Shock Tube Studies Of Biofuel Kinetics

The harmful emissions associated with the combustion of fossil fuels combined with the rapidly increasing global demand for energy present serious challenges to the long term sustainability of life on this planet. Fossil fuels currently account for approximately 81% of worldwide energy usage, and approximately 22% of global energy consumption occurs in the transportation sector. One approach for addressing the world's energy challenges is to reduce the consumption of fossil fuels by improving the numerical simulation capabilities of combustion systems, thus enabling engineers to design more efficient combustion devices. A prerequisite for this design capability is the understanding of chemical kinetics of the fuels that are being utilized. An alternative approach for reducing the consumption of fossil fuels is developing renewable energy alternatives that eliminate the need for fossil fuels altogether. Biofuels are of particular interest as an alternative fuel in the transportation sector because their net CO2 footprints can be significantly lower compared to those of traditional fossil fuels. The goal of this dissertation is to study the chemical kinetics of biofuels, which would ultimately allow them to be used more efficiently in the combustion devices of the future. This work is primarily experimental, and it can be divided into three parts: First, the chemical kinetics of butanol, a promising second generation biofuel, were investigated extensively. A variety of kinetic targets such as ignition delay times and species time-histories were measured accurately over a wide range of conditions. These high-accuracy data have been used by research groups around the world in order to validate and improve chemical kinetic models. Second, rate constants for reactions of ethanol and tert-butanol with OH radicals were investigated. These reactions are one of the primary removal pathways of fuels during combustion, and they significantly affect the combustion properties of these fuels. Measurements were performed using isotopic labeling of 18O in the alcohol group in order to eliminate the recycling of OH radicals following H-atom abstraction at [beta]-sites, which commonly perturbs measurements of rate constants for reactions of alcohols with OH radicals. Third, various experimental techniques were developed and improved while performing these measurements. This work presents the first application of isotopic labeling and laser absorption in shock tubes, which shows significant promise for future chemical kinetic studies. Furthermore, the rate constant for cyclohexene decomposition was determined with the highest accuracy to date. These measurements are likely to improve a myriad of comparative rate and chemical thermometry studies that use cyclohexene decomposition as a reference reaction. Finally, a high-temperature laser absorption diagnostic for measuring acetylene concentration was developed. Time-resolved shock tube measurements of this critical combustion intermediate should significantly improve the experimental capabilities for performing chemical kinetic studies.