Multi Regime combustion under technically relevant conditions: Experimental and numerical investigation of thermo-chemical states and flame structures

湍流燃烧可分为预混燃烧和非预混燃烧。对这两种极限情况进行了广泛的研究，建立了预混和非预混火焰的数学模型。除了这两个限制，分层和部分预混火焰也已被研究，但使用预混或非预混模型。火焰的模拟既不能归类为预混燃烧，也不能归类为非预混燃烧(多工况燃烧)，这是一个开放的科学问题。多工况燃烧存在于各种实际系统中，如燃气轮机或发动机。最近的研究表明，多工况燃烧中的局部火焰结构与两种极限情况下的火焰结构有很大的不同。目前，还没有合适的大涡模拟既能描述预混/非预混的极限，又能描述中间状态。此外，没有实验参考数据集，不同的火焰结构是通过系统地改变边界条件来实现的。因此，本研究的目标是对多工况燃烧进行系统的实验和数值研究、模型开发和分析。在实验工作包AP1中，将开发一个具有明确定义的边界条件的燃烧器，用于产生参考数据。火焰稳定是通过回流区实现的，因此可以通过改变入口速度和化学计量比来控制燃烧状态。利用高速PIV和拉曼光谱对冷态流场和混合场进行了表征。对于燃烧情况，将用拉曼/瑞利散射记录热化学态。此外，还将首次同时进行定量的OH-LIF测量。在AP2数值程序中，将求解二维火焰面方程(混合分数和进程变量公式)。为了以后在大涡模拟中的应用和与实验的比较，将基于附加的进度变量而不是标量耗散率来开发一种新的参数化方案。最初，该模型将针对三重火焰的完全分解溶液进行测试。对于LES火焰表，将分析和综合来自实验确定的联合概率密度函数的统计信息。在AP3中，将结合实验和数值方法。作为第一步，将验证来自LES的结果。随后，将进行燃烧模式的识别、局部热化学状态和火焰结构的表征。这一分析将基于本项目开发的一种新的无梯度火焰识别和火焰表征方法。该项目将与作为墨卡托研究员的Vervisch教授密切合作进行。

Turbulent combustion can be classified as premixed or non-premixed. These two limiting cases have been studied extensively and mathematical models have been developed for premixed and non-premixed flames. Besides these two limits, stratified and partially premixed flames have also been investigated, using however either premixed or non-premixed models. Modeling of flames, which can neither be categorized as premixed nor as non-premixed (multi regime combustion), is an open scientific issue. Multi regime combustion can be found in a variety of practical systems such as gas turbines or engines.Recent studies have shown that the local flame structures in multi regime combustion can differ significantly from both limiting cases. Currently, no suitable LES model exists that is capable of describing both the premixed/non-premixed limits as well as the intermediate states. Furthermore, no experimental reference data set is available, where the different flame structures are realized through systematic variations of boundary conditions. Therefore, the objective of this study is a systematic experimental and numerical investigation, model development and analysis of multi regime combustion.The research project consists of 3 work packages (AP). In the experimental work package AP1 a burner with well-defined boundary conditions for generating the reference data will be developed. Flame stabilization is achieved through recirculation zones such that the combustion regime can be controlled by varying the inlet conditions both in velocity and stoichiometry. The cold flow and mixture field will be characterized with high-speed PIV and Raman spectroscopy. For the combusting cases, the thermo-chemical state will be recorded with Raman/Rayleigh scattering. Furthermore, simultaneous quantitative OH-LIF measurements will be carried out for the first time.In the numerical AP2 two-dimensional flamelet equations (mixture fraction and progress variable formulation) will be solved. For a subsequent usage in LES and for comparison with the experiments a novel parameterization will be developed based on additional progress variables instead of scalar dissipation rates. Initially, the model will be tested against fully resolved solutions of a triple flame. For the LES flamelet tables, statistical information from experimentally determined joint probability density functions will be analyzed and integrated.In AP3 experimental and numerical methods will be combined. As a first step the results from the LES will be validated. Subsequently, the identification of combustion regimes, the characterization of the local thermo-chemical state and the flame structure will be carried out. This analysis will be based on a novel gradient-free flame identification and flame characterization method developed in this project. The project will be carried out in close collaboration with Prof. Vervisch as Mercator fellow.