【作者】 朱磊；

【导师】 黄震；

【作者基本信息】 上海交通大学 ， 动力机械及工程， 2012， 博士

【摘要】 面对日益严重的石油安全问题和环境污染问题,生物柴油作为清洁、可再生的柴油替代燃料具有巨大的潜力。本文从燃料设计的角度改善生物柴油橡胶相容性和喷雾特性,以及发动机燃烧和排放特性,同时将燃料设计和低温燃烧模式相结合,探索用燃料设计来优化柴油低温燃烧模式从而同时降低NOx排放和碳烟排放,最后从燃料分子结构微观角度来分析了生物柴油对燃烧排放的影响。根据燃料设计概念,选用乙醇和生物柴油以不同比例互溶互混,研究了混合燃料理化特性参数,并给出了这些参数与乙醇体积分数的拟合函数关系。研究发现,混合燃料绝大多数理化特性与乙醇体积分数呈线性关系。利用不同分子结构的单一脂肪酸甲酯和乙酯与柴油掺混成体积比为4:6的混合燃料,研究混合燃料的理化特性随燃料分子结构的变化关系,并给出了这些参数与碳链长度和双键个数的拟合函数关系。考察了燃料理化性质以及不同分子结构对橡胶相容性的影响,测试了发动机上常用的丁腈橡胶不同燃料中浸泡168小时前后的质量、体积、硬度、拉伸强度、扯断伸长率和撕裂强度等参数,计算这些参数的变化率,比较了普通柴油与生物柴油以及乙醇-生物柴油对于丁腈橡胶的影响,还比较了甲酯不同分子结构对橡胶的影响。为了深入了解生物柴油以及醇类混合燃料的喷雾特性,在定容压力弹内采用高速摄影的方法研究了生物柴油和乙醇-生物柴油的喷雾特性,并与常规柴油进行了比较。研究发现,在生物柴油中添加乙醇可以明显缓解生物柴油对丁腈橡胶性能的破坏,尤其是质量、体积和硬度变化,而且可以改善喷雾质量。由于生物柴油中含有10%左右的氧,会产生较多的NOx排放。因此针对生物柴油NOx排放的增加,通过燃料设计的方法改善生物柴油的NOx排放。基于燃料设计思想,在一台四缸柴油机上燃用生物柴油以及甲醇-生物柴油和乙醇-生物柴油混合燃料,分析了添加甲醇对生物柴油燃油经济性和燃烧特性的影响。重点评价了甲醇-生物柴油混合燃料对柴油机常规气体排放(HC、CO、NOx、NO2)、非常规气体排放(甲醛、乙醛、未燃甲醇、1,3-丁二烯、苯、甲苯和二甲苯)、颗粒物质量浓度和颗粒物粒径分布的影响。比较甲醇和乙醇对于生物柴油发动机排放的影响。研究发现,在生物柴油中添加甲醇可以降低生物柴油的NOx排放和颗粒物排放,但甲醛、乙醛和1,3-丁二烯排放会随之增加。虽然添加醇类燃料可以降低生物柴油的NOx排放,但改善幅度有限。本文进一步考察了在进气充量中添加稀释气体CO2后,进气稀释对欧五柴油、生物柴油、生物柴油-柴油混合燃料、甲醇生物柴油和乙醇-生物柴油混燃料燃烧特性和排放特性(HC、CO、NOx、颗粒物质量浓度和颗粒物粒径分布)的影响。研究发现,综合使用进气稀释和燃料设计可以在降低生物柴油NOx排放的同时,维持颗粒物质量浓度到一个相对较低的水平。为了实现同时降低生物柴油NOx排放和颗粒物排放的目的,本文将燃料设计思想与低温燃烧模式相结合,在发动机燃用普通柴油、纯生物柴油和甲醇-生物柴油混合燃料,并同时利用废气再循环系统,在高比例EGR率下实现了发动机的低温燃烧。研究发现,发动机燃用甲醇-生物柴油混合燃料可以在相对较低的EGR率下同时大幅降低NOx排放和碳烟排放。同时系统分析了发动机燃烧相位对高温燃烧模式和低温燃烧模式排放特性的影响,并考察了发动机低温燃烧模式下新的trade-off关系。根据本文研究结果提出了优化生物柴油低温燃烧的燃料设计原则。进一步探索了生物柴油分子结构对发动机燃烧排放特性的影响。考察了月桂酸甲酯(C12:0)、棕榈酸甲酯(C16:0)、硬脂酸甲酯(C18:0)、油酸甲酯(C18:1M)和油酸乙酯(C18:1E)与柴油的混合燃料在发动机不同工况下的燃烧排放特性。实验结果表明,在控制HC、CO和碳烟排放方面,燃料分子中碳链长度较短,且含有有双键的脂肪酸甲酯具有较大的优势。但在控制NOx排放方面,燃料分子中碳链长度较长的不含有双键的饱和脂肪酸酯具有明显的优势。更多还原

【Abstract】 Because of its cleaness and renewability, biodiesel has a great potential as the alternative of diesel fuel to confront with the increasing energy crisis and environment pollution. In this study, the fuel design concept was used to improve the elastomer compatibility, combustion and emission characteristics. In order to reduce both NOx and smoke emission of diesel engine, the combined method of fuel design concept with low temperature combustion mode was applied in this study.Effects of ethanol percentage in ethanol-biodiesel blends on the physical and chemical properties were investigated. The results show that there were linear relationships between lots of fuel properties and the ethanol percentage in blends. Different kinds of methyl esters and ethyl esters were also tested, in order to illuminate the effects of molecular structure on the physical and chemical properties of biodiesel, such as carbon chain length, number of double bonds and alcohol type. The nitrile rubbers were immersed in different kinds of fuels. After 168 hours, the properties, such as mass weight, volume, hardness, tensile strength, elongation and tearing strength, were measured to investigate the effects of biodiesel, ethanol-biodiesel blend and ester’s molecular structure on the elastomer compatibility. Spray characteristics of diesel, biodiesel and ethanol-biodiesel blend were studied via high speed digital camera. Based on the elastomer compatibility and spray test results, it was found that the addition of ethanol in blends could not only slow down the change of elastomer, especially the change of mass weight, volume and hardness, but also improve the atomization.According to the fuel design concept, the combustion, regulated emission, unregulated emission and particulate emission characteristics were studied, when the four cylinders diesel engine was fueled with biodiesel and biodiesel blended with methanol and ethanol. It was found that with increase of methanol in methanol-biodiesel blends, NOx and PM emissions could be reduced, while formaldehyde, acetaldehyde and 1,3-butadine could be enhanced. Moreover, comparison on effects of methanol against ethanol has been conducted.The effect of intake charge dilution with carbon dioxide on the combustion and emission characteristics of a 4-cylinder diesel engine fueled with EuroV diesel fuel, biodiesel, biodiesel-diesel blends, methanol-biodiesel and ethanol-biodiesel blends were investigated. The results show that charge dilution combined with fuel design could reduce NOx emission of biodiesel, and maintain the PM emission at the releatively lower level.The low temperature combustion mode of biodiesel with high EGR rate was investigated in this study, in order to reduce NOx and smoke emission simultaneously. Influence of methanol-biodiesel blends on the combustion and emission characteristics were studied in low temperature combustion mode. It was found that the NOx and smoke could be reduced simutanously at releativley lower EGR rate when the engine is fueled with methanol-biodiesel blends. Moreover, the effects of combustion phase on the emission characteristics were studied in LTC mode and HTC mode. Meanwhile, a new trade-off relationship was formed in LTC mode. The principles of fuel design concept for LTC optimization were generalized from the experimental results of this study.Different kinds of esters were used in diesel engine, in order to illustrate the relationship between molecular structure (carbon chain length, unsaturation and alcohol type) and emissions. The esters are methyl laurate (C12:0), methyl palmitate (C16:0), methyl stearate (C18:0), methyl oleate (C18:1M) and ethyl oleate (C18:1E). In the end, a comparsion of NOx, smoke opacity and particulate composition between rapeseed oil methyl ester and palm oil methyl ester was made to explain the variances between them in molecular structure. The results show that the ester with shorter carbon chain length and double bond in molecular structure could well restrain the emissions of HC, CO and smoke. While, the ester with longer carbon chain length and without double bond could produce releativley lower NOx emission.更多还原