STUDY OF PHASE TRANSITIONS DURING FLASHING AND COMBUSTION OF PARAFFIN-BASED FUELS

Svitlana Orlovska

Abstract


The kinetics of phase transitions during the ignition and combustion of a paraffin-based fuel for hybrid rocket engines was investigated. Paraffins (a mixture of alkanes) are a promising rocket fuel that meets environmental and energy requirements. Global literature reports that their use as fuel for hybrid engines can increase the regression rate several-fold. In this study, pure octadecane, a saturated hydrocarbon with the chemical formula C₁₈H₃₈, was used as the research object. The aim of this work is to study the kinetics of melting and evaporation of octadecane droplets during ignition and combustion, and to establish the patterns of phase transition effects on high-temperature heat and mass transfer characteristics (induction period, combustion time, and combustion rate). Results. As a result of experimental studies, it was established that the induction period (time until ignition) comprises the durations of three consecutive heat- and mass-transfer stages, determined by the kinetics of first-order phase transitions. In the first heating stage, at temperatures near the melting point of paraffin, a polymorphic transition between its crystalline structures occurs, resulting in a slight decrease in the effective particle diameter. The second stage is particle melting, and the third stage is liquid phase evaporation and vapor heating to a critical temperature that determines ignition. Subsequently, droplet combustion occurs, governed by the kinetics of vapor-oxidizer interaction and the droplet evaporation rate. The rate of liquid-phase formation during the melting of the octadecane particle was measured, demonstrating that the melting kinetics follow a linear law. It was found that the evaporation and vapor heating stage lasts approximately half as long as the melting stage. The combustion constant for octadecane particles was determined, and calculations of the combustion time for droplets of various diameters were performed.


Keywords


heat and mass transfer, phase transitions, melting, evaporation, paraffins, octadecane, droplets, combustion con-stant.

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DOI: https://doi.org/10.32620/aktt.2026.4sup1.15