Multiphase ignition and combustion model and its characteristics of boron particles based on dynamic experimental phenomena

Boron, renowned for its high-energy potential but challenged by combustion difficulties, emerges as an ideal fuel for solid-fuel scramjet engines. This study improved the ignition and combustion model for boron particles in wet air by refining the Penn State University extension models based on the dynamic experimental phenomena. Under atmospheric pressure, the transition in combustion mode for boron particles occurs within the diameter range of 3.5–4.9 µm, with increased ambient temperature or H₂O concentration promoting the shift towards diffusion-controlled mode. Larger particles exhibit a sequential combustion mode, transitioning from kinetics-controlled to diffusion-controlled, and back to kinetics-controlled, while smaller particles consistently remain kinetics-controlled. The ignition delay proportion increases with the particle diameter but generally stays below 10 %. Increasing the temperature significantly shortens the ignition time, while increasing the pressure significantly shortens the combustion time. Taking the combustion of 1 µm boron particles at atmospheric pressure as an example, as the temperature increases from 1700 K to 3500 K, the ignition time decreases to 0.08 %, and as the pressure increases from 0.5 atm to 15 atm, the combustion time decreases to 1.6 %. Increasing the O₂ concentration significantly shortens the combustion time, with a lesser effect on the ignition time. The addition of H₂O can reduce both ignition and combustion times, especially for boron particles with an approximate diameter of 5 µm in low temperature environments. However, once XH₂O exceeds 15 %, the combustion time stabilizes in both combustion modes. Lower ambient temperatures and smaller particles enhance the impact of solidification on the combustion of boron particles.