Internal combustion engine and operating method

Abstract

To provide an internal combustion engine which may prevent knocking while providing optimal fuel efficiency.SOLUTION: An internal combustion engine 10, according to the present invention, comprises a pressure measuring unit 16 with at least one sensor 17 for providing a signal representative of a pressure within at least one cylinder 10. The internal combustion engine 10 comprises a control unit 18 which is configured to: receive the signal of the pressure measuring unit 16; determine a knock index on basis of the signal; compare the knock index with a predetermined knock index value or knock index interval; and adapt the EGR rate, the time of an ignition event, e.g., the time of pilot ignition or the time of pilot fuel injection, and / or the amount of supplied fluid fuel if the determined knock index is below or above the knock index value or the knock index interval.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an internal combustion engine and a method for operating an internal combustion engine.

[0002] The present invention relates to an internal combustion engine, such as a large marine engine, a ship engine, or a stationary engine, preferably one in which the cylinder has an inner diameter of at least 200 mm. The engine is preferably a two-stroke engine or a two-stroke cross-head engine. [Background technology]

[0003] The engine may be a diesel engine, a gas engine, a dual-fuel engine, or a multi-fuel engine. Such engines may be capable of burning gaseous fuels, or liquid fuels and / or gaseous fuels, and may be capable of autoignition or forced ignition.

[0004] The term internal combustion engine refers to a large engine that can operate not only in diesel mode, characterized by the autoignition of fuel, but also in Otto mode, characterized by positive ignition of fuel, or in a combination of both, such as by spark ignition. Furthermore, the term internal combustion engine includes, in particular, dual-fuel engines and large engines in which the autoignition of one fuel is used for the positive ignition of another fuel.

[0005] The engine includes at least one cylinder having a piston inside. The piston is connected to the crankshaft. When the engine is running, the piston reciprocates between top dead center (TDC) and bottom dead center (BDC). The cylinder typically has at least one airflow opening for intake, an air inlet located particularly in the cylinder liner, and at least one airflow opening for exhaust, an exhaust outlet located particularly in the cylinder cover. The air inlet is preferably in fluid communication with a scavenging receiver.

[0006] The internal combustion engine can be a longitudinal scavenging two-stroke engine.

[0007] The engine rotational speed is preferably less than 800 RPM (4-stroke), and more preferably less than 200 RPM (2-stroke), which indicates a low-speed engine.

[0008] The fuel may be light oil or marine light oil, or heavy fuel oil, or emulsion, or slurry, or methanol, or ethanol, or gas such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), etc.

[0009] Further possible fuels that may be added upon request include LBG (Liquified Biogas), biofuels (e.g., algal fuel or seaweed oil), hydrogen, and synthetic fuels from CO2 (e.g., those produced by power-to-gas or power-to-liquid).

[0010] Large vessels, especially those used for cargo transport, are typically powered by internal combustion engines, particularly diesel and / or gas engines, mostly two-stroke cross-head engines. When burning liquid fuels such as heavy fuel oil, marine diesel, diesel, or other liquids, as well as gaseous fuels such as LNG, LPG, or other gaseous fuels, the exhaust from this combustion process must be purified to comply with current regulations such as IMO Tier III.

[0011] In this application, it is preferable that the internal combustion engine be operated in gas mode. A fluid fuel, such as a gaseous fuel or a pressurized gas that forms a liquid vapor within the cylinder, is supplied through a gas inlet valve and used for torque generation. In gas mode, induction ignition may also be performed by injecting small amounts of fluid fuel, sometimes referred to as pilot injection.

[0012] An internal combustion engine typically includes a supercharger that increases the amount of air supplied to the cylinders by using the exhaust gas discharged from the cylinders. The air compressed by the supercharger can be supplied to a scavenging receiver that is in fluid communication with the air flow opening for intake air.

[0013] In addition to fresh air and fluid fuel, inert gases such as exhaust gas may be introduced into the cylinder. The engine may include a high-pressure or low-pressure exhaust gas recirculation path. In the case of low-pressure exhaust gas recirculation, the exhaust gas is mixed with fresh air after passing through the turbine of the supercharger and / or after passing through the compressor of the supercharger, and then introduced into the cylinder as part of the scavenging air.

[0014] Abnormal combustion such as premature ignition, knocking, or misfire occurs especially when the ratio of fresh air to gas, that is, the air-fuel ratio or air-fuel equivalence ratio, also called lambda, is not within a specific range.

[0015] If the gas content is too high, the concentration of the air-fuel mixture becomes too high. The combustion of the mixture will be too fast or too early, for example, by self-ignition, which can lead to premature ignition or knocking of the engine. If the air content is too high, the air-fuel mixture becomes too lean, and undesirable late combustion or even misfire may occur, which can of course also have an adverse effect on the efficient and low-pollution operation of the engine. In particular, the two states of too much gas content and too much air content are designated as abnormal combustion processes. Therefore, in the gas mode, the combustion process in which the air-gas mixture does not self-ignite is what is aimed for. The combustion process shall be carried out within a range where the air-gas mixture is neither too rich nor too lean.

[0016] It is known that inert gases such as exhaust gas can be introduced into the cylinder to reduce or avoid abnormal combustion processes such as knocking. SUMMARY OF THE INVENTION [Problems that the invention aims to solve]

[0017] The object of the present invention is to avoid the drawbacks of the prior art, and in particular to provide an internal combustion engine and a method for operating an internal combustion engine that can prevent knocking while providing optimal fuel efficiency. [Means for solving the problem]

[0018] According to the present invention, the internal combustion engine is a large marine engine or a stationary engine that can operate in at least gas mode.

[0019] To be able to operate in gas mode means either that fuel gas is introduced into the cylinder, or that high-pressure fuel liquid is introduced into the cylinder and vaporizes immediately after introduction. An internal combustion engine includes at least one gas inlet valve for supplying fuel to the cylinders. Each cylinder may have a fuel fluid inlet valve. The fuel fluid may be supplied to the fuel fluid inlet valve, for example, from an LNG tank.

[0020] The internal combustion engine includes at least one cylinder having a bore of at least 200 mm. The cylinder is equipped with a pre-chamber having, for example, a pilot ignition system or a spark ignition system.

[0021] The internal combustion engine further includes an exhaust gas recirculation path. The exhaust gas recirculation path is preferably a low-pressure exhaust gas recirculation path. In particular, the internal combustion engine includes a supercharger, which is configured such that at least a portion of the exhaust gas is recirculated through the supercharger's turbine to the supercharger's compressor, and further so that the recirculated exhaust gas is supplied to the cylinders together with fresh air.

[0022] In particular, the internal combustion engine includes a scavenging receiver, from which fresh air and recirculated exhaust gases can be guided to an opening located at the bottom of the cylinder.

[0023] The internal combustion engine further includes a pressure measuring unit having at least one sensor for providing a signal representing the pressure in at least one cylinder. Preferably, the pressure measuring unit has at least one sensor for each cylinder. The sensor may be a pressure sensor.

[0024] The internal combustion engine further includes a control unit configured to receive signals from a pressure measuring unit, and in particular a control unit configured to receive all signals for all cylinders. The control unit is further configured to determine a knock index based on the signals, and in particular a knock index for each cylinder.

[0025] The control unit is further configured to compare the knock index with a predetermined knock index value or knock index interval. The knock index value and / or knock index interval can be predetermined, for example, based on the dimensions of the cylinder, based on the natural frequency of the cylinder, and / or based on empirical values ​​specified in a shop test.

[0026] The control unit is further configured to adapt the exhaust gas recirculation rate (EGR), ignition event timing such as pilot ignition timing or pilot fuel injection timing, and / or the amount of fluid fuel supplied, if the determined knock index is below or above the knock index value or knock index interval.

[0027] The control unit may be configured to determine the knock index by determining the MAPO value and / or IMPO value.

[0028] Typically, the raw pressure signal is converted into a band-pass filtered pressure signal, for example, within a band-pass range of 0.2 to 20 kHz. It is preferable to apply a band-pass filtering window of 0.5 kHz to 10 kHz.

[0029] The band-pass filter may be part of the pressure measurement unit or part of the control unit.

[0030] The absolute value may be determined from the band-pass filtered signal.

[0031] The MAPO (maximum amplitude of pressure oscillations) value is the maximum amplitude of pressure oscillations and is determined by the following equation.

number

[0032] The IMPO (integral of the modules of pressure oscillation) value is the integral of the modules of pressure oscillation and is determined by the following equation.

number

number

[0033] The knock index is also known as the integral of the modulus of pressure oscillations (IMPG), the rate of heat release (ROHR), or the net cumulative heat release (CHR). NET It can also be determined by calculating the net cumulative heat release.

[0034] It is known that exhaust gas recirculation reduces knocking. However, too much exhaust gas can reduce combustion efficiency. Therefore, the minimum amount of exhaust gas should be used to prevent knocking.

[0035] The internal combustion engine preferably includes a plurality of n cylinders, where n is greater than 1, and the pressure measuring unit provides a signal representing the pressure in each cylinder.

[0036] The control unit may be configured to perform adjustment procedures, and the control unit is configured to set a first EGR rate. The EGR rate is typically a common parameter for all cylinders supplied by one common supercharger.

[0037] The first setting may be obtained, for example, from a map predefined in factory testing.

[0038] The EGR rate may be reduced by the amount of the first EGR rate step, and a knock index may be determined for each cylinder.

[0039] If the determined knock index is below or above the knock index value or knock index interval for at least one cylinder, the control unit is configured to adjust the ignition timing, such as the pilot fuel injection timing or spark ignition timing, for each corresponding cylinder.

[0040] If more than n-2 or more than n / 2 cylinders are regulated, the EGR rate must be kept constant.

[0041] Otherwise, the EGR rate may be reduced again, and individual cylinders may be adjusted by re-determining the knock index for each cylinder and adjusting the ignition timing.

[0042] This procedure can be repeated until the EGR rate must be kept constant.

[0043] Alternatively, the EGR rate may be set according to a predetermined set point. The control unit may be configured to determine the knock index for each cylinder. If the knock index exceeds a knock index value or knock index interval for at least one cylinder, the control unit may be configured to adjust the ignition timing for each corresponding cylinder. The control unit is configured to increase the EGR rate if at least a predetermined number of cylinders out of all n cylinders, for example, at least n-2 or at least n / 2 cylinders, provide a signal that exceeds the knock index value or knock index interval.

[0044] Subsequently, a knock index may be calculated for each cylinder. The control unit may resume monitoring the knock index after each adjustment round.

[0045] The knock index may be monitored continuously to ensure that the ignition timing and EGR rate are corrected according to the procedure described above.

[0046] In this way, if knocking occurs in only a small number of units, for example, in n-2 or fewer or n / 2 or fewer cylinders, according to the defined criteria, it is possible to avoid changing the overall EGR rate.

[0047] The ignition timing can be adjusted by delaying the ignition timing, for example, by delaying the ignition by 1 to 2 degrees from the crank angle of the preceding ignition event.

[0048] The control unit may be configured to continuously perform the adjustment procedure described above after a certain time interval, particularly after 1 to 10 cycles, or more specifically, every 5 to 10 cycles of engine operation.

[0049] In this application, the term "cycle" refers to the duration of one rotation of the crankshaft during which cylinder scavenging, compression, heat release / combustion, and expansion / operating stroke occur.

[0050] In a preferred embodiment of the present invention, the internal combustion engine includes a control unit configured to distinguish between vibrational pressure waves based on ignition events and vibrational pressure waves based on knocking events, particularly before determining the knock index.

[0051] The control unit controls the first crank angle range (CR) near the crank angle of the ignition event. I ) vibration and the second crank angle range (CR) near the crank angle of the maximum value during the pressure course of one cycle II The system may be configured to determine and compare the vibrations in ) and ).

[0052] Pressure fluctuations within the combustion chamber caused by the ignition process are usually already present for a short time after the ignition event, for example, caused by pilot ignition or pilot fuel injection.

[0053] This vibration can be detected within a first crank angle range near the ignition event. The first crank angle range may cover a crank angle interval that starts at a first crank angle distance from the crank angle of the ignition event and ends at a second crank angle distance from the crank angle of the ignition event, where the second crank angle distance is greater than the first crank angle distance.

[0054] The first crank angle distance may be 2°, and the second crank angle distance may be 4°.

[0055] The first crank angle range CR I may be defined by the following equation. CR I ={θ ignition + θ1; θ ignition + θ2} Here, θ ignition is, for example, the crank angle of an ignition event caused by the injection of pilot fuel, θ1 is the first crank angle distance, and θ2 is a second crank angle distance greater than the first angle distance. The first crank angle distance θ1 and the second crank angle distance θ2 are variables that need to be set within the control system. θ ignition + θ1 may typically be approximately 1° - 2° CA later than the crank angle θ PIT at the time of pilot fuel injection. θ ignition + θ2 may typically be approximately 4° - 6° CA later than the crank angle θ PIT at the time of pilot fuel injection.

[0056] Vibrations caused by knock events typically exist within the second crank angle range, typically around the crank angle of the maximum cylinder pressure, in the later stage of the combustion process. The second crank angle range may cover a crank angle interval starting from, for example, the crank angle obtained by subtracting 5° from the crank angle of the maximum cylinder pressure and continuing up to the crank angle obtained by adding 10° to the crank angle of the maximum cylinder pressure.

[0057] The second crank angle range CR II may be defined by the following equation. CR II ={θ pmax + θ3; θ pmax + θ4} Here, θ pmaxθ is the crank angle at maximum cylinder pressure, θ3 is the third crank angle distance, and θ4 is the fourth crank angle distance. The third crank angle distance θ3 and the fourth crank angle distance θ4 are variables that need to be set within the control system. θ3 is typically approximately -10°CA to -5°CA. θ4 is typically approximately +5°CA to +10°CA.

[0058] According to possible rules, the second crank angle range CR II Pressure oscillations in the first interval CR I If the coefficient of pressure oscillation in the given region does not exceed x, then that pressure oscillation is not counted as knocking.

[0059] The coefficient x is a variable that needs to be set within the control system. Typically, x is approximately 1.5 to 2.5.

[0060] Pressure oscillations can be given by the maximum value of the pressure oscillation amplitude of the band-pass filtered pressure signal within each corresponding interval.

[0061] Alternatively, pressure oscillations can be quantified by MAPO or IMPO values ​​within their respective intervals, or by any other suitable method.

[0062] Before or after generating a filtered pressure signal, the control unit may check whether the pressure signal is evaluated as a knocking event. The control unit determines the knock index by checking the second crank angle range CR of the pressure course. II You can consider only that.

[0063] In the case of large engines, the sampling rate can be selected to prevent excessive computational load, as the vibration frequency is lower compared to smaller engines. Typically, sampling rates of 1000Hz to 5000Hz, and especially 1000 to 2500Hz, can be selected.

[0064] The knock frequencies that typically contribute most to the amplitude of pressure oscillations are the first tangential mode, the second tangential mode, and the first radial mode. Typical knock frequencies f for these modes in a two-stroke large-bore engine are... knock The frequency range is 500Hz to 2500Hz. Therefore, since the sampling rate must be at least twice the vibration frequency, a sampling rate of 5000Hz can measure the first tangential mode, the second tangential mode, and the first radial mode.

[0065] Since the first tangential mode contributes most to the pressure oscillations in the combustion chamber due to knocking, a sampling rate of 1250 Hz is sufficient to detect knocking, for example, for a large diameter of 0.92 m, and a sampling rate of 2500 Hz is sufficient for a medium diameter of 0.5 m.

[0066] The control unit may be configured to set the EGR rate by setting the ERG valve and / or the back pressure valve and / or the EGR blower.

[0067] The problem is also solved by the method of operating the internal combustion engine as described above, which includes the following steps: providing a signal representing the pressure in at least one cylinder; determining the knock index based on that signal, in particular by determining the MAPO value or IMPO value.

[0068] The knock index is compared to a predetermined knock index value or knock index interval. If the determined knock index is below or above the knock index value or knock index interval, the EGR rate, the timing of ignition events such as pilot ignition timing or pilot fuel injection timing, and / or the amount of fluid fuel supplied are modified.

[0069] Knocking process reduction may be performed using closed-loop control procedures.

[0070] The EGR rate may be decreased or increased starting from a first EGR rate, after determining the knocking index for each cylinder. If the determined knocking index is below or above the knocking index value or knocking index interval for at least one cylinder, the ignition timing is adjusted for the corresponding cylinder.

[0071] If more than n-2 or more than n / 2 cylinders are adjusted, the EGR rate should not be changed.

[0072] Otherwise, the EGR rate may be changed again, and the knock index may be determined for all cylinders and the ignition timing adjusted.

[0073] As soon as a predetermined number of cylinders, for example n-2 or n / 2 cylinders, have been adjusted, this procedure is stopped.

[0074] Alternatively, the EGR rate may be set according to predetermined setting points. A knock index may be determined for each cylinder. If the knock index exceeds the knock index value or knock index interval for at least one cylinder, the ignition timing may be adjusted for the corresponding cylinder. The control unit may increase the EGR rate if at least a predetermined number of cylinders out of all n cylinders, for example, at least n-2 or at least n / 2 cylinders, provide a signal that exceeds the knock index value or knock index interval.

[0075] Subsequently, a knock index may be calculated for each cylinder. The control unit may resume monitoring the knock index after each adjustment round.

[0076] This method preferably includes the step of distinguishing vibrational pressure waves based on knocking events from vibrational pressure waves based on ignition events such as pilot ignition or pilot fuel injection.

[0077] The internal combustion engine may include a supercharger having a turbine and a compressor.

[0078] The present invention will be further described below with reference to the drawings and embodiments. The same reference numerals indicate functionally corresponding feature points. [Brief explanation of the drawing]

[0079] [Figure 1] This shows a schematic diagram of an internal combustion engine. [Figure 2] This outlines the determination of the knock index. [Figure 3] This diagram schematically shows the oscillation of the pressure curve based on pilot combustion. [Figure 4] This diagram schematically shows the oscillation of the pressure curve due to the knocking phenomenon. [Modes for carrying out the invention]

[0080] Figure 1 shows an internal combustion engine 10 that constitutes a large marine engine, including a cylinder 11 having an inner diameter 12 of at least 200 mm.

[0081] The cylinder has a pilot injection system 13, and the cylinder has a gas introduction valve 14.

[0082] The internal combustion engine 10 includes a low-pressure exhaust gas recirculation path 16, which is configured such that the exhaust gas passes through the turbine of the supercharger 22 and is further guided, together with fresh air, through the compressor 23 of the supercharger 22 to the scavenging receiver 24.

[0083] The percentage of exhaust gas that is recirculated (EGR rate) can be set by setting the EGR valve 19 and / or the back pressure valve 20.

[0084] The internal combustion engine 10 includes a pressure measuring unit 16 having a sensor 17, such as a pressure sensor, for providing a signal representing the pressure inside the cylinder 10.

[0085] The internal combustion engine 10 further includes a control unit 18 configured to receive a signal from a pressure measuring unit 16, the control unit 18 further configured to determine a knock index based on the pressure signal. The control unit 18 is configured to compare the knock index to a predetermined knock index value and / or to a knock index interval. The control unit 18 is configured to modify the EGR rate, the premature ignition timing, and / or the amount of fluid fuel supplied.

[0086] Figure 2 schematically shows the determination of the knock index. The pressure signal p(θ), where θ is the crank angle, is passed through a band-pass filter 25 to obtain the oscillation component p related to the downward portion of the pressure signal. f (θ) is received. Next, the absolute value is determined, and from this absolute value, the MAPO value and / or IMPO value can be calculated.

[0087] Figures 3 and 4 schematically illustrate the oscillation of the pressure curve due to different reasons.

[0088] Each figure shows the corresponding pressure progression p(θ) (maximum value p) over a crank angle θ that constitutes one cycle. max (Having an upward and downward section), and a band-pass filtered cylinder pressure p f (θ) and this is shown.

[0089] Band-pass filtered cylinder pressure p f (θ) is oscillating in both cases. However, the crank angle control range CR I and CR II Due to these differences, the degree of vibration varies among the band-pass filtered cylinder pressures.

[0090] First control range CRI In this example, the crank angle θ of pilot ignition, or pilot injection. PIT The crank angle θ is considered to be a nearby angle. ignition This covers the crank angle section starting from [this point].

[0091] First control range CR I It may have a range of 8°CA.

[0092] Second control range CR II This is the maximum pressure value p during the pressure progression within the cylinder. max The crank angle θ pmax This targets the crank angle section in the surrounding area. Second control range CR II It may have a range of 12°CA, and θ pmax It may also start from -4°CA, θ pmax You can also terminate at +8°CA.

[0093] Typically, as shown in Figure 3, - First control range CR I The maximum amplitude of the band-pass filtered cylinder pressure within is greater than 0.5 bar, and - Second control range CR II The maximum amplitude of the band-pass filtered cylinder pressure within the first control range CR I If the value obtained by multiplying the maximum amplitude of the band-pass filtered cylinder pressure within by a coefficient x such that x = 2.5 is smaller than the value obtained by this multiplication, Vibration is not considered knocking.

[0094] Typically, as shown in Figure 4, - Second control range CR II The maximum amplitude of the band-pass filtered cylinder pressure within is greater than 2.5 bar, and - First control range CR I The maximum amplitude of the band-pass filtered cylinder pressure within the second control range CR IIIf the maximum amplitude of the band-pass filtered cylinder pressure within is smaller than the value obtained by dividing it by a coefficient x such that x = 2.5, The vibration was caused by a knocking event.

[0095] Therefore, each control range CR I and CR II By determining and comparing the vibrations in the system, knocking events can be distinguished from vibration pressure waves based on ignition events.

Claims

1. An internal combustion engine (10), in particular a marine or stationary engine, capable of operating at least in gas mode, comprising: The internal combustion engine (10) has at least one cylinder (11) with an inner diameter (12) of at least 200 mm; The cylinder (11) has a pre-chamber, The internal combustion engine (10) has at least one gas inlet valve (14) for supplying fluid fuel to the cylinder (11); The internal combustion engine (10) has an exhaust gas recirculation path (16), the internal combustion engine (10) having a pressure measurement unit (16) with at least one sensor (17) for providing a signal representative of the pressure in the at least one cylinder (10); The internal combustion engine (10) has a control unit (18), the control unit comprising: receiving the signal from the pressure measurement unit (16); determining a knock index based on the signal; comparing the knock index to a predetermined knock index value or knock index interval; and If the determined knock index is below or above the knock index value or the knock index interval, -EGR rate, - ignition event timing, and - the amount of fluid fuel supplied Modify at least one of the The internal combustion engine (10) is configured as follows.

2. The internal combustion engine (10) of claim 1, wherein the control unit (18) is configured to determine the knock index by determining at least one of a MAPO value and an IMPO value.

3. the internal combustion engine (10) has a plurality of n cylinders (11), the pressure measurement unit (16) providing a signal representative of the pressure in each cylinder (11); The control unit (18) is configured to perform an adjustment procedure, the control unit (18) comprising: Setting a first EGR rate; (i) decreasing the EGR rate by a first EGR rate step; (ii) determining said knock index for each cylinder; (iii) adjusting the ignition timing for each cylinder when the determined knock index is below or above the knock index value or the knock index interval for at least one cylinder; (iv) if more than a predetermined number of cylinders are adjusted, maintain the reduced EGR rate; otherwise, start again from step (i).

2. The internal combustion engine (10) of claim 1, wherein the internal combustion engine (10) is configured as follows:

4. the internal combustion engine (10) has a plurality of n cylinders (11), the pressure measurement unit (16) providing a signal representative of the pressure in each cylinder (11); The control unit (18) is configured to perform an adjustment procedure, the control unit (18) comprising: (i) determining said knock index for each cylinder; (ii) adjusting the ignition timing for each cylinder when the determined knock index is below or above the knock index value or the knock index interval for at least one cylinder; (iii) increasing the EGR rate when at least a predetermined number of cylinders are adjusted; 2. The internal combustion engine (10) of claim 1, wherein the internal combustion engine (10) is configured as follows:

5. 4. The internal combustion engine (10) of claim 3, wherein the control unit (16) is configured to perform the adjustment procedure continuously after specific time intervals.

6. An internal combustion engine (10) as described in claim 4, wherein the control unit (16) is configured to perform the adjustment procedure continuously after a specific time interval.

7. The control unit (16) determines the crank angle (θ ｉｇｎｉｔｉｏｎ ) in the first crank angle range (CR Ｉ ) and the maximum value in the pressure course of one cycle (p ｍａｘ ) crank angle (θ ｐｍａｘ ) in the second crank angle range (CR ＩＩ 2. The internal combustion engine (10) of claim 1, configured to distinguish between oscillating pressure waves due to an ignition event and oscillating pressure waves due to a knocking event by checking and comparing oscillations in the internal combustion engine (10) with oscillations in the internal combustion engine (10).

8. The internal combustion engine (10) of any preceding claim, wherein the control unit (16) is configured to determine a knock index based on the signal at a sampling rate of 1000 to 2500 Hz.

9. 2. The internal combustion engine (10) of claim 1, wherein the EGR rate is set by at least one of setting an EGR valve (19), setting a backpressure valve (20), and setting an EGR blower.

10. An internal combustion engine (10) as described in claim 1, wherein the pre-chamber has a pilot injection system (13).

11. An internal combustion engine (10) as described in claim 1 having a low-pressure exhaust gas recirculation path (16).

12. An internal combustion engine (10) as described in claim 1, wherein the ignition event timing is a pilot ignition timing or a pilot fuel injection timing.

13. An internal combustion engine (10) as described in claim 4, wherein the control unit (18) is configured to start again from step (i) after step (iii).

14. 10. A method for operating an internal combustion engine as claimed in claim 1, comprising: - providing a signal representative of the pressure in said at least one cylinder (10); - determining a knock index based on said signal; comparing said knock index with a predetermined knock index value or knock index interval; modifying at least one of (a) EGR rate, (b) ignition event timing, and (c) amount of fluid fuel delivered when the determined knock index is below or above the knock index value or knock index interval; 13. A method for operating an internal combustion engine according to any one of claims 1 to 12, comprising:

15. The method of claim 14, wherein the knock index is determined based on the signal at a sampling rate of 1000 to 2500 Hz.

16. Setting a first EGR rate; (a) decreasing the EGR rate by a first EGR rate step; (b) determining the knock index for each cylinder; (c) adjusting the pilot ignition timing for each cylinder when the determined knock index is below or above the knock index value or knock index interval for at least one cylinder; (d) maintaining the reduced EGR rate if more than n / 2 cylinders have been adjusted, otherwise starting again from step (a); 15. The method of claim 14, comprising:

17. (a) determining the knock index for each cylinder; (b) adjusting the pilot ignition timing for each cylinder when the determined knock index is below or above the knock index value or knock index interval for at least one cylinder; (c) increasing the EGR rate when at least a predetermined number of cylinders are adjusted; 15. The method of claim 14, comprising:

18. The method of claim 17, comprising starting again from step (a) after step (c).

19. The crank angle (θ ｉｇｎｉｔｉｏｎ ) in the first crank angle range (CR Ｉ ) and the maximum value in the pressure course of one cycle (p ｍａｘ ) crank angle (θ ｐｍａｘ ) in the second crank angle range (CR ＩＩ 15. The method of claim 14, including the step of distinguishing oscillating pressure waves due to knocking events from oscillating pressure waves due to ignition events by identifying and comparing oscillations in the engine speed.

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