JP2007270750A - Gas fuel internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the ignitability of an internal combustion engine employing gaseous fuel as main fuel. <P>SOLUTION: The internal combustion engine employing the gaseous fuel as the main fuel includes an ignition plug 140, a gas injection valve 32 for supplying the gaseous fuel to the engine, and a liquid injection valve 42 for injecting liquid fuel to the engine. An ECU 100 judges whether the ignitability obtained by the gaseous fuel is within an appropriate range or not. When the ECU 100 determines that the ignitability will exceed the appropriate range, the liquid fuel as auxiliary fuel for ignition is supplied to the engine in addition to the gaseous fuel. In the appropriate range of the ignitability, for example, a required discharge voltage of the ignition plug 140 is regarded as a reference. When the required discharge voltage actually exceeds a set discharge voltage of the ignition plug or when it is predicted based on required torque or the like that the required discharge voltage will exceed the set discharge voltage, the discharge voltage is lowered by employing both the gaseous fuel and the liquid fuel and the ignitability is improved by injecting the minimum amounts of the fuels. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine using gas fuel as a main fuel.

  Gas fuel internal combustion engines using hydrogen gas, LPG (Liquefied Petroleum Gas), natural gas, reformed gas obtained by reforming gasoline or the like as fuel are known. Since this gas fuel has a combustibility equivalent to or higher than that of gasoline, it can provide an internal combustion engine with good combustion efficiency when ignited, but there is a problem in its ignitability compared with gasoline fuel.

  In order to reliably ignite such low ignitability fuel, it is necessary to improve the spark plug. As shown in Non-Patent Document 1, for example, the electrode shape of the spark plug is changed or the plug is narrowed. It is conceivable to increase the diameter, adjust the plug gap, change the insulating material or electrode shape, or increase the ignition energy itself.

  Poor ignition, or misfire, is highly undesirable for internal combustion engines. For example, Patent Document 1 discloses an apparatus for detecting misfire. Here, as the cause of misfire, the misfire of the fuel system due to the lean state or the rich state of the fuel mixture, and the misfire of the ignition system due to the miss spark are shown. Further, regarding the misfire of the fuel system, there is a correlation between the misfire and the voltage (discharge voltage) held between the electrodes of the spark plug, and the period during which the discharge voltage exceeds the comparison level (comparison voltage value) is predetermined. It is disclosed that a misfire is determined when it continues for a period of time.

  Patent Document 2 discloses misfire detection in a direct-injection spark ignition engine (internal combustion engine). Similarly to Patent Document 1, it is disclosed to determine misfire based on a discharge voltage of a spark plug. In Patent Document 2, the discharge voltage of the spark plug is further compared with the reference voltage, so that the rich misfire or lean is caused by the air-fuel ratio around the spark plug being richer than the optimal air-fuel ratio. It is determined whether there is a lean misfire.

JP-A-6-213129 JP-A-10-299563 JP-A-9-21362 Kanako Mitsuo “Spark Plug” Sankaido, December 20, 1999, p94-95

  In the case of an internal combustion engine that uses gas fuel as the main fuel as described above, it is only necessary to provide an optimal spark plug for the gas fuel. However, as disclosed in Non-Patent Document 1, it has a high ignition performance improving function. An improved method requires an expensive ignition device. For this reason, there is a limit to optimization, and an increase in development cost and manufacturing cost for improvement cannot be avoided.

  Moreover, misfire is determined as described in Patent Documents 1 and 2, and misfire at the next timing can be avoided by adjusting the air supply amount and the fuel injection amount. However, the deterioration in ignitability at the lean combustion limit (lean state), which is a cause of misfire in gas fuel, is eliminated by increasing the gas fuel injection amount, and the amount of fuel used cannot be reduced. Therefore, in order to reduce the amount of fuel used, it is necessary to achieve reliable ignition even in a lean region with low ignitability, and improvement of the spark plug is required as shown in Non-Patent Document 1 above. The

  Patent Document 3 describes that a reformed gas of gasoline is used in combination with an internal combustion engine whose main fuel is gasoline. In Patent Document 3, the reformed gas is supplied only to the extinguishing layer (wall surface) region formed in the cylinder, thereby promoting combustion in the region that becomes the extinguishing layer when the gasoline fuel is burned, and hydrocarbons are not yet burned. Decreasing the minutes. In other words, the reformed gas layer is selectively generated in the flame extinguishing layer in the cylinder, and the gasoline fuel layer is generated inside the flame extinguishing layer including the spark plug proximity region, so that the spark plug is an appropriate spark for gasoline fuel. What is necessary is just to be able to ignite, and what is necessary is just to employ | adopt a conventionally known spark plug as it is. Further, Patent Document 3 states that if a reformed gas layer is generated near the spark plug at the reformed gas supply timing, the ignitability can be improved when the ignitability of the main fuel (gasoline fuel) is poor. There is no recognition of the low ignitability of gas fuel.

  The present invention aims to improve ignitability in an internal combustion engine using gas fuel as the main fuel.

  The present invention relates to an internal combustion engine that uses gas fuel as a main fuel, a gas injection valve that supplies the gas fuel to the engine, a liquid injection valve that supplies liquid fuel to the engine, and an air-fuel mixture in an engine cylinder. An ignition plug that performs spark ignition, and when the engine control unit determines whether the ignitability by the gas fuel is within an appropriate range and predicts that the gas fuel is outside the appropriate range, in addition to the gas fuel, the liquid fuel Is supplied to the engine as an ignition auxiliary fuel.

  In another aspect of the present invention, the engine control unit determines whether or not the required discharge voltage of the spark plug exceeds a predetermined voltage based on a predetermined relationship map of the fuel injection amount set in advance or a detection value of the required discharge voltage. Based on this, it is possible to predict the arrival of the gas fuel outside the appropriate range of ignitability.

  In another aspect of the present invention, there is provided a spark ignition internal combustion engine that uses gas fuel as main fuel, a gas injection valve that supplies the gas fuel to the engine, a liquid injection valve that supplies liquid fuel to the engine, and an engine An ignition plug that performs spark ignition on the air-fuel mixture in the cylinder, and the engine control unit has a relationship map of the required torque and the fuel injection amount with respect to the air-fuel mixture concentration in consideration of the limit voltage of the required discharge voltage of the ignition plug When it is determined that the required discharge voltage exceeds the limit discharge voltage based on the relationship map, the liquid fuel is supplied to the engine as an ignition auxiliary fuel in addition to the gas fuel.

  In another aspect of the present invention, there is provided a spark ignition internal combustion engine that uses gas fuel as main fuel, a gas injection valve that supplies the gas fuel to the engine, a liquid injection valve that supplies liquid fuel to the engine, and an engine An ignition plug that performs spark ignition on the air-fuel mixture in the cylinder, and a detection unit that detects a required discharge voltage when the ignition plug is ignited, and when the detected required discharge voltage exceeds a limit voltage of the ignition plug In addition to the gas fuel, the liquid fuel is supplied to the engine as an ignition auxiliary fuel.

  In another aspect of the present invention, in the internal combustion engine, the liquid fuel can be directly injected into an engine cylinder.

  Gas fuel is a fuel having a smaller relative dielectric constant than liquid fuel, and has a characteristic of low ignitability. For example, when the engine load (required torque) is large, or when the air-fuel mixture concentration is low, especially in both cases, the ignitability is markedly deteriorated. In the case of worsening beyond this, liquid fuel is used in combination with gas fuel as ignition auxiliary fuel. The liquid fuel is, for example, gasoline fuel and has a relative dielectric constant larger than that of gas fuel. Therefore, the ignitability can be improved by supplying the liquid fuel together with the gas fuel into the cylinder of the engine. Therefore, both the gas fuel and the liquid fuel can achieve the minimum injection amount, and the ignition performance can be improved without any special improvement of the spark plug.

  Here, whether or not the ignitability by the gas fuel is in an appropriate range is determined based on whether or not the required discharge voltage of the spark plug exceeds a predetermined voltage, based on a predetermined relationship map of the fuel injection amount or a detected value of the required discharge voltage. It can be easily determined by making a judgment based on the above. As described above, since the relative permittivity of gas fuel is smaller than that of liquid fuel, it is difficult to ignite (not related to the combustibility after ignition), and this is the required discharge voltage between the electrodes of the spark plug. When viewed in terms of (voltage required for discharge), the required discharge voltage is generally higher than the required discharge voltage for liquid fuel under the same conditions. Furthermore, the required discharge voltage of the spark plug for the gas fuel becomes very high under the condition that the required torque is large or the mixture concentration is low and the ignitability is deteriorated. Therefore, by determining the appropriate range of the ignitability of the gas fuel using the required discharge voltage as an index and using the liquid fuel together as an ignition assist, the required discharge voltage can be reliably reduced and the ignitability can be improved. it can.

  Further, in the present invention, by adopting a system in which liquid fuel is directly injected into the engine cylinder, gas fuel can be efficiently supplied around the spark plug, and both gas fuel and liquid fuel can be used with a minimum amount of use. The ignitability can be improved.

  Hereinafter, embodiments (embodiments) of the present invention will be described with reference to the drawings.

[Outline of Embodiment]
The present embodiment is an internal combustion engine that uses gas fuel as the main fuel, and includes an ignition plug that sparks and ignites an air-fuel mixture in a cylinder, and a gas injection valve that supplies the gas fuel to the engine. Furthermore, a liquid injection valve that supplies liquid fuel to the engine is provided.

  The engine control unit (so-called ECU: electronic control unit) judges whether or not the ignitability by the gas fuel is within an appropriate range, and when it is predicted that it will reach the outside of the appropriate range, the previous fuel is used as an ignition auxiliary fuel in addition to the gas fuel Supply to the engine. As to whether or not the ignitability due to the gas fuel is in an appropriate range, as will be described later, whether or not the required discharge voltage of the spark plug exceeds a predetermined voltage, a predetermined relationship map of the fuel injection amount, or a detected value of the required discharge voltage It is decided by judging based on.

  As the gas fuel, hydrogen gas, LPG, natural gas, or the like can be employed, and a reformed gas obtained by reforming a hydrocarbon fuel such as gasoline can also be employed. Examples of the reformed gas for the hydrocarbon fuel include a mixed gas of hydrogen and carbon monoxide obtained by reforming the hydrocarbon fuel with steam or carbon dioxide. Of course, it is not limited to these gases, The combustible desired gas fuel can be employ | adopted. As the liquid fuel used as the ignition auxiliary fuel, for example, gasoline, methanol, ethanol, light oil, heavy oil or the like can be used, and a liquid having a higher relative dielectric constant and higher ignitability than gas fuel can be used. Therefore, it can be used for water.

  In the present embodiment, the ECU's judgment as to whether or not it is within the ignitability suitability range with gas fuel can be made by the following method. For example, the necessary conditions are measured in advance for each internal combustion engine, and this is set in the ECU as a fuel injection amount map. Determine if. In other words, for example, if the fuel injection amount item corresponding to the required torque is set so that the ignitability is not appropriate only with the gas fuel, and the respective injection amounts of the gas fuel and the liquid fuel are set, the ECU responds to the set value. A quantity of gas fuel and liquid fuel are injected, and the throttle valve and the like are controlled so that the air quantity corresponding to the fuel is injected. In another method, when the required discharge voltage at the spark plug is actually measured and the voltage value exceeds the reference value, it is determined that gas fuel alone is not suitable for ignition, and liquid fuel is added to the gas fuel to assist ignition. Adopt as fuel.

  1 and 2 show the required discharge voltage of the spark plug and the equivalent ratio of the air-fuel mixture for the reformed gas mainly composed of hydrogen and carbon monoxide obtained by reforming the hydrocarbon fuel with steam or carbon dioxide. About the relationship of (equivalent ratio of fuel and air), the result of having been measured under different load (required torque) conditions is shown. 1 and 2, the vertical axis represents the required discharge voltage of the spark plug, and the horizontal axis represents the equivalence ratio of the air-fuel mixture. In addition, gasoline is used as the liquid fuel, and a conventional ignition plug for gasoline fuel is used as the ignition plug. 1 and 2, the characteristic indicated by “gasoline” is a required discharge voltage when gasoline is used as a main fuel and ignition is performed by changing the gas mixture concentration (equivalent ratio). The characteristic indicated by "is the required discharge voltage when the reformed gas is used as the main fuel and ignition is performed by changing the mixture concentration (equivalent ratio) of the reformed gas. Furthermore, the characteristic indicated by “reformed gas: gasoline = 1: 1” is a requirement when the reformed gas and gasoline are supplied at a calorific value ratio of 1: 1 and ignition is performed by changing the gas mixture concentration (equivalent ratio). Discharge voltage.

  FIG. 1 shows a measurement result in a high load state, and FIG. 2 shows a measurement result in a low load state. When gasoline fuel is used as the main fuel, the required discharge voltage at the same equivalence ratio is slightly higher at high load, but the limit voltage of the ignition system at any load condition. That is, it is sufficiently lower than the design voltage of the spark plug adopted. Therefore, when gasoline is used as fuel, it can be understood that ignition can be performed within the range of the ability of the conventional spark plug regardless of the mixture concentration (equivalent ratio).

  On the other hand, the discharge voltage of the spark plug when the reformed gas is used as the main fuel is lower than the limit voltage of the spark plug when the load is low, but exceeds the limit voltage when the load is high.

  On the other hand, as shown in FIG. 1, when gasoline is used as an ignition auxiliary fuel in addition to the reformed gas, the required discharge voltage is lowered to a voltage sufficiently lower than the limit voltage of the ignition system, and stable ignition is possible. It turns out that it becomes. Of course, even in the case of a low load, by using the reformed gas and gasoline in combination, a discharge voltage lower than the discharge voltage in the case of the reformed gas alone is obtained.

  Such characteristics can be obtained similarly when gasoline is used as the liquid fuel and hydrogen, LPG, or natural gas having a dielectric constant smaller than that of gasoline is used as the main fuel (the relative dielectric constant of gasoline is 1.9). ~ 2.5, the relative dielectric constant of reformed gas, hydrogen, LPG and natural gas is about 1.0). In addition, when the liquid fuel is not gasoline but, for example, alcohol fuel such as methanol or ethanol, the relative dielectric constant is larger and is 10 or more. Therefore, alcohol fuel or the like can be used as liquid fuel instead of gasoline, and ignitability can be improved with a smaller injection amount than gasoline due to its high dielectric constant.

  In the present embodiment, as described above, in a spark ignition internal combustion engine using gas fuel as a main fuel, ignitability, particularly at high load or lean operation, can be used in combination with liquid fuel as an ignition auxiliary fuel depending on the situation. It is possible to improve the ignitability by reducing the required discharge voltage of the ignition system at the time.

[Specific Example 1]
FIG. 3 shows a specific configuration example of the internal combustion engine according to the present embodiment. This internal combustion engine includes a main fuel supply system 30 that supplies gas fuel to the engine as main fuel, and an ignition auxiliary fuel supply system 40 that supplies liquid fuel (in this case, gasoline) as ignition auxiliary fuel. A gas fuel injection valve 32 for injecting gas fuel from the main fuel supply system 30 and a liquid fuel injection valve 42 for injecting liquid fuel from the liquid fuel supply system 40 are provided in the vicinity of the port. The ECU 100 is set with a fuel injection amount map (described later in detail) for adjusting the ignitability of the air-fuel mixture to be within an appropriate range according to conditions. The ECU 100 refers to this map, The main fuel injection amount, liquid fuel injection amount, air amount, ignition timing, and the like are controlled. Each of the fuel supply systems 30 and 40 is provided with a tank in which the fuel is stored and a pump for pumping fuel from the tank, and fuel injection valves 32 and 42 are provided at the ends thereof.

  An ignition plug 140, an intake valve 124, and an exhaust valve 126 are provided in the vicinity of the upper portion of the cylinder 110, and a piston 114 that moves up and down along the cylinder axis and is connected to the crankshaft by a connecting rod is provided in the cylinder 110. Is provided. The intake pipe 120 is provided with a throttle valve 122 to control the intake air amount of the cylinder 110. The throttle valve 122 is provided with an air flow meter (not shown) that measures the flow rate of air passing through the valve and outputs an air flow meter signal. Further, the exhaust port of the cylinder 110 is connected to the exhaust pipe 130, and an exhaust catalyst 128 made of a three-way catalyst or the like is installed at the end.

  FIG. 4 shows a fuel injection amount map set in the ECU 100. This fuel injection amount map shows the required fuel injection amount according to the required torque and the air-fuel mixture concentration, and is provided for each engine speed. In this fuel injection amount map, in the region where the required discharge voltage of the spark plug does not exceed its design voltage (limit voltage), only the injection amount of gas fuel necessary for each condition is set. Further, in an area where the design voltage is exceeded, it is set that liquid fuel is used in combination with gas fuel based on the assumption that the ignitability is not in an appropriate range with only gas fuel. Specifically, in the region outside the ignitability appropriate range, the gas fuel injection amount is reduced, and the liquid fuel injection amount corresponding to the reduction in output is set.

  The operation of the engine will be briefly described below. First, the ECU 100 refers to the fuel injection amount map for the required torque and the mixture concentration as described above, and the required discharge voltage of the spark plug exceeds the design voltage when the required torque is increased and when the mixture concentration is diluted. If it is expected, the optimum injection amount and air amount for each of the gas fuel and gasoline fuel are determined, and the injection valves 32 and 42 and the throttle valve 122 are controlled. When the required discharge voltage does not exceed the design voltage, the required gas fuel injection amount and air amount are determined with reference to the map of FIG. 4 (gasoline combustion injection is not executed). The intake port is thus supplied with the optimum amount of air and gas fuel (or a mixed fuel of gas fuel and liquid fuel in a desired ratio) under the control of the ECU 100.

  When the intake valve 124 is opened and the piston 114 is lowered in the intake stroke, an appropriate amount of air and an appropriate amount of gas fuel (or a mixed fuel of gas fuel and liquid fuel) controlled by the ECU 100 are introduced into the cylinder 110 from the intake port. The air-fuel mixture is sucked into the cylinder 110 and has an optimal equivalence ratio (air-fuel ratio).

  In the compression stroke, the intake valve 124 closes and the piston rises, and the air-fuel mixture in the cylinder is compressed. The spark plug 140 performs spark ignition on the compressed air-fuel mixture at a desired timing when the piston 114 reaches the vicinity of the top dead center under the control of the ECU 100. As described above, in the present embodiment, since the air-fuel mixture that can be ignited by the discharge voltage of the spark plug 140 is always supplied into the cylinder, the compressed air-fuel mixture is reliably ignited, burned, and expanded. Due to the expansion of the combustion gas, the pressure in the cylinder 110 rises, whereby the piston 114 is pushed down to rotate the crankshaft and obtain a torque according to the demand. In the subsequent exhaust stroke, the exhaust valve 126 is opened and the combustion gas is discharged to the exhaust port. The combustion gas is purified by the exhaust catalyst 128 and then released into the atmosphere.

  Here, in the case where gasoline is used as the liquid fuel input to assist ignition and reformed gas is used as the main fuel, taking a naturally aspirated engine as an example, this gasoline amount is at most the total fuel ( 20% (calorific value ratio) of the reformed gas and gasoline is sufficient. However, in order to improve ignitability, more may be added. However, particularly from the viewpoint of making the amount of gasoline used as small as possible, it is preferable to set the above 20% as the upper limit.

  The composition of the reformed gas obtained from a hydrocarbon fuel such as gasoline varies depending on the reforming temperature. Therefore, here, the reformed gas obtained at a high reforming temperature exceeding 700 ° C. is taken as an example, and the calorific value 20 When% is expressed as a mass ratio, it is about 12% (mass ratio) of the total fuel. In this case, the remaining 88% (mass ratio) becomes the reformed gas.

  As described above, a simple internal combustion engine without a sensor or the like is obtained by incorporating necessary conditions in advance as a fuel injection amount map and determining the combined use of gas fuel and liquid fuel and each injection amount according to the required torque and the like. Thus, the ignitability can be improved quickly.

[Specific Example 2]
Next, specific example 2 will be described. In the first specific example, the ECU 100 is provided with a fuel injection amount map for the required torque and the mixture concentration, and based on the required torque, the mixture concentration, etc., the condition that the required discharge voltage of the spark plug is predicted to exceed the design voltage Then, liquid fuel is used in addition to gas fuel. On the other hand, in the specific example 2, when the discharge voltage of the spark plug 140 is actually detected and the discharge voltage exceeds a predetermined design voltage, it is predicted that the ignitability deteriorates and falls outside the ignitability appropriate range. Therefore, gas fuel and liquid fuel are used together. FIG. 5 is a schematic diagram of an equivalent circuit of the ignition device used in the second specific example.

  The ignition device includes a spark plug 140 and an ignition coil 142. The ignition coil 142 includes a primary coil 142a and a secondary coil 142b. A switch SW and a capacitor C1 are connected in parallel to the primary coil 142a, and a battery 146 and a resistor 1 are connected between the capacitor C1 and the primary coil 142a. Are connected to each other. The secondary coil 142b is connected to a capacitor C2, a spark plug 140, and a detection unit 144 that detects a voltage (discharge voltage) between the electrodes of the spark plug 140.

  When the current from the battery 146 is supplied to the primary coil 142a and the electric charge is accumulated in the capacitor C1, the coil SW is energized by changing the switch SW from the closed state to the open state under the control of the ECU 100 or the like. The secondary current is induced in the secondary coil 142b. The secondary current is accumulated in the capacitor C2, and the voltage between the electrodes of the spark plug 140 increases. When the required discharge voltage is reached, insulation breakdown occurs between the electrodes of the spark plug 140 (air mixture), and a spark is generated between the plug electrodes. And the air-fuel mixture around the plug 140 is sparked. The required discharge voltage detector is configured such that when the energization of the primary coil 142a is cut off, the secondary current flows through the secondary coil 142b, and the maximum value of the interelectrode voltage (secondary voltage) of the spark plug 140 that rises as a result (Required discharge voltage) is detected. When a spark discharge occurs between the electrodes of the plug 140, the voltage between the electrodes rapidly decreases, and the maximum value corresponds to a voltage required for discharge, that is, a required discharge voltage.

  As shown in FIG. 1, when the mixture of gas fuel and air is lean and the load is high, the required discharge voltage becomes remarkably high, and deterioration of ignitability can be predicted. Therefore, in the specific example 2, the required discharge voltage is detected by the discharge voltage detection unit 144. The detection signal is sent to the ECU 100, and when the required discharge voltage detected becomes higher than a predetermined reference voltage, for example, a limit voltage (design voltage) of the spark plug 140 to be employed, the ECU 100 uses the gas fuel and the liquid fuel together. decide.

  Here, the ECU 100 has, for example, a fuel (gas fuel) injection amount map with respect to the required torque and mixture concentration set in advance. Therefore, when it is detected that the required discharge voltage exceeds the limit voltage, this fuel injection amount map is referred to and based on the accelerator position sensor signal (driver required torque) and the air flow meter signal (intake air amount). Thus, the injection amount of the gas fuel determined with respect to the required torque and the air amount is reduced, and an amount of liquid fuel corresponding to the reduction in output is injected from the liquid fuel injection valve. At the same time, the ECU 100 adjusts the throttle opening and ignition timing according to the combined use of gas fuel and liquid fuel.

  By actually measuring the required discharge voltage as in Example 2, it is possible to accurately predict the deterioration of ignition performance according to the ignition characteristics specific to each engine, and to ensure that the amount of fuel used is minimized. The ignitability can be improved.

[Specific Example 3]
FIG. 6 shows a schematic configuration of the internal combustion engine according to the third specific example. In addition, the same code | symbol is attached | subjected to the location corresponding to drawing already demonstrated, and description is abbreviate | omitted. In the first specific example, the liquid fuel is injected into the intake pipe 120 from the injection valve 42. However, in the third embodiment, the liquid fuel injection valve 50 is provided in the cylinder 110, and the liquid fuel from the liquid fuel supply system 40 is supplied into the cylinder. 110 is injected directly. The liquid fuel injection timing is preferably in the latter half of the compression stroke.

  The determination as to whether or not the liquid fuel is used in combination with the gas fuel may be made based on a fuel injection map that is determined in advance as in the first specific example, or as described in the second specific example. When the required discharge voltage of the spark plug is actually detected and this voltage exceeds the design voltage, the combined use of gas fuel and liquid fuel may be executed. When the method of the second specific example is employed, if the ECU 100 determines that the required discharge voltage exceeds the design voltage, the gas fuel injection amount corresponding to the required torque is reduced, and an amount of liquid corresponding to the output decrease due to the reduction. Fuel is supplied from the liquid fuel injection valve 50 into the cylinder 110 in the latter half of the compression stroke.

  More specifically, a method as shown in FIG. 7 or 8 can be adopted as a method of direct injection into the cylinder. In FIG. 7, a small amount of liquid fuel is injected from the injection valve 52 toward the vicinity of the installation of the ignition plug 140, and an air-fuel mixture layer of liquid fuel and air is positively formed in the vicinity of the ignition plug 140.

  In FIG. 8, a small amount of liquid fuel is once injected from the injection valve 54 toward the upper surface of the piston 114. The injected liquid fuel collides with the upper surface of the piston 114, and the mixture region of the liquid fuel and air is expanded by the gas dispersion action, but the mixture region of the gas fuel and air is not completely mixed. It moves to the vicinity of the spark plug 140 together with the piston 114 that rises in the compression stroke. In the system of FIG. 8, the liquid fuel-air mixture region is larger than that in FIG. 7, and the liquid fuel concentration in this liquid fuel-air mixture region is as shown in FIG. It becomes lower than the case of 7. For this reason, the method of FIG. 7 can reduce the amount of liquid fuel used for ignitability improvement. On the other hand, in the system shown in FIG. 8, since the liquid fuel injected and dispersed until reaching the spark plug 140 progresses, a uniform liquid fuel-air mixture region can be generated around the spark plug 140 and stable ignition can be achieved. Can be realized. In the case of the direct injection method as shown in FIG. 8, the required amount of liquid fuel injection can be further reduced by improving the shape of the upper surface of the piston 114 and the like.

  7 and 8, as a result, an air-fuel mixture layer of liquid fuel and air is selectively formed in the vicinity of the spark plug 140, so that a discharge voltage is generated around the spark plug 140. It is possible to improve the ignitability of the air-fuel mixture. As described above, according to the third specific example, an air-fuel mixture layer of liquid fuel and air can be selectively and effectively formed in the vicinity of the spark plug 140, and the liquid in the vicinity of the intake port as shown in FIG. The ignition performance can be improved with a small amount of liquid fuel injection, compared to the fuel injection method.

  In addition, by adopting a method in which gas fuel is directly injected into the cylinder 110, it is possible to reduce the amount of gas fuel used and further improve fuel efficiency. When the gas is directly injected into the cylinder 110, a high gas pressure is required for efficient injection. Therefore, when the pressure in the gas fuel tank is low, the gas fuel is pressurized by the pump unit. It is necessary to inject directly into the cylinder from the injection valve. In addition, when gaseous fuel is hold | maintained in a tank in a high pressure state like LPG etc., gaseous fuel can be directly injected in the cylinder 110, without providing a special pressurization means.

[Specific Example 4]
Next, an overall system schematic diagram of the engine using the reformed gas is shown in FIGS. 9 and 10, respectively. When a liquid hydrocarbon fuel such as gasoline is employed as the liquid fuel described in each of the above specific examples, a mixed gas (reformed gas) mainly composed of hydrogen and carbon monoxide is obtained by reforming the hydrocarbon fuel. Obtainable. Hereinafter, gasoline will be described as an example of the hydrocarbon fuel.

  9 and 10, a water tank 200 is provided in addition to the gasoline tank of the gasoline supply system 40, and the gasoline stored in the gasoline tank is pumped up by a pump 216, and the evaporator 220 is passed through the flow control valve 214. At the same time, water is pumped from the water tank 200 by the pump 210 and sent to the evaporator 220 via the flow rate control valve 212. The evaporator 220 is heated by the heater 222 in FIG. 9 and by the exhaust heat heat exchanger 250 in FIG. 10, and the evaporator 220 evaporates gasoline and water. The evaporated gas and water mixture is sent to the reformer 230. The reformer 230 is heated by a heater 232 in FIG. 9 and a heat exchanger 260 in FIG. Here, since the reforming reaction for generating reformed gas mainly composed of hydrogen and carbon monoxide from gasoline and water is an endothermic reaction, the reforming reaction is advanced by heating the reformer 230. ing.

  9 and 10, a condenser 234 is provided behind the reformer 230, and excess water vapor in the reformed gas is removed by the condenser 234. A pump 236 is provided between the condenser 234 and the gas fuel tank, and the reformed gas obtained by the condenser 234 is pumped up by the pump 236 and supplied to the gas fuel tank.

  When reformed gas is generated from gasoline fuel in this way and the obtained reformed gas is used as engine fuel, the internal combustion engine has both gasoline fuel and reformed gas fuel. Therefore, in such an internal combustion engine using reformed gas as a main fuel, if gasoline fuel is used as an ignition assist fuel when the ignitability of the reformed gas fuel deteriorates, a special assist fuel supply system is used. There is no need to install the fuel injection valve, and an injection valve for injecting liquid assist fuel is provided, and the ECU can control the injection amount, the injection timing, and the like to improve the ignitability.

  In addition, when the required discharge voltage of the mixture of reformed gas fuel and air exceeds the limit voltage, the required discharge voltage can be reduced by using gasoline fuel together. Therefore, without using the spark plug 140 capable of applying a high voltage for gas fuel, for example, an ignition plug having a lower limit voltage as compared with a gas fuel plug as used in a gasoline engine is used as it is. It is also possible.

  Furthermore, in the reformed gas obtained by reforming gasoline fuel as described above, the composition of the reformed gas varies greatly depending on the production environment and the like. When the gas composition changes, the required discharge voltage of the spark plug changes accordingly. Therefore, as an ignition plug for an internal combustion engine that uses reformed gas as a fuel, the required discharge voltage that is expected when the required torque is the maximum when the gas with the poorest ignitability composition is burned leanly and the required torque is maximum is ensured. An applicationable configuration is required. However, in the situation where the required discharge voltage is high as in the present embodiment, if the required discharge voltage is reduced by using gasoline fuel together, a low-cost spark plug can be used for various usage environments. It is possible to reliably operate the internal combustion engine even underneath. For this reason, it is advantageous also in the reduction of development cost and manufacturing cost.

  9 and 10, as described in the specific example 1, both the gasoline fuel and the reformed gas fuel are injected near the intake port of the intake pipe 120, but as illustrated in the specific example 3. In addition, a method of directly injecting gasoline fuel into the cylinder may be employed. In this case, the fuel injection valve 42 is attached to the cylinder 110 as shown in FIG. Of course, a method of directly injecting the reformed gas fuel into the cylinder can also be adopted.

It is a figure which shows an example of the relationship under the high load conditions of the required discharge voltage of the ignition plug which concerns on this embodiment, and air-fuel | gaseous-equivalent ratio. It is a figure which shows an example of the relationship under the low load conditions of the required discharge voltage and mixture ratio of the spark plug which concerns on this embodiment. It is a figure which shows the structural example of the internal combustion engine of the specific example 1 which concerns on this embodiment. It is a figure which shows an example of the fuel injection amount map set to ECU which can be employ | adopted by the specific example 1 which concerns on this embodiment. It is a figure which shows the schematic equivalent circuit of the ignition device of the specific example 2 which concerns on this embodiment, and the detection part of a request | required discharge voltage. It is a figure which shows the structural example of the internal combustion engine of the specific example 3 which concerns on this embodiment. FIG. 7 is a diagram showing an example of direct in-cylinder injection of fuel shown in FIG. 6. It is a figure which shows the example different from FIG. 7 of the direct injection of the fuel shown in FIG. It is a figure which shows the structural example of the internal combustion engine of the specific example 4 which concerns on this embodiment. It is a figure which shows the other example of a structure of the internal combustion engine of the specific example 4 which concerns on this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Internal combustion engine, 30 Main fuel (gas fuel) supply system, 32 Main fuel (gas fuel) injection valve, 40 Liquid fuel (gasoline) supply system, 42 Liquid fuel (gasoline) injection valve, 100 ECU (engine control part), 110 cylinder, 114 piston, 120 intake pipe, 122 throttle valve, 124 intake valve, 126 exhaust valve, 128 exhaust catalyst, 130 exhaust pipe, 140 spark plug, 200 water tank, 210, 216, 236 pump, 212, 214 flow control Valve, 220 Evaporator, 222, 232 Heater, 230 Reformer, 234 Condenser, 250, 260 Heat exchanger.

Claims (7)

An internal combustion engine using gas fuel as the main fuel,
A gas injection valve for supplying the gas fuel to the engine;
A liquid injection valve for supplying liquid fuel to the engine;
An ignition plug that performs spark ignition on the air-fuel mixture in the engine cylinder,
When the engine control unit determines whether or not the ignitability by the gas fuel is in the proper range and predicts that the gas fuel is outside the proper range, the liquid fuel is supplied to the engine as an ignition auxiliary fuel in addition to the gas fuel. An internal combustion engine characterized by the above. The internal combustion engine according to claim 1,
The engine control unit determines whether the required discharge voltage of the spark plug exceeds a predetermined voltage based on a predetermined relationship map of a predetermined fuel injection amount or a detected value of the required discharge voltage, and the gas fuel An internal combustion engine characterized by predicting that the ignitability is out of an appropriate range due to the engine. A spark ignition internal combustion engine using gas fuel as a main fuel,
A gas injection valve for supplying the gas fuel to the engine;
A liquid injection valve for supplying liquid fuel to the engine;
An ignition plug that performs spark ignition on the air-fuel mixture in the engine cylinder,
The engine control unit has a relationship map of the fuel injection amount with respect to the required torque and the mixture concentration in consideration of the limit voltage of the required discharge voltage of the spark plug, and based on the relationship map, the required discharge voltage is determined to be the limit discharge voltage. An internal combustion engine characterized by supplying the liquid fuel to the engine as an ignition auxiliary fuel in addition to the gas fuel. A spark ignition internal combustion engine using gas fuel as a main fuel,
A gas injection valve for supplying the gas fuel to the engine;
A liquid injection valve for supplying liquid fuel to the engine;
A spark plug that performs spark ignition on the air-fuel mixture in the engine cylinder;
A detection unit for detecting a required discharge voltage at the time of ignition of the spark plug; and
When the detected required discharge voltage exceeds a limit voltage of the spark plug, the liquid fuel is further supplied to the engine as an ignition auxiliary fuel in addition to the gas fuel. The internal combustion engine according to any one of claims 1 to 4,
The internal combustion engine, wherein the liquid fuel is directly injected into an engine cylinder. The internal combustion engine according to any one of claims 1 to 5,
An internal combustion engine characterized in that when the gas fuel and the liquid fuel are used together, the gas fuel injection amount is reduced, and an amount of liquid fuel corresponding to an output that decreases in accordance with the reduction of the gas fuel injection amount is injected. The internal combustion engine according to any one of claims 1 to 6,
The internal combustion engine, wherein the gas fuel is a reformed gas fuel obtained by reforming the liquid fuel.

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