乙醇和芳香烃组分对直喷汽油车颗粒物排放协同影响和作用机制研究

Particulate emissions from motor vehicles is one of the key contributors to China's PM2.5 contamination. In recent years, the rapid increase in the preservation of gasoline direct injection (GDI) vehicles further strengthens the necessity to abate particulate emissions from gasoline vehicles. Moreover, China has announced a plan to intensify the use of bio-E10 fuel nationwide by 2020. However, studies focused on the impacts of burning ethanol-gasoline on particulate emissions from gasoline vehicles are still insufficient, previous researches also hold conflicted viewpoints regarding how ethanol addition impacts particulate emissions from GDI vehicles. Few researches have paid attention to the impacts of ethanol and aromatic contents in ethanol-gasoline, and not enough explanation has been given to the influences of burning ethanol-gasoline on particulate emissions. By performing physiochemical analysis of various match-blend E10 fuels, this proposal intends to investigate the impacts of ethanol and aromatics contents on the distillation profile and vapor pressure of E10 fuels. Based on fuel property research, this proposal also plans to study how ethanol arms with aromatics and influences particulate emissions from GDI vehicles burning E10, and the mechanisms that govern particle formation by conducting steady- and transient-state tests in laboratory and real-world. Besides, this proposal will work on building a particulate emission index model with ethanol and aromatics contents being the variables. Meanwhile, particulate emission factors from typical GDI vehicles will be obtained. The research work in this proposal will provide theoretical and data support for the upcoming nationwide application of bio-E10, and further curbing PM2.5 pollution from in-use vehicle sector.

机动车颗粒物排放是造成我国大气PM2.5污染的主要原因之一。近几年，随着直喷汽油车市场份额的迅速攀升，强化汽油车颗粒物排放控制已刻不容缓。我国将于2020年在全国范围内推广使用E10生物乙醇汽油，但国内外关于E10乙醇汽油对汽油车颗粒物排放影响的研究还比较匮乏，已发表的研究成果间存在矛盾，对乙醇汽油中乙醇和芳香烃组分对汽油车颗粒物排放的综合影响关注不够，缺少乙醇汽油相关影响的科学解释。本研究拟针对乙醇和芳香烃组分对E10乙醇汽油的馏程和饱和蒸气压的影响规律开展研究，在此基础上以直喷汽油车为研究对象，采用整车台架和实际道路排放测试手段，在稳态和瞬态工况下开展研究，获得乙醇和芳香烃组分对直喷汽油车颗粒物排放的协同影响规律和作用机制，研究建立以乙醇和芳香烃含量为变量的汽油车颗粒物排放表征模型，获取典型直喷汽油车的颗粒物排放因子，为我国推广E10生物乙醇汽油和削减PM2.5排放提供理论和数据支撑。

本项目针对汽油中乙醇和芳香烃组分对直喷汽油车颗粒物排放特性的协同影响开展研究。通过调配两组、共九种能够反映我国成品汽油特点的油样并在18辆整车和1台发动机开展瞬、稳态试验，系统研究了乙醇和芳香烃组分以及不同类型芳香烃对油品理化特性、气态和颗粒物排放的影响机制。研究表明，乙醇掺混明显增加燃油馏程T40以前的挥发性而显著降低T40~T50阶段挥发性，轻质芳香烃降低燃料蒸馏曲线T60~T90温度，重质芳香烃使燃料馏程T60~终馏点温度升高。与燃用汽油相比，乙醇掺混可有效降低车队CO和THC排放，对NOx影响不显著。随着E10乙醇汽油中重质芳香烃比例的增加，CO排放略有下降，THC和NOx排放没有显示出特定的规律，温室气体排放几乎不受乙醇成分和芳香烃组分的影响。颗粒质量（PM）和颗粒数量（PN）排放与乙醇成分和芳香烃组分密切相关。乙醇掺混使混合喷射汽油车的PM、PN排放增加而令直喷汽油车的PM排放减少。试验车辆的PM和PN排放因子都随重质芳香烃成分增多而增大。与汽油相比，燃用轻质芳烃含量较高的E10乙醇汽油可使PM和PN排放减半，而重质芳烃含量较高的E10乙醇汽油则使车辆PM和PN排放成倍增长。针对当前PMI模型对C12芳香烃影响低估的问题，建立了改进的颗粒物指数模型。乙醇和芳香烃组分对试验车辆的苯系物、甲醛和乙醛排放量影响不大。在冷起动阶段，苯系物排放与燃料中甲苯的体积分数线性正相关，甲苯和二甲苯在苯系物排放中的占比与燃料总芳烃中甲苯和C8芳香烃的体积分数线性正相关。乙醇掺混使低温条件下车辆的乙醛排放显著增加。反应动力学计算表明，苯系物在燃烧过程中主要进行脱氢反应生成苯基、苄基、1-苯乙基和o−C8H9。苯乙烯和乙烯是乙苯燃烧的主要中间产物，而二甲苯的主要中间产物是苯和甲苯。苯基和环戊二烯基是萘生成的主要前体物，菲主要由C7H5或环戊二烯基生成。乙醇燃烧产生的乙醛和甲醛的最大浓度分别是芳香烃火焰中对应污染物的100倍以上和2-6倍，大量的乙醛经由乙醇→CH3CHOH→乙醛途径生成。