WO2021177184A1 - Method for designing internal combustion engine - Google Patents

Abstract

A method for designing a direct-injection internal combustion engine (10) in which fuel is injected directly into a combustion chamber (21) by an injector (30), said method including: a target combustion characteristic acquisition step (S101) for acquiring a target combustion characteristic, which is a target value for a combustion characteristic of the internal combustion engine; a target equivalent ratio distribution calculation step (S102) for using a combustion characteristic sensitivity function quantifying the sensitivity of the combustion characteristic with respect to an equivalent ratio distribution in an air-fuel mixture of air and fuel generated in the combustion chamber to calculate a target equivalent ratio distribution, which is a target value for the equivalent ratio distribution with which the target combustion characteristic can be achieved; and an injector requirement calculation step (S104) for calculating an injector requirement, which is a requirement for a design parameter of the injector for achieving the target equivalent ratio distribution.

Description

Internal combustion engine design method Cross-reference of related applications

This application is based on Japanese Application No. 2020-038254 filed on March 5, 2020, and the contents of the description are incorporated herein by reference.

This disclosure relates to a design method for an internal combustion engine.

Patent Document 1 discloses a direct-injection type internal combustion engine that directly injects fuel into the combustion chamber of the internal combustion engine. In this internal combustion engine, when ignition and fuel injection are performed during the expansion stroke of the internal combustion engine, the first injection hole and the second injection for injecting fuel for the purpose of suppressing a decrease in combustion speed and improving combustion stability. The hole is set. Specifically, after the flame core generated by the ignition of the fuel is drawn between the pair of fuel sprays from the first injection hole, the fuel spray from the second injection hole reaches the flame core. , The position, hole diameter, number, injection direction, etc. of each injection hole are set.

JP-A-2017-166379

When designing an internal combustion engine, in addition to combustion stability, there are other characteristics to consider, such as the amount of emissions contained in the exhaust gas. In Patent Document 1, in order to ensure combustion stability, the position, hole diameter, number, injection direction, etc. of each injection hole are determined in consideration of the positional relationship between the spray from each injection hole and the spark plug, penetration, and the like. Although it is set, it does not consider the reduction of emissions in the exhaust emitted by the internal combustion engine. For this reason, it is necessary to acquire data by actually operating an internal combustion engine designed based on combustion stability and repeat trials to optimize the amount of emissions, which requires a considerable amount of time and man-hours.

In view of the above problems, it is an object of the present disclosure to provide a design method capable of reducing the time and man-hours required for designing a direct injection type internal combustion engine.

The present disclosure paid attention to the equivalent ratio distribution in the air-fuel mixture generated in the combustion chamber by injecting fuel into the combustion chamber of the internal combustion engine. Then, they have found that various parameters related to the design of the internal combustion engine can be linked to the equivalent ratio distribution, and have disclosed the following internal combustion engine design method.

The present disclosure provides first to third design methods as a design method for a direct injection type internal combustion engine that directly injects fuel into a combustion chamber by an injector. The first design method is for the target combustion characteristic acquisition step of acquiring the target combustion characteristic, which is the target value of the combustion characteristic of the internal combustion engine, and the equivalent ratio distribution in the air-fuel mixture generated in the combustion chamber. Based on the combustion characteristic sensitivity function that quantifies the sensitivity of the combustion characteristics, the target equivalent ratio distribution calculation step for calculating the target equivalent ratio distribution, which is the target value of the equivalent ratio distribution that can achieve the target combustion characteristics, and the above-mentioned step of calculating the target equivalent ratio distribution. The injector requirement calculation step of calculating the injector requirement, which is a requirement required for the design parameter of the injector in order to achieve the target equal ratio distribution, is included.

According to the first design method described above, the target equivalent ratio distribution is calculated in the target equivalent ratio distribution calculation step based on the combustion characteristic sensitivity function. Since this combustion characteristic sensitivity function quantifies the sensitivity of the combustion characteristic to the equivalent ratio distribution, the equivalent that can achieve the target combustion characteristic by referring to the combustion characteristic sensitivity function based on the acquired target combustion characteristic. The ratio distribution can be calculated. That is, by using the combustion characteristic sensitivity function, various target combustion characteristics can be linked to the equivalent ratio distribution and converged to a parameter called the target equivalent ratio distribution. Therefore, by calculating the injector requirements so that the target equivalent ratio distribution can be achieved and designing the internal combustion engine based on the calculated injector requirements, various target combustion characteristics can be comprehensively achieved. Can design an internal combustion engine. As a result, the number of trials performed on the actual machine to achieve various target combustion characteristics can be reduced, and the time and man-hours required for designing the internal combustion engine can be reduced.

The second design method according to the present disclosure is a step of acquiring a target combustion characteristic, which is a target value of the combustion characteristic of the internal combustion engine, and a mixture of air and fuel generated in the combustion chamber. Based on the spray characteristic sensitivity function creation step for creating a spray characteristic sensitivity function that quantifies the sensitivity of the spray characteristics of the fuel injected into the combustion chamber to the equivalent ratio distribution by combustion simulation, and the spray characteristic sensitivity function, the target It includes an injector requirement calculation step of calculating an injector requirement, which is a requirement required for the design parameters of the injector in order to achieve the target equivalent ratio distribution, which is a target value of the equivalent ratio distribution capable of achieving combustion characteristics.

According to the second design method described above, the injector requirement is calculated in the injector requirement calculation step based on the spray characteristic sensitivity function created in the spray characteristic sensitivity function creation step. This spray characteristic sensitivity function quantifies the sensitivity of the spray characteristic to the equivalent ratio distribution and is created by combustion simulation. Since the spray characteristics change depending on the design parameters of the injector, the injector requirements for achieving the target equivalent ratio distribution can be calculated by referring to the spray characteristics sensitivity function. Therefore, by designing the internal combustion engine based on the calculated injector requirements, the target equivalent ratio distribution can be achieved, and the target combustion characteristics can be achieved. By using the spray characteristic sensitivity function created by the combustion simulation, the number of trials in the actual machine executed by changing the design parameters of various injectors can be reduced, and the time and man-hours required for designing the internal combustion engine can be reduced.

A third design method according to the present disclosure is a step of acquiring a target combustion characteristic, which is a target value of the combustion characteristic of the internal combustion engine, and a mixture of air and fuel generated in the combustion chamber. Target equivalent ratio distribution calculation that calculates the target equivalent ratio distribution, which is the target value of the equivalent ratio distribution that can achieve the target combustion characteristics, based on the combustion characteristic sensitivity function that quantifies the sensitivity of the combustion characteristics to the equivalent ratio distribution. Based on the step, the spray characteristic sensitivity function creation step for creating a spray characteristic sensitivity function that quantifies the sensitivity of the spray characteristics of the fuel injected into the combustion chamber with respect to the equivalent ratio distribution by combustion simulation, and the spray characteristic sensitivity function. Including an injector requirement calculation step of calculating an injector requirement, which is a requirement required for the design parameters of the injector in order to achieve the target equivalent ratio distribution.

According to the third design method described above, in the target equivalent ratio distribution calculation step, the target equivalent ratio distribution capable of achieving the target combustion characteristic is calculated based on the combustion characteristic sensitivity function. Then, in the injector requirement calculation step, the injector requirement that can achieve the target equivalent ratio distribution calculated in the target equivalent ratio distribution calculation step is calculated based on the spray characteristic sensitivity function created in the spray characteristic sensitivity function creation step. That is, the injector requirement that can achieve the target combustion characteristic can be calculated by associating the combustion characteristic and the spray characteristic via the equivalent ratio distribution. Therefore, by designing the internal combustion engine based on the calculated injector requirements, the internal combustion engine can be designed so that various target combustion characteristics can be comprehensively achieved. In addition, by using the spray characteristic sensitivity function created by combustion simulation, it is possible to reduce the number of trials in the actual machine that are executed by changing the design parameters of various injectors, and reduce the time and man-hours required for designing the internal combustion engine. can.

The above objectives and other objectives, features and advantages of the present disclosure will be clarified by the following detailed description with reference to the accompanying drawings. The drawing is
FIG. 1 is a schematic diagram of an engine control system. FIG. 2 is a block diagram showing a design system of an internal combustion engine. FIG. 3 is a flowchart showing the design process of the internal combustion engine. FIG. 4 is a diagram showing the relationship between PN and the fuel temperature and equivalent ratio distribution. FIG. 5 is a diagram showing an example of the equivalent ratio distribution in the combustion chamber. FIG. 6 is a sensitivity function showing the sensitivity of ignitability to the equivalent ratio distribution. FIG. 7 is a sensitivity function showing the sensitivity of the amount of NOx to the equivalent ratio distribution. FIG. 8 is a sensitivity function showing the sensitivity of the PN amount to the equivalent ratio distribution. FIG. 9 is a diagram showing the relationship between the equivalent ratio distribution and the assist amount for each combustion characteristic. FIG. 10 is a diagram showing the relationship between each combustion characteristic, the equivalent ratio distribution, and the SMD. FIG. 11 is a diagram showing the relationship between each combustion characteristic, the equivalent ratio distribution, and the initial velocity of injection. FIG. 12 is a diagram showing the relationship between the injector characteristics and the SMD and the initial velocity of injection. FIG. 13 is a diagram showing the relationship between the target Φ distribution and the injector characteristics.

The internal combustion engine design method according to the present embodiment is applied to, for example, the design of the engine 10 which is the direct injection type multi-cylinder 4-cycle gasoline engine shown in FIG. 1, and can be realized by the design system shown in FIG.

The engine control system shown in FIG. 1 includes an engine 10 and an ECU 40 as a control device. The engine 10 is a 4-cylinder engine including four cylinders. In FIG. 1, only one cylinder is shown, and the other cylinders are not shown.

The engine 10 includes an engine body 20 provided with a cylinder. Of these, the combustion chamber 21 is a space formed in the cylinder by the inner wall of the cylinder and the upper surface (top) of the piston 22.

A spark plug 29 is provided for each combustion chamber 21 in the cylinder head located above the engine body 20. An ignition pulse is applied to the spark plug 29 at a desired ignition timing through an ignition coil or the like (not shown). By applying this ignition pulse, an ignition spark is generated between the counter electrodes of each spark plug 29.

The engine body 20 is provided with an injector 30 as a fuel injection valve for each combustion chamber 21. The injector 30 is a center injection type injector that is arranged in the vicinity of the spark plug 29 in the cylinder head and injects fuel directly into the combustion chamber 21 from the upper side to the lower side of the combustion chamber 21. The injector 30 is an electromagnetically driven type, and a drive pulse is applied at a desired injection timing through a drive circuit (not shown). By applying this drive pulse, the injector 30 is opened and fuel is injected.

The injector 30 is connected to the fuel tank 25 via the fuel pipe 24. The fuel in the fuel tank 25 is pumped by the low-pressure pump 26 and then pressurized by the high-pressure pump 27. By controlling the drive of the high pressure pump 27, it is possible to variably set the pressure applied to the fuel. The high-pressure fuel increased in pressure by the high-pressure pump 27 is pumped to the delivery pipe 28 and supplied from the delivery pipe 28 to the injector 30 of each cylinder. Further, the delivery pipe 28 is provided with a fuel pressure sensor 35 that detects the pressure of the fuel supplied to the injector 30 as the fuel pressure Pf.

The intake port and the exhaust port of the engine body 20 are provided with an intake valve 18 and an exhaust valve 19 that open and close according to the rotation of a camshaft (not shown), respectively. By opening the intake valve 18, the intake air flowing through the intake passage 11 is introduced into the combustion chamber 21. Further, the exhaust gas after combustion is discharged to the exhaust passage 33 by the opening operation of the exhaust valve 19. The intake valve 18 and the exhaust valve 19 are provided with variable valve mechanisms 18A and 19A that change the opening / closing timing of the intake valve 18 and the exhaust valve 19, respectively. The variable valve mechanisms 18A and 19A adjust the relative rotation phases of the crankshaft of the engine 10 and the intake and exhaust camshafts, and the phases toward the advance and retard sides with respect to a predetermined reference position. Adjustment is possible.

The engine body 20 is provided with a crank angle sensor 34 that outputs a rectangular crank angle signal for each predetermined crank angle when the engine 10 is operated. The ECU 40 can detect the rotation speed of the output shaft 23 as the rotation speed NE based on the crank angle signal.

The intake passage 11 is provided with an air flow meter 12 for detecting the amount of intake air. A throttle valve 14 whose opening degree is adjusted by a throttle actuator 13 such as a DC motor is provided on the downstream side of the air flow meter 12. A surge tank 15 is provided on the downstream side of the throttle valve 14. Further, an intake manifold 17 for introducing air into each cylinder of the engine 10 is connected to the surge tank 15, and is connected to an intake port of each cylinder in the intake manifold 17. The exhaust passage 33 is provided with a catalyst 31 such as a three-way catalyst for purifying CO, HC, NOx and the like in the exhaust gas.

The outputs of the various sensors described above are input to the ECU 40. The ECU 40 includes a microcomputer including a CPU, ROM, RAM, etc., and controls the fuel injection amount of the injector 30 according to the engine operating state by executing various control programs stored in the ROM, and the spark plug 29. The ignition timing is variably set, and the fuel pressure is variably controlled by the high-pressure pump 27.

The design system 53 shown in FIG. 2 is connected to the input unit 51 and the output unit 52. The input unit 51 may be configured by, for example, a user interface composed of a keyboard, a pointing device, or the like. The output unit 52 may be composed of, for example, a display device such as a liquid crystal display or a printing machine such as a printer.

Similar to a well-known personal computer, the design system 53 is a CPU that performs various arithmetic processes, a ROM that stores programs and the like, a RAM that is used as a work area during program execution, and a hard disk device that stores various program data. It is composed of etc. The design system 53 is configured to be able to execute the design method of the internal combustion engine exemplified by the engine 10 by executing the program stored in the ROM.

The present discloser visualizes the equivalent ratio Φ in the air-fuel mixture generated in the combustion chamber by injecting fuel into the combustion chamber of an internal combustion engine in the numerical range and the area ratio. The idea was to link the distribution (Φ distribution) to various parameters related to the design of internal combustion engines. For example, the Φ distribution that can achieve the target value (target combustion characteristic) of the combustion characteristics (emission amount in exhaust, fuel ignitability, etc.) of the internal combustion engine is set as the target Φ distribution, and the numerical range of Φ (target Φ range). It was found that the time and manpower required for the design can be reduced by expressing it by the area ratio (target Φ area) and using it for the design.

Note that Φ means the equivalent ratio of the air-fuel mixture generated in the combustion chamber 21 of the engine 10. Φ is the ratio of the stoichiometric air-fuel ratio A to the actual air-fuel ratio F, and can be calculated by Φ = A / F. Further, the Φ distribution is preferably visualized when the combustion chamber 21 in which the spark plug 29 is installed is viewed from the top of the head. For example, the Φ distribution is displayed in a state where the color changes corresponding to the numerical range of Φ. You may.

The Φ distribution in the combustion chamber 21 can be measured by actually driving the engine 10. Specifically, it can be measured by injecting fuel into the combustion chamber 21 to ignite it and spectroscopically analyzing the radical emission of the flame surface. The Φ distribution changes, for example, by changing the fuel injection amount or fuel pressure. For this reason, by experimenting with an actual machine, the Φ distribution is changed and measured by changing the fuel injection amount and fuel pressure, and at the same time, the combustion characteristics such as the emission amount and ignitability are detected to obtain the Φ distribution. The relationship with the combustion characteristics can be obtained by measurement.

The internal combustion engine to be designed by the design system 53 may be a direct injection type internal combustion engine that directly injects fuel into the combustion chamber by an injector, and is not limited to the specific configuration of the engine 10 shown in FIG. For example, the positional relationship between the injector and the spark plug may be any positional relationship in which the Φ distribution around the spark plug can be designed. The engine 10 is a center direct injection type that injects fuel from an injector 30 arranged on the upper surface of the combustion chamber 21, but may be a side direct injection type in which an injector is arranged on the side surface of the combustion chamber 21.

The design system 53 includes a calculation unit 60 and a database (DB) unit 70. The DB unit 70 includes a combustion characteristic / Φ distribution DB 71, a Φ distribution / spray characteristic DB 72, a spray characteristic / injector requirement DB 73, and an injector requirement / injector specification DB 74.

Combustion characteristics / Φ distribution DB71 stores the relationship between combustion characteristics and Φ distribution as a database. The combustion characteristic / Φ distribution DB71 stores a combustion characteristic sensitivity function fa that quantifies the sensitivity of the combustion characteristic to the Φ distribution as a database. Examples of the combustion characteristics include the amount of emissions contained in the exhaust gas emitted by the engine 10 and the ignitability of the fuel in the engine 10. The emission amount is the amount of environmentally harmful substances contained in the exhaust, for example, the amount of nitrogen oxides (NOx amount) contained in the exhaust and the number of solid particles (PN amount) which is the number of particulate matter (PM). Can be exemplified.

More specifically, in the combustion characteristic / Φ distribution DB71, the target Φ range and the target Φ area required to achieve the target combustion characteristic are stored as the combustion characteristic sensitivity function fa for each combustion characteristic. That is, the target Φ distribution is expressed by two types of parameters, the target Φ range and the target Φ area. The combustion characteristic sensitivity function fa is obtained in advance by a trial using an actual machine, and is stored as a database in the combustion characteristic / Φ distribution DB71.

The Φ distribution / spray characteristic DB72 stores the relationship between the spray characteristic and the Φ distribution as a database. In the Φ distribution / spray characteristic DB 72, the spray characteristic sensitivity function fb that quantifies the sensitivity of the spray characteristic with respect to the Φ distribution is stored as a database. The spray characteristic is a physical quantity of spray, and examples thereof include a fuel assist amount at the time of ignition, an initial velocity of spray, and a Sauter mean diameter (SMD) of spray.

The spray characteristic sensitivity function fb can be obtained by trial with an actual machine, but it can also be obtained by executing a combustion simulation such as CFD (Computational Fluid Dynamics) based on the spray characteristics. By executing a combustion simulation based on the spray characteristics, the equivalent ratio Φ in the air-fuel mixture generated in the combustion chamber is visualized in the numerical range and the area ratio (Φ). Distribution) can be created.

The spray characteristic / injector characteristic DB73 stores the relationship between the spray characteristic and the injector characteristic as a database. More specifically, the relationship between the spray characteristics and the injector characteristics is stored as a map or a mathematical formula. The injector characteristic is an injector design parameter, and the injector requirement is a requirement required for the injector design parameter in order to achieve the target spray characteristic. Examples of injector characteristics include an increase / decrease in the injection amount, a fuel pressure at the outlet of the injection hole, an injection rate, and the like.

Injector characteristics / injector specifications DB74 stores the relationship between injector characteristics and injector specifications as a database. More specifically, the relationship between the injector characteristics and the injector specifications is stored as a map or mathematical formula. Examples of injector specifications include the fuel pressure of the fuel to be injected, the hole diameter of the injection hole, the taper angle, and the like.

The calculation unit 60 includes a target combustion characteristic acquisition unit 61, an engine specification acquisition unit 62, a target Φ distribution calculation unit 63, a sensitivity function creation unit 64, an injector requirement calculation unit 65, and an injector specification setting unit 66. It has.

The target combustion characteristic acquisition unit 61 acquires the target combustion characteristic which is the target value of various combustion characteristics of the engine 10. The target combustion characteristics may be input, for example, from a user interface that functions as the input unit 51. For example, the target PN amount and the target NOx amount defined by the upper limit values of the NOx amount and the PN amount in the exhaust can be acquired as the target combustion characteristics. In addition, the ignition requirements defined by homogeneous combustion can be obtained as the target combustion characteristics.

The engine specification acquisition unit 62 acquires the specifications of the engine 10. The engine specifications may be input from, for example, a user interface that functions as the input unit 51.

The target Φ distribution calculation unit 63 acquires the combustion characteristic sensitivity function fa from the combustion characteristic / Φ distribution DB71, and calculates the target Φ distribution based on the combustion characteristic sensitivity function fa. The target Φ distribution is a target value of the Φ distribution that can achieve the target combustion characteristics.

Specifically, the target Φ distribution calculation unit 63 determines the target Φ distribution that can achieve the target combustion characteristic from the combustion characteristic sensitivity function fa. More specifically, the target Φ range and the target Φ area are determined as the target Φ distribution. The target Φ range may be set as a numerical range of Φ that should be satisfied in order to achieve the target combustion characteristic, or may be set as a numerical range of Φ that should be avoided.

For example, when ignitability is considered as the combustion characteristic, Φ> Φf can be obtained as the target Φ range to be satisfied from the combustion characteristic sensitivity function fa. The target Φ range of Φ> Φf is an ignition requirement defined assuming homogeneous combustion. Then, Sf ≧ S1 is acquired as the target Φ area set in consideration of the variation at the time of ignition in the actual machine of the engine 10. That is, as a requirement for the Φ distribution that can ensure ignitability, the requirement that Sf ≧ S1 can be calculated for the area ratio Sf in the region where the numerical range of Φ is Φ> Φf.

The sensitivity function creation unit 64 creates a spray characteristic sensitivity function fb that quantifies the sensitivity of the spray characteristic with respect to the Φ distribution by a combustion simulation such as CFD. Specifically, the Φ distribution corresponding to the spray characteristics is created by extracting the spray characteristics that affect the combustion characteristics for which the target value is set and executing the combustion simulation in the combustion chamber 21 based on the extracted spray characteristics. do. Even when the combustion simulation is used, the equivalent ratio distribution (Φ distribution) visualized in the numerical range and the area ratio can be obtained as in the case where the engine 10 is actually driven and measured. Then, the spray characteristic sensitivity function fb can be created by quantifying the sensitivity of the spray characteristic to the Φ distribution based on the Φ distribution calculated by the combustion simulation. The spray characteristic sensitivity function fb created by the sensitivity function creation unit 64 is stored in the Φ distribution / spray characteristic DB 72.

The injector requirement calculation unit 65 extracts the spray characteristics that affect the target combustion characteristics, and acquires the spray characteristic sensitivity function fb from the Φ distribution / spray characteristics DB 72 for the extracted spray characteristics. Further, the injector requirement calculation unit 65 reads out a map, a mathematical formula, or the like showing the relationship between the spray characteristic and the injector characteristic from the spray characteristic / injector characteristic DB 73. Then, the injector requirement that can achieve the target Φ distribution is calculated based on the acquired spray characteristic sensitivity function fb and the map showing the relationship between the read spray characteristic and the injector characteristic.

The injector specification setting unit 66 reads out a map or a mathematical formula showing the relationship between the injector characteristic and the injector specification from the injector characteristic / injector specification DB 74, and sets the injector specification so that the calculated injector requirement can be achieved. do.

FIG. 3 shows a flowchart of the design process of the internal combustion engine executed by the design system 53 shown in FIG.

In step S101, the target combustion characteristic acquisition step is executed. Specifically, as the target combustion characteristics, the target values of emission and ignitability are acquired, and the engine specifications are acquired. Then, the process proceeds to step S102.

In step S102, the target Φ distribution calculation step is executed. Specifically, the combustion characteristic sensitivity function fa is read out, and the target Φ distribution is calculated from the combustion characteristic sensitivity function fa based on the emission and ignitability target values acquired in step S101. The target Φ distribution is calculated as the target Φ range and the target Φ area.

The combustion characteristic sensitivity function fa is created based on the Φ distribution obtained based on the trial with the actual machine and the relationship between the combustion characteristic and Φ, and is stored in advance in the design system 53 as a database. The relationship between the combustion characteristics and Φ has been obtained theoretically or experimentally in advance and stored in the design system 53. For example, the relationship between the amount of NOx in exhaust gas and Φ, which is an example of combustion characteristics, can be theoretically calculated from the stoichiometric ratio in the chemical reaction formula showing the generation mechanism of each NOx. More specifically, based on the prompt NOx generation mechanism, it can be theoretically derived that the amount of NOx exceeding the permissible amount is generated in Φna <Φ <Φnb.

Further, for example, regarding the relationship between the amount of PN in the exhaust and Φ, which is an example of combustion characteristics, the relationship shown in FIG. 4 can be obtained experimentally. In FIG. 4, where the combustion temperature of the fuel is on the horizontal axis and the value of Φ is on the vertical axis, it has been experimentally determined in advance that PN exceeding the permissible amount is generated in the shaded area. If the lower limit of the value of Φ in the shaded area shown in FIG. 4 is set as Φp, the amount of PN exceeds the permissible amount in the range of Φ> Φp.

FIG. 5 shows an example of the Φ distribution in the combustion chamber 21. The Φ distribution shown in FIG. 5 is measured by injecting fuel into the combustion chamber 21 of the engine 10 to ignite it and spectroscopically analyzing the radical emission of the flame surface. As shown in FIG. 5, it is possible to create a Φ distribution in which the combustion chamber 21 is visualized as viewed from the crown and the regions A0 to A4 partitioned by the numerical range of Φ are displayed. The area ratio of each region of regions A0 to A4 can be expressed by the ratio of the area of each region to the area of the total region. In FIG. 5, the Φ distribution is divided by the numerical range of Φ, but the Φ distribution may be displayed in a state where the color changes in response to the change in the numerical value of Φ.

In FIG. 5, the region A0 is a region where the numerical range of Φ is Φ> Φp, the region A1 is a region where the numerical range of Φ is Φnb ≦ Φ ≦ Φp, and the region A2 is a region where the numerical range of Φ is Φna. <Φ <Φnb, region A3 is a region where the numerical range of Φ is Φf <Φ≤Φna, and region A4 is a region where the numerical range of Φ is Φ≤Φf. As for the value of Φ in each region, A0 is the largest and A4 is the smallest.

Region A0 is a PN generation zone in which the PN amount increases, and is a region in the numerical range of Φ that should be avoided in order to achieve the target value of the PN amount. The smaller the area ratio Sp of the region A0, the more the amount of PN can be suppressed. The region A2 is a NOx generation zone in which the amount of NOx increases, and is a region in the numerical range of Φ that should be avoided in order to achieve the target value of the amount of NOx. The smaller the area ratio Sn of the region A2, the more the amount of NOx can be suppressed. The region including the regions A0 to A3 is an ignition stable zone in which the ignitability can be ensured, and is a region in the numerical range of Φ that should be satisfied in order to achieve the target value of the ignitability. The larger the area ratio Sf of the regions A0 to A3, the better the ignitability. In FIG. 5, the region A1 may not be clearly distinguishable from the adjacent region because the values of Φnb and Φp are close to each other and the region A1 becomes very small. Therefore, the region A1 is neither a PN generation zone nor a NOx generation zone, but may be treated as a region having a numerical range of Φ to be avoided, similarly to the PN generation zone and the like. For example, the design may be advanced so that the total of the area of the area A0 and the area of the area A1 satisfies the condition of the target area ratio set for the PN amount.

Based on the Φ distribution in the combustion chamber 21 as shown in FIG. 5, each combustion characteristic (ignitability, NOx amount in exhaust, in exhaust) with respect to the area ratio within the target Φ range as shown in FIGS. 6 to 8 A combustion characteristic sensitivity function fa that quantifies the sensitivity of (PN amount) is created and stored in the design system 53.

In step S102, the target Φ distribution for satisfying the target values (target combustion characteristics) for ignitability, NOx amount, and PN amount is acquired based on the combustion characteristic sensitivity function fa shown in FIGS. 6 to 8. The vertical axis of FIG. 6 shows the frequency of deterioration of ignition, and the worsening rate of ignition decreases as the area ratio Sf in the target Φ range to be satisfied in order to achieve the target value of ignition property increases. The vertical axis of FIG. 7 shows the amount of NOx in the exhaust gas, and the amount of NOx decreases as the area ratio Sn, which is the target Φ range to be avoided in order to achieve the target value of the amount of NOx, decreases. The vertical axis of FIG. 8 shows the amount of PN in the exhaust gas, and the amount of PN decreases as the area ratio Sp, which is the target Φ range to be avoided in order to achieve the target value of the amount of PN, decreases.

In FIGS. 6 to 8, the target Φ range corresponds to the range indicated by the diagonal line. Regarding the ignitability shown in FIG. 6, the target area ratio: Sf ≧ S1 can be calculated for the target Φ range to be satisfied: Φ> Φf. The amount of NOx in the exhaust gas shown in FIG. 7 can be calculated as the target area ratio: Sn ≦ S2 for the target Φ range to be avoided: Φna <Φ <Φnb. Regarding the amount of PN in the exhaust shown in FIG. 8, the target area ratio: Sp ≦ S3 can be calculated for the target Φ range: Φ> Φp to be avoided. Then, the process proceeds to step S103.

In step S103, the spray characteristic sensitivity function creation step is executed. Specifically, the spray characteristics that affect the target combustion characteristics acquired in step S101 are extracted, and for the extracted spray characteristics, a combustion simulation such as CFD is executed based on the engine specifications, and the fuel in the combustion chamber 21 is executed. Calculate the Φ distribution when ignited by injecting. By calculating by combustion simulation, it is possible to create a Φ distribution that visualizes the numerical range of Φ and the area ratio, as in FIG. In step S103, a spray characteristic sensitivity function fb that quantifies the sensitivity of the spray characteristic to the Φ distribution is created based on the Φ distribution created by the combustion simulation.

As an example of the spray characteristic sensitivity function fb, FIGS. 9 to 11 show sensitivity functions for quantifying the sensitivity of each spray characteristic with respect to the Φ distribution. The vertical axis of FIGS. 9 to 11 shows the area ratio within the target Φ range for the combustion characteristics (ignitability, NOx amount, PN amount), and the horizontal axis shows each spraying characteristic (assist amount, SMD, initial velocity of spraying). show.

As shown in FIG. 9, the area ratio within the target Φ range for ignitability changes logarithmically with the increase in the assist amount, and the increase amount of the area ratio decreases as the assist amount increases. Regarding the NOx amount and the PN amount, the area ratio within the target Φ range increases substantially in proportion to the increase in the assist amount.

As shown in FIG. 10, with respect to ignitability and NOx amount, the area ratio within the target Φ range hardly increases or decreases with respect to the change in SMD. Regarding the amount of PN, the area ratio within the target Φ range increases substantially in proportion to the larger the SMD.

As shown in FIG. 11, with respect to ignitability and NOx amount, the area ratio within the target Φ range hardly increases or decreases with respect to the change in the initial velocity of spraying. Regarding the amount of PN, the area ratio within the target Φ range decreases substantially in proportion to the faster the initial velocity of spraying. These spray characteristic sensitivity functions fb are stored in the design system 53 as a database. After step S103, the process proceeds to step S104.

In step S104, the injector requirement calculation step is executed. Specifically, first, for the spray characteristic extracted in step S103, a map showing the relationship between the spray characteristic and the injector characteristic (injector design parameter) is read out, and based on the relationship of this map, the spray characteristic sensitivity function fb Replace the spray characteristics in with the injector characteristics. As a result, the relationship between the injector characteristic and the target Φ distribution can be obtained, and based on this relationship, the injector requirement, which is the injector characteristic that can achieve the target Φ distribution, can be calculated.

FIG. 12 illustrates a diagram showing the relationship between the extracted spray characteristics and the injector characteristics. The initial spray velocity and SMD shown on the vertical and horizontal axes of FIG. 12 correspond to the spray characteristics. Points P1 to P3 shown in FIG. 12 are values obtained by experiments with different injector outlet fuel pressures (an example of injector characteristics), and the injector outlet fuel pressures are in the order of P1, P2, and P3. high. The solid line shown in FIG. 12 shows that the muzzle velocity and the SMD change depending on the fuel pressure at the outlet of the injection hole. Specifically, the higher the fuel pressure at the outlet of the injection hole, the faster the initial spray velocity and the smaller the SMD. The lower the fuel pressure at the outlet of the injection hole, the slower the initial spray velocity and the larger the SMD.

The relationship between the spray characteristics and the injector characteristics as illustrated in FIG. 12 is mapped and stored in the design system 53 as a database. In step S104, a map showing the relationship between the spray characteristic and the injector characteristic as shown in FIG. 12 is read out from the database, and is illustrated in FIG. 13 based on the relationship between the Φ distribution and the spray characteristic as shown in FIGS. 9 to 11. Find the relationship between the injector requirements and the target Φ distribution.

The figure shown in FIG. 13 shows a region R in which the target value of each combustion characteristic can be achieved, with the fuel assist amount as the horizontal axis and the injection hole outlet fuel pressure as the vertical axis. The fuel assist amount shown in FIG. 9 is directly replaced with the assist amount as an injector characteristic. The muzzle velocity and SMD as the two spray characteristics shown in FIGS. 10 and 11 are replaced with the injection hole outlet fuel pressure as one injector characteristic based on the relationship shown in FIG.

L1 is an ignitability constraint line that defines a target Φ distribution set based on ignitability. In the region where the assist amount is larger than the ignitability constraint line L1 (the region on the right side of the ignitability constraint line L1), the target Φ distribution (target Φ range: Φ> Φf and target area) set based on the ignitability target value. Rate: Sf ≧ S1) can be achieved.

L2 is a NOx amount constraint line that defines a target Φ distribution set based on the NOx amount in the exhaust gas. In the region where the assist amount is smaller than the NOx amount constraint line L2 (the area on the left side of the NOx amount constraint line L2), the target Φ distribution set based on the target value of the NOx amount (target Φ range: Φna <Φ <Φnb and Target area ratio: Sn ≦ S2) can be achieved.

L3 is a PN amount constraint line that defines a target Φ distribution set based on the PN amount in the exhaust gas. In the region where the fuel pressure at the outlet of the injection hole is higher than the PN amount constraint line L3 (the region above the PN amount constraint line L3), the target Φ distribution (target Φ range: Φ> Φp Target area ratio: Sp ≦ S3) can be achieved.

Area R is a shaded area surrounded by L1 to L3. In the region R, the target Φ distribution set based on each target value for ignitability, NOx amount and PN amount can be achieved. In step S104, the injector requirement is set within the range of the region R shaded in FIG. This allows the injector requirements to be set to achieve the respective target values for ignitability, NOx amount and PN amount. After step S104, the process proceeds to step S105.

In step S105, the injector specification setting step is executed. Specifically, a map showing the relationship between the injector characteristics and the injector specifications is read out, and the injector specifications are set so that the calculated injector requirements can be achieved based on this map. For example, the injection hole outlet fuel pressure as an injector characteristic can be replaced with injector specifications such as the fuel pressure of the fuel to be injected, the injection hole diameter, and the injection hole shape (taper angle, etc.). More specifically, the fuel pressure at the outlet of the injection hole can be increased by increasing the fuel pressure of the fuel to be injected, reducing the diameter of the injection hole, and widening the taper angle of the injection hole. On the contrary, the fuel pressure at the outlet of the injection hole can be lowered by lowering the fuel pressure of the fuel to be injected, increasing the diameter of the injection hole, and narrowing the taper angle of the injection hole. Further, the assist injection amount as an injector characteristic can be replaced with the injection amount of the fuel to be injected. The set injector specifications are output to the output unit 52. After step S105, a series of processes shown in FIG. 3 is completed.

As described above, according to the present embodiment, the target Φ distribution is set by associating the target combustion characteristic with the Φ distribution based on the combustion characteristic sensitivity function fa in step S102. Then, in step S104, the injector requirement, which is a requirement required for the injector characteristic in order to achieve the target Φ distribution, is calculated based on the spray characteristic sensitivity function fb calculated by the combustion simulation in step S103. Therefore, in step S105, by setting the injector specifications so as to satisfy the injector requirements calculated in step S104, the injector specifications can be set within a range in which the target combustion characteristics can be achieved. Even if there are multiple target combustion characteristics, the injector specifications that can achieve each target combustion characteristic are set by associating with the Φ distribution using the combustion characteristic sensitivity function fa and the spray characteristic sensitivity function fb. can. Therefore, after designing the engine 10 so as to achieve a specific target combustion characteristic, it is not necessary to repeat trials on the actual machine so that other target combustion characteristics can be achieved, and the time and man-hours required for designing the engine 10 can be reduced. Can be reduced. Further, since the spray characteristic sensitivity function fb is created by combustion simulation, it is not necessary to perform measurement with an actual machine to create the spray characteristic sensitivity function fb, and the cost, man-hours, and time for design can be reduced.

The design system 53 may be configured to be able to execute a design method for ending the design process after setting the target Φ distribution based on the target combustion characteristics input from the input unit 51. In this design method, after each process of steps S101 to S103 is executed, the set target Φ distribution is output to the output unit 52, and the process ends.

Further, the design system 53 is configured to be able to execute a design method for setting injector specifications based on the target Φ distribution input from the input unit 51 without executing the target Φ distribution setting process based on the target combustion characteristics. It may have been done. In this case, in a step prior to step S104, after executing the target Φ distribution acquisition step for acquiring the target Φ distribution, the process proceeds to the process of step S104. The target Φ distribution acquisition step may be executed at the timing of step S101, or may be executed at a timing between step S103 and step S104. Further, the design system 53 may be configured so that the above three types of design methods can be selected by the input unit 51.

According to each of the above embodiments, the following effects can be obtained.

The design system 53 is configured to be able to execute the first design method for designing the engine 10 which is a direct injection type internal combustion engine that directly injects fuel into the combustion chamber 21 by the injector 30. This design method includes a target combustion characteristic acquisition step, a target Φ distribution calculation step, and an injector requirement calculation step. In the target combustion characteristic acquisition step, the target combustion characteristic, which is the target value of the combustion characteristic of the engine 10, is acquired. In the target Φ distribution calculation step, the target Φ distribution, which is the target value of the Φ distribution that can achieve the target combustion characteristic, is calculated based on the combustion characteristic sensitivity function fa that quantifies the sensitivity of the combustion characteristic with respect to the Φ distribution. In the injector requirement calculation step, the injector requirement, which is a requirement required for the design parameters of the injector in order to achieve the target Φ distribution, is calculated. It is a Φ distribution in the air-fuel mixture generated in the combustion chamber 21 of the engine 10.

According to the first design method described above, by using the combustion characteristic sensitivity function fa, various target combustion characteristics such as emission amount and ignitability are linked to the Φ distribution and converged to the parameter of the target Φ distribution. Can be made to. Therefore, by calculating the injector requirements so that the target Φ distribution can be achieved and designing the engine 10 based on the calculated injector requirements, the engine 10 can be comprehensively achieved with various target combustion characteristics. Can be designed. That is, the engine 10 capable of achieving both the amount of emission and the ignitability can be designed by a series of design processes. As a result, it is possible to reduce the number of trials in the actual machine for achieving the target combustion characteristics, and it is possible to reduce the time and man-hours required for designing the engine 10.

Although the combustion characteristics are not particularly limited, it is preferable to include the amount of emissions contained in the exhaust gas emitted by the engine 10 and the ignitability of the fuel in the engine 10. With a small number of man-hours, it is possible to design an engine 10 having good performance in terms of both emission amount and ignitability.

The design system 53 is also configured to be able to execute the second design method of the engine 10, which includes a target combustion characteristic acquisition step, a spray characteristic sensitivity function creation step, and an injector requirement calculation step. In the spray characteristic sensitivity function creation step, a spray characteristic sensitivity function fb that quantifies the sensitivity of the spray characteristic to the Φ distribution is created by combustion simulation. In the injector requirement calculation step, the injector requirement, which is an injector characteristic that can achieve the target Φ distribution, is calculated based on the spray characteristic sensitivity function fb.

According to the second design method described above, by using the spray characteristic sensitivity function fb, the Φ distribution can be linked to various spray characteristics, and by extension, it can be linked to the injector characteristic. That is, by using the spray characteristic sensitivity function fb, the injector requirement that can achieve the target Φ distribution can be calculated. Then, by designing the engine 10 based on the calculated injector requirements, the engine 10 can be designed so that the target Φ distribution can be achieved. In addition, by using the spray characteristic sensitivity function created by the combustion simulation, it is possible to reduce the number of trials executed on the actual machine by changing the design parameters of various injectors. As a result, it is possible to reduce the number of trials in the actual machine for achieving the target Φ distribution, and it is possible to reduce the time and man-hours required for designing the engine 10.

The design system 53 is also configured to be feasible to implement a third design method of the engine 10, including a target combustion characteristic acquisition step, a target Φ distribution calculation step, a spray characteristic sensitivity function creation step, and an injector requirement calculation step. Has been done. According to the third design method described above, the injector requirement that can achieve the target combustion characteristic can be calculated by associating the combustion characteristic and the spray characteristic via the Φ distribution. Therefore, by designing the engine 10 based on the calculated injector requirements, the engine 10 can be designed so that various target combustion characteristics can be comprehensively achieved. In addition, by using the spray characteristic sensitivity function created by the combustion simulation, it is possible to reduce the number of trials executed on the actual machine by changing the design parameters of various injectors. As a result, the number of trials in the actual machine can be reduced, and the time and man-hours required for designing the engine 10 can be reduced.

The controls and methods thereof described in the present disclosure are realized by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. May be done. Alternatively, the controls and methods thereof described in the present disclosure may be implemented by a dedicated computer provided by configuring the processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and method thereof described in the present disclosure may be a combination of a processor and memory programmed to perform one or more functions and a processor composed of one or more hardware logic circuits. It may be realized by one or more dedicated computers configured. Further, the computer program may be stored in a computer-readable non-transitional tangible recording medium as an instruction executed by the computer.

Although this disclosure has been described in accordance with the examples, it is understood that the disclosure is not limited to the examples and structures. The present disclosure also includes various modifications and modifications within a uniform range. In addition, various combinations and forms, as well as other combinations and forms that include only one element, more, or less, are also within the scope of the present disclosure.

Claims (4)

1. It is a design method of a direct injection type internal combustion engine (10) that directly injects fuel into a combustion chamber (21) by an injector (30).
   The target combustion characteristic acquisition step (S101) for acquiring the target combustion characteristic, which is the target value of the combustion characteristic of the internal combustion engine, and the target combustion characteristic acquisition step (S101).
   A target of the equivalent ratio distribution capable of achieving the target combustion characteristic based on a combustion characteristic sensitivity function that quantifies the sensitivity of the combustion characteristic to the equivalent ratio distribution of the air-fuel mixture generated in the combustion chamber. The target equivalence ratio distribution calculation step (S102) for calculating the target equivalence ratio distribution, which is a value, and the target equivalence ratio distribution calculation step (S102).
   A method for designing an internal combustion engine, which includes an injector requirement calculation step (S104) for calculating an injector requirement, which is a requirement required for the design parameters of the injector in order to achieve the target equivalent ratio distribution.
2. It is a design method of a direct injection type internal combustion engine that injects fuel directly into the combustion chamber by an injector.
   The target combustion characteristic acquisition step (S101) for acquiring the target combustion characteristic, which is the target value of the combustion characteristic of the internal combustion engine, and the target combustion characteristic acquisition step (S101).
   A spray characteristic sensitivity function that quantifies the sensitivity of the spray characteristics of the fuel injected into the combustion chamber to the equivalent ratio distribution in the air-fuel mixture generated in the combustion chamber by combustion simulation. Creation step (S103) and
   Based on the spray characteristic sensitivity function, the injector requirement, which is a requirement required for the design parameters of the injector in order to achieve the target equivalent ratio distribution, which is the target value of the equivalent ratio distribution capable of achieving the target combustion characteristic, is calculated. A method for designing an internal combustion engine, which includes an injector requirement calculation step (S104).
3. It is a design method of a direct injection type internal combustion engine that injects fuel directly into the combustion chamber by an injector.
   The target combustion characteristic acquisition step (S101) for acquiring the target combustion characteristic, which is the target value of the combustion characteristic of the internal combustion engine, and the target combustion characteristic acquisition step (S101).
   A target value of the equivalent ratio distribution capable of achieving the target combustion characteristics based on quantifying the sensitivity of the combustion characteristics to the equivalent ratio distribution in the air-fuel mixture generated in the combustion chamber. The target equivalence ratio distribution calculation step (S102) for calculating the equivalence ratio distribution, and
   A spray characteristic sensitivity function creation step (S103) for creating a spray characteristic sensitivity function quantifying the sensitivity of the spray characteristics of the fuel injected into the combustion chamber with respect to the equivalent ratio distribution by combustion simulation, and
   Design of an internal combustion engine including an injector requirement calculation step (S104) for calculating an injector requirement, which is a requirement required for an injector design parameter in order to achieve the target equivalent ratio distribution based on the spray characteristic sensitivity function. Method.
4. The method for designing an internal combustion engine according to any one of claims 1 to 3, wherein the combustion characteristics include an amount of emissions contained in the exhaust gas emitted by the internal combustion engine and ignitability of fuel in the internal combustion engine.

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