弱旋流燃烧器燃料/空气预混均匀性研究

实施贫预混燃烧技术的关键是保证燃料与氧化剂的均匀混合，避免在燃烧时形成局部高温点而导致NOx排放增加。本文针对弱旋流燃烧器设计了甲烷/空气预混方案，首先通过试验结果验证了数值计算方法的可靠性，然后对当量比为0.7的预混气体进行数值模拟，分析了燃料喷射孔和弱旋流流场特性对掺混的影响机制。结果表明：喷射孔径影响燃料的初始分布，很大程度上决定了在有限空间内可以达到的最终混合效果，对给出的预混结构，存在最佳当量孔径b=0.01及对应的平均动量通量比 J =75.59，使混合效果最优。弱旋流流场由中心直流通量和外环旋流通量共同作用，其中旋流对燃料扩散起主导作用。在保证弱旋流特性的前提下，通过增大孔板阻塞比或旋流叶片几何角的方式能够强化旋流作用，从而提高预混均匀性。

Fuel/Air Premixing Uniformity of Low Swirl Burner

The key to implementing lean premixed combustion technology is to ensure that fuel and oxidant are evenly mixed, so as to avoid the formation of hot spots at the local position during combustion which further resulting in increased NOx emissions. In this paper, a methane/air premixing scheme has been designed for low swirl burner. Comparisons are performed with experimental measurements with the aim to validate the numerical method. Then a numerical simulation of premixed gas at equivalent ratio of 0.7 was conducted to investigate the influence mechanism of the characteristics of fuel orifice and low swirl flow field on premixing process. Results show that jet aperture affects the initial distribution of fuel which largely determines the final mixing efficiency that can be achieved in a limited space. For the given structure, an optimal equivalent aperture b=0.01 and a corresponding average momentum flux ratio J = 75.59 can be found to optimize the mixing efficiency. The low swirl flow field is under the interaction of central direct-current flux and outer swirling flux, wherein the swirling effect plays a leading role during the fuel diffusion process. Under the prerequisite of flowing in a low swirl state, the premixing uniformity can be improved through enhanced swirling intensity by increasing the blockage ratio of the perforated plate or the geometric angle of the swirling vane.