JP6109988B1 - EGR system - Google Patents

Abstract

An EGR system capable of operating an engine stably is provided. An exhaust gas recirculation line that recirculates a part of exhaust gas discharged from an engine as a combustion gas to the engine, an EGR blower provided in the exhaust gas recirculation line, and an exhaust gas recirculation line that supplies the engine And a control device that controls the flow rate of the combustion gas mixed with the exhaust gas and air, and the control device calculates the first target value of the EGR blower based on the engine load at the start of operation of the EGR blower. The rising speed of the frequency of the EGR blower is determined based on the first target value and a preset setting time, and the frequency of the EGR blower is increased at the rising speed during the setting time. [Selection] Figure 2

Description

  The present invention relates to an EGR system that supplies engine exhaust gas to an engine.

  An exhaust gas recirculation (EGR) system is available for reducing NOx in exhaust gas discharged from the engine. This EGR system returns a part of exhaust gas discharged from a combustion chamber of an internal combustion engine to a combustion chamber as a combustion gas (for example, Patent Document 1). Therefore, the combustion gas has a reduced oxygen concentration, and the combustion temperature is lowered by delaying the combustion speed, which is a reaction between the fuel and oxygen, and the amount of NOx generated can be reduced.

JP 2010-174661 A

  The EGR system can achieve the target oxygen concentration by adjusting the amount of exhaust gas supplied based on the oxygen concentration, that is, the amount of exhaust gas recirculated to the engine. However, since the change in the oxygen concentration is delayed, if the amount of exhaust gas supplied to the engine is controlled based on the oxygen concentration, the amount of exhaust gas supplied temporarily may become excessive. If the amount of exhaust gas supplied to the engine becomes excessive, combustion in the engine becomes unstable, and engine operation becomes unstable.

  The present invention solves the above-described problems, and an object thereof is to provide an EGR system capable of stably operating an engine.

  The present invention for achieving the above object is an EGR system comprising: an exhaust gas recirculation line for recirculating a part of exhaust gas discharged from an engine as a combustion gas to the engine; and the exhaust gas recirculation line. An EGR blower provided, and a control device that controls the flow rate of the exhaust gas supplied to the engine via the exhaust gas recirculation line, and the control device loads the engine when the EGR blower starts operation. A first target value of the EGR blower is calculated based on the first target value and a preset increase time of the EGR blower is determined based on the first target value, and during the set time, The frequency of the EGR blower is increased at the increasing speed.

  The EGR system can prevent the exhaust gas from being excessively supplied to the engine at the time of starting by limiting the rate of increase in the frequency of the EGR blower at the time of starting. As a result, the engine can be operated stably.

  An oxygen concentration detection unit that measures an oxygen concentration of the combustion gas supplied to the engine, and the control device, after the set time elapses, includes a relationship between a load of the engine and a target value of the oxygen concentration; Based on the relationship between the calculated target value of the oxygen concentration and the measurement result of the oxygen concentration detection unit, and the current frequency of the EGR blower, the frequency of the EGR blower is calculated. Is preferably calculated. The EGR system starts the control to calculate the frequency of the EGR blower based on the oxygen concentration after the set time has elapsed, so that the concentration of the air-fuel mixture supplied to the engine can be set to an appropriate concentration. Occurrence can be suppressed. In addition, by controlling the frequency of the EGR blower based on the oxygen concentration after the set time has elapsed, the difference between the current oxygen concentration and the target oxygen concentration can be reduced. Can be prevented from becoming excessive.

  An oxygen concentration detection unit for measuring an oxygen concentration of the combustion gas supplied to the engine; and the control device, after the frequency of the EGR blower reaches the first target value, The target value of the oxygen concentration is calculated based on the relationship with the target value of the oxygen concentration, the relationship between the calculated target value of the oxygen concentration and the measurement result of the oxygen concentration detector, and the current frequency of the EGR blower It is preferable to calculate the frequency of the EGR blower based on the above. The EGR system starts the control for calculating the frequency of the EGR blower based on the oxygen concentration after the EGR blower frequency reaches the first target value, so that the concentration of the air-fuel mixture supplied to the engine is set to an appropriate concentration. And generation of nitrogen oxides can be suppressed. In addition, by controlling the frequency of the EGR blower based on the oxygen concentration after reaching the first target value, the difference between the current oxygen concentration and the target oxygen concentration can be reduced. It is possible to suppress the amount of exhaust gas to be excessive.

  The first target value is preferably a value equal to or lower than the frequency when the oxygen concentration target value is reached by frequency control of the EGR blower based on the oxygen concentration. By setting the first target value in the above range, it is possible to shorten the time for the amount of exhaust gas supplied from the EGR blower to reach the final target amount while suppressing the supply of exhaust gas from being excessive.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that exhaust gas is supplied excessively to an engine at the time of start-up by restricting the rate of increase of the frequency of the EGR blower at the time of start-up. As a result, the engine can be operated stably.

FIG. 1 is a schematic diagram showing a diesel engine equipped with the EGR system of the present embodiment. FIG. 2 is a schematic configuration diagram showing the EGR system of the present embodiment. FIG. 3 is a block diagram showing a schematic configuration of the EGR control device. FIG. 4 is a graph showing the relationship between the engine output and the control value of the EGR blower frequency. FIG. 5 is a flowchart showing an example of operation control of the EGR blower. FIG. 6 is an explanatory diagram for explaining processing by the EGR control unit. FIG. 7 is a flowchart showing another example of operation control of the EGR blower.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by this embodiment, and when there are two or more embodiments, what comprises combining each embodiment is also included.

  FIG. 1 is a schematic diagram illustrating a diesel engine equipped with an EGR system, and FIG. 2 is a schematic configuration diagram illustrating the EGR system.

  As shown in FIG. 1, the marine diesel engine 10 of this embodiment includes an engine body (engine) 11, a supercharger 12, and an EGR system 13.

  As shown in FIG. 2, the engine body 11 is a propulsion engine (main engine) that drives and rotates the propeller for propulsion via a propeller shaft, although not shown. This engine body 11 is a uniflow scavenging exhaust type diesel engine, which is a two-stroke diesel engine, in which the flow of intake and exhaust in the cylinder is unidirectional from the bottom to the top so as to eliminate the residual exhaust. It is. The engine body 11 includes a plurality of cylinders (combustion chambers) 21 in which pistons move up and down, a scavenging trunk 22 that communicates with each cylinder 21, and an exhaust manifold 23 that communicates with each cylinder 21. A scavenging port 24 is provided between each cylinder 21 and the scavenging trunk 22, and an exhaust passage 25 is provided between each cylinder 21 and the exhaust manifold 23. In the engine body 11, the air supply line G <b> 1 is connected to the scavenging trunk 22, and the exhaust line G <b> 2 is connected to the exhaust manifold 23.

  The engine body 11 is provided with a rotation speed detection unit 62 and a fuel input amount detection unit 64. The rotation speed detection unit 62 detects the rotation speed of the engine body 11 (the rotation speed of the rotation shaft connected to the propeller shaft). The rotation speed detection unit 62 may detect the rotation speed of the rotation shaft inserted into the engine body 11 or may detect the rotation speed of the propeller shaft. The fuel input amount detection unit 64 detects the fuel input amount of the engine body 11.

  The engine control device 26 controls the operation of the engine body 11. The engine control device 26 controls the operation of the engine body 11 based on various input conditions such as a required load and results detected by various sensors such as the rotation speed detection unit 62 and the fuel input amount detection unit 64. The engine control device 26 controls the fuel injection amount and the rotational speed of the engine body 11 by controlling the fuel injection timing and the injection amount into the cylinder. The engine control device 26 controls the output of the engine body 11 by controlling the fuel input amount and the rotation speed.

  The supercharger 12 is configured by connecting a compressor 31 and a turbine 32 so as to rotate integrally with a rotary shaft 33. In the supercharger 12, the turbine 32 is rotated by the exhaust gas discharged from the exhaust line G2 of the engine body 11, the rotation of the turbine 32 is transmitted by the rotary shaft 33, and the compressor 31 is rotated. / Or the recirculated gas is compressed and supplied to the engine body 11 from the supply air line G1. The compressor 31 is connected to a suction line G6 that sucks air from the outside (atmosphere).

  The supercharger 12 is connected to an exhaust line G3 that discharges exhaust gas that has rotated the turbine 32. The exhaust line G3 is connected to a chimney (funnel) (not shown). An EGR system 13 is provided between the exhaust line G3 and the air supply line G1.

  The EGR system 13 includes exhaust gas recirculation lines G4, G5, and G7, a scrubber 42, a demister unit 14, an EGR blower (blower) 47, and an EGR control device 60. The EGR system 13 mixes recirculation gas, which is a part of exhaust gas discharged from the marine diesel engine 10, with air, and then compresses it by the supercharger 12 to recirculate it as a combustion gas to the marine diesel engine 10. This suppresses the generation of NOx due to combustion. Here, a part of the exhaust gas is extracted from the downstream side of the turbine 32, but a part of the exhaust gas may be extracted from the upstream side of the turbine 32.

  In the following description, the exhaust gas is exhausted from the engine body 11 to the exhaust line G2, and then exhausted to the outside from the exhaust line G3. The recirculated gas is separated from the exhaust line G3. A part of the exhaust gas is returned to the engine body 11 by the exhaust gas recirculation lines G4, G5, and G7.

  One end of the exhaust gas recirculation line G4 is connected to the middle part of the exhaust line G3. The exhaust gas recirculation line G4 is provided with an EGR inlet valve (open / close valve) 41A, and the other end is connected to the scrubber 42. The EGR inlet valve 41A opens and closes the exhaust gas recirculation line G4 to turn ON / OFF the inflow of exhaust gas that is diverted from the exhaust line G3 to the exhaust gas recirculation line G4. The flow rate of exhaust gas passing through the exhaust gas recirculation line G4 may be adjusted by using the EGR inlet valve 41A as a flow rate adjustment valve.

  The scrubber 42 is a venturi-type scrubber, and includes a throat portion 43 having a hollow shape, a venturi portion 44 into which recirculated gas is introduced, and an enlarged portion 45 that gradually returns to the original flow velocity. The scrubber 42 includes a water injection unit 46 that injects water to the recirculated gas introduced into the venturi unit 44. The scrubber 42 is connected to an exhaust gas recirculation line G5 that discharges recirculation gas from which harmful substances such as particulate matter (PM) such as SOx and dust are removed and waste water containing harmful substances. In addition, in this embodiment, although the venturi type is employ | adopted as a scrubber, it is not limited to this structure.

  The exhaust gas recirculation line G5 is provided with a demister unit 14 and an EGR blower 47.

  The demister unit 14 separates the recirculated gas from which harmful substances have been removed by water injection and mist (drainage). The demister unit 14 is provided with a drainage circulation line W <b> 1 that circulates drainage to the water injection unit 46 of the scrubber 42. The drainage circulation line W1 is provided with a hold tank 49 and a pump 50 for temporarily storing drainage.

  The EGR blower 47 guides the recirculation gas in the scrubber 42 from the exhaust gas recirculation line G5 to the demister unit 14. The EGR blower 47 sends the exhaust gas that has passed through the demister unit 47 to the compressor 31.

  The exhaust gas recirculation line G7 has one end connected to the EGR blower 47 and the other end connected to the compressor 31 via a mixer (not shown). It is done. The exhaust gas recirculation line G7 is provided with an EGR outlet valve (open / close valve or flow rate adjusting valve) 41B. The air from the suction line G6 and the recirculation gas from the exhaust gas recirculation line G7 are mixed in a mixer to generate combustion gas. This mixer may be provided separately from the silencer, or the silencer may be configured to add a function of mixing the recirculated gas and air without providing a separate mixer. The supercharger 12 can supply the combustion gas compressed by the compressor 31 from the supply line G1 to the engine main body 11, and an air cooler (cooler) 48 is provided in the supply line G1. The air cooler 48 cools the combustion gas by exchanging heat between the combustion gas compressed by the compressor 31 and having a high temperature and the cooling water. In the EGR system 13, an oxygen concentration detection unit 66 is disposed in the supply line G1. The oxygen concentration detection unit 66 of this embodiment is disposed closer to the engine body 11 than the air cooler 48. The oxygen concentration detector 66 detects the oxygen concentration of the air supplied to the engine body 11, that is, the oxygen concentration of the combustion gas in which the recirculation gas and the air are mixed when the EGR system 13 is operating.

  The EGR control device 60 controls the operation of each part of the EGR system 13. Hereinafter, the EGR control device 60 will be described with reference to FIG. FIG. 3 is a block diagram showing a schematic configuration of the EGR control device.

  The EGR control device 60 includes a rotation speed acquisition unit 72, a fuel input amount acquisition unit 74, an oxygen concentration acquisition unit 76, and an EGR control unit 78. The rotational speed acquisition unit 72 acquires information on the rotational speed of the engine body 11 from the rotational speed detection unit 62. The fuel input amount acquisition unit 74 acquires information on the fuel input amount of the engine body 11 from the fuel input amount detection unit 64. The oxygen concentration acquisition unit 76 acquires information on the oxygen concentration of the combustion gas supplied from the oxygen concentration detection unit 66 to the engine body 11. The rotation speed acquisition unit 72, the fuel input amount acquisition unit 74, and the oxygen concentration acquisition unit 76 send the acquired information to the EGR control unit 78.

  The EGR control unit 78 is supplied to the engine main body 11 with the engine speed of the engine body 11 and the fuel input amount acquired by the engine speed acquisition unit 72, the fuel input amount acquisition unit 74, and the oxygen concentration acquisition unit 76. Based on the oxygen concentration of the air, the operating state of the EGR blower 47, specifically the frequency of the motor that rotates the compressor, is controlled to control the amount of recirculated gas supplied from the EGR system 13 to the engine body 11. .

  The EGR control unit 78 includes an operation control unit 90 and an activation control unit 92. The operation control unit 90 executes processing other than when the EGR system 13 is activated. The activation control unit 92 executes processing at the time of activation of the EGR system 13. That is, the start control unit 92 does not execute control while the operation control unit 90 executes control. While the start control unit 92 is executing control, the operation control unit 90 does not execute control.

  The operation control unit 90 stores the relationship between the load of the engine body 11 and the target value of oxygen concentration, and calculates the target value of oxygen concentration according to the load. The operation control unit 90 calculates the load (output) of the engine body 11 based on the rotation speed of the engine body 11 and the fuel input amount. The operation control unit 90 calculates the target value of the oxygen concentration based on the relationship between the engine load and the target value of the oxygen concentration, and the relationship between the calculated target value of the oxygen concentration and the acquired oxygen concentration and the current EGR. Based on the frequency of the blower 47, the frequency (operating frequency) of the EGR blower is calculated. The operation control unit 90 rotates the EGR blower 47 at the calculated frequency of the EGR blower 47. When the calculated frequency of the EGR blower 47 exceeds the set limit value, the operation control unit 90 rotates the EGR blower 47 at the limit value frequency. The limit value may be a value that fluctuates based on at least one of the load (output) of the engine body 11, the rotational speed of the engine body 11, and the fuel input amount of the engine body 11, or may be a constant value. . Although the operation control unit 90 of this embodiment controls the frequency of the motor of the EGR blower 47, the operation control unit 90 may control the number of revolutions of the compressor by controlling the number of revolutions of the motor. This also applies to the activation control unit 92.

  As described above, the activation control unit 92 controls the operation of the EGR blower 47 when the EGR system 13 is activated. The activation control unit 92 stores the relationship between the engine output shown in FIG. 4 and the first target value of the EGR blower frequency. FIG. 4 is a graph showing the relationship between the engine output and the control value of the EGR blower frequency. The first target value and the final target value shown in FIG. 4 are EGR blower frequency values set for the output (load, calculated horsepower) of the engine (engine body 11). The final target value is the frequency of the EGR blower operated at each output in an ideal operating state or in a land test, corrected by oxygen concentration control. That is, the frequency of the EGR blower that can supply air with a target oxygen concentration at each output. The first target value is the number of revolutions of the EGR blower 47 that is lower than the final target value.

  The start control unit 92 determines the first target value corresponding to the current output based on the output of the engine and the relationship shown in FIG. 4 at the start of operation of the EGR blower 47, and is set in advance as the first target value. The frequency of the EGR blower is increased based on the set time, and the frequency of the EGR blower is increased at the increased speed during the set time.

  In the above embodiment, the operation control unit 90 and the activation control unit 92 of the EGR control unit 78 control the EGR blower 47. However, each unit other than the EGR blower 47, for example, the EGR inlet valve 41A, the EGR outlet valve It also controls the opening and closing of 41B, the operation of the scrubber 42, and the operation of the air cooler 48.

  Hereinafter, the operation of the EGR system of this embodiment will be described.

  As shown in FIG. 2, when combustion gas is supplied from the scavenging trunk 22 into the cylinder 21, the engine main body 11 compresses the combustion gas by a piston, and fuel is supplied to the high-temperature combustion gas. By firing, it ignites spontaneously and burns. The generated combustion gas is discharged as exhaust gas from the exhaust manifold 23 to the exhaust line G2. The exhaust gas discharged from the engine body 11 rotates the turbine 32 in the supercharger 12 and then is discharged to the exhaust line G3. When the EGR inlet valve 41A and the EGR outlet valve 41B are closed, the entire amount is exhausted. It is discharged from G3 to the outside.

  On the other hand, when the EGR inlet valve 41A and the EGR outlet valve 41B are open, part of the exhaust gas flows from the exhaust line G3 to the exhaust gas recirculation line G4 as recirculation gas. The scrubber 42 removes harmful substances from the recirculated gas that has flowed into the exhaust gas recirculation line G4. That is, the scrubber 42 injects water from the water injection unit 46 when exhaust gas passes through the venturi unit 44 at a high speed, thereby cooling the recirculated gas with this water and removing harmful substances by dropping with water. To do. Then, the waste water containing the harmful substance flows into the demister unit 14 together with the EGR gas.

  The recirculated gas from which harmful substances have been removed by the scrubber 42 is discharged to the exhaust gas recirculation line G5. After the mist (drainage) is separated by the demister unit 14, it is sent to the supercharger 12 by the exhaust gas recirculation line G7. . The recirculated gas is mixed with the air sucked from the suction line G6 to become a combustion gas, compressed by the compressor 31 of the supercharger 12, and then cooled by the air cooler 48, from the air supply line G1 to the engine. It is supplied to the main body 11.

  Next, an example of control of the EGR blower 47 by the EGR control device 60 will be described with reference to FIGS. 5 and 6. FIG. 5 is a flowchart showing an example of operation control of the EGR blower. FIG. 6 is an explanatory diagram for explaining processing by the EGR control unit. 5 and 6 show an example of the control executed by the start control unit 92 when the EGR system 13 is started up and the process started by the operation control unit 90 after the process is completed by the start control unit 92. The processing shown in FIG. 5 can be realized by the EGR control device 60 controlling the operation of each unit.

  When the EGR control device 60 determines the start of EGR operation (step S12), it calculates the output of the engine (step S14). Specifically, the rotational speed acquisition unit 72 acquires the rotational speed, the fuel input amount acquisition unit 74 acquires the fuel input amount, and calculates the output (load, calculated horsepower) based on the rotational speed and the fuel input amount. . The output value may be acquired from the engine control device 26.

  The EGR control device 60 determines the first target value of the frequency of the EGR blower 47 based on the output of the engine body 11 (step S16). The first target value uses the output of the engine main body 11 and the relationship shown in FIG. 4 to calculate a first target value corresponding to the output of the engine main body 11 and applies the calculated first target value. And

  After determining the first target value, the EGR control device 60 determines the frequency increase rate based on the first target value and the set time (step S18). The frequency increase rate is a frequency that changes (increases) per unit time. Here, the set time is a preset time. The set time can be any time, but is preferably several minutes, for example, 1 minute or more and 10 minutes or less. By setting the set time in the above range, it is possible to suppress a sudden change in the amount of exhaust gas supplied by the EGR blower 47 and a rapid change in the oxygen concentration while suppressing the start-up process from becoming long.

After determining the frequency increase rate, the EGR control device 60 increases the frequency of the EGR blower 47 for a set time based on the frequency increase rate (step S20). Thus, when sip start rising frequency to start operation of the EGR blower 47 at time t ₁ as shown in FIG. 6, the time set at a constant rate of rise, i.e. between time t ₁ of time t _2, the blower frequency (The frequency of the EGR blower 47) increases. When the blower frequency increases, the oxygen concentration (O ₂ concentration) supplied to the engine body 11 decreases. As a result, the amount of the recirculated gas supplied from time t ₁ to time t ₂ increases, so that the oxygen concentration gradually decreases from the current O _{2 at} time t ₁ .

When the set time elapses, the EGR control device 60 starts controlling the blower based on the oxygen concentration (step S22). That is, the control by the start control unit 92 is terminated, and the control by the operation control unit 90 is started. Thus, after the time t _2, the operation control unit 90, so that the oxygen concentration close to the target O ₂ calculated based on the output of the engine, controls the frequency of the EGR blower 47. Specifically, in time t _2, the order EGR blower 47 is operated at the first target value lower than the final target value, the oxygen concentration are higher than the target O _2. The operation control unit 90 increases the frequency of the EGR blower 47 so that the oxygen concentration approaches the target O _2, and sets the EGR blower 47 at a value close to the final frequency estimated value f ₂ where the oxygen concentration is close to the target O _2. drive.

The EGR control device 60 uses the activation control unit 92 to limit the ascent rate of the EGR blower 47 at the time of activation and to keep it constant, so that the oxygen concentration changes rapidly and the oxygen concentration becomes lower than the target O _2. This can be suppressed. That is, when the operation control unit 90 performs control from the start and controls the frequency of the EGR blower 47 with feedback based on the oxygen concentration, for example, the difference between the target O ₂ and the current O ₂ is large. Shoots and oxygen concentration is low. That is, the supply of recirculation gas becomes excessive, and the combustion state in the engine body 11 deteriorates. In addition, after the oxygen concentration overshoot occurs, oxygen concentration hunting occurs, which may increase the fluctuation of the rotational speed of the EGR blower 47. Further, when the control condition is such that the oxygen concentration does not overshoot, the time required for the oxygen concentration to reach the target O ₂ becomes long, and the time until the operating condition that can reduce nitrogen oxides becomes long. On the other hand, since it changes with the rising speed determined to the 1st target value, the frequency of the EGR blower 47 can be raised to the frequency close | similar to a final target value irrespective of the state of oxygen concentration. Thereby, generation | occurrence | production of an overshoot can be suppressed and it can suppress that the quantity of the recirculation gas to supply becomes excess. As described above, the EGR control device 60 can suppress the excessive supply of the recirculation gas to the engine at the time of start-up by limiting the rate of increase in the frequency of the EGR blower 47 at the time of start-up. As a result, the engine can be operated stably.

  Moreover, the EGR control device 60 can set the concentration of the air-fuel mixture supplied to the engine to an appropriate concentration by starting control for calculating the frequency of the EGR blower based on the oxygen concentration after the set time has elapsed, Generation of nitrogen oxides can be suppressed. In addition, by controlling the frequency of the EGR blower based on the oxygen concentration after the set time has elapsed, the difference between the current oxygen concentration and the target oxygen concentration can be reduced. It can suppress that the quantity of becomes excessive.

  Further, the first target value is preferably a value equal to or lower than the frequency (final target value of the EGR blower 47) when the oxygen concentration target value is reached by the frequency control of the EGR blower 47 based on the oxygen concentration. By setting the first target value to a value equal to or lower than the above frequency, it is possible to suppress an excessive supply of recirculation gas.

  Here, in the said embodiment, although control by the oxygen concentration using the operation control part 90 was started after setting time progress, it is not limited to this. Another example of the operation control will be described with reference to FIG. FIG. 7 is a flowchart showing another example of operation control of the EGR blower. Of the processes shown in FIG. 7, processes similar to those shown in FIG. 5 are given the same step numbers, and detailed description thereof is omitted.

  When the EGR control device 60 determines the start of EGR operation (step S12), it calculates the output of the engine (step S14). The EGR control device 60 determines the first target value based on the output of the engine body 11 (step S16). After determining the first target value, the EGR control device 60 determines the frequency increase rate based on the first target value and the set time (step S18).

  After determining the frequency increase rate, the EGR control device 60 increases the frequency of the EGR blower 47 based on the frequency increase rate (step S32). The EGR control device 60 determines whether the frequency of the EGR blower 47 has reached the first target value (step S34). If the EGR control device 60 determines that the frequency of the EGR blower 47 has not reached the first target value (No in step S34), the EGR control device 60 returns to step S32. The EGR control device 60 executes a process of increasing the frequency of the EGR blower 47 based on the frequency increase rate in step S32 until the frequency of the EGR blower 47 reaches the first target value.

  When it is determined that the frequency of the EGR blower 47 has reached the first target value (Yes in step S34), the EGR control device 60 starts controlling the blower based on the oxygen concentration (step S22).

  As described above, in the process shown in FIG. 7, the EGR control unit 60 starts control for calculating the frequency of the EGR blower based on the oxygen concentration after the frequency of the EGR blower reaches the first target value. Thereby, the density | concentration of the air-fuel | gaseous mixture supplied to an engine can be made into an appropriate density | concentration, and generation | occurrence | production of nitrogen oxide can be suppressed. In addition, by controlling the frequency of the EGR blower based on the oxygen concentration after reaching the first target value, the difference between the current oxygen concentration and the target oxygen concentration can be reduced. It can suppress that the quantity of the recirculation gas to perform becomes excess.

  Moreover, in embodiment mentioned above, although demonstrated using the main engine as a marine diesel engine, it is applicable also to the diesel engine used as a generator.

DESCRIPTION OF SYMBOLS 10 Marine diesel engine 11 Engine main body 12 Supercharger 13 EGR system 14 Demister unit 26 Engine control apparatus 41A EGR inlet valve 41B EGR outlet valve 42 Scrubber 47 EGR blower 48 Air cooler (cooler)
60 EGR Control Device 62 Rotational Speed Detection Unit 64 Fuel Input Amount Detection Unit 66 Oxygen Concentration Detection Unit 72 Rotation Number Acquisition Unit 74 Fuel Input Amount Acquisition Unit 76 Oxygen Concentration Acquisition Unit 78 EGR Control Unit 90 Operation Control Unit 92 Startup Control Unit G4 G5, G7 Exhaust gas recirculation line G6 Suction line W1 Drainage circulation line

Claims (4)

An exhaust gas recirculation line for recirculating a part of the exhaust gas discharged from the engine to the engine as a combustion gas;
An EGR blower provided in the exhaust gas recirculation line;
A control device for controlling the flow rate of the exhaust gas supplied to the engine via the exhaust gas recirculation line,
The control device calculates a first target value of the EGR blower based on a load of the engine at the start of operation of the EGR blower,
A frequency increase speed of the EGR blower is determined based on the first target value and a preset setting time, and the frequency of the EGR blower is increased at the increase speed during the setting time. EGR system. An oxygen concentration detector that measures the oxygen concentration of the combustion gas supplied to the engine;
The controller calculates the target value of the oxygen concentration based on the relationship between the engine load and the target value of oxygen concentration after the set time has elapsed, and calculates the target value of the oxygen concentration and the calculated target value of the oxygen concentration. 2. The EGR system according to claim 1, wherein the frequency of the EGR blower is calculated based on a relationship with a measurement result of the oxygen concentration detection unit and a current frequency of the EGR blower. An oxygen concentration detector that measures the oxygen concentration of the combustion gas supplied to the engine;
After the frequency of the EGR blower reaches the first target value, the control device calculates the target value of the oxygen concentration based on the relationship between the engine load and the target value of the oxygen concentration, The frequency of the EGR blower is calculated based on the relationship between the calculated target value of the oxygen concentration and the measurement result of the oxygen concentration detection unit and the current frequency of the EGR blower. EGR system.   The said 1st target value is a value below the frequency at the time of reaching | attaining an oxygen concentration target value by the frequency control of the said EGR blower based on oxygen concentration, The Claim 1 characterized by the above-mentioned. The EGR system described.

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