Method for operating a large turbocharged two-stroke uniflow crosshead compression-ignited internal combustion engine and such an engine

Abstract

This invention discloses a method for operating a large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine. The method involves observing the pre-injection pressure (PCP) in the corresponding cylinder within the crankshaft angle range between the pre-injection and main fuel injection, comparing the PCP with the commutation charge (CP) within the same range during the compression stroke, and increasing or decreasing the size of the pre-injection in the next revolution based on the calculated difference between the PCP and CP. The invention also relates to a large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine. By performing at least one pre-injection and adjusting the size of the pre-injection in subsequent revolutions based on the comparison of PCP and CP, robust pre-combustion of the desired size is achieved, allowing the main combustion to shift to a later stage during the expansion stroke, resulting in a significant reduction in stage 5 excitation without the risk of diesel knock.

Description

Technical Field

[0001] This invention relates to a method for operating a large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine, the internal combustion engine comprising: a plurality of cylinders having pistons therein, the pistons reciprocating between a BDC and a TDC during engine operation, the pistons being operably connected to a crankshaft via a plurality of piston rods, a plurality of crossheads and a plurality of connecting rods, the crankshaft rotating at a certain speed during engine operation; a fuel injection system comprising one or more fuel valves associated with each cylinder for injecting fuel into the cylinders for combustion, wherein the timing of fuel injection is controlled relative to the crankshaft angle of the cylinder by controlling the opening and closing of the fuel valves involved, wherein the engine operates with delayed main fuel injection at least within a certain speed range, wherein at least one pre-fuel injection is performed before the main fuel injection.

[0002] The present invention also relates to such an engine. Background Technology

[0003] Large turbocharged two-stroke compression ignition crosshead internal combustion engines are typically used as prime movers in large ocean-going vessels (such as container ships) or power plants.

[0004] In particular, torsional vibrations can be challenging to control when operating on ocean-going vessels. This torsional vibration occurs because the propeller shaft, which connects the engine to the propeller, is relatively flexible torsionally, and this relatively flexible system is exposed to varying tangential pressures (torque) from the engine. This is due to the fact that the torque from a piston engine varies significantly over one crankshaft revolution, which severely impacts the requirements for the propeller shaft system in such vessels. The large inertia of the propeller shaft connecting both the engine and the propeller creates a mechanical system with natural frequencies within the same frequency range as the excitation from the engine. The shaft stresses in these resonances are higher than those caused by the average torque under 100% engine load. This varying tangential pressure from the engine is caused by the cyclic process in each cylinder and repeats for each crankshaft revolution. This cyclic process in each cylinder produces large variations in crankshaft torque. The torque is negative during compression and positive during expansion. This... Figure 5 The diagram illustrates the cylinder pressure P and torque Q from one cylinder as a continuous line, and the combined torque from six cylinders as a discontinuous line. By distributing the torque across multiple cylinders within one revolution, the variation in crankshaft torque is reduced, but still significant. Figure 5In the example, there are actually six cycles for each revolution, where the crankshaft torque is negative. Torsional vibration problems in the load-driven driveshaft engine system are significant in 4, 5, 6, and 7-cylinder engines. These vibrations are critical when considering the flexibility of the driveshaft between the engine and the load (e.g., the propeller), where the inertia of the engine and propeller combined with the flexible shaft connecting them leads to resonance. When operation approaches resonance, excitation from torque variations becomes critical.

[0005] Spring and / or viscous torsional dampers are employed to reduce torsional vibration problems. However, torsional dampers come with significant cost increases and efficiency losses. Furthermore, even with torsional dampers, these engines often have a prohibited speed range—a range where steady-state operation is not permitted beyond a typical 60 seconds—due to reduced shaft life caused by high stresses in the shaft. Because steady-state operation is not permitted, higher stress limits are imposed within the prohibited speed range. However, due to the tendency for increasing compression and combustion pressures, further action is often required to achieve acceptable stress levels. Despite the prohibited speed range, high-strength shaft materials and heavy-duty flywheels are often required in 5- and 6-cylinder engines to achieve acceptable stress levels.

[0006] Simulations and measurements have shown that ignition / combustion delay affects cylinder pressure in a way that significantly reduces certain important levels of torque variation. Therefore, delaying fuel injection can reduce torsional excitation. However, due to diesel knocking, delaying fuel injection beyond 10° crankshaft angle after top dead center (TDC) is generally not feasible.

[0007] In DK201770489A1, the aforementioned problems associated with diesel knock are addressed by performing at least one pre-injection of fuel after the TDC (Total Combustion Control Date), thereby maintaining a higher temperature in the combustion chamber and increasing the maximum acceptable delay of the main injection without the risk of diesel knock. In this prior art document, the pre-injection is performed between 6-10°C after the TDC.

[0008] Another method of operating an internal combustion engine of the type described in the introduction is known from US2006 / 0241848 A1.

[0009] Dampers are quite expensive, often accounting for about 10% of the engine price, and especially on 5-cylinder engines. Commonly used spring-type dampers also consume significant power above the prohibited speed range. To significantly reduce stage 5 and 6 excitation to avoid the requirements of dampers, combustion must be delayed by well more than 10° of crankshaft angle after TDC. When testing at a 20° crankshaft angle, it became clear to the applicant of this invention that expansion had developed so far that the temperature during combustion was too low to prevent diesel knock. Diesel knock is a very destructive phenomenon and is unacceptable. It overloads components in the combustion chamber and can even cause hood lift.

[0010] The prohibited speed range for 5- and 6-cylinder engines typically begins at >40% of the specified maximum continuous rating (SMCR). The corresponding engine load at 40% SMCR is only 6% on the nominal propeller curve, and may be even lower during sea trials due to a slight operating margin. Pre-combustion must be kept low to achieve a positive impact on stages 5 and 6 via main combustion. Therefore, controlling the size of the fuel injection used for pre-combustion is critical. This is particularly difficult when the size is close to the minimum amount the fuel injection equipment can inject. Summary of the Invention

[0011] In view of the above, the object of the present invention is to provide a method for operating a large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine, which can operate with a very late timing main fuel injection delay at least within a given RPM bandwidth, in order to overcome or at least reduce the aforementioned problems.

[0012] Another object of the present invention is to provide such a large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine. Further embodiments are apparent in the dependent claims, the description, and the drawings.

[0013] According to a first aspect, a method is provided for operating a large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine, the internal combustion engine comprising: a plurality of cylinders having pistons therein, the pistons reciprocating between a BDC and a TDC during engine operation, the pistons being operably connected to a crankshaft via piston rods, crossheads, and connecting rods, the crankshaft rotating at a certain speed during engine operation; and a fuel injection system including one or more fuel valves associated with each cylinder for injecting fuel into the cylinder for combustion, wherein the opening of the fuel valves involved is controlled... The timing of fuel injection is controlled relative to the crankshaft angle of the cylinder involved, wherein the engine operates with delayed main fuel injection at least within a specific speed range, wherein at least one fuel pre-injection is performed before the main fuel injection, and characterized in that the integral pre-combustion pressure (PCP) in the corresponding cylinder is observed within the crankshaft angle range between the fuel pre-injection and the main fuel injection, and the PCP is compared with the integral compression pressure (CP) within the same range on the compression stroke, wherein the magnitude of the fuel pre-injection is increased or decreased in the next revolution based on the calculated difference between the PCP and the CP.

[0014] The expression "integral pre-combustion pressure (PCP)" refers to the actual pre-combustion pressure (PCP) obtained by integrating the measured cylinder pressure over the crankshaft angle range. Similarly, the expression "integral compression pressure (CP)" refers to the actual compression pressure (CP) obtained by integrating the measured cylinder pressure over the crankshaft angle range during the compression stroke.

[0015] Pressure and temperature within the combustion chamber affect the occurrence of knock. During delayed combustion, both temperature and pressure decrease due to the expansion of air in the combustion chamber. By performing at least one fuel pre-injection and adjusting the magnitude of the fuel pre-injection in subsequent cycles based on a comparison of PCP and CP, robust pre-combustion of the desired magnitude is achieved, allowing the main combustion to shift to a later stage in the expansion stroke, resulting in a significant reduction in stage 5 excitation without the risk of diesel knock. This means that the damper can be significantly reduced in size / capacity and may even be omitted for some applications.

[0016] In this case, TDC is a 0° crankshaft angle. PCP is the integral of the cylinder pressure within a angular window from a to b after TDC, where both a and b > 0, while CP is the integral of the cylinder pressure within the same angular window on the other side of TDC, from –b to –a. The difference is calculated as PCP minus CP. In practice, both PCP and CP are divided by the window width, such that the calculated difference becomes the average pressure difference between the expansion and compression sides. Therefore, when the difference between the calculated PCP and CP is greater than the internally selected setpoint, the fuel pre-injection magnitude will preferably be reduced by the engine control system (ECS), and vice versa.

[0017] Cylinder pressure is typically measured at a fixed angular distance and therefore in the two angular windows mentioned above, specifically during the compression and expansion strokes. However, sometimes it may be necessary to use measurements only in a portion of the window, and estimations / calculations in the remainder. An example could be that if combustion occurs before TDC and a pure compression cylinder pressure profile is needed to determine the integral compression pressure (CP), a model of the compression profile could be created and used to calculate the difference between CPC and CP. Such a model might utilize a portion of the cylinder pressure measurement along with thermodynamic assumptions about what typically occurs during the compression stroke.

[0018] Fuel pre-injection can be performed as late as 10° crankshaft angle after TDC; however, for more robust measurements, it is advantageous to move the fuel pre-injection closer to TDC. Therefore, preferably, fuel pre-injection is performed at least 4° crankshaft angle after TDC, more preferably at TDC + / - 2°, and most preferably at TDC. In this way, PCP and CP are calculated over a longer duration, making the comparison better and more accurate.

[0019] The amount or size of the injected fuel is typically proportional to the injection duration. For example, the duration of the fuel pre-injection is initially set to 2 ms. According to the invention, it is preferable to increase or decrease the size of the fuel pre-injection in the next cycle within a range of 0.1 ms to 0.5 ms, preferably less than 0.2 ms, based on the calculated difference between PCP and CP.

[0020] According to the present invention, the main fuel injection is preferably performed more than 12° after the TDC, more preferably more than 15° after the TDC, and most preferably more than 20° after the TDC.

[0021] However, as mentioned above, in the case of the present invention utilizing pre-combustion and late main injection, the minimum fuel index corresponds to a ~40% SMCR speed. Therefore, if the fuel index is below this threshold, a single injection will be used with a significant increase in gas excitation. Due to the lighter sea trial runs, the method according to the invention will only be applicable to engines with a prohibited speed range above about 40% to 45% SMCR speed, and therefore only to about 50% of 6-cylinder engines. According to the invention, the solution to this problem is to omit fuel injection for some cylinders if the engine operates within the prohibited speed range and if the fuel index is below the mentioned threshold. This method, with omitted injection and significantly reduced Pc / Ps, can also be applied to engines with a prohibited speed range at low engine speeds (e.g., 7- and 8-cylinder engines) to achieve cost reduction in the propulsion system. It can also be applied to vessels with controlled pitch propeller (CPP) projects, where torsional vibration dampers (TVDs) typically need to meet a 0-pitch criterion. If this is also combined with a significantly reduced Pc / Ps combination in non-combustible cylinders—the sum of the main critical stages in the prohibited speed range—gas excitation can be further reduced.

[0022] According to the present invention, the amount of fuel injected during the at least one pre-injection is significantly lower than the amount of fuel injected during the main fuel injection under full engine load.

[0023] According to the invention, fuel pre-injection includes an amount of fuel sufficient to ensure that the temperature inside the cylinder involved during delayed main fuel injection is substantially equal to the temperature inside the cylinder involved at TDC.

[0024] According to the present invention, the fuel used for main fuel injection may be gaseous fuel, and the fuel used for fuel pre-injection may be ignition liquid, wherein the ignition liquid may also be injected simultaneously with the main fuel injection.

[0025] According to a second aspect, a large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine is provided, comprising: a plurality of cylinders having pistons therein, the pistons reciprocating between BDC and TDC during engine operation, the pistons being operably connected to a crankshaft via piston rods, crossheads, and connecting rods, the crankshaft rotating at a certain speed during engine operation; a fuel injection system including one or more fuel valves associated with each cylinder for injecting fuel into the cylinders for combustion; and an electronic control unit configured to control fuel injection relative to the cylinders by controlling the opening and closing of the involved fuel valves. The timing of the crankshaft angle of the cylinder involved, wherein the electronic control unit is configured to operate the engine with delayed main fuel injection at least within a specific speed range by performing at least one fuel pre-injection before the main fuel injection, and characterized in that the electronic control unit is configured to observe the integral pre-combustion pressure (PCP) in the corresponding cylinder within the crankshaft angle range between the fuel pre-injection and the main fuel injection, compare the PCP with the integral compression pressure (CP) within the same range on the compression stroke, and increase or decrease the magnitude of the fuel pre-injection in the next revolution based on the calculated difference between the PCP and CP. Attached Figure Description

[0026] In the following detailed sections of this disclosure, the invention will be described in more detail with reference to exemplary embodiments shown in the accompanying drawings, wherein:

[0027] Figure 1 This is an elevation view showing the front end and a side view of a large two-stroke compression ignition turbocharged engine according to an example embodiment;

[0028] Figure 2 It shows Figure 1 An elevation view of the rear end of the engine and another side view;

[0029] Figure 3 It is based on Figure 1 A diagram of an engine and its intake and exhaust systems;

[0030] Figure 4 It shows the installation in a large ship Figures 1 to 3 The engine;

[0031] Figure 5 It shows the result of Figures 1 to 3 A graph showing the changes in torque produced by the engine;

[0032] Figure 6 It shows the result of Figures 1 to 3 A graph showing the effect of changes in the torque produced by the engine;

[0033] Figure 7 It shows an engine for use in the prior art and for use according to Figures 1 to 3 The graphs of combustion chamber temperature and pressure of the engine, and

[0034] Figure 8 This is a graph showing the combustion chamber pressures for two different fuel pre-injection sizes used in the engine according to the invention. Detailed Implementation

[0035] In the following detailed description, the present invention will be described with respect to a large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine, but it should be understood that the internal combustion engine may be of another type.

[0036] Figures 1 to 3 A large, low-speed turbocharged two-stroke diesel engine with a crankshaft 22, connecting rods, crosshead 23, and piston rod is shown. Figure 3 A diagram of a large, low-speed turbocharged two-stroke diesel engine and its intake and exhaust systems is shown. In this example embodiment, the engine has six cylinders 1 arranged in a row. Large turbocharged two-stroke diesel engines typically have five to sixteen cylinders arranged in a row, which are carried by an engine frame 24. The engine can be used, for example, as a main engine in ocean-going vessels or as a stationary engine for operating generators in power plants. The total output of the engine can be, for example, in the range of 5000 kW to 110000 kW.

[0037] The engine is a two-stroke, single-flow diesel (compression ignition) engine, having purge ports 19 in the form of rings with multiple piston-controlled ports in the lower region of these cylinders 1 and exhaust valves 4 at the top of these cylinders 1. Therefore, the flow in the combustion chamber is always from bottom to top, and thus the engine is so-called single-flow. Purge air is delivered from purge air receiver 2 to the purge air ports 19 of each individual cylinder 1. The piston 21, reciprocating in the cylinder 1, compresses the purge air in the combustion chamber 14. Fuel is injected into the combustion chamber 14 via two or three fuel valves 30 arranged in the cylinder head 26. The timing of fuel injection is controlled by an electronic control unit 50, which transmits fuel via a signal line (in... Figure 3 (Shown as a broken line) connected to fuel valve 30. Combustion then occurs, producing exhaust gas. When exhaust valve 4 is opened, exhaust gas flows through exhaust pipe 20 associated with the cylinder involved into exhaust receiver 3 and forward through first exhaust pipe 18 to turbine 6 of turbocharger 5. The exhaust gas flows away from turbine through second exhaust pipe 7. Turbine 6 drives compressor 9, supplied via air inlet 10, via shaft 8.

[0038] Compressor 9 delivers pressurized boosted air to boosted air duct 11 leading to boosted air receiver 2. Purge air in duct 11 passes through intercooler 12 for cooling the boosted air. The cooled boosted air is then delivered to boosted air receiver 2 via auxiliary blower 16 driven by electric motor 17, which pressurizes the boosted air flow under low or partial load conditions. Under higher load conditions, the turbocharger's compressor 9 delivers sufficient compressed purge air, which is then bypassed by auxiliary blower 16 through check valve 15.

[0039] Cylinder 1 is formed in cylinder liner 13. These cylinder liners 13 are carried by cylinder frame 25, which is supported by engine frame 24.

[0040] In a reciprocating engine, the dead point is the position where the piston is furthest or closest to the crankshaft. The former is called top dead center (TDC), and the latter is called bottom dead center (BDC).

[0041] Figure 4 The installation in the large vessel 40 is shown Figures 1 to 3 The engine 1 is mounted in an engine room relatively close to the stern of the vessel 40. A propeller shaft 42 connects the engine to a propeller 44 mounted at the stern. A torsional damper (not shown) may be installed between the propeller shaft 42 and the engine 1.

[0042] Figure 5 This is a graph showing the change in torque produced by the engine in each cylinder during an engine cycle, caused by the cycle process. The engine cycle is shown on a horizontal axis in degrees of crankshaft angle (Deg CA). Torque is negative during compression and positive during expansion. Figure 5 The diagram shows the cylinder pressure P (bar) on the vertical axis, the torque Q from one cylinder (represented by a continuous line), and the combined torque from all six cylinders (represented by a discontinuous line). The discontinuous lines clearly show that the torque fluctuates significantly, and that for each revolution of the six-cylinder engine, the torque is actually slightly below zero six times.

[0043] Figure 6 This is a graph showing the magnitude of the torsional vibration / expected effect of stress in the drive shaft (in MPa) relative to the engine speed setting (in RPM) for an engine operating without fuel pre-injection.

[0044] The graph shows a peak around 46 RPM. This large peak near 46 RPM results in a restricted speed range of approximately 42 to 49 RPM, between the two vertically extending dashed lines. The magnitude of the stress in the driveshaft caused by torsional vibration, particularly near the peak, can be reduced by enabling a later main fuel injection that precedes a smaller pre-injection.

[0045] The graph, represented by two dashed lines in a chain-like pattern, illustrates two stress limits related to rpm. Stress levels below the lower chain line are acceptable for continuous operation. Stress levels above the higher chain line are unacceptable. Stress levels between the lower and higher chain lines are acceptable for a finite time period.

[0046] Figure 7 The timing of fuel injection events for a single cylinder is shown. Discontinuous lines indicate events where the engine operates without fuel pre-injection, while continuous lines indicate events where the engine operates with fuel pre-injection. Lines denoted by P indicate pressure in combustion chamber 14, while lines denoted by T indicate temperature in the combustion chamber. Crankshaft angles relative to TDC are shown in degrees on the horizontal axis, and pressures in the combustion chamber are shown in bars on the vertical axis.

[0047] When the engine is operated without pre-injection of fuel, fuel injection is delayed until 5° after TDC. Between fuel injection at TDC 0 and 5°, both the temperature and pressure in combustion chamber 14 decrease. At 5° after TDC, fuel is injected, and from this moment on, the temperature in the combustion chamber rises until it reaches its respective maximum value.

[0048] In engines utilizing fuel pre-injection, a small fuel pre-injection is performed by an electronic control unit 50 via operation of fuel valve 30. In the illustrated example, the fuel pre-injection is performed approximately 4° after the TDC (Total Combustion Control). The pre-injection is a fuel injection with a relatively small amount of fuel compared to the subsequent main fuel injection. The amount of fuel injected pre-injected is sufficient to ensure that the temperature within the combustion chamber 14 does not significantly drop below the TDC before the main fuel injection is performed, controlled by the electronic control unit 50. The fuel pre-injection can be performed as a single injection or as a series of multiple small pre-injections, and the electronic control unit 50 is configured accordingly in the embodiments. In one embodiment, the main fuel injection is delayed until 25° after the TDC. Preferably, the main fuel injection is performed at least 12° after the TDC, more preferably at least 15° after the TDC, and most preferably at least 20° after the TDC. Tests and simulations have shown that when the pre-injection is performed shortly after the TDC, domain knock can be timed as late as 20-25° without diesel knocking or other combustion problems.

[0049] Delayed main fuel injection is typically detrimental to fuel efficiency, and therefore is generally only applied within the engine speed range where torsional vibration and resonance problems exist. Thus, in one embodiment, the electronic control unit 50 is configured to apply both pre-injection and late main fuel injection only within a predetermined speed range of the engine associated with torsional operation problems. Of course, dual injection (a late-timing main injection following a pre-injection) can also be used for other purposes, such as NOx emission reduction.

[0050] To improve known methods of operating engines with fuel pre-injection and delayed main fuel injection, the present invention proposes to observe the integral pre-combustion pressure (PCP) in the corresponding cylinder within the crankshaft angle range between fuel pre-injection and main fuel injection, and to compare the PCP with the integral compression pressure (CP) within the same range during the compression stroke. Then, based on the calculated difference between PCP and CP, the magnitude of the fuel pre-injection is increased or decreased in the next revolution.

[0051] This method achieves robust pre-combustion of the desired magnitude, allowing the main combustion to shift to a later stage during the expansion stroke, resulting in a significant reduction in stage 5 excitation without the risk of diesel knock. This means that the damper can be significantly reduced in size / capacity and may even be omitted in some installations.

[0052] To obtain more robust measurements, fuel pre-injection can be moved closer to the TDC, such as... Figure 8 As shown, fuel pre-injection begins at a crankshaft angle of 0°, i.e., when the piston is at TDC. In this way, PCP and CP are calculated over a longer duration, making the comparison better and more accurate. Figure 8 Two pressure curves, PCP1 and PCP2, are shown, where the fuel pre-injection size is approximately 2 ms for the first mentioned curve and approximately 5 ms for the latter.

[0053] Therefore, based on the calculated difference between PCP and CP, according to the present invention, the amount of fuel pre-injection is increased or decreased in the next cycle within a range of 0.1 ms to 0.5 ms, preferably less than 0.2 ms.

[0054] like Figure 8 As shown, the main fuel injection is performed approximately 20° after the TDC. If the dP / dT after the main fuel injection is too steep, the fuel pre-injection must be increased in the next cycle for safety reasons, preferably by at least 0.2 ms.

Claims

1. A method for operating a large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine, the internal combustion engine comprising: A plurality of cylinders (1), wherein each cylinder has a piston (21) that reciprocates between a BDC and a TDC during engine operation, the piston (21) being operably connected to a crankshaft (22) via a piston rod, a crosshead (23) and a connecting rod, the crankshaft (22) rotating at a certain speed during engine operation; a fuel injection system comprising one or more fuel valves (30) associated with each cylinder (1) for injecting fuel into the cylinder for combustion, wherein the fuel valves (30) are controlled relative to each other by opening and closing. The timing of fuel injection is controlled by the crankshaft angle of the cylinder involved, wherein the internal combustion engine operates with delayed main fuel injection at least within a specific speed range, wherein at least one fuel pre-injection is performed before the main fuel injection, characterized in that the integral pre-combustion pressure in the corresponding cylinder (1) is observed within the crankshaft angle range between the fuel pre-injection and the main fuel injection, and the integral pre-combustion pressure is compared with the integral compression pressure within the same range on the compression stroke, wherein the magnitude of the fuel pre-injection is increased or decreased in the next revolution based on the calculated difference between the integral pre-combustion pressure and the integral compression pressure.

2. The method according to claim 1, characterized in that, The fuel pre-injection shall be performed no later than 4° crankshaft angle after TDC.

3. The method according to claim 1, characterized in that, The fuel pre-injection shall be performed no later than TDC+ / -2°.

4. The method according to claim 1, characterized in that, The fuel pre-injection shall be performed no later than at TDC.

5. The method according to claim 1, characterized in that, Based on the calculated difference between the integral pre-combustion pressure and the integral compression pressure, the magnitude of the fuel pre-injection is increased or decreased within a range of 0.1 ms to 0.5 ms in the next cycle.

6. The method according to claim 1, characterized in that, Based on the calculated difference between the integral pre-combustion pressure and the integral compression pressure, the magnitude of the fuel pre-injection is increased or decreased within a range of 0.1 ms to less than 0.2 ms in the next cycle.

7. The method according to claim 1, characterized in that, The main fuel injection is performed 12° after TDC.

8. The method according to claim 1, characterized in that, The main fuel injection is performed 15° later than TDC.

9. The method according to claim 1, characterized in that, The main fuel injection is performed 20° later than TDC.

10. The method according to claim 1, characterized in that, The amount of fuel injected in the at least one pre-injection is lower than the amount of fuel injected in the main fuel injection at full engine load.

11. The method according to claim 1, characterized in that, The amount of fuel included in the pre-injection is sufficient to ensure that the temperature inside the cylinder involved during the delayed main fuel injection is substantially equal to the temperature inside the cylinder involved at TDC.

12. The method according to claim 1, characterized in that, The fuel used for the main fuel injection can be a gaseous fuel, and the fuel used for the fuel pre-injection can be an ignition liquid, wherein the ignition liquid can also be injected simultaneously with the main fuel injection.

13. A large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine, the internal combustion engine comprising: A plurality of cylinders (1), wherein each cylinder has a piston (21) that reciprocates between a BDC and a TDC during engine operation, the piston (21) being operably connected to a crankshaft (22) via a piston rod, a crosshead (23) and a connecting rod, the crankshaft (22) rotating at a certain speed during engine operation; a fuel injection system comprising one or more fuel valves (30) associated with each cylinder (1) for injecting fuel into the cylinder for combustion; and an electronic control unit (50) configured to control the opening and closing of the fuel valves (30) relative to the crankshaft of the cylinder (1) in question. The timing of the angle-controlled fuel injection, wherein the electronic control unit (50) is configured to cause the internal combustion engine to perform the main fuel injection operation with a delay at least within a specific speed range when the electronic control unit (50) performs at least one fuel pre-injection before the main fuel injection, characterized in that the electronic control unit (50) is configured to observe the integral pre-combustion pressure in the corresponding cylinder (1) within the crankshaft angle range between the fuel pre-injection and the main fuel injection, compare the integral pre-combustion pressure with the integral compression pressure within the same range on the compression stroke, and increase or decrease the amount of fuel pre-injection in the next revolution based on the calculated difference between the integral pre-combustion pressure and the integral compression pressure.

14. The large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine according to claim 13, characterized in that, The electronic control unit (50) is configured to perform the fuel pre-injection no later than 4° crankshaft angle after TDC.

15. The large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine according to claim 13, characterized in that, The electronic control unit (50) is configured to perform the fuel pre-injection no later than TDC+ / -2°.

16. The large turbocharged two-stroke single-flow crosshead compression ignition internal combustion engine according to claim 13, characterized in that, The electronic control unit (50) is configured to perform the fuel pre-injection no later than the TDC.

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