甲烷高压富氧燃烧层流扩散火焰的数值研究

摘要

Numerical study of three axisymmetric laminar co-flow diffusion flames at pressures between 0.1,-4.0,MPa was conducted. One flame is a methane/air flame(Flame 1),and the other two are methaneitrogen-diluted oxygen flame(Flame 2)and methane/carbon dioxide-diluted oxygen flame(Flame 3),the mass fraction of oxygen in the oxidizer of Flame 2,and Flame 3,are both 30%. Numerical model includes a skeletal mechanism derived from GRI-Mech 3.0,with 163 reaction steps and 26 species. An optically thin radiation sub-model was employed in the simula-tions to consider the thermal radiation absorption by species such as CH4,CO2,CO and H2O. As compared to Flame 1,the two oxygen-enhanced combustion flames are shorter and hotter. NO emission index in Flame 2 increases by 70%and increase monotonically with pressure. The majority of NO in Flame 2 is produced via the thermal route. The reaction step:H+CO2 ? OH+CO accounts for the high mole fraction of CO in Flame 3 near the fuel tube exit. As the pressure increases,flame temperature increases firstly and then decreases,flame radius decreases monotonically, while flame height remains almost constant.%对0.1～4.0,MPa范围内CH4富氧燃烧层流同轴射流扩散火焰进行了数值研究，研究对象包含3种工况：工况1为CH4/空气，工况2为CH4/70%N2和30%O2，工况3为CH4/70%CO2和30%O2．计算模型采用了基于GRI 3.0的骨干反应机理，该机理包含26种组分和163个反应，同时模型还考虑了 CH4、H2O、CO2、CO 的辐射换热损失．结果表明，富氧燃烧使火焰温度升高、长度变短．工况2中 NO 排放指数与工况1相比增加了70%，且随压力的提高而增大，绝大部分NO是通过热力型NO途径形成．基元反应H＋CO2？ OH＋CO使得工况3近燃烧器喷口处的CO浓度大大增加．提高压力，火焰温度先升高后降低，火焰半径逐渐变小，火焰长度几乎不变．