JP2018173063A - engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine capable of enlarging a lean limit while maintaining sufficient ignition in an ignition chamber even when a supercharging pressure fluctuates.SOLUTION: An engine includes an ignition point position adjusting section for adjusting a distance between an ignition point P as a focal position of a laser beam and a communication hole 15 in a direction along an optical axis on the basis of a supercharging pressure-related value related to a supercharging pressure by a supercharger 50.SELECTED DRAWING: Figure 1

Description

  The present invention has an ignition point cover portion that covers the ignition point and forms an ignition chamber, and is formed in the combustion chamber facing the piston and inside the ignition point cover portion in a state where the ignition point cover portion is mounted on the cylinder head. The present invention relates to an engine in which a communication hole communicating with the ignition chamber is provided in the ignition point cover portion.

Conventionally, in a spark ignition engine, an ignition chamber is formed so as to cover the ignition point of the spark plug body in order to ensure stable ignition of the lean mixture for the purpose of increasing the lean limit of the lean mixture and improving efficiency. A cylinder head may be provided with a pre-chamber plug with a plug cover.
The pre-chamber plug is configured by providing one or a plurality of communication holes in the plug cover, and the communication holes are configured to communicate the ignition chamber and the combustion chamber. The communication hole allows the air-fuel mixture of the combustion air and fuel sucked into the combustion chamber in the intake stroke to flow mainly from the combustion chamber into the ignition chamber in the compression stroke, and also in the ignition chamber in the combustion expansion stroke. The combustion flame formed by being ignited is ejected from the ignition chamber to the combustion chamber. In the combustion chamber, the air-fuel mixture is combusted by the combustion flame ejected from the communication hole (see Patent Document 1).
In particular, in the spark ignition engine as described above, in order to increase the specific output, a configuration in which a supercharger is provided to increase the supercharging pressure may be employed. Since abnormal combustion occurs, suppression of misfire associated therewith becomes a problem.

On the other hand, as described in Patent Document 2, there is known a laser ignition engine capable of condensing laser light at an ignition point of an ignition chamber communicating with a combustion chamber.
In the laser ignition type engine, a high-density laser beam is condensed at an ignition point at a desired ignition timing, thereby igniting at an ignition point in an ignition chamber at a desired ignition timing.

JP 2007-77902 A Special table 2012-518120 gazette

In the spark ignition engine disclosed in Patent Document 1, residual gas that is not discharged to the exhaust passage even in the exhaust stroke remains in the ignition chamber, and therefore flows into the ignition chamber in the intake compression stroke at the ignition timing. Fresh air and residual gas will be present inside the ignition chamber. The inventors have found that these new air and residual gas are not sufficiently mixed in the state of communication holes of a general pre-chamber plug, and are new on the combustion chamber side inside the ignition chamber. It has been confirmed that the concentration of the gas is high, the concentration of the residual gas is high on the cylinder head side, and a substantially laminar state is formed in the ignition chamber along the direction from the combustion chamber to the cylinder head.
Furthermore, in the spark ignition engine disclosed in Patent Document 1, the inventors have adopted a configuration in which a supercharger is provided to increase the supercharging pressure, so that fresh air and residual gas in the ignition chamber at the ignition timing can be reduced. The boundary region is considered to change as the boost pressure varies.
When the explanation is added, when the combustion exhaust gas is discharged from the combustion chamber and the ignition chamber in the exhaust stroke, the pressure of the residual gas partially remaining in the ignition chamber is lower than the supercharging pressure. Then, in the intake compression stroke, when fresh air with a predetermined supercharging pressure flows into the ignition chamber, the higher the supercharging pressure, the more the residual gas will be compressed. It is considered that the boundary region between fresh air and residual gas varies in the direction from the combustion chamber toward the cylinder head.
As described above, it is conceivable that a problem such as misfire occurs due to the boundary region between fresh air and residual gas fluctuating inside the ignition chamber. However, until now, no technology has been known that takes into account the variation in the boundary region between fresh air and residual gas in the ignition chamber in a pre-chamber engine that applies supercharging pressure by a supercharger.

  The present invention has been made in view of the above-mentioned problems, and its purpose is to increase the lean limit while maintaining good ignition inside the ignition chamber even when the supercharging pressure fluctuates. Is to provide an engine that can also be used.

The engine to achieve the above purpose is
The ignition point cover portion that covers the ignition point and forms an ignition chamber, and the ignition chamber formed inside the combustion chamber facing the piston and the ignition point cover portion in a state where the ignition point cover portion is mounted on the cylinder head An engine in which a communication hole communicating with the chamber is provided in the ignition point cover portion,
A laser light irradiation mechanism for condensing and igniting laser light at the ignition point through a laser light transmission window provided in the ignition point cover part, and an optical axis of the laser light between the combustion chamber and the ignition chamber Arranged in a state to pass through,
A supercharger for compressing fresh air taken into the combustion chamber by a compressor provided in the intake passage;
Ignition for adjusting a distance between the focal position of the laser beam as the ignition point and the communication hole in a direction along the optical axis based on a supercharging pressure related value related to a supercharging pressure by the supercharger The point is that a point position adjustment unit is provided.

Prior to the operation and effect of the present invention, the effect of adjusting the ignition point position will be described based on experimental results.
In this experiment, a mixture gas mixed in a premix tank is sent to a constant volume container having a pseudo combustion chamber 3 and a pseudo ignition chamber 14 as shown in FIG. 3, and spark ignition is performed inside the pseudo ignition chamber 14. In addition, the temporal change of the pressure in the pseudo combustion chamber 3 is measured, and the propagation state of the flame is imaged from the heat-resistant glass window above the pseudo combustion chamber 3 using a high-speed video camera. The pseudo combustion chamber 3 and the pseudo ignition chamber 14 are configured to communicate with each other through one communication hole 15. The combustion exhaust gas is scavenged from the pseudo combustion chamber 3 and the pseudo ignition chamber 14 by a vacuum pump for each ignition, and then the premixed gas is sucked into the pseudo combustion chamber 3 and the pseudo ignition chamber 14 and settled. Ignited. In the premix tank, a uniform constant temperature premixed gas was formed by methane and compressed air. In the constant volume container, the pseudo combustion chamber 3 has a cylindrical shape with a diameter of 70 mm and a height of 37 mm, a volume of 142.4 cm ³ , and the pseudo ignition chamber 14 is provided on the side of the pseudo combustion chamber 3 in the circumferential direction. The cylinder was 13 mm in height and 9 mm in height, and the volume was 1.2 cm ³ .

In the experiment, as shown in FIG. 3, the distance between the ignition point position and the communication hole 15 was changed inside the pseudo ignition chamber 14.
Specifically, the ignition point position is set within the pseudo ignition chamber 14 at a position 0 mm from the communication hole 15 (position indicated by P1 in FIG. 3) and at a position 4 mm from the communication hole 15. Set to the center position (position indicated by P2 in FIG. 3) and the position near the wall facing the communication hole 15 in the pseudo ignition chamber 14 at a position 9 mm from the communication hole 15 (position indicated by P3 in FIG. 3). In this case, the change with time of the pressure and the propagation state of the flame were measured.
When the ignition point position is set to a position of 0 mm from the communication hole 15 (position indicated by P1 in FIG. 3), only spherical flame propagation occurs from the communication hole 15 as shown in the captured image in the upper part of FIG. The change with time in the pressure is slow as shown in FIG. That is, a flame jet from the pseudo ignition chamber 14 to the pseudo combustion chamber 3 is not formed at the ignition point position. In such a combustion mode, when a lean mixture is used, the lean mixture cannot be burned well near the ignition timing, and it is difficult to expand the lean limit.
When the ignition point position is set at a position approximately 4 mm from the communication hole 15 at the substantially center position of the pseudo ignition chamber 14 (position indicated by P2 in FIG. 3), as shown in the captured image in the lower part of FIG. After the spherical flame propagation has occurred, a flame jet is generated, and a two-stage flame is formed. As shown in FIG. 3, the change with time of the pressure at this time is steeper than that at the position 0 mm from the communication hole 15 (the position indicated by P1 in FIG. 3), but is relatively slow.
When the ignition point position is set at a position 9 mm from the communication hole 15 and in the vicinity of the wall facing the communication hole 15 in the pseudo ignition chamber 14 (position indicated by P3 in FIG. 3), a captured image is not acquired. However, as shown in FIG. 4, the change with time of the pressure shows a sharp rise compared to the cases of 0 mm and 4 mm, and the mixture in the pseudo combustion chamber 3 is burned well by the flame jet. It is inferred that As a result, from the viewpoint of expanding the lean limit, it has been found that the ignition point position is preferably set as far as possible from the communication hole 15 in the pseudo ignition chamber 14.
That is, in the spark ignition engine having an ignition chamber, the inventors have a very important factor in increasing the lean limit in the positional relationship between the ignition point position and the communication hole in the ignition chamber. I got the knowledge.

Furthermore, as described above, in the spark ignition engine having the ignition chamber, the inventors have left residual gas that is not discharged into the exhaust passage even in the exhaust stroke in the ignition chamber. Thus, fresh air and residual gas flowing into the ignition chamber exist in the ignition chamber. The inventors have found that these new air and residual gas are not sufficiently mixed in the state of communication holes of a general pre-chamber plug, and are new on the combustion chamber side inside the ignition chamber. It has been confirmed that the concentration of the gas is high, the concentration of the residual gas is high on the cylinder head side, and a substantially laminar state is formed in the ignition chamber along the direction from the combustion chamber to the cylinder head.
Further, the inventors of the present invention, in a spark ignition engine having an ignition chamber, when adopting a configuration including a supercharger to increase the supercharging pressure, a boundary region between fresh air and residual gas inside the ignition chamber at the ignition timing. Thinks that it changes with the fluctuation of supercharging pressure.
In other words, when the atmosphere surrounding the ignition point is covered with residual gas, there is a possibility that ignition may not be performed properly during supercharging at which unstable combustion is likely to occur, and there is room for improvement. I believe there is.

According to the engine having the above-described characteristic configuration, the ignition point position adjusting unit determines whether the focal position of the laser beam as the ignition point and the communication hole are based on the supercharging pressure related value related to the supercharging pressure of the supercharger. Since the distance is adjusted in the direction along the optical axis, even if the boundary region between the fresh air and the residual gas in the ignition chamber varies with the variation of the supercharging pressure, for example, with the variation By adjusting the ignition point position to the fresh air region, it is possible to satisfactorily prevent the occurrence of unstable combustion due to supercharging.
Further, for example, the ignition point position adjusting unit generates a flame jet at the ignition timing in the form of increasing the distance between the ignition point position and the communication hole when performing lean combustion, for example, when the combustion is stable. Thus, by changing the pressure of the combustion chamber sharply and appropriately burning the lean air-fuel mixture in the combustion chamber, the lean limit can be expanded and the thermal efficiency can be improved.

Further features of the above engine
The supercharging pressure-related value is the supercharging pressure measured by a pressure sensor that measures the pressure of the fresh air supercharged by the supercharger in the intake passage,
The ignition point position adjusting unit adjusts the focal position to a side away from the communication hole as the supercharging pressure increases in the direction along the optical axis, and the distance between the focal position and the communication hole. The point is to adjust.

As described above, when the supercharging pressure fluctuates, when the combustion exhaust gas is discharged from the combustion chamber and the ignition chamber in the exhaust stroke, the pressure of the residual gas partially remaining in the ignition chamber is a pressure lower than the supercharging pressure. Become. Then, in the intake compression stroke, when fresh air with a predetermined supercharging pressure flows into the ignition chamber, the higher the supercharging pressure, the more the residual gas will be compressed. It is considered that the boundary region between fresh air and residual gas varies in the direction from the combustion chamber toward the cylinder head. In particular, the boundary region moves in a direction away from the communication hole as the supercharging pressure increases.
According to the above characteristic configuration, the ignition point position adjusting unit adjusts the ignition point to the side away from the communication hole as the boost pressure increases in the direction along the optical axis, for example, as the boost pressure increases, While the ignition point is positioned in a region where the ambient atmosphere is fresh, the ignition point can be positioned at a position away from the communication hole, which is a position where a flame jet is easily formed.

Further features of the above engine
The ignition chamber covered by the ignition point cover portion extends along an extending direction from the cylinder head toward the combustion chamber,
The communication hole is provided on the combustion chamber side in the extending direction in the ignition point cover portion,
The laser beam irradiation mechanism is provided with the optical axis along the extending direction,
The ignition point position adjustment unit adjusts the distance between the focal position and the communication hole in a direction along the extending direction and adjusts the focal position toward the cylinder head as the supercharging pressure increases. There is in point to do.

By adopting this configuration, the flow of fresh air as a whole is in the extending direction from the combustion chamber to the cylinder head in the extending direction, so the boundary between the residual gas and fresh air in the ignition chamber is It moves in the extending direction with the fluctuation of the supercharging pressure.
Then, by aligning the optical axis in the extending direction, the focal point is adjusted toward the cylinder head as the boost pressure increases along the moving direction of the boundary between the residual gas and the fresh air. That is, it can be moved in a form that increases the distance between the focal position and the communication hole. As a result, it is possible to more appropriately suppress the instability of combustion accompanying the fluctuation of the supercharging pressure.

Further features of the above engine
The residual gas remaining in the ignition chamber in the previous exhaust stroke and the fresh air newly flowing into the ignition chamber in the intake stroke are the cylinder head side in the extending direction at the ignition timing. Exists in the order of description,
A storage unit for storing a first relationship between a boundary region between the residual gas and the fresh air in the extending direction at the ignition timing, and the supercharging pressure;
The ignition point position adjusting unit is configured to detect the focal position and the focal point in a direction along the extending direction based on the supercharging pressure measured by the pressure sensor and a first relationship stored in the storage unit. The point is to adjust the distance to the communication hole.

Although the first relationship between the boundary region between the residual gas and fresh air in the extending direction at the ignition timing and the supercharging pressure varies depending on the equivalence ratio of the air-fuel mixture, the outside air temperature, etc., experiments and simulations are performed in advance. Therefore, it can be predicted.
According to the above characteristic configuration, the ignition point position adjusting unit adjusts the distance between the focal position and the communication hole in the direction along the extending direction by using the first relationship and the supercharging pressure. The position of the ignition point can be adjusted in a state in accordance with the actual change in the boundary region between the fresh air and the residual gas.

Further features of the above engine
The ignition point position adjustment unit is configured to be more in the direction along the extending direction than the boundary region based on the supercharging pressure measured by the pressure sensor and the first relationship stored in the storage unit. The point of adjusting the distance between the focal position and the communication hole is that the ignition point position is positioned on the fresh air side and in the vicinity of the boundary region.

According to the above characteristic configuration, since the ignition point is set on the fresh air side of the boundary region between the residual gas and fresh air, the atmosphere around the ignition point is set to an atmosphere where the gas in the combustible region is sufficiently present, Ignition can be performed.
Furthermore, since the ignition point is set on the fresh air side of the boundary region and in the vicinity region of the boundary region, the distance between the ignition point and the communication hole is set as large as possible, so that the flame jet is easily formed. The ignition point position can be set so as to widen the lean limit as much as possible.

Further features of the above engine
The ignition point position adjustment unit is provided with an optical element that condenses the laser light and an actuator that moves the optical element in a direction along the optical axis.

  By adopting the above characteristic configuration, it is possible to satisfactorily realize adjustment of the ignition point position by the ignition point position adjustment unit.

The engine that has been described so far is
It is preferable that a plurality of the communication holes are provided, and the plurality of the communication holes are provided in line symmetry with the optical axis as a symmetry axis.

Schematic configuration diagram of a laser ignition type engine having an ignition chamber Conceptual diagram showing the concept of adjustment of the boundary region between fresh air and residual gas associated with the supercharging pressure and the adjustment of the distance between the focal position (ignition point) and the communication hole associated with the variation Partial sectional view of the constant volume container used in the experiment Graph showing changes in pressure over time in experiments using constant volume containers Image showing flame propagation in an experiment using a constant volume container

The engine 100 according to the embodiment of the present invention relates to an engine capable of increasing the lean limit while maintaining good ignition inside the ignition chamber 14 even when the supercharging pressure fluctuates.
Hereinafter, description will be given based on the drawings.

The engine 100 is configured as a turbocharged gas engine, and as shown in FIG. 1, by compressing and burning an air-fuel mixture M of fuel gas F such as city gas 13A and air A in the combustion chamber 3. An engine body that generates rotational power, a fuel gas supply path 61 that supplies fuel gas F to an intake path 42 that is connected to the intake port 8 of the engine body, and a fuel gas F that flows through the fuel gas supply path 61 A fuel control valve 63 for adjusting the flow rate and a compressor provided in the intake passage 42 in a state where the exhaust gas E discharged from the combustion chamber 3 is supplied to the turbine 52 provided in the exhaust passage 47 of the engine body and connected to the turbine 52 A supercharger 50 that compresses the air-fuel mixture M sucked into the combustion chamber 3 by 51, and a throttle that adjusts the flow rate of the air-fuel mixture M sucked into the combustion chamber 3 in the intake passage 42 44, and a hardware group that controls the turbocharged operation by controlling the various auxiliary machines such as the throttle valve 44 based on the input signal of the measurement result of the sensor and the like. An engine control unit C) comprising a software group is provided.

  In this type of gas engine 100, although not shown in detail, an air-fuel mixture M taken as fresh air from the intake port 8 into the combustion chamber 3 is compressed by the rise of the piston 2, and an ignition chamber 14 to be described later. By igniting sparks at the ignition point P in the inside and burning and expanding, the piston 2 is pushed down to output rotational power from a rotating shaft (not shown), and exhaust gas E generated by combustion is discharged from the combustion chamber 3. It is pushed out to the exhaust passage 47 and discharged outside.

In the intake passage 42, an air cleaner 41 that purifies the air A, a venturi mixer 64 that mixes the fuel gas F with the air A at an appropriate ratio (air-fuel ratio), and an air-fuel mixture M mixed by the mixer 64 are compressed. From the upstream side of the compressor 51, the intercooler 45 that cools the air-fuel mixture M that has been heated by boosting the compressor 51, and the throttle valve 44 that can adjust the intake amount of the air-fuel mixture M to the combustion chamber 3 by adjusting the opening degree. They are provided in the order of description.
That is, in the intake passage 42, the air-fuel mixture M generated by mixing the fuel gas F and air A by the mixer 64 is compressed by the compressor 51 and then cooled by the intercooler 45, and the throttle valve 44 is And is introduced into the combustion chamber 3 of the engine body.

  A fuel gas supply path 61 that guides the fuel gas F to the mixer 64 has a differential pressure regulator that maintains a constant pressure difference between the air A in the intake path 40 upstream of the mixer 64 and the fuel gas F in the fuel gas supply path 61. 62, a fuel control valve 63 for adjusting the supply amount of the fuel gas F supplied to the combustion chamber 3 via the mixer 64 is provided.

  The supercharger 50 supplies the exhaust gas E discharged from the combustion chamber 3 to the turbine 52 provided in the exhaust passage 47 of the engine body, and is connected to the turbine 52 by the compressor 51 provided in the intake passage 42. 3 is configured as a turbo-type supercharger that compresses the air-fuel mixture M sucked into the air. That is, the supercharger 50 rotates the turbine 52 by the enthalpy and kinetic energy of the exhaust gas E flowing through the exhaust passage 47, and rotationally drives the compressor 51 disposed in the intake passage 42 by the rotational force of the turbine 52. In the form, so-called supercharging is performed, in which the air-fuel mixture M as fresh air flowing through the intake passage 42 is compressed and supplied to the combustion chamber 3.

  The engine control unit C has, for example, an engine output calculated based on an engine speed measured by a speed sensor (not shown) and a torque of a rotation shaft (not shown) of the engine body as a target output. In this case, the engine control unit C functions as the output control unit C1.

Between the throttle valve 44 of the intake passage 42 and the engine body, there is provided a pressure sensor S for measuring the mixed air pressure (an example of the supercharging pressure) of the air-fuel mixture M at the position.
Here, when the output of the engine body is controlled to the target output by the output control unit C1, the air-fuel ratio of the air-fuel mixture M supplied to the combustion chamber 3 is uniquely determined when the mixed atmospheric pressure is determined.
That is, the engine control unit C holds, for example, a map indicating the relationship between the mixed pressure and the air-fuel ratio for each target output, and the pressure sensor described above so that the target air-fuel ratio is obtained at a predetermined target output. The opening degree of at least one of the fuel control valve 63 and the throttle valve 44 is controlled so that the mixed pressure measured in S approaches the target mixed pressure corresponding to the target air-fuel ratio.
In this embodiment, the turbocharged gas engine 100 is operated by lean burn combustion (for example, the equivalence ratio is less than 1) in which the equivalence ratio of the air-fuel mixture M in the combustion chamber 3 is smaller than 1 in order to operate with high efficiency. The target air-fuel ratio and the target mixed air pressure corresponding to the target air-fuel ratio are set so as to continue to be executed.

  The engine 100 according to the present embodiment includes an ignition point cover portion 20 that covers the ignition point P and forms the ignition chamber 14, and serves as a sub chamber with respect to the combustion chamber 3 as a so-called main chamber. A configuration including an ignition chamber 14 is employed.

When the explanation is added, the ignition point cover portion 20 includes a communication hole 15 that communicates the ignition chamber 14 formed inside and the combustion chamber 3 with the cylinder head 6 mounted.
Furthermore, the ignition chamber 14 covered with the ignition point cover portion 20 extends along the extending direction from the cylinder head 6 toward the combustion chamber 3, and in the present embodiment, an axis (ignition) along the extending direction. The central axis of the chamber 14) is provided in a state that coincides with the central axis α of the combustion chamber 3.

  The ignition point cover portion 20 is configured in a bottomed cylindrical shape including a cylindrical ignition point cover base end portion 22 and a dome-shaped ignition point cover head portion 23 that closes one end of the ignition point cover base end portion 22. Has been. Further, the ignition point cover portion 20 is configured such that a male screw portion threaded into the outer peripheral portion of the cylindrical ignition point cover base end portion 22 is screwed into a female screw portion threaded into the cylinder head 6. Mounted on the cylinder head 6. The ignition point cover portion 20 has an ignition point cover collar portion 21 on the opposite side of the ignition point cover head portion 23 at the ignition point cover base end portion 22 in the direction along the extending direction. The ignition point cover collar 21 abuts on the top surface of the cylinder head 6.

In the present embodiment, a plurality of communication holes 15 are provided in the ignition point cover head portion 23 on the combustion chamber 3 side in the extending direction of the ignition point cover portion 20.
Specifically, the communication hole 15 is a portion where the ignition point cover portion 20 and the central axis α of the ignition chamber 14 intersect, and is provided at the top of the ignition point cover head portion 23 and the center of the ignition chamber 14. A plurality (four in the present embodiment: two are shown in FIG. 1) are provided on the ignition point cover head 23 with the axis α as the axis of symmetry.

Furthermore, the ignition point cover part 20 is configured to divide the interior thereof into an ignition point cover flange part 21 side and an ignition point cover head part 23 side, and a heat-resistant transmission member 34 that transmits laser light, which will be described later, It is provided inside the cylindrical ignition point cover base end portion 22. The transmission member 34 is hermetically connected to the inner wall of the ignition point cover base end portion 22 by a specific connection technique.
That is, the ignition chamber 14 is formed so as to be surrounded by the ignition point cover head portion 23, the ignition point cover base end portion 22, and the transmission member 34.
In this embodiment, a high-power pulse is transmitted through the internal space of the ignition point cover base end portion 22 of the ignition point cover portion 20 (an example of a laser light transmission window provided through the ignition point cover portion 20). A laser light irradiation mechanism 30 for condensing the laser light inside the ignition chamber 14 is provided in a state where the optical axis of the laser light passes through the combustion chamber 3 and the ignition chamber 14. More specifically, the laser light irradiation mechanism 30 is arranged in a state where the optical axis is along the extending direction, that is, in a state where the laser light irradiation mechanism 30 is along the central axis α of the ignition chamber 14.
Although not shown in detail, the laser beam irradiation mechanism 30 is assembled to the engine 100 and is arranged so as to vibrate together with the engine 100.

  In this embodiment, the distance between the ignition point P as the focal position of the laser beam and the communication hole 15 is calculated based on the supercharging pressure-related value related to the supercharging pressure by the supercharger 50. An ignition point position adjusting unit that adjusts in the direction along the axis is provided, and the description of the configuration and control by the configuration will be added below.

The ignition point position adjusting unit is an internal space of the ignition point cover base end portion 22 that is the ignition point cover unit 20, and is an optical that condenses laser light on the ignition point cover flange 21 side with respect to the transmission member 34. An optical lens 35 as an element and an actuator 36 that moves the optical lens 35 in a direction along the optical axis are provided. Based on the control by the ignition point position control unit C2 of the engine control unit C, the actuator 36 controls the optical lens 35. The focal position (ignition point) of the laser beam can be adjusted by adjusting the position in the direction along the optical axis.
With this configuration, the actuator 36 can be prevented from being exposed to the high-temperature combustion exhaust gas E.

  By condensing the laser beam to the ignition point P by the laser beam irradiation mechanism 30 and the ignition point position adjusting unit, the air-fuel mixture M flowing from the combustion chamber 3 to the ignition chamber 14 through the communication hole 15 is ignited and burned. A combustion flame (flame jet) formed by combustion is ejected to the combustion chamber 3 through the communication hole 15. In this way, the flow of the air-fuel mixture M from the combustion chamber 3 to the ignition chamber 14 and the ejection of the combustion flame (flame jet) from the ignition chamber 14 to the combustion chamber 3 are performed by the plurality of communication holes 15. The air-fuel mixture M sucked into the combustion chamber 3 is combusted. Here, in this embodiment, the mixture M flowing into the ignition chamber 14 is all the mixture M flowing from the combustion chamber 3 through the communication hole 15. The fuel G and the air-fuel mixture M are not supplied from other than the above.

  As described above, in the configuration in which the communication hole 15 is provided with respect to the ignition point cover head portion 23 of the ignition point cover portion 20 with the central axis of the ignition chamber 14 as the axis of symmetry, the ignition chamber 14 in the previous exhaust stroke is provided. The residual gas remaining inside and the fresh air newly flowing into the ignition chamber 14 during the intake stroke are present in a substantially laminar order in the order described from the cylinder head 6 side in the extending direction at the ignition timing. Become.

When the supercharging pressure fluctuates, the boundary region K between the residual gas and fresh air inside the ignition chamber 14 changes along the extending direction of the ignition chamber 14 (direction along the optical axis).
Specifically, when the supercharging pressure is low, the boundary region K moves toward the combustion chamber 3 in the extending direction inside the ignition chamber 14 as shown in the left of FIG. 2, and the supercharging pressure is high. 2, the boundary region K moves toward the cylinder head 6 in the extending direction inside the ignition chamber 14. Incidentally, on the left side of FIG. 2, the concentration distribution of the fuel concentration is illustrated. In the ignition chamber 14, the fuel concentration decreases from the combustion chamber 3 side to the cylinder head 6 side.
Here, a flame jet is appropriately injected from the ignition chamber 14 to the combustion chamber 3, and the pressure change in the combustion chamber 3 immediately after the ignition timing is assumed to be steep, so that the combustion state in the combustion chamber 3 is kept good. From the viewpoint of expanding the range of lean combustion, it is preferable to increase the distance between the ignition point P and the communication hole 15 as described above with reference to FIGS.
Therefore, the ignition point position adjusting unit moves the focal position (ignition point P) to the communication hole 15 as the supercharging pressure measured by the pressure sensor S is higher in the direction along the optical axis (direction along the extending direction). The distance between the focal position and the communication hole is adjusted in such a manner that the distance is adjusted to the side away from the center.

However, if the distance between the ignition point P and the communication hole 15 is too large, the ignition point P will be located in a region where there is little fresh air and a large amount of residual gas, which is problematic in terms of ignitability.
Therefore, the ignition point position adjusting unit according to the embodiment positions the ignition position on the fresh air side (lower side in FIG. 2) from the boundary region K in the direction along the optical axis (direction along the extending direction). The distance between the focal position and the communication hole 15 is adjusted in such a manner that the ignition point position is positioned in the vicinity of the boundary region K.
Here, as shown in FIG. 2, when a communication hole provided at the top of the ignition point cover head 23 is employed as the communication hole 15, the distance between the ignition point P <b> 3 a and the communication hole 15 when the supercharging pressure is low. L3a (shown on the left in FIG. 2) is set shorter than the distance L3b (shown on the right in FIG. 2) between the ignition point P3b and the communication hole 15 when the supercharging pressure is high.

  The engine control unit C according to the embodiment includes a storage unit C3 that stores a first relationship between the boundary region K between the residual gas and fresh air in the extending direction at the ignition timing and the supercharging pressure. ing. Then, the ignition point position adjustment unit is based on the supercharging pressure measured by the pressure sensor S and the first relationship stored in the storage unit C3, and the focal position and the communication hole in the direction along the extending direction. Adjust the distance to 15.

[Another embodiment]
(1) In the above-described embodiment, the fuel gas F is supplied to the intake passage 40 and the mixture M of fuel and combustion air is supplied to the ignition chamber 14 through the communication hole 15. .
However, a configuration including an injector that directly injects fuel into the ignition chamber 14 may be employed.

(2) In the engine 100 according to the above-described embodiment, the configuration example including the turbocharger-type supercharger 50 has been shown. You may employ | adopt the structure provided.

(3) In the above embodiment, an example in which the supercharging pressure related value is the supercharging pressure has been shown. However, for example, the rotation speed of the compressor 51 may be adopted as the supercharging pressure related value.

(4) In the above embodiment, the example in which the central axis of the ignition chamber 14 (axis in the extending direction (optical axis)) coincides with the central axis α of the combustion chamber 3 is shown. It doesn't matter.
Further, the central axis and the optical axis of the ignition chamber 14 do not have to coincide with each other.

  The configuration disclosed in the above embodiment (including another embodiment, the same shall apply hereinafter) can be applied in combination with the configuration disclosed in the other embodiment, as long as no contradiction occurs. The embodiment disclosed in this specification is an exemplification, and the embodiment of the present invention is not limited to this. The embodiment can be appropriately modified without departing from the object of the present invention.

  The engine of the present invention can be effectively used as an engine capable of expanding the lean limit while maintaining good ignition inside the ignition chamber even when the supercharging pressure fluctuates.

2: Piston 3: Combustion chamber 6: Cylinder head 14: Ignition chamber 15: Communication hole 20: Ignition point cover part 30: Laser light irradiation mechanism 34: Transmission member 35: Optical lens 36: Actuator 42: Intake passage 50: Supercharging Machine 100: Engine C2: Ignition position control unit C3: Storage unit K: Boundary region M: Air-fuel mixture P: Ignition point S: Pressure sensor α: Center axis

Claims (7)

The ignition point cover portion that covers the ignition point and forms an ignition chamber, and the ignition chamber formed inside the combustion chamber facing the piston and the ignition point cover portion in a state where the ignition point cover portion is mounted on the cylinder head An engine in which a communication hole communicating with the chamber is provided in the ignition point cover portion;
A laser light irradiation mechanism for condensing and igniting laser light at the ignition point through a laser light transmission window provided in the ignition point cover part, and an optical axis of the laser light between the combustion chamber and the ignition chamber Arranged in a state to pass through,
A supercharger for compressing fresh air taken into the combustion chamber by a compressor provided in the intake passage;
Ignition for adjusting a distance between the focal position of the laser beam as the ignition point and the communication hole in a direction along the optical axis based on a supercharging pressure related value related to a supercharging pressure by the supercharger An engine equipped with a point position adjustment unit. The supercharging pressure-related value is the supercharging pressure measured by a pressure sensor that measures the pressure of the fresh air supercharged by the supercharger in the intake passage,
The ignition point position adjusting unit adjusts the focal position to a side away from the communication hole as the supercharging pressure increases in the direction along the optical axis, and the distance between the focal position and the communication hole. The engine according to claim 1, wherein the engine is adjusted. The ignition chamber covered by the ignition point cover portion extends along an extending direction from the cylinder head toward the combustion chamber,
The communication hole is provided on the combustion chamber side in the extending direction in the ignition point cover portion,
The laser beam irradiation mechanism is provided with the optical axis along the extending direction,
The ignition point position adjustment unit adjusts the distance between the focal position and the communication hole in a direction along the extending direction and adjusts the focal position toward the cylinder head as the supercharging pressure increases. The engine according to claim 2. The residual gas remaining in the ignition chamber in the previous exhaust stroke and the fresh air newly flowing into the ignition chamber in the intake stroke are the cylinder head side in the extending direction at the ignition timing. Exists in the order of description,
A storage unit for storing a first relationship between a boundary region between the residual gas and the fresh air in the extending direction at the ignition timing, and the supercharging pressure;
The ignition point position adjusting unit is configured to detect the focal position and the focal point in a direction along the extending direction based on the supercharging pressure measured by the pressure sensor and a first relationship stored in the storage unit. The engine according to claim 3, wherein the distance from the communication hole is adjusted.   The ignition point position adjustment unit is configured to be more in the direction along the extending direction than the boundary region based on the supercharging pressure measured by the pressure sensor and the first relationship stored in the storage unit. The engine according to claim 4, wherein the distance between the focal position and the communication hole is adjusted in a form in which an ignition point position is positioned on a fresh air side and in a region near the boundary region.   The said ignition point position adjustment part is provided with the optical element which condenses the said laser beam, and the actuator which moves the said optical element in the direction along the said optical axis. Engine. A plurality of the communication holes are provided,
The engine according to any one of claims 1 to 6, wherein the plurality of communication holes are provided in line symmetry with the optical axis as a symmetry axis.

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