JP4692427B2 - Multi-fuel internal combustion engine - Google Patents

Description

  The present invention relates to a multi-fuel internal combustion engine that is operated by introducing a fuel having good fuel characteristics stored in separate fuel tanks and a mixed fuel composed of fuel having poor fuel characteristics to a combustion chamber.

  Conventionally, there is a so-called multi-fuel internal combustion engine that is provided with a fuel tank that stores fuel with good compression ignitability and bad fuel, respectively, and that is operated using a mixed fuel obtained by mixing each fuel at a predetermined set fuel mixture ratio. Are known. For example, in Patent Document 1 below, light oil with good compression ignitability and gasoline with poor compression ignitability are stored in separate fuel tanks, and the fuel mixing ratio is changed according to the operating state. A multi-fuel internal combustion engine is described.

  In Patent Document 2 below, in an internal combustion engine that switches between and uses a plurality of types of fuel stored in separate fuel tanks, a fuel in which the same type of fuel is stored as surplus fuel during operation A fuel return device that can be returned to a tank is disclosed.

JP-A-9-68061 JP 2002-327658 A

  By the way, although not mentioned in the above-mentioned Patent Document 1, actually, a fuel return device is also provided in the multi-fuel internal combustion engine. And, when the surplus mixed fuel is returned to the fuel tank for light oil with good compression ignitability by the fuel return device, gasoline with poor compression ignitability is mixed in the fuel tank for light oil, The compression ignitability of the fuel in the fuel tank for light oil (mixed fuel of light oil and gasoline) is lowered. For this reason, in such a case, self-ignition may become unstable when the fuel is injected into compressed air, and even self-ignition may not be possible as the mixing ratio of the gasoline increases. Therefore, there is a risk that stable compression auto-ignition diffusion combustion cannot be performed.

  As described above, in a multi-fuel internal combustion engine in which fuel having good fuel characteristics and fuel having bad fuel characteristics are stored in separate fuel tanks and operated using a mixed fuel composed of the respective fuels, If the surplus of the mixed fuel is returned to the fuel tank of fuel with good fuel characteristics, the fuel characteristics of the fuel in this fuel tank will deteriorate, and the combustion state in the combustion mode utilizing the fuel characteristics will deteriorate. End up.

  In view of the above, the present invention improves the disadvantages of the conventional example, and makes it possible to return and reuse the surplus of the mixed fuel composed of the fuel with good fuel characteristics and the fuel with poor fuel characteristics stored in separate fuel tanks. However, an object of the present invention is to provide a multi-fuel internal combustion engine capable of maintaining a good combustion state when operating in a combustion mode utilizing the fuel characteristics.

  In order to achieve the above object, according to the first aspect of the present invention, a first fuel tank supplied with fuel having good fuel characteristics, a second fuel tank supplied with fuel having poor fuel characteristics, and a predetermined set fuel In a multi-fuel internal combustion engine comprising: a fuel supply device that mixes fuel from a first fuel tank and fuel from a second fuel tank at the same ratio as a mixing ratio and guides the mixed fuel to a combustion chamber. A return passage is provided for returning the surplus mixed fuel in the supply device to the second fuel tank in which fuel with poor fuel characteristics is stored.

  In the multi-fuel internal combustion engine according to claim 1, while maintaining the purity of the fuel with good fuel characteristics in the first fuel tank, the deterioration of the fuel characteristics of the fuel in the second fuel tank is prevented (strictly speaking, , The fuel characteristics can be improved). Therefore, the fuel characteristics of the mixed fuel obtained by mixing the fuel from the first fuel tank and the fuel from the second fuel tank do not deteriorate with respect to the fuel characteristics of the mixed fuel having the set fuel mixing ratio.

  In order to achieve the above object, in the invention according to claim 2, in the multi-fuel internal combustion engine according to claim 1, the actual fuel mixture ratio of the mixed fuel led to the combustion chamber becomes the set fuel mixture ratio. In addition, the fuel from the first fuel tank according to the mixing ratio of the fuel with good fuel characteristics in the second fuel tank or the difference between the fuel characteristics of the mixed fuel introduced into the combustion chamber and the fuel characteristics of the mixed fuel with the set fuel mixing ratio The fuel supply device is configured so that the mixing ratio between the fuel and the fuel from the second fuel tank is adjusted.

  In the multifuel internal combustion engine according to the second aspect, the engine can be operated using the mixed fuel having the set fuel mixture ratio.

By the way, as the fuel characteristics described above, compression ignition, knock resistance, or cold startability can be considered as in the third aspect of the invention.

  For example, in the case of compression ignitability, a mixed fuel with good compression ignitability is generated, so that operation in a stable compression autoignition diffusion combustion mode can be performed. Further, in the case of knock resistance, a mixed fuel having good knock resistance is generated, so that occurrence of knocking during combustion can be suppressed. Further, in the case of cold startability, a mixed fuel with good cold startability is generated, so that the engine can be started smoothly when the engine is cold.

  The multi-fuel internal combustion engine according to the present invention is a fuel of newly generated mixed fuel even after returning the surplus of the mixed fuel composed of a plurality of types of fuel stored in the fuel tank divided into good and bad fuel characteristics. Since the characteristics can be maintained in a good state, deterioration of the combustion state in the combustion mode utilizing the fuel characteristics can be avoided.

  Embodiments of a multi-fuel internal combustion engine according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the embodiments.

  A first embodiment of a multi-fuel internal combustion engine according to the present invention will be described with reference to FIGS. The multi-fuel internal combustion engine is an internal combustion engine that is operated by introducing a mixed fuel composed of at least two types of fuels having different properties to a combustion chamber, and has a plurality of types of fuel used for the operation. Includes fuels with good and bad fuel characteristics.

  In this multifuel internal combustion engine, various control operations such as combustion control are executed by an electronic control unit (ECU) 1 shown in FIG. The electronic control unit 1 includes a CPU (Central Processing Unit) (not shown), a ROM (Read Only Memory) that stores a predetermined control program and the like, and a RAM (Random Access Memory) that temporarily stores the calculation result of the CPU. , And a backup RAM for storing information prepared in advance.

  First, the configuration of the multi-fuel internal combustion engine exemplified here will be described with reference to FIG. Although only one cylinder is shown in FIG. 1, the present invention is not limited to this, and can be applied to a multi-cylinder multifuel internal combustion engine. In the first embodiment, description will be made assuming that a plurality of cylinders are provided.

  The multifuel internal combustion engine is provided with a cylinder head 11, a cylinder block 12, and a piston 13 that form a combustion chamber CC. Here, the cylinder head 11 and the cylinder block 12 are fastened with bolts or the like via the head gasket 14 shown in FIG. 1, and the recess 11a on the lower surface of the cylinder head 11 and the cylinder bore 12a of the cylinder block 12 formed thereby. The piston 13 is disposed so as to be capable of reciprocating in the space. And the combustion chamber CC mentioned above is comprised by the space enclosed by the wall surface of the recessed part 11a of the cylinder head 11, the wall surface of the cylinder bore 12a, and the top surface 13a of the piston 13. FIG.

  The multifuel internal combustion engine of the first embodiment sends air and fuel into the combustion chamber CC according to the operating conditions such as the engine speed and engine load and the combustion mode, and executes combustion control according to the operating conditions. The air is sucked from the outside through the intake passage 21 and the intake port 11b of the cylinder head 11 shown in FIG. On the other hand, the fuel is supplied using the fuel supply device 50 shown in FIG.

  First, the air supply path will be described. On the intake passage 21 of the first embodiment, an air cleaner 22 that removes foreign matters such as dust contained in air introduced from the outside, and an air flow meter 23 that detects the amount of intake air from the outside are provided. . In this multi-fuel internal combustion engine, the detection signal of the air flow meter 23 is sent to the electronic control unit 1, and the electronic control unit 1 calculates the intake air amount, the engine load and the like based on the detection signal.

  A throttle valve 24 that adjusts the amount of intake air into the combustion chamber CC and a throttle valve actuator 25 that opens and closes the throttle valve 24 are disposed downstream of the air flow meter 23 on the intake passage 21. Is provided. The electronic control device 1 according to the first embodiment controls the throttle valve actuator 25 according to the operating conditions and the combustion mode so that the valve opening degree (in other words, the intake air amount) according to the operating conditions is obtained. The valve opening angle of the throttle valve 24 is adjusted. For example, the throttle valve 24 is adjusted so that the intake air amount necessary for achieving an air-fuel ratio corresponding to the operating conditions and the combustion mode is sucked into the combustion chamber CC. The multifuel internal combustion engine is provided with a throttle opening sensor 26 that detects the valve opening of the throttle valve 24 and transmits the detection signal to the electronic control unit 1.

  Further, one end of the intake port 11b opens to the combustion chamber CC, and an intake valve 31 for opening and closing the opening is disposed at the opening portion. The number of openings may be one or more, and an intake valve 31 is provided for each opening. Therefore, in this multi-fuel internal combustion engine, air is sucked into the combustion chamber CC from the intake port 11b by opening the intake valve 31 and closed in the combustion chamber CC by closing the intake valve 31. Inflow of air to is blocked.

  Here, as the intake valve 31, for example, there is a valve that is driven to open and close in accordance with the rotation of an intake camshaft (not shown) and the elastic force of an elastic member (string spring). In this type of intake valve 31, by interposing a power transmission mechanism such as a chain or a sprocket between the intake side camshaft and the crankshaft 15, the intake side camshaft is interlocked with the rotation of the crankshaft 15, Open / close drive is performed at a preset opening / closing timing. In the multifuel internal combustion engine of the first embodiment, the intake valve 31 that is opened and closed in synchronization with the rotation of the crankshaft 15 is applied.

  However, this multi-fuel internal combustion engine may be provided with a variable valve mechanism such as a so-called variable valve timing & lift mechanism that can change the opening / closing timing and lift amount of the intake valve 31. The opening / closing timing and the lift amount can be changed to suitable ones according to the operating conditions and the combustion mode. Furthermore, in this multi-fuel internal combustion engine, a so-called electromagnetically driven valve that opens and closes the intake valve 31 using electromagnetic force may be used in order to obtain the same effect as the variable valve mechanism.

  Next, the fuel supply device 50 will be described. The fuel supply device 50 mixes a plurality of types of individually stored fuels having different properties in advance at a predetermined set fuel mixing ratio and guides the mixed fuel into the combustion chamber CC. In the first embodiment, the first fuel F1 stored in the first fuel tank 41A and the second fuel F2 stored in the second fuel tank 41B are set to a predetermined set fuel according to the operating conditions and the combustion mode. An example is shown in which the fuel is mixed at a mixing ratio and the mixed fuel is directly injected into the combustion chamber CC.

  Specifically, the fuel supply device 50 according to the first embodiment includes a first feed pump 52A that sucks up the first fuel F1 from the first fuel tank 41A and sends it to the first fuel passage 51A, and the second fuel F2 as the second fuel F2. The second feed pump 52B sucked up from the fuel tank 41B and sent to the second fuel passage 51B, and the first and second fuels F1 and F2 sent from the first and second fuel passages 51A and 51B, respectively. Fuel mixing means 53 for mixing at a predetermined set fuel mixing ratio.

  In this fuel supply device 50, the first feed pump 52A, the second feed pump 52B, and the fuel mixing means 53 are driven and controlled by the fuel mixing control means of the electronic control device 1, whereby the predetermined fuel mixture ratio is set. The mixed fuel is generated by the fuel mixing means 53. For example, the fuel supply device 50 adjusts the actual fuel mixture ratio of the mixed fuel by adjusting the discharge amounts of the first feed pump 52A and the second feed pump 52B to the fuel mixing control means of the electronic control device 1. According to the instruction of the fuel mixing control means, the actual mixing ratio of the mixed fuel is adjusted by adjusting the mixing ratio of the first and second fuels F1 and F2 in the fuel mixing means 53. Also good. Here, in the first embodiment, an optimal set fuel mixture ratio is set according to the operating conditions and the combustion mode.

  The fuel supply device 50 includes a high-pressure fuel pump 56 that sucks up the mixed fuel generated by the fuel mixing means 53 from the fuel delivery path 54 and pressurizes the mixed fuel to the high-pressure fuel path 55, and the high-pressure fuel. A delivery passage 57 for distributing the mixed fuel in the passage 55 to the respective cylinders, and a fuel injection valve 59 for each cylinder for injecting the mixed fuel supplied from the delivery passage 57 through the fuel distribution passage 58 into the combustion chamber CC; , Is provided.

  In this fuel supply device 50, the high-pressure fuel pump 56 and the fuel injection valve 59 are driven and controlled by the fuel injection control means of the electronic control device 1, thereby the desired fuel injection amount, fuel injection timing, fuel injection period, etc. The generated mixed fuel is configured to be injected under the fuel injection conditions. For example, the fuel injection control means of the electronic control unit 1 pumps the mixed fuel from the high-pressure fuel pump 56 and causes the fuel injection valve 59 to perform injection under fuel injection conditions corresponding to operating conditions and combustion modes.

  The mixed fuel thus supplied to the combustion chamber CC is burned by the ignition operation in the ignition mode corresponding to the combustion mode in combination with the air described above. The in-cylinder gas after the combustion is discharged from the combustion chamber CC to the exhaust port 11c shown in FIG. Here, an exhaust valve 61 that opens and closes an opening between the exhaust port 11c and the combustion chamber CC is disposed. The number of openings may be one or more, and the exhaust valve 61 described above is provided for each opening. Therefore, in this multi-fuel internal combustion engine, the in-cylinder gas after combustion is discharged from the combustion chamber CC to the exhaust port 11c by opening the exhaust valve 61, and the exhaust valve 61 is closed to close the cylinder. The discharge of the internal gas to the exhaust port 11c is blocked.

  Here, as the exhaust valve 61, as in the intake valve 31 described above, a valve with a power transmission mechanism, a valve with a variable valve mechanism such as a so-called variable valve timing & lift mechanism, or a so-called electromagnetically driven valve can be used. Can be applied.

  By the way, in an internal combustion engine, combustion modes are generally divided into a diffusion combustion mode and a flame propagation combustion mode, and a compression auto-ignition mode and a premixed spark ignition mode are prepared as ignition modes corresponding to the combustion modes. Hereinafter, they are collectively referred to as a combustion mode, and are respectively referred to as a compression autoignition diffusion combustion mode and a premixed spark ignition flame propagation combustion mode.

  First, the compression self-ignition diffusion combustion mode is a method in which a part of fuel is self-ignited by injecting high-pressure fuel into high-temperature compressed air formed in the combustion chamber CC in the compression stroke, and the fuel and air Is a combustion mode in which combustion proceeds while diffusing and mixing. Here, since the compressed air in the combustion chamber CC and the fuel are difficult to be mixed instantaneously, immediately after the start of fuel injection, the air-fuel ratio varies in some places. On the other hand, it is generally preferable to use a fuel excellent in compression ignitability as described below when performing diffusion combustion, and such a fuel having good compression ignitability waits for the entire injection amount to be injected. Instead, it will ignite itself at a portion of the air-fuel ratio suitable for combustion. For this reason, in this compression self-ignition diffusion combustion mode, the fuel of the air-fuel ratio part suitable for combustion self-ignites first, and the flame formed thereby gradually advances the combustion while entraining the remaining fuel and air. Let

  In order to operate in this compressed self-ignition diffusion combustion mode, a fuel having a good compression ignitability whose ignition point is lower than the compression heat of compressed air is usually required. For example, light oil, dimethyl ether, and the like are conceivable as the fuel having good compression ignitability. Further, in recent years, GTL (Gas To Liquids) fuel has attracted attention as an alternative fuel for light oil, and this GTL fuel is easily produced in a desired property. For this reason, the GTL fuel produced | generated in order to improve compression ignition property can also be used for fuel with good compression ignition property. Such a fuel with good compression ignitability not only enables compression auto-ignition diffusion combustion, but also reduces the amount of NOx generated when operating in the compression auto-ignition diffusion combustion mode, and further reduces noise during combustion. And vibration can be suppressed.

  On the other hand, in the premixed spark ignition flame propagation combustion mode, the premixed gas in the combustion chamber CC in which fuel and air are mixed in advance is given a spark by spark ignition, and combustion is performed while propagating the flame around the fire type. It is a combustion form that advances the. Here, in this premixed spark ignition flame propagation combustion mode, homogeneous combustion for igniting a homogeneously mixed premixed gas or a high-concentration premixed gas is formed around the ignition means, and further A combustion mode such as stratified combustion in which a lean premixed gas is formed in the surroundings and ignition is performed on the rich premixed gas is included.

  As a fuel suitable for the premixed spark ignition flame propagation combustion mode, a highly evaporative fuel represented by gasoline is generally considered. And since this highly evaporable fuel is easily mixed with air, it reduces the fuel rich region and contributes to the suppression of PM, smoke, NOx and unburned hydrocarbons (unburned HC). As such highly evaporable fuel, in addition to gasoline, GTL fuel, alcohol fuel, dimethyl ether and the like produced as highly evaporable properties are known.

  The multifuel internal combustion engine of the first embodiment is operated by appropriately selecting both combustion modes. Accordingly, the multifuel internal combustion engine of the first embodiment is provided with the spark plug 71 shown in FIG. 1 for spark ignition of the premixed gas in order to enable operation in the premixed spark ignition flame propagation combustion mode. To do. The spark plug 71 executes spark ignition when the ignition timing according to the operating condition in the premixed spark ignition flame propagation combustion mode is reached in accordance with the instruction of the electronic control unit 1.

  Furthermore, in order to enable operation in both combustion modes, it is preferable that at least one fuel has excellent compression ignitability and the other fuel has excellent evaporability. On the other hand, the multi-fuel internal combustion engine of the first embodiment is premised on the use of at least two types of fuel that are divided into superiority and inferiority for specific fuel characteristics. Therefore, in the multi-fuel internal combustion engine of the first embodiment, the first and second modes that can be operated in both combustion modes while being classified as either good or bad in compression ignitability or good or bad in evaporability. It is necessary to select the fuels F1 and F2.

  Here, in order to operate in the compression self-ignition diffusion combustion mode, it is usually an essential requirement to use a fuel with good compression ignitability, and it is not possible to perform self-ignition with a fuel selected without considering this. May be possible. Therefore, in the multi-fuel internal combustion engine of the first embodiment, fuel with good compression ignitability is stored as the first fuel F1 in the first fuel tank 41A, while fuel with poor compression ignitability and high evaporability is stored in the first fuel tank 41A. The second fuel F2 is stored in the second fuel tank 41B. For example, in order to make the first and second fuels F1 and F2 such a combination, light oil or GTL fuel with high compression ignition is selected as the first fuel F1, and gasoline or alcohol fuel is used as the second fuel F2. A GTL fuel with poor compression ignitability and high evaporability may be selected. In addition, since the present Example 1 is shown about the multi-fuel internal combustion engine operate | moved with a multiple types of fuel, the combination of dimethyl ether shall not be taken into consideration.

  In addition, the electronic control device 1 according to the first embodiment is provided with combustion mode setting means for selecting and setting an optimum one from both of the above-described combustion modes. The combustion mode setting means exemplified here uses the combustion mode map data as shown in FIG. 2 with the operating conditions (engine speed Ne and engine load Kl) as parameters, and the optimal combustion mode according to the operating conditions. To select. For example, this combustion mode map data can be operated in the compression auto-ignition diffusion combustion mode under medium / high load / low rotation or high load / high rotation operation conditions, and the low load / low rotation, low medium load / high rotation, etc. This is set in advance based on experiments and simulations so as to operate in the premixed spark ignition flame propagation combustion mode under the above operating conditions. The engine speed Ne can be grasped from the detection signal of the crank angle sensor 16 shown in FIG. The crank angle sensor 16 is a sensor that detects the rotation angle of the crankshaft 15. On the other hand, the engine load Kl can be grasped from the detection signal of the air flow meter 23 described above.

  In the multifuel internal combustion engine of the first embodiment, the first fuel F1 is supplied to the fuel mixing control means of the electronic control unit 1 in accordance with the operating conditions (engine speed Ne and engine load Kl) in the combustion mode selected as described above. And the set fuel mixture ratio of the second fuel F2.

  Specifically, as in the first embodiment, the mixed fuel composed of the first fuel F1 having good compression ignitability and the second fuel F2 having high evaporability is considered in consideration of various fuel characteristics of the respective fuels F1 and F2. However, generally, when the fuel mixing ratio of the first fuel F1 is large, the fuel characteristics with good compression ignitability are obtained, and when the fuel mixing ratio of the second fuel F2 is large, the fuel characteristics with good evaporability are obtained. For this reason, the fuel mixing control means when operating in the compression self-ignition diffusion combustion mode selects a set fuel mixing ratio with a large fuel mixing ratio of the first fuel F1 so that the mixed fuel has a good compression ignitability. .

  However, for example, if this mixed fuel has the same level of compression ignitability, steep combustion tends to occur as the engine speed Ne decreases, which may lead to an increase in the amount of NOx generated and deterioration in thermal efficiency. . In this case, the fuel mixing ratio of the first fuel F1 may be reduced in accordance with the decrease in the engine speed Ne to reduce the compression ignition performance of the mixed fuel.

  Further, in the compressed self-ignition diffusion combustion mode, since fuel is injected into the compressed air, the use of low evaporative fuel makes it difficult for the fuel and air to be mixed uniformly. Since the temperature and pressure in the combustion chamber CC are reduced during the afterburning period, incomplete combustion is likely to occur and PM and smoke are likely to be generated. In particular, the amount of PM and smoke generated increases as the fuel evaporability decreases. For this reason, in this case, it is only necessary to adjust the set fuel mixture ratio to generate a mixed fuel having not only high compression ignitability but also high evaporability, and thereby the fuel introduced into the combustion chamber CC. Since the evaporability of the fuel is increased and mixing with air is promoted, the excessively concentrated region of the fuel can be reduced and the generation amount of PM and smoke can be reduced.

  Therefore, in the first embodiment, in order to realize the optimum compression auto-ignition diffusion combustion according to the operation condition such as the engine speed Ne and the operation condition such as the emission performance, the compression self-ignition is set using the operation condition as a parameter. It is preferable to prepare map data that can determine the set fuel mixture ratio during operation in the ignition diffusion combustion mode. Further, based on the same idea, it is preferable to prepare map data using the operating conditions as parameters for the set fuel mixture ratio during the premixed spark ignition flame propagation combustion mode operation.

  In the multifuel internal combustion engine of the first embodiment, after the first fuel F1 and the second fuel F2 are mixed in the fuel mixing means 53 so that the set fuel mixing ratio is set based on such an idea, The mixed fuel is supplied to the fuel injection valve 59 via the high-pressure fuel pump 56 and the delivery passage 57, and is injected into the combustion chamber CC at a fuel injection amount corresponding to the operating conditions and the combustion mode.

  By the way, in the internal combustion engine, generally, the amount of fuel supplied to the fuel injection valve is larger than the amount of fuel injection from the fuel injection valve, so that the fuel is left by the difference. For this reason, in a normal internal combustion engine, the surplus fuel is returned to the fuel tank and sent again to the fuel injection valve. This is no exception in the multi-fuel internal combustion engine of the first embodiment. For this reason, the multi-fuel internal combustion engine has a fuel return device 80 shown in FIG. 1 for returning the surplus mixed fuel in the fuel supply device 50. It is arranged. For example, the fuel return device 80 of the first embodiment is provided with a return passage 81 that guides the mixed fuel remaining without being injected by the fuel injection valve 59.

  In the multifuel internal combustion engine of the first embodiment, a common rail is adopted as the delivery passage 57. Generally, in such a common rail type internal combustion engine, a pressure adjusting valve for adjusting the pressure in the common rail is provided, and surplus fuel at the time of pressure adjustment by the pressure adjusting valve is discharged outside the common rail. Returned to the fuel tank. Therefore, also in the multifuel internal combustion engine of the first embodiment, the pressure adjusting valve 57a for adjusting the pressure in the delivery passage 57 (common rail), and the return passage 82 for guiding the mixed fuel discharged from the pressure adjusting valve 57a, Are disposed.

  Hereinafter, for the sake of convenience, the return passage 81 from the fuel injection valve 59 is referred to as a “first return passage 81”, and the return passage 82 from the pressure adjustment valve 57a is referred to as a “second return passage 82”. In the multi-fuel internal combustion engine of the first embodiment, the second return passage 82 is connected to the first return passage 81 so that all surplus mixed fuel is returned from the first return passage 81. .

  Next, the fuel tank (the first fuel tank 41A or the second fuel tank 41B) to which the surplus mixed fuel is returned will be described.

  The surplus mixed fuel of the first embodiment is a mixture of the first fuel F1 having good compression ignitability and the second fuel F2 having poor compression ignitability. For this reason, when this mixed fuel is returned to the first fuel tank 41A, the second fuel F2 with poor compression ignitability is mixed into the first fuel F1 with good compression ignitability. The compression ignitability of the fuel in the tank 41A is lowered. On the other hand, when the surplus mixed fuel is returned to the second fuel tank 41B, the first fuel F1 with good compression ignitability is mixed into the second fuel F2 with poor compression ignitability. 2 The compression ignitability of the fuel in the fuel tank 41B is increased. As described above, in the fuel tank in which the surplus mixed fuel is returned, the compression ignitability of the fuel changes compared to before the mixed fuel is mixed.

  Here, the set fuel mixing ratio of the first embodiment set by the fuel mixing control means represents the optimal mixing ratio between the first fuel F1 and the second fuel F2 in accordance with the combustion mode and operating conditions. On the other hand, the actual fuel mixing ratio of the mixed fuel produced by the fuel mixing means 53 represents the mixing ratio between the fuel from the first fuel tank 41A and the fuel from the second fuel tank 41B. is there. That is, in the fuel mixing means 53, the fuel from the first fuel tank 41A and the fuel from the second fuel tank 41B are mixed at the set fuel mixture ratio. For this reason, if another fuel is mixed in the fuel tank due to the return of the surplus mixed fuel, the mixed fuel having a desired set fuel mixing ratio is not generated.

  For example, when the surplus mixed fuel is returned to the first fuel tank 41A, the mixed fuel generated by the fuel mixing means 53 as the compression ignitability of the fuel in the first fuel tank 41A decreases. Since the fuel mixing ratio of the first fuel F1 having good compression ignitability is lowered, the compression ignitability of the mixed fuel is also lowered as compared with the mixed fuel having an accurate set fuel mixing ratio. Therefore, when the mixing ratio of the second fuel F2 having poor compression ignitability into the first fuel tank 41A becomes too high, the generated mixed fuel may not be able to self-ignite in the compressed air. . Even if it does not reach a state where self-ignition is impossible, the generated mixed fuel is lower than the desired compression ignitability (compression ignitability according to the set fuel mixture ratio). There is a risk of causing sharp combustion during combustion, leading to an increase in the amount of NOx generated and deterioration in thermal efficiency. Further, when the compressed self-ignition diffusion combustion is performed using such a mixed fuel having reduced compression ignitability, so-called diesel knock is caused, which causes deterioration of noise and vibration during combustion. Since it becomes unstable and causes severe torque fluctuations due to misfire, stable engine operation may be impossible.

  For this reason, in order to perform a stable operation in the compression auto-ignition diffusion combustion mode, it is preferable not to lower the compression ignitability of the fuel in the first fuel tank 41A.

  Therefore, in the first embodiment, the first return passage 81 is provided in the second fuel tank 41B so that the excess mixed fuel discharged from the fuel injection valve 59 and the pressure regulating valve 57a is returned to the second fuel tank 41B. Connect to. As a result, in the multifuel internal combustion engine of the first embodiment, since the surplus mixed fuel is prevented from being mixed into the first fuel tank 41A, the compression ignitability in the first fuel tank 41A is improved. The purity of the one fuel F1 (in other words, the compression ignitability of the fuel in the first fuel tank 41A) can be maintained. Further, in this multifuel internal combustion engine, the surplus mixed fuel is returned to the second fuel tank 41B, so that the fuel mixing ratio of the first fuel F1 in the mixed fuel and the original storage in the second fuel tank 41B are stored. Although it depends on the amount and the like, the compression ignitability of the fuel in the second fuel tank 41B can be kept at the same level as before mixing of the surplus mixed fuel or higher than before mixing. For this reason, the fuel mixing means 53 of the first embodiment can generate a mixed fuel having a compression ignitability equivalent to or higher than the desired compression ignitability even after the surplus mixed fuel is returned.

  As described above, in the multifuel internal combustion engine of the first embodiment, after the surplus mixed fuel is returned, the mixed fuel newly generated by the fuel mixing means 53 has a set fuel mixing ratio of the mixed fuel. The compression ignitability does not decrease. Therefore, according to the multifuel internal combustion engine of the first embodiment, even after the surplus mixed fuel is mixed, the fuel can be burned by using a good compression ignitable mixed fuel suitable for the compression auto-ignition diffusion combustion mode operation. it can. In addition, according to this multi-fuel internal combustion engine, steep combustion does not occur at the time of compression auto-ignition diffusion combustion even after surplus mixed fuel is mixed, so that the amount of NOx generated increases and thermal efficiency deteriorates (deterioration of fuel consumption, output) Reduction) can be suppressed. Further, in this multi-fuel internal combustion engine, noise and vibration during combustion by diesel knock during compression auto-ignition diffusion combustion are suppressed even after mixing of surplus mixed fuel, and ignition during compression auto-ignition diffusion combustion is suppressed. Thus, torque fluctuation due to unstable ignition and repeated combustion is suppressed.

  Next, a second embodiment of the multi-fuel internal combustion engine according to the present invention will be described with reference to FIGS.

  In the multi-fuel internal combustion engine of the first embodiment described above, the first fuel tank is mixed in the fuel mixing means 53 at the same ratio as the set fuel mixing ratio even though the first fuel F1 is mixed in the second fuel tank 41B. The fuel from 41A and the fuel from the second fuel tank 41B are mixed. For this reason, in the multi-fuel internal combustion engine of the first embodiment, a difference occurs between the actual fuel mixture ratio of the generated mixed fuel and the set fuel mixture ratio, and the optimum corresponding to the set fuel mixture ratio is generated. Compressive auto-ignition diffusion combustion may not be performed. For example, if the mixing ratio of the first fuel F1 in the second fuel tank 41B is large and the compression ignitability of the generated mixed fuel becomes too high, steep combustion is likely to be caused as the intake air temperature rises. Therefore, there is a risk of increasing the amount of NOx generated and deteriorating thermal efficiency.

Therefore, the multifuel internal combustion engine of the second embodiment is configured such that a mixed fuel having a set fuel mixing ratio is generated in the multifuel internal combustion engine of the first embodiment described above. Specifically, in the second embodiment, the fuel from the first fuel tank 41A and the second fuel tank 41B in the fuel mixing means 53 according to the mixing ratio r _T2F1 of the first fuel F1 into the second fuel tank 41B. Is adjusted so that the actual fuel mixture ratio between the first fuel F1 and the second fuel F2 in these mixed fuels becomes the set fuel mixture ratio.

First, the setting fuel mixing ratio between the second fuel F2 of the first fuel F1 and the fuel mixing ratio r _F2 of the fuel mixing ratio r _F1 "A: B" and then, the first fuel F1 in the mixed fuel during its When the fuel amount is “V _F1 ” and the fuel amount of the second fuel F 2 is “V _F2 ”, the set fuel mixture ratio α between the first fuel F 1 and the second fuel F 2 is expressed by the following formula 1. It can be expressed by a relational expression.

α = r _F1 / r _F2 = V _F1 / V _F2 = A / B (1)

Further, the mixing ratio between the fuel in the first fuel tank 41A and the fuel in the second fuel tank 41B for establishing the mixed fuel having the set fuel mixing ratio “A: B” is set to “C: D”. The fuel mixture ratio of the fuel from the first fuel tank 41A in the mixed fuel generated at this time is “r _T1 ”, and the fuel mixture ratio of the fuel from the second fuel tank 41B is “r _T2 ”. Further, the fuel amount from the first fuel tank 41A in the mixed fuel at that time is “V _T1 ”, and the fuel amount from the second fuel tank 41B is “V _T2 ”. In this case, the mixing ratio β between the fuel from the first fuel tank 41A and the fuel from the second fuel tank 41B in the generated mixed fuel can be expressed by the following relational expression (2).

β = r _T1 / r _T2 = V _T1 / V _T2 = C / D (2)

Here, since the set fuel mixture ratio α of the mixed fuel changes at any time according to the combustion mode or the like, the mixing ratio r _T2F1 of the first fuel F1 into the second fuel tank 41B is determined to be a constant value. Absent. That is, the mixing ratio γ of the first fuel F1 and the second fuel F2 in the second fuel tank 41B changes as needed by returning the surplus mixed fuel. The mixing ratio γ is _expressed by the following relational expression 3 when the fuel amount of the first fuel F1 in the second fuel tank 41B is “V _T2F1 ” and the fuel amount of the second fuel F2 is “V _T2F2 ”. Can be expressed as Further, the mixing ratio gamma, as in Equation 3 below, the first fuel F1 fuel quantity V _T2f1 from the second fuel tank 41B in the generated mixed fuel and fuel quantity V _T2F2 of the second fuel F2 It can also be expressed using.

γ = V _T2F1 / V _T2F2 = V _T2f1 / V _T2f2 (3)

Incidentally, a fuel quantity V _T2 from the second fuel tank 41B in the generated mixed fuel and fuel quantity V _T2f1 of the first fuel F1 is between the fuel quantity V _T2F2 of the second fuel F2, of the formula 4 below The relational expression is established.

V _T2 = V _T2f1 + V _T2f2 (4)

Incidentally, the fuel amount V _F1 of the first fuel F1 in the generated mixed fuel is the fuel amount V _T1 of the first fuel F1 from the first fuel tank 41A and the fuel amount of the first fuel F1 from the second fuel tank 41B. This corresponds to the sum of V _T2f1 (Formula 5).

V _F1 = V _T1 + V _T2f1 (5)

This equation 5 can be transformed into the following equation 6 using the equation 2 (V _T1 = βV _T2 ), the equation 3 (V _T2f1 = γV _T2f2 ), and the above equation 4.

V _F1 = β (γV _T2f2 + V _T2f2 ) + γV _T2f2 = (6)

Also, the fuel quantity V _F2 of the second fuel F2 in the generated mixed fuel is equivalent to a fuel quantity V _T2F2 of the second fuel F2 from the second fuel tank 41B (Equation 7).

V _F2 = V _T2f2 (7)

  Then, by substituting the formulas 6 and 7 into the formula 1, the fuel and the second fuel from the first fuel tank 41A necessary for generating the mixed fuel having the set fuel mixture ratio as the following formula 8 The mixing ratio β with the fuel from the tank 41B can be expressed.

    β = (α−γ) / (γ + 1) (8)

  Here, the set fuel mixture ratio α can be obtained from the set fuel mixture ratio set when the fuel mixing means 53 generates the mixed fuel.

  On the other hand, the mixing ratio γ of the first fuel F1 and the second fuel F2 in the second fuel tank 41B is, for example, a density meter capable of measuring the density of the first fuel F1 mixed in the second fuel tank 41B. It can be obtained based on the detection signal of the density sensor 91. For example, the density sensor 91 detects the difference in components between the first fuel F1 and the second fuel F2 and measures the density of the first fuel F1. Further, instead of the density sensor 91, a specific gravity sensor such as a hydrometer for measuring the specific gravity of the first fuel F1 in the second fuel tank 41B may be used.

The fuel mixing control means of the electronic control device 1 of the second embodiment is the first fuel tank 41B in the second fuel tank 41B obtained from the set fuel mixture ratio α obtained by itself and the detection signal of the measuring means such as the density sensor 91 and the specific gravity sensor. The mixing ratio γ of the fuel F1 and the second fuel F2 is substituted into the above equation 8, and the mixing ratio β between the fuel from the first fuel tank 41A and the fuel from the second fuel tank 41B is calculated. Then, the fuel mixing control unit causes the fuel mixing unit 53 to execute the mixing control of the fuel from the first fuel tank 41A and the fuel from the second fuel tank 41B so that the mixing ratio β is obtained. That is, in the second embodiment, the first fuel F1 mixing ratio r _T2F1 in the second fuel tank 41B is set so that the actual fuel mixing ratio of the generated mixed fuel becomes the set fuel mixing ratio. The mixing ratio between the fuel from the fuel tank 41A and the fuel from the second fuel tank 41B is adjusted.

Thereby, the _multifuel internal combustion engine of the second embodiment is not affected by the mixing ratio r _T2F1 of the first fuel F1 in the second fuel tank 41B to which the surplus mixed fuel has been returned, and the combustion mode and operation The fuel mixing means 53 can generate the mixed fuel having the optimal set fuel mixing ratio set according to the conditions. Therefore, in the multifuel internal combustion engine of the second embodiment, the compression autoignition diffusion combustion that is more stable than that of the first embodiment is performed using the optimum compression ignition mixed fuel corresponding to the set fuel mixture ratio. become. For this reason, in the _multifuel internal combustion engine of the second embodiment, even when the mixing ratio r _T2F1 of the first fuel F1 into the second fuel tank 41B becomes high, the optimum compression ignition according to the set fuel mixing ratio is _achieved. Therefore, it is possible to suppress an increase in the amount of NOx generated and the deterioration in thermal efficiency due to sharp combustion.

Further, in the multi-fuel internal combustion engine of the second embodiment, as is clear from the above equation 8, as the mixing ratio r _T2F1 of the first fuel F1 with good compression ignition to the second fuel tank 41B increases. The fuel mixing ratio r _T1 of the first fuel F1 from the first fuel tank 41A in the generated mixed fuel decreases. That is, in the multifuel internal combustion engine of the second embodiment, the mixed fuel is generated by using the first fuel F1 in the second fuel tank 41B with priority over the first fuel tank 41A. The amount of the first fuel F1 used in 41A can be reduced. Therefore, according to the multifuel internal combustion engine of the second embodiment, the replenishment timing of the first fuel F1 to the first fuel tank 41A can be delayed, and the convenience for the user is improved.

  By the way, the usage amount of the first fuel F1 in the first fuel tank 41A can be reduced as follows.

For example, when the fuel in the first fuel tank 41A and the fuel in the second fuel tank 41B are mixed at the same ratio as the set fuel mixing ratio as in the multifuel internal combustion engine of the first embodiment, the compression ignitability of the actual mixed fuel As the mixing ratio r _T2F1 of the first fuel F1 into the second fuel tank 41B becomes higher, the compression ignitability of the mixed fuel at the set fuel mixing ratio becomes better. For this reason, for example, if the difference in compression ignitability between the actual mixed fuel and the mixed fuel of the set fuel mixture ratio can be quantified and clarified, the mixture was excessively mixed with the mixed fuel of the set fuel mixture ratio The mixing amount of the first fuel F1 can be grasped, and the usage amount of the first fuel F1 in the first fuel tank 41A can be reduced by this excessive mixing amount. In the actual mixed fuel generated at that time, the fuel mixture ratio of the first fuel F1 and the second fuel F2 becomes the set fuel mixture ratio.

  Here, the compression ignitability of the fuel can be expressed using an index value obtained by indexing the quality (hereinafter referred to as “compression ignitability index value”). Therefore, in such a case, it is only necessary to provide the electronic control device 1 with fuel characteristic detection means for detecting the compression ignitability index value of the mixed fuel.

  As the compression ignitability index value, the ignition delay period during the compression self-ignition diffusion combustion mode operation can be used. The ignition delay period can be detected using detection signals from the in-cylinder pressure sensor 92 and the crank angle sensor 16. For example, the fuel characteristic detecting means calculates the ignition delay period based on the change in the in-cylinder pressure detected from the in-cylinder pressure sensor 92 during the compression auto-ignition diffusion combustion mode operation. The fuel characteristic detection means calculates the ignition delay period based on the change in the crank angular velocity detected from the crank angle sensor 16 during the compression auto-ignition diffusion combustion mode operation. Further, the ignition delay period can be calculated based on an ion current measured using an ion probe as an ignition timing sensor during the compression auto-ignition diffusion combustion mode operation.

  Furthermore, as the compression ignitability index value, a heat generation rate during compression autoignition diffusion combustion mode operation or a value equivalent thereto may be used. The heat generation rate or a value corresponding thereto can be obtained based on the in-cylinder pressure detected from the in-cylinder pressure sensor 92 and the crank angle detected from the crank angle sensor 16.

  The electronic control device 1 according to the second embodiment obtains a difference between the compression ignitability index value of the actual mixed fuel detected by the fuel characteristic detecting means and the compression ignitability index value of the mixed fuel having the set fuel mixture ratio, The amount of the first fuel F1 corresponding to this difference is calculated. Here, the compression ignitability index value of the mixed fuel having the set fuel mixture ratio is calculated and prepared in advance. For the amount of the first fuel F1 corresponding to the difference in the compression ignitability index value, the correspondence relationship between the difference in the compression ignitability index value and the amount of the first fuel F1 (excess mixture amount) was obtained in advance. Calculate using map data.

  Then, the fuel mixing control means of the electronic control unit 1 according to the second embodiment obtains the fuel amount of the first fuel tank 41A and the fuel amount of the second fuel tank 41B that have the same ratio as the set fuel mixture ratio, and the first The fuel mixing means 53 mixes the first fuel F1 obtained by subtracting the calculated amount from the fuel amount in the fuel tank 41A and the fuel amount in the second fuel tank 41B (first and second fuels F1 and F2). Let

  Thus, since the amount of the first fuel F1 in the first fuel tank 41A can be reduced even if the compression ignitability is used as a judgment material, this multi-fuel internal combustion engine is connected to the first fuel tank 41A. The replenishment time of the first fuel F1 can be delayed, and the convenience for the user can be improved.

  Next, a third embodiment of the multifuel internal combustion engine according to the present invention will be described with reference to FIG.

  In the multi-fuel internal combustion engine of the first embodiment described above, the surplus mixed fuel is returned to the second fuel tank 41B, which is a storage tank for the second fuel F2 having poor compression ignitability, and the first fuel F1 having good compression ignitability. Is mixed. For this reason, the fuel in the second fuel tank 41B is improved in compression ignitability, while the other fuel characteristics of the second fuel F2 having poor compression ignitability are deteriorated. For example, in the multifuel internal combustion engine of the first embodiment, light oil having good compression ignitability and poor evaporation is used as the first fuel F1, and gasoline having poor compression ignitability and high evaporation is used as the second fuel F2. When used, the evaporability of the fuel in the second fuel tank 41B is deteriorated by returning the surplus mixed fuel. Therefore, in the multifuel internal combustion engine of the first embodiment, the evaporability of the generated mixed fuel is lower than the evaporability of the mixed fuel having the set fuel mixing ratio, so that the premixed spark ignition flame propagation combustion mode operation is performed. Sometimes, the low evaporative mixed fuel becomes difficult to be mixed with air, which may increase the generation amount of PM, smoke, NOx and unburned HC.

  Thus, in the third embodiment, a multi-fuel internal combustion engine that enables operation utilizing the beneficial fuel characteristics of the respective fuels F1 and F2 is configured.

  Specifically, in the multifuel internal combustion engine of the third embodiment, the fuel return device 80 in the multifuel internal combustion engine of the first embodiment is replaced with a fuel return device 180 shown in FIG. The fuel tank (hereinafter referred to as “excess mixed fuel tank”) 183 is stored.

  The fuel return device 180 of the third embodiment is connected to first and second return passages 181 and 182 similar to the first and second return passages 81 and 82 of the first embodiment, and the first return passage 181. A surplus mixed fuel tank 183. Thereby, in the third embodiment, the surplus mixed fuel discharged from the fuel injection valve 59 and the pressure regulating valve 57a is stored in the surplus mixed fuel tank 183 via the first return passage 181.

  Therefore, in the third embodiment, not only the purity of the first fuel F1 having good compression ignitability in the first fuel tank 41A (compression ignitability of fuel in the first fuel tank 41A) but also the second fuel tank 41B. It is possible to maintain the purity of the second fuel F2 having poor compression ignitability (evaporability of fuel in the second fuel tank 41B). As a result, the fuel mixing means 53 can generate a mixed fuel having a set fuel mixing ratio set so as to obtain an optimal compression ignitability according to the combustion mode and operating conditions. For this reason, in the multifuel internal combustion engine of the third embodiment, stable compression autoignition diffusion combustion can be performed using the mixed fuel having the most optimal compression ignitability than that of the first embodiment. It is possible to suppress an increase in the amount of NOx generated and thermal efficiency (deterioration of fuel consumption, output reduction), suppression of noise and vibration during combustion, and suppression of torque fluctuations associated with stabilization of ignition. Further, in the multifuel internal combustion engine of the third embodiment, stable premixed spark ignition flame propagation combustion can be performed using an evaporative mixed fuel that is more optimal than that of the first embodiment. It becomes easy to mix with air, and the excessively rich region of fuel is reduced, and the generation of PM, smoke, NOx and unburned HC is suppressed.

  Thus, according to the multifuel internal combustion engine of the third embodiment, the first and second stored respectively are prevented by preventing the mixing of different fuels into the first and second fuel tanks 41A and 41B. It becomes possible to generate a mixed fuel having optimum fuel characteristics utilizing the inherent fuel characteristics (compression ignitability and evaporability) of the fuels F1 and F2. For this reason, in this multi-fuel internal combustion engine, it becomes possible to generate a mixed fuel having optimum fuel characteristics in accordance with the combustion mode and operating conditions, and to stabilize the combustion.

  Here, in the third embodiment, a feed pump 152 that sucks up the stored mixed fuel from the surplus mixed fuel tank 183 and sends it to the fuel passage 151 is provided, and the mixed fuel stored in the surplus mixed fuel tank 183 is provided. It is preferable to send the fuel to the fuel injection valve 59 preferentially. Here, the fuel passage 151 is connected to the fuel delivery path 54 (on the fuel injection valve 59 side relative to the fuel mixing means 53), and the mixed fuel is supplied to the fuel delivery path 54. Thereby, the replenishment time of the 1st and 2nd fuel F1, F2 to the 1st and 2nd fuel tank 41A, 41B can be delayed, and a user's convenience is improved. Further, since the stored mixed fuel is consumed preferentially, it is not necessary to store a large amount of mixed fuel in the surplus mixed fuel tank 183, and the capacity of the surplus mixed fuel tank 183 can be reduced. This makes it possible to improve the mountability on a vehicle.

  When the fuel mixture ratio of the mixed fuel stored in the surplus mixed fuel tank 183 is the same as the set fuel mixture ratio, only the mixed fuel in the surplus mixed fuel tank 183 may be sent to the fuel injection valve 59. This also has the same effect. Therefore, the surplus mixed fuel tank 183 has measuring means such as a density sensor 91 that can measure the fuel mixture ratio (mixing ratio δ) of the first fuel F1 and the second fuel F2 in the surplus mixed fuel tank 183. Has been deployed.

  By the way, in the multifuel internal combustion engine of each of the first to third embodiments described above, the first and second fuels F1 and F2 which are different depending on whether the compression ignitability is good or bad are exemplified. Other fuel characteristics, such as knock resistance and cold startability, may be applied as the fuel characteristics that are divided into good and bad at F2. And even if it is the case of the 1st and 2nd fuel F1 and F2 which were classified by the quality of such another fuel characteristic, if it is based on the multi-fuel internal combustion engine of Examples 1 and 2, The surplus mixed fuel is returned to the fuel tank of fuel having poor fuel characteristics.

  For example, the first fuel F1 having good knock resistance such as premium gasoline and the second fuel F2 having relatively low knock resistance such as regular gasoline are stored in the first and second fuel tanks 41A and 41B, respectively. In this case, in the multifuel internal combustion engine equivalent to the first and second embodiments, when the surplus mixed fuel is returned to the second fuel tank 41B, the purity of the first fuel F1 in the first fuel tank 41A is increased. While (knock resistance) is maintained, the knock resistance of the fuel in the second fuel tank 41B is improved. For this reason, in this multi-fuel internal combustion engine, the knock resistance of the mixed fuel produced by the fuel mixing means 53 can be kept in a good state, so that the occurrence of knocking during combustion can be suppressed. Become.

  Further, the first fuel F1 having good cold startability such as gasoline and the second fuel F2 having relatively poor cold startability such as alcohol fuel are respectively stored in the first and second fuel tanks 41A and 41B. In this case, in the multifuel internal combustion engine equivalent to the first and second embodiments, when the surplus mixed fuel is returned to the second fuel tank 41B, the purity of the first fuel F1 in the first fuel tank 41A is increased. While (cold startability) is maintained, the cold startability of the fuel in the second fuel tank 41B is improved. For this reason, in this multi-fuel internal combustion engine, the cold startability of the mixed fuel produced by the fuel mixing means 53 can be maintained in a good state, so that the engine can be started smoothly when the engine is cold. become able to.

  As described above, the multifuel internal combustion engine according to the present invention is reused by returning the surplus of the mixed fuel composed of the fuel with good fuel characteristics and the fuel with poor fuel characteristics stored in separate fuel tanks. This is useful as a technique for maintaining the fuel characteristics of the newly generated mixed fuel even after the surplus mixed fuel is returned, and in the combustion mode that makes use of the fuel characteristics. It is suitable for technologies that improve the combustion state during operation.

It is a figure shown about the structure of Example 1, 2 of the multi-fuel internal combustion engine which concerns on this invention. It is a figure which shows an example of the combustion mode map data used when setting a combustion mode. It is a figure shown about the structure of Example 3 of the multi-fuel internal combustion engine which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electronic control apparatus 41A 1st fuel tank 41B 2nd fuel tank 50 Fuel supply apparatus 53 Fuel mixing means 80,180 Fuel return apparatus 81,181 1st return path 82,182 2nd return path 91 Density sensor 92 In-cylinder pressure sensor 151 Fuel passage 152 Feed pump 183 Tank for surplus mixed fuel CC Combustion chamber F1 First fuel F2 Second fuel

Claims (3)

A first fuel tank that is supplied with fuel having good fuel characteristics, a second fuel tank that is supplied with fuel having poor fuel characteristics, and fuel from the first fuel tank at the same ratio as a predetermined set fuel mixture ratio. A multifuel internal combustion engine comprising: a fuel supply device that mixes fuel from the second fuel tank and guides the mixed fuel to a combustion chamber;
A multi-fuel internal combustion engine comprising a return passage for returning surplus mixed fuel in the fuel supply device to a second fuel tank in which fuel having poor fuel characteristics is stored.   The fuel supply device may include a mixing ratio of fuel having good fuel characteristics in the second fuel tank or the combustion chamber so that an actual fuel mixture ratio of the mixed fuel guided to the combustion chamber becomes the set fuel mixture ratio. The mixing ratio between the fuel from the first fuel tank and the fuel from the second fuel tank is adjusted according to the difference between the fuel characteristics of the mixed fuel introduced to the fuel and the fuel characteristics of the mixed fuel at the set fuel mixing ratio The multifuel internal combustion engine according to claim 1, wherein the multifuel internal combustion engine is configured as described above. The multifuel internal combustion engine according to claim 1 or 2, wherein the fuel characteristic is compression ignition, knock resistance, or cold startability.

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