Thermal Stability Of Endothermic Hydrocarbon Fuels With High Density

The critical requests of hypersonic aircraft for the space, propulsion and thermal protection have prompted the quick development of endothermic hydrocarbon fuels with high density. This dissertation mainly focuses on some fundamental aspects for the evaluation of thermal stability of endothermiv hydrocarbon fuels with high density. The main work is summarized as follows.Several methods for the evaluation of the thermal stability of hydrocarbon fuels are taken from the measurements on the decomposition conversion, gas yield, gaseous products and liquid products. The hydrogen nuclear magnetic resonance spectroscopy (1H NMR), along with the high-performance liquid chromatography (HPLC) and the gas chromatography-mass spectrometry (GC-MS), is mainly performed to moniter the products, especially the produced aromatics, in the liquid residues of the thermal decomposition. The thermal stability and decomposition degree of hydrocarbon fuels under high temperature and pressure are discussed.The thermal stability for n-octane, n-nonane, n-decane, n-undecane, and n-dodecane, as the model endothermic hydrocarbon fuels, is evaluated respectively at the temperature range from 673 K to 713 K. A simplifying assumption of the first-order reaction is used to describe the thermal decomposition of the n-alkanes.1H NMR, HPLC, and GC-MS are combined to follow the thermal decomposition process, and the influences of temperature and reaction time on the thermal stability are investigated. At the experimental temperature range, the gas yield for one of the five n-alkanes increases exponentially with increasing the conversion, and that for an alkane with a shorter chain increases more quickly with increasing the conversion. With increasing the temperature and reaction time, the total content of aromatic products increases. At the same conditions of reaction temperature and time, the rate of thermal decomposition, the conversion, or the content of produced aromatics increases with increasing the number of odd or even carbon atoms of alkanes, respectively. A scheme of the formation of aromatics for the thermal decomposition of n-alkanes is discussed. It follows that the exponential growth of the aromatics against the increasing conversion of thermal decomposition reflects, to a certain extent, the regular changes of the thermal stability and decomposition degree of a hydrocarbonThe thermal stability of 1,3-DMA under different temperature-volume-pressure conditions has been investigated. The thermal decomposition kinetics of 1,3-DMA in the batch reactor are calculated quantitatively at temperatures from 693 K to 743 K with the rate constants ranging from 4.00×10-7 s-1 at 693 K to 35.19 × 10-7 s-1 at 743 K, along with the Arrhenius parameters of A=2.39×107 s-1 and the activation energy Ea=183 kJ·mol-1. The relatively small rate constants indicate that its thermal stability is satisfactory at the given temperatures. The thermal decomposition of 1,3-DMA in the flowing reactor at temperatures from 873 K to 973 K and pressures from 0.1 MPa to 5.0 MPa is further performed. The calculated activation energy (Ea=180 kJ·mol-1) for the thermal decomposition of 1,3-DMA in the flowing reactor is consistent with the value(Ea=183 kJ·mol-1) in the batch reactor. The Arrhenius analysis for the thermal decomposition of 1,3-DMA in the flowing reactor is also compared with that of JP-10 in the flowing reactor, and the decomposition rate constants of these two compounds are similar. The main produced aromatic species in the liquid residues, quantified by GC-MS, HPLC and NMR, are detected to be toluene and xylene. They result from the continuous consumption of 1,3-DMA isomers and the destruction of cage-like structures. The extent of coking for the thermal decomposition of 1,3-DMA in the flowing reactor is much lower than that of JP-10. On the basis of the component analyses, a hypothetical mechanism of the thermal decomposition of 1,3-DMA is proposed to explain the product distribution, especially the production of toluene, xylene. It is shown that the species are mainly produced through the processes of isomerization, hydrogen transfer,?-scission, and dehydrogenation. From above fundamental observations,1,3-DMA can be considered as a pontential component of endothermic hydrocarbon fuels with high density.The physical properties and thermal decomposition for two binary systems of 1,3-DMA with n-decane/n-dodecane are studied. Densities, viscosities, surface tensions, and refractive indices for the binary mixtures are determined over the whole composition range. The excess molar volume, the viscosity deviation, the surface tension deviation, and the refractive index deviation are calculated. The thermal decomposition of the mixtures of 1,3-DMA with n-dodecane at 923 K and 3.0 MPa is further investigated. According to the decomposition results, it is found that the viscosity of the 1,3-DMA/n-dodecane mixture is decreased and the thermal stability of the mixture is improved with increasing the addition of n-dodecane. The results could provide important reference information for the development and performance of petroleum-based endothermic hydrocarbon fuels with high density.The thermal decomposition of a petroleum-based endothermic hydrocarbon fuel with high density (HEDF-1, the density higher than 0.85 g·mol-1) at 848 K-948 K and 0.1 MPa-5.0 MPa is carried out. The influences of temperature and pressure on the conversion, the product distribution and the aromatics production are investigated. The additive package (A3) is added to improve the thermal stability of HEDF-1. The aromatic content in the liquid residues for the thermal decomposition of HEDF-1A (HEDF-1+A3) is less than that of HEDF-1 under the same reaction conditions. It follows that the thermal stability of the fuel can be effectively improved by adding the additive package. To further simulate a practical engineering conditions, the thermal stability, heat sink and coke content of HEDF-1 and HEDF-1A under 3.5 MPa with the flow rate of 1.0 g·s-1 are investigated. The results demonstrate that the thermal stability of HEDF-1 is significantly improved compared with that of HEDF-1 under the same reaction conditions, and HEDF-1 A still maintains high heat sink. This fuel can be considered as a promising candidate of endothermic hydrocarbon fuels with high density.