Basic Research for Reduction of NO_x Emission in Premixed combustion

预混湍流火焰的结构分为褶皱层流火焰和分布反应区两类。分布反应区的产生需要极强的湍流，而我们对这种火焰结构的发射特性认识不足。本文设计了一种陶瓷对置射流燃烧器，以保证其绝热性。采用2台化学发光NO-NO_x分析仪测定NO_x浓度，采用3台气相色谱仪同时多组分分析系统测定稳定组分。燃烧器有钟口出口丙烷/空气混合气供应管，以消除出口周围的再循环区产生。垂直于径向拉伸涡矢量的强混合形成了纯一维浓度场。在分布反应区，火焰区形成的NO_x主要来源于prompt-NO机制，而不是Zeldovich机制，并随着当量比的增加而增加。而在完全燃烧气体区，通过Zeldovich机制形成的NO_x占主导地位，并在化学计量浓度处达到最大值。该燃烧器的NO_x排放量极低，排放指数约为1g/kg燃料。采用同步多组分分析系统，可以同时测定O_2、N_2、H_2、CO、CO_2、CH_4、C_2H_2、C_2H_4、C_2H_6、C_3H_6、C_3H_6、C_3H_8、i-C_4H_<10>、n-C_4H_<10>的浓度。用纯气体对分析系统的灵敏度进行了标定。在火焰区未燃气侧丙烷热解形成的低碳氢化合物在未燃气侧被迅速消耗。在燃烧气侧，没有发现这种低碳氢化合物，化学结构与未燃烧气侧不同。

The structure of the premixed turbulent flame is divided into two categories, namely, wrinkled laminar flame and distributed reaction zone. Extremely strong turbulence is required to produce the distributed reaction zone, and our knowledge on the emission characteristics of this flame structure is insufficient. In the present study, a ceramic opposed jet burner was designed to assure the adiabaticity. NO_x concentration was measured by two chemiluminescence NO-NO_x analyzers and the stable chemical species were measured by the simultaneous multi-species analyzing system designed using 3 gas chromatographs. The burner has the bell-mouthed exits of propane/air mixture supply tube to eliminate the production of the recirculation zones around the exits. Purely one-dimensional concentration field was established due to the strong mixing perpendicular to the radially stretched vortex vector.In the distributed reaction zone, NO_x formed in the flame zone originates mainly from the prompt-NO mechanism rather than the Zeldovich mechanism and increased with the equivalence ratio. However, in the completely burned gas region, the NO_x formed through the Zeldovich mechanism is predominant and reaches a maximum at the stoichiometric concentration. The amount of NO_x emitted from this burner is extremely small and the emission index is of the order of 1g/kgfuel.By the simultaneous multi-species analyzing system, the concentrations of O_2, N_2, H_2, CO,CO_2, CH_4, C_2H_2, C_2H_4, C_2H_6, C_3H_6, C_3H_6, C_3H_8, i-C_4H_<10>, n-C_4H_<10> are able to be measured simultaneously. The sensitivity of the analyzing system was calibrated against the pure gases. The lower hydrocarbons which are formed by pyrolysis of propane on the unburned gas side of the flame zone are consumed rapidly on the unburned gas side. On the burned gas side, no such lower hydrocarbons were found and the chemical stucture is different from that on the unburned gas side.