氨是一种高效氢载体，有望成为下一代无碳燃料，但较窄的燃烧极限和较高的NOx排放阻碍其使用。等离子体是一种高效、低能耗的助燃方法，得到广泛应用。设计搭建自制的耦合介质阻挡放电的氨/空气预混旋流燃烧台架，研究了燃烧极限、火焰形貌、O2和NOx含量的变化规律。未放电时，贫燃极限为0.75，富燃极限为1.1～1.2。当量比为0.9时，火焰传播速度最快，火焰最短；在贫/富燃极限附近时，火焰充满整个燃烧室。当量比在1.05～1.10时，NO含量保持在较低水平，未生成NO2。当量比由1.05减小至0.75时，NO体积分数由97×10-6（3.5% O2）增至2 785×10-6（3.5% O2）。随当量比降低，少量NO会进一步被氧化为NO2，当量比为0.75时，NO2体积分数达171×10-6（3.5% O2）。介质阻挡放电明显增强燃烧反应，抑制壁面猝熄的负面作用，O2略下降,燃烧极限扩展至0.65～1.30。当量比0.75～1.05生成的NOx同比减少40%～45%。分析探讨氨燃烧生成NOx机制，发现NOx主要来源于燃料，并随当量比降低，O/H浓度提高，NHi浓度降低，产生NO的副反应占比升高，有利于NOx生成。放电产生大量活性自由基，其中NHi促进NO+NHi和NHi+NHi反应是NOx减少的重要原因。等离子体辅助氨燃烧能显著扩宽燃烧极限，减少NOx生成，为氨的清洁高效燃烧提供一种新方法。

Ammonia is an efficient hydrogen carrier that is expected to become the next generation of carbon free fuel. However, its use is hindered due to the narrow combustion limit and high NOx emission. Plasma is an efficient and low energy consumption method to enhence combustion, which has been widely used. A self-made ammonia/air premixed swirl combustion platform coupled with dielectric barrier discharge was designed and constructed. The changes of combustion limit, flame shape, O2 and NOx were studied. The limit of lean combustion is 0.75 and the limit of rich combustion is 1.1-1.2 without discharge. When the equivalent ratio is 0.9, the flame propagating speed is the fastest and the flame is the shortest. The flame fills the entire combustion chamber near the low/rich combustion limit. When the equivalent ratio is 1.05-1.10, NO emissions remain at a low level and NO2 is not generated. When the equivalent ratio decreases from 1.05 to 0.75, the volume fraction of NO increases from 97×10-6 (3.5% O2) to 2 785×10-6 (3.5% O2). As the equivalent ratio decreases, a small amount of NO is further oxidized to NO2, and the volume fraction of NO2 reaches 171×10-6 (3.5% O2) at the equivalent ratio of 0.75. The dielectric barrier discharge significantly enhances the combustion reaction and inhibits the negative effect of flame quenching at the wall of combustion chamber. The O2 decreases slightly and the combustion limit extends to 0.65-1.30. Simultaneously, NOx generated from the equivalence ratio of 0.75 to 1.05 is reduced by 40%-45%. The mechanism of NOx generated by ammonia combustion was analyzed and discussed. It is found that NOx mainly comes from fuel. With the decrease of equivalent ratio, the concentration of O/H increases, the concentration of NHi decreases, and the proportion of side reaction that produce NO increases, which is more conducive to NOx generation. Discharge produces a large number of active free radicals, and the promotion of NO+NHi and NHi+NHi by NHi is an important reason for NOx reduction. Ammonia combustion assisted by plasma can significantly expand the combustion limit and reduce NOx, providing a new method for clean and efficient ammonia combustion.

0 引言

1 试验

2 结果与讨论

   2.1 DBD对燃烧极限和火焰形貌的影响

   2.2 DBD对O2和NOx的影响

   2.3 NOx生成机制

3 结论