Patent Application
20130000598
The present invention relates to a divided-chamber gas engine including an auxiliary combustion chamber (an auxiliary chamber), and particularly to nozzles (nozzle holes) through which a combustion gas is injected from the auxiliary combustion chamber of the gas engine into a main combustion chamber.
Divided-chamber gas engines include a main combustion chamber (which may be hereinafter referred to as a “main chamber”) and an auxiliary combustion chamber (which may be hereinafter referred to as an “auxiliary chamber”) connected to the main combustion chamber via nozzles. A lean air-fuel mixture (a fuel gas) is supplied to the main chamber through an air supply valve. The lean air-fuel mixture is produced by mixing a gaseous fuel and supplied air. The lean air-fuel mixture is such that air that is greater in amount than a theoretical air requirement is mixed into the fuel. Accordingly, the excess air ratio λ of the lean air-fuel mixture is high (e.g., λ is approximately 2). The auxiliary chamber is provided with a spark plug. A rich air-fuel mixture (a fuel gas for ignition), the excess air ratio λ of which is 1 or lower, is supplied to the auxiliary chamber. In the divided-chamber gas engine as above, first, the spark plug provided in the auxiliary chamber is fired and thereby the fuel gas for ignition in the auxiliary chamber is ignited. A flame produced in the auxiliary chamber propagates such that the flame front spreads from the spark plug in a spherical manner. Then, a high-temperature fuel gas jets into the main chamber in the form of jet flames through a plurality of nozzles. From the jet flames, the flame propagates to the lean fuel gas in the main chamber. At the time, the temperature of the inner wall surface of the auxiliary chamber reaches approximately 1000° C.
In the above divided-chamber gas engine, the plurality of nozzles connecting the auxiliary chamber and the main chamber are open radially at the bottom part of the auxiliary chamber. Accordingly, the jet flames that jet into the main chamber through the nozzles spread within the main chamber in a distributed manner. It is necessary for the jet flames, which are injected from the auxiliary chamber into the main chamber through the nozzles, to have sufficient intensity for igniting the fuel gas in the main chamber, that is, sufficient injection quantity and jet velocity. In consideration of the above-described combustion in the main chamber, the nozzles are designed such that the intensity of the jet flames becomes optimal.
When the rich air-fuel mixture, the excess air ratio λ of which is 1 or lower, is combusted, NOx of several thousand ppm is produced. Therefore, it is necessary to install a denitration device. However, generally speaking, in a case where the lean air-fuel mixture is combusted (i.e., lean burn), the amount of NOx to be produced is suppressed to approximately several hundred ppm. Therefore, for performing lean burn, the installation of a denitration device is unnecessary in some cases.
The inner wall of the auxiliary chamber of the divided-chamber gas engine is formed of a nickel-based alloy (e.g., Inconel). Usually, the nozzles (nozzle holes) connecting the auxiliary chamber and the main chamber of the divided-chamber gas engine are formed as straight pipes by machining. If such a conventional divided-chamber gas engine is operated for a long period of time, the edge of the nozzles' inlets at the auxiliary chamber side becomes deformed. As mentioned above, the temperature in the auxiliary chamber becomes 1000° C. or higher. Accordingly, the inner wall surface of the auxiliary chamber is repeatedly subjected to heating and cooling cycles, in which the inner wall surface expands due to exposure to a high-temperature atmosphere and contracts when cooling down. Due to such heating and cooling cycles, the inner wall of the auxiliary chamber is subjected to thermal fatigue. As a result, cracks occur. In particular, cracks mainly occur near the nozzles' opening edges at the auxiliary chamber side. If the severity of the cracks near the nozzles' opening edges at the auxiliary chamber side increases, then cracks also occur in the inner wall of the nozzles. If a high-temperature jet flame passes through such a cracked inner wall of a nozzle, then cracked portions partially come off, resulting in chipping of the edge of the nozzle's inlet (i.e., chipping of the opening edge), or the inner wall of the nozzle or the inner wall of the auxiliary chamber at the rim of the nozzle peels off, causing its surface to become rough.
Chipping and cracks at the edge of the inlet of the nozzle cause a change in the intensity of a jet flame, which may lead to a decrease in the engine's combustion performance. Usually, divided-chamber gas engines are designed so that the engines can exert predetermined functions under optimized conditions, under the assumption that the edge of the inlet of each nozzle is in perfect conditions where there is no chipping or the like at the edge. If chipping or cracks occur at the edge of the inlet of the nozzle, the cross-sectional shape of the nozzle changes. As a result, the intensity of a jet flame that jets out though the nozzle also changes. For example, if the diameter of the nozzle increases, then the intensity of the jet flame decreases. In this case, there is a possibility that the length of the jet flame becomes insufficient. Moreover, the degree of such chipping and cracks is not necessarily the same among a plurality of nozzles. Accordingly, the jet flame intensity becomes different from nozzle to nozzle. If an ignition environment in the main chamber becomes less uniform than that originally designed, it may result in a decrease in the engine's combustion efficiency.
Patent Literature 1 discloses an invention in relation to nozzle holes of a swirl chamber type combustion chamber of a diesel engine that is manually operable in a low-temperature atmosphere. Patent Literature 1 discloses that an inlet, at a swirl chamber side, of a main nozzle hole with two side nozzle holes positioned at its sides is chamfered. However, the nozzle hole used in the diesel engine disclosed in Patent Literature 1 is a single nozzle hole having a large aperture diameter. Since a fluid that passes through the nozzle hole is used as a fuel, its temperature is low and there is no possibility that crack-like flaws occur at the inlet or in the wall of the nozzle hole. Thus, the technical nature of this nozzle hole is different from the technical nature of the nozzle holes of a divided-chamber gas engine for injecting jet flames from the auxiliary chamber into the main chamber. Moreover, the chamfering disclosed in Patent Literature 1 is intended to merely form an obtuse-angled edge for the purpose of preventing a fuel that is jetted into the swirl chamber from splashing by hitting the rim of the nozzle hole.
Patent Literature 2 discloses a fuel combustion system for an engine, which is configured to supply jet flames from an auxiliary combustion chamber to a main combustion chamber through ejection passages at a speed greater than the speed of sound. Patent Literature 2 discloses that the ejection passages for ejecting a combustion gas from the auxiliary combustion chamber to the main combustion chamber include an inlet portion having a conical internal surface. The conical internal surface is inclined with respect to a central axis by an angle in the range of 15° to 30°. The conical internal surface is an inclined surface formed at the inlet side of tube-shaped ejection passages, which are formed in a venturi tube-like shape for the purpose of ejecting a fluid at high speed. Therefore, the conical internal surface does not have a function of suppressing cracks and edge chipping at the inlet portion of the passages.
PTL 1: Japanese Laid-Open Patent Application Publication No. 3-70812
PTL 2: Japanese National Phase PCT Laid-Open Publication No. 5-504185
A problem to be solved by the present invention is to provide a divided-chamber gas engine including a main combustion chamber (a main chamber) and an auxiliary combustion chamber (an auxiliary chamber), the divided-chamber gas engine being capable of maintaining stable combustion in the main combustion chamber while suppressing degradation in combustion performance.
In order to solve the above problem, a divided-chamber gas engine according to the present invention is a gas engine configured to inject a combustion gas from an auxiliary combustion chamber through a plurality of nozzles, through which the auxiliary combustion chamber and a main combustion chamber are in communication with each other, so as to ignite a fuel in the main combustion chamber. An opening edge, at the auxiliary combustion chamber side, of each of the plurality of nozzles has a chamfered shape.
In the divided-chamber gas engine, it is desired that the chamfered shape is a round chamfered shape, and the opening edge is formed to have a curved surface.
In the divided-chamber gas engine, it is preferred that a portion, having the chamfered shape, of the opening edge, at the auxiliary combustion chamber side, of each of the plurality of nozzles is spaced apart from a portion, having the chamfered shape, of the opening edge, at the auxiliary combustion chamber side, of the other of the plurality of nozzles, such that interference between the portions having the chamfered shape is prevented.
In the divided-chamber gas engine, it is preferred that the curved surface has a curvature radius greater than or equal to a diameter of each nozzle.
Alternatively, in the divided-chamber gas engine, the curved surface has a curvature radius which may be set, such that a temperature increase or decrease at the opening edge, at the auxiliary combustion chamber side, of each of the plurality of nozzles is less than a temperature increase or decrease at a portion of an inner wall of the auxiliary combustion chamber, the portion being a closest portion of the inner wall to the main combustion chamber.
In the divided-chamber gas engine according to the present invention, the edge of the inlet of each nozzle at the auxiliary combustion chamber side is formed into a curved surface. Therefore, at the inlet of the nozzle, there is no edge that tends to be chipped. This makes it possible to suppress a phenomenon where cracked portions partially come off, to prevent deformation of the nozzle's cross section, and to suppress degradation in the combustion performance in the main combustion chamber.
Hereinafter, one embodiment of a divided-chamber gas engine according to the present invention is described in detail with reference to the accompanying drawings.
The main chamber 1 is formed within a cylinder 18. Provided below the main chamber 1 is a piston 7 configured to move in a sliding manner within the cylinder 18. The piston 7 is connected to a drive shaft 19 via a crank 8. When the piston 7 moves within the cylinder 18 in a reciprocating manner, the drive shaft 19 rotates via the crank 8.
Provided above the main chamber 1 is an air supply pipe 14 connected to an air supply source 22. An air supply valve 15 configured to open and close between the air supply pipe 14 and the main chamber 1 is provided between the air supply pipe 14 and the main chamber 1. The air supply pipe 14 is connected to a fuel gas source 21 via a fuel supply pipe 24. The fuel gas is LNG, for example. The fuel supply pipe 24 is provided with a main solenoid valve 4 which is configured to adjust the amount of fuel gas supplied to the air supply pipe 14.
A controller that is not shown generates a command in synchronization with an operation of the air supply valve 15 of the main chamber 1. In response to the command, the main solenoid valve 4 opens for a predetermined period. As a result, a predetermined amount of fuel gas is supplied from the fuel gas source 21 to the air supply pipe 14 through the fuel supply pipe 24. When the fuel gas supplied to the air supply pipe 14 is mixed into a flow of air supplied from the air supply source 22, a lean air-fuel mixture (a fuel gas) is produced. It should be noted that if the air-fuel mixture is thicker than a theoretical air-fuel ratio, then the air-fuel mixture is called a rich air-fuel mixture, and also, if the air-fuel mixture is thinner than the theoretical air-fuel ratio, then the air-fuel mixture is called a lean air-fuel mixture. The produced lean air-fuel mixture is supplied from the air supply pipe 14 to the main chamber 1 when the air supply valve 15 is opened. The air-fuel mixture to be supplied to the main chamber 1 is adjusted, for example, such that the air-fuel ratio becomes approximately twice the theoretical air-fuel ratio (i.e., excess air ratio λ=2). Combustion of the lean air-fuel mixture is lean burn (lean combustion), in which the amount of NOx to be produced is small.
An exhaust gas pipe 16, which leads to an exhaust gas part 23 (i.e., to the outside), is connected to the upper part of the main chamber 1. An exhaust gas valve 17 configured to open and close between the exhaust gas pipe 16 and the main chamber 1 is provided between the exhaust gas pipe 16 and the main chamber 1. When the exhaust gas valve 17 is opened, a flue gas is discharged from the main chamber 1 to the exhaust gas part 23 through the exhaust gas pipe 16.
The auxiliary chamber 2 is provided with a spark plug 3. Further, the auxiliary chamber 2 is connected to the fuel gas source 21 via a fuel supply pipe 25. The fuel supply pipe 25 is provided with an auxiliary solenoid valve 5 for adjusting the amount of fuel gas supplied to the auxiliary chamber 2, and a check valve 6 for preventing a reverse flow of the fuel gas from the auxiliary chamber 2 to the fuel supply pipe 25. The auxiliary solenoid valve 5 opens for a predetermined period in response to a command generated by the controller which is not shown. As a result, the fuel gas that is in a necessary amount is supplied from the fuel gas source 21 to the auxiliary chamber 2 through the fuel supply pipe 25 and the check valve 6.
Next, the combustion of the air-fuel mixture in the combustion chamber is described in detail. In the divided-chamber gas engine having the above-described structure, the fuel gas is supplied to the auxiliary chamber 2 at the same time as the lean air-fuel mixture is sucked into the main chamber 1 in a suction stroke. Since the nozzles 9 are always in the state of communication, the lean air-fuel mixture flows into the auxiliary chamber 2 when the piston 7 is lifted in the following compression stroke.
For example, in the case of an engine with a compression ratio of 10, the fuel gas is supplied from the fuel gas source 21 to the auxiliary chamber 2 through the fuel supply pipe 25 in an amount that corresponds to the volume of the auxiliary chamber, and the supplied fuel gas is compressed to 1/10. Meanwhile, the lean air-fuel mixture with the excess air ratio λ of approximately 2 is supplied from the inside of the main chamber 1 to the auxiliary chamber 2 through the nozzles 9 in an amount that corresponds to 9/10 of the volume of the auxiliary chamber. The fuel gas and the lean air-fuel mixture are mixed in the auxiliary chamber 2, and becomes an air-fuel mixture with the excess air ratio λ of approximately 1, that is, an air-fuel mixture with the theoretical air-fuel ratio
When the spark plug 3 is fired in the auxiliary chamber 2 near the compression top dead center, the air-fuel mixture is ignited in the auxiliary chamber 2. The air-fuel mixture, while being combusted, jets into the main chamber 1 through the nozzles 9 in the form of high-temperature jet flames. The lean air-fuel mixture in the main chamber 1 is ignited by the jet flames and explodes, and the resultant force lowers the piston 7. When the piston 7 moves, the drive shaft 19 rotates via the crank 8, accordingly. A combustion gas that is produced in the main chamber 1 is released to the exhaust gas part 23 (i.e., to the outside) through the exhaust gas pipe 16 when the exhaust gas valve 17 is opened.
Each nozzle 9 according to the present embodiment has such a shape that the edge of the nozzle's inlet at the auxiliary chamber 2 side, i.e., the corner of the opening edge at the auxiliary chamber 2 side, is chamfered. Examples of the chamfered shape include a shape in which the corner is rounded and a shape in which the corner is cut out diagonally (the diagonal angle is not particularly limited). One of these shapes is selected depending on machining conditions. However, the chamfered shape is desirably a round chamfered shape since such a shape does not allow a sharp ridge to be formed at a position where the inner wall of the auxiliary chamber 2 and the inner wall of the nozzle join.
If a right-angled corner, or a nearly right-angled corner such as an acute-angled or obtuse-angled corner, is formed at the opening edge of the nozzle 9 at the auxiliary chamber 2 side, then the temperature of such a cornered portion increases more easily than other portions. For example, assume a case where there is a corner formed at the opening edge of the nozzle 9 at the auxiliary chamber 2 side and the temperature variation range of the corner is approximately 50 to 1000° C. In this case, the temperature variation range of other portions, different from the corner, of the bottom wall in the auxiliary chamber 2 remains approximately 50 to 700° C. That is, if there is a corner formed at the opening edge of the nozzle 9 at the auxiliary chamber 2 side, the temperature of the corner easily increases to a significantly higher temperature than the temperature of other portions. However, since there is no corner formed at the opening edge of each nozzle 9 at the auxiliary chamber 2 side according to the present embodiment, the temperature variation range of the opening edge and its surrounding portions is narrower, which realizes more uniform temperature distribution. In addition, the highest temperature in the temperature variation range is lower. Therefore, heat stress exerted on the opening edge of the nozzle 9 at the auxiliary chamber 2 side is reduced, and the degree of thermal fatigue is reduced as compared to a case where a corner is formed.
Furthermore, since there is no corner formed at the opening edge of each nozzle 9 at the auxiliary chamber 2 side, an air stream that passes through the nozzle 9 smoothly flows downward along a streamline. Accordingly, even if there are cracks formed in the wall surface in the auxiliary chamber 2 at the inlet of the nozzle 9 or in the inner wall of the nozzle 9, the following phenomenon does not easily occur: when a high-temperature jet flame passes through the nozzle 9 at high speed, cracked portions of the surface are partially torn away and thereby chipped.
The curvature radius R of the curved surface 11 formed at the opening edge of each nozzle 9 may be set in consideration of thermal conduction energy, aiming to equalize a temperature increase or decrease at the opening edge of the nozzle 9 of the auxiliary chamber 2 with a temperature increase or decrease at other portions of the inner wall of the auxiliary chamber 2. As shown in
In the auxiliary chamber forming body 40 shown in
The above Equation 1 indicates that the total of the opening thermal conduction areas A2 of n nozzles 9 formed in the auxiliary chamber forming body 40 is greater than the tip portion thermal conduction area A1 multiplied by the proportion of the opening thermal conduction distance L2 to the tip portion thermal conductive distance L1. The curvature radius R of the curved surface 11 may be any value that allows Equation 1 to be satisfied. That is, the minimum value of the curvature radius R of the curved surface 11 may be set based on Equation 1. It should be noted that it is desired that the opening thermal conduction area A2 is great since the greater the opening thermal conduction area A2, the more the amount of heat to be dissipated from the opening edge of the nozzle 9 to the cooling means 44 and the more suppressed the increase in the temperature at the opening edge of the nozzle 9.
The diameter (internal diameter) D of each nozzle 9 according to the present embodiment is several mm to ten-odd mm. The curved surface 11 formed at the opening edge of the nozzle 9 flares out toward the outside such that the diameter increases. Easily damaged portions of the wall surface in the auxiliary chamber 2 are those positioned several mm away from the inner wall of the nozzle 9. Therefore, the curvature radius R, which satisfies the relationship of the above Equation 1, of the curved surface 11 of the opening edge of the nozzle 9 at the auxiliary chamber 2 side may be, for example, greater than or equal to the nozzle diameter D. For example, if the curvature radius R of the curved surface 11 is greater than or equal to the nozzle diameter D, then the curvature radius R of the inlet of the nozzle 9 is sufficiently great and the inlet has no acute-angled portion. Therefore, an occurrence of a phenomenon where cracked portions are torn away and chipped is suppressed. Accordingly, chipping of the edge is reduced. Further, an incident angle at which an energy line from the inside of the auxiliary chamber 2 hits the curved surface 11 of the opening edge of the nozzle 9 is greater than in a case where the auxiliary chamber 2 side of the opening edge of the nozzle 9 is a flat surface. Therefore, damage to the curved surface 11 is reduced.
The maximum value of the curvature radius R of the curved surface 11 is not particularly limited. However, the length of the nozzle 9 decreases in accordance with an increase in the curvature radius R of the curved surface 11. Therefore, it is desired that the curvature radius R is in a range that allows the nozzle 9 to have such a length as to be able to jet out a jet flame.
Since the openings, at the auxiliary chamber 2 side, of the respective nozzles 9 are close to each other, if the curvature radius R of the curved surface 11 is excessively great, then the strength of the nozzles 9 cannot be maintained. Therefore, it is desired to adopt such a curvature radius R that an interference margin between the curved surfaces 11 of adjacent nozzles 9 is sufficiently small to maintain the strength of the nozzles 9, or that there is no interference margin between the curved surfaces 11 of adjacent nozzles 9.
Although in the above-described present embodiment only the opening edge at the auxiliary chamber 2 side is chamfered, the opening edge of each nozzle 9 at the main chamber 1 side may also be chambered. In other words, the edge of the inlet of each nozzle 9 at the main chamber 1 side may have such a chamfered shape that the corner of the edge is either rounded or cut out diagonally. If the opening edge of each nozzle 9 at the main chamber 1 side has such a chamfered shape, the passage resistance is reduced when the lean air-fuel mixture flows from the main chamber 1 to the auxiliary chamber 2. This makes it possible to reduce fluid pressure loss. Moreover, if the nozzle 9 has an acute-angled edge at the main chamber 1 side, then during an abnormal state, the edge may act as a flint and cause an ignition, thereby causing knocking. However, through the chamfering, the edge is made obtuse, and thereby knocking can be suppressed.
If the opening edge of the nozzle 9 at the auxiliary chamber 2 side is chipped and thereby the cross-sectional shape of the nozzle 9 changes as in the auxiliary chamber forming body according to the comparative example, then the intensity of the jet flame that jets into the main chamber 1 through the nozzle 9 changes. In particular, the jet flame becomes short if the nozzle diameter increases due to such a change in the cross-sectional shape of the nozzle 9. If the jet flame becomes shorter than the original design, spontaneous ignition of the air-fuel mixture in the cylinder 18 (i.e., knocking) tends to occur. General gas engines have a function of preventing knocking. Therefore, under conditions where knocking tends to occur, control for preventing the knocking is performed. Consequently, the combustion efficiency of the gas engine decreases.
According to the present invention, temporal changes to the shape of the nozzles (nozzle holes) of the auxiliary combustion chamber do not easily occur. This reduces changes in the jet flame intensity and variations among the nozzles in terms of the jet flame intensity. Therefore, the present invention makes it possible to provide an efficient gas engine with reduced temporal degradation in performance. Moreover, in the divided-chamber gas engine according to the present invention, distortion in the shape of the nozzles' openings at the auxiliary chamber side is prevented, and thereby an occurrence of swirl flow is suppressed. As a result, decrease in the jet flame intensity is prevented, and thus effective energy utilization is realized.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-297646 | Dec 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/007558 | 12/27/2010 | WO | 00 | 8/2/2012 |
