Dual fuel injection valve and method of operating a dual fuel injection valve

A dual fuel injection valve for independently and separately injecting two different fuels into a combustion chamber of an internal combustion engine, said dual fuel injection valve comprising:

• (a) a hollow injection valve body comprising:
• a first-fuel inlet port through which a first fuel can be introduced at injection pressure into said valve body;
• a first-fuel passage provided within said valve body and extending between said first-fuel inlet port and a first-fuel cavity;
• a second-fuel inlet port through which a second fuel can be introduced at injection pressure into said valve body;
• a second-fuel passage connecting said second-fuel inlet port to a second-fuel cavity;
• (b) a dual needle assembly comprising:
• an outer needle, which is hollow and disposed within said injection valve body, wherein said outer needle is movable between a closed position in which a first sealing surface associated with said outer needle contacts a first seat associated with said body and an open position in which said first sealing surface is spaced apart from said first seat, allowing said first fuel to flow from within said first-fuel cavity into said combustion chamber through at least one first-fuel ejection port;
• and
• an inner needle, which is disposed within said hollow outer needle, wherein said inner needle is movable between a closed position in which a second sealing surface associated with said inner needle contacts a second seat associated with said outer needle and an open position in which said second sealing surface is spaced apart from said second seat, allowing said second fuel to flow from within said second-fuel cavity into said combustion chamber through at least one second-fuel ejection port;
• (c) a first actuator assembly operable to selectively move said outer needle between said open and closed positions:
• (d) a second actuator assembly operable to selectively move said inner needle between said open and closed positions, wherein at least one of said first and second actuator assemblies comprising a hydraulic actuator;
• (e) a hydraulic fluid inlet port through which pressurized hydraulic fluid can be introduced into fluid passages and a control chamber disposed within the interior of said valve body;
• (f) a hydraulic fluid drain port through which hydraulic fluid can be drained from said control chamber;
• and
• (g) at least one control valve that is operable to selectively govern the flow of said hydraulic fluid whereby hydraulic fluid pressure within said control chamber is controllable to influence movement of at least one of said outer needle and said inner needle between respective open and closed positions;
• and
• (h) wherein said control chamber is employed to influence the position of said outer needle and said control valve is operable to selectively control the flow of hydraulic fluid between said control chamber and said drain port or between said hydraulic fluid inlet port and said control chamber, to modulate pressure within said control chamber between drain pressure, when pressure within said control chamber is substantially equal to pressure at said drain port, and rail pressure, when pressure within said control chamber substantially equal to pressure at said hydraulic fluid inlet port.