ABSTRACT

Emissions levels from current gasoline spark-ignited engines are low, and emissions changes associated with the blending of ethanol into gasoline are small and difficult to quantify. Addition of ethanol, with a high blending octane number, allows a reduction in aromatics in market gasoline. Blending behavior of ethanol is nonlinear, altering the distillation curve, including the 50% temperature point, T50. Increase in gasoline direct injection (GDI) engine technology in the fleet challenges ability of older models based on port fuel injection (PFI) results to predict the overall air quality impact of ethanol blending. Five different models derived from data collected through U.S. Environmental Protection Agency Energy Policy Act (EPAct) programs were used to predict LA92 Phase 1 particulate matter (PM) emissions for summer regular (SR) E0 (gasoline with 0% ethanol by volume), E10 (gasoline with 10% ethanol) and E15 (gasoline with 15% ethanol). Substantial reductions of PM for E10 and E15 relative to E0 were predicted when aromatics were displaced by ethanol to maintain octane rating. SR E0 and E10 were also matched to linear combinations of EPAct fuels and results showed a 35% PM reduction for SR E10 relative to SR E0. For GDI vehicles the Coordinating Research Council (CRC) E-94-3 study found that E10 had 23% or 29% PM increase. However, CRC E-129 found an E10 PM reduction of 10% when one E0 fuel and its splash blended (SB) E10 were compared. Both CRC project E-129 SB data and fuel triplets selected from the EPAct study showed variation for E15 emissions, although E-129 suggests that E15 in GDI offers about a 25% reduction of PM with respect to E0. Overall, data suggest that ethanol blending offers a modest to a substantial reduction of cold-start PM mass if aromatic levels of the finished products are reduced in response to ethanol addition.

Implications: Studies of exhaust emissions effects of ethanol blending with gasoline vary in conclusions. Blending properties are nonlinear. Modeling of real-world emissions effects must consider all fuel composition adjustments and property changes associated with ethanol addition. Aromatics are reduced in E10 or E15, compared with E0, and distillation changes. PFI-derived models show reductions in cold-start PM for expected average E10 versus E0 pump fuel, due to reduced aromatic content. Relative emissions effects from older technology (PFI) engines do not predict newer engine (GDI) results reliably, but recent GDI data show reduced cold-start PM when ethanol displaces aromatics.

摘要

当前的汽油火花点火式发动机的排放水平较低，并且与乙醇混入汽油相关的排放变化很小且难以量化。添加具有高混合辛烷值的乙醇可以减少市场上汽油中的芳烃。乙醇的混合行为是非线性的，从而改变了蒸馏曲线，包括50％温度点T50。机队中汽油直喷（GDI）发动机技术的增长挑战了基于港口燃料喷射（PFI）结果的较旧型号的能力，以预测乙醇混合对空气质量的总体影响。通过美国收集的数据得出的五个不同模型 环境保护署《能源政策法》（EPAct）程序用于预测夏季常规（SR）E0（乙醇含量为0％的汽油），E10（乙醇含量为10％的汽油）的LA92第1阶段颗粒物（PM）排放（汽油和15％的乙醇）。当芳族化合物被乙醇置换以保持辛烷值时，预计E10和E15的PM相对于E0会大幅降低。SR E0和E10也与EPAct燃料的线性组合匹配，结果表明SR E10相对于SR E0的PM降低了35％。对于GDI车辆，协调研究委员会（CRC）的E-94-3研究发现，E10的PM增加了23％或29％。但是，CRC E-129发现，将一种E0燃料及其飞溅混合（SB）E10进行比较后，E10 PM降低了10％。CRC项目的E-129 SB数据和从EPAct研究中选择的燃料三元组都显示了E15排放的变化，尽管E-129表明GDI中的E15相对于E0可使PM降低约25％。总体而言，数据表明，如果响应于添加乙醇而降低了成品的芳烃含量，则乙醇共混可以适度地大幅降低冷启动PM的质量。

启示：关于乙醇与汽油混合的废气排放影响的研究结论不同。混合特性是非线性的。对现实排放影响进行建模时，必须考虑所有燃料成分的调整以及与添加乙醇相关的特性变化。与E0相比，E10或E15中的芳烃减少，并且蒸馏发生变化。基于PFI的模型显示，由于芳烃含量降低，预期平均E10与E0泵燃料相比，冷启动PM有所降低。旧技术（PFI）发动机的相对排放影响不能可靠地预测新发动机（GDI）的结果，但是最新的GDI数据显示，当乙醇替代芳烃时，冷启动PM减少。