We are investigating ammonia-seeded diffusion flames in collaboration with researchers at the University of Heidelberg and the Technical University of Denmark. The goal of this work is to improve the understanding of NO pollutant formation due to fuel-bound nitrogen characteristic of bio-mass fuels. For these problems, data is gathered from the experiment using laser-induced fluorescence (LIF). In the two-line LIF analysis approach for temperature extraction, two frequencies associated with the NO molecule are excited by the laser over a two-dimensional sheet through the vertical midplane of the flame, and the resulting LIF signals are processed using the known temperature-dependence of the bands. The absolute NO concentration can be inferred from either signal if the temperature and mole fractions are known for all species that may quench the NO LIF signal. Unfortunately, the NO signal is strongly quenched by the oxygen molecule.
We have developed a new approach that more closely intertwines simulation and experimental data interpretation. Using a two-dimensional axisymmetric model, we compute steady diffusion flame solutions corresponding to the experimental setup. After validating the computational results against the temperature profiles inferred from the experiment using the two-line approach discussed, we use the simulation results, combined with quantum-dynamical quenching models to generate numerical LIF images. Across the range of experimental parameters, these numerical LIF images showed exceptional agreement with the raw LIF data from the experiment. A comparison of the experimentally-measured and the synthetic computational LIF is presented in the figure below.
NO-molecule excitation LIF images obtained (top) from measurement and (bottom) by synthetically processing the results of the flame simulation, for different ammonia seeding concentrations. The experimental data and the synthetic LIF intensities are shown on identical scales.
Additionally, using simulated chemical distributions directly in the quench calculations, we demonstrated very good agreement between the computed and experimentally inferred NO concentrations. This work was published in the 2002 Combustion Symposium and is available on the CCSE Publications page.
The adaptive low Mach number simulation code, an extension of CCSE code IAMR for incompressible flows, is not presently available for release. For more information about the adaptive methodology for low Mach number combustion modeling applications, or about these calculations, contact Marc Day or John Bell of CCSE.