JPH07293344A - Thermal insulation type gas engine - Google Patents

Abstract

PURPOSE:To improve thermal efficiency by setting high compression ratio of an engine. CONSTITUTION:In a cylindrical housing arranged on a lower side of a cylinder head 20, an upper subsidiary-chamber 9 and a lower subsidiary-chamber 10 are determined by means of a partition wall 12, and fuel injection nozzle 4 is arranged in an intermediate peripheral wall of the upper subsidiary-chamber 9. A subsidiary-piston 7 which is moved vertically interlockingly with intake/ exhaust valves 18, 16 is arranged inside the upper subsidiary-chamber 9. An opening/closing valve 6a which opens and closes a valve hole 13 formed on the partition wall 12 is connected to a lower end of the subsidiary-piston 7. A plurality of injection holes 14 communicated with a main combustion of injection hole 14 communicated with a main combustion chamber 25 of a cylinder main body 22 are formed on a lower end peripheral wall of the lower subsidiary-chamber 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat shield type gas engine for compression ignition of natural gas as a fuel.

[0002]

2. Description of the Related Art In a gas engine using natural gas as a fuel, the compression ratio can be set to a low value of 11 to 13 due to problems such as knocking. Since natural gas has a slow burning rate and an unstable burning state, its thermal efficiency is low. There are problems such as ......

[0003]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a heat shield type gas engine which can set a higher compression ratio and improve thermal efficiency.

[0004]

In order to achieve the above object, the structure of the present invention has a cylindrical housing provided in the lower portion of a cylinder head, and an upper sub-chamber and a lower sub-chamber are defined by a partition wall. A fuel injection nozzle is arranged on the intermediate peripheral wall of the sub chamber, a sub piston that moves up and down in conjunction with the intake and exhaust valves is fitted in the upper sub chamber, and a valve hole provided in the partition wall is opened and closed at the lower end of the sub piston. An opening / closing valve is connected, and a plurality of injection holes communicating with the main combustion chamber of the cylinder body are provided on the lower peripheral wall of the lower auxiliary chamber.

[0005]

According to the present invention, the gas fuel mainly composed of natural gas is injected into the upper sub chamber at the end of the intake stroke, and then the opening / closing valve is opened when the sub piston is lowered, and the gas fuel in the upper sub chamber is opened. After entering the lower sub-chamber, it is ignited while being mixed with intake air, and ejected from a large number of injection holes to the main combustion chamber at the end of the compression stroke.

[0006]

EXAMPLE A gas engine according to the present invention is a cylinder body 2
The main piston 24 is fitted to the cylinder 2, and the cylinder head 20 having the intake passage 17 and the exhaust passage 15 is connected to the upper end of the cylinder body 22 with the gasket 21 interposed therebetween. In the illustrated embodiment, the cylinder head 20 has two intake passages 17 and two exhaust passages 15 for each cylinder. A heat shield plate 23 made of a heat resistant structural material such as ceramics is coupled to the upper end of the main piston 24. At each intake port 17, an intake valve 18 that is separated from and in contact with the valve seat 17a at the lower end,
In the exhaust passage 15, the exhaust valve 1 which is in contact with and separates from the valve seat 15a at the lower end.
6 are provided, and the stems of the intake valve 18 and the exhaust valve 16 are opened and closed by a valve mechanism (not shown) arranged above the cylinder head 20. Such a structure is almost the same as a normal diesel engine.

According to the present invention, the cylindrical portion 19 is formed on the lower surface of the cylinder head 20 substantially at the axial center, and the cylindrical housing 8 is fitted and supported by the cylindrical portion 19. The housing 8 is partitioned by a partition wall 12 into an upper sub chamber 9 and a lower sub chamber 10.
The sub piston 7 is fitted in the upper sub chamber 9, and the stem 6 coupled to the sub piston 7 is projected upward. The sub piston 7 is fitted with a seal ring made of low friction ceramics. A spring 3 is interposed between a spring seat 2 connected to the upper end of the stem 6 via a cotter and a spring seat 5 arranged on the upper wall of the cylinder head 20. A stem (not shown) is also coupled to the upper end of the stem 6, and is vertically moved by a cam mechanism that drives an intake valve or an exhaust valve by a valve mechanism. A stem of an on-off valve 6 a that opens and closes the conical valve hole 13 of the partition wall 12 is coupled to the lower end of the sub piston 7. The fuel injection nozzle 4 is disposed on the peripheral wall between the upper sub chamber 9 and the upper and lower intermediate chambers. The fuel injection nozzle 4 intermittently injects the gas fuel into the upper sub chamber 9 in association with the reciprocating movement of the main piston 24. The lower end of the housing 8 slightly protrudes into the main combustion chamber 25, and a plurality of injection holes 14 extending obliquely downward are provided in the lower end peripheral wall of the lower auxiliary chamber 10. The heat shield plate 23 is provided with a recess 23a so as not to interfere with the lower end of the housing 8.

As shown in FIG. 3, the directions of the injection holes 14 extend in a tangential direction when seen in a plan view, and when the gas fuel in the lower sub chamber 10 is ejected into the main combustion chamber 25, a swirl flow is formed. Composed. In order to withstand a large heat load due to the high compression ratio of the gas fuel, the crown portion of the main piston 24, the auxiliary chambers 9 and 10, and the on-off valve 6a are made of a heat resistant structural material such as ceramics.

Next, the operation of the heat shield type gas engine according to the present invention will be described. The compression ratio is set to 17 to 18 in order to raise the temperature of the lower sub chamber 10 and surely ignite the gas fuel near the end of the compression stroke (top dead center). As shown in FIG. 4, the on-off valve 6a opens from near the end of the compression stroke of the main piston 24 (top dead center) to near the beginning of the intake stroke (top dead center), and closes at the end of the intake stroke (bottom dead center). ing.

At the end of the intake stroke (bottom dead center), injection of gas fuel from the fuel injection nozzle 4 into the upper sub chamber 9 starts. When the main piston 24 starts to rise in the compression stroke, the temperature of the lower sub chamber 10 rises, but the gas fuel in the upper sub chamber 9 is too rich to ignite. When the main piston 24 reaches the end of the compression stroke (top dead center), the main combustion chamber 25 and the lower sub chamber 1
The temperature of 0 rises, the on-off valve 6a opens, and the gas fuel in the upper subchamber 9 flows into the lower subchamber 10 and mixes with the high temperature, high pressure intake air. The air-fuel mixture in the lower sub-chamber 10 is ignited with an excess air ratio capable of being ignited. At the same time as the opening / closing valve 6a is opened, the sub piston 7 descends, and the gas fuel in the upper sub chamber 9 is pushed out to the lower sub chamber 10 through the valve hole 13. The dense mixture in the lower sub-chamber 10 is the injection hole 1
The amount of unburned gas that is ejected into the main combustion chamber 25 via 4 and remains in the lower sub chamber 10 becomes small. Since the air-fuel mixture blows out from the injection hole 14 to the main combustion chamber 25 in the tangential direction or the circumferential direction, mixing with the intake air is promoted, and combustion is completed within a short time.

As shown in FIG. 2, as the auxiliary piston 7 descends, the fuel injection nozzle 4 is positioned above the auxiliary piston 7, so that the fuel injection nozzle 4 is exposed to the flame for a short period of time and also has a heat load. small.

[0012]

As described above, according to the present invention, the upper sub-chamber and the lower sub-chamber are partitioned by the partition wall in the cylindrical housing provided in the lower portion of the cylinder head, and the fuel injection nozzle is provided on the intermediate peripheral wall of the upper sub-chamber. A sub-piston that moves up and down in conjunction with the intake and exhaust valves is fitted in the upper sub-chamber, and an opening / closing valve that opens and closes a valve hole provided in the partition wall is connected to the lower end of the sub-piston to form a lower sub-chamber. The lower peripheral wall of the cylinder is equipped with multiple injection holes that communicate with the main combustion chamber of the cylinder body.At the end of the compression stroke, a small amount of intake air is filled into the lower sub chamber, and the gas fuel in the upper sub chamber is charged by the sub piston. Since it is supplied to the lower sub chamber to start combustion and the gas fuel in the lower sub chamber is supplied to the main combustion chamber from the plurality of injection holes, the compression ratio is 17 to 1
It can be set as high as 8, and the thermal efficiency of the engine can be improved.

By making the injection holes of the lower auxiliary chamber tangential to each other, a strong swirling flow is generated in the main combustion chamber, and the intake air and the gas fuel are uniformly mixed and very good combustion is achieved in a lean state. There is no problem with the exhaust gas component obtained.

Since the gas fuel in the upper sub-chamber is pushed out to the lower sub-chamber by the sub-piston, the gas fuel is jetted into the main combustion chamber while being mixed with the intake air in the lower sub-chamber, and the direction of the injection holes is tangential. Therefore, the jetting energy of the air-fuel mixture is effectively used and the flame spreads to the main combustion chamber within a short period of time, resulting in a shorter combustion period in the main combustion chamber and improved thermal efficiency.

Since the fuel injection nozzle is located above the auxiliary piston at the same time as the gas fuel is ignited, the heat load on the fuel injection nozzle is reduced.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a main part of a heat shield type gas engine according to the present invention.

FIG. 2 is a front sectional view showing a lowered state of a sub piston in the gas engine.

FIG. 3 is a bottom cross-sectional view showing the lower half portion of FIG. 1 taken along the line 3A-3A.

FIG. 4 is a diagram showing a stroke of a heat shield type gas engine.

[Explanation of symbols]

4: Fuel injection nozzle 6a: Open / close valve 7: Sub piston
8: Housing 9: Upper sub chamber 10: Lower sub chamber 12: Partition wall 13: Valve hole 14: Injection hole 16: Exhaust valve 18: Intake valve 20: Cylinder head 22: Cylinder body 2
4: Main piston 25: Main combustion chamber

Claims (4)

[Claims] 1. A cylindrical housing provided in the lower part of a cylinder head, which divides an upper sub chamber and a lower sub chamber by a partition wall, and a fuel injection nozzle is arranged on an intermediate peripheral wall of the upper sub chamber. A sub-piston that moves up and down in conjunction with the intake and exhaust valves is fitted to the bottom of the sub-chamber, and an opening / closing valve that opens and closes a valve hole is connected to the lower end of the sub-piston. A heat shield type gas engine having a plurality of injection holes communicating with the combustion chamber. 2. The heat shield type gas engine according to claim 1, wherein the plurality of injection holes are arranged at equal intervals in the circumferential direction on the lower peripheral wall of the lower sub chamber, and the directions of the injection holes are tangential. 3. The heat shield type gas engine according to claim 1, wherein the housing and the crown portion of the main piston are made of a heat resistant structural material. 4. The auxiliary piston fitted in the upper auxiliary chamber has a stem protruding upwardly engaged with a valve mechanism for moving the auxiliary piston up and down in synchronization with an intake / exhaust valve. Heat shield type gas engine.