燃料在亚/超临界环境下的喷射现象学研究

Phenomenological Study on the Fuel Injecting into Sub-and Super-Critical Environments

为探究燃料在亚/超临界环境条件下喷射过程的差异,采用定容燃烧弹系统将亚临界状态的正己烷喷射到亚/超临界环境中,利用背光法记录喷射的全过程,研究亚/超临界环境下喷射形态的差异以及相关机理。结果表明:超临界环境下的喷射与亚临界环境下的喷射在形态学特征上存在较大差异,在超临界温度下,当喷射环境的压力由亚临界压力进入超临界压力时,相同喷射时刻的喷射锥角和喷射长度大幅增大,说明亚/超临界环境下喷射的气化机理存在差异,即亚临界环境下的喷射为传统的气化蒸发过程,而超临界环境下的喷射是靠跨越"伪沸腾"线,进行"类液体"向"类气体"转变的过程;超临界环境下相同喷射时刻的喷射锥角和喷射长度随着环境条件的变化波动较大,主要是燃料在临界点及"伪沸腾"线附近时热力学物性参数的剧烈变化导致。亚/超临界环境下的喷射现象学的研究表明,亚/超临界环境下喷射形态学的差异主要是喷射破碎及气化机理的差异导致,为进一步研究超临界环境下的喷射过程数值模拟提供了试验依据。

To investigate the difference of fuel injection processes in sub-and super-critical environments,N-hexane in subcritical condition was sprayed into the sub-and super-critical environments in a constant volume combustion bomb system,and the whole process of injection was recorded by the backlight method.The difference of spray shapes and related mechanism in sub-and super-critical environments were studied.The results show that the jets in super-and sub-critical environments are different in morphological characteristics.At supercritical temperature,when the pressure of the injection reaches the supercritical pressure from subcritical pressure,the spreading angle and injection length increase greatly at the same time.It shows that the gasification theory is different between sub-and super-critical environments,that is,the jet under subcritical environment is a traditional evaporation process,but it is a transition from liquid-like to gas-like across the pseudo-boiling line under supercritical environment.The spreading angle and injection length under supercritical environment fluctuate greatly with the pressure and the temperature due to the drastic change of the physical parameters near the critical point and pseudo-boiling line.The study on the spray phenomenology in sub-and super-critical environments shows that the difference of spray morphology between sub-and super-critical environments is mainly caused by the difference in jet fragmentation and gasification mechanism,which provides a test basis for further study on numerical simulation of the spraying process in supercritical environment.