JP5655214B2 - Air-fuel ratio correction control method and apparatus for premixed gas engine - Google Patents

Description

  The present invention relates to an air-fuel ratio correction control method and an air-fuel ratio correction control apparatus for a premixed gas engine in which fuel gas and air are mixed in advance and supplied to a combustion chamber.

  Effective utilization of biogas such as pyrolysis gas and digestion gas is required as an alternative to fossil energy. As one of the utilization methods of biogas, a power generation system using a gas engine using biogas as a fuel has attracted attention.

  In a gas engine, the ratio (air-fuel ratio) between fuel gas and combustion air is an important adjustment factor. If there is too much air relative to the fuel gas, misfires and combustion fluctuations will occur, and if there is too little air, combustion abnormal phenomena such as exhaust temperature rise and knocking will occur, and stable operation cannot be continued. For this reason, in a premixed gas engine, a target air-fuel ratio is set in advance, and the air-fuel ratio is kept constant by measuring the amount of air-fuel mixture. In this case, the set value of the air-fuel ratio is set using a typical characteristic of fuel gas determined in advance.

  For example, in the gas engine described in Japanese Patent Application Laid-Open No. 2009-36111 (Patent Document 1), the target value of the air-fuel ratio is set at the start of operation using high calorie gas (for example, LPG (liquefied natural gas), city gas). Is set to the value of the stoichiometric air / fuel ratio at which the fuel reacts without excess or deficiency. When switching from high-calorie gas to low-calorie gas (biogas), the target value of air-fuel ratio is set to the theoretical air-fuel ratio value, or to avoid the possibility of misfiring because the air-fuel mixture becomes lean all at once. Is set to be richer than the theoretical air-fuel ratio.

JP 2009-36111 A

  In the case of gas with stable properties such as city gas, there is no problem even if the target value of the air-fuel ratio is fixed. However, in the case of gas such as biogas whose properties change during operation of the gas engine, it is appropriate. The air / fuel ratio also changes. For this reason, if control is performed to fix the target value of the air-fuel ratio in the case of biogas, combustion abnormality occurs when the property of the fuel gas changes.

  In the case of the bioengine described in the above-mentioned patent document, the target value of the air-fuel ratio is basically fixed to the value of the theoretical air-fuel ratio, so that it cannot cope with a sudden change in the properties of the fuel gas. When the fuel gas calorie is switched, there is a problem in terms of biogas utilization efficiency because an appropriate air-fuel ratio is not obtained.

  An object of the present invention is to provide an air-fuel ratio correction control method and air-fuel ratio correction for correcting and controlling an air-fuel ratio so that a gas engine can be stably operated even in the case of biogas whose properties of fuel gas change with time. It is to provide a control device.

In summary, the present invention is an air-fuel ratio correction control method for a premixed gas engine in which a mixed gas obtained by mixing fuel gas and air is supplied. The air-fuel ratio correction control method according to the present invention has a first correspondence relationship that associates a load factor of a gas engine with a target temperature, and a second correspondence that associates a load factor of the gas engine with a theoretical air amount for correction. Presetting the relationship, obtaining the current load factor of the gas engine, measuring the temperature of the exhaust gas discharged from the combustion chamber of the gas engine using a temperature sensor, and the obtained load A step of determining a correction theoretical air amount according to the rate, a step of calculating a set value of the air-fuel ratio by multiplying the determined correction theoretical air amount by a preset excess air ratio, and a current air-fuel ratio Adjusting the supply amount of the fuel gas or air according to the set value. Here, in the step of determining the correction theoretical air amount, the deviation between the exhaust gas temperature and the target temperature corresponding to the load factor when the exhaust gas temperature is measured is based on the first correspondence relationship. A first step of determining the correction theoretical air amount by feedback control so as to decrease, and a second step of determining the correction theoretical air amount according to the load factor of the gas engine based on the second correspondence relationship. Including. The first step is executed when the load factor of the gas engine is greater than or equal to a predetermined threshold, and the second step is executed when the load factor of the gas engine is less than the threshold.

Preferably, when the load factor of the gas engine is increased gradually, the second step is performed until the load factor of the gas engine reaches a threshold, the first step is equal to or greater than the threshold load of the gas engine, and, It is executed after the first transition period starting from when the load factor of the gas engine reaches the threshold value. The step of determining the correction theoretical air amount is further executed during the first transition period, and the temperature of the exhaust gas measured when the first transition period starts is used as an initial value, or a gas engine The target value when the exhaust gas temperature and the exhaust gas temperature are measured by setting the change value that gradually increases or decreases as the load factor increases to the target temperature according to the elapsed time or the load factor of the gas engine. A step of determining a correction theoretical air amount by feedback control so that a deviation from the temperature is small ; The first transition period ends when the change value and the target temperature based on the first correspondence relationship become equal .

Preferably, In no event the load factor of the gas engine is decreased gradually, the first step is performed until the load factor of the gas engine reaches a threshold, the second step is less than the threshold load of the gas engine, And it is performed after the end of the second transition period starting when the load factor of the gas engine reaches the threshold value. The step of determining the correction theoretical air amount is further executed during the second transition period, and the passage of time with the correction theoretical air amount determined in the first step immediately before entering the second transition period as an initial value. Alternatively, the method includes the step of determining a change value that gradually increases or decreases as the load factor of the gas engine decreases in the correction theoretical air amount in accordance with the elapsed time or the load factor of the gas engine . The second transition period ends when the above change value and the correction theoretical air amount based on the second correspondence relationship become equal.

In another aspect of the present invention, the first step is executed when the temperature sensor is normal. Said 2nd step is performed after the completion | finish of the 3rd transition period started from the time of detecting failure of a temperature sensor. Determining a Tadashiyo theoretical amount of air is further performed during the third migration period, the time of the correction theoretical air quantity determined in the first step immediately before entering the third transition period as the initial value A step of determining a change value that gradually increases or decreases with the passage of time as a correction theoretical air amount according to the elapsed time; The second transition period ends when the above change value and the correction theoretical air amount based on the second correspondence relationship become equal.

Preferably, the second step includes a step of determining a reference value of the correction theoretical air amount according to the load factor of the gas engine based on the second correspondence relationship, and the temperature of the exhaust gas is a predetermined reference temperature. If the temperature of the exhaust gas does not exceed the reference temperature, the reference value is determined as a final corrected theoretical air amount, and the temperature of the exhaust gas is equal to the reference temperature. if it exceeds comprises the step of determining a value obtained by adding a predetermined offset amount to the reference value to the final correction for the theoretical amount of air.

In another aspect, the present invention is an air-fuel ratio correction control device for a premixed gas engine to which a mixed gas obtained by mixing fuel gas and air is supplied, the excess air ratio setting unit, a temperature sensor, and a correction A theoretical air amount determination unit, an air-fuel ratio calculation unit, and a gas amount adjuster are provided. The excess air ratio setting unit is configured to determine the excess air ratio corresponding to the current rotation speed and the load factor of the gas engine based on a table representing a predetermined correspondence relationship between the revolution speed and load factor of the gas engine and the excess air ratio. Set the value of. The temperature sensor measures the temperature of the exhaust gas discharged from the combustion chamber of the gas engine. The correction theoretical air amount determination unit determines the correction theoretical air amount according to the current load factor of the gas engine. The air-fuel ratio calculation unit calculates the set value of the air-fuel ratio by multiplying the determined correction theoretical air amount by the value of the excess air ratio set. The gas amount adjuster adjusts the supply amount of fuel gas or air according to the current set value of the air-fuel ratio. When the load factor of the gas engine is equal to or greater than the threshold value, the correction theoretical air amount determination unit described above calculates the temperature of the exhaust gas based on the first correspondence relationship that associates the load factor of the gas engine with the target temperature. The correction theoretical air amount is determined by feedback control so that the deviation from the target temperature corresponding to the load factor when the temperature of the exhaust gas is measured becomes small. The correction theoretical air amount determination unit determines the load of the gas engine based on the second correspondence relationship that associates the load factor of the gas engine and the correction theoretical air amount when the load factor of the gas engine is less than the threshold. The correction theoretical air amount is determined according to the rate.

In yet another aspect, the present invention provides a premixed gas engine system, a premixed gas engine, an excess air ratio setting unit, a temperature sensor, a correction theoretical air amount determination unit, and an air-fuel ratio calculation unit. And a gas amount regulator. The premixed gas engine is supplied with a mixed gas obtained by mixing fuel gas and air. The excess air ratio setting unit is configured to determine the excess air ratio corresponding to the current rotation speed and the load factor of the gas engine based on a table representing a predetermined correspondence relationship between the revolution speed and load factor of the gas engine and the excess air ratio. Set the value of. The temperature sensor measures the temperature of the exhaust gas discharged from the combustion chamber of the gas engine. The correction theoretical air amount determination unit determines the correction theoretical air amount according to the current load factor of the gas engine. The air-fuel ratio calculation unit calculates the set value of the air-fuel ratio by multiplying the determined correction theoretical air amount by the value of the excess air ratio set. The gas amount adjuster adjusts the supply amount of fuel gas or air according to the current set value of the air-fuel ratio. When the load factor of the gas engine is equal to or greater than the threshold value, the correction theoretical air amount determination unit described above calculates the temperature of the exhaust gas based on the first correspondence relationship that associates the load factor of the gas engine with the target temperature. The correction theoretical air amount is determined by feedback control so that the deviation from the target temperature corresponding to the load factor when the temperature of the exhaust gas is measured becomes small. The correction theoretical air amount determination unit determines the load of the gas engine based on the second correspondence relationship that associates the load factor of the gas engine and the correction theoretical air amount when the load factor of the gas engine is less than the threshold. The correction theoretical air amount is determined according to the rate.

  According to the present invention, by correcting the set value of the air-fuel ratio according to the temperature of the exhaust gas, the gas engine can be stably operated even in the case of biogas whose properties of fuel gas change with time. Thus, the air-fuel ratio can be controlled.

1 is a block diagram showing a configuration of a premixed gas engine system 100 according to an embodiment of the present invention. FIG. 2 is a block diagram showing an example of the configuration of an air-fuel ratio control unit 12 and a correction theoretical air amount determination unit 14 in FIG. 1. It is a figure which shows an example of the setting table of the excess air ratio memorize | stored in the memory | storage part 16 of FIG. It is a figure for demonstrating the closed loop control performed by the calculating part 31 of FIG. It is a figure for demonstrating the example of target temperature Tref of the exhaust gas memorize | stored in the memory | storage part 32 of FIG. It is a figure for demonstrating the example of theoretical air quantity Yset for correction | amendment of the air fuel ratio setting value memorize | stored in the memory | storage part 32 of FIG. It is a flowchart which shows the operation | movement of the air fuel ratio control part 12 shown in FIG. It is a flowchart which shows operation | movement of the correction | amendment theoretical air amount determination part 14 shown in FIG. It is a flowchart which shows the detail of step S17 of FIG. It is a flowchart which shows the detail of step S5 of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

[Schematic Configuration of Gas Engine System 100]
FIG. 1 is a block diagram showing a configuration of a premixed gas engine system 100 according to an embodiment of the present invention. As shown in FIG. 1, the gas engine system 100 includes a gas engine 1, a mixer 30, a fuel gas amount regulator 8, an air cleaner 7, a supercharger 4, and a throttle valve 9.

  The gas engine 1 is a premixed gas engine in which a mixed gas M in which a fuel gas F and air A are mixed in advance is sucked into the combustion chamber 2. In the gas engine 1 of the first embodiment, biogas such as pyrolysis gas or digestion gas is used as the fuel gas F. The sucked mixed gas M is ignited and burned in the combustion chamber 2, and the piston 3 is driven by the generated heat energy.

  The mixer 30 mixes the fuel gas F and the air A to generate a mixed gas M. The fuel gas amount adjuster 8 adjusts the flow rate of the fuel gas F supplied to the mixer 30. The air cleaner 7 removes dust contained in the air A supplied to the mixer 30.

  The supercharger 4 is an exhaust turbine driven supercharger (so-called turbocharger). That is, the turbine 6 is rotated by the exhaust gas E exhausted from the combustion chamber 2, and the mixed gas M supplied to the combustion chamber 2 is pressurized by the compressor 5 that rotates in conjunction with the turbine 6.

  The throttle valve 9 is provided in the path of the mixed gas M between the compressor 5 of the supercharger 4 and the combustion chamber 2, and adjusts the flow rate of the mixed gas M according to the output of the gas engine 1.

  The biogas used as the fuel gas F is different from city gas or the like, and its properties change with time. For example, the pyrolysis gas is obtained by thermally decomposing waste plastics or building waste materials, etc., and then gas reforming, and the ratio of the component gas, hydrogen and carbon monoxide, changes with time. As for digestion gas obtained by subjecting organic waste or sludge to methane fermentation by anaerobic microorganisms, the ratio of its component gas, methane and carbon dioxide, changes over time. For this reason, it is necessary to appropriately control the air-fuel ratio (ratio of air A and fuel gas F) according to the properties of the fuel gas F.

  The gas engine system 100 of FIG. 1 further includes a flow meter 11, a temperature sensor 13, an air-fuel ratio control unit 12, and a correction theoretical air amount determination unit 14 for controlling the air-fuel ratio.

  The flow meter 11 is provided in the path of the mixed gas M between the throttle valve 9 and the combustion chamber 2 and measures the flow rate of the mixed gas M. The temperature sensor 13 is provided in the path of the exhaust gas E between the combustion chamber 2 and the supercharger 4 and measures the temperature of the exhaust gas E exhausted from the combustion chamber 2.

  The air-fuel ratio control unit 12 sets the value of the excess air ratio according to the rotation speed and load factor of the gas engine 1 (the ratio of the current engine output to the rated output). The correction theoretical air amount determination unit 14 determines the correction theoretical air amount according to the type of fuel gas. The air-fuel ratio controller 12 sets the air-fuel ratio by multiplying the determined correction theoretical air amount by the excess air ratio. The air-fuel ratio control unit 12 generates a control signal according to the flow rate of the mixed gas M measured by the flow meter 11 so that the air-fuel ratio becomes the current set value, and outputs the control signal to the fuel gas amount adjuster 8. To do. As a result, the flow rate of the fuel gas F is adjusted.

  The correction theoretical air amount is a control parameter used for correcting the air-fuel ratio, and is a value corresponding to the theoretical air amount. Originally, the theoretical air amount is uniquely determined according to the properties of the fuel gas. However, in the case of biogas, it is difficult to directly detect changes in the properties of the fuel gas. Therefore, the theoretical air amount is used as a control parameter for correcting the air-fuel ratio. The correction theoretical air amount is set according to the type of fuel gas and the exhaust gas temperature when the load factor of the gas engine is equal to or greater than a predetermined threshold. When the load factor of the gas engine is less than a predetermined threshold value, a value obtained by correcting the theoretical air amount determined based on the typical properties for each type of fuel gas according to the load factor, regardless of the exhaust gas temperature. Set to the corrected theoretical air volume.

  Generally, the temperature of the exhaust gas E decreases as the air-fuel ratio increases, that is, as the mixed gas M becomes leaner. In the present invention, by utilizing this point, a change in the property of the fuel gas F is detected by monitoring a change in the temperature of the exhaust gas E. Then, the air-fuel ratio is corrected according to the temperature of the exhaust gas E. Thereby, the air-fuel ratio can be optimized according to the change in the properties of the fuel gas F. However, since the temperature follow-up of the exhaust gas E with respect to changes in the properties of the fuel gas F is slow at low loads, it is desirable to control the air-fuel ratio based on the temperature of the exhaust gas E after a certain high load is applied.

  The functions of the air-fuel ratio control unit 12 and the correction theoretical air amount determination unit 14 can be realized using a microcomputer. In FIG. 1, the air-fuel ratio control unit 12 and the correction theoretical air amount determination unit 14 have separate configurations, but they may be configured by a single microcomputer.

[Configuration of Air-Fuel Ratio Correction Control Device 10]
FIG. 2 is a block diagram showing an example of the configuration of the air-fuel ratio control unit 12 and the correction theoretical air amount determination unit 14 of FIG. As shown in FIG. 2, the air-fuel ratio control unit 12 includes a storage unit 16, an excess air ratio setting unit 15, a multiplication unit 17, and a control signal generation unit 18. The correction theoretical air amount determination unit 14 includes a calculation unit 31 and a storage unit 32. The air-fuel ratio control unit 12, the correction theoretical air amount determination unit 14, the flow meter 11, and the temperature sensor 13 constitute the air-fuel ratio correction control device 10 of the present invention.

  In the air-fuel ratio control unit 12, the storage unit 16 stores the value of the excess air ratio according to the rotation speed and the load factor. FIG. 3 is a diagram showing an example of an excess air ratio setting table stored in the storage unit 16 of FIG.

  The excess air ratio setting unit 15 reads the excess air ratio value corresponding to the rotation speed and load factor of the gas engine 1 from the storage unit 16. The rotation speed and output of the gas engine 1 in FIG. 1 are controlled by an engine control unit (not shown). The excess air ratio setting unit 15 acquires information representing the rotation speed and the load factor from the engine control unit.

The multiplying unit 17 (air-fuel ratio calculating unit) uses the set value of the excess air ratio output from the excess air ratio setting unit 15 for the correction corresponding to the type of fuel gas acquired from the corrected theoretical air amount determination unit 14. The set value of the air-fuel ratio is determined by multiplying the theoretical air amount Yout. If the excess air ratio read from the storage unit 16 is α, the final air-fuel ratio R is
R = Yout × α (1)
It is expressed as

  The control signal generator 18 adjusts the flow rate of the fuel gas F output from the fuel gas amount adjuster 8 so that the air-fuel ratio R calculated according to the flow rate of the mixed gas M detected by the flow meter 11 is obtained. A control signal for generating

  The correction theoretical air amount determination unit 14 determines the correction theoretical air amount Yout as correction of the set value of the air-fuel ratio. In this case, the correction theoretical air amount Yout is determined by closed loop control (feedback control) corresponding to the exhaust gas temperature, and the correction theoretical air amount Yout is determined by open loop control corresponding to the load factor of the gas engine 1. There is a case to do. In this specification, the case of the closed loop control is referred to as a correction mode 1, and the latter case of the open loop control is referred to as a correction mode 2. Correction mode 1 (closed loop control) is used when the load factor of the gas engine 1 is greater than or equal to a predetermined threshold, and correction mode 2 (open loop control) is used when the load factor is less than the above threshold. Even if the load factor is equal to or greater than a predetermined threshold, if the temperature sensor fails, correction mode 2 (open loop control) is used instead of correction mode 1 (closed loop control). Hereinafter, each of correction mode 1 (closed loop control) and correction mode 2 (open loop control) will be described in detail. Further, when the open loop control is shifted to the closed loop control due to an increase in the load factor of the gas engine 1 (referred to as transition mode 1), the open loop control is switched from the closed loop control due to a decrease in the load factor of the gas engine 1 or a failure of the temperature sensor 13. The case of shifting to control (referred to as transition mode 2) will be described.

(Correction mode 1: closed loop control according to exhaust gas temperature)
0
Referring to FIG. 2, in the correction mode 1, the calculation unit 31 of the correction theoretical air amount determination unit 14 has a small deviation between the temperature Tex of the exhaust gas measured by the temperature sensor 13 and the target temperature Tref. As described above, the correction theoretical air amount Yout is determined by closed loop control. The target temperature Tref is set in advance corresponding to the load factor of the gas engine 1 for each type of fuel gas, and is stored in the storage unit 32.

  FIG. 4 is a diagram for explaining the closed-loop control executed by the calculation unit 31 in FIG.

  As shown in FIG. 4, in the correction mode 1, the calculation unit 31 determines the correction theoretical air amount Yout by PID control (proportional integral derivative control) according to the exhaust gas temperature Tex. The calculation unit 31 includes a subtraction unit 21, coefficient units 22 to 24, an integration unit 25, a differentiation unit 26, and an addition unit 27 as functional blocks for performing PID control. The subtraction unit 21 calculates a deviation between the exhaust gas temperature Tex and the set target temperature Tref. The coefficient unit 22 multiplies the calculated deviation by a proportional gain (1 / Kp). The coefficient unit 23 multiplies the calculated deviation by an integral gain (1 / Ki). The output of the coefficient unit 23 is integrated by the integration unit 25. The coefficient unit 24 multiplies the calculated deviation by a differential gain (Kd). The output of the coefficient unit 24 is differentiated by the differentiation unit 26. The adding unit 27 adds the outputs of the coefficient unit 22, the integrating unit 25, and the differentiating unit 26 to generate the correction theoretical air amount Yout. By the above operation, the correction theoretical air amount Yout is determined so that the deviation between the set target temperature Tref and the exhaust gas temperature Tex is as small as possible. The values of the coefficients Kp, Ki, and Kd are experimentally determined so that the controllability of the air-fuel ratio is good.

  FIG. 5 is a diagram for explaining an example of the target temperature Tref of the exhaust gas stored in the storage unit 32 of FIG. As shown in FIG. 5, the correction theoretical air amount determination unit 14 includes a plurality of load factors (in the case of FIG. 5, X0 = 0, X1 = 15, X2 = 25, X3 = 50, X4 = 70, X5 = 85). , X6 = 100, X7 = 110 [%]), the target temperatures T0 to T7 set in advance are stored in advance. The target temperature Tref is set to a larger value as the load factor is larger. The target temperature Tref for load factors other than X0 to X7 in FIG. 5 is obtained by interpolating preset target temperatures T0 to T7. In this specification, the correspondence between the load factor of the gas engine 1 and the target temperature Tref is referred to as a first correspondence. However, since the closed loop control is not used when the load factor is less than the predetermined threshold value, for example, when the threshold value is L1 (= X3) in FIG. 5, the target temperatures T0 to T3 for the load factors X0 to X3 are actually controlled. Not used for.

(Correction mode 2: Open loop control according to load factor)
Referring to FIG. 2 again, the case of the correction mode 2 will be described. In this case, the correspondence between the load factor of the gas engine 1 and the correction theoretical air amount Yset (referred to as a second correspondence) is the storage unit 32 of the correction theoretical air amount determination unit 14 for each type of fuel gas. Is stored in advance. The computing unit 31 determines a correction theoretical air amount Yset according to the load factor of the gas engine 1 based on the second correspondence relationship. The calculation unit 31 finally has
Yout = Yset + Yos (2)
Is output to the multiplier 17 of the air-fuel ratio controller 12. In the above equation (2), Yos is an offset, and its initial value is 0. The calculation unit 31 suppresses an abnormal increase in the exhaust gas temperature by increasing the offset Yos by a predetermined amount when the exhaust gas temperature exceeds the reference temperature.

  FIG. 6 is a diagram for explaining an example of the correction theoretical air amount Yset for the air-fuel ratio set value stored in the storage unit 32 of FIG. As shown in FIG. 6, the correction theoretical air amount determination unit 14 includes a plurality of load factors (in the case of FIG. 6, X0 = 0, X1 = 15, X2 = 25, X3 = 50, X4 = 70, X5). = 85, X6 = 100, X7 = 110 [%]), respectively, the correction theoretical air amounts Y0 to Y7 are stored in advance. The value of the correction theoretical air amount Yset is set to a larger value as the load factor is larger. The correction theoretical air amount Yset corresponding to a load factor other than X0 to X7 in FIG. 6 is given by interpolating preset correction theoretical air amounts Y0 to Y7. However, when the temperature sensor 13 is normal, the open loop control is not used when the temperature sensor 13 is equal to or greater than a predetermined threshold. For example, if the threshold value is L1 (X3) in FIG. 5, the correction theoretical air amounts Y3 to Y7 for the load factors X3 to X7 are not used in actual control.

(Transition mode 1: Transition from open loop control to closed loop control)
When the load factor of the gas engine 1 gradually increases, the modes are switched in the order of correction mode 2 (open loop control), transition mode 1 and correction mode 1 (closed loop control). For example, in the case of FIG. 5, the open loop control (correction mode 2) is executed until the load factor reaches the threshold value L1 (= X3), the load factor X3 to X4 is the transition mode 1, and the load factor is Closed loop control (correction mode 1) is executed when X4 or more.

  In the transition mode 1, the arithmetic unit 31 determines the correction theoretical air amount Yout according to the load factor of the gas engine 1 by the closed loop control according to the exhaust gas temperature as in the correction mode 1, but the target temperature How to give Tref is different from that in the correction mode 1. For example, in the case of FIG. 5, at the start time of the transition mode 1 (load factor X3), the exhaust gas temperature Tex measured at the load factor X3 is set as the target temperature. At the end of transition mode 1 (load factor X4), target temperature T4 based on the first correspondence relationship used in correction mode 1 is set as the target temperature of transition mode 1. Between the load factors X3 and X4, the target temperature corresponding to each load factor is interpolated between the exhaust gas temperature Tex actually measured at the load factor X3 and the target temperature T4 based on the first correspondence relationship. (Broken line in FIG. 5) is set. Thus, a change value (dashed line in FIG. 5) that gradually increases or decreases as the load factor of the gas engine 1 increases with the exhaust gas temperature Tex measured when the transition mode 1 is started as an initial value. A target temperature corresponding to each load factor is set. And the calculating part 31 determines the correction | amendment theoretical air amount Yout by feedback control so that the deviation with exhaust gas temperature and target temperature when measuring exhaust gas temperature may become small. The transition mode 1 ends when the change value (broken line in FIG. 5) becomes equal to the target temperature (T4 in FIG. 5) based on the first correspondence (when the load factor reaches X4 in FIG. 5). .

(Transition mode 2: Transition from closed loop control to open loop control)
When the load factor of the gas engine 1 gradually decreases, the modes are switched in the order of correction mode 1 (closed loop control), transition mode 2 and correction mode 2 (open loop control). For example, in the case of FIG. 6, the closed loop control (correction mode 1) is executed until the load factor reaches the threshold value L2 (L2 is not necessarily equal to L1), and the load factor L2 to X8 is the transition mode 2. When the load factor is less than X8, open loop control (correction mode 2) is executed.

  In the transition mode 2, the calculation unit 31 determines the correction theoretical air amount Yout by open loop control according to the load factor of the gas engine 1, but unlike the correction mode 2, the calculation unit 31 determines the load factor and the correction theoretical air amount. The correspondence with Yout is not set in advance. For example, in the case of FIG. 6, the correction theoretical air amount at the start of the transition mode 2 (load factor L2) is set to the correction theoretical air amount Yout determined in the correction mode 1 immediately before entering the transition mode 2. The Thereafter, with the correction theoretical air amount Yout at the load factor L2 as an initial value, a change value that increases or decreases with the passage of time at a predetermined time change rate is set as the correction theoretical air amount corresponding to each elapsed time. The The transition mode 2 ends when the change value (broken line in FIG. 6) becomes equal to the correction theoretical air amount Yset based on the second correspondence (when the load factor reaches X8 in FIG. 6).

  Similarly, when the temperature sensor 13 fails during execution of closed loop control (correction mode 1) corresponding to the exhaust gas temperature, the mode is switched to correction mode 2 (open loop control) via the transition mode 2. In the transition mode 2, the calculation unit 31 gradually increases or decreases at a predetermined rate of change with the passage of time, with the correction theoretical air amount Yout determined in the correction mode 1 immediately before entering the transition mode 2 as an initial value. The change value to be determined is determined as the correction theoretical air amount according to the elapsed time. The correction mode 2 ends when the change value and the correction theoretical air amount Yset based on the second correspondence relationship become equal.

  Providing transition mode 1 or 2 between closed loop control (correction mode 1) and open loop control (correction mode 2) as described above prevents the correction theoretical air amount Yout from changing suddenly. Can do.

  When the load factor of the gas engine 1 gradually increases, instead of the transition mode 1 described above, as in the transition mode 2, the exhaust gas temperature at the start of the transition mode is used as an initial value, and changes with time over a predetermined time. A change value that increases or decreases at a rate may be set to a target temperature corresponding to each elapsed time.

  When the load factor of the gas engine 1 gradually decreases, instead of the transition mode 2 described above, the load factor at the start and end of the transition mode is determined in advance as in the transition mode 1, and set immediately before entering the transition mode. The correction theoretical air amount corresponding to each load factor is determined by interpolating the corrected theoretical air amount Yout and the correction theoretical air amount set according to the second correspondence in the load factor at the end. May be.

[Operation of Air-Fuel Ratio Correction Control Device 10]
FIG. 7 is a flowchart showing the operation of the air-fuel ratio control unit 12 shown in FIG. With reference to FIGS. 2 and 7, the operation of the air-fuel ratio control unit 12 will be generally described.

  In step S101, when the gas engine 1 is started, the excess air ratio setting unit 15 of the air-fuel ratio control unit 12 sets an initial value of the excess air ratio.

  In the next step S102, the air-fuel ratio control unit 12 acquires the initial value of the correction theoretical air amount from the correction theoretical air amount determination unit 14.

  In the next step S103, the multiplication unit 17 multiplies the initial value of the excess air ratio output from the excess air ratio setting unit 15 by the initial value of the correction theoretical air amount acquired from the correction theoretical air amount determination unit 14. To set the initial value of the air-fuel ratio.

  In the next step S104, the fuel gas amount adjuster 8 receives a control signal corresponding to the set initial value of the air-fuel ratio from the air-fuel ratio control unit 12, and adjusts the flow rate F of the fuel gas based on the control signal.

  When the gas engine 1 is started, an engine control unit (not shown) gradually increases the rotational speed and the load factor. In step S105, the excess air ratio setting unit 15 acquires information representing the rotation speed and the load factor from the engine control unit. In the next step S106, the excess air ratio setting unit 15 determines a set value of the excess air ratio corresponding to the rotational speed / load factor acquired from the engine control unit based on the table stored in the storage unit 16.

  In the next step S107, the air-fuel ratio control unit 12 acquires the correction theoretical air amount from the correction theoretical air amount determination unit 14.

  In the next step S108, the multiplication unit 17 multiplies the set value of the excess air ratio output from the excess air ratio setting unit 15 by the correction theoretical air amount acquired from the correction theoretical air amount determination unit 14, thereby Set the fuel ratio.

  In the next step S109, the fuel gas amount adjuster 8 receives a control signal corresponding to the current set value of the air-fuel ratio from the air-fuel ratio control unit 12, and adjusts the flow rate F of the fuel gas based on the control signal. If the engine is not stopped (NO in step S110), the procedures in steps S105 to S109 are repeated.

  FIG. 8 is a flowchart showing the operation of the correction theoretical air amount determination unit 14 shown in FIG. Hereinafter, the operation of the correction theoretical air amount determination unit 14 will be described with reference to FIGS. 2 and 8.

  Until the gas engine 1 is started and the rotational speed reaches a predetermined rated rotational speed n1 in a no-load state (NO in step S2), the calculation unit 31 sets the initial value (for example, (Yout = 5) is output (step S1).

  When the rotational speed of the gas engine 1 reaches a predetermined rated rotational speed n1 (YES in step S2), the calculation unit 31 initializes control parameters (step S3).

  In the next step S4, the calculation unit 31 determines the correction theoretical air amount Yset according to the load factor by open loop control (correction mode 2) based on the second correspondence stored in the storage unit 32. . The computing unit 31 calculates the final correction theoretical air amount Yout by adding the offset Yos according to the above-described equation (2), and outputs it to the air-fuel ratio control unit 12. The value of the offset value Yos is set to an initial value (Yos = 0) in step S3.

  In the next step S5, when the exhaust gas temperature Tex exceeds the predetermined reference temperature (Ta in FIG. 10) and abnormally increases, a step of suppressing the abnormal increase in the exhaust gas temperature is executed. Specifically, when the exhaust gas temperature exceeds the reference temperature, the calculation unit 31 suppresses an abnormal increase in the exhaust gas temperature by increasing the offset Yos of the above equation (2) by a predetermined amount. Details of step S5 will be described with reference to FIG.

  The next step S6 is provided when the gas engine 1 is stopped. Specifically, if the engine speed is equal to or less than the reference value n2 (n2 is smaller than the rated engine speed n1) (YES in step S6), the process proceeds to step S7, and if the engine is stopped (YES in step S7). The process ends. If the engine speed is equal to or less than the reference value n2 (YES in step S6), but the engine is not stopped (NO in step S7), the process returns to step S1.

  The above steps S4 to S6 are repeatedly executed until the load factor of the gas engine 1 reaches the threshold value L1 (during NO in step S8). On the other hand, when the load factor is equal to or greater than the threshold L1 (YES in step S8) and the temperature sensor 13 is normal (YES in step S9), the process proceeds to step S10, and the open loop control (correction mode 2) to the closed loop control. The mode is switched to the transition mode 1 that shifts to (correction mode 1).

  If it is confirmed in the next step S11 that the temperature sensor 13 is normal (YES in step S11), the process proceeds to step S12. In step S12, the correction theoretical air amount determination unit 14 determines the correction theoretical air amount Yout by closed loop control (correction mode 1) according to the exhaust gas temperature. If the temperature sensor 13 is out of order in step S11 (NO in step S11), the process returns to step S3 via the transition mode 2 in step S17. The procedure of step S17 will be described with reference to FIG.

  In the next step S13, the calculation unit 31 determines whether or not the absolute value (| Tex−Tref |) of the deviation between the exhaust gas temperature Tex and the target temperature Tref is equal to or higher than a predetermined reference temperature Tb. If the absolute value of the deviation is not equal to or higher than the reference temperature Tb (NO in step S13), the proportional gain and integral gain in FIG. 4 are set to standard values (step S14). On the other hand, if the absolute value of the deviation is equal to or higher than the reference temperature Tb (YES in step S13), the proportional gain and integral gain in FIG. 4 are set to a gain for change that is larger than the standard value (step S15). . That is, the coefficients Kp and Ki are set to values smaller than the coefficients in the case of standard values. Thereby, hunting can be suppressed.

  The next step S16 is provided when the gas engine 1 is stopped. When the load factor gradually decreases and becomes equal to or less than the threshold value L2 (YES in step S16), the correction theoretical air amount determination unit 14 returns the process to step S3 through the transition mode 2 in step S17. If the load factor exceeds the threshold L2 (NO in step S16), steps S11 to S15 are repeated.

  FIG. 9 is a flowchart showing details of step S17 in FIG. As already described, step S17 in FIG. 8 is a transition mode 2 executed when the temperature sensor fails (NO in step S11) or when the load factor becomes equal to or less than the threshold L2 (YES in step S16). Correspond. In the following description, it is assumed that the calculation unit 31 of the correction theoretical air amount determination unit 14 performs control at every predetermined control interval Ts.

  Referring to FIGS. 8 and 9, in step S <b> 21, calculation unit 31 reads from correction unit 32 the corrected theoretical air amount Yset that is set in accordance with the current load factor based on the second correspondence relationship. .

  In the next step S22, the calculation unit 31 has the correction theoretical air amount Yout set by the closed loop control (step S12) immediately before entering the transition mode 2 larger than the correction theoretical air amount Yset read in step S21. It is determined whether or not.

  If the correction theoretical air amount Yout is larger than the correction theoretical air amount Yset (YES in step S22), the process proceeds to step S23, and the calculation unit 31 corrects the value obtained by multiplying the time change rate Rate by the control interval Ts. It is subtracted from the theoretical air amount Yout.

  In the next step S <b> 24, the calculation unit 31 reads from the storage unit 32 the correction theoretical air amount Yset that is set according to the current load factor based on the second correspondence relationship.

  In the next step S25, it is determined whether or not the current correction theoretical air amount Yout is less than or equal to the correction theoretical air amount Yset read in step S24. If the corrected theoretical air amount Yout is not less than or equal to the corrected theoretical air amount Yset (NO in step S25), the process returns to step S23, and steps S23 to S25 are repeated.

  If the current correction theoretical air amount Yout is less than or equal to the correction theoretical air amount Yset read in step S24 (YES in step S25), the correction theoretical air amount Yset is set to the current correction theoretical air amount Yout. By substituting, transition mode 2 ends (step S29).

  On the other hand, when the correction theoretical air amount Yout is less than or equal to the correction theoretical air amount Yset (NO in step S22), the process proceeds to step S26, and the calculation unit 31 multiplies the time change rate Rate and the control interval Ts. Is added to the correction theoretical air amount Yout.

  In the next step S <b> 27, the calculation unit 31 reads from the storage unit 32 the correction theoretical air amount Yset that is set according to the current load factor based on the second correspondence relationship.

  In the next step S28, it is determined whether or not the current correction theoretical air amount Yout is equal to or larger than the correction theoretical air amount Yset read in step S27. If the correction theoretical air amount Yout is not equal to or greater than the correction theoretical air amount Yset (NO in step S28), the process returns to step S26, and steps S26 to S28 are repeated.

  When the current correction theoretical air amount Yout is equal to or larger than the correction theoretical air amount Yset read in step S27 (YES in step S28), the correction theoretical air amount Yset is set to the current correction theoretical air amount Yout. By substituting, transition mode 2 ends (step S29).

  FIG. 10 is a flowchart showing details of step S5 in FIG. FIG. 10 shows a processing procedure for suppressing the exhaust gas temperature when the exhaust gas temperature Tex rises abnormally beyond a predetermined reference temperature Ta.

  Referring to FIGS. 8 and 10, calculation unit 31 determines whether or not exhaust gas temperature Tex exceeds reference temperature Ta in step S31. Further, in step S32, the calculation unit 31 determines whether or not the elapsed time Tim (initialized to 0 in step S3 in FIG. 8) exceeds the reference time Tint. When both steps S31 and S32 are YES, the process proceeds to step S33, and the calculation unit 31 increases the offset value Yos of the correction theoretical air amount by a predetermined amount Ystep. In the next step S34, the calculation unit 31 initializes the elapsed time Tim to 0.

  When the exhaust gas temperature Tex continues to exceed the reference temperature Ta by the above processing, the offset value Yos increases by a predetermined amount Ystep every reference time Tint. As a result, the correction theoretical air amount Yout also increases by a predetermined amount Ystep every reference time Tint, so that an increase in the exhaust gas temperature can be suppressed.

  As described above, according to the gas engine system 100 according to the above-described embodiment, by correcting the set value of the air-fuel ratio according to the exhaust gas temperature Tex, the property of the fuel gas F changes with time. Even in this case, the air-fuel ratio can be controlled so that the gas engine 1 can be operated stably.

  In the above, the fuel gas amount adjuster 8 for adjusting the supply amount of the fuel gas F is provided in order to control the air-fuel ratio, but the supply amount of the air A is adjusted instead of the fuel gas amount adjuster 8. An air amount adjuster may be provided.

  The embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Gas engine, 2 Combustion chamber, 4 Supercharger, 8 Fuel gas quantity regulator, 10 Air fuel ratio correction control apparatus, 11 Flowmeter, 12 Air fuel ratio control part, 13 Temperature sensor, 14 Theoretical air quantity determination part for correction | amendment, 15 Excess air ratio setting unit, 16 storage unit, 100 gas engine system, A air, E exhaust gas, F fuel gas, M mixed gas, Tex exhaust gas temperature, Yout, Yset Theoretical air amount for correction.

Claims (7)

An air-fuel ratio correction control method for a premixed gas engine to which a mixed gas obtained by mixing fuel gas and air is supplied,
Pre-setting a first correspondence relationship that associates the load factor of the gas engine with a target temperature, and a second correspondence relationship that associates between the load factor of the gas engine and a correction theoretical air amount; ,
Obtaining a current load factor of the gas engine;
Measuring the temperature of the exhaust gas discharged from the combustion chamber of the gas engine using a temperature sensor;
Determining a correction theoretical air amount according to the acquired load factor;
Calculating a set value of the air-fuel ratio by multiplying the determined correction theoretical air amount by a preset excess air ratio;
Adjusting the supply amount of the fuel gas or the air according to the current set value of the air-fuel ratio,
The step of determining the correction theoretical air amount includes:
Based on the first correspondence relationship, the correction theoretical air amount is controlled by feedback control so that a deviation between the temperature of the exhaust gas and the target temperature corresponding to the load factor when the temperature of the exhaust gas is measured becomes small. A first step of determining
A second step of determining a correction theoretical air amount according to a load factor of the gas engine based on the second correspondence relationship;
The first step is executed when the load factor of the gas engine is equal to or greater than a predetermined threshold, and the second step is executed when the load factor of the gas engine is less than the threshold . Air-fuel ratio correction control method. In the case where the load factor of the previous SL gas engine gradually increases, the second step is performed until the load factor of the gas engine reaches the threshold value, the first step is the load factor of the gas engine is the threshold value or more And after the end of the first transition period starting from when the load factor of the gas engine reaches the threshold,
The step of determining the correction theoretical air amount further comprises:
The temperature of the exhaust gas, which is executed during the first transition period and measured when the first transition period starts, is used as an initial value, and gradually as time passes or the load factor of the gas engine increases. The change value that increases or decreases is set to the target temperature according to the elapsed time or the load factor of the gas engine, and the deviation between the exhaust gas temperature and the target temperature when the exhaust gas temperature is measured is small. Determining the correction theoretical air amount by feedback control so that
It said first transition period is terminated when the target temperature is equal based on the first correspondence relationship between the change value, the air-fuel ratio correction control method of premixing type gas engine according to claim 1. In no event the load factor of the previous SL gas engine is decreased gradually, the first step is performed until the load factor of the gas engine reaches the threshold value, the second step is the load factor of the gas engine is the threshold And after the end of the second transition period starting from when the load factor of the gas engine reaches the threshold,
The step of determining the correction theoretical air amount further comprises:
For the passage of time or the reduction of the load factor of the gas engine, using the correction theoretical air amount determined in the first step as an initial value immediately before entering the second transition period, which is executed during the second transition period. Determining a change value that gradually increases or decreases along with the elapsed time or the load factor of the gas engine as a correction theoretical air amount ,
Said second transition period is terminated when the correction theoretical air amount based on the second correspondence relationship between the change value becomes equal empty premixing gas engine according to claim 1 or 2 Fuel ratio correction control method. An air-fuel ratio correction control method for a premixed gas engine to which a mixed gas obtained by mixing fuel gas and air is supplied,
Pre-setting a first correspondence relationship that associates the load factor of the gas engine with a target temperature, and a second correspondence relationship that associates between the load factor of the gas engine and a correction theoretical air amount; ,
Obtaining a current load factor of the gas engine;
Measuring the temperature of the exhaust gas discharged from the combustion chamber of the gas engine using a temperature sensor;
Determining a correction theoretical air amount according to the acquired load factor;
Calculating a set value of the air-fuel ratio by multiplying the determined correction theoretical air amount by a preset excess air ratio;
Adjusting the supply amount of the fuel gas or the air according to the current set value of the air-fuel ratio,
The step of determining the correction theoretical air amount includes:
Based on the first correspondence relationship, the correction theoretical air amount is controlled by feedback control so that a deviation between the temperature of the exhaust gas and the target temperature corresponding to the load factor when the temperature of the exhaust gas is measured becomes small. A first step of determining
A second step of determining a correction theoretical air amount according to a load factor of the gas engine based on the second correspondence relationship;
The first step is executed when the temperature sensor is normal,
The second step is executed after the end of the third transition period starting from when the temperature sensor failure is detected,
The step of determining the correction theoretical air amount further comprises:
A change that is executed during the third transition period, and that gradually increases or decreases with the passage of time, with the correction theoretical air amount determined in the first step immediately before entering the third transition period as an initial value. Determining a value for the corrected theoretical air volume as a function of elapsed time ;
An air-fuel ratio correction control method for a premixed gas engine, wherein the third transition period ends when the change value and the correction theoretical air amount based on the second correspondence relationship become equal. The second step includes
Determining a correction theoretical air amount reference value according to a load factor of the gas engine based on the second correspondence relationship;
It is determined whether or not the temperature of the exhaust gas exceeds a predetermined reference temperature, and when the temperature of the exhaust gas does not exceed the reference temperature, the reference value is determined as a final corrected theoretical air amount, when the temperature of the exhaust gas exceeds the reference temperature and determining a value obtained by adding a predetermined offset amount to the reference value to the final correction for the theoretical amount of air, of claims 1 to 4, The air-fuel ratio correction control method for a premixed gas engine according to any one of the preceding claims. An air-fuel ratio correction control device for a premixed gas engine to which a mixed gas obtained by mixing fuel gas and air is supplied,
Based on a table representing a predetermined correspondence relationship between the rotation speed and load factor of the gas engine and the excess air ratio, a value of the excess air ratio corresponding to the current rotation speed and the load factor of the gas engine is set. An excess air ratio setting section;
A temperature sensor for measuring the temperature of exhaust gas discharged from the combustion chamber of the gas engine;
A correcting theoretical air amount determining unit that determines a correcting theoretical air amount according to the current load factor of the gas engine;
An air-fuel ratio calculation unit that calculates a set value of the air-fuel ratio by multiplying the determined theoretical air amount for correction by the value of the set excess air ratio;
A gas amount adjuster for adjusting a supply amount of the fuel gas or the air according to a current set value of the air-fuel ratio ,
The correction theoretical air amount determination unit includes:
When the load factor of the gas engine is equal to or greater than a threshold value, the temperature of the exhaust gas and the temperature of the exhaust gas are measured based on the first correspondence relationship that associates the load factor of the gas engine with a target temperature. The theoretical air amount for correction is determined by feedback control so that the deviation from the target temperature corresponding to the load factor becomes small,
When the load factor of the gas engine is less than the threshold, correction is performed according to the load factor of the gas engine based on the second correspondence relationship that associates between the load factor of the gas engine and the correction theoretical air amount. An air- fuel ratio correction control device for a premixed gas engine configured to determine a theoretical air amount for use . A premixed gas engine to which a mixed gas in which fuel gas and air are mixed is supplied;
Based on a table representing a predetermined correspondence relationship between the rotation speed and load factor of the gas engine and the excess air ratio, a value of the excess air ratio corresponding to the current rotation speed and the load factor of the gas engine is set. An excess air ratio setting section;
A temperature sensor for measuring the temperature of exhaust gas discharged from the combustion chamber of the gas engine;
A correcting theoretical air amount determining unit that determines a correcting theoretical air amount according to the current load factor of the gas engine;
An air-fuel ratio calculation unit that calculates a set value of the air-fuel ratio by multiplying the determined theoretical air amount for correction by the value of the set excess air ratio;
E Bei a gas amount regulator for regulating a supply amount of the fuel gas or the air in accordance with the current set value of the air-fuel ratio,
The correction theoretical air amount determination unit includes:
When the load factor of the gas engine is equal to or greater than a threshold value, the temperature of the exhaust gas and the temperature of the exhaust gas are measured based on the first correspondence relationship that associates the load factor of the gas engine with a target temperature. The theoretical air amount for correction is determined by feedback control so that the deviation from the target temperature corresponding to the load factor becomes small,
When the load factor of the gas engine is less than the threshold, correction is performed according to the load factor of the gas engine based on the second correspondence relationship that associates between the load factor of the gas engine and the correction theoretical air amount. A premixed gas engine system configured to determine the theoretical air volume for the engine.

Images