JP6178825B2 - Marine propulsion system - Google Patents

Description

  The present invention relates to a marine propulsion system including a gas engine.

  In recent years, a marine propulsion system including a gas engine has been developed due to the problem of the amount of crude oil resources and the problem of exhaust gas regulations (see, for example, Patent Document 1). The gas engine is equipped with a turbocharger.

JP 2014-177918 A

  As shown in FIG. 5, the gas engine has a knocking region and a misfire region due to the relationship between the air-fuel ratio (excess air ratio) and the net average effective pressure (BMEP). Accordingly, the operable range at high load is a narrow range between the knocking region and the misfire region.

  By the way, in a gas engine, misfire may occur for reasons other than the air-fuel ratio (for example, spark plug wear or ignition coil abnormality). In such a case, misfire occurs continuously between a plurality of cycles. Therefore, when misfiring continuously occurs in any cylinder of the gas engine, it is desirable to stop the fuel gas injection from the fuel injection valve corresponding to the cylinder (so-called cylinder cut). This is to prevent the fuel gas from being discharged without being burned.

  On the other hand, in order to suppress the decrease in the output of the gas engine due to the cylinder cut, it is desirable to increase the fuel gas injection amount in the other cylinders. However, if the amount of air supplied from the compressor of the supercharger to each cylinder cannot be increased, if the fuel gas injection amount is increased, the operating point is knocked as shown by arrow X in FIG. May shift into the region. In addition, since the fuel gas is not burned in the cylinder where the continuous misfire has occurred, the exhaust energy discharged from the gas engine and sent to the turbocharger turbine is reduced. For this reason, less air is supplied to the gas engine from the compressor of the supercharger. Therefore, in the other cylinders, not only the fuel gas injection amount cannot be increased, but also the fuel gas injection amount must be decreased. For this reason, the output of the gas engine may greatly drop after the cylinder is cut, and it is necessary to determine the supercharger specifications in consideration of the cylinder cut in order to continue the operation. For example, the turbocharger specifications are determined so that the compressor of the turbocharger discharges a sufficiently larger amount of air than required during normal operation, and the excess discharged from the compressor during normal operation It is conceivable to escape the air to the atmosphere. In that case, the efficiency during normal operation decreases.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a marine propulsion system that can maintain the output of a gas engine as high as possible after a cylinder cut without reducing the efficiency during normal operation.

  In order to solve the above problems, a marine propulsion system according to the present invention is provided in a variable pitch propeller including a pitch changing mechanism, a gas engine including a plurality of cylinders that rotationally drives the propeller, and the gas engine. A plurality of fuel injection valves respectively corresponding to the plurality of cylinders; a control device that controls the pitch change mechanism of the propeller and the plurality of fuel injection valves; and the control device is one of the plurality of cylinders. When misfires occur continuously, the fuel gas injection from the fuel injection valve corresponding to the cylinder is stopped, the fuel injection amount limit value of the other fuel injection valves is lowered, and the pitch of the propeller is reduced. It is characterized by making it smaller.

  According to the above configuration, since the fuel gas injection amount is high at high loads, the fuel gas injection amount is reduced by lowering the fuel injection amount limit value. As a result, although the rotational speed of the gas engine once falls, the pitch of the variable pitch propeller is reduced, so that the rotational speed of the gas engine increases accordingly. Thereby, since the exhaust energy per unit time discharged from the gas engine increases, it is possible to increase the air supplied from the compressor of the supercharger to the gas engine. As a result, the fuel gas injection amount can be increased. Therefore, the output of the gas engine can be maintained as high as possible after the cylinder is cut. In addition, the supercharger specifications can be determined without considering the cylinder cut, so that the efficiency during normal operation is not reduced.

  The limit value is a first limit value, and the control device determines the fuel injection amount of the plurality of fuel injection valves based on the temperature and pressure of air supplied to the gas engine and the actual rotational speed of the gas engine. Two limit values may be determined, and the smaller one of the first limit value and the second limit value may be adopted. According to this configuration, it is possible to reliably prevent the operating point from shifting to the knocking region.

  The control device performs PID control for adjusting the actual rotational speed of the gas engine to a target rotational speed for the plurality of fuel injection valves, and misfiring continuously occurs in any of the plurality of cylinders. In this case, the target rotational speed may be increased with the rated rotational speed as the upper limit. According to this configuration, the output of the gas engine can be kept higher.

  For example, the marine vessel propulsion system further includes a plurality of pressure gauges that respectively measure the pressures in the plurality of cylinders, and the control device performs one cycle from the measurement result of the pressure gauges in each of the plurality of cylinders. It may be determined whether or not misfire has occurred.

  The ratio of the reduced fuel injection amount limit value to the maximum fuel injection amount of each fuel injection valve is (T−M) / T, where T is the total number of cylinders and M is the number of cylinders where continuous misfire has occurred. It may be a value smaller than 10%. According to this configuration, knocking can be effectively suppressed.

  According to the present invention, the output of the gas engine can be maintained as high as possible after the cylinder is cut without reducing the efficiency during normal operation.

1 is a schematic configuration diagram of a marine propulsion system according to an embodiment of the present invention. It is a graph which shows the relationship between the rotation speed of a gas engine, and an output. It is a graph which shows the relationship between air quantity and the fuel injection amount 2nd limit value. It is a graph which shows a time-dependent change of the injection amount of fuel gas. It is a graph which shows the knocking area | region and misfiring area | region in the driving | running | working by the lean burn of a gas engine, and took the net average effective pressure on the vertical axis | shaft on the horizontal axis.

  FIG. 1 shows a marine propulsion system 1 according to an embodiment of the present invention. The system 1 includes a variable pitch propeller 15 and a gas engine 2 that rotationally drives the propeller 15. The gas engine 2 is equipped with a supercharger 11 (in FIG. 1, they are drawn apart for easy understanding of the drawing).

  The propeller 15 includes a pitch changing mechanism 16 that changes the pitch P of the propeller 15 (that is, the angle of each blade). In the present embodiment, the gas engine 2 is coupled to the propeller 15 via the speed reducer 14 and directly drives the propeller 15 to rotate. Although not shown, the propeller 15 is connected to the electric motor via the speed reducer 14, the gas engine 2 is connected to the generator, and the gas engine 2 is connected to the propeller 15 via the generator and the electric motor. May be indirectly rotated.

  In the present embodiment, the gas engine 2 is a 4-stroke engine. However, the gas engine 2 may be a two-stroke engine. The gas engine 2 may be a gas-only engine that burns only fuel gas (for example, natural gas), or may be a dual fuel engine that burns one or both of fuel gas and fuel oil. .

  Specifically, the gas engine 2 includes a plurality of cylinders 21 arranged in the axial direction of a crankshaft (not shown). The number of cylinders 21 is, for example, 5 to 18 (only three are shown in FIG. 1 for simplification of the drawing).

  A piston (not shown) is arranged in each cylinder 21. In the case of a 4-stroke engine, one cycle (supply, compression, expansion, exhaust) of the gas engine 2 is performed by reciprocating the piston twice in each cylinder 21. The phase angle (0 to 720 degrees) of the gas engine 2 during one cycle in each cylinder 21 is detected by the phase angle detector 7. As the phase angle, a crank shaft rotation angle (crank angle), a piston position, or the like can be used. For example, the phase angle detector 7 is an electromagnetic pickup, a proximity switch, or a rotary encoder. Further, the actual rotational speed N of the gas engine 2 is also detected from the phase angle detector 7.

  The cylinder 21 is connected to the compressor 12 and the turbine 13 of the supercharger 11 via the air supply path 3 and the exhaust path 4. The air supply path 3 guides the air discharged from the compressor 12 to the cylinder 21, and the exhaust path 4 guides the exhaust discharged from the cylinder 21 to the turbine 13. More specifically, the air supply path 3 includes an air supply manifold 32, a main flow path 31 that connects the air supply manifold 32 and the compressor 12, and a plurality of branch flow paths 33 that connect the air supply manifold 32 and the cylinder 21. Including. The exhaust passage 4 includes an exhaust manifold 42, a plurality of branch passages 41 that connect the cylinder 21 and the exhaust manifold 42, and a main passage 43 that connects the exhaust manifold 42 and the turbine 13.

  Further, an air supply blow-off path 17 is connected to the air supply path 31, and a flow rate control valve 18 is provided in the air supply blow-off path 17. By operating this flow control valve 18, the amount of air introduced into each cylinder 21 can be controlled. Although illustration is omitted, the amount of air introduced into each cylinder 21 is controlled by connecting an exhaust blow-off passage to the exhaust passage 43 and operating a flow control valve provided in the exhaust blow-off passage. Is also possible.

  The gas engine 2 is provided with a plurality of fuel injection valves 5 respectively corresponding to the cylinders 21. Each fuel injection valve 5 injects fuel gas into the air supplied to the corresponding cylinder 21.

  The pitch changing mechanism 16 and the fuel injection valve 5 of the propeller 15 described above are controlled by the control device 6 based on, for example, an operation amount of a boat speed lever (not shown). As shown in FIG. 2, when the pitch P of the propeller 15 is a specific value θ1, the relationship between the rotational speed and the output of the gas engine 2 draws a curve C1. When fuel gas is injected from each fuel injection valve 5 at the maximum injection amount Qm, the torque of the gas engine 2 is 100% (output is 100%), and the rotational speed is the maximum rotational speed Nm.

  The control device 6 performs PID control on the fuel injection valve 5 to adjust the actual rotational speed N of the gas engine 2 to the target rotational speed NT. The target rotational speed NT is determined according to, for example, the operation amount of the ship speed lever.

  Each cylinder 21 is provided with a pressure gauge 83 for measuring the pressure in the cylinder 21. The control device 6 determines whether or not misfire has occurred in each cylinder 21 from the measurement result of the pressure gauge 83 for each cycle. For example, the control device 6 calculates a pressure deviation in the cylinder 21 before and after top dead center, and determines that misfire has occurred when this deviation is less than a threshold value.

  In the present embodiment, a thermometer 81 and a pressure gauge 82 are provided in the main flow path 31 of the air supply path 3 described above. The thermometer 81 and each pressure gauge 82 measure the temperature and pressure of the air supplied to the cylinder 21. The temperature and pressure measured by the thermometer 81 and each pressure gauge 82 are input to the control device 6.

  Each fuel injection valve 5 has a fuel injection amount first limit value L1 corresponding to the above-described maximum injection amount Qm and the number of cylinders 21 in which misfires have occurred continuously, and an air amount supplied to each cylinder 21. A fuel injection amount second limit value L2 is determined. The control device 6 employs the smaller one of the first limit value L1 and the second limit value L2.

  In the present embodiment, the first limit value L1 at the normal time (when the cylinder is not cut: when the number of cylinders 21 in which misfires occur continuously is zero) is larger than the maximum injection amount Qm that can prevent overpower. A large value α1 is set. For example, the control device 6 stores in advance a map in which the limit value L1 is determined according to the engine speed. However, the normal first limit value L1 may be equal to the maximum injection amount Qm.

  The first limit value L1 at the time of cylinder cut (when the number of cylinders 21 in which misfires occur continuously is 1 or more) is set to a value α2 that is sufficiently smaller than the value α1. For example, the ratio of α2 to the maximum injection amount Qm (α2 / Qm) is 10% higher than (TM) / T, where T is the total number of cylinders 21 and M is the number of cylinders 21 in which continuous misfire has occurred. This is a small value. Knocking is likely to occur when α2 / Qm is close to (TM) / T, but knocking can be effectively suppressed when α2 / Qm is 10% or more smaller than (TM) / T. Was confirmed by experiments. For example, when T = 6 and M = 1, (TM) / T is about 83%, but α2 / Qm is about 60%.

  The amount of air supplied to each cylinder 21 that is the basis for the second limit value L2 is obtained from the temperature and pressure of the air supplied to the gas engine 2 and the actual rotational speed N of the gas engine 2. Therefore, the control device 6 determines the second limit value L2 of the fuel injection valve 5 based on the temperature and pressure measured by the thermometer 81 and the pressure gauge 82 and the actual rotational speed N detected by the phase angle detector 7. To do.

  When misfire occurs continuously in a plurality of cycles (for example, four cycles) in any of the cylinders 21, the control device 6 injects fuel gas from the fuel injection valve 5 corresponding to the cylinder 21. While stopping, the fuel injection amount first limit value L1 of the other fuel injection valves 5 is lowered.

  For example, it is assumed that before misfiring continuously occurs, the operating state is at a high load as indicated by a point A in FIG. 2 and fuel gas is injected from each fuel injection valve 5 at an injection amount Qc. To do. At this time, as shown in FIG. 4, the first limit value L1 is α1, which is larger than the maximum injection amount Qm. The control device 6 reduces the first limit value L1 from α1 to α2 when misfiring continuously occurs in any of the cylinders 21.

  Since the fuel gas injection amount is high at the time of high load, the fuel gas injection amount is reduced by lowering the first limit value L1, as shown in FIG. As a result, as shown in FIG. 2, the operating state changes from the point A to the point B along the curve C1, and the rotational speed of the gas engine 2 temporarily drops. In addition, when misfires occur continuously, the exhaust energy discharged from the gas engine 2 decreases, and the amount of air supplied to the cylinder 21 decreases. As a result, as shown in FIG. 4, the fuel gas injection amount is regulated by the second limit value L2, and is significantly smaller than the first limit value L1.

  On the other hand, the control device 6 reduces the pitch P of the propeller 15 (θ1 → θ2) when misfires occur continuously. For example, θ2 is 60 to 80% of θ1. As a result, the operating state is shifted to a point C on the curve C2 below the curve C1, as shown in FIG. 2, and the rotational speed of the gas engine 2 increases by the amount by which the pitch P of the propeller 15 is reduced. . Thereby, since the exhaust energy per unit time discharged from the gas engine 2 increases, the air supplied to the gas engine 2 from the compressor 12 of the supercharger 11 can be increased. As a result, as shown in FIG. 4, the fuel gas injection amount can be increased and can be close to the first limit value L1 (α2). Thereafter, along the torque line determined by the first limit value L1 (α2), the operating state transitions to point D, and the actual rotational speed N becomes the target rotational speed NT.

  As described above, in the marine propulsion system 1 of the present embodiment, as indicated by a point D in FIG. 2, the output of the gas engine 2 can be maintained as high as possible after the cylinder is cut. And since the specification of the supercharger 11 can be determined without considering the time of cylinder cut, the efficiency at the time of a normal driving | operation is not reduced.

  By the way, when misfiring continuously occurs in any of the cylinders 21, if control is performed based only on the second limit value L <b> 2 without instantaneously reducing the first limit value L <b> 1, supply to the cylinder 21 is performed. Since the detection of the decrease in the amount of air to be performed is delayed by a time lag, knocking occurs. In contrast, in the present embodiment, the first limit value L1 is instantaneously lowered, so that knocking can be prevented.

  In the present embodiment, since the smaller one of the first limit value L1 and the second limit value L2 is adopted, it is possible to reliably prevent the operating point from shifting to the knocking region.

  By the way, when the misfire continuously occurs in any of the cylinders 21, it is desirable that the control device 6 increases the target rotational speed NT with the rated rotational speed as an upper limit. According to this configuration, the output of the gas engine 2 can be kept higher.

(Modification)
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Marine propulsion system 15 Variable pitch propeller 16 Pitch change mechanism 2 Gas engine 21 Cylinder 5 Fuel injection valve 6 Control apparatus 82, 83 Pressure gauge

Claims (4)

A variable pitch propeller including a pitch changing mechanism;
A gas engine including a plurality of cylinders for rotationally driving the propeller;
A plurality of fuel injection valves respectively provided in the gas engine and corresponding to the plurality of cylinders;
A control device for controlling the pitch change mechanism of the propeller and the plurality of fuel injection valves,
When misfiring continuously occurs in any of the plurality of cylinders, the control device stops the fuel gas injection from the fuel injection valve corresponding to the cylinder and the fuel of the other fuel injection valves. Lower the injection amount limit value, reduce the pitch of the propeller , and
The fuel injection amount first limit value, which is the fuel injection amount limit value, is determined according to the number of cylinders in which misfires have occurred continuously, and the plurality of fuels are based on the pressure of air supplied to the gas engine. A marine propulsion system that determines a fuel injection amount second limit value of an injection valve and employs the smaller one of the first limit value and the second limit value . The control device performs PID control for adjusting the actual rotational speed of the gas engine to a target rotational speed for the plurality of fuel injection valves, and misfiring continuously occurs in any of the plurality of cylinders. when, the larger the target rotational speed of the rated speed as an upper limit, marine propulsion system of claim 1. A plurality of pressure gauges for measuring the pressure in each of the plurality of cylinders;
3. The marine propulsion system according to claim 1, wherein the control device determines whether or not misfiring has occurred in each cycle based on a measurement result of the pressure gauge in each of the plurality of cylinders. The ratio of the reduced fuel injection amount limit value to the maximum fuel injection amount of each fuel injection valve is (T−M) / T, where T is the total number of cylinders and M is the number of cylinders where continuous misfire has occurred. The marine propulsion system according to any one of claims 1 to 3 , wherein the marine propulsion system has a value that is 10% or more smaller than the value.

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