Pilot fuel nozzle assembly with vented venturi

A pilot fuel nozzle assembly for a combustor of a gas turbine engine, the pilot fuel nozzle assembly comprising:

• a pilot fuel nozzle defined about a fuel nozzle centerline axis;
• a pilot oxidizer inlet disposed about the pilot fuel nozzle;
• a pilot splitter arranged radially outward of the pilot fuel nozzle, a pilot inner air passage being defined between the pilot fuel nozzle and the pilot splitter and being in fluid communication with the pilot oxidizer inlet;
• a vented pilot venturi disposed radially outward of the pilot splitter and in fluid communication with the pilot oxidizer inlet, a pilot outer air passage being defined between the pilot splitter and the vented pilot venturi, wherein the vented pilot venturi comprises, an annular wall extending circumferentially about the fuel nozzle centerline axis, and extending in a longitudinal direction along the fuel nozzle centerline axis from an inlet end of the vented pilot venturi to an outlet of the vented pilot venturi, wherein the annular wall comprises an oxidizer flow passage within the annular wall, the oxidizer flow passage extending from the inlet end of the vented pilot venturi to an outlet end of the vented pilot venturi adjacent to the outlet, and the oxidizer flow passage being in fluid communication with the pilot oxidizer inlet, wherein the annular wall defines an inner venturi surface defining an open cavity through the vented pilot venturi, the inner venturi surface including:
• (a) a throat area disposed between the inlet end of the vented pilot venturi and the outlet of the vented pilot venturi, the throat area having a smaller diameter than a remaining portion of the inner venturi surface downstream of the throat area;
• and
• (b) an expansion flow surface portion disposed, in the longitudinal direction, from the throat area to the outlet of the vented pilot venturi, the expansion flow surface portion have a first diameter at the throat area and a second diameter at the outlet, the second diameter being larger than the first diameter,
• wherein the annular wall further defines a plurality of venturi oxidizer outlet ports extending from the oxidizer flow passage through the expansion flow surface portion, the plurality of venturi oxidizer outlet ports being circumferentially spaced about the fuel nozzle centerline axis,
• wherein the expansion flow surface portion comprises a first conical-shaped surface extending, in the longitudinal direction, from the throat area to a breakpoint arranged between the throat area and the outlet, the breakpoint being arranged, in the longitudinal direction along the fuel nozzle centerline axis such that a longitudinal distance from the throat area to the breakpoint is greater than a longitudinal distance from the breakpoint to the outlet, and a second conical-shaped surface extending from the breakpoint to the outlet, the first conical-shaped surface, with respect to the fuel nozzle centerline axis, being arranged at a first conical half-angle, and the second conical-shaped surface, with respect to the fuel nozzle centerline axis, being arranged at a second conical half-angle greater than the first conical half-angle,
• wherein the outlet of the vented pilot venturi comprises a rounded outlet tip portion having an outlet tip portion surface in fluid communication with a downstream end of the second conical-shaped surface and the outlet tip portion surface defining, at least on part, the outlet,
• wherein the vented pilot venturi includes a plurality of tip oxidizer outlet ports about a circumference of the rounded outlet tip portion, and the plurality of tip oxidizer outlet ports extend from the oxidizer flow passage through the rounded outlet tip portion, and
• wherein the rounded outlet tip portion is formed between and adjacent the second conical-shaped surface and an exterior surface of the annular wall that extends parallel to the fuel nozzle centerline axis.