Needle valve member with frustoconical guide segment and fuel injector using same

A fuel injector (10) includes an injector body (11) with a tip component (30) that defines at least one nozzle outlet (12). A needle valve member (40) is positioned in the injector body (11) and includes a frustoconical segment (43) positioned in a frustoconical bore (23) to separate a needle control chamber (20) from a nozzle chamber (21). The needle valve member (40) includes an opening hydraulic surface (41) exposed to fluid pressure in the nozzle chamber (21), and a closing hydraulic surface (42) exposed to fluid pressure in the needle control chamber (20). The frustoconical bore (23) and the frustoconical segment (43) have a narrowing taper in the direction of an injector tip (47). The frustoconical features tend to slow the initial opening of the nozzle outlets (12), and hasten their closure relative to a counterpart injector with cylindrical needle guide features.