Skeletal Mechanism Generation for Surrogate Fuels using Directed Relation Graph with Error Propagation and Sensitivity Analysis

Authors:   K. E. Niemeyer, C. J. Sung, and M. P. Raju

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A novel implementation for the skeletal reduction of large detailed reaction mechanisms using the directedrelationgraph with errorpropagation and sensitivityanalysis (DRGEPSA) is developed and presented with examples for three hydrocarbon components, n-heptane, iso-octane, and n-decane, relevant to surrogatefuel development. DRGEPSA integrates two previously developed methods, directedrelationgraph-aided sensitivityanalysis (DRGASA) and directedrelationgraph with errorpropagation (DRGEP), by first applying DRGEP to efficiently remove many unimportant species prior to sensitivityanalysis to further remove unimportant species, producing an optimally small skeletalmechanism for a given error limit. It is illustrated that the combination of the DRGEP and DRGASA methods allows the DRGEPSA approach to overcome the weaknesses of each, specifically that DRGEP cannot identify all unimportant species and that DRGASA shields unimportant species from removal. Skeletalmechanisms for n-heptane and iso-octane generated using the DRGEP, DRGASA, and DRGEPSA methods are presented and compared to illustrate the improvement of DRGEPSA. From a detailed reaction mechanism for n-alkanes covering n-octane to n-hexadecane with 2115 species and 8157 reactions, two skeletalmechanisms for n-decane generated using DRGEPSA, one covering a comprehensive range of temperature, pressure, and equivalence ratio conditions for autoignition and the other limited to high temperatures, are presented and validated. The comprehensive skeletalmechanism consists of 202 species and 846 reactions and the high-temperature skeletalmechanism consists of 51 species and 256 reactions. Both mechanisms are further demonstrated to well reproduce the results of the detailed mechanism in perfectly-stirred reactor and laminar flame simulations over a wide range of conditions. The comprehensive and high-temperature n-decane skeletalmechanisms are included as supplementary material with this article.

Citation:   K. E. Niemeyer, C. J. Sung, and M. P. Raju, “Skeletal Mechanism Generation for Surrogate Fuels using Directed Relation Graph with Error Propagation and Sensitivity Analysis,” Combustion and Flame 157 (9), 1760-1770 (2010).