摘要
为了研究低旋流CH_4/H_2火焰在不同H_2占比(体积分数)条件下的燃烧特性及稳定机制,对当量比为0.7的CH_4/H_2预混气体进行了数值模拟,分析了CH_4/H_2火焰的自相似特性、流场结构及火焰特性,研究了旋流数对富氢燃料回火性的影响。结果表明:随H_2占比增加,CH_4/H_2火焰仍保持自相似特性,其剪切层强度逐渐增加,内剪切层逐渐向中心低速区移动,火焰锋面逐渐向喷嘴移动,火焰形状由"碗"型逐渐变为"W"型,最后变为"V"型,而轴向、径向速度延伸率以及虚拟原点几乎不受H_2占比影响。在H_2占比从80%增加到95%时,燃料的层流火焰速度变化较大,使得流场结构和火焰锋面位置发生剧烈变化。对于中心低速区的CH_4/H_2火焰,当火焰传播速度等于当地气流速度时,火焰稳定;对于内剪切层区的CH_4/H_2火焰,速度梯度产生的旋流使得当地气流产生向下和向中心低速区移动的趋势,从而火焰产生向上移动的趋势,实现火焰稳定。适当减小旋流数,有利于减小富氢燃料回火发生的可能性。
The numerical simulation on the premixed CH4/H2 gas at an equivalence ratio of 0.7was conducted to investigate the combustion characteristics and stabilization mechanism of low swirl CH4/H2 flame in various hydrogen volume proportions.The analyses on the self-similar characteristics,the flow field structure and the flame characteristics of CH4/H2 flame were performed,and the effect of swirl number on the flashback of hydrogen-enriched fuel was studied.The results showed that with the increase of H2 volume proportion,the self-similar characteristics of CH4/H2 flame still remain;the intensity of the shear layer increases gradually and the inner shear layer moves gradually to the central low-velocity zone,which compels the flame front towards the nozzle,and the shape of the flame changes from the＂bowl＂type to＂W＂type,and then converts to＂V＂type finally.The mean axial and radial aerodynamic stretch rates and the virtual origin are almost not affected by the hydrogen volume proportion.When the hydrogen volume proportion increases from 80% to 95%,the laminar flame speed of the fuel changes greatly,leading to drastic changes in the flow field structure and the flame front.As forthe CH4/H2 flame in the central low-velocity zone,when the flame propagation velocity is equal to the local gas velocity,the flame is stable;as for the CH4/H2 flame in the shear layer,the vortex produced by the velocity gradient facilitates the local gas flowing downward and moving toward the central low-velocity zone,thus the flame moves upward and reaches a stable state.Decreasing the swirl number properly is beneficial to the reduction of the flashback of hydrogenenriched fuel.
作者
陈立
李祥晟
CHEN Li LI Xiangsheng(School of Energy and Power Engineering, Xi＇an Jiaotong University, Xi＇an 710049, China)
出处
《西安交通大学学报》
EI
CAS
CSCD
北大核心
2017年第1期72-78,共7页
Journal of Xi'an Jiaotong University
关键词
低旋流燃烧
火焰特性
稳定机制
旋流数
low swirl combustion
flame characteristics
stabilization mechanism
swirl number
