CN111094726B

CN111094726B - Engine operating method and engine system

Info

Publication number: CN111094726B
Application number: CN201780094729.1A
Authority: CN
Inventors: 黑岩隆典; 桥本彻
Original assignee: Ihi Prime Mover
Current assignee: Ihi Prime Mover
Priority date: 2017-09-11
Filing date: 2017-09-11
Publication date: 2022-08-16
Anticipated expiration: 2037-09-11
Also published as: JP6843250B2; SG11202002151WA; CN111094726A; JPWO2019049362A1; WO2019049362A1

Abstract

In a four-stroke dual-fuel engine (1) for propelling a ship, the engine is operated by switching from any one of the following modes: the gas mode takes gas fuel as a main heat source to carry out speed regulation control on the gas fuel; an assist mode for performing speed control of the liquid fuel using both the gas fuel and the liquid fuel as the fuel; and a diesel mode in which speed control is performed using only liquid fuel as fuel. A control unit (22) of an engine (1) is provided with: an operation control unit (49) for controlling the operation of the engine, a gas governor (44) for controlling the speed of the supply amount of the gas fuel, and a diesel governor (48) for controlling the speed of the supply amount of the liquid fuel. In the assist mode operation, when the output of the engine 1 enters the assist off region, which is a region including the front and rear sides of the cubic characteristic line for the ship, the operation is shifted to the gas mode. In the gas mode-based operation, when the output of the engine (1) enters an assist opening region where the output is larger than an assist closing region, the engine is shifted to an assist mode.

Description

Engine operating method and engine system

Technical Field

The present invention relates to a method of operating a four-stroke dual fuel engine for use in, for example, ship propulsion, and an engine system.

Background

In recent years, restrictions on the discharge of air pollutants from marine propulsion engines have been strengthened. Therefore, introduction of a dual fuel engine is desired which can use a gaseous fuel such as gas as a fuel, reduce the emission of air pollutants, and satisfy exhaust gas regulations. A dual fuel engine is an engine that can be used fueled by both gaseous and liquid fuels.

For example, an engine device described in patent document 1 describes fuel control when an operation state is switched between a gas mode and a diesel mode. When the operation mode is switched from the gas mode to the diesel mode, the fuel gas supply amount is controlled to be monotonically increased while the speed control is performed on the fuel gas supply amount, and when the fuel oil supply amount is equal to or more than a switching threshold, the fuel gas supply amount is monotonically decreased while the speed control is performed on the fuel oil supply amount. In the case of switching the operation mode from the diesel mode to the gas mode, the control is performed by the reverse procedure. In addition, only the gas mode can be switched to the diesel mode instantaneously.

The diesel engine described in patent document 2 discloses a two-stroke large diesel engine that scavenges air in the longitudinal direction. As an operation method of the large diesel engine, during the operation in the gas mode, if a state in which the load is strongly changed is detected, the operation is performed in the transition mode. In the transition mode, for each working cycle of a large diesel engine, there are a step of determining an upper threshold value for the gas quantity of the fuel and a step of determining an additional quantity of liquid fuel to be introduced into the combustion space in addition to the gas.

The engine control device described in patent document 3 is a method for controlling an engine that can be driven using both a liquid fuel and a gaseous fuel. In this method, it is described that the magnitude of the total output to be output from the engine is divided into the amount of contribution of the liquid fuel and the amount of contribution of the gas fuel at a predetermined ratio.

As is well known, in a dual fuel engine capable of performing both an operation using a gas fuel and an operation using a liquid fuel, the operation using the gas fuel (gas mode) is generally performed, and in an emergency or an unstable situation, the operation using the liquid fuel (diesel mode) or the operation using both the gas fuel and the liquid fuel is performed.

In addition, it is known that a diesel engine using liquid fuel is provided with a Variable Intake Valve Timing (VIVT) mechanism.

For example, in the example of the drive mechanism of the variable valve timing mechanism shown in fig. 17, the exhaust valve swing arm 103 or the intake valve swing arm 105 coupled to the rocker arm 127 via the pushrod 128 is connected to the tappet shaft 106 (the fulcrum position of the swing arm) of the crank-like link shaft 104. The phase of the crank-like link shaft 104 is changed (rotated) by the actuator, whereby the fulcrum position of the intake valve swing arm 105 or the exhaust valve swing arm 103 is changed, and as a result, the contact point position to the camshaft 108 is changed.

Thus, the timing at which the cam shaft 108 presses the exhaust valve swing arm 103 or the intake valve swing arm 105 to advance and retract the eccentric cam 108a of the cam shaft 108 is variable.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-57774

Patent document 2: japanese patent laid-open publication No. 2016-217348

Patent document 3: japanese patent No. 4975702

Disclosure of Invention

Problems to be solved by the invention

In a four-stroke engine for propelling a ship, in order to cope with various operating conditions, speed control of a fuel supply amount by a speed governor (speed control device) is performed. In this speed control, the amount of fuel to be supplied is not predetermined, but the amount of fuel supplied is controlled as needed to maintain a constant target rotational speed. In a dual-fuel engine that performs speed control, for example, as described in patent document 1, switching from a gas mode to a diesel mode can be performed in a short time. However, it is difficult to switch from the diesel mode to the gas mode in a short time.

That is, in the gas mode, since the air-fuel ratio range in which the operation with the appropriate fuel can be performed is limited to a narrow range, it is difficult to perform advanced technology for appropriately controlling the speed of the supply amount of the gas fuel while maintaining the appropriate air-fuel ratio. Further, switching from the diesel mode to the rapid gas mode causes knocking or misfire. In the case of the dual fuel engine as described in patent document 1, there is a problem that it takes several tens of seconds or more to switch from the diesel mode to the gas mode in an actual operation.

In the prior art, because it takes time to switch from the operation mode based on the speed regulation control of the liquid fuel to the operation mode based on the speed regulation control of the gas fuel, the switching to the operation mode using the liquid fuel is determined to be abnormal, and the return to the operation mode based on the speed regulation control of the gas fuel is difficult under the condition of a drastic output fluctuation.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a method of operating a dual-fuel engine and an engine system that can smoothly switch between an operation using a gaseous fuel and an operation using a liquid fuel in a shorter time when speed control of a fuel supply amount by a speed governor is performed.

Means for solving the problems

The invention provides an operation method of a dual-fuel engine, which is characterized by comprising the following steps: in a first operation in which a gaseous fuel is used as a main heat source, the speed control of the supply amount of the gaseous fuel is terminated to reduce the supply amount of the gaseous fuel to a predetermined value, and the speed control of the supply amount of the liquid fuel is started, thereby shifting to a second operation in which both the gaseous fuel and the liquid fuel are used as fuels; and in the operation of the second operation, ending the speed control of the supply amount of the liquid fuel to reduce the supply amount of the liquid fuel, and starting the speed control of the supply amount of the gas fuel, thereby returning to the first operation.

In the present invention, when the operation is shifted from the first operation to the second operation, the speed control of the supply amount of the gaseous fuel is ended, the speed control of the supply amount of the liquid fuel is started, and the supply amount of the gaseous fuel is reduced to a predetermined value. The operation of reducing the supply amount of the gaseous fuel to a predetermined value is performed for an extremely short time, for example, within about 1 second. If the supply amount of the gaseous fuel is decreased, the supply amount of the liquid fuel is increased by the action of the speed regulation control of the liquid fuel to maintain the target rotation speed of the engine. Therefore, the transition from the first operation to the second operation is performed without largely affecting the rotation speed of the engine.

When the second operation is returned to the first operation, the speed control of the supply amount of the liquid fuel is ended, the speed control of the supply amount of the gas fuel is started, and the supply amount of the liquid fuel is continuously decreased. If the supply amount of the liquid fuel is continuously decreased, the supply amount of the gaseous fuel is increased by the action of the speed regulation control of the gaseous fuel to maintain the target rotation speed of the engine. Therefore, the return from the second operation to the first operation is performed without largely affecting the rotation speed of the engine.

Preferably, the step of returning to the first operation is performed while the output of the engine is decreasing.

By performing the step of returning to the first operation while the output of the engine is decreasing, the return to the first operation in a short time becomes easy. However, since a sufficient amount of air is secured while the output of the engine is decreasing, it is easy to maintain an appropriate air-fuel ratio, and the direction of fuel supply is restricted in the speed control, so that a rapid increase in the gaseous fuel can be suppressed, and knocking or misfire is less likely to occur. Therefore, by returning to the first operation at this timing, return can be performed in a short time while maintaining appropriate combustion.

In the step of returning to the first operation, the step of reducing the supply amount of the liquid fuel preferably includes a first step of reducing the supply amount of the liquid fuel at a high speed and a second step of reducing the supply amount of the liquid fuel at a low speed.

When the mechanical fuel injection pump is used to supply the liquid fuel, the second stage corresponds to the non-injection region of the mechanical fuel injection pump, and the liquid fuel is not substantially injected.

Further, the step of returning to the first operation may be performed when the output of the engine enters a lower region of an auxiliary close line set in a range of ± 10% with respect to the cubic characteristic line for the ship, and the step of shifting to the second operation may be performed when the output of the engine enters an upper region of an auxiliary open line set above the auxiliary close line.

Here, if the assist close line is set in the output range of ± 10% with respect to the cubic characteristic line for the ship, and the output of the engine enters the area below the assist close line (assist close area), the return to the first operation is performed. If the assist open line is set above the assist close line, the output of the engine enters an area above the assist open line (assist open area), and the operation shifts to the second operation.

In the step of shifting to the second operation, the larger the output of the engine is, the larger the value of the supply amount of the gaseous fuel is.

Even in a region where the output of the engine is large, the return from the second operation to the first operation can be performed quickly.

The invention provides an engine operation method, which is characterized by comprising the following steps: performing a second operation using both the gas fuel and the liquid fuel for speed regulation control as fuels; and ending the speed control of the liquid fuel in the step, continuously reducing the supply amount of the liquid fuel, and performing a first operation of performing the speed control using the gas fuel as a main heat source.

The operation method of the engine of the invention can quickly make a transition from the second operation to the first operation.

The present invention provides an engine operating method, characterized in that the engine is operated by switching from any one of the following modes: the gas mode takes gas fuel as a main heat source to carry out speed regulation control on the gas fuel; an assist mode for performing speed control of the liquid fuel using both the gas fuel and the liquid fuel as the fuel; and a diesel mode in which speed control is performed using only liquid fuel as fuel, and the engine is shifted to a gas mode when the output of the engine enters an assist off region set along a cubic characteristic line for a ship during operation in the assist mode, and is shifted to the assist mode when the output of the engine enters an assist on region in which the output is greater than the assist off region during operation in the gas mode.

According to the present invention, since the return from the assist mode to the gas mode can be performed quickly, the switching and the return of the operation mode are performed stably at any time and quickly between the gas mode and the assist mode under the condition corresponding to the output of the engine. Thereby, occurrence of knocking or misfiring in the gas mode can be avoided in advance, and the operation in the assist mode is limited to the rich torque (トルクリッチ) region that is operated in the abnormal situation where the output is greatly increased, which is also preferable from the viewpoint of environmental measures based on exhaust gas restriction.

In the operation in the assist mode, it is preferable to use a common setting for the operation parameters to be controlled during the operation of the engine and the gas mode.

The present invention provides an engine system, comprising a control unit having: an operation control unit that controls operation of the engine; a gas governor that performs speed control of the supply amount of the gas fuel; and a diesel governor that performs speed control of a supply amount of the liquid fuel, wherein in a first operation in which the operation control unit performs the operation using the gas fuel as a main heat source, the speed control of the gas fuel by the gas governor is ended to reduce the supply amount of the gas fuel, and the speed control of the liquid fuel by the diesel governor is started, so that the operation shifts to a second operation in which both the gas fuel and the liquid fuel are used as fuels, and in the second operation, the speed control of the liquid fuel by the diesel governor is ended to reduce the supply amount of the liquid fuel, and the speed control of the gas fuel by the gas governor is started, so that the operation returns to the first operation.

In the present invention, when the first operation is shifted to the second operation by the operation control unit, the speed control of the supply amount of the gaseous fuel by the gas governor is ended, and the speed control of the supply amount of the liquid fuel by the diesel governor is started by reducing the supply amount of the gaseous fuel to a predetermined value. For example, the operation of reducing the supply amount of the gaseous fuel to a predetermined value is performed in a very short time of about 1 second or less. If the supply amount of the gaseous fuel is decreased, the supply amount of the liquid fuel is increased by the action of the speed regulation control of the liquid fuel to maintain the target rotation speed of the engine.

When the operation is returned from the second operation to the first operation, the speed control of the diesel governor on the supply amount of the liquid fuel is ended, and the supply amount of the liquid fuel is continuously reduced to start the speed control of the gas governor on the supply amount of the gas fuel. If the supply amount of the liquid fuel is decreased, the supply amount of the gaseous fuel is increased by the action of the speed regulation control of the gaseous fuel to maintain the target rotation speed of the engine. Therefore, the switching and returning between the first operation and the second operation are performed without largely affecting the rotation speed of the engine.

Effects of the invention

According to the engine operating method and the engine system provided by the present invention, the first operation and the second operation can be switched to each other, and when the operation is switched from the first operation to the second operation and from the second operation to the first operation, the respective switching can be performed smoothly in a very short time without greatly affecting the rotation speed of the engine.

In addition, occurrence of knocking or misfiring can be avoided in advance in the first operation, and since the second operation is limited to the rich torque region that is operated under unstable conditions, it is also preferable from the viewpoint of environmental measures based on exhaust gas restriction.

Drawings

Fig. 1 is a block diagram showing a main part structure of a dual fuel engine for a ship according to an embodiment of the present invention.

Fig. 2A is a diagram showing a diesel mode in the dual fuel engine.

Fig. 2B is a diagram showing a gas mode in the dual fuel engine.

Fig. 2C is a diagram showing an assist mode in a dual fuel engine.

Fig. 3 is a perspective view showing a relationship between an output, a rotational speed, and a VIVT command value.

Fig. 4 is a perspective view showing a relationship among an output, a rotation speed, and a closing timing of the intake valve.

Fig. 5 is a graph showing a relationship between an output and an optimum VIVT command value when the rotational speed of the output shaft is constant or varies.

Fig. 6 is a graph showing the relationship between the open timing of the fuel gas supply valve and the THC concentration for various VIVT command values.

Fig. 7 is a graph showing the relationship between the output and the opening timing of the fuel gas supply valve when the rotation speed of the output shaft is constant or when the rotation speed changes.

Fig. 8 is a graph showing a fuel gas supply start timing corresponding to the VIVT command value.

Fig. 9 is a diagram showing the configuration of a control device for performing PID control of a marine dual-fuel engine.

Fig. 10 is a diagram showing a process of performing PID control in the gas governor so that the actual rotational speed becomes the target rotational speed.

Fig. 11 is a diagram showing a process of performing PID control in the diesel governor so that the actual rotation speed becomes the target rotation speed.

Fig. 12 is a timing chart showing the opening and closing operations of the intake valve and the fuel gas supply valve in the normal state and in the advanced state.

Fig. 13 is a graph showing a relationship among a cubic characteristic line for a ship, an auxiliary open region, and an auxiliary close region.

Fig. 14 is a graph showing an output and a governor command value when switching from the gas mode to the assist mode.

Fig. 15 is a graph showing an output and a governor command value when returning from the assist mode to the gas mode.

Fig. 16A is a process diagram of a normal cycle of the combustion cycle of the engine.

Fig. 16B is a process diagram of the miller cycle of the combustion cycle of the engine.

Fig. 17 is a diagram showing a conventional variable intake valve timing mechanism.

Detailed Description

First, a Variable Intake Valve Timing (VIVT) mechanism will be described as a dual fuel engine of the present invention.

That is, the present inventors have found that by changing the opening timing (supply start) of the fuel gas supply valve at each VIVT angle, determining an optimum value from the THC concentration and the combustion state, and setting the opening timing of the fuel gas supply valve in accordance with the VIVT angle, it is possible to suppress knocking that occurs when the output of the gas fuel engine is increased, shorten the load increase time, and improve combustion fluctuation and rotational speed fluctuation caused by the opening timing of the fuel gas supply valve in the rich torque region and the lean torque (トルクプア) region.

As a knock suppression technique for an engine, a Variable Intake Valve Timing (VIVT) mechanism can be used to reduce an effective compression ratio. This point will be described with reference to fig. 16A and 16B. Fig. 16A shows a process of a normal four-stroke cycle, and fig. 16B shows a process of a miller cycle.

For example, in a gaseous fuel engine, the intake valve is normally closed at the bottom dead center of the piston (see fig. 16A). On the other hand, if the closing timing is set earlier than the bottom dead center as shown in fig. 16B, the expansion of the air-fuel mixture continues after the intake valve closes, and the in-cylinder temperature Ts becomes lower than that in fig. 16A (Ts < Ts). Accordingly, the maximum compression temperature at top dead center is also lowered (Tc < Tc), whereby spontaneous combustion is prevented and knocking is suppressed.

As a drawback of the miller cycle, since the compression temperature is lowered and the ignitability in the low load range is deteriorated, at the time of start-up or at the time of low load, it is necessary to return to the normal open timing of the intake valve shown in fig. 16A, and to make the open timing of the intake valve earlier only at the time of high load.

Hereinafter, as an engine according to an embodiment of the present invention, a four-stroke, for example, dual fuel engine 1 used for a marine engine will be described based on the drawings.

The marine dual fuel engine 1 (hereinafter, may be simply referred to As the engine 1) shown in fig. 1 and 2 can be switched to any one of the diesel mode D, the gas mode G, and the assist mode As during operation. A dual fuel engine 1 shown in fig. 1 includes a mechanism of a crankshaft 2 as an output shaft connected to a propeller or the like, and the crankshaft 2 is connected to a piston 4 provided in a cylinder block 3. A combustion chamber 6 is formed by a piston 4 and an engine head 5 provided in the cylinder block 3.

The combustion chamber 6 is sealed by an intake valve 8 and an exhaust valve 9 attached to the engine head 5 and a fuel injection valve 10 used in the diesel mode D. The engine head 5 is provided with a micro pilot injection valve 11 used in a gas mode. A fuel injection pump 12 is connected to the fuel injection valve 10. An intake pipe 13 is connected to an intake port of the intake valve 8 provided in the engine head 5, and an exhaust pipe 14 is provided to an exhaust port provided in the exhaust valve 9. A fuel gas supply valve 15 constituted by an electromagnetic valve that controls gas injection is provided at the intake pipe 13, and an air cooler 16 and a supercharger 17 that communicates with the exhaust pipe 14 are provided on the upstream side thereof.

Here, As shown in fig. 2A, 2B, and 2C, the dual-fuel engine 1 according to the present embodiment can be switched to any one of the diesel mode D, the gas mode G, and the assist mode As for operation. In the diesel mode D shown in fig. 2A, for example, heavy oil a or the like is supplied as fuel oil from a fuel tank, not shown, to a fuel injection pump, and compressed air mechanically injected from the fuel injection valve 10 into the combustion chamber 6 is ignited and burned.

In the gas mode G shown in fig. 2B, a fuel gas such as natural gas is supplied to the intake pipe 13 from the fuel gas supply valve 15, premixed with an air flow, and the mixture is supplied into the combustion chamber 6, and ignited by the ignition device in a compressed state of the mixture, and in this embodiment, pilot fuel is injected from the micro pilot fuel injection valve 11 to ignite and burn. The micro pilot injection valve 11 is electronically controlled, for example, and injects a small amount of pilot fuel as a strong ignition source. The fuel gas supply valve 15 is an electromagnetic valve capable of forming a large opening with a small stroke and flowing a large amount of gas in a short time.

In the assist mode As shown in fig. 2C, fuel oil is injected from the fuel injection valve 10 into the combustion chamber 6 by the throttle control, and fuel gas is supplied from the fuel gas supply valve 15 into the intake pipe 13.

The gas mode G includes both an operation mode in which ignition is performed by an ignition plug using only a gaseous fuel (gaseous fuel) as a fuel and an operation mode in which injection of a small amount of liquid fuel (pilot oil) is used for ignition of the gaseous fuel that occupies a main heat source. In the latter operation mode, the proportion of the liquid fuel in all the fuels is usually about 1% to 10% of the total heat in the heat quantity comparison at the rated output. From the viewpoint of achieving environmental restrictions on exhaust gas, 3% or less is desirable.

The assist mode As is an operation mode in which both the gas fuel and the liquid fuel are used As fuels and the speed control of the supply amount of the liquid fuel is performed. From the side of environmental measures, the assist mode As using liquid fuel preferably sets the operating time to the required minimum, returning to the gas mode immediately when the assist mode is no longer required. In the assist mode As, fuel oil is injected from the fuel injection valve 10 into the combustion chamber 6 to be combusted, and pilot fuel is also injected from the micro pilot fuel injection valve 11 into the combustion chamber 6 to be combusted.

The diesel mode D is an operation mode mainly used for starting and stopping the engine and operated using only liquid fuel as fuel.

The engine 1 is started in a diesel mode D in which liquid fuel is injected into the combustion chamber 6 through the fuel injection valve 10. After the supply of the gas pressure equal to or higher than the reference value to the engine 1 is confirmed, the gas mode G is operated in which the gas fuel is supplied to the intake pipe 13 by the fuel gas supply valve 15, mixed with air, and then flows into the combustion chamber 6 to combust the gas fuel.

When the vehicle stops, the mode is changed to the diesel mode D again, and then the vehicle stops. The diesel mode D and the gas mode G can be changed other than the start and stop.

In the steady operation, the engine 1 is theoretically operated in the gas mode in accordance with the relationship between the rotational speed and the output along the cubic characteristic line for the ship. The cubic characteristic for a ship is a characteristic of a main combustion engine (engine 1) for a ship, which outputs an output proportional to the cube of the rotation speed, in a ship using a fixed pitch propeller. In addition to the steady operation, when a ship is sailed in a storm weather or is driven for a quick route change, an output that is much higher than a normal operation region having cubic characteristics for the ship or more may be required, and the operation in the gas mode G may be insufficient and difficult to operate, and therefore, the liquid fuel is supplied into the combustion chamber 6 once and is operated in the assist mode As together with the gas fuel. The operation in the assist mode As is preferred because liquid fuel is used by the governor control, so that the process is performed in a required minimum time in consideration of the influence on the environment, and the gas mode G is quickly returned when the assist mode As is no longer required.

The dual-fuel engine 1 according to the present embodiment is provided with a gas engine system that performs output control when the load is increased in the gas mode G. The structure of the gas engine system will be explained.

In fig. 1, a rotational speed sensor 20 and a torque sensor 21 are attached to a crankshaft 2, the rotational speed (rotational speed) of the crankshaft 2 is measured by the rotational speed sensor 20, and the engine torque is measured by the torque sensor 21. As the torque sensor 21, a sensor that detects torque applied to the shaft by deformation, for example, can be used. The measurement data measured by the rotation speed sensor 20 and the torque sensor 21 are output as signals to a control unit 22 that controls the engine 1.

The control unit 22 detects the operating state of the engine 1 based on signals from the rotational speed sensor 20, the torque sensor 21, and the like. That is, the output (load) a of the engine 1 is calculated by the following equations (1) and (2) with n being the rotational speed (rotational speed) of the crankshaft 2 measured by the rotational speed sensor 20 and T being the torque measured by the torque sensor 21. Here, Lt is set as the rated output of the engine 1.

Output Lo 2 pi Tn/60 (1)

Output (load) A Lo/Lt × 100 (2)

Further, as a method of obtaining the output (load) of the engine 1, there are a method of estimating information relating to the operating state of the engine 1 other than the fuel supply amount and a method of obtaining the output by actually measuring the torque by providing the torque sensor 21 in the power transmission system of the output shaft of the engine 1. In a gas fuel engine, since a gas to be a fuel is an elastic body, it is relatively difficult to obtain an accurate supply amount of the fuel as compared with a liquid fuel. Therefore, it is preferable that the output is calculated by actually measuring the torque by the torque sensor 21.

When the rotation speed n is constant, the output a and the torque measurement value T are in a proportional relationship. It is desirable that the larger the output a, that is, the larger the torque data T, the larger the proportion of the advance angle setting of the timing of closing the intake valve 8 is, under the condition that the rotation speed n is constant.

The control unit 22 stores a first map 24 in which a first electric signal for determining the opening/closing timing of the intake valve is created in advance, and a second map 25 in which a second electric signal is determined based on the first electric signal and the opening/closing timing. The control unit 22 calculates the output a of the engine 1 by the above equations (1) and (2) based on the rotational speed data n and the torque data T corresponding to the output a of the engine 1 measured by the rotational speed sensor 20 and the torque sensor 21. The first electric signal corresponding to the opening and closing timing of the intake valve 8 is selected in the first map 24 by the rotation speed n and the output a. The opening/closing timing of the intake valve 8 corresponding to the first electric signal is determined in the second map 25 based on the first electric signal. Further, the creating methods of the first fig. 24 and the second fig. 25 are described later.

The second electric signal of the opening/closing timing set by the control unit 22 is sent to the electro-pneumatic transducer 27, and the signal of the opening/closing timing is converted into the air pressure by the electro-pneumatic transducer 27. This air pressure is sent to the actuator 28, and the driving of the variable intake valve timing mechanism 30 is controlled. The first pressure reducing regulator 34 and the electro-pneumatic converter 27 supply driving and control air pressures P1 and P2 to the actuator 28.

The air pressure supplied to the actuator 28 is compressed by an air compressor 32 and stored in an air tank 33. The air pressure in the air tank 33 is reduced to a desired pressure by the first pressure reducing regulator 34. The pressure at this time is adjusted by changing the valve opening degree of the first pressure reducing regulator 34, and is supplied to the actuator 28 as the driving air pressure P1. If the pressure P1 measured by the pressure gauge 36 is equal to or less than a predetermined value, the engine 1 cannot be started.

The second pressure reducing regulator 37 supplies the air pressure for driving the electro-pneumatic converter 27 from the first pressure reducing regulator 34 after further reducing the pressure. The electro-pneumatic converter 27 supplies the air pressure corresponding to the input second electric signal of the opening/closing timing to the actuator 28 as the air pressure P2 for adjusting the operation of the actuator 28. The variable intake valve timing mechanism 30 is operated by operating the rod 28a of the actuator 28 based on these air pressures P1, P2.

The actuator 28 is, for example, a well-known P cylinder (a cylinder with a positioner), and controls the advance and retreat of the rod 28a based on pressures P1, P2 input from the first pressure reducing regulator 34 and the electro-pneumatic transducer 27. The driving of the variable intake valve timing mechanism 30 is controlled by changing the moving length of the rod 28a of the actuator 28, and the timing of closing the intake valve 8 is advanced (advanced) or retarded (retarded) from the intake bottom dead center, thereby lowering the compression ratio for control. Since the time between the open timing and the closed timing of the intake valve 8 does not change, if the open timing is advanced from the intake bottom dead center, the closed timing is also advanced from the intake top dead center by the same time. In the present embodiment, the timing of opening and closing the valve is changed in accordance with the output of the engine 1, thereby suppressing knocking and shortening the load increase time. The opening/closing timing of the intake valve 8 is set by the first fig. 24 and the second fig. 25 in the control unit 22 based on the output a and the rotation speed n of the engine 1, and the opening/closing timing of the intake valve 8 is adjusted by the actuator 28 and the variable intake valve timing mechanism 30 so that knocking can be suppressed.

The structure of the variable intake valve timing mechanism 30 is known, and has the same configuration as that shown in fig. 17. That is, the variable intake valve timing mechanism 30 is disposed in parallel with a link shaft and a camshaft including an eccentric cam, for example, in which a rotational angle range is set according to the movement length of the rod 28a of the actuator 28. An exhaust swing arm is connected to the link shaft, and an intake swing arm is connected to a tappet shaft provided at a position eccentric to the link shaft. An intake valve 8 is connected to the intake swing arm, and an exhaust valve 9 is connected to the exhaust swing arm.

According to the rotation angle of the tappet shaft corresponding to the rotation of the connecting rod shaft, the distance between the camshaft and the intake swing arm changes, and the timing at which the eccentric cam of the camshaft starts to abut changes. This enables the valve closing timing to be changed to the advanced angle (or the retarded angle). The farther the distance from the tappet shaft to the camshaft center is, the earlier the closing timing of the intake valve 8 is. The rotation angle of the tappet shaft is changed according to the moving length of the rod 28a of the actuator 28. The moving length of the rod 28a is arbitrarily changed by the pressures P1 and P2 of the control air supplied to the actuator 28.

The opening/closing timing of the intake valve 8, that is, the magnitude of the advance angle is determined by the timing at which the eccentric cam of the camshaft starts to abut against the intake swing arm coupled to the tappet shaft of the link shaft.

The actuator 28 may be replaced with a servo motor, not shown, in the rotating device of the tappet shaft in the variable intake valve timing mechanism 30. In this case, the opening/closing timing signal transmitted from the second fig. 25 of the control unit 22 is input to the servo motor. The servo motor rotates the link shaft by an amount corresponding to the received signal to rotate the tappet shaft, thereby moving the tappet shaft closer to and away from the camshaft and changing the opening/closing timing of the intake valve 8. Further, in the case of using a servo motor, the actuator 28 and the structure from the air compressor 32 to the pressure gauge 38 are not required. In addition, the servo motor is driven by a controller instead of the electro-pneumatic transducer 27.

A supply mechanism for supplying gaseous fuel to the fuel gas supply valve 15 that controls gas injection in the intake pipe 13 will be described. In fig. 1, a gas fuel is supplied from an LNG gas tank 40 storing a gas fuel such as natural gas to a gas vaporizer 41, and the gas pressure is reduced to a desired gas pressure by a gas regulator 42.

The gas pressure is displayed on the fuel gas pressure gauge 43, and the valve opening of the gas regulator 42 is changed to adjust the gas pressure, so that the gas pressure is supplied as the fuel gas for combustion from the fuel gas supply valve 15 into the intake pipe 13. In the intake pipe 13, the gas fuel and the supercharged air cooled by the air cooler 16 are mixed and supplied to the combustion chamber 6. When the load increases, the supply amount of the gas fuel is increased by the operation of the fuel gas supply valve 15.

The second electric signal of the opening and closing timing set by the control portion 22 is sent to the fuel gas supply valve 15 via the gas governor 44 separately from the electro-pneumatic converter 27. The gas governor 44 performs speed regulation control (governor control) of the supply amount of the gas fuel in the gas mode. The gas governor 44 opens the fuel gas supply valve 15 by an advance angle according to the closing timing of the intake valve 8 to advance the valve opening timing for supplying the gaseous fuel into the intake pipe 13. A gas regulator 42 for adjusting the gas pressure and a gas governor 44 for advancing the valve opening timing of the fuel gas supply valve 15 and performing speed control are included in the fuel gas supply valve timing mechanism 45. The gas governor 44 may be provided outside the control unit 22. The fuel gas supply valve timing mechanism 45 may receive the second electric signal from the second fig. 25, and may advance the opening timing of the fuel gas supply valve 15 in accordance with the advance angle of the closing timing of the intake valve 8.

The control unit 22 is provided with a diesel governor 48 for controlling the speed of the liquid fuel in the assist mode As. The diesel governor 48 receives the second electric signal of the opening/closing timing, supplies the second electric signal to the fuel injection pump 12, and controls the supply amount of the fuel oil injected from the fuel injection valve 10 into the combustion chamber 6. The diesel governor 48 may be provided outside the control unit 22.

The diesel governor 48 performs speed control of the liquid fuel in the assist mode As to adjust the supply amount of the liquid fuel so As to meet the target rotational speed of the engine 1. When the assist mode As returns to the gas mode G, the speed control for the liquid fuel is ended.

The control unit 22 includes the configuration shown in fig. 24 and 25 as an operation control unit 49, and includes a gas governor 44 and a diesel governor 48 separately from the operation control unit 49.

Next, a method of creating the first and second fig. 24 and 25 stored in the control unit 22 will be described. Fig. 3 is a perspective view showing details of the first fig. 24 in which the VIVT command value (Intake Valve Closed crank angle, IVC), that is, the crank angle at which the Intake Valve 8 is Closed, is determined based on the rotational speed of the crankshaft 2 and the output (load factor) of the engine 1.

In fig. 3, a region B in which a usual (practical) operation is performed is indicated by a broken line. On the other hand, an arrow C indicates a change (advance angle) in the VIVT command value with respect to a change in output when the rotational speed is constant during power generation, and an arrow D indicates a change (advance angle) in the VIVT command value when the rotational speed and the output (load factor) change simultaneously during use of the ship. The arrow line D indicates the cubic characteristic for the ship. The cubic characteristic for a ship represents a representative characteristic of a main combustion engine for a ship in which an output is proportional to the cube of a rotation speed, and is a characteristic curve of a rotation speed and an output determined by a rated rotation speed and a rated output of the combustion engine. In the region of the usual operation region B, a region where the output (load factor) is higher than the cubic characteristic line D for the ship represents a rich torque region, and a region where the output (load factor) is lower than the cubic characteristic line D for the ship represents a lean torque region.

The first map 24 is created based on the following course of experimental steps (1) to (18).

In the experiment, the same model of the dual fuel engine 1 used in practice was used.

(1) The engine 1 is started and the rotational speed (number of revolutions) n is set to 400min ^－1 The output (load) a is set to 10%, and the closing timing of the intake valve 8 is set to 545deg (the closing timing which is the latest in structure).

(2) Abnormal combustion called knocking that occurs while the engine 1 is driven and the exhaust gas temperature at that time are measured. The occurrence of knocking is detected by a knock sensor, not shown, attached to each engine head 5. When the knocking phenomenon occurs, a waveform is formed in which high-frequency pressure fluctuations overlap with a normal combustion waveform.

Further, the exhaust temperature at the time of knock measurement is measured by a temperature sensor attached to the exhaust pipe 14.

(3) After the measurement of the exhaust temperature at the time of the knock measurement is completed, the closing timing of the intake valve 8 is decreased by 5deg, and the measurement of (2) is performed again. The valve closing timing was changed to 500deg (the first valve closing timing in terms of structure) and measured.

(4) After the measurement of (3) above, the output a is increased stepwise to 110% by 10% each time, and the measurements of (2) and (3) are repeated again.

(5) By the above measurements (1) to (4), it is determined that knocking is suppressed and the engine 1 can be operated safely when the knock intensity is equal to or less than the reference value and the exhaust gas temperature is equal to or less than 500 ℃.

(6) From the measurement results of the above (5), in the perspective view of fig. 4 in which the X axis is set as the output a, the Y axis is set as the rotation speed n, and the Z axis is set as the opening/closing timing, ● (black circle) is plotted at the measurement point where safe operation is possible, and X is plotted at the measurement point where unsafe operation is possible. This makes it possible to select a knock suppression range in which the output a, the rotation speed n, and the valve closing timing are related.

(7) The rotation speed n is set to be 100min at a time ^－1 Increasing the time to 900min ^－1 The measurement steps (1) to (6) are performed to measure the range of safe operation for each rotation speed n.

(8) Fig. 4 is a graph showing the measurement results of the above (7) on three axes of the rotation speed n, the output a, and the valve closing timing. In fig. 4, the range surrounded by the straight line is a range in which knocking is suppressed and the engine 1 can be operated safely.

(9) In the range of the solid region surrounded by the straight line, which is shown in fig. 4 and is capable of safely operating the engine, and which is measured by the experiments of (1) to (8) above, the experiments were further performed with the objective of finding nitrogen oxides (hereinafter referred to as NOx) at or below the reference value and setting the thermal efficiency to be the highest.

The engine rotation speed n is set to 400min ^－1 The output a is set to 10%, and the closing timing of the intake valve 8 is set to 545 deg.

(10) NOx and thermal efficiency were measured next. NOx is measured by an exhaust gas analyzer mounted on the exhaust pipe 14. The thermal efficiency is calculated by the following equation (3) from the fuel flow rate L measured from the fuel flow meter attached to the fuel piping and the output a calculated from the measurement result of the torque sensor 21.

Thermal efficiency eta is 360Lo/H/L (3)

Wherein, H: lower heating value (J/Nm) of fuel gas ³ )

Lo: current output

L: flow rate of fuel

(11) After the measurement of (10) above, the closing timing of the intake valve 8 is gradually decreased by 5deg each time, and the measurement of (10) is performed again. The valve closing timing was changed to 505deg and measured (see fig. 9).

(12) After the measurement of (10) and (11) above is completed, the output is increased stepwise to 110% by 10% each time, and the measurement of (10) and (11) is repeated again. The valve closing timing is changed within a range in which safe operation is possible as shown in fig. 4.

(13) The rotation speed n is set to be 100min at a time ^－1 Ascending to 900min in a stepped manner ^－1 The above-described measurements (9) to (12) are performed, and the measurement point having the best performance for each rotation speed is determined.

(14) The closing timing of the intake valve 8 at which NOx is equal to or less than a predetermined value and which has the highest thermal efficiency is set for each of the rotation speed n and the output a. From the result, a master of the first diagram shown in fig. 3 was created.

(15) Knock is detected by increasing the rotation speed n and the output a in an arbitrary load increase mode. The load increase mode is a state in which the output a (load factor) and the rotation speed n change with time, and changes according to the propeller specifications (shape, rotation speed) of the marine propulsion device.

(16) The valve closing timing of the measurement point at which the knock intensity detected in (15) is equal to or greater than the reference value is reduced by 3 deg.

(17) The steps (15) and (16) are repeated until the knock intensity becomes equal to or less than the reference value, and the valve closing timing at which knocking is suppressed is determined. If the valve closing timing is decreased, the thermal efficiency is deteriorated. The setting of the valve closing timing at which the results that NOx and knock intensity are equal to or less than the reference values and the thermal efficiency is highest is set as the set values of the rotation speed n and the output a.

(18) The valve closing timing at which knocking is suppressed by the above (17) is measured at each rotation speed n and output a, and a final first map 24 shown in fig. 3 is created from the result.

In fig. 3, the VIVT command value corresponding to the rotation speed and the output is shown by a graph of a solid plane, and the upper side in the figure is a direction in which the valve closing timing is further advanced. In the three-dimensional plane, the region indicated by the broken line is a practical operation region used for the actual operation of the ship propulsion device, and an example of a good load-raising pattern is indicated by the cubic characteristic line D for the ship. In a practical operating region, the load is increased, and control is performed so as to increase the advance angle of the valve closing timing as the output of the internal combustion engine increases.

In one example of a favorable load-raising mode represented by the cubic characteristic line D for a ship, the advance angle is set to be minimum at a position lower right in the figure where the rotation speed and the output are small, and the advance angle is increased as the rotation speed and the output increase. The rate of increasing the advance angle is not constant, but as a whole, the more the output increases, the larger the advance angle. Further, since the output (load factor) is obtained from the product of the torque and the rotational speed, it can also be expressed that the advance angle increases as the torque of the output shaft increases.

Next, a second fig. 25 was created by the experiment described below.

The second map 25 is created by the following steps when the variable intake valve timing mechanism 30 is rotation-controlled by the actuator 28.

(1) The valve closing timing is changed by the actuator 28, and the pressure at the time of each valve closing timing is measured.

(2) The second electric signal required for supplying the pressure of (1) above is checked according to the specification of the electro-pneumatic transducer 27.

(3) From the results of (1) and (2) above, a second graph 25 is created in which the first electric signal selected in the first graph 24 is shown on the horizontal axis and the valve closing timing (second electric signal) is shown on the vertical axis.

Note that the above description is of the case where the actuator 28 is used, and the following operation is performed for the case where the rotation of the variable intake valve timing mechanism 30 is controlled by the servo motor instead of the actuator 28.

(1) The valve closing timing is changed based on the servo motor, and the second electric signal when the valve closing timing is changed is measured.

(2) From the result of the above (1), a second graph 25 is created in which the first electric signal is represented on the horizontal axis and the valve closing timing (second electric signal) is represented on the vertical axis.

The second fig. 25 is a diagram showing a relationship between the valve closing timing (second electric signal) and the first electric signal.

In the perspective view shown in fig. 3, the optimum VIVT command value differs depending on the output on the power generation characteristic line shown by the solid line C and the ship cubic characteristic line D. That is, as shown as an example in fig. 5, even in the case where the outputs are the same, the intake valve closing crank angle of the optimum VIVT command value differs when the rotational speed differs.

In the present embodiment, the opening timing of the fuel gas supply valve 15 that supplies fuel gas to the intake pipe 13 is set so that blow-by of unburned fuel gas to the exhaust pipe 14 caused when the valves of the intake valve 8 and the exhaust valve 9 overlap becomes small in response to a change in the VIVT command value, that is, with respect to various intake valve closing crank angles. For this purpose, a VIVT command value corresponding to the rotation speed and the output is first set. Strictly speaking, it is preferable to set the thermal efficiency or NOx as the optimum value for the air-fuel ratio or ignition timing as the standard, but these conditions are not set here assuming that the engine 1 can be operated stably.

As an example of setting the open timing of the fuel gas supply valve 15, a method of determining the open timing of the fuel gas supply valve 15 by the gas governor 44 under the engine operating condition that matches the optimal VIVT command value in the cubic characteristic line D for the ship will be described below.

First, under each of the operating conditions in which the output (load factor) of the engine is 25%, 50%, 75%, and 100%, the fuel gas is supplied from the fuel gas supply valve 15 with the timing of opening the intake valve 8 as a criterion, but the fuel gas is supplied into the intake pipe 13, so the fuel gas does not instantaneously reach the intake valve 8. Therefore, the crank angle position at the valve opening timing of the fuel gas supply valve 15 is assumed in consideration of the distance from the fuel gas supply valve 15 to the intake valve 8. The crank angle position at the valve opening timing of the fuel gas supply valve 15 was changed by 5deg before and after the change, and the total hydrocarbon concentration (THC concentration) as unburned gas in the exhaust gas at the gas turbine outlet of the supercharger 17 at that time was measured. The THC concentration measurement was repeated at each operating condition. The THC concentration is preferably measured by a hydrogen flame ionization method (JIS B7956).

The open timing of the fuel gas supply valve 15 is changed according to each condition, and each VIVT command value (intake valve closing crank angle) is set to, for example, 40%, 65%, 85%, 100%, and fig. 6 shows the relationship between the fuel gas open timing and the measured THC concentration for each VIVT command value.

As shown in fig. 6, the open timing of the fuel gas supply valve 15 is set as a reference at a crank angle at which blow-by of unburned fuel gas is small and THC concentration is lowest at the time of valve overlap. On the other hand, if the opening timing of the fuel gas supply valve 15 changes abruptly due to an output change, the above-described combustion fluctuation or rotation speed fluctuation is linked. Therefore, the crank angle of the optimum fuel gas valve opening timing of the fuel gas supply valve 15 is selected from the range of ± 5deg.c.a from the selected reference so that the variation amount of the valve opening timing of the fuel gas supply valve 15 according to the output tends to be as small as possible, and the crank angle corresponding to the optimum valve opening timing of the fuel gas supply valve 15 is determined under each condition.

The broken line of the "rotation speed change" in fig. 7 shows the relationship between the crank angle and the output (load factor) of the optimum fuel gas supply valve 15 at the valve opening timing in the optimum VIVT command value of the cubic characteristic line D for the ship determined in this manner.

Similarly, the broken line of "constant rotational speed" in fig. 7 shows the relationship between the crank angle and the output (load factor) of the optimum fuel gas supply valve 15 at the opening timing of the optimum VIVT command value in the output with the constant rotational speed, which is obtained from the power generation characteristic line C in fig. 3.

As shown in fig. 7, the results are: even if the output is the same, the optimum opening timing of the fuel gas supply valve 15 differs between the condition where the rotation speed varies and the condition where the rotation speed is constant.

However, as shown in fig. 8, if the abscissa is adjusted to the VIVT command value instead of the output, the crank angle at the optimum opening timing of the fuel gas supply valve 15 in the optimum VIVT command value of the cubic characteristic line D for the marine vessel and the crank angle at the optimum opening timing of the fuel gas supply valve 15 in the optimum VIVT command value of the power generation characteristic line C (constant rotational speed) show one line pattern characteristic. That is, the valve opening timing of the fuel gas supply valve 15 determined to be optimal depends on the VIVT specified value (intake valve closing crank angle) without depending on the output.

As is apparent from fig. 8, if the closing timing of the intake valve 8 is changed by the variable intake valve timing mechanism 30, the degree of advance of the supply start timing of the fuel gas supply valve 15 increases as the closing timing of the intake valve 8 advances.

Therefore, the optimum crank angle of the open timing of the fuel gas supply valve 15 determined under each condition is set by the gas governor 44 based on the VIVT command value, whereby the open timing of the fuel gas supply valve 15 can be optimized based on the VIVT command value. In fig. 8, the non-measured VIVT command value, the fuel gas supply start timing, and the like may be determined by an approximate line connecting data before and after the measurement point.

Next, the timing control of the end of the fuel gas supply by the fuel gas supply valve 15 will be described with reference to fig. 9 to 11.

Fig. 9 shows a main part structure of the engine 1 shown in fig. 1. In fig. 9, a target rotation speed command unit 50 is provided outside the control unit 22, and a preset target rotation speed is input to the control unit 22. The gas supply time calculation unit 51 of the control unit 22 directly performs PID control of the valve opening period of the fuel gas supply valve 15 based on the deviation between the actual rotation speed calculated from the measurement value of the rotation speed sensor 20 and the target rotation speed.

The gas supply valve control unit 52 connected to the gas supply time calculation unit 51 performs feedback control as follows: the time to be opened is calculated starting from the opening timing of the fuel gas supply valve 15, and the calculated time is output to the fuel gas supply valve 15 to open the fuel gas supply valve 15.

A rack target value setting means 57 is disposed in the control unit 22, and the rack target value setting means 57 sets a target position of a control rack, not shown, by the target rotational speed set by the target rotational speed command unit 50. The rack position of the fuel injection valve 10 is feedback-controlled by the target value of the rack position set by the rack target value setting unit 57.

The closing timing of the fuel gas supply valve 15 is controlled as follows. That is, as shown in fig. 10, the control unit 22 directly performs PID control of the valve opening period of the fuel gas supply valve 15 based on the deviation between the target rotation speed set by the target rotation speed command unit 50 and the actual rotation speed. Specifically, based on the deviation between the target rotation speed and the actual rotation speed, the time for which each fuel gas supply valve 15 is opened is controlled by the gas governor 44 such that the actual rotation speed follows the target rotation speed through feedback control.

The gas supply valve control unit 52 controls the closing timing of each fuel gas supply valve 15 based on the valve opening period calculated from the opening timing of the fuel gas supply valve 15 as a starting point. The control unit 22 directly performs PID control of the valve opening period of the fuel gas supply valve 15 so that the actual rotation speed matches the target rotation speed without calculating the amount of fuel gas to be supplied in advance.

The fuel gas supply pressure is controlled so as to eliminate a deviation between a value obtained by adding the boost pressure detected by the boost pressure gauge 54 provided in the intake pipe 13 to a pressure Δ P value set using data of the output and the rotational speed of the engine 1 as parameters and a value of the fuel gas pressure gauge 43, and the fuel gas supply pressure is feedback-controlled by the fuel gas pressure regulator 55.

The fuel injection pump 12 and the fuel injection valve 10 of the liquid fuel are controlled as follows. That is, as shown in fig. 11, the control unit 22 directly performs PID control of the rack position of the fuel injection pump 12 based on the deviation between the target rotation speed set by the target rotation speed command unit 50 and the actual rotation speed. Specifically, the rack position of the fuel injection pump 12 is changed by the diesel governor 48 based on the deviation between the target rotational speed and the actual rotational speed such that the actual rotational speed follows the target rotational speed through feedback control, whereby the injection amount of the liquid fuel injected from the fuel injection valve 10 is increased or decreased, and the rotational speed of the engine 1 is increased or decreased.

Fig. 12 shows the relationship between the advance angle of the variable intake valve timing mechanism 30 and the timing of starting and ending the supply of the fuel gas supply valve 15 by the gas governor 44, which shows the above results.

Fig. 12 shows a relationship between the crank angle of the engine 1 and the valve lifts of the intake valve 8 and the exhaust valve 9. In the graph showing the opening and closing operation of the intake valve 8, the solid line shows the opening and closing operation image when the VIVT (variable intake valve timing) command value is 0%, and the dashed-dotted line shows the opening and closing operation image when the angle is advanced (the VIVT command value is 100%). Further, the valve-opening period of the fuel gas supply valve 15 at the time of the advance (the VIVT command value is 100%) becomes longer than the valve-opening period of the fuel gas supply valve 15 when the VIVT command value is 0%.

Further, it is preferable that the supply pressure of the fuel gas be raised and the fuel supply amount be increased as the closing timing of the intake valve 8 is advanced. Therefore, in fig. 9, the supply pressure of the fuel gas into the intake pipe 13 is set to a value obtained by adding a pressure Δ P to the supercharging pressure detected by the supercharging pressure gauge 54 provided in the intake pipe 13. The pressure Δ P is a parameter obtained by measuring data of the output and the rotational speed of the plurality of engines 1 in advance. As a result, the supply pressure of the fuel gas supplied from the fuel gas supply valve 15 increases with the advance of the timing of closing the intake valve 8.

Next, the relationship between the cubic characteristic line for the ship and the assist ON (ON) region and the assist OFF (OFF) region during the operation of the engine 1 controlled by the control unit 22 will be described. In the graph of fig. 13, the horizontal axis represents the rotation speed of the engine 1, and the vertical axis represents the output (kw).

The cubic characteristic line for a ship is a characteristic of a ship main combustion engine whose output is proportional to the cube of the rotation speed in a ship using a fixed pitch propeller, and is a basic control output level of the engine 1. However, the relationship between the output and the rotation speed is not limited to being exactly proportional to the cube, and may have a certain degree of deviation. In the figure, the range of plus or minus 10% with respect to the ship cubic characteristic line is shown by a broken line. The auxiliary close line is set in the range of plus or minus 10%. The auxiliary closing line is preferably set along the cubic characteristic line for the ship, and in the present embodiment, as shown by a long dashed line in the figure, the auxiliary closing line is set to a line along the cubic characteristic line for the ship slightly above the cubic characteristic line for the ship. The lower region of the auxiliary closing line is set as an auxiliary closing region. In addition, an auxiliary opening line is set above the auxiliary closing line. It is preferable to set the assist opening line in accordance with the characteristics of the engine 1 in the output of the unusual operation above a certain degree of the cubic characteristic line for the ship. In the present embodiment, as shown by the chain line in the figure, the line is set so as to exceed the cubic characteristic line for the ship at a certain ratio from the idle speed to the intermediate rotation speed and to approach the cubic characteristic line for the ship at the rated rotation speed from the intermediate rotation speed. The area above the auxiliary open line is set as an auxiliary open area. Note that these auxiliary open lines, auxiliary close lines, and the like represent concepts in control, do not mean physical lines, and are preferably functions in a program installed in a computer.

The operation in the gas mode G is stably performed in the vicinity of the cubic characteristic line for the ship, but the output may temporarily increase with respect to the rotation speed as indicated by an arrow (a). In the operation based on the gas mode G, if the output is raised and the assist on region is entered, the operation is shifted to the operation based on the assist mode As. After that, if the state of the output increased with respect to the rotation speed is canceled, the output is lowered to the vicinity of the cubic characteristic line for the ship as shown by an arrow (B). If the output decreases, the auxiliary off region is entered, and operation in the gas mode G is returned.

Since the operation in the assist mode As is limited to the rich torque region where the output is increased, it is also preferable from the side of environmental measures. In the assist mode As, As indicated by a broken line in a command image of the gas governor, the gas governor is controlled to supply a predetermined value of gas fuel in accordance with the rotational speed.

Next, the operation at the time of switching between the gas mode G and the assist mode As will be described with reference to the timing charts shown in fig. 14 and 15.

Fig. 14 is a timing chart showing an operation when the gas mode G is shifted to the assist mode As. When a ship is driven, such as when the ship is sailing or a rapid route change is performed in stormy weather, the output (load) with respect to the rotation speed increases. If the output (load) exceeds the preset assist enable line, the mode shifts to assist mode As. In this case, the gas governor 44 ends the speed control of the supply amount of the gas fuel. At substantially the same time, the diesel governor 48 starts the speed control of the supply amount of the liquid fuel, and the supply amount of the gaseous fuel by the gas governor 44 is rapidly reduced to a predetermined value corresponding to the rotational speed described with reference to fig. 13, and is stabilized at a low output. The low-output gas governor command value varies depending on the rotational speed.

The operation of reducing the supply amount of the gas fuel to a predetermined value is performed in an extremely short time (for example, within 1 second). If the supply amount of the gaseous fuel is reduced to a prescribed value, the supply amount of the liquid fuel is increased by the action of the speed regulation control of the liquid fuel to maintain the target rotation speed of the engine 1. As a result, the transition from the gas mode G to the assist mode As is performed without largely affecting the rotation speed of the engine 1. The gas governor 44 and the diesel governor 48 can switch from the gas mode G to the assist mode As in a very short time (for example, within 1 second) As in the case of switching to the diesel mode D.

Next, a timing chart showing an operation when returning from the assist mode As to the gas mode G will be described with reference to fig. 15.

In the assist mode As operation, if the output (load) with respect to the rotation speed decreases and the output (load) falls below the preset assist close line, the gas mode G is returned to. When the auxiliary mode As returns to the gas mode G, the diesel governor 48 ends the speed control of the supply amount of the liquid fuel, and the gas governor 44 starts the speed control of the supply amount of the gas fuel at substantially the same time. The diesel governor 48 continuously reduces the supply amount of the liquid fuel in two stages, for example, and finally sets the supply amount to zero or a very small amount.

The mode of continuously reducing the amount of liquid fuel supplied by the diesel governor 48 may be a straight line, a curved line, or a stepped shape having a plurality of steps having substantially the same action as these, but in the present embodiment, the mode is a mode of linearly reducing the amount of liquid fuel in two steps. As shown in fig. 15, in the first stage f1 of the mechanical fuel injection pump 12, the supply amount of the liquid fuel is relatively quickly decreased to decrease the output, and the decrease in the output is performed at a low speed in the region of the second stage f 2. The second stage f2 is substantially set to an injection-free region where liquid fuel is not injected, and the transition period during which the output is reduced is expected to be gradually reduced. At the boundary between the first stage f1 and the second stage f2, the diesel governor 48 command is set to the governor command for the idling degree.

The operation of continuously reducing the supply amount of the liquid fuel by the diesel governor 48 is desirably performed for a long time as compared with the operation of reducing the supply amount of the gaseous fuel described above. The time until the supply of the liquid fuel by the diesel governor 48 is completed varies depending on the output, but is substantially about several seconds. If the supply amount of the liquid fuel is continuously decreased, the supply amount of the gaseous fuel is increased by the action of the speed regulation control of the gaseous fuel by the gas governor 44 to maintain the target rotational speed of the engine 1. As a result, the return from the assist mode As to the gas mode G is performed without largely affecting the rotation speed of the engine 1.

Here, since a predetermined amount of the gas fuel is supplied in the assist mode As before the return to the gas mode G, the speed control of the supply amount of the gas fuel can be started immediately at the time of starting the return to the gas mode G. Generally, when the supply of the gas fuel is started from zero, the start is unstable, and it takes time to perform stable control. However, in the assist mode As, since the supply of the gaseous fuel is already continued by the supply amount of the predetermined value, the speed control of the gaseous fuel can be started quickly, and the follow-up performance of the speed control after the start is also improved.

Accordingly, although the output varies, the supply of the substantial liquid fuel can be stopped for several seconds in the transition from the assist mode As to the gas mode G.

Next, an operation method of the four-stroke dual fuel engine 1 for ship propulsion according to the present embodiment will be described.

At the start of the engine 1, it starts in the diesel mode D and moves to the gas mode G. In the gas mode G, the ship stably operates on the cubic characteristic line. In the control unit 22, the gas governor 44 controls the speed of the supply amount of the gas fuel, and in fig. 13, even if there is a deviation in the output to some extent from the cubic characteristic line for the ship, the rotation speed and the output are controlled in the gas mode G and the operation is stabilized without reaching the assist opening line. In the gas mode G, the operation is performed in any one of an operation mode in which only a gas fuel is used as a fuel and ignition is performed by an ignition plug, and an operation mode in which injection of a small amount of liquid fuel (pilot oil) is used for ignition of a gas fuel that occupies a main heat source. In the case of an operation mode including a small amount of liquid fuel, the proportion of the liquid fuel is usually about 1% to 10% of the total heat in the heat quantity comparison of the rated output, but is desirably 3% or less from the viewpoint of achieving environmental restriction with respect to the exhaust gas.

In the operation in the gas mode G, the output (load) of the engine is detected by the rotational speed sensor 20 and the torque sensor 21 provided on the crankshaft 2. The rotational speed (rotational speed) of the crankshaft 2 is measured by a rotational speed sensor 20, and the engine torque is measured by a torque sensor 21. The measurement data measured by the rotation speed sensor 20 and the torque sensor 21 are output as signals to the control unit 22 of the engine 1.

The control unit 22 detects an output of the operating state of the engine 1 based on signals from the rotation speed sensor 20, the torque sensor 21, and the like. When the output (load) increases due to acceleration and deceleration of the engine 1, a storm of the sea, or the like, and the output (load) exceeds a preset assist on line, the gas mode G is shifted to the assist mode As (see fig. 14).

When the gas mode G is switched to the auxiliary mode As, the speed control of the gas governor 44 for the gaseous fuel is terminated, the governor command value is rapidly decreased to decrease the supply amount of the gaseous fuel to a predetermined value, and the diesel governor 48 starts the speed control of the supply amount of the liquid fuel. The decrease in the supply amount of the gaseous fuel is performed in a very short time within 1 second, for example. At the same time, the speed regulation control by the diesel governor D increases the supply amount of the liquid fuel to maintain the target rotational speed of the engine. As a result, the gas mode G is shifted to the assist mode As in a short time without greatly affecting the engine rotation speed. Thereby, knocking or misfiring in the gas pattern G can be avoided in advance.

Further, since the operation in the assist mode As uses a certain amount of liquid fuel, the operation is performed for a minimum time required for the environmental measures, and the gas mode is quickly returned to when the assist mode As is no longer necessary.

When the output (load) of the engine 1 in the assist mode As decreases and becomes equal to or less than the assist close line, the assist mode As is ended and the operation proceeds to the gas mode G (see fig. 15).

When the auxiliary mode As returns to the gas mode G, the diesel governor 48 ends the speed control of the supply amount of the liquid fuel, and at substantially the same time, the speed control of the supply amount of the gas fuel is started by the gas governor 44. The diesel governor 48 continuously reduces the supply amount of the liquid fuel, for example, in two stages, and finally sets the amount to zero or a very small amount.

When the supply amount of the liquid fuel is decreased, the command value of the diesel governor 48 is rapidly decreased in the first stage f1, and the governor command value is relatively gently decreased by substantially making the liquid fuel into the non-injection state in the second stage f 2. The operation of continuously decreasing the supply amount of the liquid fuel takes a longer time, for example, several seconds, to perform as compared with the above-described operation of decreasing the supply amount of the gaseous fuel at the time of the assist mode transition.

If the supply amount of the liquid fuel is continuously decreased, the speed regulation control of the gaseous fuel by the gas governor 44 rapidly increases the supply amount of the gaseous fuel to maintain the target rotational speed of the engine 1. In this way, the return from the assist mode As to the gas mode G is performed without largely affecting the rotation speed of the engine 1.

Further, since the predetermined amount of the gas fuel is continuously supplied at the stage of the assist mode As, the speed control of the gas fuel can be started immediately when the gas mode G returns. Therefore, the speed control of the supply amount of the gaseous fuel can be started quickly, and the following performance and stability of the speed control after the start are improved. Therefore, when the assist mode As is switched to the gas mode G, the speed control of the gas fuel and the supply stop or limitation of the liquid fuel can be substantially performed in several seconds.

Further, by performing the step of returning to the gas mode G while the output of the engine 1 is decreasing, the return to the gas mode in a short time becomes easy. When returning to the gas mode, knocking or misfire may occur, but since a sufficient amount of air is secured while the output of the engine 1 is decreasing, it is easy to maintain an appropriate air-fuel ratio.

Further, since the direction of supplying the fuel is restricted in the speed control in the process of decreasing the output of the engine 1, a rapid increase in the gaseous fuel can be suppressed, and knocking or misfire is less likely to occur. Therefore, by returning to the gas pattern G at the timing when the engine output decreases, it is possible to return to the gas pattern G in a short time while maintaining appropriate combustion. The larger the output of the engine 1, the larger the value of the supply amount of the gaseous fuel in the assist mode As. This makes it possible to quickly return from the assist mode As to the gas mode G even in a region where the output of the engine 1 is large.

In the operation in the gas pattern G, even in a situation where knocking or misfire occurs due to an increase in expected load, the operation of the engine 1 can be continued by shifting from the gas pattern G to the assist pattern As. On the other hand, since the liquid fuel is used in the assist mode As in a predetermined ratio, the operation in the assist mode As is required to be minimized in view of environmental measures. Then, if the state in which the assist mode As is no longer required is reached, the operation is immediately returned to the gas mode G.

Since the relation between the output and the rotation speed of the engine 1 is represented by a cubic characteristic line for the ship, in the control of the switching to the assist mode As and the returning to the gas mode G, the switching based on the correlation and the continuity between the output and the rotation speed of the engine 1 is performed quickly, and the switching and the returning are performed appropriately even in the actual driving state in which the output and the rotation speed change complicatedly. Further, the assist mode As is performed in a torque-rich region having an output higher than the cubic characteristic line for the ship, and is therefore preferable from the viewpoint of environmental measures.

Further, since the engine 1 for propelling the ship stably operates substantially on the cubic characteristic line for the ship, the conversion to the assist mode As is performed only when necessary, and if the assist mode As is no longer necessary, the engine immediately returns to the gas mode G. Therefore, the engine 1 and the operation method thereof according to the present embodiment can be more suitably applied to an engine for a tugboat or a work boat whose output fluctuates sharply.

In the present embodiment, in the gas mode G and the diesel mode D, the operating parameters to be controlled during the operation of the engine 1, for example, a set value relating to the supercharging pressure, a set value for controlling the variable intake valve timing mechanism 30 (VIVT command value) when the closing timing of the intake valve is changed, and a set value relating to the ignition condition are set to be optimized in each operating mode. On the other hand, in the assist mode As, a set value common to the gas mode G is used for at least one or more of the set value relating to the supercharging pressure, the set value of the control (VIVT command value) of the variable intake valve timing mechanism 30 when the closing timing of the intake valve is changed, and the set value of the ignition device such As the micro pilot injection valve 11 or the ignition plug.

As described above, according to the dual-fuel engine 1 and the operating method thereof of the present embodiment, the switching control from the gas mode G to the assist mode As can be performed quickly in a very short time such As 1 second, and the switching control from the assist mode As to the return to the gas mode G can be performed quickly in a very short time such As several seconds. Therefore, occurrence of knocking or misfiring in the gas pattern G can be avoided in advance. The operation in the assist mode As is limited to the rich torque region where the output (load) is greatly increased, and in the case where the assist mode As using liquid fuel is no longer required, since the return to the gas mode G is made fast, a superior effect is obtained also in view of environmental measures.

The engine of the present invention is not limited to the dual-fuel engine 1 and the operation method thereof of the above-described embodiment, and can be appropriately modified or replaced without departing from the scope of the present invention. In the following, modifications of the present invention and the like will be described, but the same reference numerals are used for the same or similar components and the like as those described in the above-described embodiments, and the description thereof will be omitted.

INDUSTRIAL APPLICABILITY

The present invention provides an engine operating method and an engine system capable of mutually and rapidly switching between two operating states, a first operation in which a gaseous fuel is used as a main heat source and a second operation in which both a gaseous fuel and a liquid fuel are used as fuels when an output (load) increases during the first operation, in accordance with a change in the output (load).

Description of the symbols

1: dual-fuel engine

2: crank shaft

8: air inlet valve

9: air exhaust valve

10: fuel injection valve

11: miniature pilot oil injection valve

12: fuel injection pump

13: air inlet pipe

14: exhaust pipe

15: fuel gas supply valve

20: rotation speed sensor

21: torque sensor

22: control unit

24: first drawing

25: second drawing

30: variable intake valve timing mechanism

44: gas speed regulator

45: fuel gas supply valve timing mechanism

48: a diesel governor.

Claims

1. A method of operating an engine, the engine being a dual fuel engine, characterized by the steps of:

in a first operation in which a gaseous fuel is used as a main heat source, the speed control of the supply amount of the gaseous fuel is terminated to reduce the supply amount of the gaseous fuel to a predetermined value, and the speed control of the supply amount of a liquid fuel is started, thereby shifting to a second operation in which both the gaseous fuel and the liquid fuel are used as fuels; and

in the operation of the second operation, the speed control of the supply amount of the liquid fuel is terminated to reduce the supply amount of the liquid fuel, and the speed control of the supply amount of the gas fuel is started, thereby returning to the first operation,

in the step of returning to the first operation, the step of reducing the supply amount of the liquid fuel includes a first step of reducing the supply amount of the liquid fuel at a high speed and a second step of reducing the supply amount of the liquid fuel at a low speed.

2. The engine operating method according to claim 1,

the step of returning to the first operation is performed while the output of the engine is decreasing.

3. The operation method of the engine according to claim 1 or 2,

the step of returning to the first operation is performed when the output of the engine enters a lower region of an auxiliary closing line set in a range of ± 10% with respect to a cubic characteristic line for a ship,

and performing a step of shifting to the second operation when the output of the engine enters an upper region of an auxiliary open line set above the auxiliary close line.

4. The operation method of the engine according to claim 1 or 2,

5. The engine operating method according to claim 3,

6. A method of operating an engine, the engine being a dual fuel engine, characterized by the steps of:

performing a second operation using both the gas fuel and the liquid fuel for speed control as fuels; and

ending the speed control of the liquid fuel in the step to continuously reduce the supply amount of the liquid fuel and performing a first operation of performing the speed control using the gas fuel as a main heat source,

wherein the step of reducing the supply amount of the liquid fuel when returning to the first operation has a first stage of reducing the supply amount of the liquid fuel at a high speed and a second stage of reducing the supply amount of the liquid fuel at a low speed.

7. A method of operating an engine, the engine being a dual fuel engine, characterized by switching to operate the engine from any one of the following modes:

a gas mode in which a gas fuel is used as a main heat source to perform speed regulation control on the gas fuel;

an assist mode in which both the gas fuel and the liquid fuel are used as fuels and the speed of the liquid fuel is controlled; and

a diesel mode for performing a governor control using only the liquid fuel as a fuel,

wherein the content of the first and second substances,

in operation based on the assist mode, when the output of the engine enters a lower region of an assist close line set along a cubic characteristic line for a vessel above the cubic characteristic line for the vessel in a range of ± 10% with respect to the cubic characteristic line for the vessel, the engine is shifted to the gas mode,

in the operation based on the gas mode, when the output of the engine enters an upper region of an assist opening line that is offset to an upper side of the assist closing line in a speed range other than a rated rotation speed of the engine, the engine is shifted to the assist mode,

in the gas mode operation, the control of the speed of the gas fuel is terminated to reduce the supply amount of the gas fuel to a predetermined value, and the control of the speed of the liquid fuel is started, thereby shifting to the assist mode.

8. The engine operating method according to claim 7,

in the operation based on the assist mode, the operation parameters controlled during the operation of the engine are set in common with the gas mode.

9. An engine system, wherein the engine is a dual-fuel engine, comprising a control unit, the control unit comprising:

an operation control unit that controls operation of the engine;

a gas governor that performs speed control of the supply amount of the gas fuel; and

a diesel governor for controlling the rate of supply of the liquid fuel,

in a first operation in which the operation control unit uses the gaseous fuel as a main heat source, the speed control of the gaseous fuel by the gas governor is terminated to reduce the supply amount of the gaseous fuel to a predetermined value, and the speed control of the liquid fuel by the diesel governor is started, so that the operation control unit shifts to a second operation in which both the gaseous fuel and the liquid fuel are used as fuels,

in the second operation, the speed control of the liquid fuel by the diesel governor is terminated to reduce the supply amount of the liquid fuel, and the speed control of the gaseous fuel by the gas governor is started, thereby returning to the first operation,

in returning to the first operation, the supply amount of the liquid fuel is reduced at a high speed, and then the supply amount of the liquid fuel is reduced at a low speed.