OH planar laser-induced fluorescence measurement for H2/O2 jet diffusion flames in rocket combustion condition up to 7.0 MPa

This study focuses on the application of OH planar laser-induced fluorescence (OH-PLIF) in high-pressure rocket combustion conditions, up to 7.0 MPa. The signal to noise ratio of PLIF degrades in high-pressure combustion owing to effects such as line broadening and interference from intense chemiluminescence. The OH(2,0) band excitation method was applied to obtain the OH(2,1) fluorescence emitted near 290 nm and filter out the intense OH(0,0) band chemiluminescence emitted near 308 nm. The gaseous H2/O2 (GH2/GO2) jet diffusion flame was formed using a recessed coaxial shear injector. The GH2/GO2 injection Reynolds number, Re (ReH2/ReO2 ≈ 2320/22800–4660/45600), was varied to examine the variation of the flame structure and reaction zone thickness under each pressure condition Pc, and Re injection condition. In addition, the variation of the experimentally derived full width at half maximum (FWHM) of the radial OH distribution, δOH, with the Damköehler number, Da, was compared with that of the simulated FWHM of the OH mole fraction, δOH-SIM. The OH distribution was clearly observed in the instantaneous PLIF image while eliminating the intense OH chemiluminescence even in the highest pressure condition of 7.0 MPa, which is a pressure higher than any of the previous OH-PLIF studies conducted on rocket combustion. The flame structure showed the typical characteristics of a turbulent jet diffusion flame and depended on Re rather than on the chamber pressure Pc. The variation of δOH with Da corresponded qualitatively with δOH-SIM and showed the characteristics of flame stretch in the vicinity of the injector.