Working gas circulation gas engine using a gas-tight anomaly detection method and the method of working gas circulation gas engines

To provide a working gas circulation gas engines using simple methods and the methods at low cost abnormality accurately detected in the air-tightness of the working gas circulation gas engines. In A working gas circulation gas engines, fuel gas is supplied as the at least one excess gas in the circulation passage to the surplus by a predetermined amount 1 of the gas of the oxidant gas, and the working gas, the predetermined amount determining the presence or absence of an abnormality in air-tightness of the engine based on the difference between 1 and the gas amount of increment in circulating passage which is separately detected by the gas amount detecting means. .FIELD 4