Combustion device, internal combustion engine, combustion method, and knocking suppression method

Abstract

This combustion device includes: a combustion part that includes a combustion chamber and serves to combust a premixed fuel in the combustion chamber; and a flow promotion part for promoting the flow of an unburned fuel in the combustion chamber. This combustion method has: a combustion step for combusting a premixed fuel in a combustion chamber; and a flow promotion step for promoting the flow of an unburned fuel in the combustion chamber.

Description

Combustion device, internal combustion engine, combustion method, and knocking suppression method

[0001] This application claims priority to Japanese Patent Application No. 2023-193563, filed on November 14, 2023, the contents of which are incorporated herein by reference.

[0002] Non-Patent Document 1 reports that, as a result of research into SIP (Innovative Combustion Technology), by integrating the combustion technologies of ultra-lean combustion (gasoline) and high-speed spatial combustion (diesel) with loss reduction technology common to both engines, a maximum net thermal efficiency of over 50% has been achieved for both gasoline and diesel engines for passenger cars.

[0003] https: / / www.jst.go.jp / pr / announce / 20190116 / index.html

[0004] In conventional internal combustion engines such as gasoline engines and diesel engines, suppressing knocking is an important design issue. Knocking is a phenomenon in which unburned gases self-ignite, generating shock waves in the combustion chamber, which can potentially damage the internal combustion engine. In internal combustion engine design, knocking is suppressed by intentionally lowering the pressure and temperature (compression ratio) in the combustion chamber, but this type of knock suppression reduces the thermal efficiency of the internal combustion engine.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a combustion device, an internal combustion engine, a combustion method, and a knocking suppression method that are capable of suppressing the occurrence of knocking while suppressing a decrease in thermal efficiency more than conventional methods.

[0006] In order to achieve the above object, the present invention employs, as a first solution relating to a combustion device, a means comprising a combustion chamber, a combustion section that burns premixed fuel in the combustion chamber, and a flow promotion section that promotes the flow of unburned fuel in the combustion chamber.

[0007] The present invention employs, as a second solution relating to the combustion apparatus, the first solution, in which a plurality of the flow promoting portions are provided in the combustion chamber.

[0008] The present invention employs, as a third solution relating to the combustion apparatus, a solution in which, in the first or second solution, the flow promoting portion is a resonator that communicates with the combustion chamber.

[0009] The present invention employs, as a fourth solution relating to the combustion device, the third solution, further comprising an ignition unit that ignites the unburned fuel that has flowed into the resonator.

[0010] The present invention employs, as a fifth solution related to the combustion apparatus, a solution in which, in the first or second solution, the flow promoting section is a pressure generating section that generates pressure fluctuations in the combustion chamber.

[0011] The present invention provides a sixth solution relating to the combustion apparatus according to the fifth solution, in which the pressure generating section generates intermittent pressure fluctuations in the combustion chamber.

[0012] The present invention employs, as a seventh solution related to the combustion device, a solution in which, in the first or second solution, the combustion chamber includes a cylinder that accommodates the premixed fuel and a piston that compresses the premixed fuel, and the flow promoting portion is provided in the cylinder.

[0013] The present invention provides an eighth solution related to a combustion device, in which in the first or second solution, the flow promotion section causes the unburned fuel to flow so as to generate a vortex within the combustion chamber.

[0014] The present invention employs a combustion device according to any one of claims 1 to 8 as a means for solving the problem related to an internal combustion engine.

[0015] The present invention employs a combustion method having a combustion stroke for burning premixed fuel in a combustion chamber and a flow promotion stroke for promoting the flow of unburned fuel in the combustion chamber, as a solution to the problem.

[0016] The present invention employs a solution relating to a knocking suppression method that includes a flow promotion step for promoting the flow of unburned fuel in a premixed combustion field.

[0017] According to the present invention, it is possible to provide a combustion device, an internal combustion engine, a combustion method, and a knocking suppression method that are capable of suppressing the occurrence of knocking while suppressing a decrease in thermal efficiency more than ever before.

[0018] FIG. 1 is a longitudinal sectional view showing a configuration of a main part of an engine according to an embodiment of the present invention. FIG. 2 is a transverse sectional view showing a configuration of a main part of an engine according to an embodiment of the present invention. FIG. 3 is a schematic view showing a configuration of a main part of a flow promotion section according to an embodiment of the present invention. FIG. 4 is a schematic view showing a configuration of a main part of a flow promotion section according to a first modified example of an embodiment of the present invention. FIG. 5 is a schematic view showing a configuration of a main part of a flow promotion section according to a second modified example of an embodiment of the present invention. FIG. 6 is a schematic view showing a configuration of a main part of a flow promotion section according to a third modified example of an embodiment of the present invention. FIG. 7 is a flowchart showing a combustion method and a knocking suppression method according to an embodiment of the present invention. FIG. 8 is a flowchart showing a knocking prediction method according to an embodiment of the present invention. FIG. 9 is a table showing various physical quantities used in the theoretical explanation of an embodiment of the present invention. FIG. 10 is a first characteristic diagram showing a knocking prediction characteristic according to an embodiment of the present invention. FIG. 11 is a second characteristic diagram showing a knocking prediction characteristic according to an embodiment of the present invention. FIG. 12 is a third characteristic diagram showing a knocking prediction characteristic according to an embodiment of the present invention. FIG. 13 is a characteristic diagram showing a comparative example of a knocking prediction characteristic according to an embodiment of the present invention. FIG. 14 is a characteristic diagram showing the difference between a flat flame and an opposed-flow flame according to an embodiment of the present invention. FIG. 15 is a schematic view showing an opposed-flow flame according to an embodiment of the present invention. FIG. 16 is a characteristic diagram showing the characteristics of an opposed-flow flame according to an embodiment of the present invention.

[0019] An embodiment of the present invention will now be described with reference to the drawings. An engine A according to this embodiment is a four-stroke internal combustion engine that generates power by combusting various fuels, for example, liquid fuels such as gasoline and gaseous fuels such as hydrogen. The engine A is also a combustion device that generates thermal energy by combusting a premixed fuel of fuel and an oxidizer in a combustion chamber S, which will be described later.

[0020] The engine A according to this embodiment has a main structure shown in Figures 1A and 1B. Figure 1A shows a longitudinal section of the engine A, and Figure 1B shows a transverse section of the engine A. Note that although the engine A is actually a multi-cylinder internal combustion engine, Figure 1 shows only one cylinder for convenience.

[0021] As shown in FIGS. 1A and 1B, the engine A according to this embodiment includes, as its components, a cylinder 1, a piston 2, an intake valve 3, an exhaust valve 4, an injector 5, a butterfly valve 6, an ignition plug 7, four flow promoting parts 8A to 8D, and an ECU (Engine Control Unit) 9.

[0022] The cylinder 1 is a metal molded body with a cylindrical inner cavity (internal space). The cylinder 1 accommodates a piston 2 in the internal space. The cylinder 1 also forms a combustion chamber S surrounded by the circumferential surface of the inner cavity (cylinder wall) located above the piston 2 in FIG. 1A, the upper surface of the piston 2, and a cylinder head 2a provided on the top of the piston 2.

[0023] The combustion chamber S is an enclosed space in which premixed fuel, which is a mixture of fuel taken in from the outside and air (oxidizer), is burned, and corresponds to the premixed combustion field of the present invention. This combustion chamber S, together with the spark plug 7 described below, constitutes the combustion section of the present invention.

[0024] The piston 2 is a substantially cylindrical metal member, and its circumferential surface is a sliding surface against the cylinder wall of the cylinder 1. That is, the piston 2 is housed coaxially with the cylinder 1 in the internal space of the cylinder 1 and is capable of reciprocating freely in the axial direction of the internal space (the up-and-down direction in FIG. 1A ). One end (upper end) of a piston rod 2b extending downward is connected to the piston 2. The other end (lower end) of the piston rod 2b is connected to a crankshaft, which is the output shaft of the engine A.

[0025] The intake valve 3 is provided at the tip of the intake passage 2c and is an on-off valve that opens and closes in synchronization with the reciprocating motion of the piston 2, i.e., the rotation of the crankshaft. As shown in Figure 1A, the intake valve 3 is provided facing the combustion chamber S, and when closed, it shields the combustion chamber S from the intake passage 2c.

[0026] The intake valve 3 opens for a predetermined period when the premixed fuel is supplied to the combustion chamber S, and closes when a predetermined amount of premixed fuel has been taken into the combustion chamber S. In other words, the amount of premixed fuel taken into the combustion chamber S is determined mainly by the opening period of the intake valve 3.

[0027] The exhaust valve 4 is provided at the rear end of the exhaust flow path 2d and is an on-off valve that opens and closes in synchronization with the reciprocating motion of the piston 2, i.e., the rotation of the crankshaft, similar to the intake valve 3. The exhaust valve 4 is provided facing the combustion chamber S, similar to the intake valve 3, and when closed, it shields the combustion chamber S from the exhaust flow path 2d.

[0028] Although the opening timing of this exhaust valve 4 is different from that of the intake valve 3, it opens in synchronization with the reciprocating motion of the piston 2. This exhaust valve 4 opens as the piston 2 rises, allowing the combustion gas in the combustion chamber S to flow into the exhaust flow path 2d.

[0029] As shown in the figure, the injector 5 is an injection valve that is provided near the tip of the intake passage 2c and injects gasoline (fuel) into the intake passage 2c. The injector 5 injects a predetermined amount of gasoline (fuel) into the intake passage 2c based on an injection drive signal input from the ECU 9. The amount of gasoline (fuel) injected by the injector 5 is controlled by the injection drive signal.

[0030] The butterfly valve 6 is provided in the intake passage 2c upstream of the injector 5. The butterfly valve 6 is a flow control valve that adjusts the intake amount of air (oxidizer), i.e., the mixture amount of air (oxidizer) with gasoline (fuel). The butterfly valve 6 adjusts the passage area of ​​the air (oxidizer) by rotating around a central axis, and the rotation angle, i.e., the passage area, is adjusted based on an angle adjustment signal input from the ECU 9.

[0031] The spark plug 7 is an ignition component that forcibly ignites the premixed fuel in the combustion chamber S. The spark plug 7 operates based on an ignition signal input from the ECU 9, and forcibly ignites the premixed fuel. In other words, the operation timing of the spark plug 7, i.e., the ignition timing of the premixed fuel, is set to be synchronized with the reciprocating motion of the piston 2, i.e., the rotation of the crankshaft.

[0032] Here, the spark plug 7 ignites the premixed fuel taken into the combustion chamber S, thereby causing it to burn. The spark plug 7, together with the combustion chamber S, constitutes a combustion section that burns the premixed fuel in the combustion chamber S. In other words, the combustion section in the present invention is constituted by the combustion chamber S and the spark plug 7.

[0033] The four flow promotion section main parts 8A to 8D are the most characteristic components of the engine A according to this embodiment. As shown in Fig. 1A, these four flow promotion section main parts 8A to 8D are discretely arranged on the cylinder wall so as to face the combustion chamber S. More specifically, they are discretely arranged at the same positions in the axial direction of the cylinder wall.

[0034] 1B, the four flow promoting portion main parts 8A to 8D are provided at 90-degree angles with respect to the cylindrical cylinder wall. That is, the four flow promoting portion main parts 8A to 8D are discretely arranged at equal intervals in a plane perpendicular to the axial direction of the cylinder wall.

[0035] These four flow promotion portion main parts 8A to 8D forcibly fluidize the unburned fuel W that may remain in the combustion chamber S by applying an external force to the unburned fuel W. More preferably, the four flow promotion portion main parts 8A to 8D apply local pressure fluctuations (pressure vibration waves) to the unburned fuel W to generate vortices in the unburned fuel W, thereby effectively turbulently flowing the unburned fuel W.

[0036] 1A and 1B, these flow promotion parts 8A to 8D are operated based on a flow promotion signal input from the ECU 9. That is, the four flow promotion parts 8A to 8D are operated at a predetermined timing after the end of the combustion stroke of the engine A, thereby actively fluidizing the unburned fuel W remaining in the combustion chamber S.

[0037] Although details will be described later, fluidizing the unburned fuel W by the main parts 8A to 8D of the flow promoting section has the effect of suppressing knocking (self-ignition) of the engine A. That is, according to the knowledge of the present inventors, fluidizing the unburned fuel W remaining in the combustion chamber S makes it possible to suppress self-ignition of the unburned fuel W, thereby making it possible to suppress knocking of the engine A.

[0038] Here, in the engine A according to this embodiment, four flow promotion main parts 8A to 8D are provided, but the number of flow promotion main parts in the present invention is not limited to four. The number of flow promotion main parts in the present invention may be a single (one) part, or may be any number other than four.

[0039] Furthermore, when multiple flow promoters are provided, their arrangement is not limited to an angle of 90° relative to the cylinder wall. For example, when two flow promoters are provided, they may be arranged at an angle of 180°, and when three flow promoters are provided, they may be arranged at an angle of 120°.

[0040] The four flow promotion portion essential parts 8A to 8D in this embodiment have the detailed configuration shown in Fig. 2A, for example, and are pressure generating parts that generate pressure fluctuations in the combustion chamber S. That is, of the four flow promotion portion essential parts 8A to 8D, the first flow promotion portion essential part 8A includes a first resonator a1 and a first spark plug a2.

[0041] The first resonator a1 is a space that is partially connected to the combustion chamber S and resonates with pressure fluctuations of a specific frequency (specific period). The first resonator a1 resonates with pressure fluctuations of a specific frequency among pressure fluctuations in the combustion chamber S that accompany the combustion stroke of the engine A, thereby amplifying the pressure fluctuations of the specific frequency.

[0042] The first spark plug a2 is an ignition component that forcibly ignites a portion of the unburned fuel W that flows into the first resonance space. When the pressure fluctuation (speed fluctuation) caused by the first resonator a1 is insufficient, the first spark plug a2 ignites the unburned fuel W based on a first ignition signal input from the ECU 9. The first spark plug a2 ignites the unburned fuel W in the first resonator a1, thereby generating a jet from the first resonator a1, thereby further amplifying the speed fluctuation.

[0043] That is, the first flow promoting portion 8A amplifies pressure fluctuations of a specific frequency in the combustion chamber S. According to such first flow promoting portion 8A, the pressure fluctuations of the specific frequency act on the unburned fuel W in the combustion chamber S in an amplified state, so that the unburned fuel W can be fluidized effectively.

[0044] The second flow promoting portion 8B includes a second resonator b1 and a second spark plug b2. The second resonator b1 is a space that is partially connected to the combustion chamber S and resonates with the pressure fluctuations of the specific frequency. The second resonator b1 resonates with the pressure fluctuations of the specific frequency, thereby injecting the jet into the combustion chamber S and amplifying the velocity fluctuations.

[0045] The second spark plug b2 is an ignition component that forcibly ignites a portion of the unburned fuel W that flows into the resonance space. When the pressure fluctuation (speed fluctuation) caused by the second resonator b1 is insufficient, the second spark plug b2 ignites the unburned fuel W based on a second ignition signal input from the ECU 9. The second spark plug b2 ignites the unburned fuel W in the second resonator b1, thereby generating a jet from the second resonator b1, thereby further amplifying the speed fluctuation.

[0046] That is, like the first essential part 8A of the flow promotion section, the second essential part 8B of the flow promotion section amplifies pressure fluctuations of a specific frequency in the combustion chamber S. Like the first essential part 8A of the flow promotion section, the second essential part 8B of the flow promotion section acts on the unburned fuel W in the combustion chamber S in an amplified state of pressure fluctuations of a specific frequency, and therefore, the unburned fuel W can be fluidized effectively.

[0047] The third flow promoting portion 8C includes a third resonator c1 and a third spark plug c2. The third resonator c1 is a space that is partially connected to the combustion chamber S and resonates with the pressure fluctuations of the specific frequency. The third resonator c1 resonates with the pressure fluctuations of the specific frequency, thereby ejecting the jet into the combustion chamber S and amplifying the velocity fluctuations.

[0048] The third spark plug c2 is an ignition component that forcibly ignites a portion of the unburned fuel W that flows into the resonance space. When the pressure fluctuation (speed fluctuation) caused by the third resonator c1 is insufficient, the third spark plug c2 ignites the unburned fuel W based on a third ignition signal input from the ECU 9. The third spark plug c2 ignites the unburned fuel W in the third resonator c1, thereby generating a jet from the third resonator c1, thereby further amplifying the speed fluctuation.

[0049] That is, like the first and second flow promotion essential parts 8A and 8B, the third flow promotion essential part 8C amplifies pressure fluctuations of a specific frequency in the combustion chamber S. According to the third flow promotion essential part 8C, the pressure fluctuations of the specific frequency act on the unburned fuel W in the combustion chamber S in an amplified state, so that the unburned fuel W can be fluidized effectively.

[0050] The fourth flow promoting portion 8D includes a fourth resonator d1 and a fourth spark plug d2. The fourth resonator d1 is a space that is partially connected to the combustion chamber S and resonates with the pressure fluctuations of the specific frequency. The fourth resonator d1 resonates with the pressure fluctuations of the specific frequency, thereby ejecting the jet into the combustion chamber S and amplifying the velocity fluctuations.

[0051] The fourth spark plug d2 is an ignition component that forcibly ignites a portion of the unburned fuel W that flows into the resonance space. When the pressure fluctuation (speed fluctuation) caused by the fourth resonator d1 is insufficient, the fourth spark plug d2 ignites the unburned fuel W based on a fourth ignition signal input from the ECU 9. The fourth spark plug d2 ignites the unburned fuel W in the fourth resonator d1, thereby generating a jet from the fourth resonator d1, thereby further amplifying the speed fluctuation.

[0052] That is, like the first, second, and third flow promotion essential parts 8A, 8B, and 8C, the fourth flow promotion essential part 8D amplifies pressure fluctuations of a specific frequency in the combustion chamber S. According to the fourth flow promotion essential part 8D, the pressure fluctuations of the specific frequency act on the unburned fuel W in the combustion chamber S in an amplified state, so that the unburned fuel W can be fluidized effectively.

[0053] The activation timings of the first to fourth spark plugs a2 to d2 in the four flow promoting portions 8A to 8D are all set to the same timing, i.e., the first to fourth ignition signals are generated by the ECU 9 so that the first to fourth spark plugs a2 to d2 forcibly ignite the unburned fuel W in the resonance space at the same timing.

[0054] In addition to the four flow promoting portions 8A to 8D, three other variations as shown in FIGS. 2B, 3A, and 3B are possible for the flow promoting portion of the present invention.

[0055] 2B, the main flow promotion portion according to the first modified example is composed of four main flow promotion portions 8A1 to 8D1. These four main flow promotion portions 8A1 to 8D1 are pressure generating portions that generate pressure fluctuations in the combustion chamber S, similar to the four main flow promotion portions 8A to 8D described above. The four main flow promotion portions 8A1 to 8D1 are discretely arranged at the same position in the axial direction of the cylinder wall, and are also discretely arranged at equal intervals in a plane perpendicular to the axial direction of the cylinder wall.

[0056] The first flow promoting section main part 8A1 includes a first high-pressure source a3, a first siren wheel a4, and a first conduit a5. The first high-pressure source a3 is a pressure source that generates a predetermined high pressure (high pressure for flow). This high pressure for flow is higher than at least the maximum pressure in the combustion chamber S, and is supplied as a jet to the combustion chamber S via the first siren wheel a4 and the first conduit a5. As shown in the figure, the first high-pressure source a3 is provided outside the cylinder 1 together with the first siren wheel a4.

[0057] The first siren wheel a4 is a rotary shutter provided between the first high-pressure source a3 and the first conduit a5 and outside the cylinder 1. The first siren wheel a4 is a circular plate with slits formed at regular intervals on its periphery, and rotates to intermittently connect the first high-pressure source a3 and the first conduit a5.

[0058] The rotation speed of the first siren wheel a4 is controlled by a first rotation drive signal input from the ECU 9. Intermittent conduction between the first high pressure source a3 and the first conduit a5 based on the rotation of the first siren wheel a4 causes the flow high pressure of the first high pressure source a3 to be intermittently supplied to the combustion chamber S via the first conduit a5.

[0059] The first conduit a5 is a pipe that connects the combustion chamber S and the first high-pressure source a3. That is, the first conduit a5 is a rod-shaped pipe that penetrates the cylinder wall to communicate the first high-pressure source a3, which is provided outside the cylinder 1 together with the first siren wheel a4, with the combustion chamber S formed inside the cylinder 1.

[0060] The second flow promoting section main part 8B1 includes a second high-pressure source b3, a second siren wheel b4, and a second conduit b5. The second high-pressure source b3 is a pressure source that generates a predetermined high pressure (high pressure for flow). This high pressure for flow is higher than at least the maximum pressure in the combustion chamber S, and is supplied as a jet to the combustion chamber S via the second siren wheel b4 and the second conduit b5. As shown in the figure, the second high-pressure source b3 is provided outside the cylinder 1 together with the second siren wheel b4.

[0061] The second siren wheel b4 is a rotary shutter provided between the second high-pressure source b3 and the second conduit b5 and outside the cylinder 1. The second siren wheel b4 is a circular plate with slits formed at regular intervals on its periphery, and by rotating, it intermittently connects the second high-pressure source b3 and the second conduit b5.

[0062] The rotation speed of the second siren wheel b4 is controlled by a second rotation drive signal input from the ECU 9. Intermittent conduction between the second high pressure source b3 and the second conduit b5 based on the rotation of the second siren wheel b4 causes the flow high pressure of the second high pressure source b3 to be intermittently supplied to the combustion chamber S via the second conduit b5.

[0063] The second conduit b5 is a pipe that connects the combustion chamber S and the second high-pressure source b3. That is, the second conduit b5 is a rod-shaped pipe that penetrates the cylinder wall to communicate the second high-pressure source b3, which is provided outside the cylinder 1 together with the second siren wheel b4, with the combustion chamber S formed inside the cylinder 1.

[0064] The third flow promoting section 8C1 includes a third high-pressure source c3, a third siren wheel c4, and a third conduit c5. The third high-pressure source c3 is a pressure source that generates a predetermined high pressure (a high pressure for flow). This high pressure for flow is higher than at least the maximum pressure in the combustion chamber S, and is supplied as a jet to the combustion chamber S via the third siren wheel c4 and the third conduit c5. As shown in the figure, the third high-pressure source c3 is provided outside the cylinder 1 together with the third siren wheel c4.

[0065] The third siren wheel c4 is a rotary shutter provided between the third high-pressure source c3 and the third conduit c5 and outside the cylinder 1. The third siren wheel c4 is a circular plate with slits formed at regular intervals on its periphery, and rotates to intermittently connect the third high-pressure source c3 and the third conduit c5.

[0066] The rotation speed of the third siren wheel c4 is controlled by a third rotation drive signal input from the ECU 9. Intermittent conduction between the third high-pressure source c3 and the third conduit c5 based on the rotation of the third siren wheel c4 causes the flow high pressure of the third high-pressure source c3 to be intermittently supplied to the combustion chamber S via the third conduit c5.

[0067] The third conduit c5 is a pipe that connects the combustion chamber S and the third high-pressure source c3. That is, the third conduit c5 is a rod-shaped pipe that penetrates the cylinder wall to communicate the third high-pressure source c3, which is provided outside the cylinder 1 together with the third siren wheel c4, with the combustion chamber S formed inside the cylinder 1.

[0068] The fourth flow promoting section main part 8D1 includes a fourth high-pressure source d3, a fourth siren wheel d4, and a fourth conduit d5. The fourth high-pressure source d3 is a pressure source that generates a predetermined high pressure (high pressure for flow). This high pressure for flow is at least higher than the maximum pressure in the combustion chamber S, and is supplied as a jet to the combustion chamber S via the fourth siren wheel d4 and the fourth conduit d5. As shown in the figure, the fourth high-pressure source d3 is provided outside the cylinder 1 together with the fourth siren wheel d4.

[0069] The fourth siren wheel d4 is a rotary shutter provided between the fourth high pressure source d3 and the fourth conduit d5 and outside the cylinder 1. The fourth siren wheel d4 is a circular plate with slits formed at regular intervals on its periphery, and by rotating, it intermittently connects the fourth high pressure source d3 and the fourth conduit d5.

[0070] The rotation speed of the fourth siren wheel d4 is controlled by a fourth rotation drive signal input from the ECU 9. Intermittent conduction between the fourth high pressure source d3 and the fourth conduit d5 based on the rotation of the fourth siren wheel d4 causes the flow high pressure of the fourth high pressure source d3 to be intermittently supplied to the combustion chamber S via the fourth conduit d5.

[0071] The fourth conduit d5 is a pipe that connects the combustion chamber S and the fourth high-pressure source d3. That is, the fourth conduit d5 is a rod-shaped pipe that penetrates the cylinder wall to communicate the fourth high-pressure source d3, which is provided outside the cylinder 1 together with the fourth siren wheel d4, with the combustion chamber S formed inside the cylinder 1.

[0072] These four flow promotion section main parts 8A1 to 8D1 supply intermittent jets to the combustion chamber S by rotating the first to fourth siren wheels a4 to d4 at predetermined timings after the end of the combustion stroke of the engine A, thereby actively fluidizing the unburned fuel W remaining in the combustion chamber S. The fluidization of the unburned fuel W by the four flow promotion section main parts 8A1 to 8D1 suppresses knocking of the engine A.

[0073] 3A, the main part of the flow promotion section according to the second modification is composed of four main parts 8A2 to 8D2 of the flow promotion section. Similar to the four main parts 8A to 8D and 8A1 to 8D1 of the flow promotion section described above, these four main parts 8A2 to 8D2 of the flow promotion section are discretely arranged at the same position in the axial direction of the cylinder wall and are also discretely arranged at equal intervals in a plane perpendicular to the axial direction of the cylinder wall.

[0074] The first flow promoting section main part 8A2 includes a first vibration source a6, a first resonator a7, and a first conduit a8. The first vibration source a6 is provided outside the cylinder 1 and generates mechanical vibrations at a predetermined frequency (predetermined period) to mechanically vibrate the first resonator a7. The operation of the first vibration source a6 is controlled by a first vibration signal input from the ECU 9.

[0075] As shown in the figure, the first resonator a7 is provided outside the cylinder 1 and is a resonance space of a predetermined volume that communicates with the first conduit a8. The first conduit a8 is a circular pipe that penetrates the cylinder wall, one end of which communicates with the first resonator a7 and the other end of which communicates with the combustion chamber S.

[0076] In the first flow promoting portion 8A2, the first resonator a7 resonates with the mechanical vibrations generated by the first vibration source a6, causing repeated discharge and intake of a jet of fuel through the first conduit a8 between the combustion chamber S. Unburned fuel W remaining in the combustion chamber S is effectively fluidized by this repeated discharge and intake of the jet of fuel.

[0077] The second flow promoting section main part 8B2 includes a second vibration source b6, a second resonator b7, and a second conduit b8. The second vibration source b6 is provided outside the cylinder 1 and generates mechanical vibrations of a predetermined frequency (predetermined period) to mechanically vibrate the second resonator b7. The operation of the second vibration source b6 is controlled by a second vibration signal input from the ECU 9.

[0078] As shown in the figure, the second resonator b7 is provided outside the cylinder 1 and is a resonance space of a predetermined volume that communicates with the second conduit b8. The second conduit b8 is a circular pipe that penetrates the cylinder wall, with one end communicating with the second resonator b7 and the other end communicating with the combustion chamber S.

[0079] In the second flow promoting portion 8B2, the second resonator b7 resonates with the mechanical vibrations generated by the second vibration source b6, causing repeated discharge and intake of a jet of fuel through the second conduit b8 between the second flow promoting portion 8B2 and the combustion chamber S. The unburned fuel W remaining in the combustion chamber S is effectively fluidized by this repeated discharge and intake of a jet of fuel.

[0080] The third flow promoting section main part 8C2 includes a third vibration source c6, a third resonator c7, and a third conduit c8. The third vibration source c6 is provided outside the cylinder 1 and generates mechanical vibrations of a predetermined frequency (predetermined period) to mechanically vibrate the third resonator c7. The operation of the third vibration source c6 is controlled by a third vibration signal input from the ECU 9.

[0081] As shown in the figure, the third resonator c7 is provided outside the cylinder 1 and is a resonance space of a predetermined volume that communicates with the third conduit c8. The third conduit c8 is a circular pipe that penetrates the cylinder wall, one end of which communicates with the third resonator c7 and the other end of which communicates with the combustion chamber S.

[0082] In the third flow promoting portion 8C2, the second resonator b7 resonates with the mechanical vibrations generated by the second vibration source b6, causing repeated discharge and intake of a jet of fuel through the second conduit b8 between the third flow promoting portion 8C2 and the combustion chamber S. The unburned fuel W remaining in the combustion chamber S is effectively fluidized by this repeated discharge and intake of a jet of fuel.

[0083] The fourth flow promoting portion 8D2 includes a fourth vibration source d6, a fourth resonator d7, and a fourth conduit d8. The fourth vibration source d6 is provided outside the cylinder 1 and generates mechanical vibrations of a predetermined frequency (predetermined period) to mechanically vibrate the fourth resonator d7. The operation of the fourth vibration source d6 is controlled by a fourth vibration signal input from the ECU 9.

[0084] As shown in the figure, the fourth resonator d7 is provided outside the cylinder 1 and is a resonance space of a predetermined volume that communicates with the fourth conduit d8. The fourth conduit d8 is a circular pipe that penetrates the cylinder wall, one end of which communicates with the fourth resonator d7 and the other end of which communicates with the combustion chamber S.

[0085] In the fourth flow promoting portion 8D2, the second resonator b7 resonates with the mechanical vibrations generated by the second vibration source b6, causing repeated discharge and intake of a jet of fuel through the second conduit b8 between the fourth flow promoting portion 8D2 and the combustion chamber S. The unburned fuel W remaining in the combustion chamber S is effectively fluidized by this repeated discharge and intake of a jet of fuel.

[0086] 3B, the main part of the flow promotion section according to the third modification is composed of four main parts 8A3 to 8D3 of the flow promotion section. Similar to the four main parts 8A to 8D, 8A1 to 8D1, and 8A2 to 8D2 of the flow promotion section described above, these four main parts 8A3 to 8D3 of the flow promotion section are discretely arranged at the same position in the axial direction of the cylinder wall and are also discretely arranged so as to be equidistantly spaced in a plane perpendicular to the axial direction of the cylinder wall.

[0087] Each of the four flow promotion portions 8A3 to 8D3 is a resonator that resonates with pressure fluctuations at a specific frequency (specific period). That is, the four flow promotion portions 8A3 to 8D3 are equivalent to the four flow promotion portions 8A to 8D described above with the first to fourth spark plugs a2 to d2 removed. Like the four flow promotion portions 8A to 8D, the four flow promotion portions 8A3 to 8D3 are pressure generating portions that generate pressure fluctuations in the combustion chamber S.

[0088] The four flow promotion section essential parts 8A to 8D described above, equipped with the first to fourth spark plugs a2 to d2, act on the unburned fuel W in the combustion chamber S with an enhanced pressure vibration wave, whereas the four flow promotion section essential parts 8A3 to 8D3 act on the unburned fuel W as a pressure vibration wave by amplifying the pressure fluctuations through their own resonance.

[0089] That is, the four flow promotion essential parts 8A to 8D described above are active-type flow promotion essential parts that actively strengthen the pressure fluctuations amplified by resonance, whereas the four flow promotion essential parts 8A3 to 8D3 in the third modified example are passive-type flow promotion essential parts that passively cause the pressure fluctuations amplified by their own resonance to act on the unburned fuel W. These four flow promotion essential parts 8A3 to 8D3 effectively fluidize the unburned fuel W remaining in the combustion chamber S.

[0090] The ECU 9 (Engine Control Unit) is a control device that comprehensively controls the engine A. The ECU 9 is a type of control computer that controls the injector 5, butterfly valve 6, spark plug 7, and four flow promoting parts 8A to 8D, etc., based on a pre-installed engine control program.

[0091] The ECU 9 also refers to the rotation of the crankshaft when controlling the injector 5, butterfly valve 6, spark plug 7, and four essential flow promoting parts 8A to 8D. That is, the ECU 9 generates the above-mentioned various signals in synchronization with the rotation of the crankshaft, i.e., the reciprocating motion of the piston 2, thereby controlling the injector 5, butterfly valve 6, spark plug 7, and four essential flow promoting parts 8A to 8D in an integrated manner.

[0092] Next, the operation of the engine A according to this embodiment, that is, the combustion method and knocking suppression method according to this embodiment using the engine A, will be described with reference to the flowchart of FIG.

[0093] The engine A according to this embodiment is a four-stroke internal combustion engine, and as shown in FIG. 4, the crankshaft, which is the output shaft, is rotated by repeating an intake stroke (step P1), a compression stroke (step P2), a combustion stroke (step P3), a flow promotion stroke (step P4), and an exhaust stroke (step P5).

[0094] Among these intake stroke (step P1), compression stroke (step P2), combustion stroke (step P3), flow promotion stroke (step P4), and exhaust stroke (step P5), the combustion stroke (step P3) and the flow promotion stroke (step P4) constitute the combustion method according to this embodiment. The flow promotion stroke (step P4) corresponds to the knocking suppression method according to this embodiment.

[0095] During the intake stroke (step P1), the piston 2 descends within the cylinder 1, the intake valve 3 opens, and the exhaust valve 4 closes, thereby drawing premixed fuel generated in the intake passage 2c into the combustion chamber S.

[0096] Then, in the compression stroke (step P2), the intake valve 3 closes and the piston 2 moves up in the cylinder 1, compressing the premixed fuel. In the combustion stroke (step P3), the ECU 9 activates the spark plug 7 to ignite the premixed fuel while the premixed fuel is in a compressed state, causing the premixed fuel to burn.

[0097] In the combustion chamber S, combustion gas is generated by the combustion of the premixed fuel, causing a sudden rise in pressure. This sudden rise in pressure in the combustion chamber S exerts a direct force on the piston 2, causing it to move downward. This direct force is converted into rotational power by the crankshaft. Then, during the exhaust stroke (step P5), the piston 2 rises in conjunction with the rotation of the crankshaft, and the exhaust valve 4 opens, causing the combustion gas in the combustion chamber S to be exhausted into the exhaust passage 2d.

[0098] During such operation of the engine A, premixed fuel that was not fully burned in the combustion stroke (step P3), i.e., unburned fuel W, may remain in the combustion chamber S. This unburned fuel W is caused by a mismatch between the speed of transmission of combustion pressure from the ignition point (ignition point) of the spark plug 7 to the surroundings and the flame propagation speed.

[0099] Such unburned fuel W may self-ignite at a timing different from the normal ignition timing in the combustion chamber S, i.e., the operation timing of the spark plug 7, and cause so-called knocking. The engine A according to this embodiment is equipped with four flow promotion main parts 8A to 8D to suppress such knocking.

[0100] That is, in the combustion method and knocking suppression method according to this embodiment, the flow promotion stroke (step P4) is carried out during the transition from the combustion stroke (step P3) to the exhaust stroke (step P5) by using the four flow promotion section main parts 8A to 8D.

[0101] Specifically, the four flow promotion portion main parts 8A to 8D apply a pressure vibration wave to the unburned fuel W remaining in the combustion chamber S, thereby forcibly fluidizing the unburned fuel W. More preferably, the four flow promotion portion main parts 8A to 8D apply a pressure vibration wave to generate vortices in the unburned fuel W, thereby turbulently flowing the unburned fuel W.

[0102] The engine A (combustion device and internal combustion engine) according to this embodiment is equipped with a combustion chamber S and a spark plug 7 (combustion section) for burning premixed fuel, and flow promotion sections 8A-8D, 8A1-8D1, 8A2-8D2, 8A3-8D3 for promoting the flow of unburned fuel W in the combustion chamber S.

[0103] Therefore, according to this embodiment, it is possible to provide an engine A (combustion device and internal combustion engine) that can suppress the self-ignition of unburned fuel W by fluidizing (turbulentizing) the unburned fuel W, thereby suppressing the occurrence of knocking.

[0104] The combustion method according to this embodiment also includes a combustion stroke (step P3) in which premixed fuel is burned in the combustion chamber S, and a flow promotion step (step P4) in which flow promotion portions 8A to 8D, 8A1 to 8D1, 8A2 to 8D2, and 8A3 to 8D3 are used to promote the flow of unburned fuel W in the combustion chamber S. Furthermore, the knocking suppression method according to this embodiment also includes a flow promotion step (step P4) in which the flow of unburned fuel W in the combustion chamber S (premixed combustion field) is promoted.

[0105] Therefore, according to this embodiment, a combustion method and a knocking suppression method can be provided that can suppress the self-ignition of unburned fuel W by fluidizing (turbulentizing) the unburned fuel W, thereby suppressing the occurrence of the knocking phenomenon.

[0106] Next, the theoretical basis of the engine A (combustion device and internal combustion engine), combustion method, and knocking suppression method will be described with reference to FIGS.

[0107] 5 is a flowchart showing a knocking prediction method according to this embodiment. This flowchart shows the procedure for acquiring the flame propagation limit temperature, which is a condition for knocking to occur, in a combustion chamber S (premixed combustion field) where a premixed mixture of fuel and air (oxidizer) is ignited by a forced means such as spark ignition and then burned, i.e., the initial temperature at which knocking occurs.

[0108] This flowchart also shows an overview of the processing steps of a knocking prediction program (simulation program) executed by a predetermined computer. That is, this knocking prediction method is realized by information processing (simulation) using a computer.

[0109] A computer that executes this knocking prediction method, i.e., a computer that has a knocking prediction program installed therein, is the knocking prediction device of this embodiment. This knocking prediction device outputs the knocking occurrence conditions in a premixed combustion field by executing the knocking prediction program.

[0110] The premixed combustion field in this knocking prediction method is a combustion field corresponding to the combustion chamber of an internal combustion engine (prime mover), such as a gasoline engine installed in a vehicle as a power generating device. In designing gasoline engines, measures such as lowering the compression ratio are taken to prevent knocking, i.e., to prevent auto-ignition of unburned gas. Note that the above internal combustion engine includes a direct injection engine and an engine with a pre-chamber.

[0111] That is, this knocking prediction method relates to a design method for a combustion device equipped with a premixed combustion field (combustion chamber), a power generating device (prime mover), a vehicle, etc. The knocking prediction method according to this embodiment also relates to a design method for a fuel that burns in a premixed combustion field.

[0112] This knocking prediction method is based on the premise that when a spatiotemporal transformation of a flame is applied to a premixed combustion field, the temporal changes in the normalized fuel mass fraction and normalized temperature in zero-dimensional homogeneous ignition are equivalent to the spatial changes in one-dimensional laminar premixed flames. In other words, this knocking prediction method is based on the theoretical basis of the equivalence between the temporal changes in the normalized fuel mass fraction and normalized temperature in zero-dimensional homogeneous ignition and the spatial changes in one-dimensional laminar premixed flames.

[0113] According to this theoretical basis, the rate of decrease in the normalized fuel mass fraction in the preheating region of a premixed combustion field increases in the following order: Lewis number of the fuel is less than 1, Lewis number is 1 (= ignition), and Lewis number is greater than 1. Furthermore, it is derived that auto-ignition in the preheating region near the explosive transition can only occur for one-dimensional laminar premixed flames with Lewis numbers greater than 1. In other words, the time change in flame propagation is comparable in magnitude to that of compressed premixed gas or shock waves in a premixed combustion field. It is also clear that the Lewis number of the fuel in a premixed combustion field is a physical quantity that determines the existence of a premixed flame structure.

[0114] 6 is a table showing various physical quantities used in this theoretical explanation. The following equations (1) and (2) are governing equations for zero-dimensional homogeneous ignition using the normalized fuel mass fraction and temperature from the various physical quantities in this table.

[0115] The governing equations (1) and (2) are conservation laws of energy and chemical species under constant pressure and constant enthalpy, and are given by the mass fraction of the kth species, the chemical production rate of the kth species, the molecular weight of the kth species, the mass density, the temperature, the total number of chemical species, the enthalpy of the kth species, the average specific heat, and time.

[0116]

[0117] The mass density is given as the gas equation of state used for the interconversion of pressure, density, and temperature, as shown in the following equation (3): R in this equation of state (3) is a universal gas constant.

[0118]

[0119] Here, we consider the Legendre transformation from the multivariate function f. The total derivative of the multivariate function f, which indicates the characteristics of a gas mixture with temperature, mass density, mass fraction, and time as variables, is given by the following equation (4).

[0120]

[0121] In this equation (4), if the partial differential of the multivariate function f with respect to temperature is represented by "a", the multivariate function g shown in the following equation (5) is obtained. Furthermore, the total differential of this multivariate function g is expressed as the following equation (6), with the above-mentioned a, mass density, mass fraction, and time as variables. Based on equation (6), the total differential of the multivariate function g is expressed as the following equation (7).

[0122]

[0123] Furthermore, equation (8) is obtained based on a comparison between equations (6) and (7). Furthermore, since equation (5) can be defined as shown in equation (9), the relationship shown in equation (10) holds between multivariate function f and multivariate function g.

[0124]

[0125] Here, a candidate for the multivariate function f in Equation (8) and Equation (10) is the normalized temperature, and a candidate for the multivariate function g is the normalized fuel mass fraction in the case of the single-step chemical reaction model in Equation (8) or the normalized progress variable in the case of the multi-step chemical reaction model in Equation (10).

[0126] If it is assumed that once the multivariate function f or the multivariate function g at a certain time is determined, all of the variables (time, mass density, and fuel mass fraction) that represent the characteristics of the premixed gas in the premixed combustion field can be determined, that is, if it is assumed that the multivariate function f and the multivariate function g depend only on the time direction, then the above equations (8) and (10) can be rewritten from partial differential equations to ordinary differential equations.

[0127] As a result, when the normalized temperature is applied as a multivariate function f and the normalized fuel mass fraction is applied as a multivariate function g, the above equation (8) is expressed as the following equation (11), which shows the relationship between the time change of the normalized temperature and the time change of the normalized fuel mass fraction. Note that the normalized temperature is defined by the following equation (12), which uses the initial temperature and the final temperature as parameters. The normalized fuel mass fraction is defined by the following equation (13), which uses the initial fuel mass fraction and the final fuel mass fraction as parameters.

[0128]

[0129] Furthermore, when the normalized temperature is applied as a multivariate function f and the normalized progress variable of the multi-step chemical reaction model is applied as a multivariate function g, the above equation (10) is expressed as the following equation (14), which shows the relationship between the time change of the normalized temperature and the time change of the normalized progress variable.

[0130]

[0131] Here, to enable the Legendre transformation, the normalized temperature, normalized fuel mass fraction, and normalized progress variable must be convex functions. Additionally, to enable the Legendre transformation, all derivatives of the normalized temperature and the normalized progress variable must be greater than 0, and all derivatives of the normalized fuel mass fraction must be less than 0. This constraint always applies to single-step chemical reaction models and typically also applies to multi-step chemical reaction models.

[0132] In the following description, for simplicity, the normalized fuel mass fraction is used as the multivariate function g, and the signs of the normalized progress variables are simply inverted. Once either the normalized temperature or the normalized fuel mass fraction is determined, all remaining variables are determined. Based on this premise, equations (1) and (2) can be rewritten as the following equations (15) and (16) using the normalized temperature and normalized fuel mass fraction.

[0133]

[0134] As shown in equation (11) above, the relationship between normalized temperature and normalized fuel mass fraction is independent of time. Therefore, equation (11) can be rewritten as equation (17) below using residence time. Residence time is defined by equation (18) below, which is made up of the velocity and position of the fluid parcel, and is the total time spent by the fluid parcel within the control volume. The total derivative of such residence time is given by equation (19) below.

[0135]

[0136] By transforming equations (15) and (16) using equation (19), the following equations (20) and (21) are obtained. Furthermore, equation (17) can be rewritten as equation (22) using the position of the fluid parcel. Furthermore, the relationship shown in equation (23) is established based on equation (22).

[0137]

[0138] On the other hand, the conservation equations of a one-dimensional laminar premixed flame are given by the following equations (24) to (26) consisting of the laminar burning velocity, the mixing diffusion coefficient of the kth species, and the thermal conductivity of the premixed gas. Furthermore, equations (25) and (26) can be rewritten as the following equations (27) and (28) using the normalized temperature and normalized fuel mass fraction.

[0139]

[0140]

[0141] Substituting equations (22) and (23) into equation (27) gives the following equation (29): As can be seen by comparing equation (29) with equation (28), the only difference between the two equations is the first term on the right-hand side.

[0142]

[0143] Here, the Lewis number of the fuel is defined by the following equation (30). Comparing equations (28) and (29) with this Lewis number in mind, it can be seen that both equations are equivalent when the Lewis number is 1. In other words, for a fuel with a Lewis number of 1, the temporal changes in the normalized fuel mass fraction and normalized temperature in zero-dimensional homogeneous ignition are equivalent to the spatial changes in one-dimensional laminar premixed flames.

[0144]

[0145] Figure 7 shows the relationship between zero-dimensional homogeneous ignition and one-dimensional laminar premixed flames in premixed combustion fields using hydrogen, methane, propane, and SNIa as fuels. SNIa represents the carbon state in the nuclear combustion process of Type Ia supernovae and has a very high Lewis number. Hydrogen, methane, and propane have Lewis numbers of 0.36, 0.96, and 1.95, respectively.

[0146] As mentioned above, for fuels with a Lewis number of 1, zero-dimensional homogeneous ignition, as indicated by the normalized fuel mass fraction and normalized temperature, is equivalent to one-dimensional laminar premixed flames, as indicated by the normalized fuel mass fraction and normalized temperature. Also, the one-dimensional laminar premixed flame profile of fuels with a Lewis number less than 1 is downwardly convex compared to the profile of fuels with a Lewis number of 1 (zero-dimensional homogeneous ignition).

[0147] On the other hand, the profile of a one-dimensional laminar premixed flame of a fuel with a Lewis number greater than 1 is convex above the profile of a fuel with a Lewis number of 1 (zero-dimensional homogeneous ignition), and may intersect with the profile of a fuel with a Lewis number of 1 (zero-dimensional homogeneous ignition) in the high-temperature region (reaction zone) of the flame where heat release is high.

[0148] This indicates that for fuels with Lewis numbers less than 1, the mass diffusivity of the fuel is greater than the thermal diffusivity, so the fuel diffuses preferentially rather than being heated. Conversely, for fuels with Lewis numbers greater than 1, the thermal diffusivity of the fuel is greater than the mass diffusivity, so the fuel heats preferentially rather than being diffused.

[0149] That is, the fact that fuels with Lewis numbers greater than 1 are heated preferentially rather than diffused is consistent with well-known technical knowledge. The effect of the Lewis number on the relationship between temperature and fuel mass fraction is theoretically discussed in the well-known book by Buckmaster, and the characteristics in Figure 4 are consistent with that theory.

[0150] In the following, we will consider the relatively low temperature region (preheating region) of the premixed combustion field where the influence of the Lewis number is evident. In this study, we will assume that the well-known Soret effect and Dufur effect can be ignored.

[0151] 7, the consumption of normalized fuel mass fraction at a given normalized temperature can be considered as the progress of the combustion reaction, i.e., the progress of the combustion reaction is in the order of fuels with Lewis numbers less than 1, fuels with Lewis numbers of 1 (zero-dimensional homogeneous ignition), and fuels with Lewis numbers greater than 1.

[0152] Fuels with Lewis numbers smaller than 1 do not cause knocking in the preheating region. That is, even if the initial temperature and pressure in the premixed combustion field are very high, a one-dimensional laminar premixed flame can exist. In contrast, fuels with Lewis numbers larger than 1 may cause knocking in the preheating region. That is, depending on the initial temperature and pressure in the premixed combustion field, a one-dimensional laminar premixed flame cannot exist.

[0153] For example, gasoline, one of the fuels, has a Lewis number greater than 1, so knocking is expected to occur whenever the unburned gas region rises to a temperature and pressure that makes flame propagation impossible. That is, gasoline can affect the transition from flame propagation to detonation because the characteristic time of the flame behind the shock wave is similar to that at the time of ignition. Also, because gasoline has a Lewis number greater than 1, there may be a region behind the shock wave where flame propagation is impossible.

[0154] Simulations (one-dimensional steady-state analysis) of zero-dimensional homogeneous ignition and one-dimensional laminar premixed flames were performed for two types of premixed gases, namely, a premixed gas of hydrogen and air (hydrogen fuel) with a Lewis number smaller than 1, and a premixed gas of n-heptane and air (n-heptane fuel) with a Lewis number larger than 1, under the conditions of constant pressure and constant enthalpy.

[0155] This simulation performed a one-dimensional steady-state analysis of zero-dimensional homogeneous ignition and one-dimensional laminar premixed flames using a well-known multi-stage chemical reaction model. That is, this simulation performed a one-dimensional steady-state analysis of a one-dimensional laminar premixed flame propagating in one of two directions, left and right, in one dimension. The multi-stage chemical reaction model for hydrogen fuel was the well-known UT-JAXA model, and the multi-stage chemical reaction model for n-heptane fuel was the well-known Reduced SIP model.

[0156] In this simulation, the normalized temperature and normalized fuel mass fraction must be convex functions to maintain the Legendre transformation, so the calculation domain must be as short as possible. Therefore, in this simulation, the size of the domain including the unburned mixture, the flame reaction zone, and the burned gas in the premixed combustion field is set to the limit that can be encompassed by the flame. Note that the numerical conditions (initial conditions) for the pressure and equivalence ratio are fixed values, for example, 0.1 MPa and 1.0.

[0157] This simulation was also performed by varying the inlet temperature of a one-dimensional steady-state analysis of a one-dimensional laminar premixed flame from 300 to 3000 K in increments of 100 K. When calculation failure was confirmed even after reducing the calculation domain, the inlet temperature was changed in increments of 1 K to perform the numerical calculation.

[0158] Furthermore, this simulation performed a one-dimensional steady-state analysis of a one-dimensional laminar premixed flame, and then performed a numerical calculation of zero-dimensional homogeneous ignition using an initial temperature that allows calculation of a one-dimensional laminar premixed flame.

[0159] In this simulation (one-dimensional steady-state analysis), that is, in the knocking prediction method of this embodiment, the initial conditions required for the simulation, such as temperature, pressure, and the type and equivalence ratio of fuel, such as hydrogen fuel or n-heptane fuel, are first input into a knocking prediction device (computer) (step S1).

[0160] The knocking prediction device calculates the flame propagation limit temperature for each fuel by performing a one-dimensional steady-state analysis (calculation step) using the temperature, pressure, fuel type, and equivalence ratio input in step S1 and gradually increasing the inlet temperature (calculation start temperature) (step S2).

[0161] This one-dimensional steady-state analysis is a convergence calculation that shrinks the flame front and flame rear until the one-dimensional premixed flame structure becomes the narrowest calculation region that results in a unique solution. That is, the knocking prediction device sequentially calculates the burning velocity when the inlet temperature is gradually increased by one-dimensional steady-state analysis of the premixed combustion field, but the calculated burning velocity may converge or diverge depending on the set value of the inlet temperature.

[0162] The knocking prediction device performs a convergence determination (determination step) for each combustion speed calculation for a certain inlet temperature (calculation start temperature) (step S3). That is, in step S3, the knocking prediction device determines whether or not the combustion speed can no longer be obtained because a flame can no longer exist in the premixed combustion field. If the determination result in step S3 is "convergence," the knocking prediction device sets the inlet temperature even higher and executes the combustion speed calculation.

[0163] On the other hand, if the determination result in step S3 is "divergence," the knocking prediction device sets the inlet temperature corresponding to the previous combustion speed calculation as the flame propagation limit temperature (step S4). That is, the knocking prediction device acquires the flame propagation limit temperature (inlet temperature) corresponding to the last acquired combustion speed as the knocking occurrence condition. Then, the knocking prediction device outputs a simulation result including the acquired flame propagation limit temperature as the knocking occurrence condition (step S5).

[0164] Figure 8 shows an example of a simulation result (one-dimensional steady-state analysis result) of a one-dimensional laminar premixed flame, i.e., a calculation result including the knocking occurrence condition output from the calculation unit to the output unit. Also, Figure 9 shows an example of the relationship between the inlet temperature and the combustion velocity in a premixed combustion field based on such a simulation result.

[0165] Figure 9 shows that for hydrogen fuel, the burning velocity increases with increasing inlet or initial temperature, and a propagating flame exists even at an inlet temperature of 3000 K. Figure 9 also shows that for n-heptane fuel, the burning velocity increases with increasing inlet temperature, but a propagating flame cannot exist above about 1270 K.

[0166] That is, the theoretical basis of this embodiment theoretically shows that the relationship between the normalized fuel mass fraction and the normalized temperature is equivalent for zero-dimensional homogeneous ignition and one-dimensional laminar premixed flames, whose Lewis number after space-time transformation is 1. In addition, this theoretical basis theoretically shows that the Lewis number is a physical quantity that determines the existence of a premixed flame structure near the explosive transition of the flame in a premixed combustion field.

[0167] One-dimensional laminar premixed flames of fuels with Lewis numbers less than 1 do not ignite in the preheated zone, so a flame structure always exists. In contrast, one-dimensional laminar premixed flames of fuels with Lewis numbers greater than 1 may ignite in the preheated zone, so a flame structure does not exist when the temperature is above a certain threshold.

[0168] In other words, if the characteristic time of ignition and flame is on the same order of magnitude as behind a shock wave or the explosive transition of an SI engine, then ignition and flame should be discussed via the Lewis number.

[0169] 10 shows a comparative example of this embodiment. That is, this comparative example is a calculation result of the "Livengood-Wu integral" by direct numerical simulation (DNS). It is well known that direct numerical simulation (DNS) accurately simulates the combustion state of a premixed combustion field. As is well known, the "Livengood-Wu integral" indicates that knocking occurs when the time integral value becomes 1.

[0170] However, according to this calculation result, knocking does not occur at the point in time (CFI) when the time integral value becomes 1. According to this calculation result, knocking occurs at the point in time (KO) after the time integral value exceeds 1. Therefore, the knocking prediction method based on the "Livengood-Wu integral" has problems in terms of accuracy.

[0171] In contrast, the theoretical basis of this embodiment is based on the finding that for a fuel with a Lewis number of 1, the temporal changes in the normalized fuel mass fraction and normalized temperature in zero-dimensional homogeneous ignition are equivalent to the spatial changes in a one-dimensional laminar premixed flame, and therefore the accuracy is higher than that of the "Livengood-Wu integral." In other words, according to this theoretical basis, it is possible to provide a knocking prediction method and knocking prediction device that can further improve accuracy.

[0172] Here, in the knocking prediction method of this embodiment, the effectiveness of the knocking prediction method of this embodiment has been described for single-component fuels (pure substance fuels) such as "hydrogen" and "n-heptane" as examples of fuels to be evaluated for knocking prediction. However, the knocking prediction method of this embodiment can also be applied to other pure substance fuels such as methane and propane.

[0173] Furthermore, the knocking prediction method of this embodiment predicts knocking of the evaluation target fuel based on a one-dimensional steady-state analysis (simulation) of the evaluation target fuel. Therefore, the knocking prediction method of this embodiment is not limited to pure-substance fuels, and can be applied to multi-substance fuels that are mixtures of multiple components, as long as one-dimensional steady-state analysis (simulation) is possible.

[0174] As is well known, in order to perform one-dimensional steady-state analysis (simulation) of fuels, it is necessary to identify the chemical species involved in the fuel combustion phenomenon and the elementary reactions based on those chemical species. For example, fuels for which chemical species and elementary reactions have been identified at present include surrogate fuels consisting of up to five components defined in the SIP (Surrogate Innovative Combustion Technology) surrogate chemical reaction mechanism. However, for multi-component fuels consisting of six or more components, the chemical species and elementary reactions have not yet been identified in the SIP surrogate chemical reaction mechanism.

[0175] However, it is fully expected that the chemical species and elementary reactions will be identified in the future for multi-substance fuels consisting of six or more components. That is, it is fully expected that the chemical species and elementary reactions will be identified and one-dimensional steady-state analysis (simulation) will be possible for multi-substance fuels consisting of six or more components, and it is estimated that knocking prediction based on this embodiment will be fully possible.

[0176] Next, Fig. 11 is a characteristic diagram showing a combustion method and a knocking suppression method based on such a knocking prediction method. While Fig. 8 described above shows the results of a one-dimensional steady-state analysis of a one-dimensional laminar premixed flame propagating in one of two directions, left and right, in one dimension, i.e., a plane flame, Fig. 11 shows the results of a one-dimensional steady-state analysis of a counterflow flame rather than a plane flame.

[0177] That is, the one-dimensional steady-state analysis results (simulation results) in Figure 11 relate to the case where, as shown in Figure 12, premixed fuel is supplied toward the center from a pair of fuel injection ports N1, N2 arranged opposite each other and separated by a predetermined distance L, and a pair of left and right premixed flames B1, B2 propagate toward the center from two directions, left and right, in one dimension.

[0178] In such counterflow flames, a pair of premixed flames B1, B2 are stretched in accordance with the injection flow velocity of the premixed fuel injected toward the center from a pair of fuel injection ports N1, N2. A flat flame is a laminar flame in which the fluid state of the premixed fuel is laminar. In contrast, a counterflow flame is a turbulent flame in which the flow of the premixed fuel is activated, and the degree of fluidization (degree of turbulence) depends on the injection flow velocity of the premixed fuel.

[0179] As shown in Figure 11, a flat flame cannot propagate at a certain mixture temperature, making it impossible to calculate the propagation speed. On the other hand, a counterflow flame not only has a slightly increased propagation speed due to the activated flow of premixed fuel, but also does not experience a state in which the flame cannot propagate, and therefore does not experience a mixture temperature at which the propagation speed cannot be calculated.

[0180] The one-dimensional steady-state analysis results (simulation results) in Fig. 11 show that by fluidizing the premixed fuel, it is possible to shift the mixture temperature at which a flame cannot propagate to a higher temperature. In other words, the one-dimensional steady-state analysis results (simulation results) in Fig. 11 show that knocking can be suppressed by fluidizing, and more preferably, turbulently flowing, the unburned fuel in the combustion chamber S.

[0181] Figure 13 shows the results of one-dimensional steady-state analysis (simulation results) for several reference fuels (PRF0, PRF50, PRF90, and PRF95). These one-dimensional steady-state analysis results show that by fluidizing the premixed fuel and increasing the flame propagation speed, it is possible to increase the mixture temperature by approximately 10 K for the reference fuel (PRF0), for example.

[0182] The Japanese Industrial Standards (JIS) defines regular gasoline as having an octane number of 89 or higher, and premium gasoline as having an octane number of 96 or higher. The one-dimensional steady-state analysis results (simulation results) in Figure 13 show that fluidizing premixed gasoline fuel achieves the same knocking suppression effect as changing the fuel from regular gasoline to premium gasoline.

[0183] The present invention is not limited to the above-described embodiment, and the following modifications are possible, for example: (1) In the above-described embodiment, the combustion device of the present invention is described as being applied to a four-stroke internal combustion engine (engine) equipped with a cylinder 1 and a piston 2, but the present invention is not limited to this. In other words, the combustion device of the present invention is not limited to an internal combustion machine (power generator) that generates power, and may be any device that combusts premixed fuel.

[0184] (2) In the above embodiment, various flow promoting portions 8A to 8D, 8A1 to 8D1, 8A2 to 8D2, and 8A3 to 8D3 have been described, but the flow promoting portions of the present invention are not limited to these. The detailed configurations of the flow promoting portions 8A to 8D, 8A1 to 8D1, 8A2 to 8D2, and 8A3 to 8D3 described above are merely examples, and other detailed configurations may be adopted.

[0185] (3) In the above embodiment, four flow promoting portions 8A to 8D, 8A1 to 8D1, 8A2 to 8D2, and 8A3 to 8D3 are provided on the cylinder 1. However, the present invention is not limited to this. That is, the number of flow promoting portions in the present invention is not limited to four, and may be one, two, or five or more.

[0186] (4) In the above embodiment, the four flow promoting portions 8A to 8D, 8A1 to 8D1, 8A2 to 8D2, and 8A3 to 8D3 are provided at the same position in the axial direction of the cylinder 1. However, the present invention is not limited to this. In other words, when multiple flow promoting portions are provided on the cylinder 1, they may be arranged at different positions in the axial direction of the cylinder 1.

[0187] Although the embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the above-described embodiments, and it is possible to change the combination of the components in each embodiment, and to add various modifications to or omit each component, without departing from the spirit of the present invention. The present invention is not limited to the above description.

[0188] It is possible to provide a combustion device, an internal combustion engine, a combustion method, and a knocking suppression method that are capable of suppressing the occurrence of knocking while suppressing a decrease in thermal efficiency more than ever before.

[0189] A: Engine S: Combustion chamber W: Unburned fuel 1: Cylinder 2: Piston 2a: Cylinder head 2b: Piston rod 2c: Intake passage 2d: Exhaust passage 3: Intake valve 4: Exhaust valve 5: Injector 6: Butterfly valve 7: Spark plug 8A to 8D, 8A1 to 8D1, 8A2 to 8D2, 8A3 to 8D3: Flow promoting section 9: ECU

Claims

1. A combustion device comprising: a combustion section having a combustion chamber and combusting premixed fuel in the combustion chamber; and a flow promotion section that promotes the flow of unburned fuel in the combustion chamber.

2. The combustion device according to claim 1, wherein a plurality of said flow promoting sections are provided in said combustion chamber.

3. A combustion device as claimed in claim 1 or 2, wherein the flow promoting portion is a resonator communicating with the combustion chamber.

4. The combustion device according to claim 3, further comprising an ignition section for igniting the unburned fuel that has flowed into the resonator.

5. A combustion device according to claim 1 or 2, wherein the flow promoting section is a pressure generating section which generates pressure fluctuations within the combustion chamber.

6. The combustion device according to claim 5, wherein said pressure generating section generates intermittent pressure fluctuations in said combustion chamber.

7. A combustion device according to claim 1 or 2, wherein the combustion chamber comprises a cylinder that accommodates the premixed fuel and a piston that compresses the premixed fuel, and the flow promoting portion is provided in the cylinder.

8. A combustion device according to claim 1 or 2, wherein the flow promotion section causes the unburned fuel to flow so as to generate a vortex within the combustion chamber.

9. An internal combustion engine equipped with a combustion device according to claim 1 or 2.

10. A combustion method comprising: a combustion step for burning premixed fuel in a combustion chamber; and a flow promotion step for promoting the flow of unburned fuel in the combustion chamber.

11. A knocking suppression method having a flow promotion process for promoting the flow of unburned fuel in a premixed combustion field.

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