Supercritical carbon dioxide has brought about new questions on the chemical kinetics of several small hydrocarbon fuels and the effects of carbon dioxide as the primary diluent on the different fuels. This report presents work on the ignition delay times and several species time-histories of methane, ethylene and syngas over a range of conditions. All experiments were conducted behind reflected shock waves using two different shock tubes. The ignition delay times were measured using a GaP photodetector to measure the emission of light. The species time-histories were measured using single laser spectroscopy. The effect of CO2 as a diluent on the fluid dynamics of the system were also examined using high-speed camera images. It was determined that the ignition delay times and fuel time-histories were able to be accurately predicted by mechanisms in the literature for pressures up to 30 atm but the literature mechanisms were unable to predict the carbon monoxide time-histories beyond qualitative trends for the various fuels. It was also determined that the carbon monoxide had a string effect on the fluid dynamics of the experiments resulting in a significantly smaller chemical reaction zone. Experiments were also performed to examine the effects of water as a diluent with a ratio up to 66% of the total diluent on the ignition delay times. Using the experimental data, a global kinetic mechanism was created for methane and syngas to predict the ignition delay times and the carbon monoxide time-histories for pressures up to 300 atm.

In the current engine development, fuel reformulation is considered as one of the potential strategies to improve fuel efficiency, reduce petroleum consumption, and minimize pollutant formation. Oxygenated fuels can be used as neat fuels or additives in spark-ignition and diesel engines to allow for more complete combustion. To understand the influence of oxygenated fuels on engine performance, accurate comprehensive kinetic mechanisms, which can consist of hundreds to thousands of elementary reactions, are needed to describe the chemistry of the combustion events, such as autoignition and pollutant formation. The primary objective of the research presented in this dissertation is to provide reliable experimental kinetic targets, such as ignition delay times, species time histories, and direct reaction rate constant measurements, using shock tube and laser absorption techniques in order to evaluate and refine the existing kinetic mechanisms for two different types of oxygenated fuels (i.e., ketones and methyl esters) and to reexamine the kinetics of the H2 + OH reaction. The topics of this work are mainly divided into three sections: (1) H2 + OH kinetics, (2) ketone combustion chemistry, and (3) methyl ester + OH kinetics. The reaction of OH with molecular hydrogen (H2) H2 + OH → H2O + H (1) is an important chain-propagating reaction in all combustion systems, particularly in hydrogen combustion, and its direct rate constant measurements are discussed in the first part of this dissertation. The rate constant for reaction (1) was measured behind reflected shock waves over the temperature range of 902-1518 K at pressures of 1.15-1.52 atm. OH radicals were produced by rapid thermal decomposition of tert-butyl hydroperoxide (TBHP) at high temperatures, and were monitored using the narrow-linewidth ring dye laser absorption of the well-characterized R1(5) line in the OH A--X (0, 0) band near 306.69 nm. Consequently, this work aims to report the rate constant for reaction (1) with a much lower experimental scatter and overall uncertainty (as compared to the data available in the literature). Ketones are important to a variety of modern combustion processes. They are widely used as fuel tracers in planar laser-induced fluorescence (PLIF) imaging of combustion processes due to their physical similarity to gasoline surrogate components. Additionally, they are often formed as intermediate products during oxidation of large oxygenated fuels, such as alcohols and methyl esters. In the second part of this dissertation, the combustion characteristics of acetone (CH3COCH3), 2-butanone (C2H5COCH3), and 3-pentanone (C2H5COC2H5) are discussed in the context of the reflected shock wave experiments. These experiments were performed using different laser absorption methods to monitor species concentration time histories (i.e., ketones, CH3, CO, C2H4, CH4, OH, and H2O) over the temperature range of 1100-1650 K at pressures near 1.6 atm. These speciation data were then compared with the simulations from the detailed mechanisms of Pichon et al. (2009) and Serinyel et al. (2010). Consequently, the overall rate constants for the thermal decomposition reactions of acetone, 2-butanone, and 3-pentanone CH3COCH3 (+ M) → CH3 + CH3CO (+ M) (2) C2H5COCH3 (+ M) → Products (+ M) (3) C2H5COC2H5 (+ M) → Products (+ M) (4) were inferred by matching the species profiles with the simulations from the detailed mechanisms at pressures near 1.6 atm. In addition, an O-atom balance analysis from the speciation data revealed the absence of a methyl ketene removal pathway in the original models. Furthermore, the overall rate constants for the reactions of OH with a series of ketones CH3COCH3 + OH → CH3COCH2 + H2O (5) C2H5COCH3 + OH → Products (6) C2H5COC2H5 + OH → Products (7) C3H7COCH3 + OH → Products (8) were determined using UV laser absorption of OH over the temperature range of 870-1360 K at pressures of 1-2 atm. These measurements included the first direct high-temperature measurements of the overall rate constants for reactions (6)-(8), and were compared with the theoretical calculations from Zhou et al. (2011) and the estimates using the structure-activity relationship (SAR) (1995). Biodiesel, which consists of fatty acid methyl esters (FAMES), is a promising alternative to fossil fuels. The four simplest methyl esters include methyl formate (CH3OCHO), methyl acetate (CH3OC(O)CH3), methyl propanoate (CH3OC(O)C2H5), and methyl butanoate (CH3OC(O)C3H7), and their combustion chemistry is a building block for the chemistry of large methyl esters. In the third part of this dissertation, the rate constant measurements for the reactions of OH with four small methyl esters are discussed: CH3OCHO + OH → Products (9) CH3OC(O)CH3 + OH → Products (10) CH3OC(O)C2H5 + OH → Products (11) CH3OC(O)C3H7 + OH → Products (12) These reactions were studied behind reflected shock waves using UV laser absorption of OH over 876-1371 K at pressures near 1.5 atm. This study presented the first direct high-temperature rate constant measurements of reactions (9)-(12). These measurements were also compared with the estimated values from different detailed mechanisms and from the structure-activity relationship (SAR).

The ignition and combustion behind a reflected shock wave of particles stirred up from a layer of finely divided fuel by a passing shock wave have been studied experimentally. It is noted that the results of this study may be of interest for the study of the kinetics of heterogeneous combustion reactions. The fuel used was charcoal, brush carbon, or black powder. The data indicate that the fuels ignite behind shock waves at M = 2.25 and above with different ignition delays. The minimum ignition temperature was about 900K for the carbons and 800K for black powder. Pressure oscillographs showed that pressure behind the reflected shock front at the end of the tube remains constant for about 1.5 msec, then increases for 6-8 msec.

In this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% - 85% by volume. A 10% fuel concentration was consistently used throughout the experiments. This study looked at the effects of changing the equivalence ratios ([phi]), between 0.33, 0.5, and 1.0 as well as changing the fuel ratio ([theta]), hydrogen to carbon monoxide, from 0.25, 1.0 and 4.0. The study was performed at 1.61-1.77 atm and a temperature range of 1006-1162K. The high-speed imaging was performed through a quartz end wall with a Phantom V710 camera operated at 67,065 frames per second. From the experiments, when increasing the equivalence ratio, it resulted in a longer ignition delay time. In addition, when increasing the fuel ratio, a lower ignition delay time was observed. These trends are generally expected with this combustion reaction system. The high-speed imaging showed non-homogeneous combustion in the system, however, most of the light emissions were outside the visible light range where the camera is designed for. The results were compared to predictions of two combustion chemical kinetic mechanisms: GRI v3.0 and AramcoMech v2.0 mechanisms. In general, both mechanisms did not accurately predict the experimental data. The results showed that current models are inaccurate in predicting CO2 diluted environments for syngas combustion.

Stemming from a continuing demand for fuel surrogates, composed of only a few species, combustion of high-molecular-weight hydrocarbons (>C5) is of scientific interest due to their abundance in petroleum-based fuels, which contain hundreds of different hydrocarbon species, used for military, aviation, and transportation applications. Fuel surrogate development involves the use of a few hydrocarbon species to replicate the physical, chemical, combustion, and ignition properties of multi-component petroleum-based fuels, enabling fundamental studies to be performed in a more controlled manner. Of particular interest are straight-chained, saturated hydrocarbons (n-alkanes) due to the high concentration of these species in diesel and jet fuels. Prior to integrating a particular hydrocarbon into a surrogate fuel formulation, its individual properties are to be precisely known. n-Nonane (n- C9H20) is found in diesel and aviation fuels, and its combustion properties have received only minimal consideration. The present work involves first measurements of n- C9H20 oxidation in oxygen (O2) and argon (Ar), which were performed under dilute conditions at three levels of equivalence ratio ([phi] = 0.5, 1.0, and 2.0) and fixed pressure near 1.5 atm using a shock tube. Utilizing shock waves, high-temperature, fixed-pressure conditions are created within which the fuel reacts, where temperature and pressure are calculated using 1D shock theory and measurement of shock velocity. Of interest were measurements of ignition times and species time-histories of the hydroxyl (OH*) radical intermediate. A salient pre-ignition feature was observed in fuel-lean, stoichiometric, and fuel-rich OH* species profiles. The feature at each equivalence ratio was observed above 1400 K with the time-of-initiation (post reflected-shock) showing dependence on phi as the initiation time shortened with increasing phi. Relative percentage calculations reveal that the fuel-rich condition produces the largest quantity of pre-ignition OH*. Ignition delay time measurements and corresponding activation energy calculations show that the [phi] = 1.0 mixture was the most reactive, while the [phi] = 0.5 condition was least reactive.