HIGH INJECTION PRESSURE IMPINGING DIESEL SPRAY CHARACTERISTICS AND SUBSEQUENT SOOT FORMATION IN REACTING CONDITIONS

Abstract

The spray impingement in diesel engines attracts the attention of engine researchers in recent decades as the physical size of the engine is reduced. Due to the spray impingement, the atomization, vaporizing and air-fuel mixing quality is altered compared to a free spray. For emission control, soot is one of the major particulate emissions from diesel combustion and its formation in an impinged spray is worthy to be investigated. Firstly, to understand the impinged spray characteristics, the experiments for both non-vaporizing and reacting conditions were conducted in a constant volume combustion vessel. The impinged spray was captured by a high-speed camera and the instantaneous spray propagation distance and rate were obtained. For a better understanding, the microscopic behavior of the spray propagation, the curvature of the impinged spray was calculated and a relationship between local fuel distribution and soot formation was found. After that, the apparent heat release rate from an impinge spray combustion and the heat flux through the impingement were analyzed. The apparent heat release rate was obtained by the internal chamber pressure and the heat flux was measured by heat flux probes embedded in the impinging plate. Then, the soot formation of an impinged spray was both studied from experiments and simulations. In the experiments, the natural luminosity mainly due to the incandescence of soot particles was captured by the high-speed camera. A computational fluid dynamics (CFD) approach was adopted to quantitatively study the soot formation in terms of absolute soot mass and soot mass fractions in the vicinity of the wall. In the last, the film formation under different ambient temperatures, impinging distances, and oxygen concentration was investigated in terms of film area and thickness. The impact of film formation on the soot outcomes was then investigated by comparing the rate of film vaporization and soot formation. To summarize, the main goal of this dissertation is going to benefit the understanding of the impinged spray in reacting diesel-relevant engine conditions. From experiments, a global view of soot formation in an impinged spray was analyzed and the mechanism of soot formation was further revealed by the CFD simulations.