氰化氢 (HCN) 是一种剧毒的痕量排放物,可能在氨 (NH3) 混合烃燃烧过程中产生。在这项研究中,开发并验证了一种新的动力学模型来预测 NH3 混合燃烧中 HCN 的形成。对氮取代烃类物质的关键速率系数进行了严格的重新评估。使用一维自由传播火焰模型,系统分析了各种条件下层状预混 CH4/NH3/空气火焰中 HCN 的形成。结果表明,HCN 排放随当当比 (φ) 的增加而增加,随 NH3 混合比 (α) 的非单调变化。在贫窸条件下,HCN 主要由亚胺自由基分解形成,并在火焰前沿内被 O/OH 氧化。而在富集条件下,HCN 氧化发生在火焰后区域,这使得出口处的排放高度依赖于反应停留时间。因此,在常温常压下,在高 NH3 混合分数 (α > 50 %) 和超富集 (φ > 1.2) 条件下,应注意 HCN 排放。HCN 的峰值发射发生在 α = 0.7 和 φ = 1.45 处,在 1D 预混火焰复合物中达到致死浓度 (310 ppm)CHi 和 NHi 相互作用反应在 HCN 的形成中表现出来。总体形成路线可分为甲胺氧化路线和自由基组合路线,前者在所有条件下均占主导地位。由于HCN后氧化时间的增加和反应特征时间的缩短,独立升高的温度或压力将分别减少HCN的发射。当温度和压力同时升高时,HCN 的变化更复杂。 然而,当温度和压力超过 600 K 和 2 个大气压时,排放量将下降到可以忽略不计的水平,这表明在高压和高温条件下,对 CH4/NH3 燃烧中的 HCN 排放的关注微乎其微。
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Kinetic analysis on the hydrogen cyanide formation in the premixed methane/ammonia flame
Hydrogen cyanide (HCN) is a highly toxic trace emission that may be generated during ammonia (NH3) blended hydrocarbon combustion. In this study, a new kinetic model was developed and validated to predict HCN formation in NH3-blended combustion. Key rate coefficients for nitrogen-substituted hydrocarbon species were critically reevaluated. Using a one-dimensional freely propagating flame model, the formation of HCN in laminar premixed CH4/NH3/air flames was systematically analyzed under various conditions. Results indicate that HCN emission increases with increasing equivalence ratio (ϕ) and non-monotonically changes with NH3 blending ratio (α). Under lean conditions, HCN is primarily formed from the decomposition of imine radicals and oxidized by O/OH inside the flame front. While under rich conditions, the HCN oxidation takes place in the post-flame region, making the emissions at the outlet highly dependent on the reaction residential time. Consequently, attention should be paid to HCN emissions under high NH3 blending fraction (α > 50 %), and ultra-rich conditions (ϕ > 1.2) at normal temperature and pressure. The peak emission of HCN occurred at α = 0.7 and ϕ = 1.45, reaching a lethal concentration (310 ppm) in 1D premixed flame. Complex CHi and NHi interaction reactions are exhibited in the formation of HCN. The overall formation route can be divided into methylamine oxidation routes and radical combinations routes, and the former is dominant under all conditions. Independently increasing temperature or pressure will reduce the HCN emission due to the increased post-oxidation of HCN and diminished reaction characteristic time, respectively. More complicated changes in HCN were shown when temperature and pressure were increased at the same time. However, emissions will fall to a negligible level when temperature and pressure exceed 600 K and 2 atm, suggesting minimal concern for HCN emissions in CH4/NH3 combustion under elevated pressure and temperature conditions.