Study of soot production for double injections of n-dodecane in CI engine-like conditions
Study of soot production for double injections of n-dodecane in CI engine-like conditions
复制标题
DOI：
10.1016/j.combustflame.2016.08.005
复制
发表时间：
2016-11
影响因子：
4.4
通讯作者：
A. Moiz;M. Ameen;Seong-Young Lee;S. Som
中科院分区：
文献类型：
--
作者：
A. Moiz;M. Ameen;Seong-Young Lee;S. Som
多次喷射过程中碳烟的生成机理复杂，它依赖于各喷射流之间的湍流相互作用和燃烧过程。在定容燃烧室中，以正十二烷为燃料，采用0.3 ms预喷、0.5 ms驻留时间和1.2 ms主喷（命名为0.3/0.5/1.2 ms）的双喷射方案，模拟压燃式发动机的热力学工况，进行了简明的研究。在15%的环境氧水平下进行了900 K和800 K的实验环境温度变化。采用甲醛平面激光诱导荧光（PLIF）和纹影成像技术对甲醛的点火和火焰特性进行了实验分析。这些研究揭示了几乎相似的热释放率的双喷射在900 K和800 K的环境气体温度由于燃烧的较长的主喷射，这是增强了由先导燃烧事件。观察到800 K环境条件下的碳烟生成量低于900 K情况，这被认为是由于其更高的提离长度，这将允许燃料-空气混合物的稀薄燃烧。使用大涡模拟（LES）的方法进行了数值模拟，通过广泛验证900 K的双喷射条件相对于非反应蒸汽渗透曲线的两个注射，反应射流热释放速率和空间以及时间（定性）烟尘生产。作为LES工作的一部分，进行0.65 ms（0.3/0.65/1.2 ms）的停留时间变化，以揭示烟尘产生对停留时间变化的敏感性。据观察，数值略高的准稳态提离长度的0.3/0.65/1.2毫秒的注射导致周围的氧气进入火焰区域的夹带增加。与0.3/0.5/1.2ms喷射相比，这导致稍微稀薄的燃料-空气混合物的燃烧，因此相对较少的碳烟。
Soot production mechanism in multiple injections is complex since it involves its dependence on turbulent interactions of constituting injections and their combustion progress. A concise study was performed in a constant-volume combustion vessel by considering a double injection scheme of 0.3 ms pilot injection, 0.5 ms dwell time and 1.2 ms main injection (nomenclature: 0.3/0.5/1.2 ms) with n-dodecane as fuel and replicating the thermodynamic operating condition of a compression ignition (CI) engine. Experimental ambient temperature variations of 900 K and 800 K were performed at 15% ambient oxygen level. Simultaneous planar laser-induced fluorescence (PLIF) of formaldehyde and schlieren imaging techniques were employed to analyze the ignition and flame characteristics experimentally. These studies revealed almost similar heat release rates for a double injection at 900 K and 800 K ambient gas temperatures due to combustion of a longer main injection which is enhanced by pilot combustion event. A lower soot production for 800 K ambient condition over 900 K case was observed, which was concluded to be due to its higher lift-off length which would allow for a leaner combustion of fuel-air mixtures. Numerical simulations were performed using a Large Eddy Simulation (LES) approach by extensively validating the 900 K double injection condition with respect to non-reacting vapor penetration profiles of both injections, reacting jet heat release rate and spatial as well as temporal (qualitative) soot production. As part of LES work, a dwell time variation of 0.65 ms (0.3/0.65/1.2 ms) was performed to reveal the sensitivity of soot production to variations in dwell time. It was observed numerically that marginally higher quasi-steady lift-off length of the 0.3/0.65/1.2 ms injection causes increased entrainment of surrounding oxygen into the flame region. This leads to combustion of slightly leaner fuel-air mixture and hence relatively less soot when compared to a 0.3/0.5/1.2 ms injection.