High Temperature Single Pulse Shock Tube Studies of Combustion Relevant Chemistry
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An increasing demand for energy, as well as a need to decrease harmful emissions, necessitates better utilization of hydrocarbon fuels derived from biological and fossil sources. The single pulse shock tube experiment has been used extensively to gather validation data for the combustion of real and surrogate fuels, probe individual reactions, and aid the development of chemical kinetic models. A new lower pressure, single pulse shock tube has been constructed at the University of Illinois at Chicago. Its operation has been demonstrated in the 1-10 bar range, 650-1500 K, and ~1.7 ms reaction time. This thesis covers the work on three distinct, but broadly related studies. New pyrolysis experiments were conducted with n-heptane and oxidation experiments of mixtures of n-heptane-ethylene-methane and n-heptane-isooctane, examining how the reactivity may be influenced by the interactive chemistry of fuels and their pyrolytic and oxidative decomposition products. Several chemical kinetic models from literature were used in simulating the experimental results and were found to be inadequate for use in interpreting the results. In the second study, the recombination and disproportionation of allyl radicals has been studied in the lower pressure, single pulse shock tube. 1,5-hexadiene and allyl iodide were used as precursors. Simulation of the results using derived rate expressions from a complementary diaphragmless shock tube/laser schlieren densitometry study provided excellent agreement with precursor consumption and formation of all major stable intermediates. The final study focused on the chemical kinetic effects of the double bond position in unsaturated biodiesel molecules and long alkenes. High pressure, single pulse shock tube experiments were conducted with four decene isomers, two methyl nonenoate isomers, and two octene isomers. Increased reactivity was observed with decenes and octenes when the double bond was moved toward the center. Significantly different yields in most of the intermediate species measured were observed. The results for the methyl nonenoate isomers showed a difference in the relative yields of some stable intermediates but no increase in reactivity. Chemical kinetic models, developed with the aid of the Reaction Mechanism Generator and an updated database of relevant reaction rate rules, were used to interpret the results. Uncertainty analysis in the predicted results, using a simple Monte Carlo method, showed significant variation in the final results.