JP2008121641A - Multi-fuel internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve ignitability of fuel of low compression ignitability in a combustion chamber during compression self ignition diffuse combustion mode operation. <P>SOLUTION: A multi-fuel internal combustion engine operated by introducing at least one kind of fuel out of at least two kinds of fuels F1, F2 having different properties to a combustion chamber CC or introducing mixed fuel of at least the two kinds of fuels F1, F2 to the combustion chamber CC, is provided with a fuel property detection means (electronic control device 1) detecting ignitability index value which indicates compression ignitability of fuel itself introduced to the combustion chamber CC as an index, and a fuel injection control means (electronic control device 1) introducing fuel of low compression ignitability into the combustion chamber CC by injecting fuel before a predetermined time in a period from a suction stroke to a compression stroke and executing main injection after that when compression self ignition diffuse combustion is executed by using fuel in the combustion chamber CC which is judged as fuel of low compression ignitability based on the ignitability index value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multi-fuel internal combustion engine that is operated by introducing at least one of at least two types of fuels having different properties into a combustion chamber or guiding a mixed fuel composed of the at least two types of fuel into the combustion chamber.

  Conventionally, so-called multi-fuel internal combustion engines that are operated using a plurality of types of fuels having different properties are known. For example, in Patent Document 1 below, a low-octane fuel is injected into a mixture of high-octane fuel injected into an intake port, and the mixture of high-octane fuel starts from the spontaneous ignition of the low-octane fuel. A multi-fuel internal combustion engine for propagating combustion is disclosed, and it is described that knocking can be prevented because the combustion speed is increased and the time until the completion of combustion can be shortened. Patent Document 2 below discloses a multi-fuel internal combustion engine that can be operated using a fuel selected by a driver from various types of fuel such as gasoline, light oil, and ethanol. Furthermore, this Patent Document 2 also discloses a multi-fuel internal combustion engine that is operated in a spark ignition mode when the engine load is lighter than a predetermined load and that is operated in a compression auto-ignition diffusion combustion mode when the engine load is high. Are listed. Patent Document 3 below describes a multi-fuel internal combustion engine that is operated using a mixed fuel of gasoline and light oil.

JP 2004-197660 A JP 2004-245126 A JP-A-9-68061

  However, the multifuel internal combustion engine disclosed in Patent Document 1 has a limit in the knocking prevention effect because the main combustion is performed by flame propagation. On the other hand, as an effective combustion mode for suppressing the occurrence of knocking, compression self-ignition diffusion combustion is known in which diffusion fuel is burned by self-ignition of fuel injected into compressed air.

  Here, when the compression ignitability of the fuel used in the compression self-ignition diffusion combustion is low, the lower the compression ignitability, the longer the ignition delay period (time from fuel injection to ignition start). Therefore, steep combustion is caused at the time of ignition, resulting in an increase in the amount of nitrogen oxide (NOx) generated and deterioration in thermal efficiency. Therefore, in order to avoid such an increase in the amount of NOx generated, it is only necessary to mitigate suddenly progressing combustion. To that end, it is only necessary to retard the fuel injection timing. However, when performing compression auto-ignition diffusion combustion with fuel with low compression ignitability, retarding the fuel injection timing increases the generation amount of PM and smoke, which is not preferable.

  Accordingly, the present invention provides a multi-fuel internal combustion engine that can improve the inconvenience of the conventional example and improve the ignitability of the low compression ignitable fuel in the combustion chamber during the compression auto-ignition diffusion combustion mode operation. That is the purpose.

  In order to achieve the above object, according to the first aspect of the present invention, at least one of at least two types of fuels having different properties is led to the combustion chamber, or a mixed fuel composed of the at least two types of fuel is supplied to the combustion chamber. In a multi-fuel internal combustion engine that is led and operated, fuel characteristic detection means for detecting an ignitability index value obtained by indexing the compression ignitability of the fuel itself guided into the combustion chamber, and low compression based on the ignitability index value When performing compression auto-ignition diffusion combustion using the fuel in the combustion chamber determined to be ignitable, the fuel is injected prior to a predetermined time during the period from the intake stroke to the compression stroke, and then injected into the combustion chamber And a fuel injection control means for introducing low compression ignitable fuel.

  In the multi-fuel internal combustion engine according to the first aspect, the in-cylinder temperature and the in-cylinder pressure in the combustion chamber increase with combustion of the fuel injected before, so that Ignition is improved. Further, in this multi-fuel internal combustion engine, the main injection is performed with respect to the main injection fuel in the combustion chamber by performing main injection when flame nuclei are generated in association with ignition of the fuel injected before or when heat is generated. Ignitability is improved. For this reason, this multi-fuel internal combustion engine can be operated in a stable compression auto-ignition diffusion combustion mode in which knocking due to abnormal combustion does not occur, so the compression ignitability of the main injection fuel led into the combustion chamber is low. However, steep combustion does not occur, and an increase in the amount of NOx generated and thermal efficiency deterioration can be suppressed. Further, in this multi-fuel internal combustion engine, even if the compression ignitability of the fuel is low, diesel knock does not occur during the compression auto-ignition diffusion combustion, so that noise and vibration during combustion are suppressed, and the compression ignitability of the fuel is reduced. Since the ignition at the time of compression auto-ignition diffusion combustion can be stabilized even if it is low, torque fluctuation due to unstable ignition and repeated combustion is suppressed.

  Generally, as the ignitability of the fuel in the combustion chamber decreases, it takes time for the fuel to self-ignite. For this reason, in the invention according to claim 2, in the multifuel internal combustion engine according to claim 1, during the period from the intake stroke to the compression stroke, the lower the ignitability of the fuel previously injected in the combustion chamber, The fuel injection control means is configured to inject prior to an earlier time.

  Thereby, in the multifuel internal combustion engine according to claim 2, even if the compression ignitability of the prior injection fuel itself is low, the prior injection fuel can be self-ignited by the fuel injection timing of the main injection. Become.

  In order to achieve the above object, according to a third aspect of the present invention, in the multifuel internal combustion engine according to the first or second aspect, the fuel injection amount of the preceding injection is decreased as the intake pressure is lower. It constitutes an injection control means. For example, the fuel injection control means is configured to reduce the upper limit value of the fuel injection amount of the preceding injection as the intake pressure is lower, as in the fourth aspect of the invention.

  When the fuel injection amount of the prior injection is the same, the lower the intake pressure, the easier it is to cause steep combustion during compression auto-ignition diffusion combustion. However, in the multifuel internal combustion engine according to claim 3 or 4, The lower the amount, the smaller the fuel injection amount of the prior injection, so that sharp combustion can be prevented.

  In order to achieve the above object, in the invention according to claim 5, in the multifuel internal combustion engine according to claim 1, 2, 3 or 4, the fuel injection amount of the preceding injection decreases as the engine speed decreases. Thus, the fuel injection control means is configured. For example, the fuel injection control means is configured to reduce the upper limit value of the fuel injection amount of the preceding injection as the engine speed is lower, as in the invention of claim 6.

  When the fuel injection amount of the prior injection is the same, the lower the engine speed, the easier it is to cause steep combustion at the time of compression auto-ignition diffusion combustion. In the multi-fuel internal combustion engine according to claim 5 or 6, The lower the number, the smaller the fuel injection amount of the prior injection, so that sharp combustion can be prevented.

  Here, from the viewpoint of omitting control of the ignition timing, it is preferable that the previously injected fuel is self-ignited in the combustion chamber, and for this reason, the fuel includes at least a fuel excellent in compression ignitability. It is preferable that Therefore, for example, the fuel in the combustion chamber may be a mixed fuel of gasoline and light oil as in the seventh aspect of the invention.

  In order to achieve the above object, in the invention according to claim 8, in the multifuel internal combustion engine according to claim 1, the fuel to be injected in advance is a highly flammable fuel, and the fuel injection control means is injected in advance. The fuel gas mixture is ignited with sparks and then injected into the main fuel.

  In the multi-fuel internal combustion engine according to claim 8, since the injected fuel is ignited by spark ignition and burned in advance, thereby increasing the in-cylinder temperature and the in-cylinder pressure in the combustion chamber, the main injection in the combustion chamber The ignitability to fuel is improved. Further, in this multi-fuel internal combustion engine, the main fuel is injected into the combustion chamber with respect to the main fuel injected in the combustion chamber by performing main injection when flame nuclei are generated or generated by the ignition of the injected fuel by spark ignition. All the ignitability is improved. Therefore, the multifuel internal combustion engine can achieve the same effects as the multifuel internal combustion engine according to the first aspect.

  In order to achieve the above object, in the invention according to claim 9, in the multi-fuel internal combustion engine according to any one of claims 1 to 8, when the prior injection is executed, the main injection is performed. The fuel injection control means is configured so that the fuel injection timing is advanced.

  In the multi-fuel internal combustion engine according to claim 9, since steep combustion is prevented by the prior injection, the generation of PM and smoke at the time of compression auto-ignition diffusion combustion is advanced by advancing the fuel injection timing of the main injection. It will be possible to suppress.

  In the multi-fuel internal combustion engine according to the present invention, if the compression ignitability of the fuel when operating in the compression auto-ignition diffusion combustion mode is low, the fuel is injected prior to the main injection, and the in-cylinder temperature and the cylinder are utilized using the combustion reaction. The internal pressure is increased to improve the ignitability of the main injection fuel. In addition, this multi-fuel internal combustion engine enhances the ignitability of the main injection fuel with low compression ignitability by using flame nuclei and heat generated by the ignition of the injected fuel as a fire type under similar conditions. For this reason, according to this multi-fuel internal combustion engine, it is possible to perform compression auto-ignition diffusion combustion capable of suppressing the occurrence of knocking due to abnormal combustion, regardless of whether the compression ignitability of the fuel introduced into the combustion chamber is good or bad. it can. In particular, this multi-fuel internal combustion engine can perform compression auto-ignition diffusion combustion without causing steep combustion even when using low-compression ignitable fuel, thereby suppressing an increase in the amount of NOx generated and deterioration in thermal efficiency. can do. In addition, since this multi-fuel internal combustion engine performs stable ignition and combustion at the time of compression self-ignition diffusion combustion even when using a low-compression ignitable fuel, noise, vibration, and torque fluctuations during combustion can be suppressed. . On the other hand, in this multi-fuel internal combustion engine, stable compression auto-ignition diffusion combustion is possible even if the compression ignitability of the mixed fuel deteriorates, so that the mixing ratio of highly evaporable fuel can be increased, and the compression Generation of PM and smoke during self-ignition diffusion combustion can be suppressed. Thus, according to the multifuel internal combustion engine which concerns on this invention, the stable compression auto-ignition diffusion combustion mode driving | operation is enabled, The improvement of emission performance and output performance, and the improvement of a fuel consumption performance can be aimed at.

  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.

  Embodiment 1 A first embodiment of a multifuel internal combustion engine according to the present invention will be described with reference to FIGS. This multi-fuel internal combustion engine is an internal combustion engine that is operated by introducing at least one of at least two types of fuels having different properties into the combustion chamber or by introducing a mixed fuel composed of the at least two types of fuel into the combustion chamber. It is. In the first embodiment, the latter multi-fuel internal combustion engine will be described as an example.

  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 guides a plurality of types of fuel having different properties to the combustion chamber CC. In the first embodiment, two types of fuels having different properties (a first fuel F1 stored in the first fuel tank 41A and a second fuel F2 stored in the second fuel tank 41B) are preliminarily stored in a predetermined fuel. An example is shown in which the mixture is mixed at a mixing ratio and the mixed fuel is directly injected into the combustion chamber CC.

  Specifically, the fuel supply device 50 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 a second fuel F2 from the second fuel tank 41B. Fuel mixing for mixing the second feed pump 52B sucked up 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. Means 53, a high-pressure fuel pump 55 for pressurizing and feeding the mixed fuel produced by the fuel mixing means 53 to the high-pressure fuel passage 54, and a delivery passage for distributing the mixed fuel in the high-pressure fuel passage 54 to the respective cylinders 56 and a fuel injection valve 57 for each cylinder for injecting the mixed fuel supplied from the delivery passage 56 into the combustion chamber CC.

  In the 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 unit 1, thereby mixing at a predetermined fuel mixing ratio. The fuel is mixed by the fuel mixing means 53. For example, the fuel supply device 50 adjusts the fuel mixing 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. Alternatively, the fuel mixing ratio of the mixed fuel may be adjusted by adjusting the mixing ratio of the first and second fuels F1 and F2 in the fuel mixing means 53 according to the instruction of the fuel mixing control means. Here, the fuel mixture ratio may be a constant value set in advance, or may be a variable value that varies depending on the operating conditions and the combustion mode.

  In addition, the fuel supply device 50 causes the high-pressure fuel pump 55 and the fuel injection valve 57 to be driven and controlled by the fuel injection control means of the electronic control unit 1, so that a desired fuel injection amount, fuel injection timing, and fuel injection period can be obtained. The generated mixed fuel is configured to be injected under fuel injection conditions such as the above. For example, the fuel injection control means of the electronic control unit 1 pumps the mixed fuel from the high-pressure fuel pump 55 and causes the fuel injection valve 57 to perform injection under fuel injection conditions corresponding to operating conditions, combustion modes, and the like.

  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 During such compression auto-ignition diffusion combustion, abnormal combustion does not occur, and therefore knocking that is generally said in a gasoline engine does not occur. For this reason, in order to achieve high torque and high output in a high load region, it is desirable to operate in a compression autoignition diffusion combustion mode that is not subject to knocking restrictions.

  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, etc. can be considered 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. In this premixed spark ignition flame propagation combustion mode, homogeneous combustion for igniting a homogeneously mixed premixed gas or a highly concentrated premixed gas is formed around the ignition means, and further, a lean mixture is formed around the premixed spark ignition flame propagation combustion mode. It includes a combustion mode such as stratified combustion in which a premixed gas is formed and ignition is performed on the rich premixed gas.

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

  The multifuel internal combustion engine of the first embodiment is configured to enable operation in 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.

  In addition, the electronic control device 1 of the first embodiment is provided with combustion mode setting means for setting the combustion mode. 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 when operating conditions such as medium / high load / low rotation, high load / high rotation, etc., and 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.

  Here, 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 decrease 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, when operating in this compression auto-ignition diffusion combustion mode, it is only necessary to use a fuel that has not only high compression ignitability but also high evaporability, and this leads to 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.

  The “fuel introduced into the combustion chamber CC” shown here means that the mixed fuel of the fuels F1 and F2 mixed by the fuel mixing means 53 as in the multifuel internal combustion engine of the first embodiment enters the combustion chamber CC. When taking the form that is sent, it refers to the mixed fuel. Here, the fuel (first fuel F1) having high compression ignitability and low evaporability is stored in the first fuel tank 41A, and the fuel (second fuel F2) having low compression ignitability and high evaporability is stored in the second fuel tank 41B. ) Is illustrated as an example. For example, light oil is stored as the first fuel F1, and gasoline is stored as the second fuel F2. In such a case, the various fuel characteristics of the respective fuels F1 and F2 must be taken into consideration, but the fuel introduced into the combustion chamber CC is generally compressed ignition if the fuel mixing ratio of the first fuel F1 is large. The fuel characteristics are good and the evaporation characteristics are inferior, and if the fuel mixing ratio of the second fuel F2 is large, the fuel characteristics are inferior in compression ignitability and good evaporation characteristics. When the fuels F1 and F2 are individually supplied to the combustion chamber CC as in the multi-fuel internal combustion engine shown in FIG. 11, which will be described later, the supplied fuels F1 and F2 The whole thing is called “fuel guided into the combustion chamber CC”. In such a case, if the supply ratio of the first fuel F1 is large, the fuel characteristics are good with good compression ignitability and poor evaporability, and if the supply ratio of the second fuel F2 is large, the fuel has poor compression ignitability and good evaporability. It becomes a characteristic.

  As described above, the fuel characteristics of the fuel guided into the combustion chamber CC depend on the ratios of the fuels F1 and F2 to the fuel, and the compression ignition ignition diffusion is accompanied by the increase in the second fuel F2 having high evaporability. Although the generation of PM and smoke at the time of combustion can be suppressed, on the other hand, the compression ignitability of the fuel led into the combustion chamber CC decreases, so there is a possibility that self-ignition may not be possible depending on the degree of increase. is there. Even if it does not reach a state where self-ignition is not possible, fuel with low compression ignitability causes steep combustion during compression self-ignition diffusion combustion as described above, resulting in an increase in the amount of NOx generated and deterioration in thermal efficiency. I will invite you. Furthermore, when compression autoignition diffusion combustion is performed using such low-compression ignited fuel, so-called diesel knock is caused, causing deterioration of noise and vibration during combustion, and ignition is unstable. As a result, severe torque fluctuations are caused, and stable engine operation becomes impossible.

  Here, in recent years, a technique for suppressing release of PM and smoke into the atmosphere by a DPF (Diesel Particulate Filter) as a PM collection device has been developed. For this reason, if this PM trapping device is mounted on the vehicle, even if the amount of the first fuel F1 having high compression ignitability is increased to improve the compression ignitability of the fuel guided into the combustion chamber CC, PM and smoke Can be suppressed from being released into the atmosphere. Therefore, in this case, fuel with high compression ignitability can be used when performing compression auto-ignition diffusion combustion with the PM trapping device, so that an increase in the amount of NOx generated that can occur when fuel with low compression ignitability is used. And noise during combustion can be improved.

  However, in this multi-fuel internal combustion engine, depending on which combustion mode is selected, and what fuel mixture ratio is applied in the selected combustion mode, the subsequent fuel mixture ratio (ie, This greatly affects the fuel characteristics of the fuel introduced into the combustion chamber CC. For example, when the compressed self-ignition diffusion combustion mode is frequently used using a mixed fuel having a high mixing ratio of the first fuel F1 having a high compression ignitability, the second fuel F2 having a high evaporability is left in the second fuel tank 41B. There is a high possibility that the first fuel F1 will be exhausted. For this reason, when it is desired to continue the operation in the compression auto-ignition diffusion combustion mode, for example, the mixing ratio of the first fuel F1 is reduced from a certain point in time to suppress the usage amount of the first fuel F1, and the combustion chamber CC The compression ignitability of the fuel led into it must be reduced. Thus, in this multi-fuel internal combustion engine, it is not always possible to introduce good compression ignitable fuel suitable for compression self-ignition diffusion combustion at that time into the combustion chamber CC.

  On the other hand, even if the compression ignitability of the fuel itself as described above cannot be improved, the ignitability of the fuel introduced into the combustion chamber CC can be improved. For example, the ignitability of the fuel in the combustion chamber CC is improved by increasing the in-cylinder temperature and the in-cylinder pressure. In order to increase the in-cylinder temperature and the in-cylinder pressure, preliminary fuel injection (hereinafter referred to as “prior injection”) is performed before normal fuel injection (hereinafter referred to as “main injection”). The fuel of the injection prior to that may be burned in the combustion chamber CC before the main injection. In the following, the fuel injection mode with only the main injection is referred to as a normal fuel injection mode, and the fuel injection mode in which prior injection and main injection are performed is referred to as a combined fuel injection mode.

  Therefore, in the multifuel internal combustion engine of the first embodiment, the fuel injection mode is switched during the compression autoignition diffusion combustion mode operation in accordance with the ignitability of the fuel in the combustion chamber CC.

  Here, the ignitability of the fuel in the combustion chamber CC varies depending on not only the quality of the compression ignitability of the fuel itself but also the water temperature tw and the intake air temperature ta. For example, even if the fuel introduced into the combustion chamber CC has a good compression ignitability to some extent, if the water temperature tw and the intake air temperature ta are lower than a predetermined value, the ignitability with respect to the fuel is deteriorated. Thus, the ignitability with respect to the fuel in the combustion chamber CC becomes worse as the compression ignitability of the fuel itself is lower, and as the water temperature tw and the intake air temperature ta are lower. Therefore, when switching the fuel injection mode during the compression auto-ignition diffusion combustion mode operation, the fuel is introduced into the fuel by comprehensively considering the compression ignitability of the fuel guided into the combustion chamber CC, the water temperature tw, and the intake air temperature ta. Therefore, it is necessary to judge the ignitability.

  The compression ignitability of the fuel can be expressed using an index value (hereinafter referred to as “ignitability index value”) I obtained by indexing the quality. Accordingly, the electronic control unit 1 of the first embodiment is provided with fuel characteristic detection means for detecting the ignitability index value I of the fuel. Specifically, as the fuel ignitability index value I, the cetane number (cetane index) of the fuel and the ignition delay period during the compression auto-ignition diffusion combustion mode operation can be used.

  The cetane number of the fuel can be grasped from, for example, the properties of the fuels F1 and F2 recognized by the fuel characteristic detecting means. However, in the first embodiment, the respective fuels F1 and F2 are mixed in the fuel mixing means 53 at a predetermined fuel mixing ratio and then sent to the combustion chamber CC. Therefore, the fuel mixing ratio is also taken into consideration. Without it, it is impossible to grasp the exact cetane number of the fuel (mixed fuel) introduced into the combustion chamber CC. Therefore, when the cetane number of the fuel (mixed fuel) introduced into the combustion chamber CC is used as the ignitability index value I, the cetane number is used as the cetane number of each of the fuels F1 and F2 and the fuel mixture ratio. Based on the above.

  Here, regarding the properties of the respective fuels F1, F2, the vehicle may be provided with an input device that allows the fueling operator to input the properties of the fuels F1, F2 at the time of refueling. You may make it recognize by sending and receiving oil supply information, such as a property and the amount of oil supply, from a fuel supply equipment to a vehicle via each communication device. The properties of the respective fuels F1 and F2 can be estimated from detection signals of fuel property sensors (not shown) provided in the first and second fuel tanks 41A and 41B, for example. In this case, the fuel characteristic detection means causes the fuel property sensor to detect the specific gravity, viscosity, conductivity and the like of the fuel, and estimates the property of the fuel based on these.

  On the other hand, the ignition delay period during the compression self-ignition diffusion combustion mode operation can be detected using detection signals from an in-cylinder pressure sensor, an ignition timing sensor, and a crank angle sensor 16 (not shown). For example, the fuel characteristic detection means can calculate the ignition delay period based on the change in the in-cylinder pressure detected from the in-cylinder pressure sensor during the compression auto-ignition diffusion combustion mode operation. In addition, the fuel characteristic detection means can measure an ion current using an ion probe as an ignition timing sensor during the compression auto-ignition diffusion combustion mode operation, and can calculate an ignition delay period based on the ion current. The fuel characteristic detecting means can also calculate 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. In the multifuel internal combustion engine of the first embodiment, it is assumed that the in-cylinder pressure sensor is not provided.

  Further, as the ignitability index value I of the fuel, a heat generation rate during the compression auto-ignition 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 and the crank angle detected from the crank angle sensor 16.

  The fuel injection control means of the electronic control unit 1 of the first embodiment includes the ignitability index value I of the fuel guided into the combustion chamber CC detected in this way, and the water temperature tw detected from the water temperature sensor 81 shown in FIG. And the ignitability of the fuel in the combustion chamber CC based on the intake air temperature ta detected from the intake air temperature sensor 82 shown in FIG. 1, and in the compression auto-ignition diffusion combustion mode operation according to the result The fuel injection mode is switched. For example, the normal fuel injection mode and the composite fuel injection mode described above are prepared as the fuel injection mode of the first embodiment, and this fuel injection control means has an ignitability with respect to the fuel in the combustion chamber CC. If it is higher than the predetermined value, the normal fuel injection mode is selected. If the ignitability is lower than the predetermined value, the composite fuel injection mode is selected.

  As a specific measure, the fuel injection control means of the first embodiment includes a fuel injection mode switching set in consideration of the ignitability index value I of the fuel guided into the combustion chamber CC, the water temperature tw and the intake air temperature ta. The ignitability determination threshold value (hereinafter referred to as “first ignitability determination reference value”) Is1 is compared, and the fuel injection mode is selected according to the result. The first ignitability judgment reference value Is1 is a good compression autoignition diffusion in which the increase in the amount of NOx generated and the noise during combustion do not occur only by main injection in the state of the current water temperature tw and intake air temperature ta. It is an ignitability index value for the fuel having the lowest compression ignitability that enables combustion, and shows a higher value as the water temperature tw and the intake air temperature ta are lower. Here, the fuel injection mode switching condition map data of FIG. 3 is prepared in advance, in which the water temperature tw and the intake air temperature ta are used as parameters, and the lower the temperature is, the higher the first ignitability determination reference value Is1 is selected. Keep it. Therefore, the fuel injection control means of the first embodiment selects the normal fuel injection mode if the ignitability index value I is equal to or greater than the first ignitability determination reference value Is1, and the ignitability index value I is the first ignition index value I1. If it is smaller than the sex determination reference value Is1, it is set so as to select the composite fuel injection mode.

  By the way, in the compression auto-ignition diffusion combustion mode, the fuel injection timing of the main injection (hereinafter referred to as “main injection timing”) TM is usually the time when good compression auto-ignition diffusion combustion is possible in the latter half of the compression stroke. Is set. Generally, the time when the piston 13 is located near the compression top dead center is set as the main injection timing TM. For this reason, as the fuel injection timing (hereinafter referred to as “prior injection timing”) TP of the prior injection, the previously injected fuel self-ignites by the main injection timing TM and increases the in-cylinder temperature and the in-cylinder pressure. It is necessary to set it when it is possible. Here, during the compression self-ignition diffusion combustion mode operation, the lower the ignitability with respect to the fuel in the combustion chamber CC, the longer the ignition delay period. Therefore, depending on the degree of ignitability, the previously injected fuel There is a possibility that no ignition reaction will occur in the combustion chamber CC by the main injection timing TM. Therefore, it is preferable that the prior injection timing TP is advanced with respect to the main injection timing TM as the ignitability with respect to the fuel previously injected in the combustion chamber CC is lower, and from the intake stroke according to the ignitability to the compression stroke. It is set at a predetermined time during the period until. For example, here, if the ignitability of the fuel previously injected in the combustion chamber CC is higher than a predetermined value, the fuel is injected prior to a predetermined time in the initial stage of the compression stroke, and if the ignitability is lower than the predetermined value, the intake stroke is determined. The fuel is injected prior to a predetermined time.

  Specifically, in the fuel injection control means of the first embodiment, the pre-ignition value set in consideration of the ignitability index value IP (= ignitability index value I) of the fuel injected in advance, the water temperature tw and the intake air temperature ta. The threshold value for determining the ignitability (hereinafter referred to as “second ignitability determination reference value”) Is2, which is the injection timing switching condition, is compared, and the injection prior to the compression stroke or the injection prior to the intake stroke is selected according to the result. . The second ignitability determination reference value Is2 is a compression stroke in which the self-ignition by the main injection timing TM and the in-cylinder temperature and the in-cylinder pressure can be increased in the current state of the water temperature tw and the intake air temperature ta. Is the ignitability index value of the fuel having the lowest compression ignitability among the fuels injected prior to the start of the engine, and shows higher values as the water temperature tw and the intake air temperature ta are lower. Here, as in the case of the first ignitability determination reference value Is1 described above, the water temperature tw and the intake air temperature ta are used as parameters, and the lower the temperature, the higher the second ignitability determination reference value Is2 is selected. The prior injection timing switching condition map data shown in FIG. 4 is prepared in advance. Therefore, the fuel injection control means of the first embodiment calculates the prior injection timing TPc at the initial stage of the compression stroke if the ignitability index value I of the fuel to be injected is equal to or greater than the second ignitability determination reference value Is2. If the ignitability index value I is smaller than the second ignitability determination reference value Is2, it is set to calculate the injection timing TPs prior to the intake stroke. As the respective prior injection timings TPc and TPs, the earlier timing is selected as the ignitability index value I of the fuel injected in advance is smaller. Note that each of the preceding injection timings TPc and TPs may have its own specific fuel injection timing set in advance.

  Here, in the combined fuel injection mode of the first embodiment, since the sudden injection of the main injected fuel is avoided as will be described later by the combustion of the previously injected fuel, the generation amount of PM and smoke is reduced. Steep combustion can be prevented without performing retard control of the main injection timing TM, which is likely to increase. Conversely, by advancing the main injection timing TM, PM is suppressed while suppressing steep combustion. And smoke can be suppressed. Therefore, the fuel injection control means of the first embodiment sets the main injection timing TM in the composite fuel injection mode to an advance side to the extent that at least the generation of PM or the like can be suppressed.

  Further, in the fuel injection control means of the first embodiment, the fuel injection amount (hereinafter referred to as the “prior injection amount”) FP and the fuel injection amount of the main injection (hereinafter referred to as the “main injection amount”) at the time of prior injection. .) Let FM be calculated.

  Here, the increase rate of the in-cylinder temperature and the in-cylinder pressure accompanying the combustion reaction of the prior injection increases as the amount of fuel injected in advance increases. On the other hand, the rate of increase of the in-cylinder temperature and the in-cylinder pressure decreases as the compression ignitability of the previously injected fuel decreases and as the intake air temperature ta of the intake air guided into the combustion chamber CC decreases. Go. Accordingly, the in-cylinder temperature and the in-cylinder pressure at that time increase the preceding injection amount FP as the compression ignitability (ignitability index value I) of the fuel introduced into the combustion chamber CC during the prior injection and the intake air temperature ta are lower. Without it, it will not rise effectively.

  On the other hand, an excessive increase in the injection amount FP is not preferable because the combustion itself by the injected fuel becomes steep combustion and causes the above-described noise and the like as a problem before increasing the in-cylinder temperature and the in-cylinder pressure. . Here, whether or not the prior injection amount FP is excessive can be determined from the intake pressure Pin of the intake air introduced into the combustion chamber CC and the engine speed Ne. For example, if the prior injection amount FP is the same, the lower the intake pressure Pin and the engine speed Ne, the sharper the combustion by the prior injected fuel, so even if the prior injection amount FP is the same amount, The prior injection amount FP is determined to be excessive as the intake pressure Pin and the engine speed Ne decrease.

  Therefore, the prior injection amount FP takes into account the in-cylinder temperature and the in-cylinder in consideration of the compression ignitability (ignitability index value I) of the fuel injected in advance, the intake air temperature ta, the intake pressure Pin, and the engine speed Ne. An amount suitable for increasing the pressure is set. For example, in the fuel injection control means of the first embodiment, the prior injection amount (hereinafter referred to as “reference prior injection”) which is a reference in accordance with the compression ignitability (ignitability index value I) of the fuel injected prior to the intake air temperature ta. FP1 and an upper limit value (hereinafter referred to as “prior injection amount upper limit guard value”) FP2 as an increase limit value of the preceding injection amount in accordance with the intake pressure Pin and the engine speed Ne. The injection amount FP is set in advance according to these comparison results. Here, if the reference preliminary injection amount FP1 is equal to or less than the preliminary injection amount upper limit guard value FP2, the reference preliminary injection amount FP1 is set as the preliminary injection amount FP, and the reference preliminary injection amount FP1 is set to the preliminary injection amount upper limit guard value FP2. If it is larger than this, the prior injection amount upper limit guard value FP2 is set as the prior injection amount FP.

  Here, the reference prior injection amount FP1 is obtained using the reference prior injection amount selection map data of FIG. 5 in which the ignitability index value I and the intake air temperature ta are used as parameters, and the lower values are selected. On the other hand, with respect to the preceding injection amount upper limit guard value FP2, the intake pressure Pin and the engine speed Ne are used as parameters, and lower values are selected. Ask. That is, the prior injection amount upper limit guard value FP2 is lowered as the intake pressure Pin and the engine speed Ne are lower, thereby reducing the prior injection amount FP. The reference advance injection amount FP1 and the advance injection amount upper limit guard value FP2 are respectively the reference advance injection amount FPc1 and the advance injection amount upper limit guard value FPc2 at the beginning of the compression stroke, and the reference advance injection amount FPs1 and the advance injection amount upper limit in the intake stroke. It is divided into guard values FPs2. Therefore, the prior injection amount FP is also divided into the prior injection amount FPc at the beginning of the compression stroke and the prior injection amount FPs in the intake stroke.

  In FIG. 5, the reference advance injection amount FPc1 at the initial stage of the compression stroke and the reference advance injection amount FPs1 at the intake stroke are collectively shown for convenience, but strictly speaking, each reference advance injection amount selection map data is individually shown. It is prepared. Similarly, in FIG. 6, the prior injection amount upper limit guard value FPc2 and the prior injection amount upper limit guard value FPs2 of the intake stroke are collectively shown for convenience, but strictly speaking, each prior injection amount upper limit guard value is selected individually. Map data is available.

  Hereinafter, an example of the control operation of the electronic control unit 1 in the multifuel internal combustion engine of the first embodiment will be described based on the flowchart of FIG.

  First, the electronic control unit 1 of the first embodiment detects the engine speed Ne and the engine load Kl of the multifuel internal combustion engine based on detection signals from the crank angle sensor 16 and the air flow meter 23, respectively (step ST1). Then, the electronic control unit 1 causes the combustion mode setting means to obtain the optimum combustion mode for the combination of the engine speed Ne and the engine load Kl from the combustion mode map data shown in FIG. 2, and this is the compression auto-ignition diffusion combustion mode. It is determined whether or not (step ST2).

  Here, when the compression auto-ignition diffusion combustion mode is selected, the electronic control unit 1 detects the ignitability index value I of the fuel guided to the combustion chamber CC by the fuel characteristic detection means as described above. (Step ST3) Further, the first ignition is performed by comparing the water temperature tw and the intake air temperature ta of the multi-fuel internal combustion engine with the fuel injection mode switching condition map data shown in FIG. 3 and the prior injection timing switching condition map data shown in FIG. A sex determination reference value Is1 and a second ignitability determination reference value Is2 are calculated (step ST4). The first ignitability judgment reference value Is1 and the second ignitability judgment reference value Is2 at that time are higher values as the water temperature tw and the intake air temperature ta are lower (that is, the more severe the conditions are for self-ignition). Is set.

  Then, the fuel injection control means of the electronic control unit 1 determines whether or not the ignitability index value I is equal to or greater than the first ignitability determination reference value Is1 (step ST5). Here, the case where the ignitability index value I is equal to or greater than the first ignitability determination reference value Is1 indicates that the ignitability with respect to the main injection fuel in the combustion chamber CC is sufficiently ensured. . For this reason, in this case, the normal fuel injection mode is selected, and compression autoignition diffusion combustion of only main injection is performed through steps ST21 to ST23 described later.

  On the other hand, when the ignitability index value I is smaller than the first ignitability determination reference value Is1, it indicates that the ignitability with respect to the main injected fuel in the combustion chamber CC is low, so that the composite fuel Select the injection mode. In the first embodiment, after a negative determination is made in step ST5 and the composite fuel injection mode is selected, fuel injection control is performed to determine whether or not the ignitability index value I is greater than or equal to the second ignitability determination reference value Is2. The means is determined (step ST6).

  Here, the case where the ignitability index value I is greater than or equal to the second ignitability determination reference value Is2 means that the fuel self-ignites before the main injection timing TM by injecting prior to the initial stage of the compression stroke, The case where the in-cylinder pressure is increased is shown. On the other hand, when the ignitability index value I is smaller than the second ignitability determination reference value Is2, if the fuel is not pre-injected earlier as in the intake stroke, the fuel is self-ignited by the main injection timing TM and the cylinder The case where the internal temperature and the in-cylinder pressure cannot be increased is shown.

  Therefore, the fuel injection control means of the first embodiment, when an affirmative determination is made in step ST6, sets the prior injection timing TPc at the beginning of the compression stroke to the prior injected fuel in the combustion chamber CC in order to inject prior to the beginning of the compression stroke. It is determined according to the ignitability (ignitability index value I, water temperature tw and intake air temperature ta) (step ST7).

  Further, the fuel injection control means obtains a reference prior injection amount FPc1 and a prior injection amount upper limit guard value FPc2 at the beginning of the compression stroke (steps ST8 and ST9). At this time, the reference advance injection amount FPc1 is selected from the reference advance injection amount selection map data shown in FIG. 5 based on the ignitability index value I and the intake air temperature ta, and the advance injection amount upper limit guard value FPc2 is set to the intake pressure Pin and Based on the engine speed Ne, selection is made from the preceding injection amount upper limit guard value selection map data shown in FIG.

  Thereafter, the fuel injection control means compares the reference preliminary injection amount FPc1 with the preliminary injection amount upper limit guard value FPc2 (step ST10), and if the reference preliminary injection amount FPc1 is equal to or less than the preliminary injection amount upper limit guard value FPc2. For example, the reference prior injection amount FPc1 is set as the prior injection amount FPc at the beginning of the compression stroke (step ST11). If the reference prior injection amount FPc1 is larger than the prior injection amount upper limit guard value FPc2, the prior injection amount upper limit guard value FPc2 is set. It is set as the prior injection amount FPc at the beginning of the compression stroke (step ST12).

  Then, this fuel injection control means executes the prior injection at the initial stage of the compression stroke with the prior injection amount FPc set in step ST11 or step ST12 when the set prior injection timing TPc is reached (step ST13). As a result, in this multifuel internal combustion engine, the previously injected fuel is self-ignited and burned in the combustion chamber CC, and the in-cylinder temperature and the in-cylinder pressure are increased by the main injection timing TM.

  On the other hand, if a negative determination is made in step ST6, the fuel injection control means changes the injection timing TPs prior to the intake stroke to ignitability with respect to the prior injected fuel in the combustion chamber CC so as to inject prior to the intake stroke. Obtained accordingly (step ST14).

  Further, the fuel injection control means obtains a reference prior injection amount FPs1 and a prior injection amount upper limit guard value FPs2 for the intake stroke (steps ST15 and ST16). At this time, the reference preliminary injection amount FPs1 is selected from the reference preliminary injection amount selection map data shown in FIG. 5 based on the ignitability index value I and the intake air temperature ta, and the preliminary injection amount upper limit guard value FPs2 is determined based on the intake pressure Pin. Based on the engine speed Ne, selection is made from the preceding injection amount upper limit guard value selection map data shown in FIG.

  Thereafter, the fuel injection control means compares the reference preliminary injection amount FPs1 with the preliminary injection amount upper limit guard value FPs2 (step ST17), and if the reference preliminary injection amount FPs1 is equal to or less than the preliminary injection amount upper limit guard value FPs2. For example, the reference prior injection amount FPs1 is set as the prior injection amount FPs of the intake stroke (step ST18). If the reference prior injection amount FPs1 is larger than the prior injection amount upper limit guard value FPs2, the prior injection amount upper limit guard value FPs2 is set to the intake stroke. Is set as the injection amount FPs prior to (step ST19).

  Then, this fuel injection control means executes the prior injection of the intake stroke with the prior injection amount FPs set at step ST18 or step ST19 when the set prior injection timing TPs is reached (step ST20). As a result, in this multi-fuel internal combustion engine, the previously injected fuel self-ignites and burns in the combustion chamber CC during the compression stroke after a sufficient time has elapsed, and is injected into the cylinder by the main injection timing TM. Increase temperature and in-cylinder pressure.

  The fuel injection control means of the first embodiment calculates the main injection timing TM and the main injection amount FM, for example, until the fuel injected at the beginning of the compression stroke or prior to the intake stroke self-ignites (steps ST21 and ST22). ) When the main injection timing TM is reached, the main injection is executed with the main injection amount FM (step ST23).

  Here, in the multi-fuel internal combustion engine at that time, the in-cylinder temperature and the in-cylinder pressure are increased by the combustion of the fuel injected prior to the fuel in the combustion chamber CC injected main. Ignition is improved. For this reason, in this multi-fuel internal combustion engine, even if the fuel has a low compression ignitability, it becomes easy to self-ignite by the main injection timing TM. Ignition diffusion combustion can be realized.

  When a combustion mode other than the compression autoignition diffusion combustion mode is selected in step ST2, the fuel injection control means of the first embodiment executes fuel injection control for the corresponding combustion mode (step ST24). ).

  As described above, the multifuel internal combustion engine of the first embodiment is in a state where the ignitability of the main injection fuel is good regardless of whether the main injection fuel itself guided into the combustion chamber CC is good or bad in compression. Therefore, it is possible to operate in a stable compression autoignition diffusion combustion mode in which knocking due to abnormal combustion does not occur. Therefore, in this multi-fuel internal combustion engine, even if the compression ignitability of the main injection fuel is low, steep combustion does not occur at the time of compression auto-ignition diffusion combustion. Therefore, an increase in the amount of NOx generated and thermal efficiency (deterioration of fuel consumption, Output reduction) can be suppressed. Further, in this multi-fuel internal combustion engine, even if the compression ignitability of the fuel is low, diesel knock does not occur during the compression auto-ignition diffusion combustion, so that noise and vibration during combustion are suppressed, and the compression ignitability of the fuel is reduced. Since the ignition at the time of compression auto-ignition diffusion combustion can be stabilized even if it is low, torque fluctuation due to unstable ignition and repeated combustion is suppressed. Further, in this multi-fuel internal combustion engine, the main injection timing TM when the composite fuel injection mode is selected is set to the advance side, so that the occurrence of PM and smoke during compression auto-ignition diffusion combustion is also suppressed. Will be able to. Furthermore, in this multi-fuel internal combustion engine, stable compression auto-ignition diffusion combustion is possible even if the compression ignitability of the mixed fuel is deteriorated, so that the mixing ratio of the highly evaporable second fuel F2 can be increased. This also makes it possible to suppress the generation of PM and smoke during compression autoignition diffusion combustion. Further, in this multi-fuel internal combustion engine, knocking due to abnormal combustion is suppressed, so that it is possible to operate at a high load and to improve specific output and thermal efficiency.

  By the way, in the multifuel internal combustion engine of the first embodiment, the injected fuel is self-ignited in advance, but the compression ignitability of the prior injected fuel is too low to be self-ignited, or even if self-ignited, it is misfired immediately. In this case, the injected fuel may be ignited using the spark plug 71 in advance. In this case, it is preferable that the pre-injected fuel is a highly flammable fuel. For this reason, in this case, a highly flammable fuel such as hydrogen, compressed natural gas (CNG) or alcohol fuel is included in the mixed fuel. Is desirable. For example, in this case, in the above-described multi-fuel internal combustion engine, a highly flammable fuel is prepared as the second fuel F2.

  Here, in the multi-fuel internal combustion engine in this case, the mixture of the highly flammable pre-injected fuel formed in the combustion chamber CC is ignited by the ignition plug 71, and the in-cylinder temperature and the cylinder are combusted by this combustion. Increase internal pressure. Therefore, the prior injection timing TP, the prior injection amount FP, and the ignition timing of the prior injected fuel may be set so that combustion that can increase the in-cylinder temperature and the in-cylinder pressure is performed by the main injection timing TM. For example, here, by the main injection timing TM, a premixed gas of the pre-injected fuel having a high concentration is formed around the spark plug 71 in the combustion chamber CC, and a lean premixed gas is further formed around the premixed gas. The injection timing TP is set prior to the period from the intake stroke to the compression stroke, and the ignition timing is set so that the rich premixed gas is ignited and the in-cylinder temperature and the in-cylinder pressure are increased by the main injection timing TM. Thereby, also in the multi-fuel internal combustion engine in this case, favorable compression auto-ignition diffusion combustion using the low ignitability mixed fuel becomes possible, and the same effect as described above can be obtained.

  Further, in the multi-fuel internal combustion engine of the first embodiment, the mixed fuel generated by the fuel mixing means 53 is used as the prior injected fuel. Separately, a fuel dedicated to the prior injection is prepared. May be. For example, the fuel dedicated to the injection is preferably a fuel having a good compression ignitability.

  Furthermore, in the multifuel internal combustion engine of the first embodiment, the in-cylinder temperature and the in-cylinder pressure are increased by the combustion of the injected fuel in advance, thereby improving the ignitability of the main injected fuel in the combustion chamber CC. However, prior to the self-ignition of the injected fuel, the flame kernel and heat generation may be used as a fire type to promote the ignition of the main injection fuel with low compression ignitability. be able to. That is, this multi-fuel internal combustion engine performs main injection when flame nuclei are generated in association with ignition by spark ignition of the injected fuel before or when it generates heat, so that main injection fuel in the combustion chamber CC is obtained. The ignitability is improved.

  Here, in this case, in the above-described example, the prior injection timing TP when the composite fuel injection mode is selected is delayed, and the main injection timing TM comes when the prior injected fuel self-ignites or immediately thereafter. Set as follows. Therefore, when the compression ignitability of the prior injected fuel is high, the main injection timing TM may come immediately after the prior injection timing TP. Therefore, in this case, the injection timing TP is set prior to the timing according to the compression ignitability of the prior injected fuel during the period from the intake stroke to the latter half of the compression stroke. In addition, since it is difficult to perform prior injection and main injection continuously with one fuel injection valve 57, two direct injection fuel injection valves are provided in one combustion chamber CC, and each of them is used for prior injection. It may be used properly for main injection.

  Further, when the preceding injected fuel is the above-described highly flammable fuel, the preceding injection timing TP or ignition is set so that the main injection timing TM comes when the ignition plug 71 is ignited with the spark plug 71 or immediately after that. Set the time. Therefore, when the pre-injected fuel has high flammability, a pre-mixture of the pre-injected fuel having a high concentration is formed around the spark plug 71 in the combustion chamber CC by the main injection timing TM, and a lean pre-mixture is further formed therearound. The injection timing TP is set in advance during the period from the intake stroke to the compression stroke so that an air-fuel mixture is formed, and the main injection timing TM comes when a flame kernel is generated by igniting the rich pre-mixture or immediately after that. Ignition timing is set.

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

  In general, if the in-cylinder pressure in the combustion chamber CC can be detected, the ignition timing of the fuel injected prior to the pressure change and the in-cylinder pressure increase rate can be grasped. Therefore, when the in-cylinder pressure can be detected or estimated in the multi-fuel internal combustion engine of the first embodiment described above, it can be determined whether or not the previously injected fuel is abruptly burned. Further, the in-cylinder pressure increases as the prior injection amount FP increases, and the prior injection amount FP can be calculated backward from the in-cylinder pressure increase rate due to the prior injection. For this reason, the in-cylinder pressure increase rate is fed back at the time of the next prior injection, so that the appropriate prior injection amount FP can be obtained without preparing the prior injection amount upper limit guard value selection map data as shown in FIG. Can be set.

  Therefore, in the second embodiment, a multi-fuel internal combustion engine configured to detect or estimate the in-cylinder pressure will be described. Here, a multi-fuel internal combustion engine according to the first embodiment described above is provided with a cylinder pressure sensor 83 shown in FIG. 8 so that the cylinder pressure can be detected.

  Specifically, first, in the second embodiment, a threshold value (hereinafter referred to as “combustion state determination reference value”) Pr0 of the in-cylinder pressure increase rate when determining whether or not the combustion is steep is prepared. . The combustion state determination reference value Pr0 sets, for example, the maximum value of the in-cylinder pressure increase rate when the injection amount FP is increased or decreased in advance and an increase in NOx generation amount or a deterioration in thermal efficiency is caused accordingly.

  Therefore, if the maximum in-cylinder pressure increase rate Pr at the time of prior injection is smaller than the combustion state determination reference value Pr0, the prior injection amount FP at the time of the previous injection does not cause steep combustion.

  Here, in the first embodiment, by using the prior injection amount upper limit guard value selection map data, an excessive prior injection amount FP that causes steep combustion is avoided, while the maximum is within a range that does not cause steep combustion. The prior injection amount FP that can increase the in-cylinder temperature and the in-cylinder pressure as much as possible can be set. However, in the second embodiment, since the prior injection amount upper limit guard value selection map data is not used, the previously set prior injection amount FP can increase the in-cylinder temperature and the in-cylinder pressure to the maximum. It is not always a quantity. For this reason, the second embodiment is configured such that the advance injection amount FP that can raise the in-cylinder temperature and the in-cylinder pressure to the maximum is possible in a situation where there is no concern about steep combustion. For example, in the second embodiment, as in the first embodiment, the reference leading injection amount FP1 is calculated by comparing the ignitability index value I and the intake air temperature ta with the reference leading injection amount selection map data in FIG. To do. However, the reference leading injection amount selection map data of the second embodiment increases the in-cylinder temperature and the in-cylinder pressure to the maximum without causing sharp combustion under the conditions of the ignitability index value I and the intake air temperature ta. This is different from the first embodiment in that the reference leading injection amount FP1 that can be made is stored.

  On the other hand, for example, when the maximum in-cylinder pressure increase rate Pr at the time of prior injection before a predetermined cycle is equal to or higher than the combustion state determination reference value Pr0 (that is, steep combustion), prior to that time It can be inferred that the injection amount FP is too large.

  Here, since there is little possibility that the ignitability index value I and the intake air temperature ta greatly change during several cycles, it is not considered that a large difference will occur in the reference leading injection amount FP1 selected during that time. For this reason, if steep combustion occurs before a predetermined cycle, it is highly likely that the pre-injection amount FP of the same amount will be set in the future, and steep combustion will be caused again during the pre-injection. Therefore, it is necessary to reduce the injection amount FP prior to avoiding sharp combustion. For example, as described above, since there is a correlation between the in-cylinder pressure increase rate and the prior injection amount FP, the difference between the maximum in-cylinder pressure increase rate Pr and the combustion state determination reference value Pr0 for the decrease amount. A fuel injection amount corresponding to is set.

  Hereinafter, an example of the control operation of the electronic control device 1 in the multifuel internal combustion engine of the second embodiment will be described with reference to the flowchart of FIG. In addition, about the control operation similar to Example 1, it abbreviate | omits below or keeps it simple description.

  The electronic control unit 1 according to the second embodiment sets the combustion mode in the same manner as in the first embodiment (steps ST1 and ST2), and switches the fuel injection mode when the compression self-ignition diffusion combustion mode is set (step ST1). ST3 to ST6).

  Here, when the composite fuel injection mode is selected and the initial stage of the compression stroke is selected as the preceding injection timing TP, the fuel injection control means of the electronic control unit 1 is the same as in the first embodiment. The initial prior injection timing TPc and the reference prior injection amount FPc1 are calculated (steps ST7 and ST8).

  In the second embodiment, next, the fuel injection control means determines whether or not prior injection has been performed before a predetermined cycle (for example, 1 cycle here) (step ST31). The maximum in-cylinder pressure increase rate Pr by the prior injection obtained in step ST41, which will be described later in the previous cycle, is compared with the combustion state determination reference value Pr0 (step ST32). This fuel injection control means determines the reference prior injection amount obtained in step ST8 when the maximum in-cylinder pressure increase rate Pr is smaller than the combustion state determination reference value Pr0 or when a negative determination is made in step ST31. FPc1 is set as a prior injection amount FPc at the beginning of the compression stroke (step ST33). On the other hand, if the maximum in-cylinder pressure rise rate Pr is equal to or greater than the combustion state determination reference value Pr0, the fuel injection control means determines the amount of decrease α obtained to avoid steep combustion in the reference prior injection obtained in step ST8. This is subtracted from the amount FPc1, and this is set as the prior injection amount FPc at the beginning of the compression stroke (step ST34).

  Then, the fuel injection control means causes the prior injection at the initial stage of the compression stroke to be executed with the prior injection amount FPc set in step ST33 or step ST34 when the set prior injection timing TPc is reached (step ST35). As a result, also in the multifuel internal combustion engine of the second embodiment, the fuel injected prior to the self-ignition in the combustion chamber CC burns, and the in-cylinder temperature and the in-cylinder pressure are increased by the main injection timing TM. .

  On the other hand, when the combined fuel injection mode is selected and the intake stroke is selected as the preceding injection timing TP, the fuel injection control means uses the preceding injection timing TPs of the intake stroke and the reference as in the first embodiment. Prior injection amount FPs1 is calculated (steps ST14 and ST15).

  Next, the fuel injection control means according to the second embodiment determines whether or not prior injection has been performed before a predetermined cycle (for example, 1 cycle here), as in the case of performing injection prior to the initial stage of the compression stroke described above. However, if injection has been performed in advance, the maximum in-cylinder pressure increase rate Pr by the previous injection in the previous cycle is compared with the combustion state determination reference value Pr0 (step ST37). The fuel injection control means determines the reference prior injection amount obtained in step ST15 when the maximum in-cylinder pressure increase rate Pr is smaller than the combustion state determination reference value Pr0 or when a negative determination is made in step ST36. FPs1 is set as the injection amount FPs prior to the intake stroke (step ST38). On the other hand, if the maximum in-cylinder pressure increase rate Pr is equal to or greater than the combustion state determination reference value Pr0, the fuel injection control means determines the reduction amount β obtained to avoid steep combustion in the reference prior injection obtained in step ST15. Subtract from the amount FPs1 and set this as the injection amount FPs prior to the intake stroke (step ST39).

  Then, this fuel injection control means executes the prior injection of the intake stroke with the prior injection amount FPs set in step ST38 or step ST39 when the set prior injection timing TPs is reached (step ST40). As a result, even in this multi-fuel internal combustion engine, the fuel injected before the self-ignition burns in the combustion chamber CC after a sufficient time, and the in-cylinder temperature and the in-cylinder pressure are reached by the main injection timing TM. To raise.

  Subsequently, in the second embodiment, the fuel injection control means detects the ignition timing of the previously injected fuel based on the detection signal of the in-cylinder pressure sensor 83, and calculates the maximum in-cylinder pressure increase rate Pr at that time. (Step ST41).

  Further, the fuel injection control means of the second embodiment calculates the main injection timing TM and the main injection amount FM in the same manner as in the first embodiment (steps ST21 and ST22), and when the main injection timing TM is reached. The main injection is executed with the main injection amount FM (step ST23).

  Thus, in this multi-fuel internal combustion engine, as in the first embodiment, the in-cylinder temperature and the in-cylinder pressure are increased by the combustion of the injected fuel by the main injection timing TM, so that the main injection is performed there. Even if the fuel is a fuel with low compression ignitability, it becomes easy to self-ignite, and good compression auto-ignition diffusion combustion can be realized.

  As described above, the multi-fuel internal combustion engine of the second embodiment has a good ignitability with respect to the main injection fuel regardless of whether the main injection fuel itself led into the combustion chamber CC is good or bad in compression ignitability. Therefore, it is possible to operate in a stable compression autoignition diffusion combustion mode in which knocking due to abnormal combustion does not occur. Therefore, the multifuel internal combustion engine of the second embodiment can achieve the same effects as those of the first embodiment, such as improved emission performance and improved sound vibration performance during combustion.

  By the way, also in the multifuel internal combustion engine of the second embodiment, as described in the first embodiment, the compression ignitability of the injected fuel is too low to be self-ignited, or even if self-ignition, the fire is immediately misfired. In this case, the injected fuel may be ignited using the spark plug 71 in advance. In this case, the pre-injected fuel preferably contains highly flammable fuel and has high flammability. Further, in the multi-fuel internal combustion engine of the second embodiment, as described in the first embodiment, a fuel dedicated to injection is prepared in advance in addition to the mixed fuel generated by the fuel mixing means 53. Alternatively, it may be configured to promote ignition of the main injection fuel having low compression ignitability by using flame nuclei or heat generated when the injected fuel is self-ignited or ignited by the spark plug 71 in advance.

  Next, Embodiment 3 of the multifuel internal combustion engine according to the present invention will be described with reference to FIG.

  In each of the first and second embodiments described above, a so-called in-cylinder direct injection multi-fuel internal combustion engine in which the mixed fuel of the first fuel F1 and the second fuel F2 is directly injected into the combustion chamber CC has been illustrated. Shows an example of a multi-fuel internal combustion engine that injects the mixed fuel not only into the combustion chamber CC but also into the intake port 11b.

  For example, this type of multi-fuel internal combustion engine can be configured by replacing the fuel supply device 50 with the fuel supply device 150 shown in FIG. FIG. 10 shows an example based on the multifuel internal combustion engine of the first embodiment.

  Here, the fuel supply device 150 shown in FIG. 10 is a fuel pump 155 that discharges the mixed fuel generated by the fuel mixing means 53 to the fuel passage 154 in addition to the various components of the fuel supply device 50 in the first embodiment. And a delivery passage 156 that distributes the mixed fuel in the fuel passage 154 to each cylinder, and a fuel injection valve 157 for each cylinder that injects the mixed fuel supplied from the delivery passage 156 into the intake port 11b. Is.

  In the multifuel internal combustion engine of the third embodiment, as a basic fuel injection control mode, for example, when operating in the compression auto-ignition diffusion combustion mode, the in-cylinder direct injection fuel injection valve 57 is driven and controlled. The mixed fuel is injected into the combustion chamber CC, and when operating in the premixed spark ignition flame propagation combustion mode, the fuel injection valve 157 for port injection is driven and controlled to inject the mixed fuel into the intake port 11b.

  On the other hand, when the above-described combined fuel injection mode is selected in this multifuel internal combustion engine, both the prior injection and the main injection may be performed by the fuel injection valve 57 for direct in-cylinder injection, and only the prior injection is performed. The fuel injection valve 157 for port injection may be used. The multifuel internal combustion engine is controlled in the same manner as in the first embodiment, and the same effects as those of the multifuel internal combustion engine in the first embodiment can be obtained in any aspect. When the multifuel internal combustion engine according to the second embodiment is used as a base, the same control is performed as in the second embodiment and the same effect is obtained.

  By the way, also in the multifuel internal combustion engine of the third embodiment, as described in the first embodiment, the compression ignitability of the injected fuel is too low to be self-ignited, or even if self-ignition, the misfire immediately occurs. In this case, the injected fuel may be ignited using the spark plug 71 in advance. In this case, the pre-injected fuel preferably contains highly flammable fuel and has high flammability. Further, in the multi-fuel internal combustion engine of the third embodiment, as described in the first embodiment, a fuel dedicated to injection is prepared in advance in addition to the mixed fuel generated by the fuel mixing means 53. Alternatively, it may be configured to promote ignition of the main injection fuel having low compression ignitability by using flame nuclei or heat generated when the injected fuel is self-ignited or ignited by the spark plug 71 in advance.

  Next, Embodiment 4 of the multifuel internal combustion engine according to the present invention will be described with reference to FIG.

  In each of the first and second embodiments described above, the multifuel internal combustion engine operated by introducing the mixed fuel previously mixed by the fuel mixing means 53 into the combustion chamber CC is illustrated. However, in the fourth embodiment, the fuel mixing means An example of a multi-fuel internal combustion engine that can be operated by directing each fuel (first fuel F1 and second fuel F2) individually into the combustion chamber CC without using 53 is illustrated.

  For example, this type of multi-fuel internal combustion engine can be configured by replacing the fuel supply device 50 with the fuel supply device 250 shown in FIG. FIG. 11 shows an example based on the multifuel internal combustion engine of the first embodiment.

  Here, the fuel supply device 250 shown in FIG. 11 includes a first fuel supply unit that directly injects the first fuel F1 into the combustion chamber CC, and a second fuel supply unit that injects the second fuel F2 into the intake port 11b. And. The first fuel supply means sucks up the first fuel F1 from the first fuel tank 41A and sends it to the first fuel passage 51A, and the first fuel F1 in the first fuel passage 51A as high-pressure fuel. A high-pressure fuel pump 255A for pumping the passage 254A, a delivery passage 256A for distributing the first fuel F1 in the high-pressure fuel passage 254A to the respective cylinders, and the first fuel F1 supplied from the delivery passage 256A in the combustion chamber CC And a fuel injection valve 257A for each cylinder that injects into the cylinder. On the other hand, the second fuel supply means sucks up the second fuel F2 from the second fuel tank 41B and sends it to the second fuel passage 51B, and the second fuel F2 in the second fuel passage 51B is supplied to the second fuel pump 51B. A high pressure fuel pump 255B that pumps the fuel to the third fuel passage 254B, a delivery passage 256B that distributes the second fuel F2 in the third fuel passage 254B to the respective cylinders, and an intake of the second fuel F2 that is supplied from the delivery passage 256B. A fuel injection valve 257B for each cylinder that injects into the port 11b.

  For example, the fourth embodiment exemplifies a multi-fuel internal combustion engine in which a fuel having a low compression ignitability represented by gasoline or the like and having a high evaporation property is prepared as the first fuel F1. In this multi-fuel internal combustion engine, normally, the first fuel F1 is directly injected into the combustion chamber CC by the first fuel supply means, and the premixed gas of the first fuel F1 having a high concentration is formed around the spark plug 71. At the same time, a lean premixture is formed around it, and ignition is performed on the rich premixture. That is, this multi-fuel internal combustion engine operates in a premixed spark ignition flame propagation combustion mode by so-called stratified combustion.

  Here, this multi-fuel internal combustion engine causes knocking due to abnormal combustion particularly in a high load region by performing premixed spark ignition flame propagation combustion, and thus it is possible to suppress the occurrence of such knocking. It is preferable to operate at a high load in the compression auto-ignition diffusion combustion mode.

  However, in this multi-fuel internal combustion engine, since the first fuel F1 directly injected into the combustion chamber CC is a fuel having low compression ignitability, it is difficult to perform compression auto-ignition diffusion combustion using the first fuel F1. is there. On the other hand, in this multi-fuel internal combustion engine, second fuel supply means for injecting the second fuel F2 into the intake port 11b and guiding it to the combustion chamber CC is provided.

  Therefore, the multifuel internal combustion engine of the fourth embodiment is based on the same idea as in the first embodiment, and the first fuel having a low compression ignitability in the combustion chamber CC is obtained by injecting the second fuel F2 in advance. The ignitability with respect to F1 is improved, and even if such a first fuel F1 is used, the operation can be performed in the compression self-ignition diffusion combustion mode.

  For example, in the multi-fuel internal combustion engine of the fourth embodiment, as a basic fuel injection control mode, when operating in the compression auto-ignition diffusion combustion mode, only the fuel injection valve 257A for in-cylinder direct injection or both fuels When driving in the premixed spark ignition flame propagation combustion mode by driving and controlling the injection valves 257A and 257B and operating the fuel in the premixed spark ignition flame propagation combustion mode, only the fuel injection valve 257B for port injection or both fuel injection valves 257A, Drive control of 257B guides fuel into the combustion chamber CC. In this multi-fuel internal combustion engine, the fuel injection valves 257A and 257B are arranged so that the optimal fuel mixing ratio of the first fuel F1 and the second fuel F2 in the combustion chamber CC according to the combustion mode and operating conditions. The fuel injection amount is controlled.

  Also in this case, in the multifuel internal combustion engine of the fourth embodiment, the fuel injection control is executed by the electronic control unit 1 as in the flowchart of FIG. 7 of the first embodiment. For this reason, as the second fuel F2 of the fourth embodiment, a low compression ignitable fuel such as alcohol fuel may be used, or a high compression ignitable fuel such as light oil may be used. In the fourth embodiment, step ST3 of the flowchart of FIG. 7 is performed as follows: “The ignitability index values IP of the previously injected fuel (second fuel F2) and the main injected fuel (first fuel F1) guided into the combustion chamber” This is read as “IM detection”. Steps ST5 and ST6 are read as “IM ≧ Is1?” And “IP ≧ Is2?”, Respectively.

  Therefore, in the multifuel internal combustion engine of the fourth embodiment, if the compression ignitability of the second fuel F2 is low, the second fuel F2 is injected in advance at an early stage such as the intake stroke, and the combustion chamber CC is injected during the compression stroke. Self-ignite within. In this multi-fuel internal combustion engine, if the compression ignitability of the second fuel F2 is high, the second fuel F2 is injected prior to the initial stage of the compression stroke or the like and self-ignited in the combustion chamber CC. Note that if the compression ignitability of the second fuel F2 is too low for self-ignition, or if misfiring occurs immediately after self-ignition, the spark plug 71 may be used to ignite the injected fuel in advance. Thereby, in the multifuel internal combustion engine of the fourth embodiment, the in-cylinder temperature and the in-cylinder pressure rise by the main injection timing TM, and the ignitability with respect to the first fuel F1 having low compression ignitability in the combustion chamber CC is increased. As a result, the first fuel F1 is mainly injected and good compression autoignition diffusion combustion can be performed. For this reason, this multi-fuel internal combustion engine can achieve the same effects as those of the first embodiment.

  By the way, also in the multifuel internal combustion engine of the fourth embodiment, as described in the first embodiment, the compression ignitability of the injected fuel (second fuel F2) is too low to be self-ignited or self-ignited. In the case where a misfire immediately occurs, the injected fuel may be ignited using the spark plug 71 in advance. In this case, the prior injected fuel is preferably a highly flammable fuel. Further, in the multi-fuel internal combustion engine of the fourth embodiment, as described in the first embodiment, the flame kernel and the heat generated when the injected fuel self-ignitions or is ignited by the spark plug 71 are used as the fire type. In other words, the main injection fuel (first fuel F1) having a low compression ignitability may be ignited. Further, in the multifuel internal combustion engine of the fourth embodiment, the injected fuel (second fuel F2) is injected into the intake port 11b in advance, and the fuel injection valve 257B for port injection is used for in-cylinder direct injection. Instead of this, it may be configured such that the injected fuel is directly injected into the combustion chamber CC, and in this way, the same effect as described above can be obtained.

  As described above, the multifuel internal combustion engine according to the present invention improves the ignitability of the low compression ignitable fuel in the combustion chamber when operating in the compression autoignition diffusion combustion mode using the low compression ignitable fuel. Useful for technology.

It is a figure shown about the structure of Example 1 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 which shows an example of the fuel injection mode switching condition map data used at the time of switching of fuel injection mode. It is a figure which shows an example of prior injection timing switching condition map data used at the time of switching of prior injection timing. It is a figure which shows an example of the reference leading injection amount selection map data used at the time of selection of the reference leading injection amount. It is a figure which shows an example of the prior injection amount upper limit guard value selection map data used at the time of selection of a prior injection amount upper limit guard value. 3 is a flowchart illustrating a combustion injection control operation in the multifuel internal combustion engine of the first embodiment. It is a figure shown about the structure of Example 2 of the multi-fuel internal combustion engine which concerns on this invention. 7 is a flowchart illustrating a combustion injection control operation in the multifuel internal combustion engine of the second embodiment. It is a figure shown about the structure of Example 3 of the multi-fuel internal combustion engine which concerns on this invention. It is a figure shown about the structure of Example 4 of the multi-fuel internal combustion engine which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electronic controller 16 Crank angle sensor 23 Air flow meter 41A 1st fuel tank 41B 2nd fuel tank 50,150,250 Fuel supply device 57,157,257A, 257B Fuel injection valve 81 Water temperature sensor 82 Intake temperature sensor 83 In-cylinder pressure sensor CC Combustion chamber F1 First fuel F2 Second fuel FM Main injection amount FP, FPc, FPs Prior injection amount FPc1, FPs1 Reference prior injection amount FPc2, FPs2 Prior injection amount upper limit guard value I, IP, IM Ignition index value Is1 First 1 ignitability judgment reference value Is2 second ignitability judgment reference value Kl engine load Ne engine speed Pin intake pressure Pr maximum in-cylinder pressure increase rate Pr0 combustion state judgment reference value ta intake air temperature tw water temperature TM main injection timing TP, TPc, TPs prior injection timing

Claims (9)

In a multi-fuel internal combustion engine in which at least one of at least two types of fuels having different properties is led to a combustion chamber or a mixed fuel composed of the at least two types of fuel is led to a combustion chamber and operated.
Fuel characteristic detection means for detecting an ignitability index value obtained by indexing the compression ignitability of the fuel itself introduced into the combustion chamber;
When performing compression auto-ignition diffusion combustion using the fuel in the combustion chamber determined to be low compression ignitability based on the ignitability index value, the fuel is injected prior to a predetermined time during the period from the intake stroke to the compression stroke. Fuel injection control means for subsequently injecting main fuel and introducing the low compression ignitable fuel into the combustion chamber;
A multi-fuel internal combustion engine characterized by comprising:   The fuel injection control means is configured to inject earlier in the period from the intake stroke to the compression stroke as the ignitability with respect to the fuel injected earlier in the combustion chamber is lower. The multifuel internal combustion engine according to claim 1.   The multi-fuel internal combustion engine according to claim 1 or 2, wherein the fuel injection control means is configured such that the fuel injection amount of the preceding injection is reduced as the intake pressure is lower.   4. The multi-fuel internal combustion engine according to claim 3, wherein the fuel injection control means is configured to lower the upper limit value of the fuel injection amount of the preceding injection as the intake pressure is lower.   5. The multi-fuel internal combustion engine according to claim 1, 2, 3 or 4, wherein the fuel injection control means is configured such that the fuel injection amount of the preceding injection decreases as the engine speed decreases.   6. The multi-fuel internal combustion engine according to claim 5, wherein the fuel injection control means is configured to lower the upper limit value of the fuel injection amount of the preceding injection as the engine speed is lower.   The multifuel internal combustion engine according to any one of claims 1 to 6, wherein the fuel introduced into the combustion chamber is a mixed fuel of gasoline and light oil.   2. The fuel to be pre-injected is a highly flammable fuel, and the fuel injection control means is configured to spark-ignite an air-fuel mixture of the fuel injected in advance and then perform main injection. The multi-fuel internal combustion engine described.   9. The fuel injection control unit according to claim 1, wherein the fuel injection timing of the main injection is controlled to advance when the prior injection is executed. 10. A multi-fuel internal combustion engine as described in 1.

Images