The Role of Individual Rate Coefficients in the Performance of Compression Ignition Engine Models

摘要

We have continued our study of compression ignition performance using a recently developed reduced biodiesel surrogate model. Among the calculations undertaken in Ref. 1 was the study of global and local sensitivities of ignition delay times with respect to the uncertainties in the reaction rate coefficients for the biodiesel surrogate kinetic model under homogeneous conditions. In this work, we extend Ref. 1 by studying the sensitivity of ignition delay times for the biodiesel surrogate directly in the engine simulations, which are high-fidelity, three-dimensional computations. A number of reactions were theoretically characterized and analyzed in the earlier work based on their sensitivities in the homogeneous case. In the present work, it has been found that many of the reactions that showed significant sensitivities to ignition under some homogeneous conditions also appeared as sensitive reactions within the engine simulations. However, there are some reactions that have high sensitivity in the engine simulations that were low in the homogeneous ignition calculations, indicating the need for a complete global sensitivity analysis (GSA) directly in the engine simulations. Within the uncertainty calculations for the engine simulations, we also studied how features of the chemical-kinetic calculation of individual rate coefficients, for example reaction barrier heights and tunneling corrections, affected the ignition delay time in the engine simulations. The goal of the study is to eventually perform GSA of the chemical kinetics in engine simulations, and we discuss how to perform this analysis for very small sample sizes.