采用外开环喷油器的直喷汽油机燃油湿壁问题

Wall-Wetting in a GDI Engine with Outward-Opening Injector

采用激光诊断技术对外开环喷油器进行详细的喷雾测试,然后对AVL-Fire三维软件中的喷雾模型进行精确标定,最后用标定好的模型来对直喷发动机在不同喷油策略(变喷油器喷孔锥角、变喷油时刻及两段喷射)下缸内燃油湿壁进行了计算.研究表明,在一定范围内改变喷油器喷孔锥角对碰壁量无明显影响.然而不同的喷油时刻可以明显影响累积燃油湿壁量,当喷油时刻由460,°CA推迟到520,°CA时累积燃油碰壁量减小,压缩上止点时残留油膜质量增加.而采用两段喷射后可以对累积燃油碰壁及油膜生成起到显著的改善作用,与单段喷射相比,优化后的两段喷射累积燃油碰壁量、最大油膜量以及上止点时残留油膜量分别降低38%、49%和68%.

The spray characteristics of an outward-opening injector were studied using the advanced laser diagnostics. Based on the measurement results, spray models were calibrated in the AVL-Fire software. Then, the spray models was applied to a DI gasoline engine with a specific inlet and outlet ports to exam- ine the effects of cone-angle of the nozzle pintle, injection timing, injection mass ratio and dwell for the split injection strategy. Results show that different cone-angles of the nozzle pintle have little influence on the quantity of fuel impinged on the wall. However, the injection timing has a significant effect on the impinged fuel quantity, i. e., when retarding the injection timing from 460 ℃A to 520 ℃A, the fuel quantity impinged decreases while the fuel quantity of the wall-film at the end of compression stroke in- creases. An obvious improvement of fuel impingement and fuel film on the wall was observed when adopt- ing the split injection strategy. Compared to the single injection with the identical injection timing for the first injection pulse, the optimized split injection strategy decreases the fuel quantity impinged, the maximum fuel quantity residual on the wall and the mass of fuel quantity residual on the wall at the end of compression by 38%, 49% and 68% respectively.