CAREER: Droplet Vaporization under Asymmetric Conditions: Implications for Combustion at Conventional and Reduced Scales

这一职业项目的主要目标是评估不对称对流和热条件对燃料-蒸汽分布和蒸发液体-燃料液滴的点火特性的影响。该实验方法将单分散丙酮液滴置于热和对流不对称流动条件下。两个独立的流动反应器，一个加热的线性推流反应器(LPFR)和一个加热的环形库埃特流动反应器(CCFR)，为观察丙酮液滴的蒸发提供了热不对称(LPFR)、对流不对称(CCFR)和热/对流不对称(CCFR)环境。一片激光照射着蒸发的液滴流，使丙酮蒸气发出荧光。一台增强的ccd摄像机捕捉到了荧光图像。对这些图像的分析揭示了不对称的热流体条件导致燃料-蒸汽分布不均匀的程度，这反过来可能对液滴点火、燃烧和污染物形成产生不利影响。通过比较热、对流和热/对流组合不对称条件的影响，可以揭示单独和集体的影响，从而为将经典的液滴蒸发理论扩展到包括非均匀环境提供了基础。一个独立的并行数值模拟工作正在开发中，以模拟观察到的异常汽化行为，并使用并行处理架构和微尺度传输公式验证新的汽化模型。随着排放法规对传统燃烧设备的限制越来越多，环境合规性可能越来越取决于对高阶效应的理解，如不对称液滴蒸发现象。此外，非对称液滴蒸发现象可能在微型(~1 mm)燃烧室内的燃烧过程中发挥主导作用，这是一项正在开发的新兴技术，为便携式电子设备、遥控器和遥控飞行器提供动力。这样的微型燃烧室需要液体燃料，以便有与电动电池竞争所需的长时间加油间隔。然而，小型化增加了相对于燃烧室尺寸的液体燃料液滴的尺寸，并在燃烧室内部产生了更强和更显著的热流体性质梯度。因此，燃烧室的成功小型化取决于识别和了解异常燃烧现象，这些现象在常规尺度上几乎微不足道，但在这些缩小的尺度上占主导地位。这个职业项目的教育部分使用由高中、本科生和研究生组成的垂直整合的团队(“工程集体”或ECs)来开始指导科学和工程发现项目。高中生是从IIT校园周围的社区招募的，这些社区主要是非洲裔美国人和拉丁裔美国人，因此有助于扩大科学和工程领域代表性不足的群体的参与及其在IIT校园的代表性。

The primary objective of this CAREER project is to assess the impact of asymmetrical convective and thermal conditions on the fuel-vapor distributions and ignition characteristics of vaporizing liquid-fuel droplets. The experimental methodology exposes monodisperse acetone droplet streams to thermally and convectively asymmetric flow conditions. Two separate flow reactors, a heated linear plug-flow reactor (LPFR) and a heated circular Couette-flow reactor (CCFR), provide thermally asymmetric (LPFR), convectively asymmetric (CCFR), and combined thermal/convective asymmetric (CCFR) environments for observation of vaporization of acetone droplets. An Nd-YAG laser sheet illuminates the vaporizing droplet streams, causing the acetone vapor to fluoresce. An intensified CCD camera captures the fluorescence images. Analysis of these images reveals the degree to which asymmetric thermofluid conditions induce nonuniform fuel-vapor distributions, which in turn can impact adversely droplet ignition, combustion, and pollutant formation. By comparing the effects of thermal, convective, and combined thermal/convective asymmetric conditions, individual and collective effects can be exposed, thus providing the basis for extending classical droplet vaporization theory to include nonuniform environments. A separate, concurrent numerical modeling effort is being developed to simulate observed anomalous vaporization behavior and to validate new vaporization models using parallel processing architectures and micro-scale transport formulations.As emission regulations become ever more restrictive for traditional combustion devices, environmental compliance may depend increasingly on understanding higher-order effects, such as asymmetric droplet vaporization phenomena. Further, asymmetric droplet vaporization phenomena may play a dominant role in combustion processes within miniature (~ 1 mm) combustors, an emerging technology being developed to provide power for portable electronics, remote sensors, and remotely piloted vehicles. Such miniature combustors require liquid fuels in order to allow the long refueling intervals needed to compete with electric batteries. However, miniaturization increases the size of liquid fuel droplets relative to the combustor dimensions and produces stronger and more prominent thermofluid property gradients within the combustor itself. Thus, successful miniaturization of combustors depends on identifying and understanding anomalous combustion phenomena that are nearly insignificant at conventional scales but which predominate at these reduced scales.The educational component of this CAREER project uses vertically integrated teams ("Engineering Collectives" or ECs) of high school, undergraduate, and graduate students to embark upon guided science and engineering discovery projects. High school students are recruited from the neighborhoods surrounding the IIT campus, which are predominantly African-American and Latino, thereby helping to broaden the participation of underrepresented groups in science and engineering and their representation on the IIT campus.