BO₂-PLIF measurements of flame structures and combustion characteristics of boron-based fuels

AbstractBoron is a promising high-energy fuel for solid propellants, but its complex gas–solid two-phase combustion remains poorly characterized. In this study, BO₂ Planar Laser-Induced Fluorescence (BO₂-PLIF) is applied for the first time to visualize and quantify the combustion characteristics of boron-based fuels in a gas–solid mixing burner. Under well-controlled conditions with boron mass flow rates ranging from 0.04 to 0.10 g/s and a mean particle size of 62.65 μm, the BO₂-PLIF measurements reveal a dual-flame structure consisting of an inner conical ethylene/air flame and an outer BO₂-dominated zone. Quantitative analysis shows that increasing the boron concentration significantly enlarges the flame area and enhances the BO₂ fluorescence intensity, while concurrently reducing the flame cone angle from 52° to 36° and decreasing the propagation speed from 44 to 15 cm/s. By applying intensity-based thresholding to the PLIF data, single boron particle flames were isolated, revealing transient combustion behavior with flame diameters expanding up to ∼ 15 times the original particle size and a characteristic combustion duration of ∼ 8 ms. These results provide unprecedented insights into gas–solid combustion dynamics, demonstrating BO₂-PLIF as a robust diagnostic tool for boron-fueled propulsion systems.