A spark energy deposition model in mixture fraction space for simulations of turbulent non-premixed flame ignition

IF 5 Q2 ENERGY & FUELS
Hazem S.A.M. Awad, Savvas Gkantonas, Epaminondas Mastorakos
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引用次数: 0

Abstract

Predicting the ignition probability remains important for designing reliable combustors. A spark ignition model in mixture fraction space is proposed and used in a Large Eddy Simulation (LES)-Conditional Moment Closure (CMC) simulation of initiation of a n-heptane spray swirl flame. The model is based on including source terms for the enthalpy and species that mimic the effect of plasma kinetics on the gaseous thermochemical state, in contrast to previous approaches that included only a heat source to the energy equation or a burning distribution in mixture fraction space as the initial condition. The model is evaluated based on its prediction of the ignition probability against experimental data. In laminar non-premixed counterflow flames, failed ignition case with low energy deposition have been found to successfully ignite when portion of the deposited energy has been assigned for the oxygen dissociation. In the turbulent spray swirl flame, the results reveal a tendency towards a successful ignition when the spark is subjected to a higher probability of finding stochiometric mixture fraction values, lower axial velocity and higher probability of finding negative axial velocities (pointing towards the bluff-body). The terms budget of the CMC equation is investigated for the successful and failed ignition events. The sum of convection and dilatation remains the dominant term to suppress the spark for the investigated realisations, and a tendency towards a failed ignition is observed when the spark energy assumes comparable magnitudes compared to the sum of convection and dilatation. In the vicinity of the spark, convection and turbulent diffusion remain of equal importance, with the latter dominating at later sparking time instants. The present approach quantitatively captures the ignition probability spatial distributions compared to the experiment. The proposed spark ignition model can improve the spark representation in CMC-based simulations, thereby allowing more reliable simulations in realistic combustors.
紊流非预混火焰点火模拟的混合分数空间火花能量沉积模型
点火概率的预测对于设计可靠的燃烧室具有重要意义。提出了一种混合分数空间的火花点火模型,并将其应用于正庚烷喷雾旋流火焰起爆的大涡模拟(LES)-条件力矩闭合(CMC)模拟。该模型是基于包括焓和物质的源项,模拟等离子体动力学对气体热化学状态的影响,而不是以前的方法,只包括一个热源的能量方程或燃烧分布在混合分数空间作为初始条件。根据实验数据对模型进行了点火概率预测,并对模型进行了评价。在层流非预混逆流火焰中,发现了低能量沉积的点火失败情况,当沉积能量的一部分被分配给氧解离时,成功点燃。在紊流喷雾漩涡火焰中,结果表明,当火花受到较高的概率找到化学混合分数值,较低的轴向速度和较高的概率找到负轴向速度(指向钝体)时,火花有成功点火的趋势。研究了成功点火和失败点火时CMC方程的项预算。对于所研究的实现,对流和膨胀的总和仍然是抑制火花的主要因素,并且当火花能量与对流和膨胀的总和相比具有相当的大小时,观察到点火失败的趋势。在火花附近,对流和湍流扩散仍然同等重要,后者在随后的火花时刻占主导地位。与实验相比,本方法定量地捕捉了点火概率的空间分布。提出的火花点火模型可以改善基于cmc的仿真中的火花表示,从而使实际燃烧室的仿真更加可靠。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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CiteScore
4.20
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