To quickly detect a gas leakage to take a measure to the leakage by providing a control part for determining the gas leakage when a pressure drop rate is larger than a predetermined pressure drop rate threshold.
During the operation of an engine, a first cutoff valve 50 and a second cutoff valve 65 are opened, and according to a command of an injector driver 35, an injector 15 is opened and closed repeatedly. When the first cutoff valve 50 and the second cutoff valve 65 are closed, compressive natural gas is confined in a high pressure pipe 13 and a low pressure pipe 14. When no gas leakage is caused in he pipe, the pressure of the compressive natural gas is substantially constant and little drops. If gas leakage is caused, the pressure drops gradually or suddenly. Accordingly, leakage between the first cutoff valve 50 and the second cutoff valve 65 can be monitored by a first pressure sensor 31 at a control part, and a leakage between the second cutoff valve 65 and an injector 15 can be monitored by a second pressure sensor 33.
AKASAKI NAOSUKE
OTAKA AKIFUMI
GOTO HIROYUKI
