JP2005232997A - Fuel injection control method for mixed fuel direct injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the build-up of deposits on a jet portion of a fuel injection valve even when using mixed fuel different in alcohol concentration. <P>SOLUTION: An alcohol concentration sensor is used for calculating the nature of fuel, and a fuel injection amount is controlled corresponding to the nature of the fuel (Steps S10, 11). The upper limit temperature of the jet portion of an injector is estimated from th nature of the fuel, and the temperature of the jet portion is estimated from a current operated condition with a map (Steps S12, 13). When the estimated temperature of the jet portion exceeds the upper limit temperature (NO in Step S14) and a cumulative time for fuel injection performed in the condition of exceeding the upper limit temperature exceeds a preset time (YES in Steps S16, 17), fuel injection pressure is made greater under homogeneous combustion than in normal injection to clean deposits in an initial built-up condition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel injection control method for a mixed fuel direct injection engine. More specifically, even when mixed fuels having different alcohol concentrations are used, it is possible to suppress deposit adhesion on a nozzle portion of a fuel injection valve. The present invention relates to a fuel injection control method for a mixed fuel direct injection engine.

  2. Description of the Related Art Various types of fuel injection valves are provided in which an injection hole portion faces a combustion chamber of an internal combustion engine (hereinafter referred to as an engine) and fuel is directly injected into the combustion chamber. Then, the generation and deposition of deposits on the inner surface of the nozzle nozzle are suppressed by adjusting the temperature at the nozzle tip of the fuel injection valve to 90% or less of the fuel distillation temperature (hereinafter referred to as T90). A technique has been proposed (see, for example, Patent Document 1).

  By the way, in recent years, from the viewpoint of environmental protection, the use of alcohol, which is a biofuel, is increasing, and in particular, mixing with gasoline, which is a basic fuel, has been promoted. Various engine developments are also underway.

  Since the evaporation temperature of alcohol fuel is low, when it is mixed with gasoline fuel, which is the basic fuel, the distillation temperature of the mixed fuel is lower than that of gasoline fuel alone and evaporates easily, and also varies depending on the alcohol concentration. . In addition, since the concentration regulation of alcohol / gasoline mixed fuel has not been established, the actual situation is that the fuel properties vary greatly depending on the region.

  When the temperature of the nozzle part at the tip of the fuel injection valve becomes higher than the above T90, most of the fuel remaining in the nozzle part evaporates, so it is considered that the precursor that becomes the nucleus for deposit formation aggregates on the inner wall surface of the nozzle part. . The precursor in such a state is difficult to be washed away at the time of the next fuel injection, and remains in the injection hole portion, so that deposit deposition proceeds. When deposit accumulation progresses at the nozzle part of the fuel injection valve, the fuel injection amount decreases and the air-fuel ratio shifts, causing a decrease in output, and in the worst case, fuel injection may be impossible.

  In view of this, it is conceivable to apply a technique according to Patent Document 1 to an in-cylinder direct injection engine that uses alcohol and gasoline as a mixed fuel, thereby suppressing deposit adhesion to the nozzle portion of the fuel injection valve.

Japanese Patent Laid-Open No. 10-89192

  However, when the prior art according to Patent Document 1 is applied to an in-cylinder direct injection engine that uses alcohol and gasoline as a mixed fuel, the T90 of this mixed fuel is lower than that of gasoline alone, and also depending on the alcohol concentration. Since the distillation characteristics are different, there is a possibility that the temperature of the nozzle part of the fuel injection valve cannot be adjusted to T90 or less depending on the alcohol concentration. That is, depending on the alcohol concentration, there has been a problem that the amount of deposit deposited on the nozzle port of the fuel injection valve increases and the fuel injection amount decreases, which may hinder proper fuel injection.

  The present invention has been made in view of the above, and even when mixed fuels having different alcohol concentrations are used, the mixed fuel direct injection that can suppress deposit adhesion to the injection port portion of the fuel injection valve. It is an object of the present invention to provide an engine fuel injection control method.

  In order to solve the above-described problems and achieve the object, a fuel injection control method for a mixed fuel direct injection engine according to claim 1 of the present invention uses a fuel injection valve to mix a mixed fuel in which alcohol is mixed with basic fuel. A mixed fuel direct injection engine that directly injects into the cylinder, an alcohol concentration detection means that detects an alcohol concentration in the mixed fuel, a nozzle part temperature detection means that detects or estimates the temperature of the nozzle part of the fuel injection valve, The injection port upper limit temperature calculation means for calculating the upper limit temperature of the fuel injection valve injection port portion where deposit adhesion is expected based on the alcohol concentration detected by the alcohol concentration detection means, and the fuel injection pressure is set higher than that during normal injection. A fuel injection control method for a mixed fuel direct injection engine having a fuel injection pressure increasing means for increasing, wherein the fuel injection pressure detecting means is detected by the nozzle temperature detecting means or When the determined temperature exceeds the upper limit temperature calculated by the nozzle part upper limit temperature calculating means, the fuel injection pressure is increased by the fuel injection pressure increasing means under the homogeneous combustion control from that during normal injection. It is characterized by.

  According to a second aspect of the present invention, there is provided a fuel injection control method for a mixed fuel direct injection engine according to the first aspect, wherein the nozzle upper limit temperature calculated by the nozzle upper limit temperature calculating means is the alcohol The alcohol concentration detected by the concentration detection means is the 90% distillation temperature of the mixed fuel or the temperature converted by multiplying the 90% distillation temperature by a predetermined coefficient.

  According to a third aspect of the present invention, there is provided a fuel injection control method for a mixed fuel direct injection engine according to the first or second aspect, wherein the temperature detected or estimated by the nozzle part temperature detecting means is the nozzle. The time of fuel injection performed in a state exceeding the upper limit temperature calculated by the part upper limit temperature calculating means is accumulated, and when the accumulated time exceeds a predetermined time, the fuel injection pressure is increased by the fuel injection pressure increasing means. It is characterized in that it is increased as compared with normal injection.

  According to a fourth aspect of the present invention, there is provided a fuel injection control method for a mixed fuel direct injection engine according to any one of the first to third aspects, wherein the nozzle portion temperature detecting means includes an engine load and an engine. The temperature of the fuel injection valve nozzle is estimated based on the rotational speed.

  According to a fifth aspect of the present invention, there is provided a fuel injection control method for a mixed fuel direct injection engine according to any one of the first to third aspects, wherein the injection hole temperature detecting means is a temperature sensor. The temperature of a fuel injection valve nozzle part is detected.

  According to the fuel injection control method for a mixed fuel direct injection engine according to the present invention (Claim 1), even when mixed fuels having different alcohol concentrations are used, deposits adhere to the nozzle portion of the fuel injection valve. Accumulation can be suppressed, and a decrease in fuel injection amount can be suppressed. Therefore, it is possible to suppress the occurrence of problems such as a deviation in the air-fuel ratio or the inability to inject fuel.

  Further, according to the fuel injection control method for a mixed fuel direct injection engine according to the present invention (Claim 2), the temperature at which the precursor that is the nucleus of deposit generation aggregates on the inner wall surface of the nozzle part is set as the nozzle part upper limit temperature. And the start of deposit generation can be effectively suppressed.

  Further, according to the fuel injection control method for a mixed fuel direct injection engine according to the present invention (claim 3), the frequency of increasing the fuel injection pressure can be reduced, and the load of the fuel injection pressure increasing means can be reduced. it can.

  Further, according to the fuel injection control method for a mixed fuel direct injection engine according to the present invention (Claim 4), the temperature of the fuel injection valve nozzle can be estimated based on the actual operating state of the engine, and the deposit The generation / attachment conditions can be determined in detail.

  Further, according to the fuel injection control method for a mixed fuel direct injection engine according to the present invention (Claim 5), since the tip temperature of the fuel injection valve is measured by the temperature sensor, compared to the case of estimating the temperature. Further, it is possible to carry out more precise deposit adhesion suppression control.

  Embodiments of a fuel injection control method for a mixed fuel direct injection engine according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  First, the schematic configuration of an engine to which the present invention is applied and its fuel supply system will be described with reference to FIGS. Here, FIG. 2 is a sectional view showing a schematic configuration of the engine, and shows one cylinder. FIG. 3 is a schematic diagram showing a fuel supply system of an engine, and shows a four-cylinder engine as an example.

  As shown in FIG. 2, the engine (mixed fuel direct injection engine) 10 directly injects fuel, in which alcohol is mixed with gasoline, which is a basic fuel, from the injection port portion 23 a of the injector (fuel injection valve) 23 into the combustion chamber 10 a. Direct injection type. A combustion chamber 10 a of the engine 10 is configured by a cylinder bore 11, a cylinder head 13, and a piston 12 that is reciprocally disposed in the cylinder bore 11. A concave cavity 12a is formed in the intake side portion of the top surface of the piston 12 in order to establish stratified combustion.

  A spark plug 14 for igniting the air-fuel mixture is disposed substantially at the center of the combustion chamber 10a. An intake valve 16 is disposed at the intake port 15 facing the combustion chamber 10a, and an exhaust valve 20 is disposed at the exhaust port 18 facing the combustion chamber 10a. The injector 23 is disposed in the vicinity of the intake valve 16 in the combustion chamber 10a.

  Further, as shown in FIG. 3, the fuel tank 29 is for storing gasoline fuel mixed with alcohol (hereinafter simply referred to as fuel). The fuel tank 29 and the delivery pipe 33 of the engine 10 are connected by a fuel supply pipe (fuel supply system) 30 and a return pipe 31.

  The fuel supply pipe 30 is provided with a pump 32a for supplying fuel to the delivery pipe 30 and a pressure sensor 32c for detecting fuel pressure. The pump (fuel injection pressure increasing means) 32b boosts the fuel to a predetermined pressure capable of in-cylinder injection during normal operation and supplies it to the delivery pipe 33, and at the time of deposit cleaning control described later, the fuel injection pressure is higher than during normal injection. It is for increasing.

  The delivery pipe 33 is for distributing the pressurized fuel to the injectors 23. The delivery pipe 33 is a pressure sensor 33a for detecting the pressure in the delivery pipe 33 or a known alcohol concentration sensor (alcohol for detecting alcohol concentration). Density detecting means) 33b.

  As the alcohol concentration sensor 33b, for example, a known electrostatic capacitance type alcohol concentration sensor can be used. That is, the alcohol concentration sensor 33b utilizes the fact that the dielectric constant of the mixed fuel differs according to the alcohol concentration of the mixed fuel, and passes the mixed fuel between the electrode plates to measure the capacitance between the electrodes. Thus, the alcohol concentration of the mixed fuel is measured. Further, the alcohol concentration sensor 33 b can be provided in the fuel tank 29 or the fuel supply pipe 30.

  The engine 10 described above is basically controlled by an electronic control unit (hereinafter referred to as ECU) (not shown) on the basis of various sensor information in the same manner as an engine using gasoline alone as a fuel, and to the nozzle part 23a of the injector 23. In order to suppress the deposit adhesion, fuel injection is controlled as follows based on sensor information such as the pressure sensors 32c and 33a and the alcohol concentration sensor 33b.

  The ECU is a means for executing basic control of the engine 10, and deposit attachment based on the nozzle part temperature detecting means for estimating the temperature of the nozzle part 23 a of the injector 23 and the alcohol concentration detected by the alcohol concentration sensor 33 b. It is also provided with a nozzle upper limit temperature calculating means for calculating and estimating the upper limit temperature of the nozzle hole 23a of the injector 23.

  Next, the fuel injection control method according to the first embodiment will be described with reference to FIG. In that case, FIG. 2 and FIG. 3 are referred suitably. Here, FIG. 1 is a flowchart showing a fuel injection control method for the direct injection engine according to the first embodiment of the present invention.

  First, the property of the mixed fuel is calculated using the alcohol concentration sensor 33b (step S10). Then, the fuel injection amount (fuel injection time) is corrected and adjusted according to the calculated fuel property (step S11).

  In addition, the upper limit temperature of the tip temperature (injection port 23a) of the injector 23 is estimated from the fuel properties based on the map shown in FIG. 4 (step S12). Here, FIG. 4 is an example of a map showing the relationship between the alcohol concentration and the upper limit temperature at the tip of the injector 23 where deposits are expected to be deposited. The fuel properties (alcohol concentration) and the distillation characteristics of the fuel are experimentally determined in advance. (T90) and is stored in the ECU. By using such a map, it is possible to set the temperature at which the precursor, which is the nucleus for deposit generation, agglomerates on the inner wall surface of the nozzle part 23a as the upper limit temperature of the nozzle part 23a, effectively starting deposit generation. Can be suppressed. The upper limit temperature in this map is calculated by multiplying T90 by a predetermined safety coefficient from the viewpoint of suppressing deposit adhesion.

  Next, the tip temperature of the injector 23 is estimated based on the map shown in FIG. 5 from the current operating conditions (for example, the rotational speed and load) of the engine 10 (step S13). Here, FIG. 5 is an example of a map showing the tip temperature of the injector 23 estimated from the intake pipe pressure and the rotational speed of the engine. The map is preliminarily adapted only with gasoline as a basic fuel through experiments or the like and stored in the ECU. It is what has been. By using such a map, the temperature of the nozzle part 23a can be estimated based on the actual operating state of the engine 10, and the deposit generation and adhesion conditions can be determined in detail.

  Then, it is determined whether or not the tip temperature of the injector 23 obtained in step S13 is equal to or lower than the upper limit temperature obtained in step S12 (step S14). If the tip temperature of the injector 23 obtained in step S13 is equal to or lower than the upper limit temperature obtained in step S12 (Yes in step S14), it can be estimated that no deposit has adhered to the nozzle portion 23a of the injector 23, and the deposit is washed. Therefore, the normal combustion control is performed (step S15), and the process returns to step S10 for calculating the fuel property.

  On the other hand, if the tip temperature of the injector 23 obtained in step S13 is equal to or higher than the upper limit temperature obtained in step S12 (No in step S14), the fuel injection time above the upper limit temperature is accumulated, and this accumulated time is defined as S1. (Step S16). Then, it is determined whether or not the accumulated time S1 is equal to or longer than a predetermined specified time T1 (step S17).

  This specified time T1 is an empirical value, and is a time during which it is determined that the deposit can be cleaned without completely adhering to and solidifying the injection hole portion 23a of the injector 23. Therefore, if the accumulated time S1 is equal to or longer than the specified time T1 (Yes at step S17), it is necessary to perform control for cleaning the deposit.

  On the other hand, even if the temperature is equal to or higher than the upper limit temperature obtained in step S12 (No in Step S14), if the accumulated time S1 has not reached the specified time T1 (No in Step S17), deposit deposition has not progressed. Since it is not necessary to perform the cleaning control, normal combustion control is performed (step S22), and the process returns to step S10 for calculating the fuel property. By setting the specified time T1 in this way, the frequency of increasing the fuel injection pressure can be reduced, and the load on the pump 32b can be reduced.

  Since the control for deposit cleaning cannot be performed by stratified combustion without robustness, it is first determined whether or not the current combustion is stratified combustion (step S18). If it is stratified combustion (Yes in step S18), it is switched to homogeneous combustion (step S19), and the process proceeds to deposit cleaning control in step S20. If not stratified combustion (No in step S18), the process proceeds to step S20.

  In this step S20, in order to clean the deposit initially attached to the injection hole 23a of the injector 23 by high-pressure fuel injection, the fuel injection pressure is increased to the maximum pressure of the pump 32b. The injection time is corrected according to the pressure. Thereafter, homogeneous combustion control by high-pressure injection is performed until time T2 sufficient to clean the deposit.

  Thereby, it can suppress that a deposit adheres and deposits on the nozzle part 23a of the injector 23, and can suppress that a fuel injection amount falls. Therefore, it is possible to suppress the occurrence of problems such as a deviation in the air-fuel ratio or the inability to inject fuel. The specified time T2 is also an empirical value, and generally T1> T2.

  When the deposit cleaning control in step S20 is performed, the high-pressure injection cumulative time S1 in the upper limit temperature range is cleared (step S21), and the process returns to step S10 for calculating fuel properties.

  As described above, according to the fuel injection control method of the mixed fuel direct injection engine according to the first embodiment, it is possible to suppress deposits from adhering to and depositing on the injection hole portion 23a of the injector 23, and the fuel injection amount. Can be suppressed. Therefore, it is possible to suppress the occurrence of problems such as a deviation in the air-fuel ratio or the inability to inject fuel.

  In the first embodiment, the tip temperature of the injector 23 (the temperature of the nozzle portion 23a) is estimated from the map shown in FIG. 5, but in this second embodiment, the tip temperature of the injector 23 is measured by a temperature sensor, and this temperature is measured. More precise control than that of the first embodiment is performed by feeding back data.

  That is, in the second embodiment, as shown in FIG. 6, in addition to the configuration shown in FIG. 2, a temperature sensor (nozzle part temperature detecting means) 33c for measuring the temperature of the nozzle part 23a of the injector 23 is provided. . The other configurations of the engine 10 and the configuration of the fuel supply system are the same as the configurations shown in FIGS. 2 and 3, and therefore, the same reference numerals are given and redundant description is omitted. Here, FIG. 6 is a cross-sectional view showing a schematic configuration of an engine according to Embodiment 2 of the present invention.

  Next, a fuel injection control method according to the second embodiment will be described with reference to FIG. In that case, FIG. 6 and FIG. 3 are referred suitably. Here, FIG. 7 is a flowchart showing a fuel injection control method of the in-cylinder direct injection engine.

  First, the property of the mixed fuel is calculated using the alcohol concentration sensor 33b (step S30). Then, the fuel injection amount (fuel injection time) is corrected and adjusted according to the calculated fuel property (step S31). Further, the upper limit temperature of the tip temperature of the injector 23 (the temperature of the nozzle portion 23a) is estimated from the fuel properties based on the map (see FIG. 4) shown in the first embodiment (step S32).

  The upper limit temperature in the map shown in the first embodiment is converted from T90 by multiplying a predetermined safety factor from the viewpoint of suppressing deposit adhesion. In the second embodiment, as will be described later. In addition, the temperature of the tip of the injector 23 is directly measured by the temperature sensor 33c, and it is considered that the temperature related to deposit generation can be accurately detected. Therefore, it is not always necessary to use a converted value obtained by multiplying T90 by a predetermined safety factor. Alternatively, T90 may be used as it is as the upper limit value.

  Next, the tip temperature of each injector 23 is measured by the temperature sensor 33c, and the maximum temperature is calculated from the temperature data (step S33). Therefore, since the temperature data measured directly is used without estimating the tip temperature of the injector 23 by the map as in the first embodiment (see FIG. 5), the memory in the ECU for storing the map data is used. The amount can be reduced, and the following control that is more precise than the case of the first embodiment can be performed.

  That is, it is determined whether or not the maximum tip temperature of the injector 23 obtained in step S33 is equal to or lower than the upper limit temperature obtained in step S32 (step S34). If the maximum tip temperature of the injector 23 obtained in step S33 is equal to or lower than the upper limit temperature obtained in step S32 (Yes in step S34), it can be estimated that no deposit adheres to the nozzle portion 23a of the injector 23, and the deposit is reduced. Since it is not necessary to perform control for cleaning, normal combustion control is performed (step S35), and the process returns to step S30 for calculating fuel properties.

  On the other hand, if the maximum tip temperature of the injector 23 obtained in step S33 is equal to or higher than the upper limit temperature obtained in step S32 (No in step S34), the fuel injection time above the upper limit temperature is accumulated, and this accumulated time is designated as S1. (Step S36). Then, it is determined whether or not the accumulated time S1 is equal to or longer than a predetermined specified time T1 (step S37).

  This specified time T1 is an empirical value, and is a time during which it is determined that the deposit can be cleaned without completely adhering to and solidifying the injection hole portion 23a of the injector 23. Therefore, if the accumulated time S1 becomes equal to or longer than the specified time T1 (Yes at step S37), it is necessary to perform control for cleaning the deposit.

  On the other hand, even if the temperature is equal to or higher than the upper limit temperature obtained in Step S32 (No in Step S34), if the cumulative time S1 has not reached the specified time T1 (No in Step S37), deposit deposition has not progressed. Since it is not necessary to perform the cleaning control, normal combustion control is performed (step S42), and the process returns to step S30 for calculating the fuel property.

  Since the control for deposit cleaning cannot be performed by stratified combustion without robustness, it is first determined whether or not the current combustion is stratified combustion (step S38). If it is stratified combustion (Yes in step S38), it is switched to homogeneous combustion (step S39), and the routine proceeds to deposit cleaning control in step S40, and if it is not stratified combustion (No in step S38), the routine proceeds to step S40.

  In this step S40, the fuel injection pressure is increased to the maximum pressure of the pump 32b in order to clean the deposit initially attached to the nozzle portion 23a of the injector 23 by high-pressure fuel injection. The injection time is corrected according to the pressure. Thereafter, homogeneous combustion control by high-pressure injection is performed until time T2 sufficient to clean the deposit.

  Thereby, it can suppress that a deposit adheres and deposits on the nozzle part 23a of the injector 23, and can suppress that a fuel injection amount falls. Therefore, it is possible to suppress the occurrence of problems such as a deviation in the air-fuel ratio or the inability to inject fuel. The specified time T2 is also an empirical value, and generally T1> T2.

  When the deposit cleaning control in step S40 is performed, the high-pressure injection cumulative time S1 in the upper limit temperature range is cleared (step S41), and the process returns to step S30 for calculating the fuel property.

  As described above, according to the fuel injection control method of the mixed fuel direct injection engine according to the second embodiment, the tip temperature of the injector 23 is measured by the temperature sensor 33c, and the temperature data is fed back to the first embodiment. Since it is possible to suppress the occurrence of errors due to estimation and conversion errors due to a larger safety factor than in the case of, more precise control can be performed. That is, it is possible to more accurately suppress deposits from adhering and depositing on the injection hole portion 23a of the injector 23, and it is possible to suppress a decrease in the fuel injection amount. Therefore, it is possible to suppress the occurrence of problems such as a deviation in the air-fuel ratio or the inability to inject fuel.

  As described above, the fuel injection control method for a mixed fuel direct injection engine according to the present invention is useful for a mixed fuel direct injection engine in which a mixed fuel in which alcohol is mixed with basic fuel is directly injected into a cylinder by a fuel injection valve. In particular, even when mixed fuels having different alcohol concentrations are used, this is suitable for a fuel injection control method capable of suppressing deposit adhesion to the injection port portion of the fuel injection valve.

It is a flowchart which shows the fuel-injection control method of the direct injection engine which concerns on Example 1 of this invention. It is sectional drawing which shows schematic structure of an engine. It is a schematic diagram which shows the fuel supply system of an engine. It is a map which shows the relationship between alcohol concentration and the upper limit temperature of the injector front-end | tip at which deposit adhesion is anticipated. It is a map which shows the injector front-end | tip temperature estimated from the intake pipe pressure and rotation speed of an engine. It is sectional drawing which shows schematic structure of the engine which concerns on Example 2 of this invention. It is a flowchart which shows the fuel-injection control method of a cylinder direct injection engine.

Explanation of symbols

10 engine (mixed fuel direct injection engine)
23 Injector (fuel injection valve)
23a nozzle part 29 fuel tank (fuel supply system)
30 Fuel supply pipe (fuel supply system)
32b Pump (fuel injection pressure increasing means)
33 Delivery pipe 33b Alcohol concentration sensor (alcohol concentration detection means)
33c Temperature sensor (nozzle part temperature detection means)

Claims (5)

A mixed fuel direct injection engine that directly injects a mixed fuel obtained by mixing alcohol into basic fuel into a cylinder by a fuel injection valve;
Alcohol concentration detection means for detecting the alcohol concentration in the mixed fuel;
Nozzle part temperature detecting means for detecting or estimating the temperature of the nozzle part of the fuel injection valve;
A nozzle upper limit temperature calculating means for calculating an upper limit temperature of the fuel injection valve nozzle that is expected to deposit on the basis of the alcohol concentration detected by the alcohol concentration detecting means;
Fuel injection pressure increasing means for increasing the fuel injection pressure from that during normal injection;
A fuel injection control method for a mixed fuel direct injection engine comprising:
When the temperature detected or estimated by the nozzle part temperature detecting unit exceeds the upper limit temperature calculated by the nozzle part upper limit temperature calculating unit, the fuel injection pressure is increased by the fuel injection pressure increasing unit under homogeneous combustion control. A fuel injection control method for a mixed fuel direct injection engine, characterized in that the fuel injection is increased as compared with normal injection.   The injection port upper limit temperature calculated by the injection port upper limit temperature calculating means is converted by multiplying a predetermined coefficient by the 90% distillation temperature of the mixed fuel or the 90% distillation temperature at the alcohol concentration detected by the alcohol concentration detection means. The fuel injection control method for a mixed fuel direct injection engine according to claim 1, wherein the fuel injection control method is used.   The time of fuel injection performed in a state where the temperature detected or estimated by the nozzle part temperature detection unit exceeds the upper limit temperature calculated by the nozzle part upper limit temperature calculation unit is accumulated, and this accumulated time is a predetermined time. 3. The fuel injection control method for a mixed fuel direct injection engine according to claim 1, wherein the fuel injection pressure is increased by the fuel injection pressure increasing means when compared with a normal injection.   The mixed fuel direct injection according to any one of claims 1 to 3, wherein the nozzle temperature detecting means estimates the temperature of the fuel injection nozzle nozzle based on an engine load and an engine speed. Engine fuel injection control method.   The fuel injection control method for a mixed fuel direct injection engine according to any one of claims 1 to 3, wherein the nozzle part temperature detection means detects the temperature of the fuel injection valve nozzle part using a temperature sensor. .

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