Investigation of Combustion Performance of a Hybrid Airblast Atomizer Under Simulated Low Power Conditions

An aero gas turbine combustor has to meet requirements for both high and low power condition operation. Within the requirements for low power conditions, lean-blow-out (LBO) and combustion efficiency are the basic ones. A pure prefilming air blast atomizer may have difficulty meeting combustion requirements under low power conditions, such as, idle LBO, idle combustion efficiency, etc. Use of a hybrid airblast atomizer may offer a solution for such problems. A hybrid airblast atomizer is a single fuel injection unit that has both pilot and main fuel circuits. A simplex nozzle is often used for pilot fuel circuit and an airblast atomizer of the swirl cup type may be used for the main fuel circuit. For the main fuel circuit, fuel is injected from a number of plain jet holes. The fuel jets are injected towards a venturi, with the help of swirling air from another air swirler, and the main fuel is airblasted and well mixed with both swirler airflows. For low power conditions, the pilot fuel nozzle (simplex nozzle) works alone. Not all of the swirler air will mix with pilot nozzle fuel spray. With appropriate pilot nozzle pressure drop and with some airblast function, the pilot fuel is well atomized and does not fully mix with the swirler air nor with primary hole air. Thus, the low power condition combustion efficiency is improved. The investigation reported in the present paper has concentrated on hybrid atomizer combustion performance under simulated low power conditions, when only the pilot nozzle is operating. The study consists of the following parts: • Pilot nozzle drop size measurement; • Numerical simulation of combustor flow field; • Atmospheric ignition test; • Simulated idle condition LBO test; • Low power condition combustion efficiency test. Results are reported, and future work is defined.