液体酸素・水素ロケットエンジン燃焼場における同軸型噴射器の 噴射連成による非定常燃焼挙動の光学計測

抄録

Injection-coupled combustion instability is one of the critical issues of the rocket engine combustion. The detailed mechanism of the injection-coupled combustion instability has not been clarified yet. Recently, high-speed optical measurement techniques are frequently used to observe unsteady combustion behaviors, and modal decomposition techniques are widely used to extract dominant oscillation modes from the optical measurement results. In this study, injection-coupled combustion instability behaviors of a shear coaxial injector under a subcritical condition are observed with high-speed imaging techniques such as direct observation of flame and backlit image observation. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) techniques are used to extract the dominant oscillation modes. The dominant frequency of the combustion pressure and propellant injection pressures correspond to the acoustic natural frequency of the liquid oxygen post of the injector. The liquid oxygen jet deforms axisymmetrically with the observed dominant frequency. The POD and DMD analysis show that both direct images of the flame and backlit images oscillate with the observed dominant frequency, therefore, the heat release oscillation which results in the oscillation in the combustion pressure is caused by the periodic deformation of the LOX jet with the natural frequency of the LOX post.