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Technological advances for lowering the emissions of rich burn-quick mix-lean burn (RQL) combustors in response to increasingly stringent emissions regulations will be accompanied by more challenging operability issues, especially ignition along the flight envelope for both conventional and alternative aviation fuels. The aim of this paper is to research the ignition failure modes during ignition kernel propagation in swirl spray flames. These experiments were conducted on an optically accessible single fuel nozzle RQL model combustor featuring a fuel-air mixing device and combustor primary and dilution zones established by two rows of primary/dilution jets. The ignition tests were performed at both atmospheric and sub-atmospheric pressures, and the total pressure loss across the liner varied from 1% to 6%. A highspeed camera was utilized to capture images of the kernel and flame propagation during the ignition process. The camera frame speed rate was 6750 Hz with 1/51000 s exposure time and the image resolution of 768×768 pixels covering 80×80 mm field view of the combustor considered critical for the investigation. In the successful ignition case, the initial ignition kernel generated near the igniter was transported and stabilized downstream of the swirler exit, followed by stable combustion covering the entire combustor. In the failed ignition cases, the ignition kernel underwent a series of breakups following its formation. In these failure cases, parts of the sub-kernel were extinguished while the rest moved downstream towards the combustor exit, indicating that the kernel was not transported to the primary zone flame stabilizing portion of the combustor. Three ignition failure modes were determined from the high-speed images: ignition kernel “extinction”, ignition kernel “breakup”, and ignition kernel “downstream movement”. While flameout in gas turbine combustors is mainly caused by aerodynamic quenching and/or fuel starvation, the alternation of ignition failure modes can be correlated with the fuel-air ratio and air mass flow rate. INTRODUCTION Ignition performance is an elementary requirement for a practical combustion device. The initiation and subsequent establishment of combustion are vital for any combustion system, especially for an aero-engine combustor (Mastorakos, 2017). In response to increasingly stringent emissions regulations, technological advances for lowering the emissions of rich-burn quick-mix lean-burn (RQL) combustors will be accompanied by operability challenges including reliable ignition throughout the flight envelope for both conventional and alternative aviation fuels. The key design features for these ultra-low emission combustors are fuel-air mixing mechanisms and combustor primary/dilution

Ignition Failure Modes During Ignition Kernel Propagation in Swirl Spray Flame