Combustion simulations with accurate transport properties for reactive intermediates

Abstract

The effect of employing accurate transport properties in simulations of freely propagating H 2 /O 2 /He and CH 4 /O 2 flames is investigated. Transport properties for the collision pairs H 2-H 2 , H-H 2 , and H-H are computed from published tables of collision integrals. Previous calculations in our group of transport properties for H-H 2 O and H-O 2 have been extended to higher temperatures. In addition, new calculations on H-He, O-He, H 2-He, and H 2 O-He are reported. Flame simulations with two sets of transport data were compared. The first set contained transport properties obtained with the conventional method of employing parameterized Lennard-Jones (12-6) potentials, while in the second set transport properties for the above collision pairs were substituted. A modest increase in laminar flame speeds, comparable to differences found when employing different chemistry models, was found for both flames.

“Third‐body” collision parameters for hydrocarbons, alcohols, and hydroperoxides and an effective internal rotor approach for estimating them

“…Finally, we note that when more accurate values of σ and ε are deemed necessary, one can compute them directly fairly readily using the “one‐dimensional minimizations” approach 67 so long as not too many are needed. Higher‐accuracy calculations of transport properties are also possible, although these typically require somewhat more computational effort 16,21 …”

“…Higher-accuracy calculations of transport properties are also possible, although these typically require somewhat more computational effort. 16,21 The direct computation of requires a nontrivial amount of effort, and a major result from the present work is the strategy for using N eff to avoid this effort. As a demonstration, we consider 2,2,3-trimethylbutane (TMB) + Ar at 1000 K, which was not included in any of the series in Table 1.…”

“…In addition to errors associated with the use of simple combining rules, the 12/6 Lennard‐Jones model ignores anisotropy in the intermolecular PES, the internal coordinates of the colliders, and the softness of the repulsive wall. While these errors can be important, 21 particularly the error associated with the treatment of the repulsive wall, 16,36 incorporating more detailed transport models into existing kinetics codes and databases remains rare. We therefore limit attention to the prediction of the collision parameters ε and σ , despite the simplifications they represent.…”

“…[1][2][3][4][5][6][7][8][9] The role of a priori theory as an independent source of information for populating these databases and for improving the models they reflect continues to increase. [10][11][12][13] Here, we consider a priori theoretical approaches for computing collision rate constants and efficiencies relevant to the prediction of transport properties [14][15][16] and pressure dependence in elementary kinetics. [17][18][19][20] These phenomena are controlled by so-called "third-body" bath gas collisions, and we recently used trajectory-based collision parameters to compute diffusion coefficients 21 and pressure-dependent kinetics 22 with accuracies comparable to those from experiment.…”

“…Here, we consider a priori theoretical approaches for computing collision rate constants and efficiencies relevant to the prediction of transport properties 14–16 and pressure dependence in elementary kinetics 17–20 . These phenomena are controlled by so‐called “third‐body” bath gas collisions, and we recently used trajectory‐based collision parameters to compute diffusion coefficients 21 and pressure‐dependent kinetics 22 with accuracies comparable to those from experiment.…”