Characterisations of self-excited nonlinear oscillations at varied system parameters in a Rijke tube with a premixed laminar flame

Thermoacoustic instability has been one of the major concerns in various industrial combustion systems, such as Rich burn, Quick mix, Lean burn engine and aerospace engines. The complex interactions between heat release and pressure fluctuations could generate thermoacoustic oscillations with high amplitudes and frequencies in a combustion chamber, which causes many combustion problems even severe structural damage. The studies about the effects of various system parameters on thermoacoustic instability would be important due to their crucial roles in characterising the system oscillations. In this study, the effects of different system parameters in a Rijke tube, including equivalence ratio, methane flowrate, burner position and tube inner diameter, have been investigated. The time-domain analysis methods, including both phase space analysis constructed from the time-delayed method and recurrence analysis, have been conducted to explore the system characteristics under different system parameters. Furthermore, the Recurrence Quantitative Analysis (RQA) and Wayland translation error have been processed to quantify the system nonlinearity. The study has shown the effects of system parameters on system frequency response, deterministic nature and nonlinear dynamics. The system oscillation tends to be more complex and unstable when the burner is moved to lower positions or in a large diameter tube. The phase space and recurrence analysis are found to be efficient for characterising the system nonlinearity with useful insights of self-excited thermoacoustic oscillations.