Two-stage aerosol formation in low-temperature combustion
Two-stage aerosol formation in low-temperature combustion
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DOI：
10.1016/j.fuel.2021.121322
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发表时间：
2021-11
期刊：
影响因子：
7.4
通讯作者：
O. E. Hajj;Khairallah Atwi;Zezhen Cheng;Alanna L. Koritzke;M. Christianson;N. S. Dewey;B. Rotavera;R. Saleh
中科院分区：
文献类型：
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作者：
O. E. Hajj;Khairallah Atwi;Zezhen Cheng;Alanna L. Koritzke;M. Christianson;N. S. Dewey;B. Rotavera;R. Saleh
低温燃烧是减少内燃机中污染物形成的有前途的策略。然而，对于控制低温燃烧和常规燃烧之间点火差异的化学物质如何影响颗粒物（气溶胶）的排放率和物理化学性质，缺乏了解。在这里，我们在常压反应器中进行了燃烧实验，控制在恒定当量比（ε = 2.3）和O2/N2= 0.06，温度在250 °C和1035 °C之间变化。我们使用了两种燃料：具有高炭黑生成倾向的甲苯和具有相对较低炭黑生成倾向但表现出在甲苯燃烧中不存在的两阶段点火的正庚烷。我们对气溶胶粒径分布、挥发性和光吸收特性进行了实时测量。我们还进行了离线分子大小表征。这两种燃料排放的气溶胶都是由被归类为棕色碳的吸光有机物组成的。在最高燃烧温度（1035 °C）下，甲苯燃烧产生的气溶胶排放量是庚烷的20倍。从甲苯燃烧的气溶胶排放物有更多的丰富的大分子大小的物种，挥发性较低，和更多的光吸收比庚烷。对于这两种燃料，气溶胶排放因子随温度的降低而急剧下降。然而，在较低温度下，气溶胶排放量有所回升，正庚烷燃烧在290 °C时达到峰值，而甲苯则没有观察到。这是一致的化学动力学模拟，显示突出的两阶段点火行为forn-heptane，但不是甲苯。
Low-temperature combustion is a promising strategy for reducing pollutant formation in internal combustion engines. However, there is a lack of understanding of how the chemistry governing the differences in ignition between low-temperature and conventional combustion affects the emission rates and physicochemical properties of particulate matter (aerosols). Here, we conducted combustion experiments in an atmospheric-pressure reactor controlled at constant equivalence ratio (ϕ = 2.3) and O2/N2= 0.06, and at temperatures varied between 250 °C and 1035 °C. We used two fuels: toluene, which has high sooting propensity, andn-heptane, which has a comparatively lower sooting propensity but exhibits two-stage ignition that is not present in toluene combustion. We performed real-time measurements of aerosol size distributions, volatility, and light-absorption properties. We also performed offline molecular-size characterization. Aerosols emitted from both fuels were comprised of light-absorbing organics that are categorized as brown carbon. At the highest combustion temperature (1035 °C), the aerosol emissions from toluene combustion were a factor of 20 larger thann-heptane. The aerosol emissions from toluene combustion had more abundance of large molecular-size species, were less volatile, and were more light-absorbing thann-heptane. For both fuels, aerosol emission factors exhibited a steep drop with decreasing temperatures. However, there was a resurgence in aerosol emissions at lower temperatures with a peak at 290 °C forn-heptane combustion that was not observed for toluene. This is consistent with chemical kinetics simulations that show prominent two-stage ignition behavior forn-heptane, but not for toluene.