DK180922B1

DK180922B1 - Compression-ignited internal combustion engine operating on ammonia and retrofit kit

Info

Publication number: DK180922B1
Application number: DKPA202070740A
Authority: DK
Inventors: Mayer Stefan; Sjöholm Johan
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2020-11-06
Filing date: 2020-11-06
Publication date: 2022-06-27
Also published as: JP2022075566A; KR20220061879A; DK202070740A1; KR102656105B1; JP2023018060A; JP7183369B2; CN114439599A; CN114439599B

Abstract

A turbocharged compression-ignition internal combustion engine configured in at least one mode of operation for operating with ammonia as the main- or only fuel and retrofit kit. The engine comprises cylinders (1) with a reciprocating piston (10) therein and cylinder cover (22) covering each cylinder (1), a combustion chamber (15) formed inside the cylinders (10) between the reciprocating piston (10) and the cylinder cover (22), at least one pre-chamber (33) arranged in the cylinder cover (22) and connected to the combustion chamber through an opening (35), an ammonia valve (50) having a nozzle (51) with nozzle holes (52) opening to the at least one pre-chamber (33), the ammonia valve (50) having an inlet port connected to a source of pressurized liquid ammonia (40), the ammonia valve (50) being configured for injecting liquid ammonia from the source of pressurized liquid ammonia (40) through the nozzle holes (52) into the pre-chamber (33).

Description

DK 180922 B1 1 COMPRESSION-IGNITED INTERNAL COMBUSTION ENGINE OPERATING ON

AMMONIA AND RETROFIT KIT

TECHNICAL FIELD The disclosure relates to a compression igniting internal combustion engine, such as a large slow-running two-stroke compression-ignited internal combustion crosshead engine, which has at least one mode of operation in which the main fuel is ammonia.

BACKGROUND Compression ignition internal combustion engines (Diesel engines) have in the past mainly been operated with hydrocarbon fuels, such as fuel oil, e.g. diesel oil, or fuel gas, e.g. natural gas or petroleum gas. The combustion of hydrocarbon fuels releases carbon dioxide (CO2), as well as other greenhouse gases that contribute to atmospheric pollution and climate change. Unlike fossil fuel impurities that result in byproduct emissions, CO2 is an unavoidable result of hydrocarbon combustion. The energy density and CO2- footprint of a fuel depends on the hydrocarbon chain length and the complexity of its hydrocarbon molecules. Hence, gaseous hydrocarbon fuels have a lower footprint than liquid hydrocarbon fuels, with the drawback that gaseous hydrocarbon fuels are more challenging and costly to handle and store. In order to reduce the C02 footprint, non-hydrocarbon fuels are being investigated. Ammonia is a synthetic product obtained from fossil fuels, biomass, or renewable sources (wind, solar, hydro, or thermal), and when generated by renewable sources, ammonia

DK 180922 B1 2 will have virtually no carbon footprint or emit any CO2, SOX, particulate matter, or unburned hydrocarbons when combusted. Ammonia has been tested and used at a minor scale in small spark-ignition internal combustion engines but has not been used to power compression-ignition internal combustion engines. Large two-stroke uniflow scavenged turbocharged compression- ignited internal combustion crosshead engines are typically used in propulsion systems of large ships or as a prime mover in power plants. The sheer size, weight, and power output render them completely different from common combustion engines and place large two-stroke turbocharged compression- ignited internal combustion engines in a class for themselves. EP2664777 discloses a large two-stroke uniflow scavenged turbocharged compression-ignited internal combustion engine according to the preamble of claim 1. In this engine ammonia is injected into the combustion chamber as fuel and as reductant for assisting the process of reducing NOx emissions with the help of a reduction catalyst that is arranged downstream of the turbine of the turbocharger.

SUMMARY It is an object to provide a compression-ignition internal combustion engine that has at least one mode of operation in which the main fuel is ammonia. The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are

DK 180922 B1 3 apparent from the dependent claims, the description, and the figures. According to a first aspect, there is provided a large two- stroke turbocharged uniflow scavenged compression-ignition internal combustion engine configured in at least one mode of operation for operating with ammonia as the main- or only fuel, comprising at least one cylinder with a reciprocating piston therein and cylinder cover covering the cylinder, the cylinders being arranged in a cylinder liner and the cylinder liner being provided with scavenging ports, a combustion chamber formed inside the cylinder between the reciprocating piston and the cylinder cover, an exhaust valve arranged centrally in the cylinder cover, at least one pre-chamber arranged in the cylinder cover and fluidically connected to the combustion chamber through an opening, and an ammonia valve having a nozzle with nozzle holes opening to the at least one pre-chamber, the ammonia valve having an inlet port connected to a source of pressurized ammonia, and the ammonia valve being configured for injecting liquid ammonia from the source of pressurized liquid ammonia through the nozzle holes into the pre-chamber.

There are several challenges with using ammonia as a fuel. One challenge is the low power density compared to typical hydrocarbon fuels, resulting in a significantly larger volume of fuel that needs to be injected and thus resulting in a larger flow. Such a larger flow may cause flame extinction, i.e. although ignition occurs at the very start of the

DK 180922 B1 4 injection event, the following large flow and the resulting high speed of the fuel jet extinguishes (blows out) the flame. Another challenge is ammonia’s low willingness to ignite (low flammability) compared to liquid hydrocarbon fuels. Yet another challenge is ammonia’s high evaporative cooling that causes the fuel to cool upon injection, thus increasing the ignition energy required. Due to the high evaporative cooling high temperatures in the combustion area are a prerequisite for stable combustion. The combination of these challenges has so far prevented the use of ammonia as the main fuel in compression ignition engines. The inventors realized that injecting ammonia through the nozzles of the ammonia valve into a pre-chamber that is connected by an opening to the combustion chamber causes a significant deceleration of the fuel before the fuel enters the combustion chamber from the opening, and the pre-chamber can serve as a preheating chamber. Thus, the speed of the fuel is reduced when enters the combustion chamber through the opening and the temperature of the fuel is increased when entering the combustion chamber, thereby at least partially overcoming the challenges with ammonia as a fuel for a compression igniting internal combustion engine mentioned above.

In a possible implementation form of the first aspect, the engine comprises an ignition fluid valve associated with the at least one pre-chamber, the ignition fluid valve having an ignition fluid nozzle with nozzle holes and the ignition fluid valve is coupled to a source of pressurized ignition fluid. Thus, an ignition fluid can be mixed with the ammonia in the

DK 180922 B1 pre-chamber for enhancing reliable ignition of the ammonia. By injecting the ignition fluid with high pressure in the pre-chamber it is ensured that the ignition fluid is well dispersed into the ammonia and ensures that the ignition fluid 5 is already well mixed with the ammonia when the mixture enters the combustion chamber. In a possible implementation form of the first aspect, the source of pressurized ignition fluid is a source of pressurized pilot fluid or a source of pressurized ignition promoter. The pilot fluid can for example be dimethyl ether (DME) or fuel oil. The ignition promoter can for example be hydrogen, either from an external source or generated from the ammonia itself using e.g. a catalytic process.

In a possible implementation form of the first aspect, the engine is configured to inject pilot fluid through the nozzles of the ignition fluid valve followed by either only injecting ammonia through the nozzles of the ammonia valve or both pilot fluid through the ignition fluid valve and ammonia through the ammonia valve simultaneously. In a possible implementation form of the first aspect, the pre-chamber is formed in an insert arranged in the cylinder cover. Thus, if there is damage to the pre-chamber or to the opening between the pre-chamber and the combustion chamber, the pre-chamber can be easily replaced by swapping the insert,

DK 180922 B1 6 without needing to work on (machine) the complete cylinder cover. In a possible implementation form of the first aspect, the pre-chamber is formed together with the ammonia valve as a single unit, and wherein the single unit is an insert arranged in the cylinder cover. Thus, the pre-chamber and the ammonia valve can be installed in the cylinder cover in a single operation.

In a possible implementation form of the first aspect, at least a portion of a wall delimiting the pre-chamber from the combustion chamber forms a protrusion from the cylinder cover into the combustion chamber. By forming a protrusion into the combustion chamber, it is ensured that the wall delimiting the pre-chamber becomes hot during engine operation, thereby ensuring high temperatures in the pre-chamber and in the area of the combustion chamber close to the pre-chamber. Thus, high temperatures are insured in the area where the ammonia arrives, and reliable combustion is enhanced. In a possible implementation form of the first aspect, the opening has a given cross-sectional area such that the combined cross-sectional area of the nozzle holes is smaller than the cross-sectional area of the opening between the pre- chamber and the combustion chamber, preferably significantly smaller and most preferably less than half. Thereby, it is ensured that the ammonia enters the combustion chamber with

DK 180922 B1 7 a speed that is significantly lower than the speed at which it enters the pre-chamber.

In a possible implementation form of the first aspect, a plurality of pre-chambers is arranged around the exhaust valve.

In a possible implementation form of the first aspect, the source of pressurized ammonia is a source of pressurized liquid phase ammonia. In a possible implementation form of the first aspect, the engine is configured for injecting ammonia and another fuel simultaneously into the pre-chamber. In a possible implementation form of the first aspect, the engine comprises a fuel valve having a nozzle with nozzle holes opening to the at least one pre-chamber, the fuel valve having an inlet port connected to a source of pressurized other fuel, the fuel valve being configured for injecting said other fuel from the source of other fuel through the nozzle holes into the pre-chamber. According to a second aspect, there is provided a retrofit kit for a compression-ignition internal combustion engine for rendering the engine suitable in at least one mode of operation for operating with ammonia as the main- or only fuel, the engine comprising at least one cylinder with a reciprocating piston therein and cylinder cover covering the cylinder, a combustion chamber formed inside the cylinder between the reciprocating piston and the cylinder cover, the

DK 180922 B1 8 retrofit kit comprising at least one pre-chamber for installing in the cylinder cover and having an opening for connecting the pre-chamber to the combustion chamber, an ammonia valve having a nozzle with nozzle holes opening to the at least one pre-chamber, the ammonia valve having an inlet port for connecting to a source of pressurized liquid ammonia, the ammonia valve being configured for injecting liquid ammonia from the source of pressurized liquid ammonia through the nozzle holes into the pre-chamber.

These and other aspects will be apparent from and the embodiment (s) described below.

BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed portion of the present disclosure, the aspects, embodiments, and implementations will be explained in more detail with reference to the example embodiments shown in the drawings, in which: Fig. 1 is an elevated front view of a large two-stroke diesel engine according to an example embodiment. Fig. 2 is an elevated side view of the large two-stroke engine of Fig. 1. Fig. 3 is a diagrammatic representation of the large two- stroke engine according to Fig. 1. Fig. 4. is a sectional view in detail of a cylinder of the large two-stroke engine of Fig. 1, Fig. 5 is a diagrammatic representation of an ammonia valve used in the large two-stroke engine of Fig. 1,

DK 180922 B1 9 Fig. 5 is a diagrammatic representation of a fuel valve for another fuel, used in the large two-stroke engine of Fig. 1 1, Fig. 6 is a diagrammatic representation of an ignition fluid valve used in an embodiment of the large two-stroke engine of Fig. 1, and Fig. 7 is a sectional diagrammatic view of an ammonia valve and a pre-chamber forming a single unit installed in a cylinder cover of the large two-stroke engine of Fig 1.

DETAILED DESCRIPTION In the following detailed description, a compression igniting internal combustion engine will be described with reference to a large two-stroke low-speed uniflow scavenged turbocharged compression-ignited internal combustion engine with crossheads in the example embodiments, but it is understood that the compression ignited internal combustion engine could be of another type. Figs. 1, 2, and 3 show a large low-speed turbocharged two- stroke diesel engine with a crankshaft 8 and crossheads 9. Fig. 3 shows a diagrammatic representation of a large low- speed turbocharged two-stroke diesel engine with its intake and exhaust systems. In this example embodiment, the engine has six cylinders 1 in line. Large low-speed turbocharged two-stroke diesel engines have typically between four and fourteen cylinders 1 in line, carried by a cylinder frame 23 that is carried by an engine frame 11. The engine may e.g. be used as the main engine in a marine vessel or as a stationary engine for operating a generator in a power station. The total

DK 180922 B1 10 output of the engine may, for example, range from 1,000 to 110,000 kW.

The engine is in this example embodiment a compression-ignited engine of the two-stroke uniflow type with scavenging ports 18 at the lower region of the cylinder liners 1 and a central exhaust valve 4 at the top of each cylinder liner 1. The scavenge air is passed from the scavenge air receiver 2 to the scavenge ports 18 of the individual cylinders 1. A piston 10 that reciprocates in the cylinder liner 1 between the bottom dead center (BDC) and top dead center (TDC) compresses the scavenge air.

Ammonia is injected through ammonia valves 50 that are arranged in the cylinder cover 22. Combustion follows, and exhaust gas is generated.

The ammonia valves 50 are configured for injecting ammonia.

In an embodiment, the engine is additionally provided with additional fuel valves (not shown) that are suitable for injecting a conventional fuel (such as e.g. fuel oil or heavy fuel oil). In such an embodiment, the engine is a dual-fuel engine and is also provided with a conventional fuel supply system (not shown) for supplying the conventional fuel.

When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct associated with the cylinders 1 into the exhaust gas receiver 3 and onwards through a first exhaust conduit 19 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit via an economizer 20 to an outlet 21 and into the atmosphere.

Through a shaft, the turbine 6 drives a compressor 7 supplied with fresh air via an air inlet 12. The compressor 7 delivers

DK 180922 B1 11 pressurized scavenge air to a scavenge air conduit 13 leading to the scavenge air receiver 2. The scavenge air in the scavenge air conduit 13 passes an intercooler 14 for cooling the scavenge air.

The cooled scavenge air passes via an auxiliary blower 16 driven by an electric motor 17 that pressurizes the scavenge air flow when the compressor 7 of the turbocharger 5 does not deliver sufficient pressure for the scavenge air receiver 2, i.e. in low or partial load conditions of the engine. At higher engine loads the turbocharger compressor 7 delivers sufficient compressed scavenge air and then the auxiliary blower 16 is bypassed via a non-return valve 15.

The engine is in at least one operation mode operated with ammonia as the main fuel which is supplied to the ammonia valves 50 a substantially stable pressure and temperature. The ammonia can be supplied to the ammonia valves 50 in the liquid phase or in the gaseous phase. The ammonia liquid phase can be aqueous ammonia (ammonia-water blend).

The ammonia fuel system 30 forms part of a source of pressurized liquid phase ammonia 40 and supplies the ammonia valves 50 with liquid ammonia at relatively low supply pressure (e.g.30 to 80 bar pressure) via a supply conduit 31. Alternatively, the ammonia is supplied at a relatively low supply pressure (e.g. 30 to 80 bar pressure) to the ammonia valves 50 in the gaseous phase.

In an embodiment, ammonia is stored in the liquid phase in type C pressurized storage tanks (not shown) at approximately

DK 180922 B1 12 17 bar.

Ammonia is the liquid phase at a pressure above 8.6 bar and an ambient temperature of 20°C.

However, ammonia 1s preferably stored at approximately 17 bar to keep it in the liquid phase when the ambient temperature increases.

An existing engine configured for running on LPG or other gaseous fuel stored in the liquid phase requires relatively few modifications to be converted to ammonia combusting engine, i.e. an engine according to an embodiment of this disclosure, using a slightly modified version of the fuel supply system, i.e. a retrofit requires relatively few modifications since the same storage tanks can be used.

The ammonia valves 50 have an inlet port connected to the source of pressurized liquid ammonia 40. In an embodiment, the source of pressurized liquid ammonia is part of the fuel system 30 that is configured to supply pressurized liquid ammonia to the ammonia valves 50. Referring now to Fig. 4, a cylinder 1 with a cylinder cover 22 clamped thereon is carried by the cylinder frame 23. The piston 10 is shown with an interrupted line in both the bottom dead center and in the top dead center.

The combustion chamber is formed inside the cylinder between the reciprocating piston 10 and the cylinder cover 22. The cylinder cover 22 is provided with a central exhaust valve 4. For each cylinder 1, two or three ammonia valves 50 are arranged in the cylinder cover 22 around the central exhaust valve 4 (circumferentially distributed around the exhaust valve 4). The ammonia valves 50 are shown in greater detail in Fig. 5 and comprise an elongated valve body with a nozzle 51 at a

DK 180922 B1 13 front end of the elongated body. The ammonia valve 50 is provided with an ammonia inlet port. The ammonia inlet port is connected to the source of pressurized liquid phase ammonia

40. The nozzle 51 is preferably removably attached to the elongated body. The nozzle 51 is provided with one or more nozzle holes 52. The nozzle 51 and the nozzle holes 52 are arranged such that the ammonia is injected into the pre-chamber 33.

The ammonia valve 50 can be of the type that is controlled by a control signal for performing an ammonia injection event, and thus- This type of ammonia valve 50 can be connected to a common rail type supply ammonia with a substantially constant pressure. The control signal is synchronized with the engine cycle to ensure the proper timing of ammonia injection. Alternatively, the ammonia valve 50 can be of the type that opens when the supply pressure at the ammonia inlet port exceeds a given threshold and closes again when the supply pressure the ammonia inlet port falls below a given threshold. This latter type of ammonia valve 50 will require a connection to a source of pressurized liquid phase ammonia with a variable pressure that is controlled to be synchronized with the engine cycle. A pre-chamber 33 is associated with each of the ammonia valves

50. The pre-chamber 33 is arranged as a part of the cylinder cover 22, preferably in the form of an insert 55 installed, preferably removably installed, in the cylinder cover 22. By

DK 180922 B1 14 arranging the pre-chamber 33 in an insert 55, it can be maintained or repaired by simply exchanging the insert 55, without needing to exchange or repair the complete cylinder cover 22. In the embodiment shown in Fig. 7, the pre-chamber 33 is formed together with the ammonia valve 50 as a single unit.

The single unit is in turn an insert arranged/installed, preferably removably installed in the cylinder cover 22. The pre-chamber 33 is in fluid communication with the combustion chamber through an opening 35. Preferably, the opening 35 has a cross-sectional area that is substantially larger than the combined cross-sectional area of the nozzle holes 52 of the nozzle 51. Most preferably, the cross- sectional area of opening 35 double or more than double the combined cross-sectional area of nozzle holes 52. A wall delimiting the pre-chamber 33 from the combustion chamber forms a protrusion from the cylinder cover 22 into the combustion chamber.

Preferably, the opening 35 is arranged in the portion of the wall that forms the protrusion.

By arranging the wall as a protrusion into the combustion chamber ensures that the wall gets hot during engine operation and thereby the pre-chamber 33 itself will get hot during engine operation, thereby facilitating reliable ignition of the ammonia inside the pre-chamber.

In an embodiment, an ignition fluid valve 60 (shown in Fig. 6) is associated with the pre-chamber 33. Hereto, the ignition fluid valve 60 is installed in the cylinder cover 22 with an ignition fluid nozzle 61 with its nozzle holes 62 arranged such that ignition fluid is injected into the pre-chamber 33

DK 180922 B1 15 by the action of the ignition fluid valve 60. The ignition fluid valve 60 has an inlet port that is connected to a source of pressurized ignition fluid 44. The ignition fluid is in an embodiment a pilot fluid (i.e. a fluid that is injected at the start (prior or immediately at the start) of the main injection into the pre-chamber), such as fuel oil (e.g.

Diesel), DME or hydrogen (hydrogen can be used as a pilot fluid or as an ignition promoter). The operation of the ignition fluid valve 60 is synchronized with the engine cycle, so that ignition fluid is injected into the pre-chamber 33 before, and/or together with ammonia.

Thus, the engine according is in an embodiment configured to inject pilot fluid through the nozzles 61 of the ignition fluid valve 60 followed by either only injecting ammonia through the nozzles 51 of the ammonia valve 60 or both pilot fluid through the ignition fluid valve 60 and ammonia through the ammonia valve 60 simultaneously.

In another embodiment, an ignition promotor media is added to the ammonia prior to or at the time of injecting into the pre-chamber.

The ignition promoter is in an embodiment hydrogen that is mixed with ammonia that is in the gaseous phase.

However, other media with suitable ignition properties can be used as well. . For ammonia in the liquid phase, the ignition promotor is a substance that is also in the liquid phase and can thus be mixed with the liquid phase ammonia.

For ammonia that is in the gaseous phase, the ignition promotor is a substance that is also the gaseous phase and can thus be mixed with the gaseous phase ammonia.

DK 180922 B1 16 In an embodment the engine is configured for injecting ammonia and another fuel simultaneously into the pre-chamber 33. The other fuel is in an embodiment a conventional hydrocarbon fuel such as fuel oil or natural gas, i.e the other fuel can be in liquid phase or gaseous phase.

The ammonia can be supplied to the ammonia valve 50 in either liquid phase or gaseous phase.

As shown in Fig.

Sa engine can in this embodiment comprise a fuel valve 70 having a nozzle 71 with nozzle holes 72 opening to the at least one pre-chamber 33. The fuel valve 70 has an inlet port connected to a source of pressurized other fuel 49, the fuel valve 70 being configured for injecting the other fuel from the source of other fuel 49 through the nozzle holes 72 into the pre-chamber 33. A control unit (not shown) is configured to control the operation of the engine including the time the activation and deactivation of the ammonia valves 50 and the ignition fluid valves 60. By injecting pilot fluid before injecting ammonia, it is ensured that the temperature in the pre-chamber 33 is sufficiently high to ignite the ammonia when it enters the pre-chamber 33. Further, the pre-chamber 33 will in this case ensure the mixing of the pilot fuel with the ammonia as it is ejected from the pre-chamber 33 into the main chamber.

The pre-chamber 33 allows the ignition fluid and ammonia to be mixed prior to entering the combustion chamber and thereby ensures a substantially homogeneous distribution of the

DK 180922 B1 17 ignition fluid with the ammonia.

Thus, the ignition fluid is part of the ammonia jet leaving the pre-chamber 33 through the opening 35 and provides for optimum usage of the ignition fluid in terms of stabilizing the combustion process.

The hot air (compressed scavenging air) and the hot pre-chamber walls, most significantly during the initial part of the ammonia injection, thereby overcomes the problems associated with the high evaporative cooling of ammonia.

Thus, the pre-chamber 33 removes or at least minimizes the required amount of ignition fluid due to optimal mixing and increased heat transfer from the walls.

Stable combustion of ammonia in a direct injection mode provides significantly increased combustion control and stability.

The nozzles/ atomizers 51,61 are placed in the pre-chamber 33, which assist in protecting them from the harsh conditions in the combustion chamber, thereby increasing their expected lifespan.

The various aspects and implementations have been described in conjunction with various embodiments herein.

However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject-matter, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.

The mere fact that certain measures are recited in mutually different dependent claims does not

DK 180922 B1 18 indicate that a combination of these measured cannot be used to advantage.

The reference signs used in the claims shall not be construed as limiting the scope.

Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure.

As used in the description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader.

Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

Claims

DK 180922 B1 19 PATENT CLAIM

1. Large, turbocharged, longitudinally scavenged, compression-ignition two-stroke internal combustion engine configured in at least one operating mode to operate with ammonia as the main or sole fuel, comprising: - at least one cylinder (1) having a reciprocating piston (10) therein; and > cylinder cover (22), which > covers the cylinder (1), which cylinders (1) are arranged 1 a cylinder liner, and where the cylinder liner is provided with flushing ports (18), - a combustion chamber formed inside the cylinder (1) between the reciprocating piston (10) and the cylinder cover (22), - an exhaust valve (4) which is placed centrally in the cylinder cover (22), characterized by - at least one pre-chamber (33) which is placed in the cylinder cover (22) ) and fluidly connected to the combustion chamber through an opening (35), and - an ammonia valve (50) having a nozzle (51) with nozzle holes (52) opening into the at least one pre-chamber (33), - which ammonia valve ( 50) has an inlet opening that is connected to a source of pressurized ammonia (40), and - which ammonia valve (50) is configured to inject liquid ammonia from the source of pressurized liquid ammonia (40) through the nozzle holes (52) into the antechamber (33).

2. Engine according to claim 1, comprising an ignition fluid valve (60) connected to the at least one pre-chamber (33),

DK 180922 B1 20 which ignition fluid valve (60) has an ignition fluid nozzle (61) with nozzle holes (62), and the ignition fluid valve (60) is connected to a source of pressurized ignition fluid (44).

3. Engine according to claim 2, wherein the ignition fluid valve (60) is configured to inject ignition fluid through the nozzle (61) into the pre-chamber (33).

4. An engine according to claim 2 or 3, wherein the source of pressurized ignition fluid (40) is a source of pressurized pilot fluid or a source of pressurized ignition promoting agent.

An engine according to any one of claims 1 to 4, wherein the engine is configured to inject pilot fluid through the nozzles (61) of the ignition fluid valve (60) followed by either injecting only ammonia through the nozzles (51) of the ammonia valve (50) or both pilot fluid through the ignition fluid valve (60) and ammonia through the ammonia valve (50) simultaneously.

6. Engine according to any one of the preceding claims, where the pre-chamber (33) is an insert (55) that is placed in the cylinder cover (22), preferably an insert (55) that is removably mounted in the cylinder cover 22.

7. Engine according to claim 6, where the pre-chamber (33) is formed together with the ammonia valve (50) as a single unit, and where the single unit is an insert that is mounted in the cylinder cover (22), preferably removably mounted in the cylinder cover (22 ).

8. An engine according to any one of the preceding claims, wherein the at least one part of a wall delimiting the pre-chamber

DK 180922 B1 21 (33) from the combustion chamber, forms a projection from the cylinder cover (22) into the combustion chamber, preferably a projection from the side of the cylinder cover (22) that faces the combustion chamber.

An engine according to any one of the preceding claims, wherein the opening (35) has a given cross-sectional area and the combined cross-sectional area of the nozzle holes (52) is less than the cross-sectional area of the opening (35), preferably significantly less and most preferably less than half.

An engine according to any one of the preceding claims, wherein a plurality of pre-chambers (33) are arranged around the central exhaust valve (4).

An engine according to any one of claims 1 to 10, wherein the source of pressurized ammonia (40) is a source of pressurized liquid phase ammonia.

An engine according to any one of claims 1 to 11 configured to inject ammonia and another fuel simultaneously into the pre-chamber (33).

13. Engine according to claim 12, comprising a fuel valve (70) having a nozzle (71) with nozzle holes (72) opening into the at least one pre-chamber (33), which fuel valve (70) has an inlet opening which is connected to a source of a second pressurized fuel (49), which fuel valve (70) is configured to inject the second fuel from

DK 180922 B1 22 the source of second fuel (49) through the nozzle holes (72) into the antechamber (33).

14. Retrofit kit for a compression ignition internal combustion engine to make the engine suitable in at least one operating mode to operate with ammonia as the main fuel or the only fuel, which engine comprises: - at least one cylinder (1) with a reciprocating piston (10) therein and cylinder cover (22) covering the cylinder (1), - a combustion chamber formed inside the cylinder (1) between the reciprocating piston (10) and the cylinder cover (22), which retrofit kit includes: - at least one pre-chamber (33) for mounting in the cylinder cover (22) and with an opening (35) to connect the pre-chamber (35) with the combustion chamber, - an ammonia valve (50) having a nozzle (51) with nozzle holes (52) opening into the at least one antechamber (33), - which ammonia valve (50) has an inlet opening for connecting to a source of pressurized liquid ammonia (40), - which ammonia valve (50) is configured for injecting liquid ammonia from the source of pressurized t liquid ammonia (40) through the nozzle holes (52) into the antechamber (33).

15. Retrofit kit according to claim 14, where the pre-chamber (33) is formed in an insert (55) for mounting in the cylinder cover

DK 180922 B1 23 (22), preferably an insert that is removably mounted in the cylinder cover 22.

16. Retrofit kit according to claim 15, where the pre-chamber (33) is formed together with the ammonia valve (50) as a single unit, and where the single unit is an insert for mounting in the cylinder cover (22), preferably for removable mounting in the cylinder cover (22) .