应用红外和紫外PLIF技术对二氧化碳溶气燃油闪急沸腾喷射的研究

The middle-east part of China was blanketed in a thick haze in these years, which was mainly cause by the emissions from vehicles. Mixture formation and combustion control is the key problem of the low nitrogen oxides and soot emissions of a conventional diesel engine. A representative exhaust gas CO2 from diesel engine combustion is selected as a test gas, and CO2 dissolved diesel is treated as our research object. In order to study and analyze the distribution and the concentration of each component in the spray of the CO2 dissolved diesel, both the infrared laser-induced fluorescence (IR PLIF) and ultraviolet laser-induced fluorescence (UV PLIF) are implemented simultaneously to capture the images of the flash-boiling atomization. The project is expected to discuss how different mass fractions of dissolved gas CO2 at injection influence the atomization quality, turbulent mixing, the distribution and the concentration of each component in the spray, to show how the dissolved CO2 in the diesel play an active role before fuel combustion in the chamber of the internal combustion engine, and to provide a theoretical basis for the atomization of the dissolved gas fuel. The results of this project suggest the modern fuel technology using the combination or miscible intermixing technique to conduct a re-formulation of the fuels, thereby changing the composition and physicochemical properties of the fuels, to promote air-fuel mixture formation in the cylinder and to control the combustion. This CO2 dissolved fuel concept and this project are helpful and significant for the modern internal combustion engines to achieve high efficiency and low emissions.

排放的汽车尾气是影响国内雾霾天气的一个重要因素因素，混合气的形成和燃烧控制是实现传统柴油发动机的低氮氧化物和碳烟排放的关键，为此选择柴油机燃烧废气中的代表性气体-二氧化碳-作为试验气体, 以溶CO2的柴油为研究对象，同时使用红外激光诱导荧光（IR PLIF）和紫外激光诱导荧光（UV PLIF）技术，研究和分析CO2溶气燃油闪急沸腾喷雾中各组分的浓度分布。项目预期将揭示不同溶气量的CO2如何提高燃油喷雾质量，如何影响喷雾的湍流混合，为溶气燃油喷雾在内燃机燃烧室内各组分分布建立新的理论依据。项目的研究成果对于结合现代燃料技术，利用互溶、互混技术对燃料进行重新配方，从而改变燃料的成分和理化特性，促进缸内混合气形成并进行燃烧控制这一理念具有重要意义，可以为现代内燃机实现高效率,低排放目的提供科学依据。

利用多阈值图像处理法对内燃机排气再循环溶气汽油和溶气柴油通过单孔喷嘴的喷雾特性进行研究。将氮气和二氧化碳的混合气体（CO2的摩尔质量分数为20%）注入至柴油或汽油中模拟废气再循环的溶气燃料。通过高速摄像机获取喷雾图像，从喷雾图像，如宏观特征的瞬态喷雾锥角的变化和微观的液滴粒径分布进行分析，并于纯柴油和汽油的雾化特性进行比较。CO2溶气汽油在喷雾初始阶段时，喷雾前端有突然爆破的现象，并且喷雾锥角较大，这是由于被压缩的二氧化碳遇到压力骤降其气泡快速生长并爆破所引起的。同样，CO2溶气柴油喷雾在喷射时有微小的液滴稀疏地分布在喷雾边缘，这是由于压缩的CO2在流体中迅速蒸发造成的。此外为了达到项目研究目的，还对过热燃料闪急沸腾喷雾特性及多元燃料液滴蒸发进行了研究，较大的膨胀室为过热燃油的气化和沸腾提供了更多的空间和时间，其射流被高气/液质量比的两相流稀释。进口孔径小的喷嘴喷射流量小，膨胀室中蒸发潜热消耗快并导致腔内温度迅速下降，使其过热度较低，最终导致喷雾锥角小，液滴空间分布浓度低。通常高的环境温度将增加各成分的蒸发率峰值，并且缩短多元燃料液滴的存在寿命。虽然较高的环境压力可以抑制液滴蒸发，但是同时蒸发潜热的消耗降低，这使液滴被加热到更高的温度，而此时液滴温度对相平衡的影响要远远大于周围环境的影响。蒸发潜热的消耗和周围环境对液滴的热传递，这两个相互“竞争”的因素对多组分液滴的蒸发特性起着决定性的影响。