Quantification of differential diffusion in nonpremixed systems

Most attempts to quantify differential diffusion (DD) are based on the difference between different definitions of the mixture fraction. This paper presents a general method for evaluating differential diffusion in premixed or nonpremixed systems based on conservation equations for the elemental mass fractions. These measures form a basis for analysing differential diffusion. Casting these in terms of a mixture fraction gives particular insight into differential diffusion for nonpremixed systems, and provides a single DD measure. Furthermore, it allows direct evaluation of the validity of the traditional assumptions involved in writing a mixture fraction transport equation. Results are presented for one-dimensional opposed flow simulations of hydrogen and methane flames as well as direct numerical simulations (DNS) of CH4/H2–air and CO/H2–air flames. For a common definition of the mixture fraction, the DD measure can be approximated well by considering only the contribution of H2 and CH4 in methane–air flames. Differential diffusion is largely driven by production of H2 in the flame zone for hydrocarbon flames. Effects of strain rate and filter width on the relative importance of differential diffusion are examined.

[1]  S. Lam,et al.  On de-coupling of Shvab-Zel'dovich variables in the presence of diffusion , 2003 .

[2]  V. Giovangigli.  Multicomponent flow modeling , 1999 .

[3]  G. Kosály,et al.  Differentially diffusing scalars in turbulence , 1997 .

[4]  J. M. Heimerl,et al.  Results of a Study of Several Transport Algorithms for Premixed, Laminar Steady-State Flames , 1982 .

[5]  George Kosály,et al.  Differential diffusion in turbulent reacting flows , 1998 .

[6]  A. Kronenburg,et al.  Modelling Differential Diffusion in Nonpremixed Reacting Turbulent Flow: Application to Turbulent Jet Flames , 2001 .

[7]  R. Lewis,et al.  Low-storage, Explicit Runge-Kutta Schemes for the Compressible Navier-Stokes Equations , 2000 .

[8]  R. Barlow,et al.  Experiments on the scalar structure of turbulent CO/H2/N2 jet flames , 2000 .

[9]  A. Williams,et al.  Combustion Theory: Second Edition , 1985 .

[10]  John D. Ramshaw,et al.  Self-Consistent Effective Binary Diffusion in Multicomponent Gas Mixtures , 1990 .

[11]  J C Hewson,et al.  Stochastic simulation of transport and chemical kinetics in turbulent CO/H2/N2 flames , 2001 .

[12]  Robert W. Bilger,et al.  Modelling of differential diffusion effects in nonpremixed nonreacting turbulent flow , 1997 .

[13]  J.-Y. Chen,et al.  Fuel-dilution effect on differential molecular diffusion in laminar hydrogen diffusion flames , 1998 .

[14]  Richard A. Yetter,et al.  A Comprehensive Reaction Mechanism For Carbon Monoxide/Hydrogen/Oxygen Kinetics , 1991 .

[15]  Robert J. Kee,et al.  On reduced mechanisms for methaneair combustion in nonpremixed flames , 1990 .

[16]  G. B..  The Dynamical Theory of Gases , 1916, Nature.

[17]  Forman A. Williams,et al.  Laminar flow between parallel plates with injection of a reactant at high reynolds number , 1978 .

[18]  R. Yetter,et al.  Flow reactor studies and kinetic modeling of the H2/O2 reaction , 1999 .

[19]  Akademie der Wissenschaften in Wien , 2006, Naturwissenschaften.

[20]  John D. Ramshaw,et al.  Friction-Weighted Self-Consistent Effective Binary Diffusion Approximation , 1996 .

[21]  Christopher A. Kennedy,et al.  Improved boundary conditions for viscous, reacting, compressible flows , 2003 .

[22]  Ross Taylor,et al.  Multicomponent mass transfer , 1993 .

[23]  R. Barlow,et al.  Scalar profiles and NO formation in laminar opposed-flow partially premixed methane/air flames , 2001 .

[24]  N. Peters,et al.  A Consistent Flamelet Formulation for Non-Premixed Combustion Considering Differential Diffusion Effects , 1998 .

[25]  M. Carpenter,et al.  Several new numerical methods for compressible shear-layer simulations , 1994 .

[26]  R. Barlow,et al.  Laser Raman scattering measurements of differential molecular diffusion in turbulent nonpremixed jet flames of H2CO2 fuel , 1995 .