JP2019082131A - Engine system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine system capable of maintaining controllability of an exhaust gas extraction amount even when the extraction amount of exhaust gas extracted from an exhaust passage is small. An engine system according to an aspect of the present invention captures gas from a scavenging flow passage or from a downstream of an EGR blower in an EGR flow passage, and uses the taken-in gas as circulation gas rather than an EGR blower in an EGR flow passage. When the target extraction amount of the exhaust gas extracted from the exhaust flow passage is equal to or less than a predetermined lower limit value, the total amount of gas passing through the EGR blower is larger than the lower limit value. Circulating gas is supplied upstream of the EGR blower in the EGR passage. [Selection diagram] Figure 1

Description

  The present invention relates to an engine system.

  In order to comply with exhaust gas regulations that have been tightened in recent years, in an engine system for large ships, exhaust gas is extracted from the exhaust gas flow path, and the extracted exhaust gas is taken into scavenging gas of the scavenging gas flow path and circulated to the engine body Recirculation (Exhaust Gas Recirculation; EGR) has been performed (see, for example, Patent Document 1). By carrying out the EGR, the oxygen concentration of the scavenging gas is lowered, and the combustion time in the cylinder is prolonged, so that the maximum combustion temperature is lowered and the amount of NOx emission can be suppressed.

JP, 2017-160799, A

  By the way, in the case of a four-stroke type diesel engine which is often adopted in an engine system for automobiles, etc., exhausting is performed by raising the piston, so the exhaust stroke is generally more exhaust than the scavenging passage (intake passage). Since the pressure in the flow path is higher, if the EGR flow path is provided to connect the scavenging air flow path and the exhaust flow path, the exhaust gas naturally flows from the exhaust flow path toward the scavenging flow path in the EGR flow path. Flow. Therefore, if an open / close control valve is provided in the EGR flow path and the opening degree of the open / close control valve is adjusted, the supply amount of exhaust gas supplied from the exhaust flow path to the scavenging flow path, that is, extraction of exhaust gas extracted from the exhaust flow path The amount can be adjusted.

  On the other hand, in the case of a two-stroke engine which is often adopted in an engine system for a large ship or the like, the exhaust gas in the cylinder is pushed out by the scavenging gas, so the exhaust flow path is generally better than the scavenging flow path Because the pressure is low, it is not sufficient to provide the exhaust gas flow path from the exhaust flow path to the scavenging flow path only by providing the EGR flow path, and it is necessary to provide the EGR blower in the EGR flow path. In this case, in order to adjust the extraction amount of the exhaust gas, it is general to control the rotational speed of the EGR blower. However, because the amount of exhaust gas extraction required varies greatly depending on the operating state of the engine, if the amount of exhaust gas extraction is made constant regardless of the operating conditions of the engine, the amount of exhaust gas extraction may not be optimal If the amount of exhaust gas extracted is more than the optimum amount, there is a risk of misfiring due to lack of oxygen, and conversely, if it is less than the optimum amount, the combustion temperature can not be lowered sufficiently and the NOx suppression effect is increased. I can not If the required extraction amount of exhaust gas is small, the rotational speed of the EGR blower will be lowered, but it becomes difficult to stably control the rotational speed of the blower in the low rotational range, so the exhaust gas extraction amount can be finely controlled There are also cases where the number of revolutions can not be continuously operated due to the heat radiation characteristics of the blower.

  The present invention has been made in view of the above circumstances, and can maintain the controllability of the exhaust gas extraction amount even when the exhaust gas extraction amount extracted from the exhaust passage is small. The purpose is to provide an engine system.

  An engine system according to an aspect of the present invention includes an engine body, an exhaust flow path for discharging exhaust gas generated in the engine body, a scavenging flow path for supplying scavenging gas to the engine body, and the exhaust flow path An EGR flow path for extracting exhaust gas and supplying it to the scavenging flow path, an EGR blower provided in the EGR flow path, and gas from the scavenging flow path or from downstream of the EGR blower in the EGR flow path A circulation flow path which takes in and takes in the taken-in gas as a circulation gas upstream of the EGR blower in the EGR flow path, a circulation gas adjustment unit which adjusts the supply amount of the circulation gas, the EGR blower and the circulation And a controller for controlling the gas adjustment unit, wherein the controller controls the EGR block when the target extraction amount of the exhaust gas extracted from the exhaust flow path is equal to or less than a predetermined lower limit value. As the total amount of gas passing through is more than the lower limit value, and controls to supply the circulating gas to the upstream of the EGR blower of the EGR path.

  According to this configuration, even if the amount of exhaust gas extracted from the exhaust flow path is small, the total amount of gas passing through the EGR blower becomes larger than the lower limit value, so the number of revolutions of the EGR blower decreases. Thus, the controllability of the exhaust gas extraction amount can be maintained.

  In the above engine system, the circulation flow passage may be configured to take in the circulation gas from a downstream side of a junction point where the EGR passage of the scavenging flow passage merges.

  At the confluence point of the scavenging flow path, scavenging gas (new air) flowing upstream of the confluence point of the scavenging flow path and the gas flowing in the EGR flow path merge. Therefore, in the downstream of the merging point of the scavenging flow passage, the flow passage is formed larger than the upstream of the merging point of the scavenging flow passage and the EGR flow passage. Therefore, the flow of the scavenging gas is relatively stable downstream of the merging point of the scavenging flow path. Therefore, as described above, according to the configuration in which the circulating gas is extracted from the downstream of the scavenging air passage, the stable circulating gas can be supplied to the EGR passage.

  In the above engine system, the scavenging flow path has a scavenging chamber for temporarily storing scavenging gas and then supplying the scavenging gas to the engine body, and the circulation flow path is configured to take in the circulating gas from the scavenging chamber. It may be configured.

  Since the pressure fluctuation is small in the scavenging chamber, as described above, according to the configuration in which the circulating gas is extracted from the scavenging chamber, more stable circulating gas can be supplied to the EGR flow path.

  In the above engine system, when the target extraction amount is equal to or less than the lower limit value, the control device makes the number of revolutions of the EGR blower constant and makes the total amount of gas passing through the EGR blower constant. The supply amount of the circulating gas is adjusted so that the amount of exhaust gas contained in the gas passing through the blower becomes the target extraction amount, and when the target extraction amount is larger than the lower limit value, the supply of the circulation gas is The rotation speed of the EGR blower may be adjusted such that the total amount of gas passing through the EGR blower becomes the target extraction amount while the engine is stopped.

  In this configuration, when the target extraction amount is equal to or less than the lower limit value, the rotational speed of the EGR blower is kept constant to adjust the flow rate of the circulating gas, while when the target extraction amount is larger than the lower limit value, the supply of the circulating gas is stopped. Adjust the rotational speed of the EGR blower. In other words, adjustment of the exhaust gas extraction amount can be simplified because only one of the rotational speed of the EGR blower or the flow rate of the circulating gas is adjusted according to the target extraction amount.

  In the above engine system, the control system is configured to set the target extraction amount based on the oxygen concentration detected by the oximeter, and the control device includes an oximeter that detects the oxygen concentration of the scavenging gas. It is also good.

  According to this configuration, since the target extraction amount is set based on the oxygen concentration detected by the oximeter, the emission amount of NOx exhausted from the engine system can be appropriately adjusted.

  According to the above configuration, the controllability of the exhaust gas extraction amount can be maintained even when the exhaust gas extraction amount extracted from the exhaust flow passage is small.

FIG. 1 is an overall view of an engine system. FIG. 2 is a block diagram of a configuration of a control system of the engine system. FIG. 3 is a flowchart of the control program. FIG. 4 is a control block diagram of oxygen concentration control.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, the same or corresponding elements are denoted by the same reference numerals throughout all the drawings, and redundant description will be omitted.

<Overall configuration of engine system>
First, the overall configuration of engine system 100 will be described. FIG. 1 is an overall view of an engine system 100. An engine system 100 according to the present embodiment is an engine system for a large ship, and includes an engine body 10, an exhaust passage 20, a supercharger 30, a scavenging passage 40, an EGR passage 50, and an EGR blower. 60, a circulation flow passage 70, and a circulation gas adjustment unit 80. Hereinafter, each of these components will be described in order.

  The engine body 10 of the present embodiment is a main engine for propulsion of a ship, and is a large two-stroke diesel engine. The engine body 10 has a plurality of cylinders 11, and the piston 12 is driven by the explosive combustion of fuel in each of the cylinders 11. The engine body 10 is provided with a fuel supply device 13 for supplying fuel to the cylinder 11 and an engine tachometer 14 (both of which are shown in FIG. 2) for detecting the engine rotational speed.

  The exhaust flow passage 20 is a flow passage for discharging the exhaust gas generated by the explosive combustion of the fuel in the cylinder 11 to the outside. The exhaust passage 20 has an exhaust chamber 21 located near the outlet of the engine body 10. The exhaust gas generated by the engine body 10 is temporarily stored in the exhaust chamber 21 and then exhausted to the outside.

  The supercharger 30 is a device for compressing scavenged gas (fresh air). The turbocharger 30 has a turbine portion 31 provided in the exhaust flow path 20, a compressor portion 32 provided in the scavenging flow path 40, and a connecting shaft 33 connecting the turbine portion 31 and the compressor portion 32. . When the turbine unit 31 is rotated by the energy of the exhaust gas, the compressor unit 32 is also rotated accordingly. As the compressor unit 32 rotates, scavenged gas (fresh air) taken from the outside is compressed.

  The scavenging air flow path 40 is a flow path for supplying scavenging gas to the engine body 10. The scavenging gas compressed by the supercharger 30 flows through the scavenging air flow path 40, and merges with the gas supplied from the EGR flow path 50 at a junction point 41 and is supplied to the engine main body 10. The scavenging air passage 40 has a scavenging chamber 42 located near the inlet of the engine body 10. The scavenging chamber 42 temporarily supplies scavenging gas and then supplies the scavenging gas to the engine body 10. Further, in the scavenging chamber 42 of the scavenging air flow passage 40, an oxygen concentration meter 43 for detecting the oxygen concentration of the scavenging gas is provided. The installation location of the oximeter 43 is not limited to the scavenging chamber 42. For example, the oximeter 43 may be provided between the merging point 41 of the scavenging flow passage 40 and the scavenging chamber 42.

  The EGR flow path 50 is a flow path which extracts exhaust gas from the exhaust flow path 20 and supplies the extracted exhaust gas to the scavenging flow path 40. The EGR flow passage 50 is a downstream side of the exhaust flow passage 20 with respect to the exhaust chamber 21 and an upstream side of the turbine portion 31 and a downstream side of the scavenging air flow passage 40 with respect to the scavenging chamber 42. And the part of

  The EGR blower 60 is a device that is provided in the EGR passage 50 and supplies the exhaust gas extracted from the exhaust passage 20 to the scavenging passage 40. The EGR blower 60 of the present embodiment is a positive displacement blower in which the number of rotations and the air flow rate are proportional, and more specifically, it is a roots blower. However, the EGR blower 60 may be a blower other than a positive displacement type such as a turbo type. When the air flow rate is low and the rotational speed is low, the controllability of controlling the air flow rate is reduced. Further, the EGR blower 60 of the present embodiment is a self-cooling blower that drives the cooling mechanism by the rotation of the EGR blower 60 itself. Therefore, when the rotation speed of the EGR blower 60 is lowered, the cooling mechanism can not be sufficiently driven, and the cooling effect is reduced.

  The circulation flow passage 70 is a flow passage for supplying the circulation gas upstream of the EGR blower 60 of the EGR flow passage 50. The circulation flow passage 70 of the present embodiment takes in the scavenging gas from the scavenging chamber 42 and supplies the taken-in scavenging gas as a “circulating gas” upstream of the EGR blower 60 of the EGR passage 50. However, the circulation flow path 70 may take in gas from the portion other than the scavenging chamber 42 of the scavenging flow path 40 (including the portion between the junction 41 and the scavenging chamber 42), and the gas may be used as a circulation gas. A gas may be taken in from the downstream of the EGR blower 60 of the EGR flow passage 50, and the gas may be used as a circulating gas.

  However, since the exhaust gas (new air) and the gas flowing through the EGR passage 50 merge at the junction 41 of the scavenging flow passage 40, the upstream of the junction 41 of the scavenging flow passage 40 or the EGR downstream of the junction 41 is The flow path is formed larger than the flow path 50. Therefore, the flow of the scavenging gas is relatively stable downstream of the merging point 41 of the scavenging air flow passage 40. Therefore, according to the configuration in which the circulation flow path 70 is taken in from the downstream of the scavenging air flow path 40 but the gas is the circulation gas, stable circulation gas can be supplied to the EGR flow path 50.

  Furthermore, since the pressure fluctuation is small in the scavenging chamber 42, according to the configuration in which the circulation flow path 70 uses the gas taken in from the scavenging chamber 42 as the circulation gas as in the present embodiment, the circulating gas is more stable as EGR flow. The channel 50 can be supplied.

  The circulation gas adjustment unit 80 is a part that adjusts the supply amount of the circulation gas supplied to the EGR flow passage 50. The circulating gas adjustment unit 80 of the present embodiment is an on-off valve, and the amount of the circulating gas supplied can be adjusted by changing the opening degree of the on-off valve. Further, the circulation gas adjustment unit 80 may be a throttle mechanism capable of adjusting the flow rate. Further, the circulating gas adjustment unit 80 is not limited to the on-off valve, and may be, for example, a blower. In this case, the amount of circulating gas supplied can be adjusted by changing the rotational speed of the blower.

<Configuration of control system>
Next, the configuration of the control system of the engine system 100 according to the present embodiment will be described. FIG. 2 is a block diagram of a configuration of a control system of engine system 100. As shown in FIG. 2, the engine system 100 according to the present embodiment includes a control device 90. The controller 90 includes a processor, volatile memory, nonvolatile memory, I / O interface, and the like.

  The control device 90 is electrically connected to the operation control panel 91, the engine revolution meter 14, and the oximeter 43. The operator's control panel 91 is operated by the operator, and operating conditions including the target engine speed are input. The control device 90 obtains each of the target engine speed, the engine speed (actual engine speed), and the oxygen concentration of the scavenging gas (actual oxygen concentration) based on the signals transmitted from the respective devices described above. Can.

  Further, the control device 90 is electrically connected to the fuel supply device 13, the EGR blower 60, and the circulating gas adjustment unit 80, and transmits control signals to these devices to control the devices. Further, the control device 90 stores a control program and various data described later in the non-volatile memory, and the processor performs arithmetic processing using the volatile memory based on the control program.

<Control program>
Next, the control program will be described. FIG. 3 is a flowchart of the control program. The process shown in FIG. 3 is executed by the controller 90.

  As shown in FIG. 3, when the control is started, first, the control device 90 acquires driving information based on the signals transmitted from the respective devices (step S1). Specifically, based on the signals transmitted from the operation panel 91, the engine tachometer 14 and the oximeter 43, the controller 90 determines the target engine rotational speed, the actual engine rotational speed, and the actual oxygen concentration. Get each one.

  Subsequently, the control device 90 calculates a fuel injection amount such that the difference between the target engine rotation number and the actual engine rotation number becomes zero, and transmits a control signal to the fuel injection device 13 based on the calculated fuel injection amount. (Step S2).

  Subsequently, the control device 90 calculates a target oxygen concentration of the scavenging gas (step S3). The control device 90 stores map data indicating the relationship between the target oxygen concentration and the engine load, and calculates the target oxygen concentration based on the map data and the engine load. The engine load can be calculated (estimated) from the actual engine speed and the fuel injection amount.

  Subsequently, the control device 90 calculates a target extraction amount of the exhaust gas extracted from the exhaust flow passage 20 (step S4). Specifically, the target extraction amount is calculated based on the difference between the target oxygen concentration and the actual oxygen concentration and the engine load. For example, when the actual oxygen concentration is lower than the target oxygen concentration, it is necessary to reduce the proportion of the exhaust gas in the scavenging gas to increase the amount of oxygen in the scavenging gas. Therefore, the target extraction amount is reduced in this case. In addition, for example, when the engine load is large, the amount of scavenged gas supplied to the engine body 10 also increases, so the target extraction amount also increases.

  Subsequently, the control device 90 determines whether the target extraction amount calculated in step S4 is equal to or less than a predetermined lower limit value (step S5). Here, the above-mentioned "lower limit value" is an amount where the rotational speed becomes too low and the controllability deteriorates if the EGR blower 60 tries to blow a gas having a smaller amount than the lower limit value. That is, when the air flow rate of the EGR blower 60 becomes equal to or less than the lower limit value, the controllability deteriorates.

  In step S5, when it is determined that the target extraction amount is equal to or less than the lower limit (YES in step S5), the control device 90 causes the circulating gas to increase so that the total amount of gas passing through the EGR blower 60 becomes larger than the lower limit. Are supplied upstream of the EGR blower 60 of the EGR passage 50 (step S6). As a result, even if the amount of exhaust gas extracted is small, the total amount of gas passing through the EGR blower 60 is larger than the lower limit value, so that the rotational speed of the EGR blower 60 can be maintained at a certain level or more. Controllability can be ensured.

  More specifically, in step S6, the control device 90 makes the rotational speed of the EGR blower 60 constant, makes the total amount of gas passing through the EGR blower 60 constant, and is included in the gas passing through the EGR blower 60. The amount of circulating gas supplied is adjusted so that the amount of exhaust gas becomes the target extraction amount. That is, while making the total amount of gas passing through the EGR blower 60 constant, if the amount of exhaust gas is smaller than the target amount of extraction, the amount of circulating gas supplied is reduced to increase the amount of exhaust gas extraction, and the amount of exhaust gas is increased. Is larger than the target extraction amount, the circulation gas supply amount is increased to reduce the exhaust gas extraction amount.

  On the other hand, when it is determined in step S5 that the target extraction amount is larger than the lower limit value (NO in step S5), the control device 90 stops the supply of the circulating gas and makes the supply amount zero (step S7). As a matter of course, when the target extraction amount is larger than the lower limit value, the total amount of gas passing through the EGR blower 60 is larger than the lower limit value without supplying the circulating gas, so that the controllability can be secured.

  More specifically, in step S7, the control device 90 stops the supply of the circulating gas, and the total amount of the gas (that is, the exhaust gas extracted from the exhaust flow passage 20) passing through the EGR blower 60 becomes the target extraction amount. The rotational speed of the EGR blower 60 is adjusted so that That is, if the total amount (blowing amount) of gas passing through the EGR blower 60 is smaller than the target extraction amount, the rotation number is increased, and if the total amount is larger than the target extraction amount, the rotation number is decreased.

  As described above, in the present embodiment, when adjusting the extraction amount of the exhaust gas extracted from the exhaust flow passage 20 to be the target extraction amount, when the target extraction amount is equal to or less than the lower limit value, only the circulation gas supply amount is Since the adjustment is performed and only the rotational speed of the EGR blower 60 is adjusted when the target extraction amount is larger than the lower limit value, the control can be simplified. After the above steps S6 and S7, the process returns to step S1 again to repeat steps S1 to S7.

  Although the case where the target extraction amount of the exhaust gas is calculated so as to clarify the purpose of the control program has been described above, actually, for example, as shown in FIG. According to such oxygen concentration control, it is possible to obtain the same function and effect as the control program described above. The oxygen concentration control shown in FIG. 4 is calculated based on the difference between the target oxygen concentration and the actual oxygen concentration as illustrated. Then, when the manipulated value obtained by the calculation by the oxygen concentration control is smaller than the value corresponding to the lower limit value (see step S5) of the target extraction amount described above, the rotational speed of the EGR blower 60 is set constant, The opening degree of the gas adjustment unit 80 (here, the control valve) is set to decrease as the operation amount increases. Further, when the operation amount is larger than the value corresponding to the lower limit value of the target extraction amount described above, the rotational speed of the EGR blower 60 is set larger as the operation amount increases, while the circulating gas adjustment unit 80 (control valve) Set to fully closed.

DESCRIPTION OF SYMBOLS 10 Engine main body 20 Exhaust flow path 40 Scavenging flow path 41 Joining point 42 Scavenging chamber 43 Oximeter 50 EGR flow path 60 EGR blower 70 Circulation flow path 80 Circulation gas adjustment part 90 Control device 100 Engine system

Claims (5)

With the engine body,
An exhaust flow path for discharging exhaust gas generated in the engine body;
A scavenging air passage for supplying scavenging gas to the engine body;
An EGR flow path which extracts exhaust gas from the exhaust flow path and supplies it to the scavenging air flow path;
An EGR blower provided in the EGR passage;
A circulation flow path which takes in gas from the scavenging air flow path or from downstream of the EGR blower in the EGR flow path and supplies the taken-in gas as circulation gas upstream of the EGR blower in the EGR flow path;
A circulation gas adjustment unit that adjusts the supply amount of the circulation gas;
A controller configured to control the EGR blower and the circulating gas adjustment unit;
The control device is configured such that, when the target extraction amount of the exhaust gas extracted from the exhaust flow path is less than or equal to a predetermined lower limit, the circulating gas has a total amount of gas passing through the EGR blower larger than the lower limit. An engine system that controls to supply upstream of the EGR blower of the EGR passage.   The engine system according to claim 1, wherein the circulation flow passage takes in the circulating gas from a downstream side of a junction point where the EGR flow passages of the scavenging passages meet. The scavenging flow passage has a scavenging chamber for temporarily storing scavenging gas and then supplying the scavenging gas to the engine body.
The engine system according to claim 2, wherein the circulation passage takes in the circulation gas from the scavenging chamber. The controller is
When the target extraction amount is equal to or less than the lower limit value, the rotational speed of the EGR blower is made constant to make the total amount of gas passing through the EGR blower constant and at the same time the exhaust gas contained in the gas passing through the EGR blower Adjusting the supply amount of the circulating gas so that the amount becomes the target extraction amount;
When the target extraction amount is larger than the lower limit value, the supply of the circulating gas is stopped, and the rotational speed of the EGR blower is adjusted so that the total amount of gas passing through the EGR blower becomes the target extraction amount. The engine system according to any one of claims 1 to 3. Equipped with an oximeter to detect the oxygen concentration of the scavenged gas,
The engine system according to any one of claims 1 to 4, wherein the control device sets the target extraction amount based on the oxygen concentration detected by the oximeter.

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