An automated, high pressure, high flow rate batch mixing apparatus has been designed and constructed for rapid, stable, and repeatable mixing of multiple gases and vapors. The apparatus operates as an intermittent batch mixer with cycles of topping off fresh mixture to maintain pressure in an accumulator tank until consumed in an experimental apparatus. At high duty cycles, the apparatus can also function at steady state. This style of mixing is suitable for experiments such as high repetition rate shock tubes and other devices with intermittent flow demands. It is compact and portable, facilitating use in locations such as synchrotron light sources. The entire apparatus is heated to permit the mixing of vapors from species with low volatilities. The apparatus is fully automated and runs for extended periods with the only intervention being to refresh reagent supplies. The accuracy and repeatability of the apparatus were verified by periodic gas sampling and analysis with gas chromatography. Multi-component mixtures spanning a wide range of complexity, dilution, and volatility of constituents have been prepared. The compositions of the majority of the mixture were found to be stable over several filling cycles, repeatable, and with the proper calibration of set-point conditions, accurate. Challenges were encountered preparing a mixture from multi-component liquids, and potential solutions are discussed.
An experimental shock tube study of natural gas (NG) oxidation for several NG samples was carried out at nominal reaction pressures of 50-60 atm and temperatures ranging from 1100 to 1750 K over a nominal reaction time of 2.5 ms. As NG has no standard specified composition, various samples of NGs taken from the gas supply system across the United States were studied near stoichiometric conditions. In addition, a speciation study at equivalence ratios ranging from fuel lean (φ ≈ 0.5) to pyrolysis of a representative NG sample was carried out to provide a comprehensive but nonexhaustive set of experimental data, which will be useful in optimizing chemical kinetic models for NG. Temperature-dependent species yields measured in these experiments were compared with predictions from four well established chemical kinetic models. The agreement with model predictions was found to be largely inconsistent from experiment to experiment, reinforcing the need for optimization of models using comprehensive experimental data before their use predicting the oxidation products of NG.
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