不同Lewis数下层流球形预混不稳定火焰锋面非线性发展阶段的实验研究和机理探索

Intrinsic flame instability has a great influence on the complex turbulent combustion and unstable operation in IC engines. Thus it is necessary to conduct the research on the intrinsic flame instability. In this project, a dual-chamber apparatus will be used to study the nonlinear evolution of unstable flame front of laminar spherical premixed flame experimentally. Acceleration exponent, split and merge of cellular structure on the flame front will be obtained and recorded from the cellular unstable flame. Critical radius beyond which unstable flame occurs and the evolution of pulsing, traveling and spiral waves will be obtained from the pulsing unstable flame. Direct numerical simulation will be used to generate the laminar unstable spherical premixed flame numerically. We obtain the flow field, reaction rate, heat release, diffusion of the important radicals and heat of local flame front of laminar spherical premixed flame. Based on the results above, mechanism of nonlinear evolution of unstable flame front of laminar spherical premixed flame will be studied. In addition, the coupling and interaction between D-L and pulsing instabilities will also be investigated. Research in the project will have an important significance on the understanding of turbulent combustion of fuel-lean mixtures, solving the problem on the unstable operation in IC engines and development of the combustion dynamic theory.

本项目利用高压双腔定容燃烧弹实验装置对不同Lewis数下层流球形预混不稳定火焰锋面的非线性发展阶段进行实验研究。测量小Lewis数下细胞状不稳定火焰传播过程中的加速因子，定量分析火焰锋面细胞状结构的破裂和融合等过程。获得大Lewis数下脉动不稳定火焰出现时刻的临界半径，分析火焰锋面的脉动特性以及出现的行波和螺旋波等形态；利用直接数值模拟的方法对层流球形预混不稳定火焰锋面的非线性发展阶段进行机理探索。获取火焰局部位置处流场、反应速率、热释放率、燃烧反应区内重要自由基的分布迁移和质热扩散等信息，对层流球形预混火焰锋面非线性发展阶段的机理进行研究。此外，该部分还探索了脉动和动力学不稳定性的相互耦合作用。研究成果对揭示稀燃预混湍流火焰机制、解决发动机不稳定燃烧问题以及发展火焰动力学理论有着重要的作用。

燃烧室内燃烧过程的优化和合理组织是提升发动机性能的关键技术与核心思想。目前点燃式发动机采用稀燃预混的燃烧技术，但是稀燃发动机会出现不稳定工作的状况，这极大的影响发动机性能的提升。层流火焰自身不稳定性的研究是解决稀燃发动机不稳定运行问题的必然途径，同时也是完善湍流燃烧模型与基础火焰动力学理论的重要组成部分。研究主要利用定容燃烧弹实验装置对不同Lewis数下层流球形预混不稳定火焰锋面的发展阶段进行实验研究。项目获得了不同Lewis下不稳定火焰传播的过程和重要参数。明确了外在湍流与自身不稳定性的竞争机制。利用数值计算探索了不稳定火焰传播不同阶段的形态特性与机理。提出了非线性过渡阶段的概念。将层流不稳定火焰传播特性应用到气体爆炸安全方面，提出了爆炸压力曲线预测模型的修正方法。