摘要
均质充量压燃(HCCI)是发动机燃烧技术的一个重大进步,在内燃机节能和减排方面有很大潜力。随着发动机排放法规的日益严格和对发动机经济性的要求越来越高,HCCI燃烧技术逐渐引起了内燃机界的高度关注,有关HCCI燃烧的研究逐渐由理论向数值模拟及实验扩展和延伸。在HCCI燃烧过程中,化学动力学对自燃着火起控制作用,人们对化学动力学机理的研究也愈加详细与深入,对燃烧过程的预测则更为准确。
本文采用主要参比燃料正庚烷与异辛烷氧化的化学动力学反应机理,利用CHEMKIN化学动力学软件包进行敏感性分析,优化反应速率常数,并与详细反应机理进行对比;然后将此化学动力学模型嵌入三维流体力学程序中,取代传统内燃机三维数值模拟中的简化燃烧模型,建立HCCI发动机的三维CFD耦合详细化学动力学模型,模拟汽油均质压燃的燃烧过程,并将数值模拟结果与实验结果进行对比。结果表明,在运行工况相同的情况下,模拟得出的缸内温度和燃烧相位的关系与实验结果比较吻合,证明三维CFD耦合详细化学反应动力学模型能够用于HCCI发动机燃烧过程的模拟计算。
在这个基础上利用此模型分别研究了进气温度、进气压力、壁温、转速、压缩比、EGR率以及当量比的变化对缸内温度、缸内压力的影响,并利用三维模拟结果对缸内三维流场、温度分布及浓度分布进行了详细分析。
通过对汽油替代燃料的HCCI燃烧过程的三维CFD耦合详细化学动力学的数值模拟研究,了解了不同参数变化对燃烧特性的影响,为HCCI发动机燃烧过程的优化提供了依据,具有一定的理论意义和实用价值。
Homogeneous Charge Compression Ignition (HCCI) is an important improvement for the combustion technique, and it has great potential in energy saving and emission reducing of the internal combustion engine. In recent years, the study related to the HCCI combustion has expanded from theory to numerical simulation and experimental research. As is known to us, the self-ignition is dominated by the chemical kinetics, so the study of the chemical kinetics mechanism becomes more detailed.
A reduced chemical kinetic mechanism for the oxidation of primary reference fuel (PRF) was used to model internal combustion engines. Firstly, sensitivity analysis was made to optimize reaction rate constants of selected reactions; then the chemical kinetic mechanism was implemented into the three-dimensional CFD code to study the combustion process in HCCI engines, and compared to the experiment. The simulation results showed a good agreement with the experiments.
Based on that, the HCCI combustion characteristics were studied under different inlet temperature, wall temperatures, inlet pressure, engine speeds, compression ratios, equivalence ratios as well as EGRs. 3D simulation results were also used to analyze the flow field, temperature and species concentration distribution.
The results provide a detailed insight into the processes governing combustion, and are of profound theoretical significance and utility value.
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