Numerical evaluation of NOx mechanisms in methane-air counterflow premixed flames

The control of nitrogen oxides (NO_x) has been a major issue in designing combustion systems, since NO_x play a key role in ozone depletion and the generation of photochemical smog. The characteristics of NO_x emission can be essential information for the development of a clean combustor having suitable reduction methodologies. In the present study, NO_x emission characteristics were evaluated numerically, accounting for the effect of equivalence ratio, stretch rate, pressure, and initial temperature. In general, peak NO_x emission appeared near the equivalence ratio of unity case, and NO_x emission increased with pressure and initial temperature due to the temperature sensitivity in NO_x mechanism. NO_x decreased with stretch rate due to the decrease in residence time in high temperature region. Furthermore, the thermal and prompt mechanisms were evaluated with equivalence ratio for two calculation methods. The conventional methods ignore the interaction of coupled mechanism of thermal and prompt NO_x. The reaction path diagram was introduced to understand effective reaction pathways in various conditions. This paper was recommended for publication in revised form by Associate Editor Kyoung Doug Min Dr. Eun-Seong Cho received his B.S. and M.S. degrees in Mechanical Engineering from Hanyang University, Korea, in 1996 and 1998, respectively. He then received his Ph.D. degree from Seoul National University, Korea, in 2005. He was a principal engineer of KD Navien research center and currently a research associate at Delft University of Technology, The Netherlands. His research interests include eco-friendly clean combustion technology, new and renewable energy systems. Prof. Suk Ho Chung received his B.S. degree from Seoul National University, Korea, in 1976 and Ph.D. degree in Mechanical Engineering from Northwestern University, USA, in 1983. He is a Professor since 1984 in the School of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. His research interests cover combustion fundamentals, pollutant formation, laser diagnostics, and plasma-assisted combustion.