This paper presents the progress made on the development of a dual spray, direct injection airblast fuel nozzle capable of variable fuel placement. It is anticipated that by varying the fuel placement within the confines of a combustion chamber it will be possible to control localised zonal ‘Fuel Air Ratio’ and thus extend both stability and emissions performance in respect of engine power range. The extension of combustion stability is particularly desirable to high pressure, temperature and turndown ratio aero engines where the ratio between maximum and flight idle fuel flow is extreme. Target performance data for the design has been derived from anticipated future engine cycles. A number of initial concepts were examined and recent development work has focused on the most successful design to date. Combustor testing has been performed at both atmospheric and high pressure. The combustor utilised was a single sector tubular combustor with combustor volume and airflow distributions representative of the cycle for which the fuel injector was designed. Two fuel injector configurations were examined, having different design flow structures. Combustion stability testing was performed with air inlet conditions of atmospheric pressure and 293K. Stability and ignition data were derived over a range of combustor pressure drops. Fuel injector AFRs of over 100:1 were achieved. An ignition loop was also derived although optimisation studies were not performed at this stage. High pressure emissions evaluation was also performed up to 13 Bar. Idle and scaled climb-out power conditions were tested, with a range of fuel scheduling between the pilot and main. Idle efficiency of over 99.5% was achieved. Low emissions performance was also achieved with less than 10 EINOx at climb out power settings. Future work will include testing at up to 40 Bar pressure to establish actual full power performance in addition to further development work on stability and ignition performance.

This paper presents the progress made on the development of a dual spray, direct injection airblast fuel nozzle capable of variable fuel placement. It is anticipated that by varying the fuel placement within the confines of a combustion chamber it will be possible to control localised flame ‘Fuel Air Ratio’ and thus extend both stability and emissions performance in respect of engine power range. The extension of combustion stability is particularly desirable to high pressure, temperature and turndown ratio aero engines where the ratio between maximum and flight idle fuel flows is extreme. Atomiser aerodynamics have been developed that produce two different airflow re-circulating regions within the combustor. A concentric fuel filmer feeds each of these regions. By staging the fuel into each flame re-circulation zone the variation of local ‘Fuel Air Ratio’ can be more accurately controlled. A combination of bench testing and CFD has been used to analyse and manipulate airflow distribution between swirlers to form the two distinct flame regions. The work is ultimately concerned with the rationalisation of airflow distribution and fuel placement to best fit the operational envelope of the engine. The variable placement fuel injector features three or more air swirlers (inner swirler, middle swirler and dome swirler) and two ‘airblast’ fuel filmers (pilot and main). The paper describes the progress made with a number of fuel injector configurations.