JP2008038843A - Multi-fuel internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain the deterioration in emission performance when an exhaust catalyst device is not activated. <P>SOLUTION: This various-fuel internal combustion engine is operated by introducing at least one kind out of at least two kinds of fuels F1 and F2 different in properties to a combustion chamber CC or introducing mixed fuel composed of at least two kinds of fuels F1 and F2 to the combustion chamber CC, and is provided with a control device (an electronic control device 1) for switching to premixed spark ignition flame propagation combustion mode operation, by increasing an including rate of the highly ignitable fuel F1 in the combustion chamber CC more than the fuel mixing ratio of a premixed spark ignition flame propagation combustion mode when a catalyst of the exhaust catalyst device 72 is an inactive state, and thereafter, increasing an including rate of the highly evaporable fuel F2 in the combustion chamber CC more than the fuel mixing ratio of a compressed self-ignition diffusion combustion mode by starting in the compressed self-ignition diffusion combustion mode. <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, Patent Document 1 below discloses a multi-fuel internal combustion engine that is operated using a mixed fuel of gasoline and light oil. This multi-fuel internal combustion engine increases the mixing ratio of light oil with high ignitability at the time of engine start, and realizes diffusion combustion operation at the time of engine start using the highly ignitable mixed fuel generated thereby.

JP-A-9-68061

  As described above, the multifuel internal combustion engine disclosed in Patent Document 1 improves the ignitability of the fuel in the combustion chamber by using the mixed fuel having high ignitability at the time of starting the engine, and diffusion combustion at the time of starting the engine. Is possible. However, since the combustion temperature in the combustion chamber during diffusion combustion is generally low, when the exhaust catalyst device is not activated, such as during cold start, it takes time to warm up the catalyst and removes harmful components in the exhaust gas. It will be released to the atmosphere as it is.

  Accordingly, an object of the present invention is to provide a multi-fuel internal combustion engine that can improve the disadvantages of the conventional example and suppress the deterioration of the emission performance when the exhaust catalyst device is not activated.

  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, if the catalyst of the exhaust catalyst device is in an inactive state, the content of highly ignitable fuel in the combustion chamber is the fuel mixture ratio in the premixed spark ignition flame propagation combustion mode Start with the compression auto-ignition diffusion combustion mode and then increase the content of highly evaporative fuel in the combustion chamber more than the fuel mixture ratio of the compression auto-ignition diffusion combustion mode, and then premix spark ignition flame propagation combustion mode A control device for switching to operation is provided.

  In the multifuel internal combustion engine according to the first aspect, since the ignitability of the fuel introduced into the combustion chamber is increased at the time of engine start, the startability in the compression autoignition diffusion combustion mode is improved. And this multi-fuel internal combustion engine increases the content ratio of highly ignitable fuel until it switches to the premixed spark ignition flame propagation combustion mode, so that the compression self-ignition diffusion combustion is performed, so that the generation of HC and NOx is suppressed. Can do. On the other hand, since this multi-fuel internal combustion engine subsequently switched to the premixed spark ignition flame propagation combustion mode, the combustion temperature in the combustion chamber becomes higher than that in the compression auto-ignition diffusion combustion mode operation, so the higher temperature exhaust gas As a result, the catalyst temperature of the exhaust catalyst device is rapidly increased, and the HC and NOx generated by the premixed spark ignition flame propagation combustion mode operation can be purified.

  In order to achieve the above object, according to a second aspect of the present invention, in the multifuel internal combustion engine according to the first aspect, a PM collecting device for collecting PM in the exhaust gas is provided on the exhaust passage. Yes.

  Here, during the compression self-ignition diffusion combustion mode operation, PM and smoke are generated as the ignitability of the fuel guided into the combustion chamber increases. Therefore, by providing the PM trapping device on the exhaust passage as in the multifuel internal combustion engine according to the second aspect, it is possible to suppress the release of the PM and smoke into the atmosphere.

  The multi-fuel internal combustion engine according to the present invention improves the startability by the compression auto-ignition diffusion combustion mode operation in which the content ratio of highly ignitable fuel is increased, and also emits when the catalyst of the exhaust catalyst device is in an inactive state Improves performance. Also, in this multi-fuel internal combustion engine, the catalyst temperature of the exhaust catalyst device is rapidly increased by the premixed spark ignition flame propagation combustion mode operation in which the content ratio of highly evaporative fuel is increased thereafter, thereby improving the emission performance early. ing. For this reason, according to the multifuel internal combustion engine of the present invention, it is possible to suppress deterioration of the emission performance when the exhaust catalyst device is not activated as much as possible.

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

  A multifuel internal combustion engine according to a first embodiment of 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 increasing or decreasing the mixing ratio of the first and second fuels F1 and F2 in the fuel mixing means 53 in accordance with 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 (combustion 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. Accordingly, in this multi-fuel internal combustion engine, the combustion gas is discharged from the combustion chamber CC to the exhaust port 11c by opening the exhaust valve 61, and the combustion gas exhaust port is closed by closing the exhaust valve 61. The discharge to 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.

  Further, in the multi-fuel internal combustion engine of the first embodiment, the combustion gas discharged to the exhaust port 11c (hereinafter referred to as “exhaust gas”) is released to the atmosphere via the exhaust passage 71 shown in FIG. . Here, on the exhaust passage 71, an exhaust catalyst device 72 for purifying harmful components in the exhaust gas is disposed. Here, a three-way catalyst having a purification action of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) in the exhaust gas is exemplified as the exhaust catalyst device 72.

  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 having excellent ignitability as described below when performing diffusion combustion, and such a fuel with good ignitability does not have to wait for the entire injection amount to be injected. It will ignite by itself at the air fuel ratio suitable for combustion. For this reason, in this compression self-ignition diffusion combustion mode, the fuel of the air-fuel ratio part suitable for combustion self-ignites first, and the flame formed thereby gradually advances the combustion while entraining the remaining fuel and air. Let

  In order to operate in this compressed self-ignition diffusion combustion mode, a fuel with good ignitability whose ignition point is lower than the compression heat of compressed air is usually required. For example, light oil or dimethyl ether can be considered as the fuel with good 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 ignitability can also be used for fuel with good ignitability. Such a fuel with good 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. 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 excessively concentrated region of fuel when performing compression auto-ignition diffusion combustion, and contributes to suppression of PM, smoke, NOx, and unburned HC. As such highly evaporable fuel, in addition to gasoline, GTL fuel produced as a highly evaporable property, 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 81 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. This spark plug 81 performs spark ignition at the ignition timing according to the operating conditions in the premixed spark ignition flame propagation combustion mode 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 ignitability but also high evaporability, so that the fuel introduced into the combustion chamber CC can be used. Since evaporability is enhanced and mixing with air is promoted, the fuel rich region can be reduced, and the amount of PM and smoke generated 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, fuel with high ignitability and low evaporability (first fuel F1) is stored in the first fuel tank 41A, and fuel with low ignitability and high evaporability (second fuel F2) is stored in the second fuel tank 41B. It illustrates about the case where it is made to store. 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 ignitable if the fuel mixing ratio of the first fuel F1 is large. However, if the fuel mixing ratio of the second fuel F2 is large, the ignitability is poor and the fuel characteristic is good. 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. 5 to be described later, the fuels F1 and F2 supplied are 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 and the fuel characteristics are inferior in evaporation. If the supply ratio of the second fuel F2 is large, the fuel characteristics are inferior in ignition characteristics and good in evaporation characteristics. Become.

  On the other hand, when operating in the compression auto-ignition diffusion combustion mode, there is an adverse effect that the amount of HC generated increases as the evaporability of the fuel guided into the combustion chamber CC increases. There is also concern about an increase in the amount of NOx generated due to the steep combustion accompanying the decrease in ignitability. Normally, the HC and NOx are discharged together with the exhaust gas to the exhaust passage 71 and purified by the above-described exhaust catalyst device 72 to suppress release into the atmosphere. However, in order for the exhaust catalyst device 72 to perform the purification action of HC or the like, the catalyst temperature must reach the activation temperature. In this case, the HC or the like is not purified but is released to the atmosphere as it is. Will be.

  Thus, when the compression auto-ignition diffusion combustion mode is selected when the catalyst of the exhaust catalyst device 72 is in an inactive state, if the content ratio of the first fuel F1 in the combustion chamber CC is increased, generation of HC and NOx is generated. While the generation amount of PM and smoke is increased, if the content ratio of the second fuel F2 is increased, the generation amount of PM and smoke is suppressed, but the generation amount of HC and NOx is increased. Will be.

  By the way, in recent years, there is a PM trapping device called DPF (Diesel Particulate Filter) that can suppress the release of PM and smoke into the atmosphere, and the content ratio of the highly fuelable second fuel F2 has been increased. It is possible to suppress the release of PM or the like into the atmosphere without increasing it. For this reason, in the multifuel internal combustion engine of the first embodiment, the PM trapping device is mounted on the vehicle to suppress the release of PM and smoke into the atmosphere. For example, the PM collection device is prepared as an exhaust catalyst device 72 with a PM collection device included in the exhaust catalyst device 72.

  Therefore, in this multi-fuel internal combustion engine, even if the catalyst of the exhaust catalyst device 72 is in an inactive state, if the content ratio of the first fuel F1 having high ignitability is increased and compression self-ignition diffusion combustion is performed, HC and NOx are generated. It becomes possible to keep itself low. However, even if this is done, the amount of HC and NOx generated cannot be completely eliminated. Depending on the catalyst temperature of the exhaust catalyst device 72, the slightly generated HC and NOx are released into the atmosphere together with the exhaust gas. End up. In particular, after the cold start, since it takes time to raise the catalyst temperature to the activation temperature, the amount of HC and NOx discharged into the atmosphere increases. For this reason, in order not to release the generated HC or the like to the atmosphere, it is necessary to raise the catalyst temperature of the exhaust catalyst device 72 to the activation temperature at an early stage.

  Here, in general, the combustion temperature in the combustion chamber CC is higher during premixed spark ignition flame propagation combustion than during compression self-ignition diffusion combustion. Therefore, in order to increase the catalyst temperature of the exhaust catalyst device 72 early, it is preferable to operate the multi-fuel internal combustion engine in the premixed spark ignition flame propagation combustion mode.

  Therefore, in the first embodiment, if the catalyst of the exhaust catalyst device 72 is in an inactive state, the content ratio of the first fuel F1 having high ignitability is set to the fuel mixture ratio in the premixed spark ignition flame propagation combustion mode. To increase the content ratio of the highly evaporable second fuel F2 compared to the fuel mixture ratio of the compression auto-ignition diffusion combustion mode, and then the premixed spark. Operate in ignition flame propagation combustion mode. Hereinafter, such an operation mode is referred to as “catalyst warm-up operation mode” with respect to the normal operation mode. Therefore, in the first embodiment, the electronic control unit 1 is configured so that the normal operation mode and the catalyst warm-up operation mode are selectively used according to whether or not the catalyst of the exhaust catalyst device 72 is in an active state. The normal operation mode refers to, for example, an operation mode performed using the combustion mode map data of FIG. 2 described above.

  Here, whether or not the catalyst of the exhaust catalyst device 72 is in an active state may be determined by directly detecting the catalyst temperature or the catalyst carrier temperature with a temperature sensor (not shown), but here it is detected from the water temperature sensor 17. Judgment is made using the cooling water temperature Tw. For example, the temperature of the exhaust gas and the wall surface temperature in the combustion chamber CC change in response to an increase or decrease in the combustion temperature in the combustion chamber CC, and the exhaust catalyst device 72 changes in response to the temperature change of the exhaust gas. While the catalyst temperature changes, the coolant temperature Tw changes according to the wall temperature change in the combustion chamber CC. Therefore, a correlation can be found between the catalyst temperature of the exhaust catalyst device 72 and the cooling water temperature Tw, and if the cooling water temperature Tw can be grasped, the catalyst temperature of the exhaust catalyst device 72 can be estimated. Therefore, here, the cooling water temperature Tw that can be obtained from the existing water temperature sensor 17 without using a new temperature sensor is used, and this is compared with the threshold value Tw0 to determine whether the catalyst of the exhaust catalyst device 72 is in an active state. Judge whether or not. The threshold value Tw0 sets a cooling water temperature corresponding to a boundary temperature between an active state and an inactive state in the catalyst of the exhaust catalyst device 72.

  An example of the operation of the multifuel internal combustion engine of the first embodiment will be described below based on the flowchart of FIG.

  First, the detection signal of the water temperature sensor 17 is sent to the electronic control unit 1 of the first embodiment, and the cooling water temperature Tw of the multifuel internal combustion engine is input (step ST1). And this electronic control unit 1 compares the cooling water temperature Tw and threshold value Tw0 (step ST2), and selects the operation mode according to the result.

  Here, if the coolant temperature Tw is lower than the threshold value Tw0, the electronic control unit 1 determines that the catalyst of the exhaust catalyst device 72 is not in an active state and selects the catalyst warm-up operation mode (step ST3). Then, it is determined whether or not it is within t1 seconds after the engine start (in other words, whether or not it is from before the engine start to immediately after the engine start) (step ST4). For example, the predetermined time t1 seconds may be a momentary time until the start of the multifuel internal combustion engine with emphasis on starting the multifuel internal combustion engine, but switching to the premixed spark ignition flame propagation combustion mode. In consideration of later emission performance, it is preferable to set the time until the catalyst temperature of the exhaust catalyst device 72 approaches the activation temperature to some extent. Here, the latter time is set in advance as a predetermined time t1 seconds based on the experimental results and the simulation results. For the reason of the latter, the comparison determination target here is not the predetermined time t1 seconds but the catalyst temperature or the cooling water temperature Tw of the exhaust catalyst device 72 corresponding thereto. Is possible.

  When it is determined in step ST4 that it is within t1 seconds after the engine is started, the fuel mixing control means of the electronic control unit 1 includes the content ratio (mixing ratio) of the first fuel F1 having high ignitability in the combustion chamber CC. The first feed pump 52A, the second feed pump 52B, and the fuel mixing means 53 are driven and controlled so as to increase (step ST5). And the combustion mode setting means of this electronic control unit 1 selects the compression auto-ignition diffusion combustion mode (step ST6). These steps ST5 and ST6 are repeated until a negative determination is made in step ST2 or step ST4.

  Here, the content ratio of the first fuel F1 may be set so that at least the mixed fuel can be ignited in compressed air and then has an ignitability sufficient to allow diffusion combustion, and even if it is increased to a maximum of 100%. Good. Therefore, here, the content ratio of the first fuel F1 is made larger than the content ratio of the second fuel F2, but if good compression autoignition diffusion combustion is possible, the first fuel F1 As a result of increasing the content ratio compared to the fuel mixture ratio in the premixed spark ignition flame propagation combustion mode, the content ratio of the second fuel F2 may be increased.

  As a result, when the engine is started, the engine is started in the compression auto-ignition diffusion combustion mode using a mixed fuel having a high content of highly ignitable fuel (first fuel F1) and high ignitability. For example, the fuel cell is operated in the compression auto-ignition diffusion combustion mode using the highly ignitable mixed fuel. Therefore, generation of HC and NOx is suppressed in the combustion chamber CC at that time. On the other hand, since the evaporability of the mixed fuel used is low at that time, the amount of PM and smoke generated increases. It is collected. Therefore, the multifuel internal combustion engine of the first embodiment has improved startability and can suppress emission of harmful components in the exhaust gas to the atmosphere during the period from the start of the engine to immediately after the start of the engine.

  On the other hand, when it is determined in step ST4 that t1 seconds have elapsed after engine startup, the electronic control unit 1 determines whether it is within t2 (> t1) seconds after engine startup (step ST7). For example, for the predetermined time t2 seconds, it is preferable to set the time until the catalyst temperature of the exhaust catalyst device 72 reaches the activation temperature. The predetermined time t2 seconds is set in advance based on experimental results and simulation results. As in the case of the predetermined time t1 seconds described above, the comparison determination target here is not the predetermined time t2 seconds but the catalyst temperature and the cooling water temperature Tw of the exhaust catalyst device 72 corresponding thereto. It can also be used.

  If it is determined in step ST7 that it is within t2 seconds after the engine is started, the fuel mixing control means of the electronic control unit 1 contains the content ratio (mixing) of the second fuel F2 having high evaporability in the combustion chamber CC. The first feed pump 52A, the second feed pump 52B and the fuel mixing means 53 are driven and controlled so that the ratio) increases (step ST8). And the combustion mode setting means of this electronic control unit 1 selects the premixed spark ignition flame propagation combustion mode (step ST9). These steps ST8 and ST9 are repeated until a negative determination is made in step ST2 or step ST7.

  Here, the content ratio of the second fuel F <b> 2 may be set so as to have evaporability that can propagate the flame kernel generated by ignition, for example, and may be increased to a maximum of 100%. Therefore, here, the content ratio of the second fuel F2 is larger than the content ratio of the first fuel F1, but if the premixed spark ignition flame propagation combustion is possible, the second fuel F2 As a result of increasing the content ratio of F2 compared to the fuel mixture ratio in the compression auto-ignition diffusion combustion mode, the content ratio of the first fuel F1 may be increased.

  Thereby, in the multi-fuel internal combustion engine of the first embodiment, the operation is performed by switching to the premixed spark ignition flame propagation combustion mode having a higher combustion temperature than the operation in the compression auto-ignition diffusion combustion mode. Flows into the exhaust catalyst device 72 and quickly raises the catalyst temperature. Accordingly, in the exhaust catalyst device 72, since the catalyst rapidly rises to the activation temperature, HC and NOx generated in the combustion chamber CC by the operation in the premixed spark ignition flame propagation combustion mode can be purified.

  By the way, the electronic control unit 1 of the first embodiment is determined in step ST2 that the cooling water temperature Tw is a high temperature equal to or higher than the threshold value Tw0 or in step ST7 that it has exceeded t2 seconds after the engine is started. In this case, it is determined that the catalyst of the exhaust catalyst device 72 has reached the active state, the normal operation mode is selected (step ST10), and the operation is performed according to this.

  As described above, in the multifuel internal combustion engine of the first embodiment, the startability is improved and the exhaust catalyst is improved by the compression auto-ignition diffusion combustion mode operation in which the content ratio of the highly ignitable fuel (first fuel F1) is increased. The emission performance when the catalyst of the device 72 is in an inactive state is improved. Further, in this multi-fuel internal combustion engine, the catalyst temperature of the exhaust catalyst device 72 is rapidly increased by the premixed spark ignition flame propagation combustion mode operation in which the content ratio of the highly evaporative fuel (second fuel F2) is increased thereafter, Emission performance is improved early.

  Here, the multifuel internal combustion engine generates HC and NOx along with the premixed spark ignition flame propagation combustion mode operation until the catalyst of the exhaust catalyst device 72 reaches the activation temperature. However, the catalyst of the exhaust catalyst device 72 is not necessarily able to purify any harmful components in the exhaust gas unless the activation temperature is reached, and exhibits a purification action even if it is somewhat weaker if it is close to the activation temperature to some extent. be able to. For this reason, in the multifuel internal combustion engine of the first embodiment, HC and NOx generated during that time can be purified by the catalyst of the exhaust catalyst device 72 as much as possible.

  Therefore, according to the multifuel internal combustion engine of the first embodiment, it is possible to minimize the deterioration of the emission until the catalyst of the exhaust catalyst device 72 in the inactive state becomes active.

  By the way, although the multifuel internal combustion engine of the first embodiment has been illustrated with respect to the control mode at the time of cold start, for example, the catalyst temperature of the exhaust catalyst device 72 is lower than the activation temperature during normal operation. It may be applied to the case where it has been done.

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

  In the first embodiment described above, a so-called in-cylinder direct injection multi-fuel internal combustion engine that directly injects the mixed fuel of the first fuel F1 and the second fuel F2 into the combustion chamber CC is illustrated. An example of a multi-fuel internal combustion engine configured to inject mixed fuel not only into the combustion chamber CC but also into the intake port 11b will be described. 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. 4 in the multi-fuel internal combustion engine of the first embodiment.

  The fuel supply device 150 shown in FIG. 4 includes a fuel pump 155 for discharging 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, 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 of each cylinder. It is a thing.

  For example, in this multi-fuel internal combustion engine, when operating in the compression auto-ignition diffusion combustion mode, the fuel injection valve 57 is driven and controlled to inject the mixed fuel into the combustion chamber CC, and the premixed spark ignition flame propagation combustion mode. It is assumed that the fuel injection valve 157 is driven and controlled to inject the mixed fuel into the intake port 11b when operating at. Therefore, in the multi-fuel internal combustion engine of the second embodiment, when the catalyst of the exhaust catalyst device 72 is in an inactive state, the mixed fuel with a high content ratio of the highly ignitable fuel (first fuel F1) is used as the fuel injection valve. The fuel is directly injected into the combustion chamber CC from 57 and started in the compression auto-ignition diffusion combustion mode. On the other hand, after that, in this multi-fuel internal combustion engine, a mixed fuel having a high content of highly evaporative fuel (second fuel F2) is injected from the fuel injection valve 157 to the intake port 11b, and premixed spark ignition flame propagation combustion is performed. Drive in mode. As a result, the multifuel internal combustion engine of the second embodiment minimizes the deterioration of the emission until the catalyst of the exhaust catalyst device 72 in the inactive state becomes active as in the first embodiment. To the limit. In addition, PM and smoke generated during the compression auto-ignition diffusion combustion mode operation are collected by the PM collection device included in the exhaust catalyst device 72 before being released into the atmosphere, as in the first embodiment.

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

  In the first embodiment described above, a multi-fuel internal combustion engine in which the mixed fuel of the first fuel F1 and the second fuel F2 previously mixed by the fuel mixing means 53 is injected from the fuel injection valve 57 into the combustion chamber CC is illustrated. In the above-described second embodiment, the mixed fuel is illustrated as being injected into the combustion chamber CC and the intake port 11b from the two fuel injection valves 57 and 157, respectively. An example of a multi-fuel internal combustion engine configured to inject the first fuel F1 and the second fuel F2 separately without using the fuel mixing means 53 will be described. 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. 5 in the multi-fuel internal combustion engine of the first embodiment.

  The fuel supply device 250 shown in FIG. 5 includes a first fuel supply means for directly injecting the first fuel F1 (fuel having high ignitability and low evaporability) into the combustion chamber CC, and the second fuel F2 to the intake port 11b. Second fuel supply means for injecting (a highly evaporable and low ignitable fuel). 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 251A, and the first fuel F1 in the first fuel passage 251A as the high-pressure fuel. A high pressure fuel pump 255A for pumping to the passage 254A, a first delivery passage 256A for distributing the first fuel F1 in the high pressure fuel passage 254A to the respective cylinders, and a first fuel F1 supplied from the first delivery passage 256A And a fuel injection valve 257A for each cylinder that injects into the combustion chamber CC. On the other hand, the second fuel supply means sucks the second fuel F2 from the second fuel tank 41B and sends it to the second fuel passage 251B, and the second fuel F2 in the second fuel passage 251B, respectively. A second delivery passage 256B that distributes to the cylinders, and a fuel injection valve 257B for each cylinder that injects the second fuel F2 supplied from the second delivery passage 256B into the intake port 11b.

  For example, in this multi-fuel internal combustion engine, when operating in the compression auto-ignition diffusion combustion mode, only the fuel injection valve 257A or both the fuel injection valves 257A and 257B are driven and controlled, and the fuel is led into the combustion chamber CC. When operating in the premixed spark ignition flame propagation combustion mode, only the fuel injection valve 257B or both fuel injection valves 257A and 257B are driven and controlled to guide the fuel into the combustion chamber CC. At this time, in this multi-fuel internal combustion engine, the fuel injection valves 257A and 257B are driven and controlled so that the set fuel mixture ratio is obtained. Therefore, in the multifuel internal combustion engine of the third embodiment, only the fuel injection valve 257A is used so that the content ratio of the highly ignitable fuel (first fuel F1) increases when the catalyst of the exhaust catalyst device 72 is in an inactive state. Alternatively, fuel is injected from both fuel injection valves 257A and 257B and started in the compression auto-ignition diffusion combustion mode. On the other hand, after that, in this multifuel internal combustion engine, fuel is injected from only the fuel injection valve 257B or both of the fuel injection valves 257A and 257B so as to increase the content ratio of the highly evaporative fuel (second fuel F2), and premixed. Operate in spark ignition flame propagation combustion mode. As a result, in the multifuel internal combustion engine of the third embodiment, as in the first and second embodiments, the emission is deteriorated until the catalyst of the exhaust catalyst device 72 in the inactive state becomes active. Can be minimized. In addition, PM and smoke generated during the compression auto-ignition diffusion combustion mode operation are collected by the PM collection device included in the exhaust catalyst device 72 before being released into the atmosphere, as in the first embodiment.

  Next, a fourth embodiment of the multifuel internal combustion engine according to the present invention will be described.

  In each of the first to third embodiments described above, the exhaust catalyst device 72 with the PM trapping device is illustrated as an example. However, in the multifuel internal combustion engine, the PM trapping device is not necessarily provided on the exhaust passage 71. Not necessarily. Therefore, the fourth embodiment is configured so that the release of PM and smoke into the atmosphere during the compression auto-ignition diffusion combustion mode operation can be suppressed without providing a PM trap.

  First, the multi-fuel internal combustion engine of the fourth embodiment is constructed with the same components as those of the multi-fuel internal combustion engines of the first to third embodiments, except that the PM trapping device does not exist. Can do.

  In the multi-fuel internal combustion engine having such a configuration, in order to suppress the release of PM and smoke during the compression auto-ignition diffusion combustion mode operation, as described in the above-described first embodiment, What is necessary is just to increase the content rate of the 2nd fuel F2 with high evaporability. However, on the other hand, since the ignitability of the fuel guided into the combustion chamber CC decreases, self-ignition in compressed air becomes impossible or it does not reach a state where self-ignition is impossible. The amount of NOx generated increases due to steep combustion.

  Therefore, also in the fourth embodiment, when the catalyst of the exhaust catalyst device 72 is in an inactive state, the content ratio of the first fuel F1 is increased as compared with the fuel mixture ratio in the premixed spark ignition flame propagation combustion mode, Although the engine is started by compression auto-ignition diffusion combustion, in the fourth embodiment, the degree of increase is lowered to a level that can suppress the generation of PM and smoke. In the fourth embodiment, in order to compensate for the ignitability of the fuel introduced into the combustion chamber CC, which has been lowered by this, the compression auto-ignition diffusion combustion (hereinafter referred to as “spark”) while assisting ignition by spark ignition of the spark plug 81. Assisted compression self-ignition diffusion combustion ”).

  That is, in the multi-fuel internal combustion engine of the fourth embodiment, when the catalyst of the exhaust catalyst device 72 is in an inactive state, the fuel mixture ratio in the premixed spark ignition flame propagation combustion mode is considered while considering the generation of PM and smoke. The content ratio of the highly ignitable fuel (first fuel F1) in the combustion chamber CC is increased as compared with the time of, and the engine is started in the spark assist compression self-ignition diffusion combustion mode. On the other hand, thereafter, in this multifuel internal combustion engine, the content ratio of the highly evaporative fuel (second fuel F2) is increased and the premixed spark ignition flame propagation combustion is performed as in the case of each of the first to third embodiments. Drive in mode. Thereby, the multifuel internal combustion engine of the fourth embodiment minimizes the deterioration of the emission until the catalyst of the exhaust catalyst device 72 in the inactive state becomes active, as in the first to third embodiments. To the limit.

  As described above, the multi-fuel internal combustion engine according to the present invention is a catalyst for the exhaust catalyst device 72 while ensuring good emission performance when operating using at least a highly ignitable fuel and a highly evaporable fuel. It is useful for the technology which activates early.

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 the combustion mode at the time of normal operation mode. 3 is a flowchart for explaining the operation of 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. It is a figure shown about the structure of Example 3 of the multi-fuel internal combustion engine which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electronic controller 17 Water temperature sensor 41A 1st fuel tank 41B 2nd fuel tank 50,150,250 Fuel supply apparatus 57,157,257A, 257B Fuel injection valve 72 Exhaust catalyst apparatus 81 Spark plug CC Combustion chamber F1 1st fuel F2 Second fuel Tw Cooling water temperature

Claims (2)

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.
If the catalyst of the exhaust catalyst system is in an inactive state, the content ratio of highly ignitable fuel in the combustion chamber is increased compared to the fuel mixture ratio in the premixed spark ignition flame propagation combustion mode, and the engine is started in the compression autoignition diffusion combustion mode. After that, a control device is provided in which the content ratio of the highly evaporative fuel in the combustion chamber is increased compared to the fuel mixture ratio in the compression auto-ignition diffusion combustion mode and the operation is switched to the premixed spark ignition flame propagation combustion mode operation. A multi-fuel internal combustion engine.   The multifuel internal combustion engine according to claim 1, wherein a PM trapping device for trapping PM in the exhaust gas is provided on the exhaust passage.

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