Fuel injection engine and motorcycle comprising fuel injection engine

1. A fuel injection engine comprising:

an air-intake passage configured to guide air taken in from outside to a combustion chamber formed by a cylinder block and a cylinder head;

a fuel injector configured to inject fuel to an interior of the air-intake passage, wherein a part of the fuel is injected from the fuel injector along a fuel injection center line;

an exhaust passage configured to guide exhaust gases away from the combustion chamber; and

a water jacket through which cooling water flows to cool the air-intake passage and the exhaust passage;

wherein an inner wall of the air-intake passage has a crossing point where the fuel injection center line and the inner wall of the air-intake passage cross each other;

wherein the inner wall of the air-intake passage has a fuel adhering region which is a predetermined region including the crossing point;

wherein as viewed in a plane crossing an air flow direction in the air-intake passage and passing through the crossing point, the water jacket is configured to be provided in a location that does not include the fuel adhering region;

wherein a portion of the water jacket positioned between the exhaust passage and the air-intake passage has a longer wall extending along the exhaust passage to cool the exhaust passage and a shorter wall extending along the air-intake passage to suppress cooling of the fuel adhering region; and

wherein the water jacket extends along a circumferential direction of the air-intake passage from a region near one lateral end position of the fuel adhering region to a region near an opposite lateral end position of the fuel adhering region as viewed in the plane.

2. The fuel injection engine according to claim 1 , wherein the water jacket extends to a region beyond a straight line connecting the lateral end positions of the fuel adhering region of the inner wall of the air-intake passage.

3. The fuel injection engine according to claim 1 , further comprising:

a valve configured to open and close an opening of the air-intake passage that is located downstream in the air flow direction, the valve having a valve stem; wherein

the crossing point is located downstream of a location where the valve stem penetrates through the inner wall of an intake port provided in the cylinder head and forming a part of the air-intake passage.

4. The fuel injection engine according to claim 1 , wherein the fuel injector is attached to a wall portion of the air-intake passage, the engine further comprising:

a butterfly valve that is mounted upstream of the fuel injector in the air flow direction and is configured to be pivotable in the air flow direction to control an amount of the air flowing in the air-intake passage, the butterfly valve being configured to open the air-intake passage in such a manner that a portion of the butterfly valve that is closer to the fuel injector than a pivot shaft thereof is pivoted in the air flow direction.

5. A motorcycle comprising:

a fuel injection engine including:

an air-intake passage configured to guide air taken in from outside to a combustion chamber formed by a cylinder block and a cylinder head;

a fuel injector configured to inject fuel to an interior of the air-intake passage, wherein a part of the fuel is injected from the fuel injector along a fuel injection center line;

an exhaust passage configured to guide exhaust gases away from the combustion chamber; and

a water jacket through which cooling water flows to cool the air-intake passage and the exhaust passage;

wherein an inner wall of the air-intake passage has a crossing point where the fuel injection center line and the inner wall of the air-intake passage cross each other;

wherein the inner wall of the air-intake passage has a fuel adhering region which is a predetermined region including the crossing point;

wherein as viewed in a plane crossing an air flow direction in the air-intake passage and passing through the crossing point, the water jacket is configured to be provided in a location that does not include the fuel adhering region;

wherein a portion of the water jacket positioned between the exhaust passage and the air-intake passage has a longer wall extending along the exhaust passage to cool the exhaust passage and a shorter wall extending along the air-intake passage to suppress cooling of the fuel adhering region; and

wherein the water jacket extends along a circumferential direction of the air-intake passage from a region near one lateral end position of the fuel adhering region to a region near an opposite lateral end position of the fuel adhering region as viewed in the plane.