Patent Publication Number: US-2023147721-A1

Title: Engine system

Description:
TECHNICAL FIELD 
     The present disclosure relates to an engine system in which blow-by gas with a specific gravity smaller than 1 with reference to air is generatable, and to an engine system provided with a fuel supply unit that supplies a gaseous fuel to an internal space of an intake port. 
     BACKGROUND ART 
     As a related technology, an engine system (internal combustion engine) with countermeasure for blow-by gas leaking out from a combustion chamber to a crank chamber (crankcase) is known (see, for example, Patent Document 1). In the engine system according to the related technology, an intake port to take in the blow-by gas from the crank chamber is provided on an internal face portion of the crank chamber. The intake port is connected to a blow-by gas passage by an intake passage, and the engine system is so configured as to return, by the blow-by gas passage, the blow-by gas to the combustion chamber via the intake system. Here, the intake port (the blow-by gas intake portion) is placed in a position below a crank journal, thereby to avoid an interference between the blow-by gas intake portion and the crankshaft&#39;s crank journal. Also known is a dual-injection type engine system (internal combustion engine) provided with an in-cylinder injector and an intake passage injector (see, for example, Patent Document 2). In the engine system according to the related technology, adjusting (correcting) a fuel injection volume suppresses generation of a backfire seen during an execution of a purging process of fuel evaporated gas. Specifically, at the time of executing the purging process of the fuel evaporated gas seen when a sharing ratio of the in-cylinder injector and the intake passage injector is within a predetermined range, the fuel injection volume correction that corresponds to a to-be-introduced purged fuel volume is performed by changing only the fuel injection volume from the intake passage injector. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-127894 
         Patent Document 2: Japanese Unexamined Patent Application Publication No. 2006-194197 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     By the way, in an engine system using a gaseous fuel, such as hydrogen, with a specific gravity smaller than 1, for example, blow-by gas leaking out to a crank chamber is likely to stay above the crank chamber. Therefore, placing the intake port in a position below the crank journal, as in the above related technology may not be able to efficiently discharge the blow-by gas from the crank chamber. Further, in the engine system that uses the gaseous fuel such as hydrogen, for example, the fuel is, as the case may be, more easily ignited. Therefore, it is desirable, in the event of occurrence of the backfire, to perform a further backfire countermeasure in anticipation of a possible ignition of the fuel supplied in the intake port and a chain of backfires. 
     An object of the present disclosure is to provide an engine system that efficiently discharges blow-by gas from a crank chamber with ease, and an engine system that is capable of providing a further backfire countermeasure. 
     Solution to Problem 
     An engine system according to one mode of the present disclosure is an engine system in which blow-by gas with a specific gravity less than 1 with reference to air is generatable, the engine system including: a cylinder block. The cylinder block includes a cylinder and a crank chamber which are arranged in an up/down direction, the crank chamber being positioned below the cylinder. An internal peripheral face of the cylinder block has a ventilation port that connects to a ventilation passage that connects an internal space of the crank chamber with an external space out of the cylinder block, and that is open. The ventilation port is placed above a center in the up/down direction in the crank chamber. Further, the engine system according to one mode of the present disclosure, includes: an intake port, and a fuel supply unit. The intake port supplies the air to a combustion chamber. The fuel supply unit supplies a gaseous fuel to an internal space of the intake port. The fuel supply unit has an injection unit that injects the gaseous fuel. Of an internal peripheral face of the intake port, at least an intersection with a central axis of an injection area of the gaseous fuel from the injection unit has a cooled portion. 
     Advantageous Effects of Invention 
     According to the present disclosure, it is possible to provide an engine system that efficiently discharges blow-by gas from a crank chamber with ease, and an engine system that is capable of providing a further backfire countermeasure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a system diagram showing a schematic configuration of an engine system according to a first embodiment. 
         FIG.  2    is an explanatory view showing a schematic configuration of a ship provided with the engine system according to the first embodiment. 
         FIG.  3    is a schematic perspective view of an engine body of the engine system according to the first embodiment. 
         FIG.  4    is a schematic left side view of the engine body of the engine system according to the first embodiment. 
         FIG.  5    is a schematic plan view of the engine body of the engine system according to the first embodiment. 
         FIG.  6    is a schematic front view of the engine body of the engine system according to the first embodiment. 
         FIG.  7    is a schematic view partially breaking an essential portion of the engine body of the engine system according to the first embodiment. 
         FIG.  8    is a schematic explanatory view of flow of blow-by gas in the engine system according to the first embodiment. 
         FIG.  9    is a schematic view showing a ventilation passage of the engine system according to the first embodiment. 
         FIG.  10    is a schematic left side view of the engine body of the engine system according to the first embodiment. 
         FIG.  11    is a schematic view showing a positional relation between a cylinder, crank chamber, and cam chamber in a cylinder block of the engine system according to the first embodiment. 
         FIG.  12    is a schematic view of a positional relation of the cylinder, crank chamber, cam chamber, and intake manifold in the cylinder block of the engine system according to the first embodiment. 
         FIGS.  13 A to  13 D  are a schematic view showing a modified example for the positional relation between a ventilation port and gas introduction port of the engine system, and for an airflow forming portion, according to the first embodiment. 
         FIG.  14    is a schematic cross sectional view, enlarging an area around a piston of the engine system according to the first embodiment. 
         FIG.  15    is a schematic cross sectional view, enlarging the area around the piston of the engine system according to the first embodiment. 
         FIG.  16    is a schematic cross sectional view, enlarging an area around a cylinder of another example of the engine system according to the first embodiment. 
         FIG.  17    is a schematic view partially breaking an essential portion of the engine body of the engine system according to the first embodiment. 
         FIG.  18    is a schematic perspective view of showing internal configuration of a cylinder head of the engine system according to the first embodiment. 
         FIG.  19    is a schematic plan view of the internal configuration of the cylinder head of the engine system according to the first embodiment. 
         FIG.  20    is a schematic cross sectional view showing the configuration around an intake port of the engine system according to the first embodiment. 
         FIGS.  21 A and  21 B  are a schematic cross sectional view showing the configuration around the intake port of the engine system according to the first embodiment. 
         FIG.  22    is a timing chart showing an example of a controlling operation of the engine system according to the first embodiment. 
         FIG.  23    is a flowchart showing an example of the controlling operation of the engine system according to the first embodiment. 
         FIG.  24    is a flowchart showing an example of the controlling operation of the engine system according to the first embodiment. 
         FIG.  25    is a schematic view showing the positional relation between the cylinder, the crank chamber and the cam chamber in the engine system according to a modified example of the first embodiment. 
         FIG.  26    is a schematic view partially breaking an essential portion of the engine body of the engine system according to a second embodiment. 
         FIG.  27    is a schematic explanatory view of the blow-by gas flow in the engine system according to the second embodiment. 
         FIG.  28    is a schematic left side view of the engine body of the engine system according to a third embodiment. 
         FIG.  29    is a schematic cross sectional view showing the configuration around the intake port of the engine system according to a fourth embodiment. 
         FIG.  30    is a schematic cross sectional view showing the configuration around the intake port of the engine system according to a modified example of the fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A description will hereinafter be made on embodiments of the present disclosure with reference to the accompanying drawings. The following embodiments are each one example that embodies the present disclosure, and are not intended to limit the technical scope of the present disclosure. The drawings referenced in the present disclosure are all schematic views, and the respective ratios of size and thickness of each component in the drawings do not necessarily reflect the actual dimensional ratios. 
     First Embodiment 
     [1] Overall Configuration 
     First, an overall configuration of an engine system  1  according to the present embodiment will be described with reference to  FIGS.  1  to  6   .  FIG.  1    schematically shows a configuration of each portion of the engine system  1 , showing electrical connections by dashed dotted lines (toward a direction of flow of electrical signal). 
     As shown in  FIG.  1   , the engine system  1  according to the present embodiment is provided with an engine body  2  which is a main component of the engine system  1 . The term “engine” here includes an internal combustion engine that is a heat engine for generating mechanical energy (dynamic power) by combusting a fuel and that is a prime mover in which the combustion of the fuel takes place inside the engine and combustion gas is used as operation gas to convert thermal energy into the mechanical energy. That is, the engine body  2  generates the dynamic power (mechanical energy) by using the supplied fuel. 
     The engine body  2  according to the present embodiment is a reciprocating engine that converts a reciprocating movement of the piston  21  (see  FIG.  1   ) into a rotational movement, and outputs a rotational power as dynamic power. In particular, according to the present embodiment, a hydrogen fueled internal combustion engine, that is, a hydrogen fueled reciprocating engine, which uses at least hydrogen as fuel, is described as an example of the engine body  2 . 
     As an example, the present embodiment describes the engine system  1  used for a ship  10 , as shown in  FIG.  1   . This engine system  1  is mounted on a hull  100  of the ship  10 . That is, the ship  10  according to the present embodiment includes the engine system  1  and the hull  100 . The engine system  1  is used as a drive source for generating a propelling power to propel the hull  100 . 
     According to the present embodiment, the engine system  1  is further usable as a drive source for driving a generator  101  (see  FIG.  1   ) to generate electrical energy (power) for use in the hull  100 . That is, the engine system  1  is used for generating the propelling power for the hull  100  or as a drive source for driving the generator  101 . The electrical energy generated by the generator  101  may be stored in an energy storage unit. 
     The ship  10  is a moving body that sails (navigates) on water such as ocean, lake, or river. As an example of the present embodiment, the ship  10  is a “pleasure boat” that is a small-sized ship mainly used for sport, recreation, or the like. The hull  100  of the ship  10 , as shown in  FIG.  2   , has a propeller  103  and a propeller shaft  104 . By the propeller shaft  104 , the propeller  103  is connected to the engine body  2  of the engine system  1 . The ship  10  receives dynamic power generated by the engine body  2  and rotates the propeller  103  around the propeller shaft  104 , to thereby generate the propelling power to move the hull  100  forward or rearward. 
     The engine body  2  is mounted via a base platform, for example, on an internal bottom plate of an engine chamber of the hull  100 . Here, when the hull  100  is anchored on the water, the engine body  2  is placed at an inclination angle of θ 1  in one forward direction of the hull  100  relative to the horizontal plane, as shown in  FIG.  2   . Specifically, the engine body  2 , with a crankshaft  22  (see  FIG.  1   )&#39;s rotational axis Ax 1  ( FIG.  3   ) along the forward direction of the hull  100 , is placed in a “forward up” posture inclined in a manner to be higher on the forward side (side for moving forward) in the forward direction of the hull  100 . 
     Further, according to the present embodiment, the ship  10  is configured to be operated according to an operation (including a remote operation) by a person (a navigator); in particular, the ship  10  is of a manned type that can be boarded by the person as the navigator. Therefore, in the hull  100 , the ship  10  has an operation panel  102  (see  FIG.  1   ) that accepts the operation by the operator; in response to the operation on the operation panel  102 , an engine control unit  20  of the engine system  1  drives the engine body  2 . This allows the ship  10  to drive the engine body  2  in response to the navigator&#39;s operation and rotate the propeller  103 , thereby making it possible to move the hull  100  forward or rearward. Further, the hull  100  further includes various onboard facilities including a rudder mechanism, a display unit, a communication unit, and a lighting facility. When the engine system  1  is used to drive the generator  101 , the engine control unit  20  drives the engine body  2  according to a control state (generator load) of the generator  101  or the person (operator)&#39;s operation (including remote control). 
     The engine system  1  according to the present embodiment is a so-called dual-fuel engine (DF engine) which is applicable to any of a premix combustion method in which a gaseous fuel is mixed with air before flowing into a combustion chamber  50 , and a diffusion combustion method in which a liquid fuel is injected into the combustion chamber  50  for combustion. Here, the gaseous fuel is hydrogen as an example, and the liquid fuel is a fossil fuel (such as light oil or gasoline) as an example. More specifically, by using a diesel oil as the liquid fuel, the engine system  1  is applicable to any of a gas mode which uses hydrogen as fuel, and a diesel mode which uses diesel oil as fuel. Here, in the gas mode, a small volume of liquid fuel (such as light oil) may be further used as an ignition fuel. 
     For convenience of explanation, a direction along the rotational axis Ax 1  of the crankshaft  22 , as shown in  FIG.  3   , is defined as an output axis direction D 1 . Further, as shown in  FIG.  3   , a direction orthogonal to the output axis direction D 1  and along a vertical direction seen when the engine body  2  is ready for use is defined as an up/down direction D 2 , and a direction orthogonal to both the output axis direction D 1  and the up/down direction D 2  is defined as a width direction D 3 . Here, one of the output axis directions D 1  is defined as “forward” and another as “rearward”; in the crankshaft  22 , the side connected to the propeller shaft  104  (the side where a flywheel is placed) is defined as “rearward”. Similarly, one side of the width direction D 3  is defined as “leftward” and another side as “rightward”. Further, of the up/down direction D 2 , the side where a cylinder  51  (see  FIG.  1   ) is placed as seen from an after-described crank chamber  52  (see  FIG.  1   ) is defined as “upward”, and the opposite side is defined as “downward. 
     In other words, each of the directions used in the present embodiment is a direction defined with reference to the rotational axis Ax 1  of the crankshaft  22 . Here, as described above, the engine body  2 , with the crankshaft  22 &#39;s rotational axis Ax 1  along the forward direction of the hull  100 , is placed in the “forward up” posture inclined relative to the horizontal plane by the inclination angle θ 1 . Therefore, a virtual straight line extending in the up/down direction D 2  is to be inclined (to the rearward side), by the inclination angle θ 1 , relative to a vertical direction seen in a state of the engine body  2  installed on the hull  100 . However, any of the above directions is not intended to limit a use direction (a direction in use) of the engine body  2 . 
     The crankshaft  22  as an engine output shaft protrudes rearward from a rear end portion of the engine body  2 . To the crankshaft  22 , the propeller shaft  104  is connected via a reduction gear. Driving the engine body  2  thereby to rotate the crankshaft  22  around rotational axis Ax 1  rotates the propeller  103 , which connects to the propeller shaft  104 , thereby to generate a propelling power of the hull  100 . When the engine system  1  is used to drive the generator  101 , the generator  101  is connected to the crankshaft  22 . In this case, driving the engine body  2  thereby to rotate the crankshaft  22  around the rotational axis Ax 1  drives the generator  101  thereby to generate electrical energy. 
     The engine system  1  according to the present embodiment is the dual-fuel engine, as described above. Therefore, the engine system  1  can select any of the premix combustion method (gas mode) in which the gaseous fuel (hydrogen) is mixed with air for combustion, and the diffusion combustion method (diesel mode) in which the liquid fuel (light oil) is diffused for combustion, making it possible to drive the engine body  2 . Therefore, it is so configured that, the engine body  2  can be supplied with two types of fuels from outside the engine body  2 , that is, the gaseous fuel (in this case hydrogen) and the liquid fuel (in this case light oil). 
     That is, the engine system  1  has a fuel supply unit  3  for supplying the gaseous fuel and a liquid fuel supply unit  4  for supplying the liquid fuel, as shown in  FIG.  1   . 
     The fuel supply unit  3  has an injection unit  31 , a liquefied hydrogen tank  32 , a fuel supply path  33 , a vaporizer  34 , a pressure regulator valve  35 , and a gas admission valve  36 . The liquefied hydrogen tank  32  is a fuel tank that tanks the liquefied gaseous fuel (in this case hydrogen), and is connected through the fuel supply path  33  to the gas admission valve  36 . The vaporizer  34  and the pressure regulator valve  35  are inserted in the fuel supply path  33  in the following order from the upstream: vaporizer  34  and pressure regulator valve  35 . The vaporizer  34  vaporizes the liquefied hydrogen. The pressure regulator valve  35  is a gas valve unit that regulates the gaseous fuel&#39;s supply volume to the engine body  2 . From a nozzle-shaped (cylindrical) injection unit  31  into the engine body  2 , the gas admission valve  36  injects the gaseous fuel supplied through the fuel supply path  33 . 
     The liquid fuel supply unit  4  has a liquid fuel injection unit  41 . The liquid fuel supply unit  4  is connected via a liquid fuel supply path to a liquid fuel tank. From the nozzle-shaped (cylindrical) liquid fuel injection unit  41  into the engine body  2 , the liquid fuel supply unit  4  injects the liquid fuel supplied through the liquid fuel supply path. 
     Here, the injection unit  31 , which injects the gaseous fuel, is placed in a position facing the internal portion of an intake port  61  connecting to the combustion chamber  50 , and the liquid fuel injection unit  41 , which injects the liquid fuel, is placed in a position facing the combustion chamber  50 . As a result, the injection unit  31  injects the gaseous fuel into the intake port  61 , causing the gaseous fuel to mix with air thereafter to flow the mixture into the combustion chamber  50 . Meanwhile, the liquid fuel injection unit  41  directly injects the liquid fuel into the combustion chamber  50 . That is, a port injection method is used for the gaseous fuel, and a direct injection method is used for the liquid fuel. 
     The engine body  2  includes a cylinder head  6  assembled on a cylinder block  5 , as shown in  FIGS.  3  and  4   . The cylinder block  5  has a cylinder  51  (cylinder) and a crank chamber  52 . The cylinder head  6  has the intake port  61  and an exhaust port  62 . As shown in  FIG.  3   , at a lower portion of the cylinder block  5 , the crankshaft  22  is rotatably supported with the rotational axis Ax 1  in the output axis direction D 1 . 
     As shown in  FIG.  5   , the cylinder block  5  has multiple cylinders (six in the present embodiment)  51  formed to be arranged on one row (in line) along the rotational axis Ax 1  of the crankshaft  22 . That is, in the present embodiment, the engine body  2  is an in-line multi-cylinder engine (in-line 6-cylinder engine) with multiple cylinders  51  arranged in line. The output axis direction D 1  along the rotational axis Ax 1  of the crankshaft  22  and a direction of arranging the multiple cylinders  51  are consistent. In each of the cylinders  51 , as shown in  FIG.  1   , a piston  21  is housed in a manner to be slidable, i.e., reciprocable, in the up/down direction D 2 . The piston  21  is connected to the crankshaft  22  via a connecting rod  24 . 
     Multiple cylinder heads  6  are so provided as to correspond one-to-one to the multiple cylinders  51  (six in the present embodiment). The multiple cylinder heads  6  (six in the present embodiment) are fixed to the upper portion of one cylinder block  5  in a manner to cover the cylinders  51  from above, respectively. That is, of the multiple cylinder heads  6  are arranged in one row in the output axis direction D 1 . As shown in  FIG.  1   , of the internal space of each of the cylinders  51 , a space enclosed by the upper face of the piston  21  and the lower face of the cylinder head  6  functions as the combustion chamber  50 . That is, reciprocating the piston  21  the up/down direction D 2  allows the combustion chamber  50  to alternately expands and contracts. 
     In a one-to-one correspondence with the multiple cylinders  51  (six in the present embodiment), multiple head covers  71  are arranged in one row in the output axis direction D 1  to be placed on the cylinder head  6 . Inside of each of the head covers  71 , there is housed a valve operating mechanism including a push rod, a rocker arm, etc. for operating an intake valve  72  and an exhaust valve  73 . Of the intake port  61  formed in the cylinder head  6 , an opening that connects to the combustion chamber  50  is opened and closed by the intake valve  72 . Of the exhaust port  62  formed in the cylinder head  6 , an opening that connects to the combustion chamber  50  is opened and closed by the exhaust valve  73 . With this; when the intake valve  72  is open, air from the intake port  61  (intake air) can be taken into the combustion chamber  50 . When the exhaust valve  73  is open, exhaust air from the combustion chamber  50  can be discharged to the exhaust port  62 . 
     The intake valve  72  and the exhaust valve  73  are opened and closed by a camshaft  23  (see  FIG.  1   ). The camshaft  23  is housed in a cam chamber  53  placed to the left of the cylinder  51  in the cylinder block  5 , as shown in  FIGS.  1  and  6   . The cam chamber  53  is formed in the cylinder block  5  integrally with the cylinder  51 , the crank chamber  52 , etc. The cam chamber  53  extends in the output axis direction D 1 , and houses the camshaft  23  which likewise extends in the output axis direction D 1 . In conjunction with the rotation of the crankshaft  22 , the camshaft  23  rotates about the rotational axis along the output axis direction D 1 , thereby to open and close each of the intake valve  72  and the exhaust valve  73 . 
     A side cover  74  is mounted to a site above the cylinder block  5  and the left to the cylinder head  6 . That is, a step is formed at the upper portion of the left side of the engine body  2 , and the side cover  74  is so mounted as to cover this step portion. In a space covered with the side cover  74 , there are placed a liquid fuel supply rail piping, a main fuel injection pump, a pilot fuel supply rail piping, and the like. The liquid fuel supply rail piping is so placed as to extend in the output axis direction D 1 , and during combustion in the diffusion combustion method, distributes and supplies the liquid fuel to the combustion chamber  50  of each of the cylinders  51 . The liquid fuel supplied to the liquid fuel supply rail piping is distributed to the main fuel injection pump provided for each of the cylinders  51 , and the liquid fuel supplied from the main fuel injection pump is injected from the liquid fuel injection unit  41  into the combustion chamber  50 . For the purpose of the gaseous fuel ignition during the combustion in the premix combustion method, the pilot fuel supply rail piping distributes and supplies the pilot fuel to the combustion chamber  50  of each of the cylinders  51 . 
     As shown in  FIGS.  1  and  6   , on the right of the cylinder  51  in the cylinder block  5 , there is placed an intake manifold  54  for distributing and supplying, to the combustion chamber  50  of each of the cylinders  51 , the air (intake air) from outside the engine body  2 . The intake manifold  54  is formed in the cylinder block  5  integrally with the cylinder  51 , the crank chamber  52 , etc. The intake manifold  54  extends in the output axis direction D 1 , and connects to the multiple intake ports  61  formed in the multiple cylinder heads  6 . This distributes the air from the intake manifold  54  to the multiple intake ports  61 . That is, the intake manifold  54 , through the intake port  61 , communicates to the combustion chamber  50  of each of the cylinders  51 . 
     As shown in  FIG.  6   , at the upper right of the cylinder head  6 , there is placed an exhaust manifold  75  that collects the exhaust air generated by the combustion in the combustion chamber  50  of each of the cylinders  51 , thereby to discharge the exhaust air to outside of the engine body  2 . The exhaust manifold  75  extends in the output axis direction D 1 , connecting to the multiple exhaust ports  62  formed at the multiple cylinder heads  6 . This allows the exhaust air from the multiple exhaust ports  62  to be concentrated in the exhaust manifold  75 . That is, the exhaust manifold  75 , through the exhaust port  62 , communicates to the combustion chamber  50  of each of the cylinders  51 . 
     Here, the engine body  2 &#39;s main components such as the cylinder block  5 , the cylinder head  6 , and the piston  21  are made of metal materials such as aluminum alloy and cast iron. The above main components have a desired durability (including rigidity and wear resistance) and relatively excellent thermal conductivity. 
     According to the above configuration; when the engine body  2  is being driven in the diffusion combustion method, the liquid fuel is injected into the combustion chamber  50  from the liquid fuel injection unit  41 , at proper timing when the air supplied from the intake manifold  54  to each of the cylinders  51  is compressed by the piston  21 &#39;s sliding. As the liquid fuel is injected into the combustion chamber  50 , the piston  21  makes a reciprocating movement in the cylinder  51  by the propelling power acquired from an explosion caused in the combustion chamber  50 , converting the reciprocating movement of the piston  21  into a rotational movement of the crankshaft  22  via the connecting rod  24 . With this, the engine body  2  outputs the rotational power of the crankshaft  22  as dynamic power (mechanical energy). 
     Meanwhile, when the engine body  2  is being driven in the premix combustion method, the gaseous fuel supplied from the liquefied hydrogen tank  32  through the fuel supply path  33  is injected from the injection unit  31  into the intake port  61 . With this, the air supplied from the intake manifold  54  to intake port  61  mixes with the gaseous fuel in the intake port  61 . Therefore, a mixture of the air and the gaseous fuel is introduced from the intake port  61  into each of the cylinders  51 , and at the proper timing when the mixture is compressed by the piston  21 &#39;s sliding, a small volume of pilot fuel is injected into the combustion chamber  50 , thereby to ignite the gaseous fuel. The piston  21  reciprocates in the cylinder  51  by the propelling power acquired from the explosion generated in the combustion chamber  50 , converting the reciprocating movement of the piston  21  into the rotational movement of the crankshaft  22  via the connecting rod  24 . With this, the engine body  2  outputs the rotational power of the crankshaft  22  as dynamic power (mechanical energy). 
     In any of the diffusion combustion method and the premix combustion method, the exhaust air generated by the combustion (explosion) in the combustion chamber  50  is pushed out from the cylinder  51  by the movement of the piston  21 , and collected in the exhaust manifold  75  through the exhaust port  62 , followed by being discharged to the outside of the engine body  2 . 
     Further, the engine system  1  according to the present embodiment is a supercharged engine provided with a turbocharger  8  (see  FIG.  1   ) in addition to the engine body  2 . The turbocharger  8  is placed on and above the front portion of the engine body  2 , as shown in  FIGS.  3  and  4   . 
     The turbocharger  8  has an intake side turbine  81  and an exhaust side turbine  82 , as shown in  FIG.  1   . The intake side turbine  81  is placed on an intake passage  83  to take air into the intake manifold  54 . The exhaust side turbine  82  is placed on an exhaust passage  84  connecting to the exhaust manifold  75 . The exhaust side turbine  82  is connected to the intake side turbine  81 , and the flow of air (exhaust air), which is discharged through the exhaust passage  84 , rotating the exhaust side turbine  82  rotates the intake side turbine  81 . As the intake side turbine  81  rotates, the air taken in from the intake passage  83  (intake air) is compressed, and sent through an intercooler  85  to the intake manifold  54 . The intercooler  85 , as shown in  FIG.  6   , is placed along the front end face of the engine body  2 , and cools the air (intake air) compressed by the turbocharger  8 . The bold arrow in  FIG.  1    shows the flow (airflow) of air (including intake air and exhaust air). 
     By the way, in addition to the engine body  2  (and turbocharger  8 ) having the above configuration, the engine system  1  according to the present embodiment, as shown in  FIG.  1   , is further provided with the engine control unit  20 , an in-cylinder pressure sensor  76 , a revolution speed sensor  77 , etc. 
     The engine control unit  20  is mainly configured by a computer system having at least one processors such as a CPU (Central Processing Unit) and at least one storages such as a ROM (Read Only Storage) and a RAM (Random Access Storage), and executes various processes (information process). A program (engine control program) for causing at least one processor to execute the engine control method is recorded in the at least one storage in the engine control unit  20 . The engine control unit  20  outputs a control signal (electrical signal) to the pressure regulator valve  35 , the gas admission valve  36 , the liquid fuel injection unit  41 , etc., controlling the pressure regulator valve  35 , the gas admission valve  36 , the liquid fuel injection unit  41 , etc. Thereby, the engine control unit  20  can so control the engine body  2  as to adjust the engine body  2 &#39;s output (mainly, revolution speed) to an arbitrary value. 
     The in-cylinder pressure sensor  76  is placed at a position facing the combustion chamber  50  of each of the cylinders  51 , measures the pressure in the combustion chamber  50 , and outputs, to the engine control unit  20 , an electrical signal that corresponds to the measured value (pressure). The revolution speed sensor  77  measures the number of revolutions (and rotational angle) of the crankshaft  22 , and outputs, to the engine control unit  20 , an electrical signal that corresponds to the measured value (the number of revolutions). 
     [2] Definition 
     The term “blow-by gas” in the present disclosure means, of the combustion gas (exhaust), the uncombusted gas, etc. which became high in pressure in the compression stroke or combustion stroke of the engine body  2 , the gas that leaked out from the cylinder  51  (combustion chamber  50 ) to the crank chamber  52  through a gap between an internal peripheral face of the cylinder  51  and an external peripheral face of the piston  21 . That is, the term “the blow-by gas” includes “compressed leak gas”, which becomes high in pressure during the compression stroke and which is the mixture in the combustion chamber  50 , leaks out to the crank chamber  52 . That is, when the uncombusted gas, etc. in the combustion chamber  50  exceeds a piston ring (compression ring)&#39;s seal capacity for ensuring airtightness between the cylinder  51  and the piston  21 , the uncombusted gas, etc. in the combustion chamber  50  as the blow-by gas leaks out to the crank chamber  52 , as the case may be. 
     The term “specific gravity” referred to in the present disclosure means the ratio of the density of a certain substance to the density of a reference substance; the specific gravity for gas is expressed as the ratio of the gas&#39;s density to the density of air as the reference substance at the same temperature and same pressure. Therefore, when the specific gravity of the blow-by gas as a gaseous body, is smaller than “1”, the mass of the blow-by gas is smaller (i.e., lighter) than the air of the same volume (as the blow-by gas) at the same temperature and same pressure as the blow-by gas. Conversely, when the specific gravity of the blow-by gas as the gaseous body is greater than “1”, the mass of the blow-by gas is greater (i.e., heavier) than the air of the same volume (as the blow-by gas) at the same temperature and same pressure as the blow-by gas. As an example, the specific gravity of hydrogen is “0.06952” which is well below “1”, so when the main component of the blow-by gas is hydrogen, the specific gravity of the blow-by gas is smaller than “1”, therefore, the blow-by gas is lighter than the air of the same volume at the same temperature and same pressure. Alternatively, the specific gravity of the gas may be expressed as the ratio of the gas&#39;s density to the density of air as a reference substance in a standard condition (0° C., 1 atm). 
     The term “backfire” referred to in the present disclosure means, for example, a flame that is unintentionally ignited in the combustion chamber  50 , the intake port  61 , etc., in the intake stroke, and that is present in the combustion chamber  50 , the intake port  61 , etc. Therefore, when the backfire occurs in the intake stroke (with the intake valve  72  open), the intake port  61  may be exposed to the flame. 
     The term “parallel” referred to in the present disclosure means a relation that, in addition to the case where two straight lines on one plane do not intersect no matter how far they are extended, that is, the angle between the two is strictly 0 degree (or 180 degree), the angle between the two is within an error range of several degrees (less than 10 degree, for example) relative to 0 degree. Similarly, the term “orthogonal” referred to in the present disclosure means a relation that, in addition to the case where the angle of intersection between the two is exactly 90 degrees, the angle between the two is within an error range of several degrees (less than 10 degrees, for example) relative to 90 degrees. 
     [3] Configuration of Cylinder Block 
     Then, the configuration of the cylinder block  5  (and its surrounding configuration) of the engine body  2  is to be described in more detail with reference to  FIGS.  7  through  16   .  FIG.  7    shows a schematic view of the engine body  2  from the rear side (side from which the crankshaft  22  protrudes) which is one side in the output axis direction D 1 , partially breaking the cylinder block  5  and adding diagonal lines (hatching) to a main cross section.  FIG.  7    properly omits the side cover  74  and the like. 
     In the present embodiment, in addition to the cylinder  51  and the crank chamber  52 , as described above, the cylinder block  5  is formed with the cam chambers  53  and the intake manifold  54 . The cylinder  51 , the crank chamber  52 , the cam chamber  53 , and the intake manifold  54  all include compartments (chambers) that are separated from each other inside the cylinder block  5 , and each has its own internal space. Therefore, an internal peripheral face of each of the cylinders  51 , the crank chamber  52 , the cam chamber  53 , and the intake manifold  54  is included in an internal peripheral face  501  of the cylinder block  5 . Specifically, the crank chamber  52  is placed in the lower portion of the cylinder block  5 , and the cylinder  51 , the cam chamber  53 , and the intake manifold  54  are placed above crank chamber  52 . Of the cylinder  51 , the cam chamber  53  and the intake manifold  54 , the cylinder  51  is placed in the center of the width direction D 3 , the cam chamber  53  is placed to the left of the cylinder  51 , and the intake manifold  54  is placed to the right of the cylinder  51 . Thus, the cylinder block  5  includes the cylinder  51  and the crank chamber  52  which are arranged in the up/down direction D 2 , with the crank chamber  52  placed below the cylinder  51 . 
     Here, in  FIG.  7   , the cylinder  51 , the crank chamber  52 , the cam chamber  53  and the intake manifold  54  are shown one by one, but in reality, the multiple cylinders  51 (six in the present embodiment) are arranged in the output axis direction D 1  (perpendicular to the paper face in  FIG.  7   ). Meanwhile, the crank chambers  52  are partitioned in the output axis direction D 1  by a partition wall  521  placed between the adjacent cylinders  51 , but is integrally continuous by a communicating hole  522  formed at the lower portion of the partition wall  521 . That is, the crank chambers  52  include a single compartment (chamber) connecting in the output axis direction D 1 . Further, an opening portion  531  is formed in the lower face of the cam chamber  53 , and an internal space of the cam chamber  53  is continuous with an internal space Sp 1  of the crank chamber  52  through the opening portion  531 . The intake manifold  54  includes a single compartment (chamber) extending in the output axis direction D 1 . 
     The cylinder  51  is formed in the shape of a cylinder extending in the up/down direction D 2 , and inside which the piston  21  is housed for reciprocating movement along the up/down direction D 2 . The cylinder  51 &#39;s both end faces in the up/down direction D 2  are open. The piston  21  is a cylindrical member having an external diameter that corresponds to an internal diameter of the cylinder  51 , and the internal space of the cylinder  51  is bisected in the up/down direction D 2  by the piston  21 . Then, of the internal spaces of the cylinder  51 , the space above the piston  21 , i.e., the space enclosed by the upper face of the piston  21  and the lower face of cylinder head  6  is the combustion chamber  50 . Meanwhile, of the internal spaces of the cylinder  51 , the space below the piston  21  is continuous with the internal space Sp 1  of the crank chamber  52 . 
     In the present embodiment, the piston  21  is made of a hollow member with a lower face (the face facing the crank chamber  52 ) opened. That is, the piston  21  has a cylindrical portion  211  and a bulkhead  212 . The cylindrical portion  211  is a cylindrical site with both end portions open in the up/down direction D 2 , and the bulkhead  212  is a site that covers the upper face of the cylindrical portion  211 . Here, the cylindrical portion  211  and the bulkhead  212  are integrally formed, and the piston  21  as a whole is formed into a bottomed cylindrical shape. Therefore, strictly speaking, of the internal spaces of the cylinder  51 , the combustion chamber  50 , and a space continuous with the internal space Sp 1  of the crank chamber  52  are separated by the bulkhead  212 . In other words, the space above the bulkhead  212  is the combustion chamber  50 , and the space below the bulkhead  212 , including the internal space of the cylindrical portion  211 , is continuous to the internal space Sp 1  of the crank chamber  52 . The connecting rod  24 , with its upper end portion inserted into the piston  21 , is supported by the piston  21 . 
     In the present embodiment, the cylinder  51  is composed of a cylinder liner  511  that guides the piston  21 . The cylinder liner  511 , which is a cylindrical component, has the piston  21  slide relative to an internal peripheral face of the cylinder liner  511 , thereby to regulate the movement direction (up/down direction D 2 ) of the piston  21 . The cylinder liner  511  is supported at a liner support wall  55  of the cylinder block  5 . The liner support wall  55  is a cylindrical site that is one-step greater in internal diameter than the cylinder liner  511 , and the cylinder liner  511 , by being fitted into the liner support wall  55 , is fixed to the cylinder block  5 . Here, the cylinder liner  511 &#39;s dimension in the up/down direction D 2  is greater than the liner support wall  55 &#39;s dimension in the up/down direction D 2 , and the lower end portion of the cylinder liner  511  protrudes downward (toward the crankshaft  22  side) from the lower face of the liner support wall  55 . In short, in the present embodiment, the cylinder block  5  has the liner support wall  55  that supports the cylinder liner  511  included in the cylinder  51 . The lower end of the cylinder liner  511  protrudes downward from the lower end of the liner support wall  55 . 
     The crank chamber  52  is placed below the cylinder  51 , as described above. In the internal space Sp 1  of the crank chamber  52 , the crankshaft  22  is housed in a manner to be rotatable around the rotational axis Ax 1 . The crankshaft  22  is rotatably supported by the partition wall  521  and rotates in conjunction with the reciprocating movement of the piston  21  connected via the connecting rod  24 . Here, by the piston  21 , the crank chamber  52  is separated from the combustion chamber  50  that is of the internal spaces of the cylinder  51  and that is above the piston  21 . However, for example, in the compression stroke causing a high pressure in the combustion chamber  50 , the blow-by gas such as uncombusted gas, as the case may be, leaks out from the combustion chamber  50  to the crank chamber  52  through the gap between the cylinder  51  and the piston  21 , as described above. 
     By the way, as a related technology, an engine system is known that takes countermeasure against the blow-by gas leaking out from the combustion chamber  50  to the crank chamber  52 . In the engine system according to the related technology, the internal peripheral face portion of the crank chamber  52  is provided with an intake port to take in the blow-by gas from the crank chamber  52 . The intake port is connected to a blow-by gas passage by an intake passage, and the engine system is configured to return, by the blow-by gas passage, the blow-by gas to the combustion chamber  50  via an intake system. Here, the intake port (blow-by gas intake portion) is placed in a position below a crank journal, thereby to avoid an interference between the blow-by gas intake portion and the crankshaft  22 &#39;s crank journal. 
     However, in the engine system  1  that uses the gaseous fuel such as hydrogen with a specific gravity smaller than 1, for example, the blow-by gas having leaked out to the crank chamber  52  is likely to stay above the crank chamber  52 . Therefore, when the intake port is placed in the position below the crank journal as in the above related technology, the blow-by gas may not be efficiently discharged from the crank chamber  52 . 
     Therefore, in the present embodiment, adopting the configuration described below makes it possible to provide the engine system  1  that efficiently discharges the blow-by gas from the crank chamber  52  with ease. 
     That is, the engine system  1  according to the present embodiment is an engine system  1  in which the blow-by gas with a specific gravity smaller than 1 with reference to air is generatable. In the above engine system  1 , the internal peripheral face  501  of the cylinder block  5  has a ventilation port  502  that is open. The ventilation port  502  is an opening (hole) connecting to a ventilation passage  503  that connects the internal space Sp 1  of the crank chamber  52  with an external space out of the cylinder block  5 . The ventilation port  502  is placed above a center C 1  in the up/down direction D 2  in the crank chamber  52 . 
     In short, in the engine system  1  where using the gaseous fuel such as hydrogen with a specific gravity of less than 1, for example, may generate the blow-by gas with a specific gravity of less than 1 (with reference to air), adopting the above configuration makes it possible to efficiently discharge the blow-by gas. In the engine system  1  of this type, the blow-by gas leaking out to the crank chamber  52  is likely to stay above the crank chamber  52 . In the engine system  1  according to the present embodiment, the ventilation port  502  is placed above the center C 1  in the crank chamber  52 , thus making it possible to efficiently discharge, from the ventilation port  502 , the blow-by gas that stays above the crank chamber  52 . That is, since the ventilation port  502  serving as an outlet of the blow-by gas is formed in a site above the crank chamber  52 , in which site the blow-by gas stays, the blow-by gas is efficiently discharged from the internal space Sp 1  of the crank chamber  52  via the ventilation port  502  (and ventilation passage  503 ). The above can provide the engine system  1  that efficiently discharges the blow-by gas from the crank chamber  52  with ease. 
     Specifically, as shown in  FIG.  7   , the center C 1  in the crank chamber  52  in the up/down direction D 2  is set at a position that bisects the crank chamber  52 &#39;s dimension (height dimension) L 1  in the up/down direction D 2 . That is, the center C 1  is set at a position that is equidistant from both the upper end and lower end of the crank chamber  52 . The ventilation port  502  is so placed as to be positioned on the upper side in the up/down direction D 2 , that is, on the cylinder  51  side, as viewed from this center C 1 . In plan view, the ventilation port  502  is open in a circular shape (true circle) that is large enough to allow the blow-by gas to pass through, for example. However, the ventilation port  502 , not limited to the circular shape, may be open in an oval shape, a square shape, or a polygonal shape, for example. 
     More in detail, the ventilation port  502  is placed above the lower end of the cylinder  51 . That is, in the up/down direction D 2 , the ventilation port  502  is placed above the center C 1  of the crank chamber  52 , and above the lower end of the cylinder  51 . The lower end of the cylinder  51  here is the cylinder  51 &#39;s lowest site that faces the crank chamber  52 . In the present embodiment, the cylinder liner  511  included in the cylinder  51  protrudes downward from the lower end of the liner support wall  55 , as described above, so the lower end (lower face) of the cylinder liner  511  is the lower end of the cylinder  51 . As shown in  FIG.  7   , the lower end of the cylinder  51  (lower end of the cylinder liner  511 ) is placed above the center C 1  in the crank chamber  52  in the up/down direction D 2 , and the ventilation port  502  is placed further above the lower end of the above cylinder  51 . 
     With this, after leaking out from the lower end of the cylinder  51  to the crank chamber  52 , the blow-by gas which has the specific gravity of less than 1 is likely to be directed to the ventilation port  502  side positioned above the lower end of the cylinder  51 . As a result, it becomes easy to more efficiently discharge the blow-by gas from the crank chamber  52 , making it possible to improve the performance of discharging the blow-by gas. 
     The ventilation port  502  opens downward. Here, in the up/down direction D 2 , the crank chamber  52  side is “down” viewed from the cylinder  51 , so the ventilation port  502  is to open toward the crank chamber  52  side as viewed from the cylinder  51 . Since the ventilation port  502  is open in the internal peripheral face  501  of the cylinder block  5 , the ventilation port  502  is formed in the downward-facing site of the internal peripheral face  501 , i.e., the site serving as an upper face, thus realizing the ventilation port  502  open downward. It is sufficient that the ventilation port  502  should open downward, including not only a configuration that opens strictly straight down, but also a configuration that opens diagonally downward. That is, a normal of an opening face of the ventilation port  502  may be parallel to the up/down direction D 2 , or may be inclined relative to the up/down direction D 2 . 
     With this, after leaking out from the lower end of the cylinder  51  to the crank chamber  52 , the blow-by gas which has the specific gravity of less than 1 is likely to be discharged from the ventilation port  502  at the time of flowing upward. As a result, it becomes easy to more efficiently discharge the blow-by gas from the crank chamber  52 , making it possible to improve the performance of discharging the blow-by gas. 
     In the present embodiment, as described above, the cylinder block  5  connects to the crank chamber  52 , and further includes the cam chamber  53  that houses the camshaft  23 . Here, the ventilation port  502  is formed in the cam chamber  53 . In short, as shown in  FIG.  7   , the ventilation port  502  is placed in the cam chamber  53 , of the cylinder block  5  which includes the cylinder  51 , the crank chamber  52 , the cam chamber  53 , etc. Here, as an example, the ventilation port  502  is formed at the cam chamber  53 &#39;s position above the camshaft  23 , i.e., at an upper wall portion  532  of the cam chamber  53 . Here, the ventilation port  502  penetrates the upper wall portion  532  in the up/down direction D 2 . The internal space of the cam chamber  53  is continuous with the internal space Sp 1  of the crank chamber  52  through the opening portion  531 , so the blow-by gas leaking out to the crank chamber  52  is introduced into the cam chamber  53  through the opening portion  531 . 
     With this, using the space to house the camshaft  23 , without having to build a new space to form the ventilation port  502 , can efficiently discharge the blow-by gas from the crank chamber  52 . Moreover, since the cam chamber  53  is positioned above the crank chamber  52 , the blow-by gas with the specific gravity less than 1, after leaking out to the crank chamber  52 , can easily collect to the cam chamber  53  formed with the ventilation port  502 , making it possible to improve the performance of discharging the blow-by gas. 
     As an example of the present embodiment, the ventilation passage  503  is a cylindrical pipe (tube) that extends straight from the ventilation port  502  along the up/down direction D 2 , as shown in  FIG.  7   . The ventilation passage  503  is coupled to the ventilation port  502 , serving as a passage of the blow-by gas discharged from the ventilation port  502 . The tip (opposite the ventilation port  502 ) of the ventilation passage  503  is placed in a proper position of a space outside the cylinder block  5 . As an example, the tip of the ventilation passage  503  may be placed inside the side cover  74  or outside the side cover  74 . Further, the tip of the ventilation passage  503  may be positioned outside the hull  100  in which the engine body  2  is mounted or may be connected to a ventilation unit provided in the engine chamber of the hull  100 . 
     The ventilation passage  503  is, however, not limited to this configuration, and may be shaped other than cylindrical, such as a square cylinder, or may be a tube or a hose, for example. Further, as long as being able to be configured to serve as the blow-by gas&#39;s passage between the internal space Sp 1  of the crank chamber  52  and the external space out of the cylinder block  5 , the ventilation passage  503  need not even be a cylindrical member. That is, as long as the ventilation port  502  ultimately connects to the external space out of the cylinder block  5  through the ventilation passage  503 , the internal space of the side cover  74 , for example, may serve as the ventilation passage  503 . 
     According to the configuration described above, as shown in  FIG.  8   , the blow-by gas is efficiently discharged from the internal space Sp 1  of the crank chamber  52  via the ventilation port  502  (and ventilation passage  503 ). In  FIG.  8   , the flow of the blow-by gas is shown by bold arrows. That is, the uncombusted gas or the like leaks from the combustion chamber  50  to the crank chamber  52  through the gap between the cylinder  51  and the piston  21 , generating the blow-by gas. In the present embodiment, using the gaseous fuel (hydrogen) with the specific gravity smaller than 1 also makes the specific gravity smaller than 1 for the blow-by gas, thereby to cause the blow-by gas having leaked out to the crank chamber  52  to move upward in the crank chamber  52 . Above the crank chamber  52 , there is provided the cam chamber  53  connected, by the opening portion  531 , to the internal space Sp 1  of the crank chamber  52 , thereby to allow the blow-by gas, which moves upward, to flow into the cam chamber  53  through the opening portion  531 . As a result, the blow-by gas is discharged from the ventilation port  502  of the cam chamber  53 , and is discharged through the ventilation passage  503  to the external space out of the cylinder block  5 . 
     As shown in  FIG.  9   , the ventilation passage  503  has a gas/liquid separating portion  504  to separate the gas from the liquid. The gas/liquid separating portion  504 , as an example, includes a protruding wall provided inside the ventilation passage  503 . The protruding wall as the gas/liquid separating portion  504  protrudes from an internal peripheral face of the ventilation passage  503  toward a central axis of the ventilation passage  503 . In the present embodiment, multiple protruding walls as the gas/liquid separating portions  504  are so provided that, of the internal peripheral faces of the ventilation passage  503 , the protruding wall protruding from one side (left) of the width direction D 3  and the protruding wall protruding from the another side (right) of the width direction D 3  are alternately arranged in the up/down direction D 2 . The protruding wall protruding from the one side (left) of the width direction D 3  and the protruding wall protruding from the other side (right) of the width direction D 3  overlap at their tip portions in the up/down direction D 2 . 
     Providing the above gas/liquid separating portion  504  causes the inside of the ventilation passage  503  to be a labyrinth configuration, and the blow-by gas introduced from the ventilation port  502  into the ventilation passage  503  flows in the ventilation passage  503  while meandering between the protruding walls as the gas/liquid separating portions  504 . When the blow-by gas contacts the protruding wall as the gas/liquid separating portion  504 , a liquid such as oil or moisture discharged together with the blow-by gas adheres to the protruding wall as the gas/liquid separating portion  504 . With this, the liquid (oil or moisture, etc.) discharged together with the blow-by gas is captured by the gas/liquid separating portion  504  and is separated from the gas included in the blow-by gas. As a result, the blow-by gas is exhausted from the ventilation passage  503  with at least a part of the liquid component such as oil removed, connecting to suppressing of oil consumption, etc. involved in the exhausting of the blow-by gas. 
     The gas/liquid separating portion  504  is not limited to the protruding wall as described above, but is sufficient as long as having the function of separating the liquid from the blow-by gas discharged from the ventilation port  502 . The gas/liquid separating portion  504  may be, for example, a filter or the like placed in the ventilation passage  503 , or a combination of the protruding wall and the filter. 
     By the way, the engine body  2  according to the present embodiment is an in-line multi-cylinder engine (in-line 6-cylinder engine) with the multiple cylinders  51  (six in the present embodiment) arranged in line, as described above. In this type of engine, where the blow-by gas may occur for each of the multiple cylinders  51 ; according to the present embodiment, only one blow-by gas discharging ventilation port  502  is provided for the multiple cylinders  51 . In other words, the ventilation port  502  is shared by the multiple cylinders  51 . That is, according to the present embodiment, the crank chamber  52  includes a single compartment (chamber) connecting in the output axis direction D 1 , as described above. Therefore, no matter which of the multiple cylinders  51  generates the blow-by gas, the blow-by gas it so eventually leak out to the same crank chamber  52 . With this, it is sufficient to have only one blow-by gas discharging ventilation port  502  for the multiple cylinders  51 . 
     Specifically, as shown in  FIG.  10   , the multiple cylinders  51  are provided to be arranged in the output axis direction D 1 , and the multiple cylinders  51  include a one end side cylinder  51 A and another end side cylinder  51 B which are positioned on respective sides in the output axis direction D 1 . Here, the ventilation port  502  is placed at a position that corresponds to the one end side cylinder  51 A. In short, of the six cylinders  51  arranged in the output axis direction D 1 , the cylinder  51  on the one end (front end in the present embodiment) side in the output axis direction D 1  is defined as “one end side cylinder  51 A”, and the cylinder  51  on the other end (rear end in the present embodiment) side in the output axis direction D 1  is defined as “the other end side cylinder  51 B. In this case, in the cam chamber  53 , the ventilation port  502  is formed in a position that corresponds to the one end side cylinder  51 A, i.e., at the front end portion. The ventilation passage  503  is so provided as to extend upward from this ventilation port  502 . 
     Thus, it is sufficient that the ventilation port  502  should be at one position for the multiple cylinders  51 , as a result, making it possible to simplify the configuration for discharging the blow-by gas. In particular, according to the present embodiment, the engine body  2  is placed in the “front up” posture (see  FIG.  2   ), so the blow-by gas having leaked out to the crank chamber  52  is likely to be concentrated on the front end portion side positioned relatively upper. Therefore, in the configuration where the ventilation port  502  is placed at the front end portion of (the cam chamber  53  in) the cylinder block  5 , it is possible to more efficiently discharge the blow-by gas from the exhaust pipe  105  (see  FIG.  2   ) mounted in the hull  100 . 
     Further, in the present embodiment, for more smoothly exhausting the blow-by gas from the ventilation port  502 , the internal peripheral face  501  of the cylinder block  5  has a gas introduction port  505  that connects the internal space Sp 1  of the crank chamber  52  with the external space out of the cylinder block  5 , and that is open, as shown in  FIG.  11   .  FIG.  11    is a schematic view of the cylinder block  5 , schematically showing the positional relation between the cylinder  51 , the crank chamber  52 , and the cam chamber  53 . 
     Providing the above gas introduction port  505  separately from the ventilation port  502  makes it possible to take in fresh air into the internal space Sp 1  of the crank chamber  52  at the time of the exhausting of the blow-by gas from the ventilation port  502 . As a result, the ventilation (exhaust of the blow-by gas) of the internal space Sp 1  of the crank chamber  52  can be more smoothly performed. In plan view, the gas introduction port  505  has a circular (true circle) opening, for example, large enough to allow air to pass through. However, the gas introduction port  505  is not limited to the circular shape, but may have oval, square, or polygonal openings, for example. 
     As shown in  FIG.  11   , in the output axis direction D 1  along the rotational axis Ax 1  of the crankshaft  22  placed in the crank chamber  52 , the ventilation port  502  and the gas introduction port  505  are placed at positions different from each other. That is, the ventilation port  502  and the gas introduction port  505  are offset from each other in the output axis direction D 1 . In the example in  FIG.  11   , the gas introduction port  505  is placed at a position that corresponds to the other end side cylinder  51 B present on the other end side in the output axis direction D 1 , i.e., at the rear end portion of the cylinder block  5 . In short, the ventilation port  502  is placed at the one end (front end in the present embodiment) side in the output axis direction D 1 , whereas the gas introduction port  505  is placed at the other end (rear end in the present embodiment) side in the output axis direction D 1 . 
     According to this configuration, the gas (air) introduced from the gas introduction port  505  flows toward the ventilation port  502  thereby to form an airflow along the output axis direction D 1 , thus making it possible to cause the airflow to act across a wide range in the output axis direction D 1 . Therefore, the performance of discharging the blow-by gas by airflow can be further improved. 
     In particular, in the present embodiment, the ventilation port  502  is placed at the position (front end portion) that corresponds to the one end side cylinder  51 A, whereas the gas introduction port  505  is placed at the position that corresponds to the other end side cylinder  51 B (rear end section). Thus, placing the ventilation port  502  and the gas introduction ports  505  at respective end portions of the cylinder block  5  in the output axis direction D 1  can cause the airflow to act across substantially the entire area in the output axis direction D 1  in the crank chamber  52 . Therefore, the performance of discharging the blow-by gas by airflow can be further improved. 
     In the present embodiment, the ventilation port  502  and the gas introduction port  505  are, in plan view, placed on opposite sides sandwiching therebetween the rotational axis Ax 1  of the crankshaft  22  placed in the crank chamber  52 . That is, in plan view, the ventilation port  502  is placed on the one side (left side in the present embodiment) of the width direction D 3  as viewed from the rotational axis Ax 1 , while the gas introduction port  505  is placed on the other side (right side in the present embodiment) of the width direction D 3  as viewed from the rotational axis Ax 1 . The gas introduction port  505  is, as an example, so formed in the right side wall of the crank chamber  52  as to penetrate the right side wall of the crank chamber  52 . In this way, the ventilation port  502  and the gas introduction port  505  are placed on opposite sides sandwiching therebetween the rotational axis Ax 1 , making it possible to cause the airflow to act across the wide range in the width direction D 3  in the crank chamber  52 . Therefore, the performance of discharging the blow-by gas by airflow can be further improved. 
     Further, in the present embodiment, the gas introduction port  505  is placed below the center C 1  (see  FIG.  7   ) in the crank chamber  52  in the up/down direction D 2 . This allows the airflow by the gas (air) introduced from the gas introduction port  505  to flow diagonally upward toward the ventilation port  502  thereby to form the airflow along the up/down direction D 2 , making it possible to cause the airflow to act across the entirety of the crank chamber  52 . Therefore, the performance of discharging the blow-by gas by airflow can be further improved. 
     Here, the engine system  1  is further provided with an airflow forming portion  506 , as shown in  FIG.  12   . The airflow forming portion  506  forms the airflow from the gas introduction port  505  toward the ventilation port  502 .  FIG.  12    is a schematic view of the cylinder block  5 , schematically showing the positional relation between the cylinder  51 , the crank chamber  52 , the cam chamber  53 , and the intake manifold  54 . In the present embodiment, as an example, the turbocharger  8  is used for the airflow forming portion  506 . Specifically, the airflow forming portion  506  includes a bypass pipe that connects between the intake manifold  54  and the gas introduction port  505 . The bypass pipe as the airflow forming portion  506  forms, for example, an air passage from the intake manifold  54 &#39;s end position (rear end portion in the present embodiment) on the airflow&#39;s downstream side to the gas introduction port  505 . As a result, the air (intake air) compressed by the turbocharger  8  is sent through the intercooler  85  to the intake manifold  54 , and is further sent through the bypass pipe, as the airflow forming portion  506 , to the gas introduction port  505 . As a result, the compressed air causes the gas introduction port  505  to be in a state of a positive pressure relative to the internal space Sp 1  of the crank chamber  52 , generating, in the crank chamber  52 , an airflow in the direction of pushing out the gas (the blow-by gas) from the ventilation port  502 . 
     In this way, providing the airflow forming portion  506  can coercively form the airflow in the internal space Sp 1  of the crank chamber  52 , making it difficult for the blow-by gas to stay in the crank chamber  52 . That is, the airflow forming portion  506  promotes the blow-by gas&#39;s being discharged from the ventilation port  502 , making it possible to further improve the performance of discharging the blow-by gas. Moreover, the turbocharger  8  is used for the airflow forming portion  506  in the present embodiment, thus causing no need for setting a new unit to form the airflow. 
       FIGS.  13 A,  13 B,  13 C,  13 D  show a modified example about the positional relation between the ventilation port  502  and the gas introduction port  505 , and about the airflow forming portion  506 . In the modified example shown in  FIG.  13 A , the ventilation port  502  is placed in a center portion of the cylinder block  5  in the output axis direction D 1 , and the gas introduction ports  505  are placed both end portions of the cylinder block  5  in the output axis direction D 1 , respectively. In this example, the gas (air) introduced from the gas introduction ports  505  formed in the two positions flow toward the ventilation port  502  in the one position, thereby forming the air flow along the output axis direction D 1 . 
     In the modified example shown in  FIG.  13 B , the airflow forming portion  506  includes an air tank installed on the hull  100 , sending the air from the air tank into the gas introduction port  505 . In the modified example shown in  FIG.  13 C , the airflow forming portion  506  includes an electric fan, sending the air from the electric fan into the gas introduction port  505 . In any example in  FIG.  13 B  and  FIG.  13 C , the gas introduction port  505  is brought into a state of a positive pressure relative to the internal space Sp 1  of the crank chamber  52 , generating, in the crank chamber  52 , the airflow in the direction of pushing the gas (the blow-by gas) out from the ventilation port  502 . 
     Meanwhile, in the modified example shown in  FIG.  13 D , the airflow forming portion  506  includes an electric fan, drawing in the blow-by gas from the ventilation port  502 , by the electric fan. In this example, the downstream side (ventilation passage  503  side) of the ventilation port  502  becomes in a state of a negative pressure relative to the internal space Sp 1  of the crank chamber  52 , generating, in the crank chamber  52 , an airflow in the direction in which the gas (the blow-by gas) is drawn in from the gas introduction port  505  to the ventilation port  502 . Thus, the airflow forming portion  506  may form the airflow by generating any of the positive pressure and the negative pressure, or may be configured to generate both of the positive pressure and the negative pressure. In the modified examples of  FIG.  13 C  and  FIG.  13 D , a pump, for example, may be used instead of the electric fan. 
     The configuration of the piston  21  of the engine system  1  according to the present embodiment is described more in detail below, with reference to  FIGS.  14  and  15   .  FIGS.  14  and  15    are each a schematic cross sectional view of an enlarged area around the piston  21 . 
     In a piston internal space  210  formed inside the piston  21  that reciprocates along the up/down direction D 2  in the cylinder  51 , a stirring portion  213  that reciprocates along the up/down direction D 2  as the piston  21  moves is placed, as shown in  FIG.  14   . According to the present embodiment, a feather-like protrusion protruding from the internal peripheral face of the cylindrical portion  211  of the piston  21  toward the central axis of the piston  21  constitutes the stirring portion  213 . The piston internal space  210  is a cylindrical space enclosed by the cylindrical portion  211  of the piston  21 , and is a space separated from the combustion chamber  50  by the bulkhead  212  of the piston  21 . The connecting rod  24 , with its upper end portion inserted into the piston internal space  210 , is supported by the piston  21 . The stirring portions  213  are formed around the entire circumference of the cylindrical portion  211 , and are so provided in multiplicity (two in this case) as to be spaced apart in the up/down direction D 2 . 
     In short, the piston internal space  210  continuous with the internal space Sp 1  of the crank chamber  52  is provided with the stirring portion  213  that reciprocates as the piston  21  moves. Being provided in the above manner, the stirring portion  213  reciprocates in the piston internal space  210  as the piston  21  reciprocates, thus stirring the gas in the piston internal space  210 . Therefore, even if the blow-by gas such as uncombusted gas leaks out from the combustion chamber  50  to the piston internal space  210  through the gap between the cylinder  51  and the piston  21 , the blow-by gas in the piston internal space  210  is caused to actively flow, making it easy to move the blow-by gas to the crank chamber  52 . Therefore, it is easier to suppress the blow-by gas from staying in the piston internal space  210 , making it possible to expect a further improvement of the performance of discharging the blow-by gas. 
     As long as having the configuration of being provided in the piston internal space  210  and reciprocating according to the movement of the piston  21 , the stirring portion  213  is not limited to the protrusion protruding from the cylindrical portion  211  of the piston  21 , and may be a protrusion protruding from the upper end portion of the connecting rod  24 , for example. That is, the connecting rod  24 &#39;s protrusion provided above the lower end of the piston  21 , like the above stirring portion  213 , can stir the gas in the piston internal space  210  as the piston  21  reciprocates. The stirring portion  213  may be provided on both of the piston  21  and the connecting rod  24 . 
     It is preferable that, as shown in  FIG.  15   , of the piston  21  that reciprocates along the up/down direction D 2  in the cylinder  51 , the bulkhead  212  that separates the internal space of the cylinder  51  in the up/down direction D 2  has a cavity portion  214  inside. Specifically, fixing a plate  215  to the lower face (the side opposite the combustion chamber  50 ) of the bulkhead  212  by a proper method such as welding causes the bulkhead  212  to have a double-layered configuration. With this, on the upper side of the plate  215  (combustion chamber  50  side), the cavity portion  214  as a heat-insulating layer is formed. 
     In short, of the internal spaces of the cylinder  51 , the combustion chamber  50 , and the space continuous with the internal space Sp 1  of crank chamber  52  are separated by the bulkhead  212 , thus exposing the upper face of the bulkhead  212  to the combustion chamber  50 . Therefore, in the configuration without the cavity portion  214 , as shown in  FIG.  14   , heat of the upper face of the bulkhead  212  is likely to be transferred to the rear face (lower face) side of the bulkhead  212 , causing a possibility of heating the blow-by gas which is mainly composed of hydrogen, etc., for example. In contrast, according to the  FIG.  15   &#39;s configuration in which the cavity portion  214  is formed as the heat-insulating layer, the heat is unlikely to be transferred to the lower face side of the plate  215  at the cavity portion  214 . Therefore, the blow-by gas mainly composed of hydrogen and the like can be suppressed from being heated by the heat of the combustion chamber  50  can suppress the heating of. 
     In addition to or instead of the stirring portion  213 , as the configuration for actively flowing the blow-by gas in the piston internal space  210 , a stirring nozzle  216  may be provided, as shown in  FIG.  16   . In each of the cylinders  51 , the stirring nozzle  216  is provided in a position where its tip portion faces the internal space of the cylinder  51  from the lower face of the cylinder  51 . The stirring nozzle  216  intermittently or continuously injects the gas (e.g., air) or the liquid (e.g., oil) toward the internal portion of the cylinder  51 . This causes the gas in the piston internal space  210  to be stirred by the gas or liquid injected into the cylinder  51 . Therefore, even if the blow-by gas such as uncombusted gas leaks out from the combustion chamber  50  to the piston internal space  210  through the gap between the cylinder  51  and the piston  21 , the blow-by gas in the piston internal space  210  is caused to actively flow, making it easy to move the blow-by gas to the crank chamber  52 . Therefore, it is easier to suppress the blow-by gas from staying in the piston internal space  210 , making it possible to expect a further improvement of the performance of discharging the blow-by gas. 
     By the way, the above configuration regarding the piston  21  can be adopted independently of the configuration and the like (ventilation port  502 ) of the blow-by gas exhaust countermeasure. That is, the engine system  1  according to one aspect has the cylinder block  5  including the cylinder  51  and the crank chamber  52 , and in the piston internal space  210  formed inside the piston  21  that reciprocates in the cylinder  51 , the stirring portion  213  that reciprocates according to the movement of the piston  21  is placed. The engine system  1  according to another aspect has the cylinder block  5  including the cylinder  51  and the crank chamber  52 , and of the piston  21  that reciprocates in the cylinder  51 , the bulkhead  212  that separates the internal space of the cylinder  51  (in the direction in which the piston  21  reciprocates) has the cavity portion  214  inside. 
     [4] Configuration of Cylinder Head 
     Then, the configuration of the cylinder head  6  (and its surrounding configuration) of the engine body  2  is to be described more in detail with reference to  FIGS.  17  through  21   .  FIG.  17    is a schematic view of the engine body  2  viewed from the rear side (side from which the crankshaft  22  protrudes) as one side in the output axis direction D 1 , partially breaking the cylinder block  5  and cylinder head  6  and adding diagonal lines (hatching) a main cross section.  FIG.  17    properly omits the side cover  74  and the like. 
     According to the present embodiment, the cylinder head  6  has the intake ports  61  and the exhaust ports  62 , as described above. The intake port  61  and the exhaust port  62  each include compartments (chambers) that are separated from each other in the cylinder head  6 , having internal spaces respectively. There is provided a multiplicity of cylinder heads  6  (six in the present embodiment), and the multiple cylinder heads  6  adopt a common configuration. Then, unless particularly noted, the following description will focus on one cylinder head  6 . 
     As an example of the present embodiment, two each of the intake ports  61  and the exhaust ports  62  are provided at the cylinder head  6 , as shown in  FIGS.  18  and  19   . That is, for the one cylinder head  6 , two intake ports  61  and two exhaust ports  62  are formed. However, the two intake ports  61  are basically of a common configuration, and the two exhaust ports  62  are basically of a common configuration. Therefore, unless particularly noted, the following description will focus on the one intake port  61  or the one exhaust port  62 .  FIG.  18    is a schematic perspective view, showing schematic outlines of the cylinder head  6  and cylinder  51  with imaginary lines (double-dashed line), and highlighting the intake port  61  and the exhaust port  62 . Further,  FIG.  19    is a schematic plan view, showing an after-described refrigerant passage  63  with an imaginary line (double-dashed line), and highlighting the intake port  61  and the exhaust port  62 . 
     The cylinder head  6  is placed above the cylinder  51 , as shown in  FIGS.  17  and  18   . With this, of the internal spaces of the cylinder  51 , the space surrounded by the upper face of the piston  21  and the lower face of the cylinder head  6  functions as the combustion chamber  50 . Each of the intake port  61  and exhaust port  62  formed at the cylinder head  6  has an opening connecting to the combustion chamber  50 . 
     The intake port  61  is the gas (intake air)&#39;s passage that connects between the intake manifold  54 , which is formed at the cylinder block  5 , and the combustion chamber  50 . Of the intake port  61 , at the opening on the combustion chamber  50  side, that is, the opening as the downstream side of the airflow, there is provided the intake valve  72 . Therefore, the air distributed from the intake manifold  54 , with the intake valve  72  open, is supplied via the intake port  61  to the combustion chamber  50 . 
     Further, in the present embodiment, since the port injection method is adopted as the fuel supply method for the gaseous fuel, the fuel supply unit  3  supplies the gaseous fuel (hydrogen in the present embodiment) to the internal space of the intake port  61 . That is, the fuel supply unit  3 &#39;s injection unit  31  which injects the gaseous fuel is placed in a position facing the inside of the intake port  61 , injecting the gaseous fuel in the intake port  61 . The timing at which the fuel supply unit  3  injects the gaseous fuel is to be described in detail in the column “[ 5 ] Engine System Control Operation”. 
     Meanwhile, the exhaust port  62  is the gas (exhaust)&#39;s passage that connects between the exhaust manifold  75  and the combustion chamber  50 . Of the exhaust port  62 , at the opening on the combustion chamber  50  side, that is, the opening as the upstream side of the airflow, there is provided the exhaust valve  73 . Therefore, the gas discharged from the combustion chamber  50 , with the exhaust valve  73  open, is discharged (concentrated) through the exhaust port  62  to the exhaust manifold  75 . 
     As shown in  FIGS.  17  and  19   , the cylinder head  6  has the refrigerant passage  63 , in addition to the intake port  61  and the exhaust port  62 . The refrigerant passage  63  is a passage for the refrigerant to pass through. The term “refrigerant” here refers to a heat medium used to move heat in the cooling cycle, examples thereof including a liquid such as water (cooling water) or oil, or a gas such as cooling gas. That is, the refrigerant as a fluid, by flowing through the refrigerant passage  63 , can remove heat from the surrounding of the refrigerant passage  63 , making it possible to cool the surrounding of the refrigerant passage  63 . As an example of the present embodiment, the refrigerant passage  63  is a water jacket for passing the cooling water as a refrigerant. 
     As shown in  FIG.  19   , in plan view, the refrigerant passage  63  is formed as an annulus surrounding the opening on the combustion chamber  50  side of the intake port  61  and exhaust port  62 . Specifically, as shown in  FIG.  17   , the refrigerant passage  63  is placed in a position adjacent to the opening on the combustion chamber  50  side of the intake port  61 . Then, the refrigerant (coolant) cooled outside the cylinder head  6  is supplied to the refrigerant passage  63  for circulation. With this, the refrigerant flowing through the refrigerant passage  63  cools the area mainly around the opening on the combustion chamber  50  side of the intake port  61  and the exhaust port  62 . 
     By the way, as a related technology, a dual-injection type engine system provided with an in-cylinder injector and an intake passage injector is known. In the engine system according to the related technology, adjusting (correcting) a fuel injection volume suppresses generation of a backfire seen during an execution of a purging process of fuel evaporated gas. Specifically, at the time of executing the purging process of the fuel evaporated gas seen when a sharing ratio of the in-cylinder injector and the intake passage injector is within a predetermined range, the fuel injection volume correction that corresponds to a to-be-introduced purged fuel volume is performed by changing only the fuel injection volume from the intake passage injector. 
     However, in the engine system  1  that uses the gaseous fuel such as hydrogen, for example, the fuel (gaseous fuel) may be more easily ignited. Therefore, it is desirable to perform a further backfire countermeasure assuming the event of a backfire, even to such an extent that the fuel (gaseous fuel) supplied in the intake port  61  is ignited, causing a chain of backfires. 
     Therefore, in the present embodiment, adopting the configuration described below makes it possible to provide the engine system  1  that enables the further backfire countermeasure. 
     That is, the engine system  1  according to the present embodiment has the intake port  61  that supplies air to the combustion chamber  50 , and the fuel supply unit  3  that supplies the gaseous fuel to an internal space Sp 2  (see  FIG.  20   ) of the intake port  61 . The fuel supply unit  3  has the injection unit  31  that injects the gaseous fuel. Here, as shown in  FIG.  20   , of an internal peripheral face  611  of the intake port  61 , at least an intersection with a central axis Ax 2  of an injection area R 1  of the gaseous fuel from the injection unit  31  has a cooled portion  612 . In other words, the intersection between the internal peripheral face  611  of the intake port  61  and the central axis Ax 2  of the injection area R 1  of the gaseous fuel from the injection unit  31  is included in the cooled portion  612 . 
     The term “cooled portion” as used in the present disclosure means, of the internal peripheral face  611  of the intake port  61 , a site that has a relatively low temperature by being cooled. That is, the temperature of the internal peripheral face  611  facing the internal space Sp 2  of the intake port  61  is not uniform, and with temperature difference being likely to be caused depending on the site, the site that is relatively lower in temperature than any other site constitutes the cooled portion  612 . As an example, of the internal peripheral face  611  of the intake port  61 , the site that is below the reference temperature (e.g., the average or median temperature of the internal peripheral face  611 ) is the cooled portion  612 . 
     In short, for example, adopting the above configuration for the engine system  1  having adopted the port injection method in which the gaseous fuel such as hydrogen is injected to the internal space Sp 2  of the intake port  61  enables the further backfire countermeasure. In the engine system  1  of this type, in a situation where the intake port  61  is exposed to the flame due to the backfire, for example, igniting the gaseous fuel (e.g., hydrogen) injected into the intake port  61  may cause a chain of backfires. In the engine system  1  according to the present embodiment, the central axis Ax 2  of the injection area R 1  of the gaseous fuel is directed to the cooled portion  612 , thereby to better the heat sink of the gaseous fuel, making it possible to suppress, even immediately after the backfire occurring, the gaseous fuel&#39;s igniting due to heating of the gaseous fuel. This improving of the performance of cooling the gaseous fuel in the intake port  61  can suppress the chain of backfires, making it possible to provide the engine system  1  capable of making the further backfire countermeasure. 
     More in detail, as shown in  FIG.  20   , the intake port  61  has a curved portion  600  having a cross sectional shape that is convexed toward one direction. As an example of the present embodiment, the curved portion  600  is provided in the middle portion of the intake port  61 , and is so curved as to have the cross sectional shape convexed upward, to thereby cause the intake port  61  to have an inverted U-shaped cross sectional shape as a whole. Therefore, the flow (airflow) of air (intake air) in the internal space Sp 2  of the intake port  61  takes a path that draws an arc in one direction (upward in this case) along the curved portion  600 . In  FIG.  20   , the flow of the intake air is shown by a bold arrow. 
     According to the present embodiment, in the above intake port  61 , the cooled portion  612  is placed on the face on the side in the other direction (here, downward) of the curved portion  600  of the internal peripheral face  611 , i.e., on an internal peripheral side face  602  of the curved portion  600 . That is, the internal peripheral face  611  includes an external peripheral side face  601  which is a face of the curved portion  600  on the one direction (here upward) side, and the internal peripheral side face  602  which is a face of the curved portion  600  on the other direction (here downward) side, and places the cooled portion  612  on the internal peripheral side face  602 . 
     Further, the nozzle-shaped (cylindrical) injection unit  31  is placed in such a way that its tip portion protrudes from the external peripheral side face  601  into the intake port  61 , injecting the gaseous fuel from the injection unit  31  toward the cooled portion  612 . That is, the tip portion of the injection unit  31  is directed to at least the cooled portion  612  provided on the internal peripheral side face  602 . Here, the central axis Ax 2  of the injection area R 1  is the central axis of the injection area R 1  which extends in substantially a conical shape with the tip portion of the injection unit  31  as an apex, substantially coinciding with the central axis of the nozzle-shaped (cylindrical) injection unit  31 . 
     Further, in the intake port  61 , the cooled portion  612  is placed more downstream of the airflow of the air than the injection unit  31 . In the example in  FIG.  20   , because of the airflow from the right to the left is caused in the intake port  61 , the cooled portion  612  is placed on the left as downstream relative to the tip portion of the injection unit  31  of the fuel supply unit  3 . 
     Thus, the cooled portion  612  is placed downstream of the injection unit  31 , making it easier for the gaseous fuel injected from the injection unit  31  to arrive at the cooled portion  612  even if the gaseous fuel is flowed downstream by the airflow. Therefore, the gaseous fuel&#39;s cooling effect by the cooled portion  612  can be fully demonstrated. 
     By the way, specific modes of the cooled portion  612  include, for example, a first mode, a second mode, and a third mode described below. The first mode is a refrigerant cooling method using the refrigerant passage  63 , the second mode is a gasification latent heat method using the adherent refrigerant, and the third mode is an air cooling method. That is, the first, second, or third mode, or a combination thereof can realize the cooled portion  612  of the internal peripheral face  611  of the intake port  61 . 
     First, as shown in  FIG.  20   , in the first mode (refrigerant cooling method), a site near the refrigerant passage  63  is the cooled portion  612 . Specifically, the refrigerant passage  63  and the intake port  61 &#39;s internal space Sp 2  are physically separated by a bulkhead portion  64 , and the bulkhead portion  64 &#39;s face (internal peripheral face  611  of the intake port  61 ) opposite to the refrigerant passage  63  constitutes the cooled portion  612 . That is, the engine system  1  has the cylinder head  6  formed with the intake ports  61 , and the cylinder head  6  has the refrigerant passage  63  through which the refrigerant passes. Here, the cooled portion  612  is placed at the bulkhead portion  64  that physically separates at least the refrigerant passage  63  from the intake port  61 . 
     According to this configuration, the refrigerant flowing through the refrigerant passage  63  provided at the cylinder head  6  can efficiently cool the cooled portion  612 . Further, the temperature of the cooled portion  612  can be adjusted by the refrigerant&#39;s flowrate, etc., making it possible to further reliably cool the gaseous fuel. Therefore, the gaseous fuel&#39;s igniting due to heating of the gaseous fuel can be further suppressed. 
     Further, as shown in  FIG.  20   , the bulkhead portion  64  includes a thin wall portion  641  and a thick wall portion  642 . The thin wall portion  641  has a thickness Th 1  between the refrigerant passage  63  and the intake port  61  smaller than a reference thickness. The thick wall portion  642  has a thickness Th 2  between the refrigerant passage  63  and the intake port  61  greater than the reference thickness. Of the thin wall portion  641  and the thick wall portion  642 , the cooled portion  612  is provided only at the thin wall portion  641 . The term “reference thickness” here is a reference thickness of the bulkhead portion  64 , such as the average or median thickness of the bulkhead portion  64 , as an example. That is, the thickness of the bulkhead portion  64  is not uniform, and varies from site to site. And, of the bulkhead portion  64 , the cooled portion  612  is provided at the thin wall portion  641  that is relatively thin, and not at the thick wall portion  642 . 
     According to this configuration, the refrigerant flowing in the refrigerant passage  63  can more efficiently cool the cooled portion  612 . That is, of the internal peripheral face  611  of the bulkhead portion  64 , the cooled portion  612  is placed at the thin wall portion  641  which is relatively close to the refrigerant passage  63  and at which the heat is easily transmitted to the refrigerant flowing through the refrigerant passage  63 , making it possible to more reliably cool the gaseous fuel. Therefore, the gaseous fuel&#39;s igniting due to heating of the gaseous fuel can be further suppressed. 
     In the second mode (gasification latent heat method), as shown in  FIGS.  21 A and  21 B , the engine system  1  is further provided with a refrigerant supply unit  65  that adheres an adherent refrigerant  651  to a part of the internal peripheral face  611  of the intake port  61 . The cooled portion  612  is placed at least at the site to which the adherent refrigerant  651  adheres. The term “adherent refrigerant” here refers to a heat medium mainly used for gasification latent heat, such as water (cooling water), oil or the like. That is, the adherent refrigerant  651  adheres to a part of the internal peripheral face  611  of the intake port  61  thereby to take heat of the internal peripheral face  611  at the time of the adherent refrigerant  651 &#39;s gasifying, thus cooling the internal peripheral face  611 . Therefore, of the internal peripheral face  611  of the intake port  61 , making the site, to which the adherent refrigerant  651  adheres, the cooled portion  612  realizes cooling of the cooled portion  612 . The mode in which the adherent refrigerant  651  is “adhered” includes, for example, spraying, discharging, condensing, or applying of the adherent refrigerant  651 . 
     Specifically, in the example shown in  FIG.  21 A , a nozzle-shaped (cylindrical) refrigerant supply unit  65  that injects the adherent refrigerant  651  is used. The refrigerant supply unit  65  is placed in such a way that its tip portion protrudes from the external peripheral side face  601  into the intake port  61 , and the gaseous fuel is injected from the injection unit  31  toward the cooled portion  612 . That is, the tip portion of the refrigerant supply unit  65  is directed at least to the cooled portion  612  provided on the internal peripheral side face  602 . With this, the adherent refrigerant  651  injected from the refrigerant supply unit  65  adheres to the cooled portion  612  of the internal peripheral face  611  (internal peripheral side face  602 ) of the intake port  61 , cooling the cooled portion  612 . 
     In the example shown in  FIG.  21 B , the refrigerant supply unit  65  that cools the air introduced into the intake port  61  is used. The refrigerant supply unit  65  includes a coiled cooled portion, and is placed near the intake port  61 &#39;s opening on the intake manifold  54  side. Supplying the refrigerant to the refrigerant supply unit  65  cools the air passing through the refrigerant supply unit  65 ; when the water vapor volume in the air exceeds the saturated water vapor volume, condensation generates water as the adherent refrigerant  651 . The adherent refrigerant  651  is carried by the flow of the air, and adheres to at least the cooled portion  612  provided on the internal peripheral side face  602 . As a result, the adherent refrigerant  651  adheres to the cooled portion  612  of the internal peripheral face  611  (internal peripheral side face  602 ) of the intake port  61 , cooling the cooled portion  612 . It is preferable that the refrigerant supplied to the refrigerant supply unit  65  should be maintained at a low temperature, for example, by heat exchange with the liquefied hydrogen tank  32 . 
     In the example in  FIGS.  21 A and  21 B , in addition to the refrigerant supply unit  65 , the refrigerant cooling method of the first mode is used in combination by the refrigerant passage  63 ; it is not essential, however, to combine the second mode (gasification latent heat method) with the first mode. That is, when the second mode (gasification latent heat method) is adopted, the refrigerant passage  63  may be omitted, and even in this case as well, the adherent refrigerant  651  can realize the cooled portion  612 . 
     In the third mode (air-cooling method), the air flow (air current) in the internal space Sp 2  of the intake port  61  is used, thereby to form the cooled portion  612  on a part of the internal peripheral face  611  of the intake port  61 . That is, for example, the velocity of air is increased by using a fan or the like, and air is caused to impinge on a part of the internal peripheral face  611  of the intake port  61 ; thereby, the site of the internal peripheral face  611  of the intake port  61 , which site is exposed to air, is cooled by the airflow thereby to form the cooled portion  612 . According to this configuration, it is possible, without otherwise using a refrigerant, to cool a part of the internal peripheral face  611  of the intake port  61  thereby to configure the cooled portion  612 . 
     Further, in the engine system  1  according to the present embodiment, it is further useful to adopt the following configuration as the backfire countermeasure. 
     The first configuration is to provide a nozzle cooling configuration that cools the injection unit  31  of the fuel supply unit  3 , cooling the gaseous fuel itself that is injected from the injection unit  31 . The nozzle cooling configuration can be realized, as an example, by a refrigerant passage placed around the injection unit  31 . This cools the injection unit  31  by the refrigerant, and suppresses heat entry from the cylinder head  6  to the injection unit  31 , thus making it possible to suppress the temperature rise of the gaseous fuel. The refrigerant passage may, for example, extend from the cylinder head  6  in the width direction D 3 , or may extend upward from the cylinder head  6 . 
     The second configuration is to provide a heat insulation material covering the injection unit  31  of the fuel supply unit  3  thereby to reduce the heat entry to the gaseous fuel injected from the injection unit  31 . This suppresses the heat entry from the cylinder head  6  to the injection unit  31 , thus making it possible to suppress the temperature rise of the gaseous fuel. 
     [5] Control Operation of Engine System 
     Then, the control operation of the engine system  1  according to the present embodiment is to be described with reference to  FIGS.  22 ,  23  and  24   . In the present embodiment, the engine control unit  20  controls the engine system  1  as described above, so the control operation of the engine system  1  described below includes a process executed by the engine control unit  20 . 
     In the present embodiment, at the timing as shown in  FIG.  22   , the engine control unit  20  controls the fuel supply unit  3 , injecting the gaseous fuel to the intake port  61 .  FIG.  22   , with the abscissa as the crank angle, shows an opening degree G 1  of the exhaust valve  73  and an opening degree G 2  of the intake valve  72  (“valve opening degree”), the flow velocity of the intake air in the intake port  61  (“flow velocity”), and the internal peripheral face  611  (wall face)&#39;s temperature (“temperature”) in an area that is in the intake port  61  and that is near the combustion chamber  50 . Here, according to an elapse of time, the crank angle continuously changes as the piston  21  reciprocates between BDC (bottom dead center) and TDC (top dead center). Therefore, the abscissa showing the crank angle corresponds to a time axis. 
     In  FIG.  22   , it is assumed that the piston  21  is at the BDC at a time point t 0 , the piston  21  is at the TDC at a time point t 2 , the piston  21  is at the BDC at a time point t 7 , and the backfire occurred at a time point t 1 . Here, the time point t 1 , being between the time point t 0  and the time point t 2 , is a timing immediately after the intake valve  72  starts opening. In this case, at a time point t 3  after the time point t 2 ; when the exhaust valve  73  closes (opening degree G 1  is 0), then, only after a cooling period T 1  has elapsed, an injection permission period T 2  for allowing for injecting of the gaseous fuel starts. Here, when the injection of the gaseous fuel is a split injection (intermittent injection), the period from the start of the first injection to the end of the last injection is performed within the injection permission period T 2 . 
     That is, in the present embodiment, after satisfying the supply start condition which includes the exhaust valve  73 &#39;s closing, and after an elapse of the cooling period T 1 , the fuel supply unit  3  starts supplying the gaseous fuel to the internal space Sp 2  of the intake port  61 . The cooling period T 1  is a period for cooling the cooled portion  612 , and prohibits the injection of the gaseous fuel. Specifically, in addition to the exhaust valve  73 &#39;s closing (opening degree G 1  is 0), the start supply condition includes the intake valve  72 &#39;s opening (opening degree G 2  is greater than 0). In the example in  FIG.  22   , at the time point t 3 , the exhaust valve  73  is closed and the intake valve  72  is opened (at the time point t 1  therebefore), satisfying the supply start condition. Therefore, when the cooling period T 1  from the time point t 3  to a time point t 5  elapses, and the process enters the injection permission period T 2 , the fuel supply unit  3  can start injecting (supplying) the gaseous fuel. 
     According to this configuration, the cooling period T 1  has been set before the supplying (injecting) of the gaseous fuel is started; therefore, after the cooled portion  612  has been securely cooled down, supplying of the gaseous fuel to the internal space Sp 2  of the intake port  61  can be started. Therefore, even when the backfire should occur, the gaseous fuel is cooled by the cooled portion  612 , making it easy to suppress the chain of backfires. 
     The end time point of the cooling period T 1  is set at and after the time point at which the opening degree G 2  of the intake valve  72  is maximized. That is, the time point t 5  as the end time point of the cooling period T 1  is set on the retarded side of the crank angle, viewed from a time point t 4  when the opening degree G 2  of the intake valve  72  is maximized (peak of opening degree G 2 ). 
     According to this configuration, supplying of the gaseous fuel starts on and after the timing when the flow velocity of intake air in the intake port  61  is maximized, making it possible to more efficiently cooling the gaseous fuel. That is, the flow velocity of intake air in the intake port  61  is maximized when the opening degree G 2  of the intake valve  72  is maximized; starting the supplying of the gaseous fuel at and after this timing (time point t 4  in  FIG.  22   ) improves the performance of cooling the gaseous fuel. The above further suppresses the chain of backfires with ease. 
     Further, the engine system  1  according to the present embodiment is provided with the turbocharger  8  that feeds air into the intake port  61 . This makes it easier to feed the gaseous fuel into the combustion chamber  50  even if the timing of the start supplying the gaseous fuel is delayed by providing the cooling period T 1 . That is, the air velocity is accelerated by the turbocharger  8 , allowing the gaseous fuel injected in the intake port  61  to more easily flow into the combustion chamber  50 . 
     Here, as shown in  FIG.  22   , the injection permission period T 2  is set in view of a grace period T 3  inserted immediately before the intake valve  72 &#39;s closing. The grace period T 3  is a period during which injecting of the gaseous fuel is prohibited, like the cooling period T 1 . That is, from a time point t 6 , when the injection permission period T 2  ends, until a time point t 7 , when the intake valve  72  closes (opening degree G 2  is 0), injecting of the gaseous fuel is prohibited as the grace period T 3 . That is, the end time point of the cooling period T 1  is set to a time point (t 5  in  FIG.  22   ) which is back from the time point t 7 , at which the intake valve  72  closes, by a total time of the grace period T 3  and the injection permission period T 2 ). 
     According to this configuration, remaining of the gaseous fuel in the intake port  61  is suppressed, which remaining is due to the intake valve  72  being closed at the point t 6  when the injection permission period T 2  ends. That is, even if the gaseous fuel remains in the intake port  61  at the time point t 6  when the injection permission period T 2  ends, the remaining gaseous fuel can be discharged to the combustion chamber  50  during the grace period T 3 . 
     Further, it is preferable that the length of the grace period T 3  should be set based on the distance between (tip of) the injection unit  31  and the intake port  61 &#39;s opening on the combustion chamber  50  side. The above distance is a distance on the air flow path in the intake port  61 . Specifically, the longer the distance between (tip of) the injection unit  31  and the intake port  61 &#39;s opening on the combustion chamber  50  side, the longer the grace period T 3  is set. With this, the grace period T 3  is set in view of the time required for the gaseous fuel, which is injected from the injection unit  31 , to be discharged to the combustion chamber  50 , making it difficult for the gaseous fuel to remain in the intake port  61 . 
     By the way, the above configuration related to the control of the fuel supply unit  3  can be adopted independently of the configuration (ventilation port  502 ) for the blow-by gas exhaust countermeasure and independently of the cooled portion  612 , etc. That is, the engine system  1  according to the one mode has the intake port  61  that supplies air to the combustion chamber  50 , and the fuel supply unit  3  that supplies the gaseous fuel to the internal space Sp 2  of the intake port  61 . After satisfying the supply start condition including the exhaust valve  73 &#39;s closing, and after an elapse of the cooling period T 1 , the fuel supply unit  3  starts supplying the gaseous fuel to the internal space Sp 2  of the intake port  61 . 
       FIG.  23    is a flowchart showing an example of the operation (process) of the engine control unit  20  for the injection of the gaseous fuel, which is seen when the engine system  1  is used to drive the generator  101  or to propel the hull  100 . 
     That is, the engine control unit  20  first determines whether or not the engine system  1  is to be used to drive the generator  101  (S 1 ). When the engine system  1  is used to drive the generator  101  (S 1 : Yes), the engine control unit  20  determines that the process is in the power generation mode, and moves the process to step S 2 . Meanwhile, when the engine system  1  is used to propel the hull  100  (S 1 : No), the engine control unit  20  determines that the process is not in the power generation mode, and moves the process to step S 6 . 
     In step S 2 , the engine control unit  20  acquires the generator  101 &#39;s load and the engine body  2 &#39;s revolution speed (actual revolution speed). Then, in light of the “map of load—revolution speed” showing the correlation between the generator  101 &#39;s load and the engine revolution speed, the engine control unit  20  determines the gaseous fuel&#39;s injection period, i.e., the timing to start injecting the gaseous fuel (S 3 ). Then, the engine control unit  20  calculates the gaseous fuel&#39;s injection volume (S 4 ), and with an arrival of the gaseous fuel&#39;s injection time, so controls the fuel supply unit  3  as to inject the gaseous fuel (S 5 ). 
     In step S 6 , the engine control unit  20  acquires the operation amount of (throttle lever of) the operation panel  102  and the revolution speed (actual revolution speed) of the engine body  2 . Here, the engine control unit  20  sets the target revolution speed of the engine body  2  (S 7 ), and calculates the difference between the target revolution speed and the actual revolution speed (S 8 ). Further, the engine control unit  20  calculates the gaseous fuel&#39;s injection volume (deficient injection volume) that is deficient relative to the gaseous fuel&#39;s injection volume in the immediately preceding cycle. Then, in light of the “map of injection volume—injection time” showing the correlation between the gaseous fuel&#39;s injection volume and the gaseous fuel&#39;s injection time, the engine control unit  20  determines the gaseous fuel&#39;s injection time (S 10 ). Further, in light of the “map of injection volume—cooling period” showing the correlation between the gaseous fuel&#39;s injection volume and the cooling period T 1 , the engine control unit  20  determines the gaseous fuel&#39;s injection period, that is, the timing to start injecting the gaseous fuel (S 11 ). Then, with an arrival of the time for the gaseous fuel injection, the engine control unit  20  so controls the fuel supply unit  3  as to inject the gaseous fuel (S 12 ). 
     The engine control unit  20  repeatedly executes the processes in the above step S 1  to step S 12 . However, the flowchart shown in  FIG.  23    is merely one example, and therefore, the process may be properly added or omitted, or the order of the processes may be properly changed. 
       FIG.  24    is a flowchart showing an example of the operation (process) of the engine control unit  20 , where a cooling period T 1  is provided at the time of occurrence of the backfire, when the engine system  1  is used to drive the generator  101 . 
     That is, the engine control unit  20  first acquires the generator  101 &#39;s load, the revolution speed (actual revolution speed) of the engine body  2 , and the pressure (in-cylinder pressure) of the combustion chamber  50  (S 21 ). Here, the in-cylinder pressure is acquired from the in-cylinder pressure sensor  76 , and is information on whether or not the backfire should occur. Then, the engine control unit  20  determines whether or not the backfire is occurring, for example, based on the in-cylinder pressure (S 22 ). When the occurrence of backfire is detected from the waveform, etc. of the in-cylinder pressure (S 22 : Yes), the engine control unit  20  moves the process to step S 23 . Meanwhile, when no backfire is detected from the waveform, etc. of the in-cylinder pressure (S 22 : No), the engine control unit  20  moves the process to step S 24 . 
     In step S 23 , in light of the “first map of load—revolution speed” showing the correlation between the generator  101 &#39;s load and the engine revolution speed, the engine control unit  20  determines the gaseous fuel&#39;s injection period, i.e., the timing to start injecting the gaseous fuel. The “first map of load—revolution speed” is a map prepared for the occurrence of the backfire, and is for setting the gaseous fuel&#39;s injection period in view of the cooling period T 1 . 
     In step S 24 , in light of the “second map of load—revolution speed” showing the correlation between the generator  101 &#39;s load and the engine revolution speed, the engine control unit  20  determines gaseous fuel&#39;s injection period, i.e., the timing to start injecting the gaseous fuel. The “second map of load—revolution speed” is a map prepared for a steady state where the backfire is not occurring, and is for setting the gaseous fuel&#39;s injection period not in view of the cooling period T 1 . 
     Then, the engine control unit  20  calculates the gaseous fuel&#39;s injection volume (S 25 ), and with an arrival of the gaseous fuel&#39;s injection period, so controls the fuel supply unit  3  as to inject the gaseous fuel (S 26 ). 
     The engine control unit  20  repeatedly executes the processes in the above step S 21  to step S 26 . However, the flowchart shown in  FIG.  24    is merely one example, and therefore, the process may be properly added or omitted, or the order of the processes may be properly changed. 
     [6] Modified Example 
     A description will hereinafter be made on a modified example of the first embodiment. The modified examples, which will be described below, can be applied in a proper combination. 
     The engine system  1  in the present disclosure includes a computer system as the engine control unit  20 . The computer system has, as hardware, one or more processors and one or more storages. Executing the program recorded in the storage of the computer system realizes the function as the engine control unit  20  in the present disclosure. The program may be preliminarily recorded in the storage of the computer system, may be provided through an electric communication line, or may be may be provided in a manner to be recorded in a non-transitory recording medium, such as a storage card, an optical disk, a hard disk drive, or the like, each of which is readable by the computer system. Further, a part of or all of the function units included in the engine control unit  20  may be composed of an electronic circuit. 
     Further, a configuration in which at least a part of the functions of the engine system  1  is concentrated in one case is not essential for the engine system  1 , and the components of the engine system  1  may be provided in a multiplicity of cases in a distributed manner. Conversely, in the first embodiment, functions that are distributed to a multiplicity of units (such as engine body  2  and generator  101 ) may be concentrated in one case. 
     Further, not limited to being installed on the hull  100 , at least a part of the engine system  1  may be provided separate from the hull  100 . As an example, when the engine control unit  20  is embodied by a server unit provided separate from the hull  100 , a communication between the server unit and (communication unit of) the hull  100  makes it possible for the engine control unit  20  to control the engine system  1 . At least a part of the functions of the engine control unit  20  may be realized by a cloud (cloud computing) or the like. 
     The ship  10  is not limited to the pleasure boat, and may be a commercial ship such as a cargo ship or a passenger ship, a workboat such as a tugboat or a salvage boat, a special ship such as a meteorological observation ship or a training ship, a fishing ship, a naval ship, or the like. Further, the ship  10  is not limited to the ship of the manned type boarded by the navigator, and may be an unmanned type ship that can be remotely operated by a person (the navigator) or autonomously operated. In addition to the engine body  2 , the hull  100  of the ship  10  may be provided with one or more dynamic power sources such as a motor (electric motor). The engine system  1  may be used for an application other than the ship  10 . 
     The engine system  1  is not limited to the in-line multi-cylinder engine in which multiple cylinders  51  are arranged in line, but can also be, for example, a V-type engine in which multiple cylinders  51  are placed in a V-shape with the crankshaft  22 &#39;s rotational axis Ax 1  at the apex, or a horizontally opposed engine. In the case of the V-type engine, as shown in  FIG.  25   , within the bank angle between the cylinders  51  on both sides, for example, the cam chamber  53 , which connects to the internal space Sp 1  of the crank chamber  52 , is placed. Even with this configuration, the ventilation port  502  is formed in the cam chamber  53 , for example, thereby making it possible to efficiently discharge the blow-by gas from the crank chamber  52 . 
     The engine system  1  may be a single-cylinder engine provided with only one cylinder  51 . The engine system  1  is not limited to the dual-fuel engine, but can also be, for example, an engine (e.g., a hydrogen-only engine) that uses only the gaseous fuel (e.g., hydrogen) as fuel. The engine system  1  is not limited to an engine with the turbocharger, but can also be a naturally aspirated engine without the turbocharger  8 . 
     Further, the fuel supply method of the gaseous fuel is not limited to the port injection method in which the fuel is injected into the intake port  61 , but may also be a direct injection method in which the fuel is injected directly into the combustion chamber  50 . In this case, the injection unit  31 , which injects the gaseous fuel, is placed in a position facing the combustion chamber  50 . 
     Further, the ventilation port  502  is not required to be ordinarily open, and may be configured to open and close with a valve unit, for example. In this case, during the period of opening the ventilation port  502 , the blow-by gas is discharged from the ventilation port  502 , and during the period of closing the ventilation port  502 , no the blow-by gas is discharged from the ventilation port  502 . 
     Second Embodiment 
     An engine system  1 A according to the present embodiment differs from the engine system  1  according to the first embodiment in the position of the ventilation port  502 , as shown in  FIG.  26    and  FIG.  27   . Hereinafter, the same components as those in the first embodiment will be denoted by the same reference signs, and the description thereof will be properly omitted. In  FIG.  27   , the flow of the blow-by gas is shown by the bold arrow. 
     That is, as shown in  FIG.  26   , according to the present embodiment, the cylinder block  5  has the liner support wall  55  that supports the cylinder liner  511  included in the cylinder  51 . The lower end of the cylinder liner  511  protrudes downward from the lower end of the liner support wall  55 . Here, the ventilation port  502  is placed at the lower end of the liner support wall  55 . Specifically, the ventilation port  502  is formed at a circumferential part in the lower face of the cylindrical liner support wall  55  that surrounds the cylinder liner  511 . In the example in  FIG.  26   , of the lower face of the liner support wall  55 , the ventilation port  502  is formed in a position on the left of the cylinder liner  511 . Here, according to the present embodiment, as shown by the imaginary line (double-dashed line) in  FIG.  26   , the opening portion  531  of the cam chamber  53  has a cam chamber wall  533  that partitions the internal space of the cam chamber  53  from the internal space Sp 1  of the crank chamber  52 . The cam chamber wall  533  may completely separate the internal space of the cam chamber  53  from the internal space Sp 1  of the crank chamber  52 , or may partially partition the internal space of the cam chamber  53  from the internal space Sp 1  of the crank chamber  52 . 
     The ventilation passage  503  connecting to the ventilation port  502  includes a longitudinal passage  503 A which extends straight upward along the up/down direction D 2  from the ventilation port  502 , and a transverse passage  503 B which extends from the upper end portion of the longitudinal passage  503 A to the left along the width direction D 3 . The longitudinal passage  503 A may extend upward from the ventilation port  502  along the up/down direction D 2 , therefore, may extend diagonally upward from the ventilation port  502 , or may meander upward from the ventilation port  502 , for example. This ventilation passage  503  is an in-wall passage formed inside the liner support wall  55 . Thus, including the longitudinal passage  503 A and the transverse passage  503 B which have different extension directions, the ventilation passage  503  has an inflected portion  503 C (see  FIG.  27   ) at a connection site between the longitudinal passage  503 A and the transverse passage  503 B. That is, the connection site between the longitudinal passage  503 A and the transverse passage  503 B forms the inflected portion  503 C. 
     According to the configuration described above, as shown in  FIG.  27   , the blow-by gas is efficiently discharged from the internal space Sp 1  of the crank chamber  52  via the ventilation port  502  (and ventilation passage  503 ). That is, the uncombusted gas or the like leaks from the combustion chamber  50  to the crank chamber  52  through the gap between the cylinder  51  and the piston  21 , generating the blow-by gas. In the present embodiment, using the gaseous fuel (hydrogen) with the specific gravity smaller than 1 also makes the specific gravity smaller than 1 for the blow-by gas, thereby to cause the blow-by gas having leaked out to the crank chamber  52  to move upward in the crank chamber  52 . The lower end of the cylinder liner  511  protrudes downward from the lower end of the liner support wall  55 ; therefore, the blow-by gas leaking out from the lower end of the cylinder liner  511  to the crank chamber  52  moves toward the lower face of the upwardly recessed liner support wall  55 , in a manner to be folded back at the lower end of the cylinder liner  511 . As a result, the blow-by gas is discharged from the ventilation port  502  at the lower end (lower face) of the liner support wall  55 , and is discharged through the ventilation passage  503  to the external space out of the cylinder block  5 . 
     Here, the lower end (lower face) of the liner support wall  55  is inclined rather than perpendicular to the central axis of the cylinder  51 . That is, as shown in  FIG.  27   , the lower face of the liner support wall  55  has a “left upward” inclination so that the end portion (left end portion) side where the ventilation port  502  is provided is positioned higher up. Therefore, the blow-by gas that stays at the lower end of the liner support wall  55  is collected on the left end side by the inclination of the lower face of the liner support wall  55 , bypassing around the cylinder liner  511 . Thus, the blow-by gas is efficiently discharged from the ventilation port  502  provided at the left end portion of the lower end of the liner support wall  55 . 
     According to the present embodiment, the inflected portion  503 C of the ventilation passage  503  functions as the gas/liquid separating portion  504 . In short, with the above inflected portion  503 C (gas/liquid separating portion  504 ) provided, the blow-by gas introduced from the ventilation port  502  to the ventilation passage  503  flows in the ventilation passage  503  in such a manner as to impinge on an impinging face of the longitudinal passage  503 A at the time of passing the inflected portion  503 C as the gas/liquid separating portion  504 . When the blow-by gas contacts the internal peripheral face of the inflected portion  503 C as the gas/liquid separating portion  504 , the liquid such as oil or moisture that is discharged together with the blow-by gas adheres to the internal peripheral face of the inflected portion  503 C as the gas/liquid separating portion  504 . With this, the liquid (oil or moisture, etc.) discharged together with the blow-by gas is captured by the gas/liquid separating portion  504  and is separated from the gas included in the blow-by gas. 
     Thus, in the present embodiment, the ventilation passage  503  has the inflected portion  503 C that changes the direction of the gas distribution. The gas/liquid separating portion  504  includes an inflected portion  503 C. 
     As a result, the blow-by gas is exhausted from the ventilation passage  503  with at least a part of the liquid component such as oil removed, connecting to suppressing of oil consumption, etc. involved in the exhausting of the blow-by gas. 
     The cam chamber wall  533  is not an essential component, and may be properly omitted. The configuration (including the modified examples) according to the second embodiment can be adopted in proper combination with the various configurations (including the modified examples) described in the first embodiment. 
     Third Embodiment 
     An engine system  1 B according to the present embodiment differs from the engine system  1  according to the first embodiment in that, as shown in FIG.  28 , multiple ventilation ports  502  are so provided as to correspond one-to-one to the multiple cylinders  51 . Hereinafter, the same components as those in the first embodiment will be denoted by the same reference signs, and the description thereof will be properly omitted. 
     That is, according to the present embodiment, the cylinders  51  multiple (six) in number are so provided as to be arranged in the output axis direction D 1 . Here, at six positions in the output axis direction D 1 , the ventilation ports  502  are formed in the cam chamber  53  in a manner to correspond to all of the multiple cylinders  51 . The multiple ventilation passages  503  are provided in such a manner as to respectively extend upward from the multiple (six in the present embodiment) ventilation ports  502 . 
     Here, the tip positions (upper end portions) of the multiple ventilation passages  503  connect to a single common exhaust pipe  507 . The common exhaust pipe  507  extends along the output axis direction D 1 , with its tip (the rear end in the present embodiment) positioned in the external space out of the engine body  2 . With this, the blow-by gas respectively generated in the respective multiple cylinders  51  are concentrated in the common exhaust pipe  507  through the ventilation port  502  and the ventilation passage  503 , to be discharged through the common exhaust pipe  507  to the external space out of the engine body  2 . 
     In the present embodiment, the common exhaust pipe  507  is inclined rather than parallel to the rotational axis Ax 1  of the crankshaft  22 . That is, as shown in  FIG.  28   , the common exhaust pipe  507  has a “rear upward” inclination so that one end (rear end in the present embodiment) side in the output axis direction D 1  is positioned more upward. Therefore, at the tip side (rear end side) of the common exhaust pipe  507 , the inclination of the common exhaust pipe  507  collects the blow-by gas concentrated in the common exhaust pipe  507 . Thus, the blow-by gas is efficiently discharged from the common exhaust pipe  507 . 
     The configuration according to the third embodiment can be adopted in proper combination with various configurations (including the modified example) described in the first embodiment or the second embodiment. 
     Fourth Embodiment 
     An engine system  1 C according to the present embodiment differs from the engine system  1  according to the first embodiment in that the cooled portion  612  is placed on the external peripheral side face  601 , as shown in  FIG.  29   . Hereinafter, the same components as those in the first embodiment will be denoted by the same reference signs, and the description thereof will be properly omitted. 
     That is, in the present embodiment, the intake port  61  has the curved portion  600  having a cross sectional shape that is convexed toward one direction. The cooled portion  612  is placed on the curved portion  600 &#39;s face on the one direction (here upward) side, of the internal peripheral face  611  of the intake port  61 , that is, placed on the external peripheral side face  601 . That is, the internal peripheral face  611  includes the external peripheral side face  601  which is the curved portion  600 &#39;s face on the one direction (here upward) side, and the internal peripheral side face  602  which is the curved portion  600 &#39;s face on the other direction (here downward) side, placing the cooled portion  612  at the external peripheral side face  601 . 
     Thus, the cooled portion  612  is placed at the external peripheral side face  601 , making it easier for the gaseous fuel, which is injected from the injection unit  31 , to arrive at the cooled portion  612  even if being flown away by the airflow of the air. In short, since the airflow in the curved portion  600  passes mainly near the external peripheral side face  601 , the cooled portion  612 , by being present on the external peripheral side face  601 , makes it easier to cool the gaseous fuel by the cooled portion  612 . Therefore, the gaseous fuel&#39;s cooling effect by the cooled portion  612  can be fully demonstrated. 
     Here, setting the relatively long nozzle length of the injection unit  31  enhances the directivity of the gaseous fuel injected from the injection unit  31 . That is, the longer the injection unit  31  is, the more improved the directivity of the gaseous fuel injected from the injection unit  31 , further making it easier for the gaseous fuel to arrive at the cooled portion  612 . 
     By the way, as an example in the present embodiment, a valve seat portion  66  is used, as shown in  FIG.  29   , so as to realize the cooled portion  612  placed on the external peripheral side face  601 . That is, the valve seat portion  66  for seating the intake valve  72  is provided at the intake port  61 &#39;s end portion on the combustion chamber  50  side. The cooled portion  612  is placed at the valve seat portion  66 . Specifically, a refrigerant passage  661  for passing the refrigerant is formed on the valve seat portion  66 &#39;s face opposite the internal space Sp 2  of the intake port  61 . Flowing of the refrigerant in this refrigerant passage  661  cools the valve seat portion  66 , cooling the cooled portion  612  provided at the valve seat portion  66 . That is, the first mode (refrigerant cooling method) is adopted as the specific mode of the cooled portion  612 . 
     According to this configuration, the gaseous fuel can be cooled at the valve seat portion  66  closest to the combustion chamber  50 , of the intake port  61 . Therefore, even if a flame (or heated gas) flows into the intake port  61  from the combustion chamber  50  due to the backfire, the cooled portion  612  provided at the inlet (valve seat portion  66 ) of the intake port  61  can perform cooling, making it possible to further suppress the chain of backfires. 
     As a modified example of the fourth embodiment, a throttle portion  67  may be used so as to realize the cooled portion  612  placed on the external peripheral side face  601 , as shown in  FIG.  30   . Of the intake port  61 &#39;s site, the throttle portion  67  with a locally reduced cross sectional area perpendicular to the airflow, that is, the flow path&#39;s cross sectional area. That is, the flow path&#39;s cross sectional area of the intake port  61  is not uniform, that is, at least at the throttle portion  67 , is smaller (narrower) than the upstream and downstream of the throttle portion  67 . The above throttle portion  67  is embodied by a rib or the like formed on the internal peripheral face  611  of the intake port  61 . In the example shown in  FIG.  30   , the rib protruding from the internal peripheral face  611  of the intake port  61  rearward (toward the front side of the paper in  FIG.  30   ) constitutes the throttle portion  67  that locally narrows the flow path&#39;s cross sectional area of the intake port  61 . 
     With the above throttle portion  67  provided, the air with increased flow velocity seen when passing through the throttle portion  67  moves substantially linearly, thereby impinge on the internal peripheral face  611  (in this case, external peripheral side face  601 ) of the intake port  61 . This allows the site of the internal peripheral face  611  of the intake port  61 , which site is exposed to air, to be cooled by the airflow, making it possible to form the cooled portion  612 . In short, in the example shown in  FIG.  30   , the intake port  61  has the throttle portion  67  that has the partially reduced cross sectional area perpendicular to the airflow. The cooled portion  612  includes, of the internal peripheral face  611  of the intake port  61 , an intersection with a virtual line VL 1  perpendicularly extending from a cross section of the throttle portion  67  in the intake port  61  toward the downstream side of the airflow. Thus, the cooled portion  612  realized by using the throttle portion  67  is a type of the third mode (air-cooling method). 
     According to this configuration, merely providing the throttle portion  67  can realize the cooled portion  612  by the air-cooling method, without using a fan or the like to increase the air velocity. 
     Thus, it is possible to simplify the configuration for realizing the cooled portion  612 . In the example in  FIG.  30   , the refrigerant passage  661  at the valve seat portion  66  can be omitted. 
     According to the present embodiment, the refrigerant passage  63  can be properly omitted. The configuration (including the modified example) according to the fourth embodiment can be adopted in proper combination with the various configurations (including the modified examples) described in the first, second, or third embodiment. 
     REFERENCE SIGNS LIST 
     
         
           1 ,  1 A to  1 C: engine system 
           3 : fuel supply unit 
           5 : cylinder block 
           6 : cylinder head 
           8 : turbocharger 
           23 : camshaft 
           31 : injection unit 
           50 : combustion chamber 
           51 : cylinder 
           51 A: one end side cylinder 
           51 B: another end side cylinder 
           52 : crank chamber 
           53 : cam chamber 
           55 : liner support wall 
           61 : intake port 
           63 : refrigerant passage 
           64 : bulkhead portion 
           65 : refrigerant supply unit 
           66 : valve seat portion 
           67 : throttle portion 
           72 : intake valve 
           210 : in-piston space 
           212 : bulkhead 
           213 : stirring portion 
           214 : cavity portion 
           501 : internal peripheral face (of cylinder block) 
           502 : ventilation port 
           503 : ventilation passage 
           503 C: inflected portion 
           504  gas/liquid separating portion 
           511 : cylinder liner 
           505 : gas introduction port 
           506 : airflow forming portion 
           600 : curved portion 
           601 : external peripheral side face (one directional side face) 
           611 : internal peripheral face (of intake port) 
           612 : cooled portion 
           641 : thin wall portion 
           642 : thick wall portion 
           651 : adherent refrigerant 
         Ax 1 : rotational axis 
         Ax 2 : central axis 
         C 1 : center 
         D 1 : output axis direction 
         D 2 : up/down direction 
         G 2 : opening degree (of intake valve) 
         R 1 : injection area 
         Sp 1 : internal space (of crank chamber) 
         Sp 2 : internal space (of intake port) 
         T 1 : cooling period 
         VL 1 : virtual line