Combustion and Flame ( IF 5.8 ) Pub Date : 2023-05-04 , DOI: 10.1016/j.combustflame.2023.112821 Andrea Nobili , Dongsheng Zheng , Matteo Pelucchi , Alberto Cuoci , Alessio Frassoldati , Xin Hui , Tiziano Faravelli
Blending of hydrocarbon fuels with hydrogen is a practically feasible way to rapidly integrate a carbon neutral energy vector in the transport sector and to effectively reduce harmful particulate matter emissions. This work investigates the effects of hydrogen (H2) addition on soot formation in n-heptane in low strain rate counterflow diffusion flames with different oxygen mole fractions (XO2=0.3 ∼ 0.45). Flame temperature, soot volume fraction (fv), monocyclic (MAHs), and polycyclic aromatic hydrocarbons (PAHs) are measured by using OH-2C-PLIF/thermocouple, LII/LE, and PAH-LIF methods, respectively. Measurements of n-heptane flames with addition of helium (He), as an inert gas with a specific heat capacity similar to that of H2, are also carried out and compared. Numerical simulations are then performed using a soot discrete sectional model coupled with detailed gas-phase kinetics to interpret the data obtained. Temperature and soot volume fraction profiles are better predicted by 2D simulations, which account for the non-negligible impact of radial diffusion and buoyancy under low strain rate conditions. Then, it is shown that both the fv and PAH yields almost linearly decrease by increasing H2 or helium (He) addition. The reduction of PAHs and soot is larger in n-heptane/H2 flames due to H2 chemical effects, absent in the n-heptane/He flames, hampering the formation of peri‑condensed structures. The effect of O2 concentration in the oxidizer stream is also studied. Experimental and simulation results show that PAHs and soot increase with XO2 for all flames. Finally, the effects of H2/He addition varying XO2 on soot formation are investigated. With the increase of XO2, the difference in the peak flame temperatures of n-heptane/H2 and n-heptane/He flames decreases. Consequently, compared to the neat n-heptane flame, the reduction of peak fv becomes more and more pronounced in the case of hydrogen addition rather than the helium addition since the H2 soot inhibiting chemical effect prevails over the H2 temperature effect which instead promotes soot formation.
中文翻译:
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氧气对 H2/正庚烷逆流火焰中碳烟形成的影响
将碳氢化合物燃料与氢混合是一种切实可行的方法,可以在交通部门快速整合碳中和能源载体,并有效减少有害颗粒物排放。这项工作研究了在具有不同氧摩尔分数(X O2 =0.3 ∼ 0.45)的低应变率逆流扩散火焰中,添加氢 (H 2 ) 对正庚烷中烟灰形成的影响。火焰温度、烟灰体积分数 ( f v )、单环 (MAHs) 和多环芳烃 (PAHs) 分别使用 OH-2C-PLIF/热电偶、LII/LE 和 PAH-LIF 方法测量。n的测量-添加氦 (He) 的庚烷火焰,作为惰性气体,比热容与 H 2相似,也进行了比较。然后使用烟灰离散截面模型结合详细的气相动力学进行数值模拟,以解释获得的数据。二维模拟可以更好地预测温度和烟灰体积分数分布,这说明了低应变率条件下径向扩散和浮力的不可忽略的影响。然后,表明通过增加 H 2或氦 (He) 添加量, f v和 PAH 产量几乎呈线性下降。由于 H 2的存在,正庚烷/H 2火焰中 PAHs 和烟灰的减少量更大化学效应,在正庚烷/He 火焰中不存在,阻碍了围凝聚结构的形成。还研究了氧化剂流中O 2浓度的影响。实验和模拟结果表明,对于所有火焰,多环芳烃和烟尘随着 X O2的增加而增加。最后,研究了H 2 /He 添加量变化的 X O2对烟灰形成的影响。随着X O2的增加,正庚烷/H 2和正庚烷/He火焰的峰值火焰温度之差减小。因此,与纯正庚烷火焰相比,峰值f v的减少在添加氢气而不是添加氦气的情况下变得越来越明显,因为 H 2烟灰抑制化学效应胜过 H 2 温度效应,而 H 2温度效应反而促进烟灰形成。