Basic Research for Reduction of NO_x Emission in Premixed combustion

将预混湍流火焰的结构分为两类，即褶皱层流火焰和分布反应区。产生分布式反应区需要极强的湍流，而我们对这种火焰结构的排放特性的了解还不够。为了保证绝热性能，设计了一种陶瓷对置射流燃烧器。用两台化学发光NO-NOx分析仪测定NO_x浓度，用3台气相色谱仪设计的多组分同时分析系统测定稳定组分。燃烧器具有丙烷/空气混合物供应管的喇叭口出口，以消除出口周围的再循环区的产生。在分布反应区内，火焰区NO_x的生成主要来源于燃烧-NO机理，而不是Zeldovich机理，并随当量比的增大而增大。而在完全燃烧区，NO_x的生成以Zeldovich机理为主，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，排放指数为1g/kg燃料，采用多组分同时分析系统，可同时测定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_8、i-C_4 H_<10>、n-C_4 H_的浓度<10>。分析系统的灵敏度针对纯气体进行了校准。丙烷在火焰区未燃气侧热解形成的低级烃在未燃气侧迅速消耗。在已燃气侧，没有发现这种低级烃，其化学结构与未燃气侧不同。

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.