Engine System

Abstract

To provide an engine system which has a reforming cylinder generating reformed gas through partial oxidation reaction of rich mixture and maintains net thermal efficiency close to a local maximum point of an entire engine including the reforming cylinder and a normal cylinder even when an external environment such as a temperature and humidity of air supplied to the engine is fluctuated.SOLUTION: An engine system comprises: a reformed gas component concentration measuring section S which measures gas component concentration, a concentration of an arbitrary gas component of reformed gas K generated in a reforming cylinder 40d; and a control device 50 which executes air excess rate control controlling an air excess rate in the reforming cylinder 40d within a predetermined range enabling reformed gas K to be generated. In the air excess rate control, the control device 50 controls the air excess rate in the reforming cylinder 40d on the basis of the gas component concentration measured with the reformed gas component concentration measuring section S.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an engine system in which at least some of a plurality of cylinders are made to function as reforming cylinders that carry out a partial oxidation reaction of at least a portion of a mixture containing fuel and combustion air to reform it into a reformed gas containing a combustion-promoting gas that has a faster combustion speed than the fuel, and the remaining plurality of cylinders are made to function as normal cylinders to which the reformed gas reformed in the reforming cylinders is introduced. [Background technology]

[0002] Conventionally, there is known an engine system that has at least one normal cylinder having a combustion chamber that burns a mixture containing fuel and combustion air, and at least one reforming cylinder that reforms at least a portion of the mixture into a reformed gas containing a combustion-promoting gas that burns faster than the fuel by a partial oxidation reaction in the combustion chamber, and that directs the reformed gas reformed in the reforming cylinder to at least the normal cylinder (see Patent Document 1). In the reforming cylinder, for example, a rich mixture containing fuel whose main component is methane is subjected to a partial oxidation reaction to produce a reformed gas containing a combustion-promoting gas with a fast combustion rate, such as hydrogen. By introducing this reformed gas into the normal cylinder, for example, it is possible to increase the spark propagation speed in the combustion chamber of the normal cylinder, reduce misfires and combustion fluctuations, and improve thermal efficiency by burning the combustion-promoting gas. On the other hand, there is a conventionally known engine system that has a lambda sensor that measures the oxygen concentration of exhaust gas flowing through the exhaust passage in order to operate the engine at a desired thermal efficiency, and uses the output of the lambda sensor to control the excess air ratio in the combustion chamber to a predetermined excess air ratio (see Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-94930 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-278070 Summary of the Invention [Problem to be solved by the invention]

[0004] In the engine system disclosed in Patent Document 1, operating the engine at a desired thermal efficiency could be achieved by, for example, providing a lambda sensor in an exhaust passage through which combustion exhaust gas from multiple cylinders flows, and controlling engine operation based on the measurement results of the lambda sensor, as in the technology disclosed in Patent Document 2. However, in the engine system disclosed in Patent Document 1, the reforming cylinder produces a reformed gas containing a combustion-promoting gas, so the excess air ratio is set to less than 1. Even if the reformed gas from the reforming cylinder is measured with a lambda sensor, it is difficult to accurately capture changes in the concentration of hydrogen and other components in the reformed gas that occur due to changes in atmospheric temperature and humidity, making it difficult to control engine operation based on these values. For this reason, there has been a need for the development of a new technology for operating the engine system disclosed in Patent Document 1 at high thermal efficiency. In particular, as described above, in an engine system equipped with a reformed cylinder, no technology has been disclosed or suggested for maintaining a high level of engine thermal efficiency even when external environmental conditions such as the engine's intake air temperature and intake air humidity fluctuate, leaving room for improvement.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide an engine system that has a reforming cylinder that generates reformed gas by partially oxidizing an over-rich mixture, and that can maintain the overall net thermal efficiency, including the reforming cylinder and the normal cylinder, near the maximum point even when the external environment of the engine, such as the intake air temperature and intake air humidity, fluctuates. [Means for solving the problem]

[0006] The engine system for achieving the above object is an engine system in which at least some of a plurality of cylinders are made to function as reforming cylinders that reform at least part of an air-fuel mixture containing fuel and combustion air into a reformed gas containing a combustion-promoting gas that burns faster than the fuel by a partial oxidation reaction, and the remaining cylinders are made to function as normal cylinders to which the reformed gas reformed in the reforming cylinders is introduced, and the engine system is characterized by the following configuration: a reformed gas component concentration measuring unit that measures a gas component concentration, which is the concentration of at least one gas component selected from the combustion promoting gas and unburned hydrocarbons in the reformed gas generated in the reforming cylinder; a control device that executes an excess air ratio control that controls an excess air ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated; the reformed gas component concentration measuring unit includes a combustion promoting gas concentration measuring unit that measures the concentration of the combustion promoting gas in the reformed gas; In the air excess ratio control, the control device controls the air excess ratio in the reformed cylinder based on the gas component concentration measured by the reformed gas component concentration measurement unit. It is something, the control device controls the excess air ratio in the reforming cylinder so as to maximize the concentration of the combustion promoting gas measured by the combustion promoting gas concentration measuring unit in the excess air ratio control; the excess air ratio control controls the excess air ratio of the reformed cylinder in a manner that follows a reference excess air ratio that can be arbitrarily changed, the control device is configured to be able to execute an excess air ratio reduction control for reducing the excess air ratio by a predetermined determination amount from the reference excess air ratio, The control device controls the reference excess air ratio to decrease when a change in concentration of the combustion promoting gas measured by the combustion promoting gas concentration measuring unit before and after execution of the excess air ratio decrease control is positive, and controls the reference excess air ratio to increase when the change in concentration of the combustion promoting gas is negative. It's at the point. Furthermore, the engine system for achieving the above object comprises: An engine system in which at least some of a plurality of cylinders are made to function as reforming cylinders that reform at least a portion of a mixture containing fuel and combustion air into a reformed gas containing a combustion-promoting gas that burns faster than the fuel by a partial oxidation reaction, and the remaining cylinders are made to function as normal cylinders to which the reformed gas reformed in the reforming cylinders is introduced, and the engine system is characterized by the following configuration: a reformed gas component concentration measuring unit that measures a gas component concentration, which is the concentration of at least one gas component selected from the combustion promoting gas and unburned hydrocarbons in the reformed gas generated in the reforming cylinder; a control device that executes an excess air ratio control that controls an excess air ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated; the reformed gas component concentration measuring unit includes a combustion promoting gas concentration measuring unit that measures the concentration of the combustion promoting gas in the reformed gas; the control device controls the excess air ratio in the reformed cylinder based on the gas component concentration measured by the reformed gas component concentration measuring unit in the excess air ratio control, the control device controls the excess air ratio in the reforming cylinder so as to maximize the concentration of the combustion promoting gas measured by the combustion promoting gas concentration measuring unit in the excess air ratio control; the excess air ratio control controls the excess air ratio of the reformed cylinder in a manner that follows a reference excess air ratio that can be arbitrarily changed, the control device is configured to be able to execute an air excess ratio increase control for increasing the air excess ratio by a predetermined determination change amount from the reference air excess ratio, The control device controls the reference air excess ratio to increase when the change in concentration of the combustion-promoting gas measured by the combustion-promoting gas concentration measuring unit before and after executing the air excess ratio increase control is positive, and controls the reference air excess ratio to decrease when the change in concentration of the combustion-promoting gas is negative.

[0007] As a result of extensive research, the inventors of the present invention have found that, as shown in Figure 3, when the above-mentioned excess air ratio control is performed, the concentrations of hydrogen and carbon monoxide as combustion-promoting gases in the reformed gas gradually increase as the excess air ratio of the reformed cylinder is reduced from 1 to a predetermined peak excess air ratio (a value included in the range indicated by λα in Figure 3), and when the excess air ratio is reduced beyond the predetermined peak excess air ratio, the concentrations of hydrogen and carbon monoxide as combustion-promoting gases in the reformed gas gradually decrease. Furthermore, as shown in Figure 5, it was found that the net thermal efficiency of an engine including a reformed cylinder gradually increases as the excess air ratio of the reformed cylinder decreases from 1 to near a predetermined peak excess air ratio, and gradually decreases when the excess air ratio is decreased beyond near the predetermined peak excess air ratio. In other words, from the results shown in Figures 3 and 5, it is estimated that when the excess air ratio in the reformed cylinder is changed, the net thermal efficiency of the engine including the reformed cylinder has a positive correlation with the concentration of the combustion-promoting gas generated in the reformed cylinder. In this experiment, the stroke-bore ratio (stroke / bore), displacement, and engine speed of the normal cylinder and the modified cylinder were adjusted to values ​​generally used in normal engines.

[0008] According to the above characteristic configuration, the control device controls the excess air ratio in the reforming cylinder based on the gas component concentration measured by the reformed gas component concentration measuring unit in the excess air ratio control that controls the excess air ratio in the reforming cylinder within a predetermined range in which reformed gas is generated.Therefore, for example, the control device can operate the engine while maintaining the net thermal efficiency at the maximum point achieved by controlling the excess air ratio in the reforming cylinder by performing feedback control to increase the reformed gas component concentration (e.g., concentration of hydrogen, carbon monoxide, etc.) that is estimated to have a high correlation with the net thermal efficiency of the engine. In particular, this control is resistant to changes in the external environment of the engine, such as the intake air temperature and intake air humidity, because it executes control based on the reformed gas component concentration that reflects the change in the external environment, and can maintain the net thermal efficiency of the engine at its maximum point.

[0009] As described above, an engine system can be provided that has a reforming cylinder that generates reformed gas by partially oxidizing an over-rich mixture, and that can execute control to maintain the overall net thermal efficiency, including the reforming cylinder and the normal cylinder, near the maximum point even when the external environment of the engine, such as the intake air temperature or intake air humidity, fluctuates.

[0011] Furthermore, As described above, the control device controls the excess air ratio in the reformed cylinder so as to maximize the concentration of the combustion-promoting gas measured by the combustion-promoting gas measuring unit during excess air ratio control. As shown in Figures 3 and 5, this increases the concentration of the combustion-promoting gas in the reformed gas, and enables operation at a maximum net thermal efficiency in the normal cylinder, which has a positive correlation with the concentration of the combustion-promoting gas. Furthermore, as in the above-described characteristic configuration, by executing excess air ratio reduction control that reduces the excess air ratio by a determined change amount from the reference air excess ratio, or excess air ratio increase control that increases the excess air ratio by a determined change amount from the reference air excess ratio, it is possible to grasp the trend in change in concentration of the combustion-promoting gas when the excess air ratio is varied at the time of execution, and by changing the reference air excess ratio based on this trend in concentration change, it is possible to bring the reference air excess ratio closer to the peak excess air ratio that maximizes the concentration of the combustion-promoting gas. By continuously executing the excess air ratio reduction control or excess air ratio increase control at predetermined time intervals, the reference excess air ratio can be maintained at the peak excess air ratio that maximizes the concentration of combustion-promoting gas, thereby enabling the engine to continue operating at a rate that maximizes its net thermal efficiency.

[0013] Further characteristic configurations of the engine system include: the excess air ratio control controls the excess air ratio of the reformed cylinder in a manner that follows a reference excess air ratio that can be arbitrarily changed, the control device is configured to be able to execute an air excess ratio increase control for increasing the air excess ratio by a predetermined determination change amount from the reference air excess ratio, The control device controls the reference air excess ratio to increase when the change in concentration of the combustion-promoting gas measured by the combustion-promoting gas concentration measuring unit before and after executing the air excess ratio increase control is positive, and controls the reference air excess ratio to decrease when the change in concentration of the combustion-promoting gas is negative.

[0014] As per the above characteristic configuration , basis By executing excess air ratio increase control that increases the excess air ratio by a determined change amount from the quasi-air excess ratio, it is possible to grasp the trend in change in concentration of the combustion-promoting gas when the excess air ratio is varied at the time of execution. Therefore, by changing the reference excess air ratio based on this trend in change in concentration, it is possible to bring the reference excess air ratio closer to the peak excess air ratio that maximizes the concentration of the combustion-promoting gas. and , sky By continuously executing the excess air ratio increase control at predetermined time intervals, the reference excess air ratio can be maintained at the peak excess air ratio that maximizes the concentration of combustion-promoting gases, thereby enabling the engine to continue operating at a rate that maximizes its net thermal efficiency.

[0015] The engine system for achieving the above object is an engine system in which at least some of a plurality of cylinders are made to function as reforming cylinders that reform at least part of an air-fuel mixture containing fuel and combustion air into a reformed gas containing a combustion-promoting gas that burns faster than the fuel by a partial oxidation reaction, and the remaining cylinders are made to function as normal cylinders to which the reformed gas reformed in the reforming cylinders is introduced, and the engine system is characterized by the following configuration: a reformed gas component concentration measuring unit that measures a gas component concentration, which is the concentration of at least one gas component selected from the combustion promoting gas and unburned hydrocarbons in the reformed gas generated in the reforming cylinder; a control device that executes an excess air ratio control that controls an excess air ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated; the reformed gas component concentration measuring unit includes an unburned hydrocarbon concentration measuring unit that measures the concentration of unburned hydrocarbons in the reformed gas, the control device controls the excess air ratio in the reformed cylinder based on the gas component concentration measured by the reformed gas component concentration measuring unit in the excess air ratio control, the excess air ratio control controls the excess air ratio of the reformed cylinder in a manner that follows a reference excess air ratio that can be arbitrarily changed, the control device is configured to be able to execute an excess air ratio decrease control for decreasing the excess air ratio by a predetermined determination amount from the reference excess air ratio, or an excess air ratio increase control for increasing the excess air ratio by a predetermined determination amount from the reference excess air ratio, The control device controls to increase the reference air excess ratio when the absolute value of the amount of change in concentration of unburned hydrocarbons measured by the unburned hydrocarbon concentration measuring unit before and after executing the excess air ratio decrease control or the excess air ratio increase control exceeds a predetermined judgment amount of concentration change, and controls to decrease the reference air excess ratio when the absolute value of the amount of change in concentration of unburned hydrocarbons is equal to or less than the predetermined judgment amount of concentration change.

[0016] As shown in Figure 4, the inventors have found that when the excess air ratio of the reformed cylinder is varied by controlling the excess air ratio, the concentration of unburned hydrocarbons in the reformed gas gradually increases as the excess air ratio decreases, and in particular, when Figure 5 is also taken into consideration, it can be seen that the rate of change in concentration (the amount of change in the concentration of unburned hydrocarbons with respect to a change in the excess air ratio) of the unburned hydrocarbon concentration in the reformed gas increases significantly on the side of the excess air ratio that is smaller than the side at which the net thermal efficiency of the engine is maximized. According to the above characteristic configuration based on this finding, the control device increases the reference excess air ratio when the absolute value of the amount of change in the concentration of unburned hydrocarbons measured by the unburned hydrocarbon concentration measuring unit before and after executing excess air ratio decreasing control or excess air ratio increasing control exceeds a predetermined judgment amount of concentration change, and decreases the reference excess air ratio when the absolute value of the amount of change in the concentration of unburned hydrocarbons is equal to or less than the predetermined judgment amount of concentration change.By appropriately setting the predetermined judgment amount of concentration change when the excess air ratio is changed by the predetermined judgment amount of change, the control device can set the reference excess air ratio to an air excess ratio that maximizes the net thermal efficiency of the engine.

[0017] Further characteristic configurations of the engine system include: a first fuel supply unit that supplies fuel to be introduced to at least the normal cylinder, and a second fuel supply unit that supplies fuel to be introduced to the reforming cylinder; When the control device is executing the fuel ratio reduction control that reduces a fuel ratio, which is a ratio of the total fuel supply amount to all of the normal cylinders by the first fuel supply unit to the total fuel supply amount to all of the reforming cylinders by the second fuel supply unit, in a state where the control device is executing the air excess ratio control that adjusts the fuel supply amount by the second fuel supply unit to control the air excess ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated, In the excess air ratio control, the excess air ratio in the reformed cylinder is controlled based on the gas component concentration measured by the reformed gas component concentration measuring section.

[0018] The inventors of the present invention have discovered that the net thermal efficiency of an engine can be improved by lowering the fuel ratio, which is the ratio of the total fuel supply to all normal cylinders to the total fuel supply to the reformed cylinders, i.e., by increasing the amount of fuel derived from reformed gas used in the normal cylinders. Therefore, according to the above characteristic configuration, in addition to improving net thermal efficiency based on fuel ratio reduction control, net thermal efficiency can be improved by controlling the excess air ratio in the reformed cylinder based on the gas component concentration measured by the reformed gas component concentration measurement unit, so that further improvement in the net thermal efficiency of the engine can be expected.

[0019] Further characteristic configurations of the engine system include: The control device, in the air excess ratio control, performs reformed gas operation in which only the reformed gas is introduced as the fuel to the normal cylinder while controlling the air excess ratio in the reformed cylinder based on the gas component concentration measured by the reformed gas component concentration measuring unit.

[0020] As described above, the net thermal efficiency of the engine can be improved by increasing the proportion of reformed gas (combustion-promoting gas) as fuel for the normal cylinders. Therefore, by performing reformed gas operation in which only reformed gas is introduced as fuel to the normal cylinders, as in the above characteristic configuration, the net thermal efficiency of the engine can be improved. In addition, the net thermal efficiency of the engine can also be improved by controlling the excess air ratio in the reformed cylinders based on the gas component concentration measured by the reformed gas component concentration measuring unit, so a further improvement in the net thermal efficiency of the engine can be expected.

[0021] Further characteristic configurations of the engine system include: The engine is characterized by comprising a reformed engine having at least one reformed cylinder as the plurality of cylinders, and an external power engine having the normal cylinders as the plurality of cylinders.

[0022] The engine system of the present invention, as in the above-described characteristic configuration, can effectively exhibit the effects described so far even when it is configured to have a separate reformed engine with a reformed cylinder and an external output engine with a normal cylinder to which reformed gas is guided from the reformed cylinder. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic configuration diagram of an engine system according to an embodiment. [Figure 2] FIG. 10 is a flow chart showing control of maximum point tracking control of net thermal efficiency. [Figure 3] FIG. 1 is a graph showing the concentrations of hydrogen and carbon monoxide in the reformed gas for each excess air ratio in the reforming cylinder. [Figure 4] FIG. 10 is a graph showing the concentrations of unburned hydrocarbons and methane in the reformed gas for each excess air ratio in the reforming cylinder. [Figure 5] FIG. 10 is a graph showing the net thermal efficiency of the entire engine for each excess air ratio in the reformed cylinder. DETAILED DESCRIPTION OF THE INVENTION

[0024] The engine system 100 according to an embodiment of the present invention has a reforming cylinder that generates reformed gas by partially oxidizing an over-rich mixture, and is capable of maintaining the overall net thermal efficiency, including the reforming cylinder and the normal cylinder, near the maximum point even when the external environment of the engine, such as the intake air temperature or intake air humidity, fluctuates. The engine system 100 will be described below with reference to the drawings.

[0025] As shown in FIG. 1, the engine system 100 according to the embodiment includes an engine body 40, which includes normal cylinders 40a, 40b, and 40c that combust fresh air (air-fuel mixture M) containing fuel F, such as city gas 13A (an example of a hydrocarbon gas whose main component is methane), and combustion air A, and a reforming cylinder 40d that reforms at least a portion of the air-fuel mixture M through a partial oxidation reaction into reformed gas K containing a combustion-promoting gas that has a faster combustion speed than fuel F. The engine system 100 is provided with a first fuel supply unit that supplies fuel to the normal cylinders 40a, 40b, and 40c, and a second fuel supply unit that supplies fuel to the reforming cylinder 40d. The reformed gas K reformed in the reforming cylinder 40d is supplied to at least the normal cylinders 40a, 40b, and 40c (in this embodiment, it is supplied only to the normal cylinders 40a, 40b, and 40c). In the reforming cylinder 40d, steam reforming shown in the following formula 1 and the water gas shift reaction shown in the following formula 2 also proceed.

[0026] CH4+H20→CO+3H2... [Formula 1]

[0027] CO+H20→CO2+H2... [Formula 2]

[0028] An engine system 100 according to an embodiment will be described below with reference to FIG. The engine system 100 of this embodiment is configured as a turbocharged engine and includes at least one (three in this embodiment) normal cylinders 40a, 40b, 40c and at least one (one in this embodiment) reformed cylinder 40d. Furthermore, the engine system 100 includes an engine control unit (hereinafter referred to as a control device 50) that receives measurement results from sensors that detect the operating state of the engine and is composed of a group of hardware and software that controls the operation of the turbocharged engine based on the input signals.

[0029] Although detailed illustration is omitted for this type of engine system 100, the air-fuel mixture M is supplied from the main air intake pipe 20 to the combustion chambers (not shown) of the normal cylinders 40a, 40b, and 40c via intake valves (not shown), and is then compressed as the pistons rise, ignited by a spark from a spark plug (not shown), causing the mixture to burn and expand, pushing the pistons down and outputting rotational power from the rotating shaft (not shown).Exhaust gas E generated by the combustion is pushed out of the combustion chambers of the normal cylinders 40a, 40b, and 40c via exhaust valves (not shown) into the exhaust passage 27 and discharged to the outside. As will be described in detail later, the combustion air A supplied from the main air intake pipe 20 is also supplied to the reforming cylinder 40d through the reforming cylinder intake branch pipe 20d, and the piston in the reforming cylinder 40d is also pushed down, outputting rotational power from the rotary shaft. However, the reformed gas K generated as exhaust gas in the reforming cylinder 40d is not discharged to the outside, but is returned to the main air intake pipe 20 via the reformed gas passage 28 and is guided to the normal cylinders 40a, 40b, and 40c.

[0030] The main air intake pipe 20 is provided with, in the order listed from the upstream side, an air cleaner 21 that purifies the combustion air A, a Venturi-type mixer 14 that mixes the combustion air A with fuel F at an appropriate ratio (air-fuel ratio), and a throttle valve 23 for normal cylinders that can adjust the amount of air-fuel mixture M supplied to the normal cylinders 40a, 40b, and 40c by adjusting the opening. That is, in the main air intake pipe 20, the mixture M produced by mixing fuel F and combustion air A in the mixer 14 is adjusted to a predetermined flow rate via the normal cylinder throttle valve 23 and introduced into the combustion chambers of the normal cylinders 40a, 40b, and 40c.

[0031] The reforming cylinder intake branch pipe 20d, which branches off from the main intake pipe 20 upstream of the mixer 14, is provided with the following in the order listed from the upstream side: a compressor 31 as a supercharger 30 that compresses the combustion air A; an intercooler 22 that cools the combustion air A that has been heated by the pressure increase by the compressor 31; a reforming cylinder throttle valve 25 that can adjust the amount of mixture M supplied to the reforming cylinder 40d by adjusting its opening; and a Venturi-type mixer 16 that mixes the combustion air A with fuel F at an appropriate ratio (air-fuel ratio).

[0032] The first fuel supply passage 11, which introduces the fuel F to the mixer 14, is provided with a differential pressure regulator 12 that maintains a constant pressure difference between the pressure of the combustion air A in the main air intake pipe 20 upstream of the mixer 14 and the pressure of the fuel F in the first fuel supply passage 11, and a first fuel flow control valve 13 that adjusts the amount of fuel F supplied to the combustion chambers of the normal cylinders 40a, 40b, and 40c via the mixer 14. That is, the first fuel supply passage 11, the differential pressure regulator 12, the mixer 14, and the first fuel flow control valve 13 function as a first fuel supply unit.

[0033] The supercharger 30 is configured as a turbo-type supercharger 30 that supplies exhaust gas E discharged from the normal cylinders 40a, 40b, 40c to a turbine 32 provided in the exhaust passage 27 connected to the normal cylinders 40a, 40b, 40c, and compresses the air-fuel mixture M supplied to the combustion chamber of the reforming cylinder 40d by a compressor 31 provided in the reforming cylinder air intake duct 20d while connected to the turbine 32. That is, the supercharger 30 rotates the turbine 32 by the kinetic energy of the exhaust gas E flowing through the exhaust passage 27, compresses combustion air A flowing through the reforming cylinder air intake duct 20d by the rotational force of the turbine 32, and supplies the compressed combustion air A to the combustion chamber of the reforming cylinder 40d, i.e., performs so-called supercharging. That is, in this embodiment, the supercharger 30 supercharges only the combustion air A that is led to the reforming cylinder 40d.

[0034] Downstream of the air cleaner 21, the main air intake pipe 20 branches into a plurality of normal cylinder air intake branch pipes 20a, 20b, and 20c that lead combustion air A to the normal cylinders 40a, 40b, and 40c, respectively, and a reforming cylinder air intake branch pipe 20d that leads combustion air A to the reforming cylinder 40d. The reforming cylinder 40d is configured to partially oxidize a portion of the air-fuel mixture M in its combustion chamber N to generate a reformed gas K containing combustion-promoting gases such as hydrogen and carbon monoxide, which have a faster combustion speed than the fuel F (e.g., methane). Here, it is known that when methane and air are mixed and burned, the amount of hydrogen and carbon monoxide generated peaks in a fuel-rich region where the excess air ratio is less than 1 (e.g., the excess air ratio region indicated by λα in FIG. 3). Therefore, in this embodiment, in order to combust the air-fuel mixture M in a fuel rich state in the fuel chamber of the reforming cylinder 40d, a second fuel supply passage 29 that supplies fuel F via a Venturi-type mixer 16 is connected to the reforming cylinder intake branch pipe 20d that supplies the air-fuel mixture M to the reforming cylinder 40d, and the second fuel supply passage 29 is provided with a second fuel flow control valve 15 that controls the flow rate of the fuel F. A compressor (not shown) or the like is provided on the upstream side of the second fuel flow control valve 15 of the second fuel supply passage 29 in order to increase the supply pressure of the fuel F to the supercharging pressure at the outlet of the compressor 31 of the main intake pipe 20. Furthermore, a reformed gas passage 28, which carries the reformed gas K reformed in the reforming cylinder 40d, is connected to the reforming cylinder 40d, and the downstream end of the reformed gas passage 28 is connected to the downstream side of the throttle valve 23 for the normal cylinders of the main intake pipe 20. That is, in this embodiment, the reformed gas K is configured so that all of it is guided to the normal cylinders 40a, 40b, 40c. The control device 50 executes excess air ratio control to control the opening of the second fuel flow control valve 15 so that the excess air ratio in the reforming cylinder 40d is within a predetermined range for generating the reformed gas K, that is, so that the excess air ratio of the mixture M in the reforming cylinder 40d is smaller than 1. In other words, the second fuel supply passage 29, the mixer 16, and the second fuel flow control valve 15 function as a second fuel supply unit.

[0035] A rotation speed sensor that measures the rotation speed of the rotation shaft (not shown) is provided as an operating state detection unit 41 on the rotation shaft (not shown) of the engine body 40. Furthermore, a torque measurement sensor that measures the torque of the rotating shaft (not shown) of the engine body 40 is provided as an operating state detection unit 41 on the rotating shaft of the engine body 40, and the control device 50 controls the openings of the first fuel flow control valve 13, the second fuel flow control valve 15, the throttle valve 23 for the normal cylinder, and the throttle valve 25 for the reformed cylinder so that the engine output calculated based on the engine speed measured by the speed sensor and the torque measured by the torque measurement sensor becomes a target output.

[0036] As a result of extensive research, the inventors of the present invention have discovered that, as shown in Figure 3, when the above-mentioned excess air ratio control is performed, as the excess air ratio of the reforming cylinder 40d is reduced from 1 to a predetermined peak excess air ratio (a value included in the range indicated by λα in Figure 3), the concentrations of hydrogen and carbon monoxide as combustion-promoting gases in the reformed gas K gradually increase, and when the excess air ratio is reduced beyond the peak excess air ratio, the concentrations of hydrogen and carbon monoxide as combustion-promoting gases in the reformed gas K gradually decrease. Furthermore, as shown in FIG. 5, it was found that the net thermal efficiency of the engine body 40 including the reformed cylinder 40d gradually increases as the excess air ratio of the reformed cylinder 40d decreases from 1 to near the peak excess air ratio, and gradually decreases when the excess air ratio is decreased beyond near the peak excess air ratio. That is, from the results shown in Figures 3 and 5, it is estimated that when the excess air ratio is changed in the reformed cylinder 40d, the net thermal efficiency of the engine body 40 including the reformed cylinder 40d has a positive correlation with the concentration of the combustion-promoting gas generated in the reformed cylinder 40d.

[0037] Therefore, the engine system 100 according to this embodiment has the following configuration in order to maintain the overall net thermal efficiency including the reformed cylinder 40d and the normal cylinders 40a, 40b, and 40c near the maximum point. The engine system 100 is provided with a hydrogen sensor S (an example of a reformed gas component concentration measuring unit, a combustion-promoting gas concentration measuring unit) at the outlet of the reformed cylinder 40d in the reformed gas flow path 28, which measures the concentration of hydrogen, which is a combustion-promoting gas in the reformed gas K generated in the reformed cylinder 40d, and the control device 50 controls the excess air ratio in the reformed cylinder 40d based on the hydrogen concentration measured by the hydrogen sensor S in the excess air ratio control.In other words, the control device 50 controls the excess air ratio in the reformed cylinder 40d in the excess air ratio control so as to maximize the hydrogen concentration measured by the hydrogen sensor S, thereby maintaining the net thermal efficiency of the engine body 40 at a maximum point by controlling the excess air ratio of the reformed cylinder 40d.

[0038] A specific control flow of this control will be explained below based on the control flow in Fig. 2. This control maintains the excess air ratio of the reforming cylinder 40d at a value that maximizes the concentration of hydrogen in the reformed gas K, thereby maintaining the net thermal efficiency of the engine body 40 at its maximum point.

[0039] In this control, when the engine body 40 is operating at a predetermined target output, the control device 50 first controls the excess air ratio of the reformed cylinder 40d in a manner that follows a reference excess air ratio that can be set arbitrarily. First, the control device 50 controls the second fuel supply unit to set the excess air ratio of the reforming cylinder 40d to a predetermined arbitrary reference excess air ratio (in this step, for example, a maximum value less than 1 (for example, 0.95)) (#01).

[0040] The control device 50 measures and stores the concentration λC1 of hydrogen (an example of a combustion-promoting gas) using the hydrogen sensor S at the time when the excess air ratio of the reforming cylinder 40d is set to the reference excess air ratio, i.e., before the excess air ratio reduction control described below is executed (#02). Next, the control device 50 executes an excess air ratio reduction control to reduce the excess air ratio of the reformed cylinder 40d, which is set to the reference excess air ratio, by a predetermined judgment change amount λJ (for example, a value of about 0.05) (#03), and at a point after the excess air ratio reduction control, measures and stores the concentration λC2 of hydrogen (an example of a combustion-promoting gas) using the hydrogen sensor S (#04).

[0041] Next, if the amount of change in hydrogen concentration before and after performing the air excess ratio reduction control is negative (λC2-λC1<0: #05), the control device 50 increases the reference air excess ratio by a reduction control amount Δλ (for example, a value of about 0.05) (#06), and if the amount of change in hydrogen concentration before and after performing the air excess ratio reduction control is positive (λC2-λC1>0: #07), the control device 50 decreases the reference air excess ratio by a reduction control amount Δλ (for example, a value of about 0.05) (#08).

[0042] Here, the decrease control amount Δλ (absolute value) is set to be equal to or less than the above-mentioned predetermined determination change amount λJ (absolute value).

[0043] By continuously executing the processes #02 to #08 at predetermined time intervals, the excess air ratio (reference excess air ratio) of the reforming cylinder 40d is controlled so that the hydrogen concentration in the reformed gas K is maximized, and the net thermal efficiency of the entire engine body 40 based on the excess air ratio control in the reforming cylinder 40d can be maintained at its maximum point.

[0044] Furthermore, the inventors of the present application have discovered that when excess air ratio control is being performed, in fuel ratio reduction control, which reduces the fuel ratio, which is the ratio of the total fuel supply amount to all normal cylinders 40a, 40b, 40c to the total fuel supply amount to all reformed cylinders 40d, the net thermal efficiency of the engine body 40 improves as the fuel ratio is reduced. Therefore, when the control device 50 is performing excess air ratio control in the reforming cylinder 40d by adjusting the fuel supply amount by the second fuel supply unit, and is performing fuel ratio reduction control to reduce the fuel ratio, which is the ratio of the total fuel supply amount to all normal cylinders 40a, 40b, 40c by the first fuel supply unit to the total fuel supply amount to all reforming cylinders 40d by the second fuel supply unit, the control device 50 controls the excess air ratio of the reforming cylinder 40d based on the hydrogen concentration measured by the hydrogen sensor S. This control not only improves net thermal efficiency based on fuel ratio reduction control, but also improves net thermal efficiency by controlling the excess air ratio in the reforming cylinder 40d based on the hydrogen concentration measured by the hydrogen sensor S, so that further improvements in the net thermal efficiency of the engine can be expected.

[0045] [Another embodiment] (1) In the above embodiment, a configuration example was shown in which the reformed gas component concentration measuring unit includes a hydrogen sensor S that measures the concentration of hydrogen as a combustion-promoting gas in the reformed gas K. However, a configuration may also be adopted in which a carbon monoxide sensor is included that measures the concentration of carbon monoxide as a combustion-promoting gas. Furthermore, a configuration may also be adopted in which the reformed gas component concentration measuring unit includes an unburned hydrocarbon sensor that measures the concentration of unburned hydrocarbons such as methane, rather than the concentration of a combustion-promoting gas in the reformed gas K. Furthermore, a configuration may be adopted in which multiple sensors are provided among the hydrogen sensor, carbon monoxide sensor, and unburned hydrocarbon sensor.

[0046] (2) In the above embodiment, with regard to the control for maintaining the net thermal efficiency of the engine body 40 at its maximum point, the control device 50 has shown an example of a configuration in which the control device 50 executes excess air ratio reduction control to reduce the excess air ratio of the reformed cylinder 40d, which is set to the reference excess air ratio, by a predetermined judgment change amount λJ (for example, a value of about 0.05). However, the object of the present invention can also be satisfactorily achieved by a configuration in which excess air ratio increase control is executed to increase the excess air ratio. That is, the control device 50 is configured to be able to execute excess air ratio increase control, which increases the excess air ratio by a predetermined determined amount from the reference excess air ratio, and the control device 50 may be configured to increase the reference excess air ratio when the amount of change in hydrogen concentration measured by the hydrogen sensor S before and after executing excess air ratio increase control is positive, and to decrease the reference excess air ratio when the amount of change in hydrogen concentration is negative.

[0047] (3) In the above embodiment, when an unburned hydrocarbon sensor (one example of an unburned hydrocarbon concentration measuring unit: not shown) that measures the concentration of unburned hydrocarbons such as methane is provided as the reformed gas component concentration measuring unit, it is preferable to execute the following control instead of the maximum point control of the net thermal efficiency of the above embodiment in order to maintain the net thermal efficiency of the engine body 40 at the maximum point. In other words, the excess air ratio control controls the excess air ratio of the reformed cylinder 40d in a manner that follows a reference excess air ratio that can be changed arbitrarily, and the control device 50 is configured to be able to execute excess air ratio reduction control, which reduces the excess air ratio by a predetermined determined amount from the reference excess air ratio, or excess air ratio increase control, which increases the excess air ratio by a predetermined determined amount. The control device 50 increases the reference excess air ratio when the absolute value of the change in concentration of unburned hydrocarbons measured by the unburned hydrocarbon concentration sensor before and after executing the excess air ratio decrease control or excess air ratio increase control exceeds a predetermined judgment concentration change amount, and decreases the reference excess air ratio when the absolute value of the change in concentration of unburned hydrocarbons is equal to or less than the predetermined judgment concentration change amount. This control was developed by the inventors in light of the fact that the absolute value of the change in concentration of unburned hydrocarbons in the reformed gas K measured by the unburned hydrocarbon sensor increases rapidly near the point where the net thermal efficiency of the engine body 40 is at its maximum, as shown in Figures 4 and 5.

[0048] (4) In the above embodiment, the hydrogen sensor S as a reformed gas component concentration measuring unit is provided at the outlet of the reformed cylinder 40d in the reformed gas flow path 28. However, if a catalyst (not shown) that promotes the reforming of the reformed gas K is provided in the reformed gas flow path 28, it is preferable that the hydrogen sensor S be provided downstream of the catalyst.

[0049] (5) In the above embodiment, the number of normal cylinders may be any number as long as it is one or more, and the number of reformed cylinders may be any number as long as it is one or more, and the functions of the present invention can be satisfactorily exhibited.

[0050] (6) In the above embodiment, a configuration example was shown in which one engine body 40 is provided with the reforming cylinder 40d and the normal cylinders 40a, 40b, 40c to which the reformed gas K generated in the reforming cylinder 40d is introduced. Alternatively, although not shown in the figures, it is possible to adopt a configuration that includes a reformed engine having at least one reformed cylinder and an external output engine having a normal cylinder to which the reformed gas generated in the reformed cylinder of the reformed engine is introduced. Even in this configuration, the various controls performed by the control device 50 described in the above embodiment can be executed, and the effects thereof can be satisfactorily exhibited.

[0051] (7) In the fuel ratio reduction control, while oxygen-containing gas supply control is being performed, the control device 50 can also perform reformed gas operation in which the fuel ratio is set to zero and only reformed gas K is introduced as fuel to the normal cylinders 40a, 40b, and 40c. In this case, the first fuel supply passage 11, the differential pressure regulator 12, the first fuel flow control valve 13, and the mixer 14, which serve as the first fuel supply unit, can be omitted.

[0052] (8) The reformed gas flow passage 28 may be configured to be connected to the exhaust port 28a of the reformed cylinder 40d and at least one of the normal cylinder air intake pipes 20a, 20b, and 20c that supply fresh air to the normal cylinders 40a, 40b, and 40c.

[0053] (9) In the above embodiment, an example was shown in which the engine system 100 includes the supercharger 30. However, even if the engine system 100 does not include the supercharger 30, the object of the present invention can be satisfactorily achieved. As described above, in a configuration that does not include the supercharger 30, the pressure in the reforming cylinder intake pipe 20d is not boosted to the supercharging pressure, so there is no need to boost the pressure of the fuel F supplied to the mixer 16 as a second fuel supply unit, and a simple and compact configuration can be achieved that does not include a compressor or the like for boosting the pressure.Incidentally, in this case, the pressure of the fuel F supplied from the mixer 16 to the reforming cylinder intake pipe 20d is set to the normal intake pressure. Furthermore, in the above embodiment, an example in which a turbo type is provided as the supercharger 30 has been shown, but a supercharger type may also be used. Furthermore, in the above embodiment, an example of so-called single-stage supercharging, in which the supercharger 30 includes a single compressor 31 and a single turbine 32, has been shown, but it may alternatively be a multi-stage supercharger having two or more stages.

[0054] (10) In the above embodiment, the fuel F is city gas 13A. However, in the essential meaning of the present invention, the fuel F is not limited to gas fuel, and may be liquid fuel such as gasoline.

[0055] (11) In the above embodiment, the fuel F is supplied by a venturi system, but it may be injected into the reforming cylinder intake pipe 20d or directly into the reforming cylinder 40d. In this case, the excess air ratio can be controlled by adjusting the injection amount of the fuel F.

[0056] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradictions arise. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0057] The engine system of the present invention has a reforming cylinder that generates reformed gas by subjecting an over-rich mixture to a partial oxidation reaction, and can be effectively used as a system that can maintain the overall net thermal efficiency, including the reforming cylinder and the normal cylinder, near the maximum point even when the external environment of the engine, such as the intake air temperature or intake air humidity, fluctuates. [Explanation of symbols]

[0058] 40: Engine body 40a: Normal cylinder 40b: Normal cylinder 40c: Standard cylinder 40d: Modified cylinder 50: Control device S: Hydrogen sensor 100: Engine system A: Combustion air E: Exhaust gas F:Fuel K: Reformed gas M: Air-fuel mixture

Claims

1. In an engine system in which at least some of a plurality of cylinders are made to function as reforming cylinders that reform at least a portion of an air-fuel mixture containing fuel and combustion air into a reformed gas containing a combustion-promoting gas that burns faster than the fuel by a partial oxidation reaction, and the remaining cylinders are made to function as normal cylinders to which the reformed gas reformed in the reforming cylinders is introduced, a reformed gas component concentration measuring unit that measures a gas component concentration, which is the concentration of at least one gas component selected from the combustion promoting gas and unburned hydrocarbons in the reformed gas generated in the reforming cylinder; a control device that executes an excess air ratio control that controls an excess air ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated; the reformed gas component concentration measuring unit includes a combustion promoting gas concentration measuring unit that measures the concentration of the combustion promoting gas in the reformed gas; the control device controls the excess air ratio in the reformed cylinder based on the gas component concentration measured by the reformed gas component concentration measuring unit in the excess air ratio control, the control device controls the excess air ratio in the reforming cylinder so as to maximize the concentration of the combustion promoting gas measured by the combustion promoting gas concentration measuring unit in the excess air ratio control; the excess air ratio control controls the excess air ratio of the reformed cylinder in a manner that follows a reference excess air ratio that can be arbitrarily changed, the control device is configured to be able to execute an excess air ratio reduction control for reducing the excess air ratio by a predetermined determination amount from the reference excess air ratio, The control device controls the reference excess air ratio to decrease when the amount of change in concentration of the combustion-promoting gas measured by the combustion-promoting gas concentration measuring unit before and after executing the air excess ratio reduction control is positive, and controls the reference excess air ratio to increase when the amount of change in concentration of the combustion-promoting gas is negative.

2. An engine system in which at least some of a plurality of cylinders are made to function as reforming cylinders that carry out a partial oxidation reaction of at least a portion of a mixture containing fuel and combustion air to reform the mixture into a reformed gas containing a combustion-promoting gas that has a faster combustion rate than the fuel, and the remaining plurality of cylinders are made to function as normal cylinders to which the reformed gas reformed in the reforming cylinders is introduced, a reformed gas component concentration measuring unit that measures a gas component concentration, which is the concentration of at least one gas component selected from the combustion promoting gas and unburned hydrocarbons in the reformed gas generated in the reforming cylinder; a control device that executes an excess air ratio control that controls an excess air ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated; the reformed gas component concentration measuring unit includes a combustion promoting gas concentration measuring unit that measures the concentration of the combustion promoting gas in the reformed gas; the control device controls the excess air ratio in the reformed cylinder based on the gas component concentration measured by the reformed gas component concentration measuring unit in the excess air ratio control, the control device controls the excess air ratio in the reforming cylinder so as to maximize the concentration of the combustion promoting gas measured by the combustion promoting gas concentration measuring unit in the excess air ratio control; the excess air ratio control controls the excess air ratio of the reformed cylinder in a manner that follows a reference excess air ratio that can be arbitrarily changed, the control device is configured to be able to execute an air excess ratio increase control for increasing the air excess ratio by a predetermined determination change amount from the reference air excess ratio, The control device controls the reference excess air ratio to increase when the amount of change in concentration of the combustion-promoting gas measured by the combustion-promoting gas concentration measuring unit before and after executing the air excess ratio increase control is positive, and controls the reference excess air ratio to decrease when the amount of change in concentration of the combustion-promoting gas is negative.

3. An engine system in which at least some of a plurality of cylinders are made to function as reforming cylinders that carry out a partial oxidation reaction of at least a portion of a mixture containing fuel and combustion air to reform the mixture into a reformed gas containing a combustion-promoting gas that has a faster combustion rate than the fuel, and the remaining plurality of cylinders are made to function as normal cylinders to which the reformed gas reformed in the reforming cylinders is introduced, a reformed gas component concentration measuring unit that measures a gas component concentration, which is the concentration of at least one gas component selected from the combustion promoting gas and unburned hydrocarbons in the reformed gas generated in the reforming cylinder; a control device that executes an excess air ratio control that controls an excess air ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated; the reformed gas component concentration measuring unit includes an unburned hydrocarbon concentration measuring unit that measures the concentration of unburned hydrocarbons in the reformed gas, the control device controls the excess air ratio in the reformed cylinder based on the gas component concentration measured by the reformed gas component concentration measuring unit in the excess air ratio control, the excess air ratio control controls the excess air ratio of the reformed cylinder in a manner that follows a reference excess air ratio that can be arbitrarily changed, the control device is configured to be able to execute an excess air ratio decrease control for decreasing the excess air ratio by a predetermined determination amount from the reference excess air ratio, or an excess air ratio increase control for increasing the excess air ratio by a predetermined determination amount from the reference excess air ratio, The control device controls to increase the reference excess air ratio when an absolute value of a change in concentration of unburned hydrocarbons measured by the unburned hydrocarbon concentration measuring unit before and after executing the excess air ratio decreasing control or the excess air ratio increasing control exceeds a predetermined judgment concentration change amount, and controls to decrease the reference excess air ratio when the absolute value of the change in concentration of unburned hydrocarbons is equal to or less than the predetermined judgment concentration change amount.

4. the excess air ratio control controls the excess air ratio of the reformed cylinder in a manner that follows a reference excess air ratio that can be arbitrarily changed, the control device is configured to be able to execute an air excess ratio increase control for increasing the air excess ratio by a predetermined determination change amount from the reference air excess ratio, 2. The engine system according to claim 1, wherein the control device increases the reference air excess ratio when a change in concentration of the combustion promoting gas measured by the combustion promoting gas concentration measuring unit before and after executing the air excess ratio increase control is positive, and decreases the reference air excess ratio when the change in concentration of the combustion promoting gas is negative.

5. A combustion engine comprising: a first fuel supply unit that supplies fuel to be led to at least the normal cylinder; and a second fuel supply unit that supplies fuel to be led to the reforming cylinder; When the control device is executing the air excess ratio control that adjusts the fuel supply amount by the second fuel supply unit to control the air excess ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated, and is executing a fuel ratio reduction control that reduces a fuel ratio that is a ratio of the total fuel supply amount to all of the normal cylinders by the first fuel supply unit to the total fuel supply amount to all of the reforming cylinders by the second fuel supply unit, 5. The engine system according to claim 1, wherein in the air excess ratio control, the air excess ratio in the reformed cylinder is controlled based on the gas component concentration measured by the reformed gas component concentration measuring unit.

6. An engine system described in any one of claims 1 to 5, wherein the control device, in the air excess ratio control, performs reformed gas operation in which only the reformed gas is introduced as the fuel to the normal cylinder while controlling the air excess ratio in the reformed cylinder based on the gas component concentration measured by the reformed gas component concentration measuring unit.

7. An engine system described in any one of claims 1 to 6, comprising a modified engine having at least one modified cylinder as one of the plurality of cylinders, and an external output engine having normal cylinders as one of the plurality of cylinders.

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