物理化学学报 >> 2016, Vol. 32 >> Issue (8): 1941-1949.doi: 10.3866/PKU.WHXB201604223

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三维直接数值模拟部分预混发动机内的燃烧过程

张帆,尧命发*()   

  • 收稿日期:2016-01-14 发布日期:2016-07-29
  • 通讯作者: 尧命发 E-mail:y_mingfa@tju.edu.cn
  • 基金资助:
    国家自然科学基金国际（地区）合作与交流项目(51320105008);国家自然科学基金青年基金(51506146)

Three-Dimensional Direct Numerical Simulation of Partially Premixed Combustion in Engine-Related Conditions

Fan ZHANG,Ming-Fa YAO*()   

  • Received:2016-01-14 Published:2016-07-29
  • Contact: Ming-Fa YAO E-mail:y_mingfa@tju.edu.cn
  • Supported by:
    The project was supported by the Funds for International Cooperation and Exchange of National Natural Science Foundation of China(51320105008);National Natural Science Foundation of China(51506146)

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摘要：

采用三维直接数值模拟方法研究了一个类似于部分预混燃烧(PPC)发动机条件下高辛烷值燃料PRF70的着火过程。文章采用了简化的PRF化学动力学机理，包含33个组分和38步基元反应。计算中根据发动机的几何尺寸和真实运行工况加入了气缸内压缩/膨胀的效果，并考虑了燃料的两次喷射，其中第一次喷射形成了较均匀的混合气，第二次燃料喷射增加了混合物分层。研究发现，PPC的燃烧过程非常复杂，是均质压燃、预混燃烧和扩散燃烧三种主要燃烧模式的结合。在两次燃料喷射之间的区域为近化学计量比燃烧，是氮氧化物的生成区；而在化学计量比(φ)大于2的区域，混合不充分聚集了大量未燃碳氢和CO。文章使用Marching cube算法捕捉了三维火焰锋面随时间的变化。最后，使用反应锋面上高斯曲率(kg)与平均曲率(km)的联合概率密度函数(PDF)以及平均曲率随时间变化的概率密度函数，揭示了球形火焰锋面和马鞍形火焰锋面的存在，前者占主要地位，并且随着燃烧的进行，负曲率增加，主要是因为中心的燃料浓区在逐渐消耗。

关键词: 直接数值模拟, 部分预混燃烧, PRF70, 燃烧特性, PPC发动机

Abstract:

Three-dimensional direct numerical simulation is conducted to simulate the auto-ignition of the highoctane fuel PRF70 under partially premixed combustion (PPC) engine conditions. A skeletal primary reference fuel (PRF) chemical kinetic mechanism is adopted, including 33 species and 38 elementary reactions. Compression/expansion effects caused by piston motion, the real engine geometry, and the working conditions are considered. The simulation includes two injections, the first being used to form a relatively uniform base mixture and the second to forma stratified mixture and trigger the ignition. It is found that the combustion process in PPC engines is a rather complex combination of homogeneous combustion, rich premixed and diffusioncontrolled combustion. The region between the two injections is near stoichiometry, resulting in the formation of NOx, while abundant CO is retained in the region with equivalence ratio (φ) > 2, which needs to diffuse to meet the oxidizer and burn in a diffusion flame. The marching cube method is used to extract the 3D flame surface and show the temporal evolution of the reaction front. Finally, the joint PDF of the Gaussian curvature (kg) and principle mean curvature (km) and temporal evolution of the probability density function (PDF) in terms of km show that km plays a more important role and becomes negative as time evolves because of the consumption of rich premixed flame in the center.

Key words: Direct numerical simulation, Partially premixed combustion, PRF70, Combustion characteristics, PPC engine