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

分析了液体燃料喷射到热力状态超过燃料临界点的空气中时所形成的喷雾燃烧的特征过程。发现了以下几种情况。(1)尽管人们普遍认为液滴的自燃延迟时间随压力的增加而单调缩短，但在接近燃料临界点的环境状态下，液滴的自燃延迟时间出现了一个峰值。这种长期行为是由于液滴表面相平衡条件的影响。考虑到目前的柴油机在这样的条件下工作，这一知识解决了一个有趣的问题，即寻找快速燃烧的最佳喷雾条件。(2)雾化是喷雾燃烧的关键技术。然而，由于高压下的光学观测非常困难，对液体火箭发动机和柴油发动机高压喷雾中涉及的雾化机理的了解很少。目前的概念是基于在标准压力下的水射流雾化实验所获得的知识。研究了具有近临界混合面的射流的不稳定性，发现了一种新的不稳定模式，其增长率与射流速度成正比，该模式可以使液体射流在流体动力作用下破碎成间距较小的液滴。如果我们将低速液体喷流视为注入液体的湍流雾化过程中形成的液体韧带之一，这一发现从理论上为高压下形成由细小液滴组成的稠密喷雾奠定了基础。此外，我们还研究了(3)火焰通过湍流混合过程中形成的可燃旋涡的快速传播机理和(4)各种喷雾的火焰在液滴之间的传播方式。

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.