Hydrogen engine

A hydrogen engine in which hydrogen gas is supplied into a combustion chamber as fuel, comprises: an injector for injecting hydrogen gas; a pressure accumulation chamber communicating with an injection hole of the injector; a communication hole communicating with the pressure accumulation chamber and the combustion chamber; and a pressure accumulation chamber defining portion provided between the injector and the combustion chamber and defining the pressure accumulation chamber and the communication hole. The pressure accumulation chamber defining portion is formed separately from the injector and has a thermal conductivity equal to or higher than a thermal conductivity of a combustion chamber wall defining the combustion chamber.

RELATED APPLICATIONS

The present application claims priority of Japanese Patent Application No. 2022-180266 filed Nov. 10, 2022, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD

The present disclosure relates to a hydrogen engine.

BACKGROUND

Conventionally, an engine in which gaseous fuel is directly injected into a combustion chamber has been known (JP 2007-162633 A, JP 2002-221037 A). In particular, JP 2007-162633 A discloses an engine in which hydrogen gas is used as gaseous fuel. Further, in the rotary engine described in JP 2007-162633 A, the hydrogen injector is arranged so as to face the working chamber in the retard side from the compressed top dead center 100°, whereby even if premature ignition (pre-ignition) occurs in the working chamber, damage or the like to the hydrogen injector is reduced, since the hydrogen injector is located at the end of a flame or pressure wave.

SUMMARY

Since hydrogen has a high combustion speed, a low minimum ignition energy, and a wide combustible range in a mixing ratio with air, the flame easily reaches the vicinity of the wall surface constituting the combustion chamber. Therefore, if the hydrogen injector is disposed so as to face the working chamber, even if the hydrogen injector is located where the flame or the pressure wave has difficulty reaching, it is not possible to sufficiently reduce the possibility that the hydrogen injector may be damaged due to the heat in the combustion chamber.

In view of the above problems, an object of the present disclosure is to reduce the possibility of an injector for injecting hydrogen gas being damaged due to the heat in a combustion chamber.

The gist of the present disclosure is as follows.(1) A hydrogen engine in which hydrogen gas is supplied into a combustion chamber as fuel, comprising:an injector for injecting hydrogen gas;a pressure accumulation chamber communicating with an injection hole of the injector;a communication hole communicating with the pressure accumulation chamber and the combustion chamber; anda pressure accumulation chamber defining portion provided between the injector and the combustion chamber and defining the pressure accumulation chamber and the communication hole, whereinthe pressure accumulation chamber defining portion is formed separately from the injector and has a thermal conductivity equal to or higher than a thermal conductivity of a combustion chamber wall defining the combustion chamber.(2) The hydrogen engine according to above (1), wherein one or more of the communication holes are provided, andat least one of the communication holes is formed so as to have an axis that is angled with respect to an axis of the injection hole of the injector.(3) The hydrogen engine according to above (2), further comprising a piston reciprocating in a cylinder defining the combustion chamber, whereinat least one of the communication holes is formed so as to have an axis that extends obliquely to a piston side in an injection direction with respect to the axis of the injection hole of the injector.(4) The hydrogen engine according to above (2) or (3), further comprising a spark plug arranged to be exposed to the combustion chamber and igniting a mixture of hydrogen gas and air, whereinat least one of the communication holes is formed to have an axis that is inclined with respect to the axis of the injection hole of the injector so as to extend away from an ignition portion of the spark plug.(5) The hydrogen engine according to above (4), whereintwo or more communication holes are provided, andat least two of the communication holes are formed so as to have axes extending in directions spreading on both sides across the ignition portion of the spark plug when viewed in an axial direction of the combustion chamber.(6) The hydrogen engine according to any one of above (1) to (5), wherein the pressure accumulation chamber defining portion is configured as a part of a cylinder head defining the combustion chamber.(7) The hydrogen engine according to any one of above (1) to (5), wherein the pressure accumulation chamber defining portion is configured as a member separate from a cylinder head defining the combustion chamber.(8) The hydrogen engine according to any one of above (1) to (7), wherein the communication hole is formed such that a total flow path cross-sectional area thereof is smaller than a flow path cross-sectional area of the pressure accumulation chamber so as to be a throttle with respect to the pressure accumulation chamber.(9) The hydrogen engine according to above (8), wherein the communication hole is formed such that the total flow path cross-sectional area thereof is larger than a flow path cross-sectional area of a throttle portion of the injector so that a flow rate of the hydrogen gas in the throttle portion of the injector becomes a predetermined flow rate when the hydrogen gas is injected from the injector.(10) The hydrogen engine according to any one of above (1) to (9), wherein the pressure accumulation chamber is formed to have the same axis as the axis of the injection hole of the injector.(11) The hydrogen engine according to any one of above (1) to (10), further comprising a check valve provided in the pressure accumulation chamber, whereinthe check valve permits a flow of fluid from the injector to the communication hole and prohibits a flow of fluid from the communication hole to the injector.(12) The hydrogen engine according to above (11), further comprising a biasing member that biases the check valve toward the injection hole of the injector, whereinthe biasing member is fixed to the injector.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference to the drawings. In the following description, the same reference numerals are given to the same elements.

First Embodiment

<Overall Configuration of Engine>

First, with reference toFIGS.1and2, an overall configuration of a hydrogen engine (hereinafter, also simply referred to as an “engine”)1according to the first embodiment will be described. In a hydrogen engine, hydrogen gas is directly injected into a combustion chamber as fuel.FIG.1is a partial cross-sectional view schematically showing the engine1according to the present embodiment. As shown inFIG.1, the engine1includes a cylinder block2, a cylinder head3, pistons4, and connecting rods5.

The cylinder block2includes a plurality of cylinders6arranged side by side. The cylinder head3is arranged so as to contact the cylinder block2in a contact plane A, and is arranged so as to close one end of the cylinder6formed in the cylinder block2. The cylinder block2and the cylinder head3are formed of a metal such as an aluminum alloy or cast iron.

The piston4is arranged to reciprocate in a cylinder6formed in the cylinder block2. The piston4is connected to the connecting rod5via a piston pin. The connecting rod5is connected to a crankshaft (not shown) via a crankpin. The connecting rod5serves to convert the reciprocating movement of the piston4into a rotational movement of the crankshaft. The wall surface of the cylinder6of the cylinder block2, the cylinder head3, and the piston4define a combustion chamber7in which a mixture of air and hydrogen gas is combusted. In the combustion chamber7, a swirling flow of the air-fuel mixture is generated in a direction indicated by an arrow inFIG.1.

FIG.2is a partial bottom view schematically showing a bottom surface of the cylinder head3. In particular,FIG.2schematically shows a portion of the cylinder head3positioned to close one cylinder6. Further, inFIG.2, an injector51, although a pressure accumulation chamber61and communication holes62which will be described later are depicted, they are not visible in nature from the bottom surface side of the cylinder head3since they are disposed inside the cylinder head3, but they are depicted for easy understanding of the explanation.

As shown inFIGS.1and2, an intake port11and an exhaust port12are formed in the cylinder head3. The intake port11faces the combustion chamber7and communicates with the combustion chamber7via an intake opening13formed in the cylinder head3. Similarly, the exhaust port12faces the combustion chamber7and communicates with the combustion chamber7via an exhaust opening14formed in the cylinder head3.

As shown inFIG.2, in the present embodiment, two intake openings13and two exhaust openings14are provided for each combustion chamber7. The two intake openings13are arranged side by side in the same direction as the direction in which the plurality of cylinders6are arranged side by side (hereinafter, also referred to as “cylinder alignment direction”). Similarly, the two exhaust openings14are arranged side by side in the same direction as the cylinder alignment direction. Two intake openings13are arranged on one side and two exhaust openings14are arranged on the other side with respect to a central plane C extending in the cylinder alignment direction through the center of each cylinder6.

As shown inFIG.1, the cylinder head3is formed such that the upper surface of the combustion chamber7has two inclined surfaces, an intake-side inclined surface17and an exhaust-side inclined surface18. The intake-side inclined surface17is formed so that a height from the contact plane A (a length from the contact plane A in the axial line Z direction of the cylinder6) increases from the edge portion on the intake opening side toward the central plane C. The exhaust-side inclined surface18is formed so that the height from the contact plane A increases from the edge portion on the exhaust opening side toward the central plane C. Therefore, the upper surface of the combustion chamber7is inclined so as to be highest in the central plane C.

Further, the cylinder head3is provided with an intake valve21for opening and closing the intake opening13, an exhaust valve31for opening and closing the exhaust opening14, an spark plug41for igniting the air-fuel mixture in the combustion chamber7, and an injector51for directly injecting hydrogen gas into the combustion chamber7.

The intake valve21includes a valve stem22and a valve body23fixed to one end of the valve stem22. The intake valve21is arranged in the cylinder head3so as to be slidable in the direction in which the valve stem22extends, i.e., in the axial direction of the intake valve21. The intake valve21is lifted in its axial direction by an intake valve mechanism (not shown).

Similarly, the exhaust valve31includes a valve stem32and a valve body33fixed to one end of the valve stem32. The exhaust valve31is arranged in the cylinder head3so as to be slidable in the direction in which the valve stem32extends, i.e., in the axial direction of the exhaust valve31. The exhaust valve31is lifted in its axial direction by an exhaust valve operating mechanism (not shown).

The spark plug41is attached to the cylinder head3so as to be positioned on the upper surface of the combustion chamber7substantially at the center of the combustion chamber7when viewed in the axis Z (i.e., the axis of the combustion chamber7) direction of the cylinder6. Thus, the spark plug41is arranged so as to be exposed to the combustion chamber7. The spark plug41has, at its end, an electrode42which functions as an ignition unit for igniting the air-fuel mixture. Therefore, the electrode42of the spark plug41is located near the upper surface of the combustion chamber7at substantially the center of the combustion chamber7when viewed in the axis Z direction of the cylinder6.

<Configuration around the Injector>

Next, the configuration of the cylinder head3around the injector51will be described with reference toFIGS.3and4in addition toFIGS.1and2.FIG.3is an enlarged cross-sectional view taken along the line III-III ofFIG.2, showing a portion of the cylinder head3around the spark plug41and the injector51.FIG.4is an enlarged cross-sectional view of a portion ofFIG.3, showing a portion of the cylinder head3around the injector51. InFIG.4, only the tip of the injector51is depicted as representing a cross section.

As shown inFIG.2, the injector51is disposed on the intake opening side with respect to the central plane C. In particular, in the present embodiment, the injector51is arranged to inject hydrogen gas between the two intake openings13and in the vicinity of the outer periphery of the cylinder6. It should be noted that the injector51does not necessarily have to be provided between the intake openings13, and may be disposed in the cylinder head3between the exhaust openings14or in the vicinity of the center of the combustion chamber7.

Further, as shown inFIG.4, the injector51has an injection hole52for injecting hydrogen gas at the tip thereof. The injection hole52is formed so that its axis is the same as the axis of the injector51(in the figure, the axis of the injector51and the axis of the injection hole52are both represented by X). In the present embodiment, the injection hole52is formed such that the flow path cross-sectional area in a cross section perpendicular to the main flow direction of the hydrogen gas is the smallest in the injector51. Therefore, in the present embodiment, the injection hole52functions as a throttle portion for the flow of the hydrogen gas in the injector51. It should be noted that the injection hole52may be formed such that its axis is oriented in a direction different from the axis X of the injector51. In addition, the injector51may be formed so that the flow path cross-sectional area in the injector51is the smallest around a valve body of a needle valve that opens and closes the injection hole52. In this case, a region around the valve body, such as a needle valve, functions as a throttle portion for the flow of the hydrogen gas.

In addition, as shown inFIGS.3and4, the injector51is disposed in a hole45formed in the cylinder head3. The hole45is open to the outside of the cylinder head3so that the injector51can be inserted. The hole45is formed so that a cross-sectional shape perpendicular to the axial direction thereof is substantially the same as or slightly larger than the cross-sectional shape of the injector51. In addition, the hole45is formed such that the axial length of the portion of the hole45having substantially the same cross-sectional shape (in the present embodiment, a circular shape) as the cylindrical portion53having a circular cross section narrower than the other portion on the distal end side of the injector51is longer than the axial length of the cylindrical portion53. In addition, the injector51is fixed in the hole45by any method, for example, by supporting the rear portion of the injector51with another member fixed to the cylinder head3.

As shown inFIGS.3and4, between the injector51and the combustion chamber7, a pressure accumulation chamber61, a communication hole62, and a pressure accumulation chamber defining portion63that defines the pressure accumulation chamber61and the communication hole62are provided. As shown inFIG.4, the pressure accumulation chamber61communicates with the injection hole52of the injector51and communicates with the communication hole62. In addition, the communication hole62communicates with the pressure accumulation chamber61and also communicates with the combustion chamber7. In particular, in the present embodiment, the communication hole62is formed so as to open to an end surface of the pressure accumulation chamber61opposite to the injector51side. However, the communication hole62may be formed so as to open to the annular side surface of the pressure accumulation chamber61, in addition to the end surface of the pressure accumulation chamber61on the side opposite to the injector51side.

The pressure accumulation chamber61is formed so as to have the same axis as the axis X of the injection hole52of the injector51. Therefore, the annular side wall defining the pressure accumulation chamber61is prevented from becoming the flow path resistance to the hydrogen gas injected from the injector51. In addition, in the present embodiment, the pressure accumulation chamber61has a cross-sectional shape substantially the same as the cross-sectional shape of the tip of the injector51provided with the injection hole52(i.e., the cross-sectional shape of the cylindrical portion53) in a cross section perpendicular to the axis X. Therefore, in the present embodiment, the pressure accumulation chamber61has a circular cross-sectional shape. In addition, the flow path cross-sectional area of the pressure accumulation chamber61(i.e., the cross-sectional area in a cross section perpendicular to the axis X) is substantially the same as the cross-sectional area of the tip end of the injector51. Therefore, the pressure accumulation chamber61has a flow path cross-sectional area larger than the flow path cross-sectional area of the injection hole52by the thickness of the wall portion around the injection hole52of the injector51. Further, in the present embodiment, the pressure accumulation chamber61is formed in the hole45of the cylinder head3, and is formed by the axial length of the portion of the hole45having substantially the same cross-sectional shape as the cylindrical portion53of the injector51being longer than the axial length of the cylindrical portion53in the X-axis direction. The pressure accumulation chamber61may have a cross-sectional shape other than a circular shape, such as a polygonal shape or an elliptical shape.

It should be noted that the pressure accumulation chamber61may be formed to have an axis different from the axis X of the injection hole52. The pressure accumulation chamber61may have a cross-sectional shape different from the cross-sectional shape of the tip end of the injector51, and the cross-sectional area of the flow path of the pressure accumulation chamber61may be larger or smaller than the cross-sectional area of the tip end of the injector51.

In the present embodiment, two communication holes62are provided. In particular, in the present embodiment, as can be seen fromFIG.2, the communication holes62are arranged side by side when viewed in the axis Z direction of the cylinder6. In addition, the cross-sectional shape of the communication hole62in a cross section perpendicular to the main flow direction of the hydrogen gas is formed to be substantially circular. In addition, in the present embodiment, the two communication holes62are formed so that the cross-sectional shapes thereof have the same shape, and thus the cross-sectional areas thereof are the same as each other. The communication hole62may have a cross-sectional shape other than a circular shape, such as a polygonal shape or an elliptical shape.

In addition, the two communication holes62are formed so that the total flow path cross-sectional area thereof is smaller than the flow path cross-sectional area of the pressure accumulation chamber61. As a result, the communication hole62acts as a throttle in the flow of the hydrogen gas with respect to the pressure accumulation chamber61.

In addition, the two communication holes62are formed such that the total flow path cross-sectional area thereof is larger than the flow path cross-sectional area of the throttle portion of the injector51(in the present embodiment, the injection hole52) so that the flow rate of the hydrogen gas in the throttle portion of the injector51becomes a predetermined flow rate (in the present embodiment, sound velocity) when the hydrogen gas is injected from the injector51. Specifically, for example, the two communication holes62are formed such that the total flow path cross-sectional area thereof is, for example, 1.75 times or more of the flow path cross-sectional area of the throttle portion of the injector51. As described above, when the hydrogen gas is injected from the injector51, the flow rate of the hydrogen gas becomes a predetermined flow rate (for example, sound velocity), so that the supply amount of the hydrogen gas into the combustion chamber7can be adjusted only based on the time when the injector51is opened, and thus the supply amount of the hydrogen gas into the combustion chamber7can be easily controlled.

Further, in the present embodiment, as shown inFIGS.2and4, each of the two communication holes62is formed so as to have axis Y that is angled with respect to the axis X of the injection hole52of the injector51. In particular, in the present embodiment, as shown inFIG.4, the axes Y of the two communication holes62are inclined toward the piston4side (in the direction from the cylinder head3toward the cylinder block2in the axis Z direction of the cylinder6) in the injection direction of the hydrogen gas from the injection hole52with respect to the axis X of the injection hole52of the injector51. In other words, as shown inFIG.4, the axes Y of the two communication holes62extend obliquely with respect to the axis X of the injector51in a cross section including the axis Z of the cylinder6and the axis X of the injector51. The inclination angle α at this time is, for example, 5 to 30°, 7 to 20°, or 10 to 15°.

Further, in the present embodiment, as shown inFIG.2, the axis Y of the two communication holes62extends so as to be inclined away from the electrode42of the spark plug41with respect to the axis X of the injection hole52of the injector51. In other words, as shown inFIG.2, the axis Y of each of the two communication holes62extends obliquely with respect to the axis X of the injection hole52extending through the spark plug41when viewed in the axis Z direction of the cylinder6. The inclination angle β at this time is, for example, 5 to 45°, 7 to 35°, or 10 to 20°. As shown inFIG.2, the respective axes Y of the two communication holes62extend so as to be inclined in mutually opposite directions with respect to the axis X of the injection hole52when viewed in the axis Z direction of the cylinder6. Therefore, in the present embodiment, as shown inFIG.2, the axes Y of the two communication holes62extend in a direction extending to both sides across the electrode42of the spark plug41when viewed in the axis Z direction of the cylinder6.

The pressure accumulation chamber defining portion63is located around the injector51, the pressure accumulation chamber61and the communication hole62. In particular, in the present embodiment, the pressure accumulation chamber defining portion63is configured as a part of the cylinder head3. Therefore, the pressure accumulation chamber defining portion63is a portion of the cylinder head3located around the pressure accumulation chamber61and the communication hole62. Therefore, the pressure accumulation chamber defining portion63is formed of the same material as the cylinder head3(i.e., the combustion chamber wall defining the combustion chamber7). Therefore, the pressure accumulation chamber defining portion63has the same thermal conductivity as that of the cylinder head3. On the other hand, the cylinder head3is formed separately from the injector51, and thus the pressure accumulation chamber defining portion63is formed separately from the injector51.

In the hydrogen engine1configured as described above, when the hydrogen gas is injected from the injection hole52of the injector51, the injected hydrogen gas is injected through the pressure accumulation chamber61and the communication hole62from the communication hole62into the combustion chamber7. As described above, the hydrogen gas is injected from the injection hole52at a flow velocity such that the flow velocity thereof becomes sound velocity in the throttle portion of the injector51, and then flows through the pressure accumulation chamber61and the communication hole62at a velocity slower than sound velocity, and is injected into the combustion chamber7. When the hydrogen gas is injected from the communication hole62, the hydrogen gas is injected into the combustion chamber7mainly in the axial line Y direction of the communication hole62.

Incidentally, as described above, hydrogen has a high combustion speed, a low minimum ignition energy, and a wide combustible range in a mixing ratio with air. Therefore, the quenching distance is short, and the flame reaches the vicinity of the wall surface of the combustion chamber7. Therefore, the temperature of the constituent members exposed to the combustion chamber7tends to be relatively high. In addition, since the minimum ignition energy of hydrogen is low, abnormal combustion such as premature ignition (pre-ignition) is likely to occur, and when such abnormal combustion occurs, the constituent members exposed to the combustion chamber7are exposed to high temperatures.

On the other hand, in the present embodiment, the pressure accumulation chamber defining portion63provided between the injector51and the combustion chamber7is a part of the cylinder head3and has the same thermal conductivity as that of the cylinder head3, and is therefore cooled together with the cylinder head3by coolant or the like flowing in the cylinder head3. In addition, a pressure accumulation chamber61and a communication hole62are provided between the injector51and the combustion chamber7. Accordingly, the injector51is arranged at a position retracted from the other wall surface defining the combustion chamber7. Therefore, the flame in the combustion chamber7hardly reaches the tip of the injector51. Therefore, the injector51is prevented from being constantly maintained at a high temperature and thus being damaged, and the injector51is prevented from being damaged when, for example, premature ignition or the like occurs.

Further, in the present embodiment, the communication hole62is formed such that the total flow path cross-sectional area thereof is smaller than the flow path cross-sectional area of the pressure accumulation chamber61. Since the flow path cross-sectional area of the communication hole62is small in this way, the flame in the combustion chamber7is less likely to reach the inside of the pressure accumulation chamber61. Accordingly, this also prevents the injector51from being maintained at a high temperature and prevents the injector51from being damaged.

In addition, in the present embodiment, the communication hole62has the axes Y at an arbitrary angle with respect to the axis X of the injection hole52of the injector51. Therefore, while the injector51is disposed at a position retracted from another wall surface defining the combustion chamber7, the hydrogen gas can be injected in desired directions specified by the axes Y other than the axis X direction of the injection hole52of the injector51. Further, since the stoichiometric air-fuel ratio in the air-fuel mixture of the hydrogen gas is low, it is necessary to supply a large amount of hydrogen gas into the combustion chamber7, and therefore, it is preferable to increase the cross-sectional area of the injection hole52of the injector51as much as possible, and therefore it is difficult to make the direction and the shape of the injection hole52in the direction and the shape corresponding to the optimum injection direction. On the other hand, in the present embodiment, since the injection is performed in the optimum injection direction in the combustion chamber7by the communication hole62, the injection hole52of the injector51can be formed so as to extend in the axial line X direction of the injector51, and the cross-sectional area of the flow path of the injector51can be large.

In the present embodiment, the axis Y of the communication hole62is inclined toward the piston4side (downward inFIGS.1and4) at an inclination angle α with respect to the axis X of the injection hole52of the injector51. Therefore, the hydrogen gas injected into the combustion chamber7through the communication hole62is prevented from coming into contact with the uneven portion, which is likely to reach a high temperature, on the lower surface of the cylinder head3at an early stage, and thus occurrence of abnormal combustion such as premature ignition is suppressed.

Further, in the present embodiment, the axes Y of the communication hole62extend so as to be inclined away from the electrode42of the spark plug41at an inclination angle θ with respect to the axis X of the injection hole52of the injector51. Therefore, the concentration of the air-fuel mixture in the vicinity of the electrode42of the spark plug41which becomes high in temperature is prevented from becoming high, and thus the possibility of premature ignition occurring in the vicinity of the spark plug41is suppressed. In the present embodiment, the axes Y of the two communication holes62extend in a direction extending to both sides across the electrode42of the spark plug41. Therefore, a certain amount of air-fuel mixture can be formed around the electrode42of the spark plug41while suppressing an excessive increase in the concentration of the air-fuel mixture in the vicinity of the electrode42of the spark plug41, and thus the air-fuel mixture can be ignited by the spark plug41.

In the above-described embodiment, the engine1is provided with two communication holes62for each injector51. However, any number of the communication holes may be provided, as long as the number of the communication holes is one or more. Therefore, the engine1may be provided with one or more communication holes62for each injector51, and therefore, the engine1may be provided with only one communication hole62for each injector51, or may be provided with three or more communication holes62for each injector51.

In addition, in the above-described embodiment, each communication hole62is formed so that its axis Y extends at an angle with respect to the axis X of the injection hole52of the injector51. However, all or a part of the one or more communication holes62may be formed such that the axis Y thereof extends in the same direction as the axis X of the injection hole52. Further, at least a part of the communication hole62may extend such that the axis Y does not separate from the electrode42of the spark plug41with respect to the axis X of the injection hole52.

Further, in the above-described embodiment, the axes Y of the two communication holes62are inclined in the axis Z direction of the cylinder6at the same inclination angle α with respect to the axis X of the injection hole52. However, the axes Y of the two communication holes62may be inclined in the axis Z direction (i.e., upward or downward direction inFIG.4) of the cylinder6at different inclination angles with respect to the axis X of the injection hole52. In addition, in the above-described embodiment, the axes Y of the two communication holes62are inclined at the same inclination angle β in opposite directions with respect to the axis X of the injection hole52when viewed in the axis Z direction of the cylinder6. However, the axes Y of the two communication holes62may be inclined at the same inclination angle in the same direction with respect to the axis X of the injection hole52when viewed in the axis Z direction of the cylinder6(i.e., both of them may be inclined upward inFIG.2, or may be inclined downward). Alternatively, the axes Y of the two communication holes62may be inclined at different inclination angles in mutually opposite directions or in mutually identical directions with respect to the axis X of the injection hole52when viewed in the axis Z direction of the cylinder6.

FIG.5is an enlarged cross-sectional view, similar toFIG.4, showing a portion of the cylinder head3around the injector51, according to one modification. In the example shown inFIG.5, the engine1is provided with four communication holes62for each injector51. As shown inFIG.5, two communication holes62are provided side by side in the axis Z direction of the cylinder6, and these communication holes62are inclined at different inclination angles with respect to each other with respect to the axis X of the injection hole52. In particular, in the present modification, the communication holes62are formed such that the inclination angle of the communication holes62provided on the opposite side (upper side in the drawing) to the piston4is smaller than the inclination angle of the communication holes62provided on the piston4side (lower side in the drawing). Further, in the present modification, when viewed in the axis Z direction of the cylinder6, the two communication holes62are inclined at the same inclination angle β in opposite directions with respect to the axis X of the injection hole52. By forming the communication hole62in this manner, hydrogen gas can be diffused widely into the combustion chamber7.

FIG.6is an enlarged sectional view, similar toFIG.4, showing a portion of the cylinder head3around the injector51, according to another modification. In the example shown inFIG.6, only one communication hole62is provided for each injector51in the engine1. In addition, the communication hole62is formed so that its axis Y extends on the axis X of the injection hole52of the injector51. By forming the communication hole62in this manner, the communication hole62can be easily formed.

In the above-described embodiment, the flow path cross-sectional area of the pressure accumulation chamber61is formed to be larger than the flow path cross-sectional area of the injection hole52of the injector51. However, the flow path cross-sectional area of the pressure accumulation chamber61may be formed to be substantially the same as the flow path cross-sectional area of the injection hole52of the injector51. In addition, in the above-described embodiment, the total flow path cross-sectional area of the plurality of communication holes62is formed to be smaller than the flow path cross-sectional area of the pressure accumulation chamber61. However, in the case where the plurality of communication holes62are provided, the plurality of communication holes62may be formed such that the total flow path cross-sectional area thereof is substantially the same as the flow path cross-sectional area of the pressure accumulation chamber61. In addition, in the present embodiment, the communication hole62is formed such that the total flow path cross-sectional area thereof is larger than the flow path cross-sectional area of the throttle portion of the injector51. However, the communication hole62may be formed such that its flow path cross-sectional area is substantially the same as the flow path cross-sectional area of the throttle portion of the injector51.

In the above-described embodiment, the hydrogen engine1includes only the injector51that directly injects hydrogen gas into the combustion chamber7. However, the hydrogen engine1may include an injector that injects hydrogen gas or other fuel into an intake passage such as the intake port11in addition to the injector51that injects hydrogen gas directly into the combustion chamber7.

Second Embodiment

Next, a hydrogen engine1according to the second embodiment will be described with reference toFIG.7. The configuration of the hydrogen engine1according to the second embodiment is basically similar to the configuration of the hydrogen engine1according to the first embodiment. Therefore, portions different from the configuration of the hydrogen engine1according to the first embodiment will be mainly described below.

FIG.7is an enlarged cross-sectional view, similar toFIG.4, showing a portion of the cylinder head3around the injector51according to the second embodiment. As shown inFIG.7, the hole45formed in the cylinder head3is formed such that a cross-sectional shape perpendicular to the axial direction thereof is larger than a cross-sectional shape of the cylindrical portion53of the injector51. In the present embodiment, a pressure accumulation chamber defining member63′ is provided between the inner surface of the hole45and the outer surface of the cylindrical portion53in the vicinity of the distal end portion of the cylindrical portion53of the injector51. The pressure accumulation chamber defining member63′ is provided between the injector51and the combustion chamber7, and functions as a pressure accumulation chamber defining portion defining the pressure accumulation chamber61and the communication hole62. Therefore, in the present embodiment, the pressure accumulation chamber defining portion is configured as a member separate from the cylinder head3defining the combustion chamber7.

In the present embodiment, the pressure accumulation chamber defining member63′ is formed of the same material as the cylinder head3, and therefore of a metal such as an aluminum alloy or cast iron. Therefore, in the present embodiment, the pressure accumulation chamber defining member63′ has the same thermal conductivity and corrosion resistance as the cylinder head3. However, the pressure accumulation chamber defining member63′ may be formed of another material having thermal conductivity greater than or equal to the thermal conductivity of the cylinder head3used as the combustion chamber wall. In addition, the pressure accumulation chamber defining member63′ may be formed of another material having corrosion resistance higher than or equal to the corrosion resistance of the cylinder head3.

Specifically, the pressure accumulation chamber defining member63′ may be formed of, for example, beryllium copper.

As shown inFIG.7, the pressure accumulation chamber defining member63′ has a hole64into which the injector51is inserted. The hole64is formed so that a cross-sectional shape perpendicular to the axial direction thereof is substantially the same as or slightly larger than the cross-sectional shape of the cylindrical portion53of the injector51. Further, the pressure accumulation chamber defining member63′ is press-fitted into the hole45of the cylinder head3, and is configured so that the tip end of the injector51does not reach the bottom surface of the hole64of the pressure accumulation chamber defining member63′ when the injector51is inserted. As a result, the pressure accumulation chamber61is formed between the tip of the injector51and the bottom surface of the hole64of the pressure accumulation chamber defining member63′.

According to the present embodiment, since the pressure accumulation chamber defining portion is configured as a member separate from the cylinder head3, the communication hole62can be easily formed, and thus the processing accuracy of the communication hole62can be improved. In addition, the pressure accumulation chamber defining portion can be formed of a material having higher thermal conductivity and corrosion resistance than the cylinder head3, whereby the cooling property around the tip end of the injector51can be enhanced, and deformation of the shape, clogging, or the like due to corrosion of the communication hole62can be suppressed.

Third Embodiment

Next, referring toFIGS.8to12B, a hydrogen engine1according to a third embodiment will be described. The configuration of the hydrogen engine1according to the third embodiment is basically similar to the configuration of the hydrogen engine1according to the first embodiment. Therefore, portions different from the configuration of the hydrogen engine1according to the first embodiment will be mainly described below.

FIG.8is an enlarged cross-sectional view, similar toFIG.4, showing a portion of the cylinder head3around the injector51according to the third embodiment. As shown inFIG.8, the engine1according to the present embodiment includes a spherical check valve65and a coil spring66that biases the check valve65toward the injection hole52of the injector51.

The check valve65and the coil spring66are provided in the pressure accumulation chamber61. The check valve65and the coil spring66are arranged such that their axes coincide with the axis X of the injection hole52of the injector51. The coil spring66is disposed so as to be placed on an end surface of the pressure accumulation chamber61where the communication hole62opens. The check valve65is disposed between the coil spring66and the injector51.FIGS.9A to9Care views schematically showing the operation of the check valve65.

FIG.9Ashows a state where no hydrogen gas is injected from the injector51and no combustion of the air-fuel mixture is occurring in the combustion chamber7. Further,FIG.9Bshows a state where hydrogen gas is injected from the injector51. In addition,FIG.9Cshows a state where the combustion of the air-fuel mixture occurs in the combustion chamber7.

As shown inFIG.9A, when the hydrogen gas is not injected from the injector51and the combustion of the air-fuel mixture is not generated in the combustion chamber7, the check valve65is biased by the coil spring66to the injection hole52of the injector51to close the injection hole52. Then, as shown inFIG.9B, when the hydrogen gas is injected from the injector51, the check valve65is opened by the pressure of the hydrogen gas. In other words, the coil spring66biases the check valve65to the injection hole52by a biasing force such that the check valve65is opened by the pressure of the hydrogen gas when the hydrogen gas is injected from the injection hole52. As a result, the hydrogen gas flows from the injector51toward the communication hole62. On the other hand, as shown inFIG.9C, when the combustion of the air-fuel mixture occurs in the combustion chamber7, the check valve65is closed by the pressure in the combustion chamber7. As a result, the gas generated by the combustion in the combustion chamber7is prevented from flowing into the injection hole52of the injector51via the communication hole62and the pressure accumulation chamber61. In other words, in the present embodiment, the check valve65is configured to allow the flow of the hydrogen gas (fluid) from the injector51to the communication hole62and to prohibit the flow of the combustion gas (fluid) from the communication hole62to the injector51.

According to the present embodiment, the check valve65prevents the combustion gas from flowing backward from the combustion chamber7through the injection hole52into the injector51. Therefore, the durability of the injector51can be increased.

In the third embodiment, the check valve65is a spherical valve, and the coil spring66is used as a biasing member that biases the check valve65toward the injection hole52of the injector51. However, a valve of any shape other than a spherical valve, such as a plate valve or a cylindrical valve, can be used as the check valve65. As the biasing member, any elastic member such as a disc spring or a leaf spring can be used.

FIGS.10A to12Bare views schematically showing configurations around the pressure accumulation chamber61. In particular,FIGS.10A to12Bshow configurations around the pressure accumulation chamber61in which the check valves65and the biasing members have configurations differing from each other.

FIGS.10A and10Bshow an embodiment in which a plate valve65ais used as a check valve, and a conical coil spring66ais used as a biasing member.FIG.10Ashows a cross-sectional view around the pressure accumulation chamber61, andFIG.10Bshows a cross-sectional view around the pressure accumulation chamber61as viewed along the line B-B ofFIG.10A. As shown inFIG.10B, the plate valve65ais configured such that its outer periphery partially contacts the inner surface of the pressure accumulation chamber defining portion63. This limits the displacement of the plate valve65ain a direction perpendicular to the main flow direction of the hydrogen gas. In addition, the plate valve65ais configured such that its outer circumference is partially spaced apart from the inner surface of the pressure accumulation chamber defining portion63. This allows hydrogen gas to flow between the plate valve65aand the inner surface of the pressure accumulation chamber defining portion63.

In addition,FIGS.11A to11Cshow an embodiment in which a cylindrical valve65bis used as a check valve and a disc spring66bis used as a biasing member.FIG.11Ashows a cross-sectional view around the pressure accumulation chamber61, andFIG.11Bshows a cross-sectional view around the pressure accumulation chamber61as viewed along the line B-B ofFIG.11A. Further,FIG.11Cis a plan view of the disc spring66b. As shown inFIG.11C, the disc spring66bhas an annular portion67that contacts an inner surface of the pressure accumulation chamber defining portion63and is placed on the end surface where the communication hole62of the pressure accumulation chamber61opens, and a plurality of elastic portions68that extend inward from the annular portion67. The plurality of elastic portions68bias the cylindrical valve65band are circumferentially spaced apart from each other such that the hydrogen gas flows through between the resilient portions68.

Further, inFIGS.12A and12B, a spherical valve65is used as a check valve, and a disc spring66bis used as a biasing member.FIG.12Ashows a cross-sectional view around the pressure accumulation chamber61, andFIG.12Bis a plan view of the disc spring66b.

In the third embodiment, the pressure accumulation chamber defining portion63is formed as a part of the cylinder head3as in the first embodiment. However, similarly to the second embodiment, the pressure accumulation chamber defining portion may be configured as a pressure accumulation chamber defining member63′ separate from the cylinder head3.FIG.13is an enlarged cross-sectional view, similar toFIG.4, showing a portion of the cylinder head3around the injector51when the pressure accumulation chamber defining member63′ is provided. In the example shown inFIG.13, the pressure accumulation chamber defining member63′ is disposed in the hole45of the cylinder head3, and the spherical check valve65and the coil spring66are disposed in the pressure accumulation chamber61defined by the pressure accumulation chamber defining member63′.

Further, in the third embodiment, the coil spring66, which is a biasing member, is placed on an end surface of the pressure accumulation chamber61where the communication hole62opens. However, the biasing member may be fixed to the injector51.FIGS.14A and14Bare views, similar toFIGS.12A and12B, schematically showing the configuration around the pressure accumulation chamber61. As shown inFIGS.14A and14B, the biasing member66′ has an annular portion67′ formed in a cylindrical shape and a plurality of elastic portions68extending inward from an end portion of the annular portion67′ positioned away from the injector51. The end portion of the annular portion67′ on the injector51side is press-fitted onto the outer surface of the injector51, and is thus fixed to the injector51. Thus, in the embodiment shown inFIGS.14A and14B, the biasing member66′ is fixed to the injector51. By fixing the biasing member to the injector51in this manner, the check valve and the biasing member can be easily assembled.

While preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.