Micro-explosion and evaporation of blended ethanol/rocket propellant-3 droplets under high-temperature and high-pressure conditions

The development of ethanol-blended sustainable aviation fuels requires a fundamental understanding of droplet evaporation dynamics under realistic combustion conditions. While previous studies have focused on atmospheric-pressure evaporation, systematic investigations into the phase-change mechanisms and pressure effects on ethanol/rocket propellant-3 (RP-3) blends at elevated temperatures and pressures remain lacking. This study experimentally resolves the micro-explosion and evaporation behavior of ethanol/RP-3 droplets (0–50 wt. % ethanol) under coupled high-temperature (300–600 °C) and high-pressure (1–20 bar) conditions. Three distinct evaporation modes are identified: (1) micro-explosion-dominated evaporation (transient heating → fluctuating evaporation → equilibrium stages), (2) non-expansive evaporation (rapid ethanol depletion → unstable evaporation → equilibrium stages), and (3) thermal-expansion evaporation (transient heating → equilibrium stages). Key findings reveal a pressure-dependent ethanol concentration threshold governing evaporation enhancement: At 1 bar, 30 wt. % ethanol achieves the shortest total evaporation time (reduced by up to 30% vs pure RP-3) due to intensified evaporation and heating rates. Conversely, elevated pressures (10–20 bar) suppress micro-explosions, where ethanol addition always prolongs evaporation time through reduced volatility dominance. These results establish a critical trade-off between ethanol's micro-explosion benefits and volatility limitations, providing quantitative guidelines for optimizing ethanol blending ratios in aviation fuels under engine-relevant pressure conditions.