"The principal objective of this study was to investigate the fundamentals of various soot processes within turbulent non-premixed flames using non-intrusive laser diagnostics. Unconfined burners with different fuels in atmospheric-pressure air were selected to collect data in well-defined turbulent flames. Laser scattering at two angles and extinction experiments were conducted and interpreted based on an optical theory which can properly account for the actual fractal morphology of soot aggregates ... with the ultimate objective of advancing the predictions of fine-particulate matter in practical combustion applications"--Introduction, leaves 16-17.

Progress is made in this thesis in understanding the complex multi-scale chemical and physical processes governing the formation of condensed phase material from gaseous species. The formation of soot through combustion and the synthesis of functional nanomaterial through chemical vapor deposition (CVD) are examined. We first attempt to characterize the sooting tendencies of alternative fuels using different techniques. A new numerical model based on modified flamelet equations is used along with a modified chemical mechanism to predict the effect of fuel molecular structure on soot yield in gasoline surrogates. These simulations provide trends on sooting behavior and are one-dimensional calculations that neglect other phenomenon that govern soot yield and distribution. To determine how other factors influence sooting behavior in laminar flames we carry out experimental and numerical studies to understand how the addition of oxygen to the oxidizer changes soot yield and distribution. Finite-rate chemistry based Direct Numerical Simulations (DNS) are carried out for a series of methane/air flames with increasing Oxygen Index (OI) using an extensively validated, semi-detailed chemical kinetic mechanism, along with an aggregate-based soot model and the results are compared with experimental measurements. It is seen that the effect of variable OI is well captured for major flame characteristics including flame heights, soot yield, and distribution by the numerical simulations when compared to the experimental data. This study is however confined to a small fuel that may not represent behavior seen in real fuels or the constituents that make up these gasoline fuels or their surrogates. Thus, we examine the effects of premixing on soot processes in an iso-octane coflow laminar flame at atmospheric pressure. Iso-octane is chosen as a higher molecular weight fuel as it is an important component of gasoline and its surrogates. Flames at different levels of premixing are investigated ranging from jet equivalence ratios of 1 (non-premixed), 24, 12, and 6. Numerical simulations are compared against experimental measurements and good agreement is seen in soot yield and soot spatial distributions with increasing levels of premixing. While the above studies for soot were carried out for laminar flames combustion devices frequently operate at conditions that lead to turbulent flow. Therefore, to understand how soot is affected by turbulence we computationally study the effects large Polycyclic Atromatic Hydrocarbons species (PAH) have on soot yield and distribution in turbulent non-premixed sooting jet flames using ethylene and and jet fuel surrogate (JP-8). The effects of large PAH on soot are highlighted by comparing the PAH profiles, soot nucleation rate, and soot volume fraction distributions obtained from both simulations for each test flame. Comparisons are also made with experiments when available and further analysis is performed to determine the cause of the observed behavior. Finally, a new multi-scale model is proposed for the computational modeling of the synthesis of functional nanomaterials using CVD. The proposed model is applied to a W(CO)6/H2Se system that has been used by researchers at Penn State to perform WSe2 crystal growth. A force-field for W/C/O/H/Se is developed and favorable agreement is seen when compared to QM data. A reaction mechanism leading from W(CO)6 and H2Se to the crystal precursor is then developed and used in a reacting flow simulation of the custom CVD chamber at Penn State. The bulk reacting flow numerical predictions show promising results for the gas-phase and precursor species, while additional work is still being performed to make the method more robust.

Due to the complexity of the fluid dynamics and non-linear reactions in the combustion zone, a simplified approach to study this process is required. Given these complexities, it is practically very challenging to take measurements in very high temperature and pressure zones in practical combustion systems, and if by any means those measurements can be made, it is equally challenging to analyze those measurements. Hence, in order to more comprehensively understand these processes, the problem needs to be resolved into the smaller and controllable sub-category of experiments, by creating laminar flamelets. One approach used in creating these flamelets is by establishing simplified non-premixed flames in the counterflow configuration. Alongwith all the fundamental properties of combustion, it is important to study the health hazard and environmentally detrimental emissions, such as soot and polycyclic aromatic hydrocarbons (PAHs). Such combustion studies need to be carried out using the non-intrusive in-situ optical diagnostics measurement techniques, such as the Laser Induced Incandescence (LII), Planar Laser Induced Fluorescence (PLIF) and Light Extinction (LE). These measurements for renewable biofuels aid in better understanding of the soot formation process, as well as in developing the fuel specific knowledge to bring them into commercial use. Furthermore since the most practical combustion systems operate at elevated pressures, it is also important to understand the soot formation process under elevated pressure conditions. Considering these, in the current study, the soot and PAH formation processes for butane and butanol isomers (C4 fuels) at atmospheric pressure; and for ethylene at elevated pressure have been experimentally investigated and compared in a counterflow non-premixed flame configuration. Under the investigated conditions, butane isomers were observed to form more soot than butanol isomers, thereby showing the effect of the hydroxyl group. The effects of isomeric structural differences on sooting propensity were also observed within the butane and butanol isomers. In addition, while soot volume fraction was seen to increase with increasing fuel mole fraction, the ranking of sooting propensity for these C4 fuels remained unchanged. For the conditions studied, the sooting tendency ranking generally follows n-butane > iso-butane > tert-butanol > n-butanol > iso-butanol > sec-butanol. . The counterflow non-premixed flames were also simulated using the gas-phase chemical kinetic models, USC Mech II [1], Sarathy et al. [2] and Merchant et al. [3] available in the literature to compute the spatially-resolved profiles of soot precursors, including acetylene and propargyl. For these C4 fuels, the PAHs of various aromatic ring size groups (2, 3, 4, and larger aromatic rings) have been characterized and compared in non-premixed combustion configuration. In particular, the formation and growth of the PAHs of different aromatic ring sizes in these counterflow flames was examined by tracking the PAH-PLIF signals at various detection wavelengths. PAH-PLIF experiments were conducted, by blending each of the branched-chain isomers with the baseline straight-chain isomer, in order to study the synergistic effects. The fuel structure effects on the PAH formation and growth processes were also analyzed by comparing the PAH growth pathways for these C4 fuels. A chemical kinetic model, POLIMI mechanism [4-7], available in the literature that includes both the fuel oxidation and the PAH chemistry was also used to simulate and compare the PAH species up to A4 rings. Counterflow non-premixed sooting ethylene‒air flames with fuel mole fractions of 0.20‒0.40 in the pressure range of 1‒6 atm were investigated experimentally with the laser diagnostic techniques of LII, PLIF and LE. A better understating of the quantitative soot formation process has been developed for ethylene counterflow flames under elevated pressure conditions. The effect of pressure on the formation of PAHs with different aromatic ring sizes has also been determined qualitatively. With increase in pressure, the increase in soot volume fraction and PAH-PLIF signals were observed. A chemical kinetic model available in the literature, that includes both the fuel oxidation and the PAH chemistry, was also used to simulate and compare the PAH species up to A4 rings. At the incipient stage of the PAH formation, the simulated results exhibited similar behavior to the experimental observations. A chemical kinetic model, WF-PAH mechanism [8], available in the literature was also used to compute the PAHs up to four aromatic rings. This chemical kinetic model predicted enhancing PAHs formation with an increase in pressure, consistent with the experimental trend.