Nonlinear analysis of combustion oscillations in a cavity-based supersonic combustor

Abstract

Combustion oscillations in a supersonic combustor with hydrogen injection upstream of a cavity flameholder are investigated using nonlinear analysis based on experimental measurements. Time series of both flamefront and wall pressure are acquired, and the state space reconstruction approach is adopted to characterize the nonlinear behavior of the combustion oscillations. Three overall equivalence ratios, 0.038, 0.076 and 0.11, are considered. The existence of a chaotic source in the present combustion system is demonstrated. The correlation dimension and the largest Lyapunov exponent tend to become larger with the increasing equivalence ratio, indicating a more complicated and unstable combustion system. In particular, it is found that the correlation dimension for the highest equivalence ratio is much greater than those of the two lower equivalence ratios. Two possible reasons responsible for the observed nonlinear behaviors are identified. One is the shock-related instabilities and the other is the transition of combustion stabilization mode between the cavity and jet-wake stabilized mode.