JP7376995B2 - Gas engine with turbocharger and its combustion method - Google Patents

Description

The present invention relates to a turbocharged gas engine and a combustion method thereof.

Conventionally, gas engines with turbochargers are known. A turbocharger uses the exhaust flow from a gas engine to drive a compressor, increasing the density of the air the gas engine draws. This type of turbocharged gas engine is disclosed in Patent Document 1, for example.

The turbocharged gas engine disclosed in Patent Document 1 includes a cylinder in which a piston is inserted, and a pilot fuel injection valve that injects pilot fuel into the cylinder. The intake port of the cylinder is connected to the compressor of the supercharger via an intake pipe, and the exhaust port of the cylinder is connected to the exhaust turbine of the supercharger via an exhaust pipe. Gaseous fuel is supplied to the intake pipe, and a mixture of gas fuel and air is formed within the intake pipe. The pilot fuel injection valve is connected to a high-pressure fuel pipe that stores high-pressure pilot fuel. In this gas engine, an air-fuel mixture is introduced into the cylinder when the piston descends, and the air-fuel mixture is compressed as the piston rises with the intake port and exhaust port closed. When the air-fuel mixture is compressed, pilot fuel is injected from the pilot fuel injection valve, the air-fuel mixture ignites and combustion occurs, and as the cylinder internal pressure rises, the piston descends, and the piston rises due to inertia, causing combustion gas to flow out from inside the cylinder. Exhausted.

The gas engine disclosed in Patent Document 1 employs a direct injection micropilot ignition system in which a small amount of pilot fuel (for example, light oil) is directly injected into the cylinder. In order to appropriately control the ignition timing of the air-fuel mixture and avoid abnormal combustion, pilot fuel injection is combined with pre-injection that assists flame propagation combustion of the air-fuel mixture, and main injection that can control the ignition timing of the air-fuel mixture. It is divided into injection and injection.

Some ships that navigate the ocean or rivers use a gas engine with a turbocharger as described above as the main engine. In the main engine of a ship, the amount of fuel supplied to the main engine is controlled so that the rotation speed of a propulsion shaft connected to a propulsion propeller or an engine directly connected thereto becomes a given target rotation speed.

FIG. 7 is a graph showing the combustion characteristics of a typical gas engine, where the horizontal axis shows the air-fuel ratio (excess air ratio) and the vertical axis shows the net mean effective pressure (BMEP). Net average effective pressure can be an indicator of engine power for a gas engine. In the combustion characteristics of a typical gas engine, a knocking region exists in the region where the air-fuel ratio of the lean air-fuel mixture in the combustion chamber of the cylinder is low and the engine output is high, and a misfire region exists in the region where the air-fuel ratio is high and the engine output is high. exists. In order to obtain high output in lean burn, the combustion characteristics are optimal when the air-fuel ratio of the lean mixture in the combustion chamber is within the range X (operating window) between the knocking region and the misfire region. The amount is controlled to a minimum. In other words, in a gas engine during steady operation, the air supply pressure is controlled to maintain the target rotation speed so that the air-fuel ratio of the lean mixture falls between the knocking region and the misfire region. be done.

The rotational speed of a propeller for propulsion of a ship tends to change in a short period of time due to tidal currents, waves, the rudder angle of the ship, and the like. In response to such rapid load changes, in a gas engine with a turbocharger, the supply pressure does not increase immediately due to turbo lag even if the gas fuel supply amount is increased, so the gas fuel supply amount is quickly increased. I can't. Therefore, the fuel supply device for a propulsion internal combustion engine (gas engine) disclosed in Patent Document 2 calculates the predicted fuel supply amount based on the predicted torque calculated based on the predicted future ship speed of the ship, and calculates the predicted fuel supply amount based on the predicted fuel supply amount. The pressure of the air-fuel mixture supplied to the engine is controlled based on the

Patent No. 5922830 JP2016-205270A

The technique disclosed in Patent Document 2 predicts a sudden increase in the load of the gas engine and increases the air supply pressure in advance in preparation for this, and is not a technique for quickly increasing the air supply pressure. Furthermore, it is known to jet-assist a supercharger in order to quickly increase the air supply pressure, but in this case, the supercharger needs to be equipped with a jet-assist device.

In view of the above, it is an object of the present invention to provide a technology for quickly increasing the boost pressure in a turbocharged gas engine so that the amount of gas fuel supplied can be quickly increased in response to a sudden increase in engine load. purpose.

A combustion method for a gas engine according to one aspect of the present invention includes an intake stroke in which a lean mixture consisting of gas fuel and air is sucked into a combustion chamber, a compression stroke in which the lean mixture is compressed, and combustion of the lean mixture. A combustion method for a pilot ignition type turbocharged gas engine that repeats a combustion cycle consisting of an expansion stroke in which combustion gas expands and an exhaust stroke in which the combustion gas is exhausted from the combustion chamber,
When the engine load increases, a first injection of liquid fuel into the combustion chamber is performed at a first timing in the compression stroke, and the lean mixture in the combustion chamber is caused by the propagation of the flame generated by the first injection. A second injection for injecting the liquid fuel into the combustion chamber is started at a second timing in the expansion stroke in the second half of the combustion period during which combustion is occurring, and the second injection is performed for the injection amount of the first injection. The injection amount is large, and the ratio of the injection amount of the second injection to the injection amount of the first injection is greater than 1 and 15 or less,
When the engine output is continuously increased from the first output value to the second output value to the third output value in response to the increase in the engine load, the The amount of gas fuel supplied is increased and the amount of gas fuel supplied is increased so that the rate of increase in engine output is greater than the rate of increase in engine output from the second output value to the third output value. The engine output is increased from the first output value to the second output value by gradually increasing the injection amount of liquid fuel from a predetermined first injection amount to a predetermined second injection amount, and the supply amount of the gas fuel is increased. The engine output is increased from the second output value to the third output value by increasing the amount of liquid fuel and maintaining the injection amount of the liquid fuel in the first injection at the second injection amount.

Further, a gas engine with a turbo supercharger according to one aspect of the present invention,
A cylinder and a piston that form a combustion chamber, an air supply pipe that supplies a lean mixture of air and gas fuel to the combustion chamber, a gas fuel supply valve that adjusts the amount of gas fuel supplied, and a liquid in the combustion chamber. an injector that injects fuel; an intake stroke in which the piston reciprocates within the cylinder to draw the lean mixture into the combustion chamber; a compression stroke to compress the lean mixture; and a compression stroke to compress the lean mixture; A pilot ignition type turbocharged gas engine that repeats a combustion cycle consisting of an expansion stroke in which combustion gas generated by combustion of the engine expands, and an exhaust stroke in which the combustion gas is exhausted from the combustion chamber,
When the engine load increases, the injector performs a first injection at a first timing in the compression stroke, and a combustion period during which the lean air-fuel mixture in the combustion chamber is combusted by the propagation of the flame generated by the first injection. The second injection is started at a second timing in the expansion stroke in the second half of the expansion stroke, and the injection amount of the second injection is larger than the injection amount of the first injection, and the second injection is The ratio of the injection amount of the injection is greater than 1 and less than or equal to 15,
When the engine output is continuously increased from the first output value to the second output value to the third output value in response to the increase in the engine load, the The gas fuel supply valve increases the supply amount of the gas fuel so that the rate of increase in the engine output is greater than the rate of increase in the engine output from the second output value to the third output value. The injector gradually increases the injection amount of the liquid fuel in the first injection from a predetermined first injection amount to a predetermined second injection amount, thereby increasing the engine output from the first output value to the second output value. and the gas fuel supply valve increases the supply amount of the gas fuel, and the injector maintains the injection amount of the liquid fuel in the first injection at the second injection amount, thereby increasing the engine output to the second injection amount. 2 output value to the third output value .

According to the turbocharged gas engine and its combustion method, the liquid fuel injected in the second injection is not substantially used for the work of pushing down the piston, but increases the exhaust temperature by combustion. As a result, the temperature of the combustion gas sent to the turbine of the supercharger becomes higher than when the second injection is not performed, and it is possible to give more energy to the turbine. As a result, when switching from operation in which the second injection is not performed to operation in which the second injection is performed, the boost pressure can be quickly increased, making it possible to quickly increase the amount of gas fuel supplied. . Such a combustion method is suitable as a combustion method when the load of a gas engine with a turbocharger increases rapidly, and can improve the load response of the gas engine (i.e., the followability of the actual output to the required output). .

In the turbocharged gas engine and its combustion method, the gas engine may be a four-stroke engine, and the second timing may be within a range of 60° to 180° ATDC.

Thereby, the temperature of the combustion gas discharged from the combustion chamber can be increased by the additional pilot fuel by the second injection without inhibiting the normal combustion of the lean air-fuel mixture within the combustion chamber.

In the turbocharged gas engine and its combustion method, when increasing the engine output from the first output value to the second output value to the third output value, from the first output value to the second output value The injection amount of the liquid fuel in the first injection may be changed such that the output increase rate becomes larger than the output increase rate from the second output value to the third output value.

In this way, by lowering the air-fuel ratio and making the engine rich in fuel at a relatively low load, it is possible to quickly increase the rotational speed while avoiding abnormal combustion. By lowering the air-fuel ratio of the lean air-fuel mixture at a relatively high load while maintaining this momentum of increase in rotational speed, engine output can be quickly increased while avoiding abnormal combustion. Therefore, the load response of the turbocharged gas engine can be improved.

According to the present invention, it is possible to provide a technique for rapidly increasing the boost pressure in a turbocharged gas engine so that the gas fuel supply amount can be rapidly increased in response to a sudden increase in engine load.

FIG. 1 is a schematic configuration diagram of a turbocharger-equipped gas engine according to an embodiment of the present invention. FIG. 2 is a sectional view showing the structure of one of the plurality of cylinders included in the engine. FIG. 3 is a schematic configuration diagram of the air cooler. FIG. 4 is a diagram showing the configuration of a control system of a gas engine with a turbocharger. FIG. 5 is a timing chart of pilot fuel injection in sudden load operation. FIG. 6 is a chart showing time-series changes in target engine output and pilot fuel injection amount when increasing engine output in response to a sudden increase in engine load. FIG. 7 is a graph showing the combustion characteristics of a typical gas engine.

Next, embodiments of the present invention will be described with reference to the drawings. A turbocharged gas engine 1 according to the present embodiment is mounted on a ship as a main engine. However, the turbocharger-equipped gas engine 1 according to the present invention is not limited to being mounted on a ship.

[Configuration of gas engine 1 with turbocharger]
FIG. 1 is a schematic configuration diagram of a turbocharger-equipped gas engine 1 according to an embodiment of the present invention. The turbocharged gas engine 1 shown in FIG. 1 includes an engine (engine main body) 2, a supercharger 3, an air cooler 43, and a control device 7 (see FIG. 2). In this embodiment, the turbocharged gas engine 1 drives a propulsion shaft 93 to which a propulsion blade 83 is attached.

The engine 2 according to this embodiment is a four-stroke multi-cylinder gas combustion engine. However, the engine 2 is not limited to a gas-only combustion engine, and may be a dual-fuel engine that burns one or both of gas fuel and liquid fuel depending on the situation.

FIG. 2 is a sectional view showing the structure of one of the plurality of cylinders 21 included in the engine 2. A piston 22 is disposed within the cylinder 21 so as to be able to freely reciprocate, and the cylinder 21 and the piston 22 form a combustion chamber 20 .

An intake port of the cylinder 21 is connected to an air supply pipe 41. The intake port is provided with an intake valve 23 that opens and closes the intake port. The exhaust port of the cylinder 21 is connected to an exhaust pipe 42. The exhaust port is provided with an exhaust valve 24 that opens and closes the exhaust port. The combustion chamber 20 is provided with an in-cylinder pressure sensor 62 that detects the in-cylinder pressure, which is the pressure within the combustion chamber 20 .

The piston 22 is connected to a crankshaft (not shown) by a connecting rod (not shown). By reciprocating the piston 22 twice within the cylinder 21, one combustion cycle consisting of intake, compression, expansion, and exhaust is performed. The phase angle of the engine 2 during one combustion cycle in each cylinder 21 is detected by a phase angle detector 63. As the phase angle, the rotation angle (crank angle) of the crankshaft, the position of the piston 22, etc. may be used, and the phase angle detector 63 may be, for example, an electromagnetic pickup, a proximity switch, or a rotary encoder. Further, the phase angle detector 63 also functions as an actual rotation speed detector that detects the actual rotation speed of the engine 2.

Returning to FIG. 1, the supercharger 3 includes a compressor 31 and a turbine 32, which are connected by a shaft. The combustion chamber 20 within the cylinder 21 is connected to the compressor 31 via an air supply pipe 41 and to the turbine 32 via an exhaust pipe 42 . The air supply pipe 41 guides air compressed by the compressor 31 to the combustion chamber 20 of each cylinder 21. The air supply pipe 41 is provided with an air supply blow-off valve 48 that releases gas from the air supply pipe 41 to release the pressure in the air supply pipe 41 . The exhaust pipe 42 guides exhaust gas (combustion gas) from the combustion chamber 20 of each cylinder 21 to the turbine 32. The exhaust pipe 42 is provided with an exhaust wastegate valve 49 that controls the amount of gas flowing into the turbine 32 by diverting a portion of the gas from the exhaust pipe 42 . Note that the downstream part of the air supply pipe 41 and the upstream part of the exhaust pipe 42 branch from the manifold into the same number of branch paths as the cylinders 21, but in FIG. 42 is drawn as one flow path.

The air supply pipe 41 is provided with an air cooler 43 for cooling the air (supply air) that has been compressed by the compressor 31 and has reached a high temperature. As shown in FIG. 3, the air cooler 43 is a heat exchanger that exchanges heat between a refrigerant such as water flowing through the refrigerant flow path 44 and air flowing through the air supply pipe 41. A bypass path 46 is connected to the refrigerant flow path 44 , which allows the refrigerant to flow downstream from the air cooler 43 without passing through the air cooler 43 (that is, without being used for heat exchange by the air cooler 43 ). Further, the refrigerant flow path 44 is provided with a flow rate adjustment device 45 that adjusts the flow rate of the refrigerant flowing through the bypass path 46, in other words, the flow rate of the refrigerant used for heat exchange in the air cooler 43. The flow rate adjustment device 45 adjusts the flow rate of the refrigerant used for heat exchange in the air cooler 43 so that the cooled air coming out of the air cooler 43 has a predetermined temperature.

A supply air pressure sensor 61 and a supply air temperature sensor 65 are provided in the supply air pipe 41 downstream of the air cooler 43 . The air supply pressure sensor 61 detects the air supply pressure which is the discharge pressure of the compressor 31. The air supply pressure sensor 61 may be provided in each of the above-mentioned branch paths on the downstream side of the air supply pipe 41, or only one may be provided in the above-mentioned manifold. The supply air temperature sensor 65 detects the supply air temperature, which is the temperature of the air introduced into the combustion chamber 20 through the supply air pipe 41. Similarly, the supply air temperature sensor 65 may be provided in each of the branch passages described above on the downstream side of the supply air pipe 41, or only one supply air temperature sensor 65 may be provided in the manifold described above.

Further, the air supply pipe 41 is provided with a gas fuel supply valve 51 for each cylinder 21 . The gas fuel supply valve 51 supplies gas fuel into the air discharged from the compressor 31. The opening degree (or opening time) of the gas fuel supply valve 51 is operated by the gas fuel supply valve driver 50. Depending on the opening degree (or opening time) of the gas fuel supply valve 51, the amount of gas fuel supplied from the gas fuel chamber (not shown) to the air supply pipe 41 through the gas fuel supply valve 51 changes. The gas fuel supply valve driver 50 and the gas fuel supply valve 51 constitute a gas fuel supply amount adjustment device.

The engine 2 according to this embodiment employs a direct injection pilot fuel ignition method and includes a pilot fuel injector 52 that injects pilot fuel into the combustion chamber 20. The pilot fuel is, for example, liquid fuel such as light oil. Pilot fuel injector 52 is connected to common rail 53 via a fuel pipe. High-pressure pilot fuel is stored in the common rail 53, and this pilot fuel can be injected from the pilot fuel injector 52 of each cylinder 21 at any timing and at any injection pressure. Injection from pilot fuel injector 52 is operated by injector driver 54 . The injector driver 54 and the pilot fuel injector 52 constitute a pilot fuel injection amount adjusting device.

[Configuration of control system of gas engine 1 with turbocharger]
The configuration of the control system of the turbocharged gas engine 1 will be described below. FIG. 4 is a diagram showing the configuration of a control system of the gas engine 1 with a turbocharger. The control device 7 is a so-called computer, and includes an arithmetic processing section 7a such as a CPU, and a storage section 7b such as a ROM and a RAM. The storage unit 7b stores programs executed by the arithmetic processing unit 7a, various fixed data, and the like. The arithmetic processing unit 7a transmits and receives data to and from external devices. Further, the arithmetic processing unit 7a inputs detection signals from various sensors and outputs control signals to each control target. The control device 7 performs processing as each functional unit by having the arithmetic processing unit 7a read and execute software such as a program stored in the storage unit 7b. Note that the control device 7 may execute each process through centralized control by a single computer, or may execute each process through distributed control through cooperation of a plurality of computers. Further, the control device 7 may be composed of a microcontroller, a programmable logic controller (PLC), or the like.

The control device 7 is electrically connected to a rudder angle operating tool 73, a ship maneuvering operating tool 74, a turning angle sensor 66, and a boat speed meter 67.

A cockpit (not shown) provided in the hull is provided with a rudder angle operating tool 73 for operating and inputting the rudder angle, and a ship steering operating tool 74 for operating and inputting the rotation speed of the engine 2 and forward/backward movement. . Rudder angle operation information input by the driver is input to the control device 7 via the rudder angle operation tool 73 . Vessel maneuvering information input by the operator is input to the control device 7 via the marine vessel maneuvering tool 74 . These operating tools 73 and 74 may be handles or levers, for example. Further, the hull is provided with a turning angle sensor 66 that detects the turning angle of the hull, and a ship speed meter 67 that detects the ship speed.

The control device 7 determines a sudden increase in engine load or predicts a sudden increase in engine load. A sudden increase in engine load is an increase in load that causes turbo lag (i.e., the supercharger 3 does not provide sufficient supercharging and there is a delay time until the required boost pressure is reached). means. Causes of sudden increases in load include, for example, an increase in ship speed, a change in the rudder angle, strong wind and waves that the ship receives, a change in propeller pitch, and a change in turning angle if the ship is equipped with an azimuth thruster.

The control device 7 can determine that the load on the engine 2 has suddenly increased by the following method. For example, the rate of increase in the amount of gas fuel supply is calculated, and if the rate of increase in the amount of gas fuel supply exceeds a threshold value, it is determined that the load has increased rapidly, and if the rate of increase in the amount of gas fuel supply is less than the threshold value, the load is determined to have increased rapidly. It is determined that the temperature has not increased. For example, the deviation between the actual rotation speed and the target rotation speed is calculated, and if the deviation between the actual rotation speed and the target rotation speed exceeds a threshold value, it is determined that the load has increased rapidly, and the difference between the actual rotation speed and the target rotation speed is determined. If the deviation is below the threshold, it is determined that the load has not increased rapidly. For example, the output torque of the engine 2 is detected by a torque meter (not shown), and the rate of increase in the output torque is calculated, and if the rate of increase in the output torque exceeds a threshold value, it is determined that the load has increased rapidly, and the output torque is increased. If the rising speed is below the threshold value, it is determined that the load is not rising rapidly.

Further, the control device 7 performs the following operations based on the rudder angle operation information, the ship maneuvering operation information, the turning angle of the ship, the rotational speed of the gas engine 1, the ship speed, and the ship performance model stored in advance in the storage unit 7b. A sudden increase in engine load can be predicted in advance. For example, when the rudder angle of the hull is manipulated by the rudder angle operating tool 73, a sudden increase in engine load is expected in the near future. For example, when the boat maneuvering tool 74 is switched from forward to reverse, the engine load is expected to increase rapidly in the near future.

The control device 7 includes a gas fuel supply valve driver 50, an injector driver 54, an air intake pressure sensor 61, an in-cylinder pressure sensor 62, a phase angle detector 63, an air intake temperature sensor 65, an air intake blow-off valve 48, and an exhaust waist. It is electrically connected to the gate valve 49. The control device 7 operates the gas fuel supply valve driver 50 and the injector driver 54 for each cylinder 21 based on the phase angle detected by the phase angle detector 63 so that the actual rotation speed becomes the target rotation speed. , controls the supply amount and timing of gas fuel and pilot fuel. Further, the control device 7 operates the intake air blow-off valve 48 and the exhaust wastegate valve 49 based on the intake pressure detected by the intake air pressure sensor 61 to control the amount of gas inside the combustion chamber 20 according to the amount of gas fuel supplied. The air supply pressure is controlled so that the combustion characteristics are optimal, that is, the thermal efficiency is high and the amount of NOx emissions is minimized when the air-fuel ratio of the lean mixture is within the range X shown in FIG.

The control device 7 performs steady operation while the engine load hardly changes, and when a sudden increase in engine load is predicted or detected during steady operation, shifts to sudden load increase operation. The combustion method of the gas engine 1 during sudden load operation will be described below.

During the intake stroke of the combustion cycle, the piston 22 moves down with the exhaust valve 24 closed and the intake valve 23 opened, and the lean gas containing the gas fuel injected from the gas fuel supply valve 51 and the air supplied from the supercharger 3 is released. The air-fuel mixture is drawn into the combustion chamber 20 through the intake port. In the compression stroke, the piston 22 moves up to top dead center with the intake valve 23 and the exhaust valve 24 closed, and the lean air-fuel mixture in the combustion chamber 20 is compressed. Before the piston 22 reaches top dead center, the pilot fuel is directly injected into the compressed lean air-fuel mixture in the combustion chamber 20, and the pilot fuel self-ignites. This flame propagates to the lean mixture within the combustion chamber 20, and the mixture is combusted. In the expansion stroke (combustion stroke), the ignited lean air-fuel mixture is combusted, the combustion gas expands, and the piston 22 is pushed down to the bottom dead center. In the exhaust stroke, the piston 22 moves up due to inertia with the intake valve 23 closed and the exhaust valve 24 opened, and combustion gas is pushed out to the exhaust pipe 42 through the exhaust port. The combustion gas is introduced into the turbine 32 through the exhaust pipe 42 and is used as power to drive the compressor 31.

When the control device 7 starts the sudden load operation, referring to FIG. 3, the control device 7 operates the flow rate adjustment device 45 so that all of the refrigerant flowing through the refrigerant flow path 44 passes through the air cooler 43. In other words, the flow rate adjustment device 45 blocks the flow of refrigerant in the bypass path 46 . Thereby, the supply air temperature can be rapidly lowered using the full cooling capacity of the air cooler 43.

In normal combustion in the premix combustion engine 2, the ignited flame successively propagates through the unburnt mixture to complete combustion. However, if the heat load and combustion pressure within the combustion chamber 20 increase due to an increase in load, etc., the unburned air-fuel mixture will self-ignite without waiting for flame propagation. When this self-ignition occurs in a chain reaction, a strong pressure and temperature rise occurs. This is the "knocking" phenomenon. As described above, by lowering the supply air temperature, the heat load within the combustion chamber 20 can be suppressed, and the occurrence of knocking (abnormal combustion) can be suppressed.

FIG. 5 is a timing chart of pilot fuel injection in sudden load operation. In this timing chart, the vertical axis represents the pilot fuel injection amount and the in-cylinder pressure, and the horizontal axis represents the phase angle [ATDC: After Top Dead Center] of the piston 22. As shown in this timing chart, the pilot fuel injector 52 controlled by the control device 7 performs at least one first injection (main injection) and at least one second injection (post injection) in one combustion cycle. ). The control device 7 measures the injection timing based on the phase angle detected by the phase angle detector 63.

The first injection is performed at a predetermined first timing Ta before top dead center (TDC) in the compression stroke. More specifically, the pilot fuel injector 52 is opened by the injector driver 54 at the first timing Ta, and a small amount (approximately 1% of the total heat input at rated load) of pilot fuel is injected into the lean mixture in the combustion chamber 20. gushes out. The first timing Ta may be within the range of -30° to 0° ATDC.

The high-pressure pilot fuel injected into the combustion chamber 20 during the first injection ignites the lean air-fuel mixture within the combustion chamber 20. That is, the first injection determines the start timing of the combustion period. The combustion pressure of the lean mixture in the combustion chamber 20 provides the output of the engine 2.

When the piston 22 exceeds top dead center (TDC), the compression stroke shifts to the expansion stroke. The second injection is performed at a predetermined second timing Tb in the latter half of the combustion period in the expansion stroke. More specifically, the pilot fuel injector 52 is opened by the injector driver 54 at the second timing Tb, and pilot fuel is injected into the combustion chamber 20. Note that the latter half of the combustion period refers to the period during which the lean air-fuel mixture in the combustion chamber 20 is being combusted, and after the time Tc when the cylinder pressure reaches the maximum cylinder pressure.

The combustion of the pilot fuel injected in the second injection increases the temperature of the combustion gas in the cylinder. In addition, the pilot fuel injected in the second injection burns unburned gas fuel in the combustion gas in the combustion chamber 20 and the exhaust pipe 42 in the expansion stroke and the subsequent exhaust stroke. As a result, the temperature of the combustion gas sent to the turbine 32 of the supercharger 3 becomes higher than that in the case where the second injection is not performed, and larger energy can be given to the turbine 32. Therefore, the rotation speed of the turbine 32 can be increased compared to the case where the second injection is not performed, and the supercharging pressure by the supercharger 3 can be quickly increased. As a result, it is possible to eliminate or shorten turbo lag when the engine load suddenly increases.

When the first timing Ta, that is, the start timing of the combustion period, is within the range of -30° to 0° ATDC, the second injection is started before the time Tc when the cylinder pressure reaches the maximum cylinder pressure. Then, the maximum in-cylinder pressure may increase and abnormal combustion may occur. On the other hand, if the second injection is started after 180° ATDC, there is a possibility that the fuel supplied in the second injection may not be combusted. From this point of view, the second timing Tb, ie, the start timing of the second injection, may be within the range of 60° to 180° ATDC. The end timing of the second injection may be determined by the injection capacity of the pilot fuel injector 52.

Moreover, the injection amount of the second injection is larger than the injection amount of the first injection. The ratio of the injection amount of the second injection to the injection amount of the first injection is greater than 1 and less than or equal to 15, preferably greater than or equal to 8 and less than or equal to 12. If the ratio is less than 1, the exhaust temperature will not rise sufficiently, and the effect of quickly increasing the rotational speed of the turbine 32 will not be achieved. On the other hand, if the ratio is 15 or more, the exhaust gas temperature will rise excessively, and there is a possibility that the exhaust gas temperature will exceed the allowable temperature of the member.

It is known that abnormal combustion such as knocking is less likely to occur when the engine load is relatively low, and abnormal combustion is more likely to occur when the engine load is relatively high. Therefore, when increasing the engine load rapidly from a relatively low load, it is desirable to set the rate of change in engine output to two stages.

FIG. 6 shows a case in which the engine output is increased from a relatively low first output value Da, through a second output value Db, to a relatively high third output value Dc in response to a sudden increase in engine load. 2 is a chart showing time-series changes in target engine output and pilot fuel injection amount. The second output value Db is an engine output value corresponding to a boundary value between a relatively low load range in which abnormal combustion is less likely to occur and a relatively high load range in which abnormal combustion is more likely to occur. In the figure, a fixed rate of change output line L0 indicates a change in engine output when the engine output is increased at a constant rate of change in response to an increase in engine load. Here, the output change rate of the fixed change rate output line L0 is the maximum output change rate at which knocking does not occur even under high loads.

In the target output line L of the present invention, the output change rate when increasing the engine output from the first output value Da to the second output value Db is larger than the output change rate of the fixed change rate output line L0 (i.e., the tangent line (the slope is large). Further, on the target output line L, the output change rate when increasing the engine output from the second output value Db to the third output value Dc is smaller than the output change rate on the fixed rate of change output line L0 (that is, the rate of change of the output on the fixed change rate output line L0). slope is small) or the same. As a result, the target output line L can increase the output to the third output value Dc more quickly than the fixed rate of change output line L0.

The target output line L is stored in the control device 7 in advance. When rapidly increasing the engine output from the first output value Da to the third output value Dc, the control device 7 controls the amount of gas fuel supplied from the gas fuel supply valve 51 and the pilot output along the target output line L. The amount of pilot fuel injected from the fuel injector 52 during the first injection is changed.

When increasing the engine output from the first output value Da to the second output value Db, the control device 7 increases the amount of gas fuel supplied so as to increase the engine output along the target output line L. , the injection amount of pilot fuel is gradually increased from the injection amount Fa to the injection amount Fb. Note that when increasing the engine output using the conventional combustion method, the amount of gas fuel supplied is increased, but the injection amount of pilot fuel is constant at the injection amount Fa. The injection amount Fa and the injection amount Fb are set according to the gas engine 1 and are stored in the control device 7 in advance.

When increasing the engine output from the second output value Db to the third output value Dc, the control device 7 increases the amount of gas fuel supplied so as to increase the engine output along the target output line L. , the injection amount of pilot fuel is maintained at the injection amount Fb. That is, the injection amount of pilot fuel is maintained in an increased state. When the engine output reaches the third output value Dc, the control device 7 gradually reduces the injection amount of pilot fuel from the injection amount Fb to the injection amount Fa.

As described above, when the engine load suddenly increases from a relatively low load, by increasing the injection amount of pilot fuel in the first injection along the target output line L, the combustion chamber 2 The air-fuel ratio within changes on curve Y in FIG. Specifically, in a range where the engine output is low (that is, a range where the engine load is low), the air-fuel ratio is reduced to a range where knocking does not occur, resulting in a fuel-rich state. In a range where the engine output is high (that is, a range where the engine load is large), the air-fuel ratio increases to a range that does not cause a misfire.

As explained above, the turbocharged gas engine 1 of the present embodiment is a pilot ignition type turbocharged gas engine, and includes a cylinder 21 and a piston 22 that form a combustion chamber 20, An intake stroke that includes an injector 52 that injects liquid fuel (pilot fuel) into the chamber 20, and sucks a lean mixture of air and gas fuel into the combustion chamber 20 by reciprocating the piston 22 within the cylinder 21; A combustion cycle consisting of a compression stroke to compress a lean mixture, an expansion stroke to expand combustion gas produced by combustion of the lean mixture, and an exhaust stroke to exhaust the combustion gas from the combustion chamber is repeated. Then, the injector 52 performs the first injection at the first timing Ta in the compression stroke, and in the second half of the combustion period when the lean air-fuel mixture in the combustion chamber 20 is being combusted by the propagation of the flame generated by the first injection. It is characterized in that the second injection is started at the second timing Tb in the expansion stroke.

Similarly, the combustion method of the turbocharged gas engine 1 according to the present embodiment includes performing a first injection of injecting liquid fuel into the combustion chamber 20 at a first timing Ta in the compression stroke; The second injection of injecting the liquid fuel into the combustion chamber 20 is started at the second timing Tb in the expansion stroke during the second half of the combustion period when the lean mixture in the combustion chamber 20 is being combusted by the propagation of the generated flame. It is characterized by

According to the turbocharged gas engine 1 and its combustion method, the pilot fuel (liquid fuel) injected in the second injection is not substantially used for the work of pushing down the piston 22, but is exhausted by combustion. Increase temperature. As a result, the temperature of the combustion gas sent to the turbine 32 of the supercharger 3 becomes higher than that in the case where the second injection is not performed, and larger energy can be given to the turbine 32. As a result, when switching from an operation in which the second injection is not performed to an operation in which the second injection is performed, the supply air pressure sensor 61 can be quickly increased, and the amount of gas fuel supplied can be quickly increased. can. Such a combustion method is suitable as a combustion method when the load of the turbocharged gas engine 1 increases rapidly, and improves the load response of the gas engine 1 (i.e., the followability of the actual output to the required output). I can do it.

Furthermore, in the turbocharged gas engine 1 and its combustion method according to the present embodiment, the gas engine 1 is a four-stroke engine, and the second timing Tb is within the range of 60° to 180° ATDC.

Thereby, the temperature of the combustion gas discharged from the combustion chamber 20 can be increased by the additional pilot fuel by the second injection without inhibiting the normal combustion of the lean mixture in the combustion chamber 20.

Moreover, in the turbocharged gas engine 1 and its combustion method according to the present embodiment, the injection amount of the second injection is larger than the injection amount of the first injection.

Thereby, the temperature of the combustion gas discharged from the combustion chamber 20 can be increased by the additional pilot fuel by the second injection without inhibiting the normal combustion of the lean mixture in the combustion chamber 20.

Furthermore, in the turbocharged gas engine 1 and its combustion method according to the present embodiment, when increasing the engine output from the first output value Da to the second output value Db to the third output value Dc, The liquid fuel is injected in the first injection so that the rate of increase in output from the first output value Da to the second output value Db is larger than the rate of increase in output from the second output value Db to the third output value Dc. Vary the amount.

That is, the pilot ignition turbocharged gas engine 1 includes a cylinder 21 and a piston 22 that form a combustion chamber 20, and an injector 52 that injects pilot fuel (liquid fuel) into the combustion chamber 20. 52 performs main injection in the compression stroke to compress the lean air-fuel mixture sucked into the combustion chamber 20 when increasing the engine output from the first output value Da to the third output value Dc via the second output value Db, Pilot fuel is injected in main injection so that the rate of increase in output from the first output value Da to the second output value Db is greater than the rate of increase in output from the second output value Db to the third output value Dc. Vary the amount.

In this way, by lowering the air-fuel ratio and making the engine rich in fuel at a relatively low load, it is possible to quickly increase the rotational speed while avoiding abnormal combustion. By lowering the air-fuel ratio of the lean air-fuel mixture at a relatively high load while maintaining this momentum of increase in rotational speed, engine output can be quickly increased while avoiding abnormal combustion. Therefore, the load response of the turbocharged gas engine 1 can be improved.

Further, the turbocharged gas engine 1 according to the present embodiment further includes an air cooler 43 that cools the air sucked into the combustion chamber 20. The air cooler 43 includes a refrigerant flow path 44 through which the refrigerant flows, a bypass path 46 that is connected to the refrigerant flow path 44, and allows the refrigerant to flow downstream of the refrigerant flow path 44 without exchanging heat with air; It has a flow rate adjustment device 45 that adjusts the flow rate of the refrigerant flowing into the bypass path 46 among the flowing refrigerant, and the flow rate adjustment device 45 blocks the flow of refrigerant from the refrigerant flow path 44 to the bypass path when the engine load increases. do.

That is, the turbocharged gas engine 1 includes an engine 2 that obtains power by burning a lean mixture of gas fuel and air, a compressor 31 connected to the engine 2 through an air supply pipe 41, and an exhaust pipe. A supercharger 3 having a turbine 32 connected to the engine 2 by 42, a gas fuel supply device (gas fuel supply valve 51 and gas fuel supply valve driver 50) that supplies gas fuel to the intake pipe 41, and an intake pipe 41 and an air cooler 43 that cools the air passing through. The air cooler 43 includes a refrigerant passage 44 through which the refrigerant flows, a bypass passage 46 that is connected to the refrigerant passage 44 and allows the refrigerant to flow downstream of the refrigerant passage 44 without exchanging heat with air, and a refrigerant passage 44. It has a flow rate adjustment device 45 that adjusts the flow rate of the refrigerant flowing into the bypass path 46 out of the flowing refrigerant, and the flow rate adjustment device 45 blocks the flow of refrigerant from the refrigerant flow path 44 to the bypass path 46 when the engine load increases. do.

In this way, when the engine load increases, by cooling the air supplied to the engine 2 with the full cooling capacity of the air cooler 43, the heat load in the combustion chamber 20 is suppressed, and the occurrence of knocking (abnormal combustion) is suppressed. be able to.

Although the preferred embodiments of the present invention have been described above, the present invention may include modifications to the specific structure and/or functional details of the above embodiments without departing from the spirit of the present invention. .

For example, although the engine 2 of the turbocharged gas engine according to the above embodiment is a four-stroke engine, it may be a two-stroke engine. In a two-stroke engine, exhaust, intake, and compression are performed during the upward stroke of the piston 22, and combustion and exhaust are performed during the downward stroke of the piston 22.

1: Gas engine with turbocharger 2: Engine (engine body)
3: Supercharger 7: Control device 7a: Processing unit 7b: Storage unit 20: Combustion chamber 21: Cylinder 22: Piston 23: Intake valve 24: Exhaust valve 31: Compressor 32: Turbine 41: Air supply pipe 42: Exhaust Pipe 43: Air cooler 44: Refrigerant flow path 45: Flow rate adjustment device 46: Bypass path 48: Air supply blow-off valve 49: Exhaust wastegate valve 50: Gas fuel supply valve driver 51: Gas fuel supply valve 52: Pilot fuel injector 53: Common rail 54 : Injector driver 61 : Supply air pressure sensor 62 : In-cylinder pressure sensor 63 : Phase angle detector 65 : Supply air temperature sensor 66 : Turning angle sensor 67 : Ship speed meter 73 : Rudder angle operating tool 74 : Vessel steering operating tool 83: Propulsion blade 93: Propulsion shaft

Claims (7)

An intake stroke in which a lean mixture consisting of gas fuel and air is sucked into a combustion chamber, a compression stroke in which the lean mixture is compressed, an expansion stroke in which combustion gas generated by combustion of the lean mixture expands, and a combustion stroke in which the combustion gas is expanded. A combustion method for a pilot ignition turbocharged gas engine that repeats a combustion cycle consisting of an exhaust stroke for exhausting air from the combustion chamber,
When the engine load increases, a first injection of liquid fuel into the combustion chamber is performed at a first timing in the compression stroke, and the lean mixture in the combustion chamber is caused by the propagation of the flame generated by the first injection. A second injection for injecting the liquid fuel into the combustion chamber is started at a second timing in the expansion stroke in the second half of the combustion period during which combustion is occurring, and the second injection is performed for the injection amount of the first injection. The injection amount is large, and the ratio of the injection amount of the second injection to the injection amount of the first injection is greater than 1 and 15 or less,
When the engine output is continuously increased from the first output value to the second output value to the third output value in response to the increase in the engine load, the The amount of gas fuel supplied is increased and the amount of gas fuel supplied is increased so that the rate of increase in engine output is greater than the rate of increase in engine output from the second output value to the third output value. The engine output is increased from the first output value to the second output value by gradually increasing the injection amount of liquid fuel from a predetermined first injection amount to a predetermined second injection amount, and the supply amount of the gas fuel is increased. increasing the engine output from the second output value to the third output value by increasing the injection amount of the liquid fuel in the first injection and maintaining the injection amount at the second injection amount;
How gas engines burn. When the maximum rate of change in output that can increase the engine output from the first output value to the third output value without causing knocking in response to an increase in the engine load is set as a fixed rate of change. The rate of increase in the engine output from the first output value to the second output value is greater than the fixed rate of change, and the rate of increase in the engine output from the second output value to the third output value is greater than the fixed rate of change. the same as a fixed rate of change or smaller than the fixed rate of change,
The combustion method for a gas engine according to claim 1. When the engine output increases from the first output value to the second output value to the third output value, the injection amount of the liquid fuel in the first injection is changed from the second injection amount to the first injection amount. reduce ,
The combustion method for a gas engine according to claim 1 or 2. A cylinder and a piston that form a combustion chamber, an air supply pipe that supplies a lean mixture of air and gas fuel to the combustion chamber, a gas fuel supply valve that adjusts the amount of gas fuel supplied, and a liquid in the combustion chamber. an injector that injects fuel, and the piston reciprocates within the cylinder to draw the lean mixture into the combustion chamber; a compression stroke to compress the lean mixture; and a compression stroke to compress the lean mixture. A pilot ignition type turbocharged gas engine in which a combustion cycle consisting of an expansion stroke in which combustion gas generated by combustion expands and an exhaust stroke in which the combustion gas is exhausted from the combustion chamber is repeated,
When the engine load increases, the injector performs a first injection at a first timing in the compression stroke, and a combustion period during which the lean air-fuel mixture in the combustion chamber is combusted by the propagation of the flame generated by the first injection. The second injection is started at a second timing in the expansion stroke in the second half of the expansion stroke, and the injection amount of the second injection is larger than the injection amount of the first injection, and the second injection is The ratio of the injection amount of the injection is greater than 1 and less than or equal to 15,
When the engine output is continuously increased from the first output value to the second output value to the third output value in response to the increase in the engine load, the The gas fuel supply valve increases the supply amount of the gas fuel so that the rate of increase in the engine output is greater than the rate of increase in the engine output from the second output value to the third output value. The injector gradually increases the injection amount of the liquid fuel in the first injection from a predetermined first injection amount to a predetermined second injection amount, thereby increasing the engine output from the first output value to the second output value. and the gas fuel supply valve increases the supply amount of the gas fuel, and the injector maintains the injection amount of the liquid fuel in the first injection at the second injection amount, thereby increasing the engine output to the second injection amount. increasing from the second output value to the third output value ;
Gas engine with turbocharger. When the maximum rate of change in output that can increase the engine output from the first output value to the third output value without causing knocking in response to an increase in the engine load is set as a fixed rate of change. The rate of increase in the engine output from the first output value to the second output value is greater than the fixed rate of change, and the rate of increase in the engine output from the second output value to the third output value is greater than the fixed rate of change. The turbocharged gas engine according to claim 4, wherein the rate of change is equal to or smaller than the fixed rate of change . When the engine output increases from the first output value to the second output value to the third output value, the injector changes the injection amount of the liquid fuel in the first injection from the second injection amount to the third output value. Reduce the injection amount to 1,
The turbocharger-equipped gas engine according to claim 4 or 5. further comprising an air cooler that cools the air sucked into the combustion chamber,
The air cooler includes a refrigerant flow path through which a refrigerant flows, a bypass path that is connected to the refrigerant flow path and allows the refrigerant to flow downstream of the refrigerant flow path without exchanging heat with the air, and a bypass path through which the refrigerant flows through the refrigerant flow path. a flow rate adjustment device that adjusts the flow rate of the refrigerant flowing into the bypass path among the refrigerants;
The flow rate adjustment device blocks the flow of the refrigerant from the refrigerant flow path to the bypass path when the engine load increases.
The turbocharger-equipped gas engine according to any one of claims 4 to 6.

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