Comparative sensitivity analysis of transport properties and reaction rate coefficients

Transport properties of chemical species are required for many combustion models. A sensitivity analysis is conducted to assess the significance of transport properties and their underlying molecular parameterizations for atmospheric pressure premixed laminar flames for three different fuels and two different approaches to transport property calculations. The analysis is performed at both the macroscopic level of Arrhenius A-factors and transport coefficients as well as at the molecular scale. First- and second-order sensitivities of reactant, intermediate, and product species concentrations, temperature, and flame velocity were calculated with respect to various parameters, all within the mixture approximation using ADIFOR 2.0, a software package that supports exact differentiation. Parameters considered were the binary diffusion coefficients, pure species thermal conductivity coefficients, and thermal diffusion ratios. The more fundamental molecular parameters: collision diameters, well depths, dipole moments, polarizabilities, and the rotational relaxation collision numbers were also considered.

Influential transport properties are found to be as important in flame modeling as influential reaction rates, and both should be taken into account when building chemical mechanisms. Transport parameter importance was found to vary according to the independent variable being considered and the flame type. Magnitudes of sensitivities appear to be more influenced by the underlying molecular parameters than the approach used to compute the transport properties. The number of significant sensitivities to transport parameters increases for the progression: flame temperature, flame velocity, reactant species, product species, and intermediate radical species. Many dependent variables have significant sensitivities to the pure species thermal conductivities of N₂, O₂, and the fuel. At the molecular level, large sensitivities to the collision diameters of several species are also observed, but significant sensitivity to well depths, although observed is less and more rare. Large sensitivities are not observed to the rotational relaxation collision number, the dipole moment, or to the molecular polarizability. Second-order sensitivities are significant for a number of dependent variables. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 538–553, 2005