Fuel injector, a fuel injector assembly and an associated method

A fuel injector comprising a valve member, a valve member guide, a spring chamber, a fuel supply passage and a cleaning fluid supply passage;

• the valve member being movable with respect to the valve member guide into and out of contact with a valve seat of the fuel injector to thereby control discharge of a fuel out of a fuel injector outlet;
• the valve member guide defining a bore which receives the valve member, the bore being configured to guide the valve member during sliding movement of the valve member into and out of contact with the valve seat, the bore comprising a first end proximate the fuel injector outlet and a second end distal the fuel injector outlet with the bore and a portion of an outer surface of the valve member disposed between the first end and the second end of the bore defining a clearance distance between the valve member and the valve member guide, and the valve member guide defining a drainage passage extending from the bore to an outer surface of the valve member guide and intersecting the bore at a drainage port located between the first end and the second end of the bore, wherein the valve member guide comprises an annular drainage gallery defined in the bore and intersected by the drainage passage at the drainage port;
• the spring chamber containing a biasing member which biases the valve member into contact with the valve seat, the spring member being in fluid communication with the second end of the bore;
• the fuel supply passage being configured to direct a flow of the fuel at a first pressure to an outlet chamber of the fuel injector, the outlet chamber being in fluid communication with the first end of the bore and the valve member;
• wherein the fuel supply passage by-passes the spring chamber;
• and
• the cleaning fluid supply passage being in fluid communication with the spring chamber and configured to supply a pressurised cleaning fluid at a second pressure greater than the first pressure to the second end of the bore to restrict leakage of the fuel from the outlet chamber towards the second end of the bore along the clearance, and configured to simultaneously supply the pressurised cleaning fluid when the fuel supply passage is directing the flow of fuel to the outlet chamber.