A numerical study of auto-ignition in turbulent lifted flames issuing into a vitiated co-flow
A numerical study of auto-ignition in turbulent lifted flames issuing into a vitiated co-flow
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DOI：
10.1080/13647830600903472
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发表时间：
2007-04
影响因子：
1.3
通讯作者：
Robert L. Gordon;A. Masri;Stephen B. Pope;G. Goldin
中科院分区：
文献类型：
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作者：
Robert L. Gordon;A. Masri;Stephen B. Pope;G. Goldin
本文对氢氮混合气体进入同向流中的简单射流自燃过程进行了数值研究。这些火焰的稳定区域是复杂的，并且取决于流动条件，可能经历从自燃到预混火焰传播的过渡。本文的目的是开发识别这种行为的数值指标，首先在众所周知的简单的测试情况下，然后在解除湍流火焰。计算采用了一个组成概率密度函数（PDF）的方法耦合到商业CFD代码，FLUENT。原位自适应制表（ISAT）方法被用来实现详细的化学动力学。一个简单的k-ε湍流模型用于湍流沿着与低雷诺数模型接近的燃料管的固体壁。第一个指标是基于对流，扩散和化学反应条款的预算的物种运输的分析。这是一个强有力的工具，研究方面的湍流燃烧，否则将是禁止或不可能的实验研究。反应平衡的对流与最小的轴向扩散被视为自燃的指标，而扩散反应平衡，对流扩散平衡的预热区之前，是一个预混火焰的代表。第二个指标是某些自由基物质（如HO 2）在火焰区之前开始产生的相对位置。在生成H、O和OH之前的HO 2的积累被认为是自燃的另一个指标。本文首先确认了这些指标的相关性，相对于两个简单的测试情况下，代表明确的自燃和预混火焰传播。三个湍流提升火焰，然后调查和自燃的存在被确定。这些数值工具是必不可少的，在提供有价值的见解这些火焰的稳定行为，以及自动点火和预混火焰传播过程之间的分界。
This paper presents a numerical study of auto-ignition in simple jets of a hydrogen–nitrogen mixture issuing into a vitiated co-flowing stream. The stabilization region of these flames is complex and, depending on the flow conditions, may undergo a transition from auto-ignition to premixed flame propagation. The objective of this paper is to develop numerical indicators for identifying such behavior, first in well-known simple test cases and then in the lifted turbulent flames. The calculations employ a composition probability density function (PDF) approach coupled to the commercial CFD code, FLUENT. The in-situ-adaptive tabulation (ISAT) method is used to implement detailed chemical kinetics. A simple k–ϵ turbulence model is used for turbulence along with a low Reynolds number model close to the solid walls of the fuel pipe. The first indicator is based on an analysis of the species transport with respect to the budget of convection, diffusion and chemical reaction terms. This is a powerful tool for investigating aspects of turbulent combustion that would otherwise be prohibitive or impossible to examine experimentally. Reaction balanced by convection with minimal axial diffusion is taken as an indicator of auto-ignition while a diffusive–reactive balance, preceded by a convective–diffusive balanced pre-heat zone, is representative of a premixed flame. The second indicator is the relative location of the onset of creation of certain radical species such as HO2 ahead of the flame zone. The buildup of HO2 prior to the creation of H, O and OH is taken as another indicator of autoignition. The paper first confirms the relevance of these indicators with respect to two simple test cases representing clear auto-ignition and premixed flame propagation. Three turbulent lifted flames are then investigated and the presence of auto-ignition is identified. These numerical tools are essential in providing valuable insights into the stabilization behaviour of these flames, and the demarcation between processes of auto-ignition and premixed flame propagation.