Experimental and theoretical studies on thermoacoustic limit cycle oscillation in a simplified solid rocket motor using flat flame burner

Combustion instability is a common phenomenon in solid rocket motors. Coupling between pressure and heat release rate produces pressure oscillation, which seriously affects the operation and safety of the motors. It is necessary to investigate this mechanism in order to prevent or at least suppress pressure oscillations. A segmented combustor is designed, and a movable flat flame burner is used as the heating source. A stability map is plotted by moving the flat flame burner along the combustor and changing the equivalence ratio. The experimental results are predicted by employing the low-order thermoacoustic network model. When the heat source position is fixed, it is shown that the combustion changes from stable to very unstable and then returns to a stable state, with the increase of equivalence ratio from 0.9 to 1.5. The pressure oscillation is the strongest in the rich combustion region (equivalence ratio is 1.2-1.3), with the amplitude of about 122 dB. The pressure oscillation is strongest and the amplitude is about 125 dB, when the heat source is close to the nozzle exit. The calculation results by thermoacoustic network model agree well with the experimental results. The stability map and limit cycle characteristics of thermoacoustic oscillation can be accurately estimated. It indicates that this experimental method and theoretical model can be used to capture the limit cycle behavior, and provide a new scheme for predictions of thermoacoustic oscillation in solid rocket motors.

Automated summary

The study reveals that when the heat source position is fixed in solid rocket motors, combustion transitions from stable to very unstable as the equivalence ratio increases from 0.9 to 1.5, then returns to a stable state. The strongest pressure oscillations are observed in the rich combustion region and when the heat source is close to the nozzle exit, reaching approximately 122-125 dB in amplitude. The experimental method and theoretical model used can accurately estimate the stability map and limit cycle characteristics of thermoacoustic oscillation in solid rocket motors.