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Rohaly, Matthew JosephDecomposition of Aromatic Amines in a Jet Fuel Surrogate
Master of Science (M.S.), University of Dayton, 2014, Chemistry
The thermal decomposition of aromatic nitrogen containing compounds in a jet fuel surrogate was studied. The surrogate fuel's decomposition was compared to the decomposition found in natural jet fuels. Then high performance liquid chromatography was used to examine the formation of any polar products from the thermal decomposition of the surrogate fuel. Gas chromatography coupled with mass spectrometry and nuclear magnetic resonance were employed to try and identify the polar products. The large amount of hydrocarbons masking the polar products made fractional collection necessary before any identification could be attempted. After fractional collections were employed several oxygen polar compounds were found and identified from the thermal decomposition of the surrogate fuel. However no nitrogen-containing compounds could be found. This is most likely due to the low concentration of the nitrogen-containing compounds within the surrogate. Due to the effectiveness of the surrogate fuel's thermal decomposition it remains a good candidate for further jet fuel studies that look at reactivity. HPLC was also very effective at observing the formation of polar products within the jet fuel, although it could not identify these products. The fractional collection method that was employed did improve the results of the identification process, but it did not manage enough separation between the polar compounds and the hydrocarbons present in the surrogate. It is likely that a further separation method is needed. GCMS was relatively ineffective at separating and identifying polar products from this reaction. This is due to the bulk hydrocarbons masking the polar product signals. GCMS was able to identify a oxygen-containing compound, but only because the elution point from this compound was far from the elution point of any hydrocarbon. NMR was effective at identifying polar compounds that were present in significant quantities, however the extremely low concentration of the polar products made this process much less effective as well. Overall for GCMS or NMR to be considered effective techniques for this analysis a better separation process must be utilized.

Committee:

David Johnson (Advisor)

Subjects:

Chemistry

Keywords:

jet fuels; jet fuel decomposition; nitrogen contaminants in jet fuels; polar products from jet fuel decomposition; jet fuel separation techniques;

Parker, Grant HoustonPyrolytic Decomposition of Synthetic Paraffinic Kerosene Fuel Compared to JP-7 and JP-8 Aviation Fuels
Master of Science (M.S.), University of Dayton, 2013, Chemical Engineering
Every generation of advanced military aircraft fly higher and faster than previous generations. With these leaps in performance, aircrafts develop enormous heat loads which can exceed aircraft material limitations. To relieve these heat loads, aircraft can utilize the endothermic heat sink capacity of jet fuel realized through pyrolytic decomposition. Improved understanding of the effect of fuel chemical composition on supercritical pyrolytic reactivity under conditions relevant to advanced aircraft operation can assist with the successful development of viable cooling methodologies. The goal of the current study was to compare the pyrolytic reactivity, primary decomposition products, and global reaction rates of fuels with varying chemical composition. A flowing reactor system was used to explore the pyrolytic chemistry of a Synthetic Paraffinic Kerosene (SPK) and specification jet fuels JP-8 and JP-7. The SPK was comprised solely of iso- and n-paraffins, with negligible cycloparaffin and aromatic content, while the specification fuels had chemical compositions consistent with typical petroleum-derived fuels. The pyrolytic studies were performed using stainless steel tube reactors which were 37.5 cm long and 0.5 mm inside diameter, with inlet flow rates of 0.2 to 0.6 mL/min at a pressure of 3.54 MPa. External reactor wall temperatures ranged from 500C to 650C. The liquid to gas conversion by mass was used as a metric for evaluating the pyrolytic reactivity due to the complex multicomponent composition of the test fuels. SPK averaged 45% higher conversion than JP-7 and 75% higher conversion than JP-8 at each respective temperature. All fuels followed similar reactivity trends with respect to controlling reaction chemistry, such as such as decomposition of long chain nparaffins, olefin formation, cycloparaffins formation, aromatic formation, and gas (e.g.,low molecular weight compound) production. Characterization of the relative reactivity of the fuels was performed by assuming the fuels decomposed via a first order, irreversible reaction pathway with respect to the gravimetric liquid to gas conversion. The calculated reaction rates and temperature data were used to develop Arrhenius plots which yielded the following kinetic perimeters: SPK--pre-exponential (A) factor of 2.3 x 10^12 s-1 and activation energy (Ea) of 223 kcal/mol, JP-7--A of 2.1 x 10^12 s-1 and Ea of 226 kcal/mol, and JP-8--A of 4.6 x 10^12 s-1 and Ea of 235 kcal/mol. These parameters can be used to estimate the initial reactivity and decomposition of these fuels under endothermic conditions. SPK fuels are more pyrolytically reactive compared to JP-7 and JP-8 using the liquid to gas conversion metric due to the variation in the neat chemical compositions. The mildly branched paraffins of the SPK with negligible cycloparaffins and aromatics, which can act as hydrogen donors reducing propagation rate, limited the reaction pathways resulting in a high liquid to gas conversion. JP-7 and JP-8 had a lower liquid to gas conversion due to the significantly higher initial concentrations of cycloparaffins and aromatics, thereby enabling these fuels to participate in a greater number of hydrogen donor reactions which lowers the extent of propagation reactions. Implications of these results can vary depending on the heat sink design and endothermic fuel cooling strategy. The propensity of SPK to react at lower temperature can enable SPK fuels to more readily reach the endothermic heating value. Unfortunately, a fuel with a higher pyrolytic reaction rate can also produce carbon deposition more readily. Further development into the design of a hypersonic heat exchanger system and the determination of the acceptable amount of liquid to gas conversion will dictate the optimal endothermic fuel.

Committee:

Matthew DeWitt (Advisor); Kevin Myers (Committee Member); Steven Zabarnick (Committee Member); Richard Striebich (Committee Member)

Subjects:

Aerospace Engineering; Alternative Energy; Chemical Engineering

Keywords:

pyrolysis, endothermic jet fuels, synthetic paraffinic kerosene, hypersonic, endothermic heat sink, pyrolytic decomposition, JP-7, fischer tropsch, FT

Balagurunathan, JayakishanInvestigation of Ignition Delay Times of Conventional (JP-8) and Synthetic (S-8) Jet Fuels: A Shock Tube Study
Master of Science (M.S.), University of Dayton, 2012, Mechanical Engineering
The global depletion of petroleum-based fuels has led the world to more closely examine alternate fuels. Therefore, alternate fuels produced from feedstocks such as coal, soybeans, palm oil or switch grass through methods such as coal liquefaction, biomass gasification, and Fischer-Tropsch synthesis have been tested. Among these techniques, fuels generated using Fischer-Tropsch technologies are of interest because they produce clean burning hydrocarbons similar to those found in commercial fuels. Therefore, in this study the Fischer-Tropsch derived S-8 fuel was evaluated as a drop-in replacement for the jet fuel JP-8. The jet fuel JP-8 is comprised of n-, iso- and cyclo- alkanes as well as aromatics while the S-8 fuel is primarily comprised of n- and iso- alkanes. The composition of the fuel affects its ignition characteristics chemically and physically by either advancement or delay of time to ignition. Since this study focused on the chemical effects, the fuels were completely pre-vaporized and pre-mixed. A high pressure, high temperature heated single pulse shock tube was used for this study. The shock tube is an established experimental tool used to obtain ignition delay data behind reflected shock waves under operating conditions relevant to modern engines. The experiments were conducted over a temperature range of 1000-1600 K, a pressure of 19±2 atm, equivalence ratios of 0.5, 1 and 3, within a dwell time of 7.6±0.2 ms and an argon dilution of 93% (v/v). Ignition delay times were measured using the signal from the pressure transducer on the end plate with guidance from the optical diagnostic signal. Along with JP-8 and S-8, the ignition delay of n-heptane was also studied. N-heptane was chosen to represent the n-alkanes in the fuels for this study since it was present in both fuels and also to prove the fact that the n-alkanes were rate controlling. The results indicate that both S-8 and JP-8 fuels have similar ignition delays at corresponding equivalence ratios. The fuel-rich mixtures ignited faster at lower temperatures (<1150 K) and the fuel-lean mixtures ignited faster at higher temperatures (>1150 K). In the transition period between lower to higher temperatures (~1100-1200 K), the equivalence ratio had no significant effect on the ignition delay time. The results also show that the ignition delay time measurements of S-8 and JP-8 fuels are similar to the ignition delay of n-heptane at the equivalence ratio of Φ=0.5 and thereby indicate that the n-alkanes present in these fuels controlled the ignition under these conditions. The ignition delay results of S-8 and JP-8 at Φ=3.0 from this study were also compared to prior work (Kahandawala et al., 2008) on 2-methylheptane and n-heptane/toluene (80/20 liquid vol.%), respectively and found to be indistinguishable. This data serves to extend the gas phase ignition delay database for both JP-8 and S-8 and is the first known data taken for both these fuels at higher temperatures (>1000 K) for an equivalence ratio of 3.0 with argon as the diluent gas.

Committee:

Sukh Sidhu, Dr (Committee Chair); Philip Taylor, Dr (Committee Member); Moshan Kahandawala, Dr (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Alternative Energy; Automotive Engineering; Automotive Materials; Chemical Engineering; Chemistry; Energy; Engineering; Environmental Engineering; Mechanical Engineering; Petroleum Engineering; Technology

Keywords:

Ignition delay; shock tube; S-8; JP-8; Jet fuels; Fuel characteristics; heated shock tube; Fischer-Tropsch; Alternate fuels; alkanes; synthetic fuel; fuel; iso-alkanes; jayakishan balagurunathan

Nagulapalli, AdityaMethylcyclohexane Ignition Delay Times Under a Wide Range of Conditions
Master of Science (M.S.), University of Dayton, 2015, Mechanical Engineering
During the last century, our dependence on oil has increased rapidly and is projected to increase for several decades. There is a critical need to improve the design of the combustion chamber for different kinds of engines to reduce fuel consumption. Chemical kinetics of the fuel plays an important role in reducing emissions and improving engine efficiency. Studying single components of a conventional fuel allows a fuller understanding of the physical and chemical behavior of the real fuel. Many studies have been conducted on all classes of hydrocarbons, with the exception of cycloalkanes. Only a few studies exist on cycloalkanes, which is an important class of hydrocarbons. Methylcyclohexane (MCH), which is widely used as a surrogate to represent the cycloalkane portion of a fuel, was chosen as the subject of this study. The shock tube is an established tool used for measuring the ignition delay, and was used as the experimental apparatus. Ignition delay was measured using the end-plate pressure rise, the OH* and CH* chemiluminescence and white light emission. In addition, experimental results were compared with kinetic modeling data using detailed MCH mechanisms developed by Pitz et al. and Orme et al. Different modeling approaches, such as constant volume and internal energy (with and without experimental pressure profiles) and constant pressure, were used to validate the models by comparing against experimental ignition delay data. It was observed that the equivalence ratio affects the ignition delay time. For the lower argon concentration (Ar = 93%) and higher pressure (P ~ 16 atm), ignition delay times were longest for rich conditions. Additionally, they were shorter at lower temperatures (T = 1250 K) for stoichiometric conditions in comparison to lean values, but the opposite trend was observed at the higher temperatures (T > 1250 K). Ignition delay times of stoichiometric mixtures were longer than lean mixtures across the studied temperature range for low pressure (P = 2 atm) and argon concentration (Ar = 93%), as well as high pressure (P ~ 16 atm) and argon concentration (Ar = 98%). The Orme et al. model using the approach of constant U,V assumption with experimental pressure profile showed a better agreement with experimental results at low temperatures than the approach without experimental pressure profile. Both models and approaches underestimate the experimental ignition delay times at high temperatures.

Committee:

Sidhu Sukh S, Ph.D (Advisor); Philip Taylor. H. , Ph.D (Committee Member); Moshan Kahandawala, Ph.D (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

Methylcyclohexane; Ignition Delay; Jet Fuels; Surrogate Fuels; Shock Tube; Hydrocarbons;