Abstract:

An experimental and numerical study with detailed chemistry has been conducted to determine the role of water addition to the fuel side of methane-air counterflow diffusion flames. This work is relevant to combustion processes were water is incorporated in the fuel stream; e.g, methane hydrates and applications for emission reduction such as in flares and H2O/fuel emulsions. The maximum flame temperature and extinction limits were measured, while the flame structure was computed using a detailed kinetic mechanism, GRI 3.0. Predictions and experiments demonstrate that water mainly acts thermally to lower the flame temperature (1650K) until extinction. Experimentally and computationally, extinction limits (in terms of the H2O to CH4 molar ratio) decrease with increasing strain rates; that is, flames can sustain more H2O vapor at low strain rates. Maximum flame temperature at the extinction increases with increasing strain rates because there is less H2O to act as a thermal sink. Hydroxyl radical Planar Laser Induced Fluorescence measurements confirm features found in the calculations and experiments, showing a decrease of OH intensity, a decrease in the reaction zone thickness, and a movement of the flame location with water addition. Computationally, chemical effects were distinguished from thermal effects through the introduction of a nonreactive water molecule. The study suggests that water’s chemical effects are to change the production and depletion of OH, H and O radicals, especially near extinction. In particular, a sensitivity analysis shows that atomic hydrogen plays a critical role in the extinction through the chain branching reaction H+O₂ OH+O.

Bio:

Rosa Padilla completed her undergraduate studies from the University of California, Davis with a degree in Biological Systems Engineering and an emphasis in biomechanics. She obtained a Masters in Mechanical Engineering from the California State University, Los Angeles. After her studies at CSULA she moved to the University of California, Irvine where she has worked with Professor Derek Dunn Rankin in the field of combustion and is near completion for her doctoral degree in Mechanical Engineering. During her PhD she has worked with high school students as part of engineering introductory programs, Upward Bound and COSMOS, and she has mentored students through undergraduate research programs such as the California Alliance for Minority Participation and UC-LEADS.