In spite of the accelerated development of electrification, particularly for automobiles, the global reliance on liquid fuels (bio-derived or petroleum based) continues to be strong. With the ongoing use of these fuels, a need exists for sustained improvements in pollutant reduction and fuel economy. A key place to look these advancements is directly in the process of fuel injection and spray formation. This area of investigation is not new, but unfortunately it has faced daunting experimental challenges originating from the presence of a dense cloud of minuscule droplets surrounding the liquid fuel core in the early stages of spray formation. It is precisely this early stage of fuel injection that is critical in the resulting spray characteristics and is ultimately linked to issues related to fuel economy and pollutant formation. An attractive alternative being pursued in the proposed work is the use of highly-detailed computer simulations that can adequately interrogate all stages of spray formation with sufficient spatial and temporal resolution. With these tools, long-standing questions concerning the dynamics of spray formation and their sensitivity to fuel properties and injection strategies will be addressed. A key question targeted in the proposed work concerns recently observed patterns of liquid fuel breakup, which seem to hint at some universal behavior of early-stage spray development. If these patterns can be understood, there is potential for controlling and optimizing them for maximum reduction of pollutant emissions and improvements in fuel economy.
The proposed work aims to uncover the underlying causes of liquid jet breakup and provide a newer perspective to this relatively old problem by employing computer simulations. Preliminary simulation results have shown the emergence of a large-scale sinuous mode that is responsible for the atomization of the intact liquid core and is associated with the largest production of interfacial area and interphase momentum exchange. Hence, the main part of the proposed work begins with a quantitative examination of this large-scale mode. Explanation of the growth of this mode and other interfacial disturbances will then be pursued with a general instability theory and with a mathematical description based on potential flow theory (the intact liquid core is largely irrotational). To provide a more comprehensive analysis of the breakup phenomena, the simulation of the flow upstream of the injector nozzle will also be included. This upstream conditioning of the flow has been established as being a key feature in the development of interfacial instabilities and the breakup of the jet. Due to the challenges involved in the simulation of liquid sprays with interface capturing methods, new validation exercises will be undertaken, along with an automated means of evaluating the appropriateness of the numerical resolution employed.
