Study On Thermal Oxidation Stability Of High-density Fuel JP-10

High-density hydrocarbon fuel has a higher energy density than aviation kerosene RP-3,which can effectively increase aircraft load and mileage,and is widely used in the aerospace field.In current and future aircraft applications,in addition to powering the aircraft as a source of energy,high-density fuels also serve as system coolants to reduce the thermal load on high-Mach aircraft.This is related to an important characteristic of high-density fuels,the thermal oxidation stability.However,there are few studies on the thermal oxidation stability of high-density fuels.In this paper,the thermal oxidation mechanism of high-density fuel（typical fuel JP-10）has been studied,and the antioxidant addition and fuel deoxygenation methods have been used to improve its thermal oxidation stability.DFT calculation was used to study the oxidation mechanism of JP-10 as well as the formation of key intermediates,hydroperoxides.During the oxidation process of JP-10,the first-stage dehydrogenation reaction is most likely to occur at the secondary carbon site of the five-membered ring,while the tertiary carbon dehydrogenation on the six-membered ring is relatively difficult.After that,the fuel hydrocarbon radical reacts rapidly with oxygen to generate peroxy radicals（ΔH<0,ΔG<0）,which then react with fuel to produce hydroperoxide.Notably,the hydroperoxide is most likely to formed at the tertiary carbon sites.When antioxidants are added in the fuel,they can preferentially react with peroxy radicals to stabilize them,inhibiting the regeneration of fuel free radicals and slowing the oxidation of fuel.We conducted the experiments（differential scanning calorimetry and rapid small-scale oxidation test）and DFT calculation to study the effects of different phenolic antioxidants on the thermal oxidation stability of JP-10.The addition of four kinds of phenolic antioxidants can improve the thermal oxidation stability of JP-10fuel,and the order of antioxidant effect is TBMP>BHA>BHT>TBHQ.Compared with the reaction energy barrier of fuel molecule with peroxy radicals(143.44～183.39 k J·mol^-1),the activation energy of the four antioxidants with peroxy radicals can be reduced to 66.22 k J·mol^-1（TBMP）,70.24 k J·mol^-1（BHA）,71.64 k J·mol^-1（BHT）and 110.99 k J·mol^-1（TBHQ）.This indicates that these four antioxidants have practical values in improving the thermal oxidation stability of JP-10.The effects of fuel deoxygenation on the thermal oxidation stability were studied.The nitrogen was purged to remove dissolved oxygen from JP-10 and RP-3 fuels,and the effects of deoxygenation on fuel stability were evaluated by accelerated thermal oxidation（180℃,200℃,and 220℃）experiments.The nitrogen-purge method can reduce the dissolved oxygen concentration and water content in JP-10 and RP-3 fuels to<3 ppm and<8.5 ppm,without affecting their physical properties（like density,net calorific value,kinematic viscosity,etc.）.During the accelerated oxidation process,compared with the non-deoxygenated fuel,the content of hydroperoxides and acids in the deoxygenated fuel are significantly reduced,with more antioxidant BHT retained.In addition,the deoxygenation treatment also inhibits the formation of soluble macromolecular oxidation reactive species（SMORS）and insoluble products.It is proved that deoxygenation treatment can effectively improve the thermal oxidation stability of JP-10.