Dual fuel injector and method

A fuel system comprising:

• a first high pressure fuel conduit;
• a second high pressure fuel conduit;
• a fuel injector forming a first fuel inlet fluidly connected to the first high pressure fuel conduit, a first nozzle outlet, a second fuel inlet fluidly connected to the second high pressure fuel conduit, and a second nozzle outlet, and including a dual concentric check assembly having an inner check and an outer check;
• a fuel flow clearance is defined between the inner check and the outer check and forms a first nozzle supply passage extending between the first fuel inlet and the first nozzle outlet;
• a second nozzle supply passage is formed in the fuel injector and extends between the second fuel inlet and the second nozzle outlet;
• and
• a tight guide clearance is defined between the inner check and the outer check.

A method of operating a fuel system comprising:

• lifting an inner check in a dual concentric check assembly in a fuel injector to open a first nozzle outlet to inject a first fuel;
• lifting an outer check in the dual concentric check assembly in the fuel injector to open a second nozzle outlet to inject a second fuel;
• guiding the inner check during the lifting the inner check via a tight guide clearance defined between the inner check and the outer check;
• guiding the outer check during the lifting the outer check via a tight guide clearance defined between the outer check and an injector housing of the fuel injector;
• and
• feeding the first fuel through a fuel supply orifice formed in the inner check to a fuel flow clearance defined between the inner check and the outer check and forming a nozzle supply passage to the first nozzle outlet.