Technical note: Use of an atmospheric simulation chamber to investigate the effect of different engine conditions on unregulated VOC-IVOC diesel exhaust emissions
Technical note: Use of an atmospheric simulation chamber to investigate the effect of different engine conditions on unregulated VOC-IVOC diesel exhaust emissions
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DOI：
10.5194/acp-18-11073-2018
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发表时间：
2018-08
影响因子：
6.3
通讯作者：
K. Pereira;R. Dunmore;J. Whitehead;M. Alfarra;J. Allan;M. S. Alam;R. Harrison;G. Mcfiggans;J. Hamilton
中科院分区：
文献类型：
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作者：
K. Pereira;R. Dunmore;J. Whitehead;M. Alfarra;J. Allan;M. S. Alam;R. Harrison;G. Mcfiggans;J. Hamilton
抽象。将柴油机排气排放物引入大气模拟室中，采用热脱附（TD）二维气相色谱-火焰离子化检测器（GC × GC-FID）测定。进行了一组广泛的测量，以研究不同的发动机条件（即负载，速度，“驾驶场景”）和排放控制装置（有或没有柴油氧化催化剂，DOC）的影响，从轻型柴油发动机，燃料与超低硫柴油（ULSD）的非管制废气排放的组成和丰度。研究了一系列排气稀释比（范围= 1：60至1：1158），模拟了从排放源附近到下风处的排气的化学和物理转化。总共测量了废气中的16种化合物和8组化合物（芳香族化合物和单环芳香族化合物），范围从挥发性到中间挥发性（VOC-IVOC），提供了详细的化学形态和基于其结构和功能的化合物分组。测量的VOC-IVOC排放率显示出良好的再现性，从重复实验使用类似的排气稀释比。然而，在所研究的排气稀释比的极端情况下（1：60和1：1158的比较），由于再现性差，测得的VOC-IVOC排放率显示出一些不一致，并强调了重复样品测量的重要性。发现所研究的DOC去除总物种化VOC-IVOC（∑SpVOC-IVOC）排放的43± 10%（算术平均值±实验不确定度）。研究的DOC的化合物类依赖的去除效率分别为39± 12%和83± 3%的芳香族化合物和单环芳烃。DOC脂肪族的去除效率一般随着碳链长度的增加而降低。∑SpVOC-IVOC的排放率随发动机工况的不同而变化很大，从70到9268 mg kg−1（每千克燃料燃烧所排放的质量毫克数）不等。∑SpVOC-IVOC排放率一般随着发动机负荷和温度的增加而降低，并且在较小程度上随着发动机转速的增加而降低。由于发动机燃烧和DOC碳氢化合物（HC）去除效率这两个影响因素，排气成分发生了显著变化。提高发动机燃烧效率导致C7至C12正构烷烃对∑SpVOC-IVOC排放率的贡献百分比更大。相反，增加DOC HC去除效率导致C7至C12支化烃类对∑SpVOC-IVOC排放速率的更大百分比贡献。在低发动机温度（<150 ℃，低于DOC的工作温度）下，废气中正构烷烃的贡献随着燃烧效率的提高而增加，并且在城市环境中可能很重要，因为正构烷烃比其分支对应物更有效地产生二次有机气溶胶（SOA）。在发动机温度非常高的情况下（最大应用发动机速度和负载，发动机温度= 700 ℃），正构烷烃的贡献比冷启动实验中观察到的大1.6倍（最类似于未燃烧的燃料），并可能表明基于液体燃料的SOA产率估计可能与排气SOA产率不一致，特别是在高发动机速度和负载（即高发动机温度）下。排放率被发现是65倍以上，从冷启动实验比在最大应用的发动机转速和负荷。据我们所知，这是第一个研究，使用大气模拟室，以分离的DOC和燃烧效率对废气成分的影响。
Abstract. Diesel exhaust emissions were introduced into an atmospheric simulation chamber and measured using thermal desorption (TD) comprehensive two-dimensional gas chromatography coupled to a flame ionisation detector (GC × GC-FID). An extensive set of measurements were performed to investigate the effect of different engine conditions (i.e. load, speed, “driving scenarios”) and emission control devices (with or without diesel oxidative catalyst, DOC) on the composition and abundance of unregulated exhaust gas emissions from a light-duty diesel engine, fuelled with ultra-low sulfur diesel (ULSD). A range of exhaust dilution ratios were investigated (range = 1 : 60 to 1 : 1158), simulating the chemical and physical transformations of the exhaust gas from near to downwind of an emission source. In total, 16 individual and 8 groups of compounds (aliphatics and single-ring aromatics) were measured in the exhaust gas ranging from volatile to intermediate volatility (VOC-IVOC), providing both detailed chemical speciation and groupings of compounds based on their structure and functionality. Measured VOC-IVOC emission rates displayed excellent reproducibility from replicate experiments using similar exhaust dilution ratios. However, at the extremes of the investigated exhaust dilution ratios (comparison of 1 : 60 and 1 : 1158), measured VOC-IVOC emission rates displayed some disagreement owing to poor reproducibility and highlighted the importance of replicate sample measurements. The investigated DOC was found to remove 43±10 % (arithmetic mean ± experimental uncertainty) of the total speciated VOC-IVOC (∑SpVOC-IVOC) emissions. The compound class-dependant removal efficiencies for the investigated DOC were 39±12 % and 83±3 % for the aliphatics and single-ring aromatics, respectively. The DOC aliphatic removal efficiency generally decreased with increasing carbon chain length. The ∑SpVOC-IVOC emission rates varied significantly with different engine conditions, ranging from 70 to 9268 mg kg−1 (milligrams of mass emitted per kilogram of fuel burnt). ∑SpVOC-IVOC emission rates generally decreased with increasing engine load and temperature, and to a lesser degree, engine speed. The exhaust gas composition changed considerably as a result of two influencing factors: engine combustion and DOC hydrocarbon (HC) removal efficiency. Increased engine combustion efficiency resulted in a greater percentage contribution of the C7 to C12 n-alkanes to the ∑SpVOC-IVOC emission rate. Conversely, increased DOC HC removal efficiency resulted in a greater percentage contribution of the C7 to C12 branched aliphatics to the ∑SpVOC-IVOC emission rate. At low engine temperatures (<150 ∘C, below the working temperature of the DOC), the contribution of n-alkanes in the exhaust gas increased with increasing combustion efficiency and may be important in urban environments, as n-alkanes are more efficient at producing secondary organic aerosol (SOA) than their branched counterparts. At very high engine temperatures (maximum applied engine speed and load, engine temperature = 700 ∘C), the n-alkane contribution increased by a factor of 1.6 times greater than that observed in the cold-start experiment (most similar to unburnt fuel) and may suggest liquid-fuel-based estimates of SOA yields may be inconsistent with exhaust SOA yields, particularly at high engine speeds and loads (i.e. high engine temperatures). Emission rates were found to be 65 times greater from a cold-start experiment than at maximum applied engine speed and load. To our knowledge, this is the first study which uses an atmospheric simulation chamber to separate the effects of the DOC and combustion efficiency on the exhaust gas composition.