Offers a computational study of the effect of pressure on soot formation in laminar premixed flames. An existing detailed kinetic model of soot formation validated previously for low-pressure and atmospheric laminar premixed flames is extended to account for the effects associated with elevated-pressure conditions. Detailed analysis of the model predictions is then used to gain a physical understanding of the experimentally observed trends in soot formation caused by elevated pressures.

During the second twelve-month period of the project, progress has been made in the following areas: (1) The computational study of sooting limits in laminar premixed flames was completed. It was found that the critical equivalence ratios for soot appearance, both the absolute values and temperature dependencies, can be predicted fairly close to the experimental observations. Sensitivity and reaction path analyses were performed to examine the factors responsible for the predicted behavior. (2) New estimation techniques were developed and applied for calculations of standard-state enthalpies of formation and binary gaseous diffusion coefficients Of polyCyCl4C aromatic hydrocarbons (PAHs) and their radicals, thus providing critical information for accurate modeling of soot formation in flames. (3) Theoretical studies of a bench-mark ion-molecule reaction were completed. (4) Computer simulations of the effect of pressure on soot formation were initiated. (5) Several manuscripts summarizing the results obtained have been completed and submitted for publication.

Soot Formation in Combustion represents an up-to-date overview. The contributions trace back to the 1991 Heidelberg symposium entitled "Mechanism and Models of Soot Formation" and have all been reedited by Prof. Bockhorn in close contact with the original authors. The book gives an easy introduction to the field for newcomers, and provides detailed treatments for the specialists. The following list of contents illustrates the topics under review:

This is the final report of a research program considering the structure and the soot surface reaction properties of laminar nonpremixed (diffusion) flames. The study was limited to ground-based measurements of buoyant laminar jet diffusion flames at pressures of 0.1-1.0 atm. The motivation for the research is that soot formation in flames is a major unresolved problem of combustion science that influences the pollutant emissions, durability and performance of power and propulsion systems, as well as the potential for developing computational combustion. The investigation was divided into two phases considering the structure of laminar soot-containing diffusion flames and the soot surface reaction properties (soot surface growth and oxidation) of these flames, in turn. The first phase of the research addressed flame and soot structure properties of buoyant laminar jet diffusion flames at various pressures. The measurements showed that H, OH and O radical concentrations were generally in superequilibrium concentrations at atmospheric pressure but tended toward subequilibrium concentrations as pressures decreased. The measurements indicated that the original fuel decomposed into more robust compounds at elevated temperatures, such as acetylene (unless the original fuel was acetylene) and H, which are the major reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. The second phase of the research addressed soot surface reaction properties, e.g., soot surface growth and surface oxidation. It was found that soot surface growth rates in both laminar premixed and diffusion flames were in good agreement, that these rates were relatively independent of fuel type, and that these rates could be correlated by the Hydrogen-Abstraction/Carbon-Addition (HACA) mechanisms of Colket and Hall (1994), Frenklach et al. (1990,1994), and Kazakov et al. (1995). It was also fou

The present work focuses on a computational study of a simplified soot model to predict soot production and destruction in methane/oxidizer (O2 and N2) and ethylene/air flames using a one-dimensional laminar opposed diffusion flame setup. Two different detailed reaction mechanisms (361 reactions & 61 species for methane/oxidizer flame and 527 reactions & 99 species for ethylene/air flame) are used to validate the simplified soot model in each flame. The effects of strain rate and oxygen content on the soot production and destruction are studied, and the soot related properties such as soot volume fraction, particle number density and particle diameter are compared with published results. The results show reasonable agreement with data and that the soot volume fraction decreases with higher strain rate and lower oxygen content. The simplified soot model has also been used with two reduced reaction mechanisms (12-step, 16-species for methane flame and 20-species for ethylene flame) since such reduced mechanisms are computationally more efficient for practical application. The profiles of the physical properties and the major species are in excellent agreement with the results using the detailed reaction mechanisms. However, minor hydrocarbon-species such as acetylene (C2H2) that is the primary pyrolysis species in the simplified soot model is significantly over predicted and this, in turn, results in an over-prediction of soot production. Finally, the reduced reaction mechanism is modified to get more accurate prediction of the minor hydrocarbon-species. The modified reduced reaction mechanism shows that the soot prediction can be improved by improving the predictions of the key minor species.