Shock tube and laser absorption studies of small alkene spectroscopy and real fuel kinetics
Keywords: Mechanical Engineering.

Growing demand for energy coupled with increased awareness of various deleterious effects of current energy generation techniques drive a demand for more efficient utilization of current feedstocks and addition of new streams. Accomplishing both more efficient utilization of current fuels and interoperability of new streams requires detailed chemical kinetic understanding of both existing and novel fuels. Shock tube/laser absorption strategies are well-suited for these fuel kinetics studies. In this work, several new infrared laser sensor strategies have been developed that have enabled the quantitative time-history measurements of critical fuel decomposition products. Using these sensors, the decomposition products of several fuels were measured. These data have been used in the development of the HyChem model for jet fuel. An existing facility, the Kinetic Shock Tube, has been modified through heating to more readily handle distillate fuels with low vapor pressures at ambient conditions. Additionally, the fuel handling and mixing system was modified allow for the production of mixtures of distillate fuels and oxidizers or inert diluents. A novel laser-absorption-based propene diagnostic was developed using an external cavity quantum cascade laser to allow measurement of the second-smallest alkene in shock tube experiments. Existing room-temperature resolved spectra spanning the infrared absorption of propene from 1.5 to 15 microns was considered to select a target wavelength region. A series of experiments at high temperatures were done to ensure that a maximally-absorbing wavelength was selected at high temperatures. The temperaturedependence of this propene absorption feature was then measured. This diagnostic was combined with an existing CO2 gas laser ethylene diagnostic to study the decomposition of propene at elevated temperatures. Simultaneous laser-based measurements of propene and ethylene were recorded for the first time. Propene decomposition measurements were reported between 1360 and 1710 K and compared to models in the literature to provide recommendations for further model refinement. These diagnostics were then combined with other laser diagnostics, including a HeNe gas laser fuel-absorption diagnostic at 3.39 microns and an interband cavity laser diagnostic for measuring methane at 3.18 microns, to measure a variety of species during the pyrolysis of two gasolines, two jet fuels, and a synthetic jet fuel Ethylene and iso-butene were measured during the pyrolysis of two Shell gasolines between 1050 and 1390 K; propene was also measured during these experiments for one of the gasolines. These measurements were compared to predictions from a recent gasoline surrogate mechanism. Ethylene and propene were measured during the pyrolysis of two distillate jet fuels between 1070 and 1440 K; iso-butene was also measured during these experiments for one of the jet fuels. Ethylene, propene, iso-butene, and methane formation were measured during the pyrolysis of a synthetic jet fuel between 1071 and 1317 K. These measured mole fractions were then compared to an existing model for large, branched hydrocarbons. These measurements were also used to constrain in-development hybrid chemistry (HyChem) models for the respective fuels. These studies demonstrate the utility of laser absorption studies in shock tubes to investigate real fuel pyrolysis kinetics through the measurement of both product formation rates and product distributions. Subsequently, these measurements can be used to constrain new chemical kinetic models, evaluate the accuracy of existing chemical kinetic models, and select appropriate surrogate compositions for surrogate-based models.