【作者】 田国弘；

【导师】 王建昕；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2007， 博士

【摘要】 汽油均质充量压缩着火(HCCI)燃烧能显著改善发动机燃油经济性、大幅度降低NOx排放,但存在着燃烧控制困难,负荷范围有限以及瞬态工况不易控制等问题。利用汽油多段缸内喷射实现HCCI燃烧,并将发动机整个工况平面划分为几个分别以HCCI燃烧模式和火花点火(SI)燃烧模式工作的工况区以各取所长,现已成为被普遍看好的技术发展方向。本文围绕这种双模式发动机的瞬态工况控制策略进行研究,包括HCCI模式区内的工况变换控制问题和HCCI/SI模式间转换的控制问题。为了实现HCCI模式和SI模式的迅速平稳转换,采取了同步改变配气相位和多段喷油策略的技术路线,设计了一种能够切换配气相位的电-液式错位双凸轮机构,以及相应的汽油喷射与凸轮切换的电控系统,建成了一台双模式原理性试验样机。在该原理性试验样机上,对发动机排放特性和示功图进行了实时多循环测试,分析了影响HCCI瞬态过程的各种因素,提出了相应的优化控制策略,以及SI/HCCI模式转换的协同控制准则。试验结果表明,基于GDI的HCCI模式对负荷变化响应快速,且可通过调整喷油策略优化;HCCI对转速变化不敏感,燃烧稳定性好;模式转换时,由HCCI向SI转换较容易,由SI向HCCI转换难度较大;通过动态调整转换过程中的喷油开始时刻、火花点火时刻、节气门开度等参数,可以优化转换过程。经优化后的完整转换过程能在10个循环内平滑可靠地完成,没有异常燃烧现象发生,此结果表明本文提出的模式转换和瞬态过程的控制思路是可行的。为深入分析瞬态工况的规律并优化其控制策略,在Chemkin源代码程序基础上开发了能反映分层均质混合气特征的双区详细化学反应动力学发动机缸内燃烧模型,并将该双区模型和整机循环模拟软件BOOST耦合,构建了HCCI发动机工作过程循环模型。利用该模型对燃烧模式转换过程进行了模拟解析,研究了喷油时刻、喷油比例等控制参数对转换过程的影响,为HCCI发动机瞬态工况试验研究提供了指导和理论支持。更多还原

【Abstract】 Homogeneous Charge Compression Ignition (HCCI) combustion has advantages of low fuel consumption and ultra low NOx emission. However, the challenges from the autoignition control difficulty and narrow operation region limit the practical application of this technology. A hybrid combustion mode which combines SI mode and HCCI mode in separated working regions was regarded as a promising technology for HCCI engines. The purpose of this dissertation is to study the control strategies of transient process, including engine performance behavior process within HCCI region and mode switch process between HCCI and SI.A technical solution of changing the cam profile and injection strategy simultaneously was adopted to realize the rapid and smooth switch between SI mode and HCCI mode. An electrohydraulic two-stage cam profile mechanism was designed and produced, including the fuel injection and cam profile electronic control system. An SI/HCCI hybrid engine prototype was established.On the prototype test bench, the factors which influence the HCCI transient process were analyzed based on the test results of engine emission and pressure traces. The optimized strategies and its general criteria of mode switch control were proposed. The test results show that the load change in HCCI mode is rapidly responded, and can be optimized by adjusting injection strategy; the HCCI combustion is insensitive to the engine speed change, and the combustion phase can be adjusted rapidly and smoothly by changing the injection ratio; the mode switch from HCCI to SI was easy, while the switch from SI to HCCI was difficult with combustion fluctuation; by adjusting the key factors within the switch process, such as injection mass, injection timing, spark timing, throttle opening, and so on, the switch process was optimized; the switch process was completed in 10 engine cycles, rapidly, reliably and smoothly, without any abnormal combustion such as knocking and misfiring.A dual-zone detailed chemical kinetics engine model which features stratified homogeneous mixture was developed based on the Chemkin source code. An engine cycle simulation model was established by coupling the dual-zone model and software BOOST. The engine mode was utilized to simulate the switch process. Controlling parameters such as injection ratio and injection timing was evaluated. The results provide a good explanation for the experiments.更多还原