Effect of Aviation Fuel Type on Pyrolytic Reactivity and Deposition Propensity under Supercritical Conditions

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• 作者：Matthew J. DeWitt ; Tim Edwards ; Linda Shafer ; David Brooks ; Richard Striebich ; Sean P. Bagley ; Mary J. Wornat
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2011
• 出版时间：September 21, 2011
• 年：2011
• 卷：50
• 期：18
• 页码：10434-10451
• 全文大小：1504K
• 年卷期：v.50,no.18(September 21, 2011)
• ISSN：1520-5045

文摘

Development of reusable liquid-hydrocarbon-fueled hypersonic vehicles requires improved understanding of the effect of chemical composition on the controlling reaction chemistry and deposition propensity as the fuel is used to cool the system. In this effort, supercritical pyrolytic stressing studies were performed using two petroleum-derived fuels and a Synthetic Paraffinic Kerosene (SPK) comprised predominantly of normal and branched paraffins. All fuels decomposed via free radical pathways with high yields of unsaturates and lower molecular weight products consistent with pyrolysis at high pressures and moderate temperatures. However, the SPK was significantly more reactive than the petroleum-derived fuels due to a lack of efficient hydrogen donors that act to terminate chain reactions (higher net propagation rate). High-pressure liquid chromatography was used to identify and quantify polycyclic aromatic hydrocarbons (PAH) in the stressed fuels, conclusively determining that these are produced during thermal stressing. A notable observation was the presence of PAH during SPK stressing, as the neat fuel did not contain cyclic precursors for growth to PAH. During stressing with stainless-steel tubing, the formation of filamentous deposits via metal-catalyzed reactions of stressed fuel components with reactor surfaces was observed for all fuels studied. However, the SPK fuel exhibited a much higher pyrolytic deposition rate, which was attributed to higher lateral growth rates of surface filaments via noncatalytic free radical addition pathways. The PAH formed during SPK stressing are indicators of the highly reactive intermediates prone to participating in the surface coke addition pathways. Studies blending benzene with the SPK indicated that low PAH solubility in the paraffinic fuel is not the dominant cause for the high deposition propensity. Testing with the petroleum-derived fuels showed that metal sulfide filament formation can occur under endothermic conditions, and higher fuel sulfur content can increase carbon deposition propensity. Studies with surface passivated tubing (Silcosteel) suppressed filamentous carbon formation and rendered a substantial reduction in SPK deposition to levels similar to the petroleum-derived fuels. Overall, these studies provided guidance regarding the controlling chemistry during supercritical pyrolysis of current and potential synthetic hydrocarbon fuels and insight into prevalent deposition pathways.