Control device, engine system, skip fire execution determination method, and program

Abstract

Provided is a control method for avoiding backfire caused by the state of fuel in a cylinder. A control device according to the present invention performs the following: acquiring the composition of fuel supplied to a cylinder of an engine that burns an air-fuel mixture in which fuel and air are mixed, and the concentration of fuel in the air-fuel mixture; on the basis of criteria information defining the relationship of criteria set on the basis of the fuel concentration, the fuel composition, and a combustible limit, determining whether the acquired fuel composition and the acquired fuel concentration fall within a range of upper and lower limit values for the criteria; determining not to skip fire the engine if the acquired fuel composition and the acquired fuel concentration fall within said range of upper and lower limit values; and determining to skip fire the engine when the acquired fuel composition and the acquired fuel concentration fall outside said range of upper and lower limit values.

Description

Control device, engine system, skip fire execution determination method and program

[0001] The present disclosure relates to a control device, an engine system, a skip fire execution determination method, and a program. This disclosure claims priority to Japanese Patent Application No. 2024-086644, filed on May 28, 2024, the contents of which are incorporated herein by reference.

[0002] Premixed spark ignition reciprocating engines generate rotational energy by introducing a fuel-air mixture into the cylinder and igniting it with a spark. Fuels such as hydrogen, which continue to burn under ultra-lean conditions, can burn slowly if the fuel concentration in the cylinder is low or if there are many inert gases present, and combustion continues until the next cycle, which can cause a backfire during the intake stroke of the next cycle. One way to deal with backfire is to use a skip fire, which does not execute the combustion stroke.

[0003] Patent Document 1 discloses a control method that determines whether to execute skip fire based on an index indicating the engine state, such as engine output or engine speed. However, this method may not be able to deal with backfires caused by the state of fuel in the cylinder.

[0004] Special Publication No. 2015-524541

[0005] There is a need for skip fire execution control to avoid backfire due to fuel conditions in the cylinder.

[0006] The present disclosure provides a control device, an engine system, a skip fire execution determination method, and a program that can solve the above-mentioned problems.

[0007] According to one aspect of the present disclosure, a control device includes a determination unit that acquires the composition of fuel supplied to a cylinder of an engine that burns a mixture of fuel and air and the concentration of fuel in the mixture, and determines whether the acquired fuel composition and the acquired fuel concentration fall within the range of upper and lower limit values ​​of the criteria based on criteria information that defines the relationship between the fuel concentration, the fuel composition, and the flammability limit, and decides not to execute skip fire for the engine if they fall within the range of the upper and lower limit values, and decides to execute skip fire for the engine if they are outside the range of the upper and lower limit values.

[0008] According to one aspect of the present disclosure, an engine system includes an engine having one or more cylinders and the control device described above.

[0009] According to one aspect of the present disclosure, a skip fire execution determination method acquires the composition of fuel supplied to a cylinder of an engine that burns a mixture of fuel and air and the concentration of fuel in the mixture, and determines whether the acquired fuel composition and the acquired fuel concentration fall within the range of upper and lower limit values ​​of the criteria based on criteria information that defines the relationship between the fuel concentration, the fuel composition, and the flammability limit, and determines not to execute skip fire for the engine if they fall within the range of the upper and lower limit values, and determines to execute skip fire for the engine if they are outside the range of the upper and lower limit values.

[0010] According to one aspect of the present disclosure, a program causes a computer to execute a process of acquiring the composition of fuel supplied to a cylinder of an engine that combusts a mixture of fuel and air and the concentration of fuel in the mixture, determining whether the acquired fuel composition and the acquired fuel concentration fall within upper and lower limit values ​​of the criteria based on criteria information that defines the relationship between the fuel concentration, the fuel composition, and a flammability limit, and deciding not to execute skip fire for the engine if the acquired fuel composition and the acquired fuel concentration fall within the range of the upper and lower limit values, and deciding to execute skip fire for the engine if the acquired fuel composition and the acquired fuel concentration fall outside the range of the upper and lower limit values.

[0011] According to the control device, engine system, skip fire execution determination method, and program described above, it is possible to suppress the occurrence of backfire caused by the state of fuel in the cylinder.

[0012] It is a schematic diagram of an engine system according to an embodiment. It is a first diagram showing an example of a flammable limit curve according to an embodiment. It is a second diagram showing an example of a flammable limit curve according to an embodiment. It is a flowchart showing an example of a skip fire execution determination process according to an embodiment. It is a schematic diagram showing an example of a hardware configuration of a control device according to an embodiment.

[0013] <Embodiment> Hereinafter, skip fire execution control based on fuel composition and fuel concentration according to the present disclosure will be described with reference to the drawings. FIG. 1 is a schematic diagram of an engine system 1 according to this embodiment. The engine system 1 includes an engine 2 having a plurality of cylinders 4a, 4b, etc., and a control device 10 that controls the engine 2. The engine 2 is a reciprocating engine that outputs power by combusting a mixture generated by mixing fuel gas with air. The engine 2 includes an intake pipe 3a, cylinders 4a, an exhaust pipe 9a, etc. The intake pipe 3a is provided with a mixture generator 31a. Air and fuel are supplied to the mixture generator 31a, which generates a mixture of the air and fuel. The fuel has a composition of, for example, H2 and N2, or H2, N2, and CH4. The mixture generated by the mixture generator 31a is supplied to the cylinder 4a via the intake pipe 3a. Cylinder 4a includes a cylinder 5a, a piston 6a, a spark plug 7a, and the like. Spark ignition by the spark plug 7a burns the air-fuel mixture in a combustion chamber 8a defined by the cylinder 5a and the piston 6a. The exhaust gas after combustion is discharged through an exhaust pipe 9a. Other cylinders, such as 4b, included in the engine 2, also have a similar configuration. Hereinafter, when it is not necessary to distinguish between intake pipes 3a, 3b and cylinders 4a, 4b, etc., they may simply be referred to as intake pipe 3, cylinder 4, etc. While FIG. 1 illustrates a configuration in which the engine 2 includes multiple cylinders 4, the engine 2 may also include only one cylinder 4. While FIG. 1 shows PFI (Port Fuel Injection) as an example of an injection method, DI (Direct Injection) and premixed (Tecjet) methods may also be used.

[0014] The control device 10 controls the engine 2. The control device 10 includes a fuel composition acquisition unit 11, a fuel concentration acquisition unit 12, a determination unit 13, and a control unit 14. The fuel composition acquisition unit 11 acquires the composition of the fuel contained in the mixture supplied to the cylinder 4. For example, if the fuel is composed of H2 and N2, a sensor that measures the concentration of H2 or N2 is provided in the fuel pipe, and the fuel composition acquisition unit 11 calculates the ratio of H2 to N2 in the fuel supplied to the cylinder 4 (e.g., N2 / H2, which is the ratio of N2 to H2) from the concentration of H2 or N2 measured by the sensor. Alternatively, the fuel composition acquisition unit 11 may calculate and acquire the ratio of H2 to N2 by simulating the operation of the engine 2 or by a known calculation method.

[0015] The fuel concentration acquisition unit 12 acquires the concentration of fuel in the mixture supplied to the cylinder 4. For example, the air flow rate and fuel flow rate measured by a sensor that measures the air flow rate of air supplied to the mixture generation device 31 and a sensor that measures the fuel flow rate, or design values ​​or estimated values ​​of the air flow rate and fuel flow rate, are used as the air flow rate and fuel flow rate supplied to the inside of the cylinder 4a, and the fuel concentration acquisition unit 12 calculates the concentration of fuel in the mixture from the air flow rate and fuel flow rate. Alternatively, the fuel concentration acquisition unit 12 may estimate the fuel concentration using a known estimation method.

[0016] The determination unit 13 determines whether the fuel state in the cylinder 4a is likely to cause abnormal combustion such as backfire, and if it determines that there is a possibility of backfire, it decides to execute skip fire. Specifically, if the fuel concentration in the air-fuel mixture is lean or if a large amount of inert gas (e.g., N2) is present, combustion in the combustion chamber 8 becomes slow, and backfire occurs during intake as combustion continues until the next cycle. Therefore, based on the proportion of inert gas in the fuel supplied to the cylinder 4 and the fuel concentration, it determines whether the fuel state in the cylinder is likely to cause backfire, and if it determines that there is a possibility of backfire, it decides to execute skip fire.

[0017] The control unit 14 controls the operation of the engine 2. The control unit 14 executes skip fire based on the determination result of the determination unit 13. For example, when executing skip fire, the control unit 14 closes a valve (not shown) provided in the intake pipe 3 to temporarily stop the supply of the mixture to the cylinder 4, thereby executing skip fire, for example, without fuel injection once every two cycles. Alternatively, the control unit 14 may stop fuel injection to the mixture generation device 31a and execute skip fire, without fuel injection once every two cycles (introducing air but not fuel). In this case, even if combustion in a certain cylinder slows down during a certain cycle and a spark remains in the cylinder until the start of the intake stroke of the next cycle, by executing skip fire, fuel is not introduced into the cylinder during the next intake stroke, and backfire during the intake stroke can be avoided.

[0018] (Determination of Skip Fire Execution) Next, a method for determining whether to execute skip fire will be specifically described with reference to FIGS. 2 and 3. FIG. 2 shows an example of a flammability limit curve used to determine whether to execute skip fire when the fuel is a mixture of H2 and N2. The vertical axis of FIG. 2 represents the fuel concentration (flammability limit) of the mixture, and the horizontal axis represents the ratio of N2 to H2 (the ratio of inert gas). Flammability limit curves C1 for hydrogen and nitrogen mixtures are publicly known, such as those found in literature. When the relationship between the fuel concentration and the N2 / H2 ratio is within the region surrounded by the flammability limit curve C1 but is sufficiently distant from the curve C1, combustion of the H2-N2 mixture is stable. However, when the relationship is within the region surrounded by the flammability limit curve C1 but is close to the curve C1, combustion slows. When the relationship between the fuel concentration and the N2 / H2 ratio is outside the flammability limit curve C1, where the fuel is lean or excessively rich (overly rich), combustion does not occur. A curve offset by a fixed value or a fixed factor on the inside of the flammability limit curve C1 is defined as the skip fire criteria curve C2. Here, the criteria curve C2 is drawn not only on the lean side but also on the rich side, assuming that there is a risk of combustion slowing down. The risk of combustion slowing down is determined to be low within the region enclosed by the criteria curve C2. The user causes the determination unit 13 to store and retain a graph, as shown in FIG. 2 , in which the criteria curve C2 is drawn against the known flammability limit curve C1. The determination unit 13 uses the N2 / H2 ratio acquired by the fuel composition acquisition unit 11 and the fuel concentration acquired by the fuel concentration acquisition unit 12 to plot the fuel state indicated by these on the graph shown in FIG. 2 and confirms whether the state of the fuel supplied to cylinder 4 is inside or outside the criteria curve C2. For example, when the N2 / H2 ratio is X1 and the fuel concentration is Y1, the fuel state indicated by these can be represented by point P2. When the N2 / H2 ratio is X2 and the fuel concentration is Y1, the fuel state indicated by these can be represented by point P1. Point P2 is inside the criteria curve C2, and point P1 is outside the criteria curve C2. When the fuel state is at point P2, the determination unit 13 determines that combustion will not slow down and decides not to execute skip fire. On the other hand, when the fuel state is represented by point P1, the determination unit 13 determines that combustion will slow down and decides to execute skip fire.For example, if the fuel state of cylinder 4a is P1 and the fuel state of cylinder 4b is P2, the determination unit 13 determines that the engine 2a should skip fire once every two cycles, but that the engine 2b should not skip fire.

[0019] FIG. 3 shows an example of a flammability limit curve used to determine whether a skip fire should be initiated when a fuel mixture contains H2, N2, and CH4. The vertical axis of FIG. 3 represents the fuel concentration of the mixture, and the horizontal axis represents the ratio of N2 to CH4 (the ratio of inert gases). In reality, the flammability limit curve for this fuel mixture is expressed as a three-dimensional graph, with a coordinate axis representing the ratio of CH4 to H2 in addition to the coordinate axes representing the fuel concentration and N2 / CH4 shown in FIG. 3. However, the graph in FIG. 3 is a cross section of the three-dimensional graph when the ratio of CH4 to H2 is fixed at a certain value. Flammability limit curves C3 are known from literature and elsewhere. As in the case of FIG. 2, a curve offset by a fixed value or a fixed factor on the inside of the flammability limit curve C3 is defined as the skip fire criteria curve C4. The user prepares a graph (or a three-dimensional graph) for each CH4 / H2 ratio, as shown in Fig. 3, in which a criteria curve C4 is plotted against a known flammability limit curve C3, and stores and retains this graph in the determination unit 13. The determination unit 13 selects a graph (e.g., Fig. 3) including the flammability limit curve C3 and criteria curve C4 corresponding to the ratio of CH4 to H2 from the ratios of CH4, H2, and N2 acquired by the fuel composition acquisition unit 11 (or cuts out the graph from the three-dimensional graph), and plots the fuel state indicated by the N2 / CH4 ratio acquired by the fuel composition acquisition unit 11 and the fuel concentration acquired by the fuel concentration acquisition unit 12 on the selected graph shown in Fig. 3. The determination unit 13 checks whether the state of the fuel supplied to cylinder 4 is inside or outside the criteria curve C4, and determines not to execute skip fire if it is inside, and to execute skip fire if it is outside.

[0020] Here, a three-dimensional flammability limit curve is assumed to be given, but the flammability limit may be calculated using Le Chatelier's equation (1) below and the flammability limit curves C1 and C3 shown in FIGS. 2 and 3.

[0021]

[0022] v ｉ is the ratio of gas split, L ｉ is the fuel concentration at the flammable limit in the divided gases. For example, assume that the ratio of the fuel composition supplied into cylinder 4 is CH4:H2:N2=50%:20%:30%. (A) First, the determination unit 13 arbitrarily divides the CH4-H2-N2 mixed fuel into two combinations: CH4-N2 mixed gas and H2-N2 mixed gas. For example, the determination unit 13 divides into CH4:N2=50%:15% and H2:N2=20%:15%. (B) Next, each divided gas is divided into G ｉ If (i = 1, 2), the flammability limit L of the gas before division is the flammability limit L of the gas after division. ｉ This can be obtained from the above formula (1). Here, the upper limit of the flammability limit when CH4:N2 = 50%:15% is H1 and the lower limit is L1 (these can be determined from Figure 3), and the upper limit of the flammability limit when H2:N2 = 20%:15% is H2 and the lower limit is L2 (these can be determined from Figure 2). In this case, the upper limit of the flammability limit for a mixed fuel of CH4:H2:N2 = 50%:20%:30% can be calculated using the following formula (1'): Lh = 100 / ((50 / H1) + (15 / H1) + (20 / H2) + (15 / H2)) ... (1')

[0023] On the other hand, the lower flammability limit of a fuel mixture with a CH4:H2:N2 ratio of 50%:20%:30% can be calculated using the following formula (1"): Ll = 100 / ((50 / L1) + (15 / L1) + (20 / L2) + (15 / L2)) ... (1") The determination unit 13 calculates the upper limit Lh and lower limit Ll of the fuel concentration of the flammability limit for this fuel composition using formulas (1") and (1") from the ratios of CH4, H2, and N2 acquired by the fuel composition acquisition unit 11, the flammability limit curves C1 and C3, and formula (1). Furthermore, the determination unit 13 sets points offset by a certain value or a certain factor on the inside of the calculated upper limit Lh and lower limit Ll (in the direction of narrowing the range between the upper limit Lh and the lower limit Ll) as the upper limit Lh' and the lower limit Ll', respectively. The determination unit 13 then compares the fuel concentration in cylinder 4 acquired by the fuel concentration acquisition unit 12 with the calculated upper limit Lh' and lower limit Ll' of the fuel concentration. If the fuel concentration in cylinder 4 is within the range of Lh' to Ll', the determination unit 13 determines that backfire will not occur under this fuel condition and decides not to execute skip fire. On the other hand, if the fuel concentration value in cylinder 4 is greater than Lh' or less than Ll', the determination unit 13 determines that backfire may occur and decides to execute skip fire. Such calculations may be performed in advance to calculate upper and lower flammability limits according to the ratios of CH4, H2, and N2, and criteria values ​​based on the calculated upper and lower limits may be stored and held in the determination unit 13. For example, in the case of a fuel in which the ratio of CH4 to H2 is constant and only the ratio of nitrogen (N2) varies, a two-dimensional curve C1 similar to that shown in FIG. 2 for the ratio of CH4 to H2 can be obtained by changing the ratio of nitrogen (N2) to H2 and following the steps (A) and (B) described above. Criteria curve C2 is created by taking an offset from curve C1, etc. Similarly, in the case of a fuel in which the ratio of CH4 and nitrogen N2 to H2 varies, by following the steps (A) and (B) described above while changing the ratios of CH4 and N2 to H2, a three-dimensional curve is obtained by adding an axis representing the ratio of CH4 to hydrogen to the graph in Figure 2. Criteria curve C4 is created by taking an offset from this curve, etc.

[0024] (Operation) Next, the flow of the skip fire execution determination process will be described with reference to Fig. 4. Fig. 4 is a flowchart showing an example of the skip fire execution determination process according to the embodiment. As an example, it is assumed that the fuel composition is H2 and N2. It is assumed that the determination unit 13 stores and holds a graph of the criteria curve C2 shown in Fig. 2.

[0025] The fuel composition acquisition unit 11 estimates the proportion of inert gas in the fuel supplied to the cylinder 4 (step S1). For example, the fuel composition acquisition unit 11 acquires the N2 concentration from an N2 concentration sensor provided in a pipe through which fuel is supplied to the mixture generation device 31. The fuel composition acquisition unit 11 calculates the H2 concentration from the acquired N2 concentration, and calculates the ratio of the inert gas N2 to H2 (N2 / H2). Alternatively, the fuel composition acquisition unit 11 may acquire a predicted value of N2 / H2 calculated in advance by a simulation or the like, or may calculate an estimated value of N2 / H2 using a known calculation method.

[0026] The fuel concentration acquisition unit 12 estimates the fuel concentration in the mixture supplied to cylinder 4 (step S2). For example, the fuel concentration acquisition unit 12 acquires a fuel flow rate measured by a fuel flow rate sensor provided in a pipe to which fuel is supplied to the mixture generation device 31, and acquires an air flow rate measured by an air flow rate sensor provided in a pipe to which air is supplied to the mixture generation device 31. The fuel concentration acquisition unit 12 calculates the fuel concentration in the mixture by, for example, dividing the fuel flow rate by (fuel flow rate + air flow rate), and sets the calculated value as the fuel concentration in cylinder 4. The order of execution of steps S1 and S2 may be reversed, or steps may be performed simultaneously in parallel.

[0027] The determination unit 13 acquires the inert gas ratio N2 / H2 and the fuel concentration, and compares it with the criteria curve C2 to determine whether the acquired fuel concentration falls within the range between the upper and lower limits of the criteria curve C2 for the acquired N2 / H2 (step S3). If the acquired fuel concentration exceeds the upper limit of the criteria curve C2 or falls below the lower limit of the criteria curve C2 (step S3; Yes), the determination unit 13 determines to execute a skip fire (step S4). The determination unit 13 determines to execute a skip fire once every two cycles. If the acquired fuel concentration falls within the range between the upper and lower limits of the criteria curve C2 (step S3; No), the determination unit 13 determines not to execute a skip fire (step S5).

[0028] Next, the control device 10 determines whether or not to end the skip fire execution determination process (step S6). For example, when a command to stop the engine system 1 is input by the user, the control device 10 determines to end the skip fire execution determination process (step S6; Yes) and ends the process of the flowchart in Fig. 4. If the skip fire execution determination process is not to be ended (step S6; No), the process from step S1 is repeatedly executed.

[0029] (Effects) As described above, according to this embodiment, backfires caused by the state of fuel in the cylinder (caused by slow combustion) can be prevented or avoided. By utilizing the basic flammable gas-inert gas mixed fuel flammability limit curves C1, C3, etc. and Le Châtelier's equation (1), the upper and lower flammability limits can be calculated for fuels that combine a variety of flammable gases and inert gases. Backfires can be avoided by using the fuel state and the upper and lower flammability limits. While the upper and lower limit criteria are set for each ratio of inert gas to flammable gas in Figures 2 and 3, the upper and lower limit criteria may be set for each ratio of flammable gas in the fuel, each ratio of inert gas in the fuel, or each ratio of inert gas to flammable gas in the fuel.

[0030] (Another Example 1) While the above description has been given using an example of a fuel mixture composed of H2, N2, and the like, this embodiment can also be applied to a hydrogen engine fueled by H2 to determine whether to execute skip fire. In a hydrogen engine, pipes and the like are purged with nitrogen when the engine is stopped. Therefore, when the engine is started, a large amount of inert gas is present in the cylinder, which tends to slow combustion. The process of FIG. 4 can be used for skip fire control in such a situation. For example, a sensor for measuring the concentration of N2 is provided in the fuel pipe, and the N2 concentration contained in the fuel at the time of starting the engine 2 is measured. The fuel composition acquisition unit 11 estimates the N2 / H2 ratio from the measurement value of a sensor measuring the fuel flow rate in the mixture generation device 31, etc., and the measured N2 concentration (step S1). The fuel concentration acquisition unit 12 estimates the fuel concentration from the fuel flow rate and air flow rate (step S2). Then, as described above, the determination unit 13 determines whether the fuel concentration estimated in step S2 falls within the range between the upper and lower limits of the criteria curve C2 for N2 / H2 estimated in step S1 (step S3), and determines whether to execute skip fire. This makes it possible to avoid backfire in a hydrogen engine due to slow combustion when starting the engine after nitrogen purging.

[0031] In addition to the above process described with reference to FIG. 4 , the determination of whether to execute skip fire can also be performed by the following method. Method 1: (Step 1) A simulation is performed in advance using a computer external to the engine system 1 to simulate the start sequence of the engine 2, and a predicted value of the ratio of H2 to N2 in the fuel supplied to cylinder 4, for example, the time history of N2 / H2, is obtained. (Step 2) Using the predicted time history of N2 / H2, the computer calculates the time T until the fuel state (N2 / H2 and fuel concentration) in cylinder 4 falls within the region surrounded by the skip fire criteria curve C2 ( FIG. 2 ) and the risk of slow combustion is determined to be low. (Step 3) The calculated time T is stored and held in the determination unit 13 of the control device 10. (Step 4) When actually starting the hydrogen engine, the determination unit 13 determines to execute skip fire for the period from the start of the engine 2 until the time T has elapsed. After the time T has elapsed since the start of the engine 2, the execution of skip fire may be determined by the process described with reference to Fig. 4. This method can also be applied to the start of an engine that runs on a mixed fuel containing H2, N2, etc.

[0032] Method 2 (Step 1) For locations in the piping, etc. where the temperature, pressure, etc. can be obtained by calculation or sensor measurement, the volume V replaced with nitrogen during nitrogen purging is obtained in advance by simulation, experiment, etc. (Step 2) When the engine is started, the control device 10 estimates the fuel injection mass flow rate using a known calculation method, or constantly obtains it using a sensor, etc. The pressure P and temperature T of the portion replaced with nitrogen (called the inspection area) are constantly obtained. (Step 3) The control device 10 solves the following equations (2) to (4) for the inspection area replaced with nitrogen to obtain the average nitrogen density ρ of the portion replaced with nitrogen. Ｎ２ and the density of hydrogen ρ Ｈ２ Estimate.

[0033]

[0034]

[0035]

[0036] where ρ Ｈ２ is the density of H2, ρ Ｎ２ is the density of N2, m （ドット） ｉｎ＿Ｈ２ is the mass flow rate of H2 flowing into the inspection area (calculated from the measured fuel flow rate), m （ドット） ｏｕｔ＿Ｈ２ is the mass flow rate of H2 leaving the test area, m （ドット） ｏｕｔ＿Ｎ２ is the mass flow rate of N2 flowing out of the test area, m （ドット） ｏｕｔ is the fuel injection mass flow rate, m （ドット） ｏｕｔ＿Ｎ２ and m （ドット） ｏｕｔ＿Ｈ２ where V is the volume obtained in step 1, ρ is the density of the test region, R is the gas constant, P is the pressure of the test region, and T is the temperature of the test region.

[0037] (Step 4) From the result of step 3, the control device 10 calculates the ratio of H2 to N2 in the inspection area and outputs it to the determination unit 13. The fuel concentration is calculated in the same manner as in step S2 of FIG. 4 and output to the determination unit 13. (Step 5) Using the ratio of H2 to N2 and the fuel concentration received in step S4, the determination unit 13 refers to the criteria curve C2 and determines whether the fuel concentration is within or outside the range of the upper and lower limit values ​​corresponding to the ratio of H2 to N2 on the criteria curve C2. (Step 6) If the fuel concentration is outside the range, the determination unit 13 determines that combustion will slow down and decides to execute a skip fire.

[0038] (Another Example 2) When a load is cut off, the opening control of the throttle valve (not shown) provided in the intake pipe 3 for adjusting the flow rate of the air-fuel mixture may be delayed and may not follow the load change. This may result in the fuel in the cylinder 4 becoming leaner, slowing down combustion and making backfire more likely to occur. In this case, backfire can be avoided by performing the determination process described in FIG. 4 and executing skip fire.

[0039] 5 is a schematic block diagram showing the hardware configuration of a control device according to an embodiment. A computer 90 includes a processor 91, a main memory 92, a storage 93, and an interface 94. The above-described control device 10 is implemented in the computer 90. The operations of each of the above-described processing units are stored in the storage 93 in the form of a program. The processor 91 reads the program from the storage 93, loads it into the main memory 92, and executes the above-described processing in accordance with the program. The processor 91 allocates storage areas in the main memory 92 corresponding to each of the above-described storage units in accordance with the program. Examples of the processor 91 include a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), and a microprocessor.

[0040] The program may be for realizing some of the functions to be performed by the computer 90. For example, the program may be combined with other programs already stored in storage or implemented in other devices to perform the functions. In another embodiment, the computer 90 may include a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to or instead of the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), and FPGA (Field Programmable Gate Array). In this case, some or all of the functions realized by the processor 91 may be realized by the integrated circuit. Such an integrated circuit is also an example of a processor.

[0041] Examples of storage 93 include hard disk drives (HDDs), solid state drives (SSDs), magnetic disks, magneto-optical disks, compact disc read-only memories (CD-ROMs), digital versatile disc read-only memories (DVD-ROMs), and semiconductor memories. Storage 93 may be internal media directly connected to the bus of computer 90, or external media connected to computer 90 via interface 94 or a communication line. When this program is distributed to computer 90 via a communication line, computer 90 receiving the program may deploy the program in main memory 92 and execute the above-described processing. In at least one embodiment, storage 93 is a non-transitory, tangible storage medium. The program may be for implementing some of the above-described functions. Furthermore, the program may be a so-called differential file (differential program) that realizes the above-described functions in combination with other programs already stored in storage 93.

[0042] As described above, several embodiments according to the present disclosure have been described, but all of these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as defined in the claims, as well as in the scope and spirit of the invention.

[0043] <Additional Notes> The control device, engine system, skip fire execution determination method, and program described in each embodiment can be understood, for example, as follows.

[0044] (1) A control device according to a first aspect includes a determination unit that acquires a composition of fuel supplied to a cylinder of an engine that burns a mixture of fuel and air and a concentration of fuel in the mixture, determines whether the acquired fuel composition and the acquired fuel concentration fall within upper and lower limit values ​​of the criteria based on criteria information that defines a relationship between the fuel concentration, the fuel composition, and a flammability limit, and determines not to execute skip fire for the engine if the acquired fuel composition and the acquired fuel concentration fall within the upper and lower limit values, and determines to execute skip fire for the engine if the acquired fuel composition and the acquired fuel concentration fall outside the upper and lower limit values. This makes it possible to suppress backfires caused by the state of fuel in the cylinder.

[0045] (2) A control device according to a second aspect is the control device of (1), in which, when the fuel is composed of an inert gas and a flammable gas, the determination unit acquires the proportion of flammable gas in the fuel and the concentration of the fuel, and determines whether to execute skip fire using criteria information that is set by offsetting a flammability limit curve that defines the flammability limit of the concentration of the fuel for each proportion of flammable gas in the fuel to the inside. This makes it possible to determine whether to execute skip fire when the fuel is composed of an inert gas and a flammable gas.

[0046] (3) A control device according to a third aspect is the control device of (1), wherein, when the fuel is composed of an inert gas and multiple types of flammable gases, the determination unit arbitrarily divides the proportion of the inert gas in the fuel by the number of types of flammable gas, generates combinations of each of the multiple types of flammable gases with the inert gas after division as many times as the number of types of flammable gas, calculates upper and lower flammability limits for each generated combination based on the criteria information for the combination, calculates upper and lower flammability limits for the fuel based on the calculated upper and lower flammability limits for each combination and Le Chatelier's equation, and determines whether to execute skip fire using criteria set by offsetting the upper and lower limits inward as the criteria information for the fuel. This makes it possible to obtain criteria information even when the fuel is composed of an inert gas and multiple types of flammable gases.

[0047] (4) A control device according to a fourth aspect is the control device according to (1) to (2), wherein the fuel is composed of H2 and N2.

[0048] (5) A control device according to a fifth aspect is the control device according to any one of (1) to (3), wherein the fuel is composed of CH4, H2, and N2.

[0049] (6) A control device according to a sixth aspect is the control device of any one of (1) to (5), further comprising a second determination unit that acquires the time from a computer that simulates a start sequence of the engine and calculates the time until the fuel composition and the fuel concentration fall within the range of upper and lower limit values ​​of criteria set based on the flammability limit, and determines to execute skip fire for the period from the start of the engine until the time has elapsed. This makes it possible to suppress backfires caused by the state of fuel for each of the multiple engines.

[0050] (7) An engine system according to a seventh aspect includes an engine having one or more cylinders and a control device according to any one of (1) to (6).

[0051] (8) In the skip fire execution determination method according to the eighth aspect, the composition of fuel supplied to a cylinder of an engine that burns a mixture of fuel and air and the concentration of fuel in the mixture are obtained, and based on criteria information that defines the relationship between the fuel concentration, the fuel composition, and criteria set based on the flammability limit, it is determined whether the obtained fuel composition and the obtained fuel concentration fall within the range of upper and lower limit values ​​of the criteria, and if they fall within the range of the upper and lower limit values, it is determined not to execute skip fire for the engine, and if they are outside the range of the upper and lower limit values, it is determined to execute skip fire for the engine.

[0052] (9) A program according to a ninth aspect causes a computer to execute the following process: acquire the composition of fuel supplied to a cylinder of an engine that burns a mixture of fuel and air and the concentration of fuel in the mixture; determine whether the acquired fuel composition and the acquired fuel concentration fall within the range of upper and lower limit values ​​of the criteria based on criteria information that defines the relationship between the fuel concentration, the fuel composition, and the flammability limit; and decide not to execute skip fire for the engine if the acquired fuel composition and the acquired fuel concentration fall within the range of the upper and lower limit values; and decide to execute skip fire for the engine if the acquired fuel composition and the acquired fuel concentration fall outside the range of the upper and lower limit values.

[0053] According to the control device, engine system, skip fire execution determination method, and program described above, it is possible to suppress the occurrence of backfire caused by the state of fuel in the cylinder.

[0054] REFERENCE SIGNS LIST 1 engine system 2 engine 3a, 3b intake pipe 31a, 31b mixture generation device 4a, 4b cylinder 5a, 5b cylinder 6a, 6b piston 7a, 7b spark plug 8a, 8b combustion chamber 9a, 9b exhaust pipe 10 control device 11 fuel composition acquisition unit 12 fuel concentration acquisition unit 13 determination unit 14 control unit 90 computer 91 processor 92 main memory 93 storage 94 interface

Claims

1. A control device comprising a determination unit that acquires the composition of fuel supplied to a cylinder of an engine that burns a mixture of fuel and air and the concentration of fuel in the mixture, and determines whether the acquired fuel composition and concentration fall within the range of upper and lower limit values ​​of the criteria based on criteria information that defines the relationship between fuel concentration, fuel composition, and flammability limits, and decides not to execute skip fire for the engine if the acquired fuel composition and concentration fall within the range of the upper and lower limit values, and decides to execute skip fire for the engine if the acquired fuel composition and concentration fall outside the range of the upper and lower limit values.

2. The control device according to claim 1, wherein, when the fuel is composed of an inert gas and a flammable gas, the determination unit acquires the proportion of flammable gas in the fuel and the concentration of the fuel, and determines whether to execute a skip fire using criteria information that is set by offsetting inward a flammability limit curve that defines the flammability limit of the concentration of the fuel for each proportion of flammable gas in the fuel.

3. The control device according to claim 1, wherein, when the fuel is composed of an inert gas and multiple types of flammable gases, the determination unit arbitrarily divides the proportion of the inert gas in the fuel by the number of types of flammable gas, generates combinations of each of the multiple types of flammable gas and the inert gas after division as many times as the number of types of flammable gas, calculates upper and lower flammability limits for each generated combination based on the criteria information for that combination, calculates upper and lower flammability limits for the fuel based on the calculated upper and lower flammability limits for each combination and Le Chatelier's equation, and determines whether to execute a skip fire using criteria set by offsetting the upper and lower limits inward as the criteria information for the fuel.

4. The control device according to claim 1 or 2, wherein the fuel is composed of H2 and N2.

5. The control device according to claim 1 or 3, wherein the fuel is composed of CH4, H2 and N2.

6. A control device as described in claim 1 or claim 2, further comprising a second determination unit that acquires the time from a computer that simulates the engine start sequence and calculates the time until the fuel composition and concentration fall within the upper and lower limit values ​​of the criteria, and determines to execute skip fire for the period from the start of the engine until the time has elapsed.

7. An engine system comprising: an engine having one or more cylinders; and the control device according to claim 1 or 2.

8. A skip fire execution determination method, which acquires the composition of fuel supplied to a cylinder of an engine that burns a mixture of fuel and air and the concentration of fuel in said mixture, and determines whether the acquired fuel composition and the acquired fuel concentration fall within the range of upper and lower limit values ​​of the criteria based on criteria information that defines the relationship between fuel concentration, fuel composition, and criteria set based on flammability limits, and determines not to execute skip fire for the engine if they fall within the range of the upper and lower limit values, and determines to execute skip fire for the engine if they are outside the range of the upper and lower limit values.

9. A program that causes a computer to execute the following process: acquire the composition of fuel supplied to the cylinders of an engine that burns a mixture of fuel and air and the concentration of fuel in said mixture; determine whether the acquired fuel composition and the acquired fuel concentration fall within the range of upper and lower limit values ​​of the criteria based on criteria information that defines the relationship between fuel concentration, fuel composition, and flammability limits; and decide not to execute skip fire for the engine if they fall within the range of the upper and lower limit values, and decide to execute skip fire for the engine if they are outside the range of the upper and lower limit values.

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