GB2497293A - Operation of a Fuel Injection System for an Internal Combustion Engine - Google Patents

Abstract

Operating an Internal Combustion Engine 110, comprising a cylinder 125 and a fuel injector 160, comprising, performing first and second fuel injections (preferably pilot injections) with a predetermined energizing time to inject first and second fuel quantities into the cylinder 125 that are substantially equal to each other, determining an oxygen quantity value due to the first and the second fuel injections, and determining, on the basis of the oxygen quantity value a value for total fuel quantity injected. Also determining a calculated fuel quantity dividing the total fuel quantity injected by two, determining a correction factor of the energizing time of the injector as a function of the difference between the calculated fuel quantity and a nominal fuel quantity value, and using the correction factor to determine a corrected energizing time to perform subsequent fuel injections. The invention overcomes the inaccuracy problems of the currently available strategies for adjusting pilot injections based on crank wheel information or oxygen sensors.

Description

METHOD FOR OPERATING.AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method for operating an Internal Combustion Engine.

BACKGROUND

Internal combustion engines are provided with cylinders, each one having a piston coupled to rotate a crankshaft. A fuel and air mixture is injected into a combustion chamber of each cylinder and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston, the fuel being provided by injectors which in turn receive fuel at high pressure from a fuel common rail that is in fluid communication with a high pressure fuel pump.

Internal combustion engine are also generally equipped with an Electronic Control Unit (ECU) to manage various parameters of the engine and to activate the fuel injectors.

In order to improve the exhaust emissions and reduce combustion noise in engines, particularly Diesel engines having a common-rail fuel injection system, a so-called multiple fuel injection pattern is adopted, according to which the fuel quantity to be injected in each cylinder at each engine cycle is splitted into a plurality of injections Thus, a typical multiple injection pattern may include preliminary injections, also known as pilot injections, which may be in turn splitted into two or more injection pulses, followed by one or more main injection pulses, followed by a number of after and post injection pulses.

Pilot injections are injections of a small amount of fuel that are performed before a main injection event and that do not normally produce torque, but are used for various reasons such as reducing explosiveness of the main injection, reducing vibration, as well as optimising fuel consumption.

Th&pilot injéctibn pUlses duration or energizing time (ET) Is generally-mapped in-a memory of the Electronic Control Unit. The mapped values of the energizing time are predetermined with reference to an injection system having nominal characteristics, i.e. components having no drifts.

However, the fuel quantity which is actually injected by an injector into the corresponding engine cylinder is inevitably affected by drifts, with respect to the desired or nominal value and this fact, during the vehicle lifetime, causes an increase of the combustion noise and a worsening of exhaust emission characteristics.

Specific problems that affect pilot injection are the following.

If the pilot injection inject a too small fuel quantity actually injected with respect to a nominal quantity, an engine noise increase is generated.

On the contrary, if pilot injection injects a too big fuel quantity with respect to a nominal quantity, a Particulate Material emission increase occurs.

If a pilot injection misfires, besides the noise increase that inevitably occurs, also NO emissions are negatively affected.

Therefore fuel compensation strategies are used to correct the injected fuel quantity in a combustion engine during injector lifetime to periodically adjusts the injector energiz!ng time in order to have repetitive performance and increased accuracy in the fuel injected quantity along the life of the injector.

Also, pilot injections are in the range of a strong non-linearity of the injector performance and therefore more in need of being subjected to a compensation strategy.

To correct the fuel injected quantity, an injector energizing time strategy runs during engine overruns, for example when the automotive vehicle's driver releases the pressure on the accelerator pedal.

A known correction method is performed during these overruns, wherein the Electronic Control Unit of the engine commands a calibratable pilot test injection (e.g. 1 mm3 of fuel) in one of the cylinder of the engine, while the other injectors are de-energized.

The injected fuel quantity is proportional to the crankshaft acceleration, and known injector energizing time correction strategies processes crankshaft timing in order to obtain a signal that is proportional to the acceleration and so to the injected quantity.

A crank wheel study strategy such as the one above has certain limits, first of all it is quite sensitive to non-systematic disturbances like the roughness of the road and electrical loads.

Furthermore the accuracy of a crank wheel study strategy is reduced by the noise introduced by some actuators, such as when brakes are strongly pressed, or an automatic transmission clutch slipping occurs and in very high engine speed conditions.

In some countries where rough roads are frequent or in general when the Pilot Quantity Adjustment strategies based on crank wheel study cannot be effectively performed, an alternative is to perform the same task by an Oxygen sensor strategy.

With these strategies, the fuel quantity introduced in a cylinder is estimated by measuring an Oxygen value in the exhaust gasses as a result of the combustion of the fuel in the cylinder. The Oxygen value may be measured by a lambda sensor or by a NC sensor, both sensors being generally present in the exhaust line of the engine.

The main problem of a Pilot Injection adjustment strategy performed by using Oxygen values from a corresponding sensor is a matter of accuracy.

In fact, during the pilot correction learning, if the two strategies, namely Pilot injection adjustment performed by clank sensor number and Pilot Injection adjustment performed by Oxygen sensor, use the same of fuel pulses, it happens that the strategy of Pilot Injection adjustment performed by Oxygen sensor will have a worse accuracy.

In particular, the Pilot Injection adjustment strategy performed by Oxygen sensor may have a bad signal to noise ratio because the quantity injected in a single pilot injection is generally too small.

An object of an embodiment of the invention is to overcome the problems of the prior art by providing a method of operating an engine that allows to perform adjustment of the pilot injections without using the crank wheel information, therefore providing a viable alternative to that method Another object is to perform a pilot injection adjustment overcoming the bad signal to noise ratio of the Oxygen sensor.

Another object is to perform a pilot injection adjustment without using complex 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 for operating an Internal Combustion Engine, comprising an engine block defining a cylinder and a fuel injector suitable to inject fuel inside the cylinder, the engine being equipped with an exhaust line, the method comprisuig the steps of: -performing a first fuel injection using a predetermined energizing time to inject a first fuel quantity into the cylinder; -performing a second fuel injection using a predetermined modified energizing time that takes into account the effects of the first fuel injection in order to inject a second fuel quantity into the cylinder that is substantially equal to the first fuel quantity injected by the first fuel injection; -determining an Oxygen quantity value due to the combined effect of the first and the second fuel injection; -determining, on the basis of the Oxygen quantity value, a value of a total injected fuel quantity by the combination of the first and the second fuel injection; -determining a correction factor of the energizing time of the injector as a function of the difference between the determined value of the total injected fuel quantity and a preset nominal value thereof; and -using the correction factor to determine a corrected energizing time for subsequent fuel injections.

An advantage of this embodiment is that it can be performed in all situations in which a crank wheel adjustment method would not be accurate, such as in the cases of clutch slipping, brake strongly pressed or a too noisy road.

Furthermore this embodiment allows to perform a Pilot Injection Adjustment at very high engine speed.

This results in improved customer satisfaction, in emission and noise reduction that occurs also in the first kilometers of the vehicle lifetime and in non-standard roads.

According to another embodiment of the invention, the engine comprises a fuel rail and wherein the predetermined modified energizing time of the second fuel injection is determined by taking into account a fuel rail pressure disturbance value due to the first fuel injection.

An advantage of this embodiment is that it identifies and corrects one of the main causes of inaccuracy in the second injection fuel quantity.

According to another embodiment of the invention, the predetermined modified energizing time of the second fuel injection is determined by taking into account the Indicated Mean Effective Pressure in the cylinder due to the first fuel injection.

An advantage of this embodiment is that it identifies 2nd correct another cause of inaccuracy in the second injection fuel quantity.

According to another embodiment of the invention, the determination of the predetermined modified energizing time is performed in an engine test phase.

An advantage of this embodiment is that it allows to create a map that correlates the performance of the injector in the second injection when the second injection is performed immediately after the first fuel injection.

According to another embodiment of the invention, a dwell time between the first and the second fuel is chosen in order not to produce torque.

According to another embodiment of the invention, the determination of an Oxygen quantity value due to the combined effect of the first and the second fuel injection is performed by means of an Oxygen quantity sensor in the exhaust line.

This embodiment has the advantage of using a sensor generally present in current engine's exhaust rines.

According to another embodiment of the invention, the Oxygen quantity sensor is a lambda sensor or a NO sensor, According to a further embodiment of the Invention, the first and second fuel are pilot injections.

The invention further provides an apparatus for operating an Internal Combustion Engine comprising an engine block defining a cylinder and a fuel injector suitable to inject fuel inside the cylinder, the engine being equipped with an exhaust line, the apparatus comprising: -means for performing a first fuel injection using a predetermined energizing time to inject a first fuel quantity into the cylinder; -means for performing a second fuel injection using a predetermined modified energizing time that takes into account the effects of the first fuel injection in order to inject a second fuel quantity into the cylinder that is substantially equal to the first fuel quantity injected by the first fuel injection; -means for determining an Oxygen quantity value due to the combined effect of the first and the second fuel injection; -means for determining, on the basis of the Oxygen quantity value, a value of a total injected fuel quantity by the combination of the first and the second fuel injection; -means for determining a correction factor of the energizing time of the injector as a function of the difference between the determined value of the total injected fuel quantity and a preset nominal value thereof; and -means for using the correction factor to determine a corrected energizing time for subsequent fuel injections.

The invention further provides an automotive system comprising an internal combustion eiiy'rie, comprising an engine Diocic cietining a cylinder and a fuel injector and suitable to inject fuel inside the cylinder, the engine being equipped with an exhaust line, the automotive system comprising an Electronic Control Unit of the engine, wherein the Electronic Control Unit is configured to: -perform a first fuel injection using a predetermined energizing time to inject a first fuel quantity into the cylinder; -perform a second fuel injection using a predetermined modified energizing time that takes into account the effects of the first fuel injection in order to inject a second fuel quantity into the cylinder that is substantially equal to the first fuel quantity injected by the first fuel injection; -determine an Oxygen quantity value due to the combined effect of the first and the second fuel injection; -determine, on the basis of the Oxygen quantity value, a value of a total injected fuel quantity by the combination of the first and the second fuel injection; determine a correction factor of the energizing time of the injector as a function of the difference between the determined value of the total injected fuel quantity and a preset nominal value thereof; and -use the correction factor to determine a corrected energizing time for subsequent fuel injections.

The advantages of the apparatus and of the automotive system embodiments of the invention are substantially the same of those of the method for operation the of the internal combustion engine according to the various embodiments 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 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 -arrandforafrybunhjefhodclajmed

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 internal combustion engine belonging to the automotive system of figure 1; Figure 3 is a schematic representation of the main components of the automotive system employed for performing a method according to an embodiment of the invention; and Figure 4 is a schematic representation of the main steps of a method according to an embodiment 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 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 increases 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 proviutu. Notation 01 me compressor d40 increases tne 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 after-treatment 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 catalysts, lean NO, traps, hydrocarbon adsorbers, selective catalytic reduction (8CR) systems, and particulate filters. 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 crankshaft position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445.

Furthermore, as will be better explained hereinafter, the exhaust line 275 may also be provided with sensors that are suitable to measure, directly or indirectly, an Oxygen quantity in the exhaust gas, such as a lambda sensor 470 and/or a NO, sensor 480 which may send information on Oxygen concentration in the exhaust gas to the ECU 450 for further elaboration according to the various embodiments of the method explained below.

The crankshaft position sensor 420 is an electronic device used to monitor the position or rOtätiónál speed of the &ankshàft 145 and can mountea proximal to me cranicshatt itself in order to sense rotattonal displacement of the crankshaft 145 and send corresponding signals to the ECU 450.

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 Vol 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, or data carrier 460, 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.

More specifically, Figure 3 is a schematic representation of the main components of the automotive system 100 employed for performing a method according to an embodiment of the invention.

In Figure 3 the internal combustion engine 110 is represented, the engine 110 being provided with an engine block 120 defining cylinders 125. To each cylinder 125 an injector 160 is associated to inject fuel therein; for simplicity, only one injector 160 is represented in Figure 3.

The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 iniluid communication with a high pressure fuel pump 180 (visible in Figure 2) that increases the pressure of the fuel received from a fuel source 190 (also visible in Figure 2).

The engine 110 has an exhaust manifold 225, wherein from the exhaust manifold 225 an exhaust line 275 is provided.

Along the exhaust line 275 various sensors may be provided such as, in particular, a lambda sensor 470 and a NO sensor 480.

As it is known, a lambda sensor 470 may generate a voltage based on the Oxygen concentration in the exhaust gas.

Also, a NO sensor 480 may contain an oxygen concentration detection electrode for measuring the oxygen concentration in the exhaust gas.

Therefore, from the measures performed by both these sensors 470,480 an Oxygen quantity n tne exnaust gas can ye aeterminea.

The engine 110 is also associated to the Electronic Control Unit 450, this latter being equipped with a data carrier 460, and being suitable to control the operation of the injector 160 and to receive data from sensors 470,480.

The Electronic Control Unit 450 may be employed to perform the various embodiments of the method of the invention, according to a program stored in the data carrier 460.

Figure 4 is a schematic representation of the main steps of a method according to an embodiment of the invention.

As a preliminary step, the method is started when the engine 110 experiences a cutoff of fuel, for example when the driver releases the pressure on the accelerator pedal (block 10).

In this condition, according to the method, the ECU 450 activates the fuel injector 160 to perform a first test fuel injection with a predetermined energizing time ET1 to inject a first fuel quantity Q into the cylinder 125 (block IS).

Then, immediately afterwards of the first injection, the ECU 450 activates the fuel injector to perform a second fuei injection to inject a second fuel quantity Q into the cylinder (block 20).

The second fuel injection may be separated from the first injection by a predefined dwell time.

Preferably1 the dwell time between the first and the second fuel injection is chosen in order not to produce torque.

The first and the second fuel injections are preferably pilot injections, namely injections of a small amount of fuel that are performed before a main injection event and that do not normally produce torque, but are used for various reasons such as reducing explosiveness of the main injection, reducing vibration, as well as optirnising fuel consumption.

The first and the second fuel injections may therefore occur both before a specific main injection.

Since the fuel quantity actually injected by the second injection is influenced by the effects of the first injection, the second injection is performed using a predetermined modified energizing time ET2 that takes into account these effects and which is generally different form the energizing time ET of the first injection.

There are two main effects to be taken into account.

The first effect is that the fuel rail 170 experiences a fuel pressure disturbance due to the first injection.

More specifically, the fuel quantity injected in the first injection may cause a sudden drop or pressure in me raii 1 (U mat anects me immeaiateiy toitowing secona injection.

The second effect depends on the Indicated Mean Effective Pressure (IMEP) in the cylinder 125 due to the first fuel injection; this second effect has generally a lower magnitude with respect to the first effects, but may be nonetheless taken into account for increased accuracy.

Both these effects may cause the injection of a different quantity of fuel with respect to a nominal fuel value, even if the effect of IMEP may be smaller than that of the pressure disturbances in the fuel rail 170 and may, in some case, not taken into account.

Therefore a predetermined modified energizing time ET2 of the second fuel injection must be determined by taking into account the fuel rail 170 pressure disturbance due to the first fuel injection (block 25) and, eventually, the Indicated Mean Effective Pressure (IMEP) in the cylinder 125 due to the first fuel injection (block 30).

These effects are studied and calibrated in an engine test phase and maps 500,510 for each effect is stared in the data carrier 460, the maps 500,510 correlating these effects with actual fuel quantities injected for predetermined energizing times.

Using these maps 500,510 it is then possible to determine a predetermined modified energizing time ET2 for the second injection that takes into account the effects of the first fuel injection, with the aim of injecting a second fuel quantity Q into the cylinder 125 that is substantially equal to the first fuel quantity O,< injected by the first fuel injection.

After the second injection is performed, the lambda sensor 470 or the NO sensor 450 are used to determine an Oxygen quantity value O2 in the exhaust line 275 due to the combination of both the first and the second fuel injection (block 35).

On the basis of the Oxygen quantity value °2tol, a value of a total fuel quantity injected Otot by the combined effect of the first and of the second injection can be determined using a map 520 correlating these two quantities and stored in the data carrier 460 (block 40).

The total fuel quantity injected Q10 is used to determine a calculated fuel quantity To do so the ECU 450 divides (block 45) the total fuel quantity injected value Q by two, in symbols: OCaIG = Qtot /2 The calculated fuel value Qc* represents an estimation of the quantity injected by a single pilot injection under the above hypothesis that the first fuel quantity Q injected by the first injections is substantially equal to the second fuel quantity Q injected by the second fuel injections.

The calculated fuel value Ocaic can at this point considered as an actual value of fuel injected and be used to determine a correction factor CF of the energizing time of the injector 160 as a function of the difference between the calculated tuel quantity Qca/c and a nominal fuel quantity value Qoom thereof (block 50).

This correction factor CF is then used to determine a corrected energizing time ET.rr for the injector 160 (block 55).

The fuel injector 160 can be then energized (block 60) for the corrected energizing time ET011 to perform subsequent fuel injections.

The various embodiments of the method allow for an alternative way to perform apilot injection adjustment with respect to a crankshaft study strategy, that may be useful in all the cases in which such strategy cannot reliably be performed.

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 block block block

25 block block block block block 50 block block block automotive system internal combustion engine (ICE) 120 engine block cylinder cylinder head camshaft piston 145 crankshaft combustion chamber cam phaser fuel injector fuel rail 180 fuel pump fuel source intake manifold 205 air intake duct 210 intake air port 215 valves of the cylinder 220 exhaust gas port 440 exnaust rnaniioia 230 turbocharger 240 compressor 250 turbine 260 interceder 270 exhaust system 275 exhaust line 280 exhaust aftertreatment device 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 470 lambda sensor 480 NOserisor 500 map 510 map 520 map

Claims (1)

1. <claim-text>CLAIMS1. A method for operating an Internal Combustion Engine (110), comprising an engine block (120) defining a cylinder (125) and a fuel injector (160) suitable to inject fuel inside the cylinder (125), the engine being (110) equipped with an exhaust line (275), the method comprising the steps of: -performing a first fuel injection using a predetermined energizing time (ET1) to inject a first fuel quantity (Q) into the cylinder (125); -performing a second fuel injection using a predetermined modified energizing time (E12) that takes into account the effects of the first fuel injection in order to inject a second fuel quantity (Q) into the cylinder (125) that is substantially equal to the first fuel quantity (Q) injected by the first fuel injection; -determining an Oxygen quantity value (O2) due to the combined effect of the first and the second fuel injection; -determining, on the basis of the Oxygen quantity value (O2tet), a value of a total injected fuel quantity (Q0) by the combination of the first and the second fuel injection; -determining a correction factor (CF) of the energizing time of the injector (160) as a function of the difference between the determined value (Qca) of the total injected fuel quantity (Q0) and a preset nominal value (Onom) thereof; and -using the correction factor (CF) to determine a corrected energizing time (ETcorr) far subsequent fuel injections.</claim-text> <claim-text>2. A method according to claim 1, wherein the engine (110) comprises a fuel rail (170) and wherein the predetermined modified energizing time (ET2) of the second fuel injection is determined by taking into account a fuel rail (170) pressure disturbance value due to the first fuel injection.</claim-text> <claim-text>3. A method according to claim 1, wherein the predetermined modified energizing time (E12) of the second fuel injection is determined by taking into account an Indicated Mean Effective Pressure value (IMEP) in the cylinder (125) due to the firstfuelinjection. -- 4. A method accorng -to claims 2 or 3, wherein the determination of the predetermined modified energizing time (ET2) is performed during an engine test phase.5. A method according to claim 1, wherein a dwell time between the first and the second fuel is chosen in order that the combined effect of the first and second fuel injection does not produce torque.6. A method according to claim 1, wherein the determination of an Oxygen quantity value (O2tot) due to the combined effect of the first and the second fuel injection is performed by means of an Oxygen quantity sensor (470480) in the exhaust line (275).1. A method according to claim 6, wherein the Oxygen quantity sensor (470,480) is a lambda sensor (470) or a NO sensor (480).8. A method according to claim 1 in which the first and second fuel injections are pilot injections.9. An apparatus for operating an Internal Combustion Engine (110), comprising an engine block (120) defining a cylinder (125) and a fuel injector (160) suitable to inject fuel inside the cylinder (125), the engine being (110) equipped with an exhaust line (275), the apparatus comprising: -means for performing a first fuel injection using a predetermined energizing time (Eli) to inject a first fuel quantity (Q) into the cylinder (125); -means for performing a second fuel injection using a predetermined modified energizing time (E12) that takes into account the effects of the first fuel injection in order to inject a second fuel quantity (Q,) into the cylinder (125) that is substantially equal to the first fuel quantity (Q) injected by the first fuel injection; -means for determining an Oxygen quantity value (O2tot) due to the combined effect of the first and the second fuel injection; -means for determining, on the basis of the Oxygen quantity value (02t01), a value of a total injected fuel quantity (Q0) by the combination of the first and the second fuel injection; -means for determining a correction factor (CF) of the energizing time of the injector (160) as a function of the difference between the determined value (Qc&c) of the total injected fuel quantity (Qtot) and a preset nominal value (Ononi) thereof; and -means for using the correction factor (CF) to determine a corrected energizing time (ETcoir) for subsequent fuel injections. - 10. An utbmoiiv sytem è6ripdsihg an internal combustion engine (110)7 cbrnpilsing an engine block (120) defining a cylinder (125) and a fuel injector (160) and suitable to inject fuel inside the cylinder (125), the engine being (110) equipped with an exhaust line (275), the automotive system comprising an Electronic Control Unit (450) of the engine (110), wherein the Electronic Control Unit (450) is configured to: -perform a first fuel injection using a predetermined energizing time (ET1) to inject a first fuel quantity (Q) into the cylinder (125); -perform a second fuel injection using a predetermined modified enelgizing time (ET2) that takes into account the effects of the first fuel injection in order to inject a second fuel quantity (Q) into the cylinder (125) that is substantially equal to the first fuel quantity (Q) injected by the first fuel injection; -determine an Oxygen quantity value (O2tot) due to the combined effect of the first and the second fuel injection; -determine, on the basis of the Oxygen quantity value (O2jot), a value of a total injected fuel quantity (Q01) by the combination of the first and the second fuel injection; -determine a correction factor (CF) of the energizing time of the injector (160) as a function of the difference between the determined value (Qcafc) of the total injected fuel quantity (Q10) and a preset nominal value (Q00) thereof; and -use the correction factor (CF) to determine a corrected energizing time (ET01) for subsequent fuel injections.11. An internal combustion engine, in particular Diesel engine, the combustion engine (110) having associated sensors (470,480) for the measurement of combustion parameters, the engine comprising an Electronic Control Unit (450) configured for carrying out the method according to any of the claims 1-8.12. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1 -8.13. 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, a data carrier associated to the Electronic Control Unit and a computer program according to claim 12 stored in the data carrier.15. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 12.</claim-text>