Blowoff Characteristics of a Bluff-Body Stabilized, Multi-Element, Lean Premixed Pre-Vaporized Combustor for Supersonic Transport Applications

This work explores the flame stabilization and blowoff characteristics of a novel lean premixed pre-vaporized (LPP) combustor design for potential commercial supersonic transport (CST) applications. CST operating conditions involve higher combustor inlet temperatures and lower inlet pressures than encountered in conventional subsonic aeroengines. Additionally, the LPP combustor investigated in this work is a multi-element subsonic flow design, with four bluff-body stabilized, annular “main” flames surrounding a central, swirl-stabilized pilot flame. Existing blowoff studies have not explored the combined effects of multi-element flames with varying temperature and pressure simultaneously. This work presents experimental analysis of the conditions that lead to blowoff in such a combustor. The experimental data consists of simultaneous pressure fluctuations, high-speed OH* chemiluminescence imaging and low-speed kerosene planar laser induced fluorescence imaging. The operating conditions for each data set were used to evaluate the Reynolds number (Re) and Damköhler number (Da). Plots of Da versus Re indicate that the Da at blowoff is lower than that reported in literature for flames stabilized on axisymmetric bluff bodies. It is hypothesized that the observed trend is due, in part, to the presence of the central pilot flame which breaks the axisymmetry of the individual main flames and acts as an ignition source for low Da conditions. An investigation of a case with intermittent blowoff reveals the presence and effects of unforeseen hysteresis in the combustor.