Fuel ignitor, cylinder head - fuel ignitor combination, a gas operated internal combustion engine and method of converting an existing internal combustion piston engine

Abstract

Invention relates to a fuel ignitor (10) for gaseous fuel comprising a body assembly (12) having a longitudinal axis (A), and a first axial end and a second axial end. The ignitor body assembly (12) comprises a. a prechamber (20) arranged at the first axial end and having a tip, and more than two jet openings (22) arranged to the tip of prechamber (20) at the first axial end, b. a fuel inlet (26) arranged to open into the prechamber (20), c. first cavity (28) arranged to extend from the second axial end of the body assembly (12) to proximity to the prechamber (20), wherein a solenoid actuated gas admission valve unit (29) is arranged in the first cavity (28), d. second cavity arranged to extend from the second axial end of the body assembly (12) to the prechamber (20), wherein an ignition device (31) is arranged in the second cavity in cooperation with the prechamber (20) so as to initiate combustion of fuel in the prechamber (20), when in use, e. cooling channels (32) arranged at the first axial end of the ignitor body assembly (12) arranged in heat transfer connection with the prechamber (20). Invention relates also to a cylinder head - fuel ignitor combination, a gas operated internal combustion engine and method of converting an existing internal combustion piston engine.

Description

Fuel ignitor, cylinder head - fuel ignitor combination, a gas operated internal combustion engine and method of converting an existing internal combustion piston engineTechnical field

[0001] Invention relates to a fuel ignitor for an internal combustion piston engine according to preamble of claim 1.

[0002] Invention relates to a fuel ignitor - cylinder head combination.

[0003] Invention relates to gas operated internal combustion piston engine according to preamble of a second independent claim.

[0004] Invention relates to a method of converting an existing engine to gas operated internal combustion piston engine.Background art

[0005] The present invention relates large, multi-cylinder internal combustion piston engines being capable of providing power more than 150 kW per cylinder. Such engines are typically provided at least six cylinders, commonly more than eight cylinders, and are used as main or auxiliary engines in marine vessel, or as power sources in land-based power plants. Traditionally such engines have been operated by combusting heavy fuel oil or in smaller engines with light fuel oil, but due to present and potentially coming stringent emissions legislation combustion of gaseous fuel, such as natural gas, has emerged in dual fuel (DF) engines. In DF engine gas is used as a main fuel, which is ignited in cylinders of the engine with a pilot injection of light fuel oil, which facilitates compression ignition of the fuel charge.

[0006] Because there is still a need to develop internal combustion engine towards even more clean operation with decreased emissions, it is an object of theinvention is to provide a fuel ignitor which is capable of inject and ignite gaseous fuel in accurate manner.

[0007] An object of the invention is also to provide a fuel ignitor - cylinder head combination, and a gas operated internal combustion piston engine as well as providing a method of converting an existing dual fuel engine, which is configured to combust premixed gaseous fuel as its main fuel and to ignite the main fuel with a direct injected liquid pilot fuel.Disclosure of the Invention

[0008] Objects of the invention can be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

[0009] A fuel ignitor for gaseous fuel according to an aspect of the invention comprises a body assembly having a longitudinal axis, and a first axial end and a second axial end, wherein the ignitor body assembly comprises a. a prechamber arranged at the first axial end and having a tip, and more than two jet openings arranged to the tip of prechamber at the first axial end, b. a fuel inlet arranged to open into the prechamber, c. first cavity arranged to extend from the second axial end of the body assembly to proximity to the prechamber, wherein a solenoid actuated gas admission valve unit is arranged in the first cavity, d. second cavity arranged to extend from the second axial end of the body assembly to the prechamber, wherein an ignition device is arranged in the second cavity in cooperation with the pre-chamber so as to initiate combustion of fuel in the prechamber, when in use, e. cooling channels arranged at the first axial end of the ignitor body assembly arranged in heat transfer connection with the pre-chamber.

[0010] A fuel ignitor according to the invention makes it possible to operate an engine by combusting single gaseous fuel such that main portion of the gas is brought into cylinder as a lean mixture with combustion air and a smaller portion of the same gas is administered to the prechamber of the ignitor, which is thenignited with the ignition device in the prechamber. With the ignitor according to the invention is possible to efficiently combust gaseous fuel brought into combustion chamber with combustion air as a mixture providing lambda value of 1 ,8 - to 2,5, whereas in the prechamber the lambda value being 0,9 - 1 ,2. Combustion of ignition fuel in the prechamber provides high energy flame into the combustion chamber for ignition of the main fuel mixture.

[0011] Control of timing of ignition of the main fuel is accurate by ignition with a flame created by combustion of a portion of the gas in the prechamber, with ignition using the ignition device. Then the ignition fuel is administered with a solenoid actuated fuel admission valve unit, propagation of combustion first in the prechamber and the in the combustion chamber can be controlled efficiently. The fuel ignitor according to the invention makes it possible to convert a dual fuel engine, which combust a gaseous fuel, such as LNG, as a main fuel by ignition of the mail fuel with direct injected liquid pilot fuel, such as light fuel oil, marine diesel fuel or diesel fuel, which is compression ignited, such that in the conversion liquid fuel pilot injection may be abandoned, and ignition of the main fuel can be accomplished with the same main gas using the ignitor according the invention.

[0012] According to an aspect of the invention in the fuel ignitor, cooling channels comprise a first channel which extends straight through the body assembly, perpendicularly to the longitudinal axis, having a first cooling channel opening and a second cooling channel opening, and a second channel which extends from middle area of the first channel to sidewall of the body assembly near the first cooling channel opening, and a third channel which extends from middle area of the first channel to sidewall of the body assembly near the second cooling channel opening, wherein the first channel, the second channel and the third channel are in arranged in a same plane.

[0013] The cooling channels provides efficient cooling of the solenoid actuated gas admission valve in the ignitor, and it can be positioned substantially near to the prechamber, ensuring accurate control of timing of admission of ignition fuel into the prechamber.

[0014] According to an aspect of the invention in the fuel ignitor, the cooling channels comprises a fourth channel extending from middle area of the first cooling channel to side wall of the body assembly, perpendicularly to the plane, and the cooling channels comprises a fifth channel extending from middle area of the first cooling channel to side wall of the body assembly, perpendicularly to the plane, wherein the fourth channel and the fifth channel a parallel to each other.

[0015] The parallel channels make is possible to cool down the spark plug efficiently.

[0016] According to an aspect of the invention in the fuel ignitor, the ignitor body assembly comprises three axially bordered interface areas on its outer surface, bordered by at least four sealing arrangements in circumference of the body assembly, wherein a first interface area is arranged to the vicinity of the first end of the body assembly bordered by a first sealing arrangement provided to the prechamber and a second sealing arrangement arranged axially at a distance from the prechamber such that the second sealing arrangement is located axially between first and second ends of the gas admission valve unit, and wherein the cooling channels of the fuel ignitor opens to the first interface area, a second interface area is arranged axially next to the first interface area bordered by the second sealing arrangement and a third sealing arrangement which is located axially at a distance from the second sealing arrangement and in a region of second end of the gas admission valve unit, and wherein a gas inlet channel opens to the second interface area so as provide a flow path from outer surface of the ignitor body assembly at the second interface area to the gas admission valve unit, a third interface area is arranged axially next to the second interface area bordered by the third sealing arrangement and a fourth sealing arrangement which is located axially in a region of second end of the gas admission valve unit and arranged axially at a distance from the third sealing arrangement, and wherein a gas leakage outlet channel opens to the third interface area so as provide a flow path for detection of gas leakage.

[0017] By means of the first interface area the lower portion, particularly the prechamber and the solenoid actuated gas admission valve can be cooledefficiently. The second and the third interface area handle gas flow into the gas admission valve as well as possible fuel leakage handling and / or detection. Moreover, the second interface area, in addition to feeding fuel to the admission valve, participates in cooling of the solenoid actuated fuel admission valve. In other words, this way the ignitor body assembly at the region of the solenoid actuated fuel admission valve can be efficiently cooled with cooperation of actual coolant and the gas fed to the admission valve.

[0018] According to an aspect of the invention in the fuel ignitor, the ignitor body assembly comprises a prechamber part which is removably attached to the body assembly, wherein major part of volume of the prechamber is arranged to the prechamber part.

[0019] This facilitate easy maintenance of the fuel ignitor, because the prechamber is a wearing part.

[0020] According to an aspect of the invention in the fuel ignitor, cooling channels extending through the body assembly are arranged at a distance from the prechamber, which distance is less than diameter of the cooling bore nearest to the prechamber.

[0021] This way heat transfer from the prechamber is efficient and temperature of the prechamber can be maintained at desired temperature.

[0022] According to an aspect of the invention in the fuel ignitor, the second sealing arrangement comprises two similar grooves arranged to circumscribe outer wall of the ignitor body assembly configured for use of an O-ring, wherein axial distance between the grooves is less than axial length of a groove.

[0023] This way the area of the ignitor, which is not subjected to active cooling, is minimized.

[0024] According to an aspect of the invention in the fuel ignitor, the second sealing arrangement is provided with a gas detection opening of a leakage gas channel between the grooves.

[0025] This way it is possible to detect leakage of the second sealing arrangement.

[0026] According to an aspect of the invention in the fuel ignitor, the first sealing arrangement comprises a ring surface arranged to the prechamber which surface is perpendicular to the longitudinal axis of the ignitor body assembly, and facing towards the tip of the prechamber, configured for sealing with a flat sealing ring, when in use, the second sealing arrangement comprises two similar grooves arranged to circumscribe outer wall of the ignitor body assembly configured for use of an O- ring, wherein axial distance between the grooves is less than axial length of a groove, the third sealing arrangement comprises one groove arranged to circumscribe outer wall of the ignitor body assembly configured for use of an O-ring, and the fourth sealing arrangement comprises one groove arranged to circumscribe outer wall of the ignitor body assembly configured for use of an O-ring.

[0027] This way the sealings between the interface area are straightforward, easy to maintain and effective.

[0028] According to the invention a cylinder head - fuel ignitor combination comprising a cylinder head configured to close and seal a cylinder of an internal combustion engine, which cylinder head is provided with an ignitor opening configured to receive a fuel ignitor according to claim 4,5,7 or 8, such that the tip of the prechamber protrudes from the cylinder head, wherein a coolant chamber is bordered by an inner wall of the ignitor opening in the cylinder head, the first interface area in outer wall of the fuel ignitor, the first sealing arrangement and the second sealing arrangement, wherein the first sealing arrangement and the second sealing arrangement forming a seal between the fuel ignitor body assembly and the cylinder head, and wherein the cylinder head is provided with coolant channels which open into the coolant chamber at two locations, preferably next to the first sealing arrangement and next to the second sealing arrangement, a fuel feeding chamber is bordered by inner wall of the ignitor opening in the cylinder head, the second interface area in outer wall of the fuel ignitor, thesecond sealing arrangement and the third sealing arrangement, wherein the second sealing arrangement and the third sealing arrangement forming a seal between the fuel ignitor body assembly and the cylinder head, and wherein the cylinder head is provided with fuel feeding channel which opens into the fuel feeding chamber between the second sealing arrangement and the third sealing arrangement, a fuel leakage detection chamber (120) is bordered by inner wall of the ignitor opening in the cylinder head, the third interface area in outer wall of the fuel ignitor, the third sealing arrangement and the fourth sealing arrangement, wherein the third sealing arrangement and the fourth sealing arrangement forming a seal between the fuel ignitor body assembly and the cylinder head, and wherein the cylinder head is provided with leakage fuel channel which opens into the fuel leakage chamber between the third sealing arrangement and the fourth sealing arrangement.

[0029] This kind of invention a cylinder head - fuel ignitor combination makes it possible to operate an internal combustion engine by combusting one single gaseous fuel effectively. With the present invention the engine can be operated with only a single gaseous fuel and combusted the fuel in lean burn, i.e. utilizing lean fuel-air mixture to optimize the fuel economy and minimize the emissions, with reliable ignition and combustion of such mixture. With the present invention abnormal combustion, such as misfiring and knocking can be avoided due to accurate control of the fuel ignitor to provide reliably ignitable mixture into the prechamber of the fuel ignitor, which is capable then igniting and timing correctly the combustion of the main charge inside the main combustion chamber of a cylinder.

[0030] According to an aspect of the invention in the cylinder head - fuel ignitor combination, the cooling channels arranged at the first axial end of the ignitor body comprises cooling channels, including a first channel which extends straight through the body assembly, perpendicularly to the longitudinal axis, having a first cooling channel opening and a second cooling channel opening, and a second channel which extends from middle area of the first channel to sidewall of the body assembly near the first cooling channel opening, and a third channel which extends from middle area of the first channel to sidewall of the body assemblynear the second cooling channel opening, wherein the first channel, the second channel and the third channel are in arranged in a same plane.

[0031] The cooling channels provides efficient cooling of the solenoid actuated gas admission valve in the ignitor, and it can be positioned substantially near to the prechamber, ensuring accurate control of timing of admission of ignition fuel into the prechamber.

[0032] According to an aspect of the invention in in the cylinder head - fuel ignitor, the cooling channels comprises a fourth channel extending from middle area of the first cooling channel to side wall of the body assembly, perpendicularly to the plane, and the cooling channels comprises a fifth channel extending from middle area of the first cooling channel to side wall of the body assembly, perpendicularly to the plane, wherein the fourth channel and the fifth channel a parallel to each other.

[0033] The parallel channels make is possible to cool down the spark plug efficiently.

[0034] A gas operated internal combustion piston engine comprising multiple cylinders in a line of cylinders parallel to a crank shaft, preferably as in-line or v- configuration, the engine comprising a gas delivery pipe, comprising a double wall structure having an inner and an outer flow channel, extending from a first end to a second end of the line of cylinders, an air receiver extending from a first end to a second end of the line of cylinders, an air supply channel arranged in connection with each cylinder of the engine connecting the air receiver to a combustion air inlet of a cylinder head of the cylinder, a first gas admission valve unit arranged to each air supply channel, configured to administer a first portion of fuel gas, preferably a main portion, into combustion air prior to entering a combustion chamber, when in use, and a first gas feed pipe, comprising a double wall structure having an inner and an outer flow channel, for each first gas admission valve unit, is arranged to couple the first gas admission valve unit with the gas delivery pipe in gas tightmanner, such that the inner flow channels are coupled with each other, and the outer flow channels are coupled with each other, a fuel ignitor arranged to the cylinder head of each cylinder of the engine, the fuel ignitor comprising a prechamber, an ignition device arranged co-operation with the prechamber so as to initiate combustion of fuel in the prechamber when in use, and a second gas admission valve unit, comprising a solenoid actuated fuel valve, arranged to administer a second portion of the fuel into the prechamber, when in use, a second gas feed pipe, comprising a double wall structure having an inner and an outer flow channel, for each second gas admission valve unit in the fuel ignitor, is arranged to couple the second gas admission valve unit with the gas delivery pipe in gas tight manner, such that the inner flow channels are coupled with each other, and the outer flow channels are coupled with each other.

[0035] This way the gas operated engine can be run without a separate liquid fuel pilot fuel system, which makes it more simple. Omission of the second fuel brings also many other advantages in fuel handling. This provides a simple continuous double wall main fuel pipe to deliver the main fuel for the air supply channel of each cylinder, as well as to the ignitors in the cylinders. Running the engine is only one gas, also decreases emissions. Simplifying the fuel delivery to the ignitor by extracting the gaseous fuel directly from the main fuel line may expose the ignitor fuel delivery to certain amount of pressure variations in the gaseous fuel line. These pressure variations may originate either from the main fuel line or from the actuation of the gas admission valve unit in the ignitor. Thanks to the electronically controlled gas admission valve unit in the very close proximity of the prechamber both located within the ignitor the effects of such pressure variations can be effectively compensated on cycle-to- cycle basis.

[0036] According to an aspect of the invention in the gas operated internal combustion piston engine, the engine comprises multiple cylinders in two lines of cylinders in v-con- figuration, and a space is formed between cylinder heads in the lines of cylinder, whereinthe gas delivery pipe comprises a first gas delivery pipe section and a second gas delivery pipe section which both extend from a first end to a second end of the line of cylinder and which gas delivery pipe sections are in flow connection with each other, such that the inner flow channels are coupled with each other, and the outer flow channels are coupled with each other, at one end of the gas delivery pipe sections, and the first gas delivery pipe section is provided with a fuel inlet at an opposite end to the one connected with the second gas delivery pipe, and the second gas delivery pipe section is provided with flow plug at an opposite end to the one connected with the first gas delivery pipe.

[0037] In V-engines this kind of gas delivery pipe is very advantageous. It is of simple structure, and thanks to is U-shaped form is requiring less connection pipes to the engine and thus saves space.

[0038] According to an aspect of the invention in the gas operated internal combustion piston engine the piston engine comprises a fuel ignitor according to anyone of the claims 1 to 9.

[0039] According to an aspect of the invention in the gas operated internal combustion piston engine the piston engine comprises a cylinder head - fuel ignitor combination according to anyone of the claims 10-11.

[0040] Method of converting a fuel injection system of an existing engine which is configured to combust gaseous fuel as a main fuel and to ignite the main fuel by compression ignition of direct injection of liquid pilot fuel, the method comprising removing existing cylinder heads from the engine, including injectors for injecting the pilot fuel, providing a fuel ignitor for each cylinder of the engine, wherein fuel ignitor comprising a body assembly having a longitudinal axis, and a first axial end and a second axial end, wherein the ignitor body assembly comprisesa. a prechamber arranged at the first axial end and having a tip, and more than two jet openings arranged to the tip of prechamber at the first axial end, b. a fuel inlet arranged to open into the prechamber, c. second cavity arranged to extend from the second axial end of the body assembly to the prechamber, wherein an ignition device is arranged in the second cavity in cooperation with the pre-chamber so as to initiate combustion of fuel in the prechamber, when in use, d. first cavity arranged to extend from the second axial end of the body assembly to proximity to the prechamber, wherein a gas admission valve unit is arranged in the first cavity, and wherein the gas admission valve unit comprises a solenoid actuated fuel valve, e. cooling channels arranged at the first axial end of the ignitor body assembly extending transversely through the body assembly and arranged in heat transfer connection with the prechamber, and f. three axially bordered interface areas on its outer surface, bordered by at least four sealing arrangements in circumference of the body assembly, wherein i. a first interface area is arranged to the vicinity of the first end of the body assembly bordered by a first sealing arrangement provided to the prechamber and a second sealing arrangement arranged axially at a distance from the prechamber such that the second sealing arrangement is located axially between first and second ends of the gas admission valve unit, and wherein the cooling channels open into the first interface area, ii. a second interface area is arranged axially next to the first interface area bordered by the second sealing arrangement and a third sealing arrangement which is located axially at a distance from the second sealing arrangement and in a region of second end of the gas admission valve unit, and wherein a gas inletchannel opens to the second interface area so as provide a flow path from outer sur-face of the ignitor body assembly at the second interface area to the gas admission valve unit, iii. a third interface area is arranged axially next to the second interface area bordered by the third sealing arrangement and a fourth sealing arrangement which is located axially in a region of second end of the gas admission valve unit and arranged axially at a distance from the third sealing arrangement, and wherein a gas leakage outlet channel opens to the third interface area so as provide a flow path for detection of gas leakage, providing a cylinder head for each cylinder of the engine, wherein the cylinder head comprising a. an ignitor opening configured to receive the fuel ignitor provided, such that the tip of the prechamber protrudes from the cylinder head, wherein b. a coolant chamber which is bordered by an inner wall of the ignitor opening in the cylinder head, the first interface area in outer wall of the fuel ignitor, the first sealing arrangement and the second sealing arrangement, wherein the first sealing arrangement and the second sealing arrangement forming a seal between the fuel ignitor body assembly and the cylinder head, and wherein the cylinder head is provided with coolant channels which open into the coolant chamber at two locations, preferably next to the first sealing arrangement and next to the second sealing arrangement, c. a fuel feeding chamber which is bordered by inner wall of the ignitor opening in the cylinder head, the second interface area in outer wall of the fuel ignitor, the second sealing arrangement and the third sealing arrangement, wherein the second sealing arrangement and the third sealing arrangement forming a seal between the fuel ignitor body assembly and the cylinder head, andwherein the cylinder head is provided with fuel feeding channel which opens into the fuel feeding chamber between the second sealing arrangement and the third sealing arrangement, d. a fuel leakage detection chamber (120) which is bordered by inner wall of the ignitor opening in the cylinder head, the third interface area in outer wall of the fuel ignitor, the third sealing arrangement and the fourth sealing arrangement, wherein the third sealing arrangement and the fourth sealing arrangement forming a seal be-tween the fuel ignitor body assembly and the cylinder head, and wherein the cylinder head is provided with leakage fuel channel which opens into the fuel leakage chamber between the third sealing arrangement and the fourth sealing arrangement, and installing the ignitors into the cylinder heads and installing the thus formed cylinder head - fuel ignitor combination to the engine, and installing a gas feed pipe for each cylinder of the engine connecting a gas delivery pipe of the engine to gas admission valve unit in the fuel ignitor.

[0041] Conversion method brings about a possibility to improve the existing engine to operate with one gaseous fuel only. This way a need for second, pilot fuel system is removed. Engine run cleaner with pure gaseous fuel than when a separate pilot fuel is needed.

[0042] According to an aspect of the invention in converting a fuel injection system, further the existing a gas delivery pipe is re-moved from the engine, and a new gas delivery pipe, comprising a double wall structure having an inner and an outer flow channel, in installed to extend from a first end to a second end of the line of cylinders, wherein the new gas delivery pipe comprises- a first gas feed pipe for each cylinder of the engine, comprising a double wall structure having an inner and an outer flow channel an outlet for each main gas admission valve of the engine, the inner and outer flow channels connected to the inner and outer flow channels of the gas delivery pipe and main fuel gas admission valve- a second gas feed pipe for each cylinder of the engine, comprising a double wall structure having an inner and an outer flow channel, the inner and outer flow channels connected to the inner and outer flow channels of the gas delivery pipe and gas admission valve unit in the fuel ignitor in the cylinder head.

[0043] According to an aspect of the invention in converting a fuel injection system, the fuel ignitor provided is a fuel ignitor according to anyone of the claim 1 to 9.

[0044] According to an aspect of the invention in converting a fuel injection system, the cylinder head - fuel ignitor combination provided is according to anyone of the claims 10-11.

[0045] In connection with this application the word “prechamber” means a precombustion chamber connected to the main combustion chamber, which is a small auxiliary chamber that facilitates ignition and combustion of small amount of fuel in the prechamber and subsequently causes ignition of a main fuel premixed with combustion air in a cylinder of the engine. Such a small amount of fuel fed to the prechamber may be called ignition gas. Unless otherwise specified, the word “gas” is used for combustible fuel, which is in gaseous phase when delivered to an internal combustion piston engine and administered to combustion chamber and / or prechamber or the engine, i.e. gaseous fuel.

[0046] The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims.Brief Description of Drawings

[0047] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in whichFigure 1 illustrates a side view of a fuel ignitor according to an embodiment of the invention,Figure 2 illustrates a top view of the fuel ignitor shown in the figure 1 ,Figure 3 illustrates a section A-A of the fuel ignitor shown in the figure 1 ,Figure 4 illustrates a section B-B of the fuel ignitor shown in the figure 1 ,Figure 5 illustrates a section C-C of the fuel ignitor shown in the figure 1 ,Figure 6 illustrates a section D-D of the fuel ignitor shown in the figure 1 ,Figure 7 illustrates a section E-E of the fuel ignitor shown in the figure 1 ,Figure 8 illustrates a section F-F of the fuel ignitor shown in the figure 1 ,Figure 9 illustrates cooling channels in the fuel ignitor according to an embodiment of the invention,Figure 10 illustrates a cylinder head where a fuel ignitor is assembled,Figure 11 illustrates a gas operated internal combustion piston engine according to an embodiment of the invention, andFigure 12 illustrates a gas operated internal combustion piston engine according to another embodiment of the invention.Detailed Description of Drawings

[0048] Figure 1 depicts schematically a fuel ignitor 10 according to an embodiment of the invention, figure 2 shows the ignitor 10 from above and explains the sections of the ignitor shown in the figures 3 to 8. It should be understood that all of the features disclosed in the figures 1 to 8 are not essential to provide a technical effect according to an aspect of the invention, to at least some extent.

[0049] Aspects of the invention concerning mainly the ignitor, are described in the following with reference to the figures 1 to 10. Functionally the fuel ignitor10 is configured to operate as an ignitor of charge of premixed gas in a combustion chamber of an internal combustion piston engine. The fuel ignitor 10 comprises a body assembly 12, indicating that the body of the fuel ignitor is preferably an assembly of several body parts 12.1 ,12.2.12.3. The fuel ignitor is rotationally substantially symmetrical of its outer shape, in relation to it longitudinal axis A. The fuel ignitor 10 is provided with a first cavity 28 for assembly of a gas admission valve unit 29 and a second cavity 30 for assembly of a spark plug 31. The gas admission valve unit comprises a solenoid actuated gas admission valve, which means that valve means which opens or closes flows communication through the valve unit, is directly operated by a solenoid, that is, there is not hydraulic of pneumatic components in the gas admission valve unit 29, in other words the solenoid actuated valve has a direct force transmission connection between a solenoid and a valve needle, without an intermediate working fluid.

[0050] The ignitor body assembly 12 comprises a prechamber volume 20, plain prechamber in the following, which is arranged at the first axial end of the ignitor body assembly. The prechamber is preferably removably attached to the body assembly 12, and major part of volume of the prechamber is arranged to the prechamber part. In general, as is depicted in the figure 3, the prechamber 20 comprises a rotationally symmetrical space which is comprised of jet openings 22 arranged to first end of the prechamber i.e. to a tip 24 of the prechamber, a prechamber main chamber arranged at a second end, opposite to the first end of the prechamber, and a prechamber flow channel, for example a funnel type structure, which extends from the prechamber main chamber towards the first end and connects the jet openings 22 to the prechamber main chamber. The tip 24 of the prechamber 20, when assembled to a cylinder head, protrudes from a cylinder head into a combustion chamber of the engine. Using the prechamber ignites main gas fuel by igniting a small amount of gas in the prechamber, and therefore there is a fuel inlet 26 arranged to open into the prechamber.

[0051] Gas is admitted to the prechamber by means of the solenoid actuated gas admission valve unit 29, which is shown in the figure 3 only schematically. A solenoid actuated gas admission valve unit 29 is arranged in the first cavity 28, when the fuel ignitor is assembled for use. The ignition gas is administered by the solenoid actuated valve and admitted to the prechamber. The solenoidactuated gas admission valve unit 29 is generally cylindrical and in has gas inlet at its cylindrical side wall and gas outlet is arranged at a first axial end of the gas valve. In order to accommodate such a gas admission valve unit 29 into the ignitor 10, the ignitor body assembly 12 comprises the first cavity 28 extending from the second axial end of the body assembly to proximity to the prechamber 20. The second axial end may also be referred to as upper end, because the ignitor is usually installed substantially in a position where the prechamber is downwards. Thus, the second cavity is configured to receive the solenoid actuated gas admission valve unit 29, and they are compatible for installing the gas admission valve unit 29 into the cavity in sealed manner, and such that fluid exchange functions in intended manner.

[0052] The first cavity 28 includes at its end a first boring section 28.1 , being an attachment part, close to the prechamber 20. The attachment part is provided with internal thread on its surface, which is provided for attaching the gas admission valve unit 29 to the first cavity 28. The internal thread has an axial end at the side of the prechamber, which in other words means a lower edge of the thread. The gas admission valve unit 29 suitable for use has its gas outlet opening at its axial end, and a mating thread on its outer surface. The first cavity 28 has a second boring section 28.2 axially after (upwards in the figure 3) after the first boring section 28.1. The second boring section 28.2 is cylindrical, and it has larger diameter than the first boring section 28.1 at the axial location closest to the second boring section. The treaded first boring section 28.1 may be slightly conical in some practical applications. There is a radial sealing surface 28.3 arranged to the end of the second boring section 28.2, against which the gas admission valve unit 29 may be sealed when assembled to the ignitor 10. The sealing face 28.3 is substantially perpendicular to the axial direction of the first cavity 28. The first cavity 28 has a third boring section 28.4 axially after (upward in the figure 3) the second boring section 28.2. The third boring section 28.4 is cylindrical, and it has larger diameter than the second section 28.2. A transition from diameter of the second boring section 28.2 to the diameter of the third boring section 28.4 is a first conical part 28.5. Further, the first cavity 28 has a fourth boring section 28.6 axially after (upward in the figure 3) the third boring section 28.4. The fourth boring section 28.6 is cylindrical, and it has larger diameter than the third section 28.4. In a transition from diameter of the third boring section 28.4to the diameter of the fourth boring section 28.6 is a second conical part 28.7. When the gas admission valve unit 29 includes compatible shoulder at the location of the first and the second conical parts 28.5, 28.7 as sealing rings may be used for sealing the second boring section 28.2 from the third boring section 28.4.

[0053] This way the third boring section 28.6 is axially bordered by the first conical part 28.5 and the second conical part 28.7. The conical parts provide a sealing surface for the gas admission valve unit 29. When the gas admission valve unit is installed in the first cavity, there is an annular space between the gas admission valve unit 29 and first cavity 28, the second boring section 28.2 and the third boring section 28.4 thus forming separated spaces.

[0054] The body assembly 12 comprises a gas feeding flow path, preferably a boring, which extends between outer surface of the body assembly 12 and inner surface of the first cavity 28. The gas feeding boring 18 has an outlet 18.2, i.e. the opening in the inner surface of the first cavity 28, which outlet 18.2 is positioned axially in the first cavity 28 between the radial sealing surface 28.3 arranged to the end of the second boring section 28.2 and the first conical part 28.5 of the first cavity 28. Respectively, the gas admission valve unit 29 has a gas inlet within the same section 28.2 for receiving gas at delivery pressure.

[0055] The gas feeding boring 18 extends inside the body assembly axially and it opens into an inlet 18.1 arranged to an outer surface of the body assembly 12. The gas feeding boring 18 extends inside the body assembly axially and, according to an aspect of the invention, and it extends from a second interface area 14.2 on outer surface of the body assembly, to position inside the first cav- ity28 positioned between the radial sealing surface 28.3 arranged to the end of the second boring section 28.2 and the first conical part 28.5 of the first cavity 28.

[0056] The first cavity 28 is arranged in flow communication with the prechamber 20 via borings between bottom of the first cavity and the prechamber. The borings comprise a coaxial extension bore 28.8 extending downwards from the treaded first boring section 28.1 toward the prechamber 20. The extension bore has smaller diameter than diameter of the first boring section 28.1 , but diameter of the coaxial extension is such that face area of the extension bore 28.8 isgreater than gas outlet opening of the gas admission valve unit 29, so as to make possible trouble-free admission of fuel into the coaxial extension bore 28.8 and the prechamber 20. When assembled to the first cavity, the gas admission valve unit 29 feeds gas to the coaxial extension bore 28.8. In other words, the gas fuel is admitted to the prechamber via a boring, it is not directly injected into the prechamber. This way effect of heat generated in the prechamber is decreased.

[0057] The coaxial bore extension 28.8 is connected to an upper end of the prechamber 20 via a connection boring 28.9, which opens into the prechamber at its second end via the fuel inlet 26. The connection boring 28.9 extends between the coaxial extension bore 28.8 and the fuel inlet 26 in the prechamber 20. Thus, the ignitor body assembly 12 is provided with a boring between the gas admission valve gas outlet and the prechamber. The fuel inlet 26 is arranged to an upper wall of the prechamber to which also a second cavity 20 opens and the spark plug is positioned. The extension bore 28.8 is at an angle to longitudinal axis A of the ignitor body assembly 12 and it is directed towards the opening of the second cavity 30 for the spark plug 31 in the prechamber. This way it is ensured that circumstances at the vicinity of electrodes of the spark plug in the prechamber are favourable to ignition of the gas, when igniting spark is applied, in swirling motion of gas (mainly fuel and air) in the prechamber.

[0058] The second cavity 30 is arranged to extend from the second axial end of the body assembly 12 to the prechamber 20. A spark plug 31 , or more generally an ignition device, is arranged in the second cavity 30 in cooperation with the prechamber so as to initiate combustion of fuel in the prechamber, when in use. The spark plug is attached to the ignitor body assembly 12 at a bottom of the second cavity 30 such that its active part providing ignition, such as electrodes in a spark plugs, is in, or at least in direct connection with a main chamber of the prechamber 20. The first cavity 28 and the second cavity 30 are arranged in parallel to each other and to longitudinal axis of the ignitor body assembly 12.

[0059] The second cavity 30 is preferably of substantially constant diameter, except that it is provided with a first boring section 30.1 , which has smaller diameter than other parts of the second cavity 30. The first boring section 30.1 of the second cavity 30 is provided with internal thread on its surface. The internal thread has axial ends, which in other words means upper and lower edges of thethread. The internal thread is provided for attaching the spark plug to the ignitor body assembly, in the first boring section 30.1 of the second cavity 30. The first boring section 30.1 of the second cavity for the spark plug, opens into the main chamber of the prechamber 20, such that a spark can be generated into the main chamber of the prechamber by the spark plug 31. There is a radial sealing surface 30.2 arranged to the end of the second cavity 30, to the location where the first section 30.1 begins, which sealing surface 30.2 is substantially perpendicular to the longitudinal axis of the body assembly 12. The spark plug 31 is assembled with a substantially flat sealing ring which is pressed against the axial sealing surface 30.2 when the spark plug is tightened, thus sealing the prechamber.

[0060] The threaded part of the first cavity 28, i.e. the first boring section 28.1 of the first cavity 28 is axially farther from the prechamber 20 than the threaded part of the second cavity 30, i.e. first boring section 30.1 of the second cavity 30 This determines minimum distance of the (outlet) of the gas admission valve to the prechamber. This way temperature of the gas admission valve unit 29 during normal use is at suitable temperature, the temperature being lower than temperature of the spark plug 31 , or the first boring section 30.1 of the second cavity 30. This increases lifetime expectancy of the solenoid gas admission valve unit 29.. Preferably, the lower edge of the thread in the first boring section 28.1 of the first cavity above the lower edge of the internal edge in the first boring section 30.1 of the second cavity 30. Most preferably, the lower edge of the thread in the first boring section 28.1 of the first cavity above the upper edge of the internal edge in the first boring section 30.1 of the second cavity 30.

[0061] On the other hand, in order to obtain adequate control of timing of gas entering the prechamber, total length and / or volume of the coaxial extension bore 28.8 and the connection boring 28.9 between the coaxial extension bore 28.8 and the fuel inlet 26, need to be below a certain predetermined maximum limit. This determines maximum distance of the (outlet) of the gas admission valve to the prechamber. It has been found out that the coaxial extension bore 28.8 and the connection boring 28.9 have an average ratio of length to diameter between 6 - 14. This way controllability of gas admission to the prechamber with and lifetime expectancy of the solenoid gas admission valve unit 29 and is still as desired, and the gas admission valve unit 29 is axially far enough from theprechamber and / or first boring section 30.1 of the second cavity 30. Preferably the connection boring 28.9, which is closer to the prechamber than the coaxial extension bore 28.2, has smaller diameter than the coaxial extension bore 28.2. This increases velocity of admitted gas before entering the prechamber 20.

[0062] The gas admission valve unit 29 is substantially near to the prechamber 20 and therefore, with the combination of solenoid actuated gas admission valve unit and separately controllable timing of initiation of combustion of ignition gas in the prechamber provides accurate and reliable timing of ignition of the main fuel in the cylinder. Timing of admission of the fuel in the prechamber may be controlled separately to timing of ignition of the gas in the prechamber, which provides versatile controllability of combustion process.

[0063] With a reference to the figures 8 and 1 , the body assembly 12 comprises further a first leakage gas flow path, including a boring 19, which extends between outer surface of the body assembly 12 and inner surface of the first cavity 28. The first leakage gas flow path 19 has an inlet 19.1 , i.e. the opening in the inner surface of the first cavity 28, which inlet 19.1 is positioned axially in the first cavity 28 between the first conical part 28.5 of the first cavity 28 and the second conical part 28.7 of the first cavity 28. Respectively, the gas admission valve unit 29 has a leakage gas outlet within the third boring section 28.4 for safely discharging potentially leaked gas for further processing as desired.

[0064] The first leakage gas flow path 19 extends inside the body assembly axially over the third sealing arrangement 16.3 and, according to an aspect of the invention, opens into a radial space arranged between a second body part 12.2 and a third body part 12.3 of the body assembly 12 and further extends via a radial channel 19.3 to outer surface of the body assembly 12, as is shown in the detail G in the figure 1. The first leakage gas flow path thus opens in in a third fluid interface 14.3. Correct position of the second body part 12.2 and the third body part 12.3 is ensured by pins 27 as is disclosed in the figure 6.

[0065] There are cooling channels 32, as explained mainly referring the figures 4 and 9, arranged at the first axial end of the ignitor body assembly 12, to the proximity of the prechamber 12. The cooling channels comprise at least the first flow channel 32.1 which extends straight through the body assembly,perpendicularly to the longitudinal axis A, and which is arranged at a distance from the prechamber 12, which distance to the prechamber is less than diameter of the first flow channel 32.1. The first flow channel 32.1 is preferably arranged axially between the first boring section 30.1 of the second cavity 30 and the connection boring 28.8 between the coaxial extension bore 28.8 and the prechamber 20.

[0066] The cooling channels 32 are preferably formed of several interconnected channels. The cooling channels 32 are arranged in heat transfer connection with the prechamber 20, because the prechamber is the major heat source in the ignitor 10. The cooling channels are arranged generally to extend transversely through the ignitor body assembly 12 above (in the position of the figures) the prechamber 12. Figure 9 discloses a form of the channels according to an embodiment of the invention in more detailed manner. The first channel 32.1 which extends straight through the body assembly has a first cooling channel opening 32.2 and a second cooling channel opening 32.3 at opposite sides of the body assembly 12. The is a second channel 32.4 which extends from middle area of the first channel 32.1 to sidewall of the body assembly near the first cooling channel opening 32.2, above it in the figure, and a third channel 32.5 which extends from middle area of the first channel to sidewall of the body assembly near the second cooling channel opening 32.3, above it in the figure. The first channel 32.1 , the second channel 32.4 and the third channel 32.5 are arranged in a same plane with each other and with longitudinal axis of the ignitor body assembly 12. The fist cavity 28 and the second cavity 60 are opposite sides of the plane formed by the first channel 32.1 , the second channel 32.4 the third channel 32.5 and the longitudinal axis A. This way cooling effect provided by coolant flowing in the cooling channel is subjected to both the solenoid actuated gas admission valve unit 29 and the spark plug 31.

[0067] The cooling channels comprises a fourth channel 32.6 extending from middle area of the first cooling channel 32.1 to side wall of the body assembly 12, perpendicularly to the plane formed by the first channel 32.1 , the second channel 32.4 the third channel 32.5. The cooling channels further comprise a fifth channel 32.7 extending from middle area of the first cooling channel to side wall of the body assembly, which is also arranged in a direction normal of the plane.The fourth channel 32.6 and the fifth channel 32.7 a parallel to each other. The fourth and fifth channels run on both sides of the second cavity 30, enhancing cooling of the spark plug 31. Now turning to figure 1 , one can see the ignitor body assembly is provided with flow guides 33 around the openings of the fourth channel 32.6 and the fifth channel 32.7 on the side wall of the body assembly, which are configured to enhance coolant flow, flowing around the body assembly in direction towards the second end of the ignitor 10, into the fourth and the fifth cooling channels 32.5, 32.7. When the ignitor is assembled into a cylinder head the coolant flow generally upwards around the ignitor body assembly, and therefore the guides include a radial protrusion from the surface around the openings, positioned above the openings of the fourth channel 32.6 and the fifth channel 32.7. In the figure 1 the protrusions are realised by providing an axially extending recess to the outer surface of the body assembly, the recess having side wall perpendicular to the plane of the bottom of the recess, around the openings of the fourth channel 32.6 and the fifth channel 32.7.

[0068] This kind of cooling channels network provides efficient flow of coolant nearby the prechamber 23 and the first and the second cavities 28,30 keeping temperature of the ignitor, and particularly the solenoid actuated gas admission valve unit 29, at desired level.

[0069] As it can be seen in the figures 1 and 4 the ignitor body assembly is provided with axially extending, planar recesses 36, which are parallel to each other and arranged at opposite sides of the ignitor body. The recesses are arranged to the first interface area 14.1 and thus they increase locally a volume for cooling liquid space at the side of the ignitor body assembly 12, between the recess walls and inner wall of an ignitor opening in the cylinder head. This feature improves further cooling of the solenoid gas admission valve unit 29, because resistance of heat transfer is decreased due to shorter thickness of material between the first cavity 28 and the surface being in contact with coolant. Because of the recesses are symmetrically at two opposite sides of the body assembly cooling of. i.e. heat transfer from the gas admission valve unit is also symmetrical. This way temperature distribution in the gas admission valve unit is substantially even.

[0070] Next, fluid interfaces of the ignitor 10 with fluid channels of a cylinder head 102, to which the ignitor is configured to be installed, will be discussed in following with a reference to the figures 1 and 3. The interfaces are formed to an outer wall of the ignitor 10 and they communicate differently with ignitor 10. The body assembly 12 comprises separate interface areas 14.1 ,14.2,14.3 in its axial direction, that is, in the direction of the longitudinal axis A of the ignitor 10. The ignitor is provided with sealing arrangements 16.1 , 16.2, 16.3, 16.4 which border the interface areas in axial direction and fluidly separate them from each other. There are three axially bordered interface areas 14.1 ,14.2,14.3 on outer surface of the body assembly 12, bordered by four sealing arrangements. The sealing arrangement are arranged to circumscribe the body assembly and so also an interface area circumscribes the body assembly. The sealing arrangement are in fluid tight connection with counter surfaces in the cylinder head, when the ignitor 10 is assembled correctly to a cylinder head. The first interface area 14.1 is configured for exchanging coolant with the ignitor 10, the second interface area 14.2 is configured for feeding gas to the ignitor and the third interface area 14.3 is configured for leading possible leakage gas from the ignitor.

[0071] The first interface area 14.1 is arranged next to the first end of the body assembly 12, namely extending axially downwards to region of the prechamber 12. The first interface 14.1 is bordered by a first sealing arrangement16.1 at the prechamber and by a second sealing arrangement 16.2 at opposite axial end of the first interface 14.1. The first sealing arrangement 16.1 is arranged to a prechamber part 12.1 of the ignitor 10 and the second sealing arrangement16.2 is arranged axially at a distance from the prechamber part 12.1. The first sealing arrangement 16.1 comprises a radial sealing surface in the prechamber part 12.1 facing downwards towards the tip of the prechamber. The second sealing arrangement comprises two grooves 16.2’, 16.2” arranged to circumscribe outer wall of the ignitor body assembly configured for use of an O-ring. The two grooves are preferably similar.

[0072] The first interface is configured for providing flowing of cooling liquid from a cylinder head to the cooling channels 32 in the ignitor, and back to the cylinder head, as well as cool the outer wall of the body assembly 12 in the first interface area 14.1. As it becomes clear in the figure 3, the second sealingarrangement 16.2 is arranged axially at a distance from the prechamber. In respect to the first cavity 28 the second sealing arrangement 16.2 is located axially between the radial sealing surface 28.3 arranged to the end of the second boring section 28.2 and the first conical part 28.5. This way the first interface 14.1 extends axially upwards over the first boring section 28.1 and the radial sealing surface 28.3 arranged to the end of the second boring section 28.2, but lower than the first conical part 28.5 of the first cavity 28.

[0073] This way the first interface extends between the first and second ends of the gas admission valve unit 29, when assembled to the first cavity 28, and provides cooling of the gas admission valve unit 29, as well. Correspondingly the second sealing arrangement 16.2 is located axially above the first boring section 30.1 of the second cavity 30, therefore the first interface provides also cooling of the spark plug 31.

[0074] The second interface area 14.2 is arranged next to the first interface area 14.1 , above it, bordered by the second sealing arrangement 16.2 and a third sealing arrangement 16.3. The second interface area 14.2 extends radially from the second sealing arrangement 16.2. to the third sealing arrangement 16.3. The third sealing arrangement 16.3 is arranged axially above the first conical part 28.5, the third boring section 28.4 and the second conical part 28.7 in the first cavity 28. The third sealing arrangement 16.3 located axially in in a region of second end of the gas admission valve unit 29.

[0075] The second interface 14.2 is configured for feeding gas to the ignitor, more precisely to the gas admission valve unit 29. The inlet 18.1. of the gas feeding boring 18 is positioned within the second interface 14.2 as is shown in the figure 3 and the gas feeding boring extends from the second interface 14.2 inside the body assembly to the inlet 18.1 , for delivering the gas to the gas admission valve unit 29.

[0076] Both the first and second interfaces 14.1 , 14.2 provides cooling of the ignitor, because also the gas delivered to the gas admission valve unit 29 receives heat from the ignitor 10. In order to improve cooling effectiveness, axial distance between the grooves 16.2’, 16.2” of the second sealing arrangement16.2 is preferably less than axial length of a groove, so as to make an uncooled area of the ignitor 10 as small as possible, in practise.

[0077] The third interface 14.3 is arranged next to the second interface area 14.2, above it. The third interface area 14.3 extends radially from the third sealing arrangement 16.3 to the fourth sealing arrangement 16.4, which borders axially the third interface 14.3. The third sealing arrangement 16.3 is arranged axially above the second conical part 28.7 in the first cavity 28. The third sealing arrangement and the fourth sealing arrangement both comprise one groove arranged to circumscribe outer wall of the ignitor body assembly configured for use of an O-ring.

[0078] The third interface are 14.3 is configured for leading leakage gas away from the ignitor and / or for detecting a possible gas leakage. There are leakage channels preferably arranged in connection with the gas admission valve unit 29 and the second sealing arrangement 16.2. As is shown in the figure 8 and 1 the first leakage gas flow path 19 extends from the area between the first conical part 28.5 and the second conical part 28.7, via the first leakage gas flow path and further extends via radial channels 19.3 to outer surface of the body assembly 12, which located axially in the third interface 14.3. This way leakage from gas admission valve 29 may be routed to the third interface 14.3. In other words, the gas leakage flow path opens to the third interface area 14.3 so as provide a flow path for detection of gas leakage.

[0079] Now referring to the figure 7, the ignitor 10 is provided with a second leakage gas flow path 34, including an axially extending boring 34. The second leakage gas flow path 34 extends between outer surface of the body assembly 12 in the third interface area 14.3 and outer surface of the body assembly between the two grooves 16.2’, 16.2” of the second sealing arrangement 16.2.

[0080] The second leakage gas flow channel 34 has an inlet opening 34.1 i.e. the opening between the two grooves. The second leakage gas flow channel 34 extends into a radial space arranged between a second body part 12.2 and a third body part 12.3 of the body assembly 12, similarly to the first leakage channel 19, and further extends via radial channel 19.3 to outer surface of the bodyassembly 12, as is shown in the detail G in the figure 1. The second leakage gas flow path thus opens in in a third fluid interface 14.3.

[0081] In the figure 10 there is shown axial location of the first interface 14.1 is respect to coolant channels of a cylinder 102 configured for use with the ignitor 10. The cylinder is provided with coolant

[0082] Aspects of the invention concerning to the cylinder head - fuel ignitor combination 100 are described in the following with reference mainly to the figure 10. Figure 1 to 9 relate also to the cylinder head - fuel injector combination.

[0083] A cylinder head 102 for the cylinder head - fuel ignitor combination 100 is configured to close and seal a cylinder of an internal combustion engine. The cylinder head is provided with an ignitor opening 104 which configured to receive a fuel ignitor 10 according to the invention, such that the tip of the prechamber protrudes from the cylinder head into the combustion chamber of the engine. The cylinder head 102 is also provided with mating surfaces with the first sealing arrangement 16.1 , the second sealing arrangement 16.2, the third sealing arrangement 16.3 and with the fourth sealing arrangement 16.4 at location in the ignitor opening 104 corresponding to axial locations of the sealing arrangements in the ignitor body assembly 12, when assembled into the ignitor opening 104.

[0084] Aspects of the fuel ignitor 10 in the cylinder head - fuel ignitor combination 100have been described above and can be seen in the figures 1 to 9.

[0085] When the ignitor 10 is assembled to the cylinder head 102, forming the cylinder head - fuel ignitor combination 100, a coolant chamber 106 is formed, which is bordered by an inner wall of the ignitor opening 104 in the cylinder head, the first interface area 14.1 in outer wall of the fuel ignitor 10, the first sealing arrangement 16.1 and the second sealing arrangement 16.2 in the ignitor 10. The first sealing arrangement 16.1 and the second sealing arrangement 16.2 form a seal between the fuel ignitor body assembly 12 and the cylinder head 102. The cylinder head is provided with coolant channels 108 which open into the coolant chamber 106 at two axial locations 108.1 108.2, next to the first sealing arrangement 16.1 and next to the second sealing arrangement 16.2.

[0086] Coolant flow in the cylinder head - fuel ignitor combination 100 takes place as follows. The coolant flows into the cylinder from below into coolant channels 108 and flow symmetrically towards the center of the cylinder head 102. The channels 108 opens into the coolant chamber 106 a location 108.1 which is at lower end of the first interface area 14.1 in the ignitor 10. Coolant flows partially around the ignitor upwards in the coolant chamber 106 and partially through the cooling channels 32 provided in the ignitor 10, as explained above referring to the figures 1 to 9. The partial flows are combined at the second location 108.2 at the upper end of the first interface area 14.2 and coolant is removed from the coolant chamber 106 into coolant channels 106 of the cylinder for recirculation and removal of heat from the coolant.

[0087] When the ignitor 10 is assembled to the cylinder head 102 a fuel feeding chamber 110 is formed, which is bordered by inner wall of the ignitor opening 104 in the cylinder head 102, the second interface area 14.2 in outer wall of the fuel ignitor 10, the second sealing arrangement 16.2 and the third sealing arrangement 16.3 in the ignitor 10. The second sealing arrangement 16.2 and the third sealing arrangement 16.3 form a seal between the fuel ignitor body assembly 12 and the cylinder head 102. The cylinder head 102 is provided with fuel feeding channel 112 which opens into the fuel feeding chamber 110 between the second sealing arrangement 16.2 and the third sealing arrangement 16.3, that is within the second interface area 14.2.

[0088] When the ignitor 10 is assembled to the cylinder head 102 a fuel leakage chamber 120 is formed, which is bordered by inner wall of the ignitor opening 104 in the cylinder head 102, the third interface area 14.3 in outer wall of the fuel ignitor 10, the third sealing arrangement 16.3 and the fourth sealing arrangement 16.4. The third sealing arrangement 16.3 and the fourth sealing arrangement 16.4 form a seal between the fuel ignitor body assembly 12 and the cylinder head 10. The cylinder head 102 is provided with leakage fuel channel 122 which opens into the fuel leakage chamber 120 between the third sealing arrangement 16.3 and the fourth sealing arrangement 16.4, that is within the third interface area 14.3.

[0089] Aspects of the invention concerning to a gas operated internal combustion engine are described in the following with reference mainly to the figures 11 and 12.

[0090] Figure 11 discloses schematically a gas operated internal combustion piston engine 200 according to an aspect of the invention. Some of the features are common with the engine shown in the figure 12 is a so-called v-engine. The engine 200 in the figure 11 comprises multiple cylinders 201 in an in-line configuration of cylinders parallel to a crank shaft (not shown). The engine 200 comprises a gas delivery pipe 202, is of a double wall structure having an inner 202.1 and an outer flow channel 202.2 between an inner and outer wall 202.3, 202.3. The gas delivery pipe 202 extends from a first end to a second end of the line of cylinders 201. In practise this means that the gas delivery pipe 202 functions as a gas manifold which delivers gas to each one of the cylinders 201. The engine is also provided with an air receiver 204 extending from a first end to a second end of the line of cylinders. The air receiver 204 is connected to a super charger 206 which pressurized the air to suitable level. The air receiver 204 is in flow connection with each cylinder 201 via an air supply channel 206, which connects the air receiver 204 to a combustion air inlet 208 arranged to the cylinder head 102 installed to the cylinder 201. This way pressure of the combustion air is substantially equal to each one of the cylinders 201 . The fuel pressure need only to exceed the pressure of the charge air.

[0091] The engine is provided with a first gas admission valve unit 210 arranged in connection with each air supply channel 206. The first gas admission valve unit 210 is configured to administer a first portion of gas, preferably a main portion of the gas, into combustion air prior to entering a combustion chamber in the cylinder of the engine. The engine comprises a first gas feed pipe 212 for each first gas admission valve unit 210, which first gas feed pipe 212 is arranged to couple the first gas admission valve 210 unit with the gas delivery pipe 202 in gas tight manner. The first gas feed pipe 212 comprises also a double wall structure having an inner and an outer flow channel, and connection with the gas delivery pipe 202 is such that the inner flow channels of the first gas feed pipe and gas delivery pipe are coupled with each other, and the outer flow channels arecoupled with each other, respectively. This way potential leakage of the gas can be safely led to further processing, including leakage detection, from the engine.

[0092] The engine is further provided with a fuel ignitor 10 arranged to the cylinder head of each cylinder of the engine, the fuel ignitor comprising a prechamber, an ignition device, such as a spark plug, arranged in co-operation with the prechamber so as to initiate combustion of fuel in the prechamber when in use. Structure of the fuel injector 10, and its different aspects, are explained in more detailed manner with reference to the figures 1 to 9. In the fuel ignitor 10 there is a second gas admission valve unit arranged, which comprises a solenoid actuated fuel valve, which second gas admission valve unit is arranged to administer a second portion of the fuel into the prechamber, when in use. A second gas feed pipe 214 is arranged to the engine 200 in connection with each second gas admission valve unit in the ignitor 10. The second gas feed pipe 214 is arranged to couple the second gas admission valve unit with the same gas delivery pipe 202 as the first gas admission valve unit, in gas tight manner. The second gas feed pipe 214 comprises also a double wall structure having an inner and an outer flow channel, and connection with the gas delivery pipe 202 is such that the inner flow channels of the first gas feed pipe and gas delivery pipe are coupled with each other, and the outer flow channels are coupled with each other, respectively. This way potential leakage of the gas in the ignitor can be safely led to further processing, including leakage detection, from the engine.

[0093] Now turning to the figure 12 in which the engine 200 comprises multiple cylinders 201 in two lines of cylinders in v-configuration, and therefore there is a space is formed between cylinder heads 102 in the lines of cylinder. In a V engine the gas delivery pipe 202 comprises a first gas delivery pipe section 202.1 and a second gas delivery pipe section 202.1 which both extend from a first end to a second end of the line of cylinders 102 and the gas delivery pipe sections are in flow connection with each other, such that the inner flow channels are coupled with each other, and the outer flow channels are coupled with each other, at one end of the gas delivery pipe sections 202.1 ,202.2 only. In the V- engine the gas delivery pipe sections form generally a U-shaped gas delivery pipe. The first gas delivery pipe section 202.1 is provided with a fuel inlet 202.3 at an opposite end to the one connected with the second gas delivery pipe 202.2 and the secondgas delivery pipe section 202.2 is provided with flow plug 202.4, such as a flange, at an opposite end to the one connected with the first gas delivery pipe 202.1. This provides a space saving fuel delivery pipe for a V-engine.

[0094] The engine 200 is provided with a fuel ignitor 10 as described in the figures 1 to 9, which makes it possible to connect the gas admission valve units via the first and the second gas feed pipes 212, 214 to the same fuel delivery pipe 202, wherein both the fuel admission valves are configured to administer gas at the same pressure, when the first gas admission valve unit 201 is configured to the air supply channel and the second ga admission valve unit 29 in the ignitor10 is configured to administer fuel into to prechamber 20 of the ignitor. This way the engine is run successfully such that both the main and igniting fuel portions are same gas, delivered at same pressure.

[0095] The cylinder head - fuel ignitor combination in the engine, in both figures11 and 12 is shown and described in the figure 10.

[0096] Aspects of the invention concerning to method of converting an existing internal combustion piston engine are described in the following with reference mainly to the figures 11 and 12.

[0097] Method of converting a fuel injection system of an existing dual fuel engine which is configured to combust gaseous fuel as a main fuel and to ignite the main fuel by compression ignition of direct injection of liquid pilot fuel is explained in the following with the reference to the figures as follows.

[0098] An existing engine comprises a gas delivery pipe which comprises a double wall structure having an inner and an outer flow channel, extending from a first end to a second end of the line of cylinders, and there is no need to replace that. However, existing cylinder heads are removed from the engine, including injectors for injecting the pilot fuel into the cylinders. Further a fuel ignitor is provided for each cylinder of the engine, wherein fuel ignitor 10 comprising a body assembly 12 having a longitudinal axis, and a first axial end and a second axial end, wherein the ignitor body assembly 12 comprises, with reference to the figures 1 to 9:a. a prechamber 20 arranged at the first axial end and having a tip, and more than two jet openings arranged to the tip of prechamber at the first axial end, b. a fuel inlet 26 arranged to open into the prechamber, c. first cavity 28 arranged to extend from the second axial end of the body assembly to proximity to the prechamber 20, and a gas admission valve unit 29 arranged in the first cavity, and wherein the gas admission valve unit comprises a solenoid actuated fuel valve, d. second cavity 30 arranged to extend from the second axial end of the body assembly 12 to the prechamber 20, wherein an ignition device 31 is arranged in the second cavity in cooperation with the prechamber 20 so as to initiate combustion of fuel in the prechamber, when in use, e. cooling channels 32 arranged at the first axial end of the ignitor body assembly arranged in heat transfer connection with the prechamber 20, and f. three axially bordered interface areas, 14.1 ,14.2,14.3 on its outer surface, bordered by at least four sealing arrangements 16.1 ,16.2,16.3,16.4 in circumference of the body assembly 12, wherein i. a first interface area 14,1 is arranged to the vicinity of the first end of the body assembly 12 bordered by a first sealing arrangement 16.1 provided to the prechamber 20 and a second sealing arrangement 16.2 arranged axially at a distance from the prechamber 20 such that the second sealing arrangement is located axially between first and second ends of the gas admission valve unit 29, and wherein the cooling channels 32 in the body assembly 12 open into the first interface area 14.1 , ii. a second interface area 14.2 is arranged axially next to the first interface area bordered by the second sealing arrangement 16.2 and a third sealing arrangement 16.3 which is located axially at a distance from the second sealing arrangement 16.2 and in a region of second end of the gas admission valve unit, and wherein a gas inlet 18.1 channel opens to the second interface area 14.2 so as provide a flow path from outer surface of the ignitor body assembly 12 at the second interface area to the gas admission valve unit 29, iii. a third interface area 14.3 is arranged axially next to the second interface area 14.2 bordered by the third sealing arrangement 16.3 and a fourth sealing arrangement 16.4 which is located axially in a region of second end of the gas admission valve unit 29 and arranged axially at adistance from the third sealing arrangement 16.3, and wherein a gas leakage outlet channel 19.3, 34.3 opens to the third interface area 14.3 so as provide a flow path for detection of gas leakage, and further, providing a cylinder head 102 for each cylinder of the engine, wherein the cylinder head comprising a. an ignitor opening 104 configured to receive the fuel ignitor 10 provided, such that the tip 24 of the prechamber 20 protrudes from the cylinder head 102, wherein b. a coolant chamber 106 which is bordered by an inner wall of the ignitor opening 104 in the cylinder head, the first interface area 14.1 in outer wall of the fuel ignitor, the first sealing arrangement 16.1 and the second sealing arrangement 16.2, wherein the first sealing arrangement 16.1 and the second sealing arrangement 16.2 forming a seal between the fuel ignitor body assembly 12 and the cylinder head 102, and wherein the cylinder head is provided with coolant channels 108 which open into the coolant chamber 106 at two locations, preferably next to the first sealing arrangement 16.1 and next to the second sealing arrangement 16.2, c. a fuel feeding chamber 110 which is bordered by inner wall of the ignitor opening 104 in the cylinder head, the second interface area 14.2 in outer wall of the fuel ignitor 10, the second sealing arrangement 16.2 and the third sealing arrangement 16.3, wherein the second sealing arrangement and the third sealing arrangement forming a seal between the fuel ignitor body assembly 12 and the cylinder head, and wherein the cylinder head is provided with fuel feeding channel 112 which opens into the fuel feeding chamber 110 between the second sealing arrangement 16.2 and the third sealing arrangement 16.3, d. a fuel leakage detection chamber 120 which is bordered by inner wall of the ignitor opening 104 in the cylinder head, the third interface area14.3 in outer wall of the fuel ignitor 10, the third sealing arrangement 16.3 and the fourth sealing arrangement 16.4, wherein the third sealing arrangement and the fourth sealing arrangement forming a seal between the fuel ignitor body assembly 12 and the cylinder head, and wherein the cylinder head is provided with leakage fuel channel 122 which opens into the fuel leakage chamber 120 between the third sealing arrangement16.3 and the fourth sealing arrangement 16.4, andinstalling the ignitors 10 into the cylinder heads 102 forming cylinder head - fuel ignitor combinations 100 and installing the cylinder head - fuel ignitor combination to the engine and installing a gas feed pipe for each cylinder of the engine connecting a gas delivery pipe of the engine to gas admission valve unit in the fuel ignitor. The gas delivery pipe 202 and the gas feed pipes 212, 214 in the engine after the conversion are shown in the figure 11 and 12. The inner and outer flow channels gas feed pipe 212, 214 is connected in the conversion to the inner and outer flow channels of the gas delivery pipe 202.

[0099] In the step of providing a cylinder head 102 for each cylinder of the engine, cylinder heads 102 may be refurbished existing cylinder heads to include the feature of the cylinder head according to the invention as describe in the figure 10 or new cylinder heads according to the invention.

[0100] The method of converting a fuel injection system can be further develop such that the existing a gas delivery pipe is removed from the engine, in case needed, and a new gas delivery pipe, comprising a double wall structure having an inner and an outer flow channel, in installed to extend from a first end to a second end of the line of cylinders. The new gas delivery pipe comprises a first gas feed pipe 212 for each cylinder of the engine, comprising a double wall structure having an inner and an outer flow channel an outlet for each main gas admission valve of the engine, the inner and outer flow channels connected to the inner and outer flow channels of the gas delivery pipe 202 and main fuel gas admission valve 210, and a second gas feed pipe 214 for each cylinder of the engine, comprising a double wall structure having an inner and an outer flow channel, the inner and outer flow channels connected to the inner and outer flow channels of the gas delivery pipe 202 and gas admission valve unit 29 in the fuel ignitor 10 in the cylinder head.

[0101] The fuel ignitor 10 used and provided in the conversion is explained in more detailed manner in the figures 1 to 9 and the cylinder head in the figure 10.

[0102] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is obvious to the skilled person that, along with the technicalprogress, the basic idea of the invention can be implemented in many ways. The invention and its embodiments are thus not limited to the examples and samples described above but they may vary within the contents of patent claims and their legal equivalents. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.

Claims

Claims1. A fuel ignitor (10) for gaseous fuel comprising a body assembly (12) having a longitudinal axis (A), and a first axial end and a second axial end, characterized in that the ignitor body assembly (12) comprises a. a prechamber (20) arranged at the first axial end and having a tip, and more than two jet openings (22) arranged to the tip of prechamber (20) at the first axial end, b. a fuel inlet (26) arranged to open into the prechamber (20), c. first cavity (28) arranged to extend from the second axial end of the body assembly (12) to proximity to the prechamber (20), wherein a solenoid actuated gas admission valve unit (29) is arranged in the first cavity (28), d. second cavity arranged to extend from the second axial end of the body assembly (12) to the prechamber (20), wherein an ignition device (31) is arranged in the second cavity in cooperation with the prechamber (20) so as to initiate combustion of fuel in the prechamber (20), when in use, e. cooling channels (32) arranged at the first axial end of the ignitor body assembly (12) arranged in heat transfer connection with the prechamber (20).

2. A fuel ignitor (10) according to claim 1 , characterized in that cooling channels (32) comprise a first channel (32.1)which extends straight through the body assembly (12), perpendicularly to the longitudinal axis (A), having a first cooling channel opening (32.2) and a second cooling channel opening (32.3), and a second channel (32.4) which extends from middle area of the first channel (32.1) to sidewall of the body assembly (12) near the first cooling channel opening (32.2), and a third channel (32.5) which extends from middle area of the first channel to sidewall of the body assembly (12) near the second cooling channel opening, wherein the first channel (32.1), the second channel (32.4) and the third channel (32.5) are in arranged in a same plane.

3. A fuel ignitor (10) according to claim 2, characterized in that that the cooling channels (32) comprises a fourth channel (32.6) extending from middle area of the first cooling channel to side wall of the body assembly (12), perpendicularly to the plane, and that the cooling channels (32) comprises a fifth channel (32.7) extending from middle area of the first cooling channel (32.1) to side wall of the body assembly (12), perpendicularly to the plane, wherein the fourth channel (32.6) and the fifth channel (32.7) are parallel to each other.

4. A fuel ignitor (10) according to claim 1 , characterized in that the ignitor body assembly (12) comprises three axially bordered interface areas (14.1 ,14.2, 14.3) on its outer surface, bordered by at least four sealing arrangements (16.1 ,16.2,16.3,16.4) in circumference of the body assembly (12), wherein a first interface area (14.1) is arranged to the vicinity of the first end of the body assembly (12) bordered by a first sealing arrangement (16.1) provided to the prechamber (20) and a second sealing arrangement (16.2) arranged axially at a distance from the prechamber (20) such that the second sealing arrangement(16.2) is located axially between first and second ends of the gas admission valve unit (29), and wherein the cooling channels (32) of the fuel ignitor (10) opens to the first interface area (14.1), a second interface area (14.2) is arranged axially next to the first interface area(14.1) bordered by the second sealing arrangement (16.2) and a third sealing arrangement (16.3) which is located axially at a distance from the second sealing arrangement (16.2) and in a region of second end of the gas admission valve unit (29), and wherein a gas inlet channel opens to the second interface area(14.2) so as provide a flow path from outer surface of the ignitor body assembly (12) at the second interface area (14.2) to the gas admission valve unit (29), a third interface area (14.3) is arranged axially next to the second interface area(14.2) bordered by the third sealing arrangement (16.3) and a fourth sealing arrangement (16.4) which is located axially in a region of second end of the gas admission valve unit (29) and arranged axially at a distance from the third sealing arrangement (16.3), and wherein a gas leakage outlet channel (19.3, 34.3) opens to the third interface area (14.3) so as provide a flow path for detection of gas leakage.

5. A fuel ignitor (10) according to claim 1 or 4, characterized in that the ignitor body assembly (12) comprises a prechamber part (12.1) which is removably attached to the body assembly (12), wherein major part of volume of the prechamber (20) is arranged to the prechamber part.

6. A fuel ignitor (10) according to claim 1 , characterized in that cooling channels (32) extending through the body assembly (12) are arranged at a distance from the prechamber (20), which distance is less than diameter of the cooling bore nearest to the prechamber (20).

7. A fuel ignitor (10) according to claim 4, characterized in that the second sealing arrangement (16.2) comprises two similar grooves (16.2’, 16.2”) arranged to circumscribe outer wall of the ignitor body assembly (12) configured for use of an O-ring, wherein axial distance between the grooves is less than axial length of a groove.

8. A fuel ignitor (10) according to claim 7, characterized in that the second sealing arrangement (16.2) is provided with a gas detection opening (34.1) of a leakage gas channel between the grooves (16.2’, 16.2”).

9. A fuel ignitor (10) according to claim 4, characterized in that the first sealing arrangement (16.1) comprises a ring surface arranged to the prechamber (20) which surface is perpendicular to the longitudinal axis of the ignitor body assembly (12), and facing towards the tip of the prechamber (20), configured for sealing with a flat sealing ring, when in use, the second sealing arrangement (16.2) comprises two similar grooves arranged to circumscribe outer wall of the ignitor body assembly (12) configured for use of an O-ring, wherein axial distance between the grooves (16.2’, 16.2”) is less than axial length of a groove, the third sealing arrangement (16.3) comprises one groove arranged to circumscribe outer wall of the ignitor body assembly (12) configured for use of an O- ring, and the fourth sealing arrangement (16.4) comprises one groove arranged to circumscribe outer wall of the ignitor body assembly (12) configured for use of an O- ring.

10. A cylinder head - fuel ignitor combination (100), comprising a cylinder head configured to close and seal a cylinder of an internal combustion engine, which cylinder head is provided with an ignitor opening (104) configured to receive a fuel ignitor (10) according to claim 4, 5, 7 or 8, such that the tip of the prechamber (20) protrudes from the cylinder head (102), wherein a coolant chamber (106) is bordered by an inner wall of the ignitor opening (104) in the cylinder head (102), the first interface area (14.1) in outer wall of the fuel ignitor (10), the first sealing arrangement (16.1) and the second sealing arrangement (16.2), wherein the first sealing arrangement (16.1) and the second sealing arrangement (16.2) forming a seal between the fuel ignitor body assembly (12) and the cylinder head (102), and wherein the cylinder head (102) is provided with coolant channels which open into the coolant chamber (106) at two locations, preferably next to the first sealing arrangement (16.1) and next to the second sealing arrangement (16.2), a fuel feeding chamber (110) is bordered by inner wall of the ignitor opening (104) in the cylinder head (102), the second interface area (14.2) in outer wall of the fuel ignitor (10), the second sealing arrangement (16.2) and the third sealing arrangement (16.3), wherein the second sealing arrangement (16.2) and the third sealing arrangement (16.3) forming a seal between the fuel ignitor body assembly (12) and the cylinder head (102), and wherein the cylinder head (102) is provided with fuel feeding channel (112) which opens into the fuel feeding chamber (110) between the second sealing arrangement (16.2) and the third sealing arrangement (16.3), a fuel leakage detection chamber (120) is bordered by inner wall of the ignitor opening (104) in the cylinder head (102), the third interface area (14.3) in outer wall of the fuel ignitor (10), the third sealing arrangement (16.3) and the fourth sealing arrangement (16.4), wherein the third sealing arrangement (16.3) and the fourth sealing arrangement (16.4) forming a seal between the fuel ignitor body assembly (12) and the cylinder head (102), and wherein the cylinder head (102) is provided with leakage fuel channel (122) which opens into the fuel leakage chamber between the third sealing arrangement (16.3) and the fourth sealing arrangement (16.4).

11. A cylinder head - fuel ignitor combination (100) according to claims 9, characterized in that the cooling channels (32) arranged at the first axial end of the ignitor body assembly (12) comprises channel according to claim 2 or 3.

12. A gas operated internal combustion piston engine comprising multiple cylinders in a line of cylinders parallel to a crank shaft, preferably as in-line or v- configuration, the engine comprising a gas delivery pipe (202), comprising a double wall structure having an inner (202.1) and an outer flow channel (202.2), extending from a first end to a second end of the line of cylinders, an air receiver (204) extending from a first end to a second end of the line of cylinders, an air supply channel (206) arranged in connection with each cylinder of the engine connecting the air receiver to a combustion air inlet (208) of a cylinder head (102) of the cylinder, a first gas admission valve unit (210) arranged to each air supply channel, configured to administer a first portion of fuel gas, preferably a main portion, into combustion air prior to entering a combustion chamber, when in use, and a first gas feed pipe (212), comprising a double wall structure having an inner (202.1) and an outer flow channel (202.2), for each first gas admission valve unit (210), is arranged to couple the first gas admission valve unit (210) with the gas delivery pipe in gas tight manner, such that the inner flow channels are coupled with each other, and the outer flow channels are coupled with each other, a fuel ignitor (10) arranged to the cylinder head (102) of each cylinder of the engine, the fuel ignitor (10) comprising a prechamber (20), an ignition device (31) arranged cooperation with the prechamber (20) so as to initiate combustion of fuel in the prechamber (20) when in use, and a second gas admission valve unit (29), comprising a solenoid actuated fuel valve, arranged to administer a second portion of the fuel into the prechamber (20), when in use, a second gas feed pipe (214), comprising a double wall structure having an inner (202.1) and an outer flow channel (202.2), for each second gas admission valve unit (29) in the fuel ignitor (10), is arranged to couple thesecond gas admission valve unit (29) with the gas delivery pipe (202) in gas tight manner, such that the inner flow channels are coupled with each other, and the outer flow channels are coupled with each other.

13. A gas operated internal combustion piston engine according to claim 12, characterized in that the engine comprises multiple cylinders (201) in two lines of cylinders in v-configuration, and a space is formed between cylinder heads (102) in the lines of cylinder, wherein the gas delivery pipe comprises a first gas delivery pipe section (202.1) and a second gas delivery pipe section (202.2) which both extend from a first end to a second end of the line of cylinder and- which gas delivery pipe sections are in flow connection with each other, such that the inner flow channels are coupled with each other, and the outer flow channels are coupled with each other, at one end of the gas delivery pipe sections, and the first gas delivery pipe section (202.1) is provided with a fuel inlet(202.3) at an opposite end to the one connected with the second gas delivery pipe (202.1), and the second gas delivery pipe section (202.2) is provided with flow plug(202.4) at an opposite end to the one connected with the first gas delivery pipe (202.1).

14. A gas operated internal combustion piston engine according to anyone of the preceding claims 11 to 12, characterized in that piston engine comprises a fuel ignitor (10) according to anyone of the preceding claims 1 to 9.

15. A gas operated internal combustion piston engine according to anyone of the preceding claims 11 to 12, characterized in that piston engine comprises a cylinder head - fuel ignitor combination (100) according to anyone of the preceding claims 10-11.

16. Method of converting a fuel injection system of an existing engine which is configured to combust gaseous fuel as a main fuel and to ignite the main fuelby compression ignition of direct injection of liquid pilot fuel, the method comprising removing existing cylinder heads from the engine, including injectors for injecting the pilot fuel, providing a fuel ignitor (10) for each cylinder of the engine, wherein fuel ignitor (10) comprising a body assembly (12) having a longitudinal axis, and a first axial end and a second axial end, wherein the ignitor body assembly (12) comprises a. a prechamber (20) arranged at the first axial end and having a tip, and more than two jet openings (22) arranged to the tip of prechamber (20) at the first axial end, b. a fuel inlet (26) arranged to open into the prechamber (20), c. second cavity arranged to extend from the second axial end of the body assembly (12) to the prechamber (20), wherein an ignition device (31) is arranged in the second cavity in cooperation with the prechamber (20) so as to initiate combustion of fuel in the prechamber (20), when in use, d. first cavity (28) arranged to extend from the second axial end of the body assembly (12) to proximity to the prechamber (20), wherein a gas admission valve unit (29) is arranged in the first cavity (28), and wherein the gas admission valve unit (29) comprises a solenoid actuated fuel valve, e. cooling channels (32) arranged at the first axial end of the ignitor body assembly (12) extending transversely through the body assembly (12) and arranged in heat transfer connection with the prechamber (20), and f. three axially bordered interface areas on its outer surface, bordered by at least four sealing arrangements in circumference of the body assembly (12), wherein i. a first interface area (14.1) is arranged to the vicinity of the first end of the body assembly (12) bordered by a first sealing arrangement (16.1) provided to the prechamber (20) and a second sealing arrangement (16.2) arranged axially at a distance from the prechamber (20) such that the second sealing arrangement (16.2) is located axially betweenfirst and second ends of the gas admission valve unit (29), and wherein the cooling channels (32) open into the first interface area (14.1), ii. a second interface area (14.2) is arranged axially next to the first interface area (14.1) bordered by the second sealing arrangement (16.2) and a third sealing arrangement(16.3) which is located axially at a distance from the second sealing arrangement (16.2) and in a region of second end of the gas admission valve unit (29), and wherein a gas inlet channel opens to the second interface area (14.2) so as provide a flow path from outer surface of the ignitor body assembly (12) at the second interface area (14.2) to the gas admission valve unit (29), iii. a third interface area (14.3) is arranged axially next to the second interface area (14.2) bordered by the third sealing arrangement (16.3) and a fourth sealing arrangement(16.4) which is located axially in a region of second end of the gas admission valve unit (29) and arranged axially at a distance from the third sealing arrangement (16.3), and wherein a gas leakage outlet channel opens to the third interface area (14.3) so as provide a flow path for detection of gas leakage, providing a cylinder head (102) for each cylinder of the engine, wherein the cylinder head (102) comprising a. an ignitor opening (104) configured to receive the fuel ignitor (10) provided, such that the tip of the prechamber (20) protrudes from the cylinder head (102), wherein b. a coolant chamber (106) which is bordered by an inner wall of the ignitor opening (104) in the cylinder head (102), the first interface area (14.1) in outer wall of the fuel ignitor (10), the first sealing arrangement (16.1) and the second sealing arrangement (16.2), wherein the first sealing arrangement (16.1) and the second sealing arrangement (16.2) forming a seal between the fuel ignitor body assembly (12) and the cylinder head (102), and wherein the cylinder head (102) is provided with coolant channels which openinto the coolant chamber (106) at two locations, preferably next to the first sealing arrangement (16.1) and next to the second sealing arrangement (16.2), c. a fuel feeding chamber (110) which is bordered by inner wall of the ignitor opening (104) in the cylinder head (102), the second interface area (14.2) in outer wall of the fuel ignitor (10), the second sealing arrangement (16.2) and the third sealing arrangement (16.3), wherein the second sealing arrangement (16.2) and the third sealing arrangement (16.3) forming a seal between the fuel ignitor body assembly (12) and the cylinder head (102), and wherein the cylinder head (102) is provided with fuel feeding channel which opens into the fuel feeding chamber (110) between the second sealing arrangement (16.2) and the third sealing arrangement (16.3), d. a fuel leakage detection chamber (120) which is bordered by inner wall of the ignitor opening (104) in the cylinder head (102), the third interface area (14.3) in outer wall of the fuel ignitor (10), the third sealing arrangement (16.3) and the fourth sealing arrangement (16.4), wherein the third sealing arrangement (16.3) and the fourth sealing arrangement (16.4) forming a seal between the fuel ignitor body assembly (12) and the cylinder head (102), and wherein the cylinder head (102) is provided with leakage fuel channel which opens into the fuel leakage chamber between the third sealing arrangement (16.3) and the fourth sealing arrangement (16.4), and installing the ignitors into the cylinder heads and installing the thus formed cylinder head - fuel ignitor combination to the engine, and- installing a gas feed pipe for each cylinder of the engine connecting a gas delivery pipe of the engine to gas admission valve unit (29) in the fuel ignitor (10).

17. Method according to claim 16, characterized in that in the method of converting a fuel injection system, further the existing a gas delivery pipe is removedfrom the engine, and a new gas delivery pipe, comprising a double wall structure having an inner (202.1) and an outer flow channel (202.2), in installed to extend from a first end to a second end of the line of cylinders, wherein the new gas delivery pipe comprises- a first gas feed pipe for each cylinder of the engine, comprising a double wall structure having an inner (202.1) and an outer flow channel (202.2) an outlet for each main gas admission valve of the engine, the inner and outer flow channels connected to the inner and outer flow channels of the gas delivery pipe and main fuel gas admission valve- a second gas feed pipe for each cylinder of the engine, comprising a double wall structure having an inner (202.1) and an outer flow channel (202.2), the inner and outer flow channels connected to the inner and outer flow channels of the gas delivery pipe and gas admission valve unit (29) in the fuel ignitor (10) in the cylinder head (102).

18. Method according to claim 16 or 17, characterized in that the fuel ignitor provided is a fuel ignitor according to anyone of the preceding claim 1 to 9.

19. Method according to claim 16 or 17, characterized in that the cylinder head - fuel ignitor combination (100) provided is according to anyone of the preceding claims 10-11.

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