Pressure and puffing behavior in ethanol gel droplet combustion S. Bharathi, B. T. Kannan, Senthil Kumar Raman, Lakka Suneetha, Purushothaman Nandagopalan Physics of Fluids, 2025 The combustion dynamics of non-Newtonian gel fuel droplets display a unique behavior influenced by the interaction of viscoelastic properties, rapid vaporization of the base fuel, and surface tension effects. This study offers a detailed experimental investigation of pressure dynamics, phase transitions, and post-explosion behavior of ethanol gel droplets. The investigation elucidates the significance of internal pressure buildup, phase separation due to heat influx leading to bubble generation, and shell rupture in governing combustion phases. It emphasizes the distinctive puffing behavior during the post-phase III regime. The temporal evolution of internal pressure, supported by experimental data, reveals critical dynamics across various phases. During phase II, internal pressure buildup is regulated until it reaches the yield stress of the fluid, thereby delaying droplet rupture and subsequent explosion. Phase III is defined by rapid explosion, which improves fuel–air mixing and facilitates secondary atomization. The regression dynamics following phase III, PIII+, mimics the conventional droplet regression rate of Newtonian fuels. PIII+ is primarily influenced by pressure dissipation, characterized by puffing cycles resulting from transient gellant-based shell formation and depletion, which promotes efficient evaporation. The impact of the decay coefficient (α) on PIII+ pressure dynamics shows that lower values of α prolong puffing, whereas higher values expedite pressure dissipation. These findings provide essential insights into gel droplet combustion, enhancing our understanding of phase-dependent behavior and demonstrating methodologies to optimize gel fuels for high-performance energy systems.
