Studies On Thermal Stability And Coking Of Hydrocarbon Fuels

In order to characterize on the properties about thermal stability and coking of hydrocarbon fuels,several single and binary model fuels,and multiple-component hydrocarbon fuels are studied systematically in this work.The results are expected to provide experimental and theoretical information for the application of endothermic hydrocarbon fuels.The main contents are summarized as follows:1.An apparatus for the evaluation of thermal stability of hydrocarbon fuels is designed and constructed on the basis of a single heat-exchanger passage in engine.p-Xylene is chosen as a standard substance to calibrate the instrumental parameters.The heat sinks of cyclohexane at different temperatures are determined to check the accuracy.The average relative deviation of the experimental heat sink from the theroretical value is less than 2.1%,which indicates that the apparatus has sufficient accuracy to satisfy the requirements of engineering applications.The analysis characterization methods for the gas products,liquid products and cokes obtained from the pyrolysis of hydrocarbon fuels are performed with detailed operation parameters.2.In order to provide important information for the research on the thermal stability and coking of hydrocarbon fuels,the pyrolysis experiments of two model fuels,n-tridecane and decalin,are carried out under 3.5 MPa and 650?750 ? with feed rate of 1.00 g·s-1 and the steady running time of 300?1200 s.The results show that all of the conversions,the gas yields and the heat sinks of n-tridecane and decalin increase with the rise of reaction temperature.The rising reaction temperature also leads to the increase of relative contents of olefins and aromatics in liquid products,the increase of coke mass and the regular changes about the free cokes from filamentous type to granular type.The pyrolysis properties of n-tridecane and decalin are not significantly affected by the steady running time.However,the masses of attached cokes,free cokes and the total cokes are positive correlated with the steady running time,respectively.The thermal stability of decalin is higher than that of n-tridecane under 3.5 MPa and 700 ? with feed rate of 1.00 g·s-1 and the steady running time of 1200 s.The masses of total cokes of decalin and n-tridecane are determined to be 7.3 mg and 42.5mg,respectively.The coke mass for decalin is about one-sixth of that for n-tridecane.3.The pyrolytic experiments about JP-10/iso-octane binary mixtures are performed at different conditions to investigate the interactions among the components of hydrocarbon fuels during the pyrolytic process.The experimental results show that iso-octane can initiate the pyrolysis of JP-10,and the conversion of JP-10 significantly increases from 7.5%to 41.0%with the addition of iso-octane from 0 to 90%.One possible mechanism has been proposed to demonstrate the initiation effect of iso-octane on the basis of the analyses of various products.Theoretical calculation results from the density functional theory(DFT)are also used to confirm the initiation mechanism.4.A kerosene based high-density hydrocarbon fuel(HEDF-1)is prepared.The impacts of temperature,feed rate and steady running time on thermal stability and coking of HEDF-lare investigated.The changes of the conversion,gas yield,product distribution of gas/liquid,amount and morphology of cokes are considered for the evalution on the performances of HEDF-1.The results indicate that HEDF-1 can run steadily and last more than 1200 s under 3.5 MPa and 750 ? with the feed rate of 1.00 g·s-1.5.The multi-functional additive package A is designed to improve the performances of HEDF-1.The additive package can inhibit effectively the formation of both catalytic cokes and noncatalytic cokes,reduce greatly the masses of cokes.As an example,the total coke mass is reduced from 277.6 mg without package A to 16.3 mg with package A under same conditions of 3.5 MPa,the feed rate of 1.00 g·s-1 and processing temperature rising from 25 ? to 750 ? with about 3200 s.Simultaneously,the free cokes change from the filamentous to granular.With and without the additive package A,the conversion and its variety law for the pyrolysis of on the hydrocarbon fuel HEDF-1 are observed to be similar.The package itself shows little impact on the conversion,gas yield and heat sink of HEDF-1.