TECHNICAL FIELD The invention relates to a combined fuel injector and igniter, configured to inject fuel into, and ignite a fuel and air mixture in, a combustion chamber of an internal combustion engine, presenting a tip region adapted to be exposed to the combustion chamber, a fuel injection assembly comprising a fuel outlet provided in the tip region, and a corona ignition assembly comprising an electrode provided in the tip region, the fuel outlet being adapted to emit a jet of fuel into the combustion chamber, and the electrode being adapted to provide a corona discharge in the combustion chamber.

The invention also relates to a fuel injector, an internal combustion engine, and a vehicle, and also a method for injecting fuel into, and igniting a fuel and air mixture in, a combustion chamber of a cylinder of an internal combustion engine. Further the invention relates to a computer program, a computer readable medium, and a controller for performing steps of the method.

BACKGROUND

For vehicle internal combustion engines, corona ignition has been discussed for some time. For example, US6883507B2 describes an ignition system where, in order to initiate combustion, an electrode is charged to a high, radio frequency voltage potential to create a strong radio frequency electric field in the combustion chamber. In turn, this causes a portion of the fuel-air mixture in the combustion chamber to ionise, and a corona discharge to occur. The ionised fuel-air mixture forms a flame front which then becomes self-sustaining and combusts the remaining fuel-air mixture. Another example of a corona ignition system is presented in US2012199088A1. US2014123924A1 discloses a combined fuel injector and corona igniter, which has the benefit that the injection and ignition functions can be provided in the cylinder head with a single aperture for each cylinder. Although advantages of corona ignition as compared to traditional ignition methods have been discussed there is a desire to improve corona ignition solutions, in order to provide further gains in engine operations. In particular, it is desired to provide an improved combustion without affecting or complicating an internal combustion engine design.

SUMMARY

It is an object of the invention to improve the effectiveness of the combustion process in internal combustion engines. It is also an object to provide an improved effectiveness of the combustion process in internal combustion engines without significantly complicating an internal combustion engine design.

These objects are reached with a combined fuel injector and igniter, configured to inject fuel into, and ignite a fuel and air mixture in, a combustion chamber of an internal combustion engine, presenting a tip region adapted to be exposed to the combustion chamber, a fuel injection assembly comprising a fuel outlet provided in the tip region, and a corona ignition assembly comprising an electrode provided in the tip region, the fuel outlet being adapted to emit a jet of fuel into the combustion chamber, and the electrode being adapted to provide a corona discharge in the combustion chamber, characterized in that the fuel injection assembly and the corona ignition assembly are arranged to provide for at least at least a major portion of a corona discharged from the electrode being confined within the fuel jet emitted from the fuel outlet.

The fuel outlet and the electrode may be mutually arranged so that at least a major portion of a corona discharged from the electrode is confined within a fuel jet emitted from the fuel outlet. Thereby, a corona discharged from the electrode can mainly extend in a region within the outer delimitation of the fuel jet. The fuel jet is herein considered to be formed by a stream or spray of fluid extending from the fuel outlet to the delimitation of the combustion chamber, e.g. the piston or the cylinder wall.

The fuel jet presents an air and fuel mixture which, in the lateral direction of the fuel jet, is increasingly lean with increasing distance from a centreline of the fuel jet. The fuel jet delimitation in the lateral direction of the fuel jet is herein considered to be a three dimensional surface where the lambda value is 10. Thus, the electrode is adapted to provide a corona discharge dedicated to ignite a particular jet from the fuel outlet. The invention will ensure a very high efficiency of the combustion process. At the same time, with the combined fuel injector and corona igniter, the injection and ignition functions can be provided in the cylinder head with a single aperture for each cylinder. Thereby, an internal combustion engine corona ignition can be provided, which is simple to implement, for example in existing engine designs.

The invention allows for a multi-fuel capacity of engines, since most fuels can be ignited by use of the inventive concept. In addition, the ignition and injection solution allows, as opposed to spark ignition, for igniting high octane fuels, such as ethanol, methanol, and petrol (gasoline), with a high compression ratio similar to that of engines with compression ignition, thereby increasing the engine efficiency, and thereby lowering fuel consumption. The inventive ignition and injection solution could also allow for igniting natural gas.

Further, the invention provides for using the concept and design of a conventional diesel fuel injector, and adding to this injector design a corona ignition assembly comprising electrodes at the fuel outlets of the injector. This indicates that the invention can be implemented to designs available today without major revision of the injection system or other parts of the engine.

It is understood that the invention can be advantageously used in a piston internal combustion engine, in which the combustion chamber is provided in a cylinder of the engine, and in which cylinder a piston is adapted to move in a reciprocating manner by a connection to a crankshaft of the engine.

The fuel outlet can be provided as a bore in the tip region of the combined injector and ignitor. The bore can be straight, preferably cylindrical, and present a centreline which is parallel to the direction of the fuel jet which it is adapted to emit.

The electrode is preferably provided in the form of a cathode. It can be adapted to emit a radio frequency electric field to ionize a portion of a fuel-air mixture. Preferably, the electrode presents a tip and a symmetry line extending through the tip, the symmetry line being provided at an intersection of at least two symmetry planes of the electrode. Thereby, the corona provided by the electrode can be directed so as to mainly coincide with the extension of the symmetry line into the combustion chamber.

Preferably, the symmetry line forms an angle to a centreline of the fuel outlet, which angle is 2.5-17.5 degrees, preferably 2.5-12.5 degrees.

The objects are also reached with a combined fuel injector and igniter, configured to inject fuel into, and ignite a fuel and air mixture in, a combustion chamber of an internal combustion engine, presenting a tip region adapted to be exposed to the combustion chamber, a fuel injection assembly comprising a fuel outlet provided in the tip region, and a corona ignition assembly comprising an electrode provided in the tip region, the fuel outlet being adapted to emit a jet of fuel into the combustion chamber, and the electrode being adapted to provide a corona discharge in the combustion chamber, wherein the electrode presents a tip and a symmetry line extending through the tip, the symmetry line being provided at an intersection of at least two symmetry planes of the electrode, characterised in that the symmetry line forms an angle to a centreline of the fuel outlet, which angle is 2.5-17.5 degrees, preferably 2.5-12.5 degrees.

Preferably, the fuel injection assembly and the corona ignition assembly are arranged so that the corona presents a stem, and possibly one or more branches extending from the stem, and so that at least a major portion of the stem is confined within the fuel jet emitted from the fuel outlet. The corona can have an elongated shape. At least a major portion of the corona may be confined within the fuel jet if at least 50% of a line, extending from a tip of the electrode to an end of the corona being at the greatest distance from the tip, is within the outer delimitation of the fuel jet.

Preferably, where the corona ignition assembly is arranged so as to provide a corona presenting a stem, and at least a major portion of the stem is confined within a fuel jet emitted from the fuel outlet, the stem is offset from a centreline of the fuel jet. Thereby, a "centre of gravity" of the corona can be offset from the centreline of the fuel jet, and this will provide beneficial combustion conditions since the mixture at the centreline of may be too rich for initiating a combustion. Preferably, the fuel injection assembly and the corona ignition assembly are arranged so that at least a major portion of the corona discharged from the electrode is confined within a region of the fuel jet where the lambda value is 0.4-1.8, preferably 0.6-1.8, preferably 1.1-1.8, Thereby, the corona discharged from the electrode will mainly extend at a distance from a centreline of the fuel jet, where a beneficial air and fuel mixture is provided for initiating the combustion.

Preferably a plurality of fuel outlets and electrodes, i.e. at least two fuel outlets and at least two electrodes, are provided in the tip region, whereby the fuel outlets and electrodes are arranged in pairs. The distance between the fuel outlet and the electrode in a pair is preferably less than the distance from any of the fuel outlet and the electrode in the pair to any other fuel outlet or electrode in the tip region.

In some embodiments, 3-12, preferably 3-8, pairs of fuel outlets and electrodes are provided in the tip region. It should however be noted that the invention also includes embodiments with only one or two pairs of fuel outlets and electrodes, or more than 12 pairs of fuel outlets and electrodes. The tip region can present a rotationally symmetric shape and a centreline, and the pairs of fuel outlets and electrodes can be distributed around the centreline, equally spaced in a circumferential direction. The pairs of fuel outlets and electrodes can be provided at intervals in the circumferential direction of 30-120 degrees.

Where there is a plurality of fuel outlets and electrodes in the tip region, and the tip region can presents a rotationally symmetric shape and a centreline, and the fuel outlets and electrodes can be arranged at substantially equal distances from the centreline. Where there is a plurality of fuel outlets and electrodes in the tip region, the fuel outlets can be arranged so that fuel jets emitted therefrom present an umbrella angle of 90-170 degrees, preferably 130-160 degrees, for example 150 degrees. Where the electrodes each present a tip and a symmetry line extending through the tip, the symmetry line being provided at an intersection of at least two symmetry planes of the electrode, the umbrella angle of the electrode symmetry lines, and the umbrella angle of centrelines of the fuel outlets can be substantially the same.

The objects are also reached with a fuel injector, configured to inject fuel into a combustion chamber of an internal combustion engine, presenting a tip region adapted to be exposed to the combustion chamber, a fuel injection assembly comprising a plurality of fuel outlets provided in the tip region, the fuel outlets being adapted to emit respective jets of fuel into the combustion chamber, characterised in that it comprises a corona ignition assembly comprising a plurality of electrodes provided in the tip region, whereby each one of the electrodes is adapted to provide a single corona discharge dedicated to ignite a single one of the fuel jets from the fuel outlets.

Further advantageous embodiments are defined in the dependent claims 16-21. The objects are also reached with an internal combustion engine according to claim 22,

Preferably, the engine is configured so that a corona discharged from an electrode of the combined fuel injector and igniter or the fuel injector is directed to a ground position on a delimitation of the combustion chamber. Where the combined fuel injector and igniter or the fuel injector is provided with a plurality of electrodes, the latter can be arranged so that each electrode is adapted to discharge a corona directed to a single one of a plurality of ground positions on the combustion chamber delimitation. The ground position or ground positions can be predetermined. Preferably, a centreline of the fuel outlet forms an angle with an imaginary straight line, extending from a tip of the electrode to the ground position, which angle (B) is 2.5-17.5 degrees, preferably 2.5-12.5 degrees.

In such an engine, use is made of a tenancy of a corona to be directed towards the closest conductive part presenting an electric ground. Thereby, a good control is obtained of the direction of the corona, and the fuel outlet is provided such that it forms said angle to the corona, at which at least a major portion of the corona is confined within a fuel jet from the fuel outlet. As understood from the discussion above, thereby a particularly advantageous and beneficial combustion can provided with a high octane fuel and a high compression ratio.

Preferably, the ground position is provided on the surface of a piston which is arranged to undergo a reciprocating movement in the cylinder by connection to a crankshaft of the engine. The piston forms a part of the combustion chamber delimitation. Since it is at its top dead position close to the combined fuel injector and igniter, the piston is an advantageous item to provide the ground position(s) for the corona discharge(s). The ground position(s) can be position(s) on the piston surface which is closest to a tip of the electrode. In some embodiments the ground position is provided on a protrusion on the piston. Thereby, by a suitable piston design presenting such a protrusion, the corona direction can be predetermined in an accurate manner. However, the ground position can be provided on other locations, such as on a rim on the piston where the latter lias a bowl shaped top. It is also possible for the ground position to be provided on a cylinder wall of the cylinder.

The objects are also reached with a vehicle according to claim 32, and a method according to any of the claims 33-41.

The objects are also reached with a method for providing a combustion in a combustion chamber of a cylinder of an internal combustion engine, comprising emitting, at the end of a compression stroke or at the beginning of an expansion stroke of a work cycle of the cylinder, a jet of fuel into the cylinder, characterised by providing, 2-20 crankshaft angle degrees after the start of the fuel jet emission, a corona discharge in the cylinder. By providing a corona discharge 2-20 crankshaft angle degrees after the start of the fuel jet emission, an effective combustion of a high octane fuel, such as ethanol, methanol, or petrol, at a high compression ratio, can be provided. In some embodiments, the method can comprise repeating, in the same work cycle, at the end of the compression stroke or at the beginning of the expansion stroke, said steps of emitting a jet of fuel into the cylinder, and providing, 2-20 crankshaft angle degrees after the start of the fuel jet emission, a corona discharge in the cylinder. Said repetition can be made 1-4 times in the same work cycle. Thereby an effective combustion can be supported also during the subsequent emissions of fuel jets.

The combustion process quality can also be further improved by the corona being discharged so that at least a major portion of the corona is confined within the fuel jet. Advantageously, said step of emitting a jet of fuel into the cylinder can comprise emitting simultaneously a plurality of fuel jets into the cylinder, and said step of providing a corona discharge in the cylinder can comprise providing simultaneously a plurality of coronas into the cylinder, wherein each corona in said corona discharge is dedicated to ignite a respective of the fuel jets. The objects are also reached with a computer program according to claim 47, a computer readable medium according to claim 48, and a controller according to claim 49.

DESCRIPTION OF DRAWINGS

Below embodiments of the invention will be described with reference to the drawings in which

- fig. 1 shows a vehicle in the form of a truck, comprising an internal combustion

engine,

- fig. 2 shows a cross-section of a part of the internal combustion engine in the vehicle in fig. 1,

- fig. 3 shows a longitudinal cross-section of a combined fuel injector and igniter in the internal combustion engine in the vehicle in fig, 1, and devices connected thereto,

- fig. 4 shows a detail in fig. 2,

- fig. 5 show ^r s the detail in fig. 4 in a view as seen from below in fig. 4,

- fig. 6 is a view corresponding to the view in fig. 5 in a alternative embodiment of the invention,

- fig, 7 shows a diagram indicating events in a method according to an embodiment of the invention, and

- fig. 8 shows a cross-section of a part of an internal combustion engine with an

alternative embodiment of the invention.

DETAILED DESCRIPTION Fig. 1 shows vehicle in the form of a truck, comprising an internal combustion engine, part of which is shown in a cross-sectional view in fig. 2. The engine is a piston engine, with a plurality of cylinders. Fig. 2 shows a cross-sectional view of an upper part of one of the cylinders 2, whereby the section coincides with a centreline of the cylinder 2. As is known, a piston 3 is adapted to move in a reciprocating manner in the cylinder 2 by a connection to a crankshaft (not shown) of the engine. A combustion chamber 4 is provided in the cylinder 2, and is delimited by the piston 3, the cylinder wall 201, and a cylinder head 5.

Reference is made also to fig. 3, fig. 4 and fig. 5. For each cylinder 2 a combined fuel injector and igniter 6 is provided, herein also referred to as an injector/igniter 6. The injector/igniter 6 presents a tip region 601 adapted to be exposed to the combustion chamber 4. As can be seen in fig. 3, the injector/igniter 6 comprises a fuel injection assembly comprising valve stem 602 and a valve actuator 603. A pressurised fuel supply device 604 is adapted to provide pressurised fuel to the fuel injection assembly. As can be seen in fig. 4 and fig. 5, at the tip region 601, the injector/igniter 6 presents four fuel outlets 605 adapted to emit a jet of fuel into the combustion chamber. The fuel outlets 605 are provided as bores. Each bore 605 has a straight and cylindrical shape and is adapted to emit a fuel jet which is parallel to the bore centreline. As can be seen in fig. 4 and fig. 5, the injector/igniter 6 also comprises a corona ignition assembly comprising four electrodes 606 provided in the tip region 601. As can be seen in fig. 3, the electrodes are electrically connected via conductors 607 to a charging assembly 608, which is powered by an electric power source 609, e.g. a 24 volt battery pack of the vehicle. The charging assembly is adapted to charge the electrodes 606 to a potential suitable for providing corona discharges in the combustion chamber.

As suggested in fig. 3, the valve actuator 603 and the charging assembly 608 are adapted to be controlled by a control unit 7. As can be seen in fig. 5, the fuel outlets 605 and electrodes 606 are arranged in four pairs. The tip region 601 presents a rotationally symmetric shape, more specifically a circular shape, and a centreline, indicated with a broken line 610 in fig. 4. The pairs of fuel outlets 605 and electrodes 606 are distributed around the centreline 610, provided at intervals in the circumferential direction of 90 degrees. The pairs of fuel outlets 605 and electrodes 606 are further arranged at equal distances from the centreline 610.

Referring to fig. 4, the fuel outlets 605 are arranged so that fuel jets emitted therefrom present an umbrella angle A, for example 138 degrees, (fig. 4 is not to scale), since the centrelines of the fuel outlets 605 form the same angle A.

As understood from fig. 4 and fig. 5, each electrode 606 is located radially outside the fuel outlet 605 in the respective pair of electrodes and fuel outlets. Each electrode has a triangular shape which is constant throughout its thickness, indicated with a "t" in fig. 4. Each electrode 606 presents a tip 611 and a symmetry line 612 extending through the tip 611, The orientation and the position of the symmetry line 612 are provided by an intersection of the two symmetry planes of the electrode 606. The geometric shape and the orientation of the electrodes 606 provides for coronas discharged from the electrodes 606 being directed so as to mainly coincide with an extension of the symmetry line 612 into the combustion chamber 4.

As can be seen from fig. 4, in each electrode and fuel outlet pair, the electrode symmetry line 612 forms an angle B to the centreline of the fuel outlet 605. Preferably, the angle B is angle is 2.5-17.5 degrees, preferably 2.5-12.5 degrees. It should be noted that the electrode symmetry lines 612 form an umbrella angle, A+2B, which is larger than the umbrella angle A formed by the fuel outlet centrelines.

Further, the fuel injection assembly, and in particular each fuel outlet 605 is arranged so that the fuel jet emitted therefrom presents a widening angle, opening angle, or cone angle C, indicated in fig. 2. The cone angle C can for example be within the range of 5-35 degrees. The fuel injection assembly and the corona ignition assembly thereby provides for at least a major portion of the coronas discharged from the electrodes 606 being confined within the respective fuel jets emitted from the respective fuel outlets 605. Thereby, the electrodes 606 are adapted to provide corona discharges dedicated to ignite respective fuel jets from the fuel outlets 605.

It should be noted that, as the fuel jet presents an air and fuel mixture which, in the lateral direction of the fuel jet, is increasingly lean with increasing distance from a centreline of the fuel jet, the fuel jet delimitation in the lateral direction of the fuel jet is herein considered to be a three dimensional surface, for example a cone shaped surface, where the lambda value is 10.

It should be noted that changing the pressure of the fuel injected might change the fuel jet cone angle C. Thus, where the engine load control involves variation of the fuel pressure, preferably the angle B between the centreline of the fuel outlet 605 and the corona discharge direction, e.g. the electrode symmetry line 612, is such that the coronas extend within the fuel jets at all engine loads. It should be noted that the engine load changes can also be controlled with varying the duration of the fuel jets, which variation in principle does not change the fuel jet cone angle C. As suggested in fig, 2, the corona ignition assembly is arranged so as to provide coronas having elongated shapes and presenting stems 613. In each corona, one or more branches 614 might extend from the stem. At least a major portion of the stem 613 is confined within the respective jet 615 emitted from the respective fuel outlet. Preferably, at least 50% of an imaginary line, extending from a tip of the respective electrode to an end of the respective corona being at the greatest distance from the tip, is within the outer delimitation of the fuel jet. It should be noted that the stem 613 is offset from the centreline of the fuel jet 615.

The embodiment described above provides for at least a major portion of the coronas discharged from the electrodes are confined within respective regions of the fuel jets where the lambda value is 0.4-1.8, preferably 0.6-1.8, preferably 1 ,1-1.8.

Reference is made to fig. 6 with a view corresponding to the view in fig. 5. In this alternative embodiment the fuel outlets 605 and the electrodes 606 are provided at substantially the same radial distance from the centreline 606 of the injector/igniter 6. Thereby the umbrella angle of the electrode symmetry lines, and the umbrella angle of centrelines of the fuel outlets can be substantially the same. It should be noted that the electrode symmetry lines and/or the fuel outlet centrelines could present an angle in the circumferential direction, so that in each electrode and fuel outlet pair, the electrode symmetry line 612 forms an angle to the centreline of the fuel outlet 605.

Reference is made to fig. 7. In a method according to an embodiment of the invention, in an internal combustion engine with injector/igniters 6, for example as the ones described above with reference to fig. 1 to fig. 6, the following steps are undertaken in each cylinder:

At the end of a compression stroke or at the beginning of an expansion stroke of a work cycle of the cylinder, a first plurality of jets of fuel is emitted Jl into the cylinder. At the end of a predetermined first crankshaft angle (CAD) interval following the start of the first jet emission, a first plurality of coronas are discharged CI in the cylinder, whereby each of said corona discharges are dedicated to ignite a respective of the fuel jets in the first jet emission.

Subsequently, in the same work cycle, said steps are repeated four times. I.e. a second, third, fourth and fifth pluralities of jets of fuel are emitted J2, J3, J4, J5 sequentially into the cylinder. At the end of respective predetermined second, third, fourth and fifth crankshaft angle intervals following the respective starts of the second, third, fourth and fifth jet emissions, respective second, third, fourth and fifth pluralities of coronas are sequentially discharged C2, C3, C4, C5 in the cylinder. Thereby, each of the corona discharges in the second, third, fourth and fifth pluralities of coronas are dedicated to ignite a respective of the fuel jets in the second, third, fourth and fifth pluralities of jet emissions, respectively.

As can be seen in fig. 7, the duration of the third plurality of jet emissions J3 is longer than the other pluralities of jet emissions, and can be referred to as a main injection. It should be noted that the plurality of coronas C3 dedicated to ignite a respective of the fuel jets in the third plurality of jet emissions J3 are discharged at the end of a crankshaft interval from the start of the third plurality of jet emissions J3 that is longer than the crankshaft intervals between the start of the first, second, fourth and fifth pluralities of jet emissions Jl, J2, J4, J5, and the first, second, fourth and fifth pluralities of corona discharges CI, C2, C4, C5. Preferably, any crankshaft interval from the start of a plurality of jet emissions to the discharge of a plurality of coronas, each dedicated to ignite a respective of the fuel jet emissions, is 2-20 crankshaft angle degrees, CAD.

It should be noted that in some embodiments, at each cycle, the amount of corona discharges are less, or much less, than the amount of jet emissions. For example, after the emission Jl of the first plurality of jets of fuel into the cylinder, and the subsequent discharge CI of the first plurality of coronas in the cylinder, the following emissions J2, J3, J4, J5 of pluralities of jets of fuel into the cylinder could each be provided without any respective corona discharge. Thereby, the following emissions J2, J3, J4, J5 of pluralities of fuel jets would be ignited with the combustion already initiated with the first plurality of fuel jets and the discharge CI of the first plurality of coronas.

Fig. 8 shows a cross-section of a part of an internal combustion engine with an alternative embodiment of the invention. As can be seen the piston 3, forming a part of a delimitation of the combustion chamber 4, presents a protrusion 301. The protrusion is provided as a circular ridge and extends around a centreline of the piston 3. The piston is provided such that at the top dead centre, the closest distance from the piston to any electrode is from the protrusion 301 to the respective electrode 606. Thus, the shortest distance from any electrode to the piston is an imaginary straight line L, extending from the tip of the electrode 606, to a respective position, herein also referred to as a ground position 302, on the surface of the piston protrusion 301. The piston is electrically grounded, and a corona from any of the electrodes will tend to be directed towards the closest part presenting an electric ground. Hence, the arrangement in fig. 8 provides for the corona being directed, essentially along said imaginary straight line L, to the respective ground position 302 on the piston protrusion being closest to the respective electrode. Thus, the ground positions 302 can be regarded as predetermined.

Further, a centreline (indicated with broken lines in fig, 8) of each fuel outlet 605 forms an angle B with said respective imaginary straight line L, which angle B is 2.5- 17.5 degrees, preferably 2.5-12.5 degrees.

In other embodiments, the ground positions 302 can be provided on other locations. For example, where the top of the piston is bowl shaped as in fig. 8, the ground positions 302 can be provided on a rim 303 of the bowl of the piston 3. In other embodiments, the ground positions 302 can be provided on the cylinder wall 201.