INTERNAL COMBUSTION ENGINE

Abstract

 The present invention is related to an internal combustion engine (100) and a method for operating an internal combustion engine. The Internal combustion engine (100), preferably a large two-stroke internal combustion engine, has at least one cylinder (1), preferably having an inner diameter of at least 200mm.
The Internal combustion engine (100) is a low pressure fuel fluid engine or dual-fuel engine (1) comprising at least one fluid admission valve (29) for providing fuel fluid. The cylinder (1) has a plurality of scavenging ports (10) being in fluid communication with a scavenging chamber (4) which surrounds a first end side (6a) of the cylinder (1).
The internal combustion engine (100) comprises at least one mixing chamber (11) providing a mixing volume (12), which is arranged in the scavenging chamber (4). The mixing chamber (11) comprises at least one inlet port (13) for introducing scavenging air, at least one feed nozzle (14) for introducing fuel fluid into the mixing chamber, preferably at least one feed nozzle (14) arranged in each inlet port (13), and at least one outlet (15), each outlet (15) facing at least one scavenging port (10) and preferably up to four adjacent scavenging ports (10).

Description

[0001] The present invention is related to internal combustion engines and to a method for operating an internal combustion engine according to the preambles of the independent claims.

[0002] The present invention preferably relates to an internal combustion engine like a large marine or ship engine or a stationary engine whose cylinders have an inner diameter of at least 200 mm. The engine preferably is a two-stroke engine or a two-stroke cross head engine. The engine can be a gas engine, a dual fuel or a multi fuel engine. Burning of liquid and or gaseous fuels in such engines is possible as well as self-igniting or forced igniting.

[0003] The internal combustion engine can be a longitudinally flushed two-stroke engine.

[0004] The term internal combustion engine also refers to large engines which can be operated not only in diesel mode, which is characterized by the self-ignition of the fuel, but also in Otto mode, which is characterized by the positive ignition of the fuel, or in mixtures of the two. Furthermore, the term internal combustion engine includes in particular dual-fuel engines and large engines in which the self-ignition of the fuel is used for the positive ignition of another fuel.

[0005] Engine speed is preferably below 800 RPM, especially for 4-stroke engines, and more preferably below 200 RPM, especially for 2-stroke engines, which indicates the designation of low speed engines.

[0006] Fuel can be diesel or marine diesel oils or heavy fuel oils or emulsions or slurries or methanol or ethanol as well as gases like liquid natural gas (LNG) liquid petrol gas (LPG) and so on.

[0007] Further possible fuels which might be added on request are: LBG (Liquefied Biogas), biological fuels (e. g. oil made from algae or seaweed), ammonia, hydrogen, synthetic fuels from CO2 (e.g. made by Power-To-Gas or Power-To-Liquid).

[0008] Large ships, in particular vessels for transport of goods, usually are powered by internal combustion engines, in particular diesel and/or gas engines, mostly two-stroke, cross head engines.

[0009] It is known to inject high or low pressurized fuel directly into the pressurized cylinder. The timing can be chosen such that blowing through of air fuel mixture can be reduced or avoided. The mixture of the fuel fluid and the active fluid may be insufficient and the concentration of the fuel fluid may be locally increased, which may cause problems such as premature ignition and discharge of unburnt fluid.

[0010] The admission holes arranged in the cylinder liner may disturb the pressure within the ring packages of the piston.

[0011] WO2018135191 A1 discloses a two-stroke engine in which fuel is brought via nozzles into a space ahead of scavenging ports. The fuel injection starts after the scavenging ports are released from the piston and ends before the scavenging ports are closed again.

[0012] EP 3296557 B1 shows a two-stroke engine in which fuel is directed into a scavenging air chamber surrounding the cylinder. The fuel is directed from a main supply through valves into a ring line. Branching off from the ring line are fuel lines, which have holes through which the fuel can enter the scavenging chamber, where it mixes with scavenging air. Similarly to the mixing within the cylinder, mixing may be insufficient and the concentration of the fuel gas may be not be distributed homogenously which also could result in misfiring events such as pre-ignition or knocking.

[0013] It is an object of the present invention to avoid the drawbacks of the prior art and in particular to provide an internal combustion engine and a method of operating an internal combustion engine providing an increased engine efficiency.

[0014] The object is achieved by the internal combustion engines and the method for running an internal combustion engine according to the independent claims.

[0015] The internal combustion engine comprises at least one cylinder, preferably having an inner diameter of at least 200mm.

[0016] The internal combustion engine is a low pressure fuel gas engine or a dual-fuel engine, preferably is a large two-stroke internal combustion engine.

[0017] The internal combustion engine comprises at least one fluid admission valve for providing fuel fluid. Within this application a fuel fluid may be a fuel gas or a fuel liquid.

[0018] The cylinder comprises a plurality of scavenging ports, which are in fluid communication with a scavenging chamber. The scavenging chamber surrounds at least a part of a first end side of the cylinder in a stroke direction of the piston, and the scavenging air may be introduced therein.

[0019] Scavenging air may be a compressed, cooled and dehydrated active gas example including an oxidizer such as oxygen, ozone or the like, or a mixture thereof (e.g. air). Scavenging air may also comprise recirculated exhaust gas or an inert gas of a different type.

[0020] The scavenging port may be a hole which passes through from an inner circumferential surface that is an inner circumferential surface of a cylinder liner on a first end side of the cylinder to an outer circumferential surface thereof, and a plurality of scavenging ports may be provided all around the cylinder.

[0021] The scavenging ports may be opened and closed by the movement of the piston within the cylinder.

[0022] The internal combustion engine comprises at least one mixing chamber providing a mixing volume, which is arranged in the scavenging chamber.

[0023] The mixing chamber comprises at least one inlet port for introducing scavenging air, at least one feed nozzle for introducing fuel fluid into the mixing chamber and at least one outlet.

[0024] Preferably at least one feed nozzle is arranged in the inlet port, more preferably in each inlet port. Fuel fluid may enter the mixing volume together with the scavenging air. Fuel fluid may be supplied to scavenging air such that an evenly distributed mixture forms.

[0025] Each outlet faces at least one scavenging port.

[0026] The mixing chamber may comprise one outlet per scavenging port or one outlet for up to eight, preferably for up to four, adjacent scavenging ports.

[0027] The fluid admission valve may supply pressurized fuel gas or pressurized fuel liquid. In the mixing chamber the fuel gas or fuel liquids expands and is mixed up with scavenging air such that a fuel/air mixture is provided.

[0028] Due to the premixing of fuel and air, fuel enters the cylinder mixed up with scavenging air and therefore may be homogeneously distributed within the cylinder. Very lean and very fuel-rich mixture regions in the combustion chamber are reduced. In addition, by admitting the natural gas into the mixing chamber with an optimised gas admission start and gas admission end, fuel is prevented from entering combustion chamber crevices, e.g. between piston and liner, and direct fuel losses out of the cylinder during the scavenging process are reduced.

[0029] The percentage of unburned fuel, in particular methane, is reduced, the tendency for ignition before the desired ignition timing and the tendency of knocking combustion are reduced, hence the engine efficiency is increased and the engine operation cycle in dual-fuel gas-mode is improved.

[0030] As the fuel fluid is premixed with the scavenging air outside the cylinder and a well prepared fuel/air mixture enters the cylinder lower fuel pressures may be necessary.

[0031] The mixing chamber is suitable as well as for fuel gas as also for fuel liquids.

[0032] The internal combustion engine may be a uniflow scavenging two-stroke engine, which may be used as an engine of a ship. Whereas the scavenging chamber is arranged at a first end side of the cylinder, an exhaust port may be provided on a second end side in the stroke direction of the piston in the cylinder.

[0033] The exhaust port may be an opening provided at the second end side, for example in the cylinder head, located above a top dead center of the piston and is opened and closed to exhaust an exhaust gas generated in the cylinder after combustion. When the exhaust port is open, the exhaust gas is exhausted from the cylinder through the exhaust port.

[0034] The at least one mixing chamber may be arranged coaxially around at least a part of the cylinder, in particular corresponding to scavenging ports coaxially arranged in the cylinder wall. The mixing chamber may be arranged on the same axial level, that is on the same level between top dead centre and bottom dead centre, as the scavenging ports. Thus the fuel/air mixture has a short way to the cylinder volume.

[0035] One of the at least one mixing chambers may supply a mixture of fuel and scavenging air to one scavenging port, to up to a number of adjacent scavenging ports or even to all scavenging ports.

[0036] The internal combustion engine may comprise exactly one mixing chamber, which may annularly extend around the complete cylinder and may provide an annular mixing volume.

[0037] The annular mixing chamber may comprise an annular inlet port and/or an annular outlet. An annular outlet may serve all scavenging ports. Alternatively the annular mixing chamber may comprise a plurality of inlet ports and/or a plurality of outlets.

[0038] Instead of one annular mixing chamber, at least two mixing chambers may be arranged on a coaxial ring around the cylinder. A plurality of mixing chambers may be annularly arranged around the cylinder. Each mixing chamber may serve up to eight, preferably four, adjacent scavenging ports.

[0039] Each of the plurality of mixing chambers may comprise one inlet port and one feed nozzle. Alternatively, each of the plurality of mixing chambers may comprise a plurality of inlet ports and/or a plurality of outlets.

[0040] The mixing chamber may comprise a neck adjacent to and/or surrounding the outlet which preferably contacts the outside wall of the cylinder. The neck may be arranged such that the outlet covers one or a plurality of adjunct scavenging ports and provides for a guided flow of the fuel/air mixture, such that the fuel/air mixture only enters the cylinder and does not return to the scavenging chamber.

[0041] Each inlet port may comprise an inlet pipe. At least a part of the inlet pipe may comprise an axis, preferably being parallel or perpendicular to an axis of the cylinder. Scavenging air may thus be supplied to the mixing chamber axially or radially.

[0042] At least one feed nozzle may be arranged in the inlet pipe, and may preferably be arranged such that the fuel liquid is mainly supplied in direction of the pipe axis. Mixing of fuel fluid and scavenging air may start in the inlet pipe.

[0043] The inlet pipe may be formed as a Venturi mixer with feed nozzles coaxially arranged, with respect to the axis of the pipe, in a wall of an intermediate part of the pipe. The intermediate part of the pipe has a smaller diameter than an upstream part and a downstream part of the pipe.

[0044] In the intermediate part the fuel fluid must increase its velocity, whereas its pressure is reduced. As the fluid leaves the intermediate part its pressure increases back to the pipe level. The change in pressure at the intermediate part in turn effects a change in flow of supplied fuel to join and mix with the main airflow in the required proportion. Fuel fluid may be supplied without a pump or at least with reduced pump power.

[0045] The inlet pipe may alternatively comprise an intermediate part with an enlarged diameter as compared with an upstream part and a downstream part of the inlet pipe. At least one feed nozzle may be arranged within the intermediate part. Fuel fluid and scavenging air are combined under turbulent flow conditions.

[0046] A static mixer may be arranged in the inlet pipe downstream of a feed nozzle. The static mixer may improve the mixing of the combined fuel fluid and scavenging air. Hence flow path within the mixing chamber for mixing may be reduced.

[0047] A throttle valve may be arranged in the inlet pipe downstream of a feed nozzle.

[0048] By setting the throttle vale the admission of scavenging air to the mixing chamber may be controlled. The admission of scavenging air may thus be equalized with respect to other mixing chambers, in particular for combustion engines with a plurality of cylinders. Also, for lower loads, scavenging air supply may be reduced. The throttle can as well be used to improve the mixing of the fuel gas and the scavenging gas.

[0049] The internal combustion engine may comprise a control device for setting the throttle valves.

[0050] The internal combustion engine may comprise a control device for enabling opening the feed nozzle to inject fuel into the mixing chamber after the scavenging ports have started to open and for stopping injection before the scavenging ports are closed.

[0051] Thus, the risk of blowing out unburnt fuel through the exhaust outlet is reduced.

[0052] According to a further aspect the internal combustion engine comprises at least one gas admission valve for providing fuel fluid and comprises at least one fuel feeding chamber which is arranged downstream of at least one gas admission valve and upstream of the volume of the cylinder. Preferably the fuel feeding chamber is arranged upstream and fluidly connected to a plurality of feed nozzles. Preferably the internal combustion engine comprises 1 to 3 fuel feeding chambers, which may be arranged in different axial levels. Each fuel feeding chamber may be arranged downstream of 1 to 5 fluid admission valves.

[0053] The combustion engine is low pressure fuel gas engine or dual-fuel engine, preferably a large longitudinally flushed two-stroke internal combustion engine, having at least one cylinder, preferably having an inner diameter of at least 200mm. The combustion engine in particular is a combustion engine as described above.

[0054] One or more fluid admission valves may be mounted on the fuel feeding chamber. The fluid admission valves can be actuated to allow pressurised fuel to enter the fuel supply chamber. Preferably four to sixteen fluid admission valves are mounted around the cylinder.

[0055] The feed nozzles may be arranged to supply the fuel fluid to the mixing chamber or directly to the cylinder. The cylinder may comprise nozzle openings, for example 40-50 nozzle openings, in the cylinder wall defining feed nozzles. The nozzle opening may have an axis which may be directed radially or may include an angle with the radial direction. The axis of the nozzle opening may be perpendicular to the cylinder axis or may include an angle with a horizontal plane which is perpendicular to the cylinder axis.

[0056] One or more such fuel feeding chambers can be installed on one cylinder with an axial distance to optimise the fuel fresh charge mixing.

[0057] The fuel feeding chamber may be coaxially arranged around at least a part of the cylinder. Preferably one feeding chamber may extend annularly around the cylinder and may be fluidly connected to all feed nozzles.

[0058] A location of such a fuel feeding chamber in the lower half of the piston stroke is preferred. A location which allows admitting fuel into a region with a high turbulence level due to a freshly charged flow through the scavenging ports into the cylinder is advantageous.

[0059] The fuel feeding chamber may be arranged on the same axial level as the mixing chamber or above the axial level of the mixing chamber or below the axial level of the mixing chamber.

[0060] According to a further aspect the internal combustion engine comprises at least one fluid admission valve for providing fuel fluid. A check valve is arranged in a fluid path between the at least one fluid admission valve and a cylinder volume, preferably within a feed nozzle.

[0061] The combustion engine is a low-pressure fuel gas engine or dual-fuel engine, preferably a large longitudinally flushed two-stroke internal combustion engine, having at least one cylinder, preferably having an inner diameter of at least 200mm. The combustion engine in particular is a combustion engine as described above.

[0062] The check valve provides for reducing a dead volume. The dead volume is the volume from where fuel may enter the cylinder after the fluid admission valve has been closed. The check valves can as well improve the fuel dynamics within the system. As the check valves provide for a smaller dead volume, a reaction on requirement changes can happen faster. Smaller volumes result in a lower inertia of the system.

[0063] Preferably, the check valve is arranged such that the dead volume is reduced at least by 70% to 80% as compared with an arrangement without check valves.

[0064] According to a further aspect a method is provided for operating an internal combustion engine as described above comprising a cylinder with scavenging ports, a mixing chamber and feed nozzle. The method comprises the steps of opening the feed nozzle to inject fuel into the mixing chamber after the scavenging ports are open and stopping injection before the scavenging ports are closed.

[0065] In the following, the invention is further explained in embodiments by means of figures. Same reference numbers refer to functionally corresponding features.

Figure 1:

shows a schematic view of an internal combustion engine;

Figure 2:

shows a schematic view of a first example of a first end side of a cylinder in a side view;

Figure 3:

shows a schematic view of the first example in a sectional view from above;

Figure 4:

shows a schematic view of a second example of a first end side of a cylinder in a side view;

Figure 5:

shows a schematic view of a cylinder in a side view with the second example of a first end side of the cylinder;

Figure 6:

shows a schematic view of a first example of an inlet pipe;

Figure 7:

shows schematic views of a second example of an inlet pipe;

Figure 8:

shows a schematic view of a third example of an inlet pipe;

Figure 9:

shows schematic views of a fourth example of an inlet pipe;

Figure 10:

shows schematic diagram of valve settings depending on crank position/time;

Figure 11a:

shows a schematic view of a further example of an internal combustion engine in a sectional view from the side;

Figure 11b:

shows a schematic view of a further example of an internal combustion engine in a sectional view from above;

Figure 12:

shows a schematic view of a cylinder liner of a further example for an internal combustion engine in a sectional view from the side.

[0066] Figure 1 shows a schematic view of an internal combustion engine 100. The internal combustion engine is a large two-stroke internal combustion engine having at least a cylinder 1 with an inner diameter 7 of at least 200mm. A reciprocating piston 2 is connected to a crosshead not shown in the figure.

[0067] The cylinder 1 has a plurality of scavenging ports 10, for example 32 scavenging ports, which are in fluid communication with a scavenging chamber 4. The scavenging chamber 4 surrounds a first end side 6a of the cylinder 1. An exhaust port 3 is arranged on a second end side 6b of the cylinder 2.

[0068] The internal combustion engine 100 comprises at least one mixing chamber 11, which is arranged in the scavenging chamber 4.
In the mixing chamber 11 fuel fluid and scavenging air is mixed before entering the cylinder through the scavenging ports 10.

[0069] Figure 2 shows a schematic view of a first example of a first end side 6a of a cylinder 1 in a side view. On the first end side 6a a plurality of mixing chambers 11 are arranged around the cylinder 1.

[0070] Each mixing chamber 11 comprises an inlet port 13 for introducing scavenging air into the mixing chamber 11. A feed nozzle 14 for introducing fuel fluid into the mixing chamber is arranged in each of the inlet ports 13.

[0071] Each mixing chamber 11 comprises an outlet 15 facing at least one scavenging port 10.

[0072] Each mixing chamber 11 provides a mixing volume 12, where scavenging air and fuel fluid form a mixture as homogeneous as possible before entering the cylinder 1.

[0073] Figure 3 shows a schematic view of the first example in a sectional view from above. The mixing chambers 11 are arranged on a circle around the cylinder 1. Fuel fluid is supplied to the feed nozzles 14 via fuel feeding chambers 28. Each fuel feeding chamber is fluidly connected to a fluid admission valve 29. Thus each fluid admission 29 valve may supply fuel fluid to all feed nozzles 14 being connected to the respective fuel feed chamber 28.

[0074] Instead of the usage of a fuel feeding chamber 28 together with a lower number of fuel admission valves 29 than feed nozzles 14, the fuel admission valves 29 can be integrated into the feed nozzles 14, which results in the same number of fuel admission valves 29 and of feed nozzles 14.

[0075] Figure 4 shows a schematic view of a second example of a first end side 6a of a cylinder in a side view and Figure 5 shows a schematic view the second example in a side view.

[0076] In this example one mixing chamber 11 is annularly arranged around the cylinder 1. The mixing chamber 11 may comprise a plurality of inlet ports 13 (see figure 5) or may comprise on sine annular inlet port. The mixing chamber 11 comprises a plurality of feed nozzles 14. The feed nozzles 14 are fed via a single common fuel feeding chamber 28, which is supplied by four fluid admission valves 29.

[0077] Also in the case of one annular mixing chamber 11, the fuel admission valves 29 can be integrated into the feed nozzles 14, such that the same number of fuel admission valves 29 and of feed nozzles 14 are installed.

[0078] As can be seen in figure 5, the inlet ports 13 may be formed as individual inlet pipes 17 with an axis 18 parallel to the axis 9 of the cylinder 1 or the inlet port 13 may be formed as an annular collar having a single annular opening.

[0079] The mixing chamber 11 comprises a neck 16 adjacent to the outlet 15 which contacts the outside wall 8 of the cylinder 1. Hence, the mixture of fuel fluid and scavenging air is reliably guided into the cylinder.

[0080] Figure 6 shows a schematic view of a first example of an inlet pipe 17. The inlet pipe 17 comprises an intermediate part 21' with an enlarged diameter 25 as compared with an upstream part 22' and a downstream part 23' of the inlet pipe 17.
A feed nozzle 14 is arranged in the intermediate part 21'.

[0081] Scavenging air entering the inlet pipe 17 at the upstream part 22' forms a turbulent flow in the intermediate part 21' promoting a homogeneous mixture with entering fuel fluid.

[0082] Figure 7 shows schematic views of a second example of an inlet pipe 17 along the axis 18 (above) and perpendicular to the axis 18 (below).

[0083] In this example the inlet pipe 17 is formed as a Venturi mixer 19 with feed nozzles 14 coaxially arranged in a wall 20 of an intermediate part 21 of the inlet pipe 17. In this case, the intermediate part 21 has a smaller diameter 24 than an upstream part 22 and a downstream part 23 of the inlet pipe 17.

[0084] Due to the accelerated flow of the scavenging air in the intermediate part 21, fuel fluid is sucked into the inlet pipe 17.

[0085] Figure 8 shows a schematic view of a third example of an inlet pipe 17. A feed nozzle 14 is arranged in the inlet pipe 17 and downstream of the feed nozzle 14 there is a static mixer 27. Due to the flow path determined by the static mixer 27, a turbulent flow is generated providing for a mixture of scavenging air and fuel fluid.

[0086] Figure 9 shows schematic views of a fourth example of an inlet pipe 17. A throttle valve 26 is arranged in the inlet pipe 17 downstream of a feed nozzle 14.

[0087] By setting the throttle valve the inflow of scavenging air mixed up with fuel fluid may be equalized which might be necessary in cases when not all inlet pipes 17 are provided with the same pressure of scavenging air and/or fuel fluid, for example when the distances between the scavenging reservoir 5 (see Figure 1) and the inlet pipes 17 and/or the distances between the fluid admission valves 29 (see figures 3 and 4) and the feed nozzles 14 are different for each inlet pipes 17.

[0088] Figure 10 shows schematic diagram of valve settings depending on the crank angle. The dashed line schematically shows the setting of the exhaust port 3 (see figure 1), the dotted line show the setting of the fluid admission valves 29 (see figures 3 and 4) and the solid line shows the state of the scavenging ports 10 (see figure 1).

[0089] The fuel needs to be admitted within a specific crank angle interval to on the one hand avoid that a part of the fuel exits the cylinder within the scavenging process, and on the other hand to reach the best mixing result.

[0090] When the piston 2 (see figure 1) moves downwards during the working stroke, the exhaust ports 3 (see figure 1) opens and afterwards the piston opens the scavenging ports 10.

[0091] The start of fuel admission into the mixing chamber 11 should start at a time, such that the cylinder is scavenged by the fresh charge but such that as low as possible or no fuel exits the cylinder 1 via the exhaust port 3 during the scavenging process. A direct methane slip shall be prevented. To optimise the fuel and fresh charge mixing, the admission duration and timing of the fuel fluid into the fresh scavenging air needs to be optimised. The fuel fluid admission needs to stop before the piston 2 closes the scavenging ports 10 during the compression stroke.

[0092] Typically, the scavenging ports 10 open at about 40°CA (degree crank angle) before the piston reaches the bottom dead centre or 140°CA after the piston has passed the top dead centre.

[0093] Typically, the scavenging ports 10 close about 40°CA after the piston has passed the bottom dead centre or at 220°CA after the piston has passed the top dead centre.

[0094] The exhaust port closes at 240°CA to 280°CA, wherein the actual exhaust valve closure depends on the engine load.

[0095] Gas admission typically starts at 20°CA after scavenging port opening or 160°CA after the piston has passed the top dead centre. Gas admission typically ends about 5°CA before the scavenging ports 10 are closed or 215°CA after the piston has passed the top dead centre

[0096] Figure 11a shows a schematic view of a further example of an internal combustion engine 100 in a sectional view from the side, Figure 11b shows a schematic view of the same example in a sectional view from above.

[0097] Two axially distanced fuel feeding chambers 28 are arranged around the cylinder 1. Each fuel feeding chamber 28 is arranged downstream of four fluid admission valves 29 and upstream of the volume 31 of the cylinder 1. Alternatively, for each fuel feeding chamber one to ten fluid admission valves 29 may be installed.

[0098] In this case the fuel fluid nozzles 14' are arranged in the wall 20 of the cylinder 1 and provide a directed fluid stream 32, which includes a first angle γ of between -45°and 45°, preferably of between -25°and 25° with a horizontal plane 33 perpendicular to the cylinder axis 9 and a second angle β of between -70°and 70°, preferably of between -45°and 45° with a radial direction 34 in the horizontal plane 33.

[0099] The fluid nozzles 14' are arranged on the same axial level and are equally distanced.

[0100] On each fuel feeding chamber 29, generally one or more fluid admission valves 29 may be mounted. The fluid admission valves 29 can be actuated to allow pressurised fuel to enter the fuel feeding chamber 29. Generally, one or more such fuel feeding chambers 29 can be installed on one cylinder to optimise the fuel fresh charge mixing.

[0101] Figure 12 shows a schematic view of a cylinder wall 20 of a further example for an internal combustion engine in a sectional view from the side.

[0102] In this example, the fluid admission valves 29 (not shown in the figure) are mounted on the outside of the wall 20 of the cylinder 1. The nozzle volume 35 of the fluid admission valve 29 is directly connected to feed nozzles 14' which form a fluid path between the fluid admission valve 29 and the cylinder volume 31.

[0103] A check valve 30 is arranged within each feed nozzle 14'. Without pressure from the fluid admission valve 29 the check valves 30 remain closed. The dead volume downstream of the fluid admission valve 29 from where fuel fluid may get into the cylinder volume after closing the fluid admission valve 29 is reduced.

[0104] Generally, the check valve 30 may be arranged anywhere in the fluid path between the gas admission valve 29 and the cylinder volume 31, preferably close to the cylinder volume 31.

Claims

1. Internal combustion engine (100), preferably a large two-stroke internal combustion engine, having at least one cylinder (1), preferably having an inner diameter of at least 200mm,

namely a low pressure fuel fluid engine or dual-fuel engine (1) comprising at least one fluid admission valve (29) for providing fuel fluid,

the cylinder (1) having a plurality of scavenging ports (10),

being in fluid communication with a scavenging chamber (4) which surrounds a first end side (6a) of the cylinder (1), characterized in that the internal combustion engine (100) comprises at least one mixing chamber (11) providing a mixing volume (12), which is arranged in the scavenging chamber (4),

wherein the mixing chamber (11) comprises

at least one inlet port (13) for introducing scavenging air,

at least one feed nozzle (14) for introducing fuel fluid into the mixing chamber, preferably at least one feed nozzle (14) arranged in each inlet port (13), and

at least one outlet (15), each outlet (15) facing at least one scavenging port (10) and preferably up to four adjacent scavenging ports (10).

2. Internal combustion engine (100) according to claim 1,
wherein
the mixing chamber (11) is coaxially arranged around at least a part of the cylinder (1).

3. Internal combustion engine (100) according to claim 2,
wherein one mixing chamber (11) annularly extends around the complete cylinder (1) and provides an annular mixing volume (12).

4. Internal combustion engine (100) according to claim 2,
wherein a plurality of mixing chambers (11) is annularly arranged around the cylinder (1).

5. Internal combustion engine (100) according one of the preceding claims, wherein the mixing chamber (11) comprises a neck (16) adjacent to the outlet (15), which preferably contacts the outside wall (8) of the cylinder (1).

6. Internal combustion engine (100) according one of the preceding claims, wherein each inlet port (13) comprises an inlet pipe (17) having an axis (18) in particular being parallel or perpendicular to an axis (9) of the cylinder (1) .

7. Internal combustion engine (100) according to claim 6,
wherein the inlet pipe (17) is formed as a Venturi mixer (19) with feed nozzles (14) coaxially arranged in a wall (20) of an intermediate part (21) of the inlet pipe (17), the intermediate part (21) having a smaller diameter (24) than an upstream part (22) and a downstream part (23) of the inlet pipe (17).

8. Internal combustion engine (100) according to claim 6,
wherein the inlet pipe (17) comprises an intermediate part (21") with an enlarged diameter (25) as compared with an upstream part (22') and a downstream part (23') of the inlet pipe (17), and wherein at least one feed nozzle (14) is arranged in the intermediate part (21").

9. Internal combustion engine (100) according to one of claims 6-8, wherein a throttle valve (26) is arranged in the inlet pipe (17) downstream of a feed nozzle (14).

10. Internal combustion engine (100) according to one of claims 6-8, wherein a static mixer (27) is arranged in the inlet pipe (17) downstream of a feed nozzle (14).

11. Internal combustion engine (100) according to one of the preceding claims, wherein the internal combustion engine (100) comprises a control device for enabling opening the feed nozzle (14) to inject fuel into the mixing chamber (11) after the scavenging ports (10) have started to open and for stopping injection before the scavenging ports (10) are closed.

12. Internal combustion engine (100), in particular according to one of the preceding claims, preferably a large longitudinally flushed two-stroke internal combustion engine, having at least one cylinder (1), preferably having an inner diameter of at least 200mm,

namely a low pressure fuel fluid engine or dual-fuel engine (1), comprising at least one fluid admission valve (29) for providing fuel fluid,

characterized in that the internal combustion engine (100) comprises at least one fuel feeding chamber (28) which is arranged downstream of the at least one fluid admission valve (29) and upstream of a cylinder volume (31), preferably arranged upstream and fluidly connected to a plurality of feed nozzles (14; 14').

13. Internal combustion engine (100) according to claim 12,
wherein the fuel feeding chamber (28) is coaxially arranged around at least a part of the cylinder (1), preferably one feeding chamber annularly (28) extends around the cylinder (1) and is fluidly connected to all feed nozzles (14; 14').

14. Internal combustion engine (100), in particular according to one of the preceding claims, preferably a large longitudinally flushed two-stroke internal combustion engine, having at least one cylinder (1), preferably having an inner diameter of at least 200mm,

namely a low pressure fuel fluid engine or dual-fuel engine (1), comprising at least one fluid admission valve (29) for providing fuel fluid,

characterized in that a check valve (30) is arranged in a fluid path between the at least one fluid admission valve (29) and a cylinder volume (31), preferably within a feed nozzle (14').

15. Method of operating an internal combustion engine according to one of the preceding claims 1-11 comprising the steps of

- opening the feed nozzle to inject fuel into the mixing chamber after the scavenging ports are open and

- stopping injection before the scavenging ports are closed.

Drawing