Method and apparatus for delivering two fuels to a direct injection internal combustion engine

An apparatus for separately delivering a liquid fuel and a gaseous fuel into a combustion chamber of an internal combustion engine, said apparatus comprising:

• a liquid-fuel supply system comprising:
• a liquid-fuel storage vessel that is fillable with said liquid fuel;
• a liquid-fuel pump with a liquid-fuel inlet fluidly connected by a liquid-fuel passage to said liquid-fuel storage vessel;
• a liquid-fuel rail fluidly connected to an outlet of said liquid-fuel pump and to a liquid-fuel accumulator chamber inside at least one liquid-fuel injection valve that is operable to introduce said liquid fuel from said liquid-fuel accumulator chamber through a first nozzle directly into said combustion chamber;
• a gaseous-fuel supply system comprising:
• a gaseous-fuel supply pipe;
• a gaseous-fuel pressurizing device with a gaseous-fuel inlet fluidly connected by a gaseous-fuel passage to said gaseous-fuel supply pipe;
• a gaseous-fuel rail fluidly connected to an outlet of said gaseous-fuel pressurizing device and to a gaseous-fuel accumulator chamber inside at least one gaseous-fuel injection valve that is operable to introduce said gaseous fuel from said gaseous-fuel accumulator chamber through a second nozzle directly into said combustion chamber;
• and
• a drain rail with a receiving end fluidly connected to at least one drain passage from said liquid-fuel injection valve and at least one drain passage from said gaseous-fuel injection valve, and a discharge end fluidly connected to said liquid-fuel storage vessel, and a venting device through which said gaseous fuel is ventable from at least one of said drain rail and said liquid-fuel storage vessel.