Proceedings of the Combustion Institute ( IF 5.3 ) Pub Date : 2018-06-19 , DOI: 10.1016/j.proci.2018.05.103 Behrooz Ostadmohammadi Arani , Christos Emmanouil Frouzakis , John Mantzaras , Konstantinos Boulouchos
Three-dimensional direct numerical simulations of turbulent catalytic and gas-phase H2/air combustion at a fuel-lean equivalence ratio were performed in platinum-coated planar channels at two industrially-relevant flow conditions (inlet friction Reynolds numbers Reτ= 182 and 385) using detailed hetero-/homogeneous chemical reaction mechanisms. The preferential diffusion of hydrogen and oxygen, which was responsible for creating significantly higher surface equivalence ratios φw compared to the bulk gas-phase φ, was appreciably suppressed by turbulence at Reτ= 385. The higher turbulence intensity at this Reτ resulted in larger near-wall hydrogen excess that in turn yielded shorter homogeneous ignition distances compared to the lower Reτ case. Gas-phase ignition proceeded from isolated ignition kernels that subsequently formed axially elongated flames confined close to the catalytic walls. The coupling of catalytic and gas-phase chemistry inhibited homogeneous ignition, since at the vicinity of the ignition kernels the OH, H and O radical fluxes to the underlying catalytic wall were net-adsorptive and furthermore hydrogen was depleted by the catalytic reactions. The flame topology included alternating vigorously-burning and extinguished elongated streamwise stripes at or islands at . The extinguished gas-phase reaction zones at were characterized by underlying intense catalytic reaction rates. The flame topology and spatiotemporal correlation of the isolated burning and extinguished gaseous zones indicated that significant surface temperature non-uniformities could be obtained in practical catalytic reactors.
中文翻译:
在实际相关的雷诺数下H 2 /空气在Pt上的湍流催化燃烧和气相燃烧的直接数值模拟
贫燃当量比的湍流催化和气相H 2 /空气燃烧的三维直接数值模拟在两个工业相关的流动条件在铂涂覆的平坦通道进行(入口摩擦雷诺数重新τ使用详述的杂/均相化学反应机制= 182和385)。氢气和氧气的选择性扩散,这是负责创建显著更高的表面的当量比φ瓦特相比本体气相φ,被明显地由在湍流抑制再τ = 385。在此较高的湍流强度重新τ导致较大的近壁的氢气过量,这又产生了更短的均匀的点火距离比下再τ案件。气相点火从孤立的点火核开始,随后形成靠近催化剂壁的轴向细长火焰。催化化学和气相化学的耦合抑制了均匀点火,因为在点火核附近,到下面的催化壁的OH,H和O自由基通量是净吸收的,而且催化反应还耗尽了氢气。火焰拓扑包括交替剧烈燃烧和熄灭的细长流向条纹 或岛屿 。熄灭的气相反应区其特征在于潜在的强烈催化反应速率。孤立的燃烧和熄灭的气态区的火焰拓扑和时空相关性表明,在实际的催化反应器中可以获得明显的表面温度不均匀性。