Four-stroke internal combustion engine and method of operating four-stroke internal combustion engine

Disclosed is a four-stroke direct injection engine comprising a camshaft, and exhaust valve, and a control system. The control system is configured to change the timing of the camshaft to advance a closing of the exhaust valve, control a first fuel injection step during a compression stroke of the piston, control a second fuel injection step during a power stroke of the piston, and control a third fuel injection step, after the second fuel injection step, during the power stroke of the piston.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application (filed under 35 § U.S.C. 371) of PCT/SE2020/050179, filed Feb. 17, 2020 of the same title, which, in turn, claims priority to Swedish Application No. 1950212-9 filed Feb. 20, 2019; the contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The invention relates to a method of operating a four-stroke direct injection internal combustion engine, to a four-stroke direct injection internal combustion engine, and to a vehicle comprising a four-stroke direct injection internal combustion engine. The invention further relates to a computer program and to a computer-readable storage medium.

BACKGROUND

A modern four-stroke direct injection internal combustion engine, such as a diesel engine, is provided with an exhaust gas aftertreatment system in order to fulfil emission legislation, such as the European emission standard Euro6. An exhaust gas aftertreatment system may comprise e.g. a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reduction (SCR) device.

A sufficient exhaust gas temperature is required in order to ensure a proper function of the exhaust gas aftertreatment system. A particularly high exhaust gas temperature may be required for regenerating the DPF.

US 2003/0221421 discloses a control strategy for regenerating a particulate filter in an exhaust system of an engine having a variable valve actuation mechanism. A control for controlling a variable valve actuation mechanism of an internal combustion comprises an operating program for regenerating the particulate filter while the engine is running on its own power, by causing the variable valve actuation mechanism to change the timing of engine cylinder valves during an engine operating cycle, and as a result, elevate the temperature of the gas flow through the exhaust system to a temperature that is effective to combust particles trapped by the particulate filter.

US 2015/0275723 discloses a method for operating an internal combustion engine. A particulate filter is arranged in an exhaust system of the internal combustion engine, downstream of an oxidation catalyst. A closing moment of a discharge valve of a cylinder of the internal combustion engine is advanced when the temperature of the oxidation catalyst is in a first temperature range, thus, increasing the temperature of the exhaust gas. An injection valve is utilised to post-inject fuel into at least one cylinder of the internal combustion engine in order to help regenerate a particulate filter. The post-injections are performed when the temperature of the oxidation catalyst is in a second temperature range. An upper limit of the first temperature range having a lower value that an upper limit of the second temperature range.

SUMMARY

Not only temperature affects the regeneration of a particulate filter, but also NOx content of the gas flowing through the particulate filter.

It would be advantageous to achieve an alternative method of operating an internal combustion engine, ICE, which method will provide conditions for regenerating a particulate filter of an exhaust gas aftertreatment system connected to the ICE. In particular, it would be desirable to provide for an increased exhaust gas temperature as well as an increase in NOx content of the exhaust gas from an ICE. To better address this, a method of operating a four-stroke direct injection internal combustion engine having the features defined in one of the independent claims, and a four-stroke direct injection internal combustion engine defined in one of the independent claims are provided.

According to an aspect of the invention, there is provided a method of operating a four-stroke direct injection internal combustion engine, ICE, comprising at least one cylinder arrangement, a crankshaft, and a camshaft. The cylinder arrangement comprises a combustion chamber, a fuel injector, an exhaust valve, a cylinder bore, and a piston configured to reciprocate in the cylinder bore and being connected to the crankshaft. The camshaft is configured to control the opening and closing of the exhaust valve. A timing of the camshaft is controllable. The method comprises:a step of changing the timing of the camshaft to advance a closing of the exhaust valve,a first fuel injecting step during a compression stroke of the piston,a second fuel injecting step during a power stroke of the piston, anda third fuel injecting step, after the second fuel injecting step, during the power stroke of the piston.

Since the method comprises the step of changing the timing of the camshaft to advance the closing of the exhaust valve, the internal load on the ICE is increased and thus, a temperature of the exhaust gas is increased, and since the method comprises the first fuel injecting step during a compression stroke of the piston, increase of NOx content in the exhaust gas is promoted. Moreover, since the method comprises the third fuel injecting step, after the second fuel injecting step, fuel is injected into the combustion chamber, which fuel will not combust in the combustion chamber. Instead the fuel of the third injecting step is entrained with the exhaust gas for promoting exothermal reactions downstream of the exhaust valve and thus, for increasing the temperature of the exhaust gas.

In combination the steps of the method provide for high NOx content high temperature exhaust gas suitable e.g. for regenerating a particulate filter of an exhaust gas aftertreatment system connected to the ICE. The method provides high exhaust gas temperature at zero external load on the ICE. Advancing the closing of the exhaust valve in combination with the refined fuel injection strategy including the first, second, and third fuel injecting steps result in no need for external ICE load enhancing to increase exhaust gas temperature.

The four-stroke direct injection ICE may be a compression ignition ICE, such as a diesel engine. Herein, the four-stroke direct injection ICE simply may be referred to as an internal combustion engine, ICE.

The ICE may form part of a powertrain of a vehicle.

During normal operation of a four-stroke direct injection ICE, a common aim is to reduce the NOx content of the exhaust gas leaving the ICE. Thereby, the amount of NOx which has to be converted into harmless gases by the exhaust gas aftertreatment system connected to the ICE is reduced.

In contrast, the inventors have realised that under certain operating conditions of the ICE, an increased amount of NOx may be beneficial. For instance, if a particulate filter of the exhaust gas treatment system is to be regenerated, i.e. when soot is to be burned off from the particulate filter, NOx contributes to oxidation of the soot which mainly contains carbon, the regeneration resulting in inter alia CO2forming in the process.

Thus, the method may be implemented during regeneration of a particulate filter of an exhaust gas treatment system connected to the ICE. For instance, the method may be implemented when the ICE is not subjected to a high external load, e.g. when the ICE is subjected to low external load, or when a vehicle provided with the ICE is standing still.

Accordingly, the step of changing the timing of the camshaft to advance a closing of the exhaust valve provides an internal load on the ICE, which increases exhaust gas temperature compared to an ordinary timing of the camshaft. Put differently, the ICE itself produces an auxiliary load while the torque on the ICE output shaft is zero. Advancing the closing of the exhaust valve reduces the gas exchange in the cylinder bore and the combustion chamber, i.e. pumping work of the ICE is increased. The increased pumping work is overcome by adding fuel, which in turn increases exhaust gas temperature.

Alternative measures for regenerating the particulate filter are of course available, such as regeneration utilising high temperature exhaust gas produced during high external load operation of the ICE, e.g. when a vehicle provided with the ICE is travelling on an uphill gradient. Accordingly, the method may be implemented in situations where regeneration of the particulate filter is desired, or required, but when the ICE is not subjected to high external load.

As in any four-stroke ICE, the piston performs an intake stroke, a compression stroke, a power stroke, and an exhaust stroke in the cylinder bore of the cylinder arrangement. The rotation of the camshaft is synchronized with the crankshaft. The exhaust valve is configured to open and close an exhaust opening leading out of the combustion chamber, through which exhaust opening gas is admitted out of the combustion chamber. The piston is connected to the crankshaft via a connecting rod.

The cylinder arrangement comprises an intake valve which is configured to open and close an intake opening leading into the combustion chamber, through which intake opening gas is admitted into the combustion chamber. The ICE may comprise more than one cylinder arrangement, such as e.g. four, five, six, or eight cylinder arrangements.

Each of the first, second, and third fuel injecting steps involves fuel injection into the combustion chamber with the fuel injector. Each of the first, second, and third fuel injecting step comprises at least one individual fuel injecting operation. One or more of the first, second, and third fuel injecting steps may comprise two or more individual fuel injecting operations. Each individual fuel injecting operation is performed with the fuel injector.

The timing of the camshaft being controllable entails that the rotational position of the camshaft in relation to the crankshaft is changeable. This may also be referred to as cam phasing. In practice, this means that the crankshaft angle at which a valve controlled by the camshaft is opened and closed can be changed.

The step of changing the timing of the camshaft to advance a closing of the exhaust valve may be performed in any known manner. For instance, WO 2017/217908 and U.S. Pat. No. 8,714,123 disclose suitable timing control arrangements to be utilised for changing the timing of the camshaft. Other variable valve timing technology which changes the timing of the camshaft may alternatively be used.

The amount of timing change of the camshaft may be one fixed amount of timing change or a variable amount of timing change providing at least two different amounts of timing change to provide different levels of internal load on the ICE and thus, different levels of temperature increase of the exhaust gas.

Herein, reference will be made to crankshaft angle, CA, degrees when discussing timing of fuel injecting steps, and timing changes of the camshaft. One full rotation of the crankshaft is 360 CA degrees. Crankshaft angle is measured from Top Dead Centre fire, TDCf, the TDC between the compression stroke and of the power stroke, i.e. TDCf is 0 CA degrees. Negative values of CA are before TDCf, also referred to as BTDCf, positive values of CA are after TDCf, also referred to as ATDCf.

If the ICE comprises more than one exhaust valve, the step of changing the timing of the camshaft to advance the closing of the exhaust valve encompasses advancing the closing of all exhaust valves. Accordingly, if additional exhaust valves are controlled by additional camshafts, also the timing any additional camshafts have to be changed.

According to embodiments, the first fuel injecting step may comprise at least two individual fuel injecting operations. In this manner, the first individual fuel injecting operation will set off early combustion and NOx production and the second individual fuel injecting operation promotes further NOx production in the exhaust gas by supporting the combustion awaiting the second fuel injecting step taking place during the power stroke. In a similar manner, a third individual fuel injecting operation may support the combustion during the compression stroke awaiting the second fuel injecting step.

According to embodiments, the third fuel injecting step may take place after opening of the exhaust valve during the power stroke. In this manner, the fuel injected during the third fuel injecting step may be entrained with the exhaust gas escaping through the exhaust valve and further downstream to the aftertreatment system where exhaust temperature may be further increased by exothermal reactions.

According to embodiments, the second fuel injecting step may comprise at least two individual fuel injection operations. In this manner, the first individual fuel injecting operation may form the main source of combustion energy while the second individual fuel injecting operation may increase exhaust gas temperature.

According to embodiments, wherein the ICE comprises an exhaust gas aftertreatment system, which comprises a first selective catalytic reduction, SCR, device and downstream thereof a particulate filter, the method may comprise:a step of refraining from injecting urea or ammonia into the first selective catalytic reduction device. In this manner, the NOx content of the exhaust gas from the ICE is not reduced in the first selective catalytic reduction device, but will instead reach the particulate filter and thus, contribute to the regeneration of the particulate filter.

According to embodiments, the first fuel injecting step may be performed within a range of −40 to −15 CA degrees in relation to 0 CA degrees being at TDCf, i.e. 40−15 CA degrees BTDCf. In this manner, NOx content of the exhaust gas may be increased by combustion during the compression stroke. At least one individual fuel injecting operation of the first fuel injecting step may be performed within the above defined −40 to −15 CA degrees. However, all individual fuel injecting operations of the first fuel injecting step may be performed within the above defined −40 to −15 CA degrees.

According to embodiments, a second individual fuel injection operation subsequent to a first individual fuel injection operation of the second fuel injecting step may be performed within a range of 30-50 CA degrees in relation to 0 CA degrees being at TDCf, i.e. 30-50 CA degrees ATDCf. In this manner, the second individual fuel injection operation provides for an exhaust gas temperature increase.

According to a further aspect of the invention, there is provided a four-stroke direct injection internal combustion engine comprising at least one cylinder arrangement, a crankshaft, a camshaft, and a control system. The cylinder arrangement comprises a combustion chamber, a fuel injector, an exhaust valve, a cylinder bore, and a piston configured to reciprocate in the cylinder bore and being connected to the crankshaft. The fuel injector is controllable by the control system. The camshaft is configured to control the opening and closing of the exhaust valve. A timing of the camshaft is controllable by the control system. The control system is configured to:change the timing of the camshaft to advance a closing of the exhaust valve,control a first fuel injecting step during a compression stroke of the piston,control a second fuel injecting step during a power stroke of the piston, andcontrol a third fuel injecting step, after the second fuel injecting step, during the power stroke of the piston.

Similarly, as mentioned above in connection with the method, since the control system is configured to change the timing of the camshaft to advance the closing of the exhaust valve, the internal load on the ICE is increased and thus, a temperature of the exhaust gas is increased, and since the control system is configured to control a first fuel injecting step during a compression stroke of the piston, increase of NOx content in the exhaust gas is promoted. Moreover, since the control system is configured to control the third fuel injecting step, after the second fuel injecting step, fuel is injected into the combustion chamber, which fuel will not combust in the combustion chamber. Instead the fuel of the third injecting step is entrained with the exhaust gas for promoting exothermal reactions downstream of the exhaust valve and thus, for increasing the temperature of the exhaust gas.

In combination, the control measures of the control system provide for high NOx content high temperature exhaust gas suitable e.g. for regenerating a particulate filter of an exhaust gas aftertreatment system connected to the ICE. High exhaust gas temperature is provided for at zero external load on the ICE. Advancing the closing of the exhaust valve in combination with the refined fuel injection strategy including the first, second, and third fuel injecting steps result in no need for external ICE load enhancing.

According to a further aspect of the invention, there is provided a vehicle comprising a four-stroke direct injection internal combustion engine according to any one of aspects and/or embodiments discussed herein.

The vehicle may be a heavy load vehicle such as e.g. a truck, a bus, a construction vehicle, a pickup, a van, a train engine, or other similar motorized manned or unmanned vehicle, designed for land-based propulsion, on or off road.

According to a further aspect of the invention, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of aspects and/or embodiments discussed herein.

According to a further aspect of the invention, there is provided a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of aspects and/or embodiments discussed herein.

Further features of, and advantages with, the invention will become apparent when studying the appended claims and the following detailed description.

DETAILED DESCRIPTION

Aspects and/or embodiments of the invention will now be described more fully. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

FIG.1schematically illustrates a vehicle2according to embodiments. The vehicle2may be a heavy goods vehicle, designed for land-based propulsion. The vehicle2comprises a four-stroke direct injection internal combustion engine, ICE, according to any one of aspects and/or embodiments discussed herein, such as e.g. the ICE discussed below with reference toFIG.2. The ICE forms part of a powertrain of the vehicle2.

FIG.2schematically illustrates embodiments of an ICE4. The ICE4may be configured to form part of a powertrain of a vehicle, such as e.g. the vehicle2shown inFIG.1.

The ICE4is a four-stroke direct injection internal combustion engine, such as a compression ignition ICE4, e.g. a diesel engine. The ICE4comprises at least one cylinder arrangement6, a crankshaft8, a camshaft10.

The cylinder arrangement6comprises a combustion chamber12, a fuel injector14, an exhaust valve16, a cylinder bore18, and a piston20configured to reciprocate in the cylinder bore18. The piston20is connected to the crankshaft8via a connecting rod22. The movement of the exhaust valve16is controlled by the camshaft10, i.e. the camshaft10is configured to control the opening and closing of the exhaust valve16.

The ICE4comprises a further camshaft24and the cylinder arrangement6comprises an intake valve26. The movement of the intake valve26is controlled by the further camshaft24.

The intake valve26is configured for admitting gas into the combustion chamber12, and the exhaust valve16is configured for admitting gas out of the combustion chamber12. At least the timing of the camshaft10is configured to the be controlled by a timing control arrangement30as indicated by a double arrow.

In a known manner, the piston20is arranged to reciprocate in the cylinder bore18. The piston20performs four strokes in the cylinder bore18, corresponding to an intake stroke, a compression stroke, a power stroke, and an exhaust stroke, see alsoFIG.4. InFIG.2the piston20is illustrated with continuous lines at its Bottom Dead Centre, BDC, and with dashed lines at its Top Dead Centre, TDC. The combustion chamber12is formed above the piston20inside the cylinder bore18.

In a known manner, the intake valve26comprises an intake valve head configured to seal against an intake valve seat extending around an intake opening28. An inlet conduit29for fresh gas, such as air, leads to the intake opening28. The exhaust valve16comprises an exhaust valve head configured to seal against an exhaust valve seat extending around an exhaust opening32. An exhaust conduit34leads from the exhaust opening32towards an exhaust system36connected to the ICE4.

In a known manner, the camshafts10,24rotate at half the rotational speed of the crankshaft8and control the movement of the intake and exhaust valves16,26via lobes38,40arranged on the camshafts10,24. The camshaft10is arranged for controlling movement of the exhaust valve16, and opening and closing of the exhaust opening32. The camshaft10comprises a lobe38configured to abut against the exhaust valve16. Thus, the exhaust valve16will follow a contour of the lobe38. The exhaust valve16may be biased towards its closed position, e.g. by means of a non-shown spring. The movement of the intake valve26is controlled in the same manner by the further camshaft24and its lobe40.

The cylinder arrangement6has a total swept volume, Vs, in the cylinder bore18between the BDC and the TDC. According to some embodiments, the cylinder arrangement6may have a total swept volume, Vs, of within a range of 0.3 to 4 litres. Mentioned purely as an example, in the lower range of Vs, the cylinder arrangement6may form part of an internal combustion engine for a passenger car, and in the middle and higher range of Vs, the cylinder arrangement4may form part of an internal combustion engine for a heavy load vehicle such as e.g. a truck, a bus, or a construction vehicle.

The ICE4comprises a control system42. The control system42is configured to control at least fuel injection into the combustion chamber12and the timing of the camshaft10. Thus, the fuel injector14and the timing control arrangement30are controllable by the control system42.

FIG.3illustrates a control system42to be utilised in connection with the different aspects and/or embodiments of the invention. The control system42is also indicated inFIG.2. The control system42comprises at least one calculation unit50, which may take the form of substantially any suitable type of processor circuit or microcomputer, e.g. a circuit for digital signal processing (digital signal processor, DSP), a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The herein utilised expression “calculation unit” may represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The control system42comprises a memory unit52. The calculation unit50is connected to the memory unit52, which provides the calculation unit50with, e.g. stored programme code, data tables, and/or other stored data which the calculation unit50needs to enable it to do calculations and to control the ICE and optionally an exhaust gas aftertreatment system connected to the ICE. The calculation unit50is also adapted to store partial or final results of calculations in the memory unit52. The memory unit52may comprise a physical device utilised to store data or programs, i.e. sequences of instructions on a temporary or permanent basis. According to some embodiments, the memory unit52may comprise integrated circuits comprising silicon-based transistors. The memory unit52may comprise e.g. a memory card, a flash memory, a USB memory, a hard disc, or another similar volatile or non-volatile storage unit for storing data such as e.g. ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), etc. in different embodiments.

The control system42is further provided with respective devices54,56,58,60for receiving and/or sending input and output signals. These input and output signals may comprise waveforms, pulses or other attributes, which can be detect as information by signal receiving devices, and which can be converted to signals processable by the calculation unit50. Input signals are supplied to the calculation unit50. Output signal sending devices54,56,60are arranged to convert calculation results from the calculation unit50to output signals for conveying signal receiving devices of other parts of the control system42. Each of the connections to the respective devices for receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (controller area network) bus, a MOST (media orientated systems transport) bus or some other bus configuration, or a wireless connection. In the embodiment depicted, only one calculation unit50and memory52are shown, but the control system42may alternatively comprise more than one calculation unit and/or memory.

Mentioned as examples, the output signal sending devices54,56may send control signals to the fuel injector14and to a timing control arrangement30of the camshaft10. The input signal receiving device58may receive signals from the ICE, such as from a rotational speed sensor sending signals related to the rotational speed of the crankshaft of the ICE to the calculation unit50.

An example of a data table may be a table containing fuel injection quantities. Examples of data may be measured, monitored, and/or calculated data. The control system42is connected to various sensors and actuators in order to receive input and provide output for performing the various aspects and embodiments of the method discussed herein. An example of a sensor may be a rotational speed sensor. An example of an actuator may a fuel injector.

In the following reference is made toFIGS.2and3. For instance, when a particulate filter of an exhaust gas aftertreatment system connected to the ICE4is to be regenerated, the control system42is configured to:Change the timing of the camshaft10to advance a closing of the exhaust valve16. Thus, an internal load on the ICE4is produced, which causes an increase exhaust gas temperature.Control a first fuel injecting step during a compression stroke of the piston20. Thus, NOx content of exhaust gas is increased by early fuel injection into the combustion chamber12.Control a second fuel injecting step during a power stroke of the piston20. The second fuel injecting step comprise the main individual fuel injecting operation, or operations, shortly after the piston20has passed TDCf. However, later during the second fuel injecting step, before the exhaust valve16opens, a further individual fuel injecting operation may increase exhaust gas temperature.Control a third fuel injecting step, after the second fuel injecting step, during the power stroke of the piston20. Fuel injected into the combustion chamber during the third fuel injecting step will not combust in the combustion chamber. This fuel is entrained with the exhaust gas to flow downstream of the exhaust valve16, and the exhaust opening32. See also below with reference toFIGS.4and5and the method100discussed with reference toFIG.6.

According to embodiments, the third fuel injecting step may take place after opening of the exhaust valve16during the power stroke. In this manner, fuel injected during the third fuel injecting step may be entrained with the exhaust gas out of the combustion chamber12. Thus, the fuel injected during the third fuel injecting step may flow downstream of the exhaust valve16and the exhaust opening32to increase exhaust gas temperature in the exhaust system of36connected to the ICE4.

The exhaust gas increasing measures of changing the timing of the camshaft10to advance the closing of the exhaust valve16, and/or the first fuel injecting step during the compression stroke of the piston20, and/or the second fuel injecting step during the power stroke of the piston20promote exothermal reactions downstream of the exhaust valve16energised by the fuel injected in the third fuel injecting step.

According to embodiments, the third fuel injecting step may take place within a range of 0-25 CA degrees after opening the exhaust valve16during the power stroke.

According to embodiments, the change of the timing of the camshaft10to advance the closing of the exhaust valve may comprise advancing the closing of the exhaust valve16at least 60 CA degrees from an ordinary exhaust valve closing. In this manner, an internal load is put on the ICE4, which increases exhaust gas temperature.

The ordinary closing of the exhaust valve16is that, at which the exhaust valve16closes during normal operation of the ICE4, i.e. when the ICE4produces positive torque on its output shaft to drive e.g. a vehicle.

According to some embodiments, the change of the timing of the camshaft10to advance the closing of the exhaust valve may comprise advancing the closing of the exhaust valve16within a range of 1-100 CA degrees from an ordinary exhaust valve closing, preferably within a range of 60-80 CA degrees from an ordinary exhaust valve closing.

FIG.4illustrates a diagram over functionality the ICE4ofFIG.2.FIG.4illustrates the four strokes of the piston20and the movement of the exhaust valve and of the intake valve. The movement of the intake valve is indicated with a dash-dotted line. The movement of the exhaust valve during ordinary operation of the ICE is indicated with a full line.

The crankshaft of the ICE rotates 720 CA degrees as the four strokes of the piston20are performed. For each stroke, the crankshaft rotates 180 CA degrees as indicated inFIG.4. A represents the intake stroke, B represents the compression stroke, C represents the power stroke, and D represents the exhaust stroke.

The broken line indicates the movement of the exhaust valve after the timing of the camshaft has been changed to advance the closing of the exhaust valve, in accordance with the present invention. InFIG.4α indicates advancing the closing of the exhaust valve, in accordance with the change of the timing of the camshaft discussed above with reference toFIGS.2and3.

InFIG.4the advancing a indicated is approximately 60 CA degrees. That is, the exhaust valve will be closed during a large part of the last half of the exhaust stroke.

Mentioned as an example, the ordinary closing of the exhaust valve16during normal operation of the ICE4may be within a range of 350-390 CA degrees. In this example, the change of the timing of the camshaft10to advance the closing of the exhaust valve16at least 60 CA degrees from the ordinary exhaust valve closing means that the closing of the exhaust valve is advanced to 290-330 CA degrees.

FIG.5illustrates different fuel injecting steps into the combustion chamber of the ICE ofFIG.2, as discussed above with reference toFIGS.2and3. The different fuel injecting steps are indicated with ovals inFIG.5. The first fuel injecting step is indicated at62. The second fuel injecting step is indicated at64. The third fuel injecting step is indicated at66. InFIG.5, arrows indicated with roman numbers represent individual fuel injecting operations of the first, second, and third fuel injecting steps62,64,66.

In the following reference is made toFIGS.2-5and the discussions above.

According to embodiments, the first fuel injecting step62may comprise at least two individual fuel injecting operations I, II, Ill. In this manner, early combustion for increased NOx production is initiated as well as maintained.

In the embodiments ofFIG.5, three individual fuel injecting operations I, II, III during the first fuel injecting step62are provided. The first and second individual fuel injecting operations I, II promote the production of NOx in the exhaust gas, whereas the third individual fuel injecting operation III is provided for maintaining the combustion in the combustion chamber12until the second fuel injecting step64during the power stroke of the piston20.

According to embodiments, a first individual fuel injection operation I of the first fuel injecting step62may be performed within a range of −40 to −15 CA degrees in relation to 0 CA degrees at TDCf, i.e. 40-15 CA degrees BTDCf. In this manner, production of NOx in the exhaust gas may be promoted.

According to embodiments, the second fuel injecting step64may comprise at least two individual fuel injection operations IV, V. In this manner, a first individual fuel injecting operation IV of the second fuel injecting step64may form of the main individual fuel injecting operation for combustion with the aim of producing the main power during the power stroke, where as a second individual fuel injecting operation V of the second fuel injecting step64may be provided for increasing exhaust gas temperature. InFIG.5, the first individual fuel injecting operation IV is performed shortly after the piston20has passed TDCf, within a range of 10-30 CA degrees ATDCf, such as at approximately 20 CA degrees ATDCf. The second individual fuel injecting operation V is performed later during the power stroke, before the exhaust valve16has started to open with the timing of the camshaft10changed for the advanced closing, and thus also advanced opening, of the exhaust valve16. InFIG.5, the second individual fuel injecting operation V is performed within a range of 30-50 CA degrees ATDCf, such as at approximately 40 CA degrees ATDCf.

In the following reference is made toFIG.2. The exhaust system36comprises an exhaust gas aftertreatment system68, i.e. an exhaust gas aftertreatment system68is connected to the exhaust conduit34of the ICE4.

Accordingly, according to some embodiments, the internal combustion engine4may comprise an exhaust gas aftertreatment system68, which may comprise a first selective catalytic reduction, SCR, device70and downstream thereof a particulate filter72. The control system42may be configured to refrain from injecting urea or ammonia into the first SCR device70. In this manner, NOx content of the exhaust gas from the ICE4may be maintained and may be utilised in the particulate filter72for regeneration thereof.

More specifically, the first SCR device70, in a known manner, may be configured to reduce NOx content of exhaust gas utilising urea or ammonia. Thus, the first SCR device70comprises a first dosage device71configured to inject an additive comprising a urea or ammonia into the exhaust gas stream flowing into, and through, the first SCR device70. The particulate filter72may be a diesel particulate filter, DPF, configured for reducing particles in the exhaust gas stream. In accordance with these embodiments, when the particulate filter72is regenerated, the NOx content of the exhaust gas is not reduced in the first SCR device70by the control system42controlling the first dosage device71to refrain from injecting urea or ammonia into the first SCR device70. See alsoFIG.3. Thus, the NOx in the exhaust gas may contribute to the regeneration of the particulate filter72.

The exhaust gas aftertreatment system68may further comprise a second SCR device74.

Such an exhaust gas aftertreatment system68, its operation, and specific advantages, is discussed in detail in WO 2015/130211. During regeneration of the particulate filter72, any remaining NOx content of the exhaust gas passing the particulate filter72may be reduced in the second SCR device74. That is, a second dosage device75is controlled by the control system42to inject urea or ammonia into the second SCR device74.

FIG.6illustrates embodiments of a method100of operating a four-stroke ICE. The vehicle and the ICE may be a vehicle2and an ICE4as discussed above in connection withFIGS.1-5. Accordingly, in the following reference is also made toFIGS.1-5and the descriptions related thereto.

The method100comprises:a step102of changing the timing of the camshaft10to advance a closing of the exhaust valve16,a first fuel injecting step104during a compression stroke of the piston20,a second fuel injecting step106during a power stroke of the piston20, anda third fuel injecting step108, after the second fuel injecting step106, during the power stroke of the piston20.

As discussed inter alia above with reference toFIGS.2-5, and the control system42, the step102of changing the timing of the camshaft to advance the closing of the exhaust valve, increases the internal load on the ICE increases the exhaust gas temperature, the first fuel injecting step104during the compression stroke of the piston20promotes increased NOx content in the exhaust gas, the second fuel injecting step106provides a main individual fuel injecting operation and optionally an exhaust gas temperature increasing further individual fuel injecting operation, and the third fuel injecting step108provides fuel which will not combust in the combustion chamber but is entrained with the exhaust gas from the combustion chamber12.

Particularly, reference is made to the first, second, and third fuel injecting steps62,64,66discussed above with reference toFIG.5, which correspond to the respective first, second, and third fuel injecting steps104,106,108of the method100.

According to embodiments, the first fuel injecting step104may comprise at least two individual fuel injecting operations. As discussed above, the first individual fuel injecting operation will set off early combustion and NOx production and the second individual fuel injecting operation promotes further NOx production in the exhaust gas by supporting the combustion awaiting the second fuel injecting step taking place during the power stroke. In a similar manner, a third individual fuel injecting operation may support the combustion during the compression stroke awaiting the second fuel injecting step, see also above with reference toFIG.5.

According to embodiments, the third fuel injecting step108may take place after opening of the exhaust valve16during the power stroke of the piston20. As discussed above, the fuel injected during the third fuel injecting step108may be entrained with the exhaust gas escaping through the exhaust valve to promote exhaust gas temperature increase downstream of the exhaust valve.

According to embodiments, the second fuel injecting step106may comprise at least two individual fuel injection operations. As discussed above, the first individual fuel injecting operation of the second fuel injecting step106may form the main source of combustion energy while the second individual fuel injecting operation may increase exhaust gas temperature.

According to embodiments, the step102of changing the timing of the camshaft may comprise:a step110of changing the timing to advance the closing of the exhaust valve at least 60 crankshaft angle, CA, degrees from an ordinary exhaust valve closing. In this manner, the ICE4may be subjected to a substantial internal load, which will increase exhaust gas temperature.

According to embodiments, wherein the ICE comprises an exhaust gas aftertreatment system, which comprises a first selective catalytic reduction, SCR, device70and downstream thereof a particulate filter72, the method100may comprise:a step112of refraining from injecting urea or ammonia into the first selective catalytic reduction device. As mentioned above, the NOx content of the exhaust gas from the ICE4is thus, not reduced in the first selective catalytic reduction device70, but will instead reach the particulate filter72and thus, contribute to the regeneration of the particulate filter72.

According to embodiments, the first fuel injecting step104may be performed within a range of −40 to −15 CA degrees in relation to 0 CA degrees being at TDCf. As discussed above, NOx content of the exhaust gas may be increased by combustion during the compression stroke. By performing one or more individual fuel injecting operations within the above defined −40 to −15 degrees CA this may be achieved.

According to embodiments, a second individual fuel injection operation subsequent to a first individual fuel injection operation of the second fuel injecting step106may be performed within a range of 30-50 degrees crankshaft angle, CA, in relation to 0 crankshaft angle, CA, degrees being at TDCf. As discussed above, this provides for an exhaust gas temperature increase.

The method100may be implemented in situations where regeneration of the particulate filter is desired, or required, but when the ICE4is not subjected to high external load. In such situations a vehicle comprising the ICE4may be standing still. This may for instance occur during service of the ICE4and the vehicle2.

A further alternative may be to perform the method100when the ICE4is subjected to low load, which in itself does not produce a high enough exhaust gas temperature for regenerating a particulate filter.

Mentioned as an example, e.g. in such above discussed situations, the method100may be performed continuously over a time period having a length within a range of 20-120 minutes. In this manner, the particulate filter72may be regenerated.

According to an aspect there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method100according to any one of aspect and/or embodiments discussed herein, in particular with reference toFIG.6. One skilled in the art will appreciate that the method100of operating a four-stroke ICE may be implemented by programmed instructions. These programmed instructions are typically constituted by a computer program, which, when it is executed in a computer or control system, ensures that the computer or control system carries out the desired control, such as the method steps102-112according to the invention. The computer program is usually part of a computer programme product which comprises a suitable digital storage medium on which the computer program is stored.

FIG.7shows a computer-readable storage medium90according to embodiments. The computer-readable storage medium90comprises instructions which, when executed by a computer or other control system42, causes the computer or other control system42to carry out the method100according to any one of aspects and/or embodiments discussed herein. The computer-readable storage medium90may be provided for instance in the form of a data carrier carrying computer program code for performing at least some of the steps102-112according to some embodiments when being loaded into the one or more calculation units50of the control system42. The data carrier may be, e.g. a ROM (read-only memory), a PROM (programmable read-only memory), an EPROM (erasable PROM), a flash memory, an EEPROM (electrically erasable PROM), a hard disc, a CD ROM disc, a memory stick, an optical storage device, a magnetic storage device or any other appropriate medium such as a disk or tape that may hold machine readable data in a non-transitory manner. The computer-readable storage medium may furthermore be provided as computer program code on a server and may be downloaded to the control system42remotely, e.g., over an Internet or an intranet connection, or via other wired or wireless communication systems.

It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the invention, as defined by the appended claims.