A fuel injector nozzle (10, 120, 200) for a gasifier comprising, a) a fuel injector body having an upstream end and a downstream end, b) concentric inner and outer conduits (22,24,26) extending from the upstream end to the downstream end to permit segregated flow of a stream of oxygen-containing gas and a stream of carbonaceous fuel from the downstream end, c) the downstream end of the fuel injector nozzle having an outlet orifice and an annular downstream end surface, said downstream end surface (62, 126, 206) being formed with a recess (90, 130, 210) and d) an annular refractory insert (72, 150, 230) secured within said recess for providing thermal and thermo-chemical protection to the fuel injector nozzle at the downstream end, said annular refractory insert having an exposed end surface (76, 164) that is substantially coplanar With the downstream end surface of said fuel injector nozzle; characterized in that: said insert (72, 150, 230) is trapezoidal in cross section and said recess (90, 130, 210) is an annular channel with a trapezoidal cross section formed in the metal annular surface which has a shape and magnitude that are substantially complementary with the trapezoidal shape of insert (72, 150, 230) so as to accommodate the insert (72, 150, 230); said annular channel is further provided with retaining means (110, 144, 226); and said insert is provided with a groove (80, 172) on its inner circumference to receive said retaining means. a) a fuel injector body having an upstream end and a downstream end, b) concentric inner and outer conduits (22,24,26) extending from the upstream end to the downstream end to permit segregated flow of a stream of oxygen-containing gas and a stream of carbonaceous fuel from the downstream end, c) the downstream end of the fuel injector nozzle having an outlet orifice and an annular downstream end surface, said downstream end surface (62, 126, 206) being formed with a recess (90, 130, 210) and d) an annular refractory insert (72, 150, 230) secured within said recess for providing thermal and thermo-chemical protection to the fuel injector nozzle at the downstream end, said annular refractory insert having an exposed end surface (76, 164) that is substantially coplanar With the downstream end surface of said fuel injector nozzle; characterized in that: said insert (72, 150, 230) is trapezoidal in cross section and said recess (90, 130, 210) is an annular channel with a trapezoidal cross section formed in the metal annular surface which has a shape and magnitude that are substantially complementary with the trapezoidal shape of insert (72, 150, 230) so as to accommodate the insert (72, 150, 230); said annular channel is further provided with retaining means (110, 144, 226); and said insert is provided with a groove (80, 172) on its inner circumference to receive said retaining means. said insert (72, 150, 230) is trapezoidal in cross section and said recess (90, 130, 210) is an annular channel with a trapezoidal cross section formed in the metal annular surface which has a shape and magnitude that are substantially complementary with the trapezoidal shape of insert (72, 150, 230) so as to accommodate the insert (72, 150, 230); said annular channel is further provided with retaining means (110, 144, 226); and said insert is provided with a groove (80, 172) on its inner circumference to receive said retaining means.