Dynamic behavior of high-frequency combustion instability in a model sub-scale rocket engine combustor.

We experimentally explore the dynamic behavior of a transition from stable combustion to high-frequency combustion instability in a model sub-scale rocket engine combustor using the analytical methods based on complex network and symbolic dynamics. As the model sub scale rocket engine combustor, we use a cylindrical combustor with an off-center installed coaxial injector that is identical to our previous study [Aoki et al., J. Appl. Phys. 127, 224903 (2020)]. The most interesting result obtained in this work is that the dynamical state of stable combustion changes from high-dimensional chaotic oscillations to strongly correlated limit cycle oscillations via weakly correlated limit cycle oscillations. The formation of the in-phase synchronization between the acoustic pressure and heat release rate fluctuations during limit cycle oscillations is clearly identified by the symbolic dynamics-based synchronization index[K. Asami et al., EuroPhys. Lett. 139 13001 (2022); K. Baba et al., Chaos 33, 073101 (2023)] and symbolic transfer entropy [M. Staniek and K. Lehnertz, Phys. Rev. Lett. 100, 158101 (2008)]. The directional dependence between the acoustic pressure and heat release rate fluctuations switches during the transition from high-dimensional chaotic oscillations to strongly correlated limit cycle oscillations. The emergence of coherent structures in heat release rate field fulfills an important role in the transition to strongly correlated limit cycle oscillations.