Effect Of Organic Molybdenum Additives On The Stability Of Hydrocarbon Fuels

An endothermic hydrocarbon fuel, which is put forward for the thermal management of hypersonic aircraft, can be served as both coolant and propellant. Its stability is an important indicator to evaluate the fuel performance. This work mainly focuses on the study about the stability of model fuels. The main contents and the corresponding results are summarized as follows:The experimental data of density, viscosity, refractive index and freezing point are measured for the binary systems of1,1’-bicyclohexyl with methylcyclohexane, ethylcyclohexane and butylcyclohexane at different temperatures.The excess molar volumes (VmE) and the viscosity deviations (△η) are then calculated. The values of oxidation onset temperature (OT) and oxidation induction time (OIT) which reflect oxidation stability of hydrocarbon fuels are determined by differential scanning calorimeter (DSC). It follows that the thermal oxidation stability of the binary mixtures show a slight decreasing trend with the increasing addition of1,1’-bicyclohexyl.The effects of organic molybdenum (MoDTC-1, MoDTC-2) and diphenylamine antioxidants on the thermal oxidation stability of1,1’-bicyclohexyl are then studied by DSC. The results indicate that the oxidation resistance of the organic molybdenum antioxidant increases with the increase of its concentration, and the antioxidant ability of MoDTC-2is better than that of MoDTC-1. The antioxidant ability of4,4’-ditolyl-amine (DMDPA) is better than that of MoDTC-2at the same additive concentration. It is noted that the thermal oxidation stability of1,1’-bicyclohexyl is improved significantly with the combined addition of MoDTC-2with DMDPA. As an example, the oxidation onset temperature (OT) of1,1’-bicyclohexyl is increased by66℃, and the oxidative induction time (OIT) is prolonged for31min at220℃when both of the addition concentrations of MoDTC-2and DMDPA are0.5%.The effect of organic molybdenum antioxidants (MoDTC-1, MoDTC-2) on the thermal stability of two model fuels,1,1’-bicyclohexyl and n-dodecane is performed in the static (constant volume) and dynamic (constant pressure) thermal cracking apparatus.According to the results of static thermal cracking, the influence of MoDTC-1or MoDTC-2with the addition content of0.1%on the cracking conversion of1,1’-bicyclohexyl is not obvious. When the addition content is increased to0.50%, significant promotion effect on the cracking conversion of1,1’-bicyclohexyl is observed. The results of the dynamic cracking show that the influences of two kinds of the organic molybdenums on the cracking of n-dodecane are not significant, while the inhibition effects on the cracking conversion of1,1’-bicyclohexyl are detected.