JP5886356B2 - Engine system and control method - Google Patents

Description

  The present invention uses exhaust gas recirculation (EGR) that uses water emulsion fuel or returns part of the exhaust gas to the engine in order to reduce nitrogen oxide (NOx) emissions from the engine. It relates to the engine system to be performed. The present invention also relates to a method for controlling the engine system.

  One method for reducing NOx emissions from the engine is EGR that returns a portion of the exhaust gas to the engine. By returning a part of the exhaust gas to the engine, combustion is performed in a state where the oxygen concentration is low. As a result, the combustion temperature is lowered and the generation of NOx is suppressed. However, when performing EGR, a sufficient NOx reduction effect can be obtained by increasing the EGR rate (the ratio of the EGR gas in the scavenging gas), but depending on the conditions, the fuel consumption may deteriorate or the soot contained in the exhaust gas There is a problem such as the amount of increase.

  On the other hand, as another method of reducing the amount of NOx discharged from the engine, there is a method of using water emulsion fuel obtained by adding water to pure fuel (fuel to which water is not added). By using the water emulsion fuel, the combustion temperature is lowered by the heat of vaporization of water, and the generation of NOx can be suppressed. Further, when the water in the water emulsion fuel is vaporized and evaporated, the pure fuel surrounding the water particles is scattered, and the scattered pure fuel becomes particles having a small diameter. Thereby, the pure fuel in the water emulsion fuel has a large surface area per volume, that is, an area in contact with oxygen, and local incomplete combustion is reduced. As a result, the combustion efficiency is increased and the amount of soot generated is suppressed. As described above, when the water emulsion fuel is used, the amount of soot contained in the exhaust gas is suppressed although the NOx reduction effect is not large. In addition, there is an advantage that fuel consumption hardly deteriorates until a certain amount of water is added.

  In the engine described in Patent Document 1 below, control is performed to keep the flow rate of EGR gas constant, and when the EGR rate increases with a decrease in the flow rate of scavenging gas, fuel is supplied from pure fuel to water emulsion fuel. Switching (see FIGS. 1 and 2). Thus, the engine described in Patent Document 1 tries to avoid excessive soot generation when the EGR rate is high, specifically when the engine load is lower than 75%.

Special table 2012-518748 gazette

  However, the engine described in Patent Document 1 is provided with a plurality of fuel systems so that the fuel can be switched (see FIGS. 1 and 2). Therefore, the engine described in Patent Document 1 has a complicated structure.

  In addition, in patent document 1, although the ratio of the pure fuel and water supplied to an engine is changed, the structure which changes the water addition rate of water emulsion fuel instantaneously is proposed (refer FIG.3 and FIG.4), In such a configuration, it is difficult to mix pure fuel and water uniformly, and there is a problem in practical use.

  The present invention has been made in view of the above circumstances. When EGR control is performed while using water emulsion fuel, NOx generation is stably suppressed while suppressing deterioration of fuel consumption and soot generation in response to changes in the operating conditions of the engine as long as the characteristics do not cancel each other. An object of the present invention is to provide an engine system that can be reduced and that can be realized with a simple structure.

  An engine system according to an aspect of the present invention includes an engine body having a cylinder and a fuel injection valve, a fuel supply unit that generates water emulsion fuel and supplies the water emulsion fuel to the fuel injection valve, and supplies EGR gas to the engine body. The EGR unit is controlled to use the water emulsion fuel in the entire range of practical engine loads, and the flow rate of the EGR gas is controlled so that the amount of NOx discharged from the engine body becomes a predetermined value or less. And a control device configured as described above.

  Here, the “practical engine load” means an engine load in a range excluding a low engine load such as when the engine is started, that is, an engine load in a range used in normal operation, and 25 to 100% of the maximum engine load is It corresponds to this. According to the above configuration, switching between pure fuel and water emulsion fuel is basically not performed in the entire range of practical engine load. Therefore, according to the engine system described above, a mechanism necessary for instantaneously switching the fuel becomes unnecessary, and the structure can be simplified. In addition, the use of water emulsion fuel can suppress the deterioration of fuel consumption and the generation of soot, and the amount of NOx produced can be reduced by supplying EGR gas corresponding to the engine load to the engine. It is also possible to adjust the amount of NOx produced by changing the water addition rate of the water emulsion fuel, but it is very difficult to change the water addition rate instantaneously while mixing pure fuel and water uniformly. difficult. On the other hand, the flow rate of EGR gas can be quickly changed by controlling the number of revolutions of the EGR blower. Therefore, according to said structure, even if a situation changes rapidly, suppression of NOx production amount can be maintained by controlling the flow volume of EGR gas.

  In the engine system described above, the control device may be configured to maintain a constant water addition rate of the water emulsion fuel in the entire range of practical engine loads. According to such a configuration, since the water addition rate is kept constant throughout the practical engine load range, the generation of soot can be stably suppressed. Under this condition, it is easy to control the water addition rate.

  In the engine system, the control device may be configured to increase the injection time per cycle as the injection amount of the water emulsion fuel per cycle increases. According to such a configuration, even if the injection amount per cycle fluctuates greatly, the injection amount per unit time does not fluctuate greatly. Therefore, even if the variation in the injection amount per cycle is large to some extent, the water emulsion fuel can be injected with the same fuel injection valve.

  In the engine system, when the control device increases the injection time per cycle, the injection timing of the water emulsion fuel is within a range in which the maximum pressure in the cylinder does not exceed a predetermined upper limit value. It may be configured to speed up. According to such a configuration, it is possible to suppress a decrease in the maximum in-cylinder pressure resulting from the longer injection time, and the engine can be operated efficiently.

  In the engine system described above, the control device may be configured to determine the injection start time according to one or both of the water addition rate and the EGR rate. According to such a configuration, an appropriate injection start timing can be determined according to the water addition rate and the EGR rate, so that it is possible to quickly shift to an efficient operating state of the engine.

  A control method according to an aspect of the present invention includes an engine main body having a cylinder and a fuel injection valve, a fuel supply unit that generates water emulsion fuel and supplies the water emulsion fuel to the fuel injection valve, and supplies EGR gas to the engine main body. A control method for an engine system comprising an EGR unit, wherein the water emulsion fuel is used in the entire range of practical engine loads, and the amount of NOx discharged from the engine body is less than a predetermined value. The flow rate of the EGR gas is controlled.

  In the above control method, the water addition rate of the water emulsion fuel may be kept constant in the entire range of practical engine load.

  Moreover, in said control method, you may lengthen the injection time per cycle as the injection amount per cycle of the said water emulsion fuel increases.

  In the above control method, when the injection time per cycle is lengthened, the water emulsion fuel injection start timing may be advanced within a range in which the maximum pressure in the cylinder does not exceed a predetermined upper limit value. .

  In the above control method, the injection start timing may be determined according to one or both of the water addition rate and the EGR rate.

  As described above, according to the engine system described above, by using water emulsion fuel and performing EGR, it is possible to reduce the amount of NOx generated while suppressing the deterioration of fuel consumption and the generation of soot, and this It can be realized with a simple structure.

FIG. 1 is a schematic diagram of the entire engine system according to the embodiment. FIG. 2 is a block diagram of a control system of the engine system according to the embodiment. FIG. 3 is a diagram showing the relationship between the engine load, the target water addition rate, and the target EGR rate. FIG. 4 is a diagram showing the relationship between the engine load and the target EGR rate when the target water addition rate in FIG. 3 is lowered. FIG. 5 is a flowchart of fuel injection control. FIG. 6 is a conceptual diagram showing the relationship between the crank angle and the in-cylinder pressure.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Below, the same code | symbol is attached | subjected to the element which is the same or it corresponds through all the drawings, and the overlapping description is abbreviate | omitted.

<Overall configuration of engine system>
First, the overall configuration of the engine system 100 according to the present embodiment will be described. FIG. 1 is a block diagram of the engine system 100. As shown in FIG. 1, the engine system 100 includes an engine body 10, a supercharger 20, an EGR unit 30, and a fuel supply unit 40.

  The engine body 10 in the present embodiment is a main propulsion unit for a ship, and is a large two-stroke diesel engine. The engine body 10 has a plurality of cylinders 11 (only one is shown in FIG. 1). Each cylinder 11 is formed with a scavenging port 12 in the lower part and an exhaust port 13 in the upper part. Each cylinder 11 is provided with a piston 14, a fuel injection valve 15, and an exhaust valve 16. The piston 14 slides in the cylinder 11 so as to cross the scavenging port 12, and a lower end portion is connected to a crankshaft (not shown). The fuel injection valve 15 is located in the upper part of the cylinder 11 and is supplied with fuel from the fuel supply unit 40. Further, the cylinder 11 is provided with an in-cylinder pressure sensor 17 for measuring the pressure in the cylinder 11 (in-cylinder pressure), and the engine body 10 has an engine speed for measuring the number of revolutions of the engine body 10 (engine speed). A total of 18 (see FIG. 2) is provided. The engine body 10 may be a 4-stroke engine, a gas engine, or a gasoline engine.

  The supercharger 20 is a device that boosts air and supplies it to the engine body 10. The exhaust gas generated in each cylinder 11 is supplied to the turbine unit 21 of the supercharger 20 via the exhaust port 13, the exhaust pipe 24, and the exhaust passage 25. The turbine unit 21 is rotated by the energy of the supplied exhaust gas. The turbine part 21 and the compressor part 22 are connected by a connecting shaft 23, and the compressor part 22 also rotates as the turbine part 21 rotates. When the compressor unit 22 rotates, the air (fresh air) taken from the outside is increased in pressure, and the increased new air is supplied into each cylinder 11 via the scavenging flow path 26, the scavenging pipe 27, and the scavenging port 12. .

  The EGR unit 30 is provided in an EGR flow path 28 that connects the exhaust flow path 25 and the scavenging flow path 26, and extracts a part of the exhaust gas in the exhaust flow path 25 (hereinafter referred to as exhaust gas extracted from the exhaust flow path 25). This unit is a unit that supplies the EGR gas to the scavenging flow path 26. The EGR gas supplied to the scavenging passage 26 is mixed with fresh air whose pressure has been increased by the supercharger 20 and supplied as scavenging gas to the engine body 10 (each cylinder 11). As a result, the oxygen concentration of the scavenging gas supplied to each cylinder 11 decreases, and the amount of NOx discharged from the engine body 10 can be reduced. The EGR unit 30 includes a scrubber 31 that cleans the EGR gas, a cooling device 32 that cools the EGR gas, and an EGR blower 33 that boosts the EGR gas and supplies it to the scavenging flow path 26. By adjusting the rotation speed of the EGR blower 33, the flow rate of the EGR gas, and thus the EGR rate, can be changed. However, the EGR gas flow rate (and thus the EGR rate) may be changed by a flow rate adjusting valve (not shown) provided in the EGR flow path 28.

  The fuel supply unit 40 is a unit that generates water emulsion fuel and supplies it to the fuel injection valve 15. The fuel supply unit 40 includes a fuel generation unit 41 and a fuel supply unit 42. The fuel generation unit 41 is a part that mixes pure fuel and water charged into the mixing container 43 with a mixer or the like to generate water emulsion fuel having a predetermined water addition rate. In a structure in which pure fuel and water are simultaneously supplied to the fuel injection valve 15 (see FIGS. 3 and 4 of Patent Document 1), it is difficult to uniformly mix pure fuel and water. Pure fuel and water can be mixed uniformly. Note that the actual water addition rate can be calculated based on the ratio of pure fuel and water that has been added. The fuel supply unit 42 is a part that supplies the water emulsion fuel generated by the fuel generation unit 41 to the fuel injection valve 15 of the engine body 10. The fuel supply unit 42 can change the injection time and injection start timing of the water emulsion fuel injected from the fuel injection valve 15.

<Control system configuration>
Next, the configuration of the control system of the engine system 100 will be described. FIG. 2 is a block diagram of a control system of engine system 100. As shown in FIG. 2, the engine system 100 includes a control device 50 that controls the entire engine system 100. The control device 50 is configured by, for example, a CPU, a ROM, a RAM, and the like.

  The control device 50 is electrically connected to the in-cylinder pressure sensor 17, the engine tachometer 18, and the input setting unit 51. The control device 50 acquires the in-cylinder pressure, the engine speed, and the set water addition rate based on signals transmitted from these devices. The input setting unit 51 is provided in the cab of the hull in which the engine system 100 is mounted. In addition, the input setting unit 51 is configured so that the driver can input the set water addition rate and can store the input set water addition rate.

  The control device 50 performs various calculations based on the input signals from the above devices and controls each part of the engine system 100. In the present embodiment, the control device 50 is electrically connected to the EGR blower 33, the fuel generation unit 41, and the fuel supply unit 42, and sends control signals to these devices based on the results of various calculations. Send. Note that the control device 50 can acquire the actual water addition rate based on the signal transmitted from the fuel generating unit 41 as well as transmitting the control signal to the fuel generating unit 41. However, the actual water addition rate may be acquired based on a signal transmitted from the sensor provided in the flow path from the mixing container 43 to the injection valve 15 of the fuel generation unit 41 to the water addition rate. Good.

  The control device 50 includes a water addition rate control unit 52, an EGR rate control unit 53, and a fuel injection control unit 54 as functional configurations.

  The water addition rate control unit 52 is a part that controls the water addition rate of the water emulsion fuel. The water addition rate control unit 52 first sets a target water addition rate based on the set water addition rate input by the driver. In the present embodiment, the target water addition rate is set as shown by the broken line in FIG. Specifically, when the engine load is 0 to 15%, the target water addition rate is set to 0%, and when the engine load is 15 to 100%, the target water addition rate is set to the above set water addition rate. And the water addition rate control part 52 transmits a control signal to the fuel production | generation part 41, and controls it so that an actual water addition rate may turn into a target addition rate.

  Thus, in this embodiment, pure fuel is not used but only water emulsion fuel is used in the whole range of practical engine loads (engine load is 25 to 100%). Moreover, the water addition rate is constant in the practical engine load region. Therefore, according to this embodiment, a mechanism that instantaneously switches between pure fuel and water emulsion fuel and a mechanism that instantaneously changes the water addition rate are unnecessary. Further, in Patent Document 1 described above, when the pure fuel and the water emulsion fuel are switched, the fuel injection valve to be used is also switched. However, according to the present embodiment, a mechanism for switching the fuel injection valve is unnecessary. Thus, according to the present embodiment, the configuration of the engine system 100 can be simplified.

  The EGR rate control unit 53 is a part that controls the EGR rate by adjusting the flow rate of the EGR gas. The EGR rate control unit 53 first sets a target EGR rate. In this embodiment, as shown by the solid line in FIG. 3, the target EGR rate is set to 0% when the engine load is 0 to 15%, and the target EGR is increased as the engine load increases when the engine load is 15 to 100%. Set the rate to be small. The target EGR rate is a value derived by a test performed in advance, and is an EGR rate that can clear the NOx emission amount regulation, that is, an EGR rate at which the NOx emission amount becomes a predetermined value or less. The target EGR rate is stored in the EGR rate control unit 53.

  FIG. 4 is a diagram showing the relationship between the engine load and the target EGR rate when the target water addition rate in FIG. 3 is lowered. The two dotted lines in FIG. 4 correspond to the target water addition rate and the target EGR rate in FIG. 3, respectively. As shown in FIG. 4, it is assumed that the set water addition rate is lowered and the target water addition rate when the engine load is 15% or more is lowered. Then, the target EGR rate when the engine load is 15% or more is increased. This is because if the water addition rate is reduced, the NOx emission reduction effect due to the use of water emulsion fuel is reduced, so that the EGR rate must be increased in order to satisfy the NOx emission restriction.

  Subsequently, the EGR rate control unit 53 transmits a control signal to the EGR blower 33, and the actual EGR rate is calculated based on the engine load at that time (in this embodiment, the engine load is calculated based on the engine speed and the fuel injection amount). However, it may be calculated by another method, for example, it may be calculated from the number of revolutions of the supercharger 20, or may be calculated from the illustrated work obtained by the in-cylinder pressure. It is also possible to directly measure the engine load.) The EGR gas flow rate is adjusted so that the target EGR rate corresponding to the engine load is obtained. Thereby, the NOx emission regulation can be cleared. In the present embodiment, the EGR gas flow rate is adjusted by controlling the rotation speed of the EGR blower 33. However, the EGR gas flow rate may be adjusted by other methods such as a method of controlling by the flow rate control valve. Regardless of which method is used, the adjustment of the EGR gas flow rate is easy, and the responsiveness of the change in the EGR gas flow rate with respect to the situation change is very high.

  The fuel injection control unit 54 is a part that controls fuel injection (injection amount, injection time, and injection start timing) of the water emulsion fuel. FIG. 5 is a flowchart showing a method of fuel injection control of water emulsion fuel. Calculation and control described below are performed by the fuel injection control unit 54.

  First, when the process is started, the fuel injection control unit 54 reads signals transmitted from the in-cylinder pressure sensor 17, the engine tachometer 18, the fuel generation unit 41, and the like, and based on these signals, the in-cylinder pressure and the engine Various information such as the rotation speed and the water addition rate is acquired (step S1).

  Subsequently, the fuel injection control unit 54 determines the amount of water emulsion fuel to be injected per cycle (step S2). In the present embodiment, the injection amount is determined so that the engine speed can be maintained at a constant speed (100% speed). However, even if the injection amount is the same, the heat amount is different if the water addition rate is different, and the combustion efficiency is different if the EGR rate is different. Therefore, for example, when the water addition rate or the EGR rate becomes high, the injection amount is increased.

  Subsequently, the fuel injection control unit 54 determines the injection time of the water emulsion fuel to be injected per cycle (step S3). In the present embodiment, the injection time is lengthened as the fuel injection amount per cycle increases. Thereby, even if the injection amount per cycle increases, the injection amount per unit time does not increase. Therefore, even if the injection amount per cycle fluctuates to some extent, normal injection is possible using the same fuel injection valve 15.

  Subsequently, the fuel injection control unit 54 determines whether or not the injection time has been changed (step S4). As will be described later, each step is repeated, but it is determined whether or not the injection time determined in step S3 has changed from the injection time set in the previous cycle. If the fuel injection control unit 54 determines that the injection time has changed (YES in step S4), the process proceeds to step S5. On the other hand, if it is determined that the injection time has not changed (NO in step S4), the process proceeds to step S6.

  Then, when progressing to step S5, the fuel-injection control part 54 determines the injection start time (crank angle which starts injection). Specifically, based on the water addition rate, EGR rate, and engine load, the value read from the map data stored in advance is used as the injection start timing. In this embodiment, the injection start timing is determined based on the water addition rate, the EGR rate, and the engine load. However, the injection start timing is determined based on the parameters corresponding to the water addition rate, the EGR rate, and the engine load. May be. For example, the value of the oxygen concentration in the scavenging tube 27 may be used instead of the EGR rate.

  FIG. 6 is a conceptual diagram showing the relationship between the crank angle and the in-cylinder pressure. The solid line in the figure shows the case where pure fuel is used, the broken line shows the case where water emulsion fuel is used, and the dotted line shows the case where the injection start timing is advanced using water emulsion.

  When pure fuel is used as the fuel, as shown by the solid line in FIG. 6, the in-cylinder pressure reaches the first peak when the piston 14 rises and reaches top dead center (crank angle = 0 °). When fuel injection is started at this time, the in-cylinder pressure once decreases and then rises again by combustion to reach a second peak. The cylinder pressure at the second peak is the maximum cylinder pressure (Pmax). This maximum in-cylinder pressure can be adjusted by changing the fuel injection start timing. The higher the maximum in-cylinder pressure, the higher the engine efficiency. However, if the in-cylinder pressure becomes too high, the cylinder 11 may be damaged. Therefore, normally, the injection start timing is determined so that the maximum in-cylinder pressure becomes a predetermined target value (a maximum value within a range not exceeding the upper limit value). Note that the fuel injection control unit 54 may perform control to correct the injection start timing when the maximum in-cylinder pressure may exceed the upper limit value.

  On the other hand, it is assumed that water emulsion fuel is used as the fuel and fuel injection is started when the crank angle is 0 ° as in the case of pure fuel. As a result, the water emulsion fuel has a smaller calorific value per volume than the pure fuel and is injected for a relatively long period of time. Therefore, as shown by the broken line in FIG. Become. As a result, the maximum in-cylinder pressure becomes lower than a predetermined target value.

  On the other hand, water emulsion fuel is used as the fuel, but it is assumed that the injection start timing is earlier than in the case of pure fuel. Then, as shown by the dotted line in FIG. 6, the rising of the curve toward the second peak of the in-cylinder pressure starts earlier, and as a result, the maximum in-cylinder pressure can be set to a predetermined target value or a value close thereto. That is, the maximum in-cylinder pressure can be set to a predetermined target value or a value close to this by increasing the injection start timing as the injection time per cycle becomes longer.

  In the present embodiment, the injection start timing is calculated based on the water addition rate, the EGR rate, and the maximum in-cylinder pressure at a predetermined target value or a value close to the predetermined value for each engine load by a test performed in advance. The time is stored as map data. Therefore, when the water emulsion fuel injection is started at the injection start timing determined in step S5, the maximum in-cylinder pressure becomes a predetermined target value or a value close thereto.

  On the other hand, when it progresses to step S6, the fuel-injection control part 54 correct | amends an injection start time. Specifically, the fuel injection control unit 54 corrects the injection start timing so that the difference between the actual maximum in-cylinder pressure and a predetermined target value becomes small. Thus, in this embodiment, immediately after the injection time is changed, the injection start timing that is the initial value is determined based on the water addition rate and the EGR rate (step S5), and thereafter the actual maximum in-cylinder pressure is set. Based on this, the injection start timing is corrected (step S6). That is, in this embodiment, control combining feedforward control and feedback control is performed.

  Subsequently, after step S5 or S6, the fuel injection control unit 54 transmits a control signal to the fuel supply unit 42 to inject water emulsion fuel at the determined injection amount, injection time, and injection start timing ( Step S7). When step S7 ends, the fuel injection control unit 54 returns to step S1 and repeats steps S1 to S7. In the present embodiment, since the fuel injection control as described above is performed, the water emulsion fuel is injected at an appropriate injection start timing, so that the engine body 10 can be operated efficiently.

  The above is the description of the embodiment according to the present invention. The case where the feedback control and the feedforward control are combined when determining the fuel injection start timing has been described above. However, the fuel injection start timing may be determined only by the control corresponding to the feedforward control. . That is, without providing the cylinder pressure sensor 17 in the cylinder 11, the injection start timing may be determined based on the water addition rate, the EGR rate, and the engine load, and the injection start timing may be maintained.

  In the above description, the case where the water addition rate of the water emulsion fuel is constant over the entire range of the practical engine load has been described. However, the water addition rate may change gradually. Even with such an engine system, it is possible to achieve the effect of being able to reduce the amount of NOx produced while suppressing the deterioration of fuel consumption and the generation of soot with a simple structure.

  According to the engine system of the present invention, by using water emulsion fuel and performing EGR, it is possible to reduce the amount of NOx generated while suppressing the deterioration of fuel consumption and the generation of soot. Can be realized with a structure. In addition, since the EGR rate that facilitates follow-up control with respect to load fluctuations is used as a main control variable, control can be performed reliably with no control delay for NOx reduction. Since it can be realized with a simple structure, it is useful as a widely versatile NOx reduction system.

DESCRIPTION OF SYMBOLS 10 Engine main body 11 Cylinder 15 Fuel injection valve 30 EGR unit 40 Fuel supply unit 50 Control apparatus 100 Engine system

Claims (8)

An engine body having a cylinder and a fuel injection valve;
A fuel supply unit that generates water emulsion fuel and supplies it to the fuel injection valve;
An EGR unit for supplying EGR gas to the engine body;
It is configured to control the use of the water emulsion fuel in the entire range of the practical engine load, and to control the flow rate of the EGR gas so that the amount of NOx discharged from the engine body becomes a predetermined value or less. A control device comprising :
The engine system is configured to maintain a constant water addition rate of the water emulsion fuel in the entire range of practical engine loads . An engine body having a cylinder and a fuel injection valve;
A fuel supply unit that generates water emulsion fuel and supplies it to the fuel injection valve;
An EGR unit for supplying EGR gas to the engine body;
It is configured to control the use of the water emulsion fuel in the entire range of the practical engine load, and to control the flow rate of the EGR gas so that the amount of NOx discharged from the engine body becomes a predetermined value or less. A control device comprising:
The control device increases the injection time per cycle as the injection amount of the water emulsion fuel per cycle increases, and the maximum pressure in the cylinder regardless of the injection amount of the water emulsion fuel per cycle. The engine system is configured to advance the injection timing of the water emulsion fuel so that can maintain a predetermined target value. The engine system according to claim 2 , wherein the control device is configured to maintain a constant water addition rate of the water emulsion fuel in an entire range of practical engine loads. The engine system according to claim 2 or 3 , wherein the control device is configured to determine the injection start time according to one or both of the water addition rate and the EGR rate. An engine body having a cylinder and a fuel injection valve;
A fuel supply unit that generates water emulsion fuel and supplies it to the fuel injection valve;
An EGR unit for supplying EGR gas to the engine body, and a control method for an engine system,
While using the water emulsion fuel in the entire range of practical engine load, the flow rate of the EGR gas is controlled so that the amount of NOx discharged from the engine body is a predetermined value or less ,
A control method for maintaining a constant water addition rate of the water emulsion fuel in a whole range of practical engine loads . An engine body having a cylinder and a fuel injection valve;
A fuel supply unit that generates water emulsion fuel and supplies it to the fuel injection valve;
An EGR unit for supplying EGR gas to the engine body, and a control method for an engine system,
While using the water emulsion fuel in the entire range of practical engine load, the flow rate of the EGR gas is controlled so that the amount of NOx discharged from the engine body is a predetermined value or less,
As the injection amount per cycle of the water emulsion fuel increases, the injection time per cycle is lengthened, and the maximum pressure in the cylinder is a predetermined target value regardless of the injection amount per cycle of the water emulsion fuel. The control method of advancing the injection start timing of the water emulsion fuel so as to maintain the above .   The method according to claim 6, wherein a water addition rate of the water emulsion fuel is kept constant throughout a practical engine load range. The control method according to claim 6 or 7 , wherein the injection start timing is determined based on one or both of the water addition rate and the EGR rate.

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