Development of fast-sampled species and laminar flame speed measurement techniques in a shock tube
Keywords: Mechanical Engineering.

This dissertation focuses on the development of two experimental approaches for the study of low-temperature combustion kinetics in a shock tube: a combined laser absorption spectroscopy-gas chromatography (LAS-GC), fast-sampling speciation diagnostic, and a method for measuring laminar flame speeds in a shock tube at previously unexplored temperature conditions. The combined LAS-GC speciation technique was developed in three stages. First, an endwall sampling system was developed to provide species yield measurements in conventional shock tube experiments. The diagnostic was paired with an in situ ethylene laser absorption diagnostic and used to study ethylene pyrolysis at conditions ranging from 1200-2000 K at 5 atm. A methodology for accurately comparing species-yield sampling results with laser and model results is also presented. In the second stage of GC fast-sampling technique development, the endwall sampling system was used to study low-temperature n-heptane oxidation. Quasi-time-resolved endwall samples were extracted and used to quantify intermediate species present between first- and second-stage n-heptane ignition. Three laser diagnostics were simultaneously employed to measure temperature, carbon dioxide, water, and ethylene. Laser-measured ignition delay times indicate an overestimation of three primary RO2 isomerization reactions in the kinetic model used for comparison. In the third stage of technique development, long test-time shock tube experiments were conducted to allow for three consecutive, 10-ms samples to be extracted from the reacting shock tube gas before the arrival of the expansion fan. This time-resolved, fast-sampling technique was applied to the study of cyclohexene pyrolysis (980-1150 K, 7.3 atm) and ethane pyrolysis (1060-1153 K, 6.9 atm). A time-resolved ethylene laser diagnostic was simultaneously used to provide truly time-resolved, in situ results. A discrepancy between late-time GC and laser/model results was found to be caused by endwall thermal boundary layer growth. In addition to the combined LAS-GC experimental approach, a new shock tube technique was developed for measuring high-temperature (> 500 K) laminar flame speeds. Shock-heated gas mixtures are ignited via laser-induced spark-ignition and high-speed, endwall emission imaging is used to capture flame propagation in time. The technique was validated by measuring stoichiometric methane/air and propane/air flame speeds at 1 atm and unburned gas temperatures below 600 K. Stoichiometric, 1-atm, propane/modified-air flame speeds were then recorded at unburned gas temperatures exceeding 750 K, representing the highest-temperature propane laminar flame speed data available to date. Next, single line-of-sight laser absorption diagnostics were deployed in the flame speed experiments, allowing for the simultaneous measurement of laminar flame speed, temperature, species, and pressure in high-temperature, spherically expanding ethane/air flames (449-537 K, 1 atm). The burned gas, equilibrium temperature and species measurements, as well as the flame speed measurements, show close agreement with model results