Supersonic combustion sensing by the passive endoscopic flame sensor

The improvement of ramjet performance in the future wide-area flight envelope requires advanced combustion organization strategies and engine system control technology. Among them, high-dynamic frequency response sensors and actuators are one of the key technologies of the high-performance control system FADEC. Stable and reliable, simple structure, non-intrusive, low energy consumption, and light weight are the basic requirements of the ramjet online sensors. This paper develops an optical fiber flame sensor based on passive flame chemiluminescence for optical diagnosis, andpreliminarily verifies the value of the optical fiber flame sensor's data for sensing the combustion process. Based on the direct-connected supersonic combustion test bed of the Institute of Mechanics, Chinese Academy of Sciences, the flight conditions with a total incoming flow temperature of 1475 K, a total incoming pressure of 1.68 MPa and an incoming Mach number of 5.6 are simulated. Using a newly developed endoscopic fiber optic flame sensor, the combustion heat release rate characterized by CH* and the local equivalence ratio characterized by C₂*/CH* were measured under different equivalence ratios and momentum-to-flux ratios. The analysis results show that the endoscopic optical fiber sensor can sense the temporal and spatial evolution characteristics of the heat release rate of the combustion chamber; The endoscopic fiber optic sensor can sense the combustion oscillation characteristics in the frequency domain, and experiments show that there may be spanwise thermoacoustic oscillations in the combustion process; The C₂*/CH* optical signal of the endoscope optical fiber sensor can perceive the temporal and spatial evolution characteristics of the local equivalence ratio, and can be combined with the CH* optical signal to study the correlation between the mixed field and the combustion field; The statistical characteristics of the local flame centroid position characterized the shear-layer flame stabilization mode and jet wake flame stabilization mode.