Simulations of In-Cylinder Processes in a Diesel Engine Operated with Post-Injections Using an Extended CMC Model
Simulations of In-Cylinder Processes in a Diesel Engine Operated with Post-Injections Using an Extended CMC Model
复制标题
使用扩展 CMC 模型模拟后喷射柴油机的缸内过程
DOI：
10.4271/2014-01-2571
复制
发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Y. Wright
中科院分区：
文献类型：
--
作者：
N. Frapolli;M. Bolla;K. Boulouchos;Y. Wright
在这项研究中，缸内过程的数值模拟与燃料后喷射在柴油机运行在低温燃烧（LTC）已经完成。一个扩展的条件矩封闭（CMC）模型能够占任意数量的后续注射已被采用：而不是一个三饲料系统，问题已被描述为一个连续的两个饲料系统，使用的总混合物分数作为调节标量。一个简化的正庚烷的化学机制，加上一个两方程烟粒模型。数值计算结果已被验证与测量从光学访问重型柴油机安装在桑迪亚国家实验室通过比较表观放热率（AHRR）和缸内碳烟质量的演变为三个不同的开始主喷射，和广泛的后喷射停留时间。与实验结果吻合良好的AHRR报告，虽然缸内碳烟质量的演变得到了定性再现，计算的碳烟质量是相当低估。随后，数值研究不同的后喷射时间对碳烟形成和氧化过程的影响，特别强调后喷射增加混合的作用。模拟结果揭示了两个主要的竞争现象，其中支配缸内碳烟质量的演变期间和之后的后喷射：I）从主喷射的碳烟的加速氧化，和II）在后喷射期间形成的碳烟对缸内温度的依赖性。总体而言，研究结果表明，扩展CMC框架是一个很有前途的候选人在柴油发动机中的多次喷射模拟，允许更深入地了解相关的缸内过程。
In this study, numerical simulations of in-cylinder processes associated to fuel post-injection in a diesel engine operated at Low Temperature Combustion (LTC) have been performed. An extended Conditional Moment Closure (CMC) model capable of accounting for an arbitrary number of subsequent injections has been employed: instead of a three-feed system, the problem has been described as a sequential two-feed system, using the total mixture fraction as the conditioning scalar. A reduced n-heptane chemical mechanism coupled with a two-equation soot model is employed. Numerical results have been validated with measurements from the optically accessible heavy-duty diesel engine installed at Sandia National Laboratories by comparing apparent heat release rate (AHRR) and in-cylinder soot mass evolutions for three different start of main injection, and a wide range of post injection dwell times. Good agreement with the experimental results is reported for the AHRR, while qualitative reproduction of in-cylinder soot mass evolutions have been obtained, the computed soot mass is considerably underestimated. Subsequently, numerical investigations concerning the effects of different post injection timings on soot formation and oxidation processes are presented, with particular emphasis on the role of the increased mixing by post injections. The simulation results revealed two main competing phenomena which govern the evolution of the in-cylinder soot mass during and after post-injections: I) the accelerated oxidation of the soot from the main injection, and II) the dependency of soot formed during post-injection on the in-cylinder temperatures. Overall, the findings suggest that the extended CMC framework is a promising candidate for the simulation of multiple injections in diesel engines, allowing for deeper understandings of the associated in-cylinder processes.