Turbulence-chemistry interaction in lean premixed hydrogen combustion

This paper presents three-dimensional direct numerical simulations of lean premixed hydrogen flames at an equivalence ratio of phi = 0.4 over a range of turbulence levels from Ka = 1-36. The simulations form part of a larger effort to construct a DNS database that can be used by the community for model construction and validation. We have focussed on producing well-resolved simulations at conditions representative of atmospheric laboratory-scale flames. After an overview of phenomenological trends with increasing Karlovitz number, we examine the factors that lead to an observed decorrelation between fuel consumption and heat release in the flame at Ka = 36. We show that in this flame the fuel consumption is greatly enhanced in regions of positive curvature. We also show that the radical pool is enriched throughout the entire flame as Ka is increased. In particular, we identify three reactions that, driven by high molar concentrations of radicals at low temperatures, are responsible for high levels of heat release away from regions of fuel consumption, thereby accounting for the observed decorrelation between fuel consumption and heat release. (C) 2014 Published by Elsevier Inc. on behalf of The Combustion Institute.