不均一濃度場における圧縮自着火燃焼過程の数値解析

概要

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In recent years, the premixed charge compression ignition engine is attracting a great interest because it is high efficiency and capable of reducing both nitrogen oxide and particulate matter emissions significantly. However, some problems remain not resolved, such as the difficulty of controlling ignition timing and combustion rate in high load. In order to solve this problem, it is investigated using EGR system and heterogeneous mixture. In this study, the auto ignition and combustion process of heterogeneous isooctane-air mixture in a PCCI engine has been simulated by a multi-dimensional CFD computation. The chemical reaction is described by using a 5-step global reaction model for hydrocarbon fuels. The initial conditions of heterogeneity of a fuel-air mixture was given at the intake valve closing time, which generated a statistically reasonable turbulent fluctuations in both velocity and fuel mass fraction fields. The results show that the heat release rate for the heterogeneous case is more moderate than that for the homogeneous case. In addition, it is found that the distribution of fuel mass fraction is important factor for characterize a combustion processes.