An improved fuel system for a dual-fuel internal combustion engine. During normal operation, the primary fuel passes through a pressure regulator before arriving at a primary fuel rail. Further, pressurized secondary fuel is delivered to both a secondary fuel rail and to the pressure regulator for purposes of regulating the output pressure of the primary fuel that is delivered to the primary fuel rail. When the pressure at the primary fuel supply or between the primary fuel supply and the pressure regulator drops below a minimum operating pressure, the pressure regulator is isolated from the secondary fuel and the secondary fuel continues to be pressurized until it reaches a suitable pressure for operating in a limp mode. Then, the secondary fuel, which is pressurized to greater than a normal operating pressure, may be injected at the higher pressure for improved performance of the engine in the limp mode.

The present disclosure provides a high-pressure fuel pump having barrel sets comprising offset, opposing barrel units within the same plane and having plungers disposed therein. The high-pressure fuel pump further includes a camshaft having at least one offset lobe and a cam ring encircling the lobe and in contact with the plungers, which translate the rotational movement of the camshaft to longitudinal movement of the plungers, controlling inflow, compression, and outflow of fuel within the pump.

The present disclosure provides a high-pressure fuel pump having barrel sets comprising offset, opposing barrel units within the same plane and having plungers disposed therein. The high-pressure fuel pump further includes a camshaft having at least one offset lobe and a cam ring encircling the lobe and in contact with the plungers, which translate the rotational movement of the camshaft to longitudinal movement of the plungers, controlling inflow, compression, and outflow of fuel within the pump.