogen oxides NO contained in the exhaust gas and is located in the exhaust line.

A LNT is a catalytic device containing catalysts, such as Rhodium, Platinum and Palladium, and adsorbents, such as barium based elements, which provide active sites suitable for binding the nitrogen oxides (NOr) contained in the exhaust gas, in order to trap them within the device itself.

Lean NO Traps are subjected to periodic regeneration processes, whereby such regeneration processes are generally provided to release and reduce the trapped nitrogen oxides (NOr) from the LNT.

S The LNT are operated cyclically, for example by switching the engine from lean-bum operation to operation whereby an excess amount of fuel is available referred also as rich operation or regeneration phase. During normal operation of the engine, the NO are stored on a catalytic surface. When the engine is switched to rich operation, the NO stored on the adsorbent site react with the reductants in the exhaust gas and are desorbed and converted to nitrogen and ammonia, thereby regenerating the adsorbent site of the catalyst.

Due to the presence of suplhur into the fuel, the LNT is exposed to the sulphur poisoning, which heavily reduces the NOx storage capacity of the catalyst. In order to re-enable the capability of the after-treatment system, a desulphation (also called DeSOx regeneration or simply DeSOx) is needed. The DeSOx consists in a fast alternation of lean and rich atmosphere (hereafter, wobbling) at high temperature during engine The sulphur stored into the LNT is removed only during the rich eventh, but the problem is that sulphur release during DeSOx regeneration is influenced not only by rich time duration but even by working conditions.

Therefore a need exists for the estimation of the sulphur release during the regeneration process of the lean NOx trap, in order to optimize the desulphation process in term of duration and frequency.

An object of this invention is to provide a method that defines a physical model of sulphur release, taking into account the most influent parameters. This model can really predict and consequently optimize the desulphation process and will be a useful information to estimate the residual sulphur content in the Diesel Particulate Filter (DPE).

Another object is to provide a controller device which allows to per-form the above method.

These objects are achieved by a method, by a controller device, by an engine, by a computer program and computer program product, and by an electromagnetic signal having the features recited in the independent claims.

The dependent claims delineate preferred andlor especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of estimating the sulphur release during a desulphation process of a lean NOx trap, on the basis of a space velocity, a catalyst temperature, an air/fuel ratio and a DeSOx rich time duration, comprising the steps of providing a plurality of regression coefficients, modeling a line segment and calculating (2400) a sulphur released quantity in percentage.

Consequently a controller device is disclosed for estimating the sulphur release during a desulphation process of a lean NOx trap, on the basis of a space velocity, a catalyst temperature, an air/fuel ratio and a DeSOx rich time duration, comprising a block for providing a plurality of regression coefficients, a block for modeling a line segment and a block for calculating a sulphur released quantity in percentage.

An advantage of this embodiment is that it provides a method of estimating the sulphur release during the regeneration process of the lean NOx trap, by a physical model which takes into account the most influent parameters, such as catalyst temperature, air/fuel ratio, space velocity and, of course, rich time duration. Therefore this method optimizes the desulphation process in term of duration and frequency.

According to an aspect of the invention, said regression coefficients are provided at a generic time point i as function of a predetermined sulphur release quantity in percentage and corresponding space velocity, catalyst temperature and air/fuel ratio, according to the a regression function.

According to another aspect, said line segment is obtained by a linear interpolation between a sulphur release model at time point i and a sulphur release model at time point il-i.

An advantage of these aspects is that the method for estimating the sulphur release quantity can be built up by using experimental results and the Design of Experiment technique.

According to a further embodiment of the invention, said method is repeated twice for a fresh Lean NOx Trap and for an aged Lean NOx Trap and, it further comprises the step of interpolating a sulphur released quantity in percentage for a fresh Lean NOx Trap and a sulphur released quantity in percentage for an aged Lean NOx Trap by means of a calibratable ageing factor, thus providing a sulphur released quantity in percentage, also determined by the Lean NOx Trap ageing status.

An advantage of this embodiment is that it provides an estimation of the sulphur released percentage of a Lean NOx Trap, also taking into account the ageing status of the catalyst.

to According to a further embodiment, said sulphur released quantity in percentage is multiplied per a sulphur stored quantity, thus obtaining a sulphur released quantity.

An advantage of this embodiment is that whenever a sulphur stored quantity is avaiLable, for example calculated by existing physical models, a sulphur released quantity can be easily obtained.

According to a still further embodiment, said space velocity, catalyst temperature and air/fuel ratio are averaged, with respect to DeSOx rich time duration, and normalized in a range (-1, 1).

An advantage of this embodiment is that the working conditions (space velocity, catalyst temperature, air/fuel ratio), which represent the input variables for the present method, can be averaged and normalized in a range (-1, 1), which is more easily managed by available computation programs.

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 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 outthe method claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 shows an automotive system.

Figure 2 is a section of an internal combustion engine belongirtgto the automotive system of figure 1.

Figure 3 is a schematic view of the alter-treatment system according to the invention.

Figure 4 is a scheme of the DeSOx regeneration phases.

Figure 5 is a graph depicting how sulphur released quantities are calculated.

Figure 6 is a flowchart of the whole method for estimating the sulphur release quantity according to the present invention.

Figure 7 is a block diagram of a controller device for estimating the sulphur release quantity according to the method of Fig. 6.

Figure 8 is a block diagram of a controller device for estimating the sulphur release quantity according to the method of Fig, 6, which also takes in account the ageing status of the catalyst.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 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 define 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 a fuel source 190. Each of the cylinders 125 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 pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts1 lean NOx traps 281, hydrocarbon adsorbers, selective catalytic reduction (5CR) systems 282. particulate filters (OFF) or a combination of the last two devices, i.e. selective catalytic reduction system comprising a particulate fitter (SCRF) 283. Other embodiments may include an exhaust gas recircutation (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 andlor devices associated with the ICE 110 and equipped with a data canler 40. 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 cit 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 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 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 carryout out the steps of such methods and control the ICE 110.

Turning back to exhaust system 270, the proposed invention relies on the optimization of the DeSOx lean time minimum duration for a Lean NOx Trap 281. Fig. 3 shows the scheme of the aftertreatment system 280 which, advantageously could also comprise a particulate fitter (DPF) 282 to trap particulate emitted in case of a Diesel engine.

Upstream and downstream the LNT, air/fuel ratio sensors 283, 284 and temperature sensors 285, 286 can be provided.

Preferably, the LNT catalyst could be positioned as close as possible to the exit of the turbocharger to take advantage of the high temperature conditions which are beneficial for it.

The LNT reduces engine-out exhaust gas constituents (CO and HG) with high efficiency and stores NOx during lean operating conditions. During rich operating conditions, the NOx is released and converted. The LNT works properly thanks to presence in the catalyst of barium and aluminum that define its NOx storage capacity during the diesel engine lean operation.

However, due to the presence of suplhur into the fuel, the LNT is exposed to the sulphur poisoning, which heavily reduces the NOx storage capacity of the catalyst. The sulphur contained in the fuel is easily oxidized in lean atmosphere: it is stored as barium and aluminum sulphates, which are more stable compounds than the corresponding nitrates.

This process reduces the efficiency of the Trap in terms of NOx Storage: this efficiency can be restored through a desulphation process, that requires high temperature and rich atmosphere. In particular, it consists in a fast alternation of lean and rich atmosphere at high temperature during engine working condition.

The DeSOx regeneration is defined as the process which leads to the desulphation of the Lean NOx Trap. It is critical from the point of view of thermal degradation of the trap, because of the requested high temperature. It is penalizing in terms of fuel consumption as well, because of the additional injected fuel needed to provide a rich atmosphere at the inlet of the Trap. The DeSOx regeneration is based on the "wobbling" concept, shown in Fig. 4, that is to say, an alternation of lean 510 and rich 520 phases at high temperature 500. The DeSOx rich phase is needed to destabilize the chemical links between the sulphur and the barium and/or aluminium, making the barium/aluminium sites free for the NOx and restoring the NOx trapping capability of the LNT. The DeSOx lean phase is used to maintain a stable and high temperature, to restore the oxygen content in the trap and to bum the HC cumulated in the trap during the rich phase.

The effective sulphur removal occurs in the rich phase and the released quantity is a function of the sulphur already present in the trap. As easily understandable the higher is the time spent in rich atmosphere during the DeSOx, the higher is the efficiency of the regeneration. The problem is that sulphur release, during DeSOx regeneration, is influenced not only by rich time duration but even by engine working conditions.

Therefore, the present invention defines a physical model of sulphur release, taking into account the most influent parameters. This model can be coupled to existing sulphur storage models to really predict and consequently optimize the desuiphation process in term of duration and frequency.

To build up the model according to the invention, a preliminary analysis has been carried out, aimed to the identification of parameters influencing the sulphur release. As is influencing parameters have been considered the time duration in rich combustion mode, the airlfuel ratio upstream the LNT, the catalyst temperature and the exhaust flow rate.

A structured test plan has been set up through the known technique of Design of Experiments (DOE). The test has been executed in fifteen different points. Of course, the choice of these points is arbitrary, since the DOE technique is not remarkably influenced by the number of levels and by the specific values, which are adopted. In such points, the independent parameters has been chosen as follows: * 3 levels of catalyst temperature (Tern): 620°C -650°C -680°C * 2 levels of air/flow ratio upstream the LNT (Lam): 0.9-0.95 * 3 levels of exhaust flow rate (FR): 50 Kg/h-SO Kg/h -120 KgIh * As reference point (repeated three times) has been chosen: TemGSO°C, Lam 0.925, FR 80 Kg/h.

The measurements have been carried out as function of the number of rich events.

More in detail, the number of rich events is calculated by fixing the single rich time duration (for example, 15 s), the whole regeneration duration (e.g., 600 s) and the single lean time duration (for instance, 12 s). Considering the wobbling lean/rich, the number of rich events can be easily established.

The obtained results have been used to study the relationship between the independent (Tern, Lam, FR) and the response variable (sulphur release, Sris) through a regression model. More in detail, the following analysis have been performed: air/fuel ratio variation at fixed temperature values and exhaust flow rate to catch the qualitative impact of decrease/increase in air/fuel ratio: exhaust flow variation at fixed temperature values and air/fuel ratio values to catch the qualitative impact of decrease/increase in exhaust flow; temperature variation at fixed air/fuel ratio values and exhaust flow rate to catch the qualitative impact of decrease/increase in temperature. Considering the obtained results,

the following conclusions arise:

-the lower is the air/fuel ratio value, the higher is the sulphur release -the higher is the exhaust flowrate value, the higher is the sulphur release -the higher is the temperature value, the higher is the sulphur release, without a strong impact at high temperature.

Being the behavior of the sulphur release vs. the independent variables not linear, the idea behind the invention is to model the sulphur released percentage with line segment curves, function of rich time duration, air/fuel ratio upstream the LNT, catalyst temperature and exhaust flow rate. The sulphur released percentage (S115%) is related to a sulphur storage quantity in the LNT, which is supposed to be available by known models. The exhaust flowrate has been expressed in terms of space velocity (SV). The space velocity (dimensionally [5.11) inside the LNT is calculated as the ratio between the exhaust mass flow upstream LNT, the density and the LNT volume. The density is calculated as the ratio between the LNT pressure (average of pressure between LNT upstream pressure and LNT downstream pressure) and the product between LNT main temperature (average temperature between LNT upstream temperature and LNT downstream temperature) and the ideal gas constant.

With reference to Fig. 5, the line segment curves are obtained starting from the sulphur released profile in rich time, and dividing it into time points (time point 0, time point 1, time point 2 time point n, as shown in Fig. 5. Then, the model of the sulphur release at the generic time point i has been determined as function of air/fuel ratio upstream LNT (Lam), catalyst temperature (Tem) and space velocity (SV) according to a regression function: = a1 *5V2 + a2 Lam2 + a3Tem2 +a4 SVTem+a5 LantTem+a6 Larn'SV+a7 SV + a9 Tern + ag Larn + a19 where, apart the already defined variables: al, a2,...alO are the regression coefficients Having modeled the generic time point i, it is possible to build up a linear interpolation between two models: the model at time point i and the model at time point i+1 to obtain the line segment curve in function of rich time duration. Finally, as first time point it is possible to use the one corresponding to zero sulphur release. It can be modeled as regression function, as well: Offset = xl 6V2 + x2'Tem2 + x3LamSV + x4LamTem + x5Larn + x6"Tem + x7 where: Offset: time point at approximately zero sulphur release, better, as explained hereafter, time point in which the sulphur release does not overcome 2%, xl, x2,...,x7: regression coefficients The model has been obtained according to the following hypothesis: sulphur release does not depend on sulphur loading, therefore sulphur release can be calculated as a io percentage of the initial loading at the beginning of rich event; sulphur release does not depend on regeneration history but sulphur release depends on current rich time duration; the time point Offset' is the rich time duration in which sulphur release percentage could be approximated with 0. It is evaluated as the rich time in which sulphur released does not overcome 2%; the Offset' is modeled in function of air/fuel ratio upstream LNTI catalyst temperature and exhaust space velocity, as well; sulphur released quantity is calculated at the end of the DeSOx Rich event as a percentage of sulphur stored quantity.

As practical example, always with reference to Fig. 5, two line segment curves 1, 2 have been represented, having the same offset value and respectively a tern Lami, Teml, SV1 and Lam2, Tem2, SV2. It is to be understood that, according to the present method, a plurality of line segment curves can be built up, indifferently with same or different offset values. To simplify the comprehension, in Fig. 5 only two line segment curves have been shown. According to air/fuel ratio, temperature and space velocity values, the sulphur released percentage moves from curve I to curve 2 and vice versa. When calculating a specific sulphur released percentage, the following cases could happen.

First case, the point 3 lies over a line segment curve in correspondence of a time point (n in the example): this is a trivial case since the model has been built on such points and therefore the value of S% is already available. Second case, the point 4 lies in between curve I and 2 but corresponding to a time point the sulphur released percentage will be available, as in the previous case, by the model of the time point, time point 2 in the example. Third case: the point 5 lies in between curve 1 and 2 but does not correspond to a time point: in this case, following the example in Fig. 5, an interpolation will be done, between the models at the time point 2 and the time point 3.

Fig. 6 shows a complete flowchart of the above method, which can be summarized as follows. The method estimates the sulphur release quantity during a desulphation process of a lean NOx trap 281 taking into account 2000 the duration of the rich combustion phase 13 to be analyzed and the working conditions, that is to say space velocity 10, catalyst temperature 11, air/fuel ratio 12. Then, based on the working conditions, the regression coefficients to build up the line segment curves are provided 2200 and a line segment is modeled 2300. Finally the sulphur release quantity in percentage is calculated 2400.

Consequently, in Fig. 7 a block diagram of a controller device for estimating the sulphur release quantity is shown. The controller device comprises a block 22 for providing a plurality of regression coefficients, a block 23 for modeling a line segment and a block 24 for calculating a sulphur released quantity in percentage. Block 22 provided the regression coefficients at a generic time point i as function of a predetermined sulphur release quantity in percentage and corresponding space velocity, catalyst temperature and air/fuel ratio, by using the already defined regression function, while block 23 models said line segment by a linear interpolation between a sulphur release model at time point i and a sulphur release model at time point i+1.

According to another embodiment, which also takes into account the ageing status of the catalyst, two dedicated structures for a fresh and for an aged catalyst have been setup.

The logic and the algorithms are exactly the same, as shown in Fig. 6, while the controlled device is shown in Fig. 8. The controller device comprises a block 22 for providing a first plurality of regression coefficients of an aged catalyst and a block 22' for providing a second plurality of regression coefficients of a new catalyst. As well, the controller devices comprises a block 23 for modeling a line segment of an aged catalyst and a block 23' for modeling a line segment of a new catalyst. The output of such structures will be a sulphur released percentage for a fresh LNT 281 and a sulphur released percentage for an aged LNT 281'. These two values will be interpolated 2500, i.e. entered in suitable means for interpolating 25. The interpolation will be performed by means of a calibratable ageing factor and will provide a sulphur released percentage, also determined by the catalyst ageing status. According to a preferred embodiment, the interpolation is a linear interpolation, according to the following scheme: = SdS% Fresh x (1 -Ageing factor) + Sds% Aged x Ageing factor where the ageing factor runs from 0 (new catalyst) to 1 (aged catalyst).

It is to be understood that, whenever a sulphur stored quantity is available, for example calculated by existing physical models, a sulphur released quantity can be obtained multiplying 2600 sulphur released quantity in percentage per sulphur stored quantity 14.

It is to be understood, that the controller device will comprise means for multiplying 26 the above quantities.

Advantageously1 the working conditions (space velocity, catalyst temperature, airlfuel ratio), which represent the input variables for the present method, can be averaged and normalized 2100 in a range (-1, 1), which is more easily managed by available computation programs. Consequently, the controlled device will comprise means for averaging and normalizing 21.

Summarizing, the described method, by estimating the sulphur release during the desulphation process contributes to improve the LNT management thanks to a more efficient regeneration in terms of performances, fuel consumption and ageing.

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

1, 2 line segment curves 3 4 5 sulphur release calculated points block 11 block 12 block 13 block 14 block block 21 block 22, 22' blocks 23, 23' blocks 24, 24' blocks block 26 block data carrier automotive system internal combustion engine 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 pipe 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 281 lean NOx trap (LNT) 282 diesel particulate filter (DPF) 263 LNT upstream air/fuel ratio sensor 284 LNT downstream air/fuel ratio sensor 285 LNT upstream temperature sensor 286 LNT downstream temperature sensor 290 VOT actuator 300 exhaust gas recirculation 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 temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 500 Exhausttemperature 510 Combustion mode, lean phase 520 Combustion mode, rich phase 2000 block 2100 block 2200 block 2300 block 2400 block 2500 block Tern Catalyst temperature Lam Air/fuel ratio upstream the [NT FR Exhaust gas flowrate SV Exhaust gas space velocity Sris Sulphur released quantity SrIs% Sulphur released percentage S Sulphur stored quantity

Claims

CLAIMS1. Method of estimating the sulphur release during a desulphatiOn process of a lean NOx trap (281), on the basis of a space velocity (10), a catalyst temperature (11), an air/fuel ratio (12) and a DeSOx rich time duration (13), comprising the steps of providing (2200) a plurality of regression coefficients modeling (2300) a line segment and calculating (2400) a sulphur released quantity in percentage.
2. Method according to claim 1, wherein said regression coefficients are provided at a generic time point i as function of a predetermined sulphur release quantity in percentage and corresponding space velocity, catalyst temperature and air/fuel ratio, according to the following regression function Sr(s% a1 SV2+ a2'Larn2 + a3-Tem2 -1-a4 SVTem+a5 -Larn'Tern+a5 LanvSV+a7 SV + a0 Tern + a9 Lam + a10 wherein SV is the space velocity, Tern is the catalyst temperature. Lam is the air/fuel ratio and al, a2,...alO are the regression coefficients.
3. Method according to claim I or 2, wherein said line segment is obtained by a linear interpolation between a sulphur release model at time point i and a sulphur release model at time point +1 -
4. Method according to one of the previous claims, wherein said method is repeated twice fora fresh Lean NOx Trap (281) and for an aged Lean NOx Trap (281') and, it further comprises the step of interpolating (2500) a sulphur released quantity in percentage for a fresh Lean Wax Trap (281) and a sulphur released quantity in percentage for an aged Lean NOx Trap (281') by means of a calibratable ageing factor (15), thus providing a sulphur released quantity in percentage, also determined by the Lean NOx Trap ageing status.
5. Method according to one of the previous claims, wherein said sulphur released quantity in percentage is multiplied (2600) per a sulphur stored quantity (14), thus obtaining a sulphur released quantity.
6. Method according to one of the previous claims, wherein said space velocity, catalyst temperature and air/fuel ratio are averaged, with respect to DeSOx rich time duration, and noimalized (2100) in a range (-1, 1)
7. Controller device for estimating the sulphur release during a desulphation process of a lean NOx trap (281), on the basis of a space velocity (10), a catalyst temperature (11), an air/fuel ratio (12) and a DeSOx rich time duration (13), comprising a block (22) for providing a plurality of regression coefficients, a block (23) for modeling a line segment and a block (24) for calculating a sulphur released quantity in percentage.
8. Controller device according to claim 7, wherein block (22) provides said regression coefficients at a generic time point i as function of a predetermined sulphur release quantity in percentage and corresponding space velocity, catalyst temperature and air/fuel ratio, according to the following regression function 5rls%1 = a1 SV2 + a2 Lam2 + a3 *Tcnt2 +a4 SVTern+a5 LamTem+a6 LantSV+a7 SV+apTem+a9Lam+aio wherein SV is the space velocity, Tern is the catalyst temperature, Lam is the air/fuel ratio and al, a2,...alO are the regression coefficients.
9. Controller device according to claim 7 or 8, wherein block (23) models said line S segment by a linear interpolation between a sulphur release model at time point i and a sulphur release model at time point i+1 -
10. Controller device according to one of the claims from 7 to 9, wherein it further comprises a block (25) for interpolating a sulphur released quantity in percentage for a fresh Lean NOx Trap (281) and a sulphur released quantity in percentage for an aged Lean NOx Trap (281') by means of a calibratable ageing factor (15), thus providing a sulphur released quantity in percentage, also determined by the Lean NOx Trap ageing status.
11. Internal combustion engine (110) of an automotive system (100) equipped with an exhaust system (270), comprising at least an aftertreatment device (280), the after-treatment device being a lean WOx trap (281), said exhaust system also comprising at least an air/fuel ratio sensor (283, 284) and at least a temperature sensor (285, 286), the automotive system (100) comprising an electronic control unit (450) configured for carrying out the method according to claims 1-6.
12. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-6.
13. Computer program product on which the computer program according to claim 12 is stored.
14. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim 12 stored in the data carrier (40).
15. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 12.