Multi-function fuel injector valve in dual fuel system and fuel system operating method

A fuel system comprising:

• a first fuel supply of a first fuel;
• a second fuel supply of a second fuel;
• a fuel injector forming a low-pressure fuel space fluidly connected to the first fuel supply, a first-fuel nozzle supply passage, a second-fuel nozzle supply passage, a combined-fuel outlet passage extending to a plurality of nozzle outlets, and a nozzle check control cavity;
• and
• the fuel injector further including a control valve movable between a first position blocking the low-pressure fuel space from both the first-fuel nozzle supply passage and the nozzle check control cavity, and a second position at which the low-pressure fuel space is fluidly connected to both of the first-fuel nozzle supply passage and the nozzle check control cavity;
• and
• the fuel injector further including a valve seat, and the control valve is in contact with the valve seat at the first position.

A method of operating a fuel system comprising:

• feeding a first fuel to a first-fuel inlet of a fuel injector;
• feeding a second fuel to a second-fuel inlet of the fuel injector;
• operating a control valve in the fuel injector to admit the first fuel to an outlet passage in the fuel injector;
• pressurizing a fuel charge containing the first fuel in the outlet passage, including increasing a pressure of the fuel charge to an injection pressure in the outlet passage;
• and
• injecting the fuel charge via operating the control valve to relieve a closing hydraulic pressure on a nozzle check of the fuel injector.