Investigation of Pressure Effect on Thermal Cracking of n-Decane at Supercritical Pressures

Abstract

Regenerative cooling utilizing on-board endothermic hydrocarbon fuels of the high-temperature components of the scramjet engine plays a paramount role in maintaining the reliability and durability of the systems. A molecular kinetic model was proposed by modifying the Kumar–Kunzru kinetic model to describe the thermal cracking of n-decane at supercritical pressures. The apparent kinetic parameters at different pressures were optimized by the Levenberg–Marquardt algorithm. After the model validation, the role of pressure on the chemical heat absorption rate during n-decane pyrolysis was investigated using the one-dimensional plug flow model. It was found that the heat absorption rate first increases and then slightly decreases as the temperature increases at all pressures. The highest chemical heat absorption rate is located at a conversion of 41.81%, 53.34%, and 59.40% at 3, 4, and 5 MPa. In addition, the effect of pressure on n-decane pyrolysis was quantitated using the equivalence temperature. Under the simulation conditions considered in the present study, each 1 MPa increase in pressure produced the same conversion as a temperature decrease of 6.5–10 K. Finally, in order to extrapolate the kinetic model to a wider range of pressure conditions, a model extrapolation method based on the activation volume was proposed.

Impact of Pyrolysis Products on n-Decane Laminar Flame Speeds Investigated through Experimentation and Kinetic Simulations

“…According to the results of previous research, , hydrogen and C 1 –C 3 (methane, ethylene, ethane, propylene, and propane) species are the main pyrolysis products of macromolecular hydrocarbon fuel. Moreover, the effect of small hydrocarbon products on the burning properties of liquid fuels is more significant than that of other liquid pyrolysis products . The effects of primary pyrolysis gases H 2 , CH 4 , C 2 H 4 , and C 2 H 6 on S u 0 of n -decane were investigated.…”

“…Currently, regenerative cooling based on endothermic hydrocarbon fuels (EHFs) is the most suitable and effective cooling method. − Under actual conditions, the EHFs enter the pipeline outside of the combustion chamber under high pressure and pyrolyze at a certain temperature to produce small-molecule pyrolysis products (C 0 –C 4 , including H 2 and C 1 –C 4 alkanes and alkenes) and liquid hydrocarbons. − Among them, increased amounts of alkenes can significantly improve the heat absorption capacity of the fuel to provide a better cooling effect. However, as the pyrolysis pressure increases, the proportion of alkenes/alkanes in the pyrolysis products decreases rapidly. , This also leads to a decrease in the pyrolysis temperature and a significant change in the heat absorption capacity of the fuel. , The pyrolysis results of various EHFs have been studied under both low − and high pressures. − Furthermore, the formation of gas and liquid pyrolysis products leads to changes in fuel burning properties and improves the jet flow, mixing, ignition, and combustion performances of liquid fuel. − Therefore, it is extremely necessary and meaningful to research the effects of pyrolysis products on fuel burning properties. Such studies can further improve conventional regenerative cooling systems and contribute toward realizing hypersonic flight.…”

“…H 2 and C 1 –C 3 species are the primary components of n -decane pyrolysis in the supercritical state, ,, and the molarities of hydrogen, methane, ethylene, and ethane account for more than 60% of pyrolysis products. The combustion characteristics of these pure gaseous products have been extensively investigated, and their chemical properties are quite different, owing to structural differences. − Liquid fuel burning properties have also been significantly studied. − However, few studies have explored the combustion characteristics of mixtures of these gaseous species and practical jet fuels.…”

Numerical Investigations on the Molecular Reaction Model for Thermal Cracking of n-Decane at Supercritical Pressures

“…Wang et al 29 and Liu et al 30 pointed out that pressure has an effect on the pyrolysis of n-decane, so Wang 29 developed a novel global model of 38 species with secondary reactions suitable for both low and high pressures. Jiao et al 31 proposed a model extrapolation method based on activated volume, which allows the kinetic model to be extrapolated to a wider range of pressure conditions. In addition, many researchers proposed the global reaction model for aviation fuel cracking.…”

Differential Global Reaction Model with Variable Stoichiometric Coefficients for Thermal Cracking of n-Decane at Supercritical Pressures

“…Wang et al 37 simulated the thermal cracking of n-decane for conversion up to 93% using a model containing 16 species and 21 reactions, with a maximum average absolute relative error below 15%, for the methane mass fraction. Jiao et al 38 investigated the effects of the pressure on n-decane thermal cracking and developed a lumped model with all products heavier than C 4 lumped together as C 4+ . Zhang et al 39 proposed a method for n-dodecane thermal cracking by applying a PPD model for n-dodecane conversions of less than 13%.…”