Study on the Atomization Gasification, Mixing and Combustuin Processes of Liquid fuel Jets in Supercritical Enironments

本文分析了液体燃料喷入热力状态超过临界点的空气中所形成的喷雾燃烧的特征过程。结果表明：（1）尽管人们普遍认为液滴自燃延迟时间随压力的增加而单调缩短，但在燃料临界点附近的环境状态下，液滴自燃延迟时间出现一个峰值。这种长期行为是由于液滴表面相平衡条件的影响。考虑到目前的柴油发动机在这种条件下运行，这种知识解决了一个有趣的问题，找到一个最佳的喷雾条件快速燃烧。(2)雾化是喷雾燃烧的关键技术。然而，由于高压下光学观察非常困难，对液体火箭发动机和柴油发动机中高压喷雾的雾化机理的理解非常差。目前的概念是基于从标准压力下的水射流雾化实验获得的知识。研究了近临界混合面射流的不稳定性，发现了一种新的不稳定性模式，其增长率与射流速度成正比，在流体动力作用下，可使液体射流破碎成间距较小的液滴。如果我们把低速液体射流看作是在喷射液体的湍流雾化过程中形成的液体韧带之一，则这一发现在理论上是在高压下形成由细液滴组成的密集喷雾的基础。此外，我们还研究了（3）湍流混合过程中形成的可燃涡流中火焰快速传播的机理和（4）各种喷雾液滴间火焰传播的模式。

Analyzes were made of characteristic processes involved in the combustion of sprays which are formed when liquid fuel is injected into the air whose thermodynamic state exceeds the critical point of the fuel. The following were found. ( 1) Despite the convectional belief that droplet auto-ignition delay time shortens monotonically with increasing pressure, it was found that the droplet auto-ignition delay time takes a peak at the ambient states near to the fuel critical point. This secular behavior is due to the influence of the phase equilibrium condition at droplet surface. Considering that current diesel engines operate at such condition, this knowledge addresses an interesting problem of finding an optimum spray condition for fast combustion. (2) Atomization is a keytechnology to spray combustion. However, the understanding of atomization mechanism involved in high-pressure sprays used in liquid rocket engines and diesel engines are very poor because optical observation is very difficult at high pressures. The current concept is based on the knowledge obtained from the experiments of water jet atomization at standard pressure. We examined the instability of jets with near-critical mixing surface and found a new instability mode with growth rate proportional to jet speed, which can make the liquid jetbroken into droplets with short spacing with the aids of hydrodynamic action. This finding theoretically bases the formation of dense sprays constituting of fine droplets at high pressures, if we regard a low-speed liquid jet as one of the liquid ligaments formed in the turbulent atomization process of an injected liquid. Furthermore, we studies (3) the mechanism of rapid flame propagation through combustible vortices formed in the process of turbulent mixing and (4) the modes of flame spreading between droplets for a various kind of sprays.