Engine system

Abstract

To improve net thermal efficiency of an engine through adjusting a concentration of hydrogen as combustion promoting gas in reformed gas in a manner that controls a progress level of partial oxidation reaction even in a state where an air excess rate is stabilized in a reforming cylinder in a configuration capable of generating the reformed gas through partial oxidation reaction of rich mixture in a reforming cylinder.SOLUTION: An engine system comprises: water injection means capable of injecting water to air-fuel mixture supplied into 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 a state where the air excess control is in execution, the control device 50 executes water injection state control controlling a state of water injection to the air-fuel mixture supplied to the reforming cylinder 40d through the water injection means so as to adjust a concentration of hydrogen as combustion promoting gas in the reformed gas K.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an engine system capable of using at least a part of a plurality of cylinders as reforming cylinders that reform at least a part of a mixture containing fuel and combustion air into reformed gas containing combustion-promoting gas having a combustion rate higher than that of the fuel by subjecting the mixture to a partial oxidation reaction, and using the remaining part of the plurality of cylinders as normal cylinders into which the reformed gas reformed in the reforming cylinders is introduced.

Background Art

[0002] Conventionally, as an engine system, it includes 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 part of the mixture in the combustion chamber by a partial oxidation reaction into reformed gas containing combustion-promoting gas having a combustion rate higher than that of the fuel, and guides the reformed gas reformed in the reforming cylinder to at least the normal cylinder (see Patent Document 1). In the reforming cylinder, for example, by subjecting an over-rich mixture containing fuel mainly composed of methane to a partial oxidation reaction, reformed gas containing combustion-promoting gas such as hydrogen having a high combustion rate can be generated. And by guiding the reformed gas to the normal cylinder, for example, the flame propagation speed in the combustion chamber of the normal cylinder can be increased, misfire and combustion fluctuations can be reduced, and an improvement in thermal efficiency due to the combustion of the combustion-promoting gas can be expected. In the technology disclosed in Patent Document 1 above, it is shown that the production amount of reformed gas is controlled by changing the number of cylinders of the reforming cylinder according to the output of the normal cylinder that mainly contributes to the output of the engine.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As hydrogen as a combustion-promoting gas has a faster combustion rate compared to carbon monoxide as another combustion-promoting gas, it is generally considered to increase the flame propagation speed in the combustion chamber of a cylinder and contribute highly to improving the net thermal efficiency. In the engine system as disclosed in Patent Document 1 above, although there is a disclosure regarding controlling the amount of reformed gas generated itself by changing the number of cylinders of the reforming cylinder according to the output of the normal cylinder, there is neither a disclosure nor a suggestion regarding controlling the concentration of hydrogen as a combustion-promoting gas in the reformed gas, and there was room for improvement.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide an engine system that can adjust the concentration of hydrogen as a combustion-promoting gas in reformed gas by controlling the degree of promotion of the partial oxidation reaction in a reforming cylinder in a configuration capable of generating reformed gas by subjecting an overly rich air-fuel mixture to a partial oxidation reaction in the reforming cylinder, and can improve the net thermal efficiency of the engine.

[0006] An engine system for achieving the above object causes at least a part of a plurality of cylinders to act as a reforming cylinder that subjects at least a part of an air-fuel mixture containing fuel and combustion air to a partial oxidation reaction to reform it into reformed gas containing a combustion-promoting gas with a faster combustion rate than the fuel, and causes the remaining part of the plurality of cylinders to act as normal cylinders into which the reformed gas reformed in the reforming cylinder is introduced. The engine system is characterized in that it is provided with water injection means capable of injecting water into the reforming cylinder, an air supply passage connected to the reforming cylinder, or an exhaust passage connected to the reforming cylinder, it is provided with a control device that executes air excess ratio control for controlling the air excess ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated, and the control device executes water injection state control for controlling the injection state of water by the water injection means in a state where the air excess ratio control is being executed. The control device is in a state of executing the air excess ratio control , front and executes water injection state control for controlling the injection state of water by the water injection means. and adjust the concentration of hydrogen as the combustion-promoting gas in the reformed gas and at the same time, When increasing the concentration of hydrogen as the combustion-promoting gas, in the range where the concentration of the combustion-promoting gas in the reformed gas increases as the air excess ratio decreases in the air excess ratio control, as the air excess ratio in the reformed cylinder decreases, the water injection amount by the water injection means in the water injection state control is increased is the point.

[0007] As a result of intensive research, the inventors of the present invention have found that, as shown in FIG. 3, when the above-described air excess ratio control is executed, as the air excess ratio of the reforming cylinder is decreased from 1 to a predetermined peak air excess ratio, the concentrations of hydrogen and carbon monoxide as combustion-promoting gases in the reformed gas gradually increase. Furthermore, as shown in FIG. 4, when the air excess ratio of the reforming cylinder is decreased from 1 to a predetermined peak air excess ratio (a value included in the air excess ratio range indicated by λα in FIG. 3), and as the concentrations of hydrogen and carbon monoxide as the combustion-promoting gases increase, it has also been experimentally confirmed that the net thermal efficiency of the engine tends to improve. In view of these results and the fact that hydrogen as a combustion-promoting gas has a faster combustion rate than carbon monoxide, it is expected that if the hydrogen concentration in the reformed gas is increased, the net thermal efficiency of the engine can be further improved. In the experiment, the stroke-bore ratio (stroke / bore), displacement, and engine rotational speed of the normal cylinder and the reforming cylinder were adjusted to values generally used in a normal engine. Incidentally, the simulation was performed using GT-Power (Gamma Technologies).

[0008] Therefore, when the inventors changed the amount of water injected into the region where the rich mixture undergoes a partial oxidation reaction in the combustion chamber of the reforming cylinder, and fixed the heat generation profile for various reactions including the partial oxidation reaction, the change in the hydrogen concentration in the reformed gas was derived by simulation. Here, the simulation was executed with the air excess ratio in the combustion chamber set to 0.5. From the simulation results in FIG. 5, it can be seen that the concentration of hydrogen in the reformed gas may increase as the absolute humidity of the weight of the injected water increases. Incidentally, in FIG. 5, the ratio (α2 / α1) of α2 to α1 as the hydrogen concentration is about 1.40.

[0009] Furthermore, the inventors conducted an experiment showing the relationship between the opening period of a water injection injector that sprays water into the air-fuel mixture introduced into the reforming cylinder and the concentrations (vol%) of hydrogen and carbon monoxide in the reformed gas. The conditions of the experiment were as follows: the engine speed was 800 rpm, the ignition timing of the reforming cylinder was 42° before top dead center, the ignition timing of the normal cylinder was 20° before top dead center, and the air excess ratio of the reforming cylinder was 0.62. As shown in FIG. 6, it can also be seen from the experiment that as the water injection amount increases (the opening period of the water injection injector increases), the hydrogen concentration in the reformed gas increases. On the other hand, as the water injection amount increases (the opening period of the water injection injector increases), the concentration of carbon monoxide in the reformed gas decreases. This is presumably because the water-gas shift reaction of [Equation 1] proceeds as the water injection amount increases. Furthermore, as shown in FIG. 7, it can be seen that as the water injection amount increases (the opening period of the water injection injector increases), the net thermal efficiency of the engine improves, but the combustion fluctuation rate (COV) of the reforming cylinder increases and the combustion stability decreases. Also, when the water injection amount is too large (in FIGS. 6 and 7, when the opening time of the water injection injector exceeds 900 μsec), the hydrogen concentration in the reformed gas decreases, and the net thermal efficiency of the reforming cylinder also decreases. Incidentally, in FIG. 6, the ratio (β2 / β1) of β2 to β1 as the hydrogen concentration is about 0.960, the ratio (γ2 / γ1) of γ2 to γ1 as the carbon monoxide concentration is about 1.03, in FIG. 7, the ratio (η2 / η1) of η2 to η1 as the net thermal efficiency is about 1.05, and the ratio (C2 / C1) of C2 to C1 as the combustion fluctuation rate (COV) is about 5.05.

[0010] Based on these results, the inventors, as in the above-described characteristic configuration, while performing air excess ratio control , water By performing water injection state control for controlling the injection state of water by injection means, the degree of promotion of the partial oxidation reaction is controlled, and an engine system capable of adjusting the concentration of hydrogen as a combustion promoting gas in the reformed gas has been completed. As a result, an engine system capable of improving the concentration of hydrogen as a combustion promoting gas in the reforming cylinder and improving the net thermal efficiency of the engine can be realized. Further, according to the above characteristic configuration, when the control device increases the concentration of hydrogen as the combustion-promoting gas, in the range where the concentration of the combustion-promoting gas in the reformed gas increases as the air excess ratio decreases in the air excess ratio control, as the air excess ratio in the reformed cylinder decreases, the water injection amount by the water injection means in the water injection state control is increased. Therefore, for example, the water injection amount is increased in accordance with the increase in carbon monoxide accompanying the decrease in the air excess ratio, and the water-gas shift reaction is favorably performed, so that the concentration of hydrogen in the reformed gas can be increased. Furthermore, it is possible to improve the hydrogen concentration of the reformed gas at the peak air excess ratio in the air excess ratio control and push up the peak of the net thermal efficiency of the engine.

[0011] A further characteristic configuration of the engine system is In the water injection state control, when the control device increases the concentration of hydrogen as the combustion promoting gas in the reformed gas, the water injection amount by the water injection means is increased to promote the water gas shift reaction represented by the following [Equation 1]. CO + H2O → CO2 + H2 [Equation 1]

[0012] According to the above characteristic configuration, in the water injection state control, when the control device increases the concentration of hydrogen as the combustion promoting gas in the reformed gas, the water injection amount by the water injection means is increased to promote the water gas shift reaction represented by [Equation 1], so that the concentration of hydrogen can be increased in a form in which carbon monoxide in the reformed gas is replaced with hydrogen.

[0015] A further characteristic configuration of the engine system is It separately includes at least a first fuel supply unit that supplies fuel to the normal cylinders and a second fuel supply unit that supplies fuel to the reforming cylinders. In a state where the control device performs air excess ratio control for controlling the air excess ratio in the reforming cylinder within a predetermined range in which reformed gas is generated by adjusting the fuel supply amount by the second fuel supply unit, when performing fuel ratio reduction control for reducing the fuel ratio, which is the ratio of the total fuel supply amount to all the normal cylinders by the first fuel supply unit to the total fuel supply amount to all the reforming cylinders by the second fuel supply unit, the water injection state control is performed.

[0016] The inventors of the present invention have found that the net thermal efficiency of the entire engine can be improved by reducing the fuel ratio, which is the ratio of the total fuel supply to all normal cylinders to the total fuel supply to the reforming cylinder, that is, by increasing the proportion of the reformed gas-derived fuel in the fuel of the normal cylinders. According to the above-described characteristic configuration, in addition to improving the net thermal efficiency of the engine based on the fuel ratio reduction control, by executing the water injection state control to improve the concentration of hydrogen in the reformed gas, the net thermal efficiency of the engine can be further improved, so that a further improvement in the net thermal efficiency of the engine can be expected.

[0017] A further characteristic configuration of the engine system is the control device increases the water injection amount by the water injection means in the water injection state control as the fuel ratio decreases in the fuel ratio reduction control.

[0018] According to the above-described characteristic configuration, when the fuel ratio is reduced by the fuel ratio reduction control while maintaining the output of the engine to a certain extent, as the absolute amount of carbon monoxide in the reformed gas increases due to the reduction of the fuel ratio, the water injection amount by the water injection means can be increased. Therefore, for example, the water injection amount can be increased in a form that follows the increase of carbon monoxide, and the carbon monoxide in the reformed gas can be effectively replaced with hydrogen by the water gas shift reaction.

[0019] A further characteristic configuration of the engine system is the water injection means is provided penetratingly in any one of the cylinder head of the reforming cylinder, or the air supply port that guides at least the combustion air to the reforming cylinder, or the exhaust passage that discharges the reformed gas from the reforming cylinder.

[0020] According to the above-described characteristic configuration, water can be satisfactorily contained in the air-fuel mixture or reformed gas that causes the water gas shift reaction, and the water gas shift reaction can be effectively promoted.

[0021] A further characteristic configuration of the engine system is The control device is configured to perform a reformed gas operation in which only the reformed gas is introduced as the fuel into the normal cylinder while the water injection state control is being executed.

[0022] As described above, by increasing the concentration of the reformed gas (combustion-promoting gas) as the fuel in the normal cylinder, the net thermal efficiency of the engine can be improved. Therefore, by performing a reformed gas operation in which only the reformed gas is introduced as the fuel into the normal cylinder as in the above-described characteristic configuration, in addition to improving the net thermal efficiency, by executing the water injection state control, the concentration of hydrogen in the reformed gas can be increased, and the net thermal efficiency can be improved. Thus, a further improvement in the net thermal efficiency of the engine can be expected.

[0023] A further characteristic configuration of the engine system is a reformed engine including at least one of the reformed cylinders as a plurality of the cylinders, and an external output engine including the normal cylinder as a plurality of the cylinders.

[0024] The engine system of the present invention has a configuration in which a reformed engine including a reformed cylinder and an external output engine including a normal cylinder into which the reformed gas is introduced from the reformed cylinder are provided separately, and can exhibit the effects described so far satisfactorily.

Brief Description of the Drawings

[0025] [Figure 1] It is a schematic configuration diagram of an engine system according to an embodiment. [Figure 2] It is a schematic diagram of a reformed cylinder of an engine system according to an embodiment. [Figure 3] It is a graph showing the concentrations (vol%) of hydrogen and carbon monoxide in the reformed gas for each air excess ratio in the reformed cylinder. [Figure 4] It is a graph showing the net thermal efficiency of the entire engine for each air excess ratio in the reformed cylinder. [Figure 5] It is a graph obtained by simulating the water injection amount into the reformed cylinder and the concentration (vol%) of hydrogen in the reformed gas. [Figure 6] It is a graph showing the relationship between the valve opening period of the water injection injector into the reforming cylinder and the concentrations (vol%) of hydrogen and carbon monoxide in the reformed gas, which is the experimental result. [Figure 7] It is a graph showing the valve opening period of the water injection injector into the reforming cylinder, the net thermal efficiency of the entire engine, and the combustion fluctuation rate of the reforming cylinder.

Embodiments for Carrying Out the Invention

[0026] The engine system 100 according to an embodiment of the present invention is configured to generate a reformed gas by subjecting a rich air-fuel mixture to a partial oxidation reaction in a reforming cylinder, and controls the degree of promotion of the partial oxidation reaction in the reforming cylinder to adjust the concentration of hydrogen as a combustion-promoting gas in the reformed gas, and relates to an engine system capable of improving the net thermal efficiency of the engine. Hereinafter, the engine system 100 will be described with reference to the drawings.

[0027] As shown in FIG. 1, the engine system 100 according to the embodiment includes normal cylinders 40a, 40b, and 40c that burn an air-fuel mixture M (fresh air) including a fuel F such as city gas 13A (an example of a hydrocarbon gas mainly composed of methane) and combustion air A in the engine body 40, and a reforming cylinder 40d that subjects at least a part of the air-fuel mixture M to a partial oxidation reaction to reform it into a reformed gas K containing a combustion-promoting gas having a combustion rate faster than that of the fuel F. The engine system 100 separately includes 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, and guides the reformed gas K reformed in the reforming cylinder 40d to at least the normal cylinders 40a, 40b, and 40c (in this embodiment, only to the normal cylinders 40a, 40b, and 40c). Note that in the reforming cylinder 40d, steam reforming represented by the following [Equation 2] and the water gas shift reaction represented by the above [Equation 1] also proceed.

[0028] CH4 + H20 → CO + 3H2 [Equation 2]

[0029] Hereinafter, based on FIG. 1, the engine system 100 according to the embodiment will be described. The engine system 100 of this embodiment is configured as a turbocharged engine, and includes at least one or more (three in this embodiment) normal cylinders 40a, 40b, 40c and at least one or more (one in this embodiment) reformed cylinders 40d. Further, it includes an engine control unit (hereinafter referred to as the control device 50), which is composed of a hardware group and a software group that input measurement results such as sensors for detecting the operating state of the engine and control the operation of the turbocharged engine based on the input signals.

[0030] Although detailed illustration is omitted for this type of engine system 100, the air-fuel mixture M supplied from the main intake pipe 20 to the combustion chambers (not shown) of the normal cylinders 40a, 40b, 40c through an intake valve (not shown) is spark-ignited by a spark plug (not shown) in a state compressed by the upward movement of the piston, and burned and expanded, thereby pushing down the piston to output rotational power from a rotating shaft (not shown). At the same time, the exhaust gas E generated by combustion is pushed out from the combustion chambers of the normal cylinders 40a, 40b, 40c to the exhaust passage 27 through an exhaust valve (not shown) and discharged to the outside. Incidentally, although details will be described later, the combustion air A supplied from the main intake pipe 20 is also supplied to the reformed cylinder 40d through the intake branch pipe 20d for the reformed cylinder, and the reformed cylinder 40d also pushes down the piston to output rotational power from the rotating shaft. However, the reformed gas K generated as exhaust gas in the reformed cylinder 40d is not discharged to the outside, and all of it is returned to the main intake pipe 20 through the reformed gas flow passage 28 and led to the normal cylinders 40a, 40b, 40c.

[0031] An air cleaner 21 for purifying the combustion air A, a venturi-type mixer 14 for mixing the fuel F with the combustion air A at an appropriate ratio (air-fuel ratio), and a throttle valve 23 for the normal cylinders that can adjust the supply amount of the air-fuel mixture M to the normal cylinders 40a, 40b, 40c by adjusting the opening degree are provided in this order from the upstream side in the main intake pipe 20. That is, in the main intake pipe 20, the air-fuel mixture M generated by mixing the fuel F and the combustion air A in the mixer 14 is adjusted to a predetermined flow rate through the normal cylinder throttle valve 23 and introduced into the combustion chambers of the normal cylinders 40a, 40b, and 40c.

[0032] In the reforming cylinder intake branch pipe 20d that branches from the upstream side of the mixer 14 in the main intake pipe 20, a compressor 31 as a supercharger 30 that compresses the combustion air A, an intercooler 22 that cools the combustion air A heated by the pressure boost of the compressor 31, a reforming cylinder throttle valve 25 that can adjust the supply amount of the air-fuel mixture M to the reforming cylinder 40d by adjusting the opening degree, and a venturi-type mixer 16 that mixes the fuel F with the combustion air A at an appropriate ratio (air-fuel ratio) are provided in the order described from its upstream side.

[0033] In the first fuel supply path 11 that guides the fuel F to the mixer 14, a differential pressure regulator 12 that keeps the pressure difference between the combustion air A in the main intake pipe 20 on the upstream side of the mixer 14 and the fuel F in the first fuel supply path 11 constant, and a first fuel flow control valve 13 that adjusts the supply amount of the fuel F supplied to the combustion chambers of the normal cylinders 40a, 40b, and 40c through the mixer 14 are provided. That is, the first fuel supply path 11, the differential pressure regulator 12, the mixer 14, and the first fuel flow control valve 13 function as the first fuel supply unit.

[0034] The supercharger 30 supplies the exhaust gas E discharged from the normal cylinders 40a, 40b, and 40c to a turbine 32 provided in the exhaust path 27 connected to the normal cylinders 40a, 40b, and 40c, and is configured as a turbo-type supercharger 30 that 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 intake branch pipe 20d in a state of being 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 path 27, and compresses the combustion air A flowing through the reforming cylinder intake branch pipe 20d by the rotational force of the turbine 32 and supplies it to the combustion chamber of the reforming cylinder 40d, that is, performs so-called supercharging. That is, in this embodiment, the supercharger 30 supercharges only the combustion air A introduced into the reforming cylinder 40d.

[0035] The main air supply pipe 20 is branched into a main air supply pipe 20 connected to a plurality of air supply branch pipes 20a, 20b, and 20c for guiding combustion air A1 to the normal cylinders 40a, 40b, and 40c respectively on the downstream side of the air cleaner 21, and an air supply branch pipe 20d for the reforming cylinder for guiding combustion air A to the reforming cylinder 40d. The reforming cylinder 40d is configured to generate a reformed gas K containing combustion-promoting gases such as hydrogen and carbon monoxide, which have a higher combustion rate than the fuel F (for example, methane), by subjecting a part of the air-fuel mixture M to a partial oxidation reaction in its combustion chamber N. Here, the inventors have obtained the finding that hydrogen and carbon monoxide have a peak in their generation amount in the fuel-rich region where the air excess ratio is less than 1 (for example, the air excess ratio region indicated by λα in FIG. 3) when methane and air are mixed and burned. Therefore, in the present embodiment, in order to burn the air-fuel mixture M in a fuel-rich state in the fuel chamber of the reforming cylinder 40d, a second fuel supply path 29 for supplying the fuel F in a form passing through a Venturi-type mixer 16 is connected to the air supply branch pipe 20d for the reforming cylinder that supplies the air-fuel mixture M to the reforming cylinder 40d, and a second fuel flow control valve 15 for controlling the flow rate of the fuel F is provided in the second fuel supply path 29. An air compressor (not shown) or the like is provided upstream of the second fuel flow control valve 15 in the second fuel supply path 29 to boost the supply pressure of the fuel F to the supercharging pressure at the outlet of the compressor 31 of the main air supply pipe 20. Furthermore, a reformed gas flow path 28 through which the reformed gas K reformed in the reforming cylinder 40d flows is connected to the reforming cylinder 40d, and the downstream end of the reformed gas flow path 28 is connected to the downstream side of the normal cylinder throttle valve 23 of the main air supply pipe 20. That is, in the present embodiment, all of the reformed gas K is configured to be guided to the normal cylinders 40a, 40b, and 40c. The control device 50 performs air excess ratio control to control the opening degree of the second fuel flow control valve 15 so that the air excess ratio in the reforming cylinder 40d is within a predetermined range in which reformed gas is generated, that is, the air excess ratio of the air-fuel mixture M supplied to the reforming cylinder 40d is less than 1. That is, the second fuel supply passage 29, the mixer 16, and the second fuel flow control valve 15 function as a second fuel supply unit.

[0036] A rotation speed sensor for measuring the rotation speed of a rotation shaft (not shown) is provided on the rotation shaft (not shown) of the engine body 40 as an operation state detection unit 41. Furthermore, a torque measurement sensor for measuring the torque of the rotation shaft is provided on the rotation shaft (not shown) of the engine body 40 as an operation state detection unit 41. The control device 50 controls the opening degrees 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 reforming cylinder so that the engine output calculated based on the engine rotation speed measured by the rotation speed sensor and the torque measured by the torque measurement sensor becomes the target output.

[0037] Now, the engine system 100 according to the present embodiment includes the following configuration to adjust the concentration of the combustion promoting gas in the reformed gas K.

[0038] That is, as shown in FIG. 2, the reforming cylinder 40d includes a water supply passage 66 through which water from a water supply source can flow as water injection means capable of injecting water into the air-fuel mixture M supplied to the reforming cylinder 40d, a pressure pump 60 capable of pumping water into the water supply passage 66, an on-off valve 67 capable of intermittently opening and closing the water supply passage 66 on the downstream side of the pressure pump 60, and a water injection nozzle 61 capable of injecting the water intermittently supplied by the on-off valve 67 into the combustion chamber N of the reforming cylinder 40d. The control device 50 is configured to be able to perform water injection state control for controlling the water injection state into the combustion chamber N. The water injection nozzle 61 is penetratively provided in the cylinder head 62 of the reforming cylinder 40d in such a form that the tip of the nozzle is exposed to the combustion chamber N of the reforming cylinder 40d. As shown in Fig. 2, in the combustion chamber N of the reforming cylinder 40d, an intake valve 63 for opening and closing an intake port 20f to which an intake branch pipe 20d for the reforming cylinder is connected, and an exhaust valve 64 for opening and closing an exhaust port 28b to which a reformed gas flow path 28 is connected are provided. The timing at which the water injection nozzle 61 injects water into the reforming cylinder 40d may be any of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke as long as the reaction can proceed from the time before the above-described water gas shift reaction occurs until the time when the reaction can proceed.

[0039] Furthermore, regarding the control of the water injection state, when the control device 50 is in a state of executing the above-described air excess ratio control, the control device 50 executes water injection state control for controlling the water injection state into the combustion chamber N to adjust the concentration of hydrogen as a combustion promoting gas in the reformed gas K. More specifically, in the water injection state control, when the control device 50 increases the concentration of hydrogen as a combustion promoting gas in the reformed gas K, the control device 50 increases the injection time of the on-off valve 67 that is intermittently controlled as the water injection means to increase the water injection amount and promote the water gas shift reaction shown in the following [Equation 1].

[0040] CO + H2O → CO2 + H2 [Equation 1]

[0041] When promoting the water gas shift reaction, the greater the amount of carbon monoxide as a combustion promoting gas contained in the reformed gas, the greater the supply of water required. Therefore, when the control device 50 increases the concentration of hydrogen as a combustion promoting gas, the control device 50 increases the water injection amount in the water injection state control as the air excess ratio in the reforming cylinder 40d decreases.

[0042] At this time, as shown in Fig. 3, in the air excess ratio control, since the concentration (vol%) of carbon monoxide in the reformed gas K takes a maximum value in a predetermined air excess ratio range (for example, the range indicated by λα in Fig. 3), the control device 50 is in the range where the concentration of the combustion promoting gas in the reformed gas K increases as the air excess ratio decreases in the air excess ratio control (in the example of Fig. 3, the range where the air excess ratio λ is about 0.55 ≦ λ < 1), as described above, the water injection amount is increased as the air excess ratio decreases. Here, in the air excess ratio control, the determination of whether or not the concentration of the combustion promoting gas in the reformed gas K increases as the air excess ratio decreases is, for example, when the control device 50 decreases the air excess ratio, whether or not the change amount of the concentration (vol%) of carbon monoxide measured by a carbon monoxide concentration sensor (not shown) provided in the reformed gas flow path 28 increases. It can be judged by.

[0043] By executing this control, the higher the concentration (vol%) of carbon monoxide in the reformed gas K, the more the production amount of hydrogen generated by the water gas shift reaction can be increased, and the net thermal efficiency in the engine body 40 can be improved with the increase of the hydrogen. Incidentally, although illustration is omitted, in this embodiment, for the reforming cylinder 40d as well, spark ignition by a spark plug is executed. In addition, in the water injection state control, for example, when the combustion fluctuation rate (COV) of the reforming cylinder 40d derived from the detection result of a cylinder internal pressure sensor (not shown) that detects the cylinder internal pressure of the reforming cylinder 40d becomes a certain value or more, the water spray is stopped.

[0044] Furthermore, the inventors of the present application have found that in the fuel ratio reduction control in which the fuel ratio, which is the ratio of the total fuel supply amount to all the normal cylinders 40a, 40b, 40c to the total fuel supply amount to all the reforming cylinders 40d, is reduced while the air excess ratio control is being executed, the net thermal efficiency of the engine body 40 improves as the fuel ratio decreases. Therefore, the control device 50 adjusts the fuel supply amount by the second fuel supply unit and executes the water injection state control when executing the fuel ratio reduction control in which the fuel ratio, which is the ratio of the total fuel supply amount by the first fuel supply unit to all the normal cylinders 40a, 40b, 40c to the total fuel supply amount by the second fuel supply unit to all the reforming cylinders 40d, is reduced in a state where the above-described air excess ratio control is being executed in the reforming cylinder 40d. Furthermore, the control device 50 increases the water injection amount in the water injection state control as the fuel ratio decreases in the fuel ratio reduction control.

[0045] When executing fuel ratio reduction control, when attempting to maintain the output in the engine body 40, the reformed gas K generated in the reforming cylinder 40d tends to increase. When the air excess ratio in the reforming cylinder 40d is constant and there is no change in the concentration of the combustion promoting gas in the reformed gas K, the absolute amount of carbon monoxide in the reformed gas K will increase. Due to the above control, as the absolute amount of carbon monoxide in the reformed gas K increases due to the reduction of the fuel ratio, the water injection amount is increased. For example, the water injection amount is increased in a form that follows the increase in carbon monoxide, and by the water gas shift reaction, the carbon monoxide contained in the reformed gas K can be effectively replaced with hydrogen.

[0046] 〔Alternative Embodiment〕 (1) In the above embodiment, the water injection nozzle 61 is shown as a configuration example penetrating the cylinder head 62 of the reforming cylinder 40d. However, for example, a configuration may be adopted in which the water injection nozzle 61 is provided at the reforming cylinder air supply port 20e (reforming cylinder air supply branch pipe 20d) where the reforming cylinder air supply branch pipe 20d is connected to the reforming cylinder 40d. The timing of water injection from the water injection nozzle 61 can be at any time. However, in the case of this configuration, preferably, it is from the opening start point where the opening of the air supply valve 63 starts to the opening end point where the opening of the air supply valve 63 ends during the air supply stroke. The timing of this water injection varies depending on the injection position, injection pressure, specifications of the injection nozzle, etc. Also, the water gas shift reaction shown in Equation 1 is an exothermic reaction, and the equilibrium is more on the product side at lower temperatures, that is, hydrogen is more easily generated. Therefore, the water injection nozzle 61 may adopt a configuration provided at the exhaust port 28a (exhaust passage 28) where the reformed gas flow passage 28 is connected to the reforming cylinder 40d. The timing of water injection from the water injection nozzle 61 can be at any time. However, in this case, preferably, it is from the opening start point where the opening of the exhaust valve 64 starts to the opening end point where the opening of the air supply valve 63 ends during the exhaust stroke. The timing of this water injection varies depending on the injection position, injection pressure, specifications of the injection nozzle, etc.

[0047] (2) In the above-described embodiment, the number of normal cylinders may be any number as long as it is one or more, and the number of reforming cylinders may also be any number as long as it is one or more, and the functions of the present invention can be exhibited well.

[0048] (3) In the above-described embodiment, an example of a configuration is shown in which, for one engine body 40, a reforming cylinder 40d and normal cylinders 40a, 40b, 40c into which reformed gas K generated in the reforming cylinder 40d is introduced are provided. Instead of this configuration, although illustration is omitted, a configuration can be adopted that includes a reforming engine having at least one reforming cylinder and an external output engine having normal cylinders into which reformed gas generated in the reforming cylinder of the reforming engine is introduced. Even in such a configuration, various controls executed by the control device 50 described in the above embodiment can be executed, and its effects can be exhibited well.

[0049] (4) In the fuel ratio reduction control, the control device 50 can also execute a reformed gas operation in which, while executing water injection state control, the fuel ratio is set to zero and only reformed gas K is introduced as fuel into the normal cylinders 40a, 40b, 40c. In this case, the first fuel supply path 11, differential pressure regulator 12, first fuel flow control valve 13, and mixer 14 as the first fuel supply unit can be omitted.

[0050] (5) The reformed gas flow path 28 may adopt a configuration in which it is connected to at least one of the exhaust ports 28a of the reforming cylinder 40d and the intake air branch pipes 20a, 20b, 20c for normal cylinders that supply the air-fuel mixture M to the normal cylinders 40a, 40b, 40c.

[0051] (6) In the above-described embodiment, an example in which the engine system 100 includes a supercharger 30 is shown, but even in a configuration without the supercharger 30, the object of the present invention can be achieved well. As described above, in the configuration without the supercharger 30, since the intake air branch pipe 20d for the reforming cylinder is not pressurized up to the supercharging pressure, it is not necessary to increase the pressure of the fuel F supplied to the mixer 16 as the second fuel supply unit, and a simple and compact configuration without a compressor or the like for pressure increase can be achieved. Incidentally, in this case, the pressure of the fuel F supplied from the mixer 16 to the intake air branch pipe 20d for the reforming cylinder is set to the normal intake air pressure. Furthermore, in the above embodiment, an example in which a turbo-type supercharger 30 is provided has been shown, but a supercharger-type one may be used instead. Also, in the above embodiment, an example of so-called single-stage supercharging including a single compressor 31 and a single turbine 32 as the supercharger 30 has been shown, but alternatively, two-stage or more multi-stage supercharging may be used.

[0052] (7) In the above embodiment, the fuel F is the city gas 13A, but in the essential meaning of the present invention, it is not limited to gas fuel and may be liquid fuel such as gasoline.

[0053] (8) In the above embodiment, the reforming cylinder 40d includes a spark plug (not shown) and shows a configuration example in which the air-fuel mixture is spark-ignited. However, a configuration may be adopted in which a spark plug is not provided in the reforming cylinder 40d and the air-fuel mixture is self-ignited and burned.

[0054] (9) In the above embodiment, the configuration in which the fuel F is supplied by a venturi type has been shown, but a configuration in which it is injected into the intake air branch pipe 20d for the reforming cylinder or a configuration in which it is directly injected into the reforming cylinder 40d may be adopted. In this case, the air-fuel ratio can be controlled by adjusting the injection amount of the fuel F or the like.

[0055] In addition, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with the configurations disclosed in other embodiments as long as there is no contradiction. Also, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be appropriately modified within the scope not departing from the object of the present invention.

Industrial Applicability

[0056] The engine system of the present invention is configured to generate reformed gas by subjecting a rich air-fuel mixture to a partial oxidation reaction in a reforming cylinder. By controlling the degree of promotion of the partial oxidation reaction in the reforming cylinder, the concentration of hydrogen as a combustion-promoting gas in the reformed gas is adjusted, and the net thermal efficiency of the engine can be improved, making it effectively utilizable.

Description of Reference Numerals

[0057] 40: Engine body 40a: Normal cylinder 40b: Normal cylinder 40c: Normal cylinder 40d: Reforming cylinder 50: Control device 60: Feed pump 61: Water injection nozzle 62: Cylinder head 66: Water supply passage 67: On-off valve 100: Engine system A: Combustion air E: Exhaust gas F: Fuel K: Reformed gas M: Air-fuel mixture N: Combustion chamber

Claims

1. In an engine system capable of operating at least a part of a plurality of cylinders as reforming cylinders that reform at least a part of a mixture containing fuel and combustion air by subjecting it to a partial oxidation reaction to produce a reformed gas containing a combustion-promoting gas having a combustion rate faster than that of the fuel, and operating the remaining part of the plurality of cylinders as normal cylinders into which the reformed gas reformed in the reforming cylinders is introduced, water injection means capable of injecting water into the reforming cylinder, an intake passage connected to the reforming cylinder, or an exhaust passage connected to the reforming cylinder is provided, a control device that performs air excess ratio control for controlling the air excess ratio in the reforming cylinder within a predetermined range in which the reformed gas is generated is provided, the control device performs water injection state control for controlling the water injection state by the water injection means while performing the air excess ratio control, to adjust the concentration of hydrogen as the combustion-promoting gas in the reformed gas, and when increasing the concentration of hydrogen as the combustion-promoting gas, within a range in which the concentration of the combustion-promoting gas in the reformed gas increases as the air excess ratio decreases in the air excess ratio control, as the air excess ratio in the reforming cylinder decreases, the engine system that increases the water injection amount by the water injection means in the water injection state control.

2. The control device promotes the water-gas shift reaction represented by the following [Equation 1] by increasing the water injection amount by the water injection means when increasing the concentration of hydrogen as the combustion-promoting gas in the reformed gas in the water injection state control. The engine system according to Claim 1. CO + H ２ O → CO ２ + H ２ [Formula 1]

3. It separately includes a first fuel supply unit that supplies fuel to at least the normal cylinders, and a second fuel supply unit that supplies fuel to the reforming cylinders, the control device performs the water injection state control when performing fuel ratio reduction control for reducing the fuel ratio, which is the ratio of the total fuel supply amount to all the normal cylinders by the first fuel supply unit to the total fuel supply amount to all the reforming cylinders by the second fuel supply unit, while adjusting 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. The engine system according to Claim 1 or 2.

4. The engine system according to claim 3, wherein the control device increases the water injection amount by the water injection means in the water injection state control in accordance with the decrease in the fuel ratio in the fuel ratio decrease control.

5. The engine system according to any one of claims 1 to 4, wherein the water injection means is provided penetratingly in any one of the cylinder head of the reforming cylinder, an air supply port for guiding at least the combustion air to the reforming cylinder, or an exhaust passage for discharging the reformed gas from the reforming cylinder.

6. The engine system according to any one of claims 1 to 5, wherein the control device executes a reformed gas operation in which only the reformed gas is introduced as the fuel into the normal cylinder in a state where the water injection state control is being executed.

7. The engine system according to any one of claims 1 to 6, comprising a reforming engine including at least one reforming cylinder as a plurality of the cylinders, and an external output engine including the normal cylinder as a plurality of the cylinders.

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