CLALIFICATION OF FUNDAMENTAL PHENOMENA ON NON-EMISSION BURNING OF CO_2AND NOx

为了开发一种既能回收CO_2又能减少污染物排放的燃烧体系，提出了一种以CO_2/ o_2为氧化剂的新型燃烧方法。然而，具有普朗克平均吸收系数的极薄灰色气体辐射模型，没有再吸收，过高估计了发射，特别是对于“低速”火焰。数值分析了非灰辐射对CH_4/O_2/CO_2预混火焰传播和燃烧极限的影响。研究结果总结如下：1。统计窄带（SNB）模型描述的非灰色辐射对层流燃烧速度和可燃性极限的影响随着CO_2稀释比的增大而增大。光学薄模型（OTM）描述的灰色辐射在CO_2稀释比较高和当量比较低时失去有效性。在较宽的稀释比z范围内，对稀释剂（CO_2或N_2）对CH_4/（稀释剂+O_2）轴对称升力层流扩散火焰结构和稳定性的影响进行了实验和数值研究。随着Z的增大，附着火焰在Z_<lim> （CO_2稀释火焰为0.72，N_2稀释火焰为0.83）处升起，且随火焰长度的变化有稳定的响应。3 . L_f变短，升离高度H_f增大，火焰基部沿径向向外扩散直至Z_b （CO_2稀释火焰为0.78，N_2稀释火焰为0.86）。升力火焰前缘结构为三重火焰，富燃料预混翼比贫燃料预混翼小，尾焰非预混翼从起跳点立即向燃料侧倾斜。由于CO_2的高热容量和低输运率，CO_2对结构和稳定性的影响强于N_2。

To develop a combustion system that is suitable for CO_2 recovery and has less emission of pollutants, a new combustion method using CO_2/O_2as oxidant has been proposed. However, the epically thin and gray-gas radiation model with Planck mean absorption coefficient, which has no reabsorption, has overestimated the emission, especially for "low-speed" flames. The effects of nongray radiation on the propagation and flammability limit of premixed CH_4/O_2/CO_2 flames were numerically analyzed. The results can be summarized as follows :1. The nongray radiation effects described by the statistical narrow-band (SNB) model on the laminarburning velocity and flammability limit become larger as the dilution ratio of CO_2 is increased.2. The gray radiation described by the optically thin model (OTM) loses effectiveness for higher CO_2 dilution ratios and lower equivalence ratios.An experimental and numerical study of diluent (CO_2 or N_2) effects on structure and stability of axisymmetric lifted laminar diffusion CH_4/(Diluent+O_2) flames were also performed over a wide range of the dilution ratio, Z.Results showed that3. As increasing the Z, attached flames are lifted off at the Z_<lim> (0.72 for CO_2, 0.83 for N_2 diluted flame, respectively) and there were steady responses that the flame length. L_f, shortened and the lift off height, H_f, increased as well as the spreading out of the flame base in the radial direction until the Z_b (0.78 for CO_2, 0.86 for N_2 diluted flame, respectively).4. The leading edge structure of the lifted flame has a triple flame, where fuel rich premixed wing is smaller than lean one and the trailing nonpremixed flame inclines immediately to the fuel side from trip point.5. It is also shown that CO_2 effects are stronger than N_2 on the structure and stability due to high heat capacity and low transport rate of Co_2.