JP3048475B2 - 2-stroke gas engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention supplies natural gas from a gaseous fuel supply source to a sub-chamber and supplies intake air to a main chamber in which communication with the sub-chamber is closed. The present invention relates to a two-stroke gas engine for mixing and burning gas fuel.

[0002]

2. Description of the Related Art Conventionally, an engine using natural gas as a main fuel has been developed as a cogeneration type engine. In this cogeneration type engine, power is extracted as electric energy by a generator, and heat of exhaust gas energy is heated by a heat exchanger to make hot water and used for hot water supply. This cogeneration type engine is expected to be used as an electricity supply system in the city in the future.

As an engine using natural gas as a fuel, for example, there are those disclosed in JP-A-54-156911 and JP-A-1-232119.

The internal combustion engine disclosed in Japanese Patent Application Laid-Open No. 54-156911 compresses intake air and supplies it to a main combustion chamber, and supplies a part of the intake air to a jet cell ignition chamber.
The paraffinic hydrocarbon fuel is injected into the jet cell ignition chamber to form a rich mixture, the intake air and the mixture are further compressed, and the paraffinic hydrocarbon fuel is injected into the main combustion chamber, while Further compressing the intake air and the mixture to produce a lean mixture in the main combustion chamber and igniting the mixture in the jet cell ignition chamber before full compression of both mixtures is achieved to produce a hot gas stream; the flow of the heat had gas was charged to the mixture in the main combustion chamber to ignite the mixture of the main combustion chamber, thereby reducing the production of NO _X.

Further, the engine for hydrogen and liquefied natural gas disclosed in Japanese Patent Application Laid-Open No. 1-223219 supplies either hydrogen as fuel or liquefied natural gas when the engine is in a low-load operation state, A control means for supplying liquefied natural gas as a fuel when the engine is in a high load operation state is provided.

[0006]

However, in a gas engine using natural gas as a fuel, since the fuel is a gaseous substance, the fuel gas is sucked from an intake port by opening and closing an intake valve in the same manner as gasoline, by opening and closing an intake valve. Since ignition occurs, the compression ratio cannot be increased, and the theoretical thermal efficiency (η
= Heat conversion of work / heat of fuel) is not necessarily high. Generally used gas engines have a compression ratio of about 9 to 13 and a theoretical thermal efficiency of only 48%.
If the gas engine is powered by electric energy,
The net thermal efficiency is between 34 and 35%, possibly below 30%. Therefore, 65 to 70% of the fuel is released as the cooling water loss and the exhaust gas energy, and this heat energy is used to generate hot water by a heat exchanger and the hot water is supplied in an excessively large amount. It is the present situation that general use facilities cannot fully utilize the facilities.

Therefore, at the present time, it is desired to improve thermal efficiency when extracting electric energy from a gas engine. Gas engines are generally
Natural gas is used as fuel, and the fuel is gas. Therefore, when the gas is sucked in the suction stroke and then compressed, the temperature increases in a highly compressed state, and the phenomenon of self-ignition, that is, knocking occurs. Therefore, if natural gas fuel is not an engine with a compression ratio of 12 or less,
It is self-igniting. Regarding the thermal efficiency of the engine, it has been theoretically and experimentally confirmed that the smaller the compression ratio, the lower the thermal efficiency. Therefore, in the gas engine, there is a problem how to avoid the self-ignition of the gas fuel and how to increase the compression ratio.

Further, since natural gas is mainly used as a fuel for a gas engine, if an excellent engine capable of burning at a high compression ratio using this natural gas can be manufactured, natural gas, which is said to exist infinitely, can be produced. A gas engine for fuel can be completed.

Therefore, in the gas engine, in order to increase the compression ratio, gas fuel is charged into the sub chamber and compression top dead center TD
It is conceivable to open a valve that opens and closes the communication hole in the vicinity of C to communicate the sub-chamber with the main chamber to mix and ignite the highly compressed air in the main chamber and the gas fuel in the sub-chamber. In such a type of gas engine, the most important issue is to mix gas fuel and air well.

[0010] Therefore, an object of the present invention is to solve the above-mentioned problems, and the communication between the main chamber and the sub-chamber is interrupted by the communication hole, natural gas is introduced into the sub-chamber, and the main chamber is sucked. Only the air is compressed to increase the compression ratio, and in a state where the air in the main chamber is raised to a high temperature, the communication hole valve of the communication hole is opened to allow the highly compressed air in the main chamber to flow into the sub-chamber. The air and gaseous fuel are rapidly mixed in the sub-chamber by the air flow velocity flowing through the gap between the communication hole valve and the communication hole. In this state, the fuel equivalent ratio is large, and the mixture is in a rich mixture state. The fuel that has completed the process becomes an expansion flame and blows out from the communication hole into the main chamber, and the expansion flame mixes with the air in the main chamber. Configure the shape of the main chamber to achieve mixing, and transfer the flame from the sub chamber to the main chamber. Causes blown out air, to complete in a short time as much as possible uniform mixture was in secondary combustion promoting mixing of the squish flow to the main chamber and the flame, NO
A two-stroke gas fueled by a gas fuel capable of reducing the generation of _X , HC, etc., particularly increasing the thermal efficiency, preventing self-ignition of the gas fuel, preventing the occurrence of knocking, and increasing the thermal efficiency as electric energy To provide the engine.

[0011]

The present invention is configured as follows to achieve the above object. That is,
The present invention provides a cylinder block having a cylinder formed therein, a cylinder head fixed to the cylinder block, an intake / exhaust port provided at a lower portion of the cylinder, a piston reciprocating in the cylinder, and a sub-chamber formed in the cylinder head. A fuel passage formed in the cylinder head for supplying gas fuel from a gas fuel supply source to the sub-chamber, a fuel valve for opening and closing a communication state between the fuel passage and the sub-chamber, and an opening in the center of the lower surface of the head of the cylinder head A communication hole communicating the sub-chamber and the inside of the cylinder, a conical shape arranged in a valve seat provided in the communication hole, and in which a flame spouting from the sub-chamber side to the cylinder side forms an expanded ring shape. A communication hole valve having a valve face, and a shape deepening from a central portion to a peripheral portion along a streamline pattern of a blast flame from the sub chamber. Main chamber formed in the top surface of the piston,
A two-stroke gas engine having

In this two-stroke gas engine, the communication hole valve opens near the compression top dead center to allow the compressed air to flow from the cylinder side into the sub-chamber, and the compressed air and the gas fuel in the sub-chamber. Are mixed and ignited.

In the two-stroke gas engine, the outer peripheral end of the annular opening of the main chamber has a radially inwardly tapered lip for promoting squish flow to the main chamber near the end of the compression stroke. It is formed in.

[0014]

The two-stroke gas engine according to the present invention
It is configured as described above and operates as follows. That is, the two-stroke gas engine includes a fuel valve that opens and closes a fuel passage to the sub-chamber, and a communication hole valve that opens and closes a communication hole that communicates with the inside of the cylinder and the sub-chamber that is opened at the center of the lower surface of the cylinder head. And the intake / exhaust port is formed in the lower part of the cylinder, the compression ratio ε can be increased to about 18, the engine performance can be improved, and the rich mixture can be burned in the sub-chamber. _X generation can be suppressed. However, when natural gas is used as fuel, the fuel is injected into the combustion chamber and diffusion combustion occurs.However, self-ignition occurs before the compression ratio reaches 18, causing knocking and burning with fuel lean. As a result, the generation of NO _X increases.

Further, there is no need to form an intake / exhaust port in the cylinder head, so that the degree of freedom in designing the combustion chamber formed in the cylinder head is increased, and the sub-chamber can be arranged in the center of the cylinder. The shape of the main chamber can be formed in accordance with the flame erupted from the sub chamber. When the communication hole is formed in the center of the lower surface of the head and the communication hole valve is arranged in the communication hole, the cylinder central region becomes a shadow of the communication hole valve, and a combustion chamber is formed in the piston head corresponding to the cylinder central region. Is also not valid. Therefore, the shape of the main chamber formed in the piston head is such that when the communication hole valve is formed in a conical valve face, the flame spouting from the sub-chamber side to the cylinder side forms an expanding ring shape. The main chamber formed in the head is formed so as to be deeper from the central part to the peripheral part along the streamline pattern of the blast flame from the sub-chamber.

Therefore, this two-stroke gas engine supplies gas fuel to the sub-chamber by a predetermined gas mass with the communication hole valve closed, and introduces intake air into the main chamber to supply the intake air to the main chamber. Compress alone. Since gas fuel does not exist in the main chamber even when the intake air has a high compression ratio, knocking does not occur without self-ignition of gas fuel. Further, when the communication hole is opened, high-compression intake air flows from the main chamber into the sub-chamber due to an air flow rate flowing from a gap between the communication hole and the communication hole valve, and gas fuel and compressed air DOO ignites mixed rapidly, large fuel equivalence ratio in this state, generation of the NO _X ignited combustion in a fuel-rich state is suppressed.

Next, the gaseous fuel that has been mixed in the sub-chamber becomes an expansion flame and blows out from the sub-chamber through the communication hole into the main chamber, and mixes with fresh air existing in the main chamber. At this time, the gap between the communication hole valve and the communication hole is a circular gap in cross section, in other words, an annular conical gap, and the flame ejected from the sub chamber to the main chamber through the annular conical gap has an expanded ring shape. The main chamber formed on the top surface of the piston is formed in a shape that becomes deeper from the center to the periphery along the streamline pattern of the flaming flame from the sub-chamber.
The squish flow that flows into the main chamber along with the decrease in the gap between the piston top surface and the lower surface of the head crosses the flared ring-shaped blast flame and promotes the mixing of air and flame. it can.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a two-stroke gas engine according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a two-stroke gas engine according to the present invention, and FIG. 2 is a sectional view showing an open state of a communication hole valve of the two-stroke gas engine of FIG.

This two-stroke gas engine fits into a cylinder block 14 having scavenging ports, that is, an intake port 25 and an exhaust port 31, a cylinder head 7 fixed to the cylinder block 14, and a hole 21 formed in the cylinder block 14. Liner 6 forming cylinder 18 and intake port 2 formed in cylinder block 14
5. A scavenging port or intake port 20 formed in the cylinder liner 6 communicating with the cylinder line 5, and the cylinder liner 6 communicating with the exhaust port 31.
, A sub-chamber wall 3 made of ceramics forming the sub-chamber 2 disposed in the hole 19 formed in the cylinder head 7, and a piston 15 reciprocating in a cylinder 18 formed in the cylinder liner 6. , A main chamber 1 formed in the piston head 16 of the piston 15, and a communication hole 30 communicating the main chamber 1 and the sub chamber 2.

In this two-stroke gas engine,
A headliner 10 made of ceramics is fitted in a hole 9 formed in the cylinder head 7. The head liner 10 includes a liner upper part 2 that forms a part of the cylinder 18.
8 and a lower surface portion 11 of the head. A sub-chamber wall 3 forming the sub-chamber 2 is integrally formed on the upper surface of the head lower surface portion 11. The sub-chamber wall 3 has a cylinder head 7
The upper wall body 12 and the lower wall body 13 fitted in the hole 19 are formed. The communication hole 30 is formed at the center of the cylinder on the lower surface 11 of the head. The piston 15 has a piston head 16 made of ceramics such as silicon nitride having excellent heat resistance, and a coupling ring 29 attached to the piston head 16.
Skirt 17 fixed by metal flow at
It is composed of

In this two-stroke gas engine, natural gas as gas fuel is supplied through the fuel passage 8 to the sub-chamber 2.
And a gas fuel supply source for supplying the gaseous fuel. Although not shown, the gas fuel supply source includes, for example, a fuel tank containing a natural gas as a gas fuel and a pressure accumulator for accumulating the natural gas from the fuel tank. 8 through the cylinder head 7
The fuel is supplied to the sub-chamber 2 from the fuel inlet 23 formed in the above. Further, the two-stroke gas engine is arranged in a fuel valve 5 arranged at a fuel inlet 23 for adjusting gas fuel supply to the sub-chamber 2 and a communication hole 30 communicating the main chamber 1 with the sub-chamber 2. The communication hole valve 4 is provided.

In the area of the communication hole 30, the temperature becomes high due to the combustion gas.
Are manufactured from ceramics such as silicon nitride and silicon carbide having high temperature strength and excellent heat resistance. The fuel valve 5 has, for example, an electromagnetic valve driving device that is opened and closed by an electromagnetic force, and a valve opening period is determined according to an engine load. When the fuel valve 5 opens the fuel inlet 23, gas fuel, which is natural gas, is supplied from the accumulator to the sub-chamber 2 in a required amount. Further, the two-stroke gas engine is provided with a turbocharger 22, and exhaust gas discharged from an exhaust port 31 is sent to a turbine of the turbocharger 22. The turbine driven by the exhaust gas energy operates the compressor, and the air compressed by the compressor is supplied from the intake port 25 into the cylinder 18.

In particular, this two-stroke gas engine is:
The intake and exhaust ports 25 and 31 are formed in the lower part of the cylinder, and the shape of the main chamber formed in the piston head 16 is given a degree of freedom, so that the main chamber 1 having an ideal shape is formed in the piston head 16 and the fuel passage 8 is formed. And a communication hole valve 4 disposed in a communication hole 30 for communicating the sub-chamber 2 with the inside of the cylinder 18. The communication hole valve 4 is disposed in a valve seat 24 formed in a communication hole 30 opened in the center of the head lower surface portion 11 of the cylinder head 7, and is provided from the sub chamber 2 side to the cylinder 18.
The flame that blows out to the side has a conical valve face forming an expanding ring shape 33. The main chamber 1 formed in the piston head 16 is provided with a communication hole 30 from the sub-chamber 2 side.
It is formed in a shape that becomes deeper from the central part to the peripheral part along the streamline pattern of the expanding ring-shaped jet flame that jets out to the cylinder 18 side. Also, the piston head 16
Is formed on a flat surface 27 so as to be a relief when the communication hole valve 4 is opened and to reduce a waste volume. The main chamber 1 is formed in a shape that becomes deeper from the periphery of the flat surface 27 toward the periphery of the piston head 16. The outer peripheral edge of the main chamber 1 is formed on a pointed lip 34 so that a squish flow S generated by the inflow of air from the gap 26 into the main chamber 1 is formed favorably.

In this two-stroke gas engine, the communication hole valve 4 opens near the compression top dead center to allow the compressed air to flow into the sub-chamber 2 from the cylinder 18 side. It is to mix and ignite gas fuel.

In this two-stroke gas engine,
A headliner 10, which is a wall forming the main chamber 1, and a sub chamber 2
The upper wall body 12 and the lower wall body 13, the cylinder liner 6, and the piston head 16 that constitute the sub-chamber wall body 3 forming
For example, it is preferably made of ceramics such as silicon nitride and silicon carbide having excellent heat resistance. As a result, sufficient heat resistance even when the gas temperature in the later stage of combustion increases,
It has high-temperature strength, reduces emission of unburned hydrocarbons HC and the like, and can send heat energy generated in the sub-chamber 2 and the main chamber 1 to the turbocharger 22. If the turbocharger 22 is provided with a generator / motor, or if an energy recovery device is provided downstream of the turbocharger 22, the heat energy generated by the two-stroke gas engine can be reliably recovered, providing a gas engine with high thermal efficiency. can do.

This two-stroke gas engine is configured as described above and operates as follows. This 2
The stroke gas engine is operated by performing four strokes of a scavenging / suction stroke, a compression stroke, an expansion stroke, and an exhaust stroke with one rotation of the crankshaft, that is, two strokes of the piston 15, and sequentially repeating the strokes. . First, in the intake stroke, intake air is supplied into the cylinder 18 from an intake port 25 formed in the lower part of the cylinder, and the fuel valve 5 is opened with the communication hole 30 closed by the communication hole valve 4 to open the fuel passage 8. The gas fuel of the natural gas is supplied to the sub-chamber 2 from the gas fuel supply source. At this time, since the post-combustion exhaust gas slightly remains in the sub-chamber 2, when the gas fuel is introduced into the sub-chamber 2, the gas fuel receives heat and is activated in the sub-chamber 2.

In the two-stroke gas engine, in the compression stroke, the communication hole 30 is closed by the communication hole valve 4, and the intake air is highly compressed in the main chamber 1 to increase the compression ratio. Next, at the end of the compression stroke, that is, near the compression top dead center TDC, the communication hole valve 4 opens the communication hole 30, and the compressed air that has been highly compressed and raised in temperature (for example, 650 ° C.) through the communication hole 30 from the main chamber 1 to the sub-chamber. allowed to flow into the 2, the inhalation air is ignited combustion to promote mixing with gas fuel activated, burns in a state in which combustion is reduced NO _X in rapid progress to fuel-rich. Therefore, even if the intake air has a high compression ratio in the main chamber 1, the fuel does not contain gas fuel, so that the gas fuel does not self-ignite and no knocking occurs. In addition, when the communication hole 30 is opened, the highly compressed intake air flows from the main chamber 1 into the sub-chamber 2 due to the flow velocity of the air flowing from the gap between the communication hole 30 and the communication hole valve 4, and the gas fuel and the compressed air DOO ignites mixed rapidly, large fuel equivalence ratio in this state, the ignition and combustion in a fuel-rich NO _X
Is suppressed.

Next, the gaseous fuel that has been mixed in the sub-chamber ignites and burns to form an expansion flame, which is ejected from the sub-chamber 2 to the main chamber 1 through the communication hole 30, and the fresh air existing in the main chamber 1 Mix with. At this time, the gap between the communication hole valve 4 and the communication hole 30 is a passage having a circular cross section, in other words, an annular conical passage. The annular conical passage is a passage expanding toward the main chamber 1 side. The flame that passes through the sub-chamber 2 and blows out to the main chamber 1 blows out in a direction that expands into an expanded ring shape, and the main chamber 1 formed in the piston head 16 is
It is formed so as to be deeper from the center to the periphery along the streamline pattern of the flaming flame ejected from the main body, so that the gap 26 between the top surface of the piston head 16 and the head lower surface portion 11 decreases, The squish flow S flowing into the chamber 1 flows across the flared flame F in the form of the expanding ring 33 to promote mixing of the air and the blast flame in the main chamber 1.

The flame in the sub-chamber 2 blows out to the main chamber 1 and shifts to the combustion stroke, that is, the expansion stroke, and promotes the mixing with the fresh air present in the main chamber 1 to complete the secondary combustion in a short time. In this expansion stroke, the communication chamber 30 is maintained in the open state and the sub chamber 2 is moved to the main chamber 1.
The communication hole valve 4 is operated near the end of the exhaust stroke to close the communication hole 30.

As described above, this two-stroke gas engine is provided with the communication hole 30 and the fuel inlet 23 in the sub-chamber 2 and accumulates the natural gas from the fuel tank storing the natural gas in the accumulator. With the communication hole 30 closed by the communication hole valve 4, the control valve provided between the pressure accumulating chamber and the fuel passage 8 is opened to allow gas fuel to flow from the fuel inlet 23 through the fuel passage 8 into the sub-chamber 2. In a state in which the supply air is sucked into the main chamber 1 from the intake port 25 at the bottom of the cylinder and is not supplied to the sub-chamber 2 by closing the communication hole 30 with the communication hole valve 4, the piston 15 is compressed in the upward compression stroke. Therefore, even if the intake air is highly compressed in the main chamber 1, the gas fuel supplied into the sub-chamber 2 is isolated from the main chamber 1 by the communication hole valve 4 and does not self-ignite. , Knocking There is no possibility to live.

When the communication hole valve 4 opens the communication hole 30, high-compression suction air flows from the main chamber 1 into the sub-chamber 2, where gas fuel and suction air are mixed and ignited. fast burning a large fuel-rich ratio, occurrence of the NO _X is suppressed. Furthermore, the sub-chamber 2 containing exhaust gas after combustion
, A gas fuel from a gas fuel supply source is introduced, and the gas fuel receives heat in the sub-chamber 2 and is activated. In addition, this 2
In a stroke gas engine, if the fuel valve 5 is constituted by an electromagnetically driven valve driven by an electromagnetic force, the fuel valve 5 can be set so as to determine the valve opening period in response to the operating state of the engine load. An appropriate amount of gas fuel can be supplied to the sub chamber 2 according to the engine load.

[0032]

The two-stroke gas engine according to the present invention is configured as described above and has the following effects. That is, the two-stroke gas engine includes a fuel valve that opens and closes a fuel passage to the sub-chamber, and a communication hole valve that opens and closes a communication hole that communicates with the inside of the cylinder and the sub-chamber that is opened at the center of the lower surface of the cylinder head. The intake and exhaust ports are formed in the lower part of the cylinder, and it is not necessary to form them in the cylinder head.Therefore, the degree of freedom in designing the cylinder head is increased. Thus, the shape of the main chamber formed in the piston head can be formed to match the shape of the flame from the sub chamber. That is, the main chamber formed in the piston head can be formed in a shape that becomes deeper from the center to the periphery along the streamline pattern of the flaming flame from the sub-chamber.

Therefore, the communication hole valve can be formed in a conical valve face so that the flame spouting from the sub-chamber side to the cylinder side has an expanded ring shape. Then, the blast flame expanding in the shape of the expanding ring, that is, the annular cone, and the squish flow to the main chamber generated due to the decrease in the distance between the top surface of the piston head and the lower surface of the head in the compression stroke. Intersecting can promote mixing of the air with the blast flame.

In addition, since the intake hole can be supplied to the main chamber and the gas fuel can be supplied to the sub-chamber with the communication hole valve closing the communication hole, self-ignition occurs even when the intake air is highly compressed in the main chamber. And knocking does not occur. Further, since the sub-chamber is compressed and sealed in a state where no air is present, and the mass of the gas fuel is increased and supplied to the sub-chamber, it is possible to control the fuel equivalence ratio to an appropriate ratio, thereby improving the thermal efficiency. Can be. Further, after the combustion, the exhaust gas slightly remains in the sub-chamber, and when the gas fuel from the gas fuel supply source is introduced, the gas fuel receives heat and is activated in the sub-chamber. Further, even if the intake air has a high compression pressure in the main chamber, the sub-chamber is closed by the communication hole valve and is isolated from the main chamber, and the activated gas fuel in the sub-chamber is self-ignited. Without knocking.

When the communication hole valve is operated and the communication hole is opened, the air which has been highly compressed and heated from the main chamber flows into the sub-chamber at a stretch, and the gas fuel and the intake air are separated. Mixing is promoted at a stretch to ignite, and in the sub-chamber, high-speed combustion is performed in a fuel-rich state with a high equivalent ratio, so NO
_X generation is suppressed. Then, the pressure in the sub-chamber rises at once by combustion, and the combustion is promoted. At the same time, the flame gushes from the sub-chamber to the main chamber through the communication hole at a stretch, and the flame is renewed in the main chamber. Mixed with
It promotes combustion and raises the combustion speed to complete ideal secondary combustion. Accordingly, the two-stroke gas engine, NO _X, the generation of HC and the like can be significantly reduced, if produced a combustion chamber of the main chamber and the sub chamber in ceramics, sufficient thermal energy turbocharger, the energy recovery device And a gas engine with high thermal efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a two-stroke gas engine according to the present invention.

FIG. 2 is a cross-sectional view illustrating a state when a communication hole valve of the two-stroke gas engine of FIG. 1 is opened.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main chamber 2 Sub chamber 4 Communication hole valve 5 Fuel valve 7 Cylinder head 8 Fuel passage 11 Head lower surface part 14 Cylinder block 15 Piston 18 Cylinder 23 Fuel inlet 24 Valve seat 25 Intake port 30 Communication hole 31 Exhaust port

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F02B 19/02 F02B 23/02 F02B 23/06 F02B 25/14

Claims (3)

(57) [Claims] A cylinder block forming a cylinder;
A cylinder head fixed to the cylinder block, an intake / exhaust port provided at a lower portion of the cylinder, a piston reciprocating in the cylinder, a sub-chamber formed in the cylinder head, and gas fuel supplied from a gas fuel supply source to the sub-chamber. A fuel passage formed in the cylinder head, a fuel valve for opening and closing a communication state between the fuel passage and the sub-chamber, and a communication between the sub-chamber opened in the center of the lower surface of the head of the cylinder head and the inside of the cylinder. A communication hole valve having a conical valve face arranged in a valve seat provided in the communication hole, and having a flame shape spouting from the sub-chamber side to the cylinder side forming an expanded ring shape, and the piston The piston has an annular opening on the top surface of the piston and has a shape that becomes deeper from the center side to the peripheral side along the streamline pattern of the blast flame from the sub chamber. The formed main chamber, two-stroke gas engine having. 2. The communication hole valve opens near a compression top dead center to allow compressed air to flow from the cylinder side into the sub-chamber, and to mix and ignite the compressed air and gas fuel in the sub-chamber. 2. The two-stroke gas engine according to 1. 3. The lip of the main chamber is formed with a lip that is pointed radially inward to promote squish flow to the main chamber near the end of the compression stroke. 2. The two-stroke gas engine according to 1.