Single-Pulse Shock Tube Pyrolysis Study of RP-3 Jet Fuel and Kinetic Modeling

Study on the Alternative Solvent of Methylbenzene in the Total Acid Number Titration of Current Jet Fuels

Evaluation of the acidic characteristics of a jet fuel, especially for the total acid number (TAN), is of great significance to ensure flight safety. Methylbenzene is commonly used as the titration solvent; however, it is poisonous and harmful to the environment. It is highly desirable to develop an alternative solvent for methylbenzene to extract the acidic compounds from the jet fuel during the determination of the TAN. Here, we develop a desirable alternative solvent of a mixed ethanol-water solution with the volume ratio of ethanol to water of 99:1, which exhibits a value of TAN similar to that of the solvent of methylbenzene in potentiometric titration and acid-base titration methods. The TAN value derived from the different titration solvents was in the order of 2.96 μg KOH g^-1 (V _cyclohexane/V _isopropanol/V _water = 100:99:1) > 2.68 μg KOH g^-1 (V _{methylbenzene}/V _isopropanol/V _water = 100:99:1) ≈ 2.6 μg KOH g^-1 (V _{absolute ethanol}/V _water = 99:1) > 2.34 μg KOH g^-1 (V _isopropanol/V _water = 99:1). The current report presents a nontoxic and eco-friendly alternative solvent for methylbenzene, which may open up an avenue for evaluating the TAN of jet fuels.

Experimental Study on the Pyrolysis and Soot Formation Characteristics of JP-10 Jet Fuel

Experiments of high temperature pyrolysis and soot formation analysis on JP-10, one of the representatives of fuels, were conducted in order to analyze its properties and help construct its chemical kinetic mechanism. High-temperature pyrolysis and fuel-rich oxidation experiments were carried out on JP-10 fuel under different conditions using two types of shock tube equipment (SPST and HPST). The pyrolysis experiments were carried out in two working conditions with JP-10 concentrations of 200 ppm and 500 ppm (in Ar). Quantitative analyses of JP-10 pyrolysis products were carried out using gas chromatography, and a total of eight small molecule products below C4 were detected. Among these eight products, methane, ethene, and acetylene were the three main products. In the fuel-rich oxidation experiments for soot formation analysis, a total of nine working conditions were designed, but soot formation was detected only under three of them. The soot induction delay time and soot yield of JP-10 were investigated using laser absorption measurement. The SYmax (the maximum amount of soot yield) and other relevant parameters were investigated under these three different working conditions. At a pressure of 3 bar and a temperature of 1884.10 K, the soot yield reached a maximum of 14.3. In addition to practical insights from these data, they were also useful for the construction and validation of the chemical kinetic mechanism of JP-10.

Ignition Delay Time and Oxidation of a Kerosene Aviation Fuel and a Blended Jet50-Bio50 Fuel

Ignition delay and oxidation of two jet aviation fuels, Jet A-1 and its blended fuel with a bio-jet fuel in half, are investigated by experiments and numerical simulations. From their major combustion properties, derived cetane number and molecular weight of the blended fuel, Jet50-Bio50, are higher than those of Jet A-1, and its H/C ratio and threshold sooting index are lower because more n-alkanes are contained in a bio-jet fuel and aromatic compounds are not. The surrogate fuels of the two jet fuels are constructed for numerical simulations of their ignition and oxidation. Early ignition of the blended fuel measured in a shock tube experiment is investigated by comparing the speciation profiles of several products from the two fuels, and their global reactivity is measured in a laminar flow reactor. Oxidation of the blended fuel is initiated at a lower temperature than Jet A-1, and reaction pathways of the two fuels are analyzed at two temperatures of 600 and 1100 K, respectively. At a low temperature of 600 K, reaction pathways of the major surrogate components for the two fuels are significantly different, while they are almost the same at high temperatures. The active radical of OH is produced more by the oxidation of Jet50-Bio50, and its oxidation is initiated at a lower temperature than Jet A-1, leading to earlier ignition. At low temperatures, the difference between initiation times of oxidation of the two fuels is much larger than at high temperatures. At both temperatures, production rates of the major reaction steps, where OH is produced, are higher in Jet50-Bio50 than in Jet A-1.

Development of a Chemical-Kinetic Mechanism of a Four-Component Surrogate Fuel for RP-3 Kerosene

RP-3 kerosene is the most widely used aviation kerosene in China, and research on its chemical-kinetic mechanism is significant for understanding the combustion characteristics. Based on a novel four-component surrogate fuel consisting of n-dodecane, 2,5-dimethylhexane, 1,3,5-trimethylbenzene, and decalin (54, 22, 14, and 10% by mole), the detailed chemical-kinetic mechanism of the corresponding RP-3 surrogate fuel with 1333 species and 6803 reactions has been developed and then reduced to 145 species and 818 reactions for high-temperature conditions. After that, the merged surrogate mechanism of surrogate fuel was validated by various experimental data sets for each individual surrogate component. Then, the surrogate mechanism was validated by comparing the simulation and experimental data of the ignition delay times, species concentrations in a jet-stirred reactor, and laminar flame speeds. Good agreements between simulations and experiments were observed. In addition, using the sensitivity analysis method, the key reactions of RP-3 surrogate fuels were compared and analyzed. In summary, the mechanism developed in this study can accurately predict the ignition, oxidation, and flame propagation characteristics of RP-3 aviation kerosene. The novel surrogate model can help deeply understand the combustion characteristics of RP-3 aviation kerosene, and it is used for high-precision numerical simulation of combustion reaction flow.

Single-Pulse Shock Tube Experimental and Kinetic Modeling Study on Pyrolysis of a Direct Coal Liquefaction-Derived Jet Fuel and Its Blends with the Traditional RP-3 Jet Fuel

A basic understanding of the high-temperature pyrolysis process of jet fuels is not only valuable for the development of combustion kinetic models but also critical to the design of advanced aeroengines. The development and utilization of alternative jet fuels are of crucial importance in both military and civil aviation. A direct coal liquefaction (DCL) derived liquid fuel is an important alternative jet fuel, yet fundamental pyrolysis studies on this category of jet fuels are lacking. In the present work, high-temperature pyrolysis studies on a DCL-derived jet fuel and its blend with the traditional RP-3 jet fuel are carried out by using a single-pulse shock tube (SPST) facility. The SPST experiments are performed at averaged pressures of 5.0 and 10.0 bar in the temperature range around 900-1800 K for 0.05% fuel diluted by argon. Major intermediates are obtained and quantified using gas chromatography analysis. A flame-ionization detector and a thermal conductivity detector are used for species identification and quantification. Ethylene is the most abundant product for the two fuels in the pyrolysis process. Other important intermediates such as methane, ethane, propyne, acetylene, and 1,3-butadiene are also identified and quantified. The pyrolysis product distributions of the pure RP-3 jet fuel are also performed. Kinetic modeling is performed by using a modern detailed mechanism for the DCL-derived jet fuel and its blends with the RP-3 jet fuel. Rate-of-production analysis and sensitivity analysis are conducted to compare the differences of the chemical kinetics of the pyrolysis process of the two jet fuels. The present work is not only valuable for the validation and development of detailed combustion mechanisms for alternative jet fuels but also improves our understanding of the pyrolysis characteristics of alternative jet fuels.