Study on the Combustion Characteristics of Carbon Monoxide-Hydrogen-Nitrogen Mixture

本文通过详细的化学动力学数值计算，研究了甲烷与空气部分氧化生成的CO-H_2-N_2混合气的燃烧特性和NOx排放。并与CH_4-N_2和H_2-N_2混合气体的结果进行了比较。在每一种情况下，空气都被用作氧化剂。确定了上述三种燃料混合物的组成，以使化学计量燃烧的绝热火焰温度彼此相同。分别采用一维预混火焰和同向流动扩散火焰作为典型的预混火焰和典型的扩散火焰。对同向流动扩散火焰进行了实验，测量了火焰结构和NOx浓度分布，并与数值计算结果进行了详细比较。对于一维预混火焰，CO-H_2-N_2火焰的燃烧速度、燃烧极限和NOx排放指数与CH_4-N_2火焰有很大不同，而与H_2-N_2火焰相似。而同向流动扩散火焰的温度分布、火焰长度和NOx排放与CH4-N_2火焰有很大不同，而与H_2-N_2火焰相似。也就是说，与CH4-N_2火焰相比，CO-H_2-N_2火焰具有更短的火焰长度和更低的NOx排放。此外，还根据数值结果绘制了NO生成的定量反应路径图，以探讨CO-H_2-N_2火焰NOx排放低的原因。结果表明，NO主要是通过NNH生成的，CO-H_2-N_2火焰中不存在与C有关的任何大的反应途径，如瞬时NO。

In this study, the combustion characteristics and the NOx emission of the CO-H_2-N_2 mixture, which can be produced by the partial oxidation of methane with air, were investigated by a numerical calculation with detailed chemical kinetics. The results were compared with those of the CH_4-N_2 mixture and H_2-N_2 mixture. In each case air was used as the oxidizer. The compositions of the above three fuel mixtures were determined so that the adiabatic flame temperatures of the stoichiometric combustion should be identical with each other. The one-dimensional premixed flame and the coflow diffusion flame were adopted respectively as the representative premixed flame and the representative diffusion flame. Experiments were also conducted for the coflow diffusion flame, and the flame structure and the NOx concentration distribution were measured and compared in detail with the numerical results. For the one-dimensional premixed flame, it was found that the burning velocity, the flammability limits and the emission index of NOx of the CO-H_2-N_2 flame are much different from those of the CH_4-N_2 flame, and similar to those of the H_2-N_2 flame. For the coflow diffusion flame, on the other hand, it was found that the temperature distribution, the flame length and the NOx emission are much different from those of the CH_4-N_2 flame, and similar to those of the H_2-N_2 flame. That is, as compared to the CH_4-N_2 flame the CO-H_2-N_2 flame has much shorter flame length and lower NOx emission. In addition, QRPD (Quantitative Reaction Path Diagram) for NO formation was drawn based on the numerical results, in order to investigate the cause of the low NOx emission of the CO-H_2-N_2 flame. As a result, it was found that NO is formed mainly via NNH and any large reaction pathway related with C such as prompt NO does not exist in the CO-H_2-N_2 flame.