JP2017072031A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion chamber structure suitable for gas combustion in an internal combustion engine with gas fuel directly injected into a combustion chamber.SOLUTION: An internal combustion engine 1 comprises: an internal combustion engine body 2 which has a cylinder 4 with a combustion chamber ceiling section 5 provided at one end thereof; an intake port 11 and an exhaust port 12 which are opened on the combustion chamber ceiling section; a piston 7 provided with a crest surface 7A which is slidably stored in the cylinder and defines a combustion chamber 8 together with the combustion chamber ceiling section, a cavity 30 which is formed in a shape of a concave circle around a cylinder axial line A on the crest surface and has an edge wall section 30B almost vertically connected to the crest surface around an outer edge thereof, and a convex section 31 which is protruded from a bottom section 30A of the cavity with an almost conical shape around the cylinder axial line; an ignition plug 19 with an ignition section 19A protruded from the combustion chamber ceiling section; and an injector 17 which is provided at the center of the combustion chamber ceiling section and injects gas fuel toward the convex section along the cylinder axial line.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an internal combustion engine that directly injects gaseous fuel into a combustion chamber.

Gaseous fuels, including natural gas and hydrogen or the like has a low CO ₂ emissions and NO _x emissions per unit calorific value than gasoline, environmental impact is known as a low fuel. Natural gas or the like has a higher octane number than gasoline, and it is possible to increase the efficiency by setting the compression ratio of the internal combustion engine high. On the other hand, natural gas or the like has the characteristics that the energy required for ignition is larger than that of gasoline and the laminar combustion speed is low. Therefore, when using gaseous fuel such as natural gas in an internal combustion engine, how to stabilize the combustion becomes important.

  In a gasoline direct injection engine, stratified combustion is used in order to stably perform lean combustion. This stratified combustion has been attempted to be improved by various methods such as changing the shape of the piston crown and changing the layout of the injector and spark plug (for example, Patent Documents 1 and 2).

Japanese Patent No. 5549510 Japanese Patent No. 4155044

  In the case of gasoline injection, it is necessary to secure time for vaporizing gasoline after injection, but in the case of gaseous fuel injection, the time is not required, so the injection timing is different between gasoline injection and gaseous fuel injection. Will be different. Therefore, in a gasoline direct injection engine, efficient combustion cannot be performed by simply changing the fuel to be injected from gasoline to gaseous fuel. For example, in the internal combustion engine according to Patent Document 1, since the edge wall of the cavity formed on the top surface of the piston is inclined so as to spread upward, the air-fuel mixture that rebounds from the cavity is guided to the ignition part of the ignition plug. In order to form a combustible layer around the ignition part at the ignition timing, it is necessary to limit the injection timing, and it is difficult to replace the gas fuel with a different injection timing. Further, in the internal combustion engine according to Patent Document 1, the ignition part of the ignition plug is disposed in the vicinity of the injection hole of the injector, and the injection direction is directed to the ignition part. When used, the initial flame is blown out by the jet of fuel, and there is a problem that ignition stability cannot be ensured.

  In view of the above background, an object of the present invention is to provide a combustion chamber structure suitable for gaseous fuel in an internal combustion engine that directly injects gaseous fuel into the combustion chamber.

  In order to solve the above-mentioned problems, an aspect of the present invention includes an internal combustion engine body (2) including a cylinder (4) having a combustion chamber ceiling (5) at one end, and an intake port that opens to the combustion chamber ceiling. (11) and an exhaust port (12), a crown surface (7A) that is slidably received in the cylinder and defines a combustion chamber (8) in cooperation with the combustion chamber ceiling, and a cylinder on the crown surface A cavity (30) provided with an edge wall (30B) that is recessed in a circle centered on the axis (A) and is connected to the peripheral surface substantially perpendicularly to the crown surface, and protrudes into the bottom (30A) of the cavity. A piston (7) provided with a substantially conical convex part (31) centered on the cylinder axis, and an ignition plug (19) provided with an ignition part (19A) protruding from the combustion chamber ceiling part, Located in the center of the combustion chamber ceiling and along the cylinder axis Towards the convex portion to provide an internal combustion engine and having an injector (17) for injecting gaseous fuel.

  According to this aspect, the gaseous fuel injected from the injector is guided to the convex portion and flows radially in the cavity in the axial direction, and then guided to the edge wall portion of the cavity and flows toward the combustion chamber ceiling portion. Form a combustible layer. Since the edge wall portion is arranged so as to be connected substantially perpendicular to the crown surface, the gaseous fuel flows from the edge wall portion to the combustion chamber ceiling portion in parallel with the cylinder axis. For this reason, even when the injection timing is different and the piston position changes at that time, the gaseous fuel always flows toward a predetermined position on the ceiling portion of the combustion chamber and forms a combustible layer around the ignition portion. Can do. That is, the injection timing can be changed while forming a combustible layer around the ignition part. This makes it possible to adjust the injection timing according to the load and the like.

  Moreover, said aspect WHEREIN: The said ignition part is good to be arrange | positioned in the position which overlaps with the said cavity seeing from the direction along a cylinder axis line.

  According to this aspect, the gaseous fuel is guided by the edge wall portion to the region overlapping with the cavity when viewed from the direction along the cylinder axis, so that a combustible layer having a high equivalence ratio is formed around the ignition portion. It will be.

  In the above aspect, the intake port may include swirl flow generation means (11A, 11B) that promotes a swirl flow of intake air flowing from the intake port into the combustion chamber.

  According to this aspect, the combustion rate can be increased by utilizing the flow of the combustible layer by the swirl flow.

  In the above aspect, the combustion chamber ceiling portion may be formed in a flat surface.

  According to this aspect, the generation of a tumble flow is suppressed in the combustion chamber. Thereby, while spreading | diffusion of a combustible layer is suppressed, it becomes easy to maintain a swirl flow.

  In the above aspect, the boundary (30C) between the bottom of the cavity and the edge wall may be formed as a smooth curved surface. Moreover, the boundary part (33) between the bottom part and the convex part of the cavity may be formed in a smooth curved surface. In addition, the cavity and the convex portion may cooperate with each other to form a toroidal concave portion centering on the cylinder axis.

  According to these aspects, the gaseous fuel injected from the injector is smoothly guided along the convex portion and the wall surface of the cavity, and the formation of the combustible layer is further ensured.

  According to the above configuration, a combustion chamber structure suitable for gaseous fuel can be provided in an internal combustion engine that directly injects gaseous fuel into the combustion chamber.

It is sectional drawing of the internal combustion engine which concerns on this embodiment, Comprising: A piston exists in the middle vicinity in a compression stroke View of combustion chamber ceiling from below It is sectional drawing of an internal combustion engine, Comprising: The piston exists in the vicinity of a top dead center in a compression stroke The figure which shows the combustion injection timing in the high load state A graph showing the rate of change in combustion with respect to the air-fuel ratio under high load Graph showing combustion period versus air-fuel ratio under high load conditions Diagram showing combustion injection timing in low and high load conditions A graph showing the rate of combustion fluctuation with respect to the air-fuel ratio under low load conditions Graph showing combustion period versus air-fuel ratio in low load condition

  Hereinafter, an embodiment in which the present invention is applied to a 4-valve CNG direct injection engine will be described with reference to the drawings.

(Structure of internal combustion engine)
The internal combustion engine 1 is a four-stroke engine, and has an internal combustion engine body 2 including a cylinder block 2A and a cylinder head 2B fastened to the upper end surface of the cylinder block 2A as shown in FIG. The cylinder block 2A is formed with a cylinder 4 that opens to the upper end surface of the cylinder block 2A. A portion of the lower end surface of the cylinder head 2B that faces the upper end of the cylinder 4 is referred to as a combustion chamber ceiling portion 5. The combustion chamber ceiling 5 is formed in a flat surface and closes the upper end of the cylinder 4. A piston 7 is received in the cylinder 4 so as to reciprocate. A combustion chamber 8 is defined by the combustion chamber ceiling 5, the wall surface of the cylinder 4, and the crown surface 7 </ b> A of the piston 7.

  As shown in FIGS. 1 and 2, the combustion chamber ceiling 5 has two intake ports 11 and two exhaust ports 12. In the combustion chamber ceiling 5, two intake ports 11 are arranged on one side (intake side), and two exhaust ports 12 are arranged on the other side (exhaust side). Open ends of the intake port 11 and the exhaust port 12 on the combustion chamber ceiling 5 side are opened and closed by an intake valve 13 and an exhaust valve 14 which are poppet valves.

  The intake port 11 has swirl flow generation means (11A, 11B) that promotes a swirl flow of intake air flowing from the intake port 11 into the combustion chamber 8. The swirl flow generation means is realized by a known means such as the shape of the intake port 11 or a swirl generation valve. For example, the intake port 11 includes a helical port 11A in which the opening end on the combustion chamber 8 side is formed in a spiral shape centering on the axis of the opening end, and a tangential port extending in a tangential direction about the cylinder axis A It may be formed as 11B. As shown in FIG. 2, in this embodiment, one of the intake ports 11 is a helical port 11A, and the other is a tangential port 11B. As a result, a counterclockwise (counterclockwise) swirl flow is formed when viewed from below along the cylinder axis A. The swirl ratio is preferably about 1-2.

  An injector hole 16 is opened at the center of the combustion chamber ceiling 5. An injector 17 is inserted into the injector hole 16. The injector 17 is means for injecting high-pressure gaseous fuel directly into the combustion chamber 8. In this embodiment, the injector 17 is suitable for CNG and is connected to the CNG cylinder via a delivery pipe and a pressure control valve. The injection hole of the injector 17 is arranged coaxially with the cylinder axis A. CNG injected from the injection hole has a conical spray shape centered on the cylinder axis A, and is directed downward (on the piston 7 side) along the cylinder axis A.

  A spark plug hole 18 is formed in a portion between the two intake ports 11 of the combustion chamber ceiling 5. The spark plug hole 18 has a spark plug 19 that is a spark plug inserted in the spark plug hole 18. An ignition part 19 </ b> A made of a ground electrode is provided at the tip of the spark plug 19, and the ignition part 19 </ b> A protrudes into the combustion chamber 8.

  As shown in FIG. 1, a pair of disc-shaped crown portions 21, a pair of skirt portions 22 projecting downward from the peripheral edge portion of the crown portion 21, and a pair of side edges corresponding to each other of the skirt portions 22 are connected to each other. And a connecting wall portion 23. The axis of the piston 7 coincides with the cylinder axis A.

  A first annular groove, a second annular groove, and a third annular groove (reference numerals omitted) extending in the circumferential direction are formed on the outer peripheral portion of the crown portion 21 in order from the top. A compression ring 26 is fitted in each of the first annular groove and the second annular groove, and an oil ring 27 is fitted in the third annular groove.

  A crown surface 7A facing the combustion chamber 8 side of the crown portion 21 is formed in a plane perpendicular to the cylinder axis A. A cavity 30 is recessed in the center of the crown surface 7A. The cavity 30 is formed in a circular shape centered on the cylinder axis A, and has a bottom portion 30A and an edge wall portion 30B provided at the peripheral edge of the bottom portion 30A. The edge wall portion 30B is formed in a cylindrical surface centered on the cylinder axis A, and is connected perpendicularly to the crown surface 7A at the upper end. Here, the angle formed between the upper end of the edge wall portion 30B and the crown surface 7A may be substantially vertical, and may have a slight width (for example, 87 to 93 °). In the present embodiment, the angle formed by the upper end of the edge wall portion 30B and the crown surface 7A is 90 °. The surface of the corner part 30C at the boundary between the edge wall part 30B and the bottom part 30A is formed into a smooth curved surface. The wall surface of the edge wall portion 30B, the surface of the corner portion 30C, and the upper surface of the bottom portion 30A form a smoothly continuous surface.

  A substantially conical convex portion 31 centering on the cylinder axis A is projected from the center of the bottom portion 30A. The protruding end of the convex portion 31 is disposed below the crown surface 7A. That is, the height of the convex portion 31 is set to be smaller than the depth of the cavity 30. The height of the convex portion 31 may be ½ or less of the depth of the cavity 30. When viewed from the direction along the cylinder axis A, the peripheral edge of the protrusion 31 extends to the vicinity of the peripheral edge of the bottom 30A. When viewed from the direction along the cylinder axis A, the convex portion 31 is disposed so as to cover at least half of the bottom portion 30 </ b> A of the cavity 30. The protruding end of the convex portion 31 is formed into a smooth curved surface that is chamfered. Moreover, the surface of the boundary part 33 between the peripheral edge part of the convex part 31 and the bottom part 30A is formed in a smooth curved surface. The wall surface of the convex part 31, the surface of the boundary part 33, and the upper surface of the bottom part 30A form a smoothly continuous surface.

  The cavity 30 and the convex portion 31 cooperate to form a toroidal shape with the cylinder axis A as the center, and the depth of the peripheral edge portion is deeper than the central portion. The crown surface 7A including the cavity 30 and the convex portion 31 is formed in an axially symmetric shape with the cylinder axis A as an axis of symmetry.

  The ignition portion 19 </ b> A of the spark plug 19 is disposed in a portion overlapping the cavity 30 when viewed from the direction along the cylinder axis A. More specifically, the ignition part 19 </ b> A is disposed in the cavity 30 on the edge wall part 30 </ b> B side with respect to the center as viewed from the direction along the cylinder axis A.

  As shown in FIG. 1, the gaseous fuel injected from the injector 17 forms a combustible layer 35 (fuel layer), proceeds downward (on the crown surface 7A side) along the cylinder axis A, and is centered on the cylinder axis A. It spreads like a cone. Thereafter, the combustible layer 35 is guided to the wall surface of the convex portion 31 and flows radially outward (radially) around the cylinder axis A, and is guided upward by the upper surface of the bottom portion 30A and the surface of the corner portion 30C. Thereafter, the combustible layer 35 is guided to the edge wall portion 30B and flows upward in parallel with the cylinder axis A, that is, toward the combustion chamber ceiling portion 5 side. The combustible layer 35 facing the combustion chamber ceiling 5 is formed in an axisymmetric shape with the cylinder axis A as the center, and has an annular shape (cylindrical shape) with the cylinder axis A as the center in the vicinity of the combustion chamber ceiling 5. Although the swirl flow is formed in the combustion chamber 8 by the intake air flowing into the combustion chamber 8 from the intake port 11, the combustible layer 35 is axially symmetric with respect to the cylinder axis A, and therefore is affected by the swirl flow. Although it rotates around the cylinder axis A, the shape is maintained.

  Thereafter, the combustible layer 35 that forms a ring and faces upward collides with the combustion chamber ceiling 5 and flows radially inward (on the cylinder axis A side). In this way, the combustible layer 35 is formed in the vicinity of the combustion chamber ceiling 5. The combustible layer 35 that forms a ring and faces upward mainly reaches the portion of the combustion chamber ceiling 5 that faces the outer peripheral portion of the cavity 30, and therefore the equivalent ratio (fuel concentration) of this portion is near the combustion chamber ceiling 5. Higher than other parts. The equivalence ratio is a numerical value representing the concentration of fuel, and is calculated by dividing the fuel / air ratio of the actual mixture ratio by the theoretical fuel / air ratio.

  As shown in FIG. 3, the combustible layers 35 that collide with the combustion chamber ceiling portion 5 and flow radially inwardly press against each other and flow downward, and then rotate so as to form a vortex along their own flow. The combustible layer 35 diffuses in the process of rotating and mixes with the air in the combustion chamber 8 to approach a homogeneous air-fuel mixture. That is, the combustible layer 35 exists for a predetermined period from the fuel injection timing, and changes to a homogeneous air-fuel mixture over time. The concentration of the homogeneous mixture is determined by the intake air amount and the fuel injection amount, and is lower than the concentration of the combustible layer 35. When the fuel injection timing is earlier than the predetermined period with respect to the ignition timing (advance timing), a homogeneous mixture exists around the ignition portion 19A at the ignition timing, and the fuel injection timing is within the predetermined period with respect to the ignition timing. In some cases (retard timing), the combustible layer 35 exists around the ignition portion 19A at the ignition timing.

  When ignition is performed in the ignition part 19A of the spark plug 19 at the ignition timing, the initial flame propagates to the flame and the air-fuel mixture burns. At this time, as shown in FIG. 2, the flame propagation is promoted in the circumferential direction around the cylinder axis A by the flow of the swirl flow, and the flame propagation speed is increased. In particular, when ignited at a retarded timing, since an annular combustible layer 35 centering on the cylinder axis A exists in the vicinity of the combustion chamber ceiling 5, the circumferential flame propagation along the combustible layer 35 causes swirl flow. To increase the burning rate.

  In the internal combustion engine 1 according to the present embodiment, since the edge wall portion 30B is arranged so as to be connected substantially perpendicularly to the crown surface 7A, the gaseous fuel passes from the edge wall portion 30B to the combustion chamber ceiling portion 5 with the cylinder axis A. Flow in parallel. For this reason, even when the injection timing is different and the position of the piston 7 at that time changes, the gaseous fuel always flows toward a predetermined position of the combustion chamber ceiling portion 5, and the combustible layer 35 around the ignition portion 19A. Can be formed. That is, the injection timing can be changed while the combustible layer 35 is formed around the ignition portion 19A. This makes it possible to adjust the injection timing according to the load and the like.

(control)
As shown in FIG. 1, the internal combustion engine 1 includes a control device 40 (ECU), an accelerator pedal sensor 41 that detects the depression amount of the accelerator pedal, a crank angle sensor 42 that detects the rotational position of the crankshaft of the internal combustion engine 1, Have Signals from the accelerator pedal sensor 41 and the crank angle sensor 42 are input to the control device 40. The control device 40 calculates the engine speed based on the signal from the crank angle sensor 42, and calculates the load of the internal combustion engine 1 based on the engine speed and the depression amount of the accelerator pedal. The load may be calculated with reference to a predetermined map, for example. For example, the map may be set so that the load increases as the engine speed increases and the load increases as the accelerator pedal is depressed. Then, the control device 40 compares the load with a predetermined determination value. When the load is lower than the determination value, the operation state of the internal combustion engine 1 is a low load state, and when the load is equal to or higher than the determination value, The operating state of the engine 1 is a high load state. For example, a low load state corresponds to a range where IMEP (indicated mean effective pressure) is 800 kPa or less, and a high load state corresponds to a range where IMEP is greater than 800 kPa.

  The control device 40 controls the injector 17 according to the load. First, the control device 40 increases the total valve opening time in one combustion cycle of the injector 17 in accordance with an increase in load. As a result, the amount of fuel injected from the injector 17 in one combustion cycle increases as the load increases.

  Secondly, the control device 40 changes the number of injections and the injection timing in one combustion cycle according to the operating state of the internal combustion engine 1. The control device 40 controls the injector 17 to perform single-stage injection when the operating state of the internal combustion engine 1 is in a low load state, and the injector 17 operates when the operating state of the internal combustion engine 1 is in a high load state. Control to perform multi-stage injection. In the present embodiment, the control device 40 controls the injector 17 to perform injection twice per combustion cycle when in a high load state.

  When the injector 17 is in a low load state, the single stage injection is performed immediately before the ignition timing so that the combustible layer 35 having an equivalence ratio of 0.8 to 1.2 is formed around the ignition portion 19A at the ignition timing. Do. Specifically, the injector 17 starts fuel injection at a timing of −10 ms to −5 ms with the ignition timing as a reference (0 ms). In terms of crank angle, the top dead center in the compression stroke is used as a reference (0 deg CA.), and -60 deg CA. ~ -30 deg CA. At this timing, the injector 17 starts fuel injection.

  When the injector 17 is in a high load state, the first fuel injection is started in the intake stroke, and the second fuel injection is started immediately before the ignition timing in the compression stroke. The first fuel injection is started in an intake stroke relatively early from the ignition timing so that the injected fuel is uniformly mixed (premixed) at the ignition timing. Specifically, with the top dead center in the compression stroke as a reference (0 deg CA.), −300 deg CA. ~ -210degCA. At this timing, the injector 17 starts fuel injection. In the second fuel injection, the combustible layer 35 having an equivalence ratio of 0.8 to 1.2 is formed around the ignition part 19A at the ignition timing. Specifically, in the second fuel injection, the injector 17 starts fuel injection at a timing of −10 ms to −5 ms with reference to the ignition timing (0 ms). In terms of the crank angle, the injector 17 starts fuel injection at a timing of −90 deg to −60 deg with the top dead center in the compression stroke as a reference (0 deg CA.). The ratio of the first and second fuel injection amounts may be set arbitrarily. In the present embodiment, the ratio of the first and second fuel injection amounts is 1: 1.

For the internal combustion engine 1 configured as described above, an experiment was conducted on the influence of the fuel injection timing and the number of injections on the combustion stability. The specifications of the internal combustion engine 1 used in the experiment are a single cylinder, a bore diameter of 85.0 mm, a stroke of 97.1 mm, a displacement of 551 cm ³ , a compression ratio of 14.0, an expansion ratio of 14.0, an injector 17 The injection pressure is 5 MPa, and the swirl ratio is 2. The experiment was performed in two operating states: a low load state with a rotational speed of 1500 rpm and IMEP of 500 kPa, and a high load state with a rotational speed of 2000 rpm and IMEP of 1200 kPa.

  As shown in FIG. 4, in a high load state, when fuel is injected in two stages (condition 1), when single stage injection is performed at an advance timing (condition 2), and when single stage injection is performed at a retard timing (condition 3) ) Was measured. In condition 1, combustion injection with an injection duration of 4 ms is performed twice, and in conditions 2 and 3, combustion injection with an injection duration of 8 ms is performed once. In each case, the fuel injection amount in one combustion cycle is equal. In the case of condition 1, the first injection start timing is −270 degCA. The second injection start timing is -80 deg CA. In the case of condition 2, the injection start timing is −245 degCA. In the case of condition 3, the injection start timing is -110 degCA. It is. In each of conditions 1 to 3, the ignition timing is -11 deg CA. It is.

When measurement was performed for the above conditions 1 to 3, misfires occurred frequently in the case of condition 3, and a significant measurement result could not be obtained. This is because the combustible layer 35 having an equivalence ratio of 1.3 or more is formed around the ignition portion 19A at the ignition timing by performing fuel injection with a relatively large injection amount at the retard timing. I think that. Table 1 below shows ignition probabilities when a CNG mixture of each equivalent ratio is formed in a constant volume container and ignition is performed with a spark plug. From Table 1, it can be seen that when the equivalence ratio is 1.2-1.3, the ignition probability decreases. If a relatively large amount of fuel is injected at the retard timing, the combustible layer 35 is formed around the ignition portion 19A at the ignition timing, so it is unlikely that the equivalent ratio will be less than 0.6. Therefore, in the case of condition 3, it is appropriate to consider that the combustible layer 35 having an equivalence ratio of 1.3 or more is formed around the ignition part 19A at the ignition timing.

  FIG. 5 is a graph showing the combustion fluctuation rate (COV,%) with respect to the air-fuel ratio (A / F) for the conditions 1 and 2, and FIG. 6 shows the combustion period (degCA. ). From FIG. 5, it is possible to stabilize the combustion with a leaner fuel consumption when the injection is performed twice (condition 1) than when the single-stage injection is performed at the advance timing (condition 2). As can be seen from FIG. 6, this is considered to be due to the fact that the combustion speed is increased in the condition 1 than in the condition 2. Under condition 1, the combustible layer 35 is formed around the ignition portion 19A at the ignition timing by the second fuel injection, and it is considered that the combustion speed is increased by the combustible layer 35.

  As described above, in a high load state where the fuel injection amount increases, the lean limit air-fuel ratio can be expanded by dividing the injection into two times and performing stratified combustion by the second injection.

  As shown in FIG. 7, in the low load state, measurement was performed for the case where the fuel was single-stage injected at the retard timing (condition 4) and the case where the fuel was single-stage injected at the advance timing (condition 5). In the case of Condition 4 and Condition 5, the injection duration is both 4 ms, and the fuel injection amount in one combustion cycle is equal. In the case of condition 4, the injection start timing is −50 deg CA. In the case of condition 5, the injection start timing is -190 degCA. It is. In each of conditions 1 to 3, the ignition timing is -11 deg CA. It is.

  FIG. 8 is a graph showing the combustion fluctuation rate (COV,%) with respect to the air-fuel ratio (A / F) for conditions 4 and 5, and FIG. 9 shows the combustion period (degCA. ). From FIG. 8, the combustion is stabilized with a leaner fuel consumption when the single stage injection is performed at the retarded timing (condition 4) than when the single stage injection is performed at the advanced timing (condition 5). Can do. As can be seen from FIG. 9, this is considered to be caused by the increase in the combustion rate in the condition 4 than in the condition 5. Under the condition 4, the combustible layer 35 is formed around the ignition portion 19 </ b> A at the ignition timing by the fuel injection at the retard timing, and it is considered that the combustion speed is increased by the combustible layer 35.

  Although the description of the specific embodiment is finished as described above, the present invention is not limited to the above embodiment and can be widely modified. For example, in the above embodiment, an example in which CNG is used as the gaseous fuel has been described, but the gaseous fuel may be hydrogen, methane, propane, or the like. The swirl generation means may be a known swirl valve instead of the helical port 11A or the tangential port 11B. The swirl valve is provided inside the intake port 11 and may control the flow direction of the intake air by closing at least a part of the flow path of the intake port 11.

1: Internal combustion engine 2: Internal combustion engine body 4: Cylinder 5: Combustion chamber ceiling 7: Piston 7A: Crown surface 8: Combustion chamber 11: Intake port 11A: Helical port (swirl flow generating means)
11B: Tangential port (swirl flow generating means)
12: Exhaust port 17: Injector 19: Spark plug 19A: Ignition part 30: Cavity 30A: Bottom part 30B: Edge wall part 30C: Corner part 31: Convex part 33: Boundary part 35: Combustible layer 40: Controller A: Cylinder axis

Claims (7)

An internal combustion engine body comprising a cylinder having a combustion chamber ceiling at one end;
An intake port and an exhaust port that open in the ceiling of the combustion chamber;
A crown surface that is slidably received by the cylinder and cooperates with the combustion chamber ceiling portion to define a combustion chamber, and the crown surface is recessed in a circle centering on a cylinder axis, and the crown surface is formed at a peripheral portion. A piston having an edge wall connected substantially perpendicularly, and a piston provided with a substantially conical projection centered on the cylinder axis, protruding from the bottom of the cavity;
A spark plug including an ignition portion protruding from the ceiling portion of the combustion chamber;
An internal combustion engine comprising an injector provided at a center of the combustion chamber ceiling portion and injecting gaseous fuel toward the convex portion along a cylinder axis.   2. The internal combustion engine according to claim 1, wherein the ignition portion is disposed at a position overlapping the cavity when viewed from a direction along a cylinder axis.   3. The internal combustion engine according to claim 1, wherein the intake port has a swirl flow generating unit that promotes a swirl flow of intake air flowing from the intake port into the combustion chamber. 4.   The internal combustion engine according to any one of claims 1 to 3, wherein the combustion chamber ceiling portion is formed in a flat surface.   The internal combustion engine according to any one of claims 1 to 4, wherein a boundary portion between the bottom portion and the edge wall portion of the cavity is formed into a smooth curved surface.   The internal combustion engine according to any one of claims 1 to 5, wherein a boundary portion between the bottom portion and the convex portion of the cavity is formed into a smooth curved surface.   The internal combustion engine according to any one of claims 1 to 6, wherein the cavity and the convex portion cooperate with each other to form a toroidal concave portion centering on the cylinder axis. .

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