An Assessment of the Validity of Damköhler's Hypotheses for Different Choices of Reaction Progress Variable in Homogenous Mixture Moderate or Intense Low-Oxygen Dilution (MILD) Combustion
An Assessment of the Validity of Damköhler's Hypotheses for Different Choices of Reaction Progress Variable in Homogenous Mixture Moderate or Intense Low-Oxygen Dilution (MILD) Combustion
复制标题
均质混合物中度或强低氧稀释 (MILD) 燃烧中 Damköhler 假设不同反应进程变量选择的有效性评估
DOI：
10.1007/s10494-023-00520-4
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
Awad H
中科院分区：
文献类型：
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作者：
Awad H
Damköhler的假设的适用性均匀混合物（即恒定当量比）中度或强烈的低氧稀释（MILD）燃烧过程（甲烷作为燃料）已评估使用三维直接数值模拟数据与骨架机制。两种不同浓度水平的均匀MILD燃烧情况（4.8%和3.5%体积比）和不同湍流强度进行了研究，以分析稀释度的影响，湍流强度和反应过程变量定义的选择（即湍流燃烧速度和火焰表面积评估的主要物种的不同选择）Damköhler的假设在温和燃烧中的适用性。研究发现，只有当反应进程变量定义基于一个刘易斯数接近1的组分质量分数时，归一化体积积分燃烧速率才与归一化火焰表面积保持同一数量级。但是当物质质量分数的刘易斯数（基于该数定义反应进程变量）显著偏离1（例如）时，适用性水平变差。此外，它已被证明，火焰表面积计算从OH摩尔分数为基础的信息可能会导致显着偏离达姆克勒的第一个假设。还发现，归一化体积积分燃烧速率和归一化火焰表面积的相对大小显着影响的稀释水平和反应进程变量定义的选择。Damköhler的第二个假设提供了标准化湍流燃烧速度与湍流扩散系数与分子扩散系数之比之间的关系，已经发现，在均质混合物MILD燃烧中，只有当反应进程变量定义基于刘易斯数接近1的物质时（例如，但是当反应进程变量的刘易斯数显著偏离1（例如）时，不一致的程度增加。
The applicability of Damköhler’s hypotheses for homogenous mixture (i.e. constant equivalence ratio) moderate or intense low-oxygen dilution (MILD) combustion processes (with methane as the fuel) has been assessed using three-dimensional direct numerical simulation data with a skeletal mechanism. Two homogeneous MILD combustion cases with different levels ofconcentration (4.8% and 3.5% by volume) and different turbulence intensities have been investigated to analyse the influence of dilution level, turbulence intensity and the choice of the reaction progress variable definition (i.e. different choices of major species for turbulent burning velocity and flame surface area evaluations) on the applicability of Damköhler’s hypotheses in MILD combustion. It has been found that the normalized volume-integrated burning rate remains of the same order of magnitude as that of the normalized flame surface area only for the reaction progress variable definition based on a species mass fraction which has a Lewis number close to unity (e.g.) but the level of applicability deteriorates when the Lewis number of the species mass fraction, based on which the reaction progress variable is defined, deviates significantly from unity (e.g.). Moreover, it has been demonstrated that the flame surface area calculation from the OH mole fraction-based information can lead to significant departures from Damköhler’s first hypothesis. It is also found that the relative magnitudes of normalised volume-integrated burning rate and normalised flame surface area are significantly affected by the level of dilution and the choice of the reaction progress variable definition. Damköhler’s second hypothesis, which provides a relation between the normalised turbulent burning velocity and the ratio of turbulent to molecular diffusivities, has been found to hold in an order of magnitude sense in homogeneous mixture MILD combustion only for the reaction progress variable definition based on species that has a Lewis number close to unity (e.g.) but the level of disagreement increases as the Lewis number of the reaction progress variable deviates significantly from unity (e.g.).