【作者】 沈义涛；

【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， 2009， 博士

【摘要】 汽油品质对发动机性能尤其是排放性能有重要影响,燃用清洁汽油可有效控制汽油机的排放。许多国家已根据本国汽车行业和石化行业的特点进行了相关研究,并制定了严格的清洁汽油标准。我国炼油工艺与国外存在较大差异,同时缺乏汽油品质与排放相关性的研究工作积累。因此有必要开展相关研究,为制定符合我国国情的汽油标准提供依据。本文首先对国际上典型“汽车—燃油”(Auto-Oil)项目及汽油品质相关研究进展进行了系统地综述分析,总结了其主要研究结果、研究方法以及不足之处,在此基础上确定了本研究的主要技术路线。试验研究中,在不同排放水平的汽油发动机上,通过发动机台架性能试验、催化器快速硫老化试验和冷起动模拟试验研究了汽油的辛烷值、挥发性、烯烃、芳烃和硫含量对动力性、燃油经济性和排放特性的影响规律;并通过燃烧分析对试验现象进行了深入解析。结合本研究结果和相关研究进展阐述了汽油品质与排放的相关性,提出了适合我国国情的清洁汽油相关建议。试验结果表明,汽油辛烷值过高,会使燃烧持续期加长,导致燃油经济性和排放特性恶化;烯烃易于燃烧,可缩短着火落后期和燃烧持续期,显著降低THC排放,烯烃含量每增加1%v,THC排放降低1%;芳烃含量在35～45%v范围内变化对燃烧和排放的影响不明显;硫对三效催化剂(TWC)的初始活性没有影响,但对其耐久性有严重影响,硫含量增加,TWC老化后的起燃温度显著升高,同时TWC硫中毒具有一定可逆性,高温下催化剂活性可得到部分恢复;汽油挥发性提高,对改善冷起动燃烧和THC排放有利,对CO排放的影响则与具体发动机相关。针对汽油多组分燃料的特点,通过燃油热重分析试验合理确定了三组分汽油模型中的替代组分和比例,据此开发了三组分油滴蒸发模型和油膜蒸发模型,该模型较好地体现了汽油不同组分蒸发特性的差异。基于所开发的三组分汽油蒸发模型,模拟分析了汽油喷雾蒸发的规律,并应用所建立的发动机CFD数值模型研究了汽油挥发性对冷起动首循环中混合气形成和燃烧过程的影响,为理解汽油品质对燃烧和排放的影响提供了理论依据。更多还原

【Abstract】 Gasoline quality has an important role in the engine performance, especially the emissions characteristics. Exhaust emissions can be effectively controlled with clean gasoline. Many countries have performed research on gasoline quality based on the characteristics of their own automobile and oil industries, and enacted stringent gasoline specifications. The oil refinery is quite different from foreign countries and it is lack of the research on the relationships between gasoline qualities and emissions in China. Therefore, it is necessary to conduct relevant research and supply data and suggestions to Chinese or Beijing government for the stipulation of gasoline requirements.The typical international“Auto-Oil”programs and progress of relevant research on gasoline quality were investigated and analyzed, and the conclusions, research methods and the weakness in this research field were summarized. Based on the analysis, the main research contents and reasonable methods were proposed.The effects of octane number, olefins content, aromatics content, sulfur content and volatility on power output, fuel consumption and engine-out emissions were studied on two gasoline engines with different emissions level. Engine performance tests, rapid catalyst sulfur aging tests and simulated cold-start tests were conducted. Combustion characteristics were analyzed and were used to investigate the phenomenon and trends in the tests. The proposal of clean gasoline specifications to meet the 4th stage emissions standard in China was brought forward through detailed discussions on the results in this study and relevant results in previous research. Test results showed that too high octane number resulted in the prolonged combustion duration, high fuel consumption and emissions. Olefins resulted in the short combustion duration and low THC emissions. 1%v increment in olefins content resulted in 1% less THC emissions. Aromatics content had no significant effect on emissions and combustion process as it increased from 35%v to 45%v. Sulfur had little influence on catalyst initial activity. It had a great effect on catalyst aging performance. The aging light off temperature lifted significantly as sulfur content increased. Sulfur poisoning was somewhat reversible and the catalyst activity could be partially recovered through high temperature running. High volatility could improve the combustion process and reduce THC emissions during cold start. The effect of volatility on CO emissions was related to engines.Considering the multi-component characteristics of gasoline, three representative species and their fractions in the substituted gasoline model was determined by thermogravimetry analysis tests. The multi-component vaporization models for droplet and fuel film were developed, which can capture the differences of the vaporization between different gasoline components. Based on the developed vaporization models, the spray evaporation process of gasoline and the influence of gasoline volatility on mixture formation and combustion of an engine during cold start were numerically studied, which provided a theoretical explanation for understanding the effect of the gasoline quality on combustion and emissions.更多还原