디젤 엔진내 분무 과정 시뮬레이션의 격자 의존성 저감을 위한 개선된 운동량 교환 (EMC) 모델에 관한 연구

Abstract

This study aims to suggest the best solution for achieving the computational efficiency in the diesel engine simulation. In this regard, this study primarily deals with the high pressure injected spray simulation in terms of liquid phase penetrating length and atomization and evaporation characteristics. First of all, in order to provide the spray models which is well matched with the practical spray systems, the fundamental studies on the experiments in relation to the droplet behavior were performed, for example, droplet breakup and collision. The experimental data proved the actual droplet breakup and collision regimes as a function of Weber number. Then, the newly suggested spray models’ computational results were compared to the experimental result and evaluated. The suggested breakup and collision models in this study are regarded as the best choice for numerical simulation of actual spray systems. On the other hand, the standard Euler-Lagrange multiphase flow modeling for spray system model has inherent grid dependent problem, for example, the calculated results of spray tip penetration and mixture formation are much sensitive to the grid resolution. The primary reason of that originates from the inaccurate transfer rate of momentum from the droplet. In order to solve these problems, this study deals with the grid independent spray models such as Gas-jet model and Enhanced Momentum Coupling (EMC) model, and evaluate them by comparing the results form the different grid resolutions. The new grid independent model, EMC model was considered a best choice for the spray simulation because the grid dependency of calculated liquid phase and vapor phase distributions was almost eliminated. However there still remain some problems when the new spray models are adopted for the diesel engine simulation when it comes to the combustion performance such as pressure and temperature. The problem is considered to be induced by the inappropriate solution in the Eulerian CFD solution when using the coarse mesh system.