As part of an ongoing research program aimed at developing techniques capable of quantitative imaging of mixture fraction and scalar dissipation in turbulent flames, three-scalar measurements were made in a turbulent nonpremixed flame. The use of nitrogen Raman scattering to detect a passive conserved scalar made it possible to increase confidence in the two-scalar technique based on simultaneous imaging of Rayleigh scattering and fuel Raman scattering. These experiments showed that proper parameterization of mixture fraction-dependent terms appearing in the expression for mixture fraction can improve accuracy for lean values of mixture fraction as well as those near stoichiometric. Additionally, a new experimental technique was investigated which allows the extraction of velocity information from laser-based scalar imaging in turbulent flows. Preliminary results from simultaneous particle-imaging velocimetry (PIV) and optical flow velocimetry showed that this technique has potential for unseeded velocity measurements compatible with the mixture fraction imaging. The optical flow approach was based on extracting velocity vectors from the intensity variations naturally present in inhomogeneous turbulent flow images of a mixing-dependent scalar quantity.

Three-scalar measurements were made in a turbulent nonpremixed flame (Re=15000) to increase confidence in the two-scalar technique based on simultaneous imaging of Rayleigh scattering and fuel Raman scattering. Nitrogen Raman scattering was employed as an passive conserved scalar and mixture fraction was calculated by two independent approaches. These experiments showed that proper parameterization of mixture fraction-dependent terms appearing in the expression for mixture fraction can reduce deficiencies for lean values of mixture fraction and near stoichiometric. Additionally, the spatial resolution of the optical setup was characterized and determined to be sufficient for resolving scalar dissipation.

Three-scalar measurements were made in a turbulent nonpremixed flame (Re=15000) to increase confidence in the two-scalar technique based on simultaneous imaging of Rayleigh scattering and fuel Raman scattering. Nitrogen Raman scattering was employed as an passive conserved scalar and mixture fraction was calculated by two independent approaches. These experiments showed that proper parameterization of mixture fraction-dependent terms appearing in the expression for mixture fraction can reduce deficiencies for lean values of mixture fraction and near stoichiometric. Additionally, the spatial resolution of the optical setup was characterized and determined to be sufficient for resolving scalar dissipation.

A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.

Significant progress has been made in the following two research areas: (1) Nonlinear spectroscopy of micrometer-sized multicomponent droplets; and (2) Two- and three-dimensional scalar and velocity mapping. Optical diagnostics that have the potential of providing information on chemical species and temperature of multicomponent liquid droplets have been developed. A brief summary of the research accomplishments in the following three areas: (1) droplet temperature determination with thermochromic dyes; (2) enhancement of stimulated Raman scattering from droplets for identifying chemical species; and (3) modification of droplet lasing characteristics by injection seeding and Q-switching. Progress has been made in developing and applying a technique for obtaining mixture fraction and scalar dissipation in a variety of turbulent nonpremixed flames. The data from these experiments are of use for modeling these complex systems. In premixed flames, simultaneous velocity/scalar images were obtained, along with full three-dimensional gradient and OH information.

The combustion of fossil fuels remains a key technology for the foreseeable future. It is therefore important that we understand the mechanisms of combustion and, in particular, the role of turbulence within this process. Combustion always takes place within a turbulent flow field for two reasons: turbulence increases the mixing process and enhances combustion, but at the same time combustion releases heat which generates flow instability through buoyancy, thus enhancing the transition to turbulence. The four chapters of this book present a thorough introduction to the field of turbulent combustion. After an overview of modeling approaches, the three remaining chapters consider the three distinct cases of premixed, non-premixed, and partially premixed combustion, respectively. This book will be of value to researchers and students of engineering and applied mathematics by demonstrating the current theories of turbulent combustion within a unified presentation of the field.