JP6633270B2 - Uniflow scavenging two-stroke engine - Google Patents

Description

  The present invention relates to a uniflow scavenging two-cycle engine having a variable compression ratio.

  A uniflow scavenging two-stroke engine, which is also used as a ship engine, is provided with an exhaust port at one end of a cylinder and a scavenging port at the other end. Then, when the active gas is sucked into the combustion chamber from the scavenging port in the intake stroke, the exhaust gas generated by the combustion action is exhausted by being pushed out of the exhaust port by the sucked active gas.

  For example, Patent Literature 1 describes a configuration in which a scavenging port that is inclined with respect to the radial direction of a cylinder is provided. Since the scavenging gas flowing into the cylinder from the scavenging port becomes a swirl flow, it is easy to maintain a separated state from the exhaust gas layer in the cylinder, and scavenging efficiency is improved. Patent Document 2 describes a configuration in which a scavenging port is a so-called skewed port. The skew port referred to here is a port having a shape in which a portion on the exhaust port side is inclined with respect to the radial direction of the cylinder and a portion on the opposite side to the exhaust port is distorted so as to be parallel to the radial direction of the cylinder. . By making the scavenging port a skewed port, the speed at which the scavenging air travels toward the combustion chamber is leveled.

Japanese Patent No. 4395474 Japanese Patent Publication No. 02-26700

  By the way, for example, in a dual fuel engine that uses liquid fuel and fuel gas properly, the compression ratio may be variable. In an engine having a variable compression ratio, when the scavenging port is a skewed port described in Patent Literature 2, at a low compression ratio, since the scavenging speed is leveled, blow-through of fuel gas is suppressed. . On the other hand, at a high compression ratio, since liquid fuel is injected, there is no danger of fuel gas blowing through, and it is not necessary to level the scavenging speed. Therefore, at a high compression ratio, the swirl flow becomes weaker than when a scavenging port for generating a swirl flow described in Patent Document 1 is used, and the scavenging efficiency is meaninglessly reduced. .

  The present invention has been made in view of the above circumstances, and has as its object to provide a uniflow scavenging two-cycle engine capable of performing appropriate scavenging according to a compression ratio.

In order to solve the above problems, a uniflow scavenging type two-stroke engine of the present invention has an exhaust port formed at one end of a cylinder in which a piston reciprocates, and a scavenging port formed at the other end of the cylinder. A uniflow scavenging type two-stroke engine which is switched to at least two operation modes of a compression ratio mode and a high compression ratio mode in which a top dead center and a bottom dead center of a piston are located closer to an exhaust port than in a low compression ratio mode. A first fuel supply unit for injecting gaseous fuel into the scavenging gas in the low compression ratio mode, and a liquid fuel in the cylinder at one end of the cylinder with respect to the first fuel supply unit in the high compression ratio mode. comprising a second fuel supply unit for injecting the scavenging port toward the inside from the outside of the cylinder, guide an inclined direction scavenging gas with respect to the radial direction of the cylinder A swirl guide portion, a center guide portion provided on the other end side of the cylinder with respect to the swirl guide portion, and guiding the scavenging gas toward the center side of the cylinder with respect to the swirl guide portion. Is at the bottom dead center, the swirl guide is not opposed to the piston, at least a part of the center guide is opposed to the piston, and when the piston is at the bottom dead center in the low compression ratio mode, The center guide portion and the piston are not opposed to each other, or the area facing the piston is smaller than in the high compression ratio mode.

  According to the uniflow scavenging two-cycle engine of the present invention, it becomes possible to perform appropriate scavenging according to the compression ratio.

It is an explanatory view showing the whole composition of a uniflow scavenging type two-cycle engine. FIG. 3 is an explanatory diagram for explaining a first fuel supply unit. It is an explanatory view for explaining an auxiliary fuel supply unit. FIG. 4 is an explanatory diagram for explaining a compression ratio variable mechanism. It is explanatory drawing for demonstrating a scavenging port. FIG. 9 is an explanatory diagram for explaining a flow of scavenging in a comparative example. It is an explanatory view for explaining a flow of scavenging in the present embodiment.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, other specific numerical values, and the like shown in the embodiments are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the specification and the drawings, elements having substantially the same function and configuration will be denoted by the same reference numerals, and redundant description will be omitted. Elements not directly related to the present invention will be omitted. I do.

  In the following embodiments, it is possible to selectively execute any one of a gas operation mode in which fuel gas that is gaseous fuel is mainly burned and a diesel operation mode in which fuel oil that is liquid fuel is burned. A so-called dual fuel type uniflow scavenging two-cycle engine will be described. However, the type of engine is not limited to the dual fuel type, and may be any uniflow scavenging two-cycle engine.

  FIG. 1 is an explanatory diagram showing the overall configuration of a uniflow scavenging two-cycle engine 100. The uniflow scavenging two-stroke engine 100 of the present embodiment is used, for example, for ships. The uniflow scavenging two-cycle engine 100 includes a cylinder 110, a piston 112, a crosshead 114, a connecting rod 116, a crankshaft 118, an exhaust port 120, an exhaust valve driving device 122, an exhaust valve 124, A port 126, a scavenging chamber 128, a first fuel supply section 130, an auxiliary fuel supply section 132, a main combustion chamber 134a, a sub combustion chamber 134b, a second fuel supply section 136, a rotary encoder 138, a governor 140 (governor), a fuel supply control unit 142, and an exhaust control unit 144.

  In the uniflow scavenging two-stroke engine 100, the piston 112 reciprocates in the cylinder 110 through four continuous strokes of intake (supply), compression, combustion, and exhaust. One end of a piston rod 112a is fixed to the piston 112. A crosshead 114 is fixed to the other end of the piston rod 112a, and the crosshead 114 reciprocates with the piston 112. The movement of the crosshead 114 in the direction perpendicular to the stroke direction of the piston 112 (the left-right direction in FIG. 1) is restricted by the crosshead shoe 114a.

  The crosshead 114 supports one end of the connecting rod 116. The other end of the connecting rod 116 is connected to the crankshaft 118 so that the crankshaft 118 rotates with respect to the connecting rod 116. As a result, when the crosshead 114 reciprocates with the reciprocation of the piston 112, the crankshaft 118 rotates in conjunction with the reciprocation.

  In such a crosshead type reciprocating engine, the stroke in the cylinder 110 can be formed relatively long and the lateral pressure acting on the piston 112 can be received by the crosshead 114. The output of the engine 100 can be increased.

  The exhaust port 120 is provided in the cylinder head 110a located above the top dead center position of the piston 112 in FIG. That is, the exhaust port 120 is formed at one end of the cylinder 110 where the piston 112 reciprocates. The exhaust port 120 is opened and closed to exhaust the burned exhaust gas generated in the cylinder 110. The exhaust valve driving device 122 opens and closes the exhaust port 120 by sliding the exhaust valve 124 up and down at a predetermined timing. The exhaust gas exhausted through the exhaust port 120 in this way is supplied to, for example, a turbine side of a supercharger (not shown) and then exhausted to the outside.

  The scavenging port 126 is a hole penetrating from the inner peripheral surface (the inner peripheral surface of the cylinder block 110 b) on the lower end side (the other end side) of the cylinder 110 to the outer peripheral surface, and a plurality of scavenging ports 126 are provided over the entire circumference of the cylinder 110. ing. Then, the scavenging port 126 sucks the active gas into the cylinder 110 according to the sliding operation of the piston 112. Such an active gas includes an oxidizing agent such as oxygen and ozone, or a mixture thereof (for example, air). An active gas (for example, air) pressurized by a compressor of a supercharger (not shown) is sealed in the scavenging chamber 128, and the active gas is sucked from the scavenging port 126 by a pressure difference between the scavenging chamber 128 and the cylinder 110. Is done. The pressure in the scavenging chamber 128 can be substantially constant. However, when the pressure in the scavenging chamber 128 changes, a pressure gauge is provided in the scavenging port 126, and the injection amount of the fuel gas and the like are set in accordance with the measured value. Other parameters may be controlled.

  The first fuel supply unit 130 is arranged on the outer peripheral side of the cylinder 110 with respect to the scavenging port 126, and allows the premixed gas (fuel gas) to be sucked into the cylinder 110 from the scavenging port 126 together with the active gas in the gas operation mode. Hereinafter, the first fuel supply unit 130 will be described in detail with reference to FIG.

  FIG. 2 is an explanatory diagram for explaining the first fuel supply unit 130. FIG. 2A shows an extraction diagram of the vicinity of the first fuel supply unit 130 in the side view of the cylinder 110. FIG. 2B is an enlarged view of a broken line portion in FIG.

  As shown in FIG. 2A, the first fuel supply unit 130 has mixing tubes 130 a and 130 b formed separately from the cylinder 110. Each of the mixing tubes 130a and 130b is an annular member that circumferentially surrounds the outside of the cylinder 110 in the radial direction. The mixing pipe 130a is arranged on one end side (upper side in FIG. 2A) of the piston 112 with respect to the scavenging port 126, and the mixing pipe 130b is arranged with the other end of the piston 112 in the stroke direction with respect to the scavenging port 126. (Lower side in FIG. 2A).

  Inside each of the mixing pipes 130a and 130b, an annularly extending mixing chamber is formed, and in the mixing chamber, the fuel gas and the active gas are mixed to generate a premixed gas.

  One of the adjacent flow pipes 130c communicates with the mixing pipe 130a, and the other communicates with the mixing pipe 130b. The premixed gas flowing from the mixing pipe 130a or the mixing pipe 130b flows through the flow pipe 130c.

  Then, when the first fuel injection valve (not shown) is opened and the premixed gas is ejected from the injection port 130d shown in FIG. 2B, the premixed gas is directed from the scavenging chamber 128 toward the active gas flowing toward the scavenging port 126, The premixed air is blown from the injection port 130d of the first fuel supply unit 130. Hereinafter, the premixed gas is simply referred to as the fuel gas, unless the premixed gas is particularly distinguished from the fuel gas.

  Returning to FIG. 1, the auxiliary fuel supply unit 132 is an injection valve provided on the cylinder head 110a. The uniflow scavenging two-cycle engine 100 includes a main combustion chamber 134a and a sub-combustion chamber 134b as combustion chambers. The main combustion chamber 134a is surrounded by the cylinder head 110a, the cylinder liner in the cylinder block 110b, and the piston 112. The auxiliary combustion chamber 134b is formed inside the cylinder head 110a, and one end protrudes from the cylinder head 110a toward the main combustion chamber 134a.

  FIG. 3 is an explanatory diagram for explaining the auxiliary fuel supply unit 132. In FIG. 3, the illustration of the second fuel supply unit 136 is omitted for easy understanding. As shown in FIG. 3A, the auxiliary fuel supply unit 132 has a distal end opened to the auxiliary combustion chamber 134b, and injects fuel oil toward the auxiliary combustion chamber 134b in the gas operation mode.

  The fuel oil injected into the sub-combustion chamber 134b is ignited by the heat in the sub-combustion chamber 134b, as shown in FIG. Then, as shown in FIG. 3C, the fuel gas and the exhaust gas burned in the sub-combustion chamber 134b are blown out together with the flame into the main combustion chamber 134a, and the fuel gas sucked into the cylinder 110 from the scavenging port 126 is removed. Burn.

  Returning to FIG. 1, the second fuel supply unit 136 is an injection valve provided on the cylinder head 110a, and its tip is open to the main combustion chamber 134a. In the diesel operation mode, the second fuel supply unit 136 faces the main combustion chamber 134a. Inject fuel oil.

  As described above, in the gas operation mode, fuel gas is supplied from the first fuel supply unit 130 into the cylinder 110, and in the diesel operation mode, fuel oil is supplied from the second fuel supply unit 136 into the cylinder 110. At this time, an appropriate compression ratio differs between the gas operation mode and the diesel operation mode. Specifically, the compression ratio is low in the gas operation mode, and is high in the diesel operation mode. That is, the gas operation mode = low compression ratio mode, and the diesel operation mode = high compression ratio mode. Here, in order to make the compression ratio variable, a compression ratio variable mechanism is provided at a connection portion between the piston rod 112a and the crosshead 114.

  FIG. 4 is an explanatory diagram for explaining the compression ratio variable mechanism 146, and shows a connection portion between the piston rod 112a and the crosshead 114 in an extracted manner. In the gas operation mode, the piston rod 112a and the crosshead pin 114b are directly connected, as shown in FIG.

  On the other hand, in the diesel operation mode, the shim plate 148 is interposed between the piston rod 112a and the crosshead pin 114b as shown in FIG. And the position of the bottom dead center is shifted to the exhaust port 120 side. Thus, the compression ratio variable mechanism 146 can reduce the volume of the main combustion chamber 134a at the top dead center and increase the compression ratio.

  Returning to FIG. 1, the rotary encoder 138 is provided on the crankshaft 118, and detects a crankshaft angle signal (hereinafter, referred to as a crank angle signal).

  The governor 140 derives a fuel injection amount based on an engine output command value input from a host control device and an engine speed based on a crank angle signal from the rotary encoder 138, and outputs the fuel injection amount to the fuel supply control unit 142.

  The fuel supply control unit 142 controls the first fuel supply unit 130 and the second fuel supply unit 130 based on the information indicating the fuel injection amount input from the governor 140, the information indicating the operation mode, and the crank angle signal from the rotary encoder 138. The supply unit 136 is controlled.

  The exhaust control unit 144 sends an exhaust valve operation signal to the exhaust valve driving device 122 based on the information indicating the fuel injection amount from the fuel supply control unit 142, the information indicating the operation mode, and the crank angle signal from the rotary encoder 138. Is output.

  FIG. 5 is an explanatory diagram for explaining the scavenging port 126. FIG. 5 (a) shows the vicinity of the scavenging port 126 extracted from the side view of the cylinder 110, and FIG. 5 (a) shows a cross section taken along line IV (b) -IV (b), and FIG. 5 (c) shows a cross section taken along line IV (c) -IV (c) in FIG. 5 (a).

  One end of the scavenging port 126 in the stroke direction (the upper side in FIG. 5A) with respect to the stroke direction center of the piston 112 shown by a broken line in FIG. 5A serves as a swirl guide portion 126a. ing. The other end of the cylinder 110 in the stroke direction (lower side in FIG. 5A) than the swirl guide 126a is a center guide 126b.

  As shown in FIG. 5B, the swirl guide portion 126a has a shape that guides scavenging gas from the outside of the cylinder 110 to the inside in a direction inclined with respect to the radial direction of the cylinder 110. Specifically, the swirl guide 126a extends in a direction inclined with respect to the radial direction of the cylinder 110. In addition, the inclination of the swirl guide portion 126a is substantially equal in any of the scavenging ports 126 provided over the entire circumference of the cylinder 110. As a result, as shown by the arrow in FIG. 5B, the scavenging air becomes a swirl flow, rises in the cylinder 110, and flows toward the exhaust port 120 side.

  The center guide portion 126b has a shape that guides the scavenging gas toward the center of the cylinder 110 more than the swirl guide portion 126a, as indicated by an arrow in FIG. 5C. Specifically, the center guide portion 126b is open toward the center of the cylinder 110 and extends in the radial direction of the cylinder 110. As a result, as shown by an arrow in FIG. 5C, the scavenging air rises inside the cylinder 110 and flows toward the exhaust port 120 while moving toward the radial center of the cylinder 110.

  Thus, the scavenging port 126 is a so-called skewed port. The operation and problems when the scavenging port 126 is a skewed port will be described with reference to FIG.

FIG. 6 is an explanatory diagram for explaining the flow of scavenging in the comparative example. FIG. 6A shows the flow of scavenging in the first comparative example in a state where the piston 112 is at the bottom dead center position. FIG. 6B shows a scavenging flow of the second comparative example. In the first comparative example, the whole scavenging ports S ₁ is has a swirl guide portion S _{1 a,} in the second comparative example, it is assumed that the scavenging port S ₂ is a skewed port.

As shown in FIG. 6 (a), in the first comparative example, since the overall scavenging port S ₁ is a swirl guide portion S _{1 a,} swirl flow in the scavenging flow (in FIG. 6 (a), arrows ), The scavenging is easily maintained in a separated state from the exhaust gas layer in the cylinder 110, and the scavenging efficiency is improved.

  On the other hand, as can be seen from the velocity distribution of the scavenging air to the exhaust port 120 side indicated by the broken line in FIG. 6A, the velocity tends to decrease at the radial center portion of the cylinder 110. At this time, for example, in the case of the gas operation mode (low compression ratio mode), the fuel gas is mixed into the scavenging gas. Therefore, if there is a bias in the scavenging speed distribution, the fuel gas blows out from the exhaust port 120 without being burned. There is a possibility that it will.

Therefore, as in the second comparative example, when the scavenging port S ₂ and skewed port, the central guide portion S _{2 b,} since the scavenging toward the radial center side of the cylinder 110, the radial center side of the cylinder 110 At, the speed toward the exhaust port 120 is improved. As a result, as shown by a broken line in FIG. 6B, the velocity distribution of the scavenging air to the exhaust port 120 side is leveled as compared with the first comparative example, and the blow-through of the fuel gas can be suppressed.

However, when the scavenging port S ₂ and skewed port, minutes of the center guide portion S _{2 b} are provided, as shown by the arrows in FIG. 6 (b), the swirl flow is weakened than the first comparative example . For example, in the case of the diesel operation mode (high compression ratio mode), since the fuel gas is not injected from the first fuel supply unit 130 as in the gas operation mode, there is no fear of blow-through, and the state of separation between the scavenging gas and the exhaust gas is reduced. The maintenance should be given priority, but in the second modified example, since the swirl flow is weak, the scavenging efficiency is reduced.

  FIG. 7 is an explanatory diagram for explaining the flow of scavenging in the present embodiment. FIG. 7A shows a state in which the piston 112 is at the bottom dead center position in the gas operation mode, and FIG. () Shows a state in which the piston 112 is at the bottom dead center position in the diesel operation mode.

  As shown in FIG. 7A, in the gas operation mode (low compression ratio mode), as in the second comparative example, the scavenging air is directed toward the radial center of the cylinder 110 by the center guide portion 126b. Therefore, as shown by the broken line in FIG. 7A, the velocity distribution of the scavenging air to the exhaust port 120 side is more leveled than in the first comparative example, and the blow-through of the fuel gas can be suppressed.

  On the other hand, as shown in FIG. 7B, in the diesel operation mode (high compression ratio mode), the top dead center position and the bottom dead center position of the piston 112 are lower than in the gas operation mode (low compression ratio mode). It has shifted to the port 120 side. Due to this shift, in the diesel operation mode (high compression ratio mode), when the piston 112 is at the bottom dead center, the center guide portion 126b faces the piston 112 (the side wall of the piston 112) in the radial direction of the piston 112. It is a positional relationship. Therefore, the scavenging air hardly flows into the cylinder 110 from the center guide portion 126b, and the scavenging air generally flows into the cylinder 110 from the swirl guide portion 126a. As a result, as shown by the arrow in FIG. 7B, the swirl flow becomes strong, and the scavenging efficiency is improved.

  As described above, by adjusting the substantial opening degree of the center guide portion 126b of the scavenging port 126 (skew port) according to the position of the bottom dead center of the piston 112, it is possible to perform appropriate scavenging according to the compression ratio. Becomes possible.

  In the above-described embodiment, the case where the center guide portion 126b and the piston 112 are not opposed to each other when the piston 112 is at the bottom dead center in the low compression ratio mode has been described. However, it is sufficient that the area of the center guide portion 126b facing the piston 112 is smaller in the low compression ratio mode than at least in the high compression ratio mode.

  In the above-described embodiment, the case where one scavenging port 126 is formed by the swirl guide 126a and the center guide 126b has been described. However, the swirl guide 126a and the center guide 126b are formed as separate ports. Alternatively, two ports may be partially connected and formed.

  Further, in the above-described embodiment, the case has been described where the first fuel supply unit 130 ejects the premixed gas obtained by mixing the fuel gas and the active gas from the injection port 130d, but the fuel gas is injected instead of the premixed gas. The structure which injects from the mouth 130d may be sufficient.

  Further, in the above-described embodiment, the case where the first fuel supply unit 130 is arranged on the outer peripheral side of the cylinder 110 with respect to the scavenging port 126 and the fuel gas is sucked into the cylinder 110 from the scavenging port 126 has been described. However, the first fuel supply unit 130 may be provided at any position as long as it supplies fuel gas into the cylinder 110.

  Further, in the above-described embodiment, the case where the variable compression ratio mechanism 146 is configured to change the positions of the top dead center and the bottom dead center of the piston 112 depending on the presence or absence of the shim plate 148 is described. Other configurations may be used as long as the length of the piston 112 or the piston rod 112a is adjusted by hydraulic pressure.

  Further, in the above-described embodiment, the configuration in which the main combustion chamber 134a and the sub-combustion chamber 134b are provided as the combustion chambers and the fuel gas burned in the sub-combustion chamber 134b is injected into the main combustion chamber 134a in the gas operation mode has been described. . However, the fuel gas sucked from the scavenging port 126 may be ignited by injecting a small amount of fuel oil into the main combustion chamber 134a without providing the sub-combustion chamber 134b.

  In the above-described embodiment, the case where a small amount of fuel oil is injected into the sub-combustion chamber 134b to ignite the fuel gas in the sub-combustion chamber 134b has been described. May be ignited.

  Further, in the above-described embodiment, a case has been described in which two modes of the low compression ratio mode and the high compression ratio mode are provided. However, three or more modes having different compression ratios may be provided. It is sufficient that at least two modes correspond to the above-described low compression ratio mode and high compression ratio mode.

  As described above, the preferred embodiments of the present invention have been described with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such embodiments. It is obvious to those skilled in the art that various changes or modifications can be conceived within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present invention. Is done.

  INDUSTRIAL APPLICABILITY The present invention can be used for a uniflow scavenging two-cycle engine having a variable compression ratio.

100 Uniflow scavenging two-stroke engine 110 Cylinder 112 Piston 120 Exhaust port 126 Scavenging port 126a Swirl guide 126b Central guide 130 First fuel supply 136 Second fuel supply

Claims (1)

An exhaust port is formed at one end of the cylinder in which the piston reciprocates, and a scavenging port is formed at the other end of the cylinder. The low compression ratio mode and the top dead center of the piston are lower than the low compression ratio mode. And a uniflow scavenging two-stroke engine switched to at least two operation modes, and a high compression ratio mode in which a bottom dead center is located on the exhaust port side,
A first fuel supply unit that injects gaseous fuel into the scavenging gas when in the low compression ratio mode;
In the high compression ratio mode, a second fuel supply unit that injects liquid fuel into the cylinder at one end of the cylinder than the first fuel supply unit;
With
The scavenging port is
From the outside of the cylinder toward the inside, a swirl guide section for guiding scavenging gas in a direction inclined with respect to the radial direction of the cylinder,
A center guide portion provided on the other end side of the cylinder with respect to the swirl guide portion, and guiding the scavenging gas toward the center side of the cylinder with respect to the swirl guide portion;
With
When the piston is at the bottom dead center in the high compression ratio mode, the swirl guide portion is not opposed to the piston, and at least a part of the center guide portion is opposed to the piston, and the low compression ratio When the piston is at the bottom dead center in the mode, the center guide portion and the piston are not opposed to each other, or the area facing the piston is smaller than in the high compression ratio mode. Features a uniflow scavenging two-cycle engine.

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