Abstract: First gas flow passage grooves communicating with a fuel gas inlet and second gas flow passage grooves communicating with a fuel gas outlet are provided on a surface of a first separator. First and second united sections are provided at merged portions of the first gas flow passage grooves and the second gas flow passage grooves. Accordingly, the number of gas flow passage grooves is throttled from the side of the fuel gas inlet to the side of the fuel gas outlet. The turbulence is allowed to occur at the throttled portion to make it possible to improve the gas diffusion performance.

Abstract: A fuel cell stack comprises first and second separators for holding a fuel cell unit therebetween. The first separator has a fuel gas flow passage and the second separator has an oxygen-containing gas flow passage. The gas flow passages are formed by grooves with the number of grooves decreasing from the inlet to the outlet. In one embodiment, the gas flow passage comprises twelve individual first gas flow passage grooves which communicate with an inlet hole on a gas inlet side, six individual second gas flow passage grooves which communicate with the first gas flow passage grooves, and three individual third gas flow passage grooves which communicate with the second gas flow passage grooves. The third gas flow passage grooves communicate with an outlet hole on a gas outlet side.

Abstract: An intake system for an internal combustion engine includes first and second intake valve bores provided to face a combustion chamber and to be independently opened and closed by first and second intake valves, and first and second intake ports which are connected to the corresponding intake valve bores with a partition wall interposed therebetween and which communicate with a common intake passage. In a particular operation range of the engine, an imbalance is produced in the concentration of the air-fuel mixture flowing through the first and second intake valve bores into the combustion chamber on the basis of a difference between the amounts of fresh air flowing into the first and second intake ports. The intake system further includes a communication hole provided in the partition wall for putting the first and second intake ports into communication with each other. This provides for improvements in the lean combustibility and in the nature of the exhaust gas.