JP2020056316A - Control device for natural gas engine - Google Patents

Abstract

To provide a control device for a natural gas engine capable of efficiently supplying boil-off gas to improve knocking resistance.SOLUTION: A control device 100 for a natural gas engine includes: a first tank 21 for storing liquefied natural gas; a second tank 22 for storing boil-off gas; a knocking recognition section 12 for recognizing knocking on the basis of a detection result obtained by a knock sensor 3; an ignition timing calculation section 14 for calculating reference ignition timing on the basis of engine speed and engine load; and a fuel amount calculation section 13 for calculating fuel gas supply amount Q1 and boil-off gas supply amount Q2 on the basis of the engine speed, the engine load and a recognition result obtained by the knocking recognition section 12. When knocking is recognized by the knocking recognition section 12, the fuel amount calculation section 13 increases a supply ratio of the boil-off gas to the fuel gas in accordance with timing advance amount from the reference ignition timing, compared to before the knocking is recognized.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for a natural gas engine.

  2. Description of the Related Art Conventionally, as a technique related to a natural gas engine, for example, a technique described in Patent Document 1 is known. In the technology described in Patent Literature 1, a part of boil-off gas discharged from a storage tank that stores liquefied natural gas is used as fuel for a natural gas engine.

JP-A-2006-128737

  In a natural gas engine that burns an air-fuel mixture by ignition, it is conceivable to improve the knock resistance of the natural gas engine by supplying boil-off gas as a part of the air-fuel mixture. However, considering the amount of boil-off gas generated by natural vaporization, it is desired to efficiently supply the boil-off gas for improving knock resistance.

  An object of the present invention is to provide a control device for a natural gas engine that can efficiently supply boil-off gas for improving knock resistance.

  A control device for a natural gas engine according to one aspect of the present invention is a control device for a natural gas engine that controls ignition timing and fuel supply of an engine using natural gas as a fuel, wherein the first tank stores liquefied natural gas. A second tank for storing boil-off gas generated by natural vaporization of liquefied natural gas in the first tank, and a knocking recognition unit for recognizing engine knocking based on a detection result of a knock sensor provided in the engine. An ignition timing calculating unit for calculating a reference ignition timing based on an advance amount of the ignition timing based on an engine speed and an engine load; and recognition of an engine speed, an engine load, and a knocking recognition unit. Based on the result, the supply amount of the fuel gas generated by vaporizing the liquefied natural gas in the first tank to the engine and the boil-off gas in the second tank A fuel amount calculating unit for calculating an amount of supply to the engine, wherein when the knocking is recognized by the knocking recognition unit, the fuel amount calculating unit boil-offs the fuel gas in accordance with the advance amount from the reference ignition timing. The gas supply ratio is increased as compared to before the knocking was recognized.

  In the control device for a natural gas engine, when knocking is recognized by the knocking recognition unit, the supply amount of boil-off gas to fuel gas is determined by the fuel amount calculation unit in accordance with the advance amount from the reference ignition timing. Is increased compared to before recognition. Therefore, in a situation where there is a high probability that knocking can be suppressed due to the improvement in knocking resistance, the supply ratio of the boil-off gas is increased. As a result, the boil-off gas for improving the knock resistance can be more efficiently supplied than in the case where the boil-off gas is supplied in advance in such an amount that knocking does not occur at all.

  In the control device of the natural gas engine, the ignition timing calculation unit determines whether the knocking is recognized by the knocking recognition unit, and when the supply ratio is increased by the fuel amount calculation unit in accordance with the knocking recognition by the knocking recognition unit. The amount of advance may be increased. In this case, it is possible to advance the ignition timing not only when knocking is not recognized but also by improving knock resistance even if knocking is recognized, using the knocking recognition result by the knocking recognition unit. Becomes

  In the control device of the natural gas engine, when the knocking recognition unit recognizes the knocking in the high load operation state where the load of the engine is equal to or more than the predetermined load threshold, the fuel amount calculation unit compares the supply ratio with that before the knocking was recognized. May be increased, and the supply ratio may be reduced in a low-load operation state in which the engine load is less than the load threshold. In this case, the supply amount of the boil-off gas can be reduced in a low-load operation state in which knocking is less likely to occur than in a high-load operation state.

  According to the present invention, it is possible to efficiently supply a boil-off gas for improving knock resistance.

It is a schematic structure figure of a control device of a natural gas engine of a 1st embodiment. It is a block diagram of the control apparatus of the natural gas engine of FIG. (A) is a figure which shows the example of a setting of a fuel gas supply amount and a boil-off gas supply amount. (B) is a diagram showing the supply ratio of the boil-off gas to the fuel gas in the setting example of (a). It is a figure showing an example of a torque curve of a natural gas engine. 5 is a timing chart illustrating an operation example of the control device of the natural gas engine. 3 is a flowchart illustrating a fuel control process of the ECU of FIG. 2. 3 is a flowchart illustrating an ignition timing control process of the ECU of FIG. 2. It is a schematic structure figure of a control device of a natural gas engine of a 2nd embodiment. FIG. 9 is a block diagram of a control device of the natural gas engine of FIG. 8. 10 is a flowchart illustrating an ignition timing control process of the ECU of FIG. 9.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements have the same reference characters allotted, and overlapping description will be omitted.

[First Embodiment]
FIG. 1 is a schematic configuration diagram of the control device of the natural gas engine of the first embodiment. As shown in FIG. 1, the control apparatus 100 for a natural gas engine of the present embodiment includes an ECU [Electronic Control Unit] 10, a fuel gas supply unit 20, and a natural gas engine 30. Control ignition timing and fuel supply. The control device 100 for a natural gas engine is mounted on a ship V, for example.

  The natural gas engine 30 is an internal combustion engine that burns a mixture containing natural gas. Here, liquefied natural gas (LNG: [Liquefied Natural Gas]) is used as natural gas. The natural gas engine 30 has an engine body 31, a piston 32, an intake passage 33, and an exhaust passage 34.

  The engine body 31 is a main part of the natural gas engine 30 including a cylinder block 31a and a cylinder head 31b. In the engine body 31, a combustion chamber 31c is defined by a cylinder block 31a, a cylinder head 31b, and a piston 32. The intake passage 33 is a pipe for introducing a mixture of intake air and natural gas into the combustion chamber 31c. In the intake passage 33, the fuel gas supplied from the pipes 27c and 27d is mixed with the intake air supplied from an intake pipe (not shown) including a throttle valve, thereby forming an air-fuel mixture.

  In the engine body 31, the air-fuel mixture containing natural gas is supplied from the intake passage 33 to the combustion chamber 31 c by moving the piston 32 to the bottom dead center side. The ignition section 6 is provided on the cylinder head 31b of the engine body 31. In the combustion chamber 31c, the air-fuel mixture is compressed by the piston 32 moving toward the top dead center. The compressed air-fuel mixture is ignited by the ignition unit 6 and burns, and is discharged from the exhaust passage 34 as exhaust gas. In FIG. 1, the illustration of an intake valve and an exhaust valve provided in the cylinder head 31b is omitted.

  The fuel gas supply unit 20 is a system that supplies gas serving as fuel to the natural gas engine 30. The fuel gas supply unit 20 includes a first tank 21, a second tank 22, a solenoid valve 23, a pump 24, a carburetor 25, a solenoid valve 26, a first solenoid valve 7, and a second solenoid valve 8 And

  The first tank 21 is a tank that stores a liquid fuel (liquefied natural gas) L. In the first tank 21, the liquid fuel L is cooled so as to maintain the liquid state. The components of the liquid fuel L differ in composition depending on the place where natural gas is produced, but include at least methane, ethane, propane, isobutane, normal butane, normal pentane, nitrogen, and carbon dioxide. The first tank 21 may be cooled, for example, below the boiling point of methane (−162 ° C.), and may have a heat insulating structure capable of maintaining natural gas containing methane as the liquid fuel L.

In the first tank 21, vaporization of the liquid fuel L occurs by natural heat input or the like which can not be prevented even by cooling, may occur boil-off gas G _B. BOG G _B, the liquid fuel L of the first tank 21 is a gas produced naturally vaporized. Here, the natural vaporization means, for example, that the liquid fuel L evaporates due to natural heat input from the surroundings to the first tank 21 and that the liquid level of the liquid fuel L moves with the shaking of the vehicle V. This includes evaporation of the liquid fuel L due to frictional heat generated between the inner wall surface of the first tank 21 and the liquid fuel L. BOG G _B is methane has a main component, can improve the anti-knocking performance by being supplied to the natural gas engine 30. BOG G _B may contain ethane.

The first tank 21 is connected to the second tank 22 via a pipe 27a. Pipe 27a is a pipe for guiding the BOG _{G B} from the first tank 21 to second tank 22. An electromagnetic valve 23 and a pump 24 are provided in the middle of the pipe 27a. Solenoid valve 23, for example, may be switched communication and blocking of the pipe 27a in response to the occurrence amount of the BOG G _B in the first tank 21. Pump 24 may be, for example, when the solenoid valve 26 is communicated with a piping 27a, it may be pumped a second tank 22 to boil-off gas G _B from the first tank 21.

  The first tank 21 is connected to the vaporizer 25 via a pipe 27b. The pipe 27b is a pipe that guides the liquid fuel L from the first tank 21 to the vaporizer 25. An electromagnetic valve 26 is provided in the middle of the pipe 27b. The solenoid valve 26 may switch between communication and cutoff of the pipe 27b according to the load of the natural gas engine 30.

Vaporizer 25, the liquid fuel L guided through the pipe 27b from the first tank 21 is vaporized to produce a fuel gas G _F. Fuel gas G _F is a gas as a main fuel of natural gas engine 30. The carburetor 25 is connected to the intake passage 33 via a pipe 27c. Pipe 27c is a pipe for guiding the fuel gas _{G F} to the intake passage 33 from the vaporizer 25. A first solenoid valve 7 described later is provided in the middle of the pipe 27c.

The second tank 22 is a tank for storing boil-off gas _{G B.} The second tank 22 is connected to the intake passage 33 via a pipe 27d. Pipe 27d is a piping for guiding the BOG _{G B} to the intake passage 33 from the second tank 22. A second solenoid valve 8 described later is provided in the middle of the pipe 27d.

  The ECU 10 is an electronic control unit that controls the natural gas engine 30. The ECU 10 includes a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], a communication circuit, and the like. The ECU 10 implements various functions by, for example, loading a program stored in the ROM into the RAM and executing the program loaded into the RAM by the CPU. The ECU 10 may be composed of a plurality of electronic units.

  FIG. 2 is a block diagram of the control device of the natural gas engine of FIG. As shown in FIG. 2, the ECU 10 electrically connects the engine rotation sensor 1, the throttle lever sensor 2, the knock sensor 3, the tank pressure sensor 4, the ignition unit 6, the first solenoid valve 7, and the second solenoid valve 8 to each other. It is connected.

  The engine rotation sensor 1 is a detector that detects the engine speed of the natural gas engine 30. The engine rotation sensor 1 outputs a detection signal of the detected engine speed to the ECU 10. The throttle lever sensor 2 is a detector that detects an operation amount of the throttle lever. The throttle lever sensor 2 outputs a detection signal corresponding to the detected operation amount of the throttle lever to the ECU 10.

  Knock sensor 3 is, for example, a detector that is attached to cylinder block 31a of engine body 31 and detects vibration of cylinder block 31a. Knock sensor 3 may employ a sensor having a general configuration as long as it can detect vibration of cylinder block 31a including vibration due to abnormal combustion (knocking). Knock sensor 3 outputs to ECU 10 a detection signal of the detected vibration of cylinder block 31a.

Tank pressure sensor 4 is provided on the second tank 22, a detector for detecting the pressure of boil-off gas G _B which is stored in the second tank 22. Here, the pressure of the boil-off gas G _B is used as an indicator of the remaining amount of boil-off gas G _B which is stored in the second tank 22. Tank pressure sensor 4 outputs a detection signal of the pressure detected BOG G _B to ECU 10.

  The ignition unit 6 is a device for burning the air-fuel mixture in the combustion chamber 31c of the natural gas engine 30 by ignition. The ignition section 6 here includes, for example, an ignition coil and an ignition plug. The ignition timing of the ignition section 6 is controlled by the ECU 10. In the following description, for convenience of explanation, the “ignition timing” is a crank angle value (unit: ° [degree], ATDC) having a positive value on the retard side with respect to the top dead center of the piston 32 (0 °). And the “advance amount” represents the absolute value (unit: °) of the crank angle advanced from the reference ignition timing.

The first solenoid valve 7 is a valve for adjusting the supply amount of the fuel gas G _F to natural gas engine 30. The operation of the first solenoid valve 7 is controlled by the ECU 10. The first solenoid valve 7 is controlled, for example, by ECU10 as a fuel gas G _F of the feed amount corresponding to the required fuel amount and the supply ratio will be described later, it is supplied to the natural gas engine 30.

The second solenoid valve 8 is a valve for adjusting the supply amount of boil-off gas G _B to natural gas engine 30. The operation of the second solenoid valve 8 is controlled by the ECU 10. The second solenoid valve 8 is controlled, for example, by ECU10 as BOG G _B supply amount according to the required fuel amount and the supply ratio will be described later, it is supplied to the natural gas engine 30.

[Functional Configuration of ECU 10]
Next, a functional configuration of the ECU 10 will be described. The ECU 10 includes an intake load factor calculation unit 11, a knocking recognition unit 12, a fuel amount calculation unit 13, an ignition timing calculation unit 14, a fuel control unit 15, and an ignition control unit 16.

  The intake load factor calculation unit 11 calculates an intake load factor based on the engine speed detected by the engine rotation sensor 1 and the operation amount of the throttle lever detected by the throttle lever sensor 2. The intake load factor means a load (engine load) required to be output to the natural gas engine 30, and is expressed, for example, as a ratio to the total load of the natural gas engine 30. The intake load factor calculation unit 11 calculates the intake load factor based on map data in which the relationship between the engine speed, the operation amount of the throttle lever, and the intake load factor is set in advance by, for example, a test or a simulation. The intake load factor calculation unit 11 may control a throttle valve and the like so that the natural gas engine 30 takes in air in an amount corresponding to the intake load factor.

  Knock recognition section 12 recognizes knocking of natural gas engine 30 based on the detection result of knock sensor 3. For example, when the magnitude of vibration of cylinder block 31a detected by knock sensor 3 is equal to or larger than a predetermined knock threshold, knocking recognition unit 12 recognizes knocking as occurrence of vibration peculiar to abnormal combustion. The knock threshold value is a threshold value of the magnitude of vibration of the cylinder block 31a for determining whether or not knocking has occurred (whether or not abnormal combustion has occurred). The knock threshold value can be set in advance by a test or the like, for example, so that vibration specific to abnormal combustion can be distinguished from vibration caused by movement of the piston 32 and the like.

  When knocking is recognized, the knocking recognition unit 12 stores the knocking advance amount of the knocking. The knocking advance amount is the advance amount when the knocking occurs. The knock generation advance amount can be, for example, the advance amount from the reference ignition timing for the ignition that triggered the knock generation. The knocking advance amount is determined based on the latest ignition (the latest ignition actually fired by the natural gas engine 30) instructed by the ECU 10 to the ignition unit 6 before the knocking is recognized by the knocking recognition unit 12. The advance amount from the reference ignition timing may be used.

  For example, when the ignition timing for the ignition that triggered the occurrence of knocking is the reference ignition timing, knocking recognition unit 12 stores 0 ° as the knocking advance amount. For example, when the ignition timing at the time of occurrence of the knocking is an ignition timing advanced from the reference ignition timing by a certain advance amount, the knocking recognition unit 12 stores the advance amount as the knock generation advance amount. I do.

The fuel amount calculation unit 13 calculates a required fuel amount based on the engine speed and the intake load factor. Required fuel amount is, for example, the supply amount of the fuel gas G _F required according to the intake air load factor of a natural gas engine 30. The fuel amount calculation unit 13 calculates the required fuel amount based on map data in which the relationship between the engine speed, the intake load factor, and the required fuel amount is set in advance by, for example, testing and simulation.

Fuel amount calculating unit 13 based on the recognition result of the calculated required fuel amount and the knocking recognition unit 12, the fuel gas supply quantity Q1 is a supply to the natural gas engine 30 of the fuel gas G _F and, BOG G _The boil-off gas supply amount Q2, which is the supply amount of _{B to} the natural gas engine 30, is calculated. The fuel amount calculation unit 13 determines the fuel gas supply amount Q1 based on map data in which the relationship between the knocking advance amount and the fuel gas supply amount Q1 and the boil-off gas supply amount Q2 is set in advance by, for example, testing and simulation. And the boil-off gas supply amount Q2.

FIG. 3A is a diagram showing a setting example of the fuel gas supply amount and the boil-off gas supply amount. The horizontal axis in FIG. 3A represents the amount of advance from the reference ignition timing. In the horizontal axis of FIG. 3A, the left side of the reference ignition timing “0 ° [deg.]” Is the advance side. The vertical axis of FIG. 3 (a) represents the supply amount of the fuel gas G _F and boil-off gas G _B (e.g. the mass flow rate).

  In the example of FIG. 3A, the fuel gas supply amount Q1 when the advance amount is 0 ° corresponds to the required fuel amount calculated by the fuel amount calculation unit 13. The boil-off gas supply amount Q2 when the advance amount is 0 ° is 0. On the other hand, in the example of FIG. 3A, the fuel gas supply amount Q1 corresponding to the abscissa position where the advance amount is more advanced than 0 ° is the fuel gas supply amount Q1 when the advance amount is 0 °. Is more weight than. Further, the boil-off gas supply amount Q2 corresponding to the abscissa position on the advance side of the advance angle of 0 ° is larger than the boil-off gas supply amount Q2 when the advance amount is 0 °.

The curve of the boil-off gas supply amount Q2 in FIG. 3A is a downwardly convex curve. For example, the sensitivity (knocking sensitivity) as to whether or not continuous knocking occurs when the advance amount is increased by a certain value (for example, 1 °) tends to increase as the advance amount increases. Therefore, the increasing gradient (gradient) of the boil-off gas supply amount Q2 is set to increase as the advance amount increases. Incidentally, BOG supply amount Q2 may be set in consideration of less than the heat generation amount of the heat generation amount of the fuel gas G _F BOG G _B.

FIG. 3B is a diagram illustrating a supply ratio of the boil-off gas to the fuel gas in the setting example of FIG. The horizontal axis in FIG. 3B is the same as the horizontal axis in FIG. The vertical axis of FIG. 3 (b) represents the supply ratio R of BOG G _B relative to the fuel gas G _F. The supply ratio R can be obtained, for example, as a ratio obtained by dividing the boil-off gas supply amount Q2 by the fuel gas supply amount Q1 at each horizontal axis position in FIG.

When the knocking recognition unit 12 recognizes knocking in a high load operation state in which the load on the natural gas engine 30 is equal to or greater than a predetermined load threshold, the fuel amount calculation unit 13 stores the knocking advance amount stored in the knocking recognition unit 12. Accordingly, the fuel gas supply amount Q1 is reduced and the boil-off gas supply amount Q2 is increased according to the relationship shown in FIG. Accordingly, the supply ratio R of BOG G _B relative to the fuel gas G _F is increased compared with the previous recognition of the knocking according to the relationship of FIG. 3 (b).

  The fuel amount calculation unit 13 reduces the supply ratio R in a low-load operation state in which the load on the natural gas engine 30 is less than the load threshold. The fuel amount calculation unit 13 may reduce the supply ratio R by a fixed amount of time change in the low load operation state.

  The load threshold is a load of the natural gas engine 30 (for example, an operation amount of a throttle lever, an intake air amount, and the like) for determining whether the operation state of the natural gas engine 30 is a high load operation state or a low load operation state. Is the threshold value. The load threshold may be a preset constant load value, or may be map data set in advance according to the engine speed.

The fuel amount calculating unit 13, for example, if the pressure of the boil-off gas G _B detected by the tank pressure sensor 4 is equal to or less than a predetermined pressure threshold, and a small residual amount of boil-off gas G _B, fuel gas supply By increasing the amount Q1 and decreasing the boil-off gas supply amount Q2, the supply ratio R is reduced. Fuel amount calculating unit 13, if the pressure of the boil-off gas G _B is equal to or less than pressure threshold, it may reduce the supply ratio R at a predetermined time change amount.

  The ignition timing calculation unit 14 determines the reference ignition timing, the advance amount ΔSA from the reference ignition timing, and the MBT [Minimum advanced for the Best Torque] based on the engine speed, the intake load factor, and the recognition result of the knocking recognition unit 12. Calculate the ignition timing. The reference ignition timing is an ignition timing serving as a reference for the advance amount of the ignition timing. The MBT ignition timing is an ignition timing at which the output torque of the natural gas engine 30 becomes maximum under certain load conditions and fuel conditions.

  The ignition timing calculation unit 14 calculates the MBT ignition timing based on map data in which the relationship between the engine speed, the intake load factor, and the MBT ignition timing is set in advance by, for example, tests and simulations.

  The ignition timing calculator 14 calculates a reference ignition timing based on the engine speed and the intake load factor. The map data of the reference ignition timing can be set in advance as, for example, an ignition timing that is set on a more retarded side than an ignition timing (knock limit) that continuously knocks in the output torque measurement test. . The knock limit means an ignition timing at which knocking continuously and significantly occurs when the ignition timing is advanced further. The map data of the reference ignition timing may include, for example, a plurality of maps preset for each fuel condition (boil-off gas supply amount Q2).

  In the low load operation state, the knock limit is on the more advanced side than the MBT ignition timing, so that the reference ignition timing can be the same ignition timing as the MBT ignition timing. In the high-load operation state, the MBT ignition timing is on the advance side of the knock limit, and therefore, the reference ignition timing can be the ignition timing on the retard side of the knock limit.

Knock limit moves to the advance side by increasing the supply ratio R of boil-off gas G _B. That is, since the knock resistance of the natural gas engine 30 is improved by increasing the boil-off gas supply amount Q2, the advance amount ΔSA from the reference ignition timing can be increased particularly in a high-load operation state.

  When knocking is not recognized by knocking recognition section 12, ignition timing calculation section 14 determines that there is room for advance and increases advance angle amount ΔSA. When the knocking is recognized by the knocking recognition unit 12 in the high load operation state, the ignition timing calculation unit 14 increases the supply ratio R by the fuel amount calculation unit 13 in accordance with the knocking recognition by the knocking recognition unit 12. Is performed (when the knock limit moves to the advance side), the advance amount ΔSA is increased, assuming that there is room for advance. The ignition timing calculation unit 14 may increase the advance angle amount ΔSA at a constant time change amount (for example, 1 ° / sec).

  However, the ignition timing calculation unit 14 limits the advance amount ΔSA so that the ignition timing advanced by the advance amount ΔSA from the reference ignition timing does not exceed the MBT ignition timing. For example, when the ignition timing advanced from the reference ignition timing by the advance amount ΔSA is on the advance side of the MBT ignition timing, the ignition timing calculation unit 14 determines that there is no room for advance and determines that the advance amount ΔSA Without increasing, the increase of the advance angle amount ΔSA is limited. On the other hand, for example, when the ignition timing advanced from the reference ignition timing by the advance amount ΔSA is not on the advance side of the MBT ignition timing, the ignition timing calculation unit 14 determines that there is room to advance, and The amount of advance angle ΔSA is increased as described above without limiting the amount ΔSA.

  The ignition timing calculator 14 reduces the advance amount ΔSA in the low load operation state. The ignition timing calculation unit 14 may reduce the advance angle amount ΔSA by a constant time change amount in the low load operation state. The time change amount of the advance angle amount ΔSA may be faster than the time change amount of the supply ratio R.

Incidentally, the ignition timing calculation unit 14, for example, if the pressure of the boil-off gas G _B detected by the tank pressure sensor 4 is equal to or less than a predetermined pressure threshold, and a small residual amount of boil-off gas G _B, advance amount Reduce ΔSA. Ignition timing calculation unit 14, when the pressure of the boil-off gas G _B is equal to or less than pressure threshold, may reduce the advance amount ΔSA at certain time variation. The time change amount of the advance angle amount ΔSA may be faster than the time change amount of the supply ratio R.

Fuel control unit 15, the fuel gas G _F of the fuel gas supply quantity Q1 calculated by the fuel amount calculating unit 13 to supply the natural gas engine 30, and controls the first solenoid valve 7. Fuel control unit 15, the boil-off gas G _B BOG supply amount Q2 calculated by the fuel amount calculating unit 13 to supply the natural gas engine 30, and a second solenoid valve 8.

  The ignition control unit 16 controls the ignition unit 6 so as to ignite the natural gas engine 30 at an ignition timing corresponding to the advance amount ΔSA calculated by the ignition timing calculation unit 14.

  Next, details of the increase of the supply ratio R by the fuel amount calculation unit 13 and the calculation of the advance amount ΔSA by the ignition timing calculation unit 14 will be described with reference to FIGS. Here, an example will be described in which the advance amount ΔSA from the reference ignition timing SA1 is gradually increased to advance amounts dSA1, dSA2, and dSA3.

  FIG. 4 is a diagram illustrating an example of a torque curve of a natural gas engine. The torque curve is a characteristic curve showing the output torque characteristic of a natural gas engine when the ignition timing is changed under the condition of a fixed intake air amount and fuel supply amount, with the ignition timing as the horizontal axis and the output torque as the vertical axis. It is. As shown in FIG. 4, the torque curve becomes an upwardly convex curve (for example, a parabola), and the ignition timing corresponding to the peak position of the torque curve is the MBT ignition timing (for example, the ignition timing SA2 in the torque curve TC3).

In FIG. 4, the load conditions (intake air amount) of the torque curves TC1 to TC3 are substantially the same in the high load operation state. Fuel condition of the torque curve TC1 is equivalent to the fuel condition of the horizontal axis position of the "advance angle = 0 °" in FIG. 3, the supply amount of the fuel gas G _F is equal to the required fuel amount, BOG G The supply amount of _B is 0. In torque curve TC2, which corresponds to the fuel condition of the horizontal axis position of the "advance angle = DSA1" in FIG. 3, the supply amount of the fuel gas G _F is equal to the fuel gas supply amount Q11, the boil-off gas G _B The supply amount is equal to the boil-off gas supply amount Q21. In torque curve TC3, which corresponds to the fuel condition of the horizontal axis position of the "advance angle = DSA1 + DSA2" in FIG. 3, the supply amount of the fuel gas _{G F} is equal to the fuel gas supply amount Q12, the boil-off gas _{G B} The supply amount is equal to the boil-off gas supply amount Q22.

  FIG. 5 is a timing chart showing an operation example of the control device of the natural gas engine. As shown in FIGS. 4 and 5, first, it is assumed that the natural gas engine 30 is operated at the reference ignition timing (ignition timing SA1) that is more retarded than the knock limit KN1 in the torque curve TC1 until time t1. (Point P1 in FIG. 4). Next, assuming that there is room to advance from time t1 to time t2, the ignition timing is calculated by the ignition timing calculation unit 14, and the ignition timing is advanced from the ignition timing SA1 by a constant time change amount by the advance amount dSA1. It is assumed that KN1 has been reached (point P2 ′ in FIG. 4).

Since the knock limit KN1 has been reached, knocking occurs at time t2, and the knocking recognition unit 12 recognizes knocking. The knocking recognizing unit 12 stores the advance angle dSA1 as the knock generation advance angle. Further, the fuel amount calculating unit 13, in response to the horizontal axis position of the advance amount dSA1 of FIG. 3, the supply amount of the fuel gas G _F is reduced to a fuel gas supply amount Q11, the supply amount of boil-off gas G _B Is increased to the boil-off gas supply amount Q21, and the supply ratio R is increased to R1. As a result, the knock limit shifts to the torque curve TC2 that has moved to the advanced knock limit KN2 (point P2 in FIG. 4).

Next, from the supply ratio R of the boil-off gas G _B is increased to R1 at time t2, from time t2 to time t3, the ignition timing calculating section 14, as can afford to advance ignition timing in the torque curve TC2 Is further advanced. It is assumed that the ignition timing is advanced from the ignition timing SA1 by a constant time change amount by an advance amount dSA1 + dSA2 and reaches a knock limit KN2 (point P3 ′ in FIG. 4).

Since the knock limit KN2 has been reached, knocking occurs at time t3, and the knocking recognition unit 12 recognizes knocking. The knocking recognizing unit 12 stores the advance angle dSA1 + dSA2 as the knock generation advance angle. Further, the fuel amount calculating unit 13, in response to the horizontal axis position of the advance amount DSA1 + DSA2 in FIG. 3, the supply amount of the fuel gas G _F is reduced to a fuel gas supply amount Q12, the supply amount of boil-off gas G _B Is increased to the boil-off gas supply amount Q22, and the supply ratio R is increased to R2. As a result, the knock limit shifts to the torque curve TC3 that has moved to the advanced knock limit KN3 (point P3 in FIG. 4).

Next, since at time t3 supply ratio R of the boil-off gas G _B is increased to R2, from time t3 to time t4, the ignition timing calculating section 14, as can afford to advance ignition timing in the torque curve TC3 Is further advanced. It is assumed that the ignition timing is advanced from the ignition timing SA1 by a constant time change amount by an advance amount dSA1 + dSA2 + dSA3 to reach the ignition timing SA2 (point P4 in FIG. 4).

  Next, since the ignition timing SA2 is the MBT ignition timing from time t4 to time t5, the ignition timing calculation unit 14 determines that there is no room for advance, and does not further increase the advance amount ΔSA. The angle amount ΔSA is limited with dSA1 + dSA2 + dSA3.

Then, for example, at time t5, when the pressure of the boil-off gas G _B detected by the tank pressure sensor 4 and equal to or less than a predetermined pressure threshold, from time t5 to time t6, as the small remaining amount of boil-off gas G _B , The advance amount ΔSA and the supply ratio R are reduced. Here, the time change amount of the advance angle amount ΔSA is made faster than the time change amount of the supply ratio R. At time t6, the advance amount ΔSA becomes 0 °, whereas the supply ratio R It is reduced to reach 0 later than t6.

  Next, an example of a process performed by the natural gas engine control device 100 according to the first embodiment will be described with reference to FIGS. 6 and 7. The knocking recognition by the knocking recognition unit 12 is performed in parallel with the processing in FIGS. 6 and 7.

  FIG. 6 is a flowchart showing the fuel control process of the ECU 10. As shown in FIG. 6, in S <b> 11, in S <b> 11, the intake load factor calculator 11 calculates the intake load factor. The intake load factor calculation unit 11 calculates the intake load factor based on the engine speed and the operation amount of the throttle lever. In S12, the ECU 10 causes the fuel amount calculation unit 13 to calculate the required fuel amount. The fuel amount calculation unit 13 calculates a required fuel amount based on the engine speed and the intake load factor.

In S13, the ECU 10 uses the fuel amount calculation unit 13 to determine whether there is a second tank remaining amount. Fuel amount calculating unit 13, based on whether the pressure of the detected BOG G _B in tank pressure sensor 4 is less than or equal to a predetermined pressure threshold, the remaining amount of the second tank 22 is sufficient (the It is determined whether or not two tanks remain).

ECU10, in S13, when the pressure of the boil-off gas G _B detected by the tank pressure sensor 4 is above a predetermined pressure threshold, it is determined that there is a second tank remaining amount, in S14, the fuel amount calculating unit 13 Thereby, it is determined whether the operation state of the natural gas engine 30 is the high load operation state.

  When it is determined in S14 that the operation state of the natural gas engine 30 is the high-load operation state in S14, the knocking is recognized by the knocking recognition unit 12 by the fuel amount calculation unit 13 in S15 (knocking is present). Is determined.

When it is determined in S15 that knocking has occurred in S15, in S16, the fuel amount calculation unit 13 reduces the fuel gas supply amount Q1 and increases the boil-off gas supply amount Q2 in accordance with the knocking advance amount. You. Accordingly, the supply ratio R of BOG G _B relative to the fuel gas G _F is increased compared with the previous recognition of the knocking.

ECU10, in S17, the fuel control unit 15, the fuel gas G _F of the fuel gas supply quantity Q1 calculated in the fuel quantity calculating section 13 to supply the natural gas engine 30, the first solenoid valve 7 is controlled also BOG G _B BOG supply amount Q2 calculated by the fuel amount calculating unit 13 to supply the natural gas engine 30, the second solenoid valve 8 is controlled. Thereafter, the ECU 10 ends the processing of FIG.

Meanwhile, ECU 10, at S13, and the pressure of the boil-off gas G _B detected by the tank pressure sensor 4 is below a predetermined pressure threshold, less remaining amount of boil-off gas G _B (no second tank remaining amount) judgment In this case, in S18, the fuel amount calculation unit 13 increases the fuel gas supply amount Q1 and reduces the boil-off gas supply amount Q2, thereby reducing the supply ratio R. Thereafter, the process proceeds to the process of S17. Thereafter, the ECU 10 ends the processing of FIG. When the ECU 10 determines in S14 that the operation state of the natural gas engine 30 is the low-load operation state, the ECU 10 performs the processing of S18, and then shifts to the processing of S17. Thereafter, the ECU 10 ends the processing of FIG.

  FIG. 7 is a flowchart showing the ignition timing control processing of the ECU 10. The processing in FIG. 7 is performed, for example, after the processing in FIG. As shown in FIG. 7, in S21, the ignition timing calculation unit 14 calculates the MBT ignition timing in S21. The ignition timing calculation unit 14 calculates the MBT ignition timing based on the engine speed and the intake load factor. In S22, the ECU 10 causes the ignition timing calculation unit 14 to calculate a reference ignition timing. The ignition timing calculator 14 calculates a reference ignition timing based on the engine speed and the intake load factor.

  In S23, the ECU 10 uses the ignition timing calculation unit 14 to determine whether or not there is a second tank remaining amount. The ignition timing calculation unit 14 may determine whether or not there is the remaining amount of the second tank based on the determination result of S13 in FIG.

  If it is determined in S23 that there is a second tank remaining amount, the ECU 10 causes the ignition timing calculation unit 14 to determine whether or not the operation state of the natural gas engine 30 is a high load operation state in S24. The ignition timing calculation unit 14 may determine whether or not the vehicle is in the high-load operation state based on the determination result in S14 of FIG.

  When it is determined in S24 that the operation state of the natural gas engine 30 is in the high-load operation state in S24, in S25, the ignition timing calculation unit 14 determines whether there is a lead angle margin. For example, when the knocking recognition unit 12 does not recognize knocking, the ignition timing calculation unit 14 determines that there is room to advance. Further, the ignition timing calculation unit 14 is a case where the knocking is recognized by the knocking recognition unit 12, and when the supply ratio R is increased by the fuel amount calculation unit 13 in FIG. 6 (the knock limit moves to the advance side). ), It is determined that there is room to advance. In addition, the ignition timing calculation unit 14 determines that there is room to advance when the ignition timing in which the advance amount ΔSA has been increased in the process of S26 described below is not on the advance side of the MBT ignition timing.

  If it is determined in S25 that there is an advance margin, the ECU 10 increases the advance amount ΔSA by the ignition timing calculation unit 14 in S26. In S27, the ignition unit 6 is controlled by the ignition control unit 16 so as to ignite the natural gas engine 30 at an ignition timing corresponding to the advance amount ΔSA calculated by the ignition timing calculation unit 14 in S27. . Thereafter, the ECU 10 ends the processing of FIG.

  On the other hand, if it is determined in S25 that there is no advance margin, the ECU 10 does not increase the advance amount ΔSA in S26 and limits the increase in the advance amount ΔSA in S26.

  On the other hand, when the ECU 10 determines in S23 that there is no second tank remaining amount, the ignition timing calculation unit 14 reduces the advance amount ΔSA in S28. After that, the processing shifts to the processing of S27. Thereafter, the ECU 10 ends the processing of FIG. When the ECU 10 determines in S24 that the operation state of the natural gas engine 30 is the low-load operation state, the ECU 10 performs the process of S28, and then proceeds to the process of S27. Thereafter, the ECU 10 ends the processing of FIG.

[Operation and Effect of First Embodiment]
As described above, in the control device 100 of the natural gas engine, when knocking is recognized by the knocking recognition unit 12, the fuel amount calculation unit 13 calculates the advance amount from the reference ignition timing (knock generation advance amount). in response, supply ratio R of BOG G _B relative to the fuel gas G _F is increased compared with the previous recognition of the knocking. Therefore, the probability is high availability that can suppress the occurrence of knocking by improving the anti-knocking performance, so that the supply ratio R of the boil-off gas G _B is increased. As a result, it is possible to supply, for example, compared with the case of pre-feeding BOG G _B amounts so as not to completely knocking, the boil-off gas G _B for knock resistance improving efficiently.

  In the control device 100 of the natural gas engine, the ignition timing calculation unit 14 determines whether the knocking is not recognized by the knocking recognition unit 12 and the supply ratio by the fuel amount calculation unit 13 in accordance with the recognition of knocking by the knocking recognition unit 12. When R is increased, the advance angle amount ΔSA is increased. This makes it possible to advance the ignition timing not only when knocking is not recognized but also by improving knock resistance even if knocking is recognized, using the knocking recognition result by the knocking recognition unit 12. It becomes possible.

In the control device 100 of the natural gas engine, the fuel amount calculation unit 13 determines the supply ratio R when the knocking recognition unit 12 recognizes the knocking in the high load operation state where the load of the natural gas engine 30 is equal to or more than the predetermined load threshold. The supply ratio R is reduced in a low-load operation state in which the load on the natural gas engine 30 is less than the load threshold, by increasing the knocking as compared to before the knocking is recognized. Thus, in the low load operating condition is less likely to knock than the high-load operation state occurs, it is possible to reduce the supply amount of boil-off gas G _B.

The ignition timing calculation unit 14 is configured to increase the advance amount ΔSA by a constant time change amount, and set the increasing gradient (slope) of the boil-off gas supply amount Q2 to increase as the advance amount ΔSA increases. I have. Thus, as the advance amount [Delta] SA increases gradually, because the boil-off gas G _B is supplied at a feed ratio R in accordance with the knock sensitivity in advance amount [Delta] SA, while suppressing an increase in the boil-off gas supply amount Q2 Knock resistance can be improved. Therefore, the advance amount ΔSA can be increased, for example, until the ignition timing reaches the MBT ignition timing, while suppressing an increase in the boil-off gas supply amount Q2. As a result, an increase in the size of the second tank 22 and an increase in manufacturing cost can be suppressed, and the mountability of the second tank 22 can be improved. Further, even if the properties of the liquid fuel L vary due to the difference in the natural gas producing area, the robustness in increasing the advance angle ΔSA can be improved.

[Second embodiment]
Next, another embodiment of the control device 100 for a natural gas engine will be described with reference to FIGS. The control device 100A of the natural gas engine of the second embodiment is different from the natural gas engine 30 in that the in-cylinder pressure sensor 5 is provided in the natural gas engine 30 and the ECU 10A having a partially different functional configuration is provided. The configuration is different from that of the first embodiment, and the other configuration is the same as that of the control device 100 of the natural gas engine of the first embodiment.

  As shown in FIG. 8, the in-cylinder pressure sensor 5 is a detector that detects the pressure of the combustion chamber of the natural gas engine 30 as the in-cylinder pressure. The in-cylinder pressure sensor 5 is provided near the combustion chamber of the natural gas engine 30 (for example, the cylinder block 31a or the cylinder head 31b). The in-cylinder pressure sensor 5 outputs a detection signal of the detected in-cylinder pressure to the ECU 10A.

  As shown in FIG. 9, the ECU 10A includes an ignition timing calculation unit 14A instead of the ignition timing calculation unit 14. Instead of calculating the MBT ignition timing based on the map data, the ignition timing calculation unit 14A differs from the ignition timing in that the ignition timing at which the output torque becomes maximum is recognized based on the detection result of the in-cylinder pressure sensor 5. This is different from the timing calculation unit 14.

  The ignition timing calculation unit 14A detects an output torque based on the in-cylinder pressure detected by the in-cylinder pressure sensor 5 and stores the output torque. The ignition timing calculating unit 14A outputs the in-cylinder pressure detected by the in-cylinder pressure sensor 5 to the output torque every time the ignition unit 6 is controlled by the ignition control unit 16 and the natural gas engine 30 is ignited, for example. And store it. The ignition timing calculator 14A converts, for example, the in-cylinder pressure detected by the in-cylinder pressure sensor 5 into an output torque, and stores the output torque in association with the load condition and the fuel condition of the natural gas engine 30 at the time of the detection.

  In the process of increasing the advance amount ΔSA under a certain load condition and fuel condition, the ignition timing calculation unit 14A has turned from the increasing trend to the decreasing trend in the plurality of output torques stored in association with the load condition and the fuel condition. In this case, it is recognized that the output torque has become the maximum at the maximum amount of advance ΔSA at which the output torque tends to increase.

  That is, in the process of increasing the advance amount ΔSA, the ignition timing calculation unit 14A determines that there is no room for advance when the plurality of stored output torques change from an increasing tendency to a decreasing tendency, and determines that there is no room for advance. The increase of the advance angle ΔSA is limited by the advance amount at which the output torque is maximized without increasing ΔSA. On the other hand, in the process of increasing the advance amount ΔSA, the ignition timing calculation unit 14A determines that there is room to advance when the plurality of stored output torques are increasing, and determines the advance amount ΔSA. increase.

  Next, an example of the ignition timing control process of the control device 100A of the natural gas engine of the second embodiment will be described with reference to FIG. Processing other than the ignition timing calculation unit 14A is performed in the same manner as the processing in FIGS.

  FIG. 10 is a flowchart showing the ignition timing control processing of the ECU 10A. The processing in FIG. 10 is performed, for example, after the processing in FIG. As shown in FIG. 10, in S31, the ECU 10A detects and stores the output torque by the ignition timing calculation unit 14A. The ignition timing calculation unit 14A detects the output torque based on the detection result of the in-cylinder pressure sensor 5, and the ignition timing calculation unit 14A converts the output torque detected by the in-cylinder pressure sensor 5 into a natural value at the time of the detection. The load condition and the fuel condition of the gas engine 30 are stored in association with each other.

  In S32, the ignition timing calculation unit 14A calculates the reference ignition timing in S32 in the same manner as in S22. In S33, the ECU 10A uses the ignition timing calculation unit 14A to determine whether or not there is a second tank remaining amount, as in S23. In S34, similarly to S24, the ECU 10A determines whether the operating state of the natural gas engine 30 is the high load operating state by the ignition timing calculating unit 14A.

  When it is determined in S34 that the operation state of the natural gas engine 30 is in the high-load operation state in S34, the ECU 10A determines in S35 whether or not the ignition timing calculation unit 14A has an advance margin. If a plurality of stored output torques are increasing, the ignition timing calculation unit 14A determines that there is room to advance. If the ignition timing calculation unit 14 determines in S25 that there is room to advance, the ignition timing calculation unit 14A may determine that there is room to advance.

  When it is determined in S35 that there is an advance margin, the ECU 10A increases the advance amount ΔSA by the ignition timing calculation unit 14 in S36 in the same manner as in S26. In S37, in S37, the ignition control unit 16 controls the ignition unit 6 according to the advance amount ΔSA in S37 in the same manner as in S27. Thereafter, the ECU 10A ends the processing of FIG.

  On the other hand, in the ECU 10A, if it is determined in S35 that the plurality of stored output torques have changed from the increasing trend to the decreasing trend, and so on, there is no advance margin, the ignition timing calculation unit 14A increases the advance amount ΔSA in S26. Is not performed, and the increase of the advance amount ΔSA is limited by the advance amount at which the output torque is maximized.

  On the other hand, when it is determined in S33 that there is no second tank remaining amount, or when it is determined in S34 that the operation state of the natural gas engine 30 is the low load operation state, the ECU 10A proceeds to S38 in the same manner as S28. The ignition timing calculation unit 14A reduces the advance amount ΔSA. After that, the processing shifts to the processing of S37. Thereafter, the ECU 10A ends the processing of FIG.

[Operation and Effect of Second Embodiment]
According to the control device 100A for the natural gas engine, the same operation and effect as those of the control device 100 for the natural gas engine are achieved. Further, according to the control device 100A of the natural gas engine, in order to determine whether there is room to advance according to the output torque detected by the in-cylinder pressure sensor 5, for example, the MBT ignition timing is set as map data in advance. Setting can be omitted.

[Modification]
As described above, the embodiments according to the present invention have been described, but the present invention is not limited to the above embodiments.

  In the above-described embodiment, as the knock sensor, for example, the knock sensor 3 that is attached to the cylinder block 31a of the engine body 31 and detects the vibration of the cylinder block 31a is exemplified, but is not limited thereto. Any knock sensor capable of detecting abnormal combustion (knocking) of the natural gas engine 30 may be used. For example, a knock sensor capable of detecting knocking by detecting an ion current in the combustion chamber 31c, and a cylinder pressure of the combustion chamber 31c For example, a knock sensor that can detect knocking by detecting the knock can be used. In this case, the knocking advance amount may be the advance amount from the reference ignition timing for the latest ignition in the cylinder in which the knocking is recognized.

  In the above embodiment, the ignition coil and the ignition plug are illustrated as the ignition unit 6, but for example, a DDF (Diesel Dual Fuel) type ignition unit 6 using light oil as ignition oil may be used. Further, although the combustion chamber 31c is illustrated as a single chamber, it may be divided into a main chamber for combustion and a sub-chamber for ignition.

In the above embodiment has illustrated a second solenoid valve 8 for adjusting the supply amount of the first electromagnetic valve 7 and the boil-off gas G _B to adjust the supply amount of the fuel gas G _F, by use of the injector in place of the solenoid valve Is also good.

  In the above-described embodiment, in the operation examples shown in FIGS. 4 and 5, when knocking is recognized by the knocking recognition unit 12 while the advance amount ΔSA is increased, the fuel amount calculation unit 13 increases the supply ratio R. However, for example, when knocking is recognized by the knocking recognition unit 12 while the advance amount ΔSA is maintained without being increased, the fuel amount calculation unit 13 may increase the supply ratio R.

  In the above embodiment, the processing of the fuel amount calculation unit 13 and the ignition timing calculation units 14 and 14A is changed according to whether the load of the natural gas engine 30 is in the high load operation state or the low load operation state. You don't have to. For example, in the fuel amount calculation unit 13 and the ignition timing calculation units 14 and 14A, the processing of S14 of FIG. 6, S24 of FIG. 7, and S34 of FIG. 10 may be omitted.

  In the above-described embodiment, the control device 100 for the natural gas engine is mounted on the ship V. However, the present invention is not limited to this. The control device 100 may be mounted on a moving object including a vehicle. In addition, the control device 100 of the natural gas engine does not necessarily have to be mounted on the moving body.

  In the above embodiment, the ignition timing equal to the reference ignition timing is used as the reference for the advance amount. However, the ignition timing delayed by a predetermined amount from the reference ignition timing may be used as the reference for the advance amount. In the first embodiment, the ignition timing equal to the MBT ignition timing is set as the upper limit of the substantial advance amount. However, the ignition timing advanced by a predetermined amount from the reference ignition timing is set to the substantial advance amount. As an upper limit, the calculation of the MBT ignition timing may be omitted.

  In the above embodiment, the “ignition timing” is represented by a crank angle value (unit: ° [degree], ATDC) having a positive value on the retard side with reference to the top dead center of the piston 32 (0 °). Although the “angle amount” represents the absolute value (unit: °) of the crank angle advanced from the reference ignition timing, it is not limited to this. The “advance angle amount” may be represented by a crank angle value having a positive value on the retard side instead of an absolute value. The “ignition timing” may be a crank angle value having a positive value on the advanced side with respect to the top dead center of the piston 32 (0 °).

3 knock sensor, 12 knock recognition unit, 13 fuel amount calculation unit, 14 and 14A ignition timing calculation unit, 21 first tank, 22 second tank, 30 natural gas engine (engine), 100, 100A ... controller of natural gas engines, G B _... BOG, G F _... fuel gas, L ... liquid fuel (liquefied natural gas), R ... supply ratio, [Delta] SA ... advance amount.

Claims (3)

A control device for a natural gas engine that controls ignition timing and fuel supply of an engine using natural gas as a fuel,
A first tank for storing liquefied natural gas,
A second tank for storing boil-off gas generated by natural vaporization of the liquefied natural gas in the first tank;
A knocking recognition unit that recognizes knocking of the engine based on a detection result of a knock sensor provided in the engine;
An ignition timing calculation unit that calculates a reference ignition timing that is a reference for the advance amount of the ignition timing based on the engine speed and the load of the engine;
A rotation amount of the engine, a load on the engine, and a supply amount of the fuel gas generated by vaporizing the liquefied natural gas in the first tank to the engine based on a recognition result of the knocking recognition unit; and A fuel amount calculation unit that calculates a supply amount of the boil-off gas of the second tank to the engine.
When knocking is recognized by the knocking recognition unit, the fuel amount calculation unit sets a supply ratio of the boil-off gas to the fuel gas according to the advance amount from the reference ignition timing before the knocking is recognized. A control device for a natural gas engine that increases compared to that of a natural gas engine.   The ignition timing calculation unit is configured to determine whether or not the knocking is recognized by the knocking recognition unit, and when the supply ratio is increased by the fuel amount calculation unit in response to the recognition of knocking by the knocking recognition unit. The control device for a natural gas engine according to claim 1, wherein the angle amount is increased. The fuel amount calculation unit,
When knocking is recognized by the knocking recognition unit in a high load operation state in which the load of the engine is equal to or more than a predetermined load threshold, the supply ratio is increased compared to before the recognition of the knocking,
3. The natural gas engine control device according to claim 1, wherein the supply ratio is reduced in a low-load operation state in which the load of the engine is less than the load threshold. 4.

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