Research and development of combustion technologies to reduce NOx emission of aero-engines to 20% of ICAO CAEP4 is progressing as a part of a project of JAXA (Japan Aerospace Exploration Agency), the Technology Development for Clean Engine (TechCLEAN). To realize such low NOx level on aero-engines, it is necessary to use not conventional combustion system such as rich-lean combustion but advanced one such as premixed combustion. We are conducting research and development of staging fuel nozzles that use diffusion combustion for the pilot nozzle and premixed combustion for the main nozzle. As the first step, five fuel nozzles were tested experimentally in the form of single-sector combustor. Test conditions were selected as the LTO cycle of presumed small-class engines. From the result of tests, to combine the combustion efficiency in low engine power condition and low NOx emission in high power one, fuel nozzle models that have triple contrary swirler are suitable. However, the combustion efficiency in 7%MTO is lower than that of current engines. It is necessary to decrease the emission of CO.Copyright © 2009 by ASME