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

本文采用详细化学动力学数值计算方法，研究了甲烷空气部分氧化制得的CO-H_2-N_2混合气的燃烧特性和NOx排放特性。并与CH_4-N_2混合气和H_2-N_2混合气的结果进行了比较。在每种情况下，空气被用作氧化剂。确定了上述三种燃料混合物的组成，使得化学计量燃烧的绝热火焰温度应彼此相同。采用一维预混火焰和同向流扩散火焰分别作为预混火焰和扩散火焰的代表。对同向流扩散火焰进行了实验研究，测量了火焰结构和NOx浓度分布，并与数值计算结果进行了比较。对于一维预混火焰，CO-H_2-N_2火焰的燃烧速度、可燃极限和NOx排放指数与CH_4-N_2火焰有很大的不同，而与H_2-N_2火焰的相似。而同向扩散火焰的温度分布、火焰长度和NOx排放量与CH_4-N_2火焰有很大不同，而与H_2-N_2火焰相似。与CH_4-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。在此基础上绘制了NO生成的定量反应路径图（QRPD），探讨了CO-H2-N2火焰NOx排放低的原因。结果表明，在CO-H_2-N_2火焰中，NO主要通过NNH生成，不存在任何与C有关的大的反应途径，如瞬发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.