CH4/空气简化动力学机理数值验证

选择绕圆柱预混燃烧算例,验证CH4/空气三种简化动力学机理(16s41r、15s19r和53s325r).考虑均匀来流,忽略湍流和湍流与燃烧相互作用以及燃料扩散效应,假设层流有限反应速率,采用保自由流5阶WENO格式求解多组分Euler方程组,得到CH4/空气预混燃烧流场温度等值线、沿驻点线压力和温度及其CH4、CO和CO2质量百分数分布.结果表明:三种简化动力学机理给出的流场均出现弓形激波和火焰面,弓形激波和火焰驻点距离及其形状、诱导区宽度和简化动力学机理相关.当圆柱直径增大,弓形激波和火焰向圆柱上游移动,对应的驻点距离均增大,诱导区宽度变短,点火延时变小,但火焰和弓形激波位置次序未变化.53s325r模型要比16s41r模型和15s19r模型精度要高,点火延时覆盖的压力和温度范围也较宽,所有简化机理均未完全反应,在较大圆柱直径下游达到化学平衡.

Numerical Validation of Three Reduced Kinetic Mechanisms of Methane Air Mixture

Methane and air premixed combustion around a cylinder is chosen to evaluate reduced mechanisms of 16species/41steps, 15species/19steps and 53spesies/325steps. The coming flows are homogeneous. Turbulence and its interaction with combustion, fuel diffusion are neglected and finite reaction rates of chemistry are assumed in the computation. The 5th order WENO scheme that conserves free flow properties is used to mitigate derivative errors from unsmooth grids and increase solution accuracy. Pressure and temperature contours as well as their distributions along stagnation line are obtained including mass fractions of species CH₄, CO and CO₂. Bow shock and flame front both appear upstream the cylinder. Standoff distances and induction lengths are related to reduced mechanisms. With increasing cylindrical diameter, standoff distances increase and induction length decrease either for ignition delay. The bow shock and flame are both pushed upstream but they are still remained in sequence. In contrast to reduced models of 16species/41steps and 15species/19steps, 53spesies/325steps model provides good accuracy and ignition covers a wide range of pressure and temperature. Three models demonstrate incompletely burning or chemical reactions in all cases except cases of cylinders with large diameters. It shows that elementary reactions reach chemically equilibrium but the reactions are not so completely. Meanwhile, the larger cylindrical diameter, the better accuracy in evaluation of reduced chemistry mechanisms.