Dynamic Characterization of a Ducted Inverse Diffusion Flame Using Recurrence Analysis

Normal diffusion flame or partially premixed flame is used in many applications, such as aviation engines, tanks, ocean vessels, and industrial furnaces, because of its high flame stability and relatively low susceptibility to dynamic instabilities compared to lean premixed flames, which give lower emissions. However, associated with such flames are high NO<i>_x</i> and soot emissions, which are particularly high for heavier hydrocarbon fuels. Increasingly stringent environmental norms have thus dictated the search for alternate approaches; one such being the inverse diffusion flame, which is currently being used in rocket motors, for staged combustion in gas turbine combustors, and furnaces. However, the dynamic response of such a flame, particularly in ducted applications where a coupling between unsteady heat release rate and duct acoustics may occur, is relatively less explored. The present work aims to plug that knowledge gap through an experimental investigation of a laboratory-scale ducted inverse diffusion flame. Two parametric variations of the flame were performed—variation of the flame position and variation of the air flow rate. Using tools of nonlinear dynamics, such as phase space reconstruction and recurrence quantification, several interesting dynamic characteristics were observed, such as limit cycles, intermittency, and homoclinic orbits. For a constant air flow rate, the system was observed to transition from a type-II intermittency regime to a limit cycle and then again to intermittent behavior as the position of the flame within the duct was varied. A similar trend was observed when the air flow rate was varied at a fixed flame position.

常规扩散火焰或部分预混火焰因其相较于排放更低的贫燃预混火焰具备更高的火焰稳定性与更低的动态不稳定性敏感性，被广泛应用于航空发动机、坦克、远洋船舶及工业窑炉等场景。然而这类火焰会伴随产生高浓度氮氧化物 (NOₓ) 与炭黑排放，对于重质烃类燃料而言，该类排放尤为突出。日趋严苛的环境标准促使人们寻求替代燃烧方案，其中之一便是逆扩散火焰 (Inverse Diffusion Flame)，目前该火焰已应用于火箭发动机、燃气轮机燃烧室分级燃烧及工业窑炉中。但针对这类火焰的动态响应特性研究相对不足，尤其在存在非稳态放热速率与管道声学耦合效应的带管道应用场景中，相关探索更为匮乏。本研究旨在通过对实验室尺度带管道逆扩散火焰的实验研究填补这一认知空白，共开展两项火焰参数调控实验：火焰位置调控与空气流量调控。借助非线性动力学分析工具，如相空间重构 (Phase Space Reconstruction) 与递归量化分析 (Recurrence Quantification)，本研究观测到多种有趣的动态特性，包括极限环、间歇性行为与同宿轨 (Homoclinic Orbit)。在空气流量固定的条件下，随着管道内火焰位置的变化，该系统呈现出从II型间歇态 (Type-II Intermittency) 过渡至极限环，随后再次转为间歇性行为的演化过程；在火焰位置固定的条件下，改变空气流量时，同样观测到了相似的演化趋势。