The objective of the project is to enhance physical understanding of the intricate processes occurring in combustion at the microscale, in order to support and guide ongoing experimental efforts in this area. Mathematically, the problems require finding solutions to coupled, highly nonlinear partial differential equations, further complicated by inevitable temporal variations, multi-scale processes, and nontrivial boundaries. Tractable problems require judicious modeling efforts in order to capture the main features of the phenomena under consideration. The simplified models are addressed using appropriate analytical or numerical strategies in order to provide solutions that enable comparing the theoretical predictions with experimental observations. The investigator examines two sets of problems. The first set is associated with premixed combustion in an excess-enthalpy combustor where the hot combustion products are recirculated to heat up the fresh reactants, thus enhancing the burning rate and heat output. The second set of problems is associated with nonpremixed combustion in a confined slot, where the mixing zone and the resulting diffusion flame spread over the entire length of the reactor channel. The goal is to study the structure, properties and dynamics of flames in such configurations and identify conditions for steady burning, onset of instabilities, flashback or blowoff, and flame extinguishment.
Combustion is a subject of great economical and societal concern. Despite the continuing search for alternative energy sources, combustion still provides the majority of the energy consumed today. It is therefore important to ensure that combustion processes are utilized in the most efficient way, and in such a way as to minimize undesirable effects on the environment. Recent development in the field of microscale combustion has been motivated by the increased need for smaller scale and high density power sources and by the fact that hydrocarbon fuels have enormous advantages over batteries in terms of energy storage per unit mass. There are, however, important issues that need to be addressed in order to render this technology practical and efficient. Beyond the difficulties associated with fabrication, fundamental questions concerned with the underlying combustion physics need to be overcome. The development of combustion systems at the microscale requires deeper understanding at the fundamental level of fluid flow in microchannels, heat and mass transport at the small scale, combustion in small volumes and complex geometries, thermal and chemical properties of the wall materials, and fluid-wall interactions. Mathematical modeling plays an important role towards this goal; it provides means to explain experimental observations and identify the physical mechanisms responsible for these observations. The investigator, building on his earlier contributions to fluid mechanics and chemically reacting flows, studies the peculiarities of combustion at the microscale in order to improve physical understanding of these phenomena. By guiding and supporting the ongoing experimental efforts the project has an immediate effect on advancements of this new technology.
