进气门晚关米勒循环对高强化柴油机燃烧和换气影响的研究

为了探索米勒循环技术对于燃烧和换气过程的影响，在1台高强化单缸柴油机上应用进气门晚关米勒循环进行了试验和仿真研究。进气门关闭时刻分别为上止点后-110°CA（原机）、-86°CA和-70°CA. 发动机试验在转速3 600 r/min、指示升功率77 kW/L、过量空气系数1.6的高强化运行工况下展开。通过对试验平台建立一维热力学计算模型进一步分析了米勒进气相位对换气过程参数的影响。研究结果表明：随着进气门关闭时刻的推迟，由于有效压缩比的降低，缸内压缩终了工质温度和压力均显著下降，在相同功率条件下最大燃烧压力和温度、最大压力升高率、排气温度均显著下降，有助于降低高强化柴油机缸内的热力负荷；随着进气门关闭时刻的推迟，压缩过程中的米勒损失和进气回流率增加，充量系数、泵气损失均下降；进气门晚关的米勒循环还明显降低了NO_x排放，改善了燃油消耗率。

Effect of LIVC Miller Cycle on Combustion and Gas Exchange on a Highly Intensified Single-cylinder Diesel Engine

The effect of Miller cycle with late intake valve closing (LIVC) timings on the combustion and gas exchange of a highly intensified single-cylinder diesel engine is studied through experiment and simulation. Three LIVC timings, i.e., -110°CA(original engine), -86°CA and -70°CA after top dead center, are used in the research. The engine test is conducted under the operating conditions: a speed of 3 600 r/min, an indicated power density of 77 kW and an excess air ratio of 1.6. An 1-D thermodynamic simulation model is established for the engine test setup in order to further analyze the influence of LIVC Miller cycle on the gas exchange process. The results show that, as the intake valve closure (IVC) timing retards, the in-cylinder charge pressure and temperature are reduced obviously due to the reduction in the effective compression ratio. This results in a noticeable decrease in the maximum combustion pressure and temperature, the maximum pressure rise rate and the exhaust temperature. This means that LIVC Miller cycle helps to constrain the increasing mechanical and thermal loads in the highly intensified diesel engine. In addition, as the IVC timing retards, the Miller loss and backflow rate during the compression stroke increase, while the charging coefficient and pumping loss decrease. The LIVC Miller cycle is also benefit to improve fuel consumption and reduce NO_x emissions.