조건평균닫힘법과 상세화학반응에 기초한 현상학적인 디젤 엔진 연소 및 배기특성 예측

Abstract

A zero-dimensional code is developed to simulate turbulent spray combustion and emissions including NOx, HC, CO and soot in direct injection diesel engines. The code consists of two major parts

mixing calculation for the probability density function (PDF) based on the multi-zone model by Hiroyasu et al. (1983) [1] and the flame structure by the conditional moment closure (CMC) model (Klimenko & Bilger, 1999) [2]. The skeletal mechanism of n-heptane combined with NOx chemistry in GRI 3.0 is employed for heat release and the NOx prediction. The spray model accounts for the fuel evaporation and mixing based on momentum balance of the spray zones, while the CMC model incorporates the conditional flame structures with one fuel group or flame structure for each injection. The spatially integrated density-weighted PDF is defined to represent inhomogeneous mixture distribution in the cylinder. The one-equation soot model[1] is employed for prediction of the soot emission. The program has been validated over a wide range of load and rpm with different injection strategies and EGR rates. Results show good agreement with measurements for the pressure trace and the NOx emission, while predicted HC, CO and soot emissions show reasonably acceptable qualitative trends.