| Endothermic hydrocarbon fuel with chemical heat sink and physics used as the primary coolant to solve thermal protection problem caused by high temperature in the combustion chamber has been one key technology of scramjet. The components hydrocarbon fuel will always change as the endothermic pyrolysis reactions occur, which will affect the state of fuel injected into the combustion chamber and thermal management performance and design of regenerative cooling system. Therefore, accurate prediction species is essential to the pyrolysis and heat absorption capacity of the fuel.For the requirement of fuel reaction kinetic model and the utilization of heat sink in the design of regenerative cooling system of scramjet, the flow and pyrolysis of fuel in the cooling channel were taken as the research objects, and experimental and model study on the thermal and initiated pyrolysis of n-decane and the analysis of influencing factors on chemical heat sink of n-decane were carried out.Firstly, the pyrolysis of n-decane, nitromethane and their binary mixture were carried out at 4, 20 and 101 k Pa in a flow reactor with synchrotron vacuum ultraviolet photoionization mass spectrometry(SVUV-PIMS).Thirty-two products were identified and quantified pyrolysis species including stable products, unstable intermediates and free radicals, which shed light on the mechanism of n-decane and nitromethane pyrolysis, as well as the interactions of these two fuels. A detailed kinetic model with 164 species and 726 reactions for n-decane pyrolysis and a detailed kinetic model with 266 species and 1648 reactions for n-decane initiated pyrolysis were developed and validated against the mole fraction profiles of reactants, major products and important intermediates during the pyrolysis of each fuel and their binary mixture. The satisfactory model prediction to the experimental measurements permits the analysis of the kinetic effect of nitromethane initiation on the pyrolysis of n-decane. So that, the increase of the conversion rate at a lower temperature, the selectivity of decomposition products, and reduction of benzene formation are better understood.econdly, in view of that fuel in the cooling channel is usually in a supercritical state, and pyrolysis products are different as fuel under high and low pressure, mainly embodies in the formation of alkanes, so the thermal pyrolysis and initiated pyrolysis using nitromethane as the initiator of n-decane were studied by using electric heating tube flow reactor under supercritical pressure. The main pyrolysis products of n-decane are n-alkane and 1-alkenes, and the total mole fraction of alkane is about 1/3. The initial pyrolysis temperature of n-decane significantly decreases because of the addition of low concentration nitromethane. The effect of nitromethane is more obvious when conversion of n-decane is below 40%. A detail pyrolysis reaction kinetic model including 271 species and 1836 reactions for n-decane thermal pyrolysis and initiated pyrolysis by nitromethane was developed validated by the experimental results. The consumption pathways of n-decane and the generation pathways of products especially alkanes from C3-C9 under supercritical pressure were obtained by rate of production analysis(ROP). Meanwhile, the effects of nitromethane on pyrolysis of n-decane and the formation of important species, and the reasons for these phenomenons are analyzed by using the detailed kinetic model. The research results can provide the theoretical and model basis and model for the application of fuel.Thirdly, the chemical heat sink is dominated by the pyrolysis process of fuel, and the chemical heat sink of n-decane was obtained by using the of product distributions calculated by the detailed kinetic model. The results shows that conversion of fuel reflects the utilization degree of chemical heat sink and the product distribution reflects the utilization level of chemical heat sink, and the contribution of pyrolysis products to chemical heat sink and influence of changes of products selection on the chemical heat sink were analyzed. In order to analysis the effects of reactions in the model on the chemical heat sink, the important species and reactions were selected by using the flux path analysis method(PFA), and a simplified model 116 species and 679 reactions were obtained. The sensitivity of reactions to the chemical heat sink and conversion of n-decane were obtained, and the reasons for the phenomenon were analyzed.Finally, characteristics of chemical heat sink of n-decane thermal and initiated pyrolysis supercritical pressures are studied by electric heating tube flow reactor experimentally as the working parameters will affect the reaction process and the utilization of chemical heat sink. The effects of flow rate and pressure on the chemical heat sink of n-decane thermal pyrolysis and the effects of concentration of initiator and pressure on chemical heat sink of n-decane initiated pyrolysis were analyzed. The simulations of kinetic model on the experimental results further verify the accuracy model of the model. The influence mechanism of working parameters on chemical heat sink of fuel was obtained by using the model combining the experimental results, which can provide theoretical and data base for the reasonable utilization of chemical heat sink. |
PDF Full Text Request