Abstract:

A key challenge for advanced liquid-fueled combustion and high-speed propulsion systems is to develop the ability to use liquid hydrocarbons as both the fuel and coolant because of their high energy density, heat sink capacity, environmentally-friendly characteristics, costs, and availability. The use of such fuels, however, is still limited due to their high decomposition temperature for regenerative cooling and long ignition delay for short combustor residence times. As a means to address these issues, colloidal nanostructured additives, which can be suspended in liquid fuels, offer the potential to act as catalysts to lower the liquid-phase decomposition temperature and accelerate the gas-phase hydrocarbon oxidation chemistry. In the present research, platinum (Pt)-decorated functionalized graphene sheets (FGS) having high surface area, high heat of combustion, and catalytic functionalities, are examined to understand their effects on the pyrolysis, injection, ignition, and subsequent combustion of hydrocarbon fuels under elevated temperature and pressure conditions. From supercritical pyrolysis studies, Pt-decorated FGS particles are observed to accelerate fuel decomposition and yield more reactive products including hydrogen and low-carbon-number species. Combustion experiments demonstrated that the compositional change in the fuel mixture containing Pt-FGS reduced ignition delay time and increased combustion conversion efficiency. The enhancing mechanisms of the materials on pyrolysis and combustion are studied using ReaxFF molecular dynamics (MD) simulation. The simulation results support the experimental observations, showing that a combination of Pt and FGS facilitates catalytic dehydrogenation of the fuel molecules. These results demonstrate that a low mass loading of high surface area catalytic material can be used to tailor both the endothermic behavior and combustion characteristics of liquid hydrocarbon fuels under supercritical conditions. Such enhancements benefit practical propulsion systems which require high conversion efficiency in a short residence time.

Biosketch:

Hyungsub Sim will receive his Ph.D. degree in Mechanical and Nuclear Engineering from Penn State University in the Spring of 2016. Prior to that, he was a plant engineer at STX Heavy Industries in South Korea, developing traditional power, cement, and biomass power plants. He received his B.S. and M.S. degree in Mechanical Engineering from Chung-Ang University, Seoul, South Korea. During his M.S. studies, he investigated microscale thermo-optical characteristics in thin film structures and conducted extensive numerical simulations using analytical and numerical methods. His current research interests include combustion chemistry, multi-phase reacting flow dynamics, nano-engineered energetic/catalytic materials, and advanced combustion/propulsion systems.