Transport properties for combustion modeling

This review examines current approximations and approaches that underlie the evaluation of transport properties for combustion modeling applications. Discussed in the review are: the intermolecular potential and its descriptive molecular parameters; various approaches to evaluating collision integrals; supporting data required for the evaluation of transport properties; commonly used computer programs for predicting transport properties; the quality of experimental measurements and their importance for validating or rejecting approximations to property estimation; the interpretation of corresponding states; combination rules that yield pair molecular potential parameters for unlike species from like species parameters; and mixture approximations. The insensitivity of transport properties to the intermolecular forces is noted, especially the non-uniqueness of the supporting potential parameters. Viscosity experiments of pure substances and binary mixtures measured post 1970 are used to evaluate a number of approximations; the intermediate temperature range 1 < T∗ < 10, where T∗ is kT/ε, is emphasized since this is where rich data sets are available. When suitable potential parameters are used, errors in transport property predictions for pure non-polar substances and their binary mixtures are less than 5% when they are calculated using the approaches of Kee et al.; Mason, Kestin, and Uribe; Paul and Warnatz; or Ern and Giovangigli. Recommendations stemming from the review include (1) revisiting the supporting data required by the various computational approaches, and updating the data sets with accurate potential parameters, dipole moments, and polarizabilities; (2) characterizing the range of parameter space over which the fit to experimental data is good, rather than the current practice of reporting only the parameter set that best fits the data; (3) looking for improved combining rules, since existing rules were found to under-predict the viscosity of mixtures in most cases; (4) performing more transport property measurements for mixtures that include radical species, an important but neglected area; (5) using the TRANLIB approach for treating polar molecules; (6) continuing to evaluate whether a different parameterization is required for the intermolecular potential for T∗ > 10; (7) performing more accurate measurements of the molecular parameters used to evaluate the molecular heat capacity and the rotational relaxation collision number, since they affect thermal conductivity; and (8) using the EGLIB approach and computer program with improved supporting data to evaluate transport properties. EGLIB uses the TRANLIB methodology for collision integral evaluation.