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• The coking of supercritical pressure n-decane and its effect on heat transfer are investigated. • The influence of coking on heat transfer can be divided into three regions. • The coking precursor content and running time are key factors that influence the coke characteristics. • The fluid temperature and coking precursor content are key factors that influence the heat transfer. • The value of c C 2 H 4 + c C 3 H 6 e - T r e f T f is recommended as an indicator to evaluate the impact of coking on heat transfer in the pyrolytic coking region.. Coking of endothermic hydrocarbon fuels can affect heat transfer performance and block the cooling channels, threatening the safe operation of regenerative cooling system for hypersonic aircraft. In this study, an experimental investigation of the influence of coking of supercritical-pressure n-decane on heat transfer was presented. The mechanism by which coking affects heat transfer was analyzed by scanning electron microscopy (SEM), Raman spectroscopy, and other characterization methods. The influence of coke on heat transfer can be divided into three regions. In oxidative coking region, coke is generated primarily through catalytic reactions, and coking leads to a slight heat transfer deterioration. In the lower conversion region, filamentous coke is generated, which improves porosity and surface roughness, and leads to heat transfer enhancement. In the higher conversion region, the increase of coking rate leads to an increase in the thickness of the coke and uniformity of coke distribution. The thermal resistance effect exceeds that of rough surfaces, leading to heat transfer deterioration. From the heat transfer and coke characterization results, an indicator related with temperature and coking precursor content was proposed for evaluating the impact of pyrolytic coking on heat transfer. This study can help design the regenerative cooling system more accurately. [ABSTRACT FROM AUTHOR]

• Effects of secondary reactions and pressure on pyrolysis of JP-10 are investigated. • The formation of gas products is suppressed by increasing the pressure. • Gas and liquid products are categorized as two and six types, respectively. • A differential global reaction (DGR) model for JP-10 predicts pyrolysis accurately. • An increase in pressure increases residence time and chemical heatsink. Regenerative cooling is widely employed for thermal protection of hypersonic vehicles. Hydrocarbon fuels undergo pyrolysis in regenerative cooling channels at supercritical pressures, which affects the performance of regenerative cooling. Pressure and secondary reactions are the key factors that influence pyrolysis. Pyrolysis experiments of JP-10 (exo-tetrahydrodicyclopentadiene) were performed in an electrically heated vertical tube in the pressure range of 3.5–7 MPa and the conversion range of 0%–45%. The formation of gas products was suppressed by increasing the pressure. The effects of pressure and secondary reactions were significant on the distribution of some of the main products, such as ethylene and 1,3-cyclopentadiene, but not for products such as propylene. A method for categorizing gas and liquid products was proposed. The gas and liquid products of JP-10 could be divided into two and six categories, respectively. Based on the differential global reaction modeling approach, a one-step reaction model for the pyrolysis of JP-10 at supercritical pressures was proposed, in which the stoichiometric coefficients were expressed as binary functions of pressure and fuel conversion to reflect the coupling effects of pressure and secondary reactions. The proposed model was implemented in one-dimensional theoretical model and a computational fluid dynamics model to predict JP-10 pyrolysis coupled with flow and heat transfer. The results demonstrated that the model accurately predicts the effects of both pressure and secondary reactions on pyrolysis. The results also showed that an increase in pressure increases the residence time at a fixed mass flow rate, which promotes fuel conversion and chemical heat sink. [ABSTRACT FROM AUTHOR]

• Effects of pressure on supercritical pyrolysis of n-decane are investigated. • The formation of liquid products is preferred at higher pressures. • A novel global reaction modelling approach is proposed for hydrocarbon fuels. • Stoichiometric coefficients are expressed as functions of fuel conversion and pressure. • The new model predicts pyrolysis accurately at both low and high pressures. Pressure is one of the key factors in pyrolysis of hydrocarbon fuels at supercritical pressures, which changes the relation between the product distribution and fuel conversion. However, reaction model with both high accuracy and efficiency to predict pressure effects is lacking. A comprehensive experimental investigation of pressure effects on supercritical pyrolysis of n-decane in the pressure range of 3–7 MPa and temperature range of 560–670 °C is presented. The formation of liquid products is preferred at higher pressures. Gas and liquid products of n-decane pyrolysis can be categorized into three and four types, respectively, according to the formation characteristics. Results show that pressure had more profound effects on the formation of most products without C–C double bonds or benzene rings in their molecular structures (i.e., C 3 –C 9 n-paraffins or cycloparaffins). A novel global reaction modeling approach was presented to solve the effects of both pressure and secondary reactions on pyrolysis of hydrocarbon fuels, in which the stoichiometric coefficients of each product are expressed as binary functions of fuel conversion and pressure. The proposed model was implemented in a computational fluid dynamics (CFD) simulation to predict the n-decane pyrolysis coupled with flow and heat transfer. The results show that the model predicts n-decane pyrolysis more accurately at both low and high pressures. This study can help design regenerative cooling systems with high accuracy and efficiency for engineering applications. [ABSTRACT FROM AUTHOR]