JP6714198B2 - Gas engine - Google Patents

Description

The present invention relates to a gas engine including a combustion chamber including a main chamber and a sub chamber.

In a gas engine that uses gas such as CNG as a fuel, a combustion chamber is formed by a main chamber and a sub-chamber connected to the main chamber through a communication hole in order to stably perform lean combustion. A sub-chamber engine in which a fuel supply valve is arranged in the sub-chamber is known (for example, Patent Document 1). In this gas engine, the equivalence ratio of the air-fuel mixture in the sub chamber is maintained higher than that in the main chamber, so that the ignitability in the sub chamber is improved. Further, the burnt gas jet (flame) generated in the sub chamber is jetted into the main chamber from the communication hole in a torch shape, and the lean air-fuel mixture in the main chamber can be reliably ignited.

JP, 2005-232987, A

The above gas engine ignites and burns the lean air-fuel mixture in the main chamber by the burnt gas jet ejected from the communication hole, so the direction and speed of the burnt gas jet ejected from the communication hole are different from those of the lean gas mixture in the main chamber. Affects combustion. The velocity of the burnt gas jet ejected from the communication holes changes depending on the volume of the sub chamber, the diameter of the communication holes, and the total number of communication holes. However, there are countless combinations of parameters such as the volume of the sub chamber, the direction of the communication holes, the diameter, and the total number, and it is difficult to set the optimum value that maximizes the thermal efficiency. Further, as a precondition for maximizing the thermal efficiency, it is necessary to ignite the air-fuel mixture in the main chamber with good stability.

In view of the above background, the present invention mainly aims to ignite the air-fuel mixture in the main chamber with good stability in a gas engine having a main chamber and a sub chamber. Moreover, this invention makes it a secondary subject to raise thermal efficiency in the gas engine provided with the main chamber and the sub chamber.

In order to solve the above problems, one aspect of the present invention is a four-stroke gas engine (1) defined by an upper end surface of a cylinder (4) and a crown surface of a piston (7) and having a cylinder axis as a center. The main chamber (8) having a cylindrical shape and the partition wall member (17) having a cylindrical shape with a bottom provided on the upper end surface of the cylinder are partitioned from the main chamber and have a small volume with respect to the main chamber. A chamber (20), at least one communication hole (22) formed in the partition wall member and connecting the main chamber and the sub chamber, an injector (30) for injecting gaseous fuel into the sub chamber, And a spark plug (36) having an ignition part (36F) disposed in the sub chamber, wherein the injector forms a mixture having an equivalence ratio of 0.5 or more and 2.0 or less in the main chamber at ignition timing. In order to achieve this, main injection is performed in the intake stroke, and a small amount of sub-injection is made immediately before the ignition timing in order to form an air-fuel mixture having an equivalence ratio of 1.0 or more and 2.0 or less in the ignition timing. And the total opening area of the communication holes to the sub chamber and the sub chamber so that the velocity of the gas ejected from the communication hole into the main chamber after ignition is 4 m/s or more and 7 m/s or less. It is characterized in that the volume is set. The gas velocity is divided by the time required for the gas to reach a distance of 0.8 when the distance between the main chamber wall side opening end of the communication hole and the wall surface of the main chamber in the axial direction of the communication hole is 1. It is calculated by

According to this aspect, in the gas engine, the air-fuel mixture in the main chamber is ignited with good stability by the burnt gas jet flow ejected from the sub chamber through the communication hole. This mode was created based on the idea and the fact that the velocity of the gas ejected from the sub chamber through the communication hole into the main chamber affects the ignitability of the air-fuel mixture in the main chamber and the fact obtained by experiments. There is. It has been confirmed by experiments conducted by the inventors of the present application that the air-fuel mixture in the main chamber is ignited with good stability when the velocity of the gas ejected from the communication hole is in the range of 4 m/s or more and 7 m/s or less. In the region where the velocity of the gas ejected from the communication hole exceeds 7 m/s, a free shear layer is generated at the boundary between the gas ejected from the communication hole and the air-fuel mixture in the main chamber. It is presumed that the flame formation, that is, the ignition is inhibited. The velocity of the gas ejected from the communication hole increases as the energy of the burnt gas generated in the sub chamber increases, and the total opening area of the communication holes, which are the passages of the burned gas, to the sub chamber increases. Understand that it will be late. It can be understood that the energy of the burned gas in the sub chamber is determined by the equivalence ratio of the air-fuel mixture in the sub chamber and the volume of the sub chamber. Therefore, in this aspect in which the range of the equivalence ratio of the air-fuel mixture in the sub-chamber is set, the sum of the opening areas of the communication holes to the sub-chamber and the volume of the sub-chamber are appropriately set so that each of the communication holes has a main volume. The velocity of the gas ejected into the chamber can be set to 4 m/s or more and 7 m/s or less, and the ignitability of the air-fuel mixture in the main chamber is improved.

Moreover, in the above aspect, the partition member projects from the upper end surface of the cylinder toward the center of the main chamber and is arranged coaxially with the cylinder axis, and the communication holes are provided in a number of 4 or more and 6 or less. It may be arranged at equal intervals in the circumferential direction around the axis. Further, the angle formed by the axis of the communication hole with respect to the cylinder axis is 20° or more and 75° or less, the stroke bore ratio is 0.6 or more and 2.6 or less, and the sub chamber of the main chamber has a volume of the sub chamber. The volume ratio is 0.02 or more and 0.04 or less, and the diameter of the piston is in the axial direction of the communication hole from the opening end on the main chamber side of the communication hole when the piston is at the top dead center. The ratio of the distance to the surface of the piston is preferably 0.19 or more and 0.32 or less. Further, the sub chamber index obtained by dividing the volume of the sub chamber by the total opening area of the communication holes to the sub chamber is preferably 9 or more and 15 or less.

According to this aspect, the gas engine can obtain high thermal efficiency. This mode was proved by the idea and experiment that the momentum of the burnt gas jet (sub-chamber index) ejected from the sub-chamber to the main chamber through the communication hole has a great influence on the combustion of the air-fuel mixture in the main chamber. It is created based on the facts. The sub-chamber index is the volume of the sub-chamber corresponding to the total amount of burned gas (flame) generated in the sub-chamber, and is defined as the opening area of the communication hole corresponding to the outlet area from the sub-chamber to the sub-chamber. It is divided by the total sum and represents the momentum (jet strength) of the burnt gas jet ejected from the communication hole. Since it has been confirmed by experiments that the sub-chamber index has a maximum value of 9 or more and 15 or less, the sub-chamber volume, the total number of communication holes, and the diameter of the sub-chamber are set so that the sub-chamber index is in such a range. The thermal efficiency is maximized by setting it. In the positional relationship in which the auxiliary chamber is arranged in the central portion of the cylindrical main chamber, each communication hole forms an angle of 20° or more and 75° or less with respect to the cylinder axis, so that the burnt gas jet flows around the periphery of the main chamber. Since it jets out toward the corner of the, the air-fuel mixture in the main chamber can be ignited over a wide range.

Further, in the above aspect, the exhaust amount of the cylinder may is 150 cm ³ or more 800 cm ³ or less.

Further, in the above-mentioned aspect, a circular concave portion (45) is formed on a crown surface of the piston when viewed from a direction along a cylinder axis, an upper end surface of the cylinder is formed on a flat surface, and the piston is top dead. When at the point, the main chamber may be defined by the inner surface of the recess, the upper end surface of the cylinder, and the outer surface of the partition member, and the lower end of the partition member may protrude into the recess.

According to this aspect, the advancing direction of the communicating hole and the burnt gas jet ejected from the communicating hole faces the corner of the peripheral edge of the main chamber, and the air-fuel mixture in the main chamber can be efficiently ignited.

Further, in the above aspect, it is preferable that each axis of the communication holes has an intersection on the cylinder axis, and the ignition part is arranged at the intersection.

According to this aspect, the burnt gas generated in the ignition part easily passes through the communication hole, and the deceleration of the burnt gas jet and energy loss are reduced.

Another aspect of the present invention is a four-stroke gas engine (1) having a cylindrical shape defined by an upper end surface of a cylinder (4) and a crown surface of a piston (7) and having a cylinder axis as a center. The main chamber (8) is partitioned from the main chamber by a bottomed cylindrical partition wall member (17) projecting from the upper end surface of the cylinder to the center of the main chamber and arranged coaxially with the cylinder axis. A sub-chamber (20) having a small volume with respect to the chamber, and four or more and six or less arranged in the partition wall member at equal intervals in the circumferential direction around the cylinder axis and connecting the main chamber and the sub-chamber. A communication hole (22), an injector (30) for injecting gaseous fuel into the sub-chamber, and an ignition plug (36) having an ignition part (36F) arranged in the sub-chamber. , The main injection is performed in the intake stroke, and at the ignition timing, a smaller amount of the sub-injection than the main injection is made immediately before the ignition timing so as to form a mixture gas having an equivalence ratio of 1.0 or more and 2.0 or less in the sub-chamber. The angle formed by the axis of the communication hole with respect to the cylinder axis is 20° or more and 75° or less, the stroke bore ratio is 0.6 or more and 2.6 or less, and the sub chamber with respect to the volume of the main chamber is In the axial direction of the communicating hole from the opening end of the communicating hole on the main chamber side when the piston is at the top dead center with respect to the diameter of the piston. The ratio of the distance to the surface of the piston is 0.19 or more and 0.32 or less, and the sub chamber index obtained by dividing the volume of the sub chamber by the total opening area of the communication holes to the sub chamber is 9 or more 15 It is characterized by the following.

According to this aspect, the gas engine can obtain high thermal efficiency. Since it has been confirmed by experiments that the sub-chamber index has a maximum value of 9 or more and 15 or less, the sub-chamber volume, the total number of communication holes, and the diameter of the sub-chamber are set so that the sub-chamber index is in such a range. The thermal efficiency is maximized by setting it. In the positional relationship in which the auxiliary chamber is arranged in the central portion of the cylindrical main chamber, each communication hole forms an angle of 20° or more and 75° or less with respect to the cylinder axis, so that the burnt gas jet flows around the periphery of the main chamber. Since it jets out toward the corner of the, the air-fuel mixture in the main chamber can be ignited over a wide range. Further, in the range where the sub chamber index is 10 or more and 15 or less, the thermal efficiency is maximized, so that the air-fuel mixture in the main chamber is ignited with good stability by the gas ejected from the communication hole.

With the above configuration, in the gas engine including the main chamber and the sub chamber, the air-fuel mixture in the main chamber can be ignited with good stability.

Sectional view of an internal combustion engine according to an embodiment (A) Sectional drawing which expands and shows a subchamber, (B) BB sectional drawing of FIG. 2(A). FIG. 2 is a cross-sectional view of the internal combustion engine according to the embodiment, showing a state where the piston is at top dead center. Explanatory drawing showing the diameter, total number, and position of communication holes Explanatory diagram showing fuel injection timing and ignition timing φ-T map Graph showing the relationship between the diameter of the communication hole and the flame reach distance Graph showing the relationship between the total number of communication holes and the flame reach distance Graph showing the relationship between the total number of communication holes and thermal efficiency Graph showing the relationship between the volume of the sub chamber and the flame reach distance Graph showing the relationship between sub chamber index and flame arrival time Graph showing the relationship between sub-chamber index, combustion period and thermal efficiency at low load Graph showing the relationship between sub-chamber index, combustion period and thermal efficiency under high load Graph showing the relationship between sub-chamber index, flame speed, and ignitability of main chamber mixture

Hereinafter, an embodiment in which the present invention is applied to a gas engine using four-valve CNG as a fuel will be described with reference to the drawings.

The gas engine 1 is a four-stroke engine, and as shown in FIG. 1, has an engine body 2 including a cylinder block 2A and a cylinder head 2B fastened to the upper end surface of the cylinder block 2A. A cylinder 4 having a circular cross section is formed in the cylinder block 2A and opens at 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 formed into a flat surface and serves as a combustion chamber ceiling portion 5 that forms the upper end surface of the cylinder 4. The axis of the cylinder 4 is designated as the cylinder axis A. A piston 7 is reciprocally received in the cylinder 4 along a cylinder axis A. A main chamber 8 is defined by the wall surface of the cylinder 4 including the combustion chamber ceiling portion 5 and the crown surface 7A of the piston 7.

Two intake ports 11 and two exhaust ports 12 are opened in the combustion chamber ceiling portion 5. In the combustion chamber ceiling portion 5, two intake ports 11 are arranged on the intake side which is one side, and two exhaust ports 12 are arranged on the exhaust side which is the other side. Opening 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.

A support hole 16 is formed in the cylinder head 2</b>B so as to vertically penetrate therethrough and open at the lower end to the center of the combustion chamber ceiling 5. The support hole 16 is a stepped hole formed coaxially with the cylinder axis A, and has a lower portion 16A having a smaller diameter from the lower side, an intermediate portion 16B enlarged to the lower portion 16A, and an enlarged diameter to the intermediate portion 16B. Has an upper portion 16C. An annular shoulder surface 16D facing upward is formed between the lower portion 16A and the intermediate portion 16B. A female screw is formed on the inner surface of the upper portion of the intermediate portion 16B.

As shown in FIGS. 1 and 2, a bottomed cylindrical partition wall member 17 is inserted into the lower portion 16A and the intermediate portion 16B of the support hole 16. The partition wall member 17 is provided with a cylindrical tubular portion 17A arranged coaxially with the cylinder axis A, an end wall portion 17B that closes the lower end of the tubular portion 17A, and an outer peripheral surface of the upper portion of the tubular portion 17A. And an annular flange portion 17C extending in the direction. The flange portion 17C is in contact with the shoulder surface 16D via an annular seal member (reference numeral omitted). An annular support member 19 having an external thread on its outer peripheral surface that is screwed into a female thread is attached to the intermediate portion 16B. The flange portion 17C is sandwiched between the shoulder surface 16D and the lower surface of the support member 19 from above and below, and is fixed to the cylinder head 2B. An upper portion of the inner peripheral portion of the cylindrical portion 17A is a reduced diameter portion whose diameter is reduced with respect to the lower portion. The lower portion of the inner peripheral portion of the cylindrical portion 17A defines the sub chamber 20. The sub chamber 20 constitutes a combustion chamber together with the main chamber 8.

The end wall portion 17</b>B of the partition wall member 17 is formed in a substantially hemispherical shape that is convex downward, protrudes below the combustion chamber ceiling portion 5, and protrudes in the center of the main chamber 8. The lower end portion (center in plan view) of the end wall portion 17B is formed in a flat shape. The center of the end wall portion 17B formed in a substantially hemispherical shape is arranged on the cylinder axis A and on a virtual plane on which the combustion chamber ceiling portion 5 is extrapolated.

A plurality of communication holes 22 that penetrates in the thickness direction and connects the main chamber 8 and the sub chamber 20 is formed in the outer peripheral portion of the end wall portion 17B. Each communication hole 22 is inclined downward and extends linearly, and the respective axes intersect each other at one intersection B in the sub chamber 20. That is, each communication hole 22 extends radially around the intersection B. Each communication hole 22 is formed in a rotationally symmetrical shape about the cylinder axis A (the axis of the partition wall member 17), and the intersection B is located on the cylinder axis A. The intersection B coincides with the center of the end wall portion 17B formed in a substantially hemispherical shape. The angle formed by the axis of each communication hole 22 with respect to the cylinder axis A is set to 20° or more and 75° or less, more preferably 45° or more and 65° or less, and further preferably 60°.

The number of the communication holes 22 is 4 or more and 6 or less, and the communication holes 22 are arranged at equal intervals around the cylinder axis A. 1 to 3 show an example in which there are five communication holes 22. As shown in FIG. 4, when there are four communication holes 22, the communication holes 22 are arranged at 90° intervals in the circumferential direction with the cylinder axis A as the center. When the number of the communication holes 22 is 5, the communication holes 22 are arranged at intervals of 72° in the circumferential direction with the cylinder axis A as the center. When the number of the communication holes 22 is 6, the communication holes 22 are arranged at intervals of 60° in the circumferential direction with the cylinder axis A as the center. The cross section of each communication hole 22 is circular and has a constant diameter in the longitudinal direction. The diameter of each communication hole 22 is 1.2 mm or more and 2.0 mm or less. The main chamber 8 and the sub chamber 20 communicate with each other only through a plurality of communication holes 22 so that fluid can flow. The main chamber 8 and the sub chamber 20 are separated from each other except for the communication hole 22, and the fluid flow is blocked.

As shown in FIG. 1, an injector 30 is inserted in the support hole 16. The injector 30 is a means for injecting gaseous fuel. In the present embodiment, the injector 30 is adapted to CNG and is connected to the CNG cylinder via a delivery pipe and a pressure control valve. The pressure of CNG supplied to the injector 30 may be, for example, about 2 MPa. The injector 30 has a substantially cylindrical main body 30A and a nozzle 30B coaxially provided at one end of the main body 30A. An injection hole (not shown) for injecting gaseous fuel is formed at the tip of the nozzle 30B, and a fuel passage (not shown) for connecting the delivery pipe and the injection hole is formed inside the main body 30A and the nozzle 30B. There is. A valve body (not shown) that opens and closes the fuel passage is provided inside the nozzle 30B, and an actuator (not shown) that drives the valve body is provided inside the main body 30A. The actuator may use a solenoid or a piezo element.

An annular flange 30C extending in the circumferential direction is formed on the outer periphery of the main body 30A of the injector 30. The injector 30 is arranged in the support hole 16 such that the nozzle 30B passes through the upper opening D of the partition member 17 and the tip of the nozzle 30B is located in the sub chamber 20. The injector 30 is fixed to the cylinder head 2B by a holder (not shown) so that the flange 30C abuts the upper end of the support member 19. The injector 30 is arranged coaxially with the cylinder axis A. In the present embodiment, there is one injection hole, which faces downward along the cylinder axis A. The CNG injected from the injection hole has a conical spray shape centered on the cylinder axis A and spreading downward (to the piston 7 side). A seal member (reference numeral omitted) is arranged between the outer peripheral surface of the nozzle 30B and the inner peripheral surface of the cylindrical portion 17A, and the upper portion of the sub chamber 20 is hermetically closed.

A spark plug hole 33, which is a through hole, is formed between the two intake ports 11 in the cylinder head 2B. The spark plug hole 33 is a linearly extending stepped hole, extends obliquely with respect to the cylinder axis A, and has a lower end opened to the inner peripheral surface of the lower portion 16A of the support hole 16. The spark plug hole 33 is formed such that its upper portion has a larger diameter than its lower portion. In the cylinder portion 17A of the partition member 17, a through hole 34 that is a through hole and connects the auxiliary chamber 20 and the ignition plug hole 33 is formed in a portion facing the lower end opening of the ignition plug hole 33. The width of the through hole 34 is larger than the width of the lower end of the ignition plug hole 33, and the peripheral portion of the through hole 34 is in contact with the inner peripheral surface of the lower portion 16A of the support hole 16. The outer peripheral surface of the cylindrical portion 17A of the partition member 17 and the inner peripheral surface of the lower portion 16A of the support hole 16 are in close contact with each other and hermetically sealed.

As shown in FIGS. 1 and 2, a spark plug 36, which is a spark plug, is inserted into the spark plug hole 33. The spark plug 36 has an axially extending main body 36A, a center electrode 36B provided at the center of the front end of the main body 36A, and a ground electrode 36C protruding from the peripheral edge of the front end of the main body 36A. A male screw is formed on the outer peripheral surface of the body portion 36A and is screwed into a female screw formed in the lower portion of the spark plug hole 33. The center electrode 36B is connected to the power supply. The ground electrode 36C is insulated from the center electrode 36B and grounded to the cylinder head 2B via the outer peripheral portion of the main body portion 36A. The ground electrode 36C is bent at a right angle to the base end portion 36D extending substantially parallel to the axis of the ignition plug 36 from the peripheral edge of the tip end of the main body portion 36A, and is substantially perpendicular to the base end portion 36D. ) Has a tip portion 36E extending inward in the radial direction. A tip portion 36E of the ground electrode 36C faces the center electrode 36B in the axial direction of the spark plug 36 with a gap. An ignition portion 36F is provided between the center electrode 36B and the tip portion 36E of the ground electrode 36C, and a spark is generated by applying a voltage to the center electrode 36B during ignition.

As shown in FIG. 2, the ignition part 36F of the ignition plug 36 is arranged in the sub chamber 20 at a position that coincides with the intersection B of the axes of the communication holes 22. Specifically, the ignition part 36F of the ignition plug 36 is arranged in a range of less than 2 mm from the intersection B of the communication holes 22. Further, the ground electrode 36C is arranged so as to avoid each line segment C connecting the intersection B and each of the communication holes 22. Specifically, the base end portion 36D of the ground electrode 36C is arranged on the side opposite to the main chamber 8 side with respect to the center electrode 36B, that is, above the center electrode 36B. Further, the tip portion 36E of the ground electrode 36C is arranged between the line segment C connecting each of the two adjacent communication holes 22 and the intersection B when viewed from the direction along the cylinder axis A. Further, the main body portion 36A of the ignition plug 36 and the through hole 34 are arranged in parallel to each other at a position overlapping with one communication hole 22 when viewed from the direction along the cylinder axis A. Further, in the present embodiment, the ignition part 36F is arranged on the axis of the partition member 17 (sub chamber 20) and also on the center of the end wall part 17B.

As shown in FIG. 1, the piston 7 includes a disc-shaped crown portion 41, a pair of skirt portions 42 projecting downward from the peripheral edge portion of the crown portion 41, and corresponding side edges of the skirt portions 42 with respect to each other. It has a pair of connecting wall portions 43 to be connected. The axis of the piston 7 coincides with the cylinder axis A. On the outer peripheral portion of the crown portion 41, a first annular groove, a second annular groove and a third annular groove (reference numeral omitted) extending in the circumferential direction are sequentially formed from the top. A compression ring (reference numeral omitted) is fitted in each of the first annular groove and the second annular groove, and an oil ring (reference numeral omitted) is fitted in the third annular groove.

A crown surface 7A of the crown portion 41 facing the combustion chamber ceiling portion 5 side is formed in a plane perpendicular to the cylinder axis A. A cavity (recess) 45 is provided in the center of the crown surface 7A. The cavity 45 is formed in a circular shape centering on the cylinder axis A, and has a bottom portion 45A and an edge wall portion 45B provided on the peripheral edge portion of the bottom portion 45A. The edge wall portion 45B is formed in a cylindrical surface centering on the cylinder axis A, and is connected to the crown surface 7A at its upper end substantially perpendicularly. The surface of the boundary between the edge wall portion 45B and the bottom portion 45A is formed into a smooth curved surface. The ratio of the diameter of the cavity 45 to the diameter of the piston 7 is set to 0.45 or more and 0.97 or less. The ratio of the depth of the cavity 45 to the diameter of the cavity 45 (depth of the deepest part) is set to 0.1 or more and 1.0 or less.

At the center of the bottom portion 45A, a convex portion 47 having a substantially conical shape centering on the cylinder axis A is provided in a protruding manner. The protruding end of the convex portion 47 is arranged below the crown surface 7A. The peripheral portion of the convex portion 47 extends to the vicinity of the peripheral portion of the bottom portion 45A. The protruding end of the convex portion 47 is formed into a smooth chamfered curved surface. Further, the surface of the boundary between the peripheral portion of the convex portion 47 and the bottom portion 45A is formed into a smooth curved surface.

The cavity 45 and the convex portion 47 cooperate with each other to form a toroidal shape with the cylinder axis A as the center, and the depth of the peripheral portion is deeper than the central portion. The crown surface 7A including the cavity 45 and the convex portion 47 is formed in an axially symmetric shape with the cylinder axis A as the axis of symmetry.

As shown in FIG. 3, when the piston 7 is at the top dead center, the main chamber 8 is defined by the inner surface of the cavity 45, the combustion chamber ceiling portion 5 of the cylinder 4, and the outer surface of the partition member 17. Further, when the piston 7 is at the top dead center, the end wall portion 17B of the partition wall member 17 protrudes into the cavity 45 and faces the convex portion 47 through the gap so that the end wall portion 17B has a protruding length. The depth of the cavity 45 and the height of the convex portion 47 are set. The angle formed by the outer surface of the convex portion 47 and the cylinder axis A is set to be substantially equal to the angle formed by the axis of the communication hole 22 and the cylinder axis A (the axis of the partition member 17).

The volume of the sub chamber 20 is set to be smaller than both the volume of the main chamber 8 when the piston 7 is located at the bottom dead center and the volume of the main chamber 8 when the piston 7 is located at the top dead center. ing. The ratio of the volume of the sub chamber 20 to the volume of the main chamber 8 is preferably 0.02 or more and 0.04 or less. The volume of the main chamber 8 here refers to the volume of the main chamber 8 when the piston 7 is at the bottom dead center, and includes the wall surface of the cylinder 4 including the combustion chamber ceiling 5, the outer surface of the partition member 17, and the crown of the piston 7. The volume of the space defined by the surface of the surface 7A, the cavity 45, and the convex portion 47. The volume of the sub chamber 20 refers to the volume of the space defined by the inner surface of the partition member 17, the outer surface of the injector 30, and the outer surface of the spark plug 36.

Emissions of the cylinder 4, 150 cm ³ or more 800 cm ³ or less, more preferably 300 cm ³ or more 650 cm ³ or less, is set more preferably at 500 cm ³ or more 600 cm ³ or less, for example, 550 cm ^3. The stroke bore ratio (SB ratio) obtained by dividing the stroke of the piston 7 by the diameter of the cylinder 4 is set to 0.6 or more and 2.6 or less. The diameter of the cylinder 4 is set to 60 mm or more and 110 mm or less, more preferably 65 mm or more and 105 mm or less, further preferably 75 mm or more and 95 mm or less, and most preferably 85 mm. The compression ratio of the gas engine 1 is set to 10.0 or more and 16.0 or less.

A value obtained by dividing the volume V of the sub chamber 20 by the total St of opening areas of the plurality of communication holes 22 to the sub chamber 20 is defined as a sub chamber index Is (=V/St). Here, the sum St of the opening areas of the communication holes 22 to the sub chamber 20 is calculated by multiplying the opening area S of each communication hole 22 to the sub chamber 20 by the total number n of the communication holes 22. The volume V of the sub chamber 20 refers to the volume of a space defined by the inner surface of the partition member 17, the inner surface of the through hole 34, the outer surface of the injector 30, and the outer surface of the ignition plug 36. The communication hole 22 is a passage having a constant cross section in the longitudinal direction. In the present embodiment, the volume V of the sub-chamber 20, the number of communication holes 22, and the number of the communication holes 22 are set so that the sub-chamber index is 9 or more and 15 or less, more preferably 9 or more and 14 or less, or 10 or more and 15 or less. The opening area S to the sub chamber 20 is set.

As shown in FIG. 1, the gas engine 1 includes a control device 50 (ECU), an accelerator pedal sensor 51 that detects the amount of depression of an accelerator pedal, and a crank angle sensor 52 that detects the rotational position of the crankshaft of the gas engine 1. Have. The signals from the accelerator pedal sensor 51 and the crank angle sensor 52 are input to the control device 50. The control device 50 calculates the engine speed based on the signal from the crank angle sensor 52, and calculates the load of the gas engine 1 based on the engine speed and the depression amount of the accelerator pedal. The load is calculated, for example, by referring to a predetermined map. For example, the map is set so that the load increases as the engine speed increases and the load increases as the accelerator pedal depression amount increases.

The control device 50 controls the injection amount and injection timing of the injector 30 according to the load and the engine speed, and controls the ignition timing of the spark plug 36. The control device 50 increases the fuel injection period (valve opening period) in one combustion cycle of the injector 30 according to the increase of the load, and increases the fuel injection amount. Further, the control device 50 advances the injection timing of the injector 30 and the ignition timing of the spark plug 36 according to the increase of the engine speed.

As shown in FIG. 5, the injector 30 controlled by the control device 50 performs at least one main injection and at least one auxiliary injection in one combustion cycle. The sub-injection is set to have a smaller fuel injection amount than the main injection. The main injection is performed to form a lean air-fuel mixture having an equivalence ratio of 0.5 or more and 1.0 or less, more preferably 0.6 or more and 0.8 or less in the main chamber 8 at the ignition timing. The sub-injection produces a mixture that is denser than the main chamber 8 and has high ignitability at an ignition timing, and an equivalence ratio of 1.0 or more and 2.0 or less, more preferably 1.2 or more and 1.5 or less. Is done to form. In this embodiment, the injector 30 performs one main injection and one sub injection in one combustion cycle. The main injection is performed in the intake stroke. The main injection may be performed for a predetermined period within a range of −340° to −180° ATDC, for example. Here, the description that the injection is performed within the predetermined range means that both the start timing and the end (completion) timing of the injection are set within the predetermined range. Further, the main injection may be performed after the exhaust valve 14 is closed in the intake stroke. Therefore, the main injection may be performed for a predetermined period of time, for example, within the range of −330° to −180° ATDC, more preferably within the range of −285° to −240° ATDC. The injection period of the main injection may be 29° in crank angle, for example. In other embodiments, the main injection may be performed for a predetermined period of time, for example within the range of −210° to −180° ATDC. When the load on the gas engine 1 increases, the control device 50 increases the fuel injection period of the main injection and increases the fuel injection amount per combustion cycle.

The secondary injection is performed near the top dead center in the compression stroke. For example, the end timing of the auxiliary injection by the injector 30 may be in the range of −20° to −10° ATDC. The ignition timing by the spark plug 36 is controlled by the control device 50 within the range of −50° to 10° ATDC. The injection period of the sub injection may be, for example, 1.4° in crank angle. In another embodiment, the secondary injection is performed for a predetermined period within a range of 30° to 10° in crank angle before the ignition timing.

The CNG supplied to the sub chamber 20 by the main injection passes through the communication hole 22 and diffuses into the main chamber 8. Particularly, in the intake stroke, since the pressure of the main chamber 8 is lowered with respect to the sub chamber 20 due to the lowering of the piston 7, diffusion of CNG from the sub chamber 20 to the main chamber 8 is promoted. The longer the interval between the injection timing of the main injection and the ignition timing, the more the diffusion of the CNG injected by the main injection by the ignition timing progresses, so that the homogenization of the air-fuel mixture in the main chamber 8 is promoted. Since the interval between the injection timing of the sub-injection and the ignition timing is short, the CNG supplied to the sub-chamber 20 by the sub-injection cannot be sufficiently diffused, and most of the CNG remains in the sub-chamber 20 at the ignition timing. The air-fuel mixture concentration of 20 is higher than that of the main chamber 8.

The controller 50 controls the fuel injection period (fuel injection amount) in the main injection by the injector 30 so that the equivalence ratio of the main chamber 8 becomes 0.5 or more and 1.0 or less at the ignition timing. The control device 50 controls the fuel injection period (fuel injection amount) in the sub-injection by the injector 30 such that the equivalence ratio of the sub-chamber 20 becomes 1.0 or more and 2.0 or less at the ignition timing. In order to realize the above equivalence ratio in the main chamber 8 and the sub chamber 20 at the ignition timing, the ratio of the injection amount of injection to the fuel injection amount of main injection is 1/150 or more and 1/60 or less in this embodiment. Is set to.

In the gas engine 1 according to the present embodiment, when the piston 7 descends in the intake stroke, the intake valve 13 is opened and fresh air is supplied from the intake port 11 to the main chamber 8. At this time, since the pressure in the main chamber 8 is lower than that in the sub chamber 20, the burned gas generated in the previous combustion in the sub chamber 20 flows into the main chamber 8 through each communication hole 22. When the piston 7 rises in the subsequent compression stroke, the pressure in the main chamber 8 rises with respect to the sub chamber 20, so that the fresh air (air) in the main chamber 8 passes through each communication hole 22 and flows into the sub chamber 20. .. The injector 30 injects the main injection into the sub chamber 20 in at least one of the intake stroke and the compression stroke. The CNG supplied to the sub chamber 20 by the main injection passes through the communication hole 22 and flows into the main chamber 8 to form a lean air-fuel mixture in the main chamber 8. Further, the injector 30 performs a sub-injection immediately before the ignition timing to form an air-fuel mixture that is richer than the main chamber 8 in the sub-chamber 20 at the ignition timing to improve the ignitability.

At the ignition timing set near the top dead center of the compression stroke, the spark plug 36 causes the ignition part 36F to generate a spark, so that the CNG is ignited at the ignition part 36F and a flame is generated. The flame generated in the ignition part 36F spreads radially, passes through each communication hole 22 as shown in FIG. 3, and becomes a torch-like burnt gas jet (flame) from each communication hole 22 in the cavity of the main chamber 8. Eject into 45. At this time, since the piston 7 is near the top dead center, the cavity 45 occupies most of the main chamber 8. The burnt gas jets ejected from the communication holes 22 spread radially in the cavity 45 along the surface of the convex portion 47, and reliably burn the air-fuel mixture in the cavity 45.

FIG. 6 is a φ-T map showing the relationship between the combustion temperature (T) and the equivalence ratio (φ), and the production of NOx and soot. As shown in FIG. 6, since the sub chamber 20 is surrounded by the partition wall member 17 exposed to high temperature, the combustion temperature becomes higher than that in the main chamber 8 and becomes 1500K to 2400K. In this case, by setting the equivalence ratio in the sub chamber 20 to 1.0 or more, it is possible to avoid the NOx region where NOx is likely to occur. Further, when the fuel temperature is in the range of 1700K to 2000K, the soot region where soot is likely to occur can be avoided by setting the equivalence ratio to 2.0 or less.

In the gas engine 1 configured as described above, the volume V of the sub chamber 20, the total number n of the communication holes 22, and the opening area S of each communication hole 22 to the sub chamber 20 are set based on the sub chamber index Is. Therefore, the velocity of the burnt gas flow ejected from each communication hole 22 into the main chamber 8 is set to an appropriate value, and the thermal efficiency of the gas engine 1 is improved. The sub-chamber index Is is set based on the following first to third experiments.

Each experiment was performed using a constant volume combustion device that reproduced the shape of the main chamber 8 when the piston 7 was at the top dead center. In the constant volume combustion device, the relative positions of the main chamber 8, the auxiliary chamber 20, the injector 30, and the spark plug 36 are the same as the positions shown in the above embodiment. The constant volume combustion device has an optical window for optically checking the inside of the main chamber 8 from the side, and is capable of capturing a Schlieren image in the main chamber 8. Further, the constant volume combustion device has a rapid compression device (RCM) and can pressurize the main chamber 8 and the sub chamber 20. Further, the constant volume combustion device has a pressure sensor for measuring the pressure of the gas in the main chamber 8 and a temperature sensor for measuring the temperature.

The constant volume combustion device has the same combustion chamber shape as that of the gas engine 1 described above, and the diameter of the cylinder 4 is 85 mm, the diameter of the main chamber 8 (cavity 45) is 60 mm, and the depth of the main chamber 8 (cavity 45). Was 10 mm, the volume of the main chamber 8 was 42 cm ³ , and the angle of each communication hole 22 with respect to the cylinder axis A was 60°. The angle formed by the axis of each communication hole 22 and the cylinder axis A was 60°. Further, the distance from the opening end of each communication hole 22 on the main chamber 8 side to the wall surface of the main chamber 8 (the edge wall portion 45B of the cavity 45) in the axial direction of each communication hole 22 is set to 18.7 mm. In this case, the ratio of the distance from the opening end of the communication hole 22 on the main chamber side when the piston 7 is at the top dead center to the surface (wall surface) of the piston 7 in the axial direction of the communication hole 22 to the diameter of the piston 7 is , 0.22. In each of the following experiments, the total number of the communication holes 22 was set to 4, 5, or 6, the diameter of each communication hole 22 was set to 1.2 mm or 1.6 mm, and the volume of the sub-chamber 20 was adjusted. 0.89 cm ³ (volume ratio to the main chamber 8 0.021), 1.20 cm ³ (volume ratio to the main chamber 8 0.028), 1.84 cm ³ (volume ratio to the main chamber 8 0.043) did.

In each experiment, after the main chamber 8 and the sub chamber 20 were filled with atmospheric pressure air, a predetermined amount of fuel was injected from the injector 30 into the sub chamber 20. Then, after waiting for 5 minutes, the fuel was diffused in the sub chamber 20 and the main chamber 8 so that the air-fuel mixture in the main chamber 8 and the sub chamber 20 became homogeneous. The amount of fuel injected by the injector 30 was adjusted so that the equivalence ratio in the main chamber 8 and the sub chamber 20 was 0.6. After that, the pressure of the main chamber 8 and the sub chamber 20 was increased to 2.3 MPa and 540 K by the rapid compression device, and 28.3 ms after that, the ignition plug 36 ignited the air-fuel mixture in the sub chamber 20. The schlieren image in the main chamber 8 is taken at each time with the time point when the jet of burnt gas jetted into the main chamber 8 starts from the communication hole 22 as 0, and the burned gas jet jets from the communication hole 22 based on the schlieren image. The state of progress (including the flame generated by the ignition of the air-fuel mixture in the main chamber 8 by the burnt gas jet) was analyzed. Specifically, image processing of the schlieren image at each time is performed to identify the tip position of the burnt gas jet, and the distance from the outlet of the communication hole 22 to the tip position of the burnt gas jet in the axial direction of the communication hole 22. Was measured as the flame reaching distance. The flame arrival distance is a ratio where the distance from the outlet of the communication hole 22 to the main chamber wall surface is 1 in the axial direction of the communication hole 22. That is, the burnt gas jet ejected from the communication hole 22 reaches the main chamber wall surface when the distance becomes 1. Since the burnt gas jet ejected from the communication hole 22 and the flame generated by the ignition of the air-fuel mixture in the main chamber 8 due to the burnt gas jet cannot be separated from each other, they are treated as one body. .. The flame arrival distance was measured 5 times and was taken as an average value.

FIG. 7 shows the result of the first experiment in which the influence of the diameter of the communication hole 22 on the flame reach distance was measured. In the first experiment, the number of the communication holes 22 was 5, the volume of the sub chamber 20 was 1.20 cm ^3, and the diameter D of the communication holes 22 was 1.2 mm or 1.6 mm. The measurement was performed 5 times for each value of the diameter of the communication hole 22, and the average value of each was calculated. As shown in FIG. 7, the average value of 5 times when the diameter of the communication hole 22 is 1.2 mm (solid line in FIG. 7) and the average value of 5 times when the diameter of the communication hole 22 is 1.6 mm (broken line in FIG. 7) In the meantime, no significant difference in flame reach was confirmed. However, when the diameter of the communication hole 22 is 1.2 mm, the flame propagation velocity is clearer in two of the five measurements (two-dot chain line in FIG. 7) than when the diameter is 1.6 mm. It was confirmed that the flame propagation speed was obviously faster than the case of 1.6 mm in the case of being slow, and three times (one-dot chain line in FIG. 7). On the other hand, when the diameter of the communication hole 22 is 1.6 mm, the fluctuation of 1.2 mm was not confirmed, and the flame arrival distance changed in the same manner in five measurements. When the diameter of the communication hole 22 is 1.2 mm and the flame propagation speed is slow (two-dot chain line), when confirmed by the Schlieren image, the progress of the burnt gas jet stagnates from 1.2 ms to 2.0 ms. It was confirmed that combustion (ignition) of the air-fuel mixture in the main chamber 8 occurred at 2.0 ms. On the other hand, when the diameter of the communication hole 22 is 1.6 mm (solid line) or when the diameter is 1.2 mm and the flame propagation speed is high (dashed line), the region where the progress of the burnt gas jet is stagnant is No confirmation was made, and no ignition delay was confirmed. As described above, when the diameter of the communication hole 22 is 1.2 mm, ignition delay may occur, and it can be said that combustion is more unstable than when the diameter is 1.6 mm. The ignition delay in the case where the diameter of the communication hole 22 is 1.2 mm is because the cross-sectional area of the communication hole 22 becomes small, the jet speed of the burnt gas jet becomes high, and the burnt gas jet from the communication hole 22 becomes It is considered that this is due to the generation of a free shear layer at the boundary with the air-fuel mixture in the main chamber 8.

The results of the second experiment in which the influence of the total number of the communication holes 22 on the flame arrival distance and the heat generation rate was measured are shown in FIGS. 8 and 9. In the second experiment, the volume of the sub chamber 20 was 1.20 cm ³ , the diameter of the communication holes 22 was 1.6 mm, and the total number of the communication holes 22 was 4, 5, or 6. In FIG. 8, the average value of the flame reach distance at each time is shown by a plot, and the variance thereof is shown by an error bar.

As shown in FIG. 8, it was confirmed that the flame reaching distances were almost the same when the total number of the communication holes 22 was four and when the total number was five. However, it was confirmed that when the total number of the communication holes 22 was 4, the error bar was larger than when it was 5, and the fluctuation was large. It is considered that this is because the pressure of the burnt gas in the sub chamber 20 increased due to the decrease in the total number of the communication holes 22, and the jet speed of the burnt gas jet increased. When the jet speed of the burnt gas jet becomes high, a free shear layer is generated at the boundary between the jet of burnt gas jetted from the communication hole 22 and the air-fuel mixture in the main chamber 8, and ignition is impeded by the free shear layer. Guessed.

It was also confirmed that when the total number of the communication holes 22 was 6, the flame reaching distance decreased and the fluctuation became larger than when the total number was 5. It is considered that this is because the pressure of the burnt gas in the sub chamber 20 decreased due to the increase in the total number of the communication holes 22, and the velocity of the burnt gas flow decreased. Further, in the schlieren images when the total number of the communication holes 22 is five and six, the burned gas jet flow extends linearly in the case of five, whereas the schlieren image in the case of five shows that It was confirmed that the fuel gas jet was curved by being entrained in the surrounding gas flow. This indicates that when the total number of the communication holes 22 is 5, the momentum of the burnt gas jet flow is weak, and it is presumed that the burnt gas jets ejected from the communication holes 22 become non-uniform. As in the case where the total number of the communication holes 22 is 6, when a part of the burnt gas jets ejected from the communication holes 22 is delayed and combustion becomes uneven, heat is generated as shown in FIG. The rate drops.

FIG. 10 shows the result of the third experiment in which the effect of the volume of the sub chamber 20 on the flame arrival distance was measured. In the third experiment, the total number of the communication holes 22 was 5, the diameter of the communication holes 22 was 1.6 mm, and the volume of the sub chamber 20 was 1.20 cm ³ or 1.84 cm ³ . In FIG. 10, the average value of the flame arrival distance at each time is shown by a plot, and the variance thereof is shown by an error bar.

In the third experiment, it was confirmed that when the volume of the sub chamber 20 was set to 1.84 cm ³ , the flame propagation speed reached the wall surface of the main chamber 8 faster than when it was set to 1.20 cm ³ . This is because the volume of the sub-chamber 20 increases and the mass of burnt gas generated increases when the equivalence ratio is the same. However, it can be seen from the size of the error bar in FIG. 10 that the flame reach distance fluctuates when the volume of the sub chamber 20 is 1.84 cm ³ compared to when it is 1.20 cm ³ . This is because the jet velocity of the burnt gas jet becomes higher, so that a free shear layer is generated at the boundary between the burnt gas jet jetted from the communication hole 22 and the air-fuel mixture in the main chamber 8, and ignition delay occurs. It is thought to be due to that.

From the above first to third experimental results, it is understood that the diameter of the communication holes 22, the total number of the communication holes 22, and the volume of the sub chamber 20 affect the flame arrival distance and the combustion stability. It can be seen that the flame arrival distance increases as the equivalence ratio is constant, the sub chamber 20 has a larger volume, the communication holes 22 have a smaller diameter, or the total number of the communication holes 22 is smaller. From these viewpoints, it is clear that the momentum of the burnt gas jet flowing from the sub chamber 20 through the communication hole 22 and jetting into the main chamber 8 has a great influence on the combustion of the air-fuel mixture in the main chamber 8. The sub-chamber index Is was defined by using the volume V of the sub-chamber 20 as a numerator and the sum St of the opening area S of each communication hole to the sub-chamber 20 as the denominator. The sub-chamber index Is is an index representing the momentum of the burnt gas jet flow ejected from the communication hole 22, and as the volume V of the sub-chamber 20 increases, the total amount of burned gas generated and the energy increase and the burned gas is burned. As the momentum of the gas jet increases, the smaller the total St (=n×S) of the opening area S of each communication hole 22 to the sub chamber 20, which is the sum of the outlet areas of the burned gas jet, the smaller the pressure of the burned gas jet. Indicates that the momentum of the burnt gas jet increases.

FIG. 11 is a graph in which the results obtained in the first to third experiments are arranged as the sub-chamber index Is on the horizontal axis and the flame arrival time on the vertical axis. The flame arrival time [ms] is the time required for the flame to reach the distance 0.8 when the distance from the outlet of the communication hole 22 to the wall surface of the main chamber 8 in the axial direction of the communication hole 22 is 1. [Ms]. The values attached to each plot in FIG. 11 are the conditions under which the results were obtained, and from the left, the total number n of the communication holes 22, the diameter of the communication holes 22, and the volume V of the sub chamber 20. As shown in FIG. 11, the larger the sub chamber index Is, the shorter the flame arrival time. From this result, it is understood that the sub chamber index Is indicates the momentum of the flame.

FIG. 12 and FIG. 13 show the relationship between the sub chamber index Is, the combustion period and the thermal efficiency in the gas engine 1 having the same combustion chamber shape as the constant volume combustion device used in the first to third experiments. It is the result of measurement. At this time, the gas engine 1 has an exhaust volume of 551 cm ³ , a compression ratio of 14.0, and other conditions are the same as those of the constant volume combustion device. FIG. 12 shows an engine speed of 1500 rpm, an indicated mean effective pressure (IMEP) of 500 kPa, and a low load combustion chamber pressure of 1.9 MPa when the piston 7 is at the top dead center. FIG. 13 shows an engine speed of 2000 rpm. The results are shown when the indicated mean effective pressure (IMEP) is 1200 kPa and the combustion chamber pressure is 4.3 MPa when the piston 7 is at the top dead center when the load is high. The combustion period is a value that has a primary relationship with the flame arrival distance in the above-described first to third experiments, and the period from when the combustion mass ratio reaches 10% to 90% is represented by the crank angle. It was done. The values added to the plots in FIGS. 12 and 13 are the conditions under which the results were obtained, and from the left, the total number n of the communication holes 22, the diameter of the communication holes 22, and the volume V of the auxiliary chamber 20. .. The mark X in the figure is a condition in which the air-fuel mixture in the main chamber 8 did not ignite, and the corresponding thermal efficiency result was not obtained.

In the region where the sub-chamber index Is is about 5 to 12, the thermal efficiency increases in accordance with the increase of the sub-chamber index Is, and when the sub-chamber index Is is about 12 to 13, the thermal efficiency takes a maximum value. Then, in the region where the sub chamber index Is is 13 or more, the thermal efficiency decreases as the sub chamber index Is increases. In the region where the sub-chamber index Is is 12 or less, it is considered that the momentum of the burnt gas jet increases as the sub-chamber index Is increases, and the combustion period is shortened to increase the thermal efficiency. On the other hand, in the region where the sub-chamber index Is is 13 or more, the momentum of the burnt gas jet further increases as the sub-chamber index Is increases, and the burned gas jet ejected from the communication hole 22 and the air-fuel mixture in the main chamber 8 are mixed. It is presumed that a free shear layer will be generated at the boundary with. When the free shear layer is generated, flame formation of the air-fuel mixture in the main chamber 8, that is, ignition is impeded, and it is considered that combustion is nonuniform due to ignition delay. This is considered to reduce the thermal efficiency. Further, it is considered that when the velocity of the burnt gas jet increases, the timing at which the burnt gas jet contacts the wall surface that defines the main chamber 8 is advanced, and the cooling loss increases, thereby lowering the thermal efficiency. This result agrees with the results of the above-mentioned first to third experiments. From FIG. 12, it can be said that the sub chamber index Is is in the range of 9 or more and 15 or less, more preferably in the range of 10 or more and 15 or less, or in the range of 9 or more and 14 or less, which is the optimum range in which the thermal efficiency is highest. As shown in FIGS. 12 and 13, in the low region where the sub-chamber index Is is 10 or less, the velocity of the burned gas jet jetted from the communication hole 22 is weak and the velocity of the burned gas jet is slow, so that the main chamber 8 The flame propagation speed of the flame generated by the combustion of the air-fuel mixture inside becomes slow, and the combustion becomes slow. Therefore, the equal volume of combustion decreases, which leads to a decrease in thermal efficiency.

When the sub-chamber index Is is 9 or more and 15 or less, the total number n of the communication holes 22 is 5, and the diameter of the communication holes 22 is 1.6 mm, the volume V of the sub-chamber 20 is 0.88 cm ³ or more and 1.51 cm ³ It becomes the following. When the sub-chamber index Is is 10 or more and 15 or less, the total number n of the communication holes 22 is 5, and the volume V of the sub-chamber 20 is 1.2 cm ³ , the diameter of the communication hole 22 is 1.5 mm or more and 1.7 mm or less. Becomes

The relationship of the thermal efficiency with respect to the sub chamber index Is as shown in FIGS. 12 and 13 is not a phenomenon peculiar to the specifications of the gas engine 1 shown in the above-mentioned embodiment, but is different in the cylinder 4 and the piston 7 of various sizes. Occurs similarly. In particular, the angle formed by the axis of the communication hole 22 with respect to the cylinder axis is 20° or more and 75° or less, the stroke bore ratio is 0.6 or more and 2.6 or less, and the sub chamber 20 with respect to the volume of the main chamber 8 When the volume ratio is 0.02 or more and 0.04 or less and the diameter of the piston 7 is at the top dead center, the piston in the axial direction of the communication hole 22 from the main chamber side opening end of the communication hole 22. In the gas engine 1 having the condition that the distance ratio to the surface of 7 is 0.19 or more and 0.32 or less, the sub chamber index is in the range of 9 or more and 15 or less, more preferably 10 or more and 15 or less or 9 or more and 14 or less. The thermal efficiency is highest in the range of. This is because when the displacement or the volume of the cylinder 4 increases and the volume of the main chamber 8 increases, the volume of the sub chamber 20 also increases and the amount of burnt gas generated increases. In this way, the sub-chamber index is an index that takes into consideration changes in the exhaust amount and changes in the volume of the cylinder 4.

In the gas engine 1 that obtained the results of FIGS. 12 and 13 and the constant volume combustion device used in the above-described first to third experiments, the diameter of the communication holes 22, the total number of the communication holes 22, and the sub chamber 20. Of the sub-chamber index Is is realized by changing the volume of each of the sub-chambers, and the velocity (flame propagation velocity) [m/s] of the burnt gas jet ejected from the communication hole 22 to the main chamber 8 when the sub-chamber indices Is are set. ] And the result of confirming the success or failure of the ignition of the air-fuel mixture in the main chamber 8 is shown in FIG. In FIG. 14, the horizontal axis represents the sub-chamber index Is, the vertical axis represents the flame velocity (velocity of burnt gas jet), and the shape of each plot shows the success or failure of ignition. The burned gas jet velocity is 0.8 when the burned gas jet velocity is 0.8 when the distance between the opening end of the communication hole 22 on the main chamber 8 side and the wall surface of the main chamber 8 in the axial direction of the communication hole 22 is 1. It is calculated by dividing by the time required to reach. In FIG. 14, in each plot, ○ indicates the result of confirming the ignition in the main chamber 8 in both the gas engine 1 and the constant volume combustion device, and Δ indicates the ignition in the main chamber 8 in the gas engine 1. However, in the constant-volume combustion device, the result that ignition in the main chamber 8 was not confirmed was shown, and in the gas engine 1, ignition was confirmed in the main chamber 8, but in the constant-volume combustion device, ignition was confirmed in the main chamber 8. Indicates that the ignition was not confirmed, and x indicates that the ignition in the main chamber 8 was not confirmed in both the gas engine 1 and the constant volume combustion device.

As shown in FIG. 14, in the gas engine 1 and the constant volume combustion device, the burnt gas jet velocity has a relationship of increasing as the sub chamber index Is increases. Further, it is confirmed that the ignitability is lowered in the gas engine 1 and the constant volume combustion device in the region where the burnt gas jet velocity is higher than 7 m/s. This is because in the region where the burnt gas jet velocity is greater than 7 m/s, a free shear layer is generated at the boundary between the gas ejected from the communication hole 22 and the air-fuel mixture in the main chamber 8 as described above. It is assumed that the shear layer hinders the flame formation of the air-fuel mixture in the main chamber 8, that is, the ignition. Further, when the velocity of the burnt gas jet ejected from the communication hole 22 increases, it is presumed that the exposed surface of the burnt gas jet increases the exposure of the high temperature gas in which the flame is not formed, and therefore the inside of the main chamber 8 is exposed. It is assumed that the ignitability of the air-fuel mixture is reduced.

The main factors that affect the burnt gas jet velocity are the energy of burnt gas generated in the sub-chamber 20, and the opening area of the communication hole 22 that is the flow path of the burnt gas jet to the sub-chamber 20. There is a sum. The burnt gas jet velocity increases as the energy of the burnt gas generated in the sub chamber 20 increases, and the burned gas jet velocity decreases as the total opening area of the communication holes 22 to the sub chamber 20 increases. Become. The energy of the burned gas in the sub chamber 20 is determined by the equivalence ratio of the air-fuel mixture in the sub chamber 20 and the volume of the sub chamber 20. Therefore, the burnt gas jet velocity is determined by the equivalence ratio of the air-fuel mixture in the sub chamber 20, the volume of the sub chamber 20, and the total opening area of the communication holes 22 to the sub chamber 20. In a state where the equivalence ratio of the air-fuel mixture in the sub chamber 20 is set, the burnt gas jet velocity is determined by the total opening area of the communication holes 22 to the sub chamber 20 and the volume of the sub chamber 20.

Although it is expected that the equivalence ratio in the main chamber 8 and the pressure in the main chamber 8 will also affect the burnt gas jet velocity, the effects thereof are the equivalence ratio of the air-fuel mixture in the sub chamber 20 and the sub chamber 20. It is considered to be negligibly small with respect to the total volume and the total opening area of the communication holes 22 to the sub chamber 20. The equivalence ratio of the main chamber 8 at the ignition timing is 0.6 under the conditions of this experiment, but there is almost no effect on the burnt gas jet velocity in the range of 0.5 or more and 2.0 or less, and the effect is 0. It is presumed to be smaller in the range of 5 or more and 1.1 or less. In addition, the pressure of the main chamber 8 is 1.9 MPa (low load condition of the gas engine 1), 4.3 MPa (high load condition of the gas engine 1), and 2.3 MPa (constant volume combustion device) in this experiment. In the range of 1.2 MPa to 6.0 MPa, the effect on the burnt gas jet velocity is presumed to be negligibly small. When the pressure of the main chamber 8 when the piston 7 is at the top dead center is 1.2 MPa or more and 6.0 MPa, the pressure at the maximum output of the gas engine 1 from idling to 5000 rpm, that is, the normal pressure of the gas engine 1. It corresponds to the entire operating state of.

As described above, the burnt gas jet speed is set in the sub chamber 20 including the sum of the equivalence ratio of the air-fuel mixture in the sub chamber 20, the volume of the sub chamber 20, and the opening area of the communication hole 22 to the sub chamber 20. The influence of the shape of the main chamber 8 and the conditions of the air-fuel mixture in the main chamber 8 is small.

In this experiment, as shown in FIG. 14, the minimum value of the burnt gas jet velocity confirmed for ignitability was 4 m/s, and the ignitability was good when the burnt gas jet velocity was 4 m/s. Have confirmed. Although the ignitability was not confirmed in the range where the burnt gas jet velocity was less than 4 m/s, ignition was performed by both the gas engine 1 and the constant volume combustion device when the burnt gas jet velocity was 4 m/s. Since it has been confirmed that the ignitability is good, it is presumed that the region having good ignitability exists even in a range smaller than 4 m/s.

From FIG. 14, the range in which the burnt gas jet velocity is 4 m/s or more and 7 m/s or less includes all the range in which the sub chamber index Is is 9 or more and 15 or less. That is, ignitability is improved by setting the burnt gas jet velocity to 4 m/s or more and 7 m/s or less, and thermal efficiency is further improved by setting the sub chamber index Is to 9 or more and 15 or less.

Although the specific embodiments have been described above, the present invention is not limited to the above embodiments and can be widely modified and implemented. In the above-described embodiment, the example in which the main chamber 8 is defined by the inner surface of the cavity 45 and the combustion chamber ceiling portion 5 when the piston is at the top dead center has been described, but in other embodiments, the cavity 45 is omitted. Good. In this case, when the piston is at the top dead center, the main chamber 8 may be defined by the crown surface 7A of the piston 7, the combustion chamber ceiling portion 5, and the inner peripheral surface of the cylinder 4. Further, in the above-described embodiment, the injector 30 has been described as an example in which the main injection is performed once and the sub-injection is performed once, but the main injection is performed by being divided into a plurality of times during the fuel injection period described above. Good.

1: Gas engine 4: Cylinder 7: Piston 7A: Crown surface 8: Main chamber 16: Support hole 17: Partition member 20: Sub-chamber 22: Communication hole 30: Injector 33: Spark plug hole 36: Spark plug 36A: Body part 36F: Firing part 45: Cavity 47: Convex part 50: Control device A: Cylinder axis

Claims (6)

A four-stroke gas engine,
A cylindrical main chamber defined by the upper end surface of the cylinder and the crown surface of the piston and centered on the cylinder axis,
A sub chamber having a small volume with respect to the main chamber, which is partitioned from the main chamber by a bottomed cylindrical partition wall member that projects from the upper end surface of the cylinder to the center of the main chamber and is arranged coaxially with the cylinder axis. When,
4 or more and 6 or less communication holes, which are arranged in the partition member at equal intervals in the circumferential direction about the cylinder axis and connect the main chamber and the sub chamber,
An injector for injecting gaseous fuel into the sub chamber,
And a spark plug having an ignition part disposed in the sub chamber,
The injector performs the main injection in the intake stroke, and in order to form the air-fuel mixture having an equivalence ratio of 1.0 or more and 2.0 or less in the ignition timing in the sub chamber, a smaller amount than the main injection is performed immediately before the ignition timing. Perform secondary injection,
The angle formed by the axis of the communication hole with respect to the cylinder axis is 20° or more and 75° or less,
Stroke bore ratio is 0.6 or more and 2.6 or less,
The ratio of the volume of the sub chamber to the volume of the main chamber is 0.02 or more and 0.04 or less,
The ratio of the distance from the opening end of the communication hole on the main chamber side to the surface of the piston in the axial direction of the communication hole when the piston is at the top dead center relative to the diameter of the piston is 0.19 or more. 32 or less,
A gas chamber engine, wherein a sub chamber index obtained by dividing a volume of the sub chamber by a sum of opening areas of the communication holes to the sub chamber is 9 or more and 15 or less. Gas engine according to claim 1, wherein the exhaust amount of the cylinder is 150 cm ³ or more 800 cm ³ or less. A circular concave portion is formed on the crown surface of the piston when viewed from the direction along the cylinder axis,
The upper end surface of the cylinder is formed into a flat surface,
When the piston is at the top dead center, the main chamber is defined by the inner surface of the recess, the upper end surface of the cylinder, and the outer surface of the partition member, and the lower end of the partition member projects into the recess. The gas engine according to claim 1 or 2 , wherein Each axis of the communication holes has an intersection on the cylinder axis,
The gas engine according to any one of claims 1 to 3 , wherein the ignition part is arranged at the intersection. The gaseous fuel is CNG, and the velocity of the gas ejected from the communication hole into the main chamber after ignition is 4 m/s or more and 7 m/s or less throughout the normal operating state of the gas engine. The gas engine according to any one of claims 1 to 4, wherein a sum of opening areas of the communication holes to the sub chamber and a volume of the sub chamber are set. 6. The injector according to claim 1, wherein the injector performs main injection in an intake stroke so as to form an air-fuel mixture having an equivalence ratio of 0.5 or more and 2.0 or less at an ignition timing. A gas engine according to any one of the above items.

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