Evaluation of Chemical Kinetics Models for Heptane Combustion

Abstract

Computational fluid dynamic (CFD) -based predictions are presented for nonpremixed and premixed flames burning vaporized heptane fuel. Three chemical kinetics models are incorporated into a time-dependent, two-dimensional, detailed-chemistry, CFD model known as UNICORN. The first mechanism is the San Diego (SD) mechanism (52 species and 544 reactions), the second one is the Lawrence Livermore National Laboratory (LLNL) mechanism (160 species and 1540 reactions), and the third one is the National Institute of Standards and Technology (NIST) mechanism (197 species and 2926 reactions). Numerical models are validated through simulating an opposing-jet nonpremixed flame that was previously studied experimentally. Models are also tested for their accuracies in predicting strain-induced extinction and autoignition. Compared to traditional one-dimensional models for opposing-jet flames, two-dimensional simulations are found to give results closer to the experimental values. All three mechanisms are reasonably close to each other in predicting co-axial jet nonpremixed and premixed flames. SD mechanism is found to be slightly stiffer than the other two mechanisms, especially in solving for premixed combustion. While LLNL kinetics resulted in a steady Bunsen-type premixed flame, SD and NIST mechanisms yielded cellular-type flame structures for the same flow conditions.