摘要:
凝胶推进剂虽然兼具有液体推进剂流量可控和固体推进剂长期可储存等优点,但凝胶喷雾液滴蒸发燃烧问题却一直困扰着凝胶推进剂研制及燃烧室设计工作,阻碍了凝胶推进剂实际工程应用.设计实现了凝胶单液滴蒸发燃烧实验系统,通过某型有机凝胶偏二甲肼（UDMH）单液滴在四氧化二氮蒸气中的蒸发燃烧实验现象,进一步深入分析了凝胶液滴蒸发燃烧机理.根据实验中凝胶单液滴在不同阶段的蒸发特性,建立了有机凝胶喷雾液滴在胶凝剂膜形成、膨胀、破裂三个不同蒸发阶段的多组分蒸发模型,采用初步选定的模型参数及物性参数对凝胶单液滴在高温气体环境中的蒸发全过程进行了仿真计算,并与常规液体液滴的仿真结果进行了对比分析.结果表明,凝胶喷雾液滴表面胶凝荆含量在蒸发初期增加比较缓慢,但在某临界时刻后的极短时间内迅速升高至形成胶凝剂膜的质量分数95%,导致表面质量流率迅速下降至0,表面温度则快速上升至UDMH推进剂沸点.胶凝剂膜形成后,液滴半径及表面UDMH蒸气质量分数出现了实验现象中凝胶液滴反复膨胀-破裂的震荡现象,液滴表面温度维持在略高于沸点的某温度范围内,凝胶液滴内部的沸腾蒸发明显强于液体液滴表面稳态蒸发流率,使得凝胶喷雾液滴生存时问小于常规液体液滴.
Abstract:
Gel propellant has the advantage of controllable flux as liquid propellant and long-term reservation as solid propellant,however, the evaporation and combustion problem of gel spray droplet bores with the gel propellant development and combustor design all the time,and hampers gel propellant practical engineering applications.In this paper,the gel single droplet combustion experiment system is designed and constructed,and then the evaporation and combustion mechanism is explored deeply based on the experimental phenomena of organic gel unsymmetrical dimethylhydrazine（UDMH） single droplet burning in nitrogen tetroxide.The organic gel spray droplet multi-component evaporation model is developed for three different evaporation phases of the gel layer,i.e.the forming, expanding and bursting of the gel layer based on the single droplet evaporation characteristics in experiment,and then the gel single droplet vaporization in high temperature gas phase is numerically simulated and compared with the result of conventional liquid droplet using the elementary model parameters and physic property parameters.The result shows that the gel content on the droplet surface increases slowly at the beginning of evaporation,however it would increase rapidly to a mass fraction of 95%and form the gel layer in a limited time after exceeding a critical evaporation time,which results in surface mass flux dropping to 0 and surface temperature reaching the UDMH boil point rapidly.After the gel layer forming,the droplet radius and surface UDMH vapor mass fraction exhibit oscillation as the swelling-bursting phenomena in experiment.The gel droplet surface temperature holds above the boil point and the mass flux of gel droplet inner boiling evaporation is stronger than the conventional liquid droplet surface steady evaporation which makes the life time of gel droplet much shorter.
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