ABSTRACT

Understanding and characterizing the non-homogenous ignition of flammable mixtures by hot particles are important for industry safety. In this study, one-dimensional transient simulations considering detailed chemistry and transport are conducted for the ignition of static methane/air and hydrogen/air mixtures by hot particles with different radii. The objective is to assess the effects of particle size on the ignition delay time for the hot particle-induced ignition process. Unlike the nearly homogenous ignition in shock tubes or rapid compression machines, the non-homogeneous ignition caused by a hot particle depends on not only chemical kinetics but also transport of reactive species. It is found that 1D hot particle ignition is much slower than the 0D homogenous ignition (in which the mixture temperature is the same as the fixed particle temperature) since there is radical loss near the particle surface caused by mass diffusion. The ignition delay time for hot particle ignition is found to strongly depend on the particle radius and temperature. This is interpreted through the change of radical loss with particle radius and temperature. Moreover, to characterize the hot particle ignition, we introduce a Damköhler number which is the ratio between two characteristic times for chemical reaction and mass diffusion. The change of the normalized ignition delay time for 1D hot particle with the Damköhler number is discussed; and a linear relationship is observed for certain conditions.

摘要

了解和表征热粒子对可燃混合物的非均匀点燃对于工业安全很重要。在这项研究中，针对不同半径的热粒子点燃静态甲烷/空气和氢气/空气混合物，进行了考虑详细化学和传输的一维瞬态模拟。目的是评估颗粒大小对热颗粒引起的点火过程的点火延迟时间的影响。与激波管或快速压缩机中几乎均匀的点火不同，由热粒子引起的非均匀点火不仅取决于化学动力学，还取决于活性物质的传输。发现一维热粒子点火比零维均匀点火（混合温度与固定粒子温度相同）慢得多，因为在粒子表面附近存在质量扩散引起的自由基损失。发现热粒子点火的点火延迟时间强烈依赖于粒子半径和温度。这可以通过自由基损失随粒子半径和温度的变化来解释。此外，为了表征热粒子点火，我们引入了一个 Damköhler 数，它是化学反应和质量扩散的两个特征时间之间的比率。讨论了一维热粒子的归一化点火延迟时间随Damköhler数的变化；并且在某些条件下观察到线性关系。