CAREER: Investigation of Fuel Sprays and Air Mixing in Lean Direct-Injection Four-Stroke Spark-Ignition Engines

本文研究了精益直喷发动机中燃油喷射混合与燃烧的相互作用。先进的光学诊断和多维建模用于表征缸内燃料/空气混合和燃烧的光学可及，直喷发动机。光学诊断包括用于显示燃烧条件下液体和蒸汽燃料空间分布的激射荧光，用于显示液体燃料的燃料掺杂的平面激光诱导荧光（PLIF），以及用于表征液滴大小和喷雾速度的相/多普勒颗粒分析（P/DPA）。在此基础上，提出了一种利用异型液体荧光和Mie散射信号同时成像的新型平面液滴定形技术；这些信号的比率与索特平均直径成正比，该技术可以使用P/DPA测量来校准。计算是在两相反应流模型的框架内进行的，该模型已用于喷雾和发动机测量的比较。本文的研究结果将为精益直喷式火花发动机的成功设计提供基础依据。这种发动机被认为可以提高燃油经济性并减少排放，但由于对燃油喷射、混合和燃烧之间的关系了解不足，它的发展受到了阻碍。

Abstract - Lee This is a study of the interaction of fuel spray mixing and combustion in a lean direct-injection engine. Advanced optical diagnostics and multi-dimensional modeling are used to characterize in-cylinder fuel/air mixing and combustion in an optically accessible, direct-injection engine. Optical diagnostics include exciplex fluorescence for visualization of spatial distributions of liquid and vapor fuel under firing conditions, planar laser-induced fluorescence (PLIF) with fuel dopants for visualization of liquid fuel, and phase/Doppler particle analysis (P/DPA) to characterize drop size and velocity of the spray. In addition, a new planar droplet sizing technique is developed by imaging exciplex liquid fluorescence and Mie scattering signals simultaneously; the ratio of these signals is proportional to the Sauter mean diameter and the technique can be calibrated using the P/DPA measurements. Computations are performed within the framework of a model for two-phase reacting flows that has been used for comparisons of spray and engine measurements. The results of this work should provide the fundamental basis for design of a successful lean direct-injection spark-injection engine. Such an engine is believed to offer improved fuel economy and reduced emissions, but its development has been hampered by poor understanding of the relationships among fuel injection, mixing, and combustion.