考虑Stefan影响的单颗粒硼着火过程研究

Study of ignition process of boron particle with considering Stefan flow effects

针对含硼推进剂固体火箭冲压发动机内单颗粒硼的着火过程展开了系统研究.考虑硼颗粒周围气相流动以及硼颗粒与周围环境间的传热传质过程,建立了考虑Stefan流作用的一维硼颗粒着火模型,研究了硼颗粒实现着火和未能实现着火两种典型情形下硼颗粒及周围气相的参数变化规律,对两种情形下Stefan流的变化规律及其成因展开了详细分析.研究表明,在硼颗粒实现着火的过程中,液态B2O3的蒸发及硼的氧化均能在硼颗粒的反应自加热作用下急剧加速,硼颗粒表面附近的氧气和气相B2O3分布变化剧烈;在未能实现着火的过程中,液态B2O3的蒸发和氧气消耗的质量流率相对较小,并逐渐趋于稳定,硼颗粒表面附近的氧气和气相B2O3分布相对变化很小.在两种典型情形下,硼颗粒外表面的Stefan流都会经历先由周围空间流向颗粒表面,而后变为由颗粒表面流向周围空间的过程.

A one-dimensional model about the ignition process of boron particle in boron-based propellant ducted rocket is systemically investigated. The gas flow around the boron particle, the heat transfer and the mass transfer between the boron particle and the surrounding are included in the model. And the effects of Stefan flow are also proposed. The changing regularities of important parameters in the two typical cases, viz., the successful ignition case and the degenerate ignition case are studied in detail. And their reasons are analyzed. The result shows that both the evaporation of the liquid boric oxide layer and the oxidation of the boron are remarkably accelerated as the result of the self-heating exothermic oxidation in the successful ignition case, and the mass fraction profiles of the oxygen gas and those of the B2O3 gas also dramatically change in that case. However, both the mass flux of the evaporation of the liquid boric oxide layer and that of the consumption of the oxygen gas are relatively small, and both of them tend to be nearly constant in the degenerate ignition case. The mass fraction profile of the oxygen gas and that of the B2O3 gas change little in the degenerate ignition case. In the two typical cases, Stefan flow on the boron particle surface undergoes the change of flow direction, viz., Stefan flow initially comes from the surrounding and then it flows from the particle surface to the surrounding.