Characterization of flame stabilization modes in an ethylene-fueled supersonic combustor using time-resolved CH* chemiluminescence

Flame stabilization in a Ma = 2.5 direct-connect supersonic combustor was experimentally characterized with a fixed stagnation pressure of 1.0 MPa and wide ranges of stagnation temperature (T-0) from 1200 K to 1800 K and global equivalence ratio (Phi) of ethylene/air from 0.1 to 0.8. Four typical flame stabilization modes were identified by using the time resolved CH* chemiluminescence and presented as a regime nomogram in the T-0-Phi parameter space. As increasing T-0, the range of Phi for the flame stabilization modes is widened and that for the oscillation mode is therefore narrowed. The widely used quasi-1D analysis, with the experimentally determined wall static pressure distribution as input parameters, suggests that the combustor operates in a scramjet mode when the flame is stabilized in the cavity shear layer and in a ramjet mode when the flame is in the jet-wake. The flame oscillation mode, observed only for a narrow range of Phi, was found to correlate with the combustor transition between the scramjet and ramjet modes. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.