Study On Thermal Stability Of Hydrocarbon Fuels

As the hypersonic flight come true, the power system of aerocraft-fuel will face severe request. Fuel not only works as propellant, but also as coolant for engines, airframe, avionics and other subsystems; it must possess excellent thermal stability. In this thesis, pressure differential scanning calorimetry (PDSC) is used to evaluate fuel's thermal stability. The influence factors for DSC apparatus are studied, and the optimal experimental condition are determined and used for the studies in this thesis.The oxidation temperature and oxidation induction time of n-dodecane, a main component in aviation fuel, were determined by means of PDSC. These provide means for determining Arrhenius activation energies and pre-exponential factors using differential calculated ways. The oxidation activation energy and pre-exponential factors of n-dodecane obtained by two ways from Flynn-Wall-Ozawa equation are 154.37 and 154.56 kJ·mol-1, 16.60 and 16.64 min-1. The oxidation activation energy of n-dodecane calculated from Arrhenius modified equation is 139.59 kJ·mol-1. The results show thermal stability of n-dodecane from the view of chemical dynamics.The oxidation peak temperature for different structure fuel from the class of fuel, n-alkane, isomerization and saturation were studied using the means of non-isothermal. The oxidation dynamics parameters were obtained by Flynn-Wall-Ozawa equation, which was used to estimate thermal stability for different structure fuels. According to thermal stability of different structure fuels, the optimal hydrocarbon composition for improving jet fuel thermal stability is suggested.The concentration of dissolved oxygen in hydrocarbon fuels plays an important role in deposition. The detection of dissolved oxygen was detected by GC-MS apparatus. Effect of dissolved oxygen concentration on fuel thermal stability was studied through physical and chemical deoxygenating way. According to the results, the best oxygen scavenger additives-1,2,5-trimethylpyrrole for different structure hydrocarbon was determined. The result shows thermal stability of n-alkane has been obviously improved.Metal acts as catalyst or inhibitor for fuel oxidation, which influences thermal stability for fuels and affects the security of aviation system. The effect of four common-used metals on n-dodecane thermal stability was studied. The results show that copper has negative effect for n-dodecane. Addition of metal deactivator N,N′-disalicylidene-1,2-propanediamine and anti-oxidant 2,6-di-tert-4-methylphenol can reduce metal's catalyzing function.