标准旋流火焰场的燃烧特性实验与模拟研究

Experimental and Numerical Study on the Combustion Characteristics of Standard Swirl Flame

本文搭建了4.2 kW标准化的旋流燃烧机理实验台,通过调节配风构造了三种旋流强度(旋流数S=0、0.5和0.9)的燃烧工况,测量并比较了不同旋流数下的流场结构及温度特性。相比直流燃烧火焰,全旋流燃烧火焰=的长度缩短,径向展宽增大。基于OpenFOAM对各工况的数值模拟结果与试验测得的火焰形貌、回流区结构及温度分布特性吻合较好。利用拉格朗日方法追踪了直径40μm颗粒在旋流场中的运动轨迹,发现部分颗粒被回流区卷吸重新进入高温区。分析颗粒运动轨迹上的聚并核函数演化,发现其在高温回流区取值较大,在下游随着温度和湍流耗散率的降低而逐渐减小。本研究为煤粉旋流燃烧过程中的细颗粒物生成提供了前期的基础。

In this paper,we develop a 4.2 kW standard mechanistic swirl burner for pulverized coal combustion.By adjusting the primary and secondary air flowrates,three conditions with different swirl intensities(with the swirl number S=0,0.5&0.9)are investigated.We measured the flow field and temperature distributions for the three cases.Under the full-swirl condition,the flame is decreased in length and stretched in radial range,as compared to the direct-flow condition.Numerical simulation using OpenFOAM for each case agree reasonably well with the measured flame appearance,recirculation zone,and temperature distributions.We further tracked the trajectories of 40-μm inertial particles in the swirl flame,revealing that some particles flowing downstream are possible to reenter the high temperature area through recirculation.The evolution of the coagulation kernel of fine particles is quantified along the‘coal’particle trajectory.It is found that the coagulation kernel takes much larger values in the high temperature area,while flowing downstream the collision frequency decreases dramatically.This work provides insights on fine particulate formation in the swirl combustion of pulverized coal.