有机凝胶燃料液滴燃烧过程相分离现象

Phenomenon of Phase Separation in Combustion Process of Organic Gelled Fuel Droplets

关键词:  凝胶燃料  液滴燃烧  相分离  质量输运  热量输运

Key words:  Gelled fuel  Droplet combustion  Phase separation  Mass transport  Heat transport

摘要:

要掌握凝胶推进剂在燃烧室内燃烧特性,必须首先认识清楚单个凝胶推进剂液滴的燃烧机理。为了揭示凝胶燃料液滴特殊的燃烧机制,在考虑相分离阶段液滴内部温度和浓度梯度变化的基础上,完善并发展了一种新的数学模型来描述凝胶燃料液滴的相分离过程,并且用之研究了凝胶燃料单液滴蒸发/燃烧过程中的相分离特性。研究结果表明:相分离阶段,液滴的半径按d²定律收缩,与实验结果吻合；液滴点火后,火焰由初始位置向液滴外围扩展,火焰温度不断上升,并且逐渐趋于稳定；相分离前期,在液滴内部,特别是表面附近的区域,质量的输运较热量输运容易,而相分离后期则呈现相反趋势,这就导致在相应的区域相分离前期比后期有更大的温度梯度,而相分离后期比前期有更大燃料浓度梯度。

Abstract:

Understanding the combustion mechanisms of single droplet is the first stage to predict the burning characteristics of gelled fuel in the combustion chamber. Therefore, to investigate the special combustion mechanism of gelled fuel droplets, a new mathematical model was firstly developed to describe their phase separation process in the consideration of the inner gradient change of temperature and concentration. Then the model was used to investigate the phase separation characteristics of the gelled fuel droplets in their evaporation and combustion process. Results show that shrinkage of the radius obeys the d²-law and it agrees well with experimental measurements at the phase separation stage. Then, after the droplet ignited, the flame will expand from the initial location to the peripheries of droplets with temperature of the flame increasing and gradually tending to be stable. Furthermore, in the prophase of the phase separation, the mass is easier than the heat to transport inside the droplets, especially in the nearby surface region. However, the above process is on the contrary in the anaphase of the phase separation, which leads to the higher temperature gradient in the prophase of the phase separation, and the higher base fuel mass concentration gradient in the anaphase of the phase separation. 