Pyrolysis And Coking Of High Density Endothermic Hydrocarbon Fuel In Cooling Channel

High density endothermic fuel on one hand meets the heat sink demand of cooling channel through specific heat and endothermic reaction,solving the problems of thermal management of advanced aircraft at high speed flight;on the other hand,the volume of higher calorific value can effectively reduce the volume of oil tank,reduce vehicle friction resistance,and provide sufficient air propulsion.The electrically heated tube test is used to investigate the pyrolysis behavior of high density endothermic fuel systematically in the micro-channel under high pressure to get further insight into the pyrolysis mechanism and kinetics,and the stability and growth process of coke is investigated,providing data support and theoretical basis for further application of high density endothermic fuel application.The pyrolysis performance of high density endothermic hydrocarbon fuel in a certain operating range(0.7-6.0 MPa,500-750 ~oC,0.54-5.38 g/s)was investigated systematically.It is found that the elevated pressure can enhance the density of fluid flowing through the cooling channel,and thus increasing the residence time and the pyrolysis process,simultaneously promote the bimolecular hydrogen abstraction which initiates the pyrolysis of decalin,the main components of the high density endothermic hydrocarbon fuel,leading to the increase in the selectivity of alkyl-cyclohexene,whereas the formation ethylene and propylene,cyclohexene and 3-methylenecyclohexene formation is inhibited relatively.Free radicals mechanism of the reaction path is established to explain the product distribution and pressure.The electrically heated tube test with adjustable length was used to study the bulk temperature and components of the pyrolysis high density endothermic fuel along the tube under high temperature and pressure(3.5MPa,680-750 ~oC,4.0 g/s),to get deeper insight into fluid property,residence time and phase behavior.Based on the Modifed-Kumar-Kunzru model,the one-dimensional pyrolysis kinetics model for high density endothermic fuel is established,taking the effect of alkenes and cycloalkenes in liquid residuals into consideration,containing 18 substances and 24reactions,which can be used to predict conversion,product distribution and fluid propertiy of the pyrolyzed high density endothermic fuel.The stability performance(680-750,3.5MPa,4.0 g/s)and the growth process(720 ~oC,3.5MPa,30-142 min)of high temperature endothermic hydrocarbon fuel in the cooling channel were investigated.It is found that the main problem of the new type of high density hydrocarbon fuel coking stability lies in the carburization phenomenon caused by the catalytic effect of the metal atom on the hydrocarbon,which lower the physical strength to some extent.Through the study of coke growth process at different run time,the initial period of filamentous coke formation is found,and the formation filamentous coke will then accelerate the axial growth related to catalytic reaction of metal atom and radial growth related to free radical reaction.,and thus the coking rate will increase to some extent.As the reaction continues,the growth rate of filamentous coke gradually reduces because the necessary active site is covered by increasing amorphous carbon.