Alaghemandi Mohammad, Newcomb Lucas B, Green Jason R
Department of Chemistry, University of Massachusetts Boston , Boston, Massachusetts 02125, United States.
Department of Physics, University of Massachusetts Boston , Boston, Massachusetts 02125, United States.
J Phys Chem A. 2017 Mar 2;121(8):1686-1692. doi: 10.1021/acs.jpca.7b00249. Epub 2017 Feb 16.
Hydrogen is a potential substitute for fossil fuels that would reduce the combustive emission of carbon dioxide. However, the low ignition energy needed to initiate oxidation imposes constraints on the efficiency and safety of hydrogen-based technologies. Microscopic details of the combustion processes, ephemeral transient species, and complex reaction networks are necessary to control and optimize the use of hydrogen as a commercial fuel. Here, we report estimates of the ignition time of hydrogen-oxygen mixtures over a wide range of equivalence ratios from extensive reactive molecular dynamics simulations. These data show that the shortest ignition time corresponds to a fuel-lean mixture with an equivalence ratio of 0.5, where the number of hydrogen and oxygen molecules in the initial mixture are identical, in good agreement with a recent chemical kinetic model. We find two signatures in the simulation data precede ignition at pressures above 200 MPa. First, there is a peak in hydrogen peroxide that signals ignition is imminent in about 100 ps. Second, we find a strong anticorrelation between the ignition time and the rate of energy dissipation, suggesting the role of thermal feedback in stimulating ignition.
氢气是一种潜在的化石燃料替代品，可减少二氧化碳的燃烧排放。然而，引发氧化所需的低点火能量对基于氢的技术的效率和安全性施加了限制。燃烧过程的微观细节、短暂的瞬态物种和复杂的反应网络对于控制和优化氢气作为商业燃料的使用是必要的。在这里，我们通过广泛的反应分子动力学模拟报告了在很宽的当量比范围内氢氧混合物的点火时间估计。这些数据表明，最短的点火时间对应于当量比为0.5的贫燃料混合物，其中初始混合物中氢和氧分子的数量相同，这与最近的化学动力学模型非常吻合。我们发现在高于200 MPa的压力下，模拟数据中在点火之前有两个特征。首先，过氧化氢出现峰值，表明点火将在大约100皮秒内发生。其次，我们发现点火时间与能量耗散速率之间存在强烈的反相关性，这表明热反馈在刺激点火中的作用。
