Pyrolysis And Heat Sink Of Alkanes In Aviation Kerosene Fuels With HP Py-GC-MS/FID

Endothermic hydrocarbon fuels（EHFs）could provide additional heat sink through endothermic pyrolysis reactions,which can be utilized as effective coolants for thermal management.The properties of EHFs are determined by their composition and molecular structures.The relationships between hydrocarbon structure and pyrolysis/heat sink are still far from enough.The pyrolysis of a large number of aviation kerosene alkanes were conducted in a HP Py-GC-MS/FID,which provided fundamental information on the component screening and optimization of EHFs.The pyrolysis properties of 31 alkanes（9 normal alkanes,14 iso-alkanes,8cycloalkanes）were analyzed at 500-750℃,3.0 MPa to study the effect of hydrocarbon structures on pyrolysis behaviors and heat sink.Structural characteristics such as the growth of the main（side）carbon chain,the increasing substituents number,and the transfer of substituents to the central carbon atom promoted the pyrolysis conversion.The pyrolysis of polysubstituted and 2-methyl alkanes produced more C₃ or C₄ alkenes and less C₂H₄ than normal alkanes due to the less-CH₂-groups.The heat sink index（HSI）and pyrolytic coke index（PCI）of hydrocarbons were defined to characterize their cool capacity and coke tendency,the HSIs ranking for hydrocarbons with same carbon number are monoethylalkane>monomethylalkane with methyl in the center of carbon chain>normal alkane>2-methylalkane>polysubstituted alkanes>disubstituted cycloalkanes>monosubstituted cycloalkanes>bicyclicalkane.Cycloalkanes with same carbon number have the highest PCIs,followed by iso-alkanes and normal alkanes.It was found that high carbon number normal alkanes,iso-alkanes with monosubstitution in the center of carbon chain and n-alkyl substituted cyclohexane have higher HSIs and lower PCIs,which are more suitable for the design of high heat sink endothermic hydrocarbon fuel.To further explore the mixing characteristics of alkanes,the pyrolysis of 18 binary mixtures were carried out under 3.0 MPa and 700℃.The binary mixtures of normal alkanes showed a synergistic effect on their pyrolysis conversion and heat sink,while the cycloalkanes mixtures,normal/iso-alkanes mixtures,normal/cycloalkanes mixtures and iso/cycloalkanes mixtures all exhibited the inhibition-initiation effect.These interactions could be explained by the variation of free radical concentration in the pyrolysis system.The addition of polysubstituted alkanes and decalin both reduced the heat sinks and increased the coke tendency.Generally,the new insights into hydrocarbon structure-pyrolysis behaviors relationships are important for the EHFs rational design for advanced aircrafts.