Doctor of Philosophy (PhD)
In order to serve a dual role as a propellant and as a coolant, fuels in the pre-combustion environment of future high-speed aircraft will be exposed to temperatures and pressures of up to 700 °C and 130 atm—conditions that are supercritical for jet fuels. Under such conditions, fuel can undergo pyrolytic reactions leading to the formation of polycyclic aromatic hydrocarbons (PAH), which are precursors to fuel-line solid deposits that can hinder safe operation of the aircraft. Therefore, to prevent solid deposit formation, it is extremely important to understand the PAH formation pathways in the supercritical fuel pyrolysis environment. To better understand these reaction pathways, supercritical pyrolysis experiments have been conducted in an isothermal, isobaric flow reactor with the model fuel n-decane (critical temperature, 344.5 °C; critical pressure 20.7 atm), an n-alkane component of jet fuels, at temperatures from 530 to 570 °C, pressures from 40 to 94.6 atm, and at a fixed residence time of 133 sec. Experiments have also been performed at 570 °C, 94.6 atm, and 133 sec, the condition for incipient solids formation, with four dopants—2-methylnaphthalene, 1-methylnaphthalene, 1-methylphenanthrene, and fluorene—added in separate experiments at 10 to 25 times their yields from n-decane pyrolysis. The aliphatic and aromatic products of up to two aromatic rings have been analyzed by gas chromatography with flame ionization detection and mass spectrometry. The PAH products are analyzed in an isomer-specific manner by high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance and mass spectrometry. Product analyses have led to the quantification of 205 products, which include 20 aliphatics, 7 one-ring aromatics, and 178 PAH from two to nine rings. At the temperatures and pressures investigated here, PAH product yields rise dramatically with increases in either temperature or pressure, with the largest PAH exhibiting the sharpest rises as the condition for incipient solids formation is approached. The results from the doped n-decane experiments demonstrate that the reactions of resonance-stabilized radicals—arylmethyl, phenalenyl, phenalenyl-type, and 9-fluorenyl—with C2-C4 1-alkenes, the highest-yield alkene products of supercritical n-decane pyrolysis, are the principal channels of PAH growth in the supercritical n-alkane-fuel-pyrolysis environment.
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Kalpathy, Subramanian Venkateswaran, "Growth of Polycyclic Aromatic Hydrocarbons during the Supercritical Pyrolysis of n-Decane" (2016). LSU Doctoral Dissertations. 3725.
Wornat, Mary Julia (Judy)