共轨柴油机高海拔碳烟形成历程的数值模拟

Numerical Simulation of Soot Formation Histories for Common Rail Diesel Engine at High Altitude

采用AVLFIRE数值分析软件对共轨柴油机高海拔（低气压）燃烧过程的燃油浓度场、温度场分布及碳烟形成历程进行了模拟计算，研究了不同海拔大气压力对共轨柴油机低速全负荷工况燃烧过程及碳烟排放的影响．结果表明，在不同海拔（0m、3000m、4000m和5000m）条件下，计算燃烧压力和放热率与试验值具有较好的一致性，验证了所建数值分析模型的有效性．随着海拔的升高，燃烧后期浓混合气分布区域、燃烧高温区域以及碳烟形成区域明显增大．在燃烧初期，碳烟质量分数逐渐增大，在15～17°CAATDC出现峰值，且碳烟峰值随海拔的升高而增大，海拔5000m碳烟质量分数峰值是海拔0m的1．87倍；燃烧后期，随海拔的升高，碳烟氧化速率降低，排放增加．

Numerical simulation of the fuel concentration field, temperature field distribution and soot formation histories in a common rail diesel engine at high altitude （low air pressure） was carried out by means of AVL FIRE nu- merical analysis. The influences of air pressure at different altitude on combustion process and soot emissions at low speed full-load in a common rail diesel engine were investigated. The in-cylinder pressure and heat release rate from simulation are consistent with the experimental data at different altitude （0 m, 3 000 m, 4 000 m, 5 000 m）. There- fore, the effectiveness of the numerical model is verified. The results indicated that rich fuel mixture area, high com- bustion temperature area and soot formation area were enlarged obviously during the late combustion period with the altitude increasing. The mass fraction of soot increased gradually during the early combustion period and the peak value appeared at 15 -17°CA ATDC. The soot mass fraction peak value increased with the altitude increasing, and the peak value at 5 000 m was 1.87 times that at 0 m altitude. During the late combustion period, the oxidation rate of soot was reduced with the altitude increasing, which resulted in the increase of soot emission.