Characterization of Centrifugally-Loaded Flame Migration for Ultra-Compact Combustors

The Air Force Research Laboratory (AFRL) has designed an Ultra Compact Combustor (UCC) showing viable merit for significantly reducing gas turbine combustor length making it a viable candidate for implementation as an inter-turbine burner and realization of efficiency benefits from the resulting near constant temperature cycle. This concept uses an off-axis combustor cavity and projects approximately 66% length reduction over a conventional combustor. The annular nature of the cavity creates high angular acceleration levels, on the order of 500-3500 g's, resulting in strong centrifugal and buoyant forces. This unique combination works to significantly reduce the required burn time and subsequently required combustor size. However, currently tested experimental models are in the 10-20 cm diameter range while application to larger-scale commercial and military engines would require a UCC in the 50-60 cm diameter range. The Air Force Institute of Technology's Combustion Optimization and Analysis Laser (COAL) laboratory was specifically designed to study the underlying UCC dynamics and investigate the feasibility of scaling the UCC to the significantly larger diameter range. Using a sectional model of AFRL's annular UCC allows customization of the UCC model to investigate varying several parameters of interest associated with the UCC scaling. Several diagnostic methods were used such as Particle Image Velocimetry (PIV) for fowfield measurements, two-line Planar Laser-Induced Fluorescence (PLIF) of the hydroxyl (OH) radical for 2-D temperature profiles, single-line PLIF for qualitative flame location, and high-speed video to investigate flame migration trajectory. The original document contains color images.