Ammonia-powered compression ignition internal combustion engine and retrofit kit

Abstract

A turbocharged, uniflow scavenged, compression ignition internal combustion engine is provided that is configured to operate on ammonia as a primary or sole fuel in at least one operating mode. The engine includes a cylinder (1) having a reciprocating piston (10) therein and a cylinder cover (22) covering the cylinder (1), a combustion chamber formed between the reciprocating piston in the cylinder and the cylinder cover, a pre-chamber (33) disposed in the cylinder cover and fluidly connected to the combustion chamber through an opening, and an ammonia valve (50) having a nozzle opening into the pre-chamber. The ammonia valve has an inlet port connected to a source of pressurized liquid ammonia, and the ammonia valve is configured to inject the liquid ammonia into the pre-chamber.

Description

[Technical Field]

[0001] The present disclosure relates to a compression ignition internal combustion engine, such as a large, low-speed, two-stroke, crosshead compression ignition internal combustion engine, having at least one operating mode that uses ammonia as the primary fuel.

[0002] Compression-ignition internal combustion engines (diesel engines) have traditionally been powered primarily by hydrocarbon fuels, such as fuel oils like diesel oil and fuel gases like natural gas or petroleum gas. Combustion of hydrocarbon fuels results in the production of greenhouse gases, including carbon dioxide (CO2), which can contribute to air pollution and climate change. Unlike impurities in petroleum fuels that result in by-product emissions, the production of CO2 is inevitable when hydrocarbons are burned. The energy density and CO2 footprint of a fuel depend on the length of the hydrocarbon chain and the complexity of the hydrocarbon molecule. Therefore, gaseous hydrocarbon fuels have a smaller footprint than liquid hydrocarbon fuels. However, gaseous hydrocarbon fuels are more difficult and costly to handle and store. To reduce their CO2 footprint, non-hydrocarbon fuels have been explored.

[0003] Ammonia is a compound derived from petroleum, biomass, and renewable energy sources (wind, solar, hydroelectric, and geothermal). Ammonia produced using renewable energy sources has a virtually zero carbon footprint when combusted, or virtually zero emissions of CO2, SOx, particulate matter, and unburned hydrocarbons.

[0004] Ammonia has been tested and used on a small scale in spark-ignition internal combustion engines, but has not yet been used to power compression-ignition internal combustion engines.

[0005] Large turbocharged two-stroke uniflow scavenged compression internal combustion crosshead engines are typically used in the propulsion systems of large ships and as prime movers in power plants. Their size, weight, and power output set them apart from other combustion engines, placing them in a unique category.

[0006] EP2664777 discloses a large turbocharged two-stroke uniflow scavenged compression internal combustion engine according to the preamble of claim 1. In this engine, ammonia is injected into the combustion chamber as fuel and as a reducing agent. The ammonia, together with a reduction catalyst arranged downstream of the turbocharger turbine, helps to reduce NOx emissions. Summary of the Invention

[0007] The objective is to provide a compression ignition internal combustion engine having at least one mode of operation in which the primary fuel is ammonia.

[0008] These and other objects are achieved by the features of the independent claims. More specific implementations will become apparent from the dependent claims, the description and the drawings.

[0009] According to a first aspect, there is provided a large two-stroke turbocharged uniflow scavenged compression ignition internal combustion engine configured to operate on ammonia as a primary or sole fuel in at least one mode of operation, the engine comprising: At least one cylinder having a reciprocating piston therein, the cylinder having a cylinder cover covering the cylinder, and provided in a cylinder liner in which a scavenging port is arranged; a combustion chamber formed between the reciprocating piston in the cylinder and the cylinder cover; an exhaust valve disposed in the center of the cylinder cover; at least one pre-chamber disposed in the cylinder cover and connected to the combustion chamber in fluid communication through an opening; an ammonia valve opening into the at least one pre-chamber; Equipped with the ammonia valve having an inlet port connected to a source of pressurized ammonia; The ammonia valve is configured to inject liquid ammonia into the pre-chamber.

[0010] There are several technical challenges to using ammonia as a fuel. One challenge is its low power density compared to typical hydrocarbon fuels. This leads to the need for very large amounts of fuel to be injected, resulting in high flow rates. Such high flow rates can result in flame extinction; even if ignition occurs very early in the injection event, the subsequent high flow rate and associated high-velocity fuel jet can extinguish (blow out) the flame. Another challenge is the low ignition (ease of combustion) of ammonia compared to liquid hydrocarbon fuels. A further challenge is ammonia's high evaporative cooling, which cools the fuel upon injection, thus requiring a large amount of ignition energy. Due to the strong evaporative cooling, high fuel zone temperatures are a prerequisite for stable combustion. These technical challenges have strongly hindered the use of ammonia as a primary fuel in compression-ignition engines.

[0011] The inventors have realised that injecting ammonia through a nozzle in an ammonia valve into a pre-chamber leading to the combustion chamber at an opening can significantly slow down the fuel before it enters the combustion chamber through the opening, allowing the pre-chamber to act as a pre-heating chamber, thereby reducing the fuel velocity as it enters the combustion chamber through the opening and increasing the fuel temperature as it enters the combustion chamber, thereby at least partially solving the above-mentioned problems associated with using ammonia as a fuel in compression-ignition internal combustion engines.

[0012] In one implementation of the first aspect, the engine includes an ignition fluid valve associated with the at least one pre-chamber, the ignition fluid valve including an ignition fluid nozzle having a nozzle hole, the ignition fluid valve connected to a source of pressurized ignition fluid, whereby the ignition fluid mixes with the ammonia in the pre-chamber, improving reliability of ignition of the ammonia. Injecting the ignition fluid into the pre-chamber at high pressure ensures that the ignition fluid is well dispersed in the ammonia, ensuring that the ignition fluid and ammonia mixture is already well mixed when it enters the combustion chamber.

[0013] In one implementation of the first approach, the source of pressurized ignition fluid is a source of pressurized pilot fluid or a source of pressurized ignition enhancer. The pilot fluid can be, for example, dimethyl ether (GME) or fuel oil. The ignition enhancer can be, for example, hydrogen. The hydrogen can be obtained from an external source or can be produced from ammonia itself, for example, using a catalytic process.

[0014] In one example implementation of the first approach, the engine is configured to inject pilot fluid through a nozzle of an ignition fluid valve, followed by either injecting only ammonia through a nozzle of an ammonia valve, or injecting both pilot fluid through the ignition fluid valve and ammonia through the ammonia valve.

[0015] In one implementation of the first aspect, the pre-chamber takes the form of an insert in the cylinder cover, so that if damage occurs to the pre-chamber or the opening between the pre-chamber and the combustion chamber, the pre-chamber can be easily replaced by simply replacing the insert, thereby avoiding the need to repair or modify the entire cylinder cover.

[0016] In one example of an implementation of the first aspect, the pre-chamber and the ammonia valve form a single unit, and the single unit is an insert that is disposed in the cylinder cover, so that the pre-chamber and the ammonia valve can be attached to the cylinder cover in a single operation.

[0017] In one example of an implementation of the first aspect, at least a portion of the wall separating 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, the wall separating the pre-chamber is guaranteed to heat up during engine operation. This ensures that the pre-chamber is heated to a high temperature, and also ensures that a region of the combustion chamber close to the pre-chamber is heated to a high temperature. Therefore, it is guaranteed that the region where the ammonia reaches is heated to a high temperature, enhancing the reliability of combustion.

[0018] In one implementation of the first approach, 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, more preferably less than half, allowing ammonia to enter the combustion chamber at a velocity significantly slower than the velocity at which it enters the pre-chamber.

[0019] In one example of an implementation of the first aspect, a plurality of pre-chambers are arranged around the exhaust valve.

[0020] In one example implementation of the first aspect, the source of pressurized ammonia is a source of pressurized liquid-phase ammonia.

[0021] In one example implementation of the first aspect, the engine is configured to inject ammonia and another fuel simultaneously into the pre-chamber.

[0022] In one example implementation of the first aspect, the engine includes a fuel valve that opens into the at least one pre-chamber, the fuel valve having an inlet port connected to a source of pressurized other fuel and configured to inject the other fuel into the pre-chamber.

[0023] According to a second aspect, there is provided a conversion kit for a large two-stroke turbocharged uniflow scavenged compression ignition internal combustion engine for converting the engine to a condition suitable for operation on ammonia as a primary or sole fuel in at least one operating mode, the engine comprising: At least one cylinder having a reciprocating piston therein and a cylinder cover covering the cylinder; a combustion chamber formed between the reciprocating piston in the cylinder and the cylinder cover; The retrofit kit comprises: at least one pre-chamber attached to the cylinder cover, the pre-chamber having an opening for connecting the pre-chamber to the combustion chamber; an ammonia valve opening into the at least one pre-chamber; Equipped with the ammonia valve having an inlet port connected to a source of pressurized liquid ammonia; The ammonia valve is configured to inject liquid ammonia into the pre-chamber.

[0024] These and other aspects will become more apparent from the examples described below. [Brief explanation of the drawings]

[0025] Various aspects, embodiments, and implementation examples will be described in detail below with reference to exemplary embodiments shown in the drawings. [Figure 1] 1 shows a front view of a large two-stroke diesel engine according to an exemplary embodiment; FIG. [Figure 2]FIG. 2 is a diagram showing an overview of the large two-stroke engine of FIG. 1 as seen from the rear. [Figure 3] 2 is a schematic representation of the large two-stroke engine of FIG. [Figure 4] FIG. 2 is a cross-sectional view showing a detailed structure relating to a cylinder of the large two-stroke engine of FIG. 1. [Figure 5] 2 is a schematic representation of an ammonia valve used in the large two-stroke engine of FIG. [Figure 5A] 2 is a schematic representation of a fuel valve for ammonia fuel used in the large two-stroke engine of FIG. 1; [Figure 6] 2 is a schematic representation of an ignition fluid valve used in the large two-stroke engine of FIG. [Figure 7] FIG. 2 is a schematic cross-sectional view of the ammonia valve and pre-chamber forming a single unit mounted on the cylinder cover of the large two-stroke engine of FIG. 1. Detailed explanation

[0026] In the following detailed description, the compression ignition internal combustion engine will be described with reference to an exemplary crosshead type large slow speed two-stroke uniflow scavenged turbocharged compression ignition internal combustion engine, although it should be noted that in some cases the compression ignition internal combustion engine may be another type of engine.

[0027] 1-3 illustrate a turbocharged, large, slow-speed, two-stroke diesel engine. The engine has a crankshaft 8 and a crosshead 9. FIG. 3 is a schematic representation of a turbocharged, large, slow-speed, two-stroke diesel engine, along with its intake and exhaust systems. In an embodiment, the engine has six cylinders 1 arranged in series. Turbocharged, large, slow-speed, two-stroke diesel engines typically have four to fourteen cylinders arranged in series. These cylinders are supported on a cylinder frame 23. The cylinder frame 23 is supported on an engine frame 11. Such an engine can also be used, for example, as a main engine on a ship or as a stationary engine for driving a generator in a power plant. The total power output of the engine can be, for example, 1,000 kW to 110,000 kW.

[0028] The engine in this embodiment is a two-stroke uniflow compression ignition engine. Each cylinder liner 1 has a scavenging port 18 in its lower region and an exhaust valve at the top center. Scavenging air is guided to the scavenging port 18 of each cylinder 1 through a scavenging air receiver 2. The piston 10 reciprocates between bottom dead center (BDC) and top dead center (TDC) in the cylinder liner 1, compressing the scavenging air. Ammonia is injected through an ammonia valve 50. The ammonia valve 50 is disposed in the cylinder cover 22. Following the injection of ammonia, combustion occurs and exhaust gas is produced. The ammonia valve 50 is configured to inject ammonia. In some embodiments, the engine has an additional fuel valve. The additional fuel valve, not shown, is configured to inject conventional fuels such as fuel oil or heavy fuel oil. In such an embodiment, the engine is a dual-engine engine and includes a fuel supply system (not shown) for supplying conventional fuels.

[0029] When the exhaust valve 4 opens, the exhaust flows through an exhaust duct in the cylinder 1 to the exhaust receiver 3, then through a first exhaust pipe 19 to the turbine 6 of the turbocharger 5. From there, the exhaust flows through a second exhaust pipe 25 to the economizer 20 and is then released into the atmosphere through an outlet 21.

[0030] The turbine 6 drives the compressor 7 via a shaft. Outside air is supplied to the compressor 9 through an air intake 12. The compressor 7 sends compressed scavenging air into a scavenging pipe 13 connected to the scavenging air receiver 2. The scavenging air in the scavenging pipe 13 passes through an intercooler 14 to cool the scavenging air.

[0031] The cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17. The auxiliary blower 16 compresses the scavenging air flow when the compressor 7 of the turbocharger 5 cannot provide sufficient pressure for the scavenging air receiver 2, i.e. when the engine is at low or partial load. At high engine loads, the turbocharger compressor 7 can provide sufficiently compressed scavenging air and the auxiliary blower 16 is bypassed by a check valve 15.

[0032] The engine is operated in at least one mode of operation using ammonia as its primary fuel. The ammonia is supplied to the ammonia valve 50 at a substantially constant pressure and temperature. The ammonia may be supplied to the ammonia valve 50 in the liquid or gas phase. The liquid phase ammonia may be aqueous ammonia, i.e., an aqueous ammonia solution.

[0033] Ammonia fuel system 30 forms part of a source 40 of pressurized liquid phase ammonia. Ammonia fuel system 30 supplies liquid ammonia at a relatively low supply pressure (e.g., 30-80 bar) to ammonia valve 50 via supply line 31. Alternatively, ammonia is supplied to ammonia valve 50 in the gas phase at a relatively low supply pressure (e.g., 30-80 bar).

[0034] In some embodiments, the ammonia is stored in a Type C pressurized storage tank (not shown) in liquid phase at approximately 17 bar. Ammonia is in liquid phase at pressures above 8.6 bar at an ambient temperature of 20°C. However, it is preferred to store the ammonia at approximately 17 bar to ensure that it remains in liquid phase even at elevated temperatures. Existing engines configured to run on LPG or other gaseous fuels stored in liquid phase can be converted with relatively minor modifications into an ammonia-fired engine, i.e., an engine in accordance with embodiments of the invention disclosed herein. The conversion involves the use of a slightly modified fuel supply system, but the same fuel tank can be used, so the modifications are relatively minor.

[0035] The ammonia valve 50 has an inlet port connected to the pressurized liquid phase ammonia source 40. In some embodiments, the pressurized liquid phase ammonia source is part of the fuel system 30 configured to supply pressurized liquid phase ammonia to the ammonia valve 50.

[0036] Referring to Figure 4, there is shown a cylinder 1 supported by a cylinder frame 23. A cylinder cover 22 is fastened to the top of the cylinder 1. A piston 10 is also shown, with top and bottom dead centers indicated by dashed lines. A combustion chamber is formed within the cylinder. The combustion chamber is formed between the reciprocating piston 10 and the cylinder cover 22. An exhaust valve 4 is arranged in the center of the cylinder cover 22. Two or three ammonia valves 50 are arranged in the cylinder cover 22 of each cylinder 1 around (in the circumferential direction) the central exhaust valve 4.

[0037] 5 illustrates the ammonia valve 50 in more detail. The ammonia valve 50 has an elongated valve body and a nozzle 51 at the front end of the valve body. The ammonia valve 50 has 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 valve body.

[0038] The nozzle 51 has one or more nozzle holes 52. The nozzle 51 and the nozzle holes 52 are configured to inject ammonia into the pre-chamber 33.

[0039] The ammonia valve 50 can be a type of valve controlled by a control signal to execute an ammonia injection event. This type of ammonia valve 50 can be connected to a common rail type ammonia supply that is maintained at a nearly constant pressure. The control signal is synchronized to the engine cycle to ensure proper timing of ammonia injection.

[0040] Alternatively, the ammonia valve 50 can be a type of valve that opens when the supply pressure at the ammonia inlet port exceeds a given threshold and closes when the supply pressure at the ammonia inlet port falls below the given threshold. The latter type of ammonia valve 50 requires connection to a pressure-swinging, pressurized liquid-phase ammonia source that is controlled in synchronization with the engine cycle.

[0041] Associated with each ammonia valve 50 is a pre-chamber 33. The pre-chamber 33 is part of the cylinder cover 22 and preferably takes the form of an insert 55 attached to the cylinder cover 22, preferably in a removably mounted manner. Having the pre-chamber 33 as an insert 55 allows the pre-chamber 33 to be maintained or repaired by simply replacing the insert 55, without having to replace or repair the entire cylinder cover 22. In the embodiment shown in Figure 7, the pre-chamber 33 is formed as a single unit with the ammonia valve 50. This single unit is, as in the previous example, an insert attached to the cylinder cover 22, preferably in a removably mounted manner.

[0042] The bleed chamber 33 is configured so that fluid can pass between it and the combustion chamber through an opening 35. The cross-sectional area of ​​the opening 35 is preferably larger than the overall cross-sectional area of ​​the plurality of nozzle holes 52 of the nozzle 51. More preferably, the cross-sectional area of ​​the opening 35 is twice or more the overall cross-sectional area of ​​the plurality of nozzle holes 52 of the nozzle 51.

[0043] The wall separating the pre-chamber 33 from the combustion chamber forms a protrusion from the cylinder cover 22 into the combustion chamber. Preferably, the opening 35 forms part of the wall forming the protrusion. By making the wall a protrusion into the combustion chamber, the wall can heat up during engine operation, thereby allowing the pre-chamber 33 to heat up during engine operation, which helps to improve the stability of ammonia injection within the pre-chamber.

[0044] In some embodiments, an ignition fluid valve 60 (see FIG. 6 ) is associated with the pre-chamber 33. In this example, the ignition fluid valve 60 is attached to the cylinder cover 22 at the ignition fluid nozzle 61. The ignition fluid nozzle 61 has nozzle holes 62 configured to inject ignition fluid into the pre-chamber 33 upon action of the ignition fluid valve 60. The ignition fluid valve 60 has an inlet port connected to a source of pressurized ignition fluid 44. In some embodiments, the ignition fluid is a pilot fluid, i.e., a fluid injected immediately before or simultaneously with the start of fuel injection into the pre-chamber. The ignition fluid can be, for example, fuel oil (e.g., diesel), DME, hydrogen, etc. (Hydrogen can be used as a pilot fluid or ignition enhancer.) Operation of the ignition fluid valve 60 is synchronized with the engine cycle so that the ignition fluid is injected into the pre-chamber 33 before and / or together with the ammonia. Thus, an engine according to one embodiment may inject pilot fluid through nozzle 61 of ignition fluid valve 60 and subsequently inject ammonia only through nozzle 51 of ammonia valve 50, or may inject both pilot fluid through ignition fluid valve 60 and ammonia through ammonia valve 50.

[0045] In another example, an ignition enhancer is added to the ammonia before or as it is injected into the pre-chamber. In some embodiments, the ignition enhancer is hydrogen. This hydrogen is mixed with the ammonia in its gas phase. Another medium with suitable ignition properties may be used. In the case of ammonia in its liquid phase, the ignition enhancer is also a liquid phase substance and therefore can be mixed with the ammonia in its liquid phase. In the case of ammonia in its gas phase, the ignition enhancer is also a gas phase substance and therefore can be mixed with the ammonia in its gas phase.

[0046] In some embodiments, the engine is configured to simultaneously inject ammonia and another fuel into the pre-chamber 33. In some embodiments, the other fuel is a conventional hydrocarbon fuel, such as fuel oil or natural gas. That is, the other fuel can also be in liquid or vapor phase. Ammonia can be supplied to the ammonia valve 50 in either liquid or vapor phase.

[0047] As shown in Figure 5a, the engine of this embodiment includes a fuel valve 70 having a nozzle 71. The nozzle 71 has a nozzle hole 72 that opens into at least one pre-chamber 33. The fuel valve 70 has an inlet port that is connected to a source 49 of pressurized other fuel. The fuel valve 70 is configured to inject the other fuel from the source 49 through the nozzle hole 72 into the pre-chamber 33.

[0048] A control unit, not shown, is configured to control engine operation, including the activation and deactivation times of the ammonia valve 50 and the ignition fluid valve 60 .

[0049] Injecting the pilot fluid before injecting the ammonia allows the temperature within the pre-chamber 33 to be high enough to ignite the ammonia when it enters the pre-chamber 33. Additionally, in this embodiment, the pre-chamber 33 ensures that the pilot fuel and ammonia mix as they exit the pre-chamber 33 into the main combustion chamber.

[0050] The prechamber 33 allows the ignition fluid and ammonia to mix before entering the combustion chamber, thereby ensuring uniform distribution of the ammonia and ignition fluid. The ignition fluid thus becomes part of the ammonia jet escaping the prechamber 33 through the opening 35, achieving optimal use of the ignition fluid in stabilizing the combustion process. The temperature increase of the air (compressed scavenging air) and prechamber walls is most pronounced during the initial phase of ammonia injection. This also solves the problems associated with high evaporative cooling of ammonia. The prechamber 33 thus eliminates or at least minimizes the amount of ignition fluid required due to the optimal mixing and improved temperature transfer from the walls.

[0051] Stable combustion of ammonia in direct injection mode results in significant improvements in combustion control and combustion stability.

[0052] The nozzles or atomizers 51, 61 are located within the pre-chamber 33, which also has the effect of protecting the nozzles or atomizers 51, 61 from the harsh environment within the combustion chamber.

[0053] Many aspects and implementations have been described with several examples. However, upon review of the specification, drawings, and claims herein, those skilled in the art will understand and be able to embody many variations in addition to the described examples in practicing the claimed invention. The words "comprise," "have," and "include" in the claims do not exclude the presence of unrecited elements or steps. The absence of an explicit recitation of a plurality of recited elements in a claim does not exclude the presence of a plurality of such elements. The fact that several items are recited in separate dependent claims does not exclude them from being practiced in combination, and may be practiced to advantage in combination.

[0054] Reference signs used in the claims should not be construed as limiting the scope of the invention. Unless otherwise noted, the drawings are intended to be read together with the specification, which is an entire part of this disclosure. Throughout the specification, the terms "horizontal," "vertical," "left," "right," "upper," "lower," and their adjectival and adverbial forms (e.g., "horizontally," "rightwardly," "upwardly," etc.) merely refer to the orientation of the illustrated structure relative to the reader's viewing direction. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to a longitudinal axis or axis of rotation, as the context requires.

Claims

1. 1. A large two-stroke turbocharged uniflow scavenged compression ignition internal combustion engine configured to operate on ammonia as a primary or sole fuel in at least one operating mode, comprising: At least one cylinder having a reciprocating piston therein, the cylinder having a cylinder cover covering the cylinder, and provided within a cylinder liner in which a scavenging port is arranged; a combustion chamber formed between the reciprocating piston in the cylinder and the cylinder cover; an exhaust valve disposed in the center of the cylinder cover; at least one pre-chamber disposed in the cylinder cover and connected to the combustion chamber in fluid communication through an opening; an ammonia valve opening into the at least one pre-chamber; Equipped with the ammonia valve having an inlet port connected to a source of pressurized ammonia; the ammonia valve is configured to inject liquid ammonia into the pre-chamber; institution.

2. 10. The engine of claim 1, further comprising an ignition fluid valve associated with the at least one pre-chamber, the ignition fluid valve comprising an ignition fluid nozzle having a nozzle hole, the ignition fluid valve connected to a source of pressurized ignition fluid.

3. The engine of claim 2 , wherein the ignition fluid valve is configured to inject ignition fluid through the nozzle into the pre-chamber.

4. 4. An engine according to claim 2 or 3, wherein the source of pressurized ignition fluid is a source of pressurized pilot fluid or a source of pressurized ignition enhancer.

5. 5. An engine according to any one of claims 2 to 4, configured to inject pilot fluid through a nozzle of the ignition fluid valve followed by injection of ammonia alone through a nozzle of the ammonia valve, or to inject both pilot fluid through the ignition fluid valve and ammonia through the ammonia valve.

6. 6. An engine according to any one of claims 1 to 5, wherein the pre-chamber is an insert disposed in the cylinder cover, preferably an insert that is removably mounted.

7. 7. An engine according to claim 6, wherein said pre-chamber together with said ammonia valve form a single unit, said single unit being an insert mounted to said cylinder cover, preferably a removably mounted insert.

8. 8. An engine according to any one of claims 1 to 7, wherein at least part of the wall separating the pre-chamber from the combustion chamber forms a protrusion from a cylinder cover into the combustion chamber, preferably from a side of the cylinder cover facing the combustion chamber.

9. 9. An engine according to claim 1, wherein the sum of the cross-sectional areas of the plurality of nozzle holes is smaller than the cross-sectional area of ​​the opening, preferably significantly smaller, more preferably less than half.

10. 10. An engine according to claim 1, further comprising a plurality of pre-chambers arranged around the exhaust valve.

11. 11. An engine according to any preceding claim, wherein the source of pressurised ammonia is a source of pressurised liquid phase ammonia.

12. 12. An engine according to any preceding claim, configured to inject ammonia and another fuel simultaneously into the pre-chamber.

13. 13. The engine of claim 12, further comprising a fuel valve opening into the at least one pre-chamber, the fuel valve having an inlet port connected to a source of pressurized other fuel and configured to inject the other fuel into the pre-chamber.

14. 1. A conversion kit for a large two-stroke turbocharged uniflow scavenged compression ignition internal combustion engine, said conversion kit for converting said engine to a condition suitable for operation on ammonia as a primary or sole fuel in at least one mode of operation, said engine comprising: At least one cylinder having a reciprocating piston therein and a cylinder cover covering the cylinder; a combustion chamber formed between the reciprocating piston in the cylinder and the cylinder cover; The retrofit kit comprises: at least one pre-chamber attached to the cylinder cover, the pre-chamber having an opening for connecting the pre-chamber to the combustion chamber; an ammonia valve opening into the at least one pre-chamber; Equipped with the ammonia valve having an inlet port connected to a source of pressurized liquid ammonia; the ammonia valve is configured to inject liquid ammonia into the pre-chamber; Modification kit.

15. A retrofit kit according to claim 14, wherein the pre-chamber forms an insert that is mounted to the cylinder cover, preferably a removably mounted insert.

16. 16. A retrofit kit as claimed in claim 15, wherein the pre-chamber together with the ammonia valve form a single unit, the single unit being an insert that is mounted in the cylinder cover, preferably a removably mounted insert.

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