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.

Abstract:The rebound behavior of fly ash particles normally impacting a planar surface is investigated by using a dynamic model. The three forms of soft sphere physical model are obtained using static/quasi-static contact mechanics and energy dissipation theory. The influences of the particle size, the incident velocity of the particle on the damping coefficient and the impact contact time are all examined. We also predict the critical velocity for three particle sizes. It is found that the variation of the damping coefficient (η) with the normal incident velocity (v in ) can be roughly divided into the three parts. In the first part, η decreases with increasing v in . In the second part, η is little changed with increasing v in . In the third part, η rapidly increases with increasing v in . For smaller impact velocities, the viscoelastic effect plays a dominant role in the impact process, while for higher incident velocities; the energy dissipation depends mainly on plastic deformation. In addition, the critical velocity shows a distinct dependence on the particle size. Finally, the contact displacement-contact time curves are examined. The work provides a solid basis for the development of a discrete-element-method approach to study ash deposition.

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