An experimental investigation of in-cylinder processes under dual-injection conditions in a DI diesel engine
An experimental investigation of in-cylinder processes under dual-injection conditions in a DI diesel engine
复制标题
DOI：
10.4271/2004-01-1843
复制
发表时间：
2004-06
期刊：
影响因子：
--
通讯作者：
C. Mueller;Glen C. Martin;T. E. Briggs;K. Duffy
中科院分区：
文献类型：
--
作者：
C. Mueller;Glen C. Martin;T. E. Briggs;K. Duffy
每循环使用两个喷射事件的燃料喷射方案（双喷射方法）具有同时减少发动机排出的碳烟和NOx排放的潜力。这些益处在多大程度上是由于增强的混合、低温燃烧模式、改变的燃烧相位或其他因素而产生的，这一点尚未完全了解。一个传统的单次注射，早期注射，只有两个双注射的情况下进行了研究，使用一套成像诊断，包括喷雾可视化，自然光度成像，平面激光诱导荧光（PLIF）成像的一氧化氮（NO）。这些数据，再加上热释放和效率分析，用于提高缸内过程，导致观察到的排放量减少的理解。结果表明，早期喷射燃料的燃烧发生在两个阶段：冷火焰阶段，其特征在于非常弱的化学发光，其次是预混合燃烧阶段，其特征在于由明亮的烟灰白炽的局部区域。早期喷射的燃料的燃烧仅释放其化学能的一小部分。喷雾可视化图像显示，这种低燃烧效率可能至少部分是由于液体燃料渗透到缸内表面并润湿缸内表面，但仅早期喷射情况下的NO PLIF图像也显示来自未燃烧的燃料蒸气和/或冷凝的燃料液滴的强烈干扰，这表明不完全的大体积气体燃烧和裂缝中的淬火也可能起作用。传统的单次注入情况产生最高的NO PLIF信号电平。两种双注入情况都降低了NO PLIF信号电平，其中延迟主注入情况的降低最为显著。
Fuel-injection schedules that use two injection events per cycle (dual-injection approaches) have the potential to simultaneously attenuate engine-out soot and NO x emissions. The extent to which these benefits are due to enhanced mixing, low-temperature combustion modes, altered combustion phasing, or other factors is not fully understood. A traditional single-injection, an early-injection-only, and two dual-injection cases are studied using a suite of imaging diagnostics including spray visualization, natural luminosity imaging, and planar laser-induced fluorescence (PLIF) imaging of nitric oxide (NO). These data, coupled with heat-release and efficiency analyses, are used to enhance understanding of the in-cylinder processes that lead to the observed emissions reductions. Results show that combustion of the early-injected fuel occurs in two phases: a cool-flame phase characterized by very weak chemiluminescence, followed by a premixed-burn phase characterized by localized regions of bright soot incandescence. Combustion of the early-injected fuel liberates only a fraction of its chemical energy. Spray visualization images show that this low combustion efficiency could be due at least in part to liquid fuel penetrating to and wetting in-cylinder surfaces, but NO PLIF images of the early-injection-only case also show strong interferences from unburned fuel vapor and/or condensed fuel droplets, suggesting that incomplete bulk-gas combustion and quenching in crevices also may play roles. The traditional single-injection case produced the highest NO PLIF signal levels. Both dual-injection cases reduced NO PLIF signal levels, with the reduction being most dramatic for the retarded-main-injection case.