Method of predicting stability against acoustic vibrations in liquid rocket engine combustors based on combustion noise

An experimental method for determining the limiting pressure perturbations initiating acoustic instability in liquid rocket engine combustors has been developed which can be used to estimate of the stability of the working process. The method involves a statistical processing of the recorded noise pressure pulsations in the vicinity of natural resonance frequencies for all normal modes of acoustic vibrations in cylindrical combustion chambers and gas generators. The vibration damping coefficient (decrement), characterizing the difference between the generated and dissipated energy, is adopted as a diagnostic predictive criterion of the stable or unstable state of a dynamic system. The method is based on the theory of self-oscillating dynamic systems and one-dimensional Markov random processes using the apparatus of the Fokker–Planck–Kolmogorov equation. Analysis of the nonlinear differential equation with a symmetrized stochastic right-hand side describing white noise for experimentally determined amplitudes of pressure pulsations and their statistical processing using Mera software allows the state of the self-oscillating system to be identified a stable or unstable. The method is passive and applicable used without using standard external pulsed disturbing devices.