A shock tube with tunable, pulsed laser-based diagnostics

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Abstract
This article describes a unique shock tube that is interfaced with a short‐pulse, Nd:YAG‐pumped, tunable dye‐laser system to provide real‐time information on transient chemical species. The tube’s internal bore (38.1‐mm‐diam) accomodates 18 optical diagnostic ports. Pressure‐driven shock waves are generated in a double‐diaphragm driver section and are timed in the driven section by HeNe laser schlieren detectors. Incident shock speeds range between 1000 and 1500 m/s and are reproducible to ±5 m/s. Individual pulses from the laser and the gate for a photodiode array detector are synchronized with the arrival of shock fronts at the viewing station. Laser‐induced fluorescence (LIF) imaging experiments demonstrate the diagnostic power of the new apparatus. One‐dimensional (1D) LIF images are recorded in shocked mixtures of ethane, oxygen, and argon by propagating the tunable laser beam along the shock tube’s axis and collecting fluorescence from the OH radical on the 1D detector. The detection sensitivity limit for OH by LIF in this shock tube is approximately 4×1011 radicals/cm3 (0.1 ppm).