锥形预混火焰羽流脱落过程的实验诊断

Experimental Diagnosis of Flame Flickering in Premixed Conical Flame

关键词:  预混火焰  羽流脱落  粒子图像测速  动态模态分解  双热电偶法

Key words:  Premixed flame  Flame flickering  Particle image velocimetry  Dynamic mode decomposition  Two thermocouple method

摘要:

为了研究锥形预混火焰的羽流脱落特性，以丙烷-空气预混火焰为实验对象，通过粒子图像测速技术对锥形预混火焰的羽流速度场进行了实验研究，以动态模态分解法对得到的速度场进行了模态分解和主要特征重构还原。同时采用光电倍增器对火焰热释放强度信号进行实时采集，采用双热电偶法对燃后热气体的温度进行了重建。结果表明在浮力诱导下燃尽气体与周围环境空气相互剪切形成剪切层（BSL），BSL的Kelvin-Helmholtz不稳定性诱导产生了涡，涡作用于燃尽区附近的流场，扰动传至火焰面附近区域，与火焰剪切层的Darrie-Landu不稳定性耦合，表现为火焰面的脉动和火焰热释放率的脉动。通过近红外自发光成像得到的热气体自发光强度与温度信号有较强的相关性，热气体呈现出与速度场相似的周期性传播模式，为研究预混火焰的羽流脱落特性提供了新的思路。

Abstract:

In order to study the characteristics of flame flickering in premixed conical flame， the premixed propane-air flame was used as the experimental object and the velocity fields of flame flickering were experimentally studied by particle image velocimetry. Dynamic mode decomposition was used to distinguish and reconstruct the main features of the velocity fields in flickering flame. Photomultiplier tube was used to obtain the heat release rate and the two thermocouple method was used to reconstruct the temperature of hot burnt gas. Results show that the burnt gas and the surrounding gas shear each other to induce one shear layer （BSL）. The Kelvin-Helmholtz instability of the BSL induces a vortex， which acts on the flow fields near the burnt zone. The perturbation induced by vortex is transmitted to the area near the flame front， which induces the Darrie-Landu instability of flame-induced shear layer and acts on the fluctuation of the flame surface and heat release rate. Meanwhile， the luminous intensity of hot burnt gas obtained by near infrared luminescence imaging is related to temperature. The hot gas exhibits a similar periodical propagation motion with that of the velocity field， which provides a new idea for studying the flow characteristics of flame flickering.