Strategies for obtaining long constant-pressure test times in shock tubes
Several techniques have been developed for obtaining long, constant-pressure test times in reflected shock wave experiments in a shock tube, including the use of driver inserts, driver gas tailoring, helium gas diaphragm interfaces, driver extensions, and staged driver gas filling. These techniques are detailed here, including discussion on the most recent strategy, staged driver gas filling. Experiments indicate that this staged filling strategy increases available test time by roughly 20 % relative to single-stage filling of tailored driver gas mixtures, while simultaneously reducing the helium required per shock by up to 85 %. This filling scheme involves firstly mixing a tailored helium–nitrogen mixture in the driver section as in conventional driver filling and, secondly, backfilling a low-speed-of-sound gas such as nitrogen or carbon dioxide from a port close to the end cap of the driver section. Using this staged driver gas filling, in addition to the other techniques listed above, post-reflected shock test times of up to 0.102 s (102 ms) at 524 K and 1.6 atm have been obtained. Spectroscopically based temperature measurements in non-reactive mixtures have confirmed that temperature and pressure conditions remain constant throughout the length of these long test duration trials. Finally, these strategies have been used to measure low-temperature n-heptane ignition delay times.
KeywordsLong test time Driver insert Driver gas tailoring Staged driver gas filling Reflected shock Shock tube
This work was supported by the Army Research Office, with Dr. Ralph Anthenien as technical monitor. M.F.C. was supported by the Division of Chemical Sciences, Geosciences, and Biosciences, the Office of Basic Energy Sciences (BES), the US Department of Energy (DOE). Also, during a portion of this work, M.F.C. was supported by a National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. The authors wish to acknowledge Andrew Lawson and Kaley Boyce for their assistance in the configuration of the shock tube, and further wish to thank the technicians in the Stanford University plumbing shop for assistance in configuration of driver inserts.
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