Abstract:

By using the skeletal reaction mechanism, the combustion in an opposed methane jet in coaxial narrow air stream tubes is studied. The temperature, species distribution, heat flux, flame stretch rate and flame curvature are calculated. When the fuel flow rate (Q_F)=120 ml·min^-1, with increasing Q_A, the flame changes from flat-disk shape to curved one and covers the inner tube exit, and the flame is forced to move toward the exit of inner pipe. The flame is compressed and the distributions of temperature and species are compact. When equivalence ratio (ER)>1.00, with increasing Q_A, the peak temperature and the flame length along the flame surface rise and reach the maximum, while when ER≤1.00, the peak temperature and the flame length decrease. The after burning gas preheats the inlet methane through the inner pipe and the total heat flux is influenced by the flame temperature and gas flow. With the increase of Q_A, the heat flux is much stronger and the preheating increases, reaching the maximum when Q_A=2450 ml·min^-1. When Q_A>2450 ml·min^-1, the preheating goes down. When ER>1.00, the stretch rate of flame κ is small and changes slowly at the beginning, and then it rises sharply along the flame surface but finally it is no more than 65 s^-1. When ER≤1.00, along the flame surface, κ increases first and then decreases, and finally become negative with the minimum value of -262 s^-1. The increase of Q_A makes κ change seriously. The maximum of κ is 638 s^-1.

Key words: methane, numerical simulation, heat transfer, opposed flow, combustion characteristics, flame stretch

摘要：

用骨架反应机理对同轴管甲烷逆流燃烧器进行分析能够很好地了解火焰结构与燃烧器内的温度分布，并得到各处的火焰拉伸率及相关参数。随着空气流量（Q_A）的增加，火焰形状由扁平型变化为弯曲型，并逐渐将内管管口包覆，火焰厚度逐渐减小。当量比（ER）较大时，火焰附近温度与物质的分布较为稀疏，而ER较小时，其分布较为紧密。内管壁面上热通量H_f随着的Q_A增加而逐渐加强；总的传热量H在Q_A=2540 ml·min^-1达到最大。当ER≥3.00时，火焰拉伸率κ开始时缓慢变化，在越过燃烧器内管边缘后快速增加，但最终不大于65 s^-1。在ER<1.00时，火焰呈弯曲状，长度较长，κ值变化剧烈，最大可以达到638 s^-1，并在火焰末端κ值变为负数，最小值为-262 s^-1。

关键词: 甲烷, 数值模拟, 传热, 逆流, 燃烧状态, 火焰拉伸率