NO_x emissions remain a primary concern for modern and future gas turbines, particularly as we progress towards a net-zero carbon future. It is critical to identify novel strategies to mitigate environmental pollutants for both modern turbines operated on natural gas and future turbines projected to use carbon-free fuels (such as hydrogen). In the current study, NO_x emissions of a reacting methane-air jet in a vitiated crossflow are experimentally investigated in a model axially staged combustor at 5 atm. The combustion products from the main stage combustor flow into the axial stage at temperatures ranging from 1580 to 1650 °C. The axial stage contains a reacting jet in crossflow, which provides an overall temperature rise ranging from 50 to 220 °C to generate exit temperatures similar to gas turbine engines. The focus of this paper is to explore the effects of flame liftoff and ignition timescales on the NO_x contribution of this secondary jet. This is done by varying the premixed level and preheat temperature of the axial jet. The effects are explored at different momentum flux ratios (J), jet equivalence ratios (φ_jet), exit temperatures (T_exit), and main stage (headend) temperatures (T_HE). High-speed CH* chemiluminescence imaging is employed for each test case to determine the flame stabilization point. For a given temperature rise and combustor exit temperature, an increase in ignition delay was observed with a decrease in jet temperature. This provided a NO_x benefit, particularly for jets that are injected at or close to an ignitable mixture fraction. Similarly, the coaxial injector caused a significant ignition delay compared to the fully premixed injector; this also led to a NO_x benefit. Overall, the results show that a thermally driven delay in the axial stage provides a greater NO_x reduction than a mixing delay.

NO _x排放仍然是现代和未来燃气轮机的主要关注点，尤其是在我们朝着净零碳未来迈进的过程中。对于使用天然气运行的现代涡轮机和预计使用无碳燃料（如氢）的未来涡轮机，确定减轻环境污染物的新策略至关重要。在目前的研究中，NO _x在 5 个大气压的轴向分级燃烧器模型中，实验研究了在腐蚀的交叉流中反应的甲烷-空气射流的排放。来自主级燃烧器的燃烧产物在 1580 至 1650 °C 的温度范围内流入轴向级。轴向级包含一个交叉流动的反应射流，它提供了 50 到 220 °C 的整体温升，以产生类似于燃气涡轮发动机的出口温度。本文的重点是探索火焰升起和点火时间尺度对这种二次射流的 NO _x贡献的影响。这是通过改变轴向射流的预混水平和预热温度来实现的。在不同的动量通量比 ( J )、射流当量比 ( φ _jet)、出口温度 ( T _exit ) 和主级（前端）温度 ( T _HE )。每个测试案例都采用高速 CH* 化学发光成像来确定火焰稳定点。对于给定的温升和燃烧器出口温度，观察到点火延迟随着射流温度的降低而增加。这提供了 NO _x益处，特别是对于在可燃混合物分数处或接近可燃混合物分数处喷射的射流。类似地，与完全预混喷射器相比，同轴喷射器导致了显着的点火延迟；这也带来了 NO _{x 的}好处。总的来说，结果表明轴向阶段的热驱动延迟提供了更大的 NO _x 减少比混合延迟。