Patent ID: 7793622

Claim:
A method of operating a gas engine comprising introducing combustion air into a combustion chamber of the engine and, in a first mode of operation of the engine, adding gaseous fuel to the combustion air outside the combustion chamber via a first fuel feed system and injecting liquid ignition fuel into the mixture of gaseous fuel and combustion air via a second fuel feed system, in a second mode of operation of the engine, shutting down the second feed system, adding gaseous fuel to the combustion air outside the combustion chamber via the first fuel feed system and injecting liquid ignition fuel into the mixture of gaseous fuel and combustion air via a third fuel feed system, and controlling the third fuel feed system so that it injects less than 20% of the total fuel amount supplied to the engine, and supplying fuel to both the second and third fuel feed systems from a common tank, whereby the third fuel feed system provides a backup of the second fuel feed system.