A Flamelet Time Scale combustion model for turbulent combustion in KIVA

Most flamelet models for turbulent combustion assume that a turbulent diffusion flame behaves locally as a steady, one-dimensional, laminar, strained flame. While this assumption works well in many practical applications, it fails to take into account finite rate kinetic effects that occur at low Damköhler numbers. It has been shown by Cook et al. (1997) that a steady laminar flamelet model over-predicts products and that its accuracy decreases as the Damköhler number decreases. Other researchers have used methods such as the RIF formulation (Pitsch et al., 1995) and conditional moment closure models (Bilger, 1993) to account for kinetic effects. However, these models are computationally expensive. The Flamelet Time Scale (FTS) model presented here attempts to account for finite-rate kinetic effects with relatively low computational overhead. The FTS combustion model (Rao, 2001) combines the laminar flamelet combustion idea (Peters, 1984) and the characteristic time-scale concept (Reitz et al., 1983). The model is formulated such that the solution approaches a steady flamelet solution when chemistry is fast and attempts to capture finite-rate effects when chemistry cannot be neglected.