SPRAY AND COMBUSTION CHARACTERISTICS OF DIMETHYL ETHER UNDER VARIOUS AMBIENT CONDITIONS: AN EXPERIMENTAL AND MODELING STUDY

With a growing restriction on environment policy due to pollution and the global needs for replacement or alternative to conventional petroleum production, alternative fuels such as Dimethyl Ether (DME) provide the solutions in environment and economy for our future generations. As the simplest ether, DME has the physical and chemical properties that are potentially suitable for compression-ignition engine in automotive industry. There are many remaining challenges in understanding the combustion of DME, fuel handling and storage, specific fuel-oriented engine design in order to use DME effectively on transportation sector. Nonetheless, the many favorable attributes such as high cetane number (good ignitability) and very low emission of DME have led to the increasing effort on research and development of this fuel. Low and high pressure injection system are continuously improved to handle the drawback from DME properties such as low viscosity (poor lubricity), high compressibility (higher required compression work). Meanwhile, fundamental research in the combustion and emission characteristics of DME fuel is necessary to provide insights on the fuel behavior at various conditions such as ambient temperature, ambient composition, fuel injection pressure, nozzle size, etc. One of the most advanced apparatus in combustion research is combustion vessel which provide desired conditions with high accuracy for spray and combustion experiment. The current study in this work investigates spray, combustion, and consumption and formation of species (i.e. formaldehyde) using an optically accessible constant volume combustion vessel. Experimental data, for example, liquid/vapor penetration, spray and flame structure, ignition delay, heat release rate, species evolution from laser application, are collected through several data acquisition systems and high-speed cameras. Various test conditions like of temperature, oxygen concentration, injection pressure are set to provide parametric study of DME. Also, the results were processed and used as validation of several models including chemical kinetic work, 1-D spray modeling, and CFD simulation to achieve detailed understanding and develop better prediction tool set of DME combustion phenomenon. A detailed chemical kinetic mechanism work was developed from other published mechanism to study soot and NOx formation in DME reactions, while reduced mechanism was also generated for a more time efficient in computational work while still maintaining the core species and reaction pathway of DME combustion and emission. Both experimental and numerical work show important conclusions and summaries in spatially and temporally ignition, species formation, heat release rate, spray characteristics, and others that provide very good understanding of DME fuel chemistry and physical behaviors. Confirmation of smokeless combustion in DME flame is also shown as the expectation of bluish flame from literature review. In summary, the goal of this dissertation is to enhance the understanding of DME combustion in a well-controlled environment, therefore providing feedbacks to the ultimate task in future development and application of a more reliable, effective, clean-fuel system.