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Supercritical Liquid Fuel Combustion Mechanism

超临界液体燃料燃烧机理

基本信息

批准号：
01550163
负责人：
UMEMURA Akira
金额：
$ 1.22万
依托单位：
Yamagata University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1991
项目状态：
已结题

项目摘要

A numerical simulation scheme was developed to disclose the unsteady evaporation and combustion processes of a single fuel droplet immersed in an otherwise quiescent gas at a various ambient gas state beyond the critical point of the fuel, which is necessary for the design of rocket motors and high speed Diesel engines. This study was carried out, based on the author's previous theoretical work on supercritical droplet combustion wherein it was found that the transition from sub- to supercritical evaporation regime can take place only if the binary diffusion coefficient relevant vanishes at the liquid gas interface in a mixture critical condition, an expression for the diffusion coefficient which satisfies this condition was proposed and the asymptotic transition feature was revealed on an analytical basis.The condition under which the droplet experiences the transition during its lifetime was identified in terms of ambient gas temperature and pressure. Other important knowledge obtained is as follows. Consistent with experimental results no singular behavior is observed in the droplet surface temperature at the transition. The core characterized by high fuel concentration preserves the liquid-like property even after the droplet has lost its liquid-gas interface. Since continuous phase change takes place in a thin layer, usual optical observation will give images as if there still exists the droplet with surface. Once the core is about to disappear, the concentration as well as the central temperature changes abruptly to assume the gaseous state. The transition is achieved far more quickly in the presence of flame which is located closer to the droplet at higher pressure. The transition epochs the change from vaporization- to diffusion-controlled combustion, accompanying an increase in flame temperature.

为了研究单燃料液滴在静止气体中的非定常蒸发和燃烧过程，建立了一种数值模拟方法，研究了燃料液滴在超过临界点的各种环境气体状态下的非定常蒸发和燃烧过程，这对火箭发动机和高速柴油机的设计是必要的。本研究是在作者以前关于超临界液滴燃烧的理论工作的基础上进行的，其中发现，只有当在混合物临界条件下，在液-气界面处的二元扩散系数相关为零时，才能发生从亚临界蒸发状态到超临界蒸发状态的转变，给出了满足该条件的扩散系数表达式，并从解析的角度揭示了扩散系数的渐近过渡特性，给出了扩散系数满足该条件的条件液滴在其寿命期间经历的转变根据环境气体温度和压力来确定。获得的其他重要知识如下。与实验结果一致，没有观察到奇异行为的液滴表面温度在过渡。以高燃料浓度为特征的芯即使在液滴已经失去其液-气界面之后也保持液体状性质。由于连续相变发生在薄层中，通常的光学观察将给出图像，好像仍然存在具有表面的液滴。一旦核心即将消失，浓度以及中心温度突然改变，呈现气态。在火焰存在的情况下，在更高的压力下更接近液滴，过渡更快地实现。过渡时期的变化，从汽化扩散控制燃烧，伴随着火焰温度的增加。