Experimental investigation on the mixing and combustion characteristics with dual combined flame stabilizers in scramjet using simultaneous OH/kerosene-PLIF and Mie scattering measurements

Experimental investigation on the mixing and combustion characteristics with dual combined flame stabilizers in scramjet was conducted using simultaneous 10 kHz OH/kerosene-PLIF (planar laser induced fluorescence) and 1 kHz Mie scattering measurements. Signal-to-noise ratio (SNR) analysis of the image processing confirmed effective suppression of liquid-phase interference, with the SNR improving from 4 to 10. The results revealed distinct differences in flame structure and fuel distribution between scramjet and ramjet combustion modes, as well as a transition mode. In scramjet mode, the flame area reached 44.3 cm² with a relative standard deviation (RSD) of 11 %, indicating a strong, turbulent reaction zone with high combustion intensity. Ramjet modes exhibited reduced flame areas of 37.5–38.2 cm² and similar RSD values, while the transition mode showed a diminished flame area of 33.4 cm² and increased instability (RSD 12 %). Mixing area analysis showed efficient fuel distribution in scramjet and partial ramjet modes (33.4 cm², RSD 17–22 %), but significant degradation in the transition mode (20.8 cm², RSD 35 %). Further analysis using Extended Proper Orthogonal Decomposition (EPOD) and Simultaneous Dynamic Mode Decomposition (SDD) identified key spatial characteristics, confirming stronger turbulence-chemistry interactions in scramjet combustion and highlighting the differences in combustion dynamics across modes. These findings provide valuable insights into fuel–air mixing and combustion dynamics in advanced scramjet engines, offering crucial information for optimizing performance and efficiency in future air-breathing propulsion systems.