随着我国经济社会的发展，汽车保有量持续快速增长。生态环境部发布的主要城市细颗粒物（PM2.5）污染来源解析结果表明，移动源排放已成为大城市PM2.5污染的主要污染源。此外，快速机动化导致原油对外依存度不断提高，对我国的能源安全也带来重大挑战。为了应对上述问题，寻求更清洁的交通替代能源迫在眉睫。乙醇相比于普通汽油，具有高辛烷值、可再生和含氧量高等特性；但在污染物排放控制效益上受到油品特征、车辆技术和环境状况等多方面复杂因素影响，现有研究结果显示存在较大不确定性。因此，全面、系统评估乙醇汽油车的污染物排放水平及燃油经济性等关键能源和环境效益特征是推广乙醇汽油的重要前提。本研究建立了针对乙醇汽油车燃油经济性、常规污染物排放、黑碳（BC）和关键挥发性有机物组分（VOCs）等非常规污染物的采样和分析方法。选择满足不同排放标准的轻型汽油车，开展不同油品特征和不同测试条件组合下的台架排放测试，深入解析油品特征、排放标准、发动机类型、环境温度和测试工况等因素对测试车辆燃油经济性和污染物排放的影响规律。本研究发现，相比于添加甲基叔丁基醚（MTBE）的普通汽油，使用10%掺混比的低芳烃（ELA）和低烯烃（ELO）乙醇汽油可以分别降低3.1%和0.9%的CO2排放。在常规污染物排放方面，乙醇汽油碳含量低、氧含量高和易雾化的特点使得CO和THC排放呈现整体下降的趋势；NOX排放影响趋势在不同的车中有所差异，部分新车由于发动机与后处理控制较好，使用乙醇汽油能够降低NOX排放。乙醇汽油能够总体降低颗粒物质量（PM）和颗粒物数浓度（PN）排放，特别是降低一次颗粒物中BC排放；但部分乙醇汽油配方由于芳烃含量相对普通汽油更高，颗粒物排放反而有所增加。研究发现，低温下乙醇汽油车排放显著上升，主要是冷启动阶段排放增加导致，多点电喷车辆PN排放增加幅度显著高于缸内直喷车。研究系统分析了乙醇汽油车主要VOCs排放特征及影响因素，使用ELA和ELO能够相对普通汽油分别降低8%和25%的VOCs排放，特别是有利于芳烃排放的控制。研究进一步指出在较新排放控制技术的车型上使用乙醇汽油可以降低尾气管排放的臭氧生成潜势（OFP）和二次有机气溶胶（SOA）生成潜势。例如，国3和国5车使用ELO乙醇汽油的SOA生成潜势比普通汽油低26%。
With rapid social and economic development, China’s vehicle ownership has maintained a strong growth in the past decades. The official source appointment results of fine particulate matter (PM2.5) pollution in major cities released by the Ministry of Ecology and Environment indicates that mobile source emissions have become one of the most important local sources. The rapid motorization also increases the dependence of imported crude petroleum from foreign countries, posing great challenges to the national energy security. To tackle these problems, it is urgent to seek cleaner alternatives for transportation energy. Compared to conventional fossil-based gasoline, ethanol has the useful features of high octane, being renewable, and high oxygen content; however, the impacts on air pollutant emissions remain quite uncertain according to existing studies, because the fuel properties, vehicle technologies and test conditions varies substantially. Therefore, there is a clear need to conduct a comprehensive and systematic evaluation of the impacts on fuel economy and air pollutant emissions characteristics from ethanol-blended gasoline fuels to support an adequate promotion program.This study established a sampling and analysis protocol for measuring fuel economy and emissions of regulated pollutants, black carbon (BC) and key volatile organic compounds (VOCs) from light-duty gasoline vehicles by using ethanol-blended fuels. The tested vehicles comply with various emission standards, and the test fuels and conditions also vary significantly to enhance the representativeness. This study thus analyzes the complex influential factors of fuel property, emission standard, engine type, ambient temperature, and test condition in fuel economy and pollutant emissions for tested vehicles. This study found that two 10% ethanol-blended fuels with low aromatics (ELA) and low olefins (ELO) can reduce CO2 emissions by 3.1% and 0.9%, respectively, compared to regular gasoline with methyl tert-butyl ether (MTBE). In terms of regulated pollutant emissions, lower carbon content, higher oxygen content and easier atomization of ethanol-blended fuels favor the overall tendency of reducing CO and THC emissions. The impacts on NOx emissions vary among different vehicles; NOX emission can be in general reduced for certain new vehicles with advanced control technologies. Ethanol-blended fuels tend to reduce particle mass (PM) and particle number (PN) emissions, as well as black carbon (BC) emissions, but some ethanol-blended formulas with higher aromatics would increase particle emissions. In addition, this study shows pollutant emissions of light-duty gasoline vehicles are highly increased at low temperature, which is mainly caused by the increase in emissions during the cold start stage. The increase in PN emissions at low temperature is more significant for port fuel injection engines than gasoline direct injection engines.This study systematically analyzed the emission characteristics of key VOCs species and the influential factors, concluding that ELA and ELO can reduce the VOCs emissions by 8% and 25%, respectively. A particular benefit is that the ethanol-blended fuels can reduce the fraction of aromatics in total VOCs emissions. This study further pointed out that the use of ethanol blended fuel can reduce the ozone formation potential (OFP) and secondary organic aerosol (SOA) formation potential from exhaust emission for newer vehicles. For example, the ELO fuel could reduce SOA formation potential by 26% compared to the regular gasoline.
