Computationally-Efficient Implementation of Combustion Chemistry using ISAT-RCCE-GALI

Computational calculations of combustion problems involving real fuels with chemistry represented by detailed mechanisms are prohibitive, due to the large number of species and reactions involved. We present a new combined dimension reduction and tabulation algorithm for the efficient implementation of combustion chemistry. In this algorithm, the dimension reduction is performed using the rate controlled constrained-equilibrium (RCCE) method and tabulation is performed using the in situ adaptive tabulation (ISAT) algorithm. The represented species for dimension reduction are selected using the Greedy Algorithm with Local Improvement (GALI). This combined ISATRCCE-GALI methodology is tested and compared to reduced and skeletal mechanisms using the partially-stirred reactor (PaSR) for premixed combustion of (i) methane/air (using the 31-species GRI-Mech 1.2 detailed mechanism and the 16-species ARM1 reduced mechanism) and (ii) ethylene/air (using the 111-species USC-Mech II detailed mechanism, a 38-species skeletal mechanism and a 24-species reduced mechanism). Results are presented to compare the accuracy and efficiency of representing chemistry in three different ways: (i) using ISAT with a detailed mechanism; (ii) using ISAT with a skeletal or reduced mechanism; and (iii) using the combined ISAT-RCCE-GALI approach. We show that the combined ISAT-RCCE-GALI approach incurs errors comparable to using ISAT with a skeletal or reduced mechanism with fewer represented species than present in the skeletal or reduced mechanism; and also achieves errors comparable to using ISAT with a detailed mechanism with relatively fewer represented species (14 out of 31 for methane/air and 32 out of 111 for ethylene/air). We also show that the combined ISAT-RCCE-GALI approach provides significant speedup (two-fold for methane/air and fifteen-fold for ethylene/air) compared to using ISAT alone with the detailed mechanism.