Evaporation and Combustion Characteristics of Kerosene Droplets in Localized Stratified Vortex-tube Combustor: A Numerical Investigation

The combustion of AC₁₀H₂₀ droplets was investigated to explore the combustion performance of liquid fuels in localized stratified vortex-tube combustor (LSVC). The evaporation ratio, flame structure, stability limit, heat loss, and combustion efficiency in the LSVC were investigated under various equivalence ratios and fuel mass fluxes numerically. Results corroborate that the LSVC exhibits a large heat release with uniform flame front, large stability limit, low heat loss, high evaporation rate, and good combustion efficiency under lean operating conditions, indicating good potential to deal with liquid fuels directly. Then, the evaporation and stabilization mechanisms are analyzed. As for the former, the evaporation ratio in LSVC increases sharply along the axial direction toward the outlet, indicating a high evaporation rate, which is optimized through the heat produced by itself efficiently. Viz., the vortex currents can entrain the AC₁₀H₂₀ droplets to interior high-temperature region and then promote the evaporation of liquid fuels. As for the latter, the localized stratified distribution of species in the LSVC results in an edge flame structure, which differs from that in the traditional vortex-tube combustors. The local equivalence ratio increases along the radial direction toward the center. The increased local equivalence ratio of the interior is crucial for stabilization and the decreased local equivalence ratio of exterior enables the heat loss to be reduced. In the end, the edge flame structure and the low heat loss yields a large heat release in the LSVC, which can increase the flame speed, thereby ensuring the stabilization and the high burn-off rate.