Velocimetry for Gaseous Detonations Using Femtosecond Laser Electronic Excitation Tagging (FLEET)

Understanding the velocity of gases behind detonation waves is critical for improving our understanding of detonation processes and achieving more accurate simulations for detonation engines. In this work, we demonstrate femtosecond laser electronic excitation tagging (FLEET) as a means to study the flow field of a gaseous H2/O2/N2 detonation inside a detonation tube. FLEET is used to excite nitrogen in a flow in order to track molecules non-intrusively. The emission from tagged nitrogen covers a range of wavelengths and is captured with an intensified camera using delayed exposures. Then, the images are spatially resolved using custom codes to provide velocity estimates. Results from this study show that FLEET signals can be successfully extracted from gaseous regions behind detonation waves and gas velocities up to 800 m/s are be extracted for delay times as close as 60 microseconds behind the detonation wave. Using these velocity statistics, the flow profiles behind detonation waves can be analyzed in order to provide more accurate estimates for non-dimensional scaling and detonation model validation applications.